Measurement of the neutron spectrum from the T(t,2n) reaction with the National Ignition Facility (open access)

Measurement of the neutron spectrum from the T(t,2n) reaction with the National Ignition Facility

None
Date: May 3, 2013
Creator: Sayre, D. B.; Brune, C. R.; Caggiano, J. A.; Glebov, V. Y.; Hatarik, R.; Friedrich, S. et al.
System: The UNT Digital Library
Exotic Effects at the Charm Threshold and Other Novel Physics Topics at JLab-12 GeV (open access)

Exotic Effects at the Charm Threshold and Other Novel Physics Topics at JLab-12 GeV

I briefly survey a number of novel hadron physics topics which can be investigated with the 12 GeV upgrade at J-Lab. The topics include new the formation of exotic heavy quark resonances accessible above the charm threshold, intrinsic charm and strangeness phenomena, the exclusive Sivers effect, hidden-color Fock states of nuclei, local two-photon interactions in deeply virtual Compton scattering, and non-universal antishadowing.
Date: May 3, 2012
Creator: Brodsky, Stanley J.
System: The UNT Digital Library
INFLUENCE OF FILM STRUCTURE AND LIGHT ON CHARGE TRAPPING AND DISSIPATION DYNAMICS IN SPUN-CAST ORGANIC THIN-FILM TRANSISTORS MEASURED BY SCANNING KELVIN PROBE MICROSCOPY (open access)

INFLUENCE OF FILM STRUCTURE AND LIGHT ON CHARGE TRAPPING AND DISSIPATION DYNAMICS IN SPUN-CAST ORGANIC THIN-FILM TRANSISTORS MEASURED BY SCANNING KELVIN PROBE MICROSCOPY

Herein, time-dependent scanning Kelvin probe microscopy of solution processed organic thin film transistors (OTFTs) reveals a correlation between film microstructure and OTFT device performance with the location of trapped charge within the device channel. The accumulation of the observed trapped charge is concurrent with the decrease in I{sub SD} during operation (V{sub G}=-40 V, V{sub SD}= -10 V). We discuss the charge trapping and dissipation dynamics as they relate to the film structure and show that application of light quickly dissipates the observed trapped charge.
Date: May 3, 2012
Creator: Teague, L.; Moth, M. & Anthony, J.
System: The UNT Digital Library
Measuring the absolute DT neutron yield using the Magnetic Recoil Spectrometer at OMEGA and the NIF (open access)

Measuring the absolute DT neutron yield using the Magnetic Recoil Spectrometer at OMEGA and the NIF

A Magnetic Recoil Spectrometer (MRS) has been installed and extensively used on OMEGA and the National Ignition Facility (NIF) for measurements of the absolute neutron spectrum from inertial confinement fusion (ICF) implosions. From the neutron spectrum measured with the MRS, many critical implosion parameters are determined including the primary DT neutron yield, the ion temperature, and the down-scattered neutron yield. As the MRS detection efficiency is determined from first principles, the absolute DT neutron yield is obtained without cross-calibration to other techniques. The MRS primary DT neutron measurements at OMEGA and the NIF are shown to be in excellent agreement with previously established yield diagnostics on OMEGA, and with the newly commissioned nuclear activation diagnostics on the NIF.
Date: May 3, 2012
Creator: Mackinnon, A.; Casey, D.; Frenje, J. A.; Johnson, M. G.; Seguin, F. H.; Li, C. K. et al.
System: The UNT Digital Library
Simultaneous High-Resolution 2-Dimensional Spatial and 1-Dimensional Picosecond Streaked X-ray Pinhole Imaging (open access)

Simultaneous High-Resolution 2-Dimensional Spatial and 1-Dimensional Picosecond Streaked X-ray Pinhole Imaging

A Kentech x-ray streak camera was run at the LLNL Compact Multipulse Terawatt (COMET) laser to record simultaneous space- and time-resolved measurements of picosecond laser-produced plasmas. Four different x-ray energy channels were monitored using broad-band filters to record the time history of Cu targets heated at irradiances of 10{sup 16} - 10{sup 19} W/cm{sup 2}. Through the Cu filter channel, a time-resolution below 3ps was obtained. Additionally, an array of 10 {micro}m diameter pinholes was placed in front of the camera to produce multiple time-resolved x-ray images on the photocathode and time-integrated images on the phosphor with 10 and 15 times magnification, respectively, with spatial resolution of <13 {micro}m.
Date: May 3, 2012
Creator: Steel, A. B.; Nagel, S. R.; Dunn, J. & Baldis, H. A.
System: The UNT Digital Library
A User Perspective of High-Performance Computing on the Cloud (open access)

A User Perspective of High-Performance Computing on the Cloud

None
Date: May 3, 2012
Creator: Marathe, A.; Lowenthal, D.; Rountree, B.; Yuan, X.; Schulz, M. & de Supinski, B.
System: The UNT Digital Library
The Compact Salaginella Genome Identifies Changes in Gene Content Associated with the Evolution of Vascular Plants (open access)

The Compact Salaginella Genome Identifies Changes in Gene Content Associated with the Evolution of Vascular Plants

None
Date: May 3, 2011
Creator: Lucas, S.; Grigoriev, I.; Banks, J.; Nishiyama, T.; Bowman, J.; Gribskov, M. et al.
System: The UNT Digital Library
Computing the energy of a water molecule using MultiDeterminants: A simple, efficient algorithm (open access)

Computing the energy of a water molecule using MultiDeterminants: A simple, efficient algorithm

None
Date: May 3, 2011
Creator: Clark, B K; Morales, M A; McMinis, J; Kim, J & Scuseria, G
System: The UNT Digital Library
Disentangling the Mn moments on different sublattices in the half-metallic ferrimagnet Mn3?xCoxGa (open access)

Disentangling the Mn moments on different sublattices in the half-metallic ferrimagnet Mn3?xCoxGa

Ferrimagnetic Mn{sub 3-x}Co{sub x}Ga compounds have been investigated by magnetic circular dichroism in x-ray absorption (XMCD). Compounds with x > 0.5 crystallize in the CuHg{sub 2}Ti structure. A tetragonal distortion of the cubic structure occurs for x {le} 0.5. For the cubic phase, magnetometry reveals a linearly increasing magnetization of 2x Bohr magnetons per formula unit obeying the generalized Slater-Pauling rule. XMCD confirms the ferrimagnetic character with Mn atoms occupying two different sublattices with antiparallel spin orientation and different degrees of spin localization and identifies the region 0.6 < x {le} 0.8 as most promising for a high spin polarization at the Fermi level. Individual Mn moments on inequivalent sites are compared to theoretical predictions.
Date: May 3, 2011
Creator: Klaer, P.; Jenkins, C. A.; Alijani, V.; Winterlik, J.; Balke, B.; Felser, C. et al.
System: The UNT Digital Library
Electronic structure and f-orbital occupancy in Yb-substituted CeCoIn5 (open access)

Electronic structure and f-orbital occupancy in Yb-substituted CeCoIn5

The local structure and 4f orbital occupancy have been investigated in Ce{sub 1−x}Yb{sub x}CoIn{sub 5} via Yb L{sub III}-edge extended x-ray absorption fine structure (EXAFS), Ce and Yb L{sub III}-edge x-ray absorption near-edge structure (XANES), and angle-resolved photoemission spectroscopy (ARPES) measurements. Yb(III) (4f{sup 13}) is the hole analog of Ce(III) (4f{sup 1}). Yb is found to be strongly intermediate-valent in Ce{sub 1−x}Yb{sub x}CoIn{sub 5} throughout the entire doping range, including pure YbCoIn{sub 5}, with an f-hole occupancy for Yb of n{sub f} ≃ 0.3 (i.e. Yb{sup 2.3+}), independent of Yb concentration and independent of temperature down to T = 20 K. In contrast, the f-electron orbital occupancy for Ce remains close to 1 for all Yb concentrations, suggesting that there is no mutual influence on n{sub f} between neighboring Ce and Yb sites. Likewise, ARPES measurements at 12 K have found that the electronic structure along {Gamma} − X is not sensitive to the Yb substitution, suggesting that the Kondo hybridization of Ce f electrons with the conduction band is not affected by the presence of Yb impurities in the lattice. The emerging picture is that in Ce{sub 1−x}Yb{sub x}CoIn{sub 5} there are two networks, interlaced but independent, that couple …
Date: May 3, 2011
Creator: Booth, C. H.; Durakiewicz, T.; Capan, C.; Hurt, D.; Bianchi, A. D.; Joyce, J.J. et al.
System: The UNT Digital Library
Iterative Algorithms for Ptychographic Phase Retrieval (open access)

Iterative Algorithms for Ptychographic Phase Retrieval

Ptychography promises diffraction limited resolution without the need for high resolution lenses. To achieve high resolution one has to solve the phase problem for many partially overlapping frames. Here we review some of the existing methods for solving ptychographic phase retrieval problem from a numerical analysis point of view, and propose alternative methods based on numerical optimization.
Date: May 3, 2011
Creator: Yang, Chao; Qian, Jianliang; Schirotzek, Andre; Maia, Filipe & Marchesini, Stefano
System: The UNT Digital Library
Novel Insights into the Diversity of Catabolic Metabolism from Ten Haloarchaeal Genomes (open access)

Novel Insights into the Diversity of Catabolic Metabolism from Ten Haloarchaeal Genomes

The extremely halophilic archaea are present worldwide in saline environments and have important biotechnological applications. Ten complete genomes of haloarchaea are now available, providing an opportunity for comparative analysis. We report here the comparative analysis of five newly sequenced haloarchaeal genomes with five previously published ones. Whole genome trees based on protein sequences provide strong support for deep relationships between the ten organisms. Using a soft clustering approach, we identified 887 protein clusters present in all halophiles. Of these core clusters, 112 are not found in any other archaea and therefore constitute the haloarchaeal signature. Four of the halophiles were isolated from water, and four were isolated from soil or sediment. Although there are few habitat-specific clusters, the soil/sediment halophiles tend to have greater capacity for polysaccharide degradation, siderophore synthesis, and cell wall modification. Halorhabdus utahensis and Haloterrigena turkmenica encode over forty glycosyl hydrolases each, and may be capable of breaking down naturally occurring complex carbohydrates. H. utahensis is specialized for growth on carbohydrates and has few amino acid degradation pathways. It uses the non-oxidative pentose phosphate pathway instead of the oxidative pathway, giving it more flexibility in the metabolism of pentoses. These new genomes expand our understanding of haloarchaeal …
Date: May 3, 2011
Creator: Anderson, Iain; Scheuner, Carmen; Goker, Markus; Mavromatis, Kostas; Hooper, Sean D.; Porat, Iris et al.
System: The UNT Digital Library
Analysis of the Spectral Function of Nd1.85Ce0.15CuO4, Obtained by Angle Resolved Photoemission Spectroscopy (open access)

Analysis of the Spectral Function of Nd1.85Ce0.15CuO4, Obtained by Angle Resolved Photoemission Spectroscopy

Samples of Nd{sub 2-x}Ce{sub x}CuO{sub 4}, an electron-doped high temperature superconducting cuprate (HTSC), near optimal doping at x = 0.155 were measured via angle resolved photoemission (ARPES). We report a renormalization feature in the self energy ('kink') in the band dispersion at {approx} 50-60 meV present in nodal and antinodal cuts across the Fermi surface. Specifically, while the kink had been seen in the antinodal region, it is now observed also in the nodal region, reminiscent of what has been observed in hole-doped cuprates.
Date: May 3, 2010
Creator: Schmitt, F.
System: The UNT Digital Library
Angle-resolved photoemission studies of lattice polaron formation in the cuprate Ca2CuO2Cl2 (open access)

Angle-resolved photoemission studies of lattice polaron formation in the cuprate Ca2CuO2Cl2

To elucidate the nature of the single-particle excitations in the undoped parent cuprates, we have performed a detailed study of Ca{sub 2}CuO{sub 2}Cl{sub 2} using photoemission spectroscopy. The photoemission lineshapes of the lower Hubbard band are found to be well-described by a polaron model. By comparing the lineshape and temperature dependence of the lower Hubbard band with additional O 2p and Ca 3p states, we conclude that the dominant broadening mechanism arises from the interaction between the photohole and the lattice. The strength of this interaction was observed to be strongly anisotropic and may have important implications for the momentum dependence of the first doped hole states.
Date: May 3, 2010
Creator: Shen, K.M.
System: The UNT Digital Library
Anomalous Fermi-Surface Dependent Pairing in a Self-Doped High-Tc Superconductor (open access)

Anomalous Fermi-Surface Dependent Pairing in a Self-Doped High-Tc Superconductor

We report the discovery of a self-doped multi-layer high T{sub c} superconductor Ba{sub 2}Ca{sub 3}Cu{sub 4}O{sub 8}F{sub 2} (F0234) which contains distinctly different superconducting gap magnitudes along its two Fermi surface(FS) sheets. While formal valence counting would imply this material to be an undoped insulator, it is a self-doped superconductor with a T{sub c} of 60K, possessing simultaneously both electron- and hole-doped FS sheets. Intriguingly, the FS sheet characterized by the much larger gap is the electron-doped one, which has a shape disfavoring two electronic features considered to be important for the pairing mechanism: the van Hove singularity and the antiferromagnetic ({pi}/a, {pi}/a) scattering.
Date: May 3, 2010
Creator: Chen, Y.
System: The UNT Digital Library
A Direct, Biomass-Based Synthesis of Benzoic Acid: Formic Acid-Mediated Deoxygenation of the Glucose-Derived Materials Quinic Acid and Shikimic Acid (open access)

A Direct, Biomass-Based Synthesis of Benzoic Acid: Formic Acid-Mediated Deoxygenation of the Glucose-Derived Materials Quinic Acid and Shikimic Acid

An alternative biomass-based route to benzoic acid from the renewable starting materials quinic acid and shikimic acid is described. Benzoic acid is obtained selectively using a highly efficient, one-step formic acid-mediated deoxygenation method.
Date: May 3, 2010
Creator: Arceo, Elena; Ellman, Jonathan & Bergman, Robert
System: The UNT Digital Library
Direct observation of the mass renormalization in SrVO3 by angle resolved photoemission spectroscopy (open access)

Direct observation of the mass renormalization in SrVO3 by angle resolved photoemission spectroscopy

We have performed an angle-resolved photoemission study of the three-dimensional perovskite-type SrVO{sub 3}. Observed spectral weight distribution of the coherent part in the momentum space shows cylindrical Fermi surfaces consisting of the V 3d t{sub 2g} orbitals as predicted by local-density approximation (LDA) band-structure calculation. The observed energy dispersion shows a moderately enhanced effective mass compared to the LDA results, corresponding to the effective mass enhancement seen in the thermodynamic properties. Contributions from the bulk and surface electronic structures to the observed spectra are discussed based on model calculations.
Date: May 3, 2010
Creator: Yoshida, t.
System: The UNT Digital Library
Doping Dependent Charge Transfer Gap and Realistic Electronic Model of n-type Cuprate Superconductors (open access)

Doping Dependent Charge Transfer Gap and Realistic Electronic Model of n-type Cuprate Superconductors

Based on the analysis of the measurement data of angle-resolved photoemission spectroscopy (ARPES) and optics, we show that the charge transfer gap is significantly smaller than the optical one and is reduced by doping in electron doped cuprate superconductors. This leads to a strong charge fluctuation between the Zhang-Rice singlet and the upper Hubbard bands. The basic model for describing this system is a hybridized two-band t-J model. In the symmetric limit where the corresponding intra- and inter-band hopping integrals are equal to each other, this two-band model is equivalent to the Hubbard model with an antiferromagnetic exchange interaction (i.e. the t-U-J model). The mean-field result of the t-U-J model gives a good account for the doping evolution of the Fermi surface and the staggered magnetization.
Date: May 3, 2010
Creator: Xiang, T.
System: The UNT Digital Library
Doping Evolution of the Underlying Fermi Surface in La_2&#8722xSr_xCuO_4 (open access)

Doping Evolution of the Underlying Fermi Surface in La_2&#8722xSr_xCuO_4

We have performed a systematic doping dependent study of La{sub 2-x}Sr{sub x}CuO{sub 4} (LSCO) (0.03 {le} x {le} 0.3) by angle-resolved photoemission spectroscopy. In the entire doping range, the underlying 'Fermi surface' determined from the low energy spectral weight approximately satisfies Luttinger's theorem, even down to the lightly-doped region. This is in strong contrast to the result on Ca{sub 2-x}Na{sub x}CuO{sub 2}Cl{sub 2} (Na-CCOC), which shows a strong deviation from Luttinger's theorem. The differences between LSCO and Na-CCOC are correlated with the different behaviors of the chemical potential shift and spectral weight transfer induced by hole doping.
Date: May 3, 2010
Creator: Yoshida, T.
System: The UNT Digital Library
Enhanced superconducting pairing interaction in indium-doped tin telluride (open access)

Enhanced superconducting pairing interaction in indium-doped tin telluride

The ferroelectric degenerate semiconductor Sn{sub 1-{delta}}Te exhibits superconductivity with critical temperatures, T{sub c}, of up to 0.3 K for hole densities of order 10{sup 21} cm{sup -3}. When doped on the tin site with greater than x{sub c} = 1.7(3)% indium atoms, however, superconductivity is observed up to 2 K, though the carrier density does not change significantly. We present specific heat data showing that a stronger pairing interaction is present for x > x{sub c} than for x < x{sub c}. By examining the effect of In dopant atoms on both T{sub c} and the temperature of the ferroelectric structural phase transition, T{sub SPT}, we show that phonon modes related to this transition are not responsible for this T{sub c} enhancement, and discuss a plausible candidate based on the unique properties of the indium impurities.
Date: May 3, 2010
Creator: Erickson, A.S.
System: The UNT Digital Library
Fermi Surface Evolution Across Multiple Charge Density Wave Transitions in ErTe3 (open access)

Fermi Surface Evolution Across Multiple Charge Density Wave Transitions in ErTe3

None
Date: May 3, 2010
Creator: Moore, R. G.
System: The UNT Digital Library
The hierarchy of multiple many-body interaction scales in high-temperature superconductors (open access)

The hierarchy of multiple many-body interaction scales in high-temperature superconductors

To date, angle-resolved photoemission spectroscopy has been successful in identifying energy scales of the many-body interactions in correlated materials, focused on binding energies of up to a few hundred meV below the Fermi energy. Here, at higher energy scale, we present improved experimental data from four families of high-T{sub c} superconductors over a wide doping range that reveal a hierarchy of many-body interaction scales focused on: the low energy anomaly ('kink') of 0.03-0.09eV, a high energy anomaly of 0.3-0.5eV, and an anomalous enhancement of the width of the LDA-based CuO{sub 2} band extending to energies of {approx} 2 eV. Besides their universal behavior over the families, we find that all of these three dispersion anomalies also show clear doping dependence over the doping range presented.
Date: May 3, 2010
Creator: Meevasana, W.
System: The UNT Digital Library
Potential Impact of Adopting Maximum Technologies as Minimum Efficiency Performance Standards in the U.S. Residential Sector (open access)

Potential Impact of Adopting Maximum Technologies as Minimum Efficiency Performance Standards in the U.S. Residential Sector

The US Department of Energy (US DOE) has placed lighting and appliance standards at a very high priority of the U.S. energy policy. However, the maximum energy savings and CO2 emissions reduction achievable via minimum efficiency performance standards (MEPS) has not yet been fully characterized. The Bottom Up Energy Analysis System (BUENAS), first developed in 2007, is a global, generic, and modular tool designed to provide policy makers with estimates of potential impacts resulting from MEPS for a variety of products, at the international and/or regional level. Using the BUENAS framework, we estimated potential national energy savings and CO2 emissions mitigation in the US residential sector that would result from the most aggressive policy foreseeable: standards effective in 2014 set at the current maximum technology (Max Tech) available on the market. This represents the most likely characterization of what can be maximally achieved through MEPS in the US. The authors rely on the latest Technical Support Documents and Analytical Tools published by the U.S. Department of Energy as a source to determine appliance stock turnover and projected efficiency scenarios of what would occur in the absence of policy. In our analysis, national impacts are determined for the following end uses: …
Date: May 3, 2010
Creator: Letschert, Virginie; Desroches, Louis-Benoit; McNeil, Michael & Saheb, Yamina
System: The UNT Digital Library
Pressure-induced quenching of the charge-density-wave state observed by x-ray diffraction (open access)

Pressure-induced quenching of the charge-density-wave state observed by x-ray diffraction

We report an x-ray diffraction study on the charge-density-wave (CDW) LaTe{sub 3} and CeTe{sub 3} compounds as a function of pressure. We extract the lattice constants and the CDW modulation wave-vector, and provide direct evidence for a pressure-induced quenching of the CDW phase. We observe subtle differences between the chemical and mechanical compression of the lattice. We account for these with a scenario where the effective dimensionality in these CDW systems is dependent on the type of lattice compression and has a direct impact on the degree of Fermi surface nesting and on the strength of fluctuation effects.
Date: May 3, 2010
Creator: Sacchetti, A.
System: The UNT Digital Library