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5,966 Matching Results
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Vertical bridgman and gradient freeze growth of III-V compound semiconductors
Major improvements in the structural and electrical perfection of single crystals of III-V compound semiconductors have been achieved by using new vertical Bridgman-type and vertical gradient freeze techniques. A general review of experimental set-ups used for growth of large diameter crystals of GaP, InP and GaAs is presented. Crystal properties and characteristic features are discussed to illustrate advantages and disadvantages of the vertical Bridgman-type growth techniques. 22 refs., 5 figs.
Date:
July 1, 1990
Creator:
Bourret, E.D.
Object Type:
Article
System:
The UNT Digital Library
Po-210 as long-term integrating radon indicator in the indoor environment
The general objective is to improve the knowledge about the transferring processes leading from airborne radon/radon daughters to embedded Po-210 in hard surfaces in the indoor environment. The specific goal of the research is to identify situations in which the surface activity of Po-210 can be used as a long-term indicator of lung cancer risk from past or future radon exposures.
Date:
July 1, 1990
Creator:
Samuelsson, C.
Object Type:
Report
System:
The UNT Digital Library
Characterization of Nb-Ti superconductors with artificial pinning structures
A series of multifilamentary APC Nb-Ti superconductors have been made with Nb added as a normal second phase to provide flux pinning centers. Two compositions, 12.5% vol % and 25 vol % Nb in Nb-Ti, have fabricated into multifilamentary composites using two different fabrication methods. One method used hot isostatic compaction and hot extrusion thoughout the processing. The other method (bundle-and-draw process) discontinued all hot processing at an intermediate level. While the J{sub c} values of the bundle-and-draw wires are quite promising, the critical current of the extruded wires appears to be limited by poor uniformity of the filament cross-sectional area along the conductor length. The large values of the index of the resistive transition and small filament standard-deviation-to-average area ratios observed in the wires produced by the bundle-and-draw process suggest extrinsic factors have little effect on J{sub c}. The variation in J{sub c} as the wire diameter is reduced appears to be most strongly affected by intrinsic factors: Nb distribution and pinning strength. The final filament microstructure and Nb spacing are shown to be difficult to calculate, e.g., the mean Nb spacing near the final wire size may be {1/2} to 1/3 that of the calculated value. 5 refs., …
Date:
June 1, 1990
Creator:
Dietderich, D. R. & Scanlan, R. M.
Object Type:
Article
System:
The UNT Digital Library
Removal of trichloroethylene contamination from the subsurface: A comparative evaluation of different remediation strategies by means of numerical simulation
Volatile organic compounds such as petroleum hydrocarbons and halogenated hydrocarbon solvents are common contaminants of the subsurface environment. Although immiscible with water, many of these organics have large enough aqueous phase solubilities to significantly degrade the quality of groundwater with which they come in contact. In addition, many of these substances exhibit high vapor pressures, causing them to partition strongly into the gas phase in their surroundings. Because of these properties, a volatile organic compound (VOC), once introduced into the subsurface may be transported as a solute, a vapor, or as a constituent in a non- aqueous phase liquid (NAPL). This implies that at some sits, an adequate description of the migration of these contaminants in the subsurface would necessarily involve three phases, -- gas, aqueous and NAPL. For example, to design an effective aquifer remediation scheme for a site where NAPL is present, it would be wrong to focus solely on the aqueous phase while ignoring either the gas phase or the NAPL phase. In the present work, we use a simulator developed by Falta et al. (1990a), known as STMVOC,'' which models true three-phase flow in which NAPL, gas and aqueous phases can move in response to pressure, …
Date:
December 1, 1990
Creator:
Adenekan, A.E.; Pruess, K. & Falta, R.W.
Object Type:
Report
System:
The UNT Digital Library
Surface electrochemical control for fine coal and pyrite separation
Ongoing work includes the characterization of coal pyrites, the floatability evaluation typical US coal samples, the flotation behavior of coal pyrites, the electrochemical measurement of the surface properties of coal pyrites, and the characterization of species produced at pyrite surfaces.
Date:
January 1, 1990
Creator:
Hu, Weibai; Zhu, Ximeng; Bodily, D. M. & Wadsworth, M. E.
Object Type:
Report
System:
The UNT Digital Library
Biological Production of Ethanol From Coal
A batch kinetic study involving Clostridium lungdahlii in a mineral medium was carried out in order to provide baseline data for the effects of nutrients on product ratio and kinetics. The use of this minimal medium containing vitamins, minerals, select amino acids and salts showed both a lower maximum specific growth rate and a lower maximum specific uptake rate than found when using a complex medium supplemented with 0.01% yeast extract. At the same time, the product ratio was improved slightly in favor of ethanol over acetate. Future experiments will measure the effects of ammonia and phosphate limitation on product ratio and process kinetics.
Date:
January 1, 1990
Creator:
unknown
Object Type:
Report
System:
The UNT Digital Library
Automatic lighting controls demonstration
The purpose of this work was to demonstrate, in a real building situation, the energy and peak demand reduction capabilities of an electronically ballasted lighting control system that can utilize all types of control strategies to efficiently manage lighting. The project has demonstrated that a state-of-the-art electronically ballasted dimmable lighting system can reduce energy and lighting demand by as least 50% using various combinations of control strategies. By reducing light levels over circulation areas (tuning) and reducing after hours light levels to accommodate the less stringent lighting demands of the cleaning crew (scheduling), lighting energy consumption on weekdays was reduced an average of 54% relative to the initial condition. 10 refs., 14 figs., 3 tabs.
Date:
March 1, 1990
Creator:
Rubinstein, F. & Verderber, R.
Object Type:
Report
System:
The UNT Digital Library
Technological challenges of third generation synchrotron radiation sources
New third generation'' synchrotron radiation research facilities are now in construction in France, Italy, Japan, Taiwan and the USA. Designs for such facilities are being developed in several other countries. Third generation facilities are based on storage rings with low electron beam emittance and space for many undulator magnets to produce radiation with extremely high brightness and coherent power. Photon beam from these rings will greatly extend present research capabilities and open up new opportunities in imaging, spectroscopy, structural and dynamic studies and other applications. The technological problems of the third generation of synchrotron radiation facilities are reviewed. These machines are designed to emit radiation of very high intensity, extreme brightness, very short pulses, and partial coherence. These performance goals put severe requirements on the quality of the electron or positron beams. Phenomena affecting the injection process and the beam lifetime are discussed. Gas desorption by synchrotron radiation and collective effects play an important role. Low emittance lattices are more sensitive to quadrupole movements and at the same time, in order not to lose the benefits of high brilliance, require tighter tolerances on the allowed movement of the photon beam source. We discuss some of the ways that should be …
Date:
January 1, 1990
Creator:
Cornacchia, M. & Winick, H.
Object Type:
Article
System:
The UNT Digital Library
A novel process for methanol synthesis
A bench-salce reactor is being used to conduct studies of the conversion of synthesis gas to methanol by a novel process. During the last quarter, we investigated the nature of the reactions involved and the nature of the Cu-chromite catalyst being used. There is evidence that methanol is formed via a two step reaction with a methyl formate intermediate rather than by the direct hydrogenation of CO. The carbonylation reaction predominantly takes place in the liquid phase while the hydrogenolysis reaction is restricted to the surface of Cu-chromite. At steady state, the carbonylation reaction taking place in the region close to the Cu-chromite surface is probably the main source of MeF. This model also explains the increased tolerance of the process to CO. A mechanistic model is proposed to explain the interaction of different species in the reaction mixture. The topography of the Cu-chromite surface is also investigated by X-ray diffraction and scanning electron microscopy. 15 refs., 5 figs., 1 tab.
Date:
January 1, 1990
Creator:
Tierney, J. W. & Wender, I.
Object Type:
Report
System:
The UNT Digital Library
A Novel Coal Feeder for Production of Low Sulfur Fuel
A novel coal feeding system is currently undergoing testing and evaluation at the University of Cincinnati. The system consists primarily of an auger feed tube which is used to both convey and provide desulfurization of a high sulfur coal feedstock. The coal is conveyed at temperatures ranging from 350 to 550 {degrees}C and under normal atmospheric pressure. Under these mild processing conditions, the coal partially pyrolizes and emits sulfur in the form of hydrogen sulfide while maintaining a relatively high heating value in the char product. The evolved gases are evacuated from the reactor (the feed tube) to another absorbing bed where H{sub 2}S reacts with the sorbent, usually lime or limestone. The resultant sorbent utilization is substantially higher than the values found in current dry scrubbing system and the produced low-sulfur char may then be used in a conventional steam boiler.
Date:
January 1, 1990
Creator:
Keener, T. C.; Khang, S. J. & Yu, X. L.
Object Type:
Report
System:
The UNT Digital Library
Genes and gene expression: Localization, damage and control -- A multilevel and inter-disciplinary study
All projects are working toward a goal for describing the three dimensional nuclear topography in terms of relative spatial relationships among genes (specific DNA sequence). Methods are now being perfected to detect these genes, quantitatively and spatially, to perturb these genes specifically, and to measure the perturbation in order to assure specificity. We are developing methods to assay, after perturbation of the target DNA within living cells, whether or not only the target sequence are attacked while other sequences remain unharmed. We are now at the stage to do chemical gene modification or masking within living cells in a strictly sequence-specific manner. Soon, we will be able to study the function and the physical location of each gene in living cells with exquisite specificity. 25 refs., 15 figs.
Date:
September 1, 1990
Creator:
Ts'o, P.O.P.
Object Type:
Report
System:
The UNT Digital Library
Research on thermophoretic and inertial aspects of ash particle deposition on heat exchanger surfaces in coal-fired equipment
The overall goal of this research in the area of ash transport was to advance the capability of making reliable engineering predictions of the dynamics and consequences of net deposit growth for surfaces exposed to the products of coal combustion. To accomplish this for a wide variety of combustor types, coal types, and operating conditions, this capability must be based on a quantitative understanding of each of the important mechanisms of mineral matter transport, as well as the nature of the interactions between these substances and the prevailing fireside'' surface of the deposit. This level of understanding and predictive capability could ultimately be translated into very significant cost reductions for coal-fired equipment design, development and operation.
Date:
May 1, 1990
Creator:
Rosner, D.E.
Object Type:
Report
System:
The UNT Digital Library
Particle correlations in JACEE (Japanese-American Cooperative Emulsion Experiment) nucleus-nucleus collisions
Correlations in the production of charged particles and photons can be examined in detail in the central and forward rapidity range using high multiplicity ({ge}100 charged tracks) events from JACEE emulsion chambers. Results are presented on several forms of correlations studies. 9 refs., 2 figs.
Date:
January 1, 1990
Creator:
unknown
Object Type:
Article
System:
The UNT Digital Library
Proof of concept testing of an integrated dry injection system for SO sub x /NO sub x control
The objective of the subscale test program were designed to provide sorbent and additive selection guidance, and, in so doing, supply answers to the questions posed in the preceding section. The objectives are: Identify the best commercial hydrate sorbent and the best enhanced hydrate sorbent from a list of nine types, based upon S0{sub 2} removal at Ca/S=2. Determine the relative effectiveness of sodium sesquicarbonate versus sodium bicarbonate for S0{sub 2} and NO{sub x} control over the temperature range of 200{degrees}F--400{degrees}F. Identify the best NO{sub 2} suppressing additive among the group of ammonia, urea, and activated carbon.
Date:
January 1, 1990
Creator:
Helfritch, D.J.; Bortz, S.J. (Research-Cottrell, Inc., Somerville, NJ (United States). Environmental Services and Technologies Div.) & Beittel, R. (Riley Stoker Corp., Worcester, MA (United States))
Object Type:
Report
System:
The UNT Digital Library
Biological Production of Ethanol From Coal
Previous results have shown that the yeast extract concentration and the medium pH significantly affect the ratio of ethanol to acetate in the product stream when fermenting CO, CO{sub 2} and H{sub 2} in synthesis gas to products by Clostridium ljungdahlii. Further experimentation has demonstrated the impact of eliminating yeast extract from the medium (except for the slight quantity transferred with the inoculm), especially when coupled with low pH. An ethanol to acetate product ratio of 4.0 was obtained at pH 4.5 without yeast extract present in the medium when using culture previously exposed to growth-limiting H{sub 2}S. The product ratio was 2.0 at pH 4.0 (nearly three times the value of pH 4.5 and nine times the value of pH 5.0) without yeast extract present in the media when using the standard (unexposed) culture.
Date:
January 1, 1990
Creator:
unknown
Object Type:
Report
System:
The UNT Digital Library
TRAC L reactor model: Geometry review and benchmarking
The analysis of the Design Basis Loss of Coolant Acident (LOCA) for Savannah River Site (SRS) reactors involves the best estimate reactor system thermal-hydraulics code TRAC-PFI/MOD1. Power levels for the L-3.1 and P-10.2 subcycles were determined based, in part, on TRAC analyses of the first few seconds of a plenum inlet break LOCA. The TRAC code is currently being used to analyze reactor system response for the Double Ended Guillotine Break (DEGB) LOCA, the Expansion Joint Bellows Break LOCA, the Loss of Pumping Accident (LOPA), and the Pump Shaft Break event. Currently, the DEGB LOCA analysis is performed with TRAC only for the flow instability (FI) phase of the accident. This analysis provides input to the determination of operating power limits for the K-14.1 subcycle.
Date:
August 1, 1990
Creator:
Griggs, D.P. (Westinghouse Savannah River Co., Aiken, SC (United States)) & Cozzuol, J.M. (Idaho National Engineering Lab., Idaho Falls, ID (United States))
Object Type:
Report
System:
The UNT Digital Library
Chemical characterization of CTBN (carboxyl-terminated butadiene/acrylonitrile) and its epoxy adduct
This report describes the analysis of carbonxyl-terminated butadiene (CTB), carboxyl-terminated butadiene/acrylonitrile (CTBN), and a CTBN adduct prepared by reaction with Epon 828. Data from gel permeation chromatography, nuclear magnetic resonance spectroscopy, high performance liquid chromatography, and ion chromatography are presented and discussed. Quantitative methods based on carbon-13 and proton NMR for analyzing CTBN are described. Proton NMR was found to be useful in identifying lots that have an abnormal amount of CTBN protons. One such lot exhibited a phase separation of a polybutadiene impurity. Carbon-13 NMR was found to be capable of determining nitrile content directly. Carbon-13 NMR had a relative standard deviation of 8.3% and a proton NMR of 3.9%. Proton NMR was found to be useful in identifying lots that have 5% more CTBN protons than other lots. 3 refs., 11 figs., 4 tabs.
Date:
January 1, 1990
Creator:
Smith, R.E.
Object Type:
Report
System:
The UNT Digital Library
Control of alpha particle transport by spatially inhomogeneous ion cyclotron resonance heating
Control of the radial alpha particle transport by using Ion Cyclotron Range of Frequency waves is investigated in a large-aspect-ratio tokamak geometry. It is shown that spatially inhomogeneous ICRF-wave energy with properly selected frequencies and wave numbers can induce fast convective transport of alpha particles at the speed of order {upsilon}{sub alpha} {approximately} (P{sub RF}/n{sub {alpha}}{epsilon}{sub 0}) {rho}{sub p}, where P{sub RF} is the ICRF-wave power density, n{sub {alpha}} is the alpha density, {epsilon}{sub 0} is the alpha birth energy, and {rho}{sub p} is the poloidal gyroradius of alpha particles at the birth energy. Application to ITER plasmas is studied and possible antenna designs to control alpha particle flux are discussed. 8 refs., 3 figs.
Date:
February 1, 1990
Creator:
Chang, C. S.; Imre, K.; Weitzner, H. (New York Univ., NY (USA). Courant Inst. of Mathematical Sciences) & Colestock, P. (Princeton Univ., NJ (USA). Plasma Physics Lab.)
Object Type:
Report
System:
The UNT Digital Library
Bounding burnout risk power limits for the K-14 cycle
This document discusses burnout risk (BOR) power limits which are designed to protect the reactor from a significant release of fission products, due to critical heat flux (CHF) burnout of fuel and target assemblies. At expected operating power levels for the reactor restart, approximately 50% of historical full power, the risk of CHF and attendant burnout is negligible. Flow instability power limits will restrict reactor operation, and flow instability will always occur before CHF. BOR power limits must nevertheless be calculated because they are required by the reactor control computer, (2) Bounding BOR limits have been calculated for the K-14 cycle, to fulfill this requirement, and they are presented in this document. Two sets of BOR limits have been calculated: one applicable for the first subcycle, zero to 30% fuel burnup, and the other for the second subcycle, 30% to 55% fuel burnup.
Date:
October 1, 1990
Creator:
Shadday, M.A. Jr.
Object Type:
Report
System:
The UNT Digital Library
Neoclassical transport of energetic minority tail ions generated by ion-cyclotron resonance heating in tokamak geometry
Neoclassical transport of energetic minority tail ions, which are generated by high powered electromagnetic waves of the Ion Cyclotron Range of Frequencies (ICRF) at the fundamental harmonic resonance, is studied analytically in tokamak geometry. The effect of Coulomb collisions on the tail ion transport is investigated in the present work. The total tail ion transport will be the sum of the present collision-driven transport and the wave-driven transport, which is due to the ICRF-wave scattering of the tail particles as reported in the literature. The transport coefficients have been calculated kinetically, and it is found that the large tail ion viscosity, driven by the localized ICRF-heating and Coulomb slowing-down collisions, induces purely convective particle transport of the tail species, while the energy transport is both convective and diffusive. The rate of radial particle transport is shown to be usually small, but the rate of radial energy transport is larger and may not be negligible compared to the Coulomb slowing-down rate. 18 refs., 2 figs.
Date:
January 1, 1990
Creator:
Chang, C.S. (New York Univ., NY (USA). Courant Inst. of Mathematical Sciences); Hammett, G.W. & Goldston, R.J. (Princeton Univ., NJ (USA). Plasma Physics Lab.)
Object Type:
Report
System:
The UNT Digital Library
DEPOT: Database for electronics parts and other things
DEPOT has been developed to provide tracking for the Stanford Linear Collider (SLC) control system equipment. For each piece of equipment entered in the database, a complete service, maintenance, modification, certification, location history, and, optionally, a radiation exposure history, can be maintained. To facilitate data entry accuracy, efficiency, and consistency, barcoding technology has been used extensively. DEPOT has been an important tool in improving the reliability of the microsystems controlling SLC. It is now being adopted by other systems at SLAC. 6 refs., 6 figs.
Date:
January 1, 1990
Creator:
Logg, C.A.; Clancey, P.W. & Crane, G.
Object Type:
Article
System:
The UNT Digital Library
A search for. nu. sub e appearance from stopped. pi. sup + and. mu. sup + decay at LAMPF (Los Alamos Meson Physics Facility)
We report on a recent search for {bar {nu}}{sub e} appearance from stopped {pi}{sup +} {yields} {mu}{sup +}{nu}{sub {mu}} and {mu}{sup +} {yields} e{sup +}{nu}{sub e}{bar {nu}}{sub {mu}} decay made by the LAMPF experiment E645. The appearance of {bar {nu}}{sub e} may occur from {bar {nu}}{sub {mu}} {yields} {bar {nu}}{sub e}, {nu}{sub e} {yields} {bar {nu}}{sub eL}, or {nu}{sub {mu}} {yields} {bar {nu}}{sub eL} oscillations. Appearance may also occur from rare {mu}{sup +} {yields} e{sup +}{bar {nu}}{sub e}{nu}{sub {mu}} decay, which is allowed by a multiplicative lepton charge conservation law. The neutrino energies range from E{sub {nu}} = 0 to 52.8MeV. The neutrino detector, which is located 26.1 meters from the neutrino source, consists of a segmented liquid scintillator and proportional drift tube central detector surrounded by both active and passive shielding. The central detector detects {bar {nu}}{sub e} through the {bar {nu}}{sub e}p {yields} ne{sup +} Charge Current (CC) reaction, which is signaled by the direct detection of the final state positron and neutron. The hydrogen-rich liquid scintillators act as free proton targets for the {bar {nu}}{sub e}p CC reaction. The neutrons are detected through radiative neutron capture on gadolinium. We find no evidence for {bar {nu}}{sub e} appearance …
Date:
January 1, 1990
Creator:
Fujikawa, B. K.
Object Type:
Report
System:
The UNT Digital Library
Biological Production of Ethanol From Coal
Previous results have shown that the medium pH, the composition of the medium and concentration of medium constituents significantly affect the ratio of ethanol to acetate in the product stream when fermenting CO, CO{sub 2} and H{sub 2} in synthesis gas to products by Clostridium ljungdahlii. An additional batch study was carried out varying the agitation rate at pH 4, 4.5 and 5.0. It was speculated that increased agitation rates in combination with low pH might result in increased ethanol production while, at the same time, yielding higher cell concentrations which could eventually result in higher ethanol concentrations.
Date:
January 1, 1990
Creator:
unknown
Object Type:
Report
System:
The UNT Digital Library
FLOWTRAN-TF code description
FLOWTRAN-TF is a two-component (air-water), two-phase thermal-hydraulics code designed for performing accident analyses of SRS reactor fuel assemblies during the Emergency Cooling System (ECS) phase of a Double Ended Guillotine Break (DEGB) Loss of Coolant Accident (LOCA). This report provides a brief description of the physical models in the version of FLOWTRAN-TF used to compute the Recommended K-Reactor Restart ECS Power Limit. This document is viewed as an interim report and should ultimately be superseded by a comprehensive user/programmer manual. In general, only high level discussions of governing equations and constitutive laws are presented. Numerical implementation of these models, code architecture and user information are not generally covered. A companion document describing code benchmarking is available.
Date:
December 1, 1990
Creator:
Flach, G.P. (ed.)
Object Type:
Report
System:
The UNT Digital Library