Sample records for water-gas shift reaction

  1. Evaluation of Sorption-Enhanced Water Gas Shift Reaction

    SciTech Connect

    Shamsi, Abolghasem

    2008-10-01

    Water-gas shift reaction, reacting water with CO is used to change the CO/H2 ratio for chemical production and for producing pure hydrogen. Water-gas shift (WGS) reaction in combination with CO2 absorption will have many applications in fuel cell and coal/biomass processing systems and will play a significant role in reducing CO2 from fossil fuel power generating systems such as IGCC by increasing system efficiencies and reducing fuel consumption. The exothermic and reversible WGS reaction, CO(g) + H2O(g) <=> CO2 (g) + H2 (g) ?H298 = - 41 kJ/mol (1), is not thermodynamically favorable at higher temperatures and for obtaining a higher conversion excess steam plus several reactors are used. Addition of excess steam and the required number of reactors to drive the reaction is expensive and it increases the cost of operation. Therefore, it is essential to develop new and novel materials that are robust, active, selective, and tolerant (less susceptible to poisoning and fouling) to contaminants in coal and in biomass.

  2. Water gas shift reaction and in the hydroformylation and hydrohydroxyformylation reactions

    SciTech Connect

    Laine, R.M.

    1980-10-07

    In the water gas shift reaction, H2O+CO -> H2+CO2 and more particularly in hydroformylation of olefins, e.g. ethylene, a homogeneous catalysts is used. A mixed ruthenium carbonyl/iron carbonyl catalyst in solution is the improvement.

  3. Simultaneous determination of kinetic and diffusion parameters for the water-gas shift reaction

    Microsoft Academic Search

    T. Salmi; Abo Akademi

    1990-01-01

    The water-gas shift reaction was studied at 563–638 K over an industrial ferrochrome catalyst. The reaction rate data could be described by first order kinetics coupled to a diffusional resistance model for isothermal pellets. The model parameters were determined by simultaneous nonlinear regression.

  4. Enhancement of water-gas shift reaction efficiency: catalysts and the catalyst bed arrangement

    NASA Astrophysics Data System (ADS)

    Baronskaya, Natal'ya A.; Minyukova, Tat'yana P.; Khassin, Aleksandr A.; Yurieva, Tamara M.; Parmon, Valentin N.

    2010-12-01

    The results of studies devoted to the search for catalysts of water-gas shift (WGS) reaction that are highly active in a wide temperature interval are generalized. New compositions based on traditional and alternative, as regards the chemical composition, catalysts of high- and low-temperature WGS reaction are considered in detail. The single-stage arrangement of WGS reaction ensuring small temperature gradients in the radial direction of the catalyst bed are discussed.

  5. Some optimization in preparing core-shell Pt–ceria catalysts for water gas shift reaction

    Microsoft Academic Search

    Connie Mei Yu Yeung; Shik Chi Tsang

    2010-01-01

    Pt on ceria-based catalysts have been extensively investigated in recent years since they could be promising alternatives to Cu-based catalysts for hydrogen production from water gas shift reaction. A core-shell Pt in thin layer ceria prepared by microemulsion technique has earlier been shown to be highly active and selective for WGS reaction as compared to those Pt–ceria catalysts prepared by

  6. Mechanisms of the water-gas-shift reaction by iron pentacarbonyl in the gas phase.

    PubMed

    Rozanska, Xavier; Vuilleumier, Rodolphe

    2008-10-01

    We analyzed the mechanisms of the water-gas-shift reaction catalyzed by Fe(CO) 5/OH (-) in the gas phase using DFT methods. The systematic analysis of the accessible reaction mechanisms and the consideration of the Gibbs free energies allows for different reaction routes than previously suggested. In the dominant catalytic cycle, the hydride [FeH(CO) 4]- is the important intermediate. Associative reaction mechanisms are not favorable under moderate and low pressures. At high pressure, a side reaction takes over and prevents the conversion of H 2O and CO to H 2 and CO 2 and leads to the formation of HCOOH. PMID:18754658

  7. A dynamic study of the water-gas shift reaction over an industrial ferrochrome catalyst

    Microsoft Academic Search

    T. Salmi; S. Bostroem; L. E. Lindfors

    1988-01-01

    The water-gas shift reaction over an industrial ferrochrome catalysts (ICI 15-4) was studied by transient experiments in a gradientless spinning basket reactor at 563-638 K and atmospheric pressure. The responses of CO, COâ, and Hâ were measured after step changes at the reactor inlet. The stationary kinetics were described with a first-order rate expression with respect to CO. The rate

  8. A comparative study of water-gas-shift reaction over ceria supported metallic catalysts

    Microsoft Academic Search

    S Hilaire; X Wang; T Luo; R. J Gorte; J Wagner

    2001-01-01

    Water-gas-shift (WGS) reaction rates have been measured on Pd\\/ceria, Ni\\/ceria, Fe\\/ceria, Co\\/ceria, ceria, and Pd\\/silica. Pd\\/ceria exhibited much higher activities than either ceria alone or Pd\\/silica, demonstrating a cooperative effect between Pd and ceria. Pd\\/ceria and Ni\\/ceria showed essentially the same activities and were much more active than either Co\\/ceria or Fe\\/ceria. Reaction orders on Pd\\/ceria were approximately zeroth-order in

  9. Hydordesulfurization of dibenzothiophene using hydrogen generated in situ by the water-gas shift reaction in a trickle bed reactor 

    E-print Network

    Hook, Bruce David

    1984-01-01

    HYDRODESULFURIZATION OF DIBENZOTHIOPHENE USING HYDROGEN GENERATED IN SITU BY THE WATER ? GAS SHIFT REACTION IN A TRICKLE BED REACTOR A Thesis BRUCE DAVID HOOK Submitted to the Graduate College of Texas A&M University in partial fulfillment... of the requirements for the degree of MASTER OF SCIENCE December 1984 Major Subject: Chemical Engineering HYDRODESULFURIZATION OF DIBENZOTHIOPHENE USING HYDROGEN GENERATED IN SITU BY THE WATER ? GAS SHIFT REACTION IN A TRICKLE BED REACTOR A Thesis by BRUCE...

  10. PdZnAl Catalysts for the Reactions of Water-Gas-Shift, Methanol Steam Reforming, and Reverse-Water-Gas-Shift

    SciTech Connect

    Dagle, Robert A.; Platon, Alexandru; Datye, Abhaya K.; Vohs, John M.; Wang, Yong; Palo, Daniel R.

    2008-03-07

    Pd/ZnO/Al2O3 catalysts were studied for water-gas-shift (WGS), methanol steam reforming, and reverse-water-gas-shift (RWGS) reactions. WGS activity was found to be dependent on the Pd:Zn ratio with a maximum activity obtained at approximately 0.50, which was comparable to that of a commercial Pt-based catalyst. The catalyst stability was demonstrated for 100 hours time-on-stream at a temperature of 3600C without evidence of metal sintering. WGS reaction rates were approximately 1st order with respect to CO concentration, and kinetic parameters were determined to be Ea = 58.3 kJ mol-1 and k0 = 6.1x107 min-1. During methanol steam reforming, the CO selectivities were observed to be lower than the calculated equilibrium values over a range of temperatures and steam/carbon ratios studied while the reaction rate constants were approximately of the same magnitude for both WGS and methanol steam reforming. These results indicate that although Pd/ZnO/Al2O3 are active WGS catalysts, WGS is not involved in methanol steam reforming. RWGS rate constants are on the order of about 20 times lower than that of methanol steam reforming, suggesting that RWGS reaction could be one of the sources for small amount of CO formation in methanol steam reforming.

  11. Minimization of steam requirements and enhancement of water-gas shift reaction with warm gas temperature CO2 removal

    DOEpatents

    Siriwardane, Ranjani V; Fisher, II, James C

    2013-12-31

    The disclosure utilizes a hydroxide sorbent for humidification and CO.sub.2 removal from a gaseous stream comprised of CO and CO.sub.2 prior to entry into a water-gas-shift reactor, in order to decrease CO.sub.2 concentration and increase H.sub.2O concentration and shift the water-gas shift reaction toward the forward reaction products CO.sub.2 and H.sub.2. The hydroxide sorbent may be utilized for absorbtion of CO.sub.2 exiting the water-gas shift reactor, producing an enriched H.sub.2 stream. The disclosure further provides for regeneration of the hydroxide sorbent at temperature approximating water-gas shift conditions, and for utilizing H.sub.2O product liberated as a result of the CO.sub.2 absorption.

  12. Carbon capture by sorption-enhanced water-gas shift reaction process using hydrotalcite-based material

    Microsoft Academic Search

    E. R. van Selow; P. D. Cobden; P. A. Verbraeken; J. R. Hufton; R. W. van den Brink

    2009-01-01

    A novel route for precombustion decarbonization is the sorption-enhanced water-gas shift (SEWGS) process. In this process carbon dioxide is removed from a synthesis gas at elevated temperature by adsorption. Simultaneously, carbon monoxide is converted to carbon dioxide by the water-gas shift reaction. The periodic adsorption and desorption of carbon dioxide is induced by a pressure swing cycle, and the cyclic

  13. Alkali-Stabilized Pt-OHx Species Catalyze Low-Temperature Water-Gas Shift Reactions

    SciTech Connect

    Zhai, Y.; Pierre, D; Si, R; Deng, W; Ferrin, P; Nilekar, A; Peng, G; Herron, J; Bell, D; et. al.

    2010-01-01

    We report that alkali ions (sodium or potassium) added in small amounts activate platinum adsorbed on alumina or silica for the low-temperature water-gas shift (WGS) reaction (H{sub 2}O + CO {yields} H{sub 2} + CO{sub 2}) used for producing H{sub 2}. The alkali ion-associated surface OH groups are activated by CO at low temperatures ({approx}100 C) in the presence of atomically dispersed platinum. Both experimental evidence and density functional theory calculations suggest that a partially oxidized Pt-alkali-O{sub x}(OH){sub y} species is the active site for the low-temperature Pt-catalyzed WGS reaction. These findings are useful for the design of highly active and stable WGS catalysts that contain only trace amounts of a precious metal without the need for a reducible oxide support such as ceria.

  14. Hydrodesulphurization of Light Gas Oil using hydrogen from the Water Gas Shift Reaction

    NASA Astrophysics Data System (ADS)

    Alghamdi, Abdulaziz

    2009-12-01

    The production of clean fuel faces the challenges of high production cost and complying with stricter environmental regulations. In this research, the ability of using a novel technology of upgrading heavy oil to treat Light Gas Oil (LGO) will be investigated. The target of this project is to produce cleaner transportation fuel with much lower cost of production. Recently, a novel process for upgrading of heavy oil has been developed at University of Waterloo. It is combining the two essential processes in bitumen upgrading; emulsion breaking and hydroprocessing into one process. The water in the emulsion is used to generate in situ hydrogen from the Water Gas Shift Reaction (WGSR). This hydrogen can be used for the hydrogenation and hydrotreating reaction which includes sulfur removal instead of the expensive molecular hydrogen. This process can be carried out for the upgrading of the bitumen emulsion which would improve its quality. In this study, the hydrodesulphurization (HDS) of LGO was conducted using in situ hydrogen produced via the Water Gas Shift Reaction (WGSR). The main objective of this experimental study is to evaluate the possibility of producing clean LGO over dispersed molybdenum sulphide catalyst and to evaluate the effect of different promoters and syn-gas on the activity of the dispersed Mo catalyst. Experiments were carried out in a 300 ml Autoclave batch reactor under 600 psi (initially) at 391°C for 1 to 3 hours and different amounts of water. After the hydrotreating reaction, the gas samples were collected and the conversion of carbon monoxide to hydrogen via WGSR was determined using a refinery gas analyzer. The sulphur content in liquid sample was analyzed via X-Ray Fluorescence. Experimental results showed that using more water will enhance WGSR but at the same time inhibits the HDS reaction. It was also shown that the amount of sulfur removed depends on the reaction time. The plan is to investigate the effect of synthesis gas (syngas) molar ratio by varying CO to H2 ratio. It is also planned to use different catalysts promoters and compare them with the un-promoted Mo based catalysts to achieve the optimum reaction conditions for treating LGO. The results of this study showed that Ni and Co have a promoting effect over unpromoted Mo catalysts for both HDS and WGSR. Ni was found to be the best promoter for both reactions. Fe showed no significant effect for both WGSR and HDS. V and K have a good promoting effect in WGSR but they inhibited the HDS reaction. Potassium was found to be the strongest inhibitor for the HDS reaction since no sulfur was removed during the reaction. Keywords. LGO, HDS, in situ H2, WGSR, oil upgrading, syn-gas.

  15. Iron Oxides from Volcanic Soils as Potential Catalysts in the Water Gas Shift Reaction

    SciTech Connect

    Pizarro, C.; Escudey, M.; Moya, S.A. [Facultad de Quimica y Biologia, USACH, Av. L. B. O'Higgins 3363, Santiago 7254758 (Chile); Fabris, J.D. [Departamento de Quimica, ICEx-UFMG, Pampulha, 31270-901 Belo Horizonte, MG (Brazil)

    2005-04-26

    This study was focused on changes of the iron oxide mineralogy with temperature of two Chilean soils (Andisol and Ultisol) derived from volcanic materials and their use as iron-based catalysts in the water gas shift reaction (WGSR). Ultisol materials produced about twice as much hydrogen than did those from Andisol upon WGSR, but in both cases hydrogen yielding increased as the heating temperature of the soil materials increased from 124 deg. C to 500 deg. C. The room temperature Moessbauer spectra showed an increase of the relative proportion of the magnetically ordered components as temperature increased. Higher heating temperature produced a negative effect on the catalytic activity, whereas the organic matter destruction led to a positive effect, due to an increasing exposition of the iron oxide surfaces; heating the soil sample at 600 deg. C induced changes on the iron oxide mineralogy with a significant decrease of the catalytic activity.

  16. Mechanism of the Water Gas Shift Reaction on Pt: First Principles, Experiments, and Microkinetic Modeling

    SciTech Connect

    Grabow, Lars C.; Gokhale, Amit A.; Evans, Steven T.; Dumesic, James A.; Mavrikakis, Manos

    2008-03-27

    The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. We present a microkinetic model as well as experimental data for the low-temperature water gas shift (WGS) reaction catalyzed by Pt at temperatures from 523 to 573 K and for various gas compositions at a pressure of 1 atm. Thermodynamic and kinetic parameters for the model are derived from periodic, self-consistent density functional theory (DFT-GGA) calculations on Pt(111). The destabilizing effect of high CO surface coverage on the binding energies of surface species is quantified through DFT calculations and accounted for in the microkinetic model. Deviations of specific fitted model parameters from DFT calculated parameters on Pt(111) point to the possible role of steps/defects in this reaction. Our model predicts reaction rates and reaction orders in good agreement with our experiments. The calculated and experimental apparent activation energies are 67.8 kJ/mol and 71.4 kJ/mol, respectively. The model shows that the most significant reaction channel proceeds via a carboxyl (COOH) intermediate. Formate (HCOO), which has been experimentally observed and thought to be the key WGS intermediate in the literature, is shown to act only as a spectator species.

  17. The effect of PdZn particle size on reverse-water-gas-shift reaction

    SciTech Connect

    Lebarbier, Vanessa MC; Dagle, Robert A.; Datye, A. K.; Wang, Yong

    2010-05-15

    The effect of PdZn particle size on the catalytic activity of Pd/ZnO catalysts for the reverse-water-gas-shift (RWGS) reaction was studied. The PdZn particle size was varied by adjusting Pd loading and reducing the catalysts at different temperatures. XRD and IR spectroscopy characterization confirmed the absence of metallic Pd on the catalyst surface. Consequently, the effect of PdZn alloy particle size on the RWGS reaction can be unambiguously studied without the complication of reactions catalyzed by metallic Pd. The results indicated that the turnover frequency increases as the PdZn crystallite size decreases. Interestingly, this structure relationship between PdZn particle size and RWGS activity is consistent with that previously observed for the steam reforming of methanol, i.e., higher CO selectivity on smaller PdZn particles. Thus, RWGS has been identified as a likely potential reaction pathway to undesired CO formation in methanol steam reforming on Pd/ZnO catalysts for hydrogen production.

  18. Water gas shift reaction kinetics and reactor modeling for fuel cell grade hydrogen

    NASA Astrophysics Data System (ADS)

    Choi, Yongtaek; Stenger, Harvey G.

    The kinetics of the water gas shift reaction was studied to evaluate existing reaction mechanisms, test various rate expressions and simulate the performance in a methanol fuel processor for fuel cell applications. The reaction was carried out in a micro reactor testing unit using a commercial Sud-Chemie Cu/ZnO/Al 2O 3 catalyst between 120 and 250 °C with a range of feed rates and compositions. Using non-linear least squares optimization, the parameters in five rate expressions were fit to the experimental data. Based on a review of published work on the WGS reaction mechanism, our study found that a rate expression derived from a regenerative mechanism and another rate expression derived from adsorptive mechanism fit the experimental data equally well. Numerical integration of a one-dimensional PFR model was used for this parameter fitting. An empirical rate expression, rCO= kPCOPH 2O (1- ?) with activation energy of 47.4 kJ/mol was also obtained from the experimental data. Reactor performance was simulated to determine catalyst loadings required to achieve specific CO conversions as a function of temperature and water feed rate. These results are useful in studying the design trade offs available to reformer systems.

  19. Density Functional Theory and Reaction Kinetics Studies of the Water–Gas Shift Reaction on Pt–Re Catalysts

    SciTech Connect

    Carrasquillo-Flores, Ronald; Gallo, Jean Marcel R.; Hahn, Konstanze; Dumesic, James A.; Mavrikakis, Manos

    2013-12-01

    Periodic, self-consistent density functional theory calculations (DFT-GGA-PW91) on Pt(111) and Pt3Re(111) surfaces, reaction kinetics measurements, and microkinetic modeling are employed to study the mechanism of the water–gas shift (WGS) reaction over Pt and Pt–Re catalysts. The values of the reaction rates and reaction orders predicted by the model are in agreement with the ones experimentally determined; the calculated apparent activation energies are matched to within 6% of the experimental values. The primary reaction pathway is predicted to take place through adsorbed carboxyl (COOH) species, whereas formate (HCOO) is predicted to be a spectator species. We conclude that the clean Pt(111) is a good representation of the active site for the WGS reaction on Pt catalysts, whereas the active sites on the Pt–Re alloy catalyst likely contain partially oxidized metal ensembles.

  20. One-Dimensional Ceria as Catalyst for the Low-Temperature Water-Gas Shift Reaction

    SciTech Connect

    Han, W.; Wen, W; Hanson, J; Teng, X; Marinkovic, N; Rodriguez, J

    2009-01-01

    Synchrotron-based in situ time-resolved X-ray diffraction and X-ray absorption spectroscopy were used to study pure ceria and Pd-loaded ceria nanotubes and nanorods (1D-ceria) as catalysts for the water-gas shift (WGS) reaction. While bulk ceria is very poor as WGS catalysts, pure 1D-ceria displayed catalytic activity at a temperature as low as 300 C. The reduction of the pure 1D-ceria in pure hydrogen started at 150 C, which is a much lower temperature than those previously reported for the reduction of 3D ceria nanoparticles. This low reduction temperature reflects the novel morphology of the oxide systems and may be responsible for the low-temperature WGS catalytic activity seen for the 1D-ceria. Pd-loaded 1D ceria displayed significant WGS activity starting at 200 C. During pretreatment in H{sub 2}, the ceria lattice parameter increased significantly around 60 C, which indicates that Pd-oxygen interactions may facilitate the reduction of Pd-loaded 1D-ceria. Pd and ceria both participate in the formation of the active sites for the catalytic reactions. The low-temperature hydrogen pretreatment results in higher WGS activity for Pd-loaded 1D-ceria.

  1. SIC-BASED HYDROGEN SELECTIVE MEMBRANES FOR WATER-GAS-SHIFT REACTION

    SciTech Connect

    Paul K.T. Liu

    2002-10-31

    In the first two years of this project, we focused on the membrane synthesis, characterization and optimization. In the past year, we have concentrated on the product development for improving the efficiency of hydrogen recovery from coal gasifier off-gas via water-gas-shift (WGS) reaction. A mathematical simulation study has been performed to compare the performance of the membrane reactor (MR) vs conventional packed bed rector for WGS reaction. Our result demonstrates that >99.999% conversion can be accomplished via WGS-MR using the hydrogen selective membrane developed by us. Further, water/CO ratio can be reduced, and >97% hydrogen recovery and <200 ppm CO can be accomplished according to the mathematical simulation. Thus, we believe that the operating economics of WGS can be improved significantly based upon the proposed MR concept. In parallel, gas separations and hydrothermal and long-term-storage stability of the hydrogen selected membrane have been experimentally demonstrated using a pilot-scale tubular membrane under a simulated WGS environment. For the remaining period of this project, we will conduct experimental study using the hydrogen selective membrane to verify the performance projected by the mathematical simulation.

  2. Reaction intermediates of methanol synthesis and the water-gas-shift reaction on the ZnO(0001) surface

    NASA Astrophysics Data System (ADS)

    Chuasiripattana, Katawut; Warschkow, Oliver; Delley, Bernard; Stampfl, Cathy

    2010-09-01

    The polar Zn-ZnO(0001) surface is involved in the catalysis of methanol synthesis and the water-gas-shift reaction. We use density functional theory calculations to explore the favorable binding geometries and energies of adsorption of several molecular species relevant to these reactions, namely carbon monoxide (CO), carbon dioxide (CO 2), water (H 2O) and methanol (CH 3OH). We also consider several proposed reaction intermediates, including hydroxymethyl (CH 2OH), methoxyl (CH 3), formaldehyde (CH 2O), methyl (CH 3), methylene (CH 2), formic acid (HCOOH), formate (HCOO), formyl (HCO), hydroxyl (OH), oxygen (O) and hydrogen (H). For each, we identify the preferred binding geometry at a coverage of 1/4 monolayers (ML), and report calculated vibrational frequencies that could aid in the identification of these species in experiment. We further explore the effects on the binding energy when the adsorbate coverage is lowered to 1/9 and 1/16 ML.

  3. Homogeneous catalysis of the water gas shift reaction by ruthenium and other metal carbonyls: studies in alkaline solutions

    Microsoft Academic Search

    Charles Ungermann; Vincent Landis; Sergio A. Moya; Haim Cohen; Howard Walker; Ralph G. Pearson; Robert G. Rinker; Peter C. Ford

    1979-01-01

    Homogeneous catalysis of the water gas shift reaction (HâO + CO reversible Hâ + COâ) has been demonstrated for a number of metal carbonyl complexes under alkaline conditions. Characterization of the catalysts based on ruthenium carbonyl in alkaline, aqueous ethoxyethanol solution demonstrates that the principal species present under the reaction conditions are the carbonyl hydride anions HâRuâ(CO)ââ⁻ and HRuâCO)âââ». (The

  4. The water-gas shift (WGS) reaction (CO + H2O = CO2+ H2) is an important reaction for hydrogen upgrading during fuel

    E-print Network

    Napp, Nils

    Reports The water-gas shift (WGS) reaction (CO + H2O = CO2+ H2) is an important reaction for the WGS reaction (~45 kJ/mol) for gold (Au) vs. ~75 kJ/mol for platinum (3­5), can be exploited for low- temperature WGS and other reactions (6). Low-temperature activity is important to avoid multiple

  5. SiC-BASED HYDROGEN SELECTIVE MEMBRANES FOR WATER-GAS-SHIFT REACTION

    SciTech Connect

    Paul K.T. Liu

    2001-10-16

    This technical report summarizes our activities conducted in Yr II. In Yr I we successfully demonstrated the feasibility of preparing the hydrogen selective SiC membrane with a chemical vapor deposition (CVD) technique. In addition, a SiC macroporous membrane was fabricated as a substrate candidate for the proposed SiC membrane. In Yr II we have focused on the development of a microporous SiC membrane as an intermediate layer between the substrate and the final membrane layer prepared from CVD. Powders and supported thin silicon carbide films (membranes) were prepared by a sol-gel technique using silica sol precursors as the source of silicon, and phenolic resin as the source of carbon. The powders and films were prepared by the carbothermal reduction reaction between the silica and the carbon source. The XRD analysis indicates that the powders and films consist of SiC, while the surface area measurement indicates that they contain micropores. SEM and AFM studies of the same films also validate this observation. The powders and membranes were also stable under different corrosive and harsh environments. The effects of these different treatments on the internal surface area, pore size distribution, and transport properties, were studied for both the powders and the membranes using the aforementioned techniques and XPS. Finally the SiC membrane materials are shown to have satisfactory hydrothermal stability for the proposed application. In Yr III, we will focus on the demonstration of the potential benefit using the SiC membrane developed from Yr I and II for the water-gas-shift (WGS) reaction.

  6. Gold atoms stabilized on various supports catalyze the water-gas shift reaction.

    PubMed

    Flytzani-Stephanopoulos, Maria

    2014-03-18

    For important chemical reactions that are catalyzed by single-site metal centers, such as the water-gas shift (WGS) reaction that converts carbon monoxide and water to hydrogen and carbon dioxide, atomically dispersed supported metal catalysts offer maximum atom efficiency. Researchers have found that for platinum metal supported on ceria and doped ceria in the automobile exhaust catalyst, atomic Pt-Ox-Ce species are the active WGS reaction sites. More recently, preparations of gold at the nanoscale have shown that this relatively "new material" is an active and often more selective catalyst than platinum for a variety of reactions, including the WGS reaction. The activity of gold is typically attributed to a size effect, while the interface of gold with the support has also been reported as important for oxidation reactions, but exactly how this comes about has not been probed satisfactorily. Typical supported metal catalysts prepared by traditional techniques have a heterogeneous population of particles, nanoclusters, subnanometer species, and isolated atoms/ions on the support surfaces, making the identification of the active sites difficult. Both we and other researchers have clearly shown that gold nanoparticles are spectator species in the WGS reaction. Evidence has now amassed that the gold active site for the WGS reaction is atomic, that is, Au-Ox species catalyze the reaction, similar to Pt-Ox. In this Account, we review the relevant literature to conclude that the intrinsic activity of the Au-Ox(OH)-S site, where S is a support, is the same for any S. The support effect is indirect, through its carrying (or binding) capacity for the active sites. Destabilization of the gold under reducing conditions through the formation of clusters and nanoparticles is accompanied by a measurable activity loss. Therefore, it is necessary to investigate the destabilizing effect of different reaction gas mixtures on the gold atom sites and to consider regeneration methods that effectively redisperse the gold clusters into atoms. For gold catalysts, we can remove weakly bound clusters and nanoparticles from certain supports by leaching techniques. Because of this, we can prepare a uniform dispersion of gold atoms/ions strongly bound to the support surface by this two-step (loading followed by leaching) approach. Presently, one-step preparation methods to maximize the number of the single atom sites on various supports need to be developed, specific to the type of the selected support. Often, it will be beneficial to alter the surface properties of the support to enhance metal ion anchoring, for example, by shape and size control of the support or by the use of light-assisted deposition and anchoring of the metal on photoresponsive supports. Because of their importance for practical catalyst development, synthesis methods are discussed at some length in this Account. PMID:24266870

  7. Reaction-Relevant Gold Structures in the Low Temperature Water-Gas Shift Reaction on Weiling Deng, Anatoly I. Frenkel, Rui Si, and Maria Flytzani-Stephanopoulos*,

    E-print Network

    Frenkel, Anatoly

    Reaction-Relevant Gold Structures in the Low Temperature Water-Gas Shift Reaction on Au-CeO2 and can be used without activation. The reducibility and catalytic activity of CeO2 are significantly effect on ceria reducibility.7 However, deactivation of Pt-CeO2 catalysts used in realistic WGS streams8

  8. Reaction-Relevant Gold Structures in the Low Temperature Water-Gas Shift Reaction on Au-CeO2

    SciTech Connect

    Deng,W.; Frenkel, A.; Si, R.; Flytzani-Stephanopoulos, M.

    2008-01-01

    Combined in situ X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) studies have been conducted to follow gold structural changes of low-content (<1%Au) gold-ceria catalysts in water-gas shift (WGS) reaction tests at 100 and 200 C; and after heating the used catalysts in oxygen gas at 150 C. Gold in the fresh (400 C-calcined) material was atomically dispersed in cerium oxide. Under WGS reaction conditions, reduction of the oxidized gold species was observed, accompanied by gradual gold aggregation. The Au-Au coordination number is zero for the fresh material, but increases with the reaction temperature, to 6.5 {+-} 2.4 (after use at 100 C) and to 8.7 {+-} 1.5 (after 200 C) in a gas mixture containing 5% CO- 3% H2O in helium. The second important parameter is the reaction gas composition which determines the extent of Au-O reduction. The lower the reduction potential of the reaction gas mixture, the more oxidized the gold is in the used catalyst, and the higher its activity. The maximum activity of Au-CeO2 was that of the fully dispersed Au-O-Ce fresh material. Loss of surface oxygen took place during reaction, as measured by H2-TPR of the used samples, and it was commensurate with the activity loss. Attempts to reoxidize and redisperse the gold by heating in oxygen gas at 150 C were not effective. However, we report here that complete recovery of the surface oxygen amount and redispersion of gold in ceria was possible after a 400 C- oxygen treatment of both the 100 C- and 200 C- used catalyst samples, with concomitant recovery of the initial catalyst activity. These tests were conducted by consecutive H2-TPR/steady-state catalyst activity measurements in the same microreactor.

  9. The action of Pt in bimetallic Au–Pt\\/CeO 2 catalyst for water–gas shift reaction

    Microsoft Academic Search

    Qiangqiang Yu; Wei Chen; Yang Li; Mingshan Jin; Zhanghuai Suo

    2010-01-01

    Bimetallic Au–M (M=Ni, Cu, Ag, Pt, and Pd) catalysts supported on CeO2 were prepared by step-by-step impregnation method for water–gas shift reaction. Among them Au–Pt\\/CeO2 catalyst shows the highest activity with 78% conversion of CO at 250°C. The action of platinum in Au–Pt\\/CeO2 catalyst was investigated by means of X-ray diffraction, hydrogen temperature-programmed reduction, UV–vis diffuse reflection spectroscopy, and X-ray

  10. Performance of Au/M(x)O(y)/TiO(2) Catalysts in Water-Gas Shift Reaction

    SciTech Connect

    Ma, Zhen [ORNL; Dai, Sheng [ORNL; Yin, Hongfeng [ORNL

    2010-01-01

    Our group recently developed a series of Au/M{sub x}O{sub y}/TiO{sub 2} catalysts for CO oxidation, and demonstrated that some of these catalysts are still active after high-temperature treatment whereas Au/TiO{sub 2} deactivates significantly due to the sintering of gold nanoparticles at elevated temperatures (Ma Z, Overbury SH, Dai S (2007) J Mol Catal A 273:97). In the current work, the performance of Au/M{sub x}O{sub y}/TiO{sub 2} (M = Al, Ca, Fe, Zn, Ga, Y, Zr, La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb) catalysts in water-gas shift (WGS) reaction was evaluated. The influences of different metal oxide (M{sub x}O{sub y}) additives and pretreatment temperatures were investigated, and the catalyst stability as a function of reaction time on stream was tested. Some of these novel gold catalysts, with high activity and stability in water-gas shift, furnish new possibilities for further fundamental research and industrial development.

  11. Structure Sensitivity of the Low-temperature Water-gas Shift Reaction on Cu–CeO2 catalysts

    SciTech Connect

    Si, R.; Zhang, L.; Raitano, J.; Yi, N.; Chan, S.-W.; Flytzani-Stephanopoulos, M.

    2012-01-17

    We have investigated the structure sensitivity of the water-gas shift (WGS) reaction on Cu-CeO{sub 2} catalysts prepared at the nanoscale by different techniques. On the surface of ceria, different CuO{sub x} structures exist. We show here that only the strongly bound Cu-[O{sub x}]-Ce species, probably associated with the surface oxygen vacancies of ceria, are active for catalyzing the low-temperature WGS reaction. Weakly bound CuO{sub x} clusters and CuO nanoparticles are spectator species in the reaction. Isolated Cu{sup 2+} ions doping the ceria surface are not active themselves, but they are important in that they create oxygen vacancies and can be used as a reservoir of copper to replenish surface Cu removed by leaching or sintering. Accordingly, synthesis techniques such as coprecipitation that allow for extensive solubility of Cu in ceria should be preferred over impregnation, deposition-precipitation, ion exchange or another two-step method whereby the copper precursor is added to already made ceria nanocrystals. For the synthesis of different structures, we have used two methods: a homogeneous coprecipitation (CP), involving hexamethylenetetramine as the precipitating agent and the pH buffer; and a deposition-precipitation (DP) technique. In the latter case, the ceria supports were first synthesized at the nanoscale with different shapes (rods, cubes) to investigate any potential shape effect on the reaction. Cu-CeO{sub 2} catalysts with different copper contents up to ca. 20 at.% were prepared. An indirect shape effect of CeO{sub 2}, manifested by the propensity to form oxygen vacancies and strongly bind copper in the active form, was established; i.e. the water-gas shift reaction is not structure-sensitive. The apparent activation energy of the reaction on all samples was similar, 50 {+-} 10 kJ/mol, in a product-free (2% CO-10% H{sub 2}O) gas mixture.

  12. A theoretical study of the water gas shift reaction mechanism on Cu(1 1 1) model system

    NASA Astrophysics Data System (ADS)

    Tang, Qian-Lin; Chen, Zhao-Xu; He, Xiang

    2009-07-01

    The water gas shift (WGS) reaction is an important reaction system and has wide applications in several processes. However, the mechanism of the reaction is still in dispute. In this paper we have investigated the reaction mechanism on the model Cu(1 1 1) system using the density functional method and slab models. We have characterized the kinetics and the thermodynamics of the four reaction pathways containing 24 elementary steps and computed the reaction potential energy surfaces. Calculations show that the formate (HCOO) intermediate mechanism (CO + OH ? HCOO ? CO 2 + H) and the associative mechanism (CO + OH ? CO 2 + H) are kinetically unlikely because of the high formation barrier. On the other hand, the carboxyl (HOCO) intermediate mechanism (CO + OH ? HOCO ? CO 2 + H) and the redox mechanism (CO + O ? CO 2) are demonstrated to be feasible. Our calculations also indicate that surface oxygen atoms can reduce the barriers of both water dissociation and HOCO decomposition significantly. The calculated potential energy surfaces show that the water dissociation which produces OH groups is the rate-determining step at the initial stage of the reaction or in the absence of surface oxygen atoms. With the development of the reaction or in the presence of oxygen atoms on the surface, CO + OH ? HOCO and CO + O ? CO 2 become the rate-limiting step for the carboxyl and redox mechanisms, respectively.

  13. Water-gas shift reaction on oxide/Cu(111): Rational catalyst screening from density functional theory

    NASA Astrophysics Data System (ADS)

    Liu, Ping

    2010-11-01

    Developing improved catalysts based on a fundamental understanding of reaction mechanism has become one of the grand challenges in catalysis. A theoretical understanding and screening the metal-oxide composite catalysts for the water-gas shift (WGS) reaction is presented here. Density functional theory was employed to identify the key step for the WGS reaction on the Au, Cu-oxide catalysts, where the calculated reaction energy for water dissociation correlates well with the experimental measured WGS activity. Accordingly, the calculated reaction energy for water dissociation was used as the scaling descriptor to screen the inverse model catalysts, oxide/Cu(111), for the better WGS activity. Our calculations predict that the WGS activity increases in a sequence: Cu(111), ZnO/Cu(111) < TiO2/Cu(111), ZrO2/Cu(111) < MoO3/Cu(111). Our results imply that the high performances of Au, Cu-oxide nanocatalysts in the WGS reaction rely heavily on the direct participation of both oxide and metal sites. The degree that the oxide is reduced by Cu plays an important role in determining the WGS activity of oxide/Cu catalysts. The reducible oxide can be transformed from the fully oxidized form to the reduced form due to the interaction with Cu and, therefore, the transfer of electron density from Cu, which helps in releasing the bottleneck water dissociation and, therefore, facilitating the WGS reaction on copper.

  14. Water-gas Shift Reaction on oxide/Cu(111): Rational Catalyst Screening from Density Functional Theory

    SciTech Connect

    Liu, P.

    2010-11-28

    Developing improved catalysts based on a fundamental understanding of reaction mechanism has become one of the grand challenges in catalysis. A theoretical understanding and screening the metal-oxide composite catalysts for the water-gas shift (WGS) reaction is presented here. Density functional theory was employed to identify the key step for the WGS reaction on the Au, Cu-oxide catalysts, where the calculated reaction energy for water dissociation correlates well with the experimental measured WGS activity. Accordingly, the calculated reaction energy for water dissociation was used as the scaling descriptor to screen the inverse model catalysts, oxide/Cu(111), for the better WGS activity. Our calculations predict that the WGS activity increases in a sequence: Cu(111), ZnO/Cu(111) < TiO{sub 2}/Cu(111), ZrO{sub 2}/Cu(111) < MoO{sub 3}/Cu(111). Our results imply that the high performances of Au, Cu-oxide nanocatalysts in the WGS reaction rely heavily on the direct participation of both oxide and metal sites. The degree that the oxide is reduced by Cu plays an important role in determining the WGS activity of oxide/Cu catalysts. The reducible oxide can be transformed from the fully oxidized form to the reduced form due to the interaction with Cu and, therefore, the transfer of electron density from Cu, which helps in releasing the bottleneck water dissociation and, therefore, facilitating the WGS reaction on copper.

  15. In Situ Time-Resolved Characterization of Ni-MoO2 Catalysts for the Water-Gas Shift Reaction

    SciTech Connect

    Wen,W.; Calderon, J.; Brito, J.; Marinkovic, N.; Hanson, J.; Rodriquez, J.

    2008-01-01

    Active catalysts for the water-gas shift (WGS, CO + H2O ? H2 + CO2) reaction were synthesized from nickel molybdates ({beta}-NiMoO4 and nH2O{center_dot}NiMoO4) as precursors, and their structural transformations were monitored using in situ time-resolved X-ray diffraction and X-ray absorption near-edge spectroscopy. In general, the nickel molybdates were not stable and underwent partial reduction in the presence of CO or CO/H2O mixtures at high temperatures. The interaction of {beta}-NiMoO4 with the WGS reactants at 500 C led to the formation of a mixture of Ni (24 nm particle size) and MoO2 (10 nm particle size). These Ni-MoO2 systems displayed good catalytic activity at 350, 400, and 500 C. At 350 and 400 C, catalytic tests revealed that the Ni-MoO2 system was much more active than isolated Ni (some activity) or isolated MoO2 (negligible activity). Thus, cooperative interactions between the admetal and oxide support were probably responsible for the high WGS activity of Ni-MoO2. In a second synthetic approach, the NiMoO4 hydrate was reduced to a mixture of metallic Ni, NiO, and amorphous molybdenum oxide by direct reaction with H2 gas at 350 C. In the first pass of the water-gas shift reaction, MoO2 appeared gradually at 500 C with a concurrent increase of the catalytic activity. For these catalysts, the particle size of Ni (4 nm) was much smaller than that of the MoO2 (13 nm). These systems were found to be much more active WGS catalysts than Cu-MoO2, which in turn is superior to commercial low-temperature Cu-ZnO catalysts.

  16. H2 production Through the Water-gas Shift Reaction: An in Situ Time-resolved X-ray Diffraction Investigation of Manganese OMS-2 Catalyst

    SciTech Connect

    Sithambaram, S.; Wen, W; Njagi, E; Shen, X; Hanson, J; Suib, S

    2010-01-01

    Manganese oxide octahedral molecular sieve (OMS-2) catalyst prepared by the reflux method was investigated for hydrogen generation via the water-gas shift reaction. Catalysts were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), The Brunauer-Emmett-Teller (BET) surface area and determination of average oxidation state (AOS). The OMS-2 catalyst showed very good catalytic activity for the water-gas shift reaction to generate hydrogen under laboratory conditions. An in situ study was conducted to monitor the structural changes in the catalyst during the water-gas shift reaction using synchrotron radiation-based time-resolved X-ray diffraction (TR-XRD). During the water-gas shift reaction, the mixed valent OMS-2 catalyst undergoes a structural transformation to form Mn{sub 2}O{sub 3} and finally to form MnO. The study showed that OMS-2 catalysts can be used as inexpensive catalysts for hydrogen generation.

  17. H2 Production Through the Water-gas Shift Reaction: An In situ Time-resolved X-ray Diffraction Investigation of Manganese OMS-2 Catalyst

    SciTech Connect

    Hanson, J.C.; Sithambaram, S.; Wen, W.; Njagi, E.; Shen, X.-F.; Suib, S.L.

    2010-10-01

    Manganese oxide octahedral molecular sieve (OMS-2) catalyst prepared by the reflux method was investigated for hydrogen generation via the water-gas shift reaction. Catalysts were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), The Brunauer-Emmett-Teller (BET) surface area and determination of average oxidation state (AOS). The OMS-2 catalyst showed very good catalytic activity for the water-gas shift reaction to generate hydrogen under laboratory conditions. An in situ study was conducted to monitor the structural changes in the catalyst during the water-gas shift reaction using synchrotron radiation-based time-resolved X-ray diffraction (TR-XRD). During the water-gas shift reaction, the mixed valent OMS-2 catalyst undergoes a structural transformation to form Mn{sub 2}O{sub 3} and finally to form MnO. The study showed that OMS-2 catalysts can be used as inexpensive catalysts for hydrogen generation.

  18. SPRING 2014 CHEMISTRY COLLOQUIA "Fundamental Studies on the Water-gas Shift Reaction on

    E-print Network

    Tsymbal, Evgeny Y.

    /Oxide Catalysts: Active Sites and Reaction Mechanism" The high-performance of gold-ceria, copper-ceria and gold surfaces that are 20 to 30% covered by ceria or titania nanoparticles have activities comparable to those of good WGS catalysts such as Cu(110) or Cu(100). Over ceria/Au(111) and ceria/Cu(111), water dissociates

  19. The activation of gold and the water-gas shift reaction: insights from studies with model catalysts.

    PubMed

    Rodriguez, José A; Senanayake, Sanjaya D; Stacchiola, Dario; Liu, Ping; Hrbek, Jan

    2014-03-18

    The activation of gold in catalytic reactions has been the subject of intensive research that has led to the transformation of one of the least chemically reactive elements to a catalyst with excellent activity and selectivity. Scientists have performed numerous systematic experimental and theoretical studies using model systems, which have explained the role of Au in chemical reactions with progressively increasing degrees of structural and chemical complexity. We present an overview of recent studies of model Au(111), CeOx/Au(111), and Au/CeOx/TiO2(110) surfaces that use Au in different structural configurations specifically for the water-gas shift reaction (WGS, CO + H2O ? CO2 + H2), an important industrial process for the purification of CO. We demonstrate the significance of key structural components of the Au-based supported catalysts such as the metal-oxide interface (Au-Ox) toward the WGS catalytic activity, a "structure-activity" relationship. In the WGS reaction, Au(111) or Au nanoparticles have poor catalytic performance due to their inability to activate one of the most important steps of the reaction, the breaking of O-H bonds in the dissociation of water (H2O ? OH + H). The relatively large energetic barrier can be overcome by using O on Au(111) to facilitate the formation of OH at low temperatures, with eventual CO2 and H2 production upon reaction between CO and the adsorbed OH. However, the inability to replace the reacted O prevents a sustainable catalytic process from occurring on Au(111). The addition of a small concentration of CeOx nanoparticles on top of the Au(111) surface facilitates this rate-determining step and easily continues the catalytic cycle in the production of H2. We have discovered that CeOx nanoparticles in contact with Au(111) are rich in Ce(3+). They also have a distinct metal-oxide interface, which sustains excellent activity for the WGS reaction via the formation of a unique carboxylate intermediate, making CeOx/Au(111) more active than Cu/ZnO(0001?), Cu(100), and Cu(111) which are the typical catalysts for this reaction. Taking this knowledge one step further, bringing these components (oxide and metal nanoparticles) together over a second oxide in Au/CeOx/TiO2 produces a system with unique morphological and electronic properties. The result is a superior catalyst for the WGS reaction, both as a model system (Au/CeOx/TiO2(110)) and as powder material (Au/CeOx/TiO2(anatase)) optimized directly in a series of systematic investigations. PMID:24191672

  20. Controlled deposition from the gas phase of surface species on amorphous supports: Preparation of ruthenium-bipyridine catalysts for 1-hexane hydroformylation and water-gas shift reaction

    SciTech Connect

    Hirva, P.; Venaelaeinen, T.; Pakkanen, T.A. (Univ. of Joensuu (Finland))

    1994-08-01

    Controlled stepwise surface reactions were studied to prepare supported ruthenium-bipyridine catalysts. Ru[sub 3](CO)[sub 12] and 2,2[prime]-bipyridine were introduced onto the support from the gas phase in a fluidized bed reactor. With this method the introduction of the precursors can be carried out independently by successive pulses. The possibilities to control metal content, properties of the surface species, and dispersion were studied by varying the deposition conditions, e.g., temperature and carrier gas. The catalysts were tested in 1-hexane hydroformylation and the water-gas shift reaction. Deposition of the precursors from the gas phase was found to produce active catalysts for both reactions. In this water-gas shift reaction the highest activities were 2-2.5 times greater than those obtained with catalysts prepared by impregnation. 35 refs., 4 figs., 4 tabs.

  1. FTIR Study of the Low-Temperature Water–Gas Shift Reaction on Au\\/Fe 2O 3 and Au\\/TiO 2 Catalysts

    Microsoft Academic Search

    F. Boccuzzi; A. Chiorino; M. Manzoli; D. Andreeva; T. Tabakova

    1999-01-01

    An FTIR and quadrupole mass spectroscopic study of the water–gas shift (WGS), the reverse WGS reactions, and the adsorption of the individual molecules involved has been carried out on Au\\/Fe2O3 and Au\\/TiO2 catalysts. The chemisorptions and the reactions on the two catalysts have been compared with the aim of gaining a better understanding of the role played by the two

  2. Low-temperature water-gas shift reaction over Cu and Ni-loaded cerium oxide catalysts

    Microsoft Academic Search

    Yue Li; Qi Fu; Maria Flytzani-Stephanopoulos

    2000-01-01

    In this paper we report on the activity of Cu- and Ni-containing cerium oxide catalysts for low-temperature water-gas shift (WGS). Bulk catalysts were prepared in nanocrystalline form by the urea co-precipitation–gelation method. Lanthanum dopant (10at.%) was used as a structural stabilizer of ceria, while the content of Cu or Ni was in the range of 5–15at.% (2–8wt.%). At low metal

  3. Activity and stability of nanostructured gold-cerium oxide catalysts for the water-gas shift reaction

    Microsoft Academic Search

    Qi Fu

    2004-01-01

    Advanced low-temperature water-gas shift (LTS) catalysts of high activity and stability are under development to produce essentially CO-free hydrogen to feed PEM fuel cells for power generation. Materials based on nanocrystalline cerium oxide (ceria) are among the most promising LTS catalysts. Understanding the structural properties relationship with the WGS activity is fundamentally important in order to rational design the catalysts.

  4. Analysis of a duo-selecting membrane reactor for the water-gas shift

    E-print Network

    Hardy, AliciA Jillian Jackson, 1978-

    2004-01-01

    The water-gas shift reaction is an exothermic and reversible catalytic process that converts carbon monoxide and water (steam) to hydrogen and carbon dioxide. In regard to energy-related issues, the water-gas shift is part ...

  5. Water-Gas Shift and CO Methanation Reactions over Ni-CeO2(111) Catalysts

    SciTech Connect

    S Senanayake; J Evans; S Agnoli; L Barrio; T Chen; J Hrbek; J Rodriguez

    2011-12-31

    X-ray and ultraviolet photoelectron spectroscopies were used to study the interaction of Ni atoms with CeO{sub 2}(111) surfaces. Upon adsorption on CeO{sub 2}(111) at 300 K, nickel remains in a metallic state. Heating to elevated temperatures (500-800 K) leads to partial reduction of the ceria substrate with the formation of Ni{sup 2+} species that exists as NiO and/or Ce{sub 1-x}Ni{sub x}O{sub 2-y}. Interactions of nickel with the oxide substrate significantly reduce the density of occupied Ni 3d states near the Fermi level. The results of core-level photoemission and near-edge X-ray absorption fine structure point to weakly bound CO species on CeO{sub 2}(111) which are clearly distinguishable from the formation of chemisorbed carbonates. In the presence of Ni, a stronger interaction is observed with chemisorption of CO on the admetal. When the Ni is in contact with Ce{sup +3} cations, CO dissociates on the surface at 300 K forming NiC{sub x} compounds that may be involved in the formation of CH{sub 4} at higher temperatures. At medium and large Ni coverages (>0.3 ML), the Ni/CeO{sub 2}(111) surfaces are able to catalyze the production of methane from CO and H{sub 2}, with an activity slightly higher than that of Ni(100) or Ni(111). On the other hand, at small coverages of Ni (<0.3 ML), the Ni/CeO{sub 2}(111) surfaces exhibit a very low activity for CO methanation but are very good catalysts for the water-gas shift reaction.

  6. Water-Gas Shift and CO Methanation Reactions over Ni-CeO2(111) Catalysts

    SciTech Connect

    Senanayake, Sanjaya D [ORNL; Evans, Jaime [Universidad Central de Venezuela; Agnoli, Stefano [Brookhaven National Laboratory (BNL); Barrio, Laura [Brookhaven National Laboratory (BNL); Chen, Tsung-Liang [ORNL; Hrbek, Jan [Brookhaven National Laboratory (BNL); Radriguez, Jose [Brookhaven National Laboratory (BNL)

    2011-01-01

    X-ray and ultraviolet photoelectron spectroscopies were used to study the interaction of Ni atoms with CeO2(111) surfaces. Upon adsorption on CeO2(111) at 300 K, nickel remains in a metallic state. Heating to elevated temperatures (500 800 K) leads to partial reduction of the ceria substrate with the formation of Ni2? species that exists as NiO and/or Ce1-xNixO2-y. Interactions of nickel with the oxide substrate significantly reduce the density of occupied Ni 3d states near the Fermi level. The results of core-level photoemission and near-edge X-ray absorption fine structure point to weakly bound CO species on CeO2(111) which are clearly distinguishable from the formation of chemisorbed carbonates. In the presence of Ni, a stronger interaction is observed with chemisorption of CO on the admetal. When the Ni is in contact with Ce?3 cations, CO dissociates on the surface at 300 K forming NiCx compounds that may be involved in the formation of CH4 at higher temperatures. At medium and large Ni coverages ([0.3 ML), the Ni/CeO2(111) surfaces are able to catalyze the production of methane from CO and H2, with an activity slightly higher than that of Ni(100) or Ni(111). On the other hand, at small coverages of Ni (\\0.3 ML), the Ni/CeO2(111) surfaces exhibit a very low activity for CO methanation but are very good catalysts for the water gas shift reaction.

  7. Probing the Reaction Intermediates for the Water–gas Shift over Inverse CeOx / Au(1 1 1) Catalysts

    SciTech Connect

    Senanayake, S.; Stacchiola, D; Evans, J; Estrella, M; Barrio, L; Perez, M; Hrbek, J; Rodriguez, J

    2010-01-01

    The water-gas shift (WGS) is an important reaction for the production of molecular H{sub 2} from CO and H{sub 2}O. An inverse CeO{sub x}/Au(1 1 1) catalyst exhibits a very good WGS activity, better than that of copper surfaces or Cu nanoparticles dispersed on a ZnO(0 0 0 {bar 1}) substrate which model current WGS industrial catalysts. In this work we report on intermediates likely to arise during the CO + H{sub 2}O reaction over CeO{sub x}/Au(1 1 1) using soft X-ray photoemission (sXPS) and near-edge X-ray absorption fine structure (NEXAFS). Several potential intermediates including formates (HCOO), carbonates (CO{sub 3}) and carboxylates (HOCO) are considered. Adsorption of HCOOH and CO{sub 2} is used to create both HCOO and CO{sub 3} on the CeO{sub x}/Au(1 1 1) surface, respectively. HCOO appears to have greater stability with desorption temperatures up to 600 K while CO{sub 3} only survives on the surface up to 300 K. On the CeO{sub x}/Au(1 1 1) catalysts, the presence of Ce{sup 3+} leads to the dissociation of H{sub 2}O to give OH groups. We demonstrate experimentally that the OH species are stable on the surface up to 600 K and interact with CO to yield weakly bound intermediates. When there is an abundance of Ce{sup 4+}, the OH concentration is diminished and the likely intermediates are carbonates. As the surface defects are increased and the Ce{sup 3+}/Ce{sup 4+} ratio grows, the OH concentration also grows and both carbonate and formate species are observed on the surface after dosing CO to H{sub 2}O/CeO{sub x}/Au(1 1 1). The addition of ceria nanoparticles to Au(1 1 1) is essential to generate an active WGS catalyst and to increase the production and stability of key reaction intermediates (OH, HCOO and CO{sub 3}).

  8. Probing the Reaction Intermediates for the Water-Gas Shift over Inverse CeOx/Au(111) Catalysts

    SciTech Connect

    Rodriguez, J.A.; Senanayake, S.D.; Stacchiola, D.; Evans, J.; Estrella, M.; Barrio-Pliego, L.; Pérez, M.; Hrbek, J.

    2010-05-04

    The water-gas shift (WGS) is an important reaction for the production of molecular H{sub 2} from CO and H{sub 2}O. An inverse CeO{sub x}/Au(1 1 1) catalyst exhibits a very good WGS activity, better than that of copper surfaces or Cu nanoparticles dispersed on a ZnO(0 0 0 {bar 1}) substrate which model current WGS industrial catalysts. In this work we report on intermediates likely to arise during the CO + H{sub 2}O reaction over CeO{sub x}/Au(1 1 1) using soft X-ray photoemission (sXPS) and near-edge X-ray absorption fine structure (NEXAFS). Several potential intermediates including formates (HCOO), carbonates (CO{sub 3}) and carboxylates (HOCO) are considered. Adsorption of HCOOH and CO{sub 2} is used to create both HCOO and CO{sub 3} on the CeO{sub x}/Au(1 1 1) surface, respectively. HCOO appears to have greater stability with desorption temperatures up to 600 K while CO{sub 3} only survives on the surface up to 300 K. On the CeO{sub x}/Au(1 1 1) catalysts, the presence of Ce{sup 3+} leads to the dissociation of H{sub 2}O to give OH groups. We demonstrate experimentally that the OH species are stable on the surface up to 600 K and interact with CO to yield weakly bound intermediates. When there is an abundance of Ce{sup 4+}, the OH concentration is diminished and the likely intermediates are carbonates. As the surface defects are increased and the Ce{sup 3+}/Ce{sup 4+} ratio grows, the OH concentration also grows and both carbonate and formate species are observed on the surface after dosing CO to H{sub 2}O/CeO{sub x}/Au(1 1 1). The addition of ceria nanoparticles to Au(1 1 1) is essential to generate an active WGS catalyst and to increase the production and stability of key reaction intermediates (OH, HCOO and CO{sub 3}).

  9. Studies of the water-gas-shift reaction on ceria-supported Pt, Pd, and Rh: Implications for oxygen-storage properties

    Microsoft Academic Search

    T. Bunluesin; R. J. Gorte; G. W. Graham

    1998-01-01

    Steady-state, water-gas-shift kinetics were measured on model, ceria-supported, Pd, Pt, and Rh catalysts and compared to rates obtained on alumina-supported catalysts. When ceria was calcined at low temperatures prior to addition of the precious metal, the specific rates were found to be identical for each of the metals, with an activation energy of 11 ± 1 kcal\\/mol and reaction orders

  10. Supported Copper, Nickel and Copper-Nickel Nanoparticle Catalysts for Low Temperature Water-Gas-Shift Reaction

    NASA Astrophysics Data System (ADS)

    Lin, Jiann-Horng

    Hydrogen is being considered worldwide as a future replacement for gasoline, diesel fuel, natural gas in both the transportation and non-transportation sectors. Hydrogen is a versatile energy carrier that can be produced from a variety of widely available primary energy sources, including coal, natural gas, biomass, solar, wind, and nuclear power. Coal, the most abundant fossil fuel on the planet, is being looked at as the possible future major source of H2, due to the development of the integrated gasification combined cycle (IGCC) and integrated gasification fuel cell technologies (IGFC). The gasification of coal produces syngas consisting of predominately carbon monoxide and hydrogen with some remaining hydrocarbons, carbon dioxide and water. Then, the water-gas shift reaction is used to convert CO to CO2 and additional hydrogen. The present work describes the synthesis of model Cu, Ni and Cu-Ni catalysts prepared from metal colloids, and compares their behavior in the WGS reaction to that of traditional impregnation catalysts. Initially, we systematically explored the performance of traditional Cu, Ni and Cu-Ni WGS catalysts made by impregnation methods. Various bimetallic Cu-Ni catalysts were prepared by supported impregnation and compared to monometallic Cu and Ni catalysts. The presence of Cu in bimetallic catalysts suppressed undesirable methanation side reaction, while the Ni component was important for high WGS activity. Colloidal Cu, Ni and Cu-Ni alloy nanoparticles obtained by chemical reduction were deposited onto alumina to prepare supported catalysts. The resulting Cu and Ni nanoparticle catalysts were found to be 2.5 times more active in the WGS reaction per unit mass of active metal as compared to catalysts prepared by the conventional impregnation technique. The powder XRD and HAADF-STEM provided evidence supporting the formation of Cu-Ni particles containing the Cu core and Cu-Ni alloy shell. The XPS data indicated surface segregation of Cu in the bimetallic Cu-Ni catalysts after reduction. The colloidal Cu5Ni5 alloy catalyst exhibited the WGS reaction rate that was higher than that observed over colloidal Cu and Ni catalysts indicating for the very first time a favorable bimetallic effect for the Cu-Ni system. The presence of Cu in these bimetallic catalysts induced favorable structural and electronic effects not only for enhancing the WGS activity, but also for suppressing methane yield. Bimetallic Cu-Ni catalysts possessing a core-shell structure were synthesized that provided important insights into their structure-activity relationships in the WGS reaction. We employed a successive reduction route to synthesize Cu Ni and Ni Cu core-shell nanoparticles and deposited them onto alumina support to obtain supported bimetallic catalysts. The powder XRD patterns, CO chemisorption data, and UV-vis spectra indicated the formation of core-shell structures in the bimetallic Cu-Ni nanoparticles. Cu Ni catalysts showed similar WGS activities to supported Ni catalysts but lower methanation activity. Suppressed methanation activity observed for Cu Ni nanoparticles may be due to Cu segregation to the surface. Supported Ni Cu catalysts displayed WGS activity comparable to supported Cu catalysts. Therefore, these findings strongly suggested that supported Cu, Ni and Cu-Ni alloy nanoparticle catalysts prepared from metal colloids are very promising as highly active WGS catalysts.

  11. In Situ Time-Resolved Characterization of Novel Cu-MoO2 Catalysts During the Water-Gas Shift Reaction

    SciTech Connect

    Wen ,W.; Liu, J.; White, M.; Marinkovic, N.; Hanson, J.; Rodriguez, J.

    2007-01-01

    A novel and active Cu-MoO{sub 2} catalyst was synthesized by partial reduction of a precursor CuMoO{sub 4} mixed-metal oxide with CO or H{sub 2} at 200-250 C. The phase transformations of Cu-MoO{sub 2} during H{sub 2} reduction and the water-gas shift reaction could be followed by In situ time resolved XRD techniques. During the reduction process the diffraction pattern of the CuMoO{sub 4} collapsed and the copper metal lines were observed on an amorphous material background that was assigned to molybdenum oxides. During the first pass of water-gas shift (WGS) reaction, diffraction lines for Cu{sub 6}Mo{sub 5}O{sub 18} and MoO{sub 2} appeared around 350 C and Cu{sub 6}Mo{sub 5}O{sub 18} was further transformed to Cu/MoO{sub 2} at higher temperature. During subsequent passes, significant WGS catalytic activity was observed with relatively stable plateaus in product formation around 350, 400 and 500 C. The interfacial interactions between Cu clusters and MoO{sub 2} increased the water-gas shift catalytic activities at 350 and 400 C.

  12. Theoretical study of gas-phase reactions of Fe(CO){sub 5} with OH{sup {minus}} and their relevance for the water gas shift reaction

    SciTech Connect

    Torrent, M.; Sola, M. [Univ. de Girona (Spain). Institut de Quimica Computacional] [Univ. de Girona (Spain). Institut de Quimica Computacional; Frenking, G. [Philipps-Universitaet Marburg (Germany)] [Philipps-Universitaet Marburg (Germany)

    1999-07-19

    Revision of the homogeneously Fe(CO){sub 5}-catalyzed water gas shift reaction in the gas phase has been performed by means of quantum chemical calculations using gradient-corrected density functional theory (B3LYP) and ab initio methods at the CCSD(T) level. The classically assumed reaction path has been scrutinized step by step, and enlarged with novel mechanistic proposals. The calculations lend additional credit to some of the previously accepted steps in the catalytic cycle, such as the initial attack of OH{sup {minus}} to Fe(CO){sub 5} and also to the recently accepted decarboxylation of (CO){sub 4}FeCOOH{sup {minus}} (via a concerted mechanism involving a four-centered transition state), as well as to the acidification of the metal hydride (CO){sub 4}Fe{sub 4}H{sub {minus}} with water to yield the dihydride (CO){sub 4}FeH{sub 2}. The present investigation also examines in terms of energies and activation barriers the existence/participation of new intermediates (in particular, a metalloformate species, a water-hydride adduct, and a dihydrogen complex), not mentioned in prior studies. Finally, a transition-metal-containing S{sub N}2-type reaction is explored for the last stages of this chemical process as a mechanistic alternative to regenerate the starting catalyst.

  13. In Situ Time-Resolved Characterization of Au-CeO2 Catalysts During Water Gas Shift Reactions: presence of Au and O Vacancies in the Active Phase

    Microsoft Academic Search

    X. Wang; J. Rodriguez; J. Hanson; M. Perez; J. Evans

    2005-01-01

    Synchrotron-based in situ time-resolved x-ray diffraction and x-ray absorption spectroscopies were used to study the behavior of nanostructured {l_brace}Au+AuO{r_brace}-CeO catalysts under the water-gas shift (WGS) reaction. At temperatures above 250 C, a complete AuOAu transformation was observed with high catalytic activity. Photoemission results for the oxidation and reduction of Au nanoparticles supported on rough ceria films or a CeO(111) single

  14. Mechanisms of the gold-catalysed water-gas shift \\

    Microsoft Academic Search

    Geoffrey Bond

    Mechanisms proposed for the gold-catalysed Water-Gas Shift (WGS) are critically reviewed, and a complete reaction set and cycle involving activation of water on reduced support sites is considered; however, a modified route to CO 2 formation by thermal decomposition of a carboxyl species results in a simpler and therefore more probable mechanism.

  15. Advanced Water-Gas Shift Membrane Reactor

    SciTech Connect

    Sean Emerson; Thomas Vanderspurt; Susanne Opalka; Rakesh Radhakrishnan; Rhonda Willigan

    2009-01-07

    The overall objectives for this project were: (1) to identify a suitable PdCu tri-metallic alloy membrane with high stability and commercially relevant hydrogen permeation in the presence of trace amounts of carbon monoxide and sulfur; and (2) to identify and synthesize a water gas shift catalyst with a high operating life that is sulfur and chlorine tolerant at low concentrations of these impurities. This work successfully achieved the first project objective to identify a suitable PdCu tri-metallic alloy membrane composition, Pd{sub 0.47}Cu{sub 0.52}G5{sub 0.01}, that was selected based on atomistic and thermodynamic modeling alone. The second objective was partially successful in that catalysts were identified and evaluated that can withstand sulfur in high concentrations and at high pressures, but a long operating life was not achieved at the end of the project. From the limited durability testing it appears that the best catalyst, Pt-Re/Ce{sub 0.333}Zr{sub 0.333}E4{sub 0.333}O{sub 2}, is unable to maintain a long operating life at space velocities of 200,000 h{sup -1}. The reasons for the low durability do not appear to be related to the high concentrations of H{sub 2}S, but rather due to the high operating pressure and the influence the pressure has on the WGS reaction at this space velocity.

  16. Studies related to the homogeneous catalysis of the water gas shift reaction. Technical progress report, December 1, 1983-November 30, 1984

    SciTech Connect

    Ford, P.C.

    1984-01-01

    Proposed are investigations related to the catalytic activation of carbon monoxide. These studies will be concerned with the design of catalysts for the water gas shift reaction and related processes such as the hydroformylation of olefins by homogeneous solution phase systems as well as by selected metal catalysts heterogenized by complexation to functional polymers. Also under investigation will be quantitative mechanistic aspects of reactions considered key to probable catalyst cycles. These are principally concerned with the fundamental chemistry of metal carbonyl and metal carbnyl hydride complexes including acid/base properties, reductive elimination, substitution and cluster fragmentation reactions and the nucleophilic activation of metal coordinated carbonyls toward reaction with water or dihydrogen. Goal of these studies is to provide chemical guidelines for the molecular design of new and more efficient catalysts for the utilization of carbonaceous materials such as coal for the production of fuels and other organic chemicals.

  17. Studies relevant to the catalytic activation of carbon monoxide: the water gas shift reaction and related processes. Technical progress report, December 1, 1983-November 30, 1984

    SciTech Connect

    Ford, P.C.

    1984-01-01

    Proposed are investigations related to the catalytic activation of carbon monoxide. These studies will be concerned with the design of catalysts for the water gas shift reaction and related processes such as the hydroformylation of olefins by homogeneous solution phase systems as well as by selected metal catalysts heterogenized by complexation to functionalized polymers. Also under investigation will be quantitative mechanistic aspects of reactions considered key to probable catalyst cycles. These are principally concerned with the fundamental chemistry of metal carbonyl and metal carbonyl hydride complexes including acid/base properties, reductive elimination, substitution and cluster fragmentation reactions and the nucleophilic activation of metal coordinated carbonyls toward reaction with water or dihydrogen. The goal of these studies is to provide chemical guidelines for the molecular design of new and more efficient catalysts for the utilization of carbonaceous materials such as coal for the production of fuels and other organic chemicals. 70 references.

  18. Activity of CeOx and TiOx Nanoparticles Grown on Au(111) in the Water-Gas Shift Reaction

    SciTech Connect

    Rodriguez,J.; Ma, S.; Liu, P.; Hrbek, J.; Evans, J.; Perez, M.

    2007-01-01

    The high performance of Au-CeO2 and Au-TiO2 catalysts in the water-gas shift (WGS) reaction (H2O + CO->H2 + CO2) relies heavily on the direct participation of the oxide in the catalytic process. Although clean Au(111) is not catalytically active for the WGS, gold surfaces that are 20 to 30% covered by ceria or titania nanoparticles have activities comparable to those of good WGS catalysts such as Cu(111) or Cu(100). In TiO2-x/Au(111) and CeO2-x/Au(111), water dissociates on O vacancies of the oxide nanoparticles, CO adsorbs on Au sites located nearby, and subsequent reaction steps take place at the metal-oxide interface. In these inverse catalysts, the moderate chemical activity of bulk gold is coupled to that of a more reactive oxide.

  19. Pulse studies to decipher the role of surface morphology in CuO/CeO? nanocatalysts for the water gas shift reaction

    DOE PAGESBeta

    Rodriguez, Jose A.; Zhao, Fuzhen; Liu, Zongyuan; Xu, Wenqian; Yao, Siyu; Si, Rui; Johnston-Peck, Aaron C.; Martinez-Arias, Arturo; Hanson, Jonathan C.; Senanayake, Sanjaya D.

    2015-03-01

    The water-gas shift reaction (WGS, CO + H?O ? CO?) was studied over CuO/CeO? catalysts with two different ceria particle morphohologies, in the form of nanospheres (ns) and nanocubes (nc). To understand the strong dependence of the WGS reaction activity on the ceria nanoshapes, pulses of CO (without and with water vapor) were employed during in situ X-ray diffraction (XRD) and X-ray absoprtion near edge structure (XANES) measurements done to characterize the catalysts. The results showed that CuO/CeO? (ns) exhibited a substantially better activity than CuO/CeO? (nc). The higher activity was associated with the unique properties of CuO/CeO? (ns), suchmore »as the easier reduction of highly dispersed CuO to metallic Cu, the stability of metallic Cu and a larger concentration Ce³? in CeO? (ns).« less

  20. Pulse studies to decipher the role of surface morphology in CuO/CeO? nanocatalysts for the water gas shift reaction

    DOE PAGESBeta

    Rodriguez, Jose A. [Brookhaven National Lab. (BNL), Upton, NY (United States); Zhao, Fuzhen [South-Central Univ. for Nationalities, Wuhan, Hubei (China); Brookhaven National Lab., Upton, NY (United States); Liu, Zongyuan [Brookhaven National Lab. (BNL), Upton, NY (United States); Xu, Wenqian [Brookhaven National Lab. (BNL), Upton, NY (United States); Yao, Siyu [Brookhaven National Lab. (BNL), Upton, NY (United States); Si, Rui [Brookhaven National Lab. (BNL), Upton, NY (United States); Johnston-Peck, Aaron C. [Brookhaven National Lab. (BNL), Upton, NY (United States); Martinez-Arias, Arturo [Inst. de Catalisis y Petroleoquimica, Consejo Superior de Investigaciones Cientificas, Madrid (Spain); Hanson, Jonathan C. [Brookhaven National Lab. (BNL), Upton, NY (United States); Senanayake, Sanjaya D. [Brookhaven National Lab. (BNL), Upton, NY (United States)

    2015-03-01

    The water-gas shift reaction (WGS, CO + H?O ? CO?) was studied over CuO/CeO? catalysts with two different ceria particle morphohologies, in the form of nanospheres (ns) and nanocubes (nc). To understand the strong dependence of the WGS reaction activity on the ceria nanoshapes, pulses of CO (without and with water vapor) were employed during in situ X-ray diffraction (XRD) and X-ray absoprtion near edge structure (XANES) measurements done to characterize the catalysts. The results showed that CuO/CeO? (ns) exhibited a substantially better activity than CuO/CeO? (nc). The higher activity was associated with the unique properties of CuO/CeO? (ns), such as the easier reduction of highly dispersed CuO to metallic Cu, the stability of metallic Cu and a larger concentration Ce³? in CeO? (ns).

  1. In Situ Time-Resolved Characterization of Au-CeO2 Catalysts During Water Gas Shift Reactions: presence of Au and O Vacancies in the Active Phase

    SciTech Connect

    Wang,X.; Rodriguez, J.; Hanson, J.; Perez, M.; Evans, J.

    2005-01-01

    Synchrotron-based in situ time-resolved x-ray diffraction and x-ray absorption spectroscopies were used to study the behavior of nanostructured {l_brace}Au+AuO{sub x}{r_brace}-CeO{sub 2} catalysts under the water-gas shift (WGS) reaction. At temperatures above 250 C, a complete AuO{sub x}{yields}Au transformation was observed with high catalytic activity. Photoemission results for the oxidation and reduction of Au nanoparticles supported on rough ceria films or a CeO{sub 2}(111) single crystal corroborate that cationic Au{sup {delta}} species cannot be the key sites responsible for the WGS activity at high temperatures. The rate determining steps for the WGS seem to occur at the gold-ceria interface, with the active sites involving small gold clusters (<2 nm) and O vacancies.

  2. Characterization of CeO2-Supported Cu-Pd Bimetallic Catalyst for the Oxygen-Assisted Water-Gas Shift Reaction

    SciTech Connect

    Fox, Elise; Velu, Subramani; Engelhard, Mark H.; Chin, Ya-Huei; Miller, Jeffrey T.; Kropf, Jeremy; Song, Chunshan

    2008-12-10

    This study was focused to investigate the roles of Cu and Pd in CuPd/CeO2 bimetallic catalysts containing 20-30 wt% Cu and 0.5-1 wt% Pd used in the oxygen-assisted water-gas shift (OWGS) reaction employing a combined bulk and surface characterization techniques such as XRD, TPR, CO chemisorption, and in-situ XPS. The catalytic activity for CO conversion and the stability of catalyst during on-stream operation increased by the addition of Cu to Pd/CeO2 or Pd to Cu/CeO2 monometallic catalysts, especially when the OWGS reaction was performed under low temperatures, below 200oC. The bimetallic catalyst after leaching with nitric acid retained about 60% of its original activity. The TPR of monometallic Cu/CeO2 showed reduction of CuO supported on CeO2 in two distinct regions, around 150 and 250oC. The high temperature peak disappeared and reduction occurred in a single step around 150oC upon Pd addition. The Pd dispersion decreased from 38.5% for Pd/CeO2 to below 1% for CuPd/CeO2 bimetallic catalyst. In-situ XPS studies showed a shift in Cu 2p peaks toward lower binding energy (BE) with concommitant shift in the Pd 3d peaks toward higher BE. Addition of Pd decreased the surface Cu concentration while the concentration of Pd remained unaltered. All these observations indicated the formation of Cu-Pd surface alloy. The valence band XP spectra collected below 10 eV corroborated the core level XP spectra and indicated that Cu is mainly involved in the catalytic reaction. The improved catalytic activity and stability of CuPd/CeO2 bimetallic catalyst was attributed to the alloy formation.

  3. A common single-site Pt(II)-O(OH)x- species stabilized by sodium on "active" and "inert" supports catalyzes the water-gas shift reaction.

    PubMed

    Yang, Ming; Liu, Jilei; Lee, Sungsik; Zugic, Branko; Huang, Jun; Allard, Lawrence F; Flytzani-Stephanopoulos, Maria

    2015-03-18

    While it has long been known that different types of support oxides have different capabilities to anchor metals and thus tailor the catalytic behavior, it is not always clear whether the support is a mere carrier of the active metal site, itself not participating directly in the reaction pathway. We report that catalytically similar single-atom-centric Pt sites are formed by binding to sodium ions through -O ligands, the ensemble being equally effective on supports as diverse as TiO2, L-zeolites, and mesoporous silica MCM-41. Loading of 0.5 wt % Pt on all of these supports preserves the Pt in atomic dispersion as Pt(II), and the Pt-O(OH)x- species catalyzes the water-gas shift reaction from ?120 to 400 °C. Since the effect of the support is "indirect," these findings pave the way for the use of a variety of earth-abundant supports as carriers of atomically dispersed platinum for applications in catalytic fuel-gas processing. PMID:25746682

  4. Determination of CO, H{sub 2}O and H{sub 2} coverage by XANES and EXAFS on Pt and Au during water gas shift reaction.

    SciTech Connect

    Guo, N.; Fingland, B. R.; Williams, W. D.; Kispersky, V. F.; Jelic, J.; Delgass, W. N.; Ribeiro, F. H.; Meyer, R. J.; Miller, J. T.; Purdue Univ.; Univ. of Illinois

    2010-01-01

    The turn over rate (TOR) for the water gas shift (WGS) reaction at 200C, 7%CO, 9%CO{sub 2}, 22% H{sub 2}O, 37% H, and balance Ar, of 1.4 nm Au/Al{sub 2}O{sub 3} is approximately 20 times higher than that of 1.6 nm Pt.Al{sub 2}O{sub 3}. Operando EXFAS experiments at both the Au and Pt L{sub 3} edges reveal tht under reaction conditions, the catalysts are fully metallic. In the absence of adsorbates, the metal-metal bond distance of Pt and Au catalysts are 0.07 {angstrom} and 0.13 {angstrom} smaller than those of bulk Pt and Au foils, respectively. Adsorption of H{sub 2} or CO on the Pt catalysts leads to significantly longer Pt-Pt bond distances, while there is little change in the Au-Au bond distance with adsorbates. Adsorption of CO, H{sub 2} and H{sub 2}O leads to changes in the XANES spectra that can be used to determine the surface coverage of each adsorbate under reaction conditions. During WGS, the coverage of CO, H{sub 2}O and H{sub 2} are obtained by the linear combination fitting of the difference XANES or {Delta}XANES, spectra. Pt catalysts adsorb CO,H{sub 2} and H{sub 2}O more strongly than the Au, in agreement with the lower CO reaction order and higher reaction temperatures.

  5. Development of Novel Water-Gas-Shift Membrane Reactor

    E-print Network

    Development of Novel Water- Gas-Shift Membrane Reactor Addressing Barrier L: H2 Purification-22, 2003 #12;Water-Gas-Shift Membrane Reactor · Relevance/Objectives - Produce Enhanced H2 Product with ppm CO at High Pressure Used for Reforming - Overcome Barrier L: H2 Purification/CO Clean-up - Achieve

  6. Interaction of CO with OH on Au(111): HCOO, CO3, and HOCO as Key Intermediates in the Water-Gas Shift Reaction

    SciTech Connect

    Senanayake, S.; Stacchiola, D; Liu, P; Mullins, C; Hrbek, J; Rodriguez, J

    2009-01-01

    We have investigated the role of formate (HCOO), carbonate (CO{sub 3}), and carboxyl (HOCO) species as possible intermediates in the OH{sub ads} + CO{sub gas} {yields} CO{sub 2,gas} + 0.5H{sub 2,gas} reaction on Au(111) using synchrotron-based core level photoemission, near-edge X-ray absorption fine structure (NEXAFS), and infrared absorption spectroscopy (IR). Adsorbed HCOO, CO{sub 3}, and OH species were prepared by adsorbing formic acid, carbon dioxide, and water on a Au(111) surface precovered with 0.2 ML of atomic oxygen, respectively. HCOOH interacts weakly with Au(111), but on O/Au(111) it dissociates its acidic H to yield adsorbed formate. The results of NEXAFS, IR, and density-functional calculations indicate that the formate adopts a bidentate configuration on Au(111). Since the HCOO groups are stable on Au(111) up to temperatures near 350 K, it is not likely that formate is a key intermediate for the OH{sub ads} + CO{sub gas} {yields} CO{sub 2,gas} + 0.5H{sub 2,gas} reaction at low temperatures. In fact, the formation of this species could lead eventually to surface poisoning. When compared to a formate species, a carbonate species formed by the reaction of CO{sub 2} with O/Au(111) has low stability, decomposing at temperatures between 100 and 125 K, and should not poison the gold surface. Neither HCOO nor CO{sub 3} was detected during the reaction of CO with OH on Au(111) at 90-120 K. The results of photoemission and IR spectroscopy point to HO {leftrightarrow} CO interactions, consistent with the formation of an unstable HOCO intermediate which has a very short lifetime on the gold surface. The possible mechanism for the low-temperature water-gas shift on gold catalysts is discussed in light of these results.

  7. Development of Ni-Mo/Al2O3 catalyst for reverse water gas shift (RWGS) reaction.

    PubMed

    Kharaji, Abolfazl Gharibi; Shariati, Ahmad; Ostadi, Mohammad

    2014-09-01

    In the present study, Mo/Al2O3 catalyst was prepared using impregnation method. Then it was promoted with Ni ions to produce Ni-Mo/Al2O3 catalyst. The structures of the catalysts were studied using X-ray diffraction (XRD), Energy dispersive X-ray (EDAX), Brunauer-Emmett-Teller (BET), X-ray photoelectron spectroscopy (XPS), CO chemisorption, temperature programmed reduction of hydrogen (H2-TPR) and scanning electron microscope (SEM) techniques. Catalytic performances of the two catalysts were investigated in a fixed-bed reactor for RWGS reaction. The results indicated that addition of nickel promoter to Mo/Al2O3 catalyst enhances its activity. It is reasonable for the electron deficient state of the Ni species and existence of NiMoO4 phase to possess high activity in RWGS reaction. Stability test of Ni-Mo/Al2O3 catalyst was carried out in a fixed bed reactor and a high CO2 conversion for 60 h time on stream was demonstrated. This study introduces a new catalyst, Ni-Mo/Al2O3, with high activity and stability for RWGS reaction. PMID:25924339

  8. On the Importance of Metal–Oxide Interface Sites for the Water–Gas Shift Reaction Over Pt/CeO2 Catalysts

    SciTech Connect

    Aranifard, Sara; Ammal, Salai Cheettu; Heyden, Andreas

    2014-01-01

    The mechanism of water–gas shift reaction at the three-phase boundary of Pt/CeO2 catalysts has been investigated using density functional theory and microkinetic modeling to better understand the importance of metal–oxide interface sites in heterogeneous catalysis. Analysis of a microkinetic model based on parameters obtained from first principles suggests that both the “Redox pathway” and the “Associative carboxyl pathway with redox regeneration” could operate on Pt/CeO2 catalysts. Although (1) only few interfacial Pt atoms are found to be catalytically active at low temperatures due to strong adsorption of CO and (2) interfacial O–H bond breakage is difficult due to the high reducibility of ceria, interface sites are 2–3 orders of magnitude more active than Pt (1 1 1) and stepped Pt surface sites and therefore effectively determine the overall activity of Pt/CeO2. The high activity of Pt/CeO2 interface sites originates from a significantly enhanced water activation and dissociation at interfacial oxygen vacancies.

  9. CO{sub 2} SELECTIVE CERAMIC MEMBRANE FOR WATER-GAS-SHIFT REACTION WITH CONCOMITANT RECOVERY OF CO{sub 2}

    SciTech Connect

    Paul K. T. Liu

    2005-01-31

    Our CO{sub 2}-affinity material synthesis activities thus far have offered two base materials suitable for hydrogen production via low temperature water gas shift reaction (LTS-WGS) with concomitant removal of CO{sub 2} for sequestration. They include (i) a nanoporous CO{sub 2}-affinity membrane and (ii) a hydrotalcite based CO-affinity adsorbent. These two materials offer a commercially viable opportunity for implementing an innovative process concept termed the hybrid adsorbent-membrane reactor (HAMR) for LTS-WGS, proposed by us in a previous quarterly report. A complete mathematical model has been developed in this quarter to describe the HAMR system, which offers process flexibility to incorporate both catalysts and adsorbents in the reactor as well as permeate sides. In comparison with the preliminary mathematical model we reported previously, this improved model incorporates ''time'' as an independent variable to realistically simulate the unsteady state nature of the adsorptive portion of the process. In the next quarterly report, we will complete the simulation to demonstrate the potential benefit of the proposed process based upon the performance parameters experimentally obtained from the CO{sub 2}-affinity adsorbent and membrane developed from this project.

  10. CO2 SELECTIVE CERAMIC MEMBRANE FOR WATER-GAS-SHIFT REACTION WITH CONCOMITANT RECOVERY OF CO2

    SciTech Connect

    Paul K.T. Liu

    2005-06-01

    In this quarter, we have focused on the completion of the loose ends of the experimental study. A series of CO{sub 2}-affinity membranes (carbonaceous base) prepared previously were characterized and evaluated for their suitability for the proposed application The CO{sub 2} permeance and selectivity are 0.5 to >3 m{sup 3}/m{sub 2}/hr/bar and 4 to 10 for CO{sub 2} over nitrogen respectively. Based upon its performance dependence on temperature and pore size, we conclude that this type of CO{sub 2} affinity membrane shows significant surface affinity to CO{sub 2} over nitrogen even at the temperature as high as 220 C, which is within the typical operating condition for LTS-WGS. Future study should focus on mixture separations for CO/CO{sub 2}/H{sub 2} to establish the selectivity of CO{sub 2} over CO and H{sub 2} which are present in the WGS reaction of the coal gasifier off-gas.

  11. Ceria-based Catalysts for the Production of H2 Through the Water-gas-shift Reaction: Time-Resolved XRD and XAFS Studies

    SciTech Connect

    Wang,X.; Rodriguez, J.; Hanson, J.; Gamarra, D.; Marinez-Arias, A.; Fernandez-Garcia, M.

    2008-01-01

    Hydrogen is a potential alternate energy source for satisfying many of our energy needs. In this work, we studied H2 production from the water-gas-shift (WGS) reaction over Ce1-x Cu x O2 catalysts, prepared with a novel microemulsion method, using two synchrotron-based techniques: time-resolved X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS). The results are compared with those reported for conventional CuO x /CeO2 and AuO x /CeO2 catalysts obtained through impregnation of ceria. For the fresh Ce1-x Cu x O2 catalysts, the results of XAFS measurements at the Cu K-edge indicate that Cu is in an oxidation state higher than in CuO. Nevertheless, under WGS reaction conditions the Ce1-x Cu x O2 catalysts undergo reduction and the active phase contains very small particles of metallic Cu and CeO2-x . Time-resolved XRD and XAFS results also indicate that Cud+ and Aud+ species present in fresh CuO x /CeO2 and AuO x /CeO2 catalysts do not survive above 200 C under the WGS conditions. In all these systems, the ceria lattice displayed a significant increase after exposure to CO and a decrease in H2O, indicating that CO reduced ceria while H2O oxidized it. Our data suggest that H2O dissociation occurred on the Ovacancy sites or the Cu-Ovacancy and Au-Ovacancy interfaces. The rate of H2 generation by a Ce0.95Cu0.05O2 catalyst was comparable to that of a 5 wt% CuO x /CeO2 catalyst and much bigger than those of pure ceria or CuO.

  12. Unusual Physical and Chemical Properties of Ni in Ce1-xNixO2-y Oxides: Structural Characterization and Catalytic Activity for the Water Gas Shift Reaction

    SciTech Connect

    Barrio, L.; Kubacka, A; Zhou, G; Estrella, M; Martinez-Arias, A; Hanson, J; Fernandez-Garcia, M; Rodriguez, J

    2010-01-01

    The structural and electronic properties of Ce{sub 1-x}Ni{sub x}O{sub 2-y} nanosystems prepared by a reverse microemulsion method were characterized with synchrotron-based X-ray diffraction, X-ray absorption spectroscopy, Raman spectroscopy, and density functional calculations. The Ce{sub 1-x}Ni{sub x}O{sub 2-y} systems adopt a lattice with a fluorite-type structure with an acute local order where Ni displays a strongly distorted (oxygen) nearest-neighbor coordination and the presence of Ni atoms as first cation distances, pointing to the existence of Ni-O-Ni entities embedded into the ceria lattice. A Ni {leftrightarrow} Ce exchange within the CeO{sub 2} leads to a charge redistribution and the appearance of O vacancies. The Ni-O bonds in Ce{sub 1-x}Ni{sub x}O{sub 2-y} are more difficult to reduce than the bonds in pure NiO. The specific structural configuration of Ni inside the mixed-metal oxide leads to a unique catalyst with a high activity for the water gas shift (CO + H{sub 2}O {yields} H{sub 2} + CO{sub 2}) reaction and a simultaneous reduction of the methanation activity of nickel. Characterization results indicate that small particles of metallic Ni at the interface position of a ceria network may be the key for high WGS activity and that the formate-carbonate route is operative for the production of hydrogen.

  13. Unusual Physical and Chemical Properties of Ni in Ce1-xNixO2-y Oxides: Structural Characterization and Catalytic Activity for the Water Gas Shift Reaction

    SciTech Connect

    Rodriguez, J.A.; Barrio, L.; Kubacka, A.; Zhou, G.; Estrella, M.; Mart& #305; nez-Arias, A.; Hanson, J.C.; Fernandez-Garc& #305; a, M.

    2010-07-29

    The structural and electronic properties of Ce{sub 1-x}Ni{sub x}O{sub 2-y} nanosystems prepared by a reverse microemulsion method were characterized with synchrotron-based X-ray diffraction, X-ray absorption spectroscopy, Raman spectroscopy, and density functional calculations. The Ce{sub 1-x}Ni{sub x}O{sub 2-y} systems adopt a lattice with a fluorite-type structure with an acute local order where Ni displays a strongly distorted (oxygen) nearest-neighbor coordination and the presence of Ni atoms as first cation distances, pointing to the existence of Ni-O-Ni entities embedded into the ceria lattice. A Ni {leftrightarrow} Ce exchange within the CeO{sub 2} leads to a charge redistribution and the appearance of O vacancies. The Ni?O bonds in Ce{sub 1-x}Ni{sub x}O{sub 2-y} are more difficult to reduce than the bonds in pure NiO. The specific structural configuration of Ni inside the mixed-metal oxide leads to a unique catalyst with a high activity for the water gas shift (CO + H{sub 2}O {yields} H{sub 2} + CO{sub 2}) reaction and a simultaneous reduction of the methanation activity of nickel. Characterization results indicate that small particles of metallic Ni at the interface position of a ceria network may be the key for high WGS activity and that the formate?carbonate route is operative for the production of hydrogen.

  14. Flame synthesis of nanosized Cu-Ce-O, Ni-Ce-O, and Fe-Ce-O catalysts for the water-gas shift (WGS) reaction.

    PubMed

    Pati, Ranjan K; Lee, Ivan C; Hou, Sicong; Akhuemonkhan, Osifo; Gaskell, Karen J; Wang, Qi; Frenkel, Anatoly I; Chu, Deryn; Salamanca-Riba, Lourdes G; Ehrman, Sheryl H

    2009-11-01

    A flame synthesis method has been used to prepare nanosized, high-surface-area Cu-Ce-O, Ni-Ce-O, and Fe-Ce-O catalysts from aqueous solutions of metal acetate precursors. The particles were formed by vaporization of the precursors followed by reaction and then gas to particle conversion. The specific surface areas of the synthesized powders ranged from 127 to 163 m(2)/g. High-resolution transmission electron microscope imaging showed that the particle diameters for the ceria materials are in the range of 3-10 nm, and a thin layer of amorphous material was observed on the surface of the particles. The presence and surface enrichment of the transition-metal oxides (CuO, NiO, and Fe(2)O(3)) on the ceria particles were detected using X-ray photoelectron spectroscopy. Electron energy-loss spectroscopic studies suggest the formation of a core-shell structure in the as-prepared particles. Extended X-ray absorption fine structure studies suggest that the dopants in all M-Ce-O systems are almost isostructural with their oxide counterparts, indicating the doping materials form separate oxide phases (CuO, Fe(2)O(3), NiO) within the host matrix (CeO(2)). Etching results confirm that most of the transition-metal oxides are present on the surface of CeO(2), easily dissolved by nitric acid. The performance of the flame-synthesized catalysts was examined toward water-gas shift (WGS) activity for fuel processing applications. The WGS activity of metal ceria catalysts decreases in the order Cu-Ce-O > Ni-Ce-O > Fe-Ce-O > CeO(2) with a feed mixture having a hydrogen to carbon monoxide (H(2)/CO) ratio of 1. There was no methane formation for these catalysts under the tested conditions. PMID:20356136

  15. Flame Synthesis of Nanosized Cu-Ce-O, Ni-Ce-O, and Fe-Ce-O Catalysts for the Water-Gas Shift (WGS) Reaction

    SciTech Connect

    Pati, R.; Lee, I; Hou, S; Akhuemonkhan, O; Gaskell, K; Wang, Q; Frenkel, A; Chu, D; Salamanca-Riba, L; Ehrman, S

    2009-01-01

    A flame synthesis method has been used to prepare nanosized, high-surface-area Cu-Ce-O, Ni-Ce-O, and Fe-Ce-O catalysts from aqueous solutions of metal acetate precursors. The particles were formed by vaporization of the precursors followed by reaction and then gas to particle conversion. The specific surface areas of the synthesized powders ranged from 127 to 163 m{sup 2}/g. High-resolution transmission electron microscope imaging showed that the particle diameters for the ceria materials are in the range of 3-10 nm, and a thin layer of amorphous material was observed on the surface of the particles. The presence and surface enrichment of the transition-metal oxides (CuO, NiO, and Fe{sub 2}O{sub 3}) on the ceria particles were detected using X-ray photoelectron spectroscopy. Electron energy-loss spectroscopic studies suggest the formation of a core-shell structure in the as-prepared particles. Extended X-ray absorption fine structure studies suggest that the dopants in all M-Ce-O systems are almost isostructural with their oxide counterparts, indicating the doping materials form separate oxide phases (CuO, Fe{sub 2}O{sub 3}, NiO) within the host matrix (CeO{sub 2}). Etching results confirm that most of the transition-metal oxides are present on the surface of CeO{sub 2}, easily dissolved by nitric acid. The performance of the flame-synthesized catalysts was examined toward water-gas shift (WGS) activity for fuel processing applications. The WGS activity of metal ceria catalysts decreases in the order Cu-Ce-O > Ni-Ce-O > Fe-Ce-O > CeO{sub 2} with a feed mixture having a hydrogen to carbon monoxide (H{sub 2}/CO) ratio of 1. There was no methane formation for these catalysts under the tested conditions.

  16. WATER-GAS SHIFT WITH INTEGRATED HYDROGEN SEPARATION

    SciTech Connect

    Maria Flytzani-Stephanopoulos; Jerry Meldon; Xiaomei Qi

    2001-12-01

    Optimization of the water-gas shift (WGS) reaction system for hydrogen production for fuel cells is of particular interest to the energy industry. To this end, it is desirable to couple the WGS reaction to hydrogen separation using a semi-permeable membrane, with both processes carried out at high temperature to improve reaction kinetics. Reduced equilibrium conversion of the WGS reaction at high temperatures is overcome by product H{sub 2} removal via the membrane. This project involves fundamental research and development of novel cerium oxide-based catalysts for the water-gas-shift reaction and the integration of these catalysts with Pd-alloy H{sub 2}-separation membranes supplying high purity hydrogen for fuel cell use. Conditions matching the requirements of coal gasifier-exit gas streams will be examined in the project. In the first year of the project, we prepared a series of nanostructured Cu- and Fe-containing ceria catalysts by a special gelation/precipitation technique followed by air calcination at 650 C. Each sample was characterized by ICP for elemental composition analysis, BET-N2 desorption for surface area measurement, and by temperature-programmed reduction in H{sub 2} to evaluate catalyst reducibility. Screening WGS tests with catalyst powders were conducted in a flow microreactor at temperatures in the range of 200-550 C. On the basis of both activity and stability of catalysts in simulated coal gas, and in CO{sub 2}-rich gases, a Cu-CeO{sub 2} catalyst formulation was selected for further study in this project. Details from the catalyst development and testing work are given in this report. Also in this report, we present H{sub 2} permeation data collected with unsupported flat membranes of pure Pd and Pd-alloys over a wide temperature window.

  17. Water-gas shift activity of Cu surfaces and Cu nanoparticles supported on metal oxides

    Microsoft Academic Search

    J. A. Rodriguez; P. Liu; X. Wang; W. Wen; J. Hanson; J. Hrbek; M. Pérez; J. Evans

    2009-01-01

    Oxide supported Cu catalysts show significant activity for the water-gas shift reaction (WGS, CO+H2O?H2+CO2) but their performance is not fully understood and is highly dependent on the synthesis conditions or the nature of the oxide support. This article describes a series of new studies examining the water-gas shift activity of Cu\\/MgO(100) surfaces and compares it to the activities found for

  18. Catalytic Links Among the Water-Gas shift, Water-Assisted Formic Acid Decomposition, and Methanol Steam Reforming Reactions over Pt PromotedTthoria

    SciTech Connect

    Jacobs,G.; Patterson, P.; Graham, U.; Crawford, A.; Dozier, A.; Davis, B.

    2005-01-01

    Implied in the proposed water-gas shift (WGS) mechanisms for Pt/ceria and Pt/thoria catalysts is the presumption that reduced defect centers are formed on the surface. This X-ray absorption near-edge spectroscopy study provides direct results indicating that Pt facilitates reduction in the surface shell of thoria. Mechanistic arguments from in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) are provided suggesting that the active sites for WGS, water-assisted formic acid decomposition, and methanol steam reforming are associated with oxygen-deficient centers. In all cases, a high H{sub 2}O/reactant (i.e., carbon monoxide, formic acid, or methanol) ratio was used. For WGS, CO reacted with type II bridging OH groups at reduced centers to generate surface formate intermediates, the decomposition of which is suggested to be the rate-limiting step by the observation of a normal kinetic isotope effect (NKIE) associated with the formate coverage as monitored by DRIFTS under steady-state conditions using CO + H{sub 2}O and CO + D{sub 2}O feeds. The same NKIE was observed in steady-state reaction tests. Formic acid dissociated on the surface of thoria to yield the same surface formate species as observed when CO adsorbs. An identical NKIE associated with formate decomposition was observed when switching from a feed containing HCOOH + H{sub 2}O and DCOOH + H{sub 2}O, establishing two important commonalities: (1) similarity in the mechanistic pathway and (2) importance of the role of type II bridging OH groups at reduced centers in the catalysis. Methanol steam reforming likely proceeded through a mechanism involving adsorption at reduced centers to generate type II methoxy species, with subsequent conversion to formate, unidentate carbonate, and finally CO{sub 2}. The higher NKIE when switching between H-labeled and D-labeled feeds suggests that conversion of methoxy species to formate may be the rate-limiting step. The methanol steam reforming reaction was selective to CO{sub 2} at low conversion, but CO selectivity increased at higher conversions, suggesting competition with the secondary reaction of reverse WGS at higher temperature. Pt/thoria was more selective at higher conversion for CO{sub 2} than a similarly loaded Pt/ceria catalyst. These results suggest that from a mechanistic standpoint, the two materials are virtually analogs of one another.

  19. On the mechanism of the reverse water gas shift reaction: Dynamic TAP reactor studies of the oxidizing capability of CO2 on a Au/CeO2 catalyst

    E-print Network

    Pfeifer, Holger

    of the oxidizing capability of CO2 on a Au/CeO2 catalyst L.C. Wang, M. Tahvildar Khazaneh, D. Widmann, and R The mechanism of the Reverse Water Gas Shift (RWGS) reaction on a Au/CeO2 supported catalyst, in particular the role of the redox mechanism, was investigated by exploring the activity of CO2 for Au assisted CeO2

  20. High-Temperature Water-Gas Shift Membrane Reactor Study

    SciTech Connect

    Ciocco, M.V.; Iyoha, O.; Enick, R.M.; Killmeyer, R.P.

    2007-06-01

    NETL’s Office of Research and Development is exploring the integration of membrane reactors into coal gasification plants as a way of increasing efficiency and reducing costs. Water-Gas Shift Reaction experiments were conducted in membrane reactors at conditions similar to those encountered at the outlet of a coal gasifier. The changes in reactant conversion and product selectivity due to the removal of hydrogen via the membrane reactor were quantified. Research was conducted to determine the influence of residence time and H2S on CO conversion in both Pd and Pd80wt%Cu membrane reactors. Effects of the hydrogen sulfide-to-hydrogen ratio on palladium and a palladium-copper alloy at high-temperature were also investigated. These results were compared to thermodynamic calculations for the stability of palladium sulfides.

  1. WATER-GAS SHIFT WITH INTEGRATED HYDROGEN SEPARATION PROCESS

    SciTech Connect

    Maria Flytzani-Stephanopoulos; Xiaomei Qi; Scott Kronewitter

    2004-02-01

    This project involved fundamental research and development of novel cerium oxide-based catalysts for the water-gas-shift reaction and the integration of these catalysts with Pd-alloy H{sub 2} -separation membranes supplying high purity hydrogen for fuel cell use. Conditions matching the requirements of coal gasifier-exit gas streams were examined in the project. Cu-cerium oxide was identified as the most promising high-temperature water-gas shift catalyst for integration with H{sub 2}-selective membranes. Formulations containing iron oxide were found to deactivate in the presence of CO{sub 2}. Cu-containing ceria catalysts, on the other hand, showed high stability in CO{sub 2}-rich gases. This type gas will be present over much of the catalyst, as the membrane removes the hydrogen produced from the shift reaction. The high-temperature shift catalyst composition was optimized by proper selection of dopant type and amount in ceria. The formulation 10at%Cu-Ce(30at%La)O{sub x} showed the best performance, and was selected for further kinetic studies. WGS reaction rates were measured in a simulated coal-gas mixture. The apparent activation energy, measured over aged catalysts, was equal to 70.2 kJ/mol. Reaction orders in CO, H{sub 2}O, CO{sub 2} and H{sub 2} were found to be 0.8, 0.2, -0.3, and -0.3, respectively. This shows that H{sub 2}O has very little effect on the reaction rate, and that both CO{sub 2} and H{sub 2} weakly inhibit the reaction. Good stability of catalyst performance was found in 40-hr long tests. A flat (38 cm{sup 2}) Pd-Cu alloy membrane reactor was used with the catalyst washcoated on oxidized aluminum screens close coupled with the membrane. To achieve higher loadings, catalyst granules were layered on the membrane itself to test the combined HTS activity/ H{sub 2} -separation efficiency of the composite. Simulated coal gas mixtures were used and the effect of membrane on the conversion of CO over the catalyst was evidenced at high space velocities. Equilibrium CO conversion at 400 C was measured at a space velocity of 30,000 h{sup -1} with the 10{micro}m- thick Pd{sub 60}Cu{sub 40} membrane operating under a pressure differential of 100 psi. No carbon deposition took place during operation. The performance of the coupled Cu-ceria catalyst/membrane system at 400 C was stable in {approx} 30 h of continuous operation. The overall conclusion from this project is that Cu-doped ceria catalysts are suitable for use in high-temperature water-gas shift membrane reactors. CO{sub 2}-rich operation does not affect the catalyst activity or stability; neither does it affect hydrogen permeation through the Pd-Cu membrane. Operation in the temperature range of 400-430 C is recommended.

  2. WATER-GAS SHIFT WITH INTEGRATED HYDROGEN SEPARATION PROCESS

    SciTech Connect

    Maria Flytzani-Stephanopoulos, PI; Jerry Meldon, Co-PI; Xiaomei Qi

    2002-12-01

    Optimization of the water-gas shift (WGS) reaction system for hydrogen production for fuel cells is of particular interest to the energy industry. To this end, it is desirable to couple the WGS reaction to hydrogen separation using a semi-permeable membrane, with both processes carried out at high temperatures to improve reaction kinetics and permeation. Reduced equilibrium conversion of the WGS reaction at high temperatures is overcome by product H{sub 2} removal via the membrane. This project involves fundamental research and development of novel cerium oxide-based catalysts for the water-gas-shift reaction and the integration of these catalysts with Pd-alloy H{sub 2}-separation membranes supplying high purity hydrogen for fuel cell use. Conditions matching the requirements of coal gasifier-exit gas streams will be examined in the project. The first-year screening studies of WGS catalysts identified Cu-ceria as the most promising high-temperature shift catalyst for integration with H{sub 2}-selective membranes. Formulations containing iron oxide were found to deactivate in the presence of CO{sub 2}, and were thus eliminated from further consideration. Cu-containing ceria catalysts, on the other hand, showed high stability in CO{sub 2}-rich gases. This type gas will be present over much of the catalyst, as the membrane removes the hydrogen produced from the shift reaction. Several catalyst formulations were prepared, characterized and tested in the first year of study. Details from the catalyst development and testing work were given in our first annual technical report. Hydrogen permeation through Pd and Pd-alloy foils was investigated in a small membrane reactor constructed during the first year of the project. The effect of temperature on the hydrogen flux through pure Pd, Pd{sub 60}Cu{sub 40} and Pd{sub 75}Ag{sub 25} alloy membranes, each 25 {micro}m thick, was evaluated in the temperature range from 250 C to 500 C at upstream pressure of 4.4 atm and permeate hydrogen pressure of 1 atm. Flux decay was observed for the Pd-Cu membrane above 500 C. From 350-450 C, an average hydrogen flux value of 0.2 mol H{sub 2}/m{sup 2}/s was measured over this Pd-alloy membrane. These results are in good agreement with literature data. In this year's report, we discuss reaction rate measurements, optimization of catalyst kinetics by proper choice of dopant oxide (lanthana) in ceria, long-term stability studies, and H{sub 2} permeation data collected with unsupported flat, 10 {micro}m-thick Pd-Cu membranes over a wide temperature window and in various gas mixtures. The high-temperature shift catalyst composition was further improved, by proper selection of dopant type and amount. The formulation 10 at%Cu-Ce(30 at%La)Ox was the best; this was selected for further kinetic studies. WGS reaction rates were measured in a simulated coal-gas mixture. The stability of catalyst performance was examined in 40-hr long tests. A series of hydrogen permeation tests were conducted in a small flat-membrane reactor using the 10 m{micro}-thick Pd-Cu membranes. Small inhibitory effects of CO and CO{sub 2} were found at temperatures above 350 C, while H{sub 2}O vapor had no effect on hydrogen permeation. No carbon deposition took place during many hours of membrane operation. The reaction extent on the blank (catalyst-free) membrane was also negligible. A larger flat-membrane reactor will be used next year with the catalyst wash coated on screens close coupled with the Pd-Cu membrane.

  3. In Situ Studies of the Active Sites for the Water Gas Shift Reaction over Cu?CeO 2 Catalysts:  Complex Interaction between Metallic Copper and Oxygen Vacancies of Ceria

    Microsoft Academic Search

    Xianqin Wang; Jonathan C. Hanson; Daniel Gamarra; Arturo Martinez-Arias; Marcos Fernandez-Garcia

    2006-01-01

    New information about the active sites for the water gas shift (WGS) reaction over Cu-CeO2 systems was obtained using in-situ, time-resolved X-ray diffraction (TR-XRD), X-ray absorption spectroscopy (TR-XAS, Cu K and Ce L3 edges), and infrared spectroscopy (DRIFTS). Cu-CeO2 nanoparticles prepared by a novel reversed microemulsion method (doped Ce1-xCuxO2 sample) and an impregnation method (impregnated CuOx\\/ CeO2 sample) were studied.

  4. In situ time-resolved characterization of Au-CeO2 and AuOx-CeO2 catalysts during the water-gas shift reaction: Presence of Au and O vacancies in the active phase

    Microsoft Academic Search

    X. Wang; J. A. Rodriguez; J. C. Hanson; M. Pérez; J. Evans

    2005-01-01

    Synchrotron-based in situ time-resolved x-ray diffraction and x-ray absorption spectroscopies were used to study the behavior of nanostructured {Au+AuOx}-CeO2 catalysts under the water-gas shift (WGS) reaction. At temperatures above 250 °C, a complete AuOx-->Au transformation was observed with high catalytic activity. Photoemission results for the oxidation and reduction of Au nanoparticles supported on rough ceria films or a CeO2(111) single

  5. In situ time-resolved characterization of Au–CeO2 and AuOx–CeO2 catalysts during the water-gas shift reaction: Presence of Au and O vacancies in the active phase

    Microsoft Academic Search

    X. Wang; J. A. Rodriguez; J. C. Hanson; M. Pe´rez; J. Evans

    2005-01-01

    Synchrotron-based in situ time-resolved x-ray diffraction and x-ray absorption spectroscopies were used to study the behavior of nanostructured {Au+AuOx}–CeO2 catalysts under the water-gas shift (WGS) reaction. At temperatures above 250 °C, a complete AuOx?Au transformation was observed with high catalytic activity. Photoemission results for the oxidation and reduction of Au nanoparticles supported on rough ceria films or a CeO2(111) single

  6. WATER-GAS SHIFT KINETICS OVER IRON OXIDE CATALYSTS AT MEMBRANE REACTOR CONDITIONS

    Microsoft Academic Search

    Carl R. F. Lund

    2002-01-01

    The kinetics of water-gas shift were studied over ferrochrome catalysts under conditions with high carbon dioxide partial pressures, such as would be expected in a membrane reactor. The catalyst activity is inhibited by increasing carbon dioxide partial pressure. A microkinetic model of the reaction kinetics was developed. The model indicated that catalyst performance could be improved by decreasing the strength

  7. Comparison of the Activity of Au/CeO2 and Au/Fe2O3 Catalysts for the CO Oxidation and the Water-gas Shift Reactions

    SciTech Connect

    Deng,W.; Carpenter, C.; Yi, N.; Flytzani-Stephanopoulos, M.

    2007-01-01

    We compare the activity and relevant gold species of nanostructured gold-cerium oxide and gold-iron oxide catalysts for the CO oxidation by dioxygen and water. Well dispersed gold nanoparticles in reduced form provide the active sites for the CO oxidation reaction on both oxide supports. On the other hand, oxidized gold species, strongly bound on the support catalyze the water-gas shift reaction. Gold species weakly bound to ceria (doped with lanthana) or iron oxide can be removed by sodium cyanide at pH {>=}12. Both parent and leached catalysts were investigated. The activity of the leached gold-iron oxide catalyst in CO oxidation is approximately two orders of magnitude lower than that of the parent material. However, after exposure to H{sub 2} up to 400 C gold diffuses out and is in reduced form on the surface, a process accompanied by a dramatic enhancement of the CO oxidation activity. Similar results were found with the gold-ceria catalysts. On the other hand, pre-reduction of the calcined leached catalyst samples did not promote their water-gas shift activity. UV-Vis, XANES and XPS were used to probe the oxidation state of the catalysts after various treatments.

  8. Active Nonmetallic Au and Pt Species on Ceria-Based Water-Gas Shift Catalysts

    Microsoft Academic Search

    Qi Fu; Howard Saltsburg; Maria Flytzani-Stephanopoulos

    2003-01-01

    Traditional analysis of reactions catalyzed by supported metals involves the structure of the metallic particles. However, we report here that for the class of nanostructured gold- or platinum-cerium oxide catalysts, which are active for the water-gas shift reaction, metal nanoparticles do not participate in the reaction. Nonmetallic gold or platinum species strongly associated with surface cerium-oxygen groups are responsible for

  9. Oxygen-enhanced water gas shift on ceria-supported Pd–Cu and Pt–Cu bimetallic catalysts

    Microsoft Academic Search

    Junichiro Kugai; Jeffrey T. Miller; Neng Guo; Chunshan Song

    2011-01-01

    Aiming at enhancing H2 production in water gas shift (WGS) for fuel cell application, a small amount of oxygen was added to WGS reaction toward oxygen-enhanced water gas shift (OWGS) on ceria-supported bimetallic Pd–Cu and Pt–Cu catalysts. Both CO conversion and H2 yield were found to increase by the oxygen addition. The remarkable enhancement of H2 production by O2 addition

  10. Nature of Ptn/TiO2(110) Interface under Water-Gas Shift Reaction Conditions: A Constrained ab Initio Thermodynamics Study

    SciTech Connect

    Ammal, Salai Cheettu; Heyden, Andreas

    2011-10-06

    The electronic structure of small Ptn (n = 1-8) clusters supported on the stoichiometric and partially reduced rutile TiO2(110) surface have been investigated using density functional theory. Pt atoms prefer to form a close-packed structure with (111) facet near an oxygen vacancy of the TiO2 support and a less dense structure with (100) facet away from oxygen vacant sites. Themain focus of this study is on identifying a realistic catalyst model for the Pt/TiO2 interface under watergas shift (WGS) reaction conditions. Constrained ab initio thermodynamic simulations on the stability of oxygen vacancies and formation of adsorbed gas phase molecules such as oxygen, CO, and hydrogen at the metal/oxide interface reveal that under WGS reaction conditions the formation of surface oxygen vacancies are thermodynamically favorable, platinum oxide species (PtOx) can easily be reduced and should not be present, CO adsorbs only weakly on interfacial Pt atoms, and CO poisoning of these sites should be less important. While hydrogen generally interacts weakly with interfacial Pt atoms, it forms very stable hydride species on Pt atoms neighboring an oxygen vacancy of the TiO2(110) support, possibly negatively affecting the WGS reaction rate.

  11. In Situ Studies of the Active Sites for the Water Gas Shift Reaction over Cu-CeO2 Catalysts: Complex Interaction Between Metallic Copper and Oxygen Vacancies of Ceria

    SciTech Connect

    Wang,X.; Rodriguez, J.; Hanson, J.; Gamarra, D.; Martinez-Arias, A.; Fernandez-Garcia, M.

    2006-01-01

    New information about the active sites for the water gas shift (WGS) reaction over Cu-CeO{sub 2} systems was obtained using in-situ, time-resolved X-ray diffraction (TR-XRD), X-ray absorption spectroscopy (TR-XAS, Cu K and Ce L3 edges), and infrared spectroscopy (DRIFTS). Cu-CeO{sub 2} nanoparticles prepared by a novel reversed microemulsion method (doped Ce1-xCuxO2 sample) and an impregnation method (impregnated CuO{sub x}/CeO{sub 2} sample) were studied. The results from all of the samples indicate that both metallic copper and oxygen vacancies in ceria were involved in the generation of active sites for the WGS reaction. Evidence was found for a synergistic Cu-O vacancy interaction. This interaction enhances the chemical activity of Cu, and the presence of Cu facilitates the formation of O vacancies in ceria under reaction conditions. Water dissociation occurred on the O vacancy sites or the Cu-O vacancy interface. No significant amounts of formate were formed on the catalysts during the WGS reaction. The presence of strongly bound carbonates is an important factor for the deactivation of the catalysts at high temperatures. This work identifies for the first time the active sites for the WGS reaction on Cu-CeO{sub 2} catalysts and illustrates the importance of in situ structural studies for heterogeneous catalytic reactions.

  12. Iron carbonyl catalyzed reductions of model coal constituents under water gas shift conditions

    SciTech Connect

    Lynch, T.J. (Univ. of California, Los Angeles); Banah, M.; Kaesz, H.D.; Porter, C.R.

    1983-01-01

    Reslts of studies aimed at elucidating the reactivity of iron carbonyl under water gas shift (WGS) conditions towards organic substrates that model coal structure are presented. Reactions of methanol, water, and base under CO atmosphere were carried out at 150/sup 0/C to optimize the iron carbonyl catalyzed water gas shift reaction, and nitrogen heterocycles are readily hydrogenated under these conditions. Reactions with the nitrogen heterocycles were studied at a temperature of 300/sup 0/C to parallel the conditions of coal liquefaction. Chelating nitrogen heterocycles were found to activate the Fe(CO)/sub 5/ toward anthracene hydrogenation. The phase transfer catalysts were also found to have a pronounced enhancement effect on all reductions. Iron carbonyl is predicted to have high potential in hydrogenation when activated by the appropriate synergistic agents. A proposed mechanism for the reductions is an initial electron transfer process from HFe(CO)/sub 4//sup -/. (BLM)

  13. WATER-GAS SHIFT KINETICS OVER IRON OXIDE CATALYSTS AT MEMBRANE REACTOR CONDITIONS

    SciTech Connect

    Carl R.F. Lund

    2001-08-10

    This report covers the second year of a project investigating water-gas shift catalysts for use in membrane reactors. It has been established that a simple iron high temperature shift catalyst becomes ineffective in a membrane reactor because the reaction rate is severely inhibited by the build-up of the product CO{sub 2}. During the past year, an improved microkinetic model for water-gas shift over iron oxide was developed. Its principal advantage over prior models is that it displays the correct asymptotic behavior at all temperatures and pressures as the composition approaches equilibrium. This model has been used to explore whether it might be possible to improve the performance of iron high temperature shift catalysts under conditions of high CO{sub 2} partial pressure. The model predicts that weakening the surface oxygen bond strength by less than 5% should lead to higher catalytic activity as well as resistance to rate inhibition at higher CO{sub 2} partial pressures. Two promoted iron high temperature shift catalysts were studied. Ceria and copper were each studied as promoters since there were indications in the literature that they might weaken the surface oxygen bond strength. Ceria was found to be ineffective as a promoter, but preliminary results with copper promoted FeCr high temperature shift catalyst show it to be much more resistant to rate inhibition by high levels of CO{sub 2}. Finally, the performance of sulfided CoMo/Al{sub 2}O{sub 3} catalysts under conditions of high CO{sub 2} partial pressure was simulated using an available microkinetic model for water-gas shift over this catalyst. The model suggests that this catalyst might be quite effective in a medium temperature water-gas shift membrane reactor, provided that the membrane was resistant to the H{sub 2}S that is required in the feed.

  14. FTIR study of the low-temperature water-gas shift reaction on Au/Fe{sub 2}O{sub 3} and Au/TiO{sub 2} catalysts

    SciTech Connect

    Boccuzzi, F.; Chiorino, A.; Manzoli, M.; Andreeva, D.; Tabakova, T.

    1999-11-15

    An FTIR and quadruple mass spectroscopic study of the water-gas shift (WGS), the reverse WGS reactions, and the adsorption of the individual molecules involved has been carried out on Au/Fe{sub 2}O{sub 3} and Au/TiO{sub 2} catalysts. The chemisorptions and the reactions on the two catalysts have been compared with the aim of gaining a better understanding of the role played by the two phases present in these catalysts and of the synergistic interplay between them in gold catalysts tested for a low-temperature water-gas shift reaction. Evidences are reported that H{sub 2} is dissociated already at room temperature on both the catalysts on gold sites, giving rise to hydrogen atoms that can react with adsorbed oxygen atoms or spillover on the supports where they can reduce the support surface sites. It is shown that CO is adsorbed molecularly on different surface sites, on the support cations, on Au{sup 0} sites exposed at the surface of small three-dimensional particles and also on Au{sup {delta}{minus}} sites exposed at the surface of negatively charged clusters. The CO formed in the reverse WGS reaction appears chemisorbed only on the Au{sup 0} sites. The support sites and the Au{sup {delta}{minus}} sites, where the CO appears as more strongly bonded, are present but not accessible to the CO formed by CO{sub 2} reduction, probably because these sites are covered by water. Water and OH groups are adsorbed on the supports, on gold sites, and at the interface between them. The effects of CO coadsorption on water dissociation and of H{sub 2} dissociation on CO{sub 2} reduction have been evidenced. The close similarity of the catalytic activity of the two examined samples indicates that the active sties for hydrogen dissociation and for water-CO reactive interactions are located at the surface of the metallic gold small particles where the reaction can take place by a red-ox regenerative mechanism.

  15. DFT models for active sites on high temperature water-gas shift catalysts

    Microsoft Academic Search

    R. M. Van Natter; J. S. Coleman; C. R. F. Lund

    2008-01-01

    A simple two-step regenerative model for the kinetics of high temperature water-gas shift provided a good fit to published experimental data for a commercial ferrochrome catalyst. The fitting process yielded an enthalpy of localization of oxygen adatoms on the surface equal to ?611kJmol?1, and it predicted that virtually all adsorption sites were covered by oxygen adatoms at reaction conditions. Cluster

  16. Unraveling the Active Site in Copper-ceria Systems for the Water Gas Shift Reaction: In-situ Characterization of an Inverse Powder CeO2-x/CuO-Cu Catalyst

    SciTech Connect

    Rodriguez, J.A.; Barrio, L.; Estrella, M.; Zhou, G.; Wen, W.; Hanson, J.C.; Hungría, A.B.; Hornés, A.; Fernández-García, M.; Arturo Martínez-Arias, A.

    2010-03-04

    An inverse powder system composed of CeO{sub 2} nanoparticles dispersed over a CuO-Cu matrix is proposed as a novel catalyst for the water-gas shift reaction. This inverse CeO{sub 2}/CuO-Cu catalyst exhibits a higher activity than standard Cu/CeO{sub 2} catalysts. In situ synchrotron characterization techniques were employed to follow the structural changes of CeO{sub 2}/CuO-Cu under reaction conditions. Time-resolved X-ray diffraction experiments showed the transformation of CuO to metallic Cu via a Cu{sub 2}O intermediate. Short-order structural changes were followed by pair distribution function analysis and corroborated the results obtained by diffraction. Moreover, X-ray absorption spectroscopy also revealed oxidation state changes from Cu{sup 2+} to Cu{sup 0} and the partial reduction of CeOx nanoparticles. The activity data obtained by mass spectrometry revealed that hydrogen production starts once the copper has been fully reduced. The strong interaction of ceria and copper boosted the catalytic performance of the sample. The inverse catalyst was active at low temperatures, stable to several reaction runs and to redox cycles. These characteristics are highly valuable for mobile fuel cell applications. The active phases of the inverse CeO{sub 2}/CuO-Cu catalyst are partially reduced ceria nanoparticles strongly interacting with metallic copper. The nature and structure of the ceria nanoparticles are of critical importance because they are involved in processes related to water dissociation over the catalyst surface.

  17. Unraveling the Active Site in Copper-Ceria Systems for the Water-Gas Shift Reaction: In Situ Characterization of an Inverse Powder CeO2-x/CuO-Cu Catalyst

    SciTech Connect

    Barrio, L.; Estrella, M; Zhou, G; Wen, W; Hanson, J; Hungria, A; Hornes, A; Fernandez-Garcia, M; Martinez-Arias, A; Rodriguez, J

    2010-01-01

    An inverse powder system composed of CeO{sub 2} nanoparticles dispersed over a CuO-Cu matrix is proposed as a novel catalyst for the water-gas shift reaction. This inverse CeO{sub 2}/CuO-Cu catalyst exhibits a higher activity than standard Cu/CeO{sub 2} catalysts. In situ synchrotron characterization techniques were employed to follow the structural changes of CeO{sub 2}/CuO-Cu under reaction conditions. Time-resolved X-ray diffraction experiments showed the transformation of CuO to metallic Cu via a Cu{sub 2}O intermediate. Short-order structural changes were followed by pair distribution function analysis and corroborated the results obtained by diffraction. Moreover, X-ray absorption spectroscopy also revealed oxidation state changes from Cu{sup 2+} to Cu{sup 0} and the partial reduction of CeO{sub x} nanoparticles. The activity data obtained by mass spectrometry revealed that hydrogen production starts once the copper has been fully reduced. The strong interaction of ceria and copper boosted the catalytic performance of the sample. The inverse catalyst was active at low temperatures, stable to several reaction runs and to redox cycles. These characteristics are highly valuable for mobile fuel cell applications. The active phases of the inverse CeO{sub 2}/CuO-Cu catalyst are partially reduced ceria nanoparticles strongly interacting with metallic copper. The nature and structure of the ceria nanoparticles are of critical importance because they are involved in processes related to water dissociation over the catalyst surface.

  18. Reactivity of iron carbonyl complexes in a hydrated sodium-Y zeolite matrix and catalysis of the resulting hydride anion HFe/sub 3/(CO)/sub 11//sup -/ for water-gas-shift reaction

    SciTech Connect

    Iwamoto, M.; Nakamura, S.; Kusano, H.; Kagawa, S.

    1986-10-09

    Iron carbonyls Fe(CO)/sub 5/, Fe/sub 2/(CO)/sub 9/, and Fe/sub 3/(CO)/sub 12/ have been introduced into a hydrated Na-Y zeolite. Fe(CO)/sub 5/ was only weakly adsorbed on the zeolite. Fe/sub 2/(CO)/sub 9/ and Fe/sub 3/(CO)/sub 12/ were reactive in the hydrated zeolite cages to yield a hydride anion species HFe/sub 3/(CO)/sub 11//sup -/ which was characterized by IR absorption bands at 2044, 1987, 1950, and 1645 cm/sup -1/, UV-vis spectrum at 540 nm, and gas-phase analyses. The red shift of absorption band of the bridging carbonyl indicated ionic interaction of a bridging carbonyl with an Al/sup 3 +/ ion in the zeolite matrix. The formation of the anion species was not observed in a dehydrated Na-Y zeolite, indicating the importance of water or a surface hydroxyl group n the reaction. The reaction course from di- or trinuclear iron carbonyl to the hydride anion has been studied by an ESR technique. Fe/sub 2/(CO)/sub 8//sup -/, Fe(CO)/sub 4//sup -/, and Fe/sub 3/(CO)/sub 11//sup -/ species were detected as intermediates, and reaction schemes have been proposed. The resulting HFe/sub 3/(CO)/sub 11//sup -/ was stable at or below 413 K both in a vacuum or in a CO atmosphere. Above this temperature it was gradually decomposed. Catalytic activity of the HFe/sub 3/(CO)/sub 11//sup -/ species was examined for water-gas-shift reaction at 333-453 K and atmospheric pressure. The activity was very high and comparable to that reported in the homogeneous phase at high pressure. Kinetics and spectroscopic studies indicated that the reaction between HFe/sub 3/(CO)/sub 11//sup -/ and H/sub 2/O would be rate-determining.

  19. Development of an advanced water-gas shift conversion system. Final report

    SciTech Connect

    Sealock, L.J. Jr.; Elliott, D.C.; Butner, R.S.

    1985-04-01

    Pacific Northwest Laboratory has completed initial exploratory research to investigate the chemistry and use of a pressurized aqueous catalyst system for conducting the water-gas shift reaction. The research was done under sponsorship of the USDOE Morgantown Energy Technology Center. A 1.0 liter continuous bench scale reactor system was built and operated to investigate water-gas shift chemistry at high pressure. Details regarding the chemistry of the aqueous, base-catalyzed system in both batch and continuous reactors are presented for a temperature range of 200 to 350/sup 0/C and pressures from 500 to 3000 psig. The catalyst choice is sodium carbonate at a concentration of 6% in water, but any material which can generate hydroxide ions at the process conditions will effectively catalyze the reaction. This report summarizes the results of the bench-scale research on the concept and presents a discussion of optimum operating conditions, pressure effects and limitations, kinetic data, effects of gas flow rates, catalyst type, and preliminary concept evaluation. 16 refs., 29 figs., 8 tabs.

  20. WATER-GAS SHIFT KINETICS OVER IRON OXIDE CATALYSTS AT MEMBRANE REACTOR CONDITIONS

    SciTech Connect

    Carl R.F. Lund

    2002-08-02

    The kinetics of water-gas shift were studied over ferrochrome catalysts under conditions with high carbon dioxide partial pressures, such as would be expected in a membrane reactor. The catalyst activity is inhibited by increasing carbon dioxide partial pressure. A microkinetic model of the reaction kinetics was developed. The model indicated that catalyst performance could be improved by decreasing the strength of surface oxygen bonds. Literature data indicated that adding either ceria or copper to the catalyst as a promoter might impart this desired effect. Ceria-promoted ferrochrome catalysts did not perform any better than unpromoted catalyst at the conditions tested, but copper-promoted ferrochrome catalysts did offer an improvement over the base ferrochrome material. A different class of water-gas shift catalyst, sulfided CoMo/Al{sub 2}O{sub 3} is not affected by carbon dioxide and may be a good alternative to the ferrochrome system, provided other constraints, notably the requisite sulfur level and maximum temperature, are not too limiting. A model was developed for an adiabatic, high-temperature water-gas shift membrane reactor. Simulation results indicate that an excess of steam in the feed (three moles of water per mole of CO) is beneficial even in a membrane reactor as it reduces the rate of adiabatic temperature rise. The simulations also indicate that much greater improvement can be attained by improving the catalyst as opposed to improving the membrane. Further, eliminating the inhibition by carbon dioxide will have a greater impact than will increasing the catalyst activity (assuming inhibition is still operative). Follow-up research into the use of sulfide catalysts with continued kinetic and reactor modeling is suggested.

  1. Water-Gas Shift and Methane Reactivity on Reducible Perovskite-Type Oxides

    PubMed Central

    2015-01-01

    Comparative (electro)catalytic, structural, and spectroscopic studies in hydrogen electro-oxidation, the (inverse) water-gas shift reaction, and methane conversion on two representative mixed ionic–electronic conducting perovskite-type materials La0.6Sr0.4FeO3?? (LSF) and SrTi0.7Fe0.3O3?? (STF) were performed with the aim of eventually correlating (electro)catalytic activity and associated structural changes and to highlight intrinsic reactivity characteristics as a function of the reduction state. Starting from a strongly prereduced (vacancy-rich) initial state, only (inverse) water-gas shift activity has been observed on both materials beyond ca. 450 °C but no catalytic methane reforming or methane decomposition reactivity up to 600 °C. In contrast, when starting from the fully oxidized state, total methane oxidation to CO2 was observed on both materials. The catalytic performance of both perovskite-type oxides is thus strongly dependent on the degree/depth of reduction, on the associated reactivity of the remaining lattice oxygen, and on the reduction-induced oxygen vacancies. The latter are clearly more reactive toward water on LSF, and this higher reactivity is linked to the superior electrocatalytic performance of LSF in hydrogen oxidation. Combined electron microscopy, X-ray diffraction, and Raman measurements in turn also revealed altered surface and bulk structures and reactivities. PMID:26045733

  2. Iron-ceria Aerogels Doped with Palladium as Water-gas Shift Catalysts for the Production of Hydrogen

    Microsoft Academic Search

    Sumit Bali; Frank E. Huggins; Richard D. Ernst; Ronald J. Pugmire; Gerald P. Huffman; Edward M. Eyring

    2010-01-01

    Mixed 4.5% iron oxide-95.5% cerium oxide aerogels doped with 1% and 2% palladium (Pd) by weight have been synthesized, and their activities for the catalysis of water-gas shift (WGS) reaction have been determined. The aerogels were synthesized using propylene oxide as the proton scavenger for the initiation of hydrolysis and polycondensation of a homogeneous alcoholic solution of cerium(III) chloride heptahydrate

  3. Single-stage temperature-controllable water gas shift reactor with catalytic nickel plates

    NASA Astrophysics Data System (ADS)

    Park, Jin-Woo; Lee, Sung-Wook; Lee, Chun-Boo; Park, Jong-Soo; Lee, Dong-Wook; Kim, Sung-Hyun; Kim, Sung-Soo; Ryi, Shin-Kun

    2014-02-01

    In this study, a microstructured reactor with catalytic nickel plates is newly designed and developed for proper heat management in an exothermic water gas shift WGS reaction. The reactor is designed to increase the reactor capacity simply by numbering-up a set of a catalyst layers and heat exchanger layers. The WGS reactor is built up with two sets of a catalyst layers and heat exchanger layers. The performance of the reactor is verified by WGS testing with the variation of the furnace temperatures, gas hourly space velocity (GHSV) and coolant (N2) flow rate. At a GHSV of 10,000 h-1, CO conversion reaches the equilibrium value with a CH4 selectivity of ?0.5% at the furnace temperature of ?375 °C. At high GHSV (40,000 h-1), CO conversion decreases considerably because of the heat from the exothermic WGS reaction at a large reactants mass. By increasing the coolant flow rate, the heat from the WGS reaction is properly managed, leading an increase of the CO conversion to the equilibrium value at GHSV of 40,000 h-1.

  4. CERIA-BASED WATER-GAS-SHIFT CATALYSTS S. Swartz, A-M. Azad, M. Seabaugh

    E-print Network

    Azad, Abdul-Majeed

    CERIA-BASED WATER-GAS-SHIFT CATALYSTS S. Swartz, A-M. Azad, M. Seabaugh NexTech Materials, Ltd catalysts based on ceria-supported precious metals. Our work has demonstrated that Pt/ceria catalysts offer annealing; and (5) availability of conventional washcoating technologies for supporting ceria

  5. A Cu/Pt Near-Surface Alloy for Water-Gas Shift Catalysis.

    SciTech Connect

    Knudsen, Jan; Nilekar, Anand U.; Vang, Ronnie T.; Schnadt, Joachim; Kunkes, Edward L.; Dumesic, James A.; Mavrikakis, Manos; Besenbacher, Fleming

    2007-05-01

    The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. The primary route to hydrogen production from fossil fuels involves the water-gas shift (WGS) reaction, and an improvement in the efficiency of WGS catalysts could therefore lead to a major leap forward in the realization of hydrogen economy. On the basis of a combination of high-resolution scanning tunneling microscopy, X-ray photoelectron spectroscopy, and density functional theory (DFT) calculations, we suggest the existence of a new thermodynamically stable Cu/Pt near-surface alloy (NSA). Temperature-programmed desorption and DFT reveal that this Cu/Pt NSA binds CO significantly more weakly than does Pt alone, thereby implying a considerable reduction in the potential for CO poisoning of the Cu/Pt NSA surface as compared to that of pure Pt. In addition, DFT calculations show that this Cu/Pt NSA is able to activate H2O easily, which is the rate-determining step for the WGS on several metal surfaces, and, at the same time, to bind the products of that reaction and formate intermediates rather weakly, thus avoiding possible poisoning of the catalyst surface. The Cu/Pt NSA is thus a promising candidate for an improved WGS catalyst.

  6. Metal/ceria water-gas shift catalysts for automotive polymer electrolyte fuel cell system.

    SciTech Connect

    Myers, D. J.; Krebs, J. F.; Carter, J. D.; Kumar, R.; Krumpelt, M.

    2002-01-11

    Polymer electrolyte fuel cell (PEFC) systems are a leading candidate for replacing the internal combustion engine in light duty vehicles. One method of generating the hydrogen necessary for the PEFC is reforming a liquid fuel, such as methanol or gasoline, via partial oxidation, steam reforming, or autothermal reforming (a combination of partial oxidation and steam reforming). The H{sub 2}-rich reformate can contain as much as 10% carbon monoxide. Carbon monoxide has been shown to poison the platinum-based anode catalyst at concentrations as low as 10 ppm,1 necessitating removal of CO to this level before passing the reformate to the fuel cell stack. The water-gas shift (WGS) reaction, CO + H{sub 2}O {rightleftharpoons} CO{sub 2} + H{sub 2}, is used to convert the bulk of the reformate CO to CO{sub 2}. Industrially, the WGS reaction is conducted over two catalysts, which operate in different temperature regimes. One catalyst is a FeCr mixed oxide, which operates at 350-450 C and is termed the high-temperature shift (HTS) catalyst. The second catalyst is a CuZn mixed oxide, which operates at 200-250 C and is termed the low-temperature shift (LTS) catalyst. Although these two catalysts are used industrially in the production of H{sub 2} for ammonia synthesis, they have major drawbacks that make them unsuitable for transportation applications. Both the LTS and the HTS catalysts must first be ''activated'' before being used. For example, the copper in the copper oxide/zinc oxide LTS catalyst must first be reduced to elemental copper in situ before it becomes active for the WGS reaction. This reduction reaction is exothermic and must be carried out under well- controlled conditions using a dilute hydrogen stream (1 vol% H{sub 2}) to prevent high catalyst temperatures, which can result in sintering (agglomeration) of the copper particles and loss of active surface area for the WGS reaction. Also, once the catalyst has been activated by reduction, it must be protected from exposure to ambient air to prevent re-oxidation of the copper. The activated catalyst must also be protected from the condensation of liquids, for example, during start-up or transient operation. For these reasons, a more thermally rugged catalyst is needed which has sufficient activity to operate at the low temperatures that are thermodynamically necessary to achieve low CO concentrations.

  7. Au-mixed lanthanum/cerium oxide catalysts for water-gas-shift

    SciTech Connect

    Wang, Yanan; Liang, Shuang; Cao, Anmin; Thompson, Robert L; Veser, Goetz

    2010-08-01

    We report on the synthesis of highly homogeneous mixed La/Ce-oxides via a microemulsion-templated approach, and their evaluation as active supports for Au in the water gas shift (WGS) reaction. Both structure and reducibility of the oxides could be tailored by adjusting the La content across the entire range of La:Ce-ratios. The reducibility of the Au-free oxides shows an optimum at ?25% La content, which can be traced back to improved oxygen mobility due to formation of oxygen vacancies and to the formation of more strongly bound oxygen upon La addition. Deposition of Au onto these oxides gives rise to an additional, low-temperature reduction peak, presumably due to hydrogen spill-over from the noble metal onto the oxide support. The WGS activity of Au/La{sub x}Ce{sub 1?x}O{sub 2?0.5x} catalysts correlates closely with the reducibility of the oxide supports, and hence with La content, demonstrating that carefully controlled synthesis of nanostructured catalysts with uniform, tailored composition allows for fine control of reactive properties of these materials, and might ultimately open the way towards a more rational design of catalysts.

  8. DFT and in situ EXAFS investigation of gold/ceria-zirconia low-temperature water gas shift catalysts: identification of the nature of the active form of gold.

    PubMed

    Tibiletti, D; Fonseca, A Amieiro; Burch, R; Chen, Y; Fisher, J M; Goguet, A; Hardacre, C; Hu, P; Thompsett, D

    2005-12-01

    A combined experimental and theoretical investigation of the nature of the active form of gold in oxide-supported gold catalysts for the water gas shift reaction has been performed. In situ extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) experiments have shown that in the fresh catalysts the gold is in the form of highly dispersed gold ions. However, under water gas shift reaction conditions, even at temperatures as low as 100 degrees C, the evidence from EXAFS and XANES is only consistent with rapid, and essentially complete, reduction of the gold to form metallic clusters containing about 50 atoms. The presence of Au-Ce distances in the EXAFS spectra, and the fact that about 15% of the gold atoms can be reoxidized after exposure to air at 150 degrees C, is indicative of a close interaction between a fraction (ca. 15%) of the gold atoms and the oxide support. Density functional theory (DFT) calculations are entirely consistent with this model and suggest that an important aspect of the active and stable form of gold under water gas shift reaction conditions is the location of a partially oxidized gold (Audelta+) species at a cerium cation vacancy in the surface of the oxide support. It is found that even with a low loading gold catalysts (0.2%) the fraction of ionic gold under water gas shift conditions is below the limit of detection by XANES (<5%). It is concluded that under water gas shift reaction conditions the active form of gold comprises small metallic gold clusters in intimate contact with the oxide support. PMID:16853937

  9. Water-Gas Shift Activity of Cu Surfaces and Cu Nanoparticles Supported on Metal Oxides

    SciTech Connect

    Rodriguez, J.; Liu, P; Wang, X; Wen, W; Hanson, J; Hrbek, J; Perez, M; Evans, J

    2009-01-01

    Oxide supported Cu catalysts show significant activity for the water-gas shift reaction (WGS, CO + H{sub 2}O {yields} H{sub 2} + CO{sub 2}) but their performance is not fully understood and is highly dependent on the synthesis conditions or the nature of the oxide support. This article describes a series of new studies examining the water-gas shift activity of Cu/MgO(1 0 0) surfaces and compares it to the activities found for pure copper systems, Cu nanoparticles in contact with well-defined surfaces of TiO{sub 2}, ZnO, MoO{sub 2} and CeO{sub 2}, and Cu cations present in mixed-metal oxides. Catalytic tests performed over CuFe{sub 2}O{sub 4}, Ce{sub 1-x}Cu{sub x}O{sub 2} or CuMoO{sub 4} show significant WGS activity only when the Cu cations in the mixed-metal oxide are reduced to metallic copper. Thus, Cu nanoparticles were deposited on different oxide surfaces and their WGS activity was measured in a batch reactor (P{sub CO} = 20 Torr; P{sub H{sub 2}O} = 10 Torr; T = 575-650 K). The WGS activity of the Cu nanoparticles supported on MgO(1 0 0) was 2-3 times larger than that of Cu(1 0 0). Even better WGS catalysts were obtained when Cu was deposited on CeO{sub 2}(1 1 1) or TiO{sub 2}(1 1 0). An apparent activation energy of 13.8 kcal/mol was found for the WGS on Cu/MgO(1 0 0). This is smaller than the value of 15.2 kcal/mol observed on Cu(1 0 0), and substantially larger than the values of 7-9 kcal/mol seen for the apparent activation energies of the Cu/CeO2(1 1 1) and Cu/TiO2(1 1 0) catalysts. Post-reaction surface characterization pointed to the lack of O vacancies in the Cu/MgO(1 0 0) catalysts. This is in contrast to results found for Cu/CeO{sub 2}(1 1 1) and Cu/TiO{sub 2}(1 1 0), where the oxide support exhibits a significant concentration of O vacancies as a consequence of the WGS reaction. The oxygen vacancies present in Cu/CeO{sub 2}(1 1 1) and Cu/TiO{sub 2}(1 1 0) help in the dissociation of the water molecule and reduce the apparent activation energy for the WGS process. Such a phenomenon cannot occur on the Cu/MgO(0 0 1) catalysts, and the main steps of the WGS probably take place on the Cu nanoparticles.

  10. Integrated Water Gas Shift Membrane Reactors Utilizing Novel, Non Precious Metal Mixed Matrix Membrane

    SciTech Connect

    Ferraris, John

    2013-09-30

    Nanoparticles of zeolitic imidazolate frameworks and other related hybrid materials were prepared by modifying published synthesis procedures by introducing bases, changing stoichiometric ratios, or adjusting reaction conditions. These materials were stable at temperatures >300 °C and were compatible with the polymer matrices used to prepare mixed- matrix membranes (MMMs). MMMs tested at 300 °C exhibited a >30 fold increase in permeability, compared to those measured at 35 °C, while maintaining H{sub 2}/CO{sub 2} selectivity. Measurements at high pressure (up to 30 atm) and high temperature (up to 300 °C) resulted in an increase in gas flux across the membrane with retention of selectivity. No variations in permeability were observed at high pressures at either 35 or 300 °C. CO{sub 2}-induced plasticization was not observed for Matrimid®, VTEC, and PBI polymers or their MMMs at 30 atm and 300 °C. Membrane surface modification by cross-linking with ethanol diamine resulted in an increase in H{sub 2}/CO{sub 2} selectivity at 35 °C. Spectrometric analysis showed that the cross-linking was effective to temperatures <150 °C. At higher temperatures, the cross-linked membranes exhibit a H{sub 2}/CO{sub 2} selectivity similar to the uncross-linked polymer. Performance of the polybenzimidazole (PBI) hollow fibers prepared at Santa Fe Science and Technology (SFST, Inc.) showed increased flux o to a flat PBI membrane. A water-gas shift reactor has been built and currently being optimized for testing under DOE conditions.

  11. Iron-ceria Aerogels Doped with Palladium as Water-gas Shift Catalysts for the Production of Hydrogen

    SciTech Connect

    Bali, S.; Huggins, F; Ernst, R; Pugmire, R; Huffman, G; Eyring, E

    2010-01-01

    Mixed 4.5% iron oxide-95.5% cerium oxide aerogels doped with 1% and 2% palladium (Pd) by weight have been synthesized, and their activities for the catalysis of water-gas shift (WGS) reaction have been determined. The aerogels were synthesized using propylene oxide as the proton scavenger for the initiation of hydrolysis and polycondensation of a homogeneous alcoholic solution of cerium(III) chloride heptahydrate and iron(III) chloride hexahydrate precursor. Palladium was doped onto some of these materials by gas-phase incorporation (GPI) using ({eta}{sup 3}-allyl)({eta}{sup 5}-cyclopentadienyl)palladium as the volatile Pd precursor. Water-gas shift catalytic activities were evaluated in a six-channel fixed-bed reactor at atmospheric pressure and reaction temperatures ranging from 150 to 350 C. Both 1% and 2% Pd-doped 4.5% iron oxide-95.5% cerium oxide aerogels showed WGS activities that increased significantly from 150 to 350 C. The activities of 1% Pd-doped 4.5% iron oxide-95.5% cerium oxide aerogels were also compared with that of the 1% Pd-doped ceria aerogel without iron. The WGS activity of 1% Pd on 4.5% iron oxide-95.5% cerium oxide aerogels is substantially higher (5 times) than the activity of 1% Pd-doped ceria aerogel without iron. The gas-phase incorporation results in a better Pd dispersion. Ceria aerogel provides a nonrigid structure wherein iron is not significantly incorporated inside the matrix, thereby resulting in better contact between the Fe and Pd and thus enhancing the WGS activity. Further, neither Fe nor Pd is reduced during the ceria-aerogel-catalyzed WGS reaction. This behavior contrasts with that noted for other Fe-based WGS catalysts, in which the original ferric oxide is typically reduced to a nonstoichiometric magnetite form.

  12. Slurry phase Fischer-Tropsch synthesis: Cobalt plus a water-gas shift catalyst

    SciTech Connect

    Yates, I.C.; Satterfield, C.N.

    1988-01-01

    A cobalt Fischer-Tropsch catalyst (CO/MgO/silica) was reduced and slurried in combination with reduced Cu/ZnO/Al[sub 2]0[sub 3] water-gas-shift catalyst. Combined catalyst system was run at fixed process conditions for more than 400 hours. The system showed stable selectivity. The Cu/ZnO/Al[sub 2]0[sub 3] water-gas-shift catalyst remained reasonably active in the presence of the cobalt catalyst. Hydrocarbon selectivity of the cobalt and Cu/ZnO/Al[sub 2]0[sub 3] catalyst system compared favorably to selectivity of iron-based catalysts. Methane selectivity was slightly higher for the cobalt-based system, but C[sub 5][sup +] selectivity was essentially the same. The hydrocarbon product distribution appeared to exhibit a double-a behavior. a[sub 1] was near 0.80 which is higher than that of iron catalysts, while a[sub 2] was calculated to be 0.86 which is somewhat lower than would be typical for an iron-based catalyst.

  13. An innovative catalyst system for slurry-phase Fischer-Tropsch synthesis: Cobalt plus a water-gas-shift catalyst

    SciTech Connect

    Satterfield, C.N.; Yates, I.C.; Chanenchuk, C.

    1991-07-01

    The feasibility of using a mechanical mixture of a Co/MgO/SiO{sub 2} Fischer-Tropsch catalyst and a Cu-ZnO/Al{sub 2}O{sub 3} water-gas-shift (WGS) catalyst for hydrocarbon synthesis in a slurry reactor has been established. Such a mixture can combine the superior product distribution from cobalt with the high activity for the WGS reaction characteristic of iron. Weight ratios of Co/MgO/SiO{sub 2} to Cu-ZnO/Al{sub 2}O{sub 3} of 0.27 and 0.51 for the two catalysts were studied at 240{degrees}C, 0.79 MPa, and in situ H{sub 2}/CO ratios between 0.8 and 3.0. Each catalyst mixture showed stable Fischer-Tropsch activity for about 400 hours-on-stream at a level comparable to the cobalt catalyst operating alone. The Cu-ZnO/Al{sub 2}O{sub 3} catalyst exhibited a very slow loss of activity under these conditions, but when operated alone it was stable in a slurry reactor at 200--220{degrees}C, 0.79--1.48 MPa, and H{sub 2}/CO in situ ratios between 1.0 and 2.0. The presence of the water-gas-shift catalyst did not affect the long-term stability of the primary Fischer-Tropsch selectivity, but did increase the extent of secondary reactions, such as l-alkene hydrogenation and isomerization.

  14. Slurry phase Fischer-Tropsch synthesis: Cobalt plus a water-gas shift catalyst

    SciTech Connect

    Yates, I.C.; Satterfield, C.N.

    1988-01-01

    This report details experiments performed on three different copper-based catalysts: Cu/Cr[sub 2]O[sub 3], Cu/MnO/Cr[sub 2]O[sub 3] and Cu/ZnO/Al[sub 2]O[sub 3]. Of these three catalysts, the Cu/ZnO/Al[sub 2]O[sub 3] exhibits the greatest stability when slurried in octacosane. More than 1000 hours-on-stream indicate that the catalyst activity is not detrimentally affected by high pressure, high H[sub 2]/CO ratio, or the presence of alkenes. All of these are necessary stability characteristics for the water-gas shift catalyst, if it is to be used in combination with a cobalt Fischer-Tropsch catalyst. A review of documented reduction procedures for cobalt-based Fischer-Tropsch catalysts is presented.

  15. A Comparative Study of the Water Gas Shift Reaction Over Platinum Catalysts Supported on CeO2, TiO2 and Ce-Modified TiO2

    SciTech Connect

    Gonzalez, I.; Navarro, R; Wen, W; Marinkovic, N; Rodriguez, J; Rosa, F; Fierro, J

    2010-01-01

    WGS reaction has been investigated on catalysts based on platinum supported over CeO{sub 2}, TiO{sub 2} and Ce-modified TiO{sub 2}. XPS and XANES analyses performed on calcined catalysts revealed a close contact between Pt precursors and cerium species on CeO{sub 2} and Ce-modified TiO{sub 2} supports. TPR results corroborate the intimate contact between Pt and cerium entities in the Pt/Ce-TiO{sub 2} catalyst that facilitates the reducibility of the support at low temperatures while the Ce-O-Ti surface interactions established in the Ce-modified TiO{sub 2} support decreases the reduction of TiO{sub 2} at high temperature. The changes in the support reducibility leads to significant differences in the WGS activity of the studied catalysts. Pt supported on Ce-modified TiO{sub 2} support exhibits better activity than those corresponding to individual CeO{sub 2} and TiO{sub 2}-supported catalysts. Additionally, the Ce-TiO{sub 2}-supported catalyst displays better stability at reaction temperatures higher than 573 K that observed on pure TiO{sub 2}-supported counterpart. Activity measurements, when coupled with the physicochemical characterization of catalysts suggest that the modifications in the surface reducibility of the support play an essential role in the enhancement of activity and stability observed when Pt is supported on the Ce-modified TiO{sub 2} substrate.

  16. In-situ Characterization of Water-Gas Shift Catalysts using Time-Resolved X-ray Diffraction

    SciTech Connect

    Rodriguez, J.; Hanson, J; Wen, W; Wang, X; Brito, J; Martnez-Arias, A; Fernandez-Garca, M

    2009-01-01

    Time-resolved X-ray diffraction (XRD) has emerged as a powerful technique for studying the behavior of heterogeneous catalysts (metal oxides, sulfides, carbides, phosphides, zeolites, etc.) in-situ during reaction conditions. The technique can identify the active phase of a heterogeneous catalyst and how its structure changes after interacting with the reactants and products (80 K < T < 1200 K; P < 50 atm). In this article, we review a series of recent works that use in-situ time-resolved XRD for studying the water-gas shift reaction (WGS, CO + H2O ? H2 + CO2) over several mixed-metal oxides: CuMoO4, NiMoO4, Ce1-xCuxO2-d and CuFe2O4. Under reaction conditions the oxides undergo partial reduction. Neutral Cu0 (i.e. no Cu1+ or Cu2+ cations) and Ni0 are the active species in the catalysts, but interactions with the oxide support are necessary in order to obtain high catalytic activity. These studies illustrate the important role played by O vacancies in the mechanism for the WGS. In the case of Ce1-xCuxO2-d, Rietveld refinement shows expansions/contractions in the oxide lattice which track steps within the WGS process: CO(gas) + O(oxi) ? CO2(gas) + O(vac); H2O(gas) + O(vac) ? O(oxi) + H2(gas).

  17. Design of water gas shift catalysts for hydrogen production in fuel processors

    NASA Astrophysics Data System (ADS)

    Opalka, S. M.; Vanderspurt, T. H.; Radhakrishnan, R.; She, Y.; Willigan, R. R.

    2008-02-01

    Low sulfur hydrocarbon fuels can be converted to fuel cell grade H2 using a compact fuel processor architecture. The necessary high volumetric activity water gas shift (WGS) Pt on ceria-zirconia catalysts reacts CO-rich reformate with steam to yield H2 and CO2. Such highly selective, non-pyrophoric noble metal/Ce[1-(x+y)]ZrxDpyO2 catalysts were developed through coordinated atomic modeling, syntheses, structural characterization, kinetic performance tests, and micro-kinetic analyses. Density functional simulations made with the VASP code suggested that the undoped catalyst WGS activity would be limited by the strong binding of CO intermediates, blocking the reoxidation of the reduced oxide by water. These predictions were confirmed by in situ cylindrical internal reflection-Fourier transform infrared spectroscopy and by micro-kinetic analyses of the micro-reactor results. Atomic simulations were used to evaluate the impact transition metal dopants had on the surface chemistry of cubic ceria-zirconia. VASP predicted that acidic transition metal dopants such as Nb, Mo, Ta, and W would increase the oxide surface affinity for water and thus increase the turnover rate of the catalyst. The efficacy of Mo-doped ceria-zirconia compositions was confirmed at lower temperatures in replicated catalyst synthesis-reactor studies.

  18. Design of water gas shift catalysts for hydrogen production in fuel processors.

    PubMed

    Opalka, S M; Vanderspurt, T H; Radhakrishnan, R; She, Y; Willigan, R R

    2008-02-13

    Low sulfur hydrocarbon fuels can be converted to fuel cell grade H(2) using a compact fuel processor architecture. The necessary high volumetric activity water gas shift (WGS) Pt on ceria-zirconia catalysts reacts CO-rich reformate with steam to yield H(2) and CO(2). Such highly selective, non-pyrophoric noble metal/Ce([1-(x+y)])Zr(x)Dp(y)O(2) catalysts were developed through coordinated atomic modeling, syntheses, structural characterization, kinetic performance tests, and micro-kinetic analyses. Density functional simulations made with the VASP code suggested that the undoped catalyst WGS activity would be limited by the strong binding of CO intermediates, blocking the reoxidation of the reduced oxide by water. These predictions were confirmed by in situ cylindrical internal reflection-Fourier transform infrared spectroscopy and by micro-kinetic analyses of the micro-reactor results. Atomic simulations were used to evaluate the impact transition metal dopants had on the surface chemistry of cubic ceria-zirconia. VASP predicted that acidic transition metal dopants such as Nb, Mo, Ta, and W would increase the oxide surface affinity for water and thus increase the turnover rate of the catalyst. The efficacy of Mo-doped ceria-zirconia compositions was confirmed at lower temperatures in replicated catalyst synthesis-reactor studies. PMID:21693898

  19. Kinetics of oxygen-enhanced water gas shift on bimetallic catalysts and the roles of metals and support

    NASA Astrophysics Data System (ADS)

    Kugai, Junichiro

    The post-processing of reformate is an important step in producing hydrogen (H2) with low carbon monoxide (CO) for low temperature fuel cells from syn-gas. However, the conventional process consists of three steps, i.e. two steps of water gas shift (WGS) and preferential oxidation (PROX) of CO, and it is not suitable for mobile applications due to the large volume of water gas shift (WGS) catalysts and conditioning and/or regeneration necessary for these catalysts. Aiming at replacing those three steps by a simple one-step process, small amount of oxygen was added to WGS (the reaction called oxygen-enhanced water gas shift or OWGS) to promote the reaction kinetics and low pyrophoric ceria-supported bimetallic catalysts were employed for stable performance in this reaction. Not only CO conversion, but also H2 yield was found to increase by the O2 addition on CeO2-supported catalysts. The characteristics of OWGS, high H2 production rate at 200 to 300°C at short contact time where unreacted O2 exists, evidenced the impact of O2 addition on surface species on the catalyst. Around 1.5 of reaction order in CO for various CeO2-supported metal catalysts for OWGS compared to reaction orders in CO ranging from -0.1 to 0.6 depending on metal species for WGS shows O2 addition decreases CO coverage to free up the active sites for co-reactant (H2O) adsorption and activation. Among the monometallic and bimetallic catalysts, Pt-Cu and Pd-Cu bimetallic catalysts were superior to monometallic catalysts in OWGS. These bimetallic components were found to form alloys where noble metal is surrounded mainly by Cu to have strong interaction between noble metal and copper resulting in high OWGS activity and low pyrophoric property. The metal loadings were optimized for CeO2-supported Pd-Cu bimetallic system and 2 wt% Pd with 5 -- 10 wt% Cu were found to be the optimum for the present OWGS condition. In the kinetic study, Pd in Pd-Cu was shown to increase the active sites for H2O dissociation and/or the subsequent reaction with chemisorbed CO as well as Pd keeps Cu in reduced state. Cu was found to keep Pd dispersed, suppress H2 activation on Pd, and facilitate CO 2 desorption from catalyst surface. While composition and structure of metal have large impacts on OWGS performance, CeO2 was shown to create new sites for H2O activation at metal-ceria interfacial region in concert with metal. These new sites strongly activate H2O to drive OWGS and WGS compared to the pure metallic sites which are present in majority on Al2O3-supported catalyst. The observed two regimes of turnover rate, the one dependent on catalyst surface area and the other independent of surface area, strongly suggested bifunctional reaction pathway where the reaction rate is determined by activation of H2O and by association of chemisorbed CO and H 2O. The associative route was also evidenced by pulse response study where the reaction occurs only when CO and H2O pulses are supplied together, and thus pre-adsorbed species such as formate and carbonate identified by FT-IR are proven to be spectators. No correlation between WGS rate and isotopic exchange rate of molecularly adsorbed D2O with H 2 showed H2O dissociation is necessary for WGS to occur. Long duration tests revealed CeO2-supported Pd-Cu, Pt-Cu and Cu catalysts are stable in OWGS condition compared to Pt, Pd, and Al 2O3-supported Pd-Cu catalysts which exhibited continuous deactivation during about 70 hours of test. The addition of Cu prevents agglomeration of monometallic Pd and carbonate formation on monometallic Pt during the reaction. The better activity and stability of Pd-Cu and Pt-Cu bimetallic catalysts in the realistic OWGS condition were ascribed to the unique active sites consisting of highly dispersed Pd in Cu or Pt in Cu on CeO2, which are good for H2O activation with low reaction inhibition by the product gases. Pt monometallic catalyst showed and highest activity in OWGS in the absence of product gases, but this was found vulnerable in the presence of product gases due to strong adsorption of H2 and CO2 on t

  20. Microstructured reactors for diesel steam reforming, water-gas shift and preferential oxidation in the kiloWatt power range

    Microsoft Academic Search

    Gunther Kolb; Christian Hofmann; Martin O’Connell; Jochen Schürer

    2009-01-01

    The paper reports from development and testing of three microstructured reactors of the kW scale, namely an oxidative diesel steam reformer, a water-gas shift reactor and a preferential oxidation reactor as first prototypes of a future fuel processor system. The reformer (cubic shape, edge length 80mm) had a co-current flow arrangement. While oxidative diesel steam reforming was performed in one

  1. Parametric Gasification of Oak and Pine Feedstocks Using the TCPDU and Slipstream Water-Gas Shift Catalysis

    SciTech Connect

    Hrdlicka, J.; Feik, C.; Carpenter, D.; Pomeroy, M.

    2008-12-01

    With oak and pine feedstocks, the Gasification of Biomass to Hydrogen project maximizes hydrogen production using the Full Stream Reformer during water-gas shift fixed-bed reactor testing. Results indicate that higher steam-to-biomass ratio and higher thermal cracker temperature yield higher hydrogen concentration. NREL's techno-economic models and analyses indicate hydrogen production from biomass may be viable at an estimated cost of $1.77/kg (current) and $1.47/kg (advanced in 2015). To verify these estimates, NREL used the Thermochemical Process Development Unit (TCPDU), an integrated system of unit operations that investigates biomass thermochemical conversion to gaseous and liquid fuels and chemicals.

  2. Ethanol synthesis and water gas shift over bifunctional sulfide catalysts. Final technical progress report, September 12, 1991--December 11, 1994

    SciTech Connect

    Klier, K.; Herman, R.G.; Deemer, M.; Richards-Babb, M.; Carr, T.

    1995-07-01

    The objective of this research was to investigate sulfur-resistant catalysts for the conversion of synthesis gas having H{sub 2}/CO {le} 1 into C{sub 1}--C{sub 4} alcohols, especially ethanol, by a highly selective and efficient pathway, while also promoting the water gas shift reaction (WGSR). The catalysts chosen are bifunctional, base-hydrogenation, sulfur-tolerant transition metal sulfides with heavy alkali, e.g. Cs{sup +}, promoter dispersed on their surfaces. The modes of activation of H{sub 2} and CO on MoS{sub 2} and alkali-doped MoS{sub 2} were considered, and computational analyses of the thermodynamic stability of transition metal sulfides and of the electronic structure of these sulfide catalysts were carried out. In the preparation of the cesium-promoted MoS{sub 2} catalysts, a variety of preparation methods using CsOOCH were examined. In all cases, doping with CsOOCH led to a lost of surface area. The undoped molybdenum disulfide catalyst only produced hydrocarbons. Cs-doped MoS{sub 2} catalysts all produced linear alcohols, along with smaller amounts of hydrocarbons. With a 20 wt% CsOOCH/MoS{sub 2} catalyst, temperature, pressure, and flow rate dependences of the synthesis reactions were investigated in the presence and absence of H{sub 2}S in the H{sub 2}/CO = 1/1 synthesis gas during short term testing experiments. It was shown that with a carefully prepared 10 wt% CsOOCH/MoS{sub 2} catalyst, reproducible and high alcohol synthesis activity could be obtained. For example, at 295 C with H{sub 2}/CO = 1 synthesis gas at 8.3 MPa and with GHSV = 7,760 l/kg cat/hr, the total alcohol space time yield was ca 300 g/kg cat/hr (accompanied with a hydrocarbon space time yield of ca 60 g/kg cat/hr). Over a testing period of ca 130 hr, no net deactivation of the catalyst was observed. 90 refs., 82 figs., 14 tabs.

  3. An innovative catalyst system for slurry-phase Fischer-Tropsch synthesis: Cobalt plus a water-gas-shift catalyst. Final technical report

    SciTech Connect

    Satterfield, C.N.; Yates, I.C.; Chanenchuk, C.

    1991-07-01

    The feasibility of using a mechanical mixture of a Co/MgO/SiO{sub 2} Fischer-Tropsch catalyst and a Cu-ZnO/Al{sub 2}O{sub 3} water-gas-shift (WGS) catalyst for hydrocarbon synthesis in a slurry reactor has been established. Such a mixture can combine the superior product distribution from cobalt with the high activity for the WGS reaction characteristic of iron. Weight ratios of Co/MgO/SiO{sub 2} to Cu-ZnO/Al{sub 2}O{sub 3} of 0.27 and 0.51 for the two catalysts were studied at 240{degrees}C, 0.79 MPa, and in situ H{sub 2}/CO ratios between 0.8 and 3.0. Each catalyst mixture showed stable Fischer-Tropsch activity for about 400 hours-on-stream at a level comparable to the cobalt catalyst operating alone. The Cu-ZnO/Al{sub 2}O{sub 3} catalyst exhibited a very slow loss of activity under these conditions, but when operated alone it was stable in a slurry reactor at 200--220{degrees}C, 0.79--1.48 MPa, and H{sub 2}/CO in situ ratios between 1.0 and 2.0. The presence of the water-gas-shift catalyst did not affect the long-term stability of the primary Fischer-Tropsch selectivity, but did increase the extent of secondary reactions, such as l-alkene hydrogenation and isomerization.

  4. Transition metal carbides, nitrides and borides, and their oxygen containing analogs useful as water gas shift catalysts

    DOEpatents

    Thompson, Levi T.; Patt, Jeremy; Moon, Dong Ju; Phillips, Cory

    2003-09-23

    Mono- and bimetallic transition metal carbides, nitrides and borides, and their oxygen containing analogs (e.g. oxycarbides) for use as water gas shift catalysts are described. In a preferred embodiment, the catalysts have the general formula of M1.sub.A M2.sub.B Z.sub.C O.sub.D, wherein M1 is selected from the group consisting of Mo, W, and combinations thereof; M2 is selected from the group consisting of Fe, Ni, Cu, Co, and combinations thereof; Z is selected from the group consisting of carbon, nitrogen, boron, and combinations thereof; A is an integer; B is 0 or an integer greater than 0; C is an integer; O is oxygen; and D is 0 or an integer greater than 0. The catalysts exhibit good reactivity, stability, and sulfur tolerance, as compared to conventional water shift gas catalysts. These catalysts hold promise for use in conjunction with proton exchange membrane fuel cell powered systems.

  5. Iron alloy Fischer-Tropsch catalysts. III. Conversion dependence of selectivity and water-gas shift

    Microsoft Academic Search

    J. A. Amelse; L. H. Schwartz; J. B. Butt

    1981-01-01

    The performance of several silica-supported iron bimetallic and potassium-promoted iron catalysts has been investigated for the conversion of carbon monoxide to hydrocarbons. The systems studied were Fe-Ni, Fe-Co, Fe-Cu, Fe-K, and the pure metals of Fe, Ni, and Co. Alloy formation and catalyst carburization were characterized using Moessbauer effect spectroscopy. Specific reaction rates, measured in a differential flow reactor at

  6. Do Ni/Cu and Cu/Ni alloys have different catalytic performances towards water-gas shift? A density functional theory investigation.

    PubMed

    Huang, Yu Cheng; Zhou, Tao; Liu, Hai; Ling, ChongYi; Wang, SuFan; Du, Jin Yan

    2014-08-25

    Density functional calculations were preformed to investigate whether adding Ni into a Cu surface (denoted as Cu/Ni) or adding Cu into a Ni surface (Ni/Cu) is more efficient for catalyzing the water-gas shift (WGS)? The reactions of water dissociation and monoxide dissociation were selected to assess the activity and selectivity towards WGS, respectively. Our results show that Ni-atom modification of surfaces is thermodynamically favorable for both reactions. Kinetically, compared with pure Cu, water dissociation is greatly facilitated on Ni-modified surfaces, and the activity is insensitive to the Ni concentration; however, monoxide dissociation is not well-promoted on one Ni-atom-modified surfaces, but two Ni-atom modification can notably decrease the dissociation barriers. Overall, on the basis of these results, we conclude that 1) the catalytic performance of bimetallic metals is superior to monometallic ones; 2) at the same Ni concentration on the surface, Cu/Ni and Ni/Cu alloys have almost the same performance towards WGS; and 3) to acquire high WGS performance, the surface Ni atoms should either be low in concentration or highly dispersed. PMID:25044560

  7. Role of metal components in Pd–Cu bimetallic catalysts supported on CeO 2 for the oxygen-enhanced water gas shift

    Microsoft Academic Search

    Junichiro Kugai; Jeffrey T. Miller; Neng Guo; Chunshan Song

    2011-01-01

    Catalytic hydrogen production and CO removal in a post-reforming process are critical for low-temperature fuel cell applications. The present study aims at clarifying the role of metal components in bimetallic catalysts for oxygen-enhanced water gas shift (OWGS), wherein a small amount of O2 is added to H2-rich reformate gas to enhance CO shift. Among CeO2-supported bimetallic catalysts, Pd–Cu and Pt–Cu

  8. Kinetic and spectroscopic study of catalysts for water-gas shift and nitrogen oxide removal

    NASA Astrophysics Data System (ADS)

    Kispersky, Vincent Frederick

    Nitrogen oxides (NOx) are formed in high temperature combustion processes such as in power generation and motor vehicles. Increasingly stringent regulation of these harmful emissions continues to drive interest in developing, understanding and studying new catalytic formulations for exhaust aftertreatment. For mobile sources, predominantly heavy duty diesel engines, selective catalytic reduction (SCR) with NH3 has become the principal means of NO x abatement. An alternative technology developed, but now surpassed by SCR, is NOx Storage Reduction (NSR) catalysis. Both technologies have been studied in our laboratory and are the basis for this dissertation. We studied seven different lean NOx trap (LNT) monolith formulations for NSR ranging from 0.6 to 6.2 wt.% Pt and 4 to 20 wt.% Ba loadings on ?-Al 2O3. The noble metal component of a LNT oxidizes NO to NO 2 aiding in the storage of NO2 on the alkaline earth component. Before the storage component saturates, a reductant such as H2 is introduced into the vehicular exhaust and the stored NOx is released and reduced to N2. Once the storage component is free of NOx, reductant flow is ceased and storage is begun anew. Our research focused on understanding the effects that CO2 and H2O have on the storage capacity of the LNT over short as well as extended periods of time. We found that for high Ba loadings, CO 2 had a consistently detrimental effect on the fast NOx storage capacity (NSC), defined as the amount of NOx the catalyst can store before 1% of the inlet NOx is measured in the reactor outlet. Over long NOx storage periods, CO2 continued to inhibit storage compared to the same catalyst in CO2 free conditions. On low loadings of Ba, however, the inhibition of CO2 was significantly reduced. We found that the loading dependent characteristics of the Ba phase affected the way in which CO2 adsorbed on the storage component, which greatly affected the stability of the species on lower Ba loadings. The less stable adsorbed CO2 proved less competitive for NOx sorption sites, explaining the weak reduction of NSC by CO2 on low Ba loadings. Contrary to CO2, H2O exhibited both beneficial and inhibitory effects on the NSC. Over long periods of time, and at high Ba loadings, the addition of H2O in the feed increased the NSC, attributed to enhanced O2 spillover on the hydroxylated Ba surface allowing greater access to available NOx storage sites. When the Ba loading was reduced, the interaction sphere of Pt particles with the Ba storage component required for O2 to spillover to assist in NOx storage was reduced. Thus, despite the enhanced spillover capacity of oxygen on the hydroxylated storage component other NSC decreasing effects of H2O addition, such as Ba agglomeration, became more dominant and reduced the NSC. Recent developments in selective catalytic reduction have shown Cu and Fe/chabazite (CHA) based zeolites to be particularly well suited to sustaining high catalytic rates without degradation in the harsh environment of diesel engine exhaust. Little has been published about these catalysts as the academic community has just recently learned about the materials and their commercial implementation. Using operando X-ray absorption spectroscopy, combined with first-principles thermodynamics simulations and kinetic analysis, we have studied the nature of the Cu active site on Cu/SSZ-13, Cu/SAPO-34 and Cu/ZSM-5. Examining the catalysts under operando standard SCR conditions (300 ppm NO, 300 ppm NH3, 5% O2, 5% H2O and 5% CO2) showed the catalyst to be in a mixed Cu(I)-Cu(II) oxidation state. Neither the amount of Cu(I) nor Cu(II) individually correlated with the different rates measured on the various zeolite catalysts, and so we proposed that the SCR reaction progresses via a redox mechanism requiring both Cu(I) and Cu(II). First principles thermodynamic calculations found that the redox couple of Cu(I)H2O and Cu(II)(OH)2 were the most thermodynamically stable species of any of the OxHy variants modeled on Cu. The redox nature of the Cu active site was further investigated in a fo

  9. Redox cycle stability of mixed oxides used for hydrogen generation in the cyclic water gas shift process

    SciTech Connect

    Datta, Pradyot, E-mail: pradyot.datta@gmail.com

    2013-10-15

    Graphical abstract: - Highlights: • Fe{sub 2}O{sub 3} modified with CaO, SiO{sub 2} and Al{sub 2}O{sub 3} was studied in cyclic water gas shift reactor. • For the first time stability of such oxides were tested for 100 redox cycles. • Optimally added oxides significantly improved the activity and the stability of Fe{sub 2}O{sub 3}. • Increased stability was attributed to the impediment of neck formation. - Abstract: Repeated cycles of the reduction of Fe{sub 3}O{sub 4} with reductive gas, e.g. hydrogen and subsequent oxidation of the reduced iron material with water vapor can be harnessed as a process for the production of pure hydrogen. The redox behavior of iron oxide modified with various amounts of SiO{sub 2}, CaO and Al{sub 2}O{sub 3} was investigated in the present study. The total amount of the additional metal oxides was always below 15 wt%. The samples were prepared by co-precipitation using urea hydrolysis method. The influence of various metal oxides on the hydrogen production capacity and the material stability was studied in detail in terms of temperature-programmed reduction (TPR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and BET analysis. Furthermore, the activity and the stability of the samples were tested in repeated reduction with diluted H{sub 2} and re-oxidation cycles with H{sub 2}O. The results indicate that combination of several oxides as promoter increases the stability of the iron oxide material by mitigating the sintering process. The positive influence of the oxides in stabilizing the iron oxide material is attributed to the impediment of neck formation responsible for sintering.

  10. In-situ Characterization of CuFe2O4 and Cu/Fe3O4 Water-Gas Shift Catalysts

    SciTech Connect

    Rodriguez,J.A.; Estrella, M.; Barrio, L.; Zhou, G.; Wang, X.; Wang, Q.; Wen, W.; Hanson, J.C.; Frenkel, A.

    2009-08-13

    Mixtures of copper and iron oxides are used as industrial catalysts for the water-gas shift (WGS, CO + H2O ? H2 + CO2). In-situ time-resolved X-ray diffraction, X-ray absorption fine structure, and atomic pair distribution function analysis were used to study the reduction of CuFe2O4 with CO and the behavior of CuFe2O4 and Cu/Fe2O3 catalysts under WGS reaction conditions. Metal?oxygen?metal interactions enhance the stability of Cu2+ and Fe3+ in the CuFe2O4 lattice, and the mixed-metal oxide is much more difficult to reduce than CuO or Fe2O3. Furthermore, after heating mixtures of CuFe2O4/CuO in the presence of CO or CO/H2O, the cations of CuO migrate into octahedral sites of the CuFe2O4 lattice at temperatures (200-250 oC) in which CuO is not stable. Above 250 oC, copper leaves the oxide, the occupancy of the octahedral sites in CuFe2O4 decreases, and diffraction lines for metallic Cu appear. From 350 to 450 oC, there is a massive reduction of CuFe2O4 with the formation of metallic Cu and Fe3O4. At this point, the sample becomes catalytically active for the production of H2 from the reaction of H2O with CO. Neutral Cu0 (i.e. no Cu+1 or Cu+2 cations) is the active species in the catalysts, but interactions with the oxide support are necessary in order to obtain high catalytic activity. These studies illustrate the importance of in-situ characterization when dealing with mixed-metal oxide WGS catalysts.

  11. In Situ Characterization of CuFe2O4 and Cu/Fe3O4 Water-Gas Shift Catalysts

    SciTech Connect

    Estrella, M.; Barrio, L; Zhou, G; Wang, X; Wang, Q; Wen, W; Hanson, J; Frenkel, A; Rodriguez, J

    2009-01-01

    Mixtures of copper and iron oxides are used as industrial catalysts for the water-gas shift (WGS, CO + H2O f H2 + CO2). In-situ time-resolved X-ray diffraction, X-ray absorption fine structure, and atomic pair distribution function analysis were used to study the reduction of CuFe2O4 with CO and the behavior of CuFe2O4 and Cu/Fe2O3 catalysts under WGS reaction conditions. MetalToxygenTmetal interactions enhance the stability of Cu 2+ and Fe 3+ in the CuFe2O4 lattice, and the mixed-metal oxide is much more difficult to reduce than CuO or Fe2O3. Furthermore, after heating mixtures of CuFe2O4/CuO in the presence of CO or CO/H2O, the cations of CuO migrate into octahedral sites of the CuFe2O4 lattice at temperatures (200-250 C) in which CuO is not stable. Above 250 C, copper leaves the oxide, the occupancy of the octahedral sites in CuFe2O4 decreases, and diffraction lines for metallic Cu appear. From 350 to 450 C, there is a massive reduction of CuFe2O4 with the formation of metallic Cu and Fe3O4. At this point, the sample becomes catalytically active for the production of H2 from the reaction of H2O with CO. Neutral Cu 0 (i.e., no Cu 1+ or Cu 2+ cations) is the active species in the catalysts, but interactions with the oxide support cannot be neglected. These studies illustrate the importance of in situ characterization when dealing with mixed-metal oxide WGS catalysts.

  12. Magnetic susceptibility as a direct measure of oxidation state in LiFePO4 batteries and cyclic water gas shift reactors.

    PubMed

    Kadyk, Thomas; Eikerling, Michael

    2015-07-22

    The possibility of correlating the magnetic susceptibility to the oxidation state of the porous active mass in a chemical or electrochemical reactor was analyzed. The magnetic permeability was calculated using a hierarchical model of the reactor. This model was applied to two practical examples: LiFePO4 batteries, in which the oxidation state corresponds with the state-of-charge, and cyclic water gas shift reactors, in which the oxidation state corresponds to the depletion of the catalyst. In LiFePO4 batteries phase separation of the lithiated and delithiated phases in the LiFePO4 particles in the positive electrode gives rise to a hysteresis effect, i.e. the magnetic permeability depends on the history of the electrode. During fast charge or discharge, non-uniform lithium distributionin the electrode decreases the hysteresis effect. However, the overall sensitivity of the magnetic response to the state-of-charge lies in the range of 0.03%, which makes practical measurement challenging. In cyclic water gas shift reactors, the sensitivity is 4 orders of magnitude higher and without phase separation, no hysteresis occurs. This shows that the method is suitable for such reactors, in which large changes of the magnetic permeability of the active material occurs. PMID:26156571

  13. Slurry phase Fischer-Tropsch synthesis: Cobalt plus a water-gas shift catalyst. [Quarterly] report, October 1, 1988--December 31, 1988

    SciTech Connect

    Yates, I.C.; Satterfield, C.N.

    1988-12-31

    A cobalt Fischer-Tropsch catalyst (CO/MgO/silica) was reduced and slurried in combination with reduced Cu/ZnO/Al{sub 2}0{sub 3} water-gas-shift catalyst. Combined catalyst system was run at fixed process conditions for more than 400 hours. The system showed stable selectivity. The Cu/ZnO/Al{sub 2}0{sub 3} water-gas-shift catalyst remained reasonably active in the presence of the cobalt catalyst. Hydrocarbon selectivity of the cobalt and Cu/ZnO/Al{sub 2}0{sub 3} catalyst system compared favorably to selectivity of iron-based catalysts. Methane selectivity was slightly higher for the cobalt-based system, but C{sub 5}{sup +} selectivity was essentially the same. The hydrocarbon product distribution appeared to exhibit a double-a behavior. a{sub 1} was near 0.80 which is higher than that of iron catalysts, while a{sub 2} was calculated to be 0.86 which is somewhat lower than would be typical for an iron-based catalyst.

  14. Slurry phase Fischer-Tropsch synthesis: Cobalt plus a water-gas shift catalyst. [Quarterly] report, June 30, 1988--September 30, 1988

    SciTech Connect

    Yates, I.C.; Satterfield, C.N.

    1988-12-31

    This report details experiments performed on three different copper-based catalysts: Cu/Cr{sub 2}O{sub 3}, Cu/MnO/Cr{sub 2}O{sub 3} and Cu/ZnO/Al{sub 2}O{sub 3}. Of these three catalysts, the Cu/ZnO/Al{sub 2}O{sub 3} exhibits the greatest stability when slurried in octacosane. More than 1000 hours-on-stream indicate that the catalyst activity is not detrimentally affected by high pressure, high H{sub 2}/CO ratio, or the presence of alkenes. All of these are necessary stability characteristics for the water-gas shift catalyst, if it is to be used in combination with a cobalt Fischer-Tropsch catalyst. A review of documented reduction procedures for cobalt-based Fischer-Tropsch catalysts is presented.

  15. Comparative studies of low-temperature watergas shift reaction over Pt=CeO2, Au=CeO2,

    E-print Network

    Gulari, Erdogan

    Comparative studies of low-temperature water­gas shift reaction over Pt=CeO2, Au=CeO2, and Au=Fe2O3 the Pt=CeO2, Au=CeO2 and Au=Fe2O3 catalysts. The activity of these catalysts was tested concentrations have significant effects on the catalytic activity. The 1% Pt=CeO2 was substantially more active

  16. Impact of Contaminants Present in Coal-Biomass Derived Synthesis Gas on Water-gas Shift and Fischer-Tropsch Synthesis Catalysts

    SciTech Connect

    Gokhan Alptekin

    2012-09-30

    Co-gasification of biomass and coal in large-scale, Integrated Gasification Combined Cycle (IGCC) plants increases the efficiency and reduces the environmental impact of making synthesis gas ("syngas") that can be used in Coal-Biomass-to-Liquids (CBTL) processes for producing transportation fuels. However, the water-gas shift (WGS) and Fischer-Tropsch synthesis (FTS) catalysts used in these processes may be poisoned by multiple contaminants found in coal-biomass derived syngas; sulfur species, trace toxic metals, halides, nitrogen species, the vapors of alkali metals and their salts (e.g., KCl and NaCl), ammonia, and phosphorous. Thus, it is essential to develop a fundamental understanding of poisoning/inhibition mechanisms before investing in the development of any costly mitigation technologies. We therefore investigated the impact of potential contaminants (H{sub 2}S, NH{sub 3}, HCN, AsH{sub 3}, PH{sub 3}, HCl, NaCl, KCl, AS{sub 3}, NH{sub 4}NO{sub 3}, NH{sub 4}OH, KNO{sub 3}, HBr, HF, and HNO{sub 3}) on the performance and lifetime of commercially available and generic (prepared in-house) WGS and FT catalysts; ferrochrome-based high-temperature WGS catalyst (HT-WGS, Shiftmax 120�, Süd-Chemie), low-temperature Cu/ZnO-based WGS catalyst (LT-WGS, Shiftmax 230�, Süd-Chemie), and iron- and cobalt-based Fischer-Trospch synthesis catalysts (Fe-FT & Co-FT, UK-CAER). In this project, TDA Research, Inc. collaborated with a team at the University of Kentucky Center for Applied Energy Research (UK-CAER) led by Dr. Burt Davis. We first conducted a detailed thermodynamic analysis. The three primary mechanisms whereby the contaminants may deactivate the catalyst are condensation, deposition, and reaction. AsH{sub 3}, PH{sub 3}, H{sub 2}S, HCl, NH{sub 3} and HCN were found to have a major impact on the Fe-FT catalyst by producing reaction products, while NaCl, KCl and PH{sub 3} produce trace amounts of deposition products. The impact of the contaminants on the activity, selectivity, and deactivation rates (lifetime) of the catalysts was determined in bench-scale tests. Most of the contaminants appeared to adsorb onto (or react with) the HT- and LT-WGS catalysts were they were co-fed with the syngas: � 4.5 ppmv AsH{sub 3} or 1 ppmv PH{sub 3} in the syngas impacted the selectivity and CO conversion of both catalysts; � H{sub 2}S slowly degraded both WGS catalysts; - A binary mixture of H{sub 2}S (60 ppmv) and NH{sub 3} (38 ppmv) impacted the activity of the LT-WGS catalyst, but not the HT-WGS catalyst � Moderate levels of NH{sub 3} (100 ppmv) or HCN (10 ppmv) had no impact � NaCl or KCl had essentially no effect on the HT-WGS catalyst, but the activity of the LT-WGS catalyst decreased very slowly Long-term experiments on the Co-FT catalyst at 260 and 270 °C showed that all of the contaminants impacted it to some extent with the exception of NaCl and HF. Irrespective of its source (e.g., NH{sub 3}, KNO{sub 3}, or HNO{sub 3}), ammonia suppressed the activity of the Co-FT catalyst to a moderate degree. There was essentially no impact the Fe-FT catalyst when up to 100 ppmw halide compounds (NaCl and KCl), or up to 40 ppmw alkali bicarbonates (NaHCO{sub 3} and KHCO{sub 3}). After testing, BET analysis showed that the surface areas, and pore volumes and diameters of both WGS catalysts decreased during both single and binary H2S and NH3 tests, which was attributed to sintering and pore filling by the impurities. The HT-WGS catalyst was evaluated with XRD after testing in syngas that contained 1 ppmv PH{sub 3}, or 2 ppmv H{sub 2}S, or both H{sub 2}S (60 ppmv) and NH{sub 3} (38 ppmv). The peaks became sharper during testing, which was indicative of crystal growth and sintering, but no new phases were detected. After LT-WGS tests (3-33 ppmv NH{sub 3} and/or 0-88 ppmv H{sub 2}S) there were a few new phases that appeared, including sulfides. The fresh Fe-FT catalyst was nanocrystalline and amorphous. ICP-AA spectroscopy and other methods (e.g., chromatography) were used to analyze for

  17. Role of metal components in Pd?Cu bimetallic catalysts supported on CeO2 for the oxygen-enhanced water gas shift

    SciTech Connect

    Kugai, J.; Miller, J. T.; Guo, N.; Song, C. (Chemical Sciences and Engineering Division); ( PSC-USR); (Penn State Univ.)

    2011-06-01

    Catalytic hydrogen production and CO removal in a post-reforming process are critical for low-temperature fuel cell applications. The present study aims at clarifying the role of metal components in bimetallic catalysts for oxygen-enhanced water gas shift (OWGS), wherein a small amount of O{sub 2} is added to H{sub 2}-rich reformate gas to enhance CO shift. Among CeO{sub 2}-supported bimetallic catalysts, Pd-Cu and Pt-Cu combinations were found to show strong synergetic promoting effect in OWGS, which leads to much higher CO conversion and higher H{sub 2} yield than WGS at low temperature around 250 C. Temperature programmed reduction (TPR) showed strong interaction between Pd and Cu in Pd-Cu/CeO{sub 2} by a single reduction peak in contrast to multiple peaks on monometallic Cu/CeO{sub 2}. Extended X-ray absorption fine structure (EXAFS) analysis revealed that such bimetallic Pd-Cu and Pt-Cu form alloy nanoparticles, where noble metal is mainly surrounded by Cu atoms. Oxygen storage capacity (OSC) measurements point to higher resistance of Pd-Cu to oxidation indicating that Pd keeps Cu in reduced state in air pulse condition. From kinetic study, Pd in Pd-Cu was found to promote CO shift, rather than CO oxidation by increasing the number of active sites and by suppressing H{sub 2} activation (that is inherent to monometallic Pd), which minimizes both the inhibition effect of H{sub 2} and the loss of H{sub 2} by oxidation in OWGS. Transient response technique revealed that Cu in Pd-Cu enhances desorption of strongly chemisorbed CO{sub 2} on catalyst surface in contrast to very slow CO{sub 2} desorption from surface of monometallic Pd. Thus, the excellent OWGS activity of Pd-Cu catalyst has been attributed to the complementary roles of the two metals for enhancing CO shift, which is realized by its alloy structure and the accompanying strong interaction between metal components.

  18. Radiation reaction and radiative frequency shifts

    Microsoft Academic Search

    Jay R. Ackerhalt; Peter L. Knight; J. H. Eberly

    1973-01-01

    The question of quantum-electrodynamic radiative corrections to atomic ; transition frequencies is investigated. It is shown that the Heisenberg ; equations of motion allow a novel and fruitful exploitation of the concept of ; radiation reaction. (auth);

  19. Red Shift from Gravitational Back Reaction

    E-print Network

    Ernst Fischer

    2007-03-30

    Deviations from geodesic motion caused by gravitational radiation have been discussed in the last decades to describe the motion of particles or photons in strong fields around collapsed objects. On cosmological scale this effect, which in the first order is caused by the finite speed of gravitational interaction, is important also in the weak field limit. In this paper the energy loss by transfer to the gravitational potential is determined in a quasi-Newtonian approximation for the examples of a static Einstein universe and for an expanding universe with flat metric. In both cases the resulting red shift is a considerable fraction of the total red shift and requires an adjustment of the age and the matter composition in our models of the universe.

  20. Gold, copper, and platinum nanoparticles dispersed on CeO(x)/TiO(2)(110) surfaces: high water-gas shift activity and the nature of the mixed-metal oxide at the nanometer level.

    PubMed

    Park, Joon B; Graciani, Jesus; Evans, Jaime; Stacchiola, Dario; Senanayake, Sanjaya D; Barrio, Laura; Liu, Ping; Fdez Sanz, Javier; Hrbek, Jan; Rodriguez, José A

    2010-01-13

    At small coverages of ceria on TiO(2)(110), the CeO(x) nanoparticles have an unusual coordination mode. Scanning tunneling microscopy and density-functional calculations point to the presence of Ce(2)O(3) dimers, which form diagonal arrays that have specific orientations of 0, 24, and 42 degrees with respect to the [1 -1 0] direction of the titania substrate. At high coverages of ceria on TiO(2)(110), the surface exhibits two types of terraces. In one type, the morphology is not very different from that observed at low ceria coverage. However, in the second type of terrace, there is a compact array of ceria particles with structures that do not match the structures of CeO(2)(111) or CeO(2)(110). The titania substrate imposes on the ceria nanoparticles nontypical coordination modes, enhancing their chemical reactivity. This phenomenon leads to a larger dispersion of supported metal nanoparticles (M = Au, Cu, Pt) and makes possible the direct participation of the oxide in catalytic reactions. The M/CeO(x)/TiO(2)(110) surfaces display an extremely high catalytic activity for the water-gas shift reaction that follows the sequence Au/CeO(x)/TiO(2)(110) < Cu/CeO(x)/TiO(2)(110) < Pt/CeO(x)/TiO(2)(110). For low coverages of Cu and CeO(x), Cu/CeO(x)/TiO(2)(110) is 8-12 times more active than Cu(111) or Cu/ZnO industrial catalysts. In the M/CeO(x)/TiO(2)(110) systems, there is a strong coupling of the chemical properties of the admetal and the mixed-metal oxide: The adsorption and dissociation of water probably take place on the oxide, CO adsorbs on the admetal nanoparticles, and all subsequent reaction steps occur at the oxide-admetal interface. The high catalytic activity of the M/CeO(x)/TiO(2)(110) surfaces reflects the unique properties of the mixed-metal oxide at the nanometer level. PMID:19994897

  1. Gold, Copper and Platinum Nanoparticles Dispersed on CeOx/TiO2(110) Surfaces: High Water-Gas Shift Activity and the Nature of the Mixed-Metal Oxide at the Nanometer Level

    SciTech Connect

    Rodriguez, J.A.; Park, J.B.; Graciani, J.; Evans, J.; Stacchiola, D.; Senanayake, S.D.; Barrio, L.; Liu, P.; Sanz, J.F.; Hrbek, J.

    2010-01-13

    At small coverages of ceria on TiO{sub 2}(110), the CeO{sub x} nanoparticles have an unusual coordination mode. Scanning tunneling microscopy and density-functional calculations point to the presence of Ce{sub 2}O{sub 3} dimers, which form diagonal arrays that have specific orientations of 0, 24, and 42{sup o} with respect to the [1 -1 0] direction of the titania substrate. At high coverages of ceria on TiO{sub 2}(110), the surface exhibits two types of terraces. In one type, the morphology is not very different from that observed at low ceria coverage. However, in the second type of terrace, there is a compact array of ceria particles with structures that do not match the structures of CeO{sub 2}(111) or CeO{sub 2}(110). The titania substrate imposes on the ceria nanoparticles nontypical coordination modes, enhancing their chemical reactivity. This phenomenon leads to a larger dispersion of supported metal nanoparticles (M = Au, Cu, Pt) and makes possible the direct participation of the oxide in catalytic reactions. The M/CeO{sub x}/TiO{sub 2}(110) surfaces display an extremely high catalytic activity for the water-gas shift reaction that follows the sequence Au/CeO{sub x}/TiO{sub 2}(110) < Cu/CeO{sub x}/TiO{sub 2}(110) < Pt/CeO{sub x}/TiO{sub 2}(110). For low coverages of Cu and CeO{sub x}, Cu/CeO{sub x}/TiO{sub 2}(110) is 8-12 times more active than Cu(111) or Cu/ZnO industrial catalysts. In the M/CeO{sub x}/TiO{sub 2}(110) systems, there is a strong coupling of the chemical properties of the admetal and the mixed-metal oxide: The adsorption and dissociation of water probably take place on the oxide, CO adsorbs on the admetal nanoparticles, and all subsequent reaction steps occur at the oxide-admetal interface. The high catalytic activity of the M/CeO{sub x}/TiO{sub 2}(110) surfaces reflects the unique properties of the mixed-metal oxide at the nanometer level.

  2. Gold, Copper, and Platinum Nanoparticles Dispersed on CeOx/TiO2(110) Surfaces: High Water-Gas Shift Activity and the Nature of the Mixed-Metal Oxide at the Nanometer Level

    SciTech Connect

    Park, J.; Graciani, J; Evans, J; Stacchiola, D; Senanayake, S; Barrio, L; Liu, P; Fdez. Sanz, J; Hrbek, J; Rodriguez, J

    2010-01-01

    At small coverages of ceria on TiO{sub 2}(110), the CeO{sub x} nanoparticles have an unusual coordination mode. Scanning tunneling microscopy and density-functional calculations point to the presence of Ce{sub 2}O{sub 3} dimers, which form diagonal arrays that have specific orientations of 0, 24, and 42{sup o} with respect to the [1 -1 0] direction of the titania substrate. At high coverages of ceria on TiO{sub 2}(110), the surface exhibits two types of terraces. In one type, the morphology is not very different from that observed at low ceria coverage. However, in the second type of terrace, there is a compact array of ceria particles with structures that do not match the structures of CeO{sub 2}(111) or CeO{sub 2}(110). The titania substrate imposes on the ceria nanoparticles nontypical coordination modes, enhancing their chemical reactivity. This phenomenon leads to a larger dispersion of supported metal nanoparticles (M = Au, Cu, Pt) and makes possible the direct participation of the oxide in catalytic reactions. The M/CeO{sub x}/TiO{sub 2}(110) surfaces display an extremely high catalytic activity for the water-gas shift reaction that follows the sequence Au/CeO{sub x}/TiO{sub 2}(110) < Cu/CeO{sub x}/TiO{sub 2}(110) < Pt/CeO{sub x}/TiO{sub 2}(110). For low coverages of Cu and CeO{sub x}, Cu/CeO{sub x}/TiO{sub 2}(110) is 8-12 times more active than Cu(111) or Cu/ZnO industrial catalysts. In the M/CeO{sub x}/TiO{sub 2}(110) systems, there is a strong coupling of the chemical properties of the admetal and the mixed-metal oxide: The adsorption and dissociation of water probably take place on the oxide, CO adsorbs on the admetal nanoparticles, and all subsequent reaction steps occur at the oxide-admetal interface. The high catalytic activity of the M/CeO{sub x}/TiO{sub 2}(110) surfaces reflects the unique properties of the mixed-metal oxide at the nanometer level.

  3. Water gas furnace

    SciTech Connect

    Gallaro, C.

    1985-12-03

    A water gas furnace comprising an outer container to provide a housing in which coke is placed into its lower part. A water container is placed within the housing. The coke is ignited and heats the water in the container converting it into steam. The steam is ejected into the coke, which together with air, produces water gas. Preferably, pumice stones are placed above the coke. The water gas is accepted into the pores of the pumice stones, where the heated pumice stones ignite the water gas, producing heat. The heat is extracted by a heat exchanger provided about the housing.

  4. CO2 SELECTIVE CERAMIC MEMBRANE FOR WATER-GAS SHIFT REACTION WITH CONCOMITANT RECOVERY OF CO2

    SciTech Connect

    Paul K.T. Liu

    2003-05-20

    Hydrotalcite material properties, specifically its CO{sub 2} reversibility, are critical to the performance of the proposed hydrotalcite-based membrane. In this report, we summarize the fundamental study we have performed using TGA, TGA/MS, and DRIFTS to quantify the degree of CO{sub 2} reversibility for the temperature range from 200 to 300 C. Results from these three separate studies consistently exhibit the CO{sub 2} reversibility. In addition, water effect appears negligible. Finally a high-pressure experimental study was performed to determine the reversibility under the actual operating condition. The results from this high-pressure (CO{sub 2}) study also demonstrate the CO{sub 2} reversibility. In the next quarter, we will continue the high-pressure experiment in the presence of high-pressure steam to quantify its effect under the actual WGS environment. The quantitative information obtained from this study will then be incorporated in a mathematical model describing the CO{sub 2} permeance as a function of the membrane layer thickness.

  5. CO2 SELECTIVE CERAMIC MEMBRANE FOR WATER-GAS SHIFT REACTION WITH CONCOMITANT RECOVERY OF CO2

    SciTech Connect

    Paul K. T. Liu

    2003-03-14

    In this quarter, we have made progress in the three approaches selected for preparing CO{sub 2}-affinity membrane. A defect free nanoporous membrane was prepared via slip casting. This membrane will then be used for post treatment to seal the micropores to become a non-porous membrane with CO{sub 2} affinity. This post treatment study will be our focus in the next several quarters. Polymeric gel as a precursor was successfully prepared, which will be used for subsequent thin film deposition. Preparation of a defect-free thin film from this precursor will be our future focus using the sol-gel approach. Finally, the third approach, in-situ impregnation approach, was modified. Although we were able to deposit the precursor within the porous of the membrane, we have not been able to enhance the pH in-situ. Designing an unconventional approach to alternate the pH in-situ will be our focus of the next quarter.

  6. CO2 SELECTIVE CERAMIC MEMBRANE FOR WATER-GAS SHIFT REACTION WITH CONCOMITANT RECOVERY OF CO2

    SciTech Connect

    Paul K.T. Liu

    2002-08-01

    As part of our optimization effort, we have conducted a comprehensive study to investigate the morphology and crystal growth kinetics of hydrotalcite powder formation. Based upon the information obtained from this study, we resumed the membrane optimization activities. Although the selectivity of the membrane remains in the Knudsen regime, the permeance decreases along with the number of impregnation. Thus, the permeance could be reduced to a minimum through repeated impregnation. Then, the membrane can be sealed with chemical vapor deposition technique. More characterization results on the membranes prepared will be available in the next quarterly report.

  7. CO2 SELECTIVE CERAMIC MEMBRANE FOR WATER-GAS SHIFT REACTION WITH CONCOMITANT RECOVERY OF CO2

    SciTech Connect

    Paul K.T. Liu

    2002-03-01

    To become a viable CO{sub 2} transport membrane, a reversible interaction between CO{sub 2} and the membrane material at the operating condition is a must. In the past quarter, we have conducted a comprehensive reversibility study using TGA and MS at {approx}200 C for both adsorption and desorption. This quarterly report summarizes the results. Evidently, CO{sub 2} can be reversible adsorbed and desorbed on the hydrotalcite surface via a pressure swing operation (i.e., between 1 bar and vacuum). About 2wt% working capacity was obtained. Even in the presence of water, the reversibility still holds. In the next quarter, we will focus on the reversibility under other operating conditions and the kinetic aspect of the reversibility study.

  8. CO2 SELECTIVE CERAMIC MEMBRANE FOR WATER-GAS SHIFT REACTION WITH CONCOMITANT RECOVERY OF CO2

    SciTech Connect

    Paul K.T. Liu

    2001-09-30

    During Year I this project has been focused on these two topic areas: (i) understanding comprehensively the CO{sub 2} affinity vs temperature, reversibility of CO{sub 2} affinity, and the role of water in order to select an optimum hydrotalcite composition for membrane preparation, and (ii) developing a membrane synthesis protocol for depositing the hydrotalcite material into a commercially available ceramic membrane from us. This annual report documents the progress we have made in these areas. In summary, the Year I study has demonstrated the technical feasibility of preparing a hydrotalcite. The proposed membrane synthesis protocol will be refined and optimized in Year II. In addition, surface analysis techniques employing FTIR and DRIFTS have been developed. These techniques have been applied to a hydrotalcite model compound to demonstrate our ability to screen hydrotalcite materials in terms of its composition and % of cation substitution. These techniques will be utilized in Year II to formulate an optimized hydrotalcite candidate for preparing a membrane with maximized CO{sub 2} transport at the proposed process condition.

  9. Noble metal ions incorporated in lattice points of perovskites - water gas shift activity of BaCe1-xPtxO3-d

    NASA Astrophysics Data System (ADS)

    Jijil, C. P.; Rajarajan, A. K.; Devi, R. Nandini

    2012-06-01

    Recently precious metals supported on oxides were reported to be very promising catalysts for the lower-temperature WGS reaction. Here we report the synthesis of platinum doped barium cerate and its use as catalysts for WGS reaction. It has been found that maximum CO conversion was obtained at 3500C which enhanced after the first cycle. XPS analysis shows that after the first cycle more ionic Platinum species are present on the surface of the catalyst. Neutron diffraction at room temperature shows that the oxygen vacancies are in the O2 position and increases with increasing Pt substitution.

  10. The effect of platinum in Cu-Ce-Zr and Cu-Zn-Al mixed oxide catalysts for water–gas shift

    Microsoft Academic Search

    Florian Huber; John Walmsley; Hilde Venvik; Anders Holmen

    2008-01-01

    Cu-Ce-Zr and Cu-Zn-Al mixed oxide catalysts were prepared by homogeneous co-precipitation with urea. Pt was wet-impregnated on the mixed oxide catalysts. The WGS activity of Cu-Ce-Zr and Cu-Zn-Al mixed oxide catalysts can be related to the Cu reducibility in these catalysts. Low-temperature reducibility correlates with low-temperature activity. Pre-reduction is not absolutely necessary when performing the WGS reaction above the Cu

  11. Low Temperature Water-Gas Shift: Type and Loading Impacts Forward Decomposition of Pseudo-Stabilized Formate over Metal/Ceria Catalysts

    SciTech Connect

    Jacobs,G.; Ricote, S.; Graham, U.; Patterson, P.; Davis, B.

    2005-01-01

    A similar degree of surface shell reduction of ceria was obtained for a series of metal/ceria catalysts. Surface formate species were generated by reaction of CO with bridging OH groups associated with the Ce{sup 3+} defects. Forward decomposition of the pseudo-stable formates was followed in flowing H{sub 2}O, leading to the production of surface carbonate species. The forward formate decomposition rate was enhanced changing the promoter from Au to Pt, and by increasing the promoter loading (from 0.5 to 2.5%). Results suggest that formate C{single_bond}H bond breaking is not only facilitated by H{sub 2}O, but it is further enhanced by type and loading of metal promoter. From earlier kinetic isotope effect and isotopic tracer studies, the rate-limiting step of the forward formate decomposition (WGS reaction) was considered to be associated with C{single_bond}H bond rupture of the formate. The results can explain the promotion in the WGS rates observed for these samples by changing from Au to Pt and by increasing the promoter loading.

  12. Low Temperature Water-Gas Shift: Type and Loading of Metal Impacts Decomposition and Hydrogen Exchange Rates of Pseudo-stabilized Formate over Metal/ceria Catalysts

    SciTech Connect

    Jacobs,G.; Ricote, S.; Davis, B.

    2006-01-01

    In this investigation, a similar degree of surface shell reduction among a series of metal promoted ceria catalysts was established by diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) and X-ray absorption near-edge spectroscopy (XANES) measurements. Surface formate species were generated by reaction of CO with bridging OH groups associated with the Ce{sup 3+} defect sites. The thermal decomposition of the pseudo-stable formates was followed in the absence of H2O. Decomposition and exchange from H to D of the pseudo-stabilized formate was enhanced by changing the promoter from Au to Pt. Likewise, an increase was observed in both decomposition and exchange rates by increasing the promoter loading from 0.5 to 2.5 wt.%. The results suggest that C{single_bond}H bond breaking is facilitated during this thermal decomposition (i.e., reverse decomposition to CO and {single_bond}OH). Therefore, since the rate limiting step of the forward formate decomposition (i.e., the WGS reaction) is strongly suggested to be associated with C{single_bond}H bond cleaving in the formate intermediate (based on earlier kinetic isotope effect and isotopic tracer studies), the results can explain the promotion in the WGS rates as observed by changing from Au to Pt and by increased promoter loading.

  13. Shift catalysts in biomass generated synthesis gas

    Microsoft Academic Search

    Ilham Kirm; Jan Brandin; Mehri Sanati

    2007-01-01

    One of the CHRISGAS project objectives is to study the shift catalysts in biomass-generated synthesis gas. The water gas shift\\u000a reaction is ruled by equilibrium, and the state of the gas can for a given H2\\/CO ratio be shifted by addition\\/removal of water, CO2 and\\/or by a change in the temperature. Stability area in respect to gas composition, sulphur content,

  14. Water-Gas Shift Membrane Reactor Studies

    E-print Network

    Coal, Petroleum coke, Biomass, Waste, etc. Gasifier Particulate Removal Air Separator Oxygen Air Steam syngas components (CO2, H2O, CO) - conduct forward WGS using a membrane reactor at favorable conditions

  15. Low Temperature Water–gas Shift: Differences in Oxidation States Observed with Partially Reduced Pt/MnOX and Pt/CeOX Catalysts Yield Differences in OH Group Reactivity

    SciTech Connect

    Ribeiro, M.; Jacobs, G; Graham, U; Azzam, K; Linganiso, L; Davis, B

    2010-01-01

    The Pt-ceria synergy may be described as the dehydrogenation of formate formed on the surface of the partially reducible oxide (PRO), ceria, by Pt across the interface, with H{sub 2}O participating in the transition state. However, due to the rising costs of rare earth oxides like ceria, replacement by a less expensive partially reducible oxide, like manganese oxide, is desirable. In this contribution, a comparison between Pt/ceria and Pt/manganese oxide catalysts possessing comparable Pt dispersions reveals that there are significant differences and certain similarities in the nature of the two Pt/PRO catalysts. With ceria, partial reduction involves reduction of the oxide surface shell, with Ce{sup 3+} at the surface and Ce{sup 4+} in the bulk. In the case of manganese oxide, partial reduction results in a mixture of Mn{sup 3+} and Mn{sup 2+}, with Mn{sup 2+} located at the surface. With Pt/CeO{sub X}, a high density of defect-associated bridging OH groups react with CO to yield a high density of the formate intermediate. With Pt/MnO{sub X}, the fraction of reactive OH groups is low and much lower formate band intensities result upon CO adsorption; moreover, there is a greater fraction of OH groups that are essentially unreactive. Thus, much lower CO conversion rates are observed with Pt/MnO{sub X} during low temperature water-gas shift. As with ceria, increasing the Pt loading facilitates partial reduction of MnO{sub X} to lower temperature, indicating metal-oxide interactions should be taken into account.

  16. Phase shifts in alpha-frequency rhythm detected in electroencephalograms influence reaction time.

    PubMed

    Naruse, Yasushi; Takiyama, Ken; Okada, Masato; Umehara, Hiroaki; Sakaguchi, Yutaka

    2015-02-01

    Although the phase shifts in ongoing oscillations seen in electroencephalograms (EEGs) and magnetoencephalograms are an important factor in discussions of phase dynamics, such as synchrony and reset, few studies have focused specifically on the phase shift. Here we investigate the relationship between phase shifts in alpha-frequency rhythms and reaction times during a visual simple reaction task by applying our previously described method (Naruse et al., 2013), which enables detection of phase shifts from a single EEG trial. In the left, parietal, and occipital areas, the reaction times in the trials in which phase shifts were detected before the button press were significantly longer than in those in which phase shifts were not so detected. These results indicate that phase shifts in the alpha and mu rhythms relate to variability in reaction times. PMID:25150125

  17. Acceptance on the move: public reaction to shifting vaccination realities.

    PubMed

    Velan, Baruch

    2011-12-01

    This review examines four events related to vaccination that have occurred in recent years: (a) the ongoing recovery from the MMR/Autism scare in the UK, (b) the upgrading of the Varicella vaccine to a universal childhood vaccine, (c) the major effort of authorities to provide a vaccine for A/H1N1 influenza and its rejection by the public, and, d) the current attempts to change the HPV vaccine target from girls only to boys and girls. All of these changes have been met with shifts in the public acceptance of the relevant vaccine. These shifts are characterized not only by the number of people willing to be vaccinated, but also by the attitudes and the motives related to acceptance. Examination of the interrelationship between changes in vaccination realities, and changes in acceptance patterns suggests that today, the public has a better understanding of vaccination, is acting in a more reflexive way, and is capable of changing attitudes and behavior. All together, changes in vaccination enhance debates and dialogues about vaccines, and lead to higher awareness and more conscious acceptance. PMID:22108039

  18. Evaluation of C-14 as a natural tracer for injected fluids at theAidlin sector of The Geysers geothermal system through modeling ofmineral-water-gas Reactions

    SciTech Connect

    Dobson, Patrick; Sonnenthal, Eric; Lewicki, Jennifer; Kennedy, Mack

    2006-06-01

    A reactive-transport model for 14C was developed to test its applicability to the Aidlin geothermal system. Using TOUGHREACT, we developed a 1-D grid to evaluate the effects of water injection and subsequent water-rock-gas interaction on the compositions of the produced fluids. A dual-permeability model of the fracture-matrix system was used to describe reaction-transport processes in which the permeability of the fractures is many orders of magnitude higher than that of the rock matrix. The geochemical system included the principal minerals (K-feldspar, plagioclase, calcite, silica polymorphs) of the metagraywackes that comprise the geothermal reservoir rocks. Initial simulation results predict that the gas-phase CO2 in the reservoir will become more enriched in 14C as air-equilibrated injectate water (with a modern carbon signature) is incorporated into the system, and that these changes will precede accompanying decreases in reservoir temperature. The effects of injection on 14C in the rock matrix will be lessened somewhat because of the dissolution of matrix calcite with ''dead'' carbon.

  19. Mesoporous and nanostructured CeO 2 as supports of nano-sized gold catalysts for low-temperature water-gas shift reaction

    Microsoft Academic Search

    Zhong-Yong Yuan; Vasko Idakiev; Aurélien Vantomme; Tatyana Tabakova; Tie-Zhen Ren; Bao-Lian Su

    2008-01-01

    Mesoporous particles and 1D nanorods of cerium oxides have been prepared by modifying the hydrothermal route of a surfactant-assisted controllable synthesis. Mesoporous cerias were obtained in a sealed glass vessel under continuous stirring, while ceria nanorods were obtained in a Teflon-lined autoclave without stirring. The mesoporous cerias did not show long-range mesoscopic organization, exhibiting a broad mesopore size distribution in

  20. Synthesis of Na-Stabilized Nonporous tZrO2 Supports and Pt/t-ZrO2 Catalysts and Application to Water-Gas-Shift Reaction

    E-print Network

    Poeppelmeier, Kenneth R.

    °C for 20 h using NaOH as the mineralizer, was phase stable up to 600 °C in air. The t-ZrO2 calcined obtained on the Z600 supported Pt/t-ZrO2 catalyst by the Pt atomic layer deposition (ALD) method. Na ions at ambient pressure: monoclinic (m-ZrO2, room temperature-1175 °C), tetragonal (t-ZrO2, 1175-2370 °C

  1. On a thermodynamic limitation of the water-gas potentiometry using solid electrolyte cells

    Microsoft Academic Search

    Reinhold Hartung; Hans-Heinrich Möbius

    1994-01-01

    Possibilities of the water-gas potentiometry using oxide ion-conducting solid electrolytes may be restricted by side reactions in the gas being analyzed. Changes in electrode potentials caused by simultaneous interfering equilibria in the water gas were investigated over a temperature range 1200 to 400°C for different initial gas compositions. Formation reactions of carbon and methane proved to be the side reactions

  2. Sensitivity of Fischer-Tropsch Synthesis and Water-Gas Shift Catalystes to Poisons form High-Temperature High-Pressure Entrained-Flow (EF) Oxygen-Blown Gasifier Gasification of Coal\\/Biomass Mixtures

    Microsoft Academic Search

    Burton Davis; Gary Jacobs; Wenping Ma; Khalid Azzam; Janet ChakkamadathilMohandas; Wilson Shafer

    2009-01-01

    There has been a recent shift in interest in converting not only natural gas and coal derived syngas to Fischer-Tropsch synthesis products, but also converting biomass-derived syngas, as well as syngas derived from coal and biomass mixtures. As such, conventional catalysts based on iron and cobalt may not be suitable without proper development. This is because, while ash, sulfur compounds,

  3. Reactivity-Structure-Based Rate Estimation Rules for Alkyl Radical H Atom Shift and Alkenyl Radical Cycloaddition Reactions.

    PubMed

    Wang, Kun; Villano, Stephanie M; Dean, Anthony M

    2015-07-16

    Intramolecular H atom shift reactions of alkyl radicals and cycloaddition reactions of alkenyl radicals are two important reaction classes in hydrocarbon combustion and pyrolysis. In this work, we derive high-pressure rate estimation rules that are based on the results of electronic structure calculations at the CBS-QB3 level of theory combined with transition state theory calculations. The rules for the H atom shift reactions of alkyl radicals cover the 1,2- up to the 1,7-H shifts. The rules for the cycloaddition reactions of alkenyl radicals are for both the endo- and exo-cycloaddition and include the formation of three- to seven-member ring products. The results are in good agreement with available experiment measurements and other theoretical studies. Both types of reactions proceed via cyclic transition state structures. The impact of ring size and substituent groups on pre-exponential factors and activation energies are discussed in the context of a Benson-type structure-reactivity relationship. Similar relationships between the pre-exponential factors and the number of internal rotors lost in formation of the transition state are derived for both H-shift and cycloaddition reactions. The activation energies are found to be more complicated. The ring strain contribution to the barrier is much lower for the exo-cycloaddition reactions than it is for the other two investigated reaction systems. The ring strains for the H-shift and endo-cycloaddition are similar to one another and are comparable to that of cycloalkanes for three- to six-member rings, but are significantly lower for the larger rings. The results suggest that the 1,6-H shift and 1,7-endo-cycloaddition reactions might be faster than previous estimates. PMID:25563061

  4. Aromatic transition states in nonpericyclic reactions: anionic 5-endo cyclizations are aborted sigmatropic shifts.

    PubMed

    Gilmore, Kerry; Manoharan, Mariappan; Wu, Judy I-Chia; Schleyer, Paul v R; Alabugin, Igor V

    2012-06-27

    The transition states (TSs) of 5-endo-dig and 5-endo-trig anionic ring closures are the first unambiguous examples of nonpericyclic reactions with TSs stabilized by aromaticity. Their five-center, six-electron in-plane aromaticity is revealed by the diatropic dissected nucleus-independent chemical shifts, -24.1 and -13.7 ppm, respectively, resulting from the delocalization of the lone pair at the nucleophilic center, a ? CC bond, and an in-plane alkyne (or alkene) ? bond. Other seemingly analogous exo and endo cyclization TSs do not have these features. A symmetry-enhanced combination of through-space and through-bond interactions explains the anomalous geometric, energetic, and electronic features of the 5-endo ring closure transition state. Anionic 5-endo cyclizations can be considered to be "aborted" [2,3]-sigmatropic shifts. The connection between anionic cyclizations and sigmatropic shifts offers new possibilities for the design and electronic control of anionic isomerizations. PMID:22594586

  5. Sulfur tolerant metal doped Fe/Ce catalysts for high temperature WGS reaction at low steam to CO ratios XPS and Mssbauer spectroscopic study

    E-print Network

    Boolchand, Punit

    Sulfur tolerant metal doped Fe/Ce catalysts for high temperature WGS reaction at low steam to CO spectroscopy TPR XPS CeO2 Magnetite a b s t r a c t High temperature water gas shift reaction (WGS) at low, Hf and Mo have little or no effect on the WGS activity of Fe/Ce. All the catalysts exhibit excellent

  6. Solving the structure of reaction intermediates by time-resolved synchrotron x-ray absorption spectroscopy

    E-print Network

    Frenkel, Anatoly

    -structure data isolated by PCA. The method is demonstrated using reduction and reoxidation of Cu-doped ceria metal oxides CuO,1 Cu-ceria,2 Au-ceria,3 and Cu­MoO2 Ref. 4 in water-gas- shift reactions. Another area

  7. Difunctionalization of Alkenes via the Visible-Light-Induced Trifluoromethylarylation/1,4-Aryl Shift/Desulfonylation Cascade Reactions.

    PubMed

    Zheng, Lewei; Yang, Chao; Xu, ZhaoZhong; Gao, Fei; Xia, Wujiong

    2015-06-01

    A novel visible-light-induced trifluoromethylarylation/1,4-aryl shift/desulfonylation cascade reaction using CF3SO2Cl as CF3 source was described. The protocol provides an efficient approach for the synthesis of ?-aryl-?-trifluoromethyl amides and/or CF3-containing oxindoles as well as the isoquinolinediones under benign conditions. PMID:25955879

  8. Kinetic analysis of the phenyl-shift reaction in $\\beta$-O-4 lignin model compounds: A computational study.

    SciTech Connect

    Beste, Ariana [ORNL; Buchanan III, A C [ORNL

    2011-01-01

    The phenyl-shift reaction in $\\beta$-phenethyl phenyl ether ($\\beta - \\rm PhCH_2CH_2OPh$, $\\beta$-PPE) is an integral step in the pyrolysis of PPE, which is a model compound for the $\\beta$-O-4 linkage in lignin. We investigated the influence of natural occurring substituents (hydroxy, methoxy) on the reaction rate by calculating relative rate constant using density functional theory in combination with transition state theory, including anharmonic correction for low-frequency modes. The phenyl-shift reaction proceeds through an intermediate and the overall rate constants were computed invoking the steady-state approximation (its validity was confirmed). Substituents on the phenethyl group have only little influence on the rate constants. If a methoxy substituent is located in para position of the phenyl ring adjacent to the ether oxygen, the energies of the intermediate and second transition state are lowered, but the overall rate constant is not significantly altered. This is a consequence of the dominating first transition from pre-complex to intermediate in the overall rate constant. {\\it O}- and di-{\\it o}-methoxy substituents accelerate the phenyl-migration rate compared to $\\beta$-PPE.

  9. Shifting the energy landscape of multicomponent reactions using aziridine aldehyde dimers: a mechanistic study.

    PubMed

    Belding, Lee; Zaretsky, Serge; Rotstein, Benjamin H; Yudin, Andrei K; Dudding, Travis

    2014-10-17

    A multicomponent reaction between an aziridine aldehyde dimer, isocyanide, and l-proline to afford a chiral piperazinone was studied to gain insight into the stereodetermining and rate-limiting steps of the reaction. The stereochemistry of the reaction was found to be determined by isocyanide addition, while the rate-limiting step was found to deviate from traditional isocyanide-based multicomponent reactions. A first-order rate dependence on aziridine aldehyde dimer and a zero-order rate dependence on all other reagents have been obtained. Computations at the MPWPW91/6-31G(d) level supported the experimental kinetic results and provide insight into the overall mechanism and the factors contributing to stereochemical induction. These factors are similar to traditional isocyanide-based multicomponent reactions, such as the Ugi reaction. The computations revealed that selective formation of a Z-iminium ion plays a key role in controlling the stereoselectivity of isocyanide addition, and the carboxylate group of l-proline mediates stereofacial addition. These conclusions are expected to be applicable to a wide range of reported stereoselective Ugi reactions and provide a basis for understanding the related macrocyclization of peptides with aziridine aldehydes. PMID:25264960

  10. Reactivity of iron carbonyl complexes in a hydrated sodium-Y zeolite matrix and catalysis of the resulting hydride anion HFeâ(CO)âââ» for water-gas-shift reaction

    Microsoft Academic Search

    Masakazu Iwamoto; Shinichiro Nakamura; Hideto Kusano; Shuichi Kagawa

    1986-01-01

    Iron carbonyls Fe(CO)â, Feâ(CO)â, and Feâ(CO)ââ have been introduced into a hydrated Na-Y zeolite. Fe(CO)â was only weakly adsorbed on the zeolite. Feâ(CO)â and Feâ(CO)ââ were reactive in the hydrated zeolite cages to yield a hydride anion species HFeâ(CO)âââ» which was characterized by IR absorption bands at 2044, 1987, 1950, and 1645 cm⁻¹, UV-vis spectrum at 540 nm, and gas-phase

  11. Deuterium studies reveal a new mechanism for the formose reaction involving hydride shifts.

    PubMed

    Appayee, Chandrakumar; Breslow, Ronald

    2014-03-12

    In the formose reaction, formaldehyde is converted to glycolaldehyde, its dimer, under credible prebiotic conditions. Breslow proposed a mechanism for the process in 1959, but recent studies by Benner showed that it was wrong in detail. Our present studies clarify the mechanism, which involves the original Breslow intermediates but some different connecting steps. PMID:24575857

  12. A spiking neural model of strategy shifting in a simple reaction time task Trevor Bekolay1

    E-print Network

    Anderson, Charles H.

    synaptic weight changes. Simple reaction-time task House lights extinguished Foreperiod 1.0 s Lever press Lever release Premature trial Foreperiod 1.0 s Response window 0.6 s Lever press Trigger stimulus Lever release Correct trial Reward delivery Foreperiod 1.0 s Response window 0.6 s Lever press Trigger stimulus

  13. Nitrate attenuation in agricultural catchments: Shifting balances between transport and reaction

    NASA Astrophysics Data System (ADS)

    Ocampo, Carlos J.; Oldham, Carolyn E.; Sivapalan, Murugesu

    2006-01-01

    Simultaneous observations, across multiple spatial and temporal scales, are needed to understand the complex interactions between hydrological and biogeochemical processes in catchments and the primary controls on NO3- availability and mobility. This paper addresses these issues by using data collected from a detailed field experiment, carried out on two topographically different hillslopes (one steep and the other flat) located within an agricultural catchment in Western Australia. Continuous hydrometric data and measurements of chemical tracers, geochemical parameters, and NO3- concentrations taken from the shallow perched aquifer across riparian, midslope, and upland locations were analyzed and interpreted through a simple process-based numerical model of transport and reaction. The NO3- concentration data indicated that the temporal and spatial patterns of NO3- concentrations within the hillslopes are linked to the state of hydrological connectivity of the three landscape units as the shallow perched aquifer developed during the winter. Significant NO3- attenuation occurs within the riparian zones after the transport of NO3- from midslope sources begins. Application of a mixing model, which partitions the riparian zones into three water source components, and the numerical model of NO3- transport and reaction indicates that different mechanisms, dilution in the steep hillslope and denitrification in the flat hillslope, are responsible for much of the observed NO3- attenuation in the riparian zones. In this way, this work highlights the importance of hillslope topography in determining the relative roles of transport and reaction in NO3- attenuation and export from riparian zones. The experimental results also supported the use of the Damköhler number, a simple dimensionless number that is a measure of the competition between transport and reaction processes, which allowed a favorable comparison of our findings with previous results published in the literature for different geographical settings.

  14. Enhancement of Equilibrium Shift in Dehydrogenation Reactions Using A Novel Membrane Reactor

    SciTech Connect

    Franklin G. King; Shamsuddin Ilias

    1998-05-27

    Electroless deposition of palladium thin-films on a surface of microporous ceramic substrate has been used to develop a new class of perm-selective inorganic membrane. In our previous two reports, we presented mathematical models to describe transport of hydrogen the palladium-ceramic composite membrane in single-stage permeation cell in cocurrent and countercurrent flow configurations. Analysis shows that the model equations have a singular point. In this report, a method is described how to avoid the singular point in order to solve the model equations numerically. To show the usefulness of the new method, a single-stage gas permeation for a three component system, without chemical reaction under cocurrent flow configuration has been used as an example.

  15. WGS reaction in a membrane reactor using a porous stainless steel supported silica membrane

    Microsoft Academic Search

    A. Brunetti; G. Barbieri; E. Drioli; K.-H. Lee; B. Sea; D.-W. Lee

    2007-01-01

    Water gas shift reaction for hydrogen production was studied in a catalytic membrane reactor using a supported silica membrane at 220–290°C temperature and 2–6bar pressure ranges. A CO conversion higher than the thermodynamic equilibrium of a traditional reactor was obtained. The best result, 95% CO conversion, was achieved at 4bar and 280°C.The membrane was also characterized in terms of permeance

  16. Transition metal chemistry under high carbon monoxide pressure: an infrared spectroscopic study of catalysis in the Fischer-Tropsch reaction. Final technical report, May 14, 1976-September 30 1981

    SciTech Connect

    King, R.B.; King, A.D. Jr.

    1981-01-01

    A high-pressure infrared cell was used to study reactions of transition metal alkyls at elevated CO and H/sub 2/ pressures (hydroformylation). Two types of catalytic systems were investigated for the synthesis of alcohols from CO and H/sub 2/. Addition of CO to metal-metal triple bonds was studied. Kinetics of the water gas shift reaction catalyzed by transition metal carbonyls was studied. (DLC)

  17. Molecular-level understanding of the WGS and reverse WGS reactions on Rh through hierarchical multiscale approach

    E-print Network

    Maestri, Matteo; 10.1016/j.ces.2012.02.043

    2012-01-01

    Hierarchically combining semi-empirical methods and first-principles calculations we gain a novel and noteworthy picture of the molecular-level mechanisms that govern the water-gas-shift (WGS) and reverse water-gas-shift (r-WGS) reactions on Rh catalysts. Central to this picture is that the WGS and r-WGS follow two different dominant reaction mechanisms: WGS proceeds according to a carboxyl (COOH) mechanism, whereas r-WGS proceeds according to a redox (CO2 {\\to} CO + O) mechanism. The obtained results furthermore underscore the danger of common first-principles analyses that focus on a priori selected dominant paths. Not restricted to such bias, our herein proposed hierarchical approach thus constitutes a promising avenue to properly transport and incorporate the ab initio predictive-quality to a new level of system complexity.

  18. Criteria for identifying homogeneous transition metal cluster-catalyzed reactions

    SciTech Connect

    Laine, R.M.

    1980-01-01

    Four criteria were developed for distinguishing homogeneous cluster from mononuclear catalysis. A criterion based on reaction kinetics, which distinguishes catalysis by clusters from catalysis by mononuclear complexes in equilibrium with the clusters, is illustrated with the hydroformylation of 1-pentene by Ru/sub 3/(CO)/sub 12/ clusters in equilibrium with 3Ru(CO)/sub 5/ complexes in the presence of CO. A criterion based on selectivity is illustrated by the water gas shift and deuterium-exchange reactions catalyzed by ruthenium and rhodium carbonyl clusters in methanol and triethylamine; the scope of this criterion is limited to deuterium exchange reactions. A criterion based on mixed-metal catalysis, in which a mixed-metal system has higher catalytic activity than each transition metal cluster alone, is illustrated with hydroformylation of 1-pentene and the water gas shift reaction catalyzed by Ru/sub 3/(CO)/sub 12//Fe/sub 3/(CO)/sub 2/ and Rh/sub 6/(CO)/sub 16//Fe/sub 3/(CO)/sub 12/. A criterion based on changes in asymmetric induction is a special case of the selectivity criterion, in which specific starting metal complexes may produce either of two enantiomers. Catalysis by metal clusters is an analytical tool for modeling heterogeneous catalytic mechanisms.

  19. Catalytic performance of Co-Mo-Ce-K\\/?-Al 2 O 3 catalyst for the shift reaction of CO in coke oven gas

    Microsoft Academic Search

    Yuqiong Zhao; Yongfa Zhang

    2010-01-01

    The catalytic performance of Co-Mo-Ce-K\\/?-Al2O3 catalyst for the shift reaction of CO in coke oven gas is investigated using X-ray diffraction (XRD) and temperature-programmed\\u000a reduction (TPR). The results indicate that Ce and K have a synergistic effect on promoting the catalytic activity, and the\\u000a Co-Mo-Ce-K\\/?-Al2O3 catalyst with 3.0 wt-% CeO2 and 6.0 wt-% K2O exhibits the highest activity. CeO2 favors

  20. Computational Chemistry-Based Identification of Ultra-Low Temperature Water-Gas-Shift Catalysts

    Microsoft Academic Search

    Manos Mavrikakis

    2008-01-01

    The current work seeks to identify novel, catalytically-active, stable, poison-resistant LWGS catalysts that retain the superior activity typical of conventional Cu catalysts but can be operated at similar or lower temperatures. A database for the Binding Energies (BEs) of the LWGS relevant species, namely CO, O and OH on the most-stable, close-packed facets of a set of 17 catalytically relevant

  1. Computational Chemistry-Based Identification of Ultra-Low Temperature Water-Gas-Shift Catalysts

    SciTech Connect

    Manos Mavrikakis

    2008-08-31

    The current work seeks to identify novel, catalytically-active, stable, poison-resistant LWGS catalysts that retain the superior activity typical of conventional Cu catalysts but can be operated at similar or lower temperatures. A database for the Binding Energies (BEs) of the LWGS relevant species, namely CO, O and OH on the most-stable, close-packed facets of a set of 17 catalytically relevant transition metals was established. This BE data and a database of previously established segregation energies was utilized to predict the stability of bimetallic NSAs that could be synthesized by combinations of the 17 parent transition metals. NSAs that were potentially stable both in vacuo and under the influence of strong-binding WGS intermediates were then selected for adsorption studies. A set of 40 NSAs were identified that satisfied all three screener criteria and the binding energies of CO, O and OH were calculated on a set of 66, 43 and 79 NSA candidates respectively. Several NSAs were found that bound intermediates weaker than the monometallic catalysts and were thus potentially poison-resistant. Finally, kinetic studies were performed and resulted in the discovery of a specific NSA-based bimetallic catalyst Cu/Pt that is potentially a promising LWGS catalyst. This stable Cu/Pt subsurface alloy is expected to provide facile H{sub 2}O activation and remain relatively resistant from the poisoning by CO, S and formate intermediates.

  2. Desulfurization of a coal model compound by in situ hydrogen generation through water-gas shift 

    E-print Network

    Kumar, Meyyappan

    1982-01-01

    were found to be 20. 356 + 2. 6 Kcal/gmole -4 ana (8. 51 + 0. 59) x 10 gmole/gm cat. min at 80% conf idence interval. The Arrhenius constant was found to be 1. 1769 x 10 gmole/gm cat min. 4 ACRHOWLEDGEMEHT The author wishes to express his... and Conversion 62 5 Computer Results or Non-Linear Regression Analysis 98 6 Results of Kinetic Parameters Estimation 7 Statistical Analysis Results for Temperature Profile Tl 108 8 Statistical Analysis Results f or Temperature Prof ile T2 109 9...

  3. Slurry phase Fischer-Tropsch synthesis: Cobalt plus a water-gas shift catalyst

    SciTech Connect

    Yates, I.C.; Satterfield, C.N.

    1989-01-01

    The rate of synthesis gas consumption over a cobalt FischerTropsch catalyst was measured in a well-mixed, continuous-flow, slurry reactor at 220 to 240[degrees]C, 0.5 to 1.5 MPa, H[sub 2]/CO feed ratios of 1.5 to 3.5 and conversions of 7 to 68% of hydrogen and 11 to 73% of carbon monoxide. The inhibiting effect of carbon monoxide was determined quantitatively and a Langmuir-Hinshelwood-type equation of the following form was found to best represent the results: -R[sub H[sub 2+Co

  4. Desulfurization of a coal model compound by in situ hydrogen generation through water-gas shift

    E-print Network

    Kumar, Meyyappan

    1982-01-01

    I ill I. -'I c, p C a~ . vnv v av ~J molybdate catalyst containing 2. 4 '4 Co and 6. 7 0 No Conversion data were obtained with a steaoy state flow reactor packed with particles of a commercial cobalt molybdate catalyst. Givens and Venuto (1970... were found to be 20. 356 + 2. 6 Kcal/gmole -4 ana (8. 51 + 0. 59) x 10 gmole/gm cat. min at 80% conf idence interval. The Arrhenius constant was found to be 1. 1769 x 10 gmole/gm cat min. 4 ACRHOWLEDGEMEHT The author wishes to express his...

  5. Preparation of neuroprotective condensed 1,4-benzoxazepines by regio- and diastereoselective domino Knoevenagel–[1,5]-hydride shift cyclization reaction

    PubMed Central

    Tóth, László; Fu, Yan; Zhang, Hai Yan; Mándi, Attila; Kövér, Katalin E; Illyés, Tünde-Zita; Kiss-Szikszai, Attila; Balogh, Balázs; Kurtán, Tibor

    2014-01-01

    Summary Condensed O,N-heterocycles containing tetrahydro-1,4-benzoxazepine and tetrahydroquinoline moieties were prepared by a regio- and diastereoselective domino Knoevenagel–[1,5]-hydride shift cyclization reaction of a 4-aryl-2-phenyl-1,4-benzoxazepine derivative obtained from flavanone. The relative configuration of products were determined by the correlation of 3 J H,H coupling data with the geometry of major conformers accessed by DFT conformational analysis. Separated enantiomers of the products were characterized by HPLC-ECD data, which allowed their configurational assignment on the basis of TDDFT-ECD calculation of the solution conformers. Two compounds showed neuroprotective activities against hydrogen peroxide (H2O2) or ?-amyloid25–35 (A?25–35)-induced cellular injuries in human neuroblastoma SH-SY5Y cells in the range of those of positive controls. PMID:25550721

  6. Lifetimes of levels in 56Co from Doppler-shift measurements via the 56Fe(p,n)56Co reaction

    Microsoft Academic Search

    J. H. Barker; D. G. Sarantites

    1974-01-01

    The decay properties of the levels in 56Co up to 1720.12 keV have been carefully investigated via the 56Fe(p,ngamma)56Co reaction at 7.3 MeV, using a Ge(Li)-NaI(Tl) anti-Compton spectrometer. Three new weak transitions from well established levels were observed. Using the Doppler-shift attenuation method the values of 0.48+0.32-0.15, >= 1.1, 0.11+0.03-0.02, 0.63+0.36-0.18, 0.35+0.05-0.03, >= 0.6, and 0.49+0.51-0.17 psec were obtained for

  7. On the analysis of CO 2 , H 2 - and CO, H 2 -mixtures by water-gas potentiometry with solid electrolyte cells

    Microsoft Academic Search

    Reinhold Hartung

    1996-01-01

    The potentiometric analysis of CO2, H2 and CO, H2O-mixtures using oxide ion-conducting solid electrolytes requires the adjustment of the water-gas equilibrium without side\\u000a reactions in the high-temperature galvanic cell. Conventional cell designs suitable for the analysis of H2, H2O and CO, CO2-mixtures are not applicable due to the insufficient gas residence times in the cells and the insufficient catalytical activity

  8. Copper promotion of high temperature shift

    Microsoft Academic Search

    John S. Coleman; Mang Zhang; Rainee M. VanNatter; Carl R. F. Lund

    2011-01-01

    A four-step, redox kinetic mechanism provides an accurate description of the rate of water-gas shift over ferrochrome catalysts. When the heats of formation of the surface intermediates in the model are decreased by only 10kJmol?1, as might be expected when copper cations substitute for iron cations in the oxide catalyst, the model predicts increased activity and decreased inhibition by CO2.

  9. KINETIC UNDERSTANDING OF THE SYNGAS-TO-DME REACTION SYSTEM AND ITS IMPLICATIONS TO PROCESS AND ECONOMICS

    SciTech Connect

    Xiang-Dong Peng

    2002-12-01

    In a single-step synthesis gas-to-dimethyl ether process, synthesis gas (or syngas, a mixture of H{sub 2} and CO) is converted into dimethyl ether (DME) in a single reactor. The three reactions involved in this process, methanol synthesis, methanol dehydration and water gas shift, form an interesting reaction network. The interplay among these three reactions results in excellent syngas conversion or reactor productivity. A fundamental understanding of this interplay helps to explain many experimental and simulation observations, to identify optimal reaction conditions, and to provide guidelines for process development. The higher syngas conversion or reactor productivity in the syngas-to-DME reaction system, compared to that in the syngas-to-methanol reaction system, is referred to as chemical synergy. This synergy exhibits a strong dependence on the composition of the reactor feed. To demonstrate the extent of this dependence, simulations with adjusted activity for each reaction were performed to reveal the relative rate of each reaction. The results show that the water gas shift reaction is the most rapid, being practically controlled by the equilibrium. Both methanol synthesis and methanol dehydration reactions are kinetically controlled. The kinetics of the dehydration reactions is greater than that of the methanol synthesis reaction in the CO-rich regime. However, the rates of these two reactions come closer as the H{sub 2} concentration in the reactor feed increases. The role of the dehydration reaction is to remove the equilibrium barrier for the methanol synthesis reaction. The role of the water gas shift reaction is more complex; it helps the kinetics of methanol dehydration by keeping the water concentration low, which in turn enhances methanol synthesis. It also readjusts the H{sub 2}:CO ratio in the reactor as the reactions proceed. In the CO-rich regime, the water gas shift reaction supplements the limiting reactant, H{sub 2}, by reacting water with CO. This enhances both the kinetics and thermodynamic driving force of the methanol synthesis reaction. In the H{sub 2}-rich regime, water gas shift consumes the limiting reactant, CO, which harms both the kinetics and thermodynamics of methanol synthesis. An understanding of these complex roles of the methanol dehydration and water gas shift reactions and of their dependence on the syngas composition explains why the synergy is high in the CO-rich regime, but decreases with increasing H{sub 2} or CO{sub 2} content in the reactor feed. The methanol equivalent productivity of the syngas-to-DME reactor is also a strong function of the reactor feed. A mathematical approach was developed to understand this dependence. The approach divides a power law type of rate equation into two terms, the kinetic term (the rate of the forward reaction) and the thermodynamics or driving force term (1- approach to equilibrium). The equations for the best feed composition for each term were derived. The approach was developed for the single reaction system, and then extended to the syngas-to-DME reaction system. The equations provide insights into why and how the methanol synthesis in the syngasto-DME system depends on the other two reactions. They can also be used to calculate the best feed composition for a given conversion. The analysis shows that for typical commercial syngas conversion, the optimal H{sub 2}:CO ratio for the LPDME{trademark} reactor is around 1-to-1, in good agreement with the results from the simulation. While the 1-to-1 feed provides a good foundation for some process configurations, it does not match the composition of natural gas-derived syngas, which typically has a H{sub 2}:CO ratio of 2:1 or greater. The process would also produce one CO{sub 2} molecule for every DME product, both a materials utilization and an environmental problem. However, recycling CO{sub 2} to the syngas generation unit can solve all of these problems. Integration schemes with different syngas generation technologies (dry reforming, steam methane reforming and partial oxidation) were

  10. Separation of intron 22 inversion type 1 and 2 of hemophilia A by modified inverse-shifting polymerase chain reaction and capillary gel electrophoresis.

    PubMed

    Pan, Tzu-Yu; Chiou, Shyh-Shin; Wang, Chun-Chi; Wu, Shou-Mei

    2014-12-01

    An inverse-shifting polymerase chain reaction (IS-PCR) combined with short-end capillary gel electrophoresis (CGE) was developed for genotyping of intron 22 inversion Type 1 (Inv22-1) and Type 2 (Inv22-2) of hemophilia A (HA). Severe HA cases are affected by intron 22 inversion around 45-50%. Inv22-1 has higher frequency than Inv22-2. The aim of this study is to distinguish them by genotyping. In order to improve Inv22 genotyping efficiency, five primers were designed and applied to differentiate the wild type, Inv22-1, Inv22-2 and carrier. Three amplicons of 405, 457 and 512 bp were recognized for wild type; 333, 457 and 584 bp for Inv22-1; 385, 405 and 584 bp for Inv22-2. The Inv22-1 carrier has 5 amplicons including 333, 405, 457, 512, 584 bp and Inv22-2 carrier is differentiated by 385, 405, 457, 512 and 584 bp. The amplicons between Inv22-1 and Inv22-2 carriers are only different in 333 bp for Inv22-1 carrier and 385 bp for Inv22-2 carrier. Capillary gel electrophoresis (CGE) was used for separation within 5 min. The separation voltage was set at 8 kV (cathode at detector), and the temperature was kept at 25°C. The sieving matrix was 89 mM Tris, 89 mM boric acid, 2mM EDTA containing 0.4% (w/v) HPMC and 1 ?M of YO-PRO(®)-1 Iodide. Total of 50 HA patients (including 35 non-Inv22, 14 Inv22-1, and one Inv22-2 patients) and 7 HA carriers were diagnosed in the application. Seven random samples (5 patients and 2 carriers) were subjected to comparison and gave identical results of DNA sequencing and this modified IS-PCR. PMID:25159417

  11. Thermochemical cyclic system for splitting water and/or carbon dioxide by means of cerium compounds and reactions useful therein

    DOEpatents

    Bamberger, Carlos E. (Oak Ridge, TN); Robinson, Paul R. (Knoxville, TN)

    1980-01-01

    A thermochemical cyclic process for producing hydrogen from water comprises reacting ceric oxide with monobasic or dibasic alkali metal phosphate to yield a solid reaction product, oxygen and water. The solid reaction product, alkali metal carbonate or bicarbonate, and water, are reacted to yield hydrogen, ceric oxide, carbon dioxide and trialkali metal phosphate. Ceric oxide is recycled. Trialkali metal phosphate, carbon dioxide and water are reacted to yield monobasic or dibasic alkali metal phosphate and alkali metal bicarbonate, which are recycled. The cylic process can be modified for producing carbon monoxide from carbon dioxide by reacting the alkali metal cerous phosphate and alkali metal carbonate or bicarbonate in the absence of water to produce carbon monoxide, ceric oxide, carbon dioxide and trialkali metal phosphate. Carbon monoxide can be converted to hydrogen by the water gas shift reaction.

  12. Laboratory support for in situ gasification: reaction kinetics. Annual report October 1977-September 1978

    SciTech Connect

    Young, J.E.; Wong, S.H.; Johnson, J.E.; Sikand, N.; Jonke, A.A.

    1980-02-01

    This work is directed toward support studies for the national program for the development and demonstration of in situ coal gasification processes. The objective of this work is to determine the reaction-controlling variables and reaction kinetics for the gasification of chars obtained by pyrolyzing coal in simulated underground gasification conditions. The reactions being studied and to be studied include steam-char, CO/sub 2/-char, H/sub 2/-char, the water-gas shift reaction, and the methanation reaction. In this report are presented data regarding the kinetics of the reaction of steam with chars prepared from Pittsburgh seam high-volatile bituminous coal. In addition, a reaction model is described correlating the steam-char reaction rates measured earlier for Hanna subbituminous coal with operating conditions including temperature, partial pressures of steam and hydrogen, and extent of carbon gasification. Partial results are presented and discussed for an investigation of structural parameters of Hanna char as a function of pyrolysis conditions and extent of carbon gasified.

  13. Stick shift

    E-print Network

    Parness, Aaron J. (Aaron Joseph), 1981-

    2004-01-01

    Stick Shift is a novel that has undergone several rounds of significant revision. Scott, the book's main character, is a sarcastic American who travels to England to move in with an ex-girlfriend. He experiences all of the ...

  14. The Influence of Intermittency on Air-Water Gas Transfer Measurements

    E-print Network

    Garbe, Christoph S.

    . Because the gas transfer of sparingly soluble gases is con- trolled by the transport across the water18 The Influence of Intermittency on Air-Water Gas Transfer Measurements Bernd Jähne, Christopher the concentration difference between the air and the water is spatially or tem- porally inhomogeneous over

  15. A Laboratory Study of the Schmidt Number Dependency of Air-Water Gas

    E-print Network

    Jaehne, Bernd

    A Laboratory Study of the Schmidt Number Dependency of Air-Water Gas Transfer Kerstin Richter1 measurements in two different wind-wave facilities. Key Words: Schmidt number exponent, transfer velocity. Gas Transfer at Water Surfaces, Kyoto, May 17-21, 2010 copyright Kyoto University Press, 2011 #12

  16. Bridging silyl groups in sigma-bond metathesis and [1, 2] shifts. An experimental and computational study of the reaction between cerium metallocenes and MeOSiMe3

    SciTech Connect

    Werkema, Evan; Yahia, Ahmed; Maron, Laurent; Eisenstein, Odile; Andersen, Richard

    2010-04-21

    The reaction of Cp'2CeH (Cp' = 1,2,4-(Me3C)3C5H2 ) with MeOSiMe3 gives Cp'2CeOMe and HSiMe3 and the reaction of the metallacycle, Cp'[(Me3C)2C5H2C(Me) 2CH2]Ce, with MeOSiMe3 yields Cp'2CeOCH2SiMe3, formed from hypothetical Cp'2CeCH2OSiMe3 by a [1, 2] shift also known as a silyl-Wittig rearrangement. Although both cerium products are alkoxides, they are formed by different pathways. DFT calculations on the reaction of the model metallocene, Cp2CeH, and MeOSiMe3 show that the lowest energy pathway is a H for OMe exchange at Ce that occurs by way of a sigma-bond metathesis transition state as SiMe3 exchanges partners. The formation of Cp2CeOCH2SiMe3 occurs by way of a low activation barrier [1, 2]shift of the SiMe3 group in Cp2CeCH2OSiMe3. Calculations on a model metallacycle, Cp[C5H4C(Me)2CH2]Ce, show that the metallacycle favors CH bond activation over sigma-bond metathesis involving the transfer of the SiMe3 group in good agreement with experiment. The sigma-bond metathesis involving the transfer of SiMe3 and the [1, 2]shift of SiMe3 reactions have in common a pentacoordinate silicon at the transition states. A molecular orbital analysis illustrates the connection between these two Si-O bond cleavage reactions and traces the reason why they occur for a silyl but not for an alkyl group to the difference in energy required to form a pentacoordinate silicon or carbon atom in the transition state. This difference clearly distinguishes a silyl from an alkyl group as shown in the study of"Pyrolysis of Tetramethylsilane Yielding Free d-orbitals by Seyferth and Pudvin in ChemTech 1981, 11, 230-233".

  17. CHLORIDE POISONING OF WATER GAS SHIFT ACTIVITY ON NICKEL CATALYSTS DURING STEAM REFORMING. (R822721C633)

    EPA Science Inventory

    The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

  18. CHLORIDE POISONING OF WATER GAS SHIFT ACTIVITY ON NICKEL CATALYSTS DURING STEAM REFORMING. (R826694C633)

    EPA Science Inventory

    The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

  19. Shift Registers

    NSDL National Science Digital Library

    Kuphaldt, Tony R.

    All About Circuits is a website that â??provides a series of online textbooks covering electricity and electronics.â? Written by Tony R. Kuphaldt, the textbooks available here are wonderful resources for students, teachers, and anyone who is interested in learning more about electronics. This specific section, Shift Registers, is the twelfth chapter in Volume IV â??Digital. A few of the topics covered in this chapter include: Serial-in, serial-out shift register, Parallel-in, parallel-out shift register, and Ring counters. Diagrams and detailed descriptions of concepts are included throughout the chapter to provide users with a comprehensive lesson. Visitors to the site are also encouraged to discuss concepts and topics using the All About Circuits discussion forums (registration with the site is required to post materials).

  20. Fluid Shifts

    NASA Technical Reports Server (NTRS)

    Stenger, M. B.; Hargens, A.; Dulchavsky, S.; Ebert, D.; Lee, S.; Laurie, S.; Garcia, K.; Sargsyan, A.; Martin, D.; Lui, J.; Macias, B.; Arbeille, P.; Danielson, R.; Chang, D.; Gunga, H.; Johnston, S.; Westby, C.; Ribeiro, L.; Ploutz-Snyder, R.; Smith, S.

    2015-01-01

    INTRODUCTION: Mechanisms responsible for the ocular structural and functional changes that characterize the visual impairment and intracranial pressure (ICP) syndrome (VIIP) are unclear, but hypothesized to be secondary to the cephalad fluid shift experienced in spaceflight. This study will relate the fluid distribution and compartmentalization associated with long-duration spaceflight with VIIP symptoms. We also seek to determine whether the magnitude of fluid shifts during spaceflight, as well as the VIIP-related effects of those shifts, can be predicted preflight with acute hemodynamic manipulations, and also if lower body negative pressure (LBNP) can reverse the VIIP effects. METHODS: Physiologic variables will be examined pre-, in- and post-flight in 10 International Space Station crewmembers including: fluid compartmentalization (D2O and NaBr dilution); interstitial tissue thickness (ultrasound); vascular dimensions and dynamics (ultrasound and MRI (including cerebrospinal fluid pulsatility)); ocular measures (optical coherence tomography, intraocular pressure, ultrasound); and ICP measures (tympanic membrane displacement, otoacoustic emissions). Pre- and post-flight measures will be assessed while upright, supine and during 15 deg head-down tilt (HDT). In-flight measures will occur early and late during 6 or 12 month missions. LBNP will be evaluated as a countermeasure during HDT and during spaceflight. RESULTS: The first two crewmembers are in the preflight testing phase. Preliminary results characterize the acute fluid shifts experienced from upright, to supine and HDT postures (increased stroke volume, jugular dimensions and measures of ICP) which are reversed with 25 millimeters Hg LBNP. DISCUSSION: Initial results indicate that acute cephalad fluid shifts may be related to VIIP symptoms, but also may be reversible by LBNP. The effect of a chronic fluid shift has yet to be evaluated. Learning Objectives: Current spaceflight VIIP research is described, including novel hardware and countermeasures.

  1. Oxygen-regulated mRNAs for light-harvesting and reaction center complexes and for bacteriochlorophyll and carotenoid biosynthesis in Rhodobacter capsulatus during the shift from anaerobic to aerobic growth

    SciTech Connect

    Zhu, Y.S.; Cook, D.N.; Leach, F.; Armstrong, G.A.; Alberti, M.; Hearst, J.E.

    1986-12-01

    The stability and regulation by oxygen of mRNAs for the photosynthetic apparatus in Rhodobacter capsulatus have been studied by using proflavin to inhibit transcription and by shifting cells from anaerobic to aerobic conditions. The results from the inhibition experiments show that the mRNA for the light-harvesting LH-II polypeptides (..beta.., ..cap alpha..) is more stable than that for the light-harvesting LH-I polypeptides (..beta.., ..cap alpha..) during anaerobic growth, whereas the mRNAs for the reaction center polypeptides L (RC-L), M (RC-M), and H (RC-H) are less stable than both the LH-I and LH-II mRNAs. When photosynthetic cells were shifted from anaerobic to aerobic conditions, an immediate decrease in the levels of mRNA for the LH-I, LH-II, RC-L, RC-M, and RC-H proteins was observed. The levels of mRNA for the LH-II proteins, however, is more sensitive to oxygen and is reduced faster than the level of mRNA and for the LH-I proteins. These results suggest that oxygen represses the expression of genes coding for the light-harvesting antenna and reaction center complexes and may selectively accelerate the degradation of mRNA for the LH-II proteins. The mRNAs for several enzymes in the bacteriochlorophyll biosynthetic pathway are regulated by oxygen in a similar manner. The authors found that the amounts of mRNAs for carotenoid biosynthetic enzymes, relative to the amounts of mRNAs for LH and RC, increased during the shift from anaerobic to aerobic conditions. They have particularly shown that although the expression of most photosynthetic genes in R. capsulatus is repressed b oxygen, the ctA gene responds to oxygen in an opposite fashion.

  2. A fully coupled model for water-gas-heat reactive transport with methane oxidation in landfill covers.

    PubMed

    Ng, C W W; Feng, S; Liu, H W

    2015-03-01

    Methane oxidation in landfill covers is a complex process involving water, gas and heat transfer as well as microbial oxidation. The coupled phenomena of microbial oxidation, water, gas, and heat transfer are not fully understood. In this study, a new model is developed that incorporates water-gas-heat coupled reactive transport in unsaturated soil with methane oxidation. Effects of microbial oxidation-generated water and heat are included. The model is calibrated using published data from a laboratory soil column test. Moreover, a series of parametric studies are carried out to investigate the influence of microbial oxidation-generated water and heat, initial water content on methane oxidation efficiency. Computed and measured results of gas concentration and methane oxidation rate are consistent. It is found that the coupling effects between water-gas-heat transfer and methane oxidation are significant. Ignoring microbial oxidation-generated water and heat can result in a significant difference in methane oxidation efficiency by 100%. PMID:25489976

  3. Shifting Sugars and Shifting Paradigms

    PubMed Central

    Siegal, Mark L.

    2015-01-01

    No organism lives in a constant environment. Based on classical studies in molecular biology, many have viewed microbes as following strict rules for shifting their metabolic activities when prevailing conditions change. For example, students learn that the bacterium Escherichia coli makes proteins for digesting lactose only when lactose is available and glucose, a better sugar, is not. However, recent studies, including three PLOS Biology papers examining sugar utilization in the budding yeast Saccharomyces cerevisiae, show that considerable heterogeneity in response to complex environments exists within and between populations. These results join similar recent results in other organisms that suggest that microbial populations anticipate predictable environmental changes and hedge their bets against unpredictable ones. The classical view therefore represents but one special case in a range of evolutionary adaptations to environmental changes that all organisms face. PMID:25688600

  4. The combined effect of rain and wind on air water gas exchange: A feasibility study

    NASA Astrophysics Data System (ADS)

    Ho, David T.; Veron, Fabrice; Harrison, Emily; Bliven, Larry F.; Scott, Nicholas; McGillis, Wade R.

    2007-06-01

    A series of experiments were conducted at University of Delaware's Air-Sea Interaction Laboratory to examine the combined effects of rain and wind on air-water gas exchange. During this study, ASIL WRX I, a combination of 3 rain rates and 4 wind speeds were used, for a total of 12 different environmental conditions. The SF 6 evasion method was used to determine the bulk gas transfer velocities, and airside profiles of wind and CO 2 were used to estimate flux-profiles of momentum and carbon dioxide. In addition to measurements of fluxes with and without rain in a wind-wave boundary layer, measurements of wave properties were also obtained. Rain is shown to alter the wind profile in the flume, and dampen surface waves. Also, SF 6 evasion indicates that with the present experimental setup, for most of the experimental conditions, rain and wind combine linearly to influence air-water gas exchange. Flux-profile relationships for marine atmospheric boundary layers, which were performed to scale up to field measurements, were explored by a comparison between SF 6-derived bulk fluxes and airside CO 2 profile measurements.

  5. The effects of oil viscosity on sweet corrosion in multiphase oil/water/gas horizontal pipelines

    SciTech Connect

    Jepson, W.P.; Menezes, R. [Ohio Univ., Athens, OH (United States)

    1995-10-01

    Experiments were carried out in a 10 cm I.D., three phase oil/water/gas horizontal Plexiglass pipeline. Mixtures of salt water with oils of viscosities 2 cp and 96 cp ranging from 0% to 100% off were used for the liquid phase with carbon dioxide as the gas phase. Results indicate that, for both full pipe flow and slug flow, at each water percentage up to approximately 60%, the corrosion rate increased with off viscosity at each flow condition. Above 60% water, the corrosion rate decreased rapidly to negligible values. In slug flow, the corrosion rate increased with increase in Froude number. This may be attributed to presence of gas at the bottom of the pipe and the higher pressure drops across the slug front at each Froude number.

  6. Combined cycle power plant with integrated coal gasification, CO shift and CO 2 washing

    Microsoft Academic Search

    R. Pruschek; G. Oeljeklaus; V. Brand; G. Haupt; G. Zimmermann; J. S. Ribberink

    1995-01-01

    Studies on CO2 removal from coal-fired power stations indicate that net efficiencies of 40 % are feasible. About 88% of very clean CO2 can be bled off in the gaseous or liquid state of aggregation. This can be achieved with IGCC's employing water gas shift and physical absorption for CO2 separation or, potentially, H2\\/CO2 separation with membranes and the usual

  7. Air-water gas exchange of organochlorine compounds in Lake Baikal, Russia

    SciTech Connect

    McConnell, L.L. [USDA, Beltsville, MD (United States)] [USDA, Beltsville, MD (United States); Kucklick, J.R. [National Marine Fisheries Service, Charleston, SC (United States)] [National Marine Fisheries Service, Charleston, SC (United States); Bidleman, T.F. [Univ. of South Carolina, Columbia, SC (United States)] [Univ. of South Carolina, Columbia, SC (United States); Ivanov, G.P. [Limnological Inst., Irkutsk (Russian Federation)] [Limnological Inst., Irkutsk (Russian Federation); Chernyak, S.M. [Inst. of Fisheries, Moscow (Russian Federation)] [Inst. of Fisheries, Moscow (Russian Federation)

    1996-10-01

    Air and surface water samples were collected at Lake Baikal, Russia, during June 1991 to determine concentrations of organochlorine pesticides and polychlorinated biphenyl (PCB) congeners. These data were combined with Henry`s law constants to estimate the gas flux rate across the air-water interface of each compound class. Air samples were collected at Lake Baikal and from nearby Irkutsk. Water samples were collected from three mid-lake stations and at the mouth of two major tributaries. Average air concentrations of chlorinated bornanes (14 pg m{sup -3}), chlordanes (4.9 pg m{sup -3}), and hexachlorobenzene (HCB) (194 pg m{sup -3}) were similar to global backgound of Arctic levels. However, air concentrations of hexachlorocyclohexanes (HCHs), DDTs, and PCBs were closer to those observed in the Great Lakes region. Significantly higher levels of these three compound classes in air over Irkutsk suggests that regional atmospheric transport and deposition may be an important source of these persistent compounds to Lake Baikal. Air-water gas exchange calculations resulted in net depositional flux values for {alpha}-HCH, {gamma}-HCH, DDTs, and chlorinated bornanes at 112, 23, 3.6, and 2.4 ng m{sup -2} d{sup -1}, respectively. The total net flux of 22 PCB congeners, chlordanes, and HCB was from water to air (volatilization) at 47, 1.8, and 32 ng m{sup -2} d{sup -1}, respectively. 50 refs., 7 figs., 5 tabs.

  8. Gear shift control mechanism

    SciTech Connect

    Janson, D.A.

    1987-03-10

    A gear shift control mechanism is described comprising: multiple shift rods directed substantially parallel to one another, each rod carrying a shift fork for axial movement; a shift lever supported for pivotal movement about a first axis directed parallel to the axes of the shift rods and for pivotal movement about a second axis directed substantially perpendicular to the axes of the shift rods. The lever is moveable about the first axis and the second axis into engagement with a selected shift fork; interlock means located on each lateral side of the shift lever and mounted for pivotal movement about the first axis for blocking engagement with the shift forks; detent means for holding the shift lever in multiple predetermined angular positions about the second axis; and spring means located on a lateral side of the shift lever and mounted for pivotal movement about the first axis into interference contact with the shift forks for producing a force tending to resiliently bias the shift lever out of engagement with the selected shift fork.

  9. RSFQ circular shift registers

    Microsoft Academic Search

    Cess A. Mancini; Nada Vukovic; Andrea M. Herr; Kris Gaj; Mark F. Bocko; Marc J. Feldman

    1997-01-01

    The circular shift register is a versatile building block for RSFQ digital circuits. It can be used for local memory and it is essential for the proposed implementation of residue number system arithmetic. It is surprising that the successful recurrent operation of such a shift register has never been reported m the RSFQ literature. Circular shift registers have a design

  10. High Water?Gas Shift Activity in TiO2(110) Supported Cu and Au Nanoparticles: Role of the Oxide and Metal Particle Size

    SciTech Connect

    Rodriguez, J.; Evans, J; Graciani, J; Park, J; Liu, P; Hrbek, J; Sanz, J

    2009-01-01

    The deposition of Cu and Au nanoparticles on TiO{sub 2}(110) produces very good catalysts for the WGS. Although bulk metallic gold is not active as a WGS catalyst, Au nanoparticles supported on TiO{sub 2}(110) have an activity comparable to that of Cu/ZnO(000). Cu/TiO{sub 2}(110) is clearly a better catalyst than Cu/ZnO(000) or Au/TiO{sub 2}(110). The catalysts that have the highest activity for the WGS have also the lowest apparent activation energy. On Cu(111) and Cu(100), the aparent activation energies are 18.1 and 15.2 kcal/mol, respectively. The apparent activation energy decreases to 12.4 kcal/mol on Cu/ZnO(000), 10.2 on Au/TiO{sub 2}(110), and 8.3 kcal/mol on Cu/TiO{sub 2}(110). The Cu {leftrightarrow} titania interactions are substantially stronger than the Au {leftrightarrow} titania interactions. This has an effect on the growth mode of the metals on TiO{sub 2}(110). In images of scanning tunneling miscroscopy, the average particle size in Cu/TiO{sub 2}(110) is smaller than that in Au/TiO{sub 2}(110). The Cu particles are dispersed on the terraces and steps of the oxide surface, whereas the Au particles concentrate on the steps. The morphology of Cu/TiO{sub 2}(110) favors high catalytic activity. The results of density functional calculations indicate that the metal?oxide interface plays an essential role in the catalysis, helping in the dissociation of water and in the formation of an OCOH intermediate, which decomposes to yield CO{sub 2} and hydrogen.

  11. Slurry phase Fischer-Tropsch synthesis: Cobalt plus a water-gas shift catalyst. [Quarterly] report, October 1, 1989--December 31, 1989

    SciTech Connect

    Yates, I.C.; Satterfield, C.N.

    1989-12-31

    The rate of synthesis gas consumption over a cobalt FischerTropsch catalyst was measured in a well-mixed, continuous-flow, slurry reactor at 220 to 240{degrees}C, 0.5 to 1.5 MPa, H{sub 2}/CO feed ratios of 1.5 to 3.5 and conversions of 7 to 68% of hydrogen and 11 to 73% of carbon monoxide. The inhibiting effect of carbon monoxide was determined quantitatively and a Langmuir-Hinshelwood-type equation of the following form was found to best represent the results: -R{sub H{sub 2+Co}} = (a P{sub CO}P{sub H{sub 2}})/(1 + b P{sub CO}){sup 2}. The apparent activation energy was 93 to 95 kJ/mol. Data from previous studies on cobalt-based Fischer-Tropsch catalysts are also well correlated with this rate expression.

  12. REPRESENTATIONS OF SHIFTED YANGIANS

    Microsoft Academic Search

    JONATHAN BRUNDAN; ALEXANDER KLESHCHEV

    We study highest weight representations of shifted Yangians over an algebraically closed field of characteristic 0. In particular, we classify the finite dimensional irreducible representations and explain how to compute their Gelfand- Tsetlin characters in terms of known characters of standard modules and certain Kazhdan-Lusztig polynomials. Our approach exploits the relationship between shifted Yangians and the finite W-algebras associated to

  13. Generalized minimum shift keying

    NASA Astrophysics Data System (ADS)

    Korn, I.

    1980-03-01

    A generalized minimum shift keying (GMSK) signal is defined, and its equivalence to a modified offset quadrature shift keying signal is shown. A simple formula for the spectrum of a GMSK signal is presented and the spectrum and out-of-band power are computed for two examples.

  14. Gasification of biomass in water\\/gas-stabilized plasma for syngas production

    Microsoft Academic Search

    M. Hrabovsky; M. Konrad; V. Kopecky; M. Hlina; T. Kavka; G. van Oost; E. Beeckman; B. Defoort

    2006-01-01

    The experimental reactor PLASGAS for plasma pyrolysis and vitrification equipped with the hybrid gas-water stabilized torch\\u000a was used in the experiments. The plasma torch is characterized by low density, high temperature plasma with very low mass\\u000a flow rates and high enthalpy. High plasma enthalpy is advantageous for adjustment of higher reaction temperatures with high\\u000a energy efficiency. Gasification of biomass was

  15. Molecular Electronic Shift Registers

    NASA Technical Reports Server (NTRS)

    Beratan, David N.; Onuchic, Jose N.

    1990-01-01

    Molecular-scale shift registers eventually constructed as parts of high-density integrated memory circuits. In principle, variety of organic molecules makes possible large number of different configurations and modes of operation for such shift-register devices. Several classes of devices and implementations in some specific types of molecules proposed. All based on transfer of electrons or holes along chains of repeating molecular units.

  16. Strategies for improving the performance and stability of Ni-based catalysts for reforming reactions.

    PubMed

    Li, Shuirong; Gong, Jinlong

    2014-11-01

    Owing to the considerable publicity that has been given to petroleum related economic, environmental, and political problems, renewed attention has been focused on the development of highly efficient and stable catalytic materials for the production of chemical/fuel from renewable resources. Supported nickel nanoclusters are widely used for catalytic reforming reactions, which are key processes for generating synthetic gas and/or hydrogen. New challenges were brought out by the extension of feedstock from hydrocarbons to oxygenates derivable from biomass, which could minimize the environmental impact of carbonaceous fuels and allow a smooth transition from fossil fuels to a sustainable energy economy. This tutorial review describes the recent efforts made toward the development of nickel-based catalysts for the production of hydrogen from oxygenated hydrocarbons via steam reforming reactions. In general, three challenges facing the design of Ni catalysts should be addressed. Nickel nanoclusters are apt to sinter under catalytic reforming conditions of high temperatures and in the presence of steam. Severe carbon deposition could also be observed on the catalyst if the surface carbon species adsorbed on metal surface are not removed in time. Additionally, the production of hydrogen rich gas with a low concentration of CO is a challenge using nickel catalysts, which are not so active in the water gas shift reaction. Accordingly, three strategies were presented to address these challenges. First, the methodologies for the preparation of highly dispersed nickel catalysts with strong metal-support interaction were discussed. A second approach-the promotion in the mobility of the surface oxygen-is favored for the yield of desired products while promoting the removal of surface carbon deposition. Finally, the process intensification via the in situ absorption of CO2 could produce a hydrogen rich gas with low CO concentration. These approaches could also guide the design of other types of heterogeneous base-metal catalysts for high temperature processes including methanation, dry reforming, and hydrocarbon combustion. PMID:25182070

  17. Emission spectroscopy of a microhollow cathode discharge plasma in helium-water gas mixtures

    SciTech Connect

    Namba, S.; Yamasaki, T.; Hane, Y.; Fukuhara, D.; Kozue, K.; Takiyama, K. [Graduate School of Engineering, Hiroshima University, 1-4-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8527 (Japan)

    2011-10-01

    A dc microhollow cathode discharge (MHCD) plasma was generated inflowing helium gas containing water vapor. The cathode hole diameters were 0.3, 0.7, 1.0, and 2.0 mm, each with a length of 2.0 mm. Emission spectroscopy was carried out to investigate the discharge mode and to determine the plasma parameters. For the 0.3-mm cathode, stable MHCDs in an abnormal glow mode existed at pressures up to 100 kPa, whereas for larger diameters, a plasma was not generated at atmospheric pressure. An analysis of the lineshapes relevant to He at 667.8 nm and to H{alpha} at 656.3 nm implied an electron density and gas temperature of 2 x 10{sup 14} cm{sup -3} and 1100 K, respectively, for a 100-kPa discharge in the negative glow region. The dependence of the OH band, and H{alpha} intensities on the discharge current exhibited different behaviors. Specifically, the OH spectrum had a maximum intensity at a certain current, while the H atom intensity kept increasing with the discharge current. This observation implies that a high concentration of OH radicals results in quenching, leading to the production of H atoms via the reaction OH + e{sup -}{yields} O + H + e{sup -}.

  18. The origin of the "snap-in" in the force curve between AFM probe and the water/gas interface of nanobubbles.

    PubMed

    Song, Yang; Zhao, Binyu; Zhang, Lijuan; Lü, Junhong; Wang, Shuo; Dong, Yaming; Hu, Jun

    2014-02-24

    The long-range attractive force or "snap-in" is an important phenomenon usually occurring when a solid particle interacts with a water/gas interface. By using PeakForce quantitative nanomechanics the origin of snap-in in the force curve between the atomic force microscopy (AFM) probe and the water/gas interface of nanobubbles has been investigated. The snap-in frequently happened when the probe was preserved for a certain time or after being used for imaging solid surfaces under atmospheric conditions. In contrast, imaging in liquids rarely induced a snap-in. After a series of control experiments, it was found that the snap-in can be attributed to hydrophobic interactions between the water/gas interface and the AFM probe, which was either modified or contaminated with hydrophobic material. The hydrophobic contamination could be efficiently removed by a conventional plasma-cleaning treatment, which prevents the occurring of the snap-in. In addition, the adsorption of sodium dodecyl sulfate onto the nanobubble surface changed the water/gas interface into hydrophilic, which also eliminated the snap-in phenomenon. PMID:24478257

  19. VOLUME 85, NUMBER 9 P H Y S I C A L R E V I E W L E T T E R S 28 AUGUST 2000 Turbulence and Wave Breaking Effects on Air-Water Gas Exchange

    E-print Network

    Fineberg, Jay

    -made systems. For instance, in waste water treatment where bioremediation is used in large man-made water Breaking Effects on Air-Water Gas Exchange Evelyn J. Boettcher,1 Jay Fineberg,1,2 and Daniel P. Lathrop1 1 gravity waves on air-water gas exchange in standing waves. We identify two regimes that govern aeration

  20. In-Cylinder Reaction Chemistry and Kinetics During Negative Valve Overlap Fuel Injection Under Low-Oxygen Conditions

    SciTech Connect

    Kalaskar, Vickey B [ORNL] [ORNL; Szybist, James P [ORNL] [ORNL; Splitter, Derek A [ORNL] [ORNL; Pihl, Josh A [ORNL] [ORNL; Gao, Zhiming [ORNL] [ORNL; Daw, C Stuart [ORNL] [ORNL

    2013-01-01

    Fuel injection into the negative valve overlap (NVO) period is a common method for controlling combustion phasing in homogeneous charge compression ignition (HCCI) as well as other forms of advanced combustion. During this event, at least a portion of the fuel hydrocarbons can be converted to products containing significant levels of H2 and CO, as well as other short chain hydrocarbons by means of thermal cracking, water-gas shift, and partial oxidation reactions, depending on the availability of oxygen and the time-temperature-pressure history. The resulting products alter the autoignition properties of the combined fuel mixture for HCCI. Fuel-rich chemistry in a partial oxidation environment is also relevant to other high efficiency engine concepts (e.g., the dedicated EGR (D-EGR) concept from SWRI). In this study, we used a unique 6-stroke engine cycle to experimentally investigate the chemistry of a range of fuels injected during NVO under low oxygen conditions. Fuels investigated included iso-octane, iso-butanol, ethanol, and methanol. Products from NVO chemistry were highly dependent on fuel type and injection timing, with iso-octane producing less than 1.5% hydrogen and methanol producing more than 8%. We compare the experimental trends with CHEMKIN (single zone, 0-D model) predictions using multiple kinetic mechanisms available in the current literature. Our primary conclusion is that the kinetic mechanisms investigated are unable to accurately predict the magnitude and trends of major species we observed.

  1. Ambiguous Red Shifts

    E-print Network

    Carl E. Wulfman

    2010-10-11

    A one-parameter conformal invariance of Maxwell's equations allows the wavelengths of electromagnetic waves to change as they propagate, and do so even in otherwise field-free space. This produces an ambiguity in interpretations of stellar red shifts. Experiments that will determine the value of the group parameter, and thereby remove the ambiguity, are proposed. They are based on an analysis of the anomalous frequency shifts uncovered in the Pioneer 10 and 11 spacecraft studies, and physical interpretation of an isomorphism discovered by E. L. Hill. If the group parameter is found to be non-zero, Hubble's relations will have to be reinterpreted and space-time metrics will have to be altered. The cosmological consequences of the transformations are even more extensive because, though they change frequencies, they do not alter the energy and momentum conservations laws of classical and quantum-electrodynamical fields established by Cunningham and by Bialynicki-Birula.

  2. [Shifting path of industrial pollution gravity centers and its driving mechanism in Pan-Yangtze River Delta].

    PubMed

    Zhao, Hai-Xia; Jiang, Xiao-Wei; Cui, Jian-Xin

    2014-11-01

    Shifting path of industrial pollution gravity centers is the response of environmental special formation during the industry transfer process, in order to prove the responding of industrial pollution gravity centers to industry transfer in economically developed areas, this paper calculates the gravity centers of industrial wastewater, gas and solid patterns and reveals the shifting path and its driving mechanism, using the data of industrial pollution in the Pan-Yangtze River Delta from 2000 to 2010. The results show that the gravity center of the industrial waste in Pan-Yangtze River Delta shifts for sure in the last 10 years, and gravity center of solid waste shifts the maximum distance within the three wastes, which was 180.18 km, and shifting distances for waste gas and waste water were 109.51 km and 85.92 km respectively. Moreover, the gravity center of the industrial waste in Pan-Yangtze River Delta shifts westwards, and gravity centers of waste water, gas and solid shift for 0.40 degrees, 0.17 degrees and 0.03 degrees respectively. The shifting of industrial pollution gravity centers is driven by many factors. The rapid development of the heavy industry in Anhui and Jiangxi provinces results in the westward shifting of the pollutions. The optimization and adjustment of industrial structures in Yangtze River Delta region benefit to alleviating industrial pollution, and high-polluting industries shifted to Anhui and Jiangxi provinces promotes pollution gravity center shifting to west. While the development of massive clean enterprise, strong environmental management efforts and better environmental monitoring system slow the shifting trend of industrial pollution to the east in Yangtze River Delta. The study of industrial pollution gravity shift and its driving mechanism provides a new angle of view to analyze the relationship between economic development and environmental pollution, and also provides academic basis for synthetical management and control of environmental pollution in Pan-Yangtze River Delta, especially in the transition period. PMID:25639121

  3. Seasonal microbial community shift in a saline sewage treatment plant

    Microsoft Academic Search

    Qingmei Yan; Xuxiang Zhang; Tong Zhang; Herbert H. P. Fang

    2011-01-01

    Activated sludge was monthly sampled from a saline sewage treatment plant of Hong Kong (China) during June 2007 to May 2008\\u000a to analyze the microbial community shift along with environmental variations using denaturing gradient gel electrophoresis\\u000a of polymerase chain reaction amplified 16S rDNA fragments. Environmental changes resulted into a seasonal microbial community\\u000a shift characterized by alterations in species number and

  4. Strong shift equivalence theory and the shift equivalence problem

    Microsoft Academic Search

    J. B. WAGONER

    1999-01-01

    This paper discusses strong shift equivalence and counterexamples to the long standing Shift Equivalence Problem in symbolic dynamics. We also discuss how strong shift equivalence theory is closely related to areas of mathematics outside dynamics such as algebraic K-theory, cyclic homology, and topological quantum eld theory.

  5. Shifting Times Tables

    NSDL National Science Digital Library

    This activity provides students with an opportunity to recognize arithmetic sequences and at the same time reinforces identifying multiples. The interactivity displays five numbers and the student must discover the times table pattern and the numerical shift. On Levels 1 and 2, the first five numbers in the sequence are given and on Levels 3 and 4, the numbers given could be any five numbers in the sequence. The Teachers' Notes page offers rationale, suggestions for implementation, discussion questions, ideas for extension and support.

  6. Lamb Shift for static atoms outside a Schwarzschild black hole

    E-print Network

    Wenting Zhou; Hongwei Yu

    2010-11-07

    We study, by separately calculating the contributions of vacuum fluctuations and radiation reaction to the atomic energy level shift, the Lamb shift of a static two-level atom interacting with real massless scalar fields in the Boulware, Unruh and Hartle-Hawking vacuums outside a Schwarzschild black hole. We find that in the Boulware vacuum, the Lamb shift gets a correction arising as a result of the backscattering of vacuum field modes off the space-time curvature, which is reminiscent of the correction to the Lamb shift induced by the presence of cavities. However, when the Unruh and Hartle-Hawking vacua are concerned, our results show that the Lamb shift behaves as if the atom were irradiated by a thermal radiation or immersed in a thermal bath at the Hawking temperature, depending on whether the scalar field is in the Unruh or the Hartle-Hawking vacuum. Remarkably, the thermal radiation is always backscattered by the space-time geometry.

  7. Radiation reaction in quantum mechanics

    E-print Network

    Atsushi Higuchi

    1998-12-15

    The Lorentz-Dirac radiation reaction formula predicts that the position shift of a charged particle due to the radiation reaction is of first order in acceleration if it undergoes a small acceleration. A semi-classical calculation shows that this is impossible at least if the acceleration is due to a time-independent potential. Thus, the Lorentz-Dirac formula gives an incorrect classical limit in this situation. The correct classical limit of the position shift at the lowest order in acceleration is obtained by assuming that the energy loss at each time is given by the Larmor formula.

  8. Shifted nondiffractive Bessel beams

    NASA Astrophysics Data System (ADS)

    Kovalev, Alexey A.; Kotlyar, Victor V.; Porfirev, Alexey A.

    2015-05-01

    Nondiffractive Bessel beams are well known to have infinite energy and infinite orbital angular momentum (OAM). However, when normalized to unity of energy, their OAM is finite. In this work, we derive an analytical relationship for calculating the normalized OAM of the superposition of off-axis Bessel beams characterized by the same topological charge. We show that if the constituent beams of the superposition have real-valued weight coefficients, the total OAM of the superposition of the Bessel beams equals that of an individual nonshifted Bessel beam. This property enables generating nondiffractive beams with different intensity distributions but identical OAM. The superposition of a set of identical Bessel beams centered on an arbitrary-radius circle is shown to be equivalent to an individual constituent Bessel beam put in the circle center. As a result of a complex shift of the Bessel beam, the transverse intensity distribution and OAM of the beam are also shown to change. We show that, in the superposition of two or more complex-shifted Bessel beams, the OAM may remain unchanged, while the intensity distribution is changed. Numerical simulation is in good agreement with theory.

  9. Transmission shift control assembly

    SciTech Connect

    Dzioba, D.L.

    1989-04-18

    This patent describes a transmission shift control assembly mounted on a steering column having a longitudinal axis comprising: bracket means secured to the steering column; transmission shift cable means having a portion secured to the bracket means and a portion linearly movable relative to the secured portion; mounting means on the bracket cable drive arm means having an axis and being rotatably mounted on the rotary axis on the mounting means oblique to the longitudinal axis and including a cable connecting portion secured to the movable portion of the cable means and lever mounting means adjacent the mounting means; operator control means including lever means, pin means for pivotally mounting the lever means on the lever mounting means on an axis substantially perpendicular to the rotary axis and positioning arm means formed on the lever means and extending from the pin means; and detent gate means disposed on the bracket means in position to abut the positioning arm means for limiting the extent of pivotal movement of the lever means.

  10. Hydraulically actuated well shifting tool

    SciTech Connect

    Roth, B.A.

    1992-10-20

    This patent describes a hydraulically actuated shifting tool for actuating a sliding member in a well tool. It comprises: a housing having a hydraulic fluid bore therein; shifting dog means positioned on the housing for movement away and toward the housing; locking dog means positioned on the housing for movement away and toward the body; shifting dog hydraulic actuating means in fluid communication with the bore for causing engagement of the shifting dogs with the sliding member; locking dog hydraulic actuating means in communication with the bore for causing engagement of the locking dogs with the locking means; and hydraulic shifting means in communication with the bore for causing relative movement between the shifting dog means and the locking dog means for shifting the sliding sleeve.

  11. Phase shifting interferometer

    DOEpatents

    Sommargren, Gary E. (Santa Cruz, CA)

    1999-01-01

    An interferometer which has the capability of measuring optical elements and systems with an accuracy of .lambda./1000 where .lambda. is the wavelength of visible light. Whereas current interferometers employ a reference surface, which inherently limits the accuracy of the measurement to about .lambda./50, this interferometer uses an essentially perfect spherical reference wavefront generated by the fundamental process of diffraction. Whereas current interferometers illuminate the optic to be tested with an aberrated wavefront which also limits the accuracy of the measurement, this interferometer uses an essentially perfect spherical measurement wavefront generated by the fundamental process of diffraction. This interferometer is adjustable to give unity fringe visibility, which maximizes the signal-to-noise, and has the means to introduce a controlled prescribed relative phase shift between the reference wavefront and the wavefront from the optics under test, which permits analysis of the interference fringe pattern using standard phase extraction algorithms.

  12. Phase shifting diffraction interferometer

    DOEpatents

    Sommargren, Gary E. (Santa Cruz, CA)

    1996-01-01

    An interferometer which has the capability of measuring optical elements and systems with an accuracy of .lambda./1000 where .lambda. is the wavelength of visible light. Whereas current interferometers employ a reference surface, which inherently limits the accuracy of the measurement to about .lambda./50, this interferometer uses an essentially perfect spherical reference wavefront generated by the fundamental process of diffraction. This interferometer is adjustable to give unity fringe visibility, which maximizes the signal-to-noise, and has the means to introduce a controlled prescribed relative phase shift between the reference wavefront and the wavefront from the optics under test, which permits analysis of the interference fringe pattern using standard phase extraction algorithms.

  13. In situ Characterization of Pt Catalysts Supported on Ceria Modified TiO(2) for the WGS reaction: Influence of Ceria Loading

    SciTech Connect

    Rodriguez J. A.; Barrio, L.; Zhou, G.; Gonzalez, I.D.; Estrella, M.; Hanson, J.; Navarro, R.M.; Fierro, J.L.G.

    2012-01-01

    This work analyzes the influence of cerium content (6-15 wt%) on a TiO{sub 2} support over the structure and water gas shift (WGS) activity of Pt catalysts. The structural properties of these Pt/Ce-TiO{sub 2} catalysts were characterized by XRD, TEM and XANES. Physicochemical characterization of the catalysts showed differences in the structure and dispersion of Ce entities on the support with Ce loading. For the samples with low ceria content (6 wt%), cerium is deposited on the support in the form of CeO{sub x} clusters in a highly dispersed state in close interaction with the Ti atoms. The formation of CeO{sub x} clusters at low Ce-loading on the support facilitates the dispersion of small particles of Pt and improves the reducibility of ceria component at low temperatures. The changes in platinum dispersion and support reducibility with Ce-loading on the TiO{sub 2} support lead to significant differences in the WGS activity. Pt supported on the sample with lower Ce content (6 wt%) shows better activity than those corresponding to catalysts with higher Ce content (15 wt%). Activity measurements coupled with catalysts characterization suggest that the improvement in the reducibility of the support with lower Ce content was associated with the presence of CeO{sub x} clusters of high reducibility that improve the chemical activity of the oxide-metal interfaces at which the WGS reaction takes place.

  14. The influence of nano-architectured CeOx supports in RhPd/CeO? for the catalytic ethanol steam reforming reaction

    DOE PAGESBeta

    Divins, N. J.; Senanayake, S. D.; Casanovas, A.; Xu, W.; Trovarelli, A.; Llorca, J.

    2015-09-01

    The ethanol steam reforming (ESR) reaction has been tested over RhPd supported on polycrystalline ceria in comparison to structured supports composed of nanoshaped CeO? cubes and CeO? rods tailored towards the production of hydrogen. At 650-700 K the hydrogen yield follows the trend RhPd/CeO?-cubes > RhPd/CeO? -rods > RhPd/CeO?- polycrystalline, whereas at temperatures higher than 800 K the catalytic performance of all samples is similar and close to the thermodynamic equilibrium. The improved performance of RhPd/CeO?-cubes and RhPd/CeO? -rods for ESR at low temperature is mainly ascribed to higher water-gas shift activity and a strong interaction between the bimetallic -more »oxide support interaction. STEM analysis shows the existence of RhPd alloyed nanoparticles in all samples, with no apparent relationship between ESR performance and RhPd particle size. X-ray diffraction under operating conditions shows metal reorganization on {100} and {110} ceria crystallographic planes during catalyst activation and ESR, but not on {111} ceria crystallographic planes. The RhPd reconstructing and tuned activation over ceria nanocubes and nanorods is considered the main reason for better catalytic activity with respect to conventional catalysts based on polycrystalline ceria« less

  15. Possible surface reactions on Mars - Implications for Viking biology results

    NASA Technical Reports Server (NTRS)

    Ponnamperuma, C.; Shimoyama, A.; Yamada, M.; Hobo, T.; Pal, R.

    1977-01-01

    The results of two of the three biology experiments carried out on the Viking Mars landers have been simulated. The mixture of organic compounds labeled with carbon-14 used on Mars released carbon dioxide containing carbon-14 when reacted with a simulated Martian surface and atmosphere exposed to ultraviolet light (labeled release experiment). Oxygen was released when metal peroxides or superoxides were treated with water (gas exchange experiment). The simulations suggest that the results of these two Viking experiments can be explained on the basis of reactions of the Martian surface and atmosphere.

  16. Chemical Reactions

    NSDL National Science Digital Library

    National Science Teachers Association (NSTA)

    2009-05-01

    We don't often stop to think about it, but underlying many of our everyday activities are chemical reactions. From the cooking of an egg to the growth of a child, chemical reactions make things happen. Although many of the reactions that support our lives

  17. Portable shift register

    SciTech Connect

    Halbig, J.K.; Bourret, S.C.; Hansen, W.J.; Hicks, D.V.; Klosterbuer, S.F.; Krick, M.S.

    1994-01-01

    An electronics package for a small, battery-operated, self-contained, neutron coincidence counter based on a portable shift-register (PSR) has been developed. The counter was developed for applications not adequately addressed by commercial packages, including in-plant measurements to demonstrate compliance with regulations (domestic and international), in-plant process control, and in-field measurements (environmental monitoring or safeguards). Our package's features, which address these applications, include the following: Small size for portability and ease of installation;battery or mains operation; a built-in battery to power the unit and a typical detector such as a small sample counter, for over 6 h if power lines are bad or noisy, if there is a temporary absence of power, or if portability is desired; complete support, including bias, for standard neutron detectors; a powerful communications package to easily facilitate robust external control over a serial port; and a C-library to simplify creating external control programs in computers or other controllers. Whereas the PSR specifically addresses the applications mentioned above, it also performs all the measurements made by previous electronics packages for neutron coincidence counters developed at Los Alamos and commercialized. The PSR electronics package, exclusive of carrying handle, is 8 by 10 by 20 cm; it contains the circuit boards, battery, and bias supply and weighs less than 2 kg. This instrument package is the second in an emerging family of portable measurement instruments being developed; the first was the Miniature and Modular Multichannel Analyzer (M[sup 3]CA). The PSR makes extensive use of hardware and software developed for the M[sup 3]CA; like the M[sup 3]CA, it is intended primarily for use with an external controller interfaced over a serial channel.

  18. Nonlocality in deuteron stripping reactions.

    PubMed

    Timofeyuk, N K; Johnson, R C

    2013-03-15

    We propose a new method for the analysis of deuteron stripping reactions, A(d,p)B, in which the nonlocality of nucleon-nucleus interactions and three-body degrees of freedom are accounted for in a consistent way. The model deals with equivalent local nucleon potentials taken at an energy shifted by ?40??MeV from the "E(d)/2" value frequently used in the analysis of experimental data, where E(d) is the incident deuteron energy. The "E(d)/2" rule lies at the heart of all three-body analyses of (d, p) reactions performed so far with the aim of obtaining nuclear structure properties such as spectroscopic factors and asymptotic normalization coefficients that are crucial for our understanding of nuclear shell evolution in neutron- and proton-rich regions of the nuclear periodic table and for predicting the cross sections of stellar reactions. The large predicted shift arises from the large relative kinetic energy of the neutron and proton in the incident deuteron in those components of the n+p+A wave function that dominate the (d, p) reaction amplitude. The large shift reduces the effective d-A potentials and leads to a change in predicted (d, p) cross sections, thus affecting the interpretation of these reactions in terms of nuclear structure. PMID:25166525

  19. Decrease in carbonyl sulfide in the feed to Claus converters by shift catalysts

    SciTech Connect

    Gens, T.A. (BOC Group Technical Center, Murray Hill, NJ (United States))

    1994-07-01

    The principal reaction in the burner in a Claus plant is the combustion of part of the hydrogen sulfide to form sulfur dioxide, which can react with more hydrogen sulfide to form sulfur. Alumina or commercial shift catalysts were used downstream of a Claus burner to shift carbon monoxide to carbon dioxide before it could react to form carbonyl sulfide. The shift catalysts were effective in preventing formation of carbonyl sulfide, thereby decreasing sulfur losses.

  20. Study of the Suitability of a Pt-Based Catalyst for the Upgrading of a Biomass Gasification Syngas Stream via the WGS Reaction

    Microsoft Academic Search

    M. Maroño; J. M. Sánchez; E. Ruiz; A. Cabanillas

    2008-01-01

    In this article, the catalytic activity of a Pt-based water gas shift (WGS) catalyst is presented. The experimental study\\u000a has been conducted under realistic conditions typical of pressurised oxygen gasification. The effect of temperature, space\\u000a velocity, steam to carbon monoxide ratio, and gas composition on the performance of the catalyst is investigated. Despite\\u000a the high CO content in the feed

  1. Production of Synthetic Fuels by Co-Electrolysis of Steam and Carbon Dioxide

    Microsoft Academic Search

    Sune Dalgaard Ebbesen; Christopher Graves; Mogens Mogensen

    2009-01-01

    Co-electrolysis of H2O and CO2 was studied in solid oxide cells (SOCs) supported by nickel-\\/yittria-stabilized zirconia (Ni\\/YSZ) electrode. Polarization characterization indicates that electrochemical reduction of both CO2 and H2O occurs during co-electrolysis. In parallel with the electrochemical reactions, the equilibrium of the water–gas shift reaction is reached, and moreover, CO is produced via the water–gas shift reaction. The degradation observed

  2. Refining the shifted topological vertex

    SciTech Connect

    Drissi, L. B.; Jehjouh, H.; Saidi, E. H. [Faculte des Sciences, Laboratory/UFR-Physique des Hautes Energies, Rabat, 1014 (Morocco); Groupement National de Physique des Hautes Energies (GNPHE), Siege focal:FS, Rabat, 1014 (Morocco)

    2009-01-15

    We study aspects of the refining and shifting properties of the 3d MacMahon function C{sub 3}(q) used in topological string theory and BKP hierarchy. We derive the explicit expressions of the shifted topological vertex S{sub {lambda}}{sub {mu}}{sub {nu}}(q) and its refined version T{sub {lambda}}{sub {mu}}{sub {nu}}(q,t). These vertices complete results in literature.

  3. Named Reactions

    NSDL National Science Digital Library

    This Web site lists 95 of the most important named reactions in organic chemistry. Each is linked to a Web page that gives the primary reference and equations for one or more recent literature examples that illustrate the use of the reaction.

  4. Reaction Time

    NSDL National Science Digital Library

    New York Hall of Science

    1999-01-01

    In this activity, learners explore reaction time and challenge themselves to improve their coordination. Do you want to move faster? Catch that ball that you never seem to see in time? Use a simple test to help you improve your reaction (or response) time.

  5. Chemical Reactions

    NSDL National Science Digital Library

    Mrs. Hicken

    2009-05-04

    We are going go over a general view of reactions to prepare us for our unit on Chemical Reactions! Have fun learning! WARNING: If you are caught looking at ANY other site, without permission, you will be sent to the ALC, and you will not participate in any other computer activities for the rest of the year. Get your worksheet and begin! Overview Take this quiz and have me come over and sign off on your worksheet when you have completed the quiz! Overview Quiz Next let's take a look at what effect the rate of a chemical reaction. Rates of Reactions Another quiz, another check off by me! Rates of Reactions Quiz Now how do we measure how fast a ...

  6. Local $^4$He--p potentials from RGM phase shifts

    E-print Network

    S. G. Cooper; R. S. Mackintosh; A. Csoto; R. G. Lovas

    1993-09-06

    Phase shifts for $\\alpha$ + nucleon scattering generated by a multichannel RGM model of the five-nucleon system are subjected to iterative-perturbative ``mixed-case" inversion for energies below the reaction threshold. The resulting phase-equivalent potentials are compared with local potentials calculated from the inversion of empirical phase shifts. A strong similarity is revealed between the two sets of potentials, most notably in the description by a parity- and energy-dependent local potential. In particular, the RGM-derived and empirical potentials share a distinctive form of parity dependence in which the odd-parity component is of greater radial extent. Comparison with potentials representing single-channel RGM phase shifts exhibits the importance of the coupled channels in terms of local potentials. The relative wave functions derived from RGM are very different to those for the phase-equivalent local potentials.

  7. Kinetic isotopic fractionation during air-water gas transfer of O[sub 2], N[sub 2], CH[sub 4], and H[sub 2

    SciTech Connect

    Knox, M. (NOAA Atlantic Oceanographic and Meteorological Lab., Miami, FL (United States)); Quay, P.D.; Wilbur, D. (Univ. of Washington, Seattle (United States))

    1992-12-15

    The authors present experimental results that show that the kinetic isotopic fractionation during gas exchange is 0.9972 [plus minus] 0.0002 for oxygen, 0.9992 [plus minus] 0.0002 for methane, 0.9987 [plus minus] 0.0001 for nitrogen and 0.982 [plus minus] 0.002 for hydrogen, and that the equilibrium fractionation between water and gas phases is 1.037 for hydrogen. They show that the isotopic fractionation during gas transfer for these gases is not equal to the square root of their reduced mass in water, as would be predicted by an extension of the kinetic theory of ideal gases to dissolved gases. The use of isotopes as tracers of biogeochemical gases requires knowledge of the fractionation factor for air-water gas transfer; there have been few direct measurements of these factors. 31 refs., 11 figs., 1 tab.

  8. Enzyme Reactions

    NSDL National Science Digital Library

    Maryland Virtual High School

    The enzyme reaction rate activity allows students to simulate the effects of variables such as temperature and pH on the reaction rate of the enzyme catalase. This computer simulation is best used after the students have done a wet lab experiment. The value of the simulation is that it requires the students to interpret and analyze the graphical representation of data and it enables the running of mutiple experiments in a short amount of time.

  9. Shift control mechanism for a manual transmission

    SciTech Connect

    Gugin, D.G.

    1991-08-06

    This patent describes a shift control mechanism for a manual transmission having a transmission gear housing and a manual shift selecting lever. It comprises a shift selecting shaft mounted within the transmission gear housing for rotation and axial translation in response to selective manipulation of the shift selecting lever; a shift sleeve supported from the transmission gear housing; an actuating member secured to the shift selecting shaft for rotation and axial translation with the shift selecting shaft; synchronizer assemblies; the actuating member individually operating the synchronizer assemblies in response to selected manipulation of the shift selecting lever; alignment guide means interactive between the shift selecting shaft and the transmission gear housing to permit axial translation of the shift selecting shaft only when the shift selecting shaft has been rotated to align a locator means with a locating means.

  10. Broadband optical serrodyne frequency shifting.

    PubMed

    Johnson, D M S; Hogan, J M; Chiow, S-w; Kasevich, M A

    2010-03-01

    We demonstrate serrodyne frequency shifting of light from 200 MHz to 1.2 GHz with an efficiency of better than 60%. The frequency shift is imparted by an electro-optic phase modulator driven by a high-frequency high-fidelity sawtooth waveform that is passively generated by a commercially available nonlinear transmission line. We also implement a push-pull configuration using two serrodyne-driven phase modulators, allowing for continuous tuning between -1.6 GHz and +1.6 GHz. Compared with competing technologies, this technique is simple and robust, and it offers the largest available tuning range in this frequency band. PMID:20195339

  11. Illinois Shifting Gears Policy Evaluation

    ERIC Educational Resources Information Center

    Weitzel, Peter C.

    2009-01-01

    Illinois Shifting Gears is a multilevel initiative that has simultaneously created bridge programs in the field and altered state policy to facilitate the creation of more programs in the future. These efforts have informed each other, giving policymakers the opportunity to interact with practitioners, troubleshoot bridge programs, and make…

  12. Shifting Patterns of Deadly Violence.

    ERIC Educational Resources Information Center

    Seiden, Richard H.; Freitas, Raymond P.

    1980-01-01

    While it is true that the total suicide rates has varied little, this composite figure masks a dramatic shift in the risk of suicide by age. In recent years there has been a reduction of suicide at older ages reciprocated by an unprecedented increase of suicide and homicide at younger ages. (Author)

  13. A 14-h night-shift in the control room of a fire brigade.

    PubMed

    Knauth, P; Keller, J; Schindele, G; Totterdell, P

    1995-01-01

    All 29 operators in the control room of a fire brigade performed test sessions during work and leisure time at 2-h intervals on a day with a 14-h night-shift, a day off and a day with a 10-h morning shift. The test sessions consisted of a visual search choice reaction time test and two Sternberg memory search tests (1 or 5 letters had to be memorized). Furthermore, the operators recorded their oral temperature and their subjective alertness before each test session. The subject also kept a diary of work and sleep times for 14 days. The circadian rhythm of body temperature was hardly changed by a single night-shift. Parallel to the body temperature, the subjective alertness fell significantly during the night-shift reaching a minimum value at 06:00 h. The mean reaction times increased non-significantly at the end of the night-shift and the results of the two Sternberg memory search tests showed no significant trends. The sleep of the operators after the night-shift was on average reduced to 5 hs 34 min. The results of subjective rating of alertness and reaction time test are interpreted as effects of the combined influences of circadian rhythmicity, sleep loss and time on professional task. Most results support the conclusion that a 14-h night-shift without extensive breaks is not acceptable. PMID:11539390

  14. Frequency shifts in gravitational resonance spectroscopy

    E-print Network

    S. Baeßler; V. V. Nesvizhevsky; G. Pignol; K. V. Protasov; D. Rebreyend; E. A. Kupriyanova; A. Yu. Voronin

    2015-01-13

    Quantum states of ultracold neutrons in the gravitational field are to be characterized through gravitational resonance spectroscopy. This paper discusses systematic effects that appear in the spectroscopic measurements. The discussed frequency shifts, which we call Stern-Gerlach shift, interference shift, and spectator state shift, appear in conceivable measurement schemes and have general importance. These shifts have to be taken into account in precision experiments.

  15. Quantum radiation reaction and the Green's function decomposition

    SciTech Connect

    Higuchi, Atsushi; Martin, Giles D. R. [Department of Mathematics, University of York, Heslington, York YO10 5DD (United Kingdom)

    2006-12-15

    We analyze the change in position (the position shift) of the wave packet of a charged scalar particle due to radiation reaction in the ({Dirac_h}/2{pi}){yields}0 limit of quantum electrodynamics. In particular, we re-express the formula previously obtained for the position shift in terms of Green's functions for the electromagnetic field, thus clarifying the relation between the quantum and classical derivations of the radiation-reaction force.

  16. Quantum Radiation Reaction and the Green's Function Decomposition

    E-print Network

    Atsushi Higuchi; Giles D. R. Martin

    2006-08-04

    We analyze the change in position (the position shift) of the wave packet of a charged scalar particle due to radiation reaction in the $\\hbar \\to 0$ limit of quantum electrodynamics. In particular, we re-express the formula previously obtained for the position shift in terms of Green's functions for the electromagnetic field, thus clarifying the relation between the quantum and classical derivations of the radiation-reaction force.

  17. Sensitivity of Fischer-Tropsch Synthesis and Water-Gas Shift Catalysts to Poisons from High-Temperature High-Pressure Entrained-Flow (EF) Oxygen-Blown Gasifier Gasification of Coal\\/Biomass Mixtures

    Microsoft Academic Search

    Burtron Davis; Gary Jacobs; Wenping Ma; Khalid Azzam; Dennis Sparks; Wilson Shafer

    2010-01-01

    The successful adaptation of conventional cobalt and iron-based Fischer-Tropsch synthesis catalysts for use in converting biomass-derived syngas hinges in part on understanding their susceptibility to byproducts produced during the biomass gasification process. With the possibility that oil production will peak in the near future, and due to concerns in maintaining energy security, the conversion of biomass-derived syngas and syngas derived

  18. Gold, Copper and Platinum Nanoparticles Dispersed on CeOx\\/TiO2(110) Surfaces: High Water-Gas Shift Activity and the Nature of the Mixed-Metal Oxide at the Nanometer Level

    Microsoft Academic Search

    J. A. Rodriguez; Jesus Graciani; Dario Stacchiola; S. D. Senanayake; L. Barrio; Javier Fdez. Sanz

    2010-01-01

    At small coverages of ceria on TiOâ(110), the CeOâ nanoparticles have an unusual coordination mode. Scanning tunneling microscopy and density-functional calculations point to the presence of CeâOâ dimers, which form diagonal arrays that have specific orientations of 0, 24, and 42{sup o} with respect to the [1 -1 0] direction of the titania substrate. At high coverages of ceria on

  19. Peripherality of breakup reactions

    NASA Astrophysics Data System (ADS)

    Capel, P.; Nunes, F. M.

    2007-05-01

    The sensitivity of elastic breakup to the interior of the projectile wave function is analyzed. Breakup calculations of loosely bound nuclei (B8 and Be11) are performed with two different descriptions of the projectile. The descriptions differ strongly in the interior of the wave function, but exhibit identical asymptotic properties, namely the same asymptotic normalisation coefficient, and phase shifts. Breakup calculations are performed at intermediate energies (40 70 MeV/nucleon) on lead and carbon targets as well as at low energy (26 MeV) on a nickel target. No dependence on the projectile description is observed. This result confirms that breakup reactions are peripheral in the sense that they probe only the external part of the wave function. These measurements are thus not directly sensitive to the total normalization of the wave function, i.e., spectroscopic factor.

  20. Working shifts: Perceptions of African American community members and shift workers

    Microsoft Academic Search

    Ericka King-Betts

    2008-01-01

    This research study examined African American shift workers, family and friends of African American shift workers, and African American community members' perceptions of shift work. In order to gain a clearer understanding of African Americans' perceptions of shift work, focus groups were conducted. By taking a qualitative approach and examining the views held by African American shift workers, friends and

  1. Anthropometric changes and fluid shifts

    NASA Technical Reports Server (NTRS)

    Thornton, W. E.; Hoffler, G. W.; Rummel, J. A.

    1977-01-01

    In an effort to obtain the most comprehensive and coherent picture of changes under weightlessness, a set of measurements on Skylab 2 was initiated and at every opportunity, additional studies were added. All pertinent information from ancillary sources were gleaned and collated. On Skylab 2, the initial anthropometric studies were scheduled in conjunction with muscle study. A single set of facial photographs was made in-flight. Additional measurements were made on Skylab 3, with photographs and truncal and limb girth measurements in-flight. Prior to Skylab 4, it was felt there was considerable evidence for large and rapid fluid shifts, so a series of in-flight volume and center of mass measurements and infrared photographs were scheduled to be conducted in the Skylab 4 mission. A number of changes were properly documented for the first time, most important of which were the fluid shifts. The following description of Skylab anthropometrics address work done on Skylab 4 primarily.

  2. Dealing with a shifting paradigm.

    PubMed

    Kaufman, R P

    1987-01-01

    In 1970, T. S. Kuhn, in The Structure of Scientific Revolutions argued that scientists work by creating a comprehensive model--a model he called "a paradigm." A paradigm, Kuhn said, is an encompassing world view that tells us what facts to pay attention to and what to ignore. He contended that, although we may think that we consider all the facts and ask all the questions, there is always some ordering and selection going on, and we must first be prepared by our paradigm to make sense of what we see. He stated that one of the first signs that a paradigm is shifting is the discovery of facts that seem significant and indisputably true but cannot be explained by the current model. The essential elements, according to Kuhn, that are required for a paradigm to shift are a strong stimulus, a rapidly changing environment, and the realization that whether the change is good or bad is essentially of no significance. The parties most closely involved are frequently the last to appreciate that the shift has occurred. PMID:10312134

  3. Shift Work and Endocrine Disorders

    PubMed Central

    Ulhôa, M. A.; Marqueze, E. C.; Burgos, L. G. A.; Moreno, C. R. C.

    2015-01-01

    The objective of this review was to investigate the impact of shift and night work on metabolic processes and the role of alterations in the sleep-wake cycle and feeding times and environmental changes in the occurrence of metabolic disorders. The literature review was performed by searching three electronic databases for relevant studies published in the last 10 years. The methodological quality of each study was assessed, and best-evidence synthesis was applied to draw conclusions. The literature has shown changes in concentrations of melatonin, cortisol, ghrelin, and leptin among shift workers. Melatonin has been implicated for its role in the synthesis and action of insulin. The action of this hormone also regulates the expression of transporter glucose type 4 or triggers phosphorylation of the insulin receptor. Therefore, a reduction in melatonin can be associated with an increase in insulin resistance and a propensity for the development of diabetes. Moreover, shift work can negatively affect sleep and contribute to sedentarism, unhealthy eating habits, and stress. Recent studies on metabolic processes have increasingly revealed their complexity. Physiological changes induced in workers who invert their activity-rest cycle to fulfill work hours include disruptions in metabolic processes. PMID:25892993

  4. Shift work and endocrine disorders.

    PubMed

    Ulhôa, M A; Marqueze, E C; Burgos, L G A; Moreno, C R C

    2015-01-01

    The objective of this review was to investigate the impact of shift and night work on metabolic processes and the role of alterations in the sleep-wake cycle and feeding times and environmental changes in the occurrence of metabolic disorders. The literature review was performed by searching three electronic databases for relevant studies published in the last 10 years. The methodological quality of each study was assessed, and best-evidence synthesis was applied to draw conclusions. The literature has shown changes in concentrations of melatonin, cortisol, ghrelin, and leptin among shift workers. Melatonin has been implicated for its role in the synthesis and action of insulin. The action of this hormone also regulates the expression of transporter glucose type 4 or triggers phosphorylation of the insulin receptor. Therefore, a reduction in melatonin can be associated with an increase in insulin resistance and a propensity for the development of diabetes. Moreover, shift work can negatively affect sleep and contribute to sedentarism, unhealthy eating habits, and stress. Recent studies on metabolic processes have increasingly revealed their complexity. Physiological changes induced in workers who invert their activity-rest cycle to fulfill work hours include disruptions in metabolic processes. PMID:25892993

  5. Shift of voltage reversal in stacked microbial fuel cells

    NASA Astrophysics Data System (ADS)

    An, Junyeong; Kim, Bongkyu; Chang, In Seop; Lee, Hyung-Sool

    2015-03-01

    We proved that sluggish kinetics on the cathode and the imbalance of cathode kinetics cause voltage reversal in a stacked microbial fuel cell (MFC) equipped with a non-Pt cathode. Catholyte aeration to a unit MFC against passive air diffusion to the cathode in the other unit MFC shifted voltage reversal between the two units, due to improved mass transport and O2 concentration effects in the aerated MFC. The shifted voltage reversal returned to an original status when catholyte aeration was stopped. A Pt-coated cathode increased the rate of oxygen reduction reaction (ORR) by a factor of ?20, as compared to the non-Pt cathode. As a result, the anodic reaction rate that became slower than the rate on the Pt-cathode limited current density to overpotential in the stacked MFC equipped with the Pt-cathode. This work shows that dominant kinetic bottlenecks, which are the primary cause of voltage reversal, can be shifted between individual MFCs of stacked MFCs or electrodes depending on relative kinetics.

  6. U.S. Geological Survey Georgia Water Science Center and Albany Water, Gas, and Light Commission Cooperative Water Program-Summary of Activities, July 2005 through June 2006

    USGS Publications Warehouse

    Gordon, Debbie Warner

    2006-01-01

    The U.S. Geological Survey (USGS) has been working with the Albany Water, Gas, and Light Commission to monitor ground-water quality and availability since 1977. This report presents the findings for July 2005 through June 2006 and summarizes the ground-water and surface-water conditions for 2005. Water levels in 14 wells were continuously monitored in Dougherty County, Georgia. Water levels in 12 of those wells were above normal, one was normal, and one was below normal. Ground-water samples collected from the Upper Floridan aquifer indicate that nitrate levels have increased in 13 wells and decreased in two wells from a year earlier. A sample also was collected from the Flint River. A trilinear diagram showing the percent composition of selected major cations and anions indicates that the ground-water quality of the Upper Floridan aquifer at the Albany wellfield is distinctly different from the water quality of the Flint River. To improve the understanding of the ground-water flow system and nitrate movement in the Upper Floridan aquifer, the USGS is developing a ground-water flow model in the southwest Albany area, Georgia.

  7. Interpreting lateral dynamic weight shifts using a simple inverted pendulum model.

    PubMed

    Kennedy, Michael W; Bretl, Timothy; Schmiedeler, James P

    2014-05-01

    Seventy-five young, healthy adults completed a lateral weight-shifting activity in which each shifted his/her center of pressure (CoP) to visually displayed target locations with the aid of visual CoP feedback. Each subject's CoP data were modeled using a single-link inverted pendulum system with a spring-damper at the joint. This extends the simple inverted pendulum model of static balance in the sagittal plane to lateral weight-shifting balance. The model controlled pendulum angle using PD control and a ramp setpoint trajectory, and weight-shifting was characterized by both shift speed and a non-minimum phase (NMP) behavior metric. This NMP behavior metric examines the force magnitude at shift initiation and provides weight-shifting balance performance information that parallels the examination of peak ground reaction forces in gait analysis. Control parameters were optimized on a subject-by-subject basis to match balance metrics for modeled results to metric values calculated from experimental data. Overall, the model matches experimental data well (average percent error of 0.35% for shifting speed and 0.05% for NMP behavior). These results suggest that the single-link inverted pendulum model can be used effectively to capture lateral weight-shifting balance, as it has been shown to model static balance. PMID:24708905

  8. Mean Shift, Mode Seeking, and Clustering

    Microsoft Academic Search

    Yizong Cheng

    1995-01-01

    Abstract-Mean shift, a simple iterative procedure that shifts each data point to the average of data points in its neighborhood, is generalized and analyzed in this paper. This generalization makes some k-means like clustering algorithms its special cases. It is shown that mean shift is a mode-seeking process on a surface constructed with a \\

  9. SHIFTED MATROID COMPLEXES CAROLINE J. KLIVANS

    E-print Network

    Klivans, Caroline J.

    SHIFTED MATROID COMPLEXES CAROLINE J. KLIVANS Abstract. We study the class of matroids whose matroids whose complexes of independent sets are shifted. This class of shifted matroids has been used them to show that there are at least 2 n non­isomorphic matroids on n elements. They were later

  10. Algebraic Feedback Shift Registers Andrew Klapper a

    E-print Network

    Klapper, Andy

    Algebraic Feedback Shift Registers Andrew Klapper a Jinzhong Xu b a Dept. of Computer Science, 763H for the design of feedback registers based on algebra over complete rings is described. These registers generalize linear feedback shift registers and feedback with carry shift registers. Basic properties

  11. Classical and Quantum Radiation Reaction

    E-print Network

    Giles D. R. Martin

    2008-05-06

    This thesis reports on work undertaken in comparing the effects of the phenomenon of radiation reaction in classical and quantum theories of electrodynamics. Specifically, it is concerned with the prediction of the change in position of a particle due to the inclusion of the self-force in the theory. We calculate this position shift for the classical theory, treating radiation reaction as a perturbation in line with the reduction of order procedure. We calculate the contributions to the position shift in the $\\hbar\\to 0$ limit of quantum field theory to order $e^2$ in the coupling, the order of the classical self-force. These calculations contain the emission and forward scattering one loop processes of quantum electrodynamics. The quantum calculations are completed for the case of a particle represented by a scalar field wave packet and then for a particle represented by the Dirac spinor field. We additionally give an alternative derivation of the scalar results using the interpretation of radiation reaction via a Green's function decomposition, in order to explain and contrast the results achieved.

  12. Formamidine Reactions

    E-print Network

    Griffin, E. L.

    1913-05-15

    of Hantzsch. (1), and the method of Uhlenhuth (2) was found to be not very much more satisfactory owing to the fact that the methyl lsoxazolon broKe down too much on heating Better results were obtained when the oxime of acetoacetic ester was obtained...,C ~ CH RNrOM-SHR = CH.C - C::CHHKR * li , II I H-0- CO U-0- CO * E2sTHx since methyl lsoxazolon is made by the reaction of hydroxylamine hydrochlorid on acetoacetic ester, it was thought that it might be possible to maKe the amldo methylene...

  13. Gear-shift mechanism for manual transmission

    SciTech Connect

    Fukuchi, H.

    1986-07-22

    This patent describes a gear-shift mechanism for a manual transmission comprising a housing for the transmission; a movable shaft mounted in place within the housing for both axial and rotary movements and being operatively connected to a manual shift lever to be axially shifted from its neutral position to a forward or reverse position in selecting operation of the manual shift lever and to be rotated at its shifted position in shifting operation of the manual shift lever; a shift-and-select lever fixed to an intermediate portion of the movable shaft; an interlock member rotatably mounted in place on the movable shaft and having a pair of interlock arms located at the opposite sides of the shift-and-select lever; means for restricting rotary movement of the interlock member and permitting axial movement of the same; a pair of resilient means for centering the movable shaft to retain the shift-and-select lever and the interlock member in their neutral positions; and first, second and third shift heads arranged in sequence within the housing.

  14. THE GAZE-SHIFT STRATEGY IN DRAWING TITLE: The Gaze-Shift Strategy in Drawing

    E-print Network

    Miall, Chris

    THE GAZE-SHIFT STRATEGY IN DRAWING 1 TITLE: The Gaze-Shift Strategy in Drawing RUNNING HEAD: The Gaze-Shift Strategy in Drawing REVISED and accepted Sept 2013 Please cite this works as: Tchalenko J, Nam S-H, Moshe & Miall RC (2014) The Gaze-Shift Strategy in Drawing Psychol. Aesthetics. Creat

  15. SPONTANEOUS AND CATALYZED HYDROGEN SHIFTS IN RADICAL CATIONS HAVING A PHOSPHORYL OR CARBONYL GROUP

    Microsoft Academic Search

    Lisa Natasha Heydorn

    2003-01-01

    Intermolecular and intramolecular hydrogen shifts represent a key component of a vast number of chemical reactions. This is particularly true for radical cations, whose high reactivity makes them prone to isomerization and dissociation reactions. In the context of the experimental work in this thesis, hydrogen transfers involved in both the intra-and inter-molecular isomerization of radical cations containing a phosphoryl (P=O)

  16. General Biology 1, Reactions 1 CHEMICAL REACTIONS *

    E-print Network

    Prestwich, Ken

    General Biology 1, Reactions 1 CHEMICAL REACTIONS * Note: This is the first of a two-part set of notes. This set will review chemical reactions and the next will overview enzymes. What you learn and ribozymes. At their heart, organisms are complex chemical engines. However, many of the chemical reactions

  17. Intro Biology, Reactions 1 CHEMICAL REACTIONS *

    E-print Network

    Prestwich, Ken

    Intro Biology, Reactions 1 CHEMICAL REACTIONS * Note: This is the first of a two-part set of notes. This set will review chemical reactions and the next will overview enzymes. What you learn in these two and ribozymes. At their heart, organisms are complex chemical engines. However, many of the chemical reactions

  18. Two-stage coal liquefaction without gas-phase hydrogen

    DOEpatents

    Stephens, H.P.

    1986-06-05

    A process is provided for the production of a hydrogen-donor solvent useful in the liquefaction of coal, wherein the water-gas shift reaction is used to produce hydrogen while simultaneously hydrogenating a donor solvent. A process for the liquefaction of coal using said solvent is also provided. The process enables avoiding the use of a separate water-gas shift reactor as well as high pressure equipment for liquefaction. 3 tabs.

  19. Melatonin and adjustment to phase shift.

    PubMed

    Arendt; Deacon; English; Hampton; Morgan

    1995-12-01

    The pineal hormone melatonin has clear circadian phase-shifting effects in humans which have recently been formalized as a phase response curve. Its potential use in circadian rhythm disorders has been investigated in field studies of jet lag and shift work and in simulated phase shift. A substantial amount of information indicates that in the majority of subjects it hastens adaptation of both subjective and objective measures to forced shifts in time cues with few reported side-effects. Field studies of its use in adaptation to shift work are sparse and preliminary but the first indications are positive. In some blind subjects with sleep disturbance it can stabilize sleep onset time without necessarily entraining all circadian rhythms and it can advance sleep timing in delayed sleep-phase insomnia. Acute suppression of core body temperature may be an integral part of the phase-shifting mechanism. PMID:10607217

  20. Shift mechanism for engine starting apparatus

    SciTech Connect

    Colvin, J.A.; Colvill, R.G.; Smock, A.L.

    1986-04-01

    This patent describes a shift lever mechanism for translating axial movement of the plunger of a starter solenoid into axial movement of a pinion of an engine starting apparatus. This apparatus consists of, a starter solenoid having an axially shiftable plunger and a coil winding, a spring opposing pull-in movement of the plunger and a solenoid switch operated to a closed condition when the plunger is completely pulled-in, a shift lever actuator carried by the plunger for axial movement therewith. The actuator has a pair of spaced surfaces, a pivotally mounted shift lever one end of which is adapted to be coupled to the pinion. The opposite end of the shift lever has a pair of opposed shift lever surfaces that respectively engage the surfaces on the actuator. The actuator surfaces and the shift lever surfaces are substantially engaged when the shift lever is in an at rest postion. The surfaces on the shift lever are at different radial distances from the pivot point of the shift lever and are arranged relative to the surfaces on the actuator such that when the solenoid plunger pulls-in the surface on the shift lever that is at the greater radial distance from the pivot point is moved by a surface of the actuator and the other surface on the shift lever becomes separated by a predetermined amount from its cooperating surface on the actuator. The amount of separation is sufficient to allow the solenoid switch to be actuated to an open condition when the solenoid coil winding is deenergized and the spring shifts and plunger to reengage the separated surfaces.

  1. Shifting of the Kosi River, northern India

    NASA Astrophysics Data System (ADS)

    Wells, Neil A.; Dorr, John A., Jr.

    1987-03-01

    The Kosi River shifts laterally over the Himalaya foreland plain by continual minor cutoffs and bank cutting and by episodic major shifts across watersheds, by moving into and then out of preexisting, adjacent, less actively aggrading streams. Migration is unidirectional because after a channel is filled to instability, floodwater will drain preferentially into a new adjacent low rather than across it to the next watershed or back to the last abandoned channel. Major shifts seem stochastic and autocyclic; they do not correlate with the many severe quakes and floods that undoubtedly helped prime the system for shifts.

  2. EXAFS Energy Shift and Structural Parameters

    SciTech Connect

    Kelly, Shelly D.; Ravel, Bruce [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States)

    2007-02-02

    In EXAFS analysis, the energy shift parameter is used to align the theoretical calculated spectrum to the energy grid of the measured spectrum. Unrealistically large energy shift values, sometimes in excess of 20 eV, are at times published in research articles. We therefore see the need for a concise discussion of the EXAFS energy shift parameter. This paper is intended as a learning tool for the proper alignment of theory to measured EXAFS spectra and proper interpretation of the energy shift parameter.

  3. EXAFS energy shift and structural parameters.

    SciTech Connect

    Kelly, S. D.; Ravel, B.; Biosciences Division

    2007-01-01

    In EXAFS analysis, the energy shift parameter is used to align the theoretical calculated spectrum to the energy grid of the measured spectrum. Unrealistically large energy shift values, sometimes in excess of 20 eV, are at times published in research articles. We therefore see the need for a concise discussion of the EXAFS energy shift parameter. This paper is intended as a learning tool for the proper alignment of theory to measured EXAFS spectra and proper interpretation of the energy shift parameter.

  4. Light-shift-modulated photon-echo.

    PubMed

    Chanelière, Thierry; Hétet, Gabriel

    2015-04-01

    We show that the AC-Stark shift (light-shift) is a powerful and versatile tool to control the emission of a photon-echo in the context of optical storage. As a proof-of-principle, we demonstrate that the photon-echo efficiency can be fully modulated by applying light-shift control pulses in an erbium-doped solid. The control of the echo emission is attributed to the spatial gradient induced by the light-shift beam. PMID:25831316

  5. Shift work and the assessment and management of shift work disorder (SWD).

    PubMed

    Wright, Kenneth P; Bogan, Richard K; Wyatt, James K

    2013-02-01

    Nearly 20% of the labor force worldwide, work shifts that include work hours outside 07:00 h to 18:00 h. Shift work is common in many occupations that directly affect the health and safety of others (e.g., protective services, transportation, healthcare), whereas quality of life, health, and safety during shift work and the commute home can affect workers in any field. Increasing evidence indicates that shift-work schedules negatively influence worker physiology, health, and safety. Shift work disrupts circadian sleep and alerting cycles, resulting in disturbed daytime sleep and excessive sleepiness during the work shift. Moreover, shift workers are at risk for shift work disorder (SWD). This review focuses on shift work and the assessment and management of sleepiness and sleep disruption associated with shift work schedules and SWD. Management strategies include approaches to promote sleep, wakefulness, and adaptation of the circadian clock to the imposed work schedule. Additional studies are needed to further our understanding of the mechanisms underlying the health risks of shift work, understanding which shift workers are at most risk of SWD, to investigate treatment options that address the health and safety burdens associated with shift work and SWD, and to further develop and assess the comparative effectiveness of countermeasures and treatment options. PMID:22560640

  6. In-line phase shift tomosynthesis

    SciTech Connect

    Hammonds, Jeffrey C.; Price, Ronald R.; Pickens, David R.; Donnelly, Edwin F. [Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, Tennessee 37232 (United States)] [Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, Tennessee 37232 (United States)

    2013-08-15

    Purpose: The purpose of this work is to (1) demonstrate laboratory measurements of phase shift images derived from in-line phase-contrast radiographs using the attenuation-partition based algorithm (APBA) of Yan et al.[Opt. Express 18(15), 16074–16089 (2010)], (2) verify that the APBA reconstructed images obey the linearity principle, and (3) reconstruct tomosynthesis phase shift images from a collection of angularly sampled planar phase shift images.Methods: An unmodified, commercially available cabinet x-ray system (Faxitron LX-60) was used in this experiment. This system contains a tungsten anode x-ray tube with a nominal focal spot size of 10 ?m. The digital detector uses CsI/CMOS with a pixel size of 50 × 50 ?m. The phantoms used consisted of one acrylic plate, two polystyrene plates, and a habanero pepper. Tomosynthesis images were reconstructed from 51 images acquired over a ±25° arc. All phase shift images were reconstructed using the APBA.Results: Image contrast derived from the planar phase shift image of an acrylic plate of uniform thickness exceeded the contrast of the traditional attenuation image by an approximate factor of two. Comparison of the planar phase shift images from a single, uniform thickness polystyrene plate with two polystyrene plates demonstrated an approximate linearity of the estimated phase shift with plate thickness (?1600 rad vs ?2970 rad). Tomographic phase shift images of the habanero pepper exhibited acceptable spatial resolution and contrast comparable to the corresponding attenuation image.Conclusions: This work demonstrated the feasibility of laboratory-based phase shift tomosynthesis and suggests that phase shift imaging could potentially provide a new imaging biomarker. Further investigation will be needed to determine if phase shift contrast will be able to provide new tissue contrast information or improved clinical performance.

  7. Density functional studies of representative pericyclic reactions

    NASA Astrophysics Data System (ADS)

    Carpenter, John E.; Sosa, Carlos P.

    1994-07-01

    Density functional theory (DFT) has traditionally been shunned by computational chemists, but has long seen widespread use in the physics community. Recently, however, DFT has been adopted by the ab initio quantum chemistry community and much activity has been devoted to refining the methodology and exploring the range of its applicability. We investigate the use of DFT (both local (LDF) and non-local (NLDF) spin density approximations) to calculate transition and equilibrium structures for three representative pericyclic reactions: the electrocyclic ring opening reaction of cyclobutene, the [1,5] sigmatropic hydrogen shift reaction in (Z)-1,3-pentadiene, and the Diels-Alder cycloaddition reaction between ethylene and butadiene. LDF theory tends to overemphasize the stability of the ringed structures in each of these reactions. For example, LDF predicts a very low (6 kcal mol -1) barrier to reaction for the Deils-Alder reaction. NLDF theory substantially improves the calculated reaction barrier (20 kcal mol -1), but it is still low with respect to experiment.

  8. A Short History of Three Chemical Shifts

    ERIC Educational Resources Information Center

    Nagaoka, Shin-ichi

    2007-01-01

    A short history of chemical shifts in nuclear magnetic resonance (NMR), electron spectroscopy for chemical analysis (ESCA) and Mossbauer spectroscopy, which are useful for chemical studies, is described. The term chemical shift is shown to have originated in the mistaken assumption that nuclei of a given element would all undergo resonance at the…

  9. On the frequency shift of gravitational waves

    E-print Network

    Claudio M. G. de Sousa

    2010-02-15

    Considering plane gravitational waves propagating through flat spacetime, it is shown that curvatures experienced both in the starting point and during their arrival at the earth can cause a considerable shift in the frequencies as measured by earth and space-based detectors. Particularly for the case of resonant bar detectors this shift can cause noise-filters to smother the signal.

  10. The wavenumber shift in SAR interferometry

    Microsoft Academic Search

    Fabio Gatelli; Andrea Monti Guamieri; Francesco Parizzi; Paolo Pasquali; Claudio Prati; Fabio Rocca

    1994-01-01

    SAR surveys from separate passes show relative shifts of the ground wavenumber spectra that depend on the local slope and the off-nadir angle. The authors discuss the exploitation of this spectral shift for different applications: 1) generation of “low noise” interferograms benefiting phase unwrapping, 2) generation of quick-look interferograms, 3) decorrelation reduction by means of tunable SAR systems (TINSAR), 4)

  11. The Concept Shifting Test: Adult Normative Data

    ERIC Educational Resources Information Center

    Van der Elst, Wim; Van Boxtel, Martin P. J.; Van Breukelen, Gerard J. P.; Jolles, Jelle

    2006-01-01

    The Concept Shifting Test (CST) is a newly developed Trail Making Type test that measures concept shifting and executive functioning. The purpose of the present study was to determine whether CST performance was affected by age, gender, educational level, or handedness and to establish the normal range of test performance. The CST was…

  12. Shift factors in ERCOT congestion pricing

    E-print Network

    Baldick, Ross

    Shift factors in ERCOT congestion pricing Ross Baldick* March 5, 2003 1. Introduction In this paper summarize the ERCOT commercial transmission model, introducing and explaining "shift factors" and their role-run, such poor economic decisions can also encourage bad choices for the location of new generation, load

  13. Classical Ciphers: Shift Cipher Cetin Kaya Koc

    E-print Network

    ambiguity) Frequency analysis: a paragraph of ciphertext (in order to get statistically reliable frequency¸c (http://cs.ucsb.edu/~koc) ucsb cs 178 intro to crypto winter 2014 1 / 1 #12;Shift Cipher Input encryption key k = 3 Ko¸c (http://cs.ucsb.edu/~koc) ucsb cs 178 intro to crypto winter 2014 2 / 1 #12;Shift

  14. The generalized Wolf shift for cyclostationary fields

    E-print Network

    Bhargava, Rohit

    The generalized Wolf shift for cyclostationary fields Robert W. Schoonover, Brynmor J. Davis, and P of cyclostationary, random fields are predicted. This result generalizes the Wolf shift for stationary fields. E. Wolf, Introduction to the Theory of Coherence and Polarization (Cambridge University Press, 2007

  15. Spectral pictures of 2-variable weighted shifts

    Microsoft Academic Search

    Raúl E. Curto; Jasang Yoon

    2006-01-01

    We study the spectral pictures of (jointly) hyponormal 2-variable weighted shifts with commuting subnormal components. By contrast with all known results in the theory of subnormal single and 2-variable weighted shifts, we show that the Taylor essential spectrum can be disconnected. We do this by obtaining a simple sufficient condition that guarantees disconnectedness, based on the norms of the horizontal

  16. The Frequency Shifting of Femtosecond Laser Pulses

    Microsoft Academic Search

    Glenn Bryant Focht

    1990-01-01

    Two new and widely applicable methods of shifting the frequency of femtosecond laser pulses have been developed experimentally and theoretically analyzed: (1) intracavity frequency doubling, for low energy (nanojoule) pulses, and (2) blue shifting in a laser-produced plasma, for high energy (millijoule) pulses. For the first method, we efficiently extract an ultraviolet femtosecond pulse train of milliwatt average power and

  17. log on education Paradigm-shifting landmark

    E-print Network

    Shneiderman, Ben

    log on education Paradigm-shifting landmark buildings are cherished by their occupants in Fallingwater (in western Pennsylva- nia) where the waterfall sounds and leafy sur- roundings offered a stress) that promoted new team-oriented management strategies. Current opportuni- ties for architectural paradigm shifts

  18. Doppler Interpretation of Quasar Red Shifts

    Microsoft Academic Search

    Harold S. Zapolsky

    1966-01-01

    The hypothesis that the quasistellar sources (quasars) are local objects moving with velocities close to the speed of light is examined. Provided there is no observational cutoff on apparent bolometric magnitude for the quasars, the transverse Doppler effect leads to the expectation of fewer blue shifts than red shifts for an isotropic distribution of velocities. Such a distribution also yields

  19. Adaptive Hybrid Mean Shift and Particle Filter

    Microsoft Academic Search

    Phong Le; Anh Duc Duong; Hai Quan Vu; Nam Trung Pham

    2009-01-01

    The changing of dynamic models in object tracking can cause high errors in state estimation algorithms. In this paper, we propose a method, adaptive hybrid mean shift and particle filter (AHMSPF), to solve this problem. AHMSPF consists of three stages. First, the mean shift algorithm is employed to search an object candidate near the target state. Then, if this candidate

  20. Social Change and Language Shift: South Africa.

    ERIC Educational Resources Information Center

    Kamwangamalu, Nkonko M.

    2003-01-01

    Examines language shift from majority African languages, such as Sotho, Xhosa, and Zulu to English in South Africa. Examines the extent to which sociopolitical changes that have taken place in South Africa have impacted everyday linguistic interaction and have contributed to language shift from the indigenous African language to English,…

  1. Trends and Shifts in Research Methods.

    ERIC Educational Resources Information Center

    Kelly, Anthony E.; Lesh, Richard

    This chapter overviews trends and shifts in research methods in mathematics and science education. It summarizes shifts in some basic assumptions about the role of research in mathematics and science education, background factors that support the proclivities of the researchers represented in the book, foreground factors that the researchers in…

  2. Apparatus for controlling transmission gear shift selection

    SciTech Connect

    Bailey, T.M.

    1986-07-29

    In an automotive engine having an electrical power source and an automatic or semi-automatic transmission including a manually operated transmission gear shift lever having at least two forward drive positions, an apparatus is described which consists of: (a) a speed sensing means for sensing the rotation speed of the engine and generating an output signal when the engine reaches a preselected rotational speed; and (b) a gear shifting means for changing the shift positions of the gear shift lever from a first drive position to a second drive position automatically in response to the output signal from the speed sensing means, the gear shifting means including (i) a latch actuable between open and closed positions, (ii) a normally de-energized solenoid having a plunger connected to the latch and operable to move the latch to the open position when the solenoid is energized by the electrical power source, (iii) a relay means for allowing the energizing of the solenoid by the power source in response to the output signal from the speed sensing means, and (iv) an actuating means, including a spring biased linkage mechanism operably connected to the gear shift lever and the latch, for actuating the movement of the gear shift lever from the first drive position to the second drive position in response to movement of the latch from the closed to the open position, thereby causing gear shifting to occur when the engine reaches the preselected rotational speed.

  3. Commentary: With Shifting Joints Torsten Anders

    E-print Network

    Miranda, Eduardo Reck

    the listener. I applied virtual instruments, physical models comprised of cells and their connections With Shifting Joints Instrumentation Eight-channel tape piece Duration approx. 11 min. Date of Composition-channel tape piece With Shifting Joints, I composed instrumental articula- tions and placed them around

  4. Isotope shifts and electron densities in W I. II. Theoretical field shifts and configuration mixing

    Microsoft Academic Search

    P. Aufmuth; A. Steudel; W. Tegtmeier; E. Wobker

    1988-01-01

    The isotope shift in the arc spectrum of tungsten was studied in seven lines by means of a photoelectric recording Fabry-Perot spectrometer with digital data processing for the isotopes 182W, 183W, 184W and 186W using highly enriched isotope samples. The observed shifts were separated into mass shift and field shift by means of a King plot with optical reference data.

  5. Methodological aspects of shift-work research.

    PubMed

    Knutsson, Anders

    2004-01-01

    A major issue in shift-work research is to understand the possible ways in which shift work can impact performance and health. Nearly all body functions, from those of the cellular level to those of the entire body, are circadian rhythmic. Disturbances of these rhythms as well as the social consequences of odd work hours are of importance for the health and well-being of shift workers. This article reviews a number of common methodological issues which are of relevance to epidemiological studies in this area of research. It discusses conceptual problems regarding the use of the term "shift work," and it underscores the need to develop models that explain the mechanisms of disease in shift workers. PMID:15646248

  6. Shift current generation at semiconductor surfaces

    NASA Astrophysics Data System (ADS)

    Shkrebtii, A. I.; Adolph, B.; Sipe, J. E.

    2000-03-01

    Interband electron excitations in a noncentrosymmetric crystal result in the shift of the electron charge with respect to that one of ground state. This so-called ``shift photocurrent" can be induced by linear absorption of light. We have recently shown [1] that shift current generation can be described in terms of the second order optical susceptibility. Numerical calculations for cubic GaAs and hexagonal CdSe demonstrate pronounced dependence of shift current on the band structure and crystal symmetry. Because solid surfaces lack inversion symmetry, this effect should be present even at the surface of centrosymmetric covalent crystals such as Si, Ge, C. Here we calculate the shift current generation for the Si(111)(1×1)H covered surface and the Pandey Si(111)(2×1) reconstruction. Results obtained are discussed in terms of the atomic bonding at the surfaces and their symmetry. [1] J.E. Sipe, A.I. Shkrebtii, Phys. Rev. B, to be published.

  7. Expected Number of Blue-shifts and Red-shifts of Ejected Sources

    Microsoft Academic Search

    John Faulkner; JAMES E. GUNN; BRUCE A. PETERSON

    1966-01-01

    IT has recently been suggested1 that the quasi-stellar radio sources are objects that have been ejected by relatively nearby peculiar galaxies. If their large red-shifts are due to the Doppler effect, we shall show that one would, in fact, expect to see many more objects with spectral shifts towards the blue than those with shifts towards the red.

  8. Chemical-shift Imaging Utilizing the Positional Shifts along the Readout Gradient Direction

    Microsoft Academic Search

    Maria I. Altbach; Theodore P. Trouard; Rik Van De Walle; Rebecca J. Theilmann; Eric Clarkson; Harrison H. Barrett; Arthur F. Gmitro

    2001-01-01

    In this work, we describe a method that uses the linear phase acquired during the readout period due to chemical shift to generate individual magnetic resonance (MR) images of chemically shifted species. The method utilizes sets of Fourier (or -space) data acquired with different directions of the readout gradient and a postprocessing algorithm to generate chemical shift images. The methodology

  9. NightShift: NMR shift inference by general hybrid model training - a framework for NMR chemical shift prediction

    PubMed Central

    2013-01-01

    Background NMR chemical shift prediction plays an important role in various applications in computational biology. Among others, structure determination, structure optimization, and the scoring of docking results can profit from efficient and accurate chemical shift estimation from a three-dimensional model. A variety of NMR chemical shift prediction approaches have been presented in the past, but nearly all of these rely on laborious manual data set preparation and the training itself is not automatized, making retraining the model, e.g., if new data is made available, or testing new models a time-consuming manual chore. Results In this work, we present the framework NightShift (NMR Shift Inference by General Hybrid Model Training), which enables automated data set generation as well as model training and evaluation of protein NMR chemical shift prediction. In addition to this main result – the NightShift framework itself – we describe the resulting, automatically generated, data set and, as a proof-of-concept, a random forest model called Spinster that was built using the pipeline. Conclusion By demonstrating that the performance of the automatically generated predictors is at least en par with the state of the art, we conclude that automated data set and predictor generation is well-suited for the design of NMR chemical shift estimators. The framework can be downloaded from https://bitbucket.org/akdehof/nightshift. It requires the open source Biochemical Algorithms Library (BALL), and is available under the conditions of the GNU Lesser General Public License (LGPL). We additionally offer a browser-based user interface to our NightShift instance employing the Galaxy framework via https://ballaxy.bioinf.uni-sb.de/. PMID:23496927

  10. Catalysis of Photochemical Reactions.

    ERIC Educational Resources Information Center

    Albini, A.

    1986-01-01

    Offers a classification system of catalytic effects in photochemical reactions, contrasting characteristic properties of photochemical and thermal reactions. Discusses catalysis and sensitization, examples of catalyzed reactions of excepted states, complexing ground state substrates, and catalysis of primary photoproducts. (JM)

  11. Photon Frequency Shifts by its Spin and Hubble Galaxy Red Shift vs Distance

    NASA Astrophysics Data System (ADS)

    Nam, Sang Boo

    2014-03-01

    A new mechanism for the photon frequency shifts by its spin, occurring from the inertial frame to the non-inertial (rotating) frame, is discussed. The photon spin one is shown with the frequency shifts by the Maxwell equations, without quantization of the photon field. The shifts are found to be varying with the photon path length, distance between its source and its observer. With the rotation of our galaxy, they account for the Hubble galaxy red shift vs distance and red shifts via supernovae, and blue shifts via galaxies. The sunlight red and blue shifts by its spin, are predicted, with the earth-self rotation. A mechanical (rotation) scheme is given for determination of a particle spin. sangboonam@mailaps.org

  12. Adaptation to Shift Work: Physiologically Based Modeling of the Effects of Lighting and Shifts’ Start Time

    PubMed Central

    Postnova, Svetlana; Robinson, Peter A.; Postnov, Dmitry D.

    2013-01-01

    Shift work has become an integral part of our life with almost 20% of the population being involved in different shift schedules in developed countries. However, the atypical work times, especially the night shifts, are associated with reduced quality and quantity of sleep that leads to increase of sleepiness often culminating in accidents. It has been demonstrated that shift workers’ sleepiness can be improved by a proper scheduling of light exposure and optimizing shifts timing. Here, an integrated physiologically-based model of sleep-wake cycles is used to predict adaptation to shift work in different light conditions and for different shift start times for a schedule of four consecutive days of work. The integrated model combines a model of the ascending arousal system in the brain that controls the sleep-wake switch and a human circadian pacemaker model. To validate the application of the integrated model and demonstrate its utility, its dynamics are adjusted to achieve a fit to published experimental results showing adaptation of night shift workers (n?=?8) in conditions of either bright or regular lighting. Further, the model is used to predict the shift workers’ adaptation to the same shift schedule, but for conditions not considered in the experiment. The model demonstrates that the intensity of shift light can be reduced fourfold from that used in the experiment and still produce good adaptation to night work. The model predicts that sleepiness of the workers during night shifts on a protocol with either bright or regular lighting can be significantly improved by starting the shift earlier in the night, e.g.; at 21?00 instead of 00?00. Finally, the study predicts that people of the same chronotype, i.e. with identical sleep times in normal conditions, can have drastically different responses to shift work depending on their intrinsic circadian and homeostatic parameters. PMID:23308206

  13. Prolonged Instability Prior to a Regime Shift

    PubMed Central

    Spanbauer, Trisha L.; Allen, Craig R.; Angeler, David G.; Eason, Tarsha; Fritz, Sherilyn C.; Garmestani, Ahjond S.; Nash, Kirsty L.; Stone, Jeffery R.

    2014-01-01

    Regime shifts are generally defined as the point of ‘abrupt’ change in the state of a system. However, a seemingly abrupt transition can be the product of a system reorganization that has been ongoing much longer than is evident in statistical analysis of a single component of the system. Using both univariate and multivariate statistical methods, we tested a long-term high-resolution paleoecological dataset with a known change in species assemblage for a regime shift. Analysis of this dataset with Fisher Information and multivariate time series modeling showed that there was a?2000 year period of instability prior to the regime shift. This period of instability and the subsequent regime shift coincide with regional climate change, indicating that the system is undergoing extrinsic forcing. Paleoecological records offer a unique opportunity to test tools for the detection of thresholds and stable-states, and thus to examine the long-term stability of ecosystems over periods of multiple millennia. PMID:25280010

  14. Cognitive Set-Shifting in Anorexia Nervosa

    PubMed Central

    Shott, Megan E.; Filoteo, J. Vincent; Bhatnagar, Kelly A.C.; Peak, Nicole J.; Hagman, Jennifer O.; Rockwell, Roxanne; Kaye, Walter H.; Frank, Guido K.W.

    2013-01-01

    Objective Adult anorexia nervosa (AN) is associated with inefficient cognitive flexibility and set-shifting. Whether such inefficiencies also characterize adolescent AN is an important area of research. Method Adolescents with AN and matched controls were administered a computerized task that required initial learning of an explicit rule using corrective feedback and learning of a new rule after a set number of trials. Adult patients with AN and controls were also examined. Results Adolescents with AN did not differ from matched controls with respect to set-shifting cost (decrease in performance after rule change), whereas adults with AN had significantly greater set-shifting cost compared with controls. Discussion This study suggests that set-shifting inefficiencies may not be a vulnerability factor for AN development in adolescents with AN, but might become an important aspect of the disorder at later age, and could point towards developmental neurobiologic brain changes that could affect AN at different ages. PMID:22492553

  15. The Lamb shift in de Sitter spacetime

    E-print Network

    Wenting Zhou; Hongwei Yu

    2010-12-18

    We study the Lamb shift of both freely-falling and static two-level atoms in interaction with quantized conformally coupled massless scalar fields in the de Sitter-invariant vacuum. We find that the Lamb shifts of both freely-falling and static atoms are in structural similarity to that of an inertial atom immersed in a thermal bath in a Minkowski spacetime. For the freely-falling atom, the Lamb shift gets a correction as if it was immersed in a thermal bath at the Gibbons-Hawking temperature, thus revealing clearly the intrinsic thermal nature of de Sitter spacetime. For the static atom, the Lamb shift is affected by a combination of the effect of the intrinsic thermal nature of de Sitter spacetime and the Unruh effect associated with the inherent acceleration of the atom.

  16. [Sleep disorders among physicians on shift work].

    PubMed

    Schlafer, O; Wenzel, V; Högl, B

    2014-11-01

    Sleep disorders in physicians who perform shift work can result in increased risks of health problems that negatively impact performance and patient safety. Even those who cope well with shift work are likely to suffer from sleep disorders. The aim of this manuscript is to discuss possible causes, contributing factors and consequences of sleep disorders in physicians and to identify measures that can improve adaptation to shift work and treatment strategies for shift work-associated sleep disorders. The risk factors that influence the development of sleep disorders in physicians are numerous and include genetic factors (15 % of the population), age (> 50 years), undiagnosed sleep apnea,, alcohol abuse as well as multiple stress factors inherent in clinical duties (including shift work), research, teaching and family obligations. Several studies have reported an increased risk for medical errors in sleep-deprived physicians. Shift workers have an increased risk for psychiatric and cardiovascular diseases and shift work may also be a contributing factor to cancer. A relationship has been reported not only with sleep deprivation and changes in food intake but also with diabetes mellitus, obesity, hypertension and coronary heart disease. Nicotine and alcohol consumption are more frequent among shift workers. Increased sickness and accident rates among physicians when commuting (especially after night shifts) have a socioeconomic impact. In order to reduce fatigue and to improve performance, short naps during shiftwork or naps plus caffeine, have been proposed as coping strategies; however, napping during adverse circadian phases is less effective, if not impossible when unable to fall asleep. Bright and blue light supports alertness during a night shift. After shiftwork, direct sunlight exposure to the retina can be avoided by using dark sunglasses or glasses with orange lenses for commuting home. The home environment for daytime sleeping after a night shift should be very dark to allow endogenous melatonin secretion, which is a night signal and supports continuous sleep. Sleep disorders can be treated with timed light exposure, as well as behavioral and environmental strategies to compensate for sleep deprivation. Fatigue due to sleep deprivation can only be systematically treated with sleep. PMID:25213642

  17. Best focus shift mechanism for thick masks

    NASA Astrophysics Data System (ADS)

    Burkhardt, Martin; Raghunathan, Ananthan

    2015-03-01

    The best focus shift due to thick mask effects is well known, both in ArF, and more importantly in EUV, where the shorter wavelength is small compared to both mask openings and absorber height. While the effect is stronger in opaque features in clear field masks, the best focus shift is visible in dark field masks as well, and it becomes even more pronounced when scattering bars are added to non-dense features. This pattern dependent focus variation can be predicted in both exact EMF simulations and fast image calculations that are used for optical proximity correction (OPC). Even though this focus shift can be predicted and patterns can be corrected in OPC, we would like to understand the mechanism that causes this focus shift. This can help us understand if, in addition to best focus shift, the image quality is further deteriorated due to the thick mask effects. The best focus shift is found to be an interplay of the complex diffraction coefficient due to thick mask effects and the direction of the light that is incident on the mask, or coherence value ?. A change in focus adds a phase term to each of the complex diffraction coefficients, causing their rotation in a phasor diagram. Best focus is found when the phasors have an angle of 0 or 180 degrees to each other and depending on which diffracted orders are caught in the pupil and contribute to imaging. We investigate the effect of partial coherence, mask thickness, and assist feature placement on best focus shift. We observe a waveguide effect in the absorber gaps because of the reduced real index of refraction in the absorber layer, making vacuum the optically dense medium. We suggest ways to lessen the best focus shifts through assist feature placement or the use of alternative absorbers that are closer matched to the dielectric index of vacuum.

  18. Quantum Phase Shift Caused by Spatial Confinement

    Microsoft Academic Search

    B. E. Allman; A. Cimmino; S. L. Griffin; A. G. Klein

    1999-01-01

    This paper presents the results of optical interferometry experiments in which the phase of photons in one arm of a Mach-Zehnder interferometer is modified by applying a transverse constriction. An equivalent quantum interferometry experiment using neutron de Broglie waves is discussed in which the observed phase shift is in the spirit of the force-free phase shift of the Aharonov-Bohm effects.

  19. Iodine Clock Reaction

    NSDL National Science Digital Library

    This site allows the user to vary initial solution concentration and temperature for the iodine clock reaction. A simulation of the reaction lets reaction times be measured. The data can then be used to determine the order of reaction for the various components.

  20. Spatial phase-shifting lateral shearing interferometer

    NASA Astrophysics Data System (ADS)

    Guo, Xiaoxian; Zeng, Aijun; Huang, Huijie

    2008-12-01

    The phase-shifting lateral shearing interferometer is widely adopted for wavefront measurement with high accuracy. For real-time wavefront measurement, a spatial phase-shifting lateral shearing interferometer is proposed. The interferometer includes a polarization lateral shearing module, a spatial phase-shifting module and an imaging module. The polarization lateral shearing module consists of a Savart polariscope. The spatial phase-shifting module is component of a non-polarization beam splitter, a polarization beam splitter, two rectangular prisms and a half wave-plate. The imaging module includes an imaging system and a CCD. The measured wavefront is sheared by the polarization lateral shearing module. The polarization directions of the two shearing beams are perpendicular to each other. The two shearing beams are split into four groups of beams by the spatial phase-shifting module to form four interferograms in a 2x2 matrix. The phase step of the four interferograms is 90 degrees. The four interferograms are captured in a single frame image by the imaging module. In experiments, a spherical wavefront with large radius of curvature was measured. Four spatial phase-shifting interferograms of the wavefront was obtained simultaneously. The usefulness of the interferometer is verified.

  1. Calculation of isotope shifts and relativistic shifts in C I, C II, C III, and C IV J. C. Berengut*

    E-print Network

    Kozlov, Mikhail G

    Calculation of isotope shifts and relativistic shifts in C I, C II, C III, and C IV J. C. Berengut of calculating isotope shifts and relativistic shifts in atomic spectra. We test the method on neutral carbon the lifetime of the Universe. Carbon isotope shifts can be used to measure isotope abundances in gas clouds

  2. ORIGINAL ARTICLE Artificial selection shifts flowering phenology and

    E-print Network

    Galloway, Laura F.

    ORIGINAL ARTICLE Artificial selection shifts flowering phenology and other correlated traits with shifts in flowering phenologies. We conducted a three-generation artificial selection experiment to a changing climate, phenological shifts may be associated with reduced plant fitness possibly hindering

  3. Scalar Field Theories with Polynomial Shift Symmetries

    E-print Network

    Tom Griffin; Kevin T. Grosvenor; Petr Horava; Ziqi Yan

    2014-12-02

    We continue our study of naturalness in nonrelativistic QFTs of the Lifshitz type, focusing on scalar fields that can play the role of Nambu-Goldstone (NG) modes associated with spontaneous symmetry breaking. Such systems allow for an extension of the constant shift symmetry to a shift by a polynomial of degree $P$ in spatial coordinates. These "polynomial shift symmetries" in turn protect the technical naturalness of modes with a higher-order dispersion relation, and lead to a refinement of the proposed classification of infrared Gaussian fixed points available to describe NG modes in nonrelativistic theories. Generic interactions in such theories break the polynomial shift symmetry explicitly to the constant shift. It is thus natural to ask: Given a Gaussian fixed point with polynomial shift symmetry of degree $P$, what are the lowest-dimension operators that preserve this symmetry, and deform the theory into a self-interacting scalar field theory with the shift symmetry of degree $P$? To answer this (essentially cohomological) question, we develop a new graph-theoretical technique, and use it to prove several classification theorems. First, in the special case of $P=1$ (essentially equivalent to Galileons), we reproduce the known Galileon $N$-point invariants, and find their novel interpretation in terms of graph theory, as an equal-weight sum over all labeled trees with $N$ vertices. Then we extend the classification to $P>1$ and find a whole host of new invariants, including those that represent the most relevant (or least irrelevant) deformations of the corresponding Gaussian fixed points, and we study their uniqueness.

  4. Combined chemical shift changes and amino acid specific chemical shift mapping of protein-protein interactions.

    PubMed

    Schumann, Frank H; Riepl, Hubert; Maurer, Till; Gronwald, Wolfram; Neidig, Klaus-Peter; Kalbitzer, Hans Robert

    2007-12-01

    Protein-protein interactions are often studied by chemical shift mapping using solution NMR spectroscopy. When heteronuclear data are available the interaction interface is usually predicted by combining the chemical shift changes of different nuclei to a single quantity, the combined chemical shift perturbation Deltadelta comb In this paper different procedures (published and non-published) to calculate Deltadelta comb are examined that include a variety of different functional forms and weighting factors for each nucleus. The predictive power of all shift mapping methods depends on the magnitude of the overlap of the chemical shift distributions of interacting and non-interacting residues and the cut-off criterion used. In general, the quality of the prediction on the basis of chemical shift changes alone is rather unsatisfactory but the combination of chemical shift changes on the basis of the Hamming or the Euclidian distance can improve the result. The corrected standard deviation to zero of the combined chemical shift changes can provide a reasonable cut-off criterion. As we show combined chemical shifts can also be applied for a more reliable quantitative evaluation of titration data. PMID:17955183

  5. Shape resonances in ion-molecule reaction

    NASA Astrophysics Data System (ADS)

    Sakimoto, Kazuhiro

    2014-01-01

    A simple analytical formula for the probability of reaction in low-energy ion-molecule collisions is given by Wentzel-Kramers-Brillouin and uniform approximations. By using this formula, one can deal with any type of shape resonances regardless of whether the collision energy is below or above a potential barrier. The reaction probability is completely determined by three parameters: the high-energy limit (P0) of the reaction probability obtained at a collision energy much above the potential barrier, a universal measure (?) of the difference between the collision energy and the barrier top, and a scattering phase shift (?) due to short-range reactive interaction. It is very useful to draw a topographical map of the reaction probability by assuming that P0 is given as a constant and that (?, ?) are independent variables. The energy dependence of the reaction probability in a collision process is represented by the section view along a route actually allowed on this topographical map. A resonance structure appears when the actual route crosses a prominent mountain ridge. It is shown that the reaction probability can be unity at a resonance energy even if the probabilities at off-resonance energies are very small. No sharp tunnelling resonance would be expected in the collision system having P_{0}>2(\\sqrt{2}-1)=0.828.

  6. Samarium Ion-Promoted Cross-Aldol Reactions and Tandem Aldol/Evans-Tishchenko Reactions.

    PubMed

    Lu, Ling; Chang, Hung-Yu; Fang, Jim-Min

    1999-02-01

    Cross-aldol reactions of carbonyl compounds were achieved by the catalysis of SmI(2) or SmI(3), together with molecular sieves, at ambient temperature. 1,3-Dichloroacetone and 1-chloroacetone can be used as acceptor substrates in the cross-aldol reactions with donor substrates such as acetone, cyclopentanone, and cyclohexanone. The cross-aldol reactions with (R)-glyceraldehyde acetonide gave optically pure compounds 25-32, the stereochemistry of which was in agreement with a chairlike chelate transition state of dipolar mode. SmI(2)-molecular sieves or SmI(3)-molecular sieves also functioned as effective Lewis acids to catalyze tandem aldol/Evans-Tishchenko reactions. The aldol/Evans-Tishchenko reactions of methyl ketones with aldehydes occurred at 0 degrees C to give alpha,gamma-anti diol monoesters 53a-59a. When the reactions were conducted at room temperature, a certain degree of transesterification took place. The aldol/Evans-Tishchenko reactions of ethyl or benzyl ketones with aldehydes yielded alpha,beta-anti-alpha,gamma-anti diol monoesters 60a-65a. However, the aldol/Evans-Tishchenko reactions of cyclic ketones with benzaldehyde occurred with a different stereoselectivity to give alpha,beta-syn-alpha,gamma-anti diol monoesters 66a-76a. The structures of products were determined by chemical and spectroscopic methods including an X-ray diffraction analysis of 72a derived from the reaction of 4-tert-butylcyclohexanone and benzaldehyde. A reaction mechanism involving dissociation-recombination of aldols followed by intramolecular stereoselective hydride shift is proposed, based on some experimental evidence, to explain the dichotomous stereoselectivity using acyclic or cyclic ketones as the reaction substrates. PMID:11674156

  7. Moving attention - Evidence for time-invariant shifts of visual selective attention

    NASA Technical Reports Server (NTRS)

    Remington, R.; Pierce, L.

    1984-01-01

    Two experiments measured the time to shift spatial selective attention across the visual field to targets 2 or 10 deg from central fixation. A central arrow cued the most likely target location. The direction of attention was inferred from reaction times to expected, unexpected, and neutral locations. The development of a spatial attentional set with time was examined by presenting target probes at varying times after the cue. There were no effects of distance on the time course of the attentional set. Reaction times for far locations were slower than for near, but the effects of attention were evident by 150 msec in both cases. Spatial attention does not shift with a characteristic, fixed velocity. Rather, velocity is proportional to distance, resulting in a movement time that is invariant over the distances tested.

  8. Chemical Shift Prediction for Denatured Proteins

    PubMed Central

    Sahu, Sarata C.; Nkari, Wendy K.; Morris, Laura C.; Live, David; Gruta, Christian

    2013-01-01

    While chemical shift prediction has played an important role in aspects of protein NMR that include identification of secondary structure, generation of torsion angle constraints for structure determination, and assignment of resonances in spectra of intrinsically disordered proteins, interest has arisen more recently in using it in alternate assignment strategies for crosspeaks in 1H-15N HSQC spectra of sparsely labeled proteins. One such approach involves correlation of crosspeaks in the spectrum of the native protein with those observed in the spectrum of the denatured protein, followed by assignment of the peaks in the latter spectrum. As in the case of disordered proteins, predicted chemical shifts can aid in these assignments. Some previously developed empirical formulas for chemical shift prediction have depended on basis data sets of 20 pentapeptides. In each case the central residue was varied among the 20 amino common acids, with the flanking residues held constant throughout the given series. However, previous choices of solvent conditions and flanking residues make the parameters in these formulas less than ideal for general application to denatured proteins. Here, we report 1H and 15N shifts for a set of alanine based pentapeptides under the low pH urea denaturing conditions that are more appropriate for sparse label assignments. New parameters have been derived and a Perl script was created to facilitate comparison with other parameter sets. A small, but significant, improvement in shift predictions for denatured ubiquitin is demonstrated. PMID:23297019

  9. Nonlinear ferromagnetic resonance shift in nanostructures

    NASA Astrophysics Data System (ADS)

    Guo, Feng; Belova, Lyuba; McMichael, Robert

    2014-03-01

    In dynamic magnetic systems, various experiments have shown that the ferromagnetic resonance frequency can shift up or down with increasing driving power in the nonlinear regime. The resonance shift is important in understanding nonlinear physics in nanomagnets and for applications of spin-torque oscillators. Here, we present a systematic study on the sign of the nonlinear coefficient, i.e. the direction of the resonance field/frequency shift. We use ferromagnetic resonance force microscopy (FMRFM) to measure the ferromagnetic resonance of a series of submicron NiFe ellipses with varying aspect ratios. We find the sign of the resonance shift is determined by both the applied field and the anisotropy field. Our measurement and micromagnetic modeling results are in qualitative agreement with a macro-spin analysis developed by Slavin and Tiberkevich. However, both measurement and modeling results exhibit values of the nonlinear coefficient that are more positive (meaning that the resonance tends to shift toward low field direction) than are predicted by the macrospin model. We attribute the difference to the non-uniformity of the precession modes in the ellipses. By analogy with standing spin waves, we show that nonuniform precession tends to increase the nonlinear frequency coefficient through a magnetostatic mechanism.

  10. Monetary policy regime shifts: new evidence from time-varying interest rate rules

    Microsoft Academic Search

    Carmine Trecroci; Matilde Vassalli

    2006-01-01

    We estimate forward-looking interest-rate rules, for major advanced countries, allowing for time variation in their parameters. Traditional constant-parameter reaction functions likely blur the impact of i) model uncertainty, ii) conflicting objectives, iii) shifting preferences and iv) nonlinearities of policymakers choices. We find that monetary policies followed by the US, the UK, Germany, France and Italy, often described in terms of

  11. Fractal Reaction Kinetics

    NASA Astrophysics Data System (ADS)

    Kopelman, Raoul

    1988-09-01

    Classical reaction kinetics has been found to be unsatisfactory when the reactants are spatially constrained on the microscopic level by either walls, phase boundaries, or force fields. Recently discovered theories of heterogeneous reaction kinetics have dramatic consequences, such as fractal orders for elementary reactions, self-ordering and self-unmixing of reactants, and rate coefficients with temporal ``memories.'' The new theories were needed to explain the results of experiments and supercomputer simulations of reactions that were confined to low dimensions or fractal dimensions or both. Among the practical examples of ``fractal-like kinetics'' are chemical reactions in pores of membranes, excitation trapping in molecular aggregates, exciton fusion in composite materials, and charge recombination in colloids and clouds. Diffusion-controlled reactions with geometrical constraints, as found in heterogeneous kinetics, may be described by reactions on fractal domains. The hallmarks of ``fractal-like'' reactions are anomalous reaction orders and time-dependent reaction rate ``constants.'' These anomalies stem from the nonrandomness of the reactant distributions in low dimensions. For homo-bimolecular reactions (A + A --> Pr) the distribution is partially ordered, for example, quasi-periodic. However, for hetero-bimolecular reactions (A + B --> Pr) the reactants segregate. Theory, simulations, and experiments are interrelated through the formalism of fractal reaction kinetics (42).

  12. Polarization phase shifting lateral shearing interferometer

    NASA Astrophysics Data System (ADS)

    Liu, Lei; Zeng, Aijun; Zhu, Linglin; Song, Qiang; Huang, Huijie

    2013-08-01

    A polarization phase shifting lateral shearing interferometer based on a polarization beam splitting plate(PBSP) is proposed. The front surface of the PBSP is coated with polarization beam splitting film and its back surface is coated with total reflection film. The beam to be tested is split by the PBSP with an incidence angle of 45° and divided into two mutually perpendicular linearly polarization beams. Phase shifting can be introduced to the interferometer when the PBSP is combined with a polarzation temporal or spatial phase shifter. A polarizaiton temporal phase shifting lateral shearing interferometer system is built up both with the ASAP software and the experiments. The usefulness of the interferometer is verified.

  13. Team Proposes Paradigm Shift in Robotic Space Exploration Team Proposes Paradigm Shift in Robotic Space Exploration

    E-print Network

    Arizona, University of

    Team Proposes Paradigm Shift in Robotic Space Exploration Team Proposes Paradigm Shift in Robotic Space Exploration A team of interdisciplinary scientists has unveiled a proposal to make core changes in the robotic exploration of the solar system. In addition to spaceborne orbiters, the "new paradigm" would

  14. Progress in speckle-shift strain measurement

    NASA Technical Reports Server (NTRS)

    Lant, Christian T.; Barranger, John P.; Oberle, Lawrence G.; Greer, Lawrence C., III

    1991-01-01

    The Instrumentation and Control Technology Division of the Lewis Research Center has been developing an in-house capability to make one dimensional and two dimensional optical strain measurements on high temperature test specimens. The measurements are based on a two-beam speckle-shift technique. The development of composite materials for use in high temperature applications is generating interest in using the speckle-shift technique to measure strains on small diameter fibers and wires of various compositions. The results of preliminary speckle correlation tests on wire and fiber specimens are covered, and the advanced system currently under development is described.

  15. Thermometry via Light Shifts in Optical Lattices

    NASA Astrophysics Data System (ADS)

    McDonald, M.; McGuyer, B. H.; Iwata, G. Z.; Zelevinsky, T.

    2015-01-01

    For atoms or molecules in optical lattices, conventional thermometry methods are often unsuitable due to low particle numbers or a lack of cycling transitions. However, a differential spectroscopic light shift can map temperature onto the line shape with a low sensitivity to trap anharmonicity. We study narrow molecular transitions to demonstrate precise frequency-based lattice thermometry, as well as carrier cooling. This approach should be applicable down to nanokelvin temperatures. We also discuss how the thermal light shift can affect the accuracy of optical lattice clocks.

  16. Isotope shifts in methane near 6000/cm

    NASA Technical Reports Server (NTRS)

    Fox, K.; Halsey, G. W.; Jennings, D. E.

    1976-01-01

    Isotope shifts for cleanly resolved vibrational-rotational absorption lines of CH4-12 and CH4-13 were measured by a 5-m focal length Littrow spectrometer in the 6000/cm range. The methane isotopes were held in separate absorption cells: 20 torr of CH4-13 in a 1-m cell, and 5 torr of CH4-12 in a White cell of 4-m optical path length. Measured shifts for the cleanly resolved singlets R(0), R(1), Q(1) and P(1) are summarized in tabular form.

  17. Compensating For Doppler Shift In Laser Instrumentation

    NASA Technical Reports Server (NTRS)

    Schwemmer, Geary K.

    1990-01-01

    Electronic tuning system continually adjusts frequency of tunable diode laser to compensate for Doppler shift caused by motion of transmitter or receiver containing laser. Doppler-shift-compensating system intended primarily for use in transmitter or receiver of laser remote-sensing or communication system to keep frequency of received signal within frequency range of narrow-band-pass filter. By use of narrow-band filter (instead of wide-band filter required in absence of Doppler compensation), signal-to-noise ratio of laser system increased. Thus, less-powerful transmitter usable.

  18. Phase Transitions in Paradigm Shift Models

    PubMed Central

    Chae, Huiseung; Yook, Soon-Hyung; Kim, Yup

    2013-01-01

    Two general models for paradigm shifts, deterministic propagation model (DM) and stochastic propagation model (SM), are proposed to describe paradigm shifts and the adoption of new technological levels. By defining the order parameter based on the diversity of ideas, , it is studied when and how the phase transition or the disappearance of a dominant paradigm occurs as a cost in DM or an innovation probability in SM increases. In addition, we also investigate how the propagation processes affect the transition nature. From analytical calculations and numerical simulations is shown to satisfy the scaling relation for DM with the number of agents . In contrast, in SM scales as . PMID:23951043

  19. Lamb Shift of Unruh Detector Levels

    E-print Network

    Bjorn Garbrecht; Tomislav Prokopec

    2005-10-28

    We argue that the energy levels of an Unruh detector experience an effect similar to the Lamb shift in Quantum Electrodynamics. As a consequence, the spectrum of energy levels in a curved background is different from that in flat space. As examples, we consider a detector in an expanding Universe and in Rindler space, and for the latter case we suggest a new expression for the local virtual energy density seen by an accelerated observer. In the ultraviolet domain, that is when the space between the energy levels is larger than the Hubble rate or the acceleration of the detector, the Lamb shift quantitatively dominates over the thermal response rate.

  20. Lamb shift in the muonic deuterium atom

    SciTech Connect

    Krutov, A. A.; Martynenko, A. P. [Samara State University, Pavlov street 1, 443011, Samara (Russian Federation); Samara State University, Pavlov Street 1, 443011, Samara, Russia and Samara State Aerospace University named after academician S.P. Korolyov, Moskovskoye Shosse 34, 443086, Samara (Russian Federation)

    2011-11-15

    We present an investigation of the Lamb shift (2P{sub 1/2}-2S{sub 1/2}) in the muonic deuterium ({mu}D) atom using the three-dimensional quasipotential method in quantum electrodynamics. The vacuum polarization, nuclear-structure, and recoil effects are calculated with the account of contributions of orders {alpha}{sup 3}, {alpha}{sup 4}, {alpha}{sup 5}, and {alpha}{sup 6}. The results are compared with earlier performed calculations. The obtained numerical value of the Lamb shift at 202.4139 meV can be considered a reliable estimate for comparison with forthcoming experimental data.

  1. Doppler frequency shift of sound apparatus

    NASA Astrophysics Data System (ADS)

    Schier, Walter

    2011-04-01

    A large 1-m diameter rotary table with a semicircular waveguide along its periphery is the basis of the Doppler frequency shift of sound apparatus. A "button" speaker is attached to the outer edge of the rotary table and a microphone pickup is positioned on the wall of the waveguide at its midpoint. At approximate speeds of 25 mph (11 m/s), the velocity measured from the frequency shift between the approaching and receding speaker compared to the velocity measured from the repeat sound pattern agree to within 1%. The microphone output is fed successively to our 10 computer stations.

  2. Frequency shift in the moving periodic structure

    SciTech Connect

    Dong Tianlin; Xia Dan [Department of Electronics and Information, Huazhong University of Science and Technology, Wuhan, Hubei 430074 (China)

    2008-09-15

    The interaction between the electromagnetic wave and the moving periodic structure is analyzed. The main physical effect revealed by theoretical analysis is that the frequency shift of the scattered or transmitted mode is proportional to the speed and the mode order m over the period a. The frequency shift is independent of the incidence direction and the carrier frequency. The physical effect is verified by an experiment. The analysis released here is fundamental in speed measurement and may have certain significance in interdisciplinary fields.

  3. Microscale Thermite Reactions.

    ERIC Educational Resources Information Center

    Arnaiz, Francisco J.; Aguado, Rafael; Arnaiz, Susana

    1998-01-01

    Describes the adaptation of thermite (aluminum with metal oxides) reactions from whole-class demonstrations to student-run micro-reactions. Lists detailed directions and possible variations of the experiment. (WRM)

  4. Anaphylaxis-Like Reactions

    MedlinePLUS

    ... antibody) is involved. These reactions are called anaphylactoid (meaning anaphylaxis-like) reactions. While the immune system must ... Find Programs & Services Make a Donation Find a Location Connect With Us View Events Calendar Read the ...

  5. Chemical Reactions and Stoichiometry

    NSDL National Science Digital Library

    2012-07-31

    In this activity, students explore reactions in which chemical bonds are formed and broken. Students experiment with changing the temperature and the concentration of the atoms in order to see how these affect reaction rates. They also learn how to communicate what happens during a chemical reaction by writing the ratios of reactants and products, known as stoichiometry.

  6. Explaining competitive reaction effects

    Microsoft Academic Search

    Peter S. H. Leeflang; Dick R. Wittink

    2001-01-01

    Changes in promotional expenditure decisions for a brand, as in other marketing decisions, should be based on the expected impact on purchase and consumption behavior as well as on the likely reactions by competitors. Purchase behavior may be predicted from estimated demand functions. Competitive reactions can be anticipated based on estimated reaction functions, which show how changes in an instrument

  7. Reaction coordinates for electron transfer reactions

    SciTech Connect

    Rasaiah, Jayendran C. [Department of Chemistry, University of Maine, Orono, Maine 04469 (United States); Zhu Jianjun [Department of Chemistry, State University of New York, Stonybrook, New York 11790 (United States) and Department of Chemistry, Henan Normal University, Xinxiang, Henan (China)

    2008-12-07

    The polarization fluctuation and energy gap formulations of the reaction coordinate for outer sphere electron transfer are linearly related to the constant energy constraint Lagrangian multiplier m in Marcus' theory of electron transfer. The quadratic dependence of the free energies of the reactant and product intermediates on m and m+1, respectively, leads to similar dependence of the free energies on the reaction coordinates and to the same dependence of the activation energy on the reorganization energy and the standard reaction free energy. Within the approximations of a continuum model of the solvent and linear response of the longitudinal polarization to the electric field in Marcus' theory, both formulations of the reaction coordinate are expected to lead to the same results.

  8. Collisionally Induced Atomic Clock Shifts and Correlations

    E-print Network

    Y. B. Band; I. Osherov

    2011-06-23

    We develop a formalism to incorporate exchange symmetry considerations into the calculation of collisional frequency shifts and blackbody radiation effects for atomic clock transitions using a density matrix formalism. The formalism is developed for both fermionic and bosonic atomic clocks. Results for a finite temperature ${}^{87}$Sr ${}^1S_0$ ($F = 9/2$) atomic clock in a magic wavelength optical lattice are presented.

  9. Blackbody radiation shifts in optical atomic clocks.

    PubMed

    Safronova, Marianna; Kozlov, Mikhail; Clark, Charles

    2012-03-01

    A review of recent theoretical calculations of blackbody radiation (BBR) shifts in optical atomic clocks is presented. We summarize previous results for monovalent ions that were obtained by a relativistic all-order single-double method, where all single and double excitations of the Dirac- Fock wave function are included to all orders of perturbation theory. A recently developed method for accurate calculations of BBR shifts in divalent atoms is then presented. This approach combines the relativistic all-order method and the configuration interaction method, which provides for accurate treatment of correlation corrections in atoms with two valence electrons. Calculations of the BBR shifts in B+, Al+, and In+ have enabled us to reduce the present fractional uncertainties in the frequencies of their clock transitions as measured at room temperature: to 4 × 10-19 for Al+ and 10-18 for B+ and In+. These uncertainties approach recent estimates of the limits of precision of currently proposed optical atomic clocks. We discuss directions of future theoretical developments for reducing clock uncertainties resulting from blackbody radiation shifts. PMID:22481777

  10. Phase shifting in pulse tube refrigerators

    Microsoft Academic Search

    A. Hofmann; H. Pan

    1999-01-01

    Different types of pulse tube refrigerators are described by alternative phasor diagrams based on the volume flow rates applied at the ambient temperature inlets of the regenerator and of the pulse tube(s). This provides a simple means for finding the optimum phase shift between pressure and flow rate for PTRs operated with different kinds of phase shifters such as the

  11. THE SHIFTED WAVE EQUATION ON DAMEKRICCI SPACES

    E-print Network

    and the inverse dual Abel trans- form. As an application, we investigate Huygens' principle. A similar analysis clarify the role of the inverse dual Abel transform in solving the shifted wave equation. Recall, using the inverse dual Abel transform. As an applica- tion, we investigate Huygens' principle. Section 4

  12. Indexicality and context-shift Franois Recanati

    E-print Network

    Paris-Sud XI, Université de

    Indexicality and context-shift François Recanati Institut Jean Nicod/Harvard University Workshop on Indexicality, Speech Acts and Logophors Harvard University, November 20th , 2004 1. Preliminaries 1.1 Indexicality and semantic under-specification Indexicals are expressions whose semantic value systematically

  13. The Vowel Shift Rule in English.

    ERIC Educational Resources Information Center

    Krohn, Robert

    When considering vowel alternations in English, it is possible to develop a less abstract vowel system than the one developed by Chomsky and Halle by using their laxing rule as the input for a restrictive vowel-shift rule which accounts for the relative height of alternating vowels in alternations such as divine-divinity, extreme-extremity,…

  14. Adaptive Bandwidth Mean Shift Object Detection

    Microsoft Academic Search

    Xiaopeng Chen; Haiyan Huang; Haibo Zheng; Chengrong Li

    2008-01-01

    In this paper, a novel adaptive bandwidth mean shift algorithm toward 2D object detection (ABMSOD) is proposed. It can not only identify whether an object of certain classes exists or not, but also get the scale and orientation besides position very fast. The feature histogram weighted by a kernel with adaptive bandwidth is used for representing the target object model

  15. The Phase Shift in the Jumping Ring

    ERIC Educational Resources Information Center

    Jeffery, Rondo N.; Amiri, Farhang

    2008-01-01

    The popular physics demonstration experiment known as Thomson's Jumping Ring (JR) has been variously explained as a simple example of Lenz's law, or as the result of a phase shift of the ring current relative to the induced emf. The failure of the first-quadrant Lenz's law explanation is shown by the time the ring takes to jump and by levitation.…

  16. Shift Work Linked to Health Problems

    MedlinePLUS

    ... news/fullstory_152606.html Shift Work Linked to Health Problems Excess weight, sleep issues more common among those ... Medicine and Public Health, said in a Sleep Health journal news ... to experiencing sleep problems as their jobs require them to work night, ...

  17. Implications of Shifting Technology in Education

    ERIC Educational Resources Information Center

    Holland, Janet; Holland, John

    2014-01-01

    This article examines the implications of shifting technology trends by looking at what we've lost or are losing, where we are, and where we need to go for making the needed transitions in knowledge and skills. Areas of growth within new media and the tech industry are good indicators of our growing interests in mobility, improved quality,…

  18. Pedagogy of the Obsessed Shifting the Focus

    ERIC Educational Resources Information Center

    Correa, Elaine

    2006-01-01

    This paper will concentrate on the current shift from teaching to entitlement learning that has become a significant part of our educational discourse and culture. With increasing emphasis on accountability and high test score, students have become active recipients in "assessing" and "evaluating" the effectiveness of their learning experiences.…

  19. Shifting Standards and Stereotype-Based Judgments

    Microsoft Academic Search

    Monica Biernat; Melvin Manis

    1994-01-01

    Four studies tested a model of stereotype-based shifts in judgment standards developed by M. Biernat, M. Manis, and T. E. Nelson (1991). The model suggests that subjective judgments of target persons from different social groups may fail to reveal the stereotyped expectations of judges, because they invite the use of different evaluative standards; more \\

  20. Pressure Shift and Broadening of Spectral Lines

    Microsoft Academic Search

    Henry Margenau

    1932-01-01

    The pressure shift of spectral lines, unexplained by the usual theories of pressure broadening, can be adequately treated on the basis of a theory which considers the perturbations produced by neighboring atoms on the two states between which transitions occur. The analysis presented in the paper is directly applicable only to absorption lines, but its consequences are qualitatively correct for

  1. Night Shift Work, Sleep Quality, and Obesity

    PubMed Central

    Ko, Sang Baek

    2013-01-01

    Background: The aims of this study were to examine the relationship between night shift work and sleep, to investigate the correlations with various biomarkers that show the influence of sleep on obesity, and ultimately, to analyze factors that have an impact on obesity. Methods: This study used data from the National Survey of Midlife Development in the United States II (MIDUS II study) and the MIDUS II Biomarker Project. After connecting the MIDUS II study data with the MIDUS II Biomarker Project data, we analyzed data from 883 subjects to investigate the relationship between night shift work and sleep quality. We also examined the correlations with biomarkers and sleep quality. Lastly, we performed logistic regression analyses to investigate factors that had an impact on obesity. Results: Sleep quality was found to be low among night shift workers. Sleep quality was positively correlated with HbA1c, total cholesterol, and triglyceride levels, and inversely correlated with DHEA levels. Sleep quality was highly correlated with inflammatory markers and inversely correlated with antioxidant markers. Sleep quality was significantly associated with obesity (OR: 1.10, 95% CI: 1.03–1.18). Biomarkers that had an influence on obesity included diastolic blood pressure, HbA1c and triglyceride levels, inflammatory markers, and antioxidant values. Conclusion: Poor sleep quality due to night shift work disturbs the circadian rhythm, causing negative changes in metabolic, inflammatory, neuroendocrine, and antioxidant biomarkers. These changes may eventually play a role in increasing the incidence of obesity.

  2. Special Section Shifting Foundations and Metrics for

    E-print Network

    Aspbury, Andrea S. - Department of Biology, Texas State University

    Special Section Shifting Foundations and Metrics for Golden-Cheeked Warbler Recovery JEFF S University Drive, San Marcos, TX 78666, USA ABSTRACT Using the golden-cheeked warbler (Setophaga chrysoparia, density estimation, endangered species, golden-cheeked warbler, occupancy models, population viability

  3. II REGIME SHIFTS IN LAKES Introduction

    E-print Network

    changes in fish populations or communities, and coordinated shifts in food web structure (trophic cascades the patterns. In addition, the chapter introduces some models addressed in later chapters. The models are introduced graphically and conceptually. Mathematical versions of the models are presented in later chapters

  4. A Tectonic Shift in Global Higher Education

    ERIC Educational Resources Information Center

    Daniel, John; Kanwar, Asha; Uvalic-Trumbic, Stamenka

    2006-01-01

    Europeans lament that their universities are lagging behind those in the United States, while Americans worry that their academic leadership is threatened by complacency. Both groups, however, are missing the tectonic shift that will transform the map of higher education worldwide--the growth of universities in the developing world. Spreading…

  5. Critical Review--Outsourcing: A Paradigm Shift.

    ERIC Educational Resources Information Center

    Kakabadse, Nada; Kakabadse, Andrew

    2000-01-01

    Discusses trends in outsourcing, provision of goods and services to an organization that were previously delivered in house. Addresses outsourcing in the public sector, advantages and disadvantages, implications for human resource development, and the shift to the new "psychological contract" between employers and employees. (Contains 227…

  6. Photospheric spectrum line asymmetries and wavelength shifts

    Microsoft Academic Search

    D. Dravins

    1982-01-01

    Results of studies on the asymmetries of spectral lines that have hitherto been regarded as symmetric are discussed. The discrepancy between solar and laboratory wavelengths is summarized, including the limb effect. Solar line profiles have been accurately measured, revealing intrinsic asymmetries in the lines. The causes of asymmetries and shifts can be traced back to photospheric inhomogeneities, so that high

  7. Shifted polynomials in a convection problem

    E-print Network

    Ioana Dragomirescu

    2007-09-14

    The onset of convection in a horizontal layer of fluid heated from below in the presence of a gravity field varying across the layer is investigated. The eigenvalue problem governing the linear stability of the mechanical equilibria of the fluid layer in the case of free boundaries is solved using a Galerkin method based on shifted polynomials (Legendre and Chebyshev polynomials).

  8. Laplacian filtered minimum shift keying modulation

    NASA Astrophysics Data System (ADS)

    Abu-Isbeih, Ibrahim N.; Maqusi, Mohammad

    2010-09-01

    Gaussian minimum shift keying (GMSK) is a continuous-phase frequency-shift keying modulation scheme. It is similar to standard minimum-shift keying (MSK); however the digital data stream is first shaped with a Gaussian filter before being applied to a frequency modulator. This has the advantage of reducing sideband power, which in turn reduces out-of- band interference between signal carriers in adjacent frequency channels. In this paper a new method of premodulation filtered MSK called Laplacian minimum shift keying (LMSK) is proposed. LMSK is proposed as a method for achieving good spectral efficiency over regular MSK, and it turns out to achieve improvement in error rate performance over the known GMSK. To compare the behavior of the system under the proposed method, bandwidth efficiency (i.e., bps/Hz), fractional out-of-band power and error rate performance in such systems are used. Results show that the proposed LMSK attains good improvement in spectral efficiency over MSK; and in using LMSK we have also good improvement in power efficiency over GMSK.

  9. Heart-rate pulse-shift detector

    NASA Technical Reports Server (NTRS)

    Anderson, M.

    1974-01-01

    Detector circuit accurately separates and counts phase-shift pulses over wide range of basic pulse-rate frequency, and also provides reasonable representation of full repetitive EKG waveform. Single telemeter implanted in small animal monitors not only body temperature but also animal movement and heart rate.

  10. Averaged shifted chi-square test

    Microsoft Academic Search

    Jyh-Shyang Wu; Wen-Shuenn Deng

    2012-01-01

    A simple procedure based on the average of shifted chi-square statistics (ASCS) is proposed to improve the classical chi-square procedure for testing whether a random sample has been drawn from a specified continuous distribution. We repeatedly partition the sample space, say, ? times to obtain ? respective chi-square statistics. The proposed test statistic is defined as the average value of

  11. Averaged shifted chi-square test

    Microsoft Academic Search

    Jyh-Shyang Wu; Wen-Shuenn Deng

    2011-01-01

    A simple procedure based on the average of shifted chi-square statistics (ASCS) is proposed to improve the classical chi-square procedure for testing whether a random sample has been drawn from a specified continuous distribution. We repeatedly partition the sample space, say, ? times to obtain ? respective chi-square statistics. The proposed test statistic is defined as the average value of

  12. Deindustrialization and the Shift to Services.

    ERIC Educational Resources Information Center

    Kutscher, Ronald E.; Personick, Valerie A.

    1986-01-01

    Bureau of Labor Statistics data show the industrial sector as a whole in healthy shape, but a few manufacturing industries in deep trouble. These industries include tobacco manufacturers, iron and steel foundries, leather products, and steel manufacturers. Also examines shifts in employment and output, job quality, and outlook for the future. (CT)

  13. Notice From Security & Parking Services to those requiring Shift Parking

    E-print Network

    Hitchcock, Adam P.

    Notice From Security & Parking Services to those requiring Shift Parking Shift parking is issued beyond the shuttle bus hours of operation. Shift parking allows a Lot M, N, O or P transponder holder to park on central campus after 2:30 pm. Shift parking is provided at no extra charge to employees who

  14. Reaction efficiency effects on binary chemical reactions.

    PubMed

    Lazaridis, Filippos; Savara, Aditya; Argyrakis, Panos

    2014-09-14

    We study the effect of the variation of reaction efficiency in binary reactions. We use the well-known A + B ? 0 model, which has been extensively studied in the past. We perform simulations on this model where we vary the efficiency of reaction, i.e., when two particles meet they do not instantly react, as has been assumed in previous studies, but they react with a probability ?, where ? is in the range 0 < ? < 1. Our results show that at small ? values the system is reaction limited, but as ? increases it crosses over to a diffusion limited behavior. At early times, for small ? values, the particle density falls slower than for larger ? values. This fall-off goes over a crossover point, around the value of ? = 0.50 for high initial densities. Under a variety of conditions simulated, we find that the crossover point was dependent on the initial concentration but not on the lattice size. For intermediate and long times simulations, all ? values (in the depleted reciprocal density versus time plot) converge to the same behavior. These theoretical results are useful in models of epidemic reactions and epidemic spreading, where a contagion from one neighbor to the next is not always successful but proceeds with a certain probability, an analogous effect with the reaction probability examined in the current work. PMID:25217900

  15. Sleep Loss and Fatigue in Shift Work and Shift Work Disorder

    PubMed Central

    Åkerstedt, Torbjörn; Wright, Kenneth P.

    2010-01-01

    Shift work is highly prevalent in industrialized societies (>20%) but, when it includes night work, it has pronounced negative effects on sleep, subjective and physiological sleepiness, performance, accident risk, as well as on health outcomes such as cardiovascular disease and certain forms of cancer. The reason is the conflict between the day oriented circadian physiology and the requirement for work and sleep at the “wrong” biological time of day. Other factors that negatively impact work shift sleepiness and accident risk include long duration shifts greater than 12 hours and individual vulnerability for phase intolerance that may lead to a diagnosis of shift work disorder; i.e., those shift workers with the greatest sleepiness and performance impairment during the biological night and insomnia during the biological day. Whereas some countermeasures may be used to ameliorate the negative impact of shift work on nighttime sleepiness and daytime insomnia (combined countermeasures may be the best available), there seems at present to be no way to eliminate most of the negative effects of shift work on human physiology and cognition. PMID:20640236

  16. Classical toy models for the monopole shift and the quadrupole shift.

    PubMed

    Rose, Katrin; Cottenier, Stefaan

    2012-08-28

    The penetration of s- and p(1/2)-electrons into the atomic nucleus leads to a variety of observable effects. The presence of s-electrons inside the nucleus gives rise to the isotope shift in atomic spectroscopy, and to the isomer shift in Mössbauer spectroscopy. Both well-known phenomena are manifestations of the more general monopole shift. In a recent paper (Koch et al., Phys. Rev. A, 2010, 81, 032507), we discussed the existence of the formally analogous quadrupole shift: a tensor correction to the electric quadrupole interaction due to the penetration of relativistic p(1/2)-electrons into the nucleus. The quadrupole shift is predicted to be observable by high-accuracy molecular spectroscopy on a set of 4 molecules (the quadrupole anomaly). The simple physics behind all these related phenomena is easily obscured by an elaborate mathematical formalism that is required for their derivation: a multipole expansion in combination with perturbation theory, invoking quantum physics and ideally relativity. In the present paper, we take a totally different approach. We consider three classical 'toy models' that can be solved by elementary calculus, and that nevertheless contain all essential physics of the monopole and quadrupole shifts. We hope that this intuitive (yet exact) analysis will increase the understanding about multipole shift phenomena in a broader community. PMID:22782015

  17. FABRICATION OF MICHELSON INTERFEROMETER FOR PHASE SHIFTING METHOD

    Microsoft Academic Search

    Nguyen Tang Vu; Tran Thanh Nam; Ly Thuong Kiet

    Displacement measurement can be performed with high accuracy using phase-shifting method. In phase-shifting method, it is often used four steps of phase-shifting for one cycle. In conventional method, to measure the displacement of an object by interferometer, the phase of reference beam should be shifted by every ?\\/2 in four-step phase-shifting. Therefore, the error of this measurement is depended upon

  18. Postweld-shift-induced fiber alignment shifts in laser-welded laser module packages: experiments and simulations

    Microsoft Academic Search

    Yi-Cheng Hsu; Ying-Chien Tsai; Jao-Hwa Kuang; Wood-Hi Cheng

    2005-01-01

    The fiber alignment shifts induced by the postweld shift (PWS) in laser-welded transistor outline (TO)-Can-type laser module packages were studied experimentally and numerically. The PWS-induced fiber alignment shifts were quantitatively determined by four geometrical parameters, namely: 1) the lateral shift (r); 2) the position angle (?); 3) the swing angle (?); and 4) the tilt angle (?). The measured coupling

  19. Transitional Bubble in Periodic Flow Phase Shift

    NASA Technical Reports Server (NTRS)

    Talan, M.; Hourmouziadis, Jean

    2004-01-01

    One particular characteristic observed in unsteady shear layers is the phase shift relative to the main flow. In attached boundary layers this will have an effect both on the instantaneous skin friction and heat transfer. In separation bubbles the contribution to the drag is dominated by the pressure distribution. However, the most significant effect appears to be the phase shift on the transition process. Unsteady transition behaviour may determine the bursting of the bubble resulting in an un-recoverable full separation. An early analysis of the phase shift was performed by Stokes for the incompressible boundary layer of an oscillating wall and an oscillating main flow. An amplitude overshoot within the shear layer as well as a phase shift were observed that can be attributed to the relatively slow diffusion of viscous stresses compared to the fast change of pressure. Experiments in a low speed facility with the boundary layer of a flat plate were evaluated in respect to phase shift. A pressure distribution similar to that on the suction surface of a turbomachinery aerofoil was superimposed generating a typical transitional separation bubble. A periodically unsteady main flow in the suction type wind tunnel was introduced via a rotating flap downstream of the test section. The experiments covered a range of the three similarity parameters of momentum-loss-thickness Reynolds-number of 92 to 226 and Strouhal-number (reduced frequency) of 0.0001 to 0.0004 at the separation point, and an amplitude range up to 19 %. The free stream turbulence level was less than 1% .Upstream of the separation point the phase shift in the laminar boundary layer does not appear to be affected significantly bay either of the three parameters. The trend perpendicular to the wall is similar to the Stokes analysis. The problem scales well with the wave velocity introduced by Stokes, however, the lag of the main flow near the wall is less than indicated analytically. The separation point comes closest to the Stokes analysis but the phase is still 20 degrees lower at the wall.

  20. PREPARATION CHARACTERISTICS OF CATALYSTS FOR FOSSIL FUEL CONVERSION

    Microsoft Academic Search

    S. Parkash; K. Lali

    1986-01-01

    The article reviews some of the technical Intricacies which are Involved In the preparation of metal oxide containing catalysts. In processing of energy resources, representative reactions catalysed by metal oxides Include cracking, reforming, hydrofining, water-gas shift, and methanol synthesis. The preparatory methods of metal catalysts control the selectivity, stability and activity for a particular reaction.The specifics of the technique of

  1. Catalytically active gold: The role of cluster morphology T.V. Choudhary a

    E-print Network

    Goodman, Wayne

    synthesis, water gas shift reaction [10,11], environmental catalysis [2,12,13] and hydrogenation reactions dispersion and activity on the catalyst synthesis procedures, supports and pre-treatment conditions make also been successful for synthesis of highly dispersed and active Au catalysts [22]. However, use

  2. Reduction from non-injective hidden shift problem to injective hidden shift problem

    E-print Network

    Mirmojtaba Gharibi

    2012-09-25

    We introduce a simple tool that can be used to reduce non-injective instances of the hidden shift problem over arbitrary group to injective instances over the same group. In particular, we show that the average-case non-injective hidden shift problem admit this reduction. We show similar results for (non-injective) hidden shift problem for bent functions. We generalize the notion of influence and show how it relates to applicability of this tool for doing reductions. In particular, these results can be used to simplify the main results by Gavinsky, Roetteler, and Roland about the hidden shift problem for the Boolean-valued functions and bent functions, and also to generalize their results to non-Boolean domains (thereby answering an open question that they pose).

  3. Isotope shifts and electron densities in W I. I. Parametric analysis and theoretical field shifts

    Microsoft Academic Search

    P. Aufmuth; A. Steudel; E. Wobker

    1988-01-01

    The isotope shift in the arc spectrum of tungsten was studied in eight lines by means of a photoelectric recording Fabry-Perot spectrometer with digital data processing for 182,184W, 184,186W and 182,186W with the use of highly enriched isotope samples. The observed shifts were analysed by means of the parametric method. For the isotope pair 184,186W the g2 parameter yields a

  4. Is the Lamb shift chemically significant?

    NASA Technical Reports Server (NTRS)

    Dyall, Kenneth G.; Bauschlicher, Charles W., Jr.; Schwenke, David W.; Pyykko, Pekka; Arnold, James (Technical Monitor)

    2001-01-01

    The contribution of the Lamb shift to the atomization energies of some prototype molecules, BF3, AlF3, and GaF3, is estimated by a perturbation procedure. It is found to be in the range of 3-5% of the one-electron scalar relativistic contribution to the atomization energy. The maximum absolute value is 0.2 kcal/mol for GaF3. These sample calculations indicate that the Lamb shift is probably small enough to be neglected for energetics of molecules containing light atoms if the target accuracy is 1 kcal/mol, but for higher accuracy calculations and for molecules containing heavy elements it must be considered.

  5. Nuclear Sizes and the Isotope Shift

    E-print Network

    J. L. Friar; J. Martorell; D. W. L. Sprung

    1997-07-11

    Darwin-Foldy nuclear-size corrections in electronic atoms and nuclear radii are discussed from the nuclear-physics perspective. Interpretation of precise isotope-shift measurements is formalism dependent, and care must be exercised in interpreting these results and those obtained from relativistic electron scattering from nuclei. We strongly advocate that the entire nuclear-charge operator be used in calculating nuclear-size corrections in atoms, rather than relegating portions of it to the non-radiative recoil corrections. A preliminary examination of the intrinsic deuteron radius obtained from isotope-shift measurements suggests the presence of small meson-exchange currents (exotic binding contributions of relativistic order) in the nuclear charge operator, which contribute approximately 1/2%.

  6. Altitude and hypoxia as phase shift inducers.

    PubMed

    Ashkenazi, I E; Ribak, J; Avgar, D M; Klepfish, A

    1982-04-01

    The daily fluctuations in the levels of some physiological and performance parameters have been assessed in three young subjects. The assessment was carried out before and after exposing them to the combined effect of two stressors, reduced barometric pressure and hypoxia. The exposure was effectuated by a simulated flight in a low pressure chamber for 30 min. The measured altitude in the chamber was 25000 ft (7620 m). During the simulated flight, each of the individuals experienced 2-3 min of hypoxia. The examined parameters (oral temperature, peak expiratory flow, grip strength, 2 and 6 digits recognition test, addition, counting backward, and odd-even addition test) exhibited circadian rhythms whose acrophases shifted significantly after exposure to the combined effect of the two stressors. The phases continued to shift for 4 d in a concordantly synchronized pattern. On the fourth day, they exhibited a tendency to resume their original phase. PMID:7200769

  7. Time shifts and correlations in synchronized chaos.

    PubMed

    Blakely, Jonathan N; Pruitt, Matthew W; Corron, Ned J

    2008-03-01

    We introduce a new method for predicting characteristics of the synchronized state achieved by a wide class of unidirectional coupling schemes. Specifically, we derive a transfer function from the coupling model that provides estimates of the correlation between the drive and response waveforms, and of the time shift (i.e., lag or anticipation) of the synchronized state. To demonstrate the method, we apply it to a simulated system of coupled Rossler oscillators as well as to an experimental system of coupled chaotic electronic circuits. Finally, we show that the transfer function can be exploited to design novel coupling schemes that significantly improve the correlation and increase the maximum achievable time shift. PMID:18377068

  8. Pole Inflation - Shift Symmetry and Universal Corrections

    E-print Network

    Broy, Benedict J; Roest, Diederik; Westphal, Alexander

    2015-01-01

    An appealing explanation for the Planck data is provided by inflationary models with a non-canonical kinetic term: a Laurent expansion of the kinetic function translates into a potential with a nearly shift-symmetric plateau in canonical fields. The shift symmetry can be broken at large field values by including higher-order poles. We show that the resulting corrections to the inflationary dynamics and predictions are universal at lowest order, and can induce power loss at large angular scales. At lowest order there are no corrections from a pole of one order higher; this is referred to as extended no-scale in string theory and we explain why this is a general phenomenon. Finally, we outline which other corrections may arise as string loop corrections.

  9. Phase-Shifting Zernike Interferometer Wavefront Sensor

    NASA Technical Reports Server (NTRS)

    Wallace, J. Kent; Rao, Shanti; Jensen-Clem, Rebecca M.

    2011-01-01

    The canonical Zernike phase-contrast technique transforms a phase object in one plane into an intensity object in the conjugate plane. This is done by applying a static pi/2 phase shift to the central core (approx. lambda/diameter) of the PSF which is intermediate between the input and output plane. Here we present a new architecture for this sensor. First, the optical system is simple and all reflective, and second the phase shift in the central core of the PSF is dynamic and can be made arbitrarily large. This common-path, all-reflective design makes it minimally sensitive to vibration, polarization and wavelength. We review the theory of operation, describe the optical system, summarize numerical simulations and sensitivities and review results from a laboratory demonstration of this novel instrument.

  10. Soliton frequency shifts in subwavelength structures

    NASA Astrophysics Data System (ADS)

    Song, Xiaohong; Yan, Ming; Wu, Miaoli; Sheng, Zhihao; Hao, Zhizhen; Huang, Chong; Yang, Weifeng

    2015-05-01

    We investigate the soliton frequency shifts for few-cycle ultrashort laser pulses propagating through resonant media embedded within subwavelength structures, and we elucidate the underlying physics. Full-wave Maxwell–Bloch equations are solved numerically by using the finite-difference time-domain method. It is shown that both soliton blueshift and redshift can occur by changing the period of the structures. We found that the rereflected waves play an essential role in this process. When the pulse propagates through the periodic structures, the reflected waves can be rereflected back by the thin layers, which can further induce the controllable frequency shifts of the generated solitons. This suggests a way to tailor the light solitons over a large spectral range.

  11. Age Differences in Strategy Shift: Retrieval Avoidance or General Shift Reluctance?

    PubMed Central

    Frank, David J.; Touron, Dayna R.; Hertzog, Christopher

    2013-01-01

    Previous studies of metacognitive age differences in skill acquisition strategies have relied exclusively on tasks with a processing shift from an algorithm to retrieval strategy. Older adults’ demonstrated reluctance to shift strategies in such tasks could reflect either a specific aversion to a memory retrieval strategy or a general, inertial resistance to strategy change. Haider and Frensch’s (1999) alphabet verification task (AVT) affords a non-retrieval-based strategy shift. Participants verify the continuation of alphabet strings such as D E F G [4] L, with the bracketed digit indicating a number of letters to be skipped. When all deviations are restricted to the letter-digit-letter portion, participants can speed their responses by selectively attend only to that part of the stimulus. We adapted the AVT to include conditions which promoted shift to a retrieval strategy, a selective attention strategy, or both strategies. Item-level strategy reports were validated by eye movement data. Older adults shifted more slowly to the retrieval strategy but more quickly to the selective attention strategy than young adults, indicating a retrieval-strategy avoidance. Strategy confidence and perceived strategy difficulty correlated with shift to the two strategies in both age groups. Perceived speed of responses with each strategy specifically correlated with older adults’ strategy choices, suggesting that some older adults avoid retrieval because they do not appreciate its efficiency benefits. PMID:23088195

  12. Brain Shift Modeling for Use in Neurosurgery

    Microsoft Academic Search

    Oskar M. Skrinjar; Dennis D. Spencer; James S. Duncan

    1998-01-01

    Surgical navigation systems are used intraoperatively to help the surgeon to ascertain her or his position and to guide tools\\u000a within the patient frame with respect to registered structures of interest in the preoperative images. However, these systems\\u000a are subject to inaccuracy caused by intraoperative brain movement (brain shift) since they assume that the intracranial structures\\u000a are rigid. Experiments show

  13. Collisionally induced atomic clock shifts and correlations

    SciTech Connect

    Band, Y. B.; Osherov, I. [Departments of Chemistry and Electro-Optics and the Ilse Katz Center for Nano-Science, Ben-Gurion University, Beer-Sheva 84105 (Israel)

    2011-07-15

    We develop a formalism to incorporate exchange symmetry considerations into the calculation of collisional frequency shifts for atomic clocks using a density-matrix formalism. The formalism is developed for both fermionic and bosonic atomic clocks. Numerical results for a finite-temperature {sup 87}Sr {sup 1}S{sub 0} (F=9/2) atomic clock in a magic wavelength optical lattice are presented.

  14. for Shift-Variant PET Image Reconstruction

    Microsoft Academic Search

    Jeffrey A. Fessler; Scott D. Booth

    Gradient-based iterative methods often converge slowly for tomographic image reconstruction and image restoration problems, but can be accelerated by suitable preconditioners. Diagonal precondition- ers offer some improvement in convergence rate, but do not incorporate the structure of the Hessian matrices in imaging problems. Circulant preconditioners can provide remarkable acceleration for inverse problems that are approximately shift-invariant, i.e. for those with

  15. Entropy-based Concept Shift Detection

    Microsoft Academic Search

    Peter Vorburger; Abraham Bernstein

    2006-01-01

    When monitoringsensorydata (e.g.,from a wearablede- vice) the context oftentimes changes abruptly: people move from one situation (e.g., working quietly in their office) to another (e.g., being interrupted by one's manager). These context changes can be treated like concept shifts, since the underlying data generator (the concept) changes while moving from onecontext situation to another. We present an entropy based measure

  16. Paradigm Shift in Causal Thinking in Epidemiology

    Microsoft Academic Search

    S. Shapiro

    Professor Shapiro expressed concern with the general direction of epidemiology. Whereas the previous position was that we\\u000a are unable to interpret limited data, this emphasis has shifted. In particular, the randomized controlled trial (RCT) now\\u000a is unassailable in the US.\\u000a \\u000a Shapiro identified the current issues as being (1) a loss of scepticism in the field, (2) the illusion of accuracy

  17. Frontal Sinus Fractures: A Conservative Shift

    PubMed Central

    Weathers, William M.; Wolfswinkel, Erik M.; Hatef, Daniel A.; Lee, Edward I.; Brown, Rodger H.; Hollier, Larry H.

    2013-01-01

    This article reflects on the changing management of frontal sinus fractures. Severity of these injuries has decreased tremendously since the universal adoption of seat belts and air bags. Recently, there has been a shift from aggressive surgical management to more conservative management strategies, some forgoing surgery all together. New technologies, such as bioabsorbable plates and endoscopic sinus surgery, are leading the way in improved surgical management strategies and offer promising alternatives to the more traditional approaches. PMID:24436753

  18. Local Position Invariance and Vacuum Energy Shifts

    E-print Network

    C. Alvarez; R. B. Mann

    1993-10-12

    We discuss tests of the Einstein Equivalence Principle due to energies which are purely quantum mechanical in origin. In particular, we consider using Lamb Shift energies to test for possible quantum violations of Local Position Invariance. (to appear in the Proceedings of the 5th Canadian Conference on General Relativity and Relativistic Astrophysics, University of Waterloo, May 13-- 15, 1993) (acknowledgements changed to correct an omission in the originally submitted version)

  19. Electricity pricing for conservation and load shifting

    SciTech Connect

    Orans, Ren; Woo, C.K.; Horii, Brian; Chait, Michele; DeBenedictis, Andrew

    2010-04-15

    The electricity industry is facing the challenge of increasing costs of reliably meeting demand growth and fully complying with legislative renewable portfolio standards and greenhouse gas reduction targets. However, an electric utility's existing tariffs often don't have rates that increase with consumption volume or vary by time of use, thus not fully exploiting the potential benefits from customer conservation and load shifting. (author)

  20. Our shifting perspectives on the oceans

    Microsoft Academic Search

    Callum M. Roberts

    2003-01-01

    Abstract In the last 15 years new research findings,cases, to reverse impacts once inflicted. Fourthly, marine species are at risk of extinction. Loss of shallow,water have,radically reshaped,our,understanding,of human eCects on ocean ecosystems. Here I describe five major,marine habitats is proceeding as rapidly as on land, many species have small geographic ranges, and many shifts in perspective that reveal our impacts

  1. Power shifting in Thrifty Interconnection Network

    Microsoft Academic Search

    Jian Li; Wei Huang; Charles Lefurgy; Lixin Zhang; Wolfgang E. Denzel; Richard R. Treumann; Kun Wang

    2011-01-01

    This paper presents two complementary techniques to manage the power consumption of large-scale systems with a packet-switched interconnection network. First, we propose Thrifty Interconnection Network (TIN), where the network links are activated and de-activated dynamically with little or no overhead by using inherent system events to timely trigger link activation or de-activation. Second, we propose Network Power Shifting (NPS) that

  2. Bidirectional magnetic domain wall shift register

    Microsoft Academic Search

    D. E. Read; L. O'Brien; H. T. Zeng; E. R. Lewis; D. Petit; R. P. Cowburn

    2010-01-01

    Data storage devices based on magnetic domain walls (DWs) propagating through ferromagnetic nanowires have attracted a great deal of attention in recent years [1,2]. Here we experimentally demonstrate a shift register based on an open-ended chain of ferromagnetic NOT gates. When used in combination with a globally applied magnetic field such devices can support bi-directional data flow [3]. We have

  3. Real-time phase shift interference microscopy.

    PubMed

    Safrani, Avner; Abdulhalim, Ibrahim

    2014-09-01

    A real-time phase shift interference microscopy system is presented using a polarization-based Linnik interferometer operating with three synchronized, phase-masked, parallel detectors. Using this method, several important applications that require high speed and accuracy, such as dynamic focusing control, tilt measurement, submicrometer roughness measurement, and 3D profiling of fine structures, are demonstrated in 50 volumes per second and with 2 nm height repeatability. PMID:25166114

  4. The muonic hydrogen Lamb-shift experiment

    Microsoft Academic Search

    A. Antognini; F. D. Amaro; F. Biraben; J. M. R. Cardoso; C. A. N. Conde; A. Dax; S. Dhawan; L. M. P. Fernandes; T. W. Hansch; F. J. Hartmann; V. W. Hughes; O. Huot; P. Indelicato; L. Julien; P. Knowles; F. Kottmann; Y. W. Liu; L. Ludhova; C. M. B. Monteiro; F. Mulhauser; F. Nez; P. Rabinowitz; J. M. F. Dos Santos; L. A. Schaller; C. Schwob; D. Taqqu; Jf. C. A. Veloso

    2005-01-01

    The charge radius of the proton, the simplest nucleus, is known from electron-scattering experiments only with a surprisingly low precision of about 2%. The poor knowledge of the proton charge radius restricts tests of bound-state quantum electrodynamics (QED) to the precision level of about 6 x 10(-6), although the experimental data themselves (1S Lamb shift in hydrogen) have reached a

  5. Anaphylactic reactions to cinoxacin.

    PubMed

    Stricker, B H; Slagboom, G; Demaeseneer, R; Slootmaekers, V; Thijs, I; Olsson, S

    1988-12-01

    During 1981 to mid-1988 three cases of anaphylactic shock after treatment with the quinolone derivative cinoxacin were reviewed by the Netherlands Centre for Monitoring of Adverse Reactions to Drugs and 17 cases of an anaphylactic type of reaction notified to the World Health Organisation Collaborating Centre for International Drug Monitoring. In five out of six patients for whom data were available the reaction began shortly after taking a single capsule of a second or next course of treatment. Cinoxacin is related to nalidixic acid, and one patient previously treated with that agent subsequently had an anaphylactoid reaction to cinoxacin and later developed a skin reaction to nalidixic acid. There were no deaths, and patients treated as an emergency with plasma expanders or with adrenaline and corticosteroids generally recovered promptly and uneventfully. In view of the potentially fatal consequences of anaphylactic reactions to cinoxacin and other quinolones doctors should take care when prescribing these drugs. PMID:3147004

  6. Atomic clocks with suppressed blackbody radiation shift.

    PubMed

    Yudin, V I; Taichenachev, A V; Okhapkin, M V; Bagayev, S N; Tamm, Chr; Peik, E; Huntemann, N; Mehlstäubler, T E; Riehle, F

    2011-07-15

    We develop a concept of atomic clocks where the blackbody radiation shift and its fluctuations can be suppressed by 1-3 orders of magnitude independent of the environmental temperature. The suppression is based on the fact that in a system with two accessible clock transitions (with frequencies ?1 and ?2) which are exposed to the same thermal environment, there exists a "synthetic" frequency ?(syn) ? (?1 - ?12?2) largely immune to the blackbody radiation shift. For example, in the case of 171Yb+ it is possible to create a synthetic-frequency-based clock in which the fractional blackbody radiation shift can be suppressed to the level of 10(-18) in a broad interval near room temperature (300±15??K). We also propose a realization of our method with the use of an optical frequency comb generator stabilized to both frequencies ?1 and ?2, where the frequency ?(syn) is generated as one of the components of the comb spectrum. PMID:21838344

  7. Experience with the shift technical advisor position

    SciTech Connect

    Melber, B.D.; Olson, J.; Schreiber, R.E.; Winges, L.

    1984-03-01

    The provision of engineering expertise on shift at commercial nuclear power plants has mainly taken the form of the Shift Technical Advisor (STA). This person, acting in a capacity that is part engineer and part operator, is expected to advise the operations crew in the event of an emergency and review plant operating experience during normal circumstances. The position was mandated by the Nuclear Regulatory Commission following the incident at Three Mile Island. This report expands on a growing body of knowledge regarding the effectiveness of the STA. The new data presented here come from interviews with plant personnel and utility officials from nine sites. Researchers from the Pacific Northwest Laboratory (PNL) interviewed plant personnel, including the STA and immediate management, the shift supervisor and management, the training department, and ancillary staff, all of whom affect the intended performance of the STA. The conclusions of the report are that the design of the STA position results in limited contribution during emergencies; more comprehensive ways should be sought to provide the variety and specificity of engineering expertise needed during such times.

  8. Incentive processes and the peak shift

    PubMed Central

    Weiss, Stanley J.; Dacanay, Robert J.

    1982-01-01

    Intradimensional operant discrimination schedules were employed, which eliminated the covariation of response and reinforcement rates that are found on most operant baselines. In Phase 1, one keylight (S1) controlled an increase in pigeons' treadle pressing, relative to another keylight (S2), while being correlated with a decrease in frequency of reinforcement. In Phase 2 both treadle pressing and reinforcement increased in the presence of one keylight, relative to the second. In Phase 1 the relatively flat treadle-press generalization gradients peaked at S1, whereas the peaks of those in Phase 2 were shifted from S1 in a direction away from S2. It was postulated that these positive and negative stimulus-reinforcement contingencies influence the likelihood of obtaining peak shift through the operation of a classically conditioned “central motive state.” How response-reinforcement and stimulus-reinforcement contingencies might contribute to the development of inhibitory effects of S2 is discussed. Autoshaped key pecking also was produced by these procedures. During manipulations of stimuli, the gradients obtained for autoshaped key pecking were narrow and sharply peaked at the food-correlated stimulus (S2) in Phase 1. This failure to obtain peak shift for an elicited response suggests a difference in discriminative processes operating in classical and instrumental learning. PMID:16812277

  9. Microscopic Theory of the Knight Shift

    NASA Astrophysics Data System (ADS)

    Hall, Bianca

    2015-03-01

    The Knight shift has been used for detecting possible parallel spin states, such as Sr2RuO4. However an improved theory of the Knight shift is needed to explain anomalies that have been found in a variety of superconductors below the superconducting transition temperature. The standard model includes the Zeeman and hyperfine interactions of the magnetic field and the electron-electron pairing interaction necessary for superconductivity. The new model now includes a term based on the Anderson model of local moments in metals. The local electron states in the original Anderson model now correspond to local atomic electron orbitals. When these orbital energies are singly occupied and close to the Fermi energy, the spins of the electrons can interact with the nuclear spins and the spins of the electrons in the conducting bands. Additionally, the paths of the electrons in the conduction bands depend on the direction and magnitude of the magnetic induction. With these new terms included, this model has the potential to describe the anomalous behavior seen in Knight shift measurements on unconventional superconductors.

  10. Is there a shift to “active nanostructures”?

    PubMed Central

    Youtie, Jan; Porter, Alan L.; Shapira, Philip

    2009-01-01

    It has been suggested that an important transition in the long-run trajectory of nanotechnology development is a shift from passive to active nanostructures. Such a shift could present different or increased societal impacts and require new approaches for risk assessment. An active nanostructure “changes or evolves its state during its operation,” according to the National Science Foundation’s (2006) Active Nanostructures and Nanosystems grant solicitation. Active nanostructure examples include nanoelectromechanical systems (NEMS), nanomachines, self-healing materials, targeted drugs and chemicals, energy storage devices, and sensors. This article considers two questions: (a) Is there a “shift” to active nanostructures? (b) How can we characterize the prototypical areas into which active nanostructures may emerge? We build upon the NSF definition of active nanostructures to develop a research publication search strategy, with a particular intent to distinguish between passive and active nanotechnologies. We perform bibliometric analyses and describe the main publication trends from 1995 to 2008. We then describe the prototypes of research that emerge based on reading the abstracts and review papers encountered in our search. Preliminary results suggest that there is a sharp rise in active nanostructures publications in 2006, and this rise is maintained in 2007 and through to early 2008. We present a typology that can be used to describe the kind of active nanostructures that may be commercialized and regulated in the future. PMID:21170117

  11. Reaction-diffusion textures

    Microsoft Academic Search

    Andrew P. Witkin; Michael Kass

    1991-01-01

    We present a method for texture synthesis based on the simulation of a process of local nonlinear interaction, called reaction-diffusion, which has been proposed as a model of biological pattern formation. We extend traditional reaction-diffusion systems by allowing anisotropic and spatially non-uniform diffusion, as well as multiple competing directions of diffusion. We adapt reaction-diffusion system to the needs of computer

  12. Immediate Contact Reactions

    Microsoft Academic Search

    David Basketter; Arto Lahti

    \\u000a Immediate contact reactions comprise a diverse spectrum of inflammatory skin reactions of both immune and nonimmune origin\\u000a and involving several often poorly characterized mechanisms and which can be caused by an enormous variety of chemicals and\\u000a proteins. Reactions range from sensory effects through local weal and flare to a more generalized response, but all generally\\u000a characterized by a rapid onset

  13. Weathering Reactions and Soil-Groundwater Reactions

    NSDL National Science Digital Library

    David M. Sherman

    This 11-page PDF document is part of an environmental geochemistry course taught by Dr. David Sherman at the University of Bristol. The lecture explores the weathering reactions that convert primary minerals into quartz or phyllosilicate clays and iron oxide hydroxides, and the mineral-water reactions that buffer pH and the dissolved ion concentration of groundwater. Also discussed is the manner in which phyllosilicate clays, iron oxides and hydroxides sorb pollutants via ion exchange and adsorption. Helpful diagrams and illustrations accompany the text.

  14. Desosamine in multicomponent reactions.

    PubMed

    Achatz, Sepp; Dömling, Alexander

    2006-12-15

    Desosamine occurring ubiquitously in natural products is introduced into isocyanide based multicomponent reaction chemistry. Corresponding products are of potential interest for the design of novel antibiotics. PMID:17070045

  15. Radical reactions of borohydrides.

    PubMed

    Kawamoto, Takuji; Ryu, Ilhyong

    2014-12-28

    Borohydrides are an important class of reagents in both organic and inorganic chemistry. Though popular as hydride-transfer reagents for reduction, since earlier work from the 1970s, borohydride reagents have also been known to serve as hydrogen-transfer reagents. In pursuit of greener tin hydride substitutes, recent progress has been made to mediate radical C-C bond forming reactions, including Giese reactions, radical carbonylation and addition to HCHO reactions, with borohydride reagents. This review article focuses on state-of-the-art borohydride based radical reactions, also covering earlier work, kinetics and some DFT calculations with respect to the hydrogen transfer mechanism. PMID:25349957

  16. Sleeve reaction chamber system

    DOEpatents

    Northrup, M. Allen (Berkeley, CA); Beeman, Barton V. (San Mateo, CA); Benett, William J. (Livermore, CA); Hadley, Dean R. (Manteca, CA); Landre, Phoebe (Livermore, CA); Lehew, Stacy L. (Livermore, CA); Krulevitch, Peter A. (Pleasanton, CA)

    2009-08-25

    A chemical reaction chamber system that combines devices such as doped polysilicon for heating, bulk silicon for convective cooling, and thermoelectric (TE) coolers to augment the heating and cooling rates of the reaction chamber or chambers. In addition the system includes non-silicon-based reaction chambers such as any high thermal conductivity material used in combination with a thermoelectric cooling mechanism (i.e., Peltier device). The heat contained in the thermally conductive part of the system can be used/reused to heat the device, thereby conserving energy and expediting the heating/cooling rates. The system combines a micromachined silicon reaction chamber, for example, with an additional module/device for augmented heating/cooling using the Peltier effect. This additional module is particularly useful in extreme environments (very hot or extremely cold) where augmented heating/cooling would be useful to speed up the thermal cycling rates. The chemical reaction chamber system has various applications for synthesis or processing of organic, inorganic, or biochemical reactions, including the polymerase chain reaction (PCR) and/or other DNA reactions, such as the ligase chain reaction.

  17. How orbital angular momentum affects beam shifts in optical reflection

    SciTech Connect

    Merano, M.; Hermosa, N.; Woerdman, J. P.; Aiello, A. [Huygens Laboratory, Leiden University, P.O. Box 9504, NL-2300 RA Leiden (Netherlands); Max Planck Institute for the Science of Light, Guenter-Scharowsky-Strasse 1/Bau 24, D-91058 Erlangen (Germany)

    2010-08-15

    It is well known that reflection of a Gaussian light beam (TEM{sub 00}) by a planar dielectric interface leads to four beam shifts when compared to the geometrical-optics prediction. These are the spatial Goos-Haenchen (GH) shift, the angular GH shift, the spatial Imbert-Fedorov (IF) shift, and the angular IF shift. We report here, theoretically and experimentally, that endowing the beam with orbital angular momentum leads to coupling of these four shifts; this is described by a 4x4 mixing matrix.

  18. Reaction field analysis and lipid bilayer location for lipophilic fluorophores.

    PubMed

    Randles, Edward G; Bergethon, Peter R

    2013-09-01

    Environment polarity can cause changes in absorbance or emission maxima, for a given fluorophore. This is termed solvatochromism. In this study semiempirical models of solvatochromic shifts are used to predict their lipid bilayer location. Four reaction field models are analyzed and compared, to provide the most accurate prediction of fluorophore solvatochromic shifts using a modified version of the Lippert equation. For curcumin, the reaction field of Block and Walker gave the strongest agreement between experimental and predicted values (r = 0.978, p < 0.0001). For aluminum phthalocyanine disulfonic acid (AlPcS2), the reaction field of Wertheim, based on statistical mechanics, gave the best agreement (r = 0.951, p = 0.001) only when dispersion forces and solute polarizability are considered. The results of these models are correlated to the Dimroth-Reichardt ET(30) solvent polarity scale used by Frimer and colleagues. Using the model predicted values, curcumin is estimated to be 1-1.2 nm from the phospholipid-water interface, in the acyl chain region of the lipid bilayer. AlPcS2 is predicted to be 0.7-0.9 nm from the interface, at the fatty acid carbonyl. This investigation provides semiempirical methods to efficiently link fluorophore solvatochromic shifts to a location in the lipid bilayer via reaction field models. PMID:23967904

  19. Anaphylactic reactions to cinoxacin

    Microsoft Academic Search

    B. H. Stricker; G. Slagboom; R. Demaeseneer; V. Slootmaekers; I. Thijs; S. Olsson

    1988-01-01

    During 1981 to mid-1988 three cases of anaphylactic shock after treatment with the quinolone derivative cinoxacin were reviewed by the Netherlands Centre for Monitoring of Adverse Reactions to Drugs and 17 cases of an anaphylactic type of reaction notified to the World Health Organisation Collaborating Centre for International Drug Monitoring. In five out of six patients for whom data were

  20. Nuclear Reaction Data Centers

    SciTech Connect

    McLane, V.; Nordborg, C.; Lemmel, H.D.; Manokhin, V.N.

    1988-01-01

    The cooperating Nuclear Reaction Data Centers are involved in the compilation and exchange of nuclear reaction data for incident neutrons, charged particles and photons. Individual centers may also have services in other areas, e.g., evaluated data, nuclear structure and decay data, reactor physics, nuclear safety; some of this information may also be exchanged between interested centers. 20 refs., 1 tab.

  1. Pressure Shift and Gravitational Red Shift of Balmer Lines in White Dwarfs. Rediscussion

    E-print Network

    Halenka, J; Madej, J; Grabowski, B

    2015-01-01

    The Stark-induced shift and asymmetry, the so-called pressure shift (PS) of $H_\\alpha$ and $H_\\beta$ Balmer lines in spectra of DA white dwarfs (WDs), as masking effects in measurements of the gravitational red shift in WDs, have been examined in detail. The results are compared with our earlier ones from before a quarter of a century (Grabowski et al. 1987, hereafter ApJ'87; Madej and Grabowski 1990). In these earlier papers, as a dominant constituent of the Balmer-line-profiles, the standard, symmetrical Stark line profiles, shifted as the whole by PS-effect, were applied to all spectrally active layers of the WD atmosphere. At present, in each of the WD layers, the Stark-line-profiles (especially of $H_\\beta$) are immanently asymmetrical and shifted due to the effects of strong inhomogeneity of the perturbing fields in plasma. To calculate the Stark line-profiles in successive layers of the WD atmosphere we used the modified Full Computer Simulation Method (mFCSM), able to take adequately into account the ...

  2. Fractal reaction kinetics.

    PubMed

    Kopelman, R

    1988-09-23

    Classical reaction kinetics has been found to be unsatisfactory when the reactants are spatially constrained on the microscopic level by either walls, phase boundaries, or force fields. Recently discovered theories of heterogeneous reaction kinetics have dramatic consequences, such as fractal orders for elementary reactions, self-ordering and self-unmixing of reactants, and rate coefficients with temporal "memories." The new theories were needed to explain the results of experiments and supercomputer simulations of reactions that were confined to low dimensions or fractal dimensions or both. Among the practical examples of "fractal-like kinetics" are chemical reactions in pores of membranes, excitation trapping in molecular aggregates, exciton fusion in composite materials, and charge recombination in colloids and clouds. PMID:17820893

  3. Radiation reaction in quantum field theory

    E-print Network

    Atsushi Higuchi

    2004-03-30

    We investigate radiation-reaction effects for a charged scalar particle accelerated by an external potential realized as a space-dependent mass term in quantum electrodynamics. In particular, we calculate the position shift of the final-state wave packet of the charged particle due to radiation at lowest order in the fine structure constant alpha and in the small h-bar approximation. We show that it disagrees with the result obtained using the Lorentz-Dirac formula for the radiation-reaction force, and that it agrees with the classical theory if one assumes that the particle loses its energy to radiation at each moment of time according to the Larmor formula in the static frame of the potential. However, the discrepancy is much smaller than the Compton wavelength of the particle. We also point out that the electromagnetic correction to the potential has no classical limit. (Correction. Surface terms were erroneously discarded to arrive at Eq. (59). By correcting this error we find that the position shift according to the Lorentz-Dirac theory obtained from Eq. (12) is reproduced by quantum field theory in the hbar -> 0 limit. We also find that the small V(z) approximation is unnecessary for this agreement. See Sec. VII.)

  4. Strategy Shifts in Mixed Density Search

    Microsoft Academic Search

    Tim Halverson

    2004-01-01

    Visual search in an important aspect of many tasks, but it is not well understood how many aspects of layout design affect visual search. This research investigates, with reaction time and eye movement data, the effect of local density on the visual search of structured layouts of words. Layouts were all- sparse, all-dense, or mixed. Participants found targets in sparse

  5. Real-time Learning when Concepts Shift [Author Information

    E-print Network

    Cook, Diane J.

    the application of the Minimum Description Length principle to detecting real-time concept shifts. Introduction of the Minimum Description Length principle to detecting concept shifts. Sliding Window A current method used

  6. Persistent shifts in Caribbean coral microbiota are linked to the 2010 warm thermal anomaly.

    PubMed

    Tracy, Allison M; Koren, Omry; Douglas, Nancy; Weil, Ernesto; Harvell, C Drew

    2015-06-01

    The response of corals to warm temperature anomalies includes changes in coral bacterial assemblages. There are clear differences between the microbiota of bleached and healthy corals. However, few studies have tracked the microbiota of individual colonies throughout a warming event. We used 454 pyrosequencing and repeated measures to characterize bacterial assemblages in 15 Gorgonia ventalina colonies before, during, 4 months after, and 1 year after the 2010 Caribbean warm thermal anomaly. In the latter three sampling times, the G.?ventalina microbiota differed significantly from the microbiota of Orbicella faveolata colonies, which were sampled only at these three times. O. faveolata microbiota did not exhibit coordinated shifts through time. Notably, the microbiota of the repeatedly sampled G.?ventalina colonies shifted persistently from before to during, after, and long after the warming event. The same pattern emerges from the norm of reaction for the individual G.?ventalina colonies. This is the first study to show persistent shifts in coral microbiota in association with a warm thermal anomaly. Whether shifting microbiota is adaptive or maladaptive, the lasting change in bacterial assemblages following this warming event identifies a new way that coral microbiota shape the response of coral colonies under thermal stress. PMID:25683053

  7. Gas-phase reactions of Fe/sup +/ with ketones and ethers

    SciTech Connect

    Burnier, R.C.; Byrd, G.D.; Freiser, B.S.

    1981-07-29

    A pulsed laser has been used in conjunction with an ion cyclotron resonance spectrometer to generate and study the gas-phase ion-molecule reactions of Fe/sup +/ with simple carbonyl compounds and ethers. Oxidative addition reactions are observed, producing alkyl acyl, and alkoxide intermediates which undergo intramolecular rearrangement by a ..beta..-hydride shift mechanism. Decarbonylation reactions are observed with only a few small ketones. The main reaction channel is dehydrogenation for unbranched ketones and reductive elimination of methane for those branched at the ..cap alpha.. carbon. Reactions of Fe/sup +/ with diisopropyl ketone, cyclohexanone, cyclopentanone, and tetrahydrofuran suggest the existence of intermediate and stable ..pi..-ally complexes resulting from sequential ..beta..-hydride shifts.

  8. Green binary and phase shifting mask

    NASA Astrophysics Data System (ADS)

    Shy, S. L.; Hong, Chao-Sin; Wu, Cheng-San; Chen, S. J.; Wu, Hung-Yu; Ting, Yung-Chiang

    2009-12-01

    SixNy/Ni thin film green mask blanks were developed , and are now going to be used to replace general chromium film used for binary mask as well as to replace molydium silicide embedded material for AttPSM for I-line (365 nm), KrF (248 nm), ArF (193 nm) and Contact/Proximity lithography. A bilayer structure of a 1 nm thick opaque, conductive nickel layer and a SixNy layer is proposed for binary and phase-shifting mask. With the good controlling of plasma CVD of SixNy under silane (50 sccm), ammonia (5 sccm) and nitrogen (100 sccm), the pressure is 250 mTorr. and RF frequency 13.56 MHz and power 50 W. SixNy has enough deposition latitude to meet the requirements as an embedded layer for required phase shift 180 degree, and the T% in 193, 248 and 365 nm can be adjusted between 2% to 20% for binary and phase shifting mask usage. Ni can be deposited by E-gun, its sheet resistance Rs is less than 1.435 k?/square. Jeol e-beam system and I-line stepper are used to evaluate these thin film green mask blanks, feature size less than 200 nm half pitch pattern and 0.558 ?m pitch contact hole can be printed. Transmission spectrums of various thickness of SixNy film are inspected by using UV spectrometer and FTIR. Optical constants of the SixNy film are measured by n & k meter and surface roughness is inspected by using Atomic Force Microscope (AFM).

  9. Responsibility for retirement planning shifts to employees.

    PubMed

    Van Gelder, N

    1994-08-01

    In recent years, organizations have shifted away from offering their employees defined benefit plans that promise specified income streams to employees when they retire. Instead, they are offering employees defined contribution plans, which rely on investment performance, as directed by plan participants, to generate sufficient retirement income. Healthcare financial managers who work in organizations that offer retirement plans for their employees find themselves increasingly prevailed upon to play the role of instructor to plan participants. While some financial managers may not relish the role, the more successful financial managers are at helping plan participants achieve their retirement income goals, the better the chance of healthcare organizations avoiding future liability problems. PMID:10146045

  10. Polaronic Signatures in Phonon Isotopic Shifts

    SciTech Connect

    de Leon, J.M.; de Coss, R.; Rubio-Ponce, A.; Bishop, A.R.; Trugman, S.A.

    1998-06-01

    The effect of O(16) by O(18) isotopic substitution in the excitation spectrum of a model electron-phonon Hamiltonian, previously used to describe the dynamics of the O(4)-Cu(1)-O(4) cluster in YBa{sub 2}Cu{sub 3}O{sub 7}, is presented. This model includes electronic correlations and electron-phonon interactions, exhibiting the presence of polaron tunneling. The calculated isotopic shifts of phonon excitations differ from those found using harmonic or anharmonic potentials, and are consistent results of optical measurements of c-axis phonons. The isotopic substitution changes the dynamics of polaron tunneling and produces a change in the local structure.

  11. Modeling Viewpoint Shifts in Probabilistic Choice.

    PubMed

    Okubo, Tomoya; Mayekawa, Shin-Ichi

    2015-06-01

    A number of mathematical models for overcoming intransitive choice have been proposed and tested in the literature of decision theory. This article presents the development of a new stochastic choice model based on multidimensional scaling. This allows decision-makers to have multiple viewpoints, whereas current multidimensional scaling models are based on the assumption that a subject or group of subjects has only one viewpoint. The implication of our model is that subjects make an intransitive choice because they are able to shift their viewpoint. This paper also presents the maximum likelihood estimation of the proposed model, and reanalyzes Tversky's gamble experiment data. PMID:24352515

  12. A partial differential equation for pseudocontact shift.

    PubMed

    Charnock, G T P; Kuprov, Ilya

    2014-10-01

    It is demonstrated that pseudocontact shift (PCS), viewed as a scalar or a tensor field in three dimensions, obeys an elliptic partial differential equation with a source term that depends on the Hessian of the unpaired electron probability density. The equation enables straightforward PCS prediction and analysis in systems with delocalized unpaired electrons, particularly for the nuclei located in their immediate vicinity. It is also shown that the probability density of the unpaired electron may be extracted, using a regularization procedure, from PCS data. PMID:25139283

  13. Quasicrystals - a paradigm shift in crystallography?

    PubMed

    Steurer, Walter

    2014-01-01

    The discovery of quasicrystals had important consequences for our understanding of long-range order in thermodynamic equilibrium, the definition of the term 'crystal' as well as diffraction theory. Quasicrystals have been observed not only at the atomic scale in binary and ternary intermetallic systems, but also at the mesoscale in self-assembled colloids and block-copolymers, and even at the macroscale in packings of hard polyhedra. How important was the discovery of quasicrystals for crystallography? Did it usher in a scientific revolution and a paradigm shift? These questions are discussed following a short overview of the status of quasicrystal research. PMID:24801696

  14. Late-quaternary shift of fagus distribution

    Microsoft Academic Search

    Matsuo Tsukada

    1982-01-01

    Based on six resolved maps of its pollen frequency (dating 13,000, 10,000, 8,000, 6,000, 3,000 and 500 yr B.P.) at 33 sites\\u000a scattered almost throughout the Japanese Archipelago,Fagus shows principally a, unidirectional late-Quaternary shift in distribution from the southwest to the northeast. The maximum\\u000a areal coverage was from 10,000 to 7,000 years ago, although northeastern populations were not fully developed

  15. Space charge effects: tune shifts and resonances

    SciTech Connect

    Weng, W.T.

    1986-08-01

    The effects of space charge and beam-beam interactions on single particle motion in the transverse degree of freedom are considered. The space charge force and the resulting incoherent tune shift are described, and examples are given from the AGS and CERN's PSB. Equations of motion are given for resonances in the presence of the space charge force, and particle behavior is examined under resonance and space charge conditions. Resonance phase space structure is described with and without space charge. Uniform and bunched beams are compared. Beam-beam forces and resonances and beam-beam detuning are described. 18 refs., 15 figs. (LEW)

  16. Auroral Substorms: Paradigm Shifts in Research

    NASA Astrophysics Data System (ADS)

    Akasofu, Syun-Ichi

    2010-08-01

    The study of scientific advancement is the study of evolving thought. Disciplines progress as old prevailing theoretical ideas are toppled by new ones, one after another. Provided that new ideas can be independently verified, scientists at any level can greatly contribute to their field. Though space weather is a young field, it has been riddled with such paradigm shifts. As a scientist who has worked on auroral and magnetospheric substorm research during several of these moments, I have witnessed firsthand how diligence, patience, and creativity combine to advance science.

  17. Identifying potential evolutionary consequences of climate-driven phenological shifts

    Microsoft Academic Search

    Matthew J. Heard; Shelby H. Riskin; Patrick A. Flight

    Climate change is shifting the phenology of many species throughout the world. While the interspecific consequences of these\\u000a phenological shifts have been well documented, the intraspecific shifts and their resultant evolutionary consequences remain\\u000a relatively unexplored. Here, we present a conceptual framework and overview of how phenological shifts within species can\\u000a drive evolutionary change. We suggest that because the impacts of

  18. Spectral red-shifting of multi-frequency Raman orders

    NASA Astrophysics Data System (ADS)

    Cui, Z.; Chaturvedi, M.; Tian, B.; Ackert, J.; Turner, F. C.; Strickland, D.

    2013-02-01

    In this paper, the spectral characteristics of the anti-Stokes orders generated by multi-frequency Raman generation are investigated. In particular, we observe that the orders can be red-shifted from the expected Raman transition frequency. The experimental observations indicate that Stark shifting rather than four-wave mixing is responsible for the red-shift. Current numerical models are insufficient to reproduce the experimental observations of red-shifting of the anti-Stokes orders.

  19. Relativistic calculations of isotope shifts in highly charged ions

    SciTech Connect

    Tupitsyn, I.I.; Shabaev, V.M. [Department of Physics, St. Petersburg State University, Oulianovskaya 1, Petrodvorets, 198504 St. Petersburg (Russian Federation); Max-Planck Institut fuer Kernphysik, Saupfercheckweg 1, D-69117 Heidelberg (Germany); Crespo Lopez-Urrutia, J.R.; Soria Orts, R.; Ullrich, J. [Max-Planck Institut fuer Kernphysik, Saupfercheckweg 1, D-69117 Heidelberg (Germany); Draganic, I. [Max-Planck Institut fuer Kernphysik, Saupfercheckweg 1, D-69117 Heidelberg (Germany); Institute of Nuclear Sciences 'Vinca', Laboratory of Physics (010), P.O. Box 522, 11001 Belgrade (Yugoslavia)

    2003-08-01

    The isotope shifts of forbidden transitions in Be- and B-like argon ions are calculated. It is shown that only using the relativistic recoil operator can provide a proper evaluation of the mass isotope shift, which strongly dominates over the field isotope shift for the ions under consideration. Comparing the isotope shifts calculated with the current experimental uncertainties indicates very good perspectives for a first test of the relativistic theory of the recoil effect in middle-Z ions.

  20. Edge technique for measurement of laser frequency shifts including the Doppler shift

    NASA Technical Reports Server (NTRS)

    Korb, Larry (inventor)

    1991-01-01

    A method is disclosed for determining the frequency shift in a laser system by transmitting an outgoing laser beam. An incoming laser beam having a frequency shift is received. A first signal is acquired by transmitting a portion of the incoming laser beam to an energy monitor detector. A second signal is acquired by transmitting a portion of the incoming laser beam through an edge filter to an edge detector, which derives a first normalized signal which is proportional to the transmission of the edge filter at the frequency of the incoming laser beam. A second normalized signal is acquired which is proportional to the transmission of the edge filter at the frequency of the outgoing laser beam. The frequency shift is determined by processing the first and second normalized signals.

  1. Frequency Shift of Radio Signals in Curved Spacetimes

    E-print Network

    Frequency Shift of Radio Signals in Curved Spacetimes E. J. B. PERSSON March 20, 2002 #12;Abstract the frequency shift of a light or radio signal is only dependent on the endpoints of the trajectory traversed on the striations in the ionosphere. It has been suggested that the radio signal undergoes a frequency shift

  2. Method for measuring Doppler shifts in arc-heated flows.

    PubMed

    Aeschliman, D P; Hill, R A

    1972-01-01

    A novel method of determining both the Doppler and Stark shifts in a single measurement of spectral lines emitted by the arc-heated flow from a plasma jet has been successfully demonstrated. The method uses a spherical mirror arranged with its optical axis coincident with the optical axis of a Fabry-Perot interferometer and with its center of curvature at the center line of the flow. The common optical axis lies at an angle to the flow. With this system, both red-and blue-shifted line profiles are recorded in the same spectral scan. If conditions are such that the red-and blue-shifted profiles are not resolvable, the blue-shifted component is chopped so that the recorded signal consists of the envelopes of both the red-shifted profile and the superimposed red-and blue-shifted profiles. The wavelength difference between the blue-and red-shifted line profiles is exactly twice the Doppler shift integrated along a line of sight through the flow and is independent of a Stark shift. The Stark shift is given by the wavelength difference between the absolute line center and the midpoint of the red-and blue-shifted lines. Abel inversion of integrated line shift data has yielded radial velocity profiles to an accuracy of +/-3% in a supersonic, arc-heated argon flow. PMID:20111470

  3. VIEWLS Final recommendations report Shift Gear to Biofuels

    E-print Network

    VIEWLS Final recommendations report 1 Shift Gear to Biofuels Results and recommendations from the VIEWLS project November 2005 #12;Shift Gear to Biofuels Final report of the VIEWLS project 2 #12;Shift Gear to Biofuels Final report of the VIEWLS project 3 Preface Biofuels are fuels made from

  4. Hand tracking and gesture gecogniton by anisotropic kernel mean shift

    Microsoft Academic Search

    Qi Sumin; Huang Xianwu

    2008-01-01

    Mean shift algorithm is an iterative procedure that shifts each data point to the average of data points in its neighborhood. It been applied to object tracking. But traditional mean shift tracker by isotropic kernel often loses the object with the changing structure of object in video sequences, especially when object structure varies fast. This paper proposes a non-rigid object

  5. Shift-map Image Registration Linus Svarm Petter Strandmark

    E-print Network

    Lunds Universitet

    University {linus,petter}@maths.lth.se Abstract Shift-map image processing is a new framework based on energy over a Gaussian pyramid. In this paper we extend the range of applications to im- age registration possible shift-map is assigned an energy, based on a priori assumptions on what a good shift-map typ

  6. Regime Shifts Found in the Northern Hemisphere SST Field

    Microsoft Academic Search

    Sayaka YASUNAKA; Kimio HANAWA

    2002-01-01

    A 'regime shift' is characterized by an abrupt transition from one quasi-steady climatic state to another, and its transition period is much shorter than the lengths of the individual epochs of each climatic state. In the present study, we investigate when regime shifts occurred and what was the difference in climatic states before and after the shifts, using the wintertime

  7. Spectral shifts of apertured Gaussian Schell-model beam

    Microsoft Academic Search

    Q. Lin; Z. Wang; J. Chen; S. Wang

    1995-01-01

    The spectral shift of Gaussian Schell-model beam passing through a circular aperture is investigated theoretically in this paper. Various factors which have influences on the spectral shift are analysed. The numerical results show that the shift of the spectrum depends on the size of the aperture, the effective correlation length and the spectrum width of the light source. Additionally, the

  8. Observed versus cosmological spectral shift of a galaxy

    Microsoft Academic Search

    F. Graos

    1997-01-01

    Since galaxies are realistic gravitating sources, it is expected that the light emitted by a galaxy will be generally shifted, either to the red or to the blue, depending on the physical characteristics of the galaxy itself. As a result the observed shift, z_0, of the galaxy's spectrum will generally differ from the purely cosmological shift, z_c. We find the

  9. Image segmentation based on fuzzy flood fill mean shift algorihm

    Microsoft Academic Search

    Hoon Kang; Seung Hwan Lee; Jayong Lee

    2010-01-01

    In this paper, the fuzzy flood fill mean shift algorithm is introduced. This algorithm is developed for the methodology of robust segmentation by improving the mean shift algorithm through the fuzzy kernels and the flood fill technique, instead of those based on the spatial bandwidth. Due to this exchange, the flood fill mean shift involves only one parameter, the range

  10. Feedback Shift Registers, 2-Adic Span, and Combiners With Memory

    E-print Network

    Klapper, Andy

    Feedback Shift Registers, 2-Adic Span, and Combiners With Memory Andrew Klapper Mark Goresky Abstract Feedback shift registers with carry operation (FCSR's) are described, implemented, and analyzed sequences. Many parallels with the theory of linear feedback shift registers (LFSR's) are presented

  11. Package Shift in Plastic-Packaged Bandgap References

    E-print Network

    Rincon-Mora, Gabriel A.

    packages add manufacturing cost and time to IC. · Package shift needs to be compensated at circuitPackage Shift in Plastic- Packaged Bandgap References Vishal Gupta Prof. Gabriel A. Rincón-Mora #12;Abstract What is package shift? Offset in voltage of packaged bandgap reference from its unpackaged value

  12. Beam shifts to reflected light beams and their axial structure

    NASA Astrophysics Data System (ADS)

    Dennis, Mark R.; Götte, Jörg B.

    2014-12-01

    The similarities and differences of spatial shifts to the centroids of reflected beams, and their (optical vortex) structure are discussed and reviewed. The differences between vortex-induced shifts to a beam centroid on reflection, and to the distribution of the vortices themselves is discussed. We conclude by discussing the shifts of a reflected beam containing a single anisotropic vortex.

  13. Regime Shifts in Asian Equity and Real Estate Markets

    Microsoft Academic Search

    Jarl G. Kallberg; Crocker H. Liu; Paolo Pasquariello

    2002-01-01

    This paper applies a new statistical technology for identifying regime shifts to analyze recent data on real estate and equity markets in eight developing Far Eastern countries in the 1992-1998 time period. We find that regime shifts in volatility occur in the summer of 1997; however, most of the regime shifts in returns occur in the spring of 1998. While

  14. Measuring D(d,p)T fusion reactant energy spectra with Doppler shifted fusion products

    SciTech Connect

    Boris, D. R. [Naval Research Laboratory, 4555 Overlook Avenue, South West, Washington, DC 20375 (United States); Kulcinski, G. L.; Santarius, J. F.; Donovan, D. C. [Fusion Technology Institute, University of Wisconsin-Madison, 1500 Engineering Drive, Madison, Wisconsin 53706 (United States); Piefer, G. R. [Phoenix Nuclear Labs, 8123 Forsythia Street, Suite 140, Middleton, Wisconsin 53562 (United States)

    2010-06-15

    Deuterium fusion reactant energy spectra have been measured using a diagnostic that records the Doppler shift imparted to charged particle fusion products of the D(d,p)T reaction by the center-of-mass velocity of the deuterium reactants. This diagnostic, known as the fusion ion Doppler shift diagnostic (FIDO) measures fast deuterium energy spectra in the inertial electrostatic confinement (IEC) experiment at the University of Wisconsin-Madison {l_brace}Santarius et al. [Fusion Sci. Technol. 47, 1238 (2005)]{r_brace}, a device to confine high energy light ions in a spherically symmetric, electrostatic potential well. This article details the first measurements of the fusion reactant energy spectra in an IEC device as well as the design and principles of operation of the FIDO diagnostic. Scaling of reactant energy spectra with a variety of experimental parameters have been explored.

  15. Chemical amplification--cavity attenuated phase shift spectroscopy measurements of atmospheric peroxy radicals.

    PubMed

    Wood, Ezra C; Charest, John R

    2014-10-21

    We describe a new instrument for the quantification of atmospheric peroxy radicals (HO2, CH3O2, C2H5O2, etc.) using the chemical amplification method. Peroxy radicals are mixed with high concentrations of NO and CO, causing a chain reaction that produces a measurable increase in NO2 which is quantified by cavity attenuated phase shift (CAPS) spectroscopy, a highly sensitive spectroscopic detection technique. The instrument utilizes two identical reaction chambers, each with a dedicated CAPS NO2 sensor. Similar to all dual-channel chemical amplifiers, one reaction chamber operates in amplification or "ROx" mode and the other in background or "Ox" mode. The peroxy radical mixing ratio is determined by the difference between the two channels' NO2 readings divided by a laboratory-determined chain length. Each reaction chamber alternates between ROx and Ox mode on an anti-synchronized schedule, eliminating the effect of CAPS baseline offsets on the calculated peroxy radical concentrations. The chain length is determined by a new calibration method: peroxyacetyl and methyl peroxy radicals are produced by the photolysis of acetone and quantified as NO2 following reaction with excess NO. We demonstrate the performance of the instrument with results from ambient sampling in Amherst and several diagnostics of its precision. The detection limit while sampling ambient air at a relative humidity (RH) of 40% is 0.6 ppt (1 min average, signal-to-noise ratio =2), with an estimated accuracy of 25% (2?). PMID:25260158

  16. Phase shifting in pulse tube refrigerators

    NASA Astrophysics Data System (ADS)

    Hofmann, A.; Pan, H.

    1999-09-01

    Different types of pulse tube refrigerators are described by alternative phasor diagrams based on the volume flow rates applied at the ambient temperature inlets of the regenerator and of the pulse tube(s). This provides a simple means for finding the optimum phase shift between pressure and flow rate for PTRs operated with different kinds of phase shifters such as the orifice system, the inertance tube, and the double inlet arrangement. The basic features are discussed first for ideal systems with no losses. Then, those results are compared with experimental data of single- and two-stage pulse tube refrigerators and also with more comprehensive numerical calculations which take account of irreversible losses caused by friction as well as heat conduction and heat transfer. It is shown that for the pulse tube, the phase shift can be well estimated from the ideal model, whereas there is more discrepancy for the regenerator. Those phasor diagrams are shown to be helpful tools for the design of multistage systems.

  17. Shifting paradigms: from Flexner to competencies.

    PubMed

    Carraccio, Carol; Wolfsthal, Susan D; Englander, Robert; Ferentz, Kevin; Martin, Christine

    2002-05-01

    Realizing medical education is on the brink of a major paradigm shift from structure- and process-based to competency-based education and measurement of outcomes, the authors reviewed the existing medical literature to provide practical insight into how to accomplish full implementation and evaluation of this new paradigm. They searched Medline and the Educational Resource Information Clearinghouse from the 1960s until the present, reviewed the titles and abstracts of the 469 articles the search produced, and chose 68 relevant articles for full review. The authors found that in the 1970s and 1980s much attention was given to the need for and the development of professional competencies for many medical disciplines. Little attention, however, was devoted to defining the benchmarks of specific competencies, how to attain them, or the evaluation of competence. Lack of evaluation strategies was likely one of the forces responsible for the three-decade lag between initiation of the movement and wide-spread adoption. Lessons learned from past experiences include the importance of strategic planning and faculty and learner buy-in for defining competencies. In addition, the benchmarks for defining competency and the thresholds for attaining competence must be clearly delineated. The development of appropriate assessment tools to measure competence remains the challenge of this decade, and educators must be responsible for studying the impact of this paradigm shift to determine whether its ultimate effect is the production of more competent physicians. PMID:12010689

  18. Automated manual transmission shift sequence controller

    DOEpatents

    Lawrie, Robert E. (Whitmore Lake, MI); Reed, Richard G. (Royal Oak, MI); Rausen, David J. (Denver, CO)

    2000-02-01

    A powertrain system for a hybrid vehicle. The hybrid vehicle includes a heat engine, such as a diesel engine, and an electric machine, which operates as both, an electric motor and an alternator, to power the vehicle. The hybrid vehicle also includes a manual-style transmission configured to operate as an automatic transmission from the perspective of the driver. The engine and the electric machine drive an input shaft which in turn drives an output shaft of the transmission. In addition to driving the transmission, the electric machine regulates the speed of the input shaft in order to synchronize the input shaft during either an upshift or downshift of the transmission by either decreasing or increasing the speed of the input shaft. When decreasing the speed of the input shaft, the electric motor functions as an alternator to produce electrical energy which may be stored by a storage device. Operation of the transmission is controlled by a transmission controller which receives input signals and generates output signals to control shift and clutch motors to effect smooth launch, upshift shifts, and downshifts of the transmission, so that the transmission functions substantially as an automatic transmission from the perspective of the driver, while internally substantially functioning as a manual transmission.

  19. Shifting seasons, climate change and ecosystem consequences

    NASA Astrophysics Data System (ADS)

    Thackeray, Stephen; Henrys, Peter; Hemming, Deborah; Huntingford, Chris; Bell, James; Leech, David; Wanless, Sarah

    2014-05-01

    In recent decades, the seasonal timing of many biological events (e.g. flowering, breeding, migration) has shifted. These phenological changes are believed to be one of the most conspicuous biological indicators of climate change. Rates and directions of phenological change have differed markedly among species, potentially threatening the seasonal synchrony of key species interactions and ultimately ecosystem functioning. Differences in phenological change among-species at different trophic levels, and with respect to other broad species traits, are likely to be driven by variations in the climatic sensitivity of phenological events. However, as yet, inconsistencies in analytical methods have hampered broad-scale assessments of variation in climate sensitivity among taxonomic and functional groups of organisms. In this presentation, results will be presented from a current collaborative project (http://www.ceh.ac.uk/sci_programmes/shifting-seasons-uk.html) in which many UK long-term data sets are being integrated in order to assess relationships between temperature/precipitation, and the timing of seasonal events for a wide range of plants and animals. Our aim is to assess which organism groups (in which locations/habitats) are most sensitive to climate. Furthermore, the role of anthropogenic climate change as a driver of phenological change is being assessed.

  20. Metabolic Shifts during Aging and Pathology.

    PubMed

    Ma, Yina; Li, Ji

    2015-03-01

    The heart is a very special organ in the body and has a high requirement for metabolism due to its constant workload. As a consequence, to provide a consistent and sufficient energy a high steady-state demand of metabolism is required by the heart. When delicately balanced mechanisms are changed by physiological or pathophysiological conditions, the whole system's homeostasis will be altered to a new balance, which contributes to the pathologic process. So it is no wonder that almost every heart disease is related to metabolic shift. Furthermore, aging is also found to be related to the reduction in mitochondrial function, insulin resistance, and dysregulated intracellular lipid metabolism. Adenosine monophosphate-activated protein kinase (AMPK) functions as an energy sensor to detect intracellular ATP/AMP ratio and plays a pivotal role in intracellular adaptation to energy stress. During different pathology (like myocardial ischemia and hypertension), the activation of cardiac AMPK appears to be essential for repairing cardiomyocyte's function by accelerating ATP generation, attenuating ATP depletion, and protecting the myocardium against cardiac dysfunction and apoptosis. In this overview, we will talk about the normal heart's metabolism, how metabolic shifts during aging and different pathologies, and how AMPK regulates metabolic changes during these conditions. © 2015 American Physiological Society. Compr Physiol 5: 667-686, 2015. PMID:25880509

  1. Language lateralization shifts with learning by adults.

    PubMed

    Plante, Elena; Almryde, Kyle; Patterson, Dianne K; Vance, Christopher J; Asbjørnsen, Arve E

    2015-05-01

    For the majority of the population, language is a left-hemisphere lateralized function. During childhood, a pattern of increasing left lateralization for language has been described in brain imaging studies, suggesting that this trait develops. This development could reflect change due to brain maturation or change due to skill acquisition, given that children acquire and refine language skills as they mature. We test the possibility that skill acquisition, independent of age-associated maturation can result in shifts in language lateralization in classic language cortex. We imaged adults exposed to an unfamiliar language during three successive fMRI scans. Participants were then asked to identify specific words embedded in Norwegian sentences. Exposure to these sentences, relative to complex tones, resulted in consistent activation in the left and right superior temporal gyrus. Activation in this region became increasingly left-lateralized with repeated exposure to the unfamiliar language. These results demonstrate that shifts in lateralization can be produced in the short term within a learning context, independent of maturation. PMID:25285756

  2. Nuclear Reactions and Reactor Safety

    E-print Network

    Onuchic, José

    Nuclear Reactions and Reactor Safety DO NOT LICK We haven't entirely nailed down what element nuclear chain reaction, 1938 #12;Nuclear Chain Reactions Do nuclear chain reactions lead to runaway explosions? or ? -Controlled nuclear chain reactions possible: control energy release/sec -> More

  3. Distribution of rest days in 12 hour shift systems: impacts on health, wellbeing, and on shift alertness

    PubMed Central

    Tucker, P.; Smith, L.; Macdonald, I.; Folkard, S.

    1999-01-01

    OBJECTIVES: To investigate of the effects of distribution of rest days in 12 hour shift systems. Although several studies have examined the effects of compressing work schedules by comparing 8 and 12 hour shift systems, there is little published research examining the various forms of 12 hour shift system. METHODS: An abridged version of the standard shiftwork index which included retrospective alertness ratings was completed by a large sample of industrial shiftworkers. The respondents worked 12 hour shift systems that either did or did not incorporate breaks of > 24 hours between the blocks of day and night shifts. For the purposes of the analysis, each of these two groups were further subdivided into those who started their morning shift at 0600 and those who started at 0700. RESULTS: Systems which incorporated rest days between the day and night shifts were associated with slightly higher levels of on shift alertness, slightly lower levels of chronic fatigue, along with longer sleep durations when working night shifts and between rest days. Early changeovers were associated with shorter night sleeps between successive day shifts, but longer and less disturbed day sleeps between night shifts. These effects of changeover time were broadly in agreement with previous research findings. CONCLUSIONS: The distribution of rest days in 12 hour shift systems had only limited effects on the outcome measures, although the few modest differences that were found favoured systems which incorporated rest days between the day and night shifts. It is conceded that the design of the study may have obscured some subtle differences between the shift systems. Nevertheless, it is concluded that the impact of distribution of rest days seems to be minor relative to previously found effects of other features of shift systems--for example, shift duration.   PMID:10448331

  4. Some Reactions of Formamidines

    E-print Network

    Malleis, Otto Oscar

    1913-05-15

    trichloride on a mixture of a formanilide and amine. 3,- The reaction of orthoformic-ester on a primary amine. OCsHs / HalOeHs . ICdHs HC- OOaHs • = 3C«HsOH + HC^ \\ HEHCeHs MOeHs OOaHs The substituted product in case of aniline is diphenyl- formamidine... as hydrochloride b.- Piorates o.- Chloroplatinates. 2.- Reaction with compounds containing methylene hydrogen. a.- Reaction of oyanacetio ethyl ester with a substi­ tuted formamidine. OH OH I R I CHa * HO = 0 * HCHH R ^ R M a I * HER I COOCaHs COOCa...

  5. s-Wave collisional frequency shift of a fermion clock.

    PubMed

    Hazlett, Eric L; Zhang, Yi; Stites, Ronald W; Gibble, Kurt; O'Hara, Kenneth M

    2013-04-19

    We report an s-wave collisional frequency shift of an atomic clock based on fermions. In contrast to bosons, the fermion clock shift is insensitive to the population difference of the clock states, set by the first pulse area in Ramsey spectroscopy, ?(1). The fermion shift instead depends strongly on the second pulse area ?(2). It allows the shift to be canceled, nominally at ?(2)=?/2, but correlations perturb the null to slightly larger ?(2). The frequency shift is relevant for optical lattice clocks and increases with the spatial inhomogeneity of the clock excitation field, naturally larger at optical frequencies. PMID:23679589

  6. Effects of pharmacological agents on subcortical resistance shifts

    NASA Technical Reports Server (NTRS)

    Klivington, K. A.

    1975-01-01

    Microliter quantities of tetrodotoxin, tetraethylammonium chloride, and picrotoxin injected into the inferior colliculus and superior olive of unanesthetized cats differentially affect the amplitude and waveform of click-evoked potentials and evoked resistance shifts. Tetrodotoxin simultaneously reduces the negative phase of the evoked potential and eliminates the evoked resistance shift. Tetraethylammonium enhances the negative evoked potential component, presumably of postsynaptic origin, without significantly altering evoked resistance shift amplitude. Picrotoxin also enhances the negative evoked potential wave but increases evoked resistance shift amplitude. These findings implicate events associated with postsynaptic membrane depolarization in the production of the evoked resistance shift.

  7. Phase-shifting behaviour revisited: An alternative measure

    NASA Astrophysics Data System (ADS)

    Kang, Bo Soo; Ryu, Doojin; Ryu, Doowon

    2014-05-01

    This study re-examines the recently documented phase-shifting behaviour of financial markets using an alternative measure, an intraday return-based measure. While most previous studies on phase-shifting behaviour adopt the volume-imbalance measure proposed by Plerou et al. (2003), we find that our return-based measure successfully captures phase-shifting behaviour, and moreover exhibits a unique pattern of phase-shifting that is not detected when the classical volume imbalance measure is used. By analysing a high-frequency dataset of KOSPI200 futures, we also find that large trades reveal phase-shifting behaviour more clearly and significantly than smaller trades.

  8. Kinetics of and intermediates in a photocycle branching reaction of the photoactive yellow protein from Ectothiorhodospira halophila

    E-print Network

    van Stokkum, Ivo

    that absorption of a blue photon leads to cisCCtrans isomerization of the 4-hydroxy-cinnamyl chromophore of PYP Abstract We have studied the kinetics of the blue light-induced branching reaction in the photocycle/Vis spectroscopy. As compared to the parallel dark recovery reaction of the presumed blue-shifted signaling state p

  9. A specific nucleophilic ring-opening reaction of aziridines as a unique platform for the construction of hydrogen polysulfides sensors.

    PubMed

    Chen, Wei; Rosser, Ethan W; Zhang, Di; Shi, Wen; Li, Yilin; Dong, Wen-Ji; Ma, Huimin; Hu, Dehong; Xian, Ming

    2015-06-01

    A hydrogen polysulfide mediated aziridine ring-opening reaction was discovered. Based on this reaction, a novel H2Sn-specific chemosensor (AP) was developed. AP showed high sensitivity and selectivity for H2Sn. Notably, the fluorescent turn-on product (1) exhibited excellent two-photon photophysical properties, a large Stokes shift, and high solid state luminescent efficiency. PMID:25961957

  10. Untoward penicillin reactions

    PubMed Central

    Guthe, T.; Idsöe, O.; Willcox, R. R.

    1958-01-01

    The literature on untoward reactions following the administration of penicillin is reviewed. These reactions, including a certain number of deaths which have been reported, are of particular interest to health administrations and to WHO in view of the large-scale programmes for controlling the treponematoses which are now under way—programmes affecting millions of people in many parts of the world. The most serious problems are anaphylactic sensitivity phenomena and superinfection or cross-infection with penicillin-resistant organisms, and the reactions involved range in intensity from the mildest to the fatal; the incidence of the latter is estimated at 0.1-0.3 per million injections. The authors point out that with increasing use of penicillin, more persons are likely to become sensitized and the number of reactions can therefore be expected to rise. The best prevention against such an increase is the restriction of the unnecessary use of penicillin. PMID:13596877

  11. Iodine Clock Reaction.

    ERIC Educational Resources Information Center

    Mitchell, Richard S.

    1996-01-01

    Describes a combination of solutions that can be used in the study of kinetics using the iodine clock reaction. The combination slows down degradation of the prepared solutions and can be used successfully for several weeks. (JRH)

  12. Reactor for exothermic reactions

    DOEpatents

    Smith, L.A. Jr.; Hearn, D.; Jones, E.M. Jr.

    1993-03-02

    A liquid phase process is described for oligomerization of C[sub 4] and C[sub 5] isoolefins or the etherification thereof with C[sub 1] to C[sub 6] alcohols wherein the reactants are contacted in a reactor with a fixed bed acid cation exchange resin catalyst at an LHSV of 5 to 20, pressure of 0 to 400 psig and temperature of 120 to 300 F. Wherein the improvement is the operation of the reactor at a pressure to maintain the reaction mixture at its boiling point whereby at least a portion but less than all of the reaction mixture is vaporized. By operating at the boiling point and allowing a portion of the reaction mixture to vaporize, the exothermic heat of reaction is dissipated by the formation of more boil up and the temperature in the reactor is controlled.

  13. Polymerase Chain Reaction

    NSDL National Science Digital Library

    2009-09-08

    This interactive activity adapted from the University of Nebraska's Library of Crop Technologies depicts steps in the polymerase chain reaction (PCR) technique and explains how it is used to efficiently copy sections of DNA for analysis.

  14. Reactor for exothermic reactions

    DOEpatents

    Smith, Jr., Lawrence A. (Bellaire, TX); Hearn, Dennis (Houston, TX); Jones, Jr., Edward M. (Friendswood, TX)

    1993-01-01

    A liquid phase process for oligomerization of C.sub.4 and C.sub.5 isoolefins or the etherification thereof with C.sub.1 to C.sub.6 alcohols wherein the reactants are contacted in a reactor with a fixed bed acid cation exchange resin catalyst at an LHSV of 5 to 20, pressure of 0 to 400 psig and temperature of 120.degree. to 300.degree. F. Wherein the improvement is the operation of the reactor at a pressure to maintain the reaction mixture at its boiling point whereby at least a portion but less than all of the reaction mixture is vaporized. By operating at the boiling point and allowing a portion of the reaction mixture to vaporize, the exothermic heat of reaction is dissipated by the formation of more boil up and the temperature in the reactor is controlled.

  15. Bad Reaction to Cosmetics?

    MedlinePLUS

    ... Cosmetics Dietary Supplements Drugs Food Medical Devices Nutrition Radiation-Emitting Products Tobacco Products Vaccines, Blood & Biologics Articulos en Espanol Bad Reaction to Cosmetics? Tell FDA Search the Consumer Updates ...

  16. Chemisorption And Precipitation Reactions

    EPA Science Inventory

    The transport and bioavailability of chemical components within soils is, in part, controlled by partitioning between solids and solution. General terms used to describe these partitioning reactions include chemisorption and precipitation. Chemisorption is inclusive of the suit...

  17. Implementing a night-shift clinical nurse specialist.

    PubMed

    Becker, Dawn Marie

    2013-01-01

    Night-shift nurses receive fewer educational opportunities and less administrative support than do day-shift staff, tend to be newer, with less experience and fewer resources, and experience greater turnover rates, stress, and procedural errors. In an attempt to bridge the gap between day- and night-shift nursing, a night-shift clinical nurse specialist (CNS) position was created in a midsized, community teaching hospital. The goal was to provide an advanced practice presence to improve patient outcomes, communication, education, and cost-effectiveness. The night-shift CNS participated in nursing education and skill certifications, communicated new procedures and information, and created a communication committee specifically for night-shift nurses. Through regular rounding and on-call notification, the CNS was available to every area of the hospital for consultation and clinical assistance and assisted with rapid responses, codes, and traumas. Providing education during night shift reduced overtime costs and increased morale, positively affecting turnover rates. The night-shift CNS position has improved morale and equalized support for night-shift nurses. More research, most notably in specific night-shift metrics, is necessary, and with the implementation of the role in additional facilities, more can be understood about improving patient care and nursing staff satisfaction during night shift. PMID:23222025

  18. Reactions of neopentane, methylcyclohexane, and 3,3-dimethylpentane on tungsten carbides: the effect of surface oxygen on reaction pathways

    SciTech Connect

    Ribeiro, F.H.; Betta, R.A.D.; Boudart, M.; Baumgartner, J.; Iglesia, E. (Stanford Univ., CA (USA) Exxon Research and Engineering Co., Annondale, NJ (USA))

    1991-07-01

    High surface area tungsten carbides with WC and {beta}-W{sub 2}C structure were prepared by direct carburization of WO{sub 3} in CH{sub 4}-H{sub 2} mixtures. Their surfaces appear devoid of excess polymeric carbon and adsorb between 0.2 and 0.4 monolayers of CO and H. These materials are very active in neopentane hydrogenolysis. Chemisorbed oxygen inhibits hydrogenolysis reactions and leads to the appearance of isopentane among the reaction products. Neopentane isomerization to isopentane occurs only on Pt, Ir, and Au surfaces. Thus, oxygen-exposed tungsten carbides catalyze reactions characteristic of noble metal catalysts. 3,3-Dimethylpentane isomerizes much faster than neopentane on oxygen-exposed carbides; the isomer distribution suggests that isomerization proceeds via a methyl shift mechanism rather than through the C{sub 5}-ring hydrogenolysis pathways characteristic of highly dispersed Pt. The apparent involvement of 3,3-dimethyl-1-pentene reactive intermediates is consistent with carbenium-type methyl shift pathways. Secondary carbon atoms, capable of forming stable carbenium ions, are present in 3,3-dimethylpentane but not in neopentane; they account for the high 3,3-dimethylpentane isomerization rate and selectivity on oxygen-exposed tungsten carbide-powders. Both dehydrogenation and isomerization reactions of methylcyclohexane occur on these carbide powders. These results suggest the presence of a bifunctional surface that catalyzes dehydrogenation and carbenium ion reactions typically occurring on reforming catalysts. 47 refs.

  19. Phototoxic and Photoallergic Reactions

    Microsoft Academic Search

    Margarida Gonçalo

    \\u000a Phototoxic and photoallergic reactions represent skin reactions to the sun, in the presence of photoactive chemicals applied\\u000a on the skin or taken systemically. They have a highly polymorphic clinical presentation – photocontact urticaria, eczema on\\u000a sun-exposed areas sometimes with erythema multiforme, exaggerated sunburn, linear phytophotodermatitis, pseudoporphyria, photoonycholysis,\\u000a dyschromia, and lupus erythematosus. Also, skin cancers are increasingly associated with exposure to

  20. Glucose reversion reaction kinetics.

    PubMed

    Pilath, Heidi M; Nimlos, Mark R; Mittal, Ashutosh; Himmel, Michael E; Johnson, David K

    2010-05-26

    The reversion reactions of glucose in mildly acidic aqueous solutions have been studied, and the kinetics of conversion to disaccharides has been modeled. The experiments demonstrate that, at high sugar loadings, up to 12 wt % of the glucose can be converted into reversion products. The reversion products observed are primarily disaccharides; no larger oligosaccharides were observed. Only disaccharides linked to the C1 carbon of one of the glucose residues were observed. The formation of 1,6-linked disaccharides was favored, and alpha-linked disaccharides were formed at higher concentrations than beta-linked disaccharides. This observation can be rationalized on the basis of steric effects. At temperatures >140 degrees C, the disaccharides reach equilibrium with glucose and the reversion reaction competes with dehydration reactions to form 5-hydroxymethylfurfural. As a result, disaccharide formation reaches a maximum at reaction times <10 min and decreases with time. At temperatures <130 degrees C, disaccharide formation reaches a maximum at reaction times >30 min. As expected, disaccharide formation exhibits a second-order dependence upon glucose concentration. Levoglucosan formation is also observed; because it shows a first-order dependence upon glucose concentration, its formation is more significant at low concentrations (10 mg mL(-1)), whereas disaccharide formation dominates at high concentrations (200 mg mL(-1)). Experiments conducted using glucose and its disaccharides were calibrated with readily available standards. The kinetic parameters for hydrolysis of some glucodisaccharides could be compared to published literature values. From these experiments, the kinetics and activation energies for the reversion reactions have been calculated. The rate parameters can be used to model the formation of the disaccharides as a function of reaction time and temperature. A new and detailed picture of the molecular mechanism of these industrially important reversion reactions has been developed. PMID:20429509

  1. The Bílik Reaction

    Microsoft Academic Search

    Ladislav Petruš; Mária Petrušová; Zuzana Hricovíniová

    The introduction of the Bílik reaction, the molybdic acid catalyzed interconversion of epimeric aldoses, is an important milestone\\u000a in carbohydrate chemistry. The essentials of this unique, stereospecific carbon-skeleton rearrangement of epialdoses are presented.\\u000a Emphasis is laid on the latest developments in the area, namely the mutual interconversion of 2-ketoses and 2-C-(hydroxymethyl)aldoses, a reaction that is exploited for the preparation of

  2. Ligase Chain Reaction

    Microsoft Academic Search

    Carla Osiowy

    \\u000a Nucleic acid amplification technologies have greatly facilitated medical diagnostics for genetic and infectious diseases through\\u000a the exquisite sensitivity and specificity associated with these methods. Polymerase chain reaction (PCR) (see\\u000a Chapter 6) ushered in these technologies and was soon accompanied by numerous newly developed amplification techniques, including\\u000a ligase chain reaction (LCR). These nucleic acid amplification techniques result in the exponential increase

  3. GIAO DFT 13C/15N chemical shifts in regioisomeric structure determination of fused pyrazoles.

    PubMed

    Chimichi, Stefano; Boccalini, Marco; Matteucci, Alessandra; Kharlamov, Sergey V; Latypov, Shamil K; Sinyashin, Oleg G

    2010-08-01

    The combined use of two-dimensional NMR correlation experiments and gauge including atomic orbital density functional theory in (13)C NMR chemical shift (CS) calculations allowed reliable and simple structural determination of regioisomeric heterocyclic systems that originate from the reactions of acylquinolinones with substituted hydrazines. Moreover, the results of differential analysis between the calculated (15)N NMR CSs for hypothetical structures and the experimental data of the title azaheterocyclic systems were even more advantageous with respect to (13)C because there was no need for correlational analysis: structures of the regioisomeric compounds could be determined just by direct comparison. PMID:20589725

  4. Intramolecular dehydro-Diels-Alder reaction affords selective entry to arylnaphthalene or aryldihydronaphthalene lignans.

    PubMed

    Kocsis, Laura S; Brummond, Kay M

    2014-08-15

    Intramolecular dehydro-Diels-Alder (DDA) reactions are performed affording arylnaphthalene or aryldihydronaphthalene lactones selectively as determined by choice of reaction solvent. This constitutes the first report of an entirely selective formation of arylnaphthalene lactones utilizing DDA reactions of styrene-ynes. The synthetic utility of the DDA reaction is demonstrated by the synthesis of taiwanin C, retrohelioxanthin, justicidin B, isojusticidin B, and their dihydronaphthalene derivatives. Computational methods for chemical shift assignment are presented that allow for regioisomeric lignans to be distinguished. PMID:25061845

  5. Potassium-catalyzed steam gasification of petroleum coke for H 2 production: Reactivity, selectivity and gas release

    Microsoft Academic Search

    Youqing Wu; Jianjian Wang; Shiyong Wu; Sheng Huang; Jinsheng Gao

    2011-01-01

    Potassium-catalyzed steam gasification of petroleum coke for H2 production was performed using a laboratory fixed-bed reaction system with an on-line quadruple mass spectrometer. The gasification reactivity, gasification selectivity and gas release for the catalytic gasification were investigated, compared with the non-catalytic gasification. The catalytic gasification could not only effectively promote these reactions (the water–carbon reaction, the water–gas shift reaction and

  6. Shift Work, Jet Lag, and Female Reproduction

    PubMed Central

    Mahoney, Megan M.

    2010-01-01

    Circadian rhythms and “clock gene” expression are involved in successful reproductive cycles, mating, and pregnancy. Alterations or disruptions of biological rhythms, as commonly occurs in shift work, jet lag, sleep deprivation, or clock gene knock out models, are linked to significant disruptions in reproductive function. These impairments include altered hormonal secretion patterns, reduced conception rates, increased miscarriage rates and an increased risk of breast cancer. Female health may be particularly susceptible to the impact of desynchronizing work schedules as perturbed hormonal rhythms can further influence the expression patterns of clock genes. Estrogen modifies clock gene expression in the uterus, ovaries, and suprachiasmatic nucleus, the site of the primary circadian clock mechanism. Further work investigating clock genes, light exposure, ovarian hormones, and reproductive function will be critical for indentifying how these factors interact to impact health and susceptibility to disease. PMID:20224815

  7. Phase-shifting point diffraction interferometer

    DOEpatents

    Medecki, H.

    1998-11-10

    Disclosed is a point diffraction interferometer for evaluating the quality of a test optic. In operation, the point diffraction interferometer includes a source of radiation, the test optic, a beam divider, a reference wave pinhole located at an image plane downstream from the test optic, and a detector for detecting an interference pattern produced between a reference wave emitted by the pinhole and a test wave emitted from the test optic. The beam divider produces separate reference and test beams which focus at different laterally separated positions on the image plane. The reference wave pinhole is placed at a region of high intensity (e.g., the focal point) for the reference beam. This allows reference wave to be produced at a relatively high intensity. Also, the beam divider may include elements for phase shifting one or both of the reference and test beams. 8 figs.

  8. Phase-shifting point diffraction interferometer

    DOEpatents

    Medecki, Hector (Berkeley, CA)

    1998-01-01

    Disclosed is a point diffraction interferometer for evaluating the quality of a test optic. In operation, the point diffraction interferometer includes a source of radiation, the test optic, a beam divider, a reference wave pinhole located at an image plane downstream from the test optic, and a detector for detecting an interference pattern produced between a reference wave emitted by the pinhole and a test wave emitted from the test optic. The beam divider produces separate reference and test beams which focus at different laterally separated positions on the image plane. The reference wave pinhole is placed at a region of high intensity (e.g., the focal point) for the reference beam. This allows reference wave to be produced at a relatively high intensity. Also, the beam divider may include elements for phase shifting one or both of the reference and test beams.

  9. Statistical properties of phase-shift algorithms

    NASA Astrophysics Data System (ADS)

    Rathjen, C.

    1995-09-01

    Statistical properties of phase-shift algorithms are investigated for the case of additive Gaussian intensity noise. Based on a bivariate normal distribution, a generally valid probability-density function for the random phase error is derived. This new description of the random phase error shows properties that cannot be obtained through Gaussian error propagation. The assumption of a normally distributed phase error is compared with the derived probability-density function. For small signal-to-noise ratios the assumption of a normally distributed phase error is not valid. Additionally, it is shown that some advanced systematic-error-compensating algorithms have a disadvantageous effect on the random phase error. error, systematic error, additive Gaussian noise, phase-measuring interferometry.

  10. Red Shift in a Laboraory Environment

    E-print Network

    Yuriy A. Yatsunenko; Julian A. Budagov

    2011-03-04

    A hypotheses of energy loss for polarization of e-e+ vacuum by a photon passing interstellar space is considered. An excitation and relaxation of vacuum can't run with speed of light due to very small but finite fraction of e-e+ pair mass that creates a retardment in recuperation of deposited energy back to photon. This "forgotten" by many photons energy is finally splashed out in real space as a Relic Radiation. An assumption that such energy loss is proportional to a photon energy conforms to Hubble low of Red Shift and experimental data treated as accelerated expansion of Universe. A possibility of an observation of this type energy loss is considered at high-energy accelerators where energy deposition may reach up hundreds MeV in second.

  11. Phenological shifts and the fate of mutualisms

    PubMed Central

    Rafferty, Nicole E.; CaraDonna, Paul J.; Bronstein, Judith L.

    2014-01-01

    Climate change is altering the timing of life history events in a wide array of species, many of which are involved in mutualistic interactions. Because many mutualisms can form only if partner species are able to locate each other in time, differential phenological shifts are likely to influence their strength, duration and outcome. At the extreme, climate change-driven shifts in phenology may result in phenological mismatch: the partial or complete loss of temporal overlap of mutualistic species. We have a growing understanding of how, when, and why phenological change can alter one type of mutualism–pollination. However, as we show here, there has been a surprising lack of attention to other types of mutualism. We generate a set of predictions about the characteristics that may predispose mutualisms in general to phenological mismatches. We focus not on the consequences of such mismatches but rather on the likelihood that mismatches will develop. We explore the influence of three key characteristics of mutualism: 1) intimacy, 2) seasonality and duration, and 3) obligacy and specificity. We predict that the following characteristics of mutualism may increase the likelihood of phenological mismatch: 1) a non-symbiotic life history in which co-dispersal is absent; 2) brief, seasonal interactions; and 3) facultative, generalized interactions. We then review the limited available data in light of our a priori predictions and point to mutualisms that are more and less likely to be at risk of becoming phenologically mismatched, emphasizing the need for research on mutualisms other than plant–pollinator interactions. Future studies should explicitly focus on mutualism characteristics to determine whether and how changing phenologies will affect mutualistic interactions. PMID:25883391

  12. Disease associated cellular machinery in anaphylaxis – And the de novo paradigm shift

    PubMed Central

    Pushparaj, Peter Natesan; Rasool, Mahmood; Naseer, Muhammad Imran; Damiati, Laila Abdullah; Kothandaraman, Narasimhan; Gauthaman, Kalamegam; Bhalas, Sami; Manikandan, Jayapal

    2015-01-01

    Anaphylaxis is a sudden immune reaction against an allergen that can potentially lead to Anaphylactic Shock (AS). This immune reaction is characterized by an increase in Immunoglobulin-E (IgE) type of antibodies that bind with Fc?RI receptors on mast cells to release inflammatory mediators. Various intracellular signaling molecules downstream of IgE/ Fc?RI axis play a potential role in cytokine, chemokine and eicosanoid secretion as well as degranulation of immune cells causing vasodilation, vascular permeability, and reduction of intravascular volume leading to cardiovascular collapse. Here, we discuss the cellular machinery of anaphylaxis and the de novo paradigm shift in the cellular aspects of AS. PMID:25780280

  13. Classes of Chemical Reactions Reactions in aqueous media

    E-print Network

    Zakarian, Armen

    Classes of Chemical Reactions Reactions in aqueous media · Precipitation reactions · Acid + electrolytes: a substance that conducts an electric current when dissolved in water Acids are donors of H+ (this is a definition) HBr ! H3O+ + Br¯ or HBr ! H+ + Br¯ Equations for Aqueous Ionic Reactions

  14. Chemical ReactionsChemical Reactions between the Componentsbetween the Components

    E-print Network

    Beauchamp, Jack

    1 Chemical ReactionsChemical Reactions between the Componentsbetween the Components of MolecularMethodology We induce chemical reactions in molecular aggregates by collisionally activating the clusters of AMP to ATP by CID: Julian, RJ and J.L. Beauchamp IJMS 2003, 227(1), 147-159. Reaction of Gas

  15. Study of the Momentum Transfer to Target-Like Residues in Heavy Ion Reactions by Prompt Gamma Measurements

    NASA Astrophysics Data System (ADS)

    Korir, K. A.; Connell, S. H.; Sellschop, J. P. F.; Sideras-Haddad, E.; Förtsch, S. V.; Lawrie, J. J.; Newman, R. T.; Mabala, G. K.; Smit, F. D.; Steyn, G. F.; Bassini, R.; Birattari, C.; Cavinato, M.; Fabrici, E.; Gadioli, E.; Gadioli Erba, E.; Vilakazi, Z.; Becker, B.

    2001-09-01

    Doppler shift and Doppler broadening of prompt ? lines have been measured for many reaction residues in the interaction of 12C with 63Cu at 33 A MeV incident 12C energy using the AFRODITE detector array at NAC, Faure, Cape Town. A preliminary analysis of these data, which carry information of the momentum transferred in the reaction, shows that very useful information regarding reaction mechanisms can be obtained by this technique.

  16. Efficient approach to 4-sulfonamidoquinolines via copper(I)-catalyzed cascade reaction of sulfonyl azides with alkynyl imines.

    PubMed

    Cheng, Guolin; Cui, Xiuling

    2013-04-01

    A novel and efficient approach to 4-sulfonamidoquinolines via copper-catalyzed cascade reaction of sulfonyl azides with alkynyl imines has been developed in which a 1,3-dipole cycloaddition/ketenimine formation/6?-electrocyclization/[1,3]-H shift cascade reaction was involved. Various 4-sulfonamidoquinolines were afforded in up to 84% yield for 19 examples. This synthetic strategy features with atom economy, concise steps, easy operation, and mild reaction conditions. PMID:23521106

  17. Theoretical studies on the tautomerism and intramolecular hydrogen shifts of 5-amino-tetrazole in the gas phase.

    PubMed

    Zhang, Jian-Guo; Feng, Li-Na; Shu, Yuan-Jie; Zhang, Shao-Wen; Zhang, Tong-Lai; Yang, Li; Wu, Man

    2009-01-01

    The tautomerism and intramolecular hydrogen shifts of 5-amino-tetrazole in the gas phase were studied in the present work. The minimum energy path (MEP) information of 5-amino-tetrazole was obtained at the CCSD(T)/6-311G**//MP2/6-311G** level of theory. The six possible tautomers of 1H, 4H-5-imino-tetrazole (a), 1H-5-amino-tetrazole (b), 2H-5-amino-tetrazole (c), 1H, 2H-5-imino-tetrazole (d), the mesoionic form (e) and 2H, 4H-5-imino-tetrazole (f) were investigated. Among these tautomers, there are 2 amino- forms, 3 imino- forms, and 1 mesoionic structure form. In all the tautomers, 2-H form (c) is the energetically preferred one in the gas phase. In the imino- tautomers, the energy value of the compound d is similar as that of the compound f but it is higher than the energy value of the compound a. The potential energetic surface (PES) and kinetics for five reactions have been investigated. Reaction 2 (b-->c) was hydrogen shifts only in which the 1-H and 2-H rearrangement. This means that the reaction 2 (b-->c) is energetically favorable having an activation barrier of 45.66 kcal.mol(-1) and the reaction energies (DeltaE) is only 2.67 kcal.mol(-1). However, the reaction energy barrier for tautomerism of reaction 1 (b-->e) is 54.90 kcal.mol(-1). Reaction 1 (b-->a), reaction 3 (c-->d), and reaction 5 (c-->f) were amino- -->imino- tautomerism reactions. The energy barriers of amino- -->imino- tautomerism reactions required are 59.39, 65.57, 73.61 kcal.mol(-1) respectively in the gas phase. The calculated values of rate constants using TST, TST/Eckart, CVT, CVT/SCT and CVT/ZCT methods using the optimized geometries obtained at the MP2/6-311G** level of theory show the variational effects are small over the whole temperature range, while tunneling effects are big in the lower temperature range for all tautomerism reactions. PMID:18941806

  18. Shifts in oxidation states of cerium oxide nanoparticles detected inside intact hydrated cells and organelles.

    PubMed

    Szymanski, Craig J; Munusamy, Prabhakaran; Mihai, Cosmin; Xie, Yumei; Hu, Dehong; Gilles, Mary K; Tyliszczak, Tolek; Thevuthasan, Suntharampillai; Baer, Donald R; Orr, Galya

    2015-09-01

    Cerium oxide nanoparticles (CNPs) have been shown to induce diverse biological effects, ranging from toxic to beneficial. The beneficial effects have been attributed to the potential antioxidant activity of CNPs via certain redox reactions, depending on their oxidation state or Ce(3+)/Ce(4+) ratio. However, this ratio is strongly dependent on the environment and age of the nanoparticles and it is unclear whether and how the complex intracellular environment impacts this ratio and the possible redox reactions of CNPs. To identify any changes in the oxidation state of CNPs in the intracellular environment and better understand their intracellular reactions, we directly quantified the oxidation states of CNPs outside and inside intact hydrated cells and organelles using correlated scanning transmission x-ray and super resolution fluorescence microscopies. By analyzing hundreds of small CNP aggregates, we detected a shift to a higher Ce(3+)/Ce(4+) ratio in CNPs inside versus outside the cells, indicating a net reduction of CNPs in the intracellular environment. We further found a similar ratio in the cytoplasm and in the lysosomes, indicating that the net reduction occurs earlier in the internalization pathway. Together with oxidative stress and toxicity measurements, our observations identify a net reduction of CNPs in the intracellular environment, which is consistent with their involvement in potentially beneficial oxidation reactions, but also point to interactions that can negatively impact the health of the cells. PMID:26056725

  19. Science to Practice: Highly shifted proton MR imaging--a shift toward better cell tracking?

    PubMed

    Bulte, Jeff W M

    2014-09-01

    Summary A "hot spot" magnetic resonance (MR) imaging cell tracking technique has been developed that allows direct detection of dysprosium- or thulium-1,4,7,10-tetraazacyclododecane-?,?',?'',?'''-tetramethyl-1,4,7,10-tetraacetic acid (DOTMA)-labeled protons inside cells. These highly shifted protons may allow specific detection of multiple cell types because it does not rely on acquiring the proton signal from bulk water. PMID:25153271

  20. Science to Practice: Highly Shifted Proton MR imaging—A Shift toward Better Cell Tracking?

    PubMed Central

    Bulte, Jeff W. M.

    2015-01-01

    Summary A “hot spot” magnetic resonance (MR) imaging cell tracking technique has been developed that allows direct detection of dysprosium- or thulium-1,4,7,10-tetraazacyclododecane-?,??,??,??-tetramethyl-1,4,7,10-tetraacetic acid (DOTMA)–labeled protons inside cells. These highly shifted protons may allow specific detection of multiple cell types because it does not rely on acquiring the proton signal from bulk water. PMID:25153271