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Oxidation and aging in U and Pu probed by spin-orbit sum rule analysis: indications for covalent metal-oxide bonds

Description: Transmission electron microscopy is used to acquire electron energy-loss spectra from phase-specific regions of Pu and U metal, PuO{sub 2} and UO{sub 2}, and aged, self-irradiated Pu metal. The N{sub 4,5} (4d {yields} 5f) spectra are analyzed using the spin-orbit sum rule. Our results show that the technique is sensitive enough to detect changes in the branching ratio of the white-line peaks between the metal and dioxide of both U and Pu. There is a small change in the branching ratio between d… more
Date: October 7, 2005
Creator: Moore, K.; van der Laan, G.; Haire, R.; Wall, M. & Schwartz, A.
Partner: UNT Libraries Government Documents Department
open access

Data Association and Bullet Tracking Algorithms for the Fight Sight Experiment

Description: Previous LLNL investigators developed a bullet and projectile tracking system over a decade ago. Renewed interest in the technology has spawned research that culminated in a live-fire experiment, called Fight Sight, in September 2005. The experiment was more complex than previous LLNL bullet tracking experiments in that it included multiple shooters with simultaneous fire, new sensor-shooter geometries, large amounts of optical clutter, and greatly increased sensor-shooter distances. This prese… more
Date: October 7, 2005
Creator: Breitfeller, E & Roberts, R
Partner: UNT Libraries Government Documents Department
open access

On the Micromechanisms of Shock-Induced Martensitic Transformation in Tantalum

Description: Shock-induced twinning and martensitic transformation in tantalum, which exhibits no solid-state phase transformation under hydrostatic pressures up to 100 GPa, have been further investigated. Since the volume fraction and size of twin and phase domains are small in scale, they are considered foming by heterogeneous nucleation that is catalyzed by high density lattice dislocations. A dynamic dislocation mechanism is accordingly proposed based upon the observation of dense dislocation clustering… more
Date: December 7, 2005
Creator: Hsiung, L L
Partner: UNT Libraries Government Documents Department
open access

High Pressure Structure of Half-Metallic CrO2

Description: Evidence for a structural phase transition from rutile {alpha}-CrO{sub 2} phase I (P4{sub 2}/mnm) to orthorhombic {beta}-CrO{sub 2} phase II (CaCl{sub 2}-like, Pnnm) is presented using angle-resolved synchrotron x-ray diffraction and high sensitivity confocal Raman spectroscopy. The transition to the CaCl{sub 2} structure, which appears to be second-order, occurs at 12 {+-} 3 GPa without any measurable discontinuity in volume, but is accompanied by an apparent increase in compressibility. Raman… more
Date: September 7, 2005
Creator: Maddox, B.; Yoo, C. S.; Kasinathan, D.; Pickett, W. E. & Scalettar, R. T.
Partner: UNT Libraries Government Documents Department
open access

Linear scaling first-principles molecular dynamics with plane waves accuracy

Description: We propose a real-space finite differences approach for accurate and unbiased O(N) Density Functional Theory molecular dynamics simulations based on a localized orbitals representation of the electronic structure. The discretization error can be reduced systematically by adapting the mesh spacing, while the orbitals truncation error decreases exponentially with the radius of the localization regions. For regions large enough, energy conservation in microcanonical simulations is demonstrated for… more
Date: October 7, 2005
Creator: Fattebert, J. & Gygi, F.
Partner: UNT Libraries Government Documents Department
open access

Averaging of Stochastic Equations for Flow and Transport in PorousMedia

Description: It is well known that at present exact averaging of theequations of flow and transport in random porous media have been realizedfor only a small number of special fields. Moreover, the approximateaveraging methods are not yet fully understood. For example, theconvergence behavior and the accuracy of truncated perturbation seriesare not well known; and in addition, the calculation of the high-orderperturbations is very complicated. These problems for a long time havestimulated attempts to find t… more
Date: January 7, 2005
Creator: Shvidler, Mark & Karasaki, Kenzi
Partner: UNT Libraries Government Documents Department
open access

Phenomenology treatment of magnetohydrodynamic turbulence with non-equipartition and anisotropy

Description: Magnetohydrodynamics (MHD) turbulence theory, often employed satisfactorily in astrophysical applications, has often focused on parameter ranges that imply nearly equal values of kinetic and magnetic energies and length scales. However, MHD flow may have disparity magnetic Prandtl number, dissimilar kinetic and magnetic Reynolds number, different kinetic and magnetic outer length scales, and strong anisotropy. Here a phenomenology for such ''non-equipartitioned'' MHD flow is discussed. Two cond… more
Date: February 7, 2005
Creator: Zhou, Y & Matthaeus, W H
Partner: UNT Libraries Government Documents Department
open access

Defining Electron Backscatter Diffraction Resolution

Description: Automated electron backscatter diffraction (EBSD) mapping systems have existed for more than 10 years [1,2], and due to their versatility in characterizing multiple aspects of microstructure, they have become an important tool in microscale crystallographic studies. Their increasingly widespread use however raises questions about their accuracy in both determining crystallographic orientations, as well as ensuring that the orientation information is spatially correct. The issue of orientation a… more
Date: February 7, 2005
Creator: El-Dasher, B S & Rollett, A D
Partner: UNT Libraries Government Documents Department
open access

String-Corrected Black Holes

Description: We investigate the geometry of four dimensional black hole solutions in the presence of stringy higher curvature corrections to the low energy effective action. For certain supersymmetric two charge black holes these corrections drastically alter the causal structure of the solution, converting seemingly pathological null singularities into timelike singularities hidden behind a finite area horizon. We establish, analytically and numerically, that the string-corrected two-charge black hole metr… more
Date: February 7, 2005
Creator: Hubeny, Veronika; Maloney, Alexander & Rangamani, Mukund
Partner: UNT Libraries Government Documents Department
open access

South Asian Summer Monsoon and Its Relationship with ENSO in the IPCC AR4 Simulations

Description: In this paper we use the extensive integrations produced for the IPCC Fourth Assessment Report (AR4) to examine the relationship between ENSO and the monsoon at interannual and decadal timescales. We begin with an analysis of the monsoon simulation in the 20th century integrations. Six of the 18 models were found to have a reasonably realistic representation of monsoon precipitation climatology. For each of these six models SST and anomalous precipitation evolution along the equatorial Pacific … more
Date: September 7, 2005
Creator: Annamalai, H.; Hamilton, K. & Sperber, K. R.
Partner: UNT Libraries Government Documents Department
open access

Hybrid FDTD Analysis for Periodic On-Chip Terahertz (THZ) Structures

Description: We present electromagnetic analysis and radiation efficiency calculations for on-chip terahertz (THz) structures based on a hybrid, finite-difference, time-domain (HFDTD) technique. The method employs the FDTD technique to calculate S-parameters for one cell of a periodic structure. The transmission ABCD matrix is then estimated and multiplied by itself n times to obtain the n-cell periodic structure ABCD parameters that are then converted back to S-parameters. Validation of the method is carri… more
Date: June 7, 2005
Creator: Hussein, Yasser A. & Spencer, James E.
Partner: UNT Libraries Government Documents Department
open access

Determination of Longitudinal Phase Space in SLAC Main Accelerator Beams

Description: In the E164 Experiment at that Stanford Linear Accelerator Center (SLAC), we drive plasma wakes for electron acceleration using 28.5 GeV bunches from the main accelerator. These bunches can now be made with an RMS length of 12 microns, and accurate direct measurement of their lengths is not feasible shot by shot. Instead, we use an indirect technique, measuring the energy spectrum at the end of the linac and comparing with detailed simulations of the entire machine. We simulate with LiTrack, a … more
Date: June 7, 2005
Creator: Barnes, C.; Decker, F. J.; Emma, P.; Hogan, M. J.; Iverson, R.; Krejcik, P. et al.
Partner: UNT Libraries Government Documents Department
open access

Simulation of HOM Leakage in the PEP-II Bellows

Description: An important factor that limits the PEP-II from operating at high currents is higher-order-mode (HOM) heating of the bellows. One source of HOM heating is the formation of trapped modes at the bellows as a result of geometry variation in the vacuum chamber, for example, the masking near the central vertex chamber. Another source comes from HOMs generated upstream that leak through the gaps between the bellows fingers. Modeling the fine details of the bellows and the surrounding geometry require… more
Date: June 7, 2005
Creator: Ng, C. K.; Folwell, N.; Ge, L.; Langton, J.; Lee, L. Q. & Novokhatski, A.
Partner: UNT Libraries Government Documents Department
open access

Field Ionization using a 28.5 GeV Electron Beam

Description: The E164/E164X plasma wakefield experiment studies beam-plasma interactions at the Stanford Linear Acceleration Center (SLAC). Due to SLAC's recent ability to variably compress bunches longitudinally from 650 {micro}m down to 20 {micro}m, the incoming beam is sufficiently dense to field ionize the neutral lithium (Li) vapor. The field ionization effects are characterized by the beams energy loss through the Li vapor column. Experiment results are presented.
Date: June 7, 2005
Creator: O'Connell, C.; Barnes, C. D.; Decker, F. J.; Hogan, M. J.; Iverson, R.; Krejcik, P. et al.
Partner: UNT Libraries Government Documents Department
open access

A parallel computer implementation of fast low-rank QR approximation of the Biot-Savart law

Description: In this paper we present a low-rank QR method for evaluating the discrete Biot-Savart law on parallel computers. It is assumed that the known current density and the unknown magnetic field are both expressed in a finite element expansion, and we wish to compute the degrees-of-freedom (DOF) in the basis function expansion of the magnetic field. The matrix that maps the current DOF to the field DOF is full, but if the spatial domain is properly partitioned the matrix can be written as a block mat… more
Date: November 7, 2005
Creator: White, D. A.; Fasenfest, B. J. & Stowell, M. L.
Partner: UNT Libraries Government Documents Department
open access

Surface Energy Anisotropy Effects on Pore-Channel Stability:Rayleigh Instabilities in m-Plane Sapphire

Description: Internal, high-aspect-ratio pore channels with their long axes parallel to the m(10{bar 1}0) plane of sapphire were generated through sequential application of photolithography, ion-beam etching and solid-state diffusion bonding. The axial orientation of channels within the m plane was systematically varied to sample a range of bounding-surface crystallographies. The morphologic evolution of these pore channels during anneals at 1700 C was recorded by postanneal optical microscopy. The developm… more
Date: September 7, 2005
Creator: Santala, Melissa K. & Glaeser, Andreas M.
Partner: UNT Libraries Government Documents Department
open access

A Summary of Recent Damage-Initiation Experiments on KDP Crystals

Description: We summarize recent investigations of the density and morphology of bulk damage in KDP crystals as a function of pulse duration, temporal profile, wavelength, and energy fluence. As previously reported by Runkel et al., we also find that the size of bulk damage sites varies roughly linearly with pulse duration for pulses between 1 ns and 9 ns. However this trend no longer applies at pulse durations below 1 ns. Experiments measuring the damage density and size distribution as a function of wavel… more
Date: November 7, 2005
Creator: Carr, C W; Feit, M D; Rubenchik, A M; Trenholme, J B & Spaeth, M L
Partner: UNT Libraries Government Documents Department
open access

CONTAINMENT EVALUATION OF BREACHED AL-SNF FOR CASK TRANSPORT

Description: Aluminum-based spent nuclear fuel (Al-SNF) from foreign and domestic research reactors (FRR/DRR) is being shipped to the Savannah River Site. To enter the U.S., the cask with loaded fuel must be certified to comply with the requirements in the Title 10 of the U.S. Code of Federal Regulations, Part 71. The requirements include demonstration of containment of the cask with its contents under normal and accident conditions. Al-SNF is subject to corrosion degradation in water storage, and many of t… more
Date: November 7, 2005
Creator: Vinson, D. W.; Sindelar, R. L. & Iyer, N. C.
Partner: UNT Libraries Government Documents Department
open access

SAES St 909 Getter Testing at the Savannah River National Laboratory

Description: Process gas tritium stripper technology has gone from catalytic oxidation followed by absorption on molecular sieve/zeolite beds to non-evaporate metal getter technology. SAES Getters produces a number of commercial getter products including St 909. St 909, a Zr-Mn-Fe alloy, is sold in pellet form, can decompose (''crack'') a number of process gas impurities, and retains lower levels of tritium than other getters. The performance of this material to remove process impurities, especially methane… more
Date: September 7, 2005
Creator: Klein, J. E. & Holder, J. E
Partner: UNT Libraries Government Documents Department
open access

Baryon-strangeness correlations: a diagnostic of stronglyinteracting matter

Description: The correlation between baryon number and strangeness elucidates the nature of strongly interacting matter. This diagnostic can be extracted theoretically from lattice QCD calculations and experimentally from event-by-event fluctuations. The analysis of present lattice results above the critical temperature severely limits the presence of q{bar q} bound states, thus supporting a picture of independent (quasi)quarks. Details may be found in [1].
Date: October 7, 2005
Creator: Koch, Volker; Majumder, Abhijit & Randrup, Jorgen
Partner: UNT Libraries Government Documents Department
open access

Closing in on a Short-Hard Burst Progenitor: Constraints From Early-Time Optical Imaging and Spectroscopy of a Possible Host Galaxy of GRB 050509b

Description: The localization of the short-duration, hard-spectrum gamma-ray burst GRB050509b by the Swift satellite was a watershed event. Never before had a member of this mysterious subclass of classic GRBs been rapidly and precisely positioned in a sky accessible to the bevy of ground-based follow-up facilities. Thanks to the nearly immediate relay of the GRB position by Swift, we began imaging the GRB field 8 minutes after the burst and have continued during the 8 days since. Though the Swift X-ray Tel… more
Date: June 7, 2005
Creator: Bloom, Joshua S.; Prochaska, J. X.; Pooley, D.; Blake, C. W.; Foley, R. J.; Jha, S. et al.
Partner: UNT Libraries Government Documents Department
open access

EXPERIENCE MONITORING FOR LOW LEVEL NEUTRON RADIATION AT THE H-CANYON AT THE SAVANNAH RIVER SITE

Description: Department of Energy contractors are required to monitor external occupational radiation exposure of an individual likely to receive an effective dose equivalent to the whole body of 0.1 rem (0.001sievert) or more in a year. For a working year of 2000 hours, this translates to a dose rate of 0.05 mrem/hr (0.5 {micro}Sv/hr). This can be a challenging requirement for neutron exposure because traditional surveys with shielded BF{sub 3} proportional counters are difficult to conduct, particularly a… more
Date: October 7, 2005
Creator: HOGUE, MARK
Partner: UNT Libraries Government Documents Department
open access

Strength of Multiple Parallel Biological Bonds

Description: Multivalent interactions play a critical role in a variety of biological processes on both molecular and cellular levels. We have used molecular force spectroscopy to investigate the strength of multiple parallel peptide-antibody bonds using a system that allowed us to determine the rupture forces and the number of ruptured bonds independently. In our experiments the interacting molecules were attached to the surfaces of the probe and sample of the atomic force microscope with flexible polymer … more
Date: December 7, 2005
Creator: Sulchek, T A; Friddle, R W & Noy, A
Partner: UNT Libraries Government Documents Department
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