Other Physics Commons^™

Molecular Mechanisms Of Amyloid-Like Fibril Formation, Sharareh Jalali

Dissertations

Proteins play a critical role in living systems by performing most of the functions inside cells. The latter is determined by the protein's three-dimensional structure when it is folded in its native state. However, under pathological conditions, proteins can misfold and aggregate, accounting for the formation of highly ordered insoluble assemblies known as amyloid fibrils. These assemblies are associated with diseases like Parkinson's and Alzheimer's. Strong evidence suggests that three mechanisms are critical for forming amyloid fibrils. These mechanisms are the nucleation of amyloid fibrils in solution (primary nucleation) as well as on the surface of existing fibrils (secondary nucleation) …

Exploring Topological Phonons In Different Length Scales: Microtubules And Acoustic Metamaterials, Ssu-Ying Chen

Dissertations

The topological concepts of electronic states have been extended to phononic systems, leading to the prediction of topological phonons in a variety of materials. These phonons play a crucial role in determining material properties such as thermal conductivity, thermoelectricity, superconductivity, and specific heat. The objective of this dissertation is to investigate the role of topological phonons at different length scales.

Firstly, the acoustic resonator properties of tubulin proteins, which form microtubules, will be explored The microtubule has been proposed as an analog of a topological phononic insulator due to its unique properties. One key characteristic of topological materials is the …

Helioseismic Diagnostics Of Active Regions And Their Magnetic Fields, John T. Stefan

Dissertations

While two and a half decades of nearly constant observation by the Solar and Heliospheric Observatory (SOHO) and the Solar Dynamics Observatory (SDO) spacecraft have yielded key insights into the structure and dynamics of active regions, it is still unclear if active regions can be identified before emerging on the solar surface and, once emerged, whether the subsurface structure of an active region’s magnetic field can be measured. Regarding the dynamical processes associated with active regions, the height and mechanism of sunquake excitation remains poorly understood. To answer these questions, a comprehensive survey of active region magnetic fields and their …

Interactions Of Amyloid Peptides With Lipid Membranes, Yanxing Yang

Dissertations

The aggregation of amyloid proteins into fibrils is a hallmark of several diseases including Alzheimer’s (AD), Parkinson’s, and Type II diabetes. This aggregation process involves the formation of small size oligomers preceding the formation of insoluble fibrils. Recent studies have shown that these oligomers are more likely to be responsible for cell toxicity than fibrils. A possible mechanism of toxicity involves the interaction of oligomers with the cell membrane compromising its integrity. In particular, oligomers may form pore-like structures in the cell membrane affecting its permeability or they may induce lipid loss via a detergent-like effect. This dissertation aims to …

Diagnostics Of Energy Release In Solar Flares With Radio Dynamic Imaging Spectroscopy, Yingjie Luo

Dissertations

Studies of the magnetic energy release and conversion process lie at the core of solar flare physics. Radio observations serve as a unique diagnostic method. In this dissertation, taking advantage of broadband radio dynamic imaging spectroscopy observations made by the Karl G. Jansky Very Large Array (VLA), studies are carried out on the flare energy release processes using different types of radio emissions.

The VLA is a general-purpose radio observatory located in New Mexico, which provides high-quality radio dynamic imaging spectroscopic observations with an ultra-fast time cadence. In the first study, stochastic decimetric radio spike bursts are observed by the …

Waves And Oscillations In A Sunspot: Observations And Modeling Of Noaa Ar 12470, Yi Chai

Dissertations

Waves and oscillations are important solar phenomena not only because they can propagate and dissipate energy in the chromosphere, but also because they carry information about the structure of the atmosphere in which they propagate. Among these phenomena, the one of the most interesting ones occurs in the sunspot umbra. In this area, continuously propagating magnetohydrodynamic (MHD) waves generated from below the photosphere create the famous 3-minute sunspot umbral oscillations that affect the line profile of spectral lines due to temperature, density, and velocity changes of the plasma in the region. In the past decades, numerous observations and models have …

Nondestructive Evaluation Of 3d Printed, Extruded, And Natural Polymer Structures Using Terahertz Spectroscopy And Imaging, Alexander T. Clark

Dissertations

Terahertz (THz) spectroscopy and imaging are considered for the nondestructive evaluation (NDE) of various three-dimensional (3D) printed, extruded, and natural polymer structures. THz radiation is the prime candidate for many NDE challenges due to the added benefits of safety, increased contrast and depth resolution, and optical characteristic visualization when compared to other techniques. THz imaging, using a wide bandwidth pulse-based system, can evaluate the external and internal structure of most nonconductive and nonpolar materials without any permanent effects. NDE images can be created based on THz pulse attributes or a material’s spectroscopic characteristics such as refractive index, attenuation coefficient, or …

Periodic Fast Multipole Method, Ruqi Pei

Dissertations

Applications in electrostatics, magnetostatics, fluid mechanics, and elasticity often involve sources contained in a unit cell C, centered at the origin, on which periodic boundary condition are imposed. The free-space Green’s functions for many classical partial differential equations (PDE), such as the modified Helmholtz equation, are well-known. Among the existing schemes for imposing the periodicity, three common approaches are: direct discretization of the governing PDE including boundary conditions to yield a large sparse linear system of equations, spectral methods which solve the governing PDE using Fourier analysis, and the method of images based on tiling the plane with copies of …

Colloidal Quantum Dot (Cqd) Based Mid-Wavelength Infrared Optoelectronics, Shihab Bin Hafiz

Dissertations

Colloidal quantum dot (CQD) photodetectors are a rapidly emerging technology with a potential to significantly impact today’s infrared sensing and imaging technologies. To date, CQD photodetector research is primarily focused on lead-chalcogenide semiconductor CQDs which have spectral response fundamentally limited by the bulk bandgap of the constituent material, confining their applications to near-infrared (NIR, 0.7-1.0 um) and short-wavelength infrared (SWIR, 1-2.5 um) spectral regions. The overall goal of this dissertation is to investigate a new generation of CQD materials and devices that advances the current CQD photodetector research toward the technologically important thermal infrared region of 3-5 ?m, known as …

Advances In Modeling Gas Adsorption In Porous Materials For The Characterization Applications, Max A. Maximov

Dissertations

The dissertation studies methods for mesoporous materials characterization using adsorption at various levels of scale and complexity. It starts with the topic introduction, necessary notations and definitions, recognized standards, and a literature review.

Synthesis of novel materials requires tailoring of the characterization methods and their thorough testing. The second chapter presents a nitrogen adsorption characterization study for silica colloidal crystals (synthetic opals). These materials have cage-like pores in the range of tens of nanometers. The adsorption model can be described within a macroscopic approach, based on the Derjaguin-Broekhoff-de Boer (DBdB) theory of capillary condensation. A kernel of theoretical isotherms is …

Radio Diagnostics Of Particles And Plasma In The Solar Corona, Sherry Chhabra

Dissertations

Radio diagnostics, in addition to their capabilities in exploring intense, impulsive bursts, also provide a high sensitivity to much weaker events, which may not show any substantial signature in other wavelengths.

The initial case study examines a complex event consisting of multiple radio sources/bursts associated with a fast coronal mass ejection (CME) and an M 2.1 class solar flare (SOL2015-09-20). ‘First-light’ data from the Owens Valley Radio Observatory–Long Wavelength Array is put in context with observations from Large Angle and Spectrometric Coronagraph onboard the Solar and Heliospheric Observatory, along with the WAVES radio spectrograph onboard WIND, the Expanded Owens Valley …

Convergence Of The Boundary Integral Method For Interfacial Stokes Flow, Keyang Zhang

Dissertations

Boundary integral numerical methods are among the most accurate methods for interfacial Stokes flow, and are widely applied. They have the advantage that only the boundary of the domain must be discretized, which reduces the number of discretization points and allows the treatment of complicated interfaces. Despite their popularity, there is no analysis of the convergence of these methods for interfacial Stokes flow. In practice, the stability of discretizations of the boundary integral formulation can depend sensitively on details of the discretization and on the application of numerical filters. A convergence analysis of the boundary integral method for Stokes flow …

Efficient Time-Stepping Approaches For The Dispersive Shallow Water Equations, Linwan Feng

Dissertations

This dissertation focuses on developing efficient and stable (high order) time-stepping strategies for the dispersive shallow water equations (DSWE) with variable bathymetry. The DSWE extends the regular shallow water equations to include dispersive effects. Dispersion is physically important and can maintain the shape of a wave that would otherwise form a shock in the shallow water system.

In some cases, the DSWE may be simplified when the bathymetry length scales are small (or large) in relation to other length scales in the shallow water system. These simplified DSWE models, which are related to the full DSWEs, are also considered in …

Flare Emission Observed In High Resolution And Comparison With Numerical Modeling, Nengyi Huang

Dissertations

As one of the most intense activities on the solar surface, flares have been extensively observed and studied ever since the first report. The standard model of solar flares has been established and commonly accepted. However, many limitations from the researching tools have left some of the problems unsolved or controversial. For example, the density of electrons in the corona is lower than it is required to activate the observed emission in HXR, and the mechanism that these electron beams can penetrate down to lower chromosphere is unclear. Many theoretical scenarios were suggested, and more observations had been in need. …

Calculating Elastic Properties Of Confined Simple Fluids, Christopher D. Dobrzanski

Dissertations

Confinement in nanoporous materials is known to affect many properties of the fluids confined within their pores. The elastic properties are no exception. This dissertation begins with an overview of the relevant literature on ways of obtaining elastic properties of confined fluids. It outlines some fundamental gaps in our understanding. The chapters following address some of these gaps in understanding elastic properties of the confined fluid, in particular, how the shape of the confining pore matters, how supercriticality effects the properties, how an equation of state designed for confined fluids can be used to calculate elastic properties, and if an …

Morphological Study Of Voids In Ultra-Large Models Of Amorphous Silicon, Durga Prasad Paudel

Dissertations

The microstructure of voids in pure and hydrogen-rich amorphous silicon (a:Si) network was studied in ultra-large models of amorphous silicon, using classical and quantum- mechanical simulations, on the nanometer length scale. The nanostructure, particularly voids of device grade ultra-large models of a:Si was studied, in which observed three-dimensional realistic voids were extended using geometrical approach within the experimental limit of void-volume fractions. In device-grade simulated models, the effect of void morphology; size, shape, number density, and distribution on simulated scattering intensities in small- angle region were investigated. The evolution of voids on annealing below the crystallization temperature …

Rare Event Sampling In Applied Stochastic Dynamical Systems, Yiming Yu

Dissertations

Predicting rare events is a challenging problem in many complex systems arising in physics, chemistry, biology, and materials science. Simulating rare events is often prohibitive in such systems due to their high dimensionality and the numerical cost of their simulation, yet analytical expressions for rare event probabilities are usually not available. This dissertation tackles the problem of approximation of the probability of rare catastrophic events in optical communication systems and spin-torque magnetic nanodevices. With the application of the geometric minimum action method, the probability of pulse position shifts or other parameter changes in a model of an actively mode-locked laser …

Predicted Deepwater Bathymetry From Satellite Altimetry: Non-Fourier Transform Alternatives, Maxsimo Salazar

Dissertations

Robert Parker (1972) demonstrated the effectiveness of Fourier Transforms (FT) to compute gravitational potential anomalies caused by uneven, non-uniform layers of material. This important calculation relates the gravitational potential anomaly to sea-floor topography. As outlined by Sandwell and Smith (1997), a six-step procedure, utilizing the FT, then demonstrated how satellite altimetry measurements of marine geoid height are inverted into seafloor topography. However, FTs are not local in space and produce Gibb’s phenomenon around discontinuities. Seafloor features exhibit spatial locality and features such as seamounts and ridges often have sharp inclines. Initial tests compared the windowed-FT to wavelets in reconstruction of …

Structural Studies To Determine The Mechanisms Supporting Multiferroic And Ferroelectric Properties Of Complex Oxides, Han Zhang

Dissertations

Multiferroics are a class of materials which possess both magnetic and electrical polarization with possible coupling between them. They show promise to enable new sensors and data storage devices with novel features, such as the possibility of writing polarization bits with magnetic fields at low power. The coexisting magnetic and ferroelectric order parameters are usually weakly coupled, preventing practical use. The development and study of new classes of materials with large magnetoelectric couplings is of high importance. Understanding the structure of these materials is key to this effort.

As one class of these systems, the RX3(BO₃)₄ has …

Roles Of Cosolvents On Protein Stability, Zhaoqian Su

Dissertations

The function of a protein is determined by its three-dimensional structure which emerges from the delicate balance of forces involving atoms of the protein and the solvent. This balance can be perturbed by changing temperature, pressure, pH and by adding organic molecules known as cosolvents to the solution. Despite the wide use of cosolvents to perturb protein structures in the lab and in living systems, their molecular mechanisms are still not well established. Understanding these mechanisms is a problem of substantial interest, with potential application to the design of new drugs to target proteins. In this dissertation, we probe the …

The Analysis And The Three-Dimensional, Forward-Fit Modeling Of The Hard X-Ray And The Microwave Emissions Of Major Solar Flares, Natsuha Kuroda

Dissertations

Solar flares are one of the most violent and energetic space weather events that are known to cause various adverse effects on the Earth. One of the major problems that must be solved to understand flares and to be able to predict their magnitudes is how the particles in the solar atmosphere are accelerated after the magnetic reconnection. One way to help solve this problem is to investigate the properties of the high energy electrons produced during the flare impulsive phase, observed in the hard X-ray (HXR) and microwave (MW). The two emissions are considered to be produced by a …

Magnetic Reconnection In Small And Large Scales On The Sun, Xin Chen

Dissertations

Almost all solar activities observed are related to the solar magnetic field, especially the topological restructuring of magnetic fields, the so-called magnetic reconnection in solar physics. They are occurring at different scales related to various phenomena, during minimum or maximum of the solar cycle, from the photosphere to the solar corona.

For small-scale activities, type II spicules which display high velocity upflows observed at the limb, have the most possible underlying driving mechanism of magnetic reconnection. A set of tools is developed for detecting small-scale solar magnetic cancellations and the disk counterpart of type II spicules (the so-called Rapid Blueshifted …

New Facet Of Solar Activities Revealed By High-Resolution Imaging At He I 10830 Å, Zhicheng Zeng

Dissertations

Major solar activities such as major flares and associated coronal mass ejections (CMEs), have a great impact on space weather, which requires us to develop the ability to predict them. Despite the extensive studies already made, however, many basic processes, such as energy accumulation processes in solar active regions and the triggering mechanism of solar activities, are still not well understood.

One reason why the basic processes are hard to be understood is that the large-scale activities are complicated, involving many small-scale energy releases, making it hard to understand the basic picture of the events. Small-scale solar activities, such as …

Terahertz Wireless Communication Through Atmospheric Atmospheric Turbulence And Rain, Jianjun Ma

Dissertations

This dissertation focusses on terahertz (THz) wireless communication technology in different weather conditions. The performance of the communication links is mainly studied under propagation through atmospheric turbulence and rain. However, as real outdoor weather conditions are temporally and spatially varying, it is difficult to obtain reproducible atmospheric conditions to verify results of independent measurements making it a challenge to measure and analyze the impact of outdoor atmospheric weather on communication links. Consequently, dedicated indoor weather chambers are designed to produce controllable weather conditions to emulate the real outdoor weather as closely as possible. To emulate turbulent air conditions, an enclosed …

Mueller Matrix Spectroscopic Ellipsometry Of Multiferroics, Roman Basistyy

Dissertations

Multiferroics, materials which possess several ferroic orders, are the focus of research in recent years. Among these materials are oxide crystals, such as, for example, RMnO₃, RMn₂O₅, R₃Fe₅O₁₂, where R stands for rare earth ions. The most fascinating physics occurs when magnon-lattice coupling reveals itself in the far-IR spectra of multiferroics. The expected optical behavior puts multiferroics into a more general category of bi-anisotropic materials, the properties of which could be only described using anisotropic dielectric ε(ω), magnetic μ(ω), and …

Electronic, Thermoelectric And Optical Properties Of Vanadium Oxides: Vo2, V2o3 And V2o5, Chiranjivi Lamsal

Dissertations

Correlated electrons in vanadium oxides are responsible for their extreme sensitivity to external stimuli such as pressure, temperature or doping. As a result, several vanadium oxides undergo insulator-to-metal phase transition (IMT) accompanied by structural change. Unlike vanadium pentoxide (V₃O₃), vanadium dioxide (VO₃) and vanadium sesquioxide (V₃O₃) show I MT in their bulk phases. In this study, we have performed one electron Kohn-Sham electronic band-structure calculations of VO₃, V₃O₃ and V₂O₅ in both metallic and insulating phases, implementing a full ab-initio simulation package …

A Comprehensive Study Of Evolution Of Photospheric Magnetic Field And Flows Associated With Solar Eruptions, Shuo Wang

Dissertations

The rapid, irreversible change of the photospheric magnetic field has been recognized as an important element of the solar flare process. Recent theoretical work has shown that such a change would imply Lorentz force perturbations acting on both the outer solar atmosphere and the solar surface. This research uses vector magnetograms obtained with the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory to study a number of flares, which range from GOES-class C4 to X5 and occur in four active regions. In all the events, a permanent and rapid change of photospheric magnetic field closely associated with the …

Analysis Of Far-Infrared Optical Spectra Of Multiferroics, Eric C. Standard

Dissertations

The optical spectra of multiferroic crystals Dy₃Fe₅O₁₂, Tb₃Fe₅O₁₂, and four hexagonal RMnO₃ (5D= Er, Tm, Yb, Lu) are studied using intense bright synchrotonic light in the infrared spectral range. In regards to the materials analyzed, two rare earth iron garnets and four rare earth manganites in total are examined. These materials have attracted much attention due to their interesting magnetoelectric properties. They could serve as the basis for the next generation of faster and more energy efficient memory and logic devices. To examine these materials, two …

Development Of Correction Algorithm For Pulsed Terahertz Computed Tomography (Thz-Ct), Suman Mukherjee

Dissertations

For last couple of decades, there has been a considerable improvement in Terahertz (THz) science, technology, and imaging. In particular, the technique of 3-D computed tomography has been adapted to the THz range. However, it has been widely recognized that a fundamental limitation to THz computed tomography imaging is the refractive effects of the sample under study. The finite refractive index of materials in the THz range can severally refract THz beams which probe the internal structure of a sample during the acquisition of tomography data. Refractive effects lead to anomalously high local absorption coefficients in the reconstructed image near …

Investigations Into B-O Defect Formation-Dissociation In Cz-Silicon And Their Effect On Solar Cell Performance, Prakash M. Basnyat

Dissertations

About 30% of the total market share of industrial manufacture of silicon solar cells is taken by single crystalline Czochralski (CZ) grown wafers. The efficiency of solar cells fabricated on boron-doped Czochralski silicon degrades due to the formation of metastable defects when excess electrons are created by illumination or minority carrier injection during forward bias. The recombination path can be removed by annealing the cell at about 200° C but recombination returns on exposure to light.

Several mono-crystalline and multi-crystalline solar cells have been characterized by methods such as laser beam induced current (LBIC), Four-Probe electrical resistivity etc. to better …