Search Results

Dalbergia and Albizia: Plantlet Production via Tissue Culture, Karyological Evaluation, and Seed Anatomy with Scanning Electron Microscopy

Description: A publication by the National Academy of Sciences, USA (1979) outlined some of the research need for a great variety of economically important woody species whose remaining genetic resources need urgently to be collected and conserved. A viable regeneration system was established via tissue and cell suspension culture for Albizia falcataria and A. lebbeck, two important wood yielding leguminous tree species. The culture medium was standardized after several trials to obtain callus from the leaflet explants of these two tree species. The optimum use of casein hydrolysate (w/v) and coconut milk (v/v) in addition to 6-Benzylaminopurine and Indole-3-butyric acid could induce morphogenesis and somatic embryogenesis in the cultured tissue. This reports the first observation on somatic embryogenesis ofA. lebbeck using leaflets as the explants. Scanning Electron Microscopy and histological studies were done on the different stages plant development following standard techniques. Embryogenesis in suspension culture followed regeneration of plantlets in A. lebbeck. In A.falcaaria the regenerative process followed via organogenesis from the shoot buds developed on the leaf explants. After hardening the regenerated plants were transferred to the greenhouse. Some of the trees grew more than 25 feet tall within a few months outside the greenhouse. Karyotype of the three leguminous trees Albizia lebbeck, A. falcataria, and Dalbergia sissoo was analyzed. In D. sissoo, various chromosomal anomalies were observed in the cultured tissue. The abnormality indices and ploidy level varied with the age and the frequency of the subculture. In the aged culture the regenerative potential declined but was reinstated to some extent with the addition of two complex growth factors, coconut milk and casein hydrolysate. Seed anatomy of 26 species of 4 leguminous genera was studied with SEM. The main distinguishing anatomical features observed in the seed sections were uniseriate or multiseriate epidermis, epidermal projections, and number of rows …
Date: December 1998
Creator: Ghosh, Nabarun
Partner: UNT Libraries

Biogeographic Relationships of Pocket Gophers (Geomys breviceps and Geomys bursarius) in the Southeastern Portion of Their Ranges

Description: This research utilized population genetic analyses (protein starch-gel electrophoresis and DNA sequencing of the cytochrome b mtDNA gene), host-parasite specificity (lice coevolution), remote sensing of satellite data, and geographic information systems (GIS) to characterize newly discovered populations of pocket gophers (genus: Geomys) in Arkansas. These populations are isolated and occur in seemingly unsuitable habitat in the Ozark Mountains of Arkansas. Analyses of electrophoretic and ectoparasite data suggested the populations in the Ozark Mountains represented isolates allied to Geomys bursarius, a species not known to occur in Arkansas. Comparison of mitochondrial DNA sequence data of the cytochrome b gene with that of other taxa and morphometric analyses confirmed that these populations are most closely allied to G. bursarius occurring to the north in Missouri. Moreover, these mtDNA sequence analyses indicated a degree of differentiation typical of that between other subspecies of pocket gophers. Therefore, these populations represent a distinct genetic entity in an intermediate stage of speciation and should be designated as a new subspecies, Geomys bursarius ozarkensis. Molecular clock analysis revealed a time of lineage divergence for this new subspecies as approximately 511,000 YBP. Due to the isolated nature and limited distribution of this subspecies, an evaluation of critical habitat needs was initiated. Remote sensing and GIS technologies were used to identify and describe suitable habitat Computerized classification of satellite imagery of suitable vegetation, integrated with ancillary digital information on soil associations, roads, and water systems, revealed that human activity had played a positive role in the establishment and dispersal of pocket gophers in this area. This research represents an initial combination of classical systematic tools with remote sensing and GIS to investigate biogeographic patterns and evolution. This project establishes a framework for using an interdisciplinary approach to studying organisms with limited distributions, determining evolutionary status, and providing recommendations for …
Date: August 1998
Creator: Elrod, Douglas Allen
Partner: UNT Libraries

Role of α-Keto Acids In Cyanide Detoxification and Assimilation by Pseudomonas Bacteria

Description: Cyanide was rapidly removed when added to culture supernatants of seven different Pseudomonas. The ability to remove cyanide was correlated with the accumulation of α-keto acids (pyruvate and α-ketoglutarate). These compounds react with cyanide forming less toxic cyanohydrins, thus conferring a mechanism for bacterial cyanide tolerance. When added to growth media the α-keto acids were shown also to serve as effective cyanide antagonists. While all bacteria tested accumulated α-keto acids, only those capable of utilizing cyanide as a nutritional nitrogen source were able to metabolize cyanohydrins. In P. fluorescens NCIMB 11764, the same enzyme (cyanide oxygenase) shown previously to be involved in cyanide metabolism appears responsible for cyanohydrin transformation. Keto acid excretion is believed to represent a new mechanism of bacterial cyanide detoxification with further enzymatic metabolism of the cyanohydrins helping to explain how cyanide can satisfy the nitrogen requirement in cyanide-utilizing bacteria.
Date: December 1998
Creator: Pan, Guangliang
Partner: UNT Libraries

Estimated Extent and Fate of Chlorinated Solvent Contamination in the Soil of the Naval Air Station, Dallas, Texas

Description: This thesis estimates the spatial extent of chlorinated solvent contamination of the soil at the Naval Air Station, Dallas, then estimates the fate and transport of these contaminants, over time, using the Soil Transport and Fate database and the Vadose-Zone Interactive Processes (VIP) modeling software. Geostatistical analysis identifies two areas with serious chlorinated solvent contamination. Fate and transport modeling estimates that this contamination will degrade and disperse from the soil phase to below regulatory limits within one year, although there is a risk of groundwater contamination. Contaminants are estimated to persist in the water and air phases of the soil. Further sampling is recommended to confirm the results of this study.
Date: August 1998
Creator: Trescott, Jill V. (Jill Virginia)
Partner: UNT Libraries

Regulation of an S6/H4 Kinase in Crude Lymphosarcoma P1798 Preparations

Description: Purified S6/H4 kinase (Mr 60,000) requires autophosphorylation for activation. A rabbit anti-S6/H4 kinase peptide (SVIDPVPAPVGDSHVDGAAK) antibody recognized both the S6/H4 kinase holoenzyme and catalytic domain. Immunoreactivity with p60 kinase protein, and S6/H4 kinase activity were precisely correlated in fractions obtained from ion exchange chromatography of P1798 lymphosarcoma extracts. An enzyme which catalyzed the MgATP-dependent phosphorylation and activation of S6/H4 kinase coeluted with immunoreactivity from Mono 5, but not Mono Q chromatography. Since S6/H4 kinase is homologous with rac-activated PAK65, the observation that phosphorylation is also required for activation suggests a complex mechanism for in vivo activation of the S6/H4 kinase.
Date: December 1998
Creator: Taylor, Allison Antoinette
Partner: UNT Libraries

Analyses of Particulate Contaminants in Semiconductor Processing Fluids

Description: Particle contamination control is a critical issue for the semiconductor industry. In the near future, this industry will be concerned with the chemical identities of contaminant particles as small as 0.01 pm in size. Therefore, analytical techniques with both high chemical sensitivity and spatial resolution are required. Transmission electron microscopy (TEM) provides excellent spatial resolution and yields structural and compositional information. It is rarely used, however, due to the difficulty of sample preparation. The goals of this research are to promote the use of TEM as an ultrafine particle analysis tool by developing new sample preparation methods, and to exploit the new TEM techniques for analysis of particles in semiconductor processing fluids. A TEM methodology for the analysis of particulate contaminants in fluids with an elemental detectability limit as low as 0.1 part per trillion (ppt), and a particle concentration detectability limit as low as 1 particle/ml for particles greater than 0.2 pm was developed and successfully applied to the analysis of particles in HF, H202, de-ionized (DI) water, and on the surface of an electronic device. HF samples from three manufacturers were examined. For HF (B), the maximum particle concentration was 8.3 x 103 particles/ml. Both a viscous material and lath-shaped particles were observed. The Sb concentration was less than 0.6 part per billion (ppb). HF (C) was the cleanest. CaF2 and TiO2 particles were identified in HF (D). For H2 02, iron and tin oxides and hydroxides were identified. The maximum particle concentration was 990 particles/ml. The Sn and Fe concentrations were less than 0.3 ppb. Spherical and dendritic particles were observed. For DI water, spherical and dendritic particles (<2 particles/ml), and particles containing Fe or Si with concentrations less than 0.1 ppt were observed. Contaminants on an electronic device surface were also analyzed. Clusters of small particles …
Date: August 1998
Creator: Xu, Daxue
Partner: UNT Libraries

Development of an In Vitro Protoplast Culture System for Albizia Lebek (L.) Benth., an Economically Important Leguminous Tree

Description: An in vitro system of generating protoplasts from their callus cultures was established. The friable callus was more productive in terms of producing protoplasts than the green compact callus. The concentration of the various cell wall degrading enzymes had an effect on the viability of the protoplasts in the medium. The protoplast system developed from the experiments was stable and could be used for the transformation experiments of Albizia lebek and for other plant improvement practices.
Date: August 1998
Creator: Sinha, Debleena
Partner: UNT Libraries

The Tent and its Contents: a Study of the Traditional Arts of Weaving by the Otaibah Tribe in Saudi Arabia

Description: This was an ethnographic study of the woven tent objects produced by the Bedouin Otaibah tribe in Najd, central Saudi Arabia; the study examines origin, techniques, character and significance of their weavings. A major objective of the researcher was to discern the relationship between the weavers' development of traditions and the factors of technique, medium and perceived meaning. The method used was investigative fieldwork that included techniques of face to face interviews and participant observation. Interviews with 50 Bedouin female weavers in Najd were conducted for 8 months. Background information on the Otaibah tribe and their traditional way of life was provided. The review of the literature of traditional arts, folk arts and art education illustrates that there is limited accessible information concerning the general history of traditional arts in Saudi Arabia. A discussion of the aesthetic value, definitions and roles of traditional art, tribal art and the differences between art and crafts was included. Analysis of data answered the study's questions through a presentation of the findings of the fieldwork. The Otaibah tribe has its own unique style of weaving. Information gathered from participant observation and documents from the Haifa Faisal Collection of Saudi Arabian Traditional Arts in Chicago supplements information obtained by interview. The findings indicate that as a result of modernization and settlement, traditional Bedouin weavings are gradually being replaced. Weavers find themselves forced to compete with a deluge of imported machine-made goods, a development changing structure of the culture from nomadic to semi--modernized creating a new foundation of social and economic life for the society. The.results of the study provide a curriculum base for art education in Saudi Arabia. Suggestions for further studies, recommendations and the implications for art education are included.
Date: December 1998
Creator: Alruwais, Bader A.
Partner: UNT Libraries

Inner-shell photoionized x-ray lasers

Description: The inner-shell photoionized x-ray lasing scheme is an attractive method for achieving x-ray lasing at short wavelengths, via population inversion following inner-shell photoionization (ISPI). This scheme promises both a short wavelength and a short pulse source of coherent x rays with high average power. In this dissertation a very complete study of the ISPI x-ray laser scheme is done concerning target structure, filter design and lasant medium. An investigation of the rapid rise time of x-ray emission from targets heated by an ultra-short pulse high-intensity optical laser was conducted for use as the x-ray source for ISPI x-ray lasing. Lasing by this approach in C at a wavelength of 45 {angstrom} requires a short pulse (about 50 fsec) driving optical laser with an energy of 1-5 J and traveling wave optics with an accuracy of {approximately} 15 {micro}m. The optical laser is incident on a high-Z target creating a high-density plasma which emits a broadband spectrum of x rays. This x-ray source is passed through a filter to eliminate the low-energy x rays. The remaining high-energy x rays preferentially photoionize inner-shell electrons resulting in a population inversion. Inner-shell photoionized x-ray lasing relies on the large energy of a K-{alpha} transition in the initially neutral lasant. The photo energy required to pump this scheme is only slightly greater than the photon energy of the lasing transition yielding a lasing scheme with high quantum efficiency. However, the overall efficiency is reduced due to low x-ray conversion efficiency and the large probability of Auger decay yielding an overall efficiency of {approximately} 10{sup {minus}7} resulting in an output energy of {micro}J's. They calculate that a driving laser with a pulse duration of 40 fs, a 10{micro}m x 1 cm line focus, and an energy of 1 J gives an effective gain length product (gl) …
Date: June 1, 1998
Creator: Moon, S. J.
Partner: UNT Libraries Government Documents Department

Laser-plasma interactions relevant to Inertial Confinement Fusion

Description: Research into laser-driven inertial confinement fusion is now entering a critical juncture with the construction of the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL). Many of the remaining unanswered questions concerning NIF involve interactions between lasers and plasmas. With the eventual goal of fusion power in mind, laser-plasma interactions relevant to laser fusion schemes is an important topic in need of further research. This work experimentally addresses some potential shortcuts and pitfalls on the road to laser-driven fusion power. Current plans on NIF have 192 laser beams directed into a small cylindrical cavity which will contain the fusion fuel; to accomplish this the beams must cross in the entrance holes, and this intersection will be in the presence of outward-flowing plasma. To investigate the physics involved, interactions of crossing laser beams in flowing plasmas are investigated with experiments on the Nova laser facility at LLNL. It was found that in a flowing plasma, energy is transferred between two crossing laser beams, and this may have deleterious consequences for energy balance and ignition in NIF. Possible solutions to this problem are presented. A recently-proposed alternative to standard laser-driven fusion, the ''fast ignitor'' concept, is also experimentally addressed in this dissertation. Many of the laser-plasma interactions necessary for the success of the fast ignitor have not previously been explored at the relevant laser intensities. Specifically, the transfer of high-intensity laser energy to electrons at solid-target interfaces is addressed. 20-30% conversion efficiencies into forward-propagated electrons were measured, along with an average electron energy that varied with the type of target material. The directionality of the electrons was also measured, revealing an apparent beaming of the highest energy electrons. This work was extended to various intensities and pulse lengths and a relationship between conversion efficiency and laser intensity was deduced. This …
Date: November 2, 1998
Creator: Wharton, K.B.
Partner: UNT Libraries Government Documents Department

From Theory to Practice: A First Look at Success for Life - A Brain Research-Based Early Childhood Program

Description: Success For Life (SFL) is a brain research-based program for children, birth through age six. This research examined the development and implementation of SFL in 13 early childhood settings. Participants were 24 female early childhood teachers and 146 (73 male) children. Teachers included seven infant, four toddler, nine preschool and four kindergarten teachers. Children included infants(n=29), toddlers(n=27), and prek/kindergartners (n=90). A Request for Proposals was disseminated to identify possible implementation sites. After participation was confirmed, teachers attended a full day's training which included a description of brain development/function, the latest brain research, how to implement SFL and other logistics of the study. Program implementation occurred over approximately four months. A field site coordinator visited each site bimonthly to provide on-going technical assistance. This was an intervention project with a pre and post implementation design. Four instruments were used: a teacher questionnaire, a classroom environment measure, a child measure and teacher journals. Results suggested that teachers became more knowledgeable about brain development research and about how children grow and learn. Teachers were better able to make connections between brain research findings and how to apply these findings to their programs and daily activities. Likewise, the environment measure indicated that teachers were better able to arrange environments for learning. They reported that children showed significant increases in skills development and performance in the following areas: physical mastery, social relations/interactions, cognitive development, and language/communications. Additionally, teachers reported improvements in emotional expression and well-being among infants and toddlers. Toddlers and preschoolers showed significant increases in creative/ artistic expression. Finally, teachers indicated that preschoolers showed increases in initiative, use of logic/mathematics skills, and musical coordination and movement. Research findings suggest that Success For Life is able to bridge the gap between theory and practice and benefits children, teachers and programs.
Date: December 1998
Creator: Castro, R. Raquel
Partner: UNT Libraries

The influence of surface topography on the forming friction of automotive aluminum sheet

Description: Interest in utilizing aluminum alloys in automobiles has increased in recent years as a result of the desire to lower automobile weight and, consequently, increase fuel economy. While aluminum alloy use in cast parts has increased, outer body panel applications are still being investigated. The industry is interested in improving the formability of these sheet alloys by a combination of alloy design and processing. A different avenue of improving the formability of these alloys may be through patterning of the sheet surface. Surface patterns hold the lubricant during the forming process, with a resulting decrease in the sheet-die surface contact. While it has been speculated that an optimum surface pattern would consist of discrete cavities, detailed investigation into the reduction of forming friction by utilizing discrete patterns is lacking. A series of discrete patterns were investigated to determine the dependence of the forming friction of automotive aluminum alloys on pattern lubricant carrying capacity and on material strength. Automotive aluminum alloys used in outer body panel applications were rolled on experimental rolls that had been prepared with a variety of discrete patterns. All patterns for each alloy were characterized before and after testing both optically and, to determine pattern lubricant capacity, using three dimensional laser profilometry. A draw bead simulation (DBS) friction tester was designed and fabricated to determine the forming friction of the patterned sheets. Tensile testing and frictionless DBS testing were performed to ascertain the material properties of each sheet. The most striking result of this work was the inversely linear dependence of forming friction on the lubricant carrying capacity of the discrete patterns.
Date: May 1, 1998
Creator: Kramer, P. A.
Partner: UNT Libraries Government Documents Department

Seismic imaging of the shallow subsurface with high frequency seismic measurements

Description: Elastic wave propagation in highly heterogeneous media is investigated and theoretical calculations and field measurements are presented. In the first part the dynamic composite elastic medium (DYCEM) theory is derived for one-dimensional stratified media. A self-consistent method using the scattering functions of the individual layers is formulated, which allows the calculation of phase velocity, attenuation and waveform. In the second part the DYCEM theory has been generalized for three-dimensional inclusions. The specific case of spherical inclusions is calculated with the exact scattering functions and compared with several low frequency approximations. In the third part log and VSP data of partially water saturated tuffs in the Yucca Mountain region of Nevada are analyzed. The anomalous slow seismic velocities can be explained by combining self-consistent theories for pores and cracks. The fourth part analyzes an air injection experiment in a shallow fractured limestone, which has shown large effects on the amplitude, but small effects on the travel time of the transmitted seismic waves. The large amplitude decrease during the experiment is mainly due to the impedance contrast between the small velocities of gas-water mixtures inside the fracture and the formation. The slow velocities inside the fracture allow an estimation of aperture and gas concentration profiles.
Date: July 1, 1998
Creator: Kaelin, B.
Partner: UNT Libraries Government Documents Department

Numerical Simulation of Fiber and Wire Array Z-pinches With Trac-II

Description: Trac-II is a two dimensional axisymmetric resistive MHD code. It simulates all three spatial components (r, z, &phi;) of the magnetic field and fluid velocity vectors, and the plasma is treated as a single fluid with two temperatures (T<sub>e</sub>,T<sub>i</sub>). In addition, it can optionally include a self-consistent external circuit. Recent modifications to the code include the addition of the 3-T radiation model, a 4-phase (solid-liquid-vapor-plasma) equation of state model (QEOS), a 4-phase electrical/thermal conductivity model, and an implicit solution of poloidal B<sub>z</sub>,B<sub>r</sub>) magnetic field diffusion. These changes permit a detailed study of fiber and wire array Z-pinches. Specifically, Trac-II is used to study the wire array Z-pinch at the PBFA-Z pulse power generator at Sandia National Laboratory. First, in 1-D we examine the behavior of a single wire in the Z-pinch. Then, using these results as initial radial conditions in 2-D, we investigate the dynamics of wire array configurations in the r-z and r-&theta; plane. In the r-z plane we examine the growth of the m=0 or ��sausage�� instability in single wires within the array. In the r-&theta; plane we examine the merging behavior between neighboring wires. Special emphasis is placed on trying to explain how instability growth affects the performance of the Z-pinch. Lastly, we introduce Trac-III, a 3-D MHD code, and illustrate the m=1 or �"kink" instability. We also discuss how Trac-III can be modified to simulate the wire array Z-pinch.
Date: September 1, 1998
Creator: Reisman, David B.
Partner: UNT Libraries Government Documents Department

Zintl cluster chemistry in the alkali-metal-gallium systems

Description: 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 a small amount of silver to form (x {approximately} 2--6). The structure is composed of three different clusters which are interconnected to form a three-dimensional structure. The RbGa{sub 3{minus}x}Au{sub x} system is also nonstoichiometric with a three-dimensional structure composed of Ga{sub 8} dodecahedra and four-bonded gallium atoms. Unlike Na{sub 30.5}Ga{sub 60{minus}x}Ag{sub x}, the RbGa{sub 3} binary is also stable. The binary is formally a Zintl phase but the ternary is not. Some chemistry in the alkali-metal-indium system also has been explored. A new potassium-indium binary is discussed but the structure has not been completely characterized.
Date: March 27, 1998
Creator: Henning, R.
Partner: UNT Libraries Government Documents Department

Compact Intracloud Discharges

Description: No Description Available.
Date: November 1, 1998
Creator: Smith, David A.
Partner: UNT Libraries Government Documents Department

Applications of electrochemically-modulated liquid chromatography (EMLC): Separations of aromatic amino acids and polycyclic aromatic hydrocarbons

Description: 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.
Date: March 27, 1998
Creator: Deng, L.
Partner: UNT Libraries Government Documents Department

Mechanical and tribological properties of ion beam-processed surfaces

Description: The intent of this work was to broaden the applications of well-established surface modification techniques and to elucidate the various wear mechanisms that occur in sliding contact of ion-beam processed surfaces. The investigation included characterization and evaluation of coatings and modified surfaces synthesized by three surface engineering methods; namely, beam-line ion implantation, plasma-source ion implantation, and DC magnetron sputtering. Correlation among measured properties such as surface hardness, fracture toughness, and wear behavior was also examined. This dissertation focused on the following areas of research: (1) investigating the mechanical and tribological properties of mixed implantation of carbon and nitrogen into single crystal silicon by beam-line implantation; (2) characterizing the mechanical and tribological properties of diamond-like carbon (DLC) coatings processed by plasma source ion implantation; and (3) developing and evaluating metastable boron-carbon-nitrogen (BCN) compound coatings for mechanical and tribological properties. The surface hardness of a mixed carbon-nitrogen implant sample improved significantly compared to the unimplanted sample. However, the enhancement in the wear factor of this sample was found to be less significant than carbon-implanted samples. The presence of nitrogen might be responsible for the degraded wear behavior since nitrogen-implantation alone resulted in no improvement in the wear factor. DLC coatings have low friction, low wear factor, and high hardness. The fracture toughness of DLC coatings has been estimated for the first time. The wear mechanism in DLC coatings investigated with a ruby slider under a contact stress of 1 GPa was determined to be plastic deformation. The preliminary data on metastable BCN compound coatings indicated high friction, low wear factor, and high hardness.
Date: January 1, 1998
Creator: Kodali, P.
Partner: UNT Libraries Government Documents Department

Spectroscopic measurement of the MHD dynamo in the MST reversed field pinch

Description: The author has directly observed the coupling of ion velocity fluctuations and magnetic field fluctuations to produce an MHD dynamo electric field in the interior of the MST reversed field pinch. Chord averaged ion velocity fluctuations were measured with a fast spectroscopic diagnostic which collects line radiation from intrinsic carbon impurities simultaneously along two lines of sight. The chords employed for the measurements resolved long wavelength velocity fluctuations of several km/s at 8--20 kHz as tiny, fast Doppler shifts in the emitted line profile. During discrete dynamo events the velocity fluctuations, like the magnetic fluctuations, increase dramatically. The toroidal and poloidal chords with impact parameters of 0.3 a and 0.6 a respectively, resolved fluctuation wavenumbers with resonance surfaces near or along the lines of sight indicating a radial velocity fluctuation width for each mode which spans only a fraction of the plasma radius. The phase between the measured toroidal velocity fluctuations and the magnetic fluctuations matches the predictions of resistive MHD while the poloidal velocity fluctuations exhibit a phase consistent with the superposition of MHD effects and the advection of a mean flow gradient past the poloidal line of sight. Radial velocity fluctuations resolved by a chord through the center of the plasma were small compared to the poloidal and toroidal fluctuations and exhibited low coherence with the magnetic fluctuations. The ensembled nonlinear product of the ion velocity fluctuations and fluctuations in the magnetic field indicates a substantial dynamo electric field which peaks during the periods of spontaneous flux generation.
Date: September 1, 1998
Creator: Chapman, J.T.
Partner: UNT Libraries Government Documents Department

A Compton camera for spectroscopic imaging from 100 keV to 1 MeV

Description: A review of spectroscopic imaging issues, applications, and technology is presented. Compton cameras based on solid state semiconductor detectors stands out as the best system for the nondestructive assay of special nuclear materials. A camera for this application has been designed based on an efficient specific purpose Monte Carlo code developed for this project. Preliminary experiments have been performed which demonstrate the validity of the Compton camera concept and the accuracy of the code. Based on these results, a portable prototype system is in development. Proposed future work is addressed.
Date: December 31, 1998
Creator: Earnhart, J. R. D.
Partner: UNT Libraries Government Documents Department

The applicability of certain Monte Carlo methods to the analysis of interacting polymers

Description: The authors consider polymers, modeled as self-avoiding walks with interactions on a hexagonal lattice, and examine the applicability of certain Monte Carlo methods for estimating their mean properties at equilibrium. Specifically, the authors use the pivoting algorithm of Madras and Sokal and Metroplis rejection to locate the phase transition, which is known to occur at {beta}{sub crit} {approx} 0.99, and to recalculate the known value of the critical exponent {nu} {approx} 0.58 of the system for {beta} = {beta}{sub crit}. Although the pivoting-Metropolis algorithm works well for short walks (N < 300), for larger N the Metropolis criterion combined with the self-avoidance constraint lead to an unacceptably small acceptance fraction. In addition, the algorithm becomes effectively non-ergodic, getting trapped in valleys whose centers are local energy minima in phase space, leading to convergence towards different values of {nu}. The authors use a variety of tools, e.g. entropy estimation and histograms, to improve the results for large N, but they are only of limited effectiveness. Their estimate of {beta}{sub crit} using smaller values of N is 1.01 {+-} 0.01, and the estimate for {nu} at this value of {beta} is 0.59 {+-} 0.005. They conclude that even a seemingly simple system and a Monte Carlo algorithm which satisfies, in principle, ergodicity and detailed balance conditions, can in practice fail to sample phase space accurately and thus not allow accurate estimations of thermal averages. This should serve as a warning to people who use Monte Carlo methods in complicated polymer folding calculations. The structure of the phase space combined with the algorithm itself can lead to surprising behavior, and simply increasing the number of samples in the calculation does not necessarily lead to more accurate results.
Date: May 1, 1998
Creator: Krapp, D.M. Jr.
Partner: UNT Libraries Government Documents Department

A proper time dependent measurement of Delta M {sub D} using jet charge and soft lepton flavor tagging

Description: This thesis presents a proper time dependent measurement of the B{sup 0}{sub d} mixing frequency {Delta}M{sub d} using jet charge and soft lepton flavor tagging in p - {anti p} collisions at {radical}s = 1.8 TeV. The measurement uses the inclusive e and {mu} trigger data of the CDF detector from an integrated luminosity of 91 pb{sub -1}. The proper time at decay is measured from a partial reconstruction of the B associated with the trigger lepton. The measurement of {Delta}M{sub d} yields {Delta}M{sub d} = 0.50 {+-} 0.05 {+-} 0.05 {bar h} ps{sup -1} where the first error is statistical and the second systematic. The flavor tagging methods used give a measured effective efficiency {epsilon}D{sup 2} of o Jet Charge: {epsilon}D{sup 2} (0.78 + 0.12 + 0.09) % o Soft Lepton: {epsilon}D{sup 2} (1.07 + 0.09 + 0.10) % where the first error is statistical and the second systematic.
Date: August 1, 1998
Partner: UNT Libraries Government Documents Department

Advanced far infrared blocked impurity band detectors based on germanium liquid phase epitaxy

Description: This research has shown that epilayers with residual impurity concentrations of 5 x 10{sup 13} cm{sup {minus}3} can be grown by producing the purest Pb available in the world. These epilayers have extremely low minority acceptor concentrations, which is ideal for fabrication of IR absorbing layers. The Pb LPE growth of Ge also has the advantageous property of gettering Cu from the epilayer and the substrate. Epilayers have been grown with intentional Sb doping for IR absorption on lightly doped substrates. This research has proven that properly working Ge BIB detectors can be fabricated from the liquid phase as long as pure enough solvents are available. The detectors have responded at proper wavelengths when reversed biased even though the response did not quite reach minimum wavenumbers. Optimization of the Sb doping concentration should further decrease the photoionization energy of these detectors. Ge BIB detectors have been fabricated that respond to 60 cm{sup {minus}1} with low responsivity. Through reduction of the minority residual impurities, detector performance has reached responsivities of 1 A/W. These detectors have exhibited quantum efficiency and NEP values that rival conventional photoconductors and are expected to provide a much more sensitive tool for new scientific discoveries in a number of fields, including solid state studies, astronomy, and cosmology.
Date: May 1, 1998
Creator: Olsen, C.S.
Partner: UNT Libraries Government Documents Department

Gas Phase Chromatography of some Group 4, 5, and 6 Halides

Description: Gas phase chromatography using The Heavy Element Volatility Instrument (HEVI) and the On Line Gas Apparatus (OLGA III) was used to determine volatilities of ZrBr{sub 4}, HfBr{sub 4}, RfBr{sub 4}, NbBr{sub 5}, TaOBr{sub 3}, HaCl{sub 5}, WBr{sub 6}, FrBr, and BiBr{sub 3}. Short-lived isotopes of Zr, Hf, Rf, Nb, Ta, Ha, W, and Bi were produced via compound nucleus reactions at the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory and transported to the experimental apparatus using a He gas transport system. The isotopes were halogenated, separated from the other reaction products, and their volatilities determined by isothermal gas phase chromatography. Adsorption Enthalpy ({Delta}H{sub a}) values for these compounds were calculated using a Monte Carlo simulation program modeling the gas phase chromatography column. All bromides showed lower volatility than molecules of similar molecular structures formed as chlorides, but followed similar trends by central element. Tantalum was observed to form the oxybromide, analogous to the formation of the oxychloride under the same conditions. For the group 4 elements, the following order in volatility and {Delta}H{sub a} was observed: RfBr{sub 4} &gt; ZrBr{sub 4} &gt; HfBr{sub 4}. The {Delta}H{sub a} values determined for the group 4, 5, and 6 halides are in general agreement with other experimental data and theoretical predictions. Preliminary experiments were performed on Me-bromides. A new measurement of the half-life of {sup 261}Rf was performed. {sup 261}Rf was produced via the {sup 248}Cm({sup 18}O, 5n) reaction and observed with a half-life of 74{sub -6}{sup +7} seconds, in excellent agreement with the previous measurement of 78{sub -6}{sup +11} seconds. We recommend a new half-life of 75{+-}7 seconds for {sup 261}Rf based on these two measurements. Preliminary studies in transforming HEVI from an isothermal (constant temperature) gas phase chromatography instrument to a thermochromatographic (variable temperature) instrument have been completed. Thermochromatography is a …
Date: October 1, 1998
Creator: Sylwester, Eric Robert
Partner: UNT Libraries Government Documents Department