{"pid": "bdr:qe4nbxku", "id": "bdr:qe4nbxku", "json_uri": "https://repository.library.brown.edu/api/collections/bdr:qe4nbxku/", "uri": "https://repository.library.brown.edu/studio/collections/bdr:qe4nbxku/", "db_id": 355, "name": "Theses and Dissertations", "description": "", "tags": [], "facets": [{"field": "mods_type_of_resource", "name": "Format", "sort_by_count": true}, {"field": "genre", "name": "Genre", "sort_by_count": false}, {"field": "keyword", "name": "Keywords", "sort_by_count": false}], "parent_folders": [{"pid": "bdr:cdz26ads", "id": "bdr:cdz26ads", "json_uri": "https://repository.library.brown.edu/api/collections/bdr:cdz26ads/", "uri": "https://repository.library.brown.edu/studio/collections/bdr:cdz26ads/", "db_id": 354, "name": "Physics", "description": "Physics, or \u201cnatural philosophy\u201d as it was originally known, has been part of Brown\u2019s curriculum since the 18th century, and our department has a distinguished history of teaching and research.  Faculty members engage in research in astrophysics and cosmology, high energy, condensed matter and biological physics that is collaborative, interdisciplinary and international in its scope.", "tags": []}], "child_folders": [], "ancestors": ["Physics"], "items": {"numFound": 272, "start": 0, "docs": [{"pid": "bdr:386289", "object_type": "pdf", "abstract": ["A wealth of astrophysical evidence confirms that 26% of the energy density of the universe is comprised of a mysterious, non-baryonic, dark matter. A leading candidate for dark matter is the Weakly Interacting Massive Particle (WIMP) that is suggested both by the relic abundance of dark matter, and extensions to the standard model of particle physics. WIMPs interact with baryonic matter only through gravity and the weak nuclear force. The Large Underground Xenon (LUX) dark matter experiment aims to detect WIMPs through this weak interaction. LUX is a 370 kg two-phase (liquid/gas) xenon time projection chamber designed to detect nuclear recoils from interactions with WIMPs. Particle interactions in LUX are observed by 122 photomultiplier tubes (PMTs). Signals from these PMTs are processed by custom-built analog electronics. The data acquisition system (DAQ) is composed of commercial digitizers with firmware customized for the LUX experiment. The LUX DAQ is optimized to provide a high rate and a large dynamic range during precision calibrations involving radioactive sources, while also delivering a low threshold for maximum sensitivity. The LUX detector is housed in a 300 tonne water tank on the 4850 ft level of the Sanford Underground Research Facility, in Lead, SD. The first WIMP search results are based on 85.3 live-days of data-taking. This non-blind analysis yields 160 events in the WIMP search energy range in a 118kg fiducial volume. A profile likelihood analysis of this data supports the background-only hypothesis, producing the highest constraint on the WIMP-nucleon interaction cross-section to date. The minimum 90% C.L. upper limit is 7.6x10^-46 cm2 for a WIMP mass of 33 GeV/c2. In particular this run has strongly ruled out hints of signal in the low-mass regime between 6 and 20 GeV/c2 recently suggested by several direct detection experiments. LUX will continue to undergo engineering and calibrations runs to improve detector sensitivity. The subsequent 300 live-day blinded WIMP search will extend the WIMP limit of LUX by a factor of x5 above a mass of 20 GeV/c2."], "keyword": ["dark matter", "WIMPs", "Dark matter (Astronomy)", "Xenon"], "primary_title": "First WIMP Search Results from the LUX Dark Matter Experiment", "uri": "https://repository.library.brown.edu/studio/item/bdr:386289/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:386289/"}, {"pid": "bdr:386168", "object_type": "pdf", "abstract": ["The dominant component of matter in the universe, referred to as dark matter, cannot be explained by the standard model of particle physics. A leading candidate for dark matter is the weakly interacting massive particle (WIMP). The WIMP theory is well motivated by several extensions of the standard model, and has been tested directly in the laboratory over the last 30 years. The Large Underground Xenon (LUX) experiment seeks to identify the signatures of WIMP interactions with baryonic matter. LUX measures particle interactions at the keV level by the detection of single-photon signals in a 250 kg Xe target mass. The LUX detector inner fiducial region is the lowest measured background particle detector in the world at keV energies, with background rates at the level of 1E-3 counts/keV/kg/day. Low background rates are essential for identifying WIMP interactions in the detector, which occur with frequencies <1/kg/(5 years). LUX completed its first low-background science run at the Sanford Underground Research Facility in August 2013. WIMP search results are reported from an 85 live day analysis. The experiment places the tightest constraint on WIMP spin-independent interaction cross-sections to date. Results from LUX also exclude several potential dark matter signal claims from other direct detection experiments, for WIMP masses in the range 6-15 GeV. The LUX result is the product of low detector background rates and high photon signal collection efficiency. Analysis of the first WIMP search data has provided direct characterization of low-energy backgrounds in LUX. Measured background rates were found to be in agreement with expectations based on models of detector material radioactivity. The data also provides the first measurements of intrinsic radioactive contaminants in the detector, including short-lived cosmogenic Xe radioisotopes. I will describe the LUX background model, detailing work which was used in the design and early performance projections of the LUX detector, as well as background measurements which constrain and support the model."], "keyword": ["Dark matter", "LUX", "radioactive backgrounds", "Dark matter (Astronomy)", "Xenon"], "primary_title": "Measurement and Analysis of WIMP Detection Backgrounds, and Characteri- zation and Performance of the Large Underground Xenon Dark Matter Search Experiment", "uri": "https://repository.library.brown.edu/studio/item/bdr:386168/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:386168/"}, {"pid": "bdr:386208", "object_type": "pdf", "abstract": ["Fractional quantum Hall (FQH) liquids are interesting two-dimensional electron systems that possess quasiparticle excitations with fractional charges, obeying quantum statistics different from those of bosons and fermions. In particular, the FQH liquid at filling factor 5/2 was proposed to host Majorana bound state (MBS) with exotic non-Abelian statistics. A collection of MBSs can span a topological Hilbert space, in which each many-particle state is topologically distinct, depending on the historical trajectories of all the MBSs in the system. Logic operations in quantum computation can be encoded in the linear transformations in topological Hilbert space and in principle be protected against local defects and perturbations, which are topologically trivial and cannot induce transitions between different many-particle states. Despite such intriguing theoretical picture, experiments probing the nature of the 5/2 FQH liquid are controversial. In this dissertation, we provide an explanation of two seemingly contradicting experiments in the 5/2 FQH liquid, by exploring the role of electrostatic interaction closely related to the geometries of the devices. We also construct several new 5/2 FQH states, by making use of the particle-hole symmetry in FQH systems, to account for a recent experiment observing upstream neutral edge transport in the 5/2 FQH liquid, which ruled out most of the existing theories. In addition to the new particle-hole states, we propose another topological description of the 5/2 FQH liquid which reconciles all existing transport experiments. Later, we turn our attention to the MBSs in superconductor systems. We study the approaches to minimizing the decoherence of a Majorana-fermion-based qbit due to its interaction with environment, based on a full classification of the fermionic zero modes in a system of interacting Majorana fermions."], "keyword": ["topological order", "fractional quantum Hall effect", "Majorana fermion"], "primary_title": "Topological Order in Superconductors and Quantum Hall Liquids", "uri": "https://repository.library.brown.edu/studio/item/bdr:386208/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:386208/"}, {"pid": "bdr:386162", "object_type": "pdf", "abstract": ["In this thesis, we present two variations of the standard measurement technique used for making picosecond ultrasonic measurements. In the first variation, a resonant optical cavity is formed between the sample to be studied and a distributed Bragg reflector, which lies above the surface of the sample. For a highly reflecting sample, this cavity enhances the fraction of the energy of the pump pulse that is absorbed by the sample, and also increases the change in the reflection of the probe pulse that results from the change in the optical constants of the sample. The signal can be enhanced by two orders of magnitude. In the second variation, a transparent mask is placed just above the surface of the sample to be studied. This mask results in a periodic modification of the intensity of the pump and probe beams across the sample surface. We have used this grating mask to make it possible to study Rayleigh waves and to determine the elastic constants of thin films. The main experimental challenge is to position the mask close to the surface; this should not be a problem when samples are prepared and measurements are made under clean room conditions. Experimental results are presented and are in good agreement with calculated results."], "keyword": ["picosecond ultrasonics", "optical cavity", "Rayleigh waves"], "primary_title": "Picosecond Ultrasonic Measurements with Enhanced Sensitivity", "uri": "https://repository.library.brown.edu/studio/item/bdr:386162/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:386162/"}, {"pid": "bdr:386154", "object_type": "pdf", "abstract": ["It has been proposed that a hidden conformal symmetry governs the dynamics of low frequency scattering in a general Kerr black hole background, enabling a possibility of realizing the physical bulk scattering amplitudes within a conformal field theory (CFT). We investigate this correspondence by mapping higher order corrections to the massless wave equations in a Kerr background to an expansion within the CFT in terms of higher dimension operators. We find that in the low frequency regime the exact Kerr background softly breaks the conformal symmetry and the scaling dimensions of these operators run with frequency. We further extend this analysis by constructing a family of vector fields that generate local symmetries in the solution space of low frequency massless field perturbations in the general Kerr geometry. This yields a one-parameter family of SL(2R)xSL(2,R) algebras. We identify limits in which the SL(2R)xSL(2,R) algebra contracts to an SL(2,R) symmetry of the Schwarzschild background. We note that for a particular value of the free parameter, the symmetry algebra generates the quasinormal mode spectrum of a Kerr black hole in the large damping limit, suggesting a connection between the hidden conformal symmetry and a fundamental CFT underlying the quantum Kerr black hole. Finally, we consider finite frequencies. We determine how the exact mode functions decompose into representations of the SL(2R)xSL(2,R) symmetry group. This extends earlier results on the low frequency limit of the massless scalar case to finite frequencies and general spin. As an application, we numerically determine the parameters of the representations that appear in quasinormal modes. These results represent a first step to formulating a more precise mapping to a holographic dual conformal field theory for generic black holes."], "keyword": ["Conformal field theory", "AdS/CFT", "Kerr black holes"], "primary_title": "The Hidden Kerr/CFT Conjecture", "uri": "https://repository.library.brown.edu/studio/item/bdr:386154/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:386154/"}, {"pid": "bdr:419538", "object_type": "pdf", "abstract": ["We explore the geometrical and dynamic variations of self-assembled colloidal mono-membrane systems composed of filamentous fd virus in the presence of a polymer depletant using computation and theory. These mono-membranes are of one virus length thickness. First, we study the interaction of a colloidal tube, which is also a virus, piercing a mono-membrane with a depletion model developed by Yang, Barry et at. (2012) of hard rods that experience attractions due to depletion interactions. This work is based on recent experiments in which a long virus is repelled and then attracted by a mono-membrane as it pierces the membrane. Our simulations demonstrate that excluded volume effects are sufficient to describe this process, which consists of three parts, repulsion when the tube just pierces the membrane, attraction when the tube pierces deeper into the membrane, and no interaction when the tube completely penetrates the membrane. Second, in consideration of computational efficiency and implementation of molecular chirality, we employ a pairwise attractive molecular potential model proposed by Savenko and Dijkstra (2006) to study membranes consisting of mixtures of viruses. The model qualitatively renders a similar phase diagram and interaction curves as the depletion mode used in the previous part for similar experimental parameters, but quantitatively exhibits much stronger molecular interactions. We also extend the model to implement the chirality of the viruses. Finally, we discuss chiral rafts of short virus in a background of a long virus mono-membrane using the de-Gennes free energy theory. We build a two-dimensional theoretical model for the rafts and numerically solve the Euler-Lagrange equations derived from the Frank free energy of the system. We demonstrate that the free energy related to the three-dimensional deformation in the director field alone can explain the repulsion between the rafts. The repulsive force characteristic length is determined by the background virus. Based on our model, the director field is very sensitive to the virus chirality profile near the rafts edges while the interaction strength is almost insensitive."], "keyword": ["self-assembled colloidal membrane", "depletion force", "fd virus", "monte carlo simulation", "Frank free energy"], "primary_title": "Numerical Studies of Self-Assembled Colloidal Membranes", "uri": "https://repository.library.brown.edu/studio/item/bdr:419538/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:419538/"}, {"pid": "bdr:320495", "object_type": "pdf", "abstract": ["This thesis presents a measurement of the mass of the top quark. The top quarks are produced through proton-antiproton collisions with $\\sqrt{s}$=1.96 TeV at the Fermilab Tevatron collider using the D\\O\\ detector. The method employed for the measurement is called the Ideogram Technique. The events used in the measurement are selected such that the top quark decay signatures (as seen in the detector) are at least one lepton (electron or muon), four or more jets with at least one of them tagged as originating from a b-quark and missing transverse momentum. These events are then fitted using a kinematic fitter. The event-by-event likelihood is calculated using templates that depend on the kinematically reconstructed top quark mass. The events are weighted by their probability to be signal or background, using topological information. The measurement of the top quark mass is 175.7$\\pm$1.98 $GeV/c^{2}$."], "keyword": ["top quark mass", "ideogram", "D0", "Tevatron", "Jets"], "primary_title": "A Measurement of the Top Quark Mass in the Lepton + Jets Channel using the Ideogram Technique at D\\O\\", "uri": "https://repository.library.brown.edu/studio/item/bdr:320495/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:320495/"}, {"pid": "bdr:297710", "object_type": "pdf", "abstract": ["An electron injected into liquid helium strongly repels the surrounding helium atoms away due to the Pauli exclusion principle, and confines its own wavefunction inside a cavity about 2 nm in radius, called an electron bubble. Its interaction with the topological excitations in superfluid helium, namely, quantized vortices, has been a particularly attractive topic for several decades. The combination of a single electron and macroscopic condensed helium serves as a unique model system for us to study many fundamental questions on the border between classical and quantum mechanics. We first report our experiment on imaging single-electron bubble motion. Specifically, we used a strong enough planar transducer to expand electron bubbles to micron size in a large volume of the cell and trace their motion with a strong light source and a sensitive camera. A theoretical analysis on the origin of the electrons in helium due to cosmic rays is presented and some striking pictures showing bubble-vortex interactions are given. We then report our experiment on imaging micron-sized particle motion. We discuss the drag forces and the acoustic radiation forces in liquid helium and their actions on small particles. We show our observations of some particles very likely to be trapped and moving on quantized vortices, and some other objects exhibiting rather strange motions. Next, we introduce our time-dependent density functional simulations on single-electron bubbles. We display in the picosecond timescale how a fast-moving electron bubble experiences vortex nucleation and phonon radiation, and how an optically excited electron bubble undergoes shape distortion and fission at different pressures. Finally, we introduce our finite-element simulations on multi-electron bubbles, which are unique but fairly classical objects in liquid helium. We find that they are unstable at rest but can be stabilized by the Bernoulli pressure from the liquid if they are moving."], "keyword": ["electron bubble", "quantized vortex", "superfluid helium"], "primary_title": "Studies of Electron Bubbles and Quantized Vortices in Superfluid Helium-4", "uri": "https://repository.library.brown.edu/studio/item/bdr:297710/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:297710/"}, {"pid": "bdr:297711", "object_type": "pdf", "abstract": ["We systematically studied the spin-dependent transport and electrical noise characteristics of MgO-based magnetic tunnel junctions (MTJs). Utilizing the coherent tunneling effect in the MgO tunnel barrier, we have successfully fabricated MTJ devices with large tunneling magnetoresistance (TMR) ratios. To explore the magnetization properties of these devices at a fundamental level, we first investigated the magnetization dynamics of sputtered CoFeB thin films used as the free layers in MgO-based MTJ stacks by a broad-band FMR spectrometer. Then we presented a new method for estimating the magnetic anisotropy dispersion in MTJ arrays in serial configurations, using the simulated field sensitivity maps. Based on a revised Stoner-Wohlfarth model, we were able to assign dispersion parameters to an actual MTJ array with arbitrary magnetic attributes such as TMR ratio, coercivity and hysteresis loops. As a result of our work, the field sensitivity of an MTJ array was found to be inversely correlated to its anisotropy dispersion and magnetic coercivity.<br/> <br/> In the second part, we focused on the noise properties of MTJ systems. At low frequencies, the flicker noise was measured in two distinct MTJ arrays: MTJ Wheatstone bridges and MTJ discrete resistors, each in their own serial arrays. For MTJ bridges, the statistical dispersion in device resistance and normalized voltage noise were attributed to the greater-than-expected magnetization noise, whereas magnetic coupling among tightly-packed MTJ elements was found to amplify the magnetic fluctuations in the MTJ discrete resistors. Finally, high frequency shot noise measurements were carried out to study the spin-dependent charge transport in MTJ systems. The normalized shot noise, or Fano factor, exhibited a sinusoidal-like variation with a continuous change in the relative orientation between the magnetization vectors of MTJ free and reference layers. We explained the noise behavior with a model of sequential tunneling in the spin-blockade regime, in which the faster transport of majority spin electrons in tunnel barriers is modulated by the slower tunneling of minority spin electrons."], "keyword": ["magnetic tunnel junctions", "spintronic devices"], "primary_title": "Noise and Spin-dependent Transport in MgO-based Magnetic Tunnel Junctions", "uri": "https://repository.library.brown.edu/studio/item/bdr:297711/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:297711/"}, {"pid": "bdr:297718", "object_type": "pdf", "abstract": ["Several aspects of transport in fractional quantum Hall (FQH) systems are investigated. The focus is on the FQH system at filling factor 5/2, which is expected to host non-Abelian anyons.<br/><br/> <br/><br/> We study interferometry signatures of the anyonic statistics in the 5/2 state. It has been shown that non-Abelian states and the Abelian 331 states may have identical signatures in Fabry-Perot interferometry in the 5/2 FQH system. We study a Mach-Zehnder interferometer and demonstrate that current and shot noise measurements are able to distinguish the 331 states from the non-Abelian counterparts. We find that the flux-dependent Fano factor has the maximal value of 2*1.4e for the 331 state with flavor symmetry. Without such symmetry, the Fano factor can reach 2*2.3e. On the other hand, for the Pfaffian and anti-Pfaffian states the maximal Fano factor is 2*3.2e.<br/><br/> <br/><br/> We also systematically study the transport properties of long line junctions between a 5/2 FQH liquid and (i) another 5/2 liquid, (ii) an integer quantum Hall liquid, and (iii) a quantum wire. We study six candidates -- two Abelian and four non-Abelian -- for the 5/2 FQH effect. This momentum-resolved tunneling provides information about the number, propagation directions, and other features of the edge modes and thus helps distinguish several competing models of the 5/2 state.<br/><br/> <br/><br/> In the final section of the thesis, we derive a fluctuation-dissipation theorem (FDT) for a general chiral system in a non-equilibrium steady state. We consider a three-terminal system with a chiral edge channel connecting the source and drain terminals. We prove that the cross noise between the currents of the chiral edge and the third terminal is related to the differential conductance of the third terminal. The relation has the same structure as the equilibrium FDT with the nonlinear response in place of the linear conductance. The result can be useful for detecting ''upstream'' modes on quantum Hall edges. We also derive a FDT for heat and charge currents in multi-terminal setups."], "keyword": ["fractional quantum Hall effect", "Mach-Zehnder interferometry", "transport in mesoscopic systems", "non-equilibrium fluctuation-dissipation theorem", "Anyons", "Chirality"], "primary_title": "Transport in Quantum Hall Systems: Probing Anyons and Edge Physics", "uri": "https://repository.library.brown.edu/studio/item/bdr:297718/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:297718/"}, {"pid": "bdr:297719", "object_type": "pdf", "abstract": ["We present an experimental study of the driven diffusion of colloids and DNA inside a micro-channel, and interstitials in two-dimensional colloid crystal. Photo-lithography and soft-lithography were used to fabricate micrometer-sized patterns on substrates and cover stamps. Fluorescent microscopy, video microscopy and particle tracking algorithms were used for analyzing the dynamics of colloids, dyed DNA inside a channel, and defect dynamics in two-dimensional colloid crystals.<br/> In the first part, we measured first-passage-time distribution of colloids confined in a quasi-one dimensional channel driven by electro-osmotic flow. In 1915, Schr\u00f6dinger derived an exact solution for the first-passage-time distribution of a system undergoing simple biased Brownian motion, which has not yet been verified experimentally. We tested his solution under different electric fields, and observed Taylor dispersion of the effective diffusion coefficient due to the finite size effect of Debye layers in micro-channels.<br/> We also studied driven diffusion of lambda DNA inside a micro-channel. The characteristic lengths and the drag coefficients of DNA follow different scaling laws in different confinement regimes. We prepared two channels of different heights and observed the microscopic conformations of electrically driven DNA using fluorescent microscopy. Although we observed periodic changes from compact coil to stretched conformations of DNA in 150nm deep channels, we did not observe this effect in 300nm deep channels. We also verified that the fluctuation of the elongated length is caused by the electro-osmotic flow near the wall.<br/> Finally, we studied the diffusion dynamics of defects in a two-dimensional colloid crystal. Point defects play a crucial role in defining the melting processes and the mechanical properties of a crystal, but microscopic mechanisms of interstitial and vacancy diffusion are not fully understood. We studied the diffusion dynamics of interstitials by Delaunay triangulation and topological description of disclination configurations. We observed that interstitials diffuse faster than vacancies and that mono-interstitials behave more like a two-dimensional random walker, while di-interstitials have strong memory effects."], "keyword": ["interstitials", "defects", "micro-channel", "DNA", "Colloids", "Abnormalities, Human"], "primary_title": "Transport of charged colloids and DNA in micro-channels", "uri": "https://repository.library.brown.edu/studio/item/bdr:297719/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:297719/"}, {"pid": "bdr:320525", "object_type": "pdf", "abstract": ["Membranes self-assembled from rod-like molecules in aqueous suspension have attracted much attention recently. Depletion force is the key factor to make the molecules self-assemble. The membranes formed can appear in nematic and smectic-\\textit{A} phase when the concentration of the molecules themselves and the concentration of the depletant in the solution are tuned. The latter is effectively varying the strength of the depletion force. Inside the smectic-\\textit{A} phase, different shapes of the membranes are observed as flat disks, twisted ribbons and 'cookie disks'. The major goal of this work is to establish a theory to explain the appearance of these shapes, discuss their relative stabilities and study the phase transitions. In order to achieve this goal, the model free energy of the monolayer is written down by adding two parts together. The first of which is the de Gennes free energy describing the phase transition between nematic and smectic-\\textit{A} phases and the cost of deformation in the director field. The second is the Helfrich free energy related to the curvature of the membranes. The model is applied to different shapes of the membranes and the corresponding Euler-Lagrange equations are solved either analytically or numerically. The numerical methods used include a partial differential equation solver in MATLAB and a Monte Carlo (MC) method. Good results are obtained about the relative stabilities of the flat disks, twisted ribbons and 'cookie disks'. First order phase transitions are found to lie between the flat disks and twisted ribbons when the molecules are chiral and also between the flat disks and 'cookie disks' when the molecules are of opposite chiralities are mixed, which effectively makes the membrane achiral. Our theoretical results qualitatively agree with the experimental observations."], "keyword": ["smectic-A", "monolayer membrane", "fd virus", "de Gennes free energy", "Helfrich free energy", "Frank free energy", "Monte Carlo", "Monte Carlo method", "Phase diagrams"], "primary_title": "Theoretical and Numerical Studies of Entropy-Driven Self-Assembled Smectic-\\textit{A} Monolayer Membranes", "uri": "https://repository.library.brown.edu/studio/item/bdr:320525/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:320525/"}, {"pid": "bdr:297707", "object_type": "pdf", "abstract": ["The top quark is the heaviest of the six observed quarks in the Standard Model (SM). Its mass is more than an order of magnitude greater than any other SM fermion, and hence a precise measurement of this mass provides constraints on the Higgs boson and many other hypothetical particles. In this analysis, we measure the mass of the top quark using the 36 pb-1 of data collected by the CMS experiment from the collisions of the LHC at \u221as = 7 TeV center-of-mass energy during the year 2010.<br/> <br/> At the LHC, top-antitop quark pairs are expected to be produced predominantly through gluon fusion and decay almost exclusively to two W bosons and a bottom-antibottom quark pair. We consider a W boson decay leptonic if it results in a muon or an electron and label the decay channel based on the number of leptonic W decays. Here, we report on the measurement of the mass of the top quark in the dilepton channel.<br/> <br/> The dilepton final state consists of two jets originating from the bottom quarks, two charged leptons and two neutrinos. The latter are not visible to our detector, which results in six unknown parameters. Five of these can be solved for using constraints arising from transverse momentum conservation, the mass of the W boson and the equality of masses of the top and antitop quarks. To deal with the under-constrained system, we use the Analytical Matrix Weighting Technique. This method iterates over many values of the top quark mass and analytically solves the system using the top quark mass as the missing constraint. Each value of the mass is given a weight based on the kinematics of top quark production and decay. The mass estimator for each event is the value with the highest weight and the mass of the top quark is extracted from these estimators by performing a maximum likelihood fit to simulated templates constructed for various masses. The measured value of the top quark mass from this analysis is mt = 175.8 \u00b1 4.9 (stat) \u00b1 4.5 (syst) GeV/c2."], "keyword": ["CMS", "LHC", "Top Quark"], "primary_title": "Measurement of the Top Quark Mass in the Dilepton Channel at the CMS Experiment", "uri": "https://repository.library.brown.edu/studio/item/bdr:297707/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:297707/"}, {"pid": "bdr:297708", "object_type": "pdf", "abstract": ["The Ludwig-Soret effect, also known as thermal diffusion, refers to the separation of mixtures in a temperature gradient. Thermal diffusion is governed by a pair of coupled differential equations which reduce to a nonlinear partial differential equation when the temperature profile is specified. Here two solutions are given to the partial differential equation describing thermal diffusion in a linear temperature field where the components are constrained in space. The first solution considers thermal diffusion without the effects of mass diffusion and shows the underlying motion of the components of the mixture to be that of shock waves. The second solution is an exact solution of the Ludwig-Soret equation that includes both the effect of the thermal gradient and mass diffusion. An additional solution is found for the problem of thermal diffusion in unbounded space. A new experimental method was developed to monitor distributions of components of the mixture in a linear temperature field based on probing a cell containing fluorescent nanoparticles with a confocal microscope. The nanoparticles were chemically synthesized and labeled with a fluorophore that absorbed 488 nm radiation and fluoresced at a 520 nm peak. The temperature gradient in the cell was generated by cooling one surface of the cell, a sapphire plate, with flowing water and electrically heating the other surface, which was an indium tin oxide coated glass plate. The dynamics of the separation of the mixture was recorded by monitoring fluorescence from the particles with the scanning confocal microscope. Data were fitted to a new numerical solution to the full partial differential equation for thermal diffusion with mass diffusion included. The method developed here is shown to provide Soret parameters, including the thermal diffusion factor and the Soret coefficient, based on either a single recording of the terminal density fraction profile, or by fitting the density profile at several times with the results of numerical integration. Ultrasonic distillation was investigated. Experiments were carried out to verify the recently reported, perfect separation of ethanol from water by ultrasonic distillation. Ultrasonic distillation refers to the application of intense ultrasound to a liquid resulting in the formation of an ultrasonic fountain that generates both mist and vapor. Here, the composition of the vapor and aerosol above an ultrasonic fountain was determined as a function of irradiation time and compared with the results of sparging for five different solutions. The experimental apparatus for determining the efficiency of separation consists of a glass vessel containing a piezoelectric transducer driven at either 1.65 or 2.40 MHz. Dry nitrogen was passed over the ultrasonic fountain to remove the vapor and aerosol. The composition of the liquid solutions remaining in the apparatus were recorded following irradiation using gas chromatography, refractive index measurement, nuclear magnetic resonance, or spectrophotometry as diagnostics for the concentrations of the components of the mixtures. Experiments were carried out with ethanol-water and ethyl acetate-ethanol solutions, cobalt chloride in water, colloidal silica, and colloidal gold. The data show that ultrasonic distillation produces separations that are somewhat less complete than what is obtained using sparging. No evidence for the perfect separation of ethanol from water-ethanol mixtures was found."], "keyword": ["Thermal Diffusion", "a linear temperature field", "Shock waves"], "primary_title": "Thermal Diffusion Shock Waves in a Linear Temperature Field and Comparison of Ultrasonic Distillation to Sparging of Liquid Mixtures", "uri": "https://repository.library.brown.edu/studio/item/bdr:297708/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:297708/"}, {"pid": "bdr:297704", "object_type": "pdf", "abstract": ["The vortex matter in type-II superconductors continues to be a subject of great fascination in condensed matter physics. A longstanding theoretical and experimental problem is the identification of the ground state of the vortex lines in the presence of quenched atomic disorder which acts as random pinning centers. A possible edge contamination model has been proposed as a mechanism behind the seemingly contradictory experimental results for the ordered state of matter. This model could also explain the lack of universality for the peak effect behavior exhibited in samples with otherwise similar phase diagrams. Using a novel neutron diffraction technique, we report structural evidence for this edge contamination mechanism. This high-resolution method is used to study the fine structure of the vortex matter in a niobium crystal with a weak peak effect and a disordered zero-field-cooled vortex matter. We find this disordered state is metastable and that it can be restructured through a thermal cycling procedure. The results are explained in a strained lattice framework. We then perform Reverse Monte Carlo Refinements on our neutron scattering data and the possible vortex structures for our crystal agree with experimental results from an approach that combines spatial information with reciprocal space scattering. Having confirmed the existence of an edge contamination mechanism in this sample, we oxidize the surface in order to reduce the impact of the inhomogeneous surface barrier. By repeating our neutron diffraction measurements, we find that oxidation process has smoothed the magnetic field profile through the sample and improves the overall structural order of the zero-field-cooled vortex matter. On the other hand, the field-cooled vortex matter structure should be independent of any edge contamination effect but surprisingly, this scattering intensity in fact doubles after surface oxidation. This result suggests that there is another source of disorder in the niobium crystal that has been affected. We discuss our results in the context of the peak effect and Bragg glass models."], "keyword": ["vortex phyiscs", "neutron scattering", "Type II superconductors", "flux line lattice", "Niobium", "Neutrons--Scattering", "Superconductivity", "Superconductors, Type II"], "primary_title": "The Crystallography of Vortex Matter in a Niobium Crystal", "uri": "https://repository.library.brown.edu/studio/item/bdr:297704/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:297704/"}, {"pid": "bdr:297705", "object_type": "pdf", "abstract": ["In condensed matter physics the vortex lattice of type-II superconductors provides a prototype for studying the effect of random pinning on elastic systems. One important problem is to understand the structural transition from a theoretically predicted ordered Bragg glass phase to a disordered vortex liquid phase. Defects, such as screw dislocations, should play an important role in mediating this order-disorder transition. It is important to confirm the existence of these defect structures in the vortex lattice. Experimentally it is difficult to probe the detailed defect structures inside the vortex lattice. Traditional methods can only provide information on the surface configuration or an averaged picture of the bulk behavior of the vortex lattice. Here we use a novel high-resolution neutron diffraction technique to probe the angular orientation of the lattice planes as the flux lines traverse the atomic crystal. Our results provide structural evidence for screw dislocations inside the vortex lattice. The anisotropic defect structure in the underlying atomic lattice serves as a symmetry breaking field for the vortex lattice. The strong dependence of the vortex lattice structure on the growth procedure reveals that the system is metastable and can be perturbed through thermal cycling to a possible ground state. We measure the structure of the vortex lattice under different applied magnetic fields and temperatures to study the interplay between vortex-vortex interaction, vortex-atomic lattice interaction, and thermal fluctuations. This high-resolution neutron diffraction technique opens up a new way in studying the detailed structure of the vortex lattice. Our results suggest that the vortex lattice in low temperature superconductors with anisotropic defects in the atomic lattice could be an excellent candidate for exploring the entangled flux liquid phase."], "keyword": ["neutron diffraction", "vortex lattice", "screw dislocation", "Neutrons--Diffraction"], "primary_title": "3D Neutron Diffraction Studies on the Vortex Lattice", "uri": "https://repository.library.brown.edu/studio/item/bdr:297705/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:297705/"}, {"pid": "bdr:297715", "object_type": "pdf", "abstract": ["The Universe is expanding at an ever increasing rate. The mysterious source of this acceleration has been dubbed \"dark energy\" and constitutes 70% of the energy-density of the Universe. To understand the nature of this force we must measure the expansion of the universe and the growth of structure with significant precision. Clusters of galaxies are the most massive gravitationally-collapsed structures in the universe and offer an ideal probe of the growth and evolution of structure. Numerous methods for detecting and measuring cluster masses exist including X-ray flux, spectroscopic redshift, and weak gravitational lensing measurements. Weak lensing is the coherent distortion of galaxy images by intervening mass and is used as an unbiased indicator of the mass of galaxy clusters. The accuracy of each of these methods for measuring clusters masses will depend in part on the accuracy of weak lensing measurements, which will be used both as a mass calibration technique and a detection technique. It is therefore critical that we understand the factors affecting weak lensing sensitivity and the correspondence to other mass measurement techniques.<br/> Orthogonal Transfer (OT) Imagers offer significant advantages for weak lensing measurements. By correcting atmospheric distortions using real-time guide-star position information and shifting charge across the CCD they can increase the number of detected galaxies and increase the signal-to-noise of weak lensing detections. One outstanding question has been whether the charge-shifting correction induces unwanted systematic effects in weak lensing measurements. I study the systematic effects from OT guiding using stellar observations and show that the magnitude of the improvement to image quality far exceed the magnitude of any possible systematic effects. <br/> I demonstrate the utility of OT imagers for weak lensing by detecting the cluster Abell 781A using the Orthogonal Parallel Transfer Imaging Camera. I use this data to measure the sensitivity of weak lensing detections and the significant discrepancy between mass estimates of Abell 781D.<br/> Finally, I show that OT imagers can also be used to probe atmospheric conditions during observations, informing our choice of observing strategy and further illustrating the facility of OT guiding."], "keyword": ["Weak Lensing", "Clusters of Galaxies", "Orthogonal Transfer Imagers", "Galaxies--Clusters"], "primary_title": "Measuring Weak Lensing Sensitivity and Systematics", "uri": "https://repository.library.brown.edu/studio/item/bdr:297715/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:297715/"}, {"pid": "bdr:320462", "object_type": "pdf", "abstract": ["The superconductor-insulator transition (SIT) is a well-known phenomenon that is observed in many types of superconducting systems, including elemental films and high Tc superconductors. Ultrathin films provide a versatile platform from which to study this ubiquitous, and possibly universal, transition. Two different theoretical approaches have been made to describe the SIT in thin films. The first predicts that Cooper pairs (CPs) exist in the insulating phase, and the second proposes that the transition is driven by pair-breaking, yielding an insulator of localized single electrons. <br/><br/> <br/><br/> Recent experiments showing the existence of an insulating phase of localized CPs have provided significant support for the first mechanism. This CP insulating (CPI) phase exhibits dramatic transport features including a giant magnetoresistance (MR) peak. Previous work in the Valles lab found such a phase in ultrathin amorphous Bi films quench-condensed onto a substrate with a nanohoneycomb (NHC) hole array. The local Cooper pairing correlations of the CPI phase were evident from Little-Parks-like MR oscillations due to the hole array. <br/><br/> <br/><br/> This thesis describes investigations of the mechanism for CP localization and the emergence of the CPI phase in NHC films. There are three main results. First, the CPI phase appears to be induced in NHC films by the undulating surface of the substrate, which produces regular spatial variations in thickness that give rise to nanoscale CP islands. Second, the giant positive MR characteristic of the CPI phase emerges with increasing film thickness simultaneously with the MR oscillation signal, associated with local CP phase coherence. The insulating phases of the thinnest films and films in magnetic fields just beyond the MR peak likely consist of CPs totally localized to their islands. Third, amorphous holey films of uniform thickness do not exhibit a CPI phase. These films go from superconductors directly to fermionic insulators with decreasing thickness. These results lend further insight to the nature of the CPI phase and also require at least two classes of SITs: one that can describe the presence of a CPI phase and one that can describe a transition from a superconductor to a fermionic insulator.<br/><br/>"], "keyword": ["quantum phase transition", "superconductor to insulator transition", "transport in two-dimensional thin films", "nanoscale superconducting inhomogeneities", "Superconductivity"], "primary_title": "Cooper Pair Localization in Thin Films near the Superconductor-Insulator Transition", "uri": "https://repository.library.brown.edu/studio/item/bdr:320462/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:320462/"}, {"pid": "bdr:386158", "object_type": "pdf", "abstract": ["We study both analytically and numerically the experimentally observed nonaxisymmetric droplet deformation and orientation in a uniform DC electric field. The theoretical model shows that a rotational flow is induced about the droplet above a threshold electric field. As a result, drop shape becomes a general ellipsoid with major axis obliquely oriented to the applied field direction. The small deformation analytical theory is in excellent agreement with the experimental data for high viscosity drops. The numerical simulation for large distortion using boundary integral method has been validated by the 2D analytical theory (Feng (2002))."], "keyword": ["leaky dielectrics", "charge convection", "Electrohydrodynamics", "Drops"], "primary_title": "Electrorotation of a viscous droplet in a uniform direct current electric field", "uri": "https://repository.library.brown.edu/studio/item/bdr:386158/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:386158/"}, {"pid": "bdr:386188", "object_type": "pdf", "abstract": ["Nanopores can be used as sensors to probe the structure of single polymers. In a typical experiment, a thin insulating membrane containing a nanometer-scale pore separates two reservoirs of electrolyte solution. The nanopore acts as an ionic channel, permitting a current of ions to flow between the reservoirs when a voltage bias is applied to them. The presence of a single polymer inside the nanopore causes a change in the current, which is the basis of the sensing mechanism. Previous studies have quantified the dynamics of DNA molecules passing through the nanopore by electrophoresis, and examined the time course of the current to infer the physical structure of translocating polymers. In this thesis, we enhanced the ability of nanopores to study single molecules and to realize biosensing applications by juxtaposing a solid-state nanopore with a micrometer-sized cavity with a sub-micrometer opening in it. We used this newly created structure to investigate the origin of the viscous drag on DNA during translocations, and to characterize the same DNA molecule before and after it underwent a chemical reaction while entropically trapped inside the cavity. First, we describe studies of electrophoretic DNA translocations of asymmetric nanopore-cavity structures whose dimensions were designed to control the initial configurations of the DNA molecules. The structures comprise a thin SiN membrane with a nanopore that leads into a 400 nm-high cavity, which is in turn covered by a 400 nm- thick SiN membrane with a circular opening whose diameter was about 200 nm. This structure maintained a gap between the nanopore and a DNA coil translocating from the cavity side, but not one translocating from the nanopore side. The additional viscous drag on the DNA segment extending from the coil to the nanopore slowed translocations from the cavity side to less than half the average speed of translocations from the nanopore side. The speeds converged as the opening enlarged from 200 nm to micrometer diameters. That result can be explained by the DNA coil, whose radius of gyration is Rg=0.73 um, squeezing further into the opening. Our experimental results compare favorably with a quantitative model of DNA translocation speeds, similar to models by Grosberg and by Ikonen, which account for the initial configuration of the DNA coil. Next, we used the nanopore-cavity structures to enable analyses of the same DNA molecule before and after chemical interactions modified its structure. We used 1.5 um high cavities as cages which entropically trap single molecules next to a nanopore, despite the presence of a few-hundred-nanometer-wide opening. We probed the dynamics of DNA molecules inside the cage by electrically driving them in through the nanopore, removing the driving force for preset pause times, and then driving them back out through the nanopore. The saturating recapture time and high recapture probability after long pauses, their agreement with a convection-diffusion model, and the observation of trapped DNA under fluorescence microscopy all confirmed that the cage stably confines DNA. At the same time, entropic cages remained permeable to small molecules. To demonstrate these capabilities, we used a restriction endonuclease to sequence-specifically cut trapped DNA molecules into fragments whose number and sizes were analyzed upon exiting through the nanopore. The work presented in this thesis illustrates new and useful ways in which entropic cages can control a single DNA molecule before or after it translocates a nanopore."], "keyword": ["Single molecular test tube", "Nanopores", "DNA", "Nanotechnology"], "primary_title": "The Use of Entropic Cages For Trapping DNA and Controlling its Configurations in Nanopore Studies", "uri": "https://repository.library.brown.edu/studio/item/bdr:386188/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:386188/"}, {"pid": "bdr:386127", "object_type": "pdf", "abstract": ["As the CMOS downscaling continues, the requirements for lower power supply voltage and power consumption become more stringent. New device operating principles and new material platforms are being explored. Among them, band to band tunneling and vapor-liquid-solid grown semiconductor hetero-nanowires (hetero-NWs) are promising candidates as a new device operating principle and a new material platform for future high-performance switching devices, respectively. This thesis focuses on exploring the possibility of utilizing Ge and SiGe nanowires for tunneling field effect transistors (TFETs). Similar SiGe hetero-NW material is also studied for photovoltaic applications. First, we explore Ge NWs, where strong back-gate modulation of band-to-band tunneling in the axial p-n junction was characterized and modeled. Top-gated Ge NW TFETs shows promisingly high ION~20 \u03bcA/\u03bcm current with the possibility of achieving better subthreshold slope and ION/IOFF current ratio by improved surface passivation. Second, axial SiGe hetero-NW TFETs with ~50 mV/decade subthreshold slope were grown, fabricated, characterized and confirmed by 3D TCAD simulation. These devices exhibited record Si-compatible TFET performance, with high ION ~2 \u00b5A/\u03bcm and ~5 orders of magnitude ION/IOFF ratio. The same devices could be operated in standard NW FET mode with good performance. Finally, we explore the possibility of employing axial p-i-n/p-i-n junction SiGe hetero-NWs as broad-spectrum tandem solar cells. Preliminary numerical and experimental studies were carried out for axial p-i-n Si NWs, axial p-n Ge NWs, and axial p-i-n/p-i-n SiGe hetero-NWs to characterize device performance. The thesis concludes with future directions, including the possibility of a novel SiGe hetero-NW electroluminescent optical source."], "keyword": ["Germanium nanowire", "SiGe hetero-nanowire", "tunneling FET", "nanowire solar cell", "nanowire optical source"], "primary_title": "GERMANIUM AND SIGE NANOWIRE TUNNELING TRANSISTORS AND SOLAR CELLS,", "uri": "https://repository.library.brown.edu/studio/item/bdr:386127/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:386127/"}, {"pid": "bdr:386173", "object_type": "pdf", "abstract": ["The detection of the primordial B-mode spectrum of the polarized cosmic microwave background (CMB) signal may provide a probe for inflation. However, the B-mode signal is orders of magnitude weaker than the temperature and E-mode signals. Observation of such faint signals requires excellent control of systematic errors. Interferometers may have certain advantages over imaging experiments in the control of systematic effects. Current and future high resolution cosmology observations, such as those that will be carried out by the QU Bolometric Interferometer for Cosmology (QUBIC), require computationally efficient data analysis techniques. Since the observed CMB signal can be interpreted as a single realization of a random process, CMB data is most suitably analyzed in a Bayesian, rather than frequentist, approach. In comparison to alternative methods of extracting power spectra, such as maximum likelihood and pseudo-Cl estimators, the method of Gibbs sampling has the advantage of providing simultaneous inference of power spectrum and signal with similar computational complexity. We demonstrate the application of Gibbs sampling to realistic interferometric observations, including an incomplete uv-coverage, finite beam size and baseline-dependent noise, of polarized signals. We present a complete simulation pipeline of interferometric observations of the CMB polarization to understand the effects of systematic errors. A realistic, QUBIC-like interferometer design is simulated with systematics that incorporate the effects of sky rotation. Several types of systematic errors are considered including antenna pointing, gain and coupling errors as well as beam cross-polarization and shape errors. The simulated data sets are analyzed by both the maximum likelihood method and the method of Gibbs sampling. The results from both methods have been found to be consistent with each other, as well as with the analytical estimations. Our simulations determine the required levels of control of systematic effects for a QUBIC-like interferometer, which targets the B-mode polarization signal. We show that the method of Gibbs sampling naturally extends to include a Bayesian foreground separation technique. We also demonstrate that the method can be further generalized to 3D power spectrum inference from interferometric data of the redshifted 21 cm HI line."], "keyword": ["bayesian analysis", "Cosmic background radiation", "Interferometers", "Bayesian statistical decision theory", "Polarimetry"], "primary_title": "BAYESIAN ANALYSIS OF SYSTEMATIC EFFECTS IN INTERFEROMETRIC OBSERVATIONS OF THE COSMIC MICROWAVE BACKGROUND POLARIZATION", "uri": "https://repository.library.brown.edu/studio/item/bdr:386173/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:386173/"}, {"pid": "bdr:386273", "object_type": "pdf", "abstract": ["A nanopore detector is a voltage-biased nanometer-scale hole in a thin insulating membrane that can sense the threading of individual charged biopolymers, such as DNA, via partial blockages of the ionic current through the nanopore. Besides having the ability to detect a single DNA molecule, its size also compels a naturally coiled DNA molecule to go linearly through, end-to-end. Previous studies have found that the end-to-end translocation time of DNA through nanopores scales super-linearly with its length, which indicates that nanopores are sensitive to the DNA coil outside the nanopore. Here we describe studies that probe the configuration and size of DNA coils, performed using 10 nm-wide solid state nanopores. In the first, we study the statistics of 16.5 um-long lambda DNA threading through a nanopore which allows a DNA molecule to go through in a straight as well as a folded configuration. The resulting ionic current signal indicates where along its length the DNA was captured. We find a strong bias favoring the capture of molecules near their ends. A theoretical model shows that bias to be a consequence of configurational entropy, rather than a search by the polymer for an energetically favorable configuration. In this study we also quantified the fluctuations and length-dependence of the speed of simultaneously translocating polymer segments from our study of folded DNA configurations. In the second, we characterize the relaxation of lambda DNA following a translocation through a solid-state nanopore using the delayed capture and re-capture technique, also called molecular ping-pong. In DNA ping-pong, a single molecule is shuffled back and forth through the nanopore by reversing the applied voltage after each translocation. The fast translocation process drives DNA into a compressed, out-of-equilibrium state and subsequent recapture enables a quantification of its relaxation via the current blockade signal. The recaptured molecules are observed to translocate faster, which is explained by the reduced viscous drag on a compact coil. Experimental evidence supports a simple relaxation model of DNA which is also consistent with our translocation speed measurements."], "keyword": ["solid-state nanopore", "DNA translocation", "DNA dynamics", "Polymer networks"], "primary_title": "The Statistics of DNA Capture and Re-Capture by a Solid-State Nanopore", "uri": "https://repository.library.brown.edu/studio/item/bdr:386273/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:386273/"}, {"pid": "bdr:386139", "object_type": "pdf", "abstract": ["The existence of non-baryonic cold dark matter is well established through a wealth of complementary observations such as the Cosmic Microwave Background, Supernova Type Ia and Big Bang Nucleosynthesis. Despite the overwhelming cosmological evidence, the particle nature of dark matter remains unknown. The leading candidate is a Weakly Interacting Massive Particle (WIMP), a thermal relic from the Big Bang that only interacts through the gravitational and weak forces. A terrestrial detector with high target mass, low background levels and a low energy threshold (keV) should be able to record the rare, faint interactions between ordinary matter and galactic WIMP dark matter. The Large Underground Xenon (LUX) experiment is a 370 kg liquid xenon time projection chamber that aims to detect WIMP recoils with xenon nuclei. The experiment is located a mile underground at the Sanford Underground Research Facility (SURF) in Lead, South Dakota. LUX is poised to become the world's most sensitive dark matter detector after only 2 weeks of exposure and will surpass current detection limits by an order of magnitude after 300 days. The LUX experimental program consists of three phases: (1) the LUX0.1 prototype detector during 2007\u2013 2009, (2) the commissioning and operation of the LUX detector at the Sanford surface laboratory during 2009\u20132012 and (3) the underground deployment and operation of the detector beginning in 2012. This thesis describes the first two phases of the LUX program. LUX utilizes 122 Hamamatsu R8778 photomultiplier tubes (PMTs) to detect photons produced by particle interactions in liquid xenon. The LUX PMT mounting, high voltage distribution, analog signal shaping and gain calibration system are described in detail. The PMTs are shown to have low radioactive background levels, single-photon sensitivity and a 30% photon detection efficiency at the 175 nm liquid xenon scintillation wavelength. Handling protocols and vacuum integrity control based on ion-initiated afterpulses are presented. Xenon purification and energy calibration results are described for LUX0.1. During the LUX surface run, light collection and statistical position resolution measurements were obtained. Additionally, the xenon circulation path was imaged with alpha particles from a Rn222 injection."], "keyword": ["LUX", "LUX0.1", "WIMP", "dark matter", "liquid xenon", "time-projection chamber", "TPC", "photomultiplier tube", "PMT", "Dark matter (Astronomy)", "Time projection chambers (Nuclear physics)"], "primary_title": "Prototype, Surface Commissioning and Photomultiplier Tube Characterization for the Large Underground Xenon (LUX) Direct Dark Matter Search Experiment", "uri": "https://repository.library.brown.edu/studio/item/bdr:386139/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:386139/"}, {"pid": "bdr:386123", "object_type": "pdf", "abstract": ["Abstract of \u201cEpitaxial growth of SiC/AlN and Si quantum dot heterostructures by molecular beam epitaxy,\u201d by Yana Cheng, Ph.D., Brown University, May 2014 SiC has been widely studied as a template for growing graphene, which is a truly 2D material that has drawn much research attention in the past decade. Due to its incompatibility with Si CMOS processing, the bulk SiC substrate may hamper the integration of graphene into practical Si technology. The conductivity of commercially available SiC substrates makes it difficult to investigate the electronic properties of graphene separately from this substrate. Thus, a novel synthesis pathway based on a SiC/AlN/Si (111) heterostructure may overcome these obstacles in the established route. In this work, growth of SiC/AlN heterostructures has been achieved by molecular beam epitaxy at 700 \u00b0C. The optimal growth conditions for AlN yield a fairly smooth surface with root-mean-square roughness of 6 \u00c5 in a 1-\u03bcm2 scanning area. Microstructural analysis confirms the wurtzite structure of AlN with the growth alignment of AlN[0001]//Si[111]. The microstructure and composition analysis of the SiC films produced by solid-source MBE suggest a faulted stacking sequence instead of a single polytype. The low fluxes from the solid source give a growth rate of 10 nm per hour for SiC. The synthesis of Si dots on AlN/Si (111) achieves for the first time a goal that has been difficult for MBE: creation of epitaxial Si dots in an insulating matrix. The occurrence of a high density of small dots at low Si coverage, followed by a reduced density and increased dot size at higher coverage, is consistent with existing understanding of equilibrium island size in a high-mismatch system. The epitaxial orientations of the Si dots are identified as either identical, or 180\u00b0 rotated around the surface normal, compared to the orientation of the AlN relative to the Si substrate. A new route to graphene synthesis by resonant laser direct writing on SiC has been investigated. The resonant conditions for both prism and grating couplers have been studied by simulations. The prism coupler configuration yields fairly good experimental results that demonstrate critical coupling."], "keyword": ["molecular beam epitaxy,heterostructures,SiC,Si qunatum dot"], "primary_title": "EPITAXIAL GROWTH OF SiC/AlN AND Si QUANTUM DOT HETEROSTRUCTURES BY MOLECULAR BEAM EPITAXY", "uri": "https://repository.library.brown.edu/studio/item/bdr:386123/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:386123/"}, {"pid": "bdr:419354", "object_type": "pdf", "abstract": ["In recent years, weak gravitational lensing has become an indispensable method for understanding the concentration of matter on the largest scales. Galaxy clusters, the largest virialized structures in the universe, provide a crucial environment in which to examine cosmological evolution. Because most matter is non-luminous, weak lensing provides an opportunity for direct measurement of large scale mass clustering, independent of considerations involving cluster dynamics. This study takes advantage of the large amount of deep and high quality optical imaging freely available from the Subaru Telescope data archive to perform a semi-blind cluster search across an extraordinarily large field of view, 10.34 deg2 of the sky, at high source density (utilizing 1.27 \u00d7 106 galaxies). Our precise 2D mass reconstruction, spanning five low-extinction Milky Way windows, detects 90 unique cluster candidates above S/N\u22653. Of these, 67 possess S/N\u22654, and 18 possess S/N\u22655. From the fields analyzed, 43 independently confirm prior detections, 6 of these match (but with offsets in the location of the cluster barycenter), and the remaining 47 represent potential new cluster discoveries. Previous cluster candidates in these regions were uncovered through non-WL techniques, therefore, our analysis represents a significant contrast against other wide-field cluster search methods, and is one of the largest lensing surveys completed to date. Convergence reconstructions also detect SZ & X-ray cluster candidate PLCKG100.2-30.4 in multiple independent waveband data, but fails to measure the more observationally difficult PLCKG18.7+23.6. We estimate the mass of the former, as well as that of clusters Abell 383, Abell 1672, and RXCJ1651.1+0459. The scale of this project necessitated the invention of numerous automated data reduction algorithms and a comprehensive pipeline optimizing the shape information and object detections of deep-field galaxies in available imaging. Most notably, a novel flux-independent identification system for stars was created in order to find ideal stellar objects necessary for accurate PSF circularization. Our techniques allow us to stack and circularize Subaru images to better than <0.5% mean ellipticity without introducing spurious effects."], "keyword": ["Observational Astronomy", "Weak Gravitational Lensing", "Subaru Telescope", "Galaxy Clusters", "Cosmology", "Astrophysics", "Astronomy", "Galaxies--Clusters"], "primary_title": "Quality-Selected Lensing Analysis of Galaxy Clusters in Subaru Telescope Fields", "uri": "https://repository.library.brown.edu/studio/item/bdr:419354/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:419354/"}, {"pid": "bdr:419371", "object_type": "pdf", "abstract": ["The luminescence of trivalent erbium (Er3+) has been widely used in lasers and optical fiber amplifiers as well as in upconverting materials for bioimaging and photodetectors. However, some fundamental spectroscopic properties of Er3+ are still not fully understood. For example, in recent decades, it has been commonly assumed that the near-infrared emission of Er3+ at 1.5 \u03bcm originates from electric dipole (ED) transitions. As a result, essential consequences of its magnetic dipole (MD) emission have been overlooked, even though such MD emission is theoretically allowed by selection rules. Such oversight may be explained by a lack of direct experimental characterization. Therefore, a thorough study of its magnetic nature may help offer a more complete model with which to optimize the design of Er3+-based devices and may also suggest new ways to engineer light-matter interactions at telecommunication wavelengths. Here, we experimentally explore the magnetic nature of Er3+:Y2O3 light emission near 1.5 \u03bcm. The spectrally-resolved intrinsic ED and MD emission rates are first quantified using energy-momentum spectroscopy. By leveraging the local density of optical states, we can selectively direct the light emission into either ED or MD transitions. Then, using this knowledge of the spectral dependence of MD and ED emission, sub-lifetime modulation of Er3+ emission is realized by optically switching the phase of an adjacent VO2 thin film. Finally, we investigate the ED and MD effects on the spontaneous emission rates of erbium through a systematic lifetime study. We believe that this work supplies consolidated evidence for the current importance and potential significance of magnetic light emission at telecom wavelengths in erbium-based devices."], "keyword": ["Spontaneous Emission", "Modulation", "Erbium", "Magnetic dipoles", "Telecommunication"], "primary_title": "Quantifying and Controlling the Magnetic Dipole Emission of Erbium at Telecom Wavelengths", "uri": "https://repository.library.brown.edu/studio/item/bdr:419371/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:419371/"}, {"pid": "bdr:419361", "object_type": "pdf", "abstract": ["Coherent structures such as large-scale jets and vortices are ubiquitous in natural quasi-two-dimensional (2D) turbulence such as atmospheres. I study statistical approaches to 2D turbulence with the goal of predicting coherent structures from the equations of motion. The approach contrasts with the traditional approach of direct numerical simulation (DNS). First I consider equilibrium statistical mechanics of Euler flows. Coherent structures that form in numerical simulation on the torus and the sphere are compared against the truncated Miller-Robert-Sommeria equilibria where only some of the conservation laws are imposed. The description that conserves energy and enstrophy produces a complete energy condensation to the largest scales, and in the absence of rotation correctly predicts the number and polarity of coherent vortices. Perturbative imposition of the quartic Casimir constraint improves agreement with simulation by sharpening the cores and transferring some energy to smaller-scale modes. Effect of rotation is beyond the conservation of energy and enstrophy. Numerical simulation also shows nonergodicity, limiting the usefulness of equilibrium statistical mechanics. Next I investigate two nonequilibrium statistical mechanical approaches. One is direct statistical simulation implemented by systematic expansion in equal-time cumulants. The approach is illustrated on the sphere by a barotropic model of jet formation. Closures of cumulant evolution equations at second order (CE2) or third order (CE3), or an intermediate closure (CE2.5) may be used. For Euler flows, CE2 and CE2.5 both conserve angular momentum, energy and enstrophy; CE3 further conserves the cubic Casimir. Comparison with DNS shows that CE2 reproduces qualitative features of the zonal jets, and CE2.5 and CE3 further improve quantitative agreement with DNS. In the other approach, Wegner\u2019s flow equation is integrated forward numerically to a fixed point to yield the equal-time steady-state statistics that is encoded in the Hopf functional. It is applied to a system with two degrees of freedom, the Lorenz attractor, and turbulence on the sphere, with some success. The statistical approaches provide new insights into coherent structures and may also bring new tools to lead to a better understanding of astrophysical and geophysical flows."], "keyword": ["two-dimensional turbulence", "geophysical turbulence", "stationary states", "Statistical mechanics", "Computational fluid dynamics"], "primary_title": "Statistical Approaches to Two-Dimensional Turbulence", "uri": "https://repository.library.brown.edu/studio/item/bdr:419361/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:419361/"}, {"pid": "bdr:419363", "object_type": "pdf", "abstract": ["This dissertation is split into two parts with the first focusing on characterizing cell motility, and the second focusing on linking cell motility to cell mechanics. Cellular motility is routinely characterized by parameters such as migration speed, tortuosity, and persistence time. However, measurements of these parameters are not generally reproducible because their numerical values depend on experimental sampling interval and measurement error. In Part 1, we use random walk theory, simulations, and experimental data to address the need for a metric that quantifies the directionality of a migration path in a manner that decouples from technical parameters. We call this novel metric directionality time because it can be interpreted as the minimum observation time required to determine that the migratory motion is directed. Along with measures of migration speed and persistence, we used the directionality time metric to determine the directedness of chemotactic neutrophil migration paths as a function of physiologically relevant substrate stiffnesses and compositions. We find that engagement of the B2-integrin, CR3, is required for the substrate stiffness dependent regulation of neutrophil honing in 2D on fibronectin. In Part 2, we investigate the role of cell mechanics in cell motility. As cells migrate, they exert cytoskeletal driven contractile forces on their environment. Using spring models with stick-slip adhesion, we are able to predict how the mechanical properties and shape of the cell affect its dynamics and traction forces. We then switch the focus back to neutrophils and explore the relationship between neutrophil contractile force, motility, and the biological response modifier B-glucan, a substance that has shown promise as a clinic grade therapeutic. Using live cell imaging and traction force microscopy to measure neutrophil traction forces as a function of substrate stiffness and $\\beta$-glucan concentration, we report that increasing the concentration of B-glucan leads to diminished traction forces. Our findings indicate that biological response modifiers may act through the modulation of cell mechanics and motility. Further, we report an overall inverse correlation between migration speed and mechanical output that is affected by B-glucan. These data will be useful for modeling cell motility."], "keyword": ["cell motility", "cell mechanics", "random walk models", "mechanobiology", "Cells--Motility", "Cells--Mechanical properties"], "primary_title": "The Mechanics of Cell Motility and a Unifying Theory for Characterizing Directed Motion", "uri": "https://repository.library.brown.edu/studio/item/bdr:419363/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:419363/"}, {"pid": "bdr:419386", "object_type": "pdf", "abstract": ["The prefrontal cortex (PFC) is the brain region most strongly associated with many higher cognitive functions such as working memory and decision making. While decades of study have produced a wealth of data about the anatomy and physiology of the PFC, our knowledge of the mechanisms by which the PFC stores, represents and processes information is currently incomplete. Specifically, little is known about the neuronal microcircuits within the PFC that may represent the basic units underlying its various functions. A deeper understanding of the network activity of PFC will likely be critically important for understanding cognition, and for developing therapies for PFC-related disorders such as schizophrenia. The advent of functional imaging has enabled the simultaneous measurement of the activity of large numbers of neighboring neurons, setting the stage for analysis of cortical microcircuits on a spatial scale that is inaccessible by traditional electrophysiological methods. In this thesis, we use calcium imaging in acute brain slices to characterize the dynamics of networks within deep-layer medial PFC. Taking advantage of the brain slice preparation, we use pharmacological agents to manipulate two molecular systems strongly implicated in network activity: NMDA receptors and GABAA receptors. We also present a framework for analyzing the resulting movies. Whereas the majority of neurons show only sporadic activity, a subset of neurons emit spontaneous, delta-band rhythmic activity. Looking beyond the activity of individual neurons, we examine the interactions between neurons. We find that spontaneous activity under baseline conditions is weakly correlated between pairs of neurons, and that rhythmic neurons showed little coherence in their oscillations. However, we consistently observed brief bouts of synchronous activity. Using surrogate data sets, we showed that the degree of correlation and synchrony we observed could not be explained by coincidence, but must be attributed partly to network activity. Finally, we described the effects of NMDA and picrotoxin on these metrics of network dynamics, and discuss possible implications of these results for understanding the neuronal bases of cognition and brain diseases."], "keyword": ["calcium imaging", "spontaneous activity", "NMDA", "synchrony", "delta", "Prefrontal cortex"], "primary_title": "Optical Interrogation of the Spontaneous Dynamics of Prefrontal Cortical Networks", "uri": "https://repository.library.brown.edu/studio/item/bdr:419386/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:419386/"}, {"pid": "bdr:419533", "object_type": "pdf", "abstract": ["A search is performed for pair-produced new particles, either gluinos or massive color octet vector bosons (colorons or axigluons). The data sample, corresponding to an integrated luminosity of 19.7 fb of proton-proton collisions at a center-of-mass energy $\\sqrt{s}$ = 8 TeV, was collected with the CMS experiment at the LHC during 2012. Events with at least eight or ten reconstructed jets are selected, and a counting experiment is performed on the distribution of the scalar sum of transverse momenta of the selected jets. The multijet background is estimated from data events with low jet multiplicity and rescaled to higher jet multiplicities. The data are in good agreement with the multijet QCD background prediction, and upper limits are set on the signal cross section at a 95% confidence level for coloron, axigluon, and gluino models, with the mass exclusions ranging from 0.6 to 1.25 TeV for colorons, 1.15 TeV for axigluons, and 1.05 TeV for gluinos."], "keyword": ["multijet", "BSM", "CMS", "coloron", "axigluon", "RPV SUSY"], "primary_title": "Search for New Physics in 8- and 10-Jet Final States at $\\sqrt{s}$ = 8 TeV with the CMS Experiment", "uri": "https://repository.library.brown.edu/studio/item/bdr:419533/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:419533/"}, {"pid": "bdr:419521", "object_type": "pdf", "abstract": ["Solid-state nanopores are an important class of biosensor that can detect the presence of a macromolecule inside the nanopore by a corresponding blockage in the nanopore's ionic conductance. Applications of nanopores include the detection of DNA binding proteins, the convenient sizing of DNA, and the sequencing of DNA. The promise of these applications cannot be unlocked without a detailed understanding of the basic physics of polymer translocation. This understanding is lacking in some fundamental areas; for instance, we still cannot predict the translocation speed of a given polymer. In this dissertation, we study the translocations of stiff filamentous viruses and compare them to current theoretical models of DNA translocation. We observe both successful translocations and failed collisions between the filamentous virus fd and the nanopore. Successful translocations teach us about the sources of dispersion in translocation speeds. These collision signals allow us to describe the capture process of a stiff filamentous virus by a nanopore. We report translocations of fd and its lower charged mutant M13 over a range of nanopore diameters and salt concentrations. We compare our results to a recently reported electrokinetic model. This electrokinetic model is a straightforward application of the Navier-Stokes equation and the Poisson-Boltzmann equation to a nanopore's geometry. Our observations are qualitatively consistent with this electrokinetic model, but differ from the predictions quantitatively. We introduce a small but significant modification to the conventional model based on the friction between counterions and the polyelectrolyte that allows us to self-consistently describe all of our measurements. A revised model helps us better understand the physics behind a polymer's translocation speed. Surprisingly, we find that the fluctuations in translocation speed of filamentous viruses increase with the applied voltage. We show that this phenomenon is due in part to a dependence of the nanopore's pulling force on the axial position of the virus. The buckling of the trans segment of the virus likely reduces the averaging of variations in the pulling force by axial diffusion. This buckling model accounts for our observations of the dispersion in translocation speed."], "keyword": ["polymer physics", "Nanopores", "Electrokinetics"], "primary_title": "Translocations of Stiff Filamentous Viruses through Solid-State Nanopores", "uri": "https://repository.library.brown.edu/studio/item/bdr:419521/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:419521/"}, {"pid": "bdr:419516", "object_type": "pdf", "abstract": ["The nematic phase transition in Fe-based superconductors (FeSCs) has been a topic under intensive investigation. So far it is commonly accepted that the structural transition from tetragonal (C4) to orthorhombic (C2) symmetry in FeSCs has an electronic nematic origin due to the unusual anisotropy in resistivity, optical conductivity and orbital occupancy observed above the structural transition. However, recent studies of (Ba, Eu)Fe2(As1-xPx)2 by magnetic torque measurements show the existence of a \u201ctrue\u201d nematic transition well above the commonly accepted structural/nematic transition .Controversies about this \u201ctrue\u201d nematic phase transition arise as residue strains or external applied fields are known to break C4 symmetry and render the structural transition merely a crossover. We performed high resolution AC micro-calorimetry and SQUID magnetometry measurements of BaFe2(As1-xPx)2 (x=0, 0.3) to investigate the various phase transitions and to explore the \u201ctrue\u201d nematic phase transition. The advantageous design of our membrane calorimeter allows us to perform high resolution studies of the thermodynamic phase transitions without any symmetry breaking fields. Our results suggest that there is not a second order \u201ctrue\u201d nematic phase transition in BaFe2(As1-xPx)2 even though the Ginzburg-Landau model used to fit the magnetic torque data indicates that the expected thermal anomaly should be within our experimental resolution. In addition to the above, we present specific heat and magnetization studies of Ba1-xNaxFe2As2 in search of the recent discovered emergent reentrant C2 to C4 symmetry SDW transition in this series of compound. Our results indeed locate a new phase transition in Ba0.74Na0.26Fe2As2 at 45K. However, the absence of the conventional SDW transition at around 80K in our data leaves doubt about the exact nature of this new phase transition. We also systematically studied the effects of heavy ion irradiation (HII) on the anisotropy of YBCO single crystals by angular rotation specific heat measurements. We found that the anisotropy of YBCO decreases by approximately a factor of two with an irradiation dose of 6T (matching field). The dependence of anisotropy on irradiation doses agrees well with the prediction from a simple phenomenological model that takes into account the anisotropic scattering caused by columnar defects created in HII."], "keyword": ["Fe-based superconductor", "phase transitions", "Phase transformations (Statistical physics)", "Thermodynamics", "Anisotropy"], "primary_title": "Thermodynamic Studies of Phase Transitions and Emerging Orders in Unconventional Superconductors", "uri": "https://repository.library.brown.edu/studio/item/bdr:419516/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:419516/"}, {"pid": "bdr:54", "object_type": "pdf", "abstract": ["Various mechanisms govern pattern formation in chemical and biological reaction systems, giving rise to structures with distinct morphologies and physical properties. The self-organization of polymerizing microtubules (MTs) is of particular interest because of its implications for biological function. We report a study of the microscopic structure and properties of the striped patterns that spontaneously form in polymerizing tubulin solutions and propose a mechanism driving this assembly. We further present a mechanical model to explain the process and mechanism of buckling, and to infer properties of MT bundles such as packing geometry and size. Using oscillatory optical tweezers based active microrheology, the viscoelasticity of MT bundled networks were measured. This method implements forced oscillation of a 1.5\u00b5m silica bead embedded in a MT bundled network. Both moduli depend on the direction of the oscillatory motion of the bead relative to the alignment direction of the bundles. Furthermore, we have built an infrared laser tweezers setup for passive microrheology and to study the biophysics of bacterial motility and adhesion. We determined the force prole both near the center of the trap and at the far edge. Using the newly-built laser tweezers and position detection system, we studied microrheological properties of Factin in both isotropic and nematic phases. This method records the displacement of thermally driven micron-sized beads, based on which shear moduli of the underlying network were calculated. The result is consistent with that obtained by video particle tracking. In addition, we use the calibrated optical trap to determine the trapping force on a swimming Caulobacter crescentus swarmer cell during its escape from the trap center. We further apply laser tweezers to study the rotation of a trapped Caulobacter swarmer cell and the process by which the cell struggles to escape from the trap center. Aided by the laser trap, we also show that bringing the holdfast of a stalked cell close to a glass surface facilitates adhesion of the cell to the surface, consistent with the model that cells must overcome a repulsive barrier at the surface to adhere effeciently."], "keyword": ["pattern formation", "laser tweezers", "microrheology", "caulobacter", "Microtubules", "Pattern formation (Physical sciences)", "Adhesion"], "primary_title": "MT Striped Birefringence Pattern Formation and Application of Laser Tweezers in Microrheology, Bacterial Motility and Adhesion", "uri": "https://repository.library.brown.edu/studio/item/bdr:54/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:54/"}, {"pid": "bdr:48", "object_type": "pdf", "abstract": ["Two dimensional electronic systems exhibit a wide variety of phenomena including the quantum Hall effect, weak and strong localization, and metal-insulator transitions, including the superconductor to insulator transition (SIT). In each case the possibility of a universal explanation, independent of the microscopic details of the system, has tantalized researchers. In some cases, such as the temperature dependence of the conductance of metal films, or the spacing of resistance plateaus in the Hall effect, universal behavior is without doubt. Universal explanations of the amorphous film SIT revolve around the dirty Boson model, in which the sharp rise in the resistance of a film at low temperature is due to the localization of Cooper pairs. The existence of long-lived Cooper pairs in an electrically insulating system, the central assumption of the model, has remained in doubt because some measurements support the assertion and others refute it. This thesis addresses this experimental dissonance by investigating the SITs of amorphous Bismuth films perforated with a regular nanohoneycomb (NHC) array of holes. The nanoscale perforations allow a direct measurement of phase coherent Cooper pairs with an applied magnetic field. On the insulating side of the disorder driven SIT the resistance as a function of magnetic field oscillates with a period, h/2eS, where S is the area of a unit cell of holes. The 2e period betrays the presence of localized Cooper pairs in an electrically insulating state. The magnetoresistance of weak superconducting films reveals several SITs which qualitatively resemble the disorder driven SIT. The behavior of these transitions borrows heavily from both sides of a dichotomy exhibited by different materials through their field driven SITs. NHC films show activated resistances and a large peak in the magnetoresistance, analogous to the more spectacular behavior of some materials. However, they also show a weak, almost metallic, temperature dependence for a range of fields near the SIT, not unlike the metallic phase of unpatterned Bismuth and other materials. These results suggest that an underlying multiply connected geometry in ostensibly amorphous, unpatterned films may account for some of the range of material dependent behavior."], "keyword": ["superconductor insulator transition", "ultra thin", "amorphous", "nanoscale", "honeycomb", "patterning", "quench condensation", "Amorphous substances", "Bismuth"], "primary_title": "Superconductor to Insulator Transitions in Amorphous Nanohoneycomb Films", "uri": "https://repository.library.brown.edu/studio/item/bdr:48/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:48/"}, {"pid": "bdr:9", "object_type": "pdf", "abstract": ["In this thesis, new aspects of localized surface plasmon polaritons and their applications are considered in nanoscale structures. First, the optical response of pairwise electromagnetically coupled Au nanoparticles is investigated for spatially adjacent particles as a function of interparticle separation and overlap. For separated particles, renormalization of the surface plasmon energies via dipole-dipole interaction is observed. Overlapping particles, on the other hand, are found to exhibit multipolar behavior, including a very high local concentration of electromagnetic energy in the vicinity of their conductive contacts on nanometer scale. Second, enhanced fluorescence response is reported from semiconductor core-shell CdSe/ZnS quantum dots in proximity to the surface plasmon polariton fields of periodic Ag nanoparticle \"antenna\" arrays. Tuning the surface plasmon polariton resonance to the quantum dot exciton emission band is found to result in a 50-fold enhancement in the overall fluorescence efficiency. The direct impact of coupling of localized surface plasmons to the propagating modes of a continuous Ag film on the fluorescence enhancement is described. Last, a new type of electrostatically sensitive plasmonic nanoparticle probe that can detect the electrical activity in neural cells is demonstrated. The modulation of the electron density at the surface of Au nanoparticles by the extracellular action potential of a nearby neuron is found to result in an observable shift in the surface plasmon resonance frequency that can be monitored. The electrical activities of live neurons cultured on plasmonic templates are measured."], "keyword": ["surface plasmons", "coupled plasmons", "fluorescence enhancement", "neural activity", "extracellular potential"], "primary_title": "Nanoscale Optics by Localized Surface Plasmon Polaritons", "uri": "https://repository.library.brown.edu/studio/item/bdr:9/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:9/"}, {"pid": "bdr:78", "object_type": "pdf", "abstract": ["This thesis aims to elaborate the theory of ultrasonic vibration potential imaging as well as to propose and implement new electro-acoustic imaging methodology for biomedical applications based on ultrasonic vibration potential. Ultrasonic vibration potential refers to an electric signal developed across a colloidal or ionic solution with a presence of ultrasound. In colloidal suspensions, the vibration potential is generated as a consequence of the different motions of the colloidal particles and the solvent under the alternating acceleration in a sound wave. Upon passage of a sound wave, the normally spherical distribution of counter charge around those particles is periodically distorted resulting in the formation of dipoles at the sites of the colloidal particles. These dipoles add over a macroscopic distance to form a voltage. Thus, if electrodes are placed in the solution, an alternating voltage can be detected. Since possessing electrolytes and containing red blood cells, whole blood is both colloidal and ionic. Experiments have shown that the whole canine blood produces vibration potentials on the order of about 500 times as large as those from various muscle tissues, which points to application of any biological or medical problem that requires blood detection. This thesis focuses on the detailed analytical explanation and theories of both the generation of current and the distribution of potential and electric field inside colloidal solutions. Experiments with different methodologies and samples were conducted to not only give results in an excellent agreement with the theory but also help proposing and implementing a new imaging method using ultrasonic vibration potential."], "keyword": ["ultrasonic vibration potential", "ultrasound", "voltage", "current", "colloidal", "ionic", "imaging", "methodologies", "electroacoustic", "biomedical", "Electromotive force", "Colloids", "Imaging systems", "Biology", "Biophysics"], "primary_title": "Ultrasonic vibration potential imaging: theory and experiment", "uri": "https://repository.library.brown.edu/studio/item/bdr:78/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:78/"}, {"pid": "bdr:6", "object_type": "pdf", "abstract": ["This thesis presents the techniques we have developed in analyzing brain signals obtained from the most commonly used brain imaging methods, e.g., EEG/MEG and fMRI through my PHD study. An introduction of brain imaging and its computational issues are provided in chapter 1. In chapter 1, I also briefly describe the solutions we have developed in our work, details of which will be presented in the following chapters. In chapter 2 and 3, we generalize information theory of random variables to random process and apply the information theoretic approaches to measure the complexity of the signals and the interaction among different EEG channels. Unlike traditional linear methods, such as power spectrum and linear correlation methods, information theoretic approaches can discover the underlying high order processes and can measure the nonlinear interaction without specifying the dependency analytically. To evaluate our modeling of EEG and the associated feature extraction methods, we contrast our models with traditional linear techniques in their abilities to distinguish EEG signals collected under different experimental conditions. In chapter 4, we extend the classification of EEG signals to predict the stimuli across subjects. In chapter 5, we develop a clustering method to segment fMRI images. A classifier based on the clustering is introduced in chapter 6. Finally, we present extra machine learning techniques that can be potentially very useful in analyzing brain signals in the last 2 chapters. In chapter 7, we introduce a classification system for the problem where the number of training examples is very small and the dimensionality of the data is very large. In chapter 8, we propose an approximate solution to the non-homogeneous hidden Markov chain problem. It is useful in analyzing time series such as EEG and MEG where homogeneous hidden Markov assumption is often not realistic."], "keyword": ["brain signals", "Machine learning", "Information theory", "Classification"], "primary_title": "Analysis of brain signals with machine learning and information-theoretic methods", "uri": "https://repository.library.brown.edu/studio/item/bdr:6/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:6/"}, {"pid": "bdr:419425", "object_type": "pdf", "abstract": ["Research on DNA translocation through nanopore has drawn much attention because of its potential in DNA sequencing and biosensing. A lot of issues about translocation process have been found in recent years, such as capture kinetics, thermal fluctuations, electro-osmotic flow, etc. Due to the flexibility of DNA molecules, there are many complicated folded translocation events, which make the task of data analysis difficult. Here we use semi-flexible fd virus as a model system for studying translocation dynamics. The fd virus has persistent length around several micrometers, larger than the diameter of a nanopore, making folded translocation unlikely. In our study, distinct types of translocation events have been observed and a scheme of classification is developed. We also observe the subtle difference in their translocation dynamics of wild and mutant types of fd viruses due to different degrees of flexibility measured by their persistent length. A systematic method of measuring the current drops and time intervals for the fd translocations is developed and is used to construct a scatter plot, the latter led to the discovery of the Stotz-Wien effect in nanopore, nonlinear electrophoresis in strong electric field. The Stotz-Wien effect is studied with different types of virus and under different measuring salt concentrations. From comparison between experimental results and theoretic prediction, we found that electro-osmotic flow (EOF) is very crucial to the translocation process. We studied the EOF around different shaped particles and as well as within nanopores through numerical approach by using Poisson-Nernst-Planck (PNP) model. From our calculation, we confirm that Stotz-Wien effect is a consequence of polarized Debye cloud caused by the strong electric field. Finally, we show that the non-uniform distributed EOF within nanopore plays a very important role in translocation process, which should be considered when designing sequence method."], "keyword": ["solid-state nanopore", "translocation", "fd virus", "Stotz-Wien", "EOF"], "primary_title": "Nonlinear Transport in Solid-State Nanopores", "uri": "https://repository.library.brown.edu/studio/item/bdr:419425/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:419425/"}, {"pid": "bdr:419428", "object_type": "pdf", "abstract": ["Quantum emitters, such as colloidal quantum dots (QD) and nitrogen vacancy (NV) centers in diamond nanoparticles have received considerable attention as robust solid-state single photon emitters in a wide range of applications from fundamental studies of light-matter interactions to emerging quantum information technology. Although many techniques have been developed for the high precision positioning of individual quantum emitters near optical nanostructures, they all suffer from a common problem, which is, once a quantum emitter becomes photo-bleached or if different quantum emitters need to be investigated on the same nanostructures, additional fabrication steps or new samples are required. This can be time-consuming and wasteful, and more importantly, there will always be unknown variations between different samples. As a result, there is a need for iterative placement of different quantum emitters on the same nanostructures. Here, we present an electrostatic self-assembly method for the controlled scalable placement of QDs, NV center nanodiamonds, and upconverting nanoparticles, based on the reusable inorganic templates. By utilizing surface-charge-mediated self-assembly, highly ordered arrays of quantum emitters are created on different dielectric material templates. The template reusability is demonstrated through the daily cleaning and re-deposition experiments over extended (month-long and year-long) periods. Then single quantum emitter placement is confirmed by performing photon anti-bunching measurements using a Hanbury-Brown Twiss (HBT) setup. Finally, examples of integrating nanoparticles with different nanostructures are also demonstrated. We anticipate that this method could be of interest to the broad nanophotonics community, including the integration of emitters with plasmonics, metamaterials and photonic cavities. The scalability of the approach may also be advantageous for more distant applications of large arrays of single photon sources."], "keyword": ["quantum emitter", "isoelectric point", "electrostatic self-assembly", "nanofabrication"], "primary_title": "Reusable Electrostatic Self-Assembly of Quantum Emitter Nanoparticles", "uri": "https://repository.library.brown.edu/studio/item/bdr:419428/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:419428/"}, {"pid": "bdr:419422", "object_type": "pdf", "abstract": ["We use digital video microscopy to study the defects in two-dimensional colloidal crystals (2DCC). A crystalline solid, different from its liquid state, preserves long-wavelength shear rigidity and broken symmetry. Questions about how shear rigidity and long-range order disappear during melting, are unresolved in terms of the complication of defect structures and their roles in crystal melting, especially in two dimension. Colloidal crystals (CC) serve as a promising model system to directly observe the defects under optical microscope. In our first study, we report the effects of vacancies and interstitials on the phonon modes in a 2DCC. By applying the equipartition theorem, we extract the dispersion relation of the lattice vibrations using real-time video microscopy. We find that both longitudinal and transverse modes in the spectrum are softened by the existence of point defects. Second, we investigate the diffusion process of interstitials in a 2DCC. The motion is viewed as gliding of both edge dislocations along one of the crystalline axes. The microscopic process is equivalently a point mass overcoming Peierls barrier with an exponential escaping time. We also establish a new criterion to determine the ergodicity of a defect system and discover the nonergodic behavior of di-interstitials."], "keyword": ["Defects", "Colloidal crystals"], "primary_title": "Defects in Two Dimensional Colloidal Crystals", "uri": "https://repository.library.brown.edu/studio/item/bdr:419422/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:419422/"}, {"pid": "bdr:419409", "object_type": "pdf", "abstract": ["With the recent discovery of the Higgs boson at the Large Hadron Collider (LHC), the next set of goals for the Compact Muon Solenoid (CMS) experiment includes characterizing the newly discovered particle and probing for new physics beyond the Standard Model. Results from a search for new physics in the final state with a low transverse energy photon and missing transverse energy, using a data set corresponding to an integrated luminosity of 7.3/fb collected in proton-proton collisions at 8 TeV with the CMS detector is presented. Due to the large background rate for this final state, a novel strategy was used to collect this dataset from August through December of 2012. Such final state can arise from models involving dark matter production or exotic decays of the Higgs boson in low-scale supersymmetry breaking scenarios. In the absence of deviations from the Standard Model predictions, limits are set on the probability of an exotic decay of the Higgs boson. The phase space consisting of a photon with a transverse energy of at least 45 GeV and significant missing transverse energy was further examined in a model independent way by varying the selection requirements on the missing transverse energy and the transverse mass of the system. Upper limits at the 95% confidence level on production cross section of possible processes resulting in this final state were set. Additional and complementary results from a search for new physics in the final states containing a high-energy photon and missing transverse energy are also presented, using the data set corresponding to an integrated luminosity of 19.6/fb collected in proton-proton collisions at 8 TeV. In the absence of any significant deviation from the Standard Model predictions, improved limits are set on dark matter production and on the parameters of a model with large extra dimensions. Upper limits at a 95% confidence level on the production cross section of possible processes resulting in the final state with the photon transverse momentum greater than 145 GeV and missing transverse energy greater than 140 GeV were set."], "keyword": ["particle physics", "low energy photons", "CMS experiment"], "primary_title": "Search for new physics in final states with low transverse energy photon and missing transverse energy in proton-proton collisions at 8 TeV", "uri": "https://repository.library.brown.edu/studio/item/bdr:419409/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:419409/"}, {"pid": "bdr:419412", "object_type": "pdf", "abstract": ["Experiments have reported that swimming Paramecia exhibit graviresponses. They exhibit negative gravitaxis by orienting their swimming trajectories upward under gravity and negative gravikinesis by exerting stronger propulsion when swimming against gravity than moving along it. Their force sensing ability is surprising because their apparent weight is only ~ 70 pN. This study was motivated by the desire to understand how Paramecia actively or passively transduce this tiny force and other similar mechanical forces. It involved a recently developed technique for applying variable magnetic forces on swimming Paramecia using inhomogeneous magnetic fields. We could vary the apparent weights of swimming Paramecia from -8 to 10 times its normal value. We conducted an experiment to understand how Paramecia respond to the mechanical drag force changes induced by changing medium viscosity. We analyzed their helical trajectories and investigated the ciliary motor properties of swimming Paramecia under magnetically induced neutral buoyancy. We developed a phenomenological model that could describe how Paramecia adjusted their beating frequencies and geometry as viscosity changed. We concluded that Paramecia cilia exhibit two extremely different motor characteristics depending on their position on the cell body. As viscosity increased, the body-cilia operated at a constant propulsion force without changes in the beating geometry while the oral groove cilia beat at a constant speed. This result is remarkable because those cilia are known to have very similar structures. Paramecia are known to actively respond to mechanical perturbation. When stimulated by a needlelike object, they normally change their swimming patterns such as swimming speed or direction to respond to the force. To investigate their response to different physical perturbations such as the collision with flat surfaces, we adjusted their apparent weight. In particular, we observed a counterintuitive surface accumulation of swimming Paramecia. Surprisingly, they became trapped at the bottom surface as we increased their buoyancy. We introduced a purely passive model to explain this strange behavior. We found that the buoyancy decreased the turning torque on the swimming Paramecia and subsequently they became trapped to the bottom surface. The experimental results indicated that Paramecia passively interact with flat surfaces."], "keyword": ["magnetic levitation", "motor characteristics", "surface accumulation", "Paramecium", "Magnetic suspension"], "primary_title": "Investigations of Swimming Microorganisms under Variable Apparent Weight", "uri": "https://repository.library.brown.edu/studio/item/bdr:419412/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:419412/"}, {"pid": "bdr:419486", "object_type": "pdf", "abstract": ["Scattering amplitudes have undergone considerable study in the last few years. Much of the progress has come from abandoning Feynman diagram techniques and instead exploring and exploiting the physical constraints and mathematical structures underlying amplitudes. In this dissertation we present a new, unexpected structure underlying certain amplitudes: cluster algebras. Harnessing the power of cluster algebras allows us to calculate previously unknown amplitudes and points the way towards a deeper mathematical understanding of quantum field theory. We begin by introducing motivic amplitudes, which contain all of the essential mathematical content of scattering amplitudes in planar N=4 supersymmetric Yang-Mills theory. We then establish, through explicit calculations of the two-loop, seven-particle motivic amplitude as well as the n-particle two-loop differential, that the amplitude only depends on on certain preferred coordinates known in the mathematics literature as cluster X-coordinates on Conf_n(P^3). The connection between scattering amplitudes and cluster algebras prompts us to define cluster polylogarithm functions, objects which elegantly (and uniquely) contain beautiful motivic and cluster algebraic structure. In particular, cluster polylogarithms allow us to associate specific polylogarithm functions to faces of generalized associahedrons, to which cluster algebras have a natural combinatoric connection. These functions form a sufficient basis to express two-loop amplitudes, and we present an analytic formula for the two-loop seven-particle amplitude as an example. Furthermore, we find intriguing connections between motivic amplitudes and the geometry of associahedrons. For example, we show that the obstruction to the two-loop motivic amplitude being expressible in terms of classical polylogarithms is most naturally represented by certain quadrilateral faces of the appropriate associahedron."], "keyword": ["scattering amplitudes", "Quantum field theory", "Cluster algebras"], "primary_title": "Cluster Polylogarithms and Scattering Amplitudes", "uri": "https://repository.library.brown.edu/studio/item/bdr:419486/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:419486/"}, {"pid": "bdr:674367", "object_type": "pdf", "abstract": ["The last few years have seen significant interest in decaying dark matter. Specific models have been conjectured to account for observations that are not predicted by the standard cosmological model concerning issues of structure formation and anomalous particle observations. I present a study of cosmological implications of generic dark matter decays. The aim of this thesis is to understand features of dark matter decay in a general, model independent fashion. I consider two-body and many-body decaying scenarios where the parent particle decays into a massive daughter particle and one or more massless particles. In the two-body case the massive daughter particle has a possibly relativistic kick velocity and thus possesses a dynamical equation of state. In the many-body decaying scenario there are many massless daughter particles together with a massive daughter particle at rest. I implement these dark matter decaying scenarios in a broader cosmological context, and explore the lifetime and energy budget of decays throughout the history of the Universe, from the early Universe and Big Bang Nucleosynthesis to the Cosmic Microwave Background, Baryon Acoustic Oscillations and Type Ia supernovae to the present epoch."], "keyword": ["Dark Matter", "Decays", "Cosmology", "Dark matter (Astronomy)"], "primary_title": "Dark Matter Decaying in the Expanding Universe", "uri": "https://repository.library.brown.edu/studio/item/bdr:674367/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:674367/"}, {"pid": "bdr:674365", "object_type": "pdf", "abstract": ["Vector-like models with O(N) and U(N) symmetries at their critical points were seen to exhibit duality with higher spin gravitational theories of Vasiliev. In the dissertation, we study the finite temperature Vector Model/Higher Spin Duality in Large N. For CFTs given by 3d O(N) (or U(N)) vector models, I evaluate the leading and one-loop partition functions in a variety of geometries. This calculations are performed in the scheme of collective field theory, which was seen in earlier studies to represent a bulk description of Vasiliev higher spin theory. The calculations presented provide data for comparison of small fluctuation determinants, giving further evidence for the one-to-one bulk identification between the bi-local and the AdS picture. They also o er insight into the identification of coupling constants G and 1/N of the two descriptions for models based on O(N) symmetry. I also consider the canonical structure of the collective formulation of Vector Model/Higher Spin Duality in AdS4. This formulation involves a construction of bulk AdS Higher Spin fields through a time-like bi-local Map, with a Hamiltonian and canonical structure that are established to all orders in 1/N. Finally, I study the Large N dynamics of the O(N) field theory in the Thermo field dynamics approach. The question of recovering the high temperature phase and the corresponding O(N) gauging is clarified. Through the associated bi-local representation, we discuss the emergent bulk space-time and construction of (Higher spin) fields. We note the presence of \u201cevanescent\u201d modes in this construction and also the mixing of spins at finite temperature."], "keyword": ["AdS/CFT,Higher Spin,Vector Model,Thermo Field Dynamics,TFD,Free Energy"], "primary_title": "Finite Temperature Holography in Higher Spin Theory/Vector Model", "uri": "https://repository.library.brown.edu/studio/item/bdr:674365/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:674365/"}, {"pid": "bdr:674168", "object_type": "pdf", "abstract": ["A new model, based on matched asymptotic analysis, for the simulation of two-dimensional unsteady flows around structures, has been developed and tested on a wide range of cases. The fluid is incompressible and the Reynolds number is high. In the vast outer region far from the structures, the viscosity is negligible and the dynamics is dominated by the advection effect. The flow states are updated by tracking the vorticity distribution in a Lagrangian reference frame. The resulting method is well adapted to the modeling of transport phenomena. It is grid-free and concentrates its computational elements in the regions of steep gradients; it also allows a simple and exact treatment of the far-field boundary conditions. In order to account for the viscous effect, especially capture the phenomenon of vortex shedding, a more complete description, Prandtl's approximation of Navier-Stokes equations, is used in the thin region close to the body surface, the so-called boundary layer. The matching conditions at the interface between the two regions ensure the smooth advection of vorticity from boundary layer to outer region. The model can be considered as a generalization of the Kutta-condition model derived from first principles to treat bodies of arbitrary shape. It is an attempt to capture the qualitative feature of the solution, especially the vortex shedding, and is guided by quantitative arguments, but not a true limit of the Navier-Stokes equations for large Reynolds number flow. The method appears to incorporate many of the physical mechanisms of unsteady flows, and at the same time maintains high computational efficiency."], "keyword": ["boundary layer approximation", "Vortex shedding"], "primary_title": "A vortex shedding model for unsteady fluid dynamics", "uri": "https://repository.library.brown.edu/studio/item/bdr:674168/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:674168/"}, {"pid": "bdr:674158", "object_type": "pdf", "abstract": ["Colloidal quantum dots (CQDs) have emerged as an etd536cient uorescent material with tunable bandgap across the visible spectrum due to quantum connement effect. Also, studies of optical gain and stimulated emission from the CQDs have been extensively reported. However, fast-decaying non-radiative Auger recombination has been impeding further development of CQDs in the laser applications. Here, in this thesis, optical gain dynamics of our core-shell engineered type-I CQDs have been studied via transient absorption spectroscopy, and optically pumped lasers have been demonstrated as optoelectronic device applications. The role of single exciton states as a dominant optical gain mechanism in densely packed II-VI CQD lms by pump-probe laser spectroscopy has been discussed. Optimizing the Stokes shift and having narrow inhomogeneous broadening of the CQDs play the key role for empowering the single exciton states. Consequently, the single exciton gain regime is accessible without the involvement of the non-radiative Auger process. Bragg grating structures have been incorporated with the CQD gain media to create red, green and blue surface-emitting distributed feedback lasers. A compact solid-state laser whose pulse duration exceeds the Auger decay time has been used as an excitation source. Monochromatic single mode lasing actions at low threshold levels were observed with excellent spatial coherence and conversion etd536ciency. Finally, another type of CQD laser device, vertical-cavity surface-emitting laser has been fabricated using nano-porous(NP)-GaN distributed Bragg re ectors. Closepacked CQD lms were sandwiched between the two NP-GaN/GaN DBRs to achieve ultra-low threshold lasing outputs under the same optical excitation condition. This enabled the realization of the pixelated laser display devices driven by a scanning mirror system."], "keyword": ["Colloidal quantum dots", "Single exciton optical gain", "Auger recombination", "Distributed feedback laser", "Vertical-cavity surface-emitting laser", "GaN distributed Bragg reflectors", "Semiconductor nanocrystals"], "primary_title": "Single Exciton Optical Gain from Dense Colloidal Quantum Dot Films and Their Optically Pumped Laser Applications", "uri": "https://repository.library.brown.edu/studio/item/bdr:674158/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:674158/"}, {"pid": "bdr:674118", "object_type": "pdf", "abstract": ["The Large Hadron Collider (LHC) has had a very successful data-taking phase with Run 1. After the discovery of the Higgs, confirming the predictions of the Standard Model (SM), the focus is on finding new physics, especially in the context of supersymmetry (SUSY). One of the potential hiding places of natural SUSY is in models with compressed spectra, that is, models where the mass difference between the parent SUSY particle and the Lightest Supersymmetric Particle (LSP) is small. Such signals are characterized by low transverse momentum (p${_T}$) objects, low hadronic activity and missing transverse energy (MET). In this analysis, we focus on di-lepton final states, specifically in the low p${_T}$ regime. We use 7.4 fb$^{-1}$ of parked data collected at $\\sqrt{s}$ = 8 TeV. The analysis is enabled by the use of triggers that place no restrictions on the di-lepton p${_T}$, instead relying on methods like Initial State Radiation (ISR) tagging by triggering on a high p${_T}$ photon, to reduce the trigger rate. The final state we are interested in consists of a high p${_T}$ photon and two oppositely charged leptons. Since no statistically significant excess of events consistent with the presence of supersymmetric particles was found, we compute exclusion limits at a 95\\% confidence level for the cross section of stop pair production in association with a photon. We also show results for model independent limits in this channel."], "keyword": ["Large Hadron Collider", "Compressed spectra SUSY", "Large Hadron Collider (France and Switzerland)"], "primary_title": "Search for SUperSYmmetry (SUSY) in Opposite Sign (OS) Dilepton Final States with Parked Data Collected at $\\sqrt s$ = 8 TeV Using the CMS Detector", "uri": "https://repository.library.brown.edu/studio/item/bdr:674118/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:674118/"}, {"pid": "bdr:674142", "object_type": "pdf", "abstract": ["When a free electron enters the liquid helium, it repels the helium atoms around it and forms a cavity. Since 1969, people have found that there were a number of negative carriers in the liquid helium with higher mobilities than the electrons. The physical nature of these so-called \u201cexotic ions\u201d remains a mystery to researchers for decades. In this thesis I describe three approaches we have taken to study the properties of these exotic ions in the liquid helium. Firstly, the mobilities of the exotic ions are measured in a time-of-flight cell, and experimental parameters are varied to see their influence on the ion signals. Combining the results from using two different discharge tips, a total number of eighteen exotic ions with distinct mobilities have been observed. Secondly, a carbon dioxide laser is used to excite the normal electrons from the ground state (1S) to the first excited state (1P), and the change in mobility is measured, again by the time-of-flight method. Objects with shorter transit times are observed, but it is not clear if they are exotic ions. One possibility is that photo-excitation frees electrons from the vortices which they are formerly attached to, and gives rise to signals at earlier times. Finally, attempts are made to study the nucleation on the exotic ions by using a piezoelectric transducer to create a negative pressure swing in the liquid helium. Three possible models, namely impurities, negative helium ions, and fission of the electron wave function, are discussed. Each of them has difficulties but the fission model appears to be the only plausible explanation."], "keyword": ["exotic ion", "superfluid helium"], "primary_title": "Experimental Investigation of the Exotic Negative Ions in Superfluid Helium-4", "uri": "https://repository.library.brown.edu/studio/item/bdr:674142/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:674142/"}, {"pid": "bdr:674146", "object_type": "pdf", "abstract": ["Study of the combined effects of strong electronic correlations with spin-orbit coupling (SOC) represents a central issue in quantum materials research. Predicting emergent properties represents a huge theoretical problems as presence of SOC implies that the spin is not a good quantum number. A multitude of exotic quantum phases are predicted to emerge even in materials with simple cubic crystal structure such as Ba2NaOsO6. Experimental tests by local probes, such as Nuclear magnetic resonance (NMR), are highly sought for. In this thesis, we first present the temperature evolution of the 23Na NMR spectrum. It clearly reveals a geometrical distortion, preceding a formation of the long-range ordered (LRO) magnetism. We discovered from the angular dependence measurement that a cubic to orthorhombic structural phase transition occurs, induced by elongation/compression of the oxygen octahedra, and only one structurally equivalent environment exists for 23Na nuclei. Furthermore, from a lattice sum simulation we found that the low temperature LRO state is the canted two-sublattice ferromagnetic (FM) state, which gives rise to the magnetic splitting in NMR spectrum. This is the first direct observation of such exotic magnetic order in 5d transition-metal systems. Such state is predicted to occur due to multipolar spin-spin interactions on the frustrated fcc lattice. We provide evidence for the presence of complicated orbital ordering. Lastly, we studied the magnetic order within the intermediate transition region, and the possible existence of spin nematic order is discussed based on second moment analysis. This work paves the way for future NMR study of highly frustrated systems with the strong SOC and electron correlations, such as Iridates."], "keyword": ["NMR", "spin-orbit coupling", "5d transition-metal", "electron correlation", "Electron configuration"], "primary_title": "Nuclear Magnetic Resonance Study of Ferromagnetism and Local Symmetry Breaking in Double Perovskite Mott Insulator Ba2NaOsO6", "uri": "https://repository.library.brown.edu/studio/item/bdr:674146/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:674146/"}, {"pid": "bdr:674096", "object_type": "pdf", "abstract": ["Safe storage and disposal of spent fuel rods from nuclear power plants calls for the ability to model actinide complexes and compounds in the environment. The rich behavior of actinide ions may be traced to the valence electrons, especially those in the $5f$ shell. The electronic configuration of neutral uranium, for instance, is [Rn]$5f^36d^17s^2$. Typically the valence $6d$ and $7s$ electrons transfer to other atoms leaving active $5f$ orbitals that are relatively localized. Quantitative calculations of actinide reactions must overcome several obstacles. The crucial physics of relativity must be included. The Amsterdam Density Functional (ADF) and NWChem density functional theory (DFT) packages incorporate relativistic effects, and are used to model various uranium compounds species (UO$_2$F$_4^{2-}$ / UO$_2$F$_4^{-}$, UO$_2$Cl$_4^{2-}$ / UO$_2$Cl$_4^{-}$, UF$_5^-$ / UF$_5$, UCl$_5^-$ / UCl$_5$, UF$_6^-$ / UF$_6$, and UCl$_6^-$ / UCl$_6$). The converged geometry and bond lengths are consistent, and also close those predicted by coupled-cluster calculations and experimental measurements. But incorporating the physics of strong electronic correlations among the $5f$ electrons presents a greater challenge as these are poorly captured by DFT. The adiabatic detachment energy (ADE) obtained from DFT alone can differ by as much as 1.0 eV from experimental measurement. In order to solve this problem, a hybrid approach is adopted that uses DFT to construct a generalized many-body Anderson impurity model of the frontier orbitals. The continuous unitary transformation (flow equation) approach and a truncation scheme are introduced to bridge the independent-particle model and many-body Anderson impurity model. This is necessary because the Hilbert space dimension of the impurity model is exponentially large. The flow equation and truncation scheme can efficiently decouple orbital states of the uranium compounds species that hybridize less with $5f$ uranium orbitals to decrease the dimension. Exact diagonalization of the resulting sparse matrix corrects the adiabatic detachment energy obtained from DFT alone. The hybrid DFT / many-body approach yields ADE values that differ by order of 0.1 eV from experiment."], "keyword": ["Density Functional Theory", "Flow Equation", "Many-Body Anderson Impurity Model", "Actinide Compounds", "Density functionals", "Actinium compounds"], "primary_title": "Flow Equation Approach to the Hybrid DFT --- Anderson Model Description of Actinide Compounds", "uri": "https://repository.library.brown.edu/studio/item/bdr:674096/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:674096/"}, {"pid": "bdr:674102", "object_type": "pdf", "abstract": ["The Giant Spin Hall Effect (GSHE) in certain transition metals due to strong spin-orbit interaction has shown great potential in the development of novel spintronic devices, such as magnetic random access memories and spin-logic devices. The induced spin current in a thin film with GSHE imposes a spin-transfer-torque (STT) on an adjacent ferromagnetic layer, strong enough to switch the magnetization direction. In this work, we realized robust perpendicular magnetic anisotropy (PMA) in a layered structure combining various GSHE solids with ultrathin ferromagnetic films. We have achieved a critical current density of 2\u00d710^6A/cm^2 to switch the magnetization vector direction. Utilizing a macro spin model, we have determined the spin Hall angles of beta-Tungsten and beta-Tantalum to be -0.40 (in the bulk limit) and -0.11 at room temperature, respectively. These numbers are among the largest in transition-metal-based solids. Furthermore, we have investigated the thickness and temperature dependence of the GSHE, which has revealed appealing characteristics of strong spin-orbit interaction and the mechanism leading to GSHE. Next, we focus on Anomalous Hall Effect (AHE) which is also caused by the strong spin-orbit coupling. We have fabricated and studied Fe-Pt alloy thin films with varying concentrations and thicknesses. We have observed AHE with a very large Hall slope. Our systematic study on the magnetic and transport properties reveals the intrinsic and side-jump mechanisms that contribute to the AHE in Fe-Pt alloy system. Due to its metallic nature, the low-frequency electronic noise in Fe-Pt based Hall sensor is two orders of magnitude lower than that of some semiconductor Hall sensors. Finally, we have studied another type of spintronic device called magnetic tunnel junction (MTJ) using rapid electron transport measurement. We have observed voltage controlled magnetic anisotropy in MTJs. The physics is likely due to the field effect of spin-orbit coupling within the interfacial regions in the MTJ multilayered structure. We believe the integration of MTJ with GSHE structure could open the door for future spintronic applications."], "keyword": ["Spin transfer torque", "perpendicular magnetic anisotropy", "beta-W", "Spintronics"], "primary_title": "Giant Spin Hall Effect and Anomalous Hall Effect in Solids with Strong Spin-Orbit Coupling", "uri": "https://repository.library.brown.edu/studio/item/bdr:674102/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:674102/"}, {"pid": "bdr:674101", "object_type": "pdf", "abstract": ["In this thesis, I first focus on the study of the optical properties of three kinds of amorphous germanium (Ge) nanostructures: Ge ultra-thin films, Ge-SiO2 (silicon dioxide) multi-layer films and Ge quantum dots (QDs) contained oxide films. We carried out optical reflectance and transmittance measurements, comparing different methods in extracting optical absorption coefficients and optical band gaps. We have shown for thin film applications, an interference model is needed to provide accurate extraction of the absorption coefficients. We have also explored the applicability of both Tauc and Cody models in studying amorphous germanium in the nanoscale regime. Further, I present high efficiency metal-oxide-semiconductor photodetectors based on Ge QDs contained in an oxide matrix. We have demonstrated the peak internal quantum efficiencies (IQE) above ~ 700% can be achieved for the as-deposited device. Post thermal treatment was carried out and was shown to significantly increase the efficiency even further, i.e. with IQE above 1500% over a wide spectrum range achieved. We also investigated the internal working mechanism of these devices by performing transient photoresponse measurements. A response time of ~ 40 ns was achieved by reducing the active Ge QD layer thickness. The high efficiency and ease of fabrication make Ge QD photodetectors a promising candidate for the future on-chip integration of optical functionalities. Lastly, I investigate the promising application of surface plasmon polariton (SPP) waves for enhanced photodetection through milled shallow holes in a silver film (a structure also known as a plasmonic concentrator) through 2D wave interference modeling. A single nanohole can be a good SPP wave source across a wide range of incident wavelengths. The generated SPP wave can be well described by a simple 2D wave model given some input parameters. We have demonstrated efficient designs of nanohole patterns through this 2D wave interference model and compared it with the 3D finite-difference-time-domain (FDTD) simulation and experiments. In addition, we have shown Ge QD photodetectors are well suitable for the plasmonic sensing application."], "keyword": ["amorphous germanium nanostructures", "photodetectors", "plasmonics", "Optical detectors"], "primary_title": "Amorphous Germanium Nanostructures: Optical Characterization and Applications for Improved Photodetector Performance", "uri": "https://repository.library.brown.edu/studio/item/bdr:674101/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:674101/"}, {"pid": "bdr:674170", "object_type": "pdf", "abstract": ["A search for long-lived particles that are produced in proton-proton collisions at the CERN LHC, come to rest in the CMS detector, and decay to muons is presented. The decays of the stopped particles could be observed during the intervals between LHC beam crossings, at times that are well separated from any proton-proton collisions. The analysis uses 19.7 1/fb of 8 TeV data collected by CMS in 2012, during a search interval of 293 hours of trigger livetime. Massive, long-lived particles do not exist in the Standard Model, and so any sign of them would be an indication of new physics. The results are interpreted with a model that predicts a long-lived particle that has a charge of twice the electron charge and that behaves like a lepton. Cross section limits are set for each long-lived particle mass as a function of lifetime, for lifetimes between 100 ns and 10 days. These are the first limits for long-lived stopped particles that decay to muons."], "keyword": ["particle physics", "LHC", "CMS", "long-lived exotic particles", "Muons"], "primary_title": "A search for long-lived particles that stop in the CMS detector and decay to muons", "uri": "https://repository.library.brown.edu/studio/item/bdr:674170/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:674170/"}, {"pid": "bdr:674137", "object_type": "pdf", "abstract": ["Swimming bacteria move through their environment using one or more helical flagella, each of which are rotated by a flagellar motor. These rotating helical flagella generate hydrodynamic propulsive forces that balance the drag force acting on the moving cell body. Much research on motile bacteria focuses on the multi-flagellated bacterial species E. coli, which is studied as a model system. In this dissertation, I focus on the swimming of uni-flagellated bacteria, primarily using Caulobacter crescentus as a model. Previous studies have reported various bacterial species swimming in circular trajectories near solid surfaces due to increased fluid drag near the stationary boundary. I examine C. crescentus swimming near an air-water interface and observe trajectories with both clockwise and counterclockwise average curvature. Near an ideal air-water interface, cells should only swim with slight clockwise curvature, as the interface acts as a free surface. The counterclockwise trajectories are a result of high surface viscosity due to adsorption of large organic molecules at the air-water interface. Adding small amounts of surfactant to the bacterial medium reduces surface contamination through competitive adsorption and restores the exclusively clockwise trajectories seen near a free surface. Studies on E. Coli have shown contradictory results concerning the distribution of time intervals over which flagellar motors rotate in the clockwise and counterclockwise directions. Since C. crescentus only has one flagellum, the rotation direction of its flagellar motor can be determined at any time by the swimming pattern of a single cell. By observing this distribution of rotation times, I show that the process controlling switching between rotation directions is not a Poisson process, but can be described using first passage time theory. Finally, by utilizing a three parallel channel microfluidic device, I determine how changing oxygen levels alter these switching rates. C. crescentus displays aerotactic behavior by extending the length of clockwise motor rotation when moving up oxygen gradients. These effects have a large impact on the motile behavior of C. crescentus and other uni-flagellated swimmers, especially near naturally occurring and abundant air-water interfaces."], "keyword": ["bacterial motility", "flagellar motor", "aerotaxis", "surface rheology"], "primary_title": "Motility of uni-flagellated bacteria: from swimming mechanics to molecular regulation", "uri": "https://repository.library.brown.edu/studio/item/bdr:674137/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:674137/"}, {"pid": "bdr:919122", "object_type": "pdf", "abstract": ["Since the discovery of the Higgs boson in 2012, much of the effort at the Large Hadron Collider located at CERN, Switzerland has focused on searching for evidence of physics beyond the standard model. This thesis presents a search for the manifestation of new physics in the form of hypothetical heavy quark partners called vector-like quarks (VLQ). The VLQs are color charged fermions whose left- and right-hand field components transform in the same manner under the SU(2)\u00d7U(1) electroweak gauge symmetry. Specifically, this is a search for pair produced heavy vector-like top (T) quarks with charge 2e/3 and vector-like bottom (B) quarks with charge \u2212e/3. Vector-like T quarks are predicted to decay to bW, tZ, and tH. Analogously, vector-like B quarks are predicted to decay to tW, bZ, and bH. Pair production of T and B quarks would result in a wide range of final states. This thesis focuses on the final state with three or more leptons (electrons/muons), denoted as the trilepton final state. Two other final states are also considered: those with two same-sign leptons (SSDL) and with single lepton. The combined results of trilepton, SSDL, and single lepton final states are also presented. The search was carried out by the CMS detector using proton-proton collisions at the center-of-mass energy of \u221as = 13 TeV. The dataset was collected in 2016 and corresponds to an integrated luminosity of 35.9 fb\u22121. The results are presented for various T and B quark decay branching fraction combinations and exclude T quarks with masses below 1140\u20131300 GeV and B quarks with masses below 910\u20131240 GeV, extending the reach of previous CMS searches by 200\u2013600 GeV."], "keyword": ["Particles (Nuclear physics)", "Experimental Particle Physics", "Large Hadron Collider (France and Switzerland)", "CMS Experiment", "Vector-like-quarks"], "primary_title": "Search for Vector-Like Heavy Quark Partners Decaying to Leptons and Jets in pp Collisions at \u221as = 13 TeV by the CMS Experiment", "uri": "https://repository.library.brown.edu/studio/item/bdr:919122/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:919122/"}, {"pid": "bdr:919059", "object_type": "pdf", "abstract": ["Charge carriers have long been introduced into superfuid helium-4, and their mobilities measured. Electrons repel the atoms of the liquid in their vicinity, forming a small cavity, or \"bubble\". Of particular interest are the \"exotic ions\", which have mobilities larger than that of the electron bubbles. By measuring the mobilities of different charge carriers we can deduce information about the microscopic structures they form in the liquid. Four different experiments were performed. In the first experiment light of wavelength 1064 nm was used to generate optical breakdown of the helium liquid. The threshold intensity was measured over the temperature range from 1.1 to 2.8 K. Experiments were performed to study how the breakdown from one pulse modifies the probability that a subsequent pulse will result in breakdown. In the second experiment the \"fast ion\", the fastest of the exotic ions, was generated with an Americium-241 source. The experimental cell was pressurized up to 5.5 bar and the mobilities of the fast ion and normal electron bubble were measured. From these measurements we study how the radius of the fast ion changes with increasing pressure. In the third experiment the \"#2 background\", a signal from charge carriers which are continuous in mobility, was studied. This background is interpreted as electrons from the discharge which have energy above that of the barrier for entry into liquid helium, but are only partially transmitted across the vapor-liquid interface. The transmitted portion of the electron wave function is trapped, forming a bubble which contains only a fraction of the wave function. and is thus smaller than the normal electron bubble. The experiment shows that the interaction of the electron with the liquid helium does not result in a measurement that quickly determines that an electron is in the bubble or is not in the bubble. Finally, in the fourth experiment observations of new positive charge carriers with mobilities close to that of the normal He+ snowball are detailed. The temperature and field dependence of their mobilities and amplitudes in the region of 1 K are measured."], "keyword": ["Physics", "Low temperatures", "Quantum mechanics", "Liquid helium", "Bubbles"], "primary_title": "Studies of Negative and Positive Charge Carriers in Superfluid Helium-4", "uri": "https://repository.library.brown.edu/studio/item/bdr:919059/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:919059/"}, {"pid": "bdr:kt982hen", "object_type": "pdf", "abstract": ["The Standard Model of physics predicts the existence of triple-top quark production in association with a W boson or a non-top flavored quark from proton-proton collisions. However, the production of triple-top quarks is extraordinarily rare due to the combination of top quarks having a large invariant mass (173 GeV) as well as requiring electroweak interaction vertices. The cross section for Standard Model triple-top quark production at leading-order with next-to-leading order Quantum Chromodynamic corrections is 2 fb. This is nearly 10 times smaller than four-top production, 100,000 times smaller than single-top production and almost a million times smaller than top-pair production. The top-pair (1995), single-top (2008) and four-top (2023) processes have all been discovered at 5 sigma. The challenge in discovering triple-top production is both its scarcity as well as the many background processes with far greater yields. The reward in discovering triple-top quark production, however, is not only that it would confirm the Standard Model prediction, but that it has an increased sensitivity to potential Beyond the Standard Model processes due to its low cross section. To push the limits of discovery, a dedicated search strategy involving several new machine learning techniques are introduced to increase the search sensitivity and reduce sources of uncertainty. In the single lepton final state search using the Compact Muon Solenoid Run 2 dataset, we do not find evidence of triple-top production and set a 95% confidence-level upper limit on the cross section of 78 fb. Despite the absence of a discovery, the prospects improve drastically with an increased dataset to be collected during Run 3 and during the High-Luminosity Large Hadron Collider era."], "keyword": ["Experimental Particle Physics"], "primary_title": "Search for Triple-Top Quark Production in the Single Lepton Final State from 13 TeV Proton-Proton Collisions at the Large Hadron Collider with the Run 2 Compact Muon Solenoid Detector", "uri": "https://repository.library.brown.edu/studio/item/bdr:kt982hen/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:kt982hen/"}, {"pid": "bdr:npz2tp3k", "object_type": "pdf", "abstract": ["Galaxy clusters are the largest gravitationally bound structures in the universe. Their enormous scale makes them the perfect environment to host cosmological phenomena that are otherwise not prominent. About 85% of the mass of a cluster is disguised in the form of dark matter, which does not interact with baryonic matter at all. Hence, gravitational lensing becomes a great tool to study the dark matter substructure within these clusters. This work is based on the LoVoCCS survey (Sheming Fu, Ian Dell'Antonio, et al), which aims to collect data from DECam and study the weak lensing signal in 107 clusters to examine the distribution of dark matter within them. We discovered that Abell 1285 has an unusually large lensing signal compared to its X-ray luminosity. A significant disagreement exists between the traditional X-ray mass estimates provided by various catalogs, such as the MCXC catalog (Piffaretti et al), and our weak lensing estimate. The focus of the thesis is to resolve this discrepancy. A multi-cluster analysis was carried out in different domains of the electromagnetic spectrum using methods like extracting the red sequence to estimate the luminosity, looking at the Sunyaev-Zeldovich effect, and studying the dispersion of redshifts in the field. We found that our estimates for optical luminosity across all clusters show an overall decreasing trend with a small peak around Abell 1285. While our estimates are in agreement with the X-ray catalogs, we found a major contamination in the field in the X-ray and millimeter regimes. This contamination might have affected the respective estimates, depending on how the subtraction was handled."], "keyword": ["Astrophysics", "Cosmology", "Physics, Astrophysics, Galaxy Clusters, Cosmology", "Galaxies--Clusters", "Gravitational lenses"], "primary_title": "Investigating the Abnormal Weak Lensing Signal of Abell 1285", "uri": "https://repository.library.brown.edu/studio/item/bdr:npz2tp3k/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:npz2tp3k/"}, {"pid": "bdr:gz4f2gk4", "object_type": "pdf", "abstract": ["Dark matter is by nature extremely difficult to detect. The only force we are certain it interacts with is gravity, making gravitational studies a key tool for investigating different models. In this thesis, a Jeans kinematic analysis and gravitational waves are used to study the viability of dark matter models that are alternatives or complements to Cold Dark Matter. I study whether ultralight bosonic dark matter is consistent with the gravitational potential extracted from stellar kinematics. The posterior likelihood is multimodal. Particle masses of order $m\\sim10^{-22}$ eV require halos of mass in excess of $\\sim10^{10}M_\\odot$, while particle mass of order $m\\geq 10^{-20}$ eV are favored by halos of mass $\\sim[10^8-10^9]M_\\odot$, with a similar behavior to cold dark matter. Regardless of particle mass, the lower halo masses are allowed if stellar dynamics are influenced by the presence of a central black hole of mass at most $\\sim10^{-2}$ the host halo mass. There is no preference for models that contain a black hole over models that do not contain a black hole. I conclude that either the fuzzy dark matter particle mass must be $m\\geq 10^{-20}$ eV, or the Milky Way dwarfs must be unusually heavy given the expected hierarchical assembly of the Milky Way, or the Milky Way dwarfs must contain a central black hole. I find no evidence for either of the last two possibilities and consider them unlikely. I also study Primordial Black Holes as a possible explanation for the $2.6 M_\\odot$ object in the LIGO/Virgo GW190814 merger observed in gravitational waves. Primordial black holes could make up a fraction of the universe's dark matter; this object is a candidate as it would be either the heaviest neutron star or lightest black hole observed to date. I find that a primordial black hole explanation to GW190814 is unlikely as it is limited by the formation rate of the primary stellar progenitor and the time available for a pair of primordial- and stellar-origin black hole binaries to form and merge within a Hubble time."], "keyword": ["Physics", "Astrophysics", "Cosmology", "Physics, Astrophysics, Galaxy Clusters, Cosmology", "Dark matter (Astronomy)", "Gravity"], "primary_title": "Movement in the Dark: Gravitational Probes of Dark Matter Models", "uri": "https://repository.library.brown.edu/studio/item/bdr:gz4f2gk4/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:gz4f2gk4/"}, {"pid": "bdr:s36kdnna", "object_type": "pdf", "abstract": ["In this thesis, I explore possible extensions to the \u039bCDM model of cosmology, their observational signatures, and the implementation of tools from machine learning for their constraint. Part I begins by exploring the viability of early dark energy models to address the Hubble tension in cosmology. It is shown that while early dark energy can alleviate the Hubble tension, large-scale structure data disfavors it as it exacerbates the large-scale structure tension already present in \u039bCDM. Based on lessons learned from confronting early dark energy with large-scale structure data, Part I concludes by presenting a string theory-inspired model of EDE that lacks the original model's theoretical shortcomings and has dynamics that suggest it can lessen the large-scale structure tension. Part II presents the novel dynamics for cosmologies derived from alternatives to classical general relativity. First, cosmology and black hole solutions in a model proposed as a solution to the cosmological constant problem where gravity is coupled to a topological field theory (BF theory) are discussed. This is followed by considering the impact on background cosmology and perturbations in a quantized theory of first-order gravity where regions of parameter space not ruled out by data are found that can alleviate the large-scale structure tension. Finally, in Part III, tools from machine learning are explored for dark matter searches. First, it is shown in the controlled realm of simulation that convolutional neural networks have the potential to distinguish between different models of dark matter in strong lensing data. It is then demonstrated that state-of-the-art methods of domain adaptation will allow the transfer of knowledge accumulated in the controlled setting of simulation to real datasets. Finally, it is shown that computer vision methods can also be used to extract information about the presence of substructure in the Milky-Way from astrometric measurements."], "keyword": ["Cosmology"], "primary_title": "Theoretical and Computational Explorations of Beyond \u039bCDM Cosmology", "uri": "https://repository.library.brown.edu/studio/item/bdr:s36kdnna/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:s36kdnna/"}, {"pid": "bdr:7bjq26jv", "object_type": "pdf", "abstract": ["Spin, orbit, and lattice dynamics are coupled in strong spin-orbit coupling systems. The Lacunar spinel, GaTa$_{4}$Se$_{8}$, is a unique Mott insulator that hosts molecular spin-orbit J$_{eff}$-3/2 states as correlation units. However, little is known about the spin-orbital ground state and dynamics in this system. In this thesis, I discuss a series of comprehensive x-ray and neutron total scattering and inelastic neutron scattering measurements that uncover a fluctuating spin-orbital dimer phase in this cluster Mott insulator. GaTa$_{4}$Se$_{8}$ has concurrent structural and magnetic transitions at 50 K, forming a spin-orbital singlet valence bond solid ground state. As a result of strong spin-orbit coupling and orbital degeneracy, the magnetic ground state couples with lattice distortion. Our total scattering measurements show that the lattice is locally distorted up to 300 K, indicating that the spin-orbital singlet transition is an order-disorder type. Our inelastic neutron measurements directly reveal the lattice fluctuations preceding the transition and provide direct evidence of spin-orbital fluctuation. To investigate the interplay between spin-orbit coupling, the Jahn-Teller effect, and exchange coupling. We carried out a series of inelastic neutron scattering measurements on lacunar spinels GaM$_{4}$X$_{8}$ (M=V, Nb, Ta; X=S, Se). Our results reveal the phonon anomaly in stronger spin-orbit coupling compounds (M=Nb, Ta), while this feature is missing in the vanadates with dominating Jahn-Teller effect. Combining our pair distribution function, synchrotron crystallography, and density functional theory, we demonstrate the spin-orbital ordering and fluctuations in lacunar spinels. Under high pressure, GaTa$_{4}$Se$_{8}$ undergoes insulator-metal and metal-superconducting phase transitions at 5 GPa and 10 GPa, respectively. The persistence of the J$_{eff}$-3/2 ground state in both phases suggests that the superconducting phase could be unconventional and topological. To gain a better understanding of the phase transitions, we performed high-pressure x-ray diffraction to identify the structural phase transition that takes place in the superconducting phase."], "keyword": ["condensed matter physics"], "primary_title": "Spin-orbital Fluctuations and Unconventional Quantum Phases in Lacunar Spinels: Insights from Neutron and X-ray Scatterings", "uri": "https://repository.library.brown.edu/studio/item/bdr:7bjq26jv/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:7bjq26jv/"}, {"pid": "bdr:tbr2ncdb", "object_type": "pdf", "abstract": ["An electron in liquid helium repels helium atoms and forms a spherical cavity referred to as an \u201celectron bubble.\u201d In addition to this well-known normal electron bubble, mobility measurements have revealed the existence of a number of negative ions of unknown structure. These include the so-called \u201cexotic ions,\u201d and two others labeled as \u201cA\u201d and \u201cB.\u201d In this thesis we report our studies of different charge carriers in superfluid helium. The stability of few-electron bubbles containing three and eight electrons was studied by computer simulations. The pressure ranges within which these bubbles are stable were determined. A series of time-of-flight mobility measurements were performed to investigate negative and positive ions in liquid helium. First, the pressure dependences of the fast ion mobility and the He+ ion mobility were measured up to a pressure of 5.5 bars. The fast ion is the exotic ion that has the highest mobility. This measurement shows that the radius of the fast ion does not significantly vary with pressure. Next, multiple positive helium ions were observed. These ions have mobilities slightly different from that of the normal positive ion He+. Further, signals from the exotic ions were detected using an Am-241 alpha source to produce a plasma discharge in helium vapor. Moreover, experimental conditions under which the A and B ions occur were studied. Both of them have a continuous distribution of mobility. The A ions are interpreted as bubbles containing only a fraction of the single electron wave function. The simulation based on this interpretation is in reasonable agreement with the experimental results and supports the idea that liquid helium does not make a measurement to determine whether an electron is in the bubble. Other possible explanations are also discussed. Lastly, we describe experiments using a carbon dioxide laser to excite electron bubbles from the 1S state to the 1P state. Multiple current signals following the photo-excitation were detected, and possible origins of these signals were studied."], "keyword": ["Low temperatures", "Liquid helium", "Superfluidity"], "primary_title": "Electrons and Exotic Ions in Superfluid Helium-4", "uri": "https://repository.library.brown.edu/studio/item/bdr:tbr2ncdb/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:tbr2ncdb/"}, {"pid": "bdr:tqeem868", "object_type": "pdf", "abstract": ["We study scattering amplitudes in N=4 SYM, holographic models of four-dimensional flat-space scattering amplitudes in terms of two-dimensional conformal fields theories dubbed celestial CFTs (CCFT), and the structure of infrared divergences in gauge theories. We begin by enumerating the all-loop singularity structure of seven-point amplitudes in N=4 SYM. We do so by solving the Landau equations for the seven-point Ziggurat graph, and find four new cyclic classes not anticipated by the heptagon symbol alphabet. A highly constraining property of N=4 SYM is it's Yangian symmetry. We classify and enumerate the class of Yangian invariants where the particle number $n$ is related to the helicity violating degree k by n=5k. We then turn to analyzing the properties of CCFTs which are holographically dual to flat-space scattering amplitudes. We analyze the correlation functions and operator product expansions of light-ray operators appearing in the CCFT spectrum. We then turn to loop level analyses of OPEs in CCFT. Lastly, we study infrared divergences in gauge theories. These divergences arise due to the asymptotic states failing to converge appropriately to free particle states. We analyze the asymptotic angular momentum of the classical electromagnetic field in the presence of far-separated charged particles in order to quantify the deviation from free particle states. An interesting feature of the result is that, although the total angular momentum of the EM field and that of the charged particles' is independent of the Cauchy surface on which these quantities are computed, the splitting between field and particle angular momentum is dependent on the details of the Cauchy surface."], "keyword": ["scattering amplitudes", "Celestial sphere", "infrared divergences"], "primary_title": "Scattering Amplitudes in N=4 SYM and the Infrared Structure of Gauge Theories", "uri": "https://repository.library.brown.edu/studio/item/bdr:tqeem868/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:tqeem868/"}, {"pid": "bdr:45q7ruhe", "object_type": "pdf", "abstract": ["We present an analysis of systematic signals in the Epoch of Reionization (EoR) Data from Phase II of the Murchison Widefield Array (MWA). Prior work analysed the same observations and reported some previously unidentified common mode systematic signals. We test relevant searching codes and become the first one to successfully indentify systematics using 2-minute observation. We find that the appearance of systematic signals are consistent across different times. The probability of systematic appearances have a linear relationship with baseline lengths and show faint dependence on tile location. The physical origins of these systematics are still unclear but they may bring risks into 21-cm power spectrum estimation."], "keyword": ["Astrophysics", "Cosmology", "Radio astronomy"], "primary_title": "Analysis of Systematic Signals in the Epoch of Reionization Data from MWA", "uri": "https://repository.library.brown.edu/studio/item/bdr:45q7ruhe/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:45q7ruhe/"}, {"pid": "bdr:8f596sqw", "object_type": "pdf", "abstract": ["The representation theory of supersymmetry is further developed, starting from questions about the role of the symmetric group in 1D, N-extended supersymmetry and the construction of higher order supermultiplets from lower order supermultiplets. These questions lead to the discovery of an invariant ``magic\u2019\u2019 number that dictates the allowed elements in a supermultiplet analogously to a vertex graph coloring problem. The recursive construction of higher order supermultiplets from lower order supermultiplets is revealed to be operationally equivalent to the recursive construction of higher order permutohedra from lower order permutohedra. This provides a way to construct arbitrary N-extended supersymmetric theories. Conjectures are made about possible uses of this formalism in the constructon of Calabi-Yau manifolds and Grassmannians."], "keyword": ["Polytopes", "Supersymmetry", "representation theory"], "primary_title": "Recursive Construction of N-extended Supersymmetry Through Polytopic Representation Theory", "uri": "https://repository.library.brown.edu/studio/item/bdr:8f596sqw/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:8f596sqw/"}, {"pid": "bdr:11059", "object_type": "pdf", "abstract": ["At temperatures below 1K, nm thick a-Bi/Sb films, patterned with a nanohoneycomb array of holes, exhibit a novel electronic state consisting of localized Cooper pairs. The Superconductor Insulator Transition (SIT), a phenomenon where the ground state of electrons is tuned from a superconducting to an insulating state, on this patterned homogeneous system shows a clear bosonic nature with activated transport on the insulating side. To date, this homogeneous system is the only one that shows clear evidence for the localization of Cooper pairs. Experiments are described that were performed to further characterize the properties of the localized Cooper pair state and its superconductor to insulator transitions. We show that: (i) The shape of the magnetoresistance (MR) oscillations, which indicate the presence of Cooper pairs in these multiply connected systems, depends on the geometry of the underlying substrates, but not on parameters like the temperature or thickness of the films. The magnetic field tuned SITs of films that are just thick enough to superconduct at zero magnetic field exhibit a common critical sheet resistance separating the superconducting and insulating phases in the range of 3.5 to 5kOhm. We also report a new type of SIT, an incommensurability driven SIT, which occurs due to the interplay of magnetic field and disorder in the arrangement of the honeycomb array of holes. (ii) The Cooper pair insulator state exhibits a giant positive MR, which peaks at a field estimated to be sufficient to break the pairs. The electrical transport on the low field side of the peak is activated. At the highest fields, it resembles G~ log(T), which is consistent with the behavior expected for weakly localized electrons rather than strongly localized Cooper pairs. We discuss this MR peak, compare it to that observed in other amorphous systems and propose a zero temperature phase diagram for these films."], "keyword": ["low temperature physics", "superconductor insulator transition", "Hung Nguyen", "James Valles", "Low temperatures", "Superconductivity", "Magnetoresistance"], "primary_title": "Experiments on a Cooper Pair Insulator", "uri": "https://repository.library.brown.edu/studio/item/bdr:11059/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:11059/"}, {"pid": "bdr:1105474", "object_type": "pdf", "abstract": ["In this work, I consider some of the recently proposed constraints on mixed dark matter scenarios involving primordial black holes (PBHs) and Weakly Interacting Massive Particles (WIMPs). In such a model, PBHs accrete dense dark matter halos of WIMPS around them, and because of WIMP annihilations, the emission of gamma rays is an observable signature. The greater the fraction of dark matter attributed to PBHs, the greater the number of WIMP annihilations around PBHs, and the greater the gamma-ray emission. Using the Fermi Large Area Telescope (LAT) measurements of the diffuse extra-galactic gamma-ray background emission (EGB), I consider what fraction of dark matter may be attributed to PBHs based on the flux detected. I find that this fraction can be at most about one part in 10^11, suggesting that WIMPs and PBHs are incompatible and cannot coexist."], "keyword": ["Dark matter (Astronomy)", "WIMP", "Black holes (Astronomy)", "Astrophysics--Research"], "primary_title": "Can primordial black holes and WIMPs coexist?", "uri": "https://repository.library.brown.edu/studio/item/bdr:1105474/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:1105474/"}, {"pid": "bdr:11119", "object_type": "pdf", "abstract": ["Recording and modulation of large neuronal populations are essential for uncovering the dynamical properties of complex neural circuits. In the last few decades, various optical neural recording and modulation methods have been developed. In this thesis, I present the synergistic application of three different optical tools in the study of neural dynamics of two different neural systems.In the first part, we applied wide field calcium imaging with a high speed CCD camera to study development of the visual system of Xenopus laevis tadpoles. Calcium signals from up to 90 optic tectal neurons were simultaneously recorded with millisecond temporal resolution. After reconstructing the electrical neural activity from their calcium signals, we compared neural synchrony over development, and found that tectal neurons in older tadpoles responded more synchronously to whole field visual stimuli when compared to younger animals. To discover the mechanisms underlying this effect, we reared animals in different environments during a critical developmental period. Dark-rearing resulted in a severe disruption in the development of neural synchrony, indicating that visual experience is crucial for this process. Blocking NMDA receptors showed a similar but smaller effect, suggesting that NMDA receptor activation is one mechanism involved in this process. Experimental results were further explained using a spike-timing dependent plasticity-based neural network model. Moreover, using a specially fabricated matrix-addressable LED array-based image projection device to generate visual stimuli, we found that tectal neurons of older animals showed much sharper and more refined visual receptive fields.In the second part, we genetically targeted and expressed a photosensitive cation channel channelrhodopsin-2 on mouse medial dorsal nucleus (MDN) of the thalamus to study how the MDN axon inputs affect the collective activity of prefrontal cortical neurons. Photostimulation of channelrhodopsin-2 expressing MDN axons in mouse prefrontal cortical slices triggered spiking activity with millisecond temporal precision, which allows MDN-axon specific optical activation. Combined with calcium imaging, we found that MDN inputs can elicit synchronous activity in PFC, which is believed to play an essential role in working memory. This suggests that MDN may also be involved in working memory."], "keyword": ["LED array", "calcium imaging", "retinotectal system", "medial dorsal nucleus", "Optogenetics", "Prefrontal cortex"], "primary_title": "Optical Recording and Photo Modulation in the Study of Dynamics in Neural Circuits", "uri": "https://repository.library.brown.edu/studio/item/bdr:11119/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:11119/"}, {"pid": "bdr:11124", "object_type": "pdf", "abstract": ["The \"E and B mode EXperiment,\" (EBEX) is a balloon-borne telescope which aims to measure the polarization of the cosmic microwave background radiation in three frequency bands: 150, 250, and 410 GHz. EBEX had an engineering flight on June 11, 2009. It was launched from the Columbia Scientific Balloon Facility in Fort Sumner, New Mexico, and terminated near the California-Arizona border following a 14 hour flight. We present an overview of the EBEX instrument and science goals. To achieve its goal of 8 arcminute resolution, EBEX requires precise pointing, which is achieved through the use of a star camera and gyroscopes. In addition, EBEX employs several coarse sensors, including a sun sensor. The sun sensor is designed to give the position of the sun to better than 1 degree , while the star camera gives the position of the telescope to within 6 arcseconds. We discuss the design, implementation, and performance of these two pointing sensors for EBEX and review their performance during the North American flight."], "keyword": ["polarization", "cosmic microwave background", "Astrophysics", "Cosmology", "Cosmic background radiation"], "primary_title": "EBEX, a balloon-borne telescope for observing the polarization of the cosmic microwave background", "uri": "https://repository.library.brown.edu/studio/item/bdr:11124/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:11124/"}, {"pid": "bdr:11220", "object_type": "pdf", "abstract": ["We study several aspects of high energy scattering using the AdS/CFT correspondence.We begin with concise theoretical overviews of a few relevant topics. First is a generalintroduction to scattering theory, where we define most of the relevant concepts and termswhich we will use later, and introduce the physical motivation for studying them. We followthat by introducing Regge theory, which has had a storied history since its\ufffd beginnings.We discuss Regge trajectories and the Pomeron and Odderon, which we will return tolater. Next we turn to a short introduction to quantum chromodynamics. We discussasymptotic freedom and confinement in quantum chromodynamics, which allows us toexamine the main ideas from DIS processes and Pomeron exchange at weak coupling. Wethen turn to introducing relevant concepts from string theory. In particular, we study themassless spectrum of states, consisting of the graviton, Kalb-Ramond field and the dilaton,and then introduce string vertex operators and study how we can use them to calculatestring scattering amplitudes. After these introductory chapters we introduce the formalismdeveloped by Brower, Polchinski, Strassler and Tan [1], and Brower, Strassler and Tan [2, 3]to study high energy scattering in the Regge limit using string theory and the AdS/CFTcorrespondence. This involves developing a Pomeron vertex operator in AdS space stringtheory, and using it to find the eikonal approximation to the scattering amplitude. ThePomeron is found to correspond to the Regge trajectory of the graviton. Finally, wethen apply these techniques to study at strong coupling some of the relevant concepts weintroduced initially at weak coupling. We begin by keeping the next order term in theexpansion that BPST used to define the Pomeron vertex operator, and find that doing sowill correspond to defining the Odderon in AdS space. We note that due to symmetryarguments the Odderon can sometimes be the leading order exchange, and find that inAdS space it corresponds to the Regge trajectory of the Kalb-Ramond field. We next turnto the study of DIS at strong coupling."], "keyword": ["High Energy", "AdS/CFT", "DIS", "Odderon"], "primary_title": "Aspects of High Energy Scattering and AdS/CFT", "uri": "https://repository.library.brown.edu/studio/item/bdr:11220/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:11220/"}, {"pid": "bdr:11226", "object_type": "pdf", "abstract": ["Chemical reactions of the early actinide elements in aqueous solution are complex and challenging to predict. Quantitative models of actinide reactions must overcome several obstacles. First relativity and the energetics of solvation must be taken into account. At present only the density functional theory (DFT) method is capable of modeling these aspects accurately. However, incorporating the physics of strong electronic correlations among the 5f electrons presents a greater challenge as these are known to be poorly captured by DFT. This thesis takes a hybrid approach to solving these problems by using DFT to construct a generalized Anderson impurity model of the frontier orbitals. Exact diagonalization of the Anderson impurity model corrects the free energy obtained from DFT alone, yielding improved predictions for redox free energies of An(VI)/An(V), An(V)/An(IV), and An(IV)/An(III), where An is an element in the family of early actinides (U, Np, and Pu), as well as for the redox couples of Am(VI)/Am(V) and Am(V)/Am(III).The first part of this thesis discusses the ab initio part of the calculation and compares the results obtained to past calculations by other research groups. The physics of the strong electronic correlations is studied through the construction of the many-body model that describes the coulomb interaction. The essential physics is then illustrated with a simplified model. Finally, extensive details of the calculations are presented in the appendices."], "keyword": ["DFT", "Anderson impurity model", "Actinides", "Redox Potential", "Hubbard model", "Actinide elements"], "primary_title": "Strong Correlations in Aqueous Actinide Complexes", "uri": "https://repository.library.brown.edu/studio/item/bdr:11226/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:11226/"}, {"pid": "bdr:11242", "object_type": "pdf", "abstract": ["The neocortical-entorhinal-hippocampal circuit has been shown to play an important role in memory formation and consolidation. Furthermore, the entorhinal cortex (EC) and the hippocampus are thought to be key components of the brain\ufffds spatial processing system. I examine both of these aspects using quantitative analysis of single-neuron and network activity. In part 1, I investigate the dynamics of the neocortical-entorhinal-hippocampal circuit in anesthetized mice where cortical neurons alternate between a depolarized and spiking \ufffdUP\ufffd state and a hyperpolarized and quiescent \ufffdDOWN\ufffd state. I first demonstrate an explicit-duration hidden Markov model algorithm for inferring UP-DOWN states (UDS) from both membrane potential and local field potential recordings. I then apply this method to study UDS in superficial neurons of the medial and lateral EC (MEC and LEC). MEC, but not LEC, neurons are shown to selectively decouple from the neocortical UDS and exhibit persistent UP states whose duration is quantized in units of neocortical UDS cycles. In contrast, LEC, but not MEC, neurons are found to display periods of pronounced 2-4Hz oscillations which are phase-locked to the ongoing UDS. In part 2, I examine the hippocampal \ufffdrate\ufffd and \ufffdtemporal\ufffd codes for position in freely behaving mice. The spatial and temporal firing properties of hippocampal neurons in GluA1 knockout (KO) mice are found to be dramatically altered relative to wild-type mice, and the network theta and gamma oscillations are also markedly reduced in the KO animals. I then examine the precession of hippocampal neurons\ufffd spike phase relative to the theta rhythm, and demonstrate a novel dependence of the temporal code on behavior. These studies reveal important mechanisms by which the EC could shape neocortical-hippocampal interactions during sleep, and advance our understanding of how the hippocampal \ufffdrate\ufffd and \ufffdtemporal\ufffd codes are generated and relate to behavior."], "keyword": ["UP-DOWN states", "hippocampus", "entorhinal cortex", "Sea horses", "Hidden Markov models"], "primary_title": "Single-Neuron and Network Dynamics in the Neocortical-Entorhinal-Hippocampal Circuit", "uri": "https://repository.library.brown.edu/studio/item/bdr:11242/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:11242/"}, {"pid": "bdr:220", "object_type": "pdf", "abstract": ["Current heightened interest in alternative energy technologies have made nanostructured materials which integrate contrasting electronic materials subject to investigation for applications such as next-generation solar cells. One example is hybrid heterojunctions which combine high-performance organic and inorganic semiconductors as a photodetecting composite. Another case is that of subwavelength scale \"nanotexture\" in photonically active materials for enhanced light matter interaction e.g. in a densely packed nanowire(NW) environment. In this thesis, we focus on optoelectronic characterstics of two distinct semiconductor nanoscale systems while investigating electron-hole dynamics and photon capture, respectively. First, we explore (In)GaN/CuPc(copper phthalocyanine)?inorganic/organic hybrid semiconductor heterojunctions for their potential in novel photodetector applications. The details of the electronic interface states of planar thin film GaN/CuPc heterostructures are investigated by ultraviolet photoemission spectroscopy (UPS) and X-ray photoemission spectroscopy (XPS). We show quantitatively how N-polar and Ga-polar GaN exhibit striking differences in their intrinsic surface electronic states. When a CuPc overlayer is present, contrasting band bending and energy band offsets further emphasize the effects of surface termination and polarization fields for these two types of GaN substrates. Secondly, we explore photon capture in Si nanowire arrays and show how these arrays can be monolithically incorporated into novel metal-insulator-silicon (MIS) photodetectors. We quantify the enhancement in optical absorption of Si NWs by direct experimental comparison of the same types of planar Si MIS and commercial p-i-n photodetectors. In addition to their robust photoresponse, our Si NW photodetectors maintain high EQEs up to large angles of incidence suggesting that NWs might be uniquely suited for efficient and stable light harvesting."], "keyword": ["Hybrid heterojunctions", "Si nanowires", "ZnO nanocones"], "primary_title": "Interface studies on the organic-inorganic hybrid heterojunctions and device applications of nanowire materials", "uri": "https://repository.library.brown.edu/studio/item/bdr:220/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:220/"}, {"pid": "bdr:232", "object_type": "pdf", "abstract": ["Although recent studies have identified the biochemical components required to generate motile forces by actin polymerization, how the forces are generated remains unclear. To elucidate this molecular mechanism of cell motility, I investigated the biophysical conditions under which actin-based growth and motility take place. In Part I of this dissertation, I report an experimental study on the kinetics of actin assembly mediated by branching and capping proteins. The experiments were performed by fluorescence imaging and light-scattering intensity measurement. The findings confirm the recent theoretical prediction that a \"branching explosion\" occurs during polymerization. Furthermore, the branching explosion occurs over a limited range of the ratio between branching protein and capping protein concentrations. This is also consistent with the theoretical model. These results establish a natural link between the kinetic theory of actin assembly in vitro and the cytoskeletal structure and actin dynamics in motile cells. In Part II of this dissertation, I present an in vitro study of the actin-based movement of functionalized spherical beads in comparison with those of bacteria like Listeria. Long trajectories induced by the spherical beads show characteristic differences with those observed for bacteria, which have both an elongated shape and an asymmetric expression of the polymerization inducing enzyme. The experimental trajectories can be simulated using a generalized kinematic model that includes the rotation of the bead relative to the actin tail. These results imply that the trajectories of spherical beads are mechanically deterministic rather than random, as suggested in stochastic models. In Part III of this dissertation, I examine nonlinear viscoelasticity of cross-linked biopolymer networks, by rheological measurements of shear moduli and normal stresses in fibrin gels. The results for coarse fibrin gels are consistent with expectations from theories of rod-like filament networks. Comparison of rheological and optical properties shows that the filament alignment, as measured by optical retardance increases with increasing shear strain but lags behind the increase in shear moduli."], "keyword": ["in vitro actin assembly", "kinematics of actin tail growth", "nonlinear elasticity of fibrin gel"], "primary_title": "Kinetic and Kinematic Properties of Actin Network Assembly and Nonlinearity of Cross-Linked Gels", "uri": "https://repository.library.brown.edu/studio/item/bdr:232/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:232/"}, {"pid": "bdr:233", "object_type": "pdf", "abstract": ["We have fabricated and investigated the electrical and magnetic behavior of polycrystalline and epitaxial CrO2 nanostructures, grown using selective-area growth technique. Magnetic domain structures were studied by magnetic force microscopy, and in-plane, lamellar domain structure with fragmented walls aligned along the magnetic easy axis direction have been observed, indicating a large magnetocrystalline anisotropy in epitaxial CrO2 nanostructures. Low-temperature transport measurements on nanowires have shown that the dc resistivity of polycrystalline CrO2 wires is strongly dependent on the linewidth. Below a critical temperature, a transition from a positive to a negative temperature coefficient of resistivity have been observed, which we attribute to a competition between the scattering of the conduction electrons inside the grains and scattering across the grain boundaries. Using a model based on grain boundary scattering, we estimate a mean transmission probability through the grain boundaries to be on the order of 10?1. Furthermore, magnetoresistance (MR) measurement indicates that the MR behavior of polycrystalline wires is dominated by the shape anisotropy; however, for epitaxial wires, both the shape and magnetocrystalline anisotropy play important roles, and the resulting MR properties are found to be closely related to the orientation of the wire axis. By studying the MR curves, we inferred the internal domain structures in various single crystal CrO2 wires and found that the spin-dependent transport is much stronger across a grain boundary than a domain wall. We have also studied the magnetotransport properties of CrO2 nanocontacts. Manipulating the domain walls using a large dc current in the contact area yields a magnetoresistance of up to 25%, which is the largest ever seen in a single ferromagnetic film. The single domain-wall-resistance is determined to be three orders of magnitude larger than that of conventional 3d ferromagnets, as a result of the material's half-metallicity. We have measured DWR and the spin-torque effect along different crystallographic axes and at varying temperatures. Finally, we present the results of a theoretical analysis of this system, based on its half-metallic character and on the intrinsic magnetic behavior of CrO2."], "keyword": ["Chromium Dioxide", "Half-metal", "Nanostructures", "Magnetoresistance"], "primary_title": "Magnetic Domain Configurations and Huge Wall Resistivity in Half-metallic Chromium Dioxide (CrO2) Nanostructures", "uri": "https://repository.library.brown.edu/studio/item/bdr:233/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:233/"}, {"pid": "bdr:241", "object_type": "pdf", "abstract": ["A wealth of evidence indicates that ~23% of the universe is composed of dark matter. For the past two decades, several experiments have attempted to detect dark matter directly or indirectly. Nevertheless, its nature remains one of the most elusive problems in fundamental physics today. XENON10 is a direct detection experiment, using a liquid Xe Time Projection Chamber (TPC) to search for dark matter in the form of Weakly Interacting Massive Particles (WIMPs). Particle interactions in the 15 kg liquid Xe target generate scintillation (S1) and ionization (S2) signals. WIMP (and neutron) interactions produce nuclear recoils. The dominant backgrounds (gamma rays and beta particles) produce electron recoils. The S2/S1 ratio is larger for electron recoils than for nuclear recoils, allowing for the rejection of electron recoil backgrounds with ~99.6% efficiency. XENON10 operated underground at the Laboratori Nazionali Gran Sasso in Italy during 2006-2007. Analysis of its WIMP Search run of 58.6 live-days and 5.4 kg fiducial mass resulted at the time in the most sensitive limits on the Spin-Independent WIMP-nucleon cross-section, setting an upper limit of 8.8x10^-44 cm^2 for a WIMP mass of 100 GeV/c^2 (90% C.L.). The large scale experiment LUX (300 kg) is designed to improve the sensitivity to WIMP interactions by two orders of magnitude, and will be deployed in the Sanford Laboratory at the Homestake Mine in 2009-2010. Next-generation Xe TPC detectors with masses in the order of 1-10 tonnes are already in the design stage, with planned deployment in the next ten years. In dark matter search experiments, backgrounds are the biggest factor limiting sensitivity. This work presents a discussion of the use of liquid Xe detectors in dark matter experiments; details the construction of background models through the use of Monte Carlo simulations; identifies and characterizes the major sources of background; explores how shielding and detector design affect the background event rate; and explains the techniques used to reduce the effect of backgrounds on the detector sensitivity."], "keyword": ["Dark Matter", "Liquid Xenon", "Backgrounds", "Monte Carlo simulations", "Particle Astrophysics", "XENON10", "LUX", "Dark matter (Astronomy)"], "primary_title": "Optimization of Signal versus Background in Liquid Xe Detectors Used for Dark Matter Direct Detection Experiments", "uri": "https://repository.library.brown.edu/studio/item/bdr:241/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:241/"}, {"pid": "bdr:13", "object_type": "pdf", "abstract": ["When a free electron is injected into liquid helium, it forms a microscopic bubble essentially free of helium atoms, which is referred to as an electron bubble. It represents a fine example of a quantum-mechanical particle confined in a potential well. In this dissertation, we describe our studies on bubble properties, especially the optical absorption properties of ground state electron bubbles and experiments on imaging individual electron bubbles in liquid helium. We studied the effect of zero-point and thermal fluctuations on the shape of ground state electron bubbles in liquid helium. The results are used to determine the line shape for the 1S to 1P optical transition. The calculated line shape is in very good agreement with the experimental measurements of Grimes and Adams. For 1S to 2P transition, the obtained transition line width agrees well with the measured data of Zipfel over a range of pressure up to 15 bars. Fluctuations in the bubble shape also make other \"unallowed\" transitions possible. The transition cross-sections from the 1S state to the 1D and 2D states are calculated with magnitude approximately two orders smaller than that of the 1S to 1P and 2P transitions. In our electron bubble imaging experiments, a planar ultrasonic transducer was used to generate strong sound wave pulse in liquid helium. The sound pulse passed through the liquid so as to produce a transient negative pressure over a large volume (~1cc). An electron bubble that was passed by the sound pulse exploded for a fraction of a microsecond and grew to have a radius of around 10 microns. While the bubble had this large size it was illuminated with a flash lamp and its position was recorded. In this way, we can determine its position. Through the application of a series of sound pulses, we can then take images along the track of individual electrons. The motion of individual electron bubbles has been successfully monitored. Interesting bubble tracks that may relate to electrons sliding down vortices and the bending of bubble tracks in external field are observed. The possible origins of some observed electron tracks are studied."], "keyword": ["electron bubble", "optical transition", "vortices", "Liquid helium"], "primary_title": "Optical absorption properties of electron bubbles and experiments on monitoring individual electron bubbles in liquid helium", "uri": "https://repository.library.brown.edu/studio/item/bdr:13/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:13/"}, {"pid": "bdr:145", "object_type": "pdf", "abstract": ["This dissertation explores several approaches to quantum gravity, all of them adding some quantum features to an otherwise classical theory. The first part is about black holes and cosmological horizons. The latter are investigated using an approach to noncommutative geometry in which the isometry Lie algebra is deformed to a quantum group. This is applied to two- and three-dimensional de Sitter space. A particular type of 'hairy' black hole in six-dimensional dilaton gravity is also investigated, and it is shown that this does not have an extremal limit. The second part is about semi-classical strings in the AdS/CFT correspondence, and in particular giant magnons. A class of solutions in some sense T-dual to giant magnons are investigated, and by performing semiclassical quantisation these are shown not to be supersymmetric. Giant magnons are then studied in the ABJM / CP^3 duality, where there are several different kinds. The dyonic generalisation of the fundamental (or 'small') giant magnon is constructed. Finite-size corrections to all classes of giant magnons are then computed, using the algebraic curve."], "keyword": ["String Theory", "Black Holes", "AdS/CFT", "Giant Magnons", "Physics", "String models"], "primary_title": "Semi-classical Approaches to Quantum Gravity and String Theory Solitons", "uri": "https://repository.library.brown.edu/studio/item/bdr:145/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:145/"}, {"pid": "bdr:132", "object_type": "pdf", "abstract": ["Integrability of both sides of AdS/CFT has enabled many quantitative checks of the correspondence. The Bethe ansatz determines the anomalous dimensions of gauge theory operators, which at strong coupling are also encoded in the energies of classical string configurations. The ``giant magnon'' is a particular limit that simplifies the spectrum on both sides of the correspondence. In this limit a general state can have any number of elementary excitations (magnons) and their bound states. In this dissertation we construct classical string solutions describing arbitrary superpositions of scattering and bound states of multi-charged giant magnons in various spaces including $AdS_5 \\times S^5$ and $AdS_4 \\times CP^3$. We use the sigma model dressing method to construct these solutions and analyze several of their properties, such as their scattering phase shift. We also use the inverse scattering and dressing methods to find various string solutions in $AdS$ whose edges trace out complicated timelike curves on boundary. These solutions correspond to $\\sinh$-Gordon solitons and breathers and may be used to calculate certain Wilson loops via AdS/CFT. Our results provide important quantitative checks of the AdS/CFT correspondence."], "keyword": ["classical string solutions"], "primary_title": "Classical String Solutions in AdS/CFT", "uri": "https://repository.library.brown.edu/studio/item/bdr:132/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:132/"}, {"pid": "bdr:129", "object_type": "pdf", "abstract": ["The AdS/CFT correspondence is a conjecture which relates gauge theories to string theories. In order to better understand this duality, several avenues can be taken, such as the study of the internal symmetries shared by both theories and their integrability properties. Integrability of maximally symmetric field theories and classical string theory is a tool which allows a very detailed study of these theories. Also the study of classical solitonic string solutions and their semi-classical behavior can lead us toward a better understanding of the full quantum theory. In this work, I have addressed these aspects of the AdS/CFT duality, within two known examples of this duality. I first focus on the superalgebra of symmetries from a matrix model point of view, followed by a thorough study of string solitons called giant magnons, and related solutions, with detailed analysis of their semi-classical behavior and the very rich relation between their dynamics and an N-body theory. I finally focus on the the integrability of the string sigma-model and use the string Bethe ansatz to determine the spectrum of string solitons and further properties of those."], "keyword": ["AdS/CFT", "Semi-Classical Strings", "Integrable Structures", "Giant Magnons", "Symmetry Algebra", "Solitons"], "primary_title": "Aspects of AdS/CFT Correspondence: Symmetries, Integrability and Solitons", "uri": "https://repository.library.brown.edu/studio/item/bdr:129/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:129/"}, {"pid": "bdr:166", "object_type": "pdf", "abstract": ["The Standard Model (SM) is a very successful theory, whose predictions have been consistent at high precision with numerous experimental results up to the present. However, the Standard Model is not a complete theory. For example, there may exist new massive long-lived particles, such as predicted by many extensions of the Standard Model. Such particles could carry electric charge, and live long enough to travel several meters and to escape a typical collider detector before decaying. In this dissertation we present a search for such particles using the data collected by the detector at the Fermilab Tevatron p\\bar{p} collider corresponding to an integrated luminosity of 1.1 fb^{-1}. Time-of-flight information is used to search for pair produced long-lived particles. The results are interpreted in three models: tau sleptons, gaugino-like charginos, and higgsino-like charginos. We find no evidence of a signal and set upper limits on the stau production cross section (at 95\\% Confidence Level), which vary from 0.31 pb to 0.04 pb for stau masses between 60 GeV and 300 GeV. We also set lower mass limits of 206 GeV for pair produced charged gauginos, and 171 GeV for charged higgsinos, respectively."], "keyword": ["CMSP stau chargino"], "primary_title": "Search for Charged Massive Long-lived Particles Using D0 Detector", "uri": "https://repository.library.brown.edu/studio/item/bdr:166/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:166/"}, {"pid": "bdr:147", "object_type": "pdf", "abstract": ["This dissertation explores two independent projects in biophysics. Part one focuses on the liquid crystalline phase transition of F-actin. The cytoskeletal protein actin can be found in both an unordered isotropic state and an aligned nematic state, and plays an important role in cell structure and motility. The phase transition between these states is predicted to be a first order transition, yet previous results have found it to be continuous. We show here that the transition is truly first order under the proper conditions of high concentration and short average filament lengths. Under this regime, the solution spontaneously separates into ordered domains in the shape of tactoidal droplets. We explore the formation and growth mechanisms of the tactoids and find that the system is only metastable. These findings help clarify the phase separation and co-existence of actin, and may be of relevance to its biological functions. Part two examines the interaction of leukocytes with their substrate. We use polyacrylamide gels to explore the role of the mechanical environment in determining neutrophil behavior. We find that neutrophils spread more and migrate slower but more persistently on stiff substrates. Inhibition of phosphatidylinositol 3-kinase (PI3K) removes this ability of the neutrophil to sense the substrate stiffness, suggesting a role for PI3K in the mechanism responsible for neutrophil mechanosensing. Furthermore, we find that neutrophil force generation is strain limited and independent of substrate stiffness within a limited range. The greatest forces are found in the posterior of the cell, suggesting that the neutrophil pushes, rather than pulls itself forward. Finally, we use polarized T lymphocytes observed under total internal reflection fluorescence (TIRF) microscopy to explore the localization of integrins, the molecules responsible for adhesion to the extracellular matrix. Active integrins are found localized in the anterior of the cell during migration. These findings elucidate the many complex interactions between the cell and substrate, which drive leukocyte behavior. Future studies based on these findings may lead to insights concerning the physiological functions of leukocytes, and in particular how these functions are regulated by the mechanical properties of the surrounding tissues."], "keyword": ["actin", "liquid crystalline phase transition", "tactoid", "mechanosensing", "Neutrophils"], "primary_title": "The Liquid Crystalline Transition of F-actin and Neutrophil Mechanosensing", "uri": "https://repository.library.brown.edu/studio/item/bdr:147/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:147/"}, {"pid": "bdr:159", "object_type": "pdf", "abstract": ["We study the rheological properties of reconstituted actin networks by tracking the thermal motion of embedded micron-sized probe beads with four types of surface coatings. For the most slippery beads, thermal motion causes those smaller than the network mesh size to percolate through the network or hop from one confinement \"cage\" to another. Consequently, the smaller beads sense a weaker network. This trend is reversed for three other types of beads, which detect an apparently stiffer network due to the physisorption of nearby filaments to the bead surface. We also confirm the existence of a depletion layer around non- or weakly-sticky probe surfaces by confocal imaging. Analysis of these effects is necessary in order to accurately define the actin network rheology both in vitro and in vivo. We investigate microrheological properties of F-actin across the isotropic-nematic phase transition region by both video particle tracking and laser deflection particle tracking. As the nematic order parameter increases with actin concentration, the storage modulus in the perpendicular direction grows faster and larger than that in the perpendicular direction. Furthermore, we find that the viscoelasticity of F-actin network varies with the magnesium concentration more sensitively in the nematic phase than in the isotropic phase. In all, particle tracking microrheology reveals rich rheological features of F-actin affected by the isotropic-nematic phase transition and by tuning weak electrostatic interactions among the protein filaments. To address the network dynamics, we observe an abnormal slowdown of the longitudinal diffusion of F-actin across the isotropic-nematic phase transition region. We also find that the F-actin diffusion across the transition region markedly differs from the diffusion of microtubule and fd virus in F-actin solutions. Additionally, the viscous drag probed by F-actin is found to increase sharply with magnesium concentration in the nematic but not in the isotropic state. Based on these results, we propose that the abnormal slowdown is caused by the counterion induced transient association between parallel actin filaments in the nematic phase."], "keyword": ["abnormal slowdown", "counterion", "nematic phase", "surface adsorption", "hopping", "depletion", "Diffusion", "Surface active agents--Absorption and adsorption"], "primary_title": "Microrheology and Dynamics of F-actin Networks", "uri": "https://repository.library.brown.edu/studio/item/bdr:159/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:159/"}, {"pid": "bdr:179", "object_type": "pdf", "abstract": ["We present our work on the study of gigahertz ultrasound propagation in water by using the picosecond ultrasonic technique. An advanced opto-acoustic detection scheme through the use of a Fabry-Perot resonant optical cavity was developed in order for the weak opto-acoustic signals caused by the sound pulses in water to be efficiently detected with a reasonable signal to noise ratio. By using this advanced detection technique, we investigated the acoustic attenuation and dispersion in water at different temperatures. Our experimental results indicate that, in the frequency range up to 11 GHz, there is no acoustic dispersion in water. Over this frequency range, the acoustic attenuation in water is found to be proportional to the square of the frequency. We also report our picosecond acoustic interferometry measurement results of the velocity and attenuation of sound waves in water at about 5 GHz. In addition to the study of sound waves in unbounded water, we studied ultra-short sound pulse propagation in water confined in nanometer scale deep trenches. We found that the sound pulses traveling through the deep trenches have different temperature dependence from the sound pulses reflected by the tops of the semiconductor lines. Our further investigation shows that this effect is caused by the strong shear viscous force acting on the sound pulses as they travel down the trenches."], "keyword": ["ultrafast; laser; acoustics"], "primary_title": "Study of Gigahertz Ultrasound Propagation in Water Using Picosecond Ultrasonics", "uri": "https://repository.library.brown.edu/studio/item/bdr:179/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:179/"}, {"pid": "bdr:17", "object_type": "pdf", "abstract": ["Particles other than bosons and fermions can exist in two dimensions. One possibility is that when one particle makes a circle around another particle the total many-particle wave function acquires a non-trivial phase factor. Such particles are called Abelian anyons. In a more exotic situation, the action of moving one particle around other particles or in other words, particle braiding, is represented by a unitary matrix acting on the quantum-state vector. If the braiding matrices do not commute with each other, the particles are called non-Abelian anyons.\\\\ The existence of both Abelian and non-Abelian anyons has been predicted in Fractional Quantum Hall systems. Quasiparticles in the Laughlin states with filling factor $\\nu=1/(2m+1) $ are Abelian anyons. On the other hand, quasiparticles in the Moore-Read and Read-Rezayi states with filling factors $ \\nu=5/2 $ and $ \\nu=12/5 $ , respectively, are proposed to be non-Abelian anyons. However, no experimental observation of the exchange statistics of identical anyons has been reported so far. \\\\ In this thesis we demonstrate that the current and shot noise in the topologically nontrivially set-up of the electronic Mach-Zehnder interferometer can be used to detect anyonic statistics. The transport is not sensitive to the fluctuations of the topological charge inside the interferometer and hence the interference picture is not destroyed by the tunneling of low-energy neutral excitations between the edges and localized states in the interferometer. The current and noise exhibit non-Analytic dependences on small tunneling amplitudes. The low-temperature Fano factor is always below 1 for Abelian anyons and can greatly exceed 1 for non-Abelian statistics."], "keyword": ["Anyonic Statistics", "Non-Abelian Statistics", "Mach-Zehnder interferometer", "Quantum Hall effect"], "primary_title": "Probing Abelian and Non-Abelian Statistics in Fractional Quantum Hall States", "uri": "https://repository.library.brown.edu/studio/item/bdr:17/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:17/"}, {"pid": "bdr:178", "object_type": "pdf", "abstract": ["Access to ultrafast physical phenomena through the use of real-time laser spectroscopy is a vibrant field in science and engineering today. Ultrashort laser pulses with controlled energy of sub-picosecond duration can be used to probe fastest events in atomic, molecular, solid state and biochemical systems. In this thesis, we employed ultrafast lasers for light-matter interaction of selected ultrafast electronic, magnetic and acoustic processes in distinctly different media. One area of interest in this thesis is the dynamics of electron spins in ferromagnetic materials. Previous work in our group successfully demonstrated ultrafast coherent magnetization rotation in the ferromagnetic thin film triggered by ultrafast optical pulses. In this thesis we extended the study of ultrafast spin dynamics to magnetic nanostructures. In another material system, a nanocomposite of ferromagnetic and noble metals, we show how noble metal nanoparticles are capable of greatly enhancing the magneto-optical response of the hybrid nanomaterials when excited at their plasmonic resonance wavelength. We describe the physics that enables the plasmonic resonance behavior of the noble-metal nanoparticles to improve their magnetooptical response. While initially focusing on measurements of the transient magnetooptical effect in the nanocomposites by ultrashort pulse optical techniques, we discovered a strongly competing signature which originated from optically induced acoustic vibration of the nanoparticles. The pronounced acousto-optical transient phenomena led to the study of laser picosecond ultrasonics. In this part of work we address the challenges in the conventional picosecond ultrasonic measurements where the opto-acoustic signals acquired as modulated reflection of the time-delayed probe beams are small due to small piezo-optic coefficients. We have investigated the use of a Fabry-Perot optical cavity to enhance these signals. The cavity is formed between a distributed Bragg reflector and a metal thin film sample. Experimental results for Al and Cu films show enhancement of acoustic signals by up to two orders of magnitude. This technique also makes it possible to determine the actual pulse shape of the returning acoustic echoes inside the metal thin films, thereby enriching the total amount of information acquired in picosecond ultrasonic experiments."], "keyword": ["Optical Cavity", "Pump Probe", "Picosecond Ultrasonics"], "primary_title": "Ultrafast Phenomena on the Nanoscale in Solids: From Magnetic to Acoustic Phenomena", "uri": "https://repository.library.brown.edu/studio/item/bdr:178/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:178/"}, {"pid": "bdr:185", "object_type": "pdf", "abstract": ["FeSb2 is a narrow band semiconductor, whose magnetic susceptibility strongly resembles that of FeSi, an archetype example of Kondo insulator. The unusual spectral weight transfer in the optical conductivity measurement and ab initio LDA+U calculations imply that FeSb2 is an unconventional semiconductor with strong electron correlations. In order to study the anisotropy and probe the electronic structure of FeSb2, single crystals are grown by high temperature flux method and carriers are introduced into FeSb2 by substituting Fe and Sb with Co/Cr and Te respectively. We investigated the magnetic and electrical properties of FeSb2 and the doping effects. Hall measurement on FeSb2 reveals that multiple band carriers with very large mobility difference are involved in the electrical transport. This can be explained by the orbital selective hybridization of the Fe d-orbitals with Sb-p electrons in FeSb2 involving only one electronic subsystem. Band structure calculation suggests that FeSb2 is close to a magnetic instability. Indeed, various magnetic orders are experimentally observed in doped FeSb2. For example, the activated Pauli paramagnetism of FeSb2 evolves into a weak ferromagnetism in Fe1-xCoxSb2 and a complex canted antiferromagnetic structure in Fe1-xCrxSb2 and Fe(Sb1-xTex)2. Metallic states are readily induced by doping FeSb2 as a result of band filling. Positive colossal magnetoresistance mainly attributed to quasi 1D weak localization is observed in Co doped FeSb2. With Te substitution, FeSb2 evolves from a strongly correlated semiconductor into a moderate heavy fermion metal. Most of the Kondo insulator materials are cubic, with the exception of CeRhSb and CeNiSn, and 4f intermetallics. An important question is that if the Kondo insulator scenario can be applied to 3d materials, e.g. FeSi and FeSb2. FeSb2 can be obtained in single crystal form with high quality and can be readily doped with carriers, thus it represents a model system with only 3d elements to study this physics. Our results indicate that the underling physics of FeSb2 can be well described by the Kondo insulator picture and FeSb2 resembles FeSi in many ways as a prototypical example of a nonrare-earth containing Kondo insulator."], "keyword": ["Kondo Insulator", "FeSb2", "Heavy fermion", "Weak ferromagnetism", "Colossal Magnetoresistance", "Giant Mobility"], "primary_title": "Investigation of a d-electron Kondo insulator FeSb2", "uri": "https://repository.library.brown.edu/studio/item/bdr:185/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:185/"}, {"pid": "bdr:186", "object_type": "pdf", "abstract": ["Liquid crystal lasers are dye-doped distributed feedback lasing systems. Fabricated by coupling the periodic structure of a liquid crystal medium with a fluorescent dye, the emission from these systems is tunable by controlling the liquid crystal system -- be it through electric or thermal field effects, photochemical reactions, mechanical deformations, etc. The laser action arises from an extended interaction time between the radiation field, the laser emission, and the matter field, the periodic liquid crystal medium, at the edge of the photonic band gap. In this thesis, several tunable liquid crystal laser systems are investigated: cholesteric liquid crystals, holographic-polymer dispersed liquid crystals and liquid crystal polarization gratings. The primary focus has been to fabricate systems that are tunable through electrical means, as applications requiring mechanical or thermal changes are often difficult to control. Cholesteric liquid crystal lasers are helical Bragg reflectors, with a band gap for circularly polarized light of equivalent handedness to their helix. These materials were doped with a laser dye and laser emission was observed. The use of an in-plane electric field tends to unwind the helical pitch of the film and in doing so tunable emission was demonstrated for ~15 nm. Holographic-polymer dispersed liquid crystals (H-PDLCs) are grating structures consisting of alternating layers of polymer and liquid crystal, with different indices of refraction. The application of an electric field index matches these layers and `switches off' the grating. Thus, laser emission can be switched on and off through the use of an electric field. Spatially tunable H-PDLC lasers were fabricated by creating chirped gratings, formed by divergent beams. The emission was shown to tune ~5 nm as the pump beam was translated across a 1 inch film. Liquid crystal polarization gratings use photo-patterned alignment layers, through a polarization holography exposure, to induce an alignment in a liquid crystal film. Electrically tunable emission was demonstrated in these systems. Applications of liquid crystal lasers include emissive substrates or backplanes for displays or tunable emission sources for biology and medicine. The potential for such applications are discussed."], "keyword": ["Liquid crystals", "Lasers", "Optics", "Photonic crystals", "Holography"], "primary_title": "Tunable liquid crystal lasers", "uri": "https://repository.library.brown.edu/studio/item/bdr:186/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:186/"}, {"pid": "bdr:203", "object_type": "pdf", "abstract": ["This thesis presents two theoretical investigations on transport in low dimensional strongly correlated electronic systems. In the study of one dimensional system, we demonstrate that spin current can be generated by an ac voltage in a one-channel quantum wire with strong repulsive electron interactions in the presence of a non-magnetic impurity and uniform static magnetic field. We show that in a certain range of voltages, the spin current can exhibit a power dependence on the ac voltage bias with a negative exponent. The spin current expressed in units of $\\hbar/2$ per second can become much larger than the charge current in units of the electron charge per second. The spin current generation requires neither spin-polarized particle injection nor time-dependent magnetic fields. In the study of on-Abelian statistics in two dimensional quantum Hall system, we suggest an experiment which can determine the physical state for the $\\nu=5/2$ quantum Hall plateau. The proposal involves transport measurements in the geometry with three quantum Hall edges connected by two quantum point contacts. In contrast to interference experiments, this approach can distinguish the Pfaffian and anti-Pfaffian states as well as different states with identical Pfaffian or anti-Pfaffian statistics. In addition, the transport is not sensitive to the fluctuations of the number of the quasiparticles trapped in the system."], "keyword": ["Luttinger Liquid", "Bosonization", "Non-Abelian Statistics", "Quantum Wire", "Quantum Hall effect"], "primary_title": "Transport in Low Dimensional Strongly Correlated Electronic System", "uri": "https://repository.library.brown.edu/studio/item/bdr:203/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:203/"}, {"pid": "bdr:201", "object_type": "pdf", "abstract": ["Neural stimulation with spatial and temporal precision is desirable both for studying the real-time dynamics of neural networks, and for prospective clinical treatment of neurological diseases. Optical stimulation of genetically targeted neurons expressing the light sensitive channel Channelrhodopsin (ChR2) has recently been reported as a method for millisecond temporal control of neuronal spiking activities with cell-type selectivity. In this thesis, I present a novel dual-modality device which consists of a tapered coaxial optical waveguide \"optrode\" integrated into a 100 element multi-electrode microscale intracortical recording array. The structure was designed by considering general guided wave electromagnetic principles for the \"optrode\" on one hand, and the photon diffusion/scattering in the brain tissue from a micron-size shaped aperture, on the other. The dual optical delivery and electrical recording capability of the optrode was first demonstrated and validated in in vitro preparations of mouse retina, photostimulating the native retinal photoreceptors while recording light-responsive activities from ganglion cells. The dual-modality device was then used in ChR2 transfected mouse brain slices. Specifically, epileptiform events are reliably optically triggered by the optrode, and their spatiotemporal patterns are simultaneously recorded through the multi-electrode array, and shown to be consistent with models for epileptiform wave-like propagation."], "keyword": ["optogenetics,channelrhodopsin(ChR2),optrode,microelectrode array,neural stimulation,retinal recording"], "primary_title": "Optical Stimulation and Spatiotemporal Electrical Recording ni Genetically Targeted Brain Tissue", "uri": "https://repository.library.brown.edu/studio/item/bdr:201/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:201/"}, {"pid": "bdr:260", "object_type": "pdf", "abstract": ["The top quark pair production cross section measurement in the lepton+jets channel with b-tagging is described. About 900 pb-1 data collected by the D\u00d8 detector at the Fermilab Tevatron are used for this analysis. In this thesis, event selection, background estimation, and cross section calculation are discussed in detail. In addition, calibration of the Luminosity Monitor readout electronics and a new b-tagging algorithm, the SLTNN tagger, are also discussed in this thesis."], "keyword": ["Top quark", "cross section", "D\u00d8", "b-tagging algorithm"], "primary_title": "Top Quark Pair Production Cross Section in the Lepton+Jets Channel Using b-tagging at D\u00d8", "uri": "https://repository.library.brown.edu/studio/item/bdr:260/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:260/"}, {"pid": "bdr:265", "object_type": "pdf", "abstract": ["Finite-temperature quantum field theory, with a focus on Quantum Electrodynamics (QED), and its application to the scattering of an ultra-relativistic particle in a hot plasma, are presented in terms of Schwingerian functional methods and a new variant of Fradkin's representation. The phenomena of a fast moving fermion entering into a hot QED plasma is described by the finite-temperature fermion propagator in a high temperature medium under the assumption that the energy scale of the incident particle is much larger than the temperature scale of the medium. The incident particle loses energy and momentum through exchange of both virtual and thermal photons with the thermal bath, which, in turn, creates a disturbance in the medium until it becomes a part of the thermal bath. Three energy-depletion mechanisms are investigated through the damping of the finite-temperature fermion propagator in the functional approach: thermal-photon enhanced and ordinary Bremsstrahlung, and pair production. The damping of the incident particle is estimated in a non-perturbative, systematically functional way under the Bloch-Nordsieck approximation, which not only extracts contributions from soft photons, but also includes effects of momentum decreasing during the process, and the results are physically correct, gauge invariant, and free of any IR and/or UV divergence which has plagued previous perturbative attempts. In contrast to time-dependent, linear or logarithmic exponential type decays of previous perturbative calculations, the results show the incident particle experiencing much faster damping in a Gaussian fashion. The disturbance inside the QED plasma is also modeled; a symmetric \"fireball\" first rises as energy depletion of the incident particle, and subsequently damps away in the same, Gaussian fashion as the incident particle. Results of perturbative calculations and Hot Thermal Loop approximations are compared and critiqued. Thermal mass-shift, impact of gauge-dependence, and other aspects of finite-temperature QED are briefly discussed, and a possible extension to QCD is also presented."], "keyword": ["Finite Temperature Field theory", "QED", "Fermion damping", "Bloch-Nordsieck Approximation", "eikonal model", "plasma", "Quantum electrodynamics"], "primary_title": "Finite-Temperature Quantum Electrodynamics: General Theory and Bloch-Nordsieck Estimates of Fermion Damping in a Hot Medium", "uri": "https://repository.library.brown.edu/studio/item/bdr:265/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:265/"}, {"pid": "bdr:28", "object_type": "pdf", "abstract": ["Nanopore system is important for its many promising applications in rapid DNA sequencing, large biological molecule detection, polynucleotide-enzyme interaction study and etc. Following the first introduction of nanopores for polynucleotide study twelve years ago, many research studies have focused on the development of synthetic nanopore systems, due to its adjustability and adaptability for meeting various application needs, and the potential integration into future nano devices. Given the broad potential technological importance, it's highly desirable to develop a reliable yet convenient fabrication method for nanopore system. We introduce a novel fast and low-cost technique for fabricating nanopore system with soft materials, employing a low-power laser with lithography-free substrate preparation. A model of surface-tension driven mass flow is proposed to describe its mechanism of formation. We further demonstrate the soft nanopore system's capability for sensing biological molecules with DNA characterization experiments. A solid-state nanopore based system with optical access is introduced for the purpose of manipulating DNA-tethered microspheres near the nanopore using optical tweezers. We use optical trap to anchor lambda-DNA-tethered microspheres in close proximity (1 - 3 um) to the solid-state nanopore, and study the ionic conductance through the voltage-biased nanopore. At high voltage (-100 mV to -300 mV ), we observe hundreds of free-DNA-translocation-like current suppressions. We present the finding and discuss its possible underlying mechanism."], "keyword": ["Nanopores", "DNA", "Microspheres"], "primary_title": "Fabrication of nanopore systems and their application to DNA manipulation", "uri": "https://repository.library.brown.edu/studio/item/bdr:28/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:28/"}, {"pid": "bdr:1094418", "object_type": "pdf", "abstract": ["The top quark is one of the most important Standard Model particles in probing new physics beyond the Standard Model. Experimentally, this exploration can be done by studying proton-proton collisions in the Large Hadron Collider with the Compact Muon Solenoid (CMS) detector. There must, however, be a reliable method to identify top quarks or their signatures in CMS data. As the top quark events of greatest interest are often Lorentz boosted, they appear as jets in detector data and can be tagged using jet substructure techniques. Increasingly, these top tagging techniques involve the use of deep learning tools such as Deep Neural Networks (DNNs). In this study, we compare the top-tagging performance of two CMS top-tagging neural networks, the Boosted Event Shape Tagger (BEST) and DeepAK8, as well as a new DNN which takes as inputs the jet topological and kinematic BEST input variables and the particle-level features used as inputs to DeepAK8. We find that this new network, PF+BEST, performs comparably to the two established networks with significant promise for improvement and utility in future new physics searches involving coupling to top quarks."], "keyword": ["Physics", "Machine learning", "Particle Physics", "Neural Networks"], "primary_title": "Tagging Hadronically Decaying Top Quarks with Deep Neural Networks", "uri": "https://repository.library.brown.edu/studio/item/bdr:1094418/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:1094418/"}, {"pid": "bdr:1102612", "object_type": "pdf", "abstract": ["We introduce the 2dLW model, which successfully captures kinetic fragility as the liquid is supercooled. The supercooled liquid suffers a glass transition around 0.30 < Tg\u2217 < 0.35, after which the fragile dynamics crossover to strong, Arrhenius-type activated dynamics. The Vogel-Fulcher-Tamman law, which models fragile dynamics, predicts To \u2248 0.30. Much like how pseudonematic domains result in slow, power-law decay of orientational time corre- lation functions in liquid crystals, we conjecture that the slow, fragile dynamics of the 2dLW supercooled liquid are caused by molecular-orientational hexatic domains. This is in con- trast to literature expectations of the general unimportance of structure to glassy dynamics. Our findings of ordered domains suggest a microscopic mechanism behind the famous slow dynamics of supercooled liquids. 2dLW domains are mesoscopic, with lengthscale ranging from the length of a few molecules to the length of dozens of molecules. Finite-size-scaling arguments show that the structural order is truly mesoscopic rather than long-range or quasi-long-range. We find that supercooling gives rise to two nearest-neighbor lengthscales with different orientational ordering associated with each length. In summary, we find in a two-dimensional supercooled liquid and glass unexpected molecular-orientationally ordered structures that we believe are structural signatures of glassy dynamics."], "keyword": ["Soft condensed matter", "Chemistry, Physical and theoretical", "Physics", "Materials"], "primary_title": "Mesoscopic Orientational Order Accompanies the Slow Dynamics of a Two-Dimensional Supercooled Liquid", "uri": "https://repository.library.brown.edu/studio/item/bdr:1102612/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:1102612/"}, {"pid": "bdr:11027", "object_type": "pdf", "abstract": ["Alkenones are lipids produced by certain haptophyte algae and are excellent sensors of temperature change. This dissertation investigates the stable isotopic and organic geochemical aspects of alkenones from brackish Greenlandic lakes and develops their use as a paleothermometer. Alkenones are reported from brackish lakes near Kangerlussuaq, Greenland and their distribution and \u03b413C values are examined. Results indicate that 1) the Greenland alkenones are most similar to those from lakes in Germany and Austria, suggesting a common producer organism and 2) alkenone producers must either fractionate CO2 to a greater extent than other algae or access a 13C-depleted carbon source. Haptophyte-specific ribosomal DNA (rDNA) sequences from Greenlandic lake sediment and water samples are compared with rDNA of known haptophytes, and demonstrate that the Greenlandic alkenone producers represent a new taxon of haptophyte algae, and that all Greenlandic lakes of the study contain the same haptophytes. A new liquid chromatographic procedure is reported for separating alkenones having the same carbon number but different degrees of unsaturation for the purpose of compound-specific hydrogen isotopic analysis. \u03b4D measurements on individual alkenones indicate that hydrogen isotopic composition differs according to the degree of alkenone unsaturation. This suggests it is preferable to make \u03b4D measurements on individual alkenones, due to possible temperature-related effects on \"pooled\" \u03b4D values and because measurements on individual alkenones provide improved precision and accuracy. Temperature variability for the past 6,000 years in Kangerlussuaq, Greenland is reconstructed by applying alkenone paleotherrmometry to sediment cores from two lakes in the region. Temperature in the Kangerlussuaq region appears to have been controlled by changes in Meridional Overturning Circulation and the extent of the North Polar Vortex on millennial timescales, while being driven by variability in the North Atlantic Oscillation over centennial timescales. The timing of major changes in Paleo-Eskimo, Norse and Inuit occupation of Southwestern Greenland coincide with episodes of abrupt temperature change revealed by the alkenone record, indicating that climatic and environmental changes played a fundamental role in the patterns of human migration in Greenland over the past 4,500 years."], "keyword": ["alkenone", "biomarker", "climate", "holocene", "greenland", "paleoclimate", "Biochemical markers", "Isotopes", "Climatology", "Holocene Geologic Period", "Limnology", "Paleoclimatology"], "primary_title": "Development and Application of Lacustrine Alkenone Paleothermometry in Southwestern Greenland", "uri": "https://repository.library.brown.edu/studio/item/bdr:11027/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:11027/"}, {"pid": "bdr:11028", "object_type": "pdf", "abstract": ["This dissertation covers fundamental studies and application motivated research exploring the coupling between LC and polymers in unique systems. The interaction of these materials link with one another creating a mechanical path for aligning low molecular LC through polymer chain organization, or conversely organizing the polymer fibers with stimulated molecular reorientation. Such coupling is explored in several different areas including general liquid crystal alignment methods--bulk and surface alignment, memory effects, liquid crystal based actuation, and in application as the phase modulating element in a Fourier Transform Spectrometer."], "keyword": ["reactive mesogen", "FTS", "Liquid crystals", "Polymers", "Phase modulation"], "primary_title": "Liquid crystal and polymeric coupling and stressed liquid crystal technology for fourier transform spectroscopy", "uri": "https://repository.library.brown.edu/studio/item/bdr:11028/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:11028/"}, {"pid": "bdr:1104389", "object_type": "pdf", "abstract": ["Galaxy clusters are the largest gravitationally bound systems in our universe and roughly 85% of their mass is contributed by dark matter. The rest of their mass is dominated by the baryonic constituents of hot X-ray emitting gas and luminous galaxies. In this project, I compared the density distribution of dark matter and X-ray emitting gas in nearby galaxy clusters. These comparisons can shed light on the evolutionary status of the cluster. I mapped the distribution of X-ray emitting gas directly from Chandra X-ray observations. However, because dark matter doesn\u2019t directly interact with photons, it has to be detected indirectly. The presence of mass within Galaxy clusters distorts the images of elliptical galaxies behind the cluster, in an effect called gravitational lensing. The majority of lensing from clusters is in the form of weak gravitational lensing (WL), which is detected as a statistical tangential shear pattern of the background galaxies and is used to build 2-dimensional mass maps of the cluster. The vast majority of cluster mass is in the form of dark matter, so we approximate the mass distribution as that of the dark matter. By examining X-ray and dark matter morphology, we can learn about the recent mergers in clusters and their evolutionary formation histories."], "keyword": ["Galaxies--Clusters", "Dark matter (Astronomy)--Measurement"], "primary_title": "Mapping Weak Gravitational Lensing Signals from Low-Redshift Galaxy Clusters to Compare Dark Matter and X-Ray Gas Substructures", "uri": "https://repository.library.brown.edu/studio/item/bdr:1104389/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:1104389/"}, {"pid": "bdr:1104381", "object_type": "pdf", "abstract": ["Spectroscopic binaries are an essential tool in astrophysics because they provide a simple method of determining the masses and radii of stars to high precision and accuracy. The proprieties of binary star systems are used in calibration of theoretical stellar models, to determine the distance of nearby galaxies, and other asteroseismology studies. In this thesis, I use high resolution spectroscopy of two dierent binary star systems, HIP 18532, also known as Epsilon Persei, and HIP 26736. The stellar spectrum of the stars can be used to determine the reduced mass of the binary system. Specically, the shifts in the spectral lines can be used to determine the orbital period while Doppler shifts in light can be used to determine their orbital velocity. Additionally, the results of Epsilon Persei will corroborate new measurements of its orbital elements."], "keyword": ["Astrophysics", "Astronomy", "Double stars", "Spectrum analysis", "Telescopes"], "primary_title": "Observations of Spectroscopic Binaries Epsilon Persei and HIP26736", "uri": "https://repository.library.brown.edu/studio/item/bdr:1104381/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:1104381/"}, {"pid": "bdr:1104333", "object_type": "pdf", "abstract": ["Quantum Mechanics does well in its description the phenomena of small particles but suffers from some significant flaws. Most importantly, Quantum Mechanics struggles to determine the ontological and epistemological effects of measurement. This paper approaches this measurement problem from a perspective informed by the Ifa Philosophy of the Yoruba people from Southwestern Nigeria. Using Ifa's principle of integrative metaphysics, insisting that matter and spirit are equiprimordial, and applying this in conjunction with the Hidden Variable interpretation of Quantum Mechanics, this paper derives an \"Ifa interpretation\" of Quantum Mechanics."], "keyword": ["Physics", "Quantum theory", "Science and the humanities", "Religion and science", "History of Science", "Philosophy", "Metaphysics", "Africa", "Interdisciplinary research", "Joints--Range of motion--Measurement", "Nigeria", "Quantum", "Science", "Science--Philosophy", "Africana Studies", "Yoruba (African people)--Religion", "Africans--Religion", "Igbo (African people)--Religion", "Vodou", "Ifa (Religion)", "Orishas", "Orisha religion", "Olodumare (Yoruba deity)", "Obatala (Yoruba deity)", "Orunmila (Yoruba deity)", "Yemonja (Yoruba deity)", "Yemaja (Yoruba deity)", "Ogun (Yoruba deity)", "Oshun", "Shango (Yoruba deity)", "Candomble\u0301 (Religion)", "Africa, West", "Egu\u0301ngu\u0301n (Cult)", "Ancestors", "Yoruba (African people)", "Igbo (African people)", "Nigeria--Ife", "Ase", "Measurement", "Wave functions", "Collapse", "Interdisciplinary approach to knowledge", "Einstein, Albert, 1879-1955", "EPR", "De Broglie family", "Bell, J. S.", "Abimbo\u0323la, \u02bcWande"], "primary_title": "\u1eccr\u00fanmil\u00e0 n\u00ed \u00f3 \u00f2 w\u00e0\u00e1 b\u00e1 n\u00ed : Examining the Quantum Measurement Problem Through the Yoruba Philosophy of Ifa Divination", "uri": "https://repository.library.brown.edu/studio/item/bdr:1104333/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:1104333/"}, {"pid": "bdr:1104334", "object_type": "pdf", "abstract": ["This thesis explores the concepts that make up an effective classroom demonstration, derived the analytical form of gravitational wave emission from a binary system, and how a Michelson Fabry Perot interferometer can be used to detect such waves. Instructions on how to make a basic Michelson interferometer were then provided in order to use such a device as a demonstration tool. A demonstration/lecture plan was then created to introduce gravitational wave astronomy to early undergraduate students."], "keyword": ["Education", "Astrophysics", "Astronomy", "Gravity"], "primary_title": "A Pedagogical Demonstration/Lecture Plan for the Introduction of Gravitational Wave Astronomy", "uri": "https://repository.library.brown.edu/studio/item/bdr:1104334/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:1104334/"}, {"pid": "bdr:1103517", "object_type": "pdf", "abstract": ["Advances in Urban Science, particularly Urban Scaling Theory, have begun to uncover and explain urban dynamics shared by cities across time and place. This thesis extends Urban Scaling Theory to consider cities as non-isolated systems (cities interacting with other cities) of heterogeneous agents (non-uniform distributions of scaling behavior within cities). First, we analyze how cities' scaling properties are affected by their connectivity in inter-city networks. We find a significant effect on scaling behavior by inter-city interactions as measured by air traffic and presence of global firms. Second, we demonstrate how heterogeneous populations within cities scale differently across city size by characterizing income distributions across US Metropolitan Areas. We find that income inequality grows with city size. In order to understand this phenomenon, various agent-based Kinetic Exchange Models of Income and Wealth are tested in varying network structures to simulate the observed characteristics of income distributions across city size."], "keyword": ["Modeling", "Urbanization", "Cities and towns", "Scaling (Social sciences)", "Globalization", "Income distribution"], "primary_title": "Extending Urban Scaling Theory Between and Within Cities: Analyses of Inter-City Networks and Kinetic Exchange Modeling of Local Income Inequality", "uri": "https://repository.library.brown.edu/studio/item/bdr:1103517/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:1103517/"}, {"pid": "bdr:11034", "object_type": "pdf", "abstract": ["Nonperturbative issues in quantum gravity in Anti de Sitter spacetimes are addressed by means of the manifestly holographic framework of Anti de Sitter/Conformal Field theory correspondence (in Lorentzian signature). After a review of the properties of Anti de Sitter space, the map of local bulk insertions in terms of \"smeared out\" boundary CFT operators is constructed in the strictly semiclassical limit. We begin with pure AdS space in various coordinate systems where it is demonstrated how (approximate) bulk locality emerges from the dual CFT. The best result is obtained for the case of Rindler coordinates one is able to minimize the support of the complexif ied smeared CFT operators to a very compact region of the boundary. Holographic maps are also constructed for various AdS black holes. We show how bulk degrees of freedom in regions of bulk behind horizons are encoded in the dual CFT and what is the CFT interpretation of the black hole singularity. Next we model a scenario of eternal ination by embedding \"landscape\" of string theory vacua in the manifestly holographic framework of AdS/CFT duality. Bubble geometries with de Sitter interiors within an ambient Schwarzschild anti-de Sitter black hole spacetime are investigated and a characterization for the states in the dual CFT on boundary of the asymptotic AdS which code the expanding dS bubble are obtained. These can then in turn be used to specify initial conditions for cosmology. This scenario naturally interprets the entropy of de Sitter space as a (logarithm of ) subspace of states of the black hole microstates. Consistency checks are performed and a number of implications regarding cosmology are discussed including how the key problems or paradoxes of conventional eternal ination are overcome. Finally we turn to pure AdS gravity in (2+1)-dimensions which is classically equivalent to Chern-Simons theory. Recent investigations suggest that the dual CFT is holomorphically factorizable. By analyzing classical gauge"], "keyword": ["AdS/CFT", "Black Holes", "Inflation", "Chern-Simons Theory", "Black holes (Astronomy)", "Inflationary universe"], "primary_title": "Holographic description of black holes and cosmic inflation in asymptotically anti de Sitter backgrounds", "uri": "https://repository.library.brown.edu/studio/item/bdr:11034/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:11034/"}, {"pid": "bdr:11025", "object_type": "pdf", "abstract": ["The quantities and properties of the dark constituents of the universe reveal much about the past and future development of the cosmos. It is thought that dark matter provides 85% of the mass in the universe, and that it is certainly the dominant component in large structures from galaxies to superclusters. Dark matter density, clustering, and quantity have repercussions for the universe's geometry, its past and future evolution (and ultimate fate), as well as for the more specific question of how structure has formed. Weak gravitational lensing is one of the only tools available to measure dark matter densities directly; most other methods measure observables that have a poorly known, and often debated, relationship to the dark mass. Although its direct sensitivity to mass distributions provides an obvious advantage for weak lensing, because it is a statistical measurement whose signal strength typically has been of the same order of magnitude as systematic and random noise, until recently it has been difficult to adequately and convincingly control for these. For this reason, weak lensing data collection has normally been specifically designed to mitigate these factors. The unique requirements for optimal weak lensing observations combined with limited telescope time have meant that there are relatively few datasets that have been used for weak lensing. There is a huge body of past and future data designed for other types of studies for which weak lensing analysis has been considered inappropriate. However, weak gravitational lensing techniques have matured. In this work for the first time, we have applied weak lensing methods to a dataset that was not engineered for weak lensing studies. The NOAO Deep Wide-Field Survey (NDWFS) optical dataset includes almost 9 square degrees over 27 subfields with a range of best seeing from 0.66\" to 1.20\" in three different filters (I, R, and Bw). We use this dataset to show that weak lensing analysis may now be successfully applied to data formerly not considered suitable. We find that detections of cluster-sized mass densities from this dataset perform comparably to detections from previous surveys. We correlate our detections with the Chandra XBo\u00f6tes results for extended sources."], "keyword": ["weak gravitational lensing", "cluster surveys", "NDWFS", "Cosmology"], "primary_title": "Measuring Weak Gravitational Lensing in General Purpose Imaging Surveys", "uri": "https://repository.library.brown.edu/studio/item/bdr:11025/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:11025/"}, {"pid": "bdr:11023", "object_type": "pdf", "abstract": ["Recent astrophsyical observations indicate that about 23% of the matter in the universe exists as non-luminous, non-baryonic dark matter. General thermodynamic arguments suggest that if an as-yet undiscovered weakly interacting particle were in thermal equilibrium in the early universe, it could have a cosmologically interesting relic abundance today. Dark matter particles are predicted to have collapsed into isothermal halos on a galactic scale. Minimal super-symmetric extensions of the standard model predict the existence of a stable particle with a mass in the range 10-1000 GeV c<sup>-2</sup>, and a an interaction cross section with ordinary matter \u03c3\u03c7 < 10<sup>-36</sup> cm<sup>2</sup>. For the past two decades, numerous experiments have been deployed with the aim of direct or indirect detection of dark matter. XENON10 is a direct-detection liquid Xe experiment, with event-by-event 3D position reconstruction. Since dark matter does not interact electromagnetically, it's signature in a Xe detector is expected to be a low-energy nuclear recoil. Particle interactions in Xe create scintillation light (<em>S</em>1) and ionization. The ionization is drifted across the active Xe target and converted into a proportional scintillation signal (<em>S</em>2) by an external electric field. The ratio y = log10(<em>S</em>2/<em>S</em>1) is larger for \u03b2 and \u0263 background events than for nuclear recoils, as determined by neutron calibration data. This allows event-by-event discrimination of background from the expected signal. In 2007 XENON10 eclipsed CDMS II as the most sensitive direct-detection experiment, excluding the existence of particle dark matter with a cross-section (normalized to a single nucleon) \u03c3\u03c7 > 10<sup>-43</sup> cm<sup>2</sup> at a particle mass of 100 GeV c<sup>-2</sup> (90% C.L.). Liquid Xe technology is extremely promising since it is easily scaled to larger target mass, which will allow greater sensitivity to particle dark matter interactions. I discuss the XENON10 detector, deployment, operation, analysis and dark matter exclusion results. I also present a new method to determine the light yield of Xe for nuclear recoils, which is essential for calibrating the nuclear recoil energy scale and understanding the detector threshold."], "keyword": ["WIMP", "dark matter", "liquid Xe", "Dark matter (Astronomy)"], "primary_title": "A Position-Sensitive Liquid Xenon Time-Projection Chamber for Direct Detection of Dark Matter: The XENON10 Experiment", "uri": "https://repository.library.brown.edu/studio/item/bdr:11023/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:11023/"}, {"pid": "bdr:1105316", "object_type": "pdf", "abstract": ["In this thesis, I explore phase inhomogeneity in mixed halide compounds through x-ray diffraction measurements of Bragg peaks in a single-crystal. Using prior knowledge of the properties of transition metal trihalides, transition metal trihalides made of mixed halides were studied using an X-ray diffractometer. In particular, the compound of interest is chromium trichloride (CrCl3) mixed with bromine: CrCl3\u2212xBrx, where x is the amount of Br (the heavier halide) mixed with Cl (the lighter halide) in the transition metal trihalide compound. To ensure a wide range of temperature, a cryostat setup was used for low temperature measurements and a furnace assembly was designed and machined for high temperature (up to 420K) measurements. Temperature dependent X-ray diffraction measurements were taken and subsequently, 2\u03b8, d-spacing and peak width against temperature were plotted to investigate structural changes in the sample crystal. The X-ray diffraction measurement of structural changes is instrumental in investigating phase inhomogeneity: if the mixed chromium trihalide compound is homogeneous, only one structural transition should occur. However, should multiple structural transitions occur at different temperatures, it would indicate that the mixed chromium trihalide compound is in fact a material with inhomogeneous phases. Thus, the use of X-rays as a probe of structural transition in the mixed chromium trihalide enables us to disentangle the disorder from the structural changes that have been introduced. Preliminary results discussed in this thesis suggest a sin- gle temperature-induced structural transition at approximately T = 300K in a CrCl0.75Br2.25 single crystal sample."], "keyword": ["Condensed matter", "Chromium compounds", "Magnetism"], "primary_title": "Magnetic Anisotropy in Mixed Chromium Trihalides", "uri": "https://repository.library.brown.edu/studio/item/bdr:1105316/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:1105316/"}, {"pid": "bdr:11349", "object_type": "pdf", "abstract": ["A search for microscopic black hole production and decay in proton-proton collisions at a center-of-mass energy of 7 TeV has been conducted using Compact Muon Solenoid (CMS) detector at the CERN Large Hadron Collider. A total integrated luminosity of 35 pb-1 data sample, taken by CMS Collaboration in year 2010, has been analyzed. A novel background estimation for multi-jet events beyond TeV scale has been developed. A good agreement with standard model backgrounds, dominated by multi-jet production, is observed for various final-state multiplicities. Using semi-classical approximation, upper limits on minimum black hole mass at 95% confidence level are set in the range of 3.5 - 4.5 TeV for values of the Planck scale up to 3 TeV. Model-independent limits are provided to further constrain microscopic black hole models with additional regions of parameter space, as well as new physics models with multiple energetic final states. These are the first limits on microscopic black hole production at a particle accelerator."], "keyword": ["High Energy Physics", "LHC", "CMS", "Black Hole", "Particles (Nuclear physics)"], "primary_title": "Search for Microscopic Black Hole Signatures at the Large Hadron Collider", "uri": "https://repository.library.brown.edu/studio/item/bdr:11349/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:11349/"}, {"pid": "bdr:11362", "object_type": "pdf", "abstract": ["The main subject of this thesis is scattering amplitudes in N=4 super-Yang-Mills theory (SYM) and N=8 super-gravity theory (SUGRA). We study several aspects of the scattering amplitudes of these two theories using modern techniques. After the introductory chapter, we apply these methods to study the scattering amplitudes both in N=4 SYM and N=8 SUGRA. We first study two dual formulations of N=4 SYM, namely the Arkani-Hamed et al Grassmannian formulation and Witten's twistor string theory. We present a new, explicit formula for all tree-level amplitudes in N=4 SYM. The formula is written as a certain contour integral of the connected prescription of Witten's twistor string, expressed in link variables. A very simple and interesting deformation of the integrand gives directly the Grassmannian integrand proposed together with the explicit contour of integration.Then we calculate for the first time the five-point three-loop amplitudes of N=4 SYM using the leading singularity method. Using the method of obstructions we numerically evaluate two previously unfixed coefficients which appear in the three-loop BDS ansatz. After the study of N=4 SYM, we turn our journey to N=8 SUGRA by first presenting and proving a new formula for MHV scattering amplitude in SUGRA. Some of interesting features of the formula set it apart as being significantly different from many more familiar formulas. We then present an algorithm for writing down explicit formulas for all tree amplitudes in N=8 SUGRA, obtained from solving the supersymmetric on-shell recursion relations. The formula is patterned after one recently obtained for all tree amplitudes in N=4 SYM which involves nested sums of dual superconformal invariants. We find that all graviton amplitudes can be written in terms of exactly the same structure of nested sums with two modifications. To illustrate the procedure we give explicit closed-form formulas for all NMHV, NNMHV and NNNMV gravity superamplitudes. The obtained results are further simplified by applying bonus relations between gravity amplitudes, which arise from the soft behavior of tree-level gravity amplitude."], "keyword": ["string theory", "scattering amplitude", "Quantum field theory", "String models", "Supersymmetry"], "primary_title": "Scattering amplitudes in N=4 SYM and N=8 SUGRA", "uri": "https://repository.library.brown.edu/studio/item/bdr:11362/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:11362/"}, {"pid": "bdr:11370", "object_type": "pdf", "abstract": ["The top quark produced through the electroweak channel provides a direct measurement of the V_tb element in the CKM matrix which can be viewed as a transition rate of a top quark to a bottom quark. This production channel of top quark is also sensitive to different theories beyond the Standard Model such as heavy charged gauged bosons termed W'.This thesis measures the cross section of the electroweak produced top quark using a technique based on using the matrix elements of the processes under consideration. The technique is applied to 2.3 fb^-1 of data from the DZero detector. From a comparison of the matrix element discriminants between data and the signal and background model using Bayesian statistics, we measure the cross section of the top quark produced through the electroweak mechanism: \u03c3 (ppbar\u2192tb + X, tqb + X) = 4.30 +0.98 -1.20 pb.The measured result corresponds to a 4.9\u03c3 Gaussian-equivalent significance. By combining this analysis with other analyses based on the Bayesian Neural Network (BNN) and Boosted Decision Tree (BDT) method, the measured cross section is 3.94 \u00b1 0.88 pb with a significance of 5.0\u03c3, resulting in the discovery of electroweak produced top quarks. Using this measured cross section and constraining |V_tb| < 1, the 95% confidence level (C.L.) lower limit is |V_tb| > 0.78.Additionally, a search is made for the production of W' using the same samples from the electroweak produced top quark. An analysis based on the BDT method is used to separate the signal from expected backgrounds. No significant excess is found and 95% C.L. upper limits on the production cross section are set for W' with masses within 600 - 950 GeV. For four general models of W' boson production using decay channel W' -> t bbar, the lower mass limits are the following: M(W'L with SM couplings) > 840 GeV; M(W'R) > 880 GeV or 890 GeV if the right-handed neutrino is lighter or heavier than W'R; and M(W'L+R) > 915 GeV."], "keyword": ["Electroweak Top Quark", "Narain", "Heavy Gauged Bosons", "W'", "Singletop", "CKM", "Vtb"], "primary_title": "Top Quark Produced Through the Electroweak Force: Discovery Using the Matrix Element Analysis and Search for Heavy Gauge Bosons Using Boosted Decision Trees", "uri": "https://repository.library.brown.edu/studio/item/bdr:11370/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:11370/"}, {"pid": "bdr:11327", "object_type": "pdf", "abstract": ["We discuss a discontinuous Galerkin (dG) method and its application to common partial differential equations which arise in the context of general relativity. First we consider extreme mass ratio binary (EMRB) systems. When modeling EMRBs as perturbations of a Schwarzschild black hole, the metric perturbations are described by the distributionally forced Regge-Wheeler-Zerilli (RWZ) equation. Despite the presence of jump discontinuities in the solution, our dG method achieves pointwise spectral accuracy. Particular attention is given to the common choice of trivialinitial data, and we show such unphysical specification may lead to spurious solutionswhich contaminate the physical solution indefinitely. Unintended consequences of thepersistent junk solution are considered as well as a simple prescription for removing it. Using our code we compute metric perturbations, gravitational waveforms, and self-force measurements from both circular and eccentric orbits.Next, we present a dG method for evolving the spherically reduced Generalized Baumgarte-Shapiro-Shibata-Nakamura (GBSSN) system expressed in terms of second-order spatial operators. Our multi-domain method achieves global spectralaccuracy and long-time stability on short computational domains. We discuss in detail both our scheme for the GBSSN system and its implementation. A theoretical and computational verification of the proposed scheme is given.We conclude with a preliminary look at reduced basis (RB) methods for parameterized binary systems. Our algorithm aims to construct a compact RB space from which a particular solution can be quickly and accurately recovered. We apply the algorithm to compress the space of analytic chirp gravitational waveforms. Next, the RWZ equation is revisited, and we consider extensions of the algorithm to a dG solver along with numerical evidence that a RB space exists for EMRB waveforms."], "keyword": ["Numerical Relativity", "Spectral Methods", "Relativity and gravitational theory", "General relativity", "Black holes", "Discontinuous Galerkin method", "Model reduction", "Reduced Basis methods", "Collocation methods", "General relativity (Physics)"], "primary_title": "Applications of Discontinuous Galerkin Methods to Computational General Relativity", "uri": "https://repository.library.brown.edu/studio/item/bdr:11327/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:11327/"}, {"pid": "bdr:11168", "object_type": "pdf", "abstract": ["In this thesis we address the question of pattern selection in spatially extendedsystems in the presence of stochastic noise. As a model equation, we study the1D stabilized Kuramoto Sivashinsky equation with additive uncorrelated stochasticnoise. This equation is one of the simplest nonlinear equations that has a variety ofsecondary and even tertiary instabilities. We focus our attention on static stationarystates that are stable against the Eckhaus secondary instability. In the presence ofnoise the Eckhaus stable band of the deterministic equation collapses to a narrowregion near the center of the band. This is consistent with the behavior of the phasediffusion constants of these states. Some connections to the phenomenon of stateselection in driven out of equilibrium systems are made."], "keyword": ["Nonequilibrium", "Pattern formation", "dynamical system", "Pattern formation (Physical sciences)", "Dynamics"], "primary_title": "Noisy Stabilized Kuramoto-Sivashinsky: A modelfor studying state selection in far fromequilibrium systems", "uri": "https://repository.library.brown.edu/studio/item/bdr:11168/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:11168/"}, {"pid": "bdr:11182", "object_type": "pdf", "abstract": ["Silicon photonics is a rapidly-developing field at the confluence of silicon microelectronicsand fiber optics. In this talk we explore several interesting systems of light in silicon.We discuss the light generated by molecule-like emitters created in the silicon lattice viaa nanoscale patterning technique. We then introduce plasmonic particles to the nanopatternedarray and find that for a particular geometry light can be slowed to less than 0.05cin every direction. Further seeking to slow and localize light, we consider optical microcavitiesand explore the realm of subwavelength silicon microdisks which are smaller thanthe free-space wavelength of light which they store. Finally, we discuss a method for broadtuning of these optical microcavities to allow for tunable interactions with emitters or withother cavities. Device applications and systems enabled by this work are discussed."], "keyword": ["microphotonics", "Silicon", "Photonics", "Integrated optics", "Optics"], "primary_title": "Light generation, size constraints, and dynamic cavities in silicon photonics", "uri": "https://repository.library.brown.edu/studio/item/bdr:11182/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:11182/"}, {"pid": "bdr:11206", "object_type": "pdf", "abstract": ["Heavy-fermion materials provide an exceptional setting for the theoretical and experimental study of many intriguing problems of modern condensed matter physics. Quantum criticality, competition of Kondo and RKKY interactions, and unconventional superconductivity are only a few of the many examples. One of the most prominent representatives of this family of materials is CeCoIn5, which, due to its rather unique properties, has attracted intense research interest in recent years.In this thesis, we present an extensive low temperature 115In nuclear magnetic resonance (NMR) study of CeCoIn5, with a magnetic field applied parallel to the \u00e2-axis of its tetragonal crystal. Our measurements focus on the superconducting region of the H-T phase diagram, exhibiting Tc ~2.3 K and Hc2 ~11.8 T. Through a consistent and thorough analysis of the NMR observables, our investigation reveals clear evidence of two separate phases within the superconducting state and helps elucidate the details of their nature. In particular, the first phase (referred to as LFSC), which occupies most of the \"volume\" of the superconducting state, is found to be well-described by a Ginzburg-Landau model for the vortex lattice in an unconventional superconductor of dx2-y2 gap symmetry. The second phase (referred to as HFLT), stabilized at a narrow high field, low temperature corner of the phase diagram in the vicinity of Hc2, shows signs of spatially modulated superconductivity. This is interpreted as a likely realization of the elusive novel superconducting phase theoretically predicted by Fulde, Ferrell, Larkin, and Ovchinnikov in the 1960s. What is more, a long range magnetic order is established within the limits of this phase, associated with an incommensurate spin-density wave order. Lastly, an additional region of distinct behavior is identified, lying in between the LFSC and HFLT phases, which is possibly a true FFLO state in the presence of strong antiferromagnetic fluctuations.These results provide, as a whole, a remarkable insight into unconventional superconductivity and quantum magnetism, as well as their intricate interplay, not only in heavy fermion materials but in condensed matter systems in general."], "keyword": ["heavy-fermions", "unconventional superconductivity", "FFLO state", "quantum magnetism"], "primary_title": "Unravelling the mysteries of unconventional superconductivity with NMR: The curious case of CeCoIn5.", "uri": "https://repository.library.brown.edu/studio/item/bdr:11206/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:11206/"}, {"pid": "bdr:11174", "object_type": "pdf", "abstract": ["In this thesis we first study various aspects of stationary distributions of certain deterministic and stochastic dynamical systems. We look at the 30 year old proposal to use complex Langevin equations to sample complex path integral weights of quantum field theories. We solve for possible stationary distributions of complex Langevin equations and relate these to the solution space of Schwinger-Dyson equations. We introduce an effective potential for the whole complex Langevin evolution, which allows us to identify the particular stationary distribution sampled. Next we look at deterministic dynamical systems and ask a very general question: Can one engineer dynamical systems with a given stationary distribution? We explicitly engineer such systems and using this knowledge we introduce novel Monte Carlo based methods to calculate various quantities associated with these dynamical systems. Through Monte Carlo simulations and series resummations, we study the analytic structure of the associated autocorrelation functions, which gives the exponential decay constant of the power spectrum. Finally we study a first order phase transition in large Nc, N=2 SYM theory using the methods of AdS/CFT correspondence. We discuss AdS/CFT description of the latent heat in the phase transition. We further investigate an out-of-equilibrium evolution of the theory at high temperatures. Through AdS/CFT correspondence, this problem is mapped to an evolution of a D7-brane in a time-dependent gravitational background."], "keyword": ["Complex Langevin Equation", "Dynamical Systems", "AdS/CFT Correspondence", "Chiral Phase Transition", "Dynamics", "D-branes"], "primary_title": "Non-perturbative Methods in Quantum Field Theory", "uri": "https://repository.library.brown.edu/studio/item/bdr:11174/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:11174/"}, {"pid": "bdr:11129", "object_type": "pdf", "abstract": ["The objective of this thesis was to study the potential of using nanometer structured selenium for various biomedical applications. Experimental results showed much promise for selenium nanocluster coatings on traditional implants. Experimental results of this study were complimented by computer simulation results of protein interactions on the nanometer rough surfaces created by selenium nanocluster coatings. Specifically, here it was demonstrated that selenium nanocluster coatings can be readily applied to bone implant metallic materials (titanium, stainless steel) and catheter polymeric materials (PVC, PU, silicone). Selenium nanoparticles were prepared using similar synthesis processes. The selenium coatings and selenium nanoparticles were characterized using SEM, EDS, XPS and AFM. Biological experiments showed that the selenium coatings on titanium promoted healthy bone cell functions. The increase in healthy bone cell functions on selenium coated surfaces was shown to be attributed to the increase in adsorption of fibronectin, one of the most important cell adhesive proteins that regulate interactions between bone cells and an implant surface. The increase in fibronectin adsorption was hypothesized to be due to the increase in root-mean-square (RMS) nanometer roughness of the selenium coated surfaces compared to the uncoated surfaces. To test this hypothesis, computer simulation was used to simulate the adsorption of fibronectin on the generated surfaces. Simulation results showed good agreement with experimental results. Moreover, results demonstrated decreased bone cancer cell functions while increased healthy bone cell functions on selenium coated implants. The decrease in cancerous bone cell growth was shown to be due to the release of selenium into cell culture media. Healthy bone cells were not affected by the released selenium in culture media. Lastly, it was demonstrated that the selenium coatings on polymeric substrates (including PVC, PU and silicone) inhibited the growth of S. aureus, an important bacterium that infects all implants, especially catheters. It was further shown that selenium nanoparticles can be synthesized and that selenium nanoparticles also had anti-bacterial properties against S. aureus.In summary, this thesis demonstrated that nanometer structured selenium has much potential in promoting new bone growth while inhibiting the growth of bone cancer and bacteria."], "keyword": ["nanostructured", "Selenium", "Nanostructures", "Cancer", "Infection"], "primary_title": "Nanostructured Selenium for Biomedical Applications:from Theory to Practice", "uri": "https://repository.library.brown.edu/studio/item/bdr:11129/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:11129/"}, {"pid": "bdr:11140", "object_type": "pdf", "abstract": ["A colloidal semiconductor nanocrystal quantum dot (QD), representing a solid state \"artificial atom\", is an attractive test bed for light-material interaction, as well as for light emitter applications with color tunability, high stability and quantum efficiency. The objective of this thesis was to study the CdSe-based colloidal QD and implement this material in light emitting sources in three vastly different regimes of QD spatial arrangements and photonic excitation, representing a single photon emitter, a luminescent panel, and stimulated emission of radiation, respectively. The recombination of an electron hole pair in a colloidal QD creates a single photon of the band-edge energy. Implementation of CdSe-based colloidal QDs in practical single photon sources is described in the first part of the thesis. A silica shell was grown around an individual colloidal QD, increasing the nanoparticle's diameter up to 220nm. An Electrostatic Force Self-Assembly method was developed to precisely control the position of a single colloidal nanoparticle on a 2-dimensional substrate. Single photon emission characteristics from each patterned nanoparticles were confirmed and suggested prospects for room temperature on-command single photon sources. In the second part, colloidal QDs were embedded within nanoporous GaN epitaxial thin films to create a nanocomposite medium. This potentially new photonic material platform combines the well known high performance of GaN wide bandgap semiconductor family for solid state lighting (SSL) with the high efficiency wavelength-engineered luminescent colloidal CdSe-based QDs. The early results suggest the possibility for wavelength engineered light emitting nanocomposites across the visible spectrum for SSL applications.Finally, in the high excitation regime of close-packed QD thin films, stimulated emission was achieved at a record low threshold for CdSe/ZnCdS \"band structure engineered\" core/shell QDs. The formation of optical gain is considered in a model of photoinduced charging effects enhanced by the designed energetically low and spatially thin potential barrier of the ZnCdS shell. Subsequently, the new type of excitonic gain material was implemented in the first optically pumped QD Vertical Cavity Surface Emitting Laser, exhibiting well defined spatial and spectral outputs, with a low pump threshold."], "keyword": ["Colloidal quantum dots", "Single photon emitter", "Vertical cavity surface emitting laser", "Semiconductor nanocrystals", "Nanocrystals", "Lasers"], "primary_title": "CdSe-based Colloidal Semiconductor Nanocrystal Quantum Dots: From Single Photon Emitters to Lasers", "uri": "https://repository.library.brown.edu/studio/item/bdr:11140/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:11140/"}, {"pid": "bdr:11127", "object_type": "pdf", "abstract": ["Due to rapid developments in nanotechnology and the importance of nanomaterial characterization, the study of the acoustic response of small structures is of significant current interest. Frequency domain techniques such as Raman scattering and direct time-resolved pump-probe experiments are nondestructive and complementary tools to detect and identify these acoustic vibrations. A possible application of these experimental works is the determination of the geometry of a nanostructure. For this to be practical, one needs to find a way to go from a measurement of the set of frequencies of the normal modes to a determination of the values of whatever set of parameters are used to describe the shape. M. Kac drew attention to this general class of problem in a famous paper in 1966 entitled \"Can one hear the shape of a drum?\" However, in fact, the problem is more difficult than it appears because it turns out that the frequencies vary with the dimensions in a surprisingly complicated way as we will discuss in this thesis.\"Level repulsion\" related mode localization is our primary interest. In 1956 Shaw observed a prominent vibration resonance localized at the edge of a thick barium titanate disk. It is known that for certain special values of Poisson's ratio these modes are perfectly localized, are uncoupled to bulk modes, and thus do not lose energy by acoustic radiation. In this thesis we consider the conditions for mode localization in different structures, and show that regardless of the value of Poisson's ratio it is often possible to design a structure with an end shape such that a perfectly localized mode appears. This localization has interesting effects on the way that the vibrational patterns and frequencies of the normal modes of a structure are changed when the dimensions of the structure are altered."], "keyword": ["acoustic vibration", "localization", "edge mode", "Edge-localized modes"], "primary_title": "Localized Modes and the Vibrations of Nanostructures", "uri": "https://repository.library.brown.edu/studio/item/bdr:11127/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:11127/"}, {"pid": "bdr:11303", "object_type": "pdf", "abstract": ["There exists a fluidic version of the electrostatic field-effect, by which the transport of ions and charged objects in solution can be controlled in nanoscale channels. In this dissertation, we present a theory of such \"electrofluidic\" gating, the fabrication of electrically articulated nanopore devices that can exploit it, and measurements of ionic and DNA transport that quantify the effect. The basic idea behind electrofluidic gating is that the charge on a metal electrode beneath an insulating layer can induce electric fields in a thin layer of fluid above it. The fundamental structure for electrofluidic gating is a metal-oxide-electrolyte (MOE) capacitor, whose charging grants control over the electric double layer of the fluid. In this dissertation, we first present a model for the charging behavior of the MOE capacitor. Our model emphasizes the chemistry of oxide surfaces. We next describe fabrication of nanopore devices with embedded electrodes by focused ion beam and transmission electron microscope. Studies of the milling rate and its dependence on the electron flux identified sputtering as the dominant erosion mechanism. Next we describe experiments of gating the ionic conductance of a nanopore with an embedded gate electrode. The induced swings in the conductance showed strong dependencies on the pH and the ionic strength of the solution that are well described by our model. The absence of gate leakage currents confirmed the purely electrostatic origin of this field-effect. Finally, we demonstrate field-effect control over DNA translocations in a gated nanopore. The capture of DNA from solution was facilitated by the application of a positive charge to the embedded gate electrode, and the average translocation speed increased. These effects are explained by the reduced effective size of the nanopore due to electrostatic repulsion of DNA from its charged walls and by the modified electro-osmotic flow. This picture is consistent with the reduced capture rate and the increased average translocation speed of DNA as we increased the Debye length. Gated nanopore devices thus begin to mimic the single-molecule regulatory capabilities of biological nanopores, and suggest new avenues for fundamental studies and technological applications."], "keyword": ["translocation", "integrated", "Nanopores", "Electrostatics", "DNA", "Electrodes"], "primary_title": "The Electrostatic Field-Effect in Electrically Actuated Nanopores", "uri": "https://repository.library.brown.edu/studio/item/bdr:11303/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:11303/"}, {"pid": "bdr:11330", "object_type": "pdf", "abstract": ["In recent years there have been significant progresses in the understanding of scattering amplitudes at both strong and weak coupling. There are new dualities discovered, new symmetries demystified and new hidden structures unearthed. And we will discuss these aspects of planar scattering amplitudes in N = 4 Super Yang-Mills theory in this dissertation.Firstly, we review the discovery and development of a new symmetry: the dual superconformal symmetry. Inspired by this we present our study of dual conformally invariant off-shell four-point Feynman diagrams. We classify all such diagramsthrough four loops and evaluate 10 new off-shell integrals in terms of Mellin-Barnes representations, also finding explicit expression for their infrared singularities.Secondly, we discuss about the recent progress on the calculation of Wilson loops at both strong and weak coupling. A remarkable feature of light-like polygon Wilson loops is their conjectured duality to MHV scattering amplitudes, which apparentlyholds at all orders in perturbation as well as non-perturbation theories. We demonstrate, by explicit calculation, the completely unanticipated fact that the duality continues to hold at two loops through order epsilon in dimensional regularization for both the four-particle amplitude and the (parity-even part of the) five-particle amplitude.Finally, we discuss about the structure of scattering amplitudes in N = 8 Super Gravity. We present and prove a new formula for the MHV scattering amplitude of n gravitons at tree level. Some of the more interesting features of this formula, which set itapart as being significantly different from many more familiar formulas, include the absence of any vestigial reference to a cyclic ordering of the gravitons and the fact that it simultaneously manifests both Sn-2 symmetry as well as large-z behavior. The formula is seemingly related to others by an enormous simplification providedby O(n) iterated Schouten identities, but our proof relies on a complex analysis argument rather than such a brute force manipulation. We find that the formula has a very simple link representation in twistor space, where cancellations that arenon-obvious in physical space become manifest."], "keyword": ["Scattering Amplitude,Dual Conformal Symmetry,Wilson Loops,Graviton Amplitude,High Energy"], "primary_title": "Aspects of Scattering Amplitudes: Symmetry and Duality", "uri": "https://repository.library.brown.edu/studio/item/bdr:11330/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:11330/"}, {"pid": "bdr:11334", "object_type": "pdf", "abstract": ["The AdS/CFT correspondence offers a unique possibility for the nonperturbative investigation of gauge theories, through their conjectured equivalence to string theories. In the past years, there has been tremendous progress in the computation of the anomalous dimensions of gauge theory operators, or equivalently energies of string states, thanks to the integrable structures that emerge in the 't Hooft limit.In this thesis, we study the two main manifestations of integrability in gauge/string dualities, namely solitons in string theory and spin chains in gauge theory. We first review the emergence of an integrable spin chain in maximally supersymmetric Yang-Mills theory, and the identification of the string dual to a single excitation in a certain limit, the `giant magnon' solution. We then semiclassicaly quantize the solution and obtain the first quantum correction to its energy, in agreement with expectations based on symmetry. The fact that the string configuration in question amounts to a single solitary wave of the string sigma model, subsequently allows us to use a nonlinear superposition method known as dressing, in order to construct a general formula describing the scattering of an arbitrary number of solitons. We further generalize our solutions for the most recent instance of a gauge/string duality, involving the 3-dimensional super Chern-Simons theory of Aharony, Bergman, Jafferis and Maldacena (ABJM).We also study the symmetry of the integrable spin chain arising in the latter duality. In particular we compute how the Hilbert space of spin chain states of length up to 4, decomposes into irreducible representations of the superconformal group, for which we also obtain the characters. This structural information enables us to calculate the leading correction to the Hagedorn temperature of weakly coupled planar ABJM theory, and more importantly serves as a tool for the detailed spectroscopic analysis of anomalous dimensions, which we turn to next. Employing a combination of Bethe Ansatz and Hamiltonian diagonalization techniques, we find the spectrum of low-lying states of length 4 at 2 loops, and identify three new sequences of rational eigenvalues."], "keyword": ["AdS/CFT", "Integrability", "Spin Chains", "Giant Magnons", "Solitons"], "primary_title": "Solitons and Spin Chains in Gauge/String Dualities", "uri": "https://repository.library.brown.edu/studio/item/bdr:11334/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:11334/"}, {"pid": "bdr:11319", "object_type": "pdf", "abstract": ["This dissertation summarizes studies directed at a deeper understanding of the AdS/CFT correspondence, its origin and its dynamics. First, classical strings in AdS were considered and a general method for constructing string solutions was developed. The method is based on the reduction of string sigma models to integrable equations of sinh-Gordon or more generally Toda type. These equations are characterized by soliton type solutions from which the string configurations are constructed with a one-to-one correspondence between solitons of the field theory and spikes of the string. Through this correspondence the most general class of dynamical string solutions can be generated. In the case of AdS3, these general spiky strings are characterized by an arbitrary number n of spikes and two arbitrary holomorphic functions. After fixing the conformal frame, only the soliton moduli remain, giving a specification of the string moduli. This moduli space is particle-like and it is shown that the spikes follow a closed set of equations describing the dynamics of the moduli space providing a 0-brane picture of the AdS string.In the second part of the dissertation we pursue the direct construction of the AdS theory from the large N collective dynamics of its moduli. We accomplish this fully in the simplest sub-sector corresponding to the bi-local system of n=2 spikes. It is seen that higher spin massless particles originate from the cusps of the spiky strings. The large N collective construction establishes the proposal of Klebanov and Polyakov that higher-spin AdS gravity of Vasiliev's type appears as a dual to the O(N) vector model. For this an explicit mapping of the AdS4 spacetime (and of higher-spin fields) was given from collective (bi-local) fields. This construction was deduced through the identification of isometries of SO(2,3) with the conformal generators of the CFT3 in the light-cone quantization. This mapping gives an explicit derivation of the extra spatial dimension in the AdS spacetime and reconstruction of the bulk AdS theory."], "keyword": ["AdS/CFT", "string dynamics", "integrability"], "primary_title": "String Dynamics and Higher Spin Anti-de Sitter Gravity", "uri": "https://repository.library.brown.edu/studio/item/bdr:11319/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:11319/"}, {"pid": "bdr:1129247", "object_type": "pdf", "abstract": ["Dark matter (DM) is one of the biggest mysteries of mankind. Despite occupying 80% of the total matter budget and 26% of total energy budget of the universe, little is known about DM except that it is cold and does not interact strongly. In the first part of this thesis, we study the strategy in using jet substructure techniques in identifying supersymmetry, a promising theory that produces DM candidates, in a future center-of-mass energy = 100 TeV proton-proton collider. In the second part, we investigate a dissipative DM astrophysical substructure in the Milky Way, known as the thin dark disk, using the data release 2 of the Gaia satellite observation. In the last part, we forecast the ability of future DM direct detection experiments in discriminating DM models and parameters under the newly discovered DM astrophysical substructure, the Gaia-Sausage."], "keyword": ["Astrophysics", "Particles (Nuclear physics)", "Dark matter (Astronomy)", "Hadron colliders", "Supersymmetry"], "primary_title": "Dark Matter Searches in the Crescendo of the 21st Century Experiments", "uri": "https://repository.library.brown.edu/studio/item/bdr:1129247/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:1129247/"}, {"pid": "bdr:1129359", "object_type": "pdf", "abstract": ["This work studies the analytical structure of scattering amplitudes in a class of toy models, from the perspective of novel geometrical structures underlying scattering amplitudes, and utilizing discrete mathematics. We find the set of all-loop n - point Landau singularities of the first type arising in any massless planar theory using graph operations inspired by the theory of electrical circuits. We also describe how to find the set of possible branch points of amplitudes at any fixed loop order and all particle multiplicities in planar N = 4 SYM theory, using the information contained in the boundaries of the amplituhedra. Along the way, we devise a method for classifying the boundaries of amplituhedra for any loop order L and helicity k. We determine the branch points of all two-loop NMHV amplitudes by solving the Landau equations for the relevant configurations and are led thereby to a conjecture for the symbol alphabets of all such amplitudes. The study of amplituhedra is then pushed beyond the realm of N = 4 SYM theory. We provide an efficient recursive formula to compute the canonical forms of arbitrary d-dimensional simple polytopes, and illustrate our method via an application to Stokes polytopes, related to scalar theory with quartic coupling."], "keyword": ["Quantum field theory", "Graph theory", "Polytopes"], "primary_title": "Landau Singularities and Positive Geometries", "uri": "https://repository.library.brown.edu/studio/item/bdr:1129359/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:1129359/"}, {"pid": "bdr:1129413", "object_type": "pdf", "abstract": ["This work consists of two main projects: the first project describes bacterial confinement within a thin but resilient layer of liquid. The second project reports on the analysis of transient attachment and detachment of bacteria from a solid surface by applying an external electric field. In the study of flagellated bacteria trapped within thin films of liquid, I describe observations of bacteria moving in circular trajectories when they are confined within a thin layer of water around dispersed micrometer-sized particles sprinkled over a semi-solid agar gel. In this setting, E. coli and Enterobacter sp. orbit around the dispersed particles in clockwise paths. The liquid layer is shaped like a shallow tent with its height at the center set by the seeding particle and the meniscus profile set by the strong surface tension of water. The thin fluid layer is resilient due to a balance between evaporation and reinforcement of fluid that permeated out of the agar. The latter is driven by the Laplace pressure caused by the concave meniscus. In the second project, I report an experiment for Caulobacter crescentus weakly attached to a plastic surface and subjected to an electric field parallel to the surface. I observe that some individuals transiently, but repeatedly attach to the surface. While electrophoretically driven by the field, these bacteria move significantly slower than the unattached ones and their speeds exhibit large variations, frequently dropping close to zero for short intervals of time. This study sheds light on the process of bacterial interaction with surfaces and suggests applying electric field as a useful method to investigate bacteria-surface interaction."], "keyword": ["Biophysics", "Bacteriology"], "primary_title": "Bacterial Mobility in Thin Liquid Films and Near a Solid Boundary", "uri": "https://repository.library.brown.edu/studio/item/bdr:1129413/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:1129413/"}, {"pid": "bdr:1129427", "object_type": "pdf", "abstract": ["The Standard Model (SM) of particle physics successfully describes the known elementary particles and their electroweak and strong interactions. With the observation of the Higgs boson in 2012 by the A Toroidal LHC Apparatus (ATLAS) and Compact Muon Solenoid (CMS) experiments at the Large Hadron Collider (LHC), the last piece of the SM was verified. Even though the SM provides a great understanding of particle physics, there are limitations of the theory. The two-Higgs-doublet model (2HDM) extends the SM with another Higgs doublet and enriches Higgs phenomenology. Type II model of 2HDM, which forbids flavour changing neutral currents, predicts five Higgs bosons: two charged Higgs bosons (+1 or -1 times the electron charge) and three neutral Higgs bosons (light, heavy and pseudoscalar bosons). According to the model, the decay of the charged Higgs boson into top and bottom quarks is the dominant channel for charged Higgs bosons with a mass above 200 GeV. We performed a search for a charged Higgs boson in this channel with 35.9 1/fb of data collected by the CMS experiment in 13 TeV proton-proton collisions in 2016. This thesis focuses on the single lepton (electron and muon) final states. To improve the sensitivity, a multivariate analysis (MVA) utilizing Boosted Decision Tree (BDT) technique has been implemented. 95% C.L. upper limits on the charged Higgs boson production cross section times the branching ratio to top and bottom quarks are evaluated as a function of charged Higgs mass in the range of 200 GeV to 3000 GeV."], "keyword": ["Experimental Particle Physics"], "primary_title": "Searches for Charged Higgs Bosons and for Decays of Neutral Higgs Bosons to Charm Quarks", "uri": "https://repository.library.brown.edu/studio/item/bdr:1129427/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:1129427/"}, {"pid": "bdr:1129452", "object_type": "pdf", "abstract": ["From the release of the CMB at redshift z ~ 1100, when the CMB was released, to around z ~ 6, where the most distant quasars are observed, lies an unobserved stretch of cosmic history. During this time, the first large scale structures grew from small perturbations, the first stars ignited, and early galaxies emitted UV radiation which re-ionized the intergalactic medium (IGM) into the fully ionized universe we see today. This last stage, when these luminous sources heated and ionized the universe, is known as the Epoch of Reionization (EoR). The 21 cm hyperfine transition of neutral hydrogen (HI) offers a window into this period, as it can be used to directly map the three-dimensional structure of the IGM throughout cosmic history. Experiments to measure this signal must contend with foreground contaminants 5 orders of magnitude brighter than the expected signal. Though bright, these foregrounds have very smooth spectra, which allows their power to be isolated from the EoR signal in Fourier space provided the observing instrument does not introduce any spectral structure. Understanding and mitigating these sources of spectral structure has been an ongoing effort. Precise and detailed simulations of the instrument response have revealed several effects that were unknown in radio astronomy, but relevant to the challenge of 21 cm detection. Previous generations of simulators have lacked sufficient standards of verification, and made it impossible to determine whether some observed artifacts were due to the simulation architecture or realistic to the instrument. In this work, I present two new instrument simulation tools. The simulator pyuvsim has been collaboratively written within a robust test framework to provide the most precise and accurate simulated visibilities available, and has come to serve as a reference standard within the HERA collaboration. In addition, I have written a new diffuse simulator called healvis which has been validated against pyuvsim and analytic calculations. With healvis simulations, I have studied the time-correlation properties of drift-scan observations of EoR-like signals and measured the sample variance of realistic observations of such signals, as a fundamental lower limit on the precision that can be obtained from current experiments. In addition, I have looked at the impact of various instrumental effects on the spread of diffuse foreground power in Fourier space, testing the limits of what Fourier modes can be detected."], "keyword": ["Cosmology", "Computer simulation", "Epoch of reionization"], "primary_title": "Precision Simulation of Low-Frequency Radio Interferometers", "uri": "https://repository.library.brown.edu/studio/item/bdr:1129452/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:1129452/"}, {"pid": "bdr:1129461", "object_type": "pdf", "abstract": ["The lack of an efficient and stable numerical method remains a serious bottleneck for long-time simulations. Time parallel integration methods can break the bottleneck by decomposing the time domain and solving these subdomains parallel-in-time. I propose a Supervised Parallel-in-time Algorithm for Stochastic Dynamics (SPASD), which aims to significantly accelerate stochastic Lagrangian solvers for long-time simulations. Based on the bottom-up coarse-graining philosophy, stochastic particle models such as dissipative particle dynamics converge to continuum macroscopic models in the scale limit. The macroscopic system can then serve as a predictor to supervise the high-dimensional stochastic Lagrangian simulation. Even though the governing equations of the macroscopic model, generally in the form of partial differential equations, are different from those of the microscopic model, the macroscopic model can capture the correct mean-field behavior of the microscopic system in the continuum limit. In particular, an inexpensive continuum solver solves the macroscopic model in serial, and an expensive but parallelizable solver resolves the molecular details by performing stochastic microscopic simulations. In my thesis, I tested the accuracy and convergence of SPASD and showed that the transient and final solutions match the analytical/reference solutions even when our estimation to the system\u00e2\u0080\u0099s mean-field behavior is far from the true behavior. More importantly, the SPASD algorithm is able to preserve the stochastic fluctuations of the microscopic model. I demonstrated that SPASD provides better parallel efficiency and thus better scalability than the conventional domain decomposition method for long-time simulations. For a practical demonstration, I applied SPASD, in conjunction to domain decomposition, to accelerate massive Lagrangian simulations of blood flow in a zebrafish hindbrain. In this example, the complex vascular network is a digital reconstruction of a real zebrafish and is comprised with 95 branches and 57 bifurcations. To show the accuracy of SPASD, I simulated the same problem with and without the parallel-in-time scheme. I found that the maximum normalized l2 error is only on the order of one percent in our complex fluid example, and it does not grow over iterations."], "keyword": ["Computational fluid dynamics", "computational physics"], "primary_title": "Spatial and Temporal Acceleration of Mesoscopic Blood-flow Simulations", "uri": "https://repository.library.brown.edu/studio/item/bdr:1129461/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:1129461/"}, {"pid": "bdr:1129504", "object_type": "pdf", "abstract": ["The detailed physics of the first luminous objects and the subsequent Epoch of Reionization (EoR) remains largely unknown. The most promising approach for placing observational constraints on the EoR is to detect the 21 cm emission from hyper-fine spin flip transition in neutral hydrogen. By observing the redshifted 21 cm emission from the neutral intergalactic medium (IGM) we are potentially able to make a 3D map of structure evolution. However, current experiments do not have the sensitivity to directly image the 21 cm signal. We instead use a statistical quantity, the 21 cm power spectrum, to quantify the 21 cm power at various spatial scales. The Murchison Widefield Array (MWA) located in Western Australia is one of the first generation telescopes targeting the EoR. The recent Phase II upgrade to the MWA has improved the EoR power spectrum sensitivity, as well as has provided new opportunities for redundant calibration. In this work, I developed new analysis techniques to remedy the contamination from foregrounds, Radio Frequency Interference (RFI), and instrument-specific artifacts. By applying this improved instrument calibration technique, as well as better data quality evaluation metrics, the errors in traditional analysis have been mitigated, and the constraints on power spectrum has been improved. By analyzing 40 hours of MWA Phase II EoR observation, we show the measured power spectrum at $0.18hMpc^{-1}<k<1.6hMpc^{-1}$ with a lowest observed upper limit of $\\Delta^2=2.39\\times 10^3 mK^2$ at $k=0.59 hMpc^{-1}$ and $z=6.5$."], "keyword": ["Radio astronomy"], "primary_title": "The Phase II of Murchison Widefield Array Experiment: Constraining the Epoch of Reionization", "uri": "https://repository.library.brown.edu/studio/item/bdr:1129504/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:1129504/"}, {"pid": "bdr:1129233", "object_type": "pdf", "abstract": ["In the last two decades, wide and deep astronomical surveys have been conducted and lead to productive observations. Built on the experience of these past and ongoing surveys, Rubin Observatory will carry out the Legacy Survey of Space and Time (LSST) to address broad scientific goals and open new windows on the Universe in the next decade. As a precursor task for LSST, we conduct gravitational lensing analysis on both simulated and real-world imaging data with algorithms and software frameworks of LSST. We introduce the image simulation pipeline, jedisim, of galaxy cluster lensing with realistic galaxy images cut from Hubble Space Telescope (HST). The simulations represent realistic galaxy distributions and morphologies, and simulate lensing effects via a ray-tracing algorithm. The simulated images are processed and measured by the LSST Data Management (DM) pipeline. By comparing the measured reduced shear g_meas and the true reduced shear g_true, we observe non-linearity up to g~0.6. We fit polynomials to the data with quadratic correction adequate to g~0.4. This study yields a first relationship between reality and shape measurement of LSST DM pipeline, and serves as the first step of the overall goal of mass calibration in clusters. In addition, we select and observe a massive, low-redshift galaxy cluster, Abell 3628, with Dark Energy Camera (DECam). LSST DM pipeline is applied to measure lensing signals and plot mass distribution. This study provides a first map of dark matter structure in A3628, and will be a low-redshift anchor for the upcoming LSST deep survey data."], "keyword": ["Astrophysics", "Dark matter (Astronomy)", "Galaxies--Clusters", "Gravitational lenses", "Dark energy (Astronomy)"], "primary_title": "Weak and Not So Weak Lensing: Shear Calibration and Dark Matter Structure in Galaxy Clusters", "uri": "https://repository.library.brown.edu/studio/item/bdr:1129233/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:1129233/"}, {"pid": "bdr:1129472", "object_type": "pdf", "abstract": ["Perovskite solar cells have attracted considerable attention in recent years due to their rapidly increasing power conversion efficiency, which currently exceeds 24%. Despite this success achieved through improvements in the fabrication processes and compositional engineering, the underlying optoelectronic properties of these materials, including charge transport, remain controversial. Here we studied carrier transport in perovskite materials using two related photoluminescence spectroscopy methods. First, we developed a time-resolved photoluminescence imaging method for studying carrier diffusion in formamidinium lead triiodide (FAPbI3) perovskite thin films. With this method, it was found that carrier diffusivity increases when background carriers are present. This effect may be explained by trap-carrier interactions. Second, a steady state photoluminescence method was developed to study carrier diffusion. In particular it was used to study carrier transport barriers and help identify sub-grain special boundaries in FAPbI3 perovskite thin films. Interestingly, these boundaries which restrict carrier diffusion and serve as nonradiative recombination sites, cannot be observed by conventional AFM or SEM measurements. The presence of such boundaries may explain why the performance of perovskite solar cells has not scaled with apparent grain size. With this same method, carrier transport across ferroelastic twin boundaries (FTB) was studied in methylammonium lead triiodide (MAPbI3) single crystals. It was found that FTBs have little effect on carrier transport and recombination, this in contrast both to normal grain boundaries and special subgrain boundaries."], "keyword": ["Photoluminescence--Measurement"], "primary_title": "Direct Optical Characterization of Carrier Transport and Structural Properties in Halide Perovskite Materials", "uri": "https://repository.library.brown.edu/studio/item/bdr:1129472/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:1129472/"}, {"pid": "bdr:1129163", "object_type": "pdf", "abstract": ["The Large Underground Xenon (LUX) experiment is a 250~kg active mass dual-phase time-projection chamber~(TPC) operating at the 4850~ft level of the Sanford Underground Research Facility in Lead, SD. Various sources, including $^{127}$Xe, D-D neutrons, $^{83m}$Kr, Tritium, and AmBe neutrons are used to perform calibrations of detector responses to electron recoils~(ER) and nuclear recoils~(NR). I will present an ultra-low energy calibration of ER using an intrinsic $^{127}$Xe source and of NR using a short pulsed D-D neutron generator. Radioactive isotope $^{127}$Xe is formed in the LUX LXe volume due to cosmogenic activation before the detector was moved one mile underground. A measurement in the early stage of the LUX WS2013 science run unveils $\\sim$0.9 million $^{127}$Xe atoms in the LUX LXe volume, which provides an ideal source for low energy calibrations. $^{127}$Xe decay is a form of electron capture in which a high energy gamma (>~200~keV) is emitted, followed by an associated low energy X-ray cascade over the energy range of 190~eV to 33.2~keV. The relatively long mean free path~(mfp) of the gamma-ray~(>~0.9~cm) allows the EC decay to produce clearly identified 2-vertex events in the LUX detector. We observe the K~(33.2~keV), L~(5.2~keV), M~(1.1~keV), and N~(190~eV) shell cascade events and verify the relative ratio of observed events for each shell. We extract the means and sigmas of the charge signal yields associated with the K, L, M, and N shell events. The N shell cascade analysis includes single extracted electron (SE) events and represents the lowest-energy electronic recoil $\\tilt{in~situ}$ measurements that have been explored in liquid xenon. A short pulsed D-D neutron NR calibration was performed $\\tilt{in~situ}$ in the LUX detector in June 2016 after the completion of the LUX WS2013-16 science run. The calibration incorporates a pulsing technique with narrow pulses~(20~$\\upmu$s$\\matbin{/}$250~Hz). We have measured, with low systematics, the absolute rates of NR events with ionization signals down to 2~extracted electrons and zero, one or greater detected scintillation photons. A calibration measurement with absolute event rates of charge-only S2 events for the first time in a Xe TPC provides an important probe for ultra-low energy measurements of LXe Qy. This technique provides direct measurements of scintillation and charge yields down to (Ly) 0.45~keV$_\\textrm{nr}$ and (Qy) 0.27~keV$_\\textrm{nr}$, respectively. New calibration results on ultra-low energy nuclear recoil yields are crucial to determine physics search sensitivities for large mass LXe TPCs~(LZ experiment) for low mass WIMPs~(<~10~GeV) and for coherent neutrino scattering (e.g. $^8$B solar neutrino)."], "keyword": ["Experimental Particle Physics"], "primary_title": "Ultra-Low Energy Calibration of the LUX and LZ Dark Matter Detectors", "uri": "https://repository.library.brown.edu/studio/item/bdr:1129163/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:1129163/"}, {"pid": "bdr:297706", "object_type": "pdf", "abstract": ["Magnetic nanoparticles have been used extensively as drug delivery materials in recent years. The goal of this study was to treat bone diseases (such as osteoporosis and infection) by using surface modified magnetic nanoparticles. To tailor particles for orthopedic applications, magnetite (Fe3O4) were synthesized and coated with hydroxyapatite (HA). Nanoparticles were characterized via transmission electron microscopy (TEM), X-ray diffraction (XRD), dynamic light scattering (DLS) and vibrating sample magnetometry (VSM). Osteoblast (OB) cultured in the presence of nanoparticles showed increased proliferation and long term function. The studies investigated mechanism of enhanced OB activity by conducting protein adsorption and gene expression experiments. Nanoparticle uptake into osteoblast was also studied. The nanoparticles were internalized into OB via receptor-mediated endocytosis. A mathematical model was developed to explain this endocytic pathway. The bactericidal effect of iron oxide nanoparticle was investigated. Results of this in vitro study demonstrated inhibited Staphylococcus aureus activities in the presence of select magnetic nanoparticles. The thesis then focused on evaluating the applicability of magnetic nanoparticles by estimating magnetic field and force exerted on a nanoparticle. In summary, the results of this study showed that magnetic nanoparticles should be further studied for various orthopedic applications as they decrease bacteria function and promote OB function."], "keyword": ["magnetic nanoparticles", "Osteoporosis", "Infection", "Hydroxyapatite", "Bone regeneration", "Endocytosis"], "primary_title": "Synthesis, Modification and Characterization of Magnetic Nanoparticles and Applications in reversing Osteoporosis and Inhibiting Bacterial Infection", "uri": "https://repository.library.brown.edu/studio/item/bdr:297706/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:297706/"}, {"pid": "bdr:297714", "object_type": "pdf", "abstract": ["Acoustic microscopy has been used to study a variety of microstructures, material defects, and biological tissues. One of the key limitations in pulsed acoustic microscopy is the duration of sound pulses that can be generated. The goal of this ongoing project is to develop an acoustic microscope that uses ultrashort laser pulses, with durations on the order of 100 fs, to generate short sound pulses, with durations on the order of 10 ps. These short sound pulses will then be used to form images of the sample being studied analogous to a traditional acoustic microscope. This technique is referred to as scanning opto-acoustic microscopy (SOAM). <br/><br/><br/> As a first step towards the construction of a SOAM instrument, a system which contains all of the key components except for the acoustic lens and the sample scanning stages was constructed. The acoustic pulses generated by the ultrafast optical source, instead of being focused by an acoustic lens, were launched into the coupling fluid directly. This technique is referred to as planar opto-acoustic microscopy (POAM). The first samples examined were periodic groups of nanostructures. With a repeat distance in the submicron regime, the acoustic pulse was probing anywhere from 20 - 100 nanostructures at once. By comparing experimental results with simulations, the average features of groups of nanostructures, such as height and spacing, could be measured with nanometer sensitivity. The relative sizes of the echoes in the POAM data were used to infer information about the average critical dimensions and profile of groups of structures. For structures with channels that were less than 60 nm wide, the amplitude and arrival time of the echo from the bottom of the channels were very sensitive to the channel width and depth. POAM was shown to provide a way of measuring the dimensions of these features non-destructively. The dimensions inferred from the POAM data were compared to destructive measurements of the sample profiles using scanning electron microscopy. For narrow channels, the presence of slip at the water-side wall interface would have a measurable effect on the echo from the bottoms of the channels. POAM data was used to place an upper limit of 5 nm on the slip length at the water-silicon nitride interfaces.<br/><br/><br/>"], "keyword": ["picosecond ultrasonics", "ultrafast acoustics", "Acoustic microscopy"], "primary_title": "Planar Opto-acoustic Microscopy Applied to the Metrology of Periodic Nanostructures", "uri": "https://repository.library.brown.edu/studio/item/bdr:297714/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:297714/"}, {"pid": "bdr:297717", "object_type": "pdf", "abstract": ["It is known that an electron in liquid helium forms a spherical cavity of a radius of approximately 19 \u00c5 and rests in it. This structure is referred to as an electron bubble, and has been well studied both experimentally and theoretically. In the time-of-flight (TOF) measurement, electron bubbles can be employed as probes to study the properties of phonon and roton - elementary excitations of helium II - as well as the 3He impurity. The mobility of electron bubbles has been measured by TOF method under various conditions, and its behavior is theoretically understood. Besides the ordinary electron bubbles, TOF measurements have revealed a series of other negative ions of higher mobility and smaller sizes. The fastest one of these objects is named as the fast ion, the intermediate ones are named exotic ions, and accordingly, the electron bubble is renamed as the normal ion. The nature and origin of the fast and exotic ions has remained unknown for several decades since their discovery. To seek a better understanding, we have carried out some further studies on these objects by the TOF method based on the experience gained from the earlier work. A new cryogenic apparatus has been specially designed and constructed to meet the specific needs of this experiment. It can maintain a stable experimental environment for long periods of time. We have also studied the TOF method and optimized our experimental TOF structure. The signal-to-noise in the TOF measurement has been improved in order to detect a current signal on the order of a tenth of a pico-Ampere. After exploring various experimental conditions, we successfully reproduced the fast and exotic ions, measured the mobility of these objects, and have been able to summarize the experimental conditions under which they are inclined to appear. Finally, we discuss some possible theoretical explanations, and based on our experimental observations speculate on the process of ion generation."], "keyword": ["fast ion", "exotic ions", "time-of-flight method", "superfluid helium"], "primary_title": "Studies of the Fast and Exotic Ions in Superfluid Helium-4", "uri": "https://repository.library.brown.edu/studio/item/bdr:297717/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:297717/"}, {"pid": "bdr:297716", "object_type": "pdf", "abstract": ["In this dissertation, we present the results of simulation studies of nematic liquid crystals using the Lattice Boltzmann (LB) Method. In the first step of our project, we built our own simulation codes for nematic liquid crystals (LC) from the ground up after reproducing the derivation of LB solvers for two coupling governing equations, one for the evolution of the momentum and one for the evolution of the tensor (order parameter). Then, we performed the Lattice Boltzmann simulation of shear flow, to validate our LB code in comparison with analytical solutions for this simple structure. According to this numerical test, we gained a sense of the efficiency of the LB method with the adjustment of spatial and temporal parameters to produce results for different physical properties. In the second step, we simulated a nematic liquid crystal in a relatively complex (due to the complex physical boundary conditions) geometric structure namely lid-driven cavity flow. We started the simulation from a static state (2D first and then 3D) and studied the pattern variation for different geometric parameters (aspect ratios). Based on these conclusions, we simulated the driven-cavity structure balancing the competition between computational runtime and physical applicability. The limitation of the LB method and inherent instability of this dynamic structure were discussed. In the final step of our project, we moved on to an even more complex structure of 2-phase (isotropic-nematic) step flow. This step was divided into three subquestions according to their respective complexity, i) the geometric ratios; ii) 2-phase flow of ordinary immiscible fluids in the step-flow structure iii) evolving the tensor equation with coupling to momentum equation and producing the pattern for the molecular alignment constrained by the dynamic boundary (interface), i.e. its geometric shape and flow field. Due to the limitation of the 2-phase separation mechanism we applied, the speed and geometric ratio of this structure is restricted to certain extent. Finally, we conclude with suggestions for future work in this area baesd on the results of our work, mainly in two directions, such as static and dynamic analysis, respectively."], "keyword": ["LB", "LC", "2-phase flow", "interface", "immiscible fluids", "Lattice Boltzmann methods", "Liquid crystals", "Shear flow"], "primary_title": "Simulation of Nematic Liquid Crystals: Shear Flow, Driven-Cavity and 2-Phase (Isotropic-Nematic) Step Flow", "uri": "https://repository.library.brown.edu/studio/item/bdr:297716/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:297716/"}, {"pid": "bdr:297712", "object_type": "pdf", "abstract": ["In this thesis work, we have presented the concept and fabrication of the single coaxial optrode. Its dual functionality of simultaneous light delivery and electrophysiological recording has been demonstrated. We applied the coaxial optrode as a stand-alone unit in in vivo optical stimulation and recording in various experimental animal models - including transgenic mice, optogenetically transduced rodents and non-human primates. To better understand light distribution and compare optical stimulation among different fiber optical structures, we investigated the interaction between light and brain tissue, and then employed the Monte Carlo method to simulate the process of light propagation and associated issue of heating. As suggested by the simulation result, we expect relatively mild temperature increases in response to stimulation paradigms currently used in our lab. We also construct a model that describes the electric behavior of optrode, which allows the spatial sensitivity of optrodes with various coating configurations to be mathematically analyzed.<br/> In the second part of this thesis, we demonstrate an integrated optrode-microelectrode array (optrode-MEA) device that enables neuromodulation and simultaneous recording of electrophysiological responses of neuronal populations in ChR2-expressing rodents in vivo. We have showed the use of this device as an optogenetic tool for single site optical stimulation and electrical mapping of neural activity in a configuration which can be applied to other animal models. Finally, to translate these optical neuromodulation studies into non-human primates, we are working on the polymer fiber-MEA version of the device that allows multisite optical stimulation and electrical recording. Such a device could be desirable for potential clinical trials in human patients."], "keyword": ["optrode", "optical stimulation", "neuroprosthetics", "chronic recording", "Optogenetics"], "primary_title": "COMBINED OPTICAL STIMULATION AND ELECTRICAL RECORDING IN IN-VIVO NEUROMODULATION", "uri": "https://repository.library.brown.edu/studio/item/bdr:297712/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:297712/"}, {"pid": "bdr:297713", "object_type": "pdf", "abstract": ["Gene expression occurs when an organism produces proteins that correspond to genes in DNA. Interactions of these proteins cause many biological functions. Some types of low dose stressors are known to have positive effects, for example the phenomenon of dietary restriction-mediated lifespan extension. This work covers aspects of the gene expression response to low dose stressors in Drosophila melanogaster. Chapter 1 is an introduction to basic gene expression analyses and a summary of the author\u2019s work analyzing gene expression data. Chapter 2 introduces a new algorithm for comparing two sets of gene expression experimental results. Chapter 3 introduces a new data set using radiation as a low dose stress. Biological results include significant genes and functional pathways that mediate the effects of dietary restriction, gene mutations that mimic dietary restriction and low doses of radiation. Mathematical results include the use of a new statistic to determine the degree of overlap between two gene expression experiments."], "keyword": ["Low Dose Radiation", "Gene expression", "Drosophila melanogaster", "Algorithms"], "primary_title": "Stress, Aging and Gene Expression in Drosophila melanogaster", "uri": "https://repository.library.brown.edu/studio/item/bdr:297713/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:297713/"}, {"pid": "bdr:297709", "object_type": "pdf", "abstract": ["This dissertation describes the process of diamond nanowire fabrication, the identification of the samples as diamond, and the characterization of their optical and structural properties. The diamond nanowires were grown in a chemical vapor deposition (CVD) process at atmospheric pressure. These nanowires are 60 - 90 nm in diameter, and 1 - 20 \u03bcm in length. Their structure consists of a crystalline diamond core inside a graphite shell. The diamond nature of the nanowires was revealed through transmission electron microscopy, scanning electron microscopy, electron diffraction analysis and Raman spectroscopy. Photoluminescence spectroscopy of the diamond nanowires revealed a sharp, strong emission line at 415 nm. This feature may indicate that these nanowires contain the N3 defect center: three nitrogen substitutional atoms near a vacancy. This emission center could have applications for quantum information processing, biosensing, and other light emission devices. Various models were introduced to explain the growth process. Though diamond does not typically grow at atmospheric pressure, the small size of the nanowires allows them to benefit from an extra capillary pressure on the order of gigapascals. The synthesis may also have been aided by the nucleation inside a carbon nanotube pressure vessel, graphite etching by hydrogen, and the charged cluster effect. Diamond nanowires were also produced via reactive ion etching of diamond films. This process allows for fine control over the dimensions of the nanowires, and is useful for production of nanowires for various applications. Diamond is a unique material with a wide bandgap (5.5 eV), the highest known thermal conductivity, and negative electron affinity. These characteristics and more give diamond nanowires a broad potential array of applications, including quantum information processing, electron field emission, UV light detection and high-power transistors."], "keyword": ["diamond", "Nanowires", "Nanotechnology"], "primary_title": "Structural and optical characterization of diamond nanowires", "uri": "https://repository.library.brown.edu/studio/item/bdr:297709/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:297709/"}, {"pid": "bdr:292", "object_type": "pdf", "abstract": ["We investigated the microscopic structure and properties of microtubule (MT) striped patterns that spontaneously form in polymerizing tubulin solutions and propose a mechanism driving this assembly. Microscopic observations reveal that the pattern comprises wave-like MT bundles. The retardance of the solution and the fluorescence intensity of labeled MTs vary periodically in space, suggesting a coincident periodic variation in MT alignment and density. This wave-like structure forms through the development and coordinated buckling of initially aligned MT bundles. Both a static magnetic field and convective flow can induce the initial alignment. The nesting of the buckled MT bundles gives rise to density variations that are in quantitative accord with the data. We propose a mechanical buckling model for the spontaneous formation of the striated MT pattern. It describes the buckling of a single MT bundle within an elastic network formed by other similarly aligned and buckling bundles and unaligned MTs. Phase contrast and polarization microscopy studies of the temporal evolution of the pattern imply that the polymerization of MTs within the bundles creates the driving compressional force. Using the measured rate of buckling, the established MT force-velocity curve and the pattern wavelength, we obtain reasonable estimates for the MT bundle bending rigidity and the elastic constant of the network. We also studied the effects of Polyethylene Glycol (PEG, MW=35 kDa) on MT bundling and pattern formation. We found that with increasing PEG concentrations, MT solutions form progressively weaker patterns. At a sufficiently high PEG concentration (~0.5% w/w), the samples maintain a nearly uniform birefringence (i.e. no pattern) and laterally contract at a later stage. Concomitantly, on a microscopic level, the network of dispersed MTs that accompany the bundles in pure solutions disappear and the bundles become more distinct. We attribute the weakening of the pattern to the loss of the dispersed MT network, which is required to mediate the coordination of bundle buckling. We propose that the loss of the dispersed network and the enhanced bundling result from PEG associated osmotic forces that drive MTs together and osmotic torques that facilitate their bundling. Similarly, we attribute the lateral contraction of the samples to osmotic torques that tend to align crossing bundles in the network."], "keyword": ["Osmotic Effect", "Bundling", "Buckling", "Birefringence", "Pattern Formation", "Microtubules", "Refraction, Double"], "primary_title": "Microscopic Investigation and Modeling of Microtubule Self-Organization in Tubulin Solutions", "uri": "https://repository.library.brown.edu/studio/item/bdr:292/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:292/"}, {"pid": "bdr:37", "object_type": "pdf", "abstract": ["This thesis describes the development of a metallic metallic calorimeters (MMC) for a soft x-ray detection. A MMC utilize diluted concentration of a paramagnetic material in a non-magnetic metal host as a temperature sensor. The sensor is placed in a weak field and operated typically below 100~mK. The temperature rise on absorption of a particle leads to a change of the magnetization of the sensor material, which is read out by a dc SQUID magnetometer. A field of application for a MMC is x-ray astronomy as a focal plane detector for imaging and high energy resolution spectroscopy. Thin film technology is suitable to fabricate such detector arrays. Thin films of erbium diluted in gold (Au:Er) were dc magnetron sputter-deposited using Au:Er alloy targets under different conditions, and the magnetic properties of the films have been studied. The magnetization of the film agreed with that of the target material from room temperature down to 200~mK, however, the magnetization of the film showed an enhanced exchange interaction among Er ions below 200~mK. The possible origin of the interaction is discussed. Au:Er films were deposited on flux transformer chips of four pixel MMC arrays. Meander pick-up coils for each pixel also provide a magnetic field by applying a superconducting persistent current. The test results of the prototype detector arrays are presented. X-ray signals of $^{55}$Fe source are analyzed."], "keyword": ["Au:Er film,magnetic microcalorimeter,x-ray detector,detector array"], "primary_title": "Study of Vapor-Deposited Au:Er Films and Development of a Metallic Magnetic Calorimeter for Future X-ray Astronomy Missions", "uri": "https://repository.library.brown.edu/studio/item/bdr:37/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:37/"}, {"pid": "bdr:320536", "object_type": "pdf", "abstract": ["For my graduate research, I have focused on the creation of high resolution weak lensing mass maps in order to study dark matter substructure in clusters of galaxies at high redshift (z&gt;0.5). Galaxy clusters are the largest virialized structures in the universe, and are meaningful environments for tests of cosmology. Mass substructure in clusters of galaxies is important for several reasons: as a test of hierarchical Cold Dark Matter, as a way of reducing the scatter in the mass calibration of clusters for dark energy studies, and as environments for galaxy and active galactic nuclei evolution.<br/> <br/> Gravitational lensing is a powerful tool for measuring mass in astronomical objects. According to General Relativity, very massive objects bend the light of more distant objects around them, thus distorting the shape of these background objects. In the weak lensing regime, these shape distortions are small (few percent level), and thus only detected as a systematic alignment about the lensing cluster. Therefore, rigorous shape detection, extraction, and statistical analysis are required to generate mass maps.<br/> <br/> Starting with Hubble Space Telescope data, I carefully correct for the HST\u2019s Point Spread Function ellipticity pattern and stack the images for each cluster. After extracting the stack data, I perform a weak lensing analysis of the cluster. To characterize the level of substructure, I apply a cluster finding variable aperture filter. Finally, I fit an ensemble of NFW profiles to the detected matter peaks."], "keyword": ["dark matter", "weak lensing", "clusters of galaxies", "Dark matter (Astronomy)", "Galaxies--Clusters"], "primary_title": "Dark Matter Substructure in High Redshift Clusters of Galaxies", "uri": "https://repository.library.brown.edu/studio/item/bdr:320536/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:320536/"}, {"pid": "bdr:320546", "object_type": "pdf", "abstract": ["Scattering Amplitudes in maximally supersymmetric gauge and gravity theories are remarkable objects which hold the key to understanding many interesting mathe- matical structures in these theories. In this dissertation we study various techniques for computing scattering amplitudes. In the AdS/CFT duality paradigm, the computation of CFT correlation functions via Witten diagrams in AdS space can be simplified via the Mellin transform. Recently a set of Feynman rules for tree-level Mellin space amplitudes has been proposed for scalar theories. In this thesis we derive these rules for the scalar \u03c6^n theory and check their behavior under the flat space limit. Next, we explore single and multi-loop conformal integrals, such as the ones appearing in perturbative dual conformal theories in flat space. Using Mellin amplitudes in this context, a large class of higher loop integrals can be written as simple integro- differential operators on star integrals: one-loop n-gon integrals in n dimensions. We explore the geometric origin of such integrals and study specific non-trivial examples including their relation to higher loop integrals. We study N = 4 Super Yang-Mills(SYM) tree level scattering amplitudes and explore inverse soft limit idea of \u201cadding a particle to lower point amplitudes\". Using it we generate full tree-level superamplitudes of N = 4 SYM theory, by adding \u201csoft\" particles in a certain way. With the help from Britto-Cachazo-Feng-Witten recursion relations, a systematic and concrete way of adding particles is determined recursively. The method of generating amplitudes by Inverse Soft Limit can also be generalized for constructing form factors. We also study the application of non-trivial relations between gravity tree amplitudes, the bonus relations, to all tree-level amplitudes in N = 8 supergravity. We show that the relations can be used to simplify explicit formulae of supergravity tree amplitudes, by reducing the known form as a sum of (n \u2212 2)! permutations to a new form as a (n \u2212 3)!-permutation sum. We demonstrate some specific examples and then provide a general pattern of bonus coefficients for all tree-level amplitudes."], "keyword": ["Scattering Amplitudes", "String Theory", "High Energy", "String models"], "primary_title": "Techniques for computing scattering amplitudes: Mellin space, Inverse Soft Limit, Bonus Relations.", "uri": "https://repository.library.brown.edu/studio/item/bdr:320546/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:320546/"}, {"pid": "bdr:2k2t2fkd", "object_type": "pdf", "abstract": ["In this thesis we present studies of scattering amplitudes on the celestial sphere at null infinity (celestial amplitudes), the cluster adjacency structure of scattering amplitudes in planar maximally supersymmetric Yang-Mills theory (N=4 SYM), and a method to derive symbol letters for loop amplitudes in N=4 SYM. First, we show that n-particle celestial gluon tree amplitudes take the form of Aomoto-Gelfand hypergeometric functions and Gelfand A-hypergeometric functions. We then study conformal properties, conformal partial wave decomposition, and the optical theorem of four-particle celestial amplitudes in massless scalar phi-cubed theory and Yang-Mills theory. Subsequently, we derive single- and multi-soft theorems for celestial amplitudes in Yang-Mills theory. Second, we provide computational evidence that each rational Yangian invariant in N=4 SYM has poles that are cluster adjacent (belong to the same cluster in the Gr(4,n) cluster algebra) through the Sklyanin bracket test. We also use this bracket test to study cluster adjacency of the symbol of one-loop NMHV amplitudes in N=4 SYM. Finally, we suggest an algorithm for computing symbol alphabets from plabic graphs by solving matrix equations of the form C.Z = 0 to associate functions on Gr(m,n) to parameterizations of certain cells in Gr(k,n) indexed by plabic graphs. For m=4 and n=8 we show that this association precisely reproduces the 18 algebraic symbol letters of the two-loop NMHV eight-particle amplitude from four plabic graphs."], "keyword": ["scattering amplitudes", "Cluster algebras", "Supersymmetry", "Celestial sphere", "Yang-Mills Theory"], "primary_title": "Celestial Amplitudes, Cluster Adjacency, and Symbol Alphabets", "uri": "https://repository.library.brown.edu/studio/item/bdr:2k2t2fkd/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:2k2t2fkd/"}, {"pid": "bdr:30", "object_type": "pdf", "abstract": ["After ~50 years, there seems to be a convergence in the languages used to describe Quantum Field Theory and String Theory, such that it seems possible to relate objects from these two perspectives. Therefore, a deeper investigation of the properties and features of QFT is a reasonable thing to do: nonperturbative effects, dualities, emergent properties, noncommutative structures, etc. This particular line of research uses Symmetry Breaking in order to probe a few of the different topics mentioned above, i.e., Symmetry Breaking is used as an \"underlying principle\", bringing different features of QFT to the foreground. However, the understanding of Symmetry Breaking that is used here is quite different from what is done in the mainstream: Symmetry Breaking is understood as the solution set of a given QFT, its vacuum manifold, or, more modernly, its Moduli Space. Distinct solutions correspond to different sectors, phases, of the theory, which are nothing but distinct foliations of the vacuum manifold, or points in the Moduli Space (for all possible values of the parameters of the theory). Under this framework, three different problems will be attacked: \"Mollifying QFT\", \"Topological Transitions and Geometric Langlands Duality\" and \"Three-dimensional Gravity and its Phase Transitions\". The first makes use of the Moduli Space of the theory in order to construct an appropriate mollification of it, rendering it viable to simulate a QFT in Lorentzian spaces, tackling the \"sign problem\" heads-on. The connections with Lee-Yang zeros and Stokes Phenomena will be made clear. The second will show that each different phase has its own topology which can be used as Superselection Rule; moreover, the Euler Characteristic of each phase gives it quantization condition. The mechanism via which several dualities work will also be elucidated. The last one will generalize a 0dimensional QFT, via dimensional construction through its D-Module, and conjecture several connections between the Lie-algebra-valued extension of the Airy function and the recent Partition Function found for 3dimensional gravity with a negative cosmological constant. These three problems, put together, should exhibit a solid and robust framework for treating QFT under this new paradigm."], "keyword": ["symmetry breaking", "topological transition", "moduli space", "3-dimensional gravity", "Broken symmetry (Physics)", "Quantum field theory", "D-modules"], "primary_title": "Symmetry Breaking: A New Paradigm for Non-Perturbative QFT and Topological Transitions", "uri": "https://repository.library.brown.edu/studio/item/bdr:30/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:30/"}, {"pid": "bdr:320593", "object_type": "pdf", "abstract": ["The Standard Model (SM) is the most successful theory of particle physics to date. It has been experimentally verified over the past 40 years as the various properties of the SM have been measured and the particles it predicts have been detected. The only particle yet to be experimentally confirmed is the SM Higgs boson. However, recent observations at the Large Hadron Collider (LHC) give hints of a new scalar boson which is consistent with the SM Higgs boson.<br/> <br/> This thesis presents two searches for the SM Higgs boson at the LHC using data collected by the CMS detector. In 2011, the search was performed using 5 fb-1 of data at a 7 TeV center of mass energy, and in 2012, using 18.3 fb-1 of data at a 8 TeV center of mass energy. In both analyses, the SM Higgs boson was produced in association with a W boson, where the Higgs boson then decays into two b-quarks and the W boson decays into a hadronic tau lepton and a neutrino. Upper limits, at the 95% confidence level, on the WH production cross section times the branching ratio of the Higgs boson decaying into two b-quarks, with respect to the expectations for a SM Higgs boson, are derived for a Higgs boson in the mass range 110-150 GeV. At a SM Higgs boson mass of 125 GeV, the observed limit is 6.4 and the expected limit is 7.7 times the SM prediction. In both analyses, no excess of events is observed above the expected background, which is consistent with the expectation from the production of the SM Higgs boson."], "keyword": ["LHC,CMS,Higgs Boson"], "primary_title": "Search for a Higgs Boson Produced in Association with a W Boson at the LHC", "uri": "https://repository.library.brown.edu/studio/item/bdr:320593/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:320593/"}, {"pid": "bdr:320594", "object_type": "pdf", "abstract": ["We review a field theory approach to Higher Spin Gravity in 4 dimensional Anti de Sitter (AdS) space within the framework of the AdS/CFT correspondence. Based on large N collective field theory of vector type models, we develop a bi-local dipole picture of Higher Spin theory. We also describe a geometric (Kahler space) framework for the bi-local theory which applies to Sp(2N) fermions and potentially to the de Sitter (dS) correspondence. We discuss in this framework the structure and size of the bi-local Hilbert space and the implementation of (finite N) exclusion principle. For the correspondence based on free CFTs we first discuss the transformation for O(N) collective field and the Higher spin filed, and then the nature of bulk 1/N interactions through an S-matrix which by the Coleman-Mandula theorem is argued to be equal to 1."], "keyword": ["bi-local", "Higher Spin gravity", "AdS/CFT"], "primary_title": "Bi-local Approach to Higher Spin Gravity", "uri": "https://repository.library.brown.edu/studio/item/bdr:320594/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:320594/"}, {"pid": "bdr:320646", "object_type": "pdf", "abstract": ["Dark matter is an essential ingredient in our modern understanding of the Universe. However, its fundamental role in cosmology is matched only by its conspicuous absence from the Standard Model of particle physics. The last thirty years has seen a concerted theoretical and experimental effort to identify the particle nature of dark matter.<br/> <br/> In this thesis I present new work that pushes current observations to the sensitivities required to explore long-standing and broad classes of dark matter candidates. I have developed a maximally-powerful statistical framework that allows a simultaneous analysis of multiple targets, taking into account the spatial and spectral properties of individual detector events. The method is applied to search for dark matter annihilation in Milky Way dwarf galaxies. This search currently represents the most sensitive probe of dark matter parameter space, for the first time excluding annihilation cross sections which explain the observed relic abundance.<br/> <br/> In addition, I present two novel techniques developed to understand the diffuse backgrounds which limit the sensitivity of all astrophysical analyses, including dark matter searches. The first is a spacetime correlation function that is sensitive to a population of extremely faint moving sources. The second makes use of time series analyses in untangling the emission from unresolved pulsars. Both methods are intended to discover and characterize an entire population of sources even when the individual members remain undetectable."], "keyword": ["dark matter", "indirect detection", "statistical methods", "gamma-ray observations", "Dark matter (Astronomy)", "Statistics", "Astrophysics", "Cosmology"], "primary_title": "Comprehensive Approaches and Results in the Indirect Dark Matter Search", "uri": "https://repository.library.brown.edu/studio/item/bdr:320646/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:320646/"}, {"pid": "bdr:320591", "object_type": "pdf", "abstract": ["The Standard Model (SM) has stood as one of the cornerstones of modern physics for the past 40 years; yet it is likely to remain only as an effective field theory. In particular, new beyond the SM theories are required to explain both the baryon-antibaryon asymmetry observed in the Universe and the unnatural lightness of the tentatively observed Higgs boson. Such theories often predict heavy partners to the six observed quarks, which naturally explain these phenomena. <br/> <br/> In this thesis, we present two searches for a heavy top-like quark at the LHC using data collected by the CMS detector. In 2011, we searched for a sequential fourth generation quark t' using 5fb-1 of data at a 7TeV centre of mass energy. In 2012, we searched for a vector-like T that partners the SM top quark using 19.6fb-1 of data at 8TeV.<br/> <br/> In both analyses, we used a semileptonic event topology, consisting of events with exactly one lepton. No excess over SM predictions are observed and the heavy top-like quark is ruled out below the mass of 700GeV/c2 across the entire phase space. This is the first analysis of its kind and we set the most stringent limit on this entire class of beyond the SM theories to date."], "keyword": ["New physics", "heavy quarks", "top quarks", "beyond the Standard Model", "LHC", "CMS"], "primary_title": "The Search for a Heavy Top-Like Quark", "uri": "https://repository.library.brown.edu/studio/item/bdr:320591/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:320591/"}, {"pid": "bdr:320598", "object_type": "pdf", "abstract": ["Acoustic waves have been proved to be a useful tool in detecting sub-surface structures, one example being the ultrasound imaging. Similar to optical imaging, the resolution of acoustic imaging is limited by the frequency of the probing waves. Conventional piezoelectric transducers can only generate up to around 10 GHz. We built an opto-acoustical microscope based on ultrafast pump-probe experiment with sub-optical resolution (550 nm). The laser pulse can generate acoustic pulses up to around 50 GHz, with the potential of improving the resolution of acoustic imaging systems to a few tens of nanometers or less. We used nano-indentation and Focused Ion (Gallium) Beam to fabricate the sub ten-micron-meter size acoustic lens for the acoustic microscope. We also implemented finite difference time domain method to simulate the focusing effect of the acoustic lens for a single sound pulse, when it propagates from solid into liquid. A perfect match layer absorption boundary condition was adopted to eliminate the reflected sound waves from the boundary in the numerical simulation."], "keyword": ["Pulsed laser", "Pump probe", "Acoustic microscopy"], "primary_title": "Scanning Opto-Acoustical Microscopy", "uri": "https://repository.library.brown.edu/studio/item/bdr:320598/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:320598/"}, {"pid": "bdr:733355", "object_type": "pdf", "abstract": ["Amplitudeologists are interested in the general mathematical properties exhibited by amplitudes, asking questions like; which variables do planar N = 4 Super-Yang-Mills (SYM) amplitudes depend on? and what properties are common to all multi-loop and non-maximally helicity violating (MHV) amplitudes? Currently, we look at the analytic results of amplitudes calculated by alternative techniques and use newly developed mathematical tools to learn more about the properties hidden in the current formulation. Just like a change of variables can make certain symmetries more obvious, expressing the currently known amplitudes in alternative mathematical languages may uncover unknown symmetries that play an essential role. By exploiting the mathematical structure and developing tools which make amplitude properties manifest, we may be able to write down analytic functions for processes too complex to be calculated with modern techniques. Scattering amplitudes in planar super-Yang-Mills theory satisfy several basic physical and mathematical constraints, including physical constraints on their branch cut structure and various empirically discovered connections to the mathematics of cluster algebras. The power of the bootstrap program for amplitudes is inversely proportional to the size of the intersection between these physical and mathematical constraints: ideally we would like a list of constraints which determine scattering amplitudes uniquely. We explore this intersection quantitatively for two-loop six- and seven-point amplitudes. We reformulate the heptagon cluster bootstrap to take advantage of the Steinmann relations, which require certain double discontinuities of any amplitude to vanish. These constraints vastly reduce the number of functions needed to bootstrap seven-point amplitudes in planar N = 4 SYM theory, making higher-loop contributions to these amplitudes more computationally accessible. In particular, dual superconformal symmetry and well-defined collinear limits suffice to determine uniquely the symbols of the three-loop next-to-maximally helicity violating (NMHV) and four-loop MHV seven-point amplitudes. We also show that at three loops, relaxing the dual superconformal (Qbar) relations and imposing dihedral symmetry (and for NMHV the absence of spurious poles) leaves only a single ambiguity in the heptagon amplitudes."], "keyword": ["scattering amplitudes", "Quantum field theory"], "primary_title": "Cluster Bootstrap in N=4 Super-Yang-Mills Scattering Amplitudes", "uri": "https://repository.library.brown.edu/studio/item/bdr:733355/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:733355/"}, {"pid": "bdr:733314", "object_type": "pdf", "abstract": ["Single-molecule approaches enable us to follow the movement, interactions and conformational dynamics of individual molecules in real-time, thus providing novel insights in complex biochemical systems that have remained masked in the ensemble averaging of traditional bulk biochemical approaches. Recent advances in single-molecule tracking, fluorescence spectroscopy and subdiffraction optical microscopy have unveiled unprecedented views of molecular processes in live cells. To extract quantitative information from individual molecules in the high background noise, these techniques are often based on in vitro reconstituted systems with either surface-immobilized or freely-diffusing biomolecules in dilute conditions. Live cell, real-time imaging, tracking and counting biomolecules in their native, crowded intracellular environment currently remain an extremely challenging task. Based on the numerical simulation, I built the real time tracking 3D STED nanoscopy enabling single molecule detection. With the new technique, I perform oligo-nucleotide hybridization detection experiment in vitro as well as study the mechanism of RNA Polymerase II transcription in living cells at single molecule level. Basically, I reveal the accumulation of Pol II molecules and quantified nearly 10 Pol II molecules in the cluster during active transcription at a tagged mini-gene in the native environment. In addition, mini-gene transcription does not involve transient Pol II clustering at pre-initiation by kinetic analysis enabled by target-locking overVII multiple transcription rounds, arguing against the persistence of accumulated Pol IIs in the absence of transcription or extensive Pol II recycling-related spatial compartmentalization. What\u2019s more, I find that single Pol II molecules are stochastically recruited from the nucleoplasm, enter into productive elongation and are predominantly released instead of recycled upon termination. The results set up a quantitative framework for investigating Pol II dynamics at single genes at single molecule level, and also demonstrate that the potential and powerful use of real time tracking 3D STED nanoscopy in elucidating the complex biological mechanisms in vivo."], "keyword": ["Molecular biology", "Physics", "Single molecule detection", "Nanoscopy", "Optics", "RNA polymerases", "Genetic transcription"], "primary_title": "Single-molecule Nanoscopy of RNA Polymerase II Transcription at a Single Gene in Live Cells", "uri": "https://repository.library.brown.edu/studio/item/bdr:733314/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:733314/"}, {"pid": "bdr:730649", "object_type": "pdf", "abstract": ["In this thesis, we present two searches for new physics performed using the data collected by the CMS experiment at the LHC at two different center of mass energies. In the first part, we present a search for anomalous Higgs couplings. In 2012, the ATLAS and CMS experiments at the LHC discovered a new boson. This discovery completed a long search for the final missing piece of the standard model (SM). The measurements so far confirm that the new boson is consistent with the Higgs boson predicted by the SM. However, there are decay channels that are yet to be confirmed experimentally; e.g., the decay to a pair of bottom quarks. In addition, precision measurements of the Higgs couplings to all SM particles need to be performed in order to make sure there is no deviation from the predictions of the SM. We present the first search at the LHC for anomalous couplings of the Higgs boson H to vector bosons V (= W or Z) using associated Higgs production with the Higgs boson decaying to a pair of bottom quarks. We use the data collected with the CMS detector from proton-proton collisions in 2012 at a center of mass energy of 8 TeV. Even though the exclusion limit derived from this production channel alone is at the 68% CL using the 2012 data, we demonstrate the power of this channel in constraining very small anomalous Higgs couplings to vector bosons. Combining the results from this channel with the previously published H \u2192 VV channels, we put more stringent constraints on anomalous Higgs couplings to vector bosons. The second part of the thesis deals with the so called hierarchy problem, caused by quadratically divergent radiative corrections to the Higgs mass at higher energy scales. The corrections are many orders of magnitude larger than the observed mass and it requires unnatural fine-tuning to cancel out these contributions. There are different models that attempt to address this problem, one of which is the Composite Higgs Model that predicts a very heavy fermionic partner of the top quark with an electric charge of 5/3 (X5/3). X5/3 decays into a W boson and a top quark, which then decays into a bottom quark and a W boson. We analyze the events in which one of the W bosons in the X5/3 pair production final state decays into leptons and the remaining three W\u2019s decay hadronically. We present here the first study of X5/3 at the LHC in the lepton + jets decay channel using events from the data collected in 2015 with the CMS detector at a center of mass energy of 13 TeV in Run 2 of the LHC. The results are also combined with the more sensitive same-sign dilepton channel."], "keyword": ["Anomalous Higgs Couplings", "Top Quark Partners", "CMS", "Radiation Damage", "CMS Tracker"], "primary_title": "Search for Heavy Top Quark Partners with Charge 5/3 and Anomalous Higgs (\u2192 bb) Couplings to Vector Bosons", "uri": "https://repository.library.brown.edu/studio/item/bdr:730649/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:730649/"}, {"pid": "bdr:730643", "object_type": "pdf", "abstract": ["Nanowire (NW) research has emerged as a quickly growing field, mainly due to its unique electronic and optical properties. This thesis focused on utilizing Si NW arrays for solar cells and SiGe hetero-NWs for tunneling field-effect transistors (TFETs) and negative transconductance (NTC) devices. A SiGe CMOS-compatible bipolar-enhanced TFET (BET-FET) device aiming to improve the TFETs ON current was also studied. We characterized the performance of solar cells made from axial p-i- n Si NW arrays with diameter < 200 nm that were grown by vapor-liquid- solid method. Both sparse arrays and dense arrays by nanoimprint lithography were studied. The improved light absorption in NW array solar cells was verified by reflectance measurements. The improvements on photovoltaic performance for passivated samples were explained by reduced surface recombination. Higher EQE and IQE in the visible spectral range were obtained for samples with higher NW density of different NW lengths, due to improved absorption. Axial p-Ge/i- Si/n-Si hetero-NW TFETs were also fabricated and characterized. The hetero-NWs were realized using VLS method with better abruptness of axial modulation of doping and composition. The tri-gated devices showed good performance with ON current of up to 2 \u03bcA/\u03bcm and best sub threshold swing (SS) of 55 mV/decade over 3 orders of drain current. NTC behavior with highest current peak-to-valley ratio of 47.9 at reverse bias voltage of -0.2 V was observed for the same device. We explain it by the gate-induced depletion in the p-Ge section that eventually reduces the maximum electric field, which was confirmed by a 3D Sentaurus TCAD simulation. Finally, stemming from improvement of ON current in the Si/Ge hetero-NW platform, we proposed and simulated a BET-FET device with a lateral layout that is fully FDSOI compatible. The simulated device combined the sharp-switching character of the TFET and high current gain of the heterojunction bipolar transistor, and enjoyed a high ON current of 260 \u03bcA/\u03bcm and a SS well below 60 mV/decade over seven decades."], "keyword": ["Nanowire,Solar cell,Tunneling,Negative Transconductance"], "primary_title": "Nanowire array solar cells and tunneling transistors with negative transconductance and high current drive", "uri": "https://repository.library.brown.edu/studio/item/bdr:730643/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:730643/"}, {"pid": "bdr:792638", "object_type": "pdf", "abstract": ["Amorphous oxide semiconductors (AOSs) have been intensively studied during the last 15 years due to their superior properties. The major application of AOS thin film transistors (TFTs) is displays. Compared to the previous generation TFT material\u2014amorphous silicon (a-Si)\u2014AOSs have higher mobility, and can be easily deposited by various deposition techniques at room temperature on arbitrary substrates. This thesis focuses on the characteristics and stability of a specific AOS, amorphous indium zinc oxide (a-IZO), as an electronic material for TFTs. We have fabricated a-IZO TFTs with a top-gate structure by using the in-situ gate dielectric formation technique: some metals\u2014such as Al and Hf\u2014can react with IZO to form an oxide insulator layer in the absence of kinetic constraints. The in-situ dielectric formation can provide a high-quality insulator/IZO interface with a low interface trap density, leading to excellent TFT performance. The subthreshold slope in our best IZO TFTs reaches a value of 62 mV/decade, close to the room temperature theoretical limit, and our devices also show on/off current ratios above 10^7 and a high extracted field effect mobility around 100 cm2/V\u00b7s. These are state-of-the-art results in AOS TFTs. Another focus in our work is the stability of IZO TFTs, where oxygen vacancy generation and migration are used to explain the observed experimental threshold voltage shifts in a-IZO TFTs as a function of aging and applied gate bias. As a possible future research direction, the high electron mobility and controllable high electron density make a-IZO a promising candidate for high-speed, high-power radio frequency transistors. We propose a vertical transistor structure with buried multi-gate fingers. Unlike in the previously studied single-crystal nanowire or permeable base vertical transistors, the properties of a-IZO make it possible to regrow the vertical semiconductor channels without any high temperature epitaxy, lowering fabrication complexity and cost while making the vertical IZO device compatible with arbitrary substrates. Preliminary fabrication process and characterization results of the vertical-current-flow a-IZO TFT are shown and discussed."], "keyword": ["Indium zinc oxide", "Amorphous semiconductors", "Transistors"], "primary_title": "Characteristics and Stability of High Performance Indium Zinc Oxide Thin Film Transistors", "uri": "https://repository.library.brown.edu/studio/item/bdr:792638/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:792638/"}, {"pid": "bdr:792641", "object_type": "pdf", "abstract": ["Spin-orbit coupling (SOC) refers to the interaction between the orbital angular momentum and electron spin, which is typically a small perturbation in relative light elements. However, such interaction is proportional to the fourth order of the atomic number and could be quite significant for heavy elements. Exotic physics arising from significant SOC include the emergent phases in Mott insulators with strong SOC and the exploded works on topological insulators (TI). For the first research thread, the combined effects of strong electronic correlations with SOC can lead to a plethora of emergent novel quantum states. The second research thread which also involves strong SOC and correlated electrons lies at the intersection of topological insulator and Kondo insulator. In this thesis, we first present an extensive nuclear magnetic resonance (NMR) study of 23Na in Ba2NaOsO6, a typical Mott insulator with SOC. We measured 23Na NMR spectra as a function of temperature in different magnetic fields. The NMR measurements reveals a paramagnetic at high temperatures, a broken local point symmetry (BLPS) phase at intermediate temperatures and a canted ferromagnetic phase at low temperatures. Most importantly, we determine the field-temperature phase diagram of Ba2NaOsO6 which shows that the intermediate BLPS phase extends to wider range in high fields. Furthermore, by adopting numerical calculation, we confirm that the breaking of local point symmetry is not due to trivial intrinsic structure instability but is due to multipolar interaction. Next, angle dependence of NMR spectra show that the canted ferromagnetic order is suppressed along certain direction at low temperatures. Secondly, we performed NMR measurements of spin-lattice relaxation (T1) on 11B of Kondo insulator SmB6 at ultra-low temperatures in various magnetic fields. We observed constant low-energy density-of-states (DOS) which corresponds to gapless excitation."], "keyword": ["Nuclear magnetic resonance", "Spin-orbit coupling", "Transparent oxide films", "Mott Insulator", "Kondo Insulator"], "primary_title": "NMR Study of Materials with Significant Spin-Orbit Coupling and Transparent Oxide Films", "uri": "https://repository.library.brown.edu/studio/item/bdr:792641/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:792641/"}, {"pid": "bdr:78fwcpgv", "object_type": "pdf", "abstract": ["Wavenumber selection in pattern-forming systems remains a long-standing puzzle in physics. Pattern-forming systems are characterized by the growth of a band of periodic solutions from a uniform state. This raises the important question of wavenumber selection: Which state is realized for a given set of conditions? We explore the role of noise as a mechanism for wavenumber selection. In the first part of this work, we conduct an extensive numerical study of a model known as the noisy stabilized Kuramoto-Sivashinsky equation. We use a fast spectral method of integration, which enables us to investigate long-time behavior for large system sizes that could not be investigated by earlier work. We compute the stationary probability distributions of the system and find that a state with a unique wavenumber has the highest probability of occurring at very long times. We also find that this state is independent of the strength of the noise and initial conditions, thus making a convincing case for the role of noise as a means of state selection. The stationary probability distributions enable us to determine the selected wavenumber, but contain no information about why this wavenumber dominates over all others. In the second part of this work, we address this issue by analyzing the noise-averaged time evolution of each unstable mode from the spatially homogeneous state, with and without noise. We find drastic differences between the nonlinear dynamics in the two cases. In particular, we find that noise opposes the growth of Eckhaus modes close to the critical wavenumber of the model and boosts the growth of Eckhaus modes with wave numbers smaller than the critical wavenumber. We then hypothesize that the main factor responsible for this behavior is the excitation of long wavelength modes by the noise. This hypothesis is confirmed by extensive numerical simulations. We conclude by discussing directions for future work."], "keyword": ["Physics", "Statistical physics"], "primary_title": "Wavenumber Selection in the Noisy Stabilized Kuramoto-Sivashinsky Equation: Stationary Probabilities and Dynamics", "uri": "https://repository.library.brown.edu/studio/item/bdr:78fwcpgv/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:78fwcpgv/"}, {"pid": "bdr:792597", "object_type": "pdf", "abstract": ["This work sets forth the methods and first results of our study of \u223c 1E14 M\u2299 mass substructures in very low redshift (z < 0.12) galaxy clusters. We have begun by performing a detailed 2-dimensional weak gravitational lensing analysis of five nearby clusters using deep ugriz imaging from the Dark Energy Camera (DECam) at the Cerro Tololo Inter-American Observatory. In our pilot study on Abell 3128, we designed a pipeline to remove instrumental artifacts from DECam images and stack multiple dithered observations without inducing a spurious ellipticity signal. We developed a new technique to characterize the spatial variation of the point spread function and so extract the intrinsic galaxy ellipticities. In both A3128 and ensuing studies, we detected multiple high-significance substructures within the clusters. By fitting photometric redshifts to sources in the cluster observations, we selected a sample of back- ground galaxies for weak lensing analysis free from foreground contaminants. Photometric redshifts were also used to select high-redshift galaxy subsamples with which we successfully isolated the signal from several interloping background clusters. We estimate the mass of clusters in this work by fitting the tangential ellipticity of background galaxies with the weak lensing shear profile of an NFW halo, and also perform NFW fits to substructures detected in the weak lensing maps. Upper mass limits for several high-redshift clusters are also reported. This work yields some of the highest resolution mass maps of low-z clusters to date, and is the first step in a larger effort to characterize the redshift evolution of substructures in clusters. We conclude with future directions for our research, including continuing our study of substructure in more low-redshift clusters and build a substructure mass function."], "keyword": ["Physics, Astrophysics, Galaxy Clusters, Cosmology"], "primary_title": "Dark Matter Substructure in Very Low Redshift Galaxy Clusters", "uri": "https://repository.library.brown.edu/studio/item/bdr:792597/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:792597/"}, {"pid": "bdr:792673", "object_type": "pdf", "abstract": ["The Sachdev-Ye-Kitaev (SYK) model is a quantum mechanical many body system with random all-to-all interactions on fermionic N sites (N>>1). This model is shown to saturate the known maximal chaos bound of many body system and then based on this observation it is conjectured to be dual to a quantum black hole in the sense of the AdS/CFT correspondence. In this dissertation, we show that the large N physics of the SYK model is systematically described by a single bi-local field. In particular, we emphasize the appearance of the emergent conformal reparametrization symmetry at the critical IR fixed point and the corresponding divergent contribution of the symmetry modes in the propagator of the bi-local field. We discuss non-linear-level derivation of the zero modes effective action, which is given by the Schwarzian derivative for finite reparametrization symmetry. Besides the symmetry modes, which correspond to the dilaton-gravity sector in the dual AdS theory, the SYK model also predicts an infinite tower of matter fields in AdS_2. We demonstrate that this infinite spectrum can be nicely packaged into a single field in 3-dimensional space-time. Finally, we consider the question of identifying the dual space-time of the SYK model. Focusing on the signature of emergent space-time of the (Euclidean) model, we explain the need for non-local (Radon-type) transformations on external legs of n-point Green's functions. This results in a dual theory with Euclidean AdS signature with additional leg-factors. We speculate that these factors incorporate the coupling of additional bulk states similar to the discrete states of 2D string theory."], "keyword": ["Physics"], "primary_title": "Investigations on the SYK Model and its Dual Gravity Theory", "uri": "https://repository.library.brown.edu/studio/item/bdr:792673/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:792673/"}, {"pid": "bdr:792604", "object_type": "pdf", "abstract": ["Statistical descriptions are well-suited for chaotic systems and turbulent flows. A common strategy for studying the statistics of such systems is Direct Numerical Simulation (DNS). However accumulating statistics via DNS can be inefficient because convergence to a statistically steady-state is slow, especially in systems with rare but large deviations as are often found in chaotic systems and turbulent flows. Another drawback of DNS is that it is difficult to extract the physics from the computed numbers. In this thesis I present two alternative strategies to directly solve for the statistics. In the first part, a Fokker-Planck description is used to study the equal-time statistics of the stochastically-forced Lorenz attractor. In particular, the steady-state probability distribution of the attractor is solved for directly by computing the zero mode of a Fokker-Planck operator. I also investigate a perturbative expansion in the equal-time cumulants of the system, tested on the Lorenz attractor and on two idealized barotropic models. Since low-order statistics tend to be spatially smoother than the corresponding dynamical fields, this method can capture the macroscopic features of turbulent flows using fewer degrees of freedom. An added benefit of such a cumulant expansion scheme is that the small-scale modes are integrated out, leaving only large-scale modes containing information about the coherent structures of interest. These modes are associated with the low-order statistics of the system and might be described by a fixed point or slow manifold, allowing for quicker convergence to a statistically steady state. Since this perturbative expansion suffers from the \"curse of dimensionality\", I detail my efforts to resolve this issue via a dimensional reduction scheme that uses a type of unsupervised machine learning technique known as Proper Orthogonal Decomposition. This involves rotating into a new coordinate system spanned by the eigenvectors of the vorticity second cumulants of the system and retaining only the most energetic modes. A substantial basis reduction with order of magnitude computational gains is demonstrated, providing an accurate alternative to directly accessing the low-order statistics of turbulent flows."], "keyword": ["Computational fluid dynamics", "Atmospheric turbulence", "Chaotic behavior in systems", "Nonequilibrium statistical mechanics", "Fokker-Planck equation"], "primary_title": "Direct Statistical Simulation of Chaos and Turbulence", "uri": "https://repository.library.brown.edu/studio/item/bdr:792604/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:792604/"}, {"pid": "bdr:792623", "object_type": "pdf", "abstract": ["Anodized aluminum oxide (AAO) is an interesting material, occupying a unique space -- already used incredibly widely in the world, yet also commonly used for nanoscience research. However, the wealth of scientific research using it has yet to make it to the real world. Similarly, many nanoscience fields that have produced incredible results on a small scale haven\u2019t found practical use. In this dissertation, we investigate scalable applications of AAO in two fields, and then look at their potential intersection. First, we look at its use as a scalable structural coloration platform, employing a Fabry-Perot optical cavity structure that has seen a research resurgence in recent years. Structural coloration presents the potential for a more tunable, durable, and environmentally friendly coloration system than traditional methods, though it can also be used in concert with them. We present tools to analyze the full capabilities of this structure for its future use in structural coloration as a \u201ccolor by design\u201d platform and verify them with experimental probes of fabricated samples. Further, we look to mitigate assumed limitations of this system, such as sensitivity to fabrication parameters and angular dependence. Then, we present another achievement of AAO as a scalable platform: the dielectric of a Ag-AAO-Al resistive switching (RS) system used for optical rectification (OR). RS is a well researched field, but almost entirely in the electronic context, being the first realization of the memristor. OR is a promising field with potential for energy harvesting and ultrafast light sensing that has seen a resurgence in recent years, but all published methods are either highly unrepeatable or rely on advanced nanofabrication techniques. We demonstrate an intersection of the RS field, used to create a unique OR platform that offers scalability and tunability beyond any that have been reported. We investigate the electronic effects, temperature dependence, and then present possible OR effects. Lastly, we present some potential combinations of these two projects."], "keyword": ["Optics", "Nanotechnology", "Nanoscience", "nanofabrication", "filamentation", "resistive switching", "optical rectification", "structural coloration", "physical coloration", "Fabry-Perot interferometers", "fabry perot", "optical cavity", "optical resonator", "Thin films--Optical properties", "Aluminum", "Aluminum alloys", "anodized aluminum", "aao", "Aluminum--Anodic oxidation", "anodic alumina", "anodization", "Aluminum oxide", "coloration"], "primary_title": "Anodic alumina as a scalable platform for structural coloration and optical rectification", "uri": "https://repository.library.brown.edu/studio/item/bdr:792623/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:792623/"}, {"pid": "bdr:674207", "object_type": "pdf", "abstract": ["The onset of monami, the synchronous waving of seagrass beds driven by a steady flow is modelled as a linear instability of the flow. Unlike previous works, our model considers the drag exerted by the grass in establishing the steady flow profile, and in damping out perturbations to it. We find two distinct modes of instability, which we label as mode 1 and mode 2. Mode 1 is closely related to Kelvin-Helmholtz instability modified by vegetation drag, whereas mode 2 is unrelated to Kelvin-Helmholtz instability and arises from an interaction between the flow in the vegetated and unvegetated layers. The vegetation damping, according to our model, leads to a finite threshold flow for both of these modes. Experimental observations for the onset and frequency of waving compare well with the model predictions for instability onset criteria and the imaginary part of the complex growth rate respectively, but experiments lie in a parameter regime where the two modes can not be distinguished. Full scale numerical simulation of the governing equation has been performed as well. The result of this simulation agrees well with the prediction of linear stability analysis. The full scale numerical simulation of governing equation shows that initially the perturbation to the flow grows with rate predicted by linear stability analysis and then reaches a saturation. At the saturation the flow can be described by a background flow plus a steadily propagating wave whose mode shape, wavelength and frequency are the same as the one predicted by the linear stability analysis."], "keyword": ["Monami", "Flow instability", "Linear Stability Analysis"], "primary_title": "Hydrodynamic instability leading to Monami", "uri": "https://repository.library.brown.edu/studio/item/bdr:674207/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:674207/"}, {"pid": "bdr:674293", "object_type": "pdf", "abstract": ["Measurements of the Cosmic Microwave Background (CMB) made over the last 25 years have ushered in the era of precision cosmology. The E and B EXperiment (EBEX) was a long-duration balloon-borne (LDB) instrument designed to measure the polarization of the CMB. EBEX was designed to measure the B-mode polarization signal from inflationary gravitational waves, detect the gravitational lensing of the polarization of the CMB, and to characterize polarized Galactic foreground emission. Polarimetry is achieved with a rotating half-wave plate paired with a wire grid polarizer. The EBEX payload flew on scientific Antarctic LDB flight in 2012-2013. The design, construction, and deployment of the EBEX instrumentation, including pointing sensors, mechanical gondola design, and thermal management are described. The LDB flight performance of the subsystems are examined. Additionally, the analysis of EBEX LDB datasets from pointing sensors, half-wave plate synchronous time streams, and bolometer internal calibrator events are discussed as well as the progress towards the publication of final data products. Additionally, the development and characterization of a polarization sensitive mirror for use in reflective polarizers and variable-delay polarization modulators (VPMs) is discussed."], "keyword": ["polarization", "CMB", "EBEX", "b-mode polarization", "inflation", "balloon-borne", "Cosmology", "Microwaves"], "primary_title": "The Development and Deployment of Instrumentation to Measure the Polarized Microwave Sky", "uri": "https://repository.library.brown.edu/studio/item/bdr:674293/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:674293/"}, {"pid": "bdr:674323", "object_type": "pdf", "abstract": ["Picosecond ultrasonics is a non-invasive technique for thin-film metrology. The technique uses the pump-and-probe method to optically generate and detect acoustic waves. This thesis presents the results of two variations of the picosecond ultrasonic technique. The first variation is picosecond ultrasonics using an optical mask. The mask is a line-grating made from a transparent material. When the mask is placed very close to the sample surface with the grating facing the sample, the profile of the pump beam and the probe beam will be modified to give periodically alternating stripes of bright and dark regions. This makes it possible to generate and detect surface acoustic waves. In this work, we have successfully used this technique to generate and detect different modes of surface acoustic waves. The second variation is planar opto-acoustic microscopy (POAM). POAM is a metrology technique that gives information about the surface profile of a sample. The sound pulse is generated optically, and the transducer is coupled to the sample via a layer of water. The detection of the echoes returning from the sample is enhanced by using a resonant Fabry-P\u00e9rot cavity. In this work, we have conducted a systematic investigation to the metrology capability of POAM by taking measurements from series of samples with one-dimensionally periodic nanostructures that consist of channels with near-rectangular shape."], "keyword": ["picosecond ultrasonics", "Acoustic microscopy"], "primary_title": "Metrology of Nanostructures Using Picosecond Ultrasonics", "uri": "https://repository.library.brown.edu/studio/item/bdr:674323/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:674323/"}, {"pid": "bdr:674258", "object_type": "pdf", "abstract": ["A new non-perturbative, gauge-invariant, exact, finite model of quantum chromody- namics, with a particular choice of renormalization is applied to high energy elastic pp- scattering. Gauge invariance is insured by explicit cancellations of all gauge dependent gluon propagators. The result is the entire infinite sum of all gluon exchanges between two quarks/(anti)quarks. With a particular choice for renormalization, this model is tested against hadron elastic scattering at ISR energies with favorable results. The differential cross- section deduced from this model displays a diffraction dip that compares very well with those of experiments. Calculation of infinite loop chains under our renormalization scheme fits experimental data rather favorably. Extension to total scattering cross-section is expected."], "keyword": ["high energy theory", "high energy physics", "particle physics", "non-perturbative", "gauge-invariant,quantum field theory", "schwinger action", "Quantum chromodynamics", "Particles (Nuclear physics)", "Quarks", "Gluons", "Feynman diagrams", "Schwinger action principle"], "primary_title": "Analytic Quantum Chromodynamics: An Exact, Finite, Non-Perturbative, Gauge-Invariant, Realistic Model of QCD, with A Particular Choice of Renormalization with Applications to High Energy Elastic Proton-Proton Scattering.", "uri": "https://repository.library.brown.edu/studio/item/bdr:674258/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:674258/"}, {"pid": "bdr:674186", "object_type": "pdf", "abstract": ["Abstract of Holographic Techniques for Strongly Coupled Scattering, by Timothy Gillooly Raben, Ph.D., Brown University, May 2016. Quarks and gluons have historically been difficult to perform calculations with: confinement creates rich phase spaces of scattering results, simple processes necessitate the calculation of huge numbers of Feynman diagrams, and experimental collisions require an understanding of strongly coupled dynamics. The AdS/CFT correspondence has fueled new lines of investigation into the study of quarks and gluons. This strong/weak duality is a step in the direction of realizing a long sought QCD-string. Holography has given us a powerful tool set to study the strongly coupled limit of gauge theories and compare these results and predictions with that of known physics (QCD, parton-models, and others.) We aim to better describe scattering physics by using the AdS/CFT to look at strongly coupled and confined regions of large-N gauge theory. By investigating high energy limits and specific areas of phase space, one can simply scattering amplitudes and make predictions and analysis sharper. A softwall model of AdS confinement is described and compared to other softly confining and sharply confining models. High energy Pomeron exchange is described in the softwall model and is used to fit deep inelastic scattering data. e- p+ data is examined from the combined H1 and ZEUS 2010 dataset at HERA. Structure functions are fit with a \u03c72dof~1.104. In the conformal limit, Reggeon exchange is further examined via a calculation of unprotected operator anomalous dimension via an analytic \u0394(J) curve . Using integrability techniques the Pomeron and Odderon intercepts, J0, are calculated to seventh order in 1/\u03bb1/2. The leading Pomeron exchange for 5 and 6 point amplitudes can be related to inclusive scattering processes via the optical theorem. By taking discontinuities of AdS scattering amplitudes, an holographic motivated model is used to fit 7-TeV LHC data at large pT."], "keyword": ["HET", "AdS/CFT", "Strongly Coupled", "Particle Physics", "Regge theory", "Particles (Nuclear physics)"], "primary_title": "Holographic Techniques for Strongly Coupled Scattering", "uri": "https://repository.library.brown.edu/studio/item/bdr:674186/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:674186/"}, {"pid": "bdr:674209", "object_type": "pdf", "abstract": ["We propose a new technique for the calibration of nuclear recoils in large noble element dual-phase time projection chambers (TPCs) used to search for WIMP dark matter in the local galactic halo. This technique provides a measurement of the low-energy nuclear recoil response of the target media using the measured scattering angle between multiple neutron interactions within the detector volume. Several strategies for improving this calibration technique are discussed, including the creation of a new type of quasi-monoenergetic 272 keV neutron source. We report results from a time-of-flight-based measurement of the neutron energy spectrum produced by an Adelphi Technology, Inc. DD108 neutron generator, confirming its suitability for the proposed calibration. The Large Underground Xenon (LUX) experiment is a dual-phase liquid xenon TPC operating at the Sanford Underground Research Facility in Lead, South Dakota. Our proposed calibration technique for nuclear recoils in liquid xenon was performed in situ in the LUX detector using a collimated beam of mono-energetic 2.45 MeV neutrons produced by the DD108 fusion source. The nuclear recoil energy from the first neutron scatter in the TPC was reconstructed using the measured scattering angle defined by two-site neutron events within the active xenon volume. We measured the absolute charge (Qy) and light (Ly) yields at an average electric field of 180 V/cm for nuclear recoil energies spanning 0.7 to 74 keV and 1.1 to 74 keV, respectively. This calibration of the nuclear recoil signal yields will permit the further refinement of liquid xenon nuclear recoil signal models and clearly demonstrates measurable ionization and scintillation signals in this medium at recoil energies down to O(1 keV). The low-energy reach and reduced systematics of this calibration have particular significance for the low-mass WIMP sensitivity of several leading dark matter experiments."], "keyword": ["LUX", "liquid xenon", "nuclear recoil", "light yield", "charge yield", "neutron generator", "dark matter", "WIMP", "Dark matter (Astronomy)"], "primary_title": "An Absolute Calibration of Sub-1 keV Nuclear Recoils in Liquid Xenon Using D-D Neutron Scattering Kinematics in the LUX Detector", "uri": "https://repository.library.brown.edu/studio/item/bdr:674209/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:674209/"}, {"pid": "bdr:733397", "object_type": "pdf", "abstract": ["Theoretical studies have shown that, contrary to the traditional belief that noise is unwanted and an experimental nuisance, under certain circumstances noise can play a constructive role and cause a resonance like behavior. Based on the theory of stochastic resonance (SR) and resonant activation (RA), the response of a bistable nonlinear system can increase with the addition of white noise. What makes a system bistable is the presence of a barrier between two stable sites. The barrier is typically entholpic in nature, but here we ask whether a single DNA molecule can exhibit SR or RA over entropic barriers? The focus of this thesis is to create the experimental capabilities needed to test this hypothesis. We generate a controlled weak periodic force on single DNA molecules with applied pressure and a Gaussian noise with adjustable amplitude using an applied voltage. We are able to observe and analyze the motion of single molecules by taking advantage of both fluorescent microscopy and to manipulate them using micro- and nanofluidic technology in order to test the theory of SR and RA. First, we show that a single DNA molecule can be trapped entropically in nano-structured pits whose known dimensions determine the trapping strength. Then, we measure the maximum force that can be applied before most DNA molecules leave their traps, in order to find the threshold of our bistable system. We plan to apply noise in addition to the applied periodic force and measure the optimum intensity of noise for each SR and RA individually. In this thesis, I describe the processes and techniques that will be used to perform these tests."], "keyword": ["DNA", "Nanofluids", "Entropy", "Stochastic processes"], "primary_title": "Toward a Stochastic Resonator with an Entropic Barrier", "uri": "https://repository.library.brown.edu/studio/item/bdr:733397/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:733397/"}, {"pid": "bdr:733451", "object_type": "pdf", "abstract": ["The Primordial Inflation Explorer (PIXIE) is a proposed NASA-led mission designed to measure the polarization and intensity of the cosmic microwave background (CMB). PIXIE will answer key questions about the origin and evolution of the universe, from the period of inflation immediately after the Big Bang to the present day. While most other instruments designed for CMB measurements are imagers, PIXIE is a Fourier transform spectrometer (FTS). Its highly-symmetric design enables excellent control of systematic effects and its sensitivity and bandwidth allow us to distinguish cosmological signals from signals originating within our own Galaxy. This thesis introduces the PIXIE experiment and details two specific areas of PIXIE development supported by my dissertation work: modeling and mitigation of instrumental systematic effects and the development of PIXIE\u2019s multimode bolometers. PIXIE\u2019s raw instrumental systematic error terms are small, generally from hundreds of nK to a few \u03bcK. But these terms will still overwhelm our target cosmological signals; for example the predicted B-mode polarization signal of the CMB, whose detection would provide strong evidence for inflation, is expected to be < 100 nK. In this work, I analytically solve for the most important systematic error signals caused by non-idealities within the PIXIE FTS. I then show how they are mitigated to acceptable levels with simple corrective actions. PIXIE achieves background-limited sensitivity with just 4 detectors. They require a vastly different optimization from bolometers developed for focal-plane imagers. They must handle a large, near-constant optical bias (~ 120 pW) but still operate with sensitivity near the thermodynamic limit. They must have a large and mechanically robust absorbing area (30 times larger than the spider web bolometers that flew on Planck) that is sensitive to all optical frequencies of interest but is relatively insensitive to cosmic ray hits. I detail our efforts to overcome these challenges and discuss the cryogenic and environmental performance of PIXIE\u2019s prototype bolometers."], "keyword": ["Physics", "Astrophysics", "Cosmic background radiation", "Fourier transform spectroscopy", "Cosmology"], "primary_title": "Observing the Universe with a Polarizing Fourier Transform Spectrometer called PIXIE", "uri": "https://repository.library.brown.edu/studio/item/bdr:733451/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:733451/"}, {"pid": "bdr:733436", "object_type": "pdf", "abstract": ["The Standard Model (SM) of particle physics has proven to be a very successful theory in explaining many experimental observations involving electroweak and strong interactions. Nevertheless, the SM is an incomplete theory as it does not describe gravity. The inclusion of gravity requires a theory that is valid up to the Planck scale. If no new physics resides above the SM, running the SM up to the Planck scale leads to divergence terms in the Higgs mass calculation. With the observation of the Higgs boson at 125 GeV, this can only be achieved by a large amount of fine-tuning to the SM parameters, known as the Hierarchy problem. Thus, many theories Beyond the Standard Model (BSM) were proposed. This thesis presents searches for new elementary particles through their decays to tau leptons using the data collected by the Compact Muon Solenoid (CMS). First, a search for a massive Higgs boson is presented in the context of the Minimal Supersymmetry Standard Model (MSSM). The MSSM tackles the Hierarchy problem by predicting super partners to the SM particles. These new particles introduce extra correction terms in the Higgs mass calculation and automatically cancel out the diverging terms which need fine-tuning. Here, the decay channel of H \u2192 hh \u2192 \ud835\udf0f\ud835\udf0fbb is studied with a tau, anti-tau lepton pair and a b, anti-b quark pair as the final state. The second part of the thesis focuses on the search for a new neutral gauge boson, denoted as Z\u2019. Many BSM theories, ranging from Grand Unification Theories, which hope to unite the strong and electroweak interactions, to the Little Higgs Model, all predict the presence of extra gauge bosons. In this thesis, we present the search for the Z\u2019 boson through its decay into a pair of tau, anti-tau leptons in the context of the Sequential Standard Model."], "keyword": ["New Physics", "Beyond the Standard Model", "Tau Leptons", "LHC", "CMS", "Particle Physics - Experiment", "Detectors and Experimental Techniques"], "primary_title": "Search for New Physics with Tau Lepton Final States", "uri": "https://repository.library.brown.edu/studio/item/bdr:733436/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:733436/"}, {"pid": "bdr:733372", "object_type": "pdf", "abstract": ["Experiments have established the existence of a Bose Insulator phase close to the two dimensional Superconductor-Insulator transition. Here, current is carried by localized Cooper Pairs, which are usually responsible for superconductivity. Several systems show a unified picture of this phase, where Cooper Pairs themselves behave as individual bosons. However, the limits of the region of phase space that it occupies are poorly understood, and there has been limited work examining whether or not pairs survive in the limit of strong disorder. To address this question, we conducted experiments with films grown on nanostructured templates made of Anodic Aluminum Oxide (AAO). We are able to study the influence of both material and topographical properties of thin films on localization in both the bosonic and fermionic regimes. I will detail two studies examining the breadth of these regimes. In the first, finite size effects on systems of weakly coupled superconducting islands are studied by growing films on AAO substrates with small hole spacings. Some experiments show evidence of a substantial shrinking of the bose insulator phase, while others are more ambiguous. We speculate that the degree of inhomogeneity present in the substrates leads to more robust pairing in some films, enhancing the bose insulator phase relative to others. In the second approach, I study scaling of the high temperature resistance, where Cooper pairs are not expected. Since scaling is observed across many fermionic systems, deviations from it can be used as a probe to detect Cooper pairs. Our results show bosons present in the strongly localized regime, where transport is fermionic. I also detail numerical studies of the influence of inhomogeneity on scaling. The simulations show that uniform disorder does not substantially impact the results of scaling, but correlated inhomogeneities can have a drastic impact on the experimental results."], "keyword": ["Physics"], "primary_title": "Studies of the Bose Insulator to Fermi Insulator Crossover Near the Two-Dimensional Superconductor-Insulator Transition", "uri": "https://repository.library.brown.edu/studio/item/bdr:733372/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:733372/"}, {"pid": "bdr:733392", "object_type": "pdf", "abstract": ["Abstract of \u201cComputational and Experimental Methods for Resolving Solid-State Emitters: Crystal-Field Calculations and Multidimensional Spectroscopy\u201d By Jonathan A. Kurvits, Ph.D., Brown University, May 2017 The identification of new emitters for quantum optics and nanophotonics has been a challenging process. This is due both to a historical bias in optical materials research for laser systems and the prevalence of ab initio methods that have displaced earlier phenomenological approaches for electronic structure calculations. Thus, we have a wealth of knowledge about laser systems and can accurately model individual defects, but are lacking systematic methods for identifying and characterizing suitable emitter systems. In this thesis, we begin to bridge this knowledge gap by developing a computational package, based on group theory, which allows for the calculation of energy levels and magnetic dipole transition for emitters embedded in an arbitrary crystal host. Using this framework, we calculated transition rates for 3d, 4d, and 5d transition-metal free-ions, as well as 3d transition-metals embedded in magnesium oxide and gallium arsenide. Furthermore, using optical modeling software, we designed and optimized a high-throughput Fourier-based hyperspectral imaging technique which is ideally suited to characterizing multipolar transition in crystal hosts. Finally, using this experimental platform, we measured the magnetic dipole contribution to emission from chromium-doped magnesium oxide and europium-doped yttrium oxide."], "keyword": ["Optics", "Photonics"], "primary_title": "Computational and Experimental Methods for Resolving Solid-State Emitters: Crystal-Field Calculations and Multidimensional Spectroscopy", "uri": "https://repository.library.brown.edu/studio/item/bdr:733392/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:733392/"}, {"pid": "bdr:733383", "object_type": "pdf", "abstract": ["This dissertation presents two experimental studies of DNA polymers inside nanofluidic devices with well-defined topographic features. Those features include square pits and rectangular trenches etched into the surface of a nanofluidic slit to nanometer depths. The relatively deep pits and trenches are regions of greater configurational entropy for DNA; therefore, the constriction between those features and the slit presents entropic barriers to its motion. In the first study, we investigate, with experiments and computer simulations, the non-equilibrium dynamics of pressure-driven DNA crossing arrays of entropic barriers. With increasing driving pressure, the effective diffusivity of DNA rises and attains a peak value that is many times larger than its equilibrium self-diffusivity. This is an entropic manifestation of a non-equilibrium phenomenon known as \u201cgiant acceleration of diffusion\u201d. The phenomenon is sensitive to the effective energy landscape; thus, it offers a unique probe of the entropic barriers in a system driven away from equilibrium. Our results indeed hint at an evolving entropic landscape as the driving pressure is increased. In the second study, we present progress toward a technique for creating sequential restriction maps of single DNA molecules. Restriction mapping provides long range sequence information (kilobases and greater) that allows next-generation DNA sequencing (NGS) systems to resolve errors and reconstruct the sequence of a whole genome. Creating overlapping restriction maps of a single molecule, a capability that does not currently exist, would provide a factorial gain in the amount of information that is used to constrain NGS sequence reconstructions. Our idea is to perform sequential restriction digest reactions on a DNA molecule that is entropically held and elongated inside a linear trench. We trapped and extended fluorescently stained DNA inside an array of trenches and flowed restriction enzymes over them. Using optical fluorescence microscopy, we observed the DNA molecules cleaving into fragments. We measured the lengths of these fragments as they maintained their positions relative to one another inside the trench. However, we could not determine if the DNA fragmentation resulted from a restriction digest, or some other non-specific chemical reaction."], "keyword": ["DNA sequencing", "Physics", "Biophysics", "Diffusion", "Nonlinear systems", "DNA"], "primary_title": "Applications of Entropic DNA Trapping to Studies of Giant Acceleration of Diffusion and a Novel Restriction Mapping Method", "uri": "https://repository.library.brown.edu/studio/item/bdr:733383/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:733383/"}, {"pid": "bdr:792718", "object_type": "pdf", "abstract": ["This thesis is concerned with understanding features of holography in de-Sitter (dS) and Minkowski space. We give bulk-boundary mapping in dS at large N using integral transform. Operator Product Expansions for theory dual to dS is found to have essential singularity. On the Minkowski holography, we find physical interpretations of the representations of Bondi-Metzner-Sachs group. The bulk to boundary mapping for massive scalar fields is constructed, providing a de Sitter analog of the LSZ reduction formula. The set of boundary correlators thus obtained defines a potentially new class of conformal field theories based on principal series representations of the global conformal group. Conversely, we show bulk field operators in de Sitter may be reconstructed from boundary operators. While consistent at the level of the free field theory, the boundary CFT does not satisfy cluster decomposition. The resulting conformal field theory does not satisfy the basic axioms of Euclidean quantum field theory due to Osterwalder and Schrader, so is likely not well-defined once interactions are included. Global conformal invariance determines the form of two and three-point functions of quasi-primary operators in a conformal field theory, and generates nontrivial relations between terms in the operator product expansion. These ideas are generalized to the principal and complementary series representations, which play an important role in the conjectured dS/CFT correspondence. The conformal partial wave expansions are constructed for these representations which in turn determine the operator product expansion. This leads us to conclude that conformal field theories containing such representations have essential singularities, so cannot be realized as conventional field theories. We revisit unitary irreducible representations of the Bondi-Metzner-Sachs (BMS) group discovered by McCarthy. Representations are labelled by an infinite number of super-momenta in addition to four-momentum. Tensor products of these irreducible representations lead to particle-like states dressed by soft gravitational modes. Conservation of 4-momentum and supermomentum in the scattering of such states leads to a memory effect encoded in the outgoing soft modes. We note there exist irreducible representations corresponding to soft states with strictly vanishing four-momentum, which may nevertheless be produced by scattering of particle-like states. This fact has interesting implications for the S-matrix in gravitational theories."], "keyword": ["Physics", "Physics, Astrophysics, Galaxy Clusters, Cosmology", "Mathematical physics", "Quantum theory"], "primary_title": "Holography In De-Sitter And Minkowski Space", "uri": "https://repository.library.brown.edu/studio/item/bdr:792718/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:792718/"}, {"pid": "bdr:792710", "object_type": "pdf", "abstract": ["This thesis is concerned with computation of tree-level scattering amplitudes through scattering equations and derivation of soft theorems from them. Additionally, mapping of scattering amplitudes to conformal correlators on the celestial sphere is considered. We use the Cachazo-He-Yuan (CHY) scattering equations based formula which describes an n-point tree level scattering amplitude for gravitons in arbitrary dimension to prove the recently proposed sub-sub-leading soft-graviton theorem. Furthermore, we investigate the tree-level S-matrix in gauge theories and open superstring theory with several soft particles. We show that scattering amplitudes with two or three soft gluons of non-identical helicities behave universally in the limit, with non-trivial multi-soft factors. We also find new soft theorems for double soft limits of scalars and fermions in Super-Yang-Mills and double-soft-scalar limits in open superstring theory. Subsequently, we derive a CHY type formula for the leading gluon, bi-adjoint scalar, Yang-Mills-scalar and non-linear sigma model m-soft factors S_m in arbitrary dimension. The general formula is used to evaluate explicit examples for up to three soft legs analytically and up to four soft legs numerically via comparison with amplitude ratios under soft kinematics. A structural pattern for gluon m-soft factor is inferred and a simpler formula for its calculation is conjectured. We develop a polynomial reduction procedure that transforms any gauge fixed scattering equations based amplitude integrand for n scattering particles into a multivariate polynomial of what we call the standard form, which has finite size at any n. Subsequently, at tree and one-loop level, we employ the global residue theorem to derive a prescription that evaluates any scattering equations based amplitude by means of collecting simple residues at infinity only. The prescription is then applied explicitly to some tree and one-loop amplitude examples. Pasterski, Shao and Strominger have recently proposed that massless scattering amplitudes can be mapped to correlators on the celestial sphere at infinity via a Mellin transform. We apply this prescription to some n-point tree-level gluon amplitudes. The Mellin transforms of MHV amplitudes are given by generalized hypergeometric functions on the Grassmannian Gr(4,n), while generic non-MHV amplitudes are given by more complicated Gelfand A-hypergeometric functions."], "keyword": ["scattering amplitudes", "Quantum field theory"], "primary_title": "Scattering Equations, Soft Theorems, and Amplitudes on the Celestial Sphere", "uri": "https://repository.library.brown.edu/studio/item/bdr:792710/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:792710/"}, {"pid": "bdr:674408", "object_type": "pdf", "abstract": ["The Standard Model (SM) of Particle Physics has proven to be an incredible mathematical framework for describing the observed elementary particles that make up the Universe and the way in which they interact through the fundamental forces of nature. The discovery of the Higgs boson in 2012 by both the Compact Muon Solenoid (CMS) experiment, and A Toroidal LHC Apparatus (ATLAS), the two general-purpose detectors at the Large Hadron Collider (LHC), was the latest confirmation of the theory. Although the SM has been enormously successful in accurately predicting the results of many measurements, there are still ways in which it is incomplete. Many Beyond the Standard Model (BSM) theories have been developed which attempt to add to or modify the SM to remove these limitations. A common feature in many BSM theories is an extended Higgs sector with more than one Higgs field producing multiple Higgs bosons, some of which are electrically charged. This thesis presents a search for a charged Higgs boson at the LHC using data collected by the CMS detector. The search was performed with 19.7 $fb^{-1}$ of data collected by CMS during the 2012 LHC run period where protons were collided at a center of mass energy of $8~\\TeV$. The charged Higgs boson is produced in association with a top quark, and it itself is presumed to decay into a top-bottom quark pair nearly 100\\% of the time. Final states with a single muon or single electron are selected to detect the presence of charged Higgs bosons. Upper limits at the 95\\% confidence level on charged Higgs boson production cross section times the $H^\\pm\\rightarrow tb$ branching fraction are derived for a charged Higgs boson in the mass range 180 -- 600~\\GeV. Across the mass range studied, no excess over the SM was measured. Limits on the production cross section times branching fraction are set between 2.4 $pb$ for low mass charged Higgs, and 0.2 $pb$ for high mass charged Higgs."], "keyword": ["Charged Higgs", "CMS", "2HDM"], "primary_title": "A Search For Heavy Charged Higgs Bosons in the CMS Experiment", "uri": "https://repository.library.brown.edu/studio/item/bdr:674408/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:674408/"}, {"pid": "bdr:792915", "object_type": "pdf", "abstract": ["Magnetic tunnel junctions (MTJs) based on textured MgO insulating barrier are a class of quantum mechanical devices, increasingly used in technology industries as magnetic memory devices and magnetic sensors. However, improving MTJs' performance remains as a challenging task, particularly, the magnetic sensitivity has remained relatively steady for a while. New approaches are needed to make MTJs reach their potentials. One of the objectives of this work is to increase the field sensing capability of MTJs by reducing magnetic anisotropy of the constituent materials, and by implementing novel magnetic amplying components based on magnetic flux concentration. The second focus of this work is on the electrical junctions based on Mott insulators (MIs), another class of quantum materials. Due to the strong electron correlation effect in MIs, their heterojunctions have been proposed as ultrafast electrical rectifiers (e.g., diodes), with performance exceeding conventional semiconductor diodes. We have made a major attempt to fabricate high quality epitaxial MI heterojunctions, that have demonstrated the potential for future applications in electronics and in solar rectification devices. We have systematically studied many MgO-based MTJ multilayer structures. Each thin-film layer's contribution to the MTJ performance has been isolated and improved. MTJs with large tunneling magnetoresitance ratios (TMR) have been successfully fabricated using a magnetron sputtering system through the optimization of layer structures. The geometry of the MTJ sensor and magnetic annealing process have also been optimized for performance. We have introduced magnetic flux concentrator into our MTJs to significantly increase the magnetic sensing capability. The flux concentrator is a \"soft\" magnetic material with certain geometry working directly on the free layer of MTJ sensor as a magnetic field amplifier. Thin films of a special \"soft\" magnetic material (Co88Nb8Zr4) has been successfully fabricated utilizing our high vacuum magnetron sputtering technique, and characterized using magnetometry measurement. The \"soft\" magnetic concentrators have been added to the MTJ using lithography techinique. Furthermore, we have included additonal magnetic concentrators outside of the MTJ devices. With these approaches, we have increased the magnetic sensing capability of the MTJs significantly. Based on the same magnetron sputtering technique, we have successfully developed high-quality heterojunctions of epitaxial La1.9Sr0.1CuO4 (LSCO) thin films on a 0.5wt% Nb doped SrTiO3 (NSTO) single-crystal substrate. The heterojunction shows good rectification and expected temperature dependency. We have investigated the capacitance of the junctions over a broad frequency range and bias voltage range. The results were explained by considering the LSCO/NSTO junctions as a Schottky barrier with deep-level impurities. This doped Mott insulator system is quite different from traditional p-n heterojunctions and exhibited interesting interfacial properties. Our work has built a foundation for the further development of MI-based junctions as viable high frequency diodes and solar rectification energy conversion devices."], "keyword": ["spintronics"], "primary_title": "Quantum Magnetic and Electronic Heterojunctions for Ultrasensitive Magnetic Sensing and Novel Electrical Rectification", "uri": "https://repository.library.brown.edu/studio/item/bdr:792915/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:792915/"}, {"pid": "bdr:792908", "object_type": "pdf", "abstract": ["My research is motivated by an idea for a new method of sequencing individual biopolymers, including proteins and nucleic acids, that combines mass spectrometry with nanopores. The basic idea is to take advantage of a mass spectrometer\u2019s ability to identify monomers by their mass, paired with a nanopore\u2019s ability to force biopolymers into a linear configuration so that their monomers are delivered into the mass spectrometer in sequence. I address two major challenges for such a method to succeed. First, monomers must be ionized and transferred to the gas phase, necessary for mass analysis. Second, before monomers are transferred into vacuum, but after they are cleaved in solution from their parent polymer, they undergo random thermal motion which tends to randomize their sequential order. This order between neighboring monomers must be preserved between when they are cleaved and when they exit into this charged gas phase. If a strong electric field is applied to the liquid surface at the tip of a solution filled needle-like capillary, it will emit a spray of ions through a process known as electrospray. Ions emitted in this spray can leave the liquid surface in two main ways. They can leave inside large multiply charged liquid drops usually on the order of 100's nm in diameter, or they can leave the surface individually as partially solvated ions, called ion clusters. Since monomer ions trapped in drops would prevent us from obtaining sequence information, I conducted experiments on a version of electrospray known as ion evaporation in which ion clusters in solution are emitted directly from the electrospray capillary\u2019s liquid surface. I have helped to build and test a machine capable of investigating this mechanism of ion production from electrospray using capillaries with nanoscale tip openings. I present measurements of the voltages necessary to produce electrospray for capillaries in this nanoscale regime. Generally, the electrospray is composed of both ion clusters and charged droplets, and the latter must be suppressed for the success of this sequencing strategy. I compare the number of ion clusters that reach our mass spectrometer with the total number of ions leaving our nanocapillaries to explore the conditions under which ion cluster production is favored over drop formation. Finally, I present a simplified one dimensional model of the dynamics of Brownian particles in the electric fields at the tips of these electrospraying capillaries to estimate the conditions under which sequential information is preserved."], "keyword": ["Biophysics"], "primary_title": "Nanopore Mass Spectrometry", "uri": "https://repository.library.brown.edu/studio/item/bdr:792908/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:792908/"}, {"pid": "bdr:733541", "object_type": "pdf", "abstract": ["Despite significant progress in polarized light microscopy, measuring the three dimensional anisotropy is still an important challenge in the analysis of anisotropic materials. In birefringent samples, traditional imaging methods don't reveal the 3D orientation (inclination and azimuth) of the optic axis and the birefringence as an intrinsic material property. In samples that emit polarized fluorescence, it is generally not possible to discern the inclination angle of the aligned fluorophores. To overcome these problems, the Oldenbourg Lab has introduced a new imaging method, the Light Field LC-PolScope, which is a combination of light field imaging and LC-PolScope technology. In my thesis, I have used the Light Field LC-PolScope for acquiring images of simple and biological relevant test specimens for developing processing methods to reconstruct the birefringence of juvenile shells of the Atlantic hard clam and the polarized fluorescence of the labeled cell membrane of sea urchin eggs. I established acquisition and processing methods to generate 3-dimensional maps of position and orientation of these optically anisotropic structures, based on polarized light field images and, for establishing their accuracy, on traditional, more complex imaging methods. My work represents the first successful attempt to generate such maps at a lateral resolution of about 2\u00b5m and angular steps of about 5\u00b0 in terms of the azimuth and inclination angles of the optic axis. The maps of clam shell birefringence provide structural insights into the early mineralization during juvenile clam shell development."], "keyword": ["Microscopy"], "primary_title": "Measuring three dimensional anisotropy in the refractive index and in the orientation of fluorophores using the new Light Field LC-PolScope", "uri": "https://repository.library.brown.edu/studio/item/bdr:733541/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:733541/"}, {"pid": "bdr:733585", "object_type": "pdf", "abstract": ["The quantum Hall effect is a marvelous thing, a microcosm of all that is strange and beautiful and quantum. The fractional quantum Hall effect supports quasiparticles of fractional charge and exotic statistics. These systems are not just a theorist's fancy and are measurable in lab. Even for properties that are still waiting for conclusive experimental confirmation, we have strong theoretical reasons to assume their existence, giving something for experimentalists to strive for as well. After nearly 40 years, the field isn't closed and can still yield surprises. In this thesis, a number of novel probes of the nature of the topological order existing in these systems are discussed, in particular focussing on the mystery of the \\nu=5/2 filling factor. Because of the bulk gap, low energy physics in the quantum Hall effect is confined to the edges of the 2D electron liquid. The velocities of edge modes are key parameters of edge physics. They were determined in several quantum Hall systems from time-resolved measurements and high-frequency ac transport. A way is proposed to extract edge velocities from dc transport in a point contact geometry defined by narrow gates. The width of the gates assumes two different sizes at small and large distances from the point contact. The Coulomb interaction across the gates depends on the gate width and affects the conductance of the contact. The conductance exhibits two different temperature dependencies at high and low temperatures. The transition between the two regimes is determined by the edge velocity. An interesting feature of the low-temperature I-V curve is current oscillations as a function of the voltage. The oscillations emerge due to charge reflection from the interface of the regions defined by the narrow and wide sections of the gates. Numerical results suggest that the quantum Hall effect at \\nu=5/2 is described by the Pfaffian or anti-Pfaffian state in the absence of disorder and Landau level mixing. Those states are incompatible with the observed transport properties of GaAs heterostructures, where disorder and Landau level mixing are strong. We show that the recent proposal of a PH-Pfaffian topological order by Son is consistent with all experiments. The absence of the particle-hole symmetry at \\nu=5/2 is not an obstacle to the existence of the PH-Pfaffian order since the order is robust to symmetry breaking."], "keyword": ["Quantum Hall effect", "Fractional Quantum Hall Effect", "Topological Matter"], "primary_title": "Novel Probes of Topological Order in the Quantum Hall Effect", "uri": "https://repository.library.brown.edu/studio/item/bdr:733585/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:733585/"}, {"pid": "bdr:eqjnr8x6", "object_type": "pdf", "abstract": ["The field of direct dark matter detection is defined by an ever-present necessity to push the limits of sensitivity along as many fronts as are practically achievable while still properly accounting for systematics. At these limits, the physics behind a detector\u2019s response will naturally be unexplored, and so rare event searches in these regions require a rigorous approach to detector calibration in order to confidently differentiate between any discovered signal and a misunderstood aspect of the detector itself. We report on the design, experimental verification, and potential applications for two newly developed low-energy neutron calibration sources, as well as on work expanding the characterization and functionality of a third. When illuminated by a D-D neutron generator with a flux of 1700\u00b1200 n/cm^2/s, a 330 g deuterium-based Eljen EJ315 scintillator reflector was demonstrated to deliver a time-of-flight-tagged 345\u00b15 keV peaked neutron source with FWHM of 85\u00b15 keV. The source intensity is equivalent to an isotropic (1.2 \u00b1 0.1) \u00d7 10^4 neutrons/s into a 1.93 \u00d7 10^\u22123 sr solid angle scintillator detector target. When illuminated by the same D-D generator with a flux of 3400\u00b1400 n/cm^2/s, a 380 g hydrogen-based Eljen EJ200 plastic scintillator reflector was demonstrated to deliver a spectrum of individually energy-tagged neutrons across 15-160 keV with a source intensity equivalent to an isotropic (3.4\u00b10.3)\u00d710^4 neutrons/s into the same target. Applying time-of-flight, pulse area, and pulse shape analysis to the reflector signals, we show how these sources can be used to perform low systematics, low-energy nuclear recoil calibrations of the LUX-ZEPLIN (LZ) dark matter detector. Finally, we present new experimental verifications characterizing off-peak energy spectrum components of the Adelphi DD109 Neutron Generator, and a new adaptive pulsing system that has enabled the system to stably produce ultra-short 16 \u00b5s neutron pulses while maintaining an average isotropic neutron intensity within each pulse above 1.8\u00d710^9 neutrons/s."], "keyword": ["Astrophysics", "Dark matter (Astronomy)", "Neutrons--Scattering", "Detectors--Calibration"], "primary_title": "Development of Tagged Low Energy D- and H-Based Scintillator Reflector Neutron Sources and Characterizations of a D-D Neutron Generator for Calibrations of the LZ Detector", "uri": "https://repository.library.brown.edu/studio/item/bdr:eqjnr8x6/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:eqjnr8x6/"}, {"pid": "bdr:srphuqwv", "object_type": "pdf", "abstract": ["We present the loop space optimization framework for solving large $N$ multi-matrix systems. Based on the collective, loop space representations, the scheme provides a systematic and efficient numerical approach for solving both multi-matrix integrals ($c=0$ systems) and also multi-matrix quantum mechanics ($c=1$ systems). Positivity constraints are of significant importance and are addressed through master-field minimization. The framework not only facilitates the determination of large $N$ backgrounds, but also enables a systematic $1/N$ expansion. Consequently the complete fluctuation spectrum is also computable, which holds immediate physical relevance in matrix quantum mechanics. The complexity and the rapid growth of the degrees of freedom for these theories have stymied earlier attempts, and in this thesis we present significant improvement in this regard. To illustrate the effectiveness of our approach, we apply this scheme to two-matrix integrals and two-matrix quantum mechanics. These examples involve minimization and spectrum calculations with close to $10^4$ variables, providing solutions to the Migdal-Makeenko (loop) and collective field equations. Despite the large number of dynamical loop variables and the extreme nonlinearity of the problem, our scheme achieves high precision when confronted with solvable cases, demonstrating its capability to solve general two-matrix problems. Additionally, we present preliminary results for the matrix thermofield double. We also briefly discuss other available numerical methods, namely the Monte Carlo method and Matrix Bootstrap."], "keyword": ["Theoretical physics", "Matrix Model", "Large N"], "primary_title": "Loop Space Optimization for Large N Multi-Matrix Systems", "uri": "https://repository.library.brown.edu/studio/item/bdr:srphuqwv/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:srphuqwv/"}, {"pid": "bdr:dhbeqagf", "object_type": "pdf", "abstract": ["In this thesis, we present studies of the structures of loop-level amplitudes in planar $\\mathcal{N}=4$ supersymmetric Yang-Mills theory, via tensor diagrams and hyperbolic volumes, and singularity of scattering amplitudes in Yang-Mills and gravity from the celestial perspective. First, we propose to use tensor diagrams and the Fomin-Pylyavskyy conjectures to explore the connection between symbol alphabets of $n$-particle amplitudes in planar $\\mathcal{N} = 4$ super Yang-Mills theory and certain polytopes associated to the Grassmannian $G(4, n)$. We show how to assign a web (a planar tensor diagram) to each facet of these polytopes. These web diagrams encode all known rational letters, and all square roots of the known algebraic letters up to $n=9$. Second, we provide an explicit analytic result for the one-loop scalar $n$-gon Feynman integral in $n$ dimensions, for even $n$, with massless or massive internal and external edges. The result can be represented by the volume of a hyperbolic object called orthoscheme. Furthermore, we evaluate the general six-dimensional hexagon integral in terms of classical polylogarithms. Finally, we show that associativity of the tree-level OPE in a celestial CFT imposes constraints on the coupling constants of the corresponding bulk theory. The constrained theories are interesting as apparently well-defined celestial CFTs with a deformed $w_{1+\\infty}$ symmetry algebra. We explicitly work out the ramifications of these constraints on scattering amplitudes and find that all $n$-point amplitudes constructible solely from holomorphic or anti-holomorphic three-point amplitudes vanish on the support of these constraints. We then studied the regular terms of the OPE of MHV amplitudes and the partial differential equations the MHV celestial amplitudes should satisfy. These PDEs originate from BCFW recursion of bulk amplitudes. We also investigate further structures of the celestial dual of planar $\\mathcal{N}=4$ SYM theory from dual superconformal symmetry."], "keyword": ["scattering amplitudes", "celestial holography"], "primary_title": "Aspects of Scattering Amplitudes: Tensor Diagrams, Hyperbolic Volumes, and Celestial Sphere", "uri": "https://repository.library.brown.edu/studio/item/bdr:dhbeqagf/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:dhbeqagf/"}, {"pid": "bdr:7cqnxjuk", "object_type": "pdf", "abstract": ["Complex metal oxides such as perovskite oxide (ABO3-\u03b4) and ceria (CeO2) can accommodate large percentage of mixed cations and oxygen vacancies (VO) for many applications, including the two-step solar thermochemical H2 generation and actuators. Understanding the point defects\u2019 formation, interaction, local distortion, and strain is vital in the design of materials suitable for these applications. Therefore, this thesis aims to develop systematic predictive models starting from density functional theory (DFT) to understand functional defects in these complex metal oxides. In the first STCH application, VO determine the H2 generation performance, and its formation energies are tuned by A- and B-site cation mixing of ABO3-\u03b4. For multi-component systems with non-dilute vacancies, DFT was combined with Metropolis Monte Carlo method (DFT-MC) to sample many possible configurations. A statistical model considering the distribution of VO formation energy and VO interactions was proposed to predict the oxygen non-stoichiometry (\u03b4). By examining the low energy structures for (La0.75Sr0.25){MnFeCoAl}O3 w/wo VO, it was found Co to be the redox active element as confirmed by the experiment. The DFT-based predictive model further revealed the Co preference was due to the electronic state of Co and the locally stretched Co-O bonds. In the second example, the local distortion due to defects leads to macroscopic strain generated proportional to the square of the electric field. This electrostriction behavior becomes \u201cgiant\u201d in trivalent and isovalent doped ceria with and without VO, respectively, warranting different mechanisms. To compute the electric-mechanical coupling, DFT and molecular dynamics simulations were carried out. It was discovered that the smaller Zr (mis)fitted in the oxygen cage in ceria lattice exhibits large anharmonic vibration. Thus, it can produce anisotropic distortion and induce electric dipole that led to giant electrostriction. This \u201cdynamic\u201d mechanism was impaired by VO trapped by Zr dopants. In contrast, in Gd-doped-ceria, VO and Gd interact to produce permanent distortion and electric dipole and their reorientations induced \u201cgiant\u201d electrostriction. Overall, this thesis highlighted the importance of combining DFT with thermodynamics, statistical models, and MD simulation to understand the interaction and dynamics of defects in complex metal oxides."], "keyword": ["Density Functional Theory", "electrostriction", "solar thermochemical hydrogen generation", "Point defects"], "primary_title": "Computational Study of Point Defects\u2019 Formation, Interaction, Local Distortion, and Strain in Complex Metal Oxides for Hydrogen Generation and Electrostriction Applications", "uri": "https://repository.library.brown.edu/studio/item/bdr:7cqnxjuk/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:7cqnxjuk/"}, {"pid": "bdr:j55jzq9a", "object_type": "pdf", "abstract": ["This dissertation presents two innovative searches for new heavy particles beyond the Standard Model (BSM) of particle physics. The investigation focuses on two distinct signatures: the decay of a new particle into a photon and a Lorentz-boosted W boson, with the latter identified through its hadronic decay as a large-radius jet, and the decay of another new particle into three widely separated hadronic jets. These searches are based on proton-proton collision data collected with the CMS detector at the CERN LHC at 13 TeV in 2016\u20132018, corresponding to an integrated luminosity of 138 /fb. Innovative techniques are incorporated to maximize the sensitivity to the signal process, including applying advanced pile-up mitigation, jet grooming, and jet substructure algorithms for the precise W boson jet reconstruction and identification. Accurate and robust background predictions are achieved via the utilization of the discrete likelihood profiling method and the binned integration of parametric probability density functions. Although no significant deviation from Standard Model predictions was observed, these searches established the world\u2019s best, and in some cases the first, constraints on the existence of such resonances across a broad range of BSM scenarios, providing crucial guidance for the future exploration of new physics. The dissertation also highlights the author\u2019s contribution to the investigation of the communication failure of the CMS Hadron Calorimeter\u2019s Next-generation Clock and Control Modules and subsequential hardware maintenance and commissioning, an indispensable component for the continuous successful operation of the CMS detector in LHC Run 3."], "keyword": ["Experimental Particle Physics"], "primary_title": "Search for High-Mass Resonances Using Signatures with Hadronic Jets on the CMS Detector at the CERN LHC", "uri": "https://repository.library.brown.edu/studio/item/bdr:j55jzq9a/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:j55jzq9a/"}, {"pid": "bdr:s6k2jh8u", "object_type": "pdf", "abstract": ["The Epoch of Reionization (EoR) marks the period in the universe's history where the neutral hydrogen (HI) in the intergalactic medium became ionized by the first stars and galaxies. A promising probe of this period is the highly redshifted 21 cm line from HI, however, observation of this distant cosmological signal has proven difficult. One of the most significant challenges faced by 21 cm EoR experiments is dealing with foreground (FG) emission from our galaxy and extragalactic sources that is several orders of magnitude brighter than the EoR signal we wish to detect. Current experiments targeting the EoR are seeking a first detection in the form of the 21 cm power spectrum. Existing techniques to mitigate FGs during 21 cm power spectrum estimation under-utilize the data and do not properly account for the covariance between the observed EoR and FG signals. My work has focused on the development of a Bayesian framework, BayesEoR, that jointly models the instrument, FGs, and EoR and marginalizes over their uncertainties to enable extraction of statistically robust and unbiased EoR power spectrum estimates. I will present a comprehensive simulation-based study of BayesEoR detailing its performance analyzing realistic data that sees the whole sky using a model in the image domain which, due to computational constraints, is restricted to a subset of the sky. My results show that BayesEoR is capable of producing unbiased power spectrum estimates when the instrument beam sufficiently down-weights bright FG emission at high zenith angles outside the restricted image space model. For use on more realistic instruments with broad beams sensitive to the whole sky, I also present a modified version of BayesEoR that allows for all sky modelling of FGs while the modelled EoR signal remains within the primary FoV of the telescope. In addition to this work analyzing simulated data with BayesEoR, I also present preliminary work analyzing data from HERA. Finally, I present the HERA validation team's published work, highlighting my specific contributions, validating the analysis pipeline used to produce HERA's first upper limits on the EoR power spectrum."], "keyword": ["Physics, Astrophysics, Galaxy Clusters, Cosmology", "Radio astronomy", "Epoch of reionization", "21cm"], "primary_title": "A Bayesian Approach to 21 cm Power Spectrum Estimation", "uri": "https://repository.library.brown.edu/studio/item/bdr:s6k2jh8u/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:s6k2jh8u/"}, {"pid": "bdr:3ad3dkcy", "object_type": "pdf", "abstract": ["Motivated by experiments on colloidal membranes made of chiral filaments that assemble through depletion force, we develop a Monte Carlo framework and carry out simulations for such membrane systems and more generally, chiral liquid crystals on deformable surfaces. The membrane surface is modeled by a triangular mesh of beads connected by bonds in which the beads and bonds are free to move or reconnect at each Monte Carlo step, and the orientational order of constituent filaments is modeled in different ways by two phenomenological theories. One models the orientational order implicitly and only uses the geometric properties of the surface edge, three classes of shapes are found: branched polymer, disk, and vesicle. The power spectrum of the edge fluctuation shows a peak as the chirality increases, and the membrane twists into ribbons under external force, which as a function of elongation increases linearly at the beginning and then plateau. Another theory models the orientational order explicitly using the full director field of unit vectors decorating each bead on the triangular mesh. The director field on the disk-shaped membranes exhibits three patterns: isotropic, smectic-A, and cholesteric. In the smectic-A phase, the twist of the directors is expelled to the edge of the membrane, and the penetration depth is tuned by the ratio between director-director coupling and tilt coupling. In the cholesteric phase, the membrane ripples due to the coupling between tilt and surface shape. Moreover, when multiple edges are allowed, increasing chirality leads to the formation of $\\pi$-walls wrapping around the membrane and opening up of edges, and the membranes become catenoid or trinoid shapes. For a membrane with two edges, pulling on the opposite edges will make it deform from a wide catenoid to a cylinder shape, and the force applied increases rapidly at the beginning then gradually. For an elongated membrane, the directors can either align with the cylindrical surface forming a curved smectic-A phase, or align with other directors and form two regions of directors laying down on the local surface. Increasing chirality will make these regions twist into $\\pi$-walls and wrap around each other forming helical shapes."], "keyword": ["Monte Carlo method", "Membrane Mechanics", "Chirality", "Liquid crystals"], "primary_title": "Chiral Liquid Crystals on Deformable Surfaces: A Monte Carlo Study", "uri": "https://repository.library.brown.edu/studio/item/bdr:3ad3dkcy/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:3ad3dkcy/"}, {"pid": "bdr:918770", "object_type": "pdf", "abstract": ["In this work we present our contribution to the method of using Landau singularities for probing scattering amplitudes in planar massless quantum field theories. We start by proposing a simple geometric algorithm for determining the complete set of branch points of amplitudes in planar N = 4 super-Yang-Mills theory directly from the Amplituhedron, without resorting to any particular representation in terms of local Feynman integrals. This represents a step towards translating integrands directly into integrals. In particular, the algorithm provides information about the symbol alphabets of general amplitudes. First we illustrate the algorithm applied to the one- and two-loop MHV amplitudes. Then we demonstrate how to use the recent reformulation of amplituhedra in terms of `sign flips' in order to streamline the application of this algorithm to amplitudes of any helicity. In this way we recover the known branch points of all one-loop amplitudes, and we find an `emergent positivity' on boundaries of amplituhedra. Lastly, we look beyond planar N = 4 super-Yang-Mills theory, and analyze Landau singularities of general massless planar theories. In massless quantum field theories the Landau equations are invariant under graph operations familiar from the theory of electrical circuits. Using a theorem on the Y-Delta reducibility of planar circuits we prove that the set of first-type Landau singularities of an n-particle scattering amplitude in any massless planar theory, in any spacetime dimension D, at any finite loop order in perturbation theory, is a subset of those of a certain n-particle [(n-2)^2/4]-loop ``ziggurat'' graph. We determine this singularity locus explicitly for D=4 and n=6 and find that it corresponds precisely to the vanishing of the symbol letters familiar from the hexagon bootstrap in SYM theory. Further implications for SYM theory are discussed."], "keyword": ["scattering amplitudes"], "primary_title": "Landau Singularities in Planar Massless Theories", "uri": "https://repository.library.brown.edu/studio/item/bdr:918770/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:918770/"}, {"pid": "bdr:918804", "object_type": "pdf", "abstract": ["The Epoch of Reionization (EoR) is a period during the history of the Universe that as of today has been largely unconstrained by cosmological measurements. The most promising probe of reionization, the 21cm emission of neutral hydrogen, is unfortunately difficult to observe. Measurements of the 21cm reionization signal are performed using low-frequency wide-field radio interferometers. The difficulty in detecting the weak 21cm signal is further compounded by instrumental and astrophysical limitations. In an effort to overcome these issues, I present four key results. First I look at applying a hybrid foreground avoidance strategy for retaining sensitivity in the presence of Galactic and extragalactic foregrounds. I then introduce a novel method for identifying radio frequency interference (RFI) in interferometric visibilities using a Deep Fully Convolutional Neural Network (DFCN). Following this, I perform sky calibration on preliminary Hydrogen Epoch of Reionization Array (HERA) observations using the Fast Holographic Deconvolution (FHD) interferometry simulation software which provides an independent validation of the default HERA processing and calibration pipeline. Finally, I demonstrate a Convolutional Neural Network (CNN) for 21cm parameter estimation and uncertainty propagation on simulated 21cm cosmological volumes."], "keyword": ["Machine Learning", "Cosmology", "Radio astronomy", "Epoch of reionization", "21cm"], "primary_title": "A Next Generation Analysis Pipeline for 21cm Epoch of Reionization Studies", "uri": "https://repository.library.brown.edu/studio/item/bdr:918804/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:918804/"}, {"pid": "bdr:6e2fgp6g", "object_type": "pdf", "abstract": ["Terahertz scattering scanning near field optical microscopy (THz s-SNOM) has become an active research topic for its effectiveness in characterizing electronic behavior in many materials with nanoscale resolution. Motivated by a desire to understand the current techniques more deeply and to expand upon them, here we present novel methods for characterizing metals and semiconductors with THz s-SNOM. First, we perform the first side-by-side THz nanoscopy and Laser Terahertz Emission Nanoscopy (LTEN) measurement on bulk InAs and determine that LTEN may provide superior spatial resolution compared to THz nanoscopy. We also provide a new framework for simulating broadband THz reflection and emission from bulk InAs. Next, by creating THz nanoscopy images of gold microstructures, we disprove the conception that THz near-field microscopy is sensitive only to the sample\u2019s optoelectronic properties directly underneath the near-field probe tip. We show that our structure has THz waveguide-like properties, which dominate the THz reflection signal; therefore, THz nanoscopy images from a small area are highly dependent on the size, shape, and orientation of structures very far from the tip. We then demonstrate the first \u201cnonlocal\u201d near-field optical pump-terahertz probe experiments, in which we photoexcite bulk undoped GaAs and use a THz probe pulse to observe the change in reflection at an area laterally displaced from our pump. We demonstrate that this technique can be used to reveal anisotropy in a sample by highlighting directions of preferred carrier motion. Next, we expand this technique to nonlocal LTEN, in which we detect THz emission from bulk InAs at a location displaced from our pump area. We determine that both techniques can reveal properties related to carrier motion, but the latter can also illustrate mechanisms of THz generation which are poorly understood in certain materials. Finally, we demonstrate the first instance of blue light LTEN. We show that inducing THz emission in semiconductors via high-energy pumping can reveal properties of charge carriers in higher bands not observable with conventional near-infrared pumping. We create the first near-field THz emission image of bulk Si and provide a novel framework for correlating the emission strength to the Si doping profile."], "keyword": ["Nonlinear optics", "Terahertz spectroscopy", "Near-field microscopy"], "primary_title": "Linear and Nonlinear Terahertz Near-Field Microscopy for Characterizing Electronic Systems", "uri": "https://repository.library.brown.edu/studio/item/bdr:6e2fgp6g/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:6e2fgp6g/"}, {"pid": "bdr:wsn3v2du", "object_type": "pdf", "abstract": ["The existence of dark matter as the dominant form of matter in the universe is now well accepted, but the identity of dark matter remains unknown. One leading candidate for dark matter is the weakly interacting massive particle (WIMP). The motivation comes from the so-called \u201cWIMP Miracle\u201d, which refers to the fact that a particle interacting via the weak force and with a mass in the range 1 GeV to 100 TeV naturally leads to the dark matter density observed today. The Large Underground Xenon (LUX) experiment was a dual-phase liquid xenon time projection chamber (TPC) operating at the Sanford Underground Research Facility in Lead, South Dakota. which sought to detect WIMP interactions with baryonic matter, and now the LUX-ZEPLIN (LZ) experiment is taking over as the successor to LUX. WIMP interactions within the detector are expected to generate nuclear recoil events. To fully understand potential WIMP signals, the nuclear recoil response must be calibrated. An Adelphi Technology, Inc. neutron generator sends neutrons into the detector to generate nuclear recoil calibration events. I discuss design, fabrication, and integration of the hardware required by the DD neutron calibration system in LZ. Beyond generating nuclear recoil response calibrations, neutrons also create radioactive backgrounds via neutron activation. I report the studies of DD activation in LZ and show that DD neutron campaigns will generate robust nuclear recoil calibration data while producing backgrounds that remain subdominant to the inherent detector backgrounds."], "keyword": ["Physics, Astrophysics, Galaxy Clusters, Cosmology", "Dark matter (Astronomy)"], "primary_title": "Neutron Calibrations and Activation Signals in Low-Background Liquid Xenon Dark Matter Detectors", "uri": "https://repository.library.brown.edu/studio/item/bdr:wsn3v2du/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:wsn3v2du/"}, {"pid": "bdr:xf42mrd6", "object_type": "pdf", "abstract": ["The combined effect of electronic correlation and strong spin-orbit-coupling(SOC) can give rise to a variety of exotic quantum phases. Double perovskites provide a simple structure to study the spin-orbit-lattice entangled states. In this thesis, focusing on the 5d osmate double perovskite system, we conduct a combination of work including theoretical model simulation, first-principle calculation, and nuclear magnetic resonance experiments to understand the fundamental physical properties of this material system. For the 5d Mott insulator Ba2NaOsO6, by conducting spin-spin relaxation measurements and applying quadrupolar noise spectroscopy, we addressed a long-standing missing entropy problem. We found that quadrupolar noise with a Lorentzian distribution persists up to a high temperature above its structural transition, indicating quadrupolar domains which account for the missing entropy in the system. Also by carrying out a classical Monte Carlo simulation using 4 sites per unit cell for a 5d1 double perovskite model with strong SOC, we found that the non-zero quadrupolar moment Q(3z^2-r^2) arises due to additional symmetry breaking that was not captured in earlier mean-field treatment with 2 sites per unit cell, showing consistency with the two non-zero quadrupolar moments proposed in the quadrupolar phase of Ba2MgReO6. Furthermore, we improved the earlier point charge approximation calculation on the electric field gradient of Ba2NaOsO6 and we identified the local orthorhombic structural distortion for Na-O octahedra in Ba2NaOsO6 of around 0.01 angstrom. Our first principle calculation on Ba2NaOsO6 also found the existence of a staggered orbital ordering pattern accompanying its canted ferromagnetic order, which is characterized by the different selective occupation of d orbitals on the two-sublattice Os ions. Besides Ba2NaOsO6, we have also conducted comprehensive NMR measurements on its isostructural, isovalent compound Ba2LiOsO6. We found that the metamagnetic transition at 5.75T is possibly a spin-flop transition and the ground magnetic state is more likely to be a 3D antiferromagnet. Electron doping effect on 5d1 Ba2NaOsO6 has also been studied on powder compounds Ba2NaxCa(1-x)OsO6 (0 < x < 1). We found that all the doped samples remain as magnetic insulators despite the added electrons. Powder spectrum simulation indicates that similar to the Ba2NaOsO6 case, a \"broken local point symmetry\" phase with orthorhombic symmetry occurs above magnetic transition for all doped samples. Under the collinear two sublattices canted AFM model, the ground magnetic states evolve from canted FM state to collinear AFM state with the increase of doping electrons. Whether there is multipolar ordering in these samples needs further study using complementary techniques in the future."], "keyword": ["Nuclear magnetic resonance", "5d osmate double perovskite", "spin-orbit-coupled Mott insulator", "quantum materials", "condensed matter physics"], "primary_title": "Magnetic and Structural Properties of 5d Osmate Double Perovskites Probed by Nuclear Magnetic Resonance", "uri": "https://repository.library.brown.edu/studio/item/bdr:xf42mrd6/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:xf42mrd6/"}, {"pid": "bdr:qymr733v", "object_type": "pdf", "abstract": ["In this thesis, we present a study of the transition to turbulence in quasilinear models. Our focus is to use quasilinear approximation as a minimal model to describe this complex system and build bridges toward direct statistical simulation. We start the discussion by introducing the quasilinear approximation in 2D incompressible flows and studying the U(1) symmetry of the system. For the linear system, the corresponding conserved charges are the pseudomomenta for each wave mode. Then we consider three-dimensional pipe flow and simulated incompressible flows in annular pipes with the quasilinear model. The quasilinear system shows localized turbulence (puffs) and signs of the critical behavior of the transition to turbulence in annular pipe flows. Finally, dimensional reduction using Proper Orthogonal Decomposition is applied to the quasilinear model, and the critical behavior is studied in the reduced models."], "keyword": ["Physics", "Turbulence", "condensed matter physics"], "primary_title": "Simulation of Turbulence in a Quasilinear Approximation", "uri": "https://repository.library.brown.edu/studio/item/bdr:qymr733v/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:qymr733v/"}, {"pid": "bdr:w9tw9bm2", "object_type": "pdf", "abstract": ["The Standard Model of particle physics describes the fundamental ways in which the particles of our universe interact. In this description, we predict that elementary particles obtain their masses through their interaction with the non-zero vacuum excitation value of the Higgs field. For fermions, the strength of these interactions is described by a Yukawa coupling between the fermions and the Higgs which exist as free parameters in the theory. As such, the only indication of these coupling strengths has previously been from our existing knowledge of the fermion masses. However, through the Large Hadron Collider we are now able to directly measure the strength of the Yukawa coupling between real Higgs boson particles and the various species of fermions. In this thesis, I present a study in which we search for a Higgs boson particle directly interacting with second generation charm quarks through the $H\\rightarrow c\\bar{c}$ decay mode using 138 fb$^{-1}$ of $\\sqrt{s}=13$ TeV proton-proton collision data collected with the CMS detector. To perform this search, I make use of the $VH$ production mode, in which the Higgs boson is produced in association with a W or Z vector gauge boson. To validate the analysis strategy, a secondary search is also carried out in which the analysis framework is re-cast to search for diboson production in which a real Z boson decays directly to a charm quark-antiquark pair. Through combination with the results of a second analysis team within the CMS collaboration, we produce the first study to observe the $Z\\rightarrow c\\bar{c}$ decay mode in a hadron collider."], "keyword": ["Experimental Particle Physics"], "primary_title": "Search for the Decay of Standard Model Higgs Bosons to a Charm Quark-Antiquark Pair Using 128 fb^-1 of CMS Proton-Proton Collision Data at \u221as = 13 TeV", "uri": "https://repository.library.brown.edu/studio/item/bdr:w9tw9bm2/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:w9tw9bm2/"}, {"pid": "bdr:79b9vypt", "object_type": "pdf", "abstract": ["Discovery of a Higgs Boson with mass near 125 GeV in 2012 marked one of the most important milestones in particle physics. The low mass of Higgs with diverging loop corrections adds motivation to look for new physics Beyond the Standard Model (BSM). Several BSM theories introduced new heavy quark partners, called vector-like quarks (VLQ), with mass in TeV scale. In particular, the vector-like top quark ($T$) can cancel the largest correction due to top quark loops, one of the main contributions to the divergence, and stabilize the scalar Higgs mass. This analysis searches for pair production of vector-like $T$ or $B$ quark with charge $2e/3$ and $-e/3$ in proton-proton collisions at 13 TeV in the LHC. Theories predict 3 decay modes for $T$ and $B$ each : $bW$, $tZ$ , $tH$ and $tW$, $bZ$, $bH$. The branching ratios vary over different theoretical models. We focus on events where bosons decay leptonically and result in final states with multiple (3 or more) leptons or exactly two leptons with same-signed electric charge. We analyze data collected by the CMS detector in the LHC in 2017 and 2018 with integrated luminosities of 41.53 and 59.74 fb$^{-1}$. Besides Standard Model (SM) processes, lepton misidentification contributes a significant part of the background and is estimated by data-driven method. For the same-signed dilepton final state, there is also background from misidentification of electric charges. Comparing estimated background with data, and considering uncertainties/systematics, we can find the upper limit on $T\\overline{T}$ or $B\\overline{B}$ production cross section. We calculate limits at different mass points of $T$ and $B$ and different branching ratio combinations."], "keyword": ["Particles (Nuclear physics)", "Beyond Standard Model", "Experimental Particle Physics", "CMS Experiment"], "primary_title": "Search for Pair Production of Vector-Like Quarks in Leptonic Final States in Proton-Proton Collisions at 13 TeV at the CMS Detector in the LHC", "uri": "https://repository.library.brown.edu/studio/item/bdr:79b9vypt/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:79b9vypt/"}, {"pid": "bdr:m2kd22ua", "object_type": "pdf", "abstract": ["As the first galaxies and stars formed in the universe, their ultraviolet radiation ionized neutral hydrogen around them, creating bubbles of ionized gas. This time is known as the Epoch of Reionization (EoR). The time between the release of the cosmic microwave background radiation and the EoR is called the Dark Ages. We don't know much about that period of time, as the universe was dark and the cosmic microwave background didn't trace the distribution of matter. The best hope to study Dark Ages and the EoR is the 21cm hyperfine transition line of neutral hydrogen. However, there are enormous observational challenges to detecting the signal. As foregrounds are several orders of magnitude brighter than the 21cm signal, extreme precision is needed to cleanly separate the two. High precision simulations of the interferometric array can help us calibrate the data and vet new analysis pipelines to see if they meet the required precision. I present my work with pyuvsim -- a comprehensive precision simulation package for radio interferometers. I have tested pyuvsim performance extensively and it has become a reference standard within the HERA and MWA collaborations. Verifying that a simulator can recover the correct power spectrum is the most important thing we can do. My results showed that pyuvsim simulations can recover power spectrum with extraordinary precision and validated power spectrum pipelines. I also present my work on foreground modeling for the highest redshift 21cm signals. There is a new potential foreground issue for very low frequency Dark Ages experiments: opacity of the foregrounds. Foregrounds are in front of the 21cm signal, so if they are optically thick to low frequency radiation, they will obscure it entirely due to free-free absorption. My results reveal which regions of the sky might be optically thick for the highest redshift 21cm signal detection."], "keyword": ["Astrophysics", "Physics, Astrophysics, Galaxy Clusters, Cosmology", "Radio astronomy"], "primary_title": "High Precision Simulations and Foreground Modeling in 21cm Cosmology", "uri": "https://repository.library.brown.edu/studio/item/bdr:m2kd22ua/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:m2kd22ua/"}, {"pid": "bdr:xgdvrscb", "object_type": "pdf", "abstract": ["In this thesis I explore applications of non-standard cosmological and gravitational theories theories in different sectors. The thesis contains three main parts. The first is on higher spin cosmology, with a discussion on applications to the cosmological collider and to dark matter. The second is on theories which are modifications to general relativity and insights provided into these theories by gravitational waves, and the third is focused again on modified gravity but using black holes as a probe. The first section of this thesis, `Higher Spin Cosmology,' is based on two published papers on higher spin particles. First, I will discuss work which applies the `cosmological collider' formalism to higher spin supersysmmtry, and I will then introduce higher spins as a dark matter candidate. I will show that HSDM gravitationally produced during inflation can make up the entirety of the dark matter that is observed in the universe today, making it a well posed model to explain the dark matter problem and speculate on direct detection possibilities. The second section, `Probing Modified Gravity with Gravitational Waves,' discusses two works which study the gravitational wave modifications for a modified theory of gravity in which the cosmological constant is allowed to vary, and noncommutative gravity, respectively. I discuss how both of these theories can be constrained using gravitational wave observations, as well as binary pulsar observations in the case of noncommutative gravity. Lastly, I turn to dynamical Chern-Simons (dCS) gravity in Section III, `Probing Modified Gravity with Black Holes,' and explore how dCS can potentially be probed with studies of black holes, including a discussion of the `Chern-Simons caps' as well as superradiance for dCS black holes."], "keyword": ["Cosmology", "Gravity"], "primary_title": "Theoretical Applications of Non-Standard Cosmological and Gravitational Physics: Higher Spins and Modified Gravity", "uri": "https://repository.library.brown.edu/studio/item/bdr:xgdvrscb/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:xgdvrscb/"}, {"pid": "bdr:8qt58f2f", "object_type": "pdf", "abstract": ["A superfield is a compact representation of a supermultiplet. A superfield description of a supersymmetric theory ensures manifest supersymmetry. In this dissertation, we present the studies of mathematical structures of superfields, and several instances of applications in superfield supergravity, supersymmetric Sachdev-Ye-Kitaev (SYK) models, and cluster superalgebras in superamplitudes. Precisely, we tackle the following series of problems. (1) We describe a several decades old problem of higher dimensional superfields. We establish a novel method based on Lie algebras, combinatorics and graphs to solve for superfields of arbitrary spins in arbitrary dimensions. (2) We construct 10D and 11D linearized Nordstr\u00f6m supergravity theories and investigate Weyl symmetry in these superspaces. We search for additional prepotential superfields needed for complete superconformal supergravity theories in 10D and 11D. (3) We extend the simplest model of holography, the SYK model, with maximal supersymmetry, by utilizing 4D superfields and projecting down to 1D. (4) We explore the potential connections between cluster superalgebras and superamplitudes, and propose a new definition of cluster superalgebras based on superfields."], "keyword": ["Physics", "Supersymmetry", "High energy theory", "Supergravity", "Holography", "Amplitudes"], "primary_title": "Superfields in Supergravity, Holography, and Amplitudes", "uri": "https://repository.library.brown.edu/studio/item/bdr:8qt58f2f/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:8qt58f2f/"}, {"pid": "bdr:pxsrrb96", "object_type": "pdf", "abstract": ["Top quark is the heaviest known fundamental particle. In this thesis I present two studies on the top quark. The first study is a combined measurement of the mass and the decay width of the top quark in di-leptonic ttbar decay events resulting from proton-proton collisions at center-of-mass energy $\\sqrt{s}$ = 13 TeV. Data was collected with the CMS detector during Run 2 of the CERN LHC in 2016. Invariant mass of lepton and b-jet pairs, called mlb, is used as observable. Events are categorized by lepton flavor (ee, e$\\mu$, $\\mu\\mu$), b-quark jet multiplicity, and the transverse momentum of the lepton b-jet pairs. Simulated expectations for different top mass and width scenarios are compared to the data via a profile likelihood method. The second study is a search for the rare production process $t\\bar{t} t\\bar{t}$. We study the single lepton final state in which one of the four top quarks decays leptonically, and three top quarks decay hadronically. We analyze the proton-proton collision data taken in 2016, 2017 and 2018. The distributions of $H_T$, the scalar sum of jet transverse momentum $p_T$ is used in order to discriminate signal from background. In this analysis, we make use of a resolved top tagging algorithm to tag the low $p_T$ top quarks that decay hadronically. Events are categorized by lepton flavor, number of AK4 jets, number of b-tagged jets, and number of resolved top-tagged jets. We set 95\\% upper limits on the $t\\bar{t} t\\bar{t}$ production cross section. We further improve the sensitivity with a discriminant constructed by a multivariate analysis based on the Boosted Decision Tree (BDT) method."], "keyword": ["Experimental Particle Physics", "CMS Experiment", "Top quark"], "primary_title": "Top Quark Studies with the CMS Experiment: Rare Process and Precision Measurements", "uri": "https://repository.library.brown.edu/studio/item/bdr:pxsrrb96/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:pxsrrb96/"}, {"pid": "bdr:cj6ctnc2", "object_type": "pdf", "abstract": ["In this thesis, we present studies of off-shell supergravity theories in ten- and eleven-dimensional superspaces, polytopic supersymmetry representation theory, and the SUSY holography conjecture. First, inspired by the history of how Einstein constructed General Relativity, we study the linearized Nordstr\\\"om supergravity in ten- and eleven-dimensional superspaces. We found no obstacles to applying the lessons we learned in 4D to higher dimensions. We also derive infinitesimal 10D superspace Weyl transformation laws. The identification of all off-shell ten-dimensional supergeometrical Weyl field strength tensors, constructed from respective torsions, is presented. Second, since the traditional approach requires a high computational price to be paid to elucidate the $\\theta$-expansion for component fields residing within the superfields, we establish a novel approach founded by the polytopic SUSY representation theory. We realize that Lie Algebra techniques, in particular branching rules, Plethysm, and tensor product, provide the key to deciphering the \\textit{complete} list of independent fields that describe a supersymmetric multiplet in \\textit{arbitrary} spacetime dimensions efficiently. We show the explicit one-to-one correspondence between Lorentz irreps and field variables, leading to an ``adynkrafield'' formalism in which the traditional $\\theta$-monomials are replaced by Young Tableaux. Further elaborations on the ``scan'' machinery and the consequent prepotential candidates for 10D, ${\\cal N} =$1, 2A, and 2B superconformal supergravity theories are presented as well. Third, the SUSY holography conjecture proposes a way to study higher-dimensional supersymmetric models from their 1D counterparts. The problem of classifying off-shell representations of the $N$-extended 1D super Poincar\\'e algebra is closely related to the classification of its graphical representations -- adinkras. We define the adinkra ``height yielding matrix number'' (HYMN) and study HYMN equivalence classes for all ${\\cal GR}(4,4)$ valise adinkras. Another puzzle is that considering the projection from 4D, ${\\cal N} = 1$ SUSY to 1D, $N = 4$ SUSY, a dissection of $\\mathbb{S}_4$ is required to be consistent with SUSY. We show that this dissection can be seen from the symmetries of the permutahedron and the use of weak Bruhat ordering."], "keyword": ["High energy theory"], "primary_title": "Higher-dimensional Supergravity, Polytopic SUSY Representation Theory, and SUSY Holography Conjecture", "uri": "https://repository.library.brown.edu/studio/item/bdr:cj6ctnc2/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:cj6ctnc2/"}, {"pid": "bdr:h8aqjqke", "object_type": "pdf", "abstract": ["In this thesis, we present a study of the singularity structure of scattering amplitudes in maximally supersymmetric Yang-Mills (N=4 SYM). We first consider the cluster adjacency properties of the singularities, and later we discuss a method to generate symbol letters from plabic graphs. We start our discussion by making use of the Sklyanin Poisson bracket on Gr(4,n) to investigate pair-wise cluster adjacency of singularities of rational Yangian invariants in N=4 SYM, and to establish that the n-point one-loop NMHV ratio function satisfies Steinmann cluster adjacency. We also present a series of conjectures about cluster adjacency. We continue our study of Yangian invariants in N=4 SYM by classifying all positive n-particle N^kMHV Yangian invariants in the theory with n=5k. We show that this problem is equivalent to that of enumerating plane cactus graphs with k pentagons and use this to enumerate the cyclic classes of these invariants. We provide an alternative (but equivalent) classification by showing that a product of k five-brackets with disjoint sets of indices is a positive Yangian invariant if and only if the sets are all weakly separated. Finally, we suggest an algorithm for computing symbol alphabets from plabic graphs by solving matrix equations of the form C Z = 0 to associate functions on Gr(m,n) to parameterizations of certain cells of Gr(k,n) indexed by plabic graphs. For m=4 and n=8 we show that this association precisely reproduces the 18 algebraic symbol letters of the two-loop NMHV eight-particle amplitude from four plabic graphs. We also show that it is possible to obtain all rational symbol letters by solving matrix equations of the form C Z = 0 if one allows C to be an arbitrary cluster parameterization of the top cell of Gr_+(n-4,n). We finish our discussion by identifying sets of parameterizations of the top cell of Gr_+(5,9) for which the solutions produce all of (and only) the cluster variable letters of the two-loop nine-particle NMHV amplitude, and identify plabic graphs from which all of its algebraic letters originate."], "keyword": ["Physics", "scattering amplitudes", "Mathematical physics", "Cluster algebras", "Supersymmetry", "Yang-Mills Theory"], "primary_title": "Singularities of Scattering Amplitudes: Symbol Letters, Cluster Adjacency, and Plabic Graphs", "uri": "https://repository.library.brown.edu/studio/item/bdr:h8aqjqke/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:h8aqjqke/"}, {"pid": "bdr:mbmfndau", "object_type": "pdf", "abstract": ["Competing interactions between strong spin-orbit coupling (SOC) and electron correlations have recently led to widespread studies of various emergent novel quantum phases. Recent interest has been placed in Mott insulators with strong SOC, particularly those containing 5d transition metal ions where SOC and electron correlations can be of comparable magnitude. In this thesis, we present a comprehensive study on the effects of charge doping on the double perovskite Ba2NaOsO6, a Mott insulator with both strong electron correlations and SOC. Specifically, we report zero-field systematic muon spin relaxation (\u03bcSR), magnetization, and nuclear magnetic resonance (NMR) studies of the magnetic and structural phase evolution as a function of charge doping of Ba2NaxCa1\u2212xOsO6 through the Na+/Ca++ partial substitution for 0 \u2264 x \u2264 1. Similar to Ba2NaOsO6, we find the existence of an intermediate temperature region with orthorhombic electric field gradient (EFG) symmetry before the onset of magnetic ordering in Ba2NaxCa1\u2212xOsO6, indicating a breaking local point symmetry (BLPS) phase. In the low temperature magnetic state, the ferromagnetic moment component present in Ba2NaOsO6 is almost completely suppressed when x \u2265 0.125. Under a canted antiferromagnetic (AFM) model of Ba2NaOsO6, a staggered angle around 86(1) degrees was found for 0.125 \u2264 x \u2264 0.9, implying a collinear AFM state, while Jahn-Teller type structural transitions support the existence of possible quadrupolar moments. Moreover, the magnetic insulating state is preserved across all doping concentrations despite the introduction of extra electrons into the system. By constructing a magnetic and structural phase diagram as a function of charge doping, our work sheds light on the effect of electronic correlation strength in the complex interplay of magnetic, structural, and lattice degrees of freedom in the interesting 5d1 and 5d2 Mott insulator systems. Towards the end, the design and performance of a low noise probe for transport measurements and magnetic sensing with large bandwidth suited for cryogenic environments is also presented. The highly modular design of the probe facilitates the exchange of sample holder and sample-stage amplifier, which combined with its characteristic low transmission and reflection loss, makes this design ideal for sensitive measurements. The specific example of measuring the shot noise of magnetic tunnel junctions is presented."], "keyword": ["Spin-orbit coupling", "Mott Insulator", "Condensed matter--Magnetic properties", "NMR", "Transition metal oxides"], "primary_title": "Studies of the Charge Doped Mott Insulator With Strong Spin-Orbit Coupling, Ba2NaxCa1-xOsO6", "uri": "https://repository.library.brown.edu/studio/item/bdr:mbmfndau/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:mbmfndau/"}, {"pid": "bdr:bk4dfcu3", "object_type": "pdf", "abstract": ["We develop an efficient simulation package of nuclear magnetic resonance spin echo experiments in order to study the effects of strong electronic spin correlations on the dynamics of the nuclear spin ensemble. A mean-field model can be used to study long range correlated electronic phases through their hyperfine interaction with nuclear spins. We first review specific aspects of the simulation package developed for our exploration. We discuss its structure, accuracy, and the technical merits of the various approximations used to model the spin ensemble. We then explore the dynamics of the interacting nuclear ensemble and discuss the key behaviors of the system. In particular, we classify the types of temporal asymmetry the interaction induces in the system as well as a pulse-dependent shift in the spectral domain. Using these results, we discuss how careful measurement of the pulse-dependent shift can be used to extract information about the anisotropy of the interaction and how these results represent a novel tool for the examination of exotic NMR signatures in strongly correlated systems."], "keyword": ["computational physics"], "primary_title": "Dynamic Simulations of Strongly Coupled Spin Ensembles", "uri": "https://repository.library.brown.edu/studio/item/bdr:bk4dfcu3/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:bk4dfcu3/"}, {"pid": "bdr:ybkvqm5d", "object_type": "pdf", "abstract": ["Structural features of proteins often serve as signatures of their biological function and molecular binding activity. Elucidating these structural and dynamical features is essential for understanding underlying biophysical mechanisms. Significant efforts in the past decade have resulted in highly accurate all-atom protein force fields for molecular dynamics (MD) simulations of proteins. These simulations provide new insights into the underlying physics of both folded proteins, which are easy to characterize by one or a few native states, and intrinsically disordered proteins (IDPs), which are structurally heterogeneous and challenging to characterize by experiments alone. However, state-of-the-art protein force fields still display significant discrepancies in MD simulation compared to experiments. Moreover, given accurate structural ensembles obtained from MD simulation, existing methods do not have the statistical capability to robustly identify geometric and dynamic variations in these simulated protein ensembles or describe the molecular interactions underlying the biophysical behavior of the protein systems. In this thesis, I present the analytical approaches for optimizing the accuracy of MD simulations and extracting structural signatures from the simulated ensembles. In the following chapters, I present (1) a refinement to the all-atom molecular dynamic simulation force field to improve the representation of helicity for intrinsically disordered proteins, (2) a statistical approach to quantify and visualize the molecular interactions underlying the liquid-liquid phase separation of intrinsically disordered protein systems, and (3) a novel topological data analytic approach for discovering biophysical signatures in protein dynamics."], "keyword": ["Computational biology", "Gaussian processes", "Molecular dynamics", "Machine learning--Statistical methods", "computational physics", "Molecular Dynamics Simulation"], "primary_title": "Analytical Framework to Uncover Structural Signatures from All-Atom Molecular Dynamics Simulations", "uri": "https://repository.library.brown.edu/studio/item/bdr:ybkvqm5d/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:ybkvqm5d/"}, {"pid": "bdr:39emhpgx", "object_type": "pdf", "abstract": ["This dissertation presents a search for the signature of the production of previously unobserved particles being produced in the proton-proton collisions of the CERN Large Hadron Collider. The particular signature that this search focuses on is a resonant production of a Higgs boson in conjunction with a photon, a signal that various models that go beyond the standard model of particle physics predict, including theories with a Z\u2019 boson. A detailed analysis of the data collected by the Compact Muon Solenoid detector corresponding to 35.9 inverse femtobarns of data is performed to hunt for any \"bumps\" arising in the invariant mass spectrum of events that contained a photon and a jet consistent with the hadronic decay of a Higgs boson. In order to maximize the sensitivity of this search, new and innovative techniques are employed, including the application of new pile-up mitigation algorithms, advanced jet grooming algorithms, and machine-learning trained discriminating algorithms for identifying the distinctive hadronic jets that develop from the decay of a Higgs boson into a pair of bottom quarks. An overview of LHC physics and the CMS detector is given to contextualize this work."], "keyword": ["Experimental Particle Physics"], "primary_title": "A Search for Exotic Particles that Decay into a Higgs Boson and a Photon with the CMS Detector at the CERN LHC", "uri": "https://repository.library.brown.edu/studio/item/bdr:39emhpgx/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:39emhpgx/"}, {"pid": "bdr:1129383", "object_type": "pdf", "abstract": ["All physical measurements are inherently noisy. In situations where signals are weak, for example, in the case of spectroscopy of weak emitters and particle localization experiments, low signal to noise is particularly challenging. In these cases, it is interesting to consider the measurement schemes that would optimize the amount of information obtained under time constraints. This thesis illustrates the design of experiments under low signal conditions in three different contexts. First, we demonstrate the enhancement in photoluminescence of up to two orders of magnitude from weak silicon defects emitters proximal to all-dielectric symmetry-broken high contrast gratings. An array of photonic devices with a variety of geometrical parameters which enhances light emission into particular wavelengths and directions by modifying the local density of states are characterized. The engineered dispersions are measured through automated energy momentum spectroscopy with an InGaAs camera, which imposes a constraint in measurement time, and PL lifetime measurements with a single photon avalanche diode. Next, we investigate the optimal measurement schemes in spectroscopy under low-light conditions with regard to the use of hardware binning of pixels in charge coupled devices. We question the default single-pixel measurement scheme by using statistical analysis with tools such as the Cram\u00e9r-Rao lower bound for unbiased estimators. The use of numerical techniques in pixel intensity reconstruction and peak localization in spectroscopy is also discussed. Finally, we apply these methods to a broader scientific challenge. Graduate school admission is a process complicated with inherently large variances and further restricted by limited data. With a usually long completion time, feedback information acquisition is very slow. We report a method and develop software tools for obtaining and analyzing academic outcome data for graduate students, resulting in generally an order of magnitude more data for strengthening the feedback mechanism and enabling a more thorough review of admission practices."], "keyword": ["Photonics"], "primary_title": "Experimental Design under Low Signal Conditions", "uri": "https://repository.library.brown.edu/studio/item/bdr:1129383/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:1129383/"}, {"pid": "bdr:918981", "object_type": "pdf", "abstract": ["Planetary atmospheres are governed by a complex interplay of chemical, radiative, and advective processes that yield an inherently three dimensional structure. Probing the three dimensional nature of exoplanet atmospheres is challenging without the capability to spatially resolve them. Here I present the results of applying a multi-dimensional approach to the characterization of exoplanet atmospheres utilizing a broad range of observational techniques and theoretical frameworks to explore the atmospheric composition and structure of transiting exoplanets. Each analysis was performed with an emphasis on ensuring robustness of scientific results by applying multiple methodologies and engaging a diverse cross sections of the community in collaboration. I present a set of Spitzer secondary eclipse observations of five different planets, anlayzed with several of the most common methods of intrapixel sensitvity correction to investigate the performance of each technique while also probing albedo and recirculation. I also present a community analysis of an HST Wide Field Camera 3 spectroscopic transit of WASP-63b probing chemical composition and providing evidence of possible disequilibirum chemistry. Finally, I discuss the analysis of a set of multi-epoch Spitzer secondary eclipse observations and phase curves of the canonical hot jupiters HD 209458b and HD 189733b at both 3.6 and 4.5 microns probing temporal variations in eclipse depth while also providing the first three dimensional thermal map of an exoplanet atmosphere."], "keyword": ["Extrasolar planets"], "primary_title": "A Multi-Dimensional Approach to the Characterization of Exoplanetary Atmospheres", "uri": "https://repository.library.brown.edu/studio/item/bdr:918981/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:918981/"}, {"pid": "bdr:919198", "object_type": "pdf", "abstract": ["As our knowledge of exoplanets continues to grow with further discoveries, we have gained a unique perspective on hot, gaseous planets close to their host star - known as \u201chot Jupiters.\u201d These planets\u2019 atmospheres lend themselves well to analyses due to their interaction with the light from their host star. However, not all of these planets are similar - it appears as though there exists a temperature beyond which the atmospheres of these planets begin to significantly change; planets in this regime are known as ultra-hot Jupiters. Such atmospheres appear to possess a temperature inversion possibly mediated by absorption and re-radiation of stellar light by metal oxides, such as titanium oxide (TiO) and vanadium oxide (VO), or ionized hydrogen (H\u2212). WASP-121 b, an ultra-hot Jupiter (T_eff > 2000 K), has been studied in the near-infrared by the Hubble Space Telescope\u2019s Wide Field Camera 3 (WFC3). Studying WASP-121 b using the Spitzer Space Telescope at 3.6 \u03bcm and 4.5 \u03bcm can lift degeneracies in models of ultra-hot Jupiters to better understand these inversions. I fit the full phase curve of WASP-121 b at both 3.6 and 4.5 \u03bcm using BATMAN and a sinusoidal flux variation model. I found Rp/Rs as 0.1223 \u00b1 0.0003 at 3.6\u03bcm, but 0.1241\u00b1 0.0004 at 4.5 \u00b5m. The eclipse depth was 4028\u00b1576 ppm at 3.6 \u03bcm, but 5003+72 ppm at 4.5 \u00b5m. I used SPIDERMAN to find that the nightside temperature was 1664 K in Channel 1 and 1643 K in Channel 2, while the change in temperature between the dayside and nightside, was 1629 K in Channel 1, but 2143 K in Channel 2. My results suggest that mechanisms other than gaseous VO, such as hydrogen ions (H\u2212) in the upper atmosphere, may cause the observed inversion. My results also provide evidence for the presence of carbon monoxide in WASP-121 b\u2019s atmosphere, perhaps due to a high C/O ratio. These results are the first steps in an extended investigation of ultra-hot Jupiters and their atmospheres. Further work will help refine models of upper-atmosphere absorption and re-radiation in ultra-hot Jupiters while identifying promising exoplanets and novel atmospheric phenomena to be studied in new detail by the upcoming James Webb Space Telescope."], "keyword": ["Extrasolar planets", "Photometry", "Atmosphere"], "primary_title": "Methods for Phase Curve Analyses of Exoplanet Atmospheres", "uri": "https://repository.library.brown.edu/studio/item/bdr:919198/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:919198/"}, {"pid": "bdr:919218", "object_type": "pdf", "abstract": ["We review some aspects of quantum chaos in a variety of systems. We begin with a general discussion of the out-of-time-ordered correlation function, the Maldacena-Shenker-Stanford chaos bound, and the spectral form factor. These ideas are then applied to different Hamiltonians in ordinary quantum mechanics to explore their properties. Additionally, we generalize an existing quantum mechanical calculation of the four-point out-of-time-ordered correlation function for Hamiltonians with discrete spectra to those with continuous spectra. Finally, we study some aspects of quantum chaos in the Sachdev-Ye-Kitaev model. We show that the large q limit of the SYK model yields the Liouville action, and we calculate the four-point function in this limit, showing that the out-of-time-ordered analytic continuation of this correlator saturates the chaos bound. We also calculate the spectral form factor for the SYK model and compare it to the Gaussian Unitary Ensemble random matrix theory analogue."], "keyword": ["Quantum Chaos", "Quantum field theory"], "primary_title": "Quantum Chaos in Simple Systems", "uri": "https://repository.library.brown.edu/studio/item/bdr:919218/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:919218/"}, {"pid": "bdr:919201", "object_type": "pdf", "abstract": ["Post-translational modifications (PTMs) on amino acids are extremely important to cellular processes as they alter protein properties, but their discovery and localization on novel proteins has proved a difficult and complex task. Modification leads to a mass increment or deficit to the naked amino acid weight, as phosphorylation of a serine residue, for example, adds 80 Da to the 87 Da mass of the natural amino acid. Because of this, mass spectrometry (MS) techniques have advanced the field but conventional MS methods remain expensive, slow and resource heavy. We are developing a technology that uses a nanopore ion source with a new ionization mechanism to transfer single ions directly from liquid into a vacuum chamber to be analyzed by mass spectrometry, potentially increasing the sensitivity of the process. This nanopore mass spectrometer has previously analyzed simple salts, and here we study the performance of the instrument with aqueous solutions of single amino acids and the tripeptide glutathione with its acetylated and nitrosylated modifications, as well as the electrospray mechanism underlying our nanopore ion source. We bias the pH of solutions below the isoelectric point of the solute tested to positively charge the amino acids and peptides. Our spectra show singly charged solute ions that are primarily unsolvated as tip size decreases, illustrating that our nanopore ion source deviates from the Taylor cone-jet model and most closely mimics the Ion Evaporation Model (IEM) of electrospray ionization (ESI) for biopolymer ejection. These findings provide an optimistic path towards developing a technique to sequence proteins and determine post-translational modifications at the single molecule level."], "keyword": ["Nanopores", "Mass spectrometry", "Post-translational modification"], "primary_title": "Use of a Nanopore Mass Spectrometer for Analysis of Peptides and their Post-Translational Modifications", "uri": "https://repository.library.brown.edu/studio/item/bdr:919201/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:919201/"}, {"pid": "bdr:93", "object_type": "pdf", "abstract": ["The experimental realization of a two dimensional quantum spin liquid has been eagerly sought since first proposed by Anderson in 1973. Recently, Cs2CuCl4, a frustrated 2D quantum antiferromagnet (QAF), has shown potential in this regard triggering immense interest, both experimentally and theoretically. Amongst these studies, different scenarios on the nature of the spin liquid phase were proposed and the presence of exotic magnetic phases in the ground state was noticed. To this date, many of these phases are still obscured and the nature of the spin liquid state remains unsettled. To investigate the above, we present 133Cs Nuclear Magnetic Resonance (NMR)measurements on Cs2CuCl4 at temperature down to 50mK and applied magnetic field up to 15 T. We first demonstrate that Cs NMR is an effective probe of the magnetism in the compound through experiments in the paramagnetic phase. Lower temperature NMR measurements as a function of the strength and orientation of the applied magnetic field provide the most complete picture of the different phases stabilized in Cs2CuCl4. The magnetic character of these phases is discussed in the context of the interplay between quantum fuctuations, frustration and the Dzyaloshinskii-Moriya (DM) interaction. Furthermore, we find evidence of three new phase transitions, as well as an unexpected angular dependence of the saturation field. These findings suggest that the accepted Hamiltonian requires modifications, such as additional DM interactions. In order to probe the nature of the spin liquid state, local magnetization and spin-lattice relaxation rate measurements were performed. A comparison with the result of a variational calculation using Gutzwiller-projected mean-field theory demonstrates the 2D magnetic behavior of the local magnetization. In addition, both temperature and magnetic field dependence of the spin-lattice relaxation rate suggests that the relevant low energy quasiparticle excitations obey fermionic statistics."], "keyword": ["NMR", "Cs2CuCl4", "spin liquid", "quantum magnetism", "2D frustrated lattice"], "primary_title": "Nuclear Magnetic Resonance Study of the Magnetism in the 2D Frustrated Quantum Heisenberg Antiferromagnet Cs2CuCl4.", "uri": "https://repository.library.brown.edu/studio/item/bdr:93/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:93/"}, {"pid": "bdr:yt9jgfaa", "object_type": "pdf", "abstract": ["Radiation damage in silicon sensors is a topic of the utmost importance for the next generation of High Energy Physics experiments, like CMS at the LHC. The damage mechanism from radiation is discussed, as well as, the parametrizations used to characterize said damage. Silicon diodes were characterized, irradiated, and annealed in order to study the change in the properties of the silicon during these processes. The results were consistent with other studies done on the subject."], "keyword": ["Particles (Nuclear physics)", "CMS", "Radiation", "Silicon diodes--Research"], "primary_title": "Radiation Damage in Silicon Diodes", "uri": "https://repository.library.brown.edu/studio/item/bdr:yt9jgfaa/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:yt9jgfaa/"}, {"pid": "bdr:t2rkufqn", "object_type": "pdf", "abstract": ["In this thesis, I develop transport theories and propose to probe certain types of novel quantum matter, such as topological insulators and quantum spin-orbital liquids, using transport methods. I first derive a transport theory based on the Redfield equation, which can describe the transport in weakly interacting systems. Comparisons between the results obtained from the Redfield equation and non-equilibrium Green's functions (NEGFs) show excellent agreement, validating its performance. Next, I propose to use resistively detected nuclear magnetic resonance (RDNMR) to probe the helical boundary states in topological insulators. The resistance change relies on the dynamically polarized nuclei on the boundary, which backscatter the edge modes once the nuclei are flipped or depolarized by a resonant radio frequency field. In a 3-D TI in the quantum Hall regime, due to the modulation of Overhauser field when nuclei are resonating, the Landau gap on the surfaces changes, which could also result in a RDNMR signal. Lastly, I study spin transport in a quantum spin-orbital liquid described by the Yao-Lee model using NEGFs. I demonstrate that in this model, the spin transport is analogous to the free electron transport in a mesoscopic conductor, and show that the spin current-spin bias relation is highly nonlinear in the gapless phase, while the spin current conductance is quantized in the chiral gapped phase if the contacts are wide enough. These spin transport calculations give different results from the previous published work, indicating the significance of non-equilibrium spin accumulation."], "keyword": ["condensed matter theory"], "primary_title": "Theory of Transport to Characterize Quantum Matter", "uri": "https://repository.library.brown.edu/studio/item/bdr:t2rkufqn/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:t2rkufqn/"}, {"pid": "bdr:9388a5nb", "object_type": "pdf", "abstract": ["Abstract of \u201cCorrections to the Geometrical Interpretation of Bosonization\u201c by Manfred Steiner, Brown University, February 2022 Bosonization is a popular technique for solving certain strongly-correlated electron systems especially in 1 dimension. Although in use for many years it has not been critically compared to equivalent systems composed of corresponding fermion operators. In this study I conducted a side by side comparison of bosonized and fermion-based systems. Expanding their coherent state representation at least to second order (O(u4)), of a displacement function uq(k) which has bosonic field character, a noticeable di\u21b5erence between pairing diagrams of bosonized and nonbosonized systems is apparent. The ratio of non-bosonized to bosonized pairings depends on the square of the upper momentum cut-o\u21b5. Extending the analysis to 2+1 dimensions shows a similar result to that observed in 1 dimension. An interpretation of the physical meaning remains somewhat speculative but fold formation of the Fermi surface leading to disconnected pieces of the latter may be involved. Coherent states represent deformed Fermi surfaces that are parametrized by the above mentioned displacement function uq(k). To define them in terms of positive and negative deviations from the Fermi surface, a system of geometrical distortions of the Fermi surface was developed that maintained the total area covered by the Fermi sea independent of the magnitude of the surface distortions in agreement with Luttinger\u2019s theorem. Fluid dynamic considerations made it possible to show that the aspect ratio of the system could be changed, e.g. from that of a circle to an ellipse. The expectation value of the number operator as a crucial indicator of excitations close to the Fermi surface was examined in detail and as expected found to be a function of the displacement function of coherent states. The change in energy from a distorted to an undistorted Fermi surface was not dependent on the characterization of the particles as fermions or bosons. An in depth examination of the area that is very close to the Fermi surface which also includes the 1-dimensional case of two Fermi points reveals a universal behavior of the low energy excitations, quasiparticles, which is best described by Airy functions. Application of these functions to the construction of the distribution curve for the number operator revealed a distinct similarity to the characteristics that make the geometrical representation so unique."], "keyword": ["Condensed Matter Physics, Bosonization"], "primary_title": "Corrections to Geometrical Interpretation of Bosonization", "uri": "https://repository.library.brown.edu/studio/item/bdr:9388a5nb/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:9388a5nb/"}, {"pid": "bdr:919034", "object_type": "pdf", "abstract": ["Moore\u2019s law, which has governed semiconductor technology for decades, has been increasingly challenged in recent years. Rather than relying on electron charge currents, spintronics-based logic and memory devices are recognized as promising candidates for post-CMOS electronics. In this thesis, we present three advancements in the field of spintronics: efficient spin current generation via giant spin Hall effect (GSHE), field-free magnetic switching through spin-transfer-torque, and the measurement of magnetic domain-wall resistance (DWR). Since the discovery of GSHE, the spintronics research and development communities are actively searching for solids with a large spin Hall angle, which is a key parameter in many applications. We observed a record-high spin Hall angle of 63.5% in the bulk limit of \u03b2-W solid at room temperature and a weak temperature dependence of spin Hall angle. Additionally, we also studied the magnetization, magnetic anisotropy, electrical transport, spin diffusion and interfacial spin current transmission in this exemplary GSHE system over a broad temperature range of 10 to 300 K. Despite the GSHE, one challenge in application is the requirement of an external biasing field in order to deterministically control the perpendicular magnetization vector. The generation of this biasing field either complicates the device structure or consumes energy. We introduce a method of field-free switching in a structure of FM/NM/FM, where the central NM is a GSHE non-magnetic metallic layer. The bottom FM with an in-plane magnetization vector exerts a biasing field on the top FM which has an out-of-plane and switchable magnetization vector. We demonstrate complete, deterministic, and reliable field-free switching, as well as a low critical switching current density of 10^6 A/cm2. Finally, we are focused on half-metallic CrO2 epitaxial nanowire with nearly 100% spin polarization. The nanostructure with an asymmetrical neck of 50 nm provides us with a capability to generate and propagate a domain wall. By comparing sample resistance state with and without domain wall at zero field, we report the first direct-observation of DWR in half-metal. Using Levy and Zhang\u2019s model, CrO2\u2019s spin asymmetry \u03c1\u2191\u2044\u03c1\u2193 is estimated to be as high as 478 \u00b1 45 at 5 K, a very large number attesting the half-metallic electronic structure of CrO2. These advancements represent important milestones in the development of spintronics, particularly in the basic understanding of electron transport in solids with strong spin-orbit interaction or strong spin polarization. They also benefit future magnetic memory devices and ultrasensitive magnetic sensors."], "keyword": ["spintronics", "Condensed matter--Magnetic properties"], "primary_title": "Giant Spin Hall Effect in the Bulk Limit of \u03b2-Tungsten and Magnetic Domain-Wall Resistance in Half-Metallic Chromium Dioxide", "uri": "https://repository.library.brown.edu/studio/item/bdr:919034/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:919034/"}, {"pid": "bdr:919113", "object_type": "pdf", "abstract": ["Studies of the superconductor-insulator transition (SIT) arose from the investigations of metal-insulator transitions (MIT) in the two dimensional limit. The SIT is a typical example of a quantum phase transition (QFT) which involves the change of a quantum ground state caused by tuning the parameters in a Hamiltonian. This transition is realized in several different systems due to different physical effects including especially localization effects induced by disorder or Coulomb interactions. The former creates an insulator due to Anderson localization and the latter creates a Mott-like insulator. One of the central questions in the SIT field is whether superconductivity is completely destroyed on the insulating side of the transition. In our lab, thin films are prepared on nano-porous anodic aluminum oxide (AAO) substrates. Little-Parks oscillations are detected in their insulating phase providing direct evidence for Cooper pairs persisting across the SIT. The corresponding insulating state near the critical point is called a Cooper Pair Insulator (CPI). Another salient feature of the SIT investigated in our lab, as well as with many other experimental platforms, is the simply activated low temperature transport of the Cooper pair insulator. The activation energy characterizes the barriers that localize the Cooper pairs. It vanishes at the SIT. In my presentation, I will talk about a unique method to investigate the microscopic origins of the activation energy. We doped the CPI with magnetic impurities, which strongly affects the superconducting gap. The behavior of the activation energy shows that extra dissipative processes accompany Cooper pair transport. These processes, which involve virtual quasiparticle tunneling, screen the localizing Coulomb interactions to reduce the energy barrier. This model also explains the transport behavior in magnetic field where a giant magnetoresistance peak is observed."], "keyword": ["Low temperatures", "Superconductivity", "quantum phase transition", "superconductor insulator transition"], "primary_title": "Cooper Pair Insulator State Near Superconductor-Insulator Transition Probed by Magnetic Impurity", "uri": "https://repository.library.brown.edu/studio/item/bdr:919113/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:919113/"}, {"pid": "bdr:919112", "object_type": "pdf", "abstract": ["Most motile bacteria propel themselves through fluid by rotating corkscrew-like filaments called flagella. Understanding the details of how and why bacteria move the way they do can inform our tactics in the fight against disease and teach us how to overcome engineering difficulties at the microscale. Some bacteria, such as those in the open ocean, may live their entire lives in bulk fluid, but most interact with surfaces. A surface alters nutrient availability and changes how bacteria move. Many species actively adapt their behavior in the presence of a surface and some even make it their specialty. Examples of surface-centered design in bacteria include the growth of extra flagella to enable P. mirabilis to swarm across a gel, the remarkably strong holdfast structure that allows C. crescentus to anchor itself even to the smoothest glass, and the dense composite biofilm colonies formed by P. aeruginosa that confer antibiotic resistance and provide a steady source of infectious, colonizing cells. Several specific types of bacterial surface motion have been described in the literature. These include flagellum tethering, twitching, sliding, slingshotting, and gliding. We describe another mode of motility, body-tethered rotation, which has potential implications for the bacteria in terms of obtaining nutrients and initiating biofilms. It also places restrictions on the conclusions that can be drawn about the flagellar motor from these tethered cells. We describe several ways in which body tethering can be distinguished from flagellum tethering, and demonstrate this behavior for multiple uni-flagellated species. In addition, we explore the production of the torque required to rotate body-tethered cells. The transmission of the motor\u2019s torque is complicated by the angle the flagellum makes with the cell body as well as its interaction with the surface. We demonstrate and discuss puzzling oscillations in the resulting torque, as well as the curious case of cells that rotate in only one direction, but with switching between multiple torque states. These findings have bearing on important biological issues such as the ability of bacteria to consume resources and efficiently utilize their metabolic energy. They are also relevant to engineering applications such as microscale mixing and micro robotics."], "keyword": ["Pseudomonas aeruginosa", "bacterial motility", "Caulobacter crescentus", "Vibrio alginolyticus"], "primary_title": "The tethered motion of uni-flagellated bacteria", "uri": "https://repository.library.brown.edu/studio/item/bdr:919112/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:919112/"}, {"pid": "bdr:919135", "object_type": "pdf", "abstract": ["Abstract of \u201cElectrons and cavitation in liquid helium.\u201d by Yiming Yang, Ph.D., Brown University, May 2019. Liquid helium is an ideal material for the study of the cavitation process due to its high purity and simple interatomic interaction. Cavitation can result from superheating the liquid or reducing the pressure below the saturated vapor pressure. An often-used way to produce a negative pressure relative to the saturated vapor pressure is to generate an acoustic wave with a piezoelectric transducer. It has been found that the presence of electrons in the liquid reduces the critical pressure for nucleation to occur. In this work, we first studied the homogenous nucleation in liquid helium. Then we investigated in detail the effect of electrons on nucleation of bubbles in liquid helium. Electrons were introduced by a radioactive beta source and a negative pressure was achieved by focusing sound from a hemispherical transducer If an electron is near the focus and the negative going pressure swing exceeds a critical value, a cavitation bubble is produced which can be detected by light scattering. Three distinct critical pressure swings have been measured and studied as a function of temperature. The first, also the largest, corresponds to cavitation resulting from the application of a reduced pressure to liquid in which an electron bubble is already present. The theory for explaining this critical pressure has been well established. The second is the critical pressure swing needed to lead to cavitation when an electron enters the liquid at a time and place where there is already a reduced pressure. We have attempted to make theoretical predictions for this critical pressure. However, due to several complications, the agreement with our experimental data is not very good. The third critical pressure swing is very small and we have no explanation for its origin."], "keyword": ["Condensed matter", "Low temperatures"], "primary_title": "Electrons and Cavitation in Liquid Helium", "uri": "https://repository.library.brown.edu/studio/item/bdr:919135/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:919135/"}, {"pid": "bdr:919097", "object_type": "pdf", "abstract": ["The application of a second-order equal-time cumulant expansion (CE2) or, equivalently, the quasilinear approximation (QL) to planetary-scale flows has shown promise. This is in part because planetary-scale coherent structures are driven by direct interactions between the most unstable scales of turbulence with the mean-field rather than an inverse energy cascade. A relatively unexplored yet promising application of CE2/QL is to planetary boundary-layer turbulence, in which the flow of energy is in the opposite direction, from the horizontal mean field to a spectrally nonlocal instability at which coherent structures emerge. These scales cannot be resolved in Earth system models, yet the coherent structures have transport properties that often require specialized sub-grid models. This thesis studies generalized applications of CE2/QL to such planetary boundary layers using two innovations. First, in order to make the application of CE2 to nonhydrostatic three-dimensional flows computationally tractable, the combination of the horizontally averaged quasilinear approximation with a truncated model, defined by a Galerkin projection of the equations of motion onto a small subset of energetically optimized modes, is studied. It is found that basis truncation can improve upon full-basis QL/CE2 transport and turbulent-kinetic-energy statistics by breaking up wave-like structures while simultaneously speeding up execution. Second, in order to quasilinearize around coherent structures in the boundary layer, ensemble-averaged QL and CE2 are explored. It is found that ensemble CE2/QL can capture coherent structures in the mean-field and reproduce nonlinear flow statistics, the extent of which is observed to be associated with the dimensional and topological freedom of the structures to drift. Robust nonlinear coherent structure emergence in the mean field can isolate the essential part of the structure from fluctuations but also makes reduced modeling inefficient. Intermediate behavior at finite ensemble sizes serves for better reduced modeling. The mechanism of mean-field emergence is discussed. The continued development and combination of such innovations should lead to badly needed generalized sub-grid modeling frameworks applicable to a diversity of coherent structures found in planetary boundary-layer turbulence."], "keyword": ["Turbulence", "ocean modeling"], "primary_title": "Quasilinear Modeling of Planetary Boundary-Layer Turbulence", "uri": "https://repository.library.brown.edu/studio/item/bdr:919097/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:919097/"}, {"pid": "bdr:919084", "object_type": "pdf", "abstract": ["Gradients of voltage, pressure, temperature, and salinity can transport objects in micro- and nanofluidic systems by well known mechanisms. Relatively little experimental work has previously been done to explore the behavior of particles in a viscosity gradient. This thesis presents observation, analysis, theory, and simulation of a new nanofluidic transport phenomenon whereby a gradient in liquid viscosity causes an ionic current to flow inside a glass nanofluidic channel. We studied ionic transport inside nanofluidic devices in which we set up a controlled viscosity gradient by pumping fluids of known viscosity past either end of a channel with no applied voltage, pressure, or salinity gradient. We measured currents on the order of 10 to 100 pA flowing in the direction of lower viscosity through the 200 \u03bcm-long and 150 \u03bcm-wide channels using fluids with viscosities that varied from 1 to 5 mPas. The nanofluidic devices enabled us to thoroughly characterize the current's dependence on experimental parameters like the viscosities of the liquids, the length of the channel, the surface charge density, and the bulk salinity. The currents increased linearly with the gradient of the inverse viscosity and the channel's surface charge density, but were insensitive to the bulk salinity. We propose a simple model of these viscosity-driven currents in which mobile counterions screening the channels' surface charge drift with a speed equal to the gradient in their diffusivities. This model describes our data well and explains the microscopic origin of the effect. Drift in a viscosity gradient is a consequence of multiplicative (state-dependent) noise, which refers to the dependence of a particle's thermal fluctuations on its position. The mathematical It\u00f4-Stratonovich dilemma arises because one must choose whether the size of each stochastic step corresponds to the viscosity at the beginning of the step (It\u00f4 convention), the middle of the step (Stratonovich convention), the end of the step (isothermal convention), or somewhere in between. This seemingly insignificant choice has measurable consequences, as only the isothermal convention explains the existence and direction of the currents we measured. We present simulations which illuminate this surprising fact and show how the drift of ions arises from particles taking larger average steps when they move in the direction of decreasing viscosity."], "keyword": ["Physics", "Biophysics", "Nanofluids"], "primary_title": "Electrokinetic Current Driven by a Viscosity Gradient", "uri": "https://repository.library.brown.edu/studio/item/bdr:919084/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:919084/"}, {"pid": "bdr:919082", "object_type": "pdf", "abstract": ["Despite numerous attempts at explaining and experimentally probing dark matter, thus far only its gravitational e\ufb00ects have been observed. These gravitational e\ufb00ects leave us blind to the true nature and structure of the dark sector. However, recent advances in experimental techniques have opened new paths for exploration. In particular, this thesis investigates the use of primordial circular polarization, electron electric dipole moments, and modi\ufb01cations to gravitational waveforms in constraining families of dark sector models."], "keyword": ["Cosmology", "Dark matter (Astronomy)"], "primary_title": "Theoretical and Observational Windows into the Dark Sector", "uri": "https://repository.library.brown.edu/studio/item/bdr:919082/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:919082/"}, {"pid": "bdr:fuh6mw2m", "object_type": "pdf", "abstract": ["Cosmology in the 21st Century has evolved into a precision science. While \u039bCDM has been established as the standard cosmological model there are still unanswered questions and in this thesis we study an array of these open problems. In the first part of this thesis we apply constraints on self-interacting dark matter models in a thick dark disk scenario using observations from the IceCube Neutrino Observatory. In the second part of the thesis we study the cosmological implications of decaying dark matter and their potential role as a solution to the H_0 and S_8 tensions. The third part is about the merger rate of Primordial-Astrophysical Black hole binary systems and the interpretation of the origin of the gravitational wave event GW190814 as such. In the final part, we show a proof of principle of using machine learning techniques to detect and localise dark matter substructure in the Milky Way using astrometric data."], "keyword": ["Cosmology", "Dark matter (Astronomy)"], "primary_title": "Select Problems in Modern Cosmology", "uri": "https://repository.library.brown.edu/studio/item/bdr:fuh6mw2m/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:fuh6mw2m/"}, {"pid": "bdr:myhcbfhx", "object_type": "pdf", "abstract": ["One of the most special fractional quantum Hall (FQH) states has the filling factor \u03bd=5/2. It is believed that the formation of this state and other even-denominator FQH states requires a superconducting pairing between composite fermions. Different pairing mechanisms lead to different possible candidates to describe the system. Interestingly, some of the proposed candidates host non-Abelian excitations, which may be an important building block for topological quantum computation. However, the nature of the \u03bd=5/2 FQH state is still under debate. In this thesis, different topological orders for even-denominator FQH states are examined. We show that they can be uniformly described by the Kitaev's sixteenfold way. This uniform description allows us to predict different experimental signatures to identify topological orders in \u03bd=5/2 and \u03bd=1/4 FQH states. For the \u03bd= 5/2 state in GaAs heterostructure, the PH-Pfaffian order has received a strong support from the thermal Hall conductance experiment. However, the idea of partial equilibration on the sample edge leads to the possibility of other interpretations. Based on this idea, we introduce a mechanism to reconcile the thermal conductance data with the numerically supported anti-Pfaffian order. Although our mechanism requires unlikely but not impossible assumptions, the same mechanism allows us to explain the experimental results in \u03bd=8/3 FQH state naturally and makes a dramatic prediction at \u03bd= 8/5. Lastly, we examine theoretically heat transport and the temperature dependence of the thermal equilibration length at low temperature. We argue that the length satisfies a 1/T^2 scaling law in most of the topological orders. Meanwhile, a 1/T^4 law is predicted for the equilibration length in PH-Pfaffian order and negative-flux Read-Rezayi states. As a result, a dramatic growth of thermal Hall conductance at low temperature may identify these special topological orders."], "keyword": ["Fractional Quantum Hall Effect", "Condensed matter", "Anyons", "Interferometry"], "primary_title": "Topological Orders in Fractional Quantum Hall Effect: Their Identification and Thermal Equilibration", "uri": "https://repository.library.brown.edu/studio/item/bdr:myhcbfhx/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:myhcbfhx/"}, {"pid": "bdr:msftgk42", "object_type": "pdf", "abstract": ["How to effectively extract important information and conduct meaningful analyses from large collections of data is an essential problem we need to tackle in order to assist various decision-making tasks in our daily life. Due to its versatile neural network structure and powerful representation learning capacity, deep learning provides an expressive approach to handling massive quantities of data systematically. This dissertation presents novel deep learning algorithms for two major real-world applications: (1) healthcare mortality forecasting and (2) information retrieval. I will first describe my Deep Ordinal LSTM models for multi-period mortality prediction from clinical claims data for patients diagnosed with congestive heart failure. These models yield consistent, effective and reliable performance across various experiment settings. Then I will demonstrate how to incorporate profound concepts from physics into neural models for information retrieval tasks. In order to aid neural model learning, I build two general listwise learning frameworks: PoolRank and ExpertRank, inspired by the concepts of mechanical equilibrium and coarse graining. These two novel frameworks are applicable to arbitrary neural retrieval models and still provide competitive and robust learning performance. I will finish with an overview of an end-to-end Cross-Lingual Arabic Information REtrieval (CLAIRE) system that helps us to bridge the language barrier between collections and user queries."], "keyword": ["Physics", "Information storage and retrieval systems", "Bioinformatics", "Deep Learning"], "primary_title": "Data-Driven Reasoning for Personalised Healthcare Mortality Forecasting & Physics-Inspired Information Retrieval Systems", "uri": "https://repository.library.brown.edu/studio/item/bdr:msftgk42/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:msftgk42/"}, {"pid": "bdr:ng7edrhp", "object_type": "pdf", "abstract": ["Discovering dark matter (DM) and establishing its cosmological properties within the Cold Dark Matter (CDM) framework has been one of the major successes of 20th century physics. On the other hand, questions regarding the particle nature of DM, its interactions with ordinary matter beyond gravity, and its local distribution in the Milky Way galaxy remain unresolved. Recently, however, astrometric data from the Gaia mission, and well-motivated particle DM models have hinted at a novel DM phenomenology in our neighborhood, or equivalently at small length scales. As a result, there is an unprecedented program, often referred to as astroparticle physics, underway to simultaneously infer DM\u2019s astrophysical and particle physics properties. Such a research direction also provides an opportunity to empirically test the CDM framework on small scales, potentially shedding light on a new paradigm for DM physics. In this dissertation, I introduce a new approach to infer the astroparticle phenomenology of DM by applying data-driven techniques to the Gaia Data Release 2 (DR2) catalog in three distinct scenarios. First, I examine the ability of dynamical methods to estimate the local DM density, especially in the presence of exotic DM substructure such as a thin dark disk co-rotating with the Milky Way\u2019s baryonic disk. Second, I systematically study how uncertainties in DM's astrophysical distribution affects the interpretation of its particle physics parameters at upcoming nuclear and electron scattering experiments on Earth. Of particular interest is the effect of DM substructure, namely debris flow and streams, in the solar neighborhood from the recent mergers of the Sausage and Sequoia dwarf galaxies. Finally, I conclude with a discussion of general constraints on a possible relativistic DM origin of the excess in low energy electron recoil events recently reported by the XENON1T experiment. These results punctuate how searches for DM phenomenology in the coming decades will be greatly aided by complementary measurements from cosmological and astrophysical surveys as well as terrestrial direct detection experiments."], "keyword": ["Astrophysics", "Dark matter (Astronomy)", "Direct detection"], "primary_title": "Space Invaders -- Astroparticle Searches for Dark Matter Physics", "uri": "https://repository.library.brown.edu/studio/item/bdr:ng7edrhp/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:ng7edrhp/"}, {"pid": "bdr:sp7s5nxu", "object_type": "pdf", "abstract": ["Since the discovery of the Higgs boson in 2012, significant efforts have been put into establishing its coupling to fermions, which is an essential feature of the Higgs boson in the standard model of particle physics. Although the Higgs boson has the largest branching fraction for a decay into bottom quarks, the measurements in this decay mode have to rely on associated production with vector bosons to overcome the overwhelming QCD jet backgrounds. This thesis presents a novel approach that searches for inclusive $\\mathrm{H}\\to\\mathrm{b}\\overline{\\mathrm{b}}$ decays using jet substructure variables and a b tagging technique based on a deep neural network. This approach explores Higgs boson production at high transverse momentum, which is a complementary phase space region to that in conventional measurements. Results are compared with the latest theoretical predictions at full next-to-leading order accuracy, including finite top quark mass effects. The data sample was collected by the CMS experiment at the LHC at $\\sqrt{s}=13~\\mathrm{TeV}$, and corresponds to an integrated luminosity of $137~\\mathrm{fb}^{-1}$. The method is validated with $\\mathrm{Z}\\to\\mathrm{b}\\overline{\\mathrm{b}}$ decays. For a Higgs boson mass of $125~\\mathrm{GeV}$, an excess of events above the expected background is observed (expected) with a local significance of 2.54 (0,71) standard deviations. The corresponding signal strength is measured to be $\\mu_\\mathrm{H} = 3.68 \\pm 1.20(\\mathrm{stat})_{-0.66}^{+0.63}(\\mathrm{syst})_{-0.46}^{+0.81}(\\mathrm{thy})$ with respect to the standard model predictions. Additionally, an unfolded differential cross section, as a function of the Higgs boson transverse momentum is presented."], "keyword": ["LHC", "CMS Experiment", "Higgs bosons", "btagging"], "primary_title": "Inclusive Search for a Lorentz-Boosted Higgs Boson Decaying into Bottom Quarks", "uri": "https://repository.library.brown.edu/studio/item/bdr:sp7s5nxu/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:sp7s5nxu/"}, {"pid": "bdr:szkh2twr", "object_type": "pdf", "abstract": ["Bacterial swarming is one of the motility types where groups of bacteria use flagella to migrate swiftly on a wet surface. Physically, swarming is a natural example of active matter. Due to high cell density, bacterial cells in the swarm collide and align with each other, forming jets and swirls. Swarming is associated with bacterial pathogenesis and antibiotic resistance. Swarming is also known to be a phenotype inversely regulated with biofilm formation. Herein, we report a study on the biophysical properties of a novel swarming bacterial strain Enterobacter sp. SM3. When confined by PDMS microwells of specific sizes mounted on an agar surface, SM3 under swarming condition exhibits a \u201csingle-swirl\u201d motion pattern distinct from \u201cmulti-swirls\u201d formed by its concentrated planktonic counterpart. We hypothesized that a \u201crafting behavior\u201d of the swarming bacteria upon dilution might account for the motion pattern difference. We verified the conjecture via numerical simulations where swarming cells are modeled with stronger cell-cell alignment. The simulations indeed produce single swirls for stronger alignments and multiple swirls as the alignment strength is tuned down. In addition to the biophysical property, SM3 is also found to have probiotic effect against intestinal inflammation due to its swarming phenotype. We find that bacterial swarmers frequently emerge during intestinal stress and SM3 was isolated from colitic mouse feces as a dominant swarming strain. SM3, in contrast to its swarming-deficient, but swimming-competent isogenic strains abrogated intestinal inflammation in mice. Treatment of colitic mice with SM3, but not its mutants, enriched beneficial fecal anaerobes belonging to the family of Bacteroidales S24-7. In vitro co-culture assay between S24-7 and SM strains together with the race assay on tissue implies that bacterial swarming might add advantage to SM3\u2019s access to S24-7 in the intestines and the symbiosis of the two results in the protection effect. These findings suggest a new paradigm in which intestinal stress allows for the emergence of swarming bacteria, which can in turn heal intestinal inflammation."], "keyword": ["Bacteria", "bacterial motility", "swarming"], "primary_title": "A Novel Swarming Bacterial Strain Exhibits Unique Biophysical and Probiotic Properties", "uri": "https://repository.library.brown.edu/studio/item/bdr:szkh2twr/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:szkh2twr/"}, {"pid": "bdr:9rsekz9t", "object_type": "pdf", "abstract": ["This project's primary objective is to apply a quantum device called the magnetic tunnel junction (MTJ) for ultrasensitive magnetic field sensing. Towards this goal, we have systematically improved the MTJ system using novel physical ideas. Firstly, by optimizing the magnetron sputtering conditions of the magnetic flux concentrator (MFC), we managed to enhance the field detectability of MTJ to unprecedented 30 pT/\u221aHz at 10 kHz. As another way to boost sensitivity, we have also tuned the magnetic anisotropy in the MTJ free layer, where an interfacial perpendicular magnetic anisotropy (PMA) is induced. By tuning PMA with temperature, a compensation between PMA and demagnetization energy enhances the MTJ sensitivity to 1.2 %/Oe. Besides, an interesting voltage-dependent random telegraph noise is discussed. As the MTJ sensitivity is greatly enhanced by MFC and PMA, the intrinsic hysteresis still prevents MTJ from detecting small fields. Therefore we have attempted to eliminate the hysteresis at a fundamental level using a superparamagnetic free layer. We experimentally observed a transition from ferromagnetic to superparamagnetic states by raising the temperature, and the sensor in the latter state is non-hysteretic with good sensitivity. We have also resorted to the vortex magnetic states, where a topologically protected vortex magnetization in the MTJ free layer can evolve without hysteresis. The generation of vortex magnetization was revealed using the MUMAX simulation package first. We then experimentally fabricated vortex MTJ sensors, with outstanding sensing performances such as a sensitivity of 0.3 %/Oe, a thermal stability of 400 ppm/K, and an extensive dynamic range of 200 Oe. In brief, we have used MFC and PMA as methods to raise the sensitivity of MTJ. We have taken advantage of the superparamagnetic effect and vortex magnetic states to eliminate ferromagnetic hysteresis. From these results, we have generalized the scaling relation between the magnetic sensitivity and noise of MTJs in the ferromagnetic, superparamagnetic and vortex states, to propose that hysteresis elimination is indispensable for a favorable linear scaling. To demonstrate the application prospect for MTJ sensors with our improvements, we have developed a magnetic gradiometer prototype and applied the device in the wellbore crack detection. The gradiometer can detect defects with a large stand-off distance of 22 mm."], "keyword": ["spintronics", "Condensed matter--Magnetic properties"], "primary_title": "Ultrasensitive and Hysteresis-free Magnetic Sensing using Magnetic Tunnel Junctions", "uri": "https://repository.library.brown.edu/studio/item/bdr:9rsekz9t/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:9rsekz9t/"}, {"pid": "bdr:ayh954ds", "object_type": "pdf", "abstract": ["Spin dependent electron transport is the basis of spintronics which is a new type of electronics relying on electron spins. This thesis presents studies on the electron magnetotransport in nanostructures and devices with enhanced spin-dependent properties. Specifically, we studied the magneto-transport and magnetic characteristics in 100% spin polarized half metals and in materials with strong spin orbit coupling. According to the two spin current channel theory, impact of spin textures on electron transport is maximized in half metals. We quantify the spatial non-uniformity of spin textures as the spin curvature. We measured the magneto-transport in the half metallic CrO2 nanostructures and calculated the corresponding spin curvatures from the simulated spin maps. We uncovered a correlation between the spin curvature variation and the magnetoresistance (MR). When the external field is low (< 0.1 T), MR depends linearly on the spin curvature change. We investigated the domain wall resistance (DWR) in CrO2 as an example of systems with extreme spin curvature. The domain walls are induced nearby the nanoscale constrictions through external magnetic fields. We observed that the domain wall induced MR scales according to S^-1.87, where S is the cross-sectional area of the constriction. This implies that MR can be as high as 100% when S is reduced to 150 nm2. The enhancement of MR when the constriction width decreases is possibly due to the ballistic electron transport through the constriction. The large MR in a simple CrO2 nanostructure is a testimony of the importance of high spin polarization in spintronics. The second part of our studies focuses on the giant spin Hall effect (SHE), which has been discovered in metallic materials with strong spin orbit coupling. We studied the enhanced SHE in the TaxW1-x alloy and the current induced magnetic switching in CoFeB/IrMn/CoFeB system. We have obtained the structural phase diagram of TaxW1-x in the full composition range from x = 0 to x = 1 and at various thicknesses. Alloying effectively increases the spin Hall angle (SHA) in both the beta and alpha phase of TaxW1-x. In TaxW1-x, the SHA is in the range of -0.06 to -0.23, which is about one order of magnitude larger than that in alpha-W and alpha-Ta. The maximum SHA (SH = -0.59) has been obtained in beta-phase 5.3 nm-thick Ta0.25W0.75. It is the largest SHA ever observed in metals at room temperature, providing an excellent candidate for spintronics applications in magnetic memory or spin logic devices. The linear dependence of SHA on resistivity in TaxW1-x provides strong evidence that the SHE in TaxW1-x alloy is dominated by the intrinsic mechanism and quantum side jump. Finally we have achieved zero field current-induced magnetic switching in CoFeB/IrMn/CoFeB system. IrMn plays the dual role as the material that generates spin current through SHE, and as the antiferromagnetic material that couples with the adjacent ferromagnetic material to provide the exchange biasing field. We modeled the switching process based on the randomly distributed direction of exchange bias in each grain of the polycrystalline IrMn thin film. Our model successfully explains the continuous and incomplete switching at zero field and is consistent with the magneto-optic Kerr effect microscopy images measured in the switching process."], "keyword": ["Physics", "Magnetism"], "primary_title": "Electron Magneto-transport in Nanostructures with Enhanced Spin-dependent Properties", "uri": "https://repository.library.brown.edu/studio/item/bdr:ayh954ds/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:ayh954ds/"}, {"pid": "bdr:nwqbzmrw", "object_type": "pdf", "abstract": ["Accurately measuring the masses of galaxy clusters is necessary if we are to use galaxy clusters as dark matter and dark energy probes. Gravitational lensing provides an approach to measuring the mass of a cluster without assumption about intrinsic dynamics. In this dissertation we study two questions: 1) How to improve current cluster lensing mass measurement pipelines and prepare for near future surveys, for example the Rubin Observatory Legacy Survey of Space and Time (LSST), where percent-level systematics become important in ensemble studies? 2) How to use the LSST Science Pipelines and LSST-like instruments to study clusters, especially a nearby sample that have not been well studied by lensing, to prepare for and compare with the LSST? For 1), we consider the cluster blending issue in the LSST, where the light from cluster galaxies contaminates the shape measurement of background galaxies. We simulated ensembles of clusters and backgrounds using stamps of isolated galaxies and distributions from the Hubble Space Telescope surveys. For the gold sample in LSST Y10 observation, results show that on average the blending causes a decrease in measured reduced-shear g by about 1% for a representative mid-redshift spherical cluster, and the effect grows with true g and the number density of cluster galaxies nonlinearly. A two-galaxy model verifies that the mean blending effect is shear-dependent. We extended our study by building image simulations using more realistic catalogs from validated N-body simulations and found similar results. For 2), we present the early science results of the ongoing Local Volume Complete Cluster Survey that uses the Dark Energy Camera to map the dark matter distribution and galaxy population in 107 low-redshift X-ray luminous clusters which are not obscured by the Milky Way. The survey reaches LSST Y1-2 depth. We process the data using the LSST Science Pipelines and analyze the results using our pipeline, and the catalogs and analysis tools will be compatible with the LSST. We demonstrate their performance using three clusters: A3911 shows agreement between lensing and baryon maps while A3921 has discrepancies because of its merging state, and A85 gives similar lensing results to previous studies."], "keyword": ["Physics, Astrophysics, Galaxy Clusters, Cosmology", "Dark matter (Astronomy)", "Gravitational lenses", "Dark energy (Astronomy)"], "primary_title": "Studies of Gravitational Lensing Mass Measurements of Galaxy Clusters Using Simulations and Observations", "uri": "https://repository.library.brown.edu/studio/item/bdr:nwqbzmrw/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:nwqbzmrw/"}, {"pid": "bdr:fapuppz7", "object_type": "pdf", "abstract": ["Radio-frequency interference detection and flagging is one of the most difficult and urgent problems in 21 cm Epoch of Reionization research. In this work, we present \u03c7^2 from redundant calibration as a novel method for RFI detection and flagging, demonstrating it to be complementary to current state-of-the-art flagging algorithms. Beginning with a brief overview of radio interferometry and an overview of the Murchison Widefield Array, we then continue into a discussion of redundant calibration and the meaning of the \u03c7^2 metric, finally demonstrating a two-step RFI flagging algorithm which uses the values of this metric to detect faint RFI. We find that roughly 27.4% of observations have RFI from digital television channel 7 detected by at least one algorithm of the three tested: 18.0% of observations are flagged by the novel \u03c7^2 algorithm, 16.5% are flagged by SSINS, and 6.8% are flagged by AOFlagger (there is significant overlap in these percentages). Of the 27.4% of observations with detected DTV channel 7 RFI, 37.1% (10.2% of the total observations) are detected by \u03c7^2 alone, and not by either SSINS or AOFlagger, demonstrating a significant population of as-yet undetected RFI. We find that \u03c7^2 is able to detect RFI events which remain undetectable to SSINS and AOFlagger, especially in the domain of long-duration, weak RFI from digital television. We also discuss the shortcomings of this approach, and discuss examples of RFI which seems undetectable using \u03c7^2 while being successfully flagged by SSINS and/or AOFlagger."], "keyword": ["Radio interferometers", "Radio--Interference"], "primary_title": "A Novel Radio-Frequency Interference Flagging Technique for Radio-Interferometric Data from the Murchison Widefield Array", "uri": "https://repository.library.brown.edu/studio/item/bdr:fapuppz7/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:fapuppz7/"}, {"pid": "bdr:rybgpsy5", "object_type": "pdf", "abstract": ["Trivalent lanthanide ions in crystals retain much of their behavior as free ions due to their 4f valence orbitals being shielded by the 5s and 5p closed shells. This shielding allows a large part of their spectrum to be understood through the splitting of f^n configurations, and a Hamiltonian similar to one describing a multi-electron ion can effectively explain their spectroscopy. The Hamiltonian provides an expansive view of the electronic structure of trivalent lanthanide ions, producing approximate energies and wavefunctions over a range as large as 10^5 cm^-1 and describing up to a few thousand states. Revisiting this semi-empirical Hamiltonian is timely and could help navigate the complexities of lanthanide ions as complex quantum objects. The understanding of lanthanide ions has been developed by numerous researchers in the latter half of the 20th century. Their results, scattered across decades, are revisited here with necessary corrections. This dissertation includes a repository of code written in the Wolfram language, named qlanth, to preserve and refine our understanding of lanthanide ions in crystals. The dissertation argues four main theses: 1. The electronic structure calculation of lanthanide ions in crystals has deficiencies and errors that need modern solutions, including errors in tabulated files, omission of spin-spin magnetic interaction, opacity of the code used, rounding errors, and incorrect signs in the crystal field description. 2. Approximate eigenvectors of lanthanide ions in crystals provide a more useful description than traditional methods of sharing energy levels, transition rates, and oscillator strengths. 3. There is a need for a modern, clearly sourced, and self-contained code that implements the effective Hamiltonian description of lanthanide ions in crystals, integrating the method of fractional parentage, Judd-Ofelt theory, and calculations of magnetic dipole intra-configuration transition rates. 4. Collecting energies, eigenvectors, magnetic dipole oscillator strengths, and magnetic dipole transition rates of lanthanide ions in crystals is timely and useful, especially when accompanied by code and curated data. The dissertation primarily uses lanthanide ions in LaF3 as examples, with some results for LiYF4. It includes a dataset of 183 files, totaling approximately 7 GB, along with a copy of the qlanth repository."], "keyword": ["Spectroscopy", "Physics", "Lanthanide ions"], "primary_title": "qlanth: A Modern Approach to Calculating the Electronic Structure and Spectroscopic Properties of Lanthanide Ions", "uri": "https://repository.library.brown.edu/studio/item/bdr:rybgpsy5/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:rybgpsy5/"}, {"pid": "bdr:etmrb4fx", "object_type": "pdf", "abstract": ["The discovery of the Higgs boson by both the CMS and ATLAS experiments marked a historic moment for the Large Hadron Collider because it confirmed the predictions of the Standard Model of particle physics. The discovery of the Higgs boson opened the door to numerous new studies aimed at precisely measuring and understanding its properties. However, this discovery also brought to the forefront the hierarchy problem, which arises due to quadratic divergences in radiative corrections to the Higgs mass. Several Beyond Standard Model (BSM) theories that attempt to address the hierarchy problem predict the existence of vector-like quarks (VLQs). This thesis presents the search for an $X_{5/3}$, a VLQ that is a heavy fermionic partner of the top quark with an exotic electric charge of $\\pm \\frac{5e}{3}$. The search is conducted using CMS Run 2 datasets, for events with the pair production of $X_{5/3}$ in the single lepton final state. Proton-proton collision data used is collected by the CMS experiment at a center of mass energy $\\sqrt{s}$ = 13 TeV and a luminosity of 19.52 fb$^{-1}$, 16.81 fb$^{-1}$, 41.48 fb$^{-1}$ and 59.83 fb$^{-1}$ in Run II 2016 pre-VFP (APV), 2016 (post-VFP), 2017 and 2018 respectively. Two decay chains are considered. Firstly, in the Standard Model (SM) decay chain, the $X_{5/3}$ is assumed to decay to a top quark and W boson with 100\\% branching ratio. The model is extended to study the decay of VLQs to BSM particles. In this extended study, the $X_{5/3}$ is assumed to decay to a top quark and a charged Higgs with 100\\% branching ratio. A multivariate output is used in order to discriminate the signal from the background and set limits on the $X_{5/3}$ mass at 95\\% confidence level."], "keyword": ["Beyond Standard Model", "CMS", "Experimental Particle Physics", "CMS Experiment"], "primary_title": "Search for Pair Production of Heavy Top Quark Partners with Electric Charge \u00b1 5/3 |e| in the Single Lepton Final State in Proton-Proton Collisions at 13 TeV at the CMS Detector", "uri": "https://repository.library.brown.edu/studio/item/bdr:etmrb4fx/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:etmrb4fx/"}, {"pid": "bdr:crb2dz5v", "object_type": "pdf", "abstract": ["This study examines how the width of warm ocean filaments influences the formation and evolution of submesoscale eddies. Using the MITgcm in an idealized, stratified domain, we simulate filaments of varying widths to evaluate their impact on eddy kinetic energy, vertical velocity, and mixed-layer depth. Results show that narrower filaments lead to earlier and more intense central eddy interactions, while wider filaments evolve more slowly but drive deeper and longer-lasting vertical mixing. These trends reveal systematic, width-dependent behaviors in the dynamics and energetics of the system. The findings have implications for understanding oceanic heat and nutrient transport, and emphasize the importance of resolving frontal geometry in both observational and modeling frameworks."], "keyword": ["Oceanography", "ocean modeling"], "primary_title": "Width-Dependent Dynamics of Warm Filaments: Submesoscale Eddy Generation and Interaction in MITgcm", "uri": "https://repository.library.brown.edu/studio/item/bdr:crb2dz5v/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:crb2dz5v/"}, {"pid": "bdr:h52g4mp8", "object_type": "pdf", "abstract": ["This thesis investigates the rich phase space born from strongly-correlated flat band edges in rhombohedral multilayer, Bernal bilayer, and twisted bilayer graphene. We first report the experimental identification of spontaneous momentum condensation in rhombohedral hexalayer graphene, a phenomenon driven by Coulomb-induced instabilities in momentum space. This momentum-polarized state -- marked by the simultaneous breaking of rotational, time-reversal, and inversion symmetries -- is revealed by the intertwined orders of transport anisotropy, orbital ferromagnetism, and the nonlinear Hall effect. Characterizing the evolution of anisotropy with temperature, we present the first ever transport observation of a nematic transition in any known system. In the same rhombohedral multilayer system, we introduce a remarkably unique superconducting phase at large displacement fields that coexists with anomalous Hall effect and stripe charge order. We identify extreme anisotropy in the sample at low temperature, parametrized by a hard axis with activated insulating behavior and an easy axis with superconductivity - resulting in a one-dimensional-like superconductor. The phase features magnetic-field-driven switching, suggesting a chiral order parameter consistent with recent reports in a similar system. Finally we observe first-order transitions with temperature and a melting transition of the solid stripe order. In the final chapter, we develop a novel experimental approach for probing collective excitations in the flatbands of magic-angle twisted bilayer graphene with microwave photo-excitation and direct-current transport detection. We report the presence of sharp resonance features that evolve with microwave frequency and magnetic field, consistent with a collective excitations of electron spin -- i.e, magnon modes. Furthermore, the trajectory of the fundamental resonance reveals the first ever measurement of intervalley Hund\u2019s coupling in the moir\u00e9 flatband. Remarkably, the microwave resonance exhibits strong density dependence, and is strongest at half-filling of the moir\u00e9 flatband where there is strong isospin polarization and Dirac revival. In summary, angular-resolved transport measurements and microwave resonance experiments unveil significant insight into the underlying electronic order of flatband graphene systems, where we observe an intricate and exciting series of novel quantum phenomena."], "keyword": ["Superconductivity", "Quantum Transport", "Experimental condensed matter", "Two-dimensional electronics", "Low-temperature physics", "van der Waals heterostructures", "Flatband graphene systems", "Strong correlation", "Quantum phenomena", "Symmetry-breaking electronic order"], "primary_title": "Novel Pathways for Probing Correlation-Driven Electronic Orders in Multilayer Graphene", "uri": "https://repository.library.brown.edu/studio/item/bdr:h52g4mp8/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:h52g4mp8/"}, {"pid": "bdr:rzxbreb9", "object_type": "pdf", "abstract": ["Motivated by the open questions of quantum gravity, the matter-antimatter asymmetry, and the dark sector, this thesis explores theories beyond the standard cosmological and gravitational paradigms and investigates both the theoretical and observational prospects, as well as constraints, of such theories. First, we study the propagation of gravitational waves (GWs) in a particular extension of general relativity (GR), known as Chern-Simons-Gauss-Bonnet (CS-GB) gravity. We review the derivation of CS-GB gravity from heterotic string theory and derive how GW propagation is modified in such a theory. We extend a method for parametrizing the parity-violating gravitational sector to include the parity-even sector. The framework presented in this thesis thus allows one to study any correction to GR in explicitly parity-violating and parity-invariant contributions. Moreover, we use this parametrization to map the CS-GB modifications to GW observables, which allows us to place constraints on the theory parameters. We find that the parity-violating sector of CS-GB gravity is allowed to have a slightly larger contribution than the parity-conserving sector. Next, we investigate the cosmological signatures of CS-GB gravity, deriving the complete set of field equations and equations of motion of the modified gravity theory for a suite of fundamental metrics (Friedmann-Lemaitre-Robertson-Walker, Schwarzschild, spherically symmetric, and perturbed Minkowski) under no prior assumptions on the behavior of the fields. The full set of field equations and equations of motion can be numerically solved and applied to specific observables under certain assumptions, and can be used to place constraints on CS-GB gravity. Finally, we study a general class of spontaneous baryogenesis models involving a scalar field derivatively coupled to a baryon current. We compute the full set of cosmological perturbation equations and initial conditions governing such models, and in doing so we find a generalization of the gauge-invariant baryon isocurvature perturbation which has been studied in existing literature. Follow-up work involves verifying our findings numerically, which will inform us about the generalized conditions under which the baryon isocurvature perturbation may be suppressed enough for spontaneous baryogenesis models to satisfy cosmological isocurvature constraints."], "keyword": ["Cosmology", "Gravity", "Gravitational waves"], "primary_title": "Parity and Baryogenesis in Theories Beyond Standard Cosmology", "uri": "https://repository.library.brown.edu/studio/item/bdr:rzxbreb9/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:rzxbreb9/"}, {"pid": "bdr:5z34te24", "object_type": "pdf", "abstract": ["This dissertation presents measurements of the production fractions of $B^\\pm$, $B^0$, and $B_s^0$ mesons in proton-proton collisions at $\\sqrt{s} = 13,\\mathrm{TeV}$ using a special data set recorded in 2018 with high-rate triggers designed to collect an unbiased sample of $10^{10}$ $b$ hadrons with the CMS experiment at the LHC. These data enabled access to hadronic open-charm decays of $B$ mesons ($B_{(s)} \\to \\pi D_{(s)}$), where the $D$ meson decays into fully hadronic final states. Production fraction ratios as functions of $B$ meson transverse momentum ($p_T$) and rapidity ($y$) are measured using the open-charm decays in the kinematic range of $8 < p_T < 60,\\mathrm{GeV}$ and $|y| < 2.25$. In addition, the same data are used to measure relative production fraction ratios in the charmonium decay channels ($B_{(s)} \\to X J/\\psi$, with $X$ being $K$, $K^{*}(892)^0$, or $\\phi(1020)$ mesons), where the $J/\\psi$ meson decays into a pair of muons. These measurements are normalized \\textit{in situ} to the measured yields in the open-charm channels, enabling the first extraction of absolute production fractions in charmonium channels. These results also improve several world-average values of the ratios of branching fractions of $B$ meson decays to charmonium and open-charm states. Finally, isospin invariance in $B$ meson production is tested, with no significant deviation observed within the experimental uncertainties."], "keyword": ["Experimental Particle Physics"], "primary_title": "Measurement of B meson production fraction ratios in proton-proton collisions at 13TeV using hadronic open-charm and charmonium decays", "uri": "https://repository.library.brown.edu/studio/item/bdr:5z34te24/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:5z34te24/"}, {"pid": "bdr:8u4tmcwx", "object_type": "pdf", "abstract": ["The first measurement of the associated production of an \u03a5(1S) meson with a Z boson, observed in the four muon final state, is presented. The analysis is based on proton-proton collision data at \u221as = 13 TeV, collected with the CMS detector in 2016\u20132018 and cor- responding to an integrated luminosity of 138 fb\u22121. Using the production of the Z boson decaying into four muons as a normalization channel, we measure the ratio of the fiducial cross section times branching fractions \u03c3(pp \u2192 Z + \u03a5(1S))B(Z \u2192 \u03bc+\u03bc\u2212) B(\u03a5(1S) \u2192 \u03bc+\u03bc\u2212) to the fiducial cross section times branching fraction \u03c3(pp \u2192 Z)B(Z \u2192 \u03bc+\u03bc\u2212\u03bc+\u03bc\u2212). The ratio is found to be RZ+\u03a5(1S) = [21.1 \u00b1 5.5(stat) \u00b1 0.6(syst)] \u00d7 10\u22123. We also perform a calculation of the effective double-parton scattering cross section, \u03c3eff , which is found to be 13.0+7.8\u22123.5 mb. In addition, we measure \u03c3eff differentially, first as a function of the transverse momentum of the \u03a5(1S) meson, and then as a function of the transverse momentum of the Z boson."], "keyword": ["elementary particle physics"], "primary_title": "Observation and Measurements of the Production of an \u03a5(1S) Meson in Association with a Z Boson in the \u03bc+\u03bc\u2212\u03bc+\u03bc\u2212 Final State using 138 fb\u22121 of Proton-Proton Collision Data at \u221as = 13 TeV Collected with the CMS Detector at the CERN LHC from 2016\u20132018", "uri": "https://repository.library.brown.edu/studio/item/bdr:8u4tmcwx/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:8u4tmcwx/"}, {"pid": "bdr:whj8gpva", "object_type": "pdf", "abstract": ["Abstract of \"The EXoplanet Climate Infrared TElescope (EXCITE),\" by Tim Rehm, Ph.D., Brown University, May 2025 Despite thousands of detected exoplanets, there is still much to be learned about the composition and dynamics of their atmospheres. The EXoplanet Climate Infrared TElescope (EXCITE) is a NASA-funded mission that measures spectra of transiting hot Jupiters during their entire orbital periods. Hot Jupiters are a subset of exoplanets which are of the size of Jupiter, but orbit their host stars at distances less than 0.1 AU and have orbital periods between 1 to 5 days. This observing technique is called phase-resolved spectroscopy, and there are currently no instruments dedicated to making these measurements. Obtaining spectra at every phase during an orbital period reveals chemical abundances, the longitudinal brightness distribution, the global energy budget, and the heat redistribution efficiency of a hot Jupiter atmosphere. The EXCITE mission flies from a large scientific balloon at stratospheric altitudes and will fly a long-duration balloon (LDB) flight from the Antarctic for several weeks. At balloon altitudes (38 to 40 km), the foreground of the Earth is stable and transparent, and allows for continuous, multi-day observing in the 0.8-3.5 micron passband with high signal-to-noise ratios (SNR). This thesis covers the entire lifetime of the mission, from the science motivation to the design of the payload, and culminates in an engineering flight in 2024 from Fort Sumner, New Mexico. During this flight, the cryogenic receiver met all thermal requirements, and the payload demonstrated sub-arcsecond pointing stability. I discuss the payload subsystems including the telescope, balloon gondola, spectrograph, detector, cryogenic receiver, and cryocooler heat dissipation system. Using radiometric simulators for exoplanet observations, I show the process of generating mock focal plane images of the EXCITE instrument. I model and detrend balloon systematics from the simulated images in order to quantify SNRs from simulated spectra measured on a high-altitude balloon platform. The results show that EXCITE can measure secondary eclipse depths with SNR > 20 across the majority of the passband for a bright target (WASP-18b)."], "keyword": ["Astrophysics", "Extrasolar planets", "instrument design", "Telescopes", "Ballooning"], "primary_title": "The EXoplanet Climate Infrared TElescope (EXCITE)", "uri": "https://repository.library.brown.edu/studio/item/bdr:whj8gpva/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:whj8gpva/"}, {"pid": "bdr:avsdkt8w", "object_type": "pdf", "abstract": ["This thesis explores the application of machine learning techniques to simplify expressions in momentum twistor space, a mathematical framework that elegantly captures the symmetries of planar N=4 super Yang-Mills theory. We develop a transformer-based neural network architecture capable of learning the complex identities that relate different representations of scattering amplitudes. Building on recent advances in applying machine learning to symbolic mathematics, we implement both one-shot learning and contrastive learning approaches to identify and simplify complex momentum twistor expressions. Our methodology generates training data through controlled application of Pl\u00fccker relations and other momentum twistor identities, creating paired examples of equivalent expressions with varying complexity. For 5- and 6-point cases, our system achieves simplification recovery rates exceeding 97% when handling expressions with multiple scrambling operations. This work demonstrates that the manifest momentum conservation property of twistor variables significantly enhances simplification efficiency compared to traditional spinor-helicity approaches. By revealing compact representations of scattering amplitudes that would be difficult to discover manually, this interdisciplinary approach provides new computational tools for theoretical physics and suggests promising directions for future applications of machine learning to geometric formulations of quantum field theory."], "keyword": ["Machine Learning", "scattering amplitudes", "Quantum field theory", "Supersymmetry"], "primary_title": "Learning The Simplicity of Momentum Twistor Variables: Understanding Amplitudes, Geometry, and Machine Learning", "uri": "https://repository.library.brown.edu/studio/item/bdr:avsdkt8w/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:avsdkt8w/"}, {"pid": "bdr:j3hgnh5t", "object_type": "pdf", "abstract": ["This study examines how the width of warm ocean filaments influences the formation and evolution of submesoscale eddies. Using the MITgcm in an idealized, stratified domain, we simulate filaments of varying widths between 10 km and 60 km to evaluate their impact on eddy kinetic energy, vertical velocity, and mixed-layer depth. Results show that narrower filaments lead to earlier and more intense central eddy interactions, while wider filaments evolve more slowly but drive deeper and longer-lasting vertical mixing. These trends reveal systematic, width-dependent behaviors in the dynamics and energetics of the system. The findings have implications for understanding oceanic heat and nutrient transport, and emphasize the importance of resolving frontal geometry in both observational and modeling frameworks."], "keyword": ["ocean modeling", "Ocean", "ocean mixing"], "primary_title": "Width-Dependent Dynamics of Warm Filaments", "uri": "https://repository.library.brown.edu/studio/item/bdr:j3hgnh5t/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:j3hgnh5t/"}, {"pid": "bdr:kynsjexf", "object_type": "pdf", "abstract": ["During the August 2024 test flight of the EXoplanet Climate Infrared TElescope (EXCITE), a balloon-borne observatory designed to characterize exoplanet atmospheres, absolute azimuth data from the on-board GPS compass was not available throughout the flight. To supplement the pointing information, we developed a method to reconstruct the payload\u2019s azimuth using images from a 360\u00b0 action camera mounted externally on the gondola. The front-facing lens of the camera was approximately aligned with the forward (stern-bow) direction of the gondola. Through a ground-based calibration test, we determined that the camera follows an equidistant projection model, allowing sun positions in the image to be mapped to azimuth angles with a resolution of 0.5\u00b0. An automated Python pipeline was created to detect and centroid the sun in each image and to assign an azimuth relative to the camera\u2019s reference frame. These relative angles were then combined with solar ephemeris data to recover the payload\u2019s absolute azimuth. The image-derived azimuth was compared with the yaw data calculated from gyroscope in- tegration. While the two datasets showed similar trends across the flight, a growing offset was observed in the later hours, likely due to integrated bias in the gyroscope solution. An additional elevation analysis using both encoder data and image-derived solar elevation helped confirm the accuracy of the elevation relative to the Sun. The secondary mirror temperature increase near 11:30 AM (GDT-6) is consistent with reconstructed pointing that placed the telescope closely aligned with the Sun within \u00b13\u00b0 elevation and \u00b15\u00b0 azimuth relative to the Sun. This work demonstrates that 360\u00b0 imaging, combined with basic calibration and supporting flight data, can provide a robust alternative means of azimuth reconstruction. The approach offers a valuable tool for future balloon missions where direct azimuth measurements may be limited or unavailable."], "keyword": ["Physics", "Astrophysics", "Telescopes"], "primary_title": "From Images to Azimuth: A Comprehensive Study of Orientation Calibration Techniques for the EXoplanet Climate Infrared TElescope (EXCITE)", "uri": "https://repository.library.brown.edu/studio/item/bdr:kynsjexf/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:kynsjexf/"}, {"pid": "bdr:98ktayt8", "object_type": "pdf", "abstract": ["Quantum information processing (QIP) in the brain has been theorized to occur via nuclear spins despite the presumption that decoherence dominates for any relevant length of time under physiological conditions~\\cite{Fisher2015}. This theory identified that the nuclear spin (I=1/2) of phosphorus-31 (31P) could function as a neural qubit, and the phosphate ion (the chemical manifestation of phosphorus in living tissue) as the qubit transporter. Building on this theory, we develop an experimental protocol to demonstrate QIP on the two-qubit system of 31P nuclear spins in adenosine diphosphate (ADP), a neurotransmitter essential to energy transfer in all living cells. Importantly, the nuclear spins' decoherence time (T_2) is measured as 207(6) ms, significantly longer than the neuronal firing timescale of \u223c1 ms~\\cite{Katz1965}. The controlled-NOT (CNOT) quantum logic gate is successfully implemented in this two-qubit system, with a measured fidelity of 0.970(53), under the ``warm, wet, and noisy'' conditions that mimic the environment in the brain, providing evidence for QIP under physiological conditions. Additionally, the H and T gates have been demonstrated with fidelities of 0.991(55), and 0.918(70), respectively. This set of gates, combined with standard rotation gates, forms a universal gate set~\\cite{Divincenzo1995}, theoretically enabling the implementation of any computable operation with arbitrary precision. This universal gate set is then used to demonstrate effective-entangled Bell states and the implementation of the Deutsch quantum algorithm, highlighting an advantage over classical systems. These quantum advantages present new opportunities for the advancement of research in quantum biology."], "keyword": ["Quantum Computing"], "primary_title": "Quantum Information Processing in Biological Molecules", "uri": "https://repository.library.brown.edu/studio/item/bdr:98ktayt8/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:98ktayt8/"}, {"pid": "bdr:wm2ab4t2", "object_type": "pdf", "abstract": ["A wide array of experimental probes of matter have been developed in order to gain a more accurate and complete understanding of the microscopic nature of emergent quantum phenomena---a cornerstone of condensed matter research. In the study of a single system or material, multiple probes are employed in order to build a complete picture, since each probe naturally faces limitations in the information accessible to it. As our understanding of quantum phenomena expands, so must the range of tools used to study them, which motivates the development of novel quantum probes of matter. This thesis focuses on the experimental implementation of novel quantum probes that aim to expand our understanding of magnetic fluctuations in strongly correlated systems. Specifically, this work focuses on the experimental implementation of two novel quantum sensing techniques: a quantum mechanical magnetic camera that utilizes noise spectroscopy of magnetic tunneling junctions (MTJ) to detect magnetic fluctuations in materials with a high level of spatial and temporal resolution and a multi-modal spectroscopic technique that expands on standard nuclear magnetic resonance (NMR) techniques to provide a direct measure the strength and distribution of spin-spin interactions. The beginning stages of implementing the quantum mechanical magnetic camera are presented, the characterization of the intrinsic noise in MTJs, the details of a highly sensitive probe we built, and the experimental techniques implemented to accurately measure such small signals. The direct measure of spin-spin interaction strength is demonstrated by probing 31P nuclear spins in the van der Waals antiferromagnet NiPS3, which enabled the detection of a sharp change in the hybridization strength of the 31P-31P dimer at the magnetic phase transition and the absence of any distribution in the 31P-31P interaction strength above the magnetic transition. The results obtained through application of this technique provide valuable insight into the nature of magnetic interactions in this material. Finally, results of standard NMR measurements of the van der Waals antiferromagnet CoNb3S6 are presented. These measurements provide insight into the nature of the complicated magnetic order in this material and on the origins of the anomalous Hall effect that arises in the antiferromagnetic phase."], "keyword": ["Magnetism", "NMR", "condensed matter physics"], "primary_title": "Applications of Multi-Modal Spectroscopic Techniques for the Study of Magnetism in Strongly Correlated Materials", "uri": "https://repository.library.brown.edu/studio/item/bdr:wm2ab4t2/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:wm2ab4t2/"}, {"pid": "bdr:37s8v2v2", "object_type": "pdf", "abstract": ["Dark matter is one of the greatest mysteries in modern physics. Although evidence is observed across diverse scales of the universe, its properties remain elusive. The LUX-ZEPLIN (LZ) experiment is designed for direct detection of dark matter using a liquid-gas dual-phase xenon time projection chamber, located at the 4850 ft underground level of the Sanford Underground Research Facility in South Dakota. LZ utilizes Adelphi Technology's deuterium-deuterium (DD) neutron generator to produce neutrons for nuclear recoil calibrations. The DD generator is deployed outside the water tank, which is used for shielding of LZ detector. The Neutrons are collimated and transmitted to the detector through nitrogen-filled conduits. The DD generator operates in three modes, delivering a range of neutron kinetic energy. The direct mode sends monoenergetic 2.45 MeV neutrons down the conduit to the TPC directly from the neutron production surface. The D-Reflector mode reflects neutrons at selected scattering angles off a deuterium-loaded scintillator, targeting 350 keV neutrons. The H-reflector mode uses a hydrogen-loaded scintillator to deliver neutrons with energy ranging from 10 to 200 keV. A powerful advantage of reflector modes is event-by-event tagging through time-of-flight, providing kinetic energy of individual incoming neutrons. Both reflector modes were implemented for the first time in a tonne-scale xenon detector. The implementation of these modes into the LZ experiment, development of event selections, and analysis of DD calibration data are presented. The DD neutron dataset is used for direct measurement of the rate of Migdal-effect events in liquid xenon for nuclear recoils with the energy range 5\u201374 keVnr resulting from the interaction of 2.45 MeV neutrons. The Migdal effect is important to the direct detection of sub-GeV dark matter because it allows additional energy deposition through the ionization of xenon caused by perturbed electron clouds. A comprehensive nuclear recoil model is developed based on DD data with high statistics and low systematics. A detailed study of possible mechanisms for the background events is conducted. From the profile likelihood ratio (PLR) test, the data shows consistency with a background-only model with a p-value of 0.78. The one-sided 90% confidence limit on the Migdal signal strength is found to be 26% of the Ibe's theoretical prediction."], "keyword": ["Physics", "Dark matter (Astronomy)", "Detectors--Calibration", "Neutron sources", "LUX-ZEPLIN", "Migdal effect", "Liquid xenon"], "primary_title": "Implementation of a Deuterium-Deuterium Neutron Generator and its Application for Nuclear Recoil Calibration and the Search for the Migdal Effect in the LUX-ZEPLIN Experiment", "uri": "https://repository.library.brown.edu/studio/item/bdr:37s8v2v2/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:37s8v2v2/"}, {"pid": "bdr:7jaat7fh", "object_type": "pdf", "abstract": ["The LUX-ZEPLIN (LZ) Experiment is a direct detection dark matter experiment that utilizes a dual-phase time-projection chamber (TPC) containing 7 tonnes of active xenon. To observe particle interactions in the TPC, LZ has implemented 494 Hamamatsu R11410-22 photomultiplier tubes (PMTs), which are sensitive to single photons and are capable of maintaining stable performance well in excess of the expected 1000 live-days of the experiment. These PMTs underwent a rigorous testing campaign prior to their installation inside the TPC. The LZ PMT system operates at an average gain of 2\u00d7106 electrons/photon with a single-photon trigger efficiency of 96.2% and a dark rate of 4.2 \u00b1 1.6 Hz per 3-inch PMT. The performance of these PMTs is continuously monitored to verify their stability over the course of the experiment. In LZ, precision nuclear recoil (NR) calibrations are critical for understanding the signal response of dark matter interactions with the liquid xenon inside the detector. Monoenergetic 2.45 MeV neutrons from a deuterium-deuterium (DD) neutron generator enable in-situ measurements of the detector\u2019s scintillation and electroluminescence response to NRs up to the DD recoil endpoint of 74 keVnr while maintaining a ratio of intrinsic gamma contamination below 10\u22127 gammas/neutron. The Migdal effect is an atomic process in which electrons are excited or ionized due to the perturbation of the electron cloud from a recoiling nucleus. In direct-detection dark matter experiments, this can be utilized to improve sensitivity to low-mass dark matter through the elevated signal response of the primary NR due to the secondary electronic recoil (ER) of the Migdal effect. This work presents a profile likelihood ratio test using a very high statistics DD neutron calibration in LZ. The result is of the first experimental constraints on the rate of the Migdal effect from Xe-recoils in the range from 5-80 keVnr. The one-sided 90% confidence level of event rate, relative to current theoretical predictions, is \u00b590%CL \u2264 0.32 \u00d7 \u00b5theory. A p-value of 0.36 confirms the consistency be-tween the observed DD neutron data and the presented nuclear recoil model with a limited Migdal component."], "keyword": ["Dark matter (Astronomy)", "Detectors--Calibration", "Neutron sources", "Migdal effect", "Time projection chambers (Nuclear physics)", "Photoelectric multipliers"], "primary_title": "Characterization of the R11410-22 Photomultiplier Tube and the Search for a Neutron- Induced Migdal Effect in the LUX-ZEPLIN Experiment", "uri": "https://repository.library.brown.edu/studio/item/bdr:7jaat7fh/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:7jaat7fh/"}, {"pid": "bdr:vtu4f92u", "object_type": "pdf", "abstract": ["This thesis is devoted to exploring the connection between thermofield dynamics and microscopic descriptions of black holes in large N matrix quantum mechanics. We uncover a dynamical symmetry, based on which the construction of thermofield double states is given. For this we adopt a master field constrained optimization scheme to systematically evaluate thermal correlations and spectra at large N. We establish a mapping between conformal field theory and the dual gravity of BTZ black hole. We also investigate alternative approaches to bulk reconstruction and subregion duality, employing the Tomita-Takesaki theory and twisted Ishibashi states."], "keyword": ["Mathematical physics", "Matrix Model", "Large N", "Black Holes", "Thermal Field Theory"], "primary_title": "From Thermofields to Black Holes", "uri": "https://repository.library.brown.edu/studio/item/bdr:vtu4f92u/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:vtu4f92u/"}, {"pid": "bdr:psgwpsxr", "object_type": "pdf", "abstract": ["We present an analysis of the reference simulations generated using the current version of pyuvsim. Prior work identified issues regarding current repeatability of the reference simulations compared to archival results. We determine that there are additional differences between current iterations of the reference simulations compared to the prior results that cannot be accounted for by the change of file structure, nor the change from the previously used ICRS coordinates to the currently used J2000 coordinates. Following this we examine the typical difference found between simulations both found to be matching and those that do not match their archival counterparts."], "keyword": ["Physics, Astrophysics, Galaxy Clusters, Cosmology", "Radio astronomy", "computational physics", "Simulations", "Radio interferometers", "21 cm cosmology"], "primary_title": "Determining Repeatability for Reference Simulations in Pyuvsim", "uri": "https://repository.library.brown.edu/studio/item/bdr:psgwpsxr/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:psgwpsxr/"}, {"pid": "bdr:z29s5mjh", "object_type": "pdf", "abstract": ["In this thesis, we present novel perspectives on the explicit evaluation and analytic structure of correlation functions and scattering amplitudes in flat and expanding spacetimes. Specifically, we analyze wavefunction coefficients in a toy model theory of conformally coupled scalars within power-law FRW cosmologies, examine unitarity constraints on dual resonant string amplitudes, and further our understanding of the flat-space S-matrix using the framework of celestial amplitudes. First, we explore intriguing connections between positive geometries, on-shell methods, and bootstrap principles studied within the modern scattering amplitudes program to the Bunch-Davies wavefunction in toy models of FRW cosmologies. Leveraging recent advances in twisted cohomology and generalized unitarity from the Feynman integral literature, we develop an algorithm to construct a physical basis that simplifies the computation of differential equations for all tree and loop-level wavefunction contributions. Furthermore, we unravel the existence of hidden zeros in the cosmological wavefunction and demonstrate a universal factorization behavior associated with the kinematics of near-zero configurations for all tree and loop graphs. Second, we investigate the constraints of partial wave unitarity on dual resonant amplitudes from the viewpoint of the modern S-matrix bootstrap. Focusing on the Coon amplitude - a one-parameter deformation of the Veneziano amplitude with logarithmic Regge trajectories - we establish manifest positivity on certain Regge trajectories while identifying regions of unitarity violation in parameter space using tools from q-calculus and numerical methods. Finally, we make substantial advances in the study of celestial amplitudes by investigating the dual celestial conformal field theory (CCFT) and the role of light-ray operators, which are increasingly recognized as fundamental components of the CCFT spectrum. We present new computations of tree-level correlation functions for these operators, demonstrating their appearance in the operator product expansion of gluon primaries. Additionally, we examine the treatment of distributional low-point correlators by introducing a background that breaks bulk translation invariance, yielding correlators that more closely resemble those found in traditional two-dimensional CFTs."], "keyword": ["Cosmology", "scattering amplitudes", "Quantum field theory", "string theory", "conformal field theory"], "primary_title": "Aspects of Cosmological, Celestial and String Amplitudes", "uri": "https://repository.library.brown.edu/studio/item/bdr:z29s5mjh/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:z29s5mjh/"}, {"pid": "bdr:wx88cjwh", "object_type": "pdf", "abstract": ["The EXoplanet Climate Infrared TElescope (EXCITE) is an instrument designed to perform phase-resolved spectroscopy of extrasolar gas giant planets (or hot Jupiters) from a long- duration balloon (LDB) platform. EXCITE will make continuous observations in the 0.8\u2013 3.5 \u03bcm band over the course of a target\u2019s orbital period. The orbital periods of targets span 1\u2013 3 days. These measurements require high photometric stability over long integration periods and low photon noise. A JWST flight spare HAWAII-2RG (H2RG) mercury-cadmium- telluride (HgCdTe) detector is used on EXCITE and read out with an ASIC for Control and Digitization for Imagers in Astronomy (ACADIA). To meet thermal requirements of the optics and detector, the EXCITE spectrograph is housed inside of a cryogenic receiver. The receiver is cooled by two linear pulse tube mechanical cryocoolers, one dedicated to cooling the optics to a nominal 100 K and one to cooling the detector to a nominal 50 K. EXCITE is the first balloon-borne instrument to utilize linear pulse tube cryocoolers, which provide a means to meet thermal requirements while solving problems posed by traditional cryogens. The cryocoolers are driven by dual opposed pistons, which introduces a potential source of vibration to the payload. The cryocoolers also generate heat, which needs to be dissipated; this is accomplished using a fluid loop system. The cryogenic subsystem will provide millikelvin thermal stability of the H2RG and ACADIA. The cryogenic control electronics can be monitored and controlled by the ground station while also operating autonomously if necessary. This thesis outlines the EXCITE cryogenic subsystem and the design of its control electronics and software. It then discusses the exported vibrations of the cryocooler compressors and fluid loop pumps as well as the thermal control achieved during the 2024 North American test flight of EXCITE and subsequent ground-based tests."], "keyword": ["Astrophysics", "Extrasolar planets", "Instrumentation design", "Ballooning", "Electronics"], "primary_title": "Design and Performance of the Cryogenic Control Electronics for the EXoplanet Climate Infrared TElescope (EXCITE)", "uri": "https://repository.library.brown.edu/studio/item/bdr:wx88cjwh/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:wx88cjwh/"}, {"pid": "bdr:x5jkx2jw", "object_type": "pdf", "abstract": ["In this thesis, we study the mathematical structures underlying scattering amplitudes, with a focus on loop-level corrections in celestial conformal field theory, twisted cohomology in higher genus string amplitudes, and q-deformations of the Veneziano amplitude. These investigations reveal novel connections between scattering amplitudes and celestial symmetries, explore a novel formalism to study higher genus string amplitudes, as well as provide new perspectives on UV-completions and dual resonant amplitudes. First, we explore loop-level corrections to collinear limits and soft theorems in celestial conformal field theory. By analyzing their impact on gluon operator product expansions (OPEs), we uncover the logarithmic structure of celestial CFT and demonstrate how these corrections alter the infinite tower of conserved charges forming the S-algebra. This study introduces a new class of non-local soft charges with logarithmic partners, providing insights into celestial CFT spectra as well as its integrability. Secondly, we investigate the worldsheet origins of the Coon amplitude, a q-deformation of the Veneziano amplitude, through a conformal field theory based on the SUq(2) quantum group. By constructing a family of deformations and exploring their analytic continuation into extended kine- matic space, we uncover a new class of dual resonant amplitudes that respect locality, unitarity, causality, and UV finiteness. These amplitudes are compatible with the S-matrix bootstrap and provide a unique connection to q-deformed worldsheet theories. Finally, we reformulate loop-level string amplitudes using intersection theory and twisted cohomology. We study the twisted (co)homology of Riemann-Wirtinger integrals, a family of genus-one integrals related to one-loop string amplitudes in chiral splitting. These integrals, which leave the loop momentum, modulus, and one puncture unintegrated, are analytically tractable and capture key properties of string amplitudes. Using intersection numbers to define an inner product on differential forms, I derive the Gauss-Manin connection for two twisted cohomology bases, independently verifying earlier results. Furthermore, we establish a double-copy formula for the closed-string analogues of these integrals via intersection indices. This genus-one KLT-like kernel extends the KLT framework to meromorphic integrals over the torus, highlighting the interplay between twisted co-homology and double-copy structures at loop level."], "keyword": ["scattering amplitudes", "algebraic geometry", "celestial holography", "string theory", "conformal field theory", "Quantum groups", "S-matrix theory"], "primary_title": "From Celestial Amplitudes to Twisted Cohomology: New Perspectives on Quantum Scattering", "uri": "https://repository.library.brown.edu/studio/item/bdr:x5jkx2jw/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:x5jkx2jw/"}, {"pid": "bdr:hqzv9gea", "object_type": "pdf", "abstract": ["Materials with strongly interacting electrons exhibit a wide variety of unconventional ordering phenomena that are both fundamentally rich and promising for many potential technological applications. These phases often involve coupling between spin, charge, orbital, and lattice degrees of freedom, precisely tuned by a hierarchy of energy scales. They may also involve more subtle degrees of freedom that may be elusive to many common experimental probes. In this thesis, I discuss a series of resonant elastic and inelastic x-ray scattering experiments (REXS/RIXS) on complex magnetic materials to uncover the microscopic mechanisms behind the novel magnetic phenomena observed in these materials. NiRh2O4 is a S=1 frustrated diamond lattice antiferromagnet that may be in proximity to a quantum critical point. I carried out RIXS measurements to unravel the spin-orbital-lattice entangled ground state in NiRh2O4. CoNb3S6 is an intercalated transition metal dichalcogenide (iTMD) exhibiting a giant anomalous Hall effect (AHE) that cannot be explained by its putative collinear antiferromagnetic order. Using REXS, I discovered a long-wavelength modulation of the magnetic structure that gives rise to a novel striped pattern in the scalar spin chirality. The properties of iTMDs are highly sensitive to the precise stoichiometry of intercalated 3d ions. I carried out comprehensive magnetic and structural characterization on CoNb3S6 and the related material NiNb3S6 with varying Co and Ni stoichiometry to understand the dependence of the magnetic properties on sample composition. NiGa2S4 is a nearly ideal S=1 triangular lattice magnet which shows no long range magnetic order and exhibits a variety of unconventional magnetic properties. I carried out REXS measurements to probe the magnetic correlations within a small sample volume to disentangle structural and magnetic disorder. I find a correlation length that is longer than that found in previous measurements, as well as a temperature-induced shift in the magnetic wavevector. Using RIXS, I ruled out the previously reported negative charge transfer ground state and instead found a mixed valence state."], "keyword": ["Condensed matter--Magnetic properties", "quantum materials", "condensed matter physics", "X-rays--Scattering", "X-ray spectroscopy"], "primary_title": "Uncovering Novel Phases in Complex Magnetic Materials Using Resonant X-ray Scattering", "uri": "https://repository.library.brown.edu/studio/item/bdr:hqzv9gea/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:hqzv9gea/"}, {"pid": "bdr:d83hv4dv", "object_type": "pdf", "abstract": ["Topological phases of matter have recently attracted intense interest. Among topological phases, topological quantum liquids, such as fractional quantum Hall liquids and gapped quantum spin liquids, possess exotic excitations with fractional statistics, known as anyons. They are of great interest to quantum information science. The most direct method to probe anyonic statistics involves electronic interferometers, which have proven successful in fractional quantum Hall liquids very recently. This thesis gives a comprehensive description of the interferometery technique and explains how electronic interferometers can be adapted to thermal interferometry that can probe the non-Abelian anyonic statistics of charge-neutral excitations in Kitaev spin liquids. We compare the Fabry\u2013P\u00e9rot geometry and the Mach\u2013Zehnder geometry and identify unique signatures of Ising statistics in Kitaev spin liquids. Furthermore, the idea of thermal interferometry can be generalized to probe almost any Abelian or non-Abelian anyonic statistics in topological liquids. In general, the absence of interference current in a Mach\u2013Zehnder device is a smoking-gun evidence of non-trivial anyonic statistics. This thesis also addresses the problem of electronic quantum Hall interferometers with multiple edge channels, explaining how a closed inner edge channel affects the measured I\u2013V curve at a finite source-drain bias voltage. When the inner mode is completely reflected and the outer mode is partially transmitted, we find striking features at low temperatures related to the resonance of excitations of the closed inner channel. However, these features disappear rapidly with increasing temperature. Another feature brought by the closed inner channel is the exponential decay in the I\u2013V curve at a high bias, which is due to the fluctuations of the quasiparticle number on the inner channel."], "keyword": ["Fractional Quantum Hall Effect", "Topological Matter", "Fabry-Perot interferometers", "Anyons", "Interferometry", "Quantum Spin Liquid"], "primary_title": "Interferometry in Topological Quantum Liquids", "uri": "https://repository.library.brown.edu/studio/item/bdr:d83hv4dv/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:d83hv4dv/"}, {"pid": "bdr:un4458sc", "object_type": "pdf", "abstract": ["Parkinson\u2019s Disease (PD) is a degenerative neurological disorder characterized by motor dysfunction and linked to abnormal patterns of neural activity. Deep Brain Stimulation (DBS) has become a widely used treatment for its ability to disrupt pathological neural oscillations, yet traditional open-loop systems are limited by adverse side effects and an inability to adapt to real-time changes in symptom severity. Closed-loop DBS presents a promising alternative, recording live neural activity and tailoring stimulation to a patient\u2019s current pathological state. While most closed-loop approaches focus on adapting the timing of stimulation, fewer efforts have addressed optimization of the stimulation parameters themselves. In this study, we developed and tested a closed-loop framework for DBS parameter selection, using Bayesian optimization of the frequency and pulse-width of stimulation. To evaluate stimulation benefit, we targeted minimization of beta, spectral power in the 13\u201330 Hz frequency band, because of its well-established correlation to motor dysfunction in PD. We also developed a novel artifact rejection algorithm to remove stimulation artifacts from recorded local field potentials (LFPs), allowing for more accurate calculations of beta and other neural biomarkers. We showed that our artifact rejection algorithm successfully preserved temporal and spectral features of neural activity, in a way that is robust to long time scale fluctuations in the signal baseline. Additionally, we found that our Bayesian optimization method converged on low frequency/high pulse-width stimulation, highlighting the need for patient-specific parameter tuning. These results demonstrate the feasibility of using closed-loop optimization algorithms to target neural biomarkers and automate DBS parameter tuning."], "keyword": ["Parkinson's disease", "Deep Brain Stimulation", "Bayesian Parameter Optimization"], "primary_title": "Bayesian Parameter Optimization to Improve Deep Brain Stimulation for Parkinson\u2019s Disease", "uri": "https://repository.library.brown.edu/studio/item/bdr:un4458sc/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:un4458sc/"}, {"pid": "bdr:nbyx2t8f", "object_type": "pdf", "abstract": ["Magnetic tunnel junctions (MTJs), owing to the quantum mechanical tunneling magnetoresistance, have attracted attention in the field of spintronics and general condensed matter physics community for decades. The large resistance change of MTJs under rotation of the magnetization has been utilized for developing ultrasensitive magnetic sensors for applications in memory devices, biophysics, and non-destructive evaluation. The miniature size of MTJs and relative easiness of read-out also allows for a two-dimensional sensing array with high spatial resolution and low power consumption. In this thesis, we present a systematic investigation of the noise characteristics in ultrasensitive magnetic sensors with different designs, based on a well-developed noise measurement system. Optimization of sensing performance has been focused on achieving high sensitivity and low noise, while the correlation between them has been overlooked. Through careful noise and sensitivity measurement, different scaling relations between intrinsic noise and sensitivity of MTJs have been identified, which provide physical insights to the noise mechanism in MTJs. Based on the scaling relations, superparamagnetism and magnetic vortex state show higher potential in further improvement of the field detectability. Moreover, a two-dimensional sensing array of MTJs with high spatial resolution has been designed and fabricated. A simple cross-bar array is built from standard sputtering deposition and photolithography process, and the Wheatstone bridge architecture suppresses the sneak path current through unselected cells, allowing for accurate read-out from the sensing elements. Moreover, all the MTJs in the sensing array are in the magnetic vortex state, where high homogeneity in sensing output has been observed down to cryogenic temperature, and negligible correlation between neighboring elements has been demonstrated. This sensing array has shown great potential in detecting spatial and temporal variation of magnetic signals from novel quantum materials."], "keyword": ["Magnetism", "condensed matter physics"], "primary_title": "Noise Characterization of Ultrasensitive Magnetic Tunnel Junctions and Integration into a Two-dimensional Sensing Array", "uri": "https://repository.library.brown.edu/studio/item/bdr:nbyx2t8f/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:nbyx2t8f/"}, {"pid": "bdr:gas8ns8n", "object_type": "pdf", "abstract": ["This thesis presents the development and physical characterization of a nanopore ion source which emits biomolecular ions directly from aqueous solution into vacuum. The primary motivations for this work are to overcome fundamental limitations in mass spectrometry-based proteomics workflows and to develop a single molecule protein sequencing technique. Traditional electrospray ionization (ESI) methods are widely used to generate vapor phase ions for mass spectrometry, but they suffer from significant sample loss which is intrinsically linked to the ionization mechanism. ESI generates a spray of charged droplets which evaporate due to collisions with background gas molecules, and this same background gas scatters the generated ions in a wide plume and prevents most ions from entering the mass spectrometer. This sample loss limits the sensitivity of proteomic analyses which rely on ESI, and precludes comprehensive single cell or single molecule analyses. In this work, we show that by reducing the emitter size to the nanoscale, the nanopore ion source can sustain a stable water/vacuum interface which generates ions directly by ion evaporation, bypassing the droplet formation stage, eliminating the need for a background gas and minimizing sample loss. We demonstrate that the nanopore ion source can emit amino acid and small peptide ions directly into vacuum from aqueous solution. The emitted current is shown to be composed of ions rather than charged droplets as in conventional ESI, and more than 90\\% of the current can be recovered in a distant collector. Theoretical arguments support the hypothesis that for sufficiently small emitters, charge emission from aqueous solution transitions to the purely ionic regime, which has previously only been observed in liquid metals, ionic liquids, and electrolyte solutions in low volatility solvents like glycerol and formamide. We further explore the thermal and electrical properties of the nanopore ion source. A thermal model which describes the competing processes of evaporative cooling and joule heating near the tip is developed and used to show that evaporative cooling in a conical emitter scales inversely with the tip radius, explaining why nanopore ion sources can maintain stable water/vacuum interfaces without freezing. We also develop a model of the current-voltage characteristic of a nanopore ion source that generates ions by direct ion evaporation, and demonstrate that it matches the source's measured behavior. Finally, we investigate the use of ultraviolet (UV) light to fragment peptides in aqueous solution as a potential precursor to single-molecule peptide sequencing. We monitor peptide bond scission through changes in the absorption spectra following irradiation with 193~nm and 222~nm light, using a combination of real-time in situ transmission measurements and UV-vis spectroscopy. We measure the quantum yields of peptide bond scission and discuss how UV-induced fragmentation in solution could be effectively coupled with the nanopore ion source to facilitate new types of single-molecule analyses."], "keyword": ["Biophysics", "Proteomics", "Mass spectrometry", "Nanopores", "Electrohydrodynamics"], "primary_title": "The Nanopore Ion Source: Mechanisms of Direct Ion Emission from Aqueous Solutions into Vacuum", "uri": "https://repository.library.brown.edu/studio/item/bdr:gas8ns8n/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:gas8ns8n/"}, {"pid": "bdr:va9bfe5k", "object_type": "pdf", "abstract": ["The unification of quantum mechanics and general relativity is the holy grail of fundamental theoretical physics. This thesis represents a small part of that effort, where we consider a number of problems that might be of interest to the theoretical studies of black holes and quantum cosmology. Why study black holes and quantum cosmology, one might ask? The answer lies in the fact that they are the only two systems where it is necessary to apply quantum mechanics and general relativity simultaneously. In particular, they both have event horizons, which are global structures of the spacetime that prevent events from making causal contact. They therefore have become the primary arenas where logical incompatibilities of quantum mechanics and general relativity can be made most transparent. One of the most dramatic incompatibilities is the black hole information paradox, which concerns the unitarity of processes that involve the formation and the evaporation of black holes. This thesis will first discuss a proposed resolution to the information paradox called black hole complementarity, and a closely linked issue known as quantum scrambling, in particular in the context of a 2D conformal field theory. We will then present a microscopic quantum model of the de-Sitter universe that incorporates the required quantum scrambling on the cosmological horizon. This quantum model of cosmology is a so-called \"holographic\" map between the stretched horizon of the de-Sitter spacetime and the static patch (colloquially known as the \"bulk\"). Continuing in a similar vein, the rest of the thesis will be concerned with building holographic theories between flat spacetime and its boundary, and we present two holographic theories of the flat spacetime, first for massive scalar particles and then extending the results to gravitons. As these all have something to do with mappings between boundary 2-spheres and their bulk, this is therefore a story of building holography on 2-spheres. Hence the title of this thesis."], "keyword": ["Theoretical physics", "Quantum gravity"], "primary_title": "\"A Tale of 2-Spheres\": How Conformal Symmetry, Chaos, and Some Elementary Algebra Led to Insights in Black Holes and Quantum Cosmology", "uri": "https://repository.library.brown.edu/studio/item/bdr:va9bfe5k/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:va9bfe5k/"}, {"pid": "bdr:qcd2qadb", "object_type": "pdf", "abstract": ["This dissertation explores direct probes of topological order, with a focus on edge-based techniques such as interferometry and noise measurements, as well as emerging platforms where anyonic excitations can be stabilized. Recent experimental breakthroughs in directly probing braiding phases through interferometric techniques and anyon collider experiments have deepened our understanding of fractionalization and anyonic statistics. However, existing interferometric methods still face challenges, particularly in regimes with low visibility in Aharonov-Bohm oscillations. The first part of this dissertation presents an exact solution to the Mach-Zehnder interferometer in the fractional quantum Hall regime, which addresses low-visibility issues and provides an ideal approach for detecting anyon braiding in more fragile quantum Hall states. Additionally, we extend the geometry to include thermal transport measurements. Beyond interferometry, shot noise remains one of the most reliable tools for detecting fractional charge. However, recent experimental data has revealed discrepancies with theoretical predictions. In the second part of the dissertation, we propose a mechanism for correlated noise generation at low temperatures, offering a potential resolution to this longstanding problem. In the final part of this dissertation, we explore emerging platforms for topological order. We also present an alternative and intuitive derivation of a recently discovered universal upper bound on the topological energy gap. Our approach provides further insights into its generalizations, including to interacting quantum spin Hall systems. Additionally, we investigate neutral anyonic excitations in recently discovered fractional excitonic states in bilayer graphene systems. These developments lay the groundwork for manipulating and controlling anyonic quasiparticles in quantum Hall systems and beyond."], "keyword": ["Fractional Quantum Hall Effect", "Anyons", "Interferometery", "Shot noise", "Topological order"], "primary_title": "Probing Topological Order: Interferometry, Noise, and Emerging Platforms for Anyons", "uri": "https://repository.library.brown.edu/studio/item/bdr:qcd2qadb/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:qcd2qadb/"}, {"pid": "bdr:jm8ybkjj", "object_type": "pdf", "abstract": ["Magnetic materials with a high degree of frustration, whether arising from lattice geometry or competing anisotropic interactions, can host exotic ground states such as quantum spin liquids, while additional exchange terms and small perturbations often stabilize long-range magnetic orders. Investigating these ordered phases in spin-liquid candidate materials through determining their magnetic structures, studying collective excitations, and exploring local degrees of freedom, provides crucial insights into frustrated magnetism. In this thesis, I present a series of neutron and X-ray scattering experiments on novel quantum materials to investigate their magnetic properties and spin and orbital dynamics to deepen our understanding of emergent phenomena driven by frustration. K2IrCl6 is a highly frustrated J=1/2 antiferromagnet on a face-centered cubic lattice. I first present a comprehensive study of its structural behavior. Neutron pair distribution function analysis reveals dynamic rotations and distortions of IrCl6 octahedra driven by soft phonon modes and a dynamic Jahn-Teller effect. Resonant inelastic X-ray scattering shows a spin-orbit exciton propagation mediated by superexchange. Additionally, a global structural distortion that coincides with the onset of magnetic ordering provides evidence for strong pseudospin-lattice coupling. Next, I investigate magnetic excitations and ordering phenomena in K2IrCl6. Inelastic neutron scattering reveals a nodal-line spin liquid state and a large fluctuation-induced spin-wave gap. Neutron diffraction and resonant elastic X-ray scattering indicate a phase coexistence scenario, highlighting the role of quantum fluctuations. Through a quantitative comparison between theoretical calculations and experimental results, we establish this material as a striking example of order-by-disorder appearing at the brink of the nodal-line spin liquid phase. Finally, I present preliminary results on TbAgGe, a rare-earth intermetallic compound on a distorted Kagome lattice. Neutron diffraction measurements on single crystals reveal multiple magnetic phases with distinct propagation vectors, while inelastic neutron scattering on the powder sample shows a series of dispersive crystal field excitations and a potential magnon mode. These preliminary findings provide a basis for future experiments and theoretical modeling of this complex frustrated system."], "keyword": ["strongly-correlated material"], "primary_title": "Investigation on Magnetic Properties in Novel Quantum Materials through Neutron and X-ray Scattering", "uri": "https://repository.library.brown.edu/studio/item/bdr:jm8ybkjj/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:jm8ybkjj/"}, {"pid": "bdr:v5wuktdm", "object_type": "pdf", "abstract": ["This thesis explores the interplay between broken symmetry and electronic correlations in emergent quantum phenomena within low-dimensional electron systems. The first half of the thesis centers on angle-resolved transport measurements, enabled by a novel planar sunflower geometry. We develop a new experimental protocol to systematically extract the tensorial parameters that characterize both the linear and nonlinear transport regimes. In Chapter 2, we investigate the moir\u00e9 flat bands of magic-angle twisted trilayer graphene (TTG). By extracting the full conductivity matrix in the ohmic regime, we uncover an intimate link between nematicity, superconductivity, and strange metallicity, which enables a direct determination of the superconducting order parameter symmetry in TTG. We further demonstrate the capability to fully resolve the rank-3 nonlinear conductivity tensor using angle-resolved techniques. By measuring the potential distribution along the perimeter of the disk-shaped device, we provide experimental input to a comprehensive theoretical framework, allowing all nonlinear tensor components to be determined with exceptional precision. We apply this methodology to both TTG and Bernal bilayer graphene devices, and in the latter, report an unambiguous identification of the nonlinear Hall conductivity\u2014the dissipationless component of second-order transport\u2014alongside tensor components corresponding to dissipative nonlinear effects. Next, we explore excitons in the fractional quantum Hall effect in quantum Hall graphene bilayers. In the interlayer-coupled two component fractional quantum Hall regime, we observe two types of fractional excitons: one as a fractional analogue of the exciton condensate at total filling of one, and another involving fractionally charged constituents, obeying bosonic, fermionic, or anyonic statistics. In the decoupled limit, we showcase the identification and control of anyonic excitons in the Jain sequence via thermal excitation and electrostatic doping. Highlighting the rich landscape of this platform, we also demonstrate pseudospin-induced transitions and observe excitonic neutral modes at even-denominator states. Leveraging versatility of van der Waals heterostructures, we explore many-body, collective phenomena using both planar and vertical device architectures. Together, our findings offer key insights into correlated quantum phases in low-dimensional systems."], "keyword": ["Experimental", "condensed matter physics"], "primary_title": "Emergent Phenomena in Multilayer Graphene with Planar and Vertical Architectures", "uri": "https://repository.library.brown.edu/studio/item/bdr:v5wuktdm/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:v5wuktdm/"}, {"pid": "bdr:mfyhnw9u", "object_type": "pdf", "abstract": ["Light pulse atom interferometry (LPAI) is a technique capable of producing incredibly accurate measurements of an atom and can be applied to many novel forms of quantum sensing. LPAI can be used to measure gravity and has demonstrated a precision on the order of 10^-9 in other lab-based experiments, which can exceed the state of the art of classical gravimeters. Such laboratory setups are large and not constructed in a form capable of being deployed in the field. Moreover, they operate at slow repetition rates and are highly susceptible to vibration and inertial variations. This thesis presents the construction and operation of an LPAI gravimeter built in a form factor capable of being deployed on a surface ship at sea. Two at-sea excursions are demonstrated, with the gravimeter producing measurements that successfully aid in an inertial navigation solution. The coupling of the LPAI gravimeter with a high-bandwidth MEMS accelerometer forms a hybrid sensor through a \"feedforward-feedback\" scheme that enables the measurement of specific force while subject to a large range of dynamic motion. A sub-\u00b5g-scale sensitivity is achieved, with an absolute accuracy of 10 \u00b5g and a stability floor of 150 ng over multiple weeks. Additional land-based field testing is performed to demonstrate viability of the LPAI gravimeter outside of a laboratory environment. Further improvements of sensor performance are investigated, especially absolute accuracy and long-term stability, with the goal of producing a gravimeter capable of making reliable measurements of gravity at sub-\u00b5g accuracy over many years. Spurious phase shifts in the interferometer sequence that produce gravimeter accuracy errors are studied, and efforts to mitigate or suppress them are presented."], "keyword": ["Gravity--Measurement", "Atom interferometry"], "primary_title": "A Light Pulse Atom Interferometric Gravimeter in Dynamic Environments", "uri": "https://repository.library.brown.edu/studio/item/bdr:mfyhnw9u/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:mfyhnw9u/"}, {"pid": "bdr:s784pkuf", "object_type": "pdf", "abstract": ["Enterobacter sp. SM3, is a recently-isolated species of gut bacteria that proficiently spreads over nutritional substrates\u2014-a motility pattern called swarming. The connection between the motility of individual bacteria and the higher-order organization observed at the level of a swarm is not well understood and is a function of both biological and physical factors. In this defense, I will characterize and describe the motility of SM3 in liquid media, drawing physical insights from my findings. I imaged SM3, grown both as individuals and as swarmers, with two-dimensional optical microscopy. Using tracking algorithms, I extracted motility parameters including the average speed, turning time, run time, and turning angle. I found that there were distinct differences in these parameters between swimmers and swarmers\u2014with swarmers turning less often and for smaller angles, resulting in smoother trajectories. Using a mechanical model, my results show that the main difference in motility can be physically attributed to the longer length of swarmers. Taking advantage of the variable length of swarmers, I imaged swarmers of different length swimming in close proximity to a surface and studied their behavior. Generally, bacteria near surfaces swim in circular trajectories due to the counter rotation of their cell body and flagellar bundle, which hydrodynamically couple with the surface. I found that swarmers of longer length traced circular trajectories that were larger in radius than shorter ones. We modeled swimming bacteria as two counter rotating spheres separated by a distance and connected by a spring. The results of the simulation showed that the dependency of radius on cell length can be explained by the torque-dipole component of the fluid flow for our model swimmer. Finally, I imaged swimming SM3 with three-dimensional digital holographic microscopy. In nature, bacteria inhabit complex, three-dimensional environments, making 3D imaging and tracking essential tools for understanding their motility. Furthermore, 3D imaging has distinct advantages over 2D imaging, such as high-throughput, minimal surface interactions, and more robust statistics. I found that the motility parameters in 3D are similar to those in 2D, but the results are more reliable and less affected by the boundary effects of a nearby solid surface."], "keyword": ["Bacteria", "Biophysics", "Microbiology", "Cell adhesion", "Computer Vision", "Flagella (Microbiology)", "bacterial motility", "Biofilms", "swarming", "Swimming", "Holography", "Bacterial biofilms", "Enterobacter sp. SM3", "SM3", "Cell tracking", "Run-and-tumble"], "primary_title": "Swimming Kinematics of Enterobacter sp. SM3", "uri": "https://repository.library.brown.edu/studio/item/bdr:s784pkuf/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:s784pkuf/"}, {"pid": "bdr:m42dkczz", "object_type": "pdf", "keyword": ["Topological Matter", "Density Functional Theory", "Metals", "computational physics", "Quantum Monte Carlo", "condensed matter physics", "Diffusion Monte Carlo", "Topological Materials"], "primary_title": "DIFFUSION MONTE CARLO METHODS FOR STUDYING STRONGLY-CORRELATED AND TOPOLOGICAL MATERIALS", "abstract": ["Investigating condensed matter systems, to understand and predict their properties for materials design and discovery, with computational methods offers complementary insights to experimental studies. The grand challenge faced by computational methods is the development of sufficiently accurate and efficient algorithms that can solve the Schr\u00f6dinger equation for many-body systems. A variety of first-principles methods are tailored to perform electronic structure calculations\u2014 numerical solutions to the Schr\u00f6dinger equation\u2014on quantum materials, distinguished by their treatment of electron correlation, computational cost, and degree of accuracy. The most widely used method to-date is Density Functional Theory, due to its favorable scaling with system size and its well-established reliability for weakly correlated systems. However, a suite of stochastic methods, comparable in computational cost, outperforms Density Functional Theory (DFT) in the modeling of strong electronic correlation and has become a gold standard for accuracy. Namely, Quantum Monte Carlo methods use random sampling of multi-dimensional integrals to estimate material properties. With the advent of larger, more powerful supercomputers and the growth of machine-learning models that require electronic structure derived datasets as input, it is important to pursue methodological developments of Quantum Monte Carlo (QMC) methods. In this thesis, I introduce a novel method for expanding QMC\u2019s ability to identify topological materials and benchmark a new technique designed to improve its treatment of metallic systems. In Part I. I first introduce the formalisms of Density Functional Theory and Quantum Monte Carlo methods. I then discuss topological insulators, the focus of our new extension for Quantum Monte Carlo identification of topological behavior in quantum materials, and outline the challenge of modeling magnetic metals. Part II. presents our new method for detecting band inversions in topological insulators using Diffusion Monte Carlo. Band inversion is a hallmark of topological insulators: at time-reversal invariant points in the Brillouin zone, spin-orbit coupling (SOC) induces a swapping of orbital character at the bulk band edges. Our approach applies a momentum- space-resolved atomic population analysis throughout the first Brillouin zone utilizing the L\u00f6wdin method and the one-body reduced density matrix produced with Diffusion Monte Carlo (DMC). We demonstrate this new technique on the topological insulator bismuth telluride, which displays band inversion between its Bi-p and Te-p states at the \u0393-point. Additionally, we use our method to compare the degree of band inversion present in monolayer Bi2Te3, which has no interlayer van der Waals interactions, to that seen in the bilayer and bulk. Reliably detecting band inversion in solid-state systems with many-body methods would aid in identifying possible candidates for spintronics and quantum computing applications and improve our understanding of the physics behind topologically-nontrivial systems. In Part III., I report the results of benchmarking a new twist-averaging technique on the paradigmatic metals aluminum and iron, and demonstrate its application to CrTe2. The exchange-correlation functional is central to DFT and determines the accuracy of DFT in describing the interactions among electrons in solids. However, a problematic trendhasemergedinwhichmoresophisticatedfunctionalsoverestimatetheatomicmagneticmoment in simple metals; recent studies have revealed Quantum Monte Carlo methods are also susceptible to this overestimation. Metals are especially challenging for electronic structure methods because of their energy band crossings at the Fermi level, requiring careful treatment of single-particle orbital occupations near the Fermi surface. Given the computational limitations of QMC methods in the use of supercells and dense k-point sampling of the Brillouin Zone, we introduce Grand Canonical Twist-Averaging with (Spin) Adapted Fermi Levels (GCTA-(S)AFL) to improve the modeling of magnetic metals. In this work we benchmark the GCTA-(S)AFL techniques using Diffusion Monte Carlo on challenging metallic properties. Comparisons between traditional twist-averaging methods and our approach are presented for equation of state calculations of nonmagnetic aluminum, as well as for the cohesive energy and magnetic moment of \u03b1-Fe. Lastly, I apply our technique to CrTe2, a two-dimensional ferromagnetic metal, to bring new many-body insights to its magnetic phase."], "uri": "https://repository.library.brown.edu/studio/item/bdr:m42dkczz/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:m42dkczz/"}, {"pid": "bdr:fpqvqgux", "object_type": "pdf", "abstract": ["The discovery and control of novel magnetic states often spurs technological advancements, and acts as a rigorous test of our most fundamental theories of interacting systems. A unique realization of this idea is offered in the plethora of electronic properties and magnetic ordering phases discovered within strongly correlated electronic materials. The variety of material properties arise from variations in the couplings strengths between the crystal lattice, electron spin and orbital angular momenta, and charge. In this thesis, I present a series of resonant inelastic X-ray scattering (RIXS) experiments on novel magnetic materials to elucidate the coupling between the electronic structures and magnetic interactions of the materials. NaCaNi2F7 is a unique example of spin-1 Heisenberg antiferromagnet on the pyrochlore lattice, but the presence of A-site (Na1+/Ca2+) disorder complicates the local electronic and magnetic environment of the B-site (Ni2+). To elucidate the influence of A-site disorder on the B-site electronic structure, I utilized RIXS to study the energy levels of the various excited electronic states in NaCaNi2F7. I provide a comprehensive electronic structure model, demonstrate the robustness of the electronic structure to the A-site disorder, and clarify the magnitude of the Ni2+ effective magnetic moment. NiPS3 is one of the few layered van der Waals materials that exhibits both antiferromagnetic order and strong correlations, and is suggested to undergo Berezinskii-Kosterlitz-Thouless transition in the monolayer limit. I aimed to investigate this possibility through direct measurement of the thickness dependence of magnetic excitations using RIXS. I first determined the thickness dependence of the electronic structure through a series of RIXS experiments and found a decrease in electron hopping and charge-transfer energy scales approaching the 2D limit. I also uncovered a sample degradation pathway brought on by prolonged X-ray beam exposure. Through a collaboration with groups at Columbia University and Brookhaven National Laboratory, I was able to corroborate these findings with another contemporary van der Waals material, alpha-RuCl3 and graphene/RuCl3 heterostructures. Ultra-thin sample degradation of this kind has caused critical experimental failures and is a necessary obstacle to overcome in order to utilize X-ray scattering to advance our understanding of 2D magnetism. Tm3Fe5O12, a ferrimagnetic insulating garnet oxide that exhibits an inherent interfacial Dzyaloshinskii-Moriya interaction in thin films, has emerged as a promising candidate for spin-based, beyond-CMOS technologies. By utilizing the magnetic circular dichroism signal in RIXS (RIXS-MCD), and comparing to Y3Fe5O12, I present evidence that Tm3+ plays a non-trivial role in the observed MCD signal. In addition, the spectra of a fully strained and unstrained film are found to be nearly equivalent, providing support that the observed MCD signal is strain independent. I also provide an electronic structure model for Fe3+ in Tm3Fe5O12 and Y3Fe5O12 which accurately reproduces the RIXS peak positions, and qualitatively agrees with the RIXS-MCD signal."], "keyword": ["Magnetism", "X-rays--Scattering", "van der Waals materials", "Rare earth oxide thin films", "antiferromagnetic", "frustrated magnetism"], "primary_title": "Understanding Magnetic Interactions through the Electronic Structures of Strongly Correlated Materials using Resonant X-ray Scattering", "uri": "https://repository.library.brown.edu/studio/item/bdr:fpqvqgux/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:fpqvqgux/"}, {"pid": "bdr:4fjrxnrp", "object_type": "pdf", "abstract": ["Several hints of potential $B$ physics anomalies have been observed in recent years. Some of the observables, such as $R_{K}$, the ratio of branching fractions of $B^{+}\\to K^{+}\\mu^{+}\\mu^{-}$ to that of $B^{+}\\to K^{+}e^{+}e^{-}$, have exhibited deviations from the standard model prediction. This could be a sign of new physics involving lepton non-universality. In 2018, the CMS experiment implemented a novel trigger strategy called $B$-parking, which enabled the collection of an unbiased sample of $\\mathcal{O}(10^{10})$ $B$ hadron decays. This dataset provides an opportunity to measure and search for rare $B$ decays, such as the measurement of $R_{K}$. This dissertation details the use of the data parking and tag-and-probe trigger strategy to collect an enormous and unbiased sample of $B$ hadron decays, followed by a thorough analysis of the $R_{K}$ measurement using this data. To increase the sensitivity of the analysis for soft electrons, a new low-$p_T$ electron reconstruction algorithm is developed to improve the reconstruction efficiency in the low-energy region for electrons. Dedicated electron identifications are also developed for this analysis to reduce contamination from fake electrons. A machine-learning-based classifier is developed and applied to the event selection process to extract rare signals from the overwhelming background. Finally, the analysis strategy is validated through a series of cross-checks, and the first measurement of $R_K$ at CMS is reported."], "keyword": ["Experimental Particle Physics"], "primary_title": "Test of Lepton Universality using B+\u2192 K+ \u2113+ \u2113\u2212 decays", "uri": "https://repository.library.brown.edu/studio/item/bdr:4fjrxnrp/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:4fjrxnrp/"}, {"pid": "bdr:tj262ceq", "object_type": "pdf", "abstract": ["This dissertation presents a new technique to increase the accessible noise range in micro and nanofluidics using electrokinetics. We show that the application of voltage noise with the same statistical properties as fundamental thermal noise controllably amplifies the Brownian motion of lambda DNA molecules suspended in solution inside a nanoslit. We analyzed the trajectories of single molecules and found that their self-diffusivity in the direction of the applied electric field increased in proportion with the variance of the voltage noise. However, unlike thermal noise, the voltage noise causes correlated fluctuations of different molecules and their segments. Therefore, this technique unlocks a previously inaccessible effective temperature regime for studies and applications of noise-dependent phenomena. Using this new technique, we significantly increased the back and forth hopping of a DNA between neighboring nanopits inside a nanofluidic device. The second half of this dissertation presents observation, analysis, theory, and simulation of a new nanofluidic transport phenomenon where a gradient in liquid viscosity causes transport of nanoparticles inside a glass nanofluidic channel. Viscosity gradient results in multiplicative (state-dependent) noise, which refers to the dependence of a particle\u2019s thermal fluctuations on its position. To investigate the motion of particles in viscosity gradient we measured the drift and the flux of nanoparticles as well as the ionic current inside the nanochannel with no applied voltage, pressure, or salinity gradient. We show that the resulting dynamics agrees with the isothermal description for Brownian particles. We discuss the origins of the ionic current, the dynamics of the nanoparticles, and the role of the boundary conditions for the ions and the nanoparticles."], "keyword": ["Biophysics", "Nanofluids"], "primary_title": "Electrokinetic noise driven dynamics of DNA molecules and dynamics of nanoparticles in diffusivity gradients.", "uri": "https://repository.library.brown.edu/studio/item/bdr:tj262ceq/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:tj262ceq/"}, {"pid": "bdr:xj4mq2gw", "object_type": "pdf", "abstract": ["The High-Luminosity Large Hadron Collider (HL-LHC) will dramatically increase the volume collision data, giving significant challenges to current computing and storage capabilities. In this study, we explore the application of lossy compression techniques to quark and gluon particle-level jets using the Baler algorithm. We investigate three different autoencoder-based models: Conventional Auto-Encoder, Single-feature Auto-Encoder, Forked-network Auto-Encoder, to perform lossy compression on jet constituent information. To further evaluate the preservation of physical information after compression, Particle Flow Networks (PFNs) are employed for jet tagging on the reconstructed jets, and the relationship between the compression ratio and the area under the ROC curve (AUC) is expected to be analyzed systematically. Our results show that although compressed representations maintain good jet tagging performance, challenges such as information loss due to zero-padding and discrepancies in jet mass distributions remain."], "keyword": ["Physics", "Large Hadron Collider", "LHC", "Particle Physics", "AI/ML", "Jet Tagging", "Jet Substructure", "Lossy Compression"], "primary_title": "Studies of the Effects of Lossy Compression on Hadronic Jet Reconstruction and Classification", "uri": "https://repository.library.brown.edu/studio/item/bdr:xj4mq2gw/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:xj4mq2gw/"}, {"pid": "bdr:svrpvurs", "object_type": "pdf", "abstract": ["Jet tagging is the process of identifying the particle that initiates a jet. It is a critical but challenging task in high-energy particle physics due to the complex substructure of jets. Machine Learning techniques have been introduced to help handle the task; however, trade-offs between accuracy and uncertainty among different machine learning models have been detected. This study explores the use of knowledge distillation as a technique to improve model performance by transferring knowledge from complex teacher models like Particle Flow Networks (PFNs) to simpler models, including Deep Neural Networks (DNNs) and Energy Flow Networks (EFNs). Simulated high-energy collision datasets were used to evaluate the impact of knowledge distillation on quark-gluon tagging and top tagging tasks. The results show that DNNs benefit from distillation, achieving higher accuracy while maintaining or reducing uncertainty, effectively breaking the Pareto frontier. EFNs demonstrated limited improvement when distilled from PFNs. These findings highlight the potential of knowledge distillation to optimize machine learning models for jet tagging."], "keyword": ["Physics", "Large Hadron Collider", "LHC", "Particle Physics", "AI/ML", "Knowledge Distillation", "Jet Tagging", "Jet Substructure"], "primary_title": "Application of Knowledge Distillation in Jet Tagging at LHC", "uri": "https://repository.library.brown.edu/studio/item/bdr:svrpvurs/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:svrpvurs/"}, {"pid": "bdr:82vhm8gj", "object_type": "pdf", "abstract": ["Over the past several years, my research has been focused on studying nearby galaxy clusters. This has required overcoming three key challenges: reducing deep, wide-field observations from modern telescopes; classifying the properties of clusters from optical data; and estimating their masses. These challenges are addressed across several different projects that I have pursued. A new processing pipeline to support the Local Volume Complete Cluster Survey is presented and tested to confirm that it is suitable for a variety of science cases; then, processed observations from the new pipeline are used to carry out two separate studies which showcases the fidelity of the new data products. The intracluster light of Abell 3667 is explored and a new feature in the cluster is unveiled thanks to the improved sky correction, which enables a subset of low surface brightness science. The mass of the Hercules Supercluster is then estimated using weak gravitational lensing; this is only possible since systematics are corrected down to the percent-level during processing. Additionally, the influence of background clusters is explicitly included via a multi-plane lens model, a first for weak lensing studies of galaxy clusters. The work is concluded by summarizing future directions for this research, including projects with observations from the Vera C. Rubin Observatory and continued investigations into Abell 3667 along with the Hercules Supercluster."], "keyword": ["Cosmology", "Galaxies--Clusters", "Gravitational lenses"], "primary_title": "Understanding Local Clusters with Deep Optical Data", "uri": "https://repository.library.brown.edu/studio/item/bdr:82vhm8gj/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:82vhm8gj/"}, {"pid": "bdr:xmgndyba", "object_type": "pdf", "abstract": ["In this thesis, we will examine several routes taken to go beyond general relativity. After a review of general relativity, \u039bCDM cosmology, and the current state of quantum gravity, we will begin with the classical double copy, a mapping between exact solutions in general relativity and in Abelian gauge theory. Within this subject, we will expand the range of the classical double copy to all Kerr-Schild metrics, not just stationary ones as in its original formulation. Then, we will prove an analog of Birkhoff's theorem for spacetimes with Kleinian signature. After that, we will provide a proof using the Cartan-Karlhede algorithm that two spacetimes discovered using the extension of the classical double copy are diffeomorphic. We will then move to modified gravity. In that chapter, a model is postulated that seeks to explain why the weak force only interacts directly with left-handed fermions. This model is called a graviweak theory, and its goal is accomplished using spontaneous symmetry breaking of an extra scalar field. Finally, we will turn to canonical quantum gravity and study the normalizability of an exact solution called the Chern-Simons-Kodama state."], "keyword": ["Physics", "Astrophysics", "Physics, Astrophysics, Galaxy Clusters, Cosmology", "Mathematical physics", "Theoretical physics"], "primary_title": "Select Topics in Classical and Quantum Gravity", "uri": "https://repository.library.brown.edu/studio/item/bdr:xmgndyba/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:xmgndyba/"}, {"pid": "bdr:pdwba7ad", "object_type": "pdf", "abstract": ["The control of spin currents through interfacial and spin-orbit-driven effects is central to the development of next-generation spintronic technologies. This dissertation investigates how spin-orbit coupling (SOC) and interfacial symmetry govern the generation, transmission, and conversion of spin currents across three model material systems including half-metallic CrO2, RuO2/CrO2 bilayers, and Ru-Pt alloys. These systems were strategically chosen to trace the full pathway of spin manipulation: CrO2 for intrinsic spin polarization and quantum transport, RuO2/CrO2 for interfacial exchange and spin coupling, and Ru-Pt for extrinsic spin-charge conversion. Epitaxial CrO2 thin films serve as a platform for intrinsic spin current generation and quantum transport. Their nearly 100% spin polarization enables robust, coherent spin currents while low-temperature transport measurements reveal quantum oscillations and high mobility, indicative of phase-coherent electronic motion. These results establish CrO2 as an ideal half-metal for generating spin-polarized currents and exploring SOC-influenced quantum transport phenomena. RuO2/CrO2 heterostructures exemplify interfacial exchange and spin coupling where an active spin-orbit antiferromagnetic RuO2 layer interacts with the CrO2 ferromagnet. Magnetization measurements reveal spin reorientation and exchange bias effects, illustrating how SOC and broken inversion symmetry at the interface can modulate spin alignment, interlayer magnetic interactions, and the transmission of spin angular momentum across oxide heterostructures. Ru-Pt alloys provide a model for extrinsic spin-to-charge conversion, where spin currents generated in a ferromagnet are converted into measurable charge signals via the spin Hall effect. Systematic mapping of the spin Hall angle across the full composition range demonstrates how crystal structure and SOC control the efficiency of spin-charge interconversion. Beyond conventional impurity tuning, Ru-Pt demonstrates structural phase evolution as an effective tuning parameter and poses as a promising alternative for spin-orbit torque devices. These results highlight how extrinsic SOC effects can be engineered to detect, manipulate, or generate spin currents in metallic systems. Together, these studies establish a unified framework connecting intrinsic spin generation and interfacial spin coupling to extrinsic spin-to-charge conversion and detection. The results provide insight into design principles for low-power, scalable spintronic devices that exploit SOC and symmetry engineering to control spin currents across diverse material platforms."], "keyword": ["spintronics", "Spin Hall Effect", "Half metal", "Altermagnetism", "Quantum oscillations", "Exchange bias"], "primary_title": "Mechanisms of Spin and Charge Transport Across Oxide and Alloy Interfaces", "uri": "https://repository.library.brown.edu/studio/item/bdr:pdwba7ad/", "json_uri": "https://repository.library.brown.edu/api/items/bdr:pdwba7ad/"}]}}