Physical Sciences and Mathematics Commons^™

Carrier Transport Engineering In Wide Bandgap Semiconductors For Photonic And Memory Device Applications, Ravi Teja Velpula

Dissertations

Wide bandgap (WBG) semiconductors play a crucial role in the current solid-state lighting technology. The AlGaN compound semiconductor is widely used for ultraviolet (UV) light-emitting diodes (LEDs), however, the efficiency of these LEDs is largely in a single-digit percentage range due to several factors. Until recently, AlInN alloy has been relatively unexplored, though it holds potential for light-emitters operating in the visible and UV regions. In this dissertation, the first axial AlInN core-shell nanowire UV LEDs operating in the UV-A and UV-B regions with an internal quantum efficiency (IQE) of 52% are demonstrated. Moreover, the light extraction efficiency of this …

Photonic Monitoring Of Atmospheric Fauna, Adrien P. Genoud

Dissertations

Insects play a quintessential role in the Earth’s ecosystems and their recent decline in abundance and diversity is alarming. Monitoring their population is paramount to understand the causes of their decline, as well as to guide and evaluate the efficiency of conservation policies. Monitoring populations of flying insects is generally done using physical traps, but this method requires long and expensive laboratory analysis where each insect must be identified by qualified personnel. Lack of reliable data on insect populations is now considered a significant issue in the field of entomology, often referred to as a “data crisis” in the field. …

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 …

Hydrodynamic Investigation Of The Discharge Of Complex Fluids From Dispensing Bottles Using Experimental And Computational Approaches, Baran Teoman

Dissertations

The discharge of non-Newtonian, complex fluids through orifices of industrial tanks, pipes, dispensers, or packaging containers is a ubiquitous but often problematic process because of the complex rheology of such fluids and the geometry of the containers. This, in turn, reduces the discharge rate and results in residual fluid left in the container, often referred to as heel. Heel formation is undesired in general, since it causes loss of valuable material, container fouling, and cross-contamination between batches. Heel may be of significant concern not only in industrial vessels but also in consumer packaging. Despite its relevance, the research in this …

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 …

Stochastic Modeling Of Flows In Membrane Pore Networks, Binan Gu

Dissertations

Membrane filters provide immediate solutions to many urgent problems such as water purification, and effective remedies to pressing environmental concerns such as waste and air treatment. The ubiquity of applications gives rise to a significant amount of research in membrane material selection and structural design to optimize filter efficiency. As physical experiments tend to be costly, numerical simulation and analysis of fluid flow, foulant transport and geometric evolution due to foulant deposition in complex geometries become particularly relevant. In this dissertation, several mathematical modeling and analytical aspects of the industrial membrane filtration process are investigated. A first-principles mathematical model for …

Performance Analysis Of The Dominant Mode Rejection Beamformer, Enlong Hu

Dissertations

In array signal processing over challenging environments, due to the non-stationarity nature of data, it is difficult to obtain enough number of data snapshots to construct an adaptive beamformer (ABF) for detecting weak signal embedded in strong interferences. One type of adaptive method targeting for such applications is the dominant mode rejection (DMR) method, which uses a reshaped eigen-decomposition of sample covariance matrix (SCM) to define a subspace containing the dominant interferers to be rejected, thereby allowing it to detect weak signal in the presence of strong interferences. The DMR weight vector takes a form similar to the adaptive minimum …

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 …

Time-Dependent Photoionization Modeling Of Warm Absorbers In Active Galactic Nuclei, Dev Raj Sadaula

Dissertations

Warm absorber spectra are bound-bound and bound-free absorption features, seen in the X-ray and UV spectra from many active galactic nuclei (AGN). The widths and centroid energies of these features indicate they occur in outflowing gas moving with hundreds to thousands of km/s. Depending upon the energy and momentum of the outflow, it can affect the gas within the host galaxy. Thus, warm absorbers’ mass and energy budgets are of great interest. Estimates for these properties depend on models that connect the absorption features' observed strengths with the density, composition, and ionization state of the absorbing gas. Such models assume …

Studying The Synthesis Of 196Hg At Astrophysically Relevant Energies Through The Measurement Of Capture Reaction Cross-Sections Of (P, Γ) (P, N) And (P, Α) Reactions, Khushi Bhatt

Dissertations

Understanding the origin of all the chemical elements is an important question for the nuclear-astrophysics community. There are many unanswered questions like: What astrophysical events are responsible for the synthesis of what particular chemical elements? How many different elements were made in total? What is the abundance of each synthesized element? etc. Currently, scientists are largely depending upon theory and simulations to define nuclear and astrophysical reaction. This makes it critical to have accurate experimental nuclear physics data to input in astrophysical theoretical models. However, out of more than 20000 reactions involved in these calculations, only a very few are …

Probing The Equation Of State Of Neutron Stars With Heavy Ion Collisions, Om Bhadra Khanal

Dissertations

The equation of state (EOS) is a fundamental property of nuclear matter, important for studying the structure of systems as diverse as the atomic nucleus and the neutron star. Nuclear reactions, especially heavy-ion collisions in the laboratories, can produce the nuclear matter similar to those contained in neutron stars. The density and the momentum dependence of the EOS of asymmetric nuclear matter, especially the symmetry energy term, is widely unconstrained. Finding appropriate constrains, especially at higher densities of the nuclear matter, requires the development of new devices, new experimental measurements as well as advances in theoretical understanding of nuclear collisions …

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 …

Investigation Of Topological Phonons In Acoustic Metamaterials, Wenting Cheng

Dissertations

Topological acoustics is a recent and intense area of research. It merges the knowledge of mathematical topology, condensed matter physics, and acoustics. At the same time, it has been pointed out that quasiperiodicity can greatly enhance the periodic table of topological systems. Because quasiperiodic patterns have an intrinsic global degree of freedom, which exists in the topological space called the hull of a pattern, where the shape traced in this topological space is called the phason. The hull augments the physical space, which opens a door to the physics of the integer quantum Hall effect (IQHE) in arbitrary dimensions. In …

Numerical Methods For Optimal Transport And Optimal Information Transport On The Sphere, Axel G. R. Turnquist

Dissertations

The primary contribution of this dissertation is in developing and analyzing efficient, provably convergent numerical schemes for solving fully nonlinear elliptic partial differential equation arising from Optimal Transport on the sphere, and then applying and adapting the methods to two specific engineering applications: the reflector antenna problem and the moving mesh methods problem. For these types of nonlinear partial differential equations, many numerical studies have been done in recent years, the vast majority in subsets of Euclidean space. In this dissertation, the first major goal is to develop convergent schemes for the sphere. However, another goal of this dissertation is …

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 …

Type I Error Rate Controlling Procedures For Multiple Hypotheses Testing, Beibei Li

Dissertations

This dissertation addresses several different but related topics arising in the field of multiple testing, including weighted procedures and graphical approaches for controlling the familywise error rate (FWER), and stepwise procedures with control of the false discovery rate (FDR) for discrete data. It consists of three major parts.

The first part investigates weighted procedures for controlling the FWER. In many statistical applications, hypotheses may be differentially weighted according to their different importance. Many weighted multiple testing procedures (wMTPs) have been developed for controlling the FWER. Among these procedures, two weighted Holm procedures are commonly used in practice: one is based …

A New Model For Predicting The Drag And Lift Forces Of Turbulent Newtonian Flow On Arbitrarily Shaped Shells On The Seafloor, Carley R. Walker, James V. Lambers, Julian Simeonov

Dissertations

Currently, all forecasts of currents, waves, and seafloor evolution are limited by a lack of fundamental knowledge and the parameterization of small-scale processes at the seafloor-ocean interface. Commonly used Euler-Lagrange models for sediment transport require parameterizations of the drag and lift forces acting on the particles. However, current parameterizations for these forces only work for spherical particles. In this dissertation we propose a new method for predicting the drag and lift forces on arbitrarily shaped objects at arbitrary orientations with respect to the direction of flow that will ultimately provide models for predicting the sediment sorting processes that lead to …