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235U and TRU Holdup Measurements on the 321-M Sawbenches (open access)

235U and TRU Holdup Measurements on the 321-M Sawbenches

The Analytical Development Section of Savannah River Technology Center (SRTC) was requested by the Facilities Disposition Projects (FDP) to determine the holdup of enriched uranium in the 321-M facility as part of an overall deactivation project of the facility. The 321-M facility was used to fabricate enriched uranium fuel assemblies, lithium-aluminum target tubes, neptunium assemblies, and miscellaneous components for the production reactors. The results of the holdup assays are essential for determining compliance with the Waste Acceptance Criteria, Material Control & Accountability, and to meet criticality safety controls. This report covers holdup measurements on two sawbench components that were used for cutting U-Al fuel rods. The benches contained U-Al residue scattered on the bench tops and bagged up in plastic containers. It was very important to obtain an estimate of the HEU content of this residue in order to remove criticality concerns before vacuuming it into a much smaller volume. A portable high purity germanium (HPGe) detection system and a portable sodium iodide (NaI) detection system were used to determine highly enriched uranium (HEU) holdup and to determine holdup Np-237 and Am-241 that were observed in these components. The measured Np-237 and Am-241 contents were especially important in these components …
Date: July 2, 2004
Creator: Dewberry, R
Object Type: Report
System: The UNT Digital Library
Adaptive 4-8 Texture Hierarchies (open access)

Adaptive 4-8 Texture Hierarchies

We address the texture level-of-detail problem for extremely large surfaces such as terrain during real-time, view-dependent rendering. A novel texture hierarchy is introduced based on 4-8 refinement of raster tiles, in which the texture grids in effect rotate 45 degrees for each level of refinement. This hierarchy provides twice as many levels of detail as conventional quad-tree-style refinement schemes such as mipmaps, and thus provides per-pixel view-dependent filtering that is twice as close to the ideal cutoff frequency for an average pixel. Because of this more gradual change in low-pass filtering, and due to the more precise emulation of the ideal cutoff frequency, we find in practice that the transitions between texture levels of detail are not perceptible. This allows rendering systems to avoid the complexity and performance costs of per-pixel blending between texture levels of detail. The 4-8 texturing scheme is integrated into a variant of the Real-time Optimally Adapting Meshes (ROAM) algorithm for view-dependent multiresolution mesh generation. Improvements to ROAM included here are: the diamond data structure as a streamlined replacement for the triangle bintree elements, the use of low-pass-filtered geometry patches in place of individual triangles, integration of 4-8 textures, and a simple out-of-core data access mechanism …
Date: August 2, 2004
Creator: Hwa, L M; Duchaineau, M A & Joy, K I
Object Type: Article
System: The UNT Digital Library
Air Quality and Road Emission Results for Fort Stewart, Georgia (open access)

Air Quality and Road Emission Results for Fort Stewart, Georgia

The Directorate of Public Works Environmental & Natural Resources Division (Fort Stewart /Hunter Army Airfield) contracted with the Pacific Northwest National Laboratory (PNNL) to monitor particulate matter (PM) concentrations on Fort Stewart, Georgia. The purpose of this investigation was to establish a PM sampling network using monitoring equipment typically used in U.S. Environmental Protection Agency (EPA) ''saturation sampling'', to determine air quality on the installation. In this initial study, the emphasis was on training-generated PM, not receptor PM loading. The majority of PM samples were 24-hr filter-based samples with sampling frequency ranging from every other day, to once every six days synchronized with the EPA 6th day national sampling schedule. Eight measurement sites were established and used to determine spatial variability in PM concentrations and evaluate whether fluctuations in PM appear to result from training activities and forest management practices on the installation. Data collected to date indicate the average installation PM2.5 concentration is lower than that of nearby urban Savannah, Georgia. At three sites near the installation perimeter, analyses to segregate PM concentrations by direction of air flow across the installation boundary indicate that air (below 80 ft) leaving the installation contains less PM2.5 than that entering the installation. …
Date: February 2, 2004
Creator: Kirkham, Randy R.; Driver, Crystal J.; Chamness, Mickie A. & Barfuss, Brad C.
Object Type: Report
System: The UNT Digital Library
Analytic Model of Reactive Flow (open access)

Analytic Model of Reactive Flow

A simple analytic model allows prediction of rate constants and size effect behavior before a hydrocode run if size effect data exists. At infinite radius, it defines not only detonation velocity but also average detonation rate, pressure and energy. This allows the derivation of a generalized radius, which becomes larger as the explosive becomes more non-ideal. The model is applied to near-ideal PBX 9404, in-between ANFO and most non-ideal AN. The power of the pressure declines from 2.3, 1.5 to 0.8 across this set. The power of the burn fraction, F, is 0.8, 0 and 0, so that an F-term is important only for the ideal explosives. The size effect shapes change from concave-down to nearly straight to concave-up. Failure is associated with ideal explosives when the calculated detonation velocity turns in a double-valued way. The effect of the power of the pressure may be simulated by including a pressure cutoff in the detonation rate. The models allows comparison of a wide spectrum of explosives providing that a single detonation rate is feasible.
Date: August 2, 2004
Creator: Souers, P C & Vitello, P
Object Type: Article
System: The UNT Digital Library
Angle-Resolved 2D Imaging of Electron Emission Processes in Atoms and Molecules (open access)

Angle-Resolved 2D Imaging of Electron Emission Processes in Atoms and Molecules

A variety of electron emission processes have been studied in detail for both atomic and molecular systems, using a highly efficient experimental system comprising two time-of-flight (TOF) rotatable electron energy analyzers and a 3rd generation synchrotron light source. Two examples are used here to illustrate the obtained results. Firstly, electron emissions in the HCL molecule have been mapped over a 14 eV wide photon energy range over the Cl 2p ionization threshold. Particular attention is paid to the dissociative core-excited states, for which the Auger electron emission shows photon energy dependent features. Also, the evolution of resonant Auger to the normal Auger decay distorted by post-collision interaction has been observed and the resonating behavior of the valence photoelectron lines studied. Secondly, an atomic system, neon, in which excitation of doubly excited states and their subsequent decay to various accessible ionic states has been studied. Since these processes only occurs via inter-electron correlations, the many body dynamics of an atom can be probed, revealing relativistic effects, surprising in such a light atom. Angular distribution of the decay of the resonances to the parity unfavored continuum exhibits significant deviation from the LS coupling predictions.
Date: September 2, 2004
Creator: Kukk, E.; Wills, A. A.; Langer, B.; Bozek, J. D. & Berrah, N.
Object Type: Article
System: The UNT Digital Library
Applying Simple Technology Accomplishes Visual Inspection Challenges (open access)

Applying Simple Technology Accomplishes Visual Inspection Challenges

This paper discusses the successful implementation of simple video technologies at the Savannah River Site (SRS) to perform complex visual inspection, monitoring, and surveillance tasks. The constraints and challenges associated with remote viewing are discussed, and examples of applications are given. Work at SRS involves many radioactive, hazardous, and remote operations and activities, which require monitoring or surveillance. As well, many facilities, including tanks, cells, and pipelines, require inspections but are inaccessible to humans. SRTC supports SRS in these situations by applying simple remote viewing technologies to address these issues and accomplish monitoring and inspection goals.
Date: April 2, 2004
Creator: ROBINSON, CASANDRA
Object Type: Report
System: The UNT Digital Library
Assessment of Food Chain Pathway Parameters in Biosphere Models: Annual Progress Report for Fiscal Year 2004 (open access)

Assessment of Food Chain Pathway Parameters in Biosphere Models: Annual Progress Report for Fiscal Year 2004

This Annual Progress Report describes the work performed and summarizes some of the key observations to date on the U.S. Nuclear Regulatory Commission’s project Assessment of Food Chain Pathway Parameters in Biosphere Models, which was established to assess and evaluate a number of key parameters used in the food-chain models used in performance assessments of radioactive waste disposal facilities. Section 2 of this report describes activities undertaken to collect samples of soils from three regions of the United States, the Southeast, Northwest, and Southwest, and perform analyses to characterize their physical and chemical properties. Section 3 summarizes information gathered regarding agricultural practices and common and unusual crops grown in each of these three areas. Section 4 describes progress in studying radionuclide uptake in several representative crops from the three soil types in controlled laboratory conditions. Section 5 describes a range of international coordination activities undertaken by Project staff in order to support the underlying data needs of the Project. Section 6 provides a very brief summary of the status of the GENII Version 2 computer program, which is a “client” of the types of data being generated by the Project, and for which the Project will be providing training to …
Date: December 2, 2004
Creator: Napier, Bruce A.; Krupka, Kenneth M.; Fellows, Robert J.; Cataldo, Dominic A.; Valenta, Michelle M. & Gilmore, Tyler J.
Object Type: Report
System: The UNT Digital Library
Atmospheric Dispersion Analysis using MACCS2 (open access)

Atmospheric Dispersion Analysis using MACCS2

The Nuclear Regulatory Commission (NRC) Regulatory Guide 1.145 requires an evaluation of the offsite atmospheric dispersion coefficient, {Chi}/Q, as a part of the acceptance criteria in the accident analysis. In it, it requires in sequence computations of (1) the overall site 95th percentile {Chi}/Q, (2) the maximum of the sixteen sector 99.5th percentile {Chi}/Q, and (3) comparison and selection of the worst of the two values for reporting in the safety analysis report (SAR). In all cases, the site-specific meteorology and sector-specific site boundary distances are employed in the evaluation. There are sixteen 22.5-sectors, the nearest site boundary of which is determined within the 45-arc centered on each of the sixteen compass directions.
Date: February 2, 2004
Creator: Glaser, R. & Yang, J. M.
Object Type: Article
System: The UNT Digital Library
Atomic layer deposition of ZnO on ultra-low-density nanoporous silica aerogel monoliths (open access)

Atomic layer deposition of ZnO on ultra-low-density nanoporous silica aerogel monoliths

We report on atomic layer deposition of an {approx} 2-nm-thick ZnO layer on the inner surface of ultralow-density ({approx} 0.5% of the full density) nanoporous silica aerogel monoliths with an extremely large effective aspect ratio of {approx} 10{sup 5} (defined as the ratio of the monolith thickness to the average pore size). The resultant monoliths are formed by amorphous-SiO{sub 2}/wurtzite-ZnO nanoparticles which are randomly oriented and interconnected into an open-cell network with an apparent density of {approx} 3% and a surface area of {approx} 100 m{sup 2} g{sup -1}. Secondary ion mass spectrometry and high-resolution transmission electron microscopy imaging reveal excellent uniformity and crystallinity of ZnO coating. Oxygen K-edge and Zn L{sub 3}-edge soft x-ray absorption near-edge structure spectroscopy shows broadened O 2p- as well as Zn 4s-, 5s-, and 3d-projected densities of states in the conduction band.
Date: September 2, 2004
Creator: Kucheyev, S O; Biener, J; Wang, Y M; Baumann, T F; Wu, K J; van Buuren, T et al.
Object Type: Article
System: The UNT Digital Library
The BNL Super Neutrino Beam Project (open access)

The BNL Super Neutrino Beam Project

To determine the neutrino mixing amplitudes and phase accurately, as well as the CP violation parameters, a very long base line super neutrino beam facility is needed. This is possible due to the long distance and wideband nature of the neutrino beam for the observation of several oscillations from one species of the neutrino to the other [1,2]. BNL plans to upgrade the AGS proton beam from the current 0.14 MW to higher than 1.0 MW and beyond for such a neutrino facility which consists of three major subsystems. First is a 1.5 GeV superconducting linac to replace the booster as injector for the AGS, second is the performance upgrade for the AGS itself for the higher intensity and repetition rate, and finally is target and horn system for the neutrino production. The major contribution for the higher power is from the increase of the repetition rate of the AGS form 0.3 Hz to 2.5 Hz, with moderate increase from the intensity [3]. The design consideration to achieve high intensity and low losses for the linac and the AGS will be reviewed. The target horn design for high power operation and easy maintenance will also be presented.
Date: December 2, 2004
Creator: Weng, W. T. & Raparia, D.
Object Type: Article
System: The UNT Digital Library
Carbon Sequestration on Surface Mine Lands Quarterly Report (open access)

Carbon Sequestration on Surface Mine Lands Quarterly Report

The April-June 2004 quarter was dedicated to the establishment of monitoring systems for all the new research areas. Hydrology and water quality monitoring continues to be conducted on all areas as does weather data pertinent to the research. Studies assessing specific questions pertaining to carbon flux has been established and the invasion of the vegetation by small mammals is being quantified. The approval of two experimental practices associated with this research by the United States Office of Surface Mining was a major accomplishment during this period of time. These experimental practices will eventually allow for tree planting on long steep slopes with loose grading systems and for the use of loose dumped spoil on mountain top removal areas with no grading in the final layer of rooting material for tree establishment.
Date: August 2, 2004
Creator: Graves, Donald H.; Barton, Christopher; Sweigard, Richard & Warner, Richard
Object Type: Report
System: The UNT Digital Library
A cartesian grid embedded boundary method for the heat equationand poisson's equation in three dimensions (open access)

A cartesian grid embedded boundary method for the heat equationand poisson's equation in three dimensions

We present an algorithm for solving Poisson's equation and the heat equation on irregular domains in three dimensions. Our work uses the Cartesian grid embedded boundary algorithm for 2D problems of Johansen and Colella (1998, J. Comput. Phys. 147(2):60-85) and extends work of McCorquodale, Colella and Johansen (2001, J. Comput. Phys. 173(2):60-85). Our method is based on a finite-volume discretization of the operator, on the control volumes formed by intersecting the Cartesian grid cells with the domain, combined with a second-order accurate discretization of the fluxes. The resulting method provides uniformly second-order accurate solutions and gradients and is amenable to geometric multigrid solvers.
Date: November 2, 2004
Creator: Schwartz, Peter; Barad, Michael; Colella, Phillip & Ligocki, Terry
Object Type: Article
System: The UNT Digital Library
Cascade Line Testing for Hanford Single-Shell HLW Tank Closure (open access)

Cascade Line Testing for Hanford Single-Shell HLW Tank Closure

Two proof-of-principle large-scale tests were performed to simulate the flow of grout into Hanford single-shell HLW Tanks and into cascade lines which interconnect the HLW tanks. The goal of the testing was to determine whether the HLW tank grout can enter the cascade line and solidify prior to flowing into an adjacent tank. Two tests were performed as part of this task. The tests were conducted using the Phase 2 Structural Grout, SRG2, the structural grout mix that was used during scale-up testing last year.
Date: December 2, 2004
Creator: JOHN, HARBOUR
Object Type: Report
System: The UNT Digital Library
Cesium Ion Exchange Program at the Hanford River Protection Project Waste Treatment Plant (open access)

Cesium Ion Exchange Program at the Hanford River Protection Project Waste Treatment Plant

The River Protection Project - Hanford Tank Waste Treatment and Immobilization Plant will use cesium ion exchange to remove 137Cs from Low Activity Waste down to 0.3 Ci/m3 in the Immobilized LAW, ILAW product. The project baseline for cesium ion exchange is the elutable SuperLig, R, 644, SL-644, resin registered trademark of IBC Advanced Technologies, Inc., American Fork, UT or the Department of Energy approved equivalent. SL-644 is solely available through IBC Advanced Technologies. To provide an alternative to this sole-source resin supply, the RPP-WTP initiated a three-stage process for selection and qualification of an alternative ion exchange resin for cesium removal in the RPPWTP. It was recommended that resorcinol formaldehyde RF be pursued as a potential alternative to SL-644.
Date: December 2, 2004
Creator: CHARLES, NASH
Object Type: Article
System: The UNT Digital Library
Characterization of Adaptive Optics at Keck Observatory: Part Ii (open access)

Characterization of Adaptive Optics at Keck Observatory: Part Ii

None
Date: June 2, 2004
Creator: van Dam, M. A.; Mignant, D. L. & Macintosh, B. A.
Object Type: Article
System: The UNT Digital Library
Characterization of an Effective Cleaning Procedure for Aluminum Alloys: Surface Enhanced Raman Spectroscopy and Zeta Potential Analysis (open access)

Characterization of an Effective Cleaning Procedure for Aluminum Alloys: Surface Enhanced Raman Spectroscopy and Zeta Potential Analysis

We have developed a cleaning procedure for aluminum alloys for effective minimization of surface-adsorbed sub-micron particles and non-volatile residue. The procedure consists of a phosphoric acid etch followed by an alkaline detergent wash. To better understand the mechanism whereby this procedure reduces surface contaminants, we characterized the aluminum surface as a function of cleaning step using Surface Enhanced Raman Spectroscopy (SERS). SERS indicates that phosphoric acid etching re-establishes a surface oxide of different characteristics, including deposition of phosphate and increased hydration, while the subsequent alkaline detergent wash appears to remove the phosphate and modify the new surface oxide, possibly leading to a more compact surface oxide. We also studied the zeta potential of <5 micron pure aluminum and aluminum alloy 6061-T6 particles to determine how surface electrostatics may be affected during the cleaning process. The particles show a decrease in the magnitude of their zeta potential in the presence of detergent, and this effect is most pronounced for particles that have been etched with phosphoric acid. This reduction in magnitude of the surface attractive potential is in agreement with our observation that the phosphoric acid etch followed by detergent wash results in a decrease in surface-adsorbed sub-micron particulates.
Date: June 2, 2004
Creator: Cherepy, N J; Shen, T H; Esposito, A P & Tillotson, T M
Object Type: Article
System: The UNT Digital Library
Characterization of Environmental Stability of Pulsed Laser Deposited Oxide Ceramic Coatings (open access)

Characterization of Environmental Stability of Pulsed Laser Deposited Oxide Ceramic Coatings

A systematic investigation of candidate hydrogen permeation materials applied to a substrate using Pulsed Laser Deposition has been performed. The investigation focused on application of leading permeation-resistant materials types (oxide, carbides, and metals) on a stainless steel substrate. and evaluation of the stability of the applied coatings. Type 304L stainless steel substrates were coated with aluminum oxide, chromium oxide, and aluminum. Characterization of the coating-substrate system adhesion was performed using scratch adhesion testing and microindentation. Coating stability and environmental susceptibility were evaluated for two conditions-air at 350 degrees Celsius and Ar-H2 at 350 degrees Celsius for up to 100 hours. Results from this study have shown the pulsed laser deposition process to be an extremely versatile technology that is capable of producing a sound coating/substrate system for a wide variety of coating materials.
Date: March 2, 2004
Creator: Adams, Thad M.
Object Type: Article
System: The UNT Digital Library
Characterization of Supernate Samples from HLW Tanks 13H, 30H, 37H, 39H, 45F, 46F, and 49H (open access)

Characterization of Supernate Samples from HLW Tanks 13H, 30H, 37H, 39H, 45F, 46F, and 49H

This document presents work conducted in support of technical needs expressed, in part, by the Engineering, Procurement, and Construction Contractor for the Salt Waste Processing Facility (SWPF). The Department of Energy (DOE) requested that Savannah River National Laboratory (SRNL) analyze and characterize supernate waste from seven selected High Level Waste (HLW) tanks to allow classification of feed to be sent to the SWPF, verification that SWPF processes will be able to meet Saltstone Waste Acceptance Criteria (WAC), and updating of the Waste Characterization System (WCS) database. This document provides characterization data of samples obtained from Tanks 13H, 30H, 37H, 39H, 45F, 46F, and 49H and discusses results.Characterization of the waste tank samples involved several treatments and analysis at various stages of sample processing. These analytical stages included as-received liquid, post-dilution to 6.44 M sodium (target), post-acid digestion, post-filtration (at 3 filtration pore sizes), and after cesium removal using ammonium molybdophosphate (AMP). Results and observations obtained from testing include the following. All tanks will require cesium removal as well as treatment with Monosodium Titanate (MST) for 90Sr (Strontium) decontamination. A small filtration effect for 90Sr was observed for five of the seven tank wastes. No filtration effects were observed for Pu …
Date: July 2, 2004
Creator: STALLINGS, MARY
Object Type: Report
System: The UNT Digital Library
Chemical Kinetic Modeling of HMX and TATB Laser Ignition Tests (open access)

Chemical Kinetic Modeling of HMX and TATB Laser Ignition Tests

Recent laser ignition experiments on octahydro-1,3,5,7-tetranitro-1,3,5,7-terrazocine (HMX) and 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) subjected to laser fluxes ranging from 10 to 800 W/cm{sup 2} produced ignition times from seconds to milliseconds. Global chemical kinetic thermal decomposition models for HMX and TATB have been developed to calculate times to thermal explosion for experiments in the seconds to days time frame. These models are applied to the laser ignition experimental data in this paper. Excellent agreement was obtained for TATB, while the calculated ignition times were longer than experiment for HMX at lower laser fluxes. At the temperatures produced in the laser experiments, HMX melts. Melting generally increases condensed phase reaction rates so faster rates were used for three of the HMX reaction rates. This improved agreement with experiments at the lower laser fluxes but yielded very fast ignition at high fluxes. The calculated times to ignition are in reasonable agreement with the laser ignition experiments, and this justifies the use of these models for estimating reaction times at impact and shock ''hot spot'' temperatures.
Date: March 2, 2004
Creator: Tarver, C M
Object Type: Article
System: The UNT Digital Library
The CKM matrix and the unitarity triangle. Proceedings, workshop, Geneva, Switzerland, February 13-16, 2002 (open access)

The CKM matrix and the unitarity triangle. Proceedings, workshop, Geneva, Switzerland, February 13-16, 2002

This report contains the results of the Workshop on the CKM Unitarity Triangle that was held at CERN on 13-16 February 2002. There had been several Workshops on B physics that concentrated on studies at e{sup +}e{sup -} machines, at the Tevatron, or at LHC separately. Here we brought together experts of different fields, both theorists and experimentalists, to study the determination of the CKM matrix from all the available data of K, D, and B physics. The analysis of LEP data for B physics is reaching its end, and one of the goals of the Workshop was to underline the results that have been achieved at LEP, SLC, and CESR. Another goal was to prepare for the transfer of responsibility for averaging B physics properties, that has developed within the LEP community, to the present main actors of these studies, from the B factory and the Tevatron experiments. The optimal way to combine the various experimental and theoretical inputs and to fit for the apex of the Unitarity Triangle has been a contentious issue. A further goal of the Workshop was to bring together the proponents of different fitting strategies, and to compare their approaches when applied to the …
Date: April 2, 2004
Creator: Battaglia, M.; Buras, A. J.; Gambino, P. & Stocchi, A.
Object Type: Article
System: The UNT Digital Library
COMPARATIVE EVALUATION OF AMBIENT FINE PARTICULATE MATTER (PM2.5) DATA OBTAINED FROM URBAN AND RURAL MONITORING SITES ALONG THE UPPER OHIO RIVER VALLEY (open access)

COMPARATIVE EVALUATION OF AMBIENT FINE PARTICULATE MATTER (PM2.5) DATA OBTAINED FROM URBAN AND RURAL MONITORING SITES ALONG THE UPPER OHIO RIVER VALLEY

Advanced Technology Systems, Inc. (ATS), with Desert Research Institute (DRI) and Ohio University as subcontractors, was contracted by the NETL in September 1998 to manage the Upper Ohio River Valley Project (UORVP), with a goal of characterizing the ambient fine particulate in this region, including examination of urban/rural variations, correlations between PM{sub 2.5} and gaseous pollutants, and influences of artifacts on PM{sub 2.5} measurements in this region. Two urban and two rural monitoring sites were included in the UORVP. The four sites selected were all part of existing local and/or state air quality programs. One urban site was located in the Lawrenceville section of Pittsburgh, Pennsylvania at an air quality monitoring station operated by the Allegheny County Health Department. A second urban site was collocated at a West Virginia Division of Environmental Protection (WVDEP) monitoring station at the airport in Morgantown, West Virginia. One rural site was collocated with the Pennsylvania Department of Environmental Protection (PADEP) at a former NARSTO-Northeast site near Holbrook, Greene County, Pennsylvania. The other rural site was collocated at a site operated by the Ohio Environmental Protection Agency (OHEPA) and managed by the Ohio State Forestry Division in Gifford State Forest near Athens, Ohio. Previous Semi-Annual …
Date: March 2, 2004
Creator: Khosah, Robinson P. & Shimshock, John P.
Object Type: Report
System: The UNT Digital Library
Comparison of Wide-Bandgap Semiconductors for Power Electronics Applications (open access)

Comparison of Wide-Bandgap Semiconductors for Power Electronics Applications

Recent developmental advances have allowed silicon (Si) semiconductor technology to approach the theoretical limits of the Si material; however, power device requirements for many applications are at a point that the present Si-based power devices cannot handle. The requirements include higher blocking voltages, switching frequencies, efficiency, and reliability. To overcome these limitations, new semiconductor materials for power device applications are needed. For high power requirements, wide-bandgap semiconductors like silicon carbide (SiC), gallium nitride (GaN), and diamond, with their superior electrical properties, are likely candidates to replace Si in the near future. This report compares wide-bandgap semiconductors with respect to their promise and applicability for power applications and predicts the future of power device semiconductor materials.
Date: January 2, 2004
Creator: Ozpineci, B.
Object Type: Report
System: The UNT Digital Library
Compatibility of Alternative Chlorinated Solvent Source Treatment Strategies With Monitored Natural Attenuation (open access)

Compatibility of Alternative Chlorinated Solvent Source Treatment Strategies With Monitored Natural Attenuation

One of the most powerful and promising strategies for optimizing environmental restoration is the use of combinations of technologies rather than a single technology to reach the target cleanup goals. The U. S. Department of Energy (DOE) is actively working to clean up legacy contamination from its operations. Notably, DOE is responsible for the cleanup of many sites where the contamination includes chlorinated solvents (or chlorinated volatile organic contaminants (CVOCs)). At some sites, groundwater plumes containing CVOCs tend to become relatively large. Estimates for times to remediate sites often ranges up to 100s of years for these large plumes. As a result, the CVOC plumes are a concern to DOE, regulators and stakeholders. In response to this challenge, DOE initiated a project to ''provide the technical and policy support to facilitate implementing appropriate passive cleanup... leading to responsible completion of active remediation activities at high risk DOE waste sites.'' A combined approach benefits from the ability to match the invasiveness and aggressiveness of the remedial action to the amount of contamination and level of risk. This matching process is particularly important for recalcitrant contaminants such as chlorinated solvents. Highly contaminated areas justify more intense remediation action(s) while minimally contaminated areas …
Date: April 2, 2004
Creator: LOONEY, BRIANB.
Object Type: Report
System: The UNT Digital Library
Compressive and Tensile Stress in CdSe Semiconductor Quantum Dots (open access)

Compressive and Tensile Stress in CdSe Semiconductor Quantum Dots

Compressive and tensile stress in colloidal CdSe quantum dots (QDs) is examined using resonance Raman spectroscopy. We find that the dispersion of the longitudinal optical phonon mode with size does not follow theoretical calculations based on phonon confinement models. To account for these deviations, the presence of compressive or tensile stress in the QDs was proposed. We find that CdSe QDs prepared via a single source precursor (SSP) method exhibit compressive stress, while CdSe QDs prepared via high temperature lyothermal methods exhibit tensile stress. Evidence is provided that the SSP CdSe QDs stress is directly related to a surface effect.
Date: June 2, 2004
Creator: Meulenberg, R W; Jennings, T & Strouse, G F
Object Type: Article
System: The UNT Digital Library