Country
States
Decade
Month
Day
Language
3,417 Matching Results
Results open in a new window/tab.
Cobalt Source Calibration
The data obtained from these tests determine the dose rate of the two cobalt sources in SRTC. This testing used chemical dosimetry to measure the dose rate of a radioactive source.
Date:
October 25, 1999
Creator:
Barnes, M.
Object Type:
Report
System:
The UNT Digital Library
Predicting application run times using historical information.
The authors present a technique for deriving predictions for the run times of parallel applications from the run times of similar applications that have executed in the past. The novel aspect of the work is the use of search techniques to determine those application characteristics that yield the best definition of similarity for the purpose of making predictions. They use four workloads recorded from parallel computers at Argonne National Laboratory, the Cornell Theory Center, and the San Diego Supercomputer Center to evaluate the effectiveness of the approach.They show that on these workloads the techniques achieve predictions that are between 14 and 60% better than those achieved by other researchers; the approach achieves mean prediction errors that are between 41 and 65% of mean application run times.
Date:
June 25, 1999
Creator:
Foster, I.; Smith, W. & Taylor, V.
Object Type:
Article
System:
The UNT Digital Library
Development of vanadium-phosphate catalysts for methanol production by selective oxidation of methane. Quarterly technical progress report 8, January--March, 1995
Activities during this quarter focused on fine tuning of catalyst characterization and synthesis techniques. Improvements in catalyst activity test methods were also implemented but more remains to be done. Specific accomplishments include: improved characterization of vanadyl pyrophosphate (VPO) and Si promoted VPO by FTIR and FTIR of chemisorbed bases; several minor improvements in catalyst preparation technique resulting in enhanced catalyst yield, better control of catalyst composition, and generation of less waste; preliminary pulsed reaction data on methane oxidation were also acquired. Preliminary activity measurements for methane conversion (without oxygen) in a pulsed reactor over VPO indicate that the primary reaction product is CO. Carbon dioxide is also formed but selectivity to CO{sub 2} decreases with number of pulses. These results suggest that selectivity to partially oxidized products improves with catalyst reduction and suggest that some surface modification will be required to obtain oxidized hydrocarbon products. Note that catalyst activation (conversion from the precursor to VPO) has been carried out using air. For butane oxidation catalysts VPO is activated in a 1% butane/air mixture which produces a slightly reduced catalyst.
Date:
May 25, 1995
Creator:
McCormick, R.L.
Object Type:
Report
System:
The UNT Digital Library
A new global hydrogen equation of state model
Simple statistical mechanics models have been assembled into a wide-range equation of state for the hydrogen isotopes. The solid is represented by an Einstein-Grtineisen model delimited by a Lindemann melting curve. The fluid is represented by an ideal gas plus a soft-sphere fluid configurational term. Dissociation and ionization are approximated by modifying the ideal gas chemical-equilibrium formulation. The T = 0 isotherm and dissociation models have been fitted to new diamond-anvil isotherm and laser-generated shock data. The main limitation of the model is in ionization at high compression.
Date:
June 25, 1999
Creator:
Young, D
Object Type:
Article
System:
The UNT Digital Library
Importance of Material Balances and Their Statistical Evaluation in Russian Material, Protection, Control and Accounting
While substantial work has been performed in the Russian MPC&A Program, much more needs to be done at Russian nuclear facilities to complete four necessary steps. These are (1) periodically measuring the physical inventory of nuclear material, (2) continuously measuring the flows of nuclear material, (3) using the results to close the material balance, particularly at bulk processing facilities, and (4) statistically evaluating any apparent loss of nuclear material. The periodic closing of material balances provides an objective test of the facility's system of nuclear material protection, control and accounting. The statistical evaluation using the uncertainties associated with individual measurement systems involved in the calculation of the material balance provides a fair standard for concluding whether the apparent loss of nuclear material means a diversion or whether the facility's accounting system needs improvement. In particular, if unattractive flow material at a facility is not measured well, the accounting system cannot readily detect the loss of attractive material if the latter substantially derives from the former.
Date:
July 25, 1999
Creator:
Fishbone, L. G.
Object Type:
Article
System:
The UNT Digital Library
Laser system for a subpicosecond electron linac.
At the Argonne Chemistry Division efforts are underway to develop a sub-picosecond electron beam pulse radiolysis facility for chemical studies. The target output of the accelerator is to generate electron pulses that can be adjusted from 3nC in .6ps to 100nC in 45ps. In conjunction with development of the accelerator a state-of-the-art ultrafast laser system is under construction that will drive the linac's photocathode and provide probe pulses that are tunable from the UV to IR spectral regions.
Date:
September 25, 1998
Creator:
Crowell, R. A.
Object Type:
Article
System:
The UNT Digital Library
Prospects for higgs discovery at the Tevatron
This report presents the results of a Fermilab study of the sensitivity for Higgs boson production at the upgraded Tevatron in Run II. The study extends previous Tevatron results by combining all possible search channels, considering the production of higher mass Higgs bosons and interpreting the results in the context of supersymmetric Higgs production as well as Standard Model production.
Date:
October 25, 1999
Creator:
Roco, Maria Teresa P.
Object Type:
Article
System:
The UNT Digital Library
Studies of hydrogen-induced degradation processes in Pb(Zr {sub 1-x}Ti{sub x})O{sub 3} (PZT) and SrBi{sub 2}Ta{sub 2}O{sub 9} SBT ferroelectric film-based capacitors.
The integration of PZT and SBT film-based capacitors with Si integrated circuit technology requires the use of processing steps that may degrade the performance of individual device components. Hydrogen annealing to remove damage in the Si FET adversely affects both PZT and SBT, although the mechanisms of degradation are different. We have used Mass spectroscopy of recoiled ions (MSRI), X-ray diffraction (XRD), Raman spectroscopy and electrical characterization to study the mechanisms of hydrogen-induced degradation in these two materials. The mechanism responsible for degradation in SBT during hydrogen annealing appears to be hydrogen-induced volatilization of Bi from the near-surface region during film growth. Although there is a similar, but smaller, loss of Pb in PZT, the resulting change in stoichiometry is not responsible for the degradation of the ferroelectric properties. Raman spectroscopy reveals that PZT films exposed to hydrogen exhibit evidence for the formation of polar hydroxyl [OH-] bonds, which can block the movement of ions in the lattice and inhibit polarization. The possible sites for the incorporation of hydrogen are discussed in terms of ionic radii, and crystal structure.
Date:
June 25, 1999
Creator:
Krauss, A. R.
Object Type:
Article
System:
The UNT Digital Library
Localized weld metal corrosion in stainless steel water tanks
The rapidly developed leaks within the TFC and TFD tanks (LLNL groundwater treatment facilities) were caused by localized corrosion within the resolidified weld metal. The corrosion was initiated by the severe oxidation of the backsides of the welds which left the exposed surfaces in a condition highly susceptible to aqueous corrosion. The propagation of surface corrosion through the thickness of the welds occurred by localized corrosive attack. This localized attack was promoted by the presence of shielded aqueous environments provided by crevices at the root of the partial penetration welds. In addition to rapid corrosion of oxidized surfaces, calcium carbonate precipitation provided an additional source of physical shielding from the bulk tank environment. Qualification testing of alternate weld procedures showed that corrosion damage can be prevented in 304L stainless steel GTA welds by welding from both sides while preventing oxidation of the tank interior through the use of an inert backing gas such as argon. Corrosion resistance was also satisfactory in GMA welds in which oxidized surfaces were postweld cleaned by wire brushing and chemically passivated in nitric acid. Further improvements in corrosion resistance are expected from a Mo-containing grade of stainless steel such as type 316L, although test results …
Date:
May 25, 1995
Creator:
Strum, M.J.
Object Type:
Report
System:
The UNT Digital Library
Laboratory measurements of compressional and shear wave speeds through methane hydrate
Simultaneous measurements of compressional and shear wave speeds through polycrystalline methane hydrate have been made. Methane hydrate, grown directly in a wave speed measurement chamber, was uniaxially compacted to a final porosity below 2%. At 277 K, the compacted material's compressional wave speed was 3650 {+-} 50 m/s. The shear wave speed, measured simultaneously, was 1890 {+-} 30 m/s. From these wave speed measurements, we derive Vp/Vs, Poisson's Ratio, bulk, shear and Young's moduli.
Date:
October 25, 1999
Creator:
Durham, W B; Waite, WF; Pinkston, J C; Stern, L A; Kirby, S H; Helgerud, M B et al.
Object Type:
Article
System:
The UNT Digital Library
The History of the 200 Area Burial Ground Vacilities Volume 2
None
Date:
September 25, 1996
Creator:
Anderson, J. D.
Object Type:
Report
System:
The UNT Digital Library
Incorporation of radionuclides in the alteration phases of spent nuclear fuel.
Alteration may be expected for spent nuclear fuel exposed to groundwater under oxidizing conditions such as that which exist at the proposed nuclear waste repository at Yucca Mountain, Nevada. The actinide elements released during the corrosion of spent fuel may be incorporated into the structures of secondary U{sup 6+} phases. The incorporation of transuranics into the crystal structures of the alteration products may significantly decrease their mobility. A series of precipitation tests were conducted at 90 C to determine the potential incorporation of Ce{sup 4+} and Nd{sup 3+} (surrogates for Pu{sup 4+} and Am{sup 3+}, respectively) into uranyl phase. Dehydrated schoepite (UO{sub 3}{center_dot}0.8-1.0HP{sub 2}O) was produced by hydrolysis of a uranium oxyacetate solution containing either cerium or neodymium. ICP-MS analysis of the leachant, leachate, and solid phase reaction products which were dissolved in a HNO{sub 3} solution indicates that 26 ppm of Ce was incorporated into dehydrated schoepite. ICP-MS results from the Nd-doped tests indicate significant neodymium incorporation as well, however, the heterogeneous distribution of Nd in the solid phase noted during the AEM/EELS examination implies that neodymium may not incorporate into the structure of dehydrated schoepite.
Date:
August 25, 1999
Creator:
Buck, E. C.; Kim, C.-W. & Wronkiewicz, D. J.
Object Type:
Article
System:
The UNT Digital Library
In situ examination of moving crack tips in ordered intermetallics.
Recent studies have shown that high stress concentrations at moving crack tips in the intermetallic compound NiTi can induce a crystalline-to-amorphous (C-A) transformation of the crack tip region. This stress-induced C-A transformation has a temperature dependence and crystallization behavior similar to those of ion irradiation-induced C-A transformation of NiTi. The present study examines if these similarities between stress- and irradiation-induced amorphization hold true for two other intermetallic compounds, CuTi and Ni{sub 3}Ti. In situ straining was performed in an intermediate-voltage transmission electron microscope. The presence or absence of an amorphous phase was determined by dark field imaging and selected area diffraction of crack tip regions. Crack tips in both CuTi and Ni{sub 3}Ti were found to remain crystalline upon fracture. The observed absence of stress-induced amorphization in Ni{sub 3}Ti is consistent with its known absence during irradiation, but the absence in CuTi differs from its known irradiation-induced amorphization behavior. Reasons for the similarity and difference are discussed.
Date:
January 25, 1999
Creator:
Heuer, J.; Lam, N. Q.; Okamoto, P. R. & Stubbins, J. F.
Object Type:
Article
System:
The UNT Digital Library
TNX GeoSiphon Cell (TGSC-1) Phase II Minimum Flushing Velocity Deployment/Demonstration Final Report
The TNX Area is a semi-works facility for the Savannah River Technology Center (SRTC), which is located one-quarter mile from the Savannah river at the Savannah River Site. As the result of TNX operation, groundwater contamination has occurred. The predominant contaminants detected in the flood plain downgradient from TNX are trichloroethylene (TCE) and nitrate.Treatability studies into the applicability of a groundwater remediation system combining GeoSiphon Cell and zero-valent iron technologies for treatment of the TCE-contaminated groundwater at TNX have been conducted. These treatability studies have been conducted by SRTC under the sponsorship of the Environmental Restoration Department.
Date:
October 25, 1999
Creator:
Phifer, M. A.
Object Type:
Report
System:
The UNT Digital Library
The measurement of the mass of the W boson from the Tevatron.
This paper presents measurements of the mass of the W vector boson from the CDF and D0 experiments using data collected at {radical}s = 1.8 TeV during the 1994-1995 data taking run. CDF finds a preliminary mass of M{sub W} = 80.43 {+-} 0.16 GeV and D0 measures a mass of M{sub W} = 80.44 {+-} 0.12 GeV.
Date:
August 25, 1998
Creator:
Thurman-Keup, R.
Object Type:
Article
System:
The UNT Digital Library
Transport of a Partially-Neutralized Ion Beam in a Heavy-Ion Fusion Reactor Chamber
In a heavy-ion driven, inertial confinement fusion power plant, a space-charge dominated beam of heavy ions must be transported through a reactor chamber and focused on a 2-3 mm spot at the target. The spot size at the target is determined by the beam emittance and space charge, plus chromatic aberrations in the focusing lens system and errors in aiming the beam. The gain of the ICF capsule depends on the focal spot size. We are investigating low density, nearly-ballistic transport using an electromagnetic, r-z particle-in-cell code. Even at low density (n {approx} 5 {times} 10{sup 13} cm{sup {minus}3}), beam stripping may be important. To offset the effects of stripping and reduce the space charge, the beam is partially charge neutralized via a pre-formed plasma near the chamber entrance. Additional electrons for charge neutralization come from ionization of the background gas by the beam. Simulations have shown that stripping can greatly increase the spot size; however, partial neutralization can offset most of this increase.
Date:
April 25, 1995
Creator:
Callahan, D. A. & Langdon, A. B.
Object Type:
Article
System:
The UNT Digital Library
The role of selected f ions in the suppression of high-Tc superconductivity.
The initial observations of superconductivity at temperatures above 77 K in copper-oxide based materials was surprising from a variety of different perspectives. Among the unexpected findings were reports of superconductivity for the series RBa{sub 2}Cu{sub 3}O{sub 7} where R is a rare earth (Y, Nd-Tm), which may carry a large, local magnetic moment. Superconductivity was subsequently demonstrated for all 4f analogs in this series except Ce, Pr, and Tb. In addition to the RBa{sub 2}Cu{sub 3}O{sub 7} series, there are several other CuO based series of superconductors that are formed by substituting R ions. The most studied of these are listed in Table 1, together with the f ions that form isostructural compounds and their superconducting critical temperatures (T{sub c}). The presence of an R ion with a large magnetic moment does not significantly influence the superconductivity. In contrast, even the presence of small concentrations of magnetic impurity ions in a conventional superconductor inhibits superconductivity by interfering with the formation of Cooper pairs. Most R ions substitute into an isostructural series with no observable effect on the superconducting properties of the material. As can be seen from Table 1, there are notable exceptions to this observation. In particular, the rare-earth …
Date:
September 25, 1998
Creator:
Soderholm, L.
Object Type:
Article
System:
The UNT Digital Library
A numerical investigation of the scale-up effects on flow, heat transfer, and kinetics processes of FCC units.
Fluid Catalytic Cracking (FCC) technology is the most important process used by the refinery industry to convert crude oil to valuable lighter products such as gasoline. Process development is generally very time consuming especially when a small pilot unit is being scaled-up to a large commercial unit because of the lack of information to aide in the design of scaled-up units. Such information can now be obtained by analysis based on the pilot scale measurements and computer simulation that includes controlling physics of the FCC system. A Computational fluid dynamic (CFD) code, ICRKFLO, has been developed at Argonne National Laboratory (ANL) and has been successfully applied to the simulation of catalytic petroleum cracking risers. It employs hybrid hydrodynamic-chemical kinetic coupling techniques, enabling the analysis of an FCC unit with complex chemical reaction sets containing tens or hundreds of subspecies. The code has been continuously validated based on pilot-scale experimental data. It is now being used to investigate the effects of scaled-up FCC units. Among FCC operating conditions, the feed injection conditions are found to have a strong impact on the product yields of scaled-up FCC units. The feed injection conditions appear to affect flow and heat transfer patterns and the …
Date:
August 25, 1998
Creator:
Chang, S. L.
Object Type:
Article
System:
The UNT Digital Library
Workshop on Basic Research Opportunities in Photovoltaics
The Basic Research Opportunities in Photovoltaics Workshop was held on May 3, 1999, in Seattle, Washington, in conjunction with the 195th Meeting of the Electrochemical Society. The workshop was structured into eight topics. Each topic area opened with a presentation in which the participants were asked to address the following: a brief introduction of the area of research; key research issues that were identified in an earlier workshop in 1992; what fundamental research has been done since then or is currently being done to address those issues; what are the research issues that are still relevant in light of advances made since the first workshop; identification of new fundamental research opportunities that will lead to important advances and innovations; and identification of significant commonalities and common research issues that have a cross-cutting impact, such as logically exist in silicon-based thin films, II-VI, and related materials. The topic areas discussed included amorphous and microcrystalline silicon, crystalline silicon, cadmium telluride, copper indium diselenide; III-V materials; novel materials and energy conversion approaches, semiconducting oxides, and characterization. After the meeting, participants in each working topic continued discussions by electronic means, completing journal articles that are to be published as a separate section in the …
Date:
August 25, 1999
Creator:
Benner, J.; McConnell, R. & Deb, S., Editors
Object Type:
Report
System:
The UNT Digital Library
Thermal Decomposition Characteristics of Orthorhombic Ammonium Perchlorate (o-AP) and an 0-AP/HTPB-Based Propellant
A study to characterize the low-temperature reactive processes for o-AP and an AP/HTPB-based propellant (class 1.3) is being conducted in the laboratory using the techniques of simultaneous thermogravimetric modulated beam mass spectrometry (STMBMS) and scanning electron microscopy (SEM). The results presented in this paper are a follow up of the previous work that showed the overall decomposition to be complex and controlled by both physical and chemical processes. The decomposition is characterized by the occurrence of one major event that consumes up to {approx}35% of the AP, depending upon particle size, and leaves behind a porous agglomerate of AP. The major gaseous products released during this event include H{sub 2}O, O{sub 2}, Cl{sub 2}, N{sub 2}O and HCl. The recent efforts provide further insight into the decomposition processes for o-AP. The temporal behaviors of the gas formation rates (GFRs) for the products indicate that the major decomposition event consists of three chemical channels. The first and third channels are affected by the pressure in the reaction cell and occur at the surface or in the gas phase above the surface of the AP particles. The second channel is not affected by pressure and accounts for the solid-phase reactions characteristic of …
Date:
October 25, 1999
Creator:
Behrens, Richard, Jr. & Minier, Leanna M. G.
Object Type:
Article
System:
The UNT Digital Library
REVIEW OF EQUIPMENT USED IN RUSSIAN PRACTICE FOR ACCOUNTING MEASUREMENTS OF NUCLEAR MATERIALS.
The objective of this work was to analyze instrumentation and methodologies used at Russian nuclear facilities for measurement of item nuclear materials, materials in bulk form, and waste streams; specify possibilities for the application of accounting measurements; and develop recommendations for improvement. The major steps and results: Representative conversion, enrichment (gas centrifuge), fuel fabrication, spent fuel reprocessing, and chemical-metallurgical production facilities in Russia were selected; Full lists of nuclear materials were prepared; Information about measurement methods and instrumentation for each type of nuclear material were gathered; and Recommendations on methodological and instrumentation support of accounting measurements for all types of materials were formulated. The analysis showed that the existing measurement methods and instrumentation serve mostly to support the technological process control and nuclear and radiation safety control. Requirements for these applications are lower than requirements for MC and A applications. To improve the state of MC and A at Russian nuclear facilities, significant changes in instrumentation support will be required, specifically in weighing equipment, volume measurements, and destructive and non-destructive analysis equipment, along with certified reference materials.
Date:
July 25, 1999
Creator:
NEYMOTIN,L.
Object Type:
Article
System:
The UNT Digital Library
Recent developments in fissile material exemptions for shipping packages
None
Date:
February 25, 1997
Creator:
Sheaffer, M. K., LLNL
Object Type:
Article
System:
The UNT Digital Library
Methane hydrate dissociation rates as 0.1 MPa and temperatures above 272K
We performed rapid depressurization experiments on methane hydrate under isothermal conditions above 272 K to determine the amount and rate of methane evolution. Sample temperatures rapidly drop below 273 K and stabilize near 272.5 K during dissociation. This thermal anomaly and the persistence of methane hydrate are consistent with the reported recovery of partially dissociated methane hydrate from ocean drilling cores.
Date:
October 25, 1999
Creator:
Durham, W. B.; Circone, S.; Stern, L. A.; Kirby, S. H. & Pinkston, J. C.
Object Type:
Article
System:
The UNT Digital Library
A decision analysis of an exploratory studies facility
An Exploratory Studies Facility (ESF) is planned to support the characterization of a potential site for a high-level nuclear waste repository at Yucca Mountain, NV. The selection of a design for the ESF is a critical decision, because the ESF design may affect the accuracy of characterization testing and subsequent repository design. The assist the design process, a comparative evaluation was conducted to rank 34 alternative relied on techniques from formal decision analysis, including decision trees and multiattribute utility analysis (MUA). The results helped to identify favorable design features and convinced the Department of Energy to adopt the top-ranked option as the preferred ESF design.
Date:
November 25, 1991
Creator:
Merkhofer, M. W. & Gnirk, P.
Object Type:
Article
System:
The UNT Digital Library