Open Access. Powered by Scholars. Published by Universities.®

Physics Commons

Open Access. Powered by Scholars. Published by Universities.®

Doctoral Dissertations

Discipline
Institution
Keyword
Publication Year

Articles 1 - 30 of 402

Full-Text Articles in Physics

A Study On Homogeneous Sheared Stably Stratified Turbulence, Gavin Portwood Jan 2019

A Study On Homogeneous Sheared Stably Stratified Turbulence, Gavin Portwood

Doctoral Dissertations

Homogeneous sheared and stably stratified turbulence is considered as a fundamental flow relevant to the study of geophysical turbulence and, generally, anisotropic turbulence. Numerical experiments are performed via high resolution direct numerical simulation (DNS) in a geophysically-relevant parameter space previously inaccessible to simulation. Turbulent dynamics relevant to the modeling of geophysical hydrodynamics are investigated as a function of mean flow and fluid parameters.

An active tuning scheme is implemented to induce temporally stationary turbulent kinetic energy in order to evaluate turbulence that is statistically independent of initial conditions and spatio-temporally homogeneous. Subject to this constraint, the parametric dependence of the ...


Investigating Blast Fume Propagation, Concentration And Clearance In Underground Mines Using Computational Fluid Dynamics (Cfd), Raymond Ninnang Tiile Jan 2019

Investigating Blast Fume Propagation, Concentration And Clearance In Underground Mines Using Computational Fluid Dynamics (Cfd), Raymond Ninnang Tiile

Doctoral Dissertations

"Blasting activities using standard industry explosives is an essential component of underground hard rock mining operations. Blasting operations result in the release of noxious gases, presenting both safety and productivity threats. Overestimation of post-blast re-entry time results in production losses, while underestimation leads to injuries and fatalities. Research shows that most underground mines simply standardize post-blast re-entry times based on experiences and observations. Few underground mines use theoretical methods for calculating post-blast re-entry time. These theoretical methods, however, are unable to account for the variations in the blasting conditions. Literature review shows that: (i) there is currently no means of ...


Ferrite Characterization Techniques & Particle Simulations For Semiconductor Devices, Nicholas Erickson Jan 2019

Ferrite Characterization Techniques & Particle Simulations For Semiconductor Devices, Nicholas Erickson

Doctoral Dissertations

"This dissertation is divided into three papers, covering two major topics. The first topic, techniques for ferrite characterization, is discussed over the course of two papers. The second topic, particle simulations for semiconductor devices, is discussed in the last paper. In the first paper, the method for extracting permeability from ferrite materials is discussed for the Keysight 16454A permeability extraction fixture, where the ferrite material to be characterized is assumed to be homogeneous. Then the method is updated to account for layered materials. The updated method is verified through full-wave simulations. In the second paper, a planar printed circuit board ...


Decoding The History Of The Early Solar System Using Comet Volatile Compositions, Nathaniel Xavier Roth Jan 2019

Decoding The History Of The Early Solar System Using Comet Volatile Compositions, Nathaniel Xavier Roth

Doctoral Dissertations

"Understanding the evolution of the solar system, as well as its current volatile content, requires knowledge of the initial conditions present in the solar nebula. As some of the first objects to accrete in the solar nebula, cometary nuclei are among the most primitive remnants of solar system formation, and their present-day volatile composition likely reflects the composition and conditions where (and when) they formed. As such, the volatile compositions of cometary nuclei may serve as 'fossils' of solar system formation. High-resolution near-infrared spectroscopy offers a valuable tool for sampling the primary volatile (i.e., ices subliming directly from the ...


Coherent Effects In Wave Propagation Through Complex Media, Milan Koirala Jan 2019

Coherent Effects In Wave Propagation Through Complex Media, Milan Koirala

Doctoral Dissertations

"Diffusion is a powerful and versatile description of a typical wave propagation in a random scattering medium that disregards phase and, thus, a possibility of interference. Speckle, transmission fluctuations, wave localization, non-local correlations, and transmission eigenchannels are examples of persistent interference effects, which arise in the course of deterministic propagation. Such wave phenomena contain a wealth of information about the medium and the source of waves, enabling sensing and coherent control of the propagation. The nonlocal correlations and speckle statistics of the partially coherent light are used to uncover an object hidden by a diffusive cloak inside a strong scattering ...


Electromagnetic Wave-Matter Interactions In Complex Opto-Electronic Materials And Devices, Raj Kumar Vinnakota Nov 2018

Electromagnetic Wave-Matter Interactions In Complex Opto-Electronic Materials And Devices, Raj Kumar Vinnakota

Doctoral Dissertations

This dissertation explores the fundamentals of light-matter interaction towards applications in the field of Opto-electronic and plasmonic devices. In its core, this dissertation attempts and succeeds in the the modeling of light-matter interactions, which is of high importance for better understanding the rich physics underlying the dynamics of electromagnetic field interactions with charged particles. Here, we have developed a self-consistent multi-physics model of electromagnetism, semiconductor physics and thermal effects which can be readily applied to the field of plasmotronics and Selective Laser Melting (SLM). Plasmotronics; a sub-field of photonics has experienced a renaissance in recent years by providing a large ...


Effective Magnetic And Electric Response Of Composite Materials, Mona Hassan Alsaleh Nov 2018

Effective Magnetic And Electric Response Of Composite Materials, Mona Hassan Alsaleh

Doctoral Dissertations

Metamaterials (MMs) are nanocomposite materials consisting of metal-dielectric resonators much smaller in size than the wavelength of the incident light. Common examples of metamaterials are based on split ring resonators (SRRs), parallel wires or strips and fishnet structures. These types of materials are designed and fabricated in order to provide unique optical responses to the incident electromagnetic radiation that are not available in naturally existing materials. The MMs can exhibit unusual properties such as strong magnetism at terahertz (THz) and optical frequencies. Additionally, negative index materials (NIMs) can provide negative index of refraction which can be used in many applications ...


Characterization Of The Cylinderical Split Internal-Loop Photobioreactor With Scenedesmus Microalgae: Advanced Culturing, Modeling, And Hydrodynamics, Laith S. Sabri Jan 2018

Characterization Of The Cylinderical Split Internal-Loop Photobioreactor With Scenedesmus Microalgae: Advanced Culturing, Modeling, And Hydrodynamics, Laith S. Sabri

Doctoral Dissertations

"Microalgae are fast growing photoynthetic microorganisms and it have very wide range of industrial applications such as biofuels and wastewater treatment. These cells can be grown in a wide variety of systems ranging from open culture systems (e.g., ponds) to closed culture systems of photobioreactor (e.g., airlift). The open culture systems exist in the external environment, and hence, are not intrinsically controllable. However, the microalgae production in enclosed photobioreactors faces prohibitively high production costs with special difficulty in reactor design and scale-up. The light availability and utilization efficiency in the photobioreactor in terms of design and scale-up consider ...


Fully Differential Study Of Dissociative Capture In P + H₂ Collisions, Basu Ram Lamichhane Jan 2018

Fully Differential Study Of Dissociative Capture In P + H₂ Collisions, Basu Ram Lamichhane

Doctoral Dissertations

"In recent years, the key role of the projectile coherence properties has been studied in several ion-atom scattering processes. These studies strongly suggested that cross sections could be significantly affected by the projectile coherence properties, especially for fast, heavy ions. In the present study, we used such coherence effects as a tool to sensitively analyze the few- body dynamics of the scattering process. To this end, we performed three kinematically complete experiments on fragmentation of H2 by 75 keV proton impacts. A novel approach was used to analyze coherence and interference effects in the observed cross-sections. The idea was ...


First-Principle Approaches To Strongly Correlated Quantum Spin Systems, Yuan Huang Jan 2018

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 ...


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 Jan 2018

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 ...


Emergent Phenomena In Quantum Critical Systems, Kun Chen Jan 2018

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 ...


Dynamics And Structure Of Polyelectrolyte Complexes, Hamidreza Shojaei-Mahib Jan 2018

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 ...


Preparation, Mechanics And Structure Of Sphere Packings Near The Random Loose Packing Limit, Greg Robert Farrell Jan 2018

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 ...


Self-Assembling Networks In Soft Materials, Ishan Prasad Jan 2018

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 ...


Vibrated Squares As Equilibrium And Active Matter, Lee Askew Walsh Jan 2018

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 ...


Quantum Phase Transitions In Disordered Boson Systems, Zhiyuan Yao Jan 2018

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 ...


Parallel Algorithms For Time Dependent Density Functional Theory In Real-Space And Real-Time, James Kestyn Jan 2018

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 ...


Collider Tests Of Fundamental Symmetries And Neutrino Properties, Haolin Li Jan 2018

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 ...


Equilibrium Partitioning Of Binary Polymer Mixtures Into Biological Nanopores, Mehmet Alphan Aksoyoglu Jan 2018

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 ...


Geometry, Growth And Pattern Formation In Thin Elastic Structures, Salem Al-Mosleh Jan 2018

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 ...


Reduced Models Of Point Vortex Systems In Quasigeostrophic Fluid Dynamics, Jonathan Maack Jan 2018

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 ...


Measured Capillary Forces On Spheres At Liquid Interfaces And The Mechanics Of Interfacial Particulate Assemblies, Wei He Jan 2018

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 ...


Alpha Radiation Studies And Related Backgrounds In The Darkside-50 Detector, Alissa Monte Jan 2018

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 ...


Evolving Specialization In An Agent-Based Model Without Task-Switching Costs, Shane Robert Meyer Jan 2018

Evolving Specialization In An Agent-Based Model Without Task-Switching Costs, Shane Robert Meyer

Doctoral Dissertations

"This work examines the possibility of evolving the phenotypic specialization associated with division of labor in an agent-based model without task-switching costs. The model examines two groups competing for vital resources, where members of one group are capable of sharing resources with other agents in their group. Agents attempt to collect resources which allow them to reproduce, with more resources leading to a greater number of offspring by asexual reproduction. Four variants of the model are examined, with combinations of one or two resources and the presence of a foraging risk. The presence of the foraging risk can lead to ...


Nanoporous Carbon Scaffolds For Energy Storage Applications, Waruni Jayawardana Jan 2018

Nanoporous Carbon Scaffolds For Energy Storage Applications, Waruni Jayawardana

Doctoral Dissertations

"Nanoporous carbons (NCs) have become increasingly popular in various fields of research due to their unique properties including tunable pore sizes, higher pore volumes and higher surface areas, as well as being able to produce controlled nanostructures. The work presented here uses NC scaffolds with as active hosts for (1) Li-ion battery electrodes and (2) confined metal hydrides (MH) for hydrogen storage applications. In (1) we investigate the Li diffusion characteristics in hard carbons (HCs) that are important for electrochemical applications. We develop a novel method named Voltage-Relaxation Galvanostatic Intermittent Titration Technique (VR-GITT). Parameters derived from the fitting of electrochemical ...


Correlation Between Delay Time And Measured Concentration And Concentration Uncertainty By Neutron Activation Analysis, James Thomas Seman Jan 2018

Correlation Between Delay Time And Measured Concentration And Concentration Uncertainty By Neutron Activation Analysis, James Thomas Seman

Doctoral Dissertations

"For the last several decades, it has been apparent that new methods of identifying explosives can help investigators trace their origins. One way to identify an explosive is through the use of taggants: materials added to a product that encodes information about the product such as when it was manufactured.

This research investigates the survivability of a new identification taggant called the Nuclear Barcode that overcomes some of the downfalls that have been identified in prior taggants. The Nuclear Barcode encodes information as a unique combination of concentrations of rare earths (Ho, Eu, Sm, Lu, and Dy) and precious metals ...


Modeling And Characterization Of Thermo-Oxidative Behavior Of Bismaleimide Composites, Rafid Muhammad Hussein Jan 2018

Modeling And Characterization Of Thermo-Oxidative Behavior Of Bismaleimide Composites, Rafid Muhammad Hussein

Doctoral Dissertations

"High-temperature polymer matrix composites (HTPMCs) are susceptible to thermo-oxidation, which accelerates the composites' degradation and reduces the service life. Mechanical properties of HTPMCs deteriorate due to coupled thermo-oxidation and cross-linking mechanisms. Bismaleimides (BMIs) are commonly used high-temperature resins for aerospace applications. This work presents the viability of using experimental weight loss to model the spatial distribution of oxidation when the oxidized polymer matrix is not discernible. Three tasks are introduced: (1) Anisotropic oxidation prediction using optimized weight loss behavior of bismaleimide composites, (2) A multi-scale modeling of thermo-oxidative effects on the flexural behavior of cross-ply bismaleimide composites, and (3) Thermo-oxidative ...


Disorder At First-Order Classical And Quantum Phase Transitions, Ahmed Khalil Ibrahim Jan 2018

Disorder At First-Order Classical And Quantum Phase Transitions, Ahmed Khalil Ibrahim

Doctoral Dissertations

"This dissertation studies the effects of quenched disorder on classical, quantum and nonequilibrium phase transitions. After a short introduction which covers the basic concepts of phase transitions, finite-size scaling and random disorder, the dissertation focuses on four separate but related projects. First, we investigate the influence of quenched disorder with long-range spatial correlations on the nonequilibrium phase transitions in the contact process. We show that the long-range correlations increase the probability to find rare atypical regions in the sample. This leads to enhanced Griffiths singularities and changes the universality class of the transition.

Project 2 and 3 focus on disorder ...


Analysis Of Primary Stripper Foils At The Spallation Neutron Source By An Electron Beam Foil Test Stand, Eric Paul Barrowclough Dec 2017

Analysis Of Primary Stripper Foils At The Spallation Neutron Source By An Electron Beam Foil Test Stand, Eric Paul Barrowclough

Doctoral Dissertations

Diamond films are used at the Spallation Neutron Source (SNS) as the primary charge exchange foils (i.e., stripper foils) of the accelerated 1 GeV (Gigaelectron volts) hydride ions. The most common type of film used is a nanocrystalline diamond film, typically 17 mm x 45 mm (millimeter) with an aerial density of 350 μg/cm2 (microgram per square centimeter). The diamond film is deposited on a corrugated silicon substrate using plasma-assisted chemical vapor deposition. After the growth of the diamond film, 30 mm of the silicon substrate is etched away, leaving a freestanding diamond foil with a silicon ...