The N-body problem is to simulate the motion of N particles under the influence of mutual force fields based on an inverse square law. The problem has applications in several domains including astrophysics, molecular dynamics, fluid dynamics, radiosity methods in computer graphics and numerical complex analysis. Research efforts have focused on reducing the O(N{sup 2}) time per iteration required by the naive algorithm of computing each pairwise interaction. Widely respected among these are the Barnes-Hut and Greengard methods. Greengard claims his algorithm reduces the complexity to O(N) time per iteration. Throughout this thesis, we concentrate on rigorous, distribution-independent, worst-case analysis of the N-body methods. We show that Greengard`s algorithm is not O(N), as claimed. Both Barnes-Hut and Greengard`s methods depend on the same data structure, which we show is distribution-dependent. For the distribution that results in the smallest running time, we show that Greengard`s algorithm is {Omega}(N log{sup 2} N) in two dimensions and {Omega}(N log{sup 4} N) in three dimensions. We have designed a hierarchical data structure whose size depends entirely upon the number of particles and is independent of the distribution of the particles. We show that both Greengard`s and Barnes-Hut algorithms can be used in conjunction with …

The underlying theme of this thesis is the use of polymeric materials in bioapplications. Chapters 2-5 either develop a fundamental understanding of current materials used for bioapplications or establish protocols and procedures used in characterizing and synthesizing novel materials. In chapters 6 and 7 these principles and procedures are applied to the development of materials to be used for gene therapy and drug delivery. Chapter one is an introduction to the ideas that will be necessary to understand the subsequent chapters, as well as a literature review of these topics. Chapter two is a paper that has been published in the ''Journal of Controlled Release'' that examines the mechanism of drug release from a polymer gel, as well as experimental design suggestions for the evaluation of water soluble drug delivery systems. Chapter three is a paper that has been published in the ''Journal of Pharmaceutical Sciences'' that discusses the effect ionic salts have on properties of the polymer systems examined in chapter two. Chapter four is a paper published in the Materials Research Society Fall 2000 Symposium Series dealing with the design and synthesis of a pH-sensitive polymeric drug delivery device. Chapter five is a paper that has been published …

Production of {Lambda} + K{sup 0}, {Sigma}{sup 0} + K{sup 0}, and {Sigma}{sup -} + K{sup +} by 1170-MeV/c {pi}{sup -} mesons has been studied in the Lawrence Radiation Laboratory 72-inch hydrogen bubble chamber, Cross sections, angular distributions, and polarizations are presented. The polarization of the {Sigma}{sup 0} is determined at four center-of-mass angles and found to be small everywhere. Based on published results for the reaction {pi}{sup +} + p {yields} {Sigma}{sup +}, K{sup +}, a comparison of the polarizations of {Sigma}{sup +}, {Sigma}{sup -}, and {Sigma}{sup 0} is made from the charge-independence triangle. A conclusion is reached that the {Sigma}{sup -} polarization should be large, and that the {Sigma}{sup -} and {Sigma}{sup +} polarizations should be opposite in sign.

Lithium ion insertion into electrode materials is commonly used in rechargeable battery technology. The insertion implies changes in both the crystal structure and the electronic structure of the electrode material. Side-reactions may occur on the surface of the electrode which is exposed to the electrolyte and form a solid electrolyte interface (SEI). The understanding of these processes is of great importance for improving battery performance. The chemical and physical properties of water and alcohols are complicated by the presence of strong hydrogen bonding. Various experimental techniques have been used to study geometrical structures and different models have been proposed to view the details of how these liquids are geometrically organized by hydrogen bonding. However, very little is known about the electronic structure of these liquids, mainly due to the lack of suitable experimental tools. In this thesis examples of studies of lithium battery electrodes and liquid systems using soft x-ray emission spectroscopy will be presented. Monochromatized synchrotron radiation has been used to accomplish selective excitation, in terms of energy and polarization. The electronic structure of graphite electrodes has been studied, before and after lithium intercalation. Changes in the electronic structure upon lithiation due to transfer of electrons into the graphite …

this research has shown that it is possible to deposit coatings of gas atomized Cu{sub 47}Ti{sub 33}Zr{sub 11}Ni{sub 8}Si{sub 1} powders containing various levels of oxygen contamination using plasma arc spray methods. The structure of the coating was found to depend primarily on the spray environment, with an argon atmosphere producing the most amorphous samples for a given starting powder. The oxygen content of the coatings reflected the relative levels of the oxygen contamination in the starting powders. The analysis of the starting powders displayed oxygen contents ranging from 0.125-0.79 wt.%. It was shown that higher oxygen levels lead to more crystalline structure in the starting powders as determined by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). This trend was found to be true for both the starting powders and for the plasma sprayed coatings. Chemical composition for all starting powders was very close to the nominal alloy composition. Chemical changes in the coatings involved the loss of Cu in coatings where high levels of oxidation were found. Cavitation erosion testing of selected coatings showed a weak trend that coatings prepared by vacuum plasma spray (VPS) had lower damage rates, but there was no clear data to indicate which …

It is possible to produce alumina-zirconia ceramic samples through existing solidification techniques. The resulting microstructures typically consist of rods of zirconia in an alumina matrix, although a lamellar structure has been noted in some cases. In nearly all cases, colony growth was present which may possibly result from grain size, repeated nucleation events, and lamellar oscillations. In the same vein, it appears that the amount of impurities within the system might be the underlying cause for the colony growth. Colony growth was diminished through impurity control as the higher purity samples exhibited colony free behavior. In addition to colony formations, faceted alumina dendrites or nonfaceted zirconia dendrites may result in the ceramic if the sample is solidified out of the coupled zone. In all cases, for larger-sized Bridgman samples, a lower limit in the eutectic spacing was noted. The solidification model which includes the kinetic effect has been developed, although the effect appears to be negligible under present experimental conditions. A spacing limit might also occur due to the result of heat flow problems. Heat flow out of the ceramic is difficult to control, often causing radial and not axial growth. This behavior is exaggerated in the presence of impurities. …

This report discusses the following topics: Bloch oscillations and other dynamical phenomena of electrons in semiconductor superlattices; solvable dynamical model of an electron in a one-dimensional aperiodic lattice subject to a uniform electric field; and quantum dynamical phenomena of electrons in aperiodic semiconductor superlattices.

Since its development, inductively coupled plasma mass spectrometry (ICP-MS) has been a widely used analytical technique. ICP-MS offers low detection limits, easy determination of isotope ratios, and simple mass spectra from analyte elements. ICP-MS has been successfully employed for many applications including geological, environmental, biological, metallurgical, food, medical, and industrial. One specific application important to many areas of study involves elemental speciation by using ICP-MS as an element specific detector interfaced to liquid chromatography. Elemental speciation information is important and cannot be obtained by atomic spectrometric methods alone which measure only the total concentration of the element present. Part 1 of this study describes the speciation of selenium in human serum by size exclusion chromatography (SEC) and detection by ICP-MS. Although ICP-MS has been widely sued, room for improvement still exists. Difficulties in ICP-MS include noise in the background, matrix effects, clogging of the sampling orifice with deposited solids, and spectral interference caused by polyatomic ions. Previous work has shown that the addition of xenon into the central channel of the ICP decreases polyatomic ion levels. In Part 2 of this work, a fundamental study involving the measurement of the excitation temperature is carried out to further understand xenon`s role …

Senior colloquium written by a student in the UNT Honors College discussing Greek sculpture and architecture as filtered through the Fauve, Constructivist, Dada, and Pop artistic movements. The author takes examples of Grecian sculpture, recreates them in each of the other styles, and discusses the results.

This dissertation includes three different topics: general introduction of capillary electrophoresis (CE); gradient in CE and CE in biological separations; and capillary gel electrophoresis (CGE) for DNA separation. Factors such as temperature, viscosity, pH, and the surface of capillary walls affecting the separation performance are demonstrated. A pH gradient between 3.0 and 5.2 is useful to improve the resolution among eight different organic acids. A flow gradient due to the change in the concentration of surfactant, which is able to coat to the capillary wall to change the flow rate and its direction, is also shown as a good way to improve the resolution for organic compounds. A temperature gradient caused by joule heat is shown by voltage programming to enhance the resolution and shorten the separation time for several phenolic compounds. The author also shows that self-regulating dynamic control of electroosmotic flow in CE by simply running separation in different concentrations of surfactant has less matrix effect on the separation performance. One of the most important demonstrations in this dissertation is that the author proposes on-column reaction which gives several advantages including the use of a small amount of sample, low risk of contamination, and time saving and kinetic …

A new technique for in situ imaging and screening heterogeneous catalysts by using multiplexed capillary electrophoresis with absorption detection was developed. By bundling the inlets of a large number of capillaries, an imaging probe can be created that can be used to sample products formed directly from a catalytic surface with high spatial resolution. In this work, they used surfaces made of platinum, iron or gold wires as model catalytic surfaces for imaging. Various shapes were recorded including squares and triangles. Model catalytic surfaces consisting of both iron and platinum wires in the shape of a cross were also imaged successfully. Each of the two wires produced a different electrochemical product that was separated by capillary electrophoresis. Based on the collected data they were able to distinguish the products from each wire in the reconstructed image.

The research in this thesis explores the separation capabilities of a new technique termed electrochemically-modulated liquid chromatography (EMLC). The thesis begins with a general introduction section which provides a literature review of this technique as well as a brief background discussion of the two research projects in each of the next two chapters. The two papers which follow investigate the application of EMLC to the separation of a mixture of aromatic amino acids and of a mixture of polycyclic aromatic hydrocarbons (PAHs). The last section presents general conclusions and summarizes the thesis. References are compiled in the reference section of each chapter. The two papers have been removed for separate processing.

The electronic and structural properties of the ({radical}3 {times} {radical}3) R30{degrees} Ag/Si(111) and ({radical}3 {times} {radical}3) R30{degrees} Au/Si(111) surfaces are investigated using first principles total energy calculations. We have tested almost all experimentally proposed structural models for both surfaces and found the energetically most favorable model for each of them. The lowest energy model structure of the ({radical}3 {times} {radical}3) R30{degrees} Ag/Si(111) surface consists of a top layer of Ag atoms arranged as ``honeycomb-chained-trimers`` lying above a distorted ``missing top layer`` Si(111) substrate. The coverage of Ag is 1 monolayer (ML). We find that the honeycomb structure observed in STM images arise from the electronic charge densities of an empty surface band near the Fermi level. The electronic density of states of this model gives a ``pseudo-gap`` around the Fermi level, which is consistent with experimental results. The lowest energy model for the ({radical}3 {times} {radical}3) R30{degrees} Au/Si(111) surface is a conjugate honeycomb-chained-trimer (CHCT-1) configuration which consists of a top layer of trimers formed by 1 ML Au atoms lying above a ``missing top layer`` Si(111) substrate with a honeycomb-chained-trimer structure for its first layer. The structures of Au and Ag are in fact quite similar and belong to the …

This dissertation describes a variety of studies meant to improve the analytical performance of inductively coupled plasma mass spectrometry (ICP-MS) and laser ablation (LA) ICP-MS. The emission behavior of individual droplets and LA generated particles in an ICP is studied using a high-speed, high frame rate digital camera. Phenomena are observed during the ablation of silicate glass that would cause elemental fractionation during analysis by ICP-MS. Preliminary work for ICP torch developments specifically tailored for the improvement of LA sample introduction are presented. An abnormal scarcity of metal-argon polyatomic ions (MAr{sup +}) is observed during ICP-MS analysis. Evidence shows that MAr{sup +} ions are dissociated by collisions with background gas in a shockwave near the tip of the skimmer cone. Method development towards the improvement of LA-ICP-MS for environmental monitoring is described. A method is developed to trap small particles in a collodion matrix and analyze each particle individually by LA-ICP-MS.

In this work, the authors have undertaken a theoretical approach to the complex problem of modeling the flow of electromagnetic waves in photonic crystals. The focus is to address the feasibility of using the exciting phenomena of photonic gaps (PBG) in actual applications. The authors start by providing analytical derivations of the computational electromagnetic methods used in their work. They also present a detailed explanation of the physics underlying each approach, as well as a comparative study of the strengths and weaknesses of each method. The Plane Wave expansion, Transfer Matrix, and Finite Difference time Domain Methods are addressed. They also introduce a new theoretical approach, the Modal Expansion Method. They then shift the attention to actual applications. They begin with a discussion of 2D photonic crystal wave guides. The structure addressed consists of a 2D hexagonal structure of air cylinders in a layered dielectric background. Comparison with the performance of a conventional guide is made, as well as suggestions for enhancing it. The studies provide an upper theoretical limit on the performance of such guides, as they assumed no crystal imperfections and non-absorbing media. Next, they study 3D metallic PBG materials at near infrared and optical wavelengths. The main …

This thesis investigated the biology and importance of the corn flea beetle vector and its role in the Stewart's disease of corn pathosystem. This was accomplished by determining the number of corn flea beetle generations that occur in Iowa and by quantifying the proportions of those populations found to be infested with the causal agent of Stewart's disease, pantoea stewartii. In addition, a preliminary study was conducted to determine how soil temperature was influenced by air temperature and how this may be applied to forecasting for Stewart's disease of corn. Research using yellow sticky cards and sweep netting demonstrated that there are overwintering, first, and second field generations of the corn flea beetle in Iowa. It was also observed that there was a period during June of both 1999 and 2000 when corn flea beetles were not found, which is important new management information. This research has also demonstrated that the incidence of P. stewartii-infested corn flea beetles can be monitored by ELISA testing and that the incidence fluctuates greatly throughout the corn growing season. The initial level of inoculum (P. stewartii-infested corn flea beetles in the adult overwintering generation) does not remain static during the spring as was previously …

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The study of rare earth magnetic properties is undertaken to further the understanding of critical phenomena and the mechanism of magnetic ordering in solids. There is a great variety of magnetic ordering observed in the rare earth compounds, thus providing an insight to phenomena such as heat capacity, magnetostriction and crystal fields. Studies began on the magnetic properties of the rare earths and their compounds in the 1950`s.

Concurrency levels in large-scale, distributed-memory supercomputers are rising exponentially. Modern machines may contain 100,000 or more microprocessor cores, and the largest of these, IBM's Blue Gene/L, contains over 200,000 cores. Future systems are expected to support millions of concurrent tasks. In this dissertation, we focus on efficient techniques for measuring and analyzing the performance of applications running on very large parallel machines. Tuning the performance of large-scale applications can be a subtle and time-consuming task because application developers must measure and interpret data from many independent processes. While the volume of the raw data scales linearly with the number of tasks in the running system, the number of tasks is growing exponentially, and data for even small systems quickly becomes unmanageable. Transporting performance data from so many processes over a network can perturb application performance and make measurements inaccurate, and storing such data would require a prohibitive amount of space. Moreover, even if it were stored, analyzing the data would be extremely time-consuming. In this dissertation, we present novel methods for reducing performance data volume. The first draws on multi-scale wavelet techniques from signal processing to compress systemwide, time-varying load-balance data. The second uses statistical sampling to select a small …

This study examined five different branched molecular architectures to discern the effect of design on the ability of molecules to form ordered structures at interfaces. Photochromic monodendrons formed kinked packing structures at the air-water interface due to the cross-sectional area mismatch created by varying number of alkyl tails and the hydrophilic polar head group. The lower generations formed orthorhombic unit cell with long range ordering despite the alkyl tails tilted to a large degree. Favorable interactions between liquid crystalline terminal groups and the underlying substrate were observed to compel a flexible carbosilane dendrimer core to form a compressed elliptical conformation which packed stagger within lamellae domains with limited short range ordering. A twelve arm binary star polymer was observed to form two dimensional micelles at the air-water interface attributed to the higher polystyrene block composition. Linear rod-coil molecules formed a multitude of packing structures at the air-water interface due to the varying composition. Tree-like rod-coil molecules demonstrated the ability to form one-dimensional structures at the air-water interface and at the air-solvent interface caused by the preferential ordering of the rigid rod cores. The role of molecular architecture and composition was examined and the influence chemically competing fragments was shown to …

The results of magnetic x-ray resonant exchange scattering (XRES) experiments are important to the development of an understanding of magnetic interactions in materials. The advantages of high Q resolution, polarization analysis, and the ability to study many different types of materials make it a vital tool in the field of condensed matter physics. Though the concept of XRES was put forth by Platzman and Tzoar in 1970, the technique did not gain much attention until the work of Gibbs and McWhan et al. in 1988. Since then, the technique of XRES has grown immensely in use and applicability. Researchers continue to improve upon the procedure and detection capabilities in order to study magnetic materials of all kinds. The XRES technique is particularly well suited to studying the rare earth metals because of the energy range involved. The resonant L edges of these elements fall between 5-10 KeV. Resonant and nonresonant x-ray scattering experiments were performed in order to develop an understanding of the magnetic ordering in GdCo{sub 2}Ge{sub 2} and NdCo{sub 2}Ge{sub 2}.

The properties of both carbon and gold substrates are easily affected by the judicious choice of a surface modification protocol. Several such processes for altering surface composition have been published in literature. The research presented in this thesis primarily focuses on the development of on-column methods to modify carbon stationary phases used in electrochemically modulated liquid chromatography (EMLC). To this end, both porous graphitic carbon (PGC) and glassy carbon (GC) particles have been modified on-column by the electroreduction of arenediazonium salts and the oxidation of arylacetate anions (the Kolbe reaction). Once modified, the carbon stationary phases show enhanced chromatographic performance both in conventional liquid chromatographic columns and EMLC columns. Additionally, one may also exploit the creation of aryl films to by electroreduction of arenediazonium salts in the creation of nanostructured materials. The formation of mercaptobenzene film on the surface of a GC electrode provides a linking platform for the chemisorption of gold nanoparticles. After deposition of nanoparticles, the surface chemistry of the gold can be further altered by self-assembled monolayer (SAM) formation via the chemisorption of a second thiol species. Finally, the properties of gold films can be altered such that they display carbon-like behavior through the formation of benzenehexathiol …

Previous research into the alkali-metal-gallium systems has revealed a large variety of networked gallium deltahedra. The clusters are analogues to borane clusters and follow the same electronic requirements of 2n+2 skeletal electrons for closo-deltahedra. This work has focused on compounds that do not follow the typical electron counting rules. The first isolated gallium cluster was found in Cs{sub 8}Ga{sub 11}. The geometry of the Ga{sub 11}{sup 7{minus}} unit is not deltahedral but can be described as a penta-capped trigonal prism. The reduction of the charge from a closo-Ga{sub 11}{sup 13{minus}} to Ga{sub 11}{sup 7{minus}} is believed to be the driving force of the distortion. The compound is paramagnetic because of an extra electron but incorporation of a halide atom into the structure captures the unpaired electron and forms a diamagnetic compound. A second isolated cluster has been found in Na{sub 10}Ga{sub 10}Ni where the tetra-capped trigonal prismatic gallium is centered by nickel. Stabilization of the cluster occurs through Ni-Ga bonding. A simple two-dimensional network occurs in the binary K{sub 2}Ga{sub 3} Octahedra are connected through four waist atoms to form a layered structure with the potassium atoms sitting between the layers. Na{sub 30.5}Ga{sub 60{minus}x}Ag{sub x} is nonstoichiometric and needs only …

Alkali metal aluminohydrides have high potential as solid hydrogen storage materials. They have been known for their irreversible dehydrogenation process below 100 atm until Bogdanovic et al succeeded in the re-hydrogenation of NaAlH{sub 4} below 70 atm. They achieved 4 wt.% H{sub 2} reversible capacity by doping NaAlH{sub 4} with Ti and/or Fe organo-metallic compounds as catalysts. This suggests that other alkali and, possibly alkaline earth metal aluminohydrides can be used for reversible hydrogen storage when modified by proper dopants. In this research, Zr{sub 27}Ti{sub 9}Ni{sub 38}V{sub 5}Mn{sub 16}Cr{sub 5}, LaNi{sub 4.85}Sn{sub 0.15}, Al{sub 3}Ti, and PdCl{sub 2} were combined with LiAlH{sub 4} by ball-milling to study whether or not LiAlH{sub 4} is capable to both absorb and desorb hydrogen near ambient conditions. X-ray powder diffraction, differential thermal analysis, and scanning electron microscopy were employed for sample characterizations. All four compounds worked as catalysts in the dehydrogenation reactions of both LiAlH{sub 4} and Li{sub 3}AlH{sub 6} by inducing the decomposition at lower temperature. However, none of them was applicable as catalyst in the reverse hydrogenation reaction at low to moderate hydrogen pressure.