Physical Sciences and Mathematics Commons^™

Unveiling Quantum Critical Phenomena In Selected Rare Earth Intermetallic Compounds, Lekhanath Poudel

Doctoral Dissertations

The quantum critical phenomenon of CeCu_6-xAu_x (x =0.1) [gold-doped cerium copper six] presents a host of intriguing puzzles: In particular, the dynamic susceptibility showing E/T-scaling with a fractional exponent of 0.75 is a surprise and is clearly inconsistent with the established approach developed by Hertz, Millis, and Moriya (HMM). Interestingly, the phase diagram of CeCu_6-xAu_x [gold-doped cerium copper six] also suggests a zero temperature structural phase transition, raising the possibility of a structural quantum critical point (QCP). To provide a further insight into the unconventional quantum criticality and to investigate the possibility of …

Analysis Of A Market For Tradable Credits, Policy Uncertainty Effects On Investment Decisions, And The Potential To Supply A Renewable Aviation Fuel Industry With An Experimental Industrial Oilseed, Evan Lawrence Markel

Doctoral Dissertations

This research is aligned with identifying barriers throughout the alternative jet-fuel supply chain. Prices are analyzed in the market for tradable credits known as renewable identification numbers (RINs). The RIN market is a key policy instrument used in the implementation of the renewable fuel standard (RFS). The program is highly complex and drivers of RIN price are not always clear. RIN prices also exhibit multiple regimes where the price of nested RINs converge. Therefore, a smooth transition autoregressive model is employed to examine drivers of RIN price and to identify drivers of price regime change. Through research in the RIN …

Design-Structure-Property Relationships Of Purine-Based Copolymers And Chromophores, Graham Smith Collier

Doctoral Dissertations

Understanding the relationship between monomer design and polymer properties is imperative for developing polymeric systems that can find applicability in targeted technologies. Purines have been extensively studied across many scientific disciplines and are useful due to the diverse properties they possess, which is due in part to the broad scope of precise synthetic transformations that are used to tailor their properties. The overarching goal of my dissertation involves developing the synthesis of “poly(purine)s” and investigating the effect of purine monomer design on polymer properties. In this vein, poly(purine)s and purine-based donor-acceptor small-molecules are synthesized via Stille cross-coupling reactions with a …

Surface Modification Of Pillar Array Systems For Chromatography And Fluorescence Enhancement, Danielle Ruth Lincoln

Doctoral Dissertations

Thin-layer chromatography offers many advantages in the world of chemical separations due to its ease of use, high sensitivity, range of applicability, and multiplex capability. However, this technique is succeptible to band broadening effects that limit its efficiency. Attempting to resolve these effects by decreasing particle size causes a decrease in mobile phase velocity which creates its own band broadening via longitudinal diffusion. However, pillar array systems on the micro- and nanoscale have been shown as useful analogues to thin-layer chromatography which mitigate the efficiency concerns associated with the method.

The work within this dissertation is concerned with the modification …

Thermally Robust And Redox Active Catalysts: Studying Their Behavior For Ethylene And L-Lactide Polymerization, Lauren Ashley Brown

Doctoral Dissertations

The development of homogenous single-site catalysts has significantly impacted the field of organometallic chemistry. The well-defined structures of homogenous catalysts make it less cumbersome to understand and develop methods to tailor these compounds for specific catalytic processes. Currently, polymerization catalysis is a major division in organometallic chemistry due to the global demand for polymeric materials such as polyethylene (PE) and polypropylene (PP), based on their low-cost feedstock, remarkable mechanical properties, and their use in a wide range of applications. However, bioplastics have become a highly sought-after alternative to conventional petrochemical-based plastics due to their biodegradability and derivatization from renewable resources. …

Hetero-Atom Containing Functional Polymers: Synthesis, Characterization And Applications, Hongbo Feng

Doctoral Dissertations

A mission to manage ever increased energy demands and reduce carbon foot print has challenged scientists and engineers to develop new materials with superior characteristics. In this scenario, lithium-ion batteries have been the dominating technology for not only applications in consumer electronics but also are essential for clean energy storage. On the other hand, the capture and separation of CO₂ [carbon dioxide] in power generation and in industrial processes is considered to be a key to reduce the carbon footprint.

Living anionic polymerization along with controlled polymerization techniques has realized the preparation of a wide variety of functional polymers …

Properties And Manipulation Of Ionic Liquid-Solid Interfaces In Complex Oxide Materials, Anthony Thomas Wong

Doctoral Dissertations

Ionic liquids are liquid salts that are bringing rapid changes to the field of solid electronic materials. The implementation of ionic liquids in conjunction with these solid materials produces interfacial effects, especially when a bias is applied across the ionic liquid, forming an electric double layer. Electric double layers in ionic liquids are unique in their formation and the interfacial charges that are orders of magnitude higher than conventional techniques they can impart, providing new techniques for device design and implementation. In chapter 1, the fundamentals of the solid state electronic and magnetic materials are introduced, along with ionic liquids, …

Understanding Three-Body Interactions In Hexagonal Close Packed Solid He-4, Ashleigh Locke Barnes

Doctoral Dissertations

The ground state properties of hexagonal close packed (hcp) solid ⁴He [He-4] are dominated by large atomic zero point motions which make the primary contribution to the solid’s low-temperature Debye-Waller (DW) factors. Preliminary investigations have also suggested that three-body interactions can play an important role in this system, particularly at higher densities. However, due to their computational cost, these interactions are not generally incorporated into theoretical models of solid ⁴He [He-4]. In order to accurately treat both zero point motion and three-body interactions, we have developed a perturbative treatment in which the three-body energy is added as a …

Programming Models' Support For Heterogeneous Architecture, Wei Wu

Doctoral Dissertations

Accelerator-enhanced computing platforms have drawn a lot of attention due to their massive peak computational capacity. Heterogeneous systems equipped with accelerators such as GPUs have become the most prominent components of High Performance Computing (HPC) systems. Even at the node level the significant heterogeneity of CPU and GPU, i.e. hardware and memory space differences, leads to challenges for fully exploiting such complex architectures. Extending outside the node scope, only escalate such challenges.

Conventional programming models such as data- ow and message passing have been widely adopted in HPC communities. When moving towards heterogeneous systems, the lack of GPU integration causes …

Development Of High Performance Gas Separation Membranes Through Intelligent Catalyst And Monomer Design, Kevin Richard Gmernicki

Doctoral Dissertations

Polymer membranes are a valuable tool for separating components of liquid and gas mixtures. Heavily inspired by biological systems, the idea of using the intrinsic properties of polymers to perform otherwise energy-intensive tasks is attractive for applications such as water desalination, natural gas sweetening, and post-combustion carbon capture. Of particular interest to our research group, post-combustion carbon capture is a promising potential solution aimed at reducing the carbon footprint involved with production, transportation, and storage of electrical energy generation.

Every year, the United States produces close to seven billion metric tons of carbon dioxide, of which a significant portion is …

Ion Separations: Achieving Selectivity Through Rational Design In Solvent Extraction And Crystallization Systems, Neil Justin Williams

Doctoral Dissertations

The selective separation of ions from aqueous solutions has been a difficult challenge to address in the separation sciences. The difficulties associated with selective separations of ions are due to a multitude of chemical and physical differences between them. Additionally, the term ions encompass both positively charged cations and their counter parts the negatively charge anions. The work covered in this dissertation discusses the difficulties encountered during the selective separation of both oxoanions and cations. Apart from the Introduction Chapter 1 and Conclusion Chapter 10, the selective separations oxoanions and cations will be discussed separately with the dissertation being …

Robot Learning From Human Demonstration: Interpretation, Adaptation, And Interaction, Chi Zhang

Doctoral Dissertations

Robot Learning from Demonstration (LfD) is a research area that focuses on how robots can learn new skills by observing how people perform various activities. As humans, we have a remarkable ability to imitate other human’s behaviors and adapt to new situations. Endowing robots with these critical capabilities is a significant but very challenging problem considering the complexity and variation of human activities in highly dynamic environments.

This research focuses on how robots can learn new skills by interpreting human activities, adapting the learned skills to new situations, and naturally interacting with humans. This dissertation begins with a discussion of …

Improving Predictive Capabilities Of Classical Cascade Theory For Nonproliferation Analysis, David Allen Vermillion

Doctoral Dissertations

Uranium enrichment finds a direct and indispensable function in both peaceful and nonpeaceful nuclear applications. Today, over 99% of enriched uranium is produced by gas centrifuge technology. With the international dissemination of the Zippe archetypal design in 1960 followed by the widespread illicit centrifuge trafficking efforts of the A.Q. Khan network, traditional barriers to enrichment technologies are no longer as effective as they once were. Consequently, gas centrifuge technology is now regarded as a high-priority nuclear proliferation threat, and the international nonproliferation community seeks new avenues to effectively and efficiently respond to this emergent threat.

Effective response first requires an …

Utilizing Nanostructures And Nano-Mechanics For Sensitive Analyte Detection Via Surface Enhanced Raman Spectroscopy (Sers) And Micro-Cantilever Sensing Platforms, Ryan Andrew Wallace

Doctoral Dissertations

The purpose of this dissertation is to present the effective utilization of nano-structures and nano-mechanics in conjunction with surface enhanced Raman spectroscopy (SERS) and micro-cantilever (MC) mechanical sensors for sensitive analytical detection. One of the most important attributes an Analytical Chemist can possess is the ability to develop and efficiently use the tools provided to obtain precise and accurate information that can be effectively communicated. The following is a brief outline of the background concepts and studies that will be present herein.

A discussion of SERS will be presented in which the history and concepts behind the technique will be …

Experiment And Simulation Of Single-Molecule Recycling, Bo Wang

Doctoral Dissertations

This dissertation presents theoretical, numerical, and experimental research into a technique for extending the observation time of a single molecule in solution, while also enabling measurement of its diffusion coefficient. A confocal microscope is used to observe the fluorescently labelled molecule in aqueous solution, which is confined within a nanochannel. By focusing a laser beam into the nanochannel and applying electrokinetic flow along the tube, a molecule passes through the laser beam and emits a burst of photons. The molecule then passes back and forth through the focus while the voltage is repeatedly reversed at a fixed delay after each …

Impact Of Macromolecular Design On Self-Assembly Properties Of Block Copolymers: Effect Of Tunable Chain Flexibility And Chain Topology, Kamlesh Ramesh Bornani

Doctoral Dissertations

The generation of well-ordered complex structures from constituent block copolymeric building blocks by the spontaneous process of self-assembly is useful in various technologies. The well-defined 3D structures are dictated by complex energetic interplays and their shape is controllable by both preparative conditions and macromolecular design. This dissertation work aims at exploring the effect of chain flexibility and chain topology design changes on phase behavior of block copolymers in solution. Further, we exploit the tunable flexibility of the semiflexible polymers in studying dispersion and controlling macroscale thermal properties in polymer nanocomposites.

The experimental design is based on two model systems: The …

Improved Sample Utilization In Thermal Ionization Mass Spectrometry Isotope Ratio Measurements: Refined Development Of Porous Ion Emitters For Nuclear Forensic Applications, Matthew Louis Baruzzini

Doctoral Dissertations

The precise and accurate determination of isotopic composition in nuclear forensic samples is vital for assessing origin, intended use and process history. Thermal ionization mass spectrometry (TIMS) is widely accepted as the gold standard for high performance isotopic measurements and has long served as the workhorse in the isotopic ratio determination of nuclear materials. Nuclear forensic and safeguard specialists have relied heavily on such methods for both routine and atypical efforts. Despite widespread use, TIMS methods for the assay of actinide systems continue to be hindered by poor ionization efficiency, often less than tenths of a percent; the majority of …

Investigating The Properties Of Superfluid He-4 Through Density Functional Calculations, Matthew Francis Dutra

Doctoral Dissertations

We present a study of isotopically pure He-4 systems evaluated using helium density functional theory (He-DFT) with the intent of better understanding their ground state structural and energetic properties, particularly within the scope of singularly-doped helium droplets. We self-consistently solve for the density profiles and chemical potentials for a wide range of pure helium droplet sizes (up to 9500 atoms) via an imaginary time propagation method, and fit the resultant energetic data to a power law formula to be able to extrapolate values for even larger droplets. Subsequent calculations on singularly-doped droplets within the same size range yield accurate binding …

All Acrylic Based Thermoplastic Elastomers: Design And Synthesis For Improved Mechanical Performance, Wei Lu

Doctoral Dissertations

Thermoplastic elastomers (TPEs) have been widely studied because of their recyclability, good processability, low production cost and distinct performance. Compared to the widely-used styrenic TPEs, acrylate based TPEs have potential advantages including exceptional chemical, heat, oxygen and UV resistance, optical transparence, and oil resistance. However, their high entanglement molecular weight lead to “disappointing” mechanical performance as compared to styrenic TPEs. The work described in this dissertation is aimed at employing various approaches to develop the all acrylic based thermoplastic elastomers with improved mechanical performance.

The first part of this work focuses on the introduction of acrylic polymers with high glass …

Extensions Of Task-Based Runtime For High Performance Dense Linear Algebra Applications, Chongxiao Cao

Doctoral Dissertations

On the road to exascale computing, the gap between hardware peak performance and application performance is increasing as system scale, chip density and inherent complexity of modern supercomputers are expanding. Even if we put aside the difficulty to express algorithmic parallelism and to efficiently execute applications at large scale, other open questions remain. The ever-growing scale of modern supercomputers induces a fast decline of the Mean Time To Failure. A generic, low-overhead, resilient extension becomes a desired aptitude for any programming paradigm. This dissertation addresses these two critical issues, designing an efficient unified linear algebra development environment using a task-based …

Synthesis And Characterization Of Novel Single-Site Titanosilicates With Targeted Connectivites And Geometries As Selective Oxidation Catalysts, Lena Elenchin

Doctoral Dissertations

The primary focus of this research was to synthesize and characterize two families of titanosilicate catalysts, first generation and second generation, that were single site, atomically dispersed with targeted connectivities to the silicate matrices but had different geometries about the active sites. First generation catalysts have tetrahedral active sites, while second generation catalysts have altered geometries for a more accessible active site, but maintain the same targeted connectivities.

A building block methodology is employed to prepare single site, isolated, atomically dispersed titanium active sites within a silicate matrix. The synthetic approach uses a molecular precursor, i.e., building block and the …

Effects Of Switchgrass Related Land-Use Changes On Aquatic Macroinvertebrates, Latha Malar Baskaran

Doctoral Dissertations

This research examines if switchgrass-based land-management practices have the potential to influence aquatic macroinvertebrates through changes in stream flow and water quality. The number of taxa in Ephemeroptera, Plecoptera, and Trichoptera orders (EPT taxa richness/EPT-TR) is analyzed as an aquatic macroinvertebrate bioindicator in the context of regional environmental effects, and changes in stream flow and water quality. This dissertation is structured as three manuscripts that link together to address the overall research question.

The first manuscript focuses on identifying regional environmental variables that influence EPT-TR across ecoregions in Tennessee. The influences of temperature, precipitation, geology, soil, stream flow and velocity …

The Homology And Phylogeny Of The Diploporita (Blastozoa: Echinodermata), Sarah Lynne Sheffield

Doctoral Dissertations

Evolutionary relationships of extinct echinoderms are poorly understood, especially within stem-bearing blastozoans, a large group of echinoderms with unique respiratory structures and feeding brachioles. They were highly experimental in their body plans and very unlike echinoderms today (e.g., sea urchins). Many of the blastozoan subgroups recognized in recent classifications do not represent clades (natural associations of organisms derived from a single ancestor); they are either grades of organization or groups united by superficially similar features. Consequently, these ‘traditional’ groupings cannot be used to analyze evolutionary questions, such as biogeography or rates of evolution. This problem is highlighted within the diploporitan …

Surface Energy In Bond-Counting Models On Bravais And Non-Bravais Lattices, Tim Ryan Krumwiede

Doctoral Dissertations

Continuum models in computational material science require the choice of a surface energy function, based on properties of the material of interest. This work shows how to use atomistic bond-counting models and crystal geometry to inform this choice. We will examine some of the difficulties that arise in the comparison between these models due to differing types of truncation. New crystal geometry methods are required when considering materials with non-Bravais lattice structure, resulting in a multi-valued surface energy. These methods will then be presented in the context of the two-dimensional material graphene in a way that correctly predicts its equilibrium …

The Statistical Dynamics Of Nonequilibrium Control, Grant Murray Rotskoff '09

Doctoral Dissertations

Living systems, even at the scale of single molecules, are constantly adapting to changing environmental conditions. The physical response of a nanoscale system to external gradients or changing thermodynamic conditions can be chaotic, nonlinear, and hence difficult to control or predict. Nevertheless, biology has evolved systems that reliably carry out the cell’s vital functions efficiently enough to ensure survival. Moreover, the development of new experimental techniques to monitor and manipulate single biological molecules has provided a natural testbed for theoretical investigations of nonequilibrium dynamics. This work focuses on developing paradigms for both understanding the principles of nonequilibrium dynamics and also …

In-Situ Assessment Of Concrete Bridge Decks And Pavements Using Stress-Wave Based Methods, Mengxing Li

Doctoral Dissertations

"Concrete infrastructure of United States is aging and deteriorating. Accurate assessment the condition of concrete infrastructure is critical for its maintenance and rehabilitation. Stress-wave based methods, including ultrasonic surface wave (USW) and impact echo (IE), are becoming popular for characterizing defects and mechanical properties of concrete infrastructures. In this dissertation, a comprehensive literature review of seismic wave theory and common types of defects identified in concrete infrastructures, as well as stress-wave based methods used for concrete infrastructure monitoring and characterizing on a selected concrete bridge deck and two concrete pavement segments are present. The utility and reliability of both methods …

An Improved Imaging Method For Extended Targets, Sui Zhang

Doctoral Dissertations

The dissertation presents an improved method for the inverse scattering problem to obtain better numerical results. There are two main methods for solving the inverse problem: the direct imaging method and the iterative method. For the direct imaging method, we introduce the MUSIC (MUltiple SIgnal Classification) algorithm, the multi-tone method and the linear sampling method with different boundary conditions in different cases, which are the smooth case, the one corner case, and the multiple corners case. The dissertation introduces the relations between the far field data and the near field data.

When we use direct imaging methods for solving inverse …

A Study Of Mathematics Achievement, Placement, And Graduation Of Engineering Students, Sara Hahler Blazek

Doctoral Dissertations

The purpose of this study was to determine how background knowledge impacts freshmen engineering students' success at Louisiana Tech University in terms of grades in two different freshman classes and graduation. To determine what factors impact students, three different studies were implemented. The first study used linear regression to analyze which demographic and academic variables significantly impacted freshman math and engineering courses. Using regression discontinuity, the second study determined if the university's placement requirement for Pre-Calculus was appropriate. The final study analyzed factors that impact graduation for engineering students as well as other disciplines to determine which significant variables were …

Acquisition Of Active Multichannel Analysis Of Surface Waves (Masw) Data In Karst Terrain, Ghassan Salem Alsulaimani

Doctoral Dissertations

"This study was designed to verify the effects and data reproducibility when the length of receiver array, receiver spacing, source offset and array orientation parameters are changed for data acquired using multichannel analysis of surface waves (MASW), at intended target depth of 30ft (9m), and to compare the results with electrical resistivity tomography (ERT) data obtained for the same study site.

The MASW data acquired for 34 sites, along four profiles for each site using variable source offsets of 10ft (3m) and 30ft (9.1m), and variable receiver spacings of 2.5ft (0.76m) and 5.0ft (0.76m), concurrently. Out of the 272 profiles …

Electron Impact Excitation-Ionization Of Molecules, Esam Abobakr A. Ali

Doctoral Dissertations

"In the last few decades, the study of atomic collisions by electron-impact has made significant advances. The most difficult case to study is electron impact ionization of molecules for which many approximations have to be made and the validity of these approximations can only be checked by comparing with experiment.

In this thesis, I have examined the Molecular three-body distorted wave (M3DW) or Molecular four-body distorted wave (M4DW) approximations for electron-impact ionization. These models use a fully quantum mechanical approach where all particles are treated quantum mechanically and the post collision interaction (PCI) is treated to all orders of perturbation. …