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Electron emission and defect formation in the interaction of slow,highly charged ions with diamond surfaces (open access)

Electron emission and defect formation in the interaction of slow,highly charged ions with diamond surfaces

We report on electron emission and defect formation in theinteraction between slow (v~;0.3 vBohr) highly charged ions (SHCI) withinsulating (type IIa) and semiconducting (type IIb) diamonds. Electronemission induced by 31Pq+ (q=5 to 13), and 136Xeq+ (q=34 to 44) withkinetic energies of 9 kVxq increase linearly with the ion charge states,reaching over 100 electrons per ion for high xenon charge states withoutsurface passivation of the diamond with hydrogen. Yields from bothdiamond types are up to a factor of two higher then from reference metalsurfaces. Crater like defects with diameters of 25 to 40 nm are formed bythe impact of single Xe44+ ions. High secondary electron yields andsingle ion induced defects enable the formation of single dopant arrayson diamond surfaces.
Date: May 31, 2006
Creator: Sideras-Haddad, E.; Shrivastava, S.; Rebuli, D.B.; Persaud, A.; Schneider, D.H. & Schenkel, T.
System: The UNT Digital Library
A geoneutrino experiment at Homestake (open access)

A geoneutrino experiment at Homestake

A significant fraction of the 44 TW of heat dissipation from the Earth's interior is believed to originate from the decays of terrestrial uranium and thorium. The only estimates of this radiogenic heat, which is the driving force for mantle convection, come from Earth models based on meteorites, and have large systematic errors. The detection of electron antineutrinos produced by these uranium and thorium decays would allow a more direct measure of the total uranium and thorium content, and hence radiogenic heat production in the Earth. They discuss the prospect of building an electron antineutrino detector approximately 700 m{sup 3} in size in the Homestake mine at the 4850 feet level. This would allow us to make a measurement of the total uranium and thorium content with a statistical error less than the systematic error from the current knowledge of neutrino oscillation parameters. It would also allow us to test the hypothesis of a naturally occurring nuclear reactor at the center of the Earth.
Date: May 31, 2006
Creator: Tolich, Nikolai; Chan, Yuen-Dat; Currat, Charles A.; Decowski, M.Patrick; Fujikawa, Brian K.; Henning, Reyco et al.
System: The UNT Digital Library
Analytic Methods for Minimizing Hohlraum Wall Losses and the Problem of Oxygen Contamination (open access)

Analytic Methods for Minimizing Hohlraum Wall Losses and the Problem of Oxygen Contamination

The authors wish to minimize ICF hohlraum wall loss, E, in order to operate the National Ignition Facility (NIF) far from its damage threshold and still provide the capsule with the drive it requires to reach ignition. In this paper they consider cocktail walls--a mixture of materials that can improve on the conventional pure Au walls. they use Hammer and Rosen (HR) (2003) which solved the radiation diffusion/hydrodynamics problem analytically. They take Au's T, {rho} dependencies of {kappa} (opacity) and e (specific heat) to be: {kappa} = {kappa}{sub 0} {rho}{sup 0.2}/T{sup 1.5} and e = e{sub 0}T{sup 1.6}/{rho}{sup 0.14}.
Date: May 31, 2006
Creator: Rosen, M. D.
System: The UNT Digital Library
Modeling Temporal-Spatial Earthquake and Volcano Clustering at Yucca Mountain, Nevada (open access)

Modeling Temporal-Spatial Earthquake and Volcano Clustering at Yucca Mountain, Nevada

The proposed national high-level nuclear repository at Yucca Mountain is close to Quaternary faults and cinder cones. The frequency of these events is low, with indications of spatial and temporal clustering, making probabilistic assessments difficult. In an effort to identify the most likely intrusion sites, we based a 3D finite element model on the expectation that faulting and basalt intrusions are primarily sensitive to the magnitude and orientation of the least principal stress in extensional terranes. We found that in the absence of fault slip, variation in overburden pressure caused a stress state that preferentially favored intrusions at Crater Flat. However, when we allowed central Yucca Mountain faults to slip in the model, we found that magmatic clustering was not favored at Crater Flat or in the central Yucca Mountain block. Instead, we calculated that the stress field was most encouraging to intrusions near fault terminations, consistent with the location of the most recent volcanism at Yucca Mountain, the Lathrop Wells cone. We found this linked fault and magmatic system to be mutually reinforcing in the model in that dike inflation favored renewed fault slip.
Date: May 31, 2006
Creator: Parsons, T.; Thompson, G.A. & Cogbill, A.H.
System: The UNT Digital Library
The Value of Distributed Generation under Different TariffStructures (open access)

The Value of Distributed Generation under Different TariffStructures

Distributed generation (DG) may play a key role in a modern energy system because it can improve energy efficiency. Reductions in the energy bill, and therefore DG attractiveness, depend on the electricity tariff structure; a system created before widespread adoption of distributed generation. Tariffs have been designed to recover costs equitably amongst customers with similar consumption patterns. Recently, electric utilities began to question the equity of this electricity pricing structure for standby service. In particular, the utilities do not feel that DG customers are paying their fair share of transmission and distribution costs - traditionally recovered through a volumetric($/kWh) mechanism - under existing tariff structures. In response, new tariff structures with higher fixed costs for DG have been implemented in New York and in California. This work analyzes the effects of different electricity tariff structures on DG adoption. First, the effects of the new standby tariffs in New York are analyzed in different regions. Next generalized tariffs are constructed, and the sensitivity to varying levels of the volumetric and the demand ($/kW, i.e. maximum rate) charge component are analyzed on New York's standard and standby tariff as well as California's standby tariff. As expected, DG profitability is reduced with standby …
Date: May 31, 2006
Creator: Firestone, Ryan; Magnus Maribu, Karl & Marnay, Chris
System: The UNT Digital Library
New Experimental Measurements of Electron Clouds in Ion Beams with Large Tune Depression (open access)

New Experimental Measurements of Electron Clouds in Ion Beams with Large Tune Depression

None
Date: May 31, 2006
Creator: Molvik, A W; Covo, M K; Friedman, A; Cohen, R; Lund, S M; Sharp, W et al.
System: The UNT Digital Library
Analytic Expressions for Minimizing Hohlraum Wall Losses (open access)

Analytic Expressions for Minimizing Hohlraum Wall Losses

We apply our recent analytic solutions to the radiation diffusion equation to problems of interest for ICF hohlraums. The solutions provide quantitative values for absorbed energy, which are of use for generating a desired radiation temperature vs. time within the hohlraum. In particular we use analytic fits to the Rosseland mean opacity and to the specific heat of combinations of materials (''cocktails'') designed to maximize the former while minimizing the latter. By doing so we find good agreement with numerical simulations and with experimental results. In particular we find that the wall loss savings of cocktails vs. the standard gold walled hohlraums have both pulse-length and temperature dependencies. Due to those dependencies we predict that NIF cocktail hohlraums will perform better than present day cocktail experiments. In addition, we apply our solutions to finding that density of foam hohlraum walls which minimizes wall loss by being of sufficiently low density to be supersonic, thus reducing kinetic energy losses, yet high enough density to not unduly suffer from enhanced specific heat capacity.
Date: May 31, 2006
Creator: Rosen, M. D.
System: The UNT Digital Library
Where Water is Oxidized to Dioxygen: Structure of thePhotosynthetic Mn4Ca Cluster (open access)

Where Water is Oxidized to Dioxygen: Structure of thePhotosynthetic Mn4Ca Cluster

Oxidation of water to dioxygen is catalyzed withinphotosystem II (PSII) by a Mn4Ca cluster, the structure of which remainselusive. Polarized extended X-ray absorption fine structure (EXAFS)measurements on PSII single crystals constrain the Mn4Ca cluster geometryto a set of three similar high-resolution structures. Combining polarizedEXAFS and X-ray diffraction data, the cluster was placed within PSIItaking into account the overall trend of the electron density of themetal site and the putative ligands. The structure of the cluster fromthe present study is unlike either the 3.0 or 3.5 Angstrom resolutionX-ray structures, and other previously proposed models.
Date: May 31, 2006
Creator: Yano, Junko; Kern, Jan; Sauer, Kenneth; Latimer, Matthew J.; Pushkar, Yulia; Biesiadka, Jacek et al.
System: The UNT Digital Library
Nanolaminate Deformable Mirrors (open access)

Nanolaminate Deformable Mirrors

LLNL is developing nanolaminate-based deformable mirrors for terrestrial and space-based optical systems. We are combining two complementary technologies: high-spatial-density electrostatic actuators and thin, flexible, lightweight nanolaminate foils. Electrostatic actuation of MEMS-like structures provides densely-spaced, repeatable deflections on the order of 10 {micro}m. Nanolaminate foils provide a mirror surface that is simultaneously flexible enough to deform under electrostatic forces and tough enough to survive handling and bonding. We are working on two similar deformable mirrors that will demonstrate the feasibility of nanolaminate-based deformable mirrors over a wide range of size scales. The high-density device has a pitch of 1.255 mm between 1,024 square pixels. The large-scale device has a pitch of 9 mm between 76 hexagonal pixels [1], [2].
Date: May 31, 2006
Creator: Papavasiliou, A. P.; Olivier, S. S.; Barbee, T. W.; Miles, R. R.; Walton, C. C.; Cohn, M. B. et al.
System: The UNT Digital Library
Electronic Properties of LiFePO4 and Li doped LiFePO4 (open access)

Electronic Properties of LiFePO4 and Li doped LiFePO4

LiFePO{sub 4} has several potential advantages in comparison to the transition metal oxide cathode materials used in commercial lithium-ion batteries. However, its low intrinsic electronic conductivity ({approx} 10{sup -9} S/cm) is problematic. We report here a study by soft x-ray absorption/emission spectroscopy of the electronic properties of undoped LiFePO{sub 4} and Li-doped LiFePO{sub 4} in which Li{sup +} ions are substituted for Fe{sup 2+} ions in an attempt to increase the intrinsic electronic conductivity. The conductivities of the Li{sub 1+x}Fe{sub 1-x}PO{sub 4} samples were, however, essentially unchanged from that of the undoped LiFePO{sub 4}. Nonetheless, evidence for changing the electronic properties of LiFePO{sub 4} by doping with excess Li+ was observed by the XAS/XES spectroscopy. New pre-edge features the O-1s XAS spectrum of Li{sub 1.05}Fe{sub 0.95}PO4 is a direct indication that the charge compensation for substitution of Fe{sup 2+} by Li{sup +} resides in the unoccupied O-2p orbitals. A charge transfer (CT) excitation was also observed in the doped material implying that the unoccupied O-2p orbitals created by doping are strongly hybridized with unoccupied Fe-3d orbitals of neighboring sites. However, the strong covalent bonding within the (PO{sub 4}){sup 3-} anions and the large separation of the Fe cations means that …
Date: May 31, 2006
Creator: Allen, J.L.; Zhuang, G.V.; Ross, P.N.; Guo, J.-H. & Jow, T.R.
System: The UNT Digital Library
X-ray Digital Radiography and Computed Tomography of ICF and HEDP Materials, Subassemblies and Targets (open access)

X-ray Digital Radiography and Computed Tomography of ICF and HEDP Materials, Subassemblies and Targets

Inertial confinement fusion (ICF) and high energy density physics (HEDP) research are being conducted at large laser facilities, such as the University of Rochester's Laboratory for Laser Energetics OMEGA facility and the Lawrence Livermore National Laboratory's (LLNL) National Ignition Facility (NIF). At such facilities, millimeter-sized targets with micrometer structures are studied in a variety of hydrodynamic, radiation transport, equation-of-state, inertial confinement fusion and high-energy density experiments. The extreme temperatures and pressures achieved in these experiments make the results susceptible to imperfections in the fabricated targets. Targets include materials varying widely in composition ({approx}3 < Z < {approx}82), density ({approx}0.03 to {approx}20 g/cm{sup 3}), geometry (planar to spherical) and embedded structures (joints to subassemblies). Fabricating these targets with structures to the tolerances required is a challenging engineering problem the ICF and HEDP community are currently undertaking. Nondestructive characterization (NDC) provides a valuable tool in material selection, component inspection, and the final pre-shot assemblies inspection. X-rays are a key method used to NDC these targets. In this paper we discuss X-ray attenuation, X-ray phase effects, and the X-ray system used, its performance and application to characterize low-temperature Raleigh-Taylor and non-cryogenic double-shell targets.
Date: May 31, 2006
Creator: Brown, W. D. & Martz, H. E., Jr.
System: The UNT Digital Library