UNT Libraries Government Documents Department - 291 Matching Results

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open access

Synthesis, characterization, phase diagrams and superconducting and normal state magnetic properties of La{sub 2{minus}x}Sr{sub x}CuO{sub 4} (0 {le} x {le} 0.08) and electrochemically oxidized La{sub 2{minus}x}Sr{sub x}CuO{sub 4+{delta}} (0 {le} x {le} 0.33, 0 {le} {delta} {le} 0.12)

Description: La{sub 2{minus}x}Sr{sub x}CuO{sub 4} (0 {le} x {le} 0.15) can all be intercalated with oxygen by a novel electrochemical oxidation method. Bulk superconductivity is found with an onset {Tc} {approx} 40 K for the whole range 0.01 {le} x {le} 0.15; for x = 0.25 and 0.33, the electrochemical oxidation did not improve the superconducting properties. The magnetic susceptibility {chi}(T = 50--320 K) data for La{sub 2}CuO{sub 4.11} and La{sub 1.92}Sr{sub 0.08}CuO{sub 4.07} are nearly identical with th… more
Date: August 1, 1993
Creator: Chou, F.
open access

Synthesis and characterization of novel lanthanide- and actinide-containing titanates and zircono-titanates; relevance to nuclear waste disposal

Description: Before experiments using actinide elements are performed, synthetic routes are tested using lanthanides of comparable ionic radii as surrogates. Compound and solid solution formation in several lanthanide-containing titanate and zircono-titanate systems have been established using X-ray diffraction (XRD) analysis, which helped to define interesting and novel experiments, some of which have been performed and are discussed, for selected actinide elements. The aqueous solubilities of several lant… more
Date: August 1, 1995
Creator: Shoup, S.L.S.
open access

Development of new VOC exposure metrics and their relationship to ``Sick Building Syndrome`` symptoms

Description: Volatile organic compounds (VOCs) are suspected to contribute significantly to ``Sick Building Syndrome`` (SBS), a complex of subchronic symptoms that occurs during and in general decreases away from occupancy of the building in question. A new approach takes into account individual VOC potencies, as well as the highly correlated nature of the complex VOC mixtures found indoors. The new VOC metrics are statistically significant predictors of symptom outcomes from the California Healthy Building… more
Date: August 1, 1995
Creator: Ten Brinke, J.
open access

Excited state carrier dynamics in CdS{sub x}Se{sub 1-x} semisconductor alloys as studied by ultrafast fluorescence spectroscopy

Description: This dissertation discusses studies of the electron-hole pair dynamics of CdS{sub x}Se{sub 1-x} semiconductor alloys for the entire compositional range from x = 1 to x = 0 as examined by the ultrafast fluorescence techniques of time correlated single photon counting and fluorescence upconversion. Specifically, samples with x = 1, .75, .5, .25, and 0 were studied each at a spread of wavelengths about its respective emission maximum which varies according to {lambda} = 718nm - 210x nm. The decays… more
Date: August 1, 1995
Creator: Gadd, S. E.
open access

A technique using a stellar spectrographic plate to measure terrestrial ozone column depth

Description: This thesis examines the feasibility of a technique to extract ozone column depths from photographic stellar spectra in the 5000--7000 Angstrom spectral region. A stellar spectrographic plate is measured to yield the relative intensity distribution of a star`s radiation after transmission through the earth`s atmosphere. The amount of stellar radiation absorbed by the ozone Chappuis band is proportional to the ozone column depth. The measured column depth is within 10% the mean monthly value for… more
Date: August 1, 1995
Creator: Wong, A.Y.
open access

Mesozoic and Cenozoic structural geology of the CP Hills, Nevada Test Site, Nye County, Nevada; and regional implications

Description: Detailed mapping and structural analysis of upper Proterozoic and Paleozoic rocks in the CP Hills of the Nevada Test Site, together with analysis of published maps and cross sections and a reconnaissance of regional structural relations indicate that the CP thrust of Barnes and Poole (1968) actually comprises two separate, oppositely verging Mesozoic thrust systems: (1) the west-vergent CP thrust which is well exposed in the CP Hills and at Mine Mountain, and (2) the east-vergent Belted Range t… more
Date: August 1, 1991
Creator: Caskey, S.J.
open access

The use of synthetic colloids in tracer transport experiments in saturated rock fractures

Description: Studies of groundwater flow and contaminant transport in saturated, fractured geologic media are of great interest to researchers studying the potential long-term storage of hazardous wastes in or near such media. A popular technique for conducting such studies is to introduce tracers having different chemical and physical properties into a system and then observe the tracers at one or more downstream locations, inferring flow and transport mechanisms from the breakthrough characteristics of th… more
Date: August 1, 1995
Creator: Reimus, Paul William
open access

Effect of Operating Parameters and Chemical Additives on Crystal Habit and Specific Cake Resistance of Zinc Hydroxide Precipitates

Description: The effect of process parameters and chemical additives on the specific cake resistance of zinc hydroxide precipitates was investigated. The ability of a slurry to be filtered is dependent upon the particle habit of the solid and the particle habit is influenced by certain process variables. The process variables studied include neutralization temperature, agitation type, and alkalinity source used for neutralization. Several commercially available chemical additives advertised to aid in solid/… more
Date: August 1, 1999
Creator: Alwin, Jennifer Louise
open access

Using Direct Sub-Level Entity Access to Improve Nuclear Stockpile Simulation Modeling

Description: Direct sub-level entity access is a seldom-used technique in discrete-event simulation modeling that addresses the accessibility of sub-level entity information. The technique has significant advantages over more common, alternative modeling methods--especially where hierarchical entity structures are modeled. As such, direct sub-level entity access is often preferable in modeling nuclear stockpile, life-extension issues, an area to which it has not been previously applied. Current nuclear stoc… more
Date: August 1, 1999
Creator: Parker, Robert Y.
open access

Etching of UO{sub 2} in NF{sub 3} RF Plasma Glow Discharge

Description: A series of room temperature, low pressure (10.8 to 40 Pa), low power (25 to 210 W) RF plasma glow discharge experiments with UO{sub 2} were conducted to demonstrate that plasma treatment is a viable method for decontaminating UO{sub 2} from stainless steel substrates. Experiments were conducted using NF{sub 3} gas to decontaminate depleted uranium dioxide from stainless-steel substrates. Depleted UO{sub 2} samples each containing 129.4 Bq were prepared from 100 microliter solutions of uranyl n… more
Date: August 1, 1999
Creator: Veilleux, John M.
open access

Contact micromechanics in granular media with clay

Description: Many granular materials, including sedimentary rocks and soils, contain clay particles in the pores, grain contacts, or matrix. The amount and location of the clays and fluids can influence the mechanical and hydraulic properties of the granular material. This research investigated the mechanical effects of clay at grain-to-grain contacts in the presence of different fluids. Laboratory seismic wave propagation tests were conducted at ultrasonic frequencies using spherical glass beads coated wit… more
Date: August 1, 1994
Creator: Ita, S. L.
open access

Neutral particle dynamics in the Alcator C-Mod tokamak

Description: This thesis presents an experimental study of neutral particle dynamics in the Alcator C-Mod tokamak. The primary diagnostic used is a set of six neutral pressure gauges, including special-purpose gauges built for in situ tokamak operation. While a low main chamber neutral pressure coincides with high plasma confinement regimes, high divertor pressure is required for heat and particle flux dispersion in future devices such as ITER. Thus we examine conditions that optimize divertor compression, … more
Date: August 1, 1995
Creator: Niemczewski, A.P.
open access

Vitrification of cesium-contaminated organic ion exchange resin

Description: Vitrification has been declared by the Environmental Protection Agency (USEPA) as the Best Demonstrated Available Technology (BDAT) for the permanent disposal of high-level radioactive waste. Savannah River Site currently uses a sodium tetraphenylborate (NaTPB) precipitation process to remove Cs-137 from a wastewater solution created from the processing of nuclear fuel. This process has several disadvantages such as the formation of a benzene waste stream. It has been proposed to replace the pr… more
Date: August 1, 1994
Creator: Sargent, T. N., Jr.
open access

Time-frequency analysis of synthetic aperture radar signals

Description: Synthetic aperture radar (SAR) has become an important tool for remote sensing of the environment. SAR is a set of digital signal processing algorithms that are used to focus the signal returned to the radar because radar systems in themselves cannot produce the high resolution images required in remote sensing applications. To reconstruct an image, several parameters must be estimated and the quality of output image depends on the degree of accuracy of these parameters. In this thesis, we deri… more
Date: August 1, 1996
Creator: Johnston, B.
open access

Characterization of organosulfur monolayer formation at gold electrodes

Description: Among the many types of organic films, covalently-attached organosulfur monolayers have attracted a great deal of attention. The authors have focused their interest on the fundamental characterization of spontaneously adsorbed organosulfur monolayers. An introductory chapter presents general aspects of monolayer preparation and characterization, followed by a few examples that illustrate the range of applications of these films. This thesis contains two papers. In the first paper, three analogo… more
Date: August 1, 1996
Creator: Tani Woods, N.
open access

The photosynthetic acclimation of Lolium perenne in response to three years growth in a free-air CO{sub 2} enrichment (FACE) system

Description: Pure stands of Ryegrass were in their third year of growth in the field, exposed to either ambient (355 {mu}mol mol{sup -1}), or elevated (600 {mu}mol mol{sup -1}) atmospheric CO{sub 2} concentration. A Free-Air CO{sub 2} Enrichment (FACE) system was used to maintain the elevated CO{sub 2} concentration whilst limiting experimental constraints on the field conditions. The theoretically predicted increase in the net rates of CO{sub 2} uptake per unit leaf area (A {mu}mol mol{sup -1}) as a conseq… more
Date: August 1, 1996
Creator: Hymus, G.J.
open access

The risk implications of approaches to setting soil remediation goals at hazardous waste contaminated sites

Description: An integrated exposure and carcinogenic risk assessment model for organic contamination in soil, SoilRisk, was developed and used for evaluating the risk implications of both site-specific and uniform-concentration approaches to setting soil remediation goals at hazardous-waste-contaminated sites. SoilRisk was applied to evaluate the uncertainty in the risk estimate due to uncertainty in site conditions at a representative site. It was also used to evaluate the variability in risk across a regi… more
Date: August 1, 1994
Creator: Labieniec, P.A.
open access

A study of the differences in respirator fit factor values between years and masks

Description: The work described in this report was carried out at a national laboratory of the Department of Energy, during the time that the author was engaged in a Department of Energy Industrial Hygiene Graduate Fellowship. The national laboratory had a respiratory protection program with approximately 50 employees participating. The program was in place to protect employees from over-exposure to airborne contaminants while engineering and work practice controls were being installed and implemented. It w… more
Date: August 15, 1995
Creator: Longo, A.
open access

Molecular beam studies of unimolecular and bimolecular chemical reaction dynamics using VUV synchrotron radiation as a product probe

Description: This dissertation describes the use of a new molecular beam apparatus designed to use tunable VUV synchrotron radiation for photoionization of the products from scattering experiments. The apparatus was built at the recently constructed Advanced Light Source at Lawrence Berkeley National Laboratory, a third generation 1-2 GeV synchrotron radiation source. The new apparatus is applied to investigations of the dynamics of unimolecular reactions, photodissociation experiments, and bimolecular reac… more
Date: August 1, 1997
Creator: Blank, D.A.
open access

Measurement of background translocation frequencies in individuals with clones

Description: In the leukemia case the unseparated B and T lymphocytes had a high translocation frequency even after 0.0014, respectively. After purging all clones from the data, the translocation frequencies for Bio 8 and Bio 23 were 0.00750.0014 and 0.0073 metaphases were scored for chromosomal aberrations,, specifically reciprocal translocations, using fluorescence in situ hybridization (FISH). Metaphase spreads were used from two healthy, unexposed individuals (not exposed to radiation, chemotherapy or r… more
Date: August 1, 1996
Creator: Wade, M.J.
open access

Speciation of Fe in ambient aerosol and cloudwater

Description: Atmospheric iron (Fe) is thought to play an important role in cloudwater chemistry (e.g., S(IV) oxidation, oxidant production, etc.), and is also an important source of Fe to certain regions of the worlds oceans where Fe is believed to be a rate-limiting nutrient for primary productivity. This thesis focuses on understanding the chemistry, speciation and abundance of Fe in cloudwater and aerosol in the troposphere, through observations of Fe speciation in the cloudwater and aerosol samples coll… more
Date: August 15, 1996
Creator: Siefert, L.
open access

Incorporating uncertainties into risk assessment with an application to the exploratory studies facilities at Yucca Mountain

Description: A methodology that incorporates variability and reducible sources of uncertainty into the probabilistic and consequence components of risk was developed. The method was applied to the north tunnel of the Exploratory Studies Facility at Yucca Mountain in Nevada. In this assessment, variability and reducible sources of uncertainty were characterized and propagated through the risk assessment models using a Monte Carlo based software package. The results were then manipulated into risk curves at t… more
Date: August 1995
Creator: Fathauer, P. M.
open access

A two-dimensional, semi-analytic expansion method for nodal calculations

Description: Most modern nodal methods used today are based upon the transverse integration procedure in which the multi-dimensional flux shape is integrated over the transverse directions in order to produce a set of coupled one-dimensional flux shapes. The one-dimensional flux shapes are then solved either analytically or by representing the flux shape by a finite polynomial expansion. While these methods have been verified for most light-water reactor applications, they have been found to have difficulty… more
Date: August 1, 1995
Creator: Palmtag, S.P.
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