Physics Commons^™

Quantitative Binocular Assessment Using Infrared Video Photoscreening, Lei Shi

Doctoral Dissertations

Photorefraction is a technique that has been used in the past two decades for pediatric vision screening. The technique uses a digital or photographic camera to capture the examinee‟s retinal reflex from a light source that is located near the camera‟s lens. It has the advantages of being objective, binocular and low cost, which make it a good candidate for pediatric screening when compared to other methods. Although many children have been screened using this technique in the U.S., its sensitivity and other disadvantages make it unacceptable for continued use. The Adaptive Photorefraction system (APS) was developed at the Center …

Electronic Excitations In Ytio3 Using Tddft And Electronic Structure Using A Multiresolution Framework, William Scott Thornton

Doctoral Dissertations

We performed ab initio studies of the electronic excitation spectra of the ferro- magnetic, Mott-insulator YTiO3 using density functional theory (DFT) and time- dependent density functional theory (TDDFT). In the ground state description, we included a Hubbard U to account for the strong correlations present within the d states on the cation. The excitation spectra was calculated using TDDFT linear response formalism in both the optical limit and the limit of large wavevector transfer. In order to identify the local d-d transitions in the response, we also computed the density response of YTiO3 using a novel technique where the basis …

Remote Sensing Of Sediments And Volatiles On The Martian Surface And Terrestrial Analog Sites, Craig James Hardgrove

Doctoral Dissertations

The role of water and volatiles in the solar system is of critical interest in planetary science. Evidence for the past action of water or direct observation of water on a planetary body can indicate the potential to harbor life and is critical to human exploration of the solar system. We study two very different remote sensing techniques that address the issue of identifying water-related processes on the surface of other planetary bodies, and in particular, Mars. The first technique, combined thermal infrared and visible imaging, has been used extensively on Mars for determining the thermal inertia of surface materials. …

Adaptation And Stochasticity Of Natural Complex Systems, Roy David Dar

Doctoral Dissertations

The methods that fueled the microscale revolution (top-down design/fabrication, combined with application of forces large enough to overpower stochasticity) constitute an approach that will not scale down to nanoscale systems. In contrast, in nanotechnology, we strive to embrace nature’s quite different paradigms to create functional systems, such as self-assembly to create structures, exploiting stochasticity, rather than overwhelming it, in order to create deterministic, yet highly adaptable, behavior. Nature’s approach, through billions of years of evolutionary development, has achieved self-assembling, self-duplicating, self-healing, adaptive systems. Compared to microprocessors, nature’s approach has achieved eight orders of magnitude higher memory density and three orders …

Proton-Proton Correlation Functions As A Probe To Reaction, Micha A. Kilburn '95

Doctoral Dissertations

In an experiment at NSCL, proton-proton (p-p) correlation functions were measured in ⁴⁰Ca+⁴⁰Ca and ⁴⁸Ca+⁴⁸Ca reactions, both at E/A = 80 MeV. The High Resolution Array (HiRA) detected light particles with excellent energy (<200 keV) and angular (~0.2^o) resolution. The MSU 4pi Array covered 77% of the total 4pi solid angle and was used to determine the impact parameter for collisions using transverse energy (E_t) as the relevant observable.

Two-particle correlation functions are employed in this work to measure the space-time …

First-Principles Studies Of Complex Hydrides For Li-Ion Battery And Hydrogen Storage Applications, Timothy Hudson Mason

Doctoral Dissertations

"We employ density functional theory in a computational study of two energy storage systems.

In the first, we explore the thermodynamic viability of light metal hydrides as a high capacity Li-ion battery negative electrode. Given a set of solid-state and gas-phase reactants, we have determined the phase diagram in the Li-Mg-B-N-H system in the grand canonical ensemble as a function of lithium electrochemical potential. We present computational results for several new conversion reactions with predicted capacities between 2400 and 4000 mAhg⁻¹ that are thermodynamically favorable and that do not involve gas evolution. We provide experimental evidence for the reaction pathway …

Multiple Differential Study Of Fragmentation Processes In 75 Kev Proton-Molecular Hydrogen Collisions, Kisra Nayomal Egodapitiya

Doctoral Dissertations

"Double Differential Cross Sections (DDCS) were measured for single ionization of H₂ by 75 keV proton (p) impact as a function of the projectile scattering angle (θp) for a fixed energy loss (ΔE) for two different target-collimating slit distances, which determined the width of the projectile wave packet (Δx). In one case Δx was larger than the inter-nuclear separation of the H₂ molecule (coherent projectile beam), while for the other case it was much smaller than the inter-nuclear separation (incoherent projectile beam). A Young type interference pattern was observed in the coherent data, but this was not present in the …

Absorbing State Transitions In Clean And Disordered Lattice Models, Man Young Lee

Doctoral Dissertations

"Nonequilibrium systems can undergo continuous phase transitions between different steady states. These transitions are characterized by collective fluctuations over large distances and long times similar to the behavior of equilibrium critical points. They also can be divided into different universality classes according to their critical behavior.

This dissertation considers two types of nonequilibrium transitions. First study concerns absorbing state transitions on a randomly diluted lattice. Second study deals with nonequilibrium models with several absorbing states. We investigate two specific nonequilibrium lattice models, i.e., the contact process and the generalized contact process by means of both theoretical and computational approaches.

In …

Quantum Phase Transitions In The Presence Of Disorder And Dissipation, Chetan Kotabage

Doctoral Dissertations

"A quantum phase transition is a phase transition at absolute zero occurring under variations in an external non-thermal parameter such as magnetic field or pressure. Quantum phase transitions are one among the important topics currently investigated in condensed matter physics. They are observed in various systems, e.g., in the ferromagnetic-paramagnetic phase transition in LiHoF₄ or in the superconductor-metal phase transition in nanowires.

A particular class of quantum phase transitions, which is phase transitions in the presence of disorder and dissipation, is investigated here. An example of this class is the ferromagnetic-paramagnetic phase transition in Ni₁₋ₓVₓ or CePd_1-xRhₓ caused …

Quantum Electrodynamics And Fundamental Constants, Benedikt J. Wundt

Doctoral Dissertations

"The unprecedented precision achieved both in the experimental measurements as well as in the theoretical description of atomic bound states make them an ideal study object for fundamental physics and the determination of fundamental constants. This requires a careful study of the effects from quantum electrodynamics (QED) on the interaction between the electron and the nucleus.

The two theoretical approaches for the evaluation of QED corrections are presented and discussed. Due to the presence of two energy scales from the binding potential and the radiation field, an overlapping parameter has to be used in both the approaches in order to …

Spin-Lattice Coupling In The Iron-Pnictide High-Temperature Superconductors, Daniel E Parshall

Doctoral Dissertations

The recent discovery of the iron-pnictide superconductors has generated tremendous excitement, in part because there are many tantalizing similarities to the cuprate superconductors. As with the cuprates, it is strongly suspected that the spins contribute to superconductivity.

There seems to be a strong relationship between the lattice and magnetism in this system. Several authors have discussed the possibility of spin-phonon coupling, but direct experimental evidence has remained elusive.

This work discusses the relationship between the spins and the lattice in the $BaFe_{2}As_{2}$ family. We demonstrate the presence of negative thermal expansion in these materials, which is a strong indicator of …

Interplay Between Structure And Chemistry Of Materials And Their Physical Properties, Alaska Subedi

Doctoral Dissertations

First principles calculations provide a powerful tool for sorting out the interplay of chemical composition and structure with the physical properties of materials. In this dissertation, I discuss the physical properties and their microscopic basis within this framework for following illustrative examples. (i) The Zintl phase hydrides, where I find H is anionic and the formation of covalent sp2 bonds in the Al/Ga/Al-Si planes, which is a highly unusual bonding configuration for these elements. (ii) PbTe, which shows strong coupling between the longitudinal acoustic and transverse optic modes that may explain its low thermal conductivity. (iii) The double perovskites BiPbZnNbO6 …

Towards Simulations Of Binary Neutron Star Mergers And Core-Collapse Supernovae With Genasis, Reuben Donald Budiardja

Doctoral Dissertations

This dissertation describes the current version of GenASiS and reports recent progress in its development. GenASiS is a new computational astrophysics code built for large-scale and multi-dimensional computer simulations of astrophysical phenomena, with primary emphasis on the simulations of neutron star mergers and core-collapse supernovae. Neutron star mergers are of high interest to the astrophysics community because they should be the prodigious source of gravitation waves and the most promising candidates for gravitational wave detection. Neutron star mergers are also thought to be associated with the production of short-duration, hard-spectral gamma-ray bursts, though the mechanism is not well understood. In …

Ads/Cft Correspondence And Hydrodynamics Of Relativistic Heavy Ion Collisions, James Ethan Alsup

Doctoral Dissertations

The experiments performed at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Lab have discovered a state of matter called the strongly coupled quark-gluon plasma (sQGP). The strong coupling has limited the ability of the standard theory to describe such matter, namely Quantum Chromodynamics (QCD). However, string theory's anti-de Sitter/conformal field theory (AdS/CFT) correspondence has provided a new way to study the situation and in an analytical manner. So far, hydrodynamic properties of RHIC's plasma, such as elliptic flow and longitudinal expansion, have been seen to follow from classical supergravity calculations. In this dissertation I discuss some of the …

Neutron Scattering Study Of The High Tc Superconductors, Jun Zhao

Doctoral Dissertations

We carried out systematic neutron scattering experiments to investigate the magnetic properties and their relationship to the high-$T_c$ superconductivity, when the materials are tuned from their antiferromagnetic (AF) parent compounds to the superconducting regime.

We observed resonance mode in the electron doped cuprate Nd$_{1.85}$Ce$_{0.15}$CuO$_4$, demonstrating that the resonance is a general phenomenon in cuprate superconductors regardless of hole- or electron-doping. In Pr$_{0.88}$LaCe$_{0.12}$CuO$_4$, the local susceptibility displays two distinct energy scales that are broadly consistent with the bosonic modes revealed by scanning tunneling microscopy experiments. These results indicate the presence of very strong electron spin excitations couplings in electron doped cuprates. …

Theoretical Models For Wall Injected Duct Flows, Tony Saad

Doctoral Dissertations

This dissertation is concerned with the mathematical modeling of the flow in a porous cylinder with a focus on applications to solid rocket motors. After discussing the historical development and major contributions to the understanding of wall injected flows, we present an inviscid rotational model for solid and hybrid rockets with arbitrary headwall injection. Then, we address the problem of pressure integration and find that for a given divergence free velocity field, unless the vorticity transport equation is identically satisfied, one cannot find an analytic expression for the pressure by direct integration of the Navier-Stokes equations. This is followed by …

Investigations Of The Dynamical Response In Solids By Time-Dependent Density-Functional Theory, Qinghong Kou

Doctoral Dissertations

The present dissertation studies a joint theoretical-experimental investigation of the dynamical structure factor of wide-gap insulators, using lithium-fluoride as a prototype. Ground-state (energy bands and electron densities) was calculated using Linear Augmented Plane Wave (LAPW) method and local density approximation (LDA) of density functional theory (DFT). Ab-initio principal is applied to obtain a realistic description of the band structure, which is central to the current research in the condensed matter physics. Dynamical response function has been evaluated within time-dependent density functional theory (DFT) with an adiabatic approximation (TDLDA), for the exchange-correlation kernel. Our TDLDA spectra contain one adjustable parameter: a …

A Study Of Synchronization Of Nonlinear Oscillators: Application To Epileptic Seizures, Daisuke Takeshita

Doctoral Dissertations

"This dissertation focuses on several problems in neuroscience from the perspective of nonlinear dynamics and stochastic processes. The first part concerns a method to visualize the idea of the power spectrum of spike trains, which has an educational value to introductory students in biophysics. The next part consists of experimental and computational work on drug-induced epileptic seizures in the rat neocortex. In the experimental part, spatiotemporal patterns of electrical activities in the rat neocortex are measured using voltage-sensitive dye imaging. Epileptic regions show well-synchronized, in-phase activity during epileptic seizures. In the computational part, a network of a Hodgkin-Huxley type neocortical …

Theoretical Study Of Electron Impact-Ionization Of Molecules, Ola Al-Hagan

Doctoral Dissertations

"There has been impressive progress in the area of theoretical treatments of electron impact ionization (e,2e) of atoms and molecules in the last decade. Most recently, low to intermediate incident electron energies have been reported for molecular systems. In this dissertation, different theoretical models will be used to calculate the fully differential cross section (FDCS) for (e,2e) processes for low to intermediate incident electron energies for a variety of final state electron angles and energies for the diatomic molecules H₂ and N₂, the triatomic molecule H₂O, and the biomolecule HCOOH.

In addition, there has been a large amount of interest …

Weak Shear Study Of Galaxy Clusters By Simulated Gravitational Lensing, David Coss

Doctoral Dissertations

"Gravitational lensing has been simulated for numerical galaxy clusters in order to characterize the effects of substructure and shape variations of dark matter halos on the weak lensing properties of clusters. In order to analyze realistic galaxy clusters, 6 high-resolution Adaptive Refinement Tree N-body simulations of clusters with hydrodynamics are used, in addition to a simulation of one group undergoing a merger. For each cluster, the three-dimensional particle distribution is projected perpendicular to three orthogonal lines of sight, providing 21 projected mass density maps. The clusters have representative concentration and mass values for clusters in the concordance cosmology. Two gravitational …

A Study Of The Growth And Structure Of Chromium And Iron Oxide Films On Pd(001) Using X-Ray Photoelectron Diffraction And Low Energy Electron Diffraction, Tina Dhekial-Phukan

Doctoral Dissertations

"In this study, attempts were made to grow well-ordered chromium- and iron-oxide films on a Pd(001) surface, and two sample preparation techniques, the multilayer and the sequential growth techniques, were used to grow these transition metal oxide films. The study is a part of a larger project that aims to look into the interaction between metal substrates and the overlayers grown on them. Previous studies of oxide films on Ag(001) resulted in the growth of 4-fold and 3-fold symmetry oxide structures from the multilayer and sequential growth techniques respectively. The present investigation's goal was to study how the growth of …

Three-Body Dynamics In Single Ionization Of Atomic Hydrogen By 75 Kev Proton Impact, Aaron C. Laforge

Doctoral Dissertations

"Doubly differential cross sections (DDCS) for single ionization of atomic hydrogen by 75 keV proton impact have been measured as a function of the projectile scattering angle and energy loss. This pure three-body collision system represents a fundamental test case for the study of the reaction dynamics in few-body systems. A comparison between theory and experiment reveals that three-body dynamics is important at all scattering angles, and that an accurate description of the role of the projectile-target nucleus interaction as well as the second order projectile-electron interaction remains a major challenge to theory. However, progress is being made in understanding …

Quantum 1/F Noise In Infrared Detectors And Scanning Tunneling Microscopes, Amanda Marie Truong

Doctoral Dissertations

"Noise is, by definition, any random and persistent disturbance, which interferes with the clarity of a signal. Modern electronic devices are designed to limit noise, and in most cases the classical forms of noise have been eliminated or greatly reduced through careful design. However, there is a fundamental, quite unavoidable type of noise, called quantum 1/f noise, which occurs at low frequencies and is a fundamental consequence of the discrete nature of the charge carriers themselves. This quantum 1/f noise is present in any physical cross section or process rate, such as carrier mobility, diffusion rates and scattering processes. Although …

Open Heavy Flavor Measurement At Forward Angles For Cu+Cu Collisions At Center Of Mass Nn Collision Energy 200 Gev, Irakli Garishvili

Doctoral Dissertations

The main purpose of Relativistic Heavy Ion Collider (RHIC) program is to study the Quark-Gluon Plasma (QGP), a deconfined state of matter believed to be created in ultra-relativistic heavy ion collisions. Heavy quarks, expected to be produced during the earlier stages of heavy ion collisions, serve as an important probe of the QGP.‎

‎The following dissertation presents measurements of single muons resulting from the semileptonic decay of heavy flavor quarks in the rapidity range of $1.4 < \vert\eta\vert < 1.9$ for Cu+Cu nuclei collisions at $\sqrt{s_{NN}}=200$ GeV measured by the PHENIX experiment. Single muon spectra were measured for three different centrality classes (0 - 20 \% , 20 - 40 \%, 40 - 94 \%) within the $p_{T}$ range of 1.0 - 4.0 GeV/c.‎

‎To calculate single muon spectra, a full background estimate was statistically subtracted from inclusive spectra of muon candidate tracks reconstructed in the PHENIX muon …

Beta-Decay, Beta-Delayed Neutron Emission And Isomer Studies Around 78Ni, Mustafa Moiz Rajabali

Doctoral Dissertations

A study of nuclei with few nucleons outside the closed shell provides benchmarks for the nuclear shell model especially in this modern era of physics where exotic doubly magic nuclei can be tested. The subject of this thesis is to experimentally investigate the properties of nuclei near ⁷⁸Ni and to confront them with the predictions of modern large scale shell model calculations. In this regard, an experiment was performed at the National Superconducting Cyclotron Laboratory (NSCL) to measure excited states in ^71-73Ni populated via the beta-decay of ^71-73Co. Data collected from this experiment lead to partial level …

Controlled Self-Organization And Tunable Collective Phenomena In Surface-Based Nanostructures, Eun Ju Moon

Doctoral Dissertations

Nanostructure systems possessing certain desirable features can arise from the self-organization of fundamental building blocks. In this thesis we explore two types of controlled self-assembly mechanisms in hetero-epitaxy: (a) classical assembly of atom vacancies into quasi one-dimensional line structures and (b) quantum-driven assembly of atoms into atomically-smooth two-dimensional thin films. In the classical assembly phenomenon, adatom vacancies, created via elastic strain-relaxation in compressively strained atom chains on a silicon substrate, self-organize into meandering vacancy lines. The average spacing between these line defects can be varied by adjusting the chemical potential μ of the adsorbed atoms. We implemented a lattice model …

Development And Implementation Of A New Technique To Study (P,Α) Reactions Relevant To Nucleosynthesis In Binary Systems, Brian Hossain Moazen

Doctoral Dissertations

The accurate determination of the strengths and energies of resonances in (p,alpha) reactions is important for understanding the influence of reaction cycles to element synthesis in many astrophysical environments. Thus far, (p,alpha) studies in inverse kinematics have employed solid polypropylene targets. These are not always advantageous, especially when the energy loss of the incoming beam in the solid target is significantly larger than the resonance width. At the Holifield Radioactive Ion Beam Facility, a new technique has been developed for measuring the strengths and energies of (p,alpha) reactions. In this technique, a large differentially-pumped scattering chamber is filled with hydrogen …

Wide-Range Characterization Of Current Conduction In Superconductors-Tuning Their Properties By Nanoscale Modification Of Materials, Özgür Polat

Doctoral Dissertations

Significant progress has been made in the development of YBa₂Cu₃O_7-x (YBCO)-based coated conductors (CCs) since the discovery of YBCO in 1987. Nowadays, high temperature superconductor (HTS) materials are advancing toward wide application areas in medical physics, industry, and science. The successful applications of these materials require clear understanding of the mechanisms controlling the current carrying capacity. It has been demonstrated the maximum current that a HTS can support is strongly affected by the vortex dynamics within the HTS materials. In this dissertation, we employed a combination of methods: conventional transport, magnetometry in a swept magnetic …

Experimental Studies Of Exotic Negative Ions, Shaun Gerald Ard

Doctoral Dissertations

Although negative ions have been studied extensively for quite some time, their study continues to offer insight into developing and refining quantum chemical modeling techniques. Negative ion states remain difficult to treat ab initio due to the significant electron-electron correlation, thus putting a premium on experimental results to guide the way. Experimental techniques such as Electrospray Ionization (ESI) and Rydberg Electron Transfer (RET) have made study of some exotic negative ions in the gas phase possible for the first time. Multiply Charged Anions (MCAs) of several families of molecules were studied using Collision Induced Dissociation (CID) and Infrared Multi Photon …

Single Walled Carbon Nanotube Networks As Transparent Conductors, Matthew Patrick Garrett

Doctoral Dissertations

A variety of technological applications depend on transparent conducting films, and carbon nanotubes have the properties required to serve in that role. Single-walled carbon nanotube networks have been studied as transparent conductors in order to understand and optimize their electrical and optical properties. Nanotube films are complex networks of semiconducting and metallic nanotubes, bundled and branched in multifarious directions, with different strength connections between bundles. Chemical modification of nanotubes and inclusion of non-nanotube material can further alter network properties. Separating the contributions of all aspects of the network is a necessary but daunting task in order to optimize nanotube films. …