Electronic structure of titania aerogels: Soft x-ray absorption study (open access)

Electronic structure of titania aerogels: Soft x-ray absorption study

None
Date: February 12, 2004
Creator: Kucheyev, S. O.; Van Buuren, T.; Baumann, T. F.; Satcher, J. H. Jr.; Willey, T. M.; Meulenberg, R. W. et al.
System: The UNT Digital Library
The MC&A Council at SSC RF-IPPE as a Coordinating Body for System Sustainability (open access)

The MC&A Council at SSC RF-IPPE as a Coordinating Body for System Sustainability

The State Scientific Center of the Russian Federation - Institute of Physics and Power Engineering's (SSC RF - IPPE) practice of nuclear material control and accounting (MC&A) has undergone significant changes during the period of cooperation with U.S. national laboratories from 1995 to the present. These changes corresponded with general changes of the Russian system of state control and accounting of nuclear materials resulting from the new Concept of the System for State Regulating and Control of Nuclear Materials (1996) and further regulatory documents, which were developed and implemented to take into account international experience in the MC&A [1]. During the upgrades phase of Russian-U.S. cooperation, an MC&A laboratory was specially created within the SSC RF - IPPE for the purpose of guiding the creation of the upgraded MC&A system, coordinating the activities of all units involved in the creation of this system, and implementing a unified technical policy during the transition period. After five years of operation of the MC&A laboratory and the implementation of new components for the upgraded MC&A system, it was decided that a greater degree of attention must be paid to the MC&A system's operation in addition to the coordination activities carried out by the …
Date: July 12, 2004
Creator: Poplavko, V.; Skorkin, V. & Myakishev, G.
System: The UNT Digital Library
DESIGN, CONSTRUCTION, AND STATUS OF ALL NIOBIUM SUPERCONDUCTING PHOTOINJECTOR AT BNL. (open access)

DESIGN, CONSTRUCTION, AND STATUS OF ALL NIOBIUM SUPERCONDUCTING PHOTOINJECTOR AT BNL.

We present here the design and construction of an all niobium superconducting RF injector to generate high average current, high brightness electron beam. A 1/2 cell superconducting cavity has been designed, built, and tested. A cryostat has been built to cool the cavity to {approx}2 K. The RF system can deliver up to 500 W at 1.3 GHz to the cavity. A mode-locked Nd:YVO{sub 4} laser, operating at 266 nm with 0.15 W average power, phase locked to the RF, will irradiate a laser cleaned Nb surface at the back wall of the cavity. Description of critical components and their status are presented in the paper. Based on DC measurements, QE of up to 10{sup 4} can be expected from such cavity.
Date: May 12, 2004
Creator: SRINIVASAN-RAO,T. BEN-ZVI,I. BURRILL,A. CITVER,G. ET AL.
System: The UNT Digital Library
Experimental Studies of Electron and Gas Sources in a Heavy-Ion Beam (open access)

Experimental Studies of Electron and Gas Sources in a Heavy-Ion Beam

None
Date: October 12, 2004
Creator: Molvik, A W; Cohen, R H; Friedman, A; Covo, M K; Lund, S M; Seidl, P A et al.
System: The UNT Digital Library
Development of a GIS Based Dust Dispersion Modeling System. (open access)

Development of a GIS Based Dust Dispersion Modeling System.

With residential areas moving closer to military training sites, the effects upon the environment and neighboring civilians due to dust generated by training exercises has become a growing concern. Under a project supported by the Strategic Environmental Research and Development Program (SERDP) of the Department of Defense, a custom application named DUSTRAN is currently under development that integrates a system of EPA atmospheric dispersion models with the ArcGIS application environment in order to simulate the dust dispersion generated by a planned training maneuver. This integration between modeling system and GIS application allows for the use of real world geospatial data such as terrain, land-use, and domain size as input by the modeling system. Output generated by the modeling system, such as concentration and deposition plumes, can then be displayed upon accurate maps representing the training site. This paper discusses the development of this integration between modeling system and Arc GIS application.
Date: August 12, 2004
Creator: Rutz, Frederick C.; Hoopes, Bonnie L.; Crandall, Duard W. & Allwine, K Jerry
System: The UNT Digital Library
Simulation of Spheromak Evolution and Energy Confinement (open access)

Simulation of Spheromak Evolution and Energy Confinement

Simulation results are presented that illustrate the formation and decay of a spheromak plasma driven by a coaxial electrostatic plasma gun, and that model the energy confinement of the plasma. The physics of magnetic reconnection during spheromak formation is also illuminated. The simulations are performed with the three-dimensional, time-dependent, resistive magnetohydrodynamic NIMROD code. The dimensional, simulation results are compared to data from the SSPX spheromak experiment at the Lawrence Livermore National Laboratory. The simulation results are tracking the experiment with increasing fidelity (e.g., improved agreement with measurements of the magnetic field, fluctuation amplitudes, and electron temperature) as the simulation has been improved in its representations of the geometry of the experiment (plasma gun and flux conserver), the magnetic bias coils, and the detailed time dependence of the current source driving the plasma gun, and uses realistic parameters. The simulations are providing a better understanding of the dominant physics in SSPX, including when the flux surfaces close and the mechanisms limiting the efficiency of electrostatic drive.
Date: November 12, 2004
Creator: Cohen, B; Hooper, E; Cohen, R; Hill, D; McLean, H; Wood, R et al.
System: The UNT Digital Library
Deflagration of HMX-Based Explosives at High Temperatures and Pressures (open access)

Deflagration of HMX-Based Explosives at High Temperatures and Pressures

We measure the deflagration behavior of energetic materials at extreme conditions (up to 520K and 1 GPa) in the LLNL High Pressure Strand Burner, thereby obtaining reaction rate data for prediction of violence of thermal explosions. The apparatus provides both temporal pressure history and flame time-of-arrival information during deflagration, allowing direct calculation of deflagration rate as a function of pressure. Samples may be heated before testing. Here we report the deflagration behavior of several HMX-based explosives at pressures of 10-600 MPa and temperatures of 300-460 K. We find that formulation details are very important to overall deflagration behavior. Formulations with high binder content (>15 wt%) deflagrate smoothly over the entire pressure range regardless of particle size, with a larger particle size distribution leading to a slower reaction. The deflagration follows a power law function with the pressure exponent being unity. Formulations with lower binder content ({le} 10% or less by weight) show physical deconsolidation at pressures over 100-200 MPA, with transition to a rapid erratic deflagration 10-100 times faster. High temperatures have a relatively minor effect on the deflagration rate until the HMX {beta} {yields} {delta} phase transition occurs, after which the deflagration rate increases by more than a factor …
Date: May 12, 2004
Creator: Maienschein, J. L.; Wardell, J. F.; DeHaven, M. R. & Black, C. K.
System: The UNT Digital Library
Optical Propagation Modeling for the National Ignition Facility (open access)

Optical Propagation Modeling for the National Ignition Facility

Optical propagation modeling of the National Ignition Facility has been utilized extensively from conceptual design several years ago through to early operations today. In practice we routinely (for every shot) model beam propagation starting from the waveform generator through to the target. This includes the regenerative amplifier, the 4-pass rod amplifier, and the large slab amplifiers. Such models have been improved over time to include details such as distances between components, gain profiles in the laser slabs and rods, transient optical distortions due to the flashlamp heating of laser slabs, measured transmitted and reflected wavefronts for all large optics, the adaptive optic feedback loop, and the frequency converter. These calculations allow nearfield and farfield predictions in good agreement with measurements.
Date: January 12, 2004
Creator: Williams, W. H.; Auerbach, J. M.; Henesian, M. A.; Jancaitis, K. S.; Manes, K. R.; Mehta, N. C. et al.
System: The UNT Digital Library
Thermal Expansion of AuIn2 (open access)

Thermal Expansion of AuIn2

The thermal expansion of AuIn{sub 2} gold is of great interest in soldering technology. Indium containing solders have been used to make gold wire interconnects at low soldering temperature and over time, AuIn{sub 2} is formed between the gold wire and the solder due to the high heat of formation and the high inter-metallic diffusion of indium. Hence, the thermal expansion of AuIn{sub 2} alloy in comparison with that of the gold wire and the indium-containing solder is critical in determining the integrity of the connection. We present the results of x-ray diffraction measurement of the coefficient of linear expansion of AuIn{sub 2} as well as the bulk expansion and density changes over the temperature range of 30 to 500 C.
Date: July 12, 2004
Creator: Saw, C K & Siekhaus, W J
System: The UNT Digital Library
The role of Hydrogen and Creep in Intergranular Stress Corrosion Cracking of Alloy 600 and Alloy 690 in PWR Primary Water Environments ? a Review (open access)

The role of Hydrogen and Creep in Intergranular Stress Corrosion Cracking of Alloy 600 and Alloy 690 in PWR Primary Water Environments ? a Review

Intergranular attack (IGA) and intergranular stress corrosion cracking (IGSCC) of Alloy 600 in PWR steam generator environment has been extensively studied for over 30 years without rendering a clear understanding of the essential mechanisms. The lack of understanding of the IGSCC mechanism is due to a complex interaction of numerous variables such as microstructure, thermomechanical processing, strain rate, water chemistry and electrochemical potential. Hydrogen plays an important role in all these variables. The complexity, however, significantly hinders a clearer and more fundamental understanding of the mechanism of hydrogen in enhancing intergranular cracking via whatever mechanism. In this work, an attempt is made to review the role of hydrogen based on the current understanding of grain boundary structure and chemistry and intergranular fracture of nickel alloys, effect of hydrogen on electrochemical behavior of Alloy 600 and Alloy 690 (e.g. the passive film stability, polarization behavior and open-circuit potential) and effect of hydrogen on PWSCC behavior of Alloy 600 and Alloy 690. Mechanistic studies on the PWSCC are briefly reviewed. It is concluded that further studies on the role of hydrogen on intergranular cracking in both inert and primary side environments are needed. These studies should focus on the correlation of the …
Date: July 12, 2004
Creator: Rebak, R B & Hua, F H
System: The UNT Digital Library
Preparing Successful ISTC Proposals for Radiological Monitoring Projects (open access)

Preparing Successful ISTC Proposals for Radiological Monitoring Projects

The United States Science Centers Program exists because expertise relevant to the production or use of weapons of mass destruction (WMD) exists in the states formerly comprising the Soviet Union. We seek to deter the transfer of that knowledge to people or governments that would use it to do harm or terrorize. Working through the Science & Technology Centers in Moscow and Kyiv, we promote peaceful collaborative science as an alternative to the proliferation of WMD expertise. In concert, we believe that increasing the prosperity of scientists helps reduce the potential attraction of working for rogue states and groups. Therefore, we aim to help scientific groups become successful at developing stable sources of income. Towards that end, we hope to guide former WMD scientists in the successful preparation of not only research proposals to the Science Centers, but future proposals seeking other funding sources as they join the competitive global scientific community.
Date: August 12, 2004
Creator: Surano, K; Scheland, M & Witow, J
System: The UNT Digital Library
Adaptive compensation of atmospheric turbulence utilizing an interferometric wave-front sensor and a high-resolution MEMS-based spatial light modulator (open access)

Adaptive compensation of atmospheric turbulence utilizing an interferometric wave-front sensor and a high-resolution MEMS-based spatial light modulator

Horizontal path correction of optical beam propagation presents a severe challenge to adaptive optics systems due to the short transverse coherence length and the high degree of scintillation incurred by propagation along these paths. The system presented operates with nearly monochromatic light. It does not require a global reconstruction of the phase, thereby eliminating issues with branch points and making its performance relatively unaffected by scintillation. The systems pixel count, 1024, and relatively high correction speed, in excess of 800 Hz, enable its use for correction of horizontal path beam propagation. We present results from laboratory and field tests of the system in which we have achieved Strehl ratios greater than 0.5.
Date: August 12, 2004
Creator: Baker, K.; Stappaerts, E.; Gavel, D.; Tucker, J.; Silva, D.; Wilks, S. et al.
System: The UNT Digital Library
Electroweak Supersymmetry with an Approximate U(1)_PQ (open access)

Electroweak Supersymmetry with an Approximate U(1)_PQ

A predictive framework for supersymmetry at the TeV scale is presented, which incorporates the Ciafaloni-Pomarol mechanism for the dynamical determination of the \mu parameter of the MSSM. It is replaced by (\lambda S), where S is a singlet field, and the axion becomes a heavy pseudoscalar, G, by adding a mass, m_G, by hand. The explicit breaking of Peccei-Quinn (PQ) symmetry is assumed to be sufficiently weak at the TeV scale that the only observable consequence is the mass m_G. Three models for the explicit PQ breaking are given; but the utility of this framework is that the predictions for all physics at the electroweak scale are independent of the particular model for PQ breaking. Our framework leads to a theory similar to the MSSM, except that \mu is predicted by the Ciafaloni-Pomarol relation, and there are light, weakly-coupled states in the spectrum. The production and cascade decay of superpartners at colliders occurs as in the MSSM, except that there is one extra stage of the cascade chain, with the next-to-LSP decaying to its"superpartner" and \tilde{s}, dramatically altering the collider signatures for supersymmetry. The framework is compatible with terrestrial experiments and astrophysical observations for a wide range of m_G and<s>. …
Date: May 12, 2004
Creator: Hall, L.J. & Watari, T.
System: The UNT Digital Library
Measurement of total ion flux in vacuum Arc discharges (open access)

Measurement of total ion flux in vacuum Arc discharges

A vacuum arc ion source was modified allowing us to collections from arc plasma streaming through an anode mesh. The mesh had ageometric transmittance of 60 percent, which was taken into account as acorrection factor. The ion current from twenty-two cathode materials wasmeasured at an arc current of 100 A. The ion current normalized by thearc current was found to depend on the cathode material, with valuesinthe range from 5 percent to 11 percent. The normalized ion current isgenerally greater for light elements than for heavy elements. The ionerosion rates were determined fromvalues of ion currentand ion chargestates, which were previously measured in the same experimental system.The ion erosion rates range from 12-94 mu g/C.
Date: April 12, 2004
Creator: Anders, Andre; Oks, Efim M.; Yushkov, Georgy Yu. & Brown, Ian G.
System: The UNT Digital Library
Increasing robustness of indirect drive capsule designs against short wavelength hydrodynamic instabilities (open access)

Increasing robustness of indirect drive capsule designs against short wavelength hydrodynamic instabilities

Target designs are described that are meant to achieve ignition on the National Ignition Facility. Simulations of recent indirect drive cryogenic capsule designs indicate dramatically reduced growth of short wavelength hydrodynamic instabilities, resulting from two changes in the designs. First, better optimization results from systematic mapping of the ignition target performance over the parameter space of ablator and DT-ice thickness combinations, using techniques developed by one of us (Herrmann). After the space is mapped with one-dimensional simulations, exploration of it with two-dimensional simulations quantifies the dependence of instability growth on target dimensions. Low modes and high modes grow differently in different regions of the space, allowing a trade-off of the two regimes of growth. Significant improvement in high-mode stability can be achieved, relative to previous designs, with only insignificant increase in low-mode growth. This procedure produces capsule designs that, in simulations, tolerate several times the surface roughness that could be tolerated by capsules optimized by older more heuristic techniques. Another significant reduction in instability growth, by another factor of several, is achieved with ablators with 'graded dopants.' In this type of capsule the mid-Z dopant, which is needed in the ablator to minimize x-ray preheat at the ablator-ice interface, is …
Date: November 12, 2004
Creator: Haan, S. W.; Herrmann, M. C.; Dittrich, T. R.; Fetterman, A. J.; Marinak, M. M.; Munro, D. et al.
System: The UNT Digital Library
Direct numerical simulations of type Ia supernovae flames II: The Rayleigh-Taylor instability (open access)

Direct numerical simulations of type Ia supernovae flames II: The Rayleigh-Taylor instability

A Type Ia supernova explosion likely begins as a nuclear runaway near the center of a carbon-oxygen white dwarf. The outward propagating flame is unstable to the Landau-Darrieus, Rayleigh-Taylor, and Kelvin-Helmholtz instabilities, which serve to accelerate it to a large fraction of the speed of sound. We investigate the Rayleigh-Taylor unstable flame at the transition from the flamelet regime to the distributed-burning regime, around densities of 10e7 gm/cc, through detailed, fully resolved simulations. A low Mach number, adaptive mesh hydrodynamics code is used to achieve the necessary resolution and long time scales. As the density is varied, we see a fundamental change in the character of the burning--at the low end of the density range the Rayleigh-Taylor instability dominates the burning, whereas at the high end the burning suppresses the instability. In all cases, significant acceleration of the flame is observed, limited only by the size of the domain we are able to study. We discuss the implications of these results on the potential for a deflagration to detonation transition.
Date: January 12, 2004
Creator: Bell, J. B.; Day, M. S.; Rendleman, C. A.; Woosley, S. E. & Zingale, M.
System: The UNT Digital Library
Microwave transitions and nonlinear magneto-optical rotation in anti-relaxation-coated cells (open access)

Microwave transitions and nonlinear magneto-optical rotation in anti-relaxation-coated cells

Using laser optical pumping, widths and frequency shifts are determined for microwave transitions between ground-state hyperfine components of {sup 85}Rb and {sup 87}Rb atoms contained in vapor cells with alkane anti-relaxation coatings. The results are compared with data on Zeeman relaxation obtained in nonlinear magneto-optical rotation (NMOR) experiments, a comparison important for quantitative understanding of spin-relaxation mechanisms in coated cells. By comparing cells manufactured over a forty-year period we demonstrate the long-term stability of coated cells, an important property for atomic clocks and magnetometers.
Date: August 12, 2004
Creator: Budker, Dmitry; Leo, Hollberg.; Kimball, Derek F.; J., Kitching; Szymon, Pustelny & Yashchuk, Valeriy V.
System: The UNT Digital Library
Energy Systems and Population Health (open access)

Energy Systems and Population Health

It is well-documented that energy and energy systems have a central role in social and economic development and human welfare at all scales, from household and community to regional and national (41). Among its various welfare effects, energy is closely linked with people s health. Some of the effects of energy on health and welfare are direct. With abundant energy, more food or more frequent meals can be prepared; food can be refrigerated, increasing the types of food items that are consumed and reducing food contamination; water pumps can provide more water and eliminate the need for water storage leading to contamination or increased exposure to disease vectors such as mosquitoes or snails; water can be disinfected by boiling or using other technologies such as radiation. Other effects of energy on public health are mediated through more proximal determinants of health and disease. Abundant energy can lead to increased irrigation, agricultural productivity, and access to food and nutrition; access to energy can also increase small-scale income generation such as processing of agricultural commodities (e.g., producing refined oil from oil seeds, roasting coffee, drying and preserving fruits and meats) and production of crafts; ability to control lighting and heating allows education …
Date: April 12, 2004
Creator: Ezzati, Majid; Bailis, Rob; Kammen, Daniel M.; Holloway, Tracey; Price, Lynn; Cifuentes, Luis A. et al.
System: The UNT Digital Library
Recent enhancements to the MARS15 code (open access)

Recent enhancements to the MARS15 code

The MARS code is under continuous development and has recently undergone substantial improvements that further increase its reliability and predictive power in numerous shielding, accelerator, detector and space applications. The major developments and new features of the MARS15 (2004) version described in this paper concern an extended list of elementary particles and arbitrary heavy ions and their interaction cross-sections, inclusive and exclusive nuclear event generators, module for modeling particle electromagnetic interactions, enhanced geometry and histograming options, improved MAD-MARS Beam Line Builder, enhanced Graphical-User Interface, and an MPI-based parallelization of the code.
Date: May 12, 2004
Creator: al., Nikolai V. Mokhov et
System: The UNT Digital Library
Toward green systems for cleanrooms: Energy efficient fan-filter units (open access)

Toward green systems for cleanrooms: Energy efficient fan-filter units

The paper presents results of laboratory-measured performance of fan-filter units (FFUs) used for cleanrooms. A total of twenty FFUs collected from the market were tested, including thirteen 1220 mm x 610 mm (or 4 ft x 2 ft) units and seven 1220 mm x 1220 mm (or 4 ft x 4 ft) units. The paper concludes that there are wide variations in FFUs energy performance, and that there are opportunities in improving energy efficiency and lowering operating costs of FFUs. Furthermore, the paper suggests the benefits of having a uniform method for testing and reporting FFU performance. Such a testing method and recommended practice guideline is under development, with heavy input from FFU suppliers, users, and independent institutions that include Lawrence Berkeley National Laboratory (LBNL), Industrial Technology Research Institute (ITRI), and Institute of Environmental Sciences and Technology (IEST). An integrated approach with the participation from designers, suppliers, users, and utility companies can help to identify energy-efficient FFUs that are required for many cleanroom applications.
Date: July 12, 2004
Creator: Jeng, Ming-Shan; Xu, Tengfang & Lan, Chao-Ho
System: The UNT Digital Library
Future World Energy Constraints and the Direction for Solutions (open access)

Future World Energy Constraints and the Direction for Solutions

This paper was originally written in response to the concern that rising levels of CO2 in the atmosphere caused by burning of fossil fuels will ultimately contribute to global warming. Now we are beginning to see evidence of coming problems in the supply of fuels for transportation. This paper describes the benefits of adequate energy supply and the problems of future energy supply. Partial solutions are suggested for immediate application as well as longer term solutions to address both of these concerns. To evaluate the situation and solutions we must understand: (1) how much primary energy is currently used world-wide and might be needed in 2100, (2) how important energy is to the welfare of people, (3) the forms of energy sources and end uses and (4) where new sources may come from. The major portion of world primary energy demand is provided by fossil fuels. This portion dropped from 93% in 1970 to 85% in 1995, mainly because of the increased use of nuclear energy. How ever, since the mid-1990s fossil fuels have maintained their 85% share of world energy supply. The importance of the relationship between per capita energy consumption and per capita income for the world is …
Date: September 12, 2004
Creator: Lightfoot, H.D.
System: The UNT Digital Library
Towards a precision measurement of theta13 with reactor neutrinos: Initiatives in the United States (open access)

Towards a precision measurement of theta13 with reactor neutrinos: Initiatives in the United States

Recent experimental results have provided unambiguous evidence that neutrinos have a small but finite mass and mix from one type into another. The phenomenon of neutrino mixing is characterized by the coupling between the neutrino flavor (nu e,mu,tau) and mass eigenstates (nu 1,2,3) and the associated mixing angles. Previous neutrino oscillation experiments have determined two of the three mixing angles in the neutrino mixing matrix, U MNSP. Using multiple neutrino detectors placed at different distances from a nuclear power plant, a future reactor neutrino experiment has the potential to discover and measure the coupling of the electron neutrino flavor to the third mass eigenstate, Ue3, the last undetermined element of the neutrino mixing matrix. In this paper we describe recent efforts in the US towards a next-generation experiment to measure theta13 with reactor neutrinos.
Date: September 12, 2004
Creator: Heeger, Karsten M.
System: The UNT Digital Library
Parallelizing the MARS15 Code with MPI for shielding applications (open access)

Parallelizing the MARS15 Code with MPI for shielding applications

The MARS15 Monte Carlo code capabilities to deal with time-consuming deep penetration shielding problems and other computationally tough tasks in accelerator, detector and shielding applications, have been enhanced by a parallel processing option. It has been developed, implemented and tested on the Fermilab Accelerator Division Linux cluster and network of Sun workstations. The code uses MPI. It is scalable and demonstrates good performance. The general architecture of the code, specific uses of message passing, and effects of a scheduling on the performance and fault tolerance are described.
Date: May 12, 2004
Creator: Mokhov, Mikhail A. Kostin and Nikolai V.
System: The UNT Digital Library
Volume-limited SDSS/First quasars and the radio dichotomy (open access)

Volume-limited SDSS/First quasars and the radio dichotomy

Much evidence has been presented in favor of and against the existence of two distinct populations of quasars, radio-loud and radio-quiet. The SDSS differs from earlier optically selected quasar surveys in the large number of quasars and the targeting of FIRST radio source counterparts as quasar candidates. This allows a qualitatively different approach of constructing a series of samples at different redshifts which are volume-limited with respect to both radio and optical luminosity. This technique avoids any biases from the strong evolution of quasar counts with redshift and potential redshift-dependent selection effects. We find that optical and radio luminosities of quasars detected in both SDSS and FIRST are not well correlated within each redshift shell, although the fraction of radio detections among optically selected quasars remains roughly constant at 10% for z {le} 3.2. The distribution in the luminosity-luminosity plane does not appear to be strongly bimodal. The optical luminosity function is marginally flatter at higher radio luminosities.
Date: March 12, 2004
Creator: Jester, Sebastian & Kron, R.G.
System: The UNT Digital Library