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Articles 1 - 24 of 24
Full-Text Articles in Physics
Quantum Phase Transitions In Disordered Boson Systems, Zhiyuan Yao
Quantum Phase Transitions In Disordered Boson Systems, Zhiyuan Yao
Doctoral Dissertations
In this dissertation, we study the superfluid-insulator quantum phase transition in disordered boson systems. Recently, there has been considerable controversy over the validity of the scaling relations of the superfluid--Bose-glass quantum phase transition in three dimensions. Results from experimental and numerical studies on disordered quantum magnets contradict the scaling relations and the associated conventional scaling hypothesis for the singular part of the free energy. We determine various critical exponents of the superfluid--Bose-glass quantum phase transition in three-dimensional disordered Bose-Hubbard model through extensive Monte Carlo simulations. Our numerical study shows the previous studies on disordered quantum magnets were performed outside the …
Swelling Induced Deformation Of Thermally Responsive Hydrogels, Ying Zhou
Swelling Induced Deformation Of Thermally Responsive Hydrogels, Ying Zhou
Doctoral Dissertations
Hydrogels are crosslinked polymeric networks imbibed with aqueous solutions. They undertake dramatic volume changes through swelling and deswelling processes, which can be stimulated by factors like temperature, pH or different chemicals. These unique properties render hydrogels particularly interesting for shape morphing related applications. In this thesis, we focus on the swelling induced deformation of thermally responsive hydrogels with lower critical solution temperatures (LCSTs), including poly(N-isopropylacrylamide) (PNIPAm) and poly(N,N-diethylacrylamide) (PDEAm). Particularly, benzophenone containing monomers are copolymerized with NIPAm or DEAm to create photocrosslinkable temperature-responsive polymers, which allows fabrication of hydrogels with controlled shapes and crosslinking …
Alpha Radiation Studies And Related Backgrounds In The Darkside-50 Detector, Alissa Monte
Alpha Radiation Studies And Related Backgrounds In The Darkside-50 Detector, Alissa Monte
Doctoral Dissertations
DarkSide-50 is the current phase of the DarkSide direct dark matter search program, operating underground at the Laboratori Nazionali del Gran Sasso in Italy. The detector is a dual-phase argon Time Projection Chamber (TPC), designed for direct detection of Weakly Interacting Massive Particles (WIMPs), and housed within a veto system of liquid scintillator and water Cherenkov detectors. Since switching to a target of low radioactivity argon extracted from underground sources in April 2015, the background is no longer dominated by naturally occurring 39Ar. However, alpha backgrounds from radon and its daughters remain, both from the liquid argon bulk and internal …
Collider Tests Of Fundamental Symmetries And Neutrino Properties, Haolin Li
Collider Tests Of Fundamental Symmetries And Neutrino Properties, Haolin Li
Doctoral Dissertations
The CP parity of the Higgs boson and the details of the electroweak symmetry breaking are the two crucial ingredients to understand the matter-antimatter asymmetry in our universe. Electroweak baryogenesis is an intriguing solution to the puzzle of this unexplained observed asymmetry because of its testability at present and near future collider experiments. The possibilities of testing CP phase in the Two-Higgs-Doublets Models (2HDMs) and the generation of a strong first-order electroweak phase transition (SFOEWPT) in the real singlet model at the future high luminosity LHC are studied. In addition to the specific extensions to the Standard Model (SM), I …
Parallel Algorithms For Time Dependent Density Functional Theory In Real-Space And Real-Time, James Kestyn
Parallel Algorithms For Time Dependent Density Functional Theory In Real-Space And Real-Time, James Kestyn
Doctoral Dissertations
Density functional theory (DFT) and time dependent density functional theory (TDDFT) have had great success solving for ground state and excited states properties of molecules, solids and nanostructures. However, these problems are particularly hard to scale. Both the size of the discrete system and the number of needed eigenstates increase with the number of electrons. A complete parallel framework for DFT and TDDFT calculations applied to molecules and nanostructures is presented in this dissertation. This includes the development of custom numerical algorithms for eigenvalue problems and linear systems. New functionality in the FEAST eigenvalue solver presents an additional level of …
Measured Capillary Forces On Spheres At Liquid Interfaces And The Mechanics Of Interfacial Particulate Assemblies, Wei He
Doctoral Dissertations
Particle-laden interfaces have promising potentials in many fields because the particulate nature can endow the surface with physical properties that are not readily obtained from molecular-scale surfactants. In this dissertation, we first focus on measuring capillary forces on particles at fluid interfaces in order to assess the key parameters that yield effective stabilizing particles. In experiment, the force and the displacement of a millimeter-scale particle passing through a liquid interface were recorded. We find that the peak force needed to detach a particle from an interface crowded with other particles is consistently smaller than the force at a clean interface. …
Preparation, Mechanics And Structure Of Sphere Packings Near The Random Loose Packing Limit, Greg Robert Farrell
Preparation, Mechanics And Structure Of Sphere Packings Near The Random Loose Packing Limit, Greg Robert Farrell
Doctoral Dissertations
Packings of monodisperse, hard spheres serve as an important model system in the understanding of granular materials which are ubiquitous in nature and industry from sedimented river beds, to construction aggregates, to pharmaceuticals. Unlike frictionless hard spheres which are only stable at densities near the random close packing volume fraction, packings of real spheres form stable packings over a range of volume fractions. We report experimental investigations of sedimented packings of noncohesive polymethyl-methacrylate spheres over a range of volume fractions near the lower limit of this range of volume fractions. We create packings by slow sedimentation in a viscous fluid …
Geometry, Growth And Pattern Formation In Thin Elastic Structures, Salem Al-Mosleh
Geometry, Growth And Pattern Formation In Thin Elastic Structures, Salem Al-Mosleh
Doctoral Dissertations
Thin shells are abundant in nature and industry, from atomic to planetary scales. The mechanical behavior of a thin shell depends crucially on its geometry and embedding in 3 dimensions (3D). In fact, the behavior of extremely thin shells becomes scale independent and only depends on geometry. That is why the crumpling of graphene will have similarities to the crumpling of paper. In this thesis, we start by discussing the static behavior of thin shells, highlighting the role of asymptotic curves (curves with zero normal curvature) in determining the possible deformations and in controlling the folding patterns. In particular, we …
Equilibrium Partitioning Of Binary Polymer Mixtures Into Biological Nanopores, Mehmet Alphan Aksoyoglu
Equilibrium Partitioning Of Binary Polymer Mixtures Into Biological Nanopores, Mehmet Alphan Aksoyoglu
Doctoral Dissertations
The cell interior, enclosed by membrane barriers, is a condensed solution of inorganic ions, polymers, carbohydrates, polynucleotides, and a large number of other organic molecules. Within cells, transport of metabolites and biopolymers, such as polynucleotides and proteins, occurs partly through specific transmembrane pores (mesoscopic ion channels) spanning cellular compartments. Examples of such functions are translocation of matrix RNA molecules from cell nucleus through nuclear pore complexes, ejection of viral genome from bacterial virus capsids into host bacterial cells, and translocation of protein factors across toxin channels in biological membranes. All these processes, that occur in the cellular milieu, are mediated …
Application And Evaluation Of Lighthouse Technology For Precision Motion Capture, Soumitra Sitole
Application And Evaluation Of Lighthouse Technology For Precision Motion Capture, Soumitra Sitole
Masters Theses
This thesis presents the development towards a system that can capture and quantify motion for applications in biomechanical and medical fields demanding precision motion tracking using the lighthouse technology. Commercially known as SteamVR tracking, the lighthouse technology is a motion tracking system developed for virtual reality applications that makes use of patterned infrared light sources to highlight trackers (objects embedded with photodiodes) to obtain their pose or spatial position and orientation. Current motion capture systems such as the camera-based motion capture are expensive and not readily available outside of research labs. This thesis provides a case for low-cost motion capture …
Computational Modeling Of Defect-Engineered Graphene Derivatives And Graphene-Polymer Nanocomposites, Asanka Weerasinghe
Computational Modeling Of Defect-Engineered Graphene Derivatives And Graphene-Polymer Nanocomposites, Asanka Weerasinghe
Doctoral Dissertations
Graphene has unique mechanical, electronic, and thermal properties, which enable a broad range of technological applications. For example, graphene flakes can be used as filler to enhance the properties of polymer-matrix nanocomposites and graphene derivatives, generated by defect engineering and chemical functionalization of single-layer graphene, have tunable properties that are very promising for engineering electronic and thermomechanical metamaterials. A fundamental understanding of the structure-property relationships that govern the function of such nanocomposites and graphene derivatives is required for designing and developing future graphene-based metamaterials. Toward this end, we have conducted a systematic study based on extensive molecular-dynamics simulations of mechanical …
Combined Spectroscopic And Scanning Probe Studies Of Electronic Interactions In Nanostructured 1d And 2d Semiconductors, Peijian Wang
Combined Spectroscopic And Scanning Probe Studies Of Electronic Interactions In Nanostructured 1d And 2d Semiconductors, Peijian Wang
Doctoral Dissertations
This dissertation includes the exploration about the following research questions: 1. What is the correlation between the work function and ground state interactions in organic semiconductor assemblies? 2. How do non-covalent chemical doping tune the work function in MoS2? 3. Are there surface charges in the Aluminum doped ZnO nanocrystals (AZO) and what's the evolution of the surface charges and polarizabilities from undoped AZO to doped AZO? 4. How is the homogeneity like during doping in the organic thermoelectric materials? The techniques we employed in the research is the spatially registered Kelvin Probe Force Microscopy and Photoluminescence spectroscopy …
Antenna Enhanced Graphene Terahertz Emitter And Detector, And Graphene Microwave Detector, Jiayue Tong
Antenna Enhanced Graphene Terahertz Emitter And Detector, And Graphene Microwave Detector, Jiayue Tong
Doctoral Dissertations
Graphene is a promising candidate for optoelectronic and fast electronics research. In THz and sub-THz frequency regime, sensitive detectors are very difficult to make. This dissertation presents my Ph.D study of THz sources and THz/Microwave (MW) detectors made with graphene. My work demonstrates the emission and detection of 1.9 THz radiation from graphene coupled to a double-patch antenna and a silicon lens. More than 3 orders of magnitude performance improvements are achieved in a half-edge-contacted graphene thermoelectric (TE) detector operating at 1.9 THz by antenna coupling and Si lens coupling. The thermoelectric mechanism is also employed in MW detection. A …
Dynamics And Structure Of Polyelectrolyte Complexes, Hamidreza Shojaei-Mahib
Dynamics And Structure Of Polyelectrolyte Complexes, Hamidreza Shojaei-Mahib
Doctoral Dissertations
Interaction of charged macromolecules among themselves and with charged interfaces in salty aqueous medium is a common phenomenon prevalent in biology and synthetic systems. We have addressed several inter-related issues in this general context. First we present a theory of adsorption of polyelectrolytes on the interior and exterior surfaces of a charged spherical vesicle. We derive the critical adsorption condition and the density profile of the polymer in terms of various characteristics of the polymer, vesicle, and the solution, such as the length and charge density of polymer, the radius and charge of the vesicle, the salt concentration of the …
Self-Assembling Networks In Soft Materials, Ishan Prasad
Self-Assembling Networks In Soft Materials, Ishan Prasad
Doctoral Dissertations
This dissertation presents a study on heterogeneous network structure in two distinct classes of soft material systems: disordered assemblies of jammed binary spheres and ordered morphologies of block copolymer melts. The aim is to investigate the combined role of geometry and entropy in structure formation of soft matter assemblies. First, we investigate the influence of particle size asymmetry on structural properties of jammed binary sphere mixtures. We give evidence of two distinct classes of materials separated by a critical size ratio that marks the onset of a sharp transition due to simultaneous jamming of a sub-component of the packing. We …
Complex Ground States Of Vortices And Filaments, Qingyou Meng
Complex Ground States Of Vortices And Filaments, Qingyou Meng
Doctoral Dissertations
This dissertation consists of two parts. In the first part, we studied the ground state configurations of vortices with multi-scale inter-vortex interactions in layered superconductors. We found that by tuning the multi-scale interaction length, we could create vortex lattice ground states with different symmetries. It has been proposed that these structures can trap ultra-cold atoms for use in quantum emulators. In further work, we measured the phase diagram and discovered many new phases by changing the relative magnitude of the interaction ranges. In the second part, we analyzed the ground state configurations of confined filaments with long-range repulsive interactions. We …
Reduced Models Of Point Vortex Systems In Quasigeostrophic Fluid Dynamics, Jonathan Maack
Reduced Models Of Point Vortex Systems In Quasigeostrophic Fluid Dynamics, Jonathan Maack
Doctoral Dissertations
We develop a nonequilibrium statistical mechanical description of the evolution of point vortex systems governed by either the Euler, single-layer quasigeostrophic or two-layer quasigeostrophic equations. Our approach is based on a recently proposed optimal closure procedure for deriving reduced models of Hamiltonian systems. In this theory the statistical evolution is kept within a parametric family of distributions based on the resolved variables chosen to describe the macrostate of the system. The approximate evolution is matched as closely as possible to the true evolution by minimizing the mean-squared residual in the Liouville equation, a metric which quantifies the information loss rate …
First-Principle Approaches To Strongly Correlated Quantum Spin Systems, Yuan Huang
First-Principle Approaches To Strongly Correlated Quantum Spin Systems, Yuan Huang
Doctoral Dissertations
My Ph.D. research focuses on the numerical study of two quantum spin systems, one is the square-lattice Heisenberg antiferromagnet with ring-exchange interaction at the Neel to valence-bond solid state transition, which is proposed to be described by the theory of deconfined criticality; the other is the highly frustrated pyrochlore Heisenberg antiferromagnet. Both systems are known as prototypical candidates for the exotic spin-liquid state with emergent fractionalized excitations and gauge structure. Regarding the long standing controversy of deconfined criticality, our results conclude that the deconfined critical theory capture the essence of the Neel to valence-bond solid state transition at least at …
Emergent Phenomena In Quantum Critical Systems, Kun Chen
Emergent Phenomena In Quantum Critical Systems, Kun Chen
Doctoral Dissertations
A quantum critical point (QCP) is a point in the phase diagram of quantum matter where a continuous phase transition takes place at zero temperature. Low-dimensional quantum critical systems are strongly correlated, therefore hosting nontrivial emergent phenomena. In this thesis, we first address two decades-old problems on quantum critical dynamics. We then reveal two novel emergent phenomena of quantum critical impurity problems. In the first part of the thesis, we address the linear response dynamics of the $(2+1)$-dimensional $O(2)$ quantum critical universality class, which can be realized in the ultracold bosonic system near the superfluid (SF) to Mott insulator (MI) …
Streamwise Flow-Induced Oscillations Of Bluff Bodies - The Influence Of Symmetry Breaking, Tyler Gurian
Streamwise Flow-Induced Oscillations Of Bluff Bodies - The Influence Of Symmetry Breaking, Tyler Gurian
Masters Theses
The influence of symmetry breaking on the flow induced oscillations of bluff bodies in the steamwise direction is studied. First, a series of experiments is conducted on a one-degree-of-freedom circular cylinder allowed to exhibit pure translational motion in the streamwise direction over a range of reduced velocities, 1.4 < U* < 4.4, corresponding to a Reynolds number range of 970 < Re < 3370. Two distinct regions of displacements were observed in reduced velocity ranges of 1.6 < U* < 2.5 and 2.75 < U* < 3.85. Measured force coefficients in the drag and lift direction were examined, along with the wake visualization, through the range of reduced velocities, to infer the resulting wake modes. A new Alternating Symmetric (AS) mode was found. This transition from symmetric to AS shedding occurred near the end of the first region of response. Similar tests were run with a square prism in the parameter space of 2.4 < U* < 5.8 and 757 < Re < 1900 over angles of incidence of 0° ≤ α ≤ 45°. A distinct region of lock-in is observed for α = 0°, 2.5°, 5°, 7.5° over 3.2 < U* < 5.4 for α = 0°, and decreasing with increasing α. The wake structures were found to be roughly symmetric for α = 0°, but transitioned towards asymmetry …
Modeling Deformation Behavior And Strength Characteristics Of Sand-Silt Mixtures: A Micromechanical Approach, Mehrashk Meidani
Modeling Deformation Behavior And Strength Characteristics Of Sand-Silt Mixtures: A Micromechanical Approach, Mehrashk Meidani
Doctoral Dissertations
This dissertation is comprised of six chapters. In the first chapter the motivation of this research, which was modeling the deformation behavior and strength characteristics of soils under internal erosion, is briefly explained. In the second chapter a micromechanis-based stress-strain model developed for prediction of sand-silt mixtures behavior is presented. The components of the micromechanics-based model are described and undrained behavior of six different types of sand-silt mixtures is predicted for several samples with different fines contents. The need for a more comprehensive compression model for sand-silt mixtures is identified at the end of this chapter. This desired compression model …
Vibrated Squares As Equilibrium And Active Matter, Lee Askew Walsh
Vibrated Squares As Equilibrium And Active Matter, Lee Askew Walsh
Doctoral Dissertations
We study the effects of particle shape and self-propulsion on the collective behaviors of a two-dimensional granular fluid, using an experimental system of hard square grains. We energize the system by vibration, which, depending on particle shape, induces either isotropic diffusion or persistent self-propulsion in the particles. We use specially designed grains as a model system to study (i) the equilibrium packing of hard squares in two dimensions, (ii) the dynamics of athermal self-propelled particles, and (iii) the melting kinetics of an unconfined granular crystallite. The first study concerns the phase diagram of a two-dimensional fluid of hard squares, which …
Search For Long-Lived, Massive Particles Decaying Into Dimuon Vertices In Pp Collisions At 13 Tev With The Atlas Detector At The Lhc, Nathan Bernard
Search For Long-Lived, Massive Particles Decaying Into Dimuon Vertices In Pp Collisions At 13 Tev With The Atlas Detector At The Lhc, Nathan Bernard
Doctoral Dissertations
A search for long-lived, massive particles decaying into dimuon pairs, in 32.9 fb-1 of data analyzed from the ATLAS detector is presented. Two signal models are considered: GGM SUSY, where the long lived particle mass is between 300-1000 GeV, and the dark photon model, where the ZD mass is between 20-60 GeV. An excess over the predicted background is observed in the GGM channel, however the angular/kinematic distributions of the excess vertices are consistent with a detec- tor/conditions related issue. A modified selection is used for the GGM channel which increases the signal sensitivity. 95% confidence level (CL) …
Evolving Black Holes In Inflation, Ruth Gregory, David Kastor, Jennie Traschen
Evolving Black Holes In Inflation, Ruth Gregory, David Kastor, Jennie Traschen
Physics Department Faculty Publication Series
We present an analytic, perturbative solution to the Einstein equations with a scalar field that describes dynamical black holes in a slow-roll inflationary cosmology. We show that the metric evolves quasi-statically through a sequence of Schwarzschild–de Sitter like metrics with time dependent cosmological constant and mass parameters, such that the cosmological constant is instantaneously equal to the value of the scalar potential. The areas of the black hole and cosmological horizons each increase in time as the effective cosmological constant decreases, and the fractional area increase is proportional to the fractional change of the cosmological constant, times a geometrical factor. …