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Absorption Spectra of Broadened Sodium Resonance Lines in Presence of Rare Gases (open access)

Absorption Spectra of Broadened Sodium Resonance Lines in Presence of Rare Gases

The pressure broadening of alkali-metal lines is a fundamental problem with numerous applications. For example, the sodium resonance lines broadened by xenon are important in the production of broad spectra emitted in the HPS (High-Pressure Sodium) lamp and they potentially can be used for gas condition diagnostics. Broadened absorption lines of alkali-metal atoms are prominent in the optical spectra of brown dwarfs and understanding the broadening mechanism will help elucidate the chemical composition and atmospheric properties of those stars. The far-line wing spectra of sodium resonance lines broadened by rare gases are found to exhibit molecular characteristics such as satellites and hence the total absorption coefficients for vapors of Na atoms and perturbing rare gas atoms can be modeled as Na-RG (rare gas) molecular absorption spectra. In this work, using carefully chosen interatomic potentials for Na-RG molecules we carry out quantum-mechanical calculations for reduced absorption coefficients for vapors composed of Na-He, Na-Ar, and Na-Xe. Calculated spectra are compared to available experimental results and the agreement is good in the measured satellite positions and shapes.
Date: September 11, 2002
Creator: Chung, H-K; Shurgalin, M & Babb, J F
System: The UNT Digital Library
Analysis of Raster Scanning Damage and Conditioning Experiments (open access)

Analysis of Raster Scanning Damage and Conditioning Experiments

The raster scan technique is used for large optics damage tests and laser conditioning. We show that the ''effective area'' concept enables the possibility to compare various scanning schemes and to use raster scan experiments for NIF optics damage prediction. It is shown that the hexagonal lattice of laser beam imprints yields optimal use of each shot for most of the typically used parameters. The effects of beam fluence fluctuations and pointing inaccuracies on experiments are evaluated. To analyze raster scan conditioning experiments, we introduce the concept of ''effective dose'', i.e. total dose averaged over a unit cell of the scan lattice. This allows various scanning schemes to be compared quantitatively.
Date: October 11, 2002
Creator: Feit, M D & Rubenchik, A M
System: The UNT Digital Library
Applications of molecular spectroscopy methods to the study of metal dusting corrosion. (open access)

Applications of molecular spectroscopy methods to the study of metal dusting corrosion.

The interrogation of molecular vibrations in crystalline and amorphous solids by Raman and infrared spectroscopy methods can provide a wealth of revealing information concerning the composition, morphology, and spatial distribution of the extant phases. When these measurements are made in situ, such as during processes taking place in extreme environments (e.g., elevated temperature and pressure, oxidizing or reducing), where phases are evolving and/or dissipating, it is also possible to derive kinetic and mechanistic parameters. This paper summarizes the possibilities and limitations involved in using various types of Raman and infrared measurement methods to study metal dusting corrosion. Applications of conventional, microprobe, and imaging molecular spectroscopy approaches are discussed, with examples taken directly from metal dusting investigations. Some perspective is offered concerning the origin of observable condensed matter phonons emanating from the surface films and the carbon particles that accompany carbon dusting on various types of metals and alloys. Concepts for the systematic investigation of carbon dusting chemistry using molecular spectroscopy methods are presented.
Date: March 11, 2002
Creator: Maroni, V. A.
System: The UNT Digital Library
Barriers in developing and using simulation-based decision-support software (open access)

Barriers in developing and using simulation-based decision-support software

The need for proper consideration of energy-related performance aspects during building design has been identified since the energy crises of the 1970s. However, energy performance is still considered in a very small fraction of building projects, mainly because proper consideration is very expensive. It requires the use of computational software tools, which are not easy to learn and are time-consuming to use. Several attempts have been made to facilitate the use of energy simulation tools, but none has brought a significant increase in the consideration of energy performance. Energy related performance criteria are still considered only in a small fraction of buildings and, in most cases, after most of the building design is complete. This paper is focused on the main barriers in properly considering energy-related performance aspects in building decisions, which range from sociopolitical, to technical. The paper includes consideration of issues related to the general interest of the building industry in energy performance and environmental impact, current practice trends, modeling capabilities and performance of tools, compatibility of computational models and availability of data. Finally, a strategy for government-industry collaboration towards removing the barriers is presented, along with the main issues that need to be resolved towards potential implementation.
Date: March 11, 2002
Creator: Papamichael, Konstantinos & Pal, Vineeta
System: The UNT Digital Library
Beauty, charm and hyperon production at fixed-target experiments (open access)

Beauty, charm and hyperon production at fixed-target experiments

Over the years fixed-target experiments have performed numerous studies of particle production in strong interactions. The experiments have been performed with different types of beam particles of varying energies, and many different target materials. Since the physics of particle production is still not understood, ongoing research of phenomena that we observe as beauty, charm and strange-particle production is crucial if we are to gain an understanding of these fundamental processes. It is in this context that recent results from fixed-target experiments on beauty, charm, and hyperon production will be reviewed.
Date: December 11, 2002
Creator: Gottschalk, Erik
System: The UNT Digital Library
Bulk Materials Analysis Using High-Energy Positron Beams (open access)

Bulk Materials Analysis Using High-Energy Positron Beams

This article reviews some recent materials analysis results using high-energy positron beams at Lawrence Livermore National Laboratory. We are combining positron lifetime and orbital electron momentum spectroscopic methods to provide electron number densities and electron momentum distributions around positron annihilation sites. Topics covered include: correlation of positron annihilation characteristics with structural and mechanical properties of bulk metallic glasses, compositional studies of embrittling features in nuclear reactor pressure vessel steel, pore characterization in Zeolites, and positron annihilation characteristics in alkali halides.
Date: November 11, 2002
Creator: Glade, S C; Asoka-Kumar, P; Nieh, T G; Sterne, P A; Wirth, B D; Dauskardt, R H et al.
System: The UNT Digital Library
Catalytic autothermal reforming of hydrocarbon fuels for fuel cells. (open access)

Catalytic autothermal reforming of hydrocarbon fuels for fuel cells.

Fuel cell development has seen remarkable progress in the past decade because of an increasing need to improve energy efficiency as well as to address concerns about the environmental consequences of using fossil fuel for producing electricity and for propulsion of vehicles [1]. The lack of an infrastructure for producing and distributing H{sub 2} has led to a research effort to develop on-board fuel processing technology for reforming hydrocarbon fuels to generate H{sub 2} [2]. The primary focus is on reforming gasoline, because a production and distribution infrastructure for gasoline already exists to supply internal combustion engines [3]. Existing reforming technology for the production of H{sub 2} from hydrocarbon feedstocks used in large-scale manufacturing processes, such as ammonia synthesis, is cost prohibitive when scaled down to the size of the fuel processor required for transportation applications (50-80 kWe) nor is it designed to meet the varying power demands and frequent shutoffs and restarts that will be experienced during normal drive cycles. To meet the performance targets required of a fuel processor for transportation applications will require new reforming reactor technology developed to meet the volume, weight, cost, and operational characteristics for transportation applications and the development of new reforming catalysts …
Date: January 11, 2002
Creator: Krumpelt, M.; Krause, T.; Kopasz, J.; Carter, D. & Ahmed, S.
System: The UNT Digital Library
Chromium: A Stress-Processing Framework for Interactive Rendering on Clusters (open access)

Chromium: A Stress-Processing Framework for Interactive Rendering on Clusters

We describe Chromium, a system for manipulating streams of graphics API commands on clusters of workstations. Chromium's stream filters can be arranged to create sort-first and sort-last parallel graphics architectures that, in many cases, support the same applications while using only commodity graphics accelerators. In addition, these stream filters can be extended programmatically, allowing the user to customize the stream transformations performed by nodes in a cluster. Because our stream processing mechanism is completely general, any cluster-parallel rendering algorithm can be either implemented on top of or embedded in Chromium. In this paper, we give examples of real-world applications that use Chromium to achieve good scalability on clusters of workstations, and describe other potential uses of this stream processing technology. By completely abstracting the underlying graphics architecture, network topology, and API command processing semantics, we allow a variety of applications to run in different environments.
Date: January 11, 2002
Creator: Humphreys, G,; Houston, M.; Ng, Y.-R.; Frank, R.; Ahern, S.; Kirchner, P.D. et al.
System: The UNT Digital Library
Computationally mediated microscopy/microanalysis : the next frontier. (open access)

Computationally mediated microscopy/microanalysis : the next frontier.

Over the last three decades, microscopists and microanalysts have successfully developed, documented and exploited a large number of experimental techniques for the characterization of the morphology, crystallography, elemental, chemical and electronic structure of their samples. While the application of any of these now ''routine'' tools of microcharacterization remains the foundation of the work reported in the microscopy or microanalysis literature, it can be safely asserted that the technologically important problems of the next decade will demand an ever increasing sophistication in how we attack and solve the ensuing generation of problems using the resources we have at hand. It is also reasonably safe to say that while improving something as basic as the resolution of an instrument will generally facilitate studying a new class of materials, it will not fundamentally change how we work, it will only change what one studies. To truly create a new paradigm of how we, as experimentalists, enlist resources to solve vexing problems; we have to step back and consider what are all the limiting factors to employing our resources to their greatest utility, then we must come up with new ways of combining these resources to change the how we might tackle new problems.
Date: June 11, 2002
Creator: Zaluzec, N. J.
System: The UNT Digital Library
Conversion of Surplus Energetic Materials to Higher Value Products. A New Production of TATB (open access)

Conversion of Surplus Energetic Materials to Higher Value Products. A New Production of TATB

The progression of this project from a general demilitarization activity to the development of a new production of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) is described. There are four major synthetic routes to TATB. Only one of these routes has been used in the industrial production of TATB. There is a need to replace this route, which employs relatively harsh reaction conditions (elevated temperatures, strong acid) and a halocarbon starting material, with a less expensive and more environmentally friendly process. The Livermore process, which uses chemistry based on the vicarious nucleophilic substitution (VNS) of hydrogen and employment of relatively inexpensive feedstocks, is described and compared with other routes to TATB. Process development studies and the issue of TATB purification are also discussed.
Date: July 11, 2002
Creator: Mitchell, A. R.; Coburn, M. D.; Schmidt, R. D.; Pagoria, P. F. & Lee, G. S.
System: The UNT Digital Library
Current Status and Future Technical Challenges for Tokamak Magnets (open access)

Current Status and Future Technical Challenges for Tokamak Magnets

Magnet technology for fusion in the last decade has been focusing mostly on the development of magnets for tokamaks--the most advanced fusion concept at the moment. The largest and the most complex tokamak under development is ITER. To demonstrate adequate design approaches to large magnets for ITER and to develop industrial capabilities, two large model coils and three insert coils, all using full-scale conductor, were built and tested by the international collaboration during 1994-2002. The status of the magnet technology and directions of future developments are discussed in this paper.
Date: November 11, 2002
Creator: Martovetsky, N.; Minervini, J.; Okuno, K.; Salpiero, E. & Filatov, O.
System: The UNT Digital Library
Deflagration Behavior of PBXN-109 and Composition B at High Pressures and Temperatures (open access)

Deflagration Behavior of PBXN-109 and Composition B at High Pressures and Temperatures

We report deflagration rate measurements on PBXN-109 (RDWAVHTPB) and Composition B (RXDTTNThrvax) at pressures from 1,500-100,000 psi (10-700 MPa). This was done with the LLNL High Pressure Strand Burner, in which embedded wires are used to record the time-of-arrival of the burn front in the cylindrical sample as a function of pressure. The propellant samples are 6.4 mm in diameter and 6.4 mm long, with burn wires inserted between samples. Burning on the cylindrical surface is inhibited with an epoxy or polyurethane layer. With this direct measurement we do not have to account for product gas equation of state or heat losses in the system, and the burn wires allow detection of irregular burning. We report deflagration results for PBXN-109 as received, and also after it has been damaged by heating. The burn behavior of pristine PBXN-109 is very regular, and exhibits a reduction in pressure exponent from 1.32 to 0.85 at pressures above 20,000 psi (135 MPa). When PBXN-109 is thermally damaged by heating to 170-180 C, the deflagration rate is increased by more than a factor of 10. This appears to be a physical effect, as the faster burning may be explained by an increase in surface area. …
Date: March 11, 2002
Creator: Maienschein, J L & Wardell, J F
System: The UNT Digital Library
Detection of Materials of Interest to Non-Proliferation: A Novel Approach (open access)

Detection of Materials of Interest to Non-Proliferation: A Novel Approach

We propose the development of a novel detector that can locate and identify materials of interest to Nuclear Arms Non Proliferation. The device will combine nuclear acoustic resonance (NAR) with superconducting quantum interference device (SQUID) widely used in nuclear magnetic resonance (NMR), geophysics, nondestructive evaluations, and biomagnetism, to name only few. NAR works like NMR. Thus resonant absorption (of applied ultrasonic energy) by a nuclear spin system occurs when the ultrasonic frequency is equal to the appropriate frequency separations between the magnetic nuclear energy levels. Ultrasonic energy couples to the nuclear spin system via spin-phonon interaction. The resulting nuclear acoustic resonance can be detected via the changes in (a) ultrasonic attenuation, (b) ultrasonic velocity, (c) material magnetization, (d) or nuclear magnetic susceptibility, all of which carries ''intrinsic and unique signatures'' of the material under investigation. The device's sensitivity and penetration depth (into metals) will be enhanced by incorporating SQUID technology into the design. We will present the details of interaction physics and outline a plan of action needed to successfully transform the concepts into a practical detector.
Date: April 11, 2002
Creator: Ze, F; Tittmann, B R & Lehahan, P M
System: The UNT Digital Library
Determination of Primordial Metallicity and Mixing in the Type IIP Supernova 1993W (open access)

Determination of Primordial Metallicity and Mixing in the Type IIP Supernova 1993W

We present the results of a large grid of synthetic spectra and compare them to early spectroscopic observations of SN 1993W. This supernova was discovered close to its explosion date and at a recession velocity of 5400 km/s is located in the Hubble flow. We focus here on two early spectra that were obtained approximately 5 and 9 days after explosion. We parameterize the outer supernova envelope as a power-law density profile in homologous expansion. In order to extract information on the value of the parameters a large number of models was required. We show that very early spectra combined with detailed models can provide constraints on the value of the power law index, the ratio of hydrogen to helium in the surface of the progenitor, the progenitor metallicity and the amount of radioactive nickel mixed into the outer envelope of the supernova. The spectral fits reproduce the observed spectra exceedingly well. The spectral results combined with the early photometry predict that the explosion date was 4.7 {+-} 0.7 days before the first spectrum was obtained. The ability to obtain the metallicity from early spectra make SN IIP attractive probes of chemical evolution in the universe and by showing that …
Date: December 11, 2002
Creator: Baron, E.; Nugent, Peter E.; Branch, David; Hauschildt, Peter H.; Turatto, M. & Cappellaro, E.
System: The UNT Digital Library
Effects of landscape disturbance on ecohydrologic systems (open access)

Effects of landscape disturbance on ecohydrologic systems

None
Date: September 11, 2002
Creator: Newman, Brent D.; Allen, Craig Daniel; Breshears, David D. & Wilson, Cathy J.
System: The UNT Digital Library
Electron cloud instabilities in the Proton Storage Ring andSpallation Neutron Source (open access)

Electron cloud instabilities in the Proton Storage Ring andSpallation Neutron Source

Electron cloud instabilities in the Los Alamos ProtonStorage Ring (PSR) and those foreseen forthe Oak Ridge SpallationNeutron Source (SNS) are examined theoretically, numerically, andexperimentally.
Date: December 11, 2002
Creator: Blaskiewicz, M.; Furman, M. A.; Pivi, M. & Macek, R. J.
System: The UNT Digital Library
Examination of spent PWR fuel rods after 15 years in dry storage. (open access)

Examination of spent PWR fuel rods after 15 years in dry storage.

Virginia Power Surry Nuclear Station Pressurized Water Reactor (PWR) fuel was stored in a dry inert atmosphere Castor V/21 cask at the Idaho National Environmental and Engineering Laboratory (INEEL) for 15 years at peak cladding temperatures decreasing from about 350 to 150 C. Prior to the storage, the loaded cask was subjected to extensive thermal benchmark tests. The cask was opened to examine the fuel for degradation and to determine if it was suitable for extended storage. No rod breaches had occurred and no visible degradation or crud/oxide spallation were observed. Twelve rods were removed from the center of the T11 assembly and shipped from INEEL to the Argonne-West HFEF for profilometric scans. Four of these rods were punctured to determine the fission gas release from the fuel matrix and internal pressure in the rods. Three of the four rods were cut into five segments each, then shipped to the Argonne-East AGHCF for detailed examination. The test plan calls for metallographic examination of six samples from two of the rods, microhardness and hydrogen content measurements at or near the six metallographic sample locations, tensile testing of six samples from the two rods, and thermal creep testing of eight samples from …
Date: February 11, 2002
Creator: Einziger, R. E.; Tsai, H. C.; Billone, M. C. & Hilton, B. A.
System: The UNT Digital Library
Extreme Bal quasars from the Sloan Digital Sky Survey (open access)

Extreme Bal quasars from the Sloan Digital Sky Survey

The Sloan Digital Sky Survey has discovered a population of broad absorption line quasars with various extreme properties. Many show absorption from metastable states of Fe II with varying excitations; several objects are almost completely absorbed bluewards of Mg II; at least one shows stronger absorption from Fe III than Fe II, indicating temperatures T > 35000 K in the absorbing region; and one object even seems to have broad H{beta} absorption. Many of these extreme BALs are also heavily reddened, though ''normal'' BALs (particularly LoBALs) from SDSS also show evidence for internal reddening.
Date: October 11, 2002
Creator: al., Patrick B. Hall et
System: The UNT Digital Library
Fabrication and test of a racetrack magnet using pre-reacted Nb3Sn cable (open access)

Fabrication and test of a racetrack magnet using pre-reacted Nb3Sn cable

A racetrack magnet, using Nb{sub 3}Sn superconducting cable reacted before winding, has been fabricated and tested at Fermilab. It consists of two flat racetrack coils, connected in a common-coil configuration, separated by a 5 mm thick fiberglass plate. Synthetic oil was used to prevent sintering of the strands during the heat treatment. The coils were wound and vacuum impregnated in the mechanical structure. The turn-to-turn insulation, consisting of Kapton{reg_sign}and pre-impregnated fiberglass tapes as wide as the cable, was wound together with the bare cable in order to form a continuous inter-turn spacer. The coils were instrumented with voltage taps, temperature sensors, spot heaters and quench heaters. The maximum current achieved was 12675 A which is 78% of the short sample limit at 5.1 K (minimum temperature in the coil during 75 A/s ramp). Measurement of the temperature margin revealed a low degradation in the innermost turns. Quench performances at different temperatures and ramp rate effects have been measured and are presented and discussed.
Date: December 11, 2002
Creator: al., Giorgio Ambrosio et
System: The UNT Digital Library
Fermilab booster operational status: Beam loss and collimation (open access)

Fermilab booster operational status: Beam loss and collimation

Beam loss reduction and control challenges confronting the Fermilab Booster are presented in the context of the current operational status. In Summer 2002 the programmatic demand for 8 GeV protons will increase to 5E20/year. This is an order of magnitude above recent high rates and nearly as many protons as the machine has produced in its entire 30-year lifetime. Catastrophic radiation damage to accelerator components must be avoided, maintenance in an elevated residual radiation environment must be addressed, and operation within a tight safety envelope must be conducted to limit prompt radiation in the buildings and grounds around the Booster. Diagnostic and performance tracking improvements, enhanced orbit control, and a beam loss collimation/localization system are essential elements in the approach to achieving the expected level of performance and are described here.
Date: June 11, 2002
Creator: Webber, Robert C.
System: The UNT Digital Library
Fine-grain authorization for resource management in the Grid environment (open access)

Fine-grain authorization for resource management in the Grid environment

In this document we describe our work-in-progress for enabling fine-grain authorization of resource management. In particular we address the needs of Virtual Organizations (VOs) to enforce their own polices in addition to those of the resource owners 1.
Date: September 11, 2002
Creator: Keahey, K. & Welch, V.
System: The UNT Digital Library
Fireside corrosion of alloys for combustion power plants. (open access)

Fireside corrosion of alloys for combustion power plants.

A program on fireside corrosion is being conducted at Argonne National Laboratory to evaluate the performance of several structural alloys in the presence of mixtures of synthetic coal ash, alkali sulfates, and alkali chlorides. Candidate alloys are also exposed in a small-scale coal-fired combustor at the National Energy Technology Laboratory in Pittsburgh. Experiments in the present program, which addresses the effects of deposit chemistry, temperature, and alloy chemistry on the corrosion response of alloys, were conducted at temperatures in the range of 575-800 C for time periods up to {approx}1850 h. Alloys selected for the study included HR3C, 310TaN, HR120, SAVE 25, NF709, modified 800, 347HFG, and HCM12A. In addition, 800H clad with Alloy 671 was included in several of the exposures. Data were obtained on weight change, scale thickness, internal penetration, microstructural characteristics of corrosion products, mechanical integrity, and cracking of scales. Results showed that relationship of corrosion rates to temperature followed a bell-shaped curve, with peak rates at {approx}725 C, but the rate itself was dependent on the alloy chemistry. Several alloys showed acceptable rates in the sulfate-containing coal-ash environment; but NaCl in the deposit led to catastrophic corrosion at 650 and 800 C.
Date: June 11, 2002
Creator: Natesan, K.; Purohit, A. & Rink, D. L.
System: The UNT Digital Library
Generalizing Lifted Tensor-Product Wavelets to Irregular Polygonal Domains (open access)

Generalizing Lifted Tensor-Product Wavelets to Irregular Polygonal Domains

We present a new construction approach for symmetric lifted B-spline wavelets on irregular polygonal control meshes defining two-manifold topologies. Polygonal control meshes are recursively refined by stationary subdivision rules and converge to piecewise polynomial limit surfaces. At every subdivision level, our wavelet transforms provide an efficient way to add geometric details that are expanded from wavelet coefficients. Both wavelet decomposition and reconstruction operations are based on local lifting steps and have linear-time complexity.
Date: April 11, 2002
Creator: Bertram, M.; Duchaineau, M.A.; Hamann, B. & Joy, K.I.
System: The UNT Digital Library
Hierarchical Volume Representation with 3{radical}2 Subdivision and Trivariate B-Spline Wavelets (open access)

Hierarchical Volume Representation with 3{radical}2 Subdivision and Trivariate B-Spline Wavelets

Multiresolution methods provide a means for representing data at multiple levels of detail. They are typically based on a hierarchical data organization scheme and update rules needed for data value computation. We use a data organization that is based on what we call n{radical}2 subdivision. The main advantage of subdivision, compared to quadtree (n = 2) or octree (n = 3) organizations, is that the number of vertices is only doubled in each subdivision step instead of multiplied by a factor of four or eight, respectively. To update data values we use n-variate B-spline wavelets, which yields better approximations for each level of detail. We develop a lifting scheme for n = 2 and n = 3 based on the n{radical}2-subdivision scheme. We obtain narrow masks that could also provide a basis for view-dependent visualization and adaptive refinement.
Date: January 11, 2002
Creator: Linsen, L; Gray, JT; Pascucci, V; Duchaineau, M & Hamann, B
System: The UNT Digital Library