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
Transmission Electron Microscopy Study of Nonpolar a-Plane GaNGrown by Pendeo-Epitaxy on (112_0) 4H-SiC (open access)

Transmission Electron Microscopy Study of Nonpolar a-Plane GaNGrown by Pendeo-Epitaxy on (112_0) 4H-SiC

Pendeo-epitaxy has been applied to nonpolar a-plane GaN layers in order to observe if such process will lead to defect reduction in comparison with direct growth on this plane. Uncoalesced and coalesced a-plane GaN layers with thicknesses 2{micro}m and 12{micro}m, respectively have been studied by conventional and high resolution electron microscopy. The following structural defects have been observed in pendeo-epitaxial layers: (1) basal stacking faults, (2) threading dislocations and (3) prismatic stacking faults. Drastic decrease of threading dislocation density and stacking faults have been observed in 'wing' areas with respect to 'seed' areas. Cross-section images reveal cracks and voids at the areas where two coalesced wings meet each other. High resolution electron microscopy shows that the majority of stacking faults are low-energy planar defects of the types I{sub 1}, I{sub 2} and I{sub 3}. The I{sub 3} type basal stacking fault, predicted theoretically, has been observed experimentally for the first time.
Date: March 10, 2005
Creator: Zakharov, D. N.; Liliental-Weber, Z.; Wagner, B.; Reitmeier, Z. J.; Preble, E. A. & Davis, R. F.
Object Type: Article
System: The UNT Digital Library
Summary of Workshop: Barriers to Energy Efficient Residential Ventilation (open access)

Summary of Workshop: Barriers to Energy Efficient Residential Ventilation

The objectives for this workshop were to bring together those with different viewpoints on the implementation of energy efficient ventilation in homes to share their perspectives. The primary benefit of the workshop is to allow the participants to get a broader understanding of the issues involved and thereby make themselves more able to achieve their own goals in this area. In order to achieve this objective each participant was asked to address four objectives from their point of view: (1) Drivers for energy efficient residential ventilation: Why is this an important issue? Who cares about it? Where is the demand: occupants, utilities, regulation, programs, etc? What does sustainability mean in this context? (2) Markets & Technologies: What products, services and systems are out there? What kinds of things are in the pipeline? What is being installed now? Are there regional or other trends? What are the technology interactions with other equipment and the envelope? (3) Barriers to Implementation: What is stopping decision makers from implementing energy-efficient residential ventilation systems? What kind of barriers are there: technological, cost, informational, structural, etc. What is the critical path? (4) Solutions: What can be done to overcome the barriers and how can/should we do …
Date: January 10, 2008
Creator: Sherman, Max & Sherman, Max
Object Type: Report
System: The UNT Digital Library
Mg-induced increase of bandgap in Zn1-xMgxO nanorods revealed by x-ray absorption and emission spectroscopy (open access)

Mg-induced increase of bandgap in Zn1-xMgxO nanorods revealed by x-ray absorption and emission spectroscopy

X-ray absorption near-edge structure (XANES) and x-ray emission spectroscopy (XES) measurements were used to investigate the effect of Mg doping in ZnO nanorods. The intensities of the features in the O K-edge XANES spectra of Zn{sub 1-x}Mg{sub x}O nanorods are lower than those of pure ZnO nanorods, suggesting that Mg doping increases the negative effective charge of O ions. XES and XANES spectra of O 2p states indicate that Mg doping raises (lowers) the conduction-band-minimum (valence-band-maximum) and increases the bandgap. The bandgap is found to increase linearly with the Mg content, as revealed by photoluminescence and combined XANES and XES measurements.
Date: July 10, 2008
Creator: Pong, Way-Faung; Chiou, J. W.; Tsai, H. M.; Pao, C. W.; Chien, F. Z.; Pong, W. F. et al.
Object Type: Article
System: The UNT Digital Library
Fine-scale Horizontal Structure of Arctic Mixed-Phase Clouds. (open access)

Fine-scale Horizontal Structure of Arctic Mixed-Phase Clouds.

Recent in situ observations in stratiform clouds suggest that mixed phase regimes, here defined as limited cloud volumes containing both liquid and solid water, are constrained to narrow layers (order 100 m) separating all-liquid and fully glaciated volumes (Hallett and Viddaurre, 2005). The Department of Energy Atmospheric Radiation Measurement Program's (DOE-ARM, Ackerman and Stokes, 2003) North Slope of Alaska (NSA) ARM Climate Research Facility (ACRF) recently started collecting routine measurement of radar Doppler velocity power spectra from the Millimeter Cloud Radar (MMCR). Shupe et al. (2004) showed that Doppler spectra has potential to separate the contributions to the total reflectivity of the liquid and solid water in the radar volume, and thus to investigate further Hallett and Viddaurre's findings. The Mixed-Phase Arctic Cloud Experiment (MPACE) was conducted along the NSA to investigate the properties of Arctic mixed phase clouds (Verlinde et al., 2006). We present surface based remote sensing data from MPACE to discuss the fine-scale structure of the mixed-phase clouds observed during this experiment.
Date: July 10, 2006
Creator: Rambukkange,M.; Verlinde, J.; Elorante, E.; Luke, E.; Kollias, P. & Shupe, M.
Object Type: Article
System: The UNT Digital Library
Web-Ice: Integrated Data Collection and Analysis for Macromolecular Crystallography (open access)

Web-Ice: Integrated Data Collection and Analysis for Macromolecular Crystallography

New software tools are introduced to facilitate diffraction experiments involving largenumbers of crystals. While existing programs have long provided a framework for lattice indexing, Bragg spot integration, and symmetry determination, these initial data processing steps often require significant manual effort. This limits the timely availability of data analysis needed for high-throughput procedures, including the selection of the best crystals from a large sample pool, and the calculation of optimal data collection parameters to assure complete spot coverage with minimal radiation damage. To make these protocols more efficient, we developed a network of software applications and application servers, collectively known as Web-Ice. When the package is installed at a crystallography beamline, a programming interface allows the beamline control software (e.g., Blu-Ice / DCSS) to trigger data analysis automatically. Results are organized based on a list of samples that the user provides, and are examined within a Web page, accessible both locally at the beamline or remotely. Optional programming interfaces permit the user tocontrol data acquisition through the Web browser. The system as a whole is implemented to support multiple users and multiple processors, and can be expanded to provide additional scientific functionality. Web-Ice has a distributed architecture consisting of several stand-alone …
Date: October 10, 2007
Creator: Gonzalez, Ana; Gonzalez, Ana; Moorhead, Penjit; McPhillips, Scott E.; Song, Jinhu; Sharp, Ken et al.
Object Type: Article
System: The UNT Digital Library
InN Nanorods Grown on Different Planes of Al2O3 (open access)

InN Nanorods Grown on Different Planes of Al2O3

None
Date: March 10, 2007
Creator: Liliental-Weber, Z.; Park, H.J.; Mangum, J.; Anderson, T. & Kryliouk, O.
Object Type: Article
System: The UNT Digital Library
Calculation Of Change-Changing Cross Sections Of IONS Or Atoms Colliding With Fast IONS Using The Classical Trajectory Method (open access)

Calculation Of Change-Changing Cross Sections Of IONS Or Atoms Colliding With Fast IONS Using The Classical Trajectory Method

Evaluation of ion-atom charge-changing cross sections is needed for many accelerator applications. A classical trajectory Monte Carlo (CTMC) simulation has been used to calculate ionization and charge exchange cross sections. For benchmarking purposes, an extensive study has been performed for the simple case of hydrogen and helium targets in collisions with various ions. Despite the fact that the simulation only accounts for classical mechanics, the calculations are comparable to experimental results for projectile velocities in the region corresponding to the vicinity of the maximum cross section. Shortcomings of the CTMC method for multielectron target atoms are discussed.
Date: October 10, 2008
Creator: Kaganovich, I. D., Shnidman, Ariel, Mebane, Harrison, Davidson, R.C.
Object Type: Article
System: The UNT Digital Library
Shape Determination for Deformed Electromagnetic Cavities (open access)

Shape Determination for Deformed Electromagnetic Cavities

The measured physical parameters of a superconducting cavity differ from those of the designed ideal cavity. This is due to shape deviations caused by both loose machine tolerances during fabrication and by the tuning process for the accelerating mode. We present a shape determination algorithm to solve for the unknown deviations from the ideal cavity using experimentally measured cavity data. The objective is to match the results of the deformed cavity model to experimental data through least-squares minimization. The inversion variables are unknown shape deformation parameters that describe perturbations of the ideal cavity. The constraint is the Maxwell eigenvalue problem. We solve the nonlinear optimization problem using a line-search based reduced space Gauss-Newton method where we compute shape sensitivities with a discrete adjoint approach. We present two shape determination examples, one from synthetic and the other from experimental data. The results demonstrate that the proposed algorithm is very effective in determining the deformed cavity shape.
Date: December 10, 2007
Creator: Akcelik, Volkan; Ko, Kwok; Lee, Lie-Quan; Li, Zhenghai; Ng, Cho-Kuen & Xiao, Liling
Object Type: Article
System: The UNT Digital Library
The Absence of Plasma in"Spark Plasma Sintering" (open access)

The Absence of Plasma in"Spark Plasma Sintering"

Spark plasma sintering (SPS) is a remarkable method for synthesizing and consolidating a large variety of both novel and traditional materials. The process typically uses moderate uni-axial pressures (<100 MPa) in conjunction with a pulsing on-off DC current during operation. There are a number of mechanisms proposed to account for the enhanced sintering abilities of the SPS process. Of these mechanisms, the one most commonly put forth and the one that draws the most controversy involves the presence of momentary plasma generated between particles. This study employees three separate experimental methods in an attempt to determine the presence or absence of plasma during SPS. The methods employed include: in-situ atomic emission spectroscopy, direct visual observation and ultra-fast in-situ voltage measurements. It was found using these experimental techniques that no plasma is present during the SPS process. This result was confirmed using several different powders across a wide spectrum of SPS conditions.
Date: April 10, 2008
Creator: Hulbert, Dustin M.; Anders, Andre; Dudina, Dina V.; Andersson, Joakim; Jiang, Dongtao; Unuvar, Cosan et al.
Object Type: Article
System: The UNT Digital Library
Chemical imaging of biological materials by NanoSIMS using isotopic and elemental labels (open access)

Chemical imaging of biological materials by NanoSIMS using isotopic and elemental labels

The NanoSIMS 50 combines unprecedented spatial resolution (as good as 50 nm) with ultra-high sensitivity (minimum detection limit of {approx}200 atoms). The NanoSIMS 50 incorporates an array of detectors, enabling simultaneous collection of 5 species originating from the same sputtered volume of a sample. The primary ion beam (Cs{sup +} or O{sup -}) can be scanned across the sample to produce quantitative secondary ion images. This capability for multiple isotope imaging with high spatial resolution provides a novel new approach to the study of biological materials. Studies can be made of sub-regions of tissues, mammalian cells, and bacteria. Major, minor and trace element distributions can be mapped on a submicron scale, growth and metabolism can be tracked using stable isotope labels, and biogenic origin can be determined based on composition. We have applied this technique extensively to mammalian and prokaryotic cells and bacterial spores. The NanoSIMS technology enables the researcher to interrogate the fate of molecules of interest within cells and organs through elemental and isotopic labeling. Biological applications at LLNL will be discussed.
Date: April 10, 2006
Creator: Weber, P K; Fallon, S J; Pett-Ridge, J; Ghosal, S & Hutcheon, I D
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
The polarized SRF gun experiment. (open access)

The polarized SRF gun experiment.

RF electron guns are capable of producing electron bunches with high brightness, which outperform DC electron guns and may even be able to provide electron beams for the ILC without the need for a damping ring. However, all successful existing guns for polarized electrons are DC guns because the environment inside an RF gun is hostile to the GaAs cathode material necessary for polarization. While the typical vacuum pressure in a DC gun is better than 10{sup -11} torr the vacuum in an RF gun is in the order of 10{sup -9} torr. Experiments at BINP Novosibirsk show that this leads to strong ion back-bombardment and generation of dark currents, which destroy the GaAs cathode in a short time. The situation might be much more favorable in a (super-conducting) SRF gun. The cryogenic pumping of the gun cavity walls may make it possible to maintain a vacuum close to 10{sup -12} torr, solving the problem of ion bombardment and dark currents. Of concern would be contamination of the gun cavity by evaporating cathode material. This report describes an experiment that Brookhaven National Laboratory (BNL) in collaboration with Advanced Energy Systems (AES) is conducting to answer these questions.
Date: September 10, 2007
Creator: Kewisch, J.; Ben-Zvi, Ilan; Rao, T.; Burrill, A.; Pate, D.; Grover, R. et al.
Object Type: Article
System: The UNT Digital Library
The Formation of Contact and Very Close Binaries (open access)

The Formation of Contact and Very Close Binaries

We explore the possibility that all close binaries, i.e. those with periods {approx}< 3 d, including contact (W UMa) binaries, are produced from initially wider binaries (periods of say 10's of days) by the action of a triple companion through the medium of Kozai Cycles with Tidal Friction (KCTF).
Date: August 10, 2007
Creator: Kisseleva-Eggleton, L & Eggleton, P P
Object Type: Article
System: The UNT Digital Library
Plasma Suppression of Large Scale Structure Formation in the Universe (open access)

Plasma Suppression of Large Scale Structure Formation in the Universe

We point out that during the reionization epoch of the cosmic history, the plasma collective effect among the ordinary matter would suppress the large scale structure formation. The imperfect Debye shielding at finite temperature would induce a residual long-range electrostatic potential which, working together with the baryon thermal pressure, would counter the gravitational collapse. As a result the effective Jean's length, {tilde {lambda}}{sub J}, is increased by a factor, {tilde {lambda}}{sub J}/{lambda}{sub J} = {radical}8/5, relative to the conventional one. For scales smaller than the effective Jean's scale the plasma would oscillate at the ion-acoustic frequency. The modes that would be influenced by this effect depend on the starting time and the initial temperature of reionization, but roughly lie in the range 0.5hMpc{sup -1} < k, which corresponds to the region of the Lyman-{alpha} forest from the inter-galactic medium. We predict that in the linear regime of density-contrast growth, the plasma suppression of the matter power spectrum would approach 1 - ({Omega}{sub dm}/{Omega}{sub m}){sup 2} {approx} 1 -(5/6){sup 2} {approx} 30%.
Date: December 10, 2007
Creator: Chen, Pisin & Lai, Kwang-Chang
Object Type: Article
System: The UNT Digital Library
Lactonization and protonation of gluconic acid: a thermodynamicand kinetic study by potentiometry, nmr and esi-ms (open access)

Lactonization and protonation of gluconic acid: a thermodynamicand kinetic study by potentiometry, nmr and esi-ms

In acidic aqueous solutions, gluconate protonation is coupled with lactonization of gluconic acid. With the decrease of pC{sub H}, two lactones ({delta}/{gamma}) are sequentially formed. The {delta}-lactone forms more readily than the {gamma}-lactone. In 0.1 M gluconate solutions, if pC{sub H} is above 2.5, only the {delta}-lactone is generated. When pC{sub H} is decreased below 2.0, the formation of the {gamma}-lactone is observable although the {delta}-lactone predominates. At I = 0.1 M NaClO{sub 4} and room temperature, the deprotonation constant of the carboxylic group, using the NMR technique, was determined to be log K{sub a} = 3.30 {+-} 0.02; the {delta}-lactonization constant, by the batch potentiometric titrations, was obtained to be log K{sub L} = - (0.54 {+-} 0.04). Using ESI-MS, the rate constants of the {delta}-lactonization and the hydrolysis at pC{sub H} {approx} 5.0 were estimated to be k{sub 1} = 3.2 x 10{sup -5} s{sup -1} and k{sup -1} = 1.1 x 10{sup -4} s{sup -1}, respectively.
Date: January 10, 2007
Creator: Zhang, Z.; Gibson, P.; Clark, S.B.; Tian, G.; Zanonato, P. & Rao, L.
Object Type: Article
System: The UNT Digital Library
Models of Longitudinal Space-Charge Impedance for the Study of theMicrobunching Instability (open access)

Models of Longitudinal Space-Charge Impedance for the Study of theMicrobunching Instability

A 1D model of space-charge impedance, assuming atransversely uniform beam with circular cross-section, has been proposedand is being extensively used in the modelling of the microbunchinginstability of relevance for the beam delivery systems of x-ray FELs. Inthis paper we investigate the limitation of the model when applied tostudying the effect of shot noise--one of the sources of themicrobunching instability. We make comparison witha fully 3D calculationand identify the upper end of the frequency spectrum for applicability ofthe 1D model. Relaxation of the assumptions regarding axis-symmetry anduniformity of the transverse density is also reviewed.
Date: March 10, 2008
Creator: Venturini, Marco
Object Type: Article
System: The UNT Digital Library
Nuclear Dynamics in Resonant Electron Collisions with SmallPolyatomic Molecules (open access)

Nuclear Dynamics in Resonant Electron Collisions with SmallPolyatomic Molecules

None
Date: September 10, 2007
Creator: Rescigno, Thomas N.; McCurdy, C. William; Haxton, Daniel J.; Trevisan, Cynthia S. & Orel, Ann E.
Object Type: Article
System: The UNT Digital Library
Michigan Technological Center for Nanostructured and Lightweight Materials in the Department of Chemical Engineering (Phase II) (open access)

Michigan Technological Center for Nanostructured and Lightweight Materials in the Department of Chemical Engineering (Phase II)

Summaries of the followings tasks are given in this report: Task 1 - Lightweight, Thermally Conductive Bipolar Plates for Improved Thermal Management in Fuel Cells; Task 2 - Exploration of pseudomorphic nanoscale overlayer bimetallic catalysts; Task 3 - Hybrid inorganic/organic polymer nanocomposites; Task 4 - Carbonaceous Monolithic Electrodes for Fuel Cells and Rechargeable Batteries; and Task 5 - Movement and Freeze of Water in Fuel Cell Electrodes.
Date: December 10, 2009
Creator: Mullins, M.; Rogers, T.; King, J.; Holles, J.; Keith, J.; Heiden, P. et al.
Object Type: Report
System: The UNT Digital Library
A review of the properties of Nb3Sn and their variation with A15composition, morphology and strain state (open access)

A review of the properties of Nb3Sn and their variation with A15composition, morphology and strain state

None
Date: November 10, 2006
Creator: Godeke, Arno
Object Type: Article
System: The UNT Digital Library
Origin and Propagation of Cosmic Rays (Some Highlights) (open access)

Origin and Propagation of Cosmic Rays (Some Highlights)

None
Date: April 10, 2008
Creator: Moskalenko, Igor V. & /Stanford U., HEPL /KIPAC, Menlo Park
Object Type: Article
System: The UNT Digital Library
NRL FTF 0.5MJ-Class Nominal Baseline Target (open access)

NRL FTF 0.5MJ-Class Nominal Baseline Target

None
Date: December 10, 2007
Creator: LaFortune, K N & Perkins, L J
Object Type: Report
System: The UNT Digital Library
Long-term Variations of CO2 Trapped in Different Mechanisms in Deep Saline Formations: A Case Study of the Songliao Basin, China (open access)

Long-term Variations of CO2 Trapped in Different Mechanisms in Deep Saline Formations: A Case Study of the Songliao Basin, China

The geological storage of CO{sub 2} in deep saline formations is increasing seen as a viable strategy to reduce the release of greenhouse gases to the atmosphere. There are numerous sedimentary basins in China, in which a number of suitable CO{sub 2} geologic reservoirs are potentially available. To identify the multi-phase processes, geochemical changes and mineral alteration, and CO{sub 2} trapping mechanisms after CO{sub 2} injection, reactive geochemical transport simulations using a simple 2D model were performed. Mineralogical composition and water chemistry from a deep saline formation of Songliao Basin were used. Results indicate that different storage forms of CO{sub 2} vary with time. In the CO{sub 2} injection period, a large amount of CO{sub 2} remains as a free supercritical phase (gas trapping), and the amount dissolved in the formation water (solubility trapping) gradually increases. Later, gas trapping decreases, solubility trapping increases significantly due to migration and diffusion of the CO{sub 2} plume, and the amount trapped by carbonate minerals increases gradually with time. The residual CO{sub 2} gas keeps dissolving into groundwater and precipitating carbonate minerals. For the Songliao Basin sandstone, variations in the reaction rate and abundance of chlorite, and plagioclase composition affect significantly the estimates of …
Date: June 10, 2008
Creator: Zhang, Wei; Li, Yilian; Xu, Tianfu; Cheng, Huilin; Zheng, Yan & Xiong, Peng
Object Type: Article
System: The UNT Digital Library
Measurement of the Branching Fraction, Polarization, and CP Asymmetries in B0->rho0rho0 Decay, and Implications for the CKM Angle alpha (open access)

Measurement of the Branching Fraction, Polarization, and CP Asymmetries in B0->rho0rho0 Decay, and Implications for the CKM Angle alpha

We study B{sup 0} {yields} {rho}{sup 0}{rho}{sup 0} decays in a sample of 465 x 10{sup 6} {Upsilon}(4S) {yields} B{bar B} events collected with the BABAR detector at the PEP-II asymmetric-energy e{sup +}e{sup -} collider located at the Stanford Linear Accelerator Center (SLAC). We measure the branching fraction {Beta} = (0.92 {+-} 0.32 {+-} 0.14) x 10{sup -6} and longitudinal polarization fraction f{sub L} = 0.75{sub -0.14}{sup +0.11} {+-} 0.04, where the first uncertainty is statistical and the second is systematic. The evidence for the B{sup 0} {yields} {rho}{sup 0}{rho}{sup 0} signal has a significance of 3.1 standard deviations, including systematic uncertainties. We investigate the proper-time dependence of the longitudinal component in the decay and measure the CP-violating coefficients S{sub L}{sup 00} = (0.3 {+-} 0.7 {+-} 0.2) and C{sub L}{sup 00} = (0.2 {+-} 0.8 {+-} 0.3). They study the implication of these results for the unitarity triangle angle {alpha}.
Date: September 10, 2008
Creator: Aubert, B.
Object Type: Article
System: The UNT Digital Library