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Ignition of Aluminum Particles and Clouds

Description: Here we review experimental data and models of the ignition of aluminum (Al) particles and clouds in explosion fields. The review considers: (i) ignition temperatures measured for single Al particles in torch experiments; (ii) thermal explosion models of the ignition of single Al particles; and (iii) the unsteady ignition Al particles clouds in reflected shock environments. These are used to develop an empirical ignition model appropriate for numerical simulations of Al particle combustion in s… more
Date: April 7, 2010
Creator: Kuhl, A. L. & Boiko, V. M.
Partner: UNT Libraries Government Documents Department
open access

Bridging silyl groups in sigma-bond metathesis and [1, 2] shifts. An experimental and computational study of the reaction between cerium metallocenes and MeOSiMe3

Description: The reaction of Cp'2CeH (Cp' = 1,2,4-(Me3C)3C5H2 ) with MeOSiMe3 gives Cp'2CeOMe and HSiMe3 and the reaction of the metallacycle, Cp'[(Me3C)2C5H2C(Me) 2CH2]Ce, with MeOSiMe3 yields Cp'2CeOCH2SiMe3, formed from hypothetical Cp'2CeCH2OSiMe3 by a [1, 2] shift also known as a silyl-Wittig rearrangement. Although both cerium products are alkoxides, they are formed by different pathways. DFT calculations on the reaction of the model metallocene, Cp2CeH, and MeOSiMe3 show that the lowest energy pathwa… more
Date: April 21, 2010
Creator: Werkema, Evan; Yahia, Ahmed; Maron, Laurent; Eisenstein, Odile & Andersen, Richard
Partner: UNT Libraries Government Documents Department
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Dense Heterogeneous Continuum Model of Two-Phase Explosion Fields

Description: A heterogeneous continuum model is proposed to describe the dispersion of a dense Aluminum particle cloud in an explosion. Let {alpha}{sub 1} denote the volume fraction occupied by the gas and {alpha}{sub 2} the fraction occupied by the solid, satisfying the volume conservation relation: {alpha}{sub 1} + {alpha}{sub 2} = 1. When the particle phase occupies a non-negligible volume fraction (i.e., {alpha}{sub 2} > 0), additional terms, proportional to {alpha}{sub 2}, appear in the conservation… more
Date: April 7, 2010
Creator: Kuhl, A L & Bell, J B
Partner: UNT Libraries Government Documents Department
open access

High Power Picosecond Laser Pulse Recirculation

Description: We demonstrate a nonlinear crystal-based short pulse recirculation cavity for trapping the second harmonic of an incident high power laser pulse. This scheme aims to increase the efficiency and flux of Compton-scattering based light sources. We demonstrate up to 36x average power enhancement of frequency doubled sub-millijoule picosecond pulses, and 17x average power enhancement of 177 mJ, 10 ps, 10 Hz pulses.
Date: April 12, 2010
Creator: Shverdin, M Y; Jovanovic, I; Semenov, V A; Betts, S M; Brown, C; Gibson, D J et al.
Partner: UNT Libraries Government Documents Department
open access

Livermore Lab's giant laser system will bring star power to Earth

Description: In the 50 years since the laser was first demonstrated in Malibu, California, on May 16, 1960, Lawrence Livermore National Laboratory (LLNL) has been a world leader in laser technology and the home for many of the world's most advanced laser systems. That tradition continues today at LLNL's National Ignition Facility (NIF), the world's most energetic laser system. NIF's completion in March 2009 not only marked the dawn of a new era of scientific research - it could also prove to be the next big… more
Date: April 8, 2010
Creator: Moses, Edward
Partner: UNT Libraries Government Documents Department
open access

Preface to International Workshop on X-ray Mirror Design, Fabrication, and Metrology

Description: The International Workshop on X-Ray Mirror Design, Fabrication, and Metrology (IWXM), Osaka, Japan, was held as a satellite meeting of the Conference on Synchrotron Radiation Instrumentation (SRI) 2009, Melbourne, Australia, in October, 2009. The workshop was organized by a collaboration of scientists from a number of leading synchrotron institutions and universities around the World, such as Osaka University, SPring-8, KEK (Japan), ALS, APS and NSLS (USA), ELETTRA (Italy), ESRF, Synchrotron SO… more
Date: April 20, 2010
Creator: Yamauchi, Kazuto; Yashchuk, Valeriy V. & Cocco, Daniele
Partner: UNT Libraries Government Documents Department
open access

Quantifying exchange coupling in f-ion pairs using the diamagnetic substitution method

Description: One of the challenges in the chemistry of actinide and lanthanide (f-ion) is quantifying exchange coupling between f-ions. While qualitative information about exchange coupling may be readily obtained using the diamagnetic substitution approach, obtaining quantitative information is much more difficult. This article describes how exchange coupling may be quantified using the susceptibility of a magnetically isolated analog, as in the diamagnetic substitution approach, along with the anisotropy … more
Date: April 1, 2010
Creator: Lukens, Wayne W. & Walter, Marc D.
Partner: UNT Libraries Government Documents Department
open access

Splitting a C-O bond in dialkylethers with bis(1,2,4-tri-t-butylcyclopentadienyl) cerium-hydride does not occur by a sigma-bond metathesis pathway: a combined experimental and DFT computational study

Description: Addition of diethylether to [1,2,4(Me3C)3C5H2]2CeH, abbreviated Cp'2CeH, gives Cp'2CeOEt and ethane. Similarly, di-n-propyl- or di-n-butylether gives Cp'2Ce(O-n-Pr) and propane or Cp'2Ce(O-n-Bu) and butane, respectively. Using Cp'2CeD, the propane and butane contain deuterium predominantly in their methyl groups. Mechanisms, formulated on the basis of DFT computational studies, show that the reactions begin by an alpha or beta-CH activation with comparable activation barriers but only the beta-… more
Date: April 6, 2010
Creator: Werkema, Evan; Yahia, Ahmed; Maron, Laurent; Eisenstein, Odile & Andersen, Richard
Partner: UNT Libraries Government Documents Department
open access

Numerical errors in the presence of steep topography: analysis and alternatives

Description: It is well known in computational fluid dynamics that grid quality affects the accuracy of numerical solutions. When assessing grid quality, properties such as aspect ratio, orthogonality of coordinate surfaces, and cell volume are considered. Mesoscale atmospheric models generally use terrain-following coordinates with large aspect ratios near the surface. As high resolution numerical simulations are increasingly used to study topographically forced flows, a high degree of non-orthogonality is… more
Date: April 15, 2010
Creator: Lundquist, K A; Chow, F K & Lundquist, J K
Partner: UNT Libraries Government Documents Department
open access

ASPH modeling of Material Damage and Failure

Description: We describe our new methodology for Adaptive Smoothed Particle Hydrodynamics (ASPH) and its application to problems in modeling material failure. We find that ASPH is often crucial for properly modeling such experiments, since in most cases the strain placed on materials is non-isotropic (such as a stretching rod), and without the directional adaptability of ASPH numerical failure due to SPH nodes losing contact in the straining direction can compete with or exceed the physical process of failu… more
Date: April 30, 2010
Creator: Owen, J M
Partner: UNT Libraries Government Documents Department
open access

Applications of Photonuclear Physics for International Safeguards and Security

Description: Studies of nuclear resonance fluorescence based applications are presented. Important for these applications are data for isotopes such as {sup 239}Pu. Nuclear resonance fluorescence measurements of {sup 239}Pu were performed at the free electron laser facility at UC Santa Barbara using photons from a bremsstrahlung beam with an endpoint energies between 4.0 MeV and 5.5 MeV. Though no discrete states with significant confidence level were measured, we have excluded the region above 27(3) eV-bar… more
Date: April 16, 2010
Creator: Johnson, M. S.; Hall, J. M.; McNabb, D. P.; McFarland, J.; Norman, E.; Bertozzi, W. et al.
Partner: UNT Libraries Government Documents Department
open access

Importance of Full Coulomb Interactions for Understanding the Electronic Structure of Delta-Pu

Description: The solid-state properties of most elements are now well understood on the basis of quantum physics - with few exceptions, notably the element number 94, plutonium. Plutonium has six crystalline phases at ambient pressure, some of which are separated by unusual phase transitions with large discontinuities in volume, exhibit negative thermal expansion coefficients, or form exotic low-symmetry structures. The main challenge to explain these anomalous properties is that the characteristic ingredie… more
Date: April 1, 2010
Creator: Gorelov, E.; Kolorenc, J.; Wehling, T.; Hafermann, H.; Lichtenstein, A. I.; Shick, A. B. et al.
Partner: UNT Libraries Government Documents Department
open access

Structure of Oxide Nanoparticles in Fe-16Cr MA/ODS Ferritic Steel

Description: Oxide nanoparticles in Fe-16Cr ODS ferritic steel fabricated by mechanical alloying (MA) method have been examined using high-resolution transmission electron microscopy (HRTEM) techniques. A partial crystallization of oxide nanoparticles was frequently observed in as-fabricated ODS steel. The crystal structure of crystalline oxide particles is identified to be mainly Y{sub 4}Al{sub 2}O{sub 9} (YAM) with a monoclinic structure. Large nanoparticles with a diameter larger than 20 nm tend to be in… more
Date: April 6, 2010
Creator: Hsiung, L; Fluss, M & Kimura, A
Partner: UNT Libraries Government Documents Department
open access

Evolution of Static Physical Properties in Plutonium by Self-irradiation Damage

Description: The alpha-decay of plutonium leads to the age-related change in physical properties. This paper presents updated results of age-related effects on enriched and reference alloys measured from immersion density, dilatometry, and mechanical tests. After nearly 100 equivalent years of aging, both the immersion density and dilatometry show that the enriched alloys are decreasing in density by less than 0.02% per year and now exhibit a near linear density decrease, without void swelling. The tensile … more
Date: April 13, 2010
Creator: Chung, B W; Lema, K E & Hiromoto, D S
Partner: UNT Libraries Government Documents Department
open access

Fault Tolerance and Scaling in e-Science Cloud Applications: Observations from the Continuing Development of MODISAzure

Description: It can be natural to believe that many of the traditional issues of scale have been eliminated or at least greatly reduced via cloud computing. That is, if one can create a seemingly wellfunctioning cloud application that operates correctly on small or moderate-sized problems, then the very nature of cloud programming abstractions means that the same application will run as well on potentially significantly larger problems. In this paper, we present our experiences taking MODISAzure, our satell… more
Date: April 1, 2010
Creator: Li, Jie; Humphrey, Marty; Cheah, You-Wei; Ryu, Youngryel; Agarwal, Deb; Jackson, Keith et al.
Partner: UNT Libraries Government Documents Department
open access

Coarse Spaces by Algebraic Multigrid: Multigrid Convergence and Upscaled Error Estimates

Description: We give an overview of a number of algebraic multigrid methods targeting finite element discretization problems. The focus is on the properties of the constructed hierarchy of coarse spaces that guarantee (two-grid) convergence. In particular, a necessary condition known as 'weak approximation property', and a sufficient one, referred to as 'strong approximation property' are discussed. Their role in proving convergence of the TG method (as iterative method) and also on the approximation proper… more
Date: April 30, 2010
Creator: Vassilevski, P S
Partner: UNT Libraries Government Documents Department
open access

System Modeling of kJ-class Petawatt Lasers at LLNL

Description: Advanced Radiographic Capability (ARC) project at the National Ignition Facility (NIF) is designed to produce energetic, ultrafast x-rays in the range of 70-100 keV for backlighting NIF targets. The chirped pulse amplification (CPA) laser system will deliver kilo-Joule pulses at an adjustable pulse duration from 1 ps to 50 ps. System complexity requires sophisticated simulation and modeling tools for design, performance prediction, and comprehension of experimental results. We provide a brief o… more
Date: April 14, 2010
Creator: Shverdin, M Y; Rushford, M; Henesian, M A; Boley, C; Haefner, C; Heebner, J E et al.
Partner: UNT Libraries Government Documents Department
open access

Natural convection in tunnels at Yucca Mountain and impact on drift seepage

Description: The decay heat from radioactive waste that is to be disposed in the once proposed geologic repository at Yucca Mountain (YM) will significantly influence the moisture conditions in the fractured rock near emplacement tunnels (drifts). Additionally, large-scale convective cells will form in the open-air drifts and will serve as an important mechanism for the transport of vaporized pore water from the fractured rock in the drift center to the drift end. Such convective processes would also impact… more
Date: April 15, 2010
Creator: Halecky, N.; Birkholzer, J.T. & Peterson, P.
Partner: UNT Libraries Government Documents Department
open access

Upscaling solute transport in naturally fractured porous media with the continuous time random walk method

Description: Solute transport in fractured porous media is typically 'non-Fickian'; that is, it is characterized by early breakthrough and long tailing and by nonlinear growth of the Green function-centered second moment. This behavior is due to the effects of (1) multirate diffusion occurring between the highly permeable fracture network and the low-permeability rock matrix, (2) a wide range of advection rates in the fractures and, possibly, the matrix as well, and (3) a range of path lengths. As a consequ… more
Date: April 1, 2010
Creator: Geiger, S.; Cortis, A. & Birkholzer, J.T.
Partner: UNT Libraries Government Documents Department
open access

Space Charge Compensation (SSC) in Hadron Beams

Description: Longitudinal space-charge fields can generate substantial distortion of the rf-generated potential wells, fill the extraction kicker gap in the beam, affect the incoherent synchrotron tune spread, and have the potential for causing instability and longitudinal emittance growth. The net effective voltage per turn resulting from the space-charge self voltage and the ring inductive wall impedance ?0L is proportional to the slope of the beam current distribution e{beta}c {lambda}(s) and can be expr… more
Date: April 1, 2010
Creator: Shiltsev, V.
Partner: UNT Libraries Government Documents Department
open access

On the Performance of an Algebraic MultigridSolver on Multicore Clusters

Description: Algebraic multigrid (AMG) solvers have proven to be extremely efficient on distributed-memory architectures. However, when executed on modern multicore cluster architectures, we face new challenges that can significantly harm AMG's performance. We discuss our experiences on such an architecture and present a set of techniques that help users to overcome the associated problems, including thread and process pinning and correct memory associations. We have implemented most of the techniques in a … more
Date: April 29, 2010
Creator: Baker, A H; Schulz, M & Yang, U M
Partner: UNT Libraries Government Documents Department
open access

U.S. Solar Market Trends

Description: Grid-connected photovoltaic installations grew by 40% in 2009 compared with installations in 2008. California and New Jersey have the largest markets. Growth occurred in the residential and utility markets, but non-residential customer-sited installations did not change compared with the installations in 2008. Two small solar thermal electric plants were connected to the grid in 2009 with a combined capacity of 7 MW. The future prospects for solar thermal electric plants look bright, although d… more
Date: April 1, 2010
Creator: Sherwood, Larry
Partner: UNT Libraries Government Documents Department
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