UNT Libraries Government Documents Department - 182 Matching Results

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open access

1: Redox chemistry of bimetallic fulvalene complexes; 2: Oligocyclopentadienyl complexes

Description: The electrochemistry of the heterobimetallic complexes (fulvalene)WFe(CO){sub 5} (30) and (fulvalene)WRu(CO){sub 5} (31) has been investigated. Compound 30 is reduced in two one-electron processes, and this behavior was exploited synthetically to prepare a tetranuclear dimer by selective metal reduction. Complex 31 displayed a distinction between the metals upon reoxidation of the dianion, allowing the formation of a dimer by selective metal anion oxidation. The redox behavior of 30 led to an i… more
Date: November 1, 1993
Creator: Brown, D. S.
open access

Advances and applications of dynamic-angle spinning nuclear magnetic resonance

Description: This dissertation describes nuclear magnetic resonance experiments and theory which have been developed to study quadrupolar nuclei (those nuclei with spin greater than one-half) in the solid state. Primarily, the technique of dynamic-angle spinning (DAS) is extensively reviewed and expanded upon in this thesis. Specifically, the improvement in both the resolution (two-dimensional pure-absorptive phase methods and DAS angle choice) and sensitivity (pulse-sequence development), along with effect… more
Date: June 1, 1993
Creator: Baltisberger, J. H.
open access

Aging effects on the microstructure, surface characteristics and wettability of Cu pretinned with Sn-Pb solders

Description: This study investigates effects of aging in air and argon at 170 C on Cu coupons which were pretinned with 75Sn-25Pb, 8Sn-92Pb, and 5Sn-95Pb solders. Coatings were applied using electroplating or hot dipping techniques. The coating thickness was controlled between 3 to 3{mu}m and the specimens were aged for 0 hours, 2 hours, 24 hours and 2 weeks. Wetting balance tests were used to evaluate the wettability of the test specimens. Microstructural development was evaluated using X-ray diffraction, … more
Date: November 1, 1993
Creator: Linch, H. S.
open access

Analysis of the application of decontamination technologies to radioactive metal waste minimization using expert systems

Description: Radioactive metal waste makes up a significant portion of the waste currently being sent for disposal. Recovery of this metal as a valuable resource is possible through the use of decontamination technologies. Through the development and use of expert systems a comparison can be made of laser decontamination, a technology currently under development at Ames Laboratory, with currently available decontamination technologies for applicability to the types of metal waste being generated and the eff… more
Date: September 30, 1993
Creator: Bayrakal, S.
open access

Anisotropic phase separation through the metal-insulator transition in amorphous Mo-Ge and Fe-Ge alloys

Description: Since an amorphous solid is often defined as that which lacks long-range order, the atomic structure is typically characterized in terms of the high-degree of short-range order. Most descriptions of vapor-deposited amorphous alloys focus on characterizing this order, while assuming that the material is chemically homogeneous beyond a few near neighbors. By coupling traditional small-angle x-ray scattering which probes spatial variations of the electron density with anomalous dispersion which cr… more
Date: December 1, 1993
Creator: Regan, M. J.
open access

Anomalous small angle x-ray scattering studies of amorphous metal-germanium alloys

Description: This dissertation addresses the issue of composition modulation in sputtered amorphous metal-germanium thin films with the aim of understanding the intermediate range structure of these films as a function of composition. The investigative tool used in this work is anomalous small-angle X-ray scattering (ASAXS). The primary focus of this investigation is the amorphous iron-germanium (a-Fe{sub x}Ge{sub 100-x}) system with particular emphasis on the semiconductor-rich regime. Brief excursions are… more
Date: December 1, 1993
Creator: Rice, M.
open access

Application of an Electrochemical Quartz Crystal Microbalance to the study of electrocatalytic films

Description: The EQCM was used to study the deposition and composition of electrodeposited pure PbO{sub 2} and Bi-doped PbO{sub 2} active toward anodic oxygen-transfer reactions. Within the doped films, Bi is incorporated as Bi{sup +5} in the form of BiO{sub 2}A, where A is ClO{sub 4}{sup {minus}} or NO{sub 3}{sup {minus}}. For deposition of these 2 materials, changes in hydration between the Au oxide and the depositing film resulted in higher mass-to-charge ratios. XRD and XPS were used to study the films;… more
Date: September 1, 1993
Creator: Gordon, J. S., Jr.
open access

Application of semiclassical methods to reaction rate theory

Description: This work is concerned with the development of approximate methods to describe relatively large chemical systems. This effort has been divided into two primary directions: First, we have extended and applied a semiclassical transition state theory (SCTST) originally proposed by Miller to obtain microcanonical and canonical (thermal) rates for chemical reactions described by a nonseparable Hamiltonian, i.e. most reactions. Second, we have developed a method to describe the fluctuations of decay … more
Date: November 1, 1993
Creator: Hernandez, R.
open access

Applications of highly spin-polarized xenon in NMR

Description: The main goal of the work presented in this thesis is produce highly spin-polarized xenon to create much greater signal intensities (up to 54,000 times greater) so as to allow studies to be made on systems with low surface area and long spin-lattice relaxation times. The spin-exchange optical pumping technique used to create high nuclear spin polarization is described in detail in chapter two. This technique is initially applied to some multiple-pulse optically detected NMR experiments in low m… more
Date: September 1, 1993
Creator: Long, H. W.
open access

An axial approach to detection in capillary electrophoresis

Description: Our approach involves on-axis illumination of the compounds inside the capillary detection region and is applied to absorbance and fluorescence detection. Absorbance measurements were made by focussing an incident laser beam into one capillary end; by using signals collected over the entire length of analyte band, this enhances the analytical path length of conventional absorbance detection 60x. This instrument offers a 15x improvement in detection limits. Three fluorescence detection experimen… more
Date: May 1, 1993
Creator: Taylor, J. A.
open access

Behavior of the particle transport coefficients near the density limit in MTX

Description: The perturbed particle transport coefficients were determined for a range of plasma conditions in the Alcator C tokamak, a component of the Microwave Tokamak Experiment (MTX), from analysis of density perturbations created in gas modulation experiments. Density measurements from a 15 chord far-infrared interferometer were sufficiently detailed to allow radial profiles of the transport coefficients to be resolved. Gas modulation experiments were carried out on plasmas over a range of relatively … more
Date: April 1, 1993
Creator: Marinak, M. M.
open access

CCM Continuity Constraint Method: A finite-element computational fluid dynamics algorithm for incompressible Navier-Stokes fluid flows

Description: As the field of computational fluid dynamics (CFD) continues to mature, algorithms are required to exploit the most recent advances in approximation theory, numerical mathematics, computing architectures, and hardware. Meeting this requirement is particularly challenging in incompressible fluid mechanics, where primitive-variable CFD formulations that are robust, while also accurate and efficient in three dimensions, remain an elusive goal. This dissertation asserts that one key to accomplishin… more
Date: September 1, 1993
Creator: Williams, P. T.
open access

Chaos and simple determinism in reversed field pinch plasmas: Nonlinear analysis of numerical simulation and experimental data

Description: In this dissertation the possibility that chaos and simple determinism are governing the dynamics of reversed field pinch (RFP) plasmas is investigated. To properly assess this possibility, data from both numerical simulations and experiment are analyzed. A large repertoire of nonlinear analysis techniques is used to identify low dimensional chaos in the data. These tools include phase portraits and Poincare sections, correlation dimension, the spectrum of Lyapunov exponents and short term pred… more
Date: September 1, 1993
Creator: Watts, C. A.
open access

Characterization of the sodium void reactivity effect for advanced liquid metal reactor fuels

Description: This report discusses the problems of a large positive sodium void reactivity effect in liquid metal reactors which have received increased attention following the accident at Chernobyl, a light water reactor with a positive coolant void coefficient. While the probability of voiding sodium is small, a large positive sodium void reactivity effect is, in many minds, unacceptable. Analyses were performed on models of an advanced liquid metal reactors to determine the effects fuel type have on the … more
Date: December 1, 1993
Creator: Kessler, S. F.
open access

Characterization of Zns-GaP Naon-composites

Description: It proved possible to produce consistent, high-quality nanocrystalline ZnS powders with grain sizes as small as 8 nm. These powders are nano-porous and are readily impregnated with GaP precursor, although inconsistently. Both crystal structure and small grain size of the ZnS can be maintained through the use of GaP. Heat treatment of the impregnated powders results in a ZnS-GaP composite structure where the grain sizes of the phases are on the order of 10--20 nm. Conventional powder processing … more
Date: December 9, 1993
Creator: Todd, V.
open access

Chemical dynamics in time and energy space

Description: The development of a versatile picosecond ultraviolet/vacuum ultraviolet temporal spectrometer and its potential use for measuring internal energy redistribution in isolated molecules are described in detail. A detailed description of the double-pass Nd:YAG amplifier and the dye amplifiers is given with the pulse energies achieved in the visible, ultraviolet, and vacuum ultraviolet. The amplified visible pulses are shown to be of sub-picosecond duration and near transform limited. The instrumen… more
Date: April 1, 1993
Creator: Myers, J. D.
open access

Chemically modified polymeric resins for separation of cations, organic acids, and small polar moleculea by high performance liquid chromatography

Description: This thesis is divided into 4 parts: a review, ion chromatography of metal cations on carboxylic resins, separation of hydrophilic organic acids and small polar compounds on macroporous resin columns, and use of eluent modifiers for liquid chromatographic separation of carboxylic acids using conductivity detection.
Date: July 1, 1993
Creator: Morris, J. B.
open access

Chemically modified polymeric resins for solid-phase extraction and group separation prior to analysis by liquid or gas chromatography

Description: Polystyrene divinylbenzene was modified by acetyl, sulfonic acid, and quaternary ammonium groups. A resin functionalized with an acetyl group was impregnated in a PTFE membrane and used to extract and concentrate phenolic compounds from aqueous samples. The acetyl group created a surface easily wetted, making it an efficient adsorbent for polar compounds in water. The membrane stabilized the resin bed. Partially sulfonated high surface area resins are used to extract and group separate an aqueo… more
Date: July 1, 1993
Creator: Schmidt, L. W.
open access

Circular magnetic x-ray dichroism in rare earth compounds

Description: This report discusses the following topics: Circular magnetic x-ray dichroism at the ER L{sub 3} Edge; angular dependence of circular magnetic x-ray dichroism in rare earth compounds: and circular magnetic x-ray dichroism in crystalline and amorphous GDFE{sub 2}.
Date: September 30, 1993
Creator: Jonathan, L.
open access

Compressive strength, plastic flow properties, and surface frictional effects of 1100, 3003 and 6061 aluminum alloys

Description: The purpose of this study is to find aluminum alloys that are effective for use as wire vacuum seals in the 800MeV particle accelerator located at the Louis Anderson Meson Physics Facility (LAMPF) in Los Alamos, NM. Three alloys, Al 1100, Al 3003, and Al 6061, are investigated under uniaxial compression to determine stresses for a given height reduction from 0 to 70 percent, and to find plastic flow and surface interaction effects. Right-circular cylindrical specimens are compressed on-end (cyl… more
Date: December 31, 1993
Creator: Pinkerton, G.W.
open access

Computer simulation of martensitic transformations

Description: The characteristics of martensitic transformations in solids are largely determined by the elastic strain that develops as martensite particles grow and interact. To study the development of microstructure, a finite-element computer simulation model was constructed to mimic the transformation process. The transformation is athermal and simulated at each incremental step by transforming the cell which maximizes the decrease in the free energy. To determine the free energy change, the elastic ene… more
Date: November 1, 1993
Creator: Xu, Ping
open access

Conceptual study of moderately coupled plasmas and experimental comparison of laboratory x-ray sources

Description: In this thesis the fundamental concepts of moderately coupled plasmas, for which 2{approx_lt}ln{Lambda}{sub b}{approx_lt}10, are, for the first time, presented. This investigation is motivated because neither the conventional Fokker-Planck approximation [for weakly coupled plasmas (ln{Lambda}{sub b}{approx_lt}10)] nor the theory of dielectric response with correlations for strongly coupled plasmas (ln{Lambda}{sub b}{approx_lt}1) has satisfactorily addressed this regime. Specifically, herein the… more
Date: December 1993
Creator: Li, C.
open access

Convection in Type 2 supernovae

Description: Results are presented here from several two dimensional numerical calculations of events in Type II supernovae. A new 2-D hydrodynamics and neutrino transport code has been used to compute the effect on the supernova explosion mechanism of convection between the neutrinosphere and the shock. This convection is referred to as exterior convection to distinguish it from convection beneath the neutrinosphere. The model equations and initial and boundary conditions are presented along with the simul… more
Date: October 15, 1993
Creator: Miller, D. S.
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