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Band Structure and Quantum Conductance of Nanostructures from Maximally Localized Wannier Functions: The Case of Functionalized Carbon Nanotubes (open access)

Band Structure and Quantum Conductance of Nanostructures from Maximally Localized Wannier Functions: The Case of Functionalized Carbon Nanotubes

Article on band structure and quantum conductance of nanostructures from maximally localized Wannier functions.
Date: August 12, 2005
Creator: Lee, Young-Su; Buongiorno Nardelli, Marco & Marzari, Nicola
System: The UNT Digital Library
Empirical Analysis of the Spot Market Implications ofPrice-Responsive Demand (open access)

Empirical Analysis of the Spot Market Implications ofPrice-Responsive Demand

Regardless of the form of restructuring, deregulatedelectricity industries share one common feature: the absence of anysignificant, rapid demand-side response to the wholesale (or, spotmarket) price. For a variety of reasons, most electricity consumers stillpay an average cost based regulated retail tariff held over from the eraof vertical integration, even as the retailers themselves are oftenforced to purchase electricity at volatile wholesale prices set in openmarkets. This results in considerable price risk for retailers, who aresometimes additionally forbidden by regulators from signing hedgingcontracts. More importantly, because end-users do not perceive real-time(or even hourly or daily) fluctuations in the wholesale price ofelectricity, they have no incentive to adjust their consumptionaccordingly. Consequently, demand for electricity is highly inelastic,which together with the non storability of electricity that requiresmarket clearing over very short time steps spawn many other problemsassociated with electricity markets, such as exercise of market power andprice volatility. Indeed, electricity generation resources can bestretched to the point where system adequacy is threatened. Economictheory suggests that even modest price responsiveness can relieve thestress on generation resources and decrease spot prices. To quantify thiseffect, actual generator bid data from the New York control area is usedto construct supply stacks and intersect them with demand curves …
Date: August 1, 2005
Creator: Siddiqui, Afzal S.; Bartholomew, Emily S. & Marnay, Chris
System: The UNT Digital Library
Recent Developments in Neutrino Science: A Whole Lot About Almost Nothing (open access)

Recent Developments in Neutrino Science: A Whole Lot About Almost Nothing

Results from Super-K, SNO, and KamLAND provide strong evidence that neutrinos undergo flavor-changing oscillations and therefore have non-zero mass. The {nu}-disappearance observations by KamLAND, assuming CPT conservation, point to matter enhanced (MSW) oscillations with large mixing angles as the solution to the solar neutrino problem--a result consistent with the MSW parameters recently defined by these experiments. This requires that the observed neutrino flavors (e, {mu}, and tau) are not mass eigenstates, but are linear combinations of the mass eigenstates of the neutrino. However, such oscillation experiments can only determine the differences in the masses of the neutrinos, not the absolute scale of neutrino mass. What can be inferred from these experiments is that at least one species of neutrino has a mass greater than 55 meV. In fact, the WMAP observations of large-scale structure point to a sum-neutrino mass of {approx} 0.7 eV (roughly 0.25 eV/species assuming democracy between the flavors). Furthermore, there is still the important issue of whether the neutrino and anti-neutrino are distinct particles (i.e. Dirac type) or not (Majorana type). The only way to answer both of these questions is through neutrinoless double beta decay (DBD) experiments. CUORE (Cryogenic Underground Observatory for Rare Events) is a …
Date: August 22, 2005
Creator: Norman, E B
System: The UNT Digital Library
Initiation of Heated PBX-9501 Explosive When Exposed to Dynamic Loading (open access)

Initiation of Heated PBX-9501 Explosive When Exposed to Dynamic Loading

Shock initiation experiments on the heated PBX9501 explosive (95% HMX, 2.5% estane, and 2.5% nitro-plasticizer by weight) were performed at temperatures 150 C and 180 C to obtain in-situ pressure gauge data. A 101 mm diameter propellant driven gas gun was utilized to initiate the PBX9501 explosive and manganin piezo-resistive pressure gauge packages were placed between sample slices to measure time resolved local pressure histories. The run-distance-to-detonation points on the Pop-plot for these experiments showed the sensitivity of the heated material to shock loading. This work shows that heated PBX-9501 is more shock sensitive than it is at ambient conditions. Proper Ignition and Growth modeling parameters were obtained to fit the experimental data. This parameter set will allow accurate code predictions to be calculated for safety scenarios involving PBX9501 explosives at temperatures close to those at which experiments were performed.
Date: August 16, 2005
Creator: Urtiew, P A; Vandersall, K S; Tarver, C M & Garcia, F
System: The UNT Digital Library
Laser coupling to reduced-scale targets at NIF Early Light (open access)

Laser coupling to reduced-scale targets at NIF Early Light

Deposition of maximum laser energy into a small, high-Z enclosure in a short laser pulse creates a hot environment. Such targets were recently included in an experimental campaign using the first four of the 192 beams of the National Ignition Facility [J. A. Paisner, E. M. Campbell, and W. J. Hogan, Fusion Technology 26, 755 (1994)], under construction at the University of California Lawrence Livermore National Laboratory. These targets demonstrate good laser coupling, reaching a radiation temperature of 340 eV. In addition, the Raman backscatter spectrum contains features consistent with Brillouin backscatter of Raman forward scatter [A. B. Langdon and D. E. Hinkel, Physical Review Letters 89, 015003 (2002)]. Also, NIF Early Light diagnostics indicate that 20% of the direct backscatter from these reduced-scale targets is in the polarization orthogonal to that of the incident light.
Date: August 31, 2005
Creator: Hinkel, D. E.; Schneider, M. B.; Young, B. K.; Holder, J. P.; Langdon, A. B.; Baldis, H. A. et al.
System: The UNT Digital Library
Modeling NIF Experimental Designs with Adaptive Mesh Refinement and Lagrangian Hydrodynamics (open access)

Modeling NIF Experimental Designs with Adaptive Mesh Refinement and Lagrangian Hydrodynamics

Incorporation of adaptive mesh refinement (AMR) into Lagrangian hydrodynamics algorithms allows for the creation of a highly powerful simulation tool effective for complex target designs with three-dimensional structure. We are developing an advanced modeling tool that includes AMR and traditional arbitrary Lagrangian-Eulerian (ALE) techniques. Our goal is the accurate prediction of vaporization, disintegration and fragmentation in National Ignition Facility (NIF) experimental target elements. Although our focus is on minimizing the generation of shrapnel in target designs and protecting the optics, the general techniques are applicable to modern advanced targets that include three-dimensional effects such as those associated with capsule fill tubes. Several essential computations in ordinary radiation hydrodynamics need to be redesigned in order to allow for AMR to work well with ALE, including algorithms associated with radiation transport. Additionally, for our goal of predicting fragmentation, we include elastic/plastic flow into our computations. We discuss the integration of these effects into a new ALE-AMR simulation code. Applications of this newly developed modeling tool as well as traditional ALE simulations in two and three dimensions are applied to NIF early-light target designs.
Date: August 31, 2005
Creator: Koniges, A E; Anderson, R W; Wang, P; Gunney, B N; Becker, R; Eder, D C et al.
System: The UNT Digital Library
Metal-induced assembly of a semiconductor-island lattice: Getruncated pyramids on Au-patterned Si (open access)

Metal-induced assembly of a semiconductor-island lattice: Getruncated pyramids on Au-patterned Si

We report the two-dimensional alignment of semiconductor islands using rudimentary metal patterning to control nucleation and growth. In the Ge on Si system, a square array of sub-micron Au dots on the Si (001) surface induces the assembly of deposited Ge adatoms into an extensive island lattice. Remarkably, these highly ordered Ge islands form between the patterned Au dots and are characterized by a unique truncated pyramidal shape. A model based on patterned diffusion barriers explains the observed ordering and establishes general criteria for the broader applicability of such a directed assembly process to quantum dot ordering.
Date: August 28, 2005
Creator: Robinson, J. T.; Liddle, J. A.; Minor, A.; Radmilovic, V.; Yi, D. O.; Greaney, P. A. et al.
System: The UNT Digital Library
BFKL resummation effects in gamma* gamma* to rho rho (open access)

BFKL resummation effects in gamma* gamma* to rho rho

We calculate the leading order BFKL amplitude for the exclusive diffractive process {gamma}*{sub L}(Q{sub 1}{sup 2}) {gamma}*{sub L}(Q{sub 2}{sup 2}) {yields} {rho}{sub L}{sup 0}{rho}{sub L}{sup 0} in the forward direction, which can be studied in future high energy e{sup +}e{sup -} linear colliders. The resummation effects are very large compared to the fixed-order calculation. We also estimate the next-to-leading logarithmic corrections to the amplitude by using a specific resummation of higher order effects and find a substantial growth with energy, but smaller than in the leading logarithmic approximation.
Date: August 11, 2005
Creator: Enberg, R.; Pire, B.; Szymanowski, L. & Wallon, S.
System: The UNT Digital Library
Review of U.S. Neutrino Factory Studies (open access)

Review of U.S. Neutrino Factory Studies

We summarize the status of the two U.S. feasibility studies carried out by the Neutrino Factory and Muon Collider Collaboration (NFMCC) along with recent improvements to Neutrino Factory design developed during the American Physical Society (APS) Neutrino Physics Study. Suggested accelerator topics for the International Scoping Study (ISS) are also indicated.
Date: August 23, 2005
Creator: Zisman, Michael S.
System: The UNT Digital Library
Fabrication of Planar Laser Targets with Sub-Micrometer Thickness Uniformity (open access)

Fabrication of Planar Laser Targets with Sub-Micrometer Thickness Uniformity

None
Date: August 30, 2005
Creator: Bono, M.; Castro, C.; Griffith, L.; Hibbard, R.; Kass, J. & Satcher, J.
System: The UNT Digital Library
A phylogenomic gene cluster resource: The phylogeneticallyinferred groups (PhlGs) database (open access)

A phylogenomic gene cluster resource: The phylogeneticallyinferred groups (PhlGs) database

We present here the PhIGs database, a phylogenomic resource for sequenced genomes. Although many methods exist for clustering gene families, very few attempt to create truly orthologous clusters sharing descent from a single ancestral gene across a range of evolutionary depths. Although these non-phylogenetic gene family clusters have been used broadly for gene annotation, errors are known to be introduced by the artifactual association of slowly evolving paralogs and lack of annotation for those more rapidly evolving. A full phylogenetic framework is necessary for accurate inference of function and for many studies that address pattern and mechanism of the evolution of the genome. The automated generation of evolutionary gene clusters, creation of gene trees, determination of orthology and paralogy relationships, and the correlation of this information with gene annotations, expression information, and genomic context is an important resource to the scientific community.
Date: August 25, 2005
Creator: Dehal, Paramvir S. & Boore, Jeffrey L.
System: The UNT Digital Library
Improved Operation of the SSPX Spheromak (open access)

Improved Operation of the SSPX Spheromak

None
Date: August 18, 2005
Creator: Wood, R. D.; Hill, D. N.; Hooper, E. B.; Woodruff, S.; McLean, H. S. & Stallard, B. W.
System: The UNT Digital Library
Influence of Chromium and Molybdenum on the Corrosion of Nickel Based Alloys (open access)

Influence of Chromium and Molybdenum on the Corrosion of Nickel Based Alloys

The addition of chromium and molybdenum to nickel creates alloys with exceptional corrosion resistance in a diverse range of environments. This study examines the complementary roles of Cr and Mo in Ni alloy passivation. Four nickel alloys with varying amounts of chromium and molybdenum were studied in 1 molar salt solutions over a broad pH range. The passive corrosion and breakdown behavior of the alloys suggests that chromium is the primary element influencing general corrosion resistance. The breakdown potential was nearly independent of molybdenum content, while the repassivation potential is strongly dependant on the molybdenum content. This indicates that chromium plays a strong role in maintaining the passivity of the alloy, while molybdenum acts to stabilize the passive film after a localized breakdown event.
Date: August 2, 2005
Creator: Hayes, J R; Gray, J; Szmodis, A W & Orme, C A
System: The UNT Digital Library
PIMC Simulation of Ps Annihilation: From Micro to Mesopores (open access)

PIMC Simulation of Ps Annihilation: From Micro to Mesopores

Path Integral Monte Carlo (PIMC) can reproduce the results of simple analytical calculations in which a single quantum particle is used to represent positronium within an idealized, spherical pore. Our calculations improve on this approach by explicitly treating the positronium as a two-particle e{sup -}, e{sup +} system interacting via the Coulomb interaction. We study the lifetime and the internal contact density, {kappa}, which controls the self-annihilation behavior, for positronium in model spherical pores, as a function of temperature and pore size. We compare the results with both PIMC and analytical calculations for a single-particle model.
Date: August 23, 2005
Creator: Bug, A. R. & Sterne, P. A.
System: The UNT Digital Library
Establishing Ergonomics in Industrially Developing Countries (open access)

Establishing Ergonomics in Industrially Developing Countries

The introduction of ergonomics is an ongoing effort in industrially developing countries and will ultimately require an organized, programmatic approach spanning several countries and organizations. Our preliminary efforts with our partner countries of Viet Nam, Thailand, and Nicaragua have demonstrated that a one-time course is just the first step in a series of necessary events to provide skills and create an infrastructure that will have lasting impact for the host country. To facilitate that any sort of training has a lasting impact, it is recommended that host countries establish a 'contract' with class participants and the guest instructors for at least one follow-up visit so instructors can see the progress and support the participants in current and future efforts. With repeated exchanges, the class participants can become the 'in country experts' and the next generation of ergonomic trainers. Additionally, providing participants with an easy to use hazard assessment tool and methods for evaluating the financial impact of the project (cost/benefit analysis) will assist increase the likelihood of success and establish a foundation for future projects. In the future, developing trade and regionally/culturally specific 'ergonomics toolkits' can help promote broader implementation, especially where training resources may be limited.
Date: August 29, 2005
Creator: Stewart, K.; Silverstein, B. & Kiefer, M.
System: The UNT Digital Library
Nanometer-scale imaging and pore-scale fluid flow modeling inchalk (open access)

Nanometer-scale imaging and pore-scale fluid flow modeling inchalk

For many rocks of high economic interest such as chalk,diatomite, tight gas sands or coal, nanometer scale resolution is neededto resolve the 3D-pore structure, which controls the flow and trapping offluids in the rocks. Such resolutions cannot be achieved with existingtomographic technologies. A new 3D imaging method, based on serialsectioning and using the Focused Ion Beam (FIB) technology has beendeveloped. FIB allows for the milling of layers as thin as 10 nanometersby using accelerated Ga+ ions to sputter atoms from the sample surface.After each milling step, as a new surface is exposed, a 2D image of thissurface is generated. Next, the 2D images are stacked to reconstruct the3D pore or grain structure. Resolutions as high as 10 nm are achievableusing this technique. A new image processing method uses directmorphological analysis of the pore space to characterize thepetrophysical properties of diverse formations. In addition to estimationof the petrophysical properties (porosity, permeability, relativepermeability and capillary pressures), the method is used for simulationof fluid displacement processes, such as those encountered in variousimproved oil recovery (IOR) approaches. Computed with the new methodcapillary pressure curves are in good agreement with laboratory data. Themethod has also been applied for visualization of the fluid distributionat various saturations …
Date: August 23, 2005
Creator: Tomutsa, Liviu; Silin, Dmitriy & Radmilovich, Velimir
System: The UNT Digital Library
The Impact of Overhang Design on the Performance of ElectrochromicWindows (open access)

The Impact of Overhang Design on the Performance of ElectrochromicWindows

In this study, various facade designs with overhangs combined with electrochromic window control strategies were modeled with a prototypical commercial office building in a hot and cold climate using the DOE 2.1E building energy simulation program. Annual total energy use (ATE), peak electric demand (PED), average daylight illuminance (DI), and daylight glare index (DGI) were computed and compared to determine which combinations of fagade design and control strategies yielded the greatest energy efficiency, daylight amenity, and visual comfort.
Date: August 1, 2005
Creator: Tavil, Aslihan & Lee, Eleanor S.
System: The UNT Digital Library
Synthesis of Mesostructured Copper Sulfide by Cation Exchange and Liquid Crystal Templating (open access)

Synthesis of Mesostructured Copper Sulfide by Cation Exchange and Liquid Crystal Templating

The development of synthetic pathways to yield advanced functional materials is an important aspect of materials science. In particular, the ability to control and manipulate the chemical composition and structure of inorganic nanomaterials is highly desirable. Two synthetic approaches which show great promise for producing the next generation of functional inorganic nanomaterials are (1) templating of supramolecular assemblies and (2) ion exchange within nanostructured inorganic solids to manipulate chemical composition. Templating of supramolecular assemblies of surfactants and amphiphilic polymers has already proven to be a powerful technique in synthesizing various inorganic structures. Namely, numerous examples of mesostructured metal oxides (SiO{sub 2}, TiO{sub 2}, WO{sub 3}, etc.) have been synthesized by templating the liquid crystalline phases of amphiphilic polymers and surfactants (i.e. vesicles, 2D and 3D hexagonal and cubic phases, etc.) with inorganic precursors, resulting in the formation of highly ordered inorganic-organic hybrid materials. Although the templating of supramolecular assemblies has been successful in generating highly ordered mesostructured metal oxides, there are only a few examples of non-oxidic mesostructured inorganic materials. The recent developments of ion exchange within nanoparticles offer a promising approach to generating novel nanostructured inorganic materials with unique chemical compositions. Konenkamp et al. and Alivisatos et al. have …
Date: August 1, 2005
Creator: Lubeck, C R; Doyle, F M; Gash, A E; Satcher, J H & Han, T Y
System: The UNT Digital Library
Unraveling the Fanconi anaemia-DNA repair connection through DNA helicase and translocase activities (open access)

Unraveling the Fanconi anaemia-DNA repair connection through DNA helicase and translocase activities

How the Fanconi anaemia (FA) chromosome stability pathway functions to cope with interstrand crosslinks and other DNA lesions has been elusive, even after FANCD1 proved to be BRCA2, a partner of Rad51 in homologous recombination. The identification and characterization of two new Fanconi proteins having helicase motifs, FANCM and FANCJ/BRIP1/BACH1, implicates the FANC nuclear core complex as a participant in recognizing or processing damaged DNA, and the BRIP1 helicase as acting independently of this complex.
Date: August 16, 2005
Creator: Thompson, L H
System: The UNT Digital Library
Interface reconstruction and sub-zone physics models (open access)

Interface reconstruction and sub-zone physics models

None
Date: August 25, 2005
Creator: Bailey, D S; Brown, S A & Zimmerman, G B
System: The UNT Digital Library
Laser-Plasma Interactions in High-Energy Density Plasmas (open access)

Laser-Plasma Interactions in High-Energy Density Plasmas

Laser-plasma interactions (LPI) have been studied experimentally in high-temperature, high-energy density plasmas. The studies have been performed using the Omega laser at the Laboratory for Laser Energetics (LLE), Rochester, NY. Up to 10 TW of power was incident upon reduced-scale hohlraums, distributed in three laser beam cones. The hot hohlraums fill quickly with plasma. Late in the laser pulse, most of the laser energy is deposited at the laser entrance hole, where most of the LPI takes place. Due to the high electron temperature, the stimulated Raman scattering (SRS) spectrum extends well beyond {omega}{sub 0}/2, due to the Bohm-Gross shift. This high-temperature, high-energy density regime provides a unique opportunity to study LPI beyond inertial confinement fusion (ICF) conditions.
Date: August 24, 2005
Creator: Constantin, C. G.; Baldis, H. A.; Schneider, M. B.; Hinkel, D. E.; Langdon, A. B.; Seka, W. et al.
System: The UNT Digital Library
XRM2005 Conference Summary (open access)

XRM2005 Conference Summary

X-ray microscopy is at a state of rapid development. The presentations at the Conference covered the latest developments in the field.
Date: August 30, 2005
Creator: Kirz, Janos
System: The UNT Digital Library
Using Groundwater Age and Other Isotopic Signatures to Delineate Groundwater Flow and Stratification (open access)

Using Groundwater Age and Other Isotopic Signatures to Delineate Groundwater Flow and Stratification

Isotopic tracers, such as stable isotopes of the water molecule and tritium, have been used in investigations of groundwater flow and transport and recharge water source for several decades. While these data can place hard constraints on groundwater flow rates, the degree of vertical flow between aquifers and across aquitards, and recharge source area(s), they are rarely used, even for validation, in conceptual or numerical models of groundwater flow. The Groundwater Ambient Monitoring and Assessment Program, sponsored by the California State Water Resources Control Board, and carried out in collaboration with the U.S. Geological Survey, has provided the means to gather an unprecedented number of tritium-helium groundwater ages in the basins of California. As the examples below illustrate, a collection of groundwater ages in a basin allows delineation of recharge areas (youngest ages), bulk flow rates and flowpaths, as well as a means of assessing susceptibility to anthropogenic contaminants.
Date: August 31, 2005
Creator: Moran, J. E. & Hudson, G. B.
System: The UNT Digital Library
A Molecular Assessment of Phylogenetic Relationships and LineageDiversification Within the Family Salamandridae (Amphibia, Caudata) (open access)

A Molecular Assessment of Phylogenetic Relationships and LineageDiversification Within the Family Salamandridae (Amphibia, Caudata)

Phylogenetic relationships among species of the salamanderfamily Salamandridae are investigated using nearly 3000 nucleotide basesof newly reported mitochondrial DNA sequence data from the mtDNA genicregion spanning the genes tRNALeu-COI. This study uses nearlycomprehensive species-level sampling to provide the first completephylogeny for the Salamandridae. Deep phylogenetic relationships amongthe three most divergent lineages in the family Salamandrina terdigitata,a clade comprising the "True" salamanders, and a clade comprising allnewts except S. terdigitata are difficult to resolve. However, mostrelationships within the latter two lineages are resolved with robustlevels of branch support. The genera Euproctus and Triturus arestatistically shown to be nonmonophyletic, instead each contains adiverse set of lineages positioned within the large newt clade. The genusParamesotriton is also resolve as a nonmonophyletic group, with the newlydescribed species P. laoensis constituting a divergent lineage placed ina sister position to clade containing all Pachytriton species and allremaining Paramesotriton species. Sequence divergences between P.laoensis and other Paramesotriton species are as great as those comparingP. laoensis and species of the genera Cynops and Pachytriton. Analyses oflineage diversification across the Salamandridae indicate that, despiteits exceptional diversity, lineage accumulation appears to have beenconstant across time, indicating that it does not represent a truespecies radiation.
Date: August 8, 2005
Creator: Weisrock, David W.; Papenfuss, Theodore J.; Macey, J. Robert; Litvinchuk, Spartak N.; Polymeni, Rosa; Ugurtas, Ismail H. et al.
System: The UNT Digital Library