Design and testing of a control strategy for a large naturallyventilated office building (open access)

Design and testing of a control strategy for a large naturallyventilated office building

The design for the new Federal Building for San Franciscoincludes an office tower that is to be naturally ventilated. Each flooris designed to be cross-ventilated, through upper windows that arecontrolled by the building management system (BMS). Users have controlover lower windows, which can be as much as 50 percent of the totalopenable area. There are significant differences in the performance andthe control of the windward and leeward sides of the building, andseparate monitoring and control strategies are determined for each side.The performance and control of the building has been designed and testedusing a modified version of EnergyPlus. Results from studies withEnergyPlus and CFD are used in designing the control strategy. EnergyPluswas extended to model a simplified version of the airflow patterndetermined using CFD. Wind-driven cross-ventilation produces a main jetthrough the upper openings of the building, across the ceiling from thewindward to the leeward side. Below this jet, the occupied regions aresubject to a recirculating air flow. Results show that temperatureswithin the building are predicted to be satisfactory, provided a suitablecontrol strategy is implemented uses night cooling in periods of hotweather. The control strategy has 10 window opening modes. EnergyPlus wasextended to simulate the effects of these modes, and to assess …
Date: March 16, 2004
Creator: Carrilho da Graca, Guilherme; Linden, Paul F. & Haves, Philip
System: The UNT Digital Library
New experimental measurements of electron clouds in ion beams with large tune depression (open access)

New experimental measurements of electron clouds in ion beams with large tune depression

We study electron clouds in high perveance beams (K = 8E-4) with a large tune depression of 0.2 (defined as the ratio of a single particle oscillation response to the applied focusing fields, with and without space charge). These 1 MeV, 180 mA, K+ beams have a beam potential of +2 kV when electron clouds are minimized. Simulation results are discussed in a companion paper [J-L. Vay, this Conference]. We have developed the first diagnostics that quantitatively measure the accumulation of electrons in a beam [1]. This, together with measurements of electron sources, will enable the electron particle balance to be measured, and electron-trapping efficiencies determined. We, along with colleagues from GSI and CERN, have also measured the scaling of gas desorption with beam energy and dE/dx [2]. Experiments where the heavy-ion beam is transported with solenoid magnetic fields, rather than with quadrupole magnetic or electrostatic fields, are being initiated. We will discuss initial results from experiments using electrode sets (in the middle and at the ends of magnets) to either expel or to trap electrons within the magnets. We observe electron oscillations in the last quadrupole magnet when we flood the beam with electrons from an end wall. These …
Date: March 16, 2006
Creator: Molvik, A W; Covo, M K; Cohen, R H; Friedman, A; Bieniosek, F M; Leister, C M et al.
System: The UNT Digital Library
Evaluation of the effects of various culture condition on Cr (VI) reduction by Shewanella oneidensis MR-1 in a novel high-throughputmini-bioreactor (open access)

Evaluation of the effects of various culture condition on Cr (VI) reduction by Shewanella oneidensis MR-1 in a novel high-throughputmini-bioreactor

The growth and Cr(VI) reduction by Shewanella oneidensisMR-1 was examined using a mini-bioreactor system that independentlymonitors and controls pH, dissolved oxygen, and temperature for each ofits 24, 10-mL reactors. Independent monitoring and control of eachreactor in the cassette allows the exploration of a matrix ofenvironmental conditions known to influence S. oneidensis chromiumreduction. S. oneidensis MR-1 grew in minimal medium without amino acidor vitamin supplementation under aerobic conditions but required serineand glycine supplementation under anaerobic conditions. Growth wasinhibited by dissolved oxygen concentrations>80 percent. Lactatetransformation to acetate was enhanced by low concentration of dissolvedoxygen during the logarithmic growth phase. Between 11 and 35oC, thegrowth rate obeyed the Arrhenius reaction rate-temperature relationship,with a maximum growth rate occurring at 35oC. S. oneidensis MR-1 was ableto grow over a wide range of pH (6-9). At neutral pH and temperaturesranging from 30-35oC, S. oneidensis MR-1 reduced 100 mu M Cr(VI) toCr(III) within 20 minutes in the exponential growth phase, and the growthrate was not affected by the addition of chromate; it reduced chromateeven faster at temperatures between 35 and 39oC. At low temperatures(<25oC), acidic (pH<6.5), or alkaline (pH>8.5) conditions, 100mu M Cr(VI) strongly inhibited growth and chromate reduction. Themini-bioreactor system enabled the rapid determination of theseparameters …
Date: March 16, 2006
Creator: Tang, Yinjie J.; Laidlaw, David; Gani, Kishen & Keasling, Jay D.
System: The UNT Digital Library
Chromosome-specific DNA Repeat Probes (open access)

Chromosome-specific DNA Repeat Probes

In research as well as in clinical applications, fluorescence in situ hybridization (FISH) has gained increasing popularity as a highly sensitive technique to study cytogenetic changes. Today, hundreds of commercially available DNA probes serve the basic needs of the biomedical research community. Widespread applications, however, are often limited by the lack of appropriately labeled, specific nucleic acid probes. We describe two approaches for an expeditious preparation of chromosome-specific DNAs and the subsequent probe labeling with reporter molecules of choice. The described techniques allow the preparation of highly specific DNA repeat probes suitable for enumeration of chromosomes in interphase cell nuclei or tissue sections. In addition, there is no need for chromosome enrichment by flow cytometry and sorting or molecular cloning. Our PCR-based method uses either bacterial artificial chromosomes or human genomic DNA as templates with {alpha}-satellite-specific primers. Here we demonstrate the production of fluorochrome-labeled DNA repeat probes specific for human chromosomes 17 and 18 in just a few days without the need for highly specialized equipment and without the limitation to only a few fluorochrome labels.
Date: March 16, 2006
Creator: Baumgartner, Adolf; Weier, Jingly Fung & Weier, Heinz-Ulrich G.
System: The UNT Digital Library
Evidence For Departure in Self-Similarity: A New Spectral Ratio Method Using Narrowband Coda Envelopes (open access)

Evidence For Departure in Self-Similarity: A New Spectral Ratio Method Using Narrowband Coda Envelopes

This study is motivated by renewed interest within the seismic source community to resolve the long-standing question on energy scaling of earthquakes, specifically, 'Do earthquakes scale self-similarly or are large earthquakes dynamically different than small ones?' This question is important from a seismic hazard prediction point of view, as well as for understanding basic rupture dynamics for earthquakes. Estimating the total radiated energy (ER) from earthquakes requires significant broadband corrections for path and site effects. Moreover, source radiation pattern and directivity corrections can be equally significant and also must be accounted for. Regional studies have used a number of different methods, each with their own advantages and disadvantages. These methods include: integration of squared shear wave moment-rate spectra, direct integration of broadband velocity-squared waveforms, empirical Green's function deconvolution, and spectral ratio techniques. The later two approaches have gained popularity because adjacent or co-located events recorded at common stations have shared path and site effects, which therefore cancel. In spite of this, a number of such studies find very large amplitude variance across a network of stations. In this paper we test the extent to which narrowband coda envelopes can improve upon the traditional spectral ratio using direct phases, allowing a …
Date: March 16, 2007
Creator: Mayeda, K; Malagnini, L & Walter, W R
System: The UNT Digital Library
Estimation of fracture flow parameters through numerical analysis of hydromechanical pressure pulses (open access)

Estimation of fracture flow parameters through numerical analysis of hydromechanical pressure pulses

The flow parameters of a natural fracture were estimated by modeling in situ pressure pulses. The pulses were generated in two horizontal boreholes spaced 1 m apart vertically and intersecting a near-vertical highly permeable fracture located within a shallow fractured carbonate reservoir. Fracture hydromechanical response was monitored using specialized fiber-optic borehole equipment that could simultaneously measure fluid pressure and fracture displacements. Measurements indicated a significant time lag between the pressure peak at the injection point and the one at the second measuring point, located 1 m away. The pressure pulse dilated and contracted the fracture. Field data were analyzed through hydraulic and coupled hydromechanical simulations using different governing flow laws. In matching the time lag between the pressure peaks at the two measuring points, our hydraulic models indicated that (1) flow was channeled in the fracture, (2) the hydraulic conductivity tensor was highly anisotropic, and (3) the radius of pulse influence was asymmetric, in that the pulse travelled faster vertically than horizontally. Moreover, our parametric study demonstrated that the fluid pressure diffusion through the fracture was quite sensitive to the spacing and orientation of channels, hydraulic aperture, storativity and hydraulic conductivity. Comparison between hydraulic and hydromechanical models showed that the …
Date: March 16, 2008
Creator: Cappa, F.; Guglielmi, Y.; Rutqvist, J.; Tsang, C.-F. & Thoraval, A.
System: The UNT Digital Library
Material properties limiting the performance of CZT gamma-ray detectors (open access)

Material properties limiting the performance of CZT gamma-ray detectors

CdZnTe (CZT) nuclear radiation detectors are advanced sensors that utilize innovative technologies developed for wide band-gap semiconductor industry and microelectronics. They open opportunities for new types of room-temperature operating, field deployable instruments that provide accurate identification of potential radiological threats and timely awareness for both the civilian and military communities. Room-temperature radiation detectors are an emerging technology that relies on the use of high-quality CZT crystals whose availability is currently limited by material non-uniformities and the presence of extended defects. To address these issues, which are most critical to CZT sensor developments, we developed X-ray mapping and IR transmission microscopy systems to characterize both CZT crystals and devices. Since a customized system is required for such X-ray measurements, we use synchrotron radiation beams available at BNL's National Synchrotron Light Source. A highly-collimated and high-intensity X-ray beam supports measurements of areas as small as 10 x 10 {micro}m{sup 2}, and allowed us to see fluctuations in collected charge over the entire area of the detector in a reasonable time. The IR microscopy system allows for 3D visualization of Te inclusions and other extended defects. In this paper, we describe the experimental techniques used in our measurements and typical results obtained from …
Date: March 16, 2009
Creator: Bolotnikov, A. E.; Babalola, S.; Camarda, G. S.; Cui, Y.; Egarievwe, S. U.; Hossain, A. et al.
System: The UNT Digital Library
Pion and photon production in heavy ion collisions (open access)

Pion and photon production in heavy ion collisions

Measurement of neutral pions and direct photons are closely connected experimentally, on the other hand they probe quite different aspects of relativistic heavy ion collisions. In this short review of the {pi}{sup 0} results from the PHENIX experiment at RHIC our focus is on the {phi}-integrated nuclear modification factor, its energy and system size dependence, and the impact of these results on parton energy loss models. We also discuss the current status of high p{sub T} and thermal direct photon measurements both in p+p and Au+Au collisions. Recognizing the advantages of measuring not only the 'signal', but also all the 'references' needed for proper interpretation in the same experiments (with same or similar systematics) we argue that RHIC should regularly include d+A and even d+d collisions into its system size and energy scan.
Date: March 16, 2008
Creator: Gabor,D.
System: The UNT Digital Library
ADVANCES IN SE-79 ANALYSES ON SAVANNAH RIVER SITE RADIOACTIVE WASTE MATRICES (open access)

ADVANCES IN SE-79 ANALYSES ON SAVANNAH RIVER SITE RADIOACTIVE WASTE MATRICES

Waste cleanup efforts underway at the United States Department of Energy's (DOE) Savannah River Site (SRS) in South Carolina, as well as other DOE nuclear sites, have created a need to characterize {sup 79}Se in radioactive waste inventories. Successful analysis of {sup 79}Se in high activity waste matrices is challenging for a variety of reasons. As a result of these unique challenges, the successful quantification of {sup 79}Se in the types of matrices present at SRS requires an extremely efficient and selective separation of {sup 79}Se from high levels of interfering radionuclides. A robust {sup 79}Se radiochemical separation method has been developed at the Savannah River National Laboratory (SRNL) which is routinely capable of successfully purifying {sup 79}Se from a wide range of interfering radioactive species. In addition to a dramatic improvements in the Kd, ease, and reproducibility of the analysis, the laboratory time has been reduced from several days to only 6 hours.
Date: March 16, 2009
Creator: Diprete, D; C Diprete, C; Ned Bibler, N; Cj Bannochie, C & Michael Hay, M
System: The UNT Digital Library
Warped Supersymmetric Unification with Non-Unified Superparticle Spectrum (open access)

Warped Supersymmetric Unification with Non-Unified Superparticle Spectrum

We present a new supersymmetric extension of the standard model. The model is constructed in warped space, with a unified bulk symmetry broken by boundary conditions on both the Planck and TeV branes. In the supersymmetric limit, the massless spectrum contains exotic colored particles along with the particle content of the minimal supersymmetric standard model (MSSM). Nevertheless, the model still reproduces the MSSM prediction for gauge coupling unification and does not suffer from a proton decay problem. The exotic states acquire masses from supersymmetry breaking, making the model completely viable, but thereis still the possibility that these states will be detected at the LHC. The lightest of these states is most likely A_5^XY, the fifth component of the gauge field associated with the broken unified symmetry. Because supersymmetry is broken on the SU(5)-violating TeV brane, the gaugino masses generated at the TeV scale are completely independent of one another. We explore some of the unusual features that the superparticle spectrum might have as a consequence.
Date: March 16, 2004
Creator: Nomura, Yasunori; Tucker-Smith, David & Tweedie, Brock
System: The UNT Digital Library
THEORETICAL STUDY ON THE INTERACTION BETWEEN XENON AND POSITIVE SILVER CLUSTERS IN GAS PHASE AND ON THE (001) CHABAZITE SURFACE (open access)

THEORETICAL STUDY ON THE INTERACTION BETWEEN XENON AND POSITIVE SILVER CLUSTERS IN GAS PHASE AND ON THE (001) CHABAZITE SURFACE

A systematic study on the adsorption of xenon on silver clusters in the gas phase and on the (001) surface of silver-exchanged chabazite is reported. Density functional theory at the B3LYP level with the cluster model was employed. The results indicate that the dominant part of the binding is the {sigma} donation, which is the charge transfer from the 5p orbital of Xe to the 5s orbital of Ag and is not the previously suggested d{sub {pi}}-d{sub {pi}} back-donation. A correlation between the binding energy and the degree of {sigma} donation is found. Xenon was found to bind strongly to silver cluster cations and not to neutral ones. The binding strength decreases as the cluster size increases for both cases, clusters in the gas-phase and on the chabazite surface. The Ag{sup +} cation is the strongest binding site for xenon both in gas phase and on the chabazite surface with the binding energies of 73.9 and 14.5 kJ/mol, respectively. The results also suggest that the smaller silver clusters contribute to the negative chemical shifts observed in the {sup 129}Xe NMR spectra in experiments.
Date: March 16, 2009
Creator: Hunter, D.
System: The UNT Digital Library
Matter Unification in Warped Supersymmetric SO(10) (open access)

Matter Unification in Warped Supersymmetric SO(10)

We construct models of warped unification with a bulk SO(10) gauge symmetry and boundary conditions that preserve the SU(4)_C x SU(2)_L x SU(2)_R Pati-Salam gauge group (422). In the dual 4D description, these models are 422 gauge theories in which the apparent unification of gauge couplings in the minimal supersymmetric standard model is explained as a consequence of strong coupling in the ultraviolet. The weakness of the gauge couplings at low energies is ensured in this 4D picture by asymptotically non-free contributions from the conformal sector, which are universal due to an approximate SO(10) global symmetry. The 422 gauge symmetry is broken to the standard model group by a simple set of Higgs fields. An advantage of this setup relative to SU(5) models of warped unification is that matter is automatically required to fill out representations of 422, providing an elegant understanding of the quantum numbers of the standard-model quarks and leptons. The models also naturally incorporate the see-saw mechanism for neutrino masses and bottom-tau unification. Finally, they predict a rich spectrum of exotic particles near the TeV scale, including states with different quantum numbers than those that appear in SU(5) models.
Date: March 16, 2004
Creator: Nomura, Yasunori & Tucker-Smith, David
System: The UNT Digital Library
Searching for Double Beta Decay with the Enriched Xenon Observatory (open access)

Searching for Double Beta Decay with the Enriched Xenon Observatory

The Enriched Xenon Observatory (EXO) Collaboration is building a series of experiments to search for the neutrinoless double beta decay of {sup 136}Xe. The first experiment, known as EXO-200, will utilize 200 kg of xenon enriched to 80% in the isotope of interest, making it the largest double beta decay experiment to date by one order of magnitude. This experiment is rapidly being constructed, and will begin data taking in 2007. The EXO collaboration is also developing a technique to identify on an event-by-event basis the daughter barium ion of the double beta decay. If successful, this method would eliminate all conventional radioactive backgrounds to the decay, resulting in an ideal experiment. We summarize here the current status of EXO-200 construction and the barium tag R&amp;D program.
Date: March 16, 2007
Creator: Hall, C.
System: The UNT Digital Library
An Infrared Study of the Large-Scale Jet in Quasar PKS 1136-135 (open access)

An Infrared Study of the Large-Scale Jet in Quasar PKS 1136-135

We present Spitzer IRAC imaging of the large-scale jet in the quasar PKS 1136-135 at wavelengths of 3.6 and 5.8 {micro}m, combined with previous VLA, HST, and Chandra observations. We clearly detect infrared emission from the jet, resulting in the most detailed multifrequency data among the jets in lobe-dominated quasars. The spectral energy distributions of the jet knots have significant variations along the jet, like the archetypal jet in 3C 273. The infrared measurements with IRAC are consistent with the previous idea that the jet has two spectral components, namely (1) the low-energy synchrotron spectrum extending from radio to infrared, and (2) the high-energy component responsible for the X-ray flux. The optical fluxes may be a mixture of the two components. We consider three radiation models for the high-energy component: inverse Compton scattering of cosmic microwave background (CMB) photons by radio-emitting electrons in a highly relativistic jet, synchrotron radiation by a second distinct electron population, and synchrotron radiation by ultra high energy protons. Each hypothesis leads to important insights into and constraints on particle acceleration in the jet, as well as the basic physical properties of the jet such as bulk velocity, transporting power, and particle contents.
Date: March 16, 2007
Creator: Uchiyama, Yasunobu; Urry, C.Megan; Coppi, Paolo; Van Duyne, Jeffrey; Cheung, C. C.; Sambruna, Rita M. et al.
System: The UNT Digital Library
Search for the rare decay B to pi l+ l- (open access)

Search for the rare decay B to pi l+ l-

The authors have performed a search for the flavor-changing neutral-current decays B {yields} {pi}{ell}{sup +}{ell}{sup -}, where {ell}{sup +}{ell}{sup -} is either e{sup +}e{sup -} or {mu}{sup +}{mu}{sup -}, using a sample of 230 million {Upsilon}(4S) {yields} B{bar B} decays collected with the BABAR detector. They observe no evidence of a signal and measure the upper limit on the isospin-averaged branching fraction to be {Beta}(B {yields} {pi}{ell}{sup +}{ell}{sup -}) &lt; 9.1 x 10{sup -8} at 90% confidence level. They also search for the lepton-flavor-violating decays B {yields} {pi}e{sup {+-}} {mu}{sup {-+}} and measure an upper limit on the isospin-averaged branching fraction of {Beta}(B {yields} {pi}e{sup {+-}} {mu}{sup {-+}}) &lt; 9.2 x 10{sup -8} at 90% confidence level.
Date: March 16, 2007
Creator: Aubert, B.
System: The UNT Digital Library
Overview of Light-Ion Beam Therapy (open access)

Overview of Light-Ion Beam Therapy

In 1930, Ernest Orlando Lawrence at the University of California at Berkeley invented the cyclotron. One of his students, M. Stanley Livingston, constructed a 13-cm diameter model that had all the features of early cyclotrons, accelerating protons to 80 keV using less than 1 kV on a semi-circular accelerating electrode, now called the ''dee''. Soon after, Lawrence constructed the first two-dee 27-Inch (69-cm) Cyclotron, which produced protons and deuterons of 4.8 MeV. In 1939, Lawrence constructed the 60-Inch (150-cm) Cyclotron, which accelerated deuterons to 19 MeV. Just before WWII, Lawrence designed a 184-inch cyclotron, but the war prevented the building of this machine. Immediately after the war ended, the Veksler-McMillan principle of phase stability was put forward, which enabled the transformation of conventional cyclotrons to successful synchrocyclotrons. When completed, the 184-Inch Synchrocyclotron produced 340-MeV protons. Following it, more modern synchrocyclotrons were built around the globe, and the synchrocyclotrons in Berkeley and Uppsala, together with the Harvard cyclotron, would perform pioneering work in treatment of human cancer using accelerated hadrons (protons and light ions). When the 184-Inch Synchrocyclotron was built, Lawrence asked Robert Wilson, one of his former graduate students, to look into the shielding requirements for of the new accelerator. …
Date: March 16, 2006
Creator: Chu, William T.
System: The UNT Digital Library
Colloidal Synthesis of Hollow Cobalt Sulfide Nanocrystals (open access)

Colloidal Synthesis of Hollow Cobalt Sulfide Nanocrystals

Formation of cobalt sulfide hollow nanocrystals through amechanism similar to the Kirkendall Effect has been investigated indetail. It was found that performing the reaction at>120oC leads tofast formation of a single void ins ide each shell, whereas at roomtemperature multiple voids are formed within each shell, which can beattributed to strongly temperature-dependent diffusivities for vacancies.The void formation process is dominated by outward diffusion of cobaltcations; still, significant inward transport of sulfur anions can beinferred to occur as the final voids are smaller in diameter than theoriginal cobalt nanocrystals. Comparison of volume distributions forinitial and final nanostructures indicates excess apparent volume inshells implying significant porosity and/or a defective structure.Indirect evidence for shells to fracture during growth at lowertemperatures was observed in shell size statisticsand TEM of as-grownshells. An idealized model of the diffusional process imposes two minimalrequirements on material parameters for shell growth to be obtainablewithin a specific synthetic system.
Date: March 16, 2006
Creator: Yin, Yadong; Erdonmez, Can K.; Cabot, Andreu; Hughes, Steven & Alivisatos, A. Paul
System: The UNT Digital Library
Crystal Growth And Characterization of the Model High-Temperature Superconductor HgBa{sub 2}CuO{sub 4+{delta}} (open access)

Crystal Growth And Characterization of the Model High-Temperature Superconductor HgBa{sub 2}CuO{sub 4+{delta}}

Since the discovery of high-transition-temperature (T{sub c}) superconductivity in La{sub 2-x}Ba{sub x}CuO{sub 4} in 1986, the study of the lamellar copper oxides has remained at the forefront of condensed matter physics. Apart from their unusually high values of T{sub c}, these materials also exhibit a variety of complex phenomena and phases. This rich behavior is a consequence of the lamellar crystal structures, formed of copper-oxygen sheets separated by charge reservoir layers, and of the strong electron-electron correlations in the copper-oxygen sheets. After two decades of intensive research, which has stimulated many valuable new insights into correlated electron systems in general, there remains a lack of consensus regarding the correct theory for high-T{sub c} superconductivity. The ultimate technological goal of room-temperature superconductivity might only be attained after the development of a deeper understanding of the mercury-based compounds HgBa{sub 2}Ca{sub n-1}Cu{sub n}OI{sub 2n+2+{delta}}, which currently exhibit the highest T{sub c}values. One very important issue in this regard is the role of electronic versus chemical and structural inhomogeneities in these materials, and the associated need to separate material-specific properties from those that are essential to superconductivity. Unfortunately, there has been remarkably little scientific work on the mercury-based compounds because sizable crystals have not …
Date: March 16, 2007
Creator: Zhao, Xudong; Yu, Guichuan; Cho, Yong-Chan; Chabot-Couture, Guillaume; Barisic, Neven; Bourges, Philippe et al.
System: The UNT Digital Library
Compositional and Structural Control on Anion Sorption Capability of Layered Double Hydroxides (LDHS) (open access)

Compositional and Structural Control on Anion Sorption Capability of Layered Double Hydroxides (LDHS)

Layered double hydroxides (LDHs) have shown great promise as anion getters. In this paper, we demonstrate that the sorption capability of a LDH for a specific oxyanion can be greatly increased by appropriately manipulating material composition and structure. A large set of LDH materials have been synthesized with various combinations of metal cations, interlayer anions, and the molar ratios of divalent cation M(II) to trivalent cation M(III). The synthesized materials have then been tested systematically for their sorption capabilities for pertechnetate (TcO{sub 4}{sup -}). It is discovered that for a given interlayer anion (either CO{sub 3}{sup 2-} or NO{sub 3}{sup -}) the Ni-Al LDH with a Ni/Al ratio of 3:1 exhibits the highest sorption capability among all the materials tested. The distribution coefficient (K{sub d}) is determined to be as high as 307 mL/g for Ni{sub 6}Al{sub 2}(0H){sub 16}CO{sub 3}nH{sub 2}O and 1390 mL/g for Ni{sub 6}Al{sub 2}(OH){sub 16}NO{sub 3}nH{sub 2}O at a pH of 8. The sorption of TcO{sub 4}{sup -} on M(II)-M(III)-CO{sub 3} LDHs is dominated by the edge sites of LDH layers and strongly correlated with the basal spacing d{sub 003} of the materials, which increases with the decreasing radii of both divalent and trivalent cations. The …
Date: March 16, 2006
Creator: Wang, Y. & Gao, H.
System: The UNT Digital Library
Tool Support for Inspecting the Code Quality of HPC Applications (open access)

Tool Support for Inspecting the Code Quality of HPC Applications

The nature of HPC application development encourages ad hoc design and implementation, rather than formal requirements analysis and design specification as is typical in software engineering. However, we cannot simply expect HPC developers to adopt formal software engineering processes wholesale, even while there is a need to improve software structure and quality to ensure future maintainability. Therefore, we propose tools that HPC developers can use at their discretion to obtain feedback on the structure and quality of their codes. This feedback would come in the form of code quality metrics and analyses, presented when necessary in intuitive and interactive visualizations. This paper summarizes our implementation of just such a tool, which we apply to a standard HPC benchmark as ''proof-of-concept.''
Date: March 16, 2007
Creator: Panas, T; Quinlan, D & Vuduc, R
System: The UNT Digital Library
Structural conformation in a poly (ethylene oxide) film obta inedfrom X-ray emission spectroscopy (XES) (open access)

Structural conformation in a poly (ethylene oxide) film obta inedfrom X-ray emission spectroscopy (XES)

The electronic structure of poly(ethylene oxide) (PEO) in a thin (&lt; 1 {micro}) film sample was experimentally probed by X-ray emission spectroscopy. The emission spectra from this film were much sharper with more resolved fine structure than the spectra from the bulk polymer from which it was cast. Both non-resonant and resonant X-ray emission spectra were simulated using density functional theory (DFT) applied to four different models representing different conformations in the polymer. Calculated spectra were compared with experimental results for the PEO film. It was found that the best fit was obtained with the polymer conformation in PEO electrolytes from which the salt (LiMF6, M=P, As, or Sb) had been removed. This conformation is different from that in the crystalline bulk polymer and implies that film casting, commonly used to form electrolytes for Li polymer batteries, induces the same conformation in the polymer with or without the salt present.
Date: March 16, 2007
Creator: Kashtanov, S.; Zhuang, G.V.; Augustsson, A.; Guo, J.-H.; Nordgren, J.; Luo, Y. et al.
System: The UNT Digital Library
A Variable Directional Coupler for an Alternate ILC High-Power RF Distribution Scheme (open access)

A Variable Directional Coupler for an Alternate ILC High-Power RF Distribution Scheme

We describe the design and functionality of an RF directional coupler for which the power division between the output ports is mechanically variable. In an alternate power distribution scheme for the ILC, power is delivered to cavities in pairs, through hybrids. Four pairs, or eight cavities, are fed from one waveguide feed, from which one fourth, one third, and one half of the power is coupled out at consecutive directional couplers. Three such feeds are powered by a single 10 MW klystron. Experience suggests that cavities considered useable will display some variation in the operational accelerating gradient they can sustain. With fixed distribution, the klystron power must be kept below the level at which the weakest cavity out of 24 receives its power limit. This problem can be solved by installing variable attenuators, but that means wasting precious power. With adjustable coupling, distribution can be optimized for more efficient use both of available power and of the accelerating cavities. This novel device, feeding cavities paired by similar performance, can provide such benefit to the ILC.
Date: March 16, 2007
Creator: Nantista, Christopher D. & Adophsen, Chris
System: The UNT Digital Library
Enhanced vibrations at surfaces with back-bonds nearly parallel to the surface (open access)

Enhanced vibrations at surfaces with back-bonds nearly parallel to the surface

It has been discovered that several very different surfaces exhibit a common property: unusually large vibration amplitudes of the outermost atoms, well beyond the enhancement normally expected at typical clean surfaces. These special surfaces are: ice H2O(0001), alpha-Al2O3(0001), alpha-Ga(010) and Si(111)-(2x1). The root-mean-square vibration amplitudes in these surfaces are at least double the bulk values. The common cause that may explain these vibration amplitudes is that the surface atoms (or molecules in the case of ice) only have back-bonds that are nearly parallel to the surface. In this geometry, vibrations, especially perpendicular to the surface, involve primarily bond bending rather than bond stretching/compression: since bond bending is relatively soft, the corresponding vibration modes can have larger amplitudes. It is suggested that theory examine and confirm this cause of enhanced surface vibration amplitudes, and explore its implication for other phenomena such as adsorption and catalysis.
Date: March 16, 2004
Creator: Van Hove, M.A.
System: The UNT Digital Library
Atmospheric Corrosion and Precipitation Runoff From Zinc and Zinc Alloys Surfaces (open access)

Atmospheric Corrosion and Precipitation Runoff From Zinc and Zinc Alloys Surfaces

The long-term atmospheric corrosion performance of rolled zinc and three thermal-sprayed (TS) zinc materials (Zn, Zn-15Al, and Al-12Zn-0.2In) was characterized by measuring corrosion product concentrations in precipitation runoff at coastal marine and inland sites. Corrosion rates and average zinc concentrations in the runoff were greater at the site having higher annual rainfall. Higher chloride concentrations did not seem to affect either the corrosion rates or the zinc concentrations in the runoff at the coastal site compared to those of the inland site. Zinc runoff concentrations were higher for TS Zn than rolled zinc due to the greater surface area of the thermal-sprayed surface. Average cumulative zinc runoff losses for the two sites were: 64 {micro}mol Zn/L for TS Zn, 37 {micro}mol Zn/L for rolled Zn, 24 {micro}mol Zn/L for TS Zn-15Al, and 1.8 {micro}mol Zn/L for TS Al-12Zn-0.2In. Cumulative zinc runoff losses were directly related both to the precipitation rate and to the availability of Zn in metal surfaces, a consequence of surface roughness and surface chemistry properties of the metal.
Date: March 16, 2003
Creator: Matthes, S. A.; Cramer, S. D.; Bullard, S. J.; Covino, B. S., Jr. & Holcomb, G. R.
System: The UNT Digital Library