I examine the strong co-variability between the surface divergence and vorticity and how it varies with latitude in the Pacific Ocean using surface vector winds from reanalysis and satellite scatterometer observations. This analysis was motivated in part by a significant correlation between divergence and vorticity over the global oceans that...
Fast neutron detection is important to the detection of illicit nuclear materials and can help prevent those materials from being used or transported without discovery. Previous research has shown that Heavy Oxide Inorganic Scintillator crystals can be used to detect fast neutrons by capitalizing on their high inelastic scattering cross...
We now have broad consensus in the mathematics education research community that active, inquiry-based classrooms provide a wealth of learning benefits for students (Freeman et al., 2014; Laursen et al., 2014; Theobald et al., 2020). Classrooms that utilize inquiry throughout the entire structure of the course, as opposed to the...
The aim of this dissertation is to construct a virtual element method (VEM) for models in magneto-hydrodynamics (MHD), an area that studies the behavior and properties of electrically conducting fluids such as a plasma. MHD models are a coupling of the Maxwell’s equations for electromagnetics and models for fluid flow....
The Introductory Physics 20X series has developed an advanced, metacognitive curriculum which requires a high degree of active learning in order for students to succeed in the class. Recently, the series has been transferred to the online campus, Ecampus, and is now available for distance learners. My work is focused...
Slow magnetosonic shock fronts are unstable to changes made to their shape, a phenomenon known as corrugation instability. The computational models studied considers a system where plasma travels across a shock front. Using the code Linogen, the corrugation instability of a shock front can be theoretically modeled. The results show...
In this thesis we study mathematical and computational models for phenomena of flow and transport in porous media in the presence of changing pore scale geometries. The differential equations for the flow and transport models at Darcy scale involve the coefficients of permeability, porosity, and tortuosity which depend on the...
Thermodynamic potentials are energies that can describe a thermodynamic system in terms of different mathematically independent variables. Some of these potentials describe particular thermodynamic systems or processes in particularly convenient ways. In this dissertation, I discuss the different ways that students and experts reason about quantities in thermodynamics within the...
Physicists seek to understand the world and often use mathematics to aid in attaining that goal. Thus when doing mathematics they often interrogate their results in order to ensure that they align with their expectations and to gain new insight into how the world works. This seeking of coherence between...
Structure-specific synthesis processes are of key importance to the growth of polymorphic functional compounds such as TiO₂, where material properties strongly depend on structure as well as chemistry. The robust growth of the brookite polymorph of TiO₂, a promising photocatalyst, has been difficult in both powder and thin-film forms due...
High Temperature Gas Reactors (HTGRs) are positioned to disrupt local and global markets via their unique ability to produce carbon-free process heat, high efficiency power generation, and passively safe operational features. However, significant impediments still exist to delay deployment of this particular technology, including a lack of experimental data, verified...
The fundamental physics of turbulence in plasma is not well understood. Recent studies of the plasma deflagration accelerator in the High Temperature Gasdynamics Lab at Stanford University have demonstrated the presence of small scale instabilities that limit the lifetime of the jet/Z pinch and are not reproduced by coaxial plasma...
Timber harvesters are high powered industrial grade rigs used to fell, delimb, and cut to size large trees. Hydraulic motors power sprockets that drive chains around a guide bar that get extended through logs during cuts. As technological advances allow for higher speeds a phenomenon called “chain shot” has...
Collaboration is tricky, but often beneficial in the context of numerous software related activities, from learning core concepts, to the design and implementation of large software products. The growth of online classes, from small structured seminars to massive open online courses (MOOCs), and the isolation and impoverished learning experience some...
The fact that measuring a quantum system reduces it to apparently classical behavior, eliminating the interference patterns that are a hallmark of quantumness, cries out for an explanation. That explanation has been provided by the recognition of decoherence,whereby the interference is destroyed by the very interaction that acquires information.We begin...
Outflowing streams of matter or jets are a common phenomenon in the observeduniverse. The most extreme and powerful jets are relativistic, i.e., they travel at speedscomparable to the of speed light. Gamma Ray-Bursts (GRBs) and Active Galactic Nuclei(AGNs) are two sources of these relativistic jets. In this work I will...
Nuclear thermal propulsion (NTP) is a viable technology for near-term interplanetary exploration. Of the candidate mission architectures that are currently available for a crewed Mars mission, NTP permits the greatest flexibility in launch window selection and provides the shortest possible trip time, thereby reducing risks associated with cosmic ray exposure,...
Deep learning has greatly improved visual recognition in recent years. However, recent research has shown that there exist many adversarial examples that can negatively impact the performance of such an architecture. Different from previous perspectives that focus on improving the classifiers to detect the adversarial examples, this work focuses on...
This dissertation is an exploration of the material response to Terahertz (THz) radiation. Specifically we will explore the ultrafast electron dynamics in the nonperturbative regime in semiconductors that have been patterned with nanoantenna arrays using broadband, high intensity, THz radiation. Three main semiconductor materials will be studied in this work....
This dissertation presents nonlinear terahertz (THz) properties of carbon nanomaterials investigated by time-resolved high-field THz spectroscopy. In order to determine THz characteristics of nanomaterials, we performed THz power spectrum measurement, THz raster imaging, THz time-domain spectroscopy (THz-TDS) and time-resolved pump-probe experiment on two different types of single layer graphene and...
Community colleges serve various populations as part of their missions. Many community colleges serve the people who live in rural communities and are challenged with fewer financial resources. The term rural is not easily defined, and many variables need to be considered when creating academic programming for rural populations. There...
Monte-Carlo Tree Search (MCTS) is an online-planning algorithm for decision-theoretic planning in domains with stochastic and combinatorial structure. The general applicability of MCTS makes it an ideal first choice to investigate when developing planners for complex applications requiring automated control and planning. The first contribution of this thesis is to...
Many applications in computer graphics and geometry processing rely on the ability to
locally orient 2D and 3D entities on a surface, or inside a volume, such as the sinusoidal
kernels in Gabor noise, the color and geometry textures in pattern synthesis, and the
finite elements in remeshing. In these...
This thesis will cover my work relating to the developing field of terahertz (THz) science and technology. It will present experimental and theoretical studies investigating the optical and electrical properties of various material systems using novel THz imaging and spectroscopy techniques. Due to its low photon energy, THz imaging and...
Low-dimensional electronic materials offer a platform to observe biological processes with unprecedented spatial and temporal resolution. Carbon nanotubes (CNTs) are the closest physical analog to an ideal 1D system and can be scaled and integrated into multiplexed electronic circuitry. The molecular structure of a CNT is also biocompatible, making them...
Carbon Nanotubes are a unique family of nanostructures that have shown remarkable promise for mechanical, electrical, and optical applications. Fundamentally similar to the earlier discovered Buckminsterfullerene (C₆₀), carbon nanotubes are hollow cylinders formed from a single sheet of carbon atoms. The research presented in this dissertation investigates several carbon nanotube...
Mixed anion compounds that form ZrCuSiAs-type crystal structures exhibit remarkable properties such as superconductivity at low temperatures,
hole conduction with optical transparency in the visible region, and exciton absorption at room temperature. In this thesis, properties of a selected group of materials out of the very large set of mixed...
A new method for delayed gamma-ray spectrometry to quantify the relative content of fissile material is developed and demonstrated to support international efforts in bolstering non-destructive assay capabilities. Previous traditional delayed gamma-ray spectrometry techniques rely upon nuclear data that often carry very high uncertainty. The new method removes the requirement...
We present the results of our experiments designed to extend the clinical applications of commercially available Optically Stimulated Luminescence (OSL) Dosimeters. Our initial experiments demonstrate the linear response of the OSL dosimeters for doses under 200 cGy and the non-linear response of the device after 200 cGy. Our experiments show...
This research introduces an energy storage system to deliver microgrid frequency response. A doubly-fed induction generator (DFIG) and a squirrel cage induction machine (SCIM) are coupled together as a motor/generator set to deliver an immediate inertial response to a change of frequency, and an inverter and supercapacitors deliver short term...
The Run-Ahead Predictive Simulation Software (RAPSS) is an architecture designed for faster-than-real-time decision support for operators of complex networks. To enable further development of the RAPSS methodology, the necessary proof of principle is illustrated in two applications: decision support for shift technical advisors in nuclear power plant control rooms (RAPSS-STA),...
Optical potential for antikaon-nucleus strong interactions are constructed using
elementary antikaon-nucleus potentials determined previously. The optical potentials
are used to determine the existence of a kaon hypernucleus. Modern three
dimensional visualization techniques are used to study model dependences, new
methods for speeding the calculation of the optical potential are developed,...
Generalized modal analysis techniques for the characterization and modeling of dissipationless planar waveguide structures and discontinuities encountered in microwave and optical integrated circuits, as well as of quantum waveguide structures and devices, are presented. The frequency-dependent transmission properties of the curved microstrip bend are derived by utilizing a second-order perturbation...
Oversampled analog-to-digital (A/D) converter architectures have been receiving
increased attention for high-precision A/D converters. These architectures offer the
means of exchanging resolution in time for that in amplitude. Among these
oversampled A/D converters, delta-sigma modulators are the most popular method
used due to their simplicity in the analog circuitry. The...
The behavior and application of organic semiconductor materials depend strongly on their molecular structure, and molecular interactions. Several studies of intermolecular interactions in functionalized polyacene materials are presented. The degree and onset of aggregation of a functionalized anthradithiophene derivative was studied as a function of concentration in two different host...
Calcium alginate gels are widely used in the biotechnology, food, and pharmaceutical industries for cell immobilization, food additives, and controlling the release of therapeutic agents. Different gelation conditions can lead to different gel structures which affects the diffusion of solutes in gels, thus mathematical models were developed to describe diffusion...
In order to understand better the defect structure and dynamics associated
with lower valent dopants complexed with native defects in group IV oxides, In/Cd
perturbed angular correlation spectroscopy was performed in ceria and zirconia. Examining
the orientation symmetry axis of defects in ceria single crystals at low temperature
has allowed...
A high-temperature, high-pressure autoclave has been
adapted for use with a high-field nuclear magnetic
resonance spectrometer. The autoclave has an internal
pressure range of atmospheric pressure to 1.5 kbar and a
temperature range of 273 K to 1900 K. The autoclave is
usable in a high field (8 T) magnet...
We used recent phenomenological form factors to calculate the effect of on-shell
two-pion exchange in nucleon-nucleon scattering below the two-pion production
threshold. As expected, the contributions of partial wave amplitudes are all negligible.
We also noticed that the relativistic spin-operator decomposition of the
scattering amplitude is not unique at certain...
In this work, Neutron Depth Profiling (NDP) analysis capability has been added to the Oregon State University TRIGA® Reactor Prompt Gamma Neutron Activation Analysis Facility (PGNAA). This system has been implemented with an advanced digital spectroscopy system and is capable of rise time pulse shape analysis as well as coincidence...
The thermodynamic and structural effects of highly anisotropic, short-ranged attraction are investigated for single- and four-site interaction models using Wertheim's multi-density graph theory of chemical association. Both models consist of associating hard spheres, where the saturable attraction sites are described by conical wells centered in the hard core and evaluated...
Computer simulations invoking the Metropolis Algorithm and Monte Carlo techniques were constructed to model the behavior ofvarious systems of magnetic semiconductors. Among the systems modeled were bulk type II FCC antiferromagnets and simple cubic thin films and superlattices. Studies of bulk antiferromagnets revealed dependence of Neel Temperature on nearest neighbor...
One of the newer and rapidly developing approaches in quantum computing is based on "quantum walks," which are quantum processes on discrete space that evolve in either discrete or continuous time and are characterized by mixing of components at each step. The idea emerged in analogy with the classical random...
As part of a research program to study the transitional region of N=88
isotones, ¹⁵²Tb was produced by the reaction ¹⁵¹Eu(α,3n)¹⁵²Tb in the 88" cyclotron
located at LBNL. Gamma-ray spectroscopy of the radiation emitted from excited
¹⁵²Gd following the β⁺ decay of ¹⁵²Tb has been performed using an array of...
This study aimed to investigate students' models of probability in a modern physics context. The study was divided into three phases. The first phase explored student pre-knowledge about probability before modem physics instruction. The second phase investigated student understanding of concepts related to probability such as wave-particle behavior, the uncertainty...
We developed a model to investigate the dielectric properties of the
BaTiO₃ − Bi(Zn₁/₂Ti₁/₂)O₃ (BT-BZT) solid solution, which is a relaxor ferroelectric and exhibits long range disorder. The model uses ab initio methods
to determine all polarization states for every atomic configuration of 2 x 2 x 2
supercells of...
Technologies such as avionics and power electronics are driving the demand for thermal management schemes towards high heat fluxes and low surface temperatures. Typically, these applications require the dissipation of heat fluxes in the rage of 100-1000 W/cm² while maintaining surface temperatures lower than about 85 °C. Phase-change heat transfer...
A hybrid Quasi-diffusion/Monte Carlo Method for solving multigroup criticality problems in slab geometry was investigated. Analog Monte Carlo was used to calculate functionals (Eddington Factors) that were then used in solution of the quasi-diffusion equations. The hybrid method was shown to accurately and precisely predict the k-eigenvalue and fission source...
This dissertation concerns several problems in the fields of light interaction with nanostructured media, metamaterials, and plasmonics. We present a technique capable of extending operational bandwidth of hyperbolic metamaterials based on interleaved highly-doped InGaAs and undoped AlInAs multilayer stacks. The experimental results confirm theoretical predictions, exhibiting broadband negative refraction response...
The process of de-excitation of the actinides is a very important question in both pure and applied science. In this dissertation the process was studied using the neutrons emitted in coincidence with fission induced by the bombardment of ²³⁸U with 14.85 MeV deuterons. Neutrons can be emitted at multiple stages...