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Sample records for water-gas shift reaction

  1. Water-gas shift reaction

    SciTech Connect

    Newsome, D.S.

    1980-01-01

    A review covers the industrial applications of the water-gas shift reaction in hydrogen manufacturing, removing CO from ammonia synthesis feeds, and detoxifying town gas; and the catalyst characteristics, reaction kinetics, and reaction mechanisms of the water-gas shift reactions catalyzed by iron-based, copper-based, or sulfided cobalt-molybdenum catalysts.

  2. Water-gas shift reaction

    SciTech Connect

    Newsome, D.S.

    1980-01-01

    Recent kinetic and mechanistic studies of the water-gas shift reaction, H/sub 2/O(g) + CO(g) reversible CO/sub 2/ + H/sub 2/(g), catalyzed by iron and copper catalysts are reviewed. Composition, structure, active sites, preparation methods, additives, and poisons are discussed relative to each catalyst. New water-gas shift reaction catalyst systems studied are Mo-magnesia, Ni - Mo, Co - Mo, sulfided Co - Mo - Cs, sulfided Co - Mo, sulfided Ni - Mo, Co - Mo - Ni with added alkaki, and Co - Mo with added alkali, Cesium carbonate - cesium acetate - potassium carbonate or potassium acetate - Co - Mo is claimed to be an especially active catalyst. These new catalyst systems are sulfur tolerant and hold promise as catalysts for hydrogenation of high-sulfur coals. (BLM)

  3. Zeolite Membrane Reactor for Water Gas Shift Reaction for Hydrogen Production

    SciTech Connect

    Lin, Jerry Y.S.

    2013-01-29

    Gasification of biomass or heavy feedstock to produce hydrogen fuel gas using current technology is costly and energy-intensive. The technology includes water gas shift reaction in two or more reactor stages with inter-cooling to maximize conversion for a given catalyst volume. This project is focused on developing a membrane reactor for efficient conversion of water gas shift reaction to produce a hydrogen stream as a fuel and a carbon dioxide stream suitable for sequestration. The project was focused on synthesizing stable, hydrogen perm-selective MFI zeolite membranes for high temperature hydrogen separation; fabricating tubular MFI zeolite membrane reactor and stable water gas shift catalyst for membrane reactor applications, and identifying experimental conditions for water gas shift reaction in the zeolite membrane reactor that will produce a high purity hydrogen stream. The project has improved understanding of zeolite membrane synthesis, high temperature gas diffusion and separation mechanisms for zeolite membranes, synthesis and properties of sulfur resistant catalysts, fabrication and structure optimization of membrane supports, and fundamentals of coupling reaction with separation in zeolite membrane reactor for water gas shift reaction. Through the fundamental study, the research teams have developed MFI zeolite membranes with good perm-selectivity for hydrogen over carbon dioxide, carbon monoxide and water vapor, and high stability for operation in syngas mixture containing 500 part per million hydrogen sulfide at high temperatures around 500°C. The research teams also developed a sulfur resistant catalyst for water gas shift reaction. Modeling and experimental studies on the zeolite membrane reactor for water gas shift reaction have demonstrated the effective use of the zeolite membrane reactor for production of high purity hydrogen stream.

  4. Effects of water-gas shift reaction on simulated performance of a molten carbonate fuel cell

    NASA Astrophysics Data System (ADS)

    Kim, Mi-Hyun; Park, Hong-Kyu; Chung, Gui-Yung; Lim, Hee-Chun; Nam, Suk-Woo; Lim, Tae-Hoon; Hong, Seong-Ahn

    A molten carbonate fuel cell (MCFC) is simulated. In order to determine the effects of the water-gas shift reaction, the calculated results such as temperature distribution, voltage distribution, conversion and performance, are compared with those calculated excluding the shift reaction. Uniformity in the temperature profile is deteriorated due to the shift reaction. At the entrance, hydrogen is consumed rapidly in order to reach the equilibrium state of the shift reaction. The conversion of hydrogen decreases along the direction of gas flow because of hydrogen generated by the shift reaction. Therefore, when the shift reaction is excluded, the conversion of hydrogen is higher than that in a practical cell. Additionally, at the same current density, the voltage calculated without the shift reaction would be higher than the real value. The effect of the shift reaction on the voltage distribution and cell performances is quite small.

  5. Low temperature, sulfur tolerant homogeneous catalysts for the water-gas shift reaction

    SciTech Connect

    Laine, R.M.; Wood, B.J.; Krishnan, G.N.

    1986-04-01

    The objective of this project is to identify, prepare, test, characterize, and evaluate a practical, homogeneous catalyst for a water-gas shift process. The project effort is divided into the following five tasks: (1) Update SRI's recent review of the literature on the catalysis of the water-gas shift reaction (WGSR) to include references after 1982 and those in the patent literature. Based on this review, SRI will choose ten candidate systems to be evaluated as to their abilities to catalyze the WGSR using syngas derived from gasified coal. (2) Develop a test plan designed to effectively evaluate both the catalysts and, to some extent, reactor configuration for WGSR catalysis. (3) Perform a series of experiments to identify the most effective and economical of the ten candidate catalysts and then further evaluate the reaction kinetics of at least one selected catalyst system to develop sufficient data to provide the basis for the work in Task 4. (4) Develop a mathematical model of the final candidate system that uses rate expressions to describe the catalytic process. (5) Perform a techno-economical evaluation of the catalyst in terms of a proposed plant design based on the reaction model, current costs, and standard chemical engineering practice and compare the proposed design with a conventional hydrogen plant.

  6. 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.

  7. 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.

  8. Plasmon-enhanced reverse water gas shift reaction over oxide supported Au catalysts

    SciTech Connect

    Upadhye, AA; Ro, I; Zeng, X; Kim, HJ; Tejedor, I; Anderson, MA; Dumesic, JA; Huber, GW

    2015-01-01

    We show that localized surface plasmon resonance (LSPR) can enhance the catalytic activities of different oxide-supported Au catalysts for the reverse water gas shift (RWGS) reaction. Oxide-supported Au catalysts showed 30 to 1300% higher activity for RWGS under visible light compared to dark conditions. Au/TiO2 catalyst prepared by the deposition-precipitation (DP) method with 3.5 nm average Au particle size showed the highest activity for the RWGS reaction. Visible light is converted into chemical energy for this reaction with up to a 5% overall efficiency. A shift in the apparent activation energy (from 47 kJ mol(-1) in dark to 35 kJ mol(-1) in light) and apparent reaction order with respect to CO2 (from 0.5 in dark to 1.0 in light) occurs due to the LSPR. Our kinetic results indicate that the LSPR increases the rate of either the hydroxyl hydrogenation or carboxyl decomposition more than any other steps in the reaction network.

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

    SciTech Connect

    Pizarro, C.; Escudey, M.; Moya, S.A.; Fabris, J.D.

    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.

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

    NASA Astrophysics Data System (ADS)

    Pizarro, C.; Escudey, M.; Moya, S. A.; Fabris, J. D.

    2005-04-01

    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°C to 500°C. The room temperature Mössbauer 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 °C induced changes on the iron oxide mineralogy with a significant decrease of the catalytic activity.

  11. Low temperature, sulfur tolerant homogeneous catalysts for the water-gas shift reaction

    SciTech Connect

    Laine, R.M.

    1986-01-20

    The purpose of this report is to update and reorganize our recent review on homogeneous catalysis of the water-gas shift reaction (WGSR) based on recent literature publications and patents. This updated version will serve as a means of selecting 10 candidate catalyst systems for use in developing effective, sulfur-tolerant, low temperature WGSR catalysts. This report discusses the variations possible in the basic chemistry associated with WGSR catalytic cycles, including basic, acidic, and neutral conditions. Then individual mechanism for specific WGSR catalyst systems are discussed. Finally, on the basis of the literature reports, a list is presented of candidate catalysts and basic systems we have chosen for study in Task 3.

  12. Water gas shift reaction: homogeneous catalysis by ruthenium and other metal carbonyls

    SciTech Connect

    Ford, P.C.

    1981-02-01

    A number of chemical systems are active for homogeneous, solution phase catalysis of the water gas shift reaction (WGSR). Catalysis of the shift reaction appears to be a quite general property of carbonyl complexes in alkaline solutions. The key mechanistic steps for which some kinetics information is available are the activation of coordinated CO by reaction with hydroxide and the reductive elimination of dihydrogen from a resulting metal hydride. Which of these is rate limiting in a cycle is a function of the specific metal system and the specific reaction conditions. A basic solution is not a necessary condition for WGSR catalysis. Although WGSR catalysis is not as general a phenomenon in acidic media, several such systems have been characterized with activities which compare very favorably to those seen in basic solutions. While logical mechanisms have been proposed for several of the better characterized catalysts, it is clear that a more complete mechanistic understanding of the key steps in potential cycles is greatly needed. Recognition of such needs has led to fundamental studies into the acid/base natures of metal carbonyl hydride clusters, of CO activation on cluster and mononuclear metal carbonyls by bases, and of dihydrogen elimination from and declusterification and clusterification reactions of metal carbonyl hydrides. While none of these processes is in itself catalytic, the sum of several represents possible cycles. With regard to the future of homogeneous WGSR catalysts, it is obvious that under the conditions which these have been tested, the known systems are not commercially viable. Certainly, for a reaction such as the WGSR for which effective heterogeneous catalysts are known, it will take substantial advantages for a new system to be an attractive alternative to established technology.

  13. Mechanisms of the Water-Gas Shift Reaction Catalyzed by Ruthenium Carbonyl Complexes.

    PubMed

    Liu, Naying; Guo, Ling; Cao, Zhaoru; Li, Wenli; Zheng, Xiaoli; Shi, Yayin; Guo, Juan; Xi, Yaru

    2016-04-21

    Density functional theory (DFT) is employed to study the water-gas shift (WGS) reaction in the gas phase for two complexes, Ru3(CO)12 and Ru(CO)5. Here we report four mechanisms of ruthenium carbonyl complexes catalyzed for WGS reaction. The energetic span model is applied to evaluate efficiency of the four catalytic pathways. Our results indicate that mechanism C and D show a good catalytic behavior, which is in agreement with results from the literature. The mechanism C and D not only include the important intermediate Ru3(CO)11H(-) but also exclude the energy-demanding OH(-) desorption and revise an unfavorable factor of the previous mechanism. Two complexes along mechanisms B have the highest turnover frequency (TOF) values. The trinuclear carbonyl complexes-Ru3(CO)12 is preferred over mononuclear carbonyl Ru(CO)5 by comparing TOF due to the fact that metal-metal cooperativity can enhance activity to the WGS reaction. In this work, the nature of interaction between transition states and intermediates is also analyzed by the detailed electronic densities of states, and we further clarify high catalytic activity of ruthenium carbonyl complexes as well. Our conclusions provide a guide to design catalysts for the WGS reaction. PMID:27064302

  14. 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.

  15. On the Mechanism of Low-Temperature Water Gas Shift Reaction on Copper

    SciTech Connect

    Gokhale, Amit A.; Dumesic, James A.; Mavrikakis, Manos

    2008-01-30

    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. Periodic, self-consistent density functional theory (DFT-GGA) calculations are used to investigate the water gas shift reaction (WGSR) mechanism on Cu(111). The thermochemistry and activation energy barriers for all the elementary steps of the commonly accepted redox mechanism, involving complete water activation to atomic oxygen, are presented. Through our calculations, we identify carboxyl, a new reactive intermediate, which plays a central role in WGSR on Cu(111). The thermochemistry and activation energy barriers of the elementary steps of a new reaction path, involving carboxyl, are studied. A detailed DFTbased microkinetic model of experimental reaction rates, accounting for both the previous and the new WGSR mechanism show that, under relevant experimental conditions, (1) the carboxyl-mediated route is the dominant path, and (2) the initial hydrogen abstraction from water is the rate-limiting step. Formate is a stable “spectator” species, formed predominantly through CO₂ hydrogenation. In addition, the microkinetic model allows for predictions of (i) surface coverage of intermediates, (ii) WGSR apparent activation energy, and (iii) reaction orders with respect to CO, H₂O, CO₂, and H₂.

  16. 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

  17. 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.

  18. Flame made ceria supported noble metal catalysts for efficient H2 production via the water gas shift reaction

    NASA Astrophysics Data System (ADS)

    Cavusoglu, G.; Lichtenberg, H.; Gaur, A.; Goldbach, A.; Grunwaldt, J.-D.

    2016-05-01

    Rh/ceria catalysts were synthesized by flame spray pyrolysis for high temperature water gas shift (WGS) reactions. These catalysts show a high specific surface area due to a high degree of nanocrystallinity. X-ray absorption spectroscopy (XAS) unraveled the formation of small Rh particles under WGS reaction conditions. The catalytic activity was examined at atmospheric pressure by measuring CO conversion as a function of temperature. Some methane formation was observed above 310°C.

  19. In situ characterization of catalysts and membranes in a microchannel under high-temperature water gas shift reaction conditions

    NASA Astrophysics Data System (ADS)

    Cavusoglu, G.; Dallmann, F.; Lichtenberg, H.; Goldbach, A.; Dittmeyer, R.; Grunwaldt, J.-D.

    2016-05-01

    Microreactor technology with high heat transfer in combination with stable catalysts is a very attractive approach for reactions involving major heat effects such as methane steam reforming and to some extent, also the high temperature water gas shift (WGS) reaction. For this study Rh/ceria catalysts and an ultrathin hydrogen selective membrane were characterized in situ in a microreactor specially designed for x-ray absorption spectroscopic measurements under WGS conditions. The results of these experiments can serve as a basis for further development of the catalysts and membranes.

  20. Approach to equilibrium of the water-gas shift reaction on a Ni/zirconia anode under solid oxide fuel-cell conditions

    NASA Astrophysics Data System (ADS)

    Ahmed, K.; Föger, K.

    The reverse water-gas shift reaction is carried out in a solid oxide fuel-cell at a range of fuel utilization levels and the approach of this reaction to thermodynamic equilibrium is calculated from the experimental data. It is found that the water-gas shift reaction is close to equilibrium only at high levels of fuel utilization. This is an important finding for modeling and simulation of fuel-cells.

  1. Low temperature, sulfur tolerant homogeneous catalysts for the water-gas shift reaction. Task 2, Test plan

    SciTech Connect

    Laine, R.M.; Wood, B.J.; Krishnan, G.N.

    1986-04-01

    The objective of this project is to identify, prepare, test, characterize, and evaluate a practical, homogeneous catalyst for a water-gas shift process. The project effort is divided into the following five tasks: (1) Update SRI`s recent review of the literature on the catalysis of the water-gas shift reaction (WGSR) to include references after 1982 and those in the patent literature. Based on this review, SRI will choose ten candidate systems to be evaluated as to their abilities to catalyze the WGSR using syngas derived from gasified coal. (2) Develop a test plan designed to effectively evaluate both the catalysts and, to some extent, reactor configuration for WGSR catalysis. (3) Perform a series of experiments to identify the most effective and economical of the ten candidate catalysts and then further evaluate the reaction kinetics of at least one selected catalyst system to develop sufficient data to provide the basis for the work in Task 4. (4) Develop a mathematical model of the final candidate system that uses rate expressions to describe the catalytic process. (5) Perform a techno-economical evaluation of the catalyst in terms of a proposed plant design based on the reaction model, current costs, and standard chemical engineering practice and compare the proposed design with a conventional hydrogen plant.

  2. Heat Integration of the Water-Gas Shift Reaction System for Carbon Sequestration Ready IGCC Process with Chemical Looping

    SciTech Connect

    Juan M. Salazara; Stephen E. Zitney; Urmila M. Diwekara

    2010-01-01

    Integrated gasification combined cycle (IGCC) technology has been considered as an important alternative for efficient power systems that can reduce fuel consumption and CO2 emissions. One of the technological schemes combines water-gas shift reaction and chemical-looping combustion as post gasification techniques in order to produce sequestration-ready CO2 and potentially reduce the size of the gas turbine. However, these schemes have not been energetically integrated and process synthesis techniques can be applied to obtain an optimal flowsheet. This work studies the heat exchange network synthesis (HENS) for the water-gas shift reaction train employing a set of alternative designs provided by Aspen energy analyzer (AEA) and combined in a process superstructure that was simulated in Aspen Plus (AP). This approach allows a rigorous evaluation of the alternative designs and their combinations avoiding all the AEA simplifications (linearized models of heat exchangers). A CAPE-OPEN compliant capability which makes use of a MINLP algorithm for sequential modular simulators was employed to obtain a heat exchange network that provided a cost of energy that was 27% lower than the base case. Highly influential parameters for the pos gasification technologies (i.e. CO/steam ratio, gasifier temperature and pressure) were calculated to obtain the minimum cost of energy while chemical looping parameters (oxidation and reduction temperature) were ensured to be satisfied.

  3. 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.

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

    SciTech Connect

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

    2009-05-15

    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 capacity can be amplified by purging with steam. From previous studies is it known that for SEWGS applications, hydrotalcite-based materials are particularly attractive as sorbent, and commercial high-temperature shift catalysts can be used for the conversion of carbon monoxide. Tablets of a potassium promoted hydrotalcite-based material are characterized in both breakthrough and cyclic experiments in a 2 m tall fixed-bed reactor. When exposed to a mixture of carbon dioxide, steam, and nitrogen at 400{sup o}C, the material shows a breakthrough capacity of 1.4 mmol/g. In subsequent experiments the material was mixed with tablets of promoted iron-chromium shift catalyst and exposed to a mixture of carbon dioxide, carbon monoxide, steam, hydrogen, and nitrogen. It is demonstrated that carbon monoxide conversion can be enhanced to 100% in the presence of a carbon dioxide sorbent. At breakthrough, carbon monoxide and carbon dioxide simultaneously appear at the end of the bed. During more than 300 cycles of adsorption/reaction and desorption, the capture rate, and carbon monoxide conversion are confirmed to be stable. Two different cycle types are investigated: one cycle with a CO{sub 2} rinse step and one cycle with a steam rinse step. The performance of both SEWGS cycles are discussed.

  5. 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.

  6. 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.

  7. On the importance of steady-state isotopic techniques for the investigation of the mechanism of the reverse water-gas-shift reaction.

    PubMed

    Tibiletti, Daniele; Goguet, Alexandre; Meunier, Frederic C; Breen, John P; Burch, Robbie

    2004-07-21

    The formation and reactivity of surface intermediates in the reverse water-gas-shift reaction on a Pt/CeO2 catalyst are critically dependent on the reaction conditions so that conclusions regarding the reaction mechanism cannot be inferred using ex operando conditions. PMID:15263955

  8. Low temperature, sulfur tolerant homogeneous catalysts for the water-gas shift reaction. Task 1, Topical report No. 1

    SciTech Connect

    Laine, R.M.

    1986-01-20

    The purpose of this report is to update and reorganize our recent review on homogeneous catalysis of the water-gas shift reaction (WGSR) based on recent literature publications and patents. This updated version will serve as a means of selecting 10 candidate catalyst systems for use in developing effective, sulfur-tolerant, low temperature WGSR catalysts. This report discusses the variations possible in the basic chemistry associated with WGSR catalytic cycles, including basic, acidic, and neutral conditions. Then individual mechanism for specific WGSR catalyst systems are discussed. Finally, on the basis of the literature reports, a list is presented of candidate catalysts and basic systems we have chosen for study in Task 3.

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

    SciTech Connect

    Unknown

    2000-12-01

    A hydrogen selective membrane as a membrane reactor (MR) can significantly improve the power generation efficiency with a reduced capital and operating cost for the waster-gas-shift reaction. Existing hydrogen selective ceramic membranes are not suitable for the proposed MR due to their poor hydrothermal stability. In this project we have focused on the development of innovative silicon carbide (SiC) based hydrogen selective membranes, which can potentially overcome this technical barrier. During Year I, we have successfully fabricated SiC macro porous membranes via extrusion of commercially available SiC powder, which were then deposited with thin, micro-porous (6 to 40{angstrom} in pore size) films via sol-gel technique as intermediate layers. Finally, an SiC hydrogen selective thin film was deposited on this substrate via our CVD/I technique. The composite membrane thus prepared demonstrated excellent hydrogen selectivity at high temperature ({approx}600 C). More importantly, this membrane also exhibited a much improved hydrothermal stability at 600 C with 50% steam (atmospheric pressure) for nearly 100 hours. In parallel, we have explored an alternative approach to develop a H{sub 2} selective SiC membrane via pyrolysis of selected pre-ceramic polymers. Building upon the positive progress made in the Year I preliminary study, we will conduct an optimization study in Year II to develop an optimized H{sub 2} selective SiC membrane with sufficient hydrothermal stability suitable for the WGS environment.

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

    SciTech Connect

    Paul K.T. Liu

    2003-12-01

    A hydrogen selective membrane as a membrane reactor (MR) can significantly improve the power generation efficiency with a reduced capital and operating cost for the waster-gas-shift reaction. Existing hydrogen selective ceramic membranes are not suitable for the proposed MR due to their poor hydrothermal stability. In this project we have focused on the development of innovative silicon carbide (SiC) based hydrogen selective membranes, which can potentially overcome this technical barrier. SiC macro-porous membranes have been successfully fabricated via extrusion of commercially available SiC powder. Also, an SiC hydrogen selective thin film was prepared via our CVD/I technique. This composite membrane demonstrated excellent hydrogen selectivity at high temperature ({approx}600 C). More importantly, this membrane also exhibited a much improved hydrothermal stability at 600 C with 50% steam (atmospheric pressure) for nearly 100 hours. In parallel, we have explored an alternative approach to develop a H{sub 2} selective SiC membrane via pyrolysis of selected pre-ceramic polymers and sol-gel techniques. Building upon the positive progress made in the membrane development study, we conducted an optimization study to develop an H{sub 2} selective SiC membrane with sufficient hydrothermal stability suitable for the WGS environment. In addition, mathematical simulation has been performed to compare the performance of the membrane reactor (MR) vs conventional packed bed reactor 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

  11. DFT study of the water gas shift reaction on Ni(111), Ni(100) and Ni(110) surfaces

    NASA Astrophysics Data System (ADS)

    Mohsenzadeh, Abas; Richards, Tobias; Bolton, Kim

    2016-02-01

    Density functional theory (DFT) calculations were used to study the water gas shift (WGS) reaction on Ni(111), Ni(100) and Ni(110) surfaces. The adsorption energy for ten species involved in the reaction together with activation barriers and reaction energies for the nine most important elementary steps were determined using the same model and DFT methods. The results reveal that these energies are sensitive to the surface structure. In spite of this, the WGS reaction occurs mainly via the direct (also referred to as redox) pathway with the CO + O → CO2 reaction as the rate determining step on all three surfaces. The activation barrier obtained for this rate limiting step decreases in the order Ni(110) > Ni(111) > Ni(100). Therefore, if O species are present on the surfaces then the WGS reaction is fastest on the Ni(100) surface. However, the barrier for desorption of H2O (which is the source of the O species) is lower than its dissociation reaction on the Ni(111) and Ni(100) surfaces, but not on the Ni(110) surface. Hence, at low H2O(g) pressures, the direct pathway on the Ni(110) surface will dominate and will be the rate limiting step. The calculations also show that the reason that the WGS reaction does not primarily occur via the formate pathway is that this species is a stable intermediate on all surfaces. The reactions studied here support the Brønsted-Evans-Polanyi (BEP) principles with an R2 value of 0.99.

  12. The role of metals and influence of oxygen on ceria supported copper-palladium bimetallic catalysts for the oxygen-assisted water-gas shift reaction

    NASA Astrophysics Data System (ADS)

    Fox, Elise Bickford

    This study was focused to investigate the roles of Cu and Pd in CuPd/CeO 2 bimetallic catalysts containing 30 wt% Cu and 1 wt% Pd used in the oxygen-assisted water-gas shift (OWGS) reaction employing combined bulk and surface characterization techniques such as X-ray diffraction (XRD), temperature programmed reduction (TPR), CO chemisorption, and in-situ X-ray photoelectron spectroscopy (XPS). The role of oxygen in aiding the water-gas shift reaction was also studied to determine an overall mechanism for the water-gas shift reaction. The catalytic activity for CO conversion and the stability of catalyst during on-stream operation increased upon adding Pd to Cu/CeO2 monometallic catalysts, especially when the OWLS reaction was performed under low temperatures. In-situ XPS studies of reduced catalysts showed the existence of Cu and Pd in their metallic states. The spectra also showed a shift in Cu 2p peaks toward lower binding energy 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. The improved catalytic activity and stability of CuPd/CeO2 bimetallic catalyst was attributed to the Cu-Pd interaction. When the catalyst series was reduced in-situ under UHV conditions in the XPS chamber in order to better understand the metal-support interactions, it was found that the addition of 1%Pd to the Cu/CeO2 catalyst would greatly improve the reduction properties of the Cu and Ce under UHV conditions. When compared with results from the oxygen-assisted water-gas-shift reaction, it was found that the increased reduction from the addition of Pd aided in the reaction. When reaction kinetics of the water-gas shift and the oxygen-assisted water-gas shift reaction were examined, it was found that the addition of a small amount of air improved the overall reaction kinetics. In general, the activation energies decreased for the catalyst series when air was added to the

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

    NASA Astrophysics Data System (ADS)

    Fu, Qi

    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. Various gold structures, such as metallic gold nanoparticles, cluster and cations were found in gold-ceria sample containing 4--8 at% gold. To discriminate between the various gold species, leaching of the gold-ceria in sodium cyanide was conducted. The metallic gold and all other gold species not in close association with ceria were removed by leaching. A small amount of gold remained in the leached samples. The exact content of non-leachable gold was a function of the parent catalyst properties. Similar data were collected from Pt-ceria samples. STEM or HRTEM, coupled with EDX showed no gold or platinum particles remaining; only what appeared to be very fine clusters or atomically dispersed gold or platinum. Cationic gold or platinum was identified in these samples by XPS. The unexpected finding was that the catalytic activity of the leached samples was similar or slightly better than that of the parent catalyst after removal of the metallic gold or platinum particles by cyanide leaching. Thus, metallic nanoparticles are not necessary; they are mere spectators in the water-gas shift reaction. Nonmetallic gold or platinum species strongly associated with surface cerium-oxygen groups are responsible for the activity, since the extra gold or platinum present in the parent material does not increase the reaction rate; nor does it change the activation energy of the reaction. The importance of the oxide support properties became clear by this work. The amount of gold or platinum retained in active form depends on the surface properties

  14. A theoretical study of surface-structural sensitivity of the reverse water-gas shift reaction over Cu( hkl) surfaces

    NASA Astrophysics Data System (ADS)

    Wang, Gui-Chang; Jiang, Ling; Pang, Xian-Yong; Cai, Zun-Sheng; Pan, Yin-Ming; Zhao, Xue-Zhuang; Morikawa, Yoshitada; Nakamura, Junji

    2003-10-01

    The surface-structural sensitivity of the reverse water-gas shift (RWGS) reaction (CO 2 + H 2 → CO + H 2O) over the Cu(1 1 1), Cu(1 0 0), and Cu(1 1 0) surfaces has been studied by first-principle density functional calculations together with the UBI-QEP approach. Cluster models of the surface have been employed to simulate the adsorption of CO 2, H 2, H, O, OH, CO, and H 2O on the Cu( hkl) surfaces at low coverage. This sensitivity is determined by the difference in the activation barriers. It can be noticed that the most likely rate-determining step in RWGS reaction is the CO 2 dissociative adsorption, namely CO 2,g → CO s + O s. The trend in the calculated activation barriers for the reaction of CO 2 dissociative adsorption follows the order of Cu(1 1 0) < Cu(1 0 0) < Cu(1 1 1), suggesting that the most efficient crystal surface for catalyzing RWGS reaction by copper is Cu(1 1 0), and the more densely packed Cu(1 1 1) surface is the least active among the Cu( hkl) surfaces studied here. As expected, the activation barriers for the recombinative reactions over Cu( hkl) are in the order of Cu(1 1 0) > Cu(1 0 0) > Cu(1 1 1), just opposite to the dissociative reactions. The interesting thing is that there is a good correlation between the adsorption bond length and the adsorption energy: The preferred adsorption site is the one with the shortest adsorption bond length. The present calculations are in good agreement with experimental observations.

  15. Reaction mechanism of the reverse water-gas shift reaction using first-row middle transition metal catalysts L'M (M = Fe, Mn, Co): a computational study.

    PubMed

    Liu, Cong; Cundari, Thomas R; Wilson, Angela K

    2011-09-19

    The mechanism of the reverse water-gas shift reaction (CO(2) + H(2) → CO + H(2)O) was investigated using the 3d transition metal complexes L'M (M = Fe, Mn, and Co, L' = parent β-diketiminate). The thermodynamics and reaction barriers of the elementary reaction pathways were studied with the B3LYP density functional and two different basis sets: 6-311+G(d) and aug-cc-pVTZ. Plausible reactants, intermediates, transition states, and products were modeled, with different conformers and multiplicities for each identified. Different reaction pathways and side reactions were also considered. Reaction Gibbs free energies and activation energies for all steps were determined for each transition metal. Calculations indicate that the most desirable mechanism involves mostly monometallic complexes. Among the three catalysts modeled, the Mn complex shows the most favorable catalytic properties. Considering the individual reaction barriers, the Fe complex shows the lowest barrier for activation of CO(2). PMID:21838224

  16. Kinetic and equilibrium study on formic acid decomposition in relation to the water-gas-shift reaction.

    PubMed

    Yasaka, Yoshiro; Yoshida, Ken; Wakai, Chihiro; Matubayasi, Nobuyuki; Nakahara, Masaru

    2006-09-28

    Kinetics and equilibrium are studied on the hydrothermal decarbonylation and decarboxylation of formic acid, the intermediate of the water-gas-shift (WGS) reaction, in hot water at temperatures of 170-330 degrees C, to understand and control the hydrothermal WGS reaction. (1)H and (13)C NMR spectroscopy is applied to analyze as a function of time the quenched reaction mixtures in both the liquid and gas phases. Only the decarbonylation is catalyzed by HCl, and the reaction is first-order with respect to both [H(+)] and [HCOOH]. Consequently, the reaction without HCl is first and a half (1.5) order due to the unsuppressed ionization of formic acid. The HCl-accelerated decarbonylation path can thus be separated in time from the decarboxylation. The rate and equilibrium constants for the decarbonylation are determined separately by using the Henry constant (gas solubility data) for carbon monoxide in hot water. The rate constant for the decarbonylation is 1.5 x 10(-5), 2.0 x 10(-4), 3.7 x 10(-3), and 6.3 x 10(-2) mol(-1) kg s(-1), respectively, at 170, 200, 240, and 280 degrees C on the liquid branch of the saturation curve. The Arrhenius plot of the decarbonylation is linear and gives the activation energy as 146 +/- 3 kJ mol(-1). The equilibrium constant K(CO) = [CO]/[HCOOH] is 0.15, 0.33, 0.80, and 4.2, respectively, at 170, 200, 240, and 280 degrees C. The van't Hoff plot results in the enthalpy change of DeltaH = 58 +/- 6 kJ mol(-1). The decarboxylation rate is also measured at 240-330 degrees C in both acidic and basic conditions. The rate is weakly dependent on the solution pH and is of the order of 10(-4) mol kg(-1) s(-1) at 330 degrees C. Furthermore, the equilibrium constant K(CO2) = [CO(2)][H(2)]/[HCOOH] is estimated to be 1.0 x10(2) mol kg(-1) at 330 degrees C. PMID:16986841

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

    SciTech Connect

    Senanayake, Sanjaya D; Evans, Jaime; Agnoli, Stefano; Barrio, Laura; Chen, Tsung-Liang; Hrbek, Jan; Radriguez, Jose

    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.

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

    SciTech Connect

    Paul K.T. Liu

    2005-07-15

    A high temperature membrane reactor (MR) has been developed to enhance the water-gas-shift (WGS) reaction efficiency with concomitant CO{sub 2} removal for sequestration. This improved WGS-MR with CO{sub 2} recovery capability is ideally suitable for integration into the Integrated Gasification Combined-Cycle (IGCC) power generation system. Two different CO{sub 2}-affinity materials were selected in this study. The Mg-Al-CO{sub 3}-layered double hydroxide (LDH) was investigated as an adsorbent or a membrane for CO{sub 2} separation. The adsorption isotherm and intraparticle diffusivity for the LDH-based adsorbent were experimentally determined, and suitable for low temperature shift (LTS) of WGS. The LDH-based membranes were synthesized using our commercial ceramic membranes as substrate. These experimental membranes were characterized comprehensively in terms of their morphology, and CO{sub 2} permeance and selectivity to demonstrate the technical feasibility. In parallel, an alternative material-base membrane, carbonaceous membrane developed by us, was characterized, which also demonstrated enhanced CO{sub 2} selectivity at the LTS-WGS condition. With optimization on membrane defect reduction, these two types of membrane could be used commercially as CO{sub 2}-affinity membranes for the proposed application. Based upon the unique CO{sub 2} affinity of the LDHs at the LTS/WGS environment, we developed an innovative membrane reactor, Hybrid Adsorption and Membrane Reactor (HAMR), to achieve {approx}100% CO conversion, produce a high purity hydrogen product and deliver a concentrated CO{sub 2} stream for disposal. A mathematical model was developed to simulate this unique one -step process. Finally a benchtop reactor was employed to generate experimental data, which were consistent with the prediction from the HAMR mathematical model. In summary, the project objective, enhancing WGS efficiency for hydrogen production with concomitant CO{sub 2} removal for

  19. 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

  20. Charge polarization at a Au-TiC interface and the generation of highly active and selective catalysts for the low-temperature water-gas shift reaction.

    PubMed

    Rodriguez, José A; Ramírez, Pedro J; Asara, Gian Giacomo; Viñes, Francesc; Evans, Jaime; Liu, Ping; Ricart, Josep M; Illas, Francesc

    2014-10-13

    Au atoms in contact with TiC(001) undergo significant charge polarization. Strong metal-support interactions make Au/TiC(001) an excellent catalyst for the low-temperature water-gas shift (WGS), with turnover frequencies orders of magnitude larger than those observed for conventional metal/oxide catalysts. DFT calculations indicate that the WGS reaction follows an associative mechanism with HOCO as a key intermediate. PMID:25196121

  1. The synthesis of methanol and the reverse water-gas shift reaction over Zn-deposited Cu(100) and Cu(110) surfaces: comparison with Zn/Cu(111)

    NASA Astrophysics Data System (ADS)

    Nakamura, I.; Fujitani, T.; Uchijima, T.; Nakamura, J.

    1998-03-01

    The catalytic activity of Zn vapor-deposited Cu(100) and Cu(110) surfaces for methanol synthesis by the hydrogenation of CO 2 and the reverse water-gas shift reaction were studied using an XPS apparatus combined with a high-pressure flow reactor (18 atm). At a reaction temperature of 523 K, no promotional effect of Zn was observed for the methanol synthesis on both Zn/Cu(100) and Zn/Cu(110). The results were quite different from those for Zn/Cu(111), on which a significant promotion of methanol synthesis activity appeared to be due to the deposition of Zn, indicating that the promotional effect of Zn was sensitive to the surface structure of Cu. However, hysteresis was observed in the catalytic activity for methanol synthesis over the Zn/Cu(110) surface upon heating above 543 K in the reaction mixture. The activity became twice that measured before heating, which was close to the methanol synthesis activity of Zn/Cu(111) at the same Zn coverage. On the other hand, no such hysteresis was observed for the reverse water-gas shift reaction on Zn/Cu(110), indicating that the active site for methanol synthesis was not identical to that for the reverse water-gas shift reaction. In the post-reaction surface analysis, formate species was detected on both Zn/Cu(100) and Zn/Cu(110), whose coverage increased with increasing Zn coverage at 0< ΘZn<0.2. No correlation between the formate coverage and the methanol synthesis activity was obtained, which was in contrast to the results for Zn/Cu(111). Thus, the structure sensitivity observed in the catalytic activity of methanol synthesis over Zn-deposited Cu surfaces is ascribed to the significant difference in the reactivity of the formate intermediate.

  2. 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.; Frenking, G.

    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.

  3. 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.

  4. 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.

  5. 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.

  6. Analysis and modeling of PEM fuel cell stack performance: Effect of in situ reverse water gas shift reaction and oxygen bleeding

    NASA Astrophysics Data System (ADS)

    Karimi, G.; Li, Xianguo

    In this study the performance of a polymer electrolyte membrane (PEM) fuel cell stack is analyzed with a mathematical model when the stack operates on hydrocarbon reformate gas as the anode feed stream. It is shown that the effect of carbon dioxide dilution of the hydrogen dominated reformate gas has a minimal impact on the stack performance. However, the CO-poisoning effect due to the in situ reverse water gas shift reaction in the anode feed stream could have a very serious adverse impact on the stack performance, especially at high current densities. Thermodynamic calculations indicate that the equilibrium concentrations of CO could be as high as 100 ppm, generated by the in situ reverse water gas shift reaction, under the typical conditions of PEM fuel cell operation; and are influenced by the stack operating temperature and water content of the reformate anode feed. This CO-poisoning of the stack performance is shown mitigated effectively by introducing about 0.5-1% oxygen to the anode feed.

  7. Pulse studies to decipher the role of surface morphology in CuO/CeO₂ 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.

    2015-01-23

    The water-gas shift reaction (WGS, CO + H₂O → CO₂) was studied over CuO/CeO₂ 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/CeO₂ (ns) exhibited a substantially better activity than CuO/CeO₂ (nc). The higher activity was associated with the unique properties of CuO/CeO₂ (ns), suchmore » as the easier reduction of highly dispersed CuO to metallic Cu, the stability of metallic Cu and a larger concentration Ce³⁺ in CeO₂ (ns).« less

  8. Atomically Dispersed Au-(OH)x Species Bound on Titania Catalyze the Low-Temperature Water-Gas Shift Reaction

    SciTech Connect

    Yang, Ming; Allard, Lawrence F; Flytzani-Stephanopoulos, Maria

    2013-03-27

    We report a new method for stabilizing appreciable loadings (~1 wt %) of isolated gold atoms on titania and show that these catalyze the low-temperature water-gas shift reaction. The method combines a typical gold deposition/precipitation method with UV irradiation of the titania support suspended in ethanol. Dissociation of H2O on the thus-created Au–O–TiOx sites is facile. At higher gold loadings, nanoparticles are formed, but they were shown to add no further activity to the atomically bound gold on titania. Removal of this “excess” gold by sodium cyanide leaching leaves the activity intact and the atomically dispersed gold still bound on titania. The new materials may catalyze a number of other reactions that require oxidized active metal sites.

  9. Pulse studies to decipher the role of surface morphology in CuO/CeO₂ nanocatalysts for the water gas shift reaction

    SciTech Connect

    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.

    2015-01-23

    The water-gas shift reaction (WGS, CO + H₂O → CO₂) was studied over CuO/CeO₂ 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/CeO₂ (ns) exhibited a substantially better activity than CuO/CeO₂ (nc). The higher activity was associated with the unique properties of CuO/CeO₂ (ns), such as the easier reduction of highly dispersed CuO to metallic Cu, the stability of metallic Cu and a larger concentration Ce³⁺ in CeO₂ (ns).

  10. 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.

  11. On the Importance of the Associative Carboxyl Mechanism for the Water-Gas Shift Reaction at Pt/CeO2 Interface Sites

    SciTech Connect

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

    2014-03-06

    Periodic density functional theory calculations and microkinetic modeling are used to investigate the associative carboxyl pathways of the water-gas shift (WGS) reaction at the Pt/CeO2 (111) interface. Analysis of a microkinetic model based on parameters obtained from first principles suggests that the turnover frequencies for the CO-assisted associative carboxyl mechanism are comparable to experimental results. However, this microkinetic model containing various associative carboxyl pathways at interface sites cannot explain the experimentally observed activation barriers and reaction orders of Pt/CeO2 catalysts. Considering furthermore that a model of an associative carboxyl mechanism with redox regeneration, also derived from first principles and recently published by us, accurately predicts all kinetic parameters while displaying a 2 orders of magnitude higher turnover frequency, we conclude that at Pt/CeO2 interface sites, the WGS reaction follows a bifunctional Mars-van Krevelen mechanism in which support oxygen vacancies facilitate water dissociation.

  12. 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

  13. Gold(III)-CO and gold(III)-CO2 complexes and their role in the water-gas shift reaction.

    PubMed

    Roşca, Dragoş-Adrian; Fernandez-Cestau, Julio; Morris, James; Wright, Joseph A; Bochmann, Manfred

    2015-10-01

    The water-gas shift (WGS) reaction is an important process for the generation of hydrogen. Heterogeneous gold catalysts exhibit good WGS activity, but the nature of the active site, the oxidation state, and competing reaction mechanisms are very much matters of debate. Homogeneous gold WGS systems that could shed light on the mechanism are conspicuous by their absence: gold(I)-CO is inactive and gold(III)-CO complexes were unknown. We report the synthesis of the first example of an isolable CO complex of Au(III). Its reactivity demonstrates fundamental differences between the CO adducts of the neighboring d (8) ions Pt(II) and Au(III): whereas Pt(II)-CO is stable to moisture, Au(III)-CO compounds are extremely susceptible to nucleophilic attack and show WGS reactivity at low temperature. The key to understanding these dramatic differences is the donation/back-donation ratio of the M-CO bond: gold-CO shows substantially less back-bonding than Pt-CO, irrespective of closely similar ν(CO) frequencies. Key WGS intermediates include the gold-CO2 complex [(C^N^C)Au]2(μ-CO2), which reductively eliminates CO2. The species identified here are in accord with Au(III) as active species and a carboxylate WGS mechanism. PMID:26601313

  14. Genesis and Evolution of Surface Species during Pt Atomic Layer Deposition on Oxide Supports Characterized by in Situ XAFS Analysis and Water-Gas Shift Reaction

    SciTech Connect

    Setthapun, Worajit; Williams, W. Damion; Kim, Seung Min; Feng, Hao; Elam, Jeffrey W.; Rabuffetti, Federico A.; Poeppelmeier, Kenneth R.; Stair, Peter C.; Stach, Eric A.; Ribeiro, Fabio H.; Miller, Jeffrey T.; Marshall, Christopher L.

    2010-06-03

    Platinum atomic layer deposition (ALD) using MeCpPtMe₃ was employed to prepare high loadings of uniform-sized, 1-2 nm Pt nanoparticles on high surface area Al₂O₃, TiO₂, and SrTiO₃ supports. X-ray absorption fine structure was utilized to monitor the changes in the Pt species during each step of the synthesis. The temperature, precursor exposure time, treatment gas, and number of ALD cycles were found to affect the Pt particle size and density. Lower-temperature MeCpPtMe₃ adsorption yielded smaller particles due to reduced thermal decomposition. A 300 °C air treatment of the adsorbed MeCpPtMe₃ leads to PtO. In subsequent ALD cycles, the MeCpPtMe₃ reduces the PtO to metallic Pt in the ratio of one precursor molecule per PtO. A 200 °C H₂ treatment of the adsorbed MeCpPtMe₃ leads to the formation of 1-2 nm, metallic Pt nanoparticles. During subsequent ALD cycles, MeCpPtMe₃ adsorbs on the support, which, upon reduction, yields additional Pt nanoparticles with a minimal increase in size of the previously formed nanoparticles. The catalysts produced by ALD had identical water-gas shift reaction rates and reaction kinetics to those of Pt catalysts prepared by standard solution methods. ALD synthesis of catalytic nanoparticles is an attractive method for preparing novel model and practical catalysts.

  15. Gold(III)-CO and gold(III)-CO2 complexes and their role in the water-gas shift reaction

    PubMed Central

    Roşca, Dragoş-Adrian; Fernandez-Cestau, Julio; Morris, James; Wright, Joseph A.; Bochmann, Manfred

    2015-01-01

    The water-gas shift (WGS) reaction is an important process for the generation of hydrogen. Heterogeneous gold catalysts exhibit good WGS activity, but the nature of the active site, the oxidation state, and competing reaction mechanisms are very much matters of debate. Homogeneous gold WGS systems that could shed light on the mechanism are conspicuous by their absence: gold(I)–CO is inactive and gold(III)–CO complexes were unknown. We report the synthesis of the first example of an isolable CO complex of Au(III). Its reactivity demonstrates fundamental differences between the CO adducts of the neighboring d8 ions Pt(II) and Au(III): whereas Pt(II)-CO is stable to moisture, Au(III)–CO compounds are extremely susceptible to nucleophilic attack and show WGS reactivity at low temperature. The key to understanding these dramatic differences is the donation/back-donation ratio of the M–CO bond: gold-CO shows substantially less back-bonding than Pt-CO, irrespective of closely similar ν(CO) frequencies. Key WGS intermediates include the gold-CO2 complex [(C^N^C)Au]2(μ-CO2), which reductively eliminates CO2. The species identified here are in accord with Au(III) as active species and a carboxylate WGS mechanism. PMID:26601313

  16. 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

  17. Theoretical studies on the catalysis of the reverse water-gas shift reaction using first-row transition metal beta-diketiminato complexes.

    PubMed

    Liu, Cong; Munjanja, Lloyd; Cundari, Thomas R; Wilson, Angela K

    2010-06-01

    The reverse water-gas shift reaction CO(2) + H(2) --> H(2)O + CO has been investigated using a set of homogeneous catalyst models L'M(I) (L' = beta-diketiminate, C(3)N(2)H(5)(-); M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn). The thermodynamics of prototypical reaction pathways were simulated at two levels of theory: B3LYP/6-311+G(d) and B3LYP/aug-cc-pVTZ. The modeled catalytic reaction has been considered in the following steps: coordination of CO(2) by the catalyst to generate a carbon dioxide complex, L'M(CO(2)); scission of L'M(CO(2)) to yield L'M(CO) and L'M(O); L'M(O) hydrogenation to form L'M(H(2)O). The final products, H(2)O and CO, were obtained from the dissociation of L'M(H(2)O) and L'M(CO). All of the reactants, intermediates, and products were modeled, where different possible conformers and multiplicities were identified and considered as potential minima. The reaction enthalpy DeltaH, of all steps for each catalyst as a function of transition metal have been determined. The Mn and Fe catalysts show more thermodynamically accessible pathways than the other catalyst models studied. The overall reaction enthalpy has been determined not only by B3LYP/6-311+G(d) and B3LYP/aug-cc-pVTZ but also via a more rigorous ab initio electron-correlation-based approach, the correlation consistent Composite Approach (ccCA). PMID:20462216

  18. 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.

  19. 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.

  20. Highly Active and Stable Pt-Loaded Ce0.75Zr0.25O2 Yolk-Shell Catalyst for Water-Gas Shift Reaction.

    PubMed

    Shim, Jae-Oh; Hong, Young Jun; Na, Hyun-Suk; Jang, Won-Jun; Kang, Yun Chan; Roh, Hyun-Seog

    2016-07-13

    Multishelled, Pt-loaded Ce0.75Zr0.25O2 yolk-shell microspheres were prepared by a simple spray pyrolysis process for use in the water-gas shift (WGS) reaction. The Pt-loading was optimized, obtaining highly active Pt/Ce0.75Zr0.25O2 yolk-shell nanostructures for the WGS. Of the prepared catalysts, a 2% Pt loading of the Ce0.75Zr0.25O2 yolk-shell microspheres showed the highest CO conversion. The high catalytic activity of the 2% Pt/Ce0.75Zr0.2O2 catalyst was mainly due to its easier reducibility and the maintenance of active catalytic Pt species. The Pt-loaded Ce0.75Zr0.25O2 catalyst microspheres were highly resistant to Pt sintering because of their unique yolk-shell structure. Spray pyrolysis was found to be highly efficient for the production of precious-metal-loaded, multicomponent metal oxide yolk-shell microspheres for catalytic applications. PMID:27315135

  1. Water-gas shift reaction over gold nanoparticles dispersed on nanostructured CeOx-TiO2(110) surfaces: Effects of high ceria coverage

    NASA Astrophysics Data System (ADS)

    Grinter, D. C.; Park, J. B.; Agnoli, S.; Evans, J.; Hrbek, J.; Stacchiola, D. J.; Senanayake, S. D.; Rodriguez, J. A.

    2016-08-01

    Scanning tunnelling microscopy has been used to study the morphology of an overlayer of ceria in contact with a TiO2(110) substrate. Two types of domains were observed after ceria deposition. An ordered ceria film covered half of the surface and high-resolution imaging suggested a near-c(6 × 2) relationship to the underlying TiO2(110)-(1 × 1). The other half of the surface comprised CeOx nanoparticles and reconstructed TiOx supported on TiO2(110)-(1 × 1). Exposure to a small amount of gold resulted in the formation of isolated gold atoms and small clusters on the ordered ceria film and TiO2(110)-(1 × 1) areas, which exhibited significant sintering at 500 K and showed strong interaction between the sintered gold clusters and the domain boundaries of the ceria film. The Au/CeOx/TiO2(110) model system proved to be a good catalyst for the water-gas shift (WGS) exhibiting much higher turnover frequencies (TOFs) than Cu(111) and Pt(111) benchmarks, or the individual Au/TiO2(110) and Au/CeO2(111) systems. For Au/CeOx/TiO2(110) catalysts, there was a decrease in catalytic activity with increasing ceria coverage that correlates with a reduction in the concentration of Ce3 + formed during WGS reaction conditions.

  2. Morphological effects of the nanostructured ceria support on the activity and stability of CuO/CeO2 catalysts for the water-gas shift reaction.

    PubMed

    Yao, S Y; Xu, W Q; Johnston-Peck, A C; Zhao, F Z; Liu, Z Y; Luo, S; Senanayake, S D; Martínez-Arias, A; Liu, W J; Rodriguez, J A

    2014-08-28

    Three CuO/CeO2 catalyst with different morphologies of ceria, namely nanospheres, nanorods and nanocubes, were synthesized and used to catalyze the water-gas shift (WGS) reaction. The reactivity tests showed that the Cu supported on the ceria nanospheres exhibited both the highest activity and superior stability when compared with the nanocube and nanorod ceria catalysts. Operando X-ray diffraction (XRD), X-ray absorption fine structure (XAFS) and diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) methods were used to characterize these catalysts in their working state. High resolution electron microscopy (HRTEM, STEM) was used to look at the local atomic structure and nano-scale morphology. Our results show that the morphology of the ceria support, which can involve different crystal faces and concentrations of defects and imperfections, has a critical impact on the catalytic properties and influences: (1) the dispersion of CuO in the as-synthesized catalyst; (2) the particle size of metallic Cu upon reduction during the WGS reaction, (3) the stability of the metallic Cu upon variations of temperature, and (4) the dissociation of water on the ceria support. The nanosphere ceria catalyst showed an excellent water dissociation capability, the best dispersion of Cu and a strong Cu-Ce interaction, therefore delivering the best performance among the three WGS catalysts. The metallic Cu, which is the active species during the WGS reaction, was more stabilized on the nanospheres than on the nanorods and nanocubes and thus led to a better stability of the nanosphere catalyst than the other two architectures. Each catalyst exhibited a distinctive line-shape in the 800-1600 cm(-1) region of the DRIFTS spectra, pointing to the existence of different types of carbonate or carboxylate species as surface intermediates for the WGS. PMID:25012908

  3. 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.

  4. Genesis and evolution of surface species during Pt atomic layer deposition on oxide supports characterized by in-situ XAFS analysis and water-gas shift reaction.

    SciTech Connect

    Setthapun, W.; Williams, W.; Kim, S.; Feng, H.; Elam, J.; Rabuffetti, F.; Poeppelmeier, K.; Stair, P.; Stach, E.; Ribeiro, F.; Miller, J.; Marshall, C.; Northwestern Univ.; Purdue Univ.

    2010-06-03

    Platinum atomic layer deposition (ALD) using MeCpPtMe{sub 3} was employed to prepare high loadings of uniform-sized, 1-2 nm Pt nanoparticles on high surface area Al{sub 2}O{sub 3}, TiO{sub 2}, and SrTiO{sub 3} supports. X-ray absorption fine structure was utilized to monitor the changes in the Pt species during each step of the synthesis. The temperature, precursor exposure time, treatment gas, and number of ALD cycles were found to affect the Pt particle size and density. Lower-temperature MeCpPtMe{sub 3} adsorption yielded smaller particles due to reduced thermal decomposition. A 300 C air treatment of the adsorbed MeCpPtMe{sub 3} leads to PtO. In subsequent ALD cycles, the MeCpPtMe{sub 3} reduces the PtO to metallic Pt in the ratio of one precursor molecule per PtO. A 200 C H{sub 2} treatment of the adsorbed MeCpPtMe{sub 3} leads to the formation of 1-2 nm, metallic Pt nanoparticles. During subsequent ALD cycles, MeCpPtMe{sub 3} adsorbs on the support, which, upon reduction, yields additional Pt nanoparticles with a minimal increase in size of the previously formed nanoparticles. The catalysts produced by ALD had identical water-gas shift reaction rates and reaction kinetics to those of Pt catalysts prepared by standard solution methods. ALD synthesis of catalytic nanoparticles is an attractive method for preparing novel model and practical catalysts.

  5. 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.; Martınez-Arias, A.; Hanson, J.C.; Fernandez-Garcıa, 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.

  6. 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.

  7. 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.

  8. Process Intensification with Integrated Water-Gas-Shift Membrane Reactor

    SciTech Connect

    2009-11-01

    This factsheet describes a research project whose objective is to develop hydrogen-selective membranes for an innovative gas-separation process based on a water-gas-shift membrane reactor (WGS-MR) for the production of hydrogen.

  9. 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.

  10. 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.

  11. 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

  12. Unique properties of ceria nanoparticles supported on metals: novel inverse ceria/copper catalysts for CO oxidation and the water-gas shift reaction.

    PubMed

    Senanayake, Sanjaya D; Stacchiola, Dario; Rodriguez, Jose A

    2013-08-20

    a standard catalyst for reactions such as CO oxidation and the water-gas shift (WGS). This metal serves as an ideal replacement for other noble metals that are neither abundant nor cost effective. To prepare the inverse system we deposited nanoparticles (2-20 nm) of cerium oxide onto the Cu(111) surface. During this process, the Cu(111) surface grows an oxide layer that is characteristic of Cu₂O (Cu¹⁺). This oxide can influence the growth of ceria nanoparticles. Evidence suggests triangular-shaped CeO₂(111) grows on Cu₂O(111) surfaces while rectangular CeO₂(100) grows on Cu₄O₃(111) surfaces. We used the CeOx/Cu₂O/Cu(111) inverse system to study two catalytic processes: the WGS (CO + H₂O → CO₂ + H₂) and CO oxidation (2CO + O₂ → 2CO₂). We discovered that the addition of small amounts of ceria nanoparticles can activate the Cu(111) surface and achieve remarkable enhancement of catalytic activity in the investigated reactions. In the case of the WGS, the CeOx nanoparticle facilitated this process by acting at the interface with Cu to dissociate water. In the CO oxidation case, an enhancement in the dissociation of O₂ by the nanoparticles was a key factor. The strong interaction between CeOx nanoparticles and Cu(111) when preoxidized and reduced in CO resulted in a massive surface reconstruction of the copper substrate with the introduction of microterraces that covered 25-35% of the surface. This constitutes a new mechanism for surface reconstruction not observed before. These microterraces helped to facilitate a further enhancement of activity towards the WGS by opening an additional channel for the dissociation of water. In summary, inverse catalysts of CeOx/Cu(111) and CeO₂/Cu₂O/Cu(111) demonstrate the versatility of a model system to obtain insightful knowledge of catalytic processes. These systems will continue to offer a unique opportunity to probe key catalytic components and elucidate the relationship between structure and

  13. 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.

  14. 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.

  15. Selective hydrogenation of 1,3-cyclooctadiene and diphenylacetylene on copper using the water-gas shift reaction as a hydrogen source

    SciTech Connect

    Fragale, C.; Gargano, M.; Rossi, M.

    1983-04-01

    Selective catalytic hydrogenation of polyenes and acetylenes to monoolefins of a particular configuration is a matter of great interest in synthetic chemistry. Studies in this field have been principally devoted to the efficiency of catalytic systems and to the mechanism of the dihydrogen activation; many examples of stereo and regioselectivities have been discussed using either homogeneous or heterogeneous catalysts for the reduction of various compounds (substrates) with molecular hydrogen. In the course of studies on selective hydrogenation reactions catalyzed by transition metal derivatives, it has been found that water and carbon monoxide can be employed as reagents in place of the more expensive pure dihydrogen for the partial hydrogenation of 1,3-cyclooctadiene (C/sub 8/H/sub 12/) and of diphenylethyne (C/sub 14/H/sub 10/); these reactions are promoted by copper catalysts under relatively mild conditions. Experimental conditions and results are reported.

  16. Development of Novel Water-Gas Shift Membrane Reactor

    SciTech Connect

    Ho, W. S. Winston

    2004-12-29

    This report summarizes the objectives, technical barrier, approach, and accomplishments for the development of a novel water-gas-shift (WGS) membrane reactor for hydrogen enhancement and CO reduction. We have synthesized novel CO{sub 2}-selective membranes with high CO{sub 2} permeabilities and high CO{sub 2}/H{sub 2} and CO{sub 2}/CO selectivities by incorporating amino groups in polymer networks. We have also developed a one-dimensional non-isothermal model for the countercurrent WGS membrane reactor. The modeling results have shown that H{sub 2} enhancement (>99.6% H{sub 2} for the steam reforming of methane and >54% H{sub 2} for the autothermal reforming of gasoline with air on a dry basis) via CO{sub 2} removal and CO reduction to 10 ppm or lower are achievable for synthesis gases. With this model, we have elucidated the effects of system parameters, including CO{sub 2}/H{sub 2} selectivity, CO{sub 2} permeability, sweep/feed flow rate ratio, feed temperature, sweep temperature, feed pressure, catalyst activity, and feed CO concentration, on the membrane reactor performance. Based on the modeling study using the membrane data obtained, we showed the feasibility of achieving H{sub 2} enhancement via CO{sub 2} removal, CO reduction to {le} 10 ppm, and high H{sub 2} recovery. Using the membrane synthesized, we have obtained <10 ppm CO in the H{sub 2} product in WGS membrane reactor experiments. From the experiments, we verified the model developed. In addition, we removed CO{sub 2} from a syngas containing 17% CO{sub 2} to about 30 ppm. The CO{sub 2} removal data agreed well with the model developed. The syngas with about 0.1% CO{sub 2} and 1% CO was processed to convert the carbon oxides to methane via methanation to obtain <5 ppm CO in the H{sub 2} product.

  17. 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.

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

    SciTech Connect

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

    1990-01-01

    A Co/MgO/SiO[sub 2] Fischer-Tropsch catalyst was operated simultaneously with a Cu/ZnO/Al[sub 2]O[sub 3] water-gas-shift catalyst in a slurry reactor for over 400 hours. The process conditions were held constant at a temperature of 240[degrees]C, a pressure of 0.79 MPa, and a 1.1 H[sub 2]/CO feed of 0.065 Nl/min-g.cat. The Fischer-Tropsch activity remained constant at the level predicted by the operation of the Co/MgO/SiO[sub 2] catalyst alone. The water-gas-shift reaction was near equilibrium. The hydrocarbon product distribution of the combined catalyst system was stable and matched that of the CO/MgO/SiO[sub 2] operating alone under similar conditions. The combined catalyst system exhibited a high selectivity to n-alkanes. Neither catalysts's operation appeared to have a detrimental effect on that of the other, showing promise for future option.

  19. 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−δ (LSF) and SrTi0.7Fe0.3O3−δ (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

  20. The Integration of a Structural Water Gas Shift Catalyst with a Vanadium Alloy Hydrogen Transport Device

    SciTech Connect

    Barton, Thomas; Argyle, Morris; Popa, Tiberiu

    2009-06-30

    component of conventional high temperature water gas shift iron oxide based catalysts. The catalysts contained Fe-Al-Cr-Cu-O and were synthesized by co-precipitation. A series of catalysts were prepared with 5 to 50 wt% Al2O3, with 8 wt% Cr2O3, 4 wt% CuO, and the balance Fe2O3. All of the catalysts were compared to a reference WGS catalyst (88 wt% FeOx, 8 wt% Cr2O3, and 4 wt% CuO) with no alumina. Alumina addition to conventional high temperature water gas shift catalysts at concentrations of approximately 15 wt% increased CO conversion rates and increase thermal stability. A series of high temperature water gas shift catalysts containing iron, chromia, and copper oxides were prepared with small amounts of added ceria in the system Fe-Cr-Cu-Ce-O. The catalysts were also tested kinetically under WGS conditions. 2-4 wt% ceria addition (at the expense of the iron oxide content) resulted in increased reaction rates (from 22-32% higher) compared to the reference catalyst. The project goal of a 10,000 liter per day WGS-membrane reactor was achieved by a device operating on coal derived syngas containing significant amounts of carbon monoxide and hydrogen sulfide. The membrane flux was equivalent to 52 scfh/ft2 based on a 600 psi syngas inlet pressure and corresponded to membranes costing $191 per square foot. Over 40 hours of iv exposure time to syngas has been achieved for a double membrane reactor. Two modules of the Chart reactor were tested under coal syngas for over 75 hours with a single module tested for 50 hours. The permeance values for the Chart membranes were similar to the REB reactor though total flux was reduced due to significantly thicker membranes. Overall testing of membrane reactors on coal derived syngas was over 115 hours for all reactors tested. Testing of the REB double membrane device exceeded 40 hours. Performance of the double membrane reactor has been similar to the results for the single reactor with good maintenance of flux even after these long

  1. Operation, Modeling and Analysis of the Reverse Water Gas Shift Process

    NASA Technical Reports Server (NTRS)

    Whitlow, Jonathan E.

    2001-01-01

    The Reverse Water Gas Shift process is a candidate technology for water and oxygen production on Mars under the In-Situ Propellant Production project. This report focuses on the operation and analysis of the Reverse Water Gas Shift (RWGS) process, which has been constructed at Kennedy Space Center. A summary of results from the initial operation of the RWGS, process along with an analysis of these results is included in this report. In addition an evaluation of a material balance model developed from the work performed previously under the summer program is included along with recommendations for further experimental work.

  2. Nucleophilic activation of coordinated carbon monoxide. Part 3. Hydroxide and methoxide reactions with the trinuclear clusters M/sub 3/(CO)/sub 12/ (M = Fe, Ru, or Os): implications with regard to catalysis of the water gas shift reaction

    SciTech Connect

    Gross, D.C.; Ford, P.C.

    1985-02-06

    Reported are quantitative investigations of the reactions of the triangular clusters M/sub 3/(CO)/sub 12/ (M = Fe, Ru, or Os) with methoxide ion in solution. In methanol under a CO atmosphere, both the osmium and ruthenium species form stable 1:1 methoxycarbonyl adducts (M/sub 3/(CO)/sub 12/ + NaOCH/sub 3/ in equilibrium (M/sub 3/(CO)/sub 11/(CO/sub 2/CH/sub 3/))Na); however, for the triiron analogue this adduct undergoes fragmentation to give Fe(CO)/sub 4/(CO/sub 2/CH/sub 3/)/sup -/. Initial adduct formation in each case occurs with an equilibrium constant of about 10/sup 3/ M/sup -1/. In mixed tetrahydrofuran/methanol solutions, K/sub eq/ for Ru/sub 3/(CO)/sub 11/(CO/sub 2/CH/sub 3/)/sup -/ is much larger, an indication of the greater activity of NaOCH/sub 3/ in the less protic solvent. Notably, in such solvent mixtures, the presence of excess methoxide also led to the formation of 2:1 adducts. Rates of adduct formation were examined by using stopped-flow kinetics techniques, and it was shown that in methanol the second-order rate constants (25/sup 0/C) are 11.3 x 10/sup 3/, 2.1 x 10/sup 3/, and 0.6 x 10/sup 3/ M/sup -1/ s/sup -1/ for Fe/sub 3/(CO)/sub 12/, Ru/sub 3/(CO)/sub 12/, and Os/sub 3/(CO)/sub 12/, respectively. Rates were much higher in the mixed THF(tetrahydro-furan)/CH/sub 3/OH solutions; for example, k/sub 1/ (25/sup 0/C) for Ru/sub 3/(CO)/sub 12/ is 2.0 x 10/sup 5/ M/sup -1/ s/sup -1/ in 90/10 THF/CH/sub 3/OH (v/v). Monosubstitution of the ruthenium cluster with (CH/sub 3/O)/sub 3/P markedly reduced the reactivity toward the anionic nucleophile. The reaction of the triruthenium species with hydroxide (Ru/sub 3/(CO)/sub 12/ + OH/sup -/ in equilibrium Ru/sub 3/(CO)/sub 11/(CO/sub 2/H)/sup -/ ..-->.. HRu/sub 3/(CO)/sub 11//sup -/ + CO/sub 2/) was also investigated. Analysis of the reaction kinetics leads to the conclusion that formation of the initial hydroxycarbonyl adduct is somewhat less favorable and is slower than the analogous reaction of

  3. Simulation and control of water-gas shift packed bed reactor with inter-stage cooling

    NASA Astrophysics Data System (ADS)

    Saw, S. Z.; Nandong, J.

    2016-03-01

    Water-Gas Shift Reaction (WGSR) has become one of the well-known pathways for H2 production in industries. The issue with WGSR is that it is kinetically favored at high temperatures but thermodynamically favored at low temperatures, thus requiring careful consideration in the control design in order to ensure that the temperature used does not deactivate the catalyst. This paper studies the effect of a reactor arrangement with an inter-stage cooling implemented in the packed bed reactor to look at its effect on outlet temperature. A mathematical model is developed based on one-dimensional heat and mass transfers which incorporate the intra-particle effects. It is shown that the placement of the inter-stage cooling and the outlet temperature exiting the inter-stage cooling have strong influence on the reaction conversion. Several control strategies are explored for the process. It is shown that a feedback- feedforward control strategy using Multi-scale Control (MSC) is effective to regulate the reactor temperature profile which is critical to maintaining the catalysts activity.

  4. 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.

  5. 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.

  6. Microkinetics of water-gas shift over sulfided Mo/Al{sub 2}O{sub 3} catalysts

    SciTech Connect

    Lund, C.R.F.

    1996-08-01

    A microkinetic model was developed to explain the catalysis of the water-gas shift reaction by sulfided, alumina-supported molybdenum. IN this model, the reaction takes place through a regenerative (reduction-oxidation) scheme wherein the catalyst surface is alternately oxidized by water and then reduced by carbon monoxide. The surface of the catalyst is equilibrated with gas-phase H{sub 2}S under all reaction conditions studied. Coverages predicted by the model are consistent with the adsorption behavior of molybdenum sulfide catalysts. Simulations indicate that the effects of steam and H{sub 2}S levels are closely related. A maximum in CO conversion with increasing steam level may only occur at certain H{sub 2}S levels, and the ordering of CO conversion with increasing H{sub 2}S levels may invert as the steam level is changed.

  7. Catalytic and surface properties of nanocrystalline gold water gas shift catalysts

    NASA Astrophysics Data System (ADS)

    Kim, Chang Hwan

    A series of CeO2 supported gold catalysts were prepared and found to possess a high activities for the water gas shift reaction (WGS), a critical step in the production of H2 for use in petroleum refining, chemicals synthesis, and proton exchange membrane fuel cells. The deposition-precipitation method was employed in synthesizing these highly active, nanocrystalline gold catalysts. X-ray photoelectron spectroscopy (XPS), infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), and dynamic sorption analyses were performed to characterize the gold catalysts. While some of these catalysts were initially four times more active than a commercial Cu-based catalyst, they were susceptible to deactivation. Characterization using techniques including temperature programmed oxidation, XPS, and FT-IR indicated that the deactivation was caused primarily by blockage of the active sites by carbonates and/or formates. Formation of these carbonaceous species appeared to be facilitated by oxygen deficient sites on the ceria surface and may have been associated with hydroxyl groups formed on the nanocrystalline gold particles under the H2 rich conditions. The deactivation could be managed by conditioning the CeO2 surface or adding constituents to minimize oxygen deficiency. The catalytic activity was fully recovered by calcining the deactivated materials in flowing air at elevated temperatures. The gold catalyst was washcoated onto microporous Fe-Al alloy foams for use in a micro-channel WGS reactor. The performance of these coated foams was inferior to that of the powder catalyst; however, a two stage micro-channel WGS reactor employing the gold catalyst was sufficient for a 100 W fuel processor system.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. An Investigation of the Reverse Water Gas Shift Process and Operating Alternatives

    NASA Technical Reports Server (NTRS)

    Whitlow, Jonathan E.

    2002-01-01

    The Reverse Water Gas Shift (RWGS) process can produce water and ultimately oxygen through electrolysis. This technology is being investigated for possible use in the exploration of Mars as well as a potential process to aid in the regeneration of oxygen from carbon dioxide. The initial part of this report summarizes the results obtained from operation of the RWGS process at Kennedy Space Center during May and June of this year. It has been demonstrated that close to complete conversion can be achieved with the RWGS process under certain operating conditions. The report also presents results obtained through simulation for an alternative staged configuration for RWGS which eliminates the recycle compressor. This configuration looks promising and hence seems worthy of experimental investigation.

  13. 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.

  14. In situ/operando studies for the production of hydrogen through the water-gas shift on metal oxide catalysts.

    PubMed

    Rodriguez, José A; Hanson, Jonathan C; Stacchiola, Dario; Senanayake, Sanjaya D

    2013-08-01

    In this perspective article, we show how a series of in situ techniques {X-ray diffraction (XRD), pair-distribution-function analysis (PDF), X-ray absorption fine structure (XAFS), environmental transmission electron microscopy (ETEM), infrared spectroscopy (IR), ambient-pressure X-ray photoelectron spectroscopy (AP-XPS)} can be combined to perform detailed studies of the structural, electronic and chemical properties of metal oxide catalysts used for the production of hydrogen through the water-gas shift reaction (WGS, CO + H2O → H2 + CO2). Under reaction conditions most WGS catalysts undergo chemical transformations that drastically modify their composition with respect to that obtained during the synthesis process. Experiments of time-resolved in situ XRD, XAFS, and PDF indicate that the active phase of catalysts which combine Cu, Au or Pt with oxides such as ZnO, CeO2, TiO2, CeOx/TiO2 and Fe2O3 essentially involves nanoparticles of the reduced noble metals. The oxide support undergoes partial reduction and is not a simple spectator, facilitating the dissociation of water and in some cases modifying the chemical properties of the supported metal. Therefore, to optimize the performance of these catalysts one must take into consideration the properties of the metal and oxide phases. IR and AP-XPS have been used to study the reaction mechanism for the WGS on metal oxide catalysts. Data of IR spectroscopy indicate that formate species are not necessarily involved in the main reaction path for the water-gas shift on Cu-, Au- and Pt-based catalysts. Thus, a pure redox mechanism or associative mechanisms that involve either carbonate-like (CO3, HCO3) or carboxyl (HOCO) species should be considered. In the last two decades, there have been tremendous advances in our ability to study catalytic materials under reaction conditions and we are moving towards the major goal of fully understanding how the active sites for the production of hydrogen through the WGS actually

  15. Lyapunov-Based Sensor Failure Detection And Recovery For The Reverse Water Gas Shift Process

    NASA Technical Reports Server (NTRS)

    Haralambous, Michael G.

    2001-01-01

    Livingstone, a model-based AI software system, is planned for use in the autonomous fault diagnosis, reconfiguration, and control of the oxygen-producing reverse water gas shift (RWGS) process test-bed located in the Applied Chemistry Laboratory at KSC. In this report the RWGS process is first briefly described and an overview of Livingstone is given. Next, a Lyapunov-based approach for detecting and recovering from sensor failures, differing significantly from that used by Livingstone, is presented. In this new method, models used are in terms of the defining differential equations of system components, thus differing from the qualitative, static models used by Livingstone. An easily computed scalar inequality constraint, expressed in terms of sensed system variables, is used to determine the existence of sensor failures. In the event of sensor failure, an observer/estimator is used for determining which sensors have failed. The theory underlying the new approach is developed. Finally, a recommendation is made to use the Lyapunov-based approach to complement the capability of Livingstone and to use this combination in the RWGS process.

  16. LYAPUNOV-Based Sensor Failure Detection and Recovery for the Reverse Water Gas Shift Process

    NASA Technical Reports Server (NTRS)

    Haralambous, Michael G.

    2002-01-01

    Livingstone, a model-based AI software system, is planned for use in the autonomous fault diagnosis, reconfiguration, and control of the oxygen-producing reverse water gas shift (RWGS) process test-bed located in the Applied Chemistry Laboratory at KSC. In this report the RWGS process is first briefly described and an overview of Livingstone is given. Next, a Lyapunov-based approach for detecting and recovering from sensor failures, differing significantly from that used by Livingstone, is presented. In this new method, models used are in t e m of the defining differential equations of system components, thus differing from the qualitative, static models used by Livingstone. An easily computed scalar inequality constraint, expressed in terms of sensed system variables, is used to determine the existence of sensor failures. In the event of sensor failure, an observer/estimator is used for determining which sensors have failed. The theory underlying the new approach is developed. Finally, a recommendation is made to use the Lyapunov-based approach to complement the capability of Livingstone and to use this combination in the RWGS process.

  17. Modeling and Analysis of the Reverse Water Gas Shift Process for In-Situ Propellant Production

    NASA Technical Reports Server (NTRS)

    Whitlow, Jonathan E.

    2000-01-01

    This report focuses on the development of mathematical models and simulation tools developed for the Reverse Water Gas Shift (RWGS) process. This process is a candidate technology for oxygen production on Mars under the In-Situ Propellant Production (ISPP) project. An analysis of the RWGS process was performed using a material balance for the system. The material balance is very complex due to the downstream separations and subsequent recycle inherent with the process. A numerical simulation was developed for the RWGS process to provide a tool for analysis and optimization of experimental hardware, which will be constructed later this year at Kennedy Space Center (KSC). Attempts to solve the material balance for the system, which can be defined by 27 nonlinear equations, initially failed. A convergence scheme was developed which led to successful solution of the material balance, however the simplified equations used for the gas separation membrane were found insufficient. Additional more rigorous models were successfully developed and solved for the membrane separation. Sample results from these models are included in this report, with recommendations for experimental work needed for model validation.

  18. 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.

  19. Atomic level study of water-gas shift catalysts via transmission electron microscopy and x-ray spectroscopy

    NASA Astrophysics Data System (ADS)

    Akatay, Mehmed Cem

    Water-gas shift (WGS), CO + H2O ⇆ CO2 + H2 (DeltaH° = -41 kJ mol -1), is an industrially important reaction for the production of high purity hydrogen. Commercial Cu/ZnO/Al2O3 catalysts are employed to accelerate this reaction, yet these catalysts suffer from certain drawbacks, including costly regeneration processes and sulfur poisoning. Extensive research is focused on developing new catalysts to replace the current technology. Supported noble metals stand out as promising candidates, yet comprise intricate nanostructures complicating the understanding of their working mechanism. In this study, the structure of the supported Pt catalysts is explored by transmission electron microscopy and X-ray spectroscopy. The effect of the supporting phase and the use of secondary metals on the reaction kinetics is investigated. Structural heterogeneities are quantified and correlated with the kinetic descriptors of the catalysts to develop a fundamental understanding of the catalytic mechanism. The effect of the reaction environment on catalyst structure is examined by in-situ techniques. This study benefitted greatly from the use of model catalysts that provide a convenient medium for the atomic level characterization of nanostructures. Based on these studies, Pt supported on iron oxide nano islands deposited on inert spherical alumina exhibited 48 times higher WGS turnover rate (normalized by the total Pt surface area) than Pt supported on bulk iron oxide. The rate of aqueous phase glycerol reforming reaction of Pt supported on multiwall carbon nanotubes (MWCNT) is promoted by co-impregnating with cobalt. The synthesis resulted in a variety of nanostructures among which Pt-Co bimetallic nanoparticles are found to be responsible for the observed promotion. The unprecedented WGS rate of Pt supported on Mo2C is explored by forming Mo 2C patches on top of MWCNTs and the rate promotion is found to be caused by the Pt-Mo bimetallic entities.

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

    NASA Astrophysics Data System (ADS)

    Kispersky, Vincent Frederick

    Hy variants modeled on Cu. The redox nature of the Cu active site was further investigated in a follow up study isolating the reducing portion of the SCR by removing O 2 from the reaction feed. Cutting off O2 drove the catalyst into a highly reduced state dominated by Cu(I) while removing a reductant drove the Cu into the fully oxidized state. Our research shows that not only is redox a vital part of the SCR reaction on Cu/zeolites, but that the oxidation state of the active site is highly sensitive to the gas environment. The water-gas shift (WGS) reaction is an industrially important step in H2 generation from steam reforming. I have had the opportunity to contribute to a number of studies in WGS by studying the catalysts in FTIR. We studied numerous catalytic formulations including Fe promoted Pd/Al 2O3 and Au/TiO2. We found that the Fe promoted the WGS rate of the catalyst by a factor of 160 compared to the Fe free Pd/Al 2O3. The reduced Fe promoter efficiently split H2O, typically the role performed by reducible supports, and the nearby noble metal particles provided spillover H2 to maintain the reduced Fe phase necessary to split H2O. Our study of Au/TiO2 involved the development of a modified operando transmission IR cell with ultra-low dead volume allowing for fast switching isotope experiments over the catalyst. The isotope switching experiments showed that only CO adsorbed on Au0 sites was an active surface intermediate at 120°C. Counting the amount of active surface Au atoms for the reaction ruled out the Au particle surface and perimeter atoms as the dominant active sites and confirmed our previous finding that the active site was composed mostly of low coordinated corner Au atoms.

  1. Pilot Scale Water Gas Shift - Membrane Device for Hydrogen from Coal

    SciTech Connect

    Barton, Tom

    2013-06-30

    The objectives of the project were to build pilot scale hydrogen separation systems for use in a gasification product stream. This device would demonstrate fabrication and manufacturing techniques for producing commercially ready facilities. The design was a 2 lb/day hydrogen device which included composite hydrogen separation membranes, a water gas shift monolith catalyst, and stainless steel structural components. Synkera Technologies was to prepare hydrogen separation membranes with metallic rims, and to adjust the alloy composition in their membranes to a palladium-gold composition which is sulfur resistant. Chart was to confirm their brazing technology for bonding the metallic rims of the composite membranes to their structural components and design and build the 2 lbs/day device incorporating membranes and catalysts. WRI prepared the catalysts and completed the testing of the membranes and devices on coal derived syngas. The reactor incorporated eighteen 2'' by 7'' composite palladium alloy membranes. These membranes were assembled with three stacks of three paired membranes. Initial vacuum testing and visual inspection indicated that some membranes were cracked, either in transportation or in testing. During replacement of the failed membranes, while pulling a vacuum on the back side of the membranes, folds were formed in the flexible composite membranes. In some instances these folds led to cracks, primarily at the interface between the alumina and the aluminum rim. The design of the 2 lb/day device was compromised by the lack of any membrane isolation. A leak in any membrane failed the entire device. A large number of tests were undertaken to bring the full 2 lb per day hydrogen capacity on line, but no single test lasted more than 48 hours. Subsequent tests to replace the mechanical seals with brazing have been promising, but the technology remains promising but not proven.

  2. 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

  3. 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.

  4. Slurry phase Fischer-Tropsch synthesis: Cobalt plus a water-gas shift catalyst. [Quarterly] report, July 1, 1990--September 30, 1990

    SciTech Connect

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

    1990-12-31

    A Co/MgO/SiO{sub 2} Fischer-Tropsch catalyst was operated simultaneously with a Cu/ZnO/Al{sub 2}O{sub 3} water-gas-shift catalyst in a slurry reactor for over 400 hours. The process conditions were held constant at a temperature of 240{degrees}C, a pressure of 0.79 MPa, and a 1.1 H{sub 2}/CO feed of 0.065 Nl/min-g.cat. The Fischer-Tropsch activity remained constant at the level predicted by the operation of the Co/MgO/SiO{sub 2} catalyst alone. The water-gas-shift reaction was near equilibrium. The hydrocarbon product distribution of the combined catalyst system was stable and matched that of the CO/MgO/SiO{sub 2} operating alone under similar conditions. The combined catalyst system exhibited a high selectivity to n-alkanes. Neither catalysts`s operation appeared to have a detrimental effect on that of the other, showing promise for future option.

  5. 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.

  6. 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.

  7. 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.

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

    SciTech Connect

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

    1990-01-01

    Experiments to study the cobalt-catalyzed and iron-catalyzed reactions of light 1-alkenes added to synthesis gas have been performed and analyzed. On cobalt, data have been obtained at 220{degrees}C, 0.45 to 1.48 MPA and a synthesis gas flow rate between 0.015 and 0.030 Nl/gcat/min with H{sub 2}/CO feeds of 1.45 to 2.25. On fused iron, data were collected at 248{degrees}C, 0.79 to 1.48 MPa and a synthesis gas flow rate between 0.005 and 0.030 Nl/gcat/min of H{sub 2}/CO feeds of 0.5 to 1.5 C{sub 2}H{sub 4}, C{sub 3}H{sub 6}, and 1-C{sub 4}H{sub 8} were added to the synthesis gas feed in concentrations ranging from 0.5 to 1.2 mol. % of total feed. 1-Alkenes incorporate into growing chains on the catalyst surface of both catalysts, probably by initiating and/or terminating the chain growth process. Only ethene is believed to propagate chain growth significantly. The propensity of the 1-alkenes to incorporate decreases with increasing carbon number of the 1-alkene. The double-{alpha} behavior which is exhibited by most Fischer-Tropsch catalysts can be explained as the sum of two growth processes, one stepwise single-carbon growth and the other 1-alkene incorporation. Both alkene addition study data and the effects of process variables on the selectivity of Fischer-Tropsch catalysts can be explained within the framework of this theory. 19 refs., 12 figs., 2 tabs.

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

    SciTech Connect

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

    1990-01-01

    Experiments on cobalt-catalyzed reactions of light 1-alkenes added to synthesis gas were performed. Data have been collected at 220C, 0.45 to 1.48 MPa and a synthesis gas flow rate between 0.015 and 0.030 Nl/(gcat[center dot]min) with H[sub 2]/CO of 1.45 to 2.25. Ethylene, propene, and butene were added to synthesis gas feed from 0.5 to 1.2 mole% of total feed. For each material balance in which 1-alkenes were added, a material balance was performed at similar process conditions without 1-alkenes added, as base case''. Material balances without added 1-alkenes were also repeated to verify of catalyst selectivity stability. 49 material balances were performed during a single run lasting over 2,500 hours-on-stream. The hydrocarbon data have been completely analyzed; data correlations are still being made. Since C[sub 3]/C[sub 1] ratios by ethene addition, C[sub 4]/C[sub 1] ratios by propene addition, and C[sub 5]/C[sub 1] ratios by 1-butene addition, it appears that 1-alkenes may incorporate into growing chains on the surface of the catalyst. Further evidence for incorporation can be seen by comparing selectivity to n-alcohol one carbon number higher than added 1-alkene. Yield of this n-alcohol increases when alkenes are present. Sensitivity of hydrocarbon distribution to process variables seems to be greater on Co than on Fe catalysts.

  10. Robust Low-Cost Water-Gas Shift Membrane Reactor for High-Purity Hydrogen Production form Coal-Derived Syngas

    SciTech Connect

    James Torkelson; Neng Ye; Zhijiang Li; Decio Coutinho; Mark Fokema

    2008-05-31

    This report details work performed in an effort to develop a low-cost, robust water gas shift membrane reactor to convert coal-derived syngas into high purity hydrogen. A sulfur- and halide-tolerant water gas shift catalyst and a sulfur-tolerant dense metallic hydrogen-permeable membrane were developed. The materials were integrated into a water gas shift membrane reactor in order to demonstrate the production of >99.97% pure hydrogen from a simulated coal-derived syngas stream containing 2000 ppm hydrogen sulfide. The objectives of the program were to (1) develop a contaminant-tolerant water gas shift catalyst that is able to achieve equilibrium carbon monoxide conversion at high space velocity and low steam to carbon monoxide ratio, (2) develop a contaminant-tolerant hydrogen-permeable membrane with a higher permeability than palladium, (3) demonstrate 1 L/h purified hydrogen production from coal-derived syngas in an integrated catalytic membrane reactor, and (4) conduct a cost analysis of the developed technology.

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

    NASA Astrophysics Data System (ADS)

    Kispersky, Vincent Frederick

    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 Ox

  12. Reverse Water-Gas Shift or Sabatier Methanation on Ni(110)? Stable Surface Species at Near-Ambient Pressure.

    PubMed

    Roiaz, Matteo; Monachino, Enrico; Dri, Carlo; Greiner, Mark; Knop-Gericke, Axel; Schlögl, Robert; Comelli, Giovanni; Vesselli, Erik

    2016-03-30

    The interaction of CO, CO2, CO + H2, CO2 + H2, and CO + CO2 + H2 with the nickel (110) single crystal termination has been investigated at 10(-1) mbar in situ as a function of the surface temperature in the 300-525 K range by means of infrared-visible sum frequency generation (IR-vis SFG) vibrational spectroscopy and by near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS). Several stable surface species have been observed and identified. Besides atomic carbon and precursors for graphenic C phases, five nonequivalent CO species have been distinguished, evidencing the role of coadsorption effects with H and C atoms, of H-induced activation of CO, and of surface reconstruction. At low temperature, carbonate species produced by the interaction of CO2 with atomic oxygen, which stems from the dissociation of CO2 into CO + O, are found on the surface. A metastable activated CO2(-) species is also detected, being at the same time a precursor state toward dissociation into CO and O in the reverse water-gas shift mechanism and a reactive species that undergoes direct conversion in the Sabatier methanation process. Finally, the stability of ethylidyne is deduced on the basis of our spectroscopic observations. PMID:26954458

  13. Water-Gas-Shift Membrane Reactor for High-Pressure Hydrogen Production. A comprehensive project report (FY2010 - FY2012)

    SciTech Connect

    Klaehn, John; Peterson, Eric; Orme, Christopher; Bhandari, Dhaval; Miller, Scott; Ku, Anthony; Polishchuk, Kimberly; Narang, Kristi; Singh, Surinder; Wei, Wei; Shisler, Roger; Wickersham, Paul; McEvoy, Kevin; Alberts, William; Howson, Paul; Barton, Thomas; Sethi, Vijay

    2013-01-01

    Idaho National Laboratory (INL), GE Global Research (GEGR), and Western Research Institute (WRI) have successfully produced hydrogen-selective membranes for water-gas-shift (WGS) modules that enable high-pressure hydrogen product streams. Several high performance (HP) polymer membranes were investigated for their gas separation performance under simulated (mixed gas) and actual syngas conditions. To enable optimal module performance, membranes with high hydrogen (H2) selectivity, permeance, and stability under WGS conditions are required. The team determined that the VTEC PI 80-051 and VTEC PI 1388 (polyimide from Richard Blaine International, Inc.) are prime candidates for the H2 gas separations at operating temperatures (~200°C). VTEC PI 80-051 was thoroughly analyzed for its H2 separations under syngas processing conditions using more-complex membrane configurations, such as tube modules and hollow fibers. These membrane formats have demonstrated that the selected VTEC membrane is capable of providing highly selective H2/CO2 separation (α = 7-9) and H2/CO separation (α = 40-80) in humidified syngas streams. In addition, the VTEC polymer membranes are resilient within the syngas environment (WRI coal gasification) at 200°C for over 1000 hours. The information within this report conveys current developments of VTEC PI 80-051 as an effective H2 gas separations membrane for high-temperature syngas streams.

  14. Sorption-Enhanced Synthetic Natural Gas (SNG) Production from Syngas. A Novel Process Combining CO Methanation, Water-Gas Shift, and CO2 Capture

    SciTech Connect

    Lebarbier, Vanessa M.C.; Dagle, Robert A.; Kovarik, Libor; Albrecht, Karl O.; Li, Xiaohong S.; Li, Liyu; Taylor, Charles E.; Bao, Xinhe; Wang, Yong

    2013-07-08

    Synthetic natural gas (SNG) production from syngas is under investigation again due to the desire for less dependency from imports and the opportunity for increasing coal utilization and reducing green house gas emission. CO methanation is highly exothermic and substantial heat is liberated which can lead to process thermal imbalance and deactivation of the catalyst. As a result, conversion per pass is limited and substantial syngas recycle is employed in conventional processes. Furthermore, the conversion of syngas to SNG is typically performed at moderate temperatures (275 to 325°C) to ensure high CH4 yields since this reaction is thermodynamically limited. In this study, the effectiveness of a novel integrated process for the SNG production from syngas at high temperature (i.e. 600°C) was investigated. This integrated process consists of combining a CO methanation nickel-based catalyst with a high temperature CO2 capture sorbent in a single reactor. Integration with CO2 separation eliminates the reverse-water-gas shift and the requirement for a separate water-gas shift (WGS) unit. Easing of thermodynamic constraint offers the opportunity of enhancing yield to CH4 at higher operating temperature (500-700ºC) which also favors methanation kinetics and improves the overall process efficiency due to exploitation of reaction heat at higher temperatures. Furthermore, simultaneous CO2 capture eliminates green house gas emission. In this work, sorption-enhanced CO methanation was demonstrated using a mixture of a 68% CaO/32% MgAl2O4 sorbent and a CO methanation catalyst (Ni/Al2O3, Ni/MgAl2O4, or Ni/SiC) utilizing a syngas ratio (H2/CO) of 1, gas-hour-space velocity (GHSV) of 22 000 hr-1, pressure of 1 bar and a temperature of 600°C. These conditions resulted in ~90% yield to methane, which was maintained until the sorbent

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

    SciTech Connect

    Datta, Pradyot

    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.

  16. Highly Effective Pt-Based Water-Gas Shift Catalysts by Surface Modification with Alkali Hydroxide Salts

    SciTech Connect

    Kusche, Matthias; Bustillo, Karen; Agel, Friederike; Wasserscheid, Peter

    2015-01-29

    Here, we describe an economical and convenient method to improve the performance of Pt/alumina catalysts for the water–gas shift reaction through surface modification of the catalysts with alkali hydroxides according to the solid catalyst with ionic liquid layer approach. The results are in agreement with our findings reported earlier for methanol steam reforming. This report indicates that alkali doping of the catalyst plays an important role in the observed catalyst activation. In addition, the basic and hygroscopic nature of the salt coating contributes to a significant improvement in the performance of the catalyst. During the reaction, a partly liquid film of alkali hydroxide forms on the alumina surface, which increases the availability of H2O at the catalytically active sites. Kinetic studies reveal a negligible effect of the KOH coating on the rate dependence of CO and H2O partial pressures. In conclusion, TEM studies indicate an agglomeration of the active Pt clusters during catalyst preparation; restructuring of Pt nanoparticles occurs under reaction conditions, which leads to a highly active and stable system over 240h time on stream. Excessive pore fillings with KOH introduce a mass transfer barrier as indicated in a volcano-shaped curve of activity versus salt loading. The optimum KOH loading was found to be 7.5wt%.

  17. Highly Effective Pt-Based Water-Gas Shift Catalysts by Surface Modification with Alkali Hydroxide Salts

    DOE PAGESBeta

    Kusche, Matthias; Bustillo, Karen; Agel, Friederike; Wasserscheid, Peter

    2015-01-29

    Here, we describe an economical and convenient method to improve the performance of Pt/alumina catalysts for the water–gas shift reaction through surface modification of the catalysts with alkali hydroxides according to the solid catalyst with ionic liquid layer approach. The results are in agreement with our findings reported earlier for methanol steam reforming. This report indicates that alkali doping of the catalyst plays an important role in the observed catalyst activation. In addition, the basic and hygroscopic nature of the salt coating contributes to a significant improvement in the performance of the catalyst. During the reaction, a partly liquid filmmore » of alkali hydroxide forms on the alumina surface, which increases the availability of H2O at the catalytically active sites. Kinetic studies reveal a negligible effect of the KOH coating on the rate dependence of CO and H2O partial pressures. In conclusion, TEM studies indicate an agglomeration of the active Pt clusters during catalyst preparation; restructuring of Pt nanoparticles occurs under reaction conditions, which leads to a highly active and stable system over 240h time on stream. Excessive pore fillings with KOH introduce a mass transfer barrier as indicated in a volcano-shaped curve of activity versus salt loading. The optimum KOH loading was found to be 7.5wt%.« less

  18. 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.

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

    PubMed

    Kadyk, Thomas; Eikerling, Michael

    2015-08-14

    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

  20. Water Gas Shift Reaction with A Single Stage Low Temperature Membrane Reactor

    SciTech Connect

    Ciora, Richard J; Liu, Paul KT

    2013-12-31

    Palladium membrane and Palladium membrane reactor were developed under this project for hydrogen separation and purification for fuel cell applications. A full-scale membrane reactor was designed, constructed and evaluated for the reformate produced from a commercial scale methanol reformer. In addition, the Pd membrane and module developed from this project was successfully evaluated in the field for hydrogen purification for commercial fuel cell applications.

  1. 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.

  2. Ethanol synthesis and water gas shift over bifunctional sulfide catalysts. Technical progress report, September 1993--November 1993

    SciTech Connect

    Klier, K.; Herman, R.; Deemer, M.

    1994-03-01

    During calcination of the precipitated and dried MoS{sub 3} to form MOS{sub 2}, it was found that small sample sizes were needed to provide thermal control of the highly exothermic decomposition reaction in the 8 mm ID quartz tube used for this purpose. Characterization of MoS{sub 2} and Cs/MoS{sub 2} catalysts have been carried out by X-ray powder diffraction (XRD) after each synthesis step. In addition, the XRD analyses were conducted after prolonged air exposure of the Cs-doped MoS{sub 2} catalyst. It was shown that prolonged exposure to the ambient atmosphere led to segregation and crystallization of the cesium formate dopant. Thus, catalytic testing should be carried out with freshly prepared samples that are protected from the ambient atmosphere. Catalytic testing is underway to determine if there is an inverse correlation of catalytic activity and selectivity with prolonged air exposure of the catalyst.

  3. Slurry phase Fischer-Tropsch synthesis: Cobalt plus a water-gas shift catalyst, January 1, 1990--March 30, 1990

    SciTech Connect

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

    1990-01-01

    Experiments to study cobalt-catalyzed reactions of light 1-alkenes added to synthesis gas feed have been performed. Data have been collected at 220{degrees}C, 0.45 to 1.48 MPa and a synthesis gas flow rate between 0.015 and 0.030 Nl/(gcatmin) with H{sub 2}/CO of 1.45 to 2.25. C{sub 2}H{sub 4}, C{sub 3}H{sub 6}, and C{sub 4}H{sub 8} were added to the synthesis gas feed in concentrations ranging from 0.5 to 1.2 mole% of total feed. For each material balance in which 1-alkenes were added, a material balance was performed at similar process conditions without 1-alkenes added. This use of base case'' process conditions should make data analysis and interpretation easier. Material balances without 1-alkenes were also repeated to allow verification of catalyst selectivity stability. A total of 49 balances were performed during a single run which lasted over 2500 hours-on-stream. The hydrocarbon data have not yet been completed analyzed.

  4. Slurry phase Fischer-Tropsch synthesis: Cobalt plus a water-gas shift catalyst, January 1, 1990--March 30, 1990

    SciTech Connect

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

    1990-12-31

    Experiments to study cobalt-catalyzed reactions of light 1-alkenes added to synthesis gas feed have been performed. Data have been collected at 220{degrees}C, 0.45 to 1.48 MPa and a synthesis gas flow rate between 0.015 and 0.030 Nl/(gcatmin) with H{sub 2}/CO of 1.45 to 2.25. C{sub 2}H{sub 4}, C{sub 3}H{sub 6}, and C{sub 4}H{sub 8} were added to the synthesis gas feed in concentrations ranging from 0.5 to 1.2 mole% of total feed. For each material balance in which 1-alkenes were added, a material balance was performed at similar process conditions without 1-alkenes added. This use of ``base case`` process conditions should make data analysis and interpretation easier. Material balances without 1-alkenes were also repeated to allow verification of catalyst selectivity stability. A total of 49 balances were performed during a single run which lasted over 2500 hours-on-stream. The hydrocarbon data have not yet been completed analyzed.

  5. Determination of the Effect of Coal/Biomass-Derived Syngas Contaminants on the Performance of Fischer-Tropsch and Water-Gas-Shift Catalysts

    SciTech Connect

    Trembly, Jason; Cooper, Matthew; Farmer, Justin; Turk, Brian; Gupta, Raghubir

    2010-12-31

    Today, nearly all liquid fuels and commodity chemicals are produced from non-renewable resources such as crude oil and natural gas. Because of increasing scrutiny of carbon dioxide (CO{sub 2}) emissions produced using traditional fossil-fuel resources, the utilization of alternative feedstocks for the production of power, hydrogen, value-added chemicals, and high-quality hydrocarbon fuels such as diesel and substitute natural gas (SNG) is critical to meeting the rapidly growing energy needs of modern society. Coal and biomass are particularly attractive as alternative feedstocks because of the abundant reserves of these resources worldwide. The strategy of co-gasification of coal/biomass (CB) mixtures to produce syngas for synthesis of Fischer-Tropsch (FT) fuels offers distinct advantages over gasification of either coal or biomass alone. Co-feeding coal with biomass offers the opportunity to exploit economies of scale that are difficult to achieve in biomass gasification, while the addition of biomass to the coal gasifier feed leverages proven coal gasification technology and allows CO{sub 2} credit benefits. Syngas generated from CB mixtures will have a unique contaminant composition because coal and biomass possess different concentrations and types of contaminants, and the final syngas composition is also strongly influenced by the gasification technology used. Syngas cleanup for gasification of CB mixtures will need to address this unique contaminant composition to support downstream processing and equipment. To investigate the impact of CB gasification on the production of transportation fuels by FT synthesis, RTI International conducted thermodynamic studies to identify trace contaminants that will react with water-gas-shift and FT catalysts and built several automated microreactor systems to investigate the effect of single components and the synergistic effects of multiple contaminants on water-gas-shift and FT catalyst performance. The contaminants

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

    SciTech Connect

    Alptekin, Gokhan

    2013-02-15

    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 (H2S, NH3, HCN, AsH3, PH3, HCl, NaCl, KCl, AS3, NH4NO3, NH4OH, KNO3, HBr, HF, and HNO3) on the performance and lifetime of commercially available and generic (prepared in-house) WGS and FT catalysts.

  7. Effect of adding Co to MoS{sub 2}/Al{sub 2}O{sub 3} upon the kinetics of the water-gas shift

    SciTech Connect

    Lund, C.R.F.

    1996-09-01

    A microkinetic model for the kinetics of the water-gas shift over sulfided CoMo/Al{sub 2}O{sub 3} catalysts was developed starting from a similar model for unpromoted sulfided Mo/Al{sub 2}O{sub 3} catalysts. Co was found to promote the catalyst`s activity only at low CO/H{sub 2}O ratios; at high ratios the Mo catalyst was marginally more active than the CoMo catalyst. The most important different between the two models was the strength of interactions between the surface and hydroxyl groups. The addition of Co increased the stability of hydroxyl groups relative to sulfhydryl groups, and at higher H{sub 2}O concentrations this allowed oxidized surface sites to more readily participate in both steam adsorption and hydrogen desorption steps. The results are most easily reconciled in terms of a promotional model where the Co and Mo are in close proximity and the active sites are similar to sites on unpromoted Mo catalysts.

  8. Energy-shifting formulae yield reliable reaction and capture probabilities

    NASA Astrophysics Data System (ADS)

    Diaz-Torres, A.; Adamian, G. G.; Sargsyan, V. V.; Antonenko, N. V.

    2014-12-01

    Predictions of energy-shifting formulae for partial reaction and capture probabilities are compared with coupled channels calculations. The quality of the agreement notably improves with increasing mass of the system and/or decreasing mass asymmetry in the heavy-ion collision. The formulae are reliable and useful for circumventing impracticable reaction calculations at low energies.

  9. 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.

  10. Investigation of the Reverse Water Gas Shift Reaction for Production of Oxygen From Mars Atmospheric Carbon Dioxide

    NASA Technical Reports Server (NTRS)

    Meyer, Tom; Zubrin, Robert

    1997-01-01

    The first phase of the research includes a comprehensive analytical study examining the potential applications for engineering subsystems and mission strategies made possible by such RWGS based subsystems, and will include an actual experimental demonstration and performance characterization of a full-scale brassboard RWGS working unit. By the time of this presentation the laboratory demonstration unit will not yet be operational but we will present the results of our analytical studies to date and plans for the ongoing work.

  11. 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.

  12. 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

    SciTech Connect

    Burton Davis; Gary Jacobs; Wenping Ma; Dennis Sparks; Khalid Azzam; Janet Chakkamadathil Mohandas; Wilson Shafer; Venkat Ramana Rao Pendyala

    2011-09-30

    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, traces of metals, halide compounds, and nitrogen-containing chemicals will likely be lower in concentration in syngas derived from mixtures of coal and biomass (i.e., using entrained-flow oxygen-blown gasifier gasification gasification) than solely from coal, other compounds may actually be increased. Of particular concern are compounds containing alkali chemicals like the chlorides of sodium and potassium. In the first year, University of Kentucky Center for Applied Energy Research (UK-CAER) researchers completed a number of tasks aimed at evaluating the sensitivity of cobalt and iron-based Fischer-Tropsch synthesis (FT) catalysts and a commercial iron-chromia high temperature water-gas shift catalyst (WGS) to alkali halides. This included the preparation of large batches of 0.5%Pt-25%Co/Al{sub 2}O{sub 3} and 100Fe: 5.1Si: 3.0K: 2.0Cu (high alpha) catalysts that were split up among the four different entities participating in the overall project; the testing of the catalysts under clean FT and WGS conditions; the testing of the Fe-Cr WGS catalyst under conditions of co-feeding NaCl and KCl; and the construction and start-up of the continuously stirred tank reactors (CSTRs) for poisoning investigations. In the second and third years, researchers from the University of Kentucky Center for Applied Energy Research (UK-CAER) continued the project by evaluating the sensitivity of a commercial iron-chromia high temperature water-gas shift catalyst (WGS) to a number of different compounds, including KHCO{sub 3}, NaHCO{sub 3}, HCl, HBr, HF, H{sub 2}S, NH{sub 3}, and a combination of H

  13. 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.

  14. 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.

  15. Slurry phase Fischer-Tropsch synthesis: Cobalt plus a water-gas shift catalyst. [Quarterly] report, April 1, 1990--June 30, 1990

    SciTech Connect

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

    1990-12-31

    Experiments on cobalt-catalyzed reactions of light 1-alkenes added to synthesis gas were performed. Data have been collected at 220C, 0.45 to 1.48 MPa and a synthesis gas flow rate between 0.015 and 0.030 Nl/(gcat{center_dot}min) with H{sub 2}/CO of 1.45 to 2.25. Ethylene, propene, and butene were added to synthesis gas feed from 0.5 to 1.2 mole% of total feed. For each material balance in which 1-alkenes were added, a material balance was performed at similar process conditions without 1-alkenes added, as ``base case``. Material balances without added 1-alkenes were also repeated to verify of catalyst selectivity stability. 49 material balances were performed during a single run lasting over 2,500 hours-on-stream. The hydrocarbon data have been completely analyzed; data correlations are still being made. Since C{sub 3}/C{sub 1} ratios by ethene addition, C{sub 4}/C{sub 1} ratios by propene addition, and C{sub 5}/C{sub 1} ratios by 1-butene addition, it appears that 1-alkenes may incorporate into growing chains on the surface of the catalyst. Further evidence for incorporation can be seen by comparing selectivity to n-alcohol one carbon number higher than added 1-alkene. Yield of this n-alcohol increases when alkenes are present. Sensitivity of hydrocarbon distribution to process variables seems to be greater on Co than on Fe catalysts.

  16. 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

    SciTech Connect

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

    2009-09-30

    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, traces of metals, halide compounds, and nitrogen-containing chemicals will likely be lower in concentration in syngas derived from mixtures of coal and biomass (i.e., using entrained-flow oxygen-blown gasifier gasification gasification) than solely from coal, other compounds may actually be increased. Of particular concern are compounds containing alkali chemicals like the chlorides of sodium and potassium. In the first year, University of Kentucky Center for Applied Energy Research (UK-CAER) researchers completed a number of tasks aimed at evaluating the sensitivity of cobalt and iron-based Fischer-Tropsch synthesis (FT) catalysts and a commercial iron-chromia high temperature water-gas shift catalyst (WGS) to alkali halides. This included the preparation of large batches of 0.5%Pt-25%Co/Al{sub 2}O{sub 3} and 100Fe: 5.1Si: 3.0K: 2.0Cu (high alpha) catalysts that were split up among the four different entities participating in the overall project; the testing of the catalysts under clean FT and WGS conditions; the testing of the Fe-Cr WGS catalyst under conditions of co-feeding NaCl and KCl; and the construction and start-up of the continuously stirred tank reactors (CSTRs) for poisoning investigations.

  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

    SciTech Connect

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

    2010-09-30

    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 from coal/biomass blends to Fischer-Tropsch synthesis products to liquid fuels may provide a sustainable path forward, especially considering if carbon sequestration can be successfully demonstrated. However, one current drawback is that it is unknown whether conventional catalysts based on iron and cobalt will be suitable without proper development because, while ash, sulfur compounds, traces of metals, halide compounds, and nitrogen-containing chemicals will likely be lower in concentration in syngas derived from mixtures of coal and biomass (i.e., using an entrained-flow oxygen-blown gasifier) than solely from coal, other byproducts may be present in higher concentrations. The current project examines the impact of a number of potential byproducts of concern from the gasification of biomass process, including compounds containing alkali chemicals like the chlorides of sodium and potassium. In the second year, researchers from the University of Kentucky Center for Applied Energy Research (UK-CAER) continued the project by evaluating the sensitivity of a commercial iron-chromia high temperature water-gas shift catalyst (WGS) to a number of different compounds, including KHCO{sub 3}, NaHCO{sub 3}, HCl, HBr, HF, H{sub 2}S, NH{sub 3}, and a combination of H{sub 2}S and NH{sub 3}. Cobalt and iron-based Fischer-Tropsch synthesis (FT) catalysts were also subjected to a number of the same compounds in order to evaluate their sensitivities.

  18. Three model space experiments on chemical reactions. [Gibbs adsorption, equilibrium shift and electrodeposition

    NASA Technical Reports Server (NTRS)

    Grodzka, P.; Facemire, B.

    1977-01-01

    Three investigations conducted aboard Skylab IV and Apollo-Soyuz involved phenomena that are of interest to the biochemistry community. The formaldehyde clock reaction and the equilibrium shift reaction experiments conducted aboard Apollo Soyuz demonstrate the effect of low-g foams or air/liquid dispersions on reaction rate and chemical equilibrium. The electrodeposition reaction experiment conducted aboard Skylab IV demonstrate the effect of a low-g environment on an electrochemical displacement reaction. The implications of the three space experiments for various applications are considered.

  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

    2013-11-05

    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. Theoretical Investigation of Intramolecular Hydrogen Shift Reactions in 3-Methyltetrahydrofuran (3-MTHF) Oxidation.

    PubMed

    Parab, Prajakta R; Sakade, Naoki; Sakai, Yasuyuki; Fernandes, Ravi; Heufer, K Alexander

    2015-11-01

    3-Methyltetrahydrofuran (3-MTHF) is proposed to be a promising fuel component among the cyclic oxygenated species. To have detailed insight of its combustion kinetics, intramolecular hydrogen shift reactions for the ROO to QOOH reaction class are studied for eight ROO isomers of 3-MTHF. Rate constants of all possible reaction paths that involve formation of cyclic transition states are computed by employing the CBS-QB3 composite method. A Pitzer-Gwinn-like approximation has been applied for the internal rotations in reactants, products, and transition states for the accurate treatment of hindered rotors. Calculated relative barrier heights highlight that the most favorable reaction channel proceeds via a six membered transition state, which is consistent with the computed rate constants. Comparing total rate constants in ROO isomers of 3-MTHF with the corresponding isomers of methylcyclopentane depicts faster kinetics in 3-MTHF than methylcyclopentane reflecting the effect of ring oxygen on the intramolecular hydrogen shift reactions. PMID:26444499

  1. 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.

  2. 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 itsapplicability to the Aidlin geothermal system. Using TOUGHREACT, wedeveloped a 1-D grid to evaluate the effects of water injection andsubsequent water-rock-gas interaction on the compositions of the producedfluids. A dual-permeability model of the fracture-matrix system was usedto describe reaction-transport processes in which the permeability of thefractures is many orders of magnitude higher than that of the rockmatrix. The geochemical system included the principal minerals(K-feldspar, plagioclase, calcite, silica polymorphs) of themetagraywackes that comprise the geothermal reservoir rocks. Initialsimulation results predict that the gas-phase CO2 in the reservoir willbecome more enriched in 14C as air-equilibrated injectate water (with amodern carbon signature) is incorporated into the system, and that thesechanges will precede accompanying decreases in reservoir temperature. Theeffects of injection on 14C in the rock matrix will be lessened somewhatbecause of the dissolution of matrix calcite with "dead"carbon.

  3. Electronic shift register memory based on molecular electron-transfer reactions

    NASA Technical Reports Server (NTRS)

    Hopfield, J. J.; Onuchic, Jose Nelson; Beratan, David N.

    1989-01-01

    The design of a shift register memory at the molecular level is described in detail. The memory elements are based on a chain of electron-transfer molecules incorporated on a very large scale integrated (VLSI) substrate, and the information is shifted by photoinduced electron-transfer reactions. The design requirements for such a system are discussed, and several realistic strategies for synthesizing these systems are presented. The immediate advantage of such a hybrid molecular/VLSI device would arise from the possible information storage density. The prospect of considerable savings of energy per bit processed also exists. This molecular shift register memory element design solves the conceptual problems associated with integrating molecular size components with larger (micron) size features on a chip.

  4. High-Throughput Electrophoretic Mobility Shift Assays for Quantitative Analysis of Molecular Binding Reactions

    PubMed Central

    2015-01-01

    We describe a platform for high-throughput electrophoretic mobility shift assays (EMSAs) for identification and characterization of molecular binding reactions. A photopatterned free-standing polyacrylamide gel array comprised of 8 mm-scale polyacrylamide gel strips acts as a chassis for 96 concurrent EMSAs. The high-throughput EMSAs was employed to assess binding of the Vc2 cyclic-di-GMP riboswitch to its ligand. In optimizing the riboswitch EMSAs on the free-standing polyacrylamide gel array, three design considerations were made: minimizing sample injection dispersion, mitigating evaporation from the open free-standing polyacrylamide gel structures during electrophoresis, and controlling unit-to-unit variation across the large-format free-standing polyacrylamide gel array. Optimized electrophoretic mobility shift conditions allowed for 10% difference in mobility shift baseline resolution within 3 min. The powerful 96-plex EMSAs increased the throughput to ∼10 data/min, notably more efficient than either conventional slab EMSAs (∼0.01 data/min) or even microchannel based microfluidic EMSAs (∼0.3 data/min). The free-standing polyacrylamide gel EMSAs yielded reliable quantification of molecular binding and associated mobility shifts for a riboswitch–ligand interaction, thus demonstrating a screening assay platform suitable for riboswitches and potentially a wide range of RNA and other macromolecular targets. PMID:25233437

  5. Combining steam-methane reforming, water-gas shift, and CO{sub 2} removal in a single-step process for hydrogen production. Final report for period March 15, 1997 - December 14, 2000

    SciTech Connect

    Alejandro Lopez Ortiz; Bhaskar Balasubramanian; Douglas P. Harrison

    2001-02-01

    The objective of the research project was to determine the feasibility of a simpler, more energy-efficient process for the production of 95+% H{sub 2} from natural gas, and to collect sufficient experimental data on the effect of reaction parameters to guide additional larger-scale process development. The overall objectives were accomplished. 95+% H{sub 2} was produced in a single reaction step by adding a calcium-based CO{sub 2} acceptor to standard Ni-based reforming catalyst. The spent acceptor was successfully regenerated and used in a number of reaction steps with only moderate loss in activity as the number of cycles increased. Sufficient experimental data were collected to guide further larger-scale experimental work designed to investigate the economic feasibility of the process.

  6. Unusually Facile Thermal Homodienyl-[1,5]-Hydrogen Shift Reactions in Photochemically Generated Vinyl Aziridines.

    PubMed

    Knowles, Jonathan P; Booker-Milburn, Kevin I

    2016-08-01

    A range of photochemically generated tri- and tetracyclic vinyl aziridines have been found to undergo a general and surprisingly low temperature ring opening through a [1,5]-hydrogen shift reaction. The rate of the process was found to be highly dependent on the structure and substitution around the azirdine ring and the alkene terminus, with some substrates being observed to undergo ring opening at temperatures as low as 25 °C. The rigid nature of these polycyclic systems precludes a conformational explanation of these rate differences, and an Eyring study confirmed a negligible entropic barrier to the reaction. However, the Eyring plots for two different aziridines systems showed a significant difference in their enthalpies of activation. It is therefore believed that the levels of aziridine ring strain, as well as electronic effects, are the dominant factors in this sequence. PMID:27380942

  7. Ethanol synthesis and water gas shift over bifunctional sulfide catalysts

    SciTech Connect

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

    1992-06-01

    During this quarter, the high pressure (up to 100 atm), high temperature (up to 350{degrees}C) catalyst testing system was rebuilt with clean tubing, etc. A new preparation of MoS{sub 2} catalyst was carried out, and this catalyst will be doped with alkali and tested during the next quarter of research.

  8. Ethanol synthesis and water gas shift over bifunctional sulfide catalysts

    SciTech Connect

    Klier, K.; Herman, R.G.; Deemer, M.

    1992-12-01

    During this quarter, the surface areas of various catalysts were determined. The surface area of the catalyst tested last quarter was determined for the undoped catalyst, the doped catalyst before testing, and the doped catalyst after testing. These surface areas were then compared with ones reported earlier. After testing under high temperature and high pressure conditions for 551 hours, there was a loss of surface area. This might be due possibly to agglomeration of cesium formate on the surface. Higher surface area catalysts were also produced. Two samples of MoS[sub 2] were synthesized with surface areas of 96 m2/g and 91 m2/g. These were obtained by varying the heating rate of MoS[sub 3] and the calcination temperature.

  9. 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 α-aryl-β-trifluoromethyl amides and/or CF3-containing oxindoles as well as the isoquinolinediones under benign conditions. PMID:25955879

  10. Lamb shift in radical-ion pairs produces a singlet-triplet energy splitting in photosynthetic reaction centers

    NASA Astrophysics Data System (ADS)

    Vitalis, K. M.; Kominis, I. K.

    2014-09-01

    Radical-ion pairs, fundamental for understanding photosynthesis and the avian magnetic compass, were recently shown to be biological open quantum systems. We here show that the coupling of the radical-pair spin degrees of freedom to its decohering vibrational reservoir leads to a shift of the radical-pair magnetic energy levels. The Lamb shift Hamiltonian is diagonal in the singlet-triplet basis, and results in a singlet-triplet energy splitting physically indistinguishable from an exchange interaction. This could have significant implications for understanding the energy level structure and the dynamics of photosynthetic reaction centers.

  11. A surface-plasmon resonance phase modulation bio-reaction detection system with (5,1) phase-shifting algorithm

    NASA Astrophysics Data System (ADS)

    Chen, Yi-Hung; Lee, Shu-Sheng; Hsu, I.-Hung; Tseng, Eddie; Lee, Chih-Kung

    2007-12-01

    Surface plasmon resonance (SPR) is a very important metrology in biology detection. Phase modulation is one of the SPR detection technologies and the sample changes can be recognized from the phase variation. It is able to detect very tiny bio sample variation due to its high sensitivity. In this study, the optical system design based on a paraboloidal lens-based surface plasmon resonance instrument will be used to control the SPR critical angle. The charge coupled device camera (CCD camera) will be used to record the images of the bio-reaction and (5,1) phase-shifting algorithm will be adopted to retrieve the phase fringes of the whole spot from the intensity maps. The combination of the angle control SPR system and the (5,1) phase-shifting algorithm will expand the whole spot detection ability from the intensity to phase modulation because the intensity maps are going to be recorded for the (5,1) phase-shifting algorithm calculation. The difference between (5,1) phase-shifting algorithm and Five-Step Algorithm1 is that (5,1) phase-shifting algorithm only needs one image map at one time during the bio reaction and Five-Step Algorithm requires five image maps. Therefore, (5,1) phase-shifting algorithm will reduce the process of experiment and the requirement of the memory. The different concentration alcohols were measured by the optical system to verify the (5,1) phase-shifting algorithm applied in SPR phase modulation measurement and to prove the idea is workable and successful.

  12. Features of the reaction of heterocyclic analogs of chalcone with lanthanide shift reagents

    SciTech Connect

    Turov, A.V.; Khilya, V.P.

    1994-10-01

    The PMR spectra of heterocyclic analogs of 2-hydroxychalcone containing thiazole, benzofuran, triazole, imidazole, benzodioxane, or pyridine rings in the presence of lanthanide shift reagents are studied. It is found that the most effective reagent for modifying the spectra of these compounds is Yb(fod)3. The broadening of the spectra of 2-hydroxy chalcones in the presence of lanthanide shift reagents is explained by the dynamic effects of complex formation. An example is given of the determination of the conformation of molecules of 2-hydroxychalcone by the simultaneous use of lanthanide shift reagents and the homonuclear Overhauser effect. 9 refs., 1 fig., 1 tab.

  13. Nanoconfined nitrogen hydrogenation on Ru(0001): Prediction of entropy related shifts in the reaction equilibria

    NASA Astrophysics Data System (ADS)

    Polak, Micha; Rubinovich, Leonid

    2015-11-01

    Remarkable variations in NHx (x = 1,2,3) equilibrium molecular fractions are revealed by statistical-mechanical computations for a system composed of only few reactant atoms that are confined to nanoscale Ru(0001) surface. Using one of two sets of reported DFT-based reaction energetics as input, NH formation on the flat surface is enhanced up to ~ 50% compared to the thermodynamic limit (TL) of the macroscopic system. This nanoconfinement entropic effect on chemical equilibrium (NCECE), introduced and demonstrated by us before for some hypothetical reactions, originates from mixing entropy reduction in the small-system that increases the product molecular fraction in exothermic reactions, as is fully elucidated here for the case of NH. The other input set gives an opposite effect due to the reaction endothermicity on both flat and stepped surfaces. For concurrent ND and NH formation, including H - D exchange, the temperature and coverage dependent superposition of the three NCECE contributions have a significant effect on two of the three equilibrium constants of the coupled reactions, and increase/decrease the ND/NH fractions. The computed TL low fractions of NH2 and NH3 in the coupled three hydrogenation steps are further diminished by the NCECE, suggesting that from this aspect ammonia synthesis on smaller particles is expected to be less effective.

  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. Rh(II)-catalyzed reaction of alpha-diazocarbonyl compounds bearing beta-trichloroacetylamino substituent: C-H insertion versus 1,2-H shift.

    PubMed

    Zhang, Zhenhua; Shi, Weifeng; Zhang, Jian; Zhang, Bo; Liu, Bingge; Liu, Yiyang; Fan, Bo; Xiao, Fengping; Xu, Feng; Wang, Jianbo

    2010-05-01

    The Rh(II)-carbene reaction is dramatically affected by the neighboring substituents. If the neighboring substituent is an OH group, a1,2-H shift is the exclusive pathway. If it is an OAc group, a 1,2-acetoxy migration is observed. If it is p-toluenesulfonyl group, 1,3 and 1,5-C-H insertion are the major pathways, and the 1,2-H shift is completely suppressed. If the adjacent substituent is a trichloroacetyl amino group, 1,5-C-H insertion competes with the 1,2-hydride shift, and no 1,3-C-H insertion can be observed. Both electronic and steric factors are responsible for the switching of the Rh(II)-carbene reaction pathway. The highly stereoselective 1,5-C-H insertions in Rh(II)-catalyzed reaction of alpha-diazocarbonyl compounds, bearing beta-trichloroacetylamino substituent, can be utilized as a novel way to synthesize five-membered cyclic beta-amino acid derivatives. PMID:20013998

  16. Characterization of reaction between ZnO and COS

    SciTech Connect

    Sasaoka, Eiji; Taniguchi, Kazuo; Uddin, M.A.; Hirano, Shigeru; Kasaoka, Shigeaki; Sakata, Yusaku

    1996-07-01

    In order to understand the behavior of COS in a ZnO desulfurization reactor, the reaction between ZnO and COS was studied in the presence of gases which compose a coal-derived gas. The behavior of COS in the reaction zone of a ZnO packed bed can be predicted as follows: H{sub 2}S in coal-derived gas reacts more easily with ZnO than COS; most of COS is converted to H{sub 2}S by catalytic hydrolysis and then reacts with ZnO, although a part of COS may react directly with ZnO; H{sub 2} accelerates the conversion of COS to H{sub 2}S; the water-gas shift reaction accelerates the reaction between ZnO and COS; and CO{sub 2} does not affect the reaction.

  17. High-pressure catalytic reactions over single-crystal metal surfaces

    NASA Astrophysics Data System (ADS)

    Rodriguez, JoséA.; Wayne Goodman, D.

    1991-11-01

    Studies dealing with high-pressure catalytic reactions over single-crystal surfaces are reviewed. The coupling of an apparatus for the measurement of reaction kinetics at elevated pressures with an ultrahigh vacuum system for surface analysis allows detailed study of structure sensitivity, the effects of promoters and inhibitors on catalytic activity, and, in certain cases, identification of reaction intermediates by post-reaction surface analysis. Examples are provided which demonstrate the relevance of single-crystal studies for modeling the behaviour of high-surface-area supported catalysts. Studies of CO methanation and CO oxidation over single-crystal surfaces provide convincing evidence that these reactions are structure insensitive. For structure-sensitive reactions (ammonia synthesis, alkane hydrogenolysis, alkane isomerization, water-gas shift reaction, etc.) model single-crystal studies allow correlations to be established between surface structure and catalytic activity. The effects of both electronegative (S and P) and electropositive (alkali metals) impurities upon the catalytic activity of metal single crystals for ammonia synthesis, CO methanation, alkane hydrogenolysis, ethylene epoxidation and water-gas shift are discussed. The roles of "ensemble" and "ligand" effects in bimetallic catalysts are examined in light of data obtained using surfaces prepared by vapor-depositing one metal onto a crystal face of a dissimilar metal.

  18. 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.

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

    PubMed

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

    2014-01-01

    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 β-amyloid25-35 (Aβ25-35)-induced cellular injuries in human neuroblastoma SH-SY5Y cells in the range of those of positive controls. PMID:25550721

  20. 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 β-amyloid25–35 (Aβ25–35)-induced cellular injuries in human neuroblastoma SH-SY5Y cells in the range of those of positive controls. PMID:25550721

  1. Thermal cyclization of phenylallenes that contain ortho-1,3-dioxolan-2-yl groups: new cascade reactions initiated by 1,5-hydride shifts of acetalic H atoms.

    PubMed

    Alajarin, Mateo; Bonillo, Baltasar; Marin-Luna, Marta; Sanchez-Andrada, Pilar; Vidal, Angel

    2013-11-18

    A series of 2-(1,3-dioxolan-2-yl)phenylallenes that contained a range of substituents (alkyl, aryl, phosphinyl, alkoxycarbonyl, sulfonyl) at the cumulenic C3 position were prepared by using a diverse range of synthetic strategies and converted into their respective 1-(2-hydroxy)-ethoxy-2-substituted naphthalenes by smooth thermal activation in toluene solution. Electron-withdrawing groups at the C3 position accelerated these tandem processes, which consisted of 1) an initial hydride-like [1,5]-H shift of the acetalic H atom onto the central cumulene carbon atom; 2) a subsequent 6π-electrocyclic ring-closure of the resulting reactive ortho-xylylenes; and 3) a final aromatization step with concomitant ring-opening of the 1,3-dioxolane fragment. If the 1,3-dioxolane ring of the starting allenes was replaced by a dimethoxymethyl group, the reactions led to mixtures of two disubstituted naphthalenes, which were formed by the migration of either the acetalic H atom or the methoxy group, with the latter migration occurring to a lesser extent. Two of the final 1,2-disubstituted naphthalenes were converted into their corresponding naphtho-fused dioxaphosphepine or dioxepinone through an intramolecular transesterification reaction. A DFT computational study accounted for the beneficial influence of the 1,3-dioxolane fragment on the carbon atom from which the H-shift took place and also of the electron-withdrawing substituents on the allene terminus. Remarkably, in the processes that contained a sulfonyl substituent, the conrotatory 6π-electrocyclization step was of lower activation energy than the alternative disrotatory mode. PMID:24123192

  2. Shift of reaction pathway by added chloride ions in the oxidation of aromatic ketones by dichloroisocyanuric acid—A kinetic study

    NASA Astrophysics Data System (ADS)

    Kumar, Y. Lakshman; Nadh, R. Venkata; Radhakrishnamurti, P. S.

    2016-03-01

    Role of added chloride ions on the shift of reaction pathway of oxidation of aromatic ketones (acetophenone, desoxybenzoin) by dichloroisocyanuric acid (DCICA) was studied in aqueous acetic acid—perchloric acid medium. Participation of enolic and protonated forms of ketones in the rate determining steps is manifested from zero and first orders with respect to the oxidant in absence and presence of added chloride ions, respectively. Positive and negative effects of acid and dielectric constant on the reaction rate were observed. The observations deduce plausible mechanisms involving (i) rate-determining formation of enol from the conjugate acid of the ketone (SH+) in the absence of added chloride ions and (ii) rapid formation of molecular chlorine species from HOCl (hydrolytic species of DCICA) in the presence of added chloride ions, which then interacts with SH+ in a rate-determining step prior to the rapid steps of product formation. The order of Arrhenius parameters substantiate the proposed plausible mechanisms based on order of reactants both in presence and absence of added chloride ions.

  3. SurfKin: an ab initio kinetic code for modeling surface reactions.

    PubMed

    Le, Thong Nguyen-Minh; Liu, Bin; Huynh, Lam K

    2014-10-01

    In this article, we describe a C/C++ program called SurfKin (Surface Kinetics) to construct microkinetic mechanisms for modeling gas-surface reactions. Thermodynamic properties of reaction species are estimated based on density functional theory calculations and statistical mechanics. Rate constants for elementary steps (including adsorption, desorption, and chemical reactions on surfaces) are calculated using the classical collision theory and transition state theory. Methane decomposition and water-gas shift reaction on Ni(111) surface were chosen as test cases to validate the code implementations. The good agreement with literature data suggests this is a powerful tool to facilitate the analysis of complex reactions on surfaces, and thus it helps to effectively construct detailed microkinetic mechanisms for such surface reactions. SurfKin also opens a possibility for designing nanoscale model catalysts. PMID:25111729

  4. 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.

  5. A model to assess the feasibility of shifting reaction equilibrium by acetone removal in the transamination of ketones using 2-propylamine.

    PubMed

    Tufvesson, Pär; Bach, Christian; Woodley, John M

    2014-02-01

    Acetone removal by evaporation has been proposed as a simple and cheap way to shift the equilibrium in the biocatalytic asymmetric synthesis of optically pure chiral amines, when 2-propylamine is used as the amine donor. However, dependent on the system properties, this may or may not be a suitable strategy. To avoid excessive laboratory work a model was used to assess the process feasibility. The results from the current study show that a simple model of the acetone removal dependence on temperature and sparging gas flowrate can be developed and fits the experimental data well. The model for acetone removal was then coupled to a simple model for biocatalyst kinetics and also for loss of substrate ketone by evaporation. The three models were used to simulate the effects of varying the critical process parameters and reaction equilibrium constants (K eq) as well as different substrate ketone volatilities (Henry's constant). The simulations were used to estimate the substrate losses and also the maximum yield that could be expected. The approach was seen to give a clear indication for which target amines the acetone evaporation strategy would be feasible and for which amines it would not. The study also shows the value of a modeling approach in conceptual process design prior to entering a biocatalyst screening or engineering program to assess the feasibility of a particular process strategy for a given target product. PMID:23904347

  6. Water–gas shift reaction over gold nanoparticles dispersed on nanostructured CeOx–TiO2(110) surfaces: Effects of high ceria coverage

    DOE PAGESBeta

    Grinter, D. C.; Park, J. B.; Agnoli, S.; Evans, J.; Hrbek, J.; Stacchiola, D. J.; Senanayake, S. D.; Rodriguez, J. A.

    2016-08-01

    We used scanning tunnelling microscopy to study the morphology of an overlayer of ceria in contact with a TiO2(110) substrate. Two types of domains were observed after ceria deposition. An ordered ceria film covered half of the surface and high-resolution imaging suggested a near-c(6 × 2) relationship to the underlying TiO2(110)-(1 × 1). For the other half of the surface, it comprised CeOx nanoparticles and reconstructed TiOx supported on TiO2(110)-(1 × 1). Exposure to a small amount of gold resulted in the formation of isolated gold atoms and small clusters on the ordered ceria film and TiO2(110)-(1 × 1) areas,more » which exhibited significant sintering at 500 K and showed strong interaction between the sintered gold clusters and the domain boundaries of the ceria film. The Au/CeOx/TiO2(110) model system proved to be a good catalyst for the water–gas shift (WGS) exhibiting much higher turnover frequencies (TOFs) than Cu(111) and Pt(111) benchmarks, or the individual Au/TiO2(110) and Au/CeO2(111) systems. Finally, for Au/CeOx/TiO2(110) catalysts, there was a decrease in catalytic activity with increasing ceria coverage that correlates with a reduction in the concentration of Ce3 + formed during WGS reaction conditions.« less

  7. The Effect of Rain on Air-Water Gas Exchange

    NASA Technical Reports Server (NTRS)

    Ho, David T.; Bliven, Larry F.; Wanninkhof, Rik; Schlosser, Peter

    1997-01-01

    The relationship between gas transfer velocity and rain rate was investigated at NASA's Rain-Sea Interaction Facility (RSIF) using several SF, evasion experiments. During each experiment, a water tank below the rain simulator was supersaturated with SF6, a synthetic gas, and the gas transfer velocities were calculated from the measured decrease in SF6 concentration with time. The results from experiments with IS different rain rates (7 to 10 mm/h) and 1 of 2 drop sizes (2.8 or 4.2 mm diameter) confirm a significant and systematic enhancement of air-water gas exchange by rainfall. The gas transfer velocities derived from our experiment were related to the kinetic energy flux calculated from the rain rate and drop size. The relationship obtained for mono-dropsize rain at the RSIF was extrapolated to natural rain using the kinetic energy flux of natural rain calculated from the Marshall-Palmer raindrop size distribution. Results of laboratory experiments at RSIF were compared to field observations made during a tropical rainstorm in Miami, Florida and show good agreement between laboratory and field data.

  8. Shifting tools

    SciTech Connect

    Fisher, E.P.; Welch, W.R.

    1984-03-13

    An improved shifting tool connectable in a well tool string and useful to engage and position a slidable sleeve in a sliding sleeve device in a well flow conductor. The selectively profiled shifting tool keys provide better fit with and more contact area between keys and slidable sleeves. When the engaged slidable sleeve cannot be moved up and the shifting tool is not automatically disengaged, emergency disengagement means may be utilized by applying upward force to the shifting tool sufficient to shear pins and cause all keys to be cammed inwardly at both ends to completely disengage for removal of the shifting tool from the sliding sleeve device.

  9. Shifting Attention

    ERIC Educational Resources Information Center

    Ingram, Jenni

    2014-01-01

    This article examines the shifts in attention and focus as one teacher introduces and explains an image that represents the processes involved in a numeric problem that his students have been working on. This paper takes a micro-analytic approach to examine how the focus of attention shifts through what the teacher and students do and say in the…

  10. Fluid Shifts

    NASA Technical Reports Server (NTRS)

    Stenger, Michael B.; Hargens, Alan R.; Dulchavsky, Scott A.; Ebert, Douglas J.; Lee, Stuart M. C.; Laurie, Steven S.; Garcia, Kathleen M.; Sargsyan, Ashot E.; Martin, David S.; Liu, John; Macias, Brandon R.; Arbeille, Philippe; Danielson, Richard; Chang, Douglas; Gunga, Hanns-Christian; Johnston, Smith L.; Westby, Christian M.; Ploutz-Snyder, Robert J.; Smith, Scott M.

    2016-01-01

    We hypothesize that microgravity-induced cephalad fluid shifts elevate intracranial pressure (ICP) and contribute to VIIP. We will test this hypothesis and a possible countermeasure in ISS astronauts.

  11. 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

  12. 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

  13. 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".

  14. Fluid Shifts

    NASA Technical Reports Server (NTRS)

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

    2016-01-01

    NASA is focusing on long-duration missions on the International Space Station (ISS) and future exploration-class missions beyond low-Earth orbit. Visual acuity changes observed after short-duration missions were largely transient, but more than 50% of ISS astronauts experienced more profound, chronic changes with objective structural and functional findings such as papilledema and choroidal folds. Globe flattening, optic nerve sheath dilation, and optic nerve tortuosity also are apparent. This pattern is referred to as the visual impairment and intracranial pressure (VIIP) syndrome. VIIP signs and symptoms, as well as postflight lumbar puncture data, suggest that elevated intracranial pressure (ICP) may be associated with the spaceflight-induced cephalad fluid shifts, but this hypothesis has not been tested. The purpose of this study is to characterize fluid distribution and compartmentalization associated with long-duration spaceflight, and to correlate these findings with vision changes and other elements of the VIIP syndrome. We also seek to determine whether the magnitude of fluid shifts during spaceflight, as well as the VIIP-related effects of those shifts, is predicted by the crewmember's preflight conditions and responses to acute hemodynamic manipulations (such as head-down tilt). Lastly, we will evaluate the patterns of fluid distribution in ISS astronauts during acute reversal of fluid shifts through application of lower body negative pressure (LBNP) interventions to characterize and explain general and individual responses. METHODS: We will examine a variety of physiologic variables in 10 long-duration ISS crewmembers using the test conditions and timeline presented in the Figure below. Measures include: (1) fluid compartmentalization (total body water by D2O, extracellular fluid by NaBr, intracellular fluid by calculation, plasma volume by CO rebreathe, interstitial fluid by calculation); (2) forehead/eyelids, tibia, calcaneus tissue thickness (by

  15. A novel reaction-based colorimetric and ratiometric fluorescent sensor for cyanide anion with a large emission shift and high selectivity.

    PubMed

    Wang, Shaodan; Fei, Xiaoliang; Guo, Jing; Yang, Qingbiao; Li, Yaoxian; Song, Yan

    2016-02-01

    A hybrid carbazole-hemicyanine dye (Cac) has been developed as a novel colorimetric and ratiometric fluorescent sensor for cyanide detection. Upon treatment with cyanide, Cac displayed a remarkable fluorescence ratiometric response, with the emission wavelength displaying a very large emission shift (214 nm). The detection of cyanide was performed via the nucleophilic addition of cyanide anion to the indolium group of the sensor, which resulted in the blocking of the intramolecular charge transfer (ICT) process in the sensor, inducing a ratiometric fluorescence change and simultaneously an obvious color change. Furthermore, competitive anions did not showed any significant changes both in color and emission intensity ratio (I381/I595), indicating the high selectivity of the sensor to CN(-). PMID:26653444

  16. Ethanol synthesis and water gas shift over bifunctional sulfide catalysts. Technical progress report, June 1993--August 1993

    SciTech Connect

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

    1993-09-01

    Various preparation methods of synthesizing molybdenum disulfide and various alkali doping procedures were studied to determine if various preparation paramenters affected catalyst activity. Testing was performed on an undoped molybdenum disulfide sample with H{sub 2}/CO = 1 synthesis gas at 8.1 MPa and at temperatures of 245, 255, 265, 275, 280, 300, 320, and 295C, and only hydrocarbons were formed. A methanol injection experiment with undoped catalyst showed that homologation of methanol did not occur over the undoped MOS{sub 2}. Catalytic testing on a cesium formate doped molybdenum disulfide catalyst corresponding to 9 wt% Cs/MoS{sub 2} at 8.1 MPa and temperatures of 245, 255, 265, 275, 285, and 295C, mostly linear alcohols. The CS/MOS{sub 2} sample was protected from air exposure during preparation and testiag. As with the other recently tested alkali-promoted MOS{sub 2} catalysts, this cataylst was not as active as previous CS/MOS{sub 2} catalysts [1], and some deactivation during these systematic studies was observed. X-Ray powder diffraction and BET surface area measurements are being used to characterize the catalysts, and electron microscopy analyses are being carried out.

  17. Ethanol synthesis and water gas shift over bifunctional sulfide catalysts. Technical progress report, March 1993--May 1993

    SciTech Connect

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

    1993-06-01

    Study of preparation of MoS{sub 3}, decomposition to form MoS{sub 2}, and the Cs-containing reagents and techniques to achieve surface doping of the MoS{sub 2} with Cs was begun. Goal is to achieve a high surface area catalyst containing lower quantities of the Cs promoter in a highly dispersed state. Using high resolution electron spectroscopy for chemical analysis and solid state Extended Hueckel (EH) theory investigation and interpretation of electronic structure of MoS{sub 2} (hexagonal 2H form, 2 MoS{sub 2} molecules/unit cell) was carried out. The theoretical valence band of MoS{sub 2} was obtained by modification of density of states. Qualitative agreement theoretical and experimental MoS{sub 2} valence bands was obtained after parameterization of EH input ionization potentials H{sub ii} and Slater-type orbital (STO) double zeta coefficients c{sub i}. Theoretical energy dispersion curves 2-D and 3-D MoS{sub 2} also compared well with experimental energy dispersion curves. Highest occupied band of valence band is shown to consist of contributions not only from Mo 4d{sub z2} orbitals but also from Mo 4d{sub xy} and Mo 4d{sub x2-y2} orbitals. The theoretical systems 2-D MoS{sub 2} and 3-D MoS{sub 2}, containing zero for the former and an infinite number of Van der Waals gaps for the latter, exhibit direct and indirect gaps, respectively. Nature of 2H-MoS{sub 2} indirect gap is found to be directly linked to the interaction of crystal orbitals across Van der Waals gap between adjacent layers of MoS{sub 2} in the realistic 3-D model. Thus, the electronic properties and ability of adsorbing and activating hydrogen of very small and thin particles of MoS{sub 2} might be expected to be different from large bulk particles of MoS{sub 2}.

  18. Ethanol synthesis and water gas shift over bifunctional sulfide catalysts. Technical progress report, September 1992--November 1992

    SciTech Connect

    Klier, K.; Herman, R.G.; Deemer, M.

    1992-12-01

    During this quarter, the surface areas of various catalysts were determined. The surface area of the catalyst tested last quarter was determined for the undoped catalyst, the doped catalyst before testing, and the doped catalyst after testing. These surface areas were then compared with ones reported earlier. After testing under high temperature and high pressure conditions for 551 hours, there was a loss of surface area. This might be due possibly to agglomeration of cesium formate on the surface. Higher surface area catalysts were also produced. Two samples of MoS{sub 2} were synthesized with surface areas of 96 m2/g and 91 m2/g. These were obtained by varying the heating rate of MoS{sub 3} and the calcination temperature.

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

    DOEpatents

    Bamberger, C.E.; Robinson, P.R.

    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 cyclic 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.

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

    DOEpatents

    Bamberger, Carlos E.; Robinson, Paul R.

    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.

  1. Fluid Shifts

    NASA Technical Reports Server (NTRS)

    Stenger, Michael; Hargens, A.; Dulchavsky, S.; Ebert, D.; Lee, S.; Sargsyan, A.; Martin, D.; Lui, J.; Macias, B.; Arbeille, P.; Platts, S.

    2014-01-01

    NASA is focusing on long-duration missions on the International Space Station (ISS) and future exploration-class missions beyond low Earth orbit. Visual acuity changes observed after short-duration missions were largely transient, but more than 30% of ISS astronauts experience more profound, chronic changes with objective structural and functional findings such as papilledema and choroidal folds. Globe flattening, optic nerve sheath dilation, and optic nerve tortuosity also are apparent. This pattern is referred to as the visual impairment and intracranial pressure (VIIP) syndrome. VIIP signs and symptoms, as well as postflight lumbar puncture data, suggest that elevated intracranial pressure (ICP) may be associated with the space flight-induced cephalad fluid shifts, but this hypothesis has not been tested. The purpose of this study is to characterize fluid distribution and compartmentalization associated with long-duration space flight, and to correlate these findings with vision changes and other elements of the VIIP syndrome. We also seek to determine whether the magnitude of fluid shifts during space flight, as well as the VIIP-related effects of those shifts, is predicted by the crewmember's pre-flight condition and responses to acute hemodynamic manipulations (such as head-down tilt). Lastly, we will evaluate the patterns of fluid distribution in ISS astronauts during acute reversal of fluid shifts through application of lower body negative pressure (LBNP) interventions to characterize and explain general and individual responses. We will examine a variety of physiologic variables in 10 long-duration ISS crewmembers using the test conditions and timeline presented in the Figure below. Measures include: (1) fluid compartmentalization (total body water by D2O, extracellular fluid by NaBr, intracellular fluid by calculation, plasma volume by CO rebreathe, interstitial fluid by calculation); (2) forehead/eyelids, tibia, calcaneus tissue thickness (by ultrasound

  2. Effect of intramolecular Paternò-Büchi reaction on the thermodynamics and kinetics of nearly degenerate [3,3]-sigmatropic shift in fluxional polycycles.

    PubMed

    Valiulin, Roman A; Dressen, Donald G; Riggs, Jennifer R; Habte, Faven M; Kutateladze, Andrei G

    2009-05-01

    In reactions with weak dienophiles, cyclooctatetraene (COT) often yields 2:1 adducts possessing the fluxional bicyclo[5.1.0]octadiene moiety. They undergo fast, nearly degenerate Cope rearrangement with an activation barrier similar to that of the parent dihydrobullvalene. Irradiation to excite the carbonyl moiety induces an intramolecular Paterno-Buchi cyclization yielding endo-oxetanes and significantly changing the Cope-averaged NMR spectra. In this paper we examine the effect of skeletal distortion caused by intramolecular [2 + 2]-photoaddition on thermodynamics and the activation barrier of the [3,3]-sigmatropic tautomerism. Our finding is that such a distortion lifts the energetic degeneracy of the two valence tautomers, while not affecting the activation barrier. PMID:19344135

  3. The reaction of European lobster larvae (Homarus gammarus) to different quality food: effects of ontogenetic shifts and pre-feeding history.

    PubMed

    Schoo, Katherina L; Aberle, Nicole; Malzahn, Arne M; Schmalenbach, Isabel; Boersma, Maarten

    2014-02-01

    Young larval stages of many organisms represent bottlenecks in the life-history of many species. The high mortality commonly observed in, for example, decapod larvae has often been linked to poor nutrition, with most studies focussing on food quantity. Here, we focus instead on the effects of quality and have investigated its effects on the nutritional condition of lobster larvae. We established a tri-trophic food chain consisting of the cryptophyte Rhodomonas salina, the calanoid copepod Acartia tonsa and larvae of the European lobster Homarus gammarus. In a set of experiments, we manipulated the C:N:P stoichiometry of the primary producers, and accordingly those of the primary consumer. In a first experiment, R. salina was grown under N- and P-limitation and the nutrient content of the algae was manipulated by addition of the limiting nutrient to create a food quality gradient. In a second experiment, the effect on lobster larvae of long- and short-term exposure to food of varying quality during ontogenetic development was investigated. The condition of the lobster larvae was negatively affected even by subtle N- and P-nutrient limitations of the algae. Furthermore, younger lobster larvae were more vulnerable to nutrient limitation than older ones, suggesting an ontogenetic shift in the capacity of lobster larvae to cope with low quality food. The results presented here might have substantial consequences for the survival of lobster larvae in the field, as, in the light of future climate change and re-oligotrophication of the North Sea, lobster larvae might face marked changes in temperature and nutrient conditions, thus significantly altering their condition and growth. PMID:24072442

  4. 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.

  5. Acetic Acid Reforming over Rh Supported on La2O3/CeO2-ZrO2: Catalytic Performance and Reaction Pathway Analysis

    SciTech Connect

    Lemonidou, Angeliki A.; Vagia, Ekaterini C.; Lercher, Johannes A.

    2013-07-11

    Reforming of acetic acid was investigated on Rh supported on CeO2-ZrO2 modified with 3 wt % La. The active catalyst converted acetic acid to H-2-rich gas and hardly formed coke. The low rate of coke formation is concluded to be related to the presence of redox-active oxygen limiting the concentration of coke precursors. Temperature-programmed O-18(2)) isotope exchange measurements showed that the La2O3 and Rh enhanced the mobility of lattice oxygen compared with that of the parent CeO2-ZrO2. Ketonization and decarboxylation of acetic acid are the dominating reactions over the latter up to 600 degrees C, whereas above 600 degrees C, steam reforming and water gas shift also contribute. Over 0.5 wt % Rh on La2O3/CeO2-ZrO2, reforming and water gas shift reactions dominate, even below 300 degrees C, producing mostly H-2 and CO2. Using isotope labeling, it is shown that acetic acid adsorbs dissociatively on Rh, forming acetates, which sequentially decarboxylate and form surface methyl groups. The latter are in turn converted to CO, CO2, and H-2.

  6. 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

  7. The adsorption behavior of octafluoropropane at the water/gas interface

    SciTech Connect

    Giebel, Friederike; Paulus, Michael; Nase, Julia Bieder, Steffen; Kiesel, Irena; Tolan, Metin

    2014-12-14

    We studied the adsorption behavior of the gas octafluoropropane at the water/gas interface as a function of different pressures. In a custom-made measurement cell, the gas pressure was varied in a range between 1 bar and close to the condensation pressure of octafluoropropane. The electron density profiles of the adsorption layers show that the layer thickness increases with pressure. The evolution of the layer electron density indicates that the bulk electron density is reached if a layer consisting of more than one monolayer of octafluoropropane is adsorbed on the water surface.

  8. Integrated reformer and shift reactor

    SciTech Connect

    Bentley, Jeffrey M.; Clawson, Lawrence G.; Mitchell, William L.; Dorson, Matthew H.

    2006-06-27

    A hydrocarbon fuel reformer for producing diatomic hydrogen gas is disclosed. The reformer includes a first reaction vessel, a shift reactor vessel annularly disposed about the first reaction vessel, including a first shift reactor zone, and a first helical tube disposed within the first shift reactor zone having an inlet end communicating with a water supply source. The water supply source is preferably adapted to supply liquid-phase water to the first helical tube at flow conditions sufficient to ensure discharge of liquid-phase and steam-phase water from an outlet end of the first helical tube. The reformer may further include a first catalyst bed disposed in the first shift reactor zone, having a low-temperature shift catalyst in contact with the first helical tube. The catalyst bed includes a plurality of coil sections disposed in coaxial relation to other coil sections and to the central longitudinal axis of the reformer, each coil section extending between the first and second ends, and each coil section being in direct fluid communication with at least one other coil section.

  9. Fischer-Tropsch synthesis over iron-based catalysts in slurry reactors. Reaction rates, kinetics and implications for improving hydrocarbon productivity

    SciTech Connect

    Raje, A.P.; Davis, B.H.

    1996-10-01

    The Fischer-Tropsch (FT) synthesis is carried out over a high activity precipitated iron catalyst promoted with silica and potassium in a slurry reactor. Reaction rates (FTS and water gas shift) and partial pressures are evaluated over a wide range of CO conversions (10 to 90%) and space velocities at 270{degrees}C, 175 psig and a H{sub 2}/CO ratio of 0.67. The partial pressure of water exhibits a maximum at intermediate CO conversion. Both the fraction of CO converted to hydrocarbons and the hydrocarbon space time yield decrease with increasing CO conversion. This implies that it would be beneficial to have lower conversion per pass in the reactor with recycle to achieve a high overall conversion. The data as well as experiments with water and CO{sub 2} addition enable us to determine a kinetic expression for the catalyst which shows negligible inhibition of the reaction rate by water or CO{sub 2}.

  10. Unusual 1H NMR chemical shifts support (His) C(epsilon) 1...O==C H-bond: proposal for reaction-driven ring flip mechanism in serine protease catalysis.

    PubMed

    Ash, E L; Sudmeier, J L; Day, R M; Vincent, M; Torchilin, E V; Haddad, K C; Bradshaw, E M; Sanford, D G; Bachovchin, W W

    2000-09-12

    13C-selective NMR, combined with inhibitor perturbation experiments, shows that the C(epsilon)(1)H proton of the catalytic histidine in resting alpha-lytic protease and subtilisin BPN' resonates, when protonated, at 9.22 ppm and 9.18 ppm, respectively, which is outside the normal range for such protons and approximately 0.6 to 0.8 ppm further downfield than previously reported. They also show that the previous alpha-lytic protease assignments [Markley, J. L., Neves, D. E., Westler, W. M., Ibanez, I. B., Porubcan, M. A. & Baillargeon, M. W. (1980) Front. Protein Chem. 10, 31-61] were to signals from inactive or denatured protein. Simulations of linewidth vs. pH demonstrate that the true signal is more difficult to detect than corresponding signals from inactive derivatives, owing to higher imidazole pK(a) values and larger chemical shift differences between protonated and neutral forms. A compilation and analysis of available NMR data indicates that the true C(epsilon)(1)H signals from other serine proteases are similarly displaced downfield, with past assignments to more upfield signals probably in error. The downfield displacement of these proton resonances is shown to be consistent with an H-bond involving the histidine C(epsilon)(1)H as donor, confirming the original hypothesis of Derewenda et al. [Derewenda, Z. S., Derewenda, U. & Kobos, P. M. (1994) J. Mol. Biol. 241, 83-93], which was based on an analysis of literature x-ray crystal structures of serine hydrolases. The invariability of this H-bond among enzymes containing Asp-His-Ser triads indicates functional importance. Here, we propose that it enables a reaction-driven imidazole ring flip mechanism, overcoming a major dilemma inherent in all previous mechanisms, namely how these enzymes catalyze both the formation and productive breakdown of tetrahedral intermediates. PMID:10984533

  11. Unusual 1H NMR chemical shifts support (His) Cɛ1—H⋅⋅⋅O⩵C H-bond: Proposal for reaction-driven ring flip mechanism in serine protease catalysis

    PubMed Central

    Ash, Elissa L.; Sudmeier, James L.; Day, Regina M.; Vincent, Matthew; Torchilin, Ekaterina V.; Haddad, Kristin Coffman; Bradshaw, Elizabeth M.; Sanford, David G.; Bachovchin, William W.

    2000-01-01

    13C-selective NMR, combined with inhibitor perturbation experiments, shows that the Cɛ1—H proton of the catalytic histidine in resting α-lytic protease and subtilisin BPN′ resonates, when protonated, at 9.22 ppm and 9.18 ppm, respectively, which is outside the normal range for such protons and ≈0.6 to 0.8 ppm further downfield than previously reported. They also show that the previous α-lytic protease assignments [Markley, J. L., Neves, D. E., Westler, W. M., Ibanez, I. B., Porubcan, M. A. & Baillargeon, M. W. (1980) Front. Protein Chem. 10, 31–61] were to signals from inactive or denatured protein. Simulations of linewidth vs. pH demonstrate that the true signal is more difficult to detect than corresponding signals from inactive derivatives, owing to higher imidazole pKa values and larger chemical shift differences between protonated and neutral forms. A compilation and analysis of available NMR data indicates that the true Cɛ1—H signals from other serine proteases are similarly displaced downfield, with past assignments to more upfield signals probably in error. The downfield displacement of these proton resonances is shown to be consistent with an H-bond involving the histidine Cɛ1—H as donor, confirming the original hypothesis of Derewenda et al. [Derewenda, Z. S., Derewenda, U. & Kobos, P. M. (1994) J. Mol. Biol. 241, 83–93], which was based on an analysis of literature x-ray crystal structures of serine hydrolases. The invariability of this H-bond among enzymes containing Asp-His-Ser triads indicates functional importance. Here, we propose that it enables a reaction-driven imidazole ring flip mechanism, overcoming a major dilemma inherent in all previous mechanisms, namely how these enzymes catalyze both the formation and productive breakdown of tetrahedral intermediates. PMID:10984533

  12. Psychopathology of Shift Work.

    ERIC Educational Resources Information Center

    Akinnawo, Ebenezer Olutope

    1989-01-01

    Examined incidence and nature of general psychopathology among Nigerian shift workers (N=320). Found shift workers more significantly psychopathological than non-shift workers (p<0.001). Prominent disorders among shift workers were intellectual, sleep, mood, and general somatic disorders. No significant difference could be attributed to gender and…

  13. Near-surface physics during convection affecting air-water gas transfer

    NASA Astrophysics Data System (ADS)

    Fredriksson, S. T.; Arneborg, L.; Nilsson, H.; Handler, R. A.

    2016-05-01

    The gas flux at the water surface is affected by physical processes including turbulence from wind shear, microscale wave breaking, large-scale breaking, and convection due to heat loss at the surface. The main route in the parameterizations of the gas flux has been to use the wind speed as a proxy for the gas flux velocity, indirectly taking into account the dependency of the wind shear and the wave processes. The interest in the contributions from convection processes has increased as the gas flux from inland waters (with typically lower wind and sheltered conditions) now is believed to play a substantial role in the air-water gas flux budget. The gas flux is enhanced by convection through the mixing of the mixed layer as well as by decreasing the diffusive boundary layer thickness. The direct numerical simulations performed in this study are shown to be a valuable tool to enhance the understanding of this flow configuration often present in nature.

  14. Sorption enhanced reaction process (SERP) for production of hydrogen

    SciTech Connect

    Sircar, S.; Anand, M.; Carvill, B.

    1995-09-01

    Sorption Enhanced Reaction (SER) is a novel process that is being developed for the production of lower cost hydrogen by steam-methane reforming (SMR). In this process, the reaction of methane with steam is carried out in the presence of an admixture of a catalyst and a selective adsorbent for carbon dioxide. The consequences of SER are: (1) reformation reaction at a significantly lower temperature (300-500{degrees}C) than conventional SMR (800-1100{degrees}C), while achieving the same conversion of methane to hydrogen, (2) the product hydrogen is obtained at reactor pressure (200-400 psig) and at 99+% purity directly from the reactor (compared to only 70-75% H{sub 2} from conventional SMR reactor), (3) downstream hydrogen purification step is either eliminated or significantly reduced in size. The early focus of the program will be on the identification of an adsorbent/chemisorbent for CO{sub 2} and on the demonstration of the SER concept for SMR in our state-of-the-art bench scale process. In the latter stages, a pilot plant will be built to scale-up the technology and to develop engineering data. The program has just been initiated and no significant results for SMR will be reported. However, results demonstrating the basic principles and process schemes of SER technology will be presented for reverse water gas shift reaction as the model reaction. If successful, this technology will be commercialized by Air Products and Chemicals, Inc. (APCI) and used in its existing hydrogen business. APCI is the world leader in merchant hydrogen production for a wide range of industrial applications.

  15. Tandem pseudopericyclic reactions: [1,5]-X sigmatropic shift/6pi-electrocyclic ring closure converting N-(2-X-carbonyl)phenyl ketenimines into 2-X-quinolin-4(3H)-ones.

    PubMed

    Alajarín, Mateo; Ortín, María-Mar; Sanchez-Andrada, Pilar; Vidal, Angel

    2006-10-13

    N-(2-X-Carbonyl)phenyl ketenimines undergo, under mild thermal conditions, [1,5]-migration of the X group from the carbonyl carbon to the electron-deficient central carbon atom of the ketenimine fragment, followed by a 6pi-electrocyclic ring closure of the resulting ketene to provide 2-X-substituted quinolin-4(3H)-ones in a sequential one-pot manner. The X groups tested are electron-donor groups, such as alkylthio, arylthio, arylseleno, aryloxy, and amino. When involving alkylthio, arylthio, and arylseleno groups, the complete transformation takes place in refluxing toluene, whereas for aryloxy and amino groups the starting ketenimines must be heated at 230 degrees C in a sealed tube in the absence of solvent. The mechanism for the conversion of these ketenimines into quinolin-4(3H)-ones has been studied by ab initio and DFT calculations, using as model compounds N-(2-X-carbonyl)vinyl ketenimines bearing different X groups (X = F, Cl, OH, SH, NH(2), and PH(2)) converting into 4(3H)-pyridones. This computational study afforded two general reaction pathways for the first step of the sequence, the [1,5]-X shift, depending on the nature of X. When X is F, Cl, OH, or SH, the migration occurs in a concerted mode, whereas when X is NH(2) or PH(2), it involves a two-step sequence. The order of migratory aptitudes of the X substituents at the acyl group is predicted to be PH(2) > Cl > SH > NH(2) > F> OH. The second step of the full transformation, the 6pi-electrocyclic ring closure, is calculated to be concerted and with low energy barriers in all the cases. We have included in the calculations an alternative mode of cyclization of the N-(2-X-carbonyl)vinyl ketenimines, the 6pi-electrocyclic ring closure leading to 1,3-oxazines that involves its 1-oxo-5-aza-1,3,5-hexatrienic system. Additionally, the pseudopericyclic topology of the transition states for some of the [1,5]-X migrations (X = F, Cl, OH, SH), for the 6pi-electrocyclization of the ketene intermediates to the 4

  16. Energy phase shift as mechanism for catalysis

    NASA Astrophysics Data System (ADS)

    Beke-Somfai, Tamás; Feng, Bobo; Nordén, Bengt

    2012-05-01

    Catalysts are agents that by binding reactant molecules lower the energy barriers to chemical reaction. After reaction the catalyst is regenerated, its unbinding energy recruited from the environment, which is associated with an inevitable loss of energy. We show that combining several catalytic sites to become energetically and temporally phase-shifted relative to each other provides a possibility to sustain the overall reaction by internal 'energy recycling', bypassing the need for thermal activation, and in principle allowing the system to work adiabatically. Using an analytical model for superimposed, phase-shifted potentials of F1-ATP synthase provides a description integrating main characteristics of this rotary enzyme complex.

  17. 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.

  18. Theoretical study on the reaction mechanism of the gas-phase H2/CO2/Ni(3D) system.

    PubMed

    Qin, Song; Hu, Changwei; Yang, Huaqing; Su, Zhishan

    2005-07-28

    The ground-state potential energy surface (PES) in the gas-phase H2/CO2/Ni(3D) system is investigated at the CCSD(T)//B3LYP/6-311+G(2d,2p) levels in order to explore the possible reaction mechanism of the reverse water gas shift reaction catalyzed by Ni(3D). The calculations predict that the C-O bond cleavage of CO2 assisted by co-interacted H2 is prior to the dissociation of the H2, and the most feasible reaction path for Ni(3D) + H2 + CO2 --> Ni(3D) + H2O + CO is endothermic by 12.5 kJ mol(-1) with an energy barrier of 103.9 kJ mol(-1). The rate-determining step for the overall reaction is predicted to be the hydrogen migration with water formation. The promotion effect of H2 on the cleavage of C-O bond in CO2 is also discussed and compared with the analogous reaction of Ni(3D) + CO2 --> NiO + CO, and the difference between triplet and singlet H2/CO2/Ni systems is also discussed. PMID:16833994

  19. Methanol synthesis via CO2 hydrogenation over a Au/ZnO catalyst: an isotope labelling study on the role of CO in the reaction process.

    PubMed

    Hartadi, Yeusy; Widmann, Daniel; Behm, R Jürgen

    2016-04-20

    Methanol synthesis for chemical energy storage, via hydrogenation of CO2 with H2 produced by renewable energies, is usually accompanied by the undesired formation of CO via the reverse water-gas shift reaction. Aiming at a better mechanistic understanding of methanol formation from CO2/H2 on highly selective supported Au/ZnO catalysts we have investigated the role of CO in the reaction process using isotope labelling experiments. Using (13)C-labelled CO2, we found for reaction at 5 bar and 240 °C that (i) the methanol formation rate is significantly higher in CO2-containing gas mixtures than in a CO2-free mixture and (ii) in mixtures containing both CO2 and CO methanol formation from CO increases with the CO content up to 1% CO, and then remains at 20% of the total methanol formation up to a CO2/CO ratio of 1/1, making CO2 the preferred carbon source in these mixtures. A shift in the preferred carbon source for MeOH from CO2 towards CO is observed with increasing reaction temperatures between 240 °C and 300 °C. At even higher temperatures CO is expected to become the dominant carbon source. The consequences of these findings for the application of Au/ZnO catalysts for chemical storage of renewable energies are discussed. PMID:26923815

  20. In-water gas combustion in linear and annular gas bubbles

    NASA Astrophysics Data System (ADS)

    Teslenko, V. S.; Drozhzhin, A. P.; Medvedev, R. N.; Batraev, I. S.

    2014-08-01

    A new pulsed-cyclic method of in-water gas combustion was developed with separate feed of fuel gas and oxygen with the focus on development of new technologies for heat generators and submerged propellers. The results of calorimetric and hydrodynamic measurements are presented. In-water combustion of acetylene, hydrogen, and propane was tested with the operation frequency of 2-2.5 Hz and with a linear injector. The combustion dynamics of combustion of stoichiometric mixture with propane (C3H8+5O2) was studied for a bubble near a solid wall; the produced gas bubble continues expansion and oscillations (for the case of linear and annular bubbles). It was demonstrated that gas combustion in annular bubbles produces two same-magnitude pulses of force acting on the wall. The first pulse is produced due to expansion of combustion products, and the second pulse is produced due to axial cumulative processes after bubble collapse. This process shapes an annular vortex which facilitates high-speed convective processes between combustion products and liquid; and this convection produces small-size bubbles.

  1. Air-Water Gas Exchange in Wetland Water Columns Due To Wind and Thermal Convection

    NASA Astrophysics Data System (ADS)

    Poindexter, C.; Variano, E. A.

    2011-12-01

    The goal of this work is to provide a parameterization of the air-water gas transfer rate in wetlands, and do so in terms of easily measured environmental variables. This parameterization is intended to support biogeochemical modeling in wetlands by providing an interfacial flux of key importance. Our approach uses laboratory experiments describe the oxygen transfer across an air-water interface in a model wetland. The oxygen transfer is sensitive to the externally imposed wind, vegetation characteristics, and vertical thermal convection. We vary these systematically, determining the gas transfer (or "piston") velocity that describes interfacial gas flux. We measure velocity vector fields near the air-water interface using particle image velocimetry, and use these measurements to help explain the mechanisms behind the measured trends in oxygen transfer. The explanatory power of these measurements includes the relationship between plant geometry and surface divergence. We explore the potential impact of our results on wetland modeling and management, for issues such as carbon sequestration and methane emission.

  2. Molecular implementation of molecular shift register memories

    NASA Technical Reports Server (NTRS)

    Beratan, David N. (Inventor); Onuchic, Jose N. (Inventor)

    1991-01-01

    An electronic shift register memory (20) at the molecular level is described. The memory elements are based on a chain of electron transfer molecules (22) and the information is shifted by photoinduced (26) electron transfer reactions. Thus, multi-step sequences of charge transfer reactions are used to move charge with high efficiency down a molecular chain. The device integrates compositions of the invention onto a VLSI substrate (36), providing an example of a molecular electronic device which may be fabricated. Three energy level schemes, molecular implementation of these schemes, optical excitation strategies, charge amplification strategies, and error correction strategies are described.

  3. Reactions of oxygen-containing molecules on transition metal carbides: Surface science insight into potential applications in catalysis and electrocatalysis

    NASA Astrophysics Data System (ADS)

    Stottlemyer, Alan L.; Kelly, Thomas G.; Meng, Qinghe; Chen, Jingguang G.

    2012-09-01

    Historically the interest in the catalytic properties of transition metal carbides (TMC) has been inspired by their "Pt-like" properties in the transformation reactions of hydrocarbon molecules. Recent studies, however, have revealed that the reaction pathways of oxygen-containing molecules are significantly different between TMCs and Pt-group metals. Nonetheless, TMCs demonstrate intriguing catalytic properties toward oxygen-containing molecules, either as the catalyst or as the catalytically active substrate to support metal catalysts, in several important catalytic and electrocatalytic applications, including water electrolysis, alcohol electrooxidation, biomass conversion, and water gas shift reactions. In the current review we provide a summary of theoretical and experimental studies of the interaction of TMC surfaces with oxygen-containing molecules, including both inorganic (O2, H2O, CO and CO2) and organic (alcohols, aldehydes, acids and esters) molecules. We will discuss the general trends in the reaction pathways, as well as future research opportunities in surface science studies that would facilitate the utilization of TMCs as catalysts and electrocatalysts.

  4. Reactions of oxygen-containing molecules on transition metal carbides: Surface science insight into potential applications in catalysis and electrocatalysis

    NASA Astrophysics Data System (ADS)

    Stottlemyer, Alan L.; Kelly, Thomas G.; Meng, Qinghe; Chen, Jingguang G.

    2012-09-01

    Historically the interest in the catalytic properties of transition metal carbides (TMC) has been inspired by their “Pt-like” properties in the transformation reactions of hydrocarbon molecules. Recent studies, however, have revealed that the reaction pathways of oxygen-containing molecules are significantly different between TMCs and Pt-group metals. Nonetheless, TMCs demonstrate intriguing catalytic properties toward oxygen-containing molecules, either as the catalyst or as the catalytically active substrate to support metal catalysts, in several important catalytic and electrocatalytic applications, including water electrolysis, alcohol electrooxidation, biomass conversion, and water gas shift reactions. In the current review we provide a summary of theoretical and experimental studies of the interaction of TMC surfaces with oxygen-containing molecules, including both inorganic (O2, H2O, CO and CO2) and organic (alcohols, aldehydes, acids and esters) molecules. We will discuss the general trends in the reaction pathways, as well as future research opportunities in surface science studies that would facilitate the utilization of TMCs as catalysts and electrocatalysts.

  5. 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.

  6. Shifting scintillator neutron detector

    SciTech Connect

    Clonts, Lloyd G; Cooper, Ronald G; Crow, Jr., Morris Lowell; Hannah, Bruce W; Hodges, Jason P; Richards, John D; Riedel, Richard A

    2014-03-04

    Provided are sensors and methods for detecting thermal neutrons. Provided is an apparatus having a scintillator for absorbing a neutron, the scintillator having a back side for discharging a scintillation light of a first wavelength in response to the absorbed neutron, an array of wavelength-shifting fibers proximate to the back side of the scintillator for shifting the scintillation light of the first wavelength to light of a second wavelength, the wavelength-shifting fibers being disposed in a two-dimensional pattern and defining a plurality of scattering plane pixels where the wavelength-shifting fibers overlap, a plurality of photomultiplier tubes, in coded optical communication with the wavelength-shifting fibers, for converting the light of the second wavelength to an electronic signal, and a processor for processing the electronic signal to identify one of the plurality of scattering plane pixels as indicative of a position within the scintillator where the neutron was absorbed.

  7. Data for phase angle shift with frequency.

    PubMed

    Paul, T; Banerjee, D; Kargupta, K

    2016-06-01

    Phase angle shift between the current and voltage with frequency has been reported for a single phosphoric acid fuel cell in the cell temperature from 100 °C to 160 °C and the humidifier temperature from 40 °C to 90 °C. An electrochemical workbench is employed to find the shift. The figure of phase angle shift shows a peak in high humidifier temperatures. The peak in phase angle shift directs to lower frequency side with decreasing humidifier temperature. The estimation of electrochemical reaction time is also evaluated in the humidifier temperature zone from 50 °C to 90 °C. PMID:27158655

  8. Data for phase angle shift with frequency

    PubMed Central

    Paul, T.; Banerjee, D.; Kargupta, K.

    2016-01-01

    Phase angle shift between the current and voltage with frequency has been reported for a single phosphoric acid fuel cell in the cell temperature from 100 °C to 160 °C and the humidifier temperature from 40 °C to 90 °C. An electrochemical workbench is employed to find the shift. The figure of phase angle shift shows a peak in high humidifier temperatures. The peak in phase angle shift directs to lower frequency side with decreasing humidifier temperature. The estimation of electrochemical reaction time is also evaluated in the humidifier temperature zone from 50 °C to 90 °C. PMID:27158655

  9. Our World: Fluid Shift

    NASA Video Gallery

    Learn about the circulatory system and how gravity aids blood flow in our bodies here on Earth. Find out how NASA flight surgeons help the astronauts deal with the fluid shift that happens during s...

  10. Shape-Shifting Plastic

    SciTech Connect

    2015-05-20

    A new plastic developed by ORNL and Washington State University transforms from its original shape through a series of temporary shapes and returns to its initial form. The shape-shifting process is controlled through changes in temperature

  11. 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.

  12. Kinetics of the Fischer-Tropsch reaction on a precipitated promoted iron catalyst. 1. Experimental procedure and results

    SciTech Connect

    Lox, E.S.; Froment, G.F. )

    1993-01-01

    The Fischer-Tropsch reaction on a commercial promoted precipitated iron catalyst was studied in a tubular reactor under non-deactivating conditions of temperatures between 523 and 623 K, pressures between 0.6 and 2.1 MPa, hydrogen to carbon monoxide feed ratios between 3.0 and 6.0 mol/mol, and W/F[degree][sub CO] values between 9.2 and 63.0 kg[center dot]s/mol. The selectivity for carbon dioxide, methane, and hydrocarbons of different functionality with 2-15 carbon atoms in the molecule was obtained as a function of the carbon monoxide conversion, the reactor temperature, and the total pressure. The initial rate of formation of these products was measured as a function of the total pressure and the partial pressures of hydrogen and carbon monoxide at the reactor inlet. These experiments, combined with the information gained from the catalyst characterization, indicated that carbon dioxide is formed by the water gas shift reaction. Methane, n-paraffins, and 1-olefins with two and more carbon atoms in the molecule are all primary products of the Fischer-Tropsch reaction. The composition of the hydrocarbon product fraction, as a function of the number of carbon atoms in the hydrocarbon molecule, could be described by the Schulz-Flory distribution, although it is shown that the latter only approximately holds for the effluent of an integral reactor.

  13. Ammonia reactions with the stored oxygen in a commercial lean NOx trap catalyst

    DOE PAGESBeta

    Bartova, Sarka; Mracek, David; Koci, Petr; Marek, Milos; Choi, Jae -Soon

    2014-10-12

    Ammonia is an important intermediate of the NOx reduction in a NOx storage and reduction catalyst (aka lean NOx trap). NH3 formed under rich conditions in the reduced front part of the catalyst is transported by convection downstream to the unregenerated (still oxidized) zone of the catalyst, where it further reacts with the stored oxygen and NOx. In this paper, the kinetics and selectivity of NH3 reactions with the stored oxygen are studied in detail with a commercial Ba-based NOx storage catalyst containing platinum group metals (PGM), Ba and Ce oxides. Furthermore, steady-state NH3 decomposition, NH3 oxidation by O2 andmore » NO, and N2O decomposition are examined in light-off experiments. Periodic lean/rich cycling is measured first with O2 and NH3, and then with NOx + O2 and NH3 to discriminate between the NH3 reactions with the stored oxygen and the stored NOx. The reaction of NH3 with the stored O2 is highly selective towards N2, however a certain amount of NOx and N2O is also formed. The formed NOx by-product is efficiently adsorbed on the NOx storage sites such that the NOx is not detected at the reactor outlet except at high temperatures. The stored NOx reacts with NH3 feed in the next rich phase, contributing to the N2O formation. Water inhibits the reactions of NH3 with the stored oxygen. On the contrary, the presence of CO2 increases the NH3 consumption. Furthermore, CO2 is able to provide additional oxygen for NH3 oxidation, forming –CO in analogy to the reverse water gas shift reaction.« less

  14. Hot compressed water—a suitable and sustainable solvent and reaction medium?

    NASA Astrophysics Data System (ADS)

    Dinjus, E.; Kruse, A.

    2004-04-01

    cobalt-catalysed cyclotrimerization of acetylenes to form benzene derivatives or hydroformylation to produce aldehydes from olefins. There, only the addition of CO is necessary, the H2 required being formed by the equilibrium of the water-gas-shift reaction. After a homogeneous reaction in the supercritical state, the reaction mixture can be separated at subcritical conditions. In support of the chemical and technical developments and to principally understand the experimental findings fundamental aspects have to be investigated as well. Intensive studies have been devoted to chemical kinetics including the modelling with elementary reaction steps, e.g. to separate ionic and radical reaction pathways. Depending on the reaction conditions, ionic or radical reaction pathways can be favoured or suppressed, allowing for control selectivity. Furthermore, corrosion of relevant reactor materials has been investigated.

  15. Absorption driven focus shift

    NASA Astrophysics Data System (ADS)

    Harrop, N.; Wolf, S.; Maerten, O.; Dudek, K.; Ballach, S.; Kramer, R.

    2016-03-01

    Modern high brilliance near infrared lasers have seen a tremendous growth in applications throughout the world. Increased productivity has been achieved by higher laser power and increased brilliance of lasers. Positive impacts on the performance and costs of parts are opposed to threats on process stability and quality, namely shift of focus position over time. A high initial process quality will be reduced by contamination of optics, eventually leading to a focus shift or even destruction of the optics. Focus analysis at full power of multi-kilowatt high brilliance lasers is a very demanding task because of high power densities in the spot and the high power load on optical elements. With the newly developed high power projection optics, the High-Power Micro-Spot Monitor High Brilliance (HP-MSM-HB) is able to measure focus diameter as low as 20 μm at power levels up to 10 kW at very low internal focus shift. A main driving factor behind thermally induced focus shift is the absorption level of the optical element. A newly developed measuring system is designed to determine the relative absorption level in reference to a gold standard. Test results presented show a direct correlation between absorption levels and focus shift. The ability to determine the absorption level of optical elements as well as their performance at full processing power before they are put to use, enables a high level of quality assurance for optics manufacturers and processing head manufacturers alike.

  16. Development of a mechanistic model for predicting corrosion rate in multiphase oil/water/gas flows

    SciTech Connect

    Zhang, R.; Gopal, M.; Jepson, W.P.

    1997-09-01

    A mechanistic model has been developed to predict corrosion rates in multiphase (water/oil/CO{sub 2}) flow conditions. The model takes into account electrochemistry, reaction kinetics, and, mass transport effects. This paper describes the equations used to determine pH and bulk concentrations of various ions, which are then used to calculate the mass transfer rates to the corrosion surface. The result includes the determination of the mass transfer coefficients of various ionic species and corrosion rates. Details of relations used for determination of mass transfer coefficients for multiphase flows, and rates of electrochemical reaction kinetics are discussed and predicted results are compared with experimental observations. Agreement between model results and experimental data is good.

  17. Predicting catastrophic shifts.

    PubMed

    Weissmann, Haim; Shnerb, Nadav M

    2016-05-21

    Catastrophic shifts are known to pose a serious threat to ecology, and a reliable set of early warning indicators is desperately needed. However, the tools suggested so far have two problems. First, they cannot discriminate between a smooth transition and an imminent irreversible shift. Second, they aimed at predicting the tipping point where a state loses its stability, but in noisy spatial system the actual transition occurs when an alternative state invades. Here we suggest a cluster tracking technique that solves both problems, distinguishing between smooth and catastrophic transitions and to identify an imminent shift in both cases. Our method may allow for the prediction, and thus hopefully the prevention of such transitions, avoiding their destructive outcomes. PMID:26970446

  18. Isotope shift in chromium

    NASA Astrophysics Data System (ADS)

    Furmann, B.; Jarosz, A.; Stefańska, D.; Dembczyński, J.; Stachowska, E.

    2005-01-01

    Thirty-three spectral lines of chromium atom in the blue-violet region (425-465 nm) have been investigated with the method of laser-induced resonance fluorescence on an atomic beam. For all the lines, the isotope shifts for every pair of chromium isotopes have been determined. The lines can be divided into six groups, according to the configuration of the upper and lower levels. Electronic factors of the field shift and the specific mass shift ( Fik and MikSMS, respectively) have been evaluated and the values for each pure configuration involved have been determined. Comparison of the values Fik and MikSMS to the ab initio calculations results has been performed. The presence of crossed second order (CSO) effects has been observed.

  19. AUDITORY-VISUAL PERCEPTUAL SHIFTING IN SPEECH HANDICAPPED CHILDREN.

    ERIC Educational Resources Information Center

    FLOWERS, ARTHUR

    INTERACTION BETWEEN VISION AND HEARING WERE STUDIED IN 35 SPEECH HANDICAPPED FIRST-GRADE CHILDREN. THE ABILITY TO SHIFT ATTENTION FROM ONE SENSORY MODALITY TO ANOTHER WAS LABELED AS "PERCEPTUAL SHIFTING." A DEVICE DEVELOPED BY EXPERIMENTAL PSYCHOLOGISTS PRESENTED VARIOUS STIMULI TO EACH SUBJECT AND RECORDED THE SUBJECT'S REACTION TIME. STIMULI…

  20. Design of a Molecular Memory Device: The Electron Transfer Shift Register Memory

    NASA Technical Reports Server (NTRS)

    Beratan, D.

    1993-01-01

    A molecular shift register memory at the molecular level is described. The memory elements consist of molecules can exit in either an oxidized or reduced state and the bits are shifted between the cells with photoinduced electron transfer reactions.

  1. Shifting Up a Gear.

    ERIC Educational Resources Information Center

    Palmer, Martin

    1997-01-01

    Shift workers are often excluded from educational opportunities on and off the job. General education and leisure learning needs are addressed less than job-specific training needs. Providers should consider open/distance learning, creative marketing, targeted funding, and consortia of employer-developed programs. (SK)

  2. Eluding catastrophic shifts

    PubMed Central

    Villa Martín, Paula; Bonachela, Juan A.; Levin, Simon A.; Muñoz, Miguel A.

    2015-01-01

    Transitions between regimes with radically different properties are ubiquitous in nature. Such transitions can occur either smoothly or in an abrupt and catastrophic fashion. Important examples of the latter can be found in ecology, climate sciences, and economics, to name a few, where regime shifts have catastrophic consequences that are mostly irreversible (e.g., desertification, coral reef collapses, and market crashes). Predicting and preventing these abrupt transitions remains a challenging and important task. Usually, simple deterministic equations are used to model and rationalize these complex situations. However, stochastic effects might have a profound effect. Here we use 1D and 2D spatially explicit models to show that intrinsic (demographic) stochasticity can alter deterministic predictions dramatically, especially in the presence of other realistic features such as limited mobility or spatial heterogeneity. In particular, these ingredients can alter the possibility of catastrophic shifts by giving rise to much smoother and easily reversible continuous ones. The ideas presented here can help further understand catastrophic shifts and contribute to the discussion about the possibility of preventing such shifts to minimize their disruptive ecological, economic, and societal consequences. PMID:25825772

  3. Eluding catastrophic shifts.

    PubMed

    Villa Martín, Paula; Bonachela, Juan A; Levin, Simon A; Muñoz, Miguel A

    2015-04-14

    Transitions between regimes with radically different properties are ubiquitous in nature. Such transitions can occur either smoothly or in an abrupt and catastrophic fashion. Important examples of the latter can be found in ecology, climate sciences, and economics, to name a few, where regime shifts have catastrophic consequences that are mostly irreversible (e.g., desertification, coral reef collapses, and market crashes). Predicting and preventing these abrupt transitions remains a challenging and important task. Usually, simple deterministic equations are used to model and rationalize these complex situations. However, stochastic effects might have a profound effect. Here we use 1D and 2D spatially explicit models to show that intrinsic (demographic) stochasticity can alter deterministic predictions dramatically, especially in the presence of other realistic features such as limited mobility or spatial heterogeneity. In particular, these ingredients can alter the possibility of catastrophic shifts by giving rise to much smoother and easily reversible continuous ones. The ideas presented here can help further understand catastrophic shifts and contribute to the discussion about the possibility of preventing such shifts to minimize their disruptive ecological, economic, and societal consequences. PMID:25825772

  4. Trophic shift, not collapse

    USGS Publications Warehouse

    Madenjian, Charles P.; Rutherford, Edward S.; Stow, Craig A.; Roseman, Edward F.; He, Ji X.

    2013-01-01

    scientists who are closely monitoring Lake Huron’s food web, we believe that the ongoing changes are more accurately characterized as a trophic shift in which benthic pathways have become more prominent. While decreases in abundance have occurred for some species, others are experiencing improved reproduction resulting in the restoration of several important native species.

  5. Evaluating reaction pathways of hydrothermal abiotic organic synthesis at elevated temperatures and pressures using carbon isotopes

    NASA Astrophysics Data System (ADS)

    Fu, Qi; Socki, Richard A.; Niles, Paul B.

    2015-04-01

    Experiments were performed to better understand the role of environmental factors on reaction pathways and corresponding carbon isotope fractionations during abiotic hydrothermal synthesis of organic compounds using piston cylinder apparatus at 750 °C and 5.5 kbars. Chemical compositions of experimental products and corresponding carbon isotopic values were obtained by a Pyrolysis-GC-MS-IRMS system. Alkanes (methane and ethane), straight-chain saturated alcohols (ethanol and n-butanol) and monocarboxylic acids (formic and acetic acids) were generated with ethanol being the only organic compound with higher δ13C than CO2. CO was not detected in experimental products owing to the favorable water-gas shift reaction under high water pressure conditions. The pattern of δ13C values of CO2, carboxylic acids and alkanes are consistent with their equilibrium isotope relationships: CO2 > carboxylic acids > alkanes, but the magnitude of the fractionation among them is higher than predicted isotope equilibrium values. In particular, the isotopic fractionation between CO2 and CH4 remained constant at ∼31‰, indicating a kinetic effect during CO2 reduction processes. No "isotope reversal" of δ13C values for alkanes or carboxylic acids was observed, which indicates a different reaction pathway than what is typically observed during Fischer-Tropsch synthesis under gas phase conditions. Under constraints imposed in experiments, the anomalous 13C isotope enrichment in ethanol suggests that hydroxymethylene is the organic intermediate, and that the generation of other organic compounds enriched in 12C were facilitated by subsequent Rayleigh fractionation of hydroxymethylene reacting with H2 and/or H2O. Carbon isotope fractionation data obtained in this study are instrumental in assessing the controlling factors on abiotic formation of organic compounds in hydrothermal systems. Knowledge on how environmental conditions affect reaction pathways of abiotic synthesis of organic

  6. Ambiguous red shifts

    NASA Astrophysics Data System (ADS)

    Wulfman, Carl E.

    2010-12-01

    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 conservation laws of classical and quantum-electrodynamical fields established by Cunningham and by Białynicki-Birula.

  7. Shifts that divide population

    NASA Astrophysics Data System (ADS)

    Muneepeerakul, Rachata; Qubbaj, Murad; Aggarwal, Rimjhim; Anderies, John M.; Janssen, Marco

    2014-05-01

    How does a population of organisms in an ecosystem or of people in a society respond to rapid shifts in the environment? Answers to this question are critical to our ability to anticipate and cope with a changing ecohydrological system. We have developed a generic model of adaptation mechanisms, based on replicator dynamics, in which we derive a simple and insightful threshold condition that separates two important types of responses: 'cohesive transition' in which the whole population changes gradually together, and 'population-dividing transition' in which the population splits into two groups with one eventually dominating the other. The threshold depends on the magnitude of the shift and the shape of the fitness landscape. Division in populations can fundamentally alter the functioning of and induce subsequent feedbacks within the system; knowing the condition that gives rise to such division is thus fundamentally important.

  8. The shifted penalty method

    NASA Astrophysics Data System (ADS)

    Zavarise, Giorgio

    2015-07-01

    The method presented here is a variation of the classical penalty one, suited to reduce penetration of the contacting surfaces. The slight but crucial modification concerns the introduction of a shift parameter that moves the minimum point of the constrained potential toward the exact value, without any penalty increase. With respect to the classical augmentation procedures, the solution improvement is embedded within the original penalty contribution. The problem is almost consistently linearized, and the shift is updated before each Newton's iteration. However, adding few iterations, with respect to the original penalty method, a reduction of the penetration of several orders of magnitude can be achieved. The numerical tests have shown very attractive characteristics and very stable solution paths. This permits to foresee a wide area of applications, not only in contact mechanics, but for any problem, like e.g. incompressible materials, where a penalty contribution is required.

  9. Quantitative Real-Time Polymerase Chain Reaction Measurement of HLA-DRA Gene Expression in Whole Blood Is Highly Reproducible and Shows Changes That Reflect Dynamic Shifts in Monocyte Surface HLA-DR Expression during the Course of Sepsis

    PubMed Central

    Tina, Elisabet; Bäckman, Anders; Magnuson, Anders; Strålin, Kristoffer; Söderquist, Bo; Källman, Jan

    2016-01-01

    Introduction A decrease in the expression of monocyte surface protein HLA-DR (mHLA-DR), measured by flow cytometry (FCM), has been suggested as a marker of immunosuppression and negative outcome in severe sepsis. However, FCM is not always available due to sample preparation that limits its use to laboratory operational hours. In this prospective study we evaluated dynamic changes in mHLA-DR expression during sepsis in relation to changes in HLA-DRA gene expression and Class II transactivator (CIITA), measured by quantitative Real-Time Polymerase Chain Reaction (qRT-PCR). Aims The aims of this study were: 1. to validate the robustness of qRT-PCR measurement of HLA-DRA- and CIITA–mRNA expression, in terms of reproducibility; and 2. to see if changes in expression of these genes reflect changes in mHLA-DR expression during the course of severe and non-severe bacteraemic sepsis. Methods and Findings Blood samples were collected from 60 patients with bacteraemic sepsis on up to five occasions during Days 1–28 after hospital admission. We found the reproducibility of the qRT-PCR method to be high by demonstrating low threshold variations (<0.11 standard deviation (SD)) of the qRT-PCR system, low intra-assay variation of Ct-values within triplicates (≤0.15 SD) and low inter-assay variations (12%) of the calculated target gene ratios. Our results also revealed dynamic HLA-DRA expression patterns during the course of sepsis that reflected those of mHLA-DR measured by FCM. Furthermore, HLA-DRA and mHLA-DR recovery slopes in patients with non-severe sepsis differed from those in patients with severe sepsis, shown by mixed model for repeated measurements (p<0.05). However, during the first seven days of sepsis, PCR-measurements showed a higher magnitude of difference between the two sepsis groups. Mean differences (95% CI) between severe sepsis (n = 20) and non-severe sepsis (n = 40) were; on day 1–2, HLA-DRA 0.40 (0.28–0.59) p<0.001, CIITA 0.48 (0.32–0.72) p = 0

  10. 20 Years of Air-Water Gas Exchange Observations for Pesticides in the Western Arctic Ocean.

    PubMed

    Jantunen, Liisa M; Wong, Fiona; Gawor, Anya; Kylin, Henrik; Helm, Paul A; Stern, Gary A; Strachan, William M J; Burniston, Deborah A; Bidleman, Terry F

    2015-12-01

    The Arctic has been contaminated by legacy organochlorine pesticides (OCPs) and currently used pesticides (CUPs) through atmospheric transport and oceanic currents. Here we report the time trends and air-water exchange of OCPs and CUPs from research expeditions conducted between 1993 and 2013. Compounds determined in both air and water were trans- and cis-chlordanes (TC, CC), trans- and cis-nonachlors (TN, CN), heptachlor exo-epoxide (HEPX), dieldrin (DIEL), chlorobornanes (ΣCHBs and toxaphene), dacthal (DAC), endosulfans and metabolite endosulfan sulfate (ENDO-I, ENDO-II, and ENDO SUL), chlorothalonil (CHT), chlorpyrifos (CPF), and trifluralin (TFN). Pentachloronitrobenzene (PCNB and quintozene) and its soil metabolite pentachlorothianisole (PCTA) were also found in air. Concentrations of most OCPs declined in surface water, whereas some CUPs increased (ENDO-I, CHT, and TFN) or showed no significant change (CPF and DAC), and most compounds declined in air. Chlordane compound fractions TC/(TC + CC) and TC/(TC + CC + TN) decreased in water and air, while CC/(TC + CC + TN) increased. TN/(TC + CC + TN) also increased in air and slightly, but not significantly, in water. These changes suggest selective removal of more labile TC and/or a shift in chlordane sources. Water-air fugacity ratios indicated net volatilization (FR > 1.0) or near equilibrium (FR not significantly different from 1.0) for most OCPs but net deposition (FR < 1.0) for ΣCHBs. Net deposition was shown for ENDO-I on all expeditions, while the net exchange direction of other CUPs varied. Understanding the processes and current state of air-surface exchange helps to interpret environmental exposure and evaluate the effectiveness of international protocols and provides insights for the environmental fate of new and emerging chemicals. PMID:26196214

  11. Effects of surface concentration on the porphine monolayers: Molecular simulations at the nanoscale water-gas interface

    NASA Astrophysics Data System (ADS)

    Krongsuk, Sriprajak; Kerdcharoen, Teerakiat

    2011-05-01

    The effect of surface concentration on the structure and stability of porphine (PH 2) monolayers at the water-gas interface was studied by using molecular dynamics simulation. Five monolayer systems having different surface concentrations were investigated in order to cover a full range of the experimental π- A isotherm. The simulation results show that increment of a number of the PH 2 molecules not only affects the significantly decreasing water density at the interface but also the monolayer surface tensions. The calculated surface tensions of the five systems indicate that the monolayer phase transfer corresponding to gaseous, expanded, condensed, and collapsed phases are observed. The hydrogen bonding between water and the PH 2 molecules at the interface plays an important role on the monolayer film formation, especially at the lower surface concentrations. The PH 2 orientations for all surface concentrations, except the highest one, are favored to be the β-structure as observed in the copper porphyrazine (CuPz) monolayer.

  12. Influence of current velocity and wind speed on air-water gas exchange in a mangrove estuary

    NASA Astrophysics Data System (ADS)

    Ho, David T.; Coffineau, Nathalie; Hickman, Benjamin; Chow, Nicholas; Koffman, Tobias; Schlosser, Peter

    2016-04-01

    Knowledge of air-water gas transfer velocities and water residence times is necessary to study the fate of mangrove derived carbon exported into surrounding estuaries and ultimately to determine carbon balances in mangrove ecosystems. For the first time, the 3He/SF6 dual tracer technique, which has been proven to be a powerful tool to determine gas transfer velocities in the ocean, is applied to Shark River, an estuary situated in the largest contiguous mangrove forest in North America. The mean gas transfer velocity was 3.3 ± 0.2 cm h-1 during the experiment, with a water residence time of 16.5 ± 2.0 days. We propose a gas exchange parameterization that takes into account the major sources of turbulence in the estuary (i.e., bottom generated shear and wind stress).

  13. 2DCOR-GC: an application of the generalized two-dimensional correlation analysis as a route to optimization of continuous flow supercritical fluid reactions.

    PubMed

    Hyde, Jason R; Bourne, Richard A; Noda, Isao; Stephenson, Phil; Poliakoff, Martyn

    2004-11-01

    A new approach for optimization and monitoring of continuous reactions has been developed using 2D correlation methods for the analysis of GC data (2DCOR-GC). 2DCOR-GC maps are obtained following perturbation of the system that allow the effect of changing reaction parameters such as time, temperature, pressure, or concentration to be both monitored and sequenced with regard to changes in the raw GC data. In this paper, we describe the application of the 2DCOR-GC technique to monitoring the reverse water-gas shift reaction in scCO(2). 2DCOR-GC is combined with FT-IR data to validate the methodology. We also report the application of 2DCOR-GC to probe the mechanism of the alkylation of m-cresol with isopropyl alcohol in scCO(2) using Nafion SAC-13 as the catalyst. These results identify coeluting peaks that could easily be missed without exhaustive method development. PMID:15516110

  14. [Characteristics of water-gas two-phase CO2 transport in unsaturated zone].

    PubMed

    Yu, Yanxin; Chen, Jiajun; Wang, Jinsheng; Yun, Ying; Li, Shushen; Wang, Zhiming

    2003-07-01

    The migration of CO2 in soil was simulated through use of soil column, especially the transformation of CO2 between water and gas phases at wetting front was studied. The soil column in the test was 1 m long and the concentration of CO2 solution was 748 mg/L. Through analysis, it was shown that CO2 migration in water phase was governed by advection, dispersion, reaction and mass transfer between water and gas phases, that in gas phase by advection, dispersion, mass transfer between two phases. Sampling method under dynamic condition of two phase flow in soil column was approached and mass transfer coefficient from water phase to gas phase was determined as 0.00061. This showed that there was certain mass transformation of CO2 from water phase to gas phase and yet it was not so significant. This study can provide the quantitative scientific bases for safety assessment of geological disposal of low and intermediate level radioactive waste and environmental impact assessment of solid waste disposal by landfilling. PMID:14551970

  15. 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.

    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 -}.

  16. Shift of meaning and students' alternative concepts

    NASA Astrophysics Data System (ADS)

    Schmidt, Hans-Jürgen; Volke, Dagmar

    2003-11-01

    The purpose of the study was to establish a relationship between the shift of meaning of the concept oxidation that has taken place during the historical development, and students' alternative concepts. First Examination Board papers were examined. The result enabled us to specify the research question. In the main part of the study, multiple-choice items were given to 3074 senior high school students. They were asked to select the correct answer and to justify their choices. Additional illustrative material was collected in four interviews with senior high school students. The analysis of the data revealed the mechanism that some students used to interpret the reactions from NO3m to NO and from CO32m to CO2. Students' interpretations were based on the concept of a transfer of oxide ions. The mechanism explains some correct and incorrect answers to the problems. The interview study also revealed that students were reluctant to accept water as a Brønsted base. It is suggested to use students' alternative concepts about oxidation reactions in class, helping them to better understand the half-reaction method. Students should also understand that the meaning of the concept oxidation has shifted in the course of time. In the area of acid-base reactions, further research is needed.

  17. Shifted genus expanded W ∞ algebra and shifted Hurwitz numbers

    NASA Astrophysics Data System (ADS)

    Zheng, Quan

    2016-05-01

    We construct the shifted genus expanded W ∞ algebra, which is isomorphic to the central subalgebra A ∞ of infinite symmetric group algebra and to the shifted Schur symmetrical function algebra Λ* defined by Okounkov and Olshanskii. As an application, we get some differential equations for the generating functions of the shifted Hurwitz numbers; thus, we can express the generating functions in terms of the shifted genus expanded cut-and-join operators.

  18. 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

  19. 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.

  20. 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.

  1. Wind driven vertical transport in a vegetated, wetland water column with air-water gas exchange

    NASA Astrophysics Data System (ADS)

    Poindexter, C.; Variano, E. A.

    2010-12-01

    Flow around arrays of cylinders at low and intermediate Reynolds numbers has been studied numerically, analytically and experimentally. Early results demonstrated that at flow around randomly oriented cylinders exhibits reduced turbulent length scales and reduced diffusivity when compared to similarly forced, unimpeded flows (Nepf 1999). While horizontal dispersion in flows through cylinder arrays has received considerable research attention, the case of vertical dispersion of reactive constituents has not. This case is relevant to the vertical transfer of dissolved gases in wetlands with emergent vegetation. We present results showing that the presence of vegetation can significantly enhance vertical transport, including gas transfer across the air-water interface. Specifically, we study a wind-sheared air-water interface in which randomly arrayed cylinders represent emergent vegetation. Wind is one of several processes that may govern physical dispersion of dissolved gases in wetlands. Wind represents the dominant force for gas transfer across the air-water interface in the ocean. Empirical relationships between wind and the gas transfer coefficient, k, have been used to estimate spatial variability of CO2 exchange across the worlds’ oceans. Because wetlands with emergent vegetation are different from oceans, different model of wind effects is needed. We investigated the vertical transport of dissolved oxygen in a scaled wetland model built inside a laboratory tank equipped with an open-ended wind tunnel. Plastic tubing immersed in water to a depth of approximately 40 cm represented emergent vegetation of cylindrical form such as hard-stem bulrush (Schoenoplectus acutus). After partially removing the oxygen from the tank water via reaction with sodium sulfite, we used an optical probe to measure dissolved oxygen at mid-depth as the tank water re-equilibrated with the air above. We used dissolved oxygen time-series for a range of mean wind speeds to estimate the

  2. 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

  3. Shifting epidemiology of Flaviviridae.

    PubMed

    Petersen, Lyle R; Marfin, Anthony A

    2005-04-01

    The dengue, West Nile, Japanese encephalitis and yellow fever viruses are important mosquito-borne viruses whose epidemiology is shifting in response to changing societal factors, such as increasing commerce, urbanization of rural areas, and population growth. All four viruses are expanding geographically, as exemplified by the emergence of West Nile virus in the Americas and Japanese encephalitis virus in Australasia. The large, recent global outbreaks of severe neurological disease caused by West Nile virus, the increasing frequency of dengue hemorrhagic fever outbreaks in the Americas, and the emergence of yellow fever virus vaccination-associated viscerotropic disease, are new clinical epidemiologic trends. These worrisome epidemiologic trends will probably continue in coming decades, as a reversal of their societal and biological drivers is not in sight. Nevertheless, the substantial reductions in Japanese encephalitis virus incidence resulting from vaccination programs and economic development in some Asian countries provide some encouragement within this overall guarded outlook. PMID:16225801

  4. Phase shifting diffraction interferometer

    DOEpatents

    Sommargren, Gary E.

    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.

  5. Phase shifting interferometer

    DOEpatents

    Sommargren, G.E.

    1999-08-03

    An interferometer is disclosed 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. 11 figs.

  6. Phase shifting interferometer

    DOEpatents

    Sommargren, Gary E.

    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.

  7. Phase shifting diffraction interferometer

    DOEpatents

    Sommargren, G.E.

    1996-08-29

    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. 8 figs.

  8. Reactions involving shifting of the double bond in cyclic ethers

    SciTech Connect

    Ibatullin, U.G.; Petrushina, T.F.; Akhmadeeva, A.A.; Safarov, M.G.

    1985-09-01

    4-Methylenetetrahydropyran undergoes isomerization to 4-methyl-5,6-dihydropyran in the presence of sodium on aluminum oxide. Both pyrans are converted to a vinyl ether, viz., 4-methyl-2,3-dihydropyran, under the influence of iron pentacarbonyl.

  9. 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.

  10. Quantized beam shifts in graphene

    NASA Astrophysics Data System (ADS)

    Kort-Kamp, Wilton; Sinitsyn, Nikolai; Dalvit, Diego

    We show that the magneto-optical response of a graphene-on-substrate system in the presence of an external magnetic field strongly affects light beam shifts. In the quantum Hall regime, we predict quantized Imbert-Fedorov, Goos-Hänchen, and photonic spin Hall shifts. The Imbert-Fedorov and photonic spin Hall shifts are given in integer multiples of the fine structure constant α, while the Goos-Hänchen ones in discrete multiples of α2. Due to time-reversal symmetry breaking the IF shifts change sign when the direction of the applied magnetic field is reversed, while the other shifts remain unchanged. We investigate the influence on these shifts of magnetic field, temperature, and material dispersion and dissipation. An experimental demonstration of quantized beam shifts could be achieved at terahertz frequencies for moderate values of the magnetic field. We acknowledge the LANL LDRD program for financial support.

  11. Antiretroviral therapy: Shifting sands.

    PubMed

    Sashindran, V K; Chauhan, Rajeev

    2016-01-01

    HIV/AIDS has been an extremely difficult pandemic to control. However, with the advent of antiretroviral therapy (ART), HIV has now been transformed into a chronic illness in patients who have continued treatment access and excellent long-term adherence. Existing indications for ART initiation in asymptomatic patients were based on CD4 levels; however, recent evidence has broken the shackles of CD4 levels. Early initiation of ART in HIV patients irrespective of CD4 counts can have profound positive impact on morbidity and mortality. Early initiation of ART has been found not only beneficial for patients but also to community as it reduces the risk of transmission. There have been few financial concerns about providing ART to all HIV-positive people but various studies have proven that early initiation of ART not only proves to be cost-effective but also contributes to economic and social growth of community. A novel multidisciplinary approach with early initiation and availability of ART at its heart can turn the tide in our favor in future. Effective preexposure prophylaxis and postexposure prophylaxis can also lower transmission risk of HIV in community. New understanding of HIV pathogenesis is opening new vistas to cure and prevention. Various promising candidate vaccines and drugs are undergoing aggressive clinical trials, raising optimism for an ever-elusive cure for HIV. This review describes various facets of tectonic shift in management of HIV. PMID:26900224

  12. Lamb shift for static atoms outside a Schwarzschild black hole

    SciTech Connect

    Zhou Wenting; Yu Hongwei

    2010-11-15

    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.

  13. 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.

  14. [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

  15. Formation of C-C and C-O bonds and oxygen removal in reactions of alkanediols, alkanols, and alkanals on copper catalysts.

    PubMed

    Sad, María E; Neurock, Matthew; Iglesia, Enrique

    2011-12-21

    This study reports evidence for catalytic deoxygenation of alkanols, alkanals, and alkanediols on dispersed Cu clusters with minimal use of external H(2) and with the concurrent formation of new C-C and C-O bonds. These catalysts selectively remove O-atoms from these oxygenates as CO or CO(2) through decarbonylation or decarboxylation routes, respectively, that use C-atoms present within reactants or as H(2)O using H(2) added or formed in situ from CO/H(2)O mixtures via water-gas shift. Cu catalysts fully convert 1,3-propanediol to equilibrated propanol-propanal intermediates that subsequently form larger oxygenates via aldol-type condensation and esterification routes without detectable involvement of the oxide supports. Propanal-propanol-H(2) equilibration is mediated by their chemisorption and interconversion at surfaces via C-H and O-H activation and propoxide intermediates. The kinetic effects of H(2), propanal, and propanol pressures on turnover rates, taken together with measured selectivities and the established chemical events for base-catalyzed condensation and esterification reactions, indicate that both reactions involve kinetically relevant bimolecular steps in which propoxide species, acting as the base, abstract the α-hydrogen in adsorbed propanal (condensation) or attack the electrophilic C-atom at its carbonyl group (esterification). These weakly held basic alkoxides render Cu surfaces able to mediate C-C and C-O formation reactions typically catalyzed by basic sites inherent in the catalyst, instead of provided by coadsorbed organic moieties. Turnover rates for condensation and esterification reactions decrease with increasing Cu dispersion, because low-coordination corner and edge atoms prevalent on small clusters stabilize adsorbed intermediates and increase the activation barriers for the bimolecular kinetically relevant steps required for both reactions. PMID:22023723

  16. Zero-shifted accelerometer outputs

    NASA Astrophysics Data System (ADS)

    Galef, Arnold

    1986-08-01

    It is claimed that the commonly appearing zero-shift in pyroshock data is usually a symptom of a malfunctioning measurement system, so that the data can not be repaired (by high-pass filtering or equivalent) unless tests can be devised that permit the demonstration that the system is operating in a linear mode in all respects other than the shift. The likely cause of the zero-shift and its prevention are discussed.

  17. Instrument Measures Shift In Focus

    NASA Technical Reports Server (NTRS)

    Steimle, Lawrence J.

    1992-01-01

    Optical components tested at wavelengths from ultraviolet to infrared. Focus-shift-measuring instrument easy to use. Operated in lighted room, without having to make delicate adjustments while peering through microscope. Measures distance along which focal point of converging beam of light shifted by introduction of nominally plane parallel optical component into beam. Intended primarily for measuring focus shifts produced by windows and filters at wavelengths from 120 to 1,100 nanometers. Portable, compact, and relatively inexpensive for degree of precision.

  18. Quantized beam shifts in graphene

    SciTech Connect

    de Melo Kort-Kamp, Wilton Junior; Sinitsyn, Nikolai; Dalvit, Diego Alejandro Roberto

    2015-10-08

    We predict the existence of quantized Imbert-Fedorov, Goos-Hanchen, and photonic spin Hall shifts for light beams impinging on a graphene-on-substrate system in an external magnetic field. In the quantum Hall regime the Imbert-Fedorov and photonic spin Hall shifts are quantized in integer multiples of the fine structure constant α, while the Goos-Hanchen ones in multiples of α2. We investigate the influence on these shifts of magnetic field, temperature, and material dispersion and dissipation. An experimental demonstration of quantized beam shifts could be achieved at terahertz frequencies for moderate values of the magnetic field.

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

    SciTech Connect

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

    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.

  20. Shifts in fisheries management: adapting to regime shifts

    PubMed Central

    King, Jacquelynne R.; McFarlane, Gordon A.; Punt, André E.

    2015-01-01

    For many years, fisheries management was based on optimizing yield and maintaining a target biomass, with little regard given to low-frequency environmental forcing. However, this policy was often unsuccessful. In the last two to three decades, fisheries science and management have undergone a shift towards balancing sustainable yield with conservation, with the goal of including ecosystem considerations in decision-making frameworks. Scientific understanding of low-frequency climate–ocean variability, which is manifested as ecosystem regime shifts and states, has led to attempts to incorporate these shifts and states into fisheries assessment and management. To date, operationalizing these attempts to provide tactical advice has met with limited success. We review efforts to incorporate regime shifts and states into the assessment and management of fisheries resources, propose directions for future investigation and outline a potential framework to include regime shifts and changes in ecosystem states into fisheries management.

  1. On the coefficients of small eddy and surface divergence models for the air-water gas transfer velocity

    NASA Astrophysics Data System (ADS)

    Wang, Binbin; Liao, Qian; Fillingham, Joseph H.; Bootsma, Harvey A.

    2015-03-01

    Recent studies suggested that under low to moderate wind conditions without bubble entraining wave breaking, the air-water gas transfer velocity k+ can be mechanistically parameterized by the near-surface turbulence, following the small eddy model (SEM). Field measurements have supported this model in a variety of environmental forcing systems. Alternatively, surface divergence model (SDM) has also been shown to predict the gas transfer velocity across the air-water interface in laboratory settings. However, the empirically determined model coefficients (α in SEM and c1 in SDM) scattered over a wide range. Here we present the first field measurement of the near-surface turbulence with a novel floating PIV system on Lake Michigan, which allows us to evaluate the SEM and SDM in situ in the natural environment. k+ was derived from the CO2 flux that was measured simultaneously with a floating gas chamber. Measured results indicate that α and c1 are not universal constants. Regression analysis showed that α˜log>(ɛ>) while the near-surface turbulence dissipation rate ɛ is approximately greater than 10-6 m2 s-3 according to data measured for this study as well as from other published results measured in similar environments or in laboratory settings. It also showed that α scales linearly with the turbulent Reynolds number. Similarly, coefficient c1 in the SDM was found to linearly scale with the Reynolds number. These findings suggest that larger eddies are also important parameters, and the dissipation rate in the SEM or the surface divergence β' in the SDM alone may not be adequate to determine k+ completely.

  2. Biological conversion of synthesis gas culture development

    SciTech Connect

    Klasson, K.T.; Basu, R.; Johnson, E.R.; Clausen, E.C.; Gaddy, J.L.

    1992-03-01

    Research continues on the conversion of synthesis by shift reactions involving bacteria. Topics discussed here include: biological water gas shift, sulfur gas utilization, experimental screening procedures, water gas shift studies, H{sub 2}S removal studies, COS degradation by selected CO-utilizing bacteria, and indirect COS utilization by Chlorobia. (VC)

  3. The Compton Effect Red Shift

    NASA Astrophysics Data System (ADS)

    Kierein, John

    2004-05-01

    In 1923 (Phil Mag. 46, 897.) A. H. Compton noted that the Compton effect produces a red shift for all wavelengths when the scattered electron is free and not bound to an atom or molecule. He suggested that the red shift in the visible spectrum at the limb of the sun is larger than that at the center due to the Compton effect from the greater number of free electrons in the sun's atmosphere along the line of sight. Kierein and Sharp (1968, Solar Physics 3, 450) quantified this and showed a good correlation of red shift observations with the variation in the number of these electrons along the line of sight from center to limb and suggested that the quasar red shift and cosmological red shift could be similarly explained. Grote Reber mapped and measured the background hectometric radiation and found it to be unexpectedly bright. In 1968 (J. Franklin Inst. 285,1), while describing these measurements and maps he explained this brightness as being due to the Compton effect causing the cosmological red shift and accelerating intergalactic electrons. The resulting universe is static. The predicted red shift from the Compton effect deviates from Hubble's law only at large red shifts.

  4. Flexible Schedules and Shift Work.

    ERIC Educational Resources Information Center

    Beers, Thomas M.

    2000-01-01

    Flexible work hours have gained prominence, as more than 25 million workers (27.6% of all full-time workers) can now vary their schedules. However, there has been little change since the mid-1980s in the proportion who work a shift other than a regular daytime shift. (JOW)

  5. Chemical shift driven geometry optimization.

    PubMed

    Witter, Raiker; Priess, Wolfram; Sternberg, Ulrich

    2002-01-30

    A new method for refinement of 3D molecular structures by geometry optimization is presented. Prerequisites are a force field and a very fast procedure for the calculation of chemical shifts in every step of optimization. To the energy, provided by the force field (COSMOS force field), a pseudoenergy, depending on the difference between experimental and calculated chemical shifts, is added. In addition to the energy gradients, pseudoforces are computed. This requires the derivatives of the chemical shifts with respect to the coordinates. The pseudoforces are analytically derived from the integral expressions of the bond polarization theory. Single chemical shift values attributed to corresponding atoms are considered for structural correction. As a first example, this method is applied for proton position refinement of the D-mannitol X-ray structure. A crystal structure refinement with 13C chemical shift pseudoforces is carried out. PMID:11924742

  6. Dynamic phase-shifting photoelasticity.

    PubMed

    Asundi, A; Tong, L; Boay, C G

    2001-08-01

    The application of phase-shifting photoelasticity to a real-time dynamic event involves simultaneous recording of the four phase-shifted images. Here an instrument, believed to be novel, is developed and described for this purpose. Use of a Multispec Imager is introduced into digital photoelasticity for the first time to our knowledge. This device enables splitting the optical energy of an object into four identical paths, thus permitting recording of the required four phase-shifted images. Experimental demonstration is provided for validation. PMID:18360395

  7. Interpretations of cosmological spectral shifts

    NASA Astrophysics Data System (ADS)

    Østvang, Dag

    2013-03-01

    It is shown that for Robertson-Walker models with flat or closed space sections, all of the cosmological spectral shift can be attributed to the non-flat connection (and thus indirectly to space-time curvature). For Robertson-Walker models with hyperbolic space sections, it is shown that cosmological spectral shifts uniquely split up into "kinematic" and "gravitational" parts provided that distances are small. For large distances no such unique split-up exists in general. A number of common, but incorrect assertions found in the literature regarding interpretations of cosmological spectral shifts, is pointed out.

  8. Can small shifts in circadian phase affect performance?

    PubMed Central

    Burgess, Helen J.; Legasto, Carlo S.; Fogg, Louis F.; Smith, Mark R.

    2012-01-01

    Small shifts in circadian timing occur frequently as a result of daylight saving time or later weekend sleep. These subtle shifts in circadian phase have been shown to influence subjective sleepiness, but it remains unclear if they can significantly affect performance. In a retrospective analysis we examined performance on the Psychomotor Vigilance Test before bedtime and after wake time in 11 healthy adults on fixed sleep schedules based on their habitual sleep times. The dim light melatonin onset, a marker of circadian timing, was measured on two occasions. An average 1.1 hour shift away from a proposed optimal circadian phase angle (6 hours between melatonin onset and midpoint of sleep) significantly slowed mean, median and fastest 10% reaction times before bedtime and after wake time (p<0.05). These results add to previous reports that suggest that humans may be sensitive to commonly occurring small shifts in circadian timing. PMID:22695081

  9. Refining the shifted topological vertex

    SciTech Connect

    Drissi, L. B.; Jehjouh, H.; Saidi, E. H.

    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.

  10. 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

  11. Considerations Based on Reaction Rate on Char Gasification Behavior in Two-stage Gasifier for Biomass

    NASA Astrophysics Data System (ADS)

    Taniguchi, Miki; Nishiyama, Akio; Sasauchi, Kenichi; Ito, Yusuke; Akamatsu, Fumiteru

    In order to develop a small-scale gasifier in which biomass can be converted to energy with high efficiency, we planned a gasification process that consists of two parts: pyrolysis part (rotary kiln) and gasification part (downdraft gasifier). We performed fundamental experiments on gasification part and discussed the appropriate conditions such as air supply location, air ratio, air temperature and hearth load. We considered the results by calculating reaction rates of representative reactions on char gasification part and found that water gas reaction is dominant in the reduction area and its behavior gives important information to decide the adequate length of the char layer.

  12. The influence of nano-architectured CeOx supports in RhPd/CeO₂ for the catalytic ethanol steam reforming reaction

    SciTech Connect

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

    2015-01-19

    The ethanol steam reforming (ESR) reaction has been tested over RhPd supported on polycrystalline ceria in comparison to structured supports composed of nanoshaped CeO₂ cubes and CeO₂ rods tailored towards the production of hydrogen. At 650-700 K the hydrogen yield follows the trend RhPd/CeO₂-cubes > RhPd/CeO₂ -rods > RhPd/CeO₂- 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/CeO₂-cubes and RhPd/CeO₂ -rods for ESR at low temperature is mainly ascribed to higher water-gas shift activity and a strong interaction between the bimetallic - 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

  13. The influence of nano-architectured CeOx supports in RhPd/CeO₂ for the catalytic ethanol steam reforming reaction

    DOE PAGESBeta

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

    2015-01-19

    The ethanol steam reforming (ESR) reaction has been tested over RhPd supported on polycrystalline ceria in comparison to structured supports composed of nanoshaped CeO₂ cubes and CeO₂ rods tailored towards the production of hydrogen. At 650-700 K the hydrogen yield follows the trend RhPd/CeO₂-cubes > RhPd/CeO₂ -rods > RhPd/CeO₂- 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/CeO₂-cubes and RhPd/CeO₂ -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

  14. Drug Reactions

    MedlinePlus

    Most of the time, medicines make our lives better. They reduce aches and pains, fight infections, and control problems such as high blood pressure or diabetes. But medicines can also cause unwanted reactions. One problem is ...

  15. Schedule shifts, cancer and longevity

    PubMed Central

    Cornélissen, Germaine; Halberg, Julia; Halberg, Franz; de la Pena, Salvador Sanchez; Nelson, Walter; Schwartzkopff, Othild; Stoynev, Alexander; Haus, Erhard

    2008-01-01

    Prompted by a recent report of the possible carcinogenic effect of shiftwork focusing on the disruption of circadian rhythms, we review studies involving shifts in schedule implemented at varying intervals in unicells, insects and mammals, including humans. Results indicate the desirability to account for a broader-than-circadian view. They also suggest the possibility of optimizing schedule shifts by selecting intervals between consecutive shifts associated with potential side-effects such as an increase in cancer risk. Toward this goal, marker rhythmometry is most desirable. The monitoring of blood pressure and heart rate present the added benefit of assessing cardiovascular disease risks resulting not only from an elevated blood pressure but also from abnormal variability in blood pressure and/or heart rate of normotensive as well as hypertensive subjects. PMID:19227006

  16. Fracture toughness curve shift method

    SciTech Connect

    Nanstad, R.K.; Sokolov, M.A.; McCabe, D.E.

    1995-10-01

    The purpose of this task is to examine the technical basis for the currently accepted methods for shifting fracture toughness curves to account for irradiation damage, and to work through national codes and standards bodies to revise those methods, if a change is warranted. During this reporting period, data from all the relevant HSSI Programs were acquired and stored in a database and evaluated. The results from that evaluation have been prepared in a draft letter report and are summarized here. A method employing Weibull statistics was applied to analyze fracture toughness properties of unirradiated and irradiated pressure vessel steels. Application of the concept of a master curve for irradiated materials was examined and used to measure shifts of fracture toughness transition curves. It was shown that the maximum likelihood approach gave good estimations of the reference temperature, T{sub o}, determined by rank method and could be used for analyzing of data sets where application of the rank method did not prove to be feasible. It was shown that, on average, the fracture toughness shifts generally exceeded the Charpy 41-J shifts; a linear least-squares fit to the data set yielded a slope of 1.15. The observed dissimilarity was analyzed by taking into account differences in effects of irradiation on Charpy impact and fracture toughness properties. Based on these comparisons, a procedure to adjust Charpy 41-J shifts for achieving a more reliable correlation with the fracture toughness shifts was evaluated. An adjustment consists of multiplying the 41-J energy level by the ratio of unirradiated to irradiated Charpy upper shelves to determine an irradiated transition temperature, and then subtracting the unirradiated transition temperature determined at 41 J. For LUS welds, however, an unirradiated level of 20 J (15 ft-1b) was used for the corresponding adjustment for irradiated material.

  17. A molecular shift register based on electron transfer

    NASA Technical Reports Server (NTRS)

    Hopfield, J. J.; Onuchic, Josenelson; Beratan, David N.

    1988-01-01

    An electronic shift-register memory at the molecular level is described. The memory elements are based on a chain of electron-transfer molecules and the information is shifted by photoinduced electron-transfer reactions. This device integrates designed electronic molecules onto a very large scale integrated (silicon microelectronic) substrate, providing an example of a 'molecular electronic device' that could actually be made. The design requirements for such a device and possible synthetic strategies are discussed. Devices along these lines should have lower energy usage and enhanced storage density.

  18. 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

  19. The Modality Shift Experiment in Adults and Children with High Functioning Autism

    ERIC Educational Resources Information Center

    Williams, Diane L.; Goldstein, Gerald; Minshew, Nancy J.

    2013-01-01

    This study used the modality shift experiment, a relatively simple reaction time measure to visual and auditory stimuli, to examine attentional shifting within and across modalities in 33 children and 42 adults with high-functioning autism as compared to matched numbers of age- and ability-matched typical controls. An exaggerated "modality shift…

  20. Foundation Shifts Tack on Studies

    ERIC Educational Resources Information Center

    Viadero, Debra

    2006-01-01

    Five years into an eight-year study of its high school improvement efforts, the Bill & Melinda Gates Foundation is shifting its strategy for evaluating the $1.3 billion grant program. The foundation's initiative, which is underwriting change efforts in more than 1,800 schools, is the nation's largest privately funded attempt to improve high…

  1. Leadership Shifts in Changing Field

    ERIC Educational Resources Information Center

    Zubrzycki, Jaclyn

    2013-01-01

    As groups representing local and state education players struggle to remain relevant in a policy conversation often dominated by foundations, think tanks, new advocacy groups, and political and business figures, a shift in leadership has been under way at major associations. Most of the changes have come as part of the natural churn; former…

  2. 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…

  3. The Shift Needed for Sustainability

    ERIC Educational Resources Information Center

    Smith, Peter A. C.; Sharicz, Carol

    2011-01-01

    Purpose: The purpose of this action research is to begin to assess to what extent organizations have in practice begun to make the shift towards triple bottom line (TBL) sustainability. Design/methodology/approach: A definition of TBL sustainability is provided, and key elements of TBL sustainability considered necessary to success are identified…

  4. Technology Counts 2012: Virtual Shift

    ERIC Educational Resources Information Center

    Education Week, 2012

    2012-01-01

    Virtual education is moving into that intersection where rising popularity meets calls for greater accountability. How the virtual education movement responds to those calls will have a significant impact on how it evolves in K-12 over the next five to 10 years. This report tackles this shift in the virtual education landscape. It examines the…

  5. Flexible shift scheduling of physicians.

    PubMed

    Brunner, Jens O; Bard, Jonathan F; Kolisch, Rainer

    2009-09-01

    This research addresses a shift scheduling problem in which physicians at a German university hospital are assigned to demand periods over a planning horizon that can extend up to several weeks. When performing the scheduling it is necessary to take into account a variety of legal and institutional constraints that are imposed by a national labor agreement, which governs all physicians in German university hospitals. Currently, most medical departments develop their staff schedules manually at great cost and time. To solve the problem, a new modeling approach is developed that requires shifts to be generated implicitly. Rather than beginning with a predetermined number of shift types and start times, shifts are allowed to start at every pre-defined period in the planning horizon and extend up to 13 h with an hour-long break included. The objective is to find an assignment such that the total hours that have to be paid out as overtime are minimal under the restrictions given by the labor agreement. The problem is formulated as a mixed-integer program and solved with CPLEX. During the solution process individual lines-of-work are constructed for each physician. Using data from an anesthesia department, computational results indicate that high quality schedules can be obtained much more quickly than by current practice. PMID:19739361

  6. Wavelength-shifted Cherenkov radiators

    NASA Technical Reports Server (NTRS)

    Krider, E. P.; Jacobson, V. L.; Pifer, A. E.; Polakos, P. A.; Kurz, R. J.

    1976-01-01

    The scintillation and Cherenkov responses of plastic Cherenkov radiators containing different wavelength-shifting fluors in varying concentrations have been studied in beams of low energy protons and pions. For cosmic ray applications, where large Cherenkov to scintillation ratios are desired, the optimum fluor concentrations are 0.000025 by weight or less.

  7. 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)

  8. Spectral shifts near compact objects

    NASA Astrophysics Data System (ADS)

    Lake, K.; Myra, E.

    1981-10-01

    It is shown that radiation emitted from material freely falling toward a black hole or neutron star cannot be blue shifted as recently claimed by Cohen and Struble (1980). The relativistic corrections to the classical apparent limb angle are given explicitly for spherical sources in collapse.

  9. Anthropometric changes and fluid shifts

    NASA Technical Reports Server (NTRS)

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

    1974-01-01

    Several observations of body size, shape, posture, and configuration were made to document changes resulting from direct effects of weightlessness during the Skylab 4 mission. After the crewmen were placed in orbit, a number of anatomical and anthropometric changes occurred including a straightening of the thoracolumbar spine, a general decrease in truncal girth, and an increase in height. By the time of the earliest in-flight measurement on mission day 3, all crewmen had lost more than two liters of extravascular fluid from the calf and thigh. The puffy facies, the bird legs effect, the engorgement of upper body veins, and the reduced volume of lower body veins were all documented with photographs. Center-of-mass measurements confirmed a fluid shift cephalad. This shift remained throughout the mission until recovery, when a sharp reversal occurred; a major portion of the reversal was completed in a few hours. The anatomical changes are of considerable scientific interest and of import to the human factors design engineer, but the shifts of blood and extravascular fluid are of more consequence. It is hypothesized that the driving force for the fluid shift is the intrinsic and unopposed lower limb elasticity that forces venous blood and then other fluid cephalad.

  10. Field shifts in hafnium II

    NASA Astrophysics Data System (ADS)

    Aufmuth, P.; Henneberg, I.; Siminski, A.; Steudel, A.

    1991-03-01

    By means of classical interference spectroscopy, using enriched isotope samples, the isotope shift between178Hf and180Hf has been measured for 33 transitions in the Hf II spectrum. For the pure Russell-Saunders terms 5 d 26 s 4 F and2 F the parametric analysis yields a field-shift difference of 17(2) mK produced by the second-order interaction of the electrostatic operator and the field-shift operator. Semi-empirical calculations based on the non-relativistic Hartree-Fock method reproduce this value as well as the experimental field shifts if a factor of 1.68(6) is used to scale the ab initio electron densities at the nucleus. The corresponding factor for the Hf atom is much smaller. This leads to a re-evaluation of screening ratios for Hf and to a more accurate value of the nuclear parameter λ178,180 (Hf)=0.072(4) fm2.

  11. Integrated Microreactors for Reaction Automation: New Approaches to Reaction Development

    NASA Astrophysics Data System (ADS)

    McMullen, Jonathan P.; Jensen, Klavs F.

    2010-07-01

    Applications of microsystems (microreactors) in continuous-flow chemistry have expanded rapidly over the past two decades, with numerous reports of higher conversions and yields compared to conventional batch benchtop equipment. Synthesis applications are enhanced by chemical information gained from integrating microreactor components with sensors, actuators, and automated fluid handling. Moreover, miniaturized systems allow experiments on well-defined samples at conditions not easily accessed by conventional means, such as reactions at high pressure and temperatures. The wealth of synthesis information that could potentially be acquired through use of microreactors integrated with physical sensors and analytical chemistry techniques for online reaction monitoring has not yet been well explored. The increased efficiency resulting from use of continuous-flow microreactor platforms to automate reaction screening and optimization encourages a shift from current batchwise chemical reaction development to this new approach. We review advances in this new area and provide application examples of online monitoring and automation.

  12. Combined shift and methanation in a fluidized-bed reactor. Final report, 25 September 1979-31 December 1980

    SciTech Connect

    Streeter, R.C.

    1981-02-01

    The objective of this program was to demonstrate the feasibility of employing a gas-phase, catalytic, fluidized-bed reactor to carry out the water-gas shift and methanation reactions simultaneously, without product gas recycle. The major portion of the experimental work involved PEDU-scale tests in a 6-inch ID reactor, operating at 1000 psig and temperatures in the range of 900 to 1000/sup 0/F, with a nominal catalyst charge of one cubic foot. These tests included operation for extended time periods (35 to 40 hours) with feed H/sub 2/:CO ratios of 2:1 in the absence of steam, and 1:1 using steam:gas ratios of 0.1:1 to 0.2:1. Five different catalysts were evaluated. Bench-scale tests, each of approximately 10 days' duration, were also conducted. At H/sub 2/:CO = 2:1 (without steam), no significant carbon deposition occurred at temperatures of 800 and 950/sup 0/F. At 1100/sup 0/F, however, considerable carbon formation did occur, possibly due to the onset of CH/sub 4/ pyrolysis. At H/sub 2/:CO = 1:1 and 950/sup 0/F, carbon deposition took place readily in the absence of steam. Small amounts of steam in the feed (e.g., steam:gas ratio = 0.1:1) were effective in inhibiting carbon formation, although larger amounts (steam:gas ratio = 0.5:1) resulted in deactivation and loss of metal surface area through sintering. Results of auxiliary studies at Brigham Young University (BYU) on rates of carbon formation and removal are also presented. As to the relative tendencies of the various catalysts to undergo carbon deposition, results of the BYU studies generally confirmed observations made during PEDU testing at BCR. Catalyst regeneration tests at BYU with 10 percent O/sub 2/ in N/sub 2/ showed that 80 to 96 percent of the original metal surface could be restored at temperatures of 572 to 662/sup 0/F.

  13. 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.

  14. Size-Dependent Raman Shifts for nanocrystals

    PubMed Central

    Gao, Yukun; Zhao, Xinmei; Yin, Penggang; Gao, Faming

    2016-01-01

    Raman spectroscopy is a very sensitive tool for probing semiconductor nanocrystals. The underlying mechanism behind the size-dependent Raman shifts is still quite controversial. Here we offer a new theoretical method for the quantum confinement effects on the Raman spectra of semiconductor nanocrystals. We propose that the shift of Raman spectra in nanocrystals can result from two overlapping effects: the quantum effect shift and surface effect shift. The quantum effect shift is extracted from an extended Kubo formula, the surface effect shift is determined via the first principles calculations. Fairly good prediction of Raman shifts can be obtained without the use of any adjustable parameter. Closer analysis shows that the size-dependent Raman shifts in Si nanocrystals mainly result from the quantum effect shifts. For nanodiamond, the proportion of surface effect shift in Raman shift is up to about 40%. Such model can also provide a good baseline for using Raman spectroscopy as a tool to measure size. PMID:27102066

  15. Ammonia reactions with the stored oxygen in a commercial lean NOx trap catalyst

    SciTech Connect

    Bartova, Sarka; Mracek, David; Koci, Petr; Marek, Milos; Choi, Jae -Soon

    2014-10-12

    Ammonia is an important intermediate of the NOx reduction in a NOx storage and reduction catalyst (aka lean NOx trap). NH3 formed under rich conditions in the reduced front part of the catalyst is transported by convection downstream to the unregenerated (still oxidized) zone of the catalyst, where it further reacts with the stored oxygen and NOx. In this paper, the kinetics and selectivity of NH3 reactions with the stored oxygen are studied in detail with a commercial Ba-based NOx storage catalyst containing platinum group metals (PGM), Ba and Ce oxides. Furthermore, steady-state NH3 decomposition, NH3 oxidation by O2 and NO, and N2O decomposition are examined in light-off experiments. Periodic lean/rich cycling is measured first with O2 and NH3, and then with NOx + O2 and NH3 to discriminate between the NH3 reactions with the stored oxygen and the stored NOx. The reaction of NH3 with the stored O2 is highly selective towards N2, however a certain amount of NOx and N2O is also formed. The formed NOx by-product is efficiently adsorbed on the NOx storage sites such that the NOx is not detected at the reactor outlet except at high temperatures. The stored NOx reacts with NH3 feed in the next rich phase, contributing to the N2O formation. Water inhibits the reactions of NH3 with the stored oxygen. On the contrary, the presence of CO2 increases the NH3 consumption. Furthermore, CO2 is able to provide additional oxygen for NH3 oxidation, forming –CO in analogy to the reverse water gas shift reaction.

  16. Drug Reactions

    MedlinePlus

    ... using any of these products. Some types of food may also cause adverse drug reactions. For example, grapefruit and grapefruit juice, as well as alcohol and caffeine, may affect how drugs work. Every time your doctor ... interactions with any foods or beverages. What about medicines I've used ...

  17. Looping through the Lamb Shift

    SciTech Connect

    Hazi, A U

    2007-02-06

    Sometimes in science, a small measurement can have big ramifications. For a team of Livermore scientists, such was the case when they measured a small shift in the spectrum of extremely ionized atoms of uranium. The measurement involves the Lamb shift, a subtle change in the energy of an electron orbiting an atom's nucleus. The precision of the Livermore result was 10 times greater than that of existing measurements, making it the best measurement to date of a complicated correction to the simplest quantum description of how atoms behave. The measurement introduces a new realm in the search for deviations between the theory of quantum electrodynamics (QED), which is an extension of quantum mechanics, and the real world. Such deviations, if discovered, would have far-reaching consequences, indicating that QED is not a fundamental theory of nature.

  18. Josephson 32-bit shift register

    SciTech Connect

    Yuh, P.F.; Yao, C.T.; Bradley, P. )

    1991-03-01

    This paper reports on a 32-bit shift register designed by edge-triggered gates tested with {plus minus}25% bias margin and {plus minus}81% input margin for the full array. Simulations have shown {plus minus}55% bias margin at 3.3 GHz and working up to a maximum frequency of 30 GHz with a junction current density of 2000A/cm{sup 2} although the shift register has only been tested up to 500 MHz, limited by instrumentation. This edge-triggered gate consisting of a pair of conventional Josephson logic gates in series has the advantages of wide margins, short reset time, and insensitivity to global parameter-variations.

  19. Lamb shift in muonic deuterium

    SciTech Connect

    Gorchtein, Mikhail; Vanderhaeghen, Marc; Carlson, Carl E.

    2013-11-07

    We consider the two-photon exchange contribution to the 2P-2S Lamb shift in muonic deuterium in the framework of forward dispersion relations. The dispersion integrals are evaluated with minimal model dependence using experimental data on elastic deuteron form factors and inelastic electron-deuteron scattering, both in the quasielastic and hadronic range. The subtraction constant that is required to ensure convergence of the dispersion relation for the forward Compton amplitude T{sub 1} (ν,Q{sup 2}) is related to the deuteron magnetic polarizability β(Q{sup 2}) and represents the main source of uncertainty in our analysis. We obtain for the Lamb shift ΔE{sub 2P-2S} = 1.620±0.190 meV and discuss ways to further reduce this uncertainty.

  20. Metaphor shifts in stroke recovery.

    PubMed

    Boylstein, Craig; Rittman, Maude; Hinojosa, Ramon

    2007-01-01

    An illness event like stroke is generally believed to produce a biographical disruption in the individual, resulting in a reconstruction of one's self identity. One method of narrative reconstruction is the use of personal metaphor. Although previous research has illustrated a variety of illness metaphors, including that of war, there has been little research conducted on how these metaphors shift throughout a person's recovery period. The authors present data that indicate an intricate connection exists among changes in individuals' physical functioning, self-reported depression level, self-identity, and the metaphors they use to describe the stroke and stroke recovery experience. As the metaphor one uses to describe one's stroke experience shifts, so does one's sense of self. As one's self-identity changes, one's level of self-reported depression may also increase. PMID:17567259

  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. Multicolor Holography With Phase Shifting

    NASA Technical Reports Server (NTRS)

    Vikram, Chandra S.

    1996-01-01

    Prototype apparatus constructed to test feasibility of two-color holographic interferometric scheme in which data for reconstructing holographic wavefront obtained with help of phase-shifting technique. Provides two sets of data needed to solve equations for effects of temperature and concentration. Concept extended to holography at three or more wavelengths to measure three or more phenomena associated with significant variations in index of refraction

  3. Structural effects in solvolytic reactions; carbon-13 NMR studies of carbocations†: Effect of increasing electron demand on the carbon-13 NMR shifts in substituted tert-cumyl and 1-aryl-1-cyclopentyl carbocations—correlation of the data by a new set of substituent constants, σC+*†

    PubMed Central

    Brown, Herbert C.; Kelly, David P.; Periasamy, Mariappan

    1980-01-01

    The cationic carbon substituent chemical shifts (ΔδC+) for nine representative meta-substituted tert-cumyl carbocations are correlated satisfactorily by the σm+ substituent constants (slope ρ+ = -18.18, correlation coefficient r = 0.990). However, the substituent chemical shifts (ΔδC+) for the corresponding para derivatives are not correlated by the σp+ substituent constants. The possibility of developing a set of substituent constants capable of correlating such 13C NMR shifts was examined. The slope of the line defined by the meta substituents (ρ+ = -18.18) was utilized to calculate σC+ constants for both meta and para substituents. The utility of these constants was then tested by their ability to correlate the 13C NMR shifts in the cations for a different system, the 1-aryl-1-cyclopentyl cations. Indeed, these σC+ values correlate very well with the ΔδC+ values, yielding ρC+ = -16.84, r = 0.999. PMID:16592926

  4. Geometric phase shifting digital holography.

    PubMed

    Jackin, Boaz Jessie; Narayanamurthy, C S; Yatagai, Toyohiko

    2016-06-01

    A new phase shifting digital holographic technique using a purely geometric phase in Michelson interferometric geometry is proposed. The geometric phase in the system does not depend upon either optical path length or wavelength, unlike dynamic phase. The amount of geometric phase generated is controllable through a rotating wave plate. The new approach has unique features and major advantages in holographic measurement of transparent and reflecting three-dimensional (3D) objects. Experimental results on surface shape measurement and imaging of 3D objects are presented using the proposed method. PMID:27244436

  5. Cortisol shifts financial risk preferences.

    PubMed

    Kandasamy, Narayanan; Hardy, Ben; Page, Lionel; Schaffner, Markus; Graggaber, Johann; Powlson, Andrew S; Fletcher, Paul C; Gurnell, Mark; Coates, John

    2014-03-01

    Risk taking is central to human activity. Consequently, it lies at the focal point of behavioral sciences such as neuroscience, economics, and finance. Many influential models from these sciences assume that financial risk preferences form a stable trait. Is this assumption justified and, if not, what causes the appetite for risk to fluctuate? We have previously found that traders experience a sustained increase in the stress hormone cortisol when the amount of uncertainty, in the form of market volatility, increases. Here we ask whether these elevated cortisol levels shift risk preferences. Using a double-blind, placebo-controlled, cross-over protocol we raised cortisol levels in volunteers over 8 d to the same extent previously observed in traders. We then tested for the utility and probability weighting functions underlying their risk taking and found that participants became more risk-averse. We also observed that the weighting of probabilities became more distorted among men relative to women. These results suggest that risk preferences are highly dynamic. Specifically, the stress response calibrates risk taking to our circumstances, reducing it in times of prolonged uncertainty, such as a financial crisis. Physiology-induced shifts in risk preferences may thus be an underappreciated cause of market instability. PMID:24550472

  6. Sectoral shifts and aggregate unemployment

    SciTech Connect

    Loungani, P.

    1986-01-01

    Some recent research has taken the view that sectoral or industry-specific shocks significantly affect aggregate unemployment by increasing the amount of inter-industry labor reallocation required. The empirical evidence for this view rests on the finding that during the 1950s - and again during the 1970s - there was a positive correlation between aggregate unemployment and the dispersion of employment growth rates. This thesis demonstrates that this correlation arises largely because oil price shocks affect both unemployment and the dispersion of employment growth. Once the dispersion due to oil shocks is accounted for, the residual dispersion in employment has very low explanatory power for unemployment. Since the dispersion index does not measure pure sectoral shifts, an alternate measure of dispersion is developed that serves as a better proxy for the amount of inter-industry labor reallocation required each period. Estimates using this measure suggest that, during the 1950s, temporary increases in the relative price of oil were responsible for generating the observed correlation. On the other hand, sectoral shifts were important during the 1970s; in particular, the 1973 oil price increase has had significant reallocative effects on the economy. This contention is subjected to further tests by looking at the time-series behavior of employment in durable-goods industries and also by following the inter-industry movements of workers over time through the use of panel data.

  7. Differential phase shift keyed signal resolver

    NASA Technical Reports Server (NTRS)

    Hopkins, P. M.; Wallingford, W. M. (Inventor)

    1974-01-01

    A differential phase shift keyed signal resolver resolves the differential phase shift in the incoming signal to determine the data content thereof overcoming phase uncertainty without requiring a transmitted reference signal.

  8. Shift register generators and applications to coding

    NASA Technical Reports Server (NTRS)

    Morakis, J. C.

    1968-01-01

    The most important properties of shift register generated sequences are exposed. The application of shift registers as multiplication and division circuits leads to the generation of some error correcting and detecting codes.

  9. Sleep, sleepiness, fatigue, and performance of 12-hour-shift nurses.

    PubMed

    Geiger-Brown, Jeanne; Rogers, Valerie E; Trinkoff, Alison M; Kane, Robert L; Bausell, R Barker; Scharf, Steven M

    2012-03-01

    Nurses working 12-h shifts complain of fatigue and insufficient/poor-quality sleep. Objectively measured sleep times have not been often reported. This study describes sleep, sleepiness, fatigue, and neurobehavioral performance over three consecutive 12-h (day and night) shifts for hospital registered nurses. Sleep (actigraphy), sleepiness (Karolinska Sleepiness Scale [KSS]), and vigilance (Performance Vigilance Task [PVT]), were measured serially in 80 registered nurses (RNs). Occupational fatigue (Occupational Fatigue Exhaustion Recovery Scale [OFER]) was assessed at baseline. Sleep was short (mean 5.5 h) between shifts, with little difference between day shift (5.7 h) and night shift (5.4 h). Sleepiness scores were low overall (3 on a 1-9 scale, with higher score indicating greater sleepiness), with 45% of nurses having high level of sleepiness (score  > 7) on at least one shift. Nurses were progressively sleepier each shift, and night nurses were sleepier toward the end of the shift compared to the beginning. There was extensive caffeine use, presumably to preserve or improve alertness. Fatigue was high in one-third of nurses, with intershift fatigue (not feeling recovered from previous shift at the start of the next shift) being most prominent. There were no statistically significant differences in mean reaction time between day/night shift, consecutive work shift, and time into shift. Lapsing was traitlike, with rare (39% of sample), moderate (53%), and frequent (8%) lapsers. Nurses accrue a considerable sleep debt while working successive 12-h shifts with accompanying fatigue and sleepiness. Certain nurses appear more vulnerable to sleep loss than others, as measured by attention lapses. PMID:22324559

  10. Discrete radon transform with shift of coordinate

    SciTech Connect

    Wei, X.; Wu, L.

    1994-12-31

    This paper describes the Radon transform with shift of coordinates. The appropriate shift value of spatial coordinate gives less alias in the data reconstruction and the appropriate shift value of frequency coordinate makes the reconstruction stable. The method is suitable to signal processing of seismogram, an example of wave field separation to practical VSP data is shown in the paper.

  11. Balmer line shifts in quasars

    NASA Astrophysics Data System (ADS)

    Sulentic, J. W.; Marziani, P.; Del Olmo, A.; Zamfir, S.

    2016-02-01

    We offer a broad review of Balmer line phenomenology in type 1 active galactic nuclei, briefly summarising luminosity and radio loudness effects, and discussing interpretation in terms of nebular physics along the 4D eigenvector 1 sequence of quasars. We stress that relatively rare, peculiar Balmer line profiles (i.e., with large shifts with respect to the rest frame or double and multiple peaked) that start attracted attentions since the 1970s are still passable of multiple dynamical interpretation. More mainstream objects are still not fully understood as well, since competing dynamical models and geometries are possible. Further progress may come from inter-line comparison across the 4D Eigenvector 1 sequence.

  12. 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.

  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. A novel phase shifting structured illumination microscopy

    NASA Astrophysics Data System (ADS)

    Singh, Veena; Dubey, Vishesh; Ahmad, Azeem; Singh, Gyanendra; Mehta, D. S.

    2016-03-01

    This paper describes a new and novel phase shifting technique for qualitative as well as quantitative measurement in microscopy. We have developed a phase shifting device which is robust, inexpensive and involves no mechanical movement. In this method, phase shifting is implemented using LED array, beam splitters and defocused projection of Ronchi grating. The light from the LEDs are made incident on the beam splitters at spatially different locations. Due to variation in the geometrical distances of LEDs from the Ronchi grating and by sequentially illuminating the grating by switching on one LED at a time the phase shifted grating patterns are generated. The phase shifted structured patterns are projected onto the sample using microscopic objective lens. The phase shifted deformed patterns are recorded by a CCD camera. The initial alignment of the setup involves a simple procedure for the calibration for equal fringe width and intensity such that the phase shifted fringes are at equal phase difference. Three frame phase shifting algorithm is employed for the reconstruction of the phase map. The method described here is fully automated so that the phase shifted images are recorded just by switching of LEDs and has been used for the shape measurement of microscopic industrial objects. The analysis of the phase shifted images provides qualitative as well as quantitative information about the sample. Thus, the method is simple, robust and low cost compared to PZT devices commonly employed for phase shifting.

  15. Attentional shift by gaze is triggered without awareness.

    PubMed

    Sato, Wataru; Okada, Takashi; Toichi, Motomi

    2007-10-01

    Reflexive attentional shift in response to another individual's gaze direction has been reported, but it remains unknown whether this process can occur subliminally. We investigated this issue using facial stimuli consisting of drawings (Experiment 1) and photographs (Experiment 2). The gaze direction was expressed by the eye gaze direction (Experiment 1), and the eye gaze and head direction (Experiment 2). The gaze cue was presented either supraliminally or subliminally in the center of the visual field, before target presentation in the periphery. The task for participants was to localize the target as soon as possible. The reaction time needed to localize the target was consistently shorter for valid than invalid gaze cues for both types of gaze cues in both subliminal and supraliminal conditions. These findings indicate that attentional shift can be triggered even without awareness in response to another individual's eye gaze or head direction. PMID:17624520

  16. Shifting Baselines, Science, and Society

    NASA Astrophysics Data System (ADS)

    Jackson, J. B.

    2006-12-01

    All of us have a deeply personal concept of nature based upon our childhood perceptions of the world around us, and of the subsequent degradation of nature by the experiences of our lifetimes. Yet even the most rudimentary knowledge of history clearly demonstrates that the modern rise of human population and consumption have wreaked havoc on global ecosystems to the extent that nowhere is close to natural or pristine and that most places have been increasingly degraded over many centuries. This disconnect between direct personal experience and abstract historical perspective is the problem of "shifting baselines" that is the fundamental impediment to basic scientific understanding and environmental policy, and affects scientists as much as the general public, business, and government. Scientists in particular suffer from the inability to directly observe and experimentally verify causes and effects of previous changes in ecosystems that now bear so little resemblance to their natural state. Under the circumstances, it is essential for scientists to draw scientific conclusions based on imperfect data and to publicly explain, defend, and discuss their conclusions as the best possible science given present information. The failure to do so makes science virtually irrelevant to social and environmental policy and government.

  17. Dealing with a Paradigm Shift

    PubMed Central

    Pack, Allan I.

    2015-01-01

    Recent changes in policies by insurance companies with respect to mandating home sleep apnea testing rather than in-laboratory studies have a large impact on the financial viability of clinical sleep centers. Coping with this disruptive change requires forward planning. First, it is important to be well positioned with respect to facilities so that these can be quickly downsized to control costs. There is also a need to develop, in advance, an accredited home sleep study program so that centers can respond to the rapidly changing environment. Following the change there is a need to control costs by rapidly downsizing the technology workforce. Technologists can be retrained for other essential roles. Centralizing the precertification process with knowledgeable, well-trained staff and a robust auditing process is an essential component. The approach taken at the University of Pennsylvania to this change is described as is how one can ensure continued financial viability of a comprehensive sleep center program in a major academic medical center. Citation: Pack AI. Dealing with a paradigm shift. J Clin Sleep Med 2015;11(8):925–929. PMID:26094918

  18. Shifting boundaries in professional care.

    PubMed Central

    Hopkins, A; Solomon, J; Abelson, J

    1996-01-01

    The nature of the work undertaken by different health professionals and inter-professional boundaries are constantly shifting. The greater knowledge of users of health care, and the increasing technical and organizational complexity of modern medicine, have partly eroded the control of health professionals over the substance of their work. The definition of a field of work as lying within the province of any one profession is culturally rather than scientifically determined. It is evident that care of good quality should be delivered at the lowest possible cost. This might include delivery of care by a less trained person than heretofore, or by someone with limited but focused training. Sharing of skills is a more sensible subject for discussion than transfer of tasks. We review a number of studies which show the effectiveness of inter-professional substitution in various care settings, and also the effectiveness of substitution by those other than health professionals. The views of users of health services on inter-professional substitution need to be considered. Health professionals and others need to work together to devise innovative ways of delivering effective health care. The legal issues need clarification. PMID:8774532

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

    PubMed

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

    2014-01-01

    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

  20. Host shifts and evolutionary radiations of butterflies

    PubMed Central

    Fordyce, James A.

    2010-01-01

    Ehrlich and Raven proposed a model of coevolution where major host plant shifts of butterflies facilitate a burst of diversification driven by their arrival to a new adaptive zone. One prediction of this model is that reconstructions of historical diversification of butterflies should indicate an increase in diversification rate following major host shifts. Using reconstructed histories of 15 butterfly groups, I tested this prediction and found general agreement with Ehrlich and Raven's model. Butterfly lineages with an inferred major historical host shift showed evidence of diversification rate variation, with a significant acceleration following the host shift. Lineages without an inferred major host shift generally agreed with a constant-rate model of diversification. These results are consistent with the view that host plant associations have played a profound role in the evolutionary history of butterflies, and show that major shifts to chemically distinct plant groups leave a historical footprint that remains detectable today. PMID:20610430

  1. Electromagnetic tracking of the pivot-shift.

    PubMed

    Kuroda, Ryosuke; Hoshino, Yuichi

    2016-06-01

    The pivot-shift test is an important examination to assess the rotational laxity in the anterior cruciate ligament (ACL) injured and reconstructed knees. Because this examination is related to subjective knee function, we may still see cases that have residual rotational laxity after ACL reconstruction. Quantitative evaluation of the pivot-shift test is preferable to the clinical pivot-shift test but is difficult to attain mainly due to complicated movements of the pivot-shift. The electromagnetic tracking system was developed to evaluate knee kinematics during the pivot-shift, providing information related to 6-degree-of-freedom knee kinematics with a high sampling rate. Through this device, the abnormal movement of the pivot-shift is characterized in two phases: an increased anterior tibial translation and a boosted acceleration of tibial posterior reduction. Since its invention, this system has been utilized to assess rotational laxity for clinical follow-up and research after the ACL reconstruction. PMID:27007473

  2. 12-hour shifts: job satisfaction of nurses.

    PubMed

    Todd, C; Robinson, G; Reid, N

    1993-09-01

    A before and after study was carried out amongst staff of 10 wards of a county hospital before and after the introduction of a 12-hour shift system for nurses. The purpose was to investigate the impact of the shift system on job satisfaction. Some 320 nurses covering all qualified and unqualified grades were surveyed using a standard job satisfaction attitude scale. It was found that under the 12-hour shift both intrinsic and extrinsic factors of job satisfaction had been detrimentally affected. Considerable dissatisfaction was expressed about hours of work, conditions of work and the impact of the shift on domestic and social arrangements. The vast majority (83%) reported that they did not want to go on working the shift and there was support for the view that recruitment to nursing would be adversely affected by the shift. PMID:8313062

  3. 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.

  4. Theory of the Helium Isotope Shift

    NASA Astrophysics Data System (ADS)

    Pachucki, Krzysztof; Yerokhin, V. A.

    2015-09-01

    Theory of the isotope shift of the centroid energies of light few-electron atoms is reviewed. Numerical results are presented for the isotope shift of the 23P-23S and 21S-23S transition energies of 3He and 4He. By comparing theoretical predictions for the isotope shift with the experimental results, the difference of the squares of the nuclear charge radii of 3He and 4He, δR2, is determined with high accuracy.

  5. Effects of Shift Work on Cognitive Performance, Sleep Quality, and Sleepiness among Petrochemical Control Room Operators.

    PubMed

    Kazemi, Reza; Haidarimoghadam, Rashid; Motamedzadeh, Majid; Golmohamadi, Rostam; Soltanian, Alireza; Zoghipaydar, Mohamad Reza

    2016-01-01

    Shift work is associated with both sleepiness and reduced performance. The aim of this study was to examine cognitive performance, sleepiness, and sleep quality among petrochemical control room shift workers. Sixty shift workers participated in this study. Cognitive performance was evaluated using a number of objective tests, including continuous performance test, n-back test, and simple reaction time test; sleepiness was measured using the subjective Karolinska Sleepiness Scale (KSS); and sleep quality was assessed using the Pittsburgh Sleep Quality Index (PSQI) questionnaire. ANCOVA, t-test, and repeated-measures ANOVA were applied for statistical analyses, and the significance level was set at p < 0.05. All variables related to cognitive performance, except for omission error, significantly decreased at the end of both day and night shifts (p < 0.0001). There were also significant differences between the day and night shifts in terms of the variables of omission error (p < 0.027) and commission error (p < 0.036). A significant difference was also observed between daily and nightly trends of sleepiness (p < 0.0001) so that sleepiness was higher for the night shift. Participants had low sleep quality on both day and night shifts, and there were significant differences between the day and night shifts in terms of subjective sleep quality and quantity (p < 0.01). Long working hours per shift result in fatigue, irregularities in the circadian rhythm and the cycle of sleep, induced cognitive performance decline at the end of both day and night shifts, and increased sleepiness in night shift. It, thus, seems necessary to take ergonomic measures such as planning for more appropriate shift work and reducing working hours. PMID:27103934

  6. Effects of Shift Work on Cognitive Performance, Sleep Quality, and Sleepiness among Petrochemical Control Room Operators

    PubMed Central

    Kazemi, Reza; Haidarimoghadam, Rashid; Golmohamadi, Rostam; Soltanian, Alireza; Zoghipaydar, Mohamad Reza

    2016-01-01

    Shift work is associated with both sleepiness and reduced performance. The aim of this study was to examine cognitive performance, sleepiness, and sleep quality among petrochemical control room shift workers. Sixty shift workers participated in this study. Cognitive performance was evaluated using a number of objective tests, including continuous performance test, n-back test, and simple reaction time test; sleepiness was measured using the subjective Karolinska Sleepiness Scale (KSS); and sleep quality was assessed using the Pittsburgh Sleep Quality Index (PSQI) questionnaire. ANCOVA, t-test, and repeated-measures ANOVA were applied for statistical analyses, and the significance level was set at p < 0.05. All variables related to cognitive performance, except for omission error, significantly decreased at the end of both day and night shifts (p < 0.0001). There were also significant differences between the day and night shifts in terms of the variables of omission error (p < 0.027) and commission error (p < 0.036). A significant difference was also observed between daily and nightly trends of sleepiness (p < 0.0001) so that sleepiness was higher for the night shift. Participants had low sleep quality on both day and night shifts, and there were significant differences between the day and night shifts in terms of subjective sleep quality and quantity (p < 0.01). Long working hours per shift result in fatigue, irregularities in the circadian rhythm and the cycle of sleep, induced cognitive performance decline at the end of both day and night shifts, and increased sleepiness in night shift. It, thus, seems necessary to take ergonomic measures such as planning for more appropriate shift work and reducing working hours. PMID:27103934

  7. Goos-Haenchen shift in complex crystals

    SciTech Connect

    Longhi, Stefano; Della Valle, Giuseppe; Staliunas, Kestutis

    2011-10-15

    The Goos-Haenchen (GH) effect for wave scattering from complex PT-symmetric periodic potentials (complex crystals) is theoretically investigated, with specific reference to optical GH shift in photonic crystal slabs with a sinusoidal periodic modulation of both real and imaginary parts of the dielectric constant. The analysis highlights some distinct and rather unique features as compared to the GH shift found in ordinary crystals. In particular, as opposed to GH shift in ordinary crystals, which is large at the band gap edges, in complex crystals the GH shift can be large inside the reflection (amplification) band and becomes extremely large as the PT symmetry-breaking threshold is approached.

  8. Jet Lag and Shift Work Disorder.

    PubMed

    Reid, Kathryn J; Abbott, Sabra M

    2015-12-01

    Jet lag and shift work disorder are circadian rhythm sleep-wake disorders resulting from behaviorally altering the sleep-wake schedule in relation to the external environment. Not everyone who experiences trans-meridian travel or performs shift work has a disorder. The prevalence of jet lag disorder is unclear, approximately 5%-10% of shift workers have shift work disorder. Treatment aims to realign the internal circadian clock with the external environment. Behavioral therapies include sleep hygiene and management of the light-dark and sleep schedule. Pharmacologic agents are used to treat insomnia and excessive sleepiness, and melatonin is used to facilitate sleep and circadian realignment. PMID:26568127

  9. The second-order gravitational red shift

    NASA Technical Reports Server (NTRS)

    Jaffe, J.

    1973-01-01

    The direct measurement of the nonlinear term of the gravitational field equations by using very stable clocks is discussed along with measuring the perhelion advance of a planet or satellite. These are considered measurements of the second-order gravitational red shift. The exact expression for the frequency shift of light in a gravitational field is derived. Other topics discussed include: The Doppler-cancelling technique; the second-order red shift in a spherically symmetric gravitational field; finite signal transit time; and the reality and interpretation of coordinates in the second-order red shift experiment.

  10. Vibrational isotope shifts in hexafluoride molecules

    NASA Astrophysics Data System (ADS)

    McDowell, Robin S.

    Central-atom isotope frequency shifts for the v3 stretching fundamentals of octahedral hexafluorides are reviewed. Accurate shifts have been measured for the hexafluorides of S, Se, Mo, Te, W and U, and can be calculated from force fields for those of Rh, Ir, Pt, Np and Pu. A theoretical treatment of the relation between the vibrational frequency v3 and the central-atom mass m establishes the parametric dependence of the isotope shift Δ v3. This yields a semi-empirical formula Δ v3(cm -1amu -1) = -4.20 v3m-1.75, with v3 in cm -1 and m in amu. Frequency shifts calculated from this formula agree with measured shifts generally to within 5%, and it promises to be useful in estimating such shifts for Jahn—Teller hexafluorides and for hexafluoride ions. The relative precision of isotope frequency shifts and Coriolis constants in constraining the general quadratic force fields of XF 6 molecules has also been considered. For a given precision in measuring frequency shifts, Δ v3 is more effective than Δ v4, by the ratio v3/ v4, for determining the off-diagonal symmetry force constant F34. F34 is about equally well constrained by the Coriolis constants for all molecules, but the frequency shifts become much less effective for this purpose as the central-atom mass increases.

  11. EXAFS Energy Shift and Structural Parameters

    NASA Astrophysics Data System (ADS)

    Kelly, Shelly D.; Ravel, Bruce

    2007-02-01

    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.

  12. Nova reaction rates and experiments

    NASA Astrophysics Data System (ADS)

    Bishop, S.; Herlitzius, C.; Fiehl, J.

    2011-04-01

    Oxygen-neon novae form a subset of classical novae events known to freshly synthesize nuclei up to mass number A≲40. Because several gamma-ray emitters lie in this mass range, these novae are also interesting candidates for gamma-ray astronomy. The properties of excited states within those nuclei in this mass region play a critical role in determining the resonant (p,γ) reaction rates, themselves, largely unknown for the unstable nuclei. We describe herein a new Doppler shift lifetime facility at the Maier-Leibnitz tandem laboratory, Technische Universität München, with which we will map out important resonant (p,γ) nova reaction rates.

  13. Rapid shift in sleep time and acrophase of melatonin secretion in short shift work schedule.

    PubMed

    Quera-Salva, M A; Defrance, R; Claustrat, B; De Lattre, J; Guilleminault, C

    1996-09-01

    Tolerance to shift work and adaptability to shifting schedules is an issue of growing importance in industrialized society. We studied 40 registered nurses, 20 on fixed day-shifts and 20 on fixed night-shifts, to assess whether workers with rapidly shifting schedules were able to adapt their melatonin secretion and sleep-wake cycles. The day-shift worked 5 days with 2 days off and the night-shift worked 3 nights with 2 off. All night-shift personnel acknowledged shifting back to daytime schedules on their days off. Sleep-wake was determined by sleep logs and actigraphy. To measure 6-sulfatoxymelatonin levels, urine was collected at 2-hour intervals on the last work day and on the last day off. Night-shift workers slept significantly more on days off. Napping on the job occurred in 9/20 night-shift workers (mean 114 minutes) between 3 and 6 a.m. The acrophase of 6-sulfatoxymelatonin in day-shift nurses occurred at similar times on workdays and off days. In night-shift nurses, the acrophase was about 7 a.m. on days off, but had a random distribution on workdays. Further analysis revealed two subgroups of night-shift nurses: six subjects (group A).demonstrated a rapid shift in melatonin secretion (acrophase at near 12 noon on work days and at near 7 a.m. on days off) while 14 nurses (group B) did not shift. Group A nurses slept more in the daytime on work days and their total sleep time was the same as day-shift nurses. Group A was slightly younger and was composed solely of women (there were nine women and five men in group B). Age may be a factor in the ability to adapt to rapidly shifting schedules. PMID:8899932

  14. A calcium oxide sorbent process for bulk separation of carbon dioxide

    SciTech Connect

    Harrison, D.P.; Han, C.; Lee, G.

    1995-11-01

    This projects described a study of the simultaneous water-gas shift reaction and carbon dioxide removal to prove the technical feasibility of an alternate process for hydrogen production from coal derived gases. Results have been favorable.

  15. Exercise, energy balance and the shift worker.

    PubMed

    Atkinson, Greg; Fullick, Sarah; Grindey, Charlotte; Maclaren, Don

    2008-01-01

    Shift work is now common in society and is not restricted to heavy industry or emergency services, but is increasingly found amongst 'white collar' occupations and the growing number of service industries. Participation in shift work is associated with increased body mass index, prevalence of obesity and other health problems. We review the behavioural and biological disturbances that occur during shift work and discuss their impact on leisure-time physical activity and energy balance. Shift work generally decreases opportunities for physical activity and participation in sports. For those shift workers who are able to exercise, subjective and biological responses can be altered if the exercise is taken at unusual times of day and/or if the shift worker is sleep deprived. These altered responses may in turn impact on the longer-term adherence to an exercise programme. The favourable effects of exercise on body mass control and sleep quality in shift workers have not been confirmed. Similarly, recent reports of relationships between sleep duration and obesity have not been examined in a shift work context. There is no evidence that exercise can mediate certain circadian rhythm characteristics (e.g. amplitude or timing) for improved tolerance to shift work. Total energy intake and meal composition do not seem to be affected by participation in shift work. Meal frequency is generally reduced but snacking is increased on the night shift. Unavailability of preferred foods in the workplace, a lack of time, and a reduced desire to eat at night explain these findings. 'Normal' eating habits with the family are also disrupted. The metabolic responses to food are also altered by shift work-mediated disruptions to sleep and circadian rhythms. Whether any interactions on human metabolism exist between timing or content of food intake and physical activity during shift work is not known at present. There are very few randomized controlled studies on the efficacy of physical

  16. Exercise, Energy Balance and the Shift Worker

    PubMed Central

    Atkinson, Greg; Fullick, Sarah; Grindey, Charlotte; Maclaren, Don; Waterhouse, Jim

    2009-01-01

    Shift work is now common in society and is not restricted to heavy industry or emergency services, but is increasingly found amongst ‘white collar’ occupations and the growing number of service industries. Participation in shift work is associated with increased body mass index, prevalence of obesity and other health problems. We review the behavioural and biological disturbances that occur during shift work and discuss their impact on leisure-time physical activity and energy balance. Shift work generally decreases opportunities for physical activity and participation in sports. For those shift workers who are able to exercise, subjective and biological responses can be altered if the exercise is taken at unusual times of day and/or if the shift worker is sleep-deprived. These altered responses may in turn impact on the longer-term adherence to an exercise programme. The favourable effects of exercise on body mass control and sleep quality have not been confirmed in shift workers. Similarly, recent reports of relationships between sleep duration and obesity have not been examined in a shift work context. There is no evidence that exercise can mediate certain circadian rhythm characteristics (e.g. amplitude or timing) for improved tolerance to shift work. Total energy intake and meal composition do not seem to be affected by participation in shift work. Meal frequency is generally reduced but snacking is increased on the night shift. Unavailability of preferred foods in the workplace, a lack of time, and a reduced desire to eat at night explain these findings. ‘Normal’ eating habits with the family are also disrupted. The metabolic responses to food are also altered by shift work-mediated disruptions to sleep and circadian rhythms. Whether any interactions on human metabolism exist between timing or content of food intake and physical activity during shift work is not known at present. There are very few randomised controlled studies on the efficacy of

  17. In-line phase shift tomosynthesis

    SciTech Connect

    Hammonds, Jeffrey C.; Price, Ronald R.; Pickens, David R.; Donnelly, Edwin F.

    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 μm. The digital detector uses CsI/CMOS with a pixel size of 50 × 50 μm. 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.

  18. Effects of extended work shifts and shift work on patient safety, productivity, and employee health.

    PubMed

    Keller, Simone M

    2009-12-01

    It is estimated 1.3 million health care errors occur each year and of those errors 48,000 to 98,000 result in the deaths of patients (Barger et al., 2006). Errors occur for a variety of reasons, including the effects of extended work hours and shift work. The need for around-the-clock staff coverage has resulted in creative ways to maintain quality patient care, keep health care errors or adverse events to a minimum, and still meet the needs of the organization. One way organizations have attempted to alleviate staff shortages is to create extended work shifts. Instead of the standard 8-hour shift, workers are now working 10, 12, 16, or more hours to provide continuous patient care. Although literature does support these staffing patterns, it cannot be denied that shifts beyond the traditional 8 hours increase staff fatigue, health care errors, and adverse events and outcomes and decrease alertness and productivity. This article includes a review of current literature on shift work, the definition of shift work, error rates and adverse outcomes related to shift work, health effects on shift workers, shift work effects on older workers, recommended optimal shift length, positive and negative effects of shift work on the shift worker, hazards associated with driving after extended shifts, and implications for occupational health nurses. PMID:20043622

  19. A Theoretical Study of the Hydration of Methane, from the Aqueous Solution to the sI Hydrate-Liquid Water-Gas Coexistence

    PubMed Central

    Luis, Daniel Porfirio; García-González, Alcione; Saint-Martin, Humberto

    2016-01-01

    Monte Carlo and molecular dynamics simulations were done with three recent water models TIP4P/2005 (Transferable Intermolecular Potential with 4 Points/2005), TIP4P/Ice (Transferable Intermolecular Potential with 4 Points/ Ice) and TIP4Q (Transferable Intermolecular Potential with 4 charges) combined with two models for methane: an all-atom one OPLS-AA (Optimal Parametrization for the Liquid State) and a united-atom one (UA); a correction for the C–O interaction was applied to the latter and used in a third set of simulations. The models were validated by comparison to experimental values of the free energy of hydration at 280, 300, 330 and 370 K, all under a pressure of 1 bar, and to the experimental radial distribution functions at 277, 283 and 291 K, under a pressure of 145 bar. Regardless of the combination rules used for σC,O, good agreement was found, except when the correction to the UA model was applied. Thus, further simulations of the sI hydrate were performed with the united-atom model to compare the thermal expansivity to the experiment. A final set of simulations was done with the UA methane model and the three water models, to study the sI hydrate-liquid water-gas coexistence at 80, 230 and 400 bar. The melting temperatures were compared to the experimental values. The results show the need to perform simulations with various different models to attain a reliable and robust molecular image of the systems of interest. PMID:27240339

  20. A Theoretical Study of the Hydration of Methane, from the Aqueous Solution to the sI Hydrate-Liquid Water-Gas Coexistence.

    PubMed

    Luis, Daniel Porfirio; García-González, Alcione; Saint-Martin, Humberto

    2016-01-01

    Monte Carlo and molecular dynamics simulations were done with three recent water models TIP4P/2005 (Transferable Intermolecular Potential with 4 Points/2005), TIP4P/Ice (Transferable Intermolecular Potential with 4 Points/ Ice) and TIP4Q (Transferable Intermolecular Potential with 4 charges) combined with two models for methane: an all-atom one OPLS-AA (Optimal Parametrization for the Liquid State) and a united-atom one (UA); a correction for the C-O interaction was applied to the latter and used in a third set of simulations. The models were validated by comparison to experimental values of the free energy of hydration at 280, 300, 330 and 370 K, all under a pressure of 1 bar, and to the experimental radial distribution functions at 277, 283 and 291 K, under a pressure of 145 bar. Regardless of the combination rules used for σC,O, good agreement was found, except when the correction to the UA model was applied. Thus, further simulations of the sI hydrate were performed with the united-atom model to compare the thermal expansivity to the experiment. A final set of simulations was done with the UA methane model and the three water models, to study the sI hydrate-liquid water-gas coexistence at 80, 230 and 400 bar. The melting temperatures were compared to the experimental values. The results show the need to perform simulations with various different models to attain a reliable and robust molecular image of the systems of interest. PMID:27240339

  1. 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.

  2. Lamb Shift in Nonrelativistic Quantum Electrodynamics.

    ERIC Educational Resources Information Center

    Grotch, Howard

    1981-01-01

    The bound electron self-energy or Lamb shift is calculated in nonrelativistic quantum electrodynamics. Retardation is retained and also an interaction previously dropped in other nonrelativistic approaches is kept. Results are finite without introducing a cutoff and lead to a Lamb shift in hydrogen of 1030.9 MHz. (Author/JN)

  3. Four-phase differential phase shift resolver

    NASA Technical Reports Server (NTRS)

    Hopkins, P. M.; Wallingford, W. M.

    1973-01-01

    Two systems have been developed to resolve phase uncertainty without transmitting reference signals. In both methods signal is impressed on carrier as differential, rather than absolute, phase shift. At the receiver four-phase demodulation and logic process unambiguously resolves differential phase shift of input carrier.

  4. 29 CFR 102.171 - Cost shifting.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 29 Labor 2 2010-07-01 2010-07-01 false Cost shifting. 102.171 Section 102.171 Labor Regulations... By Federal Income Tax Refund Offset § 102.171 Cost shifting. Costs incurred by the Agency in... amount of the offset. Such costs may include administrative costs and attorneys fees....

  5. 29 CFR 102.165 - Cost shifting.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 29 Labor 2 2010-07-01 2010-07-01 false Cost shifting. 102.165 Section 102.165 Labor Regulations... by Administrative Offset § 102.165 Cost shifting. Costs incurred by the Agency in connection with... offset. Such costs may include administrative costs and attorneys fees....

  6. 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…

  7. 29 CFR 102.165 - Cost shifting.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 29 Labor 2 2013-07-01 2013-07-01 false Cost shifting. 102.165 Section 102.165 Labor Regulations... by Administrative Offset § 102.165 Cost shifting. Costs incurred by the Agency in connection with... offset. Such costs may include administrative costs and attorneys fees....

  8. 29 CFR 102.165 - Cost shifting.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 29 Labor 2 2012-07-01 2012-07-01 false Cost shifting. 102.165 Section 102.165 Labor Regulations... by Administrative Offset § 102.165 Cost shifting. Costs incurred by the Agency in connection with... offset. Such costs may include administrative costs and attorneys fees....

  9. 29 CFR 102.165 - Cost shifting.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 29 Labor 2 2014-07-01 2014-07-01 false Cost shifting. 102.165 Section 102.165 Labor Regulations... by Administrative Offset § 102.165 Cost shifting. Costs incurred by the Agency in connection with... offset. Such costs may include administrative costs and attorneys fees....

  10. 29 CFR 102.171 - Cost shifting.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 29 Labor 2 2014-07-01 2014-07-01 false Cost shifting. 102.171 Section 102.171 Labor Regulations... By Federal Income Tax Refund Offset § 102.171 Cost shifting. Costs incurred by the Agency in... amount of the offset. Such costs may include administrative costs and attorneys fees....

  11. 29 CFR 102.171 - Cost shifting.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 29 Labor 2 2013-07-01 2013-07-01 false Cost shifting. 102.171 Section 102.171 Labor Regulations... By Federal Income Tax Refund Offset § 102.171 Cost shifting. Costs incurred by the Agency in... amount of the offset. Such costs may include administrative costs and attorneys fees....

  12. 29 CFR 102.171 - Cost shifting.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 29 Labor 2 2012-07-01 2012-07-01 false Cost shifting. 102.171 Section 102.171 Labor Regulations... By Federal Income Tax Refund Offset § 102.171 Cost shifting. Costs incurred by the Agency in... amount of the offset. Such costs may include administrative costs and attorneys fees....

  13. Rainbow-shift mechanism behind discrete optical-potential ambiguities

    SciTech Connect

    Brandan, M.E. ); McVoy, K.W. )

    1991-03-01

    Some years ago, Drisko {ital et} {ital al}. suggested that the discrete ambiguity often encountered for elastic scattering optical potentials could be understood as being due to the interior or small-{ital l} {ital S}-matrix elements for two equivalent'' potentials differing in phase by 2{pi}, {ital l}-by-{ital l}. We point out that the {ital absence} of this phase change for peripheral partial waves is equally essential, and suggest that a deeper understanding of the ambiguity may be achieved by viewing it as a consequence of a farside interference between interior and peripheral partial waves. It is this interference which produces the broad Airy maxima'' of a nuclear rainbow, and we show that a Drisko-type phase-shift increment {delta}{sub {ital l}}{r arrow}({delta}{sub {ital l}}+{pi}) for low-{ital l} phases relative to the high-{ital l} ones is exactly what is needed to shift a farside rainbow pattern by one Airy maximum, thus providing an equivalent rainbow-shift'' interpretation of the discrete ambiguity. The physical importance of both interpretations lies in the fact that the existence of discrete ambiguities (as well as of nuclear rainbows) is explicit evidence for low-{ital l} transparency in nucleus-nucleus collisions. The essential role played by low partial waves explains why peripheral reactions have generally not proven helpful in resolving this ambiguity.

  14. Contributors to shift work tolerance in South Korean nurses working rotating shift.

    PubMed

    Jung, Hye-Sun; Lee, Bokim

    2015-05-01

    Shift workers have rapidly increased in South Korea; however, there is no published research exploring shift work tolerance among South Korean workers. This study aimed to investigate factors related to shift work tolerance in South Korean nurses. The sample comprised of 660 nurses who worked shifts in a large hospital in South Korea. A structured questionnaire included following comprehensive variables: demographic (age and number of children), individual (morningness and self-esteem), psychosocial (social support and job stress), lifestyle (alcohol consumption, physical activity, and BMI), and working condition factors (number of night shifts and working hours). Shift work tolerance was measured in terms of insomnia, fatigue, and depression. The results of hierarchical regressions indicate that all variables, except for three, number of children, BMI, and working hours, were related to at least one of the symptoms associated with shift work tolerance. Based on these results, we offer some practical implications to help improve shift work tolerance of workers. PMID:25448057

  15. Comment on the reference compound for chemical shift and Knight shift determination of (209)Bi nuclei.

    PubMed

    Nowak, Bogdan

    2015-01-01

    Several groups exploring the (209)Bi NMR in solids, including usual insulators, metallic and magnetic materials and recently diamagnetic topological materials, use different standards (usually old and invalid) for chemical shift (Knight shift) determination, ignoring IUPAC recommendations. As a consequence the published shift values exhibit considerable differences (up to 17,500 ppm). PMID:25534279

  16. The AirWaterGas Teacher Professional Development Program: Lessons Learned by Pairing Scientists and Teachers to Develop Curriculum on Global Climate Change and Regional Unconventional Oil and Gas Development

    NASA Astrophysics Data System (ADS)

    Gardiner, L. S.; Hatheway, B.; Rogers, J. D.; Casey, J. G.; Lackey, G.; Birdsell, D.; Brown, K.; Polmear, M.; Capps, S.; Rosenblum, J.; Sitterley, K.; Hafich, K. A.; Hannigan, M.; Knight, D.

    2015-12-01

    The AirWaterGas Teacher Professional Development Program, run by the UCAR Center for Science Education, brought together scientists and secondary science teachers in a yearlong program culminating in the development of curriculum related to the impacts of unconventional oil and gas development. Graduate students and research scientists taught about their research area and its relationship to oil and gas throughout three online courses during the 2015-16 school year, during which teachers and scientists engaged in active online discussions. Topics covered included climate change, oil and gas infrastructure, air quality, water quality, public health, and practices and policies relating to oil and gas development. Building upon their initial online interactions and a face-to-face meeting in March, teachers were paired with appropriate AirWaterGas team members as science advisors during a month-long residency in Boulder, Colorado. During the residency, graduate student scientists provided resources and feedback as teachers developed curriculum projects in collaboration with each other and UCAR science educators. Additionally, teachers and AirWaterGas researchers shared experiences on an oil and gas well site tour, and a short course on drilling methods with a drilling rig simulator. Here, we share lessons learned from both sides of the aisle, including initial results from program assessment conducted with the participating teachers.

  17. Cause of absorption band shift of disperse red-13 attached on silica spheres

    NASA Astrophysics Data System (ADS)

    Kim, Byoung-Ju; Kim, Hyung-Deok; Kim, Na-Rae; Bang, Byeong-Gyu; Park, Eun-Hye; Kang, Kwang-Sun

    2015-08-01

    A reversible color change and large absorption band shift have been observed for the disperse red-13 (DR-13) attached on the surface of the monodisperse silica spheres. Two step synthetic processes including urethane bond formation and hydrolysis-condensation reactions were used to attach the DR-13 on the surface of the silica spheres. After the reaction, the characteristic absorption peak at 2270 cm-1 representing the -N=C=O asymmetric stretching vibration disappeared, and the a new absorption peak at 1700 cm-1 corresponding the C=O stretching vibration appeared. A visual and reversible color change was observed before and after wetting in alcohol. Although the absorption peak of DR-13 in alcohol is at 510 nm, the absorption peak shifts to 788 nm when it is dried. The absorption peak shifts to 718 nm when it is wetted in alcohol. This result can be explained by the formation of intramolecular charge transfer band.

  18. Search for Higgs shifts in white dwarfs

    SciTech Connect

    Onofrio, Roberto; Wegner, Gary A. E-mail: gary.a.wegner@dartmouth.edu

    2014-08-20

    We report on a search for differential shifts between electronic and vibronic transitions in carbon-rich white dwarfs BPM 27606 and Procyon B. The absence of differential shifts within the spectral resolution and taking into account systematic effects such as space motion and pressure shifts allows us to set the first upper bound of astrophysical origin on the coupling between the Higgs field and the Kreschmann curvature invariant. Our analysis provides the basis for a more general methodology to derive bounds to the coupling of long-range scalar fields to curvature invariants in an astrophysical setting complementary to the ones available from high-energy physics or table-top experiments.

  19. Deterministic convergence in iterative phase shifting

    SciTech Connect

    Luna, Esteban; Salas, Luis; Sohn, Erika; Ruiz, Elfego; Nunez, Juan M.; Herrera, Joel

    2009-03-10

    Previous implementations of the iterative phase shifting method, in which the phase of a test object is computed from measurements using a phase shifting interferometer with unknown positions of the reference, do not provide an accurate way of knowing when convergence has been attained. We present a new approach to this method that allows us to deterministically identify convergence. The method is tested with a home-built Fizeau interferometer that measures optical surfaces polished to {lambda}/100 using the Hydra tool. The intrinsic quality of the measurements is better than 0.5 nm. Other possible applications for this technique include fringe projection or any problem where phase shifting is involved.

  20. Theory of the Helium Isotope Shift

    SciTech Connect

    Pachucki, Krzysztof; Yerokhin, V. A.

    2015-09-15

    Theory of the isotope shift of the centroid energies of light few-electron atoms is reviewed. Numerical results are presented for the isotope shift of the 2{sup 3}P-2{sup 3}S and 2{sup 1}S-2{sup 3}S transition energies of {sup 3}He and {sup 4}He. By comparing theoretical predictions for the isotope shift with the experimental results, the difference of the squares of the nuclear charge radii of {sup 3}He and {sup 4}He, δR{sup 2}, is determined with high accuracy.

  1. Water in low-mass star-forming regions with Herschel. The link between water gas and ice in protostellar envelopes

    NASA Astrophysics Data System (ADS)

    Schmalzl, M.; Visser, R.; Walsh, C.; Albertsson, T.; van Dishoeck, E. F.; Kristensen, L. E.; Mottram, J. C.

    2014-12-01

    Aims: Our aim is to determine the critical parameters in water chemistry and the contribution of water to the oxygen budget by observing and modelling water gas and ice for a sample of eleven low-mass protostars, for which both forms of water have been observed. Methods: A simplified chemistry network, which is benchmarked against more sophisticated chemical networks, is developed that includes the necessary ingredients to determine the water vapour and ice abundance profiles in the cold, outer envelope in which the temperature increases towards the protostar. Comparing the results from this chemical network to observations of water emission lines and previously published water ice column densities, allows us to probe the influence of various agents (e.g., far-ultraviolet (FUV) field, initial abundances, timescales, and kinematics). Results: The observed water ice abundances with respect to hydrogen nuclei in our sample are 30-80 ppm, and therefore contain only 10-30% of the volatile oxygen budget of 320 ppm. The keys to reproduce this result are a low initial water ice abundance after the pre-collapse phase together with the fact that atomic oxygen cannot freeze-out and form water ice in regions with Tdust ≳ 15 K. This requires short prestellar core lifetimes ≲0.1 Myr. The water vapour profile is shaped through the interplay of FUV photodesorption, photodissociation, and freeze-out. The water vapour line profiles are an invaluable tracer for the FUV photon flux and envelope kinematics. Conclusions: The finding that only a fraction of the oxygen budget is locked in water ice can be explained either by a short pre-collapse time of ≲0.1 Myr at densities of nH ~ 104 cm-3, or by some other process that resets the initial water ice abundance for the post-collapse phase. A key for the understanding of the water ice abundance is the binding energy of atomic oxygen on ice. Herschel is an ESA space observatory with science instruments provided by European

  2. 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.

  3. Postural Stability is Altered by Blood Shift

    NASA Astrophysics Data System (ADS)

    Marais, M.; Denise, P.; Guincetre, J. Y.; Normand, H.

    2008-06-01

    Non-vestibular influences as shift in blood volume changed perception of body posture. Then, factors affecting blood shift may alter postural control. The purpose of our study was to investigate the effects of leg venous contention on postural stability. Twelve subjects were studied on a balance plate for 5 minutes with the eyes closed, in 3 conditions: with no leg venous contention or grade 1 and 3 support stockings. Standard deviation of x and y position was calculated before and after the closure of the eyes. Strong venous contention altered postural stability, after the eyes were closed, during the first 10 s of standing. As support stockings prevent blood shift induced by upright posture, this result is in line with the hypothesis that blood shifts influence the perception of body orientation and postural control among others factors as vision, vestibular inputs... This strong venous contention could induce an increase of fall.

  4. Tracking a phase-shift-keyed signal

    NASA Technical Reports Server (NTRS)

    Villarreal, S.; Lenett, S. D.; Kobayashi, H. S.; Pawlowski, J. F.

    1977-01-01

    In detector, phase shifter is used to generate negative phase shift opposing detected phase angle. This produces converted series sideband and component carrier, with residual carrier signal and converted series sideband and component carrier added together to produce tracking signal.

  5. Gradual regime shifts in fairy circles.

    PubMed

    Zelnik, Yuval R; Meron, Ehud; Bel, Golan

    2015-10-01

    Large responses of ecosystems to small changes in the conditions--regime shifts--are of great interest and importance. In spatially extended ecosystems, these shifts may be local or global. Using empirical data and mathematical modeling, we investigated the dynamics of the Namibian fairy circle ecosystem as a case study of regime shifts in a pattern-forming ecosystem. Our results provide new support, based on the dynamics of the ecosystem, for the view of fairy circles as a self-organization phenomenon driven by water-vegetation interactions. The study further suggests that fairy circle birth and death processes correspond to spatially confined transitions between alternative stable states. Cascades of such transitions, possible in various pattern-forming systems, result in gradual rather than abrupt regime shifts. PMID:26362787

  6. Amplitude dependence of the tune shift

    SciTech Connect

    Gelfand, N.M.

    1986-03-01

    Recent studies in the Tevatron have measured the tune shift as a function of the displacement from a closed orbit. The measured values of tune shift were found to be much smaller than one would expect from the measured distribution of the normal octupole moments in the Tevatron. Tracking studies performed to see if, and under what conditions, the observed results could be obtained are reported. The effect of linear coupling is taken into consideration, and is found to significantly reduce the coefficient of the tune shift. The dependence of the tune shift on the initial coordinate of a particle in the presence of a distribution of octupole moments is calculated. The ''smear'' is calculated as a function of linear coupling. (LEW)

  7. Shift Work and Child Behavioral Outcomes

    PubMed Central

    Han, Wen-Jui

    2011-01-01

    Using a large, contemporary U.S. dataset, the National Longitudinal Survey of Youth–Child Supplement, this paper explores the relationship between maternal shift work and the behavioral outcomes of children aged 4 to 10. Special attention was given to subgroups of children (e.g., based on family type, family income, and mother’s occupation and working hours) and the patterns of parental work schedules and work hours. Regression results suggest that maternal shift work may contribute to more behavioral problems. Of all children whose mothers worked non-day shifts, the strongest associations were found for children who lived in single-mother or low-income families, whose mothers worked in cashier or service occupations, and whose mothers worked non-day shifts full-time. Implications for future research are discussed. PMID:21666886

  8. Red Shifts with Obliquely Approaching Light Sources.

    ERIC Educational Resources Information Center

    Head, C. E.; Moore-Head, M. E.

    1988-01-01

    Refutes the Doppler effect as the explanation of large red shifts in the spectra of distant galaxies and explains the relativistic effects in which the light sources approach the observer obliquely. Provides several diagrams and graphs. (YP)

  9. Illuminating geographical patterns in species' range shifts.

    PubMed

    Grenouillet, Gaël; Comte, Lise

    2014-10-01

    Species' range shifts in response to ongoing climate change have been widely documented, but although complex spatial patterns in species' responses are expected to be common, comprehensive comparisons of species' ranges over time have undergone little investigation. Here, we outline a modeling framework based on historical and current species distribution records for disentangling different drivers (i.e. climatic vs. nonclimatic) and assessing distinct facets (i.e. colonization, extirpation, persistence, and lags) of species' range shifts. We used extensive monitoring data for stream fish assemblages throughout France to assess range shifts for 32 fish species between an initial period (1980-1992) and a contemporary one (2003-2009). Our results provide strong evidence that the responses of individual species varied considerably and exhibited complex mosaics of spatial rearrangements. By dissociating range shifts in climatically suitable and unsuitable habitats, we demonstrated that patterns in climate-driven colonization and extirpation were less marked than those attributed to nonclimatic drivers, although this situation could rapidly shift in the near future. We also found evidence that range shifts could be related to some species' traits and that the traits involved varied depending on the facet of range shift considered. The persistence of populations in climatically unsuitable areas was greater for short-lived species, whereas the extent of the lag behind climate change was greater for long-lived, restricted-range, and low-elevation species. We further demonstrated that nonclimatic extirpations were primarily related to the size of the species' range, whereas climate-driven extirpations were better explained by thermal tolerance. Thus, the proposed framework demonstrated its potential for markedly improving our understanding of the key processes involved in range shifting and also offers a template for informing management decisions. Conservation strategies

  10. Sleep deprivation due to shift work.

    PubMed

    Costa, Giovanni

    2015-01-01

    Sleep deprivation due to shift work is related to perturbation of the sleep/wake cycle, associated with the modified activity/rest pattern. This may cause a significant disruption of circadian rhythms of biologic functions, driven by the body clock located in the suprachiasmatic nuclei of the hypothalamus. Shift and night workers have to change sleep times and strategies according to their duty periods; consequently, both sleep length and quality can be considerably affected depending on the variable start and finish times on different shifts. About 10% of night and rotating shift workers, aged between 18 and 65 years, have been estimated to have a diagnosable "shift-work sleep disorder," according to the International Classification of Sleep Disorders, version 2 (ICSD-2). In the long run, this may lead to persistent and severe disturbances of sleep, chronic fatigue and psychoneurotic syndromes, besides being a risk or aggravating factor for accidents, gastrointestinal, cardiovascular, and reproductive disorders, as well as, probably, for cancer. Preventive and corrective actions deal with the organization of shift schedules according to ergonomic criteria, careful health surveillance, appropriate education and training on effective countermeasures, in particular, sleep hygiene and napping. PMID:26563802

  11. Cellular cooperation with shift updating and repulsion

    PubMed Central

    Pavlogiannis, Andreas; Chatterjee, Krishnendu; Adlam, Ben; Nowak, Martin A.

    2015-01-01

    Population structure can facilitate evolution of cooperation. In a structured population, cooperators can form clusters which resist exploitation by defectors. Recently, it was observed that a shift update rule is an extremely strong amplifier of cooperation in a one dimensional spatial model. For the shift update rule, an individual is chosen for reproduction proportional to fecundity; the offspring is placed next to the parent; a random individual dies. Subsequently, the population is rearranged (shifted) until all individual cells are again evenly spaced out. For large population size and a one dimensional population structure, the shift update rule favors cooperation for any benefit-to-cost ratio greater than one. But every attempt to generalize shift updating to higher dimensions while maintaining its strong effect has failed. The reason is that in two dimensions the clusters are fragmented by the movements caused by rearranging the cells. Here we introduce the natural phenomenon of a repulsive force between cells of different types. After a birth and death event, the cells are being rearranged minimizing the overall energy expenditure. If the repulsive force is sufficiently high, shift becomes a strong promoter of cooperation in two dimensions. PMID:26602306

  12. Kinematics of the scaphoid shift test.

    PubMed

    Wolfe, S W; Gupta, A; Crisco, J J

    1997-09-01

    Twenty-five uninjured subjects (50 wrists) were examined clinically and fluoroscopically during performance of the scaphoid shift test. Wrists were placed into 3 groups on the basis of the degree of palpable carpal motion that occurred during the clinical examination. Kinematic parameters of rotation and displacement were calculated from digitized images of the carpals at rest and at maximum displacement. On clinical exam, 36% of normal individuals had positive findings on scaphoid shift test. Dorsal displacement of the scaphoid was not significantly associated with positive scaphoid shift test results in these subjects, while total displacement of the scaphoid (the sum of axial and dorsal displacement) was significantly associated with positive test results. The principle confounding factor appeared to be a high degree of displacement that occurred at the capitolunate joint in some individuals, termed a "midcarpal shift." The data demonstrate that despite a high prevalence of positive scaphoid shifts among uninjured individuals, the ability to accurately detect dorsal displacement of the scaphoid using the scaphoid shift test is limited. On the basis of their findings, the authors recommend that positive test results be confirmed fluoroscopically. PMID:9330136

  13. Primary reactions of sensory rhodopsins

    PubMed Central

    Lutz, I.; Sieg, A.; Wegener, A. A.; Engelhard, M.; Boche, I.; Otsuka, M.; Oesterhelt, D.; Wachtveitl, J.; Zinth, W.

    2001-01-01

    The first steps in the photocycles of the archaeal photoreceptor proteins sensory rhodopsin (SR) I and II from Halobacterium salinarum and SRII from Natronobacterium pharaonis have been studied by ultrafast pump/probe spectroscopy and steady-state fluorescence spectroscopy. The data for both species of the blue-light receptor SRII suggests that their primary reactions are nearly analogous with a fast decay of the excited electronic state in 300–400 fs and a transition between two red-shifted product states in 4–5 ps. Thus SRII behaves similarly to bacteriorhodopsin. In contrast for SRI at pH 6.0, which absorbs in the orange part of the spectrum, a strongly increased fluorescence quantum yield and a drastically slower and biexponential decay of the excited electronic state occurring on the picosecond time scale (5 ps and 33 ps) is observed. The results suggest that the primary reactions are controlled by the charge distribution in the vicinity of the Schiff base and demonstrate that there is no direct connection between absorption properties and reaction dynamics for the retinal protein family. PMID:11158578

  14. The Glyoxal Clock Reaction

    ERIC Educational Resources Information Center

    Ealy, Julie B.; Negron, Alexandra Rodriguez; Stephens, Jessica; Stauffer, Rebecca; Furrow, Stanley D.

    2007-01-01

    Research on the glyoxal clock reaction has led to adaptation of the clock reaction to a general chemistry experiment. This particular reaction is just one of many that used formaldehyde in the past. The kinetics of the glyoxal clock makes the reaction suitable as a general chemistry lab using a Calculator Based Laboratory (CBL) or a LabPro. The…

  15. Practice Gaps: Drug Reactions.

    PubMed

    Wolverton, Stephen E

    2016-07-01

    The term "drug reactions" is relevant to dermatology in three categories of reactions: cutaneous drug reactions without systemic features, cutaneous drug reactions with systemic features, and systemic drugs prescribed by the dermatologist with systematic adverse effects. This article uses examples from each of these categories to illustrate several important principles central to drug reaction diagnosis and management. The information presented will help clinicians attain the highest possible level of certainty before making clinical decisions. PMID:27363888

  16. A holistic view of marine regime shifts

    PubMed Central

    Conversi, Alessandra; Dakos, Vasilis; Gårdmark, Anna; Ling, Scott; Folke, Carl; Mumby, Peter J.; Greene, Charles; Edwards, Martin; Blenckner, Thorsten; Casini, Michele; Pershing, Andrew; Möllmann, Christian

    2015-01-01

    Understanding marine regime shifts is important not only for ecology but also for developing marine management that assures the provision of ecosystem services to humanity. While regime shift theory is well developed, there is still no common understanding on drivers, mechanisms and characteristic of abrupt changes in real marine ecosystems. Based on contributions to the present theme issue, we highlight some general issues that need to be overcome for developing a more comprehensive understanding of marine ecosystem regime shifts. We find a great divide between benthic reef and pelagic ocean systems in how regime shift theory is linked to observed abrupt changes. Furthermore, we suggest that the long-lasting discussion on the prevalence of top-down trophic or bottom-up physical drivers in inducing regime shifts may be overcome by taking into consideration the synergistic interactions of multiple stressors, and the special characteristics of different ecosystem types. We present a framework for the holistic investigation of marine regime shifts that considers multiple exogenous drivers that interact with endogenous mechanisms to cause abrupt, catastrophic change. This framework takes into account the time-delayed synergies of these stressors, which erode the resilience of the ecosystem and eventually enable the crossing of ecological thresholds. Finally, considering that increased pressures in the marine environment are predicted by the current climate change assessments, in order to avoid major losses of ecosystem services, we suggest that marine management approaches should incorporate knowledge on environmental thresholds and develop tools that consider regime shift dynamics and characteristics. This grand challenge can only be achieved through a holistic view of marine ecosystem dynamics as evidenced by this theme issue.

  17. Shift work and circadian dysregulation of reproduction.

    PubMed

    Gamble, Karen L; Resuehr, David; Johnson, Carl Hirschie

    2013-01-01

    Health impairments, including reproductive issues, are associated with working nights or rotating shifts. For example, shift work has been associated with an increased risk of irregular menstrual cycles, endometriosis, infertility, miscarriage, low birth weight or pre-term delivery, and reduced incidence of breastfeeding. Based on what is known about circadian regulation of endocrine rhythms in rodents (and much less in humans), the circadian clock is an integral regulatory part of the reproductive system. When this 24-h program is disordered by environmental perturbation (such as shift work) or genetic alterations, the endocrine system can be impaired. The purpose of this review is to explore the hypothesis that misalignment of reproductive hormones with the environmental light-dark cycle and/or sleep-wake rhythms can disrupt menstrual cycles, pregnancy, and parturition. We highlight the role of the circadian clock in regulating human reproductive physiology and shift work-induced pathology within each step of the reproductive axis while exploring potential mechanisms from the animal model literature. In addition to documenting the reproductive hazards of shift work, we also point out important gaps in our knowledge as critical areas for future investigation. For example, future studies should examine whether forced desynchronization disrupts gonadotropin secretion rhythms and whether there are sleep/wake schedules that are better or worse for the adaptation of the reproductive system to shift work. These studies are necessary in order to define not only whether or not shift work-induced circadian misalignment impairs reproductive capacity, but also to identify strategies for the future that can minimize this desynchronization. PMID:23966978

  18. Scalar Field Theories with Polynomial Shift Symmetries

    NASA Astrophysics Data System (ADS)

    Griffin, Tom; Grosvenor, Kevin T.; Hořava, Petr; Yan, Ziqi

    2015-12-01

    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.

  19. Personality factors related to shift work tolerance in two- and three-shift workers.

    PubMed

    Natvik, Sylvia; Bjorvatn, Bjørn; Moen, Bente Elisabeth; Magerøy, Nils; Sivertsen, Børge; Pallesen, Ståle

    2011-07-01

    This study aimed to investigate whether different personality variables were associated with shift work tolerance, and whether these potential associations were moderated by various types of shift work. The sample comprised 1505 nurses who worked either two or three rotating shifts. Personality traits were measured in terms of morningness, flexibility, languidity and hardiness. Morningness reflects the tendency to be alert relatively early in the morning and sleepy relatively early in the evening. Flexibility denotes the ability to both work and sleep at odd times of the day, while languidity concerns the tendency to become tired/sleepy when cutting down on sleep. Hardiness relates to resilience to stressful life events. The dependent variables in this study comprised of measures of insomnia, sleepiness, depression and anxiety. Hierarchical regression analyses, which controlled for demographic variables and work load, revealed that Morningness was significantly and negatively related to insomnia. The Morningness by Shift type interaction was overall significant for depressive symptoms. Morningness was near significantly associated with lower levels of depressive symptoms in three-shift workers, but unrelated to depressive symptoms in two-shift workers. Flexibility was associated with higher levels of depressive symptoms. Flexibility by Shift type interaction was significant for insomnia, indicating that flexibility was negatively associated with insomnia for three-shift workers and unrelated with insomnia for two-shift workers. Languidity was associated with higher levels of sleepiness, depressive and anxiety symptoms. Hardiness was associated with lower levels of all four dependent variables. PMID:21172694

  20. Isomer Shifts in Solid State Chemistry

    NASA Astrophysics Data System (ADS)

    Wagner, F. E.; Stievano, L.

    The isomer shift of the Mössbauer resonance is a rather unique quantity that cannot be obtained by any of the other techniques used for measuring hyperfine interactions in solids, such as NMR or perturbed angular correlations (TDPAC). It shifts the resonance pattern as a whole without affecting the magnetic dipole and electric quadrupole hyperfine splittings. Methods that measure only these hyperfine splittings are insensitive to the isomer shift. The magnitude of the observed shift is proportional to the product of a nuclear parameter, the change Δ⟨r 2⟩ of the nuclear radius that goes along with the Mössbauer transition, and to an electronic property of the material, the electron density ρ(0) at the Mössbauer nucleus or, more precisely, to the difference Δρ(0) of the electron densities at the Mössbauer nuclei in the materials of which the source and the absorber are made. The electron density at the nucleus is due to s-electrons and, to a lesser extent and mainly in heavy nuclei, to relativistic p1 / 2-electrons. All the other electrons have a vanishing density inside the nucleus and do not contribute. Thus, to a very good accuracy, the Mössbauer isomer shift enables one to obtain information on the s-electron density at the Mössbauer nuclei in solids.

  1. Social reasoning about 'second-shift' parenting.

    PubMed

    Sinno, Stefanie M; Killen, Melanie

    2011-06-01

    The present study investigated children's and adolescents' social reasoning about parenting roles in the home, specifically 'second-shift parenting' by a mother or father. Surveys were administered to children (age 10) and adolescents (age 13), nearly evenly divided by gender (N= 200) in which two hypothetical scenarios were evaluated. Participants were asked to evaluate and justify second-shift parenting arrangements for the family overall, for the parent in the role, and for the child in the family. Results showed that participants expected mothers rather than fathers to take on the second-shift role, and second-shift parenting was evaluated as more unfair for fathers than for mothers. Personal choice reasoning was used for justifying arrangements for the second-shift parent and moral reasoning was used for justifying arrangements for the child. Social reasoning about the context of parental caretaking roles was multifaceted and varied by age and gender of participant more so than by self-reported personal family arrangements. PMID:21592152

  2. Nozzle Aerodynamic Stability During a Throat Shift

    NASA Technical Reports Server (NTRS)

    Kawecki, Edwin J.; Ribeiro, Gregg L.

    2005-01-01

    An experimental investigation was conducted on the internal aerodynamic stability of a family of two-dimensional (2-D) High Speed Civil Transport (HSCT) nozzle concepts. These nozzles function during takeoff as mixer-ejectors to meet acoustic requirements, and then convert to conventional high-performance convergent-divergent (CD) nozzles at cruise. The transition between takeoff mode and cruise mode results in the aerodynamic throat and the minimum cross-sectional area that controls the engine backpressure shifting location within the nozzle. The stability and steadiness of the nozzle aerodynamics during this so called throat shift process can directly affect the engine aerodynamic stability, and the mechanical design of the nozzle. The objective of the study was to determine if pressure spikes or other perturbations occurred during the throat shift process and, if so, identify the caused mechanisms for the perturbations. The two nozzle concepts modeled in the test program were the fixed chute (FC) and downstream mixer (DSM). These 2-D nozzles differ principally in that the FC has a large over-area between the forward throat and aft throat locations, while the DSM has an over-area of only about 10 percent. The conclusions were that engine mass flow and backpressure can be held constant simultaneously during nozzle throat shifts on this class of nozzles, and mode shifts can be accomplished at a constant mass flow and engine backpressure without upstream pressure perturbations.

  3. Choice Shift in Opinion Network Dynamics

    NASA Astrophysics Data System (ADS)

    Gabbay, Michael

    Choice shift is a phenomenon associated with small group dynamics whereby group discussion causes group members to shift their opinions in a more extreme direction so that the mean post-discussion opinion exceeds the mean pre-discussion opinion. Also known as group polarization, choice shift is a robust experimental phenomenon and has been well-studied within social psychology. In opinion network models, shifts toward extremism are typically produced by the presence of stubborn agents at the extremes of the opinion axis, whose opinions are much more resistant to change than moderate agents. However, we present a model in which choice shift can arise without the assumption of stubborn agents; the model evolves member opinions and uncertainties using coupled nonlinear differential equations. In addition, we briefly describe the results of a recent experiment conducted involving online group discussion concerning the outcome of National Football League games are described. The model predictions concerning the effects of network structure, disagreement level, and team choice (favorite or underdog) are in accord with the experimental results. This research was funded by the Office of Naval Research and the Defense Threat Reduction Agency.

  4. 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.

  5. Dreaming: The functional state-shift hypothesis. A neuropsychophysiological model.

    PubMed

    Koukkou, M; Lehmann, D

    1983-03-01

    The different brain functional states during sleep and wakefulness are associated with differences in processing strategies, memory stores, and EEG patterns. Shifts of functional state occur spontaneously or as orienting reactions to processed information, and cause the formal characteristics of dreams. Forgetting of dreams is a function of the magnitude of the difference between states during storage and recall. Based on EEG similarities between sleep stages and developmental stages, brain states during sleep in adults are proposed to correspond functionally with waking states during childhood. Repeated functional regressions occur during sleep, with access to earlier memory material and cognitive strategies unavailable during waking life, so that earlier experiences can be used for current problems. This dream work constitutes the biological significance of sleep. PMID:6860875

  6. Energy shift due to anisotropic blackbody radiation

    NASA Astrophysics Data System (ADS)

    Flambaum, V. V.; Porsev, S. G.; Safronova, M. S.

    2016-02-01

    In many applications a source of the blackbody radiation (BBR) can be highly anisotropic. This leads to the BBR shift that depends on tensor polarizability and on the projection of the total angular momentum of ions and atoms in a trap. We derived a formula for the anisotropic BBR shift and performed numerical calculations of this effect for Ca+and Yb+ transitions of experimental interest. These ions were used for a design of high-precision atomic clocks, fundamental physics tests such as the search for the Lorentz invariance violation and space-time variation of the fundamental constants, and quantum information. Anisotropic BBR shift may be one of the major systematic effects in these experiments.

  7. Gradual regime shifts in fairy circles

    PubMed Central

    Zelnik, Yuval R.; Meron, Ehud; Bel, Golan

    2015-01-01

    Large responses of ecosystems to small changes in the conditions—regime shifts—are of great interest and importance. In spatially extended ecosystems, these shifts may be local or global. Using empirical data and mathematical modeling, we investigated the dynamics of the Namibian fairy circle ecosystem as a case study of regime shifts in a pattern-forming ecosystem. Our results provide new support, based on the dynamics of the ecosystem, for the view of fairy circles as a self-organization phenomenon driven by water–vegetation interactions. The study further suggests that fairy circle birth and death processes correspond to spatially confined transitions between alternative stable states. Cascades of such transitions, possible in various pattern-forming systems, result in gradual rather than abrupt regime shifts. PMID:26362787

  8. Differential Stark shifts in the hydrogen maser

    SciTech Connect

    Stuart, J.G.; Larson, D.J.; Ramsey, N.F.

    1980-11-01

    The theory of the Stark shift of hydrogen ground-state hyperfine levels has been tested at the 2.4% level of accuracy in a hydrogen maser. The quadratic-Stark-shift coefficient for the hyperfine-transition frequency was experimentally found to be delta..nu.. x 10/sup -14/ Hz (V/m)/sup -2/, where the electric field was perpendicular to the axis of quantization. The quoted uncertainty corresponds to one standard deviation. The uncertainty has contributions from the statistics of the data and from systematic effects. A number of possible sources of systematic error or unwanted frequency shifts has been tested. The theoretically predicted coefficient delta..nu.. x 10/sup -14/ Hz (V/m)/sup -2/ is in reasonable agreement with the present experimental result.

  9. The affective shift model of work engagement.

    PubMed

    Bledow, Ronald; Schmitt, Antje; Frese, Michael; Kühnel, Jana

    2011-11-01

    On the basis of self-regulation theories, the authors develop an affective shift model of work engagement according to which work engagement emerges from the dynamic interplay of positive and negative affect. The affective shift model posits that negative affect is positively related to work engagement if negative affect is followed by positive affect. The authors applied experience sampling methodology to test the model. Data on affective events, mood, and work engagement was collected twice a day over 9 working days among 55 software developers. In support of the affective shift model, negative mood and negative events experienced in the morning of a working day were positively related to work engagement in the afternoon if positive mood in the time interval between morning and afternoon was high. Individual differences in positive affectivity moderated within-person relationships. The authors discuss how work engagement can be fostered through affect regulation. PMID:21766997

  10. 12 hour shifts the Nambour Hospital experience.

    PubMed

    2007-08-01

    Union members have a lengthy history of campaigning for fair working hours and conditions. The success of such campaigns has led to the implementation of the eight hour working day and the 40 hour and then 38 hour week as industrial standards. More recently though, calls for greater flexibility in their shift arrangements by nurses at Nambour Hospital have led to a voluntary 12 hour shift being implemented in their Intensive Care Unit. While union members are protective of their hard won gains in achieving reduced working hours through the 8 hour day--ICU nurses at Nambour Hospital say the voluntary 12 hour shift initiative goes a way in addressing their work/life balance issues. PMID:17879604

  11. Shift symmetry and inflation in supergravity

    SciTech Connect

    Brax, Philippe; Martin, Jerome

    2005-07-15

    We consider models of inflation in supergravity with a shift symmetry. We focus on models with one modulus and one inflaton field. The presence of this symmetry guarantees the existence of a flat direction for the inflaton field. Mildly breaking the shift symmetry using a superpotential which depends not only on the modulus, but also on the inflaton field allows one to lift the inflaton flat direction. Along the inflaton direction, the {eta} problem is alleviated. Combining the KKLT mechanism for modulus stabilization and a shift symmetry breaking superpotential of the chaotic inflation type, we find models reminiscent of 'mutated hybrid inflation' where the inflationary trajectory is curved in the modulus-inflaton plane. We analyze the phenomenology of these models and stress their differences with both chaotic and hybrid inflation.

  12. Clock shifts in the Unitary Bose Gas

    NASA Astrophysics Data System (ADS)

    Fletcher, Richard; Man, Jay; Lopes, Raphael; Navon, Nir; Smith, Robert; Hadzibabic, Zoran

    2016-05-01

    Clock shifts are interaction-induced changes in the transition frequency between atomic spin states. So-called because of their importance as systematic errors in atomic clocks, they reveal details of both the interaction energy within a gas and the particle correlations. In this work, we employ a RF-injection technique to rapidly project a thermal Bose gas into the unitary regime on a timescale much shorter than three-body losses. Working with a two-state system, one of which exhibits strong intrastate interactions, we carry out Ramsey spectroscopy to extract the variation in the clock shift across a Feshbach resonance. Thanks to the relationship between these shifts and particle correlations, we use our measurements to infer the contact as a function of both interaction strength and degeneracy. This quantity plays a central role in the many-body physics of strongly correlated systems, offering a link between few-body and thermodynamic behaviour.

  13. Understanding and diagnosing shift work disorder.

    PubMed

    Thorpy, Michael

    2011-09-01

    A significant proportion of the workforce in industrialized countries (16%) are employed as shift workers. These workers may be susceptible to shift work disorder (SWD), a circadian rhythm sleep disorder, particularly those who work at night or on early-morning shifts. Shift work disorder remains an underdiagnosed and undertreated problem among this population. Patients with SWD have difficulty initiating sleep and waking up. Often, these patients have excessive sleepiness during their work shift. Shift work disorder has been associated with decreased productivity, impaired safety, diminished quality of life, and adverse effects on health. Several tools have been validated to assess excessive daytime sleepiness and are often used to assess excessive nighttime sleepiness, such as that experienced in patients with SWD, including the Epworth Sleepiness Scale and the Multiple Sleep Latency Test. The criteria for diagnosing SWD as established by the American Academy of Sleep Medicine (AASM) and published in the International Classification of Sleep Disorders-Second Edition (ICSD-2) were most recently updated in 2005 and thus do not contain newer agents approved for use in patients with SWD. The symptoms of SWD can be treated using behavioral, prescription, and nonprescription therapies. Current treatment guidelines suggest nonpharmacologic interventions, such as exercise and exposure to light. In addition, medications that contain melatonin or caffeine may have clinical benefits in some patients with SWD. However, modafinil and armodafinil are approved by the US Food and Drug Administration to improve wakefulness in patients with excessive sleepiness associated with SWD, and recent data suggest a clinical benefit. The use of these therapies can significantly improve sleep, performance, and quality of life for patients with SWD. PMID:21904091

  14. Shift work in a security environment

    SciTech Connect

    Longhouser, G.A. Jr.

    1993-12-31

    Human beings are diurnal species, normally active by day and asleep by night. Yet over thirty million Americans struggle with work schedules that include an off-normal work effort. The railroads, law enforcement, health services, Department of Defense, factory workers, chemical plants and public services, communications and utility workers must provide some form of around-the-clock effort. Shift work has been around since the advent of recorded history. There has always been a need for some type of off-normal service and assistance. The impact of shift work is replete with tales and factual evidence of an increased personnel error rate; disorders, both personal and family, and of course, increased accident events. In recent memory, the Three Mile Island Nuclear Plant incident, Union Carbide`s explosion in Bhopal, and the Chernobyl Nuclear Plant catastrophe all occurred during off-normal working hours. Yet management overall has done little to correct the production-driven twelve hour, seven day week shift mentality of the nineteenth century. Most schedules in use today are nothing more than cosmetic variations of the old production schedules. This could be driven by a management consideration of the worker`s response to change coupled with a reluctant buy-in of responsibility for the effects of change. Florida Power Corporation has developed for its nuclear security force, a unique work schedule which attempts to employ the sound principles of circadian rhythms coupled with a comprehensive training program to counter the problems associated with shift work. The results over the last four years have seen a marked reduction in the generic problems of personnel errors, absenteeism, unscheduled overtime and turnover rates. Utilization and understanding of this scheduling process for rotational shift work needs to be assessed to determine if the benefits are site specific or provide an expected response to the problems of shift work.

  15. 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.

  16. What are 12-hour shifts good for?

    PubMed

    In the UK many hospitals use 12-hour shifts, believing it to be a cost-efficient means of providing 24-hour nursing care on wards. While healthcare organisations need to find ways to deliver nursing care around the clock and efficiency is a key consideration, nurse leaders have raised concerns about ' whether nurses can function effectively and safely when working long hours (Calkin, 2012; Rogers et al, 2004). In this Policy Plus, we focus specifically on what is known about the impact of shift length on patient safety, employee health and quality of care. PMID:23696995

  17. 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.

  18. 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.

  19. Shift-and-add for astronomical imaging

    NASA Technical Reports Server (NTRS)

    Ribak, Erez; Hege, E. Keith; Strobel, Nicolas V.; Christou, Julian C.

    1989-01-01

    Diffraction-limited astronomical images have been obtained utilizing a variant of the shift-and-add method. It is shown that the matched filter approach for extending the weighted shift-and-add method reduces specklegrams from extended objects and from an object dominated by photon noise. The method is aberration-insensitive and yields very high dynamic range results. The iterative method for arriving at the matched filter does not automatically converge in the case of photon-noisy specklegrams for objects with more than one maximum.

  20. Response-Based Strengthening in Task Shifting: Evidence from Shift Effects Produced by Errors

    ERIC Educational Resources Information Center

    Steinhauser, Marco; Hubner, Ronald

    2006-01-01

    The hypothesis is introduced that 1 source of shift costs is the strengthening of task-related associations occurring whenever an overt response is produced. The authors tested this account by examining shift effects following errors and error compensation processes. The authors predicted that following a specific type of error, called task…

  1. Microfluidic chemical reaction circuits

    DOEpatents

    Lee, Chung-cheng; Sui, Guodong; Elizarov, Arkadij; Kolb, Hartmuth C.; Huang, Jiang; Heath, James R.; Phelps, Michael E.; Quake, Stephen R.; Tseng, Hsian-rong; Wyatt, Paul; Daridon, Antoine

    2012-06-26

    New microfluidic devices, useful for carrying out chemical reactions, are provided. The devices are adapted for on-chip solvent exchange, chemical processes requiring multiple chemical reactions, and rapid concentration of reagents.

  2. Continuous detonation reaction engine

    NASA Technical Reports Server (NTRS)

    Lange, O. H.; Stein, R. J.; Tubbs, H. E.

    1968-01-01

    Reaction engine operates on the principles of a controlled condensed detonation rather than on the principles of gas expansion. The detonation results in reaction products that are expelled at a much higher velocity.

  3. Allergic reactions (image)

    MedlinePlus

    Allergic reaction is a sensitivity to a specific substance, called an allergen, that is contacted through the skin, inhaled into the lungs, swallowed or injected. The body's reaction to an allergen can be mild, such as ...

  4. Allergic reactions (image)

    MedlinePlus

    Allergic reaction can be provoked by skin contact with poison plants, chemicals and animal scratches, as well as by ... dust, nuts and shellfish, may also cause allergic reaction. Medications such as penicillin and other antibiotics are ...

  5. 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)

  6. Electrostatic Interactions Are Key to C═O n-π* Shifts: An Experimental Proof.

    PubMed

    Haldar, Tapas; Bagchi, Sayan

    2016-06-16

    Carbonyl n-π* transitions are known to undergo blue shift in polar and hydrogen-bonding solvents. Using semiempirical expressions, previous studies hypothesized several factors like change in dipole moment and hydrogen-bond strength upon excitation to cause the blue shift. Theoretically, ground-state electrostatics has been predicted to be the key to the observed shifts, however, an experimental proof has been lacking. Our experimental results demonstrate a consistent linear correlation between IR (ground-state phenomenon) and n-π* frequency shifts (involves both ground and excited electronic-states) of carbonyls in hydrogen-bonded and non-hydrogen-bonded environments. The carbonyl hydrogen-bonding status is experimentally verified from deviation in n-π*/fluorescence correlation. The IR/n-π* correlation validates the key role of electrostatic stabilization of the ground state toward n-π* shifts and demonstrates the electrostatic nature of carbonyl hydrogen bonds. n-π* shifts show linear sensitivity to calculated electrostatic fields on carbonyls. Our results portray the potential for n-π* absorption to estimate local polarity in biomolecules and to probe chemical reactions involving carbonyl activation/stabilization. PMID:27249517

  7. Reaction coordinates for electron transfer reactions

    SciTech Connect

    Rasaiah, Jayendran C.; Zhu Jianjun

    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. Has the Education Paradigm Begun to Shift?

    ERIC Educational Resources Information Center

    Chadwick, Clifton B.

    2014-01-01

    The author reviews various elements of what may be considered as evidence that the long-awaited shift in the education paradigm is actually happening. Concepts like student-centered learning, attainment-based evaluation, knowledge-based constructivism, and effort-based intelligence are growing, are being more widely recognized as important, and…

  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. Paradigmatic Shift or Tinkering at the Edges?

    ERIC Educational Resources Information Center

    Sutherland, Margaret

    2012-01-01

    In their target paper, "Towards a systemic theory of gifted education," A. Ziegler and S. N. Phillipson present a long awaited call for a paradigmatic shift in thinking within the field of gifted education. The paper considers how educators and researchers within the field could bring about such a change. They challenge the prevailing…

  11. 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

  12. A Paradigm Shift to Improve Academic Performance

    ERIC Educational Resources Information Center

    Rulloda, Rudolfo B.

    2009-01-01

    A shift to computer skills for improving academic performances was investigated. The No Child Left Behind Act of 2001 increased the amount of high school dropouts after the Act was enacted. At-risk students were included in this research study. Several models described using teachers for core subjects and mentors to built citizenship skills, along…

  13. Shifting Paradigms: From Flexner to Competencies.

    ERIC Educational Resources Information Center

    Carraccio, Carol; Wolfsthal, Susan D.; Englander, Robert; Ferentz, Kevin; Martin, Christine

    2002-01-01

    Reviewed the literature on competency-based medical education to: (1) understand the evolution of this educational paradigm; (2) assess the evidence to date of the efficacy of competency-based education; and (3) provide practical insights into how to accomplish full implementation and evaluation of the paradigm shift. (EV)

  14. Study Predicts Dramatic Shifts in Enrollments.

    ERIC Educational Resources Information Center

    Evangelauf, Jean

    1991-01-01

    A new study detailing demographic shifts in the college-age population predicts growth in minority high school graduates and shrinkage or maintenance of White graduation rates. The report is the first to provide state-by-state figures on actual and projected graduates from 1986 through 1995 by racial and ethnic group. (MSE)

  15. Chain Shift in Second Language Phonological Acquisition.

    ERIC Educational Resources Information Center

    Lee, Shin-Sook

    2000-01-01

    Examines whether Korean students learning English as a Second Language show chain shift of a similar kind to that demonstrated in first language acquisition, and if so, whether there is any difference between first language acquisition and second language acquisition with respect to affected sounds. (Author/VWL)

  16. Improved phase-shift-keyed detector

    NASA Technical Reports Server (NTRS)

    Chandler, J.

    1969-01-01

    Improved phase-shift-keyed detector contains an active filter circuit which uses an operational amplifier and resistor-capacitor network. The detector is used in the Saturn space vehicle and Apollo telescope mount command systems to translate an analog signal from the command receiver into digital information for the command decoder.

  17. 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.…

  18. 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…

  19. Gas composition shifts in Devonian shales

    SciTech Connect

    Schettler, P.D.; Parmely, C.R. )

    1989-08-01

    Analysis of the gas composition of Devonian shale wells indicates that the composition of produced gas shifts during the production history of the well. Possible mechanisms to explain this behavior are examined in light of field and laboratory data. Application of diffusion theory is made to explain adsorption-like behavior exhibited by some shales.

  20. Survey Detects Shifting Priorities of School Boards

    ERIC Educational Resources Information Center

    Samuels, Christina A.

    2011-01-01

    The author reports the results of a nationwide survey of school board members which show a shift in focus toward student achievement and away from district-management issues known as the "killer B's": buses, buildings, books, budgets, and bonds. But today's school board members appear not to be as interested in issues that many policy observers…

  1. Ambiguity Produces Attention Shifts in Category Learning

    ERIC Educational Resources Information Center

    Vadillo, Miguel A.; Orgaz, Cristina; Luque, David; Nelson, James Byron

    2016-01-01

    It has been suggested that people and nonhuman animals protect their knowledge from interference by shifting attention toward the context when presented with information that contradicts their previous beliefs. Despite that suggestion, no studies have directly measured changes in attention while participants are exposed to an interference…

  2. RQL Fuel Shifting Sector Rig Test

    NASA Technical Reports Server (NTRS)

    Holdeman, James D. (Technical Monitor); Haid, Daniel A.; Koopman, Frederick S.; Peschke, William O. T.; Siskind, Kenneth S.

    2004-01-01

    The low emissions potential of a Rich-Quench-Lean (RQL) combustor for use in the HIgh Speed Civil transport (HSCT) application was evaluated as part of the NASA Critical Propulsion Components (CPC) Program. Fuel shifting as an approach to combustor control was evaluated in a multiple bank RQL combustor, utilizing reduced scale quench technology implemented in a convoluted linear with quench plate concept.

  3. Accurate phase-shift velocimetry in rock.

    PubMed

    Shukla, Matsyendra Nath; Vallatos, Antoine; Phoenix, Vernon R; Holmes, William M

    2016-06-01

    Spatially resolved Pulsed Field Gradient (PFG) velocimetry techniques can provide precious information concerning flow through opaque systems, including rocks. This velocimetry data is used to enhance flow models in a wide range of systems, from oil behaviour in reservoir rocks to contaminant transport in aquifers. Phase-shift velocimetry is the fastest way to produce velocity maps but critical issues have been reported when studying flow through rocks and porous media, leading to inaccurate results. Combining PFG measurements for flow through Bentheimer sandstone with simulations, we demonstrate that asymmetries in the molecular displacement distributions within each voxel are the main source of phase-shift velocimetry errors. We show that when flow-related average molecular displacements are negligible compared to self-diffusion ones, symmetric displacement distributions can be obtained while phase measurement noise is minimised. We elaborate a complete method for the production of accurate phase-shift velocimetry maps in rocks and low porosity media and demonstrate its validity for a range of flow rates. This development of accurate phase-shift velocimetry now enables more rapid and accurate velocity analysis, potentially helping to inform both industrial applications and theoretical models. PMID:27111139

  4. 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.…

  5. Shift of Meaning and Students' Alternative Concepts

    ERIC Educational Resources Information Center

    Schmidt, Hans-Jurgen; Volke, Dagmar

    2003-01-01

    The purpose of the study was to establish a relationship between the shift of meaning of the concept oxidation that has taken place during the historical development, and students' alternative concepts. First Examination Board papers were examined. The result enabled us to specify the research question. In the main part of the study,…

  6. Majors' Shift to Natural Gas, The

    EIA Publications

    2001-01-01

    The Majors' Shift to Natural Gas investigates the factors that have guided the United States' major energy producers' growth in U.S. natural gas production relative to oil production. The analysis draws heavily on financial and operating data from the Energy Information Administration's Financial Reporting System (FRS)

  7. Solvent stark effects and spectral shifts. II

    SciTech Connect

    Nicol, M; Swain, J; Shum, Y Y; Merin, R; Chen, R H.H.

    1981-03-01

    Solvent shifts of the energies of the lowest /sup 1/L/sub a/ bands of the electronic absorption spectra of anthracene, chrysene, phenanthrene, and tetracene and of the lowest /sup 1/L/sub b/ bands of the electronic absorption spectra of naphthalene, phenanthrene, chrysene, and picene are reported. The origins of these shifts are analyzed in terms of theories developed by Baur and Nicol and by Abe. Satisfactory fits of the experimental data are obtained for theoretical expressions derived from both theories, but discrepancies are observed between the relative magnitudes assigned to the various contributions to the shifts by the two theories. The magnitudes of the parameters of the Baur and Nicol theory, relating solvent shifts to the dielectric constant and refractive index of the solvent, are found to be the same within experimental precision for the /sup 1/L/sub a/ transitions in all of the molecules studied; a similar regularity of the parameters for the /sup 1/L/sub b/ transitions also is observed.

  8. Design principles of shift current photovoltaics

    NASA Astrophysics Data System (ADS)

    Cook, Ashley; Fregoso, Benjamin; de Juan, Fernando; Moore, Joel

    While the basic principles and limitations of conventional solar cells are well understood, relatively little attention has gone toward evaluating and maximizing the potential efficiency of photovoltaic devices based on shift currents. In this work, a sum rule approach is introduced and used to outline design principles for optimizing shift currents for photon energies near the band gap, which depend on wavefunctions via Berry connections as well as standard band structure. Using these we identify two new classes of shift current photovoltaics, ferroelectric polymer films and orthorhombic monochalcogenides, both of which exhibit peak photoresponsivities larger than predictions for previously-known photovoltaics of this type. Using physically-motivated tight-binding models, the full frequency dependent response of these materials is obtained. Exploring the phase space of these models, we find photoresponsivities that can exceed 100 mA/W. These results show that considering the microscopic origin of shift current via effective models allows one to improve the possible efficiency of devices using this mechanism and better grasp their potential to compete with conventional solar cells. This work was completed with the support of an NSERC Michael Smith Foreign Study Supplement.

  9. 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,…

  10. Scientists detect shift in Arctic Ocean system

    NASA Astrophysics Data System (ADS)

    Showstack, Randy

    2011-12-01

    The Arctic Ocean system has shifted to a “new normal” since 2006, and there are now a sufficient number of years of data to indicate this shift, according to a new Arctic Report Card. The report card, issued on 1 December by the U.S. National Oceanic and Atmospheric Administration (NOAA) along with the U.S. Army Corps of Engineers, other agencies, and an international team of researchers, indicates that 2011 saw significant changes to the Arctic atmosphere, sea ice and ocean, and hydrology and terrestrial cryosphere, as well as some changes to Arctic marine and terrestrial ecosystems, and this shift has widespread environmental and social implications. The report refers to 2006 because precursors that year led to dramatic sea ice loss in 2007. “The shift is characterized by the persistent decline in the thickness and summer extent of the sea ice cover and a warmer, fresher upper ocean,” according to the report, which also indicates a repeated occurrence of 2010 Arctic winter wind patterns this year that are different from the norm, among other concerns. “The 2011 report card shows that record-setting changes are occurring throughout the Arctic environmental system. Given the projection of continued global warming, it is very likely that major Arctic changes will continue in years to come, with increasing climatic, biological, and social impacts,” the report indicates.

  11. NMR crystallography: the use of chemical shifts

    NASA Astrophysics Data System (ADS)

    Harris, Robin K.

    2004-10-01

    Measurements of chemical shifts obtained from magic-angle spinning NMR spectra (together with quantum mechanical computations of shielding) can provide valuable information on crystallography. Examples are given of the determination of crystallographic asymmetric units, of molecular symmetry in the solid-state environment, and of crystallographic space group assignment. Measurements of full tensor components for 199Hg have given additional coordination information. The nature of intermolecular hydrogen bonding in cortisone acetate polymorphs and solvates is obtained from chemical shift information, also involving measurement of the full tensor parameters. The resulting data have been used as restraints, built into the computation algorithm, in the analysis of powder diffraction patterns to give full crystal structures. A combination of quantum mechanical computation of shielding and measurement of proton chemical shifts (obtained by high-speed MAS) leads to the determination of the position of a proton in an intermolecular hydrogen bond. A recently-developed computer program specifically based on crystallographic repetition has been shown to give acceptable results. Moreover, NMR chemical shifts can distinguish between static and dynamic disorder in crystalline materials and can be used to determine modes and rates of molecular exchange motion.

  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. Hispanics Find Jobs that Shift Migration

    ERIC Educational Resources Information Center

    Gilroy, Marilyn

    2007-01-01

    Economic opportunity, the force that has driven population shifts for years, is changing the face of migration as Hispanics move into parts of the nation beyond border states and traditional ports of entry. North Carolina, Tennessee, Georgia, and Indiana are experiencing a steady growth in Hispanic population. In addition, West Virginia, Ohio, and…

  14. Using LEADS to shift to high performance.

    PubMed

    Fenwick, Shauna; Hagge, Erna

    2016-03-01

    Health systems across Canada are tasked to measure results of all their strategic initiatives. Included in most strategic plans is leadership development. How to measure leadership effectiveness in relation to organizational objectives is key in determining organizational effectiveness. The following findings offer considerations for a 21(st)-century approach to shifting to high-performance systems. PMID:26872796

  15. 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.

  16. Accurate phase-shift velocimetry in rock

    NASA Astrophysics Data System (ADS)

    Shukla, Matsyendra Nath; Vallatos, Antoine; Phoenix, Vernon R.; Holmes, William M.

    2016-06-01

    Spatially resolved Pulsed Field Gradient (PFG) velocimetry techniques can provide precious information concerning flow through opaque systems, including rocks. This velocimetry data is used to enhance flow models in a wide range of systems, from oil behaviour in reservoir rocks to contaminant transport in aquifers. Phase-shift velocimetry is the fastest way to produce velocity maps but critical issues have been reported when studying flow through rocks and porous media, leading to inaccurate results. Combining PFG measurements for flow through Bentheimer sandstone with simulations, we demonstrate that asymmetries in the molecular displacement distributions within each voxel are the main source of phase-shift velocimetry errors. We show that when flow-related average molecular displacements are negligible compared to self-diffusion ones, symmetric displacement distributions can be obtained while phase measurement noise is minimised. We elaborate a complete method for the production of accurate phase-shift velocimetry maps in rocks and low porosity media and demonstrate its validity for a range of flow rates. This development of accurate phase-shift velocimetry now enables more rapid and accurate velocity analysis, potentially helping to inform both industrial applications and theoretical models.

  17. Nuclear waste vitrification efficiency: cold cap reactions

    SciTech Connect

    Hrma, Pavel R.; Kruger, Albert A.; Pokorny, Richard

    2012-12-15

    The cost and schedule of nuclear waste treatment and immobilization are greatly affected by the rate of glass production. Various factors influence the performance of a waste-glass melter. One of the most significant, and also one of the least understood, is the process of batch melting. Studies are being conducted to gain fundamental understanding of the batch reactions, particularly those that influence the rate of melting, and models are being developed to link batch makeup and melter operation to the melting rate. Batch melting takes place within the cold cap, i.e., a batch layer floating on the surface of molten glass. The conversion of batch to glass consists of various chemical reactions, phase transitions, and diffusion-controlled processes. These include water evaporation (slurry feed contains as high as 60% water), gas evolution, the melting of salts, the formation of borate melt, reactions of borate melt with molten salts and with amorphous oxides (Fe2O3 and Al2O3), the formation of intermediate crystalline phases, the formation of a continuous glass-forming melt, the growth and collapse of primary foam, and the dissolution of residual solids. To this list we also need to add the formation of secondary foam that originates from molten glass but accumulates on the bottom of the cold cap. This study presents relevant data obtained for a high-level-waste melter feed and introduces a one-dimensional (1D) mathematical model of the cold cap as a step toward an advanced three-dimensional (3D) version for a complete model of the waste glass melter. The 1D model describes the batch-to-glass conversion within the cold cap as it progresses in a vertical direction. With constitutive equations and key parameters based on measured data, and simplified boundary conditions on the cold-cap interfaces with the glass melt and the plenum space of the melter, the model provides sensitivity analysis of the response of the cold cap to the batch makeup and melter conditions

  18. NUCLEAR WASTE VITRIFICATION EFFICIENCY COLD CAP REACTIONS

    SciTech Connect

    KRUGER AA; HRMA PR; POKORNY R

    2011-07-29

    The cost and schedule of nuclear waste treatment and immobilization are greatly affected by the rate of glass production. Various factors influence the performance of a waste-glass melter. One of the most significant, and also one of the least understood, is the process of batch melting. Studies are being conducted to gain fundamental understanding of the batch reactions, particularly those that influence the rate of melting, and models are being developed to link batch makeup and melter operation to the melting rate. Batch melting takes place within the cold cap, i.e., a batch layer floating on the surface of molten glass. The conversion of batch to glass consists of various chemical reactions, phase transitions, and diffusion-controlled processes. These include water evaporation (slurry feed contains as high as 60% water), gas evolution, the melting of salts, the formation of borate melt, reactions of borate melt with molten salts and with amorphous oxides (Fe{sub 2}O{sub 3} and Al{sub 2}O{sub 3}), the formation of intermediate crystalline phases, the formation of a continuous glass-forming melt, the growth and collapse of primary foam, and the dissolution of residual solids. To this list we also need to add the formation of secondary foam that originates from molten glass but accumulates on the bottom of the cold cap. This study presents relevant data obtained for a high-level-waste melter feed and introduces a one-dimensional (1D) mathematical model of the cold cap as a step toward an advanced three-dimensional (3D) version for a complete model of the waste glass melter. The 1D model describes the batch-to-glass conversion within the cold cap as it progresses in a vertical direction. With constitutive equations and key parameters based on measured data, and simplified boundary conditions on the cold-cap interfaces with the glass melt and the plenum space of the melter, the model provides sensitivity analysis of the response of the cold cap to the batch makeup

  19. Catalytic diastereoselective petasis reactions.

    PubMed

    Muncipinto, Giovanni; Moquist, Philip N; Schreiber, Stuart L; Schaus, Scott E

    2011-08-22

    Multicomponent Petasis reactions: the first diastereoselective Petasis reaction catalyzed by chiral biphenols that enables the synthesis of syn and anti β-amino alcohols in pure form has been developed. The reaction exploits a multicomponent approach that involves boronates, α-hydroxy aldehydes, and amines. PMID:21751322

  20. Rate limiting processes in the bohr shift in human red cells

    PubMed Central

    Forster, R. E.; Steen, J. B.

    1968-01-01

    1. The rates of the Bohr shift of human red cells and some of its constituent reactions have been studied with a modified Hartridge—Roughton rapid reaction apparatus using an oxygen electrode to measure the progress of the reaction. 2. The rate of the Bohr shift was compatible with the hypothesis that the transfer of H+ across the membrane by means of CO2 exchange and reaction with buffers is generally the rate-limiting step. (a) When the Bohr off-reaction was produced by a marked increase in PCO2 around the cells, the half-time at 37° C was 0·12 sec. In this case CO2 was available initially to diffuse into the cells, the process being predominantly limited by the rate of intracellular CO2 hydration. (b) When the Bohr off-shift was produced by an increase of [H+] outside the cell, PCO2 being low and equal within and outside the cells, the half time became 0·31 sec. In this case, even at the start, the H2CO3 formed by the almost instantaneous neutralization reaction of H+ and HCO3- had to dehydrate to form CO2 and this in turn had to diffuse into and react within the red cell before the [HbO2] could change. When a carbonic anhydrase inhibitor was added to slow the CO2 reaction inside the cell, the half-time rose to 10 sec. (c) The Bohr off-shift in a haemolysed cell suspension produced by an increase in PCO2 appeared to be limited by the rate at which the CO2 could hydrate to form H+. 3. The Bohr off-shift has an average Q10 of 2·5 between 42·5 and 28° C with an activation energy of 8000 cal. 4. The pronounced importance of the CO2-bicarbonate system for rapid intracellular pH changes is discussed in connexion with some physiological situations. PMID:5664232

  1. Reaction efficiency effects on binary chemical reactions

    NASA Astrophysics Data System (ADS)

    Lazaridis, Filippos; Savara, Aditya; Argyrakis, Panos

    2014-09-01

    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 γ, where γ is in the range 0 < γ < 1. Our results show that at small γ values the system is reaction limited, but as γ increases it crosses over to a diffusion limited behavior. At early times, for small γ values, the particle density falls slower than for larger γ values. This fall-off goes over a crossover point, around the value of γ = 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 γ 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.

  2. Accessible surface area from NMR chemical shifts.

    PubMed

    Hafsa, Noor E; Arndt, David; Wishart, David S

    2015-07-01

    Accessible surface area (ASA) is the surface area of an atom, amino acid or biomolecule that is exposed to solvent. The calculation of a molecule's ASA requires three-dimensional coordinate data and the use of a "rolling ball" algorithm to both define and calculate the ASA. For polymers such as proteins, the ASA for individual amino acids is closely related to the hydrophobicity of the amino acid as well as its local secondary and tertiary structure. For proteins, ASA is a structural descriptor that can often be as informative as secondary structure. Consequently there has been considerable effort over the past two decades to try to predict ASA from protein sequence data and to use ASA information (derived from chemical modification studies) as a structure constraint. Recently it has become evident that protein chemical shifts are also sensitive to ASA. Given the potential utility of ASA estimates as structural constraints for NMR we decided to explore this relationship further. Using machine learning techniques (specifically a boosted tree regression model) we developed an algorithm called "ShiftASA" that combines chemical-shift and sequence derived features to accurately estimate per-residue fractional ASA values of water-soluble proteins. This method showed a correlation coefficient between predicted and experimental values of 0.79 when evaluated on a set of 65 independent test proteins, which was an 8.2 % improvement over the next best performing (sequence-only) method. On a separate test set of 92 proteins, ShiftASA reported a mean correlation coefficient of 0.82, which was 12.3 % better than the next best performing method. ShiftASA is available as a web server ( http://shiftasa.wishartlab.com ) for submitting input queries for fractional ASA calculation. PMID:26078090

  3. Early dynamics of the semantic priming shift

    PubMed Central

    Lavigne, Frédéric; Chanquoy, Lucile; Dumercy, Laurent; Vitu, Françoise

    2013-01-01

    Semantic processing of sequences of words requires the cognitive system to keep several word meanings simultaneously activated in working memory with limited capacity. The real- time updating of the sequence of word meanings relies on dynamic changes in the associates to the words that are activated. Protocols involving two sequential primes report a semantic priming shift from larger priming of associates to the first prime to larger priming of associates to the second prime, in a range of long SOAs (stimulus-onset asynchronies) between the second prime and the target. However, the possibility for an early semantic priming shift is still to be tested, and its dynamics as a function of association strength remain unknown. Three multiple priming experiments are proposed that cross-manipulate association strength between each of two successive primes and a target, for different values of short SOAs and prime durations. Results show an early priming shift ranging from priming of associates to the first prime only to priming of strong associates to the first prime and all of the associates to the second prime. We investigated the neural basis of the early priming shift by using a network model of spike frequency adaptive cortical neurons (e.g., Deco & Rolls, 2005), able to code different association strengths between the primes and the target. The cortical network model provides a description of the early dynamics of the priming shift in terms of pro-active and retro-active interferences within populations of excitatory neurons regulated by fast and unselective inhibitory feedback. PMID:23717346

  4. Current-induced spin wave Doppler shift

    NASA Astrophysics Data System (ADS)

    Bailleul, Matthieu

    2010-03-01

    In metal ferromagnets -namely Fe, Co and Ni and their alloys- magnetism and electrical transport are strongly entangled (itinerant magnetism). This results in a number of properties such as the tunnel and giant magnetoresistance (i.e. the dependence of the electrical resistance on the magnetic state) and the more recently addressed spin transfer (i.e. the ability to manipulate the magnetic state with the help of an electrical current). The spin waves, being the low-energy elementary excitations of any ferromagnet, also exist in itinerant magnets, but they are expected to exhibit some peculiar properties due the itinerant character of the carriers. Accessing these specific properties experimentally could shed a new light on the microscopic mechanism governing itinerant magnetism, which -in turn- could help in optimizing material properties for spintronics applications. As a simple example of these specific properties, it was predicted theoretically that forcing a DC current through a ferromagnetic metal should induce a shift of the frequency of the spin waves [1,2]. This shift can be identified to a Doppler shift undergone by the electron system when it is put in motion by the electrical current. We will show how detailed spin wave measurements allow one to access this current-induced Doppler shift [3]. From an experimental point of view, we will discuss the peculiarities of propagating spin wave spectroscopy experiments carried out at a sub-micrometer length-scale and with MHz frequency resolution. Then, we will discuss the measured value of the Doppler shift in the context of both the old two-current model of spin-polarized transport and the more recent model of adiabatic spin transfer torque. [4pt] [1] P.Lederer and D.L. Mills, Phys.Rev. 148, 542 (1966).[0pt] [2] J. Fernandez-Rossier et al., Phys. Rev. B 69, 174412 (2004)[0pt] [3] V. Vlaminck and M. Bailleul, Science 322, 410 (2008).

  5. Phenyl shifts in substituted arenes via ipso arenium ions.

    PubMed

    Ajaz, Aida; McLaughlin, Erin C; Skraba, Sarah L; Thamatam, Rajesh; Johnson, Richard P

    2012-11-01

    The isomerization of substituted arenes through ipso arenium ions is an important and general molecular rearrangement that leads to interconversions of constitutional isomers. We show here that the superacid trifluoromethanesulfonic acid (TfOH), ca. 1 M in dichloroethane (DCE), provides reliable catalytic reaction conditions for these rearrangements, easily applied at ambient temperature, reflux (84 °C), or in a microwave reactor for higher temperatures. Interconversion of terphenyl isomers in TfOH/DCE at 84 °C gives an ortho/meta/para equilibrium ratio of 0:65:35, nearly identical to values reported earlier by Olah with catalysis by AlCl(3). For the three triphenylbenzenes, TfOH-catalyzed equilibration strongly (>95%) favors the 1,3,5-triphenyl isomer. Equilibration of the three possible tetraphenylbenzenes gives a 61:39 mixture of the 1,2,3,5- and 1,2,4,5-substituted isomers. Under the reaction conditions explored, none of these structures undergoes significant Scholl cyclization. DFT calculations with inclusion of solvation support a mechanistic scheme in which all of the phenyl migrations occur among a series of ipso arenium ions. In every case studied, the preferred isomers at equilibrium are those that yield highly stable cations by the most exothermic, hence least reversible 1,2-H shift. PMID:23061916

  6. Shifting responsibilities for food safety in Europe: an introduction.

    PubMed

    Halkier, Bente; Holm, Lotte

    2006-09-01

    Following the BSE crisis in 1996, the European food sector underwent profound regulatory and institutional change. The present introductory article introduces, and sketches the background to, seven studies of the institutional reactions and initiatives that were part of, or prompted by, this reorganisation. The studies analyse the way in which the division of responsibilities for food safety has changed both across the EU as a whole and, more specifically, in six European countries. Prepared as part of the comparative research project, Trust in Food, the studies attempt to go beyond traditional policy network analysis and work on regulation. They ask which constellations of societal actors and logics are important in the shifting responsibilities of public and private actors; and they treat this as an empirical question. It emerges that, at EU level, the main strategy for restoring consumer confidence in food was to enhance the institutional independence, transparency and consumer agency. In the countries covered by the remaining six studies, by contrast, institutional reactions in the food sector varied depending on the particular configurations of state, market and civil society. PMID:16793171

  7. 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.

  8. 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

  9. 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

  10. Hospital pricing: cost shifting and competition.

    PubMed

    Morrisey, M A

    1993-05-01

    The issue of cost shifting has taken on enormous policy implications. It is estimated that unsponsored and undercompensated hospital costs--one measure of cost shifting--has totaled $21.5 billion in 1991. The health services research literature indicates that hospitals set different prices for different payers. However, the empirical evidence on hospitals' ability to raise prices to one payer to make up for unsponsored care or lower payments by other payers is mixed at best. No study has concluded that hospitals have raised prices to fully adjust for such actions. The extent of cost shifting is limited by the market. When a hospital has market power, it is able to set prices above marginal costs. However, when a buyer has enough patient/subscribers and a willingness to direct them to particular providers based on price considerations, hospitals have less flexibility in raising prices above costs. Thus, the extent of cost shifting is limited by the market. Cost shifting is not as easy as it may have been in the past because the nature of hospital and insurer competition has changed radically in the last decade. While hospital quality, services, and amenities still matter, some buyers are increasingly concerned about the price they pay. Evidence from studies of PPO and HMO negotiations with hospitals suggests that hospitals' market power is eroding, at least in some areas. In areas with relatively few hospital competitors and little PPO or HMO activity, Medicaid and Medicare price reductions and uncompensated care burdens will be partially absorbed by higher prices paid by private payers. In more price sensitive markets and in markets in which prices to private payers have risen to those commensurate with the market power of local hospitals, such cost shifting will not occur. A market-based approach in hospital pricing requires an explicit policy for the uninsured. In a competitive market, a hospital that traditionally cared for the uninsured by spending some of its

  11. 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

  12. 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.

  13. Rearrangement Reactions Catalyzed by Cytochrome P450s

    PubMed Central

    Ortiz de Montellano, Paul R.; Nelson, Sidney D.

    2010-01-01

    Cytochrome P450s promote a variety of rearrangement reactions both as a consequence of the nature of the radical and other intermediates generated during catalysis, and of the neighboring structures in the substrate that can interact either with the initial radical intermediates or with further downstream products of the reactions. This article will review several kinds of previously published cytochrome P450-catalyzed rearrangement reactions, including changes in stereochemistry, radical clock reactions, allylic rearrangements, “NIH” and related shifts, ring contractions and expansions, and cyclizations that result from neighboring group interactions. Although most of these reactions can be carried out by many members of the cytochrome P450 superfamily, some have only been observed with select P450s, including some reactions that are catalyzed by specific endoperoxidases and cytochrome P450s found in plants. PMID:20971058

  14. Confocal simultaneous phase-shifting interferometry

    SciTech Connect

    Zhao Chenguang; Tan Jiubin; Tang Jianbo; Liu Tao; Liu Jian

    2011-02-10

    In order to implement the ultraprecise measurement with large range and long working distance in confocal microscopy, confocal simultaneous phase-shifting interferometry (C-SPSI) has been presented. Four channel interference signals, with {pi}/2 phase shift between each other, are detected simultaneously in C-SPSI. The actual surface height is then calculated by combining the optical sectioning with the phase unwrapping in the main cycle of the interference phase response, and the main cycle is determined using the bipolar property of differential confocal microscopy. Experimental results showed that 1 nm of axial depth resolution was achieved for either low- or high-NA objective lenses. The reflectivity disturbance resistibility of C-SPSI was demonstrated by imaging a typical microcircuit specimen. C-SPSI breaks through the restriction of low NA on the axial depth resolution of confocal microscopy effectively.

  15. 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.

  16. Phase-Shifting Zernike Interferometer Wavefront Sensor

    NASA Technical Reports Server (NTRS)

    Wallace, J. Kent; Rao, Shanti; Jensen-Clemb, Rebecca M.; Serabyn, Gene

    2011-01-01

    The canonical Zernike phase-contrast technique1,2,3,4 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/D) of the PSF which is intermediate between the input and output planes. Here we present a new architecture for this sensor. First, the optical system is simple and all reflective. Second, the phase shift in the central core of the PSF is dynamic and or arbitrary size. 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

  17. Shape-shifting colloids via stimulated dewetting

    NASA Astrophysics Data System (ADS)

    Youssef, Mena; Hueckel, Theodore; Yi, Gi-Ra; Sacanna, Stefano

    2016-07-01

    The ability to reconfigure elementary building blocks from one structure to another is key to many biological systems. Bringing the intrinsic adaptability of biological systems to traditional synthetic materials is currently one of the biggest scientific challenges in material engineering. Here we introduce a new design concept for the experimental realization of self-assembling systems with built-in shape-shifting elements. We demonstrate that dewetting forces between an oil phase and solid colloidal substrates can be exploited to engineer shape-shifting particles whose geometry can be changed on demand by a chemical or optical signal. We find this approach to be quite general and applicable to a broad spectrum of materials, including polymers, semiconductors and magnetic materials. This synthetic methodology can be further adopted as a new experimental platform for designing and rapidly prototyping functional colloids, such as reconfigurable micro swimmers, colloidal surfactants and switchable building blocks for self-assembly.

  18. Shape-shifting colloids via stimulated dewetting.

    PubMed

    Youssef, Mena; Hueckel, Theodore; Yi, Gi-Ra; Sacanna, Stefano

    2016-01-01

    The ability to reconfigure elementary building blocks from one structure to another is key to many biological systems. Bringing the intrinsic adaptability of biological systems to traditional synthetic materials is currently one of the biggest scientific challenges in material engineering. Here we introduce a new design concept for the experimental realization of self-assembling systems with built-in shape-shifting elements. We demonstrate that dewetting forces between an oil phase and solid colloidal substrates can be exploited to engineer shape-shifting particles whose geometry can be changed on demand by a chemical or optical signal. We find this approach to be quite general and applicable to a broad spectrum of materials, including polymers, semiconductors and magnetic materials. This synthetic methodology can be further adopted as a new experimental platform for designing and rapidly prototyping functional colloids, such as reconfigurable micro swimmers, colloidal surfactants and switchable building blocks for self-assembly. PMID:27426418

  19. Shape-shifting colloids via stimulated dewetting

    PubMed Central

    Youssef, Mena; Hueckel, Theodore; Yi, Gi-Ra; Sacanna, Stefano

    2016-01-01

    The ability to reconfigure elementary building blocks from one structure to another is key to many biological systems. Bringing the intrinsic adaptability of biological systems to traditional synthetic materials is currently one of the biggest scientific challenges in material engineering. Here we introduce a new design concept for the experimental realization of self-assembling systems with built-in shape-shifting elements. We demonstrate that dewetting forces between an oil phase and solid colloidal substrates can be exploited to engineer shape-shifting particles whose geometry can be changed on demand by a chemical or optical signal. We find this approach to be quite general and applicable to a broad spectrum of materials, including polymers, semiconductors and magnetic materials. This synthetic methodology can be further adopted as a new experimental platform for designing and rapidly prototyping functional colloids, such as reconfigurable micro swimmers, colloidal surfactants and switchable building blocks for self-assembly. PMID:27426418

  20. 12C+ 12C elastic scattering excitation functions and phase shift analysis

    NASA Astrophysics Data System (ADS)

    Ledoux, R. J.; Bechara, M. J.; Ordonez, C. E.; Al-Juwair, H. A.; Cosman, E. R.

    1983-03-01

    The 12C+ 12C elastic scattering has been measured for Ec.m.=14.6-31.3 MeV, θc.m.=30°-110°. The elastic data have been analyzed via a phase shift analysis, enabling the extraction of model independent sets of phase shift parameters. The extracted Jπ values for the intermediate structure resonances at Ec.m.=18.4, 19.3, and 20.3 MeV are 12+, 12+, and 12+ or 14+, respectively. The questions of ambiguities in the phase shift analysis and the comparison with Jπ values deduced from other experiments are discussed. Evidence is presented for the existence of gross structure resonances. The elastic scattering has also been analyzed using the sum-of-differences method to directly extract the total reaction cross section. The results of these analyses are compared to existing models of the origin of intermediate structure resonances. NUCLEAR REACTIONS Measured the 12C+ 12C elastic scattering, Ec.m.=14.6-31.3 MeV, θc.m.=30°-110°. Phase shift analysis, sum-of-differences analysis.

  1. 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)

  2. Fractal tiles associated with shift radix systems.

    PubMed

    Berthé, Valérie; Siegel, Anne; Steiner, Wolfgang; Surer, Paul; Thuswaldner, Jörg M

    2011-01-15

    Shift radix systems form a collection of dynamical systems depending on a parameter r which varies in the d-dimensional real vector space. They generalize well-known numeration systems such as beta-expansions, expansions with respect to rational bases, and canonical number systems. Beta-numeration and canonical number systems are known to be intimately related to fractal shapes, such as the classical Rauzy fractal and the twin dragon. These fractals turned out to be important for studying properties of expansions in several settings. In the present paper we associate a collection of fractal tiles with shift radix systems. We show that for certain classes of parameters r these tiles coincide with affine copies of the well-known tiles associated with beta-expansions and canonical number systems. On the other hand, these tiles provide natural families of tiles for beta-expansions with (non-unit) Pisot numbers as well as canonical number systems with (non-monic) expanding polynomials. We also prove basic properties for tiles associated with shift radix systems. Indeed, we prove that under some algebraic conditions on the parameter r of the shift radix system, these tiles provide multiple tilings and even tilings of the d-dimensional real vector space. These tilings turn out to have a more complicated structure than the tilings arising from the known number systems mentioned above. Such a tiling may consist of tiles having infinitely many different shapes. Moreover, the tiles need not be self-affine (or graph directed self-affine). PMID:24068835

  3. Exploring Insight: Focus on Shifts of Attention

    ERIC Educational Resources Information Center

    Palatnik, Alik; Koichu, Boris

    2015-01-01

    The paper presents and analyses a sequence of events that preceded an insight solution to a challenging problem in the context of numerical sequences. A three­week long solution process by a pair of ninth­-grade students is analysed by means of the theory of shifts of attention. The goal for this article is to reveal the potential of this theory…

  4. Written Language Shift among Norwegian Youth

    ERIC Educational Resources Information Center

    Özerk, Kamil; Todal, Jon

    2013-01-01

    In Norway there are two written Norwegian languages, Bokmâl and Nynorsk. Of these two written languages Bokmâl is being used by the majority of the people, and Bokmâl has the highest prestige in the society. This article is about the shift of written language from Nynorsk to Bokmâl among young people in a traditional Nynorsk district in the…

  5. A fast Josephson SFQ shift register

    SciTech Connect

    Kuo, F.; Whiteley, S.R.; Faris, S.M.

    1989-03-01

    A novel Josephson shift register has been designed and fabricated. The main data latch is DC biased; the data storage is accomplished through the transfer of a single flux quantum in or out of a SQUID superconducting loop. A two-phase sinusoidal clock with offset is used to operate the circuit. Simulations verify that the operating frequency can go beyond 70 GHz, with operating margins exceeding 20%. Preliminary measurements indicate that the circuit operates as intended.

  6. 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

  7. Collisionally induced atomic clock shifts and correlations

    SciTech Connect

    Band, Y. B.; Osherov, I.

    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.

  8. 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.

  9. Semi-Supervised Kernel Mean Shift Clustering.

    PubMed

    Anand, Saket; Mittal, Sushil; Tuzel, Oncel; Meer, Peter

    2014-06-01

    Mean shift clustering is a powerful nonparametric technique that does not require prior knowledge of the number of clusters and does not constrain the shape of the clusters. However, being completely unsupervised, its performance suffers when the original distance metric fails to capture the underlying cluster structure. Despite recent advances in semi-supervised clustering methods, there has been little effort towards incorporating supervision into mean shift. We propose a semi-supervised framework for kernel mean shift clustering (SKMS) that uses only pairwise constraints to guide the clustering procedure. The points are first mapped to a high-dimensional kernel space where the constraints are imposed by a linear transformation of the mapped points. This is achieved by modifying the initial kernel matrix by minimizing a log det divergence-based objective function. We show the advantages of SKMS by evaluating its performance on various synthetic and real datasets while comparing with state-of-the-art semi-supervised clustering algorithms. PMID:26353281

  10. Set Shifting Training with Categorization Tasks

    PubMed Central

    Soveri, Anna; Waris, Otto; Laine, Matti

    2013-01-01

    The very few cognitive training studies targeting an important executive function, set shifting, have reported performance improvements that also generalized to untrained tasks. The present randomized controlled trial extends set shifting training research by comparing previously used cued training with uncued training. A computerized adaptation of the Wisconsin Card Sorting Test was utilized as the training task in a pretest-posttest experimental design involving three groups of university students. One group received uncued training (n = 14), another received cued training (n = 14) and the control group (n = 14) only participated in pre- and posttests. The uncued training group showed posttraining performance increases on their training task, but neither training group showed statistically significant transfer effects. Nevertheless, comparison of effect sizes for transfer effects indicated that our results did not differ significantly from the previous studies. Our results suggest that the cognitive effects of computerized set shifting training are mostly task-specific, and would preclude any robust generalization effects with this training. PMID:24324717

  11. Set shifting training with categorization tasks.

    PubMed

    Soveri, Anna; Waris, Otto; Laine, Matti

    2013-01-01

    The very few cognitive training studies targeting an important executive function, set shifting, have reported performance improvements that also generalized to untrained tasks. The present randomized controlled trial extends set shifting training research by comparing previously used cued training with uncued training. A computerized adaptation of the Wisconsin Card Sorting Test was utilized as the training task in a pretest-posttest experimental design involving three groups of university students. One group received uncued training (n = 14), another received cued training (n = 14) and the control group (n = 14) only participated in pre- and posttests. The uncued training group showed posttraining performance increases on their training task, but neither training group showed statistically significant transfer effects. Nevertheless, comparison of effect sizes for transfer effects indicated that our results did not differ significantly from the previous studies. Our results suggest that the cognitive effects of computerized set shifting training are mostly task-specific, and would preclude any robust generalization effects with this training. PMID:24324717

  12. 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.

  13. Bashful Ballerina: Southward shifted Heliospheric Current Sheet

    NASA Astrophysics Data System (ADS)

    Mursula, K.; Hiltula, T.

    It is known since long (Rosenberg and Coleman, 1969) that one of the two sectors of the interplanetary magnetic field (IMF) observed at the Earth's orbit dominates at high heliographic latitudes during solar minimum times, reflecting the poloidal structure of the global solar magnetic field at these times. Here we find that while this latitudinal variation of the dominant IMF sector around the solar equator is valid for both solar hemispheres during the last four solar minima covered by direct observations, it is systematically more strongly developed in the northern heliographic hemisphere. This implies that the average heliospheric current sheet is shifted or coned southward during solar minimum times, suggesting that the temporary southward shift of the heliosheet found earlier by Ulysses observations in 1995 is a persistent pattern. This also implies that the open solar magnetic field is north-south asymmetric at these times, suggesting that the solar dynamo has an asymmetric component. Accordingly, the Sun with the heliosheet is like a bashful ballerina who is repeatedly trying to push her excessively high flaring skirt downward. However, the effective shift at 1 AU is only a few degrees, allowing the Rosenberg-Coleman rule to be valid, on an average, in both hemispheres during solar minima.

  14. Bashful ballerina: Southward shifted heliospheric current sheet

    NASA Astrophysics Data System (ADS)

    Mursula, K.; Hiltula, T.

    2003-11-01

    It is known since long [Rosenberg and Coleman, 1969] that one of the two sectors of the interplanetary magnetic field (IMF) observed at the Earth's orbit dominates at high heliographic latitudes during solar minimum times, reflecting the poloidal structure of the global solar magnetic field at these times. Here we find that while this latitudinal variation of the dominant IMF sector around the solar equator is valid for both solar hemispheres during the last four solar minima covered by direct observations, it is systematically more strongly developed in the northern heliographic hemisphere. This implies that the average heliospheric current sheet is shifted or coned southward during solar minimum times, suggesting that the temporary southward shift of the heliosheet found earlier by Ulysses observations in 1995 is a persistent pattern. This also implies that the open solar magnetic field is north-south asymmetric at these times, suggesting that the solar dynamo has an asymmetric component. Accordingly, the Sun with the heliosheet is like a bashful ballerina who is repeatedly trying to push her excessively high flaring skirt downward. However, the effective shift at 1 AU is only a few degrees, allowing the Rosenberg-Coleman rule to be valid, on an average, in both hemispheres during solar minima.

  15. Photonic downconversion with tunable wideband phase shift.

    PubMed

    Jiang, Tianwei; Yu, Song; Wu, Ruihuan; Wang, Dongsheng; Gu, Wanyi

    2016-06-01

    A microwave photonic frequency downconversion system with wideband and continuous phase-shift function is proposed and experimentally demonstrated. In the proposed system, a radio frequency (RF) and a local oscillator (LO) signal drive two arms of a dual-drive Mach-Zehnder modulator (DMZM). A fiber Bragg grating (FBG) is used for reflecting the first-order sidebands of both RF and LO signals. Due to phase independence between RF and LO optical sidebands, the phase-shifting operation for an output intermediate frequency (IF) signal can be implemented either by adjusting the bias voltage of DMZM or by controlling the optical wavelength of laser. Experimental results demonstrate a full 0° to 360° phase shift, while an RF signal between 12 GHz to 20 GHz is downconverted to IFs below 4 GHz. The phase deviation is measured less than 2°, and the fluctuation of magnitude response is measured less than ±1  dB over a wideband frequency range. PMID:27244434

  16. Leaf morphology shift linked to climate change

    PubMed Central

    Guerin, Greg R.; Wen, Haixia; Lowe, Andrew J.

    2012-01-01

    Climate change is driving adaptive shifts within species, but research on plants has been focused on phenology. Leaf morphology has demonstrated links with climate and varies within species along climate gradients. We predicted that, given within-species variation along a climate gradient, a morphological shift should have occurred over time due to climate change. We tested this prediction, taking advantage of latitudinal and altitudinal variations within the Adelaide Geosyncline region, South Australia, historical herbarium specimens (n = 255) and field sampling (n = 274). Leaf width in the study taxon, Dodonaea viscosa subsp. angustissima, was negatively correlated with latitude regionally, and leaf area was negatively correlated with altitude locally. Analysis of herbarium specimens revealed a 2 mm decrease in leaf width (total range 1–9 mm) over 127 years across the region. The results are consistent with a morphological response to contemporary climate change. We conclude that leaf width is linked to maximum temperature regionally (latitude gradient) and leaf area to minimum temperature locally (altitude gradient). These data indicate a morphological shift consistent with a direct response to climate change and could inform provenance selection for restoration with further investigation of the genetic basis and adaptive significance of observed variation. PMID:22764114

  17. A phenomenological view of language shift.

    PubMed

    Tsitsipis, Lukas D

    2004-01-01

    Sociolinguistic studies of language shift have in their majority framed their research object in a horizon of theoretically received variables such as class, ethnicity, locality, attitudes etc. In spite of a limited usefulness of such conceptual variables, and of a recently emerging focus on agency, negotiation, and praxis the best results we obtain have not questioned in a coherent and theoretically sound manner the continuing hegemony of mechanistic-metaphorical models (language death, language suicide). In this paper I propose to examine language shift as a multifaceted phenomenon, joining in this respect work by other linguistic anthropologists researching similar areas. I specifically argue that by replacing vertical concepts such as age and generation, and dichotomous logics such as center and periphery with phenomenologically inspired concepts such as typifications, consociateship, contemporariness, and stream of consciousness we are in a better position to generalize about language shift dynamics. Data for this work is derived primarily from the Albanian speech communities of modern Greece, but also from other communities for comparative purposes. PMID:15156728

  18. Regime shifts in the anthropocene: drivers, risks, and resilience.

    PubMed

    Rocha, Juan Carlos; Peterson, Garry D; Biggs, Reinette

    2015-01-01

    Many ecosystems can experience regime shifts: surprising, large and persistent changes in the function and structure of ecosystems. Assessing whether continued global change will lead to further regime shifts, or has the potential to trigger cascading regime shifts has been a central question in global change policy. Addressing this issue has, however, been hampered by the focus of regime shift research on specific cases and types of regime shifts. To systematically assess the global risk of regime shifts we conducted a comparative analysis of 25 generic types of regime shifts across marine, terrestrial and polar systems; identifying their drivers, and impacts on ecosystem services. Our results show that the drivers of regime shifts are diverse and co-occur strongly, which suggests that continued global change can be expected to synchronously increase the risk of multiple regime shifts. Furthermore, many regime shift drivers are related to climate change and food production, whose links to the continued expansion of human activities makes them difficult to limit. Because many regime shifts can amplify the drivers of other regime shifts, continued global change can also be expected to increase the risk of cascading regime shifts. Nevertheless, the variety of scales at which regime shift drivers operate provides opportunities for reducing the risk of many types of regime shifts by addressing local or regional drivers, even in the absence of rapid reduction of global drivers. PMID:26267896

  19. Regime Shifts in the Anthropocene: Drivers, Risks, and Resilience

    PubMed Central

    Rocha, Juan Carlos; Peterson, Garry D.; Biggs, Reinette

    2015-01-01

    Many ecosystems can experience regime shifts: surprising, large and persistent changes in the function and structure of ecosystems. Assessing whether continued global change will lead to further regime shifts, or has the potential to trigger cascading regime shifts has been a central question in global change policy. Addressing this issue has, however, been hampered by the focus of regime shift research on specific cases and types of regime shifts. To systematically assess the global risk of regime shifts we conducted a comparative analysis of 25 generic types of regime shifts across marine, terrestrial and polar systems; identifying their drivers, and impacts on ecosystem services. Our results show that the drivers of regime shifts are diverse and co-occur strongly, which suggests that continued global change can be expected to synchronously increase the risk of multiple regime shifts. Furthermore, many regime shift drivers are related to climate change and food production, whose links to the continued expansion of human activities makes them difficult to limit. Because many regime shifts can amplify the drivers of other regime shifts, continued global change can also be expected to increase the risk of cascading regime shifts. Nevertheless, the variety of scales at which regime shift drivers operate provides opportunities for reducing the risk of many types of regime shifts by addressing local or regional drivers, even in the absence of rapid reduction of global drivers. PMID:26267896

  20. Anaphylactic reactions to cinoxacin.

    PubMed Central

    Stricker, B. H.; Slagboom, G.; Demaeseneer, R.; Slootmaekers, V.; Thijs, I.; Olsson, S.

    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 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

  1. Reactions to radiocontrast media.

    PubMed

    Hong, Sandra J; Wong, Johnson T; Bloch, Kurt J

    2002-01-01

    Adverse reactions to radiocontrast media (RCM) occur unexpectedly and may be life-threatening. This article describes an anaphylactoid reaction (AR) in one patient. The term AR refers to a syndrome clinically similar to anaphylaxis, but these reactions are independent of immunoglobulin E antibody-mediated mast cell or basophil degranulation. This article briefly reviews the literature regarding RCMs and types of reactions to RCM. The risk factors for AR to RCM infusions will be discussed along with current concepts of the pathogenesis of RCM-induced ARs. This article also describes the therapeutic management of patients who have had a previous adverse reaction to RCM and provides an approach to patients who have breakthrough reactions despite adequate premedication, but require additional radiographic studies. PMID:12476546

  2. Noncanonical Reactions of Flavoenzymes

    PubMed Central

    Sobrado, Pablo

    2012-01-01

    Enzymes containing flavin cofactors are predominantly involved in redox reactions in numerous cellular processes where the protein environment modulates the chemical reactivity of the flavin to either transfer one or two electrons. Some flavoenzymes catalyze reactions with no net redox change. In these reactions, the protein environment modulates the reactivity of the flavin to perform novel chemistries. Recent mechanistic and structural data supporting novel flavin functionalities in reactions catalyzed by chorismate synthase, type II isopentenyl diphosphate isomerase, UDP-galactopyranose mutase, and alkyl-dihydroxyacetonephosphate synthase are presented in this review. In these enzymes, the flavin plays either a direct role in acid/base reactions or as a nucleophile or electrophile. In addition, the flavin cofactor is proposed to function as a “molecular scaffold” in the formation of UDP-galactofuranose and alkyl-dihydroxyacetonephosphate by forming a covalent adduct with reaction intermediates. PMID:23203060

  3. Mechanisms in Knockout Reactions

    NASA Astrophysics Data System (ADS)

    Bazin, D.; Charity, R. J.; de Souza, R. T.; Famiano, M. A.; Gade, A.; Henzl, V.; Henzlova, D.; Hudan, S.; Lee, J.; Lukyanov, S.; Lynch, W. G.; McDaniel, S.; Mocko, M.; Obertelli, A.; Rogers, A. M.; Sobotka, L. G.; Terry, J. R.; Tostevin, J. A.; Tsang, M. B.; Wallace, M. S.

    2009-06-01

    We report the first detailed study of the relative importance of the stripping and diffraction mechanisms involved in nucleon knockout reactions, by the use of a coincidence measurement of the residue and fast proton following one-proton knockout reactions. The measurements used the S800 spectrograph in combination with the HiRA detector array at the NSCL. Results for the reactions Be9(C9,B8+X)Y and Be9(B8,Be7+X)Y are presented and compared with theoretical predictions for the two reaction mechanisms calculated using the eikonal model. The data show a clear distinction between the stripping and diffraction mechanisms and the measured relative proportions are very well reproduced by the reaction theory. This agreement adds support to the results of knockout reaction analyses and their applications to the spectroscopy of rare isotopes.

  4. Sleeve reaction chamber system

    SciTech Connect

    Northrup, M. Allen; Beeman, Barton V.; Benett, William J.; Hadley, Dean R.; Landre, Phoebe; Lehew, Stacy L.; Krulevitch, Peter A.

    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.

  5. Metal-mullite reactions

    SciTech Connect

    Loehman, R.E.; Tomsia, A.P.

    1993-11-01

    Mullite was reacted with pure Al and with Ti or Zr dissolved in Ag-Cu eutectic alloys at 1100 C in Ar. Analysis of the Ti and Zr-containing specimens showed reaction zones with compositions of Ti{sub 50}Cu{sub 3O}O{sub 20} and ZrO{sub 2}, respectively. The Al-mullite specimen showed much more extensive penetration into the ceramic and a more diffuse reaction zone than the other two systems. Al{sub 2}O{sub 3} and Si were the main reaction products for Al-mullite reaction.

  6. Pterandra pyroidea: a case of pollination shift within Neotropical Malpighiaceae

    PubMed Central

    Cappellari, Simone C.; Haleem, Muhammad A.; Marsaioli, Anita J.; Tidon, Rosana; Simpson, Beryl B.

    2011-01-01

    Background and Aims Most Neotropical species of Malpighiaceae produce floral fatty oils in calyx glands to attract pollinating oil-collecting bees, which depend on this resource for reproduction. This specialized type of pollination system tends to be lost in members of the family that occur outside the geographic distribution (e.g. Africa) of Neotropical oil-collecting bees. This study focused on the pollination ecology, chemical ecology and reproductive biology of an oil flower species, Pterandra pyroidea (Malpighiaceae) from the Brazilian Cerrado. Populations of this species consist of plants with oil-secreting (glandular) flowers, plants with non-oil-secreting flowers (eglandular) or a mix of both plant types. This study specifically aims to clarify the role of eglandular morphs in this species. Methods Data on pollinators were recorded by in situ observations. Breeding system experiments were conducted by isolating inflorescences and by enzymatic reactions. Floral resources, pollen and floral oils offered by this species were analysed by staining and a combination of various spectroscopic methods. Key Results Eglandular flowers of P. pyroidea do not act as mimics of their oil-producing conspecifics to attract pollinators. Instead, both oil-producing and oil-free flowers depend on pollen-collecting bees for reproduction, and their main pollinators are bumble-bees. Floral oils produced by glandular flowers are less complex than those described in closely related genera. Conclusions Eglandular flowers represent a shift in the pollination system in which oil is being lost and pollen is becoming the main reward of P. pyroidea flowers. Pollination shifts of this kind have hitherto not been demonstrated empirically within Neotropical Malpighiaceae and this species exhibits an unusual transition from a specialized towards a generalized pollination system in an area considered the hotspot of oil-collecting bee diversity in the Neotropics. Transitions of this type

  7. Ecohydrology by thinking outside the bog: Shifting paradigms in an era of shifting peatland ecosystems

    NASA Astrophysics Data System (ADS)

    Waddington, James; Moore, Paul

    2016-04-01

    Large shifts in vegetation distributions are occurring worldwide and at unprecedented rates. The most extreme of these regime shifts are expected to occur at ecosystem boundaries of both semi-arid and semi-humid landscapes. Despite extensive hydrological research on the interactions between water and semi-arid ecosystems, research in peatlands on the wet end of ecosystem continuum has been "bogged down" (pun fully intended) by the traditional conceptual models (paradigms?) of peatland hydrology and ecology. The consequences of this "thinking" are large given that northern peatlands provide important global and regional ecosystem services (carbon storage, water storage, and biodiversity). This is especially true because peatlands face increases in the severity, areal extent, and frequency of climate-mediated (e.g., wildfire, drought) and land-use change (e.g., drainage, flooding, and mining) disturbances placing the future security of these critical ecosystem services in doubt. We use the word doubt because while numerical modelling studies predict peatland regime shifts and the demise of global peat stocks, there is growing evidence that peatlands are self-regulating ecosystems dominated by negative ecohydrological feedbacks that stabilize the aforementioned ecosystem services through high ecosystem resilience to disturbance. This raises several important hydrological questions? "Is there field evidence of peatland regime shifts? If so, what are the potential impacts of these shifts on water resources and watershed management? If not, are researchers actually looking in the right places (or times)? In this presentation we explore the need for a "thinking outside the bog" in order to understand the ecohydrological consequences of transformative landscape change caused by peatland regime shifts. With reference to over two decades of field research, recent advances with our Peatland Hydrological Impacts model and recent research examining primary peat formation, we

  8. Insertion of the force applied to handles into centre of pressure calculation modifies the amplitude of centre of pressure shifts.

    PubMed

    Noé, Frédéric; Quaine, Franck

    2006-11-01

    This study examined situations where handles were used as additional postural supports. It aimed at determining the amplitude of centre of pressure (COP) shifts when considering or not the vertical handles reaction force. Eight healthy male subjects (24+/-6 years, body mass 65+/-5kg and height 175+/-7cm) voluntarily took part in the experiment. Subjects had to voluntarily rock on their heels or rise on their toe-tips while using handles. The vertical component of the handles forces and ground reaction force was measured and the shifts of the COP were calculated while inserting or not the handles forces. Significant differences were observed when comparing the amplitude of COP shifts calculated with or without the insertion of the handles forces. This study shows that the measurement of the handles forces should not be omitted, for a rigorous analysis of postural tasks performed in conditions including additional postural supports like handles. PMID:16300948

  9. Microbial shifts associated with necrotic enteritis.

    PubMed

    Antonissen, Gunther; Eeckhaut, Venessa; Van Driessche, Karolien; Onrust, Lonneke; Haesebrouck, Freddy; Ducatelle, Richard; Moore, Robert J; Van Immerseel, Filip

    2016-06-01

    An outbreak of necrotic enteritis (NE) is a complex process requiring one or a number of predisposing factors rather than just the presence of pathogenic Clostridium perfringens. Examples are dietary influences, such as high levels of non-starch polysaccharides and fishmeal, and factors that evoke epithelial cell damage, such as Fusarium mycotoxins in feed and Eimeria infections. Recent studies have shown that different predisposing factors induce similar shifts in the intestinal microbiota composition. Butyrate-producing-strains of the Ruminococcaceae family are decreased in abundance by both fishmeal and Eimeria. Similarly, a decreased abundance of butyrate-producing-strains belonging to the Lachnospiraceae family has been induced by fishmeal. Also shifts are observed in the lactic acid-producing bacteria, such as decreased abundance of Lactobacillus johnsonii or Weissella confusa, when broilers were fed a fishmeal-based diet or a Fusarium mycotoxin contaminated diet. Finally, the abundance of Candidatus Savagella was decreased in broilers following Eimeria challenge or feeding a fumonisins contaminated diet. The nature of the microbiota shifts indicate that immune modulatory actions of the intestinal microbiota may play a critical role in the effect on the necrosis inducing activity of C. perfringens. Indeed, colonization with butyrate-producing bacteria plays a key role in counteracting inflammation in the gut and preserving intestinal integrity, while Candidatus Savagella is involved in stimulating Th17 and immunoglobulin A responses. Lactic acid bacteria stimulate colonization of lactate-utilizing and butyrate-producing Lachnospiraceae. Future research needs to clarify the role of the microbiota changes in the pathogenesis of NE. PMID:26950294

  10. An Efficient Synthesis of Benzazocines by Gold(I)-Catalyzed Tandem 1,2-Acyloxy Shift/[3+2] Cycloaddition of Terminal 1,9-Enynyl Esters.

    PubMed

    Feng, Shangbiao; Wang, Zhengshen; Zhang, Weiwei; Xie, Xingang; She, Xuegong

    2016-08-01

    An effective synthesis of structurally diverse benzazocines was accomplished in good to excellent chemical yields (55-82 %) through a gold(I)-catalyzed cascade reaction involving tandem 1,2-acyloxy shift/[3+2] cycloaddition of terminal 1,9-enynyl esters. The reaction proceeds under extremely mild conditions and represents one of the relatively few transition-metal-catalyzed intramolecular cycloaddition reactions for the synthesis of benzazocines. PMID:27310714

  11. Interferometric fiber Bragg grating shift demodulation

    NASA Astrophysics Data System (ADS)

    Stepien, Karol; Jóźwik, Michalina; Nasilowski, Tomasz

    2015-09-01

    In this paper we present a fiber Bragg grating shift demodulator with changeable resolution based on an unbalanced fiber Mach-Zehnder interferometer. Preliminary research proves phase sensitivity to Bragg wavelength changes of 6,83 rad/mɛ. Phase sensitivity can be modified by changing the optical path difference witch is only limited by the coherence length of light reflected by the fiber Bragg grating. This solution can be used as a single sensor or as a part of a more complex system.

  12. A tentative explanation of cosmological red shift

    NASA Technical Reports Server (NTRS)

    Chang, T.; Torr, D. G.

    1990-01-01

    The authors suggest a possible alternative explanation of cosmological red shift. They consider that there exists a background field in the universe, and that light (the photon) has an extremely weak interaction with this background, and as result, experiences an energy loss. By analogy with damped oscillations, the authors introduce a dumping term with the first derivative with respect to time in the wave equation. The solution yields a linearly reduced frequency of the light with travel distance. The purpose of this exercise is to demonstrate how a simple alternative interpretation of the Hubble relation can be generated.

  13. Scaling Shift in Multicracked Fiber Bundles

    NASA Astrophysics Data System (ADS)

    Manca, Fabio; Giordano, Stefano; Palla, Pier Luca; Cleri, Fabrizio

    2014-12-01

    Bundles of fibers, wires, or filaments are ubiquitous structures in both natural and artificial materials. We investigate the bundle degradation induced by an external damaging action through a theoretical model describing an assembly of parallel fibers, progressively damaged by a random population of cracks. Fibers in our model interact by means of a lateral linear coupling, thus retaining structural integrity even after substantial damage. Monte Carlo simulations of the Young's modulus degradation for increasing crack density demonstrate a remarkable scaling shift between an exponential and a power-law regime. Analytical solutions of the model confirm this behavior, and provide a thorough understanding of the underlying physics.

  14. Scaling shift in multicracked fiber bundles.

    PubMed

    Manca, Fabio; Giordano, Stefano; Palla, Pier Luca; Cleri, Fabrizio

    2014-12-19

    Bundles of fibers, wires, or filaments are ubiquitous structures in both natural and artificial materials. We investigate the bundle degradation induced by an external damaging action through a theoretical model describing an assembly of parallel fibers, progressively damaged by a random population of cracks. Fibers in our model interact by means of a lateral linear coupling, thus retaining structural integrity even after substantial damage. Monte Carlo simulations of the Young's modulus degradation for increasing crack density demonstrate a remarkable scaling shift between an exponential and a power-law regime. Analytical solutions of the model confirm this behavior, and provide a thorough understanding of the underlying physics. PMID:25554893

  15. Ambiguity produces attention shifts in category learning.

    PubMed

    Vadillo, Miguel A; Orgaz, Cristina; Luque, David; Nelson, James Byron

    2016-04-01

    It has been suggested that people and nonhuman animals protect their knowledge from interference by shifting attention toward the context when presented with information that contradicts their previous beliefs. Despite that suggestion, no studies have directly measured changes in attention while participants are exposed to an interference treatment. In the present experiments, we adapted a dot-probe task to track participants' attention to cues and contexts while they were completing a simple category learning task. The results support the hypothesis that interference produces a change in the allocation of attention to cues and contexts. PMID:26980780

  16. Solar Doppler shifts - Sources of continuous spectra

    NASA Technical Reports Server (NTRS)

    Duvall, T. L., Jr.; Harvey, J. W.

    1986-01-01

    Oscillation observations can be used to study nonoscillatory solar phenomena that exhibit Doppler shifts. The paper discusses several effects of these phenomena and their associated temporal and spatial power spectra: (1) they limit the signal-to-noise ratio and sometimes detectability of oscillation modes; (2) there is the potential for better understanding and/or detection of solar phenomena; (3) large-scale convection may spatially modulate oscillation modes, leading to a continuous background spectrum; and (4) in regions of the spectrum where the resolution to separate modes is lacking one can determine upper limits for the integrated effects of modes.

  17. Polarization phase shifting dispersed fringe sensor.

    PubMed

    Olczak, Gene

    2012-02-13

    The dispersed fringe sensor (DFS) has been demonstrated as an effective means of measuring mirror segment piston error for telescopes with primary mirror apertures below 10 meters. With larger proposed telescopes such as The Thirty Meter Telescope (TMT) and The European Large Telescope (ELT) including ever more segments, there is a need for improvement in the co-phasing capability for segmented primary mirrors. In this paper a novel DFS that employs polarization phase shifting technology is introduced. This novel technology provides system designers and engineers with a new tool to extend the dynamic range of a DFS. PMID:22418128

  18. The Spectral Shift Function and Spectral Flow

    NASA Astrophysics Data System (ADS)

    Azamov, N. A.; Carey, A. L.; Sukochev, F. A.

    2007-11-01

    At the 1974 International Congress, I. M. Singer proposed that eta invariants and hence spectral flow should be thought of as the integral of a one form. In the intervening years this idea has lead to many interesting developments in the study of both eta invariants and spectral flow. Using ideas of [24] Singer’s proposal was brought to an advanced level in [16] where a very general formula for spectral flow as the integral of a one form was produced in the framework of noncommutative geometry. This formula can be used for computing spectral flow in a general semifinite von Neumann algebra as described and reviewed in [5]. In the present paper we take the analytic approach to spectral flow much further by giving a large family of formulae for spectral flow between a pair of unbounded self-adjoint operators D and D + V with D having compact resolvent belonging to a general semifinite von Neumann algebra {mathcal{N}} and the perturbation V in {mathcal{N}} . In noncommutative geometry terms we remove summability hypotheses. This level of generality is made possible by introducing a new idea from [3]. There it was observed that M. G. Krein’s spectral shift function (in certain restricted cases with V trace class) computes spectral flow. The present paper extends Krein’s theory to the setting of semifinite spectral triples where D has compact resolvent belonging to {mathcal{N}} and V is any bounded self-adjoint operator in {mathcal{N}} . We give a definition of the spectral shift function under these hypotheses and show that it computes spectral flow. This is made possible by the understanding discovered in the present paper of the interplay between spectral shift function theory and the analytic theory of spectral flow. It is this interplay that enables us to take Singer’s idea much further to create a large class of one forms whose integrals calculate spectral flow. These advances depend critically on a new approach to the calculus of functions of non

  19. Resonance-shifting luminescent solar concentrators

    SciTech Connect

    Giebink, Noel Christopher; Wiederrecht, Gary P; Wasielewski, Michael R

    2014-09-23

    An optical system and method to overcome luminescent solar concentrator inefficiencies by resonance-shifting, in which sharply directed emission from a bi-layer cavity into a glass substrate returns to interact with the cavity off-resonance at each subsequent reflection, significantly reducing reabsorption loss en route to the edges. In one embodiment, the system comprises a luminescent solar concentrator comprising a transparent substrate, a luminescent film having a variable thickness; and a low refractive index layer disposed between the transparent substrate and the luminescent film.

  20. Pendulum Shifts, Context, Error, and Personal Accountability

    SciTech Connect

    Harold Blackman; Oren Hester

    2011-09-01

    This paper describes a series of tools that were developed to achieve a balance in under-standing LOWs and the human component of events (including accountability) as the INL continues its shift to a learning culture where people report, are accountable and interested in making a positive difference - and want to report because information is handled correctly and the result benefits both the reporting individual and the organization. We present our model for understanding these interrelationships; the initiatives that were undertaken to improve overall performance.