Genetic algorithms (GAs), global optimization methods that mimic Darwinian evolution are well suited to the nonlinear inverse problems of geophysics. A standard genetic algorithm selects the best or ''fittest'' models from a ''population'' and then applies operators such as crossover and mutation in order to combine the most successful characteristics of each model and produce fitter models. More sophisticated operators have been developed, but the standard GA usually provides a robust and efficient search. Although the choice of parameter settings such as crossover and mutation rate may depend largely on the type of problem being solved, numerous results show that certain parameter settings produce optimal performance for a wide range of problems and difficulties. In particular, a low (about half of the inverse of the population size) mutation rate is crucial for optimal results, but the choice of crossover method and rate do not seem to affect performance appreciably. Optimal efficiency is usually achieved with smaller (< 50) populations. Lastly, tournament selection appears to be the best choice of selection methods due to its simplicity and its autoscaling properties. However, if a proportional selection method is used such as roulette wheel selection, fitness scaling is a necessity, and a high …

A novel anion-exchange resin containing three amine groups was prepared by reaction of a chloromethylated polystyrene-divinylbenzene (PS-DVB) resin with diethylenetriamine. After being protonated by contact with an aqueous acid, this resin can be used for ion chromatographic separation of anions. The charge on the resins can be varied from +1 to +3 by changing the mobile phase pH. The selectivity of the new ion exchangers for various inorganic anions was quite different from that of conventional anion exchangers. The performance of this new anion exchanger was studied by changing the pH and the concentration of the eluent, and several different eluents were used with some common anions as testing analytes. Conductivity detection and UV-visible detection were applied to detect the anions after separation. The new resin can also be used for HPLC separation of neutral organic compounds. Alkylphenols and alkylbenzenes were separated with this new polymeric resin, and excellent separations were obtained under simple conditions. This report contains Chapter 1: General introduction and Chapter 6: General conclusions.

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Magnetic flux compression generators rely on the expansion of thin ductile shells to generate magnetic fields. These thin shells are filled with high explosives, which when detonated, cause the shell to expand to over 200% strain at strain-rates on the order of 10{sup 4} s{sup {minus}1}. Experimental data indicate the development and growth of multiple plastic instabilities which appear in a quasi-periodic pattern on the surfaces of the shells. These quasi-periodic instabilities are connected by localized zones of intense shear that are oriented approximately 45{degree} from the outward radial direction. The quasi-periodic instabilities continue to develop and eventually become through-cracks, causing the shell to fragment. A viscoplastic constitutive model is formulated to model the high strain-rate expansion and provide insight into the development of plastic instabilities. The formulation of the viscoplastic constitutive model includes the effects of shock heating and damage in the form of microvoid nucleation, growth, and coalescence in the expanding shell. This model uses the Johnson-Cook strength model with the Mie-Grueneisen equation of state and a modified Gurson yield surface. The constitutive model includes the modifications proposed by Tvergaard and the plastic strain controlled nucleation introduced by Neeleman. The constitutive model is implemented as a user material …

This paper presents a review of the Direct Stator Flux Field Orientation control method. This method can be used to control an induction motor`s torque and flux directly and is the application of interest for this thesis. This control method is implemented without the traditional feedback loops and associated hardware. Predictions are made, by mathematical calculations, of the stator voltage vector. The voltage vector is determined twice a switching period. The switching period is fixed throughout the analysis. The three phase inverter duty cycle necessary to control the torque and flux of the induction machine is determined by the voltage space vector Pulse Width Modulation (PWM) technique. Transient performance of either the flux or torque requires an alternate modulation scheme which is also addressed in this thesis. A block diagram of this closed loop system is provided. 22 figs., 7 tabs.

Accurately characterizing end-to-end Internet dynamics - the performance that a user actually obtains from the lengthy series of network links that comprise a path through the Internet - is exceptionally difficult, due to the network`s immense heterogeneity. At the heart of this work is a `measurement framework` in which a number of sites around the Internet host a specialized measurement service. By coordinating `probes` between pairs of these sites one can measure end-to-end behavior along O(N{sup 2}) paths for a framework consisting of N sites. Consequently, one obtains a superlinear scaling that allows measuring a rich cross-section of Internet behavior without requiring huge numbers of observation points. 37 sites participated in this study, allowing the author to measure more than 1,000 distinct Internet paths. The first part of this work looks at the behavior of end-to-end routing: the series of routers over which a connection`s packets travel. Based on 40,000 measurements made using this framework, the author analyzes: routing `pathologies` such as loops, outages, and flutter; the stability of routes over time; and the symmetry of routing along the two directions of an end-to-end path. The author finds that pathologies increased significantly over the course of 1995 and that Internet …

This paper describes methods for solid phase extraction and high performance liquid chromatography (HPLC). The following are described: Effects of Resin Sulfonation on the Retention of Polar Organic Compounds in Solid Phase Extraction; Ion-Chromatographic Separation of Alkali Metals In Non-Aqueous Solvents; Cation-Exchange Chromatography in Non-Aqueous Solvents; and Silicalite As a Stationary Phase For HPLC.

Directional solidification of eutectic alloys shows different types of eutectic morphologies. These include lamellar, rod, oscillating and tilting modes. The growth of these morphologies occurs with a macroscopically planar interface. However, under certain conditions, the planar eutectic front becomes unstable and gives rise to a cellular or a dendritic structure. This instability leads to the cellular/dendritic structure of either a primary phase or a two-phase structure. The objective of this work is to develop a fundamental understanding of the instability of eutectic structure into cellular/dendritic structures of a single phase and of two-phases. Experimental studies have been carried out to examine the transition from a planar to two-phase cellular and dendritic structures in a ceramic system of Alumina-Zirconia (Al{sub 2}O{sub 3}-ZrO{sub 2}) and in a transparent organic system of carbon tetrabromide and hexachloroethane (CBr{sub 4}-C{sub 2}Cl{sub 6}). Several aspects of eutectic interface stability have been examined.

Working directly on affine Lie groups, we construct several new formulations of the WZW model, the gauged WZW model, and the generic affine-Virasoro action. In one formulation each of these conformal field theories (CFTs) is expressed as a one-dimensional mechanical system whose variables are coordinates on the affine Lie group. When written in terms of the affine group element, this formulation exhibits a two-dimensional WZW term. In another formulation each CFT is written as a two-dimensional field theory, with a three- dimensional WZW term, whose fields are coordinates on the affine group. On the basis of these equivalent formulations, we develop a translation dictionary in which the new formulations on the affine Lie group are understood as mode formulations of the conventional formulations on the Lie group. Using this dictionary, we also express each CFT as a three-dimensional field theory on the Lie group with a four-dimensional WZW term. 36 refs.

The potential risk of lung cancer has evoked interest in the properties of radon decay products. There are two forms of this progeny: either attached to ambient aerosols, or still in the status of ions/molecules/small clusters. This ``unattached`` activity would give a higher dose per unit of airborne activity than the ``attached`` progeny that are rather poorly deposited. In this thesis, a system for determining unattached radon decay products electrical mobility size distribution by measuring their electrical mobilities was developed, based on the fact that about 88% of {sup 218}Po atoms have unit charge at the end of their recoil after decay from {sup 222}Rn, while the remainder are neutral. Essential part of the setup is the radon-aerosol chamber with the Circular Electrical Mobility Spectrometer (CEMS) inside. CEMS is used for sampling and classifying the charged radioactive clusters produced in the chamber. An alpha- sensitive plastic, CR-39 disk, is placed in CEMS as an inlaid disk electrode and the alpha particle detector. CEMS showed good performance in fine inactive particles` classification. If it also works well for radon decay products, it can offer a convenient size distribution measurement for radioactive ultrafine particles. However, the experiments did not obtain an acceptable …

Synchrotron small angle x-ray scattering (SAXS) has been applied to the structural study of several biological systems, including the nitrogenase complex, the heat shock cognate protein (hsc70), and lysozyme folding. The structural information revealed from the SAXS experiments is complementary to information obtained by other physical and biochemical methods, and adds to our knowledge and understanding of these systems.

The interaction of aerosol particles with wall surfaces is important in modeling their behavior. This interaction is usually represented in theoretical models as a loss term. The loss rate is the rate at which particles deposit or react with the surfaces. This loss term is important in many branches of aerosol science including human health and indoor air quality. Increased surface deposition usually means lower concentrations of airborne particles and hence, lower exposure to the inhabitants. If the efficiency of the particle deposition is influenced by factors other than the particle size, such as a natural convection of the air, this has to be taken into account to evaluate the results. In this research, test aerosol sized from 15 nm to 3 {micro}m are produced by several different aerosol generators; the gas burner, the Collison nebulizer, the condensation aerosol generator, the orifice atomizer and the Vibrating Orifice Aerosol Generator (VOAG). A rectangular chamber whose dimensions are 75 x 75 x 180 cm{sup 3} was used in this study. The particles were injected into the chamber, with a known ventilation and the concentration decay was monitored by the Ultrafine Condensation Particle Counter (UCPC) and Optical Particle Counter (OPC). During the measurement, …

All models of lasing action require knowledge of the physical parameters involved, of which many can be measured or estimated. The value of the terminal level lifetime is an important parameter in modeling many high power laser systems since the terminal level lifetime can have a substantial impact on the extraction efficiency of the system. However, the values of the terminal level lifetimes for a number of important laser materials such as ND:YAG and ND:YLF are not well known. The terminal level lifetime, a measure of the time it takes for the population to drain out of the terminal (lower) lasing level, has values that can range from picoseconds to microseconds depending on the host medium, thus making it difficult to construct one definitive experiment for all materials. Until recently, many of the direct measurements of the terminal level lifetime employed complex energy extraction or gain recovery methods coupled with a numerical model which often resulted in large uncertainties in the measured lifetimes. In this report we demonstrate a novel and more accurate approach which employs a pump-probe technique to measure the terminal level lifetime of 16 neodymium-doped materials. An alternative yet indirect method, which is based on the ``Energy …

An experimental inductoslag apparatus to recycle irradiated vanadium was fabricated and tested. An experimental electroslag apparatus was also used to test possible slags. The testing was carried out with slag materials that were fabricated along with impurity bearing vanadium samples. Results obtained include computer simulated thermochemical calculations and experimentally determined removal efficiencies of the transmutation impurities. Analyses of the samples before and after testing were carried out to determine if the slag did indeed remove the transmutation impurities from the irradiated vanadium.

Hydrogenated amorphous silicon and related materials have been applied to radiation detectors, utilizing their good radiation resistance and the feasibility of making deposits over a large area at low cost. Effects of deposition parameters on various material properties of a-Si:H have been studied to produce a material satisfying the requirements for specific detection application. Thick(-{approximately}50 {mu}m), device quality a-Si:H p-i-n diodes for direct detection of minimum ionizing particles have been prepared with low internal stress by a combination of low temperature growth, He-dilution of silane, and post annealing. The structure of the new film contained voids and tiny crystalline inclusions and was different from the one observed in conventional a-Si:H. Deposition on patterned substrates was attempted as an alternative to controlling deposition parameters to minimize substrate bending and delamination of thick a-Si:H films. Growth on an inversed-pyramid pattern reduced the substrate bending by a factor of 3{approximately}4 for the same thickness film. Thin (0.1 {approximately} 0.2 {mu}m) films of a-Si:H and a-SiC:H have been applied to microstrip gas chambers to control gain instabilities due to charges on the substrate. Light sensitivity of the a-Si:H sheet resistance was minimized and the surface resistivity was successfully` controlled in the range of 10{sup …

The dynamics of inelastic and reactive collisions in atomic beam-surface scattering are presented. The inelastic scattering of hyperthermal rare gaseous atoms from three alkali halide surfaces (LiF, NaCl, GI)was studied to understand mechanical energy transfer in unreactive systems. The dynamics of the chemical reaction in the scattering of H(D) atoms from the surfaces of LIF(001) and the basal plane of graphite were also studied.

Second harmonic generation (SHG) and infrared-visible sum frequency generation (SFG) spectroscopies have been shown to be powerful and versatile for studying surfaces with submonolayer sensitivity. They have been used in this work to study bare diamond surfaces and molecular adsorption on them. In particular, infrared-visible SFG as a surface vibrational spectroscopic technique has been employed to identify and monitor in-situ surface bonds and species on the diamond (111) surface. The CH stretch spectra allow us to investigate hydrogen adsorption, desorption, abstraction, and the nature of the hydrogen termination. The C(111) surface dosed with atomic hydrogen was found to be in a monohydride configuration with the hydrogen atoms situated at top-sites. The ratio of the abstraction rate to the adsorption rate was appreciable during atomic hydrogen dosing. Kinetic parameters for thermal desorption of H on C(111) were determined showing a near first-order kinetics. For the fully H-terminated (111) surface, a large (110 cm{sup {minus}1}) anharmonicity and {approximately}19 psec lifetime were measured for the first-excited CH stretch mode. The bare reconstructed C(111)-(2 {times} l) surface showed the presence of CC stretch modes which were consistent with the Pandey {pi}-bonded chain structure. When exposed to the methyl radical, the SFG spectra of the …

This dissertation describes several three-body dissociations and the photodissociation of methyl radicals studied using photofragment translational spectroscopy. The first chapter provides an introduction to three body dissociation, examines current experimental methodology, and includes a discussion on the treatment of photofragment translational spectroscopy data arising from three-body fragmentation. The ultraviolet photodissociation of azomethane into two methyl radicals and nitrogen is discussed in chapter 2. Chapter 3 describes the photodissociation of acetone at 248 nm and 193 nm. At 248 nm the translational energy release from the initial C-C bond cleavage matches the exit barrier height and a comparison with results at 266 nm suggests that <E{sub T}> is invariant to the available energy. A fraction of the nascent CH{sub 3}CO radicals spontaneously dissociate following rotational averaging. The <E{sub T}> for the second C-C bond cleavage also matches the exit barrier height. At 193 nm the experimental data can be successfully fit assuming that the dynamics are analogous to those at 248 nm. A simplified model of energy partitioning which adequately describes the experimental results is discussed. Experiments on acetyl halides provide additional evidence to support the proposed acetone dissociation mechanism. A value of 17.0{+-}1.0 kcal/mole for the barrier height, CH{sub 3}CO …

Quantum Monte Carlo (QMC) methods have been found to give excellent results when applied to chemical systems. The main goal of the present work is to use QMC to perform electronic structure calculations. In QMC, a Monte Carlo simulation is used to solve the Schroedinger equation, taking advantage of its analogy to a classical diffusion process with branching. In the present work the author focuses on how to extend the usefulness of QMC to more meaningful molecular systems. This study is aimed at questions concerning polyatomic and large atomic number systems. The accuracy of the solution obtained is determined by the accuracy of the trial wave function`s nodal structure. Efforts in the group have given great emphasis to finding optimized wave functions for the QMC calculations. Little work had been done by systematically looking at a family of systems to see how the best wave functions evolve with system size. In this work the author presents a study of trial wave functions for C, CH, C{sub 2}H and C{sub 2}H{sub 2}. The goal is to study how to build wave functions for larger systems by accumulating knowledge from the wave functions of its fragments as well as gaining some knowledge …

Conventional solid state reactions are diffusion limited processes that require high temperatures and long reaction times to reach completion. In this work, several solution based methods were utilized to circumvent this diffusion limited reaction and achieve product formation at lower temperatures. The solution methods studied all have the common goal of trapping the homogeneity inherent in a solution and transferring this homogeneity to the solid state, thereby creating a solid atomic mixture of reactants. These atomic mixtures can yield solid state products through {open_quotes}diffusionless{close_quotes} mechanisms. The effectiveness of atomic mixtures in solid state synthesis was tested on three classes of materials, varying in complexity. A procedure was invented for obtaining the highly water soluble salt, titanyl nitrate, TiO(NO{sub 3}){sub 2}, in crystalline form, which allowed the production of titanate materials by freeze drying. The freeze drying procedures yielded phase pure, nanocrystalline BaTiO{sub 3} and the complete SYNROC-B phase assemblage after ten minute heat treatments at 600{degrees}C and 1100{degrees}C, respectively. Two novel methods were developed for the solution based synthesis of Ba{sub 2}YCu{sub 3}O{sub 7-x} and Bi{sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10}. Thin and thick films of Ba{sub 2}YCu{sub 3}O{sub 7-x} and Bi{sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10} were synthesized by …

Problems with MoSi{sub 2} include low-temperature fracture toughness, high-temperature creep resistance, and ``pest`` phenomena. Oxygen introduced by powder processing may be the cause of some of these problems. This study led to the following conclusions: Supplied powders have significant oxygen present prior to processing (up to 2.5 %), in the form of silica on the surface. This oxygen contamination did not increase by exposure to air at room temperature. An improved powder processing method was developed that uses glass encapsulation. Analysis of microstructures created from powders that contained 4900 to 24,100 ppM oxygen showed that the silica was transferred to the fully dense MoSi{sub 2} as SiO{sub 2} inclusions. A method of producing MoSi{sub 2} with less oxygen was attempted.

For the last decade, the Trahanovsky research group has focused on the study of various reactive molecules such as o-quinodimethanes (o-QDM`s) and p-quinodimethanes (p-QDM`s) derived from benzene, furan, and thiophene. These types of molecules are reactive and dimerize or polymerize at room temperature. One of the group`s interests is to understand the dimerization mechanism of these molecules. Paper 1 describes the preparation and dimerization product analyses of 2-ethylidene-5-methylene-2,5-dihydrothiophene. Insights provided by these results into the mechanism of the dimerization of 2,5-dimethylene-2,5-dihydrothiophene are discussed. In paper 2, a convenient synthesis of cyclooctadecane is presented.

This report discusses the following topics on support minimized inversion of acoustic and elastic wave scattering: Minimum support inversion; forward modelling of elastodynamic wave scattering; minimum support linearized acoustic inversion; support minimized nonlinear acoustic inversion without absolute phase; and support minimized nonlinear elastic inversion.

In this work, a measurement of the strong coupling constant {alpha}{sub s} in e{sup +}e{sup {minus}} annihilation at a center-of-mass energy of 91.6 GeV is presented. The measurement was performed with the SLD at the Stanford Linear Collider facility located at the Stanford Linear Accelerator Center in California. The procedure used consisted of measuring the rate of hard gluon radiation from the primary quarks in a sample of 9,878 hadronic events. After defining the asymptotic manifestation of partons as `jets`, various phenomenological models were used to correct for the hadronization process. A value for the QCD scale parameter {Lambda}{sub bar MS}, defined in the {sub bar MS} renormalization convention with 5 active quark flavors, was then obtained by a direct fit to O({alpha}{sub s}{sup 2}) calculations. The value of {alpha}{sub s} obtained was {alpha}{sub s}(M{sub z0}) = 0.122 {plus_minus} 0.004 {sub {minus}0.007} {sup +0.008} where the uncertainties are experimental (combined statistical and systematic) and theoretical (systematic) respectively. Equivalently, {Lambda}{sub bar MS} = 0.28 {sub {minus}0.10}{sup +0.16} GeV where the experimental and theoretical uncertainties have been combined.