A balancing domain decomposition method by constraints for advection-diffusion problems (open access)

A balancing domain decomposition method by constraints for advection-diffusion problems

The balancing domain decomposition methods by constraints are extended to solving nonsymmetric, positive definite linear systems resulting from the finite element discretization of advection-diffusion equations. A pre-conditioned GMRES iteration is used to solve a Schur complement system of equations for the subdomain interface variables. In the preconditioning step of each iteration, a partially sub-assembled finite element problem is solved. A convergence rate estimate for the GMRES iteration is established, under the condition that the diameters of subdomains are small enough. It is independent of the number of subdomains and grows only slowly with the subdomain problem size. Numerical experiments for several two-dimensional advection-diffusion problems illustrate the fast convergence of the proposed algorithm.
Date: December 10, 2008
Creator: Tu, Xuemin & Li, Jing
Object Type: Article
System: The UNT Digital Library
Band Structure Asymmetry of Bilayer Graphene Revealed by Infrared Spectroscopy (open access)

Band Structure Asymmetry of Bilayer Graphene Revealed by Infrared Spectroscopy

We report on infrared spectroscopy of bilayer graphene integrated in gated structures. We observe a significant asymmetry in the optical conductivity upon electrostatic doping of electrons and holes. We show that this finding arises from a marked asymmetry between the valence and conduction bands, which is mainly due to the inequivalence of the two sublattices within the graphene layer and the next-nearest-neighbor interlayer coupling. From the conductivity data, the energy difference of the two sublattices and the interlayer coupling energy are directly determined.
Date: December 10, 2008
Creator: Li, Z. Q.; Henriksen, E. A.; Jiang, Z.; Hao, Zhao; Martin, Michael C.; Kim, P. et al.
Object Type: Article
System: The UNT Digital Library
BDDC for nonsymmetric positive definite and symmetric indefinite problems (open access)

BDDC for nonsymmetric positive definite and symmetric indefinite problems

The balancing domain decomposition methods by constraints are extended to solving both nonsymmetric, positive definite and symmetric, indefinite linear systems. In both cases, certain nonstandard primal constraints are included in the coarse problems of BDDC algorithms to accelerate the convergence. Under the assumption that the subdomain size is small enough, a convergence rate estimate for the GMRES iteration is established that the rate is independent of the number of subdomains and depends only slightly on the subdomain problem size. Numerical experiments for several two-dimensional examples illustrate the fast convergence of the proposed algorithms.
Date: December 10, 2008
Creator: Tu, Xuemin & Li, Jing
Object Type: Article
System: The UNT Digital Library
Complexation of Lanthanides with Nitrate at Variable Temperatures: Thermodynamics and Coordination Modes (open access)

Complexation of Lanthanides with Nitrate at Variable Temperatures: Thermodynamics and Coordination Modes

Complexation of neodymium(III) with nitrate was studied at variable temperatures (25, 40, 55 and 70 C) by spectrophotometry and microcalorimetry. The NdNO{sub 3}{sup 2+} complex is weak and becomes slightly stronger as the temperature is increased. The enthalpy of complexation at 25 C was determined by microcalorimetry to be small and positive, (1.5 {+-} 0.2) kJ {center_dot} mol{sup -1}, in good agreement with the trend of the stability constant at variable temperatures. Luminescence emission spectra and lifetime of Eu(III) in nitrate solutions suggest that inner-sphere and bidentate complexes form between trivalent lanthanides (Nd{sup 3+} and Eu{sup 3+}) and nitrate in aqueous solutions. Specific Ion Interaction approach (SIT) was used to obtain the stability constants of NdNO{sub 3}{sup 2+} at infinite dilution and variable temperatures.
Date: December 10, 2008
Creator: Rao, Linfeng & Tian, Guoxin
Object Type: Article
System: The UNT Digital Library
Convergence analysis of a balalncing domain decomposition method for solving interior Helmholtz equations (open access)

Convergence analysis of a balalncing domain decomposition method for solving interior Helmholtz equations

A variant of balancing domain decomposition method by constraints (BDDC) is proposed for solving a class of indefinite system of linear equations, which arises from the finite element discretization of the Helmholtz equation of time-harmonic wave propagation in a bounded interior domain. The proposed BDDC algorithm is closely related to the dual-primal finite element tearing and interconnecting algorithm for solving Helmholtz equations (FETI-DPH). Under the condition that the diameters of the subdomains are small enough, the rate of convergence is established which depends polylogarithmically on the dimension of the individual subdomain problems and which improves with the decrease of the subdomain diameters. These results are supported by numerical experiments of solving a Helmholtz equation on a two-dimensional square domain.
Date: December 10, 2008
Creator: Li,Jing & Tu, Xuemin
Object Type: Article
System: The UNT Digital Library
Couse/Tenmile Creeks Watershed Project Implementation : 2007 Conservtion Projects. [2007 Habitat Projects Completed]. (open access)

Couse/Tenmile Creeks Watershed Project Implementation : 2007 Conservtion Projects. [2007 Habitat Projects Completed].

The Asotin County Conservation District (ACCD) is the primary entity coordinating habitat projects on private lands within Asotin County watersheds. The Tenmile Creek watershed is a 42 square mile tributary to the Snake River, located between Asotin Creek and the Grande Ronde River. Couse Creek watershed is a 24 square mile tributary to the Snake River, located between Tenmile Creek and the Grande Ronde River. Both watersheds are almost exclusively under private ownership. The Washington Department of Fish and Wildlife has documented wild steelhead and rainbow/redband trout spawning and rearing in Tenmile Creek and Couse Creek. The project also provides Best Management Practice (BMP) implementation throughout Asotin County, but the primary focus is for the Couse and Tenmile Creek watersheds. The ACCD has been working with landowners, Bonneville Power Administration (BPA), Washington State Conservation Commission (WCC), Natural Resource Conservation Service (NRCS), Farm Service Agency (FSA), Salmon Recovery Funding Board (SRFB), Washington Department of Fish and Wildlife (WDFW), U.S. Forest Service, Pomeroy Ranger District (USFS), Nez Perce Tribe (NPT), Washington Department of Ecology (DOE), National Marine Fisheries Service (NOAA Fisheries), and U.S. Fish and Wildlife Service (USFWS) to address habitat projects in Asotin County. The Asotin Subbasin Plan identified priority areas …
Date: December 10, 2008
Creator: District, Asotin County Conservation
Object Type: Report
System: The UNT Digital Library
Development of ZnO:Ga as an Ultrafast Scintillator (open access)

Development of ZnO:Ga as an Ultrafast Scintillator

We report on several methods for synthesizing the ultra-fast scintillator ZnO(Ga), and measurements of the resulting products. This material has characteristics that make it an excellent alpha detector for tagging the time and direction of individual neutrons produced by t-d and d-d neutron generators (associated particle imaging). The intensity and decay time are strongly dependent on the method used for dopant incorporation. We compare samples made by diffusion of Ga metal to samples made by solid state reaction between ZnO and Ga2O3 followed by reduction in hydrogen. The latter is much more successful and has a pure, strong near-band-edge fluorescence and an ultra-fast decay time of the x-ray-excited luminescence. The luminescence increases dramatically as the temperature is reduced to 10K. We also present results of an alternate low-temperature synthesis that produces luminescent particles with a more uniform size distribution. We examine possible mechanisms for the bright near-band-edge scintillation and favor the explanation that it is due to the recombination of Ga3+ donor electrons with ionization holes trapped on H+ ion acceptors.
Date: December 10, 2008
Creator: Bourret-Courchesne, E. D.; Derenzo, S. E. & Weber, M. J.
Object Type: Article
System: The UNT Digital Library
Disturbance of isotope systematics in meteorites during shock and thermal metamorphism and implications for shergottite chronology (open access)

Disturbance of isotope systematics in meteorites during shock and thermal metamorphism and implications for shergottite chronology

Shock and thermal metamorphism of meteorites from differentiated bodies such as the Moon and Mars have the potential to disturb chronometric information contained in these meteorites. In order to understand the impact-related mechanisms and extent of disturbance to isochrons, we undertook experiments to shock and heat samples of 10017, a 3.6 billion year old lunar basalt. One sub-sample was shocked to 55 GPa, a second subsample was heated to 1000 C for one week, and a third sub-sample was maintained as a control sample. Of the isotope systems analyzed, the Sm-Nd system was the least disturbed by shock or heat, followed by the Rb-Sr system. Ages represented by the {sup 238}U-{sup 206}Pb isotope system were degraded by shock and destroyed with heating. In no case did either shock or heating alone result in rotated or reset isochrons that represent a spurious age. In some cases the true crystallization age of the sample was preserved, and in other cases age information was degraded or destroyed. Although our results show that neither shock nor thermal metamorphism alone can account for the discordant ages represented by different isotope systems in martian meteorites, we postulate that shock metamorphism may render a meteorite more susceptible …
Date: December 10, 2008
Creator: Gaffney, Amy M.; Borg, Lars E. & Asmerom, Yemane
Object Type: Article
System: The UNT Digital Library
Inf-sup estimates for the Stokes problem in a periodic channel (open access)

Inf-sup estimates for the Stokes problem in a periodic channel

We derive estimates of the Babuska-Brezzi inf-sup constant {beta} for two-dimensional incompressible flow in a periodic channel with one flat boundary and the other given by a periodic, Lipschitz continuous function h. If h is a constant function (so the domain is rectangular), we show that periodicity in one direction but not the other leads to an interesting connection between {beta} and the unitary operator mapping the Fourier sine coefficients of a function to its Fourier cosine coefficients. We exploit this connection to determine the dependence of {beta} on the aspect ratio of the rectangle. We then show how to transfer this result to the case that h is C{sup 1,1} or even C{sup 0,1} by a change of variables. We avoid non-constructive theorems of functional analysis in order to explicitly exhibit the dependence of {beta} on features of the geometry such as the aspect ratio, the maximum slope, and the minimum gap thickness (if h passes near the substrate). We give an example to show that our estimates are optimal in their dependence on the minimum gap thickness in the C{sup 1,1} case, and nearly optimal in the Lipschitz case.
Date: December 10, 2008
Creator: Wilkening, Jon
Object Type: Article
System: The UNT Digital Library
Measurements of NaI(Tl) electron response: comparison of different samples (open access)

Measurements of NaI(Tl) electron response: comparison of different samples

This paper measures the sample to sample variation in the light yield proportionality of NaI(Tl), and so explores whether this is an invariant characteristic of the material or whether it depends on the chemical and physical properties of the tested samples. We report on the electron response of nine crystals of NaI(Tl), differing in shape, volume, age, manufacturer and quality. The proportionality has been measured at the SLYNCI facility in the energy range between 3.5 to 460 keV. We observe that while samples produced by the same manufacturer at approximately the same time have virtually identical electron response curves, there are significant sample to sample variations among crystals produced by different manufacturers or at different times. In an effort to correlate changes in the electron response with details of the scintillation mechanism, we characterized other scintillation properties, including the gamma response and the x-ray excited emission spectra and decay times, for the nine crystals. While sample to sample differences in these crystals were observed, we have been unable to identify the underlying fundamental mechanisms that are responsible for these differences.
Date: December 10, 2008
Creator: Hull, Giulia; Choong, Woon-Seng; Moses, William W.; Bizarri, Gregory; Valentine, John D.; Payne, Stephen A. et al.
Object Type: Article
System: The UNT Digital Library
Microwave Plasma Chemical Vapor Deposition of Carbon Coatings on LiNi1/3Co1/3Mn1/3O2 for Li-Ion Battery Composite Cathodes (open access)

Microwave Plasma Chemical Vapor Deposition of Carbon Coatings on LiNi1/3Co1/3Mn1/3O2 for Li-Ion Battery Composite Cathodes

In this paper, we report results of a novel synthesis method of thin film conductive carbon coatings on LiNi{sub 1/3}Co{sub 1/3}Mn{sub 1/3}O{sub 2} cathode active material powders for lithium-ion batteries. Thin layers of graphitic carbon were produced from a solid organic precursor, anthracene, by a one-step microwave plasma chemical vapor deposition (MPCVD) method. The structure and morphology of the carbon coatings were examined using SEM, TEM, and Raman spectroscopy. The composite LiNi{sub 1/3}Co{sub 1/3}Mn{sub 1/3}O{sub 2} electrodes were electrochemically tested in lithium half coin cells. The composite cathodes made of the carbon-coated LiNi{sub 1/3}Co{sub 1/3}Mn{sub 1/3}O{sub 2} powder showed superior electrochemical performance and increased capacity compared to standard composite LiNi{sub 1/3}Co{sub 1/3}Mn{sub 1/3}O{sub 2} electrodes.
Date: December 10, 2008
Creator: Doeff, Marek M.; Kostecki, Robert M.; Marcinek, Marek L. & Wilcox, James W.
Object Type: Article
System: The UNT Digital Library
Practical error estimates for Reynolds' lubrication approximation and its higher order corrections (open access)

Practical error estimates for Reynolds' lubrication approximation and its higher order corrections

Reynolds lubrication approximation is used extensively to study flows between moving machine parts, in narrow channels, and in thin films. The solution of Reynolds equation may be thought of as the zeroth order term in an expansion of the solution of the Stokes equations in powers of the aspect ratio {var_epsilon} of the domain. In this paper, we show how to compute the terms in this expansion to arbitrary order on a two-dimensional, x-periodic domain and derive rigorous, a-priori error bounds for the difference between the exact solution and the truncated expansion solution. Unlike previous studies of this sort, the constants in our error bounds are either independent of the function h(x) describing the geometry, or depend on h and its derivatives in an explicit, intuitive way. Specifically, if the expansion is truncated at order 2k, the error is O({var_epsilon}{sup 2k+2}) and h enters into the error bound only through its first and third inverse moments {integral}{sub 0}{sup 1} h(x){sup -m} dx, m = 1,3 and via the max norms {parallel} 1/{ell}! h{sup {ell}-1}{partial_derivative}{sub x}{sup {ell}}h{parallel}{sub {infinity}}, 1 {le} {ell} {le} 2k + 2. We validate our estimates by comparing with finite element solutions and present numerical evidence that suggests …
Date: December 10, 2008
Creator: Wilkening, Jon
Object Type: Article
System: The UNT Digital Library
QCD Evolution of the Transverse Momentum Dependent Correlations (open access)

QCD Evolution of the Transverse Momentum Dependent Correlations

We study the QCD evolution for the twist-three quark-gluon correlation functions associated with the transverse momentum odd quark distributions. Different from that for the leading twist quark distributions, these evolution equations involve more general twist-three functions beyond the correlation functions themselves. They provide important information on nucleon structure, and can be studied in the semi-inclusive hadron production in deep inelastic scattering and Drell-Yan lepton pair production in pp scattering process.
Date: December 10, 2008
Creator: Zhou, Jian; Liang, Zuo-Tang & Yuan, Feng
Object Type: Article
System: The UNT Digital Library
Recent Development in Proton Spin Physics (open access)

Recent Development in Proton Spin Physics

In the naive model of the proton, its 1/2 spin is carried by its quark constituents. However, experiments over the last several decades have shown that the quark spin only contribute a small portion of the proton spin. In this talk, I will present recent developments exploring this proton spin puzzle, and focus on the progress made in the last few years on the longitudinal spin physics, the generalized parton distribution physics, and the transverse spin physics.
Date: December 10, 2008
Creator: Yuan, Feng
Object Type: Article
System: The UNT Digital Library
Semi-inclusive DIS: Factorization (open access)

Semi-inclusive DIS: Factorization

In this talk, we will present a QCD factorization theorem for the semi-inclusive deep-inelastic scattering with hadrons in the current fragmentation region detected at low transverse momentum. There has been considerable experimental and theoretical interest in semi-inclusive hadron production in deep inelastic scattering (SIDIS) processes. For example, by studying the polarized and unpolarized SIDIS, one will be able to identify the sea quark distribution and polarization in nucleon, and the experimental results from the HERMES collaboration have revealed nontrivial sea structure in nucleon [1]. More recently, SIDIS opened a new window to study the transverse momentum dependent (TMD) parton distributions and fragmentation functions from the low transverse momentum hadron production. The transverse momentum distribution of the final state hadron is directly related to the transverse momentum dependence of the parton distributions and fragmentation. These studies will provide new opportunities to explore the partonic structure of nucleon, especially the three-dimension distribution of partons inside nucleon. The DIS experiments, including HERMES, COMPAS, and JLab Hall B collaborations, have studied various azimuthal asymmetries in SIDIS. In particular, the HERMES collaboration found sizable single spin asymmetries in these processes involving nontrivial QCD effects and hadron structure.
Date: December 10, 2008
Creator: Yuan, Feng
Object Type: Article
System: The UNT Digital Library
Shape optimization of a sheet swimming over a thin liquid layer (open access)

Shape optimization of a sheet swimming over a thin liquid layer

Motivated by the propulsion mechanisms adopted by gastropods, annelids and other invertebrates, we consider shape optimization of a flexible sheet that moves by propagating deformation waves along its body. The self-propelled sheet is separated from a rigid substrate by a thin layer of viscous Newtonian fluid. We use a lubrication approximation to model the dynamics and derive the relevant Euler-Lagrange equations to simultaneously optimize swimming speed, efficiency and fluid loss. We find that as the parameters controlling these quantities approach critical values, the optimal solutions become singular in a self-similar fashion and sometimes leave the realm of validity of the lubrication model. We explore these singular limits by computing higher order corrections to the zeroth order theory and find that wave profiles that develop cusp-like singularities are appropriately penalized, yielding non-singular optimal solutions. These corrections are themselves validated by comparison with finite element solutions of the full Stokes equations, and, to the extent possible, using recent rigorous a-priori error bounds.
Date: December 10, 2008
Creator: Wilkening, J. & Hosoi, A.E.
Object Type: Article
System: The UNT Digital Library
A Three-level BDDC algorithm for saddle point problems (open access)

A Three-level BDDC algorithm for saddle point problems

BDDC algorithms have previously been extended to the saddle point problems arising from mixed formulations of elliptic and incompressible Stokes problems. In these two-level BDDC algorithms, all iterates are required to be in a benign space, a subspace in which the preconditioned operators are positive definite. This requirement can lead to large coarse problems, which have to be generated and factored by a direct solver at the beginning of the computation and they can ultimately become a bottleneck. An additional level is introduced in this paper to solve the coarse problem approximately and to remove this difficulty. This three-level BDDC algorithm keeps all iterates in the benign space and the conjugate gradient methods can therefore be used to accelerate the convergence. This work is an extension of the three-level BDDC methods for standard finite element discretization of elliptic problems and the same rate of convergence is obtained for the mixed formulation of the same problems. Estimate of the condition number for this three-level BDDC methods is provided and numerical experiments are discussed.
Date: December 10, 2008
Creator: Tu, X.
Object Type: Article
System: The UNT Digital Library
Transverse Spin Physics: Recent Developments (open access)

Transverse Spin Physics: Recent Developments

Transverse-spin physics has been very active and rapidly developing in the last few years. In this talk, I will briefly summarize recent theoretical developments, focusing on the associated QCD dynamics in transverse spin physics.
Date: December 10, 2008
Creator: Yuan, Feng
Object Type: Article
System: The UNT Digital Library
Two-phase viscoelastic jetting (open access)

Two-phase viscoelastic jetting

A coupled finite difference algorithm on rectangular grids is developed for viscoelastic ink ejection simulations. The ink is modeled by the Oldroyd-B viscoelastic fluid model. The coupled algorithm seamlessly incorporates several things: (1) a coupled level set-projection method for incompressible immiscible two-phase fluid flows; (2) a higher-order Godunov type algorithm for the convection terms in the momentum and level set equations; (3) a simple first-order upwind algorithm for the convection term in the viscoelastic stress equations; (4) central difference approximations for viscosity, surface tension, and upper-convected derivative terms; and (5) an equivalent circuit model to calculate the inflow pressure (or flow rate) from dynamic voltage.
Date: December 10, 2008
Creator: Yu, J.-D.; Sakai, S. & Sethian, J. A.
Object Type: Article
System: The UNT Digital Library
Variational particle scheme for the porous medium equation and for the system of isentropic Euler equations (open access)

Variational particle scheme for the porous medium equation and for the system of isentropic Euler equations

We introduce variational particle schemes for the porous medium equation and the system of isentropic Euler equations in one space dimension. The methods are motivated by the interpretation of each of these partial differential equations as a 'steepest descent' on a suitable abstract manifold. We show that our methods capture very well the nonlinear features of the flows.
Date: December 10, 2008
Creator: Westdickenberg, Michael & Wilkening, Jon
Object Type: Article
System: The UNT Digital Library
Demonstration Assessment of Light Emitting Diode (LED) Residential Downlights and Undercabinet Lights in the Lane County Tour of Homes, Eugene, Oregon (open access)

Demonstration Assessment of Light Emitting Diode (LED) Residential Downlights and Undercabinet Lights in the Lane County Tour of Homes, Eugene, Oregon

In August 2008 the Pacific Northwest National Laboratory (PNNL) conducted a light emitting diode (LED) residential lighting demonstration project for the U.S. Department of Energy (DOE), Office of Building Technologies, as part of DOE’s Solid State Lighting (SSL) Technology Demonstration Gateway Program. Two lighting technologies, an LED replacement for downlight lamps (bulbs) and an LED undercabinet lighting fixture, were tested in the demonstration which was conducted in two homes built for the 2008 Tour of Homes in Eugene, Oregon. The homes were built by the Lane County Home Builders Association (HBA), and Future B Homes. The Energy Trust of Oregon (ETO) also participated in the demonstration project. The LED downlight product, the LR6, made by Cree LED Lighting Solutions acts as a screw-in replacement for incandescent and halogen bulbs in recessed can downlights. The second product tested is Phillips/Color Kinetics’ eW® Profile Powercore undercabinet fixture designed to mount under kitchen cabinets to illuminate the countertop and backsplash surfaces. Quantitative and qualitative measurements of light performance and electrical power usage were taken at each site before and after initially installed halogen and incandescent lamps were replaced with the LED products. Energy savings and simple paybacks were also calculated and builders who …
Date: November 10, 2008
Creator: Ton, My K.; Richman, Eric E. & Gilbride, Theresa L.
Object Type: Report
System: The UNT Digital Library
Grande Ronde Subbasin Gauging Station Operations, 2007-2008 Reporting Period. (open access)

Grande Ronde Subbasin Gauging Station Operations, 2007-2008 Reporting Period.

The Grande Ronde Basin (GRB) in Northeast Oregon is a moderately dry climate receiving between 10 and 20 inches of precipitation per year with surrounding mountains accumulating up to 100 inches. Irrigated agriculture is a major part of the economy with water being diverted or pumped from surface and ground sources from April through October. Several ESA listed species exist in the basin including Chinook, steelhead, and bulltrout. Agriculture and ESA (Endangered Species Act) listed aquatic species combined with a dry climate demonstrate the need for a network of stream gauges. The GRB covers over 5,000 square miles and includes several thousand miles of perennial flowing streams. This project is in place to operate 12 existing stream gauges in combination with USGS (4 gauges) and OWRD (one gauge) who, independent of this project, operate five additional gauges (Grande Ronde at Troy, Imnaha R. at Imnaha, Minam R. at Minam, Lookingglass Creek, and Upper Catherine Cr.) to characterizes flow in both the Grande Ronde and Imnaha subbasins. These gauges are intended to assist in irrigation water management, fisheries management, long term flow and trend analysis, TMDL and SB1010 water quality management plan effectiveness, subbasin plan implementation, and provide essential information regarding …
Date: November 10, 2008
Creator: Menton, R. Coby
Object Type: Report
System: The UNT Digital Library
Molecular Basis for Enzymatic Sulfite Oxidation -- HOW THREE CONSERVED ACTIVE SITE RESIDUES SHAPE ENZYME ACTIVITY (open access)

Molecular Basis for Enzymatic Sulfite Oxidation -- HOW THREE CONSERVED ACTIVE SITE RESIDUES SHAPE ENZYME ACTIVITY

Sulfite dehydrogenases (SDHs) catalyze the oxidation and detoxification of sulfite to sulfate, a reaction critical to all forms of life. Sulfite-oxidizing enzymes contain three conserved active site amino acids (Arg-55, His-57, and Tyr-236) that are crucial for catalytic competency. Here we have studied the kinetic and structural effects of two novel and one previously reported substitution (R55M, H57A, Y236F) in these residues on SDH catalysis. Both Arg-55 and His-57 were found to have key roles in substrate binding. An R55M substitution increased Km(sulfite)(app) by 2-3 orders of magnitude, whereas His-57 was required for maintaining a high substrate affinity at low pH when the imidazole ring is fully protonated. This effect may be mediated by interactions of His-57 with Arg-55 that stabilize the position of the Arg-55 side chain or, alternatively, may reflect changes in the protonation state of sulfite. Unlike what is seen for SDHWT and SDHY236F, the catalytic turnover rates of SDHR55M and SDHH57A are relatively insensitive to pH (~;;60 and 200 s-1, respectively). On the structural level, striking kinetic effects appeared to correlate with disorder (in SDHH57A and SDHY236F) or absence of Arg-55 (SDHR55M), suggesting that Arg-55 and the hydrogen bonding interactions it engages in are crucial for …
Date: November 10, 2008
Creator: Bailey, Susan; Rapson, Trevor; Johnson-Winters, Kayunta; Astashkin, Andrei; Enemark, John & Kappler, Ulrike
Object Type: Article
System: The UNT Digital Library
NOVEL CATALYTIC EFFECTS OF FULLERENE FOR LIBH4 HYDROGEN UPTAKE AND RELEASE (open access)

NOVEL CATALYTIC EFFECTS OF FULLERENE FOR LIBH4 HYDROGEN UPTAKE AND RELEASE

Our recent novel finding, involving a synergistic experiment and first-principles theory, shows that carbon nanostructures can be used as catalysts for hydrogen uptake/release in aluminum based complex metal hydrides (sodium alanate) and also provides an unambiguous understanding of how the catalysts work. Here we show that the same concepts can be applied to boron based complex hydride such as lithium borohydride, LiBH{sub 4}. Taking into account electronegativity and curvature effect a fullerene-LiBH{sub 4} composite demonstrates catalytic properties with not only lowered hydrogen desorption temperatures, but regenerative rehydriding at relatively lower temperature of 350 C. This catalytic effect likely originates from interfering with the charge transfer from Li to the BH4 moiety, resulting in an ionic bond between Li{sup +} and BH{sub 4}{sup -}, and a covalent bond between B and H. Interaction of LiBH{sub 4} with an electronegative substrate such as carbon fullerene affects the ability of Li to donate its charge to BH{sub 4}, consequently weakening the B-H bond and causing hydrogen to desorb at lower temperatures as well as facilitating the absorption of H{sub 2} to reverse the dehydrogenation reaction. Degradation of cycling capacity is observed and is attributed to forming irreversible intermediates or diboranes.
Date: November 10, 2008
Creator: Wellons, M; Ragaiy Zidan, R & Polly Perseth, P
Object Type: Article
System: The UNT Digital Library