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Chemical identity of atoms using core electron annihilations

Description: Positron annihilation spectroscopy is a sensitive probe for studying the electronic structure of defects in solids. The high momentum part of the Doppler-broadened annihilation spectra can be used to distinguish different elements. This is achieved by using a new two-detector coincidence system and by imposing appropriate kinematic cuts to exclude background events. The new setup improves the peak to background ratio in the annihilation spectrum to {approximately}10{sup 5}. As a result, the lin… more
Date: June 27, 1997
Creator: Asoka-Kumar, P.
Partner: UNT Libraries Government Documents Department
open access

Polarization effects in active Fresnel rhomb zig-zag slab amplifier

Description: The concept to use a slab as active element, working in zig-zag geometry, and also as Fresnel rhomb, seems to be rather attractive. However, in this case different depolarization effects in active element arc of crucial importance. We have carried out the estimations of depolarization effects arising both due to mechanical loading of an active element at its fastening and due to thermooptical distortions. To check up these rigid requirements to depolarization (0.1 % - 0.01 %) careful measuremen… more
Date: January 27, 1997
Creator: Bikmatov, R. G.; Chernyak, V. M.; Ignat`ev, L. P.; Kuznetsov, V. G.; Pergament, M. I.; Smirnov, R. V. et al.
Partner: UNT Libraries Government Documents Department
open access

Preliminary investigation of scale formation and fluid chemistry at the Dixie Valley Geothermal Field, Nevada

Description: The chemistry of geothermal, production, and injection fluids at the Dixie Valley Geothermal Field, Nevada, was characterized to address an ongoing scaling problem and to evaluate the effects of reinjection into the reservoir. Fluids generally followed mixing-dilution trends. Recharge to the Dixie Valley system apparently originates from local sources. The low-pressure brine and injection waters were saturated with respect to amorphous silica, which correlated with the ongoing scaling problem. … more
Date: June 27, 1997
Creator: Bruton, C. J.; Counce, D.; Bergfeld, D.; Goff, F.; Johnson, S. D.; Moore, J. N. et al.
Partner: UNT Libraries Government Documents Department
open access

Corrosion mechanisms of spent fuel under oxidizing conditions

Description: The release of {sup 99}Tc can be used as a reliable marker for the extent of spent oxide fuel reaction under unsaturated high-drip-rate conditions at 90{degrees}C. Evidence from leachate data and from scanning and transmission electron microscopy (SEM and TEM) examination of reacted fuel samples is presented for radionuclide release, potential reaction pathways, and the formation of alteration products. In the ATM-103 fuel, 0.03 of the total inventory of {sup 99}Tc is released in 3.7 years unde… more
Date: September 27, 1997
Creator: Finn, P.A.; Finch, R.; Buck, E. & Bates, J.
Partner: UNT Libraries Government Documents Department
open access

Scalable libraries for solving systems of nonlinear equations and unconstrained minimization problems.

Description: Developing portable and scalable software for the solution of large-scale optimization problems presents many challenges that traditional libraries do not adequately meet. Using object-oriented design in conjunction with other innovative techniques, they address these issues within the SNES (Scalable Nonlinear Equation Solvers) and SUMS (Scalable Unconstrained Minimization Solvers) packages, which are part of the multilevel PETSCs (Portable, Extensible Tools for Scientific computation) library.… more
Date: October 27, 1997
Creator: Gropp, W. D.; McInnes, L. C. & Smith, B. F.
Partner: UNT Libraries Government Documents Department
open access

Laboratory measurements of resonant contributions to Fe XXIV line emission

Description: A number of X-ray astronomy satellites are scheduled for launch in the next few years. The Advanced X-ray Astrophysics Facility (AXAF) is scheduled for launch in 1998, and the X-Ray Multi-mirror Mission (XMM) and Astro-E in 1999. These satellites will carry spectrometers with resolving powers in the Fe L-shell emission region over an order of magnitude greater than the spectrometers aboard A CA. Interpreting AXAF, XMM, Astro-E spectra will require atomic data at an accuracy significantly greate… more
Date: October 27, 1997
Creator: Gu, M.F.; Beiersdorfer, P.; Brown, G.V.; Kahn, S.M.; Liedahl, D.A.; Reed, K.J. et al.
Partner: UNT Libraries Government Documents Department
open access

Neutron study of fracton excitations in percolating antiferromagnets

Description: The authors report the results of an inelastic neutron scattering experiment on nearly-percolating Heisenberg antiferromagnets (RbMn{sub c}Mg{sub 1{minus}o}F{sub 3}), in which the Mn concentrations (C = 0.31, 0.34 and 0.39) are very close to the percolation threshold (c{sub p} = 0.312). A broad peak superimposed on Ising-cluster excitations was observed throughout the Brillouin zone. The intensity of a broad peak increased on approaching the percolation threshold. The origin of this broad peak … more
Date: June 27, 1997
Creator: Ikeda, H.; Takahashi, M.; Fernandez-Baca, J. A. & Nicklow, R. M.
Partner: UNT Libraries Government Documents Department
open access

Thermal contact resistance across a copper-silicon interface.

Description: An experimental setup to measure the thermal contact conductance across a silicon-copper (Si-Cu) interface is described, and the results obtained are presented. The resulting thermal contact resistance data are used in estimating the thermo-mechanical and optical performance of optical substrates cooled by interfaced copper cooling blocks. Several factors influence the heat transfer across solid interfaces. These include the material properties, interface pressure, flatness and roughness of the… more
Date: October 27, 1997
Creator: Khounsary, A.; Chojnowski, D.; Assoufid, L. & Worek, W. M.
Partner: UNT Libraries Government Documents Department
open access

UNT to work with six Metroplex elementary schools in national arts experiment designed to boost achievement

Description: An information release document in regards to six metroplex elementary schools plus thirty other schools nationwide were selected to participate as Arts Partner Schools in a $15 million experiment to reform education. The six schools will work with art educators at the University of North Texas, announced this month by the Annenberg Foundation, the Getty Education Institute for the Arts and the National Arts Education Consortium.
Date: March 27, 1997
Creator: LeMay, Nancy C.
Partner: UNT Libraries Special Collections
open access

Robotics and remote handling concepts for disposal of high-level nuclear waste

Description: This paper summarizes preliminary remote handling and robotic concepts being developed as part of the US Department of Energy's (DOE) Yucca Mountain Project. The DOE is currently evaluating the Yucca Mountain Nevada site for suitability as a possible underground geologic repository for the disposal of high level nuclear waste. The current advanced conceptual design calls for the disposal of more than 12,000 high level nuclear waste packages within a 225 km underground network of tunnels and emp… more
Date: April 27, 1997
Creator: McAffee, Douglas; Raczka, Norman & Schwartztrauber, Keith
Partner: UNT Libraries Government Documents Department
open access

Chamber Technology Concepts for Inertial Fusion Energy: Three Recent Examples

Description: The most serious challenges in the design of chambers for inertial fusion energy (IFE) are 1) protecting the first wall from fusion energy pulses on the order of several hundred megajoules released in the form of x rays, target debris, and high energy neutrons, and 2) operating the chamber at a pulse repetition rate of 5-10 Hz (i.e., re-establishing, the wall protection and chamber conditions needed for beam propagation to the target between pulses). In meeting these challenges, designers have … more
Date: February 27, 1997
Creator: Meier, W. R.; Moir, R. W. & Abdou, M. A.
Partner: UNT Libraries Government Documents Department
open access

Wake properties of a stripline beam kicker

Description: The transport of a high current relativistic electron beam in a stripline beam kicker is strongly dependent on the wake properties of the structure. The effect of the beam-induced fields on the steering of the beam must be determined for a prescribed trajectory within the structure. A 3-D time domain electromagnetic code is used to determine the wake fields and the resultant Lorentz force on the beam both for an ultra-relativistic electron beam moving parallel to the beamline axis as well as a … more
Date: May 27, 1997
Creator: Poole, B. R., LLNL
Partner: UNT Libraries Government Documents Department
open access

Bean Model and AC Losses in Bi{sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10}/Ag Tapes

Description: The Bean model is almost solely used to interpret ac losses in the powder-in-tube processed composite conductor, Bi{sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10}/Ag. In order to examine the limits of the applicability of the model, a detailed comparison was made between the values of critical current density J{sub c} for Bi(2223)/Ag tapes which were determined by standard four-probe-dc measurement, and which were deduced from the field dependence of the ac losses utilizing the model. A significant… more
Date: October 27, 1997
Creator: Suenaga, M.; Chiba, T.; Wiesmann, H. J. & Haldar, P.
Partner: UNT Libraries Government Documents Department
open access

Super Mirror Fabrication via Electroforming.

Description: As part of a project to develop methods of placing highly reflective multilayer coatings on the inside of Wolter I mirrors, we have been pursuing a program of measuring flat mirrors. These flats have been produced and examined at various stages of the process we plan to use to fabricate multilayer coated Wolter I mirrors. The flats were measured via optical profiler, AFM, (both done at Brookhaven National Lab) and X-ray reflection (done at the Argonne National Lab (ANL) Advanced Photon Source (… more
Date: July 27, 1997
Creator: Ulmer, M. P.; Altkorn, R.; Krieger, A.; Parsignault, D.; Chung, Y. W.; Wong, M. S. et al.
Partner: UNT Libraries Government Documents Department
open access

Defense against common mode failures in protection system design

Description: The introduction of digital instrumentation and control into reactor safety systems creates a heightened concern about common-mode failure. This paper discusses the concern and methods to cope with the concern. Common-mode failures have been a ``fact-of-life`` in existing systems. The informal introduction of defense-in-depth and diversity (D-in-D&D)-coupled with the fact that hardware common-mode failures are often distributed in time-has allowed systems to deal with past common-mode failures.… more
Date: August 27, 1997
Creator: Wyman, R. H. & Johnson, G. L.
Partner: UNT Libraries Government Documents Department
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