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Sample records for methanol temperature dependence

  1. Pressure and temperature dependence of excess enthalpies of methanol + tetraethylene glycol dimethyl ether and methanol + polyethylene glycol dimethyl ether 250

    SciTech Connect

    Lopez, E.R.; Coxam, J.Y.; Fernandez, J.; Grolier, J.P.E.

    1999-12-01

    The excess molar enthalpies at 323.15 K, 373.15 K, and 423.15 K, at 8 MPa, are reported for the binary mixtures methanol + tetraethylene glycol dimethyl ether (TEGDME) and methanol + poly(ethylene glycol) dimethyl ether 250 (PEGDME 250). Excess molar enthalpies were determined with a Setaram C-80 calorimeter equipped with a flow mixing cell. For both systems, the excess enthalpies are positive over the whole composition range, increasing with temperature. The H{sup E}(x) curves are slightly asymmetrical, and their maxima are skewed toward the methanol-rich region. The excess enthalpies slightly change with the pressure, the sign of this change being composition-dependent. In the case of mixtures with TEGDME, the experimental H{sup E} values have been compared with those predicted with the Gmehling et al. version of UNIFAC (Dortmund) and the Nitta-Chao and DISQUAC group contribution models.

  2. A note on the temperature dependence of Henry's Law coefficients for methanol and ethanol

    NASA Astrophysics Data System (ADS)

    Warneck, Peter

    Measurements reported in the literature of gas-liquid partition coefficients for methanol and ethanol dissolved in water are compiled and critically evaluated to establish the temperature dependence. The data are linearly correlated in the ln( KH[mol dm -3 atm -1]) versus reciprocal absolute temperature coordinate frame and, when treated by a linear regression analysis, yield: ln( KH)=-(12.46±0.25)+(5312.4±76.0)/ T in the case of methanol (0-80 °C) and ln( KH)=-(15.87±0.82)+(6274.0±241.6)/ T in the case of ethanol (0-60 °C). The measurements at 25 °C average to KH(298.15)=(2.16±0.14)×10 2 mol dm -3 atm -1 ( n=8) and KH(298.15)=(1.94±0.13)×10 2 mol dm -3 atm -1 ( n=8), respectively. Enthalpies of solution derived from the temperature dependence are 44.17±0.63 kJ mol -1 for methanol and 52.16±2.01 kJ mol -1 for ethanol.

  3. Temperature and site dependence of the rate of hydrogen and deuterium abstraction by methyl radicals in methanol glasses

    SciTech Connect

    Doba, T.; Ingold, K.U.; Siebrand, W.; Wildman, T.A.

    1984-07-19

    Rate constants are reported for hydrogen and deuterium abstraction by methyl radicals in CH/sub 3/OH and CD/sub 3/OD glasses in the ranges 5-89 and 77-97 K, respectively. At each temperature, they show a distribution due to a variation of radical trapping sites. The rate constants of this distribution are analyzed theoretically to yield a quantitative relation between tunneling rate and equilibrium tunneling distance. 20 references, 2 figures.

  4. Low temperature catalysts for methanol production

    DOEpatents

    Sapienza, R.S.; Slegeir, W.A.; O'Hare, T.E.; Mahajan, D.

    1986-09-30

    A catalyst and process useful at low temperatures (below about 160 C) and preferably in the range 80--120 C used in the production of methanol from carbon monoxide and hydrogen are disclosed. The catalyst is used in slurry form and comprises a complex reducing agent derived from the component structure NaH--RONa-M(OAc)[sub 2] where M is selected from the group consisting of Ni, Pd, and Co and R is a lower alkyl group containing 1--6 carbon atoms. This catalyst is preferably used alone but is also effective in combination with a metal carbonyl of a group VI (Mo, Cr, W) metal. The preferred catalyst precursor is Nic (where M = Ni and R = tertiary amyl). Mo(CO)[sub 6] is the preferred metal carbonyl if such component is used. The catalyst is subjected to a conditioning or activating step under temperature and pressure, similar to the parameters given above, to afford the active catalyst.

  5. Low temperature catalyst system for methanol production

    DOEpatents

    Sapienza, R.S.; Slegeir, W.A.; O'Hare, T.E.

    1984-04-20

    This patent discloses a catalyst and process useful at low temperatures (150/sup 0/C) and preferably in the range 80 to 120/sup 0/C used in the production of methanol from carbon monoxide and hydrogen. The catalyst components are used in slurry form and comprise (1) a complex reducing agent derived from the component structure NaH-ROH-M(OAc)/sub 2/ where M is selected from the group consisting of Ni, Pd, and Co and R is a lower alkyl group containing 1 to 6 carbon atoms and (2) a metal carbonyl of a group VI (Mo, Cr, W) metal. For the first component, Nic is preferred (where M = Ni and R = tertiary amyl). For the second component, Mo(CO)/sub 6/ is preferred. The mixture is subjected to a conditioning or activating step under temperature and pressure, similar to the parameters given above, to afford the active catalyst.

  6. Using Rare Gas Permeation to Probe Methanol Diffusion near the Glass Transition Temperature

    NASA Astrophysics Data System (ADS)

    Matthiesen, Jesper; Smith, R. Scott; Kay, Bruce D.

    2009-12-01

    The permeation of rare-gas atoms through deeply supercooled metastable liquid methanol films is used to probe the diffusivity. The technique allows for measurement of supercooled liquid mobility at temperatures near the glass transition. The temperature dependence of the diffusivity is well described by a Vogel-Fulcher-Tamman equation. These new measurements and the temperature dependent kinetic parameters obtained from their analysis provide clear evidence that methanol is a fragile liquid near the glass transition.

  7. Using rare gas permeation to probe methanol diffusion near the glass transition temperature.

    PubMed

    Matthiesen, Jesper; Smith, R Scott; Kay, Bruce D

    2009-12-11

    The permeation of rare-gas atoms through deeply supercooled metastable liquid methanol films is used to probe the diffusivity. The technique allows for measurement of supercooled liquid mobility at temperatures near the glass transition. The temperature dependence of the diffusivity is well described by a Vogel-Fulcher-Tamman equation. These new measurements and the temperature dependent kinetic parameters obtained from their analysis provide clear evidence that methanol is a fragile liquid near the glass transition. PMID:20366212

  8. Low temperature catalysts for methanol production

    DOEpatents

    Sapienza, R.S.; Slegeir, W.A.; O'Hare, T.E.; Mahajan, D.

    1986-10-28

    A catalyst and process useful at low temperatures (below about 160 C) and preferably in the range 80--120 C used in the production of methanol from carbon monoxide and hydrogen are disclosed. The catalyst is used in slurry form and comprises a complex reducing agent derived from the component structure NaH--RONa-M(OAc)[sub 2] where M is selected from the group consisting of Ni, Pd, and Co and R is a lower alkyl group containing 1-6 carbon atoms. This catalyst is preferably used alone but is also effective in combination with a metal carbonyl of a group VI (Mo, Cr, W) metal. The preferred catalyst precursor is NiC (where M = Ni and R = tertiary amyl). Mo(CO)[sub 6] is the preferred metal carbonyl if such component is used. The catalyst is subjected to a conditioning or activating step under temperature and pressure, similar to the parameters given above, to afford the active catalyst.

  9. Low temperature catalysts for methanol production

    DOEpatents

    Sapienza, R.S.; Slegeir, W.A.; O'Hare, T.E.; Mahajan, D.

    1985-03-12

    A catalyst and process useful at low temperatures (below about 160/sup 0/C) and preferably in the range 80 to 120/sup 0/C used in the production of methanol from carbon monoxide and hydrogen is disclosed. The catalyst is used in slurry form and comprises a complex reducing agent derived from the component structure NaH-RONa-M(OAc)/sub 2/ where M is selected from the group consisting of Ni, Pd, and Co and R is a lower alkyl group containing 1 to 6 carbon atoms. This catalyst is preferably used alone but is also effective in combination with a metal carbonyl of a group VI (Mo, Cr, W) metal. The preferred catalyst precursor is Nic (where M = Ni and R = tertiary amyl). Mo(CO)/sub 6/ is the preferred metal carbonyl if such component is used. The catalyst is subjected to a conditioning or activating step under temperature and pressure, similar to the parameters given above, to afford the active catalyst.

  10. Low temperature catalysts for methanol production

    DOEpatents

    Sapienza, Richard S.; Slegeir, William A.; O'Hare, Thomas E.; Mahajan, Devinder

    1986-01-01

    A catalyst and process useful at low temperatures (below about 160.degree. C.) and preferably in the range 80.degree.-120.degree. C. used in the production of methanol from carbon monoxide and hydrogen is disclosed. The catalyst is used in slurry form and comprises a complex reducing agent derived from the component structure NaH--RONa--M(OAc).sub.2 where M is selected from the group consisting of Ni, Pd, and Co and R is a lower alkyl group containing 1-6 carbon atoms. This catalyst is preferably used alone but is also effective in combination with a metal carbonyl of a group VI (Mo, Cr, W) metal. The preferred catalyst precursor is Nic (where M=Ni and R=tertiary amyl). Mo(CO).sub.6 is the preferred metal carbonyl if such component is used. The catalyst is subjected to a conditioning or activating step under temperature and pressure, similar to the parameters given above, to afford the active catalyst.

  11. Structures of protonated methanol clusters and temperature effects.

    PubMed

    Fifen, Jean Jules; Nsangou, Mama; Dhaouadi, Zoubeida; Motapon, Ousmanou; Jaidane, Nejm-Eddine

    2013-05-14

    The accurate evaluation of pKa's, or solvation energies of the proton in methanol at a given temperature is subject to the determination of the most favored structures of various isomers of protonated (H(+)(MeOH)n) and neutral ((MeOH)n) methanol clusters in the gas phase and in methanol at that temperature. Solvation energies of the proton in a given medium, at a given temperature may help in the determination of proton affinities and proton dissociation energies related to the deprotonation process in that medium and at that temperature. pKa's are related to numerous properties of drugs. In this work, we were interested in the determination of the most favored structures of various isomers of protonated methanol clusters in the gas phase and in methanol, at a given temperature. For this aim, the M062X/6-31++G(d,p) and B3LYP/6-31++G(d,p) levels of theory were used to perform geometries optimizations and frequency calculations on various isomers of (H(+)(MeOH)n) in both phases. Thermal effects were retrieved using our homemade FORTRAN code. Thus, we accessed the relative populations of various isomers of protonated methanol clusters, in both phases for temperatures ranging from 0 to 400 K. As results, in the gas phase, linear structures are entropically more favorable at high temperatures, while more compact ones are energetically more favorable at lower temperatures. The trend is somewhat different when bulk effects are taken into account. At high temperatures, the linear structure only dominates the population for n ≤ 6, while it is dominated by the cyclic structure for larger cluster sizes. At lower temperatures, compact structures still dominate the population, but with an order different from the one established in the gas phase. Hence, temperature effects dominate solvent effects in small cluster sizes (n ≤ 6), while the reverse trend is noted for larger cluster sizes. PMID:23676038

  12. Methanol Uptake by Low Temperature Aqueous Sulfuric Acid Solutions

    NASA Technical Reports Server (NTRS)

    Iraci, L. T.; Essin, A. M.; Golden, D. M.; Hipskind, R. Stephen (Technical Monitor)

    2001-01-01

    The global methanol budget is currently unbalanced, with source terms significantly larger than the sinks terms. To evaluate possible losses of gaseous methanol to sulfate aerosols, the solubility and reactivity of methanol in aqueous sulfuric acid solutions representative of upper tropospheric and lower stratospheric aerosols is under investigation. Methanol will partition into sulfate aerosols according to its Henry's law solubility. Using standard uptake techniques in a Knudsen cell reactor, we have measured the effective Henry's law coefficient, H*, for cold (196 - 220 K) solutions ranging between 45 and 70 wt % H2SO4. We have found that methanol solubility ranges from approx. 10(exp 5) - 10(exp 7) M/atm for UT/LS conditions. Solubility increases with decreasing temperature and with increasing sulfuric acid content. Although methanol is slightly more soluble than are acetone and formaldehyde, current data indicate that uptake by clean aqueous sulfuric acid particles will not be a significant sink for methanol in the UT/LS. These solubility measurements include uptake due to physical solvation and any rapid equilibria which are established in solution. Reaction between primary alcohols and sulfuric acid does occur, leading to the production of alkyl sulfates. Literature values for the rate of this reaction suggest that formation of CH3OSO3H is not significant over our experimental time scale for solutions below 80 wt % H2SO4. To confirm this directly, results obtained using a complementary equilibrium measurement technique will also be presented.

  13. Methanol Uptake By Low Temperature Aqueous Sulfuric Acid Solutions

    NASA Technical Reports Server (NTRS)

    Iraci, Laura T.; Essin, Andrew M.; Golden, David M.; Hipskind, R. Stephen (Technical Monitor)

    2001-01-01

    To evaluate the role of upper tropospheric and lower stratospheric aerosols in the global budget of methanol, the solubility and reactivity of CH3OH in aqueous sulfuric acid solutions are under investigation. Using standard uptake techniques in a Knudsen cell reactor, we have measured the effective Henry's law coefficient, H(*), for methanol dissolution into 45 to 70 percent by weight H2SO4. We find that methanol solubility ranges from 10(exp 5) to 10(exp 8) M/atm and increases with decreasing temperature and with increasing sulfuric acid content. These solubility measurements include uptake due to physical solvation and all rapid equilibria which are established in solution. Our data indicate that simple uptake by aqueous sulfuric acid particles will not be a significant sink for methanol in the UT/LS. These results differ from those recently reported in the literature, and an explanation of this disparity will be presented. In addition to solvation, reaction between primary alcohols and sulfuric acid does occur, leading to the production of alkyl sulfates. Literature values for the rate of this reaction suggest that formation of CH3OSO3H may proceed in the atmosphere but is not significant under our experimental conditions. Results obtained using a complementary equilibrium measurement technique confirm this directly. In addition, the extent of methanol sequestration via formation of mono- and dimethylsulfate will be evaluated under several atmospheric conditions.

  14. Methanol dimer formation drastically enhances hydrogen abstraction from methanol by OH at low temperature.

    PubMed

    Siebrand, Willem; Smedarchina, Zorka; Martínez-Núñez, Emilio; Fernández-Ramos, Antonio

    2016-08-10

    The kinetics of the reaction of methanol with hydroxyl radicals is revisited in light of the reported new kinetic data, measured in cold expansion beams. The rate constants exhibit an approximately 10(2)-fold increase when the temperature decreases from 200 to 50 K, a result that cannot be fully explained by tunneling, as we confirm by new calculations. These calculations also show that methanol dimers are much more reactive to hydroxyl than monomers and imply that a dimer concentration of about 30% of the equilibrium concentration can account quantitatively for the observed rates. The assumed presence of dimers is supported by the observation of cluster formation in these and other cold beams of molecules subject to hydrogen bonding. The calculations imply an important caveat with respect to the use of cold expansion beams for the study of interstellar chemistry. PMID:27479134

  15. Temperature of maximum density and excess thermodynamics of aqueous mixtures of methanol.

    PubMed

    González-Salgado, D; Zemánková, K; Noya, E G; Lomba, E

    2016-05-14

    In this work, we present a study of representative excess thermodynamic properties of aqueous mixtures of methanol over the complete concentration range, based on extensive computer simulation calculations. In addition to test various existing united atom model potentials, we have developed a new force-field which accurately reproduces the excess thermodynamics of this system. Moreover, we have paid particular attention to the behavior of the temperature of maximum density (TMD) in dilute methanol mixtures. The presence of a temperature of maximum density is one of the essential anomalies exhibited by water. This anomalous behavior is modified in a non-monotonous fashion by the presence of fully miscible solutes that partly disrupt the hydrogen bond network of water, such as methanol (and other short chain alcohols). In order to obtain a better insight into the phenomenology of the changes in the TMD of water induced by small amounts of methanol, we have performed a new series of experimental measurements and computer simulations using various force fields. We observe that none of the force-fields tested capture the non-monotonous concentration dependence of the TMD for highly diluted methanol solutions. PMID:27179493

  16. Temperature of maximum density and excess thermodynamics of aqueous mixtures of methanol

    NASA Astrophysics Data System (ADS)

    González-Salgado, D.; Zemánková, K.; Noya, E. G.; Lomba, E.

    2016-05-01

    In this work, we present a study of representative excess thermodynamic properties of aqueous mixtures of methanol over the complete concentration range, based on extensive computer simulation calculations. In addition to test various existing united atom model potentials, we have developed a new force-field which accurately reproduces the excess thermodynamics of this system. Moreover, we have paid particular attention to the behavior of the temperature of maximum density (TMD) in dilute methanol mixtures. The presence of a temperature of maximum density is one of the essential anomalies exhibited by water. This anomalous behavior is modified in a non-monotonous fashion by the presence of fully miscible solutes that partly disrupt the hydrogen bond network of water, such as methanol (and other short chain alcohols). In order to obtain a better insight into the phenomenology of the changes in the TMD of water induced by small amounts of methanol, we have performed a new series of experimental measurements and computer simulations using various force fields. We observe that none of the force-fields tested capture the non-monotonous concentration dependence of the TMD for highly diluted methanol solutions.

  17. Methanol

    Integrated Risk Information System (IRIS)

    Methanol ; CASRN 67 - 56 - 1 Human health assessment information on a chemical substance is included in the IRIS database only after a comprehensive review of toxicity data , as outlined in the IRIS assessment development process . Sections I ( Health Hazard Assessments for Noncarcinogenic Effects )

  18. Superoxide dismutase, catalase and cell dimorphism in Candida albicans cells exposed to methanol and different temperatures.

    PubMed

    Romandini, P; Bonotto, C; Bertoloni, G; Beltramini, M; Salvato, B

    1994-05-01

    The combined effects of methanol and different temperatures on Candida albicans were studied. Growth curve, cell morphology, superoxide dismutase (SOD) and catalase activity levels have been determined. Cell growth in each medium was comparable to 28 degrees C and 37 degrees C. The growth rate was not affected by methanol, in the presence of glucose, while it was much lower in the absence of sugar. Cell dimorphism appeared after thermic stress and it was also dependent on the medium composition. In all media, both SOD and catalase levels were much higher at 37 degrees C. The presence of methanol per se did not affect the enzymatic levels, while the absence of glucose gave higher SOD levels. PMID:8061958

  19. Platinum-coated porous gold nanorods in methanol electrooxidation: dependence of catalytic activity on ligament size.

    PubMed

    Yoo, Sang-Hoon; Liu, Lichun; Cho, Sang Hyun; Park, Sungho

    2012-12-01

    Here we demonstrate that, in the dealloying process of Au-Ag nanorods, temperature is the key parameter for producing porous Au nanorods with tunable ligament sizes. The vertically aligned Au-Ag alloy nanorods were first synthesized by the electrochemical co-deposition of Au and Ag onto anodic aluminum oxide (AAO) membrane templates. Porous Au nanorods were then obtained by selectively etching Ag away from the precursor Au-Ag alloy nanorods. Control of the ligament size was achieved by controlling the dealloying temperature. Pt deposited on the porous Au nanorods with smaller ligaments exhibited a higher catalytic activity during methanol electrooxidation than those deposited on nanorods with larger ligaments produced by dealloying at higher temperatures. The strong dependence of the catalytic activity on the ligament size of porous Au is principally due to different amounts of carbon monoxide (CO) generated during methanol electrooxidation. Less CO was generated as the ligament size decreased. This finding is of importance for developing highly efficient cathode materials for carrying out methanol electrooxidation in practical applications in which porous Au with a large surface area is used as a supporting substrate. PMID:23023934

  20. Mixing it up - Measuring diffusion in supercooled liquid solutions of methanol and ethanol at temperatures near the glass transition

    SciTech Connect

    Matthiesen, Jesper; Smith, R. Scott; Kay, Bruce D.

    2011-03-17

    Do liquid mixtures, cooled to temperatures below their freezing point, behave as normal liquids? We address this question using nanoscale films of methanol and ethanol supercooled liquid solutions of varying composition (7 -93% methanol) at temperatures near their glass transition,Tg. The permeation of Kr through these films is used to determine the diffusivities of the supercooled liquid mixtures. We find that the temperature dependent diffusivities of the mixtures are well-fit by a Vogel-Fulcher-Tamman equation indicating that the mixtures exhibit fragile behavior at temperatures just above their Tg. Further, for a given temperature, the composition dependent diffusivity is well-fit by a Vignes-type equation, i.e. the diffusivity of any mixture can be predicted using an exponential weighting of the diffusion of the pure methanol and ethanol diffusivities. These results show that deeply supercooled liquid mixtures can be used to provide valuable insight into the properties of normal liquid mixtures.

  1. Methanol induces low temperature resilient methanogens and improves methane generation from domestic wastewater at low to moderate temperatures.

    PubMed

    Saha, Shaswati; Badhe, Neha; De Vrieze, Jo; Biswas, Rima; Nandy, Tapas

    2015-01-01

    Low temperature (<20 °C) limits bio-methanation of sewage. Literature shows that hydrogenotrophic methanogens can adapt themselves to low temperature and methanol is a preferred substrate by methanogens in cold habitats. The study hypothesizes that methanol can induce the growth of low-temperature resilient, methanol utilizing, hydrogenotrophs in UASB reactor. The hypothesis was tested in field conditions to evaluate the impact of seasonal temperature variations on methane yield in the presence and absence of methanol. Results show that 0.04% (v/v) methanol increased methane up to 15 times and its effect was more pronounced at lower temperatures. The qPCR analysis showed the presence of Methanobacteriales along with Methanosetaceae in large numbers. This indicates methanol induced the growth of both the hydrogenotrophic and acetoclastic groups through direct and indirect routes, respectively. This study thus demonstrated that methanol can impart resistance in methanogenic biomass to low temperature and can improve performance of UASB reactor. PMID:25913884

  2. Solubility of methanol in low-temperature aqueous sulfuric acid and implications for atmospheric particle composition

    NASA Technical Reports Server (NTRS)

    Iraci, Laura T.; Essin, Andrew M.; Golden, David M.; Hipskind, R. Stephen (Technical Monitor)

    2001-01-01

    Using traditional Knudsen cell techniques, we find well-behaved Henry's law uptake of methanol in aqueous 45 - 70 wt% H2SO4 solutions at temperatures between 197 and 231 K. Solubility of methanol increases with decreasing temperature and increasing acidity, with an effective Henry's law coefficient ranging from 10(exp 5) - 10(exp 8) M/atm. Equilibrium uptake of methanol into sulfuric acid aerosol particles in the upper troposphere and lower stratosphere will not appreciably alter gas-phase concentrations of methanol. The observed room temperature reaction between methanol and sulfuric acid is too slow to provide a sink for gaseous methanol at the temperatures of the upper troposphere and lower stratosphere. It is also too slow to produce sufficient quantities of soluble reaction products to explain the large amount of unidentified organic material seen in particles of the upper troposphere.

  3. Application of Flexible Micro Temperature Sensor in Oxidative Steam Reforming by a Methanol Micro Reformer

    PubMed Central

    Lee, Chi-Yuan; Lee, Shuo-Jen; Shen, Chia-Chieh; Yeh, Chuin-Tih; Chang, Chi-Chung; Lo, Yi-Man

    2011-01-01

    Advances in fuel cell applications reflect the ability of reformers to produce hydrogen. This work presents a flexible micro temperature sensor that is fabricated based on micro-electro-mechanical systems (MEMS) technology and integrated into a flat micro methanol reformer to observe the conditions inside that reformer. The micro temperature sensor has higher accuracy and sensitivity than a conventionally adopted thermocouple. Despite various micro temperature sensor applications, integrated micro reformers are still relatively new. This work proposes a novel method for integrating micro methanol reformers and micro temperature sensors, subsequently increasing the methanol conversion rate and the hydrogen production rate by varying the fuel supply rate and the water/methanol ratio. Importantly, the proposed micro temperature sensor adequately controls the interior temperature during oxidative steam reforming of methanol (OSRM), with the relevant parameters optimized as well. PMID:22319407

  4. Absorption cross-section measurements of methane, ethane, ethylene and methanol at high temperatures

    NASA Astrophysics Data System (ADS)

    Alrefae, Majed; Es-sebbar, Et-touhami; Farooq, Aamir

    2014-09-01

    Mid-IR absorption cross-sections are measured for methane, ethane, ethylene and methanol over 2800-3400 cm-1 (2.9-3.6 μm) spectral region. Measurements are carried out using a Fourier-Transform-Infrared (FTIR) spectrometer with temperatures ranging 296-1100 K and pressures near atmospheric. As temperature increases, the peak cross-sections decrease but the wings of the bands increase as higher rotational lines appear. Integrated band intensity is also calculated over the measured spectral region and is found to be a very weak function of temperature. The absorption cross-sections of the relatively small fuels studied here show dependence on the bath gas. This effect is investigated by studying the variation of absorption cross-sections at 3.392 μm using a HeNe laser in mixtures of fuel and nitrogen, argon, or helium. Mixtures of fuel with He have the highest value of absorption cross-sections followed by Ar and N2. Molecules with narrow absorption lines, such as methane and methanol, show strong dependence on bath gas than molecules with relatively broader absorption features i.e. ethane and ethylene.

  5. Isothermal Cyclic Conversion of Methane into Methanol over Copper-Exchanged Zeolite at Low Temperature.

    PubMed

    Tomkins, Patrick; Mansouri, Ali; Bozbag, Selmi E; Krumeich, Frank; Park, Min Bum; Alayon, Evalyn Mae C; Ranocchiari, Marco; van Bokhoven, Jeroen A

    2016-04-25

    Direct partial oxidation of methane into methanol is a cornerstone of catalysis. The stepped conversion of methane into methanol currently involves activation at high temperature and reaction with methane at decreased temperature, which limits applicability of the technique. The first implementation of copper-containing zeolites in the production of methanol directly from methane is reported, using molecular oxygen under isothermal conditions at 200 °C. Copper-exchanged zeolite is activated with oxygen, reacts with methane, and is subsequently extracted with steam in a repeated cyclic process. Methanol yield increases with methane pressure, enabling reactivity with less reactive oxidized copper species. It is possible to produce methanol over catalysts that were inactive in prior state of the art systems. Characterization of the activated catalyst at low temperature revealed that the active sites are small clusters of copper, and not necessarily di- or tricopper sites, indicating that catalysts can be designed with greater flexibility than formerly proposed. PMID:27010863

  6. Process assessment of small scale low temperature methanol synthesis

    NASA Astrophysics Data System (ADS)

    Hendriyana, Susanto, Herri; Subagjo

    2015-12-01

    Biomass is a renewable energy resource and has the potential to make a significant impact on domestic fuel supplies. Biomass can be converted to fuel like methanol via several step process. The process can be split into following main steps: biomass preparation, gasification, gas cooling and cleaning, gas shift and methanol synthesis. Untill now these configuration still has a problem like high production cost, catalyst deactivation, economy of scale and a huge energy requirements. These problems become the leading inhibition for biomass conversion to methanol, which should be resolved to move towards the economical. To address these issues, we developed various process and new configurations for methanol synthesis via methyl formate. This configuration combining two reactors: the one reactor for the carbonylation of methanol and CO to form methyl formate, and the second for the hydrogenolysis of methyl formate and H2 to form two molecule of methanol. Four plant process configurations were compared with the biomass basis is 300 ton/day. The first configuration (A) is equipped with a steam reforming process for converting methane to CO and H2 for increasing H2/CO ratio. CO2 removal is necessary to avoid poisoning the catalyst. COSORB process used for the purpose of increasing the partial pressure of CO in the feed gas. The steam reforming process in B configuration is not used with the aim of reducing the number of process equipment, so expect lower investment costs. For C configuration, the steam reforming process and COSORB are not used with the aim of reducing the number of process equipment, so expect lower investment costs. D configuration is almost similar to the configuration A. This configuration difference is in the synthesis of methanol which was held in a single reactor. Carbonylation and hydrogenolysis reactions carried out in the same reactor one. These processes were analyzed in term of technical process, material and energy balance and economic

  7. Process assessment of small scale low temperature methanol synthesis

    SciTech Connect

    Hendriyana; Susanto, Herri Subagjo

    2015-12-29

    Biomass is a renewable energy resource and has the potential to make a significant impact on domestic fuel supplies. Biomass can be converted to fuel like methanol via several step process. The process can be split into following main steps: biomass preparation, gasification, gas cooling and cleaning, gas shift and methanol synthesis. Untill now these configuration still has a problem like high production cost, catalyst deactivation, economy of scale and a huge energy requirements. These problems become the leading inhibition for biomass conversion to methanol, which should be resolved to move towards the economical. To address these issues, we developed various process and new configurations for methanol synthesis via methyl formate. This configuration combining two reactors: the one reactor for the carbonylation of methanol and CO to form methyl formate, and the second for the hydrogenolysis of methyl formate and H{sub 2} to form two molecule of methanol. Four plant process configurations were compared with the biomass basis is 300 ton/day. The first configuration (A) is equipped with a steam reforming process for converting methane to CO and H{sub 2} for increasing H{sub 2}/CO ratio. CO{sub 2} removal is necessary to avoid poisoning the catalyst. COSORB process used for the purpose of increasing the partial pressure of CO in the feed gas. The steam reforming process in B configuration is not used with the aim of reducing the number of process equipment, so expect lower investment costs. For C configuration, the steam reforming process and COSORB are not used with the aim of reducing the number of process equipment, so expect lower investment costs. D configuration is almost similar to the configuration A. This configuration difference is in the synthesis of methanol which was held in a single reactor. Carbonylation and hydrogenolysis reactions carried out in the same reactor one. These processes were analyzed in term of technical process, material and energy

  8. Temperature dependent BRDF facility

    NASA Astrophysics Data System (ADS)

    Airola, Marc B.; Brown, Andrea M.; Hahn, Daniel V.; Thomas, Michael E.; Congdon, Elizabeth A.; Mehoke, Douglas S.

    2014-09-01

    Applications involving space based instrumentation and aerodynamically heated surfaces often require knowledge of the bi-directional reflectance distribution function (BRDF) of an exposed surface at high temperature. Addressing this need, the Johns Hopkins University Applied Physics Laboratory (JHU/APL) developed a BRDF facility that features a multiple-port vacuum chamber, multiple laser sources covering the spectral range from the longwave infrared to the ultraviolet, imaging pyrometry and laser heated samples. Laser heating eliminates stray light that would otherwise be seen from a furnace and requires minimal sample support structure, allowing low thermal conduction loss to be obtained, which is especially important at high temperatures. The goal is to measure the BRDF of ceramic-coated surfaces at temperatures in excess of 1000°C in a low background environment. Most ceramic samples are near blackbody in the longwave infrared, thus pyrometry using a LWIR camera can be very effective and accurate.

  9. Degradation of Coflon in Methanol at Temperatures Around 140 C

    NASA Technical Reports Server (NTRS)

    Campion, R. P.; Samulak, M.; Morgan, C. J.

    1995-01-01

    An unexpected and significant physico-chemical degradation of Coflon PVDF specimens was observed at the end of 1994 during routine scheduled exposure exercises on strained material. The intent was to age various samples, including some strained in a 4-point bend configuration, in methanol at 140 C and subsequently submit the aged samples to various tests including dynamic fatigue and fracture toughness. However, the samples deteriorated to such an extent that such testing was not possible: only when conditions were made less severe was it found possible to perform such testing. The purpose of the current report is to describe the nature of the PVDF deterioration observed during a number of tests performed to examine this phenomenon. This report also records, as Appendix 1, some SEM/X-ray microanalysis data on Coflon samples exposed to a methanol/amine mixture, and to other amine or H2S-aged samples.

  10. Biomarkers to evaluate the effects of temperature and methanol on recombinant Pichia pastoris

    PubMed Central

    Zepeda, Andrea B.; Figueroa, Carolina A.; Abdalla, Dulcineia S.P.; Maranhão, Andrea Q.; Ulloa, Patricio H.; Pessoa, Adalberto; Farías, Jorge G.

    2014-01-01

    Pichia pastoris is methylotrophic yeast used as an efficient expression system for heterologous protein production. In order to evaluate the effects of temperature (10 and 30 °C) and methanol (1 and 3% (v/v)) on genetically-modified Pichia pastoris, different biomarkers were evaluated: Heat stress (HSF-1 and Hsp70), oxidative stress (OGG1 and TBARS) and antioxidant (GLR). Three yeast cultures were performed: 3X = 3% methanol-10 °C, 4X = 3% methanol-30 °C, and 5X = 1% methanol-10°C. The expression level of HIF-1α, HSF-1, HSP-70 and HSP-90 biomarkers were measured by Western blot and in situ detection was performed by immunocytochemistry. Ours results show that at 3% methanol −30 °C there is an increase of mitochondrial OGG1 (mtOGG1), Glutathione Reductase (GLR) and TBARS. In addition, there was a cytosolic expression of HSF-1 and HSP-70, which indicates a deprotection against nucleolar fragmentation (apoptosis). On the other hand, at 3% methanol −10 °C and 1% and at methanol −10 °C conditions there was nuclear expression of OGG1, lower levels of TBARS and lower expression of GLR, cytosolic expression of HSF-1 and nuclear expression HSP-70. In conclusion, our results suggest that 3% methanol-30 °C is a condition that induces a strong oxidative stress and risk factors of apoptosis in modified-genetically P. pastoris. PMID:25242930

  11. Biomarkers to evaluate the effects of temperature and methanol on recombinant Pichia pastoris.

    PubMed

    Zepeda, Andrea B; Figueroa, Carolina A; Abdalla, Dulcineia S P; Maranhão, Andrea Q; Ulloa, Patricio H; Pessoa, Adalberto; Farías, Jorge G

    2014-01-01

    Pichia pastoris is methylotrophic yeast used as an efficient expression system for heterologous protein production. In order to evaluate the effects of temperature (10 and 30 °C) and methanol (1 and 3% (v/v)) on genetically-modified Pichia pastoris, different biomarkers were evaluated: Heat stress (HSF-1 and Hsp70), oxidative stress (OGG1 and TBARS) and antioxidant (GLR). Three yeast cultures were performed: 3X = 3% methanol-10 °C, 4X = 3% methanol-30 °C, and 5X = 1% methanol-10°C. The expression level of HIF-1α, HSF-1, HSP-70 and HSP-90 biomarkers were measured by Western blot and in situ detection was performed by immunocytochemistry. Ours results show that at 3% methanol -30 °C there is an increase of mitochondrial OGG1 (mtOGG1), Glutathione Reductase (GLR) and TBARS. In addition, there was a cytosolic expression of HSF-1 and HSP-70, which indicates a deprotection against nucleolar fragmentation (apoptosis). On the other hand, at 3% methanol -10 °C and 1% and at methanol -10 °C conditions there was nuclear expression of OGG1, lower levels of TBARS and lower expression of GLR, cytosolic expression of HSF-1 and nuclear expression HSP-70. In conclusion, our results suggest that 3% methanol-30 °C is a condition that induces a strong oxidative stress and risk factors of apoptosis in modified-genetically P. pastoris. PMID:25242930

  12. NMR analysis of diacyl peroxide decomposition in methanol in response to temperature and microwave radiation

    NASA Astrophysics Data System (ADS)

    Haidukevich, O. A.; Skakovskii, E. D.; Tychinskaya, L. Yu.; Zvereva, T. D.; Dikusar, E. A.; Lamotkin, S. A.; Rykov, S. V.

    2012-05-01

    We have studied the decomposition of benzoyl and acetyl benzoyl peroxides in methanol-d4 in response to temperature and microwave radiation. We have shown that chemically-induced dynamic nuclear polarization (CIDNP) can be observed even when the reactions are carried out in spectrometers with high magnetic fields. In this case, spin correlation persists in geminal radical pairs involving labile acyloxyl radicals. Regardless of the method used to initiate peroxide decomposition, the same amount of products are formed. Homolysis occurs according to a chain mechanism. The contribution of induced decomposition decreases over the course of the reaction. Dissolved oxygen molecules efficiently terminate the chain, decreasing the rate of peroxide decomposition. In the case of acetyl benzoyl peroxide, the product yield depends on the initiation mechanism: for microwave irradiation, the solvent molecules are more active while dissolved oxygen is less active than in thermolysis.

  13. Surface-Bound Intermediates in Low-Temperature Methanol Synthesis on Copper. Participants and Spectators

    SciTech Connect

    Yang, Yong; Mei, Donghai; Peden, Charles H.F.; Campbell, Charles T.; Mims, Charles A.

    2015-11-03

    The reactivity of surface adsorbed species present on copper catalysts during methanol synthesis at low temperatures was studied by simultaneous infrared spectroscopy (IR) and mass spectroscopy (MS) measurements during “titration” (transient surface reaction) experiments with isotopic tracing. The results show that adsorbed formate is a major bystander species present on the surface under steady-state methanol synthesis reaction conditions, but it cannot be converted to methanol by reaction with pure H2, nor with H2 plus added water. Formate-containing surface adlayers for these experiments were produced during steady state catalysis in (a) H2:CO2 (with substantial formate coverage) and (b) moist H2:CO (with no IR visible formate species). Both these reaction conditions produce methanol at steady state with relatively high rates. Adlayers containing formate were also produced by (c) formic acid adsorption. Various "titration" gases were used to probe these adlayers at modest temperatures (T = 410-450K) and 6 bar total pressure. Methanol gas (up to ~1% monolayer equivalent) was produced in "titration" from the H2:CO2 catalytic adlayers by H2 plus water, but not by dry hydrogen. The decay in the formate IR features accelerated in the presence of added water vapor. The H2:CO:H2O catalytic adlayer produced similar methanol titration yields in H2 plus water but showed no surface formate features in IR (less than 0.2% monolayer coverage). Finally, formate from formic acid chemisorption produced no methanol under any titration conditions. Even under (H2:CO2) catalytic reaction conditions, isotope tracing showed that pre-adsorbed formate from formic acid did not contribute to the methanol produced. Although non-formate intermediates exist during low temperature methanol synthesis on copper which can be converted to methanol gas

  14. Viscosity and density of methanol/water mixtures at low temperatures

    NASA Technical Reports Server (NTRS)

    Austin, J. G.; Kurata, F.; Swift, G. W.

    1968-01-01

    Viscosity and density are measured at low temperatures for three methanol/water mixtures. Viscosity is determined by a modified falling cylinder method or a calibrated viscometer. Density is determined by the volume of each mixture contained in a calibrated glass cell placed in a constant-temperature bath.

  15. Coadsorbed species explain the mechanism of methanol temperature-desorption on CeO2(111)

    DOE PAGESBeta

    Sutton, Jonathan E.; Steven H. Overbury; Beste, Ariana

    2016-03-24

    Here, we have used density functional theory calculations to investigate the temperature-programmed desorption (TPD) of methanol from CeO2(111). For the first time, low-temperature water formation and high-temperature methanol desorption are explained by our calculations. High coverages of methanol, which correspond to experimental conditions, are required to properly describe these features of the TPD spectrum. We identify a mechanism for the low-temperature formation of water involving the dissociation of two methanol molecules on the same surface O atom and filling of the resulting surface vacancy with one of the methoxy products. After water desorption, methoxy groups are stabilized on the surfacemore » and react at higher temperatures to form methanol and formaldehyde by a disproportionation mechanism. Alternatively, the stabilized methoxy groups undergo sequential C–H scission reactions to produce formaldehyde. Calculated energy requirements and methanol/formaldehyde selectivity agree with the experimental data.« less

  16. Dynamics of water, methanol, and ethanol in a room temperature ionic liquid.

    PubMed

    Kramer, Patrick L; Giammanco, Chiara H; Fayer, Michael D

    2015-06-01

    The dynamics of a series of small molecule probes with increasing alkyl chain length: water, methanol, and ethanol, diluted to low concentration in the room temperature ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, was investigated with 2D infrared vibrational echo (2D IR) spectroscopy and polarization resolved pump-probe (PP) experiments on the deuterated hydroxyl (O-D) stretching mode of each of the solutes. The long timescale spectral diffusion observed by 2D IR, capturing complete loss of vibrational frequency correlation through structural fluctuation of the medium, shows a clear but not dramatic slowing as the probe alkyl chain length is increased: 23 ps for water, 28 ps for methanol, and 34 ps for ethanol. Although in each case, only a single population of hydroxyl oscillators contributes to the infrared line shapes, the isotropic pump-probe decays (normally caused by population relaxation) are markedly nonexponential at short times. The early time features correspond to the timescales of the fast spectral diffusion measured with 2D IR. These fast isotropic pump-probe decays are produced by unequal pumping of the OD absorption band to a nonequilibrium frequency dependent population distribution caused by significant non-Condon effects. Orientational correlation functions for these three systems, obtained from pump-probe anisotropy decays, display several periods of restricted angular motion (wobbling-in-a-cone) followed by complete orientational randomization. The cone half-angles, which characterize the angular potential, become larger as the experimental frequency moves to the blue. These results indicate weakening of the angular potential with decreasing hydrogen bond strength. The slowest components of the orientational anisotropy decays are frequency-independent and correspond to the complete orientational randomization of the solute molecule. These components slow appreciably with increasing chain length: 25 ps for water

  17. Dynamics of water, methanol, and ethanol in a room temperature ionic liquid

    NASA Astrophysics Data System (ADS)

    Kramer, Patrick L.; Giammanco, Chiara H.; Fayer, Michael D.

    2015-06-01

    The dynamics of a series of small molecule probes with increasing alkyl chain length: water, methanol, and ethanol, diluted to low concentration in the room temperature ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, was investigated with 2D infrared vibrational echo (2D IR) spectroscopy and polarization resolved pump-probe (PP) experiments on the deuterated hydroxyl (O-D) stretching mode of each of the solutes. The long timescale spectral diffusion observed by 2D IR, capturing complete loss of vibrational frequency correlation through structural fluctuation of the medium, shows a clear but not dramatic slowing as the probe alkyl chain length is increased: 23 ps for water, 28 ps for methanol, and 34 ps for ethanol. Although in each case, only a single population of hydroxyl oscillators contributes to the infrared line shapes, the isotropic pump-probe decays (normally caused by population relaxation) are markedly nonexponential at short times. The early time features correspond to the timescales of the fast spectral diffusion measured with 2D IR. These fast isotropic pump-probe decays are produced by unequal pumping of the OD absorption band to a nonequilibrium frequency dependent population distribution caused by significant non-Condon effects. Orientational correlation functions for these three systems, obtained from pump-probe anisotropy decays, display several periods of restricted angular motion (wobbling-in-a-cone) followed by complete orientational randomization. The cone half-angles, which characterize the angular potential, become larger as the experimental frequency moves to the blue. These results indicate weakening of the angular potential with decreasing hydrogen bond strength. The slowest components of the orientational anisotropy decays are frequency-independent and correspond to the complete orientational randomization of the solute molecule. These components slow appreciably with increasing chain length: 25 ps for water

  18. Temperature-dependent Luttinger surfaces.

    PubMed

    Ito, T; Chainani, A; Haruna, T; Kanai, K; Yokoya, T; Shin, S; Kato, R

    2005-12-01

    The Luttinger surface of an organic metal (TTF-TCNQ), possessing charge order and spin-charge separated band dispersions, is investigated using temperature-dependent angle-resolved photoemission spectroscopy. The Luttinger surface topology, obtained from momentum distribution curves, changes from quasi-2D (dimensional) to quasi-1D with temperature. The high temperature quasi-2D surface exhibits 4kF charge-density-wave (CDW) superstructure in the TCNQ derived holon band, in the absence of 2kF order. Decreasing temperature results in quasi-1D nested 2kF CDW order in the TCNQ spinon band and in the TTF surface. The results establish the link in momentum space between charge order and spin-charge separation in a Luttinger liquid. PMID:16384402

  19. Liquid phase low temperature method for production of methanol from synthesis gas and catalyst formulations therefor

    DOEpatents

    Mahajan, Devinder

    2005-07-26

    The invention provides a homogenous catalyst for the production of methanol from purified synthesis gas at low temperature and low pressure which includes a transition metal capable of forming transition metal complexes with coordinating ligands and an alkoxide, the catalyst dissolved in a methanol solvent system, provided the transition metal complex is not transition metal carbonyl. The coordinating ligands can be selected from the group consisting of N-donor ligands, P-donor ligands, O-donor ligands, C-donor ligands, halogens and mixtures thereof.

  20. Development of Anodic Flux and Temperature Controlling System for Micro Direct Methanol Fuel Cell

    NASA Astrophysics Data System (ADS)

    Li, M. M.; Liu, C.; Liang, J. S.; Wu, C. B.; Xu, Z.

    2006-10-01

    Micro Direct Methanol Fuel Cell (μDMFC) is a kind of newly developed power sources, which effective apparatus for its performance evaluation is still in urgent need at present. In this study, a testing system was established for the purpose of testing the continuous working performance such as micro flux and temperature of μDMFC. In view of the temperature controlling for micro-flux liquid fuel, a heating block with labyrinth-like single pass channel inside for heating up the methanol solution was fabricated. A semiconductorrefrigerating chip was utilized to heat and cool the liquid flow during testing procedures. On the other hand, the two channels of a high accuracy double-channel syringe pump that can suck and pump in turn so as to transport methanol solution continuously was adopted. Based on the requirements of wide-ranged temperature and micro flux controlling, the solenoid valves and the correlative component were used. A hydraulic circuit, which can circulate the fed methanol cold to hot in turn, has also been constructed to test the fatigue life of the μDMFC. The automatic control was actualized by software module written with Visual C++. Experimental results show that the system is perfect in stability and it may provide an important and advanced evaluation apparatus to satisfy the needs for real time performance testing of μDMFC.

  1. A Catalytic Role of XoxF1 as La3+-Dependent Methanol Dehydrogenase in Methylobacterium extorquens Strain AM1

    PubMed Central

    Sasa, Kentaro; Tashiro, Shinya; Iwama, Tomonori; Hayakawa, Takashi; Kawai, Keiichi

    2012-01-01

    In the methylotrophic bacterium Methylobacterium extorquens strain AM1, MxaF, a Ca2+-dependent methanol dehydrogenase (MDH), is the main enzyme catalyzing methanol oxidation during growth on methanol. The genome of strain AM1 contains another MDH gene homologue, xoxF1, whose function in methanol metabolism has remained unclear. In this work, we show that XoxF1 also functions as an MDH and is La3+-dependent. Despite the absence of Ca2+ in the medium strain AM1 was able to grow on methanol in the presence of La3+. Addition of La3+ increased MDH activity but the addition had no effect on mxaF or xoxF1 expression level. We purified MDH from strain AM1 grown on methanol in the presence of La3+, and its N-terminal amino acid sequence corresponded to that of XoxF1. The enzyme contained La3+ as a cofactor. The ΔmxaF mutant strain could not grow on methanol in the presence of Ca2+, but was able to grow after supplementation with La3+. Taken together, these results show that XoxF1 participates in methanol metabolism as a La3+-dependent MDH in strain AM1. PMID:23209751

  2. Dehydrogenation of anhydrous methanol at room temperature by o-aminophenol-based photocatalysts

    PubMed Central

    Wakizaka, Masanori; Matsumoto, Takeshi; Tanaka, Ryota; Chang, Ho-Chol

    2016-01-01

    Dehydrogenation of anhydrous methanol is of great importance, given its ubiquity as an intermediate for the production of a large number of industrial chemicals. Since dehydrogenation of methanol is an endothermic reaction, heterogeneous or homogeneous precious-metal-based catalysts and high temperatures are usually required for this reaction to proceed. Here we report the photochemical dehydrogenation of anhydrous methanol at room temperature catalysed by o-aminophenol (apH2), o-aminophenolate (apH−) and the non-precious metal complex trans-[FeII(apH)2(MeOH)2]. Under excitation at 289±10 nm and in the absence of additional photosensitizers, these photocatalysts generate hydrogen and formaldehyde from anhydrous methanol with external quantum yields of 2.9±0.15%, 3.7±0.19% and 4.8±0.24%, respectively, which are the highest values reported so far to the best of our knowledge. Mechanistic investigations reveal that the photo-induced formation of hydrogen radicals triggers the reaction. PMID:27457731

  3. Dehydrogenation of anhydrous methanol at room temperature by o-aminophenol-based photocatalysts.

    PubMed

    Wakizaka, Masanori; Matsumoto, Takeshi; Tanaka, Ryota; Chang, Ho-Chol

    2016-01-01

    Dehydrogenation of anhydrous methanol is of great importance, given its ubiquity as an intermediate for the production of a large number of industrial chemicals. Since dehydrogenation of methanol is an endothermic reaction, heterogeneous or homogeneous precious-metal-based catalysts and high temperatures are usually required for this reaction to proceed. Here we report the photochemical dehydrogenation of anhydrous methanol at room temperature catalysed by o-aminophenol (apH2), o-aminophenolate (apH(-)) and the non-precious metal complex trans-[Fe(II)(apH)2(MeOH)2]. Under excitation at 289±10 nm and in the absence of additional photosensitizers, these photocatalysts generate hydrogen and formaldehyde from anhydrous methanol with external quantum yields of 2.9±0.15%, 3.7±0.19% and 4.8±0.24%, respectively, which are the highest values reported so far to the best of our knowledge. Mechanistic investigations reveal that the photo-induced formation of hydrogen radicals triggers the reaction. PMID:27457731

  4. Temperature dependence of basalt weathering

    NASA Astrophysics Data System (ADS)

    Li, Gaojun; Hartmann, Jens; Derry, Louis A.; West, A. Joshua; You, Chen-Feng; Long, Xiaoyong; Zhan, Tao; Li, Laifeng; Li, Gen; Qiu, Wenhong; Li, Tao; Liu, Lianwen; Chen, Yang; Ji, Junfeng; Zhao, Liang; Chen, Jun

    2016-06-01

    The homeostatic balance of Earth's long-term carbon cycle and the equable state of Earth's climate are maintained by negative feedbacks between the levels of atmospheric CO2 and the chemical weathering rate of silicate rocks. Though clearly demonstrated by well-controlled laboratory dissolution experiments, the temperature dependence of silicate weathering rates, hypothesized to play a central role in these weathering feedbacks, has been difficult to quantify clearly in natural settings at landscape scale. By compiling data from basaltic catchments worldwide and considering only inactive volcanic fields (IVFs), here we show that the rate of CO2 consumption associated with the weathering of basaltic rocks is strongly correlated with mean annual temperature (MAT) as predicted by chemical kinetics. Relations between temperature and CO2 consumption rate for active volcanic fields (AVFs) are complicated by other factors such as eruption age, hydrothermal activity, and hydrological complexities. On the basis of this updated data compilation we are not able to distinguish whether or not there is a significant runoff control on basalt weathering rates. Nonetheless, the simple temperature control as observed in this global dataset implies that basalt weathering could be an effective mechanism for Earth to modulate long-term carbon cycle perturbations.

  5. Methanol:coenzyme M methyltransferase from Methanosarcina barkeri. Zinc dependence and thermodynamics of the methanol:cob(I)alamin methyltransferase reaction.

    PubMed

    Sauer, K; Thauer, R K

    1997-10-01

    In Methanosarcina barkeri, methanogenesis from methanol is initiated by the formation of methyl-coenzyme M from methanol and coenzyme M. This methyl transfer reaction is catalyzed by two enzymes, designated methyltransferases 1 (MT1) and 2 (MT2). Transferase MT1, which is composed of a 50-kDa subunit, MtaB, and a 27-kDa corrinoid-harbouring subunit, MtaC, has been shown recently to catalyze the methylation of free cob(I)alamin with methanol [Sauer, K., Harms, U. & Thauer, R. K. (1997) Eur. J. Biochem. 243, 670-677]. We report here that this reaction is catalyzed by subunit MtaB overproduced in Escherichia coli. MtaB also catalyzed the formation of methanol from methylcobalamin and H2O, the hydrolysis being associated with a free-energy change deltaG(o)' of approximately +7.0 kJ/mol. MtaB was found to contain 1 mol zinc, and its activity to be zinc dependent (pK(Zn2+) = 9.3). The zinc dependence of the MT2 (MtaA)-catalyzed reaction is also described (pK(Zn2+) = 9.6). PMID:9363780

  6. Wavelength Dependence of UV Photoemission from Solvated Electrons in Bulk Water, Methanol, and Ethanol.

    PubMed

    Yamamoto, Yo-ichi; Karashima, Shutaro; Adachi, Shunsuke; Suzuki, Toshinori

    2016-03-01

    We have measured the wavelength dependence (340-215 nm) of one-photon photoemission from the ground electronic state of solvated electrons in bulk water, methanol, and ethanol. In every case, the vertical electron binding energy (VBE) gradually increased with photon energy, indicating that the photoelectron kinetic energy diminishes as a result of electron-vibration inelastic scattering prior to emission from the liquid surface. In contrast, the VBE of the Rydberg electron in DABCO (1,4-diazabicyclo[2,2,2]octane), which has a surface-excess density, revealed no clear wavelength dependence. These results suggest that the solvated electrons are created predominantly in the bulk and that VBEs measured using UV photoemission spectroscopy of liquids generally require energy corrections to account for inelastic scattering effects. From the wavelength dependence, we have re-estimated the VBEs of solvated electrons in bulk water, methanol, and ethanol to be 3.3, 3.1, and 3.1 eV, respectively. Hydrated electrons were also identified by photoemission spectroscopy using 90 nm radiation. PMID:26836447

  7. Catalytic Oxidation of Methane into Methanol over Copper-Exchanged Zeolites with Oxygen at Low Temperature.

    PubMed

    Narsimhan, Karthik; Iyoki, Kenta; Dinh, Kimberly; Román-Leshkov, Yuriy

    2016-06-22

    The direct catalytic conversion of methane to liquid oxygenated compounds, such as methanol or dimethyl ether, at low temperature using molecular oxygen is a grand challenge in C-H activation that has never been met with synthetic, heterogeneous catalysts. We report the first demonstration of direct, catalytic oxidation of methane into methanol with molecular oxygen over copper-exchanged zeolites at low reaction temperatures (483-498 K). Reaction kinetics studies show sustained catalytic activity and high selectivity for a variety of commercially available zeolite topologies under mild conditions (e.g., 483 K and atmospheric pressure). Transient and steady state measurements with isotopically labeled molecules confirm catalytic turnover. The catalytic rates and apparent activation energies are affected by the zeolite topology, with caged-based zeolites (e.g., Cu-SSZ-13) showing the highest rates. Although the reaction rates are low, the discovery of catalytic sites in copper-exchanged zeolites will accelerate the development of strategies to directly oxidize methane into methanol under mild conditions. PMID:27413787

  8. Catalytic Oxidation of Methane into Methanol over Copper-Exchanged Zeolites with Oxygen at Low Temperature

    PubMed Central

    2016-01-01

    The direct catalytic conversion of methane to liquid oxygenated compounds, such as methanol or dimethyl ether, at low temperature using molecular oxygen is a grand challenge in C–H activation that has never been met with synthetic, heterogeneous catalysts. We report the first demonstration of direct, catalytic oxidation of methane into methanol with molecular oxygen over copper-exchanged zeolites at low reaction temperatures (483–498 K). Reaction kinetics studies show sustained catalytic activity and high selectivity for a variety of commercially available zeolite topologies under mild conditions (e.g., 483 K and atmospheric pressure). Transient and steady state measurements with isotopically labeled molecules confirm catalytic turnover. The catalytic rates and apparent activation energies are affected by the zeolite topology, with caged-based zeolites (e.g., Cu-SSZ-13) showing the highest rates. Although the reaction rates are low, the discovery of catalytic sites in copper-exchanged zeolites will accelerate the development of strategies to directly oxidize methane into methanol under mild conditions. PMID:27413787

  9. The electrolyte challenge for a direct methanol-air polymer electrolyte fuel cell operating at temperatures up to 200 C

    NASA Technical Reports Server (NTRS)

    Savinell, Robert; Yeager, Ernest; Tryk, Donald; Landau, Uziel; Wainright, Jesse; Gervasio, Dominic; Cahan, Boris; Litt, Morton; Rogers, Charles; Scherson, Daniel

    1993-01-01

    Novel polymer electrolytes are being evaluated for use in a direct methanol-air fuel cell operating at temperatures in excess of 100 C. The evaluation includes tests of thermal stability, ionic conductivity, and vapor transport characteristics. The preliminary results obtained to date indicate that a high temperature polymer electrolyte fuel cell is feasible. For example, Nafion 117 when equilibrated with phosphoric acid has a conductivity of at least 0.4 Omega(exp -1)cm(exp -1) at temperatures up to 200 C in the presence of 400 torr of water vapor and methanol vapor cross over equivalent to 1 mA/cm(exp 2) under a one atmosphere methanol pressure differential at 135 C. Novel polymers are also showing similar encouraging results. The flexibility to modify and optimize the properties by custom synthesis of these novel polymers presents an exciting opportunity to develop an efficient and compact methanol fuel cell.

  10. Shape-dependent electrocatalysis: methanol and formic acid electrooxidation on preferentially oriented Pt nanoparticles.

    PubMed

    Solla-Gullón, J; Vidal-Iglesias, F J; López-Cudero, A; Garnier, E; Feliu, J M; Aldaz, A

    2008-07-01

    Reactivity towards methanol and formic acid electrooxidation on Pt nanoparticles with well characterised surfaces were studied and compared with the behaviour of single crystal electrodes with basal orientations. Polyoriented and preferential (100), (111) and (100)-(111) Pt nanoparticles were synthesised, cleaned preserving its surface structure, characterised and employed to evaluate the influence of the surface structure/shape of the Pt nanoparticles on these two relevant electrochemical reactions. The results pointed out that, in agreement with fundamental studies with Pt single crystal electrodes, the surface structure of the electrodes plays an important role on the reactivity of both oxidation processes, and thus the electrocatalytic properties strongly depend on the surface structure/shape of the nanoparticles, in particular on the presence of sites with (111) symmetry. These findings open the possibility of designing new and better electrocatalytic materials using decorated shape-controlled Pt nanoparticles as previously described with Pt single crystal electrodes. PMID:18563230

  11. Methanol-inducible promoter of thermotolerant methylotrophic yeast Ogataea thermomethanolica BCC16875 potential for production of heterologous protein at high temperatures.

    PubMed

    Promdonkoy, Peerada; Tirasophon, Witoon; Roongsawang, Niran; Eurwilaichitr, Lily; Tanapongpipat, Sutipa

    2014-08-01

    Methanol-utilizing metabolism is generally found in methylotrophic yeasts. Several potential promoters regulating enzymes in this pathway have been extensively studied, especially alcohol oxidase. Here, we characterized the alcohol oxidase gene promoter from thermotolerant Ogataea thermomethanolica (OthAOX). This promoter can be induced by methanol, and was shown to regulate expression of phytase up to 45 °C. The pattern of heterologous phytase N-glycosylation depends on the induction temperature. Unlike the AOX promoter from Pichia pastoris, this OthAOX initially turns on the expression of the heterologous protein at the de-repression stage in the presence of glycerol. Full induction of protein is observed when methanol is present. With this methanol-inducible promoter, target protein can be initially produced prior to the induction phase, which would help shorten the time for protein production. Being able to drive protein expression at various temperatures prompts this newly identified AOX promoter to be potential tool for heterologous protein production in high temperature conditions. PMID:24671405

  12. Nanoporous gold catalysts for selective gas-phase oxidative coupling of methanol at low temperature.

    PubMed

    Wittstock, A; Zielasek, V; Biener, J; Friend, C M; Bäumer, M

    2010-01-15

    Gold (Au) is an interesting catalytic material because of its ability to catalyze reactions, such as partial oxidations, with high selectivities at low temperatures; but limitations arise from the low O2 dissociation probability on Au. This problem can be overcome by using Au nanoparticles supported on suitable oxides which, however, are prone to sintering. Nanoporous Au, prepared by the dealloying of AuAg alloys, is a new catalyst with a stable structure that is active without any support. It catalyzes the selective oxidative coupling of methanol to methyl formate with selectivities above 97% and high turnover frequencies at temperatures below 80 degrees C. Because the overall catalytic characteristics of nanoporous Au are in agreement with studies on Au single crystals, we deduced that the selective surface chemistry of Au is unaltered but that O2 can be readily activated with this material. Residual silver is shown to regulate the availability of reactive oxygen. PMID:20075249

  13. Composition dependent structural organization in trihexyl(tetradecyl)phosphonium chloride ionic liquid-methanol mixtures

    SciTech Connect

    Gupta, Aditya; Sharma, Shobha; Kashyap, Hemant K.

    2015-04-07

    This article reports results from the molecular dynamics simulations on the structural arrangement of the ions and molecules in the mixtures of trihexyl(tetradecyl)phosphonium chloride ([P{sub 666,14}{sup +}][Cl{sup −}]) ionic liquid (IL) and methanol (MeOH) over the entire composition range. Effects of composition on the charge and polarity orderings have been investigated via computation of X-ray scattering structure function, S(q), and by using a partitioning scheme proposed for such multi-component mixtures. Except for the neat methanol liquid, the total S(q) shows two peaks in its intermolecular region for all the mole-fractions. The lowest q peak is dominated primarily by anion-anion, cation-anion, and methanol-anion correlations. Our results signify that the methanol bulk structure, which predominantly has short-distance characteristic correlations and is governed by polar group of methanol, is retained for x{sub IL} ≤ 0.1. Then, the mixture goes through gradual structural changes from methanol-like to the IL-like for 0.1 < x{sub IL} ≤ 0.7. The dipolar interaction between methanol molecules weakens in this range, and the structural landscape of the mixture is steered by strong ion-ion, anion-methanol, and nonpolar interactions. The IL-like structural arrangement is virtually recovered for x{sub IL} > 0.7. At all the compositions studied, while the cation head groups are predominantly solvated by anions and subsequently by methanol molecules, the polar hydroxyl group of methanol is preferentially solvated by the anions. The radial distribution functions of selected pair of atomic species have also confirmed these observations.

  14. Composition dependent structural organization in trihexyl(tetradecyl)phosphonium chloride ionic liquid-methanol mixtures

    NASA Astrophysics Data System (ADS)

    Gupta, Aditya; Sharma, Shobha; Kashyap, Hemant K.

    2015-04-01

    This article reports results from the molecular dynamics simulations on the structural arrangement of the ions and molecules in the mixtures of trihexyl(tetradecyl)phosphonium chloride ([P666,14+][Cl-]) ionic liquid (IL) and methanol (MeOH) over the entire composition range. Effects of composition on the charge and polarity orderings have been investigated via computation of X-ray scattering structure function, S(q), and by using a partitioning scheme proposed for such multi-component mixtures. Except for the neat methanol liquid, the total S(q) shows two peaks in its intermolecular region for all the mole-fractions. The lowest q peak is dominated primarily by anion-anion, cation-anion, and methanol-anion correlations. Our results signify that the methanol bulk structure, which predominantly has short-distance characteristic correlations and is governed by polar group of methanol, is retained for xIL ≤ 0.1. Then, the mixture goes through gradual structural changes from methanol-like to the IL-like for 0.1 < xIL ≤ 0.7. The dipolar interaction between methanol molecules weakens in this range, and the structural landscape of the mixture is steered by strong ion-ion, anion-methanol, and nonpolar interactions. The IL-like structural arrangement is virtually recovered for xIL > 0.7. At all the compositions studied, while the cation head groups are predominantly solvated by anions and subsequently by methanol molecules, the polar hydroxyl group of methanol is preferentially solvated by the anions. The radial distribution functions of selected pair of atomic species have also confirmed these observations.

  15. Reduced graphene oxide coated optical fiber for methanol and ethanol vapor detection at room temperature

    NASA Astrophysics Data System (ADS)

    Kavinkumar, T.; Sastikumar, D.; Manivannan, S.

    2014-10-01

    Successful isolation of single layer of graphene from graphite by mechanical exfoliation method, attracted a great attention due to its unique structural, optical, mechanical and electronic properties. This makes the graphene as a promising material in many possible applications such as energy-storage, sensing, electronic, optical devices and polymer composite materials. High quality of reduced graphene oxide (rGO) material was prepared by chemical reduction method at 100°C. The structural and optical properties of the rGO sheets were characterized by FT-IR, micro Raman, powder XRD and UV-vis-NIR techniques. FT-IR reveals the absence of oxygen functional groups on rGO due to the reduction process. Powder XRD shows the broad peak at 2θ=24.3° corresponding to interlayer spacing 3.66Å which is smaller than the graphene oxide (GO). UV-vis-NIR of rGO displays the absorption peak at 271 nm indicates the reduction of GO and the restoration of C=C bonds in the rGO sheets. The cladding removed and rGO coated poly-methyl methacrylate (PMMA) optical fiber is used for methanol and ethanol vapors detection in the concentration ranging from 0 to 500 ppm at room temperature. The spectral characteristics along with output intensity modulation of cladding removed and rGO coated fiber optic sensor reveal the potential of methanol and ethanol vapor sensing properties.

  16. Temperature effects on the structure of liquid D-methanol through neutron diffraction

    NASA Astrophysics Data System (ADS)

    Sahoo, A.; Sarkar, S.; Krishna, P. S. R.; Joarder, R. N.

    2004-08-01

    The study of changes in the structure (H-bonded) of liquid alcohols at elevated temperatures is rare probably due to low flash points of these liquids. An indigenously devised special quartz cell is now used to carry out the structural studies of these liquids at elevated temperatures through neutron diffraction. Here, the liquid consists of deuterated methanol and neutron data was collected on the high-Q diffractometer at Dhruva, BARC. The corrected data at elevated temperatures (BP (boiling point) and double the BP) show that there is a large change in the H-bonded structure of this liquid. The pre-peak or hump, known to be signature of H-bonded clusters appears to be present at all the three temperatures studied. In the low-Q (scattering vector) data Ornstein--Zernike (OZ) behaviour is also observed. It is, however, seen that the intramolecular structure does not change very much at higher temperatures. A detailed model analysis is in progress and would be reported later.

  17. Temperature dependence of thermopower in molecular junctions

    NASA Astrophysics Data System (ADS)

    Kim, Youngsang; Lenert, Andrej; Meyhofer, Edgar; Reddy, Pramod

    2016-07-01

    The thermoelectric properties of molecular junctions are of considerable interest due to their promise for efficient energy conversion. While the dependence of thermoelectric properties of junctions on molecular structure has been recently studied, their temperature dependence remains unexplored. Using a custom built variable temperature scanning tunneling microscope, we measured the thermopower and electrical conductance of individual benzenedithiol junctions over a range of temperatures (100 K-300 K). We find that while the electrical conductance is independent of temperature, the thermopower increases linearly with temperature, confirming the predictions of the Landauer theory.

  18. Temperature Dependence of Factors Controlling Isoprene Emissions

    NASA Technical Reports Server (NTRS)

    Duncan, Bryan N.; Yoshida, Yasuko; Damon, Megan R.; Douglass, Anne R.; Witte, Jacquelyn C.

    2009-01-01

    We investigated the relationship of variability in the formaldehyde (HCHO) columns measured by the Aura Ozone Monitoring Instrument (OMI) to isoprene emissions in the southeastern United States for 2005-2007. The data show that the inferred, regional-average isoprene emissions varied by about 22% during summer and are well correlated with temperature, which is known to influence emissions. Part of the correlation with temperature is likely associated with other causal factors that are temperature-dependent. We show that the variations in HCHO are convolved with the temperature dependence of surface ozone, which influences isoprene emissions, and the dependence of the HCHO column to mixed layer height as OMI's sensitivity to HCHO increases with altitude. Furthermore, we show that while there is an association of drought with the variation in HCHO, drought in the southeastern U.S. is convolved with temperature.

  19. Insights on the effective incorporation of a foam-based methanol reformer in a high temperature polymer electrolyte membrane fuel cell

    NASA Astrophysics Data System (ADS)

    Avgouropoulos, George; Papavasiliou, Joan; Ioannides, Theophilos; Neophytides, Stylianos

    2015-11-01

    Highly active Al-doped CuMnOx catalyst supported on metallic copper foam was prepared via the combustion method and placed adjacent to the anode electrocatalyst of a high temperature PEM fuel cell operating at 200-210 °C. The addition of aluminum oxide in the catalyst composition enhanced the specific surface area (19.1 vs. 8.6 m2 g-1) and the reducibility of the Cu-Mn spinel oxide. Accordingly, the catalytic performance of CuMnOx was also improved. The doped sample is up to 2.5 times more active than the undoped sample at 200 °C, depending on the methanol concentration at the inlet, while CO selectivity is less than 0.8% in all cases. A membrane-electrode assembly comprising the ADVENT cross-linked TPS® high-temperature polymer electrolyte was integrated with the Cu-based methanol reformer in an Internal Reforming Methanol Fuel Cell (IRMFC). In order to avoid extensive poisoning of the reforming catalyst by H3PO4, a thin separation plate was placed between the reforming catalyst and the electrooxidation catalyst. Preliminary results obtained from a single-cell laboratory prototype demonstrated the improved functionality of the unit. Indeed, promising electrochemical performance was obtained during the first 24 h, during which the required H2 for achieving 580 mV at 0.2 A cm-2, was supplied from the reformer.

  20. Escherichia coli survival in waters: Temperature dependence

    EPA Science Inventory

    Knowing the survival rates of water-borne Escherichia coli is important in evaluating microbial contamination and making appropriate management decisions. E. coli survival rates are dependent on temperature, a dependency that is routinely expressed using an analogue of the Q10 mo...

  1. E. coli survival in waters: temperature dependence

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Knowing the survival rates of water-borne Escherichia coli is important for evaluating microbial contamination and in making appropriate management decisions. E. coli survival rates are dependent on temperature; this dependency is routinely expressed using an analog of the Q10 model. This suggestion...

  2. Novel Integration Approach for In situ Monitoring of Temperature in Micro-direct Methanol Fuel Cell

    NASA Astrophysics Data System (ADS)

    Lee, Chi-Yuan; Huang, Ren-De; Chuang, Chih-Wei

    2007-10-01

    In this work, a porous silicon layer is fabricated as the gas diffusion layer (GDL) of a micro-direct methanol fuel cell (μDMFC) using micro-electro-mechanical-systems (MEMS) technology. Platinum is deposited on surface of the porous silicon layer to improve the electrical conductivity of the μDMFC. Physical vapor deposition (PVD) was utilized to deposit Pt metal and wet etching was adopted to form the conductive layer and micro-thermal sensors. The Pt acted both as a current collector and a micro-thermal sensor. We fabricated a resistance temperature detector (RTD) sensor for integration with the gas diffusion layer on the bipolar plate to measure the temperature inside the μDMFC. GDLs with pores of various sizes (10, 30, and 50 μm) were considered to test the performance of the μDMFC. A silicon wafer (500 μm) was etched using KOH wet etching to yield fuel channels with a depth of 450 μm and a width of 200 μm. Then, a porous silicon layer was formed by deep reactive ion etching (DRIE) to act as the GDL of the μDMFC. The experimental results obtained at various fuel flow rates, pore sizes and other operating conditions demonstrate that the maximum power density of the μDMFC is 1.784 mW/cm2, which was reached at 203 mV with 50-μm-diameter holes. The microsensor temperature was determined to be in the range from 20 to 46 °C and the resistance of the microsensor was in the range from 7.524 to 7.677 kΩ. Experimental results demonstrate that temperature is almost linearly related to resistance and that accuracy and sensitivity are 0.3 °C and 7.82× 10-4/°C, respectively.

  3. Corrinoid-Dependent Methyl Transfer Reactions Are Involved in Methanol and 3,4-Dimethoxybenzoate Metabolism by Sporomusa ovata

    PubMed Central

    Stupperich, Erhard; Konle, Ralph

    1993-01-01

    Washed and air-oxidized proteins from Sporomusa ovata cleaved the C-O bond of methanol or methoxyaromatics and transferred the methyl to dl-tetrahydrofolate. The reactions strictly required a reductive activation by titanium citrate, catalytic amounts of ATP, and the addition of dl-tetrahydrofolate. Methylcorrinoid-containing proteins carried the methanol methyl, which was transferred to dl-tetrahydrofolate at a specific rate of 120 nmol h-1 mg of protein-1. Tetrahydrofolate methylation diminished after the addition of 1-iodopropane or when the methyl donor methanol was replaced by 3,4-dimethoxybenzoate. However, whole Sporomusa cells utilize the methoxyl groups of 3,4-dimethoxybenzoate as a carbon source by a sequential O demethylation to 4-hydroxy-3-methoxybenzoate and 3,4-dihydroxybenzoate. The in vitro O demethylation of 3,4-[4-methoxyl-14C]dimethoxybenzoate proceeded via two distinct corrinoid-containing proteins to form 5-[14C]methyltetrahydrofolate at a specific rate of 200 nmol h-1 mg of protein-1. Proteins from 3,4-dimethoxybenzoate-grown cells efficiently used methoxybenzoates with vicinal substituents only, but they were unable to activate methanol. These results emphasized that specific enzymes are involved in methanol activation as well as in the activation of various methoxybenzoates and that similar corrinoid-dependent methyl transfer pathways are employed in 5-methyl-tetrahydrofolate formation from these substrates. Methyl-tetrahydrofolate could be demethylated by a distinct methyl transferase. That enzyme activity was present in washed and air-oxidized cell extracts from methanol-grown cells and from 3,4-dimethoxybenzoate-grown cells. It used cob(I)alamin as the methyl acceptor in vitro, which was methylated at a rate of 48 nmol min-1 mg of protein-1 even when ATP was omitted from the assay mixture. This methyl-cob(III)alamin formation made possible a spectrophotometric quantification of the preceding methyl transfers from methanol or

  4. Selective oxidation of methanol and ethanol on supported ruthenium oxide clusters at low temperatures.

    PubMed

    Liu, Haichao; Iglesia, Enrique

    2005-02-17

    RuO2 domains supported on SnO2, ZrO2, TiO2, Al2O3, and SiO2 catalyze the oxidative conversion of methanol to formaldehyde, methylformate, and dimethoxymethane with unprecedented rates and high combined selectivity (>99%) and yield at low temperatures (300-400 K). Supports influence turnover rates and the ability of RuO2 domains to undergo redox cycles required for oxidation turnovers. Oxidative dehydrogenation turnover rates and rates of stoichiometric reduction of RuO2 in H2 increased in parallel when RuO2 domains were dispersed on more reducible supports. These support effects, the kinetic effects of CH3OH and O2 on reaction rates, and the observed kinetic isotope effects with CH3OD and CD3OD reactants are consistent with a sequence of elementary steps involving kinetically relevant H-abstraction from adsorbed methoxide species using lattice oxygen atoms and with methoxide formation in quasi-equilibrated CH3OH dissociation on nearly stoichiometric RuO2 surfaces. Anaerobic transient experiments confirmed that CH3OH oxidation to HCHO requires lattice oxygen atoms and that selectivities are not influenced by the presence of O2. Residence time effects on selectivity indicate that secondary HCHO-CH3OH acetalization reactions lead to hemiacetal or methoxymethanol intermediates that convert to dimethoxymethane in reactions with CH3OH on support acid sites or dehydrogenate to form methylformate on RuO2 and support redox sites. These conclusions are consistent with the tendency of Al2O3 and SiO2 supports to favor dimethoxymethane formation, while SnO2, ZrO2, and TiO2 preferentially form methylformate. These support effects on secondary reactions were confirmed by measured CH3OH oxidation rates and selectivities on physical mixtures of supported RuO2 catalysts and pure supports. Ethanol also reacts on supported RuO2 domains to form predominately acetaldehyde and diethoxyethane at 300-400 K. The bifunctional nature of these reaction pathways and the remarkable ability of Ru

  5. Selective oxidation of methanol and ethanol on supported ruthenium oxide clusters at low temperatures

    SciTech Connect

    Liu, Haichao; Iglesia, Enrique

    2004-03-04

    RuO2 domains supported on SnO2, ZrO2, TiO2, Al2O3, and SiO2 catalyze the oxidative conversion of methanol to formaldehyde, methylformate, and dimethoxymethane with unprecedented rates and high combined selectivity (>99 percent) and yield at low temperatures (300-400 K). Supports influence turnover rates and the ability of RuO2 domains to undergo redox cycles required for oxidation turnovers. Oxidative dehydrogenation turnover rates and rates of stoichiometric reduction of RuO2 in H2 increased in parallel when RuO2 domains were dispersed on more reducible supports. These support effects, the kinetic effects of CH3OH and O2 on reaction rates, and the observed kinetic isotope effects with CH3OD and CD3OD reactants are consistent with a sequence of elementary steps involving kinetically relevant H-abstraction from adsorbed methoxide species using lattice oxygen atoms and with methoxide formation in quasi-equilibrated CH3OH dissociation on nearly stoichiometric RuO2 surfaces. Anaerobic transient experiments confirmed that CH3OH oxidation to HCHO requires lattice oxygen atoms and that selectivities are not influenced by the presence of O2. Residence time effects on selectivity indicate that secondary HCHO-CH3OH acetalization reactions lead to hemiacetal or methoxymethanol intermediates that convert to dimethoxymethane in reactions with CH3OH on support acid sites or dehydrogenate to form methylformate on RuO2 and support redox sites. These conclusions are consistent with the tendency of Al2O3 and SiO2 supports to favor dimethoxymethane formation, while SnO2, ZrO2, and TiO2 preferentially form methylformate. These support effects on secondary reactions were confirmed by measured CH3OH oxidation rates and selectivities on physical mixtures of supported RuO2 catalysts and pure supports. Ethanol also reacts on supported RuO2 domains to form predominately acetaldehyde and diethoxyethane at 300-400 K. The bifunctional nature of these reaction pathways and the remarkable

  6. Temperature dependence of sapphire fiber Raman scattering

    DOE PAGESBeta

    Liu, Bo; Yu, Zhihao; Tian, Zhipeng; Homa, Daniel; Hill, Cary; Wang, Anbo; Pickrell, Gary

    2015-04-27

    Anti-Stokes Raman scattering in sapphire fiber has been observed for the first time. Temperature dependence of Raman peaks’ intensity, frequency shift, and linewidth were also measured. Three anti-Stokes Raman peaks were observed at temperatures higher than 300°C in a 0.72-m-long sapphire fiber excited by a second-harmonic Nd YAG laser. The intensity of anti-Stokes peaks are comparable to that of Stokes peaks when the temperature increases to 1033°C. We foresee the combination of sapphire fiber Stokes and anti-Stokes measurement in use as a mechanism for ultrahigh temperature sensing.

  7. The solvent dependent shift of the amide I band of a fully solvated peptide in methanol/water mixtures as a local probe for the solvent composition in the peptide/solvent interface

    SciTech Connect

    Gnanakaran, S

    2008-01-01

    We determine the shift and line-shape of the amide I band of a model AK-peptide from molecular dynamics (MD) simulations of the peptide dissolved in methanol/water mixtures with varying composition. The IR-spectra are determined from a transition dipole coupling exciton model. A simplified empirical model Hamiltonian is employed, taking both the effect of hydrogen bonding, as well as intramolecular vibrational coupling into account. We consider a single isolated AK-peptide in a mostly helical conformation, while the solvent is represented by 2600 methanol or water molecules, simulated for a pressure of 1 bar and a temperature of 300 K. Over the course of the simulations minor reversible conformational changes at the termini are observed, which are found to only slightly affect the calculated spectral properties. Over the entire composition range, varying from pure water to the pure methanol solvent, a monotonous blue-shift of the IR amide I band of about 8 wavenumbers is observed. The shift is found to be caused by two counter-compensating effects: An intramolecular red-shift of about 1.2 wavenumbers, due to stronger intramolecular hydrogen-bonding in a methanol-rich environment. Dominating, however, is the intermolecular solvent-dependent blue-shift of about 10 wavenumbers, being attributed to the less effective hydrogen bond donor capabilities of methanol compared to water. The importance of solvent-contribution to the IR-shift, as well as the significantly different hydrogen formation capabilities of water and methanol make the amide I band sensitive to composition changes in the local environment close the peptide/solvent interface. This allows, in principle, an experimental determination of the composition of the solvent in close proximity to the peptide surface. For the AK-peptide case they observe at low methanol concentrations a significantly enhanced methanol concentration at the peptide/solvent-interface, supposedly promoted by the partially hydrophobic

  8. Durable Cu composite catalyst for hydrogen production by high temperature methanol steam reforming

    NASA Astrophysics Data System (ADS)

    Matsumura, Yasuyuki

    2014-12-01

    Durable catalysts are necessitated for the high temperature methanol steam reforming in compact hydrogen processors. The high durability at 400 °C can be obtained with a composite Cu catalyst where a small amount of Cu-ZnO-ZrO2-Y2O3-In2O3 is coprecipitated on a zirconia support. The lifetime of the composite catalyst containing 3 wt.% Cu is estimated to be as long as 53 × 102 h at 400 °C to produce the full conversion at a contact time of 250 g h m-3. The deactivation rate empirically relates to the cube of the activity. The gradual deactivation is caused by the gradual reduction of the Cu surface amount and also by the reduction of the surface activity which is believed to decrease with an increase in the Cu particle size. The interaction between the thin layer of the coprecipitate and the support surface probably suppresses the aggregation of the coprecipitate leading to Cu sintering.

  9. Non-syngas direct steam reforming of methanol to hydrogen and carbon dioxide at low temperature.

    PubMed

    Yu, Kai Man Kerry; Tong, Weiyi; West, Adam; Cheung, Kevin; Li, Tong; Smith, George; Guo, Yanglong; Tsang, Shik Chi Edman

    2012-01-01

    A non-syngas direct steam reforming route is investigated for the conversion of methanol to hydrogen and carbon dioxide over a CuZnGaO(x) catalyst at 150-200 °C. This route is in marked contrast with the conventional complex route involving steam reformation to syngas (CO/H2) at high temperature, followed by water gas shift and CO cleanup stages for hydrogen production. Here we report that high quality hydrogen and carbon dioxide can be produced in a single-step reaction over the catalyst, with no detectable CO (below detection limit of 1 ppm). This can be used to supply proton exchange membrane fuel cells for mobile applications without invoking any CO shift and cleanup stages. The working catalyst contains, on average, 3-4 nm copper particles, alongside extremely small size of copper clusters stabilized on a defective ZnGa2O4 spinel oxide surface, providing hydrogen productivity of 393.6 ml g(-1)-cat h(-1) at 150 °C. PMID:23187630

  10. Scaling temperature dependent rheology of magnetorheological fluids

    NASA Astrophysics Data System (ADS)

    Sherman, Stephen G.; Powell, Louise A.; Becnel, Andrew C.; Wereley, Norman M.

    2015-05-01

    Magnetorheological (MR) fluids are suspensions of micron-scale magnetizable particles suspended in a carrier fluid. When field is applied, MR fluids develop a field controllable yield stress and a field independent post-yield viscosity. However, this viscosity has substantial temperature dependence, varying by up to an order of magnitude over the operating temperature range of MR fluid devices. We apply non-Brownian suspension theory to explain this result and find that the majority of this effect should be caused by the temperature dependent behavior of the carrier fluid. Thus, if two fluids share the same carrier fluid, then their fluid properties should scale in temperature similarly. This result is first validated by measuring viscosity across temperature for custom model fluids designed to conform to theory, showing temperature scaling within 5% for both the MR fluids and their carrier fluid. Then, on a series of related commercially available fluids with unknown additive content, we show that the MR fluids exhibit common scaling to within 4%. We also investigate the effects of magnetic hysteresis and find that it induces a negligible increase in yield stress and no measurable change in viscosity. We conclude that our non-dimensional analysis enables the temperature dependence of novel MR fluids to be characterized with fewer experiments.

  11. Study of the use of methanol-filled Er-doped suspended-core fibres in a temperature-sensing ring laser system

    NASA Astrophysics Data System (ADS)

    Martín, J. C.; Berdejo, V.; Vallés, J. A.; Sánchez-Martín, J. A.; Díez, A.; Andrés, M. V.

    2013-10-01

    We report on an experimental/numerical investigation into the use of methanol-filled Er-doped suspended-core fibres (SCFs) in temperature-sensing ring laser systems. We have adopted a ring laser configuration that includes an Er-doped SCF as a temperature-dependent attenuator (TDA) with a step-index Er-doped fibre (EDF) as the laser active medium. The laser performance dependence on the temperature was measured both in continuous wave (CW) and transient regimes. CW laser output power and build-up time values are compared with those of similar laser systems based on other types of Er-doped PCFs or using other laser configurations. A notable variation of 0.73% °C-1 was achieved in CW operation. Then, by means of parameters obtained by numerically fitting the experimental results, the potential sensing performance of the laser configuration with an SCF as a TDA is studied. Moreover, two ring cavity laser configurations (with the SCF acting basically as an attenuator or also as the active media) are compared and the influence of the position of the coupler inside the ring cavity and the contribution of the erbium doping to improve the sensor features are analysed. The longer interaction lengths compatible with laser action using the Er-doped SCF as a TDA could provide variations of laser output power up to 8.6% °C-1 for 90 mW pump power and a 1 m methanol-filled SCF.

  12. Temperature dependence of standard model CP violation.

    PubMed

    Brauner, Tomáš; Taanila, Olli; Tranberg, Anders; Vuorinen, Aleksi

    2012-01-27

    We analyze the temperature dependence of CP violation effects in the standard model by determining the effective action of its bosonic fields, obtained after integrating out the fermions from the theory and performing a covariant gradient expansion. We find nonvanishing CP violating terms starting at the sixth order of the expansion, albeit only in the C-odd-P-even sector, with coefficients that depend on quark masses, Cabibbo-Kobayashi-Maskawa matrix elements, temperature and the magnitude of the Higgs field. The CP violating effects are observed to decrease rapidly with temperature, which has important implications for the generation of a matter-antimatter asymmetry in the early Universe. Our results suggest that the cold electroweak baryogenesis scenario may be viable within the standard model, provided the electroweak transition temperature is at most of order 1 GeV. PMID:22400822

  13. Investigations of Low Temperature Time Dependent Cracking

    SciTech Connect

    Van der Sluys, W A; Robitz, E S; Young, B A; Bloom, J

    2002-09-30

    The objective of this project was to investigate metallurgical and mechanical phenomena associated with time dependent cracking of cold bent carbon steel piping at temperatures between 327 C and 360 C. Boiler piping failures have demonstrated that understanding the fundamental metallurgical and mechanical parameters controlling these failures is insufficient to eliminate it from the field. The results of the project consisted of the development of a testing methodology to reproduce low temperature time dependent cracking in laboratory specimens. This methodology was used to evaluate the cracking resistance of candidate heats in order to identify the factors that enhance cracking sensitivity. The resultant data was integrated into current available life prediction tools.

  14. Temperature dependence of polymer photovoltaic devices

    NASA Astrophysics Data System (ADS)

    Nakazawa, Yuko

    One of many steps to develop a sustainable society is to reduce the use of fossil fuels by replacing them with renewable energy sources, such as solar energy. This dissertation concerns one of the most contemporary methods to harvest solar radiation and covert it to electricity, using thin polymer films. The photovoltaic devices in this study consisted of a thin layer of p-phenylenevinylene (PPV) based semiconducting polymer sandwiched between two metals (semi-transparent ITO and evaporated metal electrode). Two modified device structures were studied, an interfacial heterojunction device, which includes an additional layer of inorganic n-type semiconductor (Ti-oxides) and a bulk heterojunction device, which is formed by blending electron-attracting materials. Both modifications resulted in higher device performances under ambient conditions due to an increased number of dissociation sites. From studies of inorganic solar cells, it is well known that temperature has a large effect on device performance. However, there are only a few studies on organic Solar cells, concerning the temperature dependence. This thesis focuses on understanding the temperature dependent behaviors of polymer photovoltaic devices. Temperature dependence study allows us to examine how the device parameters such as short circuit current (Isc) and open circuit voltage (Voc) are affected by the material properties and the device architectures. The current-voltage relationships were measured in a temperature controlled OXFORD cryostat operating between 150K and 404K. From the dark current-voltage measurements, the field-independent hole mobility (mu0) was extracted, using a space charge limited current analysis. From the photocurrent-voltage measurements, the temperature dependence on Isc, Voc, and fill factor were studied. The temperature characteristics of Isc (T) were compared to that of mu0(T), and two different dependencies were obtained for different device architectures. The temperature

  15. Temperature dependence of fluid transport in nanopores

    NASA Astrophysics Data System (ADS)

    Xu, Baoxing; Wang, Binglei; Park, Taehyo; Qiao, Yu; Zhou, Qulan; Chen, Xi

    2012-05-01

    Understanding the temperature-dependent nanofluidic transport behavior is critical for developing thermomechanical nanodevices. By using non-equilibrium molecular dynamics simulations, the thermally responsive transport resistance of liquids in model carbon nanotubes is explored as a function of the nanopore size, the transport rate, and the liquid properties. Both the effective shear stress and the nominal viscosity decrease with the increase of temperature, and the temperature effect is coupled with other non-thermal factors. The molecular-level mechanisms are revealed through the study of the radial density profile and hydrogen bonding of confined liquid molecules. The findings are verified qualitatively with an experiment on nanoporous carbon.

  16. Temperature dependence of BCF plastic scintillation detectors

    NASA Astrophysics Data System (ADS)

    Wootton, Landon; Beddar, Sam

    2013-05-01

    We examined temperature dependence in plastic scintillation detectors (PSDs) made of BCF-60 or BCF-12 scintillating fiber coupled to optical fiber with cyanoacrylate. PSDs were subjected to a range of temperatures using a temperature-controlled water bath and irradiated at each temperature while either the dose was measured using a CCD camera or the spectral output was measured using a spectrometer. The spectrometer was used to examine the intensity and spectral distribution of scintillation light emitted by the PSDs, Cerenkov light generated within the PSD, and light transmitted through an isolated optical coupling. BCF-60 PSDs exhibited a 0.50% decrease and BCF-12 PSDs a 0.09% decrease in measured dose per °C increase, relative to dose measured at 22 °C. Spectrometry revealed that the total intensity of the light generated by BCF-60 and BCF-12 PSDs decreased by 0.32% and 0.13%, respectively, per °C increase. The spectral distribution of the light changed slightly with temperature for both PSDs, accounting for the disparity between the change in measured dose and total light output. The generation of Cerenkov light was temperature independent. However, light transmitted through optical coupling between the scintillator and the optical fiber also exhibited temperature dependence.

  17. Temperature dependence of optically induced cell deformations

    NASA Astrophysics Data System (ADS)

    Fritsch, Anatol; Kiessling, Tobias R.; Stange, Roland; Kaes, Josef A.

    2012-02-01

    The mechanical properties of any material change with temperature, hence this must be true for cellular material. In biology many functions are known to undergo modulations with temperature, like myosin motor activity, mechanical properties of actin filament solutions, CO2 uptake of cultured cells or sex determination of several species. As mechanical properties of living cells are considered to play an important role in many cell functions it is surprising that only little is known on how the rheology of single cells is affected by temperature. We report the systematic temperature dependence of single cell deformations in Optical Stretcher (OS) measurements. The temperature is changed on a scale of about 20 minutes up to hours and compared to defined temperature shocks in the range of milliseconds. Thereby, a strong temperature dependence of the mechanics of single suspended cells is revealed. We conclude that the observable differences arise rather from viscosity changes of the cytosol than from structural changes of the cytoskeleton. These findings have implications for the interpretation of many rheological measurements, especially for laser based approaches in biological studies.

  18. Effects of temperature and glycerol and methanol-feeding profiles on the production of recombinant galactose oxidase in Pichia pastoris

    PubMed Central

    Anasontzis, George E; Salazar Penã, Margarita; Spadiut, Oliver; Brumer, Harry; Olsson, Lisbeth

    2014-01-01

    Optimization of protein production from methanol-induced Pichia pastoris cultures is necessary to ensure high productivity rates and high yields of recombinant proteins. We investigated the effects of temperature and different linear or exponential methanol-feeding rates on the production of recombinant Fusarium graminearum galactose oxidase (EC 1.1.3.9) in a P. pastoris Mut+ strain, under regulation of the AOX1 promoter. We found that low exponential methanol feeding led to 1.5-fold higher volumetric productivity compared to high exponential feeding rates. The duration of glycerol feeding did not affect the subsequent product yield, but longer glycerol feeding led to higher initial biomass concentration, which would reduce the oxygen demand and generate less heat during induction. A linear and a low exponential feeding profile led to productivities in the same range, but the latter was characterized by intense fluctuations in the titers of galactose oxidase and total protein. An exponential feeding profile that has been adapted to the apparent biomass concentration results in more stable cultures, but the concentration of recombinant protein is in the same range as when constant methanol feeding is employed. © 2014 The Authors Biotechnology Progress published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers Biotechnol. Prog., 30:728–735, 2014 PMID:24493559

  19. Simultaneous Measurement of Temperature Dependent Thermophysical Properties

    NASA Astrophysics Data System (ADS)

    Czél, Balázs; Gróf, Gyula; Kiss, László

    2011-11-01

    A new evaluation method for a transient measurement of thermophysical properties is presented in this paper. The aim of the research was to couple a new automatic evaluation procedure to the BICOND thermophysical property measurement method to enhance the simultaneous determination of the temperature dependent thermal conductivity and volumetric heat capacity. The thermophysical properties of two different polymers were measured and compared with the literature data and with the measurement results that were done by well-known, traditional methods. The BICOND method involves a step-down cooling, recording the temperature histories of the inner and the outer surfaces of a hollow cylindrical sample and the thermophysical properties are evaluated from the solution of the corresponding inverse heat conduction using a genetic algorithm-based method (BIGEN) developed by the authors. The BIGEN is able to find the material properties with any kind of temperature dependency, that is illustrated through the measurement results of poly(tetrafluoroethylene) (PTFE) and polyamide (PA) samples.

  20. ESR spin trapping of radicals in methanol solution irradiated by heavy ion beams. Dependence on specific energy and LET

    NASA Astrophysics Data System (ADS)

    Nakagawa, Seiko; Murakami, Takeshi

    2015-08-01

    Radicals produced by the heavy ion (He, C, Ne, Si, Ar, and Fe) irradiation of methanol were spin trapped with PBN. Three kinds of radicals, PBN-CH3O, PBN-CH2OH, and PBN-H, were observed similar to those by γ-irradiation. The relative radical yields, PBN-CH3O/PBN-CH2OH and (PBN-CH3O + PBN-CH2OH)/PBN-H, varied depending on the LET value, the specific energy and mass of ions.

  1. The complete, temperature resolved experimental spectrum of methanol (CH{sub 3}OH) between 560 and 654 GHz

    SciTech Connect

    Fortman, Sarah M.; Neese, Christopher F.; De Lucia, Frank C.

    2014-02-20

    The complete spectrum of methanol (CH{sub 3}OH) has been characterized over a range of astrophysically significant temperatures in the 560.4-654.0 GHz spectral region. Absolute intensity calibration and analysis of 166 experimental spectra recorded over a slow 248-398 K temperature ramp provide a means for the simulation of the complete spectrum of methanol as a function of temperature. These results include contributions from v{sub t} = 3 and other higher states that are difficult to model via quantum mechanical (QM) techniques. They also contain contributions from the {sup 13}C isotopologue in terrestrial abundance. In contrast to our earlier work on semi-rigid species, such as ethyl cyanide and vinyl cyanide, significant intensity differences between these experimental values and those calculated by QM methods were found for many of the lines. Analysis of these differences shows the difficulty of the calculation of dipole matrix elements in the context of the internal rotation of the methanol molecule. These results are used to both provide catalogs in the usual line frequency, linestrength, and lower state energy format, as well as in a frequency point-by-point catalog that is particularly well suited for the characterization of blended lines.

  2. PQQ-dependent methanol dehydrogenases: rare-earth elements make a difference.

    PubMed

    Keltjens, Jan T; Pol, Arjan; Reimann, Joachim; Op den Camp, Huub J M

    2014-01-01

    Methanol dehydrogenase (MDH) catalyzes the first step in methanol use by methylotrophic bacteria and the second step in methane conversion by methanotrophs. Gram-negative bacteria possess an MDH with pyrroloquinoline quinone (PQQ) as its catalytic center. This MDH belongs to the broad class of eight-bladed β propeller quinoproteins, which comprise a range of other alcohol and aldehyde dehydrogenases. A well-investigated MDH is the heterotetrameric MxaFI-MDH, which is composed of two large catalytic subunits (MxaF) and two small subunits (MxaI). MxaFI-MDHs bind calcium as a cofactor that assists PQQ in catalysis. Genomic analyses indicated the existence of another MDH distantly related to the MxaFI-MDHs. Recently, several of these so-called XoxF-MDHs have been isolated. XoxF-MDHs described thus far are homodimeric proteins lacking the small subunit and possess a rare-earth element (REE) instead of calcium. The presence of such REE may confer XoxF-MDHs a superior catalytic efficiency. Moreover, XoxF-MDHs are able to oxidize methanol to formate, rather than to formaldehyde as MxaFI-MDHs do. While structures of MxaFI- and XoxF-MDH are conserved, also regarding the binding of PQQ, the accommodation of a REE requires the presence of a specific aspartate residue near the catalytic site. XoxF-MDHs containing such REE-binding motif are abundantly present in genomes of methylotrophic and methanotrophic microorganisms and also in organisms that hitherto are not known for such lifestyle. Moreover, sequence analyses suggest that XoxF-MDHs represent only a small part of putative REE-containing quinoproteins, together covering an unexploited potential of metabolic functions. PMID:24816778

  3. The joint effects of room temperature ionic liquids and ordered media on fluorescence characteristics of estrogens in water and methanol

    NASA Astrophysics Data System (ADS)

    Wang, Huili; Duan, Ailian; Dahlgren, Randy A.; Li, Yanyan; Li, Changli; Wang, Wenwei; Zeng, Aibing; Wang, Xuedong

    2014-07-01

    This study investigated the steady-state and time-resolved fluorescence properties of 17α-ethinylestradiol (EE2) and 17β-estradiol (E2) in the presence of ordered media (β-cyclodextrins (β-CD) and cetyltrimethylammonium bromide (CTAB)). In addition, we analyzed the effects of four room temperature ionic liquids (RTILs) on the fluorescence intensities (FIs) of EE2/β-CD and E2/β-CD inclusion complexes in methanol. Both β-CD and CTAB enhanced the fluorescence of EE2 and E2. The FIs of EE2 and E2 with β-CD or CTAB in methanol were greater than those in water, possibly resulting from decreased oxygen-quenching in H2O molecules. β-CD and CTAB may form inclusion complexes with estrogen in both water and methanol. The inclusion ratio of the complex was 1:1 and the inclusion constant (K) values in water were greater than those in methanol. The fluorescence lifetimes were 2.50 and 4.13 ns for EE2 and 2.58 and 4.03 ns for E2 in aqueous solution and methanol, respectively. The changing trend of fluorescence lifetimes for EE2 and E2 in β-CD or CTAB was similar to the steady-state FIs. The four RTILs had a significant quenching effect on the FIs of EE2/β-CD and E2/β-CD, and the quenching process for EE2/β-CD and E2/β-CD by RTILs was demonstrated to be a dynamic quenching mechanism. Fluorescent data obtained from these complex systems provide a theoretical foundation for understanding the interaction mechanisms between ordered media and RTILs in the analysis of estrogens.

  4. Temperature dependent phonon properties of thermoelectric materials

    NASA Astrophysics Data System (ADS)

    Hellman, Olle; Broido, David; Fultz, Brent

    2015-03-01

    We present recent developments using the temperature dependent effective potential technique (TDEP) to model thermoelectric materials. We use ab initio molecular dynamics to generate an effective Hamiltonian that reproduce neutron scattering spectra, thermal conductivity, phonon self energies, and heat capacities. Results are presented for (among others) SnSe, Bi2Te3, and Cu2Se proving the necessity of careful modelling of finite temperature properties for strongly anharmonic materials. Supported by the Swedish Research Council (VR) Project Number 637-2013-7296.

  5. Temperature-dependent reflectivity of silicon carbide

    NASA Technical Reports Server (NTRS)

    Ng, Daniel

    1992-01-01

    The spectral reflectivity of a commercial silicon carbide (SiC) ceramic surface was measured at wavelengths from 2.5 to 14.5 microns and at temperatures ranging from 358 to 520 K using a NASA-developed multiwavelength pyrometer. The SiC surface reflectivity was low at the short wavelengths, decreasing to almost zero at 10 microns, then increasing rapidly to a maximum at approximately 12.5 microns, and decreasing gradually thereafter. The reflectivity maximum increased in magnitude with increasing surface temperature. The wavelength and temperature dependence can be explained in terms of the classical dispersion theory of crystals and the Lorentz electron theory. Electronic transitions between the donor state and the conduction band states were responsible for the dispersion. The concentration of the donor state in SiC was determined to be approximately 4 x 10 exp 18 and its ionization energy was determined to be approximately 71 meV.

  6. Temperature dependent light transmission in ferrofluids

    NASA Astrophysics Data System (ADS)

    Brojabasi, Surajit; Mahendran, V.; Lahiri, B. B.; Philip, John

    2015-05-01

    We investigate the influence of temperature on the magnetic field induced light transmission in a kerosene based ferrofluid containing oleic acid coated Fe3O4 nanoparticles, where the direction of propagation of light is parallel to the direction of the external magnetic field. At a fixed temperature the transmitted light intensity is found to monotonically increase with incident wavelength due to reduced extinction efficiency at higher wavelength. The transmitted intensity decreases with external magnetic field due to enhanced scattering from the field induced linear chain like structures along the direction of the external magnetic field and due to the build-up of standing waves inside the scattering medium. The extinction of the field induced transmitted light intensity is found to occur at a lower external field as the sample temperature is lowered. The rate of extinction of normalized transmitted light intensity decreased linearly with increasing sample temperature due to slower field induced aggregation kinetics because of an increased Brownian motion of the suspended nanoparticles and a reduced coupling constant. The observed temperature dependent magneto-optical properties of magnetic nanofluids can be exploited for applications in optical devices.

  7. Alumina-supported Pd-Ag catalysts for low-temperature CO and methanol oxidation

    NASA Technical Reports Server (NTRS)

    Mccabe, R. W.

    1987-01-01

    Pd-Ag bimetallic catalysts, supported on gamma-Al2O3, have been evaluated as exhaust catalysts for methanol-fueled vehicles. Laboratory studies have shown that a 0.01% Pd-5% Ag catalyst has greater CO and CH3OH oxidation activity than either 0.01% Pd or 5% Ag catalysts alone. Moreover, Pd and Ag interact synergistically in the bimetallic catalyst to produce greater CO and CH3OH oxidation rates and lower yields of methanol partial oxidation products than expected from a mixture of the single-component catalysts. The Pd-Ag synergism results from Pd promoting the rate of O2 adsorption and reaction with CO and CH3OH on Ag. Rate enhancement by the bimetallic catalyst is greatest at short reactor residence times where the oxygen adsorption rate limits the overall reaction rate.

  8. Temperature dependent spin structures in Hexaferrite crystal

    NASA Astrophysics Data System (ADS)

    Chao, Y. C.; Lin, J. G.; Chun, S. H.; Kim, K. H.

    2016-01-01

    In this work, the Hexaferrite Ba0.5Sr1.5Zn2Fe12O22 (BSZFO) is studied due to its interesting characteristics of long-wavelength spin structure. Ferromagnetic resonance (FMR) is used to probe the magnetic states of BSZFO single crystal and its temperature dependence behavior is analyzed by decomposing the multiple lines of FMR spectra into various phases. Distinguished phase transition is observed at 110 K for one line, which is assigned to the ferro(ferri)-magnetic transition from non-collinear to collinear spin state.

  9. Escherichia coli survival in waters: temperature dependence.

    PubMed

    Blaustein, R A; Pachepsky, Y; Hill, R L; Shelton, D R; Whelan, G

    2013-02-01

    Knowing the survival rates of water-borne Escherichia coli is important in evaluating microbial contamination and making appropriate management decisions. E. coli survival rates are dependent on temperature, a dependency that is routinely expressed using an analogue of the Q₁₀ model. This suggestion was made 34 years ago based on 20 survival curves taken from published literature, but has not been revisited since then. The objective of this study was to re-evaluate the accuracy of the Q₁₀ equation, utilizing data accumulated since 1978. We assembled a database of 450 E. coli survival datasets from 70 peer-reviewed papers. We then focused on the 170 curves taken from experiments that were performed in the laboratory under dark conditions to exclude the effects of sunlight and other field factors that could cause additional variability in results. All datasets were tabulated dependencies "log concentration vs. time." There were three major patterns of inactivation: about half of the datasets had a section of fast log-linear inactivation followed by a section of slow log-linear inactivation; about a quarter of the datasets had a lag period followed by log-linear inactivation; and the remaining quarter were approximately linear throughout. First-order inactivation rate constants were calculated from the linear sections of all survival curves and the data grouped by water sources, including waters of agricultural origin, pristine water sources, groundwater and wells, lakes and reservoirs, rivers and streams, estuaries and seawater, and wastewater. Dependency of E. coli inactivation rates on temperature varied among the water sources. There was a significant difference in inactivation rate values at the reference temperature between rivers and agricultural waters, wastewaters and agricultural waters, rivers and lakes, and wastewater and lakes. At specific sites, the Q₁₀ equation was more accurate in rivers and coastal waters than in lakes making the value of

  10. Temperature Dependent Kinetics DNA Charge Transport

    NASA Astrophysics Data System (ADS)

    Wohlgamuth, Chris; McWilliams, Marc; Slinker, Jason

    2012-10-01

    Charge transport (CT) through DNA has been extensively studied, and yet the mechanism of this process is still not yet fully understood. Besides the benefits of understanding charge transport through this fundamental molecule, further understanding of this process will elucidate the biological implications of DNA CT and advance sensing technology. Therefore, we have investigated the temperature dependence of DNA CT by measuring the electrochemistry of DNA monolayers modified with a redox-active probe. By using multiplexed electrodes on silicon chips, we compare square wave voltammetry of distinct DNA sequences under identical experimental conditions. We vary the probe length within the well matched DNA duplex in order to investigate distance dependent kinetics. This length dependent study is a necessary step to understanding the dominant mechanism behind DNA CT. Using a model put forth by O'Dea and Osteryoung and applying a nonlinear least squares analysis we are able to determine the charge transfer rates (k), transfer coefficients (α), and the total surface concentration (&*circ;) of the DNA monolayer. Arrhenius like behavior is observed for the multiple probe locations, and the results are viewed in light of and compared to the prominent charge transport mechanisms.

  11. An introduction of CO₂ conversion by dry reforming with methane and new route of low-temperature methanol synthesis.

    PubMed

    Shi, Lei; Yang, Guohui; Tao, Kai; Yoneyama, Yoshiharu; Tan, Yisheng; Tsubaki, Noritatsu

    2013-08-20

    converted in situ via one of two main routes. The first is to use Fischer-Tropsch synthesis (FTS), a process that catalytically converts syngas to hydrocarbons of varying molecular weights. The second is methanol synthesis. The latter has better atomic economy, since the oxygen atom in CO is included in the product and CO₂ can be blended into syngas as a reactant. However, production of methanol is very inefficient in this reaction: only 10-15% one-pass conversion typically at 5.0-10.0 MPa and 523-573 K, due to the severe thermodynamic limitations of this exothermal reaction (CO + 2H₂ = CH₃OH). In this Account, we propose and develop a new route of low-temperature methanol synthesis from CO₂-containing syngas only by adding alcohols, including methanol itself. These alcohols act as homogeneous cocatalysts and the solvent, realizing 70-100% one-pass conversion at only 5.0 MPa and 443 K. The key step is the reaction of the adsorbed formate species with alcohols to yield ester species at low temperatures, followed by the hydrogenation of ester by hydrogen atoms on metallic Cu. This changes the normal reaction path of conventional, high-temperature methanol synthesis from formate via methoxy to methanol. PMID:23459583

  12. Temperature-Dependent Photoluminescence of Graphene Oxide

    NASA Astrophysics Data System (ADS)

    Jadhav, S. T.; Rajoba, S. J.; Patil, S. A.; Han, S. H.; Jadhav, L. D.

    2016-01-01

    Graphene oxide thin films have been deposited by spray pyrolysis using graphene oxide powder prepared by modified Hummers method. These thin films were characterized by different physico-chemical techniques. The x-ray diffraction studies revealed the structural properties of GO (graphene oxide) while the Raman spectrum showed the presence of D and G and two-dimensional bands. The D/G intensity ratio for spray-deposited GO film is 1.10. The x-ray photoelectron spectroscopy showed 67% and 33% atomic percentages of carbon and oxygen, respectively. The ratio of O1s/C1s was found to be 0.49. The temperature-dependent photoluminescence of GO thin film and GO solution showed a blue emission.

  13. Temperature dependent nonlinear metal matrix laminae behavior

    NASA Technical Reports Server (NTRS)

    Barrett, D. J.; Buesking, K. W.

    1986-01-01

    An analytical method is described for computing the nonlinear thermal and mechanical response of laminated plates. The material model focuses upon the behavior of metal matrix materials by relating the nonlinear composite response to plasticity effects in the matrix. The foundation of the analysis is the unidirectional material model which is used to compute the instantaneous properties of the lamina based upon the properties of the fibers and matrix. The unidirectional model assumes that the fibers properties are constant with temperature and assumes that the matrix can be modelled as a temperature dependent, bilinear, kinematically hardening material. An incremental approach is used to compute average stresses in the fibers and matrix caused by arbitrary mechanical and thermal loads. The layer model is incorporated in an incremental laminated plate theory to compute the nonlinear response of laminated metal matrix composites of general orientation and stacking sequence. The report includes comparisons of the method with other analytical approaches and compares theoretical calculations with measured experimental material behavior. A section is included which describes the limitations of the material model.

  14. DFT study of the active site of the XoxF-type natural, cerium-dependent methanol dehydrogenase enzyme.

    PubMed

    Bogart, Justin A; Lewis, Andrew J; Schelter, Eric J

    2015-01-19

    Rare-earth metal cations have recently been demonstrated to be essential co-factors for the growth of the methanotrophic bacterium Methylacidiphilum fumariolicum SolV. A crystal structure of the rare-earth-dependent methanol dehydrogenase (MDH) includes a cerium cation in the active site. Herein, the Ce-MDH active site has been analyzed through DFT calculations. The results show the stability of the Ce(III)-pyrroloquinoline quinone (PQQ) semiquinone configuration. Calculations on the active oxidized form of this complex indicate a 0.81 eV stabilization of the PQQ(0) LUMO at cerium versus calcium, supporting the observation that the cerium cation in the active site confers a competitive advantage to Methylacidiphilum fumariolicum SolV. Using reported aqueous electrochemical data, a semi-empirical correlation was established based on cerium(IV/III) redox potentials. The correlation allowed estimation of the cerium oxidation potential of +1.35 V versus saturated calomel electrode (SCE) in the active site. The results are expected to guide the design of functional model complexes and alcohol-oxidation catalysts based on lanthanide complexes of biologically relevant quinones. PMID:25421364

  15. Temperature Dependence of Photosynthesis in Cotton

    PubMed Central

    Downton, Joy; Slatyer, R. O.

    1972-01-01

    Cotton plants (Gossypium hirsutum L., var. Deltapine Smooth Leaf) were grown under controlled environmental conditions over a range of day/night temperatures from 20/15 to 40/35 C. Their photosynthetic characteristics were then measured over a comparable temperature range. Net photosynthesis tended stongly to be greatest, and intracellular resistance to CO2 transport to be lowest, when the measurement temperature corresponded to the daytime growth temperature, suggesting pronounced acclimation of the plants to the growth temperature. The preferred growth temperature was close to the 25/20 C regime, since net photosynthesis of these plants, regardless of measurement temperature, was higher and intracellular resistance lower, than in plants from any other regime. Ribulose diphosphate carboxylase activity per unit leaf area was highest in plants grown at 25/20 C, but did not show pronounced changes with growth temperature. Glycolate oxidase activity decreased and NADH-malate dehydrogenase activity tended to increase with increasing growth temperature. In contrast, changes in carbonic anhydrase activity with growth temperature showed a general similarity to changes in photosynthetic rate. This may suggest that the “chemical resistance” component of the intracellular resistance bears a relationship to the amount of carbonic anhydrase in the leaf. PMID:16658208

  16. Temperature Dependence Of Single-Event Effects

    NASA Technical Reports Server (NTRS)

    Coss, James R.; Nichols, Donald K.; Smith, Lawrence S.; Huebner, Mark A.; Soli, George A.

    1990-01-01

    Report describes experimental study of effects of temperature on vulnerability of integrated-circuit memories and other electronic logic devices to single-event effects - spurious bit flips or latch-up in logic state caused by impacts of energetic ions. Involved analysis of data on 14 different device types. In most cases examined, vulnerability to these effects increased or remain constant with temperature.

  17. Trapping of Methanol, Hydrogen Cyanide, and n-Hexane in Water Ice, above Its Transformation Temperature to the Crystalline Form

    NASA Astrophysics Data System (ADS)

    Notesco, G.; Bar-Nun, A.

    1997-04-01

    HCN and n-C 6H 14were found experimentally to be trapped in water ice, when codeposited with water vapor on a cold plate, at 140 K and CH 3OH even at 160 K. At these temperatures at least part of the water ice is cystalline. These three gases have relatively high sublimation temperatures, whereas the gases studied earlier, Ar, Kr, Xe, CO, CH 4, and N 2, which have lower sublimination temperatures, are trapped only in amorphous water ice, up to ˜100 K. It seems that the major factor determining the efficiency of gas trapping by water ice, during codeposition of a gas-water vapor mixture on a cold plate, is the sublimation temperatures of the gases to be trapped. Those with a high sublimation temperature remain, during codeposition, longer in the pores of the water ice which are open to the surface, until they are covered by additional ice layers. Only methanol seems to form a clathrate hydrate, in agreement with the experimental results of D. Blake et al.(1991), Science254, 548-551), which points to the importance of the interaction of the gas molecules with the water molecules in the ice. Consequently, comets and icy satellites that were formed in the Jupiter-Saturn region and their subnebulae could trap CH 3OH, HCN, and heavy hydrocarbons, whereas comets and icy satellites that were formed in the Uranus-Neptune region, at the outskirts of the Saturnian subnebulae (Titan), and beyond the planets in the Kuiper belt could trap also gases having lower sublimation temperatures.

  18. An Analysis of Methanol and Hydrogen Production via High-Temperature Electrolysis Using the Sodium Cooled Advanced Fast Reactor

    SciTech Connect

    Shannon M. Bragg-Sitton; Richard D. Boardman; Robert S. Cherry; Wesley R. Deason; Michael G. McKellar

    2014-03-01

    Integration of an advanced, sodium-cooled fast spectrum reactor into nuclear hybrid energy system (NHES) architectures is the focus of the present study. A techno-economic evaluation of several conceptual system designs was performed for the integration of a sodium-cooled Advanced Fast Reactor (AFR) with the electric grid in conjunction with wind-generated electricity. Cases in which excess thermal and electrical energy would be reapportioned within an integrated energy system to a chemical plant are presented. The process applications evaluated include hydrogen production via high temperature steam electrolysis and methanol production via steam methane reforming to produce carbon monoxide and hydrogen which feed a methanol synthesis reactor. Three power cycles were considered for integration with the AFR, including subcritical and supercritical Rankine cycles and a modified supercritical carbon dioxide modified Brayton cycle. The thermal efficiencies of all of the modeled power conversions units were greater than 40%. A thermal efficiency of 42% was adopted in economic studies because two of the cycles either performed at that level or could potentially do so (subcritical Rankine and S-CO2 Brayton). Each of the evaluated hybrid architectures would be technically feasible but would demonstrate a different internal rate of return (IRR) as a function of multiple parameters; all evaluated configurations showed a positive IRR. As expected, integration of an AFR with a chemical plant increases the IRR when “must-take” wind-generated electricity is added to the energy system. Additional dynamic system analyses are recommended to draw detailed conclusions on the feasibility and economic benefits associated with AFR-hybrid energy system operation.

  19. Temperature Dependence of Phonons in Pyrolitic Graphite

    DOE R&D Accomplishments Database

    Brockhouse, B. N.; Shirane, G.

    1977-01-01

    Dispersion curves for longitudinal and transverse phonons propagating along and near the c-axis in pyrolitic graphite at temperatures between 4°K and 1500°C have been measured by neutron spectroscopy. The observed frequencies decrease markedly with increasing temperature (except for the transverse optical ''rippling'' modes in the hexagonal planes). The neutron groups show interesting asymmetrical broadening ascribed to interference between one phonon and many phonon processes.

  20. Conversion of methane to methanol: nickel, palladium, and platinum (d9) cations as catalysts for the oxidation of methane by ozone at room temperature.

    PubMed

    Božović, Andrea; Feil, Stefan; Koyanagi, Gregory K; Viggiano, Albert A; Zhang, Xinhao; Schlangen, Maria; Schwarz, Helmut; Bohme, Diethard K

    2010-10-11

    The room-temperature chemical kinetics has been measured for the catalytic activity of Group 10 atomic cations in the oxidation of methane to methanol by ozone. Ni(+) is observed to be the most efficient catalyst. The complete catalytic cycle with Ni(+) is interpreted with a computed potential energy landscape and, in principle, has an infinite turnover number for the oxidation of methane, without poisoning side reactions. The somewhat lower catalytic activity of Pd(+) is reported for the first time and also explored with DFT calculations. Pt(+) is seen to be ineffective as a catalyst because of the observed failure of PtO(+) to convert methane to methanol. PMID:20827690

  1. Temperature dependence of electrical conductivity and lunar temperatures

    NASA Technical Reports Server (NTRS)

    Olhoeft, G. R.; Strangway, D. W.; Sharpe, H.; Frisillo, A. L.

    1974-01-01

    Metallic conduction mechanicsms are probably not important in lunar materials because of the small amounts of free metal and metallic oxides present. This is confirmed by the extremely low conductivities measured to date and the fact that the conductivity increases with temperature. The major conduction mechanicsm appears to be ionic. This conduction mechanism is very strongly controlled by temperature, by deviations from stoichiometry, by electric field strengths, and by oxygen fugacity.

  2. Temperature dependence of free excitons in GaN

    NASA Astrophysics Data System (ADS)

    Reynolds, D. C.; Hoelscher, J.; Litton, C. W.; Collins, T. C.

    2002-11-01

    The excitons involved in this study are the longitudinal and the Gamma5 and Gamma6 free excitons, as well as the donor bound exciton (D0),X. The temperature dependence of the energy positions of the Gamma5, Gamma6, and (D0),X excitons are well accounted for by the Varshni equation (Y. P. Varshni, Physica (Amsterdam) 34, 149 (1967)). In the same temperature range, the energy positions of the longitudinal excitons depart from the predictions of the Varshni equation. The separation between the longitudinal- and transverse-mode free excitons has been previously reported. One component of this separation is the polarizability, which has a temperature dependence. The longitudinal exciton therefore has a band-gap temperature dependence, predicted by the Varshni equation, as well as an additional dependence due to polarizability. This temperature dependence has been accounted for by the Varshni equation, plus an additional linear and a quadratic temperature dependent term.

  3. Temperature dependent electrical resistivity of liquid Sn

    NASA Astrophysics Data System (ADS)

    Prajapati, A. V.; Sonvane, Y. A.; Patel, H. P.; Thakor, P. B.

    2016-05-01

    The present paper deals with the effect of temperature variation on the electrical resistivity (ρ) of liquid Sn(Tin). We have used a new parameter free pseudopotential along with screening Taylor et al and Farid et al local field correction functions. The Percus-Yevick Hard Sphere (PYHS) reference system is used to describe structural information. Zeeman formula has been used for finding resistivity with the variation of temperature. The balanced harmonies between present data and experimental data have been achieved with a minimal deviation. So, we concluded that our newly constructed model potential is an effective one to produce the data of electrical resistivity of liquid Sn(Tin) as a function of temperature.

  4. Temperature Dependent Electrical Properties of PZT Wafer

    NASA Astrophysics Data System (ADS)

    Basu, T.; Sen, S.; Seal, A.; Sen, A.

    2016-04-01

    The electrical and electromechanical properties of lead zirconate titanate (PZT) wafers were investigated and compared with PZT bulk. PZT wafers were prepared by tape casting technique. The transition temperature of both the PZT forms remained the same. The transition from an asymmetric to a symmetric shape was observed for PZT wafers at higher temperature. The piezoelectric coefficient (d 33) values obtained were 560 pc/N and 234 pc/N, and the electromechanical coupling coefficient (k p) values were 0.68 and 0.49 for bulk and wafer, respectively. The reduction in polarization after fatigue was only ~3% in case of PZT bulk and ~7% for PZT wafer.

  5. Evidence for Temperature-Dependent Electron Band Dispersion in Pentacene

    SciTech Connect

    Koch,N.; Vollmer, A.; Salzmann, I.; Nickel, B.; Weiss, H.; Rabe, J.

    2006-01-01

    Evidence for temperature-dependent electron band dispersion in a pentacene thin film polymorph on graphite is provided by angle- and energy-dependent ultraviolet photoelectron spectroscopy. The bands derived from the highest occupied molecular orbital exhibit dispersion of {approx}190 meV at room temperature, and {approx}240 meV at 120 K. Intermolecular electronic coupling in pentacene thin films is thus confirmed to be dependent on temperature and possibly crystal structure, as suggested by additional infrared absorption measurements.

  6. Temperature dependence of soil water potential

    SciTech Connect

    Mohamed, A.M.O.; Yong, R.N. ); Cheung, S.C.H. )

    1992-12-01

    To understand the process of coupled heat and water transport, the relationship between temperature and soil water potential must be known. Two clays, Avonlea bentonite and Lake Agassiz clay, are being considered as the clay-based sealing materials for the Canadian nuclear fuel waste disposal vault. Avonlea bentonite is distinguished from Lake Agassiz clay by its high sealing potential in water. A series of experiments was performed in which the two clays were mixed with equal amounts of sand and were compacted to a dry density of 1.67 Mg/m[sup 3] under various moisture contents and temperatures. A psychrometer was placed within the compacted clay-sand to measure the soil water potential based on the electromotive force measured by the psychrometer. The results indicate that the soil water potential at a particular temperature is higher for both clay-sand mixtures than predicted by the change in the surface tension of water; this effect is much more prominent in the Avonlea bentonite and at low moisture contents. The paper presents empirical equations relating the soil water potential with the moisture content and temperature of the two clay-sand mixtures. 24 refs., 8 figs., 2 tabs.

  7. Temperature dependence of gramicidin channel conductance

    NASA Astrophysics Data System (ADS)

    Song, Hyundeok; Beck, Thomas

    2010-03-01

    The gramicidin channel is the smallest known biological ion channel, and it exhibits cation selectivity. Recently, Dr. John Cuppoletti's group at the University of Cincinnati has shown that the gramicidin channel can function at high temperatures with significant currents. This finding may have implications for fuel cell technologies. In order to explore the effect of temperature on channel conductance, we examined the gramicidin system at 300K, 330K, and 360K by computer simulation. Two forms of gramicidin, the head-to-head helical dimer and the intertwined double helix, were examined. Both the decrease of the free energy barrier and the increase of the diffusion of potassium ions inside the gramicidin channel at high temperatures imply an increase of current. We found that higher temperatures also affect the lifetime of hydrogen bonds, the distribution of the bending angle, the distribution of the distance between dimers, and the size of the pore radius for the helical dimer structure. These finding may be related to the gating of the gramicidin channel.

  8. Quasipermanent magnets of high temperature superconductor - Temperature dependence

    NASA Technical Reports Server (NTRS)

    Chen, In-Gann; Liu, Jianxiong; Ren, Yanru; Weinstein, Roy; Kozlowski, Gregory; Oberly, Charles E.

    1993-01-01

    We report on persistent field in quasi-permanent magnets of high temperature superconductors. Magnets composed of irradiated Y(1+)Ba2Cu3O7 trapped field Bt = 1.52 T at 77 K and 1.9 T at lower temperature. However, the activation magnet limited Bt at lower temperature. We present data on Jc(H,T) for unirradiated materials, and calculate Bt at various T. Based upon data at 65 K, we calculate Bt in unirradiated single grains at 20 K and find that 5.2 T will be trapped for grain diameter d about 1.2 cm, and 7.9 T for d = 2.3 cm. Irradiated grains will trap four times these values.

  9. Temperature dependence of diffusion properties of soft sticky dipole water

    NASA Astrophysics Data System (ADS)

    Tan, Ming-Liang; Brooks, Bernard R.; Ichiye, Toshiko

    2006-04-01

    The isobaric diffusivities for the soft sticky dipole water model between 230 and 330 K were studied in molecular dynamics simulations using Ewald summations for the long-range interactions. This simple single-point, angularly dependent model with parameters optimized at room temperature reproduces the experimental diffusion rates over a wide range of temperatures better than multi-point models. Its ability to reproduce the unusual temperature dependence of the diffusivities of supercooled water indicates the tetrahedral nature of water is important. Moreover, comparisons with other models indicate more tetrahedral potentials correlate with increasing the so-called Angell critical temperature and decreasing power of the temperature dependence.

  10. Temperature dependent terahertz properties of energetic materials

    NASA Astrophysics Data System (ADS)

    Azad, Abul K.; Whitley, Von H.; Brown, Kathryn E.; Ahmed, Towfiq; Sorensen, Christian J.; Moore, David S.

    2016-04-01

    Reliable detection of energetic materials is still a formidable challenge which requires further investigation. The remote standoff detection of explosives using molecular fingerprints in the terahertz spectral range has been an evolving research area for the past two decades. Despite many efforts, identification of a particular explosive remains difficult as the spectral fingerprints often shift due to the working conditions of the sample such as temperature, crystal orientation, presence of binders, etc. In this work, we investigate the vibrational spectrum of energetic materials including RDX, PETN, AN, and 1,3-DNB diluted in a low loss PTFE host medium using terahertz time domain spectroscopy (THz-TDS) at cryogenic temperatures. The measured absorptions of these materials show spectral shifts of their characteristic peaks while changing their operating temperature from 300 to 7.5 K. We have developed a theoretical model based on first principles methods, which is able to predict most of the measured modes in 1, 3-DNB between 0.3 to 2.50 THz. These findings may further improve the security screening of explosives.

  11. Electro-osmotic drag coefficient of water and methanol in polymer electrolytes at elevated temperatures

    SciTech Connect

    Weng, D.; Wainright, J.S.; Landau, U.; Savinell, R.F.

    1996-04-01

    The electro-osmotic drag coefficient of water in two polymer electrolytes was experimentally determined as a function of water activity and current density for temperatures up to 200 C. The results show that the electro-osmotic drag coefficient varies from 0.2 to 0.6 in Nafion{reg_sign}/H{sub 3}PO{sub 4} membrane electrolyte, but is essentially zero in phosphoric acid-doped PBI (polybenzimidazole) membrane electrolyte over the range of water activity considered. The near-zero electro-osmotic drag coefficient found in PBI indicates that this electrolyte should lessen the problems associated with water redistribution in proton exchange membrane fuel cells.

  12. Temperature dependence of LRE-HRE-TM thin films

    NASA Astrophysics Data System (ADS)

    Li, Zuoyi; Cheng, Xiaomin; Lin, Gengqi; Li, Zhen; Huang, Zhixin; Jin, Fang; Wang, Xianran; Yang, Xiaofei

    2003-04-01

    Temperature dependence of the properties of RE-TM thin films is very important for MO recording. In this paper, we studied the temperature dependence of the magnetic and magneto-optical properties of the amorphous LRE-HRE-TM single layer thin films and LRE-HRE-TM/HRE-TM couple-bilayered thin films. For LRE-HRE-TM single layer thin films, the temperature dependence of the magnetization was investigated by using the mean field theory. The experimental and theoretical results matched very well. With the LRE substitution in HRE-TM thin film, the compensation temperature Tcomp decreased and the curie temperature Tc remained unchanged. Kerr rotation angle became larger and the saturation magnetization Ms at room temperature increased. For LRE-HRE-TM/HRE-TM couple-bilayered thin films, comparisons of the temperature dependences of the coercivities and Kerr rotation angles were made between isolated sublayers and couple-bilayered thin film.

  13. Antioxidant Activity and ROS-Dependent Apoptotic Effect of Scurrula ferruginea (Jack) Danser Methanol Extract in Human Breast Cancer Cell MDA-MB-231.

    PubMed

    Marvibaigi, Mohsen; Amini, Neda; Supriyanto, Eko; Abdul Majid, Fadzilah Adibah; Kumar Jaganathan, Saravana; Jamil, Shajarahtunnur; Hamzehalipour Almaki, Javad; Nasiri, Rozita

    2016-01-01

    Scurrula ferruginea (Jack) Danser is one of the mistletoe species belonging to Loranthaceae family, which grows on the branches of many deciduous trees in tropical countries. This study evaluated the antioxidant activities of S. ferruginea extracts. The cytotoxic activity of the selected extracts, which showed potent antioxidant activities, and high phenolic and flavonoid contents, were investigated in human breast cancer cell line (MDA-MB-231) and non-cancer human skin fibroblast cells (HSF-1184). The activities and characteristics varied depending on the different parts of S. ferruginea, solvent polarity, and concentrations of extracts. The stem methanol extract showed the highest amount of both phenolic (273.51 ± 4.84 mg gallic acid/g extract) and flavonoid contents (163.41 ± 4.62 mg catechin/g extract) and strong DPPH• radical scavenging (IC50 = 27.81 μg/mL) and metal chelation activity (IC50 = 80.20 μg/mL). The stem aqueous extract showed the highest ABTS•+ scavenging ability. The stem methanol and aqueous extracts exhibited dose-dependent cytotoxic activity against MDA-MB-231 cells with IC50 of 19.27 and 50.35 μg/mL, respectively. Furthermore, the extracts inhibited the migration and colony formation of MDA-MB-231 cells in a concentration-dependent manner. Morphological observations revealed hallmark properties of apoptosis in treated cells. The methanol extract induced an increase in ROS generation and mitochondrial depolarization in MDA-MB-231 cells, suggesting its potent apoptotic activity. The present study demonstrated that the S. ferruginea methanol extract mediated MDA-MB-231 cell growth inhibition via induction of apoptosis which was confirmed by Western blot analysis. It may be a potential anticancer agent; however, its in vivo anticancer activity needs to be investigated. PMID:27410459

  14. Antioxidant Activity and ROS-Dependent Apoptotic Effect of Scurrula ferruginea (Jack) Danser Methanol Extract in Human Breast Cancer Cell MDA-MB-231

    PubMed Central

    Marvibaigi, Mohsen; Amini, Neda; Supriyanto, Eko; Abdul Majid, Fadzilah Adibah; Kumar Jaganathan, Saravana; Jamil, Shajarahtunnur; Hamzehalipour Almaki, Javad; Nasiri, Rozita

    2016-01-01

    Scurrula ferruginea (Jack) Danser is one of the mistletoe species belonging to Loranthaceae family, which grows on the branches of many deciduous trees in tropical countries. This study evaluated the antioxidant activities of S. ferruginea extracts. The cytotoxic activity of the selected extracts, which showed potent antioxidant activities, and high phenolic and flavonoid contents, were investigated in human breast cancer cell line (MDA-MB-231) and non-cancer human skin fibroblast cells (HSF-1184). The activities and characteristics varied depending on the different parts of S. ferruginea, solvent polarity, and concentrations of extracts. The stem methanol extract showed the highest amount of both phenolic (273.51 ± 4.84 mg gallic acid/g extract) and flavonoid contents (163.41 ± 4.62 mg catechin/g extract) and strong DPPH• radical scavenging (IC50 = 27.81 μg/mL) and metal chelation activity (IC50 = 80.20 μg/mL). The stem aqueous extract showed the highest ABTS•+ scavenging ability. The stem methanol and aqueous extracts exhibited dose-dependent cytotoxic activity against MDA-MB-231 cells with IC50 of 19.27 and 50.35 μg/mL, respectively. Furthermore, the extracts inhibited the migration and colony formation of MDA-MB-231 cells in a concentration-dependent manner. Morphological observations revealed hallmark properties of apoptosis in treated cells. The methanol extract induced an increase in ROS generation and mitochondrial depolarization in MDA-MB-231 cells, suggesting its potent apoptotic activity. The present study demonstrated that the S. ferruginea methanol extract mediated MDA-MB-231 cell growth inhibition via induction of apoptosis which was confirmed by Western blot analysis. It may be a potential anticancer agent; however, its in vivo anticancer activity needs to be investigated. PMID:27410459

  15. Temperature dependence of amino acid hydrophobicities

    PubMed Central

    Wolfenden, Richard; Lewis, Charles A.; Yuan, Yang; Carter, Charles W.

    2015-01-01

    The hydrophobicities of the 20 common amino acids are reflected in their tendencies to appear in interior positions in globular proteins and in deeply buried positions of membrane proteins. To determine whether these relationships might also have been valid in the warm surroundings where life may have originated, we examined the effect of temperature on the hydrophobicities of the amino acids as measured by the equilibrium constants for transfer of their side-chains from neutral solution to cyclohexane (Kw>c). The hydrophobicities of most amino acids were found to increase with increasing temperature. Because that effect is more pronounced for the more polar amino acids, the numerical range of Kw>c values decreases with increasing temperature. There are also modest changes in the ordering of the more polar amino acids. However, those changes are such that they would have tended to minimize the otherwise disruptive effects of a changing thermal environment on the evolution of protein structure. Earlier, the genetic code was found to be organized in such a way that—with a single exception (threonine)—the side-chain dichotomy polar/nonpolar matches the nucleic acid base dichotomy purine/pyrimidine at the second position of each coding triplet at 25 °C. That dichotomy is preserved at 100 °C. The accessible surface areas of amino acid side-chains in folded proteins are moderately correlated with hydrophobicity, but when free energies of vapor-to-cyclohexane transfer (corresponding to size) are taken into consideration, a closer relationship becomes apparent. PMID:26034278

  16. Temperature dependence of particle-particle interactions in electrorheological fluids

    NASA Astrophysics Data System (ADS)

    Gonon, P.; Foulc, J.-N.

    2000-04-01

    We report on the temperature dependence of particle-particle interactions in electrorheological (ER) fluids for the temperature range 20-100 °C. The attraction force between polyamide spheres immersed in silicone oil is measured as a function of temperature. The force-temperature characteristic shows a broad maximum around 40 °C, corresponding to an increase of about 30% compared to the force measured at room temperature. In view of these results we proposed that the temperature dependence of the shear stress in ER fluids is directly related to the variation of the local particle-particle attraction forces. Data are discussed in light of models which were proposed in the literature to describe particle-particle interactions. At high electric fields "conduction models" could explain the observed temperature dependence through the variations of the oil breakdown field with temperature. However, limitations of such models are also clearly evidenced by data obtained at low electric fields.

  17. Vaporisation characteristics of methanol, ethanol and heptane droplets in opposed stagnation flow at low temperature and pressure

    NASA Astrophysics Data System (ADS)

    Zhu, Huayang; Kee, Robert J.; Chen, Longhua; Cao, Jingjing; Xu, Min; Zhang, Yuyin

    2012-08-01

    A computational model is developed and applied to study the vaporisation behaviour of three liquid fuels. This fundamental study is motivated by a need to understand how the performance of direct-injection-spark-ignition (DISI) engines may be affected by changes in fuel composition, especially alcohols. Currently, most DISI engines are designed for homogeneous-charge combustion, where the in-cylinder fuel injection, vaporisation and mixing is accomplished during the intake and early in the compression process. Thus the temperature and pressure are low, compared to post-compression conditions. The two-phase axisymmetric model is based upon an ideal opposed stagnation flow field. Liquid droplets are carried in one air stream that is met by an opposed air flow. Because of stagnation-flow similarity, the mathematical model can be represented as a one-dimensional boundary-value problem. Results show significant differences between methanol, ethanol and heptane fuels, which have potentially important impacts on the design and modification of fuel-injection systems for direct-injection engines with alternative fuels.

  18. Crossing regimes of temperature dependence in animal movement.

    PubMed

    Gibert, Jean P; Chelini, Marie-Claire; Rosenthal, Malcolm F; DeLong, John P

    2016-05-01

    A pressing challenge in ecology is to understand the effects of changing global temperatures on food web structure and dynamics. The stability of these complex ecological networks largely depends on how predator-prey interactions may respond to temperature changes. Because predators and prey rely on their velocities to catch food or avoid being eaten, understanding how temperatures may affect animal movement is central to this quest. Despite our efforts, we still lack a mechanistic understanding of how the effect of temperature on metabolic processes scales up to animal movement and beyond. Here, we merge a biomechanical approach, the Metabolic Theory of Ecology and empirical data to show that animal movement displays multiple regimes of temperature dependence. We also show that crossing these regimes has important consequences for population dynamics and stability, which depend on the parameters controlling predator-prey interactions. We argue that this dependence upon interaction parameters may help explain why experimental work on the temperature dependence of interaction strengths has so far yielded conflicting results. More importantly, these changes in the temperature dependence of animal movement can have consequences that go well beyond ecological interactions and affect, for example, animal communication, mating, sensory detection, and any behavioral modality dependent on the movement of limbs. Finally, by not taking into account the changes in temperature dependence reported here we might not be able to properly forecast the impact of global warming on ecological processes and propose appropriate mitigation action when needed. PMID:26854767

  19. Modelling temperature and concentration dependent solid/liquid interfacial energies

    NASA Astrophysics Data System (ADS)

    Lippmann, Stephanie; Jung, In-Ho; Paliwal, Manas; Rettenmayr, Markus

    2016-01-01

    Models for the prediction of the solid/liquid interfacial energy in pure substances and binary alloys, respectively, are reviewed and extended regarding the temperature and concentration dependence of the required thermodynamic entities. A CALPHAD-type thermodynamic database is used to introduce temperature and concentration dependent melting enthalpies and entropies for multicomponent alloys in the temperature range between liquidus and solidus. Several suitable models are extended and employed to calculate the temperature and concentration dependent interfacial energy for Al-FCC with their respective liquids and compared with experimental data.

  20. Temperature dependence of the excited state absorption of alexandrite

    SciTech Connect

    Shand, M.L.; Jenssen, H.P.

    1983-03-01

    The temperature dependence from 28 to 290/sup 0/C of the excited-state absorption cross section sigma /SUB 2a/ (E) in the gain wavelength region of alexandrite has been determined from the temperature dependence of the single pass gain (SPG) and of the fluorescence. sigma /SUB 2a/ (E) and the emission cross section increase with temperature at approximately the same rate.

  1. Temperature dependence of conductivity measurement for conducting polymer

    NASA Astrophysics Data System (ADS)

    Gutierrez, Leandro; Duran, Jesus; Isah, Anne; Albers, Patrick; McDougall, Michael; Wang, Weining

    2014-03-01

    Conducting polymer-based solar cells are the newest generation solar cells. While research on this area has been progressing, the efficiency is still low because certain important parameters of the solar cell are still not well understood. It is of interest to study the temperature dependence of the solar cell parameters, such as conductivity of the polymer, open circuit voltage, and reverse saturation current to gain a better understanding on the solar cells. In this work, we report our temperature dependence of conductivity measurement using our in-house temperature-varying apparatus. In this project, we designed and built a temperature varying apparatus using a thermoelectric cooler module which gives enough temperature range as we need and costs much less than a cryostat. The set-up of the apparatus will be discussed. Temperature dependence of conductivity measurements for PEDOT:PSS films with different room-temperature conductivity will be compared and discussed. NJSGC-NASA Fellowship grant

  2. Temperature and pressure dependence of CO2 extinction coefficients.

    NASA Technical Reports Server (NTRS)

    Demore, W. B.; Patapoff, M.

    1972-01-01

    Results are presented of CO2 extinction coefficient measurements that were performed under conditions of temperature and pressure different from those used by previous investigators. The results show that, whereas pressure effects are generally negligible, temperature dependence is strong enough to invalidate the use of room temperature data for the Mars atmosphere.

  3. Unusual temperature dependence of elastic constants of an ambient-temperature discotic nematic liquid crystal.

    PubMed

    Venkata Sai, D; Mirri, G; Kouwer, P H J; Sahoo, R; Musevic, I; Dhara, Surajit

    2016-03-01

    We report the first experimental studies on the temperature dependence of viscoelastic properties of a room temperature discotic nematic liquid crystal. The splay elastic constant is greater than the bend elastic constant and both show unusual temperature and order parameter dependence. The rotational viscosity is remarkably larger than conventional calamitic liquid crystals. We provide a simple physical explanation based on the columnar short-range order to account for the the unusual temperature dependence of the elastic constants. PMID:26883494

  4. Development of methanol evaporation plate to reduce methanol crossover in a direct methanol fuel cell

    NASA Astrophysics Data System (ADS)

    Zhang, Ruiming

    This research focuses on methanol crossover reduction in direct methanol fuel cells (DMFC) through separating the methanol vapor from its liquid phase and feeding the vapor passively at low temperature range. Membrane electrode assemblies (MEAs) were fabricated by using commercial available membrane with different thickness at different anode catalyst loading levels, and tested under the operating conditions below 100°C in cell temperature and cathode exit open to ambient pressure. Liquid methanol transport from the anode through the membrane into cathode ("methanol crossover") is identified as one of the major efficiency losses in a DMFC. It is known that the methanol crossover rate in the vapor phase is much lower than in liquid phase. Vapor feed can be achieved by heating the liquid methanol to elevated temperatures (>100°C), but other issues limit the performance of the cell when operating above 100°C. High temperature membranes and much more active cathode catalyst structures are required, and a complex temperature control system must be employed. However, methanol vapor feed can also occur at a lower temperature range (<100°C) by separating its vapor from the liquid phase by evaporation through a porous body. The methanol crossover with this vapor feed mode is lower compared with the direct liquid methanol feed. A new method of using a methanol evaporation plate (MEP) to separate the vapor from its liquid phase to reduce the liquid methanol crossover at low temperature range is developed. A MEP plays the roles of liquid/vapor methanol phase separation and evaporation in a DMFC. The goal of this study is to develop a MEP with the proper properties to achieve high methanol phase separation efficiency and fast methanol evaporation rate over a wide range of temperature, i.e., from room temperature up to near boiling temperature (100°C). MEP materials were selected and characterized. MEPs made from three different types were tested extensively with different

  5. Temperature Dependence of the Free Excitons in GaN

    NASA Astrophysics Data System (ADS)

    Reynolds, D. C.; Collins, T. C.

    2002-03-01

    We are presenting the temperature dependence of the photoluminescence (PL) of the free excitons and donor bound exciton ( D^circ ,X) in GaN. The excitons involved are the longitudinal, the Γ5 and the Γ6 excitons as well as D^circ ,X. The temperature dependence of the energy positions of Γ_5, Γ_6, and D^circ ,X are well mapped out using the Varshni equation in a temperature range of 0 -- 60 K. In this temperature range, the energy positions of the longitudinal excitons depart from the predictions of the Varshni equation used for the other excitons. If more than one columnar structural direction is present, then in PL, more than one longitudinal mode might be observed. The sample being investigated shows two longitudinal modes. The energy separation between the longitudinal and transverse modes has been reported by Hopfield and Thomas. One component in the separation is the polarizability, which has some temperature dependence. The longitudinal exciton then has a band gap temperature dependence, which is predicted by the Varshni equation and an additional temperature dependence due to the polarizability. We have used the Varshni equation plus a linear and quadratic temperature dependence term to map the energy positions of the longitudinal excitons.

  6. Investigation of Methanol Formation Mechanisms in H2O+CH4 Ices Subjected to 5 keV Electrons at a 10-100 K Temperature Range

    NASA Astrophysics Data System (ADS)

    Stelmach, K. B.; Cooper, P. D.

    2014-12-01

    Methane (CH4) and water are one of the most common molecules in both planetary bodies and interstellar dust grains. Another common molecule, methanol (CH3OH), is thought to form in CH4+H2O ices. However, the exact formation mechanisms of methanol from cosmic rays are not well known, especially in the temperatures of interest. Experiments were performed using high energy electrons (5 keV) to irradiate mixtures of 1:10, 1:5, and 1:3 CH4+H2O ices under a temperature range of 10-100 Kelvin with Fourier Transform Infrared (FTIR) spectroscopy being used to identify the products. Isotopologues of the two molecules (D2O and CD4) were used to probe for the mechanisms. Other products were formed as well and their potential mechanisms are identified. The implications of the mechanisms for planetary and interstellar chemistry are discussed.

  7. Temperature dependence of the emissivity of platinum in the IR.

    PubMed

    Deemyad, Shanti; Silvera, Isaac F

    2008-08-01

    The accuracy of temperature determination by fitting the spectral irradiance to a Planck curve depends on knowledge of the emissivity at all temperatures and pressures of interest within a spectral region. Here, the emissivity of platinum is measured in the near infrared as a function of temperature. In the wavelength range of study and the temperature range of 650-1100 K, we find the emissivity to be independent of temperature to within experimental error. This result should lead to improved accuracy of temperature measurement by optical pyrometry where platinum is used as a thermal emitter. PMID:19044386

  8. Oxidation of C1 compounds by particulate fractions from Methylococcus capsulatus: properties of methanol oxidase and methanol dehydrogenase.

    PubMed Central

    Wadzinski, A M; Ribbons, D W

    1975-01-01

    Methanol (and formaldehyde) oxidizing activities in crude extracts of Methylococcus capsulatus are associated mainly with particulate fractions sedimenting between 3,000 and 40,000 X g. Most of the phenazine methosulfate (PMS)-dependent methanol (and formaldehyde) dehydrogenase activity observed resides in the soluble fraction but represents only 40% of the total (PMS dependent plus independent) activity. Both PMS-dependent methanol dehydrogenase activity and PMS-independent methanol oxidase activity are found in particulate fractions, and the PMS-dependent dehydrogenase is easily solubilized by treatment with certain phospholipases or detergents. The properties of the PMS-dependent dehydrogenase activities in the soluble fraction and that solubilized from the particles suggested that they may be identical proteins. Their pH optima, temperature dependence, thermolabilities, and sensitivities to the presence of specific antisera were indistinguishable. Homogeneous preparations of the enzyme proteins obtained from the soluble fractions of extracts and the particulate fractions solubilized by detergents had similar: (i) electrophoretic mobilities in native and denatured states (subunit size in sodium dodecyl sulfate 62,000 daltons); (ii) molecular radii under native conditions, (iii) visible absorption spectra, lambdamax 350 nm, (iv) kinetic constants for methanol and formaldehyde; (v) substrate specificity; and (vi) immunological characteristics--antisera to each enzyme preparation showed precipitin lines of identity to either of the enzymes. It is suggested that the major site of methanol and formaldehyde oxidation in M. capsulatus occurs on the intracytoplasmic membranes in vivo and is coupled to oxygen reduction. Images PMID:238947

  9. Temperature dependent electrical transport of disordered reduced graphene oxide

    NASA Astrophysics Data System (ADS)

    Muchharla, Baleeswaraiah; Narayanan, T. N.; Balakrishnan, Kaushik; Ajayan, Pulickel M.; Talapatra, Saikat

    2014-06-01

    We report on the simple route for the synthesis of chemically reduced graphene oxide (rGO) using ascorbic acid (a green chemical) as a reducing agent. Temperature-dependent electrical transport properties of rGO thin films have been studied in a wide range (50 K T 400 K) of temperature. Electrical conduction in rGO thin films was displayed in two different temperature regimes. At higher temperatures, Arrhenius-like temperature dependence of resistance was observed indicating a band gap dominating transport behavior. At lower temperatures, the rGO sample showed a conduction mechanism consistent with Mott's two-dimensional variable range hopping (2D-VRH). An unsaturated negative magnetoresistance (MR) was observed up to 3 T field. A decrease in negative MR at high temperatures is attributed to the phonon scattering of charge carriers.

  10. Temperature dependence of the HNO3 UV absorption cross sections

    NASA Technical Reports Server (NTRS)

    Burkholder, James B.; Talukdar, Ranajit K.; Ravishankara, A. R.; Solomon, Susan

    1993-01-01

    The temperature dependence of the HNO3 absorption cross sections between 240 and 360 K over the wavelength range 195 to 350 nm has been measured using a diode array spectrometer. Absorption cross sections were determined using both (1) absolute pressure measurements at 298 K and (2) a dual absorption cell arrangement in which the absorption spectrum at various temperatures is measured relative to the room temperature absorption spectrum. The HNO3 absorption spectrum showed a temperature dependence which is weak at short wavelengths but stronger at longer wavelengths which are important for photolysis in the lower stratosphere. The 298 K absorption cross sections were found to be larger than the values currently recommended for atmospheric modeling (DeMore et al., 1992). Our absorption cross section data are critically compared with the previous measurements of both room temperature and temperature-dependent absorption cross sections. Temperature-dependent absorption cross sections of HNO3 are recommended for use in atmospheric modeling. These temperature dependent HNO3 absorption cross sections were used in a two-dimensional dynamical-photochemical model to demonstrate the effects of the revised absorption cross sections on loss rate of HNO3 and the abundance of NO2 in the stratosphere.

  11. Temperature Dependence of Thermopower in Strongly Correlated Multiorbital Systems

    SciTech Connect

    Sekino, M; Okamoto, Satoshi; Koshibae, W; Mori, Michiyasu; Maekawa, Sadamichi

    2014-01-01

    Temperature dependence of thermopower in the multiorbital Hubbard model is studied by using the dynamical mean-field theory with the non-crossing approximation impurity solver. It is found that the Coulomb interaction, the Hund coupling, and the crystal filed splitting bring about nonmonotonic temperature dependence of the hermopower, including its sign reversal. The implication of our theoretical results to some materials is discussed.

  12. Identification of temperature-dependent thermal conductivity and experimental verification

    NASA Astrophysics Data System (ADS)

    Pan, Weizhen; Yi, Fajun; Zhu, Yanwei; Meng, Songhe

    2016-07-01

    A modified Levenberg–Marquardt method (LMM) for the identification of temperature-dependent thermal conductivity is proposed; the experiment and structure of the specimen for identification are also designed. The temperature-dependent thermal conductivities of copper C10200 and brass C28000 are identified to verify the effectiveness of the proposed identification method. The comparison between identified results and the measured data of laser flash diffusivity apparatus indicates the fine consistency and potential usage of the proposed method.

  13. Temperature and size-dependent Hamaker constants for metal nanoparticles.

    PubMed

    Jiang, K; Pinchuk, P

    2016-08-26

    Theoretical values of the Hamaker constant have been calculated for metal nanoparticles using Lifshitz theory. The theory describes the Hamaker constant in terms of the permittivity of the interacting bodies. Metal nanoparticles exhibit an internal size effect that alters the dielectric permittivity of the particle when its size falls below the mean free path of the conducting electrons. This size dependence of the permittivity leads to size-dependence of the Hamaker constant for metal nanoparticles. Additionally, the electron damping and the plasma frequency used to model the permittivity of the particle exhibit temperature-dependence, which lead to temperature dependence of the Hamaker constant. In this work, both the size and temperature dependence for gold, silver, copper, and aluminum nanoparticles is demonstrated. The results of this study might be of interest for studying the colloidal stability of nanoparticles in solution. PMID:27454147

  14. Temperature and size-dependent Hamaker constants for metal nanoparticles

    NASA Astrophysics Data System (ADS)

    Jiang, K.; Pinchuk, P.

    2016-08-01

    Theoretical values of the Hamaker constant have been calculated for metal nanoparticles using Lifshitz theory. The theory describes the Hamaker constant in terms of the permittivity of the interacting bodies. Metal nanoparticles exhibit an internal size effect that alters the dielectric permittivity of the particle when its size falls below the mean free path of the conducting electrons. This size dependence of the permittivity leads to size-dependence of the Hamaker constant for metal nanoparticles. Additionally, the electron damping and the plasma frequency used to model the permittivity of the particle exhibit temperature-dependence, which lead to temperature dependence of the Hamaker constant. In this work, both the size and temperature dependence for gold, silver, copper, and aluminum nanoparticles is demonstrated. The results of this study might be of interest for studying the colloidal stability of nanoparticles in solution.

  15. Temperature Dependence of Radiative and Nonradiative Rates from Time-Dependent Correlation Function Methods.

    PubMed

    Banerjee, Shiladitya; Baiardi, Alberto; Bloino, Julien; Barone, Vincenzo

    2016-02-01

    The temperature dependence of the rate constants in radiative and nonradiative decays from excited electronic states has been studied using a time-dependent correlation function approach in the framework of the adiabatic representation and the harmonic oscillator approximation. The present work analyzes the vibrational aspect of the processes, which gives rise to the temperature dependence, with the inclusion of mode-mixing, as well as of frequency change effects. The temperature dependence of the rate constants shows a contrasting nature, depending on whether the process has been addressed within the Franck-Condon approximation or beyond it. The calculation of the Duschinsky matrix and the shift vector between the normal modes of the two states can be done in Cartesian and/or internal coordinates, depending on the flexibility of the investigated molecule. A new computational code has been developed to calculate the rates of intersystem crossing, internal conversion, and fluorescence for selected molecules as functions of temperature. PMID:26683207

  16. The temperature dependence of electrical excitability in fish hearts.

    PubMed

    Vornanen, Matti

    2016-07-01

    Environmental temperature has pervasive effects on the rate of life processes in ectothermic animals. Animal performance is affected by temperature, but there are finite thermal limits for vital body functions, including contraction of the heart. This Review discusses the electrical excitation that initiates and controls the rate and rhythm of fish cardiac contraction and is therefore a central factor in the temperature-dependent modulation of fish cardiac function. The control of cardiac electrical excitability should be sensitive enough to respond to temperature changes but simultaneously robust enough to protect against cardiac arrhythmia; therefore, the thermal resilience and plasticity of electrical excitation are physiological qualities that may affect the ability of fishes to adjust to climate change. Acute changes in temperature alter the frequency of the heartbeat and the duration of atrial and ventricular action potentials (APs). Prolonged exposure to new thermal conditions induces compensatory changes in ion channel expression and function, which usually partially alleviate the direct effects of temperature on cardiac APs and heart rate. The most heat-sensitive molecular components contributing to the electrical excitation of the fish heart seem to be Na(+) channels, which may set the upper thermal limit for the cardiac excitability by compromising the initiation of the cardiac AP at high temperatures. In cardiac and other excitable cells, the different temperature dependencies of the outward K(+) current and inward Na(+) current may compromise electrical excitability at temperature extremes, a hypothesis termed the temperature-dependent depression of electrical excitation. PMID:27385752

  17. Temperature dependence of photovoltaic cells, modules, and systems

    SciTech Connect

    Emery, K.; Burdick, J.; Caiyem, Y.

    1996-05-01

    Photovoltaic (PV) cells and modules are often rated in terms of a set of standard reporting conditions defined by a temperature, spectral irradiance, and total irradiance. Because PV devices operates over a wide range of temperatures and irradiances, the temperature and irradiance related behavior must be known. This paper surveys the temperature dependence of crystalline and thin-film, state-of-the-art, research-size cells, modules, and systems measured by a variety of methods. The various error sources and measurement methods that contribute to cause differences in the temperature coefficient for a given cell or module measured with various methods are discussed.

  18. Temperature dependence of electronic transport property in ferroelectric polymer films

    NASA Astrophysics Data System (ADS)

    Zhao, X. L.; Wang, J. L.; Tian, B. B.; Liu, B. L.; Zou, Y. H.; Wang, X. D.; Sun, S.; Sun, J. L.; Meng, X. J.; Chu, J. H.

    2014-10-01

    The leakage current mechanism of ferroelectric copolymer of polyvinylidene fluoride with trifluoroethylene prepared by Langmuir-Blodgett was investigated in the temperature range from 100 K to 350 K. The electron as the dominant injected carrier was observed in the ferroelectric copolymer films. The transport mechanisms in copolymer strongly depend on the temperature and applied voltage. From 100 K to 200 K, Schottky emission dominates the conduction. With temperature increasing, the Frenkel-Poole emission instead of the Schottky emission to conduct the carrier transport. When the temperature gets to 260 K, the leakage current becomes independent of temperature, and the space charge limited current conduction was observed.

  19. Temperature dependent droplet impact dynamics on flat and textured surfaces

    SciTech Connect

    Azar Alizadeh; Vaibhav Bahadur; Sheng Zhong; Wen Shang; Ri Li; James Ruud; Masako Yamada; Liehi Ge; Ali Dhinojwala; Manohar S Sohal

    2012-03-01

    Droplet impact dynamics determines the performance of surfaces used in many applications such as anti-icing, condensation, boiling and heat transfer. We study impact dynamics of water droplets on surfaces with chemistry/texture ranging from hydrophilic to superhydrophobic and across a temperature range spanning below freezing to near boiling conditions. Droplet retraction shows very strong temperature dependence especially for hydrophilic surfaces; it is seen that lower substrate temperatures lead to lesser retraction. Physics-based analyses show that the increased viscosity associated with lower temperatures can explain the decreased retraction. The present findings serve to guide further studies of dynamic fluid-structure interaction at various temperatures.

  20. ION AND TEMPERATURE DEPENDENCE OF ELECTRICAL CONDUCTANCE FOR NATURAL WATERS

    EPA Science Inventory

    Four empirical equations describing the temperature dependence of electrical conductance of aqueous solutions are compared for the case of single electrolytes. The best method uses a modified Walden product where the log of the ratio between the conductances at two temperatures i...

  1. A temperature dependent SPICE macro-model for power MOSFETs

    SciTech Connect

    Pierce, D.G.

    1991-01-01

    The power MOSFET SPICE Macro-Model has been developed suitable for use over the temperature range {minus}55 to 125 {degrees}C. The model is comprised of a single parameter set with temperature dependence accessed through the SPICE .TEMP card. SPICE parameter extraction techniques for the model and model predictive accuracy are discussed. 7 refs., 8 figs., 1 tab.

  2. Temperature Dependence of Viscosities of Common Carrier Gases

    ERIC Educational Resources Information Center

    Sommers, Trent S.; Nahir, Tal M.

    2005-01-01

    Theoretical and experimental evidence for the dependence of viscosities of the real gases on temperature is described, suggesting that this dependence is greater than that predicted by the kinetic theory of gases. The experimental results were obtained using common modern instrumentation and could be reproduced by students in analytical or…

  3. Temperature dependence of the diffusion coefficient of nanoparticles

    NASA Astrophysics Data System (ADS)

    Rudyak, V. Ya.; Dubtsov, S. N.; Baklanov, A. M.

    2008-06-01

    The temperature dependence of the diffusion coefficient of nanoparticles in gases has been experimentally studied. It is established that this dependence significantly differs from that predicted by various correlations, in particular, by the Cunningham-Millikan-Davies correlation that is used as an instrumental basis for virtually all methods of measurement of the diffusion coefficient in aerosols.

  4. The complete, temperature resolved experimental spectrum of methanol (CH{sub 3}OH) between 214.6 and 265.4 GHz

    SciTech Connect

    McMillan, James P.; Fortman, Sarah M.; Neese, Christopher F.; De Lucia, Frank C.

    2014-11-01

    The spectrum of methanol (CH{sub 3}OH) has been characterized between 214.6 and 265.4 GHz for astrophysically significant temperatures. Four hundred and eighty-six spectra with absolute intensity calibration recorded between 240 and 389 K provided a means for the calculation of the complete experimental spectrum (CES) of methanol as a function of temperature. The CES includes contributions from v{sub t} = 3 and other higher states that are difficult to model quantum mechanically (QM). It also includes the spectrum of the {sup 13}C isotopologue in terrestrial abundance. In general the QM models provide frequencies that are within 1 MHz of their experimental values, but there are several outliers that differ by tens of MHz. As in our recent work on methanol in the 560-654 GHz region, significant intensity differences between our experimental intensities and cataloged values were found. In this work these differences are explored in the context of several QM analyses. The experimental results presented here are analyzed to provide a frequency point-by-point catalog that is well suited for the simulation of crowded and overlapped spectra. Additionally, a catalog in the usual line frequency, line strength, and lower state energy format is provided.

  5. Oxidation of Fe III porphyrins by peroxyl radicals derived from 2-propanol and methanol. Evidence for acid-dependent and acid-independent pathways

    NASA Astrophysics Data System (ADS)

    Brault, D.; Neta, P.

    1985-11-01

    Iron(III) deuteroporphyrin dimethyl ester is oxidized to the radical cation form by the peroxyl radicals CH 2(OH)O 2- and (CH 3) 2C(OH)O 2- generated by pulse radiolysis of air saturated aqueous solutions of methanol and 2-propanol, respectively. Oxidation by CH 2(OH)O 2- radicals proceeds with k = 1×10 7 M -1 s -1 independent of pH. In contrast, the electron-transfer reaction of (CH 3) 2C(OH)O 2-1 is pH-dependent. A reaction scheme, which may apply to all peroxyl radicals depending on relative rate constants, is proposed. It involves the formation of an iron porphyrin peroxyl radical adduct that decays by acid-dependent and acid-independent routes.

  6. Temperature dependence of ethanol depression in mice: dose response.

    PubMed

    Finn, D A; Syapin, P J; Bejanian, M; Jones, B L; Alkana, R L

    1994-04-01

    Manipulation of body temperature during intoxication significantly alters brain sensitivity to ethanol. The current study tested the generality of this effect within the hypnotic dose range. Drug naive, male C57BL/6J mice were injected with 3.2, 3.6, or 4.0 g/kg ethanol (20% w/v) and were exposed to 1 of 7 designated temperatures from 13 degrees to 34 degrees C to manipulate body temperature during intoxication. Rectal temperature at return of righting reflex (RORR) was significantly, positively correlated with loss of righting reflex (LORR) duration and significantly, negatively correlated with blood ethanol concentration (BEC) at RORR at all three doses. These results indicate that increasing body temperature during intoxication increased ethanol sensitivity in C57 mice at all three doses tested and demonstrate the generality of temperature dependence across hypnotic doses in these animals. Interestingly, the LORR duration was dose-dependent at each ambient temperature, but the degree of body temperature change and the BEC at RORR were not dose-dependent. Overall, these results emphasize the importance of body temperature as a variable in ethanol research. PMID:8048742

  7. The temperature dependent amide I band of crystalline acetanilide

    NASA Astrophysics Data System (ADS)

    Cruzeiro, Leonor; Freedman, Holly

    2013-10-01

    The temperature dependent anomalous peak in the amide I band of crystalline acetanilide is thought to be due to self-trapped states. On the contrary, according to the present model, the anomalous peak comes from the fraction of ACN molecules strongly hydrogen-bonded to a neighboring ACN molecule, and its intensity decreases because, on average, this fraction decreases as temperature increases. This model provides, for the first time, an integrated and theoretically consistent view of the temperature dependence of the full amide I band and a qualitative explanation of some of the features of nonlinear pump-probe experiments.

  8. Matching properties, and voltage and temperature dependence of MOS capacitors

    NASA Astrophysics Data System (ADS)

    McCreary, J. L.

    1981-12-01

    A technique for designing MOS capacitor arrays is discussed, which includes a method of calculating capacitance ratio errors and subsequent total yield. Data illustrating the sensitivity of the ratio matching to capacitor layout, structures, and technology are presented, and measured voltage coefficients of MOS capacitors as function of surface concentration are compared with the calculated coefficients. It is demonstrated that the temperature dependence of space charge capacitance, thermal expansion, and temperature dependence of the dielectric constant are the major components of the temperature coefficient of capacitance. It is also shown that to a first-order, heavily doped polysilicon accumulates and depletes similar to crystalline silicon.

  9. TEMPERATURE DEPENDENCE OF THERMAL NEUTRONS FROM THE MOON

    SciTech Connect

    R.C. LITTLE; W. FELDMAN; ET AL

    2000-10-01

    Planetary thermal neutron fluxes provide a sensitive proxy for mafic and feldspathic terranes, and are also necessary for translating measured gamma-ray line strengths to elemental abundances. Both functions require a model for near surface temperatures and a knowledge of the dependence of thermal neutron flux on temperature. We have explored this dependence for a representative sample of lunar soil compositions and surface temperatures using MCNP{trademark}. For all soil samples, the neutron density is found to be independent of temperature, in accord with neutron moderation theory. The thermal neutron flux, however, does vary with temperature in a way that depends on {Delta}, the ratio of macroscopic absorption to energy-loss cross sections of soil compositions. The weakest dependence is for the largest {Delta} (which corresponds to the Apollo 17 high Ti basalt in our soil selection), and the largest dependence is for the lowest {Delta} (which corresponds to ferroan anorthosite, [FAN] in our selection). For the lunar model simulated, the depth at which the thermal neutron population is most sensitive to temperature is {approx}30 g/cm{sup 2}.

  10. Extended temperature dependence of elastic constants in cubic crystals.

    PubMed

    Telichko, A V; Sorokin, B P

    2015-08-01

    To extend the theory of the temperature dependence of the elastic constants in cubic crystals beyond the second- and third-order elastic constants, the fourth-order elastic constants, as well as the non-linearity in the thermal expansion temperature dependence, have been taken into account. Theoretical results were represented as temperature functions of the effective elastic constants and compared with experimental data for a number of cubic crystals, such as alkali metal halides, and elements gold and silver. The relations obtained give a more accurate description of the experimental temperature dependences of second-order elastic constants for a number of cubic crystals, including deviations from linear behavior. A good agreement between theoretical estimates and experimental data has been observed. PMID:25819879

  11. Renewable Electricity Generation via Solar-Powered Methanol Reforming: Hybrid Proton Exchange Membrane Fuel Cell Systems Based on Novel Non-Concentrating, Intermediate-Temperature Solar Collectors

    NASA Astrophysics Data System (ADS)

    Real, Daniel J.

    Tremendous research efforts have been conducted studying the capturing and conversion of solar energy. Solar thermal power systems offer a compelling opportunity for renewable energy utilization with high efficiencies and excellent cost-effectiveness. The goal of this work was to design a non-concentrating collector capable of reaching temperatures above 250 °C, use this collector to power methanol steam reforming, and operate a proton exchange membrane (PEM) fuel cell using the generated hydrogen. The study presents the construction and characterization of a non-concentrating, intermediate-temperature, fin-in-tube evacuated solar collector, made of copper and capable of reaching stagnation temperatures of 268.5 °C at 1000 W/m2 irradiance. The collector was used to power methanol steam reforming, including the initial heating and vaporization of liquid reactants and the final heating of the gaseous reactants. A preferential oxidation (PROX) catalyst was used to remove CO from simulated reformate gas, and this product gas was used to operate a PEM fuel cell. The results show 1) that the outlet temperature is not limited by heat transfer from the absorber coating to the heat transfer fluid, but by the amount of solar energy absorbed. This implicates a constant heat flux description of the heat transfer process and allows for the usage of materials with lower thermal conductivity than copper. 2) It is possible to operate a PEM fuel cell from reformate gas if a PROX catalyst is used to remove CO from the gas. 3) The performance of the fuel cell is only slightly decreased (~4%) by CO2 dilution present in the reformate and PROX gas. These results provide a foundation for the first renewable electricity generation via solar-powered methanol reforming through a hybrid PEM fuel cell system based on novel non-concentrating, intermediate-temperature solar collectors.

  12. Temperature dependence of optical properties of GaAs

    NASA Technical Reports Server (NTRS)

    Yao, Huade; Snyder, Paul G.; Woollam, John A.

    1991-01-01

    The effect of temperature on the optical properties of GaAs was investigated using spectroscopic ellipsometry measurements, between room temperature and about 610 C in increments of 50 C, of pseudodielectric functions and related optical constants of GaAs. A quantitative analysis of the pseudodielectric function spectrum was carried out using a harmonic-oscillator approximation (HOA) to fit the measured dielectric functions. Good fits were obtained with this model, which provides a convenient means of reproducing the GaAs dielectric function at any temperature, by using the temperature-dependent oscillator parameters. The HOA analysis also provides information about band-gap variation with temperature. Using the measured optical constants at a number of fixed temperatures, an algorithm was developed for computing the dielectric function spectrum at an arbitrary temperature in the range 22-610 C.

  13. Temperature-dependent μ-Raman investigation of struvite crystals

    NASA Astrophysics Data System (ADS)

    Prywer, Jolanta; Kasprowicz, D.; Runka, T.

    2016-04-01

    The effect of temperature on the vibrational properties of struvite crystals grown from silica gels was systematically studied by μ-Raman spectroscopy. The time-dependent Raman spectra recorded in the process of long time annealing of struvite crystal at 353 K do not indicate structural changes in the struvite crystal with the time of annealing. The temperature-dependent Raman spectra recorded in the range 298-423 K reveal a phase transition in struvite at about 368 K. Above this characteristic temperature, some of bands assigned to vibrations of the PO4 and NH4 tetrahedra and water molecules observed in the Raman spectra in low temperatures (orthorhombic phase) change their spectral parameters or disappear, which indicates a transition to a higher symmetry structure of struvite in the range of high temperatures.

  14. Temperature dependent Raman scattering in YCrO{sub 3}

    SciTech Connect

    Mall, A. K. Sharma, Y.; Mukherjee, S.; Garg, A.; Gupta, R.

    2014-04-24

    High quality polycrystalline YCrO{sub 3} samples were synthesized using solid-state-reaction method. The samples were subsequently characterized using X-ray diffraction and magnetometry. Further, temperature dependent Raman spectroscopy over a spectral range from 100 to 800 cm{sup −1} was used to examine the variation of phonons as a function of temperature from 90 to 300 K. In the low temperature ferroelectric phase of YCrO{sub 3}, the observed phonon spectra showed softening of some Raman modes below the magnetic ordering temperature (T{sub N} ∼ 142K), suggesting a coupling between the spin and phonon degrees of freedom.

  15. Substrate-dependent temperature sensitivity of soil organic matter decomposition

    NASA Astrophysics Data System (ADS)

    Myachina, Olga; Blagodatskaya, Evgenia

    2015-04-01

    Activity of extracellular enzymes responsible for decomposition of organics is substrate dependent. Quantity of the substrate is the main limiting factor for enzymatic or microbial heterotrophic activity in soils. Different mechanisms of enzymes response to temperature suggested for low and high substrate availability were never proved for real soil conditions. We compared the temperature responses of enzymes-catalyzed reactions in soils. Basing on Michaelis-Menten kinetics we determined the enzymes affinity to substrate (Km) and mineralization potential of heterotrophic microorganisms (Vmax) 1) for three hydrolytic enzymes: β-1,4-glucosidase, N-acetyl- β -D-glucosaminidase and phosphatase by the application of fluorogenically labeled substrates and 2) for mineralization of 14C-labeled glucose by substrate-dependent respiratory response. Here we show that the amount of available substrate is responsible for temperature sensitivity of hydrolysis of polymers in soil, whereas monomers oxidation to CO2 does not depend on substrate amount and is mainly temperature governed. We also found that substrate affinity of enzymes (which is usually decreases with the temperature) differently responded to warming for the process of depolymerisation versus monomers oxidation. We suggest the mechanism to temperature acclimation based on different temperature sensitivity of enzymes kinetics for hydrolysis of polymers and for monomers oxidation.

  16. Universal temperature-dependent normalized optoacoustic response of blood

    NASA Astrophysics Data System (ADS)

    Petrova, Elena V.; Liopo, Anton; Oraevsky, Alexander A.; Ermilov, Sergey A.

    2015-03-01

    We found and interpreted the universal temperature-dependent optoacoustic (photoacoustic) response (ThOR) in blood; the normalized ThOR is invariant with respect to hematocrit at the hemoglobin's isosbestic point. The unique compartmentalization of hemoglobin, the primary optical absorber at 805 nm, inside red blood cells (RBCs) explains the effect. We studied the temperature dependence of Gruneisen parameter in blood and aqueous solutions of hemoglobin and for the first time experimentally observed transition through the zero optoacoustic response at temperature T0, which was proved to be consistent for various blood samples. On the other hand, the hemoglobin solutions demonstrated linear concentration function of the temperature T0. When this function was extrapolated to the average hemoglobin concentration inside erythrocytes, the temperature T0 was found equivalent to that measured in whole and diluted blood. The obtained universal curve of blood ThOR was validated in both transparent and light scattering media. The discovered universal optoacoustic temperature dependent blood response provides foundation for future development of non-invasive in vivo temperature monitoring in vascularized tissues and blood vessels.

  17. Temperature Dependent Constitutive Modeling for Magnesium Alloy Sheet

    SciTech Connect

    Lee, Jong K.; Lee, June K.; Kim, Hyung S.; Kim, Heon Y.

    2010-06-15

    Magnesium alloys have been increasingly used in automotive and electronic industries because of their excellent strength to weight ratio and EMI shielding properties. However, magnesium alloys have low formability at room temperature due to their unique mechanical behavior (twinning and untwining), prompting for forming at an elevated temperature. In this study, a temperature dependent constitutive model for magnesium alloy (AZ31B) sheet is developed. A hardening law based on non linear kinematic hardening model is used to consider Bauschinger effect properly. Material parameters are determined from a series of uni-axial cyclic experiments (T-C-T or C-T-C) with the temperature ranging 150-250 deg. C. The influence of temperature on the constitutive equation is introduced by the material parameters assumed to be functions of temperature. Fitting process of the assumed model to measured data is presented and the results are compared.

  18. Temperature dependence of damage coefficient in electron irradiated solar cells

    NASA Technical Reports Server (NTRS)

    Faith, T. J.

    1973-01-01

    Measurements of light-generated current vs cell temperature on electron-irradiated n/p silicon solar cells show the temperature coefficient of this current to increase with increasing fluence for both 10-ohm and 20-ohm cells. A relationship between minority-carrier diffusion length and light-generated current was derived by combining measurements of these two parameters: vs fluence at room temperature, and vs cell temperature in cells irradiated to a fluence of 1 x 10 to the 15th power e/sq cm. This relationship was used, together with the light-generated current data, to calculate the temperature dependence of the diffusion-length damage coefficient. The results show a strong decrease in the damage coefficient with increasing temperature in the range experienced by solar panels in synchronous earth orbit.

  19. Temperature Dependent Constitutive Modeling for Magnesium Alloy Sheet

    NASA Astrophysics Data System (ADS)

    Lee, Jong K.; Lee, June K.; Kim, Hyung S.; Kim, Heon Y.

    2010-06-01

    Magnesium alloys have been increasingly used in automotive and electronic industries because of their excellent strength to weight ratio and EMI shielding properties. However, magnesium alloys have low formability at room temperature due to their unique mechanical behavior (twinning and untwining), prompting for forming at an elevated temperature. In this study, a temperature dependent constitutive model for magnesium alloy (AZ31B) sheet is developed. A hardening law based on non linear kinematic hardening model is used to consider Bauschinger effect properly. Material parameters are determined from a series of uni-axial cyclic experiments (T-C-T or C-T-C) with the temperature ranging 150-250° C. The influence of temperature on the constitutive equation is introduced by the material parameters assumed to be functions of temperature. Fitting process of the assumed model to measured data is presented and the results are compared.

  20. Temperature dependent surface modification of silica spheres with methacrylate

    NASA Astrophysics Data System (ADS)

    Kang, Kwang-Sun; Kim, Byoung-Ju; Jo, Dong-Hyun; Lim, Sae-Han; Park, Jin-Young; Kim, Do-gyun

    2014-09-01

    Surface modification of silica spheres with 3-(Trimethoxysilyl)propylmethacrylate (TMSPM) has been performed at ambient condition. However, the FTIR spectra and field emission scanning electron microscope (FESEM) images show no evidence of the surface modification. The reaction temperatures were varied from 60 to 80 °C with various reaction periods. Small absorption shoulder of the C=O stretching vibration was at 1700 cm-1, and slightly increased with the increase of the reaction time at 60 °C. The clear absorption peak appeared at 1698 cm-1 for the spheres reacted for 80 min at 70 °C and shifted toward 1720 cm-1 with the increase the reaction time. Strong absorption peak showed at 1698 cm-1 and shifted toward 1725 cm-1 with the increase of the reaction time at 80 °C. The spheres were dispersed to methanol and added photoinitiator (Irgacure-184). The solution was poured to a patterned glass substrate and exposed to the 254 nm UV-light during a self-assembly process. A large area and crack-free silica sphere film was formed. To increase the mechanical stability, a cellulose acetate solution was spin-coated to the film. The film was lift-off from the glass substrate to analyze the surface nanostructures. The surface nanostructures were maintained, and the film is stable enough to use as a mold to duplicate the nanopattern and flexible.

  1. Temperature dependence of the Soret coefficient of ionic colloids

    NASA Astrophysics Data System (ADS)

    Sehnem, A. L.; Figueiredo Neto, A. M.; Aquino, R.; Campos, A. F. C.; Tourinho, F. A.; Depeyrot, J.

    2015-10-01

    The temperature dependence of the Soret coefficient ST(T ) in electrostatically charged magnetic colloids is investigated. Two different ferrofluids, with different particles' mean dimensions, are studied. In both cases we obtain a thermophilic behavior of the Soret effect. The temperature dependence of the Soret coefficient is described assuming that the nanoparticles migrate along the ionic thermoelectric field created by the thermal gradient. A model based on the contributions from the thermoelectrophoresis and variation of the double-layer energy, without fitting parameters, is used to describe the experimental results of the colloid with the bigger particles. To do so, independent measurements of the ζ potential, mass diffusion coefficient, and Seebeck coefficient are performed. The agreement of the theory and the experimental results is rather good. In the case of the ferrofluid with smaller particles, it is not possible to get experimentally reliable values of the ζ potential and the model described is used to evaluate this parameter and its temperature dependence.

  2. On the detection of precipitation dependence on temperature

    NASA Astrophysics Data System (ADS)

    Zhou, Yu; Luo, Ming; Leung, Yee

    2016-05-01

    Employing their newly proposed interannual difference method (IADM), Liu et al. (2009) and Shiu et al. (2012) reported a shocking increase of around 100% K-1 in heavy precipitation with warming global temperature in 1979-2007. Such increase is alarming and prompts us to probe into the IADM. In this study, both analytical derivations and numerical analyses demonstrate that IADM provides no additional information to that of the conventional linear regression, and also, it may give a false indication of dependence. For clarity and simplicity, we therefore recommend linear regression analysis over the IADM for the detection of dependence. We also find that heavy precipitation decreased during the global warming hiatus, and the precipitation dependence on temperature drops by almost 50% when the study period is extended to 1979-2014 and it may keep dropping in the near future. The risk of having heavy precipitation under warming global temperature may have been overestimated.

  3. A framework for elucidating the temperature dependence of fitness.

    PubMed

    Amarasekare, Priyanga; Savage, Van

    2012-02-01

    Climate warming is predicted to cause large-scale extinctions, particularly of ectothermic species. A striking difference between tropical and temperate ectotherms is that tropical species experience a mean habitat temperature that is closer to the temperature at which fitness is maximized (T(opt)) and an upper temperature limit for survival (T(max)) that is closer to T(opt) than do temperate species. Thus, even a small increase in environmental temperature could put tropical ectotherms at high risk of extinction, whereas temperate ectotherms have a wider temperature cushion. Although this pattern is widely observed, the mechanisms that produce it are not well understood. Here we develop a mathematical framework to partition the temperature response of fitness into its components (fecundity, mortality, and development) and test model predictions with data for insects. We find that fitness declines at high temperatures because the temperature responses of fecundity and mortality act in opposite ways: fecundity decreases with temperature when temperatures exceed the optimal range, whereas mortality continues to increase. The proximity of T(opt) to T(max) depends on how the temperature response of development mediates the interaction between fecundity and mortality. When development is highly temperature sensitive, mortality exceeds reproduction only after fecundity has started to decline with temperature, which causes fitness to decline rapidly to zero when temperatures exceed T(opt). The model correctly predicts empirically observed fitness-temperature relationships in insects from different latitudes. It also suggests explanations for the widely reported phenological shifts in many ectotherms and the latitudinal differences in fitness responses. PMID:22218308

  4. Temperature dependence of protein hydration hydrodynamics by molecular dynamics simulations.

    SciTech Connect

    Lau, E Y; Krishnan, V V

    2007-07-18

    The dynamics of water molecules near the protein surface are different from those of bulk water and influence the structure and dynamics of the protein itself. To elucidate the temperature dependence hydration dynamics of water molecules, we present results from the molecular dynamic simulation of the water molecules surrounding two proteins (Carboxypeptidase inhibitor and Ovomucoid) at seven different temperatures (T=273 to 303 K, in increments of 5 K). Translational diffusion coefficients of the surface water and bulk water molecules were estimated from 2 ns molecular dynamics simulation trajectories. Temperature dependence of the estimated bulk water diffusion closely reflects the experimental values, while hydration water diffusion is retarded significantly due to the protein. Protein surface induced scaling of translational dynamics of the hydration waters is uniform over the temperature range studied, suggesting the importance protein-water interactions.

  5. Origins of the temperature dependence of hammerhead ribozyme catalysis.

    PubMed Central

    Peracchi, A

    1999-01-01

    The difficulties in interpreting the temperature dependence of protein enzyme reactions are well recognized. Here, the hammerhead ribozyme cleavage was investigated under single-turnover conditions between 0 and 60 degrees C as a model for RNA-catalyzed reactions. Under the adopted conditions, the chemical step appears to be rate-limiting. However, the observed rate of cleavage is affected by pre-catalytic equilibria involving deprotonation of an essential group and binding of at least one low-affinity Mg2+ion. Thus, the apparent entropy and enthalpy of activation include contributions from the temperature dependence of these equilibria, precluding a simple physical interpretation of the observed activation parameters. Similar pre-catalytic equilibria likely contribute to the observed activation parameters for ribozyme reactions in general. The Arrhenius plot for the hammerhead reaction is substantially curved over the temperature range considered, which suggests the occurrence of a conformational change of the ribozyme ground state around physiological temperatures. PMID:10390528

  6. Temperature-dependent absorption cross sections for hydrogen peroxide vapor

    NASA Technical Reports Server (NTRS)

    Nicovich, J. M.; Wine, P. H.

    1988-01-01

    Relative absorption cross sections for hydrogen peroxide vapor were measured over the temperature ranges 285-381 K for lambda = 230 nm-295 nm and 300-381 K for lambda = 193 nm-350 nm. The well established 298 K cross sections at 202.6 and 228.8 nm were used as an absolute calibration. A significant temperature dependence was observed at the important tropospheric photolysis wavelengths lambda over 300 nm. Measured cross sections were extrapolated to lower temperatures, using a simple model which attributes the observed temperature dependence to enhanced absorption by molecules possessing one quantum of O-O stretch vibrational excitation. Upper tropospheric photodissociation rates calculated using the extrapolated cross sections are about 25 percent lower than those calculated using currently recommended 298 K cross sections.

  7. Temperature dependence of coherent oscillations in Josephson phase qubits.

    PubMed

    Lisenfeld, J; Lukashenko, A; Ansmann, M; Martinis, J M; Ustinov, A V

    2007-10-26

    We experimentally investigate the temperature dependence of Rabi oscillations and Ramsey fringes in superconducting phase qubits. In a wide range of temperatures, we find that both the decay time and the amplitude of these coherent oscillations remain nearly unaffected by thermal fluctuations. In the two-level limit, coherent qubit response rapidly vanishes as soon as the energy of thermal fluctuations k(B)T becomes larger than the energy level spacing variant Planck's over h omega of the qubit. In contrast, a sample of much shorter coherence times displayed semiclassical oscillations very similar to Rabi oscillation, but showing a qualitatively different temperature dependence. Our observations shed new light on the origin of decoherence in superconducting qubits. The experimental data suggest that, without degrading already achieved coherence times, phase qubits can be operated at temperatures much higher than those reported till now. PMID:17995313

  8. Ionisation of C60: is it temperature dependent?

    NASA Astrophysics Data System (ADS)

    Baba, M. Sai; Narasimhan, T. S. Lakshmi; Balasubramanian, R.; Mathews, C. K.

    1994-01-01

    In a recent paper, Drewello [T. Drewello, W. Kratschmer, M. Fieber-Erdmann and A. Ding, Int. J. Mass Spectrom. Ion Processes, 124 (1993) R1] reported a temperature dependent ionisation cross section for the formation of C2+60 in their photoionisation dynamic studies on C60 using synchrotron radiation. To check this, the ratio of ion intensities of C2+60 to that of C60 was determined as a function of temperature of C60 samples using a Knudsen effusion mass spectrometer. Our results indicate the absence of any temperature dependence of cross section for the formation of C2+60 in the temperature range of measurement (600-800 K) using electron impact ionisation.

  9. Temperature dependence of temporal resolution in an insect nervous system.

    PubMed

    Franz, A; Ronacher, B

    2002-05-01

    The vast majority of animals are poikilotherms, and thus face the problem that the temperature of their nervous systems rather smoothly follows the temperature changes imposed by their environment. Since basic properties of nerve cells, e.g., the time constants of ion channels, strongly depend on temperature, a temperature shift likely affects the processing of the temporal structure of sensory stimuli. This can be critical in acoustic communication systems in which time patterns of signals are decisive for recognition by the receiver. We investigated the temperature dependence of the responses of locust auditory receptors and interneurons by varying the temperature of the experimental animals during intracellular recordings. The resolution of fast amplitude modulations of acoustic signals was determined in a gap detection paradigm. In auditory receptors and local (second order) interneurons, temporal resolution was improved at higher temperatures. This gain could be attributed to a higher precision of spike timing. In a third-order neuron, a rise in temperature affected the interactions of inhibition and excitation in a complex manner, also resulting in a better resolution of gaps in the millisecond range. PMID:12012097

  10. Temperature-dependent release of volatile organic compounds of eucalypts by direct analysis in real time (DART) mass spectrometry.

    PubMed

    Maleknia, Simin D; Vail, Teresa M; Cody, Robert B; Sparkman, David O; Bell, Tina L; Adams, Mark A

    2009-08-01

    A method is described for the rapid identification of biogenic, volatile organic compounds (VOCs) emitted by plants, including the analysis of the temperature dependence of those emissions. Direct analysis in real time (DART) enabled ionization of VOCs from stem and leaf of several eucalyptus species including E. cinerea, E. citriodora, E. nicholii and E. sideroxylon. Plant tissues were placed directly in the gap between the DART ionization source skimmer and the capillary inlet of the time-of-flight (TOF) mass spectrometer. Temperature-dependent emission of VOCs was achieved by adjusting the temperature of the helium gas into the DART ionization source at 50, 100, 200 and 300 degrees C, which enabled direct evaporation of compounds, up to the onset of pyrolysis of plant fibres (i.e. cellulose and lignin). Accurate mass measurements facilitated by TOF mass spectrometry provided elemental compositions for the VOCs. A wide range of compounds was detected from simple organic compounds (i.e. methanol and acetone) to a series of monoterpenes (i.e. pinene, camphene, cymene, eucalyptol) common to many plant species, as well as several less abundant sesquiterpenes and flavonoids (i.e. naringenin, spathulenol, eucalyptin) with antioxidant and antimicrobial properties. The leaf and stem tissues for all four eucalypt species showed similar compounds. The relative abundances of methanol and ethanol were greater in stem wood than in leaf tissue suggesting that DART could be used to investigate the tissue-specific transport and emissions of VOCs. PMID:19551840

  11. Anomalous temperature dependence of the IR spectrum of polyalanine

    NASA Astrophysics Data System (ADS)

    Helenius, V.; Korppi-Tommola, J.; Kotila, S.; Nieminen, J.; Lohikoski, R.; Timonen, J.

    1997-12-01

    We have studied the temperature dependence of the infrared spectra of acetanilide (ACN), tryptophan-(alanine) 15, and tyrosine-(alanine) 15. No sidebands of the amide-I vibration were observed in the polypeptides, but two anomalous sidebands of the NH stretch with a similar temperature dependence as that of the anomalous amide-I vibrational mode at 1650 cm -1 of crystalline ACN were detected. Fermi resonance combined with the appearance of a red-shifted sideband of NH stretch through coupling to lattice modes seems to explain this band structure. Observations are indicative of excitons that may occur in polypeptides as well as in single crystals of ACN.

  12. Temperature dependence of VUV transmission of synthetic fused silica

    NASA Astrophysics Data System (ADS)

    Franke, St.; Lange, H.; Schoepp, H.; Witzke, H.-D.

    2006-07-01

    The temperature dependence of the VUV transmission of synthetic fused silica is of interest for commercial applications as well as for fundamental research. In this work the transmission properties of Suprasil 2 from Heraeus with an absorption edge at very low wavelengths is investigated. The absorption edge of this quartz glass shifts from 170 to 180 nm between 789 and 1129 K. The Urbach rule is discussed for the characterization of the temperature dependent transmission curves. The results are applied to the diagnostics of the Hg 185 nm line from a high pressure mercury discharge lamp.

  13. Temperature dependence of self-broadened halfwidths of CO2

    NASA Technical Reports Server (NTRS)

    Suarez, Carlos B.; Valero, Francisco P. J.

    1990-01-01

    The temperature dependence of self-broadened halfwidths of CO2 was studied in the temperature range 165-300 K for the band at 4978/cm. Assuming a power-law of the form gamma(T) = delta(T0)(T0/T)-exp n, the exponent has been determined for J = 6-32. An average value of n = 0.745 + or - 7 percent has been found.

  14. Models for predicting temperature dependence of material properties of aluminum

    NASA Astrophysics Data System (ADS)

    Marla, Deepak; Bhandarkar, Upendra V.; Joshi, Suhas S.

    2014-03-01

    A number of processes such as laser ablation, laser welding, electric discharge machining, etc involve high temperatures. Most of the processes involve temperatures much higher than the target melting and normal boiling point. Such large variation in target temperature causes a significant variation in its material properties. Due to the unavailability of experimental data on material properties at elevated temperatures, usually the data at lower temperatures is often erroneously extrapolated during modelling of these processes. Therefore, this paper attempts to evaluate the variation in material properties with temperature using some general and empirical theories, along with the available experimental data for aluminum. The evaluated properties of Al using the proposed models show a significant variation with temperature. Between room temperature and near-critical temperature (0.9Tc), surface reflectivity of Al varies from more than 90% to less than 50%, absorption coefficient decreases by a factor of 7, thermal conductivity decreases by a factor of 5, density decreases by a factor of 4, specific heat and latent heat of vapourization vary by a factor between 1.5 and 2. Applying these temperature-dependent material properties for modelling laser ablation suggest that optical properties have a greater influence on the process than thermophysical properties. The numerical predictions of the phase explosion threshold in laser ablation are within 5% of the experimental values.

  15. Temperature dependence of myosin-II tail fragment assembly.

    PubMed

    McMahon, Peggy M; Hostetter, Daniel R; Rice, Sarah E

    2008-01-01

    Dictyostelium myosin-II bipolar thick filament (BTF) assembly is heavily dependent on ionic strength and temperature and is reversible by the phosphorylation of just three threonines. Truncated tail fragments of Dictyostelium myosin-II are commonly used as models for BTF assembly, as they self-assemble into regular paracrystals that recapitulate the ionic strength and phosphorylation dependence of full-length Dictyostelium myosin-II BTF assembly. Here we show that Dictyostelium myosin-II tail fragment assembly is highly temperature dependent, similar to full-length Dictyostelium myosin-II. Assembly of paracrystals was far more robust at 4 degrees C than at higher temperatures. Pre-assembled paracrystals disassembled completely when shifted to 37 degrees C, indicating that assembly does not greatly improve the thermostability of these tail fragments. The melting temperatures of individual Dictyostelium myosin-II tail coiled-coils under both low and high ionic strength conditions that prohibit paracrystal assembly are extremely low, 21 degrees C and 28 degrees C, respectively. These data are consistent with reversible thermal denaturation of the coiled-coil as the most likely explanation for assembly incompetence under either very low ionic strength or high temperature conditions. Assembled paracrystals of a structurally similar fragment of nonmuscle myosin-IIA were far more thermodynamically stable than their Dictyostelium counterparts at the temperatures examined here. PMID:18784979

  16. Methanol in dark clouds

    NASA Technical Reports Server (NTRS)

    Friberg, P.; Hjalmarson, A.; Madden, S. C.; Irvine, W. M.

    1988-01-01

    The first observation of methanol in cold dark clouds TMC 1, L 134 N, and B 335 is reported. In all three clouds, the relative abundance of methanol was found to be in the range of 10 to the -9th (i.e., almost an order of magnitude more abundant than acetaldehyde), with no observable variation between the clouds. Methanol emission showed a complex velocity structure; in TMC 1, clear indications of non-LTE were observed. Dimethyl ether was searched for in L 134 N; the upper limit of the column density of dimethyl ether in L 134 N was estimated to be 4 x 10 to the 12th/sq cm, assuming 5 K rotation temperature and LTE. This limit makes the abundance ratio (CH3)2O/CH3OH not higher than 1/5, indicating that dimethyl ether is not overabundant in this dark cloud.

  17. Temperature dependence of electrical resistivity measurements: A useful infiltration tracer?

    NASA Astrophysics Data System (ADS)

    Pidlisecky, A.; Knight, R.

    2008-12-01

    As part of an ongoing monitoring project, three resistivity probes were installed to a depth of 2m below a seasonal infiltration pond on the central coast of California. The probes were instrumented with 35 resistivity electrodes and 5 temperature loggers. They were designed to monitor the change in bulk resistivity beneath the pond during infiltration. The pond was filled in January 2008 and resistivity measurements were made on each probe every hour for a period of 4 months. In addition to changes in bulk resistivity, we observed diurnal fluctuations in the apparent resistivity signal due to the temperature dependence of in-situ resistivity. By processing the resistivity data, using a band pass filter, we can recover a time-depth section of pseudo- temperature data. We refer to these data as pseudo-temperature because they can be treated as a surrogate for temperature in terms of phase but not amplitude. These pseudo-temperature sections can be used as a tracer to calculate 1D infiltration rates. When compared with in-situ temperature loggers, we see good agreement. Moreover, we note that the resistivity fluctuations correspond to temperature variations that are less than one degree Celsius. The use of the temperature dependence of measured resistivity is a promising field technique. The pseudo-temperature data may prove more robust than using traditional temperature probes given that the larger sampling volume of the resistivity measurement will limit the influence local flow path perturbations caused by probe installation. Future research will involve extending this approach to 2D tomography in hopes of providing us with a technique for obtaining spatially exhaustive estimates of near-surface infiltration rates.

  18. Temperature Dependence of Photosynthesis in Agropyron smithii Rydb. 1

    PubMed Central

    Monson, Russell K.; Stidham, Mark A.; Williams, George J.; Edwards, Gerald E.; Uribe, Ernest G.

    1982-01-01

    As part of an extensive analysis of the factors regulating photosynthesis in Agropyron smithii Rydb., a C3 grass, we have examined the response of leaf gas exchange and ribulose-1,5-bisphosphate (RuBP) carboxylase activity to temperature. Emphasis was placed on elucidating the specific processes which regulate the temperature response pattern. The inhibitory effects of above-optimal temperatures on net CO2 uptake were fully reversible up to 40°C. Below 40°C, temperature inhibition was primarily due to O2 inhibition of photosynthesis, which reached a maximum of 65% at 45°C. The response of stomatal conductance to temperature did not appear to have a significant role in determining the overall temperature response of photosynthesis. The intracellular conductance to CO2 increased over the entire experimental temperature range, having a Q10 of 1.2 to 1.4. Increases in the apparent Michaelis constant (Kc) for RuBP carboxylase were observed in both in vitro and in vivo assays. The Q10 values for the maximum velocity (Vmax) of CO2 fixation by RuBP carboxylase in vivo was lower (1.3-1.6) than those calculated from in vitro assays (1.8-2.2). The results suggest that temperature-dependent changes in enzyme capacity may have a role in above-optimum temperature limitations below 40°C. At leaf temperatures above 40°C, decreases in photosynthetic capacity were partially dependent on temperature-induced irreversible reductions in the quantum yield for CO2 uptake. PMID:16662320

  19. Temperature dependence of atomic-scale stick-slip friction.

    PubMed

    Jansen, Lars; Hölscher, Hendrik; Fuchs, Harald; Schirmeisen, André

    2010-06-25

    We report experiments of atomic stick-slip friction on graphite as an explicit function of surface temperature between 100 and 300 K under ultrahigh vacuum conditions. A statistical analysis of the individual stick-slip events as a function of the velocity reveals an agreement with the thermally activated Prandtl-Tomlinson model at all temperatures. Taking into account an explicit temperature-dependence of the attempt frequency all data points collapse onto one single master curve. PMID:20867399

  20. Temperature Dependent Fluorescence Lifetime Measurements in a Phosphor

    NASA Astrophysics Data System (ADS)

    Nettles, Charles J.; Smith, R. Seth; Heath, Jonathan J.

    2012-03-01

    This poster will describe an undergraduate senior research project involving fluorescence lifetime measurements in a LaSO4:Eu phosphor compound. Specifically, this project seeks to determine the temperature dependence of the lifetime. The temperature of the phosphor will be varied using a heater block with temperature control. The phosphor will be excited with the 337 nm output of a Nitrogen Laser. An Oriel Monochromator will be used to disperse the fluorescence, and the lifetime for a particular wavelength will be determined from a photomultiplier tube signal. At the time of the presentation, this project will be nearing completion; and I will discuss my progress, successes, and challenges.

  1. NICMOS Flats and temperature dependence of the DQE

    NASA Astrophysics Data System (ADS)

    Boeker, Torsten

    2001-07-01

    The purpose of this proposal is to obtain initial estimates of the detective quantum efficiency {DQE} of the NICMOS detectors and its temperature dependence in the previously uncharted temperature regime expected for operation under the NICMOS Cooling System {NCS}. The observations will measure the relative {via flat field morphology} and absolute DQE variation at three temperature setpoints. In addition, they will provide a monitor for particulate contamination {"Grot"} and detector lateral position {from the coronagraphic spot and FDA vignetting}. When stars are present in the field of view, they will enable a preliminary focus determination.

  2. Temperature dependent energy levels of methylammonium lead iodide perovskite

    SciTech Connect

    Foley, Benjamin J.; Marlowe, Daniel L.; Choi, Joshua J. E-mail: mgupta@virginia.edu; Sun, Keye; Gupta, Mool C. E-mail: mgupta@virginia.edu; Saidi, Wissam A.; Scudiero, Louis E-mail: mgupta@virginia.edu

    2015-06-15

    Temperature dependent energy levels of methylammonium lead iodide are investigated using a combination of ultraviolet photoemission spectroscopy and optical spectroscopy. Our results show that the valence band maximum and conduction band minimum shift down in energy by 110 meV and 77 meV as temperature increases from 28 °C to 85 °C. Density functional theory calculations using slab structures show that the decreased orbital splitting due to thermal expansion is a major contribution to the experimentally observed shift in energy levels. Our results have implications for solar cell performance under operating conditions with continued sunlight exposure and increased temperature.

  3. Temperature dependence of nucleation rate in a binary solid solution

    NASA Astrophysics Data System (ADS)

    Wang, H. Y.; Philippe, T.; Duguay, S.; Blavette, D.

    2012-12-01

    The influence of regression (partial dissolution) effects on the temperature dependence of nucleation rate in a binary solid solution has been studied theoretically. The results of the analysis are compared with the predictions of the simplest Volmer-Weber theory. Regression effects are shown to have a strong influence on the shape of the curve of nucleation rate versus temperature. The temperature TM at which the maximum rate of nucleation occurs is found to be lowered, particularly for low interfacial energy (coherent precipitation) and high-mobility species (e.g. interstitial atoms).

  4. High temperature dependence of thermal transport in graphene foam.

    PubMed

    Li, Man; Sun, Yi; Xiao, Huying; Hu, Xuejiao; Yue, Yanan

    2015-03-13

    In contrast to the decreased thermal property of carbon materials with temperature according to the Umklapp phonon scattering theory, highly porous free-standing graphene foam (GF) exhibits an abnormal characteristic that its thermal property increases with temperature above room temperature. In this work, the temperature dependence of thermal properties of free-standing GF is investigated by using the transient electro-thermal technique. Significant increase for thermal conductivity and thermal diffusivity from ∼0.3 to 1.5 W m(-1) K(-1) and ∼4 × 10(-5) to ∼2 × 10(-4) m(2) s(-1) respectively is observed with temperature from 310 K to 440 K for three GF samples. The quantitative analysis based on a physical model for porous media of Schuetz confirms that the thermal conductance across graphene contacts rather than the heat conductance inside graphene dominates thermal transport of our GFs. The thermal expansion effect at an elevated temperature makes the highly porous structure much tighter is responsible for the reduction in thermal contact resistance. Besides, the radiation heat exchange inside the pores of GFs improves the thermal transport at high temperatures. Since free-standing GF has great potential for being used as supercapacitor and battery electrode where the working temperature is always above room temperature, this finding is beneficial for thermal design of GF-based energy applications. PMID:25683178

  5. Efficiencies of thermodynamics when temperature-dependent energy levels exist.

    PubMed

    Yamano, Takuya

    2016-03-14

    Based on a generalized form of the second law of thermodynamics, in which the temperature-dependent energy levels of a system are appropriately included in entropy generation, we show that the effect reasonably appears in efficiencies of thermodynamic processes. PMID:26890276

  6. Time- and temperature-dependent failures of a bonded joint

    SciTech Connect

    Sihn, Sangwook; Miyano, Yasushi; Tsai, S.W.

    1997-07-01

    Time and temperature dependent properties of a tubular lap bonded joint are reported. The joint bonds a cast iron rod and a composite pipe together with an epoxy type of an adhesive material containing chopped glass fiber. A new fabrication method is proposed.

  7. Temperature dependence of soliton diffusion in trans-polyacetylene

    SciTech Connect

    Tang, J.; Norris, J.R.; Isoya, J.

    1997-07-01

    The temperature dependence of 1-D diffusion rate of solitons in transpolyacetylene is determined by time-domain analysis of ESR measurements. The diffusion rate appears to obey a simple power law. Monte Carlo simulation of 1-D diffusion process in impure chains indicates that overall diffusion can be much slower than that without traps.

  8. Anomalous temperature dependence of the fluorescence lifetime of phycobiliproteins

    NASA Astrophysics Data System (ADS)

    Maksimov, E. G.; Schmitt, F.-J.; Hätti, P.; Klementiev, K. E.; Paschenko, V. Z.; Renger, G.; Rubin, A. B.

    2013-05-01

    Using a single photon counting technique we have investigated fluorescence decay spectra of phycobiliproteins with picosecond time resolution. The studies were performed in a wide range of temperatures—from 4 to 300 K. Comparing the fluorescence decay kinetics of samples rapidly frozen in liquid nitrogen with samples that were frozen slowly revealed that the temperature-dependent changes of phycobiliproteins fluorescence lifetime reflect the presence of three different stages, with a phase transition between 273 and 263 K that strongly depends on the rate of freezing. When the temperature decreases from 300 to 273 K, the fluorescence lifetime increases from 1.6 to 1.8 ns. In the region from 273 to 263 K we observed a decrease of the fluorescence lifetime, which strongly depends on the freezing rate: a slight decrease at high freezing rate and a drop down to 200 ps lifetime at slow freezing rate. In the low-temperature regime from 263 to 4 K a linear increase in the fluorescence lifetime was observed for all samples. It was found that the strong temperature dependence of the phycobiliprotein fluorescence, especially in the range between 263 and 273 K, is due to the interaction of the solvent with the chromophore bound to the protein. This feature is explained by a photoisomerization of the phycobiliproteins into a quenching form which is naturally prevented by the protein environment. The formation of ice microcrystals at low freezing rate eliminates this ‘protective’ effect of the protein environment.

  9. Investigation of temperature dependence of development and aging

    NASA Technical Reports Server (NTRS)

    Sacher, G. A.

    1969-01-01

    Temperature dependence of maturation and metabolic rates in insects, and the failure of vital processes during development were investigated. The paper presented advances the general hypothesis that aging in biological systems is a consequence of the production of entropy concomitant with metabolic activity.

  10. Temperature dependence of protein folding kinetics in living cells

    PubMed Central

    Guo, Minghao; Xu, Yangfan; Gruebele, Martin

    2012-01-01

    We measure the stability and folding rate of a mutant of the enzyme phosphoglycerate kinase (PGK) inside bone tissue cells as a function of temperature from 38 to 48 °C. To facilitate measurement in individual living cells, we developed a rapid laser temperature stepping method capable of measuring complete thermal melts and kinetic traces in about two min. We find that this method yields improved thermal melts compared to heating a sample chamber or microscope stage. By comparing results for six cells with in vitro data, we show that the protein is stabilized by about 6 kJ/mole in the cytoplasm, but the temperature dependence of folding kinetics is similar to in vitro. The main difference is a slightly steeper temperature dependence of the folding rate in some cells that can be rationalized in terms of temperature-dependent crowding, local viscosity, or hydrophobicity. The observed rate coefficients can be fitted within measurement uncertainty by an effective two-state model, even though PGK folds by a multistate mechanism. We validate the effective two-state model with a three-state free energy landscape of PGK to illustrate that the effective fitting parameters can represent a more complex underlying free energy landscape. PMID:22665776

  11. Temperature-dependent absorption cross-sections of perfluorotributylamine

    NASA Astrophysics Data System (ADS)

    Godin, Paul J.; Cabaj, Alex; Conway, Stephanie; Hong, Angela C.; Le Bris, Karine; Mabury, Scott A.; Strong, Kimberly

    2016-05-01

    Cross-sections of perfluorotributylamine (PFTBA) were derived from Fourier transform spectroscopy at 570-3400 cm-1 with a resolution of 0.1 cm-1 over a temperature range of 298-344 K. These results were compared to theoretical density functional theory (DFT) calculations and to previous measurements of PFTBA made at room temperature. DFT calculations were performed using the B3LYP method and the 6-311G(d,p) basis set. We find good agreement between our experimentally derived results, DFT calculations, and previously published data. No significant temperature dependence in the PFTBA cross-sections was observed for the temperature range studied. We calculate an average integrated band strength of 7.81 × 10-16 cm/molecule for PFTBA over the spectral range studied. Radiative efficiencies (RE) and global warming potentials (GWP) for PFTBA were also derived. The calculated radiative efficiencies show no dependence on temperature and agree with prior publications. We find an average RE of 0.77 Wm-2 ppbv-1 and a range of GWP from 6874 to 7571 depending on the lifetime used. Our findings are consistent with previous studies and increase our confidence in the value of the GWP of PFTBA.

  12. Stress versus temperature dependent activation energies in creep

    NASA Technical Reports Server (NTRS)

    Freed, A. D.; Raj, S. V.; Walker, K. P.

    1990-01-01

    The activation energy for creep at low stresses and elevated temperatures is lattice diffusion, where the rate controlling mechanism for deformation is dislocation climb. At higher stresses and intermediate temperatures, the rate controlling mechanism changes from that of dislocation climb to one of obstacle-controlled dislocation glide. Along with this change, there occurs a change in the activation energy. It is shown that a temperature-dependent Gibbs free energy does a good job of correlating steady-state creep data, while a stress-dependent Gibbs free energy does a less desirable job of correlating the same data. Applications are made to copper and a LiF-22 mol. percent CaF2 hypereutectic salt.

  13. Stress versus temperature dependence of activation energies for creep

    NASA Technical Reports Server (NTRS)

    Freed, A. D.; Raj, S. V.; Walker, K. P.

    1992-01-01

    The activation energy for creep at low stresses and elevated temperatures is associated with lattice diffusion, where the rate controlling mechanism for deformation is dislocation climb. At higher stresses and intermediate temperatures, the rate controlling mechanism changes from dislocation climb to obstacle-controlled dislocation glide. Along with this change in deformation mechanism occurs a change in the activation energy. When the rate controlling mechanism for deformation is obstacle-controlled dislocation glide, it is shown that a temperature-dependent Gibbs free energy does better than a stress-dependent Gibbs free energy in correlating steady-state creep data for both copper and LiF-22mol percent CaF2 hypereutectic salt.

  14. Temperature dependence of penetration depth in thin film niobium

    NASA Technical Reports Server (NTRS)

    More, N.; Muhlfelder, B.; Lockhart, J.

    1989-01-01

    A novel technique is presented which should allow precise determination of the temperature dependence of the inductance, and hence of the penetration depth, of superconducting niobium thin-film structures. Four niobium thin-film stripline inductors are arranged in a bridge configuration, and inductance differences are measured using a potentiometric technique with a SQUID (superconducting quantum interference device) as the null detector. Numerical simulations of the stripline inductances are presented which allow the performance of the measurement technique to be evaluated. The prediction of the two-fluid model for the penetration-depth temperature dependence is given for reduced temperatures of 0.3 to 0.9. The experimental apparatus and its resolution and accuracy are discussed.

  15. Temperature dependence of angular momentum transport across interfaces

    NASA Astrophysics Data System (ADS)

    Chen, Kai; Lin, Weiwei; Chien, C. L.; Zhang, Shufeng

    2016-08-01

    Angular momentum transport in magnetic multilayered structures plays a central role in spintronic physics and devices. The angular momentum currents or spin currents are carried by either quasiparticles such as electrons and magnons, or by macroscopic order parameters such as local magnetization of ferromagnets. Based on the generic interface exchange interaction, we develop a microscopic theory that describes interfacial spin conductance for various interfaces among nonmagnetic metals, ferromagnetic insulators, and antiferromagnetic insulators. Spin conductance and its temperature dependence are obtained for different spin batteries including spin pumping, temperature gradient, and spin Hall effect. As an application of our theory, we calculate the spin current in a trilayer made of a ferromagnetic insulator, an antiferromagnetic insulator, and a nonmagnetic heavy metal. The calculated results on the temperature dependence of spin conductance quantitatively agree with the existing experiments.

  16. Temperature dependence of APD-based PET scanners

    SciTech Connect

    Keereman, Vincent; Van Holen, Roel; Vandenberghe, Stefaan; Vanhove, Christian

    2013-09-15

    Purpose: Solid state detectors such as avalanche photodiodes (APDs) are increasingly being used in PET detectors. One of the disadvantages of APDs is the strong decrease of their gain factor with increasing ambient temperature. The light yield of most scintillation crystals also decreases when ambient temperature is increased. Both effects lead to considerable temperature dependence of the performance of APD-based PET scanners. In this paper, the authors propose a model for this dependence and the performance of the LabPET8 APD-based small animal PET scanner is evaluated at different temperatures.Methods: The model proposes that the effect of increasing temperature on the energy histogram of an APD-based PET scanner is a compression of the histogram along the energy axis. The energy histogram of the LabPET system was acquired at 21 °C and 25 °C to verify the validity of this model. Using the proposed model, the effect of temperature on system sensitivity was simulated for different detector temperature coefficients and temperatures. Subsequently, the effect of short term and long term temperature changes on the peak sensitivity of the LabPET system was measured. The axial sensitivity profile was measured at 21 °C and 24 °C following the NEMA NU 4-2008 standard. System spatial resolution was also evaluated. Furthermore, scatter fraction, count losses and random coincidences were evaluated at different temperatures. Image quality was also investigated.Results: As predicted by the model, the photopeak energy at 25 °C is lower than at 21 °C with a shift of approximately 6% per °C. Simulations showed that this results in an approximately linear decrease of sensitivity when temperature is increased from 21 °C to 24 °C and energy thresholds are constant. Experimental evaluation of the peak sensitivity at different temperatures showed a strong linear correlation for short term (2.32 kcps/MBq/°C = 12%/°C, R = −0.95) and long term (1.92 kcps/MBq/°C = 10%/

  17. Finite element simulation of temperature dependent free surface flows

    NASA Technical Reports Server (NTRS)

    Engelman, M. S.; Sani, R. L.

    1985-01-01

    The method of Engelman and Sani (1984) for a finite-element simulation of incompressible surface flows with a free and/or moving fluid interface, such as encountered in crystal growth and coating and polymer technology, is extended to temperature-dependent flows, including the effect of temperature-dependent surface tension. The basic algorithm of Saito and Scriven (1981) and Ruschak (1980) has been generalized and implemented in a robust and versatile finite-element code that can be employed with relative ease for the simulation of free-surface problems in complex geometries. As a result, the costly dependence on the Newton-Raphson algorithm has been eliminated by replacing it with a quasi-Newton iterative method, which nearly retains the superior convergence properties of the Newton-Raphson method.

  18. Intensity-dependent response to temperature in hydra clones.

    PubMed

    Kaliszewicz, Anita

    2015-01-01

    The intensity of environmental factors differs in natural habitats and could shape the response of an animal that is able to assess a factor's gradient. However, intensity-dependent response to environmental factors has been only occasionally reported in animals. In laboratory experiments, I studied changes in sexual induction in response to a series of temperature decreases in different clones of Hydra oligactis. The percentage of sexually-induced clone-mates was related to the temperature gradient intensity. This intensity-dependent response was observed independently of the H. oligactis clone and gender. The magnitude of the response differed significantly between the clones originated from the distinct sites. The possible significance of the intensity-dependent response in the Hydra clones is discussed in evolutionary terms. PMID:25660699

  19. Temperature-Dependent Dielectric Properties of Al/Epoxy Nanocomposites

    NASA Astrophysics Data System (ADS)

    Wang, Zijun; Zhou, Wenying; Sui, Xuezhen; Dong, Lina; Cai, Huiwu; Zuo, Jing; Chen, Qingguo

    2016-06-01

    Broadband dielectric spectroscopy was carried out to study the transition in electrical properties of Al/epoxy nanocomposites over the frequency range of 1-107 Hz and the temperature range of -20°C to 200°C. The dielectric permittivity, dissipation factor, and electrical conductivity of the nanocomposites increased with temperature and showed an abrupt increase around the glass transition temperature ( T g). The results clearly reveal an interesting transition of the electrical properties with increasing temperature: insulator below 70°C, conductor at about 70°C. The behavior of the transition in electrical properties of the nanocomposites was explored at different temperatures. The presence of relaxation peaks in the loss tangent and electric modulus spectra of the nanocomposites confirms that the chain segmental dynamics of the polymer is accompanied by the absorption of energy given to the system. It is suggested that the temperature-dependent transition of the electric properties in the nanocomposite is closely associated with the α-relaxation. The large increase in the dissipation factor and electric conductivity depends on the direct current conduction of thermally activated charge carriers resulting from the epoxy matrix above T g.

  20. Temperature-Dependent Dielectric Properties of Al/Epoxy Nanocomposites

    NASA Astrophysics Data System (ADS)

    Wang, Zijun; Zhou, Wenying; Sui, Xuezhen; Dong, Lina; Cai, Huiwu; Zuo, Jing; Chen, Qingguo

    2016-01-01

    Broadband dielectric spectroscopy was carried out to study the transition in electrical properties of Al/epoxy nanocomposites over the frequency range of 1-107 Hz and the temperature range of -20°C to 200°C. The dielectric permittivity, dissipation factor, and electrical conductivity of the nanocomposites increased with temperature and showed an abrupt increase around the glass transition temperature (T g). The results clearly reveal an interesting transition of the electrical properties with increasing temperature: insulator below 70°C, conductor at about 70°C. The behavior of the transition in electrical properties of the nanocomposites was explored at different temperatures. The presence of relaxation peaks in the loss tangent and electric modulus spectra of the nanocomposites confirms that the chain segmental dynamics of the polymer is accompanied by the absorption of energy given to the system. It is suggested that the temperature-dependent transition of the electric properties in the nanocomposite is closely associated with the α-relaxation. The large increase in the dissipation factor and electric conductivity depends on the direct current conduction of thermally activated charge carriers resulting from the epoxy matrix above T g.

  1. TEMPERATURE-DEPENDENT INFRARED OPTICAL CONSTANTS OF OLIVINE AND ENSTATITE

    SciTech Connect

    Zeidler, S.; Mutschke, H.; Posch, Th. E-mail: harald.mutschke@uni-jena.de

    2015-01-10

    Since the Infrared Space Observatory (ISO) mission, it has become clear that dust in circumstellar disks and outflows consists partly of crystalline silicates of pyroxene and olivine type. An exact mineralogical analysis of the dust infrared emission spectra relies on laboratory spectra, which, however, have been mostly measured at room temperature so far. Given that infrared spectral features depend on the thermal excitation of the crystal's vibrational modes, laboratory spectra measured at various (low and high) temperatures, corresponding to the thermal conditions at different distances from the star, can improve the accuracy of such analyses considerably. We have measured the complex refractive index in a temperature range of 10-973 K for one mineral of each of those types of silicate, i.e., for an olivine and an enstatite of typical (terrestrial) composition. Thus, our data extend the temperature range of previous data to higher values and the compositional range to higher iron contents. We analyze the temperature dependence of oscillator frequencies and damping parameters governing the spectral characteristics of the bands and calculate absorption cross-sectional spectra that can be compared with astronomical emission spectra. We demonstrate the usefulness of our new data by comparing spectra calculated for a 100 K dust temperature with the ISO SWS spectrum of IRAS 09425-6040.

  2. Temperature Dependence of Carbon Isotope Fractionation in CAM Plants.

    PubMed

    Deleens, E; Treichel, I; O'leary, M H

    1985-09-01

    The carbon isotope fractionation associated with nocturnal malic acid synthesis in Kalanchoë daigremontiana and Bryophyllum tubiflorum was calculated from the isotopic composition of carbon-4 of malic acid, after appropriate corrections. In the lowest temperature treatment (17 degrees C nights, 23 degrees C days), the isotope fractionation for both plants is -4 per thousand (that is, malate is enriched in (13)C relative to the atmosphere). For K. daigremontiana, the isotope fractionation decreases with increasing temperature, becoming approximately 0 per thousand at 27 degrees C/33 degrees C. Detailed analysis of temperature effects on the isotope fractionation indicates that stomatal aperture decreases with increasing temperature and carboxylation capacity increases. For B. tubiflorum, the temperature dependence of the isotope fractionation is smaller and is principally attributed to the normal temperature dependences of the rates of diffusion and carboxylation steps. The small change in the isotopic composition of remaining malic acid in both species which is observed during deacidification indicates that malate release, rather than decarboxylation, is rate limiting in the deacidification process. PMID:16664371

  3. Temperature-dependent Infrared Optical Constants of Olivine and Enstatite

    NASA Astrophysics Data System (ADS)

    Zeidler, S.; Mutschke, H.; Posch, Th.

    2015-01-01

    Since the Infrared Space Observatory (ISO) mission, it has become clear that dust in circumstellar disks and outflows consists partly of crystalline silicates of pyroxene and olivine type. An exact mineralogical analysis of the dust infrared emission spectra relies on laboratory spectra, which, however, have been mostly measured at room temperature so far. Given that infrared spectral features depend on the thermal excitation of the crystal's vibrational modes, laboratory spectra measured at various (low and high) temperatures, corresponding to the thermal conditions at different distances from the star, can improve the accuracy of such analyses considerably. We have measured the complex refractive index in a temperature range of 10-973 K for one mineral of each of those types of silicate, i.e., for an olivine and an enstatite of typical (terrestrial) composition. Thus, our data extend the temperature range of previous data to higher values and the compositional range to higher iron contents. We analyze the temperature dependence of oscillator frequencies and damping parameters governing the spectral characteristics of the bands and calculate absorption cross-sectional spectra that can be compared with astronomical emission spectra. We demonstrate the usefulness of our new data by comparing spectra calculated for a 100 K dust temperature with the ISO SWS spectrum of IRAS 09425-6040.

  4. Temperature dependence of resonance Raman spectra of carotenoids

    NASA Astrophysics Data System (ADS)

    Andreeva, A.; Apostolova, I.; Velitchkova, M.

    2011-04-01

    To understand the mechanism of the photoprotective and antioxidative functions of carotenoids, it is essential to have a profound knowledge of their excited electronic and vibronic states. In the present study we investigate the most powerful antioxidants: β-carotene and lutein by means of resonance Raman spectroscopy. The aim was to study in detail their Raman spectra in solution at room temperature and their changes as a function of temperature. To measure the spectra in their natural environment pyridine has been used as a solvent. It has been chosen because of its polarizability ( n = 1.5092) which is close to that of membrane lipids and proteins. The temperature dependence of the most intensive ν1 band in the range from 77 K to 295 K at 514.5 nm excitation has been obtained. It was found that in pyridine the C dbnd C stretching frequency, its intensity, line shape, and line width are very sensitive to the temperature (the sensitivity being different for the two studied carotenoids). The observed linear temperature dependence of the C dbnd C stretching frequency is explained by a mechanism involving changes of the vibronic coupling and the extent of π-electron delocalization. The different behavior of the temperature-induced broadening of the ν1 band and its intensity for the two studied carotenoids can be associated with the different nature of their solid matrices: glassy for β-carotene and crystalline-like for lutein, owing to their different chemical structures.

  5. New application of temperature-dependent modelling of high temperature superconductors: Quench propagation and pulse magnetization

    NASA Astrophysics Data System (ADS)

    Zhang, Min; Matsuda, Koichi; Coombs, T. A.

    2012-08-01

    We present temperature-dependent modeling of high-temperature superconductors (HTS) to understand HTS electromagnetic phenomena where temperature fluctuation plays a nontrivial role. Thermal physics is introduced into the well-developed H-formulation model, and the effect of temperature-dependent parameters is considered. Based on the model, we perform extensive studies on two important HTS applications: quench propagation and pulse magnetization. A micrometer-scale quench model of HTS coil is developed, which can be used to estimate minimum quench energy and normal zone propagation velocity inside the coil. In addition, we study the influence of inhomogeneity of HTS bulk during pulse magnetization. We demonstrate how the inhomogeneous distribution of critical current inside the bulk results in varying degrees of heat dissipation and uniformity of final trapped field. The temperature-dependent model is proven to be a powerful tool to study the thermally coupled electromagnetic phenomena of HTS.

  6. On the Temperature Dependence of Enzyme-Catalyzed Rates.

    PubMed

    Arcus, Vickery L; Prentice, Erica J; Hobbs, Joanne K; Mulholland, Adrian J; Van der Kamp, Marc W; Pudney, Christopher R; Parker, Emily J; Schipper, Louis A

    2016-03-29

    One of the critical variables that determine the rate of any reaction is temperature. For biological systems, the effects of temperature are convoluted with myriad (and often opposing) contributions from enzyme catalysis, protein stability, and temperature-dependent regulation, for example. We have coined the phrase "macromolecular rate theory (MMRT)" to describe the temperature dependence of enzyme-catalyzed rates independent of stability or regulatory processes. Central to MMRT is the observation that enzyme-catalyzed reactions occur with significant values of ΔCp(‡) that are in general negative. That is, the heat capacity (Cp) for the enzyme-substrate complex is generally larger than the Cp for the enzyme-transition state complex. Consistent with a classical description of enzyme catalysis, a negative value for ΔCp(‡) is the result of the enzyme binding relatively weakly to the substrate and very tightly to the transition state. This observation of negative ΔCp(‡) has important implications for the temperature dependence of enzyme-catalyzed rates. Here, we lay out the fundamentals of MMRT. We present a number of hypotheses that arise directly from MMRT including a theoretical justification for the large size of enzymes and the basis for their optimum temperatures. We rationalize the behavior of psychrophilic enzymes and describe a "psychrophilic trap" which places limits on the evolution of enzymes in low temperature environments. One of the defining characteristics of biology is catalysis of chemical reactions by enzymes, and enzymes drive much of metabolism. Therefore, we also expect to see characteristics of MMRT at the level of cells, whole organisms, and even ecosystems. PMID:26881922

  7. Temperature dependent Raman and DFT study of creatine.

    PubMed

    Gangopadhyay, Debraj; Sharma, Poornima; Singh, Ranjan K

    2015-01-01

    Temperature dependent Raman spectra of creatine powder have been recorded in the temperature range 420-100K at regular intervals and different clusters of creatine have been optimized using density functional theory (DFT) in order to determine the effect of temperature on the hydrogen bonded network in the crystal structure of creatine. Vibrational assignments of all the 48 normal modes of the zwitterionic form of creatine have been done in terms of potential energy distribution obtained from DFT calculations. Precise analysis gives information about thermal motion and intermolecular interactions with respect to temperature in the crystal lattice. Formation of higher hydrogen bonded aggregates on cooling can be visualized from the spectra through clear signature of phase transition between 200K and 180K. PMID:26010702

  8. Temperature-dependent liquid metal flowrate control device

    DOEpatents

    Carlson, Roger D.

    1978-01-01

    A temperature-dependent liquid metal flowrate control device includes a magnet and a ferromagnetic member defining therebetween a flow path for liquid metal, the ferromagnetic member being formed of a material having a curie temperature at which a change in the flow rate of the liquid metal is desired. According to the preferred embodiment the magnet is a cylindrical rod magnet axially disposed within a cylindrical member formed of a curie material and having iron pole pieces at the ends. A cylindrical iron shunt and a thin wall stainless steel barrier are disposed in the annulus between magnet and curie material. Below the curie temperature flow between steel barrier and curie material is impeded and above the curie temperature flow impedance is reduced.

  9. Temperature dependence of contact resistance at metal/MWNT interface

    NASA Astrophysics Data System (ADS)

    Lee, Sang-Eui; Moon, Kyoung-Seok; Sohn, Yoonchul

    2016-07-01

    Although contact resistance of carbon nanotube (CNT) is one of the most important factors for practical application of electronic devices, a study regarding temperature dependence on contact resistance of CNTs with metal electrodes has not been found. Here, we report an investigation of contact resistance at multiwalled nanotube (MWNT)/Ag interface as a function of temperature, using MWNT/polydimethylsiloxane (PDMS) composite. Electrical resistance of MWNT/PDMS composite revealed negative temperature coefficient (NTC). Excluding the contact resistance with Ag electrode, the NTC effect became less pronounced, showing lower intrinsic resistivity with the activation energy of 0.019 eV. Activation energy of the contact resistance of MWNT/Ag interface was determined to be 0.04 eV, two times larger than that of MWNT-MWNT network. The increase in the thermal fluctuation assisted electron tunneling is attributed to conductivity enhancement at both MWNT/MWNT and MWNT/Ag interfaces with increasing temperature.

  10. A nanoscale temperature-dependent heterogeneous nucleation theory

    SciTech Connect

    Cao, Y. Y.; Yang, G. W.

    2015-06-14

    Classical nucleation theory relies on the hypothetical equilibrium of the whole nucleation system, and neglects the thermal fluctuations of the surface; this is because the high entropic gains of the (thermodynamically extensive) surface would lead to multiple stable states. In fact, at the nanometer scale, the entropic gains of the surface are high enough to destroy the stability of the thermal equilibrium during nucleation, comparing with the whole system. We developed a temperature-dependent nucleation theory to elucidate the heterogeneous nucleation process, by considering the thermal fluctuations based on classical nucleation theory. It was found that the temperature not only affected the phase transformation, but also influenced the surface energy of the nuclei. With changes in the Gibbs free energy barrier, nucleation behaviors, such as the nucleation rate and the critical radius of the nuclei, showed temperature-dependent characteristics that were different from those predicted by classical nucleation theory. The temperature-dependent surface energy density of a nucleus was deduced based on our theoretical model. The agreement between the theoretical and experimental results suggested that the developed nucleation theory has the potential to contribute to the understanding and design of heterogeneous nucleation at the nanoscale.

  11. Multi-Relaxation Temperature-Dependent Dielectric Model of the Arctic Soil at Positive Temperatures

    NASA Astrophysics Data System (ADS)

    Savin, I. V.; Mironov, V. L.

    2014-11-01

    Frequency spectra of the dielectric permittivity of the Arctic soil of Alaska are investigated with allowance for the dipole and ionic relaxation of molecules of the soil moisture at frequencies from 40 MHz to 16 GHz and temperatures from -5 to +25°С. A generalized temperature-dependent multi-relaxation refraction dielectric model of the humid Arctic soil is suggested.

  12. Temperature-dependent internal photoemission probe for band parameters

    NASA Astrophysics Data System (ADS)

    Lao, Yan-Feng; Perera, A. G. Unil

    2012-11-01

    The temperature-dependent characteristic of band offsets at the heterojunction interface was studied by an internal photoemission (IPE) method. In contrast to the traditional Fowler method independent of the temperature (T), this method takes into account carrier thermalization and carrier/dopant-induced band-renormalization and band-tailing effects, and thus measures the band-offset parameter at different temperatures. Despite intensive studies in the past few decades, the T dependence of this key band parameter is still not well understood. Re-examining a p-type doped GaAs emitter/undoped AlxGa1-xAs barrier heterojunction system disclosed its previously ignored T dependency in the valence-band offset, with a variation up to ˜-10-4 eV/K in order to accommodate the difference in the T-dependent band gaps between GaAs and AlGaAs. Through determining the Fermi energy level (Ef), IPE is able to distinguish the impurity (IB) and valence bands (VB) of extrinsic semiconductors. One important example is to determine Ef of dilute magnetic semiconductors such as GaMnAs, and to understand whether it is in the IB or VB.

  13. Temperature dependence of the scanning performance of an electrostatic microscanner

    NASA Astrophysics Data System (ADS)

    Ishikawa, Noriaki; Ikeda, Kentaro; Sawada, Renshi

    2016-03-01

    An optical microscanner is one examples of an optical-MEMS device, which scans a laser beam across one or two dimensions by reflecting it. The microscanner has a range of applications, such as laser printers, laser displays and bio-medical imaging. For each application, the mirror is required to oscillated at a certain frequency and optical scan angle. However, its scanning performance varies with temperature. To address this issue, the temperature dependence of the natural frequency of a 1D electrostatic microscanner formed of single-crystal silicon is investigated both theorectically and experimentally in this paper. As the temperature rises from 30 °C to 80 °C, the calculated value of the natural frequency decreased from 1910.81 Hz to 1908.68 Hz, and the experimental value decreased from 2123.85 Hz to 2120.56 Hz. The percentage changes in calculated and experimental results were  -0.11% and  -0.15%, and thus the former was consistent with the latter. The factors of the variation of natural frequency are the deformation caused by thermal expansion and the temperature dependence of shear modulus. The results of theoretical calculations indicated that the principal factor in the change of natural frequency was the shear modulus on the temperature.

  14. The mass and speed dependence of meteor air plasma temperatures

    NASA Technical Reports Server (NTRS)

    Jenniskens, Peter; Laux, Christophe O.; Wilson, Michael A.; Schaller, Emily L.

    2004-01-01

    The speed and mass dependence of meteor air plasma temperatures is perhaps the most important data needed to understand how small meteoroids chemically change the ambient atmosphere in their path and enrich the ablated meteoric organic matter with oxygen. Such chemistry can play an important role in creating prebiotic compounds. The excitation conditions in various air plasma emissions were measured from high-resolution optical spectra of Leonid storm meteors during NASA's Leonid Multi-Instrument Aircraft Campaign. This was the first time a sufficient number and range of temperature measurements were obtained to search for meteoroid mass and speed dependencies. We found slight increases in temperature with decreasing altitude, but otherwise nearly constant values for meteoroids with speeds between 35 and 72 km/s and masses between 10(-5) g and 1 g. We conclude that faster and more massive meteoroids produce a larger emission volume, but not a higher air plasma temperature. We speculate that the meteoric plasma may be in multiphase equilibrium with the ambient atmosphere, which could mean lower plasma temperatures in a CO(2)-rich early Earth atmosphere.

  15. Temperature-dependent dielectric properties of a thermoplastic gelatin

    NASA Astrophysics Data System (ADS)

    Landi, Giovanni; Neitzert, Heinz C.; Sorrentino, Andrea

    2016-05-01

    The frequency and the temperature dependence of the dielectric properties of a thermoplastic gelatin based bio-material have been investigated. At lower frequencies the dielectric response is strongly affected by charge carrier accumulation at the electrodes which modifies the dominating hopping conduction mechanism. The variation of the ac conductivity with frequency obeys a Jonscher type power law except for a small deviation in the low frequency range due to the electrode polarization effect. The master curve of the ac conductivity data shows that the conductivity relaxation of the gelatin is temperature independent.

  16. Temperature dependent stability model for graphene nanoribbon interconnects

    NASA Astrophysics Data System (ADS)

    Chanu, Waikhom Mona; Das, Debaprasad

    2016-04-01

    In this paper, a temperature dependent equivalent circuit model for graphene nanoribbon (GNR) interconnects is proposed. The stability analysis of GNR interconnects is performed using this proposed model and its performance is compared with respect to that of the copper based interconnects. The analysis is performed for different interconnect systems for 16nm ITRS technology node. With increase in the length of interconnects, the relative stability increases. GNR interconnect shows less increase of resistance with the increase in temperature as compared to Cu interconnects.

  17. Temperature dependence of the absorption edge of vitreous silica

    NASA Technical Reports Server (NTRS)

    Bates, C. W., Jr.

    1976-01-01

    During an investigation of the optical properties of high-purity vitreous silica (fused quartz), which is being developed by NASA as a reflective and ablative heat shield, some interesting properties of theoretical and experimental nature have become apparent which otherwise may have remained unnoticed. Of particular interest for the NASA application is the shift of the absorption edge toward longer wavelengths with increasing temperature. The results of studies of this shift and of the spectral dependence of the absorption edge are summarized in the present paper. Plots of the absorption edge and the absorption spectrum of fused quartz vs temperature are given and discussed.

  18. A temperature dependent SPICE macro-model for power MOSFETs

    SciTech Connect

    Pierce, D.G.

    1992-05-01

    A power MOSFET macro-model for use with the circuit simulator SPICE has been developed suitable for use over the temperature range of {minus}55 to 125{degrees}C. The model is comprised of a single parameter set with the temperature dependence accessed through the SPICE TEMP card. This report describes in detail the development of the model and the extraction algorithms used to obtain model parameters. The extraction algorithms are described in sufficient detail to allow for automated measurements which in turn allows for rapid and cost effective development of an accurate SPICE model for any power MOSFET. 22 refs.

  19. Microarray study of temperature-dependent sensitivity and selectivity of metal/oxide sensing interfaces

    NASA Astrophysics Data System (ADS)

    Tiffany, Jason; Cavicchi, Richard E.; Semancik, Stephen

    2001-02-01

    Conductometric gas microsensors offer the benefits of ppm-level sensitivity, real-time data, simple interfacing to electronics hardware, and low power consumption. The type of device we have been exploring consists of a sensor film deposited on a "microhotplate"- a 100 micron platform with built-in heating (to activate reactions on the sensing surface) and thermometry. We have been using combinatorial studies of 36-element arrays to characterize the relationship between sensor film composition, operating temperature, and response, as measured by the device's sensitivity and selectivity. Gases that have been tested on these arrays include methanol, ethanol, dichloromethane, propane, methane, acetone, benzene, hydrogen, and carbon monoxide, and are of interest in the management of environmental waste sites. These experiments compare tin oxide films modified by catalyst overlayers, and ultrathin metal seed layers. The seed layers are used as part of a chemical vapor deposition process that uses each array element's microheater to activate the deposition of SnO2, and control its microstructure. Low coverage (20 Ê) catalytic metals (Pd, Cu, Cr, In, Au) are deposited on the oxides by masked evaporation or sputtering. This presentation demonstrates the value of an array-based approach for developing film processing methods, measuring performance characteristics, and establishing reproducibility. It also illustrates how temperature-dependent response data for varied metal/oxide compositions can be used to tailor a microsensor array for a given application.

  20. Temperature dependence of predation depends on the relative performance of predators and prey

    PubMed Central

    Öhlund, Gunnar; Hedström, Per; Norman, Sven; Hein, Catherine L.; Englund, Göran

    2015-01-01

    The temperature dependence of predation rates is a key issue for understanding and predicting the responses of ecosystems to climate change. Using a simple mechanistic model, we demonstrate that differences in the relative performances of predator and prey can cause strong threshold effects in the temperature dependence of attack rates. Empirical data on the attack rate of northern pike (Esox lucius) feeding on brown trout (Salmo trutta) confirm this result. Attack rates fell sharply below a threshold temperature of +11°C, which corresponded to a shift in relative performance of pike and brown trout with respect to maximum attack and escape swimming speeds. The average attack speed of pike was an order of magnitude lower than the escape speed of brown trout at 5°C, but approximately equal at temperatures above 11°C. Thresholds in the temperature dependence of ecological rates can create tipping points in the responses of ecosystems to increasing temperatures. Thus, identifying thresholds is crucial when predicting future effects of climate warming. PMID:25473013

  1. Temperature dependence of carrier capture by defects in gallium arsenide

    SciTech Connect

    Wampler, William R.; Modine, Normand A.

    2015-08-01

    This report examines the temperature dependence of the capture rate of carriers by defects in gallium arsenide and compares two previously published theoretical treatments of this based on multi phonon emission (MPE). The objective is to reduce uncertainty in atomistic simulations of gain degradation in III-V HBTs from neutron irradiation. A major source of uncertainty in those simulations is poor knowledge of carrier capture rates, whose values can differ by several orders of magnitude between various defect types. Most of this variation is due to different dependence on temperature, which is closely related to the relaxation of the defect structure that occurs as a result of the change in charge state of the defect. The uncertainty in capture rate can therefore be greatly reduced by better knowledge of the defect relaxation.

  2. Intermittent chaos in the Bray-Liebhafsky oscillator. Temperature dependence.

    PubMed

    Bubanja, I N; Maćešić, S; Ivanović-Šašić, A; Čupić, Ž; Anić, S; Kolar-Anić, Lj

    2016-03-30

    Intermittent oscillations as a chaotic mixture of large amplitude relaxation oscillations, grouped in bursts and small-amplitude sinusoidal ones or even quiescent parts between them known as gaps, were found and examined in the Bray-Liebhafsky (BL) reaction performed in CSTR under controlled temperature variations. They were obtained in a narrow temperature range from 61.0 °C to 63.1 °C, where 61.0 °C is the critical temperature for burst emergence from the stable steady state and 63.1 °C is the critical temperature for gap emergence from regular oscillations. Since intermittencies appear gradually from the regular oscillatory state, and no hysteresis was obtained with decreasing/increasing temperature in the vicinity of these two bifurcations, a linear relationship between (τB/τ)(2) and (τG/τ)(2) (where τB, τG and τ denotes duration of bursts, gaps, and whole experiment, respectively), as a function of the temperature as the control parameter, was expected and obtained. Although these intermittent oscillations are chaotic with respect to the lengths of individual gaps as well as bursts, their deterministic behavior related to temperature was additionally established. Thus, the number of bursts or gaps per unit of time (NB/τ and NG/τ) has the form of a normal distribution function over the temperature range in the region where intermittencies are obtained. Temperature dependence of the Lyapunov exponents was also described by a function of the normal distribution form. Hence, we established some regularities in the chaotic behavior of intermittent oscillations that are common in life but difficult for determinations. PMID:27001164

  3. Temperature-dependent piezoresistivity in an MWCNT/epoxy nanocomposite temperature sensor with ultrahigh performance.

    PubMed

    Alamusi; Li, Yuan; Hu, Ning; Wu, Liangke; Yuan, Weifeng; Peng, Xianghe; Gu, Bin; Chang, Christiana; Liu, Yaolu; Ning, Huiming; Li, Jinhua; Surina; Atobe, Satoshi; Fukunaga, Hisao

    2013-11-15

    A temperature sensor was fabricated from a polymer nanocomposite with multi-walled carbon nanotube (MWCNT) as nanofiller (i.e., MWCNT/epoxy). The electrical resistance and temperature coefficient of resistance (TCR) of the temperature sensor were characterized experimentally. The effects of temperature (within the range 333-373 K) and MWCNT content (within the range 1-5 wt%) were investigated thoroughly. It was found that the resistance increases with increasing temperature and decreasing MWCNT content. However, the resistance change ratio related to the TCR increases with increasing temperature and MWCNT content. The highest value of TCR (0.021 K(-1)), which was observed in the case of 5 wt% MWCNT, is much higher than those of traditional metals and MWCNT-based temperature sensors. Moreover, the corresponding numerical simulation-conducted to explain the above temperature-dependent piezoresistivity of the nanocomposite temperature sensor-indicated the key role of a temperature-dependent tunneling effect. PMID:24121656

  4. Temperature-Dependent Conformations of Model Viscosity Index Improvers

    SciTech Connect

    Ramasamy, Uma Shantini; Cosimbescu, Lelia; Martini, Ashlie

    2015-05-01

    Lubricants are comprised of base oils and additives where additives are chemicals that are deliberately added to the oil to enhance properties and inhibit degradation of the base oils. Viscosity index (VI) improvers are an important class of additives that reduce the decline of fluid viscosity with temperature [1], enabling optimum lubricant performance over a wider range of operating temperatures. These additives are typically high molecular weight polymers, such as, but not limited to, polyisobutylenes, olefin copolymer, and polyalkylmethacrylates, that are added in concentrations of 2-5% (w/w). Appropriate polymers, when dissolved in base oil, expand from a coiled to an uncoiled state with increasing temperature [2]. The ability of VI additives to increase their molar volume and improve the temperature-viscosity dependence of lubricants suggests there is a strong relationship between molecular structure and additive functionality [3]. In this work, we aim to quantify the changes in polymer size with temperature for four polyisobutylene (PIB) based molecular structures at the nano-scale using molecular simulation tools. As expected, the results show that the polymers adopt more conformations at higher temperatures, and there is a clear indication that the expandability of a polymer is strongly influenced by molecular structure.

  5. Temperature dependent bacteriophages of a tropical bacterial pathogen

    PubMed Central

    Shan, Jinyu; Korbsrisate, Sunee; Withatanung, Patoo; Adler, Natalie Lazar; Clokie, Martha R. J.; Galyov, Edouard E.

    2014-01-01

    There is an increasing awareness of the multiple ways that bacteriophages (phages) influence bacterial evolution, population dynamics, physiology, and pathogenicity. By studying a novel group of phages infecting a soil borne pathogen, we revealed a paradigm shifting observation that the phages switch their lifestyle according to temperature. We sampled soil from an endemic area of the serious tropical pathogen Burkholderia pseudomallei, and established that podoviruses infecting the pathogen are frequently present in soil, and many of them are naturally occurring variants of a common virus type. Experiments on one phage in the related model B. thailandensis demonstrated that temperature defines the outcome of phage-bacteria interactions. At higher temperatures (37°C), the phage predominantly goes through a lytic cycle, but at lower temperatures (25°C), the phage remains temperate. This is the first report of a naturally occurring phage that follows a lytic or temperate lifestyle according to temperature. These observations fundamentally alter the accepted views on the abundance, population biology and virulence of B. pseudomallei. Furthermore, when taken together with previous studies, our findings suggest that the phenomenon of temperature dependency in phages is widespread. Such phages are likely to have a profound effect on bacterial biology, and on our ability to culture and correctly enumerate viable bacteria. PMID:25452746

  6. Temperature Dependence of Smectic Liquid Crystals Mixed With Magnetic Nanoparticles

    NASA Astrophysics Data System (ADS)

    Taylor, Jefferson W.; Kurihara, Lynn K.; Martinez-Miranda, Luz J.

    2012-02-01

    We investigate the properties of bulk liquid crystal mixed with a magnetic nanoparticle (CoFe) as a function of temperature. We compare our results to those of a heat capacity measurement of Cordoyiannis et al.ootnotetextGeorge Cordoyiannis, Lynn K. Kurihara, Luz J. Martinez-Miranda, Christ Glorieux, and Jan Thoen, Phys. Rev. E 79, 011702 (2009) and compare the way the smectic as a function of temperature the way the nematic behaves. We study how the liquid crystal reorganizes in the presence of the functionalized nanoparticles as a function of temperature and compare it to how it behaves at room temperature.ootnotetextL. J. Mart'inez-Miranda, and Lynn Kurihara, J. Appl. Phys, 105, p. 084305 (2009). The X-rays give rise to three or four peaks whose evolution in temperature varies depending on their origin. In particular the second peak does not seem to vary much with temperature, and can be associated with the first several molecular layers attached to the nanoparticles.

  7. MD Study of Stokes Shifts in Ionic Liquids: Temperature Dependence.

    PubMed

    Wu, Eric C; Kim, Hyung J

    2016-05-26

    Effects of temperature on Stokes shifts, solvation structure, and dynamics in ionic liquids EMI(+)Tf2N(-), EMI(+)PF6(-), and BMI(+)PF6(-) (EMI(+) = 1-ethyl-3-methylimidazolium, BMI(+) = 1-butyl-3-methylimidazolium, Tf2N(-) = bis(trifluoromethylsulfonyl)imide, and PF6(-) = hexafluorophosphate) are investigated via molecular dynamics (MD) computer simulations in the temperature range 350 K ≤ T ≤ 500 K. Two different types of solutes are considered: a simple model diatomic solute and realistic coumarin 153, both of which are characterized by more polar S1 and less polar S0 states. In all three ionic liquids studied, the Stokes shift tends to decrease with increasing temperature. For coumarin 153, as T increases, the Franck-Condon energy for steady-state absorption decreases, whereas that for steady-state emission increases. Our findings indicate that the effective polarity of ionic liquids decreases as T increases. Their solvation dynamics are characterized by an ultrafast initial decay in the subpicosecond time scale, followed by slow dissipative relaxation, regardless of temperature. For both solutes, the solvent frequency that quantifies initial ultrafast dynamics shows little temperature dependence. By contrast, the long-time dissipative dynamics become significantly faster with rising T. Variations of solvation structure with temperature and their connection to Stokes shift and solvation dynamics are briefly examined. PMID:27133895

  8. Temperature dependence of relaxation times and temperature mapping in ultra-low-field MRI

    NASA Astrophysics Data System (ADS)

    Vesanen, Panu T.; Zevenhoven, Koos C. J.; Nieminen, Jaakko O.; Dabek, Juhani; Parkkonen, Lauri T.; Ilmoniemi, Risto J.

    2013-10-01

    Ultra-low-field MRI is an emerging technology that allows MRI and NMR measurements in microtesla-range fields. In this work, the possibilities of relaxation-based temperature measurements with ultra-low-field MRI were investigated by measuring T1 and T2 relaxation times of agarose gel at 50 μT-52 mT and at temperatures 5-45 °C. Measurements with a 3 T scanner were made for comparison. The Bloembergen-Purcell-Pound relaxation theory was combined with a two-state model to explain the field-strength and temperature dependence of the data. The results show that the temperature dependencies of agarose gel T1 and T2 in the microtesla range differ drastically from those at 3 T; the effect of temperature on T1 is reversed at approximately 5 mT. The obtained results were used to reconstruct temperature maps from ultra-low-field scans. These time-dependent temperature maps measured from an agarose gel phantom at 50 μT reproduced the temperature gradient with good contrast.

  9. Temperature dependence of the Soret coefficient of ionic colloids.

    PubMed

    Sehnem, A L; Figueiredo Neto, A M; Aquino, R; Campos, A F C; Tourinho, F A; Depeyrot, J

    2015-10-01

    The temperature dependence of the Soret coefficient S(T)(T) in electrostatically charged magnetic colloids is investigated. Two different ferrofluids, with different particles' mean dimensions, are studied. In both cases we obtain a thermophilic behavior of the Soret effect. The temperature dependence of the Soret coefficient is described assuming that the nanoparticles migrate along the ionic thermoelectric field created by the thermal gradient. A model based on the contributions from the thermoelectrophoresis and variation of the double-layer energy, without fitting parameters, is used to describe the experimental results of the colloid with the bigger particles. To do so, independent measurements of the ζ potential, mass diffusion coefficient, and Seebeck coefficient are performed. The agreement of the theory and the experimental results is rather good. In the case of the ferrofluid with smaller particles, it is not possible to get experimentally reliable values of the ζ potential and the model described is used to evaluate this parameter and its temperature dependence. PMID:26565244

  10. Temperature dependence of hydrogenated amorphous silicon solar cell performances

    NASA Astrophysics Data System (ADS)

    Riesen, Y.; Stuckelberger, M.; Haug, F.-J.; Ballif, C.; Wyrsch, N.

    2016-01-01

    Thin-film hydrogenated amorphous silicon solar (a-Si:H) cells are known to have better temperature coefficients than crystalline silicon cells. To investigate whether a-Si:H cells that are optimized for standard conditions (STC) also have the highest energy yield, we measured the temperature and irradiance dependence of the maximum power output (Pmpp), the fill factor (FF), the short-circuit current density (Jsc), and the open-circuit voltage (Voc) for four series of cells fabricated with different deposition conditions. The parameters varied during plasma-enhanced chemical vapor deposition (PE-CVD) were the power and frequency of the PE-CVD generator, the hydrogen-to-silane dilution during deposition of the intrinsic absorber layer (i-layer), and the thicknesses of the a-Si:H i-layer and p-type hydrogenated amorphous silicon carbide layer. The results show that the temperature coefficient of the Voc generally varies linearly with the Voc value. The Jsc increases linearly with temperature mainly due to temperature-induced bandgap reduction and reduced recombination. The FF temperature dependence is not linear and reaches a maximum at temperatures between 15 °C and 80 °C. Numerical simulations show that this behavior is due to a more positive space-charge induced by the photogenerated holes in the p-layer and to a recombination decrease with temperature. Due to the FF(T) behavior, the Pmpp (T) curves also have a maximum, but at a lower temperature. Moreover, for most series, the cells with the highest power output at STC also have the best energy yield. However, the Pmpp (T) curves of two cells with different i-layer thicknesses cross each other in the operating cell temperature range, indicating that the cell with the highest power output could, for instance, have a lower energy yield than the other cell. A simple energy-yield simulation for the light-soaked and annealed states shows that for Neuchâtel (Switzerland) the best cell at STC also has the best energy

  11. Temperature Dependence of Rabi Oscillations in Phase Qubits

    NASA Astrophysics Data System (ADS)

    Ustinov, Alexey; Lisenfeld, Juergen; Wirth, Tobias; Feofanov, Alexey; Lukashenko, Alexander

    2007-03-01

    Using the experimental setup in Erlangen, we compared aluminum-based phase qubits with SiNx shunting capacitors made at UCSB with similarly designed circuits fabricated at HYPRES foundry using a standard niobium-based fabrication process with SiO2 insulation. Measured decoherence times are about 100 ns and 5 ns, respectively. In both types of circuits, energy relaxation time T1 scales inversely proportional to the area of the qubit junction, which agrees with earlier data. Rabi oscillations remain visible up to the temperature T of about 400 mK (UCSB) and 800 mK (HYPRES), where the energy level separation becomes comparable with kBT. The current pulse readout in the upper temperature range is dominated by thermal escape rather then tunneling. Temperature dependence data for the decoherence time and oscillations contrast will be presented and discussed.

  12. Temperature dependence of the properties of vapor-deposited polyimide

    NASA Astrophysics Data System (ADS)

    Tsai, F. Y.; Blanton, T. N.; Harding, D. R.; Chen, S. H.

    2003-04-01

    The Young's modulus and helium gas permeability of vapor-deposited poly(4,4'-oxydiphenylenepyromellitimide) were measured at cryogenic and elevated temperatures (10-573 K). The Young's modulus decreased with increasing temperature from 5.5 GPa at 10 K to 1.8 GPa at 573 K. The temperature dependency of the permeability followed the Arrhenius' relationship, with different activation energy for permeation for samples imidized under different conditions. The effect of the imidization conditions on the permeation properties could be explained in terms of morphology/crystallinity as determined by x-ray diffraction techniques. Imidizing in air instead of nitrogen increased the permeability while lowering the activation energy for permeation and crystallinity. Imidizing at higher heating rates (in nitrogen) resulted in higher permeability, lower activation energy for permeation, and larger and fewer crystallites with better-aligned lattice planes.

  13. Temperature dependent equation of state for HMX-based composites

    NASA Astrophysics Data System (ADS)

    Baer, Melvin; Root, S.; Gustavsen, R. L.; Pierce, T.; DeFisher, S.; Travers, B.

    2012-03-01

    In order to examine the temperature dependence of the equation of state (EOS) of HMXbased explosives, two energetic composites, PBX9501 and PBXN9, were subjected to shockless compression using the Sandia VELOCE magnetic compression system. Prior to compression, the energetic samples were heated to temperatures up to 155°C, presumed to be below the HMX β - δ phase transition at atmospheric pressure conditions. A Velocity Interferometer System for Any Reflector (VISAR) was used to measure particle velocity of the transmitted compression wave. Temperature corrections in the drive plates and windows were estimated and velocity profile data was analyzed using forward/backward integration methods along with an optimization method to determine unreacted Mie-Grüneisen EOS parameters.

  14. Pressure dependence of the melting temperature of metals

    NASA Technical Reports Server (NTRS)

    Schlosser, Herbert; Vinet, Pascal; Ferrante, John

    1989-01-01

    A new method for the analysis of the experimental data for the pressure dependence of the melting temperature of metals is presented. The method combines Lindemann's law, the Debye model, and a first-order equation of state with the experimental observation that the Grueneisen parameter divided by the volume is constant. It is observed that, based on these assumptions, in the absence of phase transitions, plots of the logarithm of the normalized melting temperature versus the logarithm of the normalized pressure are straight lines. It is found that the normalized-melting--temperature versus normalized-pressure curves accurately satisfy the linear relationship for Al, Ag, Au, Cs, Cu, K, Na, Pt, and Rb. In addition, this technique provides a sensitive tool for detecting phase transitions.

  15. Temperature dependence of charge transport in conjugated single molecule junctions

    NASA Astrophysics Data System (ADS)

    Huisman, Eek; Kamenetska, Masha; Venkataraman, Latha

    2011-03-01

    Over the last decade, the break junction technique using a scanning tunneling microscope geometry has proven to be an important tool to understand electron transport through single molecule junctions. Here, we use this technique to probe transport through junctions at temperatures ranging from 5K to 300K. We study three amine-terminated (-NH2) conjugated molecules: a benzene, a biphenyl and a terphenyl derivative. We find that amine groups bind selectively to undercoordinate gold atoms gold all the way down to 5K, yielding single molecule junctions with well-defined conductances. Furthermore, we find that the conductance of a single molecule junction increases with temperature and we present a mechanism for this temperature dependent transport result. Funded by a Rubicon Grant from The Netherlands Organisation for Scientific Research (NWO) and the NSEC program of NSF under grant # CHE-0641523.

  16. Temperature-dependent particle-number projected moment of inertia

    SciTech Connect

    Allal, N. H.; Fellah, M.; Benhamouda, N.; Oudih, M. R.

    2008-05-15

    Expressions of the parallel and perpendicular temperature-dependent particle-number projected nuclear moment of inertia have been established by means of a discrete projection method. They generalize that of the FTBCS method and are well adapted to numerical computation. The effects of particle-number fluctuations have been numerically studied for some even-even actinide nuclei by using the single-particle energies and eigenstates of a deformed Woods-Saxon mean field. It has been shown that the parallel moment of inertia is practically not modified by the use of the projection method. In contrast, the discrepancy between the projected and FTBCS perpendicular moment of inertia values may reach 5%. Moreover, the particle-number fluctuation effects vary not only as a function of the temperature but also as a function of the deformation for a given temperature. This is not the case for the system energy.

  17. Temperature Dependent Cyclic Deformation Mechanisms in Haynes 188 Superalloy

    NASA Technical Reports Server (NTRS)

    Rao, K. Bhanu Sankara; Castelli, Michael G.; Allen, Gorden P.; Ellis, John R.

    1995-01-01

    The cyclic deformation behavior of a wrought cobalt-base superalloy, Haynes 188, has been investigated over a range of temperatures between 25 and 1000 C under isothermal and in-phase thermomechanical fatigue (TMF) conditions. Constant mechanical strain rates (epsilon-dot) of 10(exp -3)/s and 10(exp -4)/s were examined with a fully reversed strain range of 0.8%. Particular attention was given to the effects of dynamic strain aging (DSA) on the stress-strain response and low cycle fatigue life. A correlation between cyclic deformation behavior and microstructural substructure was made through detailed transmission electron microscopy. Although DSA was found to occur over a wide temperature range between approximately 300 and 750 C the microstructural characteristics and the deformation mechanisms responsible for DSA varied considerably and were dependent upon temperature. In general, the operation of DSA processes led to a maximum of the cyclic stress amplitude at 650 C and was accompanied by pronounced planar slip, relatively high dislocation density, and the generation of stacking faults. DSA was evidenced through a combination of phenomena, including serrated yielding, an inverse dependence of the maximum cyclic hardening with epsilon-dot, and an instantaneous inverse epsilon-dot sensitivity verified by specialized epsilon-dot -change tests. The TMF cyclic hardening behavior of the alloy appeared to be dictated by the substructural changes occuring at the maximum temperature in the TMF cycle.

  18. Temperature dependence of DNA translocations through solid-state nanopores

    PubMed Central

    Verschueren, Daniel V.; Jonsson, Magnus P.; Dekker, Cees

    2015-01-01

    In order to gain a better physical understanding of DNA translocations through solid-state nanopores, we study the temperature dependence of λ-DNA translocations through 10 nm-in-diameter silicon-nitride nanopores, both experimentally and theoretically. The measured ionic conductance G, the DNA-induced ionic-conductance blockades ΔG and the event frequency Γ all increase with increasing temperature while the DNA translocation time τ decreases. G and ΔG are accurately described when bulk and surface conductances of the nanopore are considered and access resistance is incorporated appropriately. Viscous drag on the untranslocated part of the DNA coil is found to dominate the temperature dependence of the translocation times and the event rate is well described by a balance between diffusion and electrophoretic motion. The good fit between modeled and measured properties of DNA translocations through solid-state nanopores in this first comprehensive temperature study, suggest that our model captures the relevant physics of the process. PMID:25994084

  19. Temperature and polarization dependence of photoluminescence in monolayer tungsten diselenide

    NASA Astrophysics Data System (ADS)

    Huang, Jiani; Hoang, Thang; Mikkelsen, Maiken

    2015-03-01

    Two-dimensional transition metal dichalcogenides (TMDCs) have recently attracted considerable research interest, due to their wide direct band-gaps, strong spin-orbit couplings and inversion symmetry breaking when compared to graphene. These properties have rich physics and applications in electronics, optics and spintronics. Here, we experimentally study the evolution of photoluminescence (PL) from mechanically exfoliated monolayer tungsten diselenide (WSe2) from T = 10 K to room temperature. At T = 10 K , we observe a clear free exciton (X0) emission at 1.75 eV together with a charged trion emission at 1.72 eV, yielding a trion binding energy of 30 meV. Temperature dependent PL measurements show that both the free exciton and trion exist up to room temperature, as a result of the large exciton (~370 meV) and trion binding energies of WSe2, while other localized and defect-related emission peaks vanish above T = 65 K . Temperature dependent polarization of the exciton and trion emisisons reveal a combined effect of large exciton binding energy, anisotropic thermal expansion and exciton-phonon interaction. These findings may provide a new platform to explore the valley polarization and valley-spin coupling in monolayer TMDCs.

  20. Temperature-dependent mechanics in suspended graphene systems

    NASA Astrophysics Data System (ADS)

    Storch, Isaac Robert

    Graphene is an atomically thin material with unique electrical, optical, and mechanical properties. In this thesis, we explore some of the interesting temperature-dependent mechanics of graphene membranes. We start by presenting the typical mechanical theory used by experimentalists to model a suspended graphene membrane in the presence of an electrostatic force, and we expand it to account for various effects, such as slack, capacitive softening, and dynamic changes in tension. We also perform finite element analysis using COMSOL Multiphysics software and compare the results with the analytic solution. Then, we show how to use the transfer matrix technique to model graphene optically as an infinitesimal conducting boundary. We solve for the reflectance of a graphene sheet parallel to a perfect mirror, which is important for measurements using optical detection. Next, we summarize the first measurement of photothermal optomechanics in graphene resonators, demonstrate both self-oscillation and cooling, and develop a theory to predict the optomechanical spring constant induced by photothermal forces. Finally, we develop an optical technique for sensing the static deflection of a graphene membrane and use it to measure the temperature dependence of the Young's modulus of graphene for the first time. We find that the room temperature modulus is much softer than expected from thermal rippling theories, but it stiffens significantly at low temperature.

  1. Effect of solvent strength and temperature on retention for a polar-endcapped, octadecylsiloxane-bonded silica stationary phase with methanol-water mobile phases.

    PubMed

    Kiridena, Waruna; Poole, Colin F; Koziol, Wladyslaw W

    2004-12-10

    Synergi Hydro-RP is a new type of polar-endcapped, octadecylsiloxane-bonded silica packing for reversed-phase liquid chromatography. Its retention properties as a function of solvent strength and temperature are evaluated from the change in retention factors over the composition range (0-70% v/v methanol) and temperature range (25-65 degrees C) using the solvation parameter model and response surface methodologies. The main factors that affect retention are solute size and hydrogen-bond basicity, with minor contributions from solute hydrogen-bond acidity, dipole-type and electron lone pair interactions. Within the easily accessible range for both temperature and solvent strength, the ability to change selectivity is much greater for solvent strength than temperature. Also, a significant portion of the effect of increasing temperature is to reduce retention without changing selectivity. Response surfaces for the system constants are smooth and non-linear, except for cavity formation and dispersion interactions (v system constant), which is linear. Modeling of the response surfaces suggests that solvent strength and temperature are not independent factors for the b, s and e system constants and for the model intercept (c term). PMID:15628160

  2. Temperature dependent deformation mechanisms in pure amorphous silicon

    SciTech Connect

    Kiran, M. S. R. N. Haberl, B.; Williams, J. S.; Bradby, J. E.

    2014-03-21

    High temperature nanoindentation has been performed on pure ion-implanted amorphous silicon (unrelaxed a-Si) and structurally relaxed a-Si to investigate the temperature dependence of mechanical deformation, including pressure-induced phase transformations. Along with the indentation load-depth curves, ex situ measurements such as Raman micro-spectroscopy and cross-sectional transmission electron microscopy analysis on the residual indents reveal the mode of deformation under the indenter. While unrelaxed a-Si deforms entirely via plastic flow up to 200 °C, a clear transition in the mode of deformation is observed in relaxed a-Si with increasing temperature. Up to 100 °C, pressure-induced phase transformation and the observation of either crystalline (r8/bc8) end phases or pressure-induced a-Si occurs in relaxed a-Si. However, with further increase of temperature, plastic flow rather than phase transformation is the dominant mode of deformation. It is believed that the elevated temperature and pressure together induce bond softening and “defect” formation in structurally relaxed a-Si, leading to the inhibition of phase transformation due to pressure-releasing plastic flow under the indenter.

  3. Spin Hall and spin Nernst effects: temperature dependence

    NASA Astrophysics Data System (ADS)

    Dyrdal, Anna; Barnas, Jozef; Dugaev, Vitalii

    We have considered temperature dependence of spin Hall and spin Nernst effect in two-dimensional electron gas with spin-orbit interaction of Rashba type [arXiv:1510.03080]. In our considerations we have employed the approach based on the Matsubara Green functions. The formalism used in the case of electric field as a driving force was subsequently adopted to the situation of a spin current driven by a temperature gradient. To achieve this, we have used the concept of an auxiliary vector field. Such a description gives the possibility to consider all mechanisms leading to the spin Hall and spin Nernst effect on equal footing and also their behavior at finite temperatures. Both spin Hall and spin Nernst conductivities were calculated in the approximation including the vertex correction. The total spin Hall conductivity, including vertex correction, has been shown to vanish exactly in the whole temperature range. Thus, our results extend the earlier ones to an arbitrary temperatures. In turn, the total spin Nernst conductivity remains finite when the vertex corrections are included. Using the Ioffe-Regel localization criterion, we have also estimated the range of parameters where the calculated results for the spin Hall and spin Nernst conductivities are applicable.

  4. Temperature Dependent Studies of Conformational Vibrational Modes of Biological Molecules

    NASA Astrophysics Data System (ADS)

    Markelz, A. G.; Pawar, A.

    2001-03-01

    Low frequency vibrational modes of proteins are correlated to conformation and conformational change critical to biochemical activity, however direct measurements of these modes has been impeded by limitations in spectroscopic techniques. We are presently exploring the use of the high sensitivity FIR spectroscopic technique of pulsed terahertz spectroscopy to measure these modes as a function of conformational state. Initial measurements have been preformed using bovine heart cytochrome c and the chromophore of photoactive yellow protein, p-coumaric acid (PCA). We have measured the temperature dependence (77 K - 300 K) of the far infrared absorption (2-100 cm-1) using both solid state and solution samples. Sample preparation techniques to eliminate etalon in the spectra will be discussed. For cytochrome c, a distinct absorption at 10 cm-1 is seen at room temperature that narrows and slightly red shifts as the temperature decreases. For PCA, the FIR absorption remains broad at lower temperatures, with an overall increase in FIR absorption at lower temperatures. We will discuss the implications of these measurements for future studies of conformational dynamics in these proteins.

  5. Temperature-dependent emergence of Osmia cornifrons (Hymenoptera: Megachilidae) adults.

    PubMed

    White, Joseph; Son, Youngsoo; Park, Yong-Lak

    2009-12-01

    Japanese hornfaced bees Osmia cornifrons (Radoszkowski) (Hymenoptera: Megachilidae) are used for pollination of spring blooming fruit crops such as apple, pear, and blueberry. Because O. cornifrons has a short adult life span, synchronization of bee emergence with bloom is critical to maximize crop pollination. This study was conducted to determine lower temperature thresholds (LTDs), optimum temperatures, and required degree-day accumulation for emergence of O. cornifrons adults. Patterns of temperature-dependent emergence of O. cornifrons adults at seven temperatures (3.9, 12.0, 18.6, 26.6, 30.3, 35.6, and 42.5 degrees C) were modeled and simulated with linear and nonlinear regression analyses. Results of this study showed that required degree-days (DD) for emergence of male and female O. cornifrons adults were 125.2 DD, with LTD of 8.9 degrees C and 179.8 DD, with LTD of 8.6 degrees C, respectively. The optimum temperatures for emergence were 36.5, 30.2, and 35.7 degrees C for male, female, and both sexes combined, respectively. This study indicated that emergence of O. cornifrons adults could be manipulated to synchronize with pollination periods of target fruit crops. PMID:20069827

  6. Electron density and temperature of gas-temperature-dependent cryoplasma jet

    SciTech Connect

    Noma, Yuri; Hyuk Choi, Jai; Muneoka, Hitoshi; Terashima, Kazuo

    2011-03-01

    A microsize cryoplasma jet was developed and analyzed at plasma gas temperatures ranging from room temperature down to 5 K. Experimental results obtained from optical emission spectroscopy and current-voltage measurements indicate that the average electron density and electron temperature of the cryoplasma jet depend on the gas temperature. In particular, the electron temperature in the cryoplasma starts to decrease rapidly near 60 K from about 13 eV at 60 K to 2 eV at 5 K, while the electron density increases from about 10{sup 9} to approximately 10{sup 12} cm{sup -3} from room temperature to 5 K. This phenomenon induces an increase in the Coulomb interaction between electrons, which can be explained by the virial equation of state.

  7. Temperature-dependent Refractive Index of Silicon and Germanium

    NASA Technical Reports Server (NTRS)

    Frey, Bradley J.; Leviton, Douglas B.; Madison, Timothy J.

    2006-01-01

    Silicon and germanium are perhaps the two most well-understood semiconductor materials in the context of solid state device technologies and more recently micromachining and nanotechnology. Meanwhile, these two materials are also important in the field of infrared lens design. Optical instruments designed for the wavelength range where these two materials are transmissive achieve best performance when cooled to cryogenic temperatures to enhance signal from the scene over instrument background radiation. In order to enable high quality lens designs using silicon and germanium at cryogenic temperatures, we have measured the absolute refractive index of multiple prisms of these two materials using the Cryogenic, High-Accuracy Refraction Measuring System (CHARMS) at NASA's Goddard Space Flight Center, as a function of both wavelength and temperature. For silicon, we report absolute refractive index and thermo-optic coefficient (dn/dT) at temperatures ranging from 20 to 300 K at wavelengths from 1.1 to 5.6 pin, while for germanium, we cover temperatures ranging from 20 to 300 K and wavelengths from 1.9 to 5.5 microns. We compare our measurements with others in the literature and provide temperature-dependent Sellmeier coefficients based on our data to allow accurate interpolation of index to other wavelengths and temperatures. Citing the wide variety of values for the refractive indices of these two materials found in the literature, we reiterate the importance of measuring the refractive index of a sample from the same batch of raw material from which final optical components are cut when absolute accuracy greater than k5 x 10" is desired.

  8. Methanol Oxidation on Pt3Sn(111) for Direct Methanol Fuel Cells: Methanol Decomposition.

    PubMed

    Lu, Xiaoqing; Deng, Zhigang; Guo, Chen; Wang, Weili; Wei, Shuxian; Ng, Siu-Pang; Chen, Xiangfeng; Ding, Ning; Guo, Wenyue; Wu, Chi-Man Lawrence

    2016-05-18

    PtSn alloy, which is a potential material for use in direct methanol fuel cells, can efficiently promote methanol oxidation and alleviate the CO poisoning problem. Herein, methanol decomposition on Pt3Sn(111) was systematically investigated using periodic density functional theory and microkinetic modeling. The geometries and energies of all of the involved species were analyzed, and the decomposition network was mapped out to elaborate the reaction mechanisms. Our results indicated that methanol and formaldehyde were weakly adsorbed, and the other derivatives (CHxOHy, x = 1-3, y = 0-1) were strongly adsorbed and preferred decomposition rather than desorption on Pt3Sn(111). The competitive methanol decomposition started with the initial O-H bond scission followed by successive C-H bond scissions, (i.e., CH3OH → CH3O → CH2O → CHO → CO). The Brønsted-Evans-Polanyi relations and energy barrier decomposition analyses identified the C-H and O-H bond scissions as being more competitive than the C-O bond scission. Microkinetic modeling confirmed that the vast majority of the intermediates and products from methanol decomposition would escape from the Pt3Sn(111) surface at a relatively low temperature, and the coverage of the CO residue decreased with an increase in the temperature and decrease in partial methanol pressure. PMID:27119198

  9. Latitude-Dependent Temperature Variations at the Solar Limb

    NASA Astrophysics Data System (ADS)

    Fivian, M. D.; Hudson, H. S.; Lin, R. P.; Zahid, H. J.

    2009-12-01

    We use observations from the solar aspect sensor of RHESSI to characterize the latitude dependence of the temperature of the photosphere at the solar limb. Previous observations have suggested the presence of a polar temperature excess as large as 1.5 K. The RHESSI observations, made with a rotating telescope in space, have great advantages in the rejection of systematic errors in the very precise photometry required for such an observation. This photometry is differential, i.e. relative to a mean limb-darkening function. The data base consists of about 1,000 images per day from linear CCDs with 1.73 arc sec square pixels, observing a narrow band (12nm FWHM) at 670 nm. Each image shows a chord crossing the disk at a different location as the spacecraft rotates and precesses around its average solar pointing. We fit an average limb-darkening function and reassemble the residuals into synoptic maps of differential intensity variations as function of position angle. We further mask these images against SOHO/EIT 284A images in order to eliminate magnetic regions. The analysis establishes a limit on the quadrupole dependence of temperature (brightness) on position angle of 0.04 +/- 0.02 K. This results in a possible correction of our precise measurement of the solar oblateness which is smaller than its rms error of 0.14 mas.

  10. Pressure dependence of glass transition temperature of elastomeric glasses

    NASA Astrophysics Data System (ADS)

    Pae, K. D.; Tang, C.-L.; Shin, E.-S.

    1984-11-01

    The pressure dependence of the glass transition temperature Tg of two elastomers, Solithane 113 and 3,3-bis(azidomethyl)oxetane/tetrahydrofuran (BAMO/THF) has been determined, employing high-pressure differential thermal analysis (HP-DTA) and dielectric techniques, up to 8.5 kbar. The glasses of the elastomers were named the specific (or Pi glass) or the general glass depending on how the glasses were formed. A Pi glass was formed by lowering temperature under a constant pressure (Pi) and the pressure dependency of the Pi glass was determined after changing pressure only in the glassy state. The general glass consists of a series of specific glasses but the Tg is determined only at pressures under which the glass is formed. The Tg for both glasses increased with increasing pressure. However, the Tg for the Pi glass appears to level off at very high pressures while the Tg does not level off for the general glass. Thermodynamic analysis was made to show that for many general glasses dTg/dP=Δβ/(1+n)Δα holds, in which n=1 for Solithane and many other glasses. It is also shown that a modified Gibbs and DiMarzio theory can be used effectively to predict the observed experimental results.