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Differential utilization of allochthonous and autochthonous carbon by aquatic insects of two shrub-steppe desert spring-streams: A stable carbon isotope analysis and critique of the method

Description: The purpose of this study is to assess whether the carbon supporting stream food webs comes principally from terrestrial sources or is produced within the stream. Lacking data to resolve the allochthonous/autochthonous issue with any finality, stream ecologists have alternately postulated that stream carbon was principally autochthonous or principally allochthonous. Others argued that autochthonous and allochthonous carbon resources cannot be separated and that the allochthonous/autochthonous dependence issue is unresolvable. Many investigators have seized upon stable carbon isotopes technology as the tool to resolve the controversy. Unfortunately most investigators have conceded that the results are rarely quantitative and that the qualitative relationships are ambiguous. This study points out the fallacies of trying to conjure single isotopic values for either allochthonous or autochthonous carbon. It suggests that stable carbon isotope technology is not reliable in establishing specific consumer/food source relations and that it is not suitable for assessing allochthonous/autochthonous carbon dependence in freshwater streams.
Date: June 1, 1993
Creator: Mize, A. L.
Partner: UNT Libraries Government Documents Department

Development and application of a high speed digital data acquisition technique to study steam bubble collapse using particle image velocimetry

Description: The use of a Particle Image Velocimetry (PIV) method, which uses digital cameras for data acquisition, for studying high speed fluid flows is usually limited by the digital camera`s frame acquisition rate. The velocity of the fluid under study has to be limited to insure that the tracer seeds suspended in the fluid remain in the camera`s focal plane for at least two consecutive images. However, the use of digital cameras for data acquisition is desirable to simplify and expedite the data analysis process. A technique was developed which will measure fluid velocities with PIV techniques using two successive digital images and two different framing rates simultaneously. The first part of the method will measure changes which occur to the flow field at the relatively slow framing rate of 53.8 ms. The second part will measure changes to the same flow field at the relatively fast framing rate of 100 to 320 {mu}s. The effectiveness of this technique was tested by studying the collapse of steam bubbles in a subcooled tank of water, a relatively high speed phenomena. The tracer particles were recorded and velocity vectors for the fluid were obtained far from the steam bubble collapse.
Date: August 1, 1992
Creator: Schmidl, W. D.
Partner: UNT Libraries Government Documents Department

Interpretation of seismic reflection data from the Piledriver Event Area, Nevada Test Site; A case study for evaluation of technique for characterization of void and chimney features

Description: A remote sensing geophysical method is needed to properly characterize the void and chimney characteristics of underground nuclear tests. Various techniques were considered and a seismic reflection survey was selected. This survey was then fitted to the conditions at the test site so as to give optimum results. The data was then reduced via DOS computer and analyzed for content. The planned survey using a 50 ft offset did not show any useful information, however, a second survey with a variable longer offset was also conducted which was capable of determining the depth to the top and the bottom of the chimney with reasonable accuracy. Measurements of the horizontal spread of the structure, though, were inconclusive.
Date: December 31, 1993
Creator: Tonander, K. E.
Partner: UNT Libraries Government Documents Department

Bacterially induced precipitation of CaCO{sub 3}: An example from studies of cyanobacterial mats. Final report

Description: Bacteria induce the precipitation of calcium carbonate in the laboratory and in nature by altering their chemical environment. Geologists are recognizing the possibility that bacterially induced precipitates may form significant mineral deposits, unfortunately, there are currently no sound criteria by which they can be recognized in recent sediments, or in the rock record. Cultures of aerobic and facultative bacteria from cyanobacterial mats on Andros Island, Bahamas, and Baffin Bay, Texas, induced the precipitation of calcium carbonate under controlled conditions. Crusts, the largest features formed, are composed of 5--200{mu}m diameter bundles which are, in turn, composed of numerous individual crystals. The smallest observed features are 0.1--0.4{mu}m spheres and rods which comprise some individual crystals and crystal bundles. Crystal bundles resembling rhombohedra, tetragonal disphenoids, tetragonal dipyramids, and calcite dumbbells appear to be uniquely bacterial in origin, and they have all been observed in recent sediments. Swollen rods, discs, curved dumbbells, and 50--200{mu}m optically continuous crystals resembling brushes may be uniquely bacterial in origin, however, they have not been reported by other laboratories nor observed in natural settings. Presence of any of these forms in recent sediments should be taken as strong evidence for bacterial influence. Spheres and aragonite dumbbells have also been observed in natural environments, however, they are not always bacterial in origin. Precipitation of calcium carbonate occurs preferentially on dead cyanobacteria in the presence of bacteria. Lithification of algal mats to form stromatolites may take place in the zone of decaying organic matter due to bacterial activity.
Date: April 30, 1990
Creator: Chafetz, H. S.
Partner: UNT Libraries Government Documents Department

Seismic wave propagation in thinly-layered media with steep reflectors

Description: Seismic waves reflected from steep reflectors in the earth`s subsurface spend a significant amount of time travelling more or less horizontally. Therefore, accurate imaging of steep geologic structure requires knowledge of the behavior of these horizontally propagating waves. In particular, the effect of tunneling on seismic waves propagating in thinly-layered media must be understood. I describe a method for modeling seismic waves traveling in thinly-layered media. This method, a frequency-wavenumber finite-difference scheme coupled with the Born approximation, is useful in studying seismic waves reflected from steep geologic structures.
Date: May 1, 1992
Creator: Deng, H. L.
Partner: UNT Libraries Government Documents Department

Molecular genetic and molecular evolutionary studies on the bacteriochlorophyll synthesis genes of Rhodobacter capsulatus

Description: Rhodobacter capsulatus, purple bacterium capable of either aerobic or photosynthetic growth, has proven to be very useful in genetic studies of photosynthesis. Forty-four genes clustered together within a 46 kilobase region are required to establish photosynthetic ability in R. capsulatus. Approximately twenty of these genes are involved in bacteriochlorophyll synthesis of which eight ``bch`` genes are the subject of this thesis. Six of these genes were found to code for the two ring reductases. The first converts protochlorophyllide (PChlide) into a chlorin, the immediate precursor to chlorophyll a, and then into a bacteriochlorin. Each reductase is shown to be made up of three subunits. PChlide reductase is coded by the genes bchN, bchB, and bchL. Proteins with amino acid sequences markedly similar to those of bchN and bchL have been shown in other organisms to be required for chlorophyll synthesis; hence, their designation as chlN and chlB. A third chloroplast-encoded gene of heretofore unknown function shares amino acid identities with bchB and is probably the third subunit of the plant PChlide reductase. The bchA locus, which encodes the chlorin reductase, is found to be made up of three separate, translationally coupled genes, referred to as bchX, bchY, and bchZ. Amino acid similarities between bchX, bchL, and the nitrogenase reductase protein nifH suggest that all three classes of proteins share certain three-dimensional structural features, including elements that are central to the enzymatic mechanism of nifH. PChlide reductase and chlorin reductase are clearly derived from a common ancestor. Several lines of analysis suggests the ancestor of both enzyme systems reduced PChlide twice to produce bacteriochlorophyll supporting the concept bacteriochlorophyll as the ancestral reaction center pigment.
Date: August 1, 1992
Creator: Burke-Agueero, D. H.
Partner: UNT Libraries Government Documents Department

An analytic determination of beta poloidal and internal inductance in an elongated tokamak from magnetic probe measurements

Description: Analytic calculations of the magnetic fields available to magnetic diagnostics are performed for tokamaks with circular and elliptical cross sections. The explicit dependence of the magnetic fields on the poloidal beta and internal inductances is sought. For tokamaks with circular cross sections, Shafranov`s results are reproduced and extended. To first order in the inverse aspect ratio expansion of the magnetic fields, only a specific combination of beta poloidal and internal inductance is found to be measurable. To second order in the expansion, the measurements of beta poloidal and the internal inductance are demonstrated to be separable but excessively sensitive to experimental error. For tokamaks with elliptical cross sections, magnetic measurements are found to determine beta poloidal and the internal inductance separately. A second harmonic component of the zeroth order field in combination with the dc harmonic of the zeroth order field specifies the internal inductance. The internal inductance in hand, measurement of the first order, first harmonic component of the magnetic field then determined beta poloidal. The degeneracy implicit in Shafranov`s result (i.e. that only a combination of beta poloidal and internal inductance is measurable for a circular plasma cross section) reasserts itself as the elliptic results are collapsed to their circular limits.
Date: February 1, 1992
Creator: Sorci, J. M.
Partner: UNT Libraries Government Documents Department

Oxygen electrode reaction in molten carbonate fuel cells. Final report, September 15, 1987--September 14, 1990

Description: Molten carbonate fuel cell system is a leading candidate for the utility power generation because of its high efficiency for fuel to AC power conversion, capability for an internal reforming, and a very low environmental impact. However, the performance of the molten carbonate fuel cell is limited by the oxygen reduction reaction and the cell life time is limited by the stability of the cathode material. An elucidation of oxygen reduction reaction in molten alkali carbonate is essential because overpotential losses in the molten carbonate fuel cell are considerably greater at the oxygen cathode than at the fuel anode. Oxygen reduction on a fully-immersed gold electrode in a lithium carbonate melt was investigated by electrochemical impedance spectroscopy and cyclic voltammetry to determine electrode kinetic and mass transfer parameters. The dependences of electrode kinetic and mass transfer parameters on gas composition and temperature were examined to determine the reaction orders and the activation energies. The results showed that oxygen reduction in a pure lithium carbonate melt occurs via the peroxide mechanism. A mass transfer parameter, D{sub O}{sup 1/2}C{sub O}, estimated by the cyclic voltammetry concurred with that calculated by the EIS technique. The temperature dependence of the exchange current density and the product D{sub O}{sup 1/2}C{sub O} were examined and the apparent activation energies were determined to be about 122 and 175 kJ/ mol, respectively.
Date: July 7, 1992
Creator: Appleby, A. J. & White, R. E.
Partner: UNT Libraries Government Documents Department

A two-photon fluorescence autocorrelator for a Nd:YLF modelocked laser

Description: In this thesis, I discuss the design and implementation of an autocorrelator for an actively modelocked ND:YLF laser at wavelength 1.054{mu}m. A dye is used to generate a broadband two-photon fluorescence (TPF) signal at 570nm which is the autocorrelation of the laser pulses. Two different techniques are discussed. A colliding pulse scheme can be used to generate a TPF autocorrelation signal as a function of distance, or an interferometer technique can be used to generate an autocorrelation signal as a function of the delay in an interferometer arm. Experimental results are discussed, but they are inconclusive because of difficulties in interpreting the signal.
Date: May 1, 1991
Creator: Kner, P. A.
Partner: UNT Libraries Government Documents Department

A study of the interfacial chemistry of pyrite and coal in fine coal cleaning using flotation

Description: Surface oxidation, surface charge, and flotation properties have been systematically studied for coal, coal-pyrite and ore-pyrite. Electrochemical studies show that coal-pyrite exhibits much higher and more complex surface oxidation than ore-pyrite and its oxidation rate depends strongly on the carbon/coal content. Flotation studies indicate that pyrites have no self-induced floatability. Fuel oil significantly improves the floatability of coal and induces considerable flotation for coal-pyrite due to the hydrophobic interaction of fuel oil with the carbon/coal inclusions on the pyrite surface. Xanthate is a good collector for ore-pyrite but a poor collector for coal and coal-pyrite. The results from thermodynamic calculations, flotation and zeta potential measurements show that iron ions greatly affect the flotation of pyrite with xanthate and fuel oil. Various organic and inorganic chemicals have been examined for depressing coal-pyrite. It was found, for the first time, that sodium pyrophosphate is an effective depressant for coal-pyrite. Solution chemistry shows that pyrophosphate reacts with iron ions to form stable iron pyrophosphate complexes. Using pyrophosphate, the complete separation of pyrite from coal can be realized over a wide pH range at relatively low dosage.
Date: December 31, 1993
Creator: Jiang, C.
Partner: UNT Libraries Government Documents Department

Synthesis of higher alcohols from carbon monoxide and hydrogen in a slurry reactor

Description: Higher, i.e. C{sub 2{sup +}}, alcohols are desired as gasoline additives, feedstocks for producing ethers and as alternative fuels for automobiles. In all cases, the backbone branching of an alcohol improves octane rating, which is essential for good engine performance. These types of branched, higher alcohols are the desired products for a process converting synthesis gas, a CO and H{sub 2} mixture, often generated from coal gasification. Based on this premise, promoted ZnCr oxide catalysts appear to be as one of the best avenues for further investigation. Once this investigation is complete, a natural extension is to replace the Cr in the ZnCr oxide catalyst with Mo and W, both in the same elemental triad with Cr. Mo has already been shown as an active HAS catalyst, both on a SiO{sub 2} support and in the MoS{sub 2} form. The three catalyst combinations, ZnMo, ZnW, and MnCr oxides will be tested in the stirred autoclave system. However, if none of the three indicate any comparable activity and/or selectivity toward higher alcohols as compared with other HAS catalysts, then an investigation of the effects of Cs promotion on the ZnCr oxide methanol catalysts will be executed.
Date: August 28, 1992
Creator: McCutchen, M. S.
Partner: UNT Libraries Government Documents Department

Coherent production of pions and rho mesons in neutrino charged current interactions on neon nuclei at the Fermilab Tevatron

Description: The coherent production of single pions and and {rho} mesons in charged current interactions of neutrinos and antineutrinos on neon nuclei has been studied. The data were obtained using the Fermilab 15-foot Bubble Chamber, filled with a heavy Ne-H{sub 2} mixture and exposed to the Quadrupole Triplet neutrino beam produced by 800 GeV protons from the Tevatron. The average beam energy was 86 GeV. In a sample of 330000 frames, 1032 two-prong {nu}{sub {mu}} + {bar {nu}}{sub {mu}} charged current interactions were selected. The goal of this study was to investigate the low Q{sup 2} high {nu} region where the hadron dominance model can be tested. In this model, the vector and axial-vector parts of the weak hadronic current are dominated by the {rho} and a{sub 1} mesons respectively. Moreover, the Partially Conserved Axial Current (PCAC) hypothesis can be tested by studying the coherent production of single pions.
Date: May 1, 1992
Creator: Willocq, S.
Partner: UNT Libraries Government Documents Department

Investigation of the relative abundance of heavy versus light nuclei in primary cosmic rays using underground muon bundles

Description: We study multiple muon events (muon bundles) recorded underground at a depth of 2090 mwe. To penetrate to this depth, the muons must have energies above 0.8 TeV at the Earth`s surface; the primary cosmic ray nuclei which give rise to the observed muon bundles have energies at incidence upon the upper atmosphere of 10 to 10{sup 5}TeV. The events are detected using the Soudan 2 experiment`s fine grained tracking calorimeter which is surrounded by a 14 m {times}10 m {times} 31 m proportional tube array (the ``active shield``). Muon bundles which have at least one muon traversing the calorimeter, are reconstructed using tracks in the calorimeter together with hit patterns in the proportional tube shield. All ionization pulses are required to be coincident within 3 microseconds. A goal of this study is to investigate the relative nuclear abundances in the primary cosmic radiation around the ``knee`` region (10{sup 3} {minus} 10{sup 4} TeV) of the incident energy spectrum. Four models for the nuclear composition of cosmic rays are considered: The Linsley model, the Constant Mass Composition model (CMC), the Maryland model and the Proton-poor model. A Monte Carlo which incorporates one model at a time is used to simulate events which are then reconstructed using the same computer algorithms that are used for the data. Identical cuts and selections are applied to the data and to the simulated events.
Date: June 8, 1993
Creator: Sundaralingam, N.
Partner: UNT Libraries Government Documents Department

A kinetic study of methanol synthesis in a slurry reactor using a CuO/ZnO/Al{sub 2}O{sub 3} catalyst

Description: A kinetic model that describes the methanol production rate over a CuO/ZnO/AI{sub 2}0{sub 3} catalyst (United Catalyst L-951) at typical industrial operating conditions is developed using a slurry reactor. Different experiments are conducted in which the H{sub 2}/(CO+CO{sub 2}) ratio is equal to 2, 1, and 0.5, respectively, while the CO/CO{sub 2} ratio is held constant at 9. At each H{sub 2}/(CO+CO{sub 2}) ratio the space velocity is set at four different values in the range of 3000-13,000 1/hr kg{sub cat}. The effect of H{sub 2}/(CO+CO{sub 2}) ratio and space velocity on methanol production rate, conversions, and product composition is further investigated. The results indicate that the highest methanol production rate can be achieved at H{sub 2}/(CO+CO{sub 2}) ratio of 1 followed by H{sub 2}/(CO+CO{sub 2}) ratio of 0.5 and 2 respectively. The hydrogen and carbon monoxide conversions decrease with increasing space velocity for all H{sub 2}/(CO+CO{sub 2}) ratios tested. Carbon monoxide hydrogenation appears to be the main route to methanol at H{sub 2}/(CO+CO{sub 2}) ratio of 0.5 and 2. On the other hand, carbon dioxide hydrogenation appears to be the main route to methanol at H{sub 2}/(CO+CO{sub 2}) ratio of 1. At all H{sub 2}/(CO+CO{sub 2}) ratios, the extent of the reverse water gas shift reaction decreases with increasing space velocity. The effect of temperature on the kinetics is examined by using the same experimental approach at 508 K. It is found that a different reaction sequence takes place at each temperature. Also, a time on stream study is conducted simultaneously in order to investigate the characteristic of catalyst deactivation with time on stream. During the first 150 hours of time on stream, the catalyst loses approximately 2/3 of its initial activity before reaching a steady state activity.
Date: May 1, 1992
Creator: Al-Adwani, H. A.
Partner: UNT Libraries Government Documents Department

Rare event simulation in radiation transport

Description: This dissertation studies methods for estimating extremely small probabilities by Monte Carlo simulation. Problems in radiation transport typically involve estimating very rare events or the expected value of a random variable which is with overwhelming probability equal to zero. These problems often have high dimensional state spaces and irregular geometries so that analytic solutions are not possible. Monte Carlo simulation must be used to estimate the radiation dosage being transported to a particular location. If the area is well shielded the probability of any one particular particle getting through is very small. Because of the large number of particles involved, even a tiny fraction penetrating the shield may represent an unacceptable level of radiation. It therefore becomes critical to be able to accurately estimate this extremely small probability. Importance sampling is a well known technique for improving the efficiency of rare event calculations. Here, a new set of probabilities is used in the simulation runs. The results are multiple by the likelihood ratio between the true and simulated probabilities so as to keep the estimator unbiased. The variance of the resulting estimator is very sensitive to which new set of transition probabilities are chosen. It is shown that a zero variance estimator does exist, but that its computation requires exact knowledge of the solution. A simple random walk with an associated killing model for the scatter of neutrons is introduced. Large deviation results for optimal importance sampling in random walks are extended to the case where killing is present. An adaptive ``learning`` algorithm for implementing importance sampling is given for more general Markov chain models of neutron scatter. For finite state spaces this algorithm is shown to give with probability one, a sequence of estimates converging exponentially fast to the true solution.
Date: October 1, 1993
Creator: Kollman, C.
Partner: UNT Libraries Government Documents Department

The dynamics of azulene in liquids and compressed gases on ultrafast timescales

Description: The ultrafast dynamics of vibrationally hot ground state azulene molecules have been time resolved by picosecond transient absorption spectroscopy in a variety of solvents including hexane, chloromethanes, methanol, CClF{sub 3}, Xe and Kr. A high pressure optical cell was used to liquify gases for use as solvents and change their density and temperature, independently, over the entire liquid density range. Experimental results indicate the vibrational cooling rate is strongly solvent dependent, with cooling rates of approximately 20 psec in molecular solvents and approximately 150 psec in atomic solvents. Comparison of the rates in Xe and Kr at constant density demonstrates the strong effect of solvent mass on energy transfer. The effect of solvent temperature on vibrational cooling is minimal, as is the effect of solvent density. This latter result is quite surprising in light of earlier experiments on simpler molecular systems, such as I{sub 2} in Xe. This anomalous density effect is examined in light of Isolated Binary Collision (IBC) theory and bulk thermal transport models. Both theories accurately model all experimental results obtained with the exception of the density effort. Possible explanations for the breakdown of the IBC theory in this case are offered along with methods to improve IBC theory for application to complex three dimensional molecular systems.
Date: February 1, 1992
Creator: Schultz, K. E.
Partner: UNT Libraries Government Documents Department

Diffusion of adatoms on face-centered cubic transition metal surfaces

Description: Mechanisms and associated energetics for adatom diffusion on the (100) and (110) surfaces of Ni, Cu, Rh, Pd, and Ag are investigated. Self-diffusion was studied on (100) and (I 10) surfaces of Ni, Cu, Pd and Ag using corrected effective medium method (CEM) and approximation to CEM used for molecular dynamics and Monte Carlo studies (MD/MC-CEM). Self-diffusion on Pd(100), Ag(100), Ni(110), Cu(110), Pd(110), and Ag(110) is accomplished by classical diffusion: the adatom hops from its equilibrium adsorption site over an intervening bridge site to an adjacent equilibrium site. Self-diffusion on Ni(100) and Cu(100) proceeds by atomic-exchange diffusion: the adatom on the surface displaces an atom in the first surface layer. Aside from explicit inclusion of the kinetic-exchange-correlation energy, it is critical to include enough movable atoms in the calculation to insure correct energetics. Distortions induced by these diffusion mechanisms, especially atomic exchange, are long ranged in surface plane, owing to small distortions of many atoms being energetically favored over large distortions of few atoms. Energetics and rates of heterogeneous adatom diffusion on the (100) surfaces of Ni, Cu, Rh, Pd, and Ag show that the final state energies differ due to variation of metallic bonding with coordination for different types of metal atoms. The surface energies of the 2 metals can be used to correlate the amount of energy gained or released when the adatom displaces a surface atom. This difference in energetic stability of final configurations determines whether bridge hopping diffusion or atomic displacement is the dominant kinetic process in these heterogeneous systems.
Date: May 10, 1994
Creator: Perkins, L.
Partner: UNT Libraries Government Documents Department

The analysis and minimization of oxygen contamination in the powder processing of molybdenum disilicide

Description: 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.
Date: April 24, 1994
Creator: Shannon, K.
Partner: UNT Libraries Government Documents Department

Micromorphology, mineralogy, and genesis of soils and fracture fills and the Pajarito Plateau, New Mexico

Description: The town of Los Alamos, and the Los Alamos National Laboratory (LANL), are located on the Pajarito Plateau in north-central New Mexico. Environmental concerns have recently focused attention on the numerous fractures in the Bandelier Tuff, the series of volcanic rock units that make up most of the plateau. These fractures have come into question as possible conduits for transport of contaminants downward through the tuff. This, study arose out of a need to evaluate the potential for contaminant transport in the fractures. Because the fractures are typically filled, or partially filled, with soil-like material, and appear to be physically continuous with the soils on the surface of the Pajarito Plateau, it was decided to approach the question of the fractures from a soil genesis and morphology standpoint. Specifically, it was believed that soil characterization techniques, including soil micromorphological and mineralogical analyses, could provide information about the dominant processes (past and present) acting in the soils and fractures. The specific objectives of this research were to investigate: (1) the physical, mineralogical and chemical nature of fracture-filling materials in the Bandelier Tuff, as well as associated surface soils; (2) the relationships among fracture-fills, tuff bedrock, and surface soils of the Pajarito Plateau; (3) the processes responsible for the development of the fracture-fills; and (4) the likely sequence of events leading to the present morphology of the soils and fracture-fills.
Date: December 1, 1993
Creator: Davenport, D. W.
Partner: UNT Libraries Government Documents Department

The development of an Omegratron plasma ion mass spectrometer for Alcator C-Mod

Description: A new diagnostic device, the Omegatron Probe, has been developed to investigate relative impurity levels and impurity charge state distribution in the Alcator C-Mod Tokamak edge plasma. The Omegatron probe consists of two principal components, a ``front-end`` of independently biased grids, arranged in a gridded energy analyzer fashion and a large collection cavity. Particles enter the probe in a thin ``ribbon`` through a knife-edge slit. The grids provide a means to measure and control the parallel energy distribution of the ions. In the collection cavity, an oscillating electric field is applied perpendicularly to the ambient magnetic field. Ions whose cyclotron frequencies are resonant with this electric field oscillation will gain perpendicular energy and be collected. In this way, the probe can be operated in two modes: first, by fixing the potentials on the grids and sweeping frequencies to obtain a `` Z/m spectrum`` of ion species and second, by fixing the frequency and sweeping the grid potentials to obtain the distribution function of an individual impurity species. The Omegatron probe performed successfully in tests on a Hollow Cathode Discharge (HCD) linear plasma column. It obtained measurements of T{sub e} {approx} 5 eV, T{sub i} (H{sup +}) {approx} 2.0 {plus_minus} 0.2 eV, n{sub 0} {approx} 9 {times} 10{sup 15} m{sup {minus}3}, RMS potential fluctuation levels of {approximately} 0.5 {plus_minus} 0.05 {plus_minus} T{sub e}, and obtained ``Z/m`` spectra for the plasma ions (H{sup +}, H{sub 2}{sup +}, He{sup +}). Additional experiments confirmed the theoretical scalings of the f/{delta}f resolution with the applied electric field and magnetic field strengths. The instrument yielded an absolute level of resolution, f/{delta}f, of approximately 2.5 to 3 times the theoretical values. Finally, the results from the HCD are used to project operation on Alcator C-Mod.
Date: May 1, 1993
Creator: Thomas, E. E. Jr.
Partner: UNT Libraries Government Documents Department

Support minimized inversion of acoustic and elastic wave scattering

Description: 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.
Date: April 24, 1994
Creator: Safaeinili, A.
Partner: UNT Libraries Government Documents Department

Study of the effect of humidity, particle hygroscopicity and size on the mass loading capacity of HEPA filters

Description: The effect of humidity, particle hygroscopicity and size on the mass loading capacity of glass fiber HEPA filters has been studied. At humidifies above the deliquescent point, the pressure drop across the HEPA filter increased non-linearly with the areal loading density (mass collected/filtration area) of NaCl aerosol, thus significantly reducing the mass loading capacity of the filter compared to dry hygroscopic or non-hygroscopic particle mass loadings. The specific cake resistance, K{sub 2}, has been computed for different test conditions and used as a measure of the mass loading capacity. K. was found to decrease with increasing humidity for the non-hygroscopic aluminum oxide particles and the hygroscopic NaCl particles (at humidities below the deliquescent point). It is postulated that an increase in humidity leads to the formation of a more open particulate cake which lowers the pressure drop for a given mass loading. A formula for predicting K{sub 2} for lognormally distributed aerosols (parameters obtained from impactor data) is derived. The resistance factor, R, calculated using this formula was compared to the theoretical R calculated using the Rudnick-Happel expression. For the non-hygroscopic aluminum oxide the agreement was good but for the hygroscopic sodium chloride, due to large variation in the cake porosity estimates, the agreement was poor.
Date: September 1, 1992
Creator: Gupta, A.
Partner: UNT Libraries Government Documents Department

Radioactive waste storage issues

Description: In the United States we generate greater than 500 million tons of toxic waste per year which pose a threat to human health and the environment. Some of the most toxic of these wastes are those that are radioactively contaminated. This thesis explores the need for permanent disposal facilities to isolate radioactive waste materials that are being stored temporarily, and therefore potentially unsafely, at generating facilities. Because of current controversies involving the interstate transfer of toxic waste, more states are restricting the flow of wastes into - their borders with the resultant outcome of requiring the management (storage and disposal) of wastes generated solely within a state`s boundary to remain there. The purpose of this project is to study nuclear waste storage issues and public perceptions of this important matter. Temporary storage at generating facilities is a cause for safety concerns and underscores, the need for the opening of permanent disposal sites. Political controversies and public concern are forcing states to look within their own borders to find solutions to this difficult problem. Permanent disposal or retrievable storage for radioactive waste may become a necessity in the near future in Colorado. Suitable areas that could support - a nuclear storage/disposal site need to be explored to make certain the health, safety and environment of our citizens now, and that of future generations, will be protected.
Date: August 15, 1994
Creator: Kunz, D. E.
Partner: UNT Libraries Government Documents Department

A dip-dependent divergence correction

Description: A divergence correction is conventionally applied to zero-offset data in an effort to preserved amplitude information. The conventional divergence correction compensates for the geometrical spreading of a point source in a horizontally layered medium where velocity varies with depth only. The dip-dependent divergence correction extends the conventional correction for improved amplitude processing of dipping beds. The dip-dependent divergence correction is computed by dynamic ray tracing, and applied to stacked data using a dip decomposition technique. This correction decreases amplitudes relative to the conventional correction for steep dips and late times. In a data example from the Gulf of Mexico, the conventional correction over- amplified the reflection off a salt dome flank by a factor of 1.6. High amplitudes near salt flanks are also associated with the presence of hydrocarbons. Applying the dip-dependent divergence correction ensures that ``bright spots`` are not due to over-amplification of steep dips by the conventional correction. In areas like the Gulf of Mexico, where the velocity function varies primarily with depth, and steep beds are commonplace, the dip-dependent divergence correction is an inexpensive way to improve the amplitude information in seismic images.
Date: July 1, 1992
Creator: Fazzari, F.
Partner: UNT Libraries Government Documents Department