Substrate-dependent temperature sensitivity of soil organic matter decomposition

NASA Astrophysics Data System (ADS)

Myachina, Olga; Blagodatskaya, Evgenia

2015-04-01

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

Origins of the temperature dependence of hammerhead ribozyme catalysis.

PubMed Central

Peracchi, A

1999-01-01

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

Temperature dependence of optically induced cell deformations

NASA Astrophysics Data System (ADS)

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

2012-02-01

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

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.

Temperature dependent charge transport in poly(3-hexylthiophene) diodes

NASA Astrophysics Data System (ADS)

Rahaman, Abdulla Bin; Sarkar, Atri; Banerjee, Debamalya

2018-04-01

In this work, we present charge transport properties of poly(3-hexylthiophene) (P3HT) diodes under dark conditions. Temperature dependent current-voltage (J-V) characteristics shows that charge transport represents a transition from ohomic to trap limited current. The forward current density obeys a power law J˜Vm, m>2 represents the space charge limited current region in presence of traps within the band gap. Frequency dependent conductivity has been studied in a temperature range 150K-473K. The dc conductivity values show Arrhenius like behavior and it gives conductivity activation energy 223 meV. Temperature dependent conductivity indicates a thermodynamic transition of our system.

In vitro selection of high temperature Zn(2+)-dependent DNAzymes.

PubMed

Nelson, Kevin E; Bruesehoff, Peter J; Lu, Yi

2005-08-01

In vitro selection of Zn(2+)-dependent RNA-cleaving DNAzymes with activity at 90 degrees C has yielded a diverse spool of selected sequences. The RNA cleavage efficiency was found in all cases to be specific for Zn(2+) over Pb(2+), Ca(2+), Cd(2+), Co(2+), Hg(2+), and Mg(2+). The Zn(2+)-dependent activity assay of the most active sequence showed that the DNAzyme possesses an apparent Zn(2+)-binding dissociation constant of 234 muM and that its activity increases with increasing temperatures from 50-90 degrees C. A fit of the Arrhenius plot data gave E(a) = 15.3 kcal mol(-1). Surprisingly, the selected Zn(2+)-dependent DNAzymes showed only a modest (approximately 3-fold) activity enhancement over the background rate of cleavage of random sequences containing a single embedded ribonucleotide within an otherwise DNA oligonucleotide. The result is attributable to the ability of DNA to sustain cleavage activity at high temperature with minimal secondary structure when Zn(2+) is present. Since this effect is highly specific for Zn(2+), this metal ion may play a special role in molecular evolution of nucleic acids at high temperature.

Patterns of sarcomere activation, temperature dependence, and effect of ryanodine in chemically skinned cardiac fibers

PubMed Central

1986-01-01

Functionally skinned and electrochemically shunted myocytes were prepared by perfusing rat hearts with collagenase in order to obtain a technically improved measurement of sarcomere dynamics and to evaluate the role of sarcoplasmic reticulum in situ with respect to contractile activation. In the presence of micromolar calcium, the myocytes exhibited phasic and propagated contraction waves beginning at one end and proceeding along the myocyte. Beating rates, the propagation velocity of the activation wave, and single sarcomere shortening and relaxation velocities were obtained by manual or automated analysis of 16-mm film recorded at 170 frames/s from a camera attached to a microscope that was equipped with a temperature-controlled stage. In parallel experiments, calcium accumulation by the sarcoplasmic reticulum of the myocytes in situ was measured by direct isotopic tracer methods. The frequency (10-38 min-1) of spontaneous contractions, the velocity (1.9-7.4 microns . s-1) of sarcomere shortening, and the velocity (1.7-6.8 microns . s-1) of sarcomere relaxation displayed identical temperature dependences (Q10 = 2.2), which are similar to that of the calcium pump of sarcoplasmic reticulum and are consistent with a rate limit imposed by enzyme-catalyzed mechanisms on all these parameters. On the other hand, the velocity (77- 159 microns . s-1) of sequential sarcomere activation displayed a lower temperature dependence (Q10 = 1.5), which is consistent with a diffusion-limited and self-propagating release of calcium from one sarcomere to the other. The phasic contractile activity of the dissociated myocytes was inhibited by 10(-8)-10(6) M ryanodine (and not by myolemmal calcium blockers) under conditions in which calcium accumulation by sarcoplasmic reticulum in situ was demonstrated to proceed optimally. The effect of ryanodine is attributed to an interaction of this drug with sarcotubular structures, producing inhibition of calcium release from the sarcoplasmic

Single-residue molecular switch for high-temperature dependence of vanilloid receptor TRPV3

PubMed Central

Liu, Beiying; Qin, Feng

2017-01-01

Thermal transient receptor potential (TRP) channels, a group of ion channels from the transient receptor potential family, play important functions in pain and thermal sensation. These channels are directly activated by temperature and possess strong temperature dependence. Furthermore, their temperature sensitivity can be highly dynamic and use-dependent. For example, the vanilloid receptor transient receptor potential 3 (TRPV3), which has been implicated as a warmth detector, becomes responsive to warm temperatures only after intensive stimulation. Upon initial activation, the channel exhibits a high-temperature threshold in the noxious temperature range above 50 °C. This use dependence of heat sensitivity thus provides a mechanism for sensitization of thermal channels. However, how the channels acquire the use dependence remains unknown. Here, by comparative studies of chimeric channels between use-dependent and use-independent homologs, we have determined the molecular basis that underlies the use dependence of temperature sensitivity of TRPV3. Remarkably, the restoration of a single residue that is apparently missing in the use-dependent homologs could largely eliminate the use dependence of heat sensitivity of TRPV3. The location of the region suggests a mechanism of temperature-dependent gating of thermal TRP channels involving an intracellular region assembled around the TRP domain. PMID:28154143

The effect of concentration- and temperature-dependent dielectric constant on the activity coefficient of NaCl electrolyte solutions

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

Valiskó, Mónika; Boda, Dezső, E-mail: boda@almos.vein.hu

2014-06-21

Our implicit-solvent model for the estimation of the excess chemical potential (or, equivalently, the activity coefficient) of electrolytes is based on using a dielectric constant that depends on the thermodynamic state, namely, the temperature and concentration of the electrolyte, ε(c, T). As a consequence, the excess chemical potential is split into two terms corresponding to ion-ion (II) and ion-water (IW) interactions. The II term is obtained from computer simulation using the Primitive Model of electrolytes, while the IW term is estimated from the Born treatment. In our previous work [J. Vincze, M. Valiskó, and D. Boda, “The nonmonotonic concentration dependencemore » of the mean activity coefficient of electrolytes is a result of a balance between solvation and ion-ion correlations,” J. Chem. Phys. 133, 154507 (2010)], we showed that the nonmonotonic concentration dependence of the activity coefficient can be reproduced qualitatively with this II+IW model without using any adjustable parameter. The Pauling radii were used in the calculation of the II term, while experimental solvation free energies were used in the calculation of the IW term. In this work, we analyze the effect of the parameters (dielectric constant, ionic radii, solvation free energy) on the concentration and temperature dependence of the mean activity coefficient of NaCl. We conclude that the II+IW model can explain the experimental behavior using a concentration-dependent dielectric constant and that we do not need the artificial concept of “solvated ionic radius” assumed by earlier studies.« less

From blood oxygenation level dependent (BOLD) signals to brain temperature maps.

PubMed

Sotero, Roberto C; Iturria-Medina, Yasser

2011-11-01

A theoretical framework is presented for converting Blood Oxygenation Level Dependent (BOLD) images to brain temperature maps, based on the idea that disproportional local changes in cerebral blood flow (CBF) as compared with cerebral metabolic rate of oxygen consumption (CMRO₂) during functional brain activity, lead to both brain temperature changes and the BOLD effect. Using an oxygen limitation model and a BOLD signal model, we obtain a transcendental equation relating CBF and CMRO₂ changes with the corresponding BOLD signal, which is solved in terms of the Lambert W function. Inserting this result in the dynamic bioheat equation describing the rate of temperature changes in the brain, we obtain a nonautonomous ordinary differential equation that depends on the BOLD response, which is solved numerically for each brain voxel. Temperature maps obtained from a real BOLD dataset registered in an attention to visual motion experiment were calculated, obtaining temperature variations in the range: (-0.15, 0.1) which is consistent with experimental results. The statistical analysis revealed that significant temperature activations have a similar distribution pattern than BOLD activations. An interesting difference was the activation of the precuneus in temperature maps, a region involved in visuospatial processing, an effect that was not observed on BOLD maps. Furthermore, temperature maps were more localized to gray matter regions than the original BOLD maps, showing less activated voxels in white matter and cerebrospinal fluid.

Temperature-dependent changes in the host-seeking behaviors of parasitic nematodes.

PubMed

Lee, Joon Ha; Dillman, Adler R; Hallem, Elissa A

2016-05-06

Entomopathogenic nematodes (EPNs) are lethal parasites of insects that are of interest as biocontrol agents for insect pests and disease vectors. Although EPNs have been successfully commercialized for pest control, their efficacy in the field is often inconsistent for reasons that remain elusive. EPN infective juveniles (IJs) actively search for hosts to infect using a diverse array of host-emitted odorants. Here we investigate whether their host-seeking behavior is subject to context-dependent modulation. We find that EPN IJs exhibit extreme plasticity of olfactory behavior as a function of cultivation temperature. Many odorants that are attractive for IJs grown at lower temperatures are repulsive for IJs grown at higher temperatures and vice versa. Temperature-induced changes in olfactory preferences occur gradually over the course of days to weeks and are reversible. Similar changes in olfactory behavior occur in some EPNs as a function of IJ age. EPNs also show temperature-dependent changes in their host-seeking strategy: IJs cultured at lower temperatures appear to more actively cruise for hosts than IJs cultured at higher temperatures. Furthermore, we find that the skin-penetrating rat parasite Strongyloides ratti also shows temperature-dependent changes in olfactory behavior, demonstrating that such changes occur in mammalian-parasitic nematodes. IJs are developmentally arrested and long-lived, often surviving in the environment through multiple seasonal temperature changes. Temperature-dependent modulation of behavior may enable IJs to optimize host seeking in response to changing environmental conditions, and may play a previously unrecognized role in shaping the interactions of both beneficial and harmful parasitic nematodes with their hosts.

Investigation of temperature dependence of development and aging

NASA Technical Reports Server (NTRS)

Sacher, G. A.

1969-01-01

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

Temperature-Dependent Dielectric Properties of Al/Epoxy Nanocomposites

NASA Astrophysics Data System (ADS)

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

2016-06-01

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

Shape-Dependent Activity of Ceria for Hydrogen Electro-Oxidation in Reduced-Temperature Solid Oxide Fuel Cells.

PubMed

Tong, Xiaofeng; Luo, Ting; Meng, Xie; Wu, Hao; Li, Junliang; Liu, Xuejiao; Ji, Xiaona; Wang, Jianqiang; Chen, Chusheng; Zhan, Zhongliang

2015-11-04

Single crystalline ceria nanooctahedra, nanocubes, and nanorods are hydrothermally synthesized, colloidally impregnated into the porous La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) scaffolds, and electrochemically evaluated as the anode catalysts for reduced temperature solid oxide fuel cells (SOFCs). Well-defined surface terminations are confirmed by the high-resolution transmission electron microscopy--(111) for nanooctahedra, (100) for nanocubes, and both (110) and (100) for nanorods. Temperature-programmed reduction in H2 shows the highest reducibility for nanorods, followed sequentially by nanocubes and nanooctahedra. Measurements of the anode polarization resistances and the fuel cell power densities reveal different orders of activity of ceria nanocrystals at high and low temperatures for hydrogen electro-oxidation, i.e., nanorods > nanocubes > nanooctahedra at T ≤ 450 °C and nanooctahedra > nanorods > nanocubes at T ≥ 500 °C. Such shape-dependent activities of these ceria nanocrystals have been correlated to their difference in the local structure distortions and thus in the reducibility. These findings will open up a new strategy for design of advanced catalysts for reduced-temperature SOFCs by elaborately engineering the shape of nanocrystals and thus selectively exposing the crystal facets. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Temperature dependence of direct current conductivity in Ag-ED20 nanocomposite films

NASA Astrophysics Data System (ADS)

Novikov, G. F.; Rabenok, E. V.; Bogdanova, L. M.; Irzhak, V. I.

2017-10-01

The effect of silver nanoparticles (NPs) in the concentration range of ≤0.8 wt % have on direct current conductivity σdc of Ag-ED20 nanocomposite is studied by method of broadband dielectric spectroscopy (10-2-105 Hz) method of broadband dielectric spectroscopy. It is found that temperature dependence σdc consists of two sections: above the glass transition temperature ( T g), the dependence corresponds to the empirical Vogel-Fulcher-Tammann law (Vogel temperature T 0 does not depend on the NP concentration); below T g, the dependence is Arrhenius with activation energy E a ≈ 1.2 eV. In the region where T > T g, the σdc value grows along with NP concentration. It is concluded that the observed broken form of the temperature dependence is apparently due to a change in the conduction mechanism after the freezing of ion mobility at temperatures below T g.

Temperature dependence of plastic scintillators

NASA Astrophysics Data System (ADS)

Peralta, L.

2018-03-01

Plastic scintillator detectors have been studied as dosimeters, since they provide a cost-effective alternative to conventional ionization chambers. Several articles have reported undesired response dependencies on beam energy and temperature, which provides the motivation to determine appropriate correction factors. In this work, we studied the light yield temperature dependency of four plastic scintillators, BCF-10, BCF-60, BC-404, RP-200A and two clear fibers, BCF-98 and SK-80. Measurements were made using a 50 kVp X-ray beam to produce the scintillation and/or radioluminescence signal. The 0 to 40 °C temperature range was scanned for each scintillator, and temperature coefficients were obtained.

Temperature-Dependent Energy Gap Shift and Thermally Activated Transition in Multilayer CdTe/ZnTe Quantum Dots.

PubMed

Man, Minh Tan; Lee, Hong Seok

2015-10-01

We investigated the influence of growth conditions on carrier dynamics in multilayer CdTe/ZnTe quantum dots (QDs) by monitoring the temperature dependence of the photoluminescence emission energy. The results were analyzed using the empirical Varshni and O'Donnell relations for temperature variation of the energy gap shift. Best fit values showed that the thermally activated transition between two different states occurs due to band low-temperature quenching with values separated by 5.0-6.5 meV. The addition of stack periods in multilayer CdTe/ZnTe QDs plays an important role in the energy gap shift, where the exciton binding energy is enhanced, and, conversely, the exciton-phonon coupling strength is suppressed with an average energy of 19.3-19.8 meV.

Temperature dependence of frequency response characteristics in organic field-effect transistors

NASA Astrophysics Data System (ADS)

Lu, Xubing; Minari, Takeo; Liu, Chuan; Kumatani, Akichika; Liu, J.-M.; Tsukagoshi, Kazuhito

2012-04-01

The frequency response characteristics of semiconductor devices play an essential role in the high-speed operation of electronic devices. We investigated the temperature dependence of dynamic characteristics in pentacene-based organic field-effect transistors and metal-insulator-semiconductor capacitors. As the temperature decreased, the capacitance-voltage characteristics showed large frequency dispersion and a negative shift in the flat-band voltage at high frequencies. The cutoff frequency shows Arrhenius-type temperature dependence with different activation energy values for various gate voltages. These phenomena demonstrate the effects of charge trapping on the frequency response characteristics, since decreased mobility prevents a fast charge response for alternating current signals at low temperatures.

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.

Unraveling the Transcriptional Basis of Temperature-Dependent Pinoxaden Resistance in Brachypodium hybridum

PubMed Central

Matzrafi, Maor; Shaar-Moshe, Lidor; Rubin, Baruch; Peleg, Zvi

2017-01-01

Climate change endangers food security and our ability to feed the ever-increasing human population. Weeds are the most important biotic stress, reducing crop-plant productivity worldwide. Chemical control, the main approach for weed management, can be strongly affected by temperature. Previously, we have shown that temperature-dependent non-target site (NTS) resistance of Brachypodium hybridum is due to enhanced detoxification of acetyl-CoA carboxylase inhibitors. Here, we explored the transcriptional basis of this phenomenon. Plants were characterized for the transcriptional response to herbicide application, high-temperature and their combination, in an attempt to uncover the genetic basis of temperature-dependent pinoxaden resistance. Even though most of the variance among treatments was due to pinoxaden application (61%), plants were able to survive pinoxaden application only when grown under high-temperatures. Biological pathways and expression patterns of members of specific gene families, previously shown to be involved in NTS metabolic resistance to different herbicides, were examined. Cytochrome P450, glucosyl transferase and glutathione-S-transferase genes were found to be up-regulated in response to pinoxaden application under both control and high-temperature conditions. However, biological pathways related to oxidation and glucose conjugation were found to be significantly enriched only under the combination of pinoxaden application and high-temperature. Analysis of reactive oxygen species (ROS) was conducted at several time points after treatment using a probe detecting H2O2/peroxides. Comparison of ROS accumulation among treatments revealed a significant reduction in ROS quantities 24 h after pinoxaden application only under high-temperature conditions. These results may indicate significant activity of enzymatic ROS scavengers that can be correlated with the activation of herbicide-resistance mechanisms. This study shows that up-regulation of genes

Temperature dependency in motor skill learning.

PubMed

Immink, Maarten A; Wright, David L; Barnes, William S

2012-01-01

The present study investigated the role of temperature as a contextual condition for motor skill learning. Precision grip task training occurred while forearm cutaneous temperature was either heated (40-45 °C) or cooled (10-15 °C). At test, temperature was either reinstated or changed. Performance was comparable between training conditions while at test, temperature changes decreased accuracy, especially after hot training conditions. After cold training, temperature change deficits were only evident when concurrent force feedback was presented. These findings are the first evidence of localized temperature dependency in motor skill learning in humans. Results are not entirely accounted for by a context-dependent memory explanation and appear to represent an interaction of neuromuscular and sensory processes with the temperature present during training and test.

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.

Effects of a temperature-dependent rheology on large scale continental extension

NASA Technical Reports Server (NTRS)

Sonder, Leslie J.; England, Philip C.

1988-01-01

The effects of a temperature-dependent rheology on large-scale continental extension are investigated using a thin viscous sheet model. A vertically-averaged rheology is used that is consistent with laboratory experiments on power-law creep of olivine and that depends exponentially on temperature. Results of the calculations depend principally on two parameters: the Peclet number, which describes the relative rates of advection and diffusion of heat, and a dimensionless activation energy, which controls the temperature dependence of the rheology. At short times following the beginning of extension, deformation occurs with negligible change in temperature, so that only small changes in lithospheric strength occur due to attenuation of the lithosphere. However, after a certain critical time interval, thermal diffusion lowers temperatures in the lithosphere, strongly increasing lithospheric strength and slowing the rate of extension. This critical time depends principally on the Peclet number and is short compared with the thermal time constant of the lithosphere. The strength changes cause the locus of high extensional strain rates to shift with time from regions of high strain to regions of low strain. Results of the calculations are compared with observations from the Aegean, where maximum extensional strains are found in the south, near Crete, but maximum present-day strain rates are largest about 300 km further north.

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

Time- and temperature-dependent changes in cytochrome c oxidase activity and cyanide concentration in excised mice organs and mice cadavers.

PubMed

Singh, Poonam; Rao, Pooja; Yadav, Shiv K; Gujar, Niranjan L; Satpute, Ravindra M; Bhattacharya, Rahul

2015-01-01

Postmortem stability of cyanide biomarkers is often disputed. We assessed the time and temperature-dependent changes in cytochrome c oxidase (CCO) activity and cyanide concentration in various organs of mice succumbing to cyanide. Immediately after death, excised mice organs and mice cadavers were stored at room temperature (35°C ± 5°C) or in frozen storage (-20°C ± 2°C). At various times after death, CCO activity and cyanide concentrations were measured in excised mice organs or organs removed from mice cadavers. The study revealed that (i) measuring both the biomarkers in mice cadavers was more reliable compared to excised mice organs, (ii) measuring temporal CCO activity and cyanide concentration in vital organs from mice cadavers (room temperature) was reliable up to 24 h, and (iii) CCO activity in the brain and lungs and cyanide concentration in organs from mice cadavers (frozen) were measurable beyond 21 days. This study will be helpful in postmortem determination of cyanide poisoning. © 2014 American Academy of Forensic Sciences.

Nutrient limitation suppresses the temperature dependence of phytoplankton metabolic rates.

PubMed

Marañón, Emilio; Lorenzo, María P; Cermeño, Pedro; Mouriño-Carballido, Beatriz

2018-04-25

Climate warming has the potential to alter ecosystem function through temperature-dependent changes in individual metabolic rates. The temperature sensitivity of phytoplankton metabolism is especially relevant, since these microorganisms sustain marine food webs and are major drivers of biogeochemical cycling. Phytoplankton metabolic rates increase with temperature when nutrients are abundant, but it is unknown if the same pattern applies under nutrient-limited growth conditions, which prevail over most of the ocean. Here we use continuous cultures of three cosmopolitan and biogeochemically relevant species (Synechococcus sp., Skeletonema costatum and Emiliania huxleyi) to determine the temperature dependence (activation energy, E a ) of metabolism under different degrees of nitrogen (N) limitation. We show that both CO 2 fixation and respiration rates increase with N supply but are largely insensitive to temperature. E a of photosynthesis (0.11 ± 0.06 eV, mean ± SE) and respiration (0.04 ± 0.17 eV) under N-limited growth is significantly smaller than E a of growth rate under nutrient-replete conditions (0.77 ± 0.06 eV). The reduced temperature dependence of metabolic rates under nutrient limitation can be explained in terms of enzyme kinetics, because both maximum reaction rates and half-saturation constants increase with temperature. Our results suggest that the direct, stimulating effect of rising temperatures upon phytoplankton metabolic rates will be circumscribed to ecosystems with high-nutrient availability.

Temperature Dependence of Magnetically Active Charge Excitations in Magnetite across the Verwey Transition

NASA Astrophysics Data System (ADS)

Taguchi, M.; Chainani, A.; Ueda, S.; Matsunami, M.; Ishida, Y.; Eguchi, R.; Tsuda, S.; Takata, Y.; Yabashi, M.; Tamasaku, K.; Nishino, Y.; Ishikawa, T.; Daimon, H.; Todo, S.; Tanaka, H.; Oura, M.; Senba, Y.; Ohashi, H.; Shin, S.

2015-12-01

We study the electronic structure of bulk single crystals and epitaxial films of Fe3 O4 . Fe 2 p core level spectra show clear differences between hard x-ray (HAX) and soft x-ray photoemission spectroscopy (PES). The bulk-sensitive spectra exhibit temperature (T ) dependence across the Verwey transition, which is missing in the surface-sensitive spectra. By using an extended impurity Anderson full-multiplet model—and in contrast to an earlier peak assignment—we show that the two distinct Fe species (A and B site) and the charge modulation at the B site are responsible for the newly found double peaks in the main peak above TV and its T -dependent evolution. The Fe 2 p HAXPES spectra show a clear magnetic circular dichroism (MCD) in the metallic phase of magnetized 100-nm-thick films. The model calculations also reproduce the MCD and identify the contributions from magnetically distinct A and B sites. Valence band HAXPES shows a finite density of states at EF for the polaronic half metal with a remnant order above TV and a clear gap formation below TV. The results indicate that the Verwey transition is driven by changes in the strongly correlated and magnetically active B -site electronic states, consistent with resistivity and optical spectra.

Temperature dependence of LRE-HRE-TM thin films

NASA Astrophysics Data System (ADS)

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

2003-04-01

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

Temperature dependence of 63Ni-Si betavoltaic microbattery.

PubMed

Yunpeng, Liu; Xiao, Guo; Zhangang, Jin; Xiaobin, Tang

2018-05-01

This paper theoretically presented the temperature effects on the 63 Ni-Si betavoltaic microbattery irradiated by a source with different thicknesses and activity densities at a temperature range 170-340K. Temperature dependences of the monolayer and interbedded 63 Ni-Si betavoltaics at 213.15-333.15K were tested with respect to calculations. Results showed that the higher the thickness, activity density, and average energy of the source, the lower is the betavoltaic performance responds to temperature. With the increase in temperature, the V oc and P max of the upper, lower, and interbedded betavoltaics decreased linearly at low temperatures and decreased exponentially at high temperatures in the experiment. As predicted, the measured V oc and P max sensitivities of the lower betavoltaic with 4.90mCi/cm 2 63 Ni, -2.230mV/K and -1.132%, respectively, were lower than those with 1.96mCi/cm 2 63 Ni, -2.490mV/K and -1.348%, respectively. Compared with the calculated results, the prepared betavoltaics had lower V oc sensitivity and higher P max sensitivity. In addition, the measured V oc sensitivity of the interbedded betavoltaic in series is equal to the sum of those of the upper and lower ones as predicted. Moreover, the measured P max sensitivity of the interbedded betavoltaic is equal to the average of those of the two monolayers. Copyright © 2018 Elsevier Ltd. All rights reserved.

Temperature Dependence of Factors Controlling Isoprene Emissions

NASA Technical Reports Server (NTRS)

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

2009-01-01

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

A new temperature- and humidity-dependent surface site density approach for deposition ice nucleation

NASA Astrophysics Data System (ADS)

Steinke, I.; Hoose, C.; Möhler, O.; Connolly, P.; Leisner, T.

2015-04-01

Deposition nucleation experiments with Arizona Test Dust (ATD) as a surrogate for mineral dusts were conducted at the AIDA cloud chamber at temperatures between 220 and 250 K. The influence of the aerosol size distribution and the cooling rate on the ice nucleation efficiencies was investigated. Ice nucleation active surface site (INAS) densities were calculated to quantify the ice nucleation efficiency as a function of temperature, humidity and the aerosol surface area concentration. Additionally, a contact angle parameterization according to classical nucleation theory was fitted to the experimental data in order to relate the ice nucleation efficiencies to contact angle distributions. From this study it can be concluded that the INAS density formulation is a very useful tool to describe the temperature- and humidity-dependent ice nucleation efficiency of ATD particles. Deposition nucleation on ATD particles can be described by a temperature- and relative-humidity-dependent INAS density function ns(T, Sice) with ns(xtherm) = 1.88 ×105 · exp(0.2659 · xtherm) [m-2] , (1) where the temperature- and saturation-dependent function xtherm is defined as xtherm = -(T-273.2)+(Sice-1) ×100, (2) with the saturation ratio with respect to ice Sice >1 and within a temperature range between 226 and 250 K. For lower temperatures, xtherm deviates from a linear behavior with temperature and relative humidity over ice. Also, two different approaches for describing the time dependence of deposition nucleation initiated by ATD particles are proposed. Box model estimates suggest that the time-dependent contribution is only relevant for small cooling rates and low number fractions of ice-active particles.

Erroneous Arrhenius: Modified Arrhenius model best explains the temperature dependence of ectotherm fitness

PubMed Central

Knies, Jennifer L.; Kingsolver, Joel G.

2013-01-01

The initial rise of fitness that occurs with increasing temperature is attributed to Arrhenius kinetics, in which rates of reaction increase exponentially with increasing temperature. Models based on Arrhenius typically assume single rate-limiting reaction(s) over some physiological temperature range for which all the rate-limiting enzymes are in 100% active conformation. We test this assumption using datasets for microbes that have measurements of fitness (intrinsic rate of population growth) at many temperatures and over a broad temperature range, and for diverse ectotherms that have measurements at fewer temperatures. When measurements are available at many temperatures, strictly Arrhenius kinetics is rejected over the physiological temperature range. However, over a narrower temperature range, we cannot reject strictly Arrhenius kinetics. The temperature range also affects estimates of the temperature dependence of fitness. These results indicate that Arrhenius kinetics only apply over a narrow range of temperatures for ectotherms, complicating attempts to identify general patterns of temperature dependence. PMID:20528477

Erroneous Arrhenius: modified arrhenius model best explains the temperature dependence of ectotherm fitness.

PubMed

Knies, Jennifer L; Kingsolver, Joel G

2010-08-01

The initial rise of fitness that occurs with increasing temperature is attributed to Arrhenius kinetics, in which rates of reaction increase exponentially with increasing temperature. Models based on Arrhenius typically assume single rate-limiting reactions over some physiological temperature range for which all the rate-limiting enzymes are in 100% active conformation. We test this assumption using data sets for microbes that have measurements of fitness (intrinsic rate of population growth) at many temperatures and over a broad temperature range and for diverse ectotherms that have measurements at fewer temperatures. When measurements are available at many temperatures, strictly Arrhenius kinetics are rejected over the physiological temperature range. However, over a narrower temperature range, we cannot reject strictly Arrhenius kinetics. The temperature range also affects estimates of the temperature dependence of fitness. These results indicate that Arrhenius kinetics only apply over a narrow range of temperatures for ectotherms, complicating attempts to identify general patterns of temperature dependence.

Temperature Dependence Of Elastic Constants Of Polymers

NASA Technical Reports Server (NTRS)

Simha, Robert; Papazoglou, Elisabeth

1989-01-01

Two papers extend theory of elastic constants of disordered solids to finite temperatures below glass-transition temperatures. First paper, entitled "Elastic Constants of Disordered Solids II: Temperature Dependence," applies to cryogenic temperatures. Second paper, entitled "Theory of Thermoelastic Properties for Polymer Glasses," develops unified treatment for static compressional and elongational properties at temperatures up to glass-transition temperatures.

Mechanistic basis of temperature-dependent dwell fatigue in titanium alloys

NASA Astrophysics Data System (ADS)

Zheng, Zebang; Balint, Daniel S.; Dunne, Fionn P. E.

2017-10-01

The temperature-dependent dwell sensitivity of Ti-6242 and Ti-6246 alloys has been assessed over a temperature range from - 50∘ C to 390 °C using discrete dislocation plasticity which incorporates both thermal activation of dislocation escape from obstacles and slip transfer across grain boundaries. The worst-case load shedding in Ti-6242 alloy is found to be at or close to 120 °C under dwell fatigue loading, which diminishes and vanishes at temperatures lower than - 50∘ C or higher than 230 °C. Load shedding behaviour is predicted to occur in alloy Ti-6246 also but over a range of higher temperatures which are outside those relevant to in-service conditions. The key controlling dislocation mechanism with respect to load shedding in titanium alloys, and its temperature sensitivity, is shown to be the time constant associated with the thermal activation of dislocation escape from obstacles, with respect to the stress dwell time. The mechanistic basis of load shedding and dwell sensitivity in dwell fatigue loading is presented and discussed in the context of experimental observations.

The Effect of Temperature Dependent Material Nonlinearities on the Response of Piezoelectric Composite Plates

NASA Technical Reports Server (NTRS)

Lee, Ho-Jun; Saravanos, Dimitris A.

1997-01-01

Previously developed analytical formulations for piezoelectric composite plates are extended to account for the nonlinear effects of temperature on material properties. The temperature dependence of the composite and piezoelectric properties are represented at the material level through the thermopiezoelectric constitutive equations. In addition to capturing thermal effects from temperature dependent material properties, this formulation also accounts for thermal effects arising from: (1) coefficient of thermal expansion mismatch between the various composite and piezoelectric plies and (2) pyroelectric effects on the piezoelectric material. The constitutive equations are incorporated into a layerwise laminate theory to provide a unified representation of the coupled mechanical, electrical, and thermal behavior of smart structures. Corresponding finite element equations are derived and implemented for a bilinear plate element with the inherent capability to model both the active and sensory response of piezoelectric composite laminates. Numerical studies are conducted on a simply supported composite plate with attached piezoceramic patches under thermal gradients to investigate the nonlinear effects of material property temperature dependence on the displacements, sensory voltages, active voltages required to minimize thermal deflections, and the resultant stress states.

Temperature Dependence of Parametric Phenomenon in Airborne Ultrasound for Temperature Measurement

NASA Astrophysics Data System (ADS)

Kon, Akihiko; Wakatsuki, Naoto; Mizutani, Koichi

2008-08-01

The temperature dependence of parametric phenomenon in air was experimentally studied. It was confirmed from experimental data that the amplitude of upper sideband sound with a frequency of 36.175 kHz, which is caused by parametric phenomenon between high-power ultrasound with a frequency of 20.175 kHz and another normal sound with a frequency of 16.0 kHz, is proportional to -0.88×10-4×(T+273.15). This temperature dependence of the amplitude of upper sideband sound caused by the parametric phenomenon suggests a simple and effective method of temperature measurement.

Temperature dependence of alkali-antimonide photocathodes: Evaluation at cryogenic temperatures

DOE PAGES

Mamun, M. A.; Hernandez-Flores, M. R.; Morales, E.; ...

2017-10-24

Cs xK ySb photocathodes were manufactured on a niobium substrate and evaluated over a range of temperatures from 300 to 77 K. Vacuum conditions were identified that minimize surface contamination due to gas adsorption when samples were cooled below room temperature. Here, measurements of photocathode spectral response provided a means to evaluate the photocathode bandgap dependence on temperature and to predict photocathode quantum efficiency at 4 K, a typical temperature at which superconducting radio frequency photoguns operate.

Temperature dependence of conductivity measurement for conducting polymer

NASA Astrophysics Data System (ADS)

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

2014-03-01

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

A new temperature and humidity dependent surface site density approach for deposition ice nucleation

NASA Astrophysics Data System (ADS)

Steinke, I.; Hoose, C.; Möhler, O.; Connolly, P.; Leisner, T.

2014-07-01

Deposition nucleation experiments with Arizona Test Dust (ATD) as a surrogate for mineral dusts were conducted at the AIDA cloud chamber at temperatures between 220 and 250 K. The influence of the aerosol size distribution and the cooling rate on the ice nucleation efficiencies was investigated. Ice nucleation active surface site (INAS) densities were calculated to quantify the ice nucleation efficiency as a function of temperature, humidity and the aerosol surface area concentration. Additionally, a contact angle parameterization according to classical nucleation theory was fitted to the experimental data in order to relate the ice nucleation efficiencies to contact angle distributions. From this study it can be concluded that the INAS density formulation is a very useful tool to decribe the temperature and humidity dependent ice nucleation efficiency of ATD particles. Deposition nucleation on ATD particles can be described by a temperature and relative humidity dependent INAS density function ns(T, Sice) with ns(xtherm) = 1.88 × 105 \\centerdot exp(0.2659 \\centerdot xtherm) [m-2] (1) where the thermodynamic variable xtherm is defined as xtherm = -(T - 273.2) + (Sice-1) × 100 (2) with Sice>1 and within a temperature range between 226 and 250 K. For lower temperatures, xtherm deviates from a linear behavior with temperature and relative humidity over ice. Two different approaches for describing the time dependence of deposition nucleation initiated by ATD particles are proposed. Box model estimates suggest that the time dependent contribution is only relevant for small cooling rates and low number fractions of ice-active particles.

Model evaluation of temperature dependency for carbon and nitrogen removal in a full-scale activated sludge plant treating leather-tanning wastewater.

PubMed

Görgün, Erdem; Insel, Güçlü; Artan, Nazik; Orhon, Derin

2007-05-01

Organic carbon and nitrogen removal performance of a full-scale activated sludge plant treating pre-settled leather tanning wastewater was evaluated under dynamic process temperatures. Emphasis was placed upon observed nitrogen removal depicting a highly variable magnitude with changing process temperatures. As the plant was not specifically designed for this purpose, observed nitrogen removal could be largely attributed to simultaneous nitrification and denitrification presumably occurring at increased process temperatures (T>25 degrees C) and resulting low dissolved oxygen levels (DO<0.5 mgO2/L). Model evaluation using long-term data revealed that the yearly performance of activated sludge reactor could be successfully calibrated by means of temperature dependent parameters associated with nitrification, hydrolysis, ammonification and endogenous decay parameters. In this context, the Arrhenius coefficients of (i) for the maximum autotrophic growth rate, [image omitted]A, (ii) maximum hydrolysis rate, khs and (iii) endogenous heterotrophic decay rate, bH were found to be 1.045, 1.070 and 1.035, respectively. The ammonification rate (ka) defining the degradation of soluble organic nitrogen could not be characterized however via an Arrhenius-type equation.

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

Selecting Temperature for Protein Crystallization Screens Using the Temperature Dependence of the Second Virial Coefficient

PubMed Central

Liu, Jun; Yin, Da-Chuan; Guo, Yun-Zhu; Wang, Xi-Kai; Xie, Si-Xiao; Lu, Qin-Qin; Liu, Yong-Ming

2011-01-01

Protein crystals usually grow at a preferable temperature which is however not known for a new protein. This paper reports a new approach for determination of favorable crystallization temperature, which can be adopted to facilitate the crystallization screening process. By taking advantage of the correlation between the temperature dependence of the second virial coefficient (B 22) and the solubility of protein, we measured the temperature dependence of B 22 to predict the temperature dependence of the solubility. Using information about solubility versus temperature, a preferred crystallization temperature can be proposed. If B 22 is a positive function of the temperature, a lower crystallization temperature is recommended; if B 22 shows opposite behavior with respect to the temperature, a higher crystallization temperature is preferred. Otherwise, any temperature in the tested range can be used. PMID:21479212

Infralimbic cortex controls core body temperature in a histamine dependent manner.

PubMed

Riveros, M E; Perdomo, G; Torrealba, F

2014-04-10

An increase in body temperature accelerates biochemical reactions and behavioral and physiological responses. A mechanism to actively increase body temperature would be beneficial during motivated behaviors. The prefrontal cortex is implicated in organizing motivated behavior; the infralimbic cortex, a subregion of the medial prefrontal cortex, has the necessary connectivity to serve the role of initiating such thermogenic mechanism at the beginning of the appetitive phase of motivated behavior; further, this cortex is active during motivated behavior and its disinhibition produces a marked behavioral and vegetative arousal increase, together with increases in histamine levels. We wanted to explore if this arousal was related to histaminergic activation after pharmacological infralimbic disinhibition and during the appetitive phase of motivated behavior. We measured core temperature and motor activity in response to picrotoxin injection in the infralimbic cortex, as well as during food-related appetitive behavior, evoked by enticing hungry rats with food. Pretreatment with the H1 receptor antagonist pyrilamine decreased thermal response to picrotoxin and enticement and completely blunted motor response to enticement. Motor and temperature responses to enticement were also completely abolished by infralimbic cortex inhibition with muscimol. To assess if this histamine dependent temperature increase was produced by an active sympathetic mediated thermogenic mechanism or was just a consequence of increased locomotor activity, we injected propranolol (i.p.), a β adrenergic receptor blocker, before picrotoxin injection into the infralimbic cortex. Propranolol reduced the temperature increase without affecting locomotor activity. Altogether, these results suggest that infralimbic activation is necessary for appetitive behavior by inducing a motor and a vegetative arousal increase mediated by central histamine. Copyright © 2014 Elsevier Inc. All rights reserved.

Temperature dependence of autoxidation of perilla oil and tocopherol degradation.

PubMed

Wang, Seonyeong; Hwang, Hyunsuk; Yoon, Sukhoo; Choe, Eunok

2010-08-01

Temperature dependence of the autoxidation of perilla oil and tocopherol degradation was studied with corn oil as a reference. The oils were oxidized in the dark at 20, 40, 60, and 80 degrees C. Oil oxidation was determined by peroxide and conjugated dienoic acid values. Tocopherols in the oils were quantified by HPLC. The oxidation of both oils increased with oxidation time and temperature. Induction periods for oil autoxidation decreased with temperature, and were longer in corn oil than in perilla oil, indicating higher sensitivity of perilla oil to oxidation. However, time lag for tocopherol degradation was longer in perilla oil, indicating higher stability of tocopherols in perilla oil than in corn oil. Activation energies for oil autoxidation and tocopherol degradation were higher in perilla oil (23.9 to 24.2, 9.8 kcal/mol, respectively) than in corn oil (12.5 to 15.8, 8.8 kcal/mol, respectively) indicating higher temperature-dependence in perilla oil. Higher stability of tocopherols in perilla oil was highly related with polyphenols. The study suggests that more careful temperature control is required to decrease the autoxidation of perilla oil than that of corn oil, and polyphenols contributed to the oxidative stability of perilla oil by protecting tocopherols from degradation, especially at the early stage of oil autoxidation.

Intensity and temperature-dependent photoluminescence of tris (8-hydroxyquinoline) aluminum films

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

Ajward, A. M.; Wang, X.; Wagner, H. P.

2013-12-04

We investigate the recombination of excitons in tris (8-hydroxyquinoline) aluminum films by intensity and temperature dependent time-resolved photoluminescence (PL). At low temperature (15 K) and elevated excitation intensity the radiative emission is quenched by singlet-singlet annihilation processes. With rising temperature the PL quenching is strongly reduced resulting in a PL efficiency maximum at ∼170 K. The reduced exciton annihilation is attributed to thermally activated occupation of non-quenchable trapped exciton states. Above 170 K the PL efficiency decreases due to thermal de-trapping of radiative states and subsequent migration to non-radiative centers.

Temperature dependence of field-responsive mechanisms in lead zirconate titanate

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

Chung, Ching-Chang; Fancher, Chris M.; Isaac, Catherine

2017-05-17

An electric field loading stage was designed for use in a laboratory diffractometer that enables in situ investigations of the temperature dependence in the field response mechanisms of ferroelectric materials. The stage was demonstrated in this paper by measuring PbZr 1-xTi xO 3 (PZT) based materials—a commercially available PZT and a 1% Nb-doped PbZr 0.56Ti 0.44O 3 (PZT 56/44)—over a temperature range of 25°C to 250°C. The degree of non-180° domain alignment (η 002) of the PZT as a function of temperature was quantified. η 002 of the commercially available PZT increases exponentially with temperature, and was analyzed as amore » thermally activated process as described by the Arrhenius law. The activation energy for thermally activated domain wall depinning process in PZT was found to be 0.47 eV. Additionally, a field-induced rhombohedral to tetragonal phase transition was observed 5°C below the rhombohedral-tetragonal transition in PZT 56/44 ceramic. The field-induced tetragonal phase fraction was increased 41.8% after electrical cycling. Finally, a large amount of domain switching (η 002=0.45 at 1.75 kV/mm) was observed in the induced tetragonal phase.« less

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.

Stress and temperature dependence of screw dislocation mobility in {alpha}-Fe by molecular dynamics

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

Gilbert, M. R.; Queyreau, S.; Marian, J.

2011-11-01

The low-temperature plastic yield of {alpha}-Fe single crystals is known to display a strong temperature dependence and to be controlled by the thermally activated motion of screw dislocations. In this paper, we present molecular dynamics simulations of (1/2)<111>{l_brace}112{r_brace} screw dislocation motion as a function of temperature and stress in order to extract mobility relations that describe the general dynamic behavior of screw dislocations in pure {alpha}-Fe. We find two dynamic regimes in the stress-velocity space governed by different mechanisms of motion. Consistent with experimental evidence, at low stresses and temperatures, the dislocations move by thermally activated nucleation and propagation ofmore » kink pairs. Then, at a critical stress, a temperature-dependent transition to a viscous linear regime is observed. Critical output from the simulations, such as threshold stresses and the stress dependence of the kink activation energy, are compared to experimental data and other atomistic works with generally very good agreement. Contrary to some experimental interpretations, we find that glide on {l_brace}112{r_brace} planes is only apparent, as slip always occurs by elementary kink-pair nucleation/propagation events on {l_brace}110{r_brace} planes. Additionally, a dislocation core transformation from compact to dissociated has been identified above room temperature, although its impact on the general mobility is seen to be limited. This and other observations expose the limitations of inferring or presuming dynamic behavior on the basis of only static calculations. We discuss the relevance and applicability of our results and provide a closed-form functional mobility law suitable for mesoscale computational techniques.« less

Reconciling the temperature dependence of respiration across timescales and ecosystem types.

PubMed

Yvon-Durocher, Gabriel; Caffrey, Jane M; Cescatti, Alessandro; Dossena, Matteo; del Giorgio, Paul; Gasol, Josep M; Montoya, José M; Pumpanen, Jukka; Staehr, Peter A; Trimmer, Mark; Woodward, Guy; Allen, Andrew P

2012-07-26

Ecosystem respiration is the biotic conversion of organic carbon to carbon dioxide by all of the organisms in an ecosystem, including both consumers and primary producers. Respiration exhibits an exponential temperature dependence at the subcellular and individual levels, but at the ecosystem level respiration can be modified by many variables including community abundance and biomass, which vary substantially among ecosystems. Despite its importance for predicting the responses of the biosphere to climate change, it is as yet unknown whether the temperature dependence of ecosystem respiration varies systematically between aquatic and terrestrial environments. Here we use the largest database of respiratory measurements yet compiled to show that the sensitivity of ecosystem respiration to seasonal changes in temperature is remarkably similar for diverse environments encompassing lakes, rivers, estuaries, the open ocean and forested and non-forested terrestrial ecosystems, with an average activation energy similar to that of the respiratory complex (approximately 0.65 electronvolts (eV)). By contrast, annual ecosystem respiration shows a substantially greater temperature dependence across aquatic (approximately 0.65 eV) versus terrestrial ecosystems (approximately 0.32 eV) that span broad geographic gradients in temperature. Using a model derived from metabolic theory, these findings can be reconciled by similarities in the biochemical kinetics of metabolism at the subcellular level, and fundamental differences in the importance of other variables besides temperature—such as primary productivity and allochthonous carbon inputs—on the structure of aquatic and terrestrial biota at the community level.

Active Temperature Compensation Using a High-Temperature, Fiber Optic, Hybrid Pressure and Temperature Sensor

NASA Astrophysics Data System (ADS)

Fielder, Robert S.; Palmer, Matthew E.; Davis, Matthew A.; Engelbrecht, Gordon P.

2006-01-01

Luna Innovations has developed a novel, fiber optic, hybrid pressure-temperature sensor system for extremely high-temperature environments that is capable of reliable operation up to 1050 °C. This system is based on the extremely high-temperature fiber optic sensors already demonstrated during previous work. The novelty of the sensors presented here lies in the fact that pressure and temperature are measured simultaneously with a single fiber and a single transducer. This hybrid approach will enable highly accurate active temperature compensation and sensor self-diagnostics not possible with other platforms. Hybrid pressure and temperature sensors were calibrated by varying both pressure and temperature. Implementing active temperature compensation resulted in a ten-fold reduction in the temperature-dependence of the pressure measurement. Sensors were tested for operability in a relatively high neutron dose environment up to 6.9×1017 n/cm2. In addition to harsh environment survivability, fiber optic sensors offer a number of intrinsic advantages for space nuclear power applications including extremely low mass, immunity to electromagnetic interference, self diagnostics / prognostics, and smart sensor capability. Deploying fiber optic sensors on future space exploration missions would provide a substantial improvement in spacecraft instrumentation. Additional development is needed, however, before these advantages can be realized. This paper will highlight recent demonstrations of fiber optic sensors in environments relevant to space nuclear applications. Successes and lessons learned will be highlighted. Additionally, development needs will be covered which will suggest a framework for a coherent plan to continue work in this area.

On the temperature dependence of flammability limits of gases.

PubMed

Kondo, Shigeo; Takizawa, Kenji; Takahashi, Akifumi; Tokuhashi, Kazuaki

2011-03-15

Flammability limits of several combustible gases were measured at temperatures from 5 to 100 °C in a 12-l spherical flask basically following ASHRAE method. The measurements were done for methane, propane, isobutane, ethylene, propylene, dimethyl ether, methyl formate, 1,1-difluoroethane, ammonia, and carbon monoxide. As the temperature rises, the lower flammability limits are gradually shifted down and the upper limits are shifted up. Both the limits shift almost linearly to temperature within the range examined. The linear temperature dependence of the lower flammability limits is explained well using a limiting flame temperature concept at the lower concentration limit (LFL)--'White's rule'. The geometric mean of the flammability limits has been found to be relatively constant for many compounds over the temperature range studied (5-100 °C). Based on this fact, the temperature dependence of the upper flammability limit (UFL) can be predicted reasonably using the temperature coefficient calculated for the LFL. However, some compounds such as ethylene and dimethyl ether, in particular, have a more complex temperature dependence. Copyright © 2011 Elsevier B.V. All rights reserved.

Temperature dependence of standard model CP violation.

PubMed

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

2012-01-27

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

Reversible conformational transition gives rise to 'zig-zag' temperature dependence of the rate constant of irreversible thermoinactivation of enzymes.

PubMed

Levitsky VYu; Melik-Nubarov, N S; Siksnis, V A; Grinberg VYa; Burova, T V; Levashov, A V; Mozhaev, V V

1994-01-15

We have obtained unusual 'zig-zag' temperature dependencies of the rate constant of irreversible thermoinactivation (k(in)) of enzymes (alpha-chymotrypsin, covalently modified alpha-chymotrypsin, and ribonuclease) in a plot of log k(in) versus reciprocal temperature (Arrhenius plot). These dependencies are characterized by the presence of both ascending and descending linear portions which have positive and negative values of the effective activation energy (Ea), respectively. A kinetic scheme has been suggested that fits best for a description of these zig-zag dependencies. A key element of this scheme is the temperature-dependent reversible conformational transition of enzyme from the 'low-temperature' native state to a 'high-temperature' denatured form; the latter form is significantly more stable against irreversible thermoinactivation than the native enzyme. A possible explanation for a difference in thermal stabilities is that low-temperature and high-temperature forms are inactivated according to different mechanisms. Existence of the suggested conformational transition was proved by the methods of fluorescence spectroscopy and differential scanning calorimetry. The values of delta H and delta S for this transition, determined from calorimetric experiments, are highly positive; this fact underlies a conclusion that this heat-induced transition is caused by an unfolding of the protein molecule. Surprisingly, in the unfolded high-temperature conformation, alpha-chymotrypsin has a pronounced proteolytic activity, although this activity is much smaller than that of the native enzyme.

Stay tuned: active amplification tunes tree cricket ears to track temperature-dependent song frequency.

PubMed

Mhatre, Natasha; Pollack, Gerald; Mason, Andrew

2016-04-01

Tree cricket males produce tonal songs, used for mate attraction and male-male interactions. Active mechanics tunes hearing to conspecific song frequency. However, tree cricket song frequency increases with temperature, presenting a problem for tuned listeners. We show that the actively amplified frequency increases with temperature, thus shifting mechanical and neuronal auditory tuning to maintain a match with conspecific song frequency. Active auditory processes are known from several taxa, but their adaptive function has rarely been demonstrated. We show that tree crickets harness active processes to ensure that auditory tuning remains matched to conspecific song frequency, despite changing environmental conditions and signal characteristics. Adaptive tuning allows tree crickets to selectively detect potential mates or rivals over large distances and is likely to bestow a strong selective advantage by reducing mate-finding effort and facilitating intermale interactions. © 2016 The Author(s).

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.

Temperature dependent GaAs MMIC radiation effects

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

Anderson, W.T.; Roussos, J.A.; Gerdes, J.

1993-12-01

The temperature dependence of pulsed neutron and flash x-ray radiation effects was studied in GaAs MMICs. Above room temperature the long term current transients are dominated by electron trapping in previously existing defects. At low temperature in the range 126 to 259 K neutron induced lattice damage appears to play an increasingly important role in producing long term current transients.

Change in heat capacity for enzyme catalysis determines temperature dependence of enzyme catalyzed rates.

PubMed

Hobbs, Joanne K; Jiao, Wanting; Easter, Ashley D; Parker, Emily J; Schipper, Louis A; Arcus, Vickery L

2013-11-15

The increase in enzymatic rates with temperature up to an optimum temperature (Topt) is widely attributed to classical Arrhenius behavior, with the decrease in enzymatic rates above Topt ascribed to protein denaturation and/or aggregation. This account persists despite many investigators noting that denaturation is insufficient to explain the decline in enzymatic rates above Topt. Here we show that it is the change in heat capacity associated with enzyme catalysis (ΔC(‡)p) and its effect on the temperature dependence of ΔG(‡) that determines the temperature dependence of enzyme activity. Through mutagenesis, we demonstrate that the Topt of an enzyme is correlated with ΔC(‡)p and that changes to ΔC(‡)p are sufficient to change Topt without affecting the catalytic rate. Furthermore, using X-ray crystallography and molecular dynamics simulations we reveal the molecular details underpinning these changes in ΔC(‡)p. The influence of ΔC(‡)p on enzymatic rates has implications for the temperature dependence of biological rates from enzymes to ecosystems.

Temperature dependence of acoustic impedance for specific fluorocarbon liquids

NASA Astrophysics Data System (ADS)

Marsh, Jon N.; Hall, Christopher S.; Wickline, Samuel A.; Lanza, Gregory M.

2002-12-01

Recent studies by our group have demonstrated the efficacy of perfluorocarbon liquid nanoparticles for enhancing the reflectivity of tissuelike surfaces to which they are bound. The magnitude of this enhancement depends in large part on the difference in impedances of the perfluorocarbon, the bound substrate, and the propagating medium. The impedance varies directly with temperature because both the speed of sound and the mass density of perfluorocarbon liquids are highly temperature dependent. However, there are relatively little data in the literature pertaining to the temperature dependence of the acoustic impedance of these compounds. In this study, the speed of sound and density of seven different fluorocarbon liquids were measured at specific temperatures between 20 °C and 45 °C. All of the samples demonstrated negative, linear dependencies on temperature for both speed of sound and density and, consequently, for the acoustic impedance. The slope of sound speed was greatest for perfluorohexane (-278+/-1.5 cm/s-°C) and lowest for perfluorodichlorooctane (-222+/-0.9 cm/s-°C). Of the compounds measured, perfluorohexane exhibited the lowest acoustic impedance at all temperatures, and perfluorodecalin the highest at all temperatures. Computations from a simple transmission-line model used to predict reflectivity enhancement from surface-bound nanoparticles are discussed in light of these results.

Investigation of temperature-dependent photoluminescence in multi-quantum wells.

PubMed

Fang, Yutao; Wang, Lu; Sun, Qingling; Lu, Taiping; Deng, Zhen; Ma, Ziguang; Jiang, Yang; Jia, Haiqiang; Wang, Wenxin; Zhou, Junming; Chen, Hong

2015-07-31

Photoluminescence (PL) is a nondestructive and powerful method to investigate carrier recombination and transport characteristics in semiconductor materials. In this study, the temperature dependences of photoluminescence of GaAs-AlxGa1-xAs multi-quantum wells samples with and without p-n junction were measured under both resonant and non-resonant excitation modes. An obvious increase of photoluminescence(PL) intensity as the rising of temperature in low temperature range (T < 50 K), is observed only for GaAs-AlxGa1-xAs quantum wells sample with p-n junction under non-resonant excitation. The origin of the anomalous increase of integrated PL intensity proved to be associated with the enhancement of carrier drifting because of the increase of carrier mobility in the temperature range from 15 K to 100 K. For non-resonant excitation, carriers supplied from the barriers will influence the temperature dependence of integrated PL intensity of quantum wells, which makes the traditional methods to acquire photoluminescence characters from the temperature dependence of integrated PL intensity unavailable. For resonant excitation, carriers are generated only in the wells and the temperature dependence of integrated PL intensity is very suitable to analysis the photoluminescence characters of quantum wells.

Temperature dependence in magnetic particle imaging

NASA Astrophysics Data System (ADS)

Wells, James; Paysen, Hendrik; Kosch, Olaf; Trahms, Lutz; Wiekhorst, Frank

2018-05-01

Experimental results are presented demonstrating how temperature can influence the dynamics of magnetic nanoparticles (MNPs) in liquid suspension, when exposed to alternating magnetic fields in the kilohertz frequency range. The measurements used to probe the nanoparticle systems are directly linked to both the emerging biomedical technique of magnetic particle imaging (MPI), and to the recently proposed concept of remote nanoscale thermometry using MNPs under AC field excitation. Here, we report measurements on three common types of MNPs, two of which are currently leading candidates for use as tracers in MPI. Using highly-sensitive magnetic particle spectroscopy (MPS), we demonstrate significant and divergent thermal dependences in several key measures used in the evaluation of MNP dynamics for use in MPI and other applications. The temperature range studied was between 296 and 318 Kelvin, making our findings of particular importance for MPI and other biomedical technologies. Furthermore, we report the detection of the same temperature dependences in measurements conducted using the detection coils within an operational preclinical MPI scanner. This clearly shows the importance of considering temperature during MPI development, and the potential for temperature-resolved MPI using this system. We propose possible physical explanations for the differences in the behaviors observed between the different particle types, and discuss our results in terms of the opportunities and concerns they raise for MPI and other MNP based technologies.

Temperature dependence of the HNO3 UV absorption cross sections

NASA Technical Reports Server (NTRS)

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

1993-01-01

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

Escherichia coli survival in waters: Temperature dependence

EPA Science Inventory

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

Temperature-Dependent Kinetic Model for Nitrogen-Limited Wine Fermentations▿

PubMed Central

Coleman, Matthew C.; Fish, Russell; Block, David E.

2007-01-01

A physical and mathematical model for wine fermentation kinetics was adapted to include the influence of temperature, perhaps the most critical factor influencing fermentation kinetics. The model was based on flask-scale white wine fermentations at different temperatures (11 to 35°C) and different initial concentrations of sugar (265 to 300 g/liter) and nitrogen (70 to 350 mg N/liter). The results show that fermentation temperature and inadequate levels of nitrogen will cause stuck or sluggish fermentations. Model parameters representing cell growth rate, sugar utilization rate, and the inactivation rate of cells in the presence of ethanol are highly temperature dependent. All other variables (yield coefficient of cell mass to utilized nitrogen, yield coefficient of ethanol to utilized sugar, Monod constant for nitrogen-limited growth, and Michaelis-Menten-type constant for sugar transport) were determined to vary insignificantly with temperature. The resulting mathematical model accurately predicts the observed wine fermentation kinetics with respect to different temperatures and different initial conditions, including data from fermentations not used for model development. This is the first wine fermentation model that accurately predicts a transition from sluggish to normal to stuck fermentations as temperature increases from 11 to 35°C. Furthermore, this comprehensive model provides insight into combined effects of time, temperature, and ethanol concentration on yeast (Saccharomyces cerevisiae) activity and physiology. PMID:17616615

Temperature dependence of the elastocaloric effect in natural rubber

NASA Astrophysics Data System (ADS)

Xie, Zhongjian; Sebald, Gael; Guyomar, Daniel

2017-07-01

The temperature dependence of the elastocaloric (eC) effect in natural rubber (NR) has been studied. This material exhibits a large eC effect over a broad temperature range from 0 °C to 49 °C. The maximum adiabatic temperature change (ΔT) occurred at 10 °C and the behavior could be predicted by the temperature dependence of the strain-induced crystallization (SIC) and the temperature-induced crystallization (TIC). The eC performance of NR was then compared with that of shape memory alloys (SMAs). This study contributes to the SIC research of NR and also broadens the application of elastomers.

Temperature and size-dependent Hamaker constants for metal nanoparticles

NASA Astrophysics Data System (ADS)

Jiang, K.; Pinchuk, P.

2016-08-01

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

Temperature and size-dependent Hamaker constants for metal nanoparticles.

PubMed

Jiang, K; Pinchuk, P

2016-08-26

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

E. coli survival in waters: temperature dependence

USDA-ARS?s Scientific Manuscript database

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

Understanding Biological Rates and their Temperature Dependence, from Enzymes to Ecosystems

NASA Astrophysics Data System (ADS)

Prentice, E.; Arcus, V. L.

2017-12-01

Temperature responses over various scales in biological systems follow a similar pattern; negative curvature results in an optimum temperature (Topt) for activity/growth/turnover, with decreases in rates on either side of Topt. Previously this downturn in rates at high temperatures has been attributed to enzyme denaturation, where a failing of the basic driving units of metabolism was used to describe curvature at the enzyme and organism level. However, recent developments in our understanding of the factors governing enzyme rates at different temperatures have guided a new understanding of the responses of biological systems. Enzymes catalyse reactions by driving the substrate through a high energy species, which is tightly bound to the enzyme. Macromolecular rate theory (MMRT) has recently been developed to account for the changes in the system brought about by this tight binding, specifically the change in the physical parameter heat capacity (ΔCǂp), and the effect this has on the temperature dependence of enzyme reactions. A negative ΔCǂp imparts the signature negative curvature to rates in the absence of denaturation, and finds that Topt, ΔCǂp and curvature are all correlated, placing constraints on biological systems. The simplest of cells comprise thousands of enzymatically catalysed reactions, functioning in series and in parallel in metabolic pathways to determine the overall growth rate of an organism. Intuitively, the temperature effects of enzymes play a role in determining the overall temperature dependence of an organism, in tandem with cellular level regulatory responses. However, the effect of individual Topt values and curvature on overall pathway behaviour is less apparent. Here, this is investigated in the context of MMRT through the in vitro characterisation of a six-step metabolic pathway to understand the steps in isolation and functioning in series. Pathway behaviour is found to be approximately an average of the properties of the

Temperature dependence of photoluminescence peaks of porous silicon structures

NASA Astrophysics Data System (ADS)

Brunner, Róbert; Pinčík, Emil; Kučera, Michal; Greguš, Ján; Vojtek, Pavel; Zábudlá, Zuzana

2017-12-01

Evaluation of photoluminescence spectra of porous silicon (PS) samples prepared by electrochemical etching is presented. The samples were measured at temperatures 30, 70 and 150 K. Peak parameters (energy, intensity and width) were calculated. The PL spectrum was approximated by a set of Gaussian peaks. Their parameters were fixed using fitting a procedure in which the optimal number of peeks included into the model was estimated using the residuum of the approximation. The weak thermal dependence of the spectra indicates the strong influence of active defects.

Controlling temperature dependence of silicon waveguide using slot structure.

PubMed

Lee, Jong-Moo; Kim, Duk-Jun; Kim, Gwan-Ha; Kwon, O-Kyun; Kim, Kap-Joong; Kim, Gyungock

2008-02-04

We show that the temperature dependence of a silicon waveguide can be controlled well by using a slot waveguide structure filled with a polymer material. Without a slot, the amount of temperature-dependent wavelength shift for TE mode of a silicon waveguide ring resonator is very slightly reduced from 77 pm/ degrees C to 66 pm/ degrees C by using a polymer (WIR30-490) upper cladding instead of air upper cladding. With a slot filled with the same polymer, however, the reduction of the temperature dependence is improved by a pronounced amount and can be controlled down to -2 pm/ degrees C by adjusting several variables of the slot structure, such as the width of the slot between the pair of silicon wires, the width of the silicon wire pair, and the height of the silicon slab in our experiment. This measurement proves that a reduction in temperature dependence can be improved about 8 times more by using the slot structure.

Temperature-dependent μ-Raman investigation of struvite crystals.

PubMed

Prywer, Jolanta; Kasprowicz, D; Runka, T

2016-04-05

The effect of temperature on the vibrational properties of struvite crystals grown from silica gels was systematically studied by μ-Raman spectroscopy. The time-dependent Raman spectra recorded in the process of long time annealing of struvite crystal at 353 K do not indicate structural changes in the struvite crystal with the time of annealing. The temperature-dependent Raman spectra recorded in the range 298-423 K reveal a phase transition in struvite at about 368 K. Above this characteristic temperature, some of bands assigned to vibrations of the PO4 and NH4 tetrahedra and water molecules observed in the Raman spectra in low temperatures (orthorhombic phase) change their spectral parameters or disappear, which indicates a transition to a higher symmetry structure of struvite in the range of high temperatures. Copyright © 2016 Elsevier B.V. All rights reserved.

Ubiquitous and temperature-dependent neural plasticity in hibernators.

PubMed

von der Ohe, Christina G; Darian-Smith, Corinna; Garner, Craig C; Heller, H Craig

2006-10-11

Hibernating mammals are remarkable for surviving near-freezing brain temperatures and near cessation of neural activity for a week or more at a time. This extreme physiological state is associated with dendritic and synaptic changes in hippocampal neurons. Here, we investigate whether these changes are a ubiquitous phenomenon throughout the brain that is driven by temperature. We iontophoretically injected Lucifer yellow into several types of neurons in fixed slices from hibernating ground squirrels. We analyzed neuronal microstructure from animals at several stages of torpor at two different ambient temperatures, and during the summer. We show that neuronal cell bodies, dendrites, and spines from several cell types in hibernating ground squirrels retract on entry into torpor, change little over the course of several days, and then regrow during the 2 h return to euthermia. Similar structural changes take place in neurons from the hippocampus, cortex, and thalamus, suggesting a global phenomenon. Investigation of neural microstructure from groups of animals hibernating at different ambient temperatures revealed that there is a linear relationship between neural retraction and minimum body temperature. Despite significant temperature-dependent differences in extent of retraction during torpor, recovery reaches the same final values of cell body area, dendritic arbor complexity, and spine density. This study demonstrates large-scale and seemingly ubiquitous neural plasticity in the ground squirrel brain during torpor. It also defines a temperature-driven model of dramatic neural plasticity, which provides a unique opportunity to explore mechanisms of large-scale regrowth in adult mammals, and the effects of remodeling on learning and memory.

Determining Role of the Chain Mechanism in the Temperature Dependence of the Gas-Phase Rate of Combustion Reactions

NASA Astrophysics Data System (ADS)

Azatyan, V. V.; Bolod'yan, I. A.; Kopylov, N. P.; Kopylov, S. N.; Prokopenko, V. M.; Shebeko, Yu. N.

2018-05-01

It is shown that the strong dependence of the rate of gas-phase combustion reactions on temperature is determined by the high values of the reaction rate constants of free atoms and radicals. It is established that with a branched chain mechanism, a special role in the reaction rate temperature dependence is played by positive feedback between the concentrations of active intermediate species and the rate of their change. The role of the chemical mechanism in the temperature dependence of the process rate with and without inhibitors is considered.

Temperature-Dependent Electrical and Micromechanical Properties of Lanthanum Titanate with Additions of Yttria

NASA Technical Reports Server (NTRS)

Goldsby, Jon C.

2010-01-01

Temperature-dependent elastic properties were determined by establishing continuous flexural vibrations in the material at its lowest resonance frequency of 31tHz. The imaginary part of the complex impedance plotted as a function of frequency and temperature reveals a thermally activated peak, which decreases in magnitude as the temperature increases. Additions of yttria do not degrade the electromechanical in particularly the elastic and anelastic properties of lanthanum titanate. Y2O3/La2Ti2O7 exhibits extremely low internal friction and hence may be more mechanical fatigue-resistant at low strains.

Exploration of the mechanisms of temperature-dependent grain boundary mobility: Search for the common origin of ultrafast grain boundary motion

DOE PAGES

O’Brien, C. J.; Foiles, S. M.

2016-04-19

The temperature dependence of grain boundary mobility is complex, varied, and rarely fits ideal Arrhenius behavior. This work presents a series of case studies of planar grain boundaries in a model FCC system that were previously demonstrated to exhibit a variety of temperature-dependent mobility behaviors. It is demonstrated that characterization of the mobility versus temperature plots is not sufficient to predict the atomic motion mechanism of the grain boundaries. Herein, the temperature-dependent motion and atomistic motion mechanisms of planar grain boundaries are driven by a synthetic, orientation-dependent, driving force. The systems studied include CSL boundaries with Σ values of 5,more » 7, and 15, including both symmetric and asymmetric boundaries. These boundaries represent a range of temperature-dependent trends including thermally activated, antithermal, and roughening behaviors. Examining the atomic-level motion mechanisms of the thermally activated boundaries reveals that each involves a complex shuffle, and at least one atom that changes the plane it resides on. The motion mechanism of the antithermal boundary is qualitatively different and involves an in-plane coordinated shuffle that rotates atoms about a fixed atom lying on a point in the coincident site lattice. Furthermore, this provides a mechanistic reason for the observed high mobility, even at low temperatures, which is due to the low activation energy needed for such motion. However, it will be demonstrated that this mechanism is not universal, or even common, to other boundaries exhibiting non-thermally activated motion. This work concludes that no single atomic motion mechanism is sufficient to explain the existence of non-thermally activated boundary motion.« less

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.

Temperature effects on quasi-isolated conjugated polymers as revealed by temperature-dependent optical spectra of 16-mer oligothiophene diluted in a sold matrix.

PubMed

Kanemoto, Katsuichi; Akai, Ichiro; Sugisaki, Mitsuru; Hashimoto, Hideki; Karasawa, Tsutomu; Negishi, Nobukazu; Aso, Yoshio

2009-06-21

Temperature dependences (4-300 K) of photoluminescence (PL) and absorption spectra of 16-mer oligothiophene (16 T) extremely diluted in polypropylene (PP) have been investigated in order to clarify temperature effects on quasi-isolated conjugated polymers. The PL and absorption spectra are found to blueshift with increasing temperature. The reason for the blueshift is discussed by comparing models based on the refractive index of the solvent (PP) and on the thermal conformational change of 16 T. The blueshift is concluded to result from the thermal conformational change. Time-resolved PL spectra show a redshift of PL band following photoexcitation (spectral migration). The amount of the migration is shown to increase with increasing temperature. The increased migration is concluded to be due to the thermal conformational change. The temperature dependence of the effective conjugation length (ECL) of 16 T is calculated for the absorption and PL transitions. The calculation suggests that ECL is reduced at room temperature to two-thirds of the intrinsic chain length. The activation energy of the conformational change is estimated to be 22.4 meV from the temperature dependence of ECL. We demonstrate that the steady-state PL spectra are well reproduced by simple Franck-Condon analyses using a single Huang-Ryes factor over a wide temperature range. The analyses reveal features of temperature dependence in important spectral parameters such as the Stokes shift, linewidth, and Huang-Ryes factor.

Temperature-dependent photoluminescence in meso-porous MCM nanotubes

NASA Astrophysics Data System (ADS)

Lee, Y. C.; Liu, Y. L.; Lee, W. Z.; Wang, C. K.; Shen, J. L.; Cheng, P. W.; Cheng, C. F.; Lin, T. Y.

2004-11-01

Temperature-dependent photoluminescence (PL) was exploited to investigate the mechanism of luminescence of MCM (Mobil Composition of Matter)-41 and MCM-48 nanotubes. The PL intensity has a maximum around 40 K. Localization of the carriers involved in the radiative recombination was deduced from the PL decay profiles at various energies. A model based on competition between radiative recombination of localized carriers and nonradiative recombination is suggested to explain the temperature-dependence of PL intensity.

Temperature and pressure dependences of kimberlite melts viscosity (experimental-theoretical study)

NASA Astrophysics Data System (ADS)

Persikov, Eduard; Bykhtiyarov, Pavel; Cokol, Alexsander

2016-04-01

Experimental data on temperature and pressure dependences of viscosity of model kimberlite melts (silicate 82 + carbonate 18, wt. %, 100NBO/T = 313) have been obtained for the first time at 100 MPa of CO2 pressure and at the lithostatic pressures up to 7.5 GPa in the temperature range 1350 oC - 1950 oC using radiation high gas pressure apparatus and press free split-sphere multi - anvil apparatus (BARS). Experimental data obtained on temperature and pressure dependences of viscosity of model kimberlite melts at moderate and high pressures is compared with predicted data on these dependences of viscosity of basaltic melts (100NBO/T = 58) in the same T, P - range. Dependences of the viscosity of model kimberlite and basaltic melts on temperature are consistent to the exponential Arrenian equation in the T, P - range of experimental study. The correct values of activation energies of viscous flow of kimberlite melts have been obtained for the first time. The activation energies of viscous flow of model kimberlite melts exponentially increase with increasing pressure and are equal: E = 130 ± 1.3 kJ/mole at moderate pressure (P = 100 MPa) and E = 160 ± 1.6 kJ/mole at high pressure (P = 5.5 GPa). It has been established too that the viscosity of model kimberlite melts exponentially increases on about half order of magnitude with increasing pressures from 100 MPa to 7.5 GPa at the isothermal condition (1800 oC). It has been established that viscosity of model kimberlite melts at the moderate pressure (100 MPa) is lover on about one order of magnitude to compare with the viscosity of basaltic melts, but at high pressure range (5.5 - 7.5 GPa), on the contrary, is higher on about half order of magnitude at the same values of the temperatures. Here we use both a new experimental data on viscosity of kimberlite melts and our structural chemical model for calculation and prediction the viscosity of magmatic melts [1] to determine the fundamental features of viscosity of

On the Temperature Dependence of Enzyme-Catalyzed Rates.

PubMed

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

2016-03-29

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

Oviposition activity of Drosophila suzukii as mediated by ambient and fruit temperature

PubMed Central

2017-01-01

The invasive pest Drosophila suzukii was introduced to southern Europe in 2008 and spread throughout Central Europe in the following years. Precise reliable data on the temperature-dependent behavior of D. suzukii are scarce but will help forecasting and cultivation techniques. Depending on physico-chemical properties, surface temperature of objects may differ from ambient temperatures, determining physical activity, and affect oviposition on or into substrate, determining preimaginal development later. Therefore, the preferred ambient temperatures of D. suzukii and fruit temperature for oviposition were examined on a linear temperature gradient device. Thirty adults (15 ♀; 15 ♂) were adapted to different temperatures (10, 20, 30°C) for six days and then exposed to different temperature gradients (10–25, 20–35, 25–40°C). D. suzukii adapted to 10°C remained in cooler regions and suffered from a significantly higher mortality at the 25–40°C gradient. Animals adapted to warmer temperatures had a wider temperature preference on the gradient device. Acclimation to lower temperatures and the resulting lower temperature preferences may allow the flies to disperse better in spring to search for oviposition sites. The oviposition activity decreased continuously at a fruit temperature above 28°C and below 15°C, with highest oviposition activity in fruits with temperatures between 19.7°C and 24.8°C. The preferred fruit temperature is in accordance with the temperature optimum of reproduction biology and preimaginal development of D. suzukii reported in the literature. PMID:29121635

Temperature dependence of sapphire fiber Raman scattering

DOE PAGES

Liu, Bo; Yu, Zhihao; Tian, Zhipeng; ...

2015-04-27

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

Mechanism of H₂ histamine receptor dependent modulation of body temperature and neuronal activity in the medial preoptic nucleus.

PubMed

Tabarean, Iustin V; Sanchez-Alavez, Manuel; Sethi, Jasmine

2012-08-01

Histamine is involved in the central control of arousal, circadian rhythms and metabolism. The preoptic area, a region that contains thermoregulatory neurons is the main locus of histamine modulation of body temperature. Here we report that in mice, histamine activates H(2) subtype receptors in the medial preoptic nucleus (MPON) and induces hyperthermia. We also found that a population of glutamatergic MPON neurons express H(2) receptors and are excited by histamine or H(2) specific agonists. The agonists decreased the input resistance of the neuron and increased the depolarizing "sag" observed during hyperpolarizing current injections. Furthermore, at -60 mV holding potential, activation of H(2) receptors induced an inward current that was blocked by ZD7288, a specific blocker of the hyperpolarization activated cationic current (I(h)). Indeed, activation of H(2) receptors resulted in increased I(h) amplitude in response to hyperpolarizing voltage steps and a depolarizing shift in its voltage-dependent activation. The neurons excited by H(2) specific agonism expressed the HCN1 and HCN2 channel subunits. Our data indicate that at the level of the MPON histamine influences thermoregulation by increasing the firing rate of glutamatergic neurons that express H(2) receptors. Copyright © 2012 Elsevier Ltd. All rights reserved.

Temperature-dependent internal photoemission probe for band parameters

NASA Astrophysics Data System (ADS)

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

2012-11-01

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

Quasipermanent magnets of high temperature superconductor - Temperature dependence

NASA Technical Reports Server (NTRS)

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

1993-01-01

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

Patterns of activity and body temperature of Aldabra giant tortoises in relation to environmental temperature.

PubMed

Falcón, Wilfredo; Baxter, Rich P; Furrer, Samuel; Bauert, Martin; Hatt, Jean-Michel; Schaepman-Strub, Gabriela; Ozgul, Arpat; Bunbury, Nancy; Clauss, Marcus; Hansen, Dennis M

2018-02-01

We studied the temperature relations of wild and zoo Aldabra giant tortoises ( Aldabrachelys gigantea ) focusing on (1) the relationship between environmental temperature and tortoise activity patterns ( n  = 8 wild individuals) and (2) on tortoise body temperature fluctuations, including how their core and external body temperatures vary in relation to different environmental temperature ranges (seasons; n  = 4 wild and n  = 5 zoo individuals). In addition, we surveyed the literature to review the effect of body mass on core body temperature range in relation to environmental temperature in the Testudinidae. Diurnal activity of tortoises was bimodally distributed and influenced by environmental temperature and season. The mean air temperature at which activity is maximized was 27.9°C, with a range of 25.8-31.7°C. Furthermore, air temperature explained changes in the core body temperature better than did mass, and only during the coldest trial, did tortoises with higher mass show more stable temperatures. Our results, together with the overall Testudinidae overview, suggest that, once variation in environmental temperature has been taken into account, there is little effect of mass on the temperature stability of tortoises. Moreover, the presence of thermal inertia in an individual tortoise depends on the environmental temperatures, and we found no evidence for inertial homeothermy. Finally, patterns of core and external body temperatures in comparison with environmental temperatures suggest that Aldabra giant tortoises act as mixed conformer-regulators. Our study provides a baseline to manage the thermal environment of wild and rewilded populations of an important island ecosystem engineer species in an era of climate change.

Thermally activated TRP channels: molecular sensors for temperature detection.

PubMed

Castillo, Karen; Diaz-Franulic, Ignacio; Canan, Jonathan; Gonzalez-Nilo, Fernando; Latorre, Ramon

2018-01-24

Temperature sensing is one of the oldest capabilities of living organisms, and is essential for sustaining life, because failure to avoid extreme noxious temperatures can result in tissue damage or death. A subset of members of the transient receptor potential (TRP) ion channel family is finely tuned to detect temperatures ranging from extreme cold to noxious heat, giving rise to thermoTRP channels. Structural and functional experiments have shown that thermoTRP channels are allosteric proteins, containing different domains that sense changes in temperature, among other stimuli, triggering pore opening. Although temperature-dependence is well characterized in thermoTRP channels, the molecular nature of temperature-sensing elements remains unknown. Importantly, thermoTRP channels are involved in pain sensation, related to pathological conditions. Here, we provide an overview of thermoTRP channel activation. We also discuss the structural and functional evidence supporting the existence of an intrinsic temperature sensor in this class of channels, and we explore the basic thermodynamic principles for channel activation. Finally, we give a view of their role in painful pathophysiological conditions.

Investigations of Low Temperature Time Dependent Cracking

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

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

2002-09-30

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

Modeling temperature dependent singlet exciton dynamics in multilayered organic nanofibers

NASA Astrophysics Data System (ADS)

de Sousa, Leonardo Evaristo; de Oliveira Neto, Pedro Henrique; Kjelstrup-Hansen, Jakob; da Silva Filho, Demétrio Antônio

2018-05-01

Organic nanofibers have shown potential for application in optoelectronic devices because of the tunability of their optical properties. These properties are influenced by the electronic structure of the molecules that compose the nanofibers and also by the behavior of the excitons generated in the material. Exciton diffusion by means of Förster resonance energy transfer is responsible, for instance, for the change with temperature of colors in the light emitted by systems composed of different types of nanofibers. To study in detail this mechanism, we model temperature dependent singlet exciton dynamics in multilayered organic nanofibers. By simulating absorption and emission spectra, the possible Förster transitions are identified. Then, a kinetic Monte Carlo model is employed in combination with a genetic algorithm to theoretically reproduce time-resolved photoluminescence measurements for several temperatures. This procedure allows for the obtainment of different information regarding exciton diffusion in such a system, including temperature effects on the Förster transfer efficiency and the activation energy of the Förster mechanism. The method is general and may be employed for different systems where exciton diffusion plays a role.

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.

Temperature-dependent surface density of alkylthiol monolayers on gold nanocrystals

NASA Astrophysics Data System (ADS)

Liu, Xuepeng; Lu, Pin; Zhai, Hua; Wu, Yucheng

2018-03-01

Atomistic molecular dynamics (MD) simulations are performed to study the surface density of passivating monolayers of alkylthiol chains on gold nanocrystals at temperatures ranging from 1 to 800 K. The results show that the surface density of alkylthiol monolayer reaches a maximum value at near room temperature (200-300 K), while significantly decreases with increasing temperature in the higher temperature region (> 300 {{K}}), and slightly decreases with decreasing temperature at low temperature (< 200 {{K}}). We find that the temperature dependence of surface ligand density in the higher temperature region is attributed to the substantial ligand desorption induced by the thermal fluctuation, while that at low temperature results from the reduction in entropy caused by the change in the ordering of passivating monolayer. These results are expected helpful to understand the temperature-dependent surface coverage of gold nanocrystals.

Geomagnetic activity signature in seasonal variations of mesopause temperature over Yakutia

NASA Astrophysics Data System (ADS)

Gavrilyeva, G. A.; Ammosov, P. P.; Ammosova, A. M.; Koltovskoi, I. I.; Sivtseva, V. I.

2017-11-01

Research of the seasonal change of mesopause temperature at height of nightglow of hydroxyl excited molecules and its correlation with geomagnetic activity during the 23 solar cycle is presented. An infrared digital spectrograph installed at the Maimaga station (63°N, 129.5°E) measured P-branches of the OH(6-2) band. The rotational temperature of OH emission (TOH) is assumed to be equal to the neutral atmosphere temperature at the altitude of 87 km. The database of TOH comprises 2864 nightly average temperatures obtained from August 1999 to May 2015 is considered. The observation starts at the beginning of August and ends in the middle of May. It was revealed that the maximum flux of radio emission from the Sun with a wavelength of 10.7 cm is 2 years ahead of the maximum of seasonally averaged temperature. Temperature is correlated with a change of Ap-index which is a measure of geomagnetic activity. Nightly mean TOH were grouped in accordance with the geomagnetic activity level: the temperatures measured during years with a high activity (Ap> 8), and low activity (Ap <= 8). It was found that the mesopause temperature from October to February is higher by a factor of about ·10 K than during years with low activity (Ap <= 8). There is no dependence of the TOH on the level of geomagnetic activity in autumn and spring.

Temperature dependence of electrical characteristics of Pt/GaN Schottky diode fabricated by UHV e-beam evaporation.

PubMed

Kumar, Ashish; Arafin, Shamsul; Amann, Markus Christian; Singh, Rajendra

2013-11-15

Temperature-dependent electrical characterization of Pt/n-GaN Schottky barrier diodes prepared by ultra high vacuum evaporation has been done. Analysis has been made to determine the origin of the anomalous temperature dependence of the Schottky barrier height, the ideality factor, and the Richardson constant calculated from the I-V-T characteristics. Variable-temperature Hall effect measurements have been carried out to understand charge transport at low temperature. The modified activation energy plot from the barrier inhomogeneity model has given the value of 32.2 A/(cm2 K2) for the Richardson constant A** in the temperature range 200 to 380 K which is close to the known value of 26.4A/(cm2 K2) for n-type GaN.

The temperature dependent amide I band of crystalline acetanilide

NASA Astrophysics Data System (ADS)

Cruzeiro, Leonor; Freedman, Holly

2013-10-01

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

Temperature-dependent Study of Isobutanol Decomposition

DTIC Science & Technology

2012-11-01

dimensional Al2O3 alumina CO2 carbon dioxide FTIR Fourier transform infrared Pd palladium Rh rhodium TPD temperature-programmed desorption TPO...that increasing temperature promotes aldehyde formation on the surface of each catalyst. In addition, it is shown that palladium (Pd) activates the...formation of aldehydes and CO2 at a lower temperature than a rhodium (Rh) catalyst. 15. SUBJECT TERMS Isobutanol, FTIR, spectroscopy 16. SECURITY

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.

Temperature-dependent absorption cross sections for hydrogen peroxide vapor

NASA Technical Reports Server (NTRS)

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

1988-01-01

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

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

The temperature dependence of ponded infiltration under isothermal conditions

USGS Publications Warehouse

Constantz, J.; Murphy, F.

1991-01-01

A simple temperature-sensitive modification to the Green and Ampt infiltration equation is described; this assumes that the temperature dependence of the hydraulic conductivity is reciprocally equal to the temperature dependence of the viscosity of liquid water, and that both the transmission zone saturation and the wetting front matric potential gradient are independent of temperature. This modified Green and Ampt equation is compared with ponded, isothermal infiltration experiments run on repacked columns of Olympic Sand and Aiken Loam at 5, 25, and 60??C. Experimental results showed increases in infiltration rates of at least 300% between 5 and 60??C for both soil materials, with subsequent increases in cumulative infiltration of even greater magnitudes for the loam. There is good agreement between measured and predicted initial infiltration rates at 25??C for both soil materials, yet at 60??C, the predicted results overestimate initial infiltration rates for the sand and underestimate initial rates for the loam. Measurements of the wetting depth vs. cumulative infiltration indicate that the transmission zone saturation increased with increasing temperature for both soil materials. In spite of this increased saturation with temperature, the final infiltration rates at both 25 and 60??C were predicted accurately using the modified Green and Ampt equation. This suggests that increased saturation occurred primarily in dead-end pore spaces, so that transmission zone hydraulic conductivities were unaffected by these temperature-induced changes in saturation. In conclusion, except for initial infiltration rates at 60??C, the measured influence of temperature on infiltration rates was fully accounted for by the temperature dependence of the viscosity of liquid water. ?? 1991.

relA-dependent RNA polymerase activity in Escherichia coli.

PubMed Central

Ryals, J; Bremer, H

1982-01-01

Parameters relating to RNA synthesis were measured after a temperature shift from 30 to 42 degrees C, in a relA+ and relA- isogenic pair of Escherichia coli strains containing a temperature-sensitive valyl tRNA synthetase. The following results were obtained: (i) the rRNA chain growth rate increased 2-fold in both strains; (ii) newly synthesized rRNA became unstable in both strains; (iii) the stable RNA gene activity (rRNA and tRNA, measured as stable RNA synthesis rate relative to the total instantaneous rate of RNA synthesis) decreased 1.7-fold in the relA+ strain and increased 1.9-fold in the relA mutant; and (iv) the RNA polymerase activity (measured by the percentage of total RNA polymerase enzyme active in transcription an any instant) decreased from 20 to 3.6% in the relA+ strain and remained unchanged (or increased at most to 22%) in the relA mutant. It is suggested that both rRNA gene activity and the RNA polymerase activity depend on the intracellular concentration of guanosine tetraphosphate, whereas the altered chain elongation rate and stability of rRNA are temperature or amino acid starvation effects, respectively, without involvement of relA function. PMID:6174501

Temperature Dependent Electron Transport Properties of Gold Nanoparticles and Composites: Scanning Tunneling Spectroscopy Investigations.

PubMed

Patil, Sumati; Datar, Suwarna; Dharmadhikari, C V

2018-03-01

Scanning tunneling spectroscopy (STS) is used for investigating variations in electronic properties of gold nanoparticles (AuNPs) and its composite with urethane-methacrylate comb polymer (UMCP) as function of temperature. Films are prepared by drop casting AuNPs and UMCP in desired manner on silicon substrates. Samples are further analyzed for morphology under scanning electron microscopy (SEM) and atomic force microscopy (AFM). STS measurements performed in temperature range of 33 °C to 142 °C show systematic variation in current versus voltage (I-V) curves, exhibiting semiconducting to metallic transition/Schottky behavior for different samples, depending upon preparation method and as function of temperature. During current versus time (I-t) measurement for AuNPs, random telegraphic noise is observed at room temperature. Random switching of tunneling current between two discrete levels is observed for this sample. Power spectra derived from I-t show 1/f2 dependence. Statistical analysis of fluctuations shows exponential behavior with time width τ ≈ 7 ms. Local density of states (LDOS) plots derived from I-V curves of each sample show systematic shift in valance/conduction band edge towards/away from Fermi level, with respect to increase in temperature. Schottky emission is best fitted electron emission mechanism for all samples over certain range of bias voltage. Schottky plots are used to calculate barrier heights and temperature dependent measurements helped in measuring activation energies for electron transport in all samples.

Fracture strength of the particulate-reinforced ultra-high temperature ceramics based on a temperature dependent fracture toughness model

NASA Astrophysics Data System (ADS)

Wang, Ruzhuan; Li, Weiguo; Ji, Baohua; Fang, Daining

2017-10-01

The particulate-reinforced ultra-high temperature ceramics (pUHTCs) have been particularly developed for fabricating the leading edge and nose cap of hypersonic vehicles. They have drawn intensive attention of scientific community for their superior fracture strength at high temperatures. However, there is no proper model for predicting the fracture strength of the ceramic composites and its dependency on temperature. In order to account for the effect of temperature on the fracture strength, we proposed a concept called energy storage capacity, by which we derived a new model for depicting the temperature dependent fracture toughness of the composites. This model gives a quantitative relationship between the fracture toughness and temperature. Based on this temperature dependent fracture toughness model and Griffith criterion, we developed a new fracture strength model for predicting the temperature dependent fracture strength of pUHTCs at different temperatures. The model takes into account the effects of temperature, flaw size and residual stress without any fitting parameters. The predictions of the fracture strength of pUHTCs in argon or air agreed well with the experimental measurements. Additionally, our model offers a mechanism of monitoring the strength of materials at different temperatures by testing the change of flaw size. This study provides a quantitative tool for design, evaluation and monitoring of the fracture properties of pUHTCs at high temperatures.

Temperature dependence of the Raman spectrum of UO2

NASA Astrophysics Data System (ADS)

Elorrieta, J. M.; Bonales, L. J.; Baonza, V. G.; Cobos, J.

2018-05-01

The position of the main spectral features (located at ∼445, ∼575, ∼625, ∼925 and ∼1145 cm-1) in the Raman spectrum of UO2 has been examined from room temperature up to 600 °C. The wavenumber shifts measured for the observed bands have allowed us to obtain the temperature dependence (dω/dT) of the different vibrational modes. Our measurements corroborate the assignment of the band observed at ∼1145 cm-1 to the 2LO overtone. In addition, the temperature dependence of the bandwidths of the T2g and 2LO modes has been analysed.

Temperature dependence of the ClONO2 UV absorption spectrum

NASA Technical Reports Server (NTRS)

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

1994-01-01

The temperature dependence of the ClONO2 absorption spectrum has been measured between 220 and 298 K and between 195 and 430 nm using a diode array spectrometer. The absorption cross sections were determined using both: (1) absolute pressure measurements at 296 K and (2) measurements at various temperatures relative to 296 K using a dual absorption cell arrangement. The temperature dependence of the ClONO2 absorption spectrum shows very broad structure. The amplitude of the temperature dependence relative to that at 296 K is weak at short wavelengths, less than 2% at 215 nm and 220 K, but significant at the wavelengths important in the stratosphere, about 30% at 325 nm and 220 K. Our ClONO2 absorption cross section data are in good general agreement with the previous measurements of Molina and Molina (1979).

Temperature dependence of the electrode kinetics of oxygen reduction at the platinum/Nafion interface - A microelectrode investigation

NASA Technical Reports Server (NTRS)

Parthasarathy, Arvind; Srinivasan, Supramanian; Appleby, A. J.; Martin, Charles R.

1992-01-01

Results of a study of the temperature dependence of the oxygen reduction kinetics at the Pt/Nafion interface are presented. This study was carried out in the temperature range of 30-80 C and at 5 atm of oxygen pressure. The results showed a linear increase of the Tafel slope with temperature in the low current density region, but the Tafel slope was found to be independent of temperature in the high current density region. The values of the activation energy for oxygen reduction at the platinum/Nafion interface are nearly the same as those obtained at the platinum/trifluoromethane sulfonic acid interface but less than values obtained at the Pt/H3PO4 and Pt/HClO4 interfaces. The diffusion coefficient of oxygen in Nafion increases with temperature while its solubility decreases with temperature. These temperatures also depend on the water content of the membrane.

Mechanism of H2 histamine receptor dependent modulation of body temperature and neuronal activity in the medial preoptic nucleus

PubMed Central

Tabarean, Iustin V.; Sanchez-Alavez, Manuel; Sethi, Jasmine

2012-01-01

Histamine is involved in the central control of arousal, circadian rhythms and metabolism. The preoptic area, a region that contains thermoregulatory neurons is the main locus of histamine modulation of body temperature. Here we report that in mice histamine activates H2 subtype receptors in the medial preoptic nucleus (MPON) and induces hyperthermia. We also found that a population of glutamatergic MPON neurons express H2 receptors and are excited by histamine or H2 specific agonists. The agonists decreased the input resistance of the neuron and increased the depolarizing “sag” observed during hyperpolarizing current injections. Furthermore, at −60 mV holding potential activation of H2 receptors induced an inward current that was blocked by ZD7288, a specific blocker of the hyperpolarization activated cationic current (Ih). Indeed, activation of H2 receptors resulted in increased Ih amplitude in response to hyperpolarizing voltage steps and a depolarizing shift in its voltage-dependent activation. The neurons excited by H2 specific agonism expressed the HCN1 and HCN2 channel subunits. Our data indicate that at the level of the MPON histamine influences thermoregulation by increasing the firing rate of glutamatergic neurons that express H2 receptors. PMID:22366077

Temperature Dependence of Viscosities of Common Carrier Gases

ERIC Educational Resources Information Center

Sommers, Trent S.; Nahir, Tal M.

2005-01-01

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

Temperature-dependent liquid metal flowrate control device

DOEpatents

Carlson, Roger D.

1978-01-01

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

Multiaxial Temperature- and Time-Dependent Failure Model

NASA Technical Reports Server (NTRS)

Richardson, David; McLennan, Michael; Anderson, Gregory; Macon, David; Batista-Rodriquez, Alicia

2003-01-01

A temperature- and time-dependent mathematical model predicts the conditions for failure of a material subjected to multiaxial stress. The model was initially applied to a filled epoxy below its glass-transition temperature, and is expected to be applicable to other materials, at least below their glass-transition temperatures. The model is justified simply by the fact that it closely approximates the experimentally observed failure behavior of this material: The multiaxiality of the model has been confirmed (see figure) and the model has been shown to be applicable at temperatures from -20 to 115 F (-29 to 46 C) and to predict tensile failures of constant-load and constant-load-rate specimens with failure times ranging from minutes to months..

ABA-dependent inhibition of the ubiquitin proteasome system during germination at high temperature in Arabidopsis.

PubMed

Chiu, Rex Shun; Pan, Shiyue; Zhao, Rongmin; Gazzarrini, Sonia

2016-12-01

During germination, endogenous and environmental factors trigger changes in the transcriptome, translatome and proteome to break dormancy. In Arabidopsis thaliana, the ubiquitin proteasome system (UPS) degrades proteins that promote dormancy to allow germination. While research on the UPS has focused on the identification of proteasomal substrates, little information is known about the regulation of its activity. Here we characterized the activity of the UPS during dormancy release and maintenance by monitoring protein ubiquitination and degradation of two proteasomal substrates: Suc-LLVY-AMC, a well characterized synthetic substrate, and FUSCA3 (FUS3), a dormancy-promoting transcription factor degraded by the 26S proteasome. Our data indicate that proteasome activity and protein ubiquitination increase during imbibition at optimal temperature (21°C), and are required for seed germination. However, abscisic acid (ABA) and supraoptimal temperature (32°C) inhibit germination by dampening both protein ubiquitination and proteasome activity. Inhibition of UPS function by high temperature is reduced by the ABA biosynthesis inhibitor, fluridone, and in ABA biosynthetic mutants, suggesting that it is ABA dependent. Accordingly, inhibition of FUS3 degradation at 32°C is also dependent on ABA. Native gels show that inhibition of proteasome activity is caused by interference with the 26S/30S ratio as well as free 19S and 20S levels, impacting the proteasome degradation cycle. Transfer experiments show that ABA-mediated inhibition of proteasome activity at 21°C is restricted to the first 2 days of germination, a time window corresponding to seed sensitivity to environmental and ABA-mediated growth inhibition. Our data show that ABA and high temperature inhibit germination under unfavourable growth conditions by repressing the UPS. © 2016 The Authors The Plant Journal © 2016 John Wiley & Sons Ltd.

The Influence of Wavelength-Dependent Absorption and Temperature Gradients on Temperature Determination in Laser-Heated Diamond-Anvil Cells

NASA Astrophysics Data System (ADS)

Deng, J.; Lee, K. K. M.; Du, Z.; Benedetti, L. R.

2016-12-01

In situ temperature measurements in the laser-heated diamond-anvil cell (LHDAC) are among the most fundamental experiments undertaken in high-pressure science. Despite its importance, few efforts have been made to examine the alteration of thermal radiation spectra of hot samples by wavelength-dependent absorption of the sample itself together with temperature gradients within samples while laser heating and their influence on temperature measurement. For example, iron-bearing minerals show strong wavelength dependent absorption in the wavelength range used to determine temperature, which, together with temperature gradients can account for largely aliased apparent temperatures (e.g., 1200 K deviation for a 4000 K melting temperature) in some experiments obtained by fitting of detected thermal radiation intensities. As such, conclusions of melting temperatures, phase diagrams and partitioning behavior, may be grossly incorrect for these materials. In general, wavelength-dependent absorption and temperature gradients of samples are two key factors to consider in order to rigorously constrain temperatures, which have been largely ignored in previous LHDAC studies. A reevaluation of temperatures measured in recent high-profile papers will be reviewed.

Temperature dependence of piezoelectric properties for textured SBN ceramics.

PubMed

Kimura, Masahiko; Ogawa, Hirozumi; Kuroda, Daisuke; Sawada, Takuya; Higuchi, Yukio; Takagi, Hiroshi; Sakabe, Yukio

2007-12-01

Temperature dependences of piezoelectric properties were studied for h001i textured ceramics of bismuth layer-structured ferroelectrics, SrBi(2)Nb(2)O(9) (SBN). The textured ceramics with varied orientation degrees were fabricated by templated, grain-growth method, and the temperature dependences of resonance frequency were estimated. Excellent temperature stability of resonance frequency was obtained for the 76% textured ceramics. The resonance frequency of the 76% textured specimens varied almost linearly over a wide temperature range. Therefore, the variation was slight, even in a high temperature region above 150 degrees C. Temperature stability of a quartz crystal oscillator is generally higher than that of a ceramic resonator around room temperature. The variation of resonance frequency for the 76% textured SrBi(2)Nb(2)O(9) was larger than that of oscillation frequency for a typical quartz oscillator below 150 degrees C also in this study. However, the variation of the textured SrBi(2)Nb(2)O(9) was smaller than that of the quartz oscillator over a wide temperature range from -50 to 250 degrees C. Therefore, textured SrBi(2)Nb(2)O(9) ceramics is a major candidate material for the resonators used within a wide temperature range.

Describing Temperature-Dependent Self-Diffusion Coefficients and Fluidity of 1- and 3-Alcohols with the Compensated Arrhenius Formalism.

PubMed

Fleshman, Allison M; Forsythe, Grant E; Petrowsky, Matt; Frech, Roger

2016-09-22

The location of the hydroxyl group in monohydroxy alcohols greatly affects the temperature dependence of the liquid structure due to hydrogen bonding. Temperature-dependent self-diffusion coefficients, fluidity (the inverse of viscosity), dielectric constant, and density have been measured for several 1-alcohols and 3-alcohols with varying alkyl chain lengths. The data are modeled using the compensated Arrhenius formalism (CAF). The CAF follows a modified transition state theory using an Arrhenius-like expression to describe the transport property, which consists of a Boltzmann factor containing an energy of activation, Ea, and an exponential prefactor containing the temperature-dependent solution dielectric constant, εs(T). Both 1- and 3-alcohols show the Ea of diffusion coefficients (approximately 43 kJ mol(-1)) is higher than the Ea of fluidity (approximately 35 kJ mol(-1)). The temperature dependence of the exponential prefactor in these associated liquids is explained using the dielectric constant and the Kirkwood-Frölich correlation factor, gk. It is argued that the dielectric constant must be used to account for the additional temperature dependence due to variations in the liquid structure (e.g., hydrogen bonding) for the CAF to accurately model the transport property.

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.

Temperature dependence of O2 consumption; opposite effects of leptin and etomoxir on respiratory quotient in mice.

PubMed

Högberg, Helena; Engblom, Lars; Ekdahl, Asa; Lidell, Veronica; Walum, Erik; Alberts, Peteris

2006-04-01

The aims were to compare the temperature dependence of the metabolic rate in young ob/ob mice with that in mature ob/ob and db/db mice and to examine the effect on the metabolic substrate preference of leptin and etomoxir in ob/ob, C57BL/6J (wild-type), and db/db mice. In vivo oxygen consumption and carbon dioxide production were continuously measured by indirect calorimetry, and body temperature and total locomotor activity were measured by an implanted transponder. Leptin, etomoxir, or vehicle was administered intraperitoneally. The temperature dependence of the metabolic rate of mature ob/ob and db/db mice were similar to that in wild-type mice. In young 6-week-old ob/ob mice, the metabolic rate was almost doubled at 15 degrees C. Leptin (2 x 3 mg/kg) decreased the respiratory quotient (RQ) and carbon dioxide production but did not alter oxygen consumption, body temperature, or locomotor activity in ob/ob and C57BL/6J mice and had no effect in the db/db mice. Etomoxir (2 x 30 mg/kg) enhanced RQ and decreased oxygen consumption, carbon dioxide production, and body temperature in ob/ob, C57BL/6J, and db/db mice. Total locomotor activity was reduced in ob/ob and C57BL/6J mice. In young ob/ob mice, the temperature sensitivity was enhanced compared with mature mice. Leptin and etomoxir had opposite effects on metabolic substrate preference. Leptin and lowered environmental temperature increased the relative fat oxidation as indicated by decreased RQ, possibly through activation of the sympathetic nervous system.

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.

Temperature Dependence of Proton Electroreduction Kinetics at Gold(111) and (210) Surfaces

DTIC Science & Technology

1991-05-31

Temperature Dependence of Proton Electroreduction Kinetics at Gold (111) and (210) Surfaces 12 PERSONAL AUTHOR(S) A. Hamelin, L. Stoicoviciu, S.-C...Technical Report No. 98 Temperature Dependence of Proton Electroreduction Kinetics at Gold (lll) and (210) Surfaces by A. Hamelin, L. Stoicoviciu, S...approved for public release and sale: its distribution is unlimited. Temperature Dependence of Proton Electroreduction Kinetics at Gold (Ill) and (210

Cardiac sodium channel Markov model with temperature dependence and recovery from inactivation.

PubMed Central

Irvine, L A; Jafri, M S; Winslow, R L

1999-01-01

A Markov model of the cardiac sodium channel is presented. The model is similar to the CA1 hippocampal neuron sodium channel model developed by Kuo and Bean (1994. Neuron. 12:819-829) with the following modifications: 1) an additional open state is added; 2) open-inactivated transitions are made voltage-dependent; and 3) channel rate constants are exponential functions of enthalpy, entropy, and voltage and have explicit temperature dependence. Model parameters are determined using a simulated annealing algorithm to minimize the error between model responses and various experimental data sets. The model reproduces a wide range of experimental data including ionic currents, gating currents, tail currents, steady-state inactivation, recovery from inactivation, and open time distributions over a temperature range of 10 degrees C to 25 degrees C. The model also predicts measures of single channel activity such as first latency, probability of a null sweep, and probability of reopening. PMID:10096885

Quantitative Analysis of Temperature Dependence of Raman shift of monolayer WS2

NASA Astrophysics Data System (ADS)

Huang, Xiaoting; Gao, Yang; Yang, Tianqi; Ren, Wencai; Cheng, Hui-Ming; Lai, Tianshu

2016-08-01

We report the temperature-dependent evolution of Raman spectra of monolayer WS2 directly CVD-grown on a gold foil and then transferred onto quartz substrates over a wide temperature range from 84 to 543 K. The nonlinear temperature dependence of Raman shifts for both and A1g modes has been observed. The first-order temperature coefficients of Raman shifts are obtained to be -0.0093 (cm-1/K) and -0.0122 (cm-1/K) for and A1g peaks, respectively. A physical model, including thermal expansion and three- and four-phonon anharmonic effects, is used quantitatively to analyze the observed nonlinear temperature dependence. Thermal expansion coefficient (TEC) of monolayer WS2 is extracted from the experimental data for the first time. It is found that thermal expansion coefficient of out-plane mode is larger than one of in-plane mode, and TECs of and A1g modes are temperature-dependent weakly and strongly, respectively. It is also found that the nonlinear temperature dependence of Raman shift of mode mainly originates from the anharmonic effect of three-phonon process, whereas one of A1g mode is mainly contributed by thermal expansion effect in high temperature region, revealing that thermal expansion effect cannot be ignored.

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.

Temperature dependence of lower critical field of YBCO superconductor

NASA Astrophysics Data System (ADS)

Rani, Poonam; Hafiz, A. K.; Awana, V. P. S.

2018-05-01

We report the detailed study of the temperature dependence of the lower critical field (Hc1) of the YBa2Cu3O7 superconductor by magnetization measurements. The curve shows the multiband gap behavior of the sample. It is found that the sample is not a single BCS type superconductor. Hc1 is measured as the point at which the curve deviates from a Meissner-like linear M(H) curve to a nonlinear path. The Hc1 for YBCO at different temperatures from 10K to 85K has been determined by magnetization measurements M(H) with applied field parallel to the c-axis. The sample phase purity has been confirmed by Rietveld fitted X-ray diffraction data. The amplitude (1-17Oe) dependent AC susceptibility confirms the granular nature of superconducting compound. Using Bean model we calculated the temperature dependency of inter-grain critical current density and Jc(0) is found as 699.14kAcm-2.

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.

Use of fugacity model to analyze temperature-dependent removal of micro-contaminants in sewage treatment plants.

PubMed

Thompson, Kelly; Zhang, Jianying; Zhang, Chunlong

2011-08-01

Effluents from sewage treatment plants (STPs) are known to contain residual micro-contaminants including endocrine disrupting chemicals (EDCs) despite the utilization of various removal processes. Temperature alters the efficacy of removal processes; however, experimental measurements of EDC removal at various temperatures are limited. Extrapolation of EDC behavior over a wide temperature range is possible using available physicochemical property data followed by the correction of temperature dependency. A level II fugacity-based STP model was employed by inputting parameters obtained from the literature and estimated by the US EPA's Estimations Programs Interface (EPI) including EPI's BIOWIN for temperature-dependent biodegradation half-lives. EDC removals in a three-stage activated sludge system were modeled under various temperatures and hydraulic retention times (HRTs) for representative compounds of various properties. Sensitivity analysis indicates that temperature plays a significant role in the model outcomes. Increasing temperature considerably enhances the removal of β-estradiol, ethinyestradiol, bisphenol, phenol, and tetrachloroethylene, but not testosterone with the highest biodegradation rate. The shortcomings of BIOWIN were mitigated by the correction of highly temperature-dependent biodegradation rates using the Arrhenius equation. The model predicts well the effects of operating temperature and HRTs on the removal via volatilization, adsorption, and biodegradation. The model also reveals that an impractically long HRT is needed to achieve a high EDC removal. The STP model along with temperature corrections is able to provide some useful insight into the different patterns of STP performance, and useful operational considerations relevant to EDC removal at winter low temperatures. Copyright © 2011 Elsevier Ltd. All rights reserved.

Temperature-dependence of the QCD topological susceptibility

NASA Astrophysics Data System (ADS)

Kovacs, Tamas G.

2018-03-01

We recently obtained an estimate of the axion mass based on the hypothesis that axions make up most of the dark matter in the universe. A key ingredient for this calculation was the temperature-dependence of the topological susceptibility of full QCD. Here we summarize the calculation of the susceptibility in a range of temperatures from well below the finite temperature cross-over to around 2 GeV. The two main difficulties of the calculation are the unexpectedly slow convergence of the susceptibility to its continuum limit and the poor sampling of nonzero topological sectors at high temperature. We discuss how these problems can be solved by two new techniques, the first one with reweighting using the quark zero modes and the second one with the integration method.

Global patterns in lake ecosystem responses to warming based on the temperature dependence of metabolism.

PubMed

Kraemer, Benjamin M; Chandra, Sudeep; Dell, Anthony I; Dix, Margaret; Kuusisto, Esko; Livingstone, David M; Schladow, S Geoffrey; Silow, Eugene; Sitoki, Lewis M; Tamatamah, Rashid; McIntyre, Peter B

2017-05-01

Climate warming is expected to have large effects on ecosystems in part due to the temperature dependence of metabolism. The responses of metabolic rates to climate warming may be greatest in the tropics and at low elevations because mean temperatures are warmer there and metabolic rates respond exponentially to temperature (with exponents >1). However, if warming rates are sufficiently fast in higher latitude/elevation lakes, metabolic rate responses to warming may still be greater there even though metabolic rates respond exponentially to temperature. Thus, a wide range of global patterns in the magnitude of metabolic rate responses to warming could emerge depending on global patterns of temperature and warming rates. Here we use the Boltzmann-Arrhenius equation, published estimates of activation energy, and time series of temperature from 271 lakes to estimate long-term (1970-2010) changes in 64 metabolic processes in lakes. The estimated responses of metabolic processes to warming were usually greatest in tropical/low-elevation lakes even though surface temperatures in higher latitude/elevation lakes are warming faster. However, when the thermal sensitivity of a metabolic process is especially weak, higher latitude/elevation lakes had larger responses to warming in parallel with warming rates. Our results show that the sensitivity of a given response to temperature (as described by its activation energy) provides a simple heuristic for predicting whether tropical/low-elevation lakes will have larger or smaller metabolic responses to warming than higher latitude/elevation lakes. Overall, we conclude that the direct metabolic consequences of lake warming are likely to be felt most strongly at low latitudes and low elevations where metabolism-linked ecosystem services may be most affected. © 2016 John Wiley & Sons Ltd.

Temperature Dependence of Inorganic Nitrogen Uptake: Reduced Affinity for Nitrate at Suboptimal Temperatures in Both Algae and Bacteria

PubMed Central

Reay, David S.; Nedwell, David B.; Priddle, Julian; Ellis-Evans, J. Cynan

1999-01-01

Nitrate utilization and ammonium utilization were studied by using three algal isolates, six bacterial isolates, and a range of temperatures in chemostat and batch cultures. We quantified affinities for both substrates by determining specific affinities (specific affinity = maximum growth rate/half-saturation constant) based on estimates of kinetic parameters obtained from chemostat experiments. At suboptimal temperatures, the residual concentrations of nitrate in batch cultures and the steady-state concentrations of nitrate in chemostat cultures both increased. The specific affinity for nitrate was strongly dependent on temperature (Q10 ≈ 3, where Q10 is the proportional change with a 10°C temperature increase) and consistently decreased at temperatures below the optimum temperature. In contrast, the steady-state concentrations of ammonium remained relatively constant over the same temperature range, and the specific affinity for ammonium exhibited no clear temperature dependence. This is the first time that a consistent effect of low temperature on affinity for nitrate has been identified for psychrophilic, mesophilic, and thermophilic bacteria and algae. The different responses of nitrate uptake and ammonium uptake to temperature imply that there is increasing dependence on ammonium as an inorganic nitrogen source at low temperatures. PMID:10347046

Model for temperature-dependent magnetization of nanocrystalline materials

NASA Astrophysics Data System (ADS)

Bian, Q.; Niewczas, M.

2015-01-01

A magnetization model of nanocrystalline materials incorporating intragrain anisotropies, intergrain interactions, and texture effects has been extended to include the thermal fluctuations. The method relies on the stochastic Landau-Lifshitz-Gilbert theory of magnetization dynamics and permits to study the magnetic properties of nanocrystalline materials at arbitrary temperature below the Currie temperature. The model has been used to determine the intergrain exchange constant and grain boundary anisotropy constant of nanocrystalline Ni at 100 K and 298 K. It is found that the thermal fluctuations suppress the strength of the intergrain exchange coupling and also reduce the grain boundary anisotropy. In comparison with its value at 2 K, the interparticle exchange constant decreases by 16% and 42% and the grain boundary anisotropy constant decreases by 28% and 40% at 100 K and 298 K, respectively. An application of the model to study the grain size-dependent magnetization indicates that when the thermal activation energy is comparable to the free energy of grains, the decrease in the grain size leads to the decrease in the magnetic permeability and saturation magnetization. The mechanism by which the grain size influences the magnetic properties of nc-Ni is discussed.

The effect of CO2 activation temperature on the physical and electrochemical properties of activated carbon monolith from banana stem waste

NASA Astrophysics Data System (ADS)

Taer, E.; Susanti, Y.; Awitdrus, Sugianto, Taslim, R.; Setiadi, R. N.; Bahri, S.; Agustino, Dewi, P.; Kurniasih, B.

2018-02-01

The effect of CO2 activation on the synthesis of activated carbon monolith from banana stem waste has been studied. Physical characteristics such as density, degree of crystallinity, surface morphology and elemental content has been analyzed, supporting the finding of an excellent electrochemical properties for the supercapacitor. The synthesis of activated carbon electrode began with pre-carbonization process at temperature of 250°C for 2.5 h. Then the process was continued by chemical activation using KOH as activating agent with a concentration of 0.4 M. The pellets were formed with 8 ton hydrolic pressure. All the samples were carbonized at a temperature of 600°C, followed by physical activation using CO2 gas at a various temperatures ranging from 800°C, 850°C, 900°C and 950°C for 2 h. The carbon content was increased with increasing temperature and the optimum temperature was 900°C. The specific capacitance depends on the activation temperature with the highest specific capacitance of 104.2 F/g at the activation temperature of 900°C.

Sex reversal triggers the rapid transition from genetic to temperature-dependent sex.

PubMed

Holleley, Clare E; O'Meally, Denis; Sarre, Stephen D; Marshall Graves, Jennifer A; Ezaz, Tariq; Matsubara, Kazumi; Azad, Bhumika; Zhang, Xiuwen; Georges, Arthur

2015-07-02

Sex determination in animals is amazingly plastic. Vertebrates display contrasting strategies ranging from complete genetic control of sex (genotypic sex determination) to environmentally determined sex (for example, temperature-dependent sex determination). Phylogenetic analyses suggest frequent evolutionary transitions between genotypic and temperature-dependent sex determination in environmentally sensitive lineages, including reptiles. These transitions are thought to involve a genotypic system becoming sensitive to temperature, with sex determined by gene-environment interactions. Most mechanistic models of transitions invoke a role for sex reversal. Sex reversal has not yet been demonstrated in nature for any amniote, although it occurs in fish and rarely in amphibians. Here we make the first report of reptile sex reversal in the wild, in the Australian bearded dragon (Pogona vitticeps), and use sex-reversed animals to experimentally induce a rapid transition from genotypic to temperature-dependent sex determination. Controlled mating of normal males to sex-reversed females produces viable and fertile offspring whose phenotypic sex is determined solely by temperature (temperature-dependent sex determination). The W sex chromosome is eliminated from this lineage in the first generation. The instantaneous creation of a lineage of ZZ temperature-sensitive animals reveals a novel, climate-induced pathway for the rapid transition between genetic and temperature-dependent sex determination, and adds to concern about adaptation to rapid global climate change.

Temperature-Dependent Ellipsometry Measurements of Partial Coulomb Energy in Superconducting Cuprates

DOE PAGES

Levallois, J.; Tran, M. K.; Pouliot, D.; ...

2016-08-24

Here we performed an experimental study of the temperature and doping dependence of the energy-loss function of the bilayer and trilayer bismuth cuprates family. The primary aim is to obtain information on the energy stored in the Coulomb interaction between the conduction electrons, on the temperature dependence thereof, and on the change of Coulomb interaction when Cooper pairs are formed. We performed temperature-dependent ellipsometry measurements on several Bi 2Sr 2CaCu 2O 8₋x single crystals: underdoped with T c=60, 70, and 83 K; optimally doped with T c=91 K; overdoped with T c=84, 81, 70, and 58 K; as well asmore » optimally doped Bi 2Sr 2Ca 2Cu 3O 10+x with T c=110 K. Our first observation is that, as the temperature drops through T c, the loss function in the range up to 2 eV displays a change of temperature dependence as compared to the temperature dependence in the normal state. This effect at—or close to—T c depends strongly on doping, with a sign change for weak overdoping. The size of the observed change in Coulomb energy, using an extrapolation with reasonable assumptions about its q dependence, is about the same size as the condensation energy that has been measured in these compounds. Our results therefore lend support to the notion that the Coulomb energy is an important factor for stabilizing the superconducting phase. Lastly, because of the restriction to small momentum, our observations do not exclude a possible significant contribution to the condensation energy of the Coulomb energy associated with the region of q around (π,π).« less

Simulation study of temperature-dependent diffusion behaviors of Ag/Ag(001) at low substrate temperature

NASA Astrophysics Data System (ADS)

Cai, Danyun; Mo, Yunjie; Feng, Xiaofang; He, Yingyou; Jiang, Shaoji

2017-06-01

In this study, a model based on the First Principles calculations and Kinetic Monte Carlo simulation were established to study the growth characteristic of Ag thin film at low substrate temperature. On the basis of the interaction between the adatom and nearest-neighbor atoms, some simplifications and assumptions were made to categorize the diffusion behaviors of Ag adatoms on Ag(001). Then the barriers of all possible diffusion behaviors were calculated using the Climbing Image Nudged Elastic Band method (CI-NEB). Based on the Arrhenius formula, the morphology variation, which is attributed to the surface diffusion behaviors during the growth, was simulated with a temperature-dependent KMC model. With this model, a non-monotonic relation between the surface roughness and the substrate temperature (decreasing from 300 K to 100 K) were discovered. The analysis of the temperature dependence on diffusion behaviors presents a theoretical explanation of diffusion mechanism for the non-monotonic variation of roughness at low substrate temperature.

A Temperature-Dependent Battery Model for Wireless Sensor Networks.

PubMed

Rodrigues, Leonardo M; Montez, Carlos; Moraes, Ricardo; Portugal, Paulo; Vasques, Francisco

2017-02-22

Energy consumption is a major issue in Wireless Sensor Networks (WSNs), as nodes are powered by chemical batteries with an upper bounded lifetime. Estimating the lifetime of batteries is a difficult task, as it depends on several factors, such as operating temperatures and discharge rates. Analytical battery models can be used for estimating both the battery lifetime and the voltage behavior over time. Still, available models usually do not consider the impact of operating temperatures on the battery behavior. The target of this work is to extend the widely-used Kinetic Battery Model (KiBaM) to include the effect of temperature on the battery behavior. The proposed Temperature-Dependent KiBaM (T-KiBaM) is able to handle operating temperatures, providing better estimates for the battery lifetime and voltage behavior. The performed experimental validation shows that T-KiBaM achieves an average accuracy error smaller than 0.33%, when estimating the lifetime of Ni-MH batteries for different temperature conditions. In addition, T-KiBaM significantly improves the original KiBaM voltage model. The proposed model can be easily adapted to handle other battery technologies, enabling the consideration of different WSN deployments.

Temperature-dependent dynamical transitions of different classes of amino acid residue in a globular protein.

PubMed

Miao, Yinglong; Yi, Zheng; Glass, Dennis C; Hong, Liang; Tyagi, Madhusudan; Baudry, Jerome; Jain, Nitin; Smith, Jeremy C

2012-12-05

The temperature dependences of the nanosecond dynamics of different chemical classes of amino acid residue have been analyzed by combining elastic incoherent neutron scattering experiments with molecular dynamics simulations on cytochrome P450cam. At T = 100-160 K, anharmonic motion in hydrophobic and aromatic residues is activated, whereas hydrophilic residue motions are suppressed because of hydrogen-bonding interactions. In contrast, at T = 180-220 K, water-activated jumps of hydrophilic side chains, which are strongly coupled to the relaxation rates of the hydrogen bonds they form with hydration water, become apparent. Thus, with increasing temperature, first the hydrophobic core awakens, followed by the hydrophilic surface.

Temperature requirements for initiation of RNA-dependent RNA polymerization.

PubMed

Yang, Hongyan; Gottlieb, Paul; Wei, Hui; Bamford, Dennis H; Makeyev, Eugene V

2003-09-30

To continue the molecular characterization of RNA-dependent RNA polymerases of dsRNA bacteriophages (Cystoviridae), we purified and biochemically characterized the wild-type (wt) and a temperature-sensitive (ts) point mutant of the polymerase subunit (Pol) from bacteriophage phi12. Interestingly, initiation by both wt and the ts phi12 Pol was notably more sensitive to increased temperatures than the elongation step, the absolute value of the nonpermissive temperature being lower for the ts enzyme. Experiments with the Pol subunit of related cystovirus phi6 revealed a similar differential sensitivity of the initiation and elongation steps. This is consistent with the previous result showing that de novo initiation by RdRp from dengue virus is inhibited at elevated temperatures, whereas the elongation phase is relatively thermostable. Overall, these data suggest that de novo RNA-dependent RNA synthesis in many viral systems includes a specialized thermolabile state of the RdRp initiation complex.

Temperature dependence of the plastic scintillator detector for DAMPE

NASA Astrophysics Data System (ADS)

Wang, Zhao-Min; Yu, Yu-Hong; Sun, Zhi-Yu; Yue, Ke; Yan, Duo; Zhang, Yong-Jie; Zhou, Yong; Fang, Fang; Huang, Wen-Xue; Chen, Jun-Ling

2017-01-01

The Plastic Scintillator Detector (PSD) is one of the main sub-detectors in the DArk Matter Particle Explorer (DAMPE) project. It will be operated over a large temperature range from -10 to 30 °C, so the temperature effect of the whole detection system should be studied in detail. The temperature dependence of the PSD system is mainly contributed by the three parts: the plastic scintillator bar, the photomultiplier tube (PMT), and the Front End Electronics (FEE). These three parts have been studied in detail and the contribution of each part has been obtained and discussed. The temperature coefficient of the PMT is -0.320(±0.033)%/°C, and the coefficient of the plastic scintillator bar is -0.036(±0.038)%/°C. This result means that after subtracting the FEE pedestal, the variation of the signal amplitude of the PMT-scintillator system due to temperature mainly comes from the PMT, and the plastic scintillator bar is not sensitive to temperature over the operating range. Since the temperature effect cannot be ignored, the temperature dependence of the whole PSD has been also studied and a correction has been made to minimize this effect. The correction result shows that the effect of temperature on the signal amplitude of the PSD system can be suppressed. Supported by Strategic Priority Research Program on Space Science of the Chinese Academy of Sciences (XDA04040202-3) and Youth Innovation Promotion Association, CAS

Temperature-Dependent Friction and Wear Behavior of PTFE and MoS 2

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

Babuska, T. F.; Pitenis, A. A.; Jones, M. R.

2016-06-16

We present an investigation of the temperature-dependent friction behavior of PTFE, MoS 2, and PTFE-on- MoS 2. Friction behavior was measured while continuously varying contact temperature in the range -150 to 175°C while sliding in dry nitrogen, as well as for self-mated PTFE immersed in liquid nitrogen. These results contrast with previous reports of monotonic inverse temperature dependent friction behavior, as well as reported high-friction transitions and plateaus at temperatures below about -20°C that were not observed, providing new insights about the molecular mechanisms of macro-scale friction. The temperature-dependent friction behavior characteristic of self-mated PTFE was found also on themore » PTFE-on-MoS 2 sliding contact, suggesting that PTFE friction was defined by sub-surface deformation mechanisms and internal friction even when sliding against a lamellar lubricant with extremely low friction coefficient (μ ~ 0.02). The various relaxation temperatures of PTFE were found in the temperature-dependent friction behavior, showing excellent agreement with reported values acquired using torsional techniques measuring internal friction. Additionally, hysteresis in friction behavior suggests an increase in near-surface crystallinity at upon exceeding the high temperature relaxation, T α~ 116°C.« less

Temperature dependence of elastic and strength properties of T300/5208 graphite-epoxy

NASA Technical Reports Server (NTRS)

Milkovich, S. M.; Herakovich, C. T.

1984-01-01

Experimental results are presented for the elastic and strength properties of T300/5208 graphite-epoxy at room temperature, 116K (-250 F), and 394K (+250 F). Results are presented for unidirectional 0, 90, and 45 degree laminates, and + or - 30, + or - 45, and + or - 60 degree angle-ply laminates. The stress-strain behavior of the 0 and 90 degree laminates is essentially linear for all three temperatures and that the stress-strain behavior of all other laminates is linear at 116K. A second-order curve provides the best fit for the temperature is linear at 116K. A second-order curve provides the best fit for the temperature dependence of the elastic modulus of all laminates and for the principal shear modulus. Poisson's ratio appears to vary linearly with temperature. all moduli decrease with increasing temperature except for E (sub 1) which exhibits a small increase. The strength temperature dependence is also quadratic for all laminates except the 0 degree - laminate which exhibits linear temperature dependence. In many cases the temperature dependence of properties is nearly linear.

Time dependent temperature distribution in pulsed Ti:sapphire lasers

NASA Technical Reports Server (NTRS)

Buoncristiani, A. Martin; Byvik, Charles E.; Farrukh, Usamah O.

1988-01-01

An expression is derived for the time dependent temperature distribution in a finite solid state laser rod for an end-pumped beam of arbitrary shape. The specific case of end pumping by circular (constant) or Gaussian beam is described. The temperature profile for a single pump pulse and for repetitive pulse operation is discussed. The particular case of the temperature distribution in a pulsed titanium:sapphire rod is considered.

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.

Picosecond-Resolved Fluorescent Probes at Functionally Distinct Tryptophans within a Thermophilic Alcohol Dehydrogenase: Relationship of Temperature-Dependent Changes in Fluorescence to Catalysis

PubMed Central

2015-01-01

Two single-tryptophan variants were generated in a thermophilic alcohol dehydrogenase with the goal of correlating temperature-dependent changes in local fluorescence with the previously demonstrated catalytic break at ca. 30 °C (Kohen et al., Nature1999, 399, 496). One tryptophan variant, W87in, resides at the active site within van der Waals contact of bound alcohol substrate; the other variant, W167in, is a remote-site surface reporter located >25 Å from the active site. Picosecond-resolved fluorescence measurements were used to analyze fluorescence lifetimes, time-dependent Stokes shifts, and the extent of collisional quenching at Trp87 and Trp167 as a function of temperature. A subnanosecond fluorescence decay rate constant has been detected for W87in that is ascribed to the proximity of the active site Zn2+ and shows a break in behavior at 30 °C. For the remainder of the reported lifetime measurements, there is no detectable break between 10 and 50 °C, in contrast with previously reported hydrogen/deuterium exchange experiments that revealed a temperature-dependent break analogous to catalysis (Liang et al., Proc. Natl. Acad. Sci. U.S.A. 2004, 101, 9556). We conclude that the motions that lead to the rigidification of ht-ADH below 30 °C are likely to be dominated by global processes slower than the picosecond to nanosecond motions measured herein. In the case of collisional quenching of fluorescence by acrylamide, W87in and W167in behave in a similar manner that resembles free tryptophan in water. Stokes shift measurements, by contrast, show distinctive behaviors in which the active-site tryptophan relaxation is highly temperature-dependent, whereas the solvent-exposed tryptophan’s dynamics are temperature-independent. These data are concluded to reflect a significantly constrained environment surrounding the active site Trp87 that both increases the magnitude of the Stokes shift and its temperature-dependence. The results are discussed in the context

Temperature Dependence of Irradiation Damage to Polythene

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

TODD, G.; WILD, G. A.

1963-07-13

Comparison of measurements of radiation damage to polythene exposed to a 4.3-Mev linear accelerator and in a reactor led to the conclusion that radiation damage of polythene is temperature dependent. Applications of radiation in raising or lowering the elastic modulus of polythene are suggested. (C.H.)

A Temperature-Dependent Battery Model for Wireless Sensor Networks

PubMed Central

Rodrigues, Leonardo M.; Montez, Carlos; Moraes, Ricardo; Portugal, Paulo; Vasques, Francisco

2017-01-01

Energy consumption is a major issue in Wireless Sensor Networks (WSNs), as nodes are powered by chemical batteries with an upper bounded lifetime. Estimating the lifetime of batteries is a difficult task, as it depends on several factors, such as operating temperatures and discharge rates. Analytical battery models can be used for estimating both the battery lifetime and the voltage behavior over time. Still, available models usually do not consider the impact of operating temperatures on the battery behavior. The target of this work is to extend the widely-used Kinetic Battery Model (KiBaM) to include the effect of temperature on the battery behavior. The proposed Temperature-Dependent KiBaM (T-KiBaM) is able to handle operating temperatures, providing better estimates for the battery lifetime and voltage behavior. The performed experimental validation shows that T-KiBaM achieves an average accuracy error smaller than 0.33%, when estimating the lifetime of Ni-MH batteries for different temperature conditions. In addition, T-KiBaM significantly improves the original KiBaM voltage model. The proposed model can be easily adapted to handle other battery technologies, enabling the consideration of different WSN deployments. PMID:28241444

Temperature-Dependent Detectivity of Near-Infrared Organic Bulk Heterojunction Photodiodes.

PubMed

Wu, Zhenghui; Yao, Weichuan; London, Alexander E; Azoulay, Jason D; Ng, Tse Nga

2017-01-18

Bulk heterojunction photodiodes are fabricated using a new donor-acceptor polymer with a near-infrared absorption edge at 1.2 μm, achieving a detectivity up to 10 12 Jones at a wavelength of 1 μm and an excellent linear dynamic range of 86 dB. The photodiode detectivity is maximized by operating at zero bias to suppress dark current, while a thin 175 nm active layer is used to facilitate charge collection without reverse bias. Analysis of the temperature dependence of the dark current and spectral response demonstrates a 2.8-fold increase in detectivity as the temperature was lowered from 44 to -12 °C, a relatively small change when compared to that of inorganic-based devices. The near-infrared photodiode shows a switching speed reaching up to 120 μs without an external bias. An application using our NIR photodiode to detect arterial pulses of a fingertip is demonstrated.

The Stress-Dependent Activation Parameters for Dislocation Nucleation in Molybdenum Nanoparticles.

PubMed

Chachamovitz, Doron; Mordehai, Dan

2018-03-02

Many specimens at the nanoscale are pristine of dislocations, line defects which are the main carriers of plasticity. As a result, they exhibit extremely high strengths which are dislocation-nucleation controlled. Since nucleation is a thermally activated process, it is essential to quantify the stress-dependent activation parameters for dislocation nucleation in order to study the strength of specimens at the nanoscale and its distribution. In this work, we calculate the strength of Mo nanoparticles in molecular dynamics simulations and we propose a method to extract the activation free-energy barrier for dislocation nucleation from the distribution of the results. We show that by deforming the nanoparticles at a constant strain rate, their strength distribution can be approximated by a normal distribution, from which the activation volumes at different stresses and temperatures are calculated directly. We found that the activation energy dependency on the stress near spontaneous nucleation conditions obeys a power-law with a critical exponent of approximately 3/2, which is in accordance with critical exponents found in other thermally activated processes but never for dislocation nucleation. Additionally, significant activation entropies were calculated. Finally, we generalize the approach to calculate the activation parameters for other driving-force dependent thermally activated processes.

Mapping the temperature-dependent conformational landscapes of the dynamic enzymes cyclophilin A and urease

NASA Astrophysics Data System (ADS)

Thorne, Robert; Keedy, Daniel; Warkentin, Matthew; Fraser, James; Moreau, David; Atakisi, Hakan; Rau, Peter

Proteins populate complex, temperature-dependent ensembles of conformations that enable their function. Yet in X-ray crystallographic studies, roughly 98% of structures have been determined at 100 K, and most refined to only a single conformation. A combination of experimental methods enabled by studies of ice formation and computational methods for mining low-density features in electron density maps have been applied to determine the evolution of the conformational landscapes of the enzymes cyclophilin A and urease between 300 K and 100 K. Minority conformations of most side chains depopulate on cooling from 300 to ~200 K, below which subsequent conformational evolution is quenched. The characteristic temperatures for this depopulation are highly heterogeneous throughout each enzyme. The temperature-dependent ensemble of the active site flap in urease has also been mapped. These all-atom, site-resolved measurements and analyses rule out one interpretation of the protein-solvent glass transition, and give an alternative interpretation of a dynamical transition identified in site-averaged experiments. They demonstrate a powerful approach to structural characterization of the dynamic underpinnings of protein function. Supported by NSF MCB-1330685.

Temperature Dependence of Errors in Parameters Derived from Van't Hoff Studies.

ERIC Educational Resources Information Center

Dec, Steven F.; Gill, Stanley J.

1985-01-01

The method of Clarke and Glew is broadly applicable to studies of the temperature dependence of equilibrium constant measurements. The method is described and examples of its use in comparing calorimetric results and temperature dependent gas solubility studies are provided. (JN)

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

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

Temperature dependence of the ClONO{sub 2} UV absorption spectrum

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

Burkholder, J.B.; Talukdar, R.K.; Ravishankara, A.R.

1994-04-01

The temperature dependence of the ClONO{sub 2} absorption spectrum has been measured between 220 and 298 K and between 195 and 430 nm using a diode array spectrometer. The absorption cross sections were determined using both: (1) absolute pressure measurements at 296 K and (2) measurements at various temperatures relative to 296 K using a dual absorption cell arrangement. The temperature dependence of the ClONO{sub 2} absorption spectrum shows very broad structure. The amplitude of the temperature dependence relative to that at 296 K is weak at short wavelengths, < 2% at 215 nm and 220 K, but significant atmore » the wavelengths important in the stratosphere, {approximately} 30% at 325 nm and 220 K. The authors ClONO{sub 2} absorption cross section data are in good general agreement with the previous measurements of Molina and Molina.« less

New correlation for the temperature-dependent viscosity for saturated liquids

NASA Astrophysics Data System (ADS)

Tian, Jianxiang; Zhang, Laibin

2016-11-01

Based on the recent progress on both the temperature dependence of surface tension [H. L. Yi, J. X. Tian, A. Mulero and I. Cachading, J. Therm. Anal. Calorim. 126 (2016) 1603, and the correlation between surface tension and viscosity of liquids [J. X. Tian and A. Mulero, Ind. Eng. Chem. Res. 53 (2014) 9499], we derived a new multiple parameter correlation to describe the temperature-dependent viscosity of liquids. This correlation is verified by comparing with data from NIST Webbook for 35 saturated liquids including refrigerants, hydrocarbons and others, in a wide temperature range from the triple point temperature to the one very near to the critical temperature. Results show that this correlation predicts the NIST data with high accuracy with absolute average deviation (AAD) less than 1% for 21 liquids and more than 3% for only four liquids, and is clearly better than the popularly used Vogel-Fulcher-Tamman (VFT) correlation.

Guest concentration, bias current, and temperature-dependent sign inversion of magneto-electroluminescence in thermally activated delayed fluorescence devices

NASA Astrophysics Data System (ADS)

Deng, Junquan; Jia, Weiyao; Chen, Yingbing; Liu, Dongyu; Hu, Yeqian; Xiong, Zuhong

2017-03-01

Non-emissive triplet excited states in devices that undergo thermally activated delayed fluorescence (TADF) can be up-converted to singlet excited states via reverse intersystem crossing (RISC), which leads to an enhanced electroluminescence efficiency. Exciton-based fluorescence devices always exhibit a positive magneto-electroluminescence (MEL) because intersystem crossing (ISC) can be suppressed effectively by an external magnetic field. Conversely, TADF devices should exhibit a negative MEL because RISC is suppressed by the external magnetic field. Intriguingly, we observed a positive MEL in TADF devices. Moreover, the sign of the MEL was either positive or negative, and depended on experimental conditions, including doping concentration, current density and temperature. The MEL observed from our TADF devices demonstrated that ISC in the host material and RISC in the guest material coexisted. These competing processes were affected by the experimental conditions, which led to the sign change of the MEL. This work gives important insight into the energy transfer processes and the evolution of excited states in TADF devices.

Genetic variation in the temperature dependence of liver microsomal CYP2E1 activity, within and between species of the viviparous fish Poeciliopsis

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

Crivello, J.F.; Schultz, R.J.

1995-01-01

The temperature dependence of liver microsomal CYP2E1 (cytochrome P450 2E1) activity was examined in selected genotypes of the viviparous fish Poeciliopsis. Activity of this enzyme, as a function of incubation temperature, was determined by measuring 6-OH-chlorzoxazone formation from chlorzoxazone, a specific CYP2E1 substrate. Chlorzoxazone-6-hydroxylase activity was examined among five species of Poeciliopsis, as well as among nine genotypes within a species, P. monacha. Among Poeciliopsis genotypes, P. monacha contained the greatest activity, 9.5 [+-] 1.5 U with a temperature optimum (T[sub O]) of 25 C. The lowest activity was in P. occidentalis, 0.65 [+-] 0.11 U, with a T[sub O]more » of 27 t 28 C; P. prolifica, P. fasciata, P. lucida, and P. viriosa had intermediate levels of activities, 1.1 to 5.5 U, and T[sub O] from 25 to 31 C. To determine if metabolic differences exist within species, enzyme activity was examined from nine genotypes of P. monacha by comparing expression among P. monacha-lucida hybrids. These hybrids were given identical paternal genomes of lucida but retained the original maternal Monacha genomes sampled from wild gene pools. The greatest activity was found in genotype T70-3 P. Cw, 3.6 [+-] 0.1 U, at a T[sub O] of 29 C, and the lowest was in genotype SV73-7s, 0.40 [+-] 0.12 U, at a T[sub O] of 27 C. The other naturally occurring genotypes, M65-24, M65-26, SV73-7v, as well as the laboratory-produced synthetic hybrids, Syn4 and Syn5, had intermediate activities, 0.73 [+-] 0.38 to 2.1 [+-] 0.69 U, and T[sub O] of 25 to 27 C. No hybrid had activity levels as high as the maternal parent, P. monacha, and only one had a T[sub O] as low as either parent. Apparently the genes involved in xenobiotic activity vary widely among the closely related species of Poeciliopsis but also within species, suggesting that these phenotypes can be acted upon by natural selection.« less

Molecular players involved in temperature-dependent sex determination and sex differentiation in Teleost fish

PubMed Central

2014-01-01

The molecular mechanisms that underlie sex determination and differentiation are conserved and diversified. In fish species, temperature-dependent sex determination and differentiation seem to be ubiquitous and molecular players involved in these mechanisms may be conserved. Although how the ambient temperature transduces signals to the undifferentiated gonads remains to be elucidated, the genes downstream in the sex differentiation pathway are shared between sex-determining mechanisms. In this paper, we review recent advances on the molecular players that participate in the sex determination and differentiation in fish species, by putting emphasis on temperature-dependent sex determination and differentiation, which include temperature-dependent sex determination and genetic sex determination plus temperature effects. Application of temperature-dependent sex differentiation in farmed fish and the consequences of temperature-induced sex reversal are discussed. PMID:24735220

Anomalous temperature dependence of the IR spectrum of polyalanine

NASA Astrophysics Data System (ADS)

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

1997-12-01

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

Temperature dependence of spin-orbit torques in Cu-Au alloys

NASA Astrophysics Data System (ADS)

Wen, Yan; Wu, Jun; Li, Peng; Zhang, Qiang; Zhao, Yuelei; Manchon, Aurelien; Xiao, John Q.; Zhang, Xixiang

2017-03-01

We investigated current driven spin-orbit torques in C u40A u60/N i80F e20/Ti layered structures with in-plane magnetization. We have demonstrated a reliable and convenient method to separate dampinglike torque and fieldlike torque by using the second harmonic technique. It is found that the dampinglike torque and fieldlike torque depend on temperature very differently. Dampinglike torque increases with temperature, while fieldlike torque decreases with temperature, which are different from results obtained previously in other material systems. We observed a nearly linear dependence between the spin Hall angle and longitudinal resistivity, suggesting that skew scattering may be the dominant mechanism of spin-orbit torques.

Temperature-dependent regulation of rDNA condensation in Saccharomyces cerevisiae.

PubMed

Shen, Donglai; Skibbens, Robert V

2017-06-03

Chromatin condensation during mitosis produces detangled and discrete DNA entities required for high fidelity sister chromatid segregation during mitosis and positions DNA away from the cleavage furrow during cytokinesis. Regional condensation during G1 also establishes a nuclear architecture through which gene transcription is regulated but remains plastic so that cells can respond to changes in nutrient levels, temperature and signaling molecules. To date, however, the potential impact of this plasticity on mitotic chromosome condensation remains unknown. Here, we report results obtained from a new condensation assay that wildtype budding yeast cells exhibit dramatic changes in rDNA conformation in response to temperature. rDNA hypercondenses in wildtype cells maintained at 37°C, compared with cells maintained at 23°C. This hypercondensation machinery can be activated during preanaphase but readily inactivated upon exposure to lower temperatures. Extended mitotic arrest at 23°C does not result in hypercondensation, negating a kinetic-based argument in which condensation that typically proceeds slowly is accelerated when cells are placed at 37°C. Neither elevated recombination nor reduced transcription appear to promote this hypercondensation. This heretofore undetected temperature-dependent hypercondensation pathway impacts current views of chromatin structure based on conditional mutant gene analyses and significantly extends our understanding of physiologic changes in chromatin architecture in response to hypothermia.

Temperature-dependent regulation of rDNA condensation in Saccharomyces cerevisiae

PubMed Central

Shen, Donglai; Skibbens, Robert V.

2017-01-01

ABSTRACT Chromatin condensation during mitosis produces detangled and discrete DNA entities required for high fidelity sister chromatid segregation during mitosis and positions DNA away from the cleavage furrow during cytokinesis. Regional condensation during G1 also establishes a nuclear architecture through which gene transcription is regulated but remains plastic so that cells can respond to changes in nutrient levels, temperature and signaling molecules. To date, however, the potential impact of this plasticity on mitotic chromosome condensation remains unknown. Here, we report results obtained from a new condensation assay that wildtype budding yeast cells exhibit dramatic changes in rDNA conformation in response to temperature. rDNA hypercondenses in wildtype cells maintained at 37°C, compared with cells maintained at 23°C. This hypercondensation machinery can be activated during preanaphase but readily inactivated upon exposure to lower temperatures. Extended mitotic arrest at 23°C does not result in hypercondensation, negating a kinetic-based argument in which condensation that typically proceeds slowly is accelerated when cells are placed at 37°C. Neither elevated recombination nor reduced transcription appear to promote this hypercondensation. This heretofore undetected temperature-dependent hypercondensation pathway impacts current views of chromatin structure based on conditional mutant gene analyses and significantly extends our understanding of physiologic changes in chromatin architecture in response to hypothermia. PMID:28426272

Temperature dependence of metal-enhanced fluorescence of photosystem I from Thermosynechococcus elongatus.

PubMed

Ashraf, Imran; Konrad, Alexander; Lokstein, Heiko; Skandary, Sepideh; Metzger, Michael; Djouda, Joseph M; Maurer, Thomas; Adam, Pierre M; Meixner, Alfred J; Brecht, Marc

2017-03-23

We report the temperature dependence of metal-enhanced fluorescence (MEF) of individual photosystem I (PSI) complexes from Thermosynechococcus elongatus (T. elongatus) coupled to gold nanoparticles (AuNPs). A strong temperature dependence of shape and intensity of the emission spectra is observed when PSI is coupled to AuNPs. For each temperature, the enhancement factor (EF) is calculated by comparing the intensity of individual AuNP-coupled PSI to the mean intensity of 'uncoupled' PSI. At cryogenic temperature (1.6 K) the average EF was 4.3-fold. Upon increasing the temperature to 250 K the EF increases to 84-fold. Single complexes show even higher EFs up to 441.0-fold. At increasing temperatures the different spectral pools of PSI from T. elongatus become distinguishable. These pools are affected differently by the plasmonic interactions and show different enhancements. The remarkable increase of the EFs is explained by a rate model including the temperature dependence of the fluorescence yield of PSI and the spectral overlap between absorption and emission spectra of AuNPs and PSI, respectively.

Refractive indices of liquid crystal E7 depending on temperature and wavelengths

NASA Astrophysics Data System (ADS)

Ma, Mingjian; Li, Shuguang; Jing, Xili; Chen, Hailiang

2017-11-01

The dependence of refractive indices of liquid crystal (LC) on temperature is represented by the Haller approximation model, and its dependence on the wavelength is expressed by the extended Cauchy model. We derived the refractive indices expressions of nematic LC E7 depending on temperature and wavelength simultaneously by combining these two models. Based on the obtained expressions, one can acquire the refractive indices of E7 at arbitrary temperature and wavelengths. The birefringence, variation rate of refractive indices, macroscopic order parameter Q, and orientational order parameter ⟨P2⟩ of E7 were then discussed based on the expressions.

Spectral and temperature-dependent infrared emissivity measurements of painted metals for improved temperature estimation during laser damage testing

NASA Astrophysics Data System (ADS)

Baumann, Sean M.; Keenan, Cameron; Marciniak, Michael A.; Perram, Glen P.

2014-10-01

A database of spectral and temperature-dependent emissivities was created for painted Al-alloy laser-damage-testing targets for the purpose of improving the uncertainty to which temperature on the front and back target surfaces may be estimated during laser-damage testing. Previous temperature estimates had been made by fitting an assumed gray-body radiance curve to the calibrated spectral radiance data collected from the back surface using a Telops Imaging Fourier Transform Spectrometer (IFTS). In this work, temperature-dependent spectral emissivity measurements of the samples were made from room temperature to 500 °C using a Surface Optics Corp. SOC-100 Hemispherical Directional Reflectometer (HDR) with Nicolet FTS. Of particular interest was a high-temperature matte-black enamel paint used to coat the rear surfaces of the Al-alloy samples. The paint had been assumed to have a spectrally flat and temperatureinvariant emissivity. However, the data collected using the HDR showed both spectral variation and temperature dependence. The uncertainty in back-surface temperature estimation during laser-damage testing made using the measured emissivities was improved from greater than +10 °C to less than +5 °C for IFTS pixels away from the laser burn-through hole, where temperatures never exceeded those used in the SOC-100 HDR measurements. At beam center, where temperatures exceeded those used in the SOC-100 HDR, uncertainty in temperature estimates grew beyond those made assuming gray-body emissivity. Accurate temperature estimations during laser-damage testing are useful in informing a predictive model for future high-energy-laser weapon applications.

Upper Thermosphere Winds and Temperatures in the Geomagnetic Polar Cap: Solar Cycle, Geomagnetic Activity, and Interplanetary Magnetic Field Dependencies

NASA Technical Reports Server (NTRS)

Killeen, T. L.; Won, Y.-I.; Niciejewski, R. J.; Burns, A. G.

1995-01-01

Ground-based Fabry-Perot interferometers located at Thule, Greenland (76.5 deg. N, 69.0 deg. W, lambda = 86 deg.) and at Sondre Stromfjord, Greenland (67.0 deg. N, 50.9 deg. W, lambda = 74 deg.) have monitored the upper thermospheric (approx. 240-km altitude) neutral wind and temperature over the northern hemisphere geomagnetic polar cap since 1983 and 1985, respectively. The thermospheric observations are obtained by determining the Doppler characteristics of the (OI) 15,867-K (630.0-nm) emission of atomic oxygen. The instruments operate on a routine, automatic, (mostly) untended basis during the winter observing seasons, with data coverage limited only by cloud cover and (occasional) instrument failures. This unique database of geomagnetic polar cap measurements now extends over the complete range of solar activity. We present an analysis of the measurements made between 1985 (near solar minimum) and 1991 (near solar maximum), as part of a long-term study of geomagnetic polar cap thermospheric climatology. The measurements from a total of 902 nights of observations are compared with the predictions of two semiempirical models: the Vector Spherical Harmonic (VSH) model of Killeen et al. (1987) and the Horizontal Wind Model (HWM) of Hedin et al. (1991). The results are also analyzed using calculations of thermospheric momentum forcing terms from the Thermosphere-ionosphere General Circulation Model TGCM) of the National Center for Atmospheric Research (NCAR). The experimental results show that upper thermospheric winds in the geomagnetic polar cap have a fundamental diurnal character, with typical wind speeds of about 200 m/s at solar minimum, rising to up to about 800 m/s at solar maximum, depending on geomagnetic activity level. These winds generally blow in the antisunward direction, but are interrupted by episodes of modified wind velocity and altered direction often associated with changes in the orientation of the Interplanetary Magnetic Field (IMF). The

Temperature dependency of the emission properties from positioned In(Ga)As/GaAs quantum dots

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

Braun, T.; Schneider, C.; Maier, S.

In this letter we study the influence of temperature and excitation power on the emission linewidth from site-controlled InGaAs/GaAs quantum dots grown on nanoholes defined by electron beam lithography and wet chemical etching. We identify thermal electron activation as well as direct exciton loss as the dominant intensity quenching channels. Additionally, we carefully analyze the effects of optical and acoustic phonons as well as close-by defects on the emission linewidth by means of temperature and power dependent micro-photoluminescence on single quantum dots with large pitches.

Temperature dependence of intensities of the 8-12 micron bands of CFCl3

NASA Technical Reports Server (NTRS)

Nanes, R.; Silvaggio, P. M.; Boese, R. W.

1980-01-01

The absolute intensities of the 8-12 micron bands from Freon 11 (CFCl3) were measured at temperatures of 294 and 216 K. Intensities of the bands centered at 798, 847, 934, and 1082 per cm are all observed to depend on temperature. The temperature dependence for the 847 and 1082 per cm fundamental regions is attributed to underlying hot bands; for the nu2 + nu5 combination band (934 per cm), the observed temperature dependence is in close agreement with theoretical prediction. The implication of these results on atmospheric IR remote-sensing is briefly discussed.

Complex temperature dependence of coupling and dissipation of cavity magnon polaritons from millikelvin to room temperature

NASA Astrophysics Data System (ADS)

Boventer, Isabella; Pfirrmann, Marco; Krause, Julius; Schön, Yannick; Kläui, Mathias; Weides, Martin

2018-05-01

Hybridized magnonic-photonic systems are key components for future information processing technologies such as storage, manipulation, or conversion of data both in the classical (mostly at room temperature) and quantum (cryogenic) regime. In this work, we investigate a yttrium-iron-garnet sphere coupled strongly to a microwave cavity over the full temperature range from 290 K to 30 mK . The cavity-magnon polaritons are studied from the classical to the quantum regimes where the thermal energy is less than one resonant microwave quanta, i.e., at temperatures below 1 K . We compare the temperature dependence of the coupling strength geff(T ) , describing the strength of coherent energy exchange between spin ensemble and cavity photon, to the temperature behavior of the saturation magnetization evolution Ms(T ) and find strong deviations at low temperatures. The temperature dependence of magnonic disspation is governed at intermediate temperatures by rare-earth impurity scattering leading to a strong peak at 40 K . The linewidth κm decreases to 1.2 MHz at 30 mK , making this system suitable as a building block for quantum electrodynamics experiments. We achieve an electromagnonic cooperativity in excess of 20 over the entire temperature range, with values beyond 100 in the millikelvin regime as well as at room temperature. With our measurements, spectroscopy on strongly coupled magnon-photon systems is demonstrated as versatile tool for spin material studies over large temperature ranges. Key parameters are provided in a single measurement, thus simplifying investigations significantly.

Temperature-dependent modulation of regional lymphatic contraction frequency and flow.

PubMed

Solari, Eleonora; Marcozzi, Cristiana; Negrini, Daniela; Moriondo, Andrea

2017-11-01

Lymph drainage and propulsion are sustained by an extrinsic mechanism, based on mechanical forces acting from the surrounding tissues against the wall of lymphatic vessels, and by an intrinsic mechanism attributable to active spontaneous contractions of the lymphatic vessel muscle. Despite being heterogeneous, the mechanisms underlying the generation of spontaneous contractions share a common biochemical nature and are thus modulated by temperature. In this study, we challenged excised tissues from rat diaphragm and hindpaw, endowed with spontaneously contracting lymphatic vessels, to temperatures from 24°C (hindpaw) or 33°C (diaphragmatic vessels) to 40°C while measuring lymphatic contraction frequency ( f c ) and amplitude. Both vessel populations displayed a sigmoidal relationship between f c and temperature, each centered around the average temperature of surrounding tissue (36.7 diaphragmatic and 32.1 hindpaw lymphatics). Although the slope factor of the sigmoidal fit to the f c change of hindpaw vessels was 2.3°C·cycles -1 ·min -1 , a value within the normal range displayed by simple biochemical reactions, the slope factor of the diaphragmatic lymphatics was 0.62°C·cycles -1 ·min -1 , suggesting the added involvement of temperature-sensing mechanisms. Lymph flow calculated as a function of temperature confirmed the relationship observed on f c data alone and showed that none of the two lymphatic vessel populations would be able to adapt to the optimal working temperature of the other tissue district. This poses a novel question whether lymphatic vessels might not adapt their function to accommodate the change if exposed to a surrounding temperature, which is different from their normal condition. NEW & NOTEWORTHY This study demonstrates to what extent lymphatic vessel intrinsic contractility and lymph flow are modulated by temperature and that this modulation is dependent on the body district that the vessels belong to, suggesting a possible

Methane fluxes show consistent temperature dependence across microbial to ecosystem scales.

PubMed

Yvon-Durocher, Gabriel; Allen, Andrew P; Bastviken, David; Conrad, Ralf; Gudasz, Cristian; St-Pierre, Annick; Thanh-Duc, Nguyen; del Giorgio, Paul A

2014-03-27

Methane (CH4) is an important greenhouse gas because it has 25 times the global warming potential of carbon dioxide (CO2) by mass over a century. Recent calculations suggest that atmospheric CH4 emissions have been responsible for approximately 20% of Earth's warming since pre-industrial times. Understanding how CH4 emissions from ecosystems will respond to expected increases in global temperature is therefore fundamental to predicting whether the carbon cycle will mitigate or accelerate climate change. Methanogenesis is the terminal step in the remineralization of organic matter and is carried out by strictly anaerobic Archaea. Like most other forms of metabolism, methanogenesis is temperature-dependent. However, it is not yet known how this physiological response combines with other biotic processes (for example, methanotrophy, substrate supply, microbial community composition) and abiotic processes (for example, water-table depth) to determine the temperature dependence of ecosystem-level CH4 emissions. It is also not known whether CH4 emissions at the ecosystem level have a fundamentally different temperature dependence than other key fluxes in the carbon cycle, such as photosynthesis and respiration. Here we use meta-analyses to show that seasonal variations in CH4 emissions from a wide range of ecosystems exhibit an average temperature dependence similar to that of CH4 production derived from pure cultures of methanogens and anaerobic microbial communities. This average temperature dependence (0.96 electron volts (eV)), which corresponds to a 57-fold increase between 0 and 30°C, is considerably higher than previously observed for respiration (approximately 0.65 eV) and photosynthesis (approximately 0.3 eV). As a result, we show that both the emission of CH4 and the ratio of CH4 to CO2 emissions increase markedly with seasonal increases in temperature. Our findings suggest that global warming may have a large impact on the relative contributions of CO2 and CH

Arabidopsis HSP90 protein modulates RPP4-mediated temperature-dependent cell death and defense responses.

PubMed

Bao, Fei; Huang, Xiaozhen; Zhu, Chipan; Zhang, Xiaoyan; Li, Xin; Yang, Shuhua

2014-06-01

Plant defense responses are regulated by temperature. In Arabidopsis, the chilling-sensitive mutant chs2-1 (rpp4-1d) contains a gain-of-function mutation in the TIR-NB-LRR (Toll and interleukin 1 receptor-nucleotide binding-leucine-rich repeat) gene, RPP4 (RECOGNITION OF PERONOSPORA PARASITICA 4), which leads to constitutive activation of the defense response at low temperatures. Here, we identified and characterized two suppressors of rpp4-1d from a genetic screen, hsp90.2 and hsp90.3, which carry point mutations in the cytosolic heat shock proteins HSP90.2 and HSP90.3, respectively. The hsp90 mutants suppressed the chilling sensitivity of rpp4-1d, including seedling lethality, activation of the defense responses and cell death under chilling stress. The hsp90 mutants exhibited compromised RPM1 (RESISTANCE TO PSEUDOMONAS MACULICOLA 1)-, RPS4 (RESISTANCE TO P. SYRINGAE 4)- and RPP4-mediated pathogen resistance. The wild-type RPP4 and the mutated form rpp4 could interact with HSP90 to form a protein complex. Furthermore, RPP4 and rpp4 proteins accumulated in the cytoplasm and nucleus at normal temperatures, whereas the nuclear accumulation of the mutated rpp4 was decreased at low temperatures. Genetic analysis of the intragenic suppressors of rpp4-1d revealed the important functions of the NB-ARC and LRR domains of RPP4 in temperature-dependent defense signaling. In addition, the rpp4-1d-induced chilling sensitivity was largely independent of the WRKY70 or MOS (modifier of snc1) genes. [Correction added after online publication 11 March 2013: the expansions of TIR-NB-LRR and RPS4 were amended] This study reveals that Arabidopsis HSP90 regulates RPP4-mediated temperature-dependent cell death and defense responses. © 2014 The Authors. New Phytologist © 2014 New Phytologist Trust.

Temperature dependent empirical pseudopotential theory for self-assembled quantum dots.

PubMed

Wang, Jianping; Gong, Ming; Guo, Guang-Can; He, Lixin

2012-11-28

We develop a temperature dependent empirical pseudopotential theory to study the electronic and optical properties of self-assembled quantum dots (QDs) at finite temperature. The theory takes the effects of both lattice expansion and lattice vibration into account. We apply the theory to InAs/GaAs QDs. For the unstrained InAs/GaAs heterostructure, the conduction band offset increases whereas the valence band offset decreases with increasing temperature, and there is a type-I to type-II transition at approximately 135 K. Yet, for InAs/GaAs QDs, the holes are still localized in the QDs even at room temperature, because the large lattice mismatch between InAs and GaAs greatly enhances the valence band offset. The single-particle energy levels in the QDs show a strong temperature dependence due to the change of confinement potentials. Because of the changes of the band offsets, the electron wavefunctions confined in QDs increase by about 1-5%, whereas the hole wavefunctions decrease by about 30-40% when the temperature increases from 0 to 300 K. The calculated recombination energies of excitons, biexcitons and charged excitons show red shifts with increasing temperature which are in excellent agreement with available experimental data.

Temperature-dependence of biomass accumulation rates during secondary succession.

PubMed

Anderson, Kristina J; Allen, Andrew P; Gillooly, James F; Brown, James H

2006-06-01

Rates of ecosystem recovery following disturbance affect many ecological processes, including carbon cycling in the biosphere. Here, we present a model that predicts the temperature dependence of the biomass accumulation rate following disturbances in forests. Model predictions are derived based on allometric and biochemical principles that govern plant energetics and are tested using a global database of 91 studies of secondary succession compiled from the literature. The rate of biomass accumulation during secondary succession increases with average growing season temperature as predicted based on the biochemical kinetics of photosynthesis in chloroplasts. In addition, the rate of biomass accumulation is greater in angiosperm-dominated communities than in gymnosperm-dominated ones and greater in plantations than in naturally regenerating stands. By linking the temperature-dependence of photosynthesis to the rate of whole-ecosystem biomass accumulation during secondary succession, our model and results provide one example of how emergent, ecosystem-level rate processes can be predicted based on the kinetics of individual metabolic rate.

The mass and speed dependence of meteor air plasma temperatures

NASA Technical Reports Server (NTRS)

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

2004-01-01

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

The mass and speed dependence of meteor air plasma temperatures.

PubMed

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

2004-01-01

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

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…

Temperature dependence of surface tension of molten iron under reducing gas atmosphere

NASA Astrophysics Data System (ADS)

Ozawa, S.; Takahashi, S.; Fukuyama, H.; Watanabe, M.

2011-12-01

Surface tension of molten iron was measured under Ar-He-5vol.%H2 gas by oscillating droplet method using electromagnetic levitation furnace in consideration of the temperature dependence of oxygen partial pressure, Po2, of the gas. For comparison, the measurement was carried under Ar-He atmosphere to fix the Po2 of the inlet gas at 10-2Pa. The surface tension was successfully measured over a wide temperature range of about 780K including undercooling condition. When Po2 is fixed at 10-2 Pa, the surface tension increased and then decreased with increasing temperature like a boomerang shape. When the measurement was carried out under the H2-containing gas atmosphere, the temperature dependence of the surface tension shows unique kink at around 1810K instead of liner relationship due to competition between the temperature dependence of the Po2 and that of the equilibrium constant of oxygen adsorption reaction. The relationship between the calculated lnKad with respect to inverse temperature using Szyszkowski model was different between the atmospheric gases.

Gonadal morphogenesis and gene expression in reptiles with temperature-dependent sex determination.

PubMed

Merchant-Larios, H; Díaz-Hernández, V; Marmolejo-Valencia, A

2010-01-01

In reptiles with temperature-dependent sexual determination, the thermosensitive period (TSP) is the interval in which the sex is defined during gonadal morphogenesis. One-shift experiments in a group of eggs define the onset and the end of the TSP as all and none responses, respectively. Timing for sex-undetermined (UG) and -determined gonads (DG) differs at male- (MPT) or female-producing temperatures (FPT). During the TSP a decreasing number of embryos respond to temperature shifts indicating that in this period embryos with both UG and DG exist. Although most UG correspond to undifferentiated gonads, some embryos extend UG after the onset of histological differentiation. Thus, temperature affects gonadal cells during the process of morphogenesis, but timing of commitment depends on individual embryos. A correlation between gonadal morphogenesis, TSP, and gene expression suggests that determination of the molecular pathways modulated by temperature in epithelial cells (surface epithelium and medullary cords) holds the key for a unifying hypothesis on temperature-dependent sex determination. (c) 2010 S. Karger AG, Basel.

Cyclophilin40 isomerase activity is regulated by a temperature-dependent allosteric interaction with Hsp90.

PubMed

Blackburn, Elizabeth A; Wear, Martin A; Landré, Vivian; Narayan, Vikram; Ning, Jia; Erman, Burak; Ball, Kathryn L; Walkinshaw, Malcolm D

2015-09-01

Cyclophilin 40 (Cyp40) comprises an N-terminal cyclophilin domain with peptidyl-prolyl isomerase (PPIase) activity and a C-terminal tetratricopeptide repeat (TPR) domain that binds to the C-terminal-EEVD sequence common to both heat shock protein 70 (Hsp70) and Hsp90. We show in the present study that binding of peptides containing the MEEVD motif reduces the PPIase activity by ∼30%. CD and fluorescence assays show that the TPR domain is less stable than the cyclophilin domain and is stabilized by peptide binding. Isothermal titration calorimetry (ITC) shows that the affinity for the-MEEVD peptide is temperature sensitive in the physiological temperature range. Results from these biophysical studies fit with the MD simulations of the apo and holo (peptide-bound) structures which show a significant reduction in root mean square (RMS) fluctuation in both TPR and cyclophilin domains when-MEEVD is bound. The MD simulations of the apo-protein also highlight strong anti-correlated motions between residues around the PPIase-active site and a band of residues running across four of the seven helices in the TPR domain. Peptide binding leads to a distortion in the shape of the active site and a significant reduction in these strongly anti-correlated motions, providing an explanation for the allosteric effect of ligand binding and loss of PPIase activity. Together the experimental and MD results suggest that on heat shock, dissociation of Cyp40 from complexes mediated by the TPR domain leads to an increased pool of free Cyp40 capable of acting as an isomerase/chaperone in conditions of cellular stress. © 2015 Authors.

Cyclophilin40 isomerase activity is regulated by a temperature-dependent allosteric interaction with Hsp90

PubMed Central

Blackburn, Elizabeth A.; Wear, Martin A.; Landré, Vivian; Narayan, Vikram; Ning, Jia; Erman, Burak; Ball, Kathryn L.; Walkinshaw, Malcolm D.

2015-01-01

Cyclophilin 40 (Cyp40) comprises an N-terminal cyclophilin domain with peptidyl-prolyl isomerase (PPIase) activity and a C-terminal tetratricopeptide repeat (TPR) domain that binds to the C-terminal–EEVD sequence common to both heat shock protein 70 (Hsp70) and Hsp90. We show in the present study that binding of peptides containing the MEEVD motif reduces the PPIase activity by ∼30%. CD and fluorescence assays show that the TPR domain is less stable than the cyclophilin domain and is stabilized by peptide binding. Isothermal titration calorimetry (ITC) shows that the affinity for the–MEEVD peptide is temperature sensitive in the physiological temperature range. Results from these biophysical studies fit with the MD simulations of the apo and holo (peptide-bound) structures which show a significant reduction in root mean square (RMS) fluctuation in both TPR and cyclophilin domains when–MEEVD is bound. The MD simulations of the apo-protein also highlight strong anti-correlated motions between residues around the PPIase-active site and a band of residues running across four of the seven helices in the TPR domain. Peptide binding leads to a distortion in the shape of the active site and a significant reduction in these strongly anti-correlated motions, providing an explanation for the allosteric effect of ligand binding and loss of PPIase activity. Together the experimental and MD results suggest that on heat shock, dissociation of Cyp40 from complexes mediated by the TPR domain leads to an increased pool of free Cyp40 capable of acting as an isomerase/chaperone in conditions of cellular stress. PMID:26330616

Temperature dependent electrical transport behavior of InN/GaN heterostructure based Schottky diodes

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

Roul, Basanta; Kumar, Mahesh; Central Research Laboratory, Bharat Electronics, Bangalore 560013

InN/GaN heterostructure based Schottky diodes were fabricated by plasma-assisted molecular beam epitaxy. The temperature dependent electrical transport properties were carried out for InN/GaN heterostructure. The barrier height and the ideality factor of the Schottky diodes were found to be temperature dependent. The temperature dependence of the barrier height indicates that the Schottky barrier height is inhomogeneous in nature at the heterostructure interface. The higher value of the ideality factor and its temperature dependence suggest that the current transport is primarily dominated by thermionic field emission (TFE) other than thermionic emission (TE). The room temperature barrier height obtained by using TEmore » and TFE models were 1.08 and 1.43 eV, respectively.« less

l-Proline and RNA Duplex m-Value Temperature Dependence.

PubMed

Schwinefus, Jeffrey J; Baka, Nadia L; Modi, Kalpit; Billmeyer, Kaylyn N; Lu, Shutian; Haase, Lucas R; Menssen, Ryan J

2017-08-03

The temperature dependence of l-proline interactions with the RNA dodecamer duplex surface exposed after unfolding was quantified using thermal and isothermal titration denaturation monitored by uv-absorbance. The m-value quantifying proline interactions with the RNA duplex surface area exposed after unfolding was measured using RNA duplexes with GC content ranging between 17 and 83%. The m-values from thermal denaturation decreased with increasing GC content signifying increasingly favorable proline interactions with the exposed RNA surface area. However, m-values from isothermal titration denaturation at 25.0 °C were independent of GC content and less negative than those from thermal denaturation. The m-value from isothermal titration denaturation for a 50% GC RNA duplex decreased (became more negative) as the temperature increased and was in nearly exact agreement with the m-value from thermal denaturation. Since RNA duplex transition temperatures increased with GC content, the more favorable proline interactions with the high GC content duplex surface area observed from thermal denaturation resulted from the temperature dependence of proline interactions rather than the RNA surface chemical composition. The enthalpy contribution to the m-value was positive and small (indicating a slight increase in duplex unfolding enthalpy with proline) while the entropic contribution to the m-value was positive and increased with temperature. Our results will facilitate proline's use as a probe of solvent accessible surface area changes during biochemical reactions at different reaction temperatures.

Divergent effects of postmortem ambient temperature on organophosphorus- and carbamate-inhibited brain cholinesterase activity in birds

USGS Publications Warehouse

Hill, E.F.

1989-01-01

Time- and temperature-dependent postmortem changes in inhibited brain cholinesterase (ChE) activity may confound diagnosis of field poisoning of wildlife by anticholinesterase pesticide. Carbamate-inhibited ChE activity may return to normal within 1 to 2 days of exposure of intact carcass to moderate ambient temperature (18-32C). Organophosphorus-inhibited ChE activity becomes more depressed over the same time. Uninhibited ChE activity was resilient to above freezing temperature to 32C for 1 day and 25C for 3 days. Carbamate- and organophosphorus-inhibited ChE can be separated by incubation of homogenate for 1 hour at physiological temperatures; carbamylated ChE can be readily reactivated while phosphorylated ChE cannot.

Time-dependent crack growth behavior of alloy 617 and alloy 230 at elevated temperatures

NASA Astrophysics Data System (ADS)

Roy, Shawoon Kumar

2011-12-01

Two Ni-base solid-solution-strengthened superalloys: INCONEL 617 and HAYNES 230 were studied to check sustained loading crack growth (SLCG) behavior at elevated temperatures appropriate for Next Generation Nuclear Plant (NGNP) applictaions with constant stress intensity factor (Kmax= 27.75 MPa✓m) in air. The results indicate a time-dependent rate controlling process which can be characterized by a linear elastic fracture mechanics (LEFM) parameter -- stress intensity factor (K). At elevated temperatures, the crack growth mechanism was best described using a damage zone concept. Based on results and study, SAGBOE (stress accelerated grain boundary oxidation embrittlement) is considered the primary reason for time-dependent SLCG. A thermodynamic equation was considered to correlate all the SLCG results to determine the thermal activation energy in the process. A phenomenological model based on a time-dependent factor was developed considering the previous researcher's time-dependent fatigue crack propagation (FCP) results and current SLCG results to relate cycle-dependent and time-dependent FCP for both alloys. Further study includes hold time (3+300s) fatigue testing and no hold (1s) fatigue testing with various load ratios (R) at 700°C with a Kmax of 27.75 MPa✓m. Study results suggest an interesting point: crack growth behavior is significantly affected with the change in R value in cycle-dependent process whereas in time-dependent process, change in R does not have any significant effect. Fractography study showed intergranular cracking mode for all time-dependent processes and transgranular cracking mode for cycle-dependent processes. In Alloy 230, SEM images display intergranular cracking with carbide particles, dense oxides and dimple mixed secondary cracks for time-dependent 3+300s FCP and SLCG test. In all cases, Alloy 230 shows better crack growth resistance compared to Alloy 617.

Temperature-Dependent Kinetic Prediction for Reactions Described by Isothermal Mathematics

DOE PAGES

Dinh, L. N.; Sun, T. C.; McLean, W.

2016-09-12

Most kinetic models are expressed in isothermal mathematics. In addition, this may lead unaware scientists either to the misconception that classical isothermal kinetic models cannot be used for any chemical process in an environment with a time-dependent temperature profile or, even worse, to a misuse of them. In reality, classical isothermal models can be employed to make kinetic predictions for reactions in environments with time-dependent temperature profiles, provided that there is a continuity/conservation in the reaction extent at every temperature–time step. In this article, fundamental analyses, illustrations, guiding tables, and examples are given to help the interested readers using eithermore » conventional isothermal reacted fraction curves or rate equations to make proper kinetic predictions for chemical reactions in environments with temperature profiles that vary, even arbitrarily, with time simply by the requirement of continuity/conservation of reaction extent whenever there is an external temperature change.« less

Stimulus-Dependent Effects of Temperature on Bitter Taste in Humans

PubMed Central

Andrew, Kendra

2017-01-01

This study investigated the effects of temperature on bitter taste in humans. The experiments were conducted within the context of current understanding of the neurobiology of bitter taste and recent evidence of stimulus-dependent effects of temperature on sweet taste. In the first experiment, the bitterness of caffeine and quinine sampled with the tongue tip was assessed at 4 different temperatures (10°, 21°, 30°, and 37 °C) following pre-exposure to the same solution or to water for 0, 3, or 10 s. The results showed that initial bitterness (0-s pre-exposure) followed an inverted U-shaped function of temperature for both stimuli, but the differences across temperature were statistically significant only for quinine. Conversely, temperature significantly affected adaptation to the bitterness of quinine but not caffeine. A second experiment used the same procedure to test 2 additional stimuli, naringin and denatonium benzoate. Temperature significantly affected the initial bitterness of both stimuli but had no effect on adaptation to either stimulus. These results confirm that like sweet taste, temperature affects bitter taste sensitivity and adaptation in stimulus-dependent ways. However, the thermal effect on quinine adaptation, which increased with warming, was opposite to what had been found previously for adaptation to sweetness. The implications of these results are discussed in relation to findings from prior studies of temperature and bitter taste in humans and the possible neurobiological mechanisms of gustatory thermal sensitivity. PMID:28119357

Temperature dependence of phonons in photosynthesis proteins

NASA Astrophysics Data System (ADS)

Xu, Mengyang; Myles, Dean; Blankenship, Robert; Markelz, Andrea

Protein long range vibrations are essential to biological function. For many proteins, these vibrations steer functional conformational changes. For photoharvesting proteins, the structural vibrations play an additional critical role in energy transfer to the reaction center by both phonon assisted energy transfer and energy dissipation. The characterization of these vibrations to understand how they are optimized to balance photoharvesting and photoprotection is challenging. To date this characterization has mainly relied on fluorescence line narrowing measurements at cryogenic temperatures. However, protein dynamics has a strong temperature dependence, with an apparent turn on in anharmonicity between 180-220 K. If this transition affects intramolecular vibrations, the low temperature measurements will not represent the phonon spectrum at biological temperatures. Here we use the new technique of anisotropic terahertz microscopy (ATM) to measure the intramolecular vibrations of FMO complex. ATM is uniquely capable of isolating protein vibrations from isotropic background. We find resonances both red and blue shift with temperature above the dynamical transition. The results indicate that the characterization of vibrations must be performed at biologically relevant temperatures to properly understand the energy overlap with the excitation energy transfer. This work was supported by NSF:DBI 1556359, BioXFEL seed Grant funding from NSF:DBI 1231306, DOE: DE-SC0016317, and the Bruce Holm University at Buffalo Research Foundation Grant.

Surface Temperature Dependence of Hydrogen Ortho-Para Conversion on Amorphous Solid Water.

PubMed

Ueta, Hirokazu; Watanabe, Naoki; Hama, Tetsuya; Kouchi, Akira

2016-06-24

The surface temperature dependence of the ortho-to-para conversion of H_{2} on amorphous solid water is first reported. A combination of photostimulated desorption and resonance-enhanced multiphoton ionization techniques allowed us to sensitively probe the conversion on the surface of amorphous solid water at temperatures of 9.2-16 K. Within a narrow temperature window of 8 K, the conversion time steeply varied from ∼4.1×10^{3} to ∼6.4×10^{2}  s. The observed temperature dependence is discussed in the context of previously suggested models and the energy dissipation process. The two-phonon process most likely dominates the conversion rate at low temperatures.

Scale-dependency of the global mean surface temperature trend and its implication for the recent hiatus of global warming.

PubMed

Lin, Yong; Franzke, Christian L E

2015-08-11

Studies of the global mean surface temperature trend are typically conducted at a single (usually annual or decadal) time scale. The used scale does not necessarily correspond to the intrinsic scales of the natural temperature variability. This scale mismatch complicates the separation of externally forced temperature trends from natural temperature fluctuations. The hiatus of global warming since 1999 has been claimed to show that human activities play only a minor role in global warming. Most likely this claim is wrong due to the inadequate consideration of the scale-dependency in the global surface temperature (GST) evolution. Here we show that the variability and trend of the global mean surface temperature anomalies (GSTA) from January 1850 to December 2013, which incorporate both land and sea surface data, is scale-dependent and that the recent hiatus of global warming is mainly related to natural long-term oscillations. These results provide a possible explanation of the recent hiatus of global warming and suggest that the hiatus is only temporary.

Improved Regression Analysis of Temperature-Dependent Strain-Gage Balance Calibration Data

NASA Technical Reports Server (NTRS)

Ulbrich, N.

2015-01-01

An improved approach is discussed that may be used to directly include first and second order temperature effects in the load prediction algorithm of a wind tunnel strain-gage balance. The improved approach was designed for the Iterative Method that fits strain-gage outputs as a function of calibration loads and uses a load iteration scheme during the wind tunnel test to predict loads from measured gage outputs. The improved approach assumes that the strain-gage balance is at a constant uniform temperature when it is calibrated and used. First, the method introduces a new independent variable for the regression analysis of the balance calibration data. The new variable is designed as the difference between the uniform temperature of the balance and a global reference temperature. This reference temperature should be the primary calibration temperature of the balance so that, if needed, a tare load iteration can be performed. Then, two temperature{dependent terms are included in the regression models of the gage outputs. They are the temperature difference itself and the square of the temperature difference. Simulated temperature{dependent data obtained from Triumph Aerospace's 2013 calibration of NASA's ARC-30K five component semi{span balance is used to illustrate the application of the improved approach.

On the temperature dependence of possible S8 infrared bands in planetary atmospheres

NASA Technical Reports Server (NTRS)

Khare, B. N.; Sagan, C.

1976-01-01

Measurements of the temperature dependence between 77 and 333 K of the infrared spectrum of cyclic octatomic sulfur are reported. It is suggested that the 23 micrometer Jovian feature is not due to 3 sub 8 and that the temperature dependence of the frequency of the 835/cm band of S sub 8 may be a useful temperature marker in planetary studies.

Predicting body temperature and activity of adult Polyommatus icarus using neural network models under current and projected climate scenarios.

PubMed

Howe, P D; Bryant, S R; Shreeve, T G

2007-10-01

We use field observations in two geographic regions within the British Isles and regression and neural network models to examine the relationship between microhabitat use, thoracic temperatures and activity in a widespread lycaenid butterfly, Polyommatus icarus. We also make predictions for future activity under climate change scenarios. Individuals from a univoltine northern population initiated flight with significantly lower thoracic temperatures than individuals from a bivoltine southern population. Activity is dependent on body temperature and neural network models of body temperature are better at predicting body temperature than generalized linear models. Neural network models of activity with a sole input of predicted body temperature (using weather and microclimate variables) are good predictors of observed activity and were better predictors than generalized linear models. By modelling activity under climate change scenarios for 2080 we predict differences in activity in relation to both regional differences of climate change and differing body temperature requirements for activity in different populations. Under average conditions for low-emission scenarios there will be little change in the activity of individuals from central-southern Britain and a reduction in northwest Scotland from 2003 activity levels. Under high-emission scenarios, flight-dependent activity in northwest Scotland will increase the greatest, despite smaller predicted increases in temperature and decreases in cloud cover. We suggest that neural network models are an effective way of predicting future activity in changing climates for microhabitat-specialist butterflies and that regional differences in the thermoregulatory response of populations will have profound effects on how they respond to climate change.

Synthesis, structure and temperature dependent luminescence of Eu3+ doped hydroxyapatite

NASA Astrophysics Data System (ADS)

Luo, Xiaobing; Luo, Xiaoxia; Wang, Hongwei; Deng, Yue; Yang, Peixin; Tian, Yili

2018-01-01

A series of Eu3+ substituted hydroxyapatite (HA) were prepared by co-precipitation reactions. The phase, fluorescence and temperature dependent luminescence of the phosphors were investigated by X-ray diffraction (XRD) and photoluminescence (PL). It is found that the doped Eu3+ ions have entered the hexagonal lattice with no obvious secondary phase were detected by XRD. The 5D0 → 7F0 transition was clearly split into two even at room temperature. The predominate 573 nm peak illustrates Eu3+ ions occupy more Ca(II) sites. The temperature dependent luminescent results show HA:xEu might be applied as one potential optical thermometry material.

Denitrification Temperature Dependence in Remote, Cold, and N-Poor Lake Sediments

NASA Astrophysics Data System (ADS)

Palacin-Lizarbe, Carlos; Camarero, Lluís.; Catalan, Jordi

2018-02-01

The reservoir size and pathway rates of the nitrogen (N) cycle have been deeply modified by the human enhancement of N fixation, atmospheric emissions, and climate warming. Denitrification (DEN) transforms nitrate into nitrogenous gas and thus removes reactive nitrogen (Nr) back to the atmospheric reservoir. There is still a rather limited knowledge of the denitrification rates and their temperature dependence across ecosystems; particularly, for the abundant cold and N-poor freshwater systems (e.g., Arctic and mountain lakes). We experimentally investigated the denitrification rates of mountain lake sediments by manipulating nitrate concentration and temperature on field collected cores. DEN rates were nitrate limited in field conditions and showed a large potential for an immediate DEN increase with both warming and higher Nr load. The estimated activation energy (Ea) for denitrification at nitrate saturation was 46 ± 7 kJ mol-1 (Q10 1.7 ± 0.4). The apparent Ea increased with nitrate (μM) limitation as Ea = 46 + 419 [NO3-]-1. Accordingly, we suggest that climate warming may have a synergistic effect with N emission reduction to readjusting the N cycle. Changes of nitrate availability might be more relevant than direct temperature effects on denitrification.

Temperature-dependent errors in nuclear lattice simulations

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

Lee, Dean; Thomson, Richard

2007-06-15

We study the temperature dependence of discretization errors in nuclear lattice simulations. We find that for systems with strong attractive interactions the predominant error arises from the breaking of Galilean invariance. We propose a local 'well-tempered' lattice action which eliminates much of this error. The well-tempered action can be readily implemented in lattice simulations for nuclear systems as well as cold atomic Fermi systems.

Frequency and temperature dependence of dielectric properties of chicken meat

USDA-ARS?s Scientific Manuscript database

Dielectric properties of chicken breast meat were measured with an open-ended coaxial-line probe between 200 MHz and 20 GHz at temperatures ranging from -20 degree C to +25 degree C. At a given temperature, the frequency dependence of the dielectric constant reveals two relaxations while those of th...

Temperature-dependent photoluminescence analysis of ZnO nanowire array annealed in air

NASA Astrophysics Data System (ADS)

Sun, Yanan; Gu, Xiuquan; Zhao, Yulong; Wang, Linmeng; Qiang, Yinghuai

2018-05-01

ZnO nanowire arrays (NWAs) were prepared on transparent conducting fluorine doped tin oxide (FTO) substrates through a facile hydrothermal method, followed by a 500 °C annealing to improve their crystalline qualities and photoelectrochemical (PEC) activities. It was found that the annealing didn't change the morphology, but resulted in a significant reduction of the donor concentration. Temperature-dependent photoluminescence (PL) was carried out for a comprehensive analysis of the effect from annealing. Noteworthy, four dominant peaks were identified from the 10 K spectrum of a 500 °C annealed sample, and they were assigned to FX, D0X, (e, D0) and (e, D0) -1LO, respectively. Of them, the FX emission was only existed below 130 K, while the room-temperature (RT) PL spectrum was dominated by the D0X emission.

Changing body temperature affects the T2* signal in the rat brain and reveals hypothalamic activity.

PubMed

Vanhoutte, G; Verhoye, M; Van der Linden, A

2006-05-01

This study was designed to determine brain activity in the hypothalamus-in particular the thermoregulatory function of the hypothalamic preoptic area (PO). We experimentally changed the body temperature in rats within the physiological range (37-39 degrees C) and monitored changes in blood oxygenation level-dependent (BOLD) MR signal. To explore PO activity we had to deal with general signal changes caused by temperature-dependent alterations in the affinity of oxygen for hemoglobin, which contributes to BOLD contrast because it is partly sensitive to the amount of paramagnetic deoxyhemoglobin in the voxel. To reduce these overall temperature-induced effects, we corrected the BOLD data using brain-specific correction algorithms. The results showed activity of the PO during body warming from 38 degrees C to 39 degrees C, supported by an increased BOLD signal after correction. This is the first fMRI study on the autonomous nervous system in which hypothalamic activity elicited by changes in the internal environment (body temperature) was monitored. In this study we also demonstrate 1) that any fMRI study of anesthetized small animals should guard against background BOLD signal drift, since animals are vulnerable to body temperature fluctuations; and 2) the existence of a link between PO activity and the sympathetically-mediated opening of the arteriovenous anastomoses in a parallel study on the rat tail, a peripheral thermoregulatory organ.

Unfolding of a temperature-sensitive domain controls voltage-gated channel activation

PubMed Central

Arrigoni, Cristina; Rohaim, Ahmed; Shaya, David; Findeisen, Felix; Stein, Richard A.; Nurva, Shailika Reddy; Mishra, Smriti; Mchaourab, Hassane S.; Minor, Daniel L.

2016-01-01

Voltage-gated ion channels (VGICs) are outfitted with diverse cytoplasmic domains that impact function. To examine how such elements may affect VGIC behavior, we addressed how the bacterial voltage-gated sodium channel (BacNaV) C-terminal cytoplasmic domain (CTD) affects function. Our studies show that the BacNaV CTD exerts a profound influence on gating through a temperature-dependent unfolding transition in a discrete cytoplasmic domain, the neck domain, proximal to the pore. Structural and functional studies establish that the BacNaV CTD comprises a bi-partite four-helix bundle that bears an unusual hydrophilic core whose integrity is central to the unfolding mechanism and that couples directly to the channel activation gate. Together, our findings define a general principle for how the widespread four-helix bundle cytoplasmic domain architecture can control VGIC responses, uncover a mechanism underlying the diverse BacNaV voltage dependencies, and demonstrate that a discrete domain can encode the temperature dependent response of a channel. PMID:26919429

Modeling and Compensating Temperature-Dependent Non-Uniformity Noise in IR Microbolometer Cameras

PubMed Central

Wolf, Alejandro; Pezoa, Jorge E.; Figueroa, Miguel

2016-01-01

Images rendered by uncooled microbolometer-based infrared (IR) cameras are severely degraded by the spatial non-uniformity (NU) noise. The NU noise imposes a fixed-pattern over the true images, and the intensity of the pattern changes with time due to the temperature instability of such cameras. In this paper, we present a novel model and a compensation algorithm for the spatial NU noise and its temperature-dependent variations. The model separates the NU noise into two components: a constant term, which corresponds to a set of NU parameters determining the spatial structure of the noise, and a dynamic term, which scales linearly with the fluctuations of the temperature surrounding the array of microbolometers. We use a black-body radiator and samples of the temperature surrounding the IR array to offline characterize both the constant and the temperature-dependent NU noise parameters. Next, the temperature-dependent variations are estimated online using both a spatially uniform Hammerstein-Wiener estimator and a pixelwise least mean squares (LMS) estimator. We compensate for the NU noise in IR images from two long-wave IR cameras. Results show an excellent NU correction performance and a root mean square error of less than 0.25 ∘C, when the array’s temperature varies by approximately 15 ∘C. PMID:27447637

Dependence of Plastic TATB Shock-Wave Sensitivity on Temperature, Density and Technology Factors

NASA Astrophysics Data System (ADS)

Vlasov, Yu. A.; Kosolapov, V. B.; Fomicheva, L. V.; Khabarov, I. P.

1999-06-01

Mixed TATB-based HE is the most perspective because of the manufacture and exploitation safety of its items. At the same time the safety of these explosive, at high temperatures, which take place at emergencies, causes the certain anxiety. Plastic TATB shock-wave sensitivity (SWS) researches has shown that temperature as one of the important factors of external influence is not always the determining reason of SWS change. It is known that density influence on SWS significantly. At the same time density depends on temperature and technology of details manufacturing. In this connection in this work the temperature dependence of plastic TATB SWS was studied in view of convertible and irreversible changes of density (p) under heating at -50[C up to 90[C . It is shown that during these influences the dependence of threshold pressure of initiation (P) from temperature is explained, first of all, by change of HE density, caused by its thermal expansion (compression), and also by irreversible changes of p and HE structure, arising at heating. It is found also that the share of irreversible change of density depends on technology of HE details manufacturing and is explained by relaxation of residual pressure in them. The mentioned relaxation is finished after the first cycles of thermal influence. The value of density change, caused by this factor, depends on temperature and duration of heating.

TEMPERATURE-DEPENDENT VISCOELASTIC PROPERTIES OF THE HUMAN SUPRASPINATUS TENDON

PubMed Central

Huang, Chun-Yuh; Wang, Vincent M.; Flatow, Evan L.; Mow, Van C.

2009-01-01

Temperature effects on the viscoelastic properties of the human supraspinatus tendon were investigated using static stress-relaxation experiments and Quasi-Linear Viscoelastic (QLV) theory. Twelve supraspinatus tendons were randomly assigned to one of two test groups for tensile testing using the following sequence of temperatures: (1) 37°C, 27°C, and 17°C (Group I, n=6), or (2) 42°C, 32°C, and 22°C (Group II, n=6). QLV parameter C was found to increase at elevated temperatures, suggesting greater viscous mechanical behavior at higher temperatures. Elastic parameters A and B showed no significant difference among the six temperatures studied, implying that the viscoelastic stress response of the supraspinatus tendon is not sensitive to temperature over shorter testing durations. Using regression analysis, an exponential relationship between parameter C and test temperature was implemented into QLV theory to model temperature-dependent viscoelastic behavior. This modified approach facilitates the theoretical determination of the viscoelastic behavior of tendons at arbitrary temperatures. PMID:19159888

Characterizing the temperature dependence of electronic packaging-material properties

NASA Astrophysics Data System (ADS)

Fu, Chia-Yu; Ume, Charles

1995-06-01

A computer-controlled, temperature-dependent material characterization system has been developed for thermal deformation analysis in electronic packaging applications, especially for printed wiring assembly warpage study. For fiberglass-reinforced epoxy (FR-4 type) material, the Young's moduli decrease to as low as 20-30% of the room-temperature values, while the shear moduli decrease to as low as 60-70% of the room-temperature values. The electrical resistance strain gage technique was used in this research. The test results produced overestimated values in property measurements, and this was shown in a case study. A noncontact strau]n measurement technique (laser extensometer) is now being used to measure these properties. Discrepancies of finite-element warpage predictions using different property values increase as the temperature increases from the stress-free temperature.

How Does CIGS Performance Depend on Temperature at the Microscale?

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

Stuckelberger, Michael E.; Nietzold, Tara; West, Bradley M.

Unveiling the correlation among electrical performance, elemental distribution, and defects at the microscale is crucial for the understanding and improvement of the overall solar cell performance. While this is true in general for solar cells with polycrystalline absorber layers, it is particularly critical for defect engineering of the complex quaternary CuIn xGa 1-xSe 2 (CIGS) material system. Studying these relationships under standard ambient conditions can provide important insights but does not provide input on the behavior of the cell under real operating conditions. In this contribution, we take a close look at the complex temperature dependence of defects and voltagemore » in CIGS at the microscale. We have developed correlative X-raymicroscopymethods and adapted them for temperature-dependent measurements of the locally generated voltage and elemental compositions at the microscale. We have applied these techniques to industrial CIGS solar cells covering temperatures from room temperature up to 100 degrees C. Finally, we find underperforming areas spanning multiple grains that do not correlate with the elemental distribution of major absorber constituents. However, we demonstrate that low-performing areas perform better at higher temperatures relative to the high-performing areas.« less

How Does CIGS Performance Depend on Temperature at the Microscale?

DOE PAGES

Stuckelberger, Michael E.; Nietzold, Tara; West, Bradley M.; ...

2017-11-03

Unveiling the correlation among electrical performance, elemental distribution, and defects at the microscale is crucial for the understanding and improvement of the overall solar cell performance. While this is true in general for solar cells with polycrystalline absorber layers, it is particularly critical for defect engineering of the complex quaternary CuIn xGa 1-xSe 2 (CIGS) material system. Studying these relationships under standard ambient conditions can provide important insights but does not provide input on the behavior of the cell under real operating conditions. In this contribution, we take a close look at the complex temperature dependence of defects and voltagemore » in CIGS at the microscale. We have developed correlative X-raymicroscopymethods and adapted them for temperature-dependent measurements of the locally generated voltage and elemental compositions at the microscale. We have applied these techniques to industrial CIGS solar cells covering temperatures from room temperature up to 100 degrees C. Finally, we find underperforming areas spanning multiple grains that do not correlate with the elemental distribution of major absorber constituents. However, we demonstrate that low-performing areas perform better at higher temperatures relative to the high-performing areas.« less

Nonlinear temperature dependence of glue-induced birefringence in polarization maintaining FBG sensors

NASA Astrophysics Data System (ADS)

Hopf, Barbara; Koch, Alexander W.; Roths, Johannes

2016-05-01

Glue-induced stresses decrease the accuracy of surface-mounted fiber Bragg gratings (FBG). Significant temperature dependent glue-induced birefringence was verified when a thermally cured epoxy-based bonding technique had been used. Determining the peak separation of two azimuthally aligned FBGs in PM fibers combined with a polarization resolved measurement set-up in a temperature range between -30°C and 150°C revealed high glue-induced stresses at low temperatures. Peak separations of about 60 pm and a nonlinear temperature dependence of the glue-induced birefringence due to stress relaxation processes and a visco-elastic behavior of the used adhesive have been shown.

Temperature, illumination and fluence dependence of current and voltage in electron irradiated solar cells

NASA Technical Reports Server (NTRS)

Obenschain, A. F.; Faith, T. J.

1973-01-01

Emperical equations have been derived from measurements of solar cell photovoltaic characteristics relating light generated current, IL, and open circuit voltage, VO, to cell temperature, T, intensity of illumination, W, and 1 Mev electron fluence, phi both 2 ohm-cm and 10 ohm-cm cells were tested. The temperature dependency of IL is similar for both resistivities at 140mw/sq cm; at high temperature the coefficient varies with fluence as phi 0.18, while at low temperatures the coefficient is relatively independent of fluence. Fluence dependent degration causes a decrease in IL at a rate proportional to phi 0.153 for both resistivities. At all intensities other than 560 mw/sq cm, a linear dependence of IL on illumination was found. The temperature coefficient of voltage was, to a good approximation, independent of both temperature and illumination for both resistivities. Illumination dependence of VOC was logarithmic, while the decrease with fluence of VOC varied as phi 0.25 for both resistivities.

Temperature Dependence in the Terahertz Spectrum of Nicotinamide: Anharmonicity and Hydrogen-Bonded Network.

PubMed

Takahashi, Masae; Okamura, Nubuyuki; Fan, Xinyi; Shirakawa, Hitoshi; Minamide, Hiroaki

2017-04-06

We have investigated the terahertz-spectral property of nicotinamide focusing on the temperature dependence in the range of 14-300 K. We observed that almost all peaks in the terahertz spectrum of the nicotinamide crystal showed a remarkable shift with temperature, whereas the lowest-frequency peak at 34.8 cm -1 showed a negligible shift with temperature. By analyzing the terahertz spectrum with the dispersion-corrected density functional theory calculations, we found that the difference in the temperature dependence of the peak shift is well understood in terms of the presence/absence of stretching vibration of the intermolecular hydrogen bond in the mode and the change of cell parameters. The anharmonicity in the dissociation potential energy of very weak intermolecular hydrogen bonding causes the remarkable peak shift with temperature in the terahertz spectrum of nicotinamide. This finding suggests that the assignment and identification of peaks in the terahertz spectrum are systematically enabled by temperature-dependent measurements.

Time- and temperature-dependent failures of a bonded joint

NASA Astrophysics Data System (ADS)

Sihn, Sangwook

This dissertation summarizes my study of time- and temperature-dependent behavior of a tubular lap bonded joint to provide a design methodology for windmill blade structures. The bonded joint is between a cast-iron rod and a GFRP composite pipe. The adhesive material is an epoxy containing chopped glass fibers. We proposed a new fabrication method to make concentric and void-less specimens of the tubular joint with a thick adhesive bondline to stimulate the root bond of a blade. The thick bondline facilitates the joint assembly of actual blades. For a better understanding of the behavior of the bonded joint, we studied viscoelastic behavior of the adhesive materials by measuring creep compliance at several temperatures during loading period. We observed that the creep compliance depends highly on the period of loading and the temperature. We applied time-temperature equivalence to the creep compliance of the adhesive material to obtain time-temperature shift factors. We also performed constant-rate of monotonically increased uniaxial tensile tests to measure static strength of the tubular lap joint at several temperatures and different strain-rates. We observed two failure modes from load-deflection curves and failed specimens. One is the brittle mode, which was caused by weakness of the interfacial strength occurring at low temperature and short period of loading. The other is the ductile mode, which was caused by weakness of the adhesive material at high temperature and long period of loading. Transition from the brittle to the ductile mode appeared as the temperature or the loading period increased. We also performed tests under uniaxial tensile-tensile cyclic loadings to measure fatigue strength of the bonded joint at several temperatures, frequencies and stress ratios. The fatigue data are analyzed statistically by applying the residual strength degradation model to calculate statistical distribution of the fatigue life. Combining the time-temperature

Temperature dependent energy levels of methylammonium lead iodide perovskite

NASA Astrophysics Data System (ADS)

Foley, Benjamin J.; Marlowe, Daniel L.; Sun, Keye; Saidi, Wissam A.; Scudiero, Louis; Gupta, Mool C.; Choi, Joshua J.

2015-06-01

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

Temperature-dependent respiration-growth relations in ancestral maize cultivars

Treesearch

Bruce N. Smith; Jillian L. Walker; Rebekka L. Stone; Angela R. Jones; Lee D. Hansen

2001-01-01

Shoots from 4- to 6-day old seedlings of seven ancestral or old cultivars of Zea mays L. were placed in a calorimeter. Dark metabolic heat rate (q) and CO2 production rate (RCO2) were measured at nine temperatures (5, 10, 15, 20, 25, 30, 35, 40, and 45 °C). Temperature dependencies of q and RCO2 were used to model response of both growth and substrate carbon conversion...

A method to correct for temperature dependence and measure simultaneously dose and temperature using a plastic scintillation detector

PubMed Central

Therriault-Proulx, Francois; Wootton, Landon; Beddar, Sam

2015-01-01

Plastic scintillation detectors (PSDs) work well for radiation dosimetry. However, they show some temperature dependence, and a priori knowledge of the temperature surrounding the PSD is required to correct for this dependence. We present a novel approach to correct PSD response values for temperature changes instantaneously and without the need for prior knowledge of the temperature value. In addition to rendering the detector temperature-independent, this approach allows for actual temperature measurement using solely the PSD apparatus. With a temperature-controlled water tank, the temperature was varied from room temperature to more than 40°C and the PSD was used to measure the dose delivered from a cobalt-60 photon beam unit to within an average of 0.72% from the expected value. The temperature was measured during each acquisition with the PSD and a thermocouple and values were within 1°C of each other. The depth-dose curve of a 6-MV photon beam was also measured under warm non-stable conditions and this curve agreed to within an average of −0.98% from the curve obtained at room temperature. The feasibility of rendering PSDs temperature-independent was demonstrated with our approach, which also enabled simultaneous measurement of both dose and temperature. This novel approach improves both the robustness and versatility of PSDs. PMID:26407188

Temperature-dependent change in the nature of glass fracture under electron bombardment

NASA Astrophysics Data System (ADS)

Kravchenko, A. A.

1991-04-01

We report the experimental discovery of a temperature-dependent change in the nature of glass fracture under low-energy (<10 keV) electron bombardment. This is shown to depend on the transition from the thermal-shock to the thermalfluctuation mechanism of fracture at the limiting temperature T1 = (Tg - 150) °C. The high-temperature cleavage fracture of K8 and TF1 glasses was studied and the threshold value of the critical power initiating cleavage fracture was determined (for the glasses studied Θthr = 50 70 W·sec·cm-2).

Use Dependence of Heat Sensitivity of Vanilloid Receptor TRPV2

PubMed Central

Liu, Beiying; Qin, Feng

2016-01-01

Thermal TRP channels mediate temperature transduction and pain sensation. The vanilloid receptor TRPV2 is involved in detection of noxious heat in a subpopulation of high-threshold nociceptors. It also plays a critical role in development of thermal hyperalgesia, but the underlying mechanism remains uncertain. Here we analyze the heat sensitivity of the TRPV2 channel. Heat activation of the channel exhibits strong use dependence. Prior heat activation can profoundly alter its subsequent temperature responsiveness, causing decreases in both temperature activation threshold and slope sensitivity of temperature dependence while accelerating activation time courses. Notably, heat and agonist activations differ in cross use-dependence. Prior heat stimulation can dramatically sensitize agonist responses, but not conversely. Quantitative analyses indicate that the use dependence in heat sensitivity is pertinent to the process of temperature sensing by the channel. The use dependence of TRPV2 reveals that the channel can have a dynamic temperature sensitivity. The temperature sensing structures within the channel have multiple conformations and the temperature activation pathway is separate from the agonist activation pathway. Physiologically, the use dependence of TRPV2 confers nociceptors with a hypersensitivity to heat and thus provides a mechanism for peripheral thermal hyperalgesia. PMID:27074678

Temperature dependent photoluminescence and micromapping of multiple stacks InAs quantum dots

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

Xu, Ming, E-mail: ming.xu@lgep.supelec.fr; Jaffré, Alexandre, E-mail: ming.xu@lgep.supelec.fr; Alvarez, José, E-mail: ming.xu@lgep.supelec.fr

2015-02-27

We utilized temperature dependent photoluminescence (PL) techniques to investigate 1, 3 and 5 stack InGaAs quantum dots (QDs) grown on cross-hatch patterns. PL mapping can well reproduce the QDs distribution as AFM and position dependency of QD growth. It is possible to observe crystallographic dependent PL. The temperature dependent spectra exhibit the QDs energy distribution which reflects the size and shape. The inter-dot carrier coupling effect is observed and translated as a red shift of 120mV on the [1–10] direction peak is observed at 30K on 1 stack with regards to 3 stacks samples, which is assigned to lateral coupling.

Effects of seasonal change and experimental warming on the temperature dependence of photosynthesis in the canopy leaves of Quercus serrata.

PubMed

Yamaguchi, Daisuke P; Nakaji, Tatsuro; Hiura, Tsutom; Hikosaka, Kouki

2016-10-01

The effects of warming on the temperature response of leaf photosynthesis have become an area of major concern in recent decades. Although growth temperature (GT) and day length (DL) affect leaf gas exchange characteristics, the way in which these factors influence the temperature dependence of photosynthesis remains uncertain. We established open-top canopy chambers at the canopy top of a deciduous forest, in which average daytime leaf temperature was increased by 1.0 °C. We conducted gas exchange measurements for the canopy leaves of deciduous trees exposed to artificial warming during different seasons. The carbon dioxide assimilation rate at 20 °C (A 20 ) was not affected by warming, whereas that at 25 °C (A 25 ) tended to be higher in leaves exposed to warming. Warming increased the optimal temperature of photosynthesis by increasing the activation energy for the maximum rate of carboxylation. Regression analysis indicated that both GT and DL strongly influenced gas exchange characteristics. Sensitivity analysis revealed that DL affected A without obvious effects on the temperature dependence of A, whereas GT almost maintained constant A 20 and strongly influenced the temperature dependence. These results indicate that GT and DL have different influences on photosynthesis; GT and DL affect the 'slope' and intercept' of the temperature dependence of photosynthesis, respectively. © The Author 2016. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Inverse Temperature Dependence of Nuclear Quantum Effects in DNA Base Pairs

PubMed Central

2016-01-01

Despite the inherently quantum mechanical nature of hydrogen bonding, it is unclear how nuclear quantum effects (NQEs) alter the strengths of hydrogen bonds. With this in mind, we use ab initio path integral molecular dynamics to determine the absolute contribution of NQEs to the binding in DNA base pair complexes, arguably the most important hydrogen-bonded systems of all. We find that depending on the temperature, NQEs can either strengthen or weaken the binding within the hydrogen-bonded complexes. As a somewhat counterintuitive consequence, NQEs can have a smaller impact on hydrogen bond strengths at cryogenic temperatures than at room temperature. We rationalize this in terms of a competition of NQEs between low-frequency and high-frequency vibrational modes. Extending this idea, we also propose a simple model to predict the temperature dependence of NQEs on hydrogen bond strengths in general. PMID:27195654

Temperature-dependent behaviours are genetically variable in the nematode Caenorhabditis briggsae.

PubMed

Stegeman, Gregory W; de Mesquita, Matthew Bueno; Ryu, William S; Cutter, Asher D

2013-03-01

Temperature-dependent behaviours in Caenorhabditis elegans, such as thermotaxis and isothermal tracking, are complex behavioural responses that integrate sensation, foraging and learning, and have driven investigations to discover many essential genetic and neural pathways. The ease of manipulation of the Caenorhabditis model system also has encouraged its application to comparative analyses of phenotypic evolution, particularly contrasts of the classic model C. elegans with C. briggsae. And yet few studies have investigated natural genetic variation in behaviour in any nematode. Here we measure thermotaxis and isothermal tracking behaviour in genetically distinct strains of C. briggsae, further motivated by the latitudinal differentiation in C. briggsae that is associated with temperature-dependent fitness differences in this species. We demonstrate that C. briggsae performs thermotaxis and isothermal tracking largely similar to that of C. elegans, with a tendency to prefer its rearing temperature. Comparisons of these behaviours among strains reveal substantial heritable natural variation within each species that corresponds to three general patterns of behavioural response. However, intraspecific genetic differences in thermal behaviour often exceed interspecific differences. These patterns of temperature-dependent behaviour motivate further development of C. briggsae as a model system for dissecting the genetic underpinnings of complex behavioural traits.

Temperature dependent droplet impact dynamics on flat and textured surfaces

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

Azar Alizadeh; Vaibhav Bahadur; Sheng Zhong

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

Temperature-Dependent Implicit-Solvent Model of Polyethylene Glycol in Aqueous Solution.

PubMed

Chudoba, Richard; Heyda, Jan; Dzubiella, Joachim

2017-12-12

A temperature (T)-dependent coarse-grained (CG) Hamiltonian of polyethylene glycol/oxide (PEG/PEO) in aqueous solution is reported to be used in implicit-solvent material models in a wide temperature (i.e., solvent quality) range. The T-dependent nonbonded CG interactions are derived from a combined "bottom-up" and "top-down" approach. The pair potentials calculated from atomistic replica-exchange molecular dynamics simulations in combination with the iterative Boltzmann inversion are postrefined by benchmarking to experimental data of the radius of gyration. For better handling and a fully continuous transferability in T-space, the pair potentials are conveniently truncated and mapped to an analytic formula with three structural parameters expressed as explicit continuous functions of T. It is then demonstrated that this model without further adjustments successfully reproduces other experimentally known key thermodynamic properties of semidilute PEG solutions such as the full equation of state (i.e., T-dependent osmotic pressure) for various chain lengths as well as their cloud point (or collapse) temperature.

From powder to solution: hydration dependence of human hemoglobin dynamics correlated to body temperature.

PubMed

Stadler, A M; Digel, I; Embs, J P; Unruh, T; Tehei, M; Zaccai, G; Büldt, G; Artmann, G M

2009-06-17

A transition in hemoglobin (Hb), involving partial unfolding and aggregation, has been shown previously by various biophysical methods. The correlation between the transition temperature and body temperature for Hb from different species, suggested that it might be significant for biological function. To focus on such biologically relevant human Hb dynamics, we studied the protein internal picosecond motions as a response to hydration, by elastic and quasielastic neutron scattering. Rates of fast diffusive motions were found to be significantly enhanced with increasing hydration from fully hydrated powder to concentrated Hb solution. In concentrated protein solution, the data showed that amino acid side chains can explore larger volumes above body temperature than expected from normal temperature dependence. The body temperature transition in protein dynamics was absent in fully hydrated powder, indicating that picosecond protein dynamics responsible for the transition is activated only at a sufficient level of hydration. A collateral result from the study is that fully hydrated protein powder samples do not accurately describe all aspects of protein picosecond dynamics that might be necessary for biological function.

A study on the dependence of nuclear viscosity on temperature

NASA Astrophysics Data System (ADS)

Vardaci, E.; Di Nitto, A.; Nadtochy, P. N.; La Rana, G.; Cinausero, M.; Prete, G.; Gelli, N.; Ashaduzzaman, M.; Davide, F.; Pulcini, A.; Quero, D.; Kozulin, E. M.; Knyazheva, G. N.; Itkis, I. M.

2018-05-01

Nuclear viscosity is an irreplaceable ingredient of nuclear fission collective dynamical models. It drives the exchange of energy between the collective variables and the thermal bath of single particle degrees of freedom. Its dependence on the shape and temperature is a matter of controversy. By using systems of intermediate fissility we have demonstrated in a recent study that the viscosity parameters is larger for compact shapes, and decreases for larger deformations of the fissioning system, at variance with the conclusions of the statistical model modified to include empirically viscosity and time scales. In this contribution we propose an experimental scenario to highlight the possible dependence of the viscosity from the temperature.

Temperature- and Length-Dependent Energetics of Formation for Polyalanine Helices in Water: Assignment of wAla(n,T) and Temperature-Dependent CD Ellipticity Standards

PubMed Central

Job, Gabriel E.; Kennedy, Robert J.; Heitmann, Björn; Miller, Justin S.; Walker, Sharon M.; Kemp*, Daniel S.

2006-01-01

Length-dependent helical propensities wAla(n,T) at T = 10, 25, and 60 °C are assigned from t/c values and NMR 13C chemical shifts for series 1 peptides TrpLysmInp2tLeu–AlantLeuInp2LysmNH2, n = 15, 19, and 25, m = 5, in water. Van’t Hoff analysis of wAla(n,T) show that α-helix formation is primarily enthalpy-driven. For series 2 peptides Ac–Trp Lys5Inp2tLeu–βAspHel–Alan–beta–tLeuInp2Lys5NH2, n = 12 and 22, which contain exceptionally helical Alan cores, protection factor-derived fractional helicities FH are assigned in the range 10–30 °C in water and used to calibrate temperature-dependent CD ellipticities [θ]λ,H,n,T. These are applied to CD data for series 1 peptides, 12 ≤ n ≤ 45, to confirm the wAla(n,T) assignments at T = 25 and 60 °C. The [θ]λ,H,n,T are temperature dependent within the wavelength region, 222 ± 12 nm, and yield a temperature correction for calculation of FH from experimental values of [θ]222,n,T,Exp. PMID:16787087

Temperature-dependent and optimized thermal emission by spheres

NASA Astrophysics Data System (ADS)

Nguyen, K. L.; Merchiers, O.; Chapuis, P.-O.

2018-03-01

We investigate the temperature and size dependencies of thermal emission by homogeneous spheres as a function of their dielectric properties. Different power laws obtained in this work show that the emitted power can depart strongly from the usual fourth power of temperature given by Planck's law and from the square or the cube of the radius. We also show how to optimize the thermal emission by selecting permittivities leading to resonances, which allow for the so-called super-Planckian regime. These results will be useful as spheres, i.e. the simplest finite objects, are often considered as building blocks of more complex objects.

Orientation and Temperature Dependence of Work-Hardening Rate in Cd Single Crystals

NASA Astrophysics Data System (ADS)

Uçar, N.

1997-03-01

The orientation and temperature dependence of the work-hardening rate (WHR) has been investigated in tension in the temperature range from room temperature to 500 K in Cd single crystals. The WHR was found to decrease rapidly with increasing temperature. For 21-1-3 orientated crystals, the WHR increases firstly with increasing temperature until it passes a maximum at about 350 K.

Predicting Long-term Temperature Increase for Time-Dependent SAR Levels with a Single Short-term Temperature Response

PubMed Central

Carluccio, Giuseppe; Bruno, Mary; Collins, Christopher M.

2015-01-01

Purpose Present a novel method for rapid prediction of temperature in vivo for a series of pulse sequences with differing levels and distributions of specific energy absorption rate (SAR). Methods After the temperature response to a brief period of heating is characterized, a rapid estimate of temperature during a series of periods at different heating levels is made using a linear heat equation and Impulse-Response (IR) concepts. Here the initial characterization and long-term prediction for a complete spine exam are made with the Pennes’ bioheat equation where, at first, core body temperature is allowed to increase and local perfusion is not. Then corrections through time allowing variation in local perfusion are introduced. Results The fast IR-based method predicted maximum temperature increase within 1% of that with a full finite difference simulation, but required less than 3.5% of the computation time. Even higher accelerations are possible depending on the time step size chosen, with loss in temporal resolution. Correction for temperature-dependent perfusion requires negligible additional time, and can be adjusted to be more or less conservative than the corresponding finite difference simulation. Conclusion With appropriate methods, it is possible to rapidly predict temperature increase throughout the body for actual MR examinations. (200/200 words) PMID:26096947

Predicting long-term temperature increase for time-dependent SAR levels with a single short-term temperature response.

PubMed

Carluccio, Giuseppe; Bruno, Mary; Collins, Christopher M

2016-05-01

Present a novel method for rapid prediction of temperature in vivo for a series of pulse sequences with differing levels and distributions of specific energy absorption rate (SAR). After the temperature response to a brief period of heating is characterized, a rapid estimate of temperature during a series of periods at different heating levels is made using a linear heat equation and impulse-response (IR) concepts. Here the initial characterization and long-term prediction for a complete spine exam are made with the Pennes' bioheat equation where, at first, core body temperature is allowed to increase and local perfusion is not. Then corrections through time allowing variation in local perfusion are introduced. The fast IR-based method predicted maximum temperature increase within 1% of that with a full finite difference simulation, but required less than 3.5% of the computation time. Even higher accelerations are possible depending on the time step size chosen, with loss in temporal resolution. Correction for temperature-dependent perfusion requires negligible additional time and can be adjusted to be more or less conservative than the corresponding finite difference simulation. With appropriate methods, it is possible to rapidly predict temperature increase throughout the body for actual MR examinations. © 2015 Wiley Periodicals, Inc.

Cloud droplet activation through oxidation of organic aerosol influenced by temperature and particle phase state: CLOUD ACTIVATION BY AGED ORGANIC AEROSOL

DOE PAGES

Slade, Jonathan H.; Shiraiwa, Manabu; Arangio, Andrea; ...

2017-02-04

Chemical aging of organic aerosol (OA) through multiphase oxidation reactions can alter their cloud condensation nuclei (CCN) activity and hygroscopicity. However, the oxidation kinetics and OA reactivity depend strongly on the particle phase state, potentially influencing the hydrophobic-to-hydrophilic conversion rate of carbonaceous aerosol. Here, amorphous Suwannee River fulvic acid (SRFA) aerosol particles, a surrogate humic-like substance (HULIS) that contributes substantially to global OA mass, are oxidized by OH radicals at different temperatures and phase states. When oxidized at low temperature in a glassy solid state, the hygroscopicity of SRFA particles increased by almost a factor of two, whereas oxidation ofmore » liquid-like SRFA particles at higher temperatures did not affect CCN activity. Low-temperature oxidation appears to promote the formation of highly-oxygenated particle-bound fragmentation products with lower molar mass and greater CCN activity, underscoring the importance of chemical aging in the free troposphere and its influence on the CCN activity of OA.« less

Temperature Dependence of Radiation Induced Conductivity in Insulators

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

Dennison, J. R.; Gillespie, Jodie; Hodges, Joshua

2009-03-10

This study measures Radiation Induced Conductivity (RIC) of Low Density Polyethylene (LDPE) over temperatures ranging from {approx}110 K to {approx}350 K. RIC occurs when incident ionizing radiation deposits energy and excites electrons into the conduction band of insulators. Conductivity was measured when a voltage was applied across vacuum-baked, thin film LDPE polymer samples in a parallel plate geometry. RIC was calculated as the difference in sample conductivity under no incident radiation and under an incident {approx}4 MeV electron beam at low incident fluxes of 10{sup -4}-10{sup -1} Gr/sec. The steady-state RIC was found to agree well with the standard powermore » law relation, {sigma}{sub RIC} = k{sub RIC}{center_dot}D ring {sup {delta}} between conductivity, {sigma} and adsorbed dose rate, D ring . Both the proportionality constant, k{sub RIC}, and the power, {delta}, were found to be temperature dependant above {approx}250 K, with behavior consistent with photoconductivity models developed for localized trap states in disordered semiconductors. Below {approx}250 K, kRIC and {delta} exhibited little change. The observed difference in temperature dependence might be related to a structural phase transition seen at T{sub {beta}}{approx}256 K in prior studies of mechanical and thermodynamic properties of LDPE.« less

One-shot calculation of temperature-dependent optical spectra and phonon-induced band-gap renormalization

NASA Astrophysics Data System (ADS)

Zacharias, Marios; Giustino, Feliciano

2016-08-01

Recently, Zacharias et al. [Phys. Rev. Lett. 115, 177401 (2015), 10.1103/PhysRevLett.115.177401] developed an ab initio theory of temperature-dependent optical absorption spectra and band gaps in semiconductors and insulators. In that work, the zero-point renormalization and the temperature dependence were obtained by sampling the nuclear wave functions using a stochastic approach. In the present work, we show that the stochastic sampling of Zacharias et al. can be replaced by fully deterministic supercell calculations based on a single optimal configuration of the atomic positions. We demonstrate that a single calculation is able to capture the temperature-dependent band-gap renormalization including quantum nuclear effects in direct-gap and indirect-gap semiconductors, as well as phonon-assisted optical absorption in indirect-gap semiconductors. In order to demonstrate this methodology, we calculate from first principles the temperature-dependent optical absorption spectra and the renormalization of direct and indirect band gaps in silicon, diamond, and gallium arsenide, and we obtain good agreement with experiment and with previous calculations. In this work we also establish the formal connection between the Williams-Lax theory of optical transitions and the related theories of indirect absorption by Hall, Bardeen, and Blatt, and of temperature-dependent band structures by Allen and Heine. The present methodology enables systematic ab initio calculations of optical absorption spectra at finite temperature, including both direct and indirect transitions. This feature will be useful for high-throughput calculations of optical properties at finite temperature and for calculating temperature-dependent optical properties using high-level theories such as G W and Bethe-Salpeter approaches.

Temperature-dependent innate defense against the common cold virus limits viral replication at warm temperature in mouse airway cells.

PubMed

Foxman, Ellen F; Storer, James A; Fitzgerald, Megan E; Wasik, Bethany R; Hou, Lin; Zhao, Hongyu; Turner, Paul E; Pyle, Anna Marie; Iwasaki, Akiko

2015-01-20

Most isolates of human rhinovirus, the common cold virus, replicate more robustly at the cool temperatures found in the nasal cavity (33-35 °C) than at core body temperature (37 °C). To gain insight into the mechanism of temperature-dependent growth, we compared the transcriptional response of primary mouse airway epithelial cells infected with rhinovirus at 33 °C vs. 37 °C. Mouse airway cells infected with mouse-adapted rhinovirus 1B exhibited a striking enrichment in expression of antiviral defense response genes at 37 °C relative to 33 °C, which correlated with significantly higher expression levels of type I and type III IFN genes and IFN-stimulated genes (ISGs) at 37 °C. Temperature-dependent IFN induction in response to rhinovirus was dependent on the MAVS protein, a key signaling adaptor of the RIG-I-like receptors (RLRs). Stimulation of primary airway cells with the synthetic RLR ligand poly I:C led to greater IFN induction at 37 °C relative to 33 °C at early time points poststimulation and to a sustained increase in the induction of ISGs at 37 °C relative to 33 °C. Recombinant type I IFN also stimulated more robust induction of ISGs at 37 °C than at 33 °C. Genetic deficiency of MAVS or the type I IFN receptor in infected airway cells permitted higher levels of viral replication, particularly at 37 °C, and partially rescued the temperature-dependent growth phenotype. These findings demonstrate that in mouse airway cells, rhinovirus replicates preferentially at nasal cavity temperature due, in part, to a less efficient antiviral defense response of infected cells at cool temperature.

Temperature dependence of the chromium(III) R1 linewidth in emerald

NASA Astrophysics Data System (ADS)

Carceller-Pastor, Ivana; Hutchison, Wayne D.; Riesen, Hans

2013-03-01

The temperature dependent contribution to the R1 (2E ← 4A2) linewidth in emerald, Be3Al2Si6O18:Cr3, has been measured by employing spectral hole-burning, fluorescence line narrowing and conventional luminescence experiments. The contribution varies from 0.6 MHz at 6.5 K to ˜420 GHz at 240 K and the line red-shifts by ˜570 GHz. Above 60 K, the dependence is well described by a non-perturbative formalism for two-phonon Raman scattering. Below this temperature the direct one-phonon process between the levels of the split 2E excited state dominates. However, it appears that a localized low-energy phonon leads to a deviation from the standard pattern at lowest temperatures.

In-situ observation of the temperature and orientation dependence of the surface concentration of Ni adatoms deposited on Pd

NASA Astrophysics Data System (ADS)

Zimnik, Samantha; Dickmann, Marcel; Hugenschmidt, Christoph

2017-10-01

We report the direct observation of the in-situ temperature-dependent migration of Ni adatoms in Pd using Positron annihilation induced Auger Electron Spectroscopy (PAES). For this study, a single atomic layer of Ni was grown on Pd with the crystallographic orientations Pd(111), Pd(110) and Pd(100). The sample temperature was increased from room temperature to 350 °C and the intensity of the Ni and Pd signal was evaluated from the recorded PAES spectra. Due to the outstanding surface sensitivity of PAES a clear tendency for Pd segregation at the surface was observed for all samples. Moreover the activation temperature T0 for surface segregation was found to depend strongly on the surface orientation: We determined T0 to 172± 4 °C, 261± 12 °C and 326± 11 °C for Pd(111), Pd(100) and Pd(110), respectively.

Temperature- and field-dependent characterization of a conductor on round core cable

NASA Astrophysics Data System (ADS)

Barth, C.; van der Laan, D. C.; Bagrets, N.; Bayer, C. M.; Weiss, K.-P.; Lange, C.

2015-06-01

The conductor on round core (CORC) cable is one of the major high temperature superconductor cable concepts combining scalability, flexibility, mechanical strength, ease of fabrication and high current density; making it a possible candidate as conductor for large, high field magnets. To simulate the boundary conditions of such magnets as well as the temperature dependence of CORC cables a 1.16 m long sample consisting of 15, 4 mm wide SuperPower REBCO tapes was characterized using the ‘FBI’ (force—field—current) superconductor test facility of the Institute for Technical Physics of the Karlsruhe Institute of Technology. In a five step investigation, the CORC cable’s performance was determined at different transverse mechanical loads, magnetic background fields and temperatures as well as its response to swift current changes. In the first step, the sample’s 77 K, self-field current was measured in a liquid nitrogen bath. In the second step, the temperature dependence was measured at self-field condition and compared with extrapolated single tape data. In the third step, the magnetic background field was repeatedly cycled while measuring the current carrying capabilities to determine the impact of transverse Lorentz forces on the CORC cable sample’s performance. In the fourth step, the sample’s current carrying capabilities were measured at different background fields (2-12 T) and surface temperatures (4.2-51.5 K). Through finite element method simulations, the surface temperatures are converted into average sample temperatures and the gained field- and temperature dependence is compared with extrapolated single tape data. In the fifth step, the response of the CORC cable sample to rapid current changes (8.3 kA s-1) was observed with a fast data acquisition system. During these tests, the sample performance remains constant, no degradation is observed. The sample’s measured current carrying capabilities correlate to those of single tapes assuming

Frequency and Temperature Dependent Dielectric Properties of Free-standing Strontium Titanate Thin Films.

NASA Astrophysics Data System (ADS)

Dalberth, Mark J.; Stauber, Renaud E.; Anderson, Britt; Price, John C.; Rogers, Charles T.

1998-03-01

We will report on the frequency and temperature dependence of the complex dielectric function of free-standing strontium titanate (STO) films. STO is an incipient ferroelectric with electric-field tunable dielectric properties of utility in microwave electronics. The films are grown epitaxially via pulsed laser deposition on a variety of substrates, including lanthanum aluminate (LAO), neodymium gallate (NGO), and STO. An initial film of yttrium barium cuprate (YBCO) is grown on the substrate, followed by deposition of the STO layer. Following deposition, the sacrificial YBCO layer is chemically etched away in dilute nitric acid, leaving the substrate and a released, free-standing STO film. Coplanar capacitor structures fabricated on the released films allow us to measure the dielectric response. We observe a peak dielectric function in excess of 5000 at 35K, change in dielectric constant of over a factor of 8 for 10Volt/micron electric fields, and temperature dependence above 50K that is very similar to bulk material. The dielectric loss shows two peaks, each with a thermally activated behavior, apparently arising from two types of polar defects. We will discuss the correlation between dielectric properties, growth conditions, and strain in the free-standing STO films.

Carrier concentration dependence of donor activation energy in n-type GaN epilayers grown on Si (1 1 1) by plasma-assisted MBE

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

Kumar, Mahesh; Central Research Laboratory, Bharat Electronics, Bangalore 560 013; Bhat, Thirumaleshwara N.

Highlights: ► The n-type GaN layers were grown by plasma-assisted molecular beam epitaxy. ► The optical characteristics of a donor level in Si-doped GaN were studied. ► Activation energy of a Si-related donor was estimated from temperature dependent PL measurements. ► PL peak positions, FWHM of PL and activation energies are found to be proportional to the cube root of carrier density. ► The involvement of donor levels is supported by the temperature-dependent electron concentration measurements. -- Abstract: The n-type GaN layers were grown by plasma-assisted MBE and either intentionally doped with Si or unintentionally doped. The optical characteristics ofmore » a donor level in Si-doped, GaN were studied in terms of photoluminescence (PL) spectroscopy as a function of electron concentration. Temperature dependent PL measurements allowed us to estimate the activation energy of a Si-related donor from temperature-induced decay of PL intensity. PL peak positions, full width at half maximum of PL and activation energies are found to be proportional to the cube root of carrier density. The involvement of donor levels is supported by the temperature-dependent electron concentration measurements.« less

Temperature-Dependent Conformations of Model Viscosity Index Improvers

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

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

2015-05-01

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

Temperature dependence of ice-on-rock friction at realistic glacier conditions

PubMed Central

Savage, H.; Nettles, M.

2017-01-01

Using a new biaxial friction apparatus, we conducted experiments of ice-on-rock friction in order to better understand basal sliding of glaciers and ice streams. A series of velocity-stepping and slide–hold–slide tests were conducted to measure friction and healing at temperatures between −20°C and melting. Experimental conditions in this study are comparable to subglacial temperatures, sliding rates and effective pressures of Antarctic ice streams and other glaciers, with load-point velocities ranging from 0.5 to 100 µm s−1 and normal stress σn = 100 kPa. In this range of conditions, temperature dependences of both steady-state friction and frictional healing are considerable. The friction increases linearly with decreasing temperature (temperature weakening) from μ = 0.52 at −20°C to μ = 0.02 at melting. Frictional healing increases and velocity dependence shifts from velocity-strengthening to velocity-weakening behaviour with decreasing temperature. Our results indicate that the strength and stability of glaciers and ice streams may change considerably over the range of temperatures typically found at the ice–bed interface. This article is part of the themed issue ‘Microdynamics of ice’. PMID:28025297

Use Dependence of Heat Sensitivity of Vanilloid Receptor TRPV2.

PubMed

Liu, Beiying; Qin, Feng

2016-04-12

Thermal TRP channels mediate temperature transduction and pain sensation. The vanilloid receptor TRPV2 is involved in detection of noxious heat in a subpopulation of high-threshold nociceptors. It also plays a critical role in development of thermal hyperalgesia, but the underlying mechanism remains uncertain. Here we analyze the heat sensitivity of the TRPV2 channel. Heat activation of the channel exhibits strong use dependence. Prior heat activation can profoundly alter its subsequent temperature responsiveness, causing decreases in both temperature activation threshold and slope sensitivity of temperature dependence while accelerating activation time courses. Notably, heat and agonist activations differ in cross use-dependence. Prior heat stimulation can dramatically sensitize agonist responses, but not conversely. Quantitative analyses indicate that the use dependence in heat sensitivity is pertinent to the process of temperature sensing by the channel. The use dependence of TRPV2 reveals that the channel can have a dynamic temperature sensitivity. The temperature sensing structures within the channel have multiple conformations and the temperature activation pathway is separate from the agonist activation pathway. Physiologically, the use dependence of TRPV2 confers nociceptors with a hypersensitivity to heat and thus provides a mechanism for peripheral thermal hyperalgesia. Copyright © 2016 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Temperature Dependence of Brillouin Light Scattering Spectra of Acoustic Phonons in Silicon

NASA Astrophysics Data System (ADS)

Somerville, Kevin; Klimovich, Nikita; An, Kyongmo; Sullivan, Sean; Weathers, Annie; Shi, Li; Li, Xiaoqin

2015-03-01

Thermal management represents an outstanding challenge in many areas of technology. Electrons, optical phonons, and acoustic phonons are often driven out of local equilibrium in electronic devices or during laser-material interaction processes. Interest in non-equilibrium transport processes has motivated the development of Raman spectroscopy as a local temperature sensor of optical phonons and intermediate frequency acoustic phonons, whereas Brillouin light scattering (BLS) has recently been explored as a temperature sensor of low-frequency acoustic phonons. Here, we report temperature dependent BLS spectra of silicon, with Raman spectra taken simultaneously for comparison. The origins of the observed temperature dependence of the BLS peak position, linewidth, and intensity are examined in order to evaluate their potential use as temperature sensors for acoustic phonons. We determine that the integrated BLS intensity can be used measure the temperature of specific acoustic phonon modes. This work is supported by National Science Foundation (NSF) Thermal Transport Processes Program under Grant CBET-1336968.

The temperature dependence of the anisotropy constants for nickel

NASA Astrophysics Data System (ADS)

Szpunar, B.

1984-04-01

A universal function is suggested for the description of the temperature dependence of the anisotropy constants for Ni. The function has been obtained from the extended Stevens operators for J→ {1}/{2}. The prediction is in good agreement with experimental data.

Temperature dependence of bromine activation due to reaction of bromide with ozone in a proxy for organic aerosols and its importance for chemistry in surface snow.

NASA Astrophysics Data System (ADS)

Edebeli, Jacinta; Ammann, Markus; Gilgen, Anina; Trachsel, Jürg; Avak, Sven; Eichler, Anja; Schneebeli, Martin; Bartels-Rausch, Thorsten

2017-04-01

Tropospheric ozone depletion events (ODEs) via halogen activation are observed in both cold and warm climates [1-3]. Very recently, it was suggested that this multiphase halogen activation chemistry dominates in the tropical and subtropical upper troposphere [4]. These occurrences beg the question of temperature dependence of halogen activation in sea-salt aerosol, which are often mixtures of sea-salt and organic molecules [3, 5]. With the application of flow-tubes, the aim of this study is to investigate the temperature dependence of bromine activation via ozone interaction in a bromide containing film as a proxy for mixed organic - sea-salt aersol. Citric acid is used in this study as a hygroscopically characterized matrix and a proxy for oxidized organics, which is of relevance to atmospheric chemistry. Here, we present reactive ozone uptake measured between 258 and 289 K. The data show high reproducibility. With available knowledge, we have reproduced the measured uptake with modelled bulk uptake while accounting for temperature dependence of the substrate's properties as diffusivity, viscosity, and gas solubility. This work is part of a cross-disciplinary project with the aim to investigate the impact of metamorphism on impurity location in aging snow and its consequences for chemical reactivity. Metamorphism drastically shapes the structure and physical properties of snow, which has impacts on heat transfer, albedo, and avalanche formation. Such changes can be driven by water vapour fluxes in dry metamorphism with a mass turnover of as much as 60% per day - much greater than previously thought [6]. The consequences for atmospheric science are a current question of research [7]. Here, we show first results of a joint experiment to probe the re-distribution of impurities during snow metamorphism in artificial snow combined with an investigation of the samples structural changes. Future work is planned with the goal to investigate to which extend the observed re

Rapid nondestructive spectrometric measurement of temperature-dependent gas-liquid solubility equilibria.

PubMed

Ma, Jian; Dasgupta, Purnendu K; Yang, Bingcheng

2011-02-01

Gas-liquid solubility equilibria (Henry's Law behavior) are of basic interest to many different areas. Temperature-dependent aqueous solubilities of various organic compounds are of fundamental importance in many branches of environmental science. In a number of situations, the gas/dissolved solute of interest has characteristic spectroscopic absorption that is distinct from that of the solvent. For such cases, we report facile nondestructive rapid measurement of the temperature-dependent Henry's law constant (K(H)) in a static sealed spectrometric cell. Combined with a special cell design, multiwavelength measurement permits a large range of K(H) to be spanned. It is possible to derive the K(H) values from the absorbance measured in the gas phase only, the liquid phase only (preferred), and both phases. Underlying principles are developed, and all three approaches are illustrated for a solute like acetone in water. A thermostatic spectrophotometer cell compartment, widely used and available, facilitates rapid temperature changes and allows rapid temperature-dependent equilibrium measurements. Applicability is shown for both acetone and methyl isobutyl ketone. Very little sample is required for the measurement; the K(H) for 4-hydroxynonenal, a marker for oxidative stress, is measured to be 56.9 ± 2.6 M/atm (n = 3) at 37.4 °C with 1 mg of the material available.

Temperature dependence of the anisotropy field of L10 FePt near the Curie temperature

NASA Astrophysics Data System (ADS)

Richter, H. J.; Parker, G. J.

2017-06-01

Near the Curie temperature, the anisotropy field of magnetically uniaxial L10 FePt is expected to follow the scaling law (1 - T/Tc)β, where T is the temperature and Tc is the Curie temperature. In the literature, β values between 0.36 and 0.65 have been reported. Based on recording measurements and micromagnetic analysis, we show that only the values of β near the low end of the reported range are compatible with the data. We also conclude that thermally activated magnetization reversal at temperatures near Tc cannot be ignored, even at time scales smaller than 1 ns. We demonstrate that thermally activated magnetization reversal at temperatures close to Tc is well described by conventional theory with a frequency factor f0 of the order of 1012 Hz. It is reasoned that the unusually high value for f0 is a consequence of the temperature-induced reduction of the degree of alignment of the micro-spins within the grains.

Temperature-dependent residual shear strength characteristics of smectite-bearing landslide soils

NASA Astrophysics Data System (ADS)

Shibasaki, Tatsuya; Matsuura, Sumio; Hasegawa, Yoichi

2017-02-01

This paper presents experimental investigations regarding the effect of temperature on the residual strength of landslide soils at slow-to-moderate shearing velocities. We performed ring-shear tests on 23 soil samples at temperatures of 6-29°C. The test results show that the shear strength of smectite-rich soils decreased when temperatures were relatively low. These positive temperature effects (strength losses at lower temperatures) observed for smectite-bearing soils are typical under relatively slow shearing rates. In contrast, under relatively high shearing rates, strength was gained as temperature decreased. As rheological properties of smectite suspensions are sensitive to environmental factors, such as temperature, pH, and dissolved ions, we inferred that temperature-dependent residual strengths of smectitic soils are also attributed to their specific rheological properties. Visual and scanning electron microscope observations of Ca-bentonite suggest that slickensided shear surfaces at slow shearing rates are very shiny and smooth, whereas those at moderate shearing rates are not glossy and are slightly turbulent, indicating that platy smectite particles are strongly orientated at slow velocities. The positive temperature effect is probably due to temperature-dependent microfriction that is mobilized in the parallel directions of the sheet structure of hydrous smectite particles. On the contrary, the influence of microviscous resistance, which appears in the vertical directions of the lamination, is assumed to increase at faster velocities. Our results imply that if slip-surface soils contain high fractions of smectite, decreases in ground temperature can lead to lowered shear resistance of the slip surface and trigger slow landslide movement.

Rate of egg maturation in marine turtles exhibits 'universal temperature dependence'.

PubMed

Weber, Sam B; Blount, Jonathan D; Godley, Brendan J; Witt, Matthew J; Broderick, Annette C

2011-09-01

1. The metabolic theory of ecology (MTE) predicts that, after correcting for body mass variation among organisms, the rates of most biological processes will vary as a universal function of temperature. However, empirical support for 'universal temperature dependence' (UTD) is currently equivocal and based on studies of a limited number of traits. 2. In many ectothermic animals, the rate at which females produce mature eggs is temperature dependent and may be an important factor in determining the costs of reproduction. 3. We tested whether the rate of egg maturation in marine turtles varies with environmental temperature as predicted by MTE, using the time separating successive clutches of individual females to estimate the rate at which eggs are formed. We also assessed the phenotypic contribution to this rate, by using radio telemetry to make repeated measurements of interclutch intervals for individual green turtles (Chelonia mydas). 4. Rates of egg maturation increased with seasonally increasing water temperatures in radio-tracked green turtles, but were not repeatable for individual females, and did not vary according to maternal body size or reproductive investment (number and size of eggs produced). 5. Using a collated data set from several different populations and species of marine turtles, we then show that a single relationship with water temperature explains most of the variation in egg maturation rates, with a slope that is statistically indistinguishable from the UTD predicted by MTE. However, several alternative statistical models also described the relationship between temperature and egg maturation rates equally parsimoniously. 6. Our results offer novel support for the MTE's predicted UTD of biological rates, although the underlying mechanisms require further study. The strong temperature dependence of egg maturation combined with the apparently weak phenotypic contribution to this rate has interesting behavioural implications in ectothermic

Temperature dependence of damage coefficient in electron irradiated solar cells

NASA Technical Reports Server (NTRS)

Faith, T. J.

1973-01-01

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

Temperature-dependent physical properties of egg white for HIFU applications

NASA Astrophysics Data System (ADS)

Liu, Yunbo; Maruvada, Subha; Herman, Bruce A.; Harris, Gerald R.

2012-10-01

Because egg white denatures at elevated temperature due to its protein content, it has the potential for use as a blood coagulation surrogate in pre-clinical evaluations of thermal therapy procedures such as high intensity focused ultrasound (HIFU) surgery. We therefore have measured the relevant physical properties of egg white, including coagulation temperature, frequency-dependent attenuation, sound speed, viscosity, and thermal properties, as a function of temperature (20 - 95°C). Thermal coagulation and attenuation (5-12 MHz) of cow blood, pig blood, and human blood also were assessed and compared with egg white. For a 30 s thermal exposure, both egg white and blood samples started to denature at 65°C and coagulate into an elastic gel at 85°C. The temperature-dependent parameters were found to be similar to that of the blood samples. For example, the attenuation of egg white ranged from 0.23f1.09 to 2.7f0.5 dB/cm over the 20°C - 95°C range. These results suggest that egg white would make a useful blood mimic for bench testing of therapeutic ultrasound devices.

Corticosteroid dependent and independent effects of a cannabinoid agonist on core temperature, motor activity, and prepulse inhibition of the acoustic startle reflex in Wistar rats.

PubMed

Avdesh, Avdesh; Cornelisse, Vincent; Martin-Iverson, Mathew Thomas

2012-03-01

There are inconsistent reports on the effects of cannabinoid agonists on prepulse inhibition of the startle reflex (PPI) with increases, decreases, and no effects. It has been hypothesized that the conflicting observations may be as a result of modulation of the effects of cannabinoid agonists by the regulation of corticosteroid release. The purpose of the present study was to determine the effects of CP55940, a cannabinoid agonist, and metyrapone, a corticosteroid synthesis inhibitor on core temperature, motor activity, the startle reflex, and PPI. Startle responses were measured in 64 male Wistar rats while varying startling stimulus intensities, analogous to dose-response curves. A stimulus potency measure (ES(50)) and a response measure, the maximal achievable response (R (MAX)) were derived from the stimulus-response curves. CP55940 reduced core temperature and motor activity; these effects were potentiated by metyrapone. CP55940 increased R (MAX) of startle in the absence of a prepulse by a corticosteroid-dependent mechanism but decreased it when metyrapone was administered before CP55940, a corticosteroid-independent mechanism. The inverse of stimulus potency (ES(50)) was not affected by either drug alone but was increased by the combined drugs. CP55940 increased the prepulse motor gating effects and decreased the prepulse sensory gating effects of the same prepulses but only when given after metyrapone. The most parsimonious interpretation of these effects is that CP55940 has some effects through corticosteroid-dependent actions and opposite effects by corticosteroid-independent actions. These two putative sites of actions affect stimulus gating opposite to their effects on response gating.

Motor-substrate interactions in mycoplasma motility explains non-Arrhenius temperature dependence.

PubMed

Chen, Jing; Neu, John; Miyata, Makoto; Oster, George

2009-12-02

Mycoplasmas exhibit a novel, substrate-dependent gliding motility that is driven by approximately 400 "leg" proteins. The legs interact with the substrate and transmit the forces generated by an assembly of ATPase motors. The velocity of the cell increases linearly by nearly 10-fold over a narrow temperature range of 10-40 degrees C. This corresponds to an Arrhenius factor that decreases from approximately 45 k(B)T at 10 degrees C to approximately 10 k(B)T at 40 degrees C. On the other hand, load-velocity curves at different temperatures extrapolate to nearly the same stall force, suggesting a temperature-insensitive force-generation mechanism near stall. In this article, we propose a leg-substrate interaction mechanism that explains the intriguing temperature sensitivity of this motility. The large Arrhenius factor at low temperature comes about from the addition of many smaller energy barriers arising from many substrate-binding sites at the distal end of the leg protein. The Arrhenius dependence attenuates at high temperature due to two factors: 1), the reduced effective multiplicity of energy barriers intrinsic to the multiple-site binding mechanism; and 2), the temperature-sensitive weakly facilitated leg release that curtails the power stroke. The model suggests an explanation for the similar steep, sub-Arrhenius temperature-velocity curves observed in many molecular motors, such as kinesin and myosin, wherein the temperature behavior is dominated not by the catalytic biochemistry, but by the motor-substrate interaction.

Motor-Substrate Interactions in Mycoplasma Motility Explains Non-Arrhenius Temperature Dependence

PubMed Central

Chen, Jing; Neu, John; Miyata, Makoto; Oster, George

2009-01-01

Abstract Mycoplasmas exhibit a novel, substrate-dependent gliding motility that is driven by ∼400 “leg” proteins. The legs interact with the substrate and transmit the forces generated by an assembly of ATPase motors. The velocity of the cell increases linearly by nearly 10-fold over a narrow temperature range of 10–40°C. This corresponds to an Arrhenius factor that decreases from ∼45 kBT at 10°C to ∼10 kBT at 40°C. On the other hand, load-velocity curves at different temperatures extrapolate to nearly the same stall force, suggesting a temperature-insensitive force-generation mechanism near stall. In this article, we propose a leg-substrate interaction mechanism that explains the intriguing temperature sensitivity of this motility. The large Arrhenius factor at low temperature comes about from the addition of many smaller energy barriers arising from many substrate-binding sites at the distal end of the leg protein. The Arrhenius dependence attenuates at high temperature due to two factors: 1), the reduced effective multiplicity of energy barriers intrinsic to the multiple-site binding mechanism; and 2), the temperature-sensitive weakly facilitated leg release that curtails the power stroke. The model suggests an explanation for the similar steep, sub-Arrhenius temperature-velocity curves observed in many molecular motors, such as kinesin and myosin, wherein the temperature behavior is dominated not by the catalytic biochemistry, but by the motor-substrate interaction. PMID:19948122

Unfolding of a Temperature-Sensitive Domain Controls Voltage-Gated Channel Activation.

PubMed

Arrigoni, Cristina; Rohaim, Ahmed; Shaya, David; Findeisen, Felix; Stein, Richard A; Nurva, Shailika Reddy; Mishra, Smriti; Mchaourab, Hassane S; Minor, Daniel L

2016-02-25

Voltage-gated ion channels (VGICs) are outfitted with diverse cytoplasmic domains that impact function. To examine how such elements may affect VGIC behavior, we addressed how the bacterial voltage-gated sodium channel (BacNa(V)) C-terminal cytoplasmic domain (CTD) affects function. Our studies show that the BacNa(V) CTD exerts a profound influence on gating through a temperature-dependent unfolding transition in a discrete cytoplasmic domain, the neck domain, proximal to the pore. Structural and functional studies establish that the BacNa(V) CTD comprises a bi-partite four-helix bundle that bears an unusual hydrophilic core whose integrity is central to the unfolding mechanism and that couples directly to the channel activation gate. Together, our findings define a general principle for how the widespread four-helix bundle cytoplasmic domain architecture can control VGIC responses, uncover a mechanism underlying the diverse BacNa(V) voltage dependencies, and demonstrate that a discrete domain can encode the temperature-dependent response of a channel. Copyright © 2016 Elsevier Inc. All rights reserved.

Temperature-dependent layer breathing modes in two-dimensional materials

NASA Astrophysics Data System (ADS)

Maity, Indrajit; Maiti, Prabal K.; Jain, Manish

2018-04-01

Relative out-of-plane displacements of the constituent layers of two-dimensional materials give rise to unique low-frequency breathing modes. By computing the height-height correlation functions from molecular dynamics simulations, we show that the layer breathing modes (LBMs) can be mapped consistently to vibrations of a simple linear chain model. Our calculated thickness dependence of LBM frequencies for few-layer (FL) graphene and molybdenum disulfide (MoS2) are in excellent agreement with available experiments. Our results show a redshift of LBM frequency with an increase in temperature, which is a direct consequence of anharmonicities present in the interlayer interaction. We also predict the thickness and temperature dependence of LBM frequencies for FL hexagonal boron nitride. Our Rapid Communication provides a simple and efficient way to probe the interlayer interaction for layered materials and their heterostructures with the inclusion of anharmonic effects.

Size and Temperature Dependence of Electron Transfer between CdSe Quantum Dots and a TiO 2 Nanobelt

DOE PAGES

Tafen, De Nyago; Prezhdo, Oleg V.

2015-02-24

Understanding charge transfer reactions between quantum dots (QD) and metal oxides is fundamental for improving photocatalytic, photovoltaic and electronic devices. The complexity of these processes makes it difficult to find an optimum QD size with rapid charge injection and low recombination. We combine time-domain density functional theory with nonadiabatic molecular dynamics to investigate the size and temperature dependence of the experimentally studied electron transfer and charge recombination at CdSe QD-TiO 2 nanobelt (NB) interfaces. The electron injection rate shows strong dependence on the QD size, increasing for small QDs. The rate exhibits Arrhenius temperature dependence, with the activation energy ofmore » the order of millielectronvolts. The charge recombination process occurs due to coupling of the electronic subsystem to vibrational modes of the TiO 2 NB. Inelastic electron-phonon scattering happens on a picosecond time scale, with strong dependence on the QD size. Our simulations demonstrate that the electron-hole recombination rate decreases significantly as the QD size increases, in excellent agreement with experiments. The temperature dependence of the charge recombination rates can be successfully modeled within the framework of the Marcus theory through optimization of the electronic coupling and the reorganization energy. Our simulations indicate that by varying the QD size, one can modulate the photoinduced charge separation and charge recombination, fundamental aspects of the design principles for high efficiency devices.« less

Temperature dependence of nucleation rate in a binary solid solution

NASA Astrophysics Data System (ADS)

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

2012-12-01

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

Temperature dependence of thermal pressure for NaCl

NASA Astrophysics Data System (ADS)

Singh, Chandra K.; Pande, Brijesh K.; Pandey, Anjani K.

2018-05-01

Engineering applications of the materials can be explored upto the desired limit of accuracy with the better knowledge of its mechanical and thermal properties such as ductility, brittleness and Thermal Pressure. For the resistance to fracture (K) and plastic deformation (G) the ratio K/G is treated as an indication of ductile or brittle character of solids. In the present work we have tested the condition of ductility and brittleness with the calculated values of K/G for the NaCl. It is concluded that the nature of NaCl can be predicted upto high temperature simply with the knowledge of its elastic stiffness constant only. Thermoelastic properties of materials at high temperature is directly related to thermal pressure and volume expansion of the materials. An expression for the temperature dependence of thermal pressure is formulated using basic thermodynamic identities. It is observed that thermal pressure ΔPth calculated for NaCl by using Kushwah formulation is in good agreement with the experimental values also the thermal pressure increases with the increase in temperature.

Sequence and Temperature Dependence of the End-to-End Collision Dynamics of Single-Stranded DNA

PubMed Central

Uzawa, Takanori; Isoshima, Takashi; Ito, Yoshihiro; Ishimori, Koichiro; Makarov, Dmitrii E.; Plaxco, Kevin W.

2013-01-01

Intramolecular collision dynamics play an essential role in biomolecular folding and function and, increasingly, in the performance of biomimetic technologies. To date, however, the quantitative studies of dynamics of single-stranded nucleic acids have been limited. Thus motivated, here we investigate the sequence composition, chain-length, viscosity, and temperature dependencies of the end-to-end collision dynamics of single-stranded DNAs. We find that both the absolute collision rate and the temperature dependencies of these dynamics are base-composition dependent, suggesting that base stacking interactions are a significant contributor. For example, whereas the end-to-end collision dynamics of poly-thymine exhibit simple, linear Arrhenius behavior, the behavior of longer poly-adenine constructs is more complicated. Specifically, 20- and 25-adenine constructs exhibit biphasic temperature dependencies, with their temperature dependences becoming effectively indistinguishable from that of poly-thymine above 335 K for 20-adenines and 328 K for 25-adenines. The differing Arrhenius behaviors of poly-thymine and poly-adenine and the chain-length dependence of the temperature at which poly-adenine crosses over to behave like poly-thymine can be explained by a barrier friction mechanism in which, at low temperatures, the energy barrier for the local rearrangement of poly-adenine becomes the dominant contributor to its end-to-end collision dynamics. PMID:23746521

The flavoprotein Tah18-dependent NO synthesis confers high-temperature stress tolerance on yeast cells

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

Nishimura, Akira; Kawahara, Nobuhiro; Takagi, Hiroshi, E-mail: hiro@bs.naist.jp

Highlights: Black-Right-Pointing-Pointer NO is produced from L-arginine in response to elevated temperature in yeast. Black-Right-Pointing-Pointer Tah18 was first identified as the yeast protein involved in NO synthesis. Black-Right-Pointing-Pointer Tah18-dependent NO synthesis confers tolerance to high-temperature on yeast cells. -- Abstract: Nitric oxide (NO) is a ubiquitous signaling molecule involved in the regulation of a large number of cellular functions. In the unicellular eukaryote yeast, NO may be involved in stress response pathways, but its role is poorly understood due to the lack of mammalian NO synthase (NOS) orthologues. Previously, we have proposed the oxidative stress-induced L-arginine synthesis and its physiologicalmore » role under stress conditions in yeast Saccharomyces cerevisiae. Here, our experimental results indicated that increased conversion of L-proline into L-arginine led to NO production in response to elevated temperature. We also showed that the flavoprotein Tah18, which was previously reported to transfer electrons to the Fe-S cluster protein Dre2, was involved in NO synthesis in yeast. Gene knockdown analysis demonstrated that Tah18-dependent NO synthesis confers high-temperature stress tolerance on yeast cells. As it appears that such a unique cell protection mechanism is specific to yeasts and fungi, it represents a promising target for antifungal activity.« less

Temperature dependence of single-event burnout in n-channel power MOSFET's

NASA Astrophysics Data System (ADS)

Johnson, G. H.; Schrimpf, R. D.; Galloway, K. F.; Koga, R.

1994-03-01

The temperature dependence of single-event burnout (SEB) in n-channel power metal-oxide-semiconductor field effect transistors (MOSFET's) is investigated experimentally and analytically. Experimental data are presented which indicate that the SEB susceptibility of the power MOSFET decreases with increasing temperature. A previously reported analytical model that describes the SEB mechanism is updated to include temperature variations. This model is shown to agree with the experimental trends.

Temperature dependent x-ray diffraction and dielectric studies of multiferroic GaFeO{sub 3}

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

Kumar, Rajeev; Mall, Ashish Kumar, E-mail: ashishm@iitk.ac.in; Gupta, Rajeev

2016-05-06

Polycrystalline GaFeO{sub 3} (GFO) samples were synthesized by sol-gel method. The structural and dielectric properties of GaFeO{sub 3} ceramic have been investigated by a combination of XRD and permittivity measurement. The X-ray diffraction spectra shows single phase orthorhombically distorted perovskite structure with Pc2{sub 1}n symmetry over a wide range of temperature 300 K to 600 K, with no evidence of any phase transition. Refined lattice parameters (a, b, c and V) increases with increasing temperature. Temperature dependent dielectric properties were investigated in the frequency range from 100Hz–5MHz. Impedance spectroscopy study on the sample showed that the dielectric constant and acmore » conductivity with frequency increases on increasing the temperature. Cole-Cole plots suggest that the response from grain is dominant at low temperature whereas grain boundary response overcomes as temperature increases. The relaxation activation energy (calculated from Cole-Cole plots) value is found to be 0.32 eV for the grain boundary. We believe that the oxygen ion vacancies play an important role in conduction processes at higher temperatures.« less

Dependence of cerebral-cortex activation in women on environmental factors

NASA Astrophysics Data System (ADS)

Pavlov, K. I.; Mukhin, V. N.; Kamenskaya, V. G.; Klimenko, V. M.

2016-12-01

The investigation of female physiological reactions to different meteorological conditions and space weather is relevant, since there are little experimental findings in this field. The purpose of this work is to determine how the level of cerebral-cortex activity in women depends on the meteorological and cosmophysical parameters of weather and space processes. We studied electroencephalograms (EEGs) recorded at rest in the sitting position and with eyes closed. We performed four series of measurements of brain bioelectrical activity from February to June 2013. We found that the level of cortical activity recorded by EEG changed significantly during these 6 months. Significant differences were detected between the cortical activity and the parameters of weather and space processes; namely, an increase in the air temperature and a decrease in the wind speed and cosmic-ray energy result in a decrease in the activity rate of the right occipital lobe.

Temperature dependent characteristics of the random telegraph noise on contact resistive random access memory

NASA Astrophysics Data System (ADS)

Chang, Liang-Shun; Lin, Chrong Jung; King, Ya-Chin

2014-01-01

The temperature dependent characteristics of the random telegraphic noise (RTN) on contact resistive random access memory (CRRAM) are studied in this work. In addition to the bi-level switching, the occurrences of the middle states in the RTN signal are investigated. Based on the unique its temperature dependent characteristics, a new temperature sensing scheme is proposed for applications in ultra-low power sensor modules.

On rate-dependent polycrystal deformation: the temperature sensitivity of cold dwell fatigue

PubMed Central

Zhang, Zhen; Cuddihy, M. A.; Dunne, F. P. E.

2015-01-01

A temperature and rate-dependent crystal plasticity framework has been used to examine the temperature sensitivity of stress relaxation, creep and load shedding in model Ti-6Al polycrystal behaviour under dwell fatigue conditions. A temperature close to 120°C is found to lead to the strongest stress redistribution and load shedding, resulting from the coupling between crystallographic slip rate and slip system dislocation hardening. For temperatures in excess of about 230°C, grain-level load shedding from soft to hard grains diminishes because of the more rapid stress relaxation, leading ultimately to the diminution of the load shedding and hence, it is argued, the elimination of the dwell debit. Under conditions of cyclic stress dwell, at temperatures between 20°C and 230°C for which load shedding occurs, the rate-dependent accumulation of local slip by ratcheting is shown to lead to the progressive cycle-by-cycle redistribution of stress from soft to hard grains. This phenomenon is termed cyclic load shedding since it also depends on the material's creep response, but develops over and above the well-known dwell load shedding, thus providing an additional rationale for the incubation of facet nucleation. PMID:26528078

Spectroscopy of infrared-active phonons in high-temperature superconductors

NASA Technical Reports Server (NTRS)

Litvinchuk, A. P.; Thomsen, C.; Cardona, M.; Borjesson, L.

1995-01-01

For a large variety of superconducting materials both experimental and theoretical lattice dynamical studies have been performed to date. The assignment of the observed infrared- and Raman-active phonon modes to the particular lattice eigenmodes is generally accepted. We will concentrate here upon the analysis of the changes of the infrared-phonon parameters (frequency and linewidth) upon entering the superconducting state which, as will be shown, may provide information on the magnitude of the superconductivity-related gap and its dependence on the superconducting transition temperature Tc.

Negative Temperature Dependence of Recrystallized Grain Size: Formulation and Experimental Confirmation on Copper

PubMed Central

Elmasry, Mohamed; Liu, Fan; Jiang, Yao; Mao, Ze Ning; Liu, Ying; Wang, Jing Tao

2017-01-01

The catalyzing effect on nucleation of recrystallization from existing grains resulting from previous lower temperature deformation is analyzed, analogous to the size effect of foreign nucleus in heterogeneous nucleation. Analytical formulation of the effective nucleation site for recrystallization leads to a negative temperature dependence of recrystallized grain size of metals. Non-isochronal annealing—where annealing time is set just enough for the completion of recrystallization at different temperatures—is conducted on pure copper after severe plastic deformation. More homogeneous and smaller grains are obtained at higher annealing temperature. The good fit between analytical and experimental results unveils the intrinsic feature of this negative temperature dependence of recrystallized grain size. PMID:28772676

Temperature-dependent growth of Botrytis cinerea isolates from potted plants.

PubMed

Martínez, J A; Gómez-Bellot, M J; Bañón, S

2009-01-01

Botrytis cinereo is a common aggressive saprophyte fungus which also invades injured plant tissues, causing Botrytis blight (Grey mould) in many ornamental plants, including potted flowering plants. Several B. cinerea isolates from potted plants (Pelargonium x hortorum, Lantana camara, Lonicera japonica, Hydrangea macrophylla, and Cyclamen persicum) affected by Botrytis blight in the south of Spain were studied and identified by PCR. The isolates showed phenotypic differences between them, as previously reported by the authors. In this work we demonstrate that these isolates show different temperature-dependent growth phenomena, expressed as mycelial growth rates, conidiation (measured as the number of conidia per colony and time of appearance), mass of both aerial and submerged mycelia, and sclerotia production. Growth rates were assessed from differences in colony area and mass of both aerial and submerged mycelium growing in potato dextrose agar culture medium (PDA). Three temperatures were used to measure these variables (6, 16, and 26 degrees C) and to establish the differences among isolates by modelling the effects of temperature on the growth variables. B. cinerea showed a high degree of phenotypic variability and differences in its growth kinetics, depending on temperature and isolate in question. The isolate from P. x hortorum showed the greatest conidiation although this process did not depend on the temperatures assayed. The growth rate of the isolates from P. x hortorum was the highest. The growth rates in all the isolates were determined and the growth kinetics could be fitted to a typical equation of fungi growing on solid culture medium. The isolate from P. x hortorum was the most vigorous, while the least vigorous was the isolate from L. japonica. A relationship between mycelial growth rate, conidiation and aerial mycelium could be established. A temperature of 26 degrees C accelerated sclerotia production, but only in the isolate from C. persicum

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

Temperature dependent dispersion and electron-phonon coupling surface states on Be(1010)

NASA Astrophysics Data System (ADS)

Tang, Shu-Jung; Ismail; Sprunger, Philip; Plummer, Ward

2002-03-01

Temperature dependent dispersion and electron-phonon coupling surface states on Be(10-10) S.-J Tang*, Ismail* , P.T . Sprunger#, E. W. Plummer* * Department of Physics and Astronomy, University of Tennessee, Knoxville, TN37996 , # Center for Advanced Microstructures and Devices (CAMD), Louisiana State University The surface states dispersing in a large band gap from -A to -Γ in Be(10-10) were studied with high-resolution, angle-resolved photoemission. Spectra reveal that the two zone-boundary surface states, S1 and S2, behave significantly different with respect to band dispersion, the temperature dependence of binding energies, and the electron-phonon coupling. The band dispersion of S1 is purely free-electron like with the maximum binding energy of 0.37+-0.05 eV at -A and effective mass m*/m =0835. However, the maximum binding energy 2.74+-0.05 eV of the S2 is located 0.2Åaway from -A and disperses into the bulk band edge at a binding energy of 1.75+-0.05 eV. Temperature dependent data reveal that the binding energies of S1 and S2 at -A shift in opposite directions at the rate of (-0.61+-0.3)+- 10E-4 eV/K and (1.71+-0.8)+-10E-4 eV/K, respectively. Moreover, from the temperature-dependent spectral widths of the surface states S1 and S2 at , the electron-phonon coupling parameters,λ, have been determined. Unusually different, the coupling strength λ for S1 and S2 are 0.67+-0.03 and 0.51+-0.04, respectively. The differences between the electron-phonon coupling, temperature dependent binding energies, and dispersions between these two zone-centered surface states will be discussed in light unique bonding at the surface and localization.

Temperature Dependence of IP3-Mediated Local and Global Ca2+ Signals

PubMed Central

Dickinson, George D.; Parker, Ian

2013-01-01

We examined the effect of temperature (12–40°C) on local and global Ca2+ signals mediated by inositol trisphosphate receptor/channels (IP3R) in human neuroblastoma (SH-SY5Y) cells. The amplitudes and spatial spread of local signals arising from single IP3R (blips) and clusters of IP3R (puffs) showed little temperature dependence, whereas their kinetics (durations and latencies) were markedly accelerated by increasing temperature. In contrast, the amplitude of global Ca2+ waves increased appreciably at lower temperatures, probably as a result of the longer duration of IP3R channel opening. Several parameters, including puff and blip durations, puff latency and frequency, and frequency of repetitive Ca2+ waves, showed a biphasic temperature dependence on Arrhenius plots. In all cases the transition temperature occurred at ∼25°C, possibly reflecting a phase transition in the lipids of the endoplasmic reticulum membrane. Although the IP3-evoked Ca2+ signals were qualitatively similar at 25°C and 36°C, one should consider the temperature sensitivity of IP3-mediated signal amplitudes when extrapolating from room temperature to physiological temperature. Conversely, further cooling may be advantageous to improve the optical resolution of channel gating kinetics. PMID:23442860

Coronal temperatures of selected active cool stars as derived from low resolution Einstein observations

NASA Technical Reports Server (NTRS)

Vilhu, Osmi; Linsky, Jeffrey L.

1990-01-01

Mean coronal temperatures of some active G-K stars were derived from Rev1-processed Einstein-observatory's IPC-spectra. The combined X-ray and transition region emission line data are in rough agreement with static coronal loop models. Although the sample is too small to derive any statistically significant conclusions, it suggests that the mean coronal temperature depends linearly on the inverse Rossby-number, with saturation at short rotation periods.

The temperature dependence of intermediate range oxygen-oxygen correlations in liquid water

NASA Astrophysics Data System (ADS)

Schlesinger, Daniel; Wikfeldt, K. Thor; Skinner, Lawrie B.; Benmore, Chris J.; Nilsson, Anders; Pettersson, Lars G. M.

2016-08-01

We analyze the recent temperature dependent oxygen-oxygen pair-distribution functions from experimental high-precision x-ray diffraction data of bulk water by Skinner et al. [J. Chem. Phys. 141, 214507 (2014)] with particular focus on the intermediate range where small, but significant, correlations are found out to 17 Å. The second peak in the pair-distribution function at 4.5 Å is connected to tetrahedral coordination and was shown by Skinner et al. to change behavior with temperature below the temperature of minimum isothermal compressibility. Here we show that this is associated also with a peak growing at 11 Å which strongly indicates a collective character of fluctuations leading to the enhanced compressibility at lower temperatures. We note that the peak at ˜13.2 Å exhibits a temperature dependence similar to that of the density with a maximum close to 277 K or 4 °C. We analyze simulations of the TIP4P/2005 water model in the same manner and find excellent agreement between simulations and experiment albeit with a temperature shift of ˜20 K.

Mild Hyperthermia Downregulates Receptor-dependent Neutrophil Function

PubMed Central

Fröhlich, Dieter; Wittmann, Sigrid; Rothe, Gregor; Sessler, Daniel I.; Vogel, Peter; Taeger, Kai

2005-01-01

Mild hypothermia impairs resistance to infection and, reportedly, impairs phagocytosis and oxidative killing of un-opsonized bacteria. We evaluated various functions at 33 to 41°C in neutrophils taken from volunteers. Adhesion on endothelial cells was determined using light microscopy. Adhesion molecules expression and receptors, phagocytosis, and release of reactive oxidants were assessed using flow cytometric assays. Adhesion protein CD11b expression on resting neutrophils was temperature independent. However, upregulation of CD11b with TNF-α was increased by hypothermia and decreased with hyperthermia. Neutrophil adhesion to either resting or activated endothelial cells was not temperature dependent. Bacterial uptake was inversely related to temperature, more so with E. coli than S. aureus. Temperature dependence of phagocytosis occurred only with opsonized bacteria. Hypothermia slightly increased N-Formyl-L-methionyl-L-leucyl-phenylalanine (FMLP) receptors on neutrophils: hyperthermia decreased expression, especially with TNF-α. FMLP-induced H2O2 production was inversely related to temperature, especially in the presence of TNF-α. Conversely, phorbol-13-myristate-12-acetate, an activator of protein kinase C, induced an extreme and homogenous release of reactive oxidants that increased with temperature. In contrast to non-receptor dependent phagocytosis and oxidative killing, several crucial receptor-dependent neutrophil activities show temperature-dependent regulation, with hypothermia increasing function. The temperature dependence of neutrophil function is thus more complicated than previously appreciated. PMID:15281545

Activation of Phosphorylase Kinase by Physiological Temperature.

PubMed

Herrera, Julio E; Thompson, Jackie A; Rimmer, Mary Ashley; Nadeau, Owen W; Carlson, Gerald M

2015-12-29

In the six decades since its discovery, phosphorylase kinase (PhK) from rabbit skeletal muscle has usually been studied at 30 °C; in fact, not a single study has examined functions of PhK at a rabbit's body temperature, which is nearly 10 °C greater. Thus, we have examined aspects of the activity, regulation, and structure of PhK at temperatures between 0 and 40 °C. Between 0 and 30 °C, the activity at pH 6.8 of nonphosphorylated PhK predictably increased; however, between 30 and 40 °C, there was a dramatic jump in its activity, resulting in the nonactivated enzyme having a far greater activity at body temperature than was previously realized. This anomalous change in properties between 30 and 40 °C was observed for multiple functions, and both stimulation (by ADP and phosphorylation) and inhibition (by orthophosphate) were considerably less pronounced at 40 °C than at 30 °C. In general, the allosteric control of PhK's activity is definitely more subtle at body temperature. Changes in behavior related to activity at 40 °C and its control can be explained by the near disappearance of hysteresis at physiological temperature. In important ways, the picture of PhK that has emerged from six decades of study at temperatures of ≤30 °C does not coincide with that of the enzyme studied at physiological temperature. The probable underlying mechanism for the dramatic increase in PhK's activity between 30 and 40 °C is an abrupt change in the conformations of the regulatory β and catalytic γ subunits between these two temperatures.

Temperature dependence dynamical permeability characterization of magnetic thin film using near-field microwave microscopy

NASA Astrophysics Data System (ADS)

Hung, Le Thanh; Phuoc, Nguyen N.; Wang, Xuan-Cong; Ong, C. K.

2011-08-01

A temperature dependence characterization system of microwave permeability of magnetic thin film up to 5 GHz in the temperature range from room temperature up to 423 K is designed and fabricated as a prototype measurement fixture. It is based on the near field microwave microscopy technique (NFMM). The scaling coefficient of the fixture can be determined by (i) calibrating the NFMM with a standard sample whose permeability is known; (ii) by calibrating the NFMM with an established dynamic permeability measurement technique such as shorted microstrip transmission line perturbation method; (iii) adjusting the real part of the complex permeability at low frequency to fit the value of initial permeability. The algorithms for calculating the complex permeability of magnetic thin films are analyzed. A 100 nm thick FeTaN thin film deposited on Si substrate by sputtering method is characterized using the fixture. The room temperature permeability results of the FeTaN film agree well with results obtained from the established short-circuited microstrip perturbation method. Temperature dependence permeability results fit well with the Landau-Lifshitz-Gilbert equation. The temperature dependence of the static magnetic anisotropy H_K^{sta}, the dynamic magnetic anisotropy H_K^{dyn}, the rotational anisotropy Hrot, together with the effective damping coefficient αeff, ferromagnetic resonance fFMR, and frequency linewidth Δf of the thin film are investigated. These temperature dependent magnetic properties of the magnetic thin film are important to the high frequency applications of magnetic devices at high temperatures.

Temperature dependent transport characteristics of graphene/n-Si diodes

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

Parui, S.; Ruiter, R.; Zomer, P. J.

2014-12-28

Realizing an optimal Schottky interface of graphene on Si is challenging, as the electrical transport strongly depends on the graphene quality and the fabrication processes. Such interfaces are of increasing research interest for integration in diverse electronic devices as they are thermally and chemically stable in all environments, unlike standard metal/semiconductor interfaces. We fabricate such interfaces with n-type Si at ambient conditions and find their electrical characteristics to be highly rectifying, with minimal reverse leakage current (<10{sup −10} A) and rectification of more than 10{sup 6}. We extract Schottky barrier height of 0.69 eV for the exfoliated graphene and 0.83 eV for themore » CVD graphene devices at room temperature. The temperature dependent electrical characteristics suggest the influence of inhomogeneities at the graphene/n-Si interface. A quantitative analysis of the inhomogeneity in Schottky barrier heights is presented using the potential fluctuation model proposed by Werner and Güttler.« less

Temperature dependence of exciton and charge carrier dynamics in organic thin films

NASA Astrophysics Data System (ADS)

Platt, A. D.; Kendrick, M. J.; Loth, M.; Anthony, J. E.; Ostroverkhova, O.

2011-12-01

We report on physical mechanisms behind the temperature-dependent optical absorption, photoluminescence (PL), and photoconductivity in spin-coated films of a functionalized anthradithiophene (ADT) derivative, ADT-triethylsilylethynyl (TES)-F, and its composites with C60 and another ADT derivative, ADT-TIPS-CN. Measurements of absorption and PL spectra, PL lifetimes, and transient photocurrent were performed at temperatures between 98 and 300 K as a function of applied electric field. In pristine ADT-TES-F films, absorptive and emissive species were identified to be disordered H aggregates whose properties are affected by static and dynamic disorder. The exciton bandwidths were ≤0.06 and ˜0.115 eV for absorptive and emissive aggregates, respectively, indicative of higher disorder in the emissive species. The exciton in the latter was found to be delocalized over approximately four to five molecules. The PL properties were significantly modified upon adding a guest molecule to the ADT-TES-F host. In ADT-TES-F/C60 composites, the PL was considerably quenched due to photoinduced electron transfer from ADT-TES-F to C60, while in ADT-TES-F/ADT-TIPS-CN blends, the PL was dominated by emission from an exciplex formed between ADT-TES-F and ADT-TIPS-CN molecules. In all materials, the PL quantum yield dramatically decreased as the temperature increased due to thermally activated nonradiative recombination. Considerable electric-field-induced PL quenching was observed at low temperatures at electric fields above ˜105 V/cm due to tunneling into dark states. No significant contribution of ADT-TES-F emissive exciton dissociation to transient photocurrent was observed. In all materials, charge carriers were photogenerated at sub-500-ps time scales, limited by the laser pulse width, with temperature- and electric-field-independent photogeneration efficiency. In ADT-TES-F/C60 (2%) composites, the photogeneration efficiency was a factor of 2-3 higher than that in pristine ADT

Plate-like convection in fluids with temperature-dependent viscosity

NASA Astrophysics Data System (ADS)

Curbelo, J.; Mancho, A. M.

2015-12-01

The study of instabilities in fluids in which viscosity experiences a transition at a certain temperature range is of great interest for the understanding of planetary interiors, since this phenomena is suitable for representing a very viscous lithosphere (and thus rather rigid) over a convecting mantle. To this end, we study a 2D convection problem in which viscosity depends on temperature by abruptly changing its value within a narrow temperature gap. Notable solutions are found for a sharp transition viscosity law which are fundamentally related to the presence of a symmetry in the problem. For instance, cyclic series are found consisting of spontaneous plate-like behaviors emerging sporadically through abrupt bursts, and rapidly evolving towards a stagnant lid regime. The plate-like evolution alternates motions towards either right or left, introducing temporary asymmetries on the convecting styles. Further time-dependent regimes with stagnant and plate-like lids are described, which are also greatly influenced by the presence of the symmetry. These results provide convection examples of moving plates, that coexist with subsurface upwards and downwards meandering jets, but without a proper subduction, and can be particularly illustrative for understanding convective styles of the Earth prior to subduction, or that of other planetary bodies.

Convective stirring efficiency in strongly temperature-dependent, infinite Prandtl number fluids: application to planetary mantles.

NASA Astrophysics Data System (ADS)

Tosi, N.; Samuel, H.

2017-12-01

Many rocky planetary bodies currently exhibit solid-state convection, or have experienced this process during their histories.Such a style of convection is characterized by the negligible influence of inertia, and a rheology known to be strongly temperature-dependent. Convective motion within such planetary envelopes determine their ability to preserve or to homogenize compositional heterogeneities.Therefore, understanding the efficiency of convective stirring is key to the interpretation of petrological, geochemical, and cosmochemical data originating on the Earth from sampled erupted lava, or inferred from meteorite analysis (e.g., Mars). In order to study this problem we have conducted series of numerical experiments in 2D and 3D Cartesian domains heated from below and cooled from above. We varied systematically the Rayleigh number and the activation energy using a strongly temperature-dependent viscosity based on the Arrhenius law for diffusion creep. Given the large values of activation energy considered, all our experiments fall into the stagnant lid regime. Stirring efficiency is determined by computing the finite-time Lyapunov exponents, which provide a measure of the Lagrangian deformation.This systematic exploration allows the degree of heterogeneity and its spatial variability to be quantified, and yields mixing times for both 2D and 3D geometries.Our results indicate significant differences between geometries: 2D cases lead more frequently to steady solutions, for which stirring efficiency is spatially heterogeneous and mostly weak. On the other hand, 3D cases show more time dependence of the velocity field and generally yield more efficient convective stirring, even for cases with a weak time-dependence of the flow. Scaling laws for stirring efficiencies are derived, and will serve as a basis to discuss the application to planetary mantles.

Temperature dependence of interlayer coupling in perpendicular magnetic tunnel junctions with GdOx barriers

DOE PAGES

Newhouse-Illige, T.; Xu, Y. H.; Liu, Y. H.; ...

2018-02-13

Perpendicular magnetic tunnel junctions with GdO X tunneling barriers have shown a unique voltage controllable interlayer magnetic coupling effect. Here we investigate the quality of the GdO X barrier and the coupling mechanism in these junctions by examining the temperature dependence of the tunneling magnetoresistance and the interlayer coupling from room temperature down to 11 K. The barrier is shown to be of good quality with the spin independent conductance only contributing a small portion, 14%, to the total room temperature conductance, similar to AlO X and MgO barriers. The interlayer coupling, however, shows an anomalously strong temperature dependence includingmore » sign changes below 80 K. This non-trivial temperature dependence is not described by previous models of interlayer coupling and may be due to the large induced magnetic moment of the Gd ions in the barrier.« less

Temperature dependence of interlayer coupling in perpendicular magnetic tunnel junctions with GdOx barriers

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

Newhouse-Illige, T.; Xu, Y. H.; Liu, Y. H.

Perpendicular magnetic tunnel junctions with GdO X tunneling barriers have shown a unique voltage controllable interlayer magnetic coupling effect. Here we investigate the quality of the GdO X barrier and the coupling mechanism in these junctions by examining the temperature dependence of the tunneling magnetoresistance and the interlayer coupling from room temperature down to 11 K. The barrier is shown to be of good quality with the spin independent conductance only contributing a small portion, 14%, to the total room temperature conductance, similar to AlO X and MgO barriers. The interlayer coupling, however, shows an anomalously strong temperature dependence includingmore » sign changes below 80 K. This non-trivial temperature dependence is not described by previous models of interlayer coupling and may be due to the large induced magnetic moment of the Gd ions in the barrier.« less

High temperature dependence of thermal transport in graphene foam.

PubMed

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

2015-03-13

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

Temperature dependent structural and vibrational properties of liquid indium

NASA Astrophysics Data System (ADS)

Patel, A. B.; Bhatt, N. K.

2018-05-01

The influence of the temperature effect on both the structure factor and the phonon dispersion relation of liquid indium have been investigated by means of pseudopotential theory. The Percus-Yevick Hard Sphere reference system is applied to describe the structural calculation. The effective electron-ion interaction is explained by using modified empty core potential due to Hasegawa et al. along with a local field correction function due to Ichimaru-Utsumi (IU). The temperature dependence of pair potential needed at higher temperatures was achieved by multiplying the damping factor exp(- π/kBT2k F r ) in the pair potential. Very close agreement of static structure factor, particularly, at elevated temperatures confirms the validity of the local potential. A positive dispersion is found in low-q region and the correct trend of phonon dispersion branches like the experimental; shows all broad features of collective excitations in liquid metals.

Temperature dependence of the dynamics of zone boundary phonons in ZnO:Li

NASA Astrophysics Data System (ADS)

Yadav, Harish Kumar; Sreenivas, K.; Gupta, Vinay; Katiyar, R. S.

2008-12-01

Investigations of zone boundary phonons in ZnO:Li system (Li concentration: 10%) and their dynamics with temperature are reported. Additional modes at 127, 157, and 194 cm-1 are observed and assigned to zone boundary phonons at critical point M in the Brillouin zone [J. M. Calleja and M. Cardona, Phys. Rev. B 16, 3753 (1977)] due to breakdown of crystal translational symmetry with Li incorporation in ZnO. Anharmonicity in peak frequency and linewidth of the zone boundary phonons in a temperature range from 100 to 1000 K is also analyzed taking into account the decay of zone boundary phonons into three- and four-phonon modes (cubic and quadratic anharmonicities). The anharmonic behavior of peak frequency is found to be feebly dependent on three-phonon decay process but thermal expansion of lattice together with four-phonon decay process appropriately defines the temperature dependence. Linewidths, however, follow the simple four-phonon decay mechanism. E2(low) mode, on the other hand, shows a linear temperature dependency and therefore follows a three-phonon decay channel. The calculated values of phonon lifetimes at 100 K for the 127, 157, 194 cm-1, and E2(low) modes are 8.23, 6.54, 5.32, and 11.39 ps. Decay of the zone boundary phonon modes compared to E2(low) mode reveals that dopant induced disorder has a strong temperature dependency.

Temperature dependent electrical characteristics of Zn/ZnSe/n-GaAs/In structure

NASA Astrophysics Data System (ADS)

Sağlam, M.; Güzeldir, B.

2016-04-01

We have reported a study of the I-V characteristics of Zn/ZnSe/n-GaAs/In sandwich structure in a wide temperature range of 80-300 K by a step of 20 K, which are prepared by Successive Ionic Layer Adsorption and Reaction (SILAR) method. The main electrical parameters, such as ideality factor and zero-bias barrier height determined from the forward bias I-V characteristics were found strongly depend on temperature and when the increased, the n decreased with increasing temperature. The ideality factor and barrier height values as a function of the sample temperature have been attributed to the presence of the lateral inhomogeneities of the barrier height. Furthermore, the series resistance have been calculated from the I-V measurements as a function of temperature dependent.

Temperature Dependence of Interband Transitions in Wurtzite InP Nanowires.

PubMed

Zilli, Attilio; De Luca, Marta; Tedeschi, Davide; Fonseka, H Aruni; Miriametro, Antonio; Tan, Hark Hoe; Jagadish, Chennupati; Capizzi, Mario; Polimeni, Antonio

2015-04-28

Semiconductor nanowires (NWs) formed by non-nitride III-V compounds grow preferentially with wurtzite (WZ) lattice. This is contrary to bulk and two-dimensional layers of the same compounds, where only zincblende (ZB) is observed. The absorption spectrum of WZ materials differs largely from their ZB counterparts and shows three transitions, referred to as A, B, and C in order of increasing energy, involving the minimum of the conduction band and different critical points of the valence band. In this work, we determine the temperature dependence (T = 10-310 K) of the energy of transitions A, B, and C in ensembles of WZ InP NWs by photoluminescence (PL) and PL excitation (PLE) spectroscopy. For the whole temperature and energy ranges investigated, the PL and PLE spectra are quantitatively reproduced by a theoretical model taking into account contribution from both exciton and continuum states. WZ InP is found to behave very similarly to wide band gap III-nitrides and II-VI compounds, where the energy of A, B, and C displays the same temperature dependence. This finding unveils a general feature of the thermal properties of WZ materials that holds regardless of the bond polarity and energy gap of the crystal. Furthermore, no differences are observed in the temperature dependence of the fundamental band gap energy in WZ InP NWs and ZB InP (both NWs and bulk). This result points to a negligible role played by the WZ/ZB differences in determining the deformation potentials and the extent of the electron-phonon interaction that is a direct consequence of the similar nearest neighbor arrangement in the two lattices.

Optofluidic intracavity spectroscopy for spatially, temperature, and wavelength dependent refractometry

NASA Astrophysics Data System (ADS)

Kindt, Joel D.

A microfluidic refractometer was designed based on previous optofluidic intracavity spectroscopy (OFIS) chips utilized to distinguish healthy and cancerous cells. The optofluidic cavity is realized by adding high reflectivity dielectric mirrors to the top and bottom of a microfluidic channel. This creates a plane-plane Fabry-Perot optical cavity in which the resonant wavelengths are highly dependent on the optical path length inside the cavity. Refractometry is a useful method to determine the nature of fluids, including the concentration of a solute in a solvent as well as the temperature of the fluid. Advantages of microfluidic systems are the easy integration with lab-on-chip devices and the need for only small volumes of fluid. The unique abilities of the microfluidic refractometer in this thesis include its spatial, temperature, and wavelength dependence. Spatial dependence of the transmission spectrum is inherent through a spatial filtering process implemented with an optical fiber and microscope objective. A sequence of experimental observations guided the change from using the OFIS chip as a cell discrimination device to a complimentary refractometer. First, it was noted the electrode structure within the microfluidic channel, designed to trap and manipulate biological cells with dielectrophoretic (DEP) forces, caused the resonant wavelengths to blue-shift when the electrodes were energized. This phenomenon is consistent with the negative dn/dT property of water and water-based solutions. Next, it was necessary to develop a method to separate the optical path length into physical path length and refractive index. Air holes were placed near the microfluidic channel to exclusively measure the cavity length with the known refractive index of air. The cavity length was then interpolated across the microfluidic channel, allowing any mechanical changes to be taken into account. After the separation of physical path length and refractive index, it was of interest

A study on the temperature dependence of the threshold switching characteristics of Ge2Sb2Te5

NASA Astrophysics Data System (ADS)

Lee, Suyoun; Jeong, Doo Seok; Jeong, Jeung-hyun; Zhe, Wu; Park, Young-Wook; Ahn, Hyung-Woo; Cheong, Byung-ki

2010-01-01

We investigated the temperature dependence of the threshold switching characteristics of a memory-type chalcogenide material, Ge2Sb2Te5. We found that the threshold voltage (Vth) decreased linearly with temperature, implying the existence of a critical conductivity of Ge2Sb2Te5 for its threshold switching. In addition, we investigated the effect of bias voltage and temperature on the delay time (tdel) of the threshold switching of Ge2Sb2Te5 and described the measured relationship by an analytic expression which we derived based on a physical model where thermally activated hopping is a dominant transport mechanism in the material.

Temperature-dependent magnetostriction as the key factor for martensite reorientation in magnetic field

NASA Astrophysics Data System (ADS)

L'vov, Victor A.; Kosogor, Anna

2016-09-01

The magnetic field application leads to spatially inhomogeneous magnetostriction of twinned ferromagnetic martensite. When the increasing field and magnetostrictive strain reach certain threshold values, the motion of twin boundaries and magnetically induced reorientation (MIR) of twinned martensite start. The MIR leads to giant magnetically induced deformation of twinned martensite. In the present article, the threshold field (TF) and temperature range of observability of MIR were calculated for the Ni-Mn-Ga martensite assuming that the threshold strain (TS) is temperature-independent. The calculations show that if the TS is of the order of 10-4, the TF strongly depends on temperature and MIR can be observed only above the limiting temperature (~220 K). If the TS is of the order of 10-6, the TF weakly depends on temperature and MIR can be observed at extremely low temperatures. The obtained theoretical results are in agreement with available experimental data.

Temperature dependence of fast carbonyl backbone dynamics in chicken villin headpiece subdomain

PubMed Central

Vugmeyster, Liliya; Ostrovsky, Dmitry

2012-01-01

Temperature-dependence of protein dynamics can provide information on details of the free energy landscape by probing the characteristics of the potential responsible for the fluctuations. We have investigated the temperature-dependence of picosecond to nanosecond backbone dynamics at carbonyl carbon sites in chicken villin headpiece subdomain protein using a combination of three NMR relaxation rates: 13C′ longitudinal rate, and two cross-correlated rates involving dipolar and chemical shift anisotropy (CSA) relaxation mechanisms, 13C′/13C′−13Cα CSA/dipolar and 13C′/13C′−15N CSA/dipolar. Order parameters have been extracted using the Lipari-Szabo model-free approach assuming a separation of the time scales of internal and molecular motions in the 2–16°C temperature range. There is a gradual deviation from this assumption from lower to higher temperatures, such that above 16°C the separation of the time scales is inconsistent with the experimental data and, thus, the Lipari-Szabo formalism can not be applied. While there are variations among the residues, on the average the order parameters indicate a markedly steeper temperature dependence at backbone carbonyl carbons compared to that probed at amide nitrogens in an earlier study. This strongly advocates for probing sites other than amide nitrogen for accurate characterization of the potential and other thermodynamics characteristics of protein backbone. PMID:21416162

Dependence of the critical temperature in overdoped copper oxides on superfluid density

NASA Astrophysics Data System (ADS)

Božović, I.; He, X.; Wu, J.; Bollinger, A. T.

2016-08-01

The physics of underdoped copper oxide superconductors, including the pseudogap, spin and charge ordering and their relation to superconductivity, is intensely debated. The overdoped copper oxides are perceived as simpler, with strongly correlated fermion physics evolving smoothly into the conventional Bardeen-Cooper-Schrieffer behaviour. Pioneering studies on a few overdoped samples indicated that the superfluid density was much lower than expected, but this was attributed to pair-breaking, disorder and phase separation. Here we report the way in which the magnetic penetration depth and the phase stiffness depend on temperature and doping by investigating the entire overdoped side of the La2-xSrxCuO4 phase diagram. We measured the absolute values of the magnetic penetration depth and the phase stiffness to an accuracy of one per cent in thousands of samples; the large statistics reveal clear trends and intrinsic properties. The films are homogeneous; variations in the critical superconducting temperature within a film are very small (less than one kelvin). At every level of doping the phase stiffness decreases linearly with temperature. The dependence of the zero-temperature phase stiffness on the critical superconducting temperature is generally linear, but with an offset; however, close to the origin this dependence becomes parabolic. This scaling law is incompatible with the standard Bardeen-Cooper-Schrieffer description.

Investigation on the effects of temperature dependency of material parameters on a thermoelastic loading problem

NASA Astrophysics Data System (ADS)

Kumar, Anil; Mukhopadhyay, Santwana

2017-08-01

The present work is concerned with the investigation of thermoelastic interactions inside a spherical shell with temperature-dependent material parameters. We employ the heat conduction model with a single delay term. The problem is studied by considering three different kinds of time-dependent temperature and stress distributions applied at the inner and outer surfaces of the shell. The problem is formulated by considering that the thermal properties vary as linear function of temperature that yield nonlinear governing equations. The problem is solved by applying Kirchhoff transformation along with integral transform technique. The numerical results of the field variables are shown in the different graphs to study the influence of temperature-dependent thermal parameters in various cases. It has been shown that the temperature-dependent effect is more prominent in case of stress distribution as compared to other fields and also the effect is significant in case of thermal shock applied at the two boundary surfaces of the spherical shell.

Temperature-dependent Refractive Index of Silicon and Germanium

NASA Technical Reports Server (NTRS)

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

2006-01-01

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

Temperature-dependent plastic hysteresis in highly confined polycrystalline Nb films

NASA Astrophysics Data System (ADS)

Waheed, S.; Hao, R.; Zheng, Z.; Wheeler, J. M.; Michler, J.; Balint, D. S.; Giuliani, F.

2018-02-01

In this study, the effect of temperature on the cyclic deformation behaviour of a confined polycrystalline Nb film is investigated. Micropillars encapsulating a thin niobium interlayer are deformed under cyclic axial compression at different test temperatures. A distinct plastic hysteresis is observed for samples tested at elevated temperatures, whereas negligible plastic hysteresis is observed for samples tested at room temperature. These results are interpreted using planar discrete dislocation plasticity incorporating slip transmission across grain boundaries. The effect of temperature-dependent grain boundary energy and dislocation mobility on dislocation penetration and, consequently, the size of plastic hysteresis is simulated to correlate with the experimental results. It is found that the decrease in grain boundary energy barrier caused by the increase in temperature does not lead to any appreciable change in the cyclic response. However, dislocation mobility significantly affects the size of plastic hysteresis, with high mobilities leading to a larger hysteresis. Therefore, it is postulated that the experimental observations are predominantly caused by an increase in dislocation mobility as the temperature is increased above the critical temperature of body-centred cubic niobium.

Temperature dependent Raman investigation of multiwall carbon nanotubes

NASA Astrophysics Data System (ADS)

Dilawar Sharma, Nita; Singh, Jasveer; Vijay, Aditi

2018-04-01

We report anomalous observations in our investigations of the temperature dependent Raman spectroscopic measurement of multiwall carbon nanotubes. The Micro-Raman spectra were recorded with the laser source having 514.5 nm wavelength and within the temperature range of 80-440 K. The major Raman bands, the G and D band, are observed at 1584 and 1348 cm-1, respectively, at ambient. The absence of the radial breathing mode confirms the multiwall nature of carbon nanotubes. It has been observed that with an increase in the temperature above 120 K, there is a shift in Raman bands towards the higher wave-number region. However, a drop in the G and D bands is observed from 80 to 120 K which was not observed for the second order band. Thereafter, all Raman modes exhibited mode hardening up to about 320 K followed by mild softening of the phonon modes. Linear temperature coefficients were found to have higher contribution to mode hardening as compared to higher order terms. Total anharmonicity estimation shows a predominant effect of the quasi-harmonic term as compared to the true anharmonic term.

Strong Temperature Dependence in the Reactivity of H 2 on RuO 2 (110)

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

Henderson, Michael A.; Dahal, Arjun; Dohnálek, Zdenek

2016-08-04

The ability of hydrogen to facilitate many types of heterogeneous catalysis starts with its adsorption. As such, understanding the temperature-dependence sticking of H2 is critical toward controlling and optimizing catalytic conditions in those cases where adsorption is rate-limiting. In this work, we examine the temperature-dependent sticking of H2/D2 to the clean RuO2(110) surface using the King & Wells molecular beam approach, temperature programmed desorption (TPD) and scanning tunneling microscopy (STM). We show that the sticking probability (molecular or dissociative) of H2/D2 on this surface is highly temperature-dependent, decreasing from ~0.4-0.5 below 25 K to effectively zero above 200 K. Bothmore » STM and TPD reveal that OH/OD formation is severely limited for adsorption temperatures above ~150 K. Previous literature reports of extensive surface hydroxylation from H2/D2 exposures at room temperature were most likely the result of inadvertent contamination brought about from dosing by chamber backfilling.« less

Temperature-dependent subunit exchange and chaperone-like activities of Hsp16.3, a small heat shock protein from Mycobacterium tuberculosis.

PubMed

Fu, Xinmiao; Chang, Zengyi

2004-04-02

Small heat shock proteins (sHsps) usually exist as oligomers that undergo dynamic oligomeric dissociation/re-association, with the dissociated oligomers as active forms to bind substrate proteins under heat shock conditions. In this study, however, we found that Hsp16.3, one sHsp from Mycobacterium tuberculosis, is able to sensitively modulate its chaperone-like activity in a range of physiological temperatures (from 25 to 37.5 degrees C) while its native oligomeric size is still maintained. Further analysis demonstrated that Hsp16.3 exposes higher hydrophobic surfaces upon temperatures increasing and that a large soluble complex between Hsp16.3 and substrate is formed only in the condition of heating temperature up to 35 and 37.5 degrees C. Structural analysis by fluorescence anisotropy showed that Hsp16.3 nonameric structure becomes more dynamic and variable at elevated temperatures. Moreover, subunit exchange between Hsp16.3 oligomers was found to occur faster upon temperatures increasing as revealed by fluorescence energy resonance transfer. These observations indicate that Hsp16.3 is able to modulate its chaperone activity by adjusting the dynamics of oligomeric dissociation/re-association process while maintaining its static oligomeric size unchangeable. A kinetic model is therefore proposed to explain the mechanism of sHsps-binding substrate proteins through oligomeric dissociation. The present study also implied that Hsp16.3 is at least capable of binding non-native proteins in vivo while expressing in the host organism that survives at 37 degrees C.

The temperature dependences of electromechanical properties of PLZT ceramics

NASA Astrophysics Data System (ADS)

Czerwiec, M.; Zachariasz, R.; Ilczuk, J.

2008-02-01

The mechanical and electrical properties in lanthanum modified lead zirconate-titanate ceramics of 5/50/50 and 10/50/50 were studied by mechanical loss Q - 1, Young's modulus E, electric permittivity ɛ and tangent of dielectric loss of angle tgδ measurements. The internal friction Q - 1 and Young modulus E measured from 290 K to 600 K shows that Curie temperature TC is located at 574 K and 435 K (1st cycle of heating) respectively for ceramic samples 5/50/50 and 10/50/50. The movement of TC in second cycle of heating to lower temperature (561 K for 5/50/50 and 420 K for 10/50/50) has been observed. Together with Q - 1 and E measurements, temperature dependences of ɛ=f(T) and tgδ=f(T) were determinated in temperature range from 300 K to 730 K. The values of TC obtained during ɛ and tgδ measurements were respectively: 560 K for 5/50/50 and 419 K for 10/50/50. These temperatures are almost as high as the temperatures obtained by internal friction Q - 1 measurements in second cycle of heating. In ceramic sample 10/50/50 the additional maximum on internal friction Q - 1 curve at the temperature 316 K was observed.

Linear dependence of surface expansion speed on initial plasma temperature in warm dense matter

DOE PAGES

Bang, Woosuk; Albright, Brian James; Bradley, Paul Andrew; ...

2016-07-12

Recent progress in laser-driven quasi-monoenergetic ion beams enabled the production of uniformly heated warm dense matter. Matter heated rapidly with this technique is under extreme temperatures and pressures, and promptly expands outward. While the expansion speed of an ideal plasma is known to have a square-root dependence on temperature, computer simulations presented here show a linear dependence of expansion speed on initial plasma temperature in the warm dense matter regime. The expansion of uniformly heated 1–100 eV solid density gold foils was modeled with the RAGE radiation-hydrodynamics code, and the average surface expansion speed was found to increase linearly withmore » temperature. The origin of this linear dependence is explained by comparing predictions from the SESAME equation-of-state tables with those from the ideal gas equation-of-state. In conclusion, these simulations offer useful insight into the expansion of warm dense matter and motivate the application of optical shadowgraphy for temperature measurement.« less

Temperature dependent electrical properties of rare-earth metal Er Schottky contact on p-type InP

NASA Astrophysics Data System (ADS)

Rao, L. Dasaradha; Reddy, N. Ramesha; Kumar, A. Ashok; Reddy, V. Rajagopal

2013-06-01

The current-voltage (I-V) characteristics of the Er/p-InP Schottky barrier diodes (SBDs) have been investigated in the temperature range of 300-400K in steps of 25K. The electrical parameters such as ideality factor (n) and zero-bias barrier height (Φbo) are found to be strongly temperature dependent. It is observed that ΦI-V decreases whereas n increases with decreasing temperature. The series resistance is also calculated from the forward I-V characteristics of Er/p-InP SBD and it is found to be strongly dependent on temperature. Further, the temperature dependence of energy distribution of interface state density (NSS) profiles is determined from the forward I-V measurements by taking into account the bias dependence of the effective barrier height and ideality factor. It is observed that the NSS values increase with a decrease in temperature.

Temperature Dependence of the Mechanical Properties of Equiatomic Solid Solution Alloys with FCC Crystal Structures

DOE PAGES

Wu, Zhenggang; Bei, Hongbin; Pharr, George M.; ...

2014-10-03

We found that compared to decades-old theories of strengthening in dilute solid solutions, the mechanical behavior of concentrated solid solutions is relatively poorly understood. A special subset of these materials includes alloys in which the constituent elements are present in equal atomic proportions, including the high-entropy alloys of recent interest. A unique characteristic of equiatomic alloys is the absence of “solvent” and “solute” atoms, resulting in a breakdown of the textbook picture of dislocations moving through a solvent lattice and encountering discrete solute obstacles. Likewise, to clarify the mechanical behavior of this interesting new class of materials, we investigate heremore » a family of equiatomic binary, ternary and quaternary alloys based on the elements Fe, Ni, Co, Cr and Mn that were previously shown to be single-phase face-centered cubic (fcc) solid solutions. The alloys were arc-melted, drop-cast, homogenized, cold-rolled and recrystallized to produce equiaxed microstructures with comparable grain sizes. Tensile tests were performed at an engineering strain rate of 10 -3 s -1 at temperatures in the range 77–673 K. Unalloyed fcc Ni was processed similarly and tested for comparison. The flow stresses depend to varying degrees on temperature, with some (e.g. NiCoCr, NiCoCrMn and FeNiCoCr) exhibiting yield and ultimate strengths that increase strongly with decreasing temperature, while others (e.g. NiCo and Ni) exhibit very weak temperature dependencies. Moreover, to better understand this behavior, the temperature dependencies of the yield strength and strain hardening were analyzed separately. Lattice friction appears to be the predominant component of the temperature-dependent yield stress, possibly because the Peierls barrier height decreases with increasing temperature due to a thermally induced increase of dislocation width. In the early stages of plastic flow (5–13% strain, depending on material), the temperature

Temperature Dependence of the Thermal Conductivity of Single Wall Carbon Nanotubes

NASA Technical Reports Server (NTRS)

Osman, Mohamed A.; Srivastava, Deepak

2000-01-01

The thermal conductivity of several single wall carbon nanotubes (CNT) has been calculated over a temperature range of 100-500 K using molecular dynamics simulations with Tersoff-Brenner potential for C-C interactions. In all cases, starting from similar values at 100K, thermal conductivities show a peaking behavior before falling off at higher temperatures. The peak position shifts to higher temperatures for nanotubes of larger diameter, and no significant dependence on the tube chirality is observed. It is shown that this phenomenon is due to onset of Umklapp scattering, which shifts to higher temperatures for nanotubes of larger diameter.

Diffractometric measurement of the temperature dependence of piezoelectric tensor in GMO monocrystal

NASA Astrophysics Data System (ADS)

Breczko, Teodor; Lempaszek, Andrzej

2007-04-01

Functional materials, of which an example is ferroelectric, ferroelastic monocrystal of molybdate (III) gadolinium (VI), are often used in the micro-motor operators (micro-servo motors) working in changeable environment conditions. Most frequently this change refers to temperature. That is why the important practical problem is the precise measurement of the value of piezoelectric tensor elements in dependence on the temperature of a particular monocrystal. In the presented article for this kind of measurements, the use of X-ray diffractometer has been shown. The advantage of the method presented is that, apart from precise dependence measurement between the temperature of a monocrystal and the value of piezoelectric tensor elements, it enables synchronous measurement of the value of thermal expansion tensor elements for a monocrystal.

Temperature Dependence of Smectic Liquid Crystals Mixed With Magnetic Nanoparticles

NASA Astrophysics Data System (ADS)

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

2012-02-01

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

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.

Extraction of temperature dependent electrical resistivity and thermal conductivity from silicon microwires self-heated to melting temperature

NASA Astrophysics Data System (ADS)

Bakan, Gokhan; Adnane, Lhacene; Gokirmak, Ali; Silva, Helena

2012-09-01

Temperature-dependent electrical resistivity, ρ(T), and thermal conductivity, k(T), of nanocrystalline silicon microwires self-heated to melt are extracted by matching simulated current-voltage (I-V) characteristics to experimental I-V characteristics. Electrical resistivity is extracted from highly doped p-type wires on silicon dioxide in which the heat losses are predominantly to the substrate and the self-heating depends mainly on ρ(T) of the wires. The extracted ρ(T) decreases from 11.8 mΩ cm at room-temperature to 5.2 mΩ cm at 1690 K, in reasonable agreement with the values measured up to ˜650 K. Electrical resistivity and thermal conductivity are extracted from suspended highly doped n-type silicon wires in which the heat losses are predominantly through the wires. In this case, measured ρ(T) (decreasing from 20.5 mΩ cm at room temperature to 12 mΩ cm at 620 K) is used to extract ρ(T) at higher temperatures (decreasing to 1 mΩ cm at 1690 K) and k(T) (decreasing from 30 W m-1 K-1 at room temperature to 20 W m-1 K-1 at 1690 K). The method is tested by using the extracted parameters to model wires with different dimensions. The experimental and simulated I-V curves for these wires show good agreement up to high voltage and temperature levels. This technique allows extraction of the electrical resistivity and thermal conductivity up to very high temperatures from self-heated microstructures.

Temperature-dependent thermal properties of ex vivo liver undergoing thermal ablation.

PubMed

Guntur, Sitaramanjaneya Reddy; Lee, Kang Il; Paeng, Dong-Guk; Coleman, Andrew John; Choi, Min Joo

2013-10-01

Thermotherapy uses a heat source that raises temperatures in the target tissue, and the temperature rise depends on the thermal properties of the tissue. Little is known about the temperature-dependent thermal properties of tissue, which prevents us from accurately predicting the temperature distribution of the target tissue undergoing thermotherapy. The present study reports the key thermal parameters (specific heat capacity, thermal conductivity and heat diffusivity) measured in ex vivo porcine liver while being heated from 20 ° C to 90 ° C and then naturally cooled down to 20 ° C. The study indicates that as the tissue was heated, all the thermal parameters resulted in plots with asymmetric quasi-parabolic curves with temperature, being convex downward with their minima at the turning temperature of 35-40 ° C. The largest change was observed for thermal conductivity, which decreased by 9.6% from its initial value (at 20 ° C) at the turning temperature (35 ° C) and rose by 45% at 90 ° C from its minimum (at 35 ° C). The minima were 3.567 mJ/(m(3) ∙ K) for specific heat capacity, 0.520 W/(m.K) for thermal conductivity and 0.141 mm(2)/s for thermal diffusivity. The minimum at the turning temperature was unique, and it is suggested that it be taken as a characteristic value of the thermal parameter of the tissue. On the other hand, the thermal parameters were insensitive to temperature and remained almost unchanged when the tissue cooled down, indicating that their variations with temperature were irreversible. The rate of the irreversible rise at 35 ° C was 18% in specific heat capacity, 40% in thermal conductivity and 38.3% in thermal diffusivity. The study indicates that the key thermal parameters of ex vivo porcine liver vary largely with temperature when heated, as described by asymmetric quasi-parabolic curves of the thermal parameters with temperature, and therefore, substantial influence on the temperature distribution of the tissue undergoing

Energetic radiation influence on temperature dependency of Brillouin frequency in optical fibers

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

Pheron, X.; Ouerdane, Y.; Delepine-Lesoille, S.

We present a post mortem study of the influence of energetic radiation on optical fiber Brillouin sensors, both Brillouin spectrum and its temperature dependency in two different fibers, a photosensitive optical fiber and a SMF28. The target application is nuclear wastes repository monitoring where optical fiber Brillouin sensors might be exposed to energetic radiation. UV exposure induced optical losses, Brillouin frequency shifts up to 28 MHz and even a variation of the temperature dependency. The photosensitive optical fiber resulted more sensitive than SMF28{sup TM}. (authors)

On the effect of ballistic overflow on the temperature dependence of the quantum efficiency of InGaN/GaN multiple quantum well light-emitting diodes

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

Prudaev, I. A., E-mail: funcelab@gmail.com; Kopyev, V. V.; Romanov, I. S.

The dependences of the quantum efficiency of InGaN/GaN multiple quantum well light-emitting diodes on the temperature and excitation level are studied. The experiment is performed for two luminescence excitation modes. A comparison of the results obtained during photo- and electroluminescence shows an additional (to the loss associated with Auger recombination) low-temperature loss in the high-density current region. This causes inversion of the temperature dependence of the quantum efficiency at temperatures lower than 220–300 K. Analysis shows that the loss is associated with electron leakage from the light-emitting-diode active region. The experimental data are explained using the ballistic-overflow model. The simulationmore » results are in qualitative agreement with the experimental dependences of the quantum efficiency on temperature and current density.« less

Brassinosteroid signaling-dependent root responses to prolonged elevated ambient temperature.

PubMed

Martins, Sara; Montiel-Jorda, Alvaro; Cayrel, Anne; Huguet, Stéphanie; Roux, Christine Paysant-Le; Ljung, Karin; Vert, Grégory

2017-08-21

Due to their sessile nature, plants have to cope with and adjust to their fluctuating environment. Temperature elevation stimulates the growth of Arabidopsis aerial parts. This process is mediated by increased biosynthesis of the growth-promoting hormone auxin. How plant roots respond to elevated ambient temperature is however still elusive. Here we present strong evidence that temperature elevation impinges on brassinosteroid hormone signaling to alter root growth. We show that elevated temperature leads to increased root elongation, independently of auxin or factors known to drive temperature-mediated shoot growth. We further demonstrate that brassinosteroid signaling regulates root responses to elevated ambient temperature. Increased growth temperature specifically impacts on the level of the brassinosteroid receptor BRI1 to downregulate brassinosteroid signaling and mediate root elongation. Our results establish that BRI1 integrates temperature and brassinosteroid signaling to regulate root growth upon long-term changes in environmental conditions associated with global warming.Moderate heat stimulates the growth of Arabidopsis shoots in an auxin-dependent manner. Here, Martins et al. show that elevated ambient temperature modifies root growth by reducing the BRI1 brassinosteroid-receptor protein level and downregulating brassinosteroid signaling.

Review of temperature dependence of thermal properties, dielectric properties, and perfusion of biological tissues at hyperthermic and ablation temperatures.

PubMed

Rossmanna, Christian; Haemmerich, Dieter

2014-01-01

The application of supraphysiological temperatures (>40°C) to biological tissues causes changes at the molecular, cellular, and structural level, with corresponding changes in tissue function and in thermal, mechanical and dielectric tissue properties. This is particularly relevant for image-guided thermal treatments (e.g. hyperthermia and thermal ablation) delivering heat via focused ultrasound (FUS), radiofrequency (RF), microwave (MW), or laser energy; temperature induced changes in tissue properties are of relevance in relation to predicting tissue temperature profile, monitoring during treatment, and evaluation of treatment results. This paper presents a literature survey of temperature dependence of electrical (electrical conductivity, resistivity, permittivity) and thermal tissue properties (thermal conductivity, specific heat, diffusivity). Data of soft tissues (liver, prostate, muscle, kidney, uterus, collagen, myocardium and spleen) for temperatures between 5 to 90°C, and dielectric properties in the frequency range between 460 kHz and 3 GHz are reported. Furthermore, perfusion changes in tumors including carcinomas, sarcomas, rhabdomyosarcoma, adenocarcinoma and ependymoblastoma in response to hyperthmic temperatures up to 46°C are presented. Where appropriate, mathematical models to describe temperature dependence of properties are presented. The presented data is valuable for mathematical models that predict tissue temperature during thermal therapies (e.g. hyperthermia or thermal ablation), as well as for applications related to prediction and monitoring of temperature induced tissue changes.

Review of temperature dependence of thermal properties, dielectric properties, and perfusion of biological tissues at hyperthermic and ablation temperatures

PubMed Central

Rossmann, Christian; Haemmerich, Dieter

2016-01-01

The application of supraphysiological temperatures (>40°C) to biological tissues causes changes at the molecular, cellular, and structural level, with corresponding changes in tissue function and in thermal, mechanical and dielectric tissue properties. This is particularly relevant for image-guided thermal treatments (e.g. hyperthermia and thermal ablation) delivering heat via focused ultrasound (FUS), radiofrequency (RF), microwave (MW), or laser energy; temperature induced changes in tissue properties are of relevance in relation to predicting tissue temperature profile, monitoring during treatment, and evaluation of treatment results. This paper presents a literature survey of temperature dependence of electrical (electrical conductivity, resistivity, permittivity) and thermal tissue properties (thermal conductivity, specific heat, diffusivity). Data of soft tissues (liver, prostate, muscle, kidney, uterus, collagen, myocardium and spleen) for temperatures between 5 to 90°C, and dielectric properties in the frequency range between 460 kHz and 3 GHz are reported. Furthermore, perfusion changes in tumors including carcinomas, sarcomas, rhabdomyosarcoma, adenocarcinoma and ependymoblastoma in response to hyperthmic temperatures up to 46°C are presented. Where appropriate, mathematical models to describe temperature dependence of properties are presented. The presented data is valuable for mathematical models that predict tissue temperature during thermal therapies (e.g. hyperthermia or thermal ablation), as well as for applications related to prediction and monitoring of temperature induced tissue changes. PMID:25955712

Temperature dependence of resonant secondary emission in NaNO 2: Spectral behavior

NASA Astrophysics Data System (ADS)

Kato, Riso; Kawaguchi, Yoshizo; Ashida, Masaaki

1990-05-01

Spectral behavior of resonant secondary emission in NaNO 2 has been investigated in the temperature range from 2 to 30 K under the excitation near the v00 line of the lowest singlet absorption. With increasing temperature, luminescence lines separated from multiple-order Raman lines become detectable even under the excitation with the off-resonance energy Δ c ≳ 13 cm -1. The intensity of the luminescence line IL( T) increases with temperature in proportion to the phonon number n( hvp, T) in the temperature range T ≲ Δ c/ k, while it increases more steeply in the range T ≳ Δ c/ k. The temperature dependence of IL( T) is ascribed to the increase in the luminescence from the v00 level after the one-phonon assisted transition to the level induced by the off-resonant incident light. The intensity of the Raman line IR( T) decreases gradually in 2-12 K range and shows rapid drop above 12 K. The temperature dependence of IR( T) is ascribed to the dephasing of the intermediate state due to the two-phonon interaction with the reservoir.

The temperature dependence of intermediate range oxygen-oxygen correlations in liquid water

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

Schlesinger, Daniel; Pettersson, Lars G. M., E-mail: Lars.Pettersson@fysik.su.se; Wikfeldt, K. Thor

We analyze the recent temperature dependent oxygen-oxygen pair-distribution functions from experimental high-precision x-ray diffraction data of bulk water by Skinner et al. [J. Chem. Phys. 141, 214507 (2014)] with particular focus on the intermediate range where small, but significant, correlations are found out to 17 Å. The second peak in the pair-distribution function at 4.5 Å is connected to tetrahedral coordination and was shown by Skinner et al. to change behavior with temperature below the temperature of minimum isothermal compressibility. Here we show that this is associated also with a peak growing at 11 Å which strongly indicates a collectivemore » character of fluctuations leading to the enhanced compressibility at lower temperatures. We note that the peak at ∼13.2 Å exhibits a temperature dependence similar to that of the density with a maximum close to 277 K or 4 °C. We analyze simulations of the TIP4P/2005 water model in the same manner and find excellent agreement between simulations and experiment albeit with a temperature shift of ∼20 K.« less

The temperature dependence of intermediate range oxygen-oxygen correlations in liquid water

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

Schlesinger, Daniel; Wikfeldt, K. Thor; Skinner, Lawrie B.

Here, we analyze the recent temperature dependent oxygen-oxygen pair-distribution functions from experimental high-precision x-ray diffraction data of bulk water by Skinner et al. [J. Chem. Phys. 141, 214507 (2014)] with particular focus on the intermediate range where small, but significant, correlations are found out to 17 Å. The second peak in the pair-distribution function at 4.5 Å is connected to tetrahedral coordination and was shown by Skinner et al. to change behavior with temperature below the temperature of minimum isothermal compressibility. Here we show that this is associated also with a peak growing at 11 Å which strongly indicates amore » collective character of fluctuations leading to the enhanced compressibility at lower temperatures. We note that the peak at ~13.2 Å exhibits a temperature dependence similar to that of the density with a maximum close to 277 K or 4 °C. We analyze simulations of the TIP4P/2005 water model in the same manner and find excellent agreement between simulations and experiment albeit with a temperature shift of ~20 K.« less

The temperature dependence of intermediate range oxygen-oxygen correlations in liquid water

DOE PAGES

Schlesinger, Daniel; Wikfeldt, K. Thor; Skinner, Lawrie B.; ...

2016-08-25

Here, we analyze the recent temperature dependent oxygen-oxygen pair-distribution functions from experimental high-precision x-ray diffraction data of bulk water by Skinner et al. [J. Chem. Phys. 141, 214507 (2014)] with particular focus on the intermediate range where small, but significant, correlations are found out to 17 Å. The second peak in the pair-distribution function at 4.5 Å is connected to tetrahedral coordination and was shown by Skinner et al. to change behavior with temperature below the temperature of minimum isothermal compressibility. Here we show that this is associated also with a peak growing at 11 Å which strongly indicates amore » collective character of fluctuations leading to the enhanced compressibility at lower temperatures. We note that the peak at ~13.2 Å exhibits a temperature dependence similar to that of the density with a maximum close to 277 K or 4 °C. We analyze simulations of the TIP4P/2005 water model in the same manner and find excellent agreement between simulations and experiment albeit with a temperature shift of ~20 K.« less

The effects of temperature dependent recombination rates on performance of InGaN/GaN blue superluminescent light emitting diodes

NASA Astrophysics Data System (ADS)

Moslehi Milani, N.; Mohadesi, V.; Asgari, A.

2015-07-01

The effects of temperature dependent radiative and nonradiative recombination (Shockley-Read-Hall, spontaneous radiative, and Auger coefficients) on the spectral and power characteristics of a blue multiple quantum well (MQW) superluminescent light emitting diode (SLD or SLED) have been studied. The study is based on the rate equations model, where three rate equations corresponding to MQW active region, separate confinement heterostructure (SCH) layer, and spectral density of optical power are solved self-consistently with no k-selection energy dependent gain and quasi-Fermi level functions at steady state. We have taken into account the temperature effects on Shockley-Read-Hall (SRH), spontaneous radiative, and Auger recombination in the rate equations and have investigated the effects of temperature rising from 300 K to 375 K at a fixed current density. We examine this procedure for a moderate current density and interpret the spectral radiation power and light output power diagrams. The investigation reveals that the main loss due to temperature is related to Auger coefficient.

Temperature Dependence of Nonelectrolyte Permeation across Red Cell Membranes

PubMed Central

Galey, W. R.; Owen, J. D.; Solomon, A. K.

1973-01-01

The temperature dependence of permeation across human red cell membranes has been determined for a series of hydrophilic and lipophilic solutes, including urea and two methyl substituted derivatives, all the straight-chain amides from formamide through valeramide and the two isomers, isobutyramide and isovaleramide. The temperature coefficient for permeation by all the hydrophilic solutes is 12 kcal mol-1 or less, whereas that for all the lipophilic solutes is 19 kcal mol-1 or greater. This difference is consonant with the view that hydrophilic molecules cross the membrane by a path different from that taken by the lipophilic ones. The thermodynamic parameters associated with lipophile permeation have been studied in detail. ΔG is negative for adsorption of lipophilic amides onto an oil-water interface, whereas it is positive for transfer of the polar head from the aqueous medium to bulk lipid solvent. Application of absolute reaction rate theory makes it possible to make a clear distinction between diffusion across the water-red cell membrane interface and diffusion within the membrane. Diffusion coefficients and apparent activation enthalpies and entropies have been computed for each process. Transfer of the polar head from the solvent into the interface is characterized by ΔG ‡ = 0 kcal mol-1 and ΔS ‡ negative, whereas both of these parameters have large positive values for diffusion within the membrane. Diffusion within the membrane is similar to what is expected for diffusion through a highly associated viscous fluid. PMID:4708405

Temperature Dependence of Faraday Effect-Induced Bias Error in a Fiber Optic Gyroscope

PubMed Central

Li, Xuyou; Guang, Xingxing; Xu, Zhenlong; Li, Guangchun

2017-01-01

Improving the performance of interferometric fiber optic gyroscope (IFOG) in harsh environments, such as magnetic field and temperature field variation, is necessary for its practical applications. This paper presents an investigation of Faraday effect-induced bias error of IFOG under varying temperature. Jones matrix method is utilized to formulize the temperature dependence of Faraday effect-induced bias error. Theoretical results show that the Faraday effect-induced bias error changes with the temperature in the non-skeleton polarization maintaining (PM) fiber coil. This phenomenon is caused by the temperature dependence of linear birefringence and Verdet constant of PM fiber. Particularly, Faraday effect-induced bias errors of two polarizations always have opposite signs that can be compensated optically regardless of the changes of the temperature. Two experiments with a 1000 m non-skeleton PM fiber coil are performed, and the experimental results support these theoretical predictions. This study is promising for improving the bias stability of IFOG. PMID:28880203

Temperature Dependence of Faraday Effect-Induced Bias Error in a Fiber Optic Gyroscope.

PubMed

Li, Xuyou; Liu, Pan; Guang, Xingxing; Xu, Zhenlong; Guan, Lianwu; Li, Guangchun

2017-09-07

Improving the performance of interferometric fiber optic gyroscope (IFOG) in harsh environments, such as magnetic field and temperature field variation, is necessary for its practical applications. This paper presents an investigation of Faraday effect-induced bias error of IFOG under varying temperature. Jones matrix method is utilized to formulize the temperature dependence of Faraday effect-induced bias error. Theoretical results show that the Faraday effect-induced bias error changes with the temperature in the non-skeleton polarization maintaining (PM) fiber coil. This phenomenon is caused by the temperature dependence of linear birefringence and Verdet constant of PM fiber. Particularly, Faraday effect-induced bias errors of two polarizations always have opposite signs that can be compensated optically regardless of the changes of the temperature. Two experiments with a 1000 m non-skeleton PM fiber coil are performed, and the experimental results support these theoretical predictions. This study is promising for improving the bias stability of IFOG.

Corresponding states correlation for temperature dependent surface tension of normal saturated liquids

NASA Astrophysics Data System (ADS)

Yi, Huili; Tian, Jianxiang

2014-07-01

A new simple correlation based on the principle of corresponding state is proposed to estimate the temperature-dependent surface tension of normal saturated liquids. The correlation is a linear one and strongly stands for 41 saturated normal liquids. The new correlation requires only the triple point temperature, triple point surface tension and critical point temperature as input and is able to represent the experimental surface tension data for these 41 saturated normal liquids with a mean absolute average percent deviation of 1.26% in the temperature regions considered. For most substances, the temperature covers the range from the triple temperature to the one beyond the boiling temperature.

Temperature dependence of the isotope chemistry of the heavy elements.

PubMed Central

Bigeleisen, J

1996-01-01

The temperature coefficient of equilibrium isotope fractionation in the heavy elements is shown to be larger at high temperatures than that expected from the well-studied vibrational isotope effects. The difference in the isotopic behavior of the heavy elements as compared with the light elements is due to the large nuclear isotope field shifts in the heavy elements. The field shifts introduce new mechanisms for maxima, minima, crossovers, and large mass-independent isotope effects in the isotope chemistry of the heavy elements. The generalizations are illustrated by the temperature dependence of the isotopic fractionation in the redox reaction between U(VI) and U(IV) ions. PMID:8790340

(abstract) Ulysses Solar Wind Ion Temperatures: Radial, Latitudinal, and Dynamical Dependencies

NASA Technical Reports Server (NTRS)

Goldstein, B. E.; Smith, E. J.; Gosling, J. T.; McComas, D. J.; Balogh, A.

1996-01-01

Observations of the Ulysses SWOOPS plasma experiment are used to determine the dependencies of solar wind ion temperatures upon radial distance, speed, and other parameters, and to estimate solar wind heating. Comparisons with three dimensional temperature estimates determined from the ion spectra by a least squares fitting program will be provided (only small samples of data have been reduced with this program).

Temperature dependence of carrier capture by defects in gallium arsenide

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

Wampler, William R.; Modine, Normand A.

2015-08-01

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

Charge transport and activation energy of amorphous silicon carbide thin film on quartz at elevated temperature

NASA Astrophysics Data System (ADS)

Dinh, Toan; Viet Dao, Dzung; Phan, Hoang-Phuong; Wang, Li; Qamar, Afzaal; Nguyen, Nam-Trung; Tanner, Philip; Rybachuk, Maksym

2015-06-01

We report on the temperature dependence of the charge transport and activation energy of amorphous silicon carbide (a-SiC) thin films grown on quartz by low-pressure chemical vapor deposition. The electrical conductivity as characterized by the Arrhenius rule was found to vary distinctly under two activation energy thresholds of 150 and 205 meV, corresponding to temperature ranges of 300 to 450 K and 450 to 580 K, respectively. The a-SiC/quartz system displayed a high temperature coefficient of resistance ranging from -4,000 to -16,000 ppm/K, demonstrating a strong feasibility of using this material for highly sensitive thermal sensing applications.

Low and moderate photosynthetically active radiation affects the flavonol glycosides and hydroxycinnamic acid derivatives in kale (Brassica oleracea var. sabellica) dependent on two low temperatures.

PubMed

Neugart, Susanne; Fiol, Michaela; Schreiner, Monika; Rohn, Sascha; Zrenner, Rita; Kroh, Lothar W; Krumbein, Angelika

2013-11-01

Kale (Brassica oleracea var. sabellica) contains a large number of naturally occurring structurally different non-acylated and acylated flavonol glycosides as well as hydroxycinnamic acid derivatives. The objective of this study was to determine the effect of low and moderate photosynthetic active radiation (PAR) and how these levels interact with low temperature in these phenolic compounds. Juvenile kale plants were treated with PAR levels from 200 to 800 μmol m(-2) s(-1) at 5 and 10 °C under defined conditions in climate chambers. Of the investigated 20 compounds, 11 and 17 compounds were influenced by PAR and temperature, respectively. In addition, an interaction between PAR and temperature was found for eight compounds. The response of the phenolic compounds to PAR was structure-dependent. While quercetin triglycosides increased with higher PAR at 5 and 10 °C, the kaempferol triglycosides exhibited the highest concentrations at 400 μmol m(-2) s(-1). In contrast, kaempferol diglycosides exhibited the highest concentrations at increased PAR levels of 600 and 800 μmol m(-2) s(-1) at 10 °C. However, key genes of flavonol biosynthesis were influenced by temperature but remained unaffected by PAR. Furthermore, there was no interaction between the PAR level and the low temperature in the response of hydroxycinnamic acid derivatives in kale with the exception of caffeoylquinic acid, which decreased with higher PAR levels of 600 and 800 μmol m(-2) s(-1) and at a lower temperature. In conclusion, PAR and its interaction with temperature could be a suitable tool for modifying the profile of phenolic compounds. Copyright © 2013 Elsevier Masson SAS. All rights reserved.

Temperature-dependent sorption of naphthalene, phenanthrene, and pyrene to low organic carbon aquifer sediments

USGS Publications Warehouse

Piatt, Joseph J.; Backhus, Debera A.; Capel, Paul D.; Eisenreich, Steven J.

1996-01-01

Sorption experiments were conducted with naphthalene, phenanthrene, and pyrene on low organic carbon sediments at 4 and 26 °C using batch and column techniques. Experimental controls ensured the absence of biologic and photolytic activity and colloid-free solution supernatants. Equilibrium distribution coefficients (Kd) increased 1.1−1.6 times with a decrease in temperature of 22 °C. Fraction instantaneous sorption (F) values did not change significantly with a decrease in temperature of 22 °C. Desorption rate constants (k2) decreased 1.2−2.6 times with a decrease in temperature of 22 °C. Times to equilibrium were at least 40 h. The magnitude of observed Kd and k2 values and the effect of temperature on Kd (e.g., low enthalpy of sorption) are consistent with sorbate partitioning between the aqueous phase and small amounts of organic matter (foc = 0.02%) on the sediments. The temperature dependence of Kd and k2 may be small as compared to the effects of heterogeneities in field-scale aquifer systems. Thus, thermal gradients may not be of major importance in most saturated subsurface regimes when predicting solute transport. However, aquifer remediation pump-and-treat times could be decreased because increased temperature decreases both retardation and tailing.

Temperature-dependent elastic anisotropy and mesoscale deformation in a nanostructured ferritic alloy

DOE PAGES

Stoica, G. M.; Stoica, A. D.; Miller, M. K.; ...

2014-10-10

Nanostructured ferritic alloys (NFA) are a new class of ultrafine-grained oxide dispersion-strengthened steels, promising for service in extreme environments of high temperature and high irradiation in the next-generation of nuclear reactors. This is owing to the remarkable stability of their complex microstructures containing a high density of Y-Ti-O nanoclusters within grains and along the grain boundaries. While nanoclusters have been recognized to be the primary contributor to the exceptional resistance to irradiation and high-temperature creep, very little is known about the mechanical roles of the polycrystalline grains that constitute the bulk ferritic matrix. Here we report the mesoscale characterization ofmore » anisotropic responses of the ultrafine NFA grains to tensile stresses at various temperatures using the state-of-the-art in situ neutron diffraction. We show the first experimental determination of temperature-dependent single-crystal elastic constants for the NFA, and reveal a strong temperature-dependent elastic anisotropy due to a sharp decrease in the shear stiffness constant [c'=(c_11-c_12)/2] when a critical temperature ( T_c ) is approached, indicative of elastic softening and instability of the ferritic matrix. We also show, from anisotropy-induced intergranular strain/stress accumulations, that a common dislocation slip mechanism operates at the onset of yielding for low temperatures, while there is a deformation crossover from low-temperature lattice hardening to high temperature lattice softening in response to extensive plastic deformation.« less

Some like it hot, some like it cold: Temperature dependent biotechnological applications and improvements in extremophilic enzymes.

PubMed

Siddiqui, Khawar Sohail

2015-12-01

The full biotechnological exploitation of enzymes is still hampered by their low activity, low stability and high cost. Temperature-dependent catalytic properties of enzymes are a key to efficient and cost-effective translation to commercial applications. Organisms adapted to temperature extremes are a rich source of enzymes with broad ranging thermal properties which, if isolated, characterized and their structure-function-stability relationship elucidated, could underpin a variety of technologies. Enzymes from thermally-adapted organisms such as psychrophiles (low-temperature) and thermophiles (high-temperature) are a vast natural resource that is already under scrutiny for their biotechnological potential. However, psychrophilic and thermophilic enzymes show an activity-stability trade-off that necessitates the use of various genetic and chemical modifications to further improve their properties to suit various industrial applications. This review describes in detail the properties and biotechnological applications of both cold-adapted and thermophilic enzymes. Furthermore, the review critically examines ways to improve their value for biotechnology, concluding by proposing an integrated approach involving thermally-adapted, genetically and magnetically modified enzymes to make biocatalysis more efficient and cost-effective. Copyright © 2015 Elsevier Inc. All rights reserved.

Phonon focusing and temperature dependences of thermal conductivity of silicon nanofilms

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

Kuleyev, I. I., E-mail: kuleev@imp.uran.ru; Bakharev, S. M.; Kuleyev, I. G.

2015-04-15

The effect of phonon focusing on the anisotropy and temperature dependences of the thermal conductivities of silicon nanofilms is analyzed using the three-mode Callaway model. The orientations of the film planes and the directions of the heat flux for maximal or minimal heat removal from silicon chip elements at low temperatures, as well as at room temperature, are determined. It is shown that in the case of diffuse reflection of phonons from the boundaries, the plane with the (100) orientation exhibits the lowest scattering ability (and the highest thermal conductivity), while the plane with the (111) orientation is characterized bymore » the highest scattering ability (and the lowest thermal conductivity). The thermal conductivity of wide films is determined to a considerable extent by the orientation of the film plane, while for nanowires with a square cross section, the thermal conductivity is mainly determined by the direction of the heat flux. The effect of elastic energy anisotropy on the dependences of the thermal conductivity on the geometrical parameters of films is analyzed. The temperatures of transition from boundary scattering to bulk relaxation mechanisms are determined.« less

Evaluation of molecular volume change of block copolymer depending on temperature: A SANS study

DOE PAGES

Kim, Tae-Hwan; Do, Changwoo; Han, Young-Soo

2017-12-24

Amphiphilic Pluronic triblock copolymers form various self-assembled structures such as sphere, cylinder, lamellae and so on, depending on temperature, leading to the increase of hydrophobicity of block copolymers. However, the effective molecular volume change of the block copolymer has not been fully exploited yet, when temperature increases. Here in this paper, we have investigated the effective molecular volume change of the block copolymer upon heating by using the contrast variation small angle neutron scattering. The scattering length densities (SLDs) of the block copolymer were experimentally obtained from the neutron scattering contrast variation method between the solvent and the block copolymermore » at varying temperature. Even though the SLD, which is the intrinsic property of the material, should not be changed by temperature elevation, it was dependent on temperature, indicating that the molecular volume is changed. Therefore, we obtained the increase rate of the molecular volume change of the block copolymer (the effective molecular volume change) from the comparison of the calculated SLD and the standard SLD, which is evaluated by plotting the SANS intensity at the first order Bragg peak as the function of temperature at each volume fraction of D 2O and H 2O that is about 25.5%–51.3% depending on temperature.« less

Evaluation of molecular volume change of block copolymer depending on temperature: A SANS study

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

Kim, Tae-Hwan; Do, Changwoo; Han, Young-Soo

Amphiphilic Pluronic triblock copolymers form various self-assembled structures such as sphere, cylinder, lamellae and so on, depending on temperature, leading to the increase of hydrophobicity of block copolymers. However, the effective molecular volume change of the block copolymer has not been fully exploited yet, when temperature increases. Here in this paper, we have investigated the effective molecular volume change of the block copolymer upon heating by using the contrast variation small angle neutron scattering. The scattering length densities (SLDs) of the block copolymer were experimentally obtained from the neutron scattering contrast variation method between the solvent and the block copolymermore » at varying temperature. Even though the SLD, which is the intrinsic property of the material, should not be changed by temperature elevation, it was dependent on temperature, indicating that the molecular volume is changed. Therefore, we obtained the increase rate of the molecular volume change of the block copolymer (the effective molecular volume change) from the comparison of the calculated SLD and the standard SLD, which is evaluated by plotting the SANS intensity at the first order Bragg peak as the function of temperature at each volume fraction of D 2O and H 2O that is about 25.5%–51.3% depending on temperature.« less

Cannibalism by damselflies increases with rising temperature

PubMed Central

Kirk, Devin; Shea, Dylan

2017-01-01

Trophic interactions are likely to change under climate warming. These interactions can be altered directly by changing consumption rates, or indirectly by altering growth rates and size asymmetries among individuals that in turn affect feeding. Understanding these processes is particularly important for intraspecific interactions, as direct and indirect changes may exacerbate antagonistic interactions. We examined the effect of temperature on activity rate, growth and intraspecific size asymmetries, and how these temperature dependencies affected cannibalism in Lestes congener, a damselfly with marked intraspecific variation in size. Temperature increased activity rates and exacerbated differences in body size by increasing growth rates. Increased activity and changes in body size interacted to increase cannibalism at higher temperatures. We argue that our results are likely to be general to species with life-history stages that vary in their temperature dependencies, and that the effects of climate change on communities may depend on the temperature dependencies of intraspecific interactions. PMID:28515331

Cannibalism by damselflies increases with rising temperature.

PubMed

Start, Denon; Kirk, Devin; Shea, Dylan; Gilbert, Benjamin

2017-05-01

Trophic interactions are likely to change under climate warming. These interactions can be altered directly by changing consumption rates, or indirectly by altering growth rates and size asymmetries among individuals that in turn affect feeding. Understanding these processes is particularly important for intraspecific interactions, as direct and indirect changes may exacerbate antagonistic interactions. We examined the effect of temperature on activity rate, growth and intraspecific size asymmetries, and how these temperature dependencies affected cannibalism in Lestes congener , a damselfly with marked intraspecific variation in size. Temperature increased activity rates and exacerbated differences in body size by increasing growth rates. Increased activity and changes in body size interacted to increase cannibalism at higher temperatures. We argue that our results are likely to be general to species with life-history stages that vary in their temperature dependencies, and that the effects of climate change on communities may depend on the temperature dependencies of intraspecific interactions. © 2017 The Author(s).

Spatial organization and time dependence of Jupiter's tropospheric temperatures, 1980-1993

NASA Technical Reports Server (NTRS)

Orton, Glenn S.; Friedson, A. James; Yanamandra-Fisher, Padmavati A.; Caldwell, John; Hammel, Heidi B.; Baines, Kevin H.; Bergstralh, Jay T.; Martin, Terry Z.; West, Robert A.; Veeder, Glenn J., Jr.

1994-01-01

The spatial organization and time dependence of Jupiter's temperature near 250-millibar pressure were measured through a jovian year by imaging thermal emission at 18 micrometers. The temperature field is influenced by seasonal radiative forcing, and its banded organization is closely correlated with the visible cloud field. Evidence was found for a quasi-periodic oscillation of temperatures in the Equatorial Zone, a correlation between tropospheric and stratospheric waves in the North Equatorial Belt, and slowly moving thermal features in the North and South Equatorial Belts. There appears to be no common relation between temporal changes of temperature and changes in the visual albedo of the various axisymmetric bands.

Temperature-dependent vibrational spectroscopy to study order-disorder transitions in charge transfer complexes

NASA Astrophysics Data System (ADS)

Isaac, Rohan; Goetz, Katelyn P.; Roberts, Drew; Jurchescu, Oana D.; McNeil, L. E.

2018-02-01

Charge-transfer (CT) complexes are a promising class of materials for the semiconductor industry because of their versatile properties. This class of compounds shows a variety of phase transitions, which are of interest because of their potential impact on the electronic characteristics. Here temperature-dependent vibrational spectroscopy is used to study structural phase transitions in a set of organic CT complexes. Splitting and broadening of infrared-active phonons in the complex formed between pyrene and pyromellitic dianhydride (PMDA) confirm the structural transition is of the order-disorder type and complement previous x-ray diffraction (XRD) results. We show that this technique is a powerful tool to characterize transitions, and apply it to a range of binary CT complexes composed of polyaromatic hyrdocarbons (anthracene, perylene, phenanthrene, pyrene, and stilbene) and PMDA. We extend the understanding of transitions in perylene-PMDA and pyrene-PMDA, and show that there are no order-disorder transitions present in anthracene-PMDA, stilbene-PMDA and phenanthrene-PMDA in the temperature range investigated here.

Transition from Arrhenius to non-Arrhenius temperature dependence of structural relaxation time in glass-forming liquids: continuous versus discontinuous scenario.

PubMed

Popova, V A; Surovtsev, N V

2014-09-01

The temperature dependences of α relaxation time τ(α)(T) of three glass-forming liquids (salol, o-terphenyl, and α-picoline) were investigated by a depolarized light scattering technique. A detailed description of τ(α)(T) near T(A), the temperature of the transition from the Arrhenius law at high temperatures to a non-Arrhenius behavior of τ(α)(T) at lower temperatures, was done. It was found that this transition is quite sharp. If the transition is described as switching from the Arrhenius law to the Vogel-Fulcher-Tammann law, it occurs within the temperature range of about 15 K or less. Most of the known expressions for τ(α)(T) cannot describe this sharp transition. Our analysis revealed that this transition can be described either as a discontinuous transition in the spirit of the frustration-limited domain theory [D. Kivelson, G. Tarjus, X. Zhao, and S. A. Kivelson, Phys. Rev. E 53, 751 (1996)], implying a phase transition, or by a phenomenological expression recently suggested [B. Schmidtke, N. Petzold, R. Kahlau, M. Hofmann, and E. A. Rössler, Phys. Rev. E 86, 041507 (2012)], where the activation energy includes the term depending exponentially on temperature.

Temperature-dependent mid-IR absorption spectra of gaseous hydrocarbons

NASA Astrophysics Data System (ADS)

Klingbeil, Adam E.; Jeffries, Jay B.; Hanson, Ronald K.

2007-10-01

Quantitative mid-IR absorption spectra (2500 3400 cm-1) for 12 pure hydrocarbon compounds are measured at temperatures ranging from 25 to 500 °C using an FTIR spectrometer. The hydrocarbons studied are n-pentane, n-heptane, n-dodecane, 2,2,4-trimethyl-pentane (iso-octane), 2-methyl-butane, 2-methyl-pentane, 2,4,4-trimethyl-1-pentene, 2-methyl-2-butene, propene, toluene, m-xylene, and ethylbenzene. Room-temperature measurements of neat hydrocarbon vapor were made with an instrument resolution of both 0.1 and 1 cm-1 (FWHM) to confirm that the high-resolution setting was required only to resolve the propene absorption spectrum while the spectra of the other hydrocarbons could be resolved with 1 cm-1 resolution. High-resolution (0.1 cm-1), room-temperature measurements of neat hydrocarbons were made at low pressure (˜1 Torr, 133 Pa) and compared to measurements of hydrocarbon/N2 mixtures at atmospheric pressure to verify that no pressure broadening could be observed over this pressure range. The temperature was varied between 25 and 500 °C for atmospheric-pressure measurements of hydrocarbon/N2 mixtures (Xhydrocarbon˜0.06 1.5%) and it was found that the absorption cross section shows simple temperature-dependent behavior for a fixed wavelength over this temperature range. Comparisons with previous FTIR data over a limited temperature range and with high-resolution laser absorption data over a wide temperature range show good agreement.

Temperature dependence of the vibrational spectra of acetanilide: Davydov solitons or Fermi coupling?

NASA Astrophysics Data System (ADS)

Johnston, Clifford T.; Swanson, Basil I.

1985-03-01

The unusual temperature dependence of the amide-I region in the IR spectrum of acetanilide (C 6H 5NHCOCH 3) has recently been attributed to a self-trapped Davydov-like soliton. The temperature dependence of the single-crystal Raman scattering, from acetanilide and its ND and 13CO substituted analogs in the phonon and internal mode regions has now been studied. The behavior of the amide-I region in the Raman spectra of the normal isotopic species is similar to that observed earlier in infrared studies. However, on the basis of results obtained from the ND and 13CO substituted species the unusual temperature dependence in the 1650 cm -1 region has been attributed to Fermi coupling of the amide-I fundamental and a combination band involving the in-plane NH deformation and a low-frequency torsional mode. As temperature is lowered, the strong blue-shift of the torsional mode results in a commensurate blue-shift in the combination level thereby increasing the Fermi coupling. Temperature tuning of the Fermi coupling results in the anomalous intensity changes observed in the IR and Raman spectra of the amide-I region for the normal isotopic species.

Finite-temperature time-dependent variation with multiple Davydov states

NASA Astrophysics Data System (ADS)

Wang, Lu; Fujihashi, Yuta; Chen, Lipeng; Zhao, Yang

2017-03-01

The Dirac-Frenkel time-dependent variational approach with Davydov Ansätze is a sophisticated, yet efficient technique to obtain an accurate solution to many-body Schrödinger equations for energy and charge transfer dynamics in molecular aggregates and light-harvesting complexes. We extend this variational approach to finite temperature dynamics of the spin-boson model by adopting a Monte Carlo importance sampling method. In order to demonstrate the applicability of this approach, we compare calculated real-time quantum dynamics of the spin-boson model with that from numerically exact iterative quasiadiabatic propagator path integral (QUAPI) technique. The comparison shows that our variational approach with the single Davydov Ansätze is in excellent agreement with the QUAPI method at high temperatures, while the two differ at low temperatures. Accuracy in dynamics calculations employing a multitude of Davydov trial states is found to improve substantially over the single Davydov Ansatz, especially at low temperatures. At a moderate computational cost, our variational approach with the multiple Davydov Ansatz is shown to provide accurate spin-boson dynamics over a wide range of temperatures and bath spectral densities.

The role of phosphodiesterase activity on the temperature-dependent responses of calf cardiac vein.

PubMed

Nurullahoglu, Z U

2013-01-01

To evaluate the role of phosphodiesterase (PDE) activity in the cooling (to 28 °C) and warming (41 °C)-induced effects of carbachol on calf cardiac vein. Rings obtained from calf hearts were suspended in organ baths containing 25 ml of Krebs-Henseleit solution, maintained at 37 °C, continuously gassed with 95%O2-5%CO2. At the end of the resting period the preparations were contracted with carbachol (10-9-3x10-4M), at 37 °C. The same protocol was repeated at 28 °C and 41 °C after the preparations were allowed to equilibrate at this temperature for 60 min. In order to analyze the role of PDE activity in the cooling-and warming-induced vascular response, carbachol (10-9-3x10-4M) was applied in the presence of cilostazol (10-6 M), IBMX (10-6 M) and rolipram (10-6 M), respectively. The sensitivity of carbachol was significantly lower during cooling, and higher during warming. Cooling to 28 and warming to 41 °C, after treatment with IBMX, cilostazol or rolipram, significantly decreased the sensitivity to carbachol (p<0.05). The results of the present study suggest that PDE activity plays an essential role in cooling-and warming-induced changes of calf cardiac vein treated with carbachol (Tab. 1, Fig. 2, Ref. 34). Text in PDF www.elis.sk.

Temperature dependence of underdense nanostructure formation in tungsten under helium irradiation

DOE PAGES

Valles, G.; Martin-Bragado, I.; Nordlund, K.; ...

2017-04-19

Recently, tungsten has been found to form a highly underdense nanostructured morphology (“W fuzz”) when bombarded by an intense flux of He ions, but only in the temperature window 900–2000 K. Furthermore, using object kinetic Monte Carlo simulations (pseudo-3D simulations) parameterized from first principles, we show that this temperature dependence can be understood based on He and point defect clustering, cluster growth, and detrapping reactions. At low temperatures (<900 K), fuzz does not grow because almost all He is trapped in very small He-vacancy clusters. At high temperatures (>2300 K), all He is detrapped from clusters, preventing the formation ofmore » the large clusters that lead to fuzz growth in the intermediate temperature range.« less

Analyzing the Coordinated Gene Network Underlying Temperature-Dependent Sex Determination in Reptiles

PubMed Central

Shoemaker, Christina M.; Crews, David

2009-01-01

Although gonadogenesis has been extensively studied in vertebrates with genetic sex determination, investigations at the molecular level in nontraditional model organisms with temperature-dependent sex determination are a relatively new area of research. Results show that while the key players of the molecular network underlying gonad development appear to be retained, their functions range from conserved to novel roles. In this review, we summarize experiments investigating candidate molecular players underlying temperature-dependent sex determination. We discuss some of the problems encountered unraveling this network, pose potential solutions, and suggest rewarding future directions of research. PMID:19022389

Assessing the Temperature Dependence of Narrow-Band Raman Water Vapor Lidar Measurements: A Practical Approach

NASA Technical Reports Server (NTRS)

Whiteman, David N.; Venable, Demetrius D.; Walker, Monique; Cardirola, Martin; Sakai, Tetsu; Veselovskii, Igor

2013-01-01

Narrow-band detection of the Raman water vapor spectrum using the lidar technique introduces a concern over the temperature dependence of the Raman spectrum. Various groups have addressed this issue either by trying to minimize the temperature dependence to the point where it can be ignored or by correcting for whatever degree of temperature dependence exists. The traditional technique for performing either of these entails accurately measuring both the laser output wavelength and the water vapor spectral passband with combined uncertainty of approximately 0.01 nm. However, uncertainty in interference filter center wavelengths and laser output wavelengths can be this large or larger. These combined uncertainties translate into uncertainties in the magnitude of the temperature dependence of the Raman lidar water vapor measurement of 3% or more. We present here an alternate approach for accurately determining the temperature dependence of the Raman lidar water vapor measurement. This alternate approach entails acquiring sequential atmospheric profiles using the lidar while scanning the channel passband across portions of the Raman water vapor Q-branch. This scanning is accomplished either by tilt-tuning an interference filter or by scanning the output of a spectrometer. Through this process a peak in the transmitted intensity can be discerned in a manner that defines the spectral location of the channel passband with respect to the laser output wavelength to much higher accuracy than that achieved with standard laboratory techniques. Given the peak of the water vapor signal intensity curve, determined using the techniques described here, and an approximate knowledge of atmospheric temperature, the temperature dependence of a given Raman lidar profile can be determined with accuracy of 0.5% or better. A Mathematica notebook that demonstrates the calculations used here is available from the lead author.

Determination of the Temperature Dependence of Heat Capacity for Some Molecular Crystals of Nitro Compounds

NASA Astrophysics Data System (ADS)

Kovalev, Yu. M.; Kuropatenko, V. F.

2018-05-01

An analysis of the existing approximations used for describing the dependence of heat capacity at a constant volume on the temperature of a molecular crystal has been carried out. It is shown that the considered Debye and Einstein approximations do not enable one to adequately describe the dependence of heat capacity at a constant volume on the temperature of the molecular crystals of nitro compounds. This inference requires the development of special approximations that would describe both low-frequency and high-frequency parts of the vibrational spectra of molecular crystals. This work presents a universal dependence allowing one to describe the dependence of heat capacity at a constant volume on temperature for a number of molecular crystals of nitro compounds.

Temperature Dependence of Raman-Active In-Plane E2g Phonons in Layered Graphene and h-BN Flakes

NASA Astrophysics Data System (ADS)

Li, Xiaoli; Liu, Jian; Ding, Kai; Zhao, Xiaohui; Li, Shuai; Zhou, Wenguang; Liang, Baolai

2018-01-01

Thermal properties of sp2 systems such as graphene and hexagonal boron nitride (h-BN) have attracted significant attention because of both systems being excellent thermal conductors. This research reports micro-Raman measurements on the in-plane E2g optical phonon peaks ( 1580 cm-1 in graphene layers and 1362 cm-1 in h-BN layers) as a function of temperature from - 194 to 200 °C. The h-BN flakes show higher sensitivity to temperature-dependent frequency shifts and broadenings than graphene flakes. Moreover, the thermal effect in the c direction on phonon frequency in h-BN layers is more sensitive than that in graphene layers but on phonon broadening in h-BN layers is similar as that in graphene layers. These results are very useful to understand the thermal properties and related physical mechanisms in h-BN and graphene flakes for applications of thermal devices.

Ultrawideband temperature-dependent dielectric properties of animal liver tissue in the microwave frequency range.

PubMed

Lazebnik, Mariya; Converse, Mark C; Booske, John H; Hagness, Susan C

2006-04-07

The development of ultrawideband (UWB) microwave diagnostic and therapeutic technologies, such as UWB microwave breast cancer detection and hyperthermia treatment, is facilitated by accurate knowledge of the temperature- and frequency-dependent dielectric properties of biological tissues. To this end, we characterize the temperature-dependent dielectric properties of a representative tissue type-animal liver-from 0.5 to 20 GHz. Since discrete-frequency linear temperature coefficients are impractical and inappropriate for applications spanning wide frequency and temperature ranges, we propose a novel and compact data representation technique. A single-pole Cole-Cole model is used to fit the dielectric properties data as a function of frequency, and a second-order polynomial is used to fit the Cole-Cole parameters as a function of temperature. This approach permits rapid estimation of tissue dielectric properties at any temperature and frequency.

Temperature-dependent resetting of the molecular circadian oscillator in Drosophila

PubMed Central

Goda, Tadahiro; Sharp, Brandi; Wijnen, Herman

2014-01-01

Circadian clocks responsible for daily time keeping in a wide range of organisms synchronize to daily temperature cycles via pathways that remain poorly understood. To address this problem from the perspective of the molecular oscillator, we monitored temperature-dependent resetting of four of its core components in the fruitfly Drosophila melanogaster: the transcripts and proteins for the clock genes period (per) and timeless (tim). The molecular circadian cycle in adult heads exhibited parallel responses to temperature-mediated resetting at the levels of per transcript, tim transcript and TIM protein. Early phase adjustment specific to per transcript rhythms was explained by clock-independent temperature-driven transcription of per. The cold-induced expression of Drosophila per contrasts with the previously reported heat-induced regulation of mammalian Period 2. An altered and more readily re-entrainable temperature-synchronized circadian oscillator that featured temperature-driven per transcript rhythms and phase-shifted TIM and PER protein rhythms was found for flies of the ‘Tim 4’ genotype, which lacked daily tim transcript oscillations but maintained post-transcriptional temperature entrainment of tim expression. The accelerated molecular and behavioural temperature entrainment observed for Tim 4 flies indicates that clock-controlled tim expression constrains the rate of temperature cycle-mediated circadian resetting. PMID:25165772

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

Challenges in Modelling of Lightning-Induced Delamination; Effect of Temperature-Dependent Interfacial Properties

NASA Technical Reports Server (NTRS)

Naghipour, P.; Pineda, E. J.; Arnold, S.

2014-01-01

Lightning is a major cause of damage in laminated composite aerospace structures during flight. Due to the dielectric nature of Carbon fiber reinforced polymers (CFRPs), the high energy induced by lightning strike transforms into extreme, localized surface temperature accompanied with a high-pressure shockwave resulting in extensive damage. It is crucial to develop a numerical tool capable of predicting the damage induced from a lightning strike to supplement extremely expensive lightning experiments. Delamination is one of the most significant failure modes resulting from a lightning strike. It can be extended well beyond the visible damage zone, and requires sophisticated techniques and equipment to detect. A popular technique used to model delamination is the cohesive zone approach. Since the loading induced from a lightning strike event is assumed to consist of extreme localized heating, the cohesive zone formulation should additionally account for temperature effects. However, the sensitivity to this dependency remains unknown. Therefore, the major focus point of this work is to investigate the importance of this dependency via defining various temperature dependency profiles for the cohesive zone properties, and analyzing the corresponding delamination area. Thus, a detailed numerical model consisting of multidirectional composite plies with temperature-dependent cohesive elements in between is subjected to lightning (excessive amount of heat and pressure) and delamination/damage expansion is studied under specified conditions.

Temperature-Dependent Nanofabrication on Silicon by Friction-Induced Selective Etching.

PubMed

Jin, Chenning; Yu, Bingjun; Xiao, Chen; Chen, Lei; Qian, Linmao

2016-12-01

Friction-induced selective etching provides a convenient and practical way for fabricating protrusive nanostructures. A further understanding of this method is very important for establishing a controllable nanofabrication process. In this study, the effect of etching temperature on the formation of protrusive hillocks and surface properties of the etched silicon surface was investigated. It is found that the height of the hillock produced by selective etching increases with the etching temperature before the collapse of the hillock. The temperature-dependent selective etching rate can be fitted well by the Arrhenius equation. The etching at higher temperature can cause rougher silicon surface with a little lower elastic modulus and hardness. The contact angle of the etched silicon surface decreases with the etching temperature. It is also noted that no obvious contamination can be detected on silicon surface after etching at different temperatures. As a result, the optimized condition for the selective etching was addressed. The present study provides a new insight into the control and application of friction-induced selective nanofabrication.

Composition-dependent damping and relaxation dynamics in miscible polymer blends above glass transition temperature by anelastic spectroscopy

NASA Astrophysics Data System (ADS)

Wu, Xuebang; Shang, Shuying; Xu, Qiaoling; Liu, Changsong; Zhu, Zhengang; Zhang, Guangzhao

2008-07-01

Anelastic spectroscopy is used to study the composition dependence of the damping and molecular relaxation dynamics in miscible poly(ethylene oxide) (PEO)/poly(methyl methacrylate) (PMMA) blends above the glass transition temperature. The ultrahigh damping peak of the relaxation type is shown to be associated with the liquid-liquid transition of PMMA. A higher PEO concentration leads to a higher damping performance and a lower transition temperature. The decreasing activation energy with increasing PEO concentration indicates a drastic increase in molecular mobility. Moreover, the relaxation time reveals a transition from the Vogel-Fulcher-Tamman behavior to the Arrhenius behavior due to the intermolecular guest-host interactions.

Temperature dependence of the formation of sulfate aerosols in the stratosphere

NASA Technical Reports Server (NTRS)

Yue, G. K.; Deepak, A.

1982-01-01

Classical nucleation theory is used in calculations of the temperature dependence of the characteristics and nucleation rates of sulfate aerosols in the binary H2SO4-H2O vapor mixture, in order to assess the influence of temperature on the formation of sulfate aerosols in the stratosphere, and to explore the possibility of new particle formation through homogeneous nucleation processes at regions where temperature is as low as -75 C, rather than the often-assumed -50 or -55 C. Calculation results indicate that the number of particles formed at a lower temperature is larger by several orders of magnitude than at higher temperatures, when water and sulfuric acid vapor concentrations are kept constant, and that large quantities of ultrafine particles which cannot be detected by conventional methods may exist at low-temperature stratospheric regions.

Shock temperature dependent rate law for plastic bonded explosives

NASA Astrophysics Data System (ADS)

Aslam, Tariq D.

2018-04-01

A reactive flow model for the tri-amino-tri-nitro-benzene (TATB) based plastic bonded explosive PBX 9502 (95% TATB, 5% polymeric binder Kel-F 800) is presented. This newly devised model is based primarily on the shock temperature of the material, along with local pressure, and accurately models a broader range of detonation and initiation scenarios. Specifically, sensitivity changes to the initial explosive temperature are accounted for naturally and with a single set of parameters. The equation of state forms for the reactants and products, as well as the thermodynamic closure of pressure and temperature equilibration, are carried over from the Wescott-Stewart-Davis (WSD) model [Wescott et al., J. Appl. Phys. 98, 053514 (2005) and "Modeling detonation diffraction and dead zones in PBX-9502," in Proceedings of the Thirteenth International Detonation Symposium (2006)]. This newly devised model, with Arrhenius state dependence on the shock temperature, based on the WSD equation of states, is denoted by AWSD. Modifying an existing implementation of the WSD model to the AWSD model in a hydrocode is a rather straightforward procedure.

Monte Carlo method for photon heating using temperature-dependent optical properties.

PubMed

Slade, Adam Broadbent; Aguilar, Guillermo

2015-02-01

The Monte Carlo method for photon transport is often used to predict the volumetric heating that an optical source will induce inside a tissue or material. This method relies on constant (with respect to temperature) optical properties, specifically the coefficients of scattering and absorption. In reality, optical coefficients are typically temperature-dependent, leading to error in simulation results. The purpose of this study is to develop a method that can incorporate variable properties and accurately simulate systems where the temperature will greatly vary, such as in the case of laser-thawing of frozen tissues. A numerical simulation was developed that utilizes the Monte Carlo method for photon transport to simulate the thermal response of a system that allows temperature-dependent optical and thermal properties. This was done by combining traditional Monte Carlo photon transport with a heat transfer simulation to provide a feedback loop that selects local properties based on current temperatures, for each moment in time. Additionally, photon steps are segmented to accurately obtain path lengths within a homogenous (but not isothermal) material. Validation of the simulation was done using comparisons to established Monte Carlo simulations using constant properties, and a comparison to the Beer-Lambert law for temperature-variable properties. The simulation is able to accurately predict the thermal response of a system whose properties can vary with temperature. The difference in results between variable-property and constant property methods for the representative system of laser-heated silicon can become larger than 100K. This simulation will return more accurate results of optical irradiation absorption in a material which undergoes a large change in temperature. This increased accuracy in simulated results leads to better thermal predictions in living tissues and can provide enhanced planning and improved experimental and procedural outcomes. Copyright �

The instantaneous rate dependence in low temperature laboratory rock friction and rock deformation experiments

USGS Publications Warehouse

Beeler, N.M.; Tullis, T.E.; Kronenberg, A.K.; Reinen, L.A.

2007-01-01

Earthquake occurrence probabilities that account for stress transfer and time-dependent failure depend on the product of the effective normal stress and a lab-derived dimensionless coefficient a. This coefficient describes the instantaneous dependence of fault strength on deformation rate, and determines the duration of precursory slip. Although an instantaneous rate dependence is observed for fracture, friction, crack growth, and low temperature plasticity in laboratory experiments, the physical origin of this effect during earthquake faulting is obscure. We examine this rate dependence in laboratory experiments on different rock types using a normalization scheme modified from one proposed by Tullis and Weeks [1987]. We compare the instantaneous rate dependence in rock friction with rate dependence measurements from higher temperature dislocation glide experiments. The same normalization scheme is used to compare rate dependence in friction to rock fracture and to low-temperature crack growth tests. For particular weak phyllosilicate minerals, the instantaneous friction rate dependence is consistent with dislocation glide. In intact rock failure tests, for each rock type considered, the instantaneous rate dependence is the same size as for friction, suggesting a common physical origin. During subcritical crack growth in strong quartzofeldspathic and carbonate rock where glide is not possible, the instantaneous rate dependence measured during failure or creep tests at high stress has long been thought to be due to crack growth; however, direct comparison between crack growth and friction tests shows poor agreement. The crack growth rate dependence appears to be higher than the rate dependence of friction and fracture by a factor of two to three for all rock types considered. Copyright 2007 by the American Geophysical Union.

Temperature dependence of emission measure in solar X-ray plasmas. 1: Non-flaring active regions

NASA Technical Reports Server (NTRS)

Phillips, K. J. H.

1974-01-01

X-ray and ultraviolet line emission from hot, optically thin material forming coronal active regions on the sun may be described in terms of an emission measure distribution function, Phi (T). A relationship is developed between line flux and Phi (T), a theory which assumes that the electron density is a single-valued function of temperature. The sources of error involved in deriving Phi (T) from a set of line fluxes are examined in some detail. These include errors in atomic data (collisional excitation rates, assessment of other mechanisms for populating excited states of transitions, element abundances, ion concentrations, oscillator strengths) and errors in observed line fluxes arising from poorly - known instrumental responses. Two previous analyses are discussed in which Phi (T) for a non-flaring active region is derived. A least squares method of Batstone uses X-ray data of low statistical significance, a fact which appears to influence the results considerably. Two methods for finding Phi (T) ab initio are developed. The coefficients are evaluated by least squares. These two methods should have application not only to active-region plasmas, but also to hot, flare-produced plasmas.

Temperature dependent lattice constant of InSb above room temperature

NASA Astrophysics Data System (ADS)

Breivik, Magnus; Nilsen, Tron Arne; Fimland, Bjørn-Ove

2013-10-01

Using temperature dependent X-ray diffraction on two InSb single crystalline substrates, the bulk lattice constant of InSb was determined between 32 and 325 °C. A polynomial function was fitted to the data: a(T)=6.4791+3.28×10-5×T+1.02×10-8×T2 Å (T in °C), which gives slightly higher values than previously published (which go up to 62 °C). From the fit, the thermal expansion of InSb was calculated to be α(T)=5.062×10-6+3.15×10-9×T K-1 (T in °C). We found that the thermal expansion coefficient is higher than previously published values above 100 °C (more than 10% higher at 325 °C).

Time/Temperature Dependent Tensile Strength of SiC and Al2O3-Based Fibers

NASA Technical Reports Server (NTRS)

Yun, Hee Mann; DiCarlo, James A.

1997-01-01

In order to understand and model the thermomechanical behavior of fiber-reinforced composites, stress-rupture, fast-fracture, and warm-up rupture studies were conducted on various advanced SiC and Al2O3-based fibers in the,temperature range from 20 to 1400 C in air as well as in inert environments. The measured stress-rupture, fast fracture, and warm-up rupture strengths were correlated into a single master time/temperature-dependent strength plot for each fiber type using thermal activation and slow crack growth theories. It is shown that these plots are useful for comparing and selecting fibers for CMC and MMC reinforcement and that, in comparison to stress rupture tests, the fast-fracture and warm-up tests can be used for rapid generation of these plots.

Temperature dependence of Er³⁺ ionoluminescence and photoluminescence in Gd₂O₃:Bi nanopowder.

PubMed

Boruc, Zuzanna; Gawlik, Grzegorz; Fetliński, Bartosz; Kaczkan, Marcin; Malinowski, Michał

2014-06-01

Ionoluminescence (IL) and photoluminescence (PL) of trivalent erbium ions (Er(3+)) in Gd2O3 nanopowder host activated with Bi(3+) ions has been studied in order to establish the link between changes in luminescent spectra and temperature of the sample material. IL measurements have been performed with H2 (+) 100 keV ion beam bombarding the target material for a few seconds, while PL spectra have been collected for temperatures ranging from 20 °C to 700 °C. The PL data was used as a reference in determining the temperature corresponding to IL spectra. The collected data enabled the definition of empirical formula based on the Boltzmann distribution, which allows the temperature to be determined with a maximum sensitivity of 9.7 × 10(-3) °C(-1). The analysis of the Er(3+) energy level structure in terms of tendency of the system to stay in thermal equilibrium, explained different behaviors of the line intensities. This work led to the conclusion that temperature changes during ion excitation can be easily defined with separately collected PL spectra. The final result, which is empirical formula describing dependence of fluorescence intensity ratio on temperature, raises the idea of an application of method in temperature control, during processes like ion implantation and some nuclear applications.

Temperature dependent recombination dynamics in InP/ZnS colloidal nanocrystals

NASA Astrophysics Data System (ADS)

Shirazi, R.; Kopylov, O.; Kovacs, A.; Kardynał, B. E.

2012-08-01

In this letter, we investigate exciton recombination in InP/ZnS core-shell colloidal nanocrystals over a wide temperature range. Over the entire range between room temperature and liquid helium temperature, multi-exponential exciton decay curves are observed and well explained by the presence of bright and dark exciton states, as well as defect states. Two different types of defect are present: one located at the core-shell interface and the other on the surface of the nanocrystal. Based on the temperature dependent contributions of all four states to the total photoluminescence signal, we estimate that the four states are distributed within a 20 meV energy band in nanocrystals that emit at 1.82 eV.

Time dependent and temperature dependent properties of the forward voltage characteristic of InGaN high power LEDs

NASA Astrophysics Data System (ADS)

Fulmek, P. L.; Haumer, P.; Wenzl, F. P.; Nemitz, W.; Nicolics, J.

2017-03-01