Effects of atmospheric composition on apparent activation energy of silicate weathering: I. Model formulation

NASA Astrophysics Data System (ADS)

Kanzaki, Yoshiki; Murakami, Takashi

2018-07-01

We have developed a weathering model to comprehensively understand the determining factors of the apparent activation energy of silicate weathering in order to better estimate the silicate-weathering flux in the Precambrian. The model formulates the reaction rate of a mineral as a basis, then the elemental loss by summing the reaction rates of whole minerals, and finally the weathering flux from a given weathering profile by integrating the elemental losses along the depth of the profile. The rate expressions are formulated with physicochemical parameters relevant to weathering, including solution and atmospheric compositions. The apparent activation energies of silicate weathering are then represented by the temperature dependences of the physicochemical parameters based on the rate expressions. It was found that the interactions between individual mineral-reactions and the compositions of solution and atmosphere are necessarily accompanied by those of temperature-dependence counterparts. Indeed, the model calculates the apparent activation energy of silicate weathering as a function of the temperature dependence of atmospheric CO2 (Δ HCO2‧) . The dependence of the apparent activation energy of silicate weathering on Δ HCO2‧ may explain the empirical dependence of silicate weathering on the atmospheric composition. We further introduce a compensation law between the apparent activation energy and the pre-exponential factor to obtain the relationship between the silicate-weathering flux (FCO2), temperature and the apparent activation energy. The model calculation and the compensation law enable us to predict FCO2 as a function of temperature, once Δ HCO2‧ is given. The validity of the model is supported by agreements between the model prediction and observations of the apparent activation energy and FCO2 in the modern weathering systems. The present weathering model will be useful for the estimation of FCO2 in the Precambrian, for which Δ HCO2‧ can be deduced from the greenhouse effect of atmospheric CO2.

Temperature-independent energy expenditure in early development of the African clawed frog Xenopus laevis.

PubMed

Nagano, Yatsuhisa; Ode, Koji L

2014-08-01

The thermal dissipation of activated eggs and embryos undergoing development from cleavage to the tailbud stage of the African clawed frog Xenopus laevis was measured as a function of incubation time at temperatures ranging from T = 288.2 K to 295.2 K, using a high-precision isothermal calorimeter. A23187-mediated activation of mature eggs induced stable periodic thermal oscillations lasting for 8-34 h. The frequency agreed well with the cell cycle frequency of initial cleavages at the identical temperature. In the developing embryo, energy metabolism switches from embryonic to adult features during gastrulation. The thermal dissipation after gastrulation fit well with a single modified Avrami equation, which has been used for modeling crystal-growth. Both the oscillation frequency of the activated egg and the growth rate of the embryo strongly depend on temperature with the same apparent activation energy of approximately 87 kJ mole(-1). This result suggests that early development proceeds as a single biological time, attributable to a single metabolic rate. A temperature-independent growth curve was derived by scaling the thermogram to the biological time, indicating that the amount of energy expenditure during each developmental stage is constant over the optimal temperature range.

Arrhenius activation energy of damage to catalase during spray-drying.

PubMed

Schaefer, Joachim; Lee, Geoffrey

2015-07-15

The inactivation of catalase during spray-drying over a range of outlet gas temperatures could be closely represented by the Arrhenius equation. From this an activation energy for damage to the catalase could be calculated. The close fit to Arrhenius suggests that the thermally-induced part of inactivation of the catalase during the complex drying and particle-formation processes takes place at constant temperature. These processes are rapid compared with the residence time of the powder in the collecting vessel of the cyclone where dried catalase is exposed to a constant temperature equal to approximately the drying gas outlet temperature. A lower activation energy after spray drying with the ultrasonic nozzle was found than with the 2-fluid nozzle under otherwise identical spray drying conditions. It is feasible that the ultrasonic nozzle when mounted in the lid of the spray dryer heats up toward the drying gas inlet temperature much more that the air-cooled 2-fluid nozzle. Calculation of the Arrhenius activation energy also showed how the stabilizing efficacy of trehalose and mannitol on the catalase varies in strength across the range of drying gas inlet and outlet temperatures examined. Copyright © 2015 Elsevier B.V. All rights reserved.

Solar Cell Polymer Based Active Ingredients PPV and PCBM

NASA Astrophysics Data System (ADS)

Hardeli, H.; Sanjaya, H.; Resikarnila, R.; Nitami H, R.

2018-04-01

A polymer solar cell is a solar cell based on a polymer bulk heterojunction structure using the method of thin film, which can convert solar energy into electrical energy. Absorption of light is carried by active material layer PPV: PCBM. This study aims to make solar cells tandem and know the value of converting solar energy into electrical energy and increase the value of efficiency generated through morphological control, ie annealing temperature and the ratio of active layer mixture. The active layer is positioned above the PEDOT:PSS layer on ITO glass substrate. The characterization results show the surface morphology of the PPV:PCBM active layer is quite evenly at annealing temperature of 165 ° C. The result of conversion of electrical energy with a UV light source in annealing samples with temperature 165 ° C is 0.03 mA and voltage of 4.085 V with an efficiency of 2.61% and mixed ratio variation was obtained in comparison of P3HT: PCBM is 1: 3

Elevated Temperature Creep Deformation in Solid Solution <001> NiAL-3.6Ti Single Crystals

NASA Technical Reports Server (NTRS)

Whittenberger, J. Daniel; Noebe, Ronald D.; Darolia, Ram

2003-01-01

The 1100 to 1500 K slow plastic strain rate compressive properties of <001> oriented NiAl-3.6Ti single crystals have been measured, and the results suggests that two deformation processes exist. While the intermediate temperature/faster strain rate mechanism is uncertain, plastic flow at elevated temperature/slower strain rates in NiAl-3.6Ti appears to be controlled by solute drag as described by the Cottrell-Jaswon solute drag model for gliding b = a(sub 0)<101> dislocations. While the calculated activation energy of deformation is much higher (approximately 480 kJ/mol) than the activation energy for diffusion (approximately 290 kJ/mol) used in the Cottrell-Jaswon creep model, a forced temperature compensated - power law fit using the activation energy for diffusion was able to adequately (greater than 90%) predict the observed creep properties. Thus we conclude that the rejection of a diffusion controlled mechanism can not be simply based on a large numerical difference between the activation energies for deformation and diffusion.

Strain-rate/temperature behavior of high density polyethylene in compression

NASA Technical Reports Server (NTRS)

Clements, L. L.; Sherby, O. D.

1978-01-01

The compressive strain rate/temperature behavior of highly linear, high density polyethylene was analyzed in terms of the predictive relations developed for metals and other crystalline materials. For strains of 5 percent and above, the relationship between applied strain rate, dotted epsilon, and resulting flow stress, sigma, was found to be: dotted epsilon exp times (Q sub f/RT) = k'(sigma/sigma sub c) to the nth power; the left-hand side is the activation-energy-compensated strain rate, where Q sub f is activation energy for flow, R is gas constant, and T is temperature; k is a constant, n is temperature-independent stress exponent, and sigma/sigma sub c is structure-compensated stress. A master curve resulted from a logarithmic plot of activation-energy-compensated strain rate versus structure-compensated stress.

Estimation of shelf life of natural rubber latex exam-gloves based on creep behavior.

PubMed

Das, Srilekha Sarkar; Schroeder, Leroy W

2008-05-01

Samples of full-length glove-fingers cut from chlorinated and nonchlorinated latex medical examination gloves were aged for various times at several fixed temperatures and 25% relative humidity. Creep testing was performed using an applied stress of 50 kPa on rectangular specimens (10 mm x 8 mm) of aged and unaged glove fingers as an assessment of glove loosening during usage. Variations in creep curves obtained were compared to determine the threshold aging time when the amount of creep became larger than the initial value. These times were then used in various models to estimate shelf lives at lower temperatures. Several different methods of extrapolation were used for shelf-life estimation and comparison. Neither Q-factor nor Arrhenius activation energies, as calculated from 10 degrees C interval shift factors, were constant over the temperature range; in fact, both decreased at lower temperatures. Values of Q-factor and activation energies predicted up to 5 years of shelf life. Predictions are more sensitive to values of activation energy as the storage temperature departs from the experimental aging data. Averaging techniques for prediction of average activation energy predicted the longest shelf life as the curvature is reduced. Copyright 2007 Wiley Periodicals, Inc.

Control of electrothermal heating during regeneration of activated carbon fiber cloth.

PubMed

Johnsen, David L; Mallouk, Kaitlin E; Rood, Mark J

2011-01-15

Electrothermal swing adsorption (ESA) of organic gases generated by industrial processes can reduce atmospheric emissions and allow for reuse of recovered product. Desorption energy efficiency can be improved through control of adsorbent heating, allowing for cost-effective separation and concentration of these gases for reuse. ESA experiments with an air stream containing 2000 ppm(v) isobutane and activated carbon fiber cloth (ACFC) were performed to evaluate regeneration energy consumption. Control logic based on temperature feedback achieved select temperature and power profiles during regeneration cycles while maintaining the ACFC's mean regeneration temperature (200 °C). Energy requirements for regeneration were independent of differences in temperature/power oscillations (1186-1237 kJ/mol of isobutane). ACFC was also heated to a ramped set-point, and the average absolute error between the actual and set-point temperatures was small (0.73%), demonstrating stable control as set-point temperatures vary, which is necessary for practical applications (e.g., higher temperatures for higher boiling point gases). Additional logic that increased the maximum power application at lower ACFC temperatures resulted in a 36% decrease in energy consumption. Implementing such control logic improves energy efficiency for separating and concentrating organic gases for post-desorption liquefaction of the organic gas for reuse.

Reduced annealing temperatures in silicon solar cells

NASA Technical Reports Server (NTRS)

Weinberg, I.; Swartz, C. K.

1981-01-01

Cells irradiated to a fluence of 5x10,000,000,000,000/square cm showed short circuit current on annealing at 200 C, with complete annealing occurring at 275 C. Cells irradiated to 100,000,000,000,000/square cm showed a reduction in annealing temperature from the usual 500 to 300 C. Annealing kinetic studies yield an activation energy of (1.5 + or - 2) eV for the low fluence, low temperature anneal. Comparison with activation energies previously obtained indicate that the presently obtained activation energy is consistent with the presence of either the divacancy or the carbon interstitial carbon substitutional pair, a result which agrees with the conclusion based on defect behavior in boron-doped silicon.

Improving Models of Photosynthetic Thermal Acclimation: Which Parameters are Most Important and How Many Should Be Modified?

NASA Astrophysics Data System (ADS)

Stinziano, J. R.; Way, D.; Bauerle, W.

2017-12-01

Photosynthetic temperature acclimation could strongly affect coupled vegetation-atmosphere feedbacks in the global carbon cycle, especially as the climate warms. Thermal acclimation of photosynthesis can be modelled as changes in the parameters describing the direct effect of temperature on photosynthetic capacity (activation energy, Ea; deactivation energy, Hd; entropy parameter, ΔS) or the basal value of photosynthetic capacity (i.e. photosynthetic capacity measured at 25 °C), however the impact of acclimating these parameters (individually or in combination) on vegetative carbon gain is relatively unexplored. Here we compare the ability of 66 photosynthetic temperature acclimation scenarios to improve predictions of a spatially explicit canopy carbon flux model, MAESTRA, for eddy covariance data from a loblolly pine forest. We show that: 1) incorporating seasonal temperature acclimation of basal photosynthetic capacity improves the model's ability to capture seasonal changes in carbon fluxes; 2) multifactor scenarios of photosynthetic temperature acclimation provide minimal (if any) improvement in model performance over single factor acclimation scenarios; 3) acclimation of enzyme activation energies should be restricted to the temperature ranges of the data from which the equations are derived; and 4) model performance is strongly affected by the choice of deactivation energy. We suggest that a renewed effort be made into understanding the thermal acclimation of enzyme activation and deactivation energies across broad temperature ranges to better understand the mechanisms underlying thermal photosynthetic acclimation.

Isothermal reduction kinetics of Panzhihua ilmenite concentrate under 30vol% CO-70vol% N2 atmosphere

NASA Astrophysics Data System (ADS)

Zhang, Ying-yi; Lü, Wei; Lü, Xue-wei; Li, Sheng-ping; Bai, Chen-guang; Song, Bing; Han, Ke-xi

2017-03-01

The reduction of ilmenite concentrate in 30vol% CO-70vol% N2 atmosphere was characterized by thermogravimetric and differential thermogravimetric (TG-DTG) analysis methods at temperatures from 1073 to 1223 K. The isothermal reduction results show that the reduction process comprised two stages; the corresponding apparent activation energy was obtained by the iso-conversional and model-fitting methods. For the first stage, the effect of temperature on the conversion degree was not obvious, the phase boundary chemical reaction was the controlling step, with an apparent activation energy of 15.55-40.71 kJ·mol-1. For the second stage, when the temperatures was greater than 1123 K, the reaction rate and the conversion degree increased sharply with increasing temperature, and random nucleation and subsequent growth were the controlling steps, with an apparent activation energy ranging from 182.33 to 195.95 kJ·mol-1. For the whole reduction process, the average activation energy and pre-exponential factor were 98.94-118.33 kJ·mol-1 and 1.820-1.816 min-1, respectively.

A Role-Play to Illustrate the Energy Changes Occurring in an Exothermic Reaction.

ERIC Educational Resources Information Center

Tyas, Toby; Cabot, John

1999-01-01

Describes a role-play activity designed to help students understand the energy changes involved in an exothermic reaction by modeling the concepts of bond-breaking takes in energy, activation energy, temperature rise, and bond breaking gives out energy. (WRM)

Thermodynamics and Cation Diffusion in the Oxygen Ion Conductor Lsgm

NASA Astrophysics Data System (ADS)

Martin, M.; Schulz, O.

Perovskite type oxides based on LaGaO3 are of large technical interest because of their high oxygen-ion conductivity. Lanthanum gallate doped with Sr on A- and Mg on B-sites, La1-xSrxGa1-yMgyO3-(x+y)/2 (LSGM), reaches higher oxygen-ion conductivities than yttria-doped zirconia (YSZ). Thus LSGM represents a promising alternative for YSZ as electrolyte in solid oxide fuel cells (SOFC). Cells using thin LSGM-layers as electrolyte are expected to operate at intermediate temperatures around 700°C for more than 30000 hours without severe degradation. A potential long term degradation effect of LSGM is kinetic demixing of the electrolyte, caused by different cation diffusion coefficients. In this paper we report on experimental studies concerning the phase diagram of LSGM and the diffusion of cations. Cation self-diffusion of 139La, 84Sr and 25Mg and cation impurity diffusion of 144Nd, 89Y and 56Fe in polycrystalline LSGM samples was investigated by secondary ion mass spectrometry (SIMS) for temperatures between 900°C and 1400°C. It was found that diffusion occurs by means of bulk and grain boundaries. The bulk diffusion coefficients are similar for all cations with activation energies which are strongly dependent on temperature. At high temperatures, the activation energies are about 5 eV, while at low temperatures values of about 2 eV are found. These results are explained by a frozen in defect structure at low temperatures. This means that the observed activation energy at low temperatures represents only the migration energy of the different cations while the observed activation energy at high temperatures is the sum of the defect formation energy and the migration energy. The migration energies for all cations are nearly identical, although 139La, 84Sr and 144Nd are occupying A-sites while 25Mg and 56Fe are occupying B-sites in the perovskite-structure. To explain these experimental findings we propose a defect cluster containing cation vacancies in both the A- and the B-sublattice and anion vacancies as well.

Elevated temperature and PCO2 shift metabolic pathways in differentially oxidative tissues of Notothenia rossii.

PubMed

Strobel, Anneli; Leo, Elettra; Pörtner, Hans O; Mark, Felix C

2013-09-01

Mitochondrial plasticity plays a central role in setting the capacity for acclimation of aerobic metabolism in ectotherms in response to environmental changes. We still lack a clear picture if and to what extent the energy metabolism and mitochondrial enzymes of Antarctic fish can compensate for changing temperatures or PCO2 and whether capacities for compensation differ between tissues. We therefore measured activities of key mitochondrial enzymes (citrate synthase (CS), cytochrome c oxidase (COX)) from heart, red muscle, white muscle and liver in the Antarctic fish Notothenia rossii after warm- (7°C) and hypercapnia- (0.2kPa CO2) acclimation vs. control conditions (1°C, 0.04kPa CO2). In heart, enzymes showed elevated activities after cold-hypercapnia acclimation, and a warm-acclimation-induced upward shift in thermal optima. The strongest increase in enzyme activities in response to hypercapnia occurred in red muscle. In white muscle, enzyme activities were temperature-compensated. CS activity in liver decreased after warm-normocapnia acclimation (temperature-compensation), while COX activities were lower after cold- and warm-hypercapnia exposure, but increased after warm-normocapnia acclimation. In conclusion, warm-acclimated N. rossii display low thermal compensation in response to rising energy demand in highly aerobic tissues, such as heart and red muscle. Chronic environmental hypercapnia elicits increased enzyme activities in these tissues, possibly to compensate for an elevated energy demand for acid-base regulation or a compromised mitochondrial metabolism, that is predicted to occur in response to hypercapnia exposure. This might be supported by enhanced metabolisation of liver energy stores. These patterns reflect a limited capacity of N. rossii to reorganise energy metabolism in response to rising temperature and PCO2. © 2013.

Glass transition in thaumatin crystals revealed through temperature-dependent radiation-sensitivity measurements.

PubMed

Warkentin, Matthew; Thorne, Robert E

2010-10-01

The temperature-dependence of radiation damage to thaumatin crystals between T = 300 and 100 K is reported. The amount of damage for a given dose decreases sharply as the temperature decreases from 300 to 220 K and then decreases more gradually on further cooling below the protein-solvent glass transition. Two regimes of temperature-activated behavior were observed. At temperatures above ∼200 K the activation energy of 18.0 kJ mol(-1) indicates that radiation damage is dominated by diffusive motions in the protein and solvent. At temperatures below ∼200 K the activation energy is only 1.00 kJ mol(-1), which is of the order of the thermal energy. Similar activation energies describe the temperature-dependence of radiation damage to a variety of solvent-free small-molecule organic crystals over the temperature range T = 300-80 K. It is suggested that radiation damage in this regime is vibrationally assisted and that the freezing-out of amino-acid scale vibrations contributes to the very weak temperature-dependence of radiation damage below ∼80 K. Analysis using the radiation-damage model of Blake and Phillips [Blake & Phillips (1962), Biological Effects of Ionizing Radiation at the Molecular Level, pp. 183-191] indicates that large-scale conformational and molecular motions are frozen out below T = 200 K but become increasingly prevalent and make an increasing contribution to damage at higher temperatures. Possible alternative mechanisms for radiation damage involving the formation of hydrogen-gas bubbles are discussed and discounted. These results have implications for mechanistic studies of proteins and for studies of the protein glass transition. They also suggest that data collection at T ≃ 220 K may provide a viable alternative for structure determination when cooling-induced disorder at T = 100 is excessive.

Reliability of vapor-grown planar In/sub 0. 53/Ga/sub 0. 47/As/InP p-i-n photodiodes with very high failure activation energy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Forrest, S.R.; Ban, V.S.; Gasparian, G.

1988-05-01

The authors measured the mean time to failure (MTTF) for a statistically significant population of planar In/sub 0.53/Ga/sub 0.47/As/InP heterostructure p-i-n photodetectors at several elevated temperatures. The probability for failure is fit to a log-normal distribution, with the result that the width of the failure distribution is sigma = 0.55 +- 0.2, and is roughly independent of temperature. From the temperature dependence of the MTFF data, they find that the failure mechanism is thermally activated, with an activation energy of 1.5 +- 0.2 eV measured in the temperature range of 170 - 250/sup 0/C. This extrapolates to a MTTF ofmore » less than 0.1 failure in 10/sup 9/ h (or < 0.1 FIT) at 70/sup 0/C, indicating that such devices are useful for systems requiring extremely high reliable components, even if operated at elevated temperatures for significant time periods. To the authors' knowledge, this activation energy is the highest value reported for In/sub 0.53/Ga/sub 0.47/As/InP photodetectors, and is significantly higher than the energies of -- 0.85 eV often suspected to these devices.« less

An activated energy approach for accelerated testing of the deformation of UHMWPE in artificial joints.

PubMed

Galetz, Mathias Christian; Glatzel, Uwe

2010-05-01

The deformation behavior of ultrahigh molecular polyethylene (UHMWPE) is studied in the temperature range of 23-80 degrees C. Samples are examined in quasi-static compression, tensile and creep tests to determine the accelerated deformation of UHMWPE at elevated temperatures. The deformation mechanisms under compression load can be described by one strain rate and temperature dependent Eyring process. The activation energy and volume of that process do not change between 23 degrees C and 50 degrees C. This suggests that the deformation mechanism under compression remains stable within this temperature range. Tribological tests are conducted to transfer this activated energy approach to the deformation behavior under loading typical for artificial knee joints. While this approach does not cover the wear mechanisms close to the surface, testing at higher temperatures is shown to have a significant potential to reduce the testing time for lifetime predictions in terms of the macroscopic creep and deformation behavior of artificial joints. Copyright 2010. Published by Elsevier Ltd.

Microplastics have a more profound impact than elevated temperatures on the predatory performance, digestion and energy metabolism of an Amazonian cichlid.

PubMed

Wen, Bin; Zhang, Nan; Jin, Shi-Rong; Chen, Zai-Zhong; Gao, Jian-Zhong; Liu, Ying; Liu, Han-Peng; Xu, Zhe

2018-02-01

Knowledge on the impacts of microplastics (MPs) pollution on freshwater environments and biota remains limited. Meanwhile, freshwater ecosystems have been threatened by elevated temperatures caused by climate change. To date, no information exists on how MPs-especially under elevated temperature conditions-affect predatory performance, digestive processes and metabolic pathways in freshwater organisms. Here, we examined MPs, elevated temperature and their combined effects on juveniles (0+ group) of an Amazonian cichlid, the discus fish (Symphysodon aequifasciatus). For 30 days, fish were exposed to ambient or elevated temperatures (i.e., 28 or 31 °C) in the absence or presence of MPs (i.e., 0 or 200 μg/L). The following metrics were quantified: MPs accumulation; predatory performance; and biomarkers involved in neurotransmission, digestion and energy production. The results showed that survival rate and body length were not affected by MPs, elevated temperatures or their combination. Elevated temperatures resulted in an increase in MP concentrations in fish bodies. Exposure to MPs decreased the post-exposure predatory performance (PEPP) at ambient temperatures but not at elevated temperatures. Elevated temperatures, however, had no effect on the PEPP but antagonistically interacted with MPs, leading to similar predatory performances under present and future conditions. Acetylcholinesterase (AChE) activity was only affected by MPs and decreased in the presence of MPs, indicating adverse effects in nervous and neuromuscular function and, thus, potentially in predatory performance. Trypsin activity was only influenced by MPs and decreased during exposure to MPs. Elevated temperatures or MPs alone increased the amylase activity but interacted antagonistically. Lipase activity was not influenced by either of the two stressors. In contrast, alkaline phosphatase (ALP) activity was affected by MPs or elevated temperatures alone and decreased with both stressors. Such results indicate deficits in the digestive capabilities of early-stage S. aequifasciatus under elevated temperature conditions and especially during exposure to MPs. Electron transport system (ETS) activity was not influenced by either of the two stressors. Both elevated temperatures and MPs alone increased LDH activity; however, the interaction between the two stressors cancelled activity but was still higher than activity in present conditions. Citrate synthase (CS) activity decreased with elevated temperature but increased during exposure to MPs. Cytochrome c oxidase (COX) activity was only influenced by MPs and increased in the presence of MPs. Thus, S. aequifasciatus juveniles exposed to elevated temperatures and MPs not only relied on anaerobic glycolysis for energy production but also depended on aerobic metabolism in the presence of MPs. Overall, these findings suggested that MPs showed a greater impact than elevated temperatures on the predatory performance, digestion and energy production of S. aequifasciatus. Nevertheless, juvenile survival and growth were minimally impacted, and thus, S. aequifasciatus could cope with near-future temperature increases and MP exposure. Copyright © 2017 Elsevier B.V. All rights reserved.

A thermal extrapolation method for the effective temperatures and internal energies of activated ions

NASA Astrophysics Data System (ADS)

Meot-Ner (Mautner), Michael; Somogyi, Árpád

2007-11-01

The internal energies of dissociating ions, activated chemically or collisionally, can be estimated using the kinetics of thermal dissociation. The thermal Arrhenius parameters can be combined with the observed dissociation rate of the activated ions using kdiss = Athermalexp(-Ea,thermal/RTeff). This Arrhenius-type relation yields the effective temperature, Teff, at which the ions would dissociate thermally at the same rate, or yield the same product distributions, as the activated ions. In turn, Teff is used to calculate the internal energy of the ions and the energy deposited by the activation process. The method yields an energy deposition efficiency of 10% for a chemical ionization proton transfer reaction and 8-26% for the surface collisions of various peptide ions. Internal energies of ions activated by chemical ionization or by gas phase collisions, and of ions produced by desorption methods such as fast atom bombardment, can be also evaluated. Thermal extrapolation is especially useful for ion-molecule reaction products and for biological ions, where other methods to evaluate internal energies are laborious or unavailable.

HIgh Temperature Photocatalysis over Semiconductors

NASA Astrophysics Data System (ADS)

Westrich, Thomas A.

Due in large part to in prevalence of solar energy, increasing demand of energy production (from all sources), and the uncertain future of petroleum energy feedstocks, solar energy harvesting and other photochemical systems will play a major role in the developing energy market. This dissertation focuses on a novel photochemical reaction process: high temperature photocatalysis (i.e., photocatalysis conducted above ambient temperatures, T ≥ 100°C). The overarching hypothesis of this process is that photo-generated charge carriers are able to constructively participate in thermo-catalytic chemical reactions, thereby increasing catalytic rates at one temperature, or maintaining catalytic rates at lower temperatures. The photocatalytic oxidation of carbon deposits in an operational hydrocarbon reformer is one envisioned application of high temperature photocatalysis. Carbon build-up during hydrocarbon reforming results in catalyst deactivation, in the worst cases, this was shown to happen in a period of minutes with a liquid hydrocarbon. In the presence of steam, oxygen, and above-ambient temperatures, carbonaceous deposits were photocatalytically oxidized over very long periods (t ≥ 24 hours). This initial experiment exemplified the necessity of a fundamental assessment of high temperature photocatalytic activity. Fundamental understanding of the mechanisms that affect photocatalytic activity as a function of temperatures was achieved using an ethylene photocatalytic oxidation probe reaction. Maximum ethylene photocatalytic oxidation rates were observed between 100 °C and 200 °C; the maximum photocatalytic rates were approximately a factor of 2 larger than photocatalytic rates at ambient temperatures. The loss of photocatalytic activity at temperatures above 200 °C is due to a non-radiative multi-phonon recombination mechanism. Further, it was shown that the fundamental rate of recombination (as a function of temperature) can be effectively modeled as a temperature-dependent quantum efficiency term, and is directly driven by bulk photocatalyst crystal parameters: maximum phonon energy and the number of phonons allowed per unit cell. This analysis extends to multiple photocatalysts and can explain experimental observations of photocatalytic oxidation rates with varied reactant concentrations. Lastly, this dissertation applies this knowledge to a thermo-catalytic reaction (CO-oxidation) using a Au/TiO 2 catalyst. The combined photo/thereto-catalytic reaction showed a 10-25% increase in CO conversion during a temperature programmed reaction experiment.

The analysis of energy efficiency in water electrolysis under high temperature and high pressure

NASA Astrophysics Data System (ADS)

Hourng, L. W.; Tsai, T. T.; Lin, M. Y.

2017-11-01

This paper aims to analyze the energy efficiency of water electrolysis under high pressure and high temperature conditions. The effects of temperature and pressure on four different kinds of reaction mechanisms, namely, reversible voltage, activation polarization, ohmic polarization, and concentration polarization, are investigated in details. Results show that the ohmic and concentration over-potentials are increased as temperature is increased, however, the reversible and activation over-potentials are decreased as temperature is increased. Therefore, the net efficiency is enhanced as temperature is increased. The efficiency of water electrolysis at 350°C/100 bars is increased about 17%, compared with that at 80°C/1bar.

Measuring temperature-dependent activation energy in thermally activated processes: a 2D Arrhenius plot method.

PubMed

Li, Jian V; Johnston, Steven W; Yan, Yanfa; Levi, Dean H

2010-03-01

Thermally activated processes are characterized by two key quantities, activation energy (E(a)) and pre-exponential factor (nu(0)), which may be temperature dependent. The accurate measurement of E(a), nu(0), and their temperature dependence is critical for understanding the thermal activation mechanisms of non-Arrhenius processes. However, the classic 1D Arrhenius plot-based methods cannot unambiguously measure E(a), nu(0), and their temperature dependence due to the mathematical impossibility of resolving two unknown 1D arrays from one 1D experimental data array. Here, we propose a 2D Arrhenius plot method to solve this fundamental problem. Our approach measures E(a) at any temperature from matching the first and second moments of the data calculated with respect to temperature and rate in the 2D temperature-rate plane, and therefore is able to unambiguously solve E(a), nu(0), and their temperature dependence. The case study of deep level emission in a Cu(In,Ga)Se(2) solar cell using the 2D Arrhenius plot method reveals clear temperature dependent behavior of E(a) and nu(0), which has not been observable by its 1D predecessors.

Activation of AMP-activated protein kinase in response to temperature elevation shows seasonal variation in the zebra mussel, Dreissena polymorpha.

PubMed

Jost, Jennifer A; Keshwani, Sarah S; Abou-Hanna, Jacob J

2015-04-01

Global climate change is affecting ectothermic species, and a variety of studies are needed on thermal tolerances, especially from cellular and physiological perspectives. This study utilized AMP-activated protein kinase (AMPK), a key regulator of cellular energy levels, to examine the effects of high water temperatures on zebra mussel (Dreissena polymorpha) physiology. During heating, AMPK activity increased as water temperature increased to a point, and maximum AMPK activity was detected at high, but sublethal, water temperatures. This pattern varied with season, suggesting that cellular mechanisms of seasonal thermal acclimatization affect basic metabolic processes during sublethal heat stress. There was a greater seasonal variation in the water temperature at which maximum AMPK activity was measured than in lethal water temperature. Furthermore, baseline AMPK activity varied significantly across seasons, most likely reflecting altered metabolic states during times of growth and reproduction. In addition, when summer-collected mussels were lab-acclimated to winter and spring water temperatures, patterns of heat stress mirrored those of field-collected animals. These data suggest that water temperature is the main driver of the seasonal variation in physiology. This study concluded that AMPK activity, which reflects changes in energy supply and demand during heat stress, can serve as a sensitive and early indicator of temperature stress in mussels. Copyright © 2014 Elsevier Inc. All rights reserved.

Removing the barrier to the calculation of activation energies: Diffusion coefficients and reorientation times in liquid water.

PubMed

Piskulich, Zeke A; Mesele, Oluwaseun O; Thompson, Ward H

2017-10-07

General approaches for directly calculating the temperature dependence of dynamical quantities from simulations at a single temperature are presented. The method is demonstrated for self-diffusion and OH reorientation in liquid water. For quantities which possess an activation energy, e.g., the diffusion coefficient and the reorientation time, the results from the direct calculation are in excellent agreement with those obtained from an Arrhenius plot. However, additional information is obtained, including the decomposition of the contributions to the activation energy. These results are discussed along with prospects for additional applications of the direct approach.

Activation energy for diamond growth from the carbon-hydrogen gas system at low substrate temperatures

NASA Astrophysics Data System (ADS)

Stiegler, J.; Lang, T.; von Kaenel, Y.; Michler, J.; Blank, E.

1997-01-01

The growth kinetics of diamond films deposited at low substrate temperatures (600-400 °C) from the carbon-hydrogen gas system have been studied. When the substrate temperature alone was varied, independently of all other process parameters in the microwave plasma reactor, an activation energy in the order of 7 kcal/mol was observed. This value did not change with different carbon concentrations in hydrogen. It is supposed that growth kinetics in this temperature range are controlled by a single chemical reaction, probably the abstraction of surface bonded hydrogen by gas phase atomic hydrogen.

Changes in energy metabolism accompanying pitting in blueberries stored at low temperature.

PubMed

Zhou, Qian; Zhang, Chunlei; Cheng, Shunchang; Wei, Baodong; Liu, Xiuying; Ji, Shujuan

2014-12-01

Low-temperature storage and transport of blueberries is widely practiced in commercial blueberry production. In this research, the storage life of blueberries was extended at low temperature, but fruit stored for 30 d at 0°C pitted after 2d at room-temperature. Fruit cellular structure and physiological parameters accompanying pitting in blueberries were changed. The objective of this research was to characterise properties of energy metabolism accompanying pitting in blueberries during storage, including adenosine phosphates and mitochondrial enzymes involved in stress responses. Physiological and metabolic disorders, changes in cell ultrastructure, energy content and ATPase enzyme activity were observed in pitting blueberries. Energy shortages and increased activity of phenylalanine ammonia lyase (PAL) and lipoxygenase (LOX) were observed in fruit kept at shelf life. The results suggested that sufficient available energy status and a stable enzymatic system in blueberries collectively contribute to improve chilling tolerance, thereby alleviating pitting and maintaining quality of blueberry fruit in long-term cold storage. Copyright © 2014 Elsevier Ltd. All rights reserved.

Hand-to-hand coupling and strategies to minimize unintentional energy transfer during laparoscopic surgery.

PubMed

Overbey, Douglas M; Hilton, Sarah A; Chapman, Brandon C; Townsend, Nicole T; Barnett, Carlton C; Robinson, Thomas N; Jones, Edward L

2017-11-01

Energy-based devices are used in nearly every laparoscopic operation. Radiofrequency energy can transfer to nearby instruments via antenna and capacitive coupling without direct contact. Previous studies have described inadvertent energy transfer through bundled cords and nonelectrically active wires. The purpose of this study was to describe a new mechanism of stray energy transfer from the monopolar instrument through the operating surgeon to the laparoscopic telescope and propose practical measures to decrease the risk of injury. Radiofrequency energy was delivered to a laparoscopic L-hook (monopolar "bovie"), an advanced bipolar device, and an ultrasonic device in a laparoscopic simulator. The tip of a 10-mm telescope was placed adjacent but not touching bovine liver in a standard four-port laparoscopic cholecystectomy setup. Temperature increase was measured as tissue temperature from baseline nearest the tip of the telescope which was never in contact with the energy-based device after a 5-s open-air activation. The monopolar L-hook increased tissue temperature adjacent to the camera/telescope tip by 47 ± 8°C from baseline (P < 0.001). By having an assistant surgeon hold the camera/telescope (rather than one surgeon holding both the active electrode and the camera/telescope), temperature change was reduced to 26 ± 7°C (P < 0.001). Alternative energy devices significantly reduced temperature change in comparison to the monopolar instrument (47 ± 8°C) for both the advanced bipolar (1.2 ± 0.5°C; P < 0.001) and ultrasonic (0.6 ± 0.3°C; P < 0.001) devices. Stray energy transfers from the monopolar "bovie" instrument through the operating surgeon to standard electrically inactive laparoscopic instruments. Hand-to-hand coupling describes a new form of capacitive coupling where the surgeon's body acts as an electrical conductor to transmit energy. Strategies to reduce stray energy transfer include avoiding the same surgeon holding the active electrode and laparoscopic camera or using alternative energy devices. Copyright © 2017 Elsevier Inc. All rights reserved.

Expanding the capability of reaction-diffusion codes using pseudo traps and temperature partitioning: Applied to hydrogen uptake and release from tungsten

DOE Office of Scientific and Technical Information (OSTI.GOV)

Simmonds, M. J.; Yu, J. H.; Wang, Y. Q.

Simulating the implantation and thermal desorption evolution in a reaction-diffusion model requires solving a set of coupled differential equations that describe the trapping and release of atomic species in Plasma Facing Materials (PFMs). These fundamental equations are well outlined by the Tritium Migration Analysis Program (TMAP) which can model systems with no more than three active traps per atomic species. To overcome this limitation, we have developed a Pseudo Trap and Temperature Partition (PTTP) scheme allowing us to lump multiple inactive traps into one pseudo trap, simplifying the system of equations to be solved. For all temperatures, we show themore » trapping of atoms from solute is exactly accounted for when using a pseudo trap. However, a single effective pseudo trap energy can not well replicate the release from multiple traps, each with its own detrapping energy. However, atoms held in a high energy trap will remain trapped at relatively low temperatures, and thus there is a temperature range in which release from high energy traps is effectively inactive. By partitioning the temperature range into segments, a pseudo trap can be defined for each segment to account for multiple high energy traps that are actively trapping but are effectively not releasing atoms. With increasing temperature, as in controlled thermal desorption, the lowest energy trap is nearly emptied and can be removed from the set of coupled equations, while the next higher energy trap becomes an actively releasing trap. Each segment is thus calculated sequentially, with the last time step of a given segment solution being used as an initial input for the next segment as only the pseudo and actively releasing traps are modeled. This PTTP scheme is then applied to experimental thermal desorption data for tungsten (W) samples damaged with heavy ions, which display six distinct release peaks during thermal desorption. Without modifying the TMAP7 source code the PTTP scheme is shown to successfully model the D retention in all six traps. In conclusion, we demonstrate the full reconstruction from the plasma implantation phase through the controlled thermal desorption phase with detrapping energies near 0.9, 1.1, 1.4, 1.7, 1.9 and 2.1 eV for a W sample damaged at room temperature.« less

Expanding the capability of reaction-diffusion codes using pseudo traps and temperature partitioning: Applied to hydrogen uptake and release from tungsten

DOE PAGES

Simmonds, M. J.; Yu, J. H.; Wang, Y. Q.; ...

2018-06-04

Simulating the implantation and thermal desorption evolution in a reaction-diffusion model requires solving a set of coupled differential equations that describe the trapping and release of atomic species in Plasma Facing Materials (PFMs). These fundamental equations are well outlined by the Tritium Migration Analysis Program (TMAP) which can model systems with no more than three active traps per atomic species. To overcome this limitation, we have developed a Pseudo Trap and Temperature Partition (PTTP) scheme allowing us to lump multiple inactive traps into one pseudo trap, simplifying the system of equations to be solved. For all temperatures, we show themore » trapping of atoms from solute is exactly accounted for when using a pseudo trap. However, a single effective pseudo trap energy can not well replicate the release from multiple traps, each with its own detrapping energy. However, atoms held in a high energy trap will remain trapped at relatively low temperatures, and thus there is a temperature range in which release from high energy traps is effectively inactive. By partitioning the temperature range into segments, a pseudo trap can be defined for each segment to account for multiple high energy traps that are actively trapping but are effectively not releasing atoms. With increasing temperature, as in controlled thermal desorption, the lowest energy trap is nearly emptied and can be removed from the set of coupled equations, while the next higher energy trap becomes an actively releasing trap. Each segment is thus calculated sequentially, with the last time step of a given segment solution being used as an initial input for the next segment as only the pseudo and actively releasing traps are modeled. This PTTP scheme is then applied to experimental thermal desorption data for tungsten (W) samples damaged with heavy ions, which display six distinct release peaks during thermal desorption. Without modifying the TMAP7 source code the PTTP scheme is shown to successfully model the D retention in all six traps. In conclusion, we demonstrate the full reconstruction from the plasma implantation phase through the controlled thermal desorption phase with detrapping energies near 0.9, 1.1, 1.4, 1.7, 1.9 and 2.1 eV for a W sample damaged at room temperature.« less

Temperature and photoperiod as environmental cues affect body mass and thermoregulation in Chinese bulbuls, Pycnonotus sinensis.

PubMed

Hu, Shi-Nan; Zhu, Ying-Yang; Lin, Lin; Zheng, Wei-Hong; Liu, Jin-Song

2017-03-01

Seasonal changes in temperature and photoperiod are important environmental cues used by small birds to adjust their body mass ( M b ) and thermogenesis. However, the relative importance of these cues with respect to seasonal adjustments in M b and thermogenesis is difficult to distinguish. In particular, the effects of temperature and photoperiod on energy metabolism and thermoregulation are not well known in many passerines. To address this problem, we measured the effects of temperature and photoperiod on M b , energy intake, resting metabolic rate (RMR), organ mass and physiological and biochemical markers of metabolic activity in the Chinese bulbul ( Pycnonotus sinensis ). Groups of Chinese bulbuls were acclimated in a laboratory to the following conditions: (1) warm and long photoperiod, (2) warm and short photoperiod, (3) cold and long photoperiod, and (4) cold and short photoperiod, for 4 weeks. The results indicate that Chinese bulbuls exhibit adaptive physiological regulation when exposed to different temperatures and photoperiods. M b , RMR, gross energy intake and digestible energy intake were higher in cold-acclimated than in warm-acclimated bulbuls, and in the short photoperiod than in the long photoperiod. The resultant flexibility in energy intake and RMR allows Chinese bulbuls exposed to different temperatures and photoperiods to adjust their energy balance and thermogenesis accordingly. Cold-acclimated birds had heightened state-4 respiration and cytochrome c oxidase activity in their liver and muscle tissue compared with warm-acclimated birds indicating the cellular mechanisms underlying their adaptive thermogenesis. Temperature appears to be a primary cue for adjusting energy budget and thermogenic ability in Chinese bulbuls; photoperiod appears to intensify temperature-induced changes in energy metabolism and thermoregulation. © 2017. Published by The Company of Biologists Ltd.

Buckling of thermally fluctuating spherical shells: Parameter renormalization and thermally activated barrier crossing

NASA Astrophysics Data System (ADS)

Baumgarten, Lorenz; Kierfeld, Jan

2018-05-01

We study the influence of thermal fluctuations on the buckling behavior of thin elastic capsules with spherical rest shape. Above a critical uniform pressure, an elastic capsule becomes mechanically unstable and spontaneously buckles into a shape with an axisymmetric dimple. Thermal fluctuations affect the buckling instability by two mechanisms. On the one hand, thermal fluctuations can renormalize the capsule's elastic properties and its pressure because of anharmonic couplings between normal displacement modes of different wavelengths. This effectively lowers its critical buckling pressure [Košmrlj and Nelson, Phys. Rev. X 7, 011002 (2017), 10.1103/PhysRevX.7.011002]. On the other hand, buckled shapes are energetically favorable already at pressures below the classical buckling pressure. At these pressures, however, buckling requires to overcome an energy barrier, which only vanishes at the critical buckling pressure. In the presence of thermal fluctuations, the capsule can spontaneously overcome an energy barrier of the order of the thermal energy by thermal activation already at pressures below the critical buckling pressure. We revisit parameter renormalization by thermal fluctuations and formulate a buckling criterion based on scale-dependent renormalized parameters to obtain a temperature-dependent critical buckling pressure. Then we quantify the pressure-dependent energy barrier for buckling below the critical buckling pressure using numerical energy minimization and analytical arguments. This allows us to obtain the temperature-dependent critical pressure for buckling by thermal activation over this energy barrier. Remarkably, both parameter renormalization and thermal activation lead to the same parameter dependence of the critical buckling pressure on temperature, capsule radius and thickness, and Young's modulus. Finally, we study the combined effect of parameter renormalization and thermal activation by using renormalized parameters for the energy barrier in thermal activation to obtain our final result for the temperature-dependent critical pressure, which is significantly below the results if only parameter renormalization or only thermal activation is considered.

Real versus Artificial Variation in the Thermal Sensitivity of Biological Traits.

PubMed

Pawar, Samraat; Dell, Anthony I; Savage, Van M; Knies, Jennifer L

2016-02-01

Whether the thermal sensitivity of an organism's traits follows the simple Boltzmann-Arrhenius model remains a contentious issue that centers around consideration of its operational temperature range and whether the sensitivity corresponds to one or a few underlying rate-limiting enzymes. Resolving this issue is crucial, because mechanistic models for temperature dependence of traits are required to predict the biological effects of climate change. Here, by combining theory with data on 1,085 thermal responses from a wide range of traits and organisms, we show that substantial variation in thermal sensitivity (activation energy) estimates can arise simply because of variation in the range of measured temperatures. Furthermore, when thermal responses deviate systematically from the Boltzmann-Arrhenius model, variation in measured temperature ranges across studies can bias estimated activation energy distributions toward higher mean, median, variance, and skewness. Remarkably, this bias alone can yield activation energies that encompass the range expected from biochemical reactions (from ~0.2 to 1.2 eV), making it difficult to establish whether a single activation energy appropriately captures thermal sensitivity. We provide guidelines and a simple equation for partially correcting for such artifacts. Our results have important implications for understanding the mechanistic basis of thermal responses of biological traits and for accurately modeling effects of variation in thermal sensitivity on responses of individuals, populations, and ecological communities to changing climatic temperatures.

Central Nervous System Regulation of Brown Adipose Tissue

PubMed Central

Morrison, Shaun F.; Madden, Christopher J.

2015-01-01

Thermogenesis, the production of heat energy, in brown adipose tissue is a significant component of the homeostatic repertoire to maintain body temperature during the challenge of low environmental temperature in many species from mouse to man and plays a key role in elevating body temperature during the febrile response to infection. The sympathetic neural outflow determining brown adipose tissue (BAT) thermogenesis is regulated by neural networks in the CNS which increase BAT sympathetic nerve activity in response to cutaneous and deep body thermoreceptor signals. Many behavioral states, including wakefulness, immunologic responses, and stress, are characterized by elevations in core body temperature to which central command-driven BAT activation makes a significant contribution. Since energy consumption during BAT thermogenesis involves oxidation of lipid and glucose fuel molecules, the CNS network driving cold-defensive and behavioral state-related BAT activation is strongly influenced by signals reflecting the short and long-term availability of the fuel molecules essential for BAT metabolism and, in turn, the regulation of BAT thermogenesis in response to metabolic signals can contribute to energy balance, regulation of body adipose stores and glucose utilization. This review summarizes our understanding of the functional organization and neurochemical influences within the CNS networks that modulate the level of BAT sympathetic nerve activity to produce the thermoregulatory and metabolic alterations in BAT thermogenesis and BAT energy expenditure that contribute to overall energy homeostasis and the autonomic support of behavior. PMID:25428857

Theoretical and experimental study on the effects of particle size and temperature on the reaction kinetics of cubic nano-Cu2O

NASA Astrophysics Data System (ADS)

Tang, Huanfeng; Huang, Zaiyin; Xiao, Ming; Liang, Min; Chen, Liying; Tan, XueCai

2017-09-01

The activities, selectivities, and stabilities of nanoparticles in heterogeneous reactions are size-dependent. In order to investigate the influencing laws of particle size and temperature on kinetic parameters in heterogeneous reactions, cubic nano-Cu2O particles of four different sizes in the range of 40-120 nm have been controllably synthesized. In situ microcalorimetry has been used to attain thermodynamic data on the reaction of Cu2O with aqueous HNO3 and, combined with thermodynamic principles and kinetic transition-state theory, the relevant reaction kinetic parameters have been evaluated. The size dependences of the kinetic parameters are discussed in terms of the established kinetic model and the experimental results. It was found that the reaction rate constants increased with decreasing particle size. Accordingly, the apparent activation energy, pre-exponential factor, activation enthalpy, activation entropy, and activation Gibbs energy decreased with decreasing particle size. The reaction rate constants and activation Gibbs energies increased with increasing temperature. Moreover, the logarithms of the apparent activation energies, pre-exponential factors, and rate constants were found to be linearly related to the reciprocal of particle size, consistent with the kinetic models. The influence of particle size on these reaction kinetic parameters may be explained as follows: the apparent activation energy is affected by the partial molar enthalpy, the pre-exponential factor is affected by the partial molar entropy, and the reaction rate constant is affected by the partial molar Gibbs energy. [Figure not available: see fulltext.

High energy bursts from a solid state laser operated in the heat capacity limited regime

DOEpatents

Albrecht, G.; George, E.V.; Krupke, W.F.; Sooy, W.; Sutton, S.B.

1996-06-11

High energy bursts are produced from a solid state laser operated in a heat capacity limited regime. Instead of cooling the laser, the active medium is thermally well isolated. As a result, the active medium will heat up until it reaches some maximum acceptable temperature. The waste heat is stored in the active medium itself. Therefore, the amount of energy the laser can put out during operation is proportional to its mass, the heat capacity of the active medium, and the temperature difference over which it is being operated. The high energy burst capacity of a heat capacity operated solid state laser, together with the absence of a heavy, power consuming steady state cooling system for the active medium, will make a variety of applications possible. Alternately, cooling takes place during a separate sequence when the laser is not operating. Industrial applications include new material working processes. 5 figs.

High energy bursts from a solid state laser operated in the heat capacity limited regime

DOEpatents

Albrecht, Georg; George, E. Victor; Krupke, William F.; Sooy, Walter; Sutton, Steven B.

1996-01-01

High energy bursts are produced from a solid state laser operated in a heat capacity limited regime. Instead of cooling the laser, the active medium is thermally well isolated. As a result, the active medium will heat up until it reaches some maximum acceptable temperature. The waste heat is stored in the active medium itself. Therefore, the amount of energy the laser can put out during operation is proportional to its mass, the heat capacity of the active medium, and the temperature difference over which it is being operated. The high energy burst capacity of a heat capacity operated solid state laser, together with the absence of a heavy, power consuming steady state cooling system for the active medium, will make a variety of applications possible. Alternately, cooling takes place during a separate sequence when the laser is not operating. Industrial applications include new material working processes.

Activation energy of tantalum-tungsten oxide thermite reactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cervantes, Octavio G.; Munir, Zuhair A.; Chemical Engineering and Materials Science, University of California, Davis, CA

2011-01-15

The activation energy of a sol-gel (SG) derived tantalum-tungsten oxide thermite composite was determined using the Kissinger isoconversion method. The SG derived powder was consolidated using the high-pressure spark plasma sintering (HPSPS) technique at 300 and 400 C. The ignition temperatures were investigated under high heating rates (500-2000 C min{sup -1}). Such heating rates were required in order to ignite the thermite composite. Samples consolidated at 300 C exhibit an abrupt change in temperature response prior to the main ignition temperature. This change in temperature response is attributed to the crystallization of the amorphous WO{sub 3} in the SG derivedmore » Ta-WO{sub 3} thermite composite and not to a pre-ignition reaction between the constituents. Ignition temperatures for the Ta-WO{sub 3} thermite ranged from approximately 465 to 670 C. The activation energies of the SG derived Ta-WO{sub 3} thermite composite consolidated at 300 and 400 C were determined to be 38{+-} 2 kJ mol{sup -1} and 57 {+-} 2 kJ mol{sup -1}, respectively. (author)« less

Activation energy associated with the electromigration of oligosaccharides through viscosity modifier and polymeric additive containing background electrolytes.

PubMed

Kerékgyártó, Márta; Járvás, Gábor; Novák, Levente; Guttman, András

2016-02-01

The activation energy related to the electromigration of oligosaccharides can be determined from their measured electrophoretic mobilities at different temperatures. The effects of a viscosity modifier (ethylene glycol) and a polymeric additive (linear polyacrylamide) on the electrophoretic mobility of linear sugar oligomers with α1-4 linked glucose units (maltooligosaccharides) were studied in CE using the activation energy concept. The electrophoretic separations of 8-aminopyrene-1,3,6-trisulfonate-labeled maltooligosaccharides were monitored by LIF detection in the temperature range of 20-50°C, using either 0-60% ethylene glycol (viscosity modifier) or 0-3% linear polyacrylamide (polymeric additive) containing BGEs. Activation energy curves were constructed based on the slopes of the Arrhenius plots. With the use of linear polyacrylamide additive, solute size-dependent activation energy variations were found for the maltooligosaccharides with polymerization degrees below and above maltoheptaose (DP 7), probably due to molecular conformation changes and possible matrix interaction effects. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Recombination activity of light-activated copper defects in p-type silicon studied by injection- and temperature-dependent lifetime spectroscopy

NASA Astrophysics Data System (ADS)

Inglese, Alessandro; Lindroos, Jeanette; Vahlman, Henri; Savin, Hele

2016-09-01

The presence of copper contamination is known to cause strong light-induced degradation (Cu-LID) in silicon. In this paper, we parametrize the recombination activity of light-activated copper defects in terms of Shockley—Read—Hall recombination statistics through injection- and temperature dependent lifetime spectroscopy (TDLS) performed on deliberately contaminated float zone silicon wafers. We obtain an accurate fit of the experimental data via two non-interacting energy levels, i.e., a deep recombination center featuring an energy level at Ec-Et=0.48 -0.62 eV with a moderate donor-like capture asymmetry ( k =1.7 -2.6 ) and an additional shallow energy state located at Ec-Et=0.1 -0.2 eV , which mostly affects the carrier lifetime only at high-injection conditions. Besides confirming these defect parameters, TDLS measurements also indicate a power-law temperature dependence of the capture cross sections associated with the deep energy state. Eventually, we compare these results with the available literature data, and we find that the formation of copper precipitates is the probable root cause behind Cu-LID.

Determination of Wetting Behavior, Spread Activation Energy, and Quench Severity of Bioquenchants

NASA Astrophysics Data System (ADS)

Prabhu, K. Narayan; Fernandes, Peter

2007-08-01

An investigation was conducted to study the suitability of vegetable oils such as sunflower, coconut, groundnut, castor, cashewnut shell (CNS), and palm oils as quench media (bioquenchants) for industrial heat treatment by assessing their wetting behavior and severity of quenching. The relaxation of contact angle was sharp during the initial stages, and it became gradual as the system approached equilibrium. The equilibrium contact angle decreased with increase in the temperature of the substrate and decrease in the viscosity of the quench medium. A comparison of the relaxation of the contact angle at various temperatures indicated the significant difference in spreading of oils having varying viscosity. The spread activation energy was determined using the Arrhenius type of equation. Oils with higher viscosity resulted in lower cooling rates. The quench severity of various oil media was determined by estimating heat-transfer coefficients using the lumped capacitance method. Activation energy for spreading determined using the wetting behavior of oils at various temperatures was in good agreement with the severity of quenching assessed by cooling curve analysis. A high quench severity is associated with oils having low spread activation energy.

Photoconduction in amorphous thin films of Se90Sb10-xAgx glassy alloys

NASA Astrophysics Data System (ADS)

Sharma, Suresh Kumar; Shukla, R. K.; Dwivedi, Prabhat K.; Kumar, A.

2017-10-01

The present paper reports the steady state photoconductivity and photosensitivity response of thermally evaporated amorphous thin films of Se90Sb10-xAgx(x = 2, 4, 6, 8, 10). Temperature dependence of dark conductivity is studied and activation energy is calculated for different samples. Temperature dependence of photoconductivity is also studied at different intensities. From temperature dependence of photoconductivity activation energy is computed at different intensities which are found to vary from 0.26 to 0.47 eV. Intensity dependence of photoconductivity has also been studied at different temperatures. These curves are plotted on logarithmic scale and found to be straight lines which show that photoconductivity follows a power law with intensity. Composition dependence of dark conductivity, activation energy of DC conduction and photosensitivity show that these parameters are highly. composition dependent and show a discontinuity at a particular composition when Ag concentration becomes 6 at. %. This is explained in terms of transition from floppy state to mechanically stabilized state at this composition.

Impacts of shallow geothermal energy production on redox processes and microbial communities.

PubMed

Bonte, Matthijs; Röling, Wilfred F M; Zaura, Egija; van der Wielen, Paul W J J; Stuyfzand, Pieter J; van Breukelen, Boris M

2013-12-17

Shallow geothermal systems are increasingly being used to store or harvest thermal energy for heating or cooling purposes. This technology causes temperature perturbations exceeding the natural variations in aquifers, which may impact groundwater quality. Here, we report the results of laboratory experiments on the effect of temperature variations (5-80 °C) on redox processes and associated microbial communities in anoxic unconsolidated subsurface sediments. Both hydrochemical and microbiological data showed that a temperature increase from 11 °C (in situ) to 25 °C caused a shift from iron-reducing to sulfate-reducing and methanogenic conditions. Bioenergetic calculations could explain this shift. A further temperature increase (>45 °C) resulted in the emergence of a thermophilic microbial community specialized in fermentation and sulfate reduction. Two distinct maxima in sulfate reduction rates, of similar orders of magnitude (5 × 10(-10) M s(-1)), were observed at 40 and 70 °C. Thermophilic sulfate reduction, however, had a higher activation energy (100-160 kJ mol(-1)) than mesophilic sulfate reduction (30-60 kJ mol(-1)), which might be due to a trade-off between enzyme stability and activity with thermostable enzymes being less efficient catalysts that require higher activation energies. These results reveal that while sulfate-reducing functionality can withstand a substantial temperature rise, other key biochemical processes appear more temperature sensitive.

Electrical characterization of 6H crystalline silicon carbide. M.S. Thesis Final Report

NASA Technical Reports Server (NTRS)

Lempner, Stephen E.

1994-01-01

Crystalline silicon carbide (SiC) substrates and epilayers, undoped as well as n- and p-doped, have been electrically characterized by performing Hall effect and resistivity measurements (van der Pauw) over the temperature range of approximately 85 K to 650 K (200 K to 500 K for p-type sample). By fitting the measured temperature dependent carrier concentration data to the single activation energy theoretical model: (1) the activation energy for the nitrogen donor ranged from 0.078 eV to 0.101 eV for a doping concentration range of 10(exp 17) cm(exp -3) to 10(exp 18) cm(exp -3) and (2) the activation energy for the aluminum acceptor was 0.252 eV for a doping concentration of 4.6 x 10(exp 18) cm(exp -3). By fitting the measured temperature dependent carrier concentration data to the double activation energy level theoretical model for the nitrogen donor: (1) the activation energy for the hexagonal site was 0.056 eV and 0.093 eV corresponding to doping concentrations of 3.33 x 10 (exp 17) cm(exp -3) and 1.6 x 10(exp 18) cm(exp -3) and (2) the activation energy for the cubic site was 0.113 and 0.126 eV corresponding to doping concentrations of 4.2 x 10(exp 17) cm(exp -3) and 5.4 x 10(exp 18) cm(exp -3).

Energetics of photosynthetic glow peaks

PubMed Central

DeVault, Don; Govindjee; Arnold, William

1983-01-01

By postulating temperature-dependent equilibria between two or more electron carriers acting as traps for electrons or holes, it is possible to modify the Randall-Wilkins theory of thermoluminescence so as to explain the abnormally large apparent activation energies and apparent frequency factors observed in photosynthetic glow curves when fitted by unmodified Randall-Wilkins theory. The equilibria serve to inhibit the formation of the light-emitting excited state by withholding the needed precursor state. When the inhibition is released at higher temperature by shift of equilibrium with temperature, the rise of the glow peak can be much faster than would result from Arrhenius behavior based on the true activation energy and so appears to correspond to a higher activation energy accompanied by a larger frequency factor. From another viewpoint, the enthalpy changes, ΔH, of the equilibria tend to add to the activation energy. Similarly the entropy changes, ΔS, of the equilibria tend to add to the entropy of activation, giving the large apparent frequency factors. The positive values of ΔS needed would correspond to entropy decreases in the forward early electron transport. A comparison of the glow peaks obtained by different workers is also presented. PMID:16593283

Temperature dependence of regioselectivity in nucleophilic photosubstitution of 4-nitroanisole. The activation energy criterion for regioselectivity.

PubMed

Wubbels, Gene G; Danial, Hanan; Policarpio, Danielle

2010-11-19

Photosubstitution of the nitro group vs the methoxy group of triplet 4-nitroanisole by hydroxide ion in water leads to product yields of about 80% 4-methoxyphenol and 20% 4-nitrophenol. The ratio depends slightly on temperature from 3 to 73 °C. The slight temperature variation in the yield ratio is reproduced almost perfectly with a simple Arrhenius model for a mechanism involving bonding of hydroxide ion with the triplet state of 4-nitroanisole. The competing transition states have activation energies of 2.2 and 2.6 kcal/mol, respectively. Correct prediction of regioselectivity can be done for this case by quantum chemical calculation of the competing triplet transition-state energies, or those of the corresponding triplet σ-complexes. Other models for aromatic photosubstitution regioselectivity in mechanisms of the S(N)2Ar* type, such as those based on calculated electron densities, HOMO/LUMO coefficients, or energy gap sizes, are discussed and shown to be inferior to the relative activation energies model. The photoreaction in alcohol solvents, claimed by others to generate the same products as in water and to have an exceedingly large variation of the product ratio with temperature, may reflect chemical changes other than those reported.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Warkentin, Matthew, E-mail: maw64@cornell.edu; Thorne, Robert E.

Radiation damage to protein crystals exhibits two regimes of temperature-activated behavior between T = 300 and 100 K, with a crossover at the protein glass transition near 200 K. These results have implications for mechanistic studies of proteins and for structure determination when cooling to T = 100 K creates excessive disorder. The temperature-dependence of radiation damage to thaumatin crystals between T = 300 and 100 K is reported. The amount of damage for a given dose decreases sharply as the temperature decreases from 300 to 220 K and then decreases more gradually on further cooling below the protein-solvent glassmore » transition. Two regimes of temperature-activated behavior were observed. At temperatures above ∼200 K the activation energy of 18.0 kJ mol{sup −1} indicates that radiation damage is dominated by diffusive motions in the protein and solvent. At temperatures below ∼200 K the activation energy is only 1.00 kJ mol{sup −1}, which is of the order of the thermal energy. Similar activation energies describe the temperature-dependence of radiation damage to a variety of solvent-free small-molecule organic crystals over the temperature range T = 300–80 K. It is suggested that radiation damage in this regime is vibrationally assisted and that the freezing-out of amino-acid scale vibrations contributes to the very weak temperature-dependence of radiation damage below ∼80 K. Analysis using the radiation-damage model of Blake and Phillips [Blake & Phillips (1962 ▶), Biological Effects of Ionizing Radiation at the Molecular Level, pp. 183–191] indicates that large-scale conformational and molecular motions are frozen out below T = 200 K but become increasingly prevalent and make an increasing contribution to damage at higher temperatures. Possible alternative mechanisms for radiation damage involving the formation of hydrogen-gas bubbles are discussed and discounted. These results have implications for mechanistic studies of proteins and for studies of the protein glass transition. They also suggest that data collection at T ≃ 220 K may provide a viable alternative for structure determination when cooling-induced disorder at T = 100 is excessive.« less

Nucleation and crystallization kinetics of hydrated amorphous lactose above the glass transition temperature.

PubMed

Schmitt, E A; Law, D; Zhang, G G

1999-03-01

The crystallization kinetics of amorphous lactose in the presence and absence of seed crystals were investigated at 57.5% relative humidity. Isothermal crystallization studies were conducted gravimetrically in an automated vacuum moisture balance at several temperatures between 18 and 32 degrees C. The crystallization rate constants were then determined from Johnson-Mehl-Avrami (JMA) treatment and isothermal activation energies were obtained from Arrhenius plots. Based on microscopic observations, a reaction order of 3 was used for JMA analysis. The nonisothermal activation energies were determined by differential scanning calorimetry using Kissinger's analysis. Isothermal activation energies for amorphous lactose with and without seed crystals were 89.5 (+/-5.6) kJ/mol and 186.5 (+/-17.6) kJ/mol, respectively. Nonisothermal activation energies with and without seed crystals were 71 (+/-7.5) kJ/mol and 80.9 (+/-8.9) kJ/mol, respectively. The similarity of the isothermal and nonisothermal activation energies for the sample with seeds suggested that crystallization was occurring by growth from a fixed number of preexisting nuclei. Markedly different isothermal and nonisothermal activation energies in the absence of seeds suggested a site-saturated nucleation mechanism, and therefore allowed calculation of an activation energy for nucleation of 317 kJ/mol.

Active optimal control strategies for increasing the efficiency of photovoltaic cells

NASA Astrophysics Data System (ADS)

Aljoaba, Sharif Zidan Ahmad

Energy consumption has increased drastically during the last century. Currently, the worldwide energy consumption is about 17.4 TW and is predicted to reach 25 TW by 2035. Solar energy has emerged as one of the potential renewable energy sources. Since its first physical recognition in 1887 by Adams and Day till nowadays, research in solar energy is continuously developing. This has lead to many achievements and milestones that introduced it as one of the most reliable and sustainable energy sources. Recently, the International Energy Agency declared that solar energy is predicted to be one of the major electricity production energy sources by 2035. Enhancing the efficiency and lifecycle of photovoltaic (PV) modules leads to significant cost reduction. Reducing the temperature of the PV module improves its efficiency and enhances its lifecycle. To better understand the PV module performance, it is important to study the interaction between the output power and the temperature. A model that is capable of predicting the PV module temperature and its effects on the output power considering the individual contribution of the solar spectrum wavelengths significantly advances the PV module edsigns toward higher efficiency. In this work, a thermoelectrical model is developed to predict the effects of the solar spectrum wavelengths on the PV module performance. The model is characterized and validated under real meteorological conditions where experimental temperature and output power of the PV module measurements are shown to agree with the predicted results. The model is used to validate the concept of active optical filtering. Since this model is wavelength-based, it is used to design an active optical filter for PV applications. Applying this filter to the PV module is expected to increase the output power of the module by filtering the spectrum wavelengths. The active filter performance is optimized, where different cutoff wavelengths are used to maximize the module output power. It is predicted that if the optimized active optical filter is applied to the PV module, the module efficiency is predicted to increase by about 1%. Different technologies are considered for physical implementation of the active optical filter.

Thermal energy conversion by coupled shape memory and piezoelectric effects

NASA Astrophysics Data System (ADS)

Zakharov, Dmitry; Lebedev, Gor; Cugat, Orphee; Delamare, Jerome; Viala, Bernard; Lafont, Thomas; Gimeno, Leticia; Shelyakov, Alexander

2012-09-01

This work gives experimental evidence of a promising method of thermal-to-electric energy conversion by coupling shape memory effect (SME) and direct piezoelectric effect (DPE) for harvesting quasi-static ambient temperature variations. Two original prototypes of thermal energy harvesters have been fabricated and tested experimentally. The first is a hybrid laminated composite consisting of TiNiCu shape memory alloy (SMA) and macro fiber composite piezoelectric. This composite comprises 0.1 cm3 of active materials and harvests 75 µJ of energy for each temperature variation of 60 °C. The second prototype is a SME/DPE ‘machine’ which uses the thermally induced linear strains of the SMA to bend a bulk PZT ceramic plate through a specially designed mechanical structure. The SME/DPE ‘machine’ with 0.2 cm3 of active material harvests 90 µJ over a temperature increase of 35 °C (60 µJ when cooling). In contrast to pyroelectric materials, such harvesters are also compatible with both small and slow temperature variations.

Atomic-layered Au clusters on α-MoC as catalysts for the low-temperature water-gas shift reaction

DOE PAGES

Yao, Siyu; Zhang, Xiao; Zhou, Wu; ...

2017-06-22

Here, the water-gas shift (WGS) reaction (where carbon monoxide plus water yields dihydrogen and carbon dioxide) is an essential process for hydrogen generation and carbon monoxide removal in various energy-related chemical operations. This equilibrium-limited reaction is favored at a low working temperature. Potential application in fuel cells also requires a WGS catalyst to be highly active, stable, and energy-efficient and to match the working temperature of on-site hydrogen generation and consumption units. We synthesized layered gold (Au) clusters on a molybdenum carbide (α-MoC) substrate to create an interfacial catalyst system for the ultralow-temperature WGS reaction. Water was activated over α-MoCmore » at 303 kelvin, whereas carbon monoxide adsorbed on adjacent Au sites was apt to react with surface hydroxyl groups formed from water splitting, leading to a high WGS activity at low temperatures.« less

The Differential Gibbs Free Energy of Activation and its Implications in the Transition-State of Enzymatic Reactions

NASA Astrophysics Data System (ADS)

Maggi, F.; Riley, W. J.

2016-12-01

We propose a mathematical framework to introduce the concept of differential free energy of activation in enzymatically catalyzed reactions, and apply it to N uptake by microalgae and bacteria. This framework extends the thermodynamic capabilities of the classical transition-state theory in and harmonizes the consolidated definitions of kinetic parameters with their thermodynamic and physical meaning. Here, the activation energy is assumed to be a necessary energetic level for equilibrium complexation between reactants and activated complex; however, an additional energy contribution is required for the equilibrium activated complex to release reaction products. We call this "differential free energy of activation"; it can be described by a Boltzmann distribution, and corresponds to a free energy level different from that of complexation. Whether this level is above or below the free energy of activation depends on the reaction, and defines energy domains that correspond to "superactivated", "activated", and "subactivated" complexes. The activated complex reaching one of those states will eventually release the products from an energy level different than that of activation. The concept of differential free energy of activation was tested on 57 independent experiments of NH­4+ and NO3- uptake by various microalgae and bacteria at temperatures ranging between 1 and 45oC. Results showed that the complexation equilibrium always favored the activated complex, but the differential energy of activation led to an apparent energy barrier consistent with observations. Temperature affected all energy levels within this framework but did not alter substantially these thermodynamic features. Overall the approach: (1) provides a thermodynamic and mathematical link between Michaelis-Menten and rate constants; (2) shows that both kinetic parameters can be described or approximated by Arrhenius' like equations; (3) describes the likelihood of formation of sub-, super-, and activated complexes; and (4) shows direction and thermodynamic likelihood of each reaction branch within the transition state. The approach suites particularly well for calibration of kinetic parameters against experimentally acquired reaction dynamics measurements of nutrient biogeochemical cycles.

Dark and photo conductivity analysis of Cu doped CdSe-PVA nanocomposites synthesized by chemical route

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rani, Amita; Kurchania, Rajnish; Tripathi, S. K., E-mail: surya@pu.ac.in

2016-05-06

Present communication deals with the study of electrical conductivity measurements of Cu doped CdSe-PVA nanocomposite via chemical method. In electrical measurements, the dark conductivity (σ{sub d}) and the photoconductivity (σ{sub ph}) of CdSe prepared thin films have been studied in the temperature range of 308–343 K. The effect of temperature and the intensity on conductivity has been analyzed for CdSe and CdSe:Cu nanocomposite films. The conductivity of all the samples increases with increasing temperature indicating the semiconducting behavior of the samples. The value of photo activation energy is less than the dark activation energy due to the shift in energy levelsmore » under illumination.« less

Influence of Surrounding Dielectrics on the Data Retention Time of Doped Sb2Te Phase Change Material

NASA Astrophysics Data System (ADS)

Jedema, Friso; in `t Zandt, Micha; Wolters, Rob; Gravesteijn, Dirk

2011-02-01

The crystallization properties of as-deposited and laser written amorphous marks of doped Sb2Te phase change material are found to be only dependent on the top dielectric layer. A ZnS:SiO2 top dielectric layer yields a higher crystallization temperature and a larger crystal growth activation energy as compared to a SiO2 top dielectric layer, leading to superior data retention times at ambient temperatures. The observed correlation between the larger crystallization temperatures and larger crystal growth activation energies indicates that the viscosity of the phase change material in the amorphous state is dependent on the interfacial energy between the phase change material and the top dielectric layer.

Morphology, Structural and Dielectric Properties of Vacuum Evaporated V2O5 Thin Films

NASA Astrophysics Data System (ADS)

Sengodan, R.; Shekar, B. Chandar; Sathish, S.

Vanadium pentoxide (V2O5) thin films were deposited on well cleaned glass substrate using evaporation technique under the pressure of 10-5 Torr. The thickness of the films was measured by the multiple beam interferometry technique and cross checked by using capacitance method. Metal-Insulator-Metal (MIM) structure was fabricated by using suitable masks to study dielectric properties. The dielectric properties were studied by employing LCR meter in the frequency range 12 Hz to 100 kHz for various temperatures. The temperature co- efficient of permittivity (TCP), temperature co-efficient of capacitance (TCC) and dielectric constant (ɛ) were calculated. The activation energy was calculated and found to be very low. The activation energy was found to be increasing with increase in frequency. The obtained low value of activation energy suggested that the hopping conduction may be due to electrons rather than ions.

Antenna coupling explains unintended thermal injury caused by common operating room monitoring devices.

PubMed

Townsend, Nicole T; Jones, Edward L; Paniccia, Alessandro; Vandervelde, Joel; McHenry, Jennifer R; Robinson, Thomas N

2015-04-01

Unintended thermal injury from patient monitoring devices (eg, electrocardiogram pads, neuromonitoring leads) results in third-degree burns. A mechanism for these injuries is not clear. The monopolar "bovie" emits radiofrequency energy that transfers to nearby, nonelectrically active cables or wires without direct contact by capacitive and antenna coupling. The purpose of this study was to determine if, and to what extent, radiofrequency energy couples to common patient monitoring devices. In an ex vivo porcine model, monopolar radiofrequency energy was delivered to a handheld "bovie" pencil. Nonelectrically active neuromonitoring and cardiac-monitoring leads were placed in proximity to the monopolar pencil and its cord. Temperature changes of tissue touched by the monitoring lead were measured using a thermal camera immediately after a 5-second activation. The energy-device cords were then separated by 15 cm, the power was reduced from 30 W coag to 15 W coag and different cord angulation was tested. An advanced bipolar device, a plasma-based device, and an ultrasonic device were also tested at standard settings. The neuromonitoring lead increased tissue temperature at the insertion site by 39 ± 13°C (P<0.001) creating visible char at the skin. The electrocardiogram lead raised tissue temperature by 1.3 ± 0.5°C (P<0.001). Decreasing generator power from 30 W to 15 W and separating the bovie cord from the neuromonitoring cord by 15 cm significantly reduced the temperature change (39 ± 13°C vs. 26±5°C; P<0.001 and 39 ± 13°C vs. 10 ± 5°C; P<0.001, respectively). Lastly, monopolar energy increased tissue temperatures significantly more than argon beam energy (34 ± 15°C), advanced bipolar energy (0.2 ± 0.4°C), and ultrasonic energy (0 ± 0.3°C) (all P<0.001). Stray energy couples to commonly used patient monitoring devices resulting in potentially significant thermal injury. The handheld bovie cord transfers energy via antenna coupling to neuromonitoring leads that can raise tissue temperatures over 100°F (39°C) using standard settings. The most effective ways to decrease this energy coupling is to reduce generator power, increase the separation between wires, or utilize lower voltage energy devices such as ultrasonic or bipolar energy.

An analysis of the temperature dependence of the gate current in complementary heterojunction field-effect transistors

NASA Technical Reports Server (NTRS)

Cunningham, Thomas J.; Fossum, Eric R.; Baier, Steven M.

1992-01-01

The temperature dependence of the gate current versus the gate voltage in complementary heterojunction field-effect transistors (CHFET's) is examined. An analysis indicates that the gate conduction is due to a combination of thermionic emission, thermionic-field emission, and conduction through a temperature-activated resistance. The thermionic-field emission is consistent with tunneling through the AlGaAs insulator. The activation energy of the resistance is consistent with the ionization energy associated with the DX center in the AlGaAs. Methods reducing the gate current are discussed.

Vortex pinning properties in Fe-chalcogenides

NASA Astrophysics Data System (ADS)

Leo, A.; Grimaldi, G.; Guarino, A.; Avitabile, F.; Nigro, A.; Galluzzi, A.; Mancusi, D.; Polichetti, M.; Pace, S.; Buchkov, K.; Nazarova, E.; Kawale, S.; Bellingeri, E.; Ferdeghini, C.

2015-12-01

Among the families of iron-based superconductors, the 11-family is one of the most attractive for high field applications at low temperatures. Optimization of the fabrication processes for bulk, crystalline and/or thin film samples is the first step in producing wires and/or tapes for practical high power conductors. Here we present the results of a comparative study of pinning properties in iron-chalcogenides, investigating the flux pinning mechanisms in optimized Fe(Se{}1-xTe x ) and FeSe samples by current-voltage characterization, magneto-resistance and magnetization measurements. In particular, from Arrhenius plots in magnetic fields up to 9 T, the activation energy is derived as a function of the magnetic field, {U}0(H), whereas the activation energy as a function of temperature, U(T), is derived from relaxation magnetization curves. The high pinning energies, high upper critical field versus temperature slopes near critical temperatures, and highly isotropic pinning properties make iron-chalcogenide superconductors a technological material which could be a real competitor to cuprate high temperature superconductors for high field applications.

A theory for the phase behavior of mixtures of active particles.

PubMed

Takatori, Sho C; Brady, John F

2015-10-28

Systems at equilibrium like molecular or colloidal suspensions have a well-defined thermal energy kBT that quantifies the particles' kinetic energy and gauges how "hot" or "cold" the system is. For systems far from equilibrium, such as active matter, it is unclear whether the concept of a "temperature" exists and whether self-propelled entities are capable of thermally equilibrating like passive Brownian suspensions. Here we develop a simple mechanical theory to study the phase behavior and "temperature" of a mixture of self-propelled particles. A mixture of active swimmers and passive Brownian particles is an ideal system for discovery of the temperature of active matter and the quantities that get shared upon particle collisions. We derive an explicit equation of state for the active/passive mixture to compute a phase diagram and to generalize thermodynamic concepts like the chemical potential and free energy for a mixture of nonequilibrium species. We find that different stability criteria predict in general different phase boundaries, facilitating considerations in simulations and experiments about which ensemble of variables are held fixed and varied.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yao, Siyu; Zhang, Xiao; Zhou, Wu

Here, the water-gas shift (WGS) reaction (where carbon monoxide plus water yields dihydrogen and carbon dioxide) is an essential process for hydrogen generation and carbon monoxide removal in various energy-related chemical operations. This equilibrium-limited reaction is favored at a low working temperature. Potential application in fuel cells also requires a WGS catalyst to be highly active, stable, and energy-efficient and to match the working temperature of on-site hydrogen generation and consumption units. We synthesized layered gold (Au) clusters on a molybdenum carbide (α-MoC) substrate to create an interfacial catalyst system for the ultralow-temperature WGS reaction. Water was activated over α-MoCatmore » 303 kelvin, whereas carbon monoxide adsorbed on adjacent Au sites was apt to react with surface hydroxyl groups formed from water splitting, leading to a high WGS activity at low temperatures.« less

Activation thermodynamics of virus adsorption to solids.

PubMed Central

Preston, D R; Farrah, S R

1988-01-01

The kinetics of bacteriophage MS2, T2, and f2 adsorption to powdered nitrocellulose and disrupted Seitz S1 filters at pH 7 were determined as a function of temperature. Data from these studies were combined with data produced in a previous study on MS2 adsorption to clay by Stagg et al. (Appl. Environ. Microbiol. 33:385-391, 1977). These workers studied the adsorption of MS2 to bentonite clay as a function of temperature. Data from both this previous study and the current one were used to calculate the thermodynamic parameters of virus adsorption. The results show that adsorption of bacteriophages to the solids tested is a physical process (energy of activation, less than 40 kcal [168 J]/mol) rather than a chemical process (energy of activation, greater than 40 kcal/mol). The free energy of activation showed a high negative correlation (r = -0.904, r2 = 0.817) with the percentage of virus adsorption to the solids tested. The energy of activation was highly negatively correlated with the percentage of virus adsorption to nitrocellulose and clay (r = -0.913, r2 = 0.834) but poorly correlated with the percentage of virus adsorption to disrupted Seitz S1 filters (r = -0.348, r2 = 0.121). In general, under conditions in which the percentage of virus adsorption was low, the energy of activation, the free energy of activation, and the entropy of activation were high. Increasing the percentage of virus adsorbed by changing the adsorbing conditions or changing the adsorbing solid decreased the energy of activation, the free energy of activation, and the entropy of activation. PMID:3214152

Kinetics of cellular dissolution in a Cu-Cd alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nakkalil, R.; Gupta, S.P.

1989-07-01

Dissolution of the cellular precipitate by cell boundary migration has been studied in a Cu-2 at.% Cd alloy in the temperature range 777--878 K. Microstructural observations have revealed that the process of dissolution begins at the original position of the grain boundary as well as the cell boundary. The steady state rate of cell boundary migration decreased with decreasing temperature of dissolution and became zero at approximately 770 K, which is about 30 K below the equilibrium solves temperature. The boundary diffusivities were determined at a number of temperatures by using the theory of Petermann and Hornbogen modified for dissolution.more » The diffusivity values calculated from the experimental data are seven orders of magnitude higher than the corresponding volume diffusivities. From the temperature dependence of the diffusivity, an activation energy of 157 kJ mol{sup {minus} 1} is obtained, which is bout three-quarters of the activation energy for the bulk diffusion of Cd into Cu. From the diffusivity and activation energy values, it is concluded that the diffusion of Cd along the migrating grain boundaries control the dissolution of the cellular precipitate in this alloy.« less

Thermodynamic limitations on the temperature sensitivity of cell-membrane ion channels: Trouble with enthalpy uncertainty

NASA Astrophysics Data System (ADS)

Zheltikov, A. M.

2018-06-01

Energy exchange between a thermodynamic ensemble of heat- and cold-activated cell-membrane ion channels and the surrounding heat reservoir is shown to impose fundamental limitations on the performance of such channels as temperature-controlled gates for thermal cell activation. Analysis of unavoidable thermodynamic internal-energy fluctuations caused by energy exchange between the ion channels and the heat bath suggests that the resulting enthalpy uncertainty is too high for a robust ion-current gating by a single ion channel, implying that large ensembles of ion channels are needed for thermal cell activation. We argue, based on this thermodynamic analysis, that, had thermosensitive cell-membrane ion channels operated individually, rather than as large ensembles, robust thermal cell activation would have been impossible because of thermodynamic fluctuations.

Removing the barrier to the calculation of activation energies

DOE PAGES

Mesele, Oluwaseun O.; Thompson, Ward H.

2016-10-06

Approaches for directly calculating the activation energy for a chemical reaction from a simulation at a single temperature are explored with applications to both classical and quantum systems. The activation energy is obtained from a time correlation function that can be evaluated from the same molecular dynamics trajectories or quantum dynamics used to evaluate the rate constant itself and thus requires essentially no extra computational work.

Apparent Activation Energies Associated with Protein Dynamics on Hydrophobic and Hydrophilic Surfaces

PubMed Central

Langdon, Blake B.; Kastantin, Mark; Schwartz, Daniel K.

2012-01-01

With the use of single-molecule total internal reflection fluorescence microscopy (TIRFM), the dynamics of bovine serum albumin (BSA) and human fibrinogen (Fg) at low concentrations were observed at the solid-aqueous interface as a function of temperature on hydrophobic trimethylsilane (TMS) and hydrophilic fused silica (FS) surfaces. Multiple dynamic modes and populations were observed and characterized by their surface residence times and squared-displacement distributions (surface diffusion). Characteristic desorption and diffusion rates for each population/mode were generally found to increase with temperature, and apparent activation energies were determined from Arrhenius analyses. The apparent activation energies of desorption and diffusion were typically higher on FS than on TMS surfaces, suggesting that protein desorption and mobility were hindered on hydrophilic surfaces due to favorable protein-surface and solvent-surface interactions. The diffusion of BSA on TMS appeared to be activationless for several populations, whereas diffusion on FS always exhibited an apparent activation energy. All activation energies were small in absolute terms (generally only a few kBT), suggesting that most adsorbed protein molecules are weakly bound and move and desorb readily under ambient conditions. PMID:22713578

Pressure and Temperature Effects on the Activity and Structure of the Catalytic Domain of Human MT1-MMP

PubMed Central

Decaneto, Elena; Suladze, Saba; Rosin, Christopher; Havenith, Martina; Lubitz, Wolfgang; Winter, Roland

2015-01-01

Membrane type 1-matrix metalloproteinase (MT1-MMP or MMP-14) is a zinc-transmembrane metalloprotease involved in the degradation of extracellular matrix and tumor invasion. While changes in solvation of MT1-MMP have been recently studied, little is known about the structural and energetic changes associated with MT1-MMP while interacting with substrates. Steady-state kinetic and thermodynamic data (including activation energies and activation volumes) were measured over a wide range of temperatures and pressures by means of a stopped-flow fluorescence technique. Complementary temperature- and pressure-dependent Fourier-transform infrared measurements provided corresponding structural information of the protein. MT1-MMP is stable and active over a wide range of temperatures (10–55°C). A small conformational change was detected at 37°C, which is responsible for the change in activity observed at the same temperature. Pressure decreases the enzymatic activity until complete inactivation occurs at 2 kbar. The inactivation is associated with changes in the rate-limiting step of the reaction caused by additional hydration of the active site upon compression and/or minor conformational changes in the active site region. Based on these data, an energy and volume diagram could be established for the various steps of the enzymatic reaction. PMID:26636948

Non-Arrhenius ionic conductivities in glasses due to a distribution of activation energies.

PubMed

Bischoff, C; Schuller, K; Beckman, S P; Martin, S W

2012-08-17

Previously observed non-Arrhenius behavior in fast ion conducting glasses [J. Kincs and S. W. Martin, Phys. Rev. Lett. 76, 70 (1996)] occurs at temperatures near the glass transition temperature, T(g), and is attributed to changes in the ion mobility due to ion trapping mechanisms that diminish the conductivity and result in a decreasing conductivity with increasing temperature. It is intuitive that disorder in glass will also result in a distribution of the activation energies (DAE) for ion conduction, which should increase the conductivity with increasing temperature, yet this has not been identified in the literature. In this Letter, a series of high precision ionic conductivity measurements are reported for 0.5Na(2)S + 0.5[xGeS(2) + (1-x)PS(5/2)] glasses with compositions ranging from 0 ≤ x ≤ 1. The impact of the cation site disorder on the activation energy is identified and explained using a DAE model. The absence of the non-Arrhenius behavior in other glasses is explained and it is predicted which glasses are expected to accentuate the DAE effect on the ionic conductivity.

Application of the compensated arrhenius formalism to dielectric relaxation.

PubMed

Petrowsky, Matt; Frech, Roger

2009-12-17

The temperature dependence of the dielectric rate constant, defined as the reciprocal of the dielectric relaxation time, is examined for several groups of organic solvents. Early studies of linear alcohols using a simple Arrhenius equation found that the activation energy was dependent on the chain length of the alcohol. This paper re-examines the earlier data using a compensated Arrhenius formalism that assumes the presence of a temperature-dependent static dielectric constant in the exponential prefactor. Scaling temperature-dependent rate constants to isothermal rate constants so that the dielectric constant dependence is removed results in calculated energies of activation E(a) in which there is a small increase with chain length. These energies of activation are very similar to those calculated from ionic conductivity data using compensated Arrhenius formalism. This treatment is then extended to dielectic relaxation data for n-alkyl bromides, n-nitriles, and n-acetates. The exponential prefactor is determined by dividing the temperature-dependent rate constants by the Boltzmann term exp(-E(a)/RT). Plotting the prefactors versus the static dielectric constant places the data on a single master curve for each group of solvents.

Incomplete Ionization of a 110 meV Unintentional Donor in Beta-Ga2O3 and its Effect on Power Devices (Postprint)

DTIC Science & Technology

2017-10-16

characterized via temperature dependent Hall effect measurements up to 1000 K and found to have a donor energy of 110 meV. The existence of the...unintentional donor is confirmed by temperature dependent admittance spectroscopy, with an activation energy of 131 meV determined via that technique, in...characterized via temperature dependent Hall effect measurements up to 1000 K and found to have a donor energy of 110 meV. The existence of the

Activation energy measurements in rheological analysis of cheese

USDA-ARS?s Scientific Manuscript database

Activation energy of flow (Ea) was calculated from temperature sweeps of cheeses with contrasting characteristics to determine its usefulness in predicting rheological behavior upon heating. Cheddar, Colby, whole milk Mozzarella, low moisture part skim Mozzarella, Parmesan, soft goat, and Queso Fre...

Generic temperature compensation of biological clocks by autonomous regulation of catalyst concentration

PubMed Central

Hatakeyama, Tetsuhiro S.; Kaneko, Kunihiko

2012-01-01

Circadian clocks—ubiquitous in life forms ranging from bacteria to multicellular organisms—often exhibit intrinsic temperature compensation; the period of circadian oscillators is maintained constant over a range of physiological temperatures, despite the expected Arrhenius form for the reaction coefficient. Observations have shown that the amplitude of the oscillation depends on the temperature but the period does not; this suggests that although not every reaction step is temperature independent, the total system comprising several reactions still exhibits compensation. Here we present a general mechanism for such temperature compensation. Consider a system with multiple activation energy barriers for reactions, with a common enzyme shared across several reaction steps. The steps with the highest activation energy rate-limit the cycle when the temperature is not high. If the total abundance of the enzyme is limited, the amount of free enzyme available to catalyze a specific reaction decreases as more substrates bind to the common enzyme. We show that this change in free enzyme abundance compensates for the Arrhenius-type temperature dependence of the reaction coefficient. Taking the example of circadian clocks with cyanobacterial proteins KaiABC, consisting of several phosphorylation sites, we show that this temperature compensation mechanism is indeed valid. Specifically, if the activation energy for phosphorylation is larger than that for dephosphorylation, competition for KaiA shared among the phosphorylation reactions leads to temperature compensation. Moreover, taking a simpler model, we demonstrate the generality of the proposed compensation mechanism, suggesting relevance not only to circadian clocks but to other (bio)chemical oscillators as well. PMID:22566655

Generic temperature compensation of biological clocks by autonomous regulation of catalyst concentration.

PubMed

Hatakeyama, Tetsuhiro S; Kaneko, Kunihiko

2012-05-22

Circadian clocks--ubiquitous in life forms ranging from bacteria to multicellular organisms--often exhibit intrinsic temperature compensation; the period of circadian oscillators is maintained constant over a range of physiological temperatures, despite the expected Arrhenius form for the reaction coefficient. Observations have shown that the amplitude of the oscillation depends on the temperature but the period does not; this suggests that although not every reaction step is temperature independent, the total system comprising several reactions still exhibits compensation. Here we present a general mechanism for such temperature compensation. Consider a system with multiple activation energy barriers for reactions, with a common enzyme shared across several reaction steps. The steps with the highest activation energy rate-limit the cycle when the temperature is not high. If the total abundance of the enzyme is limited, the amount of free enzyme available to catalyze a specific reaction decreases as more substrates bind to the common enzyme. We show that this change in free enzyme abundance compensates for the Arrhenius-type temperature dependence of the reaction coefficient. Taking the example of circadian clocks with cyanobacterial proteins KaiABC, consisting of several phosphorylation sites, we show that this temperature compensation mechanism is indeed valid. Specifically, if the activation energy for phosphorylation is larger than that for dephosphorylation, competition for KaiA shared among the phosphorylation reactions leads to temperature compensation. Moreover, taking a simpler model, we demonstrate the generality of the proposed compensation mechanism, suggesting relevance not only to circadian clocks but to other (bio)chemical oscillators as well.

Acutely Decreased Thermoregulatory Energy Expenditure or Decreased Activity Energy Expenditure Both Acutely Reduce Food Intake in Mice

PubMed Central

Kaiyala, Karl J.; Morton, Gregory J.; Thaler, Joshua P.; Meek, Thomas H.; Tylee, Tracy; Ogimoto, Kayoko; Wisse, Brent E.

2012-01-01

Despite the suggestion that reduced energy expenditure may be a key contributor to the obesity pandemic, few studies have tested whether acutely reduced energy expenditure is associated with a compensatory reduction in food intake. The homeostatic mechanisms that control food intake and energy expenditure remain controversial and are thought to act over days to weeks. We evaluated food intake in mice using two models of acutely decreased energy expenditure: 1) increasing ambient temperature to thermoneutrality in mice acclimated to standard laboratory temperature or 2) exercise cessation in mice accustomed to wheel running. Increasing ambient temperature (from 21°C to 28°C) rapidly decreased energy expenditure, demonstrating that thermoregulatory energy expenditure contributes to both light cycle (40±1%) and dark cycle energy expenditure (15±3%) at normal ambient temperature (21°C). Reducing thermoregulatory energy expenditure acutely decreased food intake primarily during the light cycle (65±7%), thus conflicting with the delayed compensation model, but did not alter spontaneous activity. Acute exercise cessation decreased energy expenditure only during the dark cycle (14±2% at 21°C; 21±4% at 28°C), while food intake was reduced during the dark cycle (0.9±0.1 g) in mice housed at 28°C, but during the light cycle (0.3±0.1 g) in mice housed at 21°C. Cumulatively, there was a strong correlation between the change in daily energy expenditure and the change in daily food intake (R2 = 0.51, p<0.01). We conclude that acutely decreased energy expenditure decreases food intake suggesting that energy intake is regulated by metabolic signals that respond rapidly and accurately to reduced energy expenditure. PMID:22936977

Electrical characterization and vibrational spectroscopic investigations of order-disorder phase transitions in [N(C3H7)4]2CoCl4 compound

NASA Astrophysics Data System (ADS)

Moutia, N.; Ben Gzaiel, M.; Oueslati, A.; Khirouni, K.

2017-04-01

The present paper accounts for the vibrational spectroscopy and electrical characterization of a bis-tetrapropylammonium tetrachlorocobaltate grown at room temperature by slow evaporation of aqueous solution. The Raman spectra were studied in the range of 50-3500 cm-1 as a function of temperature of 318 K-421 K. The most important changes are observed for the band at 1032 cm-1 associated to δ(C - C - C) + t(CH2) + ω(CH2) . A detail analysis of the frequency and half-width is quantitatively described in term of an order-disorder model allowed to obtain information relative to the thermal coefficient and activation energy. The decrease of the activation energy with increasing temperature has been interpreted in term of a change in the re-orientation motion of the cationic parts [N(C3H7)4]+. Besides, the impedance measurements indicate that the electrical properties are strongly temperature dependent. Nyquist plots (-Z″versus Z‧) show that the conductivity behavior is accurately represented by an equivalent circuit models which consists of a series combination of grains interior and grains boundary. The conductivity follows the Arrhenius relation with different activation energies and conduction mechanisms: three temperature regions with activation energies EaI = 0.78 eV and EaII = 0.81 eV and EaIII = 0.93 eV. Furthermore, the modulus plots can be characterized by full width at half height or in term of a non-experiential decay function ϕ(t) = exp(-1/τ) β .

Nanostructured complex oxides as a route towards thermal behavior in artificial spin ice systems

NASA Astrophysics Data System (ADS)

Chopdekar, R. V.; Li, B.; Wynn, T. A.; Lee, M. S.; Jia, Y.; Liu, Z. Q.; Biegalski, M. D.; Retterer, S. T.; Young, A. T.; Scholl, A.; Takamura, Y.

2017-07-01

We have used soft x-ray photoemission electron microscopy to image the magnetization of single-domain L a0.7S r0.3Mn O3 nanoislands arranged in geometrically frustrated configurations such as square ice and kagome ice geometries. Upon thermal randomization, ensembles of nanoislands with strong interisland magnetic coupling relax towards low-energy configurations. Statistical analysis shows that the likelihood of ensembles falling into low-energy configurations depends strongly on the annealing temperature. Annealing to just below the Curie temperature of the ferromagnetic film (TC=338 K ) allows for a much greater probability of achieving low-energy configurations as compared to annealing above the Curie temperature. At this thermally active temperature of 325 K, the ensemble of ferromagnetic nanoislands explore their energy landscape over time and eventually transition to lower energy states as compared to the frozen-in configurations obtained upon cooling from above the Curie temperature. Thus, this materials system allows for a facile method to systematically study thermal evolution of artificial spin ice arrays of nanoislands at temperatures modestly above room temperature.

A Rigidifying Salt-Bridge Favors the Activity of Thermophilic Enzyme at High Temperatures at the Expense of Low-Temperature Activity

PubMed Central

Lam, Sonia Y.; Yeung, Rachel C. Y.; Yu, Tsz-Ha; Sze, Kong-Hung; Wong, Kam-Bo

2011-01-01

Background Thermophilic enzymes are often less active than their mesophilic homologues at low temperatures. One hypothesis to explain this observation is that the extra stabilizing interactions increase the rigidity of thermophilic enzymes and hence reduce their activity. Here we employed a thermophilic acylphosphatase from Pyrococcus horikoshii and its homologous mesophilic acylphosphatase from human as a model to study how local rigidity of an active-site residue affects the enzymatic activity. Methods and Findings Acylphosphatases have a unique structural feature that its conserved active-site arginine residue forms a salt-bridge with the C-terminal carboxyl group only in thermophilic acylphosphatases, but not in mesophilic acylphosphatases. We perturbed the local rigidity of this active-site residue by removing the salt-bridge in the thermophilic acylphosphatase and by introducing the salt-bridge in the mesophilic homologue. The mutagenesis design was confirmed by x-ray crystallography. Removing the salt-bridge in the thermophilic enzyme lowered the activation energy that decreased the activation enthalpy and entropy. Conversely, the introduction of the salt-bridge to the mesophilic homologue increased the activation energy and resulted in increases in both activation enthalpy and entropy. Revealed by molecular dynamics simulations, the unrestrained arginine residue can populate more rotamer conformations, and the loss of this conformational freedom upon the formation of transition state justified the observed reduction in activation entropy. Conclusions Our results support the conclusion that restricting the active-site flexibility entropically favors the enzymatic activity at high temperatures. However, the accompanying enthalpy-entropy compensation leads to a stronger temperature-dependency of the enzymatic activity, which explains the less active nature of the thermophilic enzymes at low temperatures. PMID:21423654

A rigidifying salt-bridge favors the activity of thermophilic enzyme at high temperatures at the expense of low-temperature activity.

PubMed

Lam, Sonia Y; Yeung, Rachel C Y; Yu, Tsz-Ha; Sze, Kong-Hung; Wong, Kam-Bo

2011-03-01

Thermophilic enzymes are often less active than their mesophilic homologues at low temperatures. One hypothesis to explain this observation is that the extra stabilizing interactions increase the rigidity of thermophilic enzymes and hence reduce their activity. Here we employed a thermophilic acylphosphatase from Pyrococcus horikoshii and its homologous mesophilic acylphosphatase from human as a model to study how local rigidity of an active-site residue affects the enzymatic activity. Acylphosphatases have a unique structural feature that its conserved active-site arginine residue forms a salt-bridge with the C-terminal carboxyl group only in thermophilic acylphosphatases, but not in mesophilic acylphosphatases. We perturbed the local rigidity of this active-site residue by removing the salt-bridge in the thermophilic acylphosphatase and by introducing the salt-bridge in the mesophilic homologue. The mutagenesis design was confirmed by x-ray crystallography. Removing the salt-bridge in the thermophilic enzyme lowered the activation energy that decreased the activation enthalpy and entropy. Conversely, the introduction of the salt-bridge to the mesophilic homologue increased the activation energy and resulted in increases in both activation enthalpy and entropy. Revealed by molecular dynamics simulations, the unrestrained arginine residue can populate more rotamer conformations, and the loss of this conformational freedom upon the formation of transition state justified the observed reduction in activation entropy. Our results support the conclusion that restricting the active-site flexibility entropically favors the enzymatic activity at high temperatures. However, the accompanying enthalpy-entropy compensation leads to a stronger temperature-dependency of the enzymatic activity, which explains the less active nature of the thermophilic enzymes at low temperatures.

Solid composite electrolytes for lithium batteries

DOEpatents

Kumar, Binod; Scanlon, Jr., Lawrence G.

2001-01-01

Solid composite electrolytes are provided for use in lithium batteries which exhibit moderate to high ionic conductivity at ambient temperatures and low activation energies. In one embodiment, a polymer-ceramic composite electrolyte containing poly(ethylene oxide), lithium tetrafluoroborate and titanium dioxide is provided in the form of an annealed film having a room temperature conductivity of from 10.sup.-5 S cm.sup.-1 to 10.sup.-3 S cm.sup.-1 and an activation energy of about 0.5 eV.

Molecular Insight into the Slipperiness of Ice.

PubMed

Weber, Bart; Nagata, Yuki; Ketzetzi, Stefania; Tang, Fujie; Smit, Wilbert J; Bakker, Huib J; Backus, Ellen H G; Bonn, Mischa; Bonn, Daniel

2018-05-16

Measurements of the friction coefficient of steel-on-ice over a large temperature range reveal very high friction at low temperatures (-100 °C) and a steep decrease in the friction coefficient with increasing temperature. Very low friction is only found over the limited temperature range typical for ice skating. The strong decrease in the friction coefficient with increasing temperature exhibits Arrhenius behavior with an activation energy of E a ≈ 11.5 kJ mol -1 . Remarkably, molecular dynamics simulations of the ice-air interface reveal a very similar activation energy for the mobility of surface molecules. Weakly hydrogen-bonded surface molecules diffuse over the surface in a rolling motion, their number and mobility increasing with increasing temperature. This correlation between macroscopic friction and microscopic molecular mobility indicates that slippery ice arises from the high mobility of its surface molecules, making the ice surface smooth and the shearing of the weakly bonded surface molecules easy.

Quantitative magneto-optical analysis of the role of finite temperatures on the critical state in YBCO thin films

NASA Astrophysics Data System (ADS)

Albrecht, Joachim; Brück, Sebastian; Stahl, Claudia; Ruoß, Stephen

2016-11-01

We use quantitative magneto-optical microscopy to investigate the influence of finite temperatures on the critical state of thin YBCO films. In particular, temperature and time dependence of supercurrents in inhomogeneous and anisotropic films are analyzed to extract the role of temperature on the supercurrents themselves and the influence of thermally activated relaxation. We find that inhomogeneities and anisotropies of the current density distribution correspond to a different temperature dependence of local supercurrents. In addition, the thermally activated decay of supercurrents can be used to extract local vortex pinning energies. With these results the modification of vortex pinning introduced by substrate structures is studied. In summary the local investigation of supercurrent densities allows the full description of the vortex pinning landscape with respect to pinning forces and energies in superconducting films with complex properties under the influence of finite temperatures.

Comparison of the anaerobic digestion at the mesophilic and thermophilic temperature regime of organic wastes from the agribusiness.

PubMed

Almeida Streitwieser, Daniela

2017-10-01

An overall kinetic power law model has been successfully applied to study the anaerobic digestion of agricultural wastes. In this comparative kinetic study feed composition, organic load rate, residence time and process temperature have been systematically varied in an automated semi-continuous fermentation system to obtain the dependency of the rate of degradation as biogas production on the organic load rate and temperature. The results show that the overall reaction order depend only on the Chemical Oxygen Demand (COD) at values between 3.6 and 3.7. The Arrhenius approach shows a shift in the rate determining step between the mesophilic and thermophilic temperature regimes. The activation energy at the temperature insensitive mesophilic regime is very small at 8.9 (kJ/mole), while the activation energy at the temperature sensitive thermophilic regime lies around 117 (kJ/mole). Copyright © 2017 Elsevier Ltd. All rights reserved.

Radiant heat affects thermoregulation and energy expenditure during rewarming from torpor.

PubMed

Geiser, F; Drury, R L

2003-02-01

The high expenditure of energy required for endogenous rewarming is one of the widely perceived disadvantages of torpor. However, recent evidence demonstrates that passive rewarming either by the increase of ambient temperature or by basking in the sun appears to be common in heterothermic birds and mammals. As it is presently unknown how radiant heat affects energy expenditure during rewarming from torpor and little is known about how it affects normothermic thermoregulation, we quantified the effects of radiant heat on body temperature and metabolic rate of the small (body mass 25 g) marsupial Sminthopsis macroura in the laboratory. Normothermic resting individuals exposed to radiant heat were able to maintain metabolic rates near basal levels (at 0.91 ml O(2) g(-1) h(-1)) and a constant body temperature down to an ambient temperature of 12 degrees C. In contrast, metabolic rates of individuals without access to radiant heat were 4.5-times higher at an ambient temperature of 12 degrees C and body temperature fell with ambient temperature. During radiant heat-assisted passive rewarming from torpor, animals did not employ shivering but appeared to maximise uptake of radiant heat. Their metabolic rate increased only 3.2-times with a 15- degrees C rise of body temperature (Q(10)=2.2), as predicted by Q(10) effects. In contrast, during active rewarming shivering was intensive and metabolic rates showed an 11.6-times increase. Although body temperature showed a similar absolute change between the beginning and the end of the rewarming process, the overall energetic cost during active rewarming was 6.3-times greater than that during passive, radiant heat-assisted rewarming. Our study demonstrates that energetic models assuming active rewarming from torpor at low ambient temperatures can substantially over-estimate energetic costs. The low energy expenditure during passive arousal provides an alternative explanation as to why daily torpor is common in sunny regions and suggests that the prevalence of torpor in low latitudes may have been under-estimated in the past.

Merriam's kangaroo rats (Dipodomys merriami) voluntarily select temperatures that conserve energy rather than water.

PubMed

Banta, Marilyn R

2003-01-01

Desert endotherms such as Merriam's kangaroo rat (Dipodomys merriami) use both behavioral and physiological means to conserve energy and water. The energy and water needs of kangaroo rats are affected by their thermal environment. Animals that choose temperatures within their thermoneutral zone (TNZ) minimize energy expenditure but may impair water balance because the ratio of water loss to water gain is high. At temperatures below the TNZ, water balance may be improved because animals generate more oxidative water and reduce evaporative water loss; however, they must also increase energy expenditure to maintain a normal body temperature. Hence, it is not possible for kangaroo rats to choose thermal environments that simultaneously minimize energy expenditure and increase water conservation. I used a thermal gradient to test whether water stress, energy stress, simultaneous water and energy stress, or no water/energy stress affected the thermal environment selected by D. merriami. During the night (i.e., active phase), animals in all four treatments chose temperatures near the bottom of their TNZ. During the day (i.e., inactive phase), animals in all four treatments settled at temperatures near the top of their TNZ. Thus, kangaroo rats chose thermal environments that minimized energy requirements, not water requirements. Because kangaroo rats have evolved high water use efficiency, energy conservation may be more important than water conservation to the fitness of extant kangaroo rats.

Effect of annealing temperatures on the electrical conductivity and dielectric properties of Ni1.5Fe1.5O4 spinel ferrite prepared by chemical reaction at different pH values

NASA Astrophysics Data System (ADS)

Aneesh Kumar, K. S.; Bhowmik, R. N.

2017-12-01

The electrical conductivity and dielectric properties of Ni1.5Fe1.5O4 ferrite has been controlled by varying the annealing temperature of the chemical routed samples. The frequency activated conductivity obeyed Jonscher’s power law and universal scaling suggested semiconductor nature. An unusual metal like state has been revealed in the measurement temperature scale in between two semiconductor states with different activation energy. The metal like state has been affected by thermal annealing of the material. The analysis of electrical impedance and modulus spectra has confirmed non-Debye dielectric relaxation with contributions from grains and grain boundaries. The dielectric relaxation process is thermally activated in terms of measurement temperature and annealing temperature of the samples. The hole hopping process, due to presence of Ni3+ ions in the present Ni rich ferrite, played a significant role in determining the thermal activated conduction mechanism. This work has successfully applied the technique of a combined variation of annealing temperature and pH value during chemical reaction for tuning electrical parameters in a wide range; for example dc limit of conductivity ~10-4-10-12 S cm-1, and unusually high activation energy ~0.17-1.36 eV.

On the relation between the activation energy for electron attachment reactions and the size of their thermal rate coefficients.

PubMed

Hotop, H; Ruf, M-W; Kopyra, J; Miller, T M; Fabrikant, I I

2011-02-14

Rate coefficients k(T) for dissociative electron attachment (DEA) to molecules in many cases exhibit a more or less strong rise with increasing temperature T (the electron temperature T(e) and the molecular temperature T(G) are assumed to be in thermal equilibrium, i.e., T = T(e) = T(G)). This rise is frequently modeled by the Arrhenius equation k(T) = k(A) exp[-E(a)∕(k(B)T)], and an activation energy E(a) is deduced from fits to the experimental data k(T). This behavior reflects the presence of an energy barrier for the anion on its path to the dissociated products. In a recent paper [J. Kopyra, J. Wnorowska, M. Foryś, and I. Szamrej, Int. J. Mass Spectrom. 268, 60 (2007)] it was suggested that the size of the rate coefficients for DEA reactions at room temperature exhibits an exponential dependence on the activation energy, i.e., k(E(a); T ≈ 300 K) = k(1) exp[-E(a)∕E(0)]. More recent experimental data for molecules with high barriers [T. M. Miller, J. F. Friedman, L. C. Schaffer, and A. A. Viggiano, J. Chem. Phys. 131, 084302 (2009)] are compatible with such a correlation. We investigate the validity and the possible origin of this dependence by analyzing the results of R-matrix calculations for temperature-dependent rate coefficients of exothermic DEA processes with intermediate barrier toward dissociation. These include results for model systems with systematically varied barrier height as well as results of molecule-specific calculations for CH(3)Cl, CH(3)Br, CF(3)Cl, and CH(2)Cl(2) (activation energies above 0.2 eV) involving appropriate molecular parameters. A comparison of the experimental and theoretical results for the considered class of molecules (halogenated alkanes) supports the idea that the exponential dependence of k(T = 300 K) on the activation energy reflects a general phenomenon associated with Franck-Condon factors for getting from the initial neutral vibrational levels to the dissociating final anion state in a direct DEA process. Cases are discussed for which the proposed relation does not apply.

Glutamatergic Preoptic Area Neurons That Express Leptin Receptors Drive Temperature-Dependent Body Weight Homeostasis.

PubMed

Yu, Sangho; Qualls-Creekmore, Emily; Rezai-Zadeh, Kavon; Jiang, Yanyan; Berthoud, Hans-Rudolf; Morrison, Christopher D; Derbenev, Andrei V; Zsombok, Andrea; Münzberg, Heike

2016-05-04

The preoptic area (POA) regulates body temperature, but is not considered a site for body weight control. A subpopulation of POA neurons express leptin receptors (LepRb(POA) neurons) and modulate reproductive function. However, LepRb(POA) neurons project to sympathetic premotor neurons that control brown adipose tissue (BAT) thermogenesis, suggesting an additional role in energy homeostasis and body weight regulation. We determined the role of LepRb(POA) neurons in energy homeostasis using cre-dependent viral vectors to selectively activate these neurons and analyzed functional outcomes in mice. We show that LepRb(POA) neurons mediate homeostatic adaptations to ambient temperature changes, and their pharmacogenetic activation drives robust suppression of energy expenditure and food intake, which lowers body temperature and body weight. Surprisingly, our data show that hypothermia-inducing LepRb(POA) neurons are glutamatergic, while GABAergic POA neurons, originally thought to mediate warm-induced inhibition of sympathetic premotor neurons, have no effect on energy expenditure. Our data suggest a new view into the neurochemical and functional properties of BAT-related POA circuits and highlight their additional role in modulating food intake and body weight. Brown adipose tissue (BAT)-induced thermogenesis is a promising therapeutic target to treat obesity and metabolic diseases. The preoptic area (POA) controls body temperature by modulating BAT activity, but its role in body weight homeostasis has not been addressed. LepRb(POA) neurons are BAT-related neurons and we show that they are sufficient to inhibit energy expenditure. We further show that LepRb(POA) neurons modulate food intake and body weight, which is mediated by temperature-dependent homeostatic responses. We further found that LepRb(POA) neurons are stimulatory glutamatergic neurons, contrary to prevalent models, providing a new view on thermoregulatory neural circuits. In summary, our study significantly expands our current understanding of central circuits and mechanisms that modulate energy homeostasis. Copyright © 2016 the authors 0270-6474/16/365034-13$15.00/0.

Glutamatergic Preoptic Area Neurons That Express Leptin Receptors Drive Temperature-Dependent Body Weight Homeostasis

PubMed Central

Qualls-Creekmore, Emily; Rezai-Zadeh, Kavon; Jiang, Yanyan; Berthoud, Hans-Rudolf; Morrison, Christopher D.; Derbenev, Andrei V.; Zsombok, Andrea

2016-01-01

The preoptic area (POA) regulates body temperature, but is not considered a site for body weight control. A subpopulation of POA neurons express leptin receptors (LepRbPOA neurons) and modulate reproductive function. However, LepRbPOA neurons project to sympathetic premotor neurons that control brown adipose tissue (BAT) thermogenesis, suggesting an additional role in energy homeostasis and body weight regulation. We determined the role of LepRbPOA neurons in energy homeostasis using cre-dependent viral vectors to selectively activate these neurons and analyzed functional outcomes in mice. We show that LepRbPOA neurons mediate homeostatic adaptations to ambient temperature changes, and their pharmacogenetic activation drives robust suppression of energy expenditure and food intake, which lowers body temperature and body weight. Surprisingly, our data show that hypothermia-inducing LepRbPOA neurons are glutamatergic, while GABAergic POA neurons, originally thought to mediate warm-induced inhibition of sympathetic premotor neurons, have no effect on energy expenditure. Our data suggest a new view into the neurochemical and functional properties of BAT-related POA circuits and highlight their additional role in modulating food intake and body weight. SIGNIFICANCE STATEMENT Brown adipose tissue (BAT)-induced thermogenesis is a promising therapeutic target to treat obesity and metabolic diseases. The preoptic area (POA) controls body temperature by modulating BAT activity, but its role in body weight homeostasis has not been addressed. LepRbPOA neurons are BAT-related neurons and we show that they are sufficient to inhibit energy expenditure. We further show that LepRbPOA neurons modulate food intake and body weight, which is mediated by temperature-dependent homeostatic responses. We further found that LepRbPOA neurons are stimulatory glutamatergic neurons, contrary to prevalent models, providing a new view on thermoregulatory neural circuits. In summary, our study significantly expands our current understanding of central circuits and mechanisms that modulate energy homeostasis. PMID:27147656

Global Ultraviolet Imager (GUVI) investigation

NASA Technical Reports Server (NTRS)

Christensen, Andrew B.

1995-01-01

This report covers the activities performed under NAS5-32572. The results of those activities are included in this Final Report. TIMED Science Objectives: (1) To determine the temperature, density, and wind structure of the MLTI (mixed layer thermal inertia), including the seasonal and latitudinal variations; and (2) To determine the relative importance of the various radiative, chemical, electrodynamical, and dynamical sources and sinks of energy for the thermal structure of the MLTI. GUVI Science Goals: (1) Determine the spatial and temporal variations of temperature and constituent densities in the lower thermosphere; and (2) Determine the importance of auroral energy sources and solar EUV (extreme ultraviolet) to the energy balance of the region.

Regulation of body temperature and brown adipose tissue thermogenesis by bombesin receptor subtype-3

PubMed Central

Lateef, Dalya M.; Abreu-Vieira, Gustavo; Xiao, Cuiying

2014-01-01

Bombesin receptor subtype-3 (BRS-3) regulates energy homeostasis, with Brs3 knockout (Brs3−/y) mice being hypometabolic, hypothermic, and hyperphagic and developing obesity. We now report that the reduced body temperature is more readily detected if body temperature is analyzed as a function of physical activity level and light/dark phase. Physical activity level correlated best with body temperature 4 min later. The Brs3−/y metabolic phenotype is not due to intrinsically impaired brown adipose tissue function or in the communication of sympathetic signals from the brain to brown adipose tissue, since Brs3−/y mice have intact thermogenic responses to stress, acute cold exposure, and β3-adrenergic activation, and Brs3−/y mice prefer a cooler environment. Treatment with the BRS-3 agonist MK-5046 increased brown adipose tissue temperature and body temperature in wild-type but not Brs3−/y mice. Intrahypothalamic infusion of MK-5046 increased body temperature. These data indicate that the BRS-3 regulation of body temperature is via a central mechanism, upstream of sympathetic efferents. The reduced body temperature in Brs3−/y mice is due to altered regulation of energy homeostasis affecting higher center regulation of body temperature, rather than an intrinsic defect in brown adipose tissue. PMID:24452453

Electric Field-aided Selective Activation for Indium-Gallium-Zinc-Oxide Thin Film Transistors.

PubMed

Lee, Heesoo; Chang, Ki Soo; Tak, Young Jun; Jung, Tae Soo; Park, Jeong Woo; Kim, Won-Gi; Chung, Jusung; Jeong, Chan Bae; Kim, Hyun Jae

2016-10-11

A new technique is proposed for the activation of low temperature amorphous InGaZnO thin film transistor (a-IGZO TFT) backplanes through application of a bias voltage and annealing at 130 °C simultaneously. In this 'electrical activation', the effects of annealing under bias are selectively focused in the channel region. Therefore, electrical activation can be an effective method for lower backplane processing temperatures from 280 °C to 130 °C. Devices fabricated with this method exhibit equivalent electrical properties to those of conventionally-fabricated samples. These results are analyzed electrically and thermodynamically using infrared microthermography. Various bias voltages are applied to the gate, source, and drain electrodes while samples are annealed at 130 °C for 1 hour. Without conventional high temperature annealing or electrical activation, current-voltage curves do not show transfer characteristics. However, electrically activated a-IGZO TFTs show superior electrical characteristics, comparable to the reference TFTs annealed at 280 °C for 1 hour. This effect is a result of the lower activation energy, and efficient transfer of electrical and thermal energy to a-IGZO TFTs. With this approach, superior low-temperature a-IGZO TFTs are fabricated successfully.

Arrhenius temperature dependence of in vitro tissue plasminogen activator thrombolysis.

PubMed

Shaw, George J; Dhamija, Ashima; Bavani, Nazli; Wagner, Kenneth R; Holland, Christy K

2007-06-07

Stroke is a devastating disease and a leading cause of death and disability. Currently, the only FDA approved therapy for acute ischemic stroke is the intravenous administration of the thrombolytic medication, recombinant tissue plasminogen activator (tPA). However, this treatment has many contraindications and can have dangerous side effects such as intra-cerebral hemorrhage. These treatment limitations have led to much interest in potential adjunctive therapies, such as therapeutic hypothermia (T

Arrhenius temperature dependence of in vitro tissue plasminogen activator thrombolysis

NASA Astrophysics Data System (ADS)

Shaw, George J.; Dhamija, Ashima; Bavani, Nazli; Wagner, Kenneth R.; Holland, Christy K.

2007-06-01

Stroke is a devastating disease and a leading cause of death and disability. Currently, the only FDA approved therapy for acute ischemic stroke is the intravenous administration of the thrombolytic medication, recombinant tissue plasminogen activator (tPA). However, this treatment has many contraindications and can have dangerous side effects such as intra-cerebral hemorrhage. These treatment limitations have led to much interest in potential adjunctive therapies, such as therapeutic hypothermia (T <= 35 °C) and ultrasound enhanced thrombolysis. Such interest may lead to combining these therapies with tPA to treat stroke, however little is known about the effects of temperature on the thrombolytic efficacy of tPA. In this work, we measure the temperature dependence of the fractional clot mass loss Δm(T) resulting from tPA exposure in an in vitro human clot model. We find that the temperature dependence is well described by an Arrhenius temperature dependence with an effective activation energy Eeff of 42.0 ± 0.9 kJ mole-1. Eeff approximates the activation energy of the plasminogen-to-plasmin reaction of 48.9 kJ mole-1. A model to explain this temperature dependence is proposed. These results will be useful in predicting the effects of temperature in future lytic therapies.

The activation energy for nanocrystalline diamond films deposited from an Ar/H2/CH4 hot-filament reactor.

PubMed

Barbosa, D C; Melo, L L; Trava-Airoldi, V J; Corat, E J

2009-06-01

In this work we have investigated the effect of substrate temperature on the growth rate and properties of nanocrystalline diamond thin films deposited by hot filament chemical vapor deposition (HFCVD). Mixtures of 0.5 vol% CH4 and 25 vol% H2 balanced with Ar at a pressure of 50 Torr and typical deposition time of 12 h. We present the measurement of the activation energy by accurately controlling the substrate temperature independently of other CVD parameters. Growth rates have been measured in the temperature range from 550 to 800 degrees C. Characterization techniques have involved Raman spectroscopy, high resolution X-ray difractometry and scanning electron microscopy. We also present a comparison with most activation energy for micro and nanocrystalline diamond determinations in the literature and propose that there is a common trend in most observations. The result obtained can be an evidence that the growth mechanism of NCD in HFCVD reactors is very similar to MCD growth.

Determination of reaction rates and activation energy in aerobic composting processes for yard waste.

PubMed

Uma, R N; Manjula, G; Meenambal, T

2007-04-01

The reaction rates and activation energy in aerobic composting processes for yard waste were determined using specifically designed reactors. Different mixture ratios were fixed before the commencement of the process. The C/N ratio was found to be optimum for a mixture ratio of 1:6 containing one part of coir pith to six parts of other waste which included yard waste, yeast sludge, poultry yard waste and decomposing culture (Pleurotosis). The path of stabilization of the wastes was continuously monitored by observing various parameters such as temperature, pH, Electrical Conductivity, C.O.D, VS at regular time intervals. Kinetic analysis was done to determine the reaction rates and activation energy for the optimum mixture ratio under forced aeration condition. The results of the analysis clearly indicated that the temperature dependence of the reaction rates followed the Arrhenius equation. The temperature coefficients were also determined. The degradation of the organic fraction of the yard waste could be predicted using first order reaction model.

Analysis of activation energy in Couette-Poiseuille flow of nanofluid in the presence of chemical reaction and convective boundary conditions

NASA Astrophysics Data System (ADS)

Zeeshan, A.; Shehzad, N.; Ellahi, R.

2018-03-01

The motivation of the current article is to explore the energy activation in MHD radiative Couette-Poiseuille flow nanofluid in horizontal channel with convective boundary conditions. The mathematical model of Buongiorno [1] effectively describes the current flow analysis. Additionally, the impact of chemical reaction is also taken in account. The governing flow equations are simplified with the help of boundary layer approximations. Non-linear coupled equations for momentum, energy and mass transfer are tackled with analytical (HAM) technique. The influence of dimensionless convergence parameter like Brownian motion parameter, radiation parameter, buoyancy ratio parameter, dimensionless activation energy, thermophoresis parameter, temperature difference parameter, dimensionless reaction rate, Schmidt number, Brinkman number, Biot number and convection diffusion parameter on velocity, temperature and concentration profiles are discussed graphically and in tabular form. From the results, it is elaborate that the nanoparticle concentration is directly proportional to the chemical reaction with activation energy and the performance of Brownian motion on nanoparticle concentration gives reverse pattern to that of thermophoresis parameter.

Temperature-dependent regioselectivity of nucleophilic aromatic photosubstitution. Evidence that activation energy controls reactivity.

PubMed

Wubbels, Gene G; Tamura, Ryo; Gannon, Emmett J

2013-05-17

Irradiation (λ > 330 nm) of 2-chloro-4-nitroanisole (1) at 25 °C in aqueous NaOH forms three substitution photoproducts: 2-methoxy-5-nitrophenol (2), 2-chloro-4-nitrophenol (3), and 3-chloro-4-methoxyphenol (4), in chemical yields of 69.2%, 14.3%, and 16.5%. The activation energies for the elementary steps from the triplet state at 25 °C were determined to be 1.8, 2.4, and 2.7 kcal/mol, respectively. The chemical yields of each of the three products were determined for exhaustive irradiations at 0, 35, and 70 °C. The variation with temperature of the experimental yields is reproduced almost exactly by the yields calculated with the Arrhenius equation. This indicates that activation energy is the fundamental property related to regioselectivity in nucleophilic aromatic photosubstitution of the S(N)2 Ar* type. The many methods proposed for predicting regioselectivity in reactions of this type have had limited success and have not been related to activation energy.

Development of next generation tempered and ODS reduced activation ferritic/martensitic steels for fusion energy applications

DOE PAGES

Zinkle, S. J.; Boutard, J. L.; Hoelzer, D. T.; ...

2017-06-09

Reduced activation ferritic/martensitic steels are currently the most technologically mature option for the structural material of proposed fusion energy reactors. Advanced next-generation higher performance steels offer the opportunity for improvements in fusion reactor operational lifetime and reliability, superior neutron radiation damage resistance, higher thermodynamic efficiency, and reduced construction costs. The two main strategies for developing improved steels for fusion energy applications are based on (1) an evolutionary pathway using computational thermodynamics modelling and modified thermomechanical treatments (TMT) to produce higher performance reduced activation ferritic/martensitic (RAFM) steels and (2) a higher risk, potentially higher payoff approach based on powder metallurgy techniquesmore » to produce very high strength oxide dispersion strengthened (ODS) steels capable of operation to very high temperatures and with potentially very high resistance to fusion neutron-induced property degradation. The current development status of these next-generation high performance steels is summarized, and research and development challenges for the successful development of these materials are outlined. In conclusion, material properties including temperature-dependent uniaxial yield strengths, tensile elongations, high-temperature thermal creep, Charpy impact ductile to brittle transient temperature (DBTT) and fracture toughness behaviour, and neutron irradiation-induced low-temperature hardening and embrittlement and intermediate-temperature volumetric void swelling (including effects associated with fusion-relevant helium and hydrogen generation) are described for research heats of the new steels.« less

Development of next generation tempered and ODS reduced activation ferritic/martensitic steels for fusion energy applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zinkle, S. J.; Boutard, J. L.; Hoelzer, D. T.

Reduced activation ferritic/martensitic steels are currently the most technologically mature option for the structural material of proposed fusion energy reactors. Advanced next-generation higher performance steels offer the opportunity for improvements in fusion reactor operational lifetime and reliability, superior neutron radiation damage resistance, higher thermodynamic efficiency, and reduced construction costs. The two main strategies for developing improved steels for fusion energy applications are based on (1) an evolutionary pathway using computational thermodynamics modelling and modified thermomechanical treatments (TMT) to produce higher performance reduced activation ferritic/martensitic (RAFM) steels and (2) a higher risk, potentially higher payoff approach based on powder metallurgy techniquesmore » to produce very high strength oxide dispersion strengthened (ODS) steels capable of operation to very high temperatures and with potentially very high resistance to fusion neutron-induced property degradation. The current development status of these next-generation high performance steels is summarized, and research and development challenges for the successful development of these materials are outlined. In conclusion, material properties including temperature-dependent uniaxial yield strengths, tensile elongations, high-temperature thermal creep, Charpy impact ductile to brittle transient temperature (DBTT) and fracture toughness behaviour, and neutron irradiation-induced low-temperature hardening and embrittlement and intermediate-temperature volumetric void swelling (including effects associated with fusion-relevant helium and hydrogen generation) are described for research heats of the new steels.« less

Development of next generation tempered and ODS reduced activation ferritic/martensitic steels for fusion energy applications

NASA Astrophysics Data System (ADS)

Zinkle, S. J.; Boutard, J. L.; Hoelzer, D. T.; Kimura, A.; Lindau, R.; Odette, G. R.; Rieth, M.; Tan, L.; Tanigawa, H.

2017-09-01

Reduced activation ferritic/martensitic steels are currently the most technologically mature option for the structural material of proposed fusion energy reactors. Advanced next-generation higher performance steels offer the opportunity for improvements in fusion reactor operational lifetime and reliability, superior neutron radiation damage resistance, higher thermodynamic efficiency, and reduced construction costs. The two main strategies for developing improved steels for fusion energy applications are based on (1) an evolutionary pathway using computational thermodynamics modelling and modified thermomechanical treatments (TMT) to produce higher performance reduced activation ferritic/martensitic (RAFM) steels and (2) a higher risk, potentially higher payoff approach based on powder metallurgy techniques to produce very high strength oxide dispersion strengthened (ODS) steels capable of operation to very high temperatures and with potentially very high resistance to fusion neutron-induced property degradation. The current development status of these next-generation high performance steels is summarized, and research and development challenges for the successful development of these materials are outlined. Material properties including temperature-dependent uniaxial yield strengths, tensile elongations, high-temperature thermal creep, Charpy impact ductile to brittle transient temperature (DBTT) and fracture toughness behaviour, and neutron irradiation-induced low-temperature hardening and embrittlement and intermediate-temperature volumetric void swelling (including effects associated with fusion-relevant helium and hydrogen generation) are described for research heats of the new steels.

Effect of annealing on structural changes and oxygen diffusion in amorphous HfO2 using classical molecular dynamics

NASA Astrophysics Data System (ADS)

Shen, Wenqing; Kumari, Niru; Gibson, Gary; Jeon, Yoocharn; Henze, Dick; Silverthorn, Sarah; Bash, Cullen; Kumar, Satish

2018-02-01

Non-volatile memory is a promising alternative to present memory technologies. Oxygen vacancy diffusion has been widely accepted as one of the reasons for the resistive switching mechanism of transition-metal-oxide based resistive random access memory. In this study, molecular dynamics simulation is applied to investigate the diffusion coefficient and activation energy of oxygen in amorphous hafnia. Two sets of empirical potential, Charge-Optimized Many-Body (COMB) and Morse-BKS (MBKS), were considered to investigate the structural and diffusion properties at different temperatures. COMB predicts the activation energy of 0.53 eV for the temperature range of 1000-2000 K, while MBKS predicts 2.2 eV at high temperature (1600-2000 K) and 0.36 eV at low temperature (1000-1600 K). Structural changes and appearance of nano-crystalline phases with increasing temperature might affect the activation energy of oxygen diffusion predicted by MBKS, which is evident from the change in coordination number distribution and radial distribution function. None of the potentials make predictions that are fully consistent with density functional theory simulations of both the structure and diffusion properties of HfO2. This suggests the necessity of developing a better multi-body potential that considers charge exchange.

Activation Energy of Tantalum-Tungsten Oxide Thermite Reaction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cervantes, O; Kuntz, J; Gash, A

2010-02-25

The activation energy of a high melting temperature sol-gel (SG) derived tantalum-tungsten oxide thermite composite was determined using the Kissinger isoconversion method. The SG derived powder was consolidated using the High Pressure Spark Plasma Sintering (HPSPS) technique to 300 and 400 C to produce pellets with dimensions of 5 mm diameter by 1.5 mm height. A custom built ignition setup was developed to measure ignition temperatures at high heating rates (500-2000 C {center_dot} min{sup -1}). Such heating rates were required in order to ignite the thermite composite. Unlike the 400 C samples, results show that the samples consolidated to 300more » C undergo an abrupt change in temperature response prior to ignition. This change in temperature response has been attributed to the crystallization of the amorphous WO{sub 3} in the SG derived Ta-WO{sub 3} thermite composite and not to a pre-ignition reaction between the constituents. Ignition temperatures for the Ta-WO{sub 3} thermite ranged from approximately 465-670 C. The activation energy of the SG derived Ta-WO{sup 3} thermite composite consolidated to 300 and 400 C were determined to be 37.787 {+-} 1.58 kJ {center_dot} mol{sup -1} and 57.381 {+-} 2.26 kJ {center_dot} mol{sup -1}, respectively.« less

A Simple Method to Calculate the Temperature Dependence of the Gibbs Energy and Chemical Equilibrium Constants

ERIC Educational Resources Information Center

Vargas, Francisco M.

2014-01-01

The temperature dependence of the Gibbs energy and important quantities such as Henry's law constants, activity coefficients, and chemical equilibrium constants is usually calculated by using the Gibbs-Helmholtz equation. Although, this is a well-known approach and traditionally covered as part of any physical chemistry course, the required…

Effect of Impedance Relaxation in Conductance Mechanisms in TiO2/ITO/ZnO:Al/p-Si Heterostructure

NASA Astrophysics Data System (ADS)

Nouiri, M.; El Mir, L.

2018-03-01

The electrical conduction of a TiO2/ITO/ZnO:Al/p-Si structure under alternating-current excitation was investigated in the temperature range of 80 K to 300 K. The frequency dependence of the capacitance and conductance revealed the response of a thermally activated trap characterized by activation energy of about 140 meV. The frequency dependence of the conductance obeyed the universal dynamic response according to the common relation G = Aωs . The temperature dependence of the frequency exponent s illustrates that, in the low frequency range, conduction is governed by the correlated barrier hopping (CBH) mechanism involving two distinct energy levels for all investigated temperatures. For the high frequency region, conduction takes place according to the overlapping large-polaron tunneling mechanism at low temperatures but the CBH mechanism becomes dominant in the high temperature region. This difference in electrical behavior between low and high temperatures can be attributed to the dominance of dielectric relaxation at low compared with high temperatures.

Estimation of the activation energy in the Belousov-Zhabotinsky reaction by temperature effect on excitable waves.

PubMed

Zhang, Jinzhong; Zhou, Luqun; Ouyang, Qi

2007-02-15

We report the temperature effect on the propagation of excitable traveling waves in a quasi-two-dimensional Belousov-Zhabotinsky reaction-diffusion system. The onset of excitable waves as a function of the sulfuric acid concentration and temperature is identified, on which the sulfuric acid concentration exhibits an Arrhenius dependence on temperature. On the basis of this experimental data, the activation energy of the self-catalyzed reaction in the Oregonator model is estimated to be 83-113 kJ/mol, which is further supported by our numerical simulations. The estimation proceeds without analyzing detailed reaction steps but rather through observing the global dynamic behaviors in the BZ reaction. For a supplement, the wave propagation velocities are calculated based on our results and compared with the experimental observations.

Investigation of second grade fluid through temperature dependent thermal conductivity and non-Fourier heat flux

NASA Astrophysics Data System (ADS)

Hayat, T.; Ahmad, Salman; Khan, M. Ijaz; Alsaedi, A.; Waqas, M.

2018-06-01

Here we investigated stagnation point flow of second grade fluid over a stretchable cylinder. Heat transfer is characterized by non-Fourier law of heat flux and thermal stratification. Temperature dependent thermal conductivity and activation energy are also accounted. Transformations procedure is applying to transform the governing PDE's into ODE's. Obtained system of ODE's are solved analytically by HAM. Influence of flow variables on velocity, temperature, concentration, skin friction and Sherwood number are analyzed. Obtained outcome shows that velocity enhanced through curvature parameter, viscoelastic parameter and velocities ratio variable. Temperature decays for larger Prandtl number, thermal stratification, thermal relaxation and curvature parameter. Sherwood number and concentration field show opposite behavior for higher estimation of activation energy, reaction rate, curvature parameter and Schmidt number.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Duan, Guo Xing; Hatchtel, Jordan; Shen, Xiao

Here, we investigate negative-bias temperature instabilities in SiGe pMOSFETs with SiO 2/HfO 2 gate dielectrics. The activation energies we measured for interface-trap charge buildup during negative-bias temperature stress were lower for SiGe channel pMOSFETs with SiO 2/HfO 2 gate dielectrics and Si capping layers than for conventional Si channel pMOSFETs with SiO 2 gate dielectrics. Electron energy loss spectroscopy and scanning transmission electron microscopy images demonstrate that Ge atoms can diffuse from the SiGe layer into the Si capping layer, which is adjacent to the SiO 2/HfO 2 gate dielectric. Density functional calculations show that these Ge atoms reduce themore » strength of nearby Si-H bonds and that Ge-H bond energies are still lower, thereby reducing the activation energy for interface-trap generation for the SiGe devices. Moreover, activation energies for oxide-trap charge buildup during negative-bias temperature stress are similarly small for SiGe pMOSFETs with SiO 2/HfO 2 gate dielectrics and Si pMOSFETs with SiO 2 gate dielectrics, suggesting that, in both cases, the oxide-trap charge buildup likely is rate-limited by hole tunneling into the near-interfacial SiO 2.« less

Temperature-Dependent Lithium-Ion Diffusion and Activation Energy of Li1.2Co0.13Ni0.13Mn0.54O2 Thin-Film Cathode at Nanoscale by Using Electrochemical Strain Microscopy.

PubMed

Yang, Shan; Yan, Binggong; Wu, Jiaxiong; Lu, Li; Zeng, Kaiyang

2017-04-26

This paper presents the in situ mapping of temperature-dependent lithium-ion diffusion at the nanometer level in thin film Li 1.2 Co 0.13 Ni 0.13 Mn 0.54 O 2 cathode using electrochemical strain microscopy. The thin-film Li 1.2 Co 0.13 Ni 0.13 Mn 0.54 O 2 cathode exhibits higher lithium-ion diffusivities with increasing temperature, which explains the higher capacity observed in the lithium-ion batteries with a Li-rich cathode at elevated temperature. In addition, the activation energy for lithium-ion diffusion can be extracted in an Arrhenius-type plot at the level of grain structure with the assumption that the ionic movement is diffusion controlled. Compared with the grain interiors, the grain boundaries show relatively lower activation energy; hence, it is the preferred diffusion path for lithium ions. This study has bridged the gap between atomistic calculations and traditional macroscopic experiments, showing direct evidence as well as mechanisms for ionic diffusion for Li-rich cathode material.

Microinhomogeneities in Semi-Insulating Cd(Zn)Te

DOE PAGES

Fochuk, P.; Nykoniuk, Y.; Zakharuk, Z.; ...

2017-09-04

Here, we investigated the temperature dependences (TDs) in the range of 290-423 K for the Hall constant R H and the Hall carrier mobility μn (σ R H) in semi-insulating Cd 0.9 Zn 0.1 Te:In (CZT) crystals. As-grown, CZT material has nonequilibrium distributions of native and impurity-related defects. Thus, before taking any measurements, the samples were kept inside the test chamber in the dark at 423 K to reach an equilibrium state at T <; 423 K. For all the tested samples, the R H TD could be described by two activation energies. At the transitional point, the TD ofmore » the carrier mobility also changes from “normal” at high temperatures to “exponential” at low temperatures. The latter is a result of the collective effect of drift barriers due to microinhomogeneity. Therefore, only the high-temperature activation energies can be assigned to the ionization energies of the compensated deep donors (ε D). For different samples, the values for ε D 0 (at absolute zero) were found to be in the range of 0.50-0.78 eV, and the degree of donor compensation [D +]/[D] is between 0.3 and 0.98. The low-temperature region, where there are strong effects of crystal microinhomogeneities, cannot be used to characterize the ionization energy of donors. Therefore, we describe the activation energy as ε 1 = ε D - αε b, where ε b is the drift barrier height found from the TD of the carrier mobility and α takes a value close to unity. Values of ε b for our studied samples lie within (0.05-0.35) eV.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fochuk, P.; Nykoniuk, Y.; Zakharuk, Z.

Here, we investigated the temperature dependences (TDs) in the range of 290-423 K for the Hall constant R H and the Hall carrier mobility μn (σ R H) in semi-insulating Cd 0.9 Zn 0.1 Te:In (CZT) crystals. As-grown, CZT material has nonequilibrium distributions of native and impurity-related defects. Thus, before taking any measurements, the samples were kept inside the test chamber in the dark at 423 K to reach an equilibrium state at T <; 423 K. For all the tested samples, the R H TD could be described by two activation energies. At the transitional point, the TD ofmore » the carrier mobility also changes from “normal” at high temperatures to “exponential” at low temperatures. The latter is a result of the collective effect of drift barriers due to microinhomogeneity. Therefore, only the high-temperature activation energies can be assigned to the ionization energies of the compensated deep donors (ε D). For different samples, the values for ε D 0 (at absolute zero) were found to be in the range of 0.50-0.78 eV, and the degree of donor compensation [D +]/[D] is between 0.3 and 0.98. The low-temperature region, where there are strong effects of crystal microinhomogeneities, cannot be used to characterize the ionization energy of donors. Therefore, we describe the activation energy as ε 1 = ε D - αε b, where ε b is the drift barrier height found from the TD of the carrier mobility and α takes a value close to unity. Values of ε b for our studied samples lie within (0.05-0.35) eV.« less

Temperature-Responsive Luminescent Solar Concentrators: Tuning Energy Transfer in a Liquid Crystalline Matrix.

PubMed

Sol, Jeroen A H P; Dehm, Volker; Hecht, Reinhard; Würthner, Frank; Schenning, Albertus P H J; Debije, Michael G

2018-01-22

Temperature-responsive luminescent solar concentrators (LSCs) have been fabricated in which the Förster resonance energy transfer (FRET) between a donor-acceptor pair in a liquid crystalline solvent can be tuned. At room temperatures, the perylene bisimide (PBI) acceptor is aggregated and FRET is inactive; while after heating to a temperature above the isotropic phase of the liquid crystal solvent, the acceptor PBI completely dissolves and FRET is activated. This unusual temperature control over FRET was used to design a color-tunable LSC. The device has been shown to be highly stable towards consecutive heating and cooling cycles, making it an appealing device for harvesting otherwise unused solar energy. © 2017 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

Marcus Bell-Shaped Electron Transfer Kinetics Observed in an Arrhenius Plot.

PubMed

Waskasi, Morteza M; Kodis, Gerdenis; Moore, Ana L; Moore, Thomas A; Gust, Devens; Matyushov, Dmitry V

2016-07-27

The Marcus theory of electron transfer predicts a bell-shaped dependence of the reaction rate on the reaction free energy. The top of the "inverted parabola" corresponds to zero activation barrier when the electron-transfer reorganization energy and the reaction free energy add up to zero. Although this point has traditionally been reached by altering the chemical structures of donors and acceptors, the theory suggests that it can also be reached by varying other parameters of the system including temperature. We find here dramatic evidence of this phenomenon from experiments on a fullerene-porphyrin dyad. Following photoinduced electron transfer, the rate of charge recombination shows a bell-shaped dependence on the inverse temperature, first increasing with cooling and then decreasing at still lower temperatures. This non-Arrhenius rate law is a result of a strong, approximately hyperbolic temperature variation of the reorganization energy and the reaction free energy. Our results provide potentially the cleanest confirmation of the Marcus energy gap law so far since no modification of the chemical structure is involved.

On the crystallization of amorphous germanium films

NASA Astrophysics Data System (ADS)

Edelman, F.; Komem, Y.; Bendayan, M.; Beserman, R.

1993-06-01

The incubation time for crystallization of amorphous Ge (a-Ge) films, deposited by e-gun, was studied as a function of temperature between 150 and 500°C by means of both in situ transmission electron microscopy and Raman scattering spectroscopy. The temperature dependence of t0 follows an Arrhenius curve with an activation energy of 2.0 eV for free-sustained a-Ge films. In the case where the a-Ge films were on Si 3N 4 substrate, the activation energy of the incubation process was 1.3 eV.

Influence of several metal ions on the gelation activation energy of silicon tetraethoxide

NASA Technical Reports Server (NTRS)

Bansal, Narottam P.

1988-01-01

The effects of nine metal cations (Li(+), Na(+), Mg(2+), Ca(2+), Sr(2+), Cu(2+), Al(3+), La(3+), and Y(3+) on silica gel formation has been investigated by studying the hydrolysis and polycondensation of silicon tetraethoxide (TEOS) in the presence of metal nitrates. The influence of water: TEOS mole ratio, metal ion concentration, and the reaction temperature has been investigated. The overall activation energy for gel formation has been determined from the temperature dependence of the time of gelation for each system. The activation energy for -Si-O-Si- network formation is found to be 54.5 kJ/mol. The gel formation time as well as the activation energy sharply increase in the presence of Cu(2+), Al(3+), La(3+) and Y(3+). In contrast, the presence of Li(+), Na(+), Mg(2+), Ca(2+), or, Sr(2+) lowers the gelation time, but has no appreciable effect on the activation energy. This difference may be attributed to the participation or nonparticipation of the metal ions in the formation of the three-dimensional polymeric network during the polycondensation step. The concentration of metal ion (Mg(2+), Ca(2+), Y(3+) or the water: TEOS mole ratio had no appreciable effect on the gelation activation energy. A simple test has been proposed to determine whether a metal ion would act as a network intermediate or modifier in silica and other glassy networks.

Central Neural Regulation of Brown Adipose Tissue Thermogenesis and Energy Expenditure

PubMed Central

Tupone, Domenico

2014-01-01

SUMMARY Thermogenesis, the production of heat energy, is the specific, neurally-regulated, metabolic function of brown adipose tissue (BAT) and contributes to the maintenance of body temperature during cold exposure and to the elevated core temperature during several behavioral states, including wakefulness, the acute phase response (fever), and stress. BAT energy expenditure requires metabolic fuel availability and contributes to energy balance. This review summarizes the functional organization and neurochemical influences within the CNS networks governing the level of BAT sympathetic nerve activity to produce the thermoregulatory and metabolically-driven alterations in BAT thermogenesis and energy expenditure that contribute to overall energy homeostasis. PMID:24630813

Activation energy measurements of cheese

USDA-ARS?s Scientific Manuscript database

Temperature sweeps of cheeses using small amplitude oscillatory shear tests produced values for activation energy of flow (Ea) between 30 and 44 deg C. Soft goat cheese and Queso Fresco, which are high-moisture cheeses and do not flow when heated, exhibited Ea values between 30 and 60 kJ/mol. The ...

Analysis of temperature difference on the total of energy expenditure during static bicycle exercise

NASA Astrophysics Data System (ADS)

Sugiono

2016-04-01

How to manage energy expenditure for cyclist is very crucial part to achieve a good performance. As the tropical situation, the differences of temperature level might be contributed in energy expenditure and durability. The aim of the paper is to estimate and to analysis the configuration of energy expenditure for static cycling activity based on heart rate value in room with air conditioning (AC)/no AC treatment. The research is started with study literatures of climate factors, temperature impact on human body, and definition of energy expenditure. The next step is design the experiment for 5 participants in 2 difference models for 26.80C - 74% relative humidity (room no AC) and 23,80C - 54.8% relative humidity (room with AC). The participants’ heart rate and blood pressure are measured in rest condition and in cycling condition to know the impact of difference temperature in energy expenditure profile. According to the experiment results, the reducing of the temperature has significantly impact on the decreasing of energy expenditure at average 0.3 Kcal/minute for all 5 performers. Finally, the research shows that climate condition (temperature and relative humidity) are very important factors to manage and to reach a higher performance of cycling sport.

Warm up I: potential mechanisms and the effects of passive warm up on exercise performance.

PubMed

Bishop, David

2003-01-01

Despite limited scientific evidence supporting their effectiveness, warm-up routines prior to exercise are a well-accepted practice. The majority of the effects of warm up have been attributed to temperature-related mechanisms (e.g. decreased stiffness, increased nerve-conduction rate, altered force-velocity relationship, increased anaerobic energy provision and increased thermoregulatory strain), although non-temperature-related mechanisms have also been proposed (e.g. effects of acidaemia, elevation of baseline oxygen consumption (.VO(2)) and increased postactivation potentiation). It has also been hypothesised that warm up may have a number of psychological effects (e.g. increased preparedness). Warm-up techniques can be broadly classified into two major categories: passive warm up or active warm up. Passive warm up involves raising muscle or core temperature by some external means, while active warm up utilises exercise. Passive heating allows one to obtain the increase in muscle or core temperature achieved by active warm up without depleting energy substrates. Passive warm up, although not practical for most athletes, also allows one to test the hypothesis that many of the performance changes associated with active warm up can be largely attributed to temperature-related mechanisms.

Production of oxygen from lunar ilmenite

NASA Technical Reports Server (NTRS)

Shadman, F.; Zhao, Y.

1991-01-01

The kinetics and the mechanism of reduction of synthetic ilmenite by hydrogen in the temperature range of 807 to 1014 C were investigated. At temperatures below 876 C, the temporal profiles of conversion have a sigmoidal shape and indicate the presence of three different stages (induction, acceleration, and deceleration) during the reduction reaction. The apparent activation energy for the reaction is 22.3 kcal/mole, whereas the intrinsic activation energy is 16.9 kcal/mole. Scanning electron microscopy and energy dispersive x-ray analyses show that the diffusion of Fe product away from the reaction front and through the TiO2 phase, followed by the nucleation and growth of a separate Fe phase is an important step affecting the process kinetics. X-ray diffraction and wavelength dispersive x-ray results indicate that the TiO2 can be reduced to lower oxides of titanium at temperatures higher than 876 C.

Desorption Kinetics of H2O from Cab-O-Sil-M-7D and Hi-Sil-233 Silica Particles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dinh, L.; Balooch, M.; LeMay, J.D.

2000-01-26

Temperature programmed desorption (TPD) was performed at temperatures up to 850K on Cab-O-Sil-M-7D and Hi-Sil-233 silica particles. Physisorbed water molecules on both types of silica had activation energies in the range of 9-14.5 kcal/mol. However, the activation energies of desorption for chemisorbed water varied from {approx} 19 kcal/mol to > 59 kcal/mol for Cab-O-Sil-M-7D, and {approx} 23-37 kcal/mol for Hi-Sil-233. Our results suggest that physisorbed water can be effectively pumped away at room temperature (or preferably at 320 K) in a matter of hours. Chemisorbed water with high activation energies of desorption (>30 kcal/mol) will not escape the silica surfacesmore » in 100 years even at 320 K, while a significant amount of the chemisorbed water with medium activation energies (19-26 kcal/mol) will leave the silica surfaces in that time span. Most of the chemisorbed water with activation energies < 30 kcal/mol can be pumped away in a matter of days in a good vacuum environment at 500 K. We had previously measured about 0.1-0.4 wt. % of water in M9787 polysiloxane formulations containing {approx} 21% Cab-O-Sil-M-7D and {approx} 4% Hi-Sil-233. Comparing present results with these formulations, we conclude that absorbed H{sub 2}O and Si-OH bonds on the silica surfaces are the major contributors to water outgassing from M97 series silicones.« less

Effects of biopretreatment of corn stover with white-rot fungus on low-temperature pyrolysis products.

PubMed

Yang, Xuewei; Ma, Fuying; Yu, Hongbo; Zhang, Xiaoyu; Chen, Shulin

2011-02-01

The thermal decomposition of biopretreated corn stover during the low temperature has been studied by using the Py-GC/MS analysis and thermogravimetric analysis with the distributed activation energy model (DAEM). Results showed that biopretreatment with white-rot fungus Echinodontium taxodii 2538 can improve the low-temperature pyrolysis of biomass, by increasing the pyrolysis products of cellulose, hemicellulose (furfural and sucrose increased up to 4.68-fold and 2.94-fold respectively) and lignin (biophenyl and 3,7,11,15-tetramethyl-2-hexadecen-1-ol increased 2.45-fold and 4.22-fold, respectively). Calculated by DAEM method, it showed that biopretreatment can decrease the activation energy during the low temperature range, accelerate the reaction rate and start the thermal decomposition with lower temperature. ATR-FTIR results showed that the deconstruction of lignin and the decomposition of the main linkages between hemicellulose and lignin could contribute to the improvement of the pyrolysis at low temperature. Copyright © 2010 Elsevier Ltd. All rights reserved.

Radioluminescence as a function of temperature and low temperature thermoluminescence of BaY2F8:Ce and BaY2F8:Nd crystals

NASA Astrophysics Data System (ADS)

Kowalski, Z.; Kaczmarek, S. M.; Brylew, K.; Drozdowski, W.

2016-09-01

Radioluminescence spectra at temperatures ranging from 10 to 320 K and low temperature thermoluminescence glow curves of BaY2F8:Ce and BaY2F8:Nd scintillator crystals have been investigated. In both materials the intensities of the excitonic and the activator ion's emission at X-ray excitation vary with temperature, anticorrelating with each other, which provides valuable information on the host-to-ion energy transfer. Detailed thermoluminescence studies, in turn, prove the existence of charge traps, which introduce quasi-continuous distributions of energy levels into the bandgap.

The effective temperature of Peptide ions dissociated by sustained off-resonance irradiation collisional activation in fourier transform mass spectrometry.

PubMed

Schnier, P D; Jurchen, J C; Williams, E R

1999-01-28

A method for determining the internal energy of biomolecule ions activated by collisions is demonstrated. The dissociation kinetics of protonated leucine enkephalin and doubly protonated bradykinin were measured using sustained off-resonance irradiation (SORI) collisionally activated dissociation (CAD) in a Fourier transform mass spectrometer. Dissociation rate constants are obtained from these kinetic data. In combination with Arrhenius parameters measured with blackbody infrared radiative dissociation, the "effective" temperatures of these ions are obtained. Effects of excitation voltage and frequency and the ion cell pressure were investigated. With typical SORI-CAD experimental conditions, the effective temperatures of these peptide ions range between 200 and 400 degrees C. Higher temperatures can be easily obtained for ions that require more internal energy to dissociate. The effective temperatures of both protonated leucine enkephalin and doubly protonated bradykinin measured with the same experimental conditions are similar. Effective temperatures for protonated leucine enkephalin can also be obtained from the branching ratio of the b(4) and (M + H - H(2)O)(+) pathways. Values obtained from this method are in good agreement with those obtained from the overall dissociation rate constants. Protonated leucine enkephalin is an excellent "thermometer" ion and should be well suited to establishing effective temperatures of ions activated by other dissociation techniques, such as infrared photodissociation, as well as ionization methods, such as matrix assisted laser desorption/ionization.

The Effective Temperature of Peptide Ions Dissociated by Sustained Off-Resonance Irradiation Collisional Activation in Fourier Transform Mass Spectrometry

PubMed Central

Schnier, Paul D.; Jurchen, John C.; Williams, Evan R.

2005-01-01

A method for determining the internal energy of biomolecule ions activated by collisions is demonstrated. The dissociation kinetics of protonated leucine enkephalin and doubly protonated bradykinin were measured using sustained off-resonance irradiation (SORI) collisionally activated dissociation (CAD) in a Fourier transform mass spectrometer. Dissociation rate constants are obtained from these kinetic data. In combination with Arrhenius parameters measured with blackbody infrared radiative dissociation, the “effective” temperatures of these ions are obtained. Effects of excitation voltage and frequency and the ion cell pressure were investigated. With typical SORI–CAD experimental conditions, the effective temperatures of these peptide ions range between 200 and 400 °C. Higher temperatures can be easily obtained for ions that require more internal energy to dissociate. The effective temperatures of both protonated leucine enkephalin and doubly protonated bradykinin measured with the same experimental conditions are similar. Effective temperatures for protonated leucine enkephalin can also be obtained from the branching ratio of the b4 and (M + H − H2O)+ pathways. Values obtained from this method are in good agreement with those obtained from the overall dissociation rate constants. Protonated leucine enkephalin is an excellent “thermometer” ion and should be well suited to establishing effective temperatures of ions activated by other dissociation techniques, such as infrared photodissociation, as well as ionization methods, such as matrix assisted laser desorption/ionization. PMID:16614752

Auroral origin of medium scale gravity waves in neutral composition and temperature

NASA Technical Reports Server (NTRS)

Chandra, S.; Spencer, N. W.; Krankowsky, D.; Laemmerzahl, P.

1979-01-01

The kinetic temperature and neutral composition data obtained from the Aeros B neutral atmosphere temperature experiment and the neutral and ion mass spectrometer show spatial structures characteristic of medium scale gravity waves with a wavelength in the range of several hundred kilometers. These waves are associated with auroral activity, and their spatial structure reflects the time history of the auroral electrojet. The medium scale gravity waves tend to propagate to mid-latitudes on the nightside. On the dayside their range is limited to high latitudes. Gravity waves are carriers of auroral energy to middle and low latitudes where they may cause irreversible changes in temperature via viscous dissipation. Since auroral activity occurs frequently, it is suggested that this energy reaches the mid-latitude region of the thermosphere much more frequently than is indicated by planetary magnetic indices.

Statistical evaluation of accelerated stability data obtained at a single temperature. I. Effect of experimental errors in evaluation of stability data obtained.

PubMed

Yoshioka, S; Aso, Y; Takeda, Y

1990-06-01

Accelerated stability data obtained at a single temperature is statistically evaluated, and the utility of such data for assessment of stability is discussed focussing on the chemical stability of solution-state dosage forms. The probability that the drug content of a product is observed to be within the lower specification limit in the accelerated test is interpreted graphically. This probability depends on experimental errors in the assay and temperature control, as well as the true degradation rate and activation energy. Therefore, the observation that the drug content meets the specification in the accelerated testing can provide only limited information on the shelf-life of the drug, without the knowledge of the activation energy and the accuracy and precision of the assay and temperature control.

Temperature dependence of rat liver mitochondrial respiration with uncoupling of oxidative phosphorylation by fatty acids. Influence of inorganic phosphate.

PubMed

Samartsev, V N; Chezganova, S A; Polishchuk, L S; Paydyganov, A P; Vidyakina, O V; Zeldi, I P

2003-06-01

The respiration rate of liver mitochondria in the course of succinate oxidation depends on temperature in the presence of palmitate more strongly than in its absence (in state 4). In the Arrhenius plot, the temperature dependence of the palmitate-induced stimulation of respiration has a bend at 22 degrees C which is characterized by transition of the activation energy from 120 to 60 kJ/mol. However, a similar dependence of respiration in state 4 is linear over the whole temperature range and corresponds to the activation energy of 17 kJ/mol. Phosphate partially inhibits the uncoupling effect of palmitate. This effect of phosphate is increased on decrease in temperature. In the presence of phosphate the temperature dependence in the Arrhenius plot also has a bend at 22 degrees C, and the activation energy increases from 128 to 208 kJ/mol in the range from 13 to 22 degrees C and from 56 to 67 kJ/mol in the range from 22 to 37 degrees C. Mersalyl (10 nmol/mg protein), an inhibitor of the phosphate carrier, similarly to phosphate, suppresses the uncoupling effect of laurate, and the effects of mersalyl and phosphate are not additive. The recoupling effects of phosphate and mersalyl seem to show involvement of the phosphate carrier in the uncoupling effect of fatty acids in liver mitochondria. Possible mechanisms of involvement of the phosphate carrier in the uncoupling effect of fatty acids are discussed.

THE KINETICS AND THERMODYNAMICS OF REVERSIBLE DENATURATION OF CRYSTALLINE SOYBEAN TRYPSIN INHIBITOR

PubMed Central

Kunitz, M.

1948-01-01

Crystalline soybean trypsin inhibitor protein undergoes denaturation on heating which is reversed on cooling. In the range of temperature of 35 to 50°C. a solution of the protein consists of a mixture of native and denatured forms in equilibrium with each other. The equilibrium is only slowly established and its final value at any temperature is the same whether a heated, denatured solution of the protein is cooled to the given temperature or whether a fresh solution is raised to that temperature. The kinetics of reversible denaturation of the soybean protein as well as the reversal of denaturation is that of a reversible unimolecular reaction, each process consisting at a given temperature of the same two simultaneous reactions acting in opposite directions. The experimental data on the effect of temperature on the velocity and the equilibrium constants of the opposing reaction were utilized in evaluating the reaction energies and activation energies. The reaction energies for denaturation were found to be as follows:— Change in total heat of reaction ΔH = 57,000 calories per mole Change in entropy of reaction ΔS = 180 calories per degree per mole The heat of activation ΔH 1 ‡ for denaturation = 55,000 The heat of activation ΔH 2 ‡ for the reversal of denaturation = –1900 The entropy ΔS 1 ‡ for denaturation = 95 The entropy ΔS 2 ‡ for reversal of denaturation = –84 PMID:18891149

Validation and divergence of the activation energy barrier crossing transition at the AOT/lecithin reverse micellar interface.

PubMed

Narayanan, S Shankara; Sinha, Sudarson Sekhar; Sarkar, Rupa; Pal, Samir Kumar

2008-03-13

In this report, the validity and divergence of the activation energy barrier crossing model for the bound to free type water transition at the interface of the AOT/lecithin mixed reverse micelle (RM) has been investigated for the first time in a wide range of temperatures by time-resolved solvation of fluorophores. Here, picosecond-resolved solvation dynamics of two fluorescent probes, ANS (1-anilino-8-naphthalenesulfonic acid, ammonium salt) and Coumarin 500 (C-500), in the mixed RM have been carefully examined at 293, 313, 328, and 343 K. Using the dynamic light scattering (DLS) technique, the size of the mixed RMs at different temperatures was found to have an insignificant change. The solvation process at the reverse micellar interface has been found to be the activation energy barrier crossing type, in which interface-bound type water molecules get converted into free type water molecules. The activation energies, Ea, calculated for ANS and C-500 are 7.4 and 3.9 kcal mol(-1), respectively, which are in good agreement with that obtained by molecular dynamics simulation studies. However, deviation from the regular Arrhenius type behavior was observed for ANS around 343 K, which has been attributed to the spatial heterogeneity of the probe environments. Time-resolved fluorescence anisotropy decay of the probes has indicated the existence of the dyes in a range of locations in RM. With the increase in temperature, the overall anisotropy decay becomes faster revealing the lability of the microenvironment at elevated temperatures.

Geothermal Energy.

ERIC Educational Resources Information Center

Bufe, Charles Glenn

1983-01-01

Major activities, programs, and conferences in geothermal energy during 1982 are highlighted. These include first comprehensive national assessment of U.S. low-temperature geothermal resources (conducted by U.S. Geological Survey and Department of Energy), map production by U.S. Geological Survey, geothermal plant production, and others. (JN)

Kinetic and thermodynamic studies of a novel acid protease from Aspergillus foetidus.

PubMed

Souza, Paula Monteiro; Aliakbarian, Bahar; Filho, Edivaldo Ximenes Ferreira; Magalhães, Pérola Oliveira; Junior, Adalberto Pessoa; Converti, Attilio; Perego, Patrizia

2015-11-01

The kinetics of a thermostable extracellular acid protease produced by an Aspergillus foetidus strain was investigated at different pH, temperatures and substrate concentrations. The enzyme exhibited maximal activity at pH 5.0 and 55°C, and its irreversible deactivation was well described by first-order kinetics. When temperature was raised from 55 to 70°C, the deactivation rate constant increased from 0.018 to 5.06h(-1), while the half-life decreased from 37.6 to 0.13h. The results of activity collected at different temperatures were then used to estimate, the activation energy of the hydrolysis reaction (E*=19.03kJ/mol) and the standard enthalpy variation of reversible enzyme unfolding (ΔH°U=19.03kJ/mol). The results of residual activity tests carried out in the temperature range 55-70°C allowed estimating the activation energy (E(*)d=314.12kJ/mol), enthalpy (311.27≤(ΔH°d≤311.39kJ/mol), entropy (599.59≤ΔS(*)d≤610.49kJ/mol K) and Gibbs free energy (103.18≤ΔG(*)d≤113.87kJ/mol) of the enzyme irreversible denaturation. These thermodynamic parameters suggest that this new protease is highly thermostable and could be important for industrial applications. To the best of our knowledge, this is the first report on thermodynamic parameters of an acid protease produced by A. foetidus. Copyright © 2015 Elsevier B.V. All rights reserved.

Thermal stability and degradation kinetics of kenaf/sol-gel silica hybrid

NASA Astrophysics Data System (ADS)

Yusof, F. A. M.; Hashim, A. S.; Tajudin, Z.

2017-12-01

Thermal stability and degradation kinetics of kenaf/sol-gel silica hybrid materials was investigated by thermogravimetric analysis (TGA). Model-free iso-conversion Flynn-Wall-Ozawa (FWO) and Coats-Redfern-modified (CRm) were chosen to evaluate the activation energy of the kenaf (KF) and kenaf/sol-gel silica (KFS) at heating rates (β) of 10, 20, 30 and 40 °C/min. The results shows that an apparent activation energy was increased for the kenaf/sol-gel silica hybrid (211.59 kJ/mol for FWO and 191.55 kJ/mol for CRm) as compared to kenaf fiber (202.84 kJ/mol for FWO and 186.20 kJ/mol for CRm). Other parameters such as integral procedure decomposition temperature (IPDT), final residual weight (Rf), temperature of maximum degradation rate (Tmax) and residual at maximum temperature (RTmax) were obtained from TGA curves, additionally confirmed the thermal stability of the kenaf/sol-gel silica hybrid. These activation energy values and other findings developed the simplified approach in order to understand the thermal stability and degradation kinetics behavior of kenaf/sol-gel silica hybrid materials.

Kinetics of coffee industrial residue pyrolysis using distributed activation energy model and components separation of bio-oil by sequencing temperature-raising pyrolysis.

PubMed

Chen, Nanwei; Ren, Jie; Ye, Ziwei; Xu, Qizhi; Liu, Jingyong; Sun, Shuiyu

2016-12-01

This study was carried out to investigate the kinetics of coffee industrial residue (CIR) pyrolysis, the effect of pyrolysis factors on yield of bio-oil component and components separation of bio-oil. The kinetics of CIR pyrolysis was analyzed using distributed activation energy model (DAEM), based on the experiments in thermogravimetric analyzer (TGA), and it indicated that the average of activation energy (E) is 187.86kJ·mol -1 . The bio-oils were prepared from CIR pyrolysis in vacuum tube furnace, and its components were determined by gas chromatography/mass spectrometry (GC-MS). Among pyrolysis factors, pyrolysis temperature is the most influential factor on components yield of bio-oil, directly concerned with the volatilization and yield of components (palmitic acid, linoleic acid, oleic acid, octadecanoic acid and caffeine). Furthermore, a new method (sequencing temperature-raising pyrolysis) was put forward and applied to the components separation of bio-oil. Based on experiments, a solution of components separation of bio-oil was come out. Copyright © 2016 Elsevier Ltd. All rights reserved.

Temperature and chain length dependence of ultrafast vibrational dynamics of thiocyanate in alkylimidazolium ionic liquids: A random walk on a rugged energy landscape.

PubMed

Brinzer, Thomas; Garrett-Roe, Sean

2017-11-21

Ultrafast two-dimensional infrared spectroscopy of a thiocyanate vibrational probe (SCN - ) was used to investigate local dynamics in alkylimidazolium bis-[trifluoromethylsulfonyl]imide ionic liquids ([Im n,1 ][Tf 2 N], n = 2, 4, 6) at temperatures from 5 to 80 °C. The rate of frequency fluctuations reported by SCN - increases with increasing temperature and decreasing alkyl chain length. Temperature-dependent correlation times scale proportionally to temperature-dependent bulk viscosities of each ionic liquid studied. A multimode Brownian oscillator model demonstrates that very low frequency (<10 cm -1 ) modes primarily drive the observed spectral diffusion and that these modes broaden and blue shift on average with increasing temperature. An Arrhenius analysis shows activation barriers for local motions around the probe between 5.5 and 6.5 kcal/mol that are very similar to those for translational diffusion of ions. [Im 6,1 ][Tf 2 N] shows an unexpected decrease in activation energy compared to [Im 4,1 ][Tf 2 N] that may be related to mesoscopically ordered polar and nonpolar domains. A model of dynamics on a rugged potential energy landscape provides a unifying description of the observed Arrhenius behavior and the Brownian oscillator model of the low frequency modes.

Electronic transport in smectic liquid crystals

NASA Astrophysics Data System (ADS)

Shiyanovskaya, I.; Singer, K. D.; Twieg, R. J.; Sukhomlinova, L.; Gettwert, V.

2002-04-01

Time-of-flight measurements of transient photoconductivity have revealed bipolar electronic transport in phenylnaphthalene and biphenyl liquid crystals (LC), which exhibit several smectic mesophases. In the phenylnaphthalene LC, the hole mobility is significantly higher than the electron mobility and exhibits different temperature and phase behavior. Electron mobility in the range ~10-5 cm2/V s is temperature activated and remains continuous at the phase transitions. However, hole mobility is nearly temperature independent within the smectic phases, but is very sensitive to smectic order, 10-3 cm2/V s in the smectic-B (Sm-B) and 10-4 cm2/V s in the smectic-A (Sm-A) mesophases. The different behavior for holes and electron transport is due to differing transport mechanisms. The electron mobility is apparently controlled by rate-limiting multiple shallow trapping by impurities, but hole mobility is not. To explain the lack of temperature dependence for hole mobility within the smectic phases we consider two possible polaron transport mechanisms. The first mechanism is based on the hopping of Holstein small polarons in the nonadiabatic limit. The polaron binding energy and transfer integral values, obtained from the model fit, turned out to be sensitive to the molecular order in smectic mesophases. A second possible scenario for temperature-independent hole mobility involves the competion between two different polaron mechanisms involving so-called nearly small molecular polarons and small lattice polarons. Although the extracted transfer integrals and binding energies are reasonable and consistent with the model assumptions, the limited temperature range of the various phases makes it difficult to distinguish between any of the models. In the biphenyl LCs both electron and hole mobilities exhibit temperature activated behavior in the range of 10-5 cm2/V s without sensitivity to the molecular order. The dominating transport mechanism is considered as multiple trapping in the impurity sites. Temperature-activated mobility was treated within the disorder formalism, and activation energy and width of density of states have been calculated.

Negligible carrier freeze-out facilitated by impurity band conduction in highly p-type GaN

NASA Astrophysics Data System (ADS)

Gunning, Brendan; Lowder, Jonathan; Moseley, Michael; Alan Doolittle, W.

2012-08-01

Highly p-type GaN films with hole concentrations exceeding 6 × 1019 cm-3 grown by metal-modulated epitaxy are electrically characterized. Temperature-dependent Hall effect measurements at cryogenic temperatures reveal minimal carrier freeze-out in highly doped samples, while less heavily doped samples exhibited high resistivity and donor-compensated conductivity as is traditionally observed. Effective activation energies as low as 43 meV were extracted, and a maximum Mg activation efficiency of 52% was found. In addition, the effective activation energy was found to be negatively correlated to the hole concentration. These results indicate the onset of the Mott-Insulator transition leading to impurity band conduction.

Activation energy and energy density: a bioenergetic framework for assessing soil organic matter stability

NASA Astrophysics Data System (ADS)

Williams, E. K.; Plante, A. F.

2017-12-01

The stability and cycling of natural organic matter depends on the input of energy needed to decompose it and the net energy gained from its decomposition. In soils, this relationship is complicated by microbial enzymatic activity which decreases the activation energies associated with soil organic matter (SOM) decomposition and by chemical and physical protection mechanisms which decreases the concentrations of the available organic matter substrate and also require additional energies to overcome for decomposition. In this study, we utilize differential scanning calorimetry and evolved CO2 gas analysis to characterize differences in the energetics (activation energy and energy density) in soils that have undergone degradation in natural (bare fallow), field (changes in land-use), chemical (acid hydrolysis), and laboratory (high temperature incubation) experimental conditions. We will present this data in a novel conceptual framework relating these energy dynamics to organic matter inputs, decomposition, and molecular complexity.

Computing the Viscosity of Supercooled Liquids: Markov Network Model

PubMed Central

Li, Ju; Kushima, Akihiro; Eapen, Jacob; Lin, Xi; Qian, Xiaofeng; Mauro, John C.; Diep, Phong; Yip, Sidney

2011-01-01

The microscopic origin of glass transition, when liquid viscosity changes continuously by more than ten orders of magnitude, is challenging to explain from first principles. Here we describe the detailed derivation and implementation of a Markovian Network model to calculate the shear viscosity of deeply supercooled liquids based on numerical sampling of an atomistic energy landscape, which sheds some light on this transition. Shear stress relaxation is calculated from a master-equation description in which the system follows a transition-state pathway trajectory of hopping among local energy minima separated by activation barriers, which is in turn sampled by a metadynamics-based algorithm. Quantitative connection is established between the temperature variation of the calculated viscosity and the underlying potential energy and inherent stress landscape, showing a different landscape topography or “terrain” is needed for low-temperature viscosity (of order 107 Pa·s) from that associated with high-temperature viscosity (10−5 Pa·s). Within this range our results clearly indicate the crossover from an essentially Arrhenius scaling behavior at high temperatures to a low-temperature behavior that is clearly super-Arrhenius (fragile) for a Kob-Andersen model of binary liquid. Experimentally the manifestation of this crossover in atomic dynamics continues to raise questions concerning its fundamental origin. In this context this work explicitly demonstrates that a temperature-dependent “terrain” characterizing different parts of the same potential energy surface is sufficient to explain the signature behavior of vitrification, at the same time the notion of a temperature-dependent effective activation barrier is quantified. PMID:21464988

Investigation on Hot Workability of Homogenized Al-Zn-Mg-Cu Alloy Based on Activation Energy and Processing Map

NASA Astrophysics Data System (ADS)

Peng, Xiaoyan; Su, Wusen; Xiao, Dan; Xu, Guofu

2018-06-01

Hot deformation behaviors of the homogenized Al-Zn-Mg-Cu alloy were studied by uniaxial compression tests carried out at 623-743 K and strain rates of 0.01-10 s-1. The constitutive equation was developed for the activation energy, and thus the activation energy map was constructed. During the hot deformation, the dominated softening mechanisms were the dynamic recovery and dynamic recrystallization, which were most likely to be driven with increasing temperature and decreasing activation energy. Based on the superposition of the activation energy map and the processing map, together with the microstructure characteristics, the optimized hot workability of the alloy was proposed at the domain (670-743 K and 0.01-0.16 s-1), where the peak efficiency was 0.39 and the activation energy range was 196-260 kJ mol-1.

Thermodynamic Derivation of the Activation Energy for Ice Nucleation

NASA Technical Reports Server (NTRS)

Barahona, D.

2015-01-01

Cirrus clouds play a key role in the radiative and hydrological balance of the upper troposphere. Their correct representation in atmospheric models requires an understanding of the microscopic processes leading to ice nucleation. A key parameter in the theoretical description of ice nucleation is the activation energy, which controls the flux of water molecules from the bulk of the liquid to the solid during the early stages of ice formation. In most studies it is estimated by direct association with the bulk properties of water, typically viscosity and self-diffusivity. As the environment in the ice-liquid interface may differ from that of the bulk, this approach may introduce bias in calculated nucleation rates. In this work a theoretical model is proposed to describe the transfer of water molecules across the ice-liquid interface. Within this framework the activation energy naturally emerges from the combination of the energy required to break hydrogen bonds in the liquid, i.e., the bulk diffusion process, and the work dissipated from the molecular rearrangement of water molecules within the ice-liquid interface. The new expression is introduced into a generalized form of classical nucleation theory. Even though no nucleation rate measurements are used to fit any of the parameters of the theory the predicted nucleation rate is in good agreement with experimental results, even at temperature as low as 190 K, where it tends to be underestimated by most models. It is shown that the activation energy has a strong dependency on temperature and a weak dependency on water activity. Such dependencies are masked by thermodynamic effects at temperatures typical of homogeneous freezing of cloud droplets; however, they may affect the formation of ice in haze aerosol particles. The new model provides an independent estimation of the activation energy and the homogeneous ice nucleation rate, and it may help to improve the interpretation of experimental results and the development of parameterizations for cloud formation.

The temperature-dependent diffusion coefficient of helium in zirconium carbide studied with first-principles calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Xiao-Yong; Lu, Yong; Zhang, Ping, E-mail: zhang-ping@iapcm.ac.cn

2015-04-28

The temperature-dependent diffusion coefficient of interstitial helium in zirconium carbide (ZrC) matrix is calculated based on the transition state theory. The microscopic parameters in the activation energy and prefactor are obtained from first-principles total energy and phonon frequency calculations including the all atoms. The obtained activation energy is 0.78 eV, consistent with experimental value. Besides, we evaluated the influence of C and Zr vacancies as the perturbation on helium diffusion, and found the C vacancy seems to confine the mobility of helium and the Zr vacancy promotes helium diffusion in some extent. These results provide a good reference to understand themore » behavior of helium in ZrC matrix.« less

Diffusion and aggregation of subsurface radiation defects in lithium fluoride nanocrystals

NASA Astrophysics Data System (ADS)

Voitovich, A. P.; Kalinov, V. S.; Martynovich, E. F.; Stupak, A. P.; Runets, L. P.

2015-09-01

Lithium fluoride nanocrystals were irradiated by gamma rays at a temperature below the temperature corresponding to the mobility of anion vacancies. The kinetics of the aggregation of radiation-induced defects in subsurface layers of nanocrystals during annealing after irradiation was elucidated. The processes that could be used to determine the activation energy of the diffusion of anion vacancies were revealed. The value of this energy in subsurface layers was obtained. For subsurface layers, the concentrations ratio of vacancies and defects consisting of one vacancy and two electrons was found. The factors responsible for the differences in the values of the activation energies and concentration ratios in subsurface layers and in the bulk of the crystals were discussed.

From boiling point to glass transition temperature: transport coefficients in molecular liquids follow three-parameter scaling.

PubMed

Schmidtke, B; Petzold, N; Kahlau, R; Hofmann, M; Rössler, E A

2012-10-01

The phenomenon of the glass transition is an unresolved problem in condensed matter physics. Its prominent feature, the super-Arrhenius temperature dependence of the transport coefficients, remains a challenge to be described over the full temperature range. For a series of molecular glass formers, we combined τ(T) collected from dielectric spectroscopy and dynamic light scattering covering a range 10(-12) s < τ(T) < 10(2) s. Describing the dynamics in terms of an activation energy E(T), we distinguish a high-temperature regime characterized by an Arrhenius law with a constant activation energy E(∞) and a low-temperature regime for which E(coop)(T) ≡ E(T)-E(∞) increases exponentially while cooling. A scaling is introduced, specifically E(coop)(T)/E(∞) [proportionality] exp[-λ(T/T(A)-1)], where λ is a fragility parameter and T(A) a reference temperature proportional to E(∞). In order to describe τ(T) still the attempt time τ(∞) has to be specified. Thus, a single interaction parameter E(∞) describing the high-temperature regime together with λ controls the temperature dependence of low-temperature cooperative dynamics.

High-Capacity, High-Voltage Composite Oxide Cathode Materials

NASA Technical Reports Server (NTRS)

Hagh, Nader M.

2015-01-01

This SBIR project integrates theoretical and experimental work to enable a new generation of high-capacity, high-voltage cathode materials that will lead to high-performance, robust energy storage systems. At low operating temperatures, commercially available electrode materials for lithium-ion (Li-ion) batteries do not meet energy and power requirements for NASA's planned exploration activities. NEI Corporation, in partnership with the University of California, San Diego, has developed layered composite cathode materials that increase power and energy densities at temperatures as low as 0 degC and considerably reduce the overall volume and weight of battery packs. In Phase I of the project, through innovations in the structure and morphology of composite electrode particles, the partners successfully demonstrated an energy density exceeding 1,000 Wh/kg at 4 V at room temperature. In Phase II, the team enhanced the kinetics of Li-ion transport and electronic conductivity at 0 degC. An important feature of the composite cathode is that it has at least two components that are structurally integrated. The layered material is electrochemically inactive; however, upon structural integration with a spinel material, the layered material can be electrochemically activated and deliver a large amount of energy with stable cycling.

"Cooking the sample": radiofrequency induced heating during solid-state NMR experiments.

PubMed

d'Espinose de Lacaillerie, Jean-Baptiste; Jarry, Benjamin; Pascui, Ovidiu; Reichert, Detlef

2005-09-01

Dissipation of radiofrequency (RF) energy as heat during continuous wave decoupling in solid-state NMR experiment was examined outside the conventional realm of such phenomena. A significant temperature increase could occur while performing dynamic NMR measurements provided the sample contains polar molecules and the sequence calls for relatively long applications of RF power. It was shown that the methyl flip motion in dimethylsulfone (DMS) is activated by the decoupling RF energy conversion to heat during a CODEX pulse sequence. This introduced a significant bias in the correlation time-temperature dependency measurement used to obtain the activation energy of the motion. By investigating the dependency of the temperature increase in hydrated lead nitrate on experimental parameters during high-power decoupling one-pulse experiments, the mechanisms for the RF energy deposition was identified. The samples were heated due to dissipation of the energy absorbed by dielectric losses, a phenomenon commonly known as "microwave" heating. It was thus established that during solid-state NMR experiments at moderate B0 fields, RF heating could lead to the heating of samples containing polar molecules such as hydrated polymers and inorganic solids. In particular, this could result in systematic errors for slow dynamics measurements by solid-state NMR.

Electric Field-aided Selective Activation for Indium-Gallium-Zinc-Oxide Thin Film Transistors

NASA Astrophysics Data System (ADS)

Lee, Heesoo; Chang, Ki Soo; Tak, Young Jun; Jung, Tae Soo; Park, Jeong Woo; Kim, Won-Gi; Chung, Jusung; Jeong, Chan Bae; Kim, Hyun Jae

2016-10-01

A new technique is proposed for the activation of low temperature amorphous InGaZnO thin film transistor (a-IGZO TFT) backplanes through application of a bias voltage and annealing at 130 °C simultaneously. In this ‘electrical activation’, the effects of annealing under bias are selectively focused in the channel region. Therefore, electrical activation can be an effective method for lower backplane processing temperatures from 280 °C to 130 °C. Devices fabricated with this method exhibit equivalent electrical properties to those of conventionally-fabricated samples. These results are analyzed electrically and thermodynamically using infrared microthermography. Various bias voltages are applied to the gate, source, and drain electrodes while samples are annealed at 130 °C for 1 hour. Without conventional high temperature annealing or electrical activation, current-voltage curves do not show transfer characteristics. However, electrically activated a-IGZO TFTs show superior electrical characteristics, comparable to the reference TFTs annealed at 280 °C for 1 hour. This effect is a result of the lower activation energy, and efficient transfer of electrical and thermal energy to a-IGZO TFTs. With this approach, superior low-temperature a-IGZO TFTs are fabricated successfully.

Electric Field-aided Selective Activation for Indium-Gallium-Zinc-Oxide Thin Film Transistors

PubMed Central

Lee, Heesoo; Chang, Ki Soo; Tak, Young Jun; Jung, Tae Soo; Park, Jeong Woo; Kim, Won-Gi; Chung, Jusung; Jeong, Chan Bae; Kim, Hyun Jae

2016-01-01

A new technique is proposed for the activation of low temperature amorphous InGaZnO thin film transistor (a-IGZO TFT) backplanes through application of a bias voltage and annealing at 130 °C simultaneously. In this ‘electrical activation’, the effects of annealing under bias are selectively focused in the channel region. Therefore, electrical activation can be an effective method for lower backplane processing temperatures from 280 °C to 130 °C. Devices fabricated with this method exhibit equivalent electrical properties to those of conventionally-fabricated samples. These results are analyzed electrically and thermodynamically using infrared microthermography. Various bias voltages are applied to the gate, source, and drain electrodes while samples are annealed at 130 °C for 1 hour. Without conventional high temperature annealing or electrical activation, current-voltage curves do not show transfer characteristics. However, electrically activated a-IGZO TFTs show superior electrical characteristics, comparable to the reference TFTs annealed at 280 °C for 1 hour. This effect is a result of the lower activation energy, and efficient transfer of electrical and thermal energy to a-IGZO TFTs. With this approach, superior low-temperature a-IGZO TFTs are fabricated successfully. PMID:27725695

Reliability Assessment and Activation Energy Study of Au and Pd-Coated Cu Wires Post High Temperature Aging in Nanoscale Semiconductor Packaging.

PubMed

Gan, C L; Hashim, U

2013-06-01

Wearout reliability and high temperature storage life (HTSL) activation energy of Au and Pd-coated Cu (PdCu) ball bonds are useful technical information for Cu wire deployment in nanoscale semiconductor device packaging. This paper discusses the influence of wire type on the wearout reliability performance of Au and PdCu wire used in fine pitch BGA package after HTSL stress at various aging temperatures. Failure analysis has been conducted to identify the failure mechanism after HTSL wearout conditions for Au and PdCu ball bonds. Apparent activation energies (Eaa) of both wire types are investigated after HTSL test at 150 °C, 175 °C and 200 °C aging temperatures. Arrhenius plot has been plotted for each ball bond types and the calculated Eaa of PdCu ball bond is 0.85 eV and 1.10 eV for Au ball bond in 110 nm semiconductor device. Obviously Au ball bond is identified with faster IMC formation rate with IMC Kirkendall voiding while PdCu wire exhibits equivalent wearout and or better wearout reliability margin compare to conventional Au wirebond. Lognormal plots have been established and its mean to failure (t 50 ) have been discussed in this paper.

Transformation Stasis Phenomenon of Bainite Formation in Low-Carbon, Multicomponent Alloyed Steel

NASA Astrophysics Data System (ADS)

Lan, Liangyun; Kong, Xiangwei

2017-11-01

The transformation stasis phenomenon of bainite formation in low-carbon steel was detected using a high-resolution dilatometer. The phenomenon occurred at different stages for different isothermal temperatures. In combination with microstructural observation, the calculated overall activation energy of transformation and interface migration velocity shed new light on the cause of formation of the stasis phenomenon. The temporary stasis formed at the initial stage of phase transformation for high isothermal temperature was attributed to the drag effect of substitutional atoms, which leads to low-interface migration velocity and large overall activation energy.

Thermally induced evolution of hydrogenated amorphous carbon

NASA Astrophysics Data System (ADS)

Mangolini, Filippo; Rose, Franck; Hilbert, James; Carpick, Robert W.

2013-10-01

The thermally induced structural evolution of hydrogenated amorphous carbon (a-C:H) films was investigated in situ by X-ray photoelectron spectroscopy for annealing temperatures up to 500 °C. A model for the conversion of sp3- to sp2-hybridized carbon in a-C:H vs. temperature and time was developed and applied to determine the ranges of activation energies for the thermally activated processes occurring. The energies are consistent with ordering and clustering of sp2 carbon, scission of sp3 carbon-hydrogen bonds and formation of sp2 carbon, and direct transformation of sp3- to sp2-hybridized carbon.

Why Are Some Reactions Slower at Higher Temperatures?

ERIC Educational Resources Information Center

Revell, Laura E.; Williamson, Bryce E.

2013-01-01

It is well understood by most chemistry students at advanced undergraduate levels that chemical reactions generally follow the Arrhenius law of temperature dependence with positive activation energies, proceeding faster at elevated temperatures. It is much less widely known that the rates of some Arrhenius-compliant reactions are retarded by…

Temperature Dependence of Field-Effect Mobility in Organic Thin-Film Transistors: Similarity to Inorganic Transistors.

PubMed

Okada, Jun; Nagase, Takashi; Kobayashi, Takashi; Naito, Hiroyoshi

2016-04-01

Carrier transport in solution-processed organic thin-film transistors (OTFTs) based on dioctylbenzothienobenzothiophene (C8-BTBT) has been investigated in a wide temperature range from 296 to 10 K. The field-effect mobility shows thermally activated behavior whose activation energy becomes smaller with decreasing temperature. The temperature dependence of field-effect mobility found in C8-BTBT is similar to that of others materials: organic semiconducting polymers, amorphous oxide semiconductors and hydrogenated amorphous silicon. These results indicate that hopping transport between isoenergetic localized states becomes dominated in a low temperature regime in these materials.

Oxygen consumption and body temperature of active and resting honeybees.

PubMed

Stabentheiner, Auton; Vollmann, Jutta; Kovac, Helmut; Crailsheim, Karl

2003-09-01

We measured the energy turnover (oxygen consumption) of honeybees (Apis mellifera carnica), which were free to move within Warburg vessels. Oxygen consumption of active bees varied widely depending on ambient temperature and level of activity, but did not differ between foragers (>18 d) and middle-aged hive bees (7-10 d). In highly active bees, which were in an endothermic state ready for flight, it decreased almost linearly, from a maximum of 131.4 microl O(2) min(-1) at 15 degrees C ambient temperature to 81.1 microl min(-1) at 25 degrees C, and reached a minimum of 29.9 microl min(-1) at 40 degrees C. In bees with low activity, it decreased from 89.3 microl O(2) min(-1) at 15 degrees C to 47.9 microl min(-1) at 25 degrees C and 14.7 microl min(-1) at 40 degrees C. Thermographic measurements of body temperature showed that with increasing activity, the bees invested more energy to regulate the thorax temperature at increasingly higher levels (38.8-41.2 degrees C in highly active bees) and were more accurate. Resting metabolism was determined in young bees of 1-7 h age, which are not yet capable of endothermic heat production with their flight muscles. Their energy turnover increased from 0.21 microl O(2) min(-1) at 10 degrees C to 0.38 microl min(-1) at 15 degrees C, 1.12 microl min(-1) at 25 degrees C, and 3.03 microl min(-1) at 40 degrees C. At 15, 25 and 40 degrees C, this was 343, 73 and 10 times below the values of the highly active bees, respectively. The Q(10) value of the resting bees, however, was not constant but varied in a U-shaped manner with ambient temperature. It decreased from 4.24 in the temperature range 11-21 degrees C to 1.35 in the range 21-31 degrees C, and increased again to 2.49 in the range 30-40 degrees C. We conclude that attempts to describe the temperature dependence of the resting metabolism of honeybees by Q(10) values can lead to considerable errors if the measurements are performed at only two temperatures. An acceptable approximation can be derived by calculation of an interpolated Q(10) according to the exponential function (V(O(2))=0.151 x 1.0784(T(a))) (interpolated Q(10)=2.12).

Room temperature chemical vapor deposition of c-axis ZnO

NASA Astrophysics Data System (ADS)

Barnes, Teresa M.; Leaf, Jacquelyn; Fry, Cassandra; Wolden, Colin A.

2005-02-01

Highly (0 0 2) oriented ZnO films have been deposited at temperatures between 25 and 230 °C by high-vacuum plasma-assisted chemical vapor deposition (HVP-CVD) on glass and silicon substrates. The HVP-CVD process was found to be weakly activated with an apparent activation energy of ∼0.1 eV, allowing room temperature synthesis. Films deposited on both substrates displayed a preferential c-axis texture over the entire temperature range. Films grown on glass demonstrated high optical transparency throughout the visible and near infrared.

Crossover from weak to strong localization in quasi-1D = conductors.

NASA Astrophysics Data System (ADS)

Gershenson, M. E.; Khavin, Y. B.; Mikhalchuk, A. G.; Bozler, H. M.; Bogdanov, A. L.

1997-03-01

A crossover from weak localization (WL) to strong localization (SL) with decreasing temperature has been observed in the resistance of quasi-1D channels in Si delta-doped GaAs structures. The crossover occurs when the phase-breaking length becomes comparable to the localization length. In the SL regime, an activation temperature dependence R(T) is observed. The activation energy is very close to the spacing between the energy levels of the localized electrons within the localization domain. The activation energy decreases by half in strong magnetic fields, as a result, an exponentially strong negative magnetoresistance is developed. All the features of the magnetoresistance in the SL regime are in good agreement with the theory of doubling of the localization length in quasi-1D conductors in strong fields. The magnetoresistance provides a direct measurement of the localization length. Supported by RNFBR, INTAS 943862, and NSF DRM-9623716 (A.G.M. and H.M.B.)

Kinetics of copper nanoparticle precipitation in phosphate glass: an isothermal plasmonic approach.

PubMed

Sendova, Mariana; Jiménez, José A; Smith, Robert; Rudawski, Nicholas

2015-01-14

The kinetics of copper nanoparticle (NP) precipitation in melt-quenched barium-phosphate glass has been studied by in situ isothermal optical micro-spectroscopy. A spectroscopically based approximation technique is proposed to obtain information about the activation energies of nucleation and growth in a narrow temperature range (530-570 °C). Pre-plasmonic and plasmonic NP precipitation stages are identified separated in time. The process as a whole is discussed employing classical nucleation/growth theory and the Kolmogorov-Johnson-Mehl-Avrami phase change model. Activation energies of 3.9(7) eV and 2.6(5) eV have been estimated for the pre-plasmonic and plasmonic spectroscopically assessed stages, respectively. High resolution transmission electron microscopy, differential scanning calorimetry, and Raman spectroscopy were used as complementary techniques for studying the nanoparticulate phase and glass host structure. An empirical linear dependence of the diffusion activation energy on the glass transition temperature with broad applicability is suggested.

Effect of temperature on crack growth rates of stress corrosion cracks in metal alloys exposed to water

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vogt, H.; Speidel, M.O.

1996-12-01

The effect of temperature on stress corrosion crack growth rates was studied using four commercial alloys: an Al-Mg-Zn alloy (7000-Series), an Al-Cu alloy (2000-Series), a Mg-rare earth alloy and a Zr 2.5% Nb alloy. Stress Corrosion crack growth rate data were obtained using fracture mechanic specimens which were tested in high purity water in the temperature range of {minus}10 C to 320 C, depending on the alloy. Attention was directed towards region 2 behavior, where the crack propagation rate is independent of stress intensity but sensitive to test temperature. The experimental activation energies of the different alloys were compared withmore » literature on rate-controlling steps in order to identify the possible stress corrosion cracking mechanisms. The results were also compared with the activation energies obtained from general corrosion and hydrogen diffusion experiments.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Sang-Eui; Moon, Kyoung-Seok; Sohn, Yoonchul, E-mail: yoonchul.son@samsung.com

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/Agmore » 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.« less

Modeling Initial Stage of Ablation Material Pyrolysis: Graphitic Precursor Formation and Interfacial Effects

NASA Technical Reports Server (NTRS)

Desai, Tapan G.; Lawson, John W.; Keblinski, Pawel

2010-01-01

Reactive molecular dynamics simulations are used to study initial stage of pyrolysis of ablation materials and their composites with carbon nanotubes and carbon fibers. The products formed during pyrolysis are characterized and water is found as the primary product in all cases. The water formation mechanisms are analyzed and the value of the activation energy for water formation is estimated. A detailed study on graphitic precursor formation reveals the presence of two temperature zones. In the lower temperature zone (less than 2000 K) polymerization occurs resulting in formation of large, stable graphitic precursors, and in the high temperature zone (greater than 2000 K) polymer scission results in formation of short polymer chains/molecules. Simulations performed in the high temperature zone on the phenolic resin composites (with carbon nanotubes and carbon fibers) shows that the presence of interfaces had no substantial effect on the chain scission rate or the activation energy value for water formation.

Temperature, field activity and post-feeding metabolic response in the Asian house gecko, Hemidactylus frenatus.

PubMed

Lei, Juan; Booth, David T

2014-10-01

Temperature has significant effects on physiological activities and geographical distribution of ectotherms. The Asian house gecko Hemidactylus frenatus has become one of the most widely distributed reptiles in the world and is an invasive species in Australia. Since being introduced into northern Australia, Asian house geckos have spread rapidly and expanded into south-east Queensland and northern New South Wales. Despite their rapid spread, there have been few studies that address thermal adaptability of this species. In order to understand how temperature might limit the distribution and feeding behavior of H. frenatus we observed gecko foraging activities in the wild over the winter period, measured the temperature at which voluntary feeding ceases, and assessed the effect of temperature (30, 25, 20, and 18 °C) on post-feeding metabolic rate. Resting metabolic rate and post-feeding peak in metabolic rate decreased with low temperature, while the duration of elevated metabolic rate after feeding increased at lower temperature. The SDA coefficient (a ratio of the energy expended due to the post-feeding rise in metabolic rate to the energy contained within the meal) did not change systematically with ambient temperature. Field observations and voluntary feeding experiments showed that H. frenatus stop feeding when ambient temperature drops below 17 °C, so that persistent night time temperatures below 17 °C may be limiting the distribution of this species. Copyright © 2014 Elsevier Ltd. All rights reserved.

Seasonal metabolic acclimatization in the herbivorous desert lizard Uromastyx philbyi (Reptilia: Agamidea) from western Saudi Arabia.

PubMed

Zari, Talal A

2016-08-01

Many ectotherms adjust their metabolic rate seasonally in association with variations in environmental temperatures. The range and direction of these seasonal changes in reptilian metabolic rates are thought to be linked to the seasonality of activity and energy requirements. The present study was conducted to measure the standard metabolic rate (SMR) of seasonally-acclimatized Uromastyx philbyi with different body masses at 20, 25, 30, 35 and 40°C using open-flow respirometry during the four seasons. SMR was mass-dependent. The mean exponent of mass, "b", in the metabolism-body mass relation was 0.76 (variance=0.0007). Likewise, SMR increased as temperature increased with low Q10 values at high temperatures and high Q10 values at low temperatures. The lowest and highest Q10 values were achieved for temperature ranges of 30-35°C for summer-acclimatized dhabbs (Q10=1.6) and 20-25°C for winter-acclimatized dhabbs (Q10=3.9). Seasonal acclimatization effects were obvious at all temperatures (20-40°C). Winter-acclimatized dhabbs had the lowest metabolic rates at all temperatures. The seasonal acclimatization patterns displayed by U. philbyi may represent a valuable adaptation for herbivorous desert lizards that inhabit subtropical deserts to facilitate activity during their active seasons and to conserve energy during inactivity at low temperatures. Copyright © 2016 Elsevier Ltd. All rights reserved.

Locomotor Activity and Body Temperature Patterns over a Temperature Gradient in the Highveld Mole-Rat (Cryptomys hottentotus pretoriae).

PubMed

Haupt, Meghan; Bennett, Nigel C; Oosthuizen, Maria K

2017-01-01

African mole-rats are strictly subterranean mammals that live in extensive burrow systems. High humidity levels in the burrows prevent mole-rats from thermoregulating using evaporative cooling. However, the relatively stable environment of the burrows promotes moderate temperatures and small daily temperature fluctuations. Mole-rats therefore display a relatively wide range of thermoregulation abilities. Some species cannot maintain their body temperatures at a constant level, whereas others employ behavioural thermoregulation. Here we test the effect of ambient temperature on locomotor activity and body temperature, and the relationship between the two parameters, in the highveld mole-rat. We exposed mole-rats to a 12L:12D and a DD light cycle at ambient temperatures of 30°C, 25°C and 20°C while locomotor activity and body temperature were measured simultaneously. In addition, we investigated the endogenous rhythms of locomotor activity and body temperature at different ambient temperatures. Mole-rats displayed nocturnal activity at all three ambient temperatures and were most active at 20°C, but least active at 30°C. Body temperature was highest at 30°C and lowest at 20°C, and the daily cycle was highly correlated with locomotor activity. We show that the mole-rats have endogenous rhythms for both locomotor activity and body temperature. However, the endogenous body temperature rhythm appears to be less robust compared to the locomotor activity rhythm. Female mole-rats appear to be more sensitive to temperature changes than males, increased heterothermy is evident at lower ambient temperatures, whilst males show smaller variation in their body temperatures with changing ambient temperatures. Mole-rats may rely more heavily on behavioural thermoregulation as it is more energy efficient in an already challenging environment.

Locomotor Activity and Body Temperature Patterns over a Temperature Gradient in the Highveld Mole-Rat (Cryptomys hottentotus pretoriae)

PubMed Central

Haupt, Meghan; Bennett, Nigel C.

2017-01-01

African mole-rats are strictly subterranean mammals that live in extensive burrow systems. High humidity levels in the burrows prevent mole-rats from thermoregulating using evaporative cooling. However, the relatively stable environment of the burrows promotes moderate temperatures and small daily temperature fluctuations. Mole-rats therefore display a relatively wide range of thermoregulation abilities. Some species cannot maintain their body temperatures at a constant level, whereas others employ behavioural thermoregulation. Here we test the effect of ambient temperature on locomotor activity and body temperature, and the relationship between the two parameters, in the highveld mole-rat. We exposed mole-rats to a 12L:12D and a DD light cycle at ambient temperatures of 30°C, 25°C and 20°C while locomotor activity and body temperature were measured simultaneously. In addition, we investigated the endogenous rhythms of locomotor activity and body temperature at different ambient temperatures. Mole-rats displayed nocturnal activity at all three ambient temperatures and were most active at 20°C, but least active at 30°C. Body temperature was highest at 30°C and lowest at 20°C, and the daily cycle was highly correlated with locomotor activity. We show that the mole-rats have endogenous rhythms for both locomotor activity and body temperature. However, the endogenous body temperature rhythm appears to be less robust compared to the locomotor activity rhythm. Female mole-rats appear to be more sensitive to temperature changes than males, increased heterothermy is evident at lower ambient temperatures, whilst males show smaller variation in their body temperatures with changing ambient temperatures. Mole-rats may rely more heavily on behavioural thermoregulation as it is more energy efficient in an already challenging environment. PMID:28072840

Electronic transport mechanism in intrinsic and doped nanocrystalline silicon films deposited by RF-magnetron sputtering at low temperature

NASA Astrophysics Data System (ADS)

Benlakehal, D.; Belfedal, A.; Bouizem, Y.; Sib, J. D.; Chahed, L.; Zellama, K.

2016-12-01

The dependence on the temperature range, T, of the electronic transport mechanism in intrinsic and doped hydrogenated nanocrystalline silicon films, deposited by radiofrequency-magnetron sputtering at low substrate temperature, has been studied. Electrical conductivity measurements σ(T) have been conducted on these films, as a function of temperature, in the 93-450 K range. The analysis of these results clearly shows a thermally activated conduction process in the 273-450 K range which allows us to estimate the associated activation energy as well as the preexponential conductivity factor. While, in the lower temperature range (T < 273 K), a non-ohmic behavior is observed for the conductivity changes. The conductivity σ(T) presents a linear dependence on (T-1/4) , and a hopping mechanism is suggested to explain these results. By using the Percolation theory, further information can be gained about the density of states near the Fermi level as well as the range and the hopping energy.

High temperature two component explosive

DOEpatents

Mars, James E.; Poole, Donald R.; Schmidt, Eckart W.; Wang, Charles

1981-01-01

A two component, high temperature, thermally stable explosive composition comprises a liquid or low melting oxidizer and a liquid or low melting organic fuel. The oxidizer and fuel in admixture are incapable of substantial spontaneous exothermic reaction at temperatures on the order of 475.degree. K. At temperatures on the order of 475.degree. K., the oxidizer and fuel in admixture have an activation energy of at least about 40 kcal/mol. As a result of the high activation energy, the preferred explosive compositions are nondetonable as solids at ambient temperature, and become detonable only when heated beyond the melting point. Preferable oxidizers are selected from alkali or alkaline earth metal nitrates, nitrites, perchlorates, and/or mixtures thereof. Preferred fuels are organic compounds having polar hydrophilic groups. The most preferred fuels are guanidinium nitrate, acetamide and mixtures of the two. Most preferred oxidizers are eutectic mixtures of lithium nitrate, potassium nitrate and sodium nitrate, of sodium nitrite, sodium nitrate and potassium nitrate, and of potassium nitrate, calcium nitrate and sodium nitrate.

Solid composite electrolytes for lithium batteries

DOEpatents

Kumar, Binod; Scanlon, Jr., Lawrence G.

2000-01-01

Solid composite electrolytes are provided for use in lithium batteries which exhibit moderate to high ionic conductivity at ambient temperatures and low activation energies. In one embodiment, a ceramic-ceramic composite electrolyte is provided containing lithium nitride and lithium phosphate. The ceramic-ceramic composite is also preferably annealed and exhibits an activation energy of about 0.1 eV.

10 CFR Appendix B1 to Subpart B of... - Uniform Test Method for Measuring the Energy Consumption of Freezers

Code of Federal Regulations, 2011 CFR

2011-01-01

... defrost control. The energy consumption in kilowatt-hours per day shall be calculated equivalent to: ET... though the consumer-activated compartment temperature controls were preset so that the desired... calculated effect of operating a freezer for a period of 24 hours with the consumer-activated controls other...

DOE Office of Scientific and Technical Information (OSTI.GOV)

Machado, Thales R.; QIO-UJI, Universitat Jaume I, 12071 Castellón; Sczancoski, Júlio C.

Defect-related photoluminescence (PL) in materials have attracted interest for applications including near ultraviolet (NUV) excitable light-emitting diodes and in biomedical field. In this paper, hydroxyapatite [Ca{sub 10}(PO{sub 4}){sub 6}(OH){sub 2}] nanorods with intense PL bands (bluish- and yellowish-white emissions) were obtained when excited under NUV radiation at room temperature. These nanoparticles were synthesized via chemical precipitation at 90 °C followed by distinct heat treatments temperatures (200–800 °C). Intense and broad emission profiles were achieved at 350 °C (380–750 nm) and 400 °C (380–800 nm). UV–Vis spectroscopy revealed band gap energies (5.58–5.78 eV) higher than the excitation energies (~3.54 and ~2.98more » eV at 350 and 415 nm, respectively), confirming the contribution of defect energy levels within the forbidden zone for PL emissions. The structural features were characterized by X-ray diffraction, Rietveld refinement, thermogravimetric analysis, and Fourier transform infrared spectroscopy. By means of these techniques, the relation between structural order-disorder induced by defects, chemical reactions at both lattice and surface of the materials as well as the PL, without activator centers, was discussed in details. - Graphical abstract: The self-activated photoluminescence emissions of chemically precipitated hydroxyapatite nanorods were improved by different heat treatment temperatures. - Highlights: • HA nanorods were synthesized with improved self-activated PL at room temperature. • PL profile and intensity dependents on the temperature of posterior heat treatments. • Bluish- and yellowish-white emissions under NUV excitation (350 and 415 nm). • Broad and intense profiles achieved at 350 °C (380–750 nm) and 400 °C (380–800 nm). • PL from the e′–h{sup •} recombination between defect energy levels within the band gap.« less

Effect of borides on hot deformation behavior and microstructure evolution of powder metallurgy high borated stainless steel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, Xuan

To investigate borides effect on the hot deformation behavior and microstructure evolution of powder metallurgy high borated stainless steel, hot compression tests at the temperatures of 950– 1150 °C and the strain rates of 0.01– 10 s{sup −1} were performed. Flow stress curves indicated that borides increased the material's stress level at low temperature but the strength was sacrificed at temperatures above 1100 °C. A hyperbolic-sine equation was used to characterize the dependence of the flow stress on the deformation temperature and strain rate. The hot deformation activation energy and stress exponent were determined to be 355 kJ/mol and 3.2,more » respectively. The main factors leading to activation energy and stress exponent of studied steel lower than those of commercial 304 stainless steel were discussed. Processing maps at the strains of 0.1, 0.3, 0.5, and 0.7 showed that flow instability mainly concentrated at 950– 1150 °C and strain rate higher than 0.6 s{sup −1}. Results of microstructure illustrated that dynamic recrystallization was fully completed at both high temperature-low strain rate and low temperature-high strain rate. In the instability region cracks were generated in addition to cavities. Interestingly, borides maintained a preferential orientation resulting from particle rotation during compression. - Highlights: •The decrement of activation energy was affected by boride and boron solution. •The decrease of stress exponent was influenced by composition and Cottrell atmosphere. •Boride represented a preferential orientation caused by particle rotation.« less

Caffeine Extraction from Raw and Roasted Coffee Beans.

PubMed

Chiang, Donyau; Lin, Chih-Yang; Hu, Chen-Ti; Lee, Sanboh

2018-04-01

Coffee is a stimulant, psychoactive, popular daily beverage, and its caffeine affects human physiological health and behavior. These important issues prompted us to study caffeine extraction from both the raw and roasted coffee beans of 3 types at different temperatures. A hemispheric model is developed to simulate the extraction process of the caffeine from the coffee beans of hemisphere is proposed. The experimental data are in good agreement with the predicted model. The effective diffusivities of caffeine in both the raw and roasted beans increase with temperature in all 3 types. An incubation period, decreasing with increasing temperature, is observed in all samples studied. Caffeine extraction in roasted beans is more rapid than that for the raw beans and the time difference is significant at low temperatures. In both the raw and roasted samples, caffeine diffusion in the raw beans and the incubation behavior are thermally activated processes. Single activation energies are obtained for diffusion within the extraction temperature range for all beans tested with the exception of one type of the coffee beans, Mandheling, which exhibits 2 activation energies in raw samples. The surface energies of the epidermis of the raw beans and roasted beans obtained from the contact angle measurements are used to interpret the difference of incubation periods. This study has a potential application to the decaffeinated coffee industry.Caffeine affects human physiological health and behavior so that caffeine extraction from coffee beans of different types at different temperatures is important for product refining and customers. © 2018 Institute of Food Technologists®.

Energy saving incineration of waste

NASA Astrophysics Data System (ADS)

Meierzukoecker, H.; Voegtli, R.

1982-11-01

The machanism and the dimension of the preoxidation of the pollutants in the heat exchanger were investigated. A temperature control system was developed and tested. It is found that the preoxidation in the heat exchanger depends on the peculiarity of the pollutants and is inhibited by inactive walls with increasing of the specific surface. Active materials like copper only promote the oxidation of all pollutants in the low temperature region. Savings of supplemental energy about 25% are possible using process controlled auxiliary firing and combustion enthalpy of pollutants as a substitute for the supplemental energy.

Carrier trapping and activation at short-period wurtzite/zinc-blende stacking sequences in polytypic InAs nanowires

NASA Astrophysics Data System (ADS)

Becker, J.; Morkötter, S.; Treu, J.; Sonner, M.; Speckbacher, M.; Döblinger, M.; Abstreiter, G.; Finley, J. J.; Koblmüller, G.

2018-03-01

We explore the effects of random and short-period crystal-phase intermixing in InAs nanowires (NW) on the carrier trapping and thermal activation behavior using correlated optical and electrical transport spectroscopy. The polytypic InAs NWs are grown by catalyst-free molecular beam epitaxy under different temperatures, resulting in different fractions of wurtzite (WZ) and zincblende (ZB) and variable short-period (˜1-4 nm) WZ/ZB stacking sequences. Temperature-dependent microphotoluminescence (μ PL) studies reveal that variations in the WZ/ZB stacking govern the emission energy and carrier confinement properties. The optical transition energies are modeled for a wide range of WZ/ZB stacking sequences using a Kronig-Penney type effective mass approximation, while comparison with experimental results suggests that polarization sheet charges on the order of ˜0.0016-0.08 C/m along the WZ/ZB interfaces need to be considered to best describe the data. The thermal activation characteristics of carriers trapped inside the short-period WZ/ZB structure are directly reproduced in the temperature-dependent carrier density evolution (4-300 K) probed by four-terminal (4T) NW-field effect transistor measurements. In particular, we find that activation of carriers in-between ˜1016-1017c m-3 follows a two-step process, with activation at low temperature attributed to WZ/ZB traps and activation at high temperature being linked to surface states and electron accumulation at the InAs NW surface.

Ac conductivity and dielectric properties of bulk tin phthalocyanine dichloride (SnPcCl 2)

NASA Astrophysics Data System (ADS)

El-Nahass, M. M.; Farid, A. M.; Abd El-Rahman, K. F.; Ali, H. A. M.

2008-07-01

The ac conductivity, σac( ω), has been measured for bulk tin phthalocyanine dichloride (SnPcCl 2) in the form of compressed pellet with evaporated ohmic Au electrodes in a temperature range 303-403 K. Ac conductivity, σac( ω), is found to vary as ωs in the frequency range 42 Hz-5×10 6 Hz. At low range of frequency, s<1 and it decreases with the increase in temperature indicating a dominant hopping process. At high range of frequency, s is found to be equal to ≈1.09 and is temperature independent. The dielectric constant, ε1, and dialectic loss, ε2, have been determined for bulk SnPcCl 2. Both ε1 and ε2 decrease with the increase in frequency and increase with the increase in temperature. The Cole-Cole types have been used to determine some parameters such as; the macroscopic relaxation time ( τo), the molecular relaxation time ( τ), the activation energy for relaxation ( Eo) and the distribution parameter ( α). The temperature dependence of τ is expressed by a thermally activated process with the activation energy of 0.299 eV.

Phase 1 drilling operations at the Magma Energy Exploratory Well (LVF 51-20)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Finger, J.T.; Jacobson, R.D.

1990-12-01

This report describes the Phase 1 drilling operations for the Magma Energy Exploratory Well near Mammoth Lakes, California. An important part of the Department of Energy's Magma Energy Program, this well is designed to reach an ultimate depth of 20,000 feet or a bottomhole temperature of 500{degree}C, whichever comes first. There will be four drilling phases, at least a year apart, with scientific investigations in the borehole between the drilling intervals. Phase 1 of this project resulted in a 20 inch cased hole to 2558 feet, with 185 feet of coring beyond that. This document comprises a narrative of themore » daily activities, copies of the daily mud and lithologic reports, time breakdowns of rig activities, inventories of lost circulation materials, temperature logs of the cored hole, and a strip chart mud log. 2 figs.« less

Prompt isothermal decay properties of the Sr4Al14O25 co-doped with Eu2+ and Dy3+ persistent luminescent phosphor

NASA Astrophysics Data System (ADS)

Asal, Eren Karsu; Polymeris, George S.; Gultekin, Serdar; Kitis, George

2018-06-01

Thermoluminescence (TL) techniques are very useful in the research of the persistent Luminescence (PL) phosphors research. It gives information about the existence of energy levels within the forbidden band, its activation energy, kinetic order, lifetime etc. The TL glow curve of Sr4Al14O25 :Eu2+,Dy3+ persistent phosphor, consists of two well separated glow peaks. The TL techniques used to evaluate activation energy were the initial rise, prompt isothermal decay (PID) of TL of each peak at elevated temperatures and the glow - curve fitting. The behavior of the PID curves of the two peak is very different. According to the results of the PID procedure and the subsequent data analysis it is suggested that the mechanism behind the low temperature peak is a delocalized transition. On the other hand the mechanism behind the high temperature peak is localized transition involving a tunneling recombination between electron trap and luminescence center.

Impact of different temperatures on survival and energy metabolism in the Asian citrus psyllid, Diaphorina citri Kuwayama.

PubMed

El-Shesheny, Ibrahim; Hijaz, Faraj; El-Hawary, Ibrahim; Mesbah, Ibrahim; Killiny, Nabil

2016-02-01

Temperature influences the life history and metabolic parameters of insects. Asian citrus psyllid (ACP), Diaphorina citri is a tropical and subtropical pest. ACP invaded new regions around the world and threatened the citrus industry as a vector for Huanglongbing (HLB) disease. ACP is widely distributed and can survive high (up to 45 °C) and low temperatures (as low as -6 °C). The precise mechanism of temperature tolerance in ACP is poorly understood. We investigated adult survival, cellular energy balance, gene expression, and nucleotide and sugar-nucleotide changes under the effect of different temperature regimes (0 °C to 45 °C with 5 °C intervals). The optimum temperatures for survival were 20 and 25 °C. Low temperatures of 0 °C and 5 °C caused 50% mortality after 2 and 4 days respectively, while one day at high temperature (40 °C and 45 °C) caused more than 95% mortality. The lowest quantity of ATP (3.69 ± 1.6 ng/insect) and the maximum ATPase enzyme activities (57.43 ± 7.6 μU/insect) were observed at 25 °C. Correlation between ATP quantities and ATPase activity was negative. Gene expression of hsp 70, V-type proton ATPase catalytic subunit A and ATP synthase α subunit matched these results. Twenty-four nucleotides and sugar-nucleotides were quantified using HPLC in ACP adults maintained at low, high, and optimum temperatures. The nucleotide profiles were different among treatments. The ratios between AMP:ATP and ADP:ATP were significantly decreased and positively correlated to adults survival, whereas the adenylate energy charge was increased in response to low and high temperatures. Exploring energy metabolic regulation in relation with adult survival might help in understanding the physiological basis of how ACP tolerates newly invaded regions. Copyright © 2015 Elsevier Inc. All rights reserved.

The Effect of Temperature on the Enzyme-Catalyzed Reaction: Insights from Thermodynamics

ERIC Educational Resources Information Center

Aledo, Juan Carlos; Jimenez-Riveres, Susana; Tena, Manuel

2010-01-01

When teaching the effect of temperature on biochemical reactions, the problem is usually oversimplified by confining the thermal effect to the catalytic constant, which is identified with the rate constant of the elementary limiting step. Therefore, only positive values for activation energies and values greater than 1 for temperature coefficients…

The Oxidation Kinetics of Continuous Carbon Fibers in a Cracked Ceramic Matrix Composite. Degree awarded by Case Western Reserve Univ., May 2000

NASA Technical Reports Server (NTRS)

Halbig, Michael C.

2001-01-01

Experimental observations and results suggest two primary regimes as a function of temperature, i.e., diffusion and reaction controlled kinetics. Thermogravimetric analysis of carbon fiber in flowing oxygen gave an activation energy of 64.1 kJ/mol in the temperature range of 500 to 600 C and an apparent activation energy of 7.6 kJ/mol for temperatures from 600 to 1400 C. When C/SiC composite material was unstressed, matrix effects at temperatures from 900 to 1400 C protected the internal fibers. When under stress, self-protection was not observed. Increasing the stress from 10 to 25 ksi caused a 67 to 82 percent reduction in times to failure at temperatures from 750 to 1500 C. Based on experimental results, observation, and theory, a finite difference model was developed, which simulates the diffusion of oxygen into a matrix crack that is bridged by carbon fibers. The model allows the influence of important variables on oxidation kinetics to be studied systematically, i.e., temperature, reaction rate constant, diffusion coefficient, environment, and sample geometry.

Effect of temperature on a miniaturized microbial fuel cell (MFC)

NASA Astrophysics Data System (ADS)

Ren, Hao; Jiang, Chenming; Chae, Junseok

2017-12-01

A microbial fuel cell (MFC) is a bioinspired energy converter which directly converts biomass into electricity through the catalytic activity of a specific species of bacteria. The effect of temperature on a miniaturized microbial fuel cell with Geobacter sulfurreducens dominated mixed inoculum is investigated in this paper for the first time. The miniaturized MFC warrants investigation due to its small thermal mass, and a customized setup is built for the temperature effect characterization. The experiment demonstrates that the optimal temperature for the miniaturized MFC is 322-326 K (49-53 °C). When the temperature is increased from 294 to 322 K, a remarkable current density improvement of 282% is observed, from 2.2 to 6.2 Am-2. Furthermore, we perform in depth analysis on the effect of temperature on the miniaturized MFC, and found that the activation energy for the current limiting mechanism of the MFC is approximately between 0.132 and 0.146 eV, and the result suggest that the electron transfer between cytochrome c is the limiting process for the miniaturized MFC.

Intrinsic Brightness Temperatures of AGN Jets

NASA Astrophysics Data System (ADS)

Homan, D. C.; Kovalev, Y. Y.; Lister, M. L.; Ros, E.; Kellermann, K. I.; Cohen, M. H.; Vermeulen, R. C.; Zensus, J. A.; Kadler, M.

2006-05-01

We present a new method for studying the intrinsic brightness temperatures of the parsec-scale jet cores of active galactic nuclei (AGNs). Our method uses observed superluminal motions and observed brightness temperatures for a large sample of AGNs to constrain the characteristic intrinsic brightness temperature of the sample as a whole. To study changes in intrinsic brightness temperature, we assume that the Doppler factors of individual jets are constant in time, as justified by their relatively small changes in observed flux density. We find that in their median-low brightness temperature state, the sources in our sample have a narrow range of intrinsic brightness temperatures centered on a characteristic temperature, Tint~=3×1010 K, which is close to the value expected for equipartition, when the energy in the radiating particles equals the energy stored in the magnetic fields. However, in their maximum brightness state, we find that sources in our sample have a characteristic intrinsic brightness temperature greater than 2×1011 K, which is well in excess of the equipartition temperature. In this state, we estimate that the energy in radiating particles exceeds the energy in the magnetic field by a factor of ~105. We suggest that the excess of particle energy when sources are in their maximum brightness state is due to injection or acceleration of particles at the base of the jet. Our results suggest that the common method of estimating jet Doppler factors by using a single measurement of observed brightness temperature, the assumption of equipartition, or both may lead to large scatter or systematic errors in the derived values.

Work patterns dictate energy demands and thermal strain during wildland firefighting.

PubMed

Cuddy, John S; Sol, Joseph A; Hailes, Walter S; Ruby, Brent C

2015-06-01

The purpose of this investigation was to characterize the effects of self-selected work activity on energy expenditure, water turnover, and thermal strain during wildland fire suppression. A secondary aim was to contrast current data with data collected 15 years ago using similar methods to determine whether job demands have changed. Participants (n=15, 26±3 years, 179±6 cm, 78.3±8.6 kg) were monitored for 3 days for total energy expenditure, water turnover, core and chest skin temperature, physical activity, and heart rate. Participants arrived to the mobile laboratory each morning, submitted a nude weight, ingested a temperature transmitter, provided a urine sample, and were equipped with a physiological and activity monitor. Participants completed live wildland fire suppression during their work shifts. Mean core temperature was 37.6°±0.2°C, mean chest skin temperature was 34.1°±1.0°C, mean heart rate was 112±13 beats/min, and the mean physiological strain index score was 3.3±1.0. Wildland firefighters spent 49±8%, 39±6%, and 12±2% in the sedentary, light, and moderate-vigorous intensity categories, respectively. The mean total energy expenditure was 19.1±3.9 MJ/d, similar to 1997 (17.5±6.9 MJ/d). The mean water turnover in 2012 was 9.5±1.7 L/d, which was higher (P<.05) compared with 1997-98 (7.0±1.7 L/d). Wildland firefighters do not induce consistently high cardiovascular and thermal strain while completing arduous work in a hot environment despite fairly high chest skin temperatures. The total energy expenditure in the current study suggests job demands are similar to those of 15 years ago, while the increased water turnover may reflect a change in drinking habits. Copyright © 2015 Wilderness Medical Society. Published by Elsevier Inc. All rights reserved.

On the validity of the Arrhenius equation for electron attachment rate coefficients.

PubMed

Fabrikant, Ilya I; Hotop, Hartmut

2008-03-28

The validity of the Arrhenius equation for dissociative electron attachment rate coefficients is investigated. A general analysis allows us to obtain estimates of the upper temperature bound for the range of validity of the Arrhenius equation in the endothermic case and both lower and upper bounds in the exothermic case with a reaction barrier. The results of the general discussion are illustrated by numerical examples whereby the rate coefficient, as a function of temperature for dissociative electron attachment, is calculated using the resonance R-matrix theory. In the endothermic case, the activation energy in the Arrhenius equation is close to the threshold energy, whereas in the case of exothermic reactions with an intermediate barrier, the activation energy is found to be substantially lower than the barrier height.

A reanalysis of the HCO(+)/HOC(+) abundance ratio in dense interstellar clouds

NASA Technical Reports Server (NTRS)

Jarrold, M. F.; Bowers, M. T.; Defrees, D. J.; Mclean, A. D.; Herbst, E.

1986-01-01

New theoretical and experimental results have prompted a reinvestigation of the HCO(+)/HOC(+) abundance ratio in dense interstellar clouds. These results pertain principally but not exclusively to the reaction between HOC(+) and H2, which was previously calculated by DeFrees et al. (1984) to possess a large activation energy barrier. New calculations, reported here, indicate that this activation energy barrier is quite small and may well be zero. In addition, experimental results at higher energy and temperature indicate strongly that the reaction proceeds efficiently at interstellar temperatures. If HOC(+) does indeed react efficiently with H2 in interstellar clouds, the calculated HCO(+)/HOC(+) abundance ratio rises to a substantially greater value under standard dense cloud conditions than is deduced via the tentative observation of HOC(+) in Sgr B2.

Estimation of activation energy for electroporation and pore growth rate in liquid crystalline and gel phases of lipid bilayers using molecular dynamics simulations.

PubMed

Majhi, Amit Kumar; Kanchi, Subbarao; Venkataraman, V; Ayappa, K G; Maiti, Prabal K

2015-11-28

Molecular dynamics simulations of electroporation in POPC and DPPC lipid bilayers have been carried out at different temperatures ranging from 230 K to 350 K for varying electric fields. The dynamics of pore formation, including threshold field, pore initiation time, pore growth rate, and pore closure rate after the field is switched off, was studied in both the gel and liquid crystalline (Lα) phases of the bilayers. Using an Arrhenius model of pore initiation kinetics, the activation energy for pore opening was estimated to be 25.6 kJ mol(-1) and 32.6 kJ mol(-1) in the Lα phase of POPC and DPPC lipids respectively at a field strength of 0.32 V nm(-1). The activation energy decreases to 24.2 kJ mol(-1) and 23.7 kJ mol(-1) respectively at a higher field strength of 1.1 V nm(-1). At temperatures below the melting point, the activation energy in the gel phase of POPC and DPPC increases to 28.8 kJ mol(-1) and 34.4 kJ mol(-1) respectively at the same field of 1.1 V nm(-1). The pore closing time was found to be higher in the gel than in the Lα phase. The pore growth rate increases linearly with temperature and quadratically with field, consistent with viscosity limited growth models.

Effects of chronic exposure to cadmium and temperature, alone or combined, on the threespine stickleback (Gasterosteus aculeatus): Interest of digestive enzymes as biomarkers.

PubMed

Hani, Younes Mohamed Ismail; Turies, Cyril; Palluel, Olivier; Delahaut, Laurence; Gaillet, Véronique; Bado-Nilles, Anne; Porcher, Jean-Marc; Geffard, Alain; Dedourge-Geffard, Odile

2018-06-01

The development of predictive, sensitive and reliable biomarkers is of crucial importance for aquatic biomonitoring to assess the effects of chemical substances on aquatic organisms, especially when it comes to combined effects with other stressors (e.g. temperature). The first purpose of the present study was to evaluate the single and combined effects of 90 days of exposure to an environmental cadmium concentration (0.5 μg L -1 ) and two water temperatures (16 and 21 °C) on different parameters. These parameters are involved in (i) the antioxidant system (superoxide dismutase activity -SOD- and total glutathione levels -GSH-), (ii) the energy metabolism, i.e. energy reserves (glycogen, lipids, proteins) and digestive enzymes (trypsin, amylase, intestinal alkaline phosphatase -IAP-), and (iii) biometric parameters (weight, length, Fulton's condition factor, and the gonadosomatic index -GSI-) of threespine stickleback (Gasterosteus aculeatus). The second purpose was to determine the interest of the three digestive enzymes as biomarkers in comparison with the other parameters. The higher temperature (21 °C) impacted the anti-oxidant and energy reserve parameters. In liver, GSH levels increased on day 60, while SOD decreased on days 15 and 90, with a significant decrease of protein and lipid energy reserves on day 90. In muscle, the higher temperature decreased SOD activity only on day 90. G. aculeatus biometric parameters were also impacted by the higher temperature, which limited stickleback growth after 90 days of exposure. In female sticklebacks, the GSI peaked on day 60 and decreased sharply on day 90, while the highest values were reached at day 90 in the control groups, suggesting impaired reproduction in sticklebacks raised at 21 °C. These results suggest that 21 °C is an upper-limit temperature for long-term physiological processes in sticklebacks. In contrast, very low-concentration cadmium exposure had no effect on classical biomarkers (energy reserves, antioxidant parameters, biometric parameters). However, digestive enzymes showed an interesting sensitivity to cadmium, which was emphasized by high temperature. The activity of the three digestive enzymes decreased significantly on day 90 when sticklebacks were exposed to cadmium alone, while the decrease was stronger and was recorded earlier (from day 15) when they were exposed to the cadmium-temperature combination. Compared to conventional measurements, digestive enzymes responded rapidly. This could be an important advantage for them to be used as early warning tools to reflect the health status of organisms, particularly for trypsin and IAP activities. Copyright © 2018 Elsevier B.V. All rights reserved.

Inferring the temperature dependence of population parameters: the effects of experimental design and inference algorithm

PubMed Central

Palamara, Gian Marco; Childs, Dylan Z; Clements, Christopher F; Petchey, Owen L; Plebani, Marco; Smith, Matthew J

2014-01-01

Understanding and quantifying the temperature dependence of population parameters, such as intrinsic growth rate and carrying capacity, is critical for predicting the ecological responses to environmental change. Many studies provide empirical estimates of such temperature dependencies, but a thorough investigation of the methods used to infer them has not been performed yet. We created artificial population time series using a stochastic logistic model parameterized with the Arrhenius equation, so that activation energy drives the temperature dependence of population parameters. We simulated different experimental designs and used different inference methods, varying the likelihood functions and other aspects of the parameter estimation methods. Finally, we applied the best performing inference methods to real data for the species Paramecium caudatum. The relative error of the estimates of activation energy varied between 5% and 30%. The fraction of habitat sampled played the most important role in determining the relative error; sampling at least 1% of the habitat kept it below 50%. We found that methods that simultaneously use all time series data (direct methods) and methods that estimate population parameters separately for each temperature (indirect methods) are complementary. Indirect methods provide a clearer insight into the shape of the functional form describing the temperature dependence of population parameters; direct methods enable a more accurate estimation of the parameters of such functional forms. Using both methods, we found that growth rate and carrying capacity of Paramecium caudatum scale with temperature according to different activation energies. Our study shows how careful choice of experimental design and inference methods can increase the accuracy of the inferred relationships between temperature and population parameters. The comparison of estimation methods provided here can increase the accuracy of model predictions, with important implications in understanding and predicting the effects of temperature on the dynamics of populations. PMID:25558365

Wind shear and wet and dry thermodynamic indices as predictors of thunderstorm motion and severity and application to the AVE 4 experimental data

NASA Technical Reports Server (NTRS)

Connell, J. R.; Ey, L.

1977-01-01

Two types of parameters are computed and mapped for use in assessing their individual merits as predictors of occurrence and severity of thunderstorms. The first group is comprised of equivalent potential temperature, potential temperature, water vapor mixing ratio, and wind speed. Equivalent potential temperature maxima and strong gradients of equivalent potential temperature at the surface correlate well with regions of thunderstorm activity. The second type, comprised of the energy index, shear index, and energy shear index, incorporates some model dynamics of thunderstorms, including nonthermodynamic forcing. The energy shear index is found to improve prediction of tornadic and high-wind situations slightly better than other indices. It is concluded that further development and refinement of nonthermodynamic aspects of predictive indices are definitely warranted.

Design of wearable hybrid generator for harvesting heat energy from human body depending on physiological activity

NASA Astrophysics Data System (ADS)

Kim, Myoung-Soo; Kim, Min-Ki; Kim, Kyongtae; Kim, Yong-Jun

2017-09-01

We developed a prototype of a wearable hybrid generator (WHG) that is used for harvesting the heat energy of the human body. This WHG is constructed by integrating a thermoelectric generator (TEG) in a circular mesh polyester knit fabric, circular-shaped pyroelectric generator (PEG), and quick sweat-pickup/dry-fabric. The fabric packaging enables the TEG part of the WHG to generate energy steadily while maintaining a temperature difference in extreme temperature environments. Moreover, when the body sweats, the evaporation heat of the sweat leads to thermal fluctuations in the WHG. This phenomenon further leads to an increase in the output power of the WHG. These characteristics of the WHG make it possible to produce electrical energy steadily without reduction in the conversion efficiency, as both TEG and PEG use the same energy source of the human skin and the ambient temperature. Under a temperature difference of ˜6.5 °C and temperature change rate of ˜0.62 °C s-1, the output power and output power density of the WHG, respectively, are ˜4.5 nW and ˜1.5 μW m-2. Our hybrid approach will provide a framework to enhance the output power of the wearable generators that harvest heat energy from human body in various environments.

Kinetics of Ta ions penetration into porous low-k dielectrics under bias-temperature stress

NASA Astrophysics Data System (ADS)

He, Ming; Ou, Ya; Wang, Pei-I.; Lu, Toh-Ming

2010-05-01

It is known that Ta, a popular diffusion barrier material, can itself penetrate into low-k dielectrics under bias-temperature stress. In this work, we derived a model which directly correlates the diffusivity of Ta ions to the rate of flatband voltage shift (FBS) of the Ta/methyl silsesquixane (MSQ)/Si capacitors. From our experimentally measured constant FBS rate, the Ta diffusivity and activation energy were determined. It appears that an increase in the porosity of MSQ film enhances the Ta diffusivity but does not affect the associated activation energy. This suggests the Ta ion diffusion is mainly through interconnected pore surfaces.

Anomalously small resistivity and thermopower of strongly compensated semiconductors and topological insulators

NASA Astrophysics Data System (ADS)

Chen, Tianran; Shklovskii, B. I.

2013-04-01

In the recent paper, we explained why the maximum bulk resistivity of topological insulators (TIs) such as Bi2Se3 is so small [B. Skinner, T. Chen, and B. I. Shklovskii, Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.109.176801 109, 176801 (2012)]. Using the model of completely compensated semiconductor we showed that when the Fermi level is pinned in the middle of the gap the activation energy of resistivity is Δ=0.3(Eg/2), where Eg is the semiconductor gap. In this paper, we consider a strongly compensated n-type semiconductor. We find the position of the Fermi level μ calculated from the bottom of the conduction band Ec and the activation energy of resistivity Δ as a function of compensation K, and show that Δ=0.3(Ec-μ) holds at any 0<1-K≪1. In the same range of relatively high temperatures, the Peltier energy (heat) Π is even smaller: Π≃Δ/2=0.15(Ec-μ). We also show that at low temperatures, the activated conductivity crosses over to variable range hopping (VRH) and find the characteristic temperature of VRH, TES, as a function of K.

Key role of temperature monitoring in interpretation of microwave effect on transesterification and esterification reactions for biodiesel production.

PubMed

Mazubert, Alex; Taylor, Cameron; Aubin, Joelle; Poux, Martine

2014-06-01

Microwave effects have been quantified, comparing activation energies and pre-exponential factors to those obtained in a conventionally-heated reactor for biodiesel production from waste cooking oils via transesterification and esterification reactions. Several publications report an enhancement of biodiesel production using microwaves, however recent reviews highlight poor temperature measurements in microwave reactors give misleading reaction performances. Operating conditions have therefore been carefully chosen to investigate non-thermal microwave effects alone. Temperature is monitored by an optical fiber sensor, which is more accurate than infrared sensors. For the transesterification reaction, the activation energy is 37.1kJ/mol (20.1-54.2kJ/mol) in the microwave-heated reactor compared with 31.6kJ/mol (14.6-48.7kJ/mol) in the conventionally-heated reactor. For the esterification reaction, the activation energy is 45.4kJ/mol (31.8-58.9kJ/mol) for the microwave-heated reactor compared with 56.1kJ/mol (55.7-56.4kJ/mol) for conventionally-heated reactor. The results confirm the absence of non-thermal microwave effects for homogenous-catalyzed reactions. Copyright © 2014 Elsevier Ltd. All rights reserved.

Estimation of excess energies and activity coefficients for the penternary Ni-Cr-Co-Al-Mo system and its subsystems

NASA Astrophysics Data System (ADS)

Dogan, A.; Arslan, H.; Dogan, T.

2015-06-01

Using different prediction methods, such as the General Solution Model of Kohler and Muggianu, the excess energy and activities of molybdenum for the sections of the phase diagram for the penternary Ni-Cr-Co-Al-Mo system with mole ratios xNi/ xMo = 1, xCr/ xMo = 1, xCo/ xMo = 1, and xAl/ xMo = r = 0.5 and 1, were thermodynamically investigated at a temperature of 2000 K, whereas the excess energy and activities of Bi for the section corresponding to the ternary Bi-Ga-Sb system with mole ratio xGa/ xSb = 1/9 were thermodynamically investigated at a temperature of 1073 K. In the case of r = 0.5 and 1 in the alloys Ni-Cr-Co-Al-Mo, a positive deviation in the activity coefficient was revealed, as molybdenum content increased. Moreover, in the calculations performed in Chou's GSM model, the obtained values for excess Gibbs energies are negative in the whole concentration range of bismuth at 1073 K and exhibit the minimum of about -2.2 kJ/mol at the mole ratio xGa/ xSb = 1/9 in the alloy Bi-Ga-Sb.

Insight into Temperature Dependence of GTPase Activity in Human Guanylate Binding Protein-1

PubMed Central

Rahman, Safikur; Deep, Shashank; Sau, Apurba Kumar

2012-01-01

Interferon-γ induced human guanylate binding protein-1(hGBP1) belongs to a family of dynamin related large GTPases. Unlike all other GTPases, hGBP1 hydrolyzes GTP to a mixture of GDP and GMP with GMP being the major product at 37°C but GDP became significant when the hydrolysis reaction was carried out at 15°C. The hydrolysis reaction in hGBP1 is believed to involve with a number of catalytic steps. To investigate the effect of temperature in the product formation and on the different catalytic complexes of hGBP1, we carried out temperature dependent GTPase assays, mutational analysis, chemical and thermal denaturation studies. The Arrhenius plot for both GDP and GMP interestingly showed nonlinear behaviour, suggesting that the product formation from the GTP-bound enzyme complex is associated with at least more than one step. The negative activation energy for GDP formation and GTPase assay with external GDP together indicate that GDP formation occurs through the reversible dissociation of GDP-bound enzyme dimer to monomer, which further reversibly dissociates to give the product. Denaturation studies of different catalytic complexes show that unlike other complexes the free energy of GDP-bound hGBP1 decreases significantly at lower temperature. GDP formation is found to be dependent on the free energy of the GDP-bound enzyme complex. The decrease in the free energy of this complex at low temperature compared to at high is the reason for higher GDP formation at low temperature. Thermal denaturation studies also suggest that the difference in the free energy of the GTP-bound enzyme dimer compared to its monomer plays a crucial role in the product formation; higher stability favours GMP but lower favours GDP. Thus, this study provides the first thermodynamic insight into the effect of temperature in the product formation of hGBP1. PMID:22859948

Accelerated Testing Of Photothermal Degradation Of Polymers

NASA Technical Reports Server (NTRS)

Kim, Soon Sam; Liang, Ranty Hing; Tsay, Fun-Dow

1989-01-01

Electron-spin-resonance (ESR) spectroscopy and Arrhenius plots used to determine maximum safe temperature for accelerated testing of photothermal degradation of polymers. Aging accelerated by increasing illumination, temperature, or both. Results of aging tests at temperatures higher than those encountered in normal use valid as long as mechanism of degradation same throughout range of temperatures. Transition between different mechanisms at some temperature identified via transition between activation energies, manifesting itself as change in slope of Arrhenius plot at that temperature.

Central control of body temperature

PubMed Central

Morrison, Shaun F.

2016-01-01

Central neural circuits orchestrate the behavioral and autonomic repertoire that maintains body temperature during environmental temperature challenges and alters body temperature during the inflammatory response and behavioral states and in response to declining energy homeostasis. This review summarizes the central nervous system circuit mechanisms controlling the principal thermoeffectors for body temperature regulation: cutaneous vasoconstriction regulating heat loss and shivering and brown adipose tissue for thermogenesis. The activation of these thermoeffectors is regulated by parallel but distinct efferent pathways within the central nervous system that share a common peripheral thermal sensory input. The model for the neural circuit mechanism underlying central thermoregulatory control provides a useful platform for further understanding of the functional organization of central thermoregulation, for elucidating the hypothalamic circuitry and neurotransmitters involved in body temperature regulation, and for the discovery of novel therapeutic approaches to modulating body temperature and energy homeostasis. PMID:27239289

Central control of body temperature.

PubMed

Morrison, Shaun F

2016-01-01

Central neural circuits orchestrate the behavioral and autonomic repertoire that maintains body temperature during environmental temperature challenges and alters body temperature during the inflammatory response and behavioral states and in response to declining energy homeostasis. This review summarizes the central nervous system circuit mechanisms controlling the principal thermoeffectors for body temperature regulation: cutaneous vasoconstriction regulating heat loss and shivering and brown adipose tissue for thermogenesis. The activation of these thermoeffectors is regulated by parallel but distinct efferent pathways within the central nervous system that share a common peripheral thermal sensory input. The model for the neural circuit mechanism underlying central thermoregulatory control provides a useful platform for further understanding of the functional organization of central thermoregulation, for elucidating the hypothalamic circuitry and neurotransmitters involved in body temperature regulation, and for the discovery of novel therapeutic approaches to modulating body temperature and energy homeostasis.

Active thermal isolation for temperature responsive sensors

NASA Technical Reports Server (NTRS)

Martinson, Scott D. (Inventor); Gray, David L. (Inventor); Carraway, Debra L. (Inventor); Reda, Daniel C. (Inventor)

1994-01-01

The detection of flow transition between laminar and turbulent flow and of shear stress or skin friction of airfoils is important in basic research for validation of airfoil theory and design. These values are conventionally measured using hot film nickel sensors deposited on a polyimide substrate. The substrate electrically insulates the sensor and underlying airfoil but is prevented from thermally isolating the sensor by thickness constraints necessary to avoid flow contamination. Proposed heating of the model surface is difficult to control, requires significant energy expenditures, and may alter the basic flow state of the airfoil. A temperature responsive sensor is located in the airflow over the specified surface of a body and is maintained at a constant temperature. An active thermal isolator is located between this temperature responsive sensor and the specific surface of the body. The total thickness of the isolator and sensor avoid any contamination of the flow. The temperature of this isolator is controlled to reduce conductive heat flow from the temperature responsive sensor to the body. This temperature control includes (1) operating the isolator at the same temperature as the constant temperature of the sensor; and (2) establishing a fixed boundary temperature which is either less than or equal to, or slightly greater than the sensor constant temperature. The present invention accordingly thermally isolates a temperature responsive sensor in an energy efficient, controllable manner while avoiding any contamination of the flow.

Optical properties of self-assembled ZnTe quantum dots grown by molecular-beam epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, C.S.; Lai, Y.J.; Chou, W.C.

2005-02-01

The morphology and the size-dependent photoluminescence (PL) spectra of the type-II ZnTe quantum dots (QDs) grown in a ZnSe matrix were obtained. The coverage of ZnTe varied from 2.5 to 3.5 monolayers (MLs). The PL peak energy decreased as the dot size increased. Excitation power and temperature-dependent PL spectra are used to characterize the optical properties of the ZnTe quantum dots. For 2.5- and 3.0-ML samples, the PL peak energy decreased monotonically as the temperature increased. However, for the 3.5-ML sample, the PL peak energy was initially blueshifted and then redshifted as the temperature increased above 40 K. Carrier thermalizationmore » and carrier transfer between QDs are used to explain the experimental data. A model of temperature-dependent linewidth broadening is employed to fit the high-temperature data. The activation energy, which was found by the simple PL intensity quenching model, of the 2.5, 3.0, and 3.5 MLs were determined to be 6.35, 9.40, and 18.87 meV, respectively.« less

Sequential ultrasound and low-temperature thermal pretreatment: Process optimization and influence on sewage sludge solubilization, enzyme activity and anaerobic digestion.

PubMed

Neumann, Patricio; González, Zenón; Vidal, Gladys

2017-06-01

The influence of sequential ultrasound and low-temperature (55°C) thermal pretreatment on sewage sludge solubilization, enzyme activity and anaerobic digestion was assessed. The pretreatment led to significant increases of 427-1030% and 230-674% in the soluble concentrations of carbohydrates and proteins, respectively, and 1.6-4.3 times higher enzymatic activities in the soluble phase of the sludge. Optimal conditions for chemical oxygen demand solubilization were determined at 59.3kg/L total solids (TS) concentration, 30,500kJ/kg TS specific energy and 13h thermal treatment time using response surface methodology. The methane yield after pretreatment increased up to 50% compared with the raw sewage sludge, whereas the maximum methane production rate was 1.3-1.8 times higher. An energy assessment showed that the increased methane yield compensated for energy consumption only under conditions where 500kJ/kg TS specific energy was used for ultrasound, with up to 24% higher electricity recovery. Copyright © 2017 Elsevier Ltd. All rights reserved.

Coverage-dependent adsorption and desorption of oxygen on Pd(100)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dunnen, Angela den; Jacobse, Leon; Wiegman, Sandra

2016-06-28

We have studied the adsorption and desorption of O{sub 2} on Pd(100) by supersonic molecular beam techniques and thermal desorption spectroscopy. Adsorption measurements on the bare surface confirm that O{sub 2} initially dissociates for all kinetic energies between 56 and 380 meV and surface temperatures between 100 and 600 K via a direct mechanism. At and below 150 K, continued adsorption leads to a combined O/O{sub 2} overlayer. Dissociation of molecularly bound O{sub 2} during a subsequent temperature ramp leads to unexpected high atomic oxygen coverages, which are also obtained at high incident energy and high surface temperature. At intermediatemore » temperatures and energies, these high final coverages are not obtained. Our results show that kinetic energy of the gas phase reactant and reaction energy dissipated during O{sub 2} dissociation on the cold surface both enable activated nucleation of high-coverage surface structures. We suggest that excitation of local substrate phonons may play a crucial role in oxygen dissociation at any coverage.« less

Metabolic energy sensors (AMPK and SIRT1), protein carbonylation and cardiac failure as biomarkers of thermal stress in an intertidal limpet: linking energetic allocation with environmental temperature during aerial emersion.

PubMed

Han, Guo-dong; Zhang, Shu; Marshall, David J; Ke, Cai-huan; Dong, Yun-wei

2013-09-01

The effects of heat stress on organisms are manifested at the levels of organ function, metabolic activity, protein stability and gene expression. Here, we examined effects of high temperature on the intertidal limpet Cellana toreuma to determine how the temperatures at which (1) organ failure (cardiac function), (2) irreversible protein damage (carbonylation) and (3) expression of genes encoding proteins involved in molecular chaperoning (hsp70 and hsp90) and metabolic regulation (ampk and sirt1) occur compare with field temperatures, which commonly exceed 30°C and can reach 46°C. Heart failure, indexed by the Arrhenius break temperature, occurred at 34.3°C. Protein carbonylation rose significantly at 38°C. Genes for heat shock proteins HSP70 (hsp70) and HSP90 (hsp90), for two subunits of AMP-activated protein kinase (AMPK) (ampkα and ampkβ) and for histone/protein deacetylase SIRT1 (sirt1) all showed increased expression at 30°C. Temperatures of maximal expression differed among genes, as did temperatures at which upregulation ceased. Expression patterns for ampk and sirt1 indicate that heat stress influenced cellular energy homeostasis; above ~30°C, upregulation of ATP-generating pathways is suggested by elevated expression of genes for ampk; an altered balance between reliance on carbohydrate and lipid fuels is indicated by changes in expression of sirt1. These results show that C. toreuma commonly experiences temperatures that induce expression of genes associated with the stress response (hsp70 and hsp90) and regulation of energy metabolism (ampk and sirt1). At high temperatures, there is likely to be a shift away from anabolic processes such as growth to catabolic processes, to provide energy for coping with stress-induced damage, notably to proteins.

Electrical Conductivity, Thermal Stability, and Lattice Defect Evolution During Cyclic Channel Die Compression of OFHC Copper

NASA Astrophysics Data System (ADS)

Satheesh Kumar, S. S.; Raghu, T.

2015-02-01

Oxygen-free high-conductivity (OFHC) copper samples are severe plastically deformed by cyclic channel die compression (CCDC) technique at room temperature up to an effective plastic strain of 7.2. Effect of straining on variation in electrical conductivity, evolution of deformation stored energy, and recrystallization onset temperatures are studied. Deformation-induced lattice defects are quantified using three different methodologies including x-ray diffraction profile analysis employing Williamson-Hall technique, stored energy based method, and electrical resistivity-based techniques. Compared to other severe plastic deformation techniques, electrical conductivity degrades marginally from 100.6% to 96.6% IACS after three cycles of CCDC. Decrease in recrystallization onset and peak temperatures is noticed, whereas stored energy increases and saturates at around 0.95-1.1J/g after three cycles of CCDC. Although drop in recrystallization activation energy is observed with the increasing strain, superior thermal stability is revealed, which is attributed to CCDC process mechanics. Low activation energy observed in CCDC-processed OFHC copper is corroborated to synergistic influence of grain boundary characteristics and lattice defects distribution. Estimated defects concentration indicated continuous increase in dislocation density and vacancy with strain. Deformation-induced vacancy concentration is found to be significantly higher than equilibrium vacancy concentration ascribed to hydrostatic stress states experienced during CCDC.

Understanding the high-temperature deformation

NASA Astrophysics Data System (ADS)

Gyurko, Angela M.; Vignoul, Gregory E.; Tien, John K.; Sanchez, Juan M.

1992-11-01

Engineering, University of Texas at Austin, Austin, TX 78712 While much of the high-temperature intermetallics research has centered around Ni3Al and other aluminum-based systems, the present study focuses on the Engel-Brewer Ll2 intermetallic Ir3Zr, which has a melting temperature approaching that of ceramics (2280 °C). Due to limited material availability, the technique of microindentation was used to study both the temperature and time dependence of strength. Because of the widely held belief that certain mechanical properties of intermetallics scale roughly with temperature, Ir3Zr was expected to exhibit high strength. The microhardness was observed to vary from 225 MPa at room temperature to 75 MPa at 1400 °C, which is significantly lower than the behavior of Ni3Al. The activation energy for creep was determined to be 467 kJ/mole, and the stress exponent was found to be 18.2. The ordering energy of this system was calculated to be 0.114 eV. If it can be assumed that high ordering energy correlates to a high antiphase boundary (APB) energy, then the behavior of this system is consistent with a model that predicts highly glissile dislocation cores.

An Integrated, Layered-Spinel Composite Cathode for Energy Storage Applications

NASA Technical Reports Server (NTRS)

Hagh, Nader; Skandan, Ganesh

2012-01-01

At low operating temperatures, commercially available electrode materials for lithium-ion batteries do not fully meet the energy and power requirements for NASA fs exploration activities. The composite cathode under development is projected to provide the required energy and power densities at low temperatures and its usage will considerably reduce the overall volume and weight of the battery pack. The newly developed composite electrode material can provide superior electrochemical performance relative to a commercially available lithium cobalt system. One advantage of using a composite cathode is its higher energy density, which can lead to smaller and lighter battery packs. In the current program, different series of layered-spinel composite materials with at least two different systems in an integrated structure were synthesized, and the volumetric and gravimetric energy densities were evaluated. In an integrated network of a composite electrode, the effect of the combined structures is to enhance the capacity and power capabilities of the material to levels greater than what is possible in current state-of-the-art cathode systems. The main objective of the current program is to implement a novel cathode material that meets NASA fs low temperature energy density requirements. An important feature of the composite cathode is that it has at least two components (e.g., layered and spinel) that are structurally integrated. The layered material by itself is electrochemically inactive; however, upon structural integration with a spinel material, the layered material can be electrochemically activated, thereby delivering a large amount of energy with stable cycling. A key aspect of the innovation has been the development of a scalable process to produce submicronand micron-scale particles of these composite materials. An additional advantage of using such a composite electrode material is its low irreversible loss (.5%), which is primarily due to the unique activation of the composite. High columbic efficiency (greater than 99%) upon cycling may indicate the formation of a stable SEI (solid-electrolyte interface) layer, which can contribute to long cycle life. The innovation in the current program, when further developed, will enable the system to maintain high energy and power densities at low temperatures, improve efficiency, and further stabilize and enhance the safety of the cell.

Assessment of Uncertainty in the Determination of Activation Energy for Polymeric Materials

NASA Technical Reports Server (NTRS)

Darby, Stephania P.; Landrum, D. Brian; Coleman, Hugh W.

1998-01-01

An assessment of the experimental uncertainty in obtaining the kinetic activation energy from thermogravimetric analysis (TGA) data is presented. A neat phenolic resin, Borden SC1O08, was heated at three heating rates to obtain weight loss vs temperature data. Activation energy was calculated by two methods: the traditional Flynn and Wall method based on the slope of log(q) versus 1/T, and a modification of this method where the ordinate and abscissa are reversed in the linear regression. The modified method produced a more accurate curve fit of the data, was more sensitive to data nonlinearity, and gave a value of activation energy 75 percent greater than the original method. An uncertainty analysis using the modified method yielded a 60 percent uncertainty in the average activation energy. Based on this result, the activation energy for a carbon-phenolic material was doubled and used to calculate the ablation rate In a typical solid rocket environment. Doubling the activation energy increased surface recession by 3 percent. Current TGA data reduction techniques that use the traditional Flynn and Wall approach to calculate activation energy should be changed to the modified method.

Evaluating pen-day interactions in body temperature bilogistic mixed model for handling of feedlot heifers during heat stress

USDA-ARS?s Scientific Manuscript database

Daily activities consume the energy of heifers, subsequently causing an elevation of body temperature, depending on the ambient conditions. A better understanding of the dynamics of body temperature (Tb) would be helpful when deciding how to process and handle heifers. It would also lead to specific...

The effects of fasting on swimming performance in juvenile qingbo (Spinibarbus sinensis) at two temperatures.

PubMed

Pang, Xu; Yuan, Xing-Zhong; Cao, Zhen-Dong; Fu, Shi-Jian

2014-05-01

We measured the following variables to investigate the effects of fasting and temperature on swimming performance in juvenile qingbo (Spinibarbus sinensis): the critical swimming speed (Ucrit), resting metabolic rate (ṀO2rest) and active metabolic rate (ṀO2active) of fish fasting for 0 (control), 1, 2 and 4 weeks at low and high acclimation temperatures (15 and 25°C). Both fasting treatment and temperature acclimation had significant effects on all parameters measured (P<0.05). Fasting at the higher temperature had a negative effect on all measured parameters after 1 week (P<0.05). However, when acclimated to the lower temperature, fasting had a negative effect on Ucrit until week 2 and on (ṀO2rest), (ṀO2active) and metabolic scope (MS, (ṀO2active)-(ṀO2rest)) until week 4 (P<0.05). The values of all parameters at the lower temperature were significantly lower than those at the higher temperature in the identical fasting period groups except for (ṀO2rest) of the fish that fasted for 2 weeks. The relationship between fasting time (T) and Ucrit was described as Ucrit(15)=-0.302T(2)-0.800T+35.877 (r=0.781, n=32, P<0.001) and Ucrit(25)=0.471T(2)-3.781T+50.097 (r=0.766, n=32, P<0.001) at 15 and 25°C, respectively. The swimming performance showed less decrease in the early stage of fasting but more decrease in the later stage at the low temperature compared to the high temperature, which might be related to thermal acclimation time, resting metabolism, respiratory capacity, energy stores, enzyme activity in muscle tissue and energy substrate utilization changes with fasting between low and high temperatures. The divergent response of the swimming performance to fasting in qingbo at different temperatures might be an adaptive strategy to seasonal temperature and food resource variation in their habitat. Copyright © 2014. Published by Elsevier Ltd.

Tandem mass spectrometry of large biomolecule ions by blackbody infrared radiative dissociation.

PubMed

Price, W D; Schnier, P D; Williams, E R

1996-03-01

A new method for the dissociation of large ions formed by electrospray ionization is demonstrated. Ions trapped in a Fourier transform mass spectrometer at pressures below 10(-)(8) Torr are dissociated by elevating the vacuum chamber to temperatures up to 215 °C. Rate constants for dissociation are measured and found to be independent of pressure below 10(-)(7) Torr. This indicates that the ions are activated by absorption of blackbody radiation emitted from the chamber walls. Dissociation efficiencies as high as 100% are obtained. There is no apparent mass limit to this method; ions as large as ubiquitin (8.6 kDa) are readily dissociated. Thermally stable ions, such as melittin 3+ (2.8 kDa), did not dissociate at temperatures up to 200 °C. This method is highly selective for low-energy fragmentation, from which limited sequence information can be obtained. From the temperature dependence of the dissociation rate constants, Arrhenius activation energies in the low-pressure limit are obtained. The lowest energy dissociation processes for the singly and doubly protonated ions of bradykinin are loss of NH(3) and formation of the b(2)/y(7) complementary pair, with activation energies of 1.3 and 0.8 eV, respectively. No loss of NH(3) is observed for the doubly protonated ion; some loss of H(2)O occurs. These results show that charge-charge interactions not only lower the activation energy for dissociation but also can dramatically change the fragmentation, most likely through changes in the gas-phase conformation of the ion. Dissociation of ubiquitin ions produces fragmentation similar to that obtained by IRMPD and SORI-CAD. Higher charge state ions dissociate to produce y and b ions; the primary fragmentation process for low charge state ions is loss of H(2)O.

Torpor and activity in a free-ranging tropical bat: implications for the distribution and conservation of mammals?

NASA Astrophysics Data System (ADS)

Geiser, Fritz; Stawski, Clare; Bondarenco, Artiom; Pavey, Chris R.

2011-05-01

Bats are most diverse in the tropics, but there are no quantitative data on torpor use for energy conservation by any tropical bat in the wild. We examined the thermal biology, activity patterns and torpor use of two tree-roosting long-eared bats ( Nyctophilus geoffroyi, 7.8 g) in tropical northern Australia in winter using temperature telemetry. Bats commenced activity about 20 min after sunset, ended activity about 2.5 h before sunrise and entered torpor everyday in the early morning even when minimum ambient temperatures ( T a) were as high as 23°C. On average, bats remained torpid for almost 5 h, mean minimum skin temperature ( T skin) measured was 22.8 ± 0.1°C and daily T skin minima were correlated with T a. Our study shows that even in the tropics, torpor is frequently employed by bats, suggesting that worldwide most bat species are heterothermic and use torpor for energy conservation. We propose that the ability of employing torpor and the resulting highly plastic energy requirements may partially explain why these small insectivorous bats can inhabit almost the entire Australian continent despite vastly different climatic and likely trophic conditions. Reduced energy requirements also may permit survival in degraded or modified habitats, reduce the need for foraging and reduce exposure to predators. Thus, the ability to employ torpor may be one important reason for why most Australian bats and other heterothermic mammals have not gone extinct whereas many obligatory homeothermic mammals that cannot employ torpor and have high energy and foraging requirements have suffered high rates of extinctions.

Modeling of mid-infrared quantum cascade lasers: The role of temperature and operating field strength on the laser performance

NASA Astrophysics Data System (ADS)

Yousefvand, Hossein Reza

2017-07-01

In this paper a self-consistent numerical approach to study the temperature and bias dependent characteristics of mid-infrared (mid-IR) quantum cascade lasers (QCLs) is presented which integrates a number of quantum mechanical models. The field-dependent laser parameters including the nonradiative scattering times, the detuning and energy levels, the escape activation energy, the backfilling excitation energy and dipole moment of the optical transition are calculated for a wide range of applied electric fields by a self-consistent solution of Schrodinger-Poisson equations. A detailed analysis of performance of the obtained structure is carried out within a self-consistent solution of the subband population rate equations coupled with carrier coherent transport equations through the sequential resonant tunneling, by taking into account the temperature and bias dependency of the relevant parameters. Furthermore, the heat transfer equation is included in order to calculate the carrier temperature inside the active region levels. This leads to a compact predictive model to analyze the temperature and electric field dependent characteristics of the mid-IR QCLs such as the light-current (L-I), electric field-current (F-I) and core temperature-electric field (T-F) curves. For a typical mid-IR QCL, a good agreement was found between the simulated temperature-dependent L-I characteristic and experimental data, which confirms validity of the model. It is found that the main characteristics of the device such as output power and turn-on delay time are degraded by interplay between the temperature and Stark effects.

A theoretical model of grain boundary self-diffusion in metals with phase transitions (case study into titanium and zirconium)

NASA Astrophysics Data System (ADS)

Semenycheva, Alexandra V.; Chuvil'deev, Vladimir N.; Nokhrin, Aleksey V.

2018-05-01

The paper offers a model describing the process of grain boundary self-diffusion in metals with phase transitions in the solid state. The model is based on ideas and approaches found in the theory of non-equilibrium grain boundaries. The range of application of basic relations contained in this theory is shown to expand, as they can be used to calculate the parameters of grain boundary self-diffusion in high-temperature and low-temperature phases of metals with a phase transition. The model constructed is used to calculate grain boundary self-diffusion activation energy in titanium and zirconium and an explanation is provided as to their abnormally low values in the low-temperature phase. The values of grain boundary self-diffusion activation energy are in good agreement with the experiment.

Dielectric and AC conductivity studies on SrBi4Ti4O15

NASA Astrophysics Data System (ADS)

Jose, Roshan; Saravanan, K. Venkata

2018-05-01

The four layered SrBi4Ti4O15 ceramics which belong to the aurivillius family of oxide was prepared by conventional solid state reaction technique. Analysis of the dielectric data as a function of temperature and frequency revealed normal phase transition. The frequency dependent ac conductivity follows Jonscher's universal power law. Frequency exponent (n), pre-exponential factor (A), bulk dc conductivity (σdc), and hopping frequency (ωp) were determined from the fitting curves. The variation of frequency exponent with temperature indicates that large polaron hopping mechanism up to curie-temperature, then its changes to small polaron hopping. The activation energies were calculated from ac conductivity, bulk dc conductivity and hopping frequency. The activation energies revealed that conductivity had contributions from migrations of oxygen vacancies, bismuth ion vacancies and strontium ion vacancies.

Temperature factors effect on occurrence of stress corrosion cracking of main gas pipeline

NASA Astrophysics Data System (ADS)

Nazarova, M. N.; Akhmetov, R. R.; Krainov, S. A.

2017-10-01

The purpose of the article is to analyze and compare the data in order to contribute to the formation of an objective opinion on the issue of the growth of stress corrosion defects of the main gas pipeline. According to available data, a histogram of the dependence of defects due to stress corrosion on the distance from the compressor station was constructed, and graphs of the dependence of the accident density due to stress corrosion in the winter and summer were also plotted. Data on activation energy were collected and analyzed in which occurrence of stress corrosion is most likely constructed, a plot of activation energy versus temperature is plotted, and the process of occurrence of stress corrosion by the example of two different grades of steels under the action of different temperatures was analyzed.

Quenching And Luminescence Efficiency Of Nd3+ In YAG

NASA Astrophysics Data System (ADS)

Lupei, Voicu; Lupei, Aurelia; Georgescu, Serban; Ionescu, Christian I.; Yen, William M.

1989-05-01

The effect of the concentration luminescence quenching of the 4F 3/2, level of Nd3+ in YAG on the relative efficiency is presented. Based on the analysis of the decay curves in terms of the energy transfer theory, an analytical expression for the relative luminescence efficiency is obtained. In the low concentration range (up to q,1.5 at % Nd3+), the efficiency linearly decreases when Nd3+ concentration increases. It is also stressed that pairs quenching contribute about 20 % to the nonradiative energy transfer losses. Quantum efficiency of luminescence is an important parameter for the characterization of laser active media; its lowering is due to either multiphonon relaxation or energy transfer processes. The multiphonon non-radiative probability depends on the energy gap between levels, on the phonon energy and temperature; usually at low activator doping it is practically independent on concentration. On the other hand, energy transfer losses show a marked dependence on activator concentration, a fact that severely limits the range of useful con-centration of active centers in some laser crystals. In the YAG:Nd case the minimum energy gap between the Stark components of the 4F,I.) and the next lower level 4F15/2 is of about 4700 cm-1. Since in YAG tree phonons most effdbtively coupled to the Rare pi.th ions have an energy of 1, 700 cm-1, the probability for multiphonon relaxation from the 'F3/, level, even at room temperature, is very low and therefore for low Nd 3+ concentrations quantum efficiency is expected to be close to 1.

Evidence of superconductivity-induced phonon spectra renormalization in alkali-doped iron selenides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Opačić, M.; Lazarević, N.; Šćepanović, M.

2015-11-16

Polarized Raman scattering spectra of superconducting K xFe 2-ySe 2 and nonsuperconducting K 0.8Fe 1.8Co 0.2Se 2 single crystals were measured in a temperature range from 10 K up to 300 K. Two Raman active modes from the I4/mmm phase and seven from the I4/m phase are observed in frequency range from 150 to 325 cm -1 in both compounds, suggesting that K 0.8Fe 1.8Co 0.2Se 2 single crystal also has two-phase nature. Temperature dependence of Raman mode energy is analyzed in terms of lattice thermal expansion and phonon-phonon interaction. Temperature dependence of Raman mode linewidth is considered as temperature-inducedmore » anharmonic effects. It is shown that change of Raman mode energy with temperature is dominantly driven by thermal expansion of the crystal lattice. Abrupt change of the A 1g mode energy near T C was observed in K xFe 2-ySe 2 , whereas it is absent in K 0.8Fe 1.8Co 0.2Se 2. Phonon energy hardening at low temperatures in the superconducting sample is a consequence of superconductivity-induced redistribution of the electronic states below critical temperature.« less

Systematic variation in the temperature dependence of physiological and ecological traits.

PubMed

Dell, Anthony I; Pawar, Samraat; Savage, Van M

2011-06-28

To understand the effects of temperature on biological systems, we compile, organize, and analyze a database of 1,072 thermal responses for microbes, plants, and animals. The unprecedented diversity of traits (n = 112), species (n = 309), body sizes (15 orders of magnitude), and habitats (all major biomes) in our database allows us to quantify novel features of the temperature response of biological traits. In particular, analysis of the rising component of within-species (intraspecific) responses reveals that 87% are fit well by the Boltzmann-Arrhenius model. The mean activation energy for these rises is 0.66 ± 0.05 eV, similar to the reported across-species (interspecific) value of 0.65 eV. However, systematic variation in the distribution of rise activation energies is evident, including previously unrecognized right skewness around a median of 0.55 eV. This skewness exists across levels of organization, taxa, trophic groups, and habitats, and it is partially explained by prey having increased trait performance at lower temperatures relative to predators, suggesting a thermal version of the life-dinner principle-stronger selection on running for your life than running for your dinner. For unimodal responses, habitat (marine, freshwater, and terrestrial) largely explains the mean temperature at which trait values are optimal but not variation around the mean. The distribution of activation energies for trait falls has a mean of 1.15 ± 0.39 eV (significantly higher than rises) and is also right-skewed. Our results highlight generalities and deviations in the thermal response of biological traits and help to provide a basis to predict better how biological systems, from cells to communities, respond to temperature change.

Systematic variation in the temperature dependence of physiological and ecological traits

PubMed Central

Dell, Anthony I.; Pawar, Samraat; Savage, Van M.

2011-01-01

To understand the effects of temperature on biological systems, we compile, organize, and analyze a database of 1,072 thermal responses for microbes, plants, and animals. The unprecedented diversity of traits (n = 112), species (n = 309), body sizes (15 orders of magnitude), and habitats (all major biomes) in our database allows us to quantify novel features of the temperature response of biological traits. In particular, analysis of the rising component of within-species (intraspecific) responses reveals that 87% are fit well by the Boltzmann–Arrhenius model. The mean activation energy for these rises is 0.66 ± 0.05 eV, similar to the reported across-species (interspecific) value of 0.65 eV. However, systematic variation in the distribution of rise activation energies is evident, including previously unrecognized right skewness around a median of 0.55 eV. This skewness exists across levels of organization, taxa, trophic groups, and habitats, and it is partially explained by prey having increased trait performance at lower temperatures relative to predators, suggesting a thermal version of the life-dinner principle—stronger selection on running for your life than running for your dinner. For unimodal responses, habitat (marine, freshwater, and terrestrial) largely explains the mean temperature at which trait values are optimal but not variation around the mean. The distribution of activation energies for trait falls has a mean of 1.15 ± 0.39 eV (significantly higher than rises) and is also right-skewed. Our results highlight generalities and deviations in the thermal response of biological traits and help to provide a basis to predict better how biological systems, from cells to communities, respond to temperature change. PMID:21606358

Non-invasive energy meter for fixed and variable flow systems

DOEpatents

Menicucci, David F.; Black, Billy D.

2005-11-01

An energy metering method and apparatus for liquid flow systems comprising first and second segments of one or more conduits through which a liquid flows, comprising: attaching a first temperature sensor for connection to an outside of the first conduit segment; attaching a second temperature sensor for connection to an outside of the second conduit segment; via a programmable control unit, receiving data from the sensors and calculating energy data therefrom; and communicating energy data from the meter; whereby the method and apparatus operate without need to temporarily disconnect or alter the first or second conduit segments. The invention operates with both variable and fixed flow systems, and is especially useful for both active and passive solar energy systems.

High temperature underground thermal energy storage system for solar energy

NASA Technical Reports Server (NTRS)

Collins, R. E.

1980-01-01

The activities feasibility of high temperature underground thermal storage of energy was investigated. Results indicate that salt cavern storage of hot oil is both technically and economically feasible as a method of storing huge quantities of heat at relatively low cost. One particular system identified utilizes a gravel filled cavern leached within a salt dome. Thermal losses are shown to be less than one percent of cyclically transferred heat. A system like this having a 40 MW sub t transfer rate capability and over eight hours of storage capacity is shown to cost about $13.50 per KWh sub t.

A cold-adapted endoglucanase from camel rumen with high catalytic activity at moderate and low temperatures: an anomaly of truly cold-adapted evolution in a mesophilic environment.

PubMed

Khalili Ghadikolaei, Kamran; Gharechahi, Javad; Haghbeen, Kamahldin; Akbari Noghabi, Kambiz; Hosseini Salekdeh, Ghasem; Shahbani Zahiri, Hossein

2018-03-01

Endoglucanases are important enzymes in plant biomass degradation. They have current and potential applications in various industrial sectors including human and animal food processing, textile, paper, and renewable biofuel production. It is assumed that the cold-active endoglucanases, with high catalytic rates in moderate and cold temperatures, can improve the cost-effectiveness of industrial processes by lowering the need for heating and, thus, energy consumption. In this study, the endoglucanase CelCM3 was procured from a camel rumen metagenome via gene cloning and expression in Escherichia coli BL21 (DE3). The maximum activity of the enzyme on carboxymethyl cellulose (CMC) was obtained at pH 5 and 30 °C with a V max and K m of 339 U/mg and 2.57 mg/ml, respectively. The enzyme with an estimated low melting temperature of 45 °C and about 50% activity at 4 °C was identified to be cold-adapted. A thermodynamic analysis corroborated that CelCM3 with an activation energy (E a ), enthalpy of activation (ΔH), and Gibb's free energy (ΔG) of, respectively, 18.47 kJ mol -1 , 16.12 kJ mol -1 , and 56.09 kJ mol -1 is a cold-active endoglucanase. In addition, CelCM3 was tolerant of metal ions, non-ionic detergents, urea, and organic solvents. Given these interesting characteristics, CelCM3 shows promise to meet the requirements of industrial applications.

Transmission, reflection and thermoluminescence studies on GaS{sub 0.75}Se{sub 0.25} layered single crystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Delice, S., E-mail: sdelice@metu.edu.tr; Isik, M.; Gasanly, N.M.

2015-10-15

Highlights: • Optical and thermoluminescence properties of Ga{sub 4}S{sub 3}Se crystals were investigated. • Indirect and direct band gap energies were found as 2.39 and 2.53 eV, respectively. • The activation energy of the trap center was determined as 495 meV. - Abstract: Optical and thermoluminescence properties on GaS{sub 0.75}Se{sub 0.25} crystals were investigated in the present work. Transmission and reflection measurements were performed at room temperature in the wavelength range of 400–1000 nm. Analysis revealed the presence of indirect and direct transitions with band gap energies of 2.39 and 2.53 eV, respectively. TL spectra obtained at low temperatures (10–300more » K) exhibited one peak having maximum temperature of 168 K. Observed peak was analyzed using curve fitting, initial rise and peak shape methods to calculate the activation energy of the associated trap center. All applied methods were consistent with the value of 495 meV. Attempt-to-escape-frequency and capture cross section of the trap center were determined using the results of curve fitting. Heating rate dependence studies of the glow curve in the range of 0.4–0.8 K/s resulted with decrease of TL intensity and shift of the peak maximum temperature to higher values.« less

Synthesis and Electrical Resistivity of Nickel Polymethacrylate

NASA Astrophysics Data System (ADS)

Chohan, M. H.; Khalid, A. H.; Zulfiqar, M.; Butt, P. K.; Khan, Farah; Hussain, Rizwan

Synthesis of nickel polymethacrylate was carried out using methanolic solutions of sodium hydroxide and polymethacrylic acid. The electrical resistivity of the pellets made from Ni-polymethacrylate was measured at different voltages and temperatures. Results showed that the electrical resistivity of Ni-polymethacrylate decreases significantly with voltage in high temperature regions but the decrease is insignificant at temperatures nearing room temperature. The activation energy at low temperatures is approximately 0.8 eV whereas at high temperature it is in the range 0.21-0.27 eV.

Activation Energy of the Low-pH-Induced Lamellar to Bicontinuous Cubic Phase Transition in Dioleoylphosphatidylserine/Monoolein.

PubMed

Oka, Toshihiko; Saiki, Takahiro; Alam, Jahangir Md; Yamazaki, Masahito

2016-02-09

Electrostatic interaction is an important factor for phase transitions between lamellar liquid-crystalline (Lα) and inverse bicontinuous cubic (QII) phases. We investigated the effect of temperature on the low-pH-induced Lα to double-diamond cubic (QII(D)) phase transition in dioleoylphosphatidylserine (DOPS)/monoolein (MO) using time-resolved small-angle X-ray scattering with a stopped-flow apparatus. Under all conditions of temperature and pH, the Lα phase was directly transformed into an intermediate inverse hexagonal (HII) phase, and subsequently the HII phase slowly converted to the QII(D) phase. We obtained the rate constants of the initial step (i.e., the Lα to HII phase transition) and of the second step (i.e., the HII to QII(D) phase transition) using the non-negative matrix factorization method. The rate constant of the initial step increased with temperature. By analyzing this result, we obtained the values of its apparent activation energy, Ea (Lα → HII), which did not change with temperature but increased with an increase in pH. In contrast, the rate constant of the second step decreased with temperature at pH 2.6, although it increased with temperature at pH 2.7 and 2.8. These results indicate that the value of Ea (HII → QII(D)) at pH 2.6 increased with temperature, but the values of Ea (HII → QII(D)) at pH 2.7 and 2.8 were constant with temperature. The values of Ea (HII → QII(D)) were smaller than those of Ea (Lα → HII) at the same pH. We analyzed these results using a modified quantitative theory on the activation energy of phase transitions of lipid membranes proposed initially by Squires et al. (Squires, A. M.; Conn, C. E.; Seddon, J. M.; Templer, R. H. Soft Matter 2009, 5, 4773). On the basis of these results, we discuss the mechanism of this phase transition.

Radiofrequency energy antenna coupling to common laparoscopic instruments: practical implications.

PubMed

Jones, Edward L; Robinson, Thomas N; McHenry, Jennifer R; Dunn, Christina L; Montero, Paul N; Govekar, Henry R; Stiegmann, Greg V

2012-11-01

Electromagnetic coupling can occur between the monopolar "Bovie" instrument and other laparoscopic instruments without direct contact by a phenomenon termed antenna coupling. The purpose of this study was to determine if, and to what extent, radiofrequency energy couples to other common laparoscopic instruments and to describe practical steps that can minimize the magnitude of antenna coupling. In a laparoscopic simulator, monopolar radiofrequency energy was delivered to an L-hook. The tips of standard, nonelectrical laparoscopic instruments (either an unlit 10 mm telescope or a 5 mm grasper) were placed adjacent to bovine liver tissue and were never in contact with the active electrode. Thermal imaging quantified the change in tissue temperature nearest the tip of the telescope or grasper at the end of a 5 s activation of the active electrode. A 5 s activation (30 watts, coagulation mode, 4 cm separation between instruments) increased tissue temperature compared with baseline adjacent to the grasper tip (2.2 ± 2.2 °C; p = 0.013) and telescope tip (38.2 ± 8.0 °C; p < 0.001). The laparoscopic telescope tip increased tissue temperature more than the laparoscopic grasper tip (p < 0.001). Lowering the generator power from 30 to 15 Watts decreased the heat generated at the telescope tip (38.2 ± 8.0 vs. 13.5 ± 7.5 °C; p < 0.001). Complete separation of the camera/light cords and the active electrode cord decreased the heat generated near the telescope tip compared with parallel bundling of the cords (38.2 ± 8.0 vs. 15.7 ± 11.6 °C; p < 0.001). Commonly used laparoscopic instruments couple monopolar radiofrequency energy without direct contact with the active electrode, a phenomenon that results in heat transfer from a nonelectrically active instrument tip to adjacent tissue. Practical steps to minimize heat transfer resulting from antenna coupling include reducing the monopolar generator power setting and avoiding of parallel bundling of the telescope and active electrode cords.

Summer declines in activity and body temperature offer polar bears limited energy savings

USGS Publications Warehouse

Whiteman, J.P.; Harlow, H.J.; Durner, George M.; Anderson-Sprecher, R.; Albeke, Shannon E.; Regehr, Eric V.; Amstrup, Steven C.; Ben-David, M.

2015-01-01

Polar bears (Ursus maritimus) summer on the sea ice or, where it melts, on shore. Although the physiology of “ice” bears in summer is unknown, “shore” bears purportedly minimize energy losses by entering a hibernation-like state when deprived of food. Such a strategy could partially compensate for the loss of on-ice foraging opportunities caused by climate change. However, here we report gradual, moderate declines in activity and body temperature of both shore and ice bears in summer, resembling energy expenditures typical of fasting, nonhibernating mammals. Also, we found that to avoid unsustainable heat loss while swimming, bears employed unusual heterothermy of the body core. Thus, although well adapted to seasonal ice melt, polar bears appear susceptible to deleterious declines in body condition during the lengthening period of summer food deprivation.

Mass and energy flow in prominences

NASA Technical Reports Server (NTRS)

Poland, Arthur I.

1990-01-01

Mass and energy flow in quiescent prominences is considered based on the hypothesis that active region prominences have a different structure and thus different mass and energy flow characteristics. Several important physical parameters have been plotted using the computational model, representing the evolutionary process after the prominence formation. The temperature, velocity, conductive flux, and enthalpy flux are plotted against distance from the highest point in the loop to the coolest part of the prominence. It is shown that the maximum velocity is only about 5 km/s. The model calculations indicate that the transition region of prominences is dominated by complex processes. It is necessary to take into account mass flow at temperatures below 200,000 K, and both mass flow and optical depth effects in hydrogen at temperatures below 30,000 K. Both of these effects lead to a less steep temperature gradient through the prominence corona interface than can be obtained from the conduction alone.

Determination of the Activation Energy of the Enzymatic Biodegradation Process in Microfabricated Polyhydroxyalkanoate Thin Films Using In-Situ, Real Time Atomic Force Microscopy

NASA Astrophysics Data System (ADS)

Morse, Clinton; Latuga, Brian M.; Delfaus, Stephen; Devore, Thomas C.; Augustine, Brian H.; Hughes, W. Christopher; Warne, Paul G.

2003-11-01

Using the liquid cell capability of the atomic force microscope (AFM), we report the determination of the activation energy of the biodegradation process of the enzymatic biodegradation of poly 3-hydroxybutyrate / poly 3-hydroxyvalerate [P(3HB-HV)] thin films. We have prepared P(3HB-3HV) copolymer microstructures by the selective dewetting of soft lithographically patterned gold substrates with features sizes down to 10 mm. These have been then used as an internal height standard to measure the volume of material as a function of biodegradation time. Biodegradation is measured in-situ and real time using contact mode AFM in an enzymatic solution produced from Streptomyces sp. bacteria. The temperature dependent biodegradation has been measured over a temperature range from 23oC to 40oC. We will discuss the calculation of the activation energy of this process as well as a physical model to describe three distinct regions in the biodegradation process that have been observed.

Coal char oxidation kinetics in air medium

NASA Astrophysics Data System (ADS)

Slyusarskiy, K. V.; Jankovskiy, S. A.; Korotkikh, A. G.; Sorokin, I. V.

2017-01-01

Research on oxidation in air medium process of three different coal chars with various carbon content was presented. The anthracite, T-grade bituminous coal and 2B-grade lignite char powders with particle size less than 80 µm were studied. The coal char oxidation was studied by isothermal method using coupled TG-DSC analyzer Netzsch STA 449 Jupiter F3 in the temperature range 1000-1200 °C. Experiments were carried out at ambient pressure. Volumetric flow rate of oxidation medium into analyzer chamber was 250 ml/min and consisted of oxygen and argon with volumetric ratio 24:1. Based on experimental data, the average rate of carbon oxidation reaction values were defined at each temperature. Kinetic constants (frequency factor and activation energy) of reaction were defined as well via 1st order Arrhenius equation. Activation energy values are in good agreement with the data presented in the literature. Activation energy values for anthracite char are 1.6-1.7 times higher than those for bituminous coal and lignite chars, respectively.

Combustion characteristics of Malaysian oil palm biomass, sub-bituminous coal and their respective blends via thermogravimetric analysis (TGA).

PubMed

Idris, Siti Shawalliah; Rahman, Norazah Abd; Ismail, Khudzir

2012-11-01

The combustion characteristics of Malaysia oil palm biomass (palm kernel shell (PKS), palm mesocarp fibre (PMF) and empty fruit bunches (EFB)), sub-bituminous coal (Mukah Balingian) and coal/biomass blends via thermogravimetric analysis (TGA) were investigated. Six weight ratios of coal/biomass blends were prepared and oxidised under dynamic conditions from temperature 25 to 1100°C at four heating rates. The thermogravimetric analysis demonstrated that the EFB and PKS evolved additional peak besides drying, devolatilisation and char oxidation steps during combustion. Ignition and burn out temperatures of blends were improved in comparison to coal. No interactions were observed between the coal and biomass during combustion. The apparent activation energy during this process was evaluated using iso-conversional model free kinetics which resulted in highest activation energy during combustion of PKS followed by PMF, EFB and MB coal. Blending oil palm biomass with coal reduces the apparent activation energy value. Copyright © 2012 Elsevier Ltd. All rights reserved.

Detailed kinetics of titanium nitride synthesis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rode, H.; Hlavacek, V.

1995-02-01

A thermogravimetric analyzer is used to study the synthesis of TiN from Ti powder over a wide range of temperature, conversion and heating rate, and for two Ti precursor powders with different morphologies. Conversions to TiN up to 99% are obtained with negligible oxygen contamination. Nonisothermal initial rate and isothermal data are used in a nonlinear least-squares minimization to determine the most appropriate rate law. The logarithmic rate law offers an excellent agreement between the experimental and calculated conversions to TiN and can predict afterburning, which is an important experimentally observed phenomenon. Due to the form of the logarithmic ratemore » law, the observed activation energy is a function of effective particle size, extent of conversion, and temperature even when the intrinsic activation energy remains constant. This aspect explains discrepancies among activation energies obtained in previous studies. The frequently used sedimentation particle size is a poor measure of the powder reactivity. The BET surface area indicates the powder reactivity much better.« less

Injury of the cell's respiratory system by heat and by formaldehyde. Thermokinetics and early molecular events.

PubMed

Johnson, H A; Wiske, P S

1976-08-01

This is a study of the manner in which the respiratory system of the cell is injured either by elevated temperature or by exposure to diluted formaldehyde. Molecular mechanisms were identified by thermokinetic measurements. The rates at which respiratory failure developed in mouse liver slices in an injurious environment were measured at various temperatures. The data were fitted to the Arrhenius equation, and the effective activation energies of the injury processes were calculated. These data show that (1) the thermokinetics of injury to the cell's respiratory system, whether by thermal or chemical means, follows the Arrhenius law. (2) Thermal injury of the cell's respiratory system has a high activation energy, indicating that the critical, rate-determining event is a protein denaturation. Other mechanisms such as imbalance of metabolic reaction rates and thermal liquefaction of membrane lipids can be ruled out. (3) Repression of cell respiration by diluted formaldehyde has an activation energy compatible with a chemical reaction but low enough to exclude protein denaturation as a mechanism.

Electrical properties of granite with implications for the lower crust.

USGS Publications Warehouse

Olhoeft, G.R.

1981-01-01

The electrical properties of granite appear to be dominantly controlled by the amount of free water in the granite and by temperature. Minor contributions to the electrical properties are provided by hydrostatic and lithostatic pressure, structurally bound water, oxygen fugacity, and other parameters. The effect of sulphur fugacity may be important but is experimentally unconfirmed. In addition to changing the magnitude of electrical properties, the amount and chemistry of water in granite significantly changes the temperature dependence of the electrical properties. With increasing temperature, changes in water content retain large, but lessened, effects on electrical properties. Near room temperature, a monolayer of water will decrease the electrical resistivity by an order of magnitude. Several weight-percent water may decrease the electrical resistivity by as much as nine orders of magnitude and decrease the thermal activation energy by a factor of five. At elevated temperatures just below granitic melting, a few weight-percent water may still decrease the resistivity by as much as 3 orders of magnitude and the activation energy by a factor of two.-Author

Linking energetics and overwintering in temperate insects.

PubMed

Sinclair, Brent J

2015-12-01

Overwintering insects cannot feed, and energy they take into winter must therefore fuel energy demands during autumn, overwintering, warm periods prior to resumption of development in spring, and subsequent activity. Insects primarily consume lipids during winter, but may also use carbohydrate and proteins as fuel. Because they are ectotherms, the metabolic rate of insects is temperature-dependent, and the curvilinear nature of the metabolic rate-temperature relationship means that warm temperatures are disproportionately important to overwinter energy use. This energy use may be reduced physiologically, by reducing the slope or elevation of the metabolic rate-temperature relationship, or because of threshold changes, such as metabolic suppression upon freezing. Insects may also choose microhabitats or life history stages that reduce the impact of overwinter energy drain. There is considerable capacity for overwinter energy drain to affect insect survival and performance both directly (via starvation) or indirectly (for example, through a trade-off with cryoprotection), but this has not been well-explored. Likewise, the impact of overwinter energy drain on growing-season performance is not well understood. I conclude that overwinter energetics provides a useful lens through which to link physiology and ecology and winter and summer in studies of insect responses to their environment. Copyright © 2014 Elsevier Ltd. All rights reserved.

Thermal analysis and kinetics of coal during oxy-fuel combustion

NASA Astrophysics Data System (ADS)

Kosowska-Golachowska, Monika

2017-08-01

The pyrolysis and oxy-fuel combustion characteristics of Polish bituminous coal were studied using non-isothermal thermogravimetric analysis. Pyrolysis tests showed that the mass loss profiles were almost similar up to 870°C in both N2 and CO2 atmospheres, while further mass loss occurred in CO2 atmosphere at higher temperatures due to char-CO2 gasification. Replacement of N2 in the combustion environment by CO2 delayed the combustion of bituminous coal. At elevated oxygen levels, TG/DTG profiles shifted through lower temperature zone, ignition and burnout temperatures decreased and mass loss rate significantly increased and complete combustion was achieved at lower temperatures and shorter times. Kinetic analysis for the tested coal was performed using Kissinger-Akahira-Sunose (KAS) method. The activation energies of bituminous coal combustion at the similar oxygen content in oxy-fuel with that of air were higher than that in air atmosphere. The results indicated that, with O2 concentration increasing, the activation energies decreased.

Melting temperature and enthalpy variations of phase change materials (PCMs): a differential scanning calorimetry (DSC) analysis

NASA Astrophysics Data System (ADS)

Sun, Xiaoqin; Lee, Kyoung Ok; Medina, Mario A.; Chu, Youhong; Li, Chuanchang

2018-06-01

Differential scanning calorimetry (DSC) analysis is a standard thermal analysis technique used to determine the phase transition temperature, enthalpy, heat of fusion, specific heat and activation energy of phase change materials (PCMs). To determine the appropriate heating rate and sample mass, various DSC measurements were carried out using two kinds of PCMs, namely N-octadecane paraffin and calcium chloride hexahydrate. The variations in phase transition temperature, enthalpy, heat of fusion, specific heat and activation energy were observed within applicable heating rates and sample masses. It was found that the phase transition temperature range increased with increasing heating rate and sample mass; while the heat of fusion varied without any established pattern. The specific heat decreased with the increase of heating rate and sample mass. For accuracy purpose, it is recommended that for PCMs with high thermal conductivity (e.g. hydrated salt) the focus will be on heating rate rather than sample mass.

The excited-state decay of 1-methyl-2(1H)-pyrimidinone is an activated process.

PubMed

Ryseck, Gerald; Schmierer, Thomas; Haiser, Karin; Schreier, Wolfgang; Zinth, Wolfgang; Gilch, Peter

2011-07-11

The photophysics of 1-methyl-2(1H)-pyrimidinone (1MP) dissolved in water is investigated by steady-state and time-resolved fluorescence, UV/Vis absorption, and IR spectroscopy. In the experiments, excitation light is tuned to the lowest-energy absorption band of 1MP peaking at 302 nm. At room temperature (291 K) its fluorescence lifetime amounts to 450 ps. With increasing temperature this lifetime decreases and equals 160 ps at 338 K. Internal conversion (IC) repopulating the ground state and intersystem crossing (ISC) to a triplet state are the dominant decay channels of the excited singlet state. At room temperature both channels contribute equally to the decay, that is, the quantum yields of IC and ISC are both approximately 0.5. The temperature dependence of UV/Vis transient absorption signals shows that the activation energy of the IC process (2140 cm(-1)) is higher than that of the ISC process (640 cm(-1)). Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Optimization of KOH etching parameters for quantitative defect recognition in n- and p-type doped SiC

NASA Astrophysics Data System (ADS)

Sakwe, S. A.; Müller, R.; Wellmann, P. J.

2006-04-01

We have developed a KOH-based defect etching procedure for silicon carbide (SiC), which comprises in situ temperature measurement and control of melt composition. As benefit for the first time reproducible etching conditions were established (calibration plot, etching rate versus temperature and time); the etching procedure is time independent, i.e. no altering in KOH melt composition takes place, and absolute melt temperature values can be set. The paper describes this advanced KOH etching furnace, including the development of a new temperature sensor resistant to molten KOH. We present updated, absolute KOH etching parameters of n-type SiC and new absolute KOH etching parameters for low and highly p-type doped SiC, which are used for quantitative defect analysis. As best defect etching recipes we found T=530 °C/5 min (activation energy: 16.4 kcal/mol) and T=500 °C/5 min (activation energy: 13.5 kcal/mol) for n-type and p-type SiC, respectively.

Dielectric relaxation study of amorphous TiTaO thin films in a large operating temperature range

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rouahi, A.; Kahouli, A.; Laboratoire Materiaux, Organisation et Proprietes

2012-11-01

Two relaxation processes have been identified in amorphous TiTaO thin films deposited by reactive magnetron sputtering. The parallel angle resolved x-ray photoelectron spectroscopy and field emission scanning electron microscopy analyses have shown that this material is composed of an agglomerates mixture of TiO{sub 2}, Ta{sub 2}O{sub 5}, and Ti-Ta bonds. The first relaxation process appears at low temperature with activation energy of about 0.26 eV and is related to the first ionisation of oxygen vacancies and/or the reduction of Ti{sup 4+} to Ti{sup 3+}. The second relaxation process occurs at high temperature with activation energy of 0.95 eV. This lastmore » peak is associated to the diffusion of the doubly ionized oxygen vacancies V{sub O}e. The dispersion phenomena observed at high temperature can be attributed to the development of complex defect such as (V{sub O}e - 2Ti{sup 3+}).« less

High temperature tensile and creep behaviour of low pressure plasma-sprayed Ni-Co-Cr-Al-Y coating alloy

NASA Technical Reports Server (NTRS)

Hebsur, M. G.; Miner, R. V.

1986-01-01

The high temperature tensile and creep behavior of low pressure plasma-sprayed plates of a typical Ni-Co-Cr-Al-Y alloy has been studied. From room temperature to 800 K, the Ni-Co-Cr-Al-Y alloy studied has nearly a constant low ductility and a high strength. At higher temperatures, it becomes weak and highly ductile. At and above 1123 K, the behavior is highly dependent on strain rate and exhibits classic superplastic characteristics with a high ductility at intermediate strain rates and a strain rate sensitivity of about 0.5. At either higher or lower strain rates, the ductility decreases and the strain rate sensitivities are about 0.2. In the superplastic deformation range, the activation energy for creep is 120 + or - 20 kJ/mol, suggesting a diffusion-aided grain boundary sliding mechanism. Outside the superplastic range, the activation energy for creep is calculated to be 290 + or - 20 kJ/mol.

Temperature Dependence of Wavelength Selectable Zero-Phonon Emission from Single Defects in Hexagonal Boron Nitride.

PubMed

Jungwirth, Nicholas R; Calderon, Brian; Ji, Yanxin; Spencer, Michael G; Flatté, Michael E; Fuchs, Gregory D

2016-10-12

We investigate the distribution and temperature-dependent optical properties of sharp, zero-phonon emission from defect-based single photon sources in multilayer hexagonal boron nitride (h-BN) flakes. We observe sharp emission lines from optically active defects distributed across an energy range that exceeds 500 meV. Spectrally resolved photon-correlation measurements verify single photon emission, even when multiple emission lines are simultaneously excited within the same h-BN flake. We also present a detailed study of the temperature-dependent line width, spectral energy shift, and intensity for two different zero-phonon lines centered at 575 and 682 nm, which reveals a nearly identical temperature dependence despite a large difference in transition energy. Our temperature-dependent results are well described by a lattice vibration model that considers piezoelectric coupling to in-plane phonons. Finally, polarization spectroscopy measurements suggest that whereas the 575 nm emission line is directly excited by 532 nm excitation, the 682 nm line is excited indirectly.

Solar collector apparatus having increased energy rejection during stagnation

DOEpatents

Moore, S.W.

1981-01-16

An active solar collector having increased energy rejection during stagnation is disclosed. The collector's glazing is brought into substantial contact with absorber during stagnation to increase re-emittance and thereby to maintan lower temperatures when the collector is not in operation.

Pressure and temperature interactions on aerobic metabolism in migrating silver eels: results in vitro.

PubMed

Scaion, D; Vettier, A; Sébert, P

2008-01-01

The European eel (Anguilla anguilla) migrates (6000 km) from European coast towards the supposed spawning area: the Sargasso Sea. This intensive and sustained swimming activity is performed without feeding and by using essentially red muscle i.e. aerobic metabolism. Temperature and hydrostatic pressure vary during migration and have known effects on energy metabolism, mainly on mitochondrial functioning. We raise the question about the existence of a pressure-temperature combination that optimizes energy metabolism. We have measured the maximal oxygen consumption (MO2) of red muscle fibres of silver eel (migrating stage) in a temperature range (5 to 25 degrees C) covering what can be reasonably expected during the migration. We have combined (random order) three temperatures (5, 15, 25 degrees C) with 5 different pressures steps from 0.1 to 10.1 MPa (corresponding to depths from surface to 1000 m). The results show that when an adequate temperature is chosen as a reference, pressure effects and pressure sensitivity depend on the temperature. Based on the fact that energy budget is limited in migrating eels, we consider that the best conditions are low temperature and high pressure.

A characteristic energy scale in glasses.

PubMed

Lerner, Edan; Bouchbinder, Eran

2018-06-07

Intrinsically generated structural disorder endows glassy materials with a broad distribution of various microscopic quantities-such as relaxation times and activation energies-without an obvious characteristic scale. At the same time, macroscopic glassy responses-such as Newtonian (linear) viscosity and nonlinear plastic deformation-are widely interpreted in terms of a characteristic energy scale, e.g., an effective temperature-dependent activation energy in Arrhenius relations. Nevertheless, despite its fundamental importance, such a characteristic energy scale has not been robustly identified. Inspired by the accumulated evidence regarding the crucial role played by disorder- and frustration-induced soft quasilocalized excitations in determining the properties and dynamics of glasses, we propose that the bulk average of the glass response to a localized force dipole defines such a characteristic energy scale. We show that this characteristic glassy energy scale features remarkable properties: (i) It increases dramatically in underlying inherent structures of equilibrium supercooled states approaching the glass transition temperature T g , significantly surpassing the corresponding increase in the macroscopic shear modulus, dismissing the common view that structural variations in supercooled liquids upon vitrification are minute. (ii) Its variation with annealing and system size is very similar in magnitude and form to that of the energy of the softest non-phononic vibrational mode, thus establishing a nontrivial relation between a rare glassy fluctuation and a bulk average response. (iii) It exhibits striking dependence on spatial dimensionality and system size due to the long-ranged fields associated with quasilocalization, which are speculated to be related to peculiarities of the glass transition in two dimensions. In addition, we identify a truly static growing lengthscale associated with the characteristic glassy energy scale and discuss possible connections between the increase of this energy scale and the slowing down of dynamics near the glass transition temperature. Open questions and future directions are discussed.

Influence of silver nanoparticles on relaxation processes and efficiency of dipole – dipole energy transfer between dye molecules in polymethylmethacrylate films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bryukhanov, V V; Borkunov, R Yu; Tsarkov, M V

The fluorescence and phosphorescence of dyes in thin polymethylmethacrylate (PMMA) films in the presence of ablated silver nanoparticles has been investigated in a wide temperature range by methods of femtosecond and picosecond laser photoexcitation. The fluorescence and phosphorescence times, as well as spectral and kinetic characteristics of rhodamine 6G (R6G) molecules in PMMA films are measured in a temperature range of 80 – 330 K. The temperature quenching activation energy of the fluorescence of R6G molecules in the presence of ablated silver nanoparticles is found. The vibrational relaxation rate of R6G in PMMA films is estimated, the efficiency of themore » dipole – dipole electron energy transfer between R6G and brilliant green molecules (enhanced by plasmonic interaction with ablated silver nanoparticles) is analysed, and the constants of this energy transfer are determined. (nanophotonics)« less

Zero-point fluctuations in naphthalene and their effect on charge transport parameters.

PubMed

Kwiatkowski, Joe J; Frost, Jarvist M; Kirkpatrick, James; Nelson, Jenny

2008-09-25

We calculate the effect of vibronic coupling on the charge transport parameters in crystalline naphthalene, between 0 and 400 K. We find that nuclear fluctuations can cause large changes in both the energy of a charge on a molecule and on the electronic coupling between molecules. As a result, nuclear fluctuations cause wide distributions of both energies and couplings. We show that these distributions have a small temperature dependence and that, even at high temperatures, vibronic coupling is dominated by the effect of zero-point fluctuations. Because of the importance of zero-point fluctuations, we find that the distributions of energies and couplings have substantial width, even at 0 K. Furthermore, vibronic coupling with high energy modes may be significant, even though these modes are never thermally activated. Our results have implications for the temperature dependence of charge mobilities in organic semiconductors.

High-frequency dielectric study of proustite crystals Ag3AsS3

NASA Astrophysics Data System (ADS)

Bordovsky, V. A.; Gunia, N. Yu; Castro, R. A.

2014-12-01

The dielectric properties of the crystals proustite in the frequency of 106-109 Hz and a temperature range of 173 to 473 K were studied. The dispersion of the dielectric parameters indicates the existence of non-Debye relaxation mechanism correlates with structural changes in the phase transition region. The charge transfer is temperature activated with an activation energy of 2.40 ± 0.01 eV.

Thermophilic anaerobic digestion in compact systems: investigations by modern microbiological techniques and mathematical simulation.

PubMed

Lübken, M; Wichern, M; Letsiou, I; Kehl, O; Bischof, F; Horn, H

2007-01-01

Thermophilic anaerobic digestion in compact systems can be an economical and ecological reasonable decentralised process technique, especially for rural areas. Thermophilic process conditions are important for a sufficient removal of pathogens. The high energy demand, however, can make such systems unfavourable in terms of energy costs. This is the case when low concentrated wastewater is treated or the system is operated at low ambient temperatures. In this paper we present experimental results of a compact thermophilic anaerobic system obtained with fluorescent in situ hybridisation (FISH) analysis and mathematical simulation. The system was operated with faecal sludge for a period of 135 days and with a model substrate consisting of forage and cellulose for a period of 60 days. The change in the microbial community due to the two different substrates treated could be well observed by the FISH analysis. The Anaerobic Digestion Model no. 1 (ADM1) was used to evaluate system performance at different temperature conditions. The model was extended to contribute to decreased methanogenic activity at lower temperatures and was used to calculate energy production. A model was developed to calculate the major parts of energy consumed by the digester itself at different temperature conditions. It was demonstrated by the simulation study that a reduction of the process temperature can lead to higher net energy yield. The simulation study additionally showed that the effect of temperature on the energy yield is higher when a substrate is treated with high protein content.

Temperature-dependent endogenous oxygen concentration regulates microsomal oleate desaturase in developing sunflower seeds.

PubMed

Rolletschek, Hardy; Borisjuk, Ljudmilla; Sánchez-García, Alicia; Gotor, Cecilia; Romero, Luis C; Martínez-Rivas, José M; Mancha, Manuel

2007-01-01

Oleoyl-phosphatidylcholine desaturase (FAD2) is a key enzyme involved in fatty acid desaturation in oilseeds, which is affected by environmental temperature. The results of this study show that FAD2 is regulated in vivo via temperature-dependent endogenous oxygen concentrations in developing sunflower (Helianthus annuus L.) seeds. By combining in vivo oxygen profiling, in situ hybridization of FAD2 genes, an assay of energy status, fatty acid analysis, and an in vitro FAD2 enzyme activity assay, it is shown that: (i) the oil-storing embryo is characterized by a very low oxygen level that is developmentally regulated. Oxygen supply is mainly limited by the thin seed coat. (ii) Elevations of external oxygen supply raised the energy status of seed and produced a dramatic increase of the FAD2 enzyme activity as well as the linoleic acid content. (iii) A clear negative correlation exists between temperature and internal oxygen concentration. The changes occurred almost instantly and the effect was fully reversible. The results indicate that the internal oxygen level acts as a key regulator for the activity of the FAD2 enzyme. It is concluded that a major mechanism by which temperature modifies the unsaturation degree of the sunflower oil is through its effect on dissolved oxygen levels in the developing seed.

In-situ short circuit protection system and method for high-energy electrochemical cells

DOEpatents

Gauthier, Michel; Domroese, Michael K.; Hoffman, Joseph A.; Lindeman, David D.; Noel, Joseph-Robert-Gaetan; Radewald, Vern E.; Rouillard, Jean; Rouillard, Roger; Shiota, Toshimi; Trice, Jennifer L.

2000-01-01

An in-situ thermal management system for an energy storage device. The energy storage device includes a plurality of energy storage cells each being coupled in parallel to common positive and negative connections. Each of the energy storage cells, in accordance with the cell's technology, dimensions, and thermal/electrical properties, is configured to have a ratio of energy content-to-contact surface area such that thermal energy produced by a short-circuit in a particular cell is conducted to a cell adjacent the particular cell so as to prevent the temperature of the particular cell from exceeding a breakdown temperature. In one embodiment, a fuse is coupled in series with each of a number of energy storage cells. The fuses are activated by a current spike capacitively produced by a cell upon occurrence of a short-circuit in the cell, thereby electrically isolating the short-circuited cell from the common positive and negative connections.

In-situ short-circuit protection system and method for high-energy electrochemical cells

DOEpatents

Gauthier, Michel; Domroese, Michael K.; Hoffman, Joseph A.; Lindeman, David D.; Noel, Joseph-Robert-Gaetan; Radewald, Vern E.; Rouillard, Jean; Rouillard, Roger; Shiota, Toshimi; Trice, Jennifer L.

2003-04-15

An in-situ thermal management system for an energy storage device. The energy storage device includes a plurality of energy storage cells each being coupled in parallel to common positive and negative connections. Each of the energy storage cells, in accordance with the cell's technology, dimensions, and thermal/electrical properties, is configured to have a ratio of energy content-to-contact surface area such that thermal energy produced by a short-circuit in a particular cell is conducted to a cell adjacent the particular cell so as to prevent the temperature of the particular cell from exceeding a breakdown temperature. In one embodiment, a fuse is coupled in series with each of a number of energy storage cells. The fuses are activated by a current spike capacitively produced by a cell upon occurrence of a short-circuit in the cell, thereby electrically isolating the short-circuited cell from the common positive and negative connections.

Dielectric properties and activation behavior of gadolinium doped nanocrystalline yttrium chromite

NASA Astrophysics Data System (ADS)

Sinha, R.; Basu, S.; Meikap, A. K.

2018-04-01

Gadolinium doped Yttrium Chromite nanoparticles are synthesized following sol-gel method. The formation of the nanoparticles are confirmed by XRD and TEM measurements. Dielectric permittivity and dielectric loss are estimated within the temperature range 298K to 523K and in the frequency range 20 Hz to 1 MHz. Dielectric permittivity follows the power law ɛ'(f) ∝ Tm. It is observed that the temperature exponent m increases with the decreasing frequency. The temperature variation of resistivity shows that the samples have semiconducting behavior. The activation energy is also measured.

Effect of Mechanical Activation Treatment on the Recovery of Vanadium from Converter Slag

NASA Astrophysics Data System (ADS)

Xiang, Junyi; Huang, Qingyun; Lv, Xuewei; Bai, Chenguang

2017-10-01

The high roasting temperature and low leaching efficiency of vanadium from vanadium-bearing converter slag are regarded as the main factors significantly influencing the application of calcification roasting-acid leaching processes in the cleaner production of vanadium. In this study, a mechanical activation treatment was performed to enhance the extraction of vanadium from converter slag. The enhancement effects obtained from mechanical activation were comprehensively evaluated through indices such as the roasting temperature and leaching efficiency. The effects of mechanical activation time, roasting temperature, leaching temperature, solid to liquid ratio, particle size, and acid concentration on the leaching efficiency were investigated. Microstructure morphology and elemental analyses of the raw materials and leaching residue were also investigated using scanning electron microscopy and energy-dispersive X-ray spectroscopy. The results demonstrated that the mechanical activation significantly decreased the optimum roasting temperature from 1173 K to 1073 K (900 °C to 800 °C) and increased the leaching efficiency from 86.0 to 90.9 pct.

Thermal activation in Au-based bulk metallic glass characterized by high-temperature nanoindentation

NASA Astrophysics Data System (ADS)

Yang, Bing; Wadsworth, Jeffrey; Nieh, Tai-Gang

2007-02-01

High-temperature nanoindentation experiments have been conducted on a Au49Ag5.5Pd2.3Cu26.9Si16.3 bulk metallic glass from 30to140°C, utilizing loading rates ranging from 0.1to100mN/s. Generally, the hardness decreased with increasing temperature. An inhomogeneous-to-homogeneous flow transition was clearly observed when the test temperature approached the glass transition temperature. Analyses of the pop-in pattern and hardness variation showed that the inhomogeneous-to-homogeneous transition temperature was loading-rate dependent. Using a free-volume model, the authors deduced the size of the basic flow units and the activation energy for the homogeneous flow. In addition, the strain rate dependency of the transition temperature was predicted.

Balloons and Bottles: Activities on Air-Sea Heat Exchange.

ERIC Educational Resources Information Center

Murphree, Tom

1998-01-01

Presents an activity designed to demonstrate how heating and cooling an air mass affects its temperature, volume, density, and pressure. Illustrates how thermal energy can cause atmospheric motion such as expansion, contraction, and winds. (Author/WRM)

New distributed activation energy model: numerical solution and application to pyrolysis kinetics of some types of biomass.

PubMed

Cai, Junmeng; Liu, Ronghou

2008-05-01

In the present paper, a new distributed activation energy model has been developed, considering the reaction order and the dependence of frequency factor on temperature. The proposed DAEM cannot be solved directly in a closed from, thus a method was used to obtain the numerical solution of the new DAEM equation. Two numerical examples to illustrate the proposed method were presented. The traditional DAEM and new DAEM have been used to simulate the pyrolytic process of some types of biomass. The new DAEM fitted the experimental data much better than the traditional DAEM as the dependence of the frequency factor on temperature was taken into account.

Membrane hydraulic permeability changes during cooling of mammalian cells.

PubMed

Akhoondi, Maryam; Oldenhof, Harriëtte; Stoll, Christoph; Sieme, Harald; Wolkers, Willem F

2011-03-01

In order to predict optimal cooling rates for cryopreservation of cells, the cell-specific membrane hydraulic permeability and corresponding activation energy for water transport need to be experimentally determined. These parameters should preferably be determined at subzero temperatures in the presence of ice. There is, however, a lack of methods to study membrane properties of cells in the presence of ice. We have used Fourier transform infrared spectroscopy to study freezing-induced membrane dehydration of mouse embryonic fibroblast (3T3) cells and derived the subzero membrane hydraulic permeability and the activation energy for water transport from these data. Coulter counter measurements were used to determine the suprazero membrane hydraulic permeability parameters from cellular volume changes of cells exposed to osmotic stress. The activation energy for water transport in the ice phase is about three fold greater compared to that at suprazero temperatures. The membrane hydraulic permeability at 0 °C that was extrapolated from suprazero measurements is about five fold greater compared to that extrapolated from subzero measurements. This difference is likely due to a freezing-induced dehydration of the bound water around the phospholipid head groups. Using Fourier transform infrared spectroscopy, two distinct water transport processes, that of free and membrane bound water, can be identified during freezing with distinct activation energies. Dimethylsulfoxide, a widely used cryoprotective agent, did not prevent freezing-induced membrane dehydration but decreased the activation energy for water transport. Copyright © 2010 Elsevier B.V. All rights reserved.

Temperature effect on bacterial azo bond reduction kinetics: an Arrhenius plot analysis.

PubMed

Angelova, Blaga; Avramova, Tatyana; Stefanova, Lilyana; Mutafov, Sava

2008-06-01

Studied was the effect of temperature in the range 12-46 degrees C on the rate of bacterial decolorization of the mono-azo dye Acid Orange 7 by Alcaligenes faecalis 6132 and Rhodococcus erythropolis 24. With both strains the raise of temperature led to a corresponding raise of decolorization rate better manifested by R. erythropolis. The analysis of the Arrhenius plot revealed a break near the middle of the temperature range. The regression analysis showed practically complete identity of the observed break point temperatures (T (BP)): 20.7 degrees C for Alc. faecalis and 20.8 degrees C for R. erythropolis. The values of the activation energy of the decolorization reaction (E (a)) were found to depend on both the organism and the temperature range. In the range below T (BP) the estimated values of E (a) were 138 +/- 7 kJ mol(-1) for Alc. faecalis and 160 +/- 8 kJ mol(-1) for R. erythropolis. In the range above T (BP) they were 54.2 +/- 1.8 kJ mol(-1) for Alc. faecalis and 37.6 +/- 4.1 kJ mol(-1) for R. erythropolis. Discussed are the possible reasons for the observed abrupt change of the activation energy.

Dynamic Mechanical Response of Biomedical 316L Stainless Steel as Function of Strain Rate and Temperature

PubMed Central

Lee, Woei-Shyan; Chen, Tao-Hsing; Lin, Chi-Feng; Luo, Wen-Zhen

2011-01-01

A split Hopkinson pressure bar is used to investigate the dynamic mechanical properties of biomedical 316L stainless steel under strain rates ranging from 1 × 103 s−1 to 5 × 103 s−1 and temperatures between 25°C and 800°C. The results indicate that the flow stress, work-hardening rate, strain rate sensitivity, and thermal activation energy are all significantly dependent on the strain, strain rate, and temperature. For a constant temperature, the flow stress, work-hardening rate, and strain rate sensitivity increase with increasing strain rate, while the thermal activation energy decreases. Catastrophic failure occurs only for the specimens deformed at a strain rate of 5 × 103 s−1 and temperatures of 25°C or 200°C. Scanning electron microscopy observations show that the specimens fracture in a ductile shear mode. Optical microscopy analyses reveal that the number of slip bands within the grains increases with an increasing strain rate. Moreover, a dynamic recrystallisation of the deformed microstructure is observed in the specimens tested at the highest temperature of 800°C. PMID:22216015

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bozkurt, Y.; Misirlioglu, Z.; Sinag, A.

The reactivities of chars obtained by pyrolysis of Bursa Mustafa Kemal Pasa Alpagut lignite and Balkesir Dursunbey Cakiirca lignite (Turkey) at different temperatures were determined by CO{sub 2} gasification and by combustion with O{sub 2}. Catalytic effect of Na{sub 2}CO{sub 3} on the CO{sub 2} and O{sub 2} gasification reactivity of chars was investigated. Gasification tests were performed in the fixed bed reactors operating at ambient pressure. Reactivity of chars during the CO{sub 2} gasification reactions was determined by calculating the reaction rate constants and reactivity of chars during the O{sub 2} gasification was determined by using ignition temperatures ofmore » the samples. Activation energies and Arrhenius constants of the chars on the CO{sub 2} gasification reactions were also calculated by the help of Arrhenius curves. The activation energy for CO{sub 2} gasification was generally decreased with pyrolysis temperature, due to the different surface characteristics and different nature of carbon atoms gasified as the gasification reactions proceed. Generally, the increase in pyrolysis temperature leads to an increase in gasification reactivity with CO{sub 2}. The reactivity of chars in catalytic gasification was higher than the corresponding non-catalytic reactivity of the same chars. Ignition temperature increased with increasing pyrolysis temperature.« less

High-Temperature Annealing Induced He Bubble Evolution in Low Energy He Ion Implanted 6H-SiC

NASA Astrophysics Data System (ADS)

Liu, Yu-Zhu; Li, Bing-Sheng; Zhang, Li

2017-05-01

Bubble evolution in low energy and high dose He-implanted 6H-SiC upon thermal annealing is studied. The < 0001> -oriented 6H-SiC wafers are implanted with 15 keV helium ions at a dose of 1× 1017 cm-2 at room temperature. The samples with post-implantation are annealed at temperatures of 1073, 1173, 1273, and 1473 K for 30 min. He bubbles in the wafers are examined via cross-sectional transmission electron microscopy (XTEM) analysis. The results present that nanoscale bubbles are almost homogeneously distributed in the damaged layer of the as-implanted sample, and no significant change is observed in the He-implanted sample after 1073 K annealing. Upon 1193 K annealing, almost full recrystallization of He-implantation-induced amorphization in 6H-SiC is observed. In addition, the diameters of He bubbles increase obviously. With continually increasing temperatures to 1273 K and 1473 K, the diameters of He bubbles increase and the number density of lattice defects decreases. The growth of He bubbles after high temperature annealing abides by the Ostwald ripening mechanism. The mean diameter of He bubbles located at depths of 120-135 nm as a function of annealing temperature is fitted in terms of a thermal activated process which yields an activation energy of 1.914+0.236 eV. Supported by the National Natural Science Foundation of China under Grant No 11475229.

Decreases in activation energy and substrate affinity in cold-adapted A4-lactate dehydrogenase: evidence from the Antarctic notothenioid fish Chaenocephalus aceratus.

PubMed

Fields, Peter A; Houseman, Daniel E

2004-12-01

Enzyme function is strongly affected by temperature, and orthologs from species adapted to different thermal environments often show temperature compensation in kinetic properties. Antarctic notothenioid fishes live in a habitat of constant, extreme cold (-1.86 +/- 2 degrees C), and orthologs of the enzyme A4-lactate dehydrogenase (A4-LDH) in these species have adapted to this environment through higher catalytic rates, lower Arrhenius activation energies (Ea), and increases in the apparent Michaelis constant for the substrate pyruvate (Km(PYR)). Here, site-directed mutagenesis was used to determine which amino acid substitutions found in A4-LDH of the notothenioid Chaenocephalus aceratus, with respect to orthologs from warm-adapted teleosts, are responsible for these adaptive changes in enzyme function. Km(PYR) was measured in eight single and two double mutants, and Ea was tested in five single and two double mutants in the temperature range 0 degrees C-20 degrees C. Of the four mutants that had an effect on these parameters, two increased Ea but did not affect Km(PYR) (Gly224Ser, Ala310Pro), and two increased both Ea and Km(PYR) (Glu233Met, Gln317Val). The double mutants Glu233Met/Ala310Pro and Glu233Met/Gln317Val increased Km(PYR) and Ea to levels not significantly different from the A4-LDH of a warm temperate fish (Gillichthys mirabilis, habitat temperature 10 degrees C-35 degrees C). The four single mutants are associated with two alpha-helices that move during the catalytic cycle; those that affect Ea but not Km(PYR) are further from the active site than those that affect both parameters. These results provide evidence that (1) cold adaptation in A4-LDH involves changes in mobility of catalytically important molecular structures; (2) these changes may alter activation energy alone or activation energy and substrate affinity together; and (3) the extent to which these parameters are affected may depend on the location of the substitutions within the mobile alpha-helices, perhaps due to differences in proximity to the active site.

Influence of temperature and electrolyte on the performance of activated-carbon supercapacitors

NASA Astrophysics Data System (ADS)

Liu, Ping; Verbrugge, Mark; Soukiazian, Souren

For hybrid electric vehicle traction applications, energy storage devices with high power density and energy efficiency are required. A primary attribute of supercapacitors is that they retain their high power density and energy efficiency even at -30 °C, the lowest temperature at which unassisted starting must be provided to customers. More abuse-tolerant electrolytes are preferred to the high-conductivity acetonitrile-based systems commonly employed. Propylene carbonate based electrolytes are a promising alternative. In this work, we compare the electrochemical performance of two high-power density electrical double layer supercapacitors employing acetonitrile and propylene carbonate as solvents. From this study, we are able to elucidate phenomena that control the resistance of supercapacitor at lower temperatures, and quantify the difference in performance associated with the two electrolytes.

Control of plasma properties in a short direct-current glow discharge with active boundaries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adams, S. F.; Demidov, V. I., E-mail: vladimir.demidov@mail.wvu.edu; West Virginia University, Morgantown, West Virginia 26506

2016-02-15

To demonstrate controlling electron/metastable density ratio and electron temperature by applying negative voltages to the active (conducting) discharge wall in a low-pressure plasma with nonlocal electron energy distribution function, modeling has been performed in a short (lacking the positive-column region) direct-current glow discharge with a cold cathode. The applied negative voltage can modify the trapping of the low-energy part of the energetic electrons that are emitted from the cathode sheath and that arise from the atomic and molecular processes in the plasma within the device volume. These electrons are responsible for heating the slow, thermal electrons, while production of slowmore » electrons (ions) and metastable atoms is mostly due to the energetic electrons with higher energies. Increasing electron temperature results in increasing decay rate of slow, thermal electrons (ions), while decay rate of metastable atoms and production rates of slow electrons (ions) and metastable atoms practically are unchanged. The result is in the variation of electron/metastable density ratio and electron temperature with the variation of the wall negative voltage.« less

Halogen and LED light curing of composite: temperature increase and Knoop hardness.

PubMed

Schneider, L F; Consani, S; Correr-Sobrinho, L; Correr, A B; Sinhoreti, M A

2006-03-01

This study assessed the Knoop hardness and temperature increase provided by three light curing units when using (1) the manufacturers' recommended times of photo-activation and (2) standardizing total energy density. One halogen--XL2500 (3M/ESPE)--and two light-emitting diode (LED) curing units--Freelight (3M/ESPE) and Ultrablue IS (DMC)--were used. A type-K thermocouple registered the temperature change produced by the composite photo-activation in a mold. Twenty-four hours after the photo-activation procedures, the composite specimens were submitted to a hardness test. Both temperature increase and hardness data were submitted to ANOVA and Tukey's test (5% significance). Using the first set of photo-activation conditions, the halogen unit produced a statistically higher temperature increase than did both LED units, and the Freelight LED resulted in a lower hardness than did the other curing units. When applying the second set of photo-activation conditions, the two LED units produced statistically greater temperature increase than did the halogen unit, whereas there were no statistical differences in hardness among the curing units.

Digital Interface Modules for Active-Readout X-Ray Spectrometer.

DTIC Science & Technology

1985-03-01

strategy. Emitting a significant fraction of its total energy as complex series of high temperature characteristic x-ray lines, the PRS source is used for...0.001’ for the Reticon RL1024S detector). This is done by calculating the increment in photon energy dE that maps into a sensor width dg. The required...peak signal to r.m.s. noise). For most work the effects of temperature on the SSPA and other electronics will be more significant to the repeatability

Solar collector apparatus having increased energy rejection during stagnation

DOEpatents

Moore, Stanley W.

1983-07-12

The disclosure relates to an active solar collector having increased energy rejection during stagnation. The collector's glazing is brought into substantial contact with absorber during stagnation to increase re-emittance and thereby to maintain lower temperatures when the collector is not in operation.

Excited state intramolecular charge transfer reaction in nonaqueous electrolyte solutions: Temperature dependence

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pradhan, Tuhin; Gazi, Harun Al Rasid; Biswas, Ranjit

2009-08-07

Temperature dependence of the excited state intramolecular charge transfer reaction of 4-(1-azetidinyl)benzonitrile (P4C) in ethyl acetate (EA), acetonitrile (ACN), and ethanol at several concentrations of lithium perchlorate (LiClO{sub 4}) has been investigated by using the steady state and time resolved fluorescence spectroscopic techniques. The temperature range considered is 267-343 K. The temperature dependent spectral peak shifts and reaction driving force (-{Delta}G{sub r}) in electrolyte solutions of these solvents can be explained qualitatively in terms of interaction between the reactant molecule and ion-atmosphere. Time resolved studies indicate that the decay kinetics of P4C is biexponential, regardless of solvents, LiClO{sub 4} concentrations,more » and temperatures considered. Except at higher electrolyte concentrations in EA, reaction rates in solutions follow the Arrhenius-type temperature dependence where the estimated activation energy exhibits substantial electrolyte concentration dependence. The average of the experimentally measured activation energies in these three neat solvents is found to be in very good agreement with the predicted value based on data in room temperature solvents. While the rate constant in EA shows a electrolyte concentration induced parabolic dependence on reaction driving force (-{Delta}G{sub r}), the former in ethanol and ACN increases only linearly with the increase in driving force (-{Delta}G{sub r}). The data presented here also indicate that the step-wise increase in solvent reorganization energy via sequential addition of electrolyte induces the ICT reaction in weakly polar solvents to crossover from the Marcus inverted region to the normal region.« less

Apatite U-Pb thermochronolgy applied to complex geological settings - insights from geo/thermochronology and geochemistry

NASA Astrophysics Data System (ADS)

Paul, Andre; Spikings, Richard; Ulyanov, Alexey; Chew, David

2016-04-01

Application of high temperature (>350oC) thermochronology is limited to the U-Pb system of accessory minerals, such as apatite, under the assumption that radiogenic lead is lost to thermally activated volume diffusion into an infinite reservoir. Cochrane et al. (2015) have demonstrated a working example from the northern Andes of South America. Predictions from volume diffusion theory were compared with measured single grain U-Pb date correlated to shortest diffusion radius and in-situ profiles measured by LA-ICP-MS. Results from both techniques were found to be in agreement with predictions from thermally activated, volume diffusion. However, outliers from the ID-TIMS data suggested some complexity, as grains were found to be too young relative to their diffusion radius. Interaction of multiple processes can be responsible for the alteration of apatite U-Pb dates such as: (1) metamorphic (over)growth, (2) fluid aided alteration/recrystallization and (3) metamictization and fracturing of the grain. Further, predictions from volume diffusion rely on the input parameters: (a) diffusivity, (b) activation energy and (c) shortest diffusion radius. Diffusivity and activation energy are potentially influenced by the chemical composition and subsequent changes in crystal structure. Currently there is one value for diffusion parameter and activation energy established for (Durango) apatite (Cherniak et al., 1991). Correlation between diffusivity/activation energy and composition has not been established. We investigate if correlations exist between diffusivity/activation energy and composition by obtaining single grain apatite U-Pb date and chemical compostion and correlating these to their diffusion radius. We test the consistency of apatite closure temperature, by comparing the apatite U-Pb dates with lower temperature thermochronometers such as white mica and K-feldspar Ar/Ar and by petrographic observations. We test if chemical information can be a proxy to identify metamorphic (over)growth and fluid aided alteration/recrystallization. We seek to evaluate if apatite U-Pb thermochronology can be applied to a broad range of rock types and geological environments or if limitations must be drawn.

Temperature environment for 9975 packages stored in KAC

DOE Office of Scientific and Technical Information (OSTI.GOV)

Daugherty, W. L.

Plutonium materials are stored in the K Area Complex (KAC) in shipping packages, typically the 9975 shipping package. In order to estimate realistic degradation rates for components within the shipping package (i.e. the fiberboard overpack and O-ring seals), it is necessary to understand actual facility temperatures, which can vary daily and seasonally. Relevant facility temperature data available from several periods throughout its operating history have been reviewed. The annual average temperature within the Crane Maintenance Area has ranged from approximately 70 to 74 °F, although there is significant seasonal variation and lesser variation among different locations within the facility. Themore » long-term average degradation rate for 9975 package components is very close to that expected if the component were to remain continually at the annual average temperature. This result remains valid for a wide range of activation energies (which describes the variation in degradation rate as the temperature changes), if the activation energy remains constant over the seasonal range of component temperatures. It is recommended that component degradation analyses and service life estimates incorporate these results. Specifically, it is proposed that future analyses assume an average facility ambient air temperature of 94 °F. This value is bounding for all packages, and includes margin for several factors such as increased temperatures within the storage arrays, the addition of more packages in the future, and future operational changes.« less

Effect of O2 plasma treatment on density-of-states in a-IGZO thin film transistors

NASA Astrophysics Data System (ADS)

Ding, Xingwei; Huang, Fei; Li, Sheng; Zhang, Jianhua; Jiang, Xueyin; Zhang, Zhilin

2017-01-01

This work reports an efficient route for enhancing the performance of amorphous InGaZnO (a-IGZO) thin film transistors (TFT). The mobility was greatly improved by about 38% by means of O2 plasma treatment. Temperature-stress was carried out to investigate the stability and extract the parameters related to activation energy ( E a) and density-of-states (DOS). The DOS was calculated on the basis of the experimentally obtained E a, which can explain the experimental observation. A lower activation energy ( E a, 0.72 eV) and a smaller DOS were obtained in the O2 plasma treatment TFT based on the temperature-dependent transfer curves. The results showed that temperature stability and electrical properties enhancements in a-IGZO thin film transistors were attributed to the smaller DOS. [Figure not available: see fulltext.

Effect of temperature and grain size on the dominant diffusion process for superplastic flow in an AZ61 magnesium alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Watanabe, H.; Mukai, T.; Kohzu, M.

1999-10-26

The effect of temperature and grain size on superplastic flow was investigated using a relatively coarse-grained ({approximately}20 {micro}m) Mg-Al-Zn alloy for the inclusive understanding of the dominant diffusion process. Tensile tests revealed that the strain rate was inversely proportional to the square of the grain size and to the second power of stress. The activation energy was close to that for grain boundary diffusion at 523--573 K, and was close to that for lattice diffusion at 598--673 K. From the analysis of the stress exponent, the grain size exponent and activation energy, it was suggested that the dominant diffusion processmore » was influenced by temperature and grain size. It was demonstrated that the notion of effective diffusivity explained the experimental results.« less

AC and DC conductivity due to hopping mechanism in double ion doped ceramics

NASA Astrophysics Data System (ADS)

Rizwana, Mahboob, Syed; Sarah, P.

2018-04-01

Sr1-2xNaxNdxBi4Ti4O15 (x = 0.1, 0.2 and 0.4) system is prepared by sol gel method involving Pechini process of modified polymeric precursor method. Phase identification is done using X-ray diffraction. Conduction in prepared materials involves different mechanisms and is explained through detailed AC and DC conductivity studies. AC conductivity studies carried out on the samples at different frequencies and different temperatures gives more information about electrical transport. Exponents used in two term power relation helps us to understand the different hopping mechanism involved at low as well as high frequencies. Activation energies calculated from the Arrhenius plots are used to calculate activation energies at different temperatures and frequencies. Hopping frequency calculated from the measured data explains hopping of charge carriers at different temperatures. DC conductivity studies help us to know the role of oxygen vacancies in conduction.

Low temperature time resolved photoluminescence in ordered and disordered Cu2ZnSnS4 single crystals

NASA Astrophysics Data System (ADS)

Raadik, Taavi; Krustok, Jüri; Kauk-Kuusik, M.; Timmo, K.; Grossberg, M.; Ernits, K.; Bleuse, J.

2017-03-01

In this work we performed time-resolved micro-photoluminescence (TRPL) studies of Cu2ZnSnS4 (CZTS) single crystals grown in molten KI salt. The order/disorder degree of CZTS was varied by the thermal post treatment temperature. Photoluminescence spectra measured at T=8 K showed an asymmetric band with a peak position of 1.33 eV and 1.27 eV for partially ordered and disordered structures, respectively. Thermal activation energies were found to be ET (PO) =65±9 meV for partially ordered and ET (PD) =27±4 meV for partially disordered. These low activation energy values indicating to the defect cluster recombination model for both partially ordered and disordered structures. TRPL was measured for both crystals and their decay curves were fitted with a stretched exponential function, in order to describe the charge carriers' recombination dynamics at low temperature.

Accelerated life testing effects on CMOS microcircuit characteristics

NASA Technical Reports Server (NTRS)

1980-01-01

The 250 C, 200C and 125C accelerated tests are described. The wear-out distributions from the 250 and 200 C tests were used to estimate the activation energy between the two test temperatures. The duration of the 125 C test was not sufficient to bring the test devices into the wear-out region. It was estimated that, for the most complex of the three devices types, the activation energy between 200 C and 125 C should be at least as high as that between 250 C and 200 C. The practicality of the use of high temperature for the accelerated life tests from the point of view of durability of equipment is assessed. Guidlines for the development of accelerated life-test conditions are proposed. The use of the silicon nitride overcoat to improve the high temperature accelerated life-test characteristics of CMOS microcircuits is described.

A review of catalyst-enhanced magnesium hydride as a hydrogen storage material

NASA Astrophysics Data System (ADS)

Webb, C. J.

2015-09-01

Magnesium hydride remains an attractive hydrogen storage material due to the high hydrogen capacity and low cost of production. A high activation energy and poor kinetics at practical temperatures for the pure material have driven research into different additives to improve the sorption properties. This review details the development of catalytic additives and their effect on the activation energy, kinetics and thermodynamic properties of magnesium hydride.

Nuclear magnetic resonance investigation of dynamics in poly(ethylene oxide)-based lithium polyether-ester-sulfonate ionomers

DOE PAGES

Roach, David J.; Dou, Shichen; Colby, Ralph H.; ...

2012-01-06

Nuclear magnetic resonance (NMR) spectroscopy has been utilized to investigate the dynamics of poly(ethylene oxide)-based lithium sulfonate ionomer samples that have low glass transition temperatures. 1H and 7Li spin-lattice relaxation times (T 1) of the bulk polymer and lithium ions, respectively, were measured and analyzed in samples with a range of ion contents. The temperature dependence of T 1 values along with the presence of minima in T 1 as a function of temperature enabled correlation times and activation energies to be obtained for both the segmental motion of the polymer backbone and the hopping motion of lithium cations. Similarmore » activation energies for motion of both the polymer and lithium ions in the samples with lower ion content indicate that the polymer segmental motion and lithium ion hopping motion are correlated in these samples, even though their respective correlation times differ significantly. A divergent trend is observed for correlation times and activation energies of the highest ion content sample with 100% lithium sulfonation due to the presence of ionic aggregation. Details of the polymer and cation dynamics on the nanosecond timescale are discussed and complement the findings of X-ray scattering and Quasi Elastic Neutron Scattering experiments.« less

Flow behaviour of magnesium alloy AZ31B processed by equal-channel angular pressing

NASA Astrophysics Data System (ADS)

Arun, M. S.; Chakkingal, U.

2014-08-01

Magnesium alloys are characterised by their low density, high specific strength and stiffness. But, the potential application of Mg is limited by its low room-temperature ductility & formability. Formability can be improved by developing an ultrafine grained (UFG) structure. Equal channel angular pressing (ECAP) is a well known process that can be used to develop an ultrafine grained microstructure. The aim of this study was to investigate the flow behaviour of AZ31B magnesium alloy after ECAP. The specimen was subjected to three passes of ECAP with a die angle of 120° using processing route Bc. The processing temperature was 523 K for the first pass and 423 K for the subsequent two passes. The microstructure characterisation was done. Compression tests of ECAPed and annealed specimens were carried out at strain rates of 0.01 - 1s-1 and deformation temperatures of 200 - 300°C using computer servo-controlled Gleeble-3800 system. The value of activation energy Q and the empirical materials constants of A and n were determined. The equations relating flow stress and Zener-Hollomon parameter were proposed. In the case annealed AZ31, the activation energy was determined to be 154 kJ/mol, which was slightly higher than the activation energy of 144 kJ/mol for ECAPed AZ31.

A characteristic energy scale in glasses

NASA Astrophysics Data System (ADS)

Lerner, Edan; Bouchbinder, Eran

2018-06-01

Intrinsically generated structural disorder endows glassy materials with a broad distribution of various microscopic quantities—such as relaxation times and activation energies—without an obvious characteristic scale. At the same time, macroscopic glassy responses—such as Newtonian (linear) viscosity and nonlinear plastic deformation—are widely interpreted in terms of a characteristic energy scale, e.g., an effective temperature-dependent activation energy in Arrhenius relations. Nevertheless, despite its fundamental importance, such a characteristic energy scale has not been robustly identified. Inspired by the accumulated evidence regarding the crucial role played by disorder- and frustration-induced soft quasilocalized excitations in determining the properties and dynamics of glasses, we propose that the bulk average of the glass response to a localized force dipole defines such a characteristic energy scale. We show that this characteristic glassy energy scale features remarkable properties: (i) It increases dramatically in underlying inherent structures of equilibrium supercooled states approaching the glass transition temperature Tg, significantly surpassing the corresponding increase in the macroscopic shear modulus, dismissing the common view that structural variations in supercooled liquids upon vitrification are minute. (ii) Its variation with annealing and system size is very similar in magnitude and form to that of the energy of the softest non-phononic vibrational mode, thus establishing a nontrivial relation between a rare glassy fluctuation and a bulk average response. (iii) It exhibits striking dependence on spatial dimensionality and system size due to the long-ranged fields associated with quasilocalization, which are speculated to be related to peculiarities of the glass transition in two dimensions. In addition, we identify a truly static growing lengthscale associated with the characteristic glassy energy scale and discuss possible connections between the increase of this energy scale and the slowing down of dynamics near the glass transition temperature. Open questions and future directions are discussed.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xiong, L. H.; Wang, X. D.; Yu, Q.

Temperature-dependent atomistic structure evolution of liquid gallium (Ga) has been investigated by using in situ high energy X-ray diffraction experiment and ab initio molecular dynamics simulation. Both experimental and theoretical results reveal the existence of a liquid structural change around 1000 K in liquid Ga. Below and above this temperature the liquid exhibits differences in activation energy for selfdiffusion, temperature-dependent heat capacity, coordination numbers, density, viscosity, electric resistivity and thermoelectric power, which are reflected from structural changes of the bond-orientational order parameter Q6, fraction of covalent dimers, averaged string length and local atomic packing. This finding will trigger more studiesmore » on the liquid-to-liquid crossover in metallic melts.« less

Pressure-induced photoluminescence in Mn2+-doped BaF2 and SrF2 fluorites

NASA Astrophysics Data System (ADS)

Hernández, Ignacio; Rodríguez, Fernando

2003-01-01

This work reports an effective way for inducing room temperature photoluminescence (PL) in Mn2+-doped BaF2 and SrF2 using high-pressure techniques. The aim is to understand the surprising PL behavior exhibited by Mn2+ at the cubal site of the fluorite structure. While Mn2+-doped CaF2 shows a green PL with quantum yield close to 1 at room temperature, Mn2+-doped MF2 (M=Ba,Sr) is not PL either at room temperature (SrF2) or at any temperature (BaF2) at ambient pressure. We associate the loss of Mn2+ PL on passing from CaF2 to SrF2 or BaF2 with nonradiative multiphonon relaxation whose thermal activation energy decreases along the series CaF2→SrF2→BaF2. A salient feature of this work deals with the increase of activation energy induced by pressure. It leads to a quantum yield enhancement, which favors PL recovery. Furthermore, the activation energy mainly depends on the crystal volume per molecule irrespective of the crystal structure or the local symmetry around the impurity. In this way, the relevance of the fluorite-to-cotunnite phase transition is analyzed in connection with the PL properties of the investigated compounds. The PL spectrum and the corresponding lifetime are reported for both structural phases as a function of pressure.

The relief of microtherm inhibition for p-fluoronitrobenzene mineralization using electrical stimulation at low temperatures.

PubMed

Zhang, Xueqin; Feng, Huajun; Liang, Yuxiang; Zhao, Zhiqing; Long, Yuyang; Fang, Yuan; Wang, Meizhen; Yin, Jun; Shen, Dongsheng

2015-05-01

Low temperature aggravates biological treatment of refractory p-fluoronitrobenzene (p-FNB) because of microtherm inhibition of microbial activity. Considering the potential characterization of energy supply for microbial metabolism and spurring microbial activity by electrical stimulation, a bioelectrochemical system (BES) was established to provide sustaining electrical stimulation for p-FNB mineralization at a low temperature. Electrical stimulation facilitated p-FNB treatment and bioelectrochemical reaction rate constants for the removal and defluorination of p-FNB at 10 °C were 0.0931 and 0.0054 h(-1), which were higher than the sums of the rates found using a biological system and an electrocatalytic system by 62.8 and 64.8%, respectively. At a low temperature, microbial activity in terms of dehydrogenase and ATPase was found to be higher with electrical stimulation, being 121.1 and 100.1% more active than that in the biological system. Moreover, stronger antioxidant ability was observed in the BES, which implied a better cold-resistance and relief of microtherm inhibition by electrical stimulation. Bacterial diversity analysis revealed a significant evolution of microbial community by electrical stimulation, and Clostridia was uniquely enriched. One bacterial sequence close to Pseudomonas became uniquely predominant, which appeared to be crucial for excellent p-FNB treatment performance in the BES at a low temperature. Economic evaluation revealed that the energy required to mineralize an extra mole of p-FNB was found to be 247 times higher by heating the system than by application of electrical stimulation. These results indicated that application of electrical stimulation is extremely promising for treating refractory waste at low temperatures.

First principles calculations of point defect diffusion in CdS buffer layers: Implications for Cu(In,Ga)(Se,S){sub 2} and Cu{sub 2}ZnSn(Se,S){sub 4}-based thin-film photovoltaics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Varley, J. B.; Lordi, V.; He, X.

2016-01-14

We investigate point defects in CdS buffer layers that may arise from intermixing with Cu(In,Ga)Se{sub 2} (CIGSe) or Cu{sub 2}ZnSn(S,Se){sub 4} (CZTSSe) absorber layers in thin-film photovoltaics (PV). Using hybrid functional calculations, we characterize the migration barriers of Cu, In, Ga, Se, Sn, Zn, Na, and K impurities and assess the activation energies necessary for their diffusion into the bulk of the buffer. We find that Cu, In, and Ga are the most mobile defects in CIGS-derived impurities, with diffusion expected to proceed into the buffer via interstitial-hopping and cadmium vacancy-assisted mechanisms at temperatures ∼400 °C. Cu is predicted to stronglymore » favor migration paths within the basal plane of the wurtzite CdS lattice, which may facilitate defect clustering and ultimately the formation of Cu-rich interfacial phases as observed by energy dispersive x-ray spectroscopic elemental maps in real PV devices. Se, Zn, and Sn defects are found to exhibit much larger activation energies and are not expected to diffuse within the CdS bulk at temperatures compatible with typical PV processing temperatures. Lastly, we find that Na interstitials are expected to exhibit slightly lower activation energies than K interstitials despite having a larger migration barrier. Still, we find both alkali species are expected to diffuse via an interstitially mediated mechanism at slightly higher temperatures than enable In, Ga, and Cu diffusion in the bulk. Our results indicate that processing temperatures in excess of ∼400 °C will lead to more interfacial intermixing with CdS buffer layers in CIGSe devices, and less so for CZTSSe absorbers where only Cu is expected to significantly diffuse into the buffer.« less

The Kinetics of Heterogeneous Electron Transfer Reactions in Polar Solvents

DTIC Science & Technology

1994-04-20

focussed on systems for which rate constants and activation parameters are available as a function of the solvent, and as a function of temperature . The... temperature . The role of reactant structure in determining the kinetic parameters is also considered. Double layer effects both at unmodified and...that the Gibbs activation energy to form a monovalent cation from a neutral molecule via electrooxidation is different from that to form a monovalent

Modelling of nectarine drying under near infrared - Vacuum conditions.

PubMed

Alaei, Behnam; Chayjan, Reza Amiri

2015-01-01

Drying of nectarine slices was performed to determine the thermal and physical properties in order to reduce product deterioration due to chemical reactions, facilitate storage and lower transportation costs. Because nectarine slices are sensitive to heat with long drying period, the selection of a suitable drying approach is a challenging task. Infrared-vacuum drying can be used as an appropriate method for susceptible materials with high moisture content such as nectarine slices. Modelling of nectarine slices drying was carried out in a thin layer near infraredvacuum conditions. Drying of the samples was implemented at the absolute pressures of 20, 40 and 60 kPa and drying temperatures of 50, 60 and 70°C. Drying behaviour of nectarine slices, as well as the effect of drying conditions on moisture loss trend, drying rate, effective diffusion coefficient, activation energy, shrinkage, colour and energy consumption of nectarine slices, dried in near infrared-vacuum dryer are discussed in this study. Six mathematical models were used to predict the moisture ratio of the samples in thin layer drying. The Midilli model had supremacy in prediction of nectarine slices drying behaviour. The maximum drying rates of the samples were between 0.014-0.047 gwater/gdry material·min. Effective moisture diffusivity of the samples was estimated in the ranges of 2.46·10-10 to 6.48·10-10 m2/s. Activation energy were computed between 31.28 and 35.23 kJ/mol. Minimum shrinkage (48.4%) and total colour difference (15.1) were achieved at temperature of 50°C and absolute pressure of 20 kPa. Energy consumption of the tests was estimated in the ranges of 0.129 to 0.247 kWh. Effective moisture diffusivity was increased with decrease of vacuum pressure and increase of drying temperature but effect of drying temperature on effective moisture diffusivity of nectarine slices was more than vacuum pressure. Activation energy was decreased with decrease in absolute pressure. Total colour difference and shrinkage of nectarine slices on near infrared-vacuum drying was decreased with decrease of vacuum pressure and decrease of drying temperature.

Energetics of Na + Transport through the Electrode/Cathode Interface in Single Solvent Electrolytes

DOE PAGES

Browning, Katie L.; Sacci, Robert L.; Veith, Gabriel M.

2017-01-27

Here, the activation energy of desolvation for Na-ion electrolyte systems were studied using temperature dependent electrochemical impedance spectroscopy (EIS). Propylene carbonate (PC) and tetraglyme were chosen as solvents in single solvent electrolyte solution coupled with NaClO 4, NaPF 6, NaAsF 6, NaBF 4, and NaOFt salts. The results demonstrate the insertion and desolvation processes are extremely fast at or above room temperature. The data shows under optimal salt chemistry the desolvation activation energy is less than 21 kJ/mole. This is in contrast to the ~50 kJ/mole measured for analogous Li systems. The dominant factor affecting performance was the anion. Indeed,more » anions with lower donor numbers (PF 6 –, AsF 6 –) had more than 30 kJ/mole lower desolvation energies than species like NaBF 4 and NaOFt.« less

Animal physiology. Summer declines in activity and body temperature offer polar bears limited energy savings.

PubMed

Whiteman, J P; Harlow, H J; Durner, G M; Anderson-Sprecher, R; Albeke, S E; Regehr, E V; Amstrup, S C; Ben-David, M

2015-07-17

Polar bears (Ursus maritimus) summer on the sea ice or, where it melts, on shore. Although the physiology of "ice" bears in summer is unknown, "shore" bears purportedly minimize energy losses by entering a hibernation-like state when deprived of food. Such a strategy could partially compensate for the loss of on-ice foraging opportunities caused by climate change. However, here we report gradual, moderate declines in activity and body temperature of both shore and ice bears in summer, resembling energy expenditures typical of fasting, nonhibernating mammals. Also, we found that to avoid unsustainable heat loss while swimming, bears employed unusual heterothermy of the body core. Thus, although well adapted to seasonal ice melt, polar bears appear susceptible to deleterious declines in body condition during the lengthening period of summer food deprivation. Copyright © 2015, American Association for the Advancement of Science.

A physically constrained classical description of the homogeneous nucleation of ice in water.

PubMed

Koop, Thomas; Murray, Benjamin J

2016-12-07

Liquid water can persist in a supercooled state to below 238 K in the Earth's atmosphere, a temperature range where homogeneous nucleation becomes increasingly probable. However, the rate of homogeneous ice nucleation in supercooled water is poorly constrained, in part, because supercooled water eludes experimental scrutiny in the region of the homogeneous nucleation regime where it can exist only fleetingly. Here we present a new parameterization of the rate of homogeneous ice nucleation based on classical nucleation theory. In our approach, we constrain the key terms in classical theory, i.e., the diffusion activation energy and the ice-liquid interfacial energy, with physically consistent parameterizations of the pertinent quantities. The diffusion activation energy is related to the translational self-diffusion coefficient of water for which we assess a range of descriptions and conclude that the most physically consistent fit is provided by a power law. The other key term is the interfacial energy between the ice embryo and supercooled water whose temperature dependence we constrain using the Turnbull correlation, which relates the interfacial energy to the difference in enthalpy between the solid and liquid phases. The only adjustable parameter in our model is the absolute value of the interfacial energy at one reference temperature. That value is determined by fitting this classical model to a selection of laboratory homogeneous ice nucleation data sets between 233.6 K and 238.5 K. On extrapolation to temperatures below 233 K, into a range not accessible to standard techniques, we predict that the homogeneous nucleation rate peaks between about 227 and 231 K at a maximum nucleation rate many orders of magnitude lower than previous parameterizations suggest. This extrapolation to temperatures below 233 K is consistent with the most recent measurement of the ice nucleation rate in micrometer-sized droplets at temperatures of 227-232 K on very short time scales using an X-ray laser technique. In summary, we present a new physically constrained parameterization for homogeneous ice nucleation which is consistent with the latest literature nucleation data and our physical understanding of the properties of supercooled water.

Energy Management Checklist for the Home.

ERIC Educational Resources Information Center

Pifer, Glenda

This booklet contains a checklist of equipment and activities for the individual's use in home energy management. The categories covered include: (1) insulation; (2) windows; (3) temperature control; (4) lighting; (5) heating water; (6) laundry; (7) cleaning and maintenance; (8) cooking; (9) refrigeration; (10) dishwashing; (11) recreation; and…

Thioesterase superfamily member 1 suppresses cold thermogenesis by limiting the oxidation of lipid droplet-derived fatty acids in brown adipose tissue.

PubMed

Okada, Kosuke; LeClair, Katherine B; Zhang, Yongzhao; Li, Yingxia; Ozdemir, Cafer; Krisko, Tibor I; Hagen, Susan J; Betensky, Rebecca A; Banks, Alexander S; Cohen, David E

2016-05-01

Non-shivering thermogenesis in brown adipose tissue (BAT) plays a central role in energy homeostasis. Thioesterase superfamily member 1 (Them1), a BAT-enriched long chain fatty acyl-CoA thioesterase, is upregulated by cold and downregulated by warm ambient temperatures. Them1 (-/-) mice exhibit increased energy expenditure and resistance to diet-induced obesity and diabetes, but the mechanistic contribution of Them1 to the regulation of cold thermogenesis remains unknown. Them1 (-/-) and Them1 (+/+) mice were subjected to continuous metabolic monitoring to quantify the effects of ambient temperatures ranging from thermoneutrality (30 °C) to cold (4 °C) on energy expenditure, core body temperature, physical activity and food intake. The effects of Them1 expression on O2 consumption rates, thermogenic gene expression and lipolytic protein activation were determined ex vivo in BAT and in primary brown adipocytes. Them1 suppressed thermogenesis in mice even in the setting of ongoing cold exposure. Without affecting thermogenic gene transcription, Them1 reduced O2 consumption rates in both isolated BAT and primary brown adipocytes. This was attributable to decreased mitochondrial oxidation of endogenous but not exogenous fatty acids. These results show that Them1 may act as a break on uncontrolled heat production and limit the extent of energy expenditure. Pharmacologic inhibition of Them1 could provide a targeted strategy for the management of metabolic disorders via activation of brown fat.

Evidence of superconductivity-induced phonon spectra renormalization in alkali-doped iron selenides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Opačić, M.; Lazarević, N.; Šćepanović, M.

2015-11-16

Polarized Raman scattering spectra of superconducting K x Fe2-y Se2 and non-superconducting K0.8Fe1.8Co0.2Se2 single crystals were measured in the temperature range from 10 K up to 300 K. Two Raman active modes from the I4/mmm phase and seven from the I4/m phase are observed in the frequency range from 150 to 325 cm-1 in both compounds, suggesting that the K0.8Fe1.8Co0.2Se2 single crystal also has a two-phase nature. The temperature dependence of the Raman mode energy is analyzed in terms of lattice thermal expansion and phonon–phonon interaction. The temperature dependence of the Raman mode linewidth is dominated by temperature-induced anharmonic effects. It is shown that the change in Raman mode energy with temperature is dominantly driven by thermal expansion of the crystal lattice. An abrupt change of the A1g mode energy nearmore » $${{T}_{\\text{C}}}$$ was observed in K x Fe2-y Se2, whereas it is absent in non-superconducting K0.8Fe1.8Co0.2Se2. Phonon energy hardening at low temperatures in the superconducting sample is a consequence of superconductivity-induced redistribution of the electronic states below the critical temperature.« less

Complex coupled metabolic and prokaryotic community responses to increasing temperatures in anaerobic marine sediments: critical temperatures and substrate changes

PubMed Central

Roussel, Erwan G.; Cragg, Barry A.; Webster, Gordon; Sass, Henrik; Tang, Xiaohong; Williams, Angharad S.; Gorra, Roberta; Weightman, Andrew J.; Parkes, R. John

2015-01-01

The impact of temperature (0–80°C) on anaerobic biogeochemical processes and prokaryotic communities in marine sediments (tidal flat) was investigated in slurries for up to 100 days. Temperature had a non-linear effect on biogeochemistry and prokaryotes with rapid changes over small temperature intervals. Some activities (e.g. methanogenesis) had multiple ‘windows’ within a large temperature range (∼10 to 80°C). Others, including acetate oxidation, had maximum activities within a temperature zone, which varied with electron acceptor [metal oxide (up to ∼34°C) and sulphate (up to ∼50°C)]. Substrates for sulphate reduction changed from predominantly acetate below, and H2 above, a 43°C critical temperature, along with changes in activation energies and types of sulphate-reducing Bacteria. Above ∼43°C, methylamine metabolism ceased with changes in methanogen types and increased acetate concentrations (>1 mM). Abundances of uncultured Archaea, characteristic of deep marine sediments (e.g. MBGD Euryarchaeota, ‘Bathyarchaeota’) changed, indicating their possible metabolic activity and temperature range. Bacterial cell numbers were consistently higher than archaeal cells and both decreased above ∼15°C. Substrate addition stimulated activities, widened some activity temperature ranges (methanogenesis) and increased bacterial (×10) more than archaeal cell numbers. Hence, additional organic matter input from climate-related eutrophication may amplify the impact of temperature increases on sedimentary biogeochemistry. PMID:26207045

Characterization of a dielectric barrier discharge in contact with liquid and producing a plasma activated water

NASA Astrophysics Data System (ADS)

Neretti, G.; Taglioli, M.; Colonna, G.; Borghi, C. A.

2017-01-01

In this work a low-temperature plasma source for the generation of plasma activated water (PAW) is developed and characterized. The plasma reactor was operated by means of an atmospheric-pressure air dielectric barrier discharge (DBD). The plasma generated is in contact with the water surface and is able to chemically activate the liquid medium. Electrodes were supplied by both sinusoidal and nanosecond-pulsed voltage waveforms. Treatment times were varied from 2 to 12 min to increase the energy dose released to the water by the DBD plasma. The physics of the discharge was studied by means of electrical, spectroscopic and imaging diagnostics. The interaction between the plasma and the liquid was investigated as well. Temperature and composition of the treated water were detected. Images of the discharges showed a filamentary behaviour in the sinusoidal case and a more homogeneous behaviour in the nanosecond-pulsed one. The images and the electrical measurements allowed to evaluate an average electron number density of about 4  ×  1019 and 6  ×  1017 m-3 for the sinusoidal and nanosecond-pulsed discharges respectively. Electron temperatures in the range of 2.1÷2.6 eV were measured by using spectroscopic diagnostics. Rotational temperatures in the range of 318-475 K were estimated by fitting synthetic spectra with the measured ones. Water temperature and pH level did not change significantly after the exposure to the DBD plasma. The production of ozone and hydrogen peroxide within the water was enhanced by increasing the plasma treatment time and the energy dose. Numerical simulations of the nanosecond-pulsed discharge were performed by using a self-consistent coupling of state-to-state kinetics of the air mixture with the Boltzmann equation of free electron kinetics. Temporal evolution of the electron energy distribution function shows departure from the Maxwellian distribution especially during the afterglow phase of the discharge. When limited deviations from Maxwellian distribution were observed, calculated electron temperature is in good agreement with the one measured by means of spectroscopic diagnostics. Computed temporal evolution of the energy delivered to the discharge is comparable with the one obtained from electrical measurements. The electrical discharges supplied by both voltage waveforms produce plasma activated water with negligible thermal effects and pH variations.

Trap densities and transport properties of pentacene metal-oxide-semiconductor transistors. I. Analytical modeling of time-dependent characteristics

NASA Astrophysics Data System (ADS)

Basile, A. F.; Cramer, T.; Kyndiah, A.; Biscarini, F.; Fraboni, B.

2014-06-01

Metal-oxide-semiconductor (MOS) transistors fabricated with pentacene thin films were characterized by temperature-dependent current-voltage (I-V) characteristics, time-dependent current measurements, and admittance spectroscopy. The channel mobility shows almost linear variation with temperature, suggesting that only shallow traps are present in the semiconductor and at the oxide/semiconductor interface. The admittance spectra feature a broad peak, which can be modeled as the sum of a continuous distribution of relaxation times. The activation energy of this peak is comparable to the polaron binding energy in pentacene. The absence of trap signals in the admittance spectra confirmed that both the semiconductor and the oxide/semiconductor interface have negligible density of deep traps, likely owing to the passivation of SiO2 before pentacene growth. Nevertheless, current instabilities were observed in time-dependent current measurements following the application of gate-voltage pulses. The corresponding activation energy matches the energy of a hole trap in SiO2. We show that hole trapping in the oxide can explain both the temperature and the time dependences of the current instabilities observed in pentacene MOS transistors. The combination of these experimental techniques allows us to derive a comprehensive model for charge transport in hybrid architectures where trapping processes occur at various time and length scales.

Temperature dependence of the triplet diffusion and quenching rates in films of an Ir(ppy)3 -cored dendrimer

NASA Astrophysics Data System (ADS)

Ribierre, J. C.; Ruseckas, A.; Samuel, I. D. W.; Staton, S. V.; Burn, P. L.

2008-02-01

We study photoluminescence and triplet-triplet exciton annihilation in a neat film of a fac-tris(2-phenylpyridyl)iridium(III) [Ir(ppy)3] -cored dendrimer and in its blend with a 4,4' -bis( N -carbazolyl)biphenyl host for the temperature range of 77-300K . The nearest neighbor hopping rate of triplet excitons is found to increase by a factor of 2 with temperature between 150 and 300K and is temperature independent at lower temperature. The intermolecular quenching rate follows the Arrhenius law with an activation energy of 7meV , which can be explained by stronger dipole-dipole interactions with the donor molecule in the higher triplet substate. The results indicate that energy disorder has no significant effect on triplet transport and quenching in these materials.

Study of temperature dependent electrical properties of Se80-xTe20Bix (x = 0, 3, 6) glasses

NASA Astrophysics Data System (ADS)

Deepika, Singh, Hukum

2018-05-01

This paper reports the variation in electrical properties of Se80-xTe20Bix (x = 0, 3, 6) glasses studied at different temperatures. The amorphous samples were prepared using the melt quenching method and the electrical measurements were performed on Keithley Electrometer in the temperature ranging from 298-373 K. The I-V characteristics were noted at different temperatures and the data obtained was analysed to get dc electrical conductivity and activation energy of electrical conduction. Further, Mott's 3D VRH model has been applied to obtain density of states, hopping range and hopping energy at different temperatures. The obtained results show that dc electrical conductivity increases with increase in Bi composition in Se-Te system. These compositions also show close agreement to Mott's VRH model.

A review of high temperature co-electrolysis of H2O and CO2 to produce sustainable fuels using solid oxide electrolysis cells (SOECs): advanced materials and technology.

PubMed

Zheng, Yun; Wang, Jianchen; Yu, Bo; Zhang, Wenqiang; Chen, Jing; Qiao, Jinli; Zhang, Jiujun

2017-03-06

High-temperature solid oxide electrolysis cells (SOECs) are advanced electrochemical energy storage and conversion devices with high conversion/energy efficiencies. They offer attractive high-temperature co-electrolysis routes that reduce extra CO 2 emissions, enable large-scale energy storage/conversion and facilitate the integration of renewable energies into the electric grid. Exciting new research has focused on CO 2 electrochemical activation/conversion through a co-electrolysis process based on the assumption that difficult C[double bond, length as m-dash]O double bonds can be activated effectively through this electrochemical method. Based on existing investigations, this paper puts forth a comprehensive overview of recent and past developments in co-electrolysis with SOECs for CO 2 conversion and utilization. Here, we discuss in detail the approaches of CO 2 conversion, the developmental history, the basic principles, the economic feasibility of CO 2 /H 2 O co-electrolysis, and the diverse range of fuel electrodes as well as oxygen electrode materials. SOEC performance measurements, characterization and simulations are classified and presented in this paper. SOEC cell and stack designs, fabrications and scale-ups are also summarized and described. In particular, insights into CO 2 electrochemical conversions, solid oxide cell material behaviors and degradation mechanisms are highlighted to obtain a better understanding of the high temperature electrolysis process in SOECs. Proposed research directions are also outlined to provide guidelines for future research.

The Catalytic Function of Enzymes.

ERIC Educational Resources Information Center

Splittgerber, Allan G.

1985-01-01

Discusses: structure of the enzyme molecule; active site; reaction mechanism; transition state; factors affecting enzyme reaction rates, concentration of enzyme; concentration of substrate; product concentration; temperature effects and pH effects; factors causing a lowering of activation energy; proximity and orientation effects; substrate strain…

18F-FDG uptake in the colon is modulated by metformin but not associated with core body temperature and energy expenditure.

PubMed

Bahler, Lonneke; Holleman, Frits; Chan, Man-Wai; Booij, Jan; Hoekstra, Joost B; Verberne, Hein J

2017-01-01

Physiological colonic 18F-fluorodeoxyglucose (18F-FDG) uptake is a frequent finding on 18F-FDG positron emission tomography computed tomography (PET-CT). Interestingly, metformin, a glucose lowering drug associated with moderate weight loss, is also associated with an increased colonic 18F-FDG uptake. Consequently, increased colonic glucose use might partly explain the weight losing effect of metformin when this results in an increased energy expenditure and/or core body temperature. Therefore, we aimed to determine whether metformin modifies the metabolic activity of the colon by increasing glucose uptake. In this open label, non-randomized, prospective mechanistic study, we included eight lean and eight overweight males. We measured colonic 18F-FDG uptake on PET-CT, energy expenditure and core body temperature before and after the use of metformin. The maximal colonic 18F-FDG uptake was measured in 5 separate segments (caecum, colon ascendens,-transversum,-descendens and sigmoid). The maximal colonic 18F-FDG uptake increased significantly in all separate segments after the use of metformin. There was no significant difference in energy expenditure or core body temperature after the use of metformin. There was no correlation between maximal colonic 18F-FDG uptake and energy expenditure or core body temperature. Metformin significantly increases colonic 18F-FDG uptake, but this increased uptake is not associated with an increase in energy expenditure or core body temperature. Although the colon might be an important site of the glucose plasma lowering actions of metformin, this mechanism of action does not explain directly any associated weight loss.

Hot Ductility and Compression Deformation Behavior of TRIP980 at Elevated Temperatures

NASA Astrophysics Data System (ADS)

Zhang, Mei; Li, Haiyang; Gan, Bin; Zhao, Xue; Yao, Yi; Wang, Li

2018-02-01

The hot ductility tests of a kind of 980 MPa class Fe-0.31C (wt pct) TRIP steel (TRIP980) with the addition of Ti/V/Nb were conducted on a Gleeble-3500 thermomechanical simulator in the temperatures ranging from 873 K to 1573 K (600 °C to 1300 °C) at a constant strain rate of 0.001 s-1. It is found that the hot ductility trough ranges from 873 K to 1123 K (600 °C to 850 °C). The recommended straightening temperatures are from 1173 K to 1523 K (900 °C to 1250 °C). The isothermal hot compression deformation behavior was also studied by means of Gleeble-3500 in the temperatures ranging from 1173 K to 1373 K (900 °C to 1100 °C) at strain rates ranging from 0.01 s-1 to 10 s-1. The results show that the peak stress decreases with the increasing temperature and the decreasing strain rate. The deformation activation energy of the test steel is 436.7 kJ/mol. The hot deformation equation of the steel has been established, and the processing maps have been developed on the basis of experimental data and the principle of dynamic materials model (DMM). By analyzing the processing maps of strains of 0.5, 0.7, and 0.9, it is found that dynamic recrystallization occurs in the peak power dissipation efficiency domain, which is the optimal area of hot working. Finally, the factors influencing hot ductility and thermal activation energy of the test steel were investigated by means of microscopic analysis. It indicates that the additional microalloying elements play important roles both in the loss of hot ductility and in the enormous increase of deformation activation energy for the TRIP980 steel.

Phytochemicals content and antioxidant properties of sea buckthorn (Hippophae rhamnoides L.) as affected by heat treatment - Quantitative spectroscopic and kinetic approaches.

PubMed

Ursache, Florentina-Mihaela; Ghinea, Ioana Otilia; Turturică, Mihaela; Aprodu, Iuliana; Râpeanu, Gabriela; Stănciuc, Nicoleta

2017-10-15

The effect of thermal processing (50-100°C) on the degradation of the phytochemicals in sea buckthorn extract was investigated using chromatographic, fluorescence and FT-IR spectroscopy techniques and degradation kinetics. Heating the sea buckthorn extract resulted in structural changes that led to red- or blue-shifts in maximum emission, depending on temperature and excitation wavelengths. The attenuated total reflectance analysis of the sea buckthorn extract revealed a satisfactory thermostability of compounds at high temperatures. A fractional conversion kinetic model was used to describe the mechanism of degradation in terms of rate and activation energy. Activation energies for total carotenoids, polyphenolic, flavonoids, and antioxidant activity were 8.45±0.93kJ/mol, 2.50±0.66kJ/mol, 22.50±7.26kJ/mol and 15.22±2.75kJ/mol, respectively. The kinetic parameters evidence a higher thermal stability of carotenoids and polyphenols, suggesting higher degradation rates for flavonoids and antioxidant activity. Our results demonstrate that industrial process optimization in terms of time-temperature combinations demands product specific kinetic data. Copyright © 2017 Elsevier Ltd. All rights reserved.

X-ray Diffraction Investigation of Annealing Behavior of Peened Surface Deformation Layer on Precipitation Hardening Stainless Steel

NASA Astrophysics Data System (ADS)

Huang, Junjie; Wang, Zhou; Gan, Jin; Yang, Ying; Huang, Feng; Wu, Gang; Meng, Qingshuai

2018-05-01

In order to investigate the recrystallization behavior of peened surface deformation layer of precipitation hardening stainless steel, a classic x-ray diffraction line profile analysis, Voigt method, was carried out on peened 17-4PH with different isothermal annealing temperatures. The activation energy of domain boundary migration ( Q a) and the activation energy of microstrain relaxation ( Q b) were calculated by regression analysis in different annealing temperature conditions. The results show that the value of Q a decreases with annealing temperature increasing, which is due to the influence of precipitation (ɛ-Cu) size on the movements of grain and subgrain boundaries. The maximum growth rate of ɛ-Cu particles occurs during 400 to 500 °C interval. Compared with growth behavior of domain size, microstrain relaxation behavior is less sensitive to precipitation particle size. The effects of annealing temperature and time on dislocation density are both significant when annealing temperature is lower than 500 °C. However, the effect of annealing temperature on dislocation density becomes insignificant when annealing temperature is higher than 500 °C. 300 °C annealing temperature only leads to the microstrain relaxation but nearly cannot lead to the domain size growth even if prolonging annealing time. Microstructure enhancement effect still exists in plastic deformation layer when 300 °C annealing temperature lasts for 60 min but nearly disappears when 600 °C annealing temperature lasts for 20 min.

X-ray Diffraction Investigation of Annealing Behavior of Peened Surface Deformation Layer on Precipitation Hardening Stainless Steel

NASA Astrophysics Data System (ADS)

Huang, Junjie; Wang, Zhou; Gan, Jin; Yang, Ying; Huang, Feng; Wu, Gang; Meng, Qingshuai

2018-04-01

In order to investigate the recrystallization behavior of peened surface deformation layer of precipitation hardening stainless steel, a classic x-ray diffraction line profile analysis, Voigt method, was carried out on peened 17-4PH with different isothermal annealing temperatures. The activation energy of domain boundary migration (Q a) and the activation energy of microstrain relaxation (Q b) were calculated by regression analysis in different annealing temperature conditions. The results show that the value of Q a decreases with annealing temperature increasing, which is due to the influence of precipitation (ɛ-Cu) size on the movements of grain and subgrain boundaries. The maximum growth rate of ɛ-Cu particles occurs during 400 to 500 °C interval. Compared with growth behavior of domain size, microstrain relaxation behavior is less sensitive to precipitation particle size. The effects of annealing temperature and time on dislocation density are both significant when annealing temperature is lower than 500 °C. However, the effect of annealing temperature on dislocation density becomes insignificant when annealing temperature is higher than 500 °C. 300 °C annealing temperature only leads to the microstrain relaxation but nearly cannot lead to the domain size growth even if prolonging annealing time. Microstructure enhancement effect still exists in plastic deformation layer when 300 °C annealing temperature lasts for 60 min but nearly disappears when 600 °C annealing temperature lasts for 20 min.

Kinetic study of solid waste pyrolysis using distributed activation energy model.

PubMed

Bhavanam, Anjireddy; Sastry, R C

2015-02-01

The pyrolysis characteristics of municipal solid waste, agricultural residues such as ground nut shell, cotton husk and their blends are investigated using non-isothermal thermogravimetric analysis (TGA) with in a temperature range of 30-900 °C at different heating rates of 10 °C, 30 °C and 50 °C/min in inert atmosphere. From the thermograms obtained from TGA, it is observed that the maximum rate of degradation occurred in the second stage of the pyrolysis process for all the solid wastes. The distributed activation energy model (DAEM) is used to study the pyrolysis kinetics of the solid wastes. The kinetic parameters E (activation energy), k0 (frequency factor) are calculated from this model. It is found that the range of activation energies for agricultural residues are lower than the municipal solid waste. The activation energies for the municipal solid waste pyrolysis process drastically decreased with addition of agricultural residues. The proposed DAEM is successfully validated with TGA experimental data. Copyright © 2014 Elsevier Ltd. All rights reserved.

Fundamental Pathways for the Adsorption and Transport of Hydrogen on TiO2 Surfaces: Origin for Effective Sensing at about Room Temperature.

PubMed

Wang, Zhuo; Xia, Xiaohong; Guo, Meilan; Shao, Guosheng

2016-12-28

Effective detection of hydrogen at lowered temperature is highly desirable in promoting safety in using this abundant gas as a clean energy source. Through first-principle calculations in the framework of density functional theory, we find that the high-energy (002) surface for rutile TiO 2 is significantly more effective in adsorbing hydrogen atoms through dissociating hydrogen molecules. The pathways for the dissociation of hydrogen molecules and sequential migration of hydrogen atoms are identified through searching along various transitional states. Pathways of low potential barriers indicate promise for hydrogen sensing, even close to room temperature. This has been proven through sensors made of thin films of well-aligned rutile nanorods, wherein the high-energy (002) surface dictates the top surface of the active layer of the sensors.

Oxidation kinetics of crystal violet by potassium permanganate in acidic medium

NASA Astrophysics Data System (ADS)

Khan, Sameera Razi; Ashfaq, Maria; Mubashir; Masood, Summyia

2016-05-01

The oxidation kinetics of crystal violet (a triphenylmethane dye) by potassium permanganate was focused in an acidic medium by the spectrophotometric method at 584 nm. The oxidation reaction of crystal violet by potassium permanganate is carried out in an acidic medium at different temperatures ranging within 298-318 K. The kinetic study was carried out to investigate the effect of the concentration, ionic strength and temperature. The reaction followed first order kinetics with respect to potassium permanganate and crystal violet and the overall rate of the reaction was found to be second order. Thermodynamic activation parameters like the activation energy ( E a), enthalpy change (Δ H*), free energy change (Δ G*), and entropy change (Δ S*) have also been evaluated.

Temperature dependence of negative bias under illumination stress and recovery in amorphous indium gallium zinc oxide thin film transistors

NASA Astrophysics Data System (ADS)

Hossain Chowdhury, Md Delwar; Migliorato, Piero; Jang, Jin

2013-04-01

We have investigated the temperature dependence of negative bias under illumination stress and recovery. The transfer characteristics exhibits a non-rigid shift towards negative gate voltages. For both stress and recovery, the voltage shift in deep depletion is twice that in accumulation. The results support the mechanism we previously proposed, which is creation and annealing of a double donor, likely to be an oxygen vacancy. The time dependence of stress and recovery can be fitted to stretched exponentials. Both processes are thermally activated with activation energies 1.06 eV and 1.25 eV for stress and recovery, respectively. A potential energy diagram is proposed to explain the results.

Freezing-induced cellular and membrane dehydration in the presence of cryoprotective agents.

PubMed

Akhoondi, Maryam; Oldenhof, Harriëtte; Sieme, Harald; Wolkers, Willem F

2012-09-01

FTIR and cryomicroscopy have been used to study mouse embryonic fibroblast cells (3T3) during freezing in the absence and presence of DMSO and glycerol. The results show that cell volume changes as observed by cryomicroscopy typically end at temperatures above -15°C, whereas membrane phase changes may continue until temperatures as low as -30°C. This implies that cellular dehydration precedes dehydration of the bound water surrounding the phospholipid head groups. Both DMSO and glycerol increase the membrane hydraulic permeability at subzero temperature and reduce the activation energy for water transport. Cryoprotective agents facilitate dehydration to continue at low subzero temperatures thereby decreasing the incidence of intracellular ice formation. The increased subzero membrane hydraulic permeability likely plays an important role in the cryoprotective action of DMSO and glycerol. In the presence of DMSO water permeability was found to be greater compared to that in the presence of glycerol. Two temperature regimes were identified in an Arrhenius plot of the membrane hydraulic permeability. The activation energy for water transport at temperature ranging from 0 to -10°C was found to be greater than that below -10°C. The non-linear Arrhenius behavior of Lp has been implemented in the water transport model to simulate cell volume changes during freezing. At a cooling rate of 1°C min(-1), ∼5% of the initial osmotically active water volume is trapped inside the cells at -30°C.

The effect of a broad activation energy distribution on deuteron spin-lattice relaxation.

PubMed

Ylinen, E E; Punkkinen, M; Birczyński, A; Lalowicz, Z T

2015-10-01

Deuteron NMR spectra and spin-lattice relaxation were studied experimentally in zeolite NaY(2.4) samples containing 100% or 200% of CD3OH or CD3OD molecules of the total coverage of Na atoms in the temperature range 20-150K. The activation energies describing the methyl and hydroxyl motions show broad distributions. The relaxation data were interpreted by improving a recent model (Stoch et al., 2013 [16]) in which the nonexponential relaxation curves are at first described by a sum of three exponentials with adjustable relaxation rates and weights. Then a broad distribution of activation energies (the mean activation energy A0 and the width σ) was assumed for each essentially different methyl and hydroxyl position. The correlation times were calculated from the Arrhenius equation (containing the pre-exponential factor τ0), individual relaxation rates computed and classified into three classes, and finally initial relaxation rates and weights for each class formed. These were compared with experimental data, motional parameters changed slightly and new improved rates and weights for each class calculated, etc. This method was improved by deriving for the deuterons of the A and E species methyl groups relaxation rates, which depend explicitly on the tunnel frequency ωt. The temperature dependence of ωt and of the low-temperature correlation time were obtained by using the solutions of the Mathieu equation for a threefold potential. These dependencies were included in the simulations and as the result sets of A0, σ and τ0 obtained, which describe the methyl and hydroxyl motions in different positions in zeolite. Copyright © 2015 Elsevier Inc. All rights reserved.

Glass transition and crystallization kinetics of a barium borosilicate glass by a non-isothermal method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lopes, Andreia A. S.; Soares, Roque S.; Lima, Maria M. A.

2014-01-28

The glass transition and crystallization kinetics of a glass with a molar composition 60BaO-30B{sub 2}O{sub 3}-10SiO{sub 2} were investigated by differential scanning calorimetry (DSC) under non-isothermal conditions. DSC curves exhibited an endothermic peak associated with the glass transition and two partially overlapped exothermic peaks associated with the crystallization of the glass. The dependence of the glass transition temperature (T{sub g}) and of the maximum crystallization temperature (T{sub p}) on the heating rate was used to determine the activation energy associated with the glass transition (E{sub g}), the activation energy for crystallization (E{sub c}), and the Avrami exponent (n). X-ray diffractionmore » (XRD) revealed that barium borate (β-BaB{sub 2}O{sub 4}) was the first crystalline phase to be formed followed by the formation of barium silicate (Ba{sub 5}Si{sub 8}O{sub 21}). The variations of activation energy for crystallization and of Avrami exponent with the fraction of crystallization (χ) were also examined. When the crystallization fraction (χ) increased from 0.1 to 0.9, the value of local activation energy (E{sub c}(χ)) decreased from 554 to 458 kJ/mol for the first exothermic peak and from 1104 to 831 kJ/mol for the second exothermic peak. The value determined for the Avrami exponent was near 2 indicating a similar one-dimensional crystallization mechanism for both crystalline phases. This was confirmed by the morphological studies performed by scanning electron microscopy (SEM) on glass samples heat-treated at the first and at the second crystallization temperatures.« less

12 J, 10 Hz diode-pumped Nd:YAG distributed active mirror amplifier chain with ASE suppression.

PubMed

Liu, Tinghao; Sui, Zhan; Chen, Lin; Li, Zhupeng; Liu, Qiang; Gong, Mali; Fu, Xing

2017-09-04

Experimental amplification of 10-ns pulses to an energy of 12.2 J at the repetition rate of 1-10 Hz is reported from a diode-pumped room-temperature distributed active mirror amplifier chain (DAMAC) based on Nd:YAG slabs. Efficient power scaling at the optical-optical efficiency of 20.6% was achieved by suppressing the transverse parasitic oscillation with ASE absorbers. To the best of our knowledge, this is the first demonstration of a diode-pumped Nd:YAG active-mirror laser with nanosecond pulse energy beyond 10 joules. The verified DAMAC concept holds the promise of scaling the energy to a 50 J level and higher by adding 10-12 more pieces of active mirror in the chain.

Combined modified atmosphere packaging and low temperature storage delay lignification and improve the defense response of minimally processed water bamboo shoot.

PubMed

Song, Lili; Chen, Hangjun; Gao, Haiyan; Fang, Xiangjun; Mu, Honglei; Yuan, Ya; Yang, Qian; Jiang, Yueming

2013-09-04

Minimally processed water bamboo shoot (WBS) lignifies and deteriorates rapidly at room temperature, which limits greatly its marketability. This study was to investigate the effect of modified atmosphere packaging (MAP) on the sensory quality index, lignin formation, production of radical oxygen species (ROS) and activities of scavenging enzymes, membrane integrity and energy status of minimally processed WBS when packaged with or without the sealed low-density polyethylene (LDPE) bags, and then stored at 20°C for 9 days or 2°C for 60 days. The sensory quality of minimally processed WBS decreased quickly after 6 days of storage at 20°C. Low temperature storage maintained a higher sensory quality index within the first 30 days, but exhibited higher contents of lignin and hydrogen peroxide (H2O2) as compared with non-MAP shoots at 20°C. Combined MAP and low temperature storage not only maintained good sensory quality after 30 days, but also reduced significantly the increases in lignin content, superoxide anion (O2.-) production rate, H2O2 content and membrane permeability, maintained high activities of superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX), and reduced the increase in activities of lipase, phospholipase D (PLD) and lipoxygenase (LOX). Furthermore, the minimally processed WBS under MAP condition exhibited higher energy charge (EC) and lower adenosine monophosphate (AMP) content by the end of storage (60 days) at 2°C than those without MAP or stored for 9 days at 20°C. These results indicated that MAP in combination with low temperature storage reduced lignification of minimally processed WBS, which was closely associated with maintenance of energy status and enhanced activities of antioxidant enzymes, as well as reduced alleviation of membrane damage caused by ROS.

Combined modified atmosphere packaging and low temperature storage delay lignification and improve the defense response of minimally processed water bamboo shoot

PubMed Central

2013-01-01

Background Minimally processed water bamboo shoot (WBS) lignifies and deteriorates rapidly at room temperature, which limits greatly its marketability. This study was to investigate the effect of modified atmosphere packaging (MAP) on the sensory quality index, lignin formation, production of radical oxygen species (ROS) and activities of scavenging enzymes, membrane integrity and energy status of minimally processed WBS when packaged with or without the sealed low-density polyethylene (LDPE) bags, and then stored at 20°C for 9 days or 2°C for 60 days. Results The sensory quality of minimally processed WBS decreased quickly after 6 days of storage at 20°C. Low temperature storage maintained a higher sensory quality index within the first 30 days, but exhibited higher contents of lignin and hydrogen peroxide (H2O2) as compared with non-MAP shoots at 20°C. Combined MAP and low temperature storage not only maintained good sensory quality after 30 days, but also reduced significantly the increases in lignin content, superoxide anion (O2.-) production rate, H2O2 content and membrane permeability, maintained high activities of superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX), and reduced the increase in activities of lipase, phospholipase D (PLD) and lipoxygenase (LOX). Furthermore, the minimally processed WBS under MAP condition exhibited higher energy charge (EC) and lower adenosine monophosphate (AMP) content by the end of storage (60 days) at 2°C than those without MAP or stored for 9 days at 20°C. Conclusion These results indicated that MAP in combination with low temperature storage reduced lignification of minimally processed WBS, which was closely associated with maintenance of energy status and enhanced activities of antioxidant enzymes, as well as reduced alleviation of membrane damage caused by ROS. PMID:24006941

Interactions between temperature and nutrients across levels of ecological organization.

PubMed

Cross, Wyatt F; Hood, James M; Benstead, Jonathan P; Huryn, Alexander D; Nelson, Daniel

2015-03-01

Temperature and nutrient availability play key roles in controlling the pathways and rates at which energy and materials move through ecosystems. These factors have also changed dramatically on Earth over the past century as human activities have intensified. Although significant effort has been devoted to understanding the role of temperature and nutrients in isolation, less is known about how these two factors interact to influence ecological processes. Recent advances in ecological stoichiometry and metabolic ecology provide a useful framework for making progress in this area, but conceptual synthesis and review are needed to help catalyze additional research. Here, we examine known and potential interactions between temperature and nutrients from a variety of physiological, community, and ecosystem perspectives. We first review patterns at the level of the individual, focusing on four traits--growth, respiration, body size, and elemental content--that should theoretically govern how temperature and nutrients interact to influence higher levels of biological organization. We next explore the interactive effects of temperature and nutrients on populations, communities, and food webs by synthesizing information related to community size spectra, biomass distributions, and elemental composition. We use metabolic theory to make predictions about how population-level secondary production should respond to interactions between temperature and resource supply, setting up qualitative predictions about the flows of energy and materials through metazoan food webs. Last, we examine how temperature-nutrient interactions influence processes at the whole-ecosystem level, focusing on apparent vs. intrinsic activation energies of ecosystem processes, how to represent temperature-nutrient interactions in ecosystem models, and patterns with respect to nutrient uptake and organic matter decomposition. We conclude that a better understanding of interactions between temperature and nutrients will be critical for developing realistic predictions about ecological responses to multiple, simultaneous drivers of global change, including climate warming and elevated nutrient supply. © 2014 John Wiley & Sons Ltd.

Accelerated aggregation of donor nitrogen in diamond containing NV centers

NASA Astrophysics Data System (ADS)

Lobanov, Sergey; Vins, Victor; Yelisseev, Alexander; Afonin, Dmitry; Blinkov, Alexander; Maximov, Yuriy

2010-05-01

The aggregation of donor nitrogen (C centers) into nitrogen pairs (A centers) is considered to be a second-order chemical reaction and the kinetics of this reaction can be written as follows: Kt = 1-- -1- Ct C0 where K is the aggregation rate constant that depends exponentially on temperature and activation energy K = Aexp (- Ea-kT ) and C0 and CT are C center concentrations before and after the aggregation. The activation energy Ea in natural diamonds is equal to 5±0.3 eV. However, it was shown by Vins (2004) that Ea varied in synthetic diamonds depending on Ni concentration from 3 to 6 eV; and in synthetic diamonds containing cobalt the activation energy exceeded 4 eV. The aggregation rate of C centers also increased dramatically in diamonds irradiated with high-energy electrons (Collins, 1980). An HPHT diamond single crystal grown in the Fe-Co-C system using the TGG method was studied. The initial C center concentration determined from the intensity of the 1130 cm-1 IR absorption band was equal to 118 ppm. In order to determine the influence of NV centers on the activation energy of aggregation, the crystal was at first irradiated with high-energy electrons (3MeV, 2×1018cm-2) and annealed in a quartz ampoule in vacuum (8000C, 2 hrs). This led to the formation of over 5 ppm of NV centers. After that the sample was annealed at high temperatures in the argon flow (15300C, 30 minutes). The IR absorption spectra revealed an

High-temperature deformation processing of Ti-24Al-20Nb

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sagar, P.K.; Banerjee, D.; Muraleedharan, K.

1996-09-01

Power dissipation maps have been generated in the temperature range of 900 C to 1,150 C and strain rate range of 10{sup {minus}3} to 10 s{sup {minus}1} for a cast aluminide alloy Ti-24Al-20Nb using dynamic material model. The results define two distinct regimes of temperature and strain rate in which efficiency of power dissipation is maximum. The first region, centered around 975 C/0.1 s{sup {minus}1}, is shown to correspond to dynamic recrystallization of the {alpha}{sub 2} phase and the second, centered around 1,150 C/0.001 s{sup {minus}1}, corresponds to dynamic recovery and superplastic deformation of the {beta} phase. Thermal activation analysismore » using the power law creep equation yielded apparent activation energies of 854 and 627 kJ/mol for the first and second regimes, respectively. Reanalyzing the data by alternate methods yielded activation energies in the range of 170 to 220 kJ/mol and 220 to 270 kJ/mol for the first and second regimes, respectively. Cross slip was shown to constitute the activation barrier in both cases. Two distinct regimes of processing instability--one at high strain rates and the other at the low strain rates in the lower temperature regions--have been identified, within which shear bands are formed.« less

Ultrafast multi-pulse transient absorption spectroscopy of fucoxanthin chlorophyll a protein from Phaeodactylum tricornutum.

PubMed

West, Robert G; Bína, David; Fuciman, Marcel; Kuznetsova, Valentyna; Litvín, Radek; Polívka, Tomáš

2018-05-01

We have applied femtosecond transient absorption spectroscopy in pump-probe and pump-dump-probe regimes to study energy transfer between fucoxanthin and Chl a in fucoxanthin-Chl a complex from the pennate diatom Phaeodactylum tricornutum. Experiments were carried out at room temperature and 77 K to reveal temperature dependence of energy transfer. At both temperatures, the ultrafast (<100 fs) energy transfer channel from the fucoxanthin S 2 state is active and is complemented by the second pathway via the combined S 1 /ICT state. The S 1 /ICT-Chl a pathway has two channels, the fast one characterized by sub-picosecond energy transfer, and slow having time constants of 4.5 ps at room temperature and 6.6 ps at 77 K. The overall energy transfer via the S 1 /ICT is faster at 77 K, because the fast component gains amplitude upon lowering the temperature. The pump-dump-probe regime, with the dump pulse centered in the spectral region of ICT stimulated emission at 950 nm and applied at 2 ps after excitation, proved that the S 1 and ICT states of fucoxanthin in FCP are individual, yet coupled entities. Analysis of the pump-dump-probe data suggested that the main energy donor in the slow S 1 /ICT-Chl a route is the S 1 part of the S 1 /ICT potential surface. Copyright © 2018 Elsevier B.V. All rights reserved.

Diffusion and the Thermal Stability of Amorphous Copper-Zirconium

NASA Astrophysics Data System (ADS)

Stelter, Eric Carl

Measurements have been made of diffusion and thermal relaxation in amorphous Cu(,50)Zr(,50). Samples were prepared by melt-spinning under vacuum. Diffusion measurements were made over the temperature range from 317 to 385 C, using Ag and Au as substitutional impurities, by means of Auger electron spectrometry (AES) and Rutherford backscattering spectrometry (RBS). Thermal measurements were made by differential scanning calorimetry (DSC) up to 550 C. The diffusion coefficients of Ag and Au in amorphous Cu(,50)Zr(,50) are found to be somewhat higher than, but very close in magnitude to the coefficient of self-diffusion in crystalline Cu at the same temperatures. The activation energies for diffusion in the amorphous alloy are 0.72 to 1.55 eV/atom, much closer to the activation energy for self-diffusion in liquid Cu, 0.42 eV/atom, than that for the crystalline solid, 2.19 eV/atom. The mechanism for diffusion in the amorphous metal is presumably quite different from the monovacancy mechanism dominant in the crystalline solid. The pre-exponential terms are found to be extremely small, on the order of 10('-10) to 10('-11) cm('2)/sec for Ag diffusion. This indicates that diffusion in amorphous Cu(,50)Zr(,50) may involve an extended defect of 10 or more atoms. Analysis of the data in terms of the free -volume model also lends strength to this conclusion and indicates that the glass is composed of liquid-like clusters of 15 to 20 atoms. The initial stage of relaxation in amorphous CuZr occurs with a spectrum of activation energies. The lowest activation energy involved, 0.78 eV/atom, is almost identical to the average activation energy of Ag diffusion in the glass, 0.77 eV/atom, indicating that relaxation occurs primarily through diffusion. The activation energy of crystallization, determined by Kissinger's method, is 3.10 eV/atom. The large difference, on the order of 2.3 eV/atom, between the activation energies of crystallization and diffusion is attributed to the energy required to nucleate the crystalline phase.

Sensitizing properties of luminescence centers on the emission of Er3+ in Si-rich SiO2 film

NASA Astrophysics Data System (ADS)

Fu, Qianyu; Gao, Yuhan; Li, Dongsheng; Yang, Deren

2016-05-01

In this paper, we report on the luminescence-center (LC)-mediated excitation of Er3+ as a function of annealing temperature in Er-doped Si-rich SiO2 (SRO) films fabricated by electron beam evaporation. It is found that the annealing temperature has significant effects on the emission of Er3+ and the specific optical-active point-defects called LCs within Er-doped SRO films. Different luminescence centers generated by the evolution of microstructures during annealing process act as efficient sensitizers for Er3+ in the films when the annealing temperature is below 1100 °C. Moreover, the temperature dependence of the energy coupling between LCs and Er3+ demonstrates the effective phonon-mediated energy transfer process. In addition, when the annealing temperature reaches 1100 °C, the decreased density of activable erbium ions induced by the aggregation of Er will bring detrimental effects on the emission of Er3+. It is demonstrated that an appropriate annealing process can be designed to achieve efficiently enhanced emissions from Er3+ ions by optimizing the density of LCs and the coupling between Er3+ and LCs.

On the origin of temperature dependence of the emission maxima of Eu2+and Ce3+- activated phosphors

NASA Astrophysics Data System (ADS)

Yan, Shirun

2018-05-01

In this paper, temperature dependence of the emission maxima of Eu2+ and Ce3+-activated phosphors and various explanations for the thermal red-shift or blue-shift proposed by different authors are reviewed. Depending on the host lattice, doping concentration of Eu2+ or Ce3+, or the temperature range at which the PL spectrum was monitored, both the way and magnitude of emission spectrum shifting were quite different. Various explanations for the thermal shifts of the emission maxima were proposed. Nonetheless, a close inspection of a collection of the data indicates that some popular explanations seemingly plausible for the thermal red/blue-shifts of the emission maxima of Eu2+ and Ce3+-activated phosphors are highly questionable, because they either misused the Varshni equation or discussed the energy of the 5d-4f transitions of Eu2+ and Ce3+ in isolation without considering simultaneous change of the host lattice. An explanation of lattice dynamic induced thermal shifts of the emission maxima of Eu2+ and Ce3+-activated phosphors is proposed in this paper. By considering the dominant contribution to the energy of the 5d-4f transitions either from a lattice dilatation or from the interactions between the 5d electrons and phonons, the complex temperature dependences of the emission maxima of various Eu2+ and Ce3+-activated phosphors experimentally observed in literature could be explained reasonably.

The Arrhenius equation revisited.

PubMed

Peleg, Micha; Normand, Mark D; Corradini, Maria G

2012-01-01

The Arrhenius equation has been widely used as a model of the temperature effect on the rate of chemical reactions and biological processes in foods. Since the model requires that the rate increase monotonically with temperature, its applicability to enzymatic reactions and microbial growth, which have optimal temperature, is obviously limited. This is also true for microbial inactivation and chemical reactions that only start at an elevated temperature, and for complex processes and reactions that do not follow fixed order kinetics, that is, where the isothermal rate constant, however defined, is a function of both temperature and time. The linearity of the Arrhenius plot, that is, Ln[k(T)] vs. 1/T where T is in °K has been traditionally considered evidence of the model's validity. Consequently, the slope of the plot has been used to calculate the reaction or processes' "energy of activation," usually without independent verification. Many experimental and simulated rate constant vs. temperature relationships that yield linear Arrhenius plots can also be described by the simpler exponential model Ln[k(T)/k(T(reference))] = c(T-T(reference)). The use of the exponential model or similar empirical alternative would eliminate the confusing temperature axis inversion, the unnecessary compression of the temperature scale, and the need for kinetic assumptions that are hard to affirm in food systems. It would also eliminate the reference to the Universal gas constant in systems where a "mole" cannot be clearly identified. Unless proven otherwise by independent experiments, one cannot dismiss the notion that the apparent linearity of the Arrhenius plot in many food systems is due to a mathematical property of the model's equation rather than to the existence of a temperature independent "energy of activation." If T+273.16°C in the Arrhenius model's equation is replaced by T+b, where the numerical value of the arbitrary constant b is substantially larger than T and T(reference), the plot of Ln k(T) vs. 1/(T+b) will always appear almost perfectly linear. Both the modified Arrhenius model version having the arbitrary constant b, Ln[k(T)/k(T(reference)) = a[1/ (T(reference)+b)-1/ (T+b)], and the exponential model can faithfully describe temperature dependencies traditionally described by the Arrhenius equation without the assumption of a temperature independent "energy of activation." This is demonstrated mathematically and with computer simulations, and with reprocessed classical kinetic data and published food results.

Investigation of thermal effects of infrared lasers on the rabbit retina: a study in the course of development of an active subretinal prosthesis.

PubMed

Sailer, Heiko; Shinoda, Kei; Blatsios, Georgios; Kohler, Konrad; Bondzio, Lars; Zrenner, Eberhart; Gekeler, Florian

2007-08-01

Retinal implants are intended to replace photoreceptors in patients suffering from degenerative retinal diseases such as retinitis pigmentosa. Data show that photodiodes in subretinal implants are not powerful enough to stimulate overlying retinal tissue by simply transforming light energy into electrical energy. Therefore, infrared (IR) irradiation has been envisioned to supply additional energy. While epiretinal implants mostly use induction coils for wireless energy transfer, IR irradiation seems to be an additional option. This study investigated the feasibility of an IR energy supply for an active subretinal implant by assessing thermal effects of IR irradiation onto the rabbit retina. Polyimide foil strips carrying an optical sensor as well as a thermal sensor were implanted into the subretinal space of the eyes of nine rabbits using a transchoroidal surgical approach. The area of the thermal sensor was irradiated by an IR laser (830 nm) focused on the device. The sensor provided simultaneous real-time measurements of absolute temperature and irradiation density, allowing direct correlation of the temperature increase to different intensities of IR irradiation. Possible IR-related damage to the retina was examined in histological sections. Temperature changes in living and dead animals were evaluated as a function of IR irradiation power of between 0.1 mW and 40 mW (0.03 mW/mm2-12.7 mW/mm2). We found an exponential relationship between IR irradiation power and temperature increase over the whole range (up to 12.7 mW/mm2) in the living animal. The maximum temperature increase caused by IR irradiation of 40 mW (12.7 mW/mm2) was 4.5 degrees C. The ratio of temperature increase to IR irradiation density postmortem (i.e., without ocular blood flow) was linear over the whole range, with 1.15 degrees C per 1 mW/mm2. Thus, the cooling effect of ocular blood flow varied depending on IR irradiance density. In histological sections, no IR-induced damage to the retina was detected. A temperature increase of 3.2 degrees C in the living rabbit eye is to be expected when powering a subretinal implant with 15 mW (4.8 mW/mm2) IR power, the wattage used in an external power supply for an active implant with 1,500 electrodes. This appears to be a tolerable increase for ocular tissue.

Hot heads & cool bodies: The conundrums of human brown adipose tissue (BAT) activity research.

PubMed

Bahler, Lonneke; Holleman, Frits; Booij, Jan; Hoekstra, Joost B; Verberne, Hein J

2017-05-01

Brown adipose tissue is able to increase energy expenditure by converting glucose and fatty acids into heat. Therefore, BAT is able to increase energy expenditure and could thereby facilitate weight loss or at least weight maintenance. Since cold is a strong activator of BAT, most prospective research is performed during cold to activate BAT. In current research, there are roughly two methods of cooling. Cooling by lowering ambient air temperature, which uses a fixed temperature for all subjects and personalized cooling, which uses cooling blankets or vests with temperatures that can be adjusted to the individual set point of shivering. These methods might trigger mechanistically different cold responses and hence result in a different BAT activation. This hypothesis is underlined by two studies with the same research question (difference in BAT activity between Caucasians and South Asians) one study found no differences in BAT activity whereas the other did found differences in BAT activity. Since most characteristics (e.g. age, BMI) were similar in the two studies, the best explanation for the differences in outcomes is the use of different cooling protocols. One of the reasons for differences in outcomes might be the sensory input from the facial skin, which might be important for the activation of BAT. In this review we will elaborate on the differences between the two cooling protocols used to activate BAT. Copyright © 2017 European Federation of Internal Medicine. Published by Elsevier B.V. All rights reserved.

A study of the effect of gamma and laser irradiation on the thermal, optical and structural properties of CR-39 nuclear track detector

NASA Astrophysics Data System (ADS)

Nouh, S. A.; Atta, M. R.; El-Melleegy, W. M.

2004-08-01

A comparative study of the effect of gamma and laser irradiation on the thermal, optical and structural properties of the CR-39 diglycol carbonate solid state nuclear track detector has been carried out. Samples from CR-39 polymer were classified into two main groups: the first group was irradiated by gamma rays with doses at levels between 20 and 300 kGy, whereas the second group was exposed to infrared laser radiation with energy fluences at levels between 0.71 and 8.53 J/cm(2). Non-isothermal studies were carried out using thermogravimetry, differential thermogravimetry and differential thermal analysis to obtain activation energy of decomposition and transition temperatures for the non-irradiated and all irradiated CR-39 samples. In addition, optical and structural property studies were performed on non-irradiated and irradiated CR-39 samples using refractive index and X-ray diffraction measurements. Variation in the onset temperature of decomposition T-o, activation energy of decomposition E-a, melting temperature T-m, refractive index n and the mass fraction of the amorphous phase after gamma and laser irradiation were studied. It was found that many changes in the thermal, optical and structural properties of the CR-39 polymer could be produced by gamma irradiation via degradation and cross-linking mechanisms. Also, the gamma dose has an advantage of increasing the correlation between thermal stability of the CR-39 polymer and bond formation created by the ionizing effect of gamma radiation. On the other hand, higher laser-energy fluences in the range 4.27-8.53 J/cm(2) decrease the melting temperature of the CR-39 polymer and this is most suitable for applications requiring molding of the polymer at lower temperatures.

Non-arrhenius behavior in the unfolding of a short, hydrophobic alpha-helix. Complementarity of molecular dynamics and lattice model simulations.

PubMed

Collet, Olivier; Chipot, Christophe

2003-05-28

The unfolding of the last, C-terminal residue of AcNH(2)-(l-Leu)(11)-NHMe in its alpha-helical form has been investigated by measuring the variation of free energy involved in the alpha(R) to beta conformational transition. These calculations were performed using large-scale molecular dynamics simulations in conjunction with the umbrella sampling method. For different temperatures ranging from 280 to 370 K, the free energy of activation was estimated. Concurrently, unfolding simulations of a homopolypeptide formed by twelve hydrophobic residues were carried out, employing a three-dimensional lattice model description of the peptide, with a temperature-dependent interaction potential. Using a Monte Carlo approach, the lowest free energy conformation, an analogue of a right-handed alpha-helix, was determined in the region where the peptide chain is well ordered. The free energy barrier separating this state from a distinct, compact conformation, analogue to a beta-strand, was determined over a large enough range of temperatures. The results of these molecular dynamics and lattice model simulations are consistent and indicate that the kinetics of the unfolding of a hydrophobic peptide exhibits a non-Arrhenius behavior closely related to the temperature dependence of the hydrophobic effect. These results further illuminate the necessity to include a temperature dependence in potential energy functions designed for coarse-grained models of proteins.

Sintering in Ceramics and Solid Oxide Fuel Cells

NASA Astrophysics Data System (ADS)

Hunt, Clay Dale

Nature's propensity to minimize energy, and the change in energy with respect to position, drives diffusion. Diffusion is a means by which mass transport resulting in the bonding of the particles of a powder compact can be achieved without melting. This phenomenon occurs in powdered materials near their melting temperature, and is referred to as "sintering". Because of the extreme melting temperature of some materials, sintering might be the only practical means of processing. The complexity and subtlety of sintering ceramics motivated the evaluation of empirical data and existing sintering models. This project examined polycrystalline cubic-zirconia sintering with and without transition-metal oxide additions that change sintering behavior. This study was undertaken to determine how sintering aids affect the driving force, and activation energy, the energy barrier that must be overcome in order for an atom or ion to diffuse, of the densification occurring during sintering. Examination of commercially-available cubic-zirconia powder sintering behavior was undertaken with dilatometry, which allows monitoring of the length change a material undergoes as it sinters, and with scanning electron microscopy, which facilitates the study of sintered-sample microstructure. MATLAB algorithms quantifying sintering results were developed. Results from this work include proposed definitions of a 26-year-old undefined function of density factor in a well-accepted mathematical model of sintering. These findings suggest activation energy is not changing with density, as is suggested by recent published results. The first numerical integration of the studied sintering model has been performed. With these tools, a measure of the activation energy of densification of cubic-zirconia with and without the addition of cobalt-oxide as a sintering aid has been performed. The resulting MATLAB algorithms can be used in future sintering studies. It is concluded that sintering enhancement achieved with cobalt-oxide addition comes from reduction in activation energy of densification of cubic-zirconia. Further, it is suggested that the activation energy of densification does not change with material density. This conclusion is supported by the sensitivity of the numerical integration of the aforementioned sintering model to changes in activation energy.

Catalytic power of enzymes decreases with temperature: New insights for understanding soil C cycling and microbial ecology under warming.

PubMed

Alvarez, Gaël; Shahzad, Tanvir; Andanson, Laurence; Bahn, Michael; Wallenstein, Matthew D; Fontaine, Sébastien

2018-04-23

Most current models of soil C dynamics predict that climate warming will accelerate soil C mineralization, resulting in a long-term CO 2 release and positive feedback to global warming. However, ecosystem warming experiments show that CO 2 loss from warmed soils declines to control levels within a few years. Here, we explore the temperature dependence of enzymatic conversion of polymerized soil organic C (SOC) into assimilable compounds, which is presumed the rate-limiting step of SOC mineralization. Combining literature review, modelling and enzyme assays, we studied the effect of temperature on activity of enzymes considering their thermal inactivation and catalytic activity. We defined the catalytic power of enzymes (E power ) as the cumulative amount of degraded substrate by one unit of enzyme until its complete inactivation. We show a universal pattern of enzyme's thermodynamic properties: activation energy of catalytic activity (EA cat ) < activation energy of thermal inactivation (EA inact ). By investing in stable enzymes (high EA inact ) having high catalytic activity (low EA cat ), microorganisms may maximize the E power of their enzymes. The counterpart of such EAs' hierarchical pattern is the higher relative temperature sensitivity of enzyme inactivation than catalysis, resulting in a reduction in E power under warming. Our findings could explain the decrease with temperature in soil enzyme pools, microbial biomass (MB) and carbon use efficiency (CUE) reported in some warming experiments and studies monitoring the seasonal variation in soil enzymes. They also suggest that a decrease in soil enzyme pools due to their faster inactivation under warming contributes to the observed attenuation of warming effect on soil C mineralization. This testable theory predicts that the ultimate response of SOC degradation to warming can be positive or negative depending on the relative temperature response of E power and microbial production of enzymes. © 2018 John Wiley & Sons Ltd.

Development and testing of thermal energy storage modules for use in active solar heating and cooling systems

NASA Technical Reports Server (NTRS)

Parker, J. C.

1981-01-01

The project development requirements and criteria are presented along with technical data for the modules. Performance tests included: ducting, temperature, pressure and air flow measurements, dry and wet bulb temperature; duct pressure measurements; and air conditioning apparatus checks; installation, operation, and maintenance instructions are included.

Morphology-based differences in the thermal response of freshwater phytoplankton.

PubMed

Segura, Angel M; Sarthou, Florencia; Kruk, Carla

2018-05-01

The thermal response of maximum growth rate in morphology-based functional groups (MBFG) of freshwater phytoplankton is analysed. Contrasting an exponential Boltzmann-Arrhenius with a unimodal model, three main features were evaluated: (i) the activation energy of the rise ( E r ), (ii) the presence of a break in the thermal response and (iii) the activation energy of the fall ( E f ). The whole dataset ( N = 563) showed an exponential increase ( E r ∼ 0.5), a break around 24°C and no temperature dependence after the breakpoint ( E f = 0). Contrasting thermal responses among MBFG were found. All groups showed positive activation energy ( E r > 0), four showed no evidence of decline in growth rate (temperature range = 0-35°C) and two presented a breakpoint followed by a sharp decrease in growth rate. Our results evidenced systematic differences between MBFG in the thermal response and a coherent response significantly related to morphological traits other than size (i.e. within MBFG). These results provide relevant information for water quality modelling and climate change predictions. © 2018 The Author(s).

Impedance Spectroscopy Analysis of Mg4Nb2O9 Ceramics with Different Additions of V2O5 for Microwave and Radio Frequency Applications

NASA Astrophysics Data System (ADS)

Filho, J. M. S.; Rodrigues Junior, C. A.; Sousa, D. G.; Oliveira, R. G. M.; Costa, M. M.; Barroso, G. C.; Sombra, A. S. B.

2017-07-01

The complex impedance spectroscopy study of magnesium niobate Mg4Nb2O9 (MN) ceramics with different additions of V2O5 (0%, 2%, 5%) was performed in this present paper. The preparation of MN samples were carried out by using the solid-state reaction method with a high-energy milling machine. Frequency and temperature dependence of the complex impedance, complex modulus analysis, and conductivity were measured and calculated at different temperatures by using a network impedance analyzer. A non-Debye type relaxation was observed showing a decentralization of the semicircles. Cole-Cole formalism was adopted here with the help of a computer program used to fit the experimental data. A typical universal dielectric response in the frequency-dependent conductivity at different temperatures was found. The frequency dependent ac conductivity at different temperatures indicates that the conduction process is thermally activated. The activation energy was obtained from the Arrhenius fitting by using conductivity and electrical modules data. The results would help to understand deeply the relaxation process in these types of materials.

Thermal stability of epitaxial SrRuO3 films as a function of oxygen pressure

NASA Astrophysics Data System (ADS)

Lee, Ho Nyung; Christen, Hans M.; Chisholm, Matthew F.; Rouleau, Christopher M.; Lowndes, Douglas H.

2004-05-01

The thermal stability of electrically conducting SrRuO3 thin films grown by pulsed-laser deposition on (001) SrTiO3 substrates has been investigated by atomic force microscopy and reflection high-energy electron diffraction (RHEED) under reducing conditions (25-800 °C in 10-7-10-2 Torr O2). The as-grown SrRuO3 epitaxial films exhibit atomically flat surfaces with single unit-cell steps, even after exposure to air at room temperature. The films remain stable at temperatures as high as 720 °C in moderate oxygen ambients (>1 mTorr), but higher temperature anneals at lower pressures result in the formation of islands and pits due to the decomposition of SrRuO3. Using in situ RHEED, a temperature and oxygen pressure stability map was determined, consistent with a thermally activated decomposition process having an activation energy of 88 kJ/mol. The results can be used to determine the proper conditions for growth of additional epitaxial oxide layers on high quality electrically conducting SrRuO3.

Non-isothermal crystallization kinetics of ternary Se90Te10-xPbx glasses

NASA Astrophysics Data System (ADS)

Atyia, H. E.; Farid, A. S.

2016-02-01

Ternary Se90Te10-xPbx with (x=2 and 6 at%) glass compositions have been prepared using a melt quenching technique and performed the non-isothermal kinetics by differential thermal analysis (DTA) at various heating rates. The glassy state of the studied samples has been characterized using x-ray diffraction analysis. The glass transition temperature Tg, the onset temperature of crystallization Tc and the peak temperature of crystallization Tp are found to be composition and heating rate dependent. From heating rate dependence of Tg and Tp, the glass transition activation energies Eg and the crystallization activation energies Ec have been determined according to different methods. The transformation mechanisms have been examined by the values of Avrami exponent n and dimensionality of growth m. Thermal stability and glass formation ability have been monitored through the calculation of the thermal stability S, temperature difference ΔT, Hurby parameter Hr, frequency factor Ko, crystallization rate factor K and fragility index F. The compositional dependence of the above-mentioned parameters indicate that, the stability of the studied glass samples decreases with increasing Pb at% content.

Permeation of oxygen through high purity, large grain silver

NASA Technical Reports Server (NTRS)

Outlaw, R. A.; Peregoy, W. K.; Hoflund, Gar B.

1987-01-01

The permeation of high purity, large grain Ag membranes by oxygen has been studied over the temperature range 400 to 800 C. The permeability was found to be quite linear and repeatable, but the magnitude was 3.2 times smaller than that determined by past research. Since previous investigators studied substantially less pure Ag and conducted experiments within much poorer vacuum environments (which indicates that their grain boundary density was much greater), the data presented here suggest oxygen transport through the membrane is primarily by grain boundary diffusion. The diffusivity measurements were found to exhibit two distinct linear regions, one above and one below a critical temperature of 630 C. The high-temperature data have an activation energy (11.1 kcal/mole) similar to that reported by others, but the low-temperature data have a higher activation energy (15.3 kcal/mole), which can be explained by impurity trapping in the grain boundaries. Vacuum desorption of the oxygen-saturated Ag was found to occur at a threshold of 630 C, which is consistent with the onset of increased mobility within the grain boundaries.

The inverse problem of argon diffusion from minerals: Determination of kinetic parameters from stepwise-heating experiments

USGS Publications Warehouse

Brandt, Stephen B.; Rasskazov, S.V.; Brandt, I.S.; Ivanov, A.V.; Kunk, Michael J.

1997-01-01

Results of two routine 40Ar/39Ar stepwise heating experiments on a biotite and a basanite are interpreted in terms of Fick's and Arrhenius' laws. Both patterns represent a saddle-shaped 39Ar release. Argon isotope spectra are suggested to be controlled by the activation energy of diffusion E and the frequency factor D(o). The activation energy of 39Ar is lower than the one of 40Ar. This results in a preferable release of 40Ar relatively to 39Ar at high-temperature steps and an increasing high-temperature wing in the saddle-shaped age spectrum. At low temperatures, considerable losses and irregularities in release of mainly 39Ar are observed, which cause the decreasing low-temperature wing in the 'saddle'. The suggestion of argon losses (mainly of 39Ar) from a loose, 'unstable' zone of the mineral structures becomes justified. The n-irradiation of the samples and the shift of E of 39Ar towards lower values seems to explain the saddle-shaped age-spectra often encountered in 40Ar/39Ar-geochronometry.

Suppressing Nonradiative Recombination in Crown-Shaped Quantum Wells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Park, Kwangwook; Ju, Gunwu; Na, Byung Hoon

We examined the structural and optical properties of a crown-shaped quantum well (CSQW) to suppress nonradiative recombination. To reduce carrier loss in defect traps at the well/barrier interface, the CSQW was designed to concentrate carriers in the central region by tailoring the bandgap energy. Temperature-dependent photoluminescence measurements showed that the CSQW had a high activation energy and low potential fluctuation. In addition, the long carrier lifetime of the CSQW at high temperatures can be interpreted as indicating a decrease in carrier loss at defect traps.

Aircraft Emissions: Potential Effects on Ozone and Climate - A Review and Progress Report

DTIC Science & Technology

1977-03-01

which itself absorbs and reemits energy over a wide spectral range. In addition to such direct effects, various possible feedback effects can be...4.3.3 COMESA Climatic Effect Studies 4-17 4.4 Computed Mean Temperature Effects--Fleet Effects 4-24 4.4.1 Introduction 4-24 4.4.2 Mean Temperature Impact ...M B-13 B-2 The Chemical Kinetic Mechanism Used In . Model A B-19 B-3 Rate Coefficients for Model B (with Activation Energy in cal/mole) B-20 B-4

Emission mechanisms in stabilized iron-passivated porous silicon: Temperature and laser power dependences

NASA Astrophysics Data System (ADS)

Rahmani, M.; Moadhen, A.; Mabrouk Kamkoum, A.; Zaïbi, M.-A.; Chtourou, R.; Haji, L.; Oueslati, M.

2012-02-01

Photoluminescence (PL) measurements of porous silicon (PS) and iron-porous silicon nanocomposites (PS/Fe) with stable optical properties versus temperature and laser power density have been investigated. The presence of iron in PS matrix is confirmed by Raman spectroscopy. The PL intensity of PS and PS/Fe increases at low temperature, the evolution of integrated PL intensity follows the modified Arrhenius model. The incorporation of iron in PS matrix reduces the activation energy traducing the existence of shallow levels related to iron atoms. Also, the temperature dependence of the porous silicon PL peak position follows a linear evolution at high temperature and a quadratic one at low temperature. Such evolution is due to the thermal carriers' redistribution and an energy transfer. Similarly, we have compared the laser power dependence of the PL in PS and PS/Fe layers. The results prove that the recombination process in PS is realised through the lower energy traps localised in the electronic gap. However, the observed emission in PS/Fe is essentially due to direct transitions. So, we can conclude that the presence of iron in PS matrix induces a strong modification of the PL mechanisms.

Oxidation kinetics of model compounds of metabolic waste in supercritical water

NASA Technical Reports Server (NTRS)

Webley, Paul A.; Holgate, Henry R.; Stevenson, David M.; Tester, Jefferson W.

1990-01-01

In this NASA-funded study, the oxidation kinetics of methanol and ammonia in supercritical water have been experimentally determined in an isothermal plug flow reactor. Theoretical studies have also been carried out to characterize key reaction pathways. Methanol oxidation rates were found to be proportional to the first power of methanol concentration and independent of oxygen concentration and were highly activated with an activation energy of approximately 98 kcal/mole over the temperature range 480 to 540 C at 246 bar. The oxidation of ammonia was found to be catalytic with an activation energy of 38 kcal/mole over temperatures ranging from 640 to 700 C. An elementary reaction model for methanol oxidation was applied after correction for the effect of high pressure on the rate constants. The conversion of methanol predicted by the model was in good agreement with experimental data.

Influence of carbon conductive additives on electrochemical double-layer supercapacitor parameters

NASA Astrophysics Data System (ADS)

Kiseleva, E. A.; Zhurilova, M. A.; Kochanova, S. A.; Shkolnikov, E. J.; Tarasenko, A. B.; Zaitseva, O. V.; Uryupina, O. V.; Valyano, G. V.

2018-01-01

Electrochemical double-layer capacitors (EDLC) offer energy storage technology, highly demanded for rapid transition processes in transport and stationary applications, concerned with fast power fluctuations. Rough structure of activated carbon, widely used as electrode material because of its high specific area, leads to poor electrode conductivity. Therefore there is the need for conductive additive to decrease internal resistance and to achieve high specific power and high specific energy. Usually carbon blacks are widely used as conductive additive. In this paper electrodes with different conductive additives—two types of carbon blacks and single-walled carbon nanotubes—were prepared and characterized in organic electrolyte-based EDLC cells. Electrodes are based on original wood derived activated carbon produced by potassium hydroxide high-temperature activation at Joint Institute for High Temperatures RAS. Electrodes were prepared from slurry by cold-rolling. For electrode characterization cyclic voltammetry, impedance spectra analysis, equivalent series resistance measurements and galvanostatic charge-discharge were used.

Huddling Conserves Energy, Decreases Core Body Temperature, but Increases Activity in Brandt's Voles (Lasiopodomys brandtii)

PubMed Central

Sukhchuluun, Gansukh; Zhang, Xue-Ying; Chi, Qing-Sheng; Wang, De-Hua

2018-01-01

Huddling as social thermoregulatory behavior is commonly used by small mammals to reduce heat loss and energy expenditure in the cold. Our study aimed to determine the effect of huddling behavior on energy conservation, thermogenesis, core body temperature (Tb) regulation and body composition in Brandt's voles (Lasiopodomys brandtii). Adult captive-bred female Brandt's voles (n = 124) (~50 g) in 31 cages with 4 individuals each were exposed to cool (23 ± 1°C) and cold (4 ± 1°C) ambient temperatures (Ta) and were allowed to huddle or were physically separated. The cold huddling (Cold-H) groups significantly reduced food intake by 29% and saved digestible energy 156.99 kJ/day compared with cold separated groups (Cold-S); in cool huddling groups (Cool-H) the reduction in food intake was 26% and digestible energy was saved by 105.19 kJ/day in comparison to the separated groups (Cool-S). Resting metabolic rate (RMR) of huddling groups was 35.7 and 37.2% lower than in separated groups at cold and cool Tas, respectively. Maximum non-shivering thermogenesis (NSTmax) of huddling voles was not affected by Ta, but in Cold-S voles it was significantly increased in comparison to Cool-S. Huddling groups decreased wet thermal conductance by 39% compared with separated groups in the cold, but not in the cool Ta. Unexpectedly, huddling voles significantly decreased Tb by 0.25 – 0.50°C at each Ta. Nevertheless, activity of Cold-H voles was higher than in Cold-S voles. Thus, huddling is energetically highly effective because of reduced metabolic rate, thermogenic capacity and relaxed Tb regulation despite the increase of activity. Therefore, Brandt's voles can remain active and maintain their body condition without increased energetic costs during cold exposure. This study highlights the ecological significance of huddling behavior for maintenance of individual fitness at low costs, and thus survival of population during severe winter in small mammals. PMID:29867585

Effects of temperature and water availability on light energy utilization in photosynthetic processes of Deschampsia antarctica.

PubMed

Sáez, Patricia L; Rivera, Betsy K; Ramírez, Constanza F; Vallejos, Valentina; Cavieres, Lohengrin A; Corcuera, Luis J; Bravo, León A

2018-03-30

Regional climate change in Antarctica would favor the carbon assimilation of Antarctic vascular plants, because rising temperatures are approaching their photosynthetic optimum (10-19°C). This could be detrimental for photoprotection mechanisms, mainly those associated with thermal dissipation, making plants more susceptible to eventual drought predicted by climate change models. With the purpose to study the effect of temperature and water availability on light energy utilization and putative adjustments in photoprotective mechanisms of Deschampsia antarctica Desv., plants were collected from two Antarctic provenances: King George Island and Lagotellerie Island. Plants were cultivated at 5°, 10° and 16°C under well-watered (WW) and water-deficit (WD, at 35% of the field capacity) conditions. Chlorophyll fluorescence, pigment content, and de-epoxidation state were evaluated. Regardless of provenances, D. antarctica showed similar morphological, biochemical, and functional responses to growth temperature. Higher temperature triggered an increase in photochemical activity (i.e. ETR, and photochemical quenching), and a decrease in thermal dissipation capacity (i.e. lower xanthophyll pool, Chl a/b, and β carotene/neoxanthin ratios). LMA was reduced at higher temperature, and was only affected in plants exposed to WD at 16°C and exhibiting lower ETR and chlorophylls. D. antarctica is adapted to frequent freezing events, which may induce a form of physiological water stress. Photoprotective responses observed under WD contribute to maintain a stable photochemical activity. Thus, it is possible that short-term temperature increases could favor the photochemical activity of this species. However, long-term effects will depend on the magnitude of changes and the plant's ability to adjust to new growth temperature. This article is protected by copyright. All rights reserved.

Development of a Novel Method for in vivo Determination of Activation Energy of Glucose Transport Across S. cerevisiae Cellular Membranes. A Biosensor-like Approach.

PubMed

Kormes, Diego J; Cortón, Eduardo

2009-01-01

Whereas biosensors have been usually proposed as analytical tools, used to investigate the surrounding media pursuing an analytical answer, we have used a biosensor-like device to characterize the microbial cells immobilized on it. We have studied the kinetics of transport and degradation of glucose at different concentrations and temperatures. When glucose concentrations of 15 and 1.5 mM were assayed, calculated activation energies were 25.2 and 18.4 kcal mol(-1), respectively, in good agreement with previously published data. The opportunity and convenience of using Arrhenius plots to estimate the activation energy in metabolic-related processes is also discussed.

Application of the compensated Arrhenius formalism to self-diffusion: implications for ionic conductivity and dielectric relaxation.

PubMed

Petrowsky, Matt; Frech, Roger

2010-07-08

Self-diffusion coefficients are measured from -5 to 80 degrees C in a series of linear alcohols using pulsed field gradient NMR. The temperature dependence of these data is studied using a compensated Arrhenius formalism that assumes an Arrhenius-like expression for the diffusion coefficient; however, this expression includes a dielectric constant dependence in the exponential prefactor. Scaling temperature-dependent diffusion coefficients to isothermal diffusion coefficients so that the exponential prefactors cancel results in calculated energies of activation E(a). The exponential prefactor is determined by dividing the temperature-dependent diffusion coefficients by the Boltzmann term exp(-E(a)/RT). Plotting the prefactors versus the dielectric constant places the data on a single master curve. This procedure is identical to that previously used to study the temperature dependence of ionic conductivities and dielectric relaxation rate constants. The energies of activation determined from self-diffusion coefficients in the series of alcohols are strikingly similar to those calculated for the same series of alcohols from both dielectric relaxation rate constants and ionic conductivities of dilute electrolytes. The experimental results are described in terms of an activated transport mechanism that is mediated by relaxation of the solution molecules. This microscopic picture of transport is postulated to be common to diffusion, dielectric relaxation, and ionic transport.

Determination of electrical properties of degraded mixed ionic conductors: Impedance studies with applied dc voltage

NASA Astrophysics Data System (ADS)

Bayer, T. J. M.; Carter, J. J.; Wang, Jian-Jun; Klein, Andreas; Chen, Long-Qing; Randall, C. A.

2017-12-01

Under electrical bias, mixed ionic conductors such as SrTiO3 are characterized by oxygen vacancy migration which leads to resistance degradation. The defect chemistry to describe the relationship between conductivity and oxygen vacancies is usually obtained by high temperature conductivity data or quenching experiments. These techniques can investigate the equilibrated state only. Here, we introduce a new approach using in-situ impedance studies with applied dc voltage to analyze the temperature dependent electrical properties of degraded SrTiO3 single crystals. This procedure is most beneficial since it includes electric field driven effects. The benefits of the approach are highlighted by comparing acceptor doped and undoped SrTiO3. This approach allows the determination of the temperature activation of both anodic and cathodic conductivity of Fe-doped SrTiO3 in the degraded state. The anodic activation energy matches well with the published results, while the activation energy of the degraded cathode region reported here is not in agreement with earlier assumptions. The specific discrepancies of the experimental data and the published defect chemistry are discussed, and a defect chemistry model that includes the strong temperature dependence of the electron conductivity in the cathode region is proposed.

Low temperature regeneration of activated carbons using microwaves: revising conventional wisdom.

PubMed

Calışkan, E; Bermúdez, J M; Parra, J B; Menéndez, J A; Mahramanlıoğlu, M; Ania, C O

2012-07-15

The purpose of this work was to explore the application of microwaves for the low temperature regeneration of activated carbons saturated with a pharmaceutical compound (promethazine). Contrary to expectations, microwave-assisted regeneration did not lead to better results than those obtained under conventional electric heating. At low temperatures the regeneration was incomplete either under microwave and conventional heating, being this attributed to the insufficient input energy. At mild temperatures, a fall in the adsorption capacity upon cycling was obtained in both devices, although this was much more pronounced for the microwave. These results contrast with previous studies on the benefits of microwaves for the regeneration of carbon materials. The fall in the adsorption capacity after regeneration was due to the thermal cracking of the adsorbed molecules inside the carbon porous network, although this effect applies to both devices. When microwaves are used, along with the thermal heating of the carbon bed, a fraction of the microwave energy seemed to be directly used in the decomposition of promethazine through the excitation of the molecular bonds by microwaves (microwave-lysis). These results point out that the nature of the adsorbate and its ability to interact with microwave are key factors that control the application of microwaves for regeneration of exhausted activated carbons. Copyright © 2012 Elsevier Ltd. All rights reserved.

Dielectric and impedance spectral characteristics of bulk ZnIn2Se4

NASA Astrophysics Data System (ADS)

El-Nahass, M. M.; Attia, A. A.; Salem, G. F.; Ali, H. A. M.; Ismail, M. I.

2014-02-01

The frequency and temperature dependence of ac conductivity, dielectric constant and dielectric loss of ZnIn2Se4 in a pellet form were investigated in the frequency range of 102-106 Hz and temperature range of 293-356 K. The behavior of ac conductivity was interpreted by the correlated barrier hopping (CBH) model. Temperature dependence of ac conductivity indicates that ac conduction is a thermally activated process. The density of localized states N(EF) and ac activation energy were estimated for various frequencies. Dielectric constant and dielectric loss showed a decrease with increasing frequency and an increase with increasing in temperature. The frequency dependence of real and imaginary parts of the complex impedance was investigated. The relaxation time decreases with the increase in temperature. The impedance spectrum exhibits the appearance of the single semicircular arc. The radius of semicircular arcs decreases with increasing temperature which suggests a mechanism of temperature-dependent on relaxation.

Temperature sensitivity of ligand-gated ion channels: ryanodine receptor case

NASA Astrophysics Data System (ADS)

Iaparov, B. I.; Moskvin, A. S.; Solovyova, O. E.

2017-11-01

Temperature influences all biochemical processes, in particular, excitation-contraction coupling(ECC) in cardiac cells. In this work we propose a theoretical explanation of temperature effects on an isolated ryanodine receptor calcium release channel (RyR channel) within the electron-conformational (EC) model. We show that the EC model with an Arrhenius-like temperature dependence of the “internal” and “external” frictions and a specific thermosensitivity of the tunnelling “open ↔ closed” transitions can provide both qualitative and quantitative description of the temperature effects for isolated RyR channels. Interestingly that a small change of the activation energy for the “internal” friction can make an ion channel either heat-inhibited or heat-activated while the “external” friction doesn’t play a key role in temperature sensitivity: neglect of “external” friction doesn’t change the channel’s temperature sensitivity qualitatively.

Small within-day increases in temperature affects boldness and alters personality in coral reef fish.

PubMed

Biro, Peter A; Beckmann, Christa; Stamps, Judy A

2010-01-07

Consistent individual differences in behaviour, termed personality, are common in animal populations and can constrain their responses to ecological and environmental variation, such as temperature. Here, we show for the first time that normal within-daytime fluctuations in temperature of less than 3 degrees C have large effects on personality for two species of juvenile coral reef fish in both observational and manipulative experiments. On average, individual scores on three personality traits (PTs), activity, boldness and aggressiveness, increased from 2.5- to sixfold as a function of temperature. However, whereas most individuals became more active, aggressive and bold across temperature contexts (were plastic), others did not; this changed the individual rank order across temperatures and thus altered personality. In addition, correlations between PTs were consistent across temperature contexts, e.g. fish that were active at a given temperature also tended to be both bold and aggressive. These results (i) highlight the importance of very carefully controlling for temperature when studying behavioural variation among and within individuals and (ii) suggest that individual differences in energy metabolism may contribute to animal personality, given that temperature has large direct effects on metabolic rates in ectotherms.

Study on the optimum PCM melting temperature for energy savings in residential buildings worldwide

NASA Astrophysics Data System (ADS)

Saffari, M.; de Gracia, A.; Fernández, C.; Zsembinszki, G.; Cabeza, L. F.

2017-10-01

To maintain comfort conditions in residential buildings along a full year period, the use of active systems is generally required to either supply heating or cooling. The heating and cooling demands strongly depend on the climatic conditions, type of building and occupants’ behaviour. The overall annual energy consumption of the building can be reduced by the use of renewable energy sources and/or passive systems. The use of phase change materials (PCM) as passive systems in buildings enhances the thermal mass of the envelope, and reduces the indoor temperature fluctuations. As a consequence, the overall energy consumption of the building is generally lower as compared to the case when no PCM systems are used. The selection of the PCM melting temperature is a key issue to reduce the energy consumption of the buildings. The main focus of this study is to determine the optimum PCM melting temperature for passive heating and cooling according to different weather conditions. To achieve that, numerical simulations were carried out using EnergyPlus v8.4 coupled with GenOpt® v3.1.1 (a generic optimization software). A multi-family residential apartment was selected from ASHRAE Standard 90.1- 2013 prototype building model, and different climate conditions were considered to determine the optimum melting temperature (in the range from 20ºC to 26ºC) of the PCM contained in gypsum panels. The results confirm that the optimum melting temperature of the PCM strongly depends on the climatic conditions. In general, in cooling dominant climates the optimum PCM temperature is around 26ºC, while in heating dominant climates it is around 20ºC. Furthermore, the results show that an adequate selection of the PCM as passive system in building envelope can provide important energy savings for both heating dominant and cooling dominant regions.

Effect of gamma-ray irradiation on isothermal crystallization of biodegradable poly(ethylene succinate)

NASA Astrophysics Data System (ADS)

Chuang, Yu-Fan; Chou, Yu-Cheng; Yang, Fuqian; Lee, Sanboh

2016-09-01

The effects of gamma-ray irradiation on the isothermal crystallization of biodegradable poly(ethylene succinate) (PESu) and the growth behavior of PESu spherulites have been studied by differential scanning calorimetry and polarized optical microscopy. The irradiation doses used in the study are 0, 200, 400, and 600 kGy. The kinetic parameters for the isothermal crystallization have been determined, using the Avrami relationship. The nucleation constants and activation energy for the growth of the PESu spherulites have been analyzed, using the Lauritzen-Hoffman growth theory. Triple melting points have been observed for all the irradiated PESu. The gamma irradiation has no observable effect on the Avrami exponent, and the composite rate constant increases first with the increase of the crystallization temperature, reaches maximum at the crystallization temperature of 35 °C, and then decreases with the increase of the crystallization temperature for both the non-irradiated and irradiated PESu. There exists a transition of the growth of the PESu spherulites from regime II to regime III. Both the nucleation constants and activation energy increase with increasing the irradiation dose. The gamma irradiation increases the energy barrier for the migration of polymer chains.

Different behaviors in the transformation of PATP adsorbed on Ag or Au nanoparticles investigated by surface-enhanced Raman spectroscopy - A study of the effects from laser energy and annealing

NASA Astrophysics Data System (ADS)

Xu, Jian-Fang; Luo, Shi-Yi; Liu, Guo-Kun

2015-05-01

In order to explore the key role of surface plasmon resonance (SPR) and active 3O2 for the chemical transformation to 4,4-dimercaptoazobenzene (DMAB) from p-aminothiophenol (PATP) adsorbed on Ag or Au NPs, we systematically investigated the laser wavelength and temperature dependent surface-enhanced Raman spectra of PATP capped Ag and Au NPs. DMAB can be easily observed at the 514.5 nm laser for Ag NPs but at the 632.8 nm laser for Au NPs, indicating that a suitable energy level is necessary for the formation of DMAB. The tendency is consistent with the wavelength dependent SPR properties of Ag or Au NPs accordingly. With the energy provided by annealing, the transformation of PATP to DMAB is much easier on Ag NPs at a lower temperature, and more DMAB can be observed at the same temperature, compared to the case of Au NPs under the same condition. It is mainly due to the active 3O2 on Ag surfaces could be more easily formed than that on Au surfaces.

Effective moisture diffusivity and activation energy of rambutan seed under different drying methods to promote storage stability

NASA Astrophysics Data System (ADS)

Ahmad, So'bah; Shamsul Anuar, Mohd; Saleena Taip, Farah; Shamsudin, Rosnah; M, Siti Roha A.

2017-05-01

The effects of two drying methods, oven and microwave drying on the effective moisture diffusivity and activation energy of rambutan seed were studied. Effective moisture diffusivity and activation energy are the main indicators used for moisture movement within the material. Hence, it is beneficial to determine an appropriate drying method to attain a final moisture content of rambutan seed that potentially could be used as secondary sources in the industry. An appropriate final moisture content will provide better storage stability that can extend the lifespan of the rambutan seed. The rambutan seeds were dried with two drying methods (oven and microwave) at two level of the process variables (oven temperature; 40°C and 60°C and microwave power; 250W and 1000W) at constant initial moisture contents. The result showed that a higher value of effective moisture diffusivity and less activation energy were observed in microwave drying compared to oven drying. This finding portrays microwave drying expedites the moisture removal to achieve the required final moisture content and the most appropriate drying method for longer storage stability for rambutan seed. With respect to the process variables; higher oven temperatures and lower microwave powers also exhibit similar trends. Hopefully, this study would provide a baseline data to determine an appropriate drying method for longer storage period for turning waste to by-products.

Entropy-scaling laws for diffusion coefficients in liquid metals under high pressures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cao, Qi-Long, E-mail: qlcao@mail.ustc.edu.cn; Shao, Ju-Xiang; Wang, Fan-Hou, E-mail: eatonch@gmail.com

2015-04-07

Molecular dynamic simulations on the liquid copper and tungsten are used to investigate the empirical entropy-scaling laws D{sup *}=A exp(BS{sub ex}), proposed independently by Rosenfeld and Dzugutov for diffusion coefficient, under high pressure conditions. We show that the scaling laws hold rather well for them under high pressure conditions. Furthermore, both the original diffusion coefficients and the reduced diffusion coefficients exhibit an Arrhenius relationship D{sub M}=D{sub M}{sup 0} exp(−E{sub M}/K{sub B}T), (M=un,R,D) and the activation energy E{sub M} increases with increasing pressure, the diffusion pre-exponential factors (D{sub R}{sup 0} and D{sub D}{sup 0}) are nearly independent of the pressure and element. Themore » pair correlation entropy, S{sub 2}, depends linearly on the reciprocal temperature S{sub 2}=−E{sub S}/T, and the activation energy, E{sub S}, increases with increasing pressure. In particular, the ratios of the activation energies (E{sub un}, E{sub R}, and E{sub D}) obtained from diffusion coefficients to the activation energy, E{sub S}, obtained from the entropy keep constants in the whole pressure range. Therefore, the entropy-scaling laws for the diffusion coefficients and the Arrhenius law are linked via the temperature dependence of entropy.« less

Spectroscopic Evidence of Alfvén Wave Damping in the Off-limb Solar Corona

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gupta, G. R., E-mail: girjesh@iucaa.in

We investigate the off-limb active-region and quiet-Sun corona using spectroscopic data. The active region is clearly visible in several spectral lines formed in the temperature range of 1.1–2.8 MK. We derive the electron number density using the line ratio method, and the nonthermal velocity in the off-limb region up to the distance of 140 Mm. We compare density scale heights derived from several spectral line pairs with expected scale heights per the hydrostatic equilibrium model. Using several isolated and unblended spectral line profiles, we estimate nonthermal velocities in the active region and quiet Sun. Nonthermal velocities obtained from warm linesmore » in the active region first show an increase and then later either a decrease or remain almost constant with height in the far off-limb region, whereas nonthermal velocities obtained from hot lines show consistent decrease. However, in the quiet-Sun region, nonthermal velocities obtained from various spectral lines show either a gradual decrease or remain almost constant with height. Using these obtained parameters, we further calculate Alfvén wave energy flux in both active and quiet-Sun regions. We find a significant decrease in wave energy fluxes with height, and hence provide evidence of Alfvén wave damping. Furthermore, we derive damping lengths of Alfvén waves in the both regions and find them to be in the range of 25–170 Mm. Different damping lengths obtained at different temperatures may be explained as either possible temperature-dependent damping or by measurements obtained in different coronal structures formed at different temperatures along the line of sight. Temperature-dependent damping may suggest some role of thermal conduction in the damping of Alfvén waves in the lower corona.« less

Room Temperature, Hybrid Sodium-Based Flow Batteries with Multi-Electron Transfer Redox Reactions

PubMed Central

Shamie, Jack S.; Liu, Caihong; Shaw, Leon L.; Sprenkle, Vincent L.

2015-01-01

We introduce a new concept of hybrid Na-based flow batteries (HNFBs) with a molten Na alloy anode in conjunction with a flowing catholyte separated by a solid Na-ion exchange membrane for grid-scale energy storage. Such HNFBs can operate at ambient temperature, allow catholytes to have multiple electron transfer redox reactions per active ion, offer wide selection of catholyte chemistries with multiple active ions to couple with the highly negative Na alloy anode, and enable the use of both aqueous and non-aqueous catholytes. Further, the molten Na alloy anode permits the decoupled design of power and energy since a large volume of the molten Na alloy can be used with a limited ion-exchange membrane size. In this proof-of-concept study, the feasibility of multi-electron transfer redox reactions per active ion and multiple active ions for catholytes has been demonstrated. The critical barriers to mature this new HNFBs have also been explored. PMID:26063629

Room temperature, hybrid sodium-based flow batteries with multi-electron transfer redox reactions

DOE PAGES

Shamie, Jack S.; Liu, Caihong; Shaw, Leon L.; ...

2015-06-11

We introduce a new concept of hybrid Na-based flow batteries (HNFBs) with a molten Na alloy anode in conjunction with a flowing catholyte separated by a solid Na-ion exchange membrane for grid-scale energy storage. Such HNFBs can operate at ambient temperature, allow catholytes to have multiple electron transfer redox reactions per active ion, offer wide selection of catholyte chemistries with multiple active ions to couple with the highly negative Na alloy anode, and enable the use of both aqueous and non-aqueous catholytes. Further, the molten Na alloy anode permits the decoupled design of power and energy since a large volumemore » of the molten Na alloy can be used with a limited ion-exchange membrane size. In this proof-of-concept study, the feasibility of multielectron transfer redox reactions per active ion and multiple active ions for catholytes has been demonstrated. Furthermore, the critical barriers to mature this new HNFBs have also been explored.« less

Changes in Temperature Sensitivity and Activation Energy of Soil Organic Matter Decomposition in Different Qinghai-Tibet Plateau Grasslands.

PubMed

Li, Jie; He, Nianpeng; Wei, Xuehong; Gao, Yang; Zuo, Yao

2015-01-01

Qinghai-Tibet Plateau grasslands are unique geographical regions and store substantial soil organic matter (SOM) in the soil surface, which make them very sensitive to global climate change. Here, we focused on three main grassland types (alpine meadow, steppe, and desert) and conducted a soil incubation experiment at five different temperatures (5, 10, 15, 20, and 25°C) to investigate SOM decomposition rates (R), temperature sensitivity (Q10), and activation energy (Ea). The results showed that grassland type and incubation temperature had significant impact on R (P < 0.001), and the values of R were exponential correlated with incubation temperature in three alpine grasslands. At the same temperature, R was in the following order: alpine meadow > alpinesteppe > alpine desert. The Q10 values differed significantly among different grasslands, and the overall trends were as follows: alpine meadow (1.56 ± 0.09) < alpine steppe (1.88 ± 0.23) < alpine desert (2.39 ± 0.32). Moreover, the Ea values differed significantly across different grassland types (P < 0.001) and increased with increasing incubation time. The exponential negative correlations between Ea and R at 20°C across all grassland types (all Ps < 0.001) indicated that the substrate-quality temperature hypothesis is applicable to the alpine grasslands. Our findings provide new insights for understanding the responses of SOM decomposition and storage to warming scenarios in this Plateau.

Synthesis of charge transfer complex of chloranilic acid as acceptor with p-nitroaniline as donor: Crystallographic, UV-visible spectrophotometric and antimicrobial studies

NASA Astrophysics Data System (ADS)

Zulkarnain; Khan, Ishaat M.; Ahmad, Afaq; Miyan, Lal; Ahmad, Musheer; Azizc, Nafe

2017-08-01

The charge transfer interaction between p-nitroaniline (PNA) and chloranilic (CAA) acid was studied spectrophotometrically in methanol at different temperatures within the range 298-328 K. This experimental work explores the nature of charge-transfer interactions that play a significant role in chemistry and biology. Structure of synthesized charge transfer (CT) complex was investigated by different technique such as X-ray crystallography, FTIR, 1HNMR, UV-visible spectroscopy, XRD and TGA-DTA, which indicates the presence of N+sbnd Hrbd2bd O- bond between donor and acceptor moieties. Spectrophotometric studies of CT complexes were carried out in methanol at different temperatures to estimate thermodynamic parameters such as formation constant (KCT), molar absorptivity (εCT), free energy change (ΔG), enthalpy change (ΔH), resonance energy (RN), oscillator strength (f), transition dipole moment (μEN) and interaction energy (ECT) were also calculated. The effect of temperatures on all the parameters was studied in methanol. 1:1 stoichiometric of CT-complex was ascertained by Benesi-Hildebrand plots giving straight line, which are good agreement with other analysis. Synthesized CT complex was screened for its antimicrobial activity such as antibacterial activity against two gram-positive bacteria, Staphylococcus aureus and bacillus subtilis and two gram negative bacteria Escherichia coli and pseudomonas aeruginosa, and antifungal activity against fungi Fusarium oxysporum, and Aspergillus flavus.

Improved thermal stability of methylsilicone resins by compositing with N-doped graphene oxide/Co3O4 nanoparticles

NASA Astrophysics Data System (ADS)

Jiang, Bo; Zhao, Liwei; Guo, Jiang; Yan, Xingru; Ding, Daowei; Zhu, Changcheng; Huang, Yudong; Guo, Zhanhu

2016-06-01

Nanoparticles play important roles in enhancing the thermal-resistance of hosting polymer resins. Despite tremendous efforts, developing thermally stable methylsilicone resin at high temperatures is still a challenge. Herein, we report a strategy to increase the activation energy to slow down the decomposition/degradation of methylsilicone resin using synergistic effects between the Co3O4 nanoparticles and the nitrogen doped graphene oxide. The N-doped graphene oxides composited with Co3O4 nanoparticles were prepared by hydrolysis of cobalt nitrate hexahydrate in the presence of graphene oxide and were incorporated into the methylsilicone resin. Two-stage decompositions were observed, i.e., 200-300 and 400-500 °C. The activation energy for the low temperature region was enhanced by 47.117 kJ/mol (vs. 57.76 kJ/mol for pure resin). The enhanced thermal stability was due to the fact that the nanofillers prevented the silicone hydroxyl chain ends ``biting'' to delay the degradation. The activation energy for high-temperature region was enhanced by 11.585 kJ/mol (vs. 171.95 kJ/mol for pure resin). The nanofillers formed a protective layer to isolate oxygen from the hosting resin. The mechanism for the enhanced thermal stability through prohibited degradation with synergism of these nitrogen-doped graphene oxide nanocomposites was proposed as well.

Accelerated life testing effects on CMOS microcircuit characteristics

NASA Technical Reports Server (NTRS)

1980-01-01

This report covers the time period from May 1976 to December 1979 and encompasses the three phases of accelerated testing: Phase 1, the 250 C testing; Phase 2, the 200 C testing; and Phase 3, the 125 C testing. The duration of the test in Phase 1 and Phase 2 was sufficient to take the devices into the wear out region. The wear out distributions were used to estimate the activation energy between the 250 C and the 200 C test temperatures. The duration of the 125 C test, 20,000 hours, was not sufficient to bring the test devices into the wear out region; consequently the third data point at 125 C for determining the consistency of activation energy could not be obtained. It was estimated that, for the most complex of the three device types, the activation energy between 200 C and 125 C should be at least as high as that between 250 C and 200 C. The practicality of the use of high temperature for the accelerated life tests from the point of view of durability of equipment was assessed. Guidelines for the development of accelerated life test conditions were proposed. The use of the silicon nitride overcoat to improve the high temperature accelerated life test characteristics of CMOS microcircuits was explored in Phase 4 of this study and is attached as an appendix to this report.

Assessment of reduction behavior of hematite iron ore pellets in coal fines for application in sponge ironmaking

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar, M.; Patel, S.K.

2009-07-01

Studies on isothermal reduction kinetics (with F grade coal) in fired pellets of hematite iron ores, procured from four different mines of Orissa, were carried out in the temperature range of 850-1000C to provide information for the Indian sponge iron plants. The rate of reduction in all the fired iron ore pellets increased markedly with a rise of temperature up to 950C, and thereafter it decreased at 1000C. The rate was more intense in the first 30 minutes. All iron ores exhibited almost complete reduction in their pellets at temperatures of 900 and 950C in 2 hours' heating time duration,more » and the final product morphologies consisted of prominent cracks. The kinetic model equation 1-(1-a){sup 1/3}=kt was found to fit best to the experimental data, and the values of apparent activation energy were evaluated. Reductions of D. R. Pattnaik and M. G. Mohanty iron ore pellets were characterized by higher activation energies (183 and 150 kJ mol{sup -1}), indicating carbon gasification reaction to be the rate-controlling step. The results established lower values of activation energy (83 and 84 kJ mol{sup -1}) for the reduction of G. M. OMC Ltd. and Sakaruddin iron ore pellets, proposing their overall rates to be controlled by indirect reduction reactions.« less

Chemical vapour deposition growth of carbon nanotube forests: kinetics, morphology, composition, and their mechanisms

NASA Astrophysics Data System (ADS)

Vinten, Phillip

This thesis analyzes the chemical vapour deposition (CVD) growth of vertically aligned carbon nanotube (CNT) forests in order to understand how CNT forests grow, why they stop growing, and how to control the properties of the synthesized CNTs. in situ kinetics data of the growth of CNT forests are gathered by in situ optical microscopy. The overall morphology of the forests and the characteristics of the individual CNTs in the forests are investigated using scanning electron microscopy and Raman spectroscopy. The in situ data show that forest growth and termination are activated processes (with activation energies on the order of 1 eV), suggesting a possible chemical origin. The activation energy changes at a critical temperature for ethanol CVD (approximately 870°C). These activation energies and critical temperature are also seen in the temperature dependence of several important characteristics of the CNTs, including the defect density as determined by Raman spectroscopy. This observation is seen across several CVD processes and suggests a mechanism of defect healing. The CNT diameter also depends on the growth temperature. In this thesis, a thermodynamic model is proposed. This model predicts a temperature and pressure dependence of the CNT diameter from the thermodynamics of the synthesis reaction and the effect of strain on the enthalpy of formation of CNTs. The forest morphology suggests significant interaction between the constituent CNTs. These interactions may play a role in termination. The morphology, in particular a microscale rippling feature that is capable of diffracting light, suggest a non-uniform growth rate across the forest. A gas phase diffusion model predicts a non-uniform distribution of the source gas. This gas phase diffusion is suggested as a possible explanation for the non-uniform growth rate. The gas phase diffusion is important because growth by acetylene CVD is found to be very efficient (approximately 30% of the acetylene is converted to CNTs). It is seen that multiple mechanisms are active during CNT growth. The results of this thesis provide insight into both the basic understanding of the microscopic processes involved in CVD growth and how to control the properties of the synthesized CNTs.

Second Annual Progress Report on Radiation Tolerance of Controlled Fusion Welds in High Temperature Oxidation Resistant FeCrAl Alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Field, Kevin G.; Gussev, Maxim N.; Yamamoto, Yukinori

2016-12-30

The present report summarizes and discusses the current results and on-going activity towards developing a modern, nuclear grade FeCrAl alloy designed to have enhanced radiation tolerance and weldability under the Department of Energy (DOE) Nuclear Energy Enabling Technologies (NEET) program.

Thermal energy storage

NASA Technical Reports Server (NTRS)

1980-01-01

The planning and implementation of activities associated with lead center management role and the technical accomplishments pertaining to high temperature thermal energy storage subsystems are described. Major elements reported are: (1) program definition and assessment; (2) research and technology development; (3) industrial storage applications; (4) solar thermal power storage applications; and (5) building heating and cooling applications.

A New Exploration of the Torsional Energy Surface of N-Pentane Using Molecular Modeling Software

ERIC Educational Resources Information Center

Galembeck, Sergio E.; Caramori, Giovanni F.; Romero, Jose Ricardo

2005-01-01

The torsional potential energy surface of a chemical compounds, the accessible conformations at a specified temperature and the transition states that connect these confirmations establishes many chemical properties such as dynamic behavior, reactivity and biological activity. A conformational search of n-pentane is presented using computational…

Syntheses, Characterization and Kinetics of Nickel-Tungsten Nitride Catalysts for Hydrotreating of Gas Oil

NASA Astrophysics Data System (ADS)

Botchwey, Christian

This thesis summarizes the methods and major findings of Ni-W(P)/gamma-Al 2O3 nitride catalyst synthesis, characterization, hydrotreating activity, kinetic analysis and correlation of the catalysts' activities to their synthesis parameters and properties. The range of parameters for catalyst synthesis were W (15-40 wt%), Ni (0-8 wt%), P (0-5 wt%) and nitriding temperature (TN) (500-900 °C). Characterization techniques used included: N2 sorption studies, chemisorption, elemental analysis, temperature programmed studies, x-ray diffraction, scanning electron microscopy, energy dispersive x-ray, infrared spectroscopy, transmission electron microscopy and x-ray absorption near edge structure. Hydrodesulfurization (HDS), hydrodenitrogenation (HDN) and hydrodearomatization (HDA) were performed at: temperature (340-380 °C), pressure (6.2-9.0 MPa), liquid hourly space velocity (1-3 h-1) and hydrogen to oil ratio (600 ml/ml, STP). The predominant species on the catalyst surface were Ni3N, W2N and bimetallic Ni2W3N. The bimetallic Ni-W nitride species was more active than the individual activities of the Ni3N and W2N. P increased weak acid sites while nitriding temperature decreased amount of strong acid sites. Low nitriding temperature enhanced dispersion of metal particles. P interacted with Al 2O3 which increased the dispersion of metal nitrides on the catalyst surface. HDN activity increased with Ni and P loading but decreased with increase in nitriding temperature (optimum conversion; 60 wt%). HDS and HDA activities went through a maximum with increase in the synthesis parameters (optimum conversions; 88. wt% for HDS and 47 wt% for HDA). Increase in W loading led to increase in catalyst activity. The catalysts were stable to deactivation and had the nitride structure conserved during hydrotreating in the presence of hydrogen sulfide. The results showed good correlation between hydrotreating activities (HDS and HDN) and the catalyst nitrogen content, number of exposed active sites, catalyst particle size and BET surface area. HDS and HDN kinetic analyses, using Langmuir-Hinshelwood models, gave activation energies of 66 and 32 kJ/mol, respectively. There were no diffusion limitations in the reaction process. Two active sites were involved in HDS reaction while one site was used for HDN. HDS and HDN activities of the Ni-W(P)/gamma-Al 2O3 nitride catalysts were comparable to the corresponding sulfides.

Temperature dependence of the distribution of the thermally activated energy barriers in Tl2Ba2CaCu2O8 film

NASA Astrophysics Data System (ADS)

Ren, C.; Lin, F. Y.; Ding, S. Y.; Li, Z. M.; Aruna, S. A.; Qiu, L.; Yao, X. X.; Yan, S. L.; Si, M. S.

1999-06-01

The effects of frequency and ac amplitude on ac susceptibility have been measured for a thin Tl2Ba2CaCu2O8 film in the range 100 Hz-100 kHz in magnetic field 0.52 T. A phenomenological equation with an asymmetrical distribution of thermally activated energy barriers has been used to analyse these frequency and amplitude dependences of the ac susceptibility icons/Journals/Common/chi" ALT="chi" ALIGN="TOP"/>(icons/Journals/Common/omega" ALT="omega" ALIGN="TOP"/>,hac) in the vicinity of the peak temperature of icons/Journals/Common/chi" ALT="chi" ALIGN="TOP"/>´´. We obtain the effective energy barrier U against amplitude hac (current density j): Uicons/Journals/Common/propto" ALT="propto" ALIGN="TOP"/> hac-0.38. This U(j) relationship shows that the flux lines are in the 3D collective creep regime. Therefore, we conclude that the effective energy barrier is in fact an average of the barrier's distribution, and the distribution function is a distinguished asymmetrical one in this 3D collective creep regime.

Phase field crystal simulation of stress induced localized solid-state amorphization in nanocrystalline materials

NASA Astrophysics Data System (ADS)

Xi, Wen; Song, Xiaoqing; Hu, Shi; Chen, Zheng

2017-11-01

In this work, the phase field crystal (PFC) method is used to study the localized solid-state amorphization (SSA) and its dynamic transformation process in polycrystalline materials under the uniaxial tensile deformation with different factors. The impacts of these factors, including strain rates, temperatures and grain sizes, are analyzed. Kinetically, the ultra-high strain rate causes the lattice to be seriously distorted and the grain to gradually collapse, so the dislocation density rises remarkably. Therefore, localized SSA occurs. Thermodynamically, as high temperature increases the activation energy, the atoms are active and prefer to leave the original position, which induce atom rearrangement. Furthermore, small grain size increases the percentage of grain boundary and the interface free energy of the system. As a result, Helmholtz free energy increases. The dislocations and Helmholtz free energy act as the seed and driving force for the process of the localized SSA. Also, the critical diffusion-time step and the percentage of amorphous region areas are calculated. Through this work, the PFC method is proved to be an effective means to study localized SSA under uniaxial tensile deformation.

Phase field crystal simulation of stress induced localized solid-state amorphization in nanocrystalline materials.

PubMed

Xi, Wen; Song, Xiaoqing; Hu, Shi; Chen, Zheng

2017-11-29

In this work, the phase field crystal (PFC) method is used to study the localized solid-state amorphization (SSA) and its dynamic transformation process in polycrystalline materials under the uniaxial tensile deformation with different factors. The impacts of these factors, including strain rates, temperatures and grain sizes, are analyzed. Kinetically, the ultra-high strain rate causes the lattice to be seriously distorted and the grain to gradually collapse, so the dislocation density rises remarkably. Therefore, localized SSA occurs. Thermodynamically, as high temperature increases the activation energy, the atoms are active and prefer to leave the original position, which induce atom rearrangement. Furthermore, small grain size increases the percentage of grain boundary and the interface free energy of the system. As a result, Helmholtz free energy increases. The dislocations and Helmholtz free energy act as the seed and driving force for the process of the localized SSA. Also, the critical diffusion-time step and the percentage of amorphous region areas are calculated. Through this work, the PFC method is proved to be an effective means to study localized SSA under uniaxial tensile deformation.

Arrhenius plot for a reaction catalyzed by a single molecule of β-galactosidase.

PubMed

Craig, Douglas B; Chase, Linden N

2012-02-21

The activity of a single enzyme molecule of Escherichia coli β-galactosidase was measured using a capillary electrophoresis continuous flow assay. As the enzyme molecule traversed the capillary the incubation temperature was increased from 27 to 37 °C, providing a continuous record of the change in rate with temperature. This data was used to develop a single enzyme molecule Arrhenius plot, from which the activation energy of the reaction was determined to be 31 kJ mol(-1).

Darcy-Forchheimer flow of Maxwell nanofluid flow with nonlinear thermal radiation and activation energy

NASA Astrophysics Data System (ADS)

Sajid, T.; Sagheer, M.; Hussain, S.; Bilal, M.

2018-03-01

The present article is about the study of Darcy-Forchheimer flow of Maxwell nanofluid over a linear stretching surface. Effects like variable thermal conductivity, activation energy, nonlinear thermal radiation is also incorporated for the analysis of heat and mass transfer. The governing nonlinear partial differential equations (PDEs) with convective boundary conditions are first converted into the nonlinear ordinary differential equations (ODEs) with the help of similarity transformation, and then the resulting nonlinear ODEs are solved with the help of shooting method and MATLAB built-in bvp4c solver. The impact of different physical parameters like Brownian motion, thermophoresis parameter, Reynolds number, magnetic parameter, nonlinear radiative heat flux, Prandtl number, Lewis number, reaction rate constant, activation energy and Biot number on Nusselt number, velocity, temperature and concentration profile has been discussed. It is viewed that both thermophoresis parameter and activation energy parameter has ascending effect on the concentration profile.

Energy data report: Solar collector manufacturing activity, July - December 1980

NASA Astrophysics Data System (ADS)

1981-03-01

Statistics on solar collector manufacturing activity for both solar thermal collectors and photovoltaic modules through 1980 are presented. Summary data are given for the number of manufacturers and collector area produced each year from 1974 through 1980; data for collector type are included, i.e., low temperature or medium temperature and special collectors. Producer shipments are tabulated according to location of company headquarters, producer size, and collector types. headquarters The number of companies engaged in activities related to solar collector manufacturing for 1978 through 1980 are listed; and the number of manufacturers and market sector are tabulated for photovoltaic modules manufacturing activities.

18F-FDG uptake in the colon is modulated by metformin but not associated with core body temperature and energy expenditure

PubMed Central

Bahler, Lonneke; Holleman, Frits; Chan, Man-Wai; Booij, Jan; Hoekstra, Joost B.; Verberne, Hein J.

2017-01-01

Purpose Physiological colonic 18F-fluorodeoxyglucose (18F-FDG) uptake is a frequent finding on 18F-FDG positron emission tomography computed tomography (PET-CT). Interestingly, metformin, a glucose lowering drug associated with moderate weight loss, is also associated with an increased colonic 18F-FDG uptake. Consequently, increased colonic glucose use might partly explain the weight losing effect of metformin when this results in an increased energy expenditure and/or core body temperature. Therefore, we aimed to determine whether metformin modifies the metabolic activity of the colon by increasing glucose uptake. Methods In this open label, non-randomized, prospective mechanistic study, we included eight lean and eight overweight males. We measured colonic 18F-FDG uptake on PET-CT, energy expenditure and core body temperature before and after the use of metformin. The maximal colonic 18F-FDG uptake was measured in 5 separate segments (caecum, colon ascendens,—transversum,—descendens and sigmoid). Results The maximal colonic 18F-FDG uptake increased significantly in all separate segments after the use of metformin. There was no significant difference in energy expenditure or core body temperature after the use of metformin. There was no correlation between maximal colonic 18F-FDG uptake and energy expenditure or core body temperature. Conclusion Metformin significantly increases colonic 18F-FDG uptake, but this increased uptake is not associated with an increase in energy expenditure or core body temperature. Although the colon might be an important site of the glucose plasma lowering actions of metformin, this mechanism of action does not explain directly any associated weight loss. PMID:28464031

Stereodynamical Origin of Anti-Arrhenius Kinetics: Negative Activation Energy and Roaming for a Four-Atom Reaction.

PubMed

Coutinho, Nayara D; Silva, Valter H C; de Oliveira, Heibbe C B; Camargo, Ademir J; Mundim, Kleber C; Aquilanti, Vincenzo

2015-05-07

The OH + HBr → H2O + Br reaction, prototypical of halogen-atom liberating processes relevant to mechanisms for atmospheric ozone destruction, attracted frequent attention of experimental chemical kinetics: the nature of the unusual reactivity drop from low to high temperatures eluded a variety of theoretical efforts, ranking this one among the most studied four-atom reactions. Here, inspired by oriented molecular-beams experiments, we develop a first-principles stereodynamical approach. Thermalized sets of trajectories, evolving on a multidimensional potential energy surface quantum mechanically generated on-the-fly, provide a map of most visited regions at each temperature. Visualizations of rearrangements of bonds along trajectories and of the role of specific angles of reactants' mutual approach elucidate the mechanistic change from the low kinetic energy regime (where incident reactants reorient to find the propitious alignment leading to reaction) to high temperature (where speed hinders adjustment of directionality and roaming delays reactivity).

Karasek Home, Blackstone, Massachusetts solar-energy-system performance evaluation, Nov. 1981 - Mar. 1982

NASA Astrophysics Data System (ADS)

Raymond, M.

1982-06-01

The Karasek Home is a single family Massachusetts residence whose active-solar-energy system is equipped with 640 square feet of trickle-down liquid flat-plate collectors, storage in a 300-gallon tank and a 2000-gallon tank embedded in a rock bin in the basement, and an oil-fired glass-lined 40-gallon domestic hot water tank for auxiliary water and space heating. Monthly performance data are tabulated for the overall system and for the collector, storage, space heating, and domestic hot water subsystems. For each month a graph is presented of collector array efficiency versus the difference between the inlet water temperature and ambient temperature divided by insolation. Typical system operation is illustrated by graphs of insolation and temperatures at different parts of the system versus time for a typical day. The typical system operating sequence for a day is also graphed as well as solar energy utilization and heat losses.

Impact of long-term moderate hypercapnia and elevated temperature on the energy budget of isolated gills of Atlantic cod (Gadus morhua).

PubMed

Kreiss, Cornelia M; Michael, Katharina; Bock, Christian; Lucassen, Magnus; Pörtner, Hans-O

2015-04-01

Effects of severe hypercapnia have been extensively studied in marine fishes, while knowledge on the impacts of moderately elevated CO2 levels and their combination with warming is scarce. Here we investigate ion regulation mechanisms and energy budget in gills from Atlantic cod acclimated long-term to elevated PCO2 levels (2500 μatm) and temperature (18°C). Isolated perfused gill preparations were established to determine gill thermal plasticity during acute exposures (10-22°C) and in vivo costs of Na(+)/K(+)-ATPase activity, protein and RNA synthesis. Maximum enzyme capacities of F1Fo-ATPase, H(+)-ATPase and Na(+)/K(+)-ATPase were measured in vitro in crude gill homogenates. After whole animal acclimation to elevated PCO2 and/or warming, branchial oxygen consumption responded more strongly to acute temperature change. The fractions of gill respiration allocated to protein and RNA synthesis remained unchanged. In gills of fish CO2-exposed at both temperatures, energy turnover associated with Na(+)/K(+)-ATPase activity was reduced by 30% below rates of control fish. This contrasted in vitro capacities of Na(+)/K(+)-ATPase, which remained unchanged under elevated CO2 at 10°C, and earlier studies which had found a strong upregulation under severe hypercapnia. F1Fo-ATPase capacities increased in hypercapnic gills at both temperatures, whereas Na(+)/K(+)ATPase and H(+)-ATPase capacities only increased in response to elevated CO2 and warming indicating the absence of thermal compensation under CO2. We conclude that in vivo ion regulatory energy demand is lowered under moderately elevated CO2 levels despite the stronger thermal response of total gill respiration and the upregulation of F1Fo-ATPase. This effect is maintained at elevated temperature. Copyright © 2014 Elsevier Inc. All rights reserved.

Comparative study of energy-transducing properties of cytoplasmic membranes from mesophilic and thermophilic Bacillus species.

PubMed Central

De Vrij, W; Bulthuis, R A; Konings, W N

1988-01-01

The properties of enzymes involved in energy transduction from a mesophilic (Bacillus subtilis) and a thermophilic (B. stearothermophilus) bacterium were compared. Membrane preparations of the two organisms contained dehydrogenases for NADH, succinate, L-alpha-glycerophosphate, and L-lactate. Maximum NADH and cytochrome c oxidation rates were obtained at the respective growth temperatures of the two bacteria. The enzymes involved in the oxidation reactions in membranes of the thermophilic species were more thermostable than those of the mesophilic species. The apparent microviscosities of the two membrane preparations were studied at different temperatures. At the respective optimal growth temperatures, the apparent microviscosities of the membranes of the two organisms were remarkably similar. The transition from the gel to the liquid-crystalline state occurred at different temperatures in the two species. In the two species, the oxidation of physiological (NADH) and nonphysiological (N,N,N',N'-tetramethyl-p-phenylenediamine or phenazine methosulfate) electron donors led to generation of a proton motive force which varied strongly with temperature. At increasing temperatures, the efficiency of energy transduction declined because of increasing H+ permeability. At the growth temperature, the efficiency of energy transduction was lower in B. stearothermophilus than in the mesophilic species. Extremely high respiratory activities enabled B. stearothermophilus to maintain a high proton motive force at elevated temperatures. The pH dependence of proton motive force generation appeared to be similar in the two membrane preparations. The highest proton motive forces were generated at low external pH, mainly because of a high pH gradient. At increasing external pH, the proton motive force declined. PMID:2834342

Studies on biomass char gasification and dynamics

NASA Astrophysics Data System (ADS)

You, Zhanping; You, Shijun; Ma, Xiaoyan

2018-01-01

The gasification performances of two kinds of biomass char by experiment methods are studied, including conversion rate and gasification gas component with temperature and time. Experimental results show that gasification temperature has important effects on the conversion rate and gas component. In the range of experimental temperature, char conversion rates are no more than 30.0%. The apparent activation energies and apparent reaction frequency factors of two biomass chars are obtained through kinetic studies.

Kinetic Analysis of the Main Temperature Stage of Fast Pyrolysis

NASA Astrophysics Data System (ADS)

Yang, Xiaoxiao; Zhao, Yuying; Xu, Lanshu; Li, Rui

2017-10-01

Kinetics of the thermal decomposition of eucalyptus chips was evaluated using a high-rate thermogravimetric analyzer (BL-TGA) designed by our research group. The experiments were carried out under non-isothermal condition in order to determine the fast pyrolysis behavior of the main temperature stage (350-540ºC) at heating rates of 60, 120, 180, and 360ºC min-1. The Coats-Redfern integral method and four different reaction mechanism models were adopted to calculate the kinetic parameters including apparent activation energy and pre-exponential factor, and the Flynn-Wall-Ozawa method was employed to testify apparent activation energy. The results showed that estimation value was consistent with the values obtained by linear fitting equations, and the best-fit model for fast pyrolysis was found.

Influence of the growth method on degradation of InGaN laser diodes

NASA Astrophysics Data System (ADS)

Bojarska, Agata; Muzioł, Grzegorz; Skierbiszewski, Czesław; Grzanka, Ewa; Wiśniewski, Przemysław; Makarowa, Irina; Czernecki, Robert; Suski, Tadek; Perlin, Piotr

2017-09-01

We demonstrate the influence of the operation current density and temperature on the degradation rate of InGaN laser diodes grown via metalorganic vapor-phase epitaxy (MOVPE) and plasma-assisted molecular beam epitaxy (PAMBE). The degradation rate of the MOVPE devices shows an exponential dependence on the temperature, with an activation energy of 0.38-0.43 eV, and a linear dependence on the operating current density. In comparison, the MBE-grown lasers exhibit a higher activation energy, on the order of 1 eV, and typically a lower degradation rate, resulting in a service time exceeding 50,000 h. We suggest that this difference may be related to the lower concentration of H in the Mg-doped MBE-grown GaN.

Enhancing the stability of copper chromite catalysts for the selective hydrogenation of furfural using ALD overcoating

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Hongbo; Lei, Yu; Kropf, A. Jeremy

2014-08-01

The stability of a gas-phase furfural hydrogenation catalyst (CuCr2O4 center dot CuO) was enhanced by depositing a thin Al2O3 layer using atomic layer deposition (ALD). Based on temperature-programed reduction (TPR) measurements, the reduction temperature of Cu was raised significantly, and the activation energy for furfural reduction was decreased following the ALD treatment. Thinner ALD layers yielded higher furfural hydrogenation activities. X-ray absorption fine structure (XAFS) spectroscopy studies indicated that Cu1+/Cu-0 are the active species for furfural reduction.

Thermally Stimulated Currents in Nanocrystalline Titania

PubMed Central

Bruzzi, Mara; Mori, Riccardo; Baldi, Andrea; Cavallaro, Alessandro; Scaringella, Monica

2018-01-01

A thorough study on the distribution of defect-related active energy levels has been performed on nanocrystalline TiO2. Films have been deposited on thick-alumina printed circuit boards equipped with electrical contacts, heater and temperature sensors, to carry out a detailed thermally stimulated currents analysis on a wide temperature range (5–630 K), in view to evidence contributions from shallow to deep energy levels within the gap. Data have been processed by numerically modelling electrical transport. The model considers both free and hopping contribution to conduction, a density of states characterized by an exponential tail of localized states below the conduction band and the convolution of standard Thermally Stimulated Currents (TSC) emissions with gaussian distributions to take into account the variability in energy due to local perturbations in the highly disordered network. Results show that in the low temperature range, up to 200 K, hopping within the exponential band tail represents the main contribution to electrical conduction. Above room temperature, electrical conduction is dominated by free carriers contribution and by emissions from deep energy levels, with a defect density ranging within 1014–1018 cm−3, associated with physio- and chemi-sorbed water vapour, OH groups and to oxygen vacancies. PMID:29303976

Thermally Stimulated Currents in Nanocrystalline Titania.

PubMed

Bruzzi, Mara; Mori, Riccardo; Baldi, Andrea; Carnevale, Ennio Antonio; Cavallaro, Alessandro; Scaringella, Monica

2018-01-05

A thorough study on the distribution of defect-related active energy levels has been performed on nanocrystalline TiO₂. Films have been deposited on thick-alumina printed circuit boards equipped with electrical contacts, heater and temperature sensors, to carry out a detailed thermally stimulated currents analysis on a wide temperature range (5-630 K), in view to evidence contributions from shallow to deep energy levels within the gap. Data have been processed by numerically modelling electrical transport. The model considers both free and hopping contribution to conduction, a density of states characterized by an exponential tail of localized states below the conduction band and the convolution of standard Thermally Stimulated Currents (TSC) emissions with gaussian distributions to take into account the variability in energy due to local perturbations in the highly disordered network. Results show that in the low temperature range, up to 200 K, hopping within the exponential band tail represents the main contribution to electrical conduction. Above room temperature, electrical conduction is dominated by free carriers contribution and by emissions from deep energy levels, with a defect density ranging within 10 14 -10 18 cm -3 , associated with physio- and chemi-sorbed water vapour, OH groups and to oxygen vacancies.

A hypothalamic circuit that controls body temperature.

PubMed

Zhao, Zheng-Dong; Yang, Wen Z; Gao, Cuicui; Fu, Xin; Zhang, Wen; Zhou, Qian; Chen, Wanpeng; Ni, Xinyan; Lin, Jun-Kai; Yang, Juan; Xu, Xiao-Hong; Shen, Wei L

2017-02-21

The homeostatic control of body temperature is essential for survival in mammals and is known to be regulated in part by temperature-sensitive neurons in the hypothalamus. However, the specific neural pathways and corresponding neural populations have not been fully elucidated. To identify these pathways, we used cFos staining to identify neurons that are activated by a thermal challenge and found induced expression in subsets of neurons within the ventral part of the lateral preoptic nucleus (vLPO) and the dorsal part of the dorsomedial hypothalamus (DMD). Activation of GABAergic neurons in the vLPO using optogenetics reduced body temperature, along with a decrease in physical activity. Optogenetic inhibition of these neurons resulted in fever-level hyperthermia. These GABAergic neurons project from the vLPO to the DMD and optogenetic stimulation of the nerve terminals in the DMD also reduced body temperature and activity. Electrophysiological recording revealed that the vLPO GABAergic neurons suppressed neural activity in DMD neurons, and fiber photometry of calcium transients revealed that DMD neurons were activated by cold. Accordingly, activation of DMD neurons using designer receptors exclusively activated by designer drugs (DREADDs) or optogenetics increased body temperature with a strong increase in energy expenditure and activity. Finally, optogenetic inhibition of DMD neurons triggered hypothermia, similar to stimulation of the GABAergic neurons in the vLPO. Thus, vLPO GABAergic neurons suppressed the thermogenic effect of DMD neurons. In aggregate, our data identify vLPO→DMD neural pathways that reduce core temperature in response to a thermal challenge, and we show that outputs from the DMD can induce activity-induced thermogenesis.

Hybrid Perovskite Phase Transition and Its Ionic, Electrical and Optical Properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hoque, Md Nadim Ferdous; Islam, Nazifah; Zhu, Kai

Hybrid perovskite solar cells (PSCs) under normal operation will reach a temperature above ~ 60 °C, across the tetragonal-cubic structural phase transition of methylammonium lead iodide (MAPbI 3). Whether the structural phase transition could result in dramatic changes of ionic, electrical and optical properties that may further impact the PSC performances should be studied. Herein, we report a structural phase transition temperature of MAPbI 3thin film at ~ 55 °C, but a striking contrast occurred at ~ 45 °C in the ionic and electrical properties of MAPbI 3due to a change of the ion activation energy from 0.7 eV tomore » 0.5 eV. The optical properties exhibited no sharp transition except for the steady increase of the bandgap with temperature. It was also observed that the activation energy for ionic migration steadily increased with increased grain sizes, and reduction of the grain boundary density reduced the ionic migration.« less

Drying kinetics of onion ( Allium cepa L.) slices with convective and microwave drying

NASA Astrophysics Data System (ADS)

Demiray, Engin; Seker, Anıl; Tulek, Yahya

2017-05-01

Onion slices were dried using two different drying techniques, convective and microwave drying. Convective drying treatments were carried out at different temperatures (50, 60 and 70 °C). Three different microwave output powers 328, 447 and 557 W were used in microwave drying. In convective drying, effective moisture diffusivity was estimated to be between 3.49 × 10-8 and 9.44 × 10-8 m2 s-1 within the temperature range studied. The effect of temperature on the diffusivity was described by the Arrhenius equation with an activation energy of 45.60 kJ mol-1. At increasing microwave power values, the effective moisture diffusivity values ranged from 2.59 × 10-7 and 5.08 × 10-8 m2 s-1. The activation energy for microwave drying of samples was calculated using an exponential expression based on Arrhenius equation. Among of the models proposed, Page's model gave a better fit for all drying conditions used.

Temperature-dependent field-effect carrier mobility in organic thin-film transistors with a gate SiO2 dielectric modified by H2O2 treatment

NASA Astrophysics Data System (ADS)

Lin, Yow-Jon; Hung, Cheng-Chun

2018-02-01

The effect of the modification of a gate SiO2 dielectric using an H2O2 solution on the temperature-dependent behavior of carrier transport for pentacene-based organic thin-film transistors (OTFTs) is studied. H2O2 treatment leads to the formation of Si(-OH) x (i.e., the formation of a hydroxylated layer) on the SiO2 surface that serves to reduce the SiO2 capacitance and weaken the pentacene-SiO2 interaction, thus increasing the field-effect carrier mobility ( µ) in OTFTs. The temperature-dependent behavior of carrier transport is dominated by the multiple trapping model. Note that H2O2 treatment leads to a reduction in the activation energy. The increased value of µ is also attributed to the weakening of the interactions of the charge carriers with the SiO2 dielectric that serves to reduce the activation energy.

CdS quantum dots in a novel glass with a very low activation energy and its variation of diffusivity with temperature

NASA Astrophysics Data System (ADS)

Nagpal, Swati

2011-07-01

CdS quantum dots of different average sizes in the range 2 to 3.8 nm were grown by diffusion-limited growth process in indigenously made silicate glass. The absorption spectra showed a strong quantum confinement effect with a blue shift of the order of 500 meV depending on the average size. Critical radius of quantum dots was found to be 1.8 nm. The size dispersion decreased from 15.2 to 12.5% with a 20% increase in the particle size. The activation energy for diffusion was found to be very low i.e. 193 kJ mol-1 and the diffusion coefficient increased by 60% for 10 K rise in temperature. The PL emission spectra showed the presence of only deep traps around 600 nm with a red shift of 200 nm. No shallow traps or band edge emission was observed. The PL peak position changed from 560 to 640 nm with a 35 K increase in annealing temperature.

Investigating pyrolysis characteristics of moso bamboo through TG-FTIR and Py-GC/MS.

PubMed

Liang, Fang; Wang, Ruijuan; Hongzhong, Xiang; Yang, Xiaomeng; Zhang, Tao; Hu, Wanhe; Mi, Bingbing; Liu, Zhijia

2018-05-01

This study was carried out to investigate pyrolysis characteristics of moso bamboo (Phyllostachys pubescens), including outer layer (OB), middle layer (MB) and inner layer (IB) and bamboo leaves (BL), through TG-FTIR and Py-GC/MS. The results showed that 70% of weight loss occurred at rapid pyrolysis stage with temperature of 200-400 °C. With increase in heating rate, pyrolysis process shifted toward higher temperature. IB, OB, MB and BL had a different activation energy at different conversion rates. BL had a higher activation energy than IB, OB and MB. The volatiles of bamboo was complicated with 2-30 of C atoms. IB, OB and MB mainly released benzofuran, hydroxyacetaldehyde and 2-Pentanone. BL released furan, acetic acid and phenol. The main pyrolysis products included H 2 O, CH 4 , CO 2 , CO, carboxylic acids, NO, NO 2 . Pyrolysis products of IB was the most and that of BL was the lowest. MB had the lowest pyrolysis temperature. Copyright © 2018 Elsevier Ltd. All rights reserved.

Novel localized heating technique on centrifugal microfluidic disc with wireless temperature monitoring system.

PubMed

Joseph, Karunan; Ibrahim, Fatimah; Cho, Jongman

2015-01-01

Recent advances in the field of centrifugal microfluidic disc suggest the need for electrical interface in the disc to perform active biomedical assays. In this paper, we have demonstrated an active application powered by the energy harvested from the rotation of the centrifugal microfluidic disc. A novel integration of power harvester disc onto centrifugal microfluidic disc to perform localized heating technique is the main idea of our paper. The power harvester disc utilizing electromagnetic induction mechanism generates electrical energy from the rotation of the disc. This contributes to the heat generation by the embedded heater on the localized heating disc. The main characteristic observed in our experiment is the heating pattern in relative to the rotation of the disc. The heating pattern is monitored wirelessly with a digital temperature sensing system also embedded on the disc. Maximum temperature achieved is 82 °C at rotational speed of 2000 RPM. The technique proves to be effective for continuous heating without the need to stop the centrifugal motion of the disc.

Effect of atomic order on the martensitic and magnetic transformations in Ni-Mn-Ga ferromagnetic shape memory alloys.

PubMed

Sánchez-Alarcos, V; Pérez-Landazábal, J I; Recarte, V; Rodríguez-Velamazán, J A; Chernenko, V A

2010-04-28

The influence of long-range L2(1) atomic order on the martensitic and magnetic transformations of Ni-Mn-Ga shape memory alloys has been investigated. In order to correlate the structural and magnetic transformation temperatures with the atomic order, calorimetric, magnetic and neutron diffraction measurements have been performed on polycrystalline and single-crystalline alloys subjected to different thermal treatments. It is found that both transformation temperatures increase with increasing atomic order, showing exactly the same linear dependence on the degree of L2(1) atomic order. A quantitative correlation between atomic order and transformation temperatures has been established, from which the effect of atomic order on the relative stability between the structural phases has been quantified. On the other hand, the kinetics of the post-quench ordering process taking place in these alloys has been studied. It is shown that the activation energy of the ordering process agrees quite well with the activation energy of the Mn self-diffusion process.

The crossover between tunnel and hopping conductivity in granulated films of noble metals

NASA Astrophysics Data System (ADS)

Kavokin, Alexey; Kutrovskaya, Stella; Kucherik, Alexey; Osipov, Anton; Vartanyan, Tigran; Arakelyan, Sergey

2017-11-01

The conductivity of thin films composed by clusters of gold and silver nanoparticles has been studies in a wide range of temperatures. The switch from a temperature independence to an exponential thermal dependence of the conductivity manifests the crossover between the tunnel and thermally activated hopping regimes of the electronic transport at the temperature of 60 °C. The characteristic thermal activation energy that governs hopping of electrons between nanoparticles is estimated as 1.3 eV. We have achieved a good control of the composition and thicknesses of nano-cluster films by use of the laser ablation method in colloidal solutions.

Strontium cobaltite oxygen sponge catalyst and methods of use

DOEpatents

Lee, Ho Nyung; Jeen, Hyoungjeen; Choi, Woo Seok; Biegalski, Michael; Folkman, Chad M.; Tung, I-Cheng; Fong, Dillon D.; Freeland, John W.; Shin, Dongwon; Ohta, Hiromichi; Chisholm, Matthew F.

2017-01-24

Rapid, reversible redox activity may be accomplished at significantly reduced temperatures, as low as about 200.degree. C., from epitaxially stabilized, oxygen vacancy ordered SrCoO.sub.2.5 and thermodynamically unfavorable perovskite SrCoO.sub.3-.delta.. The fast, low temperature redox activity in SrCoO.sub.3-.delta. may be attributed to a small Gibbs free energy difference between the two topotactic phases. Epitaxially stabilized thin films of strontium cobaltite provide a catalyst adapted to rapidly transition between oxidation states at substantially low temperatures. Methods of transitioning a strontium cobaltite catalyst from a first oxidation state to a second oxidation state are described.

A ratiometric fluorescent molecular probe for visualization of mitochondrial temperature in living cells.

PubMed

Homma, Mitsumasa; Takei, Yoshiaki; Murata, Atsushi; Inoue, Takafumi; Takeoka, Shinji

2015-04-11

Mitochondrial thermodynamics is the key to understand cellular activities related to homeostasis and energy balance. Here, we report the first ratiometric fluorescent molecular probe (Mito-RTP) that is selectively localized in the mitochondria and visualize the temperature. We confirmed that Mito-RTP could work as a ratiometric thermometer in a cuvette and living cells.

Responses of plant growth and metabolism to environmental variables predicted from laboratory measurements

Treesearch

Lee D. Hansen; Bruce N. Smith; Richard S. Criddle; J. N. Church

2001-01-01

The Arrhenius activation energies, and therefore temperature coefficients, for rates of catabolic production of ATP and for anabolic use of ATP differ. Because the intracellular concentration of ATP and the phosphorylation potential must be controlled within a narrow range for cell survival, a mechanism must exist to balance these rates during temperature variation in...

Ferroelectric properties and polarization dynamics in Ba{sub 4}Sm{sub 2}Ti{sub 4}Ta{sub 6}O{sub 30} tungsten bronze ceramics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, Xiao Li, E-mail: xiaolizi0618@zju.edu.cn; Chen, Xiang Ming

2016-04-11

Ferroelectricity and polarization reversal dynamics in Ba{sub 4}Sm{sub 2}Ti{sub 4}Ta{sub 6}O{sub 30} tungsten bronze ceramics were investigated by measuring dielectric spectra and the evolution of hysteresis loops over a wide temperature range. With decreasing temperature, the dielectric properties and differential scanning calorimetry results showed diffuse peaks at ∼280 K with large thermal hysteresis, suggesting a first order ferroelectric transition. A dielectric relaxation was observed at low temperature that followed the Vogel–Fulcher relationship. The saturation and remanent polarizations of the Ba{sub 4}Sm{sub 2}Ti{sub 4}Ta{sub 6}O{sub 30} ceramics showed remarkable dependence on the applied field and temperature. The temperature dependence of the coercivemore » field was divided into three linear regions and fitted to the Vopsaroiu model. Activation energies for polarization reversal of 0.73, 0.79, and 0.65 eV were determined for the following three regions: (I) the diffuse ferroelectric transition region (323.15–293.15 K), (II) the region just below the ferroelectric transition temperature (293.15–233.15 K), and (III) the low temperature relaxation region (233.15–173.15 K), respectively. The decrease of the activation energy in region III was attributed to the low temperature relaxation of Ba{sub 4}Sm{sub 2}Ti{sub 4}Ta{sub 6}O{sub 30}.« less

The Effect of Temperature on Kinetics and Diffusion Coefficients of Metallocene Derivatives in Polyol-Based Deep Eutectic Solvents

PubMed Central

Bahadori, Laleh; Chakrabarti, Mohammed Harun; Manan, Ninie Suhana Abdul; Hashim, Mohd Ali; Mjalli, Farouq Sabri; AlNashef, Inas Muen; Brandon, Nigel

2015-01-01

The temperature dependence of the density, dynamic viscosity and ionic conductivity of several deep eutectic solvents (DESs) containing ammonium-based salts and hydrogen bond donvnors (polyol type) are investigated. The temperature-dependent electrolyte viscosity as a function of molar conductivity is correlated by means of Walden’s rule. The oxidation of ferrocene (Fc/Fc+) and reduction of cobaltocenium (Cc+/Cc) at different temperatures are studied by cyclic voltammetry and potential-step chronoamperometry in DESs. For most DESs, chronoamperometric transients are demonstrated to fit an Arrhenius-type relation to give activation energies for the diffusion of redox couples at different temperatures. The temperature dependence of the measured conductivities of DES1 and DES2 are better correlated with the Vogel-Tamman-Fulcher equation. The kinetics of the Fc/Fc+ and Cc+/Cc electrochemical systems have been investigated over a temperature range from 298 to 338 K. The heterogeneous electron transfer rate constant is then calculated at different temperatures by means of a logarithmic analysis. The glycerol-based DES (DES5) appears suitable for further testing in electrochemical energy storage devices. PMID:26642045

Prediction of air temperature for thermal comfort of people in outdoor environments

NASA Astrophysics Data System (ADS)

Huang, Jianhua

2007-05-01

Current thermal comfort indices do not take into account the effects of wind and body movement on the thermal resistance and vapor resistance of clothing. This may cause public health problem, e.g. cold-related mortality. Based on the energy balance equation and heat exchanges between a clothed body and the outdoor environment, a mathematical model was developed to determine the air temperature at which an average adult, wearing a specific outdoor clothing and engaging in a given activity, attains thermal comfort under outdoor environment condition. The results indicated low clothing insulation, less physical activity and high wind speed lead to high air temperature prediction for thermal comfort. More accurate air temperature prediction is able to prevent wearers from hypothermia under cold conditions.

Voltage gating by molecular subunits of Na+ and K+ ion channels: higher-dimensional cubic kinetics, rate constants, and temperature

PubMed Central

2015-01-01

The structural similarity between the primary molecules of voltage-gated Na and K channels (alpha subunits) and activation gating in the Hodgkin-Huxley model is brought into full agreement by increasing the model's sodium kinetics to fourth order (m3 → m4). Both structures then virtually imply activation gating by four independent subprocesses acting in parallel. The kinetics coalesce in four-dimensional (4D) cubic diagrams (16 states, 32 reversible transitions) that show the structure to be highly failure resistant against significant partial loss of gating function. Rate constants, as fitted in phase plot data of retinal ganglion cell excitation, reflect the molecular nature of the gating transitions. Additional dimensions (6D cubic diagrams) accommodate kinetically coupled sodium inactivation and gating processes associated with beta subunits. The gating transitions of coupled sodium inactivation appear to be thermodynamically irreversible; response to dielectric surface charges (capacitive displacement) provides a potential energy source for those transitions and yields highly energy-efficient excitation. A comparison of temperature responses of the squid giant axon (apparently Arrhenius) and mammalian channel gating yields kinetic Q10 = 2.2 for alpha unit gating, whose transitions are rate-limiting at mammalian temperatures; beta unit kinetic Q10 = 14 reproduces the observed non-Arrhenius deviation of mammalian gating at low temperatures; the Q10 of sodium inactivation gating matches the rate-limiting component of activation gating at all temperatures. The model kinetics reproduce the physiologically large frequency range for repetitive firing in ganglion cells and the physiologically observed strong temperature dependence of recovery from inactivation. PMID:25867741

The role of CCK2 receptors in energy homeostasis: insights from the CCK2 receptor-deficient mouse.

PubMed

Weiland, Tracey J; Voudouris, Nicholas J; Kent, Stephen

2004-09-15

The present study explored the contribution of type 2 cholecystokinin (CCK) receptors in energy regulation. A total of 78 CCK2 receptor-deficient mice and 80 wild-type controls were acclimated to a 12:12 light-dark cycle at 30 +/- 1 degrees C. Using a computer-monitored biotelemetry system, circadian patterns of body temperature, food intake, and activity were monitored for 4 days. Body weight and water consumption were manually recorded during this period. Results indicate that CCK2 receptor invalidation produces elevated body temperature during both the photophase and scotophase (by 0.38 and 0.12 degrees C, respectively), increased body weight (29.3 +/- 0.2 vs. 26.8 +/- 0.2 g) and water consumption (4.1 +/- 0.1 vs. 3.2 +/- 0.1 ml), and decreased scotophase locomotor activity (WT: 7.0 +/- 0.2 vs. KO: 6.1 +/- 0.2 counts/min). These findings suggest an important role for CCK2 receptors in processes underlying energy regulation during basal and possibly pathological states.

Ground coupled solar heat pumps: analysis of four options

DOE Office of Scientific and Technical Information (OSTI.GOV)

Andrews, J.W.

Heat pump systems which utilize both solar energy and energy withdrawn from the ground are analyzed using a simplified procedure which optimizes the solar storage temperature on a monthly basis. Four ways of introducing collected solar energy to the system are optimized and compared. These include use of actively collected thermal input to the heat pump; use of collected solar energy to heat the load directly (two different ways); and use of a passive option to reduce the effective heating load.

Hyperphagia, lower body temperature, and reduced running wheel activity precede development of morbid obesity in New Zealand obese mice.

PubMed

Jürgens, Hella S; Schürmann, Annette; Kluge, Reinhart; Ortmann, Sylvia; Klaus, Susanne; Joost, Hans-Georg; Tschöp, Matthias H

2006-04-13

Among polygenic mouse models of obesity, the New Zealand obese (NZO) mouse exhibits the most severe phenotype, with fat depots exceeding 40% of total body weight at the age of 6 mo. Here we dissected the components of energy balance including feeding behavior, locomotor activity, energy expenditure, and thermogenesis compared with the related lean New Zealand black (NZB) and obese B6.V-Lep(ob)/J (ob/ob) strains (11% and 65% fat at 23 wk, respectively). NZO mice exhibited a significant hyperphagia that, when food intake was expressed per metabolic body mass, was less pronounced than that of the ob/ob strain. Compared with NZB, NZO mice exhibited increased meal frequency, meal duration, and meal size. Body temperature as determined by telemetry with implanted sensors was reduced in NZO mice, but again to a lesser extent than in the ob/ob strain. In striking contrast to ob/ob mice, NZO mice were able to maintain a constant body temperature during a 20-h cold exposure, thus exhibiting a functioning cold-induced thermogenesis. No significant differences in spontaneous home cage activity were observed among NZO, NZB, and ob/ob strains. When mice had access to voluntary running wheels, however, running activity was significantly lower in NZO than NZB mice and even lower in ob/ob mice. These data indicate that obesity in NZO mice, just as in humans, is due to a combination of hyperphagia, reduced energy expenditure, and insufficient physical activity. Because NZO mice differ strikingly from the ob/ob strain in their resistance to cold stress, we suggest that the molecular defects causing hyperphagia in NZO mice are located distal from leptin and its receptor.

The performance of a piezoelectric-sensor-based SHM system under a combined cryogenic temperature and vibration environment

NASA Astrophysics Data System (ADS)

Qing, Xinlin P.; Beard, Shawn J.; Kumar, Amrita; Sullivan, Kevin; Aguilar, Robert; Merchant, Munir; Taniguchi, Mike

2008-10-01

A series of tests have been conducted to determine the survivability and functionality of a piezoelectric-sensor-based active structural health monitoring (SHM) SMART Tape system under the operating conditions of typical liquid rocket engines such as cryogenic temperature and vibration loads. The performance of different piezoelectric sensors and a low temperature adhesive under cryogenic temperature was first investigated. The active SHM system for liquid rocket engines was exposed to flight vibration and shock environments on a simulated large booster LOX-H2 engine propellant duct conditioned to cryogenic temperatures to evaluate the physical robustness of the built-in sensor network as well as operational survivability and functionality. Test results demonstrated that the developed SMART Tape system can withstand operational levels of vibration and shock energy on a representative rocket engine duct assembly, and is functional under the combined cryogenic temperature and vibration environment.

Simultaneous application of microwave energy and hot air to whole drying process of apple slices: drying kinetics, modeling, temperature profile and energy aspect

NASA Astrophysics Data System (ADS)

Horuz, Erhan; Bozkurt, Hüseyin; Karataş, Haluk; Maskan, Medeni

2018-02-01

Drying kinetics, modeling, temperature profile and energy indices were investigated in apple slices during drying by a specially designed microwave-hot air domestic hybrid oven at the following conditions: 120, 150 and 180 W microwave powers coupled with 50, 60 and 70 °C air temperatures. Both sources of energy were applied simultaneously during the whole drying processes. The drying process continued until the moisture content of apple slices reached to 20% from 86.3% (wet basis, w.b). Drying times ranged from 330 to 800 min and decreased with increasing microwave power and air temperatures. The constant rate period was only observed at low microwave powers and air temperatures. Two falling rate periods were observed. Temperature of apple slices sharply increased within the first 60 min, then reached equilibrium with drying medium and finally increased at the end of the drying process. In order to describe drying behavior of apple slices nine empirical models were applied. The Modified Logistic Model fitted the best our experimental data ( R 2 = 0.9955-0.9998; χ 2 = 3.46 × 10-5-7.85 × 10-4 and RMSE = 0.0052-0.0221). The effective moisture and thermal diffusivities were calculated by Fick's second law and ranged from 1.42 × 10-9 to 3.31 × 10-9 m2/s and 7.70 × 10-9 to 12.54 × 10-9 m2/s, respectively. The activation energy ( Ea) values were calculated from effective moisture diffusivity ( Deff), thermal diffusivity ( α) and the rate constant of the best model ( k). The Ea values found from these three terms were similar and varied from 13.04 to 33.52 kJ/mol. Energy consumption and specific energy requirement of the hybrid drying of apple slices decreased and energy efficiency of the drying system increased with increasing microwave power and air temperature. Apples can be dried rapidly and effectively by use of the hybrid technique.

Dielectric Properties of Tungsten Copper Barium Ceramic as Promising Colossal-Permittivity Material

NASA Astrophysics Data System (ADS)

Wang, Juanjuan; Chao, Xiaolian; Li, Guangzhao; Feng, Lajun; Zhao, Kang; Ning, Tiantian

2017-08-01

Ba(Cu0.5W0.5)O3 (BCW) ceramic has been fabricated and its dielectric properties investigated for use in energy-storage applications, revealing a very large dielectric constant (˜104) at 1 kHz. Moreover, the colossal-permittivity BCW ceramic exhibited fine microstructure and optimal temperature stability over a wide temperature range from room temperature to 500°C. The internal barrier layer capacitor mechanism was considered to be responsible for its high dielectric properties. Based on activation values, it is concluded that doubly ionized oxygen vacancies make a substantial contribution to the conduction and relaxation behaviors at grain boundaries. This study suggests that this kind of material has potential for use in high-density energy storage applications.

Central Control of Brown Adipose Tissue Thermogenesis

PubMed Central

Morrison, Shaun F.; Madden, Christopher J.; Tupone, Domenico

2011-01-01

Thermogenesis, the production of heat energy, is an essential component of the homeostatic repertoire to maintain body temperature during the challenge of low environmental temperature and plays a key role in elevating body temperature during the febrile response to infection. Mitochondrial oxidation in brown adipose tissue (BAT) is a significant source of neurally regulated metabolic heat production in many species from mouse to man. BAT thermogenesis is regulated by neural networks in the central nervous system which responds to feedforward afferent signals from cutaneous and core body thermoreceptors and to feedback signals from brain thermosensitive neurons to activate BAT sympathetic nerve activity. This review summarizes the research leading to a model of the feedforward reflex pathway through which environmental cold stimulates BAT thermogenesis and includes the influence on this thermoregulatory network of the pyrogenic mediator, prostaglandin E2, to increase body temperature during fever. The cold thermal afferent circuit from cutaneous thermal receptors, through second-order thermosensory neurons in the dorsal horn of the spinal cord ascends to activate neurons in the lateral parabrachial nucleus which drive GABAergic interneurons in the preoptic area (POA) to inhibit warm-sensitive, inhibitory output neurons of the POA. The resulting disinhibition of BAT thermogenesis-promoting neurons in the dorsomedial hypothalamus activates BAT sympathetic premotor neurons in the rostral ventromedial medulla, including the rostral raphe pallidus, which provide excitatory, and possibly disinhibitory, inputs to spinal sympathetic circuits to drive BAT thermogenesis. Other recently recognized central sites influencing BAT thermogenesis and energy expenditure are also described. PMID:22389645

Genetic variation in brown fat activity and body weight regulation in mice: lessons for human studies.

PubMed

Kozak, Leslie P

2014-03-01

The recent characterization of brown fat in humans has generated much excitement on the possibility that increased energy expenditure by heat production by this tissue will be able to reduce obesity. This expectation has largely been stimulated by studies with mice that show strong associations between increased brown fat activity and reductions in obesity and insulin resistance. Research in the mouse has been largely based upon the induction or suppression of brown fat and mitochondrial uncoupling protein by genetic methods. The review of this research literature underscores the idea that reductions in obesity in mice are secondary to the primary role of brown adipose tissue in the regulation of body temperature. Given that the variation in brown fat in humans, as detected by PET imaging, is highly associated with administration of adrenergic agonists and reductions in ambient temperature, the effects on obesity in humans may also be secondary to the regulation of body temperature. Induction of thermogenesis by reduced ambient temperature now becomes like muscle and physical activity, another natural method of increased energy expenditure to combat obesity. Furthermore, there is no evidence to indicate that heat production by adrenergic stimulation via cold exposure or drug treatment or the enriched physical environment is restricted to the thermogenic activity of the brown adipocyte. This article is part of a Special Issue entitled: Modulation of Adipose Tissue in Health and Disease. Copyright © 2013 Elsevier B.V. All rights reserved.

Metabolic plasticity and critical temperatures for aerobic scope in a eurythermal marine invertebrate (Littorina saxatilis, Gastropoda: Littorinidae) from different latitudes.

PubMed

Sokolova, Inna M; Pörtner, Hans-Otto

2003-01-01

Effects of latitudinal cold adaptation and cold acclimation on metabolic rates and aerobic scope were studied in the eurythermal marine gastropod Littorina saxatilis from temperate North Sea and sub-arctic White Sea areas. Animals were acclimated for 6-8 weeks at control temperature (13 degrees C) or at 4 degrees C, and their respiration rates were measured during acute temperature change (1-1.5 degrees C h(-1)) in a range between 0 degrees C and 32 degrees C. In parallel, the accumulation of anaerobic end products and changes in energy status were monitored. Starting from 0 degrees C, aerobic metabolic rates of L. saxatilis rose quickly with increasing temperatures up to a point at or slightly above the respective acclimation temperature. Beyond this value, thermal sensitivity of oxygen consumption rate V((O(2))) greatly decreased in a wide, 15 degrees C range of experimental temperatures. This change in metabolic regulation was also reflected in the activation energy of aerobic metabolism (E(a)), which was approximately seven times lower at temperatures above Arrhenius breakpoint temperatures (ABTs) than at temperatures below ABTs. Warming progressively led to a discrepancy between energy demand and energy production, as demonstrated by a decrease in the levels of high-energy phosphates [phosho-L-arginine (PLA) and ATP], and resulted in the onset of anaerobiosis at critically high temperatures, indicating a limitation of aerobic scope. The comparison of aerobic and anaerobic metabolic rates in L. saxatilis in air and water suggests that the heat-induced onset of anaerobiosis is due to the insufficient oxygen supply to tissues at high temperatures. Cold acclimation led to an increase in aerobic metabolic rates and a considerable downward shift of the upper critical temperature in North Sea L. saxatilis but not in White Sea L. saxatilis. Limited metabolic plasticity in response to cold acclimation in sub-arctic White Sea snails as compared with their temperate North Sea counterparts suggests that metabolic depression occurs during overwintering under the more extreme winter conditions at the White Sea.

Behavioural and physiological consequences of male reproductive trade-offs in edible dormice ( Glis glis)

NASA Astrophysics Data System (ADS)

Fietz, Joanna; Klose, Stefan M.; Kalko, Elisabeth K. V.

2010-10-01

Testosterone mediates male reproductive trade-offs in vertebrates including mammals. In male edible dormice ( Glis glis), reproductivity linked to high levels of testosterone reduces their ability to express torpor, which may be expected to dramatically increase thermoregulatory costs. Aims of this study were therefore to analyse behavioural and physiological consequences of reproductive activity in male edible dormice under ecologically and evolutionary relevant conditions in the field. As we frequently encountered sleeping groups in the field, we hypothesized that social thermoregulation should be an important measure to reduce energy expenditure especially in sexually active male edible dormice. Our results revealed that the occurrence of sleeping groups was negatively influenced by male body mass but not by reproductive status or ambient temperature. In reproductive as in non-reproductive males, the number of individuals huddling together was negatively influenced by their body mass. Thus in general males with a high body mass were sitting in smaller groups than males with a low body mass. However, in reproductive males group size was further negatively affected by ambient temperature and positively by testes size. Thus breeders formed larger sleeping groups at lower ambient temperatures and males with larger testes were found in larger groups than males with smaller testes. Measurements of oxygen consumption demonstrated that grouping behaviour represents an efficient strategy to reduce energy expenditure in edible dormice as it reduced energy requirements by almost 40%. In summary, results of this field study showcase how sexually active male edible dormice may, through behavioural adjustment, counterbalance high thermoregulatory costs associated with reproductive activity.

Developing a Repertoire of Activities for Teaching Physical Science.

ERIC Educational Resources Information Center

Cain, Peggy W.

This activity manual is divided into 15 units which focus on: the nature of science; metric measurements; properties of matter; energy; atomic structure; chemical reactions; acids, bases, and salts; temperature and heat; readioactivity; mechanics; wave motion, sound, and light; static charges and current electricity magnetism and electromagnetism;…

The Significance of Temperature Based Approach Over the Energy Based Approaches in the Buildings Thermal Assessment

NASA Astrophysics Data System (ADS)

Albatayneh, Aiman; Alterman, Dariusz; Page, Adrian; Moghtaderi, Behdad

2017-05-01

The design of low energy buildings requires accurate thermal simulation software to assess the heating and cooling loads. Such designs should sustain thermal comfort for occupants and promote less energy usage over the life time of any building. One of the house energy rating used in Australia is AccuRate, star rating tool to assess and compare the thermal performance of various buildings where the heating and cooling loads are calculated based on fixed operational temperatures between 20 °C to 25 °C to sustain thermal comfort for the occupants. However, these fixed settings for the time and temperatures considerably increase the heating and cooling loads. On the other hand the adaptive thermal model applies a broader range of weather conditions, interacts with the occupants and promotes low energy solutions to maintain thermal comfort. This can be achieved by natural ventilation (opening window/doors), suitable clothes, shading and low energy heating/cooling solutions for the occupied spaces (rooms). These activities will save significant amount of operating energy what can to be taken into account to predict energy consumption for a building. Most of the buildings thermal assessment tools depend on energy-based approaches to predict the thermal performance of any building e.g. AccuRate in Australia. This approach encourages the use of energy to maintain thermal comfort. This paper describes the advantages of a temperature-based approach to assess the building's thermal performance (using an adaptive thermal comfort model) over energy based approach (AccuRate Software used in Australia). The temperature-based approach was validated and compared with the energy-based approach using four full scale housing test modules located in Newcastle, Australia (Cavity Brick (CB), Insulated Cavity Brick (InsCB), Insulated Brick Veneer (InsBV) and Insulated Reverse Brick Veneer (InsRBV)) subjected to a range of seasonal conditions in a moderate climate. The time required for heating and/or cooling using the adaptive thermal comfort approach and AccuRate predictions were estimated. Significant savings (of about 50 %) in energy consumption in minimising the time required for heating and cooling were achieved by using the adaptive thermal comfort model.

Energy Exchange by Thermal Radiation: Hints and Suggestions for an Inquiry Based Lab Approach

NASA Astrophysics Data System (ADS)

Battaglia, Onofrio Rosario; Fazio, Claudio; Pizzolato, Nicola; Mineo, Rosa Maria Sperandeo

In this paper we present some laboratory activities developed in the framework of an inquiry-based approach to the study of energy exchange by thermal radiation. These activities were developed in the context of "Establish", a FP7 European Project aimed at promoting and developing Inquiry Based Science Education in European Secondary Schools. By starting from real life students are engaged in designing and carrying out laboratory activities by collecting, processing and analysing data. Particular attention is paid in building data interpretation by taking into account the effects of parameters like the environmental temperature.

Spectral characteristics of plasma sheet ion and electron populations during disturbed geomagnetic conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Christon, S.P., Williams, D.J.; Mitchell, D.G.; Huang, C.Y.

1991-01-01

The authors have determined the spectral characteristics of central plasma sheet ions and electrons observed during 71 hours when geomagnetic activity was at moderate to high levels (AE {ge} 100nT). Particle data from the low-energy proton and electron differential energy analyzer and the medium energy particle instrument on ISEE 1 are combined to obtain differential energy spectra (measured in units of particles/cm{sup 2} s sr keV) in the kinetic energy range {approximately}30 eV/e to {approximately}1 MeV at geocentric radial distances >12R{sub e}. Nearly isotropic central plasma sheet total ion and electron populations were chosen for analysis and were measured tomore » be continuous particle distributions from the lowest to highest energies. During these high AE periods the >24 keV particle fluxes and the temperature of the entire particle distribution kT are significantly higher than during low AE periods (AE < 100 nT). The temperatures kT{sub i} and kT{sub e} are highly correlated during both quiet and disturbed periods. The active period spectral shape appears softer for ions and somewhat harder for electrons than during quiet periods. They find that the observed active period spectrum typically is complex and cannot be represented in general by a single functional form, as during quiet periods when it can be represented by the kappa distribution function. In a limited energy range near the knee of the ion spectra, the spectral shape can often be fit with a Maxwellian form, thus rolling over faster than the typical quiet time spectrum. Electron spectra also display this spectral characteristic, although at a lower occurence frequency than for ions. The electron spectra are predominantly kappalike at energies near and above the knee. The authors conclude that both ions and electrons participate in at least two separate accerlation mechanisms as geomagnetic activity evolves from low AE to high AE values.« less

Energy. Stop Faking It! Finally Understanding Science So You Can Teach It.

ERIC Educational Resources Information Center

Robertson, William C.

This book explains science concepts in a manner in which non-science teachers and parents can understand and learn science through activities. The concepts covered in this book include energy, simple machines, temperature, and heat transfer. Each chapter is supported with internet resources available at SciLinks and ends with a summary and…

Energy-Storage Modules for Active Solar Heating and Cooling

NASA Technical Reports Server (NTRS)

Parker, J. C.

1982-01-01

34 page report describes a melting salt hydrate that stores 12 times as much heat as rocks and other heavy materials. Energy is stored mostly as latent heat; that is, heat that can be stored and recovered without any significant change in temperature. Report also describes development, evaluation and testing of permanently sealed modules containing salt hydrate mixture.

Development of a Novel Method for in vivo Determination of Activation Energy of Glucose Transport Across S. cerevisiae Cellular Membranes. A Biosensor-like Approach

PubMed Central

Kormes, Diego J.; Cortón, Eduardo

2009-01-01

Whereas biosensors have been usually proposed as analytical tools, used to investigate the surrounding media pursuing an analytical answer, we have used a biosensor-like device to characterize the microbial cells immobilized on it. We have studied the kinetics of transport and degradation of glucose at different concentrations and temperatures. When glucose concentrations of 15 and 1.5 mM were assayed, calculated activation energies were 25.2 and 18.4 kcal mol−1, respectively, in good agreement with previously published data. The opportunity and convenience of using Arrhenius plots to estimate the activation energy in metabolic-related processes is also discussed. PMID:22573975

First principles investigation of heterogeneous catalysis on metal oxide surfaces

NASA Astrophysics Data System (ADS)

Ghoussoub, Mireille

Metal oxides possess unique electronic and structural properties that render them highly favourable for applications in heterogeneous catalysis. In this study, computational atomistic modelling based on Density Functional Theory was used to investigate the reduction of carbon dioxide over hydroxylated indium oxide nanoparticles, as well at the activation of methane over oxygen-covered bimetallic surfaces. The first study employed metadynamics-biased ab initio molecular dynamics to obtain the free energy surface of the various reaction steps at finite temperature. In the second study, the nudged elastic band method was used to probe the C-H activation mechanisms for different surface configurations. In both cases, activation energies, reaction energies, transition state structures, and charge analysis results are used to explain the underlying mechanistic pathways.

High Temperature Annealing of MBE-grown Mg-doped GaN

NASA Astrophysics Data System (ADS)

Contreras, S.; Konczewicz, L.; Peyre, H.; Juillaguet, S.; Khalfioui, M. Al; Matta, S.; Leroux, M.; Damilano, B.; Brault, J.

2017-06-01

In this report, are shown the results of high temperature resistivity and Hall Effect studies of Mg-doped GaN epilayers. The samples studied were grown on (0001) (c-plane) sapphire by molecular beam epitaxy and 0.5 μm GaN:Mg layers have been achieved on low temperature buffers of GaN (30 nm) and AlN ( 150 nm). The experiments were carried out in the temperature range from 300 K up to 900 K. Up to about 870 K a typical thermally activated conduction process has been observed with the activation energy value EA = 215 meV. However, for higher temperatures, an annealing effect is observed in all the investigated samples. The increase of the free carrier concentration as a function of time leads to an irreversible decrease of sample resistivity of more than 60%.

Skin temperature, thermal comfort, sweating, clothing and activity of men sledging in Antarctica

PubMed Central

Budd, G. M.

1966-01-01

1. Three men were studied while dog-sledging 320 km in 12 days in Antarctica. Conventional Antarctic clothing (`sweaters and windproofs') was worn. Four hundred observations were made of medial thigh skin temperature, thermal comfort, sweating, clothing, activity and environmental conditions. 2. Work occupied an average of 11·0 hr/day and sleep 7·5 hr. Estimated daily energy expenditure averaged 5100 kcal (range 2740-6660 kcal). 3. Skin temperature fell on exposure to cold despite the clothing worn, but was not changed by the level of activity. Sweating, and thermal comfort, were directly related to both skin temperature and activity. 4. Inside the tent, the modal value of skin temperature was 33° C (range 27-36° C) and the men were comfortable in 94% of observations. 5. During the 9·2 hr/day spent outdoors the modal value of skin temperature was 27° C (range 18-33° C) and the men felt too cold (but did not shiver) in 11% (range 7-20%) of observations, suggesting that cold stress was not negligible. However, they also felt too hot in 20% of observations and were sweating in 23%. PMID:5914254

Effects of Light and Temperature on Daily Activity and Clock Gene Expression in Two Mosquito Disease Vectors.

PubMed

Rivas, Gustavo B S; Teles-de-Freitas, Rayane; Pavan, Márcio G; Lima, José B P; Peixoto, Alexandre A; Bruno, Rafaela Vieira

2018-06-01

Most organisms feature an endogenous circadian clock capable of synchronization with their environment. The most well-known synchronizing agents are light and temperature. The circadian clock of mosquitoes, vectors of many pathogens, drives important behaviors related to vectoral capacity, including oviposition, host seeking, and hematophagy. Main clock gene expression, as well as locomotor activity patterns, has been identified in Aedes aegypti and Culex quinquefasciatus under artificial light-dark cycles. Given that these mosquito species thrive in tropical areas, it is reasonable to speculate that temperature plays an important role in the circadian clock. Here, we provide data supporting a different hierarchy of light and temperature as zeitgebers of two mosquito species. We recorded their locomotor activity and quantified mRNA expression of the main clock genes in several combinations of light and temperature cycles. We observed that A. aegypti is more sensitive to temperature, while C. quinquefasciatus is more responsive to light. These variations in clock gene expression and locomotor activity may have affected the mosquito species' metabolism, energy expenditure, fitness cost, and pathogen transmission efficiency. Our findings are relevant to chronobiology studies and also have epidemiological implications.

Fluorescence and room temperature activity of Y₂O₃:(Eu³⁺,Au³⁺)/palygorskite nanocomposite.

PubMed

He, Xi; Yang, Huaming

2015-01-28

The fluorescence and room temperature activity of a palygorskite supported Y2O3:(Eu(3+),Au(3+)) nanocomposite were investigated to design a fluorescence-indicated catalyst. The effects of Au(3+) doping on the structure and surface properties of the host material were systematically characterized. The fluorescence intensity of Y2O3:Eu(3+) was affected by Au(3+) doping, which was related to the crystallinity of Y2O3. Excess Au(3+) ions were segregated to the host surface and reduced to metallic Au. The local symmetry of Eu(3+) was reduced by Au(3+) doping, which benefited the energy transfer between Eu(3+) and Au(3+). Energy absorbed by Eu(3+) was transferred from Au(3+) to metallic Au, where electrons were produced. These electrons were absorbed by O2 to change into O2(-), which acted as the oxidant for ortho-dichlorobenzene (o-DCB). The variation of fluorescence intensity during the catalytic reaction was observed. The room temperature catalytic activity of the nanocomposite under UV irradiation was revealed. The as-synthesized nanocomposite might have potential applications in environmental fields.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chesny, D. L.; Oluseyi, H. M.; Orange, N. B.

Ubiquitous solar atmospheric coronal and transition region bright points (BPs) are compact features overlying strong concentrations of magnetic flux. Here, we utilize high-cadence observations from the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory to provide the first observations of extreme ultraviolet quiet-Sun (QS) network BP activity associated with sigmoidal structuring. To our knowledge, this previously unresolved fine structure has never been associated with such small-scale QS events. This QS event precedes a bi-directional jet in a compact, low-energy, and low-temperature environment, where evidence is found in support of the typical fan-spine magnetic field topology. As in active regionsmore » and micro-sigmoids, the sigmoidal arcade is likely formed via tether-cutting reconnection and precedes peak intensity enhancements and eruptive activity. Our QS BP sigmoid provides a new class of small-scale structuring exhibiting self-organized criticality that highlights a multi-scaled self-similarity between large-scale, high-temperature coronal fields and the small-scale, lower-temperature QS network. Finally, our QS BP sigmoid elevates arguments for coronal heating contributions from cooler atmospheric layers, as this class of structure may provide evidence favoring mass, energy, and helicity injections into the heliosphere.« less

Sensitizing properties of luminescence centers on the emission of Er{sup 3+} in Si-rich SiO{sub 2} film

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fu, Qianyu; Gao, Yuhan; Li, Dongsheng, E-mail: mselds@zju.edu.cn

2016-05-28

In this paper, we report on the luminescence-center (LC)-mediated excitation of Er{sup 3+} as a function of annealing temperature in Er-doped Si-rich SiO{sub 2} (SRO) films fabricated by electron beam evaporation. It is found that the annealing temperature has significant effects on the emission of Er{sup 3+} and the specific optical-active point-defects called LCs within Er-doped SRO films. Different luminescence centers generated by the evolution of microstructures during annealing process act as efficient sensitizers for Er{sup 3+} in the films when the annealing temperature is below 1100 °C. Moreover, the temperature dependence of the energy coupling between LCs and Er{sup 3+}more » demonstrates the effective phonon-mediated energy transfer process. In addition, when the annealing temperature reaches 1100 °C, the decreased density of activable erbium ions induced by the aggregation of Er will bring detrimental effects on the emission of Er{sup 3+}. It is demonstrated that an appropriate annealing process can be designed to achieve efficiently enhanced emissions from Er{sup 3+} ions by optimizing the density of LCs and the coupling between Er{sup 3+} and LCs.« less

Auto-ignitions of a methane/air mixture at high and intermediate temperatures

NASA Astrophysics Data System (ADS)

Leschevich, V. V.; Martynenko, V. V.; Penyazkov, O. G.; Sevrouk, K. L.; Shabunya, S. I.

2016-09-01

A rapid compression machine (RCM) and a shock tube (ST) have been employed to study ignition delay times of homogeneous methane/air mixtures at intermediate-to-high temperatures. Both facilities allow measurements to be made at temperatures of 900-2000 K, at pressures of 0.38-2.23 MPa, and at equivalence ratios of 0.5, 1.0, and 2.0. In ST experiments, nitrogen served as a diluent gas, whereas in RCM runs the diluent gas composition ranged from pure nitrogen to pure argon. Recording pressure, UV, and visible emissions identified the evolution of chemical reactions. Correlations of ignition delay time were generated from the data for each facility. At temperatures below 1300 K, a significant reduction of average activation energy from 53 to 15.3 kcal/mol was obtained. Moreover, the RCM data showed significant scatter that dramatically increased with decreasing temperature. An explanation for the abnormal scatter in the data was proposed based on the high-speed visualization of auto-ignition phenomena and experiments performed with oxygen-free and fuel-free mixtures. It is proposed that the main reason for such a significant reduction of average activation energy is attributable to the premature ignition of ultrafine particles in the reactive mixture.

Kinetics and Mechanism of the Oxidation of Cyclic Methylsiloxanes by Hydroxyl Radical in the Gas Phase: An Experimental and Theoretical Study.

PubMed

Xiao, Ruiyang; Zammit, Ian; Wei, Zongsu; Hu, Wei-Ping; MacLeod, Matthew; Spinney, Richard

2015-11-17

The ubiquitous presence of cyclic volatile methylsiloxanes (cVMS) in the global atmosphere has recently raised environmental concern. In order to assess the persistence and long-range transport potential of cVMS, their second-order rate constants (k) for reactions with hydroxyl radical ((•)OH) in the gas phase are needed. We experimentally and theoretically investigated the kinetics and mechanism of (•)OH oxidation of a series of cVMS, hexamethylcyclotrisiloxane (D3), octamethycyclotetrasiloxane (D4), and decamethycyclopentasiloxane (D5). Experimentally, we measured k values for D3, D4, and D5 with (•)OH in a gas-phase reaction chamber. The Arrhenius activation energies for these reactions in the temperature range from 313 to 353 K were small (-2.92 to 0.79 kcal·mol(-1)), indicating a weak temperature dependence. We also calculated the thermodynamic and kinetic behaviors for reactions at the M06-2X/6-311++G**//M06-2X/6-31+G** level of theory over a wider temperature range of 238-358 K that encompasses temperatures in the troposphere. The calculated Arrhenius activation energies range from -2.71 to -1.64 kcal·mol(-1), also exhibiting weak temperature dependence. The measured k values were approximately an order of magnitude higher than the theoretical values but have the same trend with increasing size of the siloxane ring. The calculated energy barriers for H-atom abstraction at different positions were similar, which provides theoretical support for extrapolating k for other cyclic siloxanes from the number of abstractable hydrogens.

Bound exciton and free exciton states in GaSe thin slab.

PubMed

Wei, Chengrong; Chen, Xi; Li, Dian; Su, Huimin; He, Hongtao; Dai, Jun-Feng

2016-09-22

The photoluminescence (PL) and absorption experiments have been performed in GaSe slab with incident light polarized perpendicular to c-axis of sample at 10 K. An obvious energy difference of about 34 meV between exciton absorption peak and PL peak (the highest energy peak) is observed. By studying the temperature dependence of PL and absorption spectra, we attribute it to energy difference between free exciton and bound exciton states, where main exciton absorption peak comes from free exciton absorption, and PL peak is attributed to recombination of bound exciton at 10 K. This strong bound exciton effect is stable up to 50 K. Moreover, the temperature dependence of integrated PL intensity and PL lifetime reveals that a non-radiative process, with activation energy extracted as 0.5 meV, dominates PL emission.

Atomistic simulations of materials: Methods for accurate potentials and realistic time scales

NASA Astrophysics Data System (ADS)

Tiwary, Pratyush

This thesis deals with achieving more realistic atomistic simulations of materials, by developing accurate and robust force-fields, and algorithms for practical time scales. I develop a formalism for generating interatomic potentials for simulating atomistic phenomena occurring at energy scales ranging from lattice vibrations to crystal defects to high-energy collisions. This is done by fitting against an extensive database of ab initio results, as well as to experimental measurements for mixed oxide nuclear fuels. The applicability of these interactions to a variety of mixed environments beyond the fitting domain is also assessed. The employed formalism makes these potentials applicable across all interatomic distances without the need for any ambiguous splining to the well-established short-range Ziegler-Biersack-Littmark universal pair potential. We expect these to be reliable potentials for carrying out damage simulations (and molecular dynamics simulations in general) in nuclear fuels of varying compositions for all relevant atomic collision energies. A hybrid stochastic and deterministic algorithm is proposed that while maintaining fully atomistic resolution, allows one to achieve milliseconds and longer time scales for several thousands of atoms. The method exploits the rare event nature of the dynamics like other such methods, but goes beyond them by (i) not having to pick a scheme for biasing the energy landscape, (ii) providing control on the accuracy of the boosted time scale, (iii) not assuming any harmonic transition state theory (HTST), and (iv) not having to identify collective coordinates or interesting degrees of freedom. The method is validated by calculating diffusion constants for vacancy-mediated diffusion in iron metal at low temperatures, and comparing against brute-force high temperature molecular dynamics. We also calculate diffusion constants for vacancy diffusion in tantalum metal, where we compare against low-temperature HTST as well. The robustness of the algorithm with respect to the only free parameter it involves is ascertained. The method is then applied to perform tensile tests on gold nanopillars on strain rates as low as 100/s, bringing out the perils of high strain-rate molecular dynamics calculations. We also calculate temperature and stress dependence of activation free energy for surface nucleation of dislocations in pristine gold nanopillars under realistic loads. While maintaining fully atomistic resolution, we reach the fraction-of-a-second time scale regime. It is found that the activation free energy depends significantly and nonlinearly on the driving force (stress or strain) and temperature, leading to very high activation entropies for surface dislocation nucleation.

Reduced deuterium retention in simultaneously damaged and annealed tungsten

NASA Astrophysics Data System (ADS)

Simmonds, M. J.; Wang, Y. Q.; Barton, J. L.; Baldwin, M. J.; Yu, J. H.; Doerner, R. P.; Tynan, G. R.

2017-10-01

Deuterium (D) retention in polycrystalline tungsten (W) with copper (Cu) ion damage concurrently produced at elevated surface temperature is investigated. An in situ heated stage held W samples at a controlled temperature up to 1243 K, which were subjected to displacement damage produced by 3.4 MeV Cu ions. D retention is subsequently explored by exposure of the W samples held at 383 K to a D2 plasma ion fluence of 1024 D+/m2. Nuclear reaction analysis (NRA), utilizing the D(3He,p)4He nuclear reaction, is used to probe the D concentration in the near surface up to 6 μm. Thermal desorption spectroscopy (TDS) is used to measure outgassed HD and D2 molecules to determine the bulk D concentration. Both NRA and TDS measure a significant reduction in D retention for samples damaged at elevated temperature. TDS quantitatively shows that the lowest energy trap remains largely unaffected while higher energy traps, induced by Cu ions, are annealed and approach intrinsic concentrations as the temperature during ion damage approaches 1243 K. Analysis of TDS data yields an activation energy of (0.10 ± 0.02) eV for recovery of ion-damage induced traps at elevated temperature.

The Effects of Acid Etching on the Nanomorphological Surface Characteristics and Activation Energy of Titanium Medical Materials.

PubMed

Hung, Kuo-Yung; Lin, Yi-Chih; Feng, Hui-Ping

2017-10-11

The purpose of this study was to characterize the etching mechanism, namely, the etching rate and the activation energy, of a titanium dental implant in concentrated acid and to construct the relation between the activation energy and the nanoscale surface topographies. A commercially-pure titanium (CP Ti) and Ti-6Al-4V ELI surface were tested by shot blasting (pressure, grain size, blasting distance, blasting angle, and time) and acid etching to study its topographical, weight loss, surface roughness, and activation energy. An Arrhenius equation was applied to derive the activation energy for the dissolution of CP Ti/Ti-6Al-4V ELI in sulfuric acid (H₂SO₄) and hydrochloric acid (HCl) at different temperatures. In addition, white-light interferometry was applied to measure the surface nanomorphology of the implant to obtain 2D or 3D roughness parameters (Sa, Sq, and St). The nanopore size that formed after etching was approximately 100-500 nm. The surface roughness of CP Ti and Ti-6Al-4V ELI decreased as the activation energy decreased but weight loss increased. Ti-6Al-4V ELI has a higher level of activation energy than Ti in HCl, which results in lower surface roughness after acid etching. This study also indicates that etching using a concentrated hydrochloric acid provided superior surface modification effects in titanium compared with H₂SO₄.

Dynamic-compliance and viscosity of PET and PEN

NASA Astrophysics Data System (ADS)

Weick, Brian L.

2016-05-01

Complex dynamic-compliance and in-phase dynamic-viscosity data are presented and analyzed for PET and PEN advanced polyester substrates used for magnetic tapes. Frequency-temperature superposition is used to predict long-term behavior. Temperature and frequency ranges for the primary glass transition and secondary transitions are discussed and compared for PET and PEN. Shift factors from frequency-temperature superposition are used to determine activation energies for the transitions, and WLF parameters are determined for the polyester substrates.

Dynamic-compliance and viscosity of PET and PEN

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weick, Brian L.

Complex dynamic-compliance and in-phase dynamic-viscosity data are presented and analyzed for PET and PEN advanced polyester substrates used for magnetic tapes. Frequency-temperature superposition is used to predict long-term behavior. Temperature and frequency ranges for the primary glass transition and secondary transitions are discussed and compared for PET and PEN. Shift factors from frequency-temperature superposition are used to determine activation energies for the transitions, and WLF parameters are determined for the polyester substrates.

Electrical conductivity of Gd doped BiFeO3-PbZrO3 composite

NASA Astrophysics Data System (ADS)

Satpathy, Santosh Kumar; Mohanty, Nilaya Kumar; Behera, Ajay Kumar; Behera, Banarji; Nayak, Pratibindhya

2013-09-01

The composite, 0.5(BiGd0.15Fe0.85O3)-0.5(PbZrO3), was synthesized using the solid-state reaction technique. The formation of the compound was confirmed by XRD with an orthorhombic structure at room temperature. The impedance parameters were studied using an impedance analyzer in a wide range of frequency (102-106 Hz) at different temperatures. The Nyquist plot suggests the contribution of bulk effect and a slight indication of grain boundary effect and the bulk resistance decreases with a rise in temperature. The presence of temperature-dependent relaxation process occurs in the material. Electrical modulus reveals the presence of the hopping mechanism in the materials. The value of exponent n, pre-factor A and σ dc were obtained by fitting ac conductivity data with Jonscher's universal power law. The activation energies calculated from the ac conductivity were found to be 0.50, 0.46, 0.44, 0.43, 0.42 and 0.38 eV at 1, 10, 50, 100, 500 kHz and 1 MHz respectively in the temperature region of 110°C-350°C. The dc conductivity was found to increase with the rise in temperature. The activation energy calculated from complex impedance plot and from the fitted Jonscher's power law are very close, which results similar type of charge carrier exist in conduction mechanism of the material.

Deformation, Stress Relaxation, and Crystallization of Lithium Silicate Glass Fibers Below the Glass Transition Temperature

NASA Technical Reports Server (NTRS)

Ray, Chandra S.; Brow, Richard K.; Kim, Cheol W.; Reis, Signo T.

2004-01-01

The deformation and crystallization of Li(sub 2)O (center dot) 2SiO2 and Li(sub 2)O (center dot) 1.6SiO2 glass fibers subjected to a bending stress were measured as a function of time over the temperature range -50 to -150 C below the glass transition temperature (Tg). The glass fibers can be permanently deformed at temperatures about 100 C below T (sub)g, and they crystallize significantly at temperatures close to, but below T,, about 150 C lower than the onset temperature for crystallization for these glasses in the no-stress condition. The crystallization was found to occur only on the surface of the glass fibers with no detectable difference in the extent of crystallization in tensile and compressive stress regions. The relaxation mechanism for fiber deformation can be best described by a stretched exponential (Kohlrausch-Williams-Watt (KWW) approximation), rather than a single exponential model.The activation energy for stress relaxation, Es, for the glass fibers ranges between 175 and 195 kJ/mol, which is considerably smaller than the activation energy for viscous flow, E, (about 400 kJ/mol) near T, for these glasses at normal, stress-free condition. It is suspected that a viscosity relaxation mechanism could be responsible for permanent deformation and crystallization of the glass fibers below T,

Spin texture and magnetoroton excitations at nu=1/3.

PubMed

Groshaus, Javier G; Dujovne, Irene; Gallais, Yann; Hirjibehedin, Cyrus F; Pinczuk, Aron; Tan, Yan-Wen; Stormer, Horst; Dennis, Brian S; Pfeiffer, Loren N; West, Ken W

2008-02-01

Neutral spin texture (ST) excitations at nu=1/3 are directly observed for the first time by resonant inelastic light scattering. They are determined to involve two simultaneous spin flips. At low magnetic fields, the ST energy is below that of the magnetoroton minimum. With increasing in-plane magnetic field these mode energies cross at a critical ratio of the Zeeman and Coulomb energies of eta(c)=0.020+/-0.001. Surprisingly, the intensity of the ST mode grows with temperature in the range in which the magnetoroton modes collapse. The temperature dependence is interpreted in terms of a competition between coexisting phases supporting different excitations. We consider the role of the ST excitations in activated transport at nu=1/3.

Coronae on stars

NASA Technical Reports Server (NTRS)

Haisch, B. M.

1986-01-01

Three lines of evidence are noted to point to a flare heating source for stellar coronae: a strong correlation between time-averaged flare energy release and coronal X-ray luminosity, the high temperature flare-like component of the spectral signature of coronal X-ray emission, and the observed short time scale variability that indicates continuous flare activity. It is presently suggested that flares may represent only the extreme high energy tail of a continuous distribution of coronal energy release events.

Integration of thermocouple microelectrode in the scanning electrochemical microscope at variable temperatures: simultaneous temperature and electrochemical imaging and its kinetic studies.

PubMed

Pan, He; Zhang, Hailing; Lai, Junhui; Gu, Xiaoxin; Sun, Jianjun; Tang, Jing; Jin, Tao

2017-03-24

We describe herein a method for the simultaneous measurement of temperature and electrochemical signal with a new type of thermocouple microelectrode. The thermocouple microelectrode can be used not only as a thermometer but also as a scanning electrochemical microscope (SECM) tip in the reaction between tip-generated bromine and a heated Cu sample. The influence of temperature on the SECM imaging process and the related kinetic parameters have been studied, such as kinetic constant and activation energy.

Integration of thermocouple microelectrode in the scanning electrochemical microscope at variable temperatures: simultaneous temperature and electrochemical imaging and its kinetic studies

PubMed Central

Pan, He; Zhang, Hailing; Lai, Junhui; Gu, Xiaoxin; Sun, Jianjun; Tang, Jing; Jin, Tao

2017-01-01

We describe herein a method for the simultaneous measurement of temperature and electrochemical signal with a new type of thermocouple microelectrode. The thermocouple microelectrode can be used not only as a thermometer but also as a scanning electrochemical microscope (SECM) tip in the reaction between tip-generated bromine and a heated Cu sample. The influence of temperature on the SECM imaging process and the related kinetic parameters have been studied, such as kinetic constant and activation energy. PMID:28338002

Controllability of the Coulomb charging energy in close-packed nanoparticle arrays.

PubMed

Duan, Chao; Wang, Ying; Sun, Jinling; Guan, Changrong; Grunder, Sergio; Mayor, Marcel; Peng, Lianmao; Liao, Jianhui

2013-11-07

We studied the electronic transport properties of metal nanoparticle arrays, particularly focused on the Coulomb charging energy. By comparison, we confirmed that it is more reasonable to estimate the Coulomb charging energy using the activation energy from the temperature-dependent zero-voltage conductance. Based on this, we systematically and comprehensively investigated the parameters that could be used to tune the Coulomb charging energy in nanoparticle arrays. We found that four parameters, including the particle core size, the inter-particle distance, the nearest neighboring number, and the dielectric constant of ligand molecules, could significantly tune the Coulomb charging energy.

Dual reactor for in situ/operando fluorescent mode XAS studies of sample containing low-concentration 3d or 5d metal elements

NASA Astrophysics Data System (ADS)

Nguyen, Luan; Tang, Yu; Li, Yuting; Zhang, Xiaoyan; Wang, Ding; Tao, Franklin Feng

2018-05-01

Transition metal elements are the most important elements of heterogeneous catalysts used for chemical and energy transformations. Many of these catalysts are active at a temperature higher than 400 °C. For a catalyst containing a 3d or 5d metal element with a low concentration, typically their released fluorescence upon the K-edge or L-edge adsorption of X-rays is collected for the analysis of chemical and coordination environments of these elements. However, it is challenging to perform in situ/operando X-ray absorption spectroscopy (XAS) studies of elements of low-energy absorption edges at a low concentration in a catalyst during catalysis at a temperature higher than about 450 °C. Here a unique reaction system consisting two reactors, called a dual reactor system, was designed for performing in situ or operando XAS studies of these elements of low-energy absorption edges in a catalyst at a low concentration during catalysis at a temperature higher than 450 °C in a fluorescent mode. This dual-reactor system contains a quartz reactor for preforming high-temperature catalysis up to 950 °C and a Kapton reactor remaining at a temperature up to 450 °C for collecting data in the same gas of catalysis. With this dual reactor, chemical and coordination environments of low-concentration metal elements with low-energy absorption edges such as the K-edge of 3d metals including Ti, V, Cr, Mn, Fe, Co, Ni, and Cu and L edge of 5d metals including W, Re, Os, Ir, Pt, and Au can be examined through first performing catalysis at a temperature higher than 450 °C in the quartz reactor and then immediately flipping the catalyst in the same gas flow to the Kapton reactor remained up to 450 °C to collect data. The capability of this dual reactor was demonstrated by tracking the Mn K-edge of the MnOx/Na2WO4 catalyst during activation in the temperature range of 300-900 °C and catalysis at 850 °C.

Low Temperature Soda-Oxygen Pulping of Bagasse.

PubMed

Yue, Fengxia; Chen, Ke-Li; Lu, Fachuang

2016-01-13

Wood shortages, environmental pollution and high energy consumption remain major obstacles hindering the development of today's pulp and paper industry. Energy-saving and environmental friendly pulping processes are still needed, especially for non-woody materials. In this study, soda-oxygen pulping of bagasse was investigated and a successful soda-oxygen pulping process for bagasse at 100 °C was established. The pulping parameters of choice were under active alkali charge of 23%, maximum cooking temperature 100 °C, time hold at maximum temperature 180 min, initial pressure of oxygen 0.6 MPa, MgSO4 charge 0.5%, and de-pithed bagasse consistency 12%. Properties of the resultant pulp were screened yield 60.9%, Kappa number 14, viscosity 766 dm³/kg, and brightness 63.7% ISO. Similar pulps were also obtained at 110 °C or 105 °C with a cooking time of 90 min. Compared with pulps obtained at higher temperatures (115-125 °C), this pulp had higher screened yield, brightness, and acceptable viscosity, while the delignification degree was moderate. These results indicated that soda-oxygen pulping at 100 °C, the lowest cooking temperature reported so far for soda-oxygen pulping, is a suitable process for making chemical pulp from bagasse. Pulping at lower temperature and using oxygen make it an environmental friendly and energy-saving pulping process.

The effect of temperature on postprandial metabolism of yellowfin tuna (Thunnus albacares).

PubMed

Klinger, Dane H; Dale, Jonathan J; Gleiss, Adrian C; Brandt, Tyler; Estess, Ethan E; Gardner, Luke; Machado, Benjamin; Norton, Alex; Rodriguez, Luis; Stiltner, James; Farwell, Charles; Block, Barbara A

2016-05-01

Specific dynamic action (SDA), the increase in metabolic expenditure associated with consumption of a meal, represents a substantial portion of fish energy budgets and is highly influenced by ambient temperature. The effect of temperature on SDA has not been studied in yellowfin tuna (Thunnus albacares, Bonnaterre 1788), an active pelagic predator that occupies temperate and subtropical waters. The energetic cost and duration of SDA were calculated by comparing routine and post-prandial oxygen consumption rates. Mean routine metabolic rates in yellowfin tuna increased with temperature, from 136 mg O2 kg(-1)h(-1) at 20 °C to 211 mg O2 kg(-1)h at 24 °C. The mean duration of SDA decreased from 40.2h at 20 °C to 33.1h at 24 °C, while mean SDA coefficient, the percentage of energy in a meal that is consumed during digestion, increased from 5.9% at 20 °C to 12.7% at 24 °C. Digestion in yellowfin tuna is faster at a higher temperature but requires additional oxidative energy. Enhanced characterization of the role of temperature in SDA of yellowfin tuna deepens our understanding of tuna physiology and can help improve management of aquaculture and fisheries. Copyright © 2016 Elsevier Inc. All rights reserved.

A neutron spectrometer based on temperature variations in superheated drop compositions

NASA Astrophysics Data System (ADS)

Apfel, Robert E.; d'Errico, Francesco

2002-01-01

The response of superheated drop detectors (SDDs) to neutron radiation varies in a self-consistent manner with variations in temperature and pressure, making such compositions suitable for neutron spectrometry. The advantage of this approach is that the response functions of candidate materials versus energy as the temperature or pressure is varied are nested and have distinct thresholds, with no thermal neutron response. These characteristics permit unfolding without the uncertainties associated with other spectrometry techniques, where multiple solutions are possible, thus requiring an initial guess of the spectrum. A spectrometer was developed based on the well-established technology for acoustic sensing of bubble events interfaced with a proportional-integral-derivative temperature controller. The active monitor for neutrons, called REMbrandt™, was used as the platform for controlling temperature on a SDD probe and for data acquisition, thereby automating the process of measuring the neutron energy spectrum. The new instrument, called REM-SPEC™, implements and automates the original BINS approach: it adjusts the temperature of the SDD vial in increasing steps and measures the bubble event rate at each step. By using two distinct SDD materials with overlapping responses, the 0.1-20 MeV range of energies relevant to practical spectrometry is readily covered. Initial experiments with an Am-Be source validate the operational protocols of this device.

Activation energy and entropy for viscosity of wormlike micelle solutions.

PubMed

Chandler, H D

2013-11-01

The viscosities of two surfactant solutions which form wormlike micelles (WLMs) were studied over a range of temperatures and strain rates. WLM solutions appear to differ from many other shear thinning systems in that, as the shear rate increases, stress-shear rate curves tend to converge with temperature rather than diverge and this can sometimes lead to higher temperature curves crossing those at lower. Behaviour was analysed in terms of activation kinetics. It is suggested that two mechanisms are involved: Newtonian flow, following an Arrhenius law superimposed on a non-Newtonian flow described by a stress assisted kinetic law, this being a more general form of the Arrhenius law. Anomalous flow is introduced into the kinetic equation via a stress dependent activation entropy term. Copyright © 2013 Elsevier Inc. All rights reserved.

High-energy green supercapacitor driven by ionic liquid electrolytes as an ultra-high stable next-generation energy storage device

NASA Astrophysics Data System (ADS)

Thangavel, Ranjith; Kannan, Aravindaraj G.; Ponraj, Rubha; Thangavel, Vigneysh; Kim, Dong-Won; Lee, Yun-Sung

2018-04-01

Development of supercapacitors with high energy density and long cycle life using sustainable materials for next-generation applications is of paramount importance. The ongoing challenge is to elevate the energy density of supercapacitors on par with batteries, while upholding the power and cyclability. In addition, attaining such superior performance with green and sustainable bio-mass derived compounds is very crucial to address the rising environmental concerns. Herein, we demonstrate the use of watermelon rind, a bio-waste from watermelons, towards high energy, and ultra-stable high temperature green supercapacitors with a high-voltage ionic liquid electrolyte. Supercapacitors assembled with ultra-high surface area, hierarchically porous carbon exhibits a remarkable performance both at room temperature and at high temperature (60 °C) with maximum energy densities of ∼174 Wh kg-1 (25 °C), and 177 Wh kg-1 (60 °C) - based on active mass of both electrodes. Furthermore, an ultra-high specific power of ∼20 kW kg-1 along with an ultra-stable cycling performance with 90% retention over 150,000 cycles has been achieved even at 60 °C, outperforming supercapacitors assembled with other carbon based materials. These results demonstrate the potential to develop high-performing, green energy storage devices using eco-friendly materials for next generation electric vehicles and other advanced energy storage systems.

Kinetic Analysis of Isothermal Decomposition Process of Sodium Bicarbonate Using the Weibull Probability Function—Estimation of Density Distribution Functions of the Apparent Activation Energies

NASA Astrophysics Data System (ADS)

Janković, Bojan

2009-10-01

The decomposition process of sodium bicarbonate (NaHCO3) has been studied by thermogravimetry in isothermal conditions at four different operating temperatures (380 K, 400 K, 420 K, and 440 K). It was found that the experimental integral and differential conversion curves at the different operating temperatures can be successfully described by the isothermal Weibull distribution function with a unique value of the shape parameter ( β = 1.07). It was also established that the Weibull distribution parameters ( β and η) show independent behavior on the operating temperature. Using the integral and differential (Friedman) isoconversional methods, in the conversion (α) range of 0.20 ≤ α ≤ 0.80, the apparent activation energy ( E a ) value was approximately constant ( E a, int = 95.2 kJmol-1 and E a, diff = 96.6 kJmol-1, respectively). The values of E a calculated by both isoconversional methods are in good agreement with the value of E a evaluated from the Arrhenius equation (94.3 kJmol-1), which was expressed through the scale distribution parameter ( η). The Málek isothermal procedure was used for estimation of the kinetic model for the investigated decomposition process. It was found that the two-parameter Šesták-Berggren (SB) autocatalytic model best describes the NaHCO3 decomposition process with the conversion function f(α) = α0.18(1-α)1.19. It was also concluded that the calculated density distribution functions of the apparent activation energies ( ddfE a ’s) are not dependent on the operating temperature, which exhibit the highly symmetrical behavior (shape factor = 1.00). The obtained isothermal decomposition results were compared with corresponding results of the nonisothermal decomposition process of NaHCO3.

Exposure of embryos to cyclically cold incubation temperatures durably affects energy metabolism and antioxidant pathways in broiler chickens.

PubMed

Loyau, T; Collin, A; Yenisey, C; Crochet, S; Siegel, P B; Akşit, M; Yalçin, S

2014-08-01

Cyclically cold incubation temperatures have been suggested as a means to improve resistance of broiler chickens to ascites; however, the underlying mechanisms are not known. Nine hundred eggs obtained from 48 wk Ross broiler breeders were randomly assigned to 2 incubation treatments: control I eggs were incubated at 37.6°C throughout, whereas for cold I eggs the incubation temperature was reduced by 1°C for 6 h daily from 10 to 18 d of incubation. Thereafter, chickens were reared at standard temperatures or under cold exposure that was associated or not with a postnatal cold acclimation at d 5 posthatch. At hatch, hepatic catalase activity and malondialdehyde content were measured. Serum thyroid hormone and triglyceride concentrations, and muscle expression of several genes involved in the regulation of energy metabolism and oxidative stress were also measured at hatch and 5 and 25 d posthatch. Cold incubation induced modifications in antioxidant pathways with higher catalase activity, but lower expression of avian uncoupling protein 3 at hatch. However, long-term enhancement in the expression of avian uncoupling protein 3 was observed, probably caused by an increase in the expression of the transcription factor peroxisome proliferator activated receptor-γ coactivator-1α. These effects were not systematically associated with an increase in serum triiodothyronine concentrations that were observed only in chickens exposed to both cold incubation and later acclimation at 5 d with cold rearing. Our results suggest that these conditions of cyclically cold incubation resulted in the long-term in changes in antioxidant pathways and energy metabolism, which could enhance the health of chickens reared under cold conditions. © Poultry Science Association Inc.

The kinetics of the decompositions of the proton bound dimers of 1,4-dimethylpyridine and dimethyl methylphosphonate from atmospheric pressure ion mobility spectra

NASA Astrophysics Data System (ADS)

Ewing, R. G.; Eiceman, G. A.; Harden, C. S.; Stone, J. A.

2006-09-01

The rate constants for the dissociations, A2H+ --> AH+ + A, of the symmetrical proton bound dimers of 2,4-dimethylpyridine and dimethyl methylphosphonate have been determined using an ion mobility spectrometer operating with air as drift gas at ambient pressure. Reaction time was varied by varying the drift electric field. The rate constants were derived from the mobility spectra by determining the rate at which ions decomposed in the drift region. Arrhenius plots with a drift gas containing water vapor at 5 ppmv gave the following activation energies and pre-exponential factors: 2,4-dimethylpyridine, 94 +/- 2 kJ mol-1, log A (s-1) = 15.9 +/- 0.4; dimethyl methylphosphonate, 127 +/- 3 kJ mol-1, log A (s-1) = 15.6 +/- 0.3. The enthalpy changes for the decompositions calculated from the activation energies are in accord with literature values for symmetrical proton bound dimers of oxygen and nitrogen bases. The results for dimethyl methylphosphonate were obtained over the temperature range 478-497 K and are practically independent of water concentration (5-2000 ppmv). The activation energy for 2,4-dimethylpyridine, obtained over the temperature range 340-359 K, decreased to 31 kJ mol-1 in the presence of 2.0 x 103 ppmv of water. At the low temperature, a displacement reaction involving water may account for the decrease. The reduced mobilities of the protonated molecules and the proton bound dimers have been determined over a wide temperature range. While the values for the dimers are essentially independent of the water concentration in the drift gas, those of the protonated molecules show a strong dependence.

Some notes on hydrogen-related point defects and their role in the isotope exchange and electrical conductivity in olivine

NASA Astrophysics Data System (ADS)

Karato, Shun-ichiro

2015-11-01

Nominally anhydrous minerals such as olivine dissolve hydrogen in a variety of forms including free (or interstitial) proton (Hrad) and two protons trapped at the M-site ((2 H)M×). The strength of chemical bonding between protons and the surrounding atoms are different among different species, and consequently protons belonging to different species likely have different mobility (diffusion coefficients). I discuss the role of diffusion of protons in different species in the isotope exchange and hydrogen-assisted electrical conductivity adding a few notes to the previous work by Karato (2013) including a new way to test the model. I conclude that in the case of isotope exchange, the interaction among these species is strong because diffusion is heterogeneous, whereas there is no strong interaction among different species in electrical conduction where diffusion is homogeneous (in an infinite crystal). Consequently, the slowest diffusing species controls the rate of isotope exchange, whereas the fastest diffusing species controls electrical conductivity leading to a different temperature dependence of activation energy and anisotropy. This model explains the differences in the activation energy and anisotropy between isotope diffusion and electrical conductivity, and predicts that the mechanism of electrical conductivity changes with temperature providing an explanation for most of the discrepancies among different experimental observations at different temperatures except for those by Poe et al. (2010) who reported anomalously high water content dependence and highly anisotropic activation energy. When the results obtained at high temperatures are used, most of the geophysically observed high and highly anisotropic electrical conductivity in the asthenosphere can be explained without invoking partial melting.

Frequency dependent electrical characteristics of ferroelectric Pb{4.0}K{1.0}Li{1.0}Nb{10}O{30} ceramics

NASA Astrophysics Data System (ADS)

Rao, K. S.; Krishna, P. M.; Prasad, D. M.; Latha, T. S.; Hussain, M.

2007-09-01

Dielectric, impedance, modulus and conductivity studies were performed over temperature 35 °C 600 °C and frequency 45 Hz 5 MHz range on the Lead Potassium Lithium Niobate (Pb{4.0}K{1.0}Li{1.0}Nb{10}O{30}, PKLN) ceramics. These studies established the conduction ion motion and polarization mechanism in the material. The dispersive dielectric loss at high temperature reveals the ionic conductivity. From frequency variation of \\varepsilonl response the pre-factor A(T) and critical exponent n(T) are evaluated, and are used in Jonscher's dielectric dispersion relation for \\varepsilon ' to fit with the experimental data. Complex impedance plots showed a non Debye type relaxation, are used to evaluate the grain and grain boundary conduction and relaxation activation energies. DC and ac conduction activation energies are estimated from Arrhenius plots. Occupancy of Li+ for C-sites gave a completely filled structure and enhanced the phase transition temperature to 520 °C compared to PKN. This is supported by the conduction activation energy in ferro region is more than the para region. Also, the dc conductivity characterized from bulk resistance and M^ll peak frequency. Polaron hoping mechanism at room temperature has been confirmed via the linear variation of the plot log (σ ac-σ dc) as a function of log ω 2. Stretched exponential parameter, β (0 < β ≤slant 1) has been evaluated from impedance plots, interpreted as a result of correlated motions between the Li+ ions and distribution of dielectric relaxation. Compared the results from different techniques, and discussed the conduction mechanism in the material.

Temperature dependence of ion transport: the compensated Arrhenius equation.

PubMed

Petrowsky, Matt; Frech, Roger

2009-04-30

The temperature-dependent conductivity originating in a thermally activated process is often described by a simple Arrhenius expression. However, this expression provides a poor description of the data for organic liquid electrolytes and amorphous polymer electrolytes. Here, we write the temperature dependence of the conductivity as an Arrhenius expression and show that the experimentally observed non-Arrhenius behavior is due to the temperature dependence of the dielectric constant contained in the exponential prefactor. Scaling the experimentally measured conductivities to conductivities at a chosen reference temperature leads to a "compensated" Arrhenius equation that provides an excellent description of temperature-dependent conductivities. A plot of the prefactors as a function of the solvent dielectric constant results in a single master curve for each family of solvents. These data suggest that ion transport in these and related systems is governed by a single activated process differing only in the activation energy for each family of solvents. Connection is made to the shift factor used to describe electrical and mechanical relaxation in a wide range of phenomena, suggesting that this scaling procedure might have broad applications.

Influence of Elevated Temperatures on Pet-Concrete Properties

NASA Astrophysics Data System (ADS)

Albano, C.; Camacho, N.; Hernández, M.; Matheus, A.; Gutiérrez, A.

2008-08-01

Lightweight aggregate is an important material in reducing the unit weight of concrete complying with special concrete structures of large high-rise buildings. Besides, the use of recycled PET bottles as lightweight aggregate in concrete is an effective contribution for environment preservation. So, the objective of the present work was to study experimentally the flexural strength of the PET -concrete blends and the thermal degradation of the PET in the concrete, when the blends with 10 and 20% in volume of PET were exposed to different temperatures (200, 400, 600 °C). The flexural strength of concrete-PET exposed to a heat source is strongly dependent on the temperature, water/cement ratio, as well as the content and particle size of PET. However, the activation energy is affected by the temperature, location of the PET particles on the slabs and the water/cement ratio. Higher water content originates thermal and hydrolytic degradation on the PET, while on the concrete, a higher vapor pressure which causes an increase in crack formation. The values of the activation energy are higher on the center of the slabs than on the surface, since concrete is a poor heat conductor.

Oxidative processes in soybean and pea seeds: effect of light, temperature, and water content

NASA Technical Reports Server (NTRS)

Vertucci, C. W.; Leopold, A. C.

1987-01-01

Oxidative processes are probable determinants of longevity of seeds in storage. Measurements of actual oxygen uptake rates were made for soybean and pea seeds as a comparison of short and long lived seeds when light, temperature, and moisture contents were varied. In both peas and soybeans, the oxygen uptake was depressed at low temperatures (<16 degrees C) and low water contents (< 0.25 gram H2O per gram dry weight). Apparent activation energies under these conditions are very high, while apparent activation energies of seeds at higher water contents and at temperatures greater than 22 degrees C are much less. Light enhances the level of oxygen uptake in pea, but reduces the level of oxygen uptake in soybean. The complexities of the interactions of oxygen uptake with environmental conditions in soybean compared to pea suggest that oxidative processes occur in soybean at low water contents, but are essentially absent in pea. It is suggested that the additional oxidative processes in soybean with moisture contents between 0.10 and 0.24 gram per gram may contribute to the poorer longevity of soybean seed compared to pea seed.

The influence of composition and final pyrolysis temperature variations on global kinetics of combustion of segregated municipal solid waste

NASA Astrophysics Data System (ADS)

Pranoto; Himawanto, D. A.; Arifin, N. A.

2017-04-01

The combustion of segregated municipal solid waste (MSW) and the resulted char from the pyrolysis process were investigated in this research. The segregated MSW that was collected and used can be divided into organic and inorganic waste materials. The organic materials were bamboo and banana leaves and the inorganic materials were Styrofoam and snack wrappings. The composition ratio of the waste was based on the percentage of weight of each sample. The thermal behaviour of the segregated MSW was investigated by thermo gravimetric analysis. For the pyrolysis process the prepared samples of 200gram were heated from ambient temperature until a variance of final pyrolysis temperature of 550°C, 650°C and 750°C at a constant heating rate of 25°C/min. It was found that the highest activation energy of the raw materials is achieved from sample CC1 (Char with 100% inorganic materials). The activation energy of the raw materials is relatively lower than that of the char. The higher the final pyrolysis temperature, the lower the calorific value of char. The calorific value gradually increases with the amount of inorganic materials.

Protein Surface Softness Is the Origin of Enzyme Cold-Adaptation of Trypsin

PubMed Central

Isaksen, Geir Villy; Åqvist, Johan; Brandsdal, Bjørn Olav

2014-01-01

Life has effectively colonized most of our planet and extremophilic organisms require specialized enzymes to survive under harsh conditions. Cold-loving organisms (psychrophiles) express heat-labile enzymes that possess a high specific activity and catalytic efficiency at low temperatures. A remarkable universal characteristic of cold-active enzymes is that they show a reduction both in activation enthalpy and entropy, compared to mesophilic orthologs, which makes their reaction rates less sensitive to falling temperature. Despite significant efforts since the early 1970s, the important question of the origin of this effect still largely remains unanswered. Here we use cold- and warm-active trypsins as model systems to investigate the temperature dependence of the reaction rates with extensive molecular dynamics free energy simulations. The calculations quantitatively reproduce the catalytic rates of the two enzymes and further yield high-precision Arrhenius plots, which show the characteristic trends in activation enthalpy and entropy. Detailed structural analysis indicates that the relationship between these parameters and the 3D structure is reflected by significantly different internal protein energy changes during the reaction. The origin of this effect is not localized to the active site, but is found in the outer regions of the protein, where the cold-active enzyme has a higher degree of softness. Several structural mechanisms for softening the protein surface are identified, together with key mutations responsible for this effect. Our simulations further show that single point-mutations can significantly affect the thermodynamic activation parameters, indicating how these can be optimized by evolution. PMID:25165981

Thermal electron attachment to chlorinated alkenes in the gas phase

NASA Astrophysics Data System (ADS)

Wnorowski, K.; Wnorowska, J.; Michalczuk, B.; Jówko, A.; Barszczewska, W.

2017-01-01

This paper reports the measurements of the rate coefficients and the activation energies of the electron capture processes with various chlorinated alkenes. The electron attachment processes in the mixtures of chlorinated alkenes with carbon dioxide have been investigated using a Pulsed Townsend technique. This study has been performed in the temperature range (298-378) K. The obtained rate coefficients more or less depended on temperature in accordance to Arrhenius equation. The activation energies (Ea's) were determined from the fit to the experimental data points with function ln(k) = ln(A) - Ea/kBT. The rate coefficients at 298 K were equal to 1.0 × 10-10 cm3 s-1, 2.2 × 10-11 cm3 s-1, 1.6 × 10-9 cm3 s-1, 4.4 × 10-8 cm3 s-1, 2.9 × 10-12 cm3 s-1 and 7.3 × 10-12 cm3 s-1 and activation energies were: 0.27 eV, 0.26 eV, 0.25 eV, 0.21 eV, 0.55 eV and 0.42 eV, for trans-1,2-dichloroethylene, cis-1,2-dichloroethylene, trichloroethylene, tetrachloroethylene, 2-chloropropene, 3-chloropropene respectively.

Glutamine Hydrolysis by Imidazole Glycerol Phosphate Synthase Displays Temperature Dependent Allosteric Activation

PubMed Central

Lisi, George P.; Currier, Allen A.; Loria, J. Patrick

2018-01-01

The enzyme imidazole glycerol phosphate synthase (IGPS) is a model for studies of long-range allosteric regulation in enzymes. Binding of the allosteric effector ligand N'-[5'-phosphoribulosyl)formimino]-5-aminoimidazole-4-carboxamide-ribonucleotide (PRFAR) stimulates millisecond (ms) timescale motions in IGPS that enhance its catalytic function. We studied the effect of temperature on these critical conformational motions and the catalytic mechanism of IGPS from the hyperthermophile Thermatoga maritima in an effort to understand temperature-dependent allostery. Enzyme kinetic and NMR dynamics measurements show that apo and PRFAR-activated IGPS respond differently to changes in temperature. Multiple-quantum Carr-Purcell-Meiboom-Gill (CPMG) relaxation dispersion experiments performed at 303, 323, and 343 K (30, 50, and 70°C) reveal that millisecond flexibility is enhanced to a higher degree in apo IGPS than in the PRFAR-bound enzyme as the sample temperature is raised. We find that the flexibility of the apo enzyme is nearly identical to that of its PRFAR activated state at 343 K, whereas conformational motions are considerably different between these two forms of the enzyme at room temperature. Arrhenius analyses of these flexible sites show a varied range of activation energies that loosely correlate to allosteric communities identified by computational methods and reflect local changes in dynamics that may facilitate conformational sampling of the active conformation. In addition, kinetic assays indicate that allosteric activation by PRFAR decreases to 65-fold at 343 K, compared to 4,200-fold at 303 K, which mirrors the decreased effect of PRFAR on ms motions relative to the unactivated enzyme. These studies indicate that at the growth temperature of T. maritima, PFRAR is a weaker allosteric activator than it is at room temperature and illustrate that the allosteric mechanism of IGPS is temperature dependent. PMID:29468164

Changes in Temperature Sensitivity and Activation Energy of Soil Organic Matter Decomposition in Different Qinghai-Tibet Plateau Grasslands

PubMed Central

Li, Jie; He, Nianpeng; Wei, Xuehong; Gao, Yang; Zuo, Yao

2015-01-01

Qinghai-Tibet Plateau grasslands are unique geographical regions and store substantial soil organic matter (SOM) in the soil surface, which make them very sensitive to global climate change. Here, we focused on three main grassland types (alpine meadow, steppe, and desert) and conducted a soil incubation experiment at five different temperatures (5, 10, 15, 20, and 25°C) to investigate SOM decomposition rates (R), temperature sensitivity (Q 10), and activation energy (E a). The results showed that grassland type and incubation temperature had significant impact on R (P < 0.001), and the values of R were exponential correlated with incubation temperature in three alpine grasslands. At the same temperature, R was in the following order: alpine meadow > alpinesteppe > alpine desert. The Q 10 values differed significantly among different grasslands, and the overall trends were as follows: alpine meadow (1.56 ± 0.09) < alpine steppe (1.88 ± 0.23) < alpine desert (2.39 ± 0.32). Moreover, the E a values differed significantly across different grassland types (P < 0.001) and increased with increasing incubation time. The exponential negative correlations between E a and R at 20°C across all grassland types (all Ps < 0.001) indicated that the substrate-quality temperature hypothesis is applicable to the alpine grasslands. Our findings provide new insights for understanding the responses of SOM decomposition and storage to warming scenarios in this Plateau. PMID:26176705

The activation energy of stabilised/solidified contaminated soils.

PubMed

Chitambira, B; Al-Tabbaa, A; Perera, A S R; Yu, X D

2007-03-15

Developing an understanding of the time-related performance of cement-treated materials is essential in understanding their durability and long-term effectiveness. A number of models have been developed to predict this time-related performance. One such model is the maturity concept which involves use of the 'global' activation energy which derives from the Arrhenius equation. The accurate assessment of the activation energy is essential in the realistic modelling of the accelerated ageing of cement-treated soils. Experimentally, this model is applied to a series of tests performed at different elevated temperatures. Experimental work, related to the results of a time-related performance on a contaminated site in the UK treated with in situ stabilisation/solidification was carried out. Three different cement-based grouts were used on two model site soils which were both contaminated with a number of heavy metals and a hydrocarbon. Uncontaminated soils were also tested. Elevated temperatures up to 60 degrees C and curing periods up to 90 days were used. The resulting global activation energies for the uncontaminated and contaminated soils were compared. Lower values were obtained for the contaminated soils reflecting the effect of the contaminants. The resulting equivalent ages for the uncontaminated and contaminated mixes tested were 5.1-7.4 and 0.8-4.1 years, respectively. This work shows how a specific set of contaminants affect the E(a) values for particular cementitious systems and how the maturity concept can be applied to cement-treated contaminated soils.

Structural instability and phase co-existence driven non-Gaussian resistance fluctuations in metal nanowires at low temperatures.

PubMed

Bid, Aveek; Raychaudhuri, A K

2016-11-11

We report a detailed experimental study of the resistance fluctuations measured at low temperatures in high quality metal nanowires ranging in diameter from 15-200 nm. The wires exhibit co-existing face-centered-cubic and 4H hcp phases of varying degrees as determined from the x-ray diffraction data. We observe the appearance of a large non-Gaussian noise for nanowires of diameter smaller than 50 nm over a certain temperature range around ≈30 K. The diameter range ∼30 nm, where the noise has maxima coincides with the maximum volume fraction of the co-existing 4H hcp phase thus establishing a strong link between the fluctuation and the phase co-existence. The resistance fluctuation in the same temperature range also shows a deviation of [Formula: see text] behavior at low frequency with appearance of single frequency Lorentzian type contribution in the spectral power density. The fluctuations are thermally activated with an activation energy [Formula: see text] meV, which is of same order as the activation energy of creation of stacking fault in FCC metals that leads to the co-existing crystallographic phases. Combining the results of crystallographic studies of the nanowires and analysis of the resistance fluctuations we could establish the correlation between the appearance of the large resistance noise and the onset of phase co-existence in these nanowires.

Influence of shell thickness on thermal stability of bimetallic Al-Pd nanoparticles

NASA Astrophysics Data System (ADS)

Wen, John Z.; Nguyen, Ngoc Ha; Rawlins, John; Petre, Catalin F.; Ringuette, Sophie

2014-07-01

Aluminum-based bimetallic core-shell nanoparticles have shown promising applications in civil and defense industries. This study addresses the thermal stability of aluminum-palladium (Al-Pd) core/shell nanoparticles with a varying shell thickness of 5, 6, and 7 Å, respectively. The classic molecular dynamics (MD) simulations are performed in order to investigate the effects of the shell thickness on the ignition mechanism and subsequent energetic processes of these nanoparticles. The histograms of temperature change and structural evolution clearly show the inhibition role of the Pd shell during ignition. While the nanoparticle with a thicker shell is more thermally stable and hence requires more excess energy, stored as the potential energy of the nanoparticle and provided through numerically heating, to initiate the thermite reaction, a higher adiabatic temperature can be produced from this nanoparticle, thanks to its greater content of Pd. The two-stage thermite reactions are discussed with their activation energy based on the energy balance processes during MD heating and production. Analyses of the simulation results reveal that the inner pressure of the core-shell nanoparticle increases with both temperature and the absorbed thermal energy during heating, which may result in a breakup of the Pd shell.

Differential temperature effects on dissipation of excess light energy and energy partitioning in lut2 mutant of Arabidopsis thaliana under photoinhibitory conditions.

PubMed

Popova, Antoaneta V; Dobrev, Konstantin; Velitchkova, Maya; Ivanov, Alexander G

2018-05-03

The high-light-induced alterations in photosynthetic performance of photosystem II (PSII) and photosystem I (PSI) as well as effectiveness of dissipation of excessive absorbed light during illumination for different periods of time at room (22 °C) and low (8-10 °C) temperature of leaves of Arabidopsis thaliana, wt and lut2, were followed with the aim of unraveling the role of lutein in the process of photoinhibition. Photosynthetic parameters of PSII and PSI were determined on whole leaves by PAM fluorometer and oxygen evolving activity-by a Clark-type electrode. In thylakoid membranes, isolated from non-illuminated and illuminated for 4.5 h leaves of wt and lut2 the photochemical activity of PSII and PSI and energy interaction between the main pigment-protein complexes was determined. Results indicate that in non-illuminated leaves of lut2 the maximum rate of oxygen evolution and energy utilization in PSII is lower, excitation pressure of PSII is higher and cyclic electron transport around PSI is faster than in wt leaves. Under high-light illumination, lut2 leaves are more sensitive in respect to PSII performance and the extent of increase of excitation pressure of PSII, Φ NO , and cyclic electron transport around PSI are higher than in wt leaves, especially when illumination is performed at low temperature. Significant part of the excessive light energy is dissipated via mechanism, not dependent on ∆pH and to functioning of xanthophyll cycle in LHCII, operating more intensively in lut2 leaves.

The Interplay of Energy Balance and Daily Timing of Activity in a Subterranean Rodent: A Laboratory and Field Approach.

PubMed

Tachinardi, Patricia; Valentinuzzi, Verónica S; Oda, Gisele A; Buck, C Loren

The tuco-tuco (Ctenomys aff. knighti) is among the rodent species known to be nocturnal under standard laboratory conditions and diurnal under natural conditions. The circadian thermoenergetics (CTE) hypothesis postulates that switches in activity timing are a response to energetic challenges; daytime activity reduces thermoregulatory costs by consolidating activity to the warmest part of the day. Studying wild animals under both captive and natural conditions can increase understanding of how temporal activity patterns are shaped by the environment and could serve as a test of the CTE hypothesis. We estimated the effects of activity timing on energy expenditure for the tuco-tuco by combining laboratory measurements of metabolic rate with environmental temperature records in both winter and summer. We showed that, in winter, there would be considerable energy savings if activity is allocated at least partially during daylight, lending support to the CTE hypothesis. In summer, the impact of activity timing on energy expenditure is small, suggesting that during this season other factors, such as predation risk, water balance, and social interaction, may have more important roles than energetics in the determination of activity time.

Tested Demonstrations.

ERIC Educational Resources Information Center

Gilbert, George L., Ed.

1988-01-01

Details three demonstrations for use in chemistry classrooms. Includes: "A Demonstration of Corrosion by Differential Aeration"; "A Simple Demonstration of the Activation Energy Concept"; and "A Boiling Demonstration at Room Temperature." Each description includes equipment, materials, and methods. (CW)

SERI Solar Energy Storage Program: FY 1984

NASA Astrophysics Data System (ADS)

Luft, W.; Bohn, M.; Copeland, R. J.; Kreith, F.; Nix, R. G.

1985-02-01

The activities of the Solar Energy Research Institute's Solar Energy Research Institute's Solar Energy Storage Program during its sixth year are summarized. During FY 1984 a study was conducted to identify the most promising high-temperature containment concepts considering corrosion resistance, material strength at high temperature, reliability of performance, and cost. Of the two generic types of high-temperature thermal storage concepts, the single-tank system was selected using a two-medium approach to the thermocline maintenance. This concept promises low costs, but further research is required. A conceptual design for a sand-to-air direct-contact heat exchanger was developed using dual-lock hoppers to introduce the sand into the fluidized-bed exchanger, and using cyclones to remove sand particles from the output air stream. Preliminary cost estimates indicate heat exchanger subsystem annual levelized costs of about $4/GJ with compressor costs of an additional $0.75/GJ. An economic analysis comparing sensible and latent heat storage for nitrate and carbonate salts with solely sensible heat storage showed 3%-21% cost savings with combined sensible and latent heat storage.

Porphyrin-Based Symmetric Redox-Flow Batteries towards Cold-Climate Energy Storage.

PubMed

Ma, Ting; Pan, Zeng; Miao, Licheng; Chen, Chengcheng; Han, Mo; Shang, Zhenfeng; Chen, Jun

2018-03-12

Electrochemical energy storage with redox-flow batteries (RFBs) under subzero temperature is of great significance for the use of renewable energy in cold regions. However, RFBs are generally used above 10 °C. Herein we present non-aqueous organic RFBs based on 5,10,15,20-tetraphenylporphyrin (H 2 TPP) as a bipolar redox-active material (anode: [H 2 TPP] 2- /H 2 TPP, cathode: H 2 TPP/[H 2 TPP] 2+ ) and a Y-zeolite-poly(vinylidene fluoride) (Y-PVDF) ion-selective membrane with high ionic conductivity as a separator. The constructed RFBs exhibit a high volumetric capacity of 8.72 Ah L -1 with a high voltage of 2.83 V and excellent cycling stability (capacity retention exceeding 99.98 % per cycle) in the temperature range between 20 and -40 °C. Our study highlights principles for the design of RFBs that operate at low temperatures, thus offering a promising approach to electrochemical energy storage under cold-climate conditions. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Degradation analysis of a Ni-based layered positive-electrode active material cycled at elevated temperatures studied by scanning transmission electron microscopy and electron energy-loss spectroscopy

NASA Astrophysics Data System (ADS)

Kojima, Y.; Muto, S.; Tatsumi, K.; Kondo, H.; Oka, H.; Horibuchi, K.; Ukyo, Y.

We investigate the local structural changes in a positive electrode of a lithium ion secondary battery (LiNi 0.8Co 0.15Al 0.05O 2 (NCA) as the active material) associated with charge-discharge cycling at elevated temperatures by scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS). STEM-EELS spectral imaging reveals the evolution of a NiO-like phase localized near the surface and grain boundary regions after many cycles. The amounts of capacity fading and resistance increase are discussed based on the results of the semiquantitative estimation of NiO-like and other product phases. We also identify the chemical state of lithium in the NiO-like phase substituting for Ni.

Atomic steps on an ultraflat Si(111) surface upon sublimation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sitnikov, S. V., E-mail: sitnikov@isp.nsc.ru; Latyshev, A. V.; Kosolobov, S. S.

2016-05-15

The kinetics of atomic steps on an ultraflat Si(111) surface is studied by in situ ultrahigh-vacuum reflection electron microscopy at temperatures of 1050–1350°C. For the first time it is experimentally shown that the rate of displacement of an atomic step during sublimation nonlinearly depends on the width of the adjacent terrace. It is established that the atomic mechanism of mass-transport processes at the surface at temperatures higher than 1200°C is controlled by nucleation and the diffusion of surface vacancies rather than of adsorbed Si atoms. The studies make it possible to estimate the activation energy of the dissolution of vacanciesmore » from the surface into the bulk of Si. The estimated activation energy is (4.3 ± 0.05) eV.« less

First observation of HO˙ reactivity in water under high energy ions at elevated temperature.

PubMed

Balcerzyk, A; Boughattas, I; Pin, S; Balanzat, E; Baldacchino, G

2014-11-21

This communication reports the first observation of the formation of HO˙ produced under two different High energy ion beams, (18)O(8+) and (36)Ar(18+) having Linear Energy Transfers (LET) of 65 and 350 eV nm(-1) respectively, at temperatures up to 411 K. Both scavenging with various concentrations of SCN(-) and heavy-ion pulse radiolysis methods are used with an original temperature and pressure regulated optical cell. Deconvolution of kinetics is used to analyze the evolution of HO˙ track segment yields as a function of time and temperature. It takes care of involving the ionic strength effect and Arrhenius expression in the rate constants correction. The results show a fast decay of HO˙ yields in the 10(-10)-10(-8) s range which denotes an efficient reactivity of this species in the track structure of the ion beam. This effect is enhanced with the lowest LET of O(8+). Increasing the temperature also accelerates the decays for both ions. These observations are discussed in terms of temperature activation of reactions and the track structure exhibiting the formation of HO˙ in a "low LET" penumbra around the ionization tracks. HO˙ track segment yields at 100 ns, of 0.4 × 10(-7) and 0.6 × 10(-7) mol J(-1), respectively for 350 and 65 eV nm(-1), are not affected by temperature.

Warming reduces metabolic rate in marine snails: adaptation to fluctuating high temperatures challenges the metabolic theory of ecology.

PubMed

Marshall, David J; McQuaid, Christopher D

2011-01-22

The universal temperature-dependence model (UTD) of the metabolic theory of ecology (MTE) proposes that temperature controls mass-scaled, whole-animal resting metabolic rate according to the first principles of physics (Boltzmann kinetics). Controversy surrounds the model's implication of a mechanistic basis for metabolism that excludes the effects of adaptive regulation, and it is unclear how this would apply to organisms that live in fringe environments and typically show considerable metabolic adaptation. We explored thermal scaling of metabolism in a rocky-shore eulittoral-fringe snail (Echinolittorina malaccana) that experiences constrained energy gain and fluctuating high temperatures (between 25°C and approximately 50°C) during prolonged emersion (weeks). In contrast to the prediction of the UTD model, metabolic rate was often negatively related to temperature over a benign range (30-40°C), the relationship depending on (i) the temperature range, (ii) the degree of metabolic depression (related to the quiescent period), and (iii) whether snails were isolated within their shells. Apparent activation energies (E) varied between 0.05 and -0.43 eV, deviating excessively from the UTD's predicted range of between 0.6 and 0.7 eV. The lowering of metabolism when heated should improve energy conservation in a high-temperature environment and challenges both the theory's generality and its mechanistic basis.

Effect of heat exposure and exercise on food intake regulation: A randomized crossover study in young healthy men.

PubMed

Faure, Cécile; Charlot, Keyne; Henri, Stéphane; Hardy-Dessources, Marie-Dominique; Hue, Olivier; Antoine-Jonville, Sophie

2016-10-01

The effect of physical activity on food intake regulation may be moderated by environmental temperature. The aim of the study was to determine the single and combined effects of metabolic activity and temperature on energy intake and its hormonal regulation. A randomized crossover study was conducted in the laboratory. Ten healthy and physically active young Afro-Caribbean men participated in four experimental sessions (rest at 22°C and 31°C and cycling at 60% of their maximal oxygen uptake at 22°C and 31°C, all for 40 min). Each test period was followed by a 30-min recovery period and then an ad libitum meal. The main outcome measures were energy balance, subjective appetite, and plasma pancreatic polypeptide (PP), cholecystokinin (CCK) and ghrelin concentrations. Relative energy intake was significantly decreased whereas plasma PP was increased in the exercise conditions (p=0.004 and p=0.002, respectively). Postprandial levels of CCK were elevated only in the rest conditions. Exposure to heat induced a decrease in plasma ghrelin (p=0.031). Exercise induced a short-term energy deficit. However, modifications in the hormonal regulation of food intake in response to short-term heat or heat and exercise exposure seem to be minor and did not induce changes in energy intake. This trial was registered at clinicaltrials.gov as NCT02157233. Copyright © 2016. Published by Elsevier Inc.

Thermally responsive polymer electrolytes for inherently safe electrochemical energy storage

NASA Astrophysics Data System (ADS)

Kelly, Jesse C.

Electrochemical double layer capacitors (EDLCs), supercapacitors and Li-ion batteries have emerged as premier candidates to meet the rising demands in energy storage; however, such systems are limited by thermal hazards, thermal runaway, fires and explosions, all of which become increasingly more dangerous in large-format devices. To prevent such scenarios, thermally-responsive polymer electrolytes (RPEs) that alter properties in electrochemical energy storage devices were designed and tested. These RPEs will be used to limit or halt device operation when temperatures increase beyond a predetermined threshold, therefore limiting further heating. The development of these responsive systems will offer an inherent safety mechanism in electrochemical energy storage devices, while preserving the performance, lifetimes, and versatility that large-format systems require. Initial work focused on the development of a model system that demonstrated the concept of RPEs in an electrochemical device. Aqueous electrolyte solutions of polymers exhibiting properties that change in response to temperature were developed for applications in EDLCs and supercapacitors. These "smart materials" provide a means to control electrochemical systems where polymer phase separation at high temperatures affects electrolyte properties and inhibits device performance. Aqueous RPEs were synthesized using N-isopropylacrylamide, which governs the thermal properties, and fractions of acrylic acid or vinyl sulfonic acids, which provide ions to the solution. The molecular properties of these aqueous RPEs, specifically the ionic composition, were shown to influence the temperature-dependent electrolyte properties and the extent to which these electrolytes control the energy storage characteristics of a supercapacitor device. Materials with high ionic content provided the highest room temperature conductivity and electrochemical activity; however, RPEs with low ionic content provided the highest "on-off" ratio in electrochemical activity at elevated temperatures. Overall, solution pH and conductivity were altered by an order of magnitude and device performance (ability to store charge) decreased by over 70%. After demonstration of a model responsive electrolyte in an aqueous system, ionic liquid (IL) based electrolytes were developed as a means of controlling the electrochemical performance in the non-aqueous environments that batteries, specifically Li-ion, require. Here, two systems were developed: (1) an electrolyte comprising poly(ethylene oxide) (PEO), the IL, [EMIM][BF4], and a lithium salt and (2) an electrolyte comprising poly(benzyl methacrylate) (PBzMA), the IL, [EMIM][TFSI], and a lithium salt. In each system, the polymer-IL phase separation inhibited device operation at elevated temperatures. For the PEO/IL electrolyte, the thermally induced liquid-liquid phase separation was shown to decrease the ionic conductivity, thereby affecting the concentration of ions at the electrode. Additionally, an increasing charge transfer resistance associated with the phase separated polymer coating the porous electrode was shown to limit electrochemical activity significantly. For the PBzMA/IL electrolyte, the solid-liquid phase separation did not show a change in conductivity, but did cause a drastic increase in charge transfer resistance, effectively shutting off Li-ion battery operation at high temperatures. Such responsive mixtures provide a transformative approach to regulating electrochemical processes, which is necessary to achieve inherently safe operation in large format energy storage with EDLCs, supercapacitors and Li-ion batteries.

Effect of H2 binding on the nonadiabatic transition probability between singlet and triplet states of the [NiFe]-hydrogenase active site.

PubMed

Kaliakin, Danil S; Zaari, Ryan R; Varganov, Sergey A

2015-02-12

We investigate the effect of H2 binding on the spin-forbidden nonadiabatic transition probability between the lowest energy singlet and triplet electronic states of [NiFe]-hydrogenase active site model, using a velocity averaged Landau-Zener theory. Density functional and multireference perturbation theories were used to provide parameters for the Landau-Zener calculations. It was found that variation of the torsion angle between the terminal thiolate ligands around the Ni center induces an intersystem crossing between the lowest energy singlet and triplet electronic states in the bare active site and in the active site with bound H2. Potential energy curves between the singlet and triplet minima along the torsion angle and H2 binding energies to the two spin states were calculated. Upon H2 binding to the active site, there is a decrease in the torsion angle at the minimum energy crossing point between the singlet and triplet states. The probability of nonadiabatic transitions at temperatures between 270 and 370 K ranges from 35% to 32% for the active site with bound H2 and from 42% to 38% for the bare active site, thus indicating the importance of spin-forbidden nonadiabatic pathways for H2 binding on the [NiFe]-hydrogenase active site.

Nonadiabatic coupling reduces the activation energy in thermally activated delayed fluorescence.

PubMed

Gibson, J; Penfold, T J

2017-03-22

The temperature dependent rate of a thermally activated process is given by the Arrhenius equation. The exponential decrease in the rate with activation energy, which this imposes, strongly promotes processes with small activation barriers. This criterion is one of the most challenging during the design of thermally activated delayed fluorescence (TADF) emitters used in organic light emitting diodes. The small activation energy is usually achieved with donor-acceptor charge transfer complexes. However, this sacrifices the radiative rate and is therefore incommensurate with the high luminescence quantum yields required for applications. Herein we demonstrate that the spin-vibronic mechanism, operative for efficient TADF, overcomes this limitation. Nonadiabatic coupling between the lowest two triplet states give rise to a strong enhancement of the rate of reserve intersystem crossing via a second order mechanism and promotes population transfer between the T 1 to T 2 states. Consequently the rISC mechanism is actually operative between initial and final state exhibiting an energy gap that is smaller than between the T 1 and S 1 states. This contributes to the small activation energies for molecules exhibiting a large optical gap, identifies limitations of the present design procedures and provides a basis from which to construct TADF molecules with simultaneous high radiative and rISC rates.

A review of limits on microbial activity in the cryosphere: temperature and water availability

NASA Astrophysics Data System (ADS)

Bakermans, C.

2017-12-01

The extent of microbial activity in the cryosphere likely depends on many things: the presence of liquid water, an adequate energy and nutrient supply (amount and flux), the absence of damaging conditions, exposure to low temperatures, and the time to evolve adaptations to low temperature conditions. Determining the extent of microbial activity in the cryosphere is a challenge complicated by the reduced availability of liquid water as water freezes and the low rates of diffusion and reaction brought on by low temperatures. Despite these limitations, many studies have demonstrated that reproduction by microorganisms is possible at temperatures of -10 to -20°C and that metabolism continues to even lower temperatures of about -30°C. In addition, microcosm studies in frozen soils and permafrost have demonstrated respiration down to temperatures of -18°C and DNA synthesis at temperatures from 0 to -20°C. In the environment, low temperature conditions (and lack of liquid water) appear to limit microbial activity in a few places like Don Juan Pond and University Valley in Antarctica. Microorganisms may be metabolically active in Arctic permafrost, but metabolism may be so exceptionally slow as to escape detection. Given the slow metabolism expected and the short geological age of permafrost (3 million years at the longest), there is probably insufficient time for microorganisms to evolve to become better adapted to live at subfreezing temperatures. Indeed, terrestrial life may never have the chance to evolve to exploit the low temperature capabilities of its biomolecules in view of the limited times at which cold environments persist on Earth. These observational studies of microorganisms in low temperature environments of the Polar regions expose how the extent of microbial activity at low temperature is entangled with other factors (perhaps inextricably); how the lack of liquid water at low temperatures appears to be the true limit on activity at low temperatures, and not low temperature per se; and that time at low temperatures may limit cold adaptation of microorganisms.

Duality picture of Superconductor-insulator transitions on Superconducting nanowire.

PubMed

Makise, Kazumasa; Terai, Hirotaka; Tominari, Yukihiro; Tanaka, Shukichi; Shinozaki, Bunju

2016-06-17

In this study, we investigated the electrical transport properties of niobium titanium nitride (NbTiN) nanowire with four-terminal geometries to clarify the superconducting phase slip phenomena and superconducting-insulator transitions (SIT) for one-dimensional superconductors. We fabricated various nanowires with different widths and lengths from epitaxial NbTiN films using the electron beam lithography method. The temperature dependence of resistance R(T) below the superconducting transition temperature Tc was analyzed using thermal activation phase slip (TAPS) and quantum phase slip (QPS) theories. Although the accuracy of experimental data at low temperatures can deviate when using the TAPS model, the QPS model thoroughly represents the R(T) characteristic with resistive tail at low temperatures. From the analyses of data on Tc, we found that NbTiN nanowires exhibit SIT because of the change in the ratio of kinetic inductance energy and QPS amplitude energy with respect to the flux-charge duality theory.

Possible observation of the Berezinskii-Kosterlitz-Thouless transition in boron-doped diamond films

NASA Astrophysics Data System (ADS)

Coleman, Christopher; Bhattacharyya, Somnath

2017-11-01

The occurrence of the Berezinskii-Kosterlitz-Thouless (BKT) transition is investigated in heavily boron-doped nanocrystalline diamond films through a combination of current-voltage and resistance measurements. We observe transport features suggesting a robust BKT transition along with transport features related to vortex pinning in nanocrystalline diamond films with smaller grain size. The vortex core energy determined through analysis of the resistance temperature curves was found to be anti-correlated to the BKT transition temperatures. It is also observed that the higher BKT temperature is related to an increased vortex-antivortex binding energy derived from the activated transport regions. Further, the magnetic field induced superconductor insulator transition shows the possibility of the charge glass state. The consequences of granularity such as localization and vortex pinning can lead to tuneable BKT temperatures and strongly affects the field induced insulating state.

Transparent and conducting ZnO films grown by spray pyrolysis

NASA Astrophysics Data System (ADS)

Hadjeris, Lazhar; Herissi, Labidi; Badreddine Assouar, M.; Easwarakhanthan, Thomas; Bougdira, Jamal; Attaf, Nadhir; Salah Aida, M.

2009-03-01

ZnO films were prepared using the simple, flexible and cost-effective spray pyrolysis technique at different substrate temperatures and precursor molarity values. The films' structural, optical and electrical properties were investigated by x-ray diffraction, UV-VIS transmittance spectroscopy, profilometry and voltage-current-temperature (VIT) measurements. The films prepared at substrate temperatures above 400 °C appear better crystallized with (0 0 2) preferred orientation and exhibit higher visible transmittance (65-80%), higher electrical n-type semiconductor conductivity (10-50 (Ω cm)-1), lower activation energy (<0.35 eV) and smaller Urbach energy (80 meV). These results indicate that such sprayed ZnO films are chemically purer and have many fewer defects and less disorder owing to an almost complete chemical decomposition of the precursor droplets. ZnO films having desired optical and electrical properties for cheaper large-area solar cells may thus be tailored through the substrate temperature and the precursor molarity.

Integrated Model-Based Controls and PHM for Improving Turbine Engine Performance, Reliability, and Cost

DTIC Science & Technology

2009-09-01

capable of surviving the high-temperature, high- vibration environment of a jet engine. Active control spans active surge/stall control and three...other closely related areas, viz., active combustion control (references 21-22), active noise control, and active vibration control. All of these are...self-powered sensors that harvest energy from engine heat or vibrations replace sensors that require power. The long-term vision is one of a

Fractional quantum Hall effect at Landau level filling ν = 4/11

DOE PAGES

Pan, W.; Baldwin, K. W.; West, K. W.; ...

2015-01-09

In this study, we report low temperature electronic transport results on the fractional quantum Hall effect of composite fermions at Landau level filling ν = 4/11 in a very high mobility and low density sample. Measurements were carried out at temperatures down to 15mK, where an activated magnetoresistance R xx and a quantized Hall resistance R xy, within 1% of the expected value of h/(4/11)e 2, were observed. The temperature dependence of the R xx minimum at 4/11 yields an activation energy gap of ~ 7 mK. Developing Hall plateaus were also observed at the neighboring states at ν =more » 3/8 and 5/13.« less

Direct measurement of free-energy barrier to nucleation of crystallites in amorphous silicon thin films

NASA Technical Reports Server (NTRS)

Shi, Frank G.

1994-01-01

A method is introduced to measure the free-energy barrier W(sup *), the activation energy, and activation entropy to nucleation of crystallites in amorphous solids, independent of the energy barrier to growth. The method allows one to determine the temperature dependence of W(sup *), and the effect of the preparation conditions of the initial amorphous phase, the dopants, and the crystallization methds on W(sup *). The method is applied to determine the free-energy barrier to nucleation of crystallites in amorphous silicon (a-Si) thin films. For thermally induced nucleation in a-Si thin films with annealing temperatures in the range of from 824 to 983 K, the free-energy barrier W(sup *) to nucleation of silicon crystals is about 2.0 - 2.1 eV regardless of the preparation conditions of the films. The observation supports the idea that a-Si transforms into an intermediate amorphous state through the structural relaxation prior to the onset of nucleation of crystallites in a-Si. The observation also indicates that the activation entropy may be an insignificant part of the free-energy barrier for the nucleation of crystallites in a-Si. Compared with the free-energy barrier to nucleation of crystallites in undoped a-Si films, a significant reduction is observed in the free-energy barrier to nucleation in Cu-doped a-Si films. For a-Si under irradiation of Xe(2+) at 10(exp 5) eV, the free-energy barrier to ion-induced nucleation of crystallites is shown to be about half of the value associated with thermal-induced nucleation of crystallites in a-Si under the otherwise same conditions, which is much more significant than previously expected. The present method has a general kinetic basis; it thus should be equally applicable to nucleation of crystallites in any amorphous elemental semiconductors and semiconductor alloys, metallic and polymeric glasses, and to nucleation of crystallites in melts and solutions.

Ambient-temperature NO oxidation over amorphous CrOx-ZrO 2 mixed oxide catalysts: Significant promoting effect of ZrO 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Aiyong; Guo, Yanglong; Gao, Feng

2017-03-01

Three series of Cr-based mixed oxides (Cr-Co, Cr-Fe, and Cr-Ni oxides) with high specific surface areas and amorphous textures are synthesized using a novel sol-gel method. These mixed oxides, in comparison to their pure metal oxide (CrOx, Co3O4, FeOx and NiO) counterparts, display enhanced performance for catalytic oxidation of low-concentration NO at room temperature. Over best performing catalysts, 100% NO conversion can be maintained up to 30 h of operation at a high space velocity of 45,000 ml g-1 h-1. The amorphous structure is found to be critical for these catalysts to maintain high activity and durability. Cr/M (M=Co, Femore » and Ni) molar ratio, nitrate precursor decomposition temperature and catalyst calcination temperature are important criteria for the synthesis of the highly active catalysts. This work was supported by National Basic Research Program of China (2013CB933200), National Natural Science Foundation of China (21577035, 21577034), Commission of Science and Technology of Shanghai Municipality (15DZ1205305) and 111 Project (B08021). Aiyong Wang gratefully acknowledges the China Scholarship Council for the Joint-Training Scholarship Program with the Pacific Northwest National Laboratory (PNNL). PNNL is operated for the U.S. Department of Energy (DOE) by Battelle. FG and CHFP are supported by the U.S. DOE/Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Office.« less

Electrical conductivity and modulus formulation in zinc modified bismuth boro-tellurite glasses

NASA Astrophysics Data System (ADS)

Dhankhar, Sunil; Kundu, R. S.; Dult, Meenakshi; Murugavel, S.; Punia, R.; Kishore, N.

2016-09-01

The ac conductivity of zinc modified tellurium based quaternary glasses having composition 60 TeO2-10 B2O3-(30 - x) Bi2O3-x ZnO; x = 10, 15, 20, 25 and 30 has been investigated in the frequency range 10-1-105 Hz and in temperature range 483-593 K. Frequency and temperature dependent ac conductivity found to obey Jonscher power law modified by Almond-West. DC conductivity, crossover frequency and frequency exponent have been estimated from the fitting of the experimental data of conductivity with Jonscher power law modified by Almond-West. The ac conductivity and its frequency exponent have been analyzed by various theoretical models. In presently studied glasses ac conduction takes place via tunneling of overlapping large polaron tunneling. Activation energy is found to be increased with increase in zinc content and dc conduction takes place via variable range hopping proposed by Mott with some modification suggested by Punia et al. The value of the stretched exponent ( β) obtained by fitting of M^' ' }} reveals the presence of non-Debye type relaxation. Scaling spectra of ac conductivity and electric modulus collapse into a single master curve for all compositions and temperatures, reveals the presence of composition and temperature independent conduction and relaxation process in these glasses. Activation energy of conduction ( W) and electric modulus ( E R ) are nearly equal, indicating that polaron have to overcome the same energy barrier during conduction as well as relaxation processes.

Observation of Tunneling in the Hydrogenation of Atomic Nitrogen on the Ru(001) Surface to Form NH.

PubMed

Waluyo, Iradwikanari; Ren, Yuan; Trenary, Michael

2013-11-07

The kinetics of NH and ND formation and dissociation reactions on Ru(001) were studied using time-dependent reflection absorption infrared spectroscopy (RAIRS). Our results indicate that NH and ND formation and dissociation on Ru(001) follow first-order kinetics. In our reaction temperature range (320-390 K for NH and 340-390 K for ND), the apparent activation energies for NH and ND formation were found to be 72.2 ± 1.9 and 87.1 ± 1.8 kJ/mol, respectively, while NH and ND dissociation reactions between 370 and 400 K have apparent activation barriers of 106.9 ± 4.1 and 101.8 ± 4.8 kJ/mol, respectively. The lower apparent activation energy for NH formation than that for ND as well as the comparison between experimentally measured isotope effects with theoretical results strongly indicates that tunneling already starts to play a role in this reaction at a temperature as high as 340 K.