Physical Sciences and Mathematics Commons^™

Methodology For Generating Simplified Cross Section Data Sets For Neutron Transport Calculations, Thomas Jay Harrison

Doctoral Dissertations

Neutron shielding problems involve radiation transport calculations over a wide range of energies. Fission neutrons have initial energy on the order of MeV, fusion neutrons have initial energy on the order of 10s of MeV, and space-origin neutrons have initial energy on the order of 100s of MeV or higher. Shielding calculations must track the neutrons from their initial energies until they are no longer of interest; for deep-penetration neutrons, this final energy can be on the order of eV before the neutron is no longer tracked. Thus, for deep-penetration space radiation shielding problems, the calculation may require tracking the …

Understanding The Influence Of Non-Covalent Interactions And Nanoparticle Geometries In Carbon Based Polymer Nanocomposites, Bradley Carroll Miller

Doctoral Dissertations

Low-loading polymer nanocomposites (PNC) are an area of great interest in polymer science. As nanoparticles (NP) are typically expensive in comparison to matrix materials; the low loading regime makes the most efficient use of materials, and represents the optimum for realizing cost effective, high-performance PNCs. However, formulating effective low-loading composites is not without challenges. In addition to the typical requirement of good dispersion for efficient translation of NP properties to the bulk, low-loading composites can sometimes exhibit anomalous (non-classical) dynamics, and unpredictable properties. It is within this context that this thesis aims to examine the effects of NP geometry and …

Rare Earth Production And Characterization Studies, Jake Anson Stewart

Doctoral Dissertations

The rare earths include elements Sc, Y, and La through Lu are important in many modern technologies. With the exception of Sc and Ce the rare earths are all have similar chemical behaviors with the preferred oxidation state in aqueous solution being +3. Currently, industrial purification of the rare earths is completed by counter current solvent extraction (CCSX). In most CCSX separations, Y extracts with Ho making their separation difficult. However, in a few systems Y exhibits an itinerant behavior. Carboxylic acids of varying sizes and substitutions were investigated in a study of Y itinerant behavior. It was found when …

Spontaneously Generated Inhomogeneous Phases Via Holography, Kübra Yeter Aydeniz

Doctoral Dissertations

We discuss a holographic model consisting of a U(1) gauge field and a scalar field coupled to a charged AdS (anti-de Sitter) black hole under a spatially homogeneous chemical potential. By turning on a higher-derivative interaction term between the U(1) gauge field and the scalar field, a spatially dependent profile of the scalar field is generated spontaneously. We calculate the critical temperature at which the transition to the inhomogeneous phase occurs for various values of the parameters of the system. We solve the equations of motion below the critical temperature, and show that the dual gauge theory on the boundary …

Interface And Morphology Engineering In Solution-Processed Electronic And Optoelectronic Devices, Sanjib Das

Doctoral Dissertations

The first part of this dissertation focuses on interface and morphology engineering in polymer- and small molecule-based organic solar cells. High-performance devices were fabricated, and the device performance was correlated with nanoscale structures using various electrical, spectroscopic and microscopic characterization techniques, providing guidelines for high-efficiency cell design.

The second part focuses on perovskite solar cells (PSCs), an emerging photovoltaic technology with skyrocketing rise in power conversion efficiency (PCE) and currently showing comparable PCEs with those of existing thin film photovoltaic technologies such as CIGS and CdTe. Fabrication of large-area PSCs without compromising reproducibility and device PCE requires formation of dense, …

Solution And Surface Properties Of Architecturally- And Compositionally-Complex Block Copolymers And Their Binary Mixtures, Jesse Lawrence Davis

Doctoral Dissertations

The spontaneous generation of complex structures from polymeric building blocks provides a simple yet effective route to create useful soft matter structures having potential application in a variety of nanotechnologies. The topology, chemical structure, block composition, and sequence of the constituent building blocks of polymers are tunable through synthetic chemistry. This tunability offers attractive opportunities to generate complex, yet well-defined structures with control over the geometry, packing symmetry, and microdomain structure. This thesis work involves the study of the self-assembly behaviors of architecturally complex amphiphilic block copolymers (ABCs). ABCs are composed of two or more chemically distinct blocks that are …

Effective Field Theory Approach To Collective Motion In Atomic Nuclei, Eduardo Antonio Coello Perez

Doctoral Dissertations

Collective motion in heavy nuclei has been studied within collective and algebraic models, and within density functional theory. While they reproduce the energy spectra of these systems, their predictions for some electromagnetic transitions and moments do not lie within experimental uncertainty; in other words, these predictions are inconsistent with experimental data. An effective field theory approach to collective motion in heavy nuclei solves this long standing problem. Based on symmetry arguments only, the effective field theories, constructed as expansions in powers of a small parameter, consistently describe the energy spectra of nuclei exhibiting collective motion at low order in the …

Solar Modulation Of The Cosmic Ray Intensity And The Measurement Of The Cerenkov Reemission In Nova’S Liquid Scintillator, Philip James Mason

Doctoral Dissertations

The NOνA (NuMI Off-axis electron neutrino Appearance) experiment is a long baseline neutrino oscillation experiment at Fermi National Accelerator Laboratory. Its purpose is to observe the oscillation of ν_μ (muon neutrino) to ν_e (electron neutrino) and to investigate the neutrino mass hierarchy and CP violation in the neutrino sector. Two detectors have been built for this purpose, a Near Detector 300 feet underground at Fermilab, and a Far Detector, on the surface at Ash River, Minnesota.

The completion of NOνA’s Far Detector in October 2014 enabled not only the recent measurement of neutrino oscillations, but an array of …

Computational Simulation Of Mass Transport And Energy Transfer In The Microbial Fuel Cell System, Shiqi Ou

Doctoral Dissertations

This doctoral dissertation introduces the research in the computational modeling and simulation for the microbial fuel cell (MFC) system which is a bio-electrochemical system that drives a current by using bacteria and mimicking bacterial interactions found in nature. The numerical methods, research approaches and simulation comparison with the experiments in the microbial fuel cells are described; the analysis and evaluation for the model methods and results that I have achieved are presented in this dissertation.

The development of the renewable energy has been a hot topic, and scientists have been focusing on the microbial fuel cell, which is an environmentally-friendly …

Neuron Clustering For Mitigating Catastrophic Forgetting In Supervised And Reinforcement Learning, Benjamin Frederick Goodrich

Doctoral Dissertations

Neural networks have had many great successes in recent years, particularly with the advent of deep learning and many novel training techniques. One issue that has affected neural networks and prevented them from performing well in more realistic online environments is that of catastrophic forgetting. Catastrophic forgetting affects supervised learning systems when input samples are temporally correlated or are non-stationary. However, most real-world problems are non-stationary in nature, resulting in prolonged periods of time separating inputs drawn from different regions of the input space.

Reinforcement learning represents a worst-case scenario when it comes to precipitating catastrophic forgetting in neural networks. …

Algorithm-Based Fault Tolerance For Two-Sided Dense Matrix Factorizations, Yulu Jia

Doctoral Dissertations

The mean time between failure (MTBF) of large supercomputers is decreasing, and future exascale computers are expected to have a MTBF of around 30 minutes. Therefore, it is urgent to prepare important algorithms for future machines with such a short MTBF. Eigenvalue problems (EVP) and singular value problems (SVP) are common in engineering and scientific research. Solving EVP and SVP numerically involves two-sided matrix factorizations: the Hessenberg reduction, the tridiagonal reduction, and the bidiagonal reduction. These three factorizations are computation intensive, and have long running times. They are prone to suffer from computer failures.

We designed algorithm-based fault tolerant (ABFT) …

Novel Thermoplastic Elastomers Based On Benzofulvene: Synthesis And Mechanical Properties, Weiyu Wang

Doctoral Dissertations

Thermoplastic elastomers (TPEs) are of great importance both academically and technologically. Currently TPEs are the predominated form of styrene-diene copolymers. However, these styrenic TPEs have serious limitations in applications, especially at higher temperature, because of their low upper service temperature (UST). The work described in this dissertation aimed to developing thermoplastic elastomers with a higher UST and lower cost.

In order to develop TPEs with a higher UST, we employed benzofulvene, an anionically polymerizable monomer in hydrocarbon solvent at room temperature, as the glassy block and copolymerized it with isoprene to prepare polybenzofulvene-polyisoprene-polybenzofulvene (FIF) triblock copolymers. Among all triblock copolymers …

All-Acrylic Multigraft Copolymers: Synthesis And Structure-Property Relationship For Producing Next Generation Thermoplastic Elastomers, Andrew Brown Goodwin

Doctoral Dissertations

Polymer architecture and the advancement of molecular design using anionic and other controlled polymerization methods continues to be of significant research interest because of the tunable approach it provides, which can impact numerous applications ranging from thermoplastics to drug delivery systems. Among the numerous branched structures currently investigated, comb and graft copolymers continue to provide tailored materials which exhibit superior mechanical properties when compared to their di- and triblock linear counterparts. More specifically, the incorporation of two or more monomers into graft and multigraft constructions where the side chains are composed of a plastic (high T_g [glass transition temperature]) …

The Effect Of Composition And Architecture On Polymer Behavior In Homopolymer Blends And Inter-Filament Bonding In 3d Printed Models, Edward Roy Duranty

Doctoral Dissertations

This dissertation presents work that increases our understanding of the effects of composition and architecture on copolymer structure and dynamics and how they affect material diffusion between filaments in a 3D printed model. Copolymers are polymer chains made up of at least two different monomers. The ordering and arrangement of the two monomer species within a copolymer can have drastic effects on the behavior and properties of the copolymer.

The first chapter of this dissertation examines how the copolymer composition affects the structure and dynamics of the chain in a homopolymer blend. This study used a modified Monte Carlo BFM …

Batched Linear Algebra Problems On Gpu Accelerators, Tingxing Dong

Doctoral Dissertations

The emergence of multicore and heterogeneous architectures requires many linear algebra algorithms to be redesigned to take advantage of the accelerators, such as GPUs. A particularly challenging class of problems, arising in numerous applications, involves the use of linear algebra operations on many small-sized matrices. The size of these matrices is usually the same, up to a few hundred. The number of them can be thousands, even millions.

Compared to large matrix problems with more data parallel computation that are well suited on GPUs, the challenges of small matrix problems lie in the low computing intensity, the large sequential operation …

Bacterial Diversity And Function Within An Epigenic Cave System And Implications For Other Limestone Cave Systems, Kathleen Merritt Brannen-Donnelly

Doctoral Dissertations

There are approximately 48,000 known cave systems in the United States of America, with caves formed in carbonate karst terrains being the most common. Epigenic systems develop from the downward flow of meteoric water through carbonate bedrock and the solutional enlargement of interconnected subsurface conduits. Despite carbonate karst aquifers being globally extensive and important drinking water sources, microbial diversity and function are poorly understood compared to other Earth environments. After several decades of research, studies have shown that microorganisms in caves affect water quality, rates of carbonate dissolution and precipitation, and ecosystem nutrition through organic matter cycling. However, limited prior …

Investigating Advection Control In Competitive Pde Systems And Environmental Transmission In Johne's Disease Ode Models, Kokum Rekha De Silva

Doctoral Dissertations

We extend the work on optimal control of advective direction in a reaction-diffusion population model to a system representing two competing populations. We investigate the choice of movement direction to benefit a population. First, the advective direction in one of the populations in a competition model is the control. Next, we extend the work by taking the advective directions of both populations as controls. In both these cases the objective is to maximize a weighted combination of the two populations while minimizing the cost involved in the species movement. Mathematical analysis is completed to derive the optimality system and numerical …

Automated Style Feedback For Advanced Beginner Java Programmers, Hannah Blau

Doctoral Dissertations

FrenchPress is an Eclipse plug-in that partially automates the task of giving students feedback on their Java programs. It is designed not for novices but for students taking their second or third Java course: students who know enough Java to write a working program but lack the judgment to recognize bad code when they see it. FrenchPress does not diagnose compile-time or run-time errors, or logical errors that produce incorrect output. It targets silent flaws, flaws the student is unable to identify for himself because nothing in the programming environment alerts him. FrenchPress diagnoses flaws characteristic of programmers who have …

Content Placement As A Key To A Content-Dominated, Highly Mobile Internet, Abhigyan Sharma

Doctoral Dissertations

Most of the Internet traffic is content, and most of the Internet connected hosts are mobile. Our work focuses on the design of infrastructure services needed to support such a content-dominated, highly mobile Internet. In the design of these services, three sets of decisions arise frequently: (1) Content placment for selecting the locations where a content is placed, (2) request redirection for selecting the location where a particular request is served from and (3) network routing for selecting the physical path between clients and the services they are accessing. Our central thesis is that content placement is a powerful factor, …

Informed Search For Learning Causal Structure, Brian J. Taylor

Doctoral Dissertations

Over the past twenty-five years, a large number of algorithms have been developed to learn the structure of causal graphical models. Many of these algorithms learn causal structures by analyzing the implications of observed conditional independence among variables that describe characteristics of the domain being analyzed. They do so by applying inference rules, data analysis operations such as the conditional independence tests, each of which can eliminate large parts of the space of possible causal structures. Results show that the sequence of inference rules used by PC, a widely applied algorithm for constraint-based learning of causal models, is effective but …

The Impact Of Terrestrial Noise On The Detectability And Reconstruction Of Gravitational Wave Signals From Core-Collapse Supernovae, Jessica Mciver

Doctoral Dissertations

Among of the wide range of potentially interesting astrophysical sources for gravitational wave detectors Advanced LIGO and Advanced Virgo are galactic core-collapse supernovae. Although detectable core-collapse supernovae have a low expected rate (a few per century, or less) these signals would yield a wealth of new physics. Of particular interest is the insight into the explosion mechanism driving core-collapse supernovae that can be gleaned from the reconstructed gravitational wave signal. A well-reconstructed waveform will allow us to assess the likelihood of different explosion models, perform model selection, and potentially map unexpected features to new physics. This dissertation presents a series …

Utilizing In Silico And/Or Native Esi Approaches To Provide New Insights On Haptoglobin/Globin And Haptoglobin/Receptor Interactions, Ololade Fatunmbi

Doctoral Dissertations

Haptoglobin (Hp), an acute phase protein, binds free hemoglobin (Hb) dimers in one of the strongest non-covalent interactions known in biology. This interaction protects Hb from causing potentially severe oxidative damage and limiting nitric oxide bioavailability. Once Hb/Hp complexes are formed, they proceed to bind CD163, a cell surface receptor on macrophages leading to complex internalization and catabolism. Myoglobin, (Mb) a monomeric protein, that is normally found in the muscle but can be released into the blood in high concentrations during myocardial injury, is homologous to Hb and shares many conserved Hb/Hp interface residues. Both monomeric Hb and Mb species …

An Empirical Approach To Understanding Of Star Formation In Dark Matter Halos, Zhankui Lu

Doctoral Dissertations

We present a data-driven approach to understand the star formation in dark matter halos over cosmic time. With a simple empirical model and advanced tools for Bayesian inference, we try to constrain how galaxies have assembled their stars across cosmic time using stellar mass functions (SMFs) and the luminosity function of cluster galaxies. The key ingredients of the empirical model include dark halo merger trees and a generic function that links star formation rate (SFR) to the host halos. We found a new characteristic redshift z_c ~ 2 above which the SFR in low mass halos < 10¹¹ solar mass …

Exploiting Social Media Sources For Search, Fusion And Evaluation, Chia-Jung Lee

Doctoral Dissertations

The web contains heterogeneous information that is generated with different characteristics and is presented via different media. Social media, as one of the largest content carriers, has generated information from millions of users worldwide, creating material rapidly in all types of forms such as comments, images, tags, videos and ratings, etc. In social applications, the formation of online communities contributes to conversations of substantially broader aspects, as well as unfiltered opinions about subjects that are rarely covered in public media. Information accrued on social platforms, therefore, presents a unique opportunity to augment web sources such as Wikipedia or news pages, …

Contact Angles And Contact Lines Around Particles At Isotropic And Anisotropic Liquid Interfaces, Nesrin Senbil

Doctoral Dissertations

Liquid interfaces, capillarity and self-assembly of particles at interfaces are important in nature and technology. When a particle is adsorbed to a liquid interface, the contact line of the particle with the liquid interface and the associated contact angle are the crucial parameters that drive assembly of the particles. We looked at how the shape of the liquid interface and the shape of the particle affect the contact angle and the shape of the contact line. We used millimeter-sized PDMS-coated glass spheres and measured the contact angles at isotropic (planar) and anisotropic interfaces (saddle and cylindrical in shape). Anisotropy of …

Inkjet Printing For Biosensing And Security Applications, Brian Creran

Doctoral Dissertations

The adaptation of inkjet printing technology has recently been used to create controlled high throughput micro- and nano-scaled structures. Coupling this technique with gold nanoparticles in our research has produced new platforms for biosensors, chemical patterning, and anti-counterfeiting applications. In this presentation, we will highlight promising fabrication strategies including the development of test strips for the determination of bacteria in drinking water as well as the use of patterned nanoparticles for security applications.

Impact Of Fabrication Parameters On The Internal Structure Of Poly(3-Hexylthiophene) Nanoparticles, Dana Desiree Algaier

Doctoral Dissertations

Morphological control of organic functional materials is central to understanding and improving upon current technologies. The ability to create hierarchical assemblies with purposeful design from nano to meso scale has remained largely unattainable. This body of work aims to provide a foundation for creating nanoscale domains of poly (3-hexylthiophene) (P3HT) that can be used as building blocks to larger scale assemblies. We present a method for the fabrication of P3HT nanoparticles on the ability to vary the particle size and more importantly, the internal structure. We have identified the oil phase and surfactant as parameters able to influence the nature …

Safe Reinforcement Learning, Philip S. Thomas

Doctoral Dissertations

This dissertation proposes and presents solutions to two new problems that fall within the broad scope of reinforcement learning (RL) research. The first problem, high confidence off-policy evaluation (HCOPE), requires an algorithm to use historical data from one or more behavior policies to compute a high confidence lower bound on the performance of an evaluation policy. This allows us to, for the first time, provide the user of any RL algorithm with confidence that a newly proposed policy (which has never actually been used) will perform well. The second problem is to construct what we call a safe reinforcement learning …

Estimation Problems In Complex Field Studies With Deep Interactions: Time-To-Event And Local Regression Models For Environmental Effects On Vital Rates, Krzysztof M. Sakrejda

Doctoral Dissertations

Field studies that measure vital rates in context over extended time periods are a cornerstone of our understanding of population processes. These studies inform us about the relationship between biological process and environmental noise in an irreplaceable way. These data sets bring ``big data'' and ``big model'' challenges, which limit the application of standard software (e.g., \textbf{BUGS}). The environmental sensitivity of vital rates is also expected to exhibit interactions and non-linearity, which typically result in difficult model selection questions in large data sets. Finally, long-term ecological data sets often contain complex temporal structure. In commonly applied discrete-time models complex temporal …

From Molecular Scale To Mesoscale: Establishing Structural Control Organic Photovoltaics Using Organic Nanoparticles, Timothy S. Gehan

Doctoral Dissertations

Organic photovoltaic devices use an active layer of organic materials that absorbs light and creates free charges to generate electricity. Such organic photovoltaics have many desirable properties as the final devices can be very lightweight, thin, flexible, have low manufacturing costs, and be semitransparent. These properties make them particularly advantageous for myriad of applications: e.g., use on non-planar surfaces, as tinted coatings on windows, any use for charging low power devices. One of the biggest problems preventing organic photovoltaics from being commercialized is controlling the packing of the organic materials within the active layer from the molecular scale through the …