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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
New developments for the site-specific attachment of protein to surfaces (open access)

New developments for the site-specific attachment of protein to surfaces

Protein immobilization on surfaces is of great importance in numerous applications in biology and biophysics. The key for the success of all these applications relies on the immobilization technique employed to attach the protein to the corresponding surface. Protein immobilization can be based on covalent or noncovalent interaction of the molecule with the surface. Noncovalent interactions include hydrophobic interactions, hydrogen bonding, van der Waals forces, electrostatic forces, or physical adsorption. However, since these interactions are weak, the molecules can get denatured or dislodged, thus causing loss of signal. They also result in random attachment of the protein to the surface. Site-specific covalent attachment of proteins onto surfaces, on the other hand, leads to molecules being arranged in a definite, orderly fashion and uses spacers and linkers to help minimize steric hindrances between the protein surface. This work reviews in detail some of the methods most commonly used as well as the latest developments for the site-specific covalent attachment of protein to solid surfaces.
Date: May 12, 2005
Creator: Camarero, J A
System: The UNT Digital Library
A Chemical Approach to 3-D Lithographic Patterning of Si and GeNanocrystals (open access)

A Chemical Approach to 3-D Lithographic Patterning of Si and GeNanocrystals

Ion implantation into silica followed by thermal annealingis an established growth method for Si and Ge nanocrystals. Wedemonstrate that growth of Group IV semiconductor nanocrystals can besuppressed by co-implantation of oxygen prior to annealing. For Sinanocrystals, at low Si/O dose ratios, oxygen co-implantation leads to areduction of the average nanocrystal size and a blue-shift of thephotoluminescence emission energy. For both Si and Ge nanocrystals, atlarger Si/O or Ge/O dose ratios, the implanted specie is oxidized andnanocrystals do not form. This chemical deactivation was utilized toachieve patterned growth of Si and Ge nanocrystals. Si was implanted intoa thin SiO2 film on a Si substrate followed by oxygen implantationthrough an electron beam lithographically defined stencil mask. Thermalannealing of the co-implanted structure yields two-dimensionallypatterned growth of Si nanocrystals under the masked regions. We applieda previously developed process to obtain exposed nanocrystals byselective HF etching of the silica matrix to these patterned structures.Atomic force microscopy (AFM) of etched structures revealed that exposednanocrystals are not laterally displaced from their original positionsduring the etching process. Therefore, this process provides a means ofachieving patterned structures of exposed nanocrystals. The possibilitiesfor scaling this chemical-based lithography process to smaller featuresand for extending it to 3-D patterning is discussed.
Date: December 12, 2005
Creator: Sharp, I. D.; Xu, Q.; Yi, D. O.; Liao, C. Y.; Ager, J. W., III; Beeman, J. W. et al.
System: The UNT Digital Library
Performance Verification of the Astro-E2 X-ray spectrometer in the flight configuration (open access)

Performance Verification of the Astro-E2 X-ray spectrometer in the flight configuration

The X-ray Spectrometer (XRS) is a high resolution, non-dispersive cryogenic detector on board the X-ray satellite, Astro-E2 (Suzaku), which was successfully launched on July 10, 2005. The XRS achieves an energy resolution of 6 eV at 6 keV (FWHM) and covers a broad energy range of {approx} 0.07-10 keV. The XRS will enable powerful plasma diagnostics of a variety of astrophysical objects such as the dynamics of gas in clusters of galaxies. The XRS was integrated to the spacecraft in September 2004, and took a series of spacecraft tests until April 2005. We describe results of the XRS performance verification in the spacecraft configuration. First, the noise level was extremely low on the spacecraft, and most of the pixels achieved an energy resolution of 5-6 eV at 5.9 keV. Microphonics from the mechanical cooler was one of the concerns, but they did not interfere with the detector, when the dewar was integrated to the spacecraft and filled with solid neon. To attain the best energy resolution, however, correction of gain drift is mandatory. The XRS has a dedicated calibration pixel for that purpose, and drift correction using the calibration pixel is very effective when the gain variation is due to …
Date: September 12, 2005
Creator: Ota, N.; Boyce, K. R.; Brown, G. V.; Cottam, J.; Fujimoto, R.; Furusho, T. et al.
System: The UNT Digital Library
Verification of high-order mixed FEM solution of transient Magnetic diffusion problems (open access)

Verification of high-order mixed FEM solution of transient Magnetic diffusion problems

We develop and present high order mixed finite element discretizations of the time dependent electromagnetic diffusion equations for solving eddy current problems on 3D unstructured grids. The discretizations are based on high order H(grad), H(curl) and H(div) conforming finite element spaces combined with an implicit and unconditionally stable generalized Crank-Nicholson time differencing method. We develop three separate electromagnetic diffusion formulations, namely the E (electric field), H (magnetic field) and the A-{phi} (potential) formulations. For each formulation, we also provide a consistent procedure for computing the secondary variables F (current flux density) and B (magnetic flux density), as these fields are required for the computation of electromagnetic force and heating terms. We verify the error convergence properties of each formulation via a series of numerical experiments on canonical problems with known analytic solutions. The key result is that the different formulations are equally accurate, even for the secondary variables J and B, and hence the choice of which formulation to use depends mostly upon relevance of the Natural and Essential boundary conditions to the problem of interest. In addition, we highlight issues with numerical verification of finite element methods which can lead to false conclusions on the accuracy of the methods.
Date: May 12, 2005
Creator: Rieben, R. & White, D. A.
System: The UNT Digital Library
Dust-Particle Transport in Tokamak Edge Plasmas (open access)

Dust-Particle Transport in Tokamak Edge Plasmas

Dust particulates in the size range of 10nm-100{micro}m are found in all fusion devices. Such dust can be generated during tokamak operation due to strong plasma/material-surface interactions. Some recent experiments and theoretical estimates indicate that dust particles can provide an important source of impurities in the tokamak plasma. Moreover, dust can be a serious threat to the safety of next-step fusion devices. In this paper, recent experimental observations on dust in fusion devices are reviewed. A physical model for dust transport simulation, and a newly developed code DUSTT, are discussed. The DUSTT code incorporates both dust dynamics due to comprehensive dust-plasma interactions as well as the effects of dust heating, charging, and evaporation. The code tracks test dust particles in realistic plasma backgrounds as provided by edge-plasma transport codes. Results are presented for dust transport in current and next-step tokamaks. The effect of dust on divertor plasma profiles and core plasma contamination is examined.
Date: September 12, 2005
Creator: Pigarov, A Y; Krasheninnikov, S I; Soboleva, T K & Rognlien, T D
System: The UNT Digital Library
DIII-D Diagnostic Systems (open access)

DIII-D Diagnostic Systems

None
Date: October 12, 2005
Creator: Boivin, R. L.; Luxon, J. L.; Austin, M. E.; Brooks, N. H.; Burrell, K. H.; Doyle, E. J. et al.
System: The UNT Digital Library
Beam Measurements and Upgrade at BL 7.2, the Second DiagnosticsBeamline of the Advanced Light Source (open access)

Beam Measurements and Upgrade at BL 7.2, the Second DiagnosticsBeamline of the Advanced Light Source

Beamline 7.2 of the Advanced Light Source (ALS) at theLawrence Berkeley National Laboratory (LBNL) is a beam diagnostics systemthat uses the synchrotron radiation emitted by a dipole magnet. Itconsists of two branches; in the first one the x-ray portion of theradiation is used in a pinhole camera system for measuring the transverseprofile of the beam. The second branch is equipped with an x-ray beamposition monitor (BPM) and with a multipurpose port where the visible andthe far-infrared part of the radiation can be used for variousapplications such as bunch length measurements and IR coherentsynchrotron radiation experiments. The pinhole system has been operatingsuccessfully since the end of 2003. The installation of the second branchhas been completed recently and the results of its commissioning arepresented in this paper together with examples of beam measurementsperformed at BL 7.2.
Date: May 12, 2005
Creator: Scarvie, Tom; Sannibale, Fernando; Biocca, Alan; Kelez, Nicholas; Martin, Michael C.; Nishimura, Toshiro et al.
System: The UNT Digital Library
Gamma-Ray Imaging With Coaxial HPGe Detector (open access)

Gamma-Ray Imaging With Coaxial HPGe Detector

We report on the first experimental demonstration of Compton imaging of gamma rays with a single coaxial high-purity germanium (HPGe) detector. This imaging capability is realized by two-dimensional segmentation of the outside contact in combination with digital pulse-shape analysis, which enables to image gamma rays in 4{pi} without employing a collimator. We are able to demonstrate the ability to image the 662keV gamma ray from a {sup 137}Cs source with preliminary event selection with an angular accuracy of 5 degree with an relative efficiency of 0.2%. In addition to the 4{pi} imaging capability, such a system is characterized by its excellent energy resolution and can be implemented in any size possible for Ge detectors to achieve high efficiency.
Date: April 12, 2005
Creator: Niedermayr, T.; Vetter, K.; Mihailescu, L.; Schmid, G. J.; Beckedahl, D.; Kammeraad, J. et al.
System: The UNT Digital Library
Solid-Solid Phase Transition Kinetics of FOX-7 (open access)

Solid-Solid Phase Transition Kinetics of FOX-7

Since it was developed in the late 1990s, 1,1-diamino-2,2-dinitroethene (FOX-7), with lower sensitivity and comparable performance to RDX, has received increasing interest. This paper will present our results for the phase changes of FOX-7 using DSC and HFC (Heat Flow Calorimetry). DSC thermal curves recorded at linear heating rates of 0.10, 0.35 and 1.0 C min{sup -1} show two endothermic peaks and two exothermic peaks. The two endothermic peaks represent solid-solid phase transitions, which have been observed in the literature at 114 C ({beta}-{gamma}) and 159 C ({gamma}-{delta}) by both DSC and XPD (X-ray powder diffraction) measurements. The first transition shifts from 114.5 to 115.8 C as the heating rate increases from 0.10 to 1.0 C min{sup -1}, while the second transition shifts from 158.5 to 160.4 C. Cyclical heating experiments show the endotherms and exotherms for a first heating through the {gamma} phase to the {delta} phase, a cooling and reversion to the {alpha} or {beta} phase, and a second heating to the {gamma} and {delta} phases. The data are interpreted using kinetic models with thermodynamic constraints.
Date: July 12, 2005
Creator: Burnham, A K; Weese, R K; Wang, R; Kwok, Q M & Jones, D G
System: The UNT Digital Library
Production of [15O] Water at Low-Energy Proton Cyclotrons (open access)

Production of [15O] Water at Low-Energy Proton Cyclotrons

We report a simple system for producing [15O]H2O from nitrogen-15 in a nitrogen/hydrogen gas target with recycling of the target nitrogen, allowing production on low-energy proton-only accelerators with minimal consumption of isotopically enriched nitrogen-15. The radiolabeled water is separated from the target gas and radiolytically produced ammonia by temporary freezing in a small trap at -40 C.
Date: December 12, 2005
Creator: Powell, James & O'Neil, James P.
System: The UNT Digital Library
Tritium Effects on Fracture Toughness of Stainless Steel Weldments (open access)

Tritium Effects on Fracture Toughness of Stainless Steel Weldments

The effects of tritium on the fracture toughness properties of Type 304L and Type 21-6-9 stainless steel weldments were measured. Weldments were tritium-charged-and-aged and then tested in order to measure the effect of the increasing decay helium content on toughness. The results were compared to uncharged and hydrogen-charged samples. For unexposed weldments having 8-12 volume percent retained delta ferrite, fracture toughness was higher than base metal toughness. At higher levels of weld ferrite, the fracture toughness decreased to values below that of the base metal. Hydrogen-charged and tritium-charged weldments had lower toughness values than similarly charged base metals and toughness decreased further with increasing weld ferrite content. The effect of decay helium content was inconclusive because of tritium off-gassing losses during handling, storage and testing. Fracture modes were dominated by the dimpled rupture process in unexposed weldments. In hydrogen and tritium-exposed weldments, the fracture modes depended on the weld ferrite content. At high ferrite contents, hydrogen-induced transgranular fracture of the weld ferrite phase was observed.
Date: May 12, 2005
Creator: Morgan, Michael; Chapman, G. K.; Tosten, M. H. & West, S. L.
System: The UNT Digital Library
Molecular dynamics simulation of liquid water: Hybrid density functionals (open access)

Molecular dynamics simulation of liquid water: Hybrid density functionals

The structure, dynamical and electronic properties of liquid water utilizing different hybrid density functionals were tested within the plane wave framework of first principles molecular dynamics simulations. The computational approach, which employs modified functionals with short-ranged Hartree-Fock exchange, was first tested in calculations of the structural and bonding properties of the water dimer and cyclic water trimer. Liquid water simulations were performed at the state point of 350 K at the experimental density. Simulations included three different hybrid functionals, a meta functional, four gradient corrected functionals, the local density and Hartree-Fock approximation. It is found that hybrid functionals are superior in reproducing the experimental structure and dynamical properties as measured by the radial distribution function and self diffusion constant when compared to the pure density functionals. The local density and Hartree-Fock approximations show strongly over- and under-structured liquids, respectively. Hydrogen bond analysis shows that the hybrid functionals give slightly smaller averaged numbers of hydrogen bonds and similar hydrogen bond populations as pure density functionals. The average molecular dipole moments in the liquid from the three hybrid functionals are lower than from the corresponding pure density functionals.
Date: September 12, 2005
Creator: Todorova, T.; Seitsonen, A.; Hutter, J.; Kuo, W. & Mundy, C.
System: The UNT Digital Library
The ICF Status and Plans in the United States (open access)

The ICF Status and Plans in the United States

The United States continues to maintain its leadership in ICF as it moves toward the goal of ignition. The flagship of the program is the National Ignition Facility (NIF) presently under construction at LLNL. Experiments had begun on the first four beams of the National Ignition Facility just at the time of the last IFSA Conference. Several new successful campaigns have been conducted since then in planar hydrodynamics and hohlraums as well as activating the VISAR diagnostic for equation of state experiments. Highlights of these results will be reviewed. Presently, the four beam experimental capability has been suspended while the first eight beams are being installed as the first step in building out the project. Meanwhile, much progress has been made in developing ignition designs for using NIF. An array of designs having several ablator materials have been shown computationally to ignite with energies ranging from the design energy to as low as 1 MJ of laser energy. Alternative direct drive designs in the NIF indirect drive configuration have been developed by LLE. This wide array of design choices has increased the chance of achieving ignition sooner on the facility. Plans are now being developed to begin an ignition experimental …
Date: October 12, 2005
Creator: Moses, E.; Miller, G. & Kauffman, R.
System: The UNT Digital Library
Enabling HCCI modeling: The RIOT/CMCS Web Service for Automatic Reaction Mechanism Reduction (open access)

Enabling HCCI modeling: The RIOT/CMCS Web Service for Automatic Reaction Mechanism Reduction

New approaches are being developed to facilitate multidisciplinary collaborative research of Homogeneous Charge Compression Ignition (HCCI) combustion processes. In this paper, collaborative sharing of the Range Identification and Optimization Toolkit (RIOT) and related data and models is discussed. RIOT is a developmental approach to reduce the computational complexity of detailed chemical kinetic mechanisms, enabling their use in modeling kinetically-controlled combustion applications such as HCCI. These approaches are being developed and piloted as a part of the Collaboratory for Multiscale Chemical Sciences (CMCS) project. The capabilities of the RIOT code are shared through a portlet in the CMCS portal that allows easy specification and processing of RIOT inputs, remote execution of RIOT, tracking of data pedigree and translation of RIOT outputs (such as the reduced model) to a table view and to the commonly-used CHEMKIN mechanism format. The reduced model is thus immediately ready to be used for more efficient simulation of the chemically reacting system of interest. This effort is motivated by the need to improve computational efficiency in modeling HCCI systems. Preliminary use of the web service to obtain reduced models for this application has yielded computational speedup factors of up to 20 as presented in this paper.
Date: December 12, 2005
Creator: Oluwole, O; Pitz, W J; Schuchardt, K; Rahn, L A; Green, Jr., W H; Leahy, D et al.
System: The UNT Digital Library
Spectroscopic Observations and Analysis of the Unusual Type Ia SN1999ac (open access)

Spectroscopic Observations and Analysis of the Unusual Type Ia SN1999ac

The authors present optical spectra of the peculiar Type Ia supernova (SN Ia) 1999ac. The data extend from -15 to +42 days with respect to B-band maximum and reveal an event that is unusual in several respects. prior to B-band maximum, the spectra resemble those of SN 1999aa, a slowly declining event, but possess stronger Si II and Ca II signatures (more characteristic of a spectroscopically normal SN). Spectra after B-band maximum appear more normal. The expansion velocities inferred from the Iron lines appear to be lower than average; whereas, the expansion velocity inferred from Calcium H and K are higher than average. The expansion velocities inferred from the Iron lines appear to be lower than average; whereas, the expansion velocity inferred from Calcium H and K are higher than average. The expansion velocities inferred from Si II are among the slowest ever observed, though SN 1999ac is not particularly dim. The analysis of the parameters v{sub 10}(Si II), R(Si II), v, and {Delta}m{sub 15} further underlines the unique characteristics of SN 1999ac. They find convincing evidence of C II {lambda}6580 in the day -15 spectrum with ejection velocity v > 16,000 km s{sup -1}, but this signature disappears by …
Date: July 12, 2005
Creator: Garavini, G.; Aldering, G.; Amadon, A.; Amanullah, R.; Astier, P.; Balland, C. et al.
System: The UNT Digital Library
The Development of a Detailed Chemical Kinetic Mechanism for Diisobutylene and Comparison to Shock Tube Ignition Times (open access)

The Development of a Detailed Chemical Kinetic Mechanism for Diisobutylene and Comparison to Shock Tube Ignition Times

None
Date: December 12, 2005
Creator: Metcalfe, W K; Pitz, W J; Curran, H J; Simmie, J M & Westbrook, C K
System: The UNT Digital Library
Modeling and Experimental Investigation of Methylcyclohexane Ignition in a Rapid Compression Machine (open access)

Modeling and Experimental Investigation of Methylcyclohexane Ignition in a Rapid Compression Machine

None
Date: December 12, 2005
Creator: Pitz, W J; Naik, C V; Mhaold?in, T N; Westbrook, C K; Curran, H J; Orme, J P et al.
System: The UNT Digital Library
Chemical Identification of Dubnium as a Decay Product of Element 115 (open access)

Chemical Identification of Dubnium as a Decay Product of Element 115

None
Date: December 12, 2005
Creator: Shaughnessy, D A; Kenneally, J M; Moody, K J; Landrum, J H; Wilk, P A; Stoyer, M A et al.
System: The UNT Digital Library
B Decays to Open And Hidden Charm at BaBar (open access)

B Decays to Open And Hidden Charm at BaBar

A wealth of new measurements of hadronic B decays to open charm and charmonium have been performed on the data sample collected by the BaBar experiment at the PEP-II e{sup +}e{sup -} B-factory. We report the first measurement of the rates for inclusive charm production separately for charged and neutral B mesons. Combining measurements of the decay rate of B{sup 0} {yields} D*{sub s}{sup +}D*{sup -} obtained with a partial reconstruction technique and the complete reconstruction of B{sup 0} {yields} D*{sub s}{sup +}D*{sup -} with D{sub s}{sup +} {yields} {phi}{pi}{sup +}, we obtain the most precise measurement of {Beta}(D{sub s}{sup +} {yields} {phi}{pi}{sup +}). We present an update of the measurements of the branching fractions of exclusive B decays to J/{psi}, {psi}(2S), {chi}{sub c1}, {chi}{sub c2} and a kaon or a K*. In addition, we show preliminary results on exclusive decay rates to final states with baryons, or newly-discovered particles, such as D*{sub sJ}(2317), D{sub sJ}(2460){sup +}, and the X(3872).
Date: October 12, 2005
Creator: Ricciardi, S. & /Royal Holloway, U. of London
System: The UNT Digital Library
Finding the Magnetic Center of a Quadrupole to High Resolution (open access)

Finding the Magnetic Center of a Quadrupole to High Resolution

In a companion pro, collposal it is proposed to align quadrupoles of a transport line to within transverse tolerances of 5 to 10 micrometers. Such a proposal is meaningful only if the effective magnetic center of such lenses can in fact be repeatably located with respect to some external mechanical tooling to comparable accuracy. It is the purpose of this note to describe some new methods and procedures that will accomplish this aim. It will be shown that these methods are capable of yielding greater sensitivity than the more traditional methods used in the past. The notion of the ''nodal'' point is exploited.
Date: August 12, 2005
Creator: Fischer, G. E.; Cobb, J. K. & Jenson, D. R.
System: The UNT Digital Library
On the Significance of the Contribution of Multiple-Electron Capture Processes to Cometary X-Ray Emission (open access)

On the Significance of the Contribution of Multiple-Electron Capture Processes to Cometary X-Ray Emission

We report laboratory studies of the role played by multiple-electron capture (MEC) in solar wind induced cometary X-ray emission. Collisions of Ne{sup 10+} with He, Ne, Ar, CO, and CO{sub 2} have been investigated by means of the traditional singles X-ray spectroscopy in addition to the triple-coincidence measurements of X-rays, scattered projectile, and target recoil ions for the atomic targets. The coincidence measurements enable the reduction of the singles X-ray spectra into partial spectra originating in single-electron capture (SEC) and MEC collisions. The measurements provide unequivocal evidence for a significant role played by MEC, and strongly suggest that models based solely on SEC are bound to yield erroneous conclusions on the solar wind composition and velocities and on cometary atmospheres. The experimental relative importance of MEC collisions is compared with molecular classical-over-the-barrier model (MCBM), classical trajectory Monte Carlo (CTMC), and multi-channel Landau-Zener (MCLZ), calculations which can qualitatively reproduce the experimental trends.
Date: May 12, 2005
Creator: Ali, R.; Neill, P. A.; Beiersdorfer, P.; Harris, C. L.; Rakovi?, M. J.; Wang, J. G. et al.
System: The UNT Digital Library
Registration and Fusion of X-Ray and Ultrasound Images for As-Built Modeling (open access)

Registration and Fusion of X-Ray and Ultrasound Images for As-Built Modeling

None
Date: September 12, 2005
Creator: Clark, G A & Jackson, J A
System: The UNT Digital Library
DETERMINATION OF INVENTORIES AND POWER DISTRIBUTIONS FOR THE NSBR. (open access)

DETERMINATION OF INVENTORIES AND POWER DISTRIBUTIONS FOR THE NSBR.

This memo presents the details of the methodology for developing fuel inventories for the NBSR along with power distributions predicted with this set of inventories. Several improvements have been made to the MCNP model of the NBSR since a set of calculations was performed in 2002 in support of the NBSR relicensing and SAR update. One of the most significant changes in the model was to divide the fuel elements into upper and lower halves so the effects of uneven burn between the two halves (due to the shim arms) can be determined. The present set of power distributions are provided for comparison with the previous safety analyses.
Date: September 12, 2005
Creator: Hanson, A. L. & DIAMOND, D. J.
System: The UNT Digital Library