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Tunable Electronic And Optical Properties Of Low-Dimensional Materials, Shiyuan Gao

Arts & Sciences Electronic Theses and Dissertations

Two-dimensional (2D) materials with single or a few atomic layers, such as graphene, hexagonal boron nitride (h-BN) and transition metal dichalcogenides (TMDCs), and the heterostructures or one-dimensional (1D) nanostructures they form, have attracted much attention recently as unique platforms for studying many condensed-matter phenomena and holds great potentials for nanoelectronics and optoelectronic applications. Apart from their unique intrinsic properties which has been intensively studied for over a decade by now, they also allow external control of many degrees of freedom, such as electrical gating, doping and layer stacking. In this thesis, I present a theoretical study of the electronic and …

Fast Objective Coupled Planar Illumination Microscopy, Cody Jonathan Greer

Arts & Sciences Electronic Theses and Dissertations

Among optical imaging techniques light sheet fluorescence microscopy stands out as one of the most attractive for capturing high-speed biological dynamics unfolding in three dimensions. The technique is potentially millions of times faster than point-scanning techniques such as two-photon microscopy. This potential is especially poignant for neuroscience applications due to the fact that interactions between neurons transpire over mere milliseconds within tissue volumes spanning hundreds of cubic microns. However current-generation light sheet microscopes are limited by volume scanning rate and/or camera frame rate. We begin by reviewing the optical principles underlying light sheet fluorescence microscopy and the origin of these …

Linking Structure And Dynamics In Metallic Liquids: A Combined Experimental And Molecular Dynamics Approach, Robert Ashcraft

Arts & Sciences Electronic Theses and Dissertations

A major outstanding problem in condensed matter physics is the nature of the glass transition, in which a rapidly cooled liquid can bypass the transition into a crystalline state and the liquid structure is "frozen-in" due to kinetic arrest. To characterize the fundamental features behind this transition the liquid, both in the high temperature (equilibrium) and supercooled state, needs to be better understood. By examining the relationship between structure and dynamics a better characterization of the liquid state and a determination of the mechanisms that are ultimately important for the formation of the glass can be gained. In this dissertation, …

Instrumentation For Cryogenic Dynamic Nuclear Polarization And Electron Decoupling In Rotating Solids, Faith Joellen Scott

Arts & Sciences Electronic Theses and Dissertations

Dynamic nuclear polarization (DNP) increases the sensitivity of nuclear magnetic resonance (NMR) using the higher polarization of electron radical spins compared to nuclear spins. The addition of electron radicals for DNP to the sample can cause hyperfine broadening, which decreases the resolution of the NMR resonances due to hyperfine interactions between electron and nuclear spins. Electron decoupling has been shown to attenuate the effects of hyperfine coupling in rotating solids. Magic angle spinning (MAS) DNP with electron decoupling requires a high electron Rabi frequency provided by a high-power microwave source such as a frequency-agile gyrotron. This dissertation describes the development …

Dualities, Topological Properties, And Degeneracies Of Classical And Quantum Lattice Models, Seyyed Mohammad Sadegh Vaezi

Arts & Sciences Electronic Theses and Dissertations

We study various nontrivial facets of Ҥegeneracyӭ a concept of paramount importance in numerous physical systems.

In the first part of this thesis, we challenge the folklore that if the ground state degeneracy of a physical system depends on topology then this system must necessarily realize an unconventional, so-called Ҵopological quantumӬ order. To this end, we introduce a classical rendition of the Toric Code model that displays such a topological degeneracy yet exhibits conventional Landau order. As the ground states of this classical system may be distinguished by local measurements, this example illustrates that, on its own, topological degeneracy is …

Spin Alignment Generated In Inelastic Nuclear Reactions, Daniel Hoff

Arts & Sciences Electronic Theses and Dissertations

The spin alignment of inelastically excited 7Li projectiles, when the target remains in its ground state, was determined through angular-correlation measurements between the breakup fragments of 7Li_ (_ + t). It was found that 7Li_ is largely aligned along the beam axis (longitudinal) in this type of inelastic reaction, regardless of the target. This longitudinal alignment is well described by DWBA calculations, which can be explained by an angular-momentum-excitation-energy mismatch condition. These calculations also explain the longitudinal spin alignment of excited nuclei in several other systems, showing the phenomenon is more general. The experiment involving 7Li was performed at the …

Topics In Pt-Symmetric Quantum Mechanics And Classical Systems, Nima Hassanpour

Arts & Sciences Electronic Theses and Dissertations

Space-time reflection symmetry, or PT symmetry, first proposed in quantum mechanics by Bender and Boettcher in 1998 [2], has become an active research area in fundamental physics. This dissertation contains several research problems which are more or less related to this field of study. After an introduction on complementary topics for the main projects in Chap.1, we discuss about an idea which is originated from the remarkable paper by Chandrasekar et al in Chap.2. They showed that the (second-order constant-coefficient) classical equation of motion for a damped harmonic oscillator can be derived from a Hamiltonian having one degree of freedom. …

Simulation Of Black Hole Inner Accretion Disk-Corona And Optimization Of The Hard X-Ray Polarimeter, X-Calibur, Banafsheh Beheshtipour

Arts & Sciences Electronic Theses and Dissertations

Mass accreting stellar mass and supermassive black holes are strong sources of X-rays. The X- ray observations enable studies of the process of black hole accretion and give us information about the spacetime background. In the framework of my thesis work, I have continued the development of a general-relativistic ray-tracing code enabling the simulation of the Comptonization of photons in the hot accretion disk corona. I use the code to investigate the impact of various approximation schemes for modeling the Comptonization finding that a fully relativistic treatment is needed for accurate predictions in the soft and hard X- ray regimes …

Deuterium Mas Nmr Studies Of Mg-Ti Deuteride Formed During High Pressure Ball Milling, Samuel Emery

Arts & Sciences Electronic Theses and Dissertations

Magnesium hydride has long been considered a candidate onboard hydrogen storage material for hydrogen fuel cell powered vehicles due to its low cost, abundance (of magnesium metal), and high hydrogen content (7.6 wt%). However, its use has been limited by the poor kinetics and thermodynamics of the reversible hydriding/dehydriding reaction. Improvements to hydrogen uptake and release have been previously demonstrated when Mg is alloyed with Sc. The resulting MgSc-hydride adopts a cubic, fluorite crystal structure (as opposed to the rutile, tetragonal structure for bulk MgH2) that exhibits a significantly lower activation energy for thermally driven hydrogen motion. However, Sc is …

Lattice Scales From Gradient Flow And Chiral Analysis On The Milc Collaboration's Hisq Ensembles, Nathan Joseph Brown

Arts & Sciences Electronic Theses and Dissertations

The interactions of quarks and gluons form most of the visible matter around us. Yet, extracting precise predictions from the field theory describing them, Quantum Chromodynamics (QCD), is notoriously difficult. By simulating the QCD interaction on a Euclidean space time lattice, the field theory can be regularized non-perturbatively and familiar statistical techniques from classical statistical mechanics can be applied. Then, by systematically improving each component of the process, high precision results can be obtained. Some of the possible components to be improved include the discretization of the continuum action, the determination of the lattice scale(s), the generation of gauge field …

Quantum Fields In Extreme Backgrounds, Leandro Medina De Oliveira

Arts & Sciences Electronic Theses and Dissertations

Quantum field theories behave in interesting and nontrivial ways in the presence of intense electric and/or magnetic fields. Describing such behavior correctly, particularly at finite (nonzero) temperature and density, is of importance for particle physics, nuclear physics, astrophysics, condensed matter physics, and cosmology. Incorporating these conditions as external parameters also provides useful probes into the nonperturbative structure of gauge theories.

In this work, formalism for describing matter in a variety of extreme conditions is developed and implemented. We develop several expansions of one-loop finite temperature effects for spinor particles in the presence of magnetic fields, including the effects of confinement, …