Discrimination between spin-dependent charge transport and spin-dependent recombination in π-conjugated polymers by correlated current and electroluminescence-detected magnetic resonance

NASA Astrophysics Data System (ADS)

Kavand, Marzieh; Baird, Douglas; van Schooten, Kipp; Malissa, Hans; Lupton, John M.; Boehme, Christoph

2016-08-01

Spin-dependent processes play a crucial role in organic electronic devices. Spin coherence can give rise to spin mixing due to a number of processes such as hyperfine coupling, and leads to a range of magnetic field effects. However, it is not straightforward to differentiate between pure single-carrier spin-dependent transport processes which control the current and therefore the electroluminescence, and spin-dependent electron-hole recombination which determines the electroluminescence yield and in turn modulates the current. We therefore investigate the correlation between the dynamics of spin-dependent electric current and spin-dependent electroluminescence in two derivatives of the conjugated polymer poly(phenylene-vinylene) using simultaneously measured pulsed electrically detected (pEDMR) and optically detected (pODMR) magnetic resonance spectroscopy. This experimental approach requires careful analysis of the transient response functions under optical and electrical detection. At room temperature and under bipolar charge-carrier injection conditions, a correlation of the pEDMR and the pODMR signals is observed, consistent with the hypothesis that the recombination currents involve spin-dependent electronic transitions. This observation is inconsistent with the hypothesis that these signals are caused by spin-dependent charge-carrier transport. These results therefore provide no evidence that supports earlier claims that spin-dependent transport plays a role for room-temperature magnetoresistance effects. At low temperatures, however, the correlation between pEDMR and pODMR is weakened, demonstrating that more than one spin-dependent process influences the optoelectronic materials' properties. This conclusion is consistent with prior studies of half-field resonances that were attributed to spin-dependent triplet exciton recombination, which becomes significant at low temperatures when the triplet lifetime increases.

Temperature, concentration, and frequency dependence of the dielectric constant near the critical point of the binary liquid mixture nitrobenzene-tetradecane

NASA Astrophysics Data System (ADS)

Leys, Jan; Losada-Pérez, Patricia; Cordoyiannis, George; Cerdeiriña, Claudio A.; Glorieux, Christ; Thoen, Jan

2010-03-01

Detailed results are reported for the dielectric constant ɛ as a function of temperature, concentration, and frequency near the upper critical point of the binary liquid mixture nitrobenzene-tetradecane. The data have been analyzed in the context of the recently developed concept of complete scaling. It is shown that the amplitude of the low frequency critical Maxwell-Wagner relaxation (with a relaxation frequency around 10 kHz) along the critical isopleth is consistent with the predictions of a droplet model for the critical fluctuations. The temperature dependence of ɛ in the homogeneous phase can be well described with a combination of a (1-α) power law term (with α the heat capacity critical exponent) and a linear term in reduced temperature with the Ising value for α. For the proper description of the temperature dependence of the difference Δɛ between the two coexisting phases below the critical temperature, it turned out that good fits with the Ising value for the order parameter exponent β required the addition of a corrections-to-scaling contribution or a linear term in reduced temperature. Good fits to the dielectric diameter ɛd require a (1-α) power law term, a 2β power law term (in the past considered as spurious), and a linear term in reduced temperature, consistent with complete scaling.

Semi-empirical anzatz for Helmholtz free energy calculation: Thermal properties of silver along shock Hugoniot

NASA Astrophysics Data System (ADS)

Joshi, R. H.; Thakore, B. Y.; Bhatt, N. K.; Vyas, P. R.; Jani, A. R.

2018-02-01

A density functional theory along with electronic contribution is used to compute quasiharmonic total energy for silver, whereas explicit phonon anharmonic contribution is added through perturbative term in temperature. Within the Mie-Grüneisen approach, we propose a consistent computational scheme for calculating various thermophysical properties of a substance, in which the required Grüneisen parameter γth is calculated from the knowledge of binding energy. The present study demonstrates that no separate relation for volume dependence for γth is needed, and complete thermodynamics under simultaneous high-temperature and high-pressure condition can be derived in a consistent manner. We have calculated static and dynamic equation of states and some important thermodynamic properties along the shock Hugoniot. A careful examination of temperature dependence of Grüneisen parameter reveals the importance of temperature-effect on various thermal properties.

Progressive failure site generation in AlGaN/GaN high electron mobility transistors under OFF-state stress: Weibull statistics and temperature dependence

NASA Astrophysics Data System (ADS)

Sun, Huarui; Bajo, Miguel Montes; Uren, Michael J.; Kuball, Martin

2015-01-01

Gate leakage degradation of AlGaN/GaN high electron mobility transistors under OFF-state stress is investigated using a combination of electrical, optical, and surface morphology characterizations. The generation of leakage "hot spots" at the edge of the gate is found to be strongly temperature accelerated. The time for the formation of each failure site follows a Weibull distribution with a shape parameter in the range of 0.7-0.9 from room temperature up to 120 °C. The average leakage per failure site is only weakly temperature dependent. The stress-induced structural degradation at the leakage sites exhibits a temperature dependence in the surface morphology, which is consistent with a surface defect generation process involving temperature-associated changes in the breakdown sites.

Theory of the magnetic susceptibility including zero-point spin fluctuations of itinerant nearly ferromagnetic compounds

NASA Astrophysics Data System (ADS)

Konno, Rikio; Hatayama, Nobukuni; Takahashi, Yoshinori

2018-05-01

We have investigated the temperature dependence of the magnetic susceptibility of itinerant nearly ferromagnetic compounds based on the spin fluctuation theory. It is based on the conservation of the local spin amplitude that consists of both the thermal and the zero-point components. The linear dependence of the zero-point spin fluctuation amplitude on the inverse of magnetic susceptibility is usually assumed. The purpose of our present study is to include its higher order terms and to see their effects on the magnetic susceptibility. For the thermal amplitude, it shows T2-linear temperature dependence at low temperatures.

Temperature-dependent magnetic anisotropy in the layered magnetic semiconductors Cr I3 and CrB r3

NASA Astrophysics Data System (ADS)

Richter, Nils; Weber, Daniel; Martin, Franziska; Singh, Nirpendra; Schwingenschlögl, Udo; Lotsch, Bettina V.; Kläui, Mathias

2018-02-01

Chromium trihalides are layered and exfoliable semiconductors and exhibit unusual magnetic properties with a surprising temperature dependence of the magnetization. By analyzing the evolution of the magnetocrystalline anisotropy with temperature in chromium iodide Cr I3 , we find it strongly changes from Ku=300 ±50 kJ / m3 at 5 K to Ku=43 ±7 kJ / m3 at 60 K , close to the Curie temperature. We draw a direct comparison to CrB r3 , which serves as a reference, and where we find results consistent with literature. In particular, we show that the anisotropy change in the iodide compound is more than 3 times larger than in the bromide. We analyze this temperature dependence using a classical model, showing that the anisotropy constant scales with the magnetization at any given temperature below the Curie temperature, indicating that the temperature dependence can be explained by a dominant uniaxial anisotropy where this scaling results from local spin clusters having thermally induced magnetization directions that deviate from the overall magnetization.

The electrical transport properties of liquid Rb using pseudopotential theory

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

Patel, A. B., E-mail: amit07patel@gmail.com; Bhatt, N. K., E-mail: amit07patel@gmail.com; Thakore, B. Y., E-mail: amit07patel@gmail.com

2014-04-24

Certain electric transport properties of liquid Rb are reported. The electrical resistivity is calculated by using the self-consistent approximation as suggested by Ferraz and March. The pseudopotential due to Hasegawa et al for full electron-ion interaction, which is valid for all electrons and contains the repulsive delta function due to achieve the necessary s-pseudisation was used for the calculation. Temperature dependence of structure factor is considered through temperature dependent potential parameter in the pair potential. Finally, thermo-electric power and thermal conductivity are obtained. The outcome of the present study is discussed in light of other such results, and confirms themore » applicability of pseudopotential at very high temperature via temperature dependent pair potential.« less

Coherent energy scale revealed by ultrafast dynamics of UX3 (X = Al, Sn, Ga) single crystals

NASA Astrophysics Data System (ADS)

Nair, Saritha K.; Zhu, J.-X.; Sarrao, J. L.; Taylor, A. J.; Chia, Elbert E. M.

2012-09-01

The temperature dependence of relaxation dynamics of UX3 (X = Al, Ga, Sn) compounds is studied using the time-resolved pump-probe technique in reflectance geometry. For UGa3, our data are consistent with the formation of a spin density wave gap as evidenced from the quasidivergence of the relaxation time τ near the Néel temperature TN. For UAl3 and USn3, the relaxation dynamics shows a change from single-exponential to two-exponential behavior below a particular temperature, suggestive of coherence formation of the 5f electrons with the conduction band electrons. This particular temperature can be attributed to the spin fluctuation temperature Tsf, a measure of the strength of Kondo coherence. Our Tsf is consistent with other data such as resistivity and susceptibility measurements. The temperature dependence of the relaxation amplitude and time of UAl3 and USn3 were also fitted by the Rothwarf-Taylor model. Our results show that ultrafast optical spectroscopy is sensitive to c-f Kondo hybridization in the f-electron systems.

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.

Progressive failure site generation in AlGaN/GaN high electron mobility transistors under OFF-state stress: Weibull statistics and temperature dependence

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

Sun, Huarui, E-mail: huarui.sun@bristol.ac.uk; Bajo, Miguel Montes; Uren, Michael J.

2015-01-26

Gate leakage degradation of AlGaN/GaN high electron mobility transistors under OFF-state stress is investigated using a combination of electrical, optical, and surface morphology characterizations. The generation of leakage “hot spots” at the edge of the gate is found to be strongly temperature accelerated. The time for the formation of each failure site follows a Weibull distribution with a shape parameter in the range of 0.7–0.9 from room temperature up to 120 °C. The average leakage per failure site is only weakly temperature dependent. The stress-induced structural degradation at the leakage sites exhibits a temperature dependence in the surface morphology, which ismore » consistent with a surface defect generation process involving temperature-associated changes in the breakdown sites.« less

Calculated temperature dependence of elastic constants and phonon dispersion of hcp and bcc beryllium

NASA Astrophysics Data System (ADS)

Hahn, Steven; Arapan, Sergiu; Harmon, Bruce; Eriksson, Olle

2011-03-01

Conventional first principle methods for calculating lattice dynamics are unable to calculate high temperature thermophysical properties of materials containing modes that are entropically stabilized. In this presentation we use a relatively new approach called self-consistent ab initio lattice dynamics (SCAILD) to study the hcp to bcc transition (1530 K) in beryllium. The SCAILD method goes beyond the harmonic approximation to include phonon-phonon interactions and produces a temperature-dependent phonon dispersion. In the high temperature bcc structure, phonon-phonon interactions dynamically stabilize the N-point phonon. Fits to the calculated phonon dispersion were used to determine the temperature dependence of the elastic constants in the hcp and bcc phases. Work at the Ames Laboratory was supported by the Department of Energy-Basic Energy Sciences under Contract No. DE-AC02-07CH11358.

Friction Durability of Extremely Thin Diamond-Like Carbon Films at High Temperature

PubMed Central

Miyake, Shojiro; Suzuki, Shota; Miyake, Masatoshi

2017-01-01

To clarify the friction durability, both during and after the high-temperature heating of nanometer-thick diamond-like carbon (DLC) films, deposited using filtered cathodic vacuum arc (FCVA) and plasma chemical vapor deposition (P-CVD) methods, the dependence of the friction coefficient on the load and sliding cycles of the DLC films, were evaluated. Cluster-I consisted of a low friction area in which the DLC film was effective, while cluster-II consisted of a high friction area in which the lubricating effect of the DLC film was lost. The friction durability of the films was evaluated by statistical cluster analysis. Extremely thin FCVA-DLC films exhibited an excellent wear resistance at room temperature, but their friction durability was decreased at high temperatures. In contrast, the durability of the P-CVD-DLC films was increased at high temperatures when compared with that observed at room temperature. This inverse dependence on temperature corresponded to the nano-friction results obtained by atomic force microscopy. The decrease in the friction durability of the FCVA-DLC films at high temperatures, was caused by a complex effect of temperature and friction. The tribochemical reaction produced by the P-CVD-DLC films reduced their friction coefficient, increasing their durability at high temperatures. PMID:28772520

Friction Durability of Extremely Thin Diamond-Like Carbon Films at High Temperature.

PubMed

Miyake, Shojiro; Suzuki, Shota; Miyake, Masatoshi

2017-02-10

To clarify the friction durability, both during and after the high-temperature heating of nanometer-thick diamond-like carbon (DLC) films, deposited using filtered cathodic vacuum arc (FCVA) and plasma chemical vapor deposition (P-CVD) methods, the dependence of the friction coefficient on the load and sliding cycles of the DLC films, were evaluated. Cluster-I consisted of a low friction area in which the DLC film was effective, while cluster-II consisted of a high friction area in which the lubricating effect of the DLC film was lost. The friction durability of the films was evaluated by statistical cluster analysis. Extremely thin FCVA-DLC films exhibited an excellent wear resistance at room temperature, but their friction durability was decreased at high temperatures. In contrast, the durability of the P-CVD-DLC films was increased at high temperatures when compared with that observed at room temperature. This inverse dependence on temperature corresponded to the nano-friction results obtained by atomic force microscopy. The decrease in the friction durability of the FCVA-DLC films at high temperatures, was caused by a complex effect of temperature and friction. The tribochemical reaction produced by the P-CVD-DLC films reduced their friction coefficient, increasing their durability at high temperatures.

Long tailed trions in monolayer MoS2: Temperature dependent asymmetry and resulting red-shift of trion photoluminescence spectra.

PubMed

Christopher, Jason W; Goldberg, Bennett B; Swan, Anna K

2017-10-25

Monolayer molybdenum disulfide (MoS 2 ) has emerged as a model system for studying many-body physics because the low dimensionality reduces screening leading to tightly bound states stable at room temperature. Further, the many-body states possess a pseudo-spin degree of freedom that corresponds with the two direct-gap valleys of the band structure, which can be optically manipulated. Here we focus on one bound state, the negatively charged trion. Unlike excitons, trions can radiatively decay with non-zero momentum by kicking out an electron, resulting in an asymmetric trion photoluminescence (PL) peak with a long low-energy tail and peak position that differs from the zero momentum trion energy. The asymmetry of the trion PL peak and resulting peak red-shift depends both on the trion size and a temperature-dependent contribution. Ignoring the trion asymmetry will result in over estimating the trion binding energy by nearly 20 meV at room temperature. We analyze the temperature-dependent PL to reveal the effective trion size, consistent with the literature, and the temperature dependence of the band gap and spin-orbit splitting of the valence band. This is the first time the temperature-dependence of the trion PL has been analyzed with such detail in any system.

Electron-temperature dependence of dissociative recombination of electrons with N2/+/.N2 dimer ions

NASA Technical Reports Server (NTRS)

Whitaker, M.; Biondi, M. A.; Johnsen, R.

1981-01-01

The variation with electron temperature of the dissociative recombination of electrons with N2(+).N2 dimer ions is investigated in light of the importance of such ions in the lower ionosphere and in laser plasmas. Dissociative recombination coefficients were determined by means of a microwave afterglow mass spectrometer technique for electron temperatures from 300-5600 K and an ion and neutral temperature of 300 K. The recombination coefficient is found to be proportional to the -0.41 power of the electron temperature in this range, similar to that observed for the CO(+).CO dimer ion and consistent with the expected energy dependence for a fast dissociative process.

On the Enthalpy and Entropy of Point Defect Formation in Crystals

NASA Astrophysics Data System (ADS)

Kobelev, N. P.; Khonik, V. A.

2018-03-01

A standard way to determine the formation enthalpy H and entropy S of point defect formation in crystals consists in the application of the Arrhenius equation for the defect concentration. In this work, we show that a formal use of this method actually gives the effective (apparent) values of these quantities, which appear to be significantly overestimated. The underlying physical reason lies in temperature-dependent formation enthalpy of the defects, which is controlled by temperature dependence of the elastic moduli. We present an evaluation of the "true" H- and S-values for aluminum, which are derived on the basis of experimental data by taking into account temperature dependence of the formation enthalpy related to temperature dependence of the elastic moduli. The knowledge of the "true" activation parameters is needed for a correct calculation of the defect concentration constituting thus an issue of major importance for different fundamental and application issues of condensed matter physics and chemistry.

Inelastic Light Scattering Measurements of a Pressure-Induced Quantum Liquid in KCuF3

NASA Astrophysics Data System (ADS)

Yuan, S.; Kim, M.; Seeley, J. T.; Lee, J. C. T.; Lal, S.; Abbamonte, P.; Cooper, S. L.

2012-11-01

Pressure-dependent, low-temperature inelastic light (Raman) scattering measurements of KCuF3 show that applied pressure above P*˜7kbar suppresses a previously observed structural phase transition temperature to zero temperature in KCuF3, resulting in the development of a fluctuational (quasielastic) response near T˜0K. This pressure-induced fluctuational response—which we associate with slow fluctuations of the CuF6 octahedral orientation—is temperature independent and exhibits a characteristic fluctuation rate that is much larger than the temperature, consistent with quantum fluctuations of the CuF6 octahedra. A model of pseudospin-phonon coupling provides a qualitative description of both the temperature- and pressure-dependent evolution of the Raman spectra of KCuF3.

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

Investigation of the temperature dependent field emission from individual ZnO nanowires for evidence of field-induced hot electrons emission.

PubMed

Chen, Yicong; Zhang, Zhipeng; Li, Zhi-Bing; She, Juncong; Deng, Shaozhi; Xu, Ning-Sheng; Chen, Jun

2018-06-27

ZnO nanowires as field emitters have important applications in flat panel display and X-ray source. Understanding the intrinsic field emission mechanism is crucial for further improving the performance of ZnO nanowire field emitters. In this article, the temperature dependent field emission from individual ZnO nanowires was investigated by an in-situ measurement in ultra-high vacuum. The divergent temperature-dependent Fowler-Nordheim plots is found in the low field region. A field-induced hot electrons emission model that takes into account penetration length is proposed to explain the results. The carrier density and temperature dependence of the field-induced hot electrons emission current are derived theoretically. The obtained results are consistent with the experimental results, which could be attributed to the variation of effective electron temperature. All of these are important for a better understanding on the field emission process of semiconductor nanostructures. © 2018 IOP Publishing Ltd.

Development of constitutive models for cyclic plasticity and creep behavior of super alloys at high temperature

NASA Technical Reports Server (NTRS)

Haisler, W. E.

1983-01-01

An uncoupled constitutive model for predicting the transient response of thermal and rate dependent, inelastic material behavior was developed. The uncoupled model assumes that there is a temperature below which the total strain consists essentially of elastic and rate insensitive inelastic strains only. Above this temperature, the rate dependent inelastic strain (creep) dominates. The rate insensitive inelastic strain component is modelled in an incremental form with a yield function, blow rule and hardening law. Revisions to the hardening rule permit the model to predict temperature-dependent kinematic-isotropic hardening behavior, cyclic saturation, asymmetric stress-strain response upon stress reversal, and variable Bauschinger effect. The rate dependent inelastic strain component is modelled using a rate equation in terms of back stress, drag stress and exponent n as functions of temperature and strain. A sequence of hysteresis loops and relaxation tests are utilized to define the rate dependent inelastic strain rate. Evaluation of the model has been performed by comparison with experiments involving various thermal and mechanical load histories on 5086 aluminum alloy, 304 stainless steel and Hastelloy X.

Momentum-dependent hybridization gap and dispersive in-gap state of the Kondo semiconductor SmB6

NASA Astrophysics Data System (ADS)

Miyazaki, Hidetoshi; Hajiri, Tetsuya; Ito, Takahiro; Kunii, Satoru; Kimura, Shin-ichi

2012-08-01

We report the temperature-dependent three-dimensional angle-resolved photoemission spectra of the Kondo semiconductor SmB6. We found a difference in the temperature dependence of the peaks at the X and Γ points, due to hybridization between the Sm 5d conduction band and the nearly localized Sm 4f state. The peak intensity at the X point has the same temperature dependence as the valence transition below 120 K, while that at the Γ point is consistent with the magnetic excitation at Q=(0.5,0.5,0.5) below 30 K. This suggests that the hybridization with the valence transition mainly occurs near the X point, and the initial state of the magnetic excitation is located near the Γ point.

Magnetoresistance behavior in nanobulk assembled Bi2Se3 topological insulator

NASA Astrophysics Data System (ADS)

Bera, Sumit; Behera, P.; Mishra, A. K.; Krishnan, M.; Patidar, Manju Mishra; Singh, Durgesh; Venkatesh, R.; Phase, D. M.; Ganesan, V.

2018-05-01

Temperature and magnetic field dependent magnetoresistance (MR) including structural, morphological studies of Bi2Se3 nanoflower like structure synthesized by microwave assisted solvothermal method has been investigated. Powder X-ray diffraction (XRD) has confirmed the formation of single phase. Morphology of the material shows nanoflower kind of structures with edge to edge size of around 4 µm and such occurrences are quite high. The temperature dependent resistance invokes a metallic behavior up to a certain lower temperature, below which it follows -ln(T) behavior that has been elucidated in literature using electron-electron interaction and weak anti-localization effects. High temperature magnetoresistance is consistent with parabolic field dependence indicating a classical magnetoresistance in metals as a result of Lorenz force. In low temperature regime magnetoresistance as a function of magnetic field at different temperatures obeys power law near low field which indicates a three dimensional weak-antilocalization. A linear magnetoresistance at low temperature and high magnetic field shows the domination of surface state conduction.

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.

First Measurements of Time-Dependent Nucleation as a Function of Composition in Na2O.2CaO.3SiO2 Glasses

NASA Technical Reports Server (NTRS)

Kelton, K. F.; Narayan, K. Lakshmi

1996-01-01

The first measurements in any system of the composition dependence of the time-dependent nucleation rate are presented Nucleation rates of the stoichiometric crystalline phase, Na2O.2CaO.3SiO2, from quenched glasses made with different SiO2 concentrations were determined as a function of temperature and glass composition. A strong compositional dependence of the nucleation rates and a weak dependence for the induction times are observed. Using measured values of the liquidus temperatures and growth velocities as a function of glass composition, these data are shown to be consistent with predictions from the classical theory of nucleation, assuming a composition-dependent interfacial energy.

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.

Accurate MR thermometry by hyperpolarized 129 Xe.

PubMed

Zhang, Le; Burant, Alex; McCallister, Andrew; Zhao, Victor; Koshlap, Karl M; Degan, Simone; Antonacci, Michael; Branca, Rosa Tamara

2017-09-01

To investigate the temperature dependence of the resonance frequency of lipid-dissolved xenon (LDX) and to assess the accuracy of LDX-based MR thermometry. The chemical shift temperature dependence of water protons, methylene protons, and LDX was measured from samples containing tissues with varying fat contents using a high-resolution NMR spectrometer. LDX results were then used to acquire relative and absolute temperature maps in vivo and the results were compared with PRF-based MR thermometry. The temperature dependence of proton resonance frequency (PRF) is strongly affected by the specific distribution of water and fat. A redistribution of water and fat compartments can reduce the apparent temperature dependence of the water chemical shift from -0.01 ppm/°C to -0.006 ppm, whereas the LDX chemical shift shows a consistent temperature dependence of -0.21 ppm/°C. The use of the methylene protons resonance frequency as internal reference improves the accuracy of LDX-based MR thermometry, but degrades that of PRF-based MR thermometry, as microscopic susceptibility gradients affected lipid and water spins differently. The LDX resonance frequency, with its higher temperature dependence, provides more accurate and precise temperature measurements, both in vitro and in vivo. More importantly, the resonance frequency of nearby methylene protons can be used to extract absolute temperature information. Magn Reson Med 78:1070-1079, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.

Does the Arrhenius Temperature Dependence of the Johari-Goldstein Relaxation Persist above Tg?

NASA Astrophysics Data System (ADS)

Paluch, M.; Roland, C. M.; Pawlus, S.; Zioło, J.; Ngai, K. L.

2003-09-01

Dielectric spectra of the polyalcohols sorbitol and xylitol were measured under isobaric pressures up to 1.8GPa. At elevated pressure, the separation between the α and β relaxation peaks is larger than at ambient pressure, enabling the β relaxation times to be unambiguously determined. Taking advantage of this, we show that the Arrhenius temperature dependence of the β relaxation time does not persist for temperatures above Tg. This result, consistent with inferences drawn from dielectric relaxation measurements at ambient pressure, is obtained directly, without the usual problematic deconvolution the β and α processes.

Temperature rise due to mechanical energy dissipation in undirectional thermoplastic composites(AS4/PEEK)

NASA Technical Reports Server (NTRS)

Georgious, I. T.; Sun, C. T.

1992-01-01

The history of temperature rise due to internal dissipation of mechanical energy in insulated off-axis uniaxial specimens of the unidirectional thermoplastic composite (AS4/PEEK) has been measured. The experiment reveals that the rate of temperature rise is a polynomial function of stress amplitude: It consists of a quadratic term and a sixth power term. This fact implies that the specific heat of the composite depends on the stretching its microstructure undergoes during deformation. The Einstein theory for specific heat is used to explain the dependence of the specific heat on the stretching of the microstructure.

Bulk viscosity of strongly interacting matter in the relaxation time approximation

DOE PAGES

Czajka, Alina; Hauksson, Sigtryggur; Shen, Chun; ...

2018-04-24

Here, we show how thermal mean field effects can be incorporated consistently in the hydrodynamical modeling of heavy-ion collisions. The nonequilibrium correction to the distribution function resulting from a temperature-dependent mass is obtained in a procedure which automatically satisfies the Landau matching condition and is thermodynamically consistent. The physics of the bulk viscosity is studied here for Boltzmann and Bose-Einstein gases within the Chapman-Enskog and 14-moment approaches in the relaxation time approximation. Constant and temperature-dependent masses are considered in turn. It is shown that, in the small mass limit, both methods lead to the same value of the ratio ofmore » the bulk viscosity to its relaxation time. The inclusion of a temperature-dependent mass leads to the emergence of the β λ function in that ratio, and it is of the expected parametric form for the Boltzmann gas, while for the Bose-Einstein case it is affected by the infrared cutoff. This suggests that the relaxation time approximation may be too crude to obtain a reliable form of ς/τ R for gases obeying Bose-Einstein statistics.« less

Bulk viscosity of strongly interacting matter in the relaxation time approximation

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

Czajka, Alina; Hauksson, Sigtryggur; Shen, Chun

Here, we show how thermal mean field effects can be incorporated consistently in the hydrodynamical modeling of heavy-ion collisions. The nonequilibrium correction to the distribution function resulting from a temperature-dependent mass is obtained in a procedure which automatically satisfies the Landau matching condition and is thermodynamically consistent. The physics of the bulk viscosity is studied here for Boltzmann and Bose-Einstein gases within the Chapman-Enskog and 14-moment approaches in the relaxation time approximation. Constant and temperature-dependent masses are considered in turn. It is shown that, in the small mass limit, both methods lead to the same value of the ratio ofmore » the bulk viscosity to its relaxation time. The inclusion of a temperature-dependent mass leads to the emergence of the β λ function in that ratio, and it is of the expected parametric form for the Boltzmann gas, while for the Bose-Einstein case it is affected by the infrared cutoff. This suggests that the relaxation time approximation may be too crude to obtain a reliable form of ς/τ R for gases obeying Bose-Einstein statistics.« less

Bulk viscosity of strongly interacting matter in the relaxation time approximation

NASA Astrophysics Data System (ADS)

Czajka, Alina; Hauksson, Sigtryggur; Shen, Chun; Jeon, Sangyong; Gale, Charles

2018-04-01

We show how thermal mean field effects can be incorporated consistently in the hydrodynamical modeling of heavy-ion collisions. The nonequilibrium correction to the distribution function resulting from a temperature-dependent mass is obtained in a procedure which automatically satisfies the Landau matching condition and is thermodynamically consistent. The physics of the bulk viscosity is studied here for Boltzmann and Bose-Einstein gases within the Chapman-Enskog and 14-moment approaches in the relaxation time approximation. Constant and temperature-dependent masses are considered in turn. It is shown that, in the small mass limit, both methods lead to the same value of the ratio of the bulk viscosity to its relaxation time. The inclusion of a temperature-dependent mass leads to the emergence of the βλ function in that ratio, and it is of the expected parametric form for the Boltzmann gas, while for the Bose-Einstein case it is affected by the infrared cutoff. This suggests that the relaxation time approximation may be too crude to obtain a reliable form of ζ /τR for gases obeying Bose-Einstein statistics.

The topological susceptibility in finite temperature QCD and axion cosmology

DOE PAGES

Petreczky, Peter; Schadler, Hans-Peter; Sharma, Sayantan

2016-10-06

We study the topological susceptibility in 2+1 flavor QCD above the chiral crossover transition temperature using Highly Improved Staggered Quark action and several lattice spacings corresponding to temporal extent of the lattice, N τ=6,8,10 and 12. We observe very distinct temperature dependences of the topological susceptibility in the ranges above and below 250MeV. While for temperatures above 250MeV, the dependence is found to be consistent with dilute instanton gas approximation, at lower temperatures the fall-off of topological susceptibility is milder. We discuss the consequence of our results for cosmology wherein we estimate the bounds on the axion decay constant andmore » the oscillation temperature if indeed the QCD axion is a possible dark matter candidate.« less

The topological susceptibility in finite temperature QCD and axion cosmology

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

Petreczky, Peter; Schadler, Hans-Peter; Sharma, Sayantan

We study the topological susceptibility in 2+1 flavor QCD above the chiral crossover transition temperature using Highly Improved Staggered Quark action and several lattice spacings corresponding to temporal extent of the lattice, N τ=6,8,10 and 12. We observe very distinct temperature dependences of the topological susceptibility in the ranges above and below 250MeV. While for temperatures above 250MeV, the dependence is found to be consistent with dilute instanton gas approximation, at lower temperatures the fall-off of topological susceptibility is milder. We discuss the consequence of our results for cosmology wherein we estimate the bounds on the axion decay constant andmore » the oscillation temperature if indeed the QCD axion is a possible dark matter candidate.« less

Temperature-dependent growth of Geomyces destructans, the fungus that causes bat white-nose syndrome

USGS Publications Warehouse

Verant, Michelle L.; Boyles, Justin G.; Waldrep, William; Wibbelt, Gudrun; Blehert, David S.

2012-01-01

White-nose syndrome (WNS) is an emergent disease estimated to have killed over five million North American bats. Caused by the psychrophilic fungus Geomyces destructans, WNS specifically affects bats during hibernation. We describe temperature-dependent growth performance and morphology for six independent isolates of G. destructans from North America and Europe. Thermal performance curves for all isolates displayed an intermediate peak with rapid decline in performance above the peak. Optimal temperatures for growth were between 12.5 and 15.8°C, and the upper critical temperature for growth was between 19.0 and 19.8°C. Growth rates varied across isolates, irrespective of geographic origin, and above 12°C all isolates displayed atypical morphology that may have implications for proliferation of the fungus. This study demonstrates that small variations in temperature, consistent with those inherent of bat hibernacula, affect growth performance and physiology of G. destructans, which may influence temperature-dependent progression and severity of WNS in wild bats.

Velocity-dependent quantum phase slips in 1D atomic superfluids.

PubMed

Tanzi, Luca; Scaffidi Abbate, Simona; Cataldini, Federica; Gori, Lorenzo; Lucioni, Eleonora; Inguscio, Massimo; Modugno, Giovanni; D'Errico, Chiara

2016-05-18

Quantum phase slips are the primary excitations in one-dimensional superfluids and superconductors at low temperatures but their existence in ultracold quantum gases has not been demonstrated yet. We now study experimentally the nucleation rate of phase slips in one-dimensional superfluids realized with ultracold quantum gases, flowing along a periodic potential. We observe a crossover between a regime of temperature-dependent dissipation at small velocity and interaction and a second regime of velocity-dependent dissipation at larger velocity and interaction. This behavior is consistent with the predicted crossover from thermally-assisted quantum phase slips to purely quantum phase slips.

Temperature dependence of Coulomb oscillations in a few-layer two-dimensional WS2 quantum dot.

PubMed

Song, Xiang-Xiang; Zhang, Zhuo-Zhi; You, Jie; Liu, Di; Li, Hai-Ou; Cao, Gang; Xiao, Ming; Guo, Guo-Ping

2015-11-05

Standard semiconductor fabrication techniques are used to fabricate a quantum dot (QD) made of WS2, where Coulomb oscillations were found. The full-width-at-half-maximum of the Coulomb peaks increases linearly with temperature while the height of the peaks remains almost independent of temperature, which is consistent with standard semiconductor QD theory. Unlike graphene etched QDs, where Coulomb peaks belonging to the same QD can have different temperature dependences, these results indicate the absence of the disordered confining potential. This difference in the potential-forming mechanism between graphene etched QDs and WS2 QDs may be the reason for the larger potential fluctuation found in graphene QDs.

Temperature dependence of Coulomb oscillations in a few-layer two-dimensional WS2 quantum dot

PubMed Central

Song, Xiang-Xiang; Zhang, Zhuo-Zhi; You, Jie; Liu, Di; Li, Hai-Ou; Cao, Gang; Xiao, Ming; Guo, Guo-Ping

2015-01-01

Standard semiconductor fabrication techniques are used to fabricate a quantum dot (QD) made of WS2, where Coulomb oscillations were found. The full-width-at-half-maximum of the Coulomb peaks increases linearly with temperature while the height of the peaks remains almost independent of temperature, which is consistent with standard semiconductor QD theory. Unlike graphene etched QDs, where Coulomb peaks belonging to the same QD can have different temperature dependences, these results indicate the absence of the disordered confining potential. This difference in the potential-forming mechanism between graphene etched QDs and WS2 QDs may be the reason for the larger potential fluctuation found in graphene QDs. PMID:26538164

Soil and vegetation parameter uncertainty on future terrestrial carbon sinks

NASA Astrophysics Data System (ADS)

Kothavala, Z.; Felzer, B. S.

2013-12-01

We examine the role of the terrestrial carbon cycle in a changing climate at the centennial scale using an intermediate complexity Earth system climate model that includes the effects of dynamic vegetation and the global carbon cycle. We present a series of ensemble simulations to evaluate the sensitivity of simulated terrestrial carbon sinks to three key model parameters: (a) The temperature dependence of soil carbon decomposition, (b) the upper temperature limits on the rate of photosynthesis, and (c) the nitrogen limitation of the maximum rate of carboxylation of Rubisco. We integrated the model in fully coupled mode for a 1200-year spin-up period, followed by a 300-year transient simulation starting at year 1800. Ensemble simulations were conducted varying each parameter individually and in combination with other variables. The results of the transient simulations show that terrestrial carbon uptake is very sensitive to the choice of model parameters. Changes in net primary productivity were most sensitive to the upper temperature limit on the rate of photosynthesis, which also had a dominant effect on overall land carbon trends; this is consistent with previous research that has shown the importance of climatic suppression of photosynthesis as a driver of carbon-climate feedbacks. Soil carbon generally decreased with increasing temperature, though the magnitude of this trend depends on both the net primary productivity changes and the temperature dependence of soil carbon decomposition. Vegetation carbon increased in some simulations, but this was not consistent across all configurations of model parameters. Comparing to global carbon budget observations, we identify the subset of model parameters which are consistent with observed carbon sinks; this serves to narrow considerably the future model projections of terrestrial carbon sink changes in comparison with the full model ensemble.

Spatial patterns and broad-scale weather cues of beech mast seeding in Europe.

PubMed

Vacchiano, Giorgio; Hacket-Pain, Andrew; Turco, Marco; Motta, Renzo; Maringer, Janet; Conedera, Marco; Drobyshev, Igor; Ascoli, Davide

2017-07-01

Mast seeding is a crucial population process in many tree species, but its spatio-temporal patterns and drivers at the continental scale remain unknown . Using a large dataset (8000 masting observations across Europe for years 1950-2014) we analysed the spatial pattern of masting across the entire geographical range of European beech, how it is influenced by precipitation, temperature and drought, and the temporal and spatial stability of masting-weather correlations. Beech masting exhibited a general distance-dependent synchronicity and a pattern structured in three broad geographical groups consistent with continental climate regimes. Spearman's correlations and logistic regression revealed a general pattern of beech masting correlating negatively with temperature in the summer 2 yr before masting, and positively with summer temperature 1 yr before masting (i.e. 2T model). The temperature difference between the two previous summers (DeltaT model) was also a good predictor. Moving correlation analysis applied to the longest eight chronologies (74-114 yr) revealed stable correlations between temperature and masting, confirming consistency in weather cues across space and time. These results confirm widespread dependency of masting on temperature and lend robustness to the attempts to reconstruct and predict mast years using temperature data. © 2017 The Authors. New Phytologist © 2017 New Phytologist Trust.

Temperature calibration of amino acid racemization: age implications for the Yuha skeleton

USGS Publications Warehouse

Bischoff, J.L.; Childers, W.M.

1979-01-01

D/L of aspartic acid ranged from 0.52 to 0.56 for femur samples of the Yuha skeleton. Subsurface temperature measurements made at the burial site indicate average annual temperature is 18??C and diagenetic temperature is 21.6??C. These data and a relation derived for the dependence of the aspartic acid rate constant on diagenetic temperature indicate an age of 23,600. The result is consistent with 14C and 230Th dating of calcrete found coating the bones. ?? 1979.

Observations of Time-Dependent Behavior in the Two-Layer Rayleigh-Benard System

NASA Technical Reports Server (NTRS)

Andereck, C. David; Colovas, Peter W.; Degen, Michael M.

1996-01-01

In this paper we present results from experiments with a system consisting of two immiscible fluid layers in rectangular and annular geometries, driven by a vertical temperature gradient. Time-dependent variations in the type of coupling observed between the two layers are described and characterized.

Signature of quantum entanglement in NH{sub 4}CuPO{sub 4}·H{sub 2}O

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

Chakraborty, Tanmoy, E-mail: tanmoy@iiserkol.ac.in; Singh, Harkirat; Mitra, Chiranjib, E-mail: chiranjib@iiserkol.ac.in

2014-01-21

Entangled solid state systems have gained a great deal of attention due to their fruitful applications in modern quantum technologies. Herein, detection of entanglement content from experimental magnetic susceptibility and specific heat data is reported for NH{sub 4}CuPO{sub 4}·H{sub 2}O in its solid state crystalline form. NH{sub 4}CuPO{sub 4}·H{sub 2}O is a prototype of Heisenberg spin 1/2 dimer system. Temperature dependent magnetic susceptibility and specific data are fitted to an isolated dimer model and the exchange coupling constant is determined. Field dependent magnetization isotherms taken at different temperatures are plotted in a three dimensional plot. Subsequently, entanglement is detected bothmore » from susceptibility and specific heat through two different entanglement measures; entanglement witness and entanglement of formation. The temperature evolution of entanglement is studied and the critical temperature is determined up to which entanglement exists. Temperature dependent nature of entanglement extracted from susceptibility and specific heat shows good consistency with each other. Moreover, the field dependent entanglement is also investigated.« less

Radar attenuation and temperature within the Greenland Ice Sheet

USGS Publications Warehouse

MacGregor, Joseph A; Li, Jilu; Paden, John D; Catania, Ginny A; Clow, Gary D.; Fahnestock, Mark A; Gogineni, Prasad S.; Grimm, Robert E.; Morlighem, Mathieu; Nandi, Soumyaroop; Seroussi, Helene; Stillman, David E

2015-01-01

The flow of ice is temperature-dependent, but direct measurements of englacial temperature are sparse. The dielectric attenuation of radio waves through ice is also temperature-dependent, and radar sounding of ice sheets is sensitive to this attenuation. Here we estimate depth-averaged radar-attenuation rates within the Greenland Ice Sheet from airborne radar-sounding data and its associated radiostratigraphy. Using existing empirical relationships between temperature, chemistry, and radar attenuation, we then infer the depth-averaged englacial temperature. The dated radiostratigraphy permits a correction for the confounding effect of spatially varying ice chemistry. Where radar transects intersect boreholes, radar-inferred temperature is consistently higher than that measured directly. We attribute this discrepancy to the poorly recognized frequency dependence of the radar-attenuation rate and correct for this effect empirically, resulting in a robust relationship between radar-inferred and borehole-measured depth-averaged temperature. Radar-inferred englacial temperature is often lower than modern surface temperature and that of a steady state ice-sheet model, particularly in southern Greenland. This pattern suggests that past changes in surface boundary conditions (temperature and accumulation rate) affect the ice sheet's present temperature structure over a much larger area than previously recognized. This radar-inferred temperature structure provides a new constraint for thermomechanical models of the Greenland Ice Sheet.

Self-consistent mean-field approach to the statistical level density in spherical nuclei

NASA Astrophysics Data System (ADS)

Kolomietz, V. M.; Sanzhur, A. I.; Shlomo, S.

2018-06-01

A self-consistent mean-field approach within the extended Thomas-Fermi approximation with Skyrme forces is applied to the calculations of the statistical level density in spherical nuclei. Landau's concept of quasiparticles with the nucleon effective mass and the correct description of the continuum states for the finite-depth potentials are taken into consideration. The A dependence and the temperature dependence of the statistical inverse level-density parameter K is obtained in a good agreement with experimental data.

Comparison of temperature effects on E. coli, Salmonella, and Enterococcus survival in surface waters

USDA-ARS?s Scientific Manuscript database

The objective of this study was to compare the dependencies of survival rates on temperature for indicator organisms E. coli and Enterococcus and the pathogen Salmonella in surface waters. A database consisting of 86 survival datasets from peer-reviewed papers on inactivation of E. coli, Salmonella...

A common thermal niche among geographically diverse populations of the widely distributed tree species Eucalyptus tereticornis: No evidence for adaptation to climate-of-origin.

PubMed

Drake, John E; Vårhammar, Angelica; Kumarathunge, Dushan; Medlyn, Belinda E; Pfautsch, Sebastian; Reich, Peter B; Tissue, David T; Ghannoum, Oula; Tjoelker, Mark G

2017-12-01

Impacts of climate warming depend on the degree to which plants are constrained by adaptation to their climate-of-origin or exhibit broad climatic suitability. We grew cool-origin, central and warm-origin provenances of Eucalyptus tereticornis in an array of common temperature environments from 18 to 35.5°C to determine if this widely distributed tree species consists of geographically contrasting provenances with differentiated and narrow thermal niches, or if provenances share a common thermal niche. The temperature responses of photosynthesis, respiration, and growth were equivalent across the three provenances, reflecting a common thermal niche despite a 2,200 km geographic distance and 13°C difference in mean annual temperature at seed origin. The temperature dependence of growth was primarily mediated by changes in leaf area per unit plant mass, photosynthesis, and whole-plant respiration. Thermal acclimation of leaf, stem, and root respiration moderated the increase in respiration with temperature, but acclimation was constrained at high temperatures. We conclude that this species consists of provenances that are not differentiated in their thermal responses, thus rejecting our hypothesis of adaptation to climate-of-origin and suggesting a shared thermal niche. In addition, growth declines with warming above the temperature optima were driven by reductions in whole-plant leaf area and increased respiratory carbon losses. The impacts of climate warming will nonetheless vary across the geographic range of this and other such species, depending primarily on each provenance's climate position on the temperature response curves for photosynthesis, respiration, and growth. © 2017 John Wiley & Sons Ltd.

Temperature-dependent index of refraction of monoclinic Ga2O3 single crystal.

PubMed

Bhaumik, Indranil; Bhatt, R; Ganesamoorthy, S; Saxena, A; Karnal, A K; Gupta, P K; Sinha, A K; Deb, S K

2011-11-01

We present temperature-dependent refractive index along crystallographic b[010] and a direction perpendicular to (100)-plane for monoclinic phase (β) Ga(2)O(3) single crystal grown by the optical floating zone technique. The experimental results are consistent with the theoretical result of Litimein et al.1. Also, the Sellmeier equation for wavelengths in the range of 0.4-1.55 μm is formulated at different temperatures in the range of 30-175 °C. The thermal coefficient of refractive index in the above specified range is ~10(-5)/°C. © 2011 Optical Society of America

[Investigation on the impact of hot temperature methods of the tissue dissection and coagulation on parenchymatous organs in experiment].

PubMed

Sukhin, I A; Khudets'kyĭ, I Iu; Kachan, S H; Bilylovets', O M

2013-01-01

There are adduced the results of experimental operations on mongrel rabbits with dissection and coagulation of the liver and the spleen, using highly temperature coagulation apparatuses of various kinds. There was established, that while application of various highly temperature technologies a typical process occurs, consisting of the heat spreading inside the organ. The temperature raising grade depends on the method and duration of the impact.

Temperature effect on the small-to-large crossover lengthscale of hydrophobic hydration

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

Djikaev, Y. S., E-mail: idjikaev@buffalo.edu; Ruckenstein, E.

2013-11-14

The thermodynamics of hydration is expected to change gradually from entropic for small solutes to enthalpic for large ones. The small-to-large crossover lengthscale of hydrophobic hydration depends on the thermodynamic conditions of the solvent such as temperature, pressure, presence of additives, etc. We attempt to shed some light on the temperature dependence of the crossover lengthscale by using a probabilistic approach to water hydrogen bonding that allows one to obtain an analytic expression for the number of bonds per water molecule as a function of both its distance to a solute and solute radius. Incorporating that approach into the densitymore » functional theory, one can examine the solute size effects on its hydration over the entire small-to-large lengthscale range at a series of different temperatures. Knowing the dependence of the hydration free energy on the temperature and solute size, one can also obtain its enthalpic and entropic contributions as functions of both temperature and solute size. These functions can provide some interesting insight into the temperature dependence of the crossover lengthscale of hydrophobic hydration. The model was applied to the hydration of spherical particles of various radii in water in the temperature range from T = 293.15 K to T = 333.15 K. The model predictions for the temperature dependence of the hydration free energy of small hydrophobes are consistent with the experimental and simulational data on the hydration of simple molecular solutes. Three alternative definitions for the small-to-large crossover length-scale of hydrophobic hydration are proposed, and their temperature dependence is obtained. Depending on the definition and temperature, the small-to-large crossover in the hydration mechanism is predicted to occur for hydrophobes of radii from one to several nanometers. Independent of its definition, the crossover length-scale is predicted to decrease with increasing temperature.« less

Temperature dependent barrier height and ideality factor of electrodeposited n-CdSe/Cu Schottky barrier diode

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

Mahato, S., E-mail: som.phy.ism@gmail.com; Shiwakoti, N.; Kar, A. K.

2015-06-24

This article reports the measurement of temperature-dependent barrier height and ideality factor of n-CdSe/Cu Schottky barrier diode. The Cadmium Selenide (CdSe) thin films have been deposited by simple electrodeposition technique. The XRD measurements ravels the deposited single phase CdSe films are highly oriented on (002) plane and the average particle size has been calculated to be ~18 nm. From SEM characterization, it is clear that the surface of CdSe thin films are continuous, homogeneous and the film is well adhered to the substrate and consists of fine grains which are irregular in shape and size. Current-Voltage characteristics have been measured atmore » different temperatures in the range (298 K – 353 K). The barrier height and ideality factor are found to be strongly temperature dependent. The inhomogenious barrier height increases and ideality factor decreases with increase in temperature. The expectation value has been calculated and its value is 0.30 eV.« less

Spectral Line Parameters Including Temperature Dependences of Self- and Air-Broadening in the 2 (left arrow) 0 Band of CO at 2.3 micrometers

NASA Technical Reports Server (NTRS)

Devi, V. Malathy; Benner, D. Chris; Smith, M. A. H.; Mantz, A. W.; Sung, K.; Brown, L. R.; Predoi-Cross, A.

2012-01-01

Temperature dependences of pressure-broadened half-width and pressure-induced shift coefficients along with accurate positions and intensities have been determined for transitions in the 2<--0 band of C-12 O-16 from analyzing high-resolution and high signal-to-noise spectra recorded with two different Fourier transform spectrometers. A total of 28 spectra, 16 self-broadened and 12 air-broadened, recorded using high- purity (greater than or equal to 99.5% C-12-enriched) CO samples and CO diluted with dry air(research grade) at different temperatures and pressures, were analyzed simultaneously to maximize the accuracy of the retrieved parameters. The sample temperatures ranged from 150 to 298K and the total pressures varied between 5 and 700 Torr. A multispectrum nonlinear least squares spectrum fitting technique was used to adjust the rovibrational constants (G, B, D, etc.) and intensity parameters (including Herman-Wallis coefficients), rather than determining individual line positions and intensities. Self-and air-broadened Lorentz half-width coefficients, their temperature dependence exponents, self- and air-pressure-induced shift coefficients, their temperature dependences, self- and air-line mixing coefficients, their temperature dependences and speed dependence have been retrieved from the analysis. Speed-dependent line shapes with line mixing employing off-diagonal relaxation matrix element formalism were needed to minimize the fit residuals. This study presents a precise and complete set of spectral line parameters that consistently reproduce the spectrum of carbon monoxide over terrestrial atmospheric conditions.

An Elevated-Temperature Tension-Compression Test and Its Application to Magnesium AZ31B

NASA Astrophysics Data System (ADS)

Piao, Kun

Many metals, particularly ones with HCP crystal structures, undergo deformation by combinations of twinning and slip, the proportion of which depends on variables such as temperature and strain rate. Typical techniques to reveal such mechanisms rely on metallography, x-ray diffraction, or electron optics. Simpler, faster, less expensive mechanical tests were developed in the current work and applied to Mg AZ31B. An apparatus was designed, simulated, optimized, and constructed to enable the large-strain, continuous tension/compression testing of sheet materials at elevated temperature. Thermal and mechanical FE analyses were used to locate cartridge heaters, thus enabling the attainment of temperatures up to 350°C within 15 minutes of start-up, and ensuring temperature uniformity throughout the gage length within 8°C. The low-cost device also makes isothermal testing possible at strain rates higher than corresponding tests in air. Analysis was carried out to predict the attainable compressive strains using novel finite element (FE) modeling and a single parameter characteristic of the machine and fixtures. The limits of compressive strain vary primarily with the material thickness and the applied-side-force-to-material-strength ratio. Predictions for a range of sheet alloys with measured buckling strains from -0.04 to -0.17 agreed within a standard deviation of 0.025 (0.015 excluding one material that was not initially flat). In order to demonstrate the utility of the new method, several sheet materials were tested over a range of temperatures. Some of the data obtained is the first of its kind. Magnesium AZ31B sheets were tested at temperatures up to 250°C with strain rate of 0.001/s. The inflected stress-strain curve observed in compression at room temperature disappeared between 125°C and 150°C, corresponding to the suppression of twinning, and suggesting a simple method for identifying the deformation mechanism transition temperature. The temperature-dependent behavior of selected advanced high strength steels (TWIP and DP) was revealed by preliminary tests at room temperature, 150°C and 250°C. For Mg AZ31B alloy sheets, the curvature of compressive stress-strain plots over a fixed strain range was found to be a consistent indicator of twinning magnitude, independent of temperature and strain rate. The relationship between curvature and areal fraction of twins is presented. Transition temperatures determined based on stress-strain curvature were consistent with ones determined by metallographic analysis and flow stresses, and depended on strain rate by the Zener-Hollomon parameter, a critical value for which was measured. The transition temperature was found to depend significantly on grain size, a relationship for which was established. Finally, it was shown that the transition temperature can be determined consistently, and much faster, using a single novel "Step-Temperature" test.

Simulation of the real efficiencies of high-efficiency silicon solar cells

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

Sachenko, A. V., E-mail: sach@isp.kiev.ua; Skrebtii, A. I.; Korkishko, R. M.

The temperature dependences of the efficiency η of high-efficiency solar cells based on silicon are calculated. It is shown that the temperature coefficient of decreasing η with increasing temperature decreases as the surface recombination rate decreases. The photoconversion efficiency of high-efficiency silicon-based solar cells operating under natural (field) conditions is simulated. Their operating temperature is determined self-consistently by simultaneously solving the photocurrent, photovoltage, and energy-balance equations. Radiative and convective cooling mechanisms are taken into account. It is shown that the operating temperature of solar cells is higher than the ambient temperature even at very high convection coefficients (~300 W/m{sup 2}more » K). Accordingly, the photoconversion efficiency in this case is lower than when the temperature of the solar cells is equal to the ambient temperature. The calculated dependences for the open-circuit voltage and the photoconversion efficiency of high-quality silicon solar cells under concentrated illumination are discussed taking into account the actual temperature of the solar cells.« less

Dmrt1 induces the male pathway in a turtle species with temperature-dependent sex determination.

PubMed

Ge, Chutian; Ye, Jian; Zhang, Haiyan; Zhang, Yi; Sun, Wei; Sang, Yapeng; Capel, Blanche; Qian, Guoying

2017-06-15

The molecular mechanism underlying temperature-dependent sex determination (TSD) has been a long-standing mystery; in particular, the thermosensitive genetic triggers for gonadal sex differentiation are largely unknown. Here, we have characterized a conserved DM domain gene, Dmrt1 , in the red-eared slider turtle Trachemys scripta ( T. scripta ), which exhibits TSD. We found that Dmrt1 has a temperature-dependent, sexually dimorphic expression pattern, preceding gonadal sex differentiation, and is capable of responding rapidly to temperature shifts and aromatase inhibitor treatment. Most importantly, loss- and gain-of-function analyses provide solid evidence that Dmrt1 is both necessary and sufficient to initiate male development in T. scripta Furthermore, the DNA methylation dynamics of the Dmrt1 promoter are tightly correlated with temperature and could mediate the impact of temperature on sex determination. Collectively, our findings demonstrate that Dmrt1 is a candidate master male sex-determining gene in this TSD species, consistent with the idea that DM domain genes are conserved during the evolution of sex determination mechanisms. © 2017. Published by The Company of Biologists Ltd.

Analytic, empirical and delta method temperature derivatives of D-D and D-T fusion reactivity formulations, as a means of verification

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

Langenbrunner, James R.; Booker, Jane M.

We examine the derivatives with respect to temperature, for various deuterium-tritium (DT) and deuterium-deuterium (D-D) fusion-reactivity formulations. Langenbrunner and Makaruk [1] had studied this as a means of understanding the time and temperature domain of reaction history measured in dynamic fusion experiments. Presently, we consider the temperature derivative dependence of fusion reactivity as a means of exercising and verifying the consistency of the various reactivity formulations.

Radiation-induced polymerization of glass-forming systems. V. Initial polymerization rate in binary glass-forming systems

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

Kaetsu, Isao; Okubo, Hiroshi; Ito, Akihiko

1973-06-01

The radiation-induced polymerization of binary systems consisting of glass-forming monomer and glass-forming solvent in supercooled phase was studied. The initial polymerization rates were markedly affected by T/sub g/ (glass transition temperature) and T/sub v/ of the system (30-50 deg C higher than T/sub g/), which are functions of the composition. The composition and temperature dependence of initial polymerization rate in binary glass-forming systems were much affected by homogeneity of the polymerization system and the T of the glass- forming solvent. The composition and temperature dependences in the glycidyl methacrylate --triacetin system as a typical homogeneous polymerization system were studied inmore » detail, and the polymerizations of hydroxyethyl methacrylate triacetln and hydroxyethyl methacrylate --isoamyl acetate systems were studied for the heterogeneous polymerization systems; the former illustrates the combination of lower T/sub g/ monomer and higher T/sub g/ solvent and the latter typifies a system consisting of higher T/sub g/ monomer and lower T/sub g/ solvent. All experimental results for the composition and temperature dependence of initial polymerization rate in binary glass-forming systems could be explained by considering the product of the effect of the physical effect relating to T/sub v/ and T/sub g/ of the system and the effect of composition in normal solution polymerization at higher temperature, which was also the product of a dilution effect and a chemical or physical acceleration effect. (auth)« less

Electron spin resonance in Cu1-xFexCr2Se4 nanoparticles synthesized with the thermal decomposition method

NASA Astrophysics Data System (ADS)

Edelman, I. S.; Zharkov, S. M.; Pankrats, A. I.; Vorotynov, A. M.; Tugarinov, V. I.; Ivantsov, R. D.; Petrov, D. A.; Velikanov, D. A.; Lin, Chun-Rong; Chen, Chin-Chang; Tseng, Yaw-Teng; Hsu, Hua-Shu

2017-08-01

In this paper, we present a study of the electron spin resonance (ESR) of nanoparticles (NPs) of Cu1-xFexCr2Se4 chalcogenides with x = 0, 0.2, and 0.4. NPs were synthesized via the thermal decomposition of metal chloride salts and selenium powder in a high-temperature organic solvent. According to the XRD and HRTEM data, the NPs were single crystalline nearly hexagonal plates with the structure close to CuCr2Se4 (Fd-3m, a = 10.337 Å). For x = 0 and 0.2, the NPs tend to form long stacks consisting of the plates ;face to face; attached to each other due to the magnetostatic interparticle interaction. Only separate NPs were observed in the case of x = 0.4. Peculiarities were revealed in the ESR temperature behavior for the NPs with x = 0 and 0.2 consistent with the features in the temperature dependences of the NPs magnetization. The non-monotonous dependence of the resonance field Hres on the temperature with a kink near 130 K and the energy gap in the resonance spectrum depending on the type of nanoparticle compacting are the distinct peculiarities. One of the main factors is discussed in order to explain the peculiarities: the coexistence of two types of anisotropy in the Cu1-xFexCr2Se4 NPs, in-plain shape anisotropy and magnetocrystalline anisotropy with four easy axes, which increases strongly with the temperature decrease.

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

Liu, Liwang, E-mail: liwang.liu@hotmail.com; Meng, Lei; Wang, Ling

The temperature dependence of the fluorescence spectrum of CdSe−ZnS core–shell quantum dots embedded in a polystyrene matrix is characterized between 30 °C and 60 °C. The spectrally integrated photoluminescence intensity is found to linearly decrease with −1.3%/ °C. This feature is exploited in a dual coating-substrate-configuration, consisting of a layer of this nanocomposite material, acting as a temperature sensor with optical readout, on top of an optically absorbing and opaque layer, acting as a photothermal excitation source, and covering a substrate material or structure of interest. From the frequency dependence of the optically detected photothermal signal in the frequency range between 5 Hz andmore » 150 Hz, different thermal parameters of the constituent layers are determined. The fitted values of thermal properties of the different layers, determined in different scenarios in terms of the used a priori information about the layers, are found to be internally consistent, and consistent with literature values.« less

Temperature measurement systems in wearable electronics

NASA Astrophysics Data System (ADS)

Walczak, S.; Gołebiowski, J.

2014-08-01

The aim of this paper is to present the concept of temperature measurement system, adapted to wearable electronics applications. Temperature is one of the most commonly monitored factor in smart textiles, especially in sportswear, medical and rescue products. Depending on the application, measured temperature could be used as an initial value of alert, heating, lifesaving or analysis system. The concept of the temperature measurement multi-point system, which consists of flexible screen-printed resistive sensors, placed on the T-shirt connected with the central unit and the power supply is elaborated in the paper.

Observation of Wigner crystal phase and ripplon-limited mobility behavior in monolayer CVD MoS2 with grain boundary.

PubMed

Chen, Jyun-Hong; Zhong, Yuan-Liang; Li, Lain-Jong; Chen, Chii-Dong

2018-06-01

Two-dimensional electron gas (2DEG) is crucial in condensed matter physics and is present on the surface of liquid helium and at the interface of semiconductors. Monolayer MoS 2 of 2D materials also contains 2DEG in an atomic layer as a field effect transistor (FET) ultrathin channel. In this study, we synthesized double triangular MoS 2 through a chemical vapor deposition method to obtain grain boundaries for forming a ripple structure in the FET channel. When the temperature was higher than approximately 175 K, the temperature dependence of the electron mobility μ was consistent with those in previous experiments and theoretical predictions. When the temperature was lower than approximately 175 K, the mobility behavior decreased with the temperature; this finding was also consistent with that of the previous experiments. We are the first research group to explain the decreasing mobility behavior by using the Wigner crystal phase and to discover the temperature independence of ripplon-limited mobility behavior at lower temperatures. Although these mobility behaviors have been studied on the surface of liquid helium through theories and experiments, they have not been previously analyzed in 2D materials and semiconductors. We are the first research group to report the similar temperature-dependent mobility behavior of the surface of liquid helium and the monolayer MoS 2 .

Observation of Wigner crystal phase and ripplon-limited mobility behavior in monolayer CVD MoS2 with grain boundary

NASA Astrophysics Data System (ADS)

Chen, Jyun-Hong; Zhong, Yuan-Liang; Li, Lain-Jong; Chen, Chii-Dong

2018-06-01

Two-dimensional electron gas (2DEG) is crucial in condensed matter physics and is present on the surface of liquid helium and at the interface of semiconductors. Monolayer MoS2 of 2D materials also contains 2DEG in an atomic layer as a field effect transistor (FET) ultrathin channel. In this study, we synthesized double triangular MoS2 through a chemical vapor deposition method to obtain grain boundaries for forming a ripple structure in the FET channel. When the temperature was higher than approximately 175 K, the temperature dependence of the electron mobility μ was consistent with those in previous experiments and theoretical predictions. When the temperature was lower than approximately 175 K, the mobility behavior decreased with the temperature; this finding was also consistent with that of the previous experiments. We are the first research group to explain the decreasing mobility behavior by using the Wigner crystal phase and to discover the temperature independence of ripplon-limited mobility behavior at lower temperatures. Although these mobility behaviors have been studied on the surface of liquid helium through theories and experiments, they have not been previously analyzed in 2D materials and semiconductors. We are the first research group to report the similar temperature-dependent mobility behavior of the surface of liquid helium and the monolayer MoS2.

Temperature dependency of the repair of sublethal damage in cultured fish cells

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

Mitani, H.; Egami, N.

1984-01-01

Established culture fish cells, CAF-MMMI, derived form the goldfish, Carassium auratus, were able to grow and form colonies over a temperature range from 20 to 33/sup 0/ C. While the growth rate of these cells was dependent on incubation temperature, colony formation had no effect on cell survival after ..gamma.. irradiation at high dose rates. The lethal effect of ..gamma.. rays was decreased at low dose rates at 20-33/sup 0/ C, but not at 6/sup 0/ C. Similarly, split-dose experiments showed that recovery from sublethal damage occurred at the higher temperatures, but not at 6/sup 0/ C. These data aremore » consistent with the in vivo data on the effect of temperature on the radiosensitivity and repair of sublethal damage reported previously for live fish.« less

Development of the III-V Barrier PhotoDetector Heterostructures for Spectral Range Above 10 microns

DTIC Science & Technology

2016-02-14

Figure 5. Quantum efficiency spectra (a) and temperature dependence of dark current (b) in heterostructures consisting of bulk InAsSb absorber and...compositions covering the range from 20 to 65 %. The solved challenges include selection of the buffer grade composition rate and growth temperature ...absorbers can operate at elevated temperatures and with faster response compared to those in detectors with n-type absorbers. It was important to

Experimental Identification and Simulation of Time and/or Rate Dependent Reversible and Irreversible Deformation Regions for both a Titanium and Nickel Alloy

NASA Technical Reports Server (NTRS)

Arnold, Steven M.; Lerch, Bradley A.; Sellers, Cory

2013-01-01

In this paper time and/or rate dependent deformation regions are experimentally mapped out as a function of temperature. It is clearly demonstrated that the concept of a threshold stress (a stress that delineate reversible and irreversible behavior) is valid and necessary at elevated temperatures and corresponds to the classical yield stress at lower temperatures. Also the infinitely slow modulus, (Es) i.e. the elastic modulus of the material if it was loaded at an infinitely slow strain rate, and the "dynamic modulus", modulus, Ed, which represents the modulus of the material if it is loaded at an infinitely fast rate are used to delineate rate dependent from rate independent regions. As demonstrated at elevated temperatures there is a significant difference between the two modulus values, thus indicating both significant time-dependence and rate dependence. In the case of the nickel-based super alloy, ME3, this behavior is also shown to be grain size specific. Consequently, at higher temperatures viscoelastic behavior exist below k (i.e., the threshold stress) and at stresses above k the behavior is viscoplastic. Finally a multi-mechanism, stress partitioned viscoelastic model, capable of being consistently coupled to a viscoplastic model is characterized over the full temperature range investigated for Ti-6-4 and ME3.

Temperature dependence of ballistic mobility in a metamorphic InGaAs/InAlAs high electron mobility transistor

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

Lee, Jongkyong; Gang, Suhyun; Jo, Yongcheol

We have investigated the temperature dependence of ballistic mobility in a 100 nm-long InGaAs/InAlAs metamorphic high-electron-mobility transistor designed for millimeter-wavelength RF applications. To extract the temperature dependence of quasi-ballistic mobility, our experiment involves measurements of the effective mobility in the low-bias linear region of the transistor and of the collision-dominated Hall mobility using a gated Hall bar of the same epitaxial structure. The data measured from the experiment are consistent with that of modeled ballistic mobility based on ballistic transport theory. These results advance the understanding of ballistic transport in various transistors with a nano-scale channel length that is comparable tomore » the carrier's mean free path in the channel.« less

Measurements of the Temperature-Dependent Total Hemispherical Emissivity Using an Electrostatic Levitation Facility

NASA Astrophysics Data System (ADS)

Gangopadhyay, A. K.; Kelton, K. F.

2017-01-01

Among the three fundamental processes of heat transfer (conduction, convection, and radiation), radiation is the most dominant at high temperatures. The total hemispherical emissivity is an important property that determines the amount of heat loss by radiation. Unfortunately, the emissivity, especially its temperature dependence (ɛ (T)), is unknown for most materials. Here, we demonstrate the feasibility of measuring ɛ (T) using an electrostatic levitation (ESL) technique that allows such measurements to be made on levitated solid and liquid samples in a contamination-free, high-vacuum environment. The ɛ (T) for solid Ni and liquid Zr_{60}Al_{10}Cu_{18}Ni9Co3 from these measurements is consistent with the existing literature data.

Acoustic and relaxation behaviors of polydimethylsiloxane studied by using brillouin and dielectric spectroscopies

NASA Astrophysics Data System (ADS)

Lee, Byoung Wan; Ko, Jae-Hyeon; Park, Jaehoon; Shin, Dong-Myeong; Hwang, Yoon-Hwae

2016-04-01

The temperature dependences of the acoustic properties and the dielectric relaxation times of polydimethylsiloxane were investigated by using high-resolution Brillouin and broadband dielectric spectroscopies. The longitudinal sound velocity showed a large increase upon approaching the glass transition temperature while the acoustic absorption coefficient exhibited a maximum at ~263 K. Comparison of these results with previous ultrasonic data revealed a substantial frequency dispersion of the acoustic properties of this silicone-based elastomer. The relaxation times derived from the acoustic absorption peaks were consistent with the temperature dependence of the dielectric relaxation time of the structural a process, indicating a strong coupling between the acoustic waves and the segmental motions of the main chains.

Temperature-induced Lifshitz transition in WTe 2

DOE PAGES

Wu, Yun; Jo, Na Hyun; Ochi, Masayuki; ...

2015-10-12

In this study, we use ultrahigh resolution, tunable, vacuum ultraviolet laser-based, angle-resolved photoemission spectroscopy (ARPES), temperature- and field-dependent resistivity, and thermoelectric power (TEP) measurements to study the electronic properties of WTe 2, a compound that manifests exceptionally large, temperature-dependent magnetoresistance. The Fermi surface consists of two pairs of electron and two pairs of hole pockets along the X–Γ–X direction. Using detailed ARPES temperature scans, we find a rare example of a temperature-induced Lifshitz transition at T≃160 K, associated with the complete disappearance of the hole pockets. Our electronic structure calculations show a clear and substantial shift of the chemical potentialmore » μ(T) due to the semimetal nature of this material driven by modest changes in temperature. This change of Fermi surface topology is also corroborated by the temperature dependence of the TEP that shows a change of slope at T≈175 K and a breakdown of Kohler’s rule in the 70–140 K range. Our results and the mechanisms driving the Lifshitz transition and transport anomalies are relevant to other systems, such as pnictides, 3D Dirac semimetals, and Weyl semimetals.« less

Large but uneven reduction in fish size across species in relation to changing sea temperatures.

PubMed

van Rijn, Itai; Buba, Yehezkel; DeLong, John; Kiflawi, Moshe; Belmaker, Jonathan

2017-09-01

Ectotherms often attain smaller body sizes when they develop at higher temperatures. This phenomenon, known as the temperature-size rule, has important consequences for global fisheries, whereby ocean warming is predicted to result in smaller fish and reduced biomass. However, the generality of this phenomenon and the mechanisms that drive it in natural populations remain unresolved. In this study, we document the maximal size of 74 fish species along a steep temperature gradient in the Mediterranean Sea and find strong support for the temperature-size rule. Importantly, we additionally find that size reduction in active fish species is dramatically larger than for more sedentary species. As the temperature dependence of oxygen consumption depends on activity levels, these findings are consistent with the hypothesis that oxygen is a limiting factor shaping the temperature-size rule in fishes. These results suggest that ocean warming will result in a sharp, but uneven, reduction in fish size that will cause major shifts in size-dependent interactions. Moreover, warming will have major implications for fisheries as the main species targeted for harvesting will show the most substantial declines in biomass. © 2017 John Wiley & Sons Ltd.

Temperature dependence of quantized states in an InGaAs/GaAs strained asymmetric triangular quantum well

NASA Astrophysics Data System (ADS)

Chi, W. S.; Lin, D. Y.; Huang, Y. S.; Qiang, H.; Pollak, F. H.; Mathine, D. L.; Maracas, G. N.

1996-03-01

Photoreflectance (PR), contactless electroreflectance (CER) and piezoreflectance (PzR) measurements of an InGaAs/GaAs strained asymmetric triangular quantum well (ATQW) heterostructure as a function of temperature in the range of 20 to 300 K have been carried out. The structure was fabricated by molecular beam epitaxy using the digital alloy compositional grading method. A careful analysis of the PR, CER and PzR spectra has led to the identification of various excitonic transitions, mnH(L), between the mth conduction band state to the nth heavy(light)-hole band state. Comparison of the observed intersubband transitions with a theoretical calculation based on the envelope function model, including the effects of strain, provide a self-consistent check of the ATQW composition profile. The detailed study of the temperature dependence of the excitonic transition energies indicates that the potential profile of the ATQW varies at different temperatures. The parameters that describe the temperature dependence of 0268-1242/11/3/012/img8 are evaluated. The anomalous behaviour of the temperature dependence of the linewidth of 11H, 0268-1242/11/3/012/img9, is compared with recent results for GaAs/AlGaAs and InGaAs/GaAs symmetric rectangular quantum wells of comparable dimensions.

A temperature-dependent coarse-grained model for the thermoresponsive polymer poly(N-isopropylacrylamide).

PubMed

Abbott, Lauren J; Stevens, Mark J

2015-12-28

A coarse-grained (CG) model is developed for the thermoresponsive polymer poly(N-isopropylacrylamide) (PNIPAM), using a hybrid top-down and bottom-up approach. Nonbonded parameters are fit to experimental thermodynamic data following the procedures of the SDK (Shinoda, DeVane, and Klein) CG force field, with minor adjustments to provide better agreement with radial distribution functions from atomistic simulations. Bonded parameters are fit to probability distributions from atomistic simulations using multi-centered Gaussian-based potentials. The temperature-dependent potentials derived for the PNIPAM CG model in this work properly capture the coil-globule transition of PNIPAM single chains and yield a chain-length dependence consistent with atomistic simulations.

Weak antilocalization of composite fermions in graphene

NASA Astrophysics Data System (ADS)

Laitinen, Antti; Kumar, Manohar; Hakonen, Pertti J.

2018-02-01

We demonstrate experimentally that composite fermions in monolayer graphene display weak antilocalization. Our experiments deal with fractional quantum Hall (FQH) states in high-mobility, suspended graphene Corbino disks in the vicinity of ν =1 /2 . We find a strong temperature dependence of conductivity σ away from half filling, which is consistent with the expected electron-electron interaction-induced gaps in the FQH state. At half filling, however, the temperature dependence of conductivity σ (T ) becomes quite weak, as anticipated for a Fermi sea of composite fermions, and we find a logarithmic dependence of σ on T . The sign of this quantum correction coincides with the weak antilocalization of graphene composite fermions, indigenous to chiral Dirac particles.

Temperature effect on pyrene as a polarity probe for supercritical fluid and liquid solutions

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

Chen, H.H.; McGuffin, V.L.

1994-05-01

The effect of temperature on the fluorescence spectrum of pyrene in supercritical and liquid carbon dioxide and liquid organic solvents is systematically studied. The Py parameter (intensity ratio of vibronic bands 1 and 3) is found to increase with the density of supercritical carbon dioxide in the range from 0.54 to 0.75 g/cm{sup 3}. This observation is consistent with the fact that dispersion forces which represent the major interaction between pyrene and carbon dioxide, depend inversely on the sixth power of distance. However, the Py parameter of both supercritical and liquid carbon dioxide is also found to decrease with temperaturemore » at constant density, which is not consistent with expectations for dispersion forces. Carbon dioxide, which is generally regarded as a nonpopular solvent, shows a temperature effect comparable to that for polar liquid solvents. The origin of this temperature effect is examined in this study by computer simulation using both semispherical molecular orbital and molecular mechanic methods. On the basis of these simulations, a strong electrostatic attraction arises between pyrene and carbon dioxide which is similiar in magnitude to that with polar solvents. The temperature dependence of the Py parameter can be qualitatively explained by these simulation results. 45 refs., 15 fig., 5 tab.« less

Molecular Dynamics Simulations of Star Polymeric Molecules with Diblock Arms, a Comparative Study.

PubMed

Swope, William C; Carr, Amber C; Parker, Amanda J; Sly, Joseph; Miller, Robert D; Rice, Julia E

2012-10-09

We have performed all atom explicit solvent molecular dynamics simulations of three different star polymeric systems in water, each star molecule consisting of 16 diblock copolymer arms bound to a small adamantane core. The arms of each system consist of an inner "hydrophobic" block (either polylactide, polyvalerolactone, or polyethylene) and an outer hydrophilic block (polyethylene oxide, PEO). These models exhibit unusual structure very close to the core (clearly an artifact of our model) but which we believe becomes "normal" or bulk-like at relatively short distances from this core. We report on a number of temperature-dependent thermodynamic (structural/energetic) properties as well as kinetic properties. Our observations suggest that under physiological conditions, the hydrophobic regions of these systems may be solid and glassy, with only rare and shallow penetration by water, and that a sharp boundary exists between the hydrophobic cores and either the PEO or water. The PEO in these models is seen to be fully water-solvated at low temperatures but tends to phase separate from water as the temperature is increased, reminiscent of a lower critical solution temperature exhibited by PEO-water mixtures. Water penetration concentration and depth is composition and temperature dependent with greater water penetration for the most ester-rich star polymer.

Modeling the thermo-acoustic effects of thermal-dependent speed of sound and acoustic absorption of biological tissues during focused ultrasound hyperthermia.

PubMed

López-Haro, S A; Gutiérrez, M I; Vera, A; Leija, L

2015-10-01

To evaluate the effects of thermal dependence of speed of sound (SOS) and acoustic absorption of biological tissues during noninvasive focused ultrasound (US) hyperthermia therapy. A finite element (FE) model was used to simulate hyperthermia therapy in the liver by noninvasive focused US. The model consisted of an ultrasonic focused transducer radiating a four-layer biological medium composed of skin, fat, muscle, and liver. The acoustic field and temperature distribution along the layers were obtained after 15 s of hyperthermia therapy using the bio-heat equation. The model solution was found with and without the thermal dependence of SOS and acoustic absorption of biological tissues. The inclusion of the thermal dependence of the SOS generated an increment of 0.4 mm in the longitudinal focus axis of the acoustic field. Moreover, results indicate an increment of the hyperthermia area (zone with temperature above 43 °C), and a maximum temperature difference of almost 3.5 °C when the thermal dependence of absorption was taken into account. The increment of the achieved temperatures at the treatment zone indicated that the effects produced by the thermal dependence of SOS and absorption must be accounted for when planning hyperthermia treatment in order to avoid overheating undesired regions.

Noctilucent cloud formation and the effects of water vapor variability on temperatures in the middle atmosphere

NASA Technical Reports Server (NTRS)

Mckay, C. P.

1985-01-01

To investigate the occurrence of low temperatures and the formation of noctilucent clouds in the summer mesosphere, a one-dimensional time-dependent photochemical-thermal numerical model of the atmosphere between 50 and 120 km has been constructed. The model self-consistently solves the coupled photochemical and thermal equations as perturbation equations from a reference state assumed to be in equilibrium and is used to consider the effect of variability in water vapor in the lower mesosphere on the temperature in the region of noctilucent cloud formation. It is found that change in water vapor from an equilibrium value of 5 ppm at 50 km to a value of 10 ppm, a variation consistent with observations, can produce a roughly 15 K drop in temperature at 82 km. It is suggested that this process may produce weeks of cold temperatures and influence noctilucent cloud formation.

Capacity of a nickel hydrogen boilerplate cell as a function of temperature

NASA Technical Reports Server (NTRS)

Rodgers, H. H.; Dalton, P. J.; Tinker, L. A.

1981-01-01

An evaluation of the components was conducted with special emphasis on positive electrodes. Electrochemically impregnated positive electrodes were used which were made on a slurry plaque by using a perforated steel substrate. The capacity of the test cell was consistent with the loading level used and the effect of temperature on capacity seems to depend on the cobalt level.

Evaluation of the Thermosensitive Release Properties of Microspheres Containing an Agrochemical Compound.

PubMed

Terada, Takatoshi; Ohtsubo, Toshiro; Iwao, Yasunori; Noguchi, Shuji; Itai, Shigeru

2017-01-01

The purpose of this study was to develop a deeper understanding of the key physicochemical parameters involved in the release profiles of microsphere-encapsulated agrochemicals at different temperatures. Microspheres consisting of different polyurethanes (PUs) were prepared using our previously reported solventless microencapsulation technique. Notably, these microspheres exhibited considerable differences in their thermodynamic characteristics, including their glass transition temperature (T g ), extrapolated onset temperature (T o ) and extrapolated end temperature (T e ). At test temperatures below the T o of the PU, only 5-10% of the agrochemical was rapidly released from the microspheres within 1 d, and none was released thereafter. However, at test temperatures above the T o of the PU, the rate of agrochemical release gradually increased with increasing temperatures, and the rate of release from the microspheres was dependent on the composition of the PU. Taken together, these results show that the release profiles of the microspheres were dependent on their thermodynamic characteristics and changes in their PU composition.

Spin Hall magnetoresistance in the non-collinear ferrimagnet GdIG close to the compensation temperature

DOE PAGES

Dong, Bo -Wen; Cramer, Joel; Ganzhorn, Kathrin; ...

2017-12-14

We investigate the spin Hall magnetoresistance (SMR) in a gadolinium iron garnet (GdIG)/platinum (Pt) heterostructure by angular dependent magnetoresistance measurements. The magnetic structure of the ferromagnetic insulator GdIG is non-collinear near the compensation temperature, while it is collinear far from the compensation temperature. In the collinear regime, the SMR signal in GdIG is consistent with the usualmore » $${\\rm si}{{{\\rm n}}^{2}}\\theta $$ relation well established in the collinear magnet yttrium iron garnet, with $$\\theta $$ the angle between magnetization and spin Hall spin polarization direction. In the non-collinear regime, both an SMR signal with inverted sign and a more complex angular dependence with four maxima are observed within one sweep cycle. The number of maxima as well as the relative strength of different maxima depend strongly on temperature and field strength. Lastly, our results evidence a complex SMR behavior in the non-collinear magnetic regime that goes beyond the conventional formalism developed for collinear magnetic structures.« less

Ultrasonic Study of Dislocation Dynamics in Lithium -

NASA Astrophysics Data System (ADS)

Han, Myeong-Deok

1987-09-01

Experimental studies of dislocation dynamics in LiF single crystals, using ultrasonic techniques combined with dynamic loading, were performed to investigate the time evolution of the plastic deformation process under a short stress pulse at room temperature, and the temperature dependence of the dislocation damping mechanism in the temperature range 25 - 300(DEGREES)K. From the former, the time dependence of the ultrasonic attenuation was understood as resulting from dislocation multiplication followed by the evolution of mobile dislocations to immobile ones under large stress. From the latter, the temperature dependence of the ultrasonic attenuation was interpreted as due to the motion of the dislocation loops overcoming the periodic Peierls potential barrier in a manner analogous to the motion of a thermalized sine-Gordon chain under a small stress. The Peierls stress obtained from the experimental results by application of Seeger's relaxation model with exponential dislocation length distribution was 4.26MPa, which is consistent with the lowest stress for the linear relation between the dislocation velocity and stress observed by Flinn and Tinder.

Spin Hall magnetoresistance in the non-collinear ferrimagnet GdIG close to the compensation temperature

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

Dong, Bo -Wen; Cramer, Joel; Ganzhorn, Kathrin

We investigate the spin Hall magnetoresistance (SMR) in a gadolinium iron garnet (GdIG)/platinum (Pt) heterostructure by angular dependent magnetoresistance measurements. The magnetic structure of the ferromagnetic insulator GdIG is non-collinear near the compensation temperature, while it is collinear far from the compensation temperature. In the collinear regime, the SMR signal in GdIG is consistent with the usualmore » $${\\rm si}{{{\\rm n}}^{2}}\\theta $$ relation well established in the collinear magnet yttrium iron garnet, with $$\\theta $$ the angle between magnetization and spin Hall spin polarization direction. In the non-collinear regime, both an SMR signal with inverted sign and a more complex angular dependence with four maxima are observed within one sweep cycle. The number of maxima as well as the relative strength of different maxima depend strongly on temperature and field strength. Lastly, our results evidence a complex SMR behavior in the non-collinear magnetic regime that goes beyond the conventional formalism developed for collinear magnetic structures.« less

Temperature dependence of the superconducting energy gaps in Ca9.35La0.65(Pt3As8)(Fe2As2)5 single crystal.

PubMed

Seo, Yu-Il; Choi, Woo-Jae; Ahmad, D; Kimura, Shin-Ichi; Kwon, Yong Seung

2018-06-05

We measured the optical reflectivity R(ω) for an underdoped (Ca 0.935 La 0.065 ) 10 (Pt 3 As 8 )(Fe 2 As 2 ) 5 single crystal and obtained the optical conductivity [Formula: see text] using the K-K transformation. The normal state [Formula: see text] at 30 K is well fitted by a Drude-Lorentz model with two Drude components (ω p1  = 1446 cm -1 and ω p2  = 6322 cm -1 ) and seven Lorentz components. Relative reflectometry was used to accurately determine the temperature dependence of the superconducting gap at various temperatures below T c . The results clearly show the opening of a superconducting gap with a weaker second gap structure; the magnitudes for the gaps are estimated from the generalized Mattis-Bardeen model to be Δ 1  = 30 and Δ 2  = 50 cm -1 , respectively, at T = 8 K, which both decrease with increasing temperature. The temperature dependence of the gaps was not consistent with one-band BCS theory but was well described by a two-band (hence, two gap) BCS model with interband interactions. The temperature dependence of the superfluid density is flat at low temperatures, indicating an s-wave full-gap superconducting state.

Low-temperature transport properties of TaxN thin films (0.72 <= x <= 0.83)

NASA Astrophysics Data System (ADS)

Očko, Miroslav; Žonja, Sanja; Nelson, G. L.; Freericks, J. K.; Yu, Lei; Newman, N.

2010-11-01

We report on low-temperature (4-320 K) transport properties of TaxN thin films deposited on an amorphous SiO2 substrate. In this work, TaxN thin films were restricted to a narrow range of x: 0.72 <= x <= 0.83 yet show considerable and nonmonotonic variation of their transport properties with Ta concentration. This behaviour is consistent with a local minimum in the density of electronic states at the Fermi level, as calculated for the rock salt intermetallic Ta4N5, and a rigid band model for describing the transport. The temperature dependence of the resistivity is best fit to the unusual form exp(-T/T0). Interestingly enough, the fit parameter T0 correlates well with the temperature of the maximum of the corresponding thermopower. Both of these characteristics, the fit and the correlation with the thermopower, are consistent with the Jonson-Mahan many-body formalism for charge and thermal transport when one has a nontrivial temperature dependence of the chemical potential. At the lowest temperatures measured, we have also found that the resistivity and thermopower show signatures of electron-electron interactions. We discuss also our results in the light of some theories usually used for describing transport of thin films and to other experimental investigations that have been performed on TaxN.

Reversible clustering of pH- and temperature-responsive Janus magnetic nanoparticles.

PubMed

Isojima, Tatsushi; Lattuada, Marco; Vander Sande, John B; Hatton, T Alan

2008-09-23

Janus nanoparticles have been synthesized consisting of approximately 5 nm magnetite nanoparticles coated on one side with a pH-dependent and temperature-independent polymer (poly(acrylic acid), PAA), and functionalized on the other side by a second (tail) polymer that is either a pH-independent polymer (polystyrene sodium sulfonate, PSSNa) or a temperature-dependent polymer (poly(N-isopropyl acrylamide), PNIPAM). These Janus nanoparticles are dispersed stably as individual particles at high pH values and low temperatures, but can self-assemble at low pH values (PSSNa) or at high temperatures (>31 degrees C) (PNIPAM) to form stable dispersions of clusters of approximately 80-100 nm in hydrodynamic diameter. The Janus nanoparticle compositions were verified using FTIR and XPS, and their structures observed directly by TEM. Their clustering behavior is analyzed by dynamic light scattering and zeta potential measurements.

Temperature- and Bias-Dependence of Magnetoresistance in Doped Manganite Thin Film Trilayer Junctions

NASA Astrophysics Data System (ADS)

Sun, J. Z.; Xiao, Gang

1998-03-01

Large low-field magnetoresistance, up to a factor of five change in resistance, was observed in trilayer junctions formed by epitaxial thin films of La_0.67Sr_0.33 MnO3 - SrTiO3 - La_0.67Sr_0.33MnO3 at 4.2K and 100 Oe. Such magnetoresistance decreases with increasing sample temperature, and disappears for temperatures above 150K. The magnetoresistance also decreases upon increasing bias voltage across the junction. We present systematic experimental studies of both temperature and bias-dependence. These results in manganite trilayer junctions at low temperatures are similar to what has been observed in metallic trilayer magnetic tunneling valves, and are qualitatively consistent with the interface magnon excitation model proposed by Zhang et al.(S. Zhang, P. M. Levy, A. C. Marley and S. S. P. Parkin, Phys. Rev. Lett. 79), 3744 (1997).

Extended investigation of intermartensitic transitions in Ni-Mn-Ga magnetic shape memory alloys: A detailed phase diagram determination

NASA Astrophysics Data System (ADS)

Ćakιr, Aslι; Righi, Lara; Albertini, Franca; Acet, Mehmet; Farle, Michael; Aktürk, Selçuk

2013-11-01

Martensitic transitions in shape memory Ni-Mn-Ga Heusler alloys take place between a high temperature austenite and a low temperature martensite phase. However, intermartensitic transformations have also been encountered that occur from one martensite phase to another. To examine intermartensitic transitions in magnetic shape memory alloys in detail, we carried out temperature dependent magnetization, resistivity, and x-ray diffraction measurements to investigate the intermartensitic transition in Ni50Mn50-xGax in the composition range 12≤x≤25 at. %. Rietveld refined x-ray diffraction results are found to be consistent with magnetization and resistivity data. Depending on composition, we observe that intermartensitic transitions occur in the sequences 7M→L10, 5M →7M, and 5M→7M→L10 with decreasing temperature. The L10 non-modulated structure is most stable at low temperature.

Bainitic stabilization of austenite in low alloy sheet steels

NASA Astrophysics Data System (ADS)

Brandt, Mitchell L.

The stabilization of retained austenite in 'triple phase' ferrite/bainite/austenite sheet steels by isothermal bainite transformation after intercritical annealing has been studied in 0.27C-1.5Si steels with 0.8 to 2.4Mn. Dilatometric studies show that cooling rates comparable to CAPL processing result in approximately 30% conversion of austenite to epitaxial ferrite, but the reaction can be suppressed by the faster cooling rate of salt bath quenching. Measured isothermal transformation kinetics at 350 to 450sp°C shows a maximum overall rate near 400sp°C. X-ray diffraction shows that the amount of austenite retained from 400sp°C treatment peaks at 3 minutes but the carbon content increases monotonically to a saturation level. The stability of austenite in this type of steel has been quantified for the first time by direct measurement of the characteristic Msbsps{sigma} temperature. With variations in processing conditions and test temperatures, the tensile uniform ductility has been correlated with the amount and stability of retained austenite, while maintaining a constant 3% flow of 83 ksi. Consistent with previous transformations plasticity studies an optimal austenite stability is found at approximately 10 K above the Msbsps{sigma} temperature, demonstrating a maximum uniform ductility of 44% for an austenite content of 16%. Correlations indicate that desired uniform ductility levels of 20 to 25% could be achieved with only approximately 5% austenite if stability is optimized by placing Msbsps{sigma} 10 K below ambient temperature. Measured uniform ductility in plane strain tension shows similar trends with processing conditions, but models predict that stress state effects will shift the Msbsps{sigma} temperature approximately 5 K higher than that for uniaxial tension. The measured dependence of Msbsps{sigma} on austenite composition and particle size has been modeled via heterogeneous nucleation theory. The composition dependence is consistent with contributions from the transformation chemical driving force and the interfacial frictional work from solution hardening. An inverse dependence on the log of the particle volume is consistent with statistics of heterogeneous nucleation. The observed austenite carbon content at the end of bainitic transformation is consistent with paraequilibrium calculations adding a stored energy term to the bainitic ferrite. The model predicts that optimal austenite stability for maximum uniform ductility can be achieved at fixed particle size by lowering Mn and/or reducing the isothermal bainite transformation temperature.

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.

Systematics of the temperature-dependent interplane resistivity in Ba(Fe 1-xM x)₂As₂ (M=Co, Rh, Ni, and Pd)

DOE PAGES

Tanatar, M. A.; Ni, N.; Thaler, A.; ...

2011-07-27

Temperature-dependent interplane resistivity ρ c(T) was measured systematically as a function of transition-metal substitution in the iron-arsenide superconductors Ba(Fe 1-xM x)₂As₂, M=Ni, Pd, Rh. The data are compared with the behavior found in Ba(Fe 1-xCo x)₂As₂, revealing resistive signatures of pseudogap. In all compounds we find resistivity crossover at a characteristic pseudogap temperature T* from nonmetallic to metallic temperature dependence on cooling. Suppression of T* proceeds very similarly in cases of Ni and Pd doping and much faster than in similar cases of Co and Rh doping. In cases of Co and Rh doping an additional minimum in the temperature-dependentmore » ρ c emerges for high dopings, when superconductivity is completely suppressed. These features are consistent with the existence of a charge gap covering part of the Fermi surface. The part of the Fermi surface affected by this gap is notably larger for Ni- and Pd-doped compositions than in Co- and Rh-doped compounds.« less

Role of electron-phonon coupling in finite-temperature dielectric functions of Au, Ag, and Cu

NASA Astrophysics Data System (ADS)

Xu, Meng; Yang, Jia-Yue; Zhang, Shangyu; Liu, Linhua

2017-09-01

Realistic representation of finite temperature dielectric functions of noble metals is crucial in describing the optical properties of advancing applications in plasmonics and optical metamaterials. However, the atomistic origins of the temperature dependence of noble metals' dielectric functions still lack full explanation. In this paper, we implement electronic structure calculations as well as ellipsometry experiments to study the finite temperature dielectric functions of noble metals Au, Ag, and Cu. Theoretically, the intraband dielectric function is described by the Drude model, of which the important quantity electron lifetime is obtained by considering the electron-phonon, electron-electron, and electron-surface scattering mechanism. The electron-phonon coupling is key to determining the temperature dependence of electron lifetime and intraband dielectric function. For the interband dielectric function, it arises from the electronic interband transition. Due to the limitation of incorporating electron-phonon coupling into the interband transition scheme, the temperature dependence of the interband dielectric function is mainly determined by the thermal expansion effect. Experimentally, variable angle spectroscopic ellipsometry measures the dielectric functions of Au and Ag over the temperature range of 300-700 K and spectral range of 2-20 µm. Those experimental measurements are consistent with theoretical results and thus verify the theoretical models for the finite temperature dielectric function.

Detecting trap states in planar PbS colloidal quantum dot solar cells

PubMed Central

Jin, Zhiwen; Wang, Aiji; Zhou, Qing; Wang, Yinshu; Wang, Jizheng

2016-01-01

The recently developed planar architecture (ITO/ZnO/PbS-TBAI/PbS-EDT/Au) has greatly improved the power conversion efficiency of colloidal quantum dot photovoltaics (QDPVs). However, the performance is still far below the theoretical expectations and trap states in the PbS-TBAI film are believed to be the major origin, characterization and understanding of the traps are highly demanded to develop strategies for continued performance improvement. Here employing impedance spectroscopy we detect trap states in the planar PbS QDPVs. We determined a trap state of about 0.34 eV below the conduction band with a density of around 3.2 × 1016 cm−3 eV−1. Temperature dependent open-circuit voltage analysis, temperature dependent diode property analysis and temperature dependent build-in potential analysis consistently denotes an below-bandgap activation energy of about 1.17–1.20 eV. PMID:27845392

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.

Temperature and composition dependence of Mg-based amorphous-alloy structure factors

NASA Astrophysics Data System (ADS)

From, M.; Muir, W. B.

1992-01-01

Measurements of the x-ray total structure factors for amorphous Mg70Zn30, Ca70Mg30, and Mg85.5Cu14.5 at 9, 150, and 300 K have been made. The composition dependence of the room-temperature structure factors of MgxZn1-x have also been measured for values of x=0.65, 0.70, and 0.75. These compositional changes can be accounted for by the increase in average atomic size as the fraction of the larger Mg atoms increases with x. Also the Perkus-Yevick hard-sphere model is sufficient to calculate the change in structure factor with composition if an experimental structure factor is available from which the sphere diameters and packing fraction can be extracted. The temperature dependence of the structure factors is consistent with the observed thermal expansion and a Debye phonon model with Meisel and Cote's approximation for the multiphonon contribution to the structure factor.

Development of electroluminescence based pressure-sensitive paint system.

PubMed

Iijima, Yoshimi; Sakaue, Hirotaka

2011-01-01

We introduce a pressure-sensitive paint (PSP) measurement system based on an electroluminescence (EL) as a surface illumination. This consists of an inorganic EL as the illumination, a short-pass filter, and a platinum-porphyrin based PSP. The short-pass filter, which passes below 500 nm, was used to separate an overlay of the EL illumination and the PSP emission. The EL shows an opposite temperature dependency to that of the PSP. It gives a uniform illumination compared to that of a point illumination source such as a xenon lamp. Under atmospheric conditions, the resultant EL-PSP system reduces the temperature dependency by 54% compared to that of a conventional PSP system. An application of the EL-PSP system to a sonic jet impingement shows that the system demonstrated its reduction of the temperature dependency by 75% in a pressure measurement and reduces an image misalignment error.

In-situ neutron diffraction characterization of temperature dependence deformation in α-uranium

NASA Astrophysics Data System (ADS)

Calhoun, C. A.; Garlea, E.; Sisneros, T. A.; Agnew, S. R.

2018-04-01

In-situ strain neutron diffraction measurements were conducted at temperature on specimens coming from a clock-rolled α-uranium plate, and Elasto-Plastic Self-Consistent (EPSC) modeling was employed to interpret the findings. The modeling revealed that the active slip systems exhibit a thermally activated response, while deformation twinning remains athermal over the temperature ranges explored (25-150 °C). The modeling also allowed assessment of the effects of thermal residual stresses on the mechanical response during compression. These results are consistent with those from a prior study of room-temperature deformation, indicating that the thermal residual stresses strongly influence the internal strain evolution of grain families, as monitored with neutron diffraction, even though accounting for these residual stresses has little effect on the macroscopic flow curve, except in the elasto-plastic transition.

The temperature dependence of the tensile properties of thermally treated Alloy 690 tubing

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

Harrod, D.L.; Gold, R.E.; Larsson, B.

1992-12-31

Tensile tests were run in air on full tube cross-sections of 22.23 mm OD by 1.27 mm wall thickness Alloy 690 steam generator production tubes from ten (10) heats of material at eight (8) temperatures between room temperature and 760{degrees}C. The tubing was manufactured to specification requirements consistent with the EPRI guidelines for Alloy 690 tubing. The room temperature stress-strain curves are described quite well by the Voce equation. Ductile fracture by dimpled rupture was observed at all test temperatures. The elevated temperature tensile properties are compared with design data given in the ASME Code.

Chiral dynamics in the low-temperature phase of QCD

NASA Astrophysics Data System (ADS)

Brandt, Bastian B.; Francis, Anthony; Meyer, Harvey B.; Robaina, Daniel

2014-09-01

We investigate the low-temperature phase of QCD and the crossover region with two light flavors of quarks. The chiral expansion around the point (T,m=0) in the temperature vs quark-mass plane indicates that a sharp real-time excitation exists with the quantum numbers of the pion. An exact sum rule is derived for the thermal modification of the spectral function associated with the axial charge density; the (dominant) pion pole contribution obeys the sum rule. We determine the two parameters of the pion dispersion relation using lattice QCD simulations and test the applicability of the chiral expansion. The time-dependent correlators are also analyzed using the maximum entropy method, yielding consistent results. Finally, we test the predictions of the chiral expansion around the point (T=0,m=0) for the temperature dependence of static observables.

Flux flow induced microwave absorption in high temperature superconductor Bi 2-XPb XSr 2Ca N-1Cu NO 4+2N

NASA Astrophysics Data System (ADS)

Owens, F. J.

1990-12-01

Direct measurements of microwave absorption without use of rf H field modulation in granular composites of the 115 K superconductor Bi 2-XPb XSr 2Ca N-1Cu NO 4+2N as a function of magnetic field above 0.1 T reveal a continuing increase of absorption of microwave energy increasing magnetic field. The temperature and magnetic field dependence of the absorption are very different from the low magnetic field (<0.01 T) absorption arising from weak links in the material. The magnetic field and temperature dependence are consistent with the behavior of thermally activated flux flow resistance suggesting the absorption is due to flux creep.

Quantum dynamics at finite temperature: Time-dependent quantum Monte Carlo study

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

Christov, Ivan P., E-mail: ivan.christov@phys.uni-sofia.bg

2016-08-15

In this work we investigate the ground state and the dissipative quantum dynamics of interacting charged particles in an external potential at finite temperature. The recently devised time-dependent quantum Monte Carlo (TDQMC) method allows a self-consistent treatment of the system of particles together with bath oscillators first for imaginary-time propagation of Schrödinger type of equations where both the system and the bath converge to their finite temperature ground state, and next for real time calculation where the dissipative dynamics is demonstrated. In that context the application of TDQMC appears as promising alternative to the path-integral related techniques where the realmore » time propagation can be a challenge.« less

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.

Low-temperature magnetic properties of greigite (Fe3S4)

NASA Astrophysics Data System (ADS)

Chang, Liao; Roberts, Andrew P.; Rowan, Christopher J.; Tang, Yan; Pruner, Petr; Chen, Qianwang; Horng, Chorng-Shern

2009-01-01

We provide comprehensive low-temperature magnetic results for greigite (Fe3S4) across the spectrum from superparamagnetic (SP) to multidomain (MD) behavior. It is well known that greigite has no low-temperature magnetic transitions, but we also document that it has strong domain-state dependence of magnetic properties at low temperatures. Blocking of SP grains and increasing thermal stability with decreasing temperature is apparent in many magnetic measurements. Thermally stable single-domain greigite undergoes little change in magnetic properties below room temperature. For pseudo-single-domain (PSD)/MD greigite, hysteresis properties and first-order reversal curve diagrams exhibit minor changes at low temperatures, while remanence continuously demagnetizes because of progressive domain wall unpinning. The low-temperature demagnetization is grain size dependent for PSD/MD greigite, with coarser grains undergoing larger remanence loss. AC susceptibility measurements indicate consistent blocking temperatures (TB) for all synthetic and natural greigite samples, which are probably associated with surficial oxidation. Low-temperature magnetic analysis provides much more information about magnetic mineralogy and domain state than room temperature measurements and enables discrimination of individual components within mixed magnetic mineral assemblages. Low-temperature rock magnetometry is therefore a useful tool for studying magnetic mineralogy and granulometry of greigite-bearing sediments.

MAVEN observations of dayside peak electron densities in the ionosphere of Mars

NASA Astrophysics Data System (ADS)

Vogt, Marissa F.; Withers, Paul; Fallows, Kathryn; Andersson, Laila; Girazian, Zachary; Mahaffy, Paul R.; Benna, Mehdi; Elrod, Meredith K.; Connerney, John E. P.; Espley, Jared R.; Eparvier, Frank G.; Jakosky, Bruce M.

2017-01-01

The peak electron density in the dayside Martian ionosphere is a valuable diagnostic of the state of the ionosphere. Its dependence on factors like the solar zenith angle, ionizing solar irradiance, neutral scale height, and electron temperature has been well studied. The Mars Atmosphere and Volatile EvolutioN spacecraft's September 2015 "deep dip" orbits, in which the orbital periapsis was lowered to 125 km, provided the first opportunity since Viking to sample in situ a complete dayside electron density profile including the main peak. Here we present peak electron density measurements from 37 deep dip orbits and describe conditions at the altitude of the main peak, including the electron temperature and composition of the ionosphere and neutral atmosphere. We find that the dependence of the peak electron density and the altitude of the main peak on solar zenith angle are well described by analytical photochemical theory. Additionally, we find that the electron temperatures at the main peak display a dependence on solar zenith angle that is consistent with the observed variability in the peak electron density. Several peak density measurements were made in regions of large crustal magnetic field, but there is no clear evidence that the crustal magnetic field strength influences the peak electron density, peak altitude, or electron temperature. Finally, we find that the fractional abundance of O2+ and CO2+ at the peak altitude is variable but that the two species together consistently represent 95% of the total ion density.

Fundamental solutions to the bioheat equation and their application to magnetic fluid hyperthermia.

PubMed

Giordano, Mauricio A; Gutierrez, Gustavo; Rinaldi, Carlos

2010-01-01

Methods of predicting temperature profiles during local hyperthermia treatment are very important to avoid damage to healthy tissue. With this aim, fundamental solutions of Pennes' bioheat equation are derived in rectangular, cylindrical, and spherical coordinates. The medium is idealised as isotropic with effective thermal properties. Temperature distributions due to space- and time-dependent heat sources are obtained by the solution method presented. Applications of the fundamental solutions are addressed with emphasis on a particular problem of Magnetic Fluid Hyperthermia (MFH) consisting of a thin shell of magnetic nanoparticles in the outer surface of a spherical solid tumour. It is observed from the solution of this particular problem that the temperature profiles are strongly dependent on the distribution of the magnetic nanoparticles within the tissue. An almost uniform temperature profile is obtained inside the tumour with little penetration of therapeutic temperatures to the outer region of healthy tissue. The fundamental solutions obtained can be used to develop boundary element methods to predict temperature profiles with more complicated geometries.

A temperature-dependent coarse-grained model for the thermoresponsive polymer poly(N-isopropylacrylamide)

DOE PAGES

Abbott, Lauren J.; Stevens, Mark J.

2015-12-22

In this study, a coarse-grained (CG) model is developed for the thermoresponsive polymer poly(N-isopropylacrylamide) (PNIPAM), using a hybrid top-down and bottom-up approach. Nonbonded parameters are fit to experimental thermodynamic data following the procedures of the SDK (Shinoda, DeVane, and Klein) CG force field, with minor adjustments to provide better agreement with radial distribution functions from atomistic simulations. Bonded parameters are fit to probability distributions from atomistic simulations using multi-centered Gaussian-based potentials. The temperature-dependent potentials derived for the PNIPAM CG model in this work properly capture the coil–globule transition of PNIPAM single chains and yield a chain-length dependence consistent with atomisticmore » simulations.« less

Simulating Damage Due to a Lightning Strike Event: Effects of Temperature Dependent Properties on Interlaminar Damage

NASA Technical Reports Server (NTRS)

Ghezeljeh, Paria Naghipour; Pineda, Evan Jorge

2014-01-01

A multidirectional, carbon fiber-epoxy, composite panel is subjected to a simulated lightning strike, within a finite element method framework, and the effect of material properties on the failure (delamination) response is investigated through a detailed numerical study. The numerical model of the composite panel consists of individual homogenized plies with user-defined, cohesive interface elements between them. Lightning strikes are simulated as an assumed combination of excessive heat and high pressure loadings. It is observed that the initiation and propagation of lightning-induced delamination is a significant function of the temperature dependency of interfacial fracture toughness. This dependency must be defined properly in order to achieve reliable predictions of the present lightning-induced delamination in the composite panel.

The Influence of Phonons and Phonon Decay on the Optical Properties of GaN

NASA Astrophysics Data System (ADS)

Song, D. Y.; Basavaraj, M.; Nikishin, S. A.; Holtz, M.; Soukhoveev, V.; Usikov, A.; Dmitriev, V.

2006-03-01

The temperature dependences of vibrational and optical properties of high-quality GaN are studied using Raman and photoluminescence (PL) spectroscopies in the range 20 to 325 K. The Raman-active A1(LO) phonon has temperature dependence described well by combined two- and three-phonon decay. The temperature dependences of E2^2 phonon are almost entirely dominated by the thermal expansion, and the contribution of three-phonon decay process is very small throughout interested temperature range. The shallow neutral donor-bound exciton (D^0,X) and two free excitons (XA and XB) are observed at low temperatrue PL spectra. Also seen are two A1(LO) phonon sidebands (PSBs), originating from the XB free exciton, with the characteristic asymmetry attributed to interactions between discrete and continuum states. Analysis of the band-edge excitons reveals that energy gap shrinkage and exciton linewidths are completely described based on electron-phonon interactions with phonon properties consistent with the Raman analysis. First and second PSBs have temperature dependence associated with the A1(LO) phonon. The shift, broadening, and asymmetry of the PSBs are explained by Segall-Mahan theory adding the decay mechanism of A1(LO) phonon and the exciton broadening from electron-phonon interactions. Work at Texas Tech University supported by National Science Foundation grant ECS-0323640.

Constraints on temperature-dependent sex determination in the leopard gecko ( Eublepharis macularius): response to Kratochvil et al.

NASA Astrophysics Data System (ADS)

Huang, Victoria; Sakata, Jon T.; Rhen, Turk; Coomber, Patricia; Simmonds, Sarah; Crews, David

2008-12-01

Kratochvil et al. (Naturwissenschaften 95:209 215, 2008) reported recently that in the leopard gecko ( Eublepharis macularius) of the family Eublepharidae with temperature-dependent sex determination (TSD), clutches in which eggs were incubated at the same temperature produce only same-sex siblings. Interpreting this result in light of studies of sex steroid hormone involvement in sex determination, they suggested that maternally derived yolk steroid hormones could constrain sex-determining mechanisms in TSD reptiles. We have worked extensively with this species and have routinely incubated clutches at constant temperatures. To test the consistency of high frequency same-sex clutches across different incubation temperatures, we examined our records of clutches at the University of Texas at Austin from 1992 to 2001. We observed that clutches in which eggs were incubated at the same incubation temperature produced mixed-sex clutches as well as same-sex clutches. Furthermore, cases in which eggs within a clutch were separated and incubated at different temperatures produced the expected number of mixed-sex clutches. These results suggest that maternal influences on sex determination are secondary relative to incubation temperature effects.

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.

Determination of Scattering and Absorption Coefficients for Plasma-Sprayed Yttria-Stabilized Zirconia Thermal Barrier Coatings at Elevated Temperatures

NASA Technical Reports Server (NTRS)

Eldridge, Jeffrey I.; Spuckler, Charles M.; Markham, James R.

2009-01-01

The temperature dependence of the scattering and absorption coefficients for a set of freestanding plasma-sprayed 8 wt% yttria-stabilized zirconia (8YSZ) thermal barrier coatings (TBCs) was determined at temperatures up to 1360 C in a wavelength range from 1.2 micrometers up to the 8YSZ absorption edge. The scattering and absorption coefficients were determined by fitting the directional-hemispherical reflectance and transmittance values calculated by a four-flux Kubelka Munk method to the experimentally measured hemispherical-directional reflectance and transmittance values obtained for five 8YSZ thicknesses. The scattering coefficient exhibited a continuous decrease with increasing wavelength and showed no significant temperature dependence. The scattering is primarily attributed to the relatively temperature-insensitive refractive index mismatch between the 8YSZ and its internal voids. The absorption coefficient was very low (less than 1 per centimeter) at wavelengths between 2 micrometers and the absorption edge and showed a definite temperature dependence that consisted of a shift of the absorption edge to shorter wavelengths and an increase in the weak absorption below the absorption edge with increasing temperature. The shift in the absorption edge with temperature is attributed to strongly temperature-dependent multiphonon absorption. While TBC hemispherical transmittance beyond the absorption edge can be predicted by a simple exponential decrease with thickness, below the absorption edge, typical TBC thicknesses are well below the thickness range where a simple exponential decrease in hemispherical transmittance with TBC thickness is expected. [Correction added after online publication August 11, 2009: "edge to a shorter wavelengths" has been updated as edge to shorter wavelengths."

Dynamical mean-field theoretical approach to explore the temperature-dependent magnetization in Ta-doped TiO2

NASA Astrophysics Data System (ADS)

Majidi, M. A.; Umar, A. S.; Rusydi, A.

2017-04-01

TiO2 has, in recent years, become a hot subject as it holds a promise for spintronic application. Recent experimental study on anatase Ti1-x Ta x O2 (x ~ 0.05) thin films shows that the system changes from non-magnetic to ferromagnetic due to Ti vacancies that are formed when a small percentage of Ti atoms are substituted by Ta. Motivated by those results that reveal the ferromagnetic phase at room temperature, we conduct a theoretical study on the temperature-dependent magnetization and the Currie temperature of that system. We hypothesize that when several Ti vacancies are formed in the system, each of them induces a local magnetic moment, then such moments couple each other through Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, forming a ferromagnetic order. To study the temperature dependence of the magnetization and predict the Curie temperature, we construct a tight-binding based Hamiltonian for this system and use the method of dynamical mean-field theory to perform calculations for various temperatures. Our work is still preliminary. The model and method may need further improvement to be consistent with known existing facts. We present our preliminary results to show how the present model works.

Global convergence in leaf respiration from estimates of thermal acclimation across time and space.

PubMed

Vanderwel, Mark C; Slot, Martijn; Lichstein, Jeremy W; Reich, Peter B; Kattge, Jens; Atkin, Owen K; Bloomfield, Keith J; Tjoelker, Mark G; Kitajima, Kaoru

2015-09-01

Recent compilations of experimental and observational data have documented global temperature-dependent patterns of variation in leaf dark respiration (R), but it remains unclear whether local adjustments in respiration over time (through thermal acclimation) are consistent with the patterns in R found across geographical temperature gradients. We integrated results from two global empirical syntheses into a simple temperature-dependent respiration framework to compare the measured effects of respiration acclimation-over-time and variation-across-space to one another, and to a null model in which acclimation is ignored. Using these models, we projected the influence of thermal acclimation on: seasonal variation in R; spatial variation in mean annual R across a global temperature gradient; and future increases in R under climate change. The measured strength of acclimation-over-time produces differences in annual R across spatial temperature gradients that agree well with global variation-across-space. Our models further project that acclimation effects could potentially halve increases in R (compared with the null model) as the climate warms over the 21st Century. Convergence in global temperature-dependent patterns of R indicates that physiological adjustments arising from thermal acclimation are capable of explaining observed variation in leaf respiration at ambient growth temperatures across the globe. © 2015 The Authors. New Phytologist © 2015 New Phytologist Trust.

Characterization of Full Set Material Constants and Their Temperature Dependence for Piezoelectric Materials Using Resonant Ultrasound Spectroscopy

PubMed Central

Tang, Liguo; Cao, Wenwu

2016-01-01

During the operation of high power electromechanical devices, a temperature rise is unavoidable due to mechanical and electrical losses, causing the degradation of device performance. In order to evaluate such degradations using computer simulations, full matrix material properties at elevated temperatures are needed as inputs. It is extremely difficult to measure such data for ferroelectric materials due to their strong anisotropic nature and property variation among samples of different geometries. Because the degree of depolarization is boundary condition dependent, data obtained by the IEEE (Institute of Electrical and Electronics Engineers) impedance resonance technique, which requires several samples with drastically different geometries, usually lack self-consistency. The resonant ultrasound spectroscopy (RUS) technique allows the full set material constants to be measured using only one sample, which can eliminate errors caused by sample to sample variation. A detailed RUS procedure is demonstrated here using a lead zirconate titanate (PZT-4) piezoceramic sample. In the example, the complete set of material constants was measured from room temperature to 120 °C. Measured free dielectric constants and  were compared with calculated ones based on the measured full set data, and piezoelectric constants d15 and d33 were also calculated using different formulas. Excellent agreement was found in the entire range of temperatures, which confirmed the self-consistency of the data set obtained by the RUS. PMID:27168336

Microwave radiometer for subsurface temperature measurement

NASA Technical Reports Server (NTRS)

Porter, R. A.; Bechis, K. P.

1976-01-01

A UHF radiometer, operating at a frequency of 800 MHz, was modified to provide an integral, three frequency voltage standing wave ratio (VSWR) circuit in the radio frequency (RF) head. The VSWR circuit provides readings of power transmission at the antenna-material interface with an accuracy of plus or minus 5 percent. The power transmission readings are numerically equal to the emissivity of the material under observation. Knowledge of material emissivity is useful in the interpretation of subsurface apparent temperatures obtained on phantom models of biological tissue. The emissivities of phantom models consisting of lean beefsteak were found to lie in the range 0.623 to 0.779, depending on moisture content. Radiometric measurements performed on instrumented phantoms showed that the radiometer was capable of sensing small temperature changes occurring at depths of at least 19 to 30 mm. This is consistent with previously generated data which showed that the radiometer could sense temperatures at a depth of 38 mm.

Liquid state isomorphism, Rosenfeld-Tarazona temperature scaling, and Riemannian thermodynamic geometry.

PubMed

Mausbach, Peter; Köster, Andreas; Vrabec, Jadran

2018-05-01

Aspects of isomorph theory, Rosenfeld-Tarazona temperature scaling, and thermodynamic geometry are comparatively discussed on the basis of the Lennard-Jones potential. The first two approaches approximate the high-density fluid state well when the repulsive interparticle interactions become dominant, which is typically the case close to the freezing line. However, previous studies of Rosenfeld-Tarazona scaling for the isochoric heat capacity and its relation to isomorph theory reveal deviations for the temperature dependence. It turns out that a definition of a state region in which repulsive interactions dominate is required for achieving consistent results. The Riemannian thermodynamic scalar curvature R allows for such a classification, indicating predominantly repulsive interactions by R>0. An analysis of the isomorphic character of the freezing line and the validity of Rosenfeld-Tarazona temperature scaling show that these approaches are consistent only in a small state region.

The effect of side-chain substitution and hot processing on diketopyrrolopyrrole-based polymers for organic solar cells.

PubMed

Heintges, Gaël H L; Leenaers, Pieter J; Janssen, René A J

2017-07-14

The effects of cold and hot processing on the performance of polymer-fullerene solar cells are investigated for diketopyrrolopyrrole (DPP) based polymers that were specifically designed and synthesized to exhibit a strong temperature-dependent aggregation in solution. The polymers, consisting of alternating DPP and oligothiophene units, are substituted with linear and second position branched alkyl side chains. For the polymer-fullerene blends that can be processed at room temperature, hot processing does not enhance the power conversion efficiencies compared to cold processing because the increased solubility at elevated temperatures results in the formation of wider polymer fibres that reduce charge generation. Instead, hot processing seems to be advantageous when cold processing is not possible due to a limited solubility at room temperature. The resulting morphologies are consistent with a nucleation-growth mechanism for polymer fibres during drying of the films.

Experimental evidence consistent with a magnon Nernst effect in the antiferromagnetic insulator MnPS3

NASA Astrophysics Data System (ADS)

Shiomi, Y.; Takashima, R.; Saitoh, E.

2017-10-01

A magnon Nernst effect, an antiferromagnetic analog of the magnon Hall effect in ferromagnetic insulators, has been studied experimentally for the layered antiferromagnetic insulator MnPS3 in contact with two Pt strips. Thermoelectric voltage in the Pt strips grown on MnPS3 single crystals exhibits nonmonotonic temperature dependence at low temperatures, which is unlikely to be explained by electronic origins in Pt but can be ascribed to the inverse spin Hall voltage induced by a magnon Nernst effect. Control of antiferromagnetic domains in the MnPS3 crystal by magnetoelectric cooling is found to modulate the low-temperature thermoelectric voltage in Pt, which is evidence consistent with the emergence of the magnon Nernst effect in Pt-MnPS3 hybrid structures.

Ab-initio study of high temperature lattice dynamics of BCC zirconium (β-Zr) and uranium (γ-U)

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

Ghosh, Partha S., E-mail: parthasarathi13@gmail.com; Arya, A., E-mail: parthasarathi13@gmail.com; Dey, G. K., E-mail: parthasarathi13@gmail.com

2014-04-24

Using self consistent ab-initio lattice dynamics calculations, we show that bcc structures of Zr and U phases become stable at high temperature by phonon-phonon interactions. The calculated temperature dependent phonon dispersion curve (PDC) of β-Zr match excellently with experimental PDC. But the calculated PDC for γ-U shows negative phonon frequencies even at solid to liquid transition temperature. We show that this discrepancy is due to an overestimation of instability depth of bcc U phase which is removed by incorporation of spin-orbit coupling in the electronic structure calculations.

Nearly Perfect Fluidity in a High Temperature Superconductor

DOE PAGES

Rameau, J. D.; Reber, T. J.; Yang, H. -B.; ...

2014-10-13

Perfect fluids are characterized as having the smallest ratio of shear viscosity to entropy density, η/s, consistent with quantum uncertainty and causality. So far, nearly perfect fluids have only been observed in the quark-gluon plasma and in unitary atomic Fermi gases, exotic systems that are amongst the hottest and coldest objects in the known universe, respectively. We use angle resolved photoemission spectroscopy to measure the temperature dependence of an electronic analog of η/s in an optimally doped cuprate high-temperature superconductor, finding it too is a nearly perfect fluid around, and above, its superconducting transition temperature T c.

Nearly perfect fluidity in a high-temperature superconductor

NASA Astrophysics Data System (ADS)

Rameau, J. D.; Reber, T. J.; Yang, H.-B.; Akhanjee, S.; Gu, G. D.; Johnson, P. D.; Campbell, S.

2014-10-01

Perfect fluids are characterized as having the smallest ratio of shear viscosity to entropy density, η /s, consistent with quantum uncertainty and causality. So far, nearly perfect fluids have only been observed in the quark-gluon plasma and in unitary atomic Fermi gases, exotic systems that are amongst the hottest and coldest objects in the known universe, respectively. We use angle resolved photoemission spectroscopy to measure the temperature dependence of an electronic analog of η /s in an optimally doped cuprate high-temperature superconductor, finding it too is a nearly perfect fluid around, and above, its superconducting transition temperature Tc.

Spectroscopic Study of Deep Level Emissions from Acceptor Defects in ZnO Thin Films with Oxygen Rich Stoichiometry

NASA Astrophysics Data System (ADS)

Ilyas, Usman; Rawat, R. S.; Tan, T. L.

2013-10-01

This paper reports the tailoring of acceptor defects in oxygen rich ZnO thin films at different post-deposition annealing temperatures (500-800°C) and Mn doping concentrations. The XRD spectra exhibited the nanocrystalline nature of ZnO thin films along with inconsistent variation in lattice parameters suggesting the temperature-dependent activation of structural defects. Photoluminescence emission spectra revealed the temperature dependent variation in deep level emissions (DLE) with the presence of acceptors as dominating defects. The concentration of native defects was estimated to be increased with temperature while a reverse trend was observed for those with increasing doping concentration. A consistent decrease in DLE spectra, with increasing Mn content, revealed the quenching of structural defects in the optical band gap of ZnO favorable for good quality thin films with enhanced optical transparency.

Neutral atmospheric models compatible with satellite orbital decay and incoherent scatter measurements

NASA Technical Reports Server (NTRS)

Rohrbaugh, J. L.

1972-01-01

A correlation study was made of the variations of the exospheric temperature extrema with various combinations of the monthly mean and daily values of the 2800 MHz and Ca:2 solar indices. The phase and amplitude of the semi-annual component and the term dependent on Kp were found to remain almost the same for the maximum and minimum temperature. The term dependent on the 27 day component of the solar activity was found to be about four times as large for the diurnal maximum as for the minimum. Measurements at Arecibo have shown that temperature gradient changes at 125 km are consistent with the phase difference between the neutral temperature and density maxima. This is used to develop an empirical model which is compatible with both the satellite measurements and the available incoherent scatter measurements. A main feature of this model is that day length is included as a major model parameter.

Low-temperature structural and transport anomalies in Cu2Se

NASA Astrophysics Data System (ADS)

Chi, Hang; Kim, Hyoungchul; Thomas, John C.; Shi, Guangsha; Sun, Kai; Abeykoon, Milinda; Bozin, Emil S.; Shi, Xiaoya; Li, Qiang; Shi, Xun; Kioupakis, Emmanouil; Van der Ven, Anton; Kaviany, Massoud; Uher, Ctirad

2014-05-01

Through systematic examination of symmetrically nonequivalent configurations, first-principles calculations have identified a new ground state of Cu2Se, which is constructed by repeating sextuple layers of Se-Cu-Cu-Cu-Cu-Se. The layered nature is in accord with electron and x-ray diffraction studies at and below room temperature and also is consistent with transport properties. Magnetoresistance measurements at liquid helium temperatures exhibit cusp-shaped field dependence at low fields and evolve into quasilinear field dependence at intermediate and high fields. These results reveal the existence of weak antilocalization effect, which has been analyzed using a modified Hikami, Larkin, and Nagaoka model, including a quantum interference term and a classical quadratic contribution. Fitting parameters suggest a quantum coherence length L of 175 nm at 1.8 K. With increasing temperature, the classical parabolic behavior becomes more dominant, and L decreases as a power law of T-0.83.

Phase-field simulation of microstructure formation in technical castings - A self-consistent homoenthalpic approach to the micro-macro problem

NASA Astrophysics Data System (ADS)

Böttger, B.; Eiken, J.; Apel, M.

2009-10-01

Performing microstructure simulation of technical casting processes suffers from the strong interdependency between latent heat release due to local microstructure formation and heat diffusion on the macroscopic scale: local microstructure formation depends on the macroscopic heat fluxes and, in turn, the macroscopic temperature solution depends on the latent heat release, and therefore on the microstructure formation, in all parts of the casting. A self-consistent homoenthalpic approximation to this micro-macro problem is proposed, based on the assumption of a common enthalpy-temperature relation for the whole casting which is used for the description of latent heat production on the macroscale. This enthalpy-temperature relation is iteratively obtained by phase-field simulations on the microscale, thus taking into account the specific morphological impact on the latent heat production. This new approach is discussed and compared to other approximations for the coupling of the macroscopic heat flux to complex microstructure models. Simulations are performed for the binary alloy Al-3at%Cu, using a multiphase-field solidification model which is coupled to a thermodynamic database. Microstructure formation is simulated for several positions in a simple model plate casting, using a one-dimensional macroscopic temperature solver which can be directly coupled to the microscopic phase-field simulation tool.

Modeling the glass transition of amorphous networks for shape-memory behavior

NASA Astrophysics Data System (ADS)

Xiao, Rui; Choi, Jinwoo; Lakhera, Nishant; Yakacki, Christopher M.; Frick, Carl P.; Nguyen, Thao D.

2013-07-01

In this paper, a thermomechanical constitutive model was developed for the time-dependent behaviors of the glass transition of amorphous networks. The model used multiple discrete relaxation processes to describe the distribution of relaxation times for stress relaxation, structural relaxation, and stress-activated viscous flow. A non-equilibrium thermodynamic framework based on the fictive temperature was introduced to demonstrate the thermodynamic consistency of the constitutive theory. Experimental and theoretical methods were developed to determine the parameters describing the distribution of stress and structural relaxation times and the dependence of the relaxation times on temperature, structure, and driving stress. The model was applied to study the effects of deformation temperatures and physical aging on the shape-memory behavior of amorphous networks. The model was able to reproduce important features of the partially constrained recovery response observed in experiments. Specifically, the model demonstrated a strain-recovery overshoot for cases programmed below Tg and subjected to a constant mechanical load. This phenomenon was not observed for materials programmed above Tg. Physical aging, in which the material was annealed for an extended period of time below Tg, shifted the activation of strain recovery to higher temperatures and increased significantly the initial recovery rate. For fixed-strain recovery, the model showed a larger overshoot in the stress response for cases programmed below Tg, which was consistent with previous experimental observations. Altogether, this work demonstrates how an understanding of the time-dependent behaviors of the glass transition can be used to tailor the temperature and deformation history of the shape-memory programming process to achieve more complex shape recovery pathways, faster recovery responses, and larger activation stresses.

Single-Walled Carbon Nanotubes, Carbon Nanofibers and Laser-Induced Incandescence

NASA Technical Reports Server (NTRS)

Schubert, Kathy (Technical Monitor); VanderWal, Randy L.; Ticich, Thomas M.; Berger, Gordon M.; Patel, Premal D.

2004-01-01

Laser induced incandescence applied to a heterogeneous, multi-element reacting flows is characterized by a) temporally resolved emission spectra, time-resolved emission at selected detection wavelengths and fluence dependence. Laser fluences above 0.6 Joules per square centimeter at 1064 nm initiate laser-induced vaporization, yielding a lower incandescence intensity, as found through fluence dependence measurements. Spectrally derived temperatures show that values of excitation laser fluence beyond this value lead to a super-heated plasma, well above the vaporization of temperature of carbon. The temporal evolution of the emission signal at these fluences is consistent with plasma dissipation processes, not incandescence from solid-like structures.

Pressure dependence of coherence-incoherence crossover behavior in KFe2As2 observed by resistivity and 75As-NMR/NQR

NASA Astrophysics Data System (ADS)

Wiecki, P.; Taufour, V.; Chung, D. Y.; Kanatzidis, M. G.; Bud'ko, S. L.; Canfield, P. C.; Furukawa, Y.

2018-02-01

We present the results of 75As nuclear magnetic resonance (NMR), nuclear quadrupole resonance (NQR), and resistivity measurements in KFe2As2 under pressure (p ). The temperature dependence of the NMR shift, nuclear spin-lattice relaxation time (T1), and resistivity show a crossover between a high-temperature incoherent, local-moment behavior and a low-temperature coherent behavior at a crossover temperature (T*). T* is found to increase monotonically with pressure, consistent with increasing hybridization between localized 3 d orbital-derived bands with the itinerant electron bands. No anomaly in T* is seen at the critical pressure pc=1.8 GPa where a change of slope of the superconducting (SC) transition temperature Tc(p ) has been observed. In contrast, Tc(p ) seems to correlate with antiferromagnetic spin fluctuations in the normal state as measured by the NQR 1 /T1 data, although such a correlation cannot be seen in the replacement effects of A in the A Fe2As2 (A =K , Rb, Cs) family. In the superconducting state, two T1 components are observed at low temperatures, suggesting the existence of two distinct local electronic environments. The temperature dependence of the short T1 s indicates a nearly gapless state below Tc. On the other hand, the temperature dependence of the long component 1 /T1 L implies a large reduction in the density of states at the Fermi level due to the SC gap formation. These results suggest a real-space modulation of the local SC gap structure in KFe2As2 under pressure.

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.

Thermal processing of diblock copolymer melts mimics metallurgy

NASA Astrophysics Data System (ADS)

Kim, Kyungtae; Schulze, Morgan W.; Arora, Akash; Lewis, Ronald M.; Hillmyer, Marc A.; Dorfman, Kevin D.; Bates, Frank S.

2017-05-01

Small-angle x-ray scattering experiments conducted with compositionally asymmetric low molar mass poly(isoprene)-b-poly(lactide) diblock copolymers reveal an extraordinary thermal history dependence. The development of distinct periodic crystalline or aperiodic quasicrystalline states depends on how specimens are cooled from the disordered state to temperatures below the order-disorder transition temperature. Whereas direct cooling leads to the formation of documented morphologies, rapidly quenched samples that are then heated from low temperature form the hexagonal C14 and cubic C15 Laves phases commonly found in metal alloys. Self-consistent mean-field theory calculations show that these, and other associated Frank-Kasper phases, have nearly degenerate free energies, suggesting that processing history drives the material into long-lived metastable states defined by self-assembled particles with discrete populations of volumes and polyhedral shapes.

Temperature evolution of the structural properties of monodomain ferroelectric thin film

NASA Astrophysics Data System (ADS)

Janolin, Pierre-Eymeric; Le Marrec, Françoise; Chevreul, Jacques; Dkhil, Brahim

2007-05-01

The structural evolution of epitaxial monodomain (only 180° domains) ferroelectric PbTiO3 thin film has been investigated, using high-resolution, temperature-dependent, x-ray diffraction. The full set of lattice parameters was obtained from room temperature up to 850K. It allowed the calculation of the different strains stored in the film at room temperature, underlying the difference between the mechanical strain and the misfit strain. The evolution of the misfit strain as a function of temperature was also calculated and was found to be consistent with the theoretical temperature-misfit strain phase diagram. These data strongly suggest that the film remains ferroelectric and tetragonal up to 940K.

Temperature dependence of differential conductance in Co-based Heusler alloy Co2TiSn and superconductor Pb junctions

NASA Astrophysics Data System (ADS)

Ooka, Ryutaro; Shigeta, Iduru; Umetsu, Rie Y.; Nomura, Akiko; Yubuta, Kunio; Yamauchi, Touru; Kanomata, Takeshi; Hiroi, Masahiko

2018-05-01

We investigated temperature dependence of differential conductance G (V) in planar junctions consisting of Co-based Heusler alloy Co2TiSn and superconductor Pb. Ferromagnetic Co2TiSn was predicted to be half-metal by first-principles band calculations. The spin polarization P of Co2TiSn was deduced to be 60.0% at 1.4 K by the Andreev reflection spectroscopy. The G (V) spectral shape was smeared gradually with increasing temperature and its structure was disappeared above the superconducting transition temperature Tc. Theoretical model analysis revealed that the superconducting energy gap Δ was 1.06 meV at 1.4 K and the Tc was 6.8 K , indicating that both values were suppressed from bulk values. However, the temperature dependent Δ (T) behavior was in good agreement with that of the Bardeen-Cooper-Schrieffer (BCS) theory. The experimental results exhibit that the superconductivity of Pb attached to half-metallic Co2TiSn was kept the conventional BCS mechanism characterized strong-coupling superconductors while its superconductivity was slightly suppressed by the superconducting proximity effect at the Co2TiSn/Pb interface.

Constraints on global temperature target overshoot.

PubMed

Ricke, K L; Millar, R J; MacMartin, D G

2017-11-07

In the aftermath of the Paris Agreement, the climate science and policy communities are beginning to assess the feasibility and potential benefits of limiting global warming to 1.5 °C or 2 °C above preindustrial. Understanding the dependence of the magnitude and duration of possible temporary exceedance (i.e., "overshoot") of temperature targets on sustainable energy decarbonization futures and carbon dioxide (CO 2 ) removal rates will be an important contribution to this policy discussion. Drawing upon results from the mitigation literature and the IPCC Working Group 3 (WG3) scenario database, we examine the global mean temperature implications of differing, independent pathways for the decarbonization of global energy supply and the implementation of negative emissions technologies. We find that within the scope of scenarios broadly-consistent with the WG3 database, the magnitude of temperature overshoot is more sensitive to the rate of decarbonization. However, limiting the duration of overshoot to less than two centuries requires ambitious deployment of both decarbonization and negative emissions technology. The dependencies of temperature target overshoot's properties upon currently untested negative emissions technologies suggests that it will be important to consider how climate impacts depend on both the magnitude and duration of overshoot, not just long term residual warming.

Temperature dependence of the structural relaxation time in equilibrium below the nominal T(g): results from freestanding polymer films.

PubMed

Ngai, K L; Capaccioli, Simone; Paluch, Marian; Prevosto, Daniele

2014-05-22

When the thickness is reduced to nanometer scale, freestanding high molecular weight polymer thin films undergo large reduction of degree of cooperativity and coupling parameter n in the Coupling Model (CM). The finite-size effect together with the surfaces with high mobility make the α-relaxation time of the polymer in nanoconfinement, τ(α)(nano)(T), much shorter than τ(α)(bulk)(T) in the bulk. The consequence is avoidance of vitrification at and below the bulk glass transition temperature, T(g)(bulk), on cooling, and the freestanding polymer thin film remains at thermodynamic equilibrium at temperatures below T(g)(bulk). Molecular dynamics simulations have shown that the specific volume of the freestanding film is the same as the bulk glass-former at equilibrium at the same temperatures. Extreme nanoconfinement renders total or almost total removal of cooperativity of the α-relaxation, and τ(α)(nano)(T) becomes the same or almost the same as the JG β-relaxation time τ(β)(bulk)(T) of the bulk glass-former at equilibrium and at temperatures below T(g)(bulk). Taking advantage of being able to obtain τ(β)(bulk)(T) at equilibrium density below T(g)(bulk) by extreme nanoconfinement of the freestanding films, and using the CM relation between τ(α)(bulk)(T) and τ(β)(bulk)(T), we conclude that the Vogel-Fulcher-Tammann-Hesse (VFTH) dependence of τ(α)(bulk)(T) cannot hold for glass-formers in equilibrium at temperatures significantly below T(g)(bulk). In addition, τ(α)(bulk)(T) does not diverge at the Vogel temperature, T₀, as suggested by the VFTH-dependence and predicted by some theories of glass transition. Instead, τ(α)(bulk)(T) of the glass-former at equilibrium has a much weaker temperature dependence than the VFTH-dependence at temperature below T(g)(bulk) and even below T₀. This conclusion from our analysis is consistent with the temperature dependence of τ(α)(bulk)(T) found experimentally in polymers aged long enough time to attain the equilibrium state at various temperatures below T(g)(bulk).

Photoluminescence study of MBE grown InGaN with intentional indium segregation

NASA Astrophysics Data System (ADS)

Cheung, Maurice C.; Namkoong, Gon; Chen, Fei; Furis, Madalina; Pudavar, Haridas E.; Cartwright, Alexander N.; Doolittle, W. Alan

2005-05-01

Proper control of MBE growth conditions has yielded an In0.13Ga0.87N thin film sample with emission consistent with In-segregation. The photoluminescence (PL) from this epilayer showed multiple emission components. Moreover, temperature and power dependent studies of the PL demonstrated that two of the components were excitonic in nature and consistent with indium phase separation. At 15 K, time resolved PL showed a non-exponential PL decay that was well fitted with the stretched exponential solution expected for disordered systems. Consistent with the assumed carrier hopping mechanism of this model, the effective lifetime, , and the stretched exponential parameter, , decrease with increasing emission energy. Finally, room temperature micro-PL using a confocal microscope showed spatial clustering of low energy emission.

Consistency of signal intensity and T2* in frozen ex vivo heart muscle, kidney, and liver tissue.

PubMed

Kaye, Elena A; Josan, Sonal; Lu, Aiming; Rosenberg, Jarrett; Daniel, Bruce L; Pauly, Kim Butts

2010-03-01

To investigate tissue dependence of the MRI-based thermometry in frozen tissue by quantification and comparison of signal intensity and T2* of ex vivo frozen tissue of three different types: heart muscle, kidney, and liver. Tissue samples were frozen and imaged on a 0.5 Tesla MRI scanner with ultrashort echo time (UTE) sequence. Signal intensity and T2* were determined as the temperature of the tissue samples was decreased from room temperature to approximately -40 degrees C. Statistical analysis was performed for (-20 degrees C, -5 degrees C) temperature interval. The findings of this study demonstrate that signal intensity and T2* are consistent across three types of tissue for (-20 degrees C, -5 degrees C) temperature interval. Both parameters can be used to calculate a single temperature calibration curve for all three types of tissue and potentially in the future serve as a foundation for tissue-independent MRI-based thermometry.

57Fe Mössbauer study of Lu 2Fe 3Si 5 iron silicide superconductor

DOE PAGES

Ma, Xiaoming; Ran, Sheng; Pang, Hua; ...

2015-03-28

With the advent of Fe–As based superconductivity it has become important to study how superconductivity manifests itself in details of 57Fe Mössbauer spectroscopy of conventional, Fe-bearing superconductors. The iron-based superconductor Lu 2Fe 3Si 5 has been studied by 57Fe Mössbauer spectroscopy over the temperature range from 4.4 K to room temperature with particular attention to the region close to the superconducting transition temperature (T c=6.1 K). Consistent with the two crystallographic sites for Fe in this structure, the observed spectra appear to have a pattern consisting of two doublets over the whole temperature range. Furthermore, the value of Debye temperaturemore » was estimated from temperature dependence of the isomer shift and the total spectral area and compared with the specific heat capacity data. Neither abnormal behavior of the hyperfine parameters at or near T c, nor phonon softening were observed.« less

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 CH4 to total greenhouse gas emissions from aquatic ecosystems, terrestrial wetlands and rice paddies.

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 field- and temperature dependence as published by the manufacturer.

Radiation-induced polymerization of glass-forming systems. IV. Effect of the homogeneity of polymerization phase and polymer concentration on temperature dependence of initial polymerization rate

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

Kaetsu, I.; Ito, A.; Hayashi, K.

1973-06-01

The effect of homogeneity of polymerization phase and monomer concentration on the temperature dependence of initial polymerization rate was studied in the radiation-induced radical polymerization of binary systems consisting of glass-forming monomer and solvent. In the polymerization of a completely homogeneous system such as HEMA-propylene glycol, a maximum and a minimum in polymerization rates as a function of temperature, characteristic of the polymerization in glass-forming systems, were observed for all monomer concentrations. However, in the heterogeneous polymerization systems such as HEMA-triacetin and HEMAisoamyl acetate, maximum and minimum rates were observed in monomer-rich compositions but not at low monomer concentrations. Furthermore,more » in the HEMA-dioctyl phthalate polymerization system, which is extremely heterogeneous, no maximum and minimum rates were observed at any monomer concentration. The effect of conversion on the temperature dependence of polymerization rate in homogeneous bulk polymerization of HEMA and GMA was investigated. Maximum and minimum rates were observed clearly in conversions less than 10% in the case of HEMA and less than 50% in the case of GMA, but the maximum and minimum changed to a mere inflection in the curve at higher conversions. A similar effect of polymer concentration on the temperature dependence of polymerization rate in the GMA-poly(methyl methacrylate) system was also observed. It is deduced that the change in temperature dependence of polymerization rate is attributed to the decrease in contribution of mutual termination reaction of growing chain radicals to the polymerization rate. (auth)« less

Dynamic and temperature dependent response of physical vapor deposited Se in freely standing nanometric thin films

NASA Astrophysics Data System (ADS)

Yoon, Heedong; McKenna, Gregory B.

2016-05-01

Here, we report results from an investigation of nano-scale size or confinement effects on the glass transition and viscoelastic properties of physical vapor deposited selenium films. The viscoelastic response of freely standing Se films was determined using a biaxial membrane inflation or bubble inflation method [P. A. O'Connell and G. B. McKenna, Science 307, 1760-1763 (2005)] on films having thicknesses from 60 to 267 nm and over temperatures ranging from Tg, macroscopic - 15 °C to Tg, macroscopic + 21 °C. Time-temperature superposition and time-thickness superposition were found to hold for the films in the segmental dispersion. The responses are compared with macroscopic creep and recoverable creep compliance data for selenium [K. M. Bernatz et al., J. Non-Cryst. Solids 307, 790-801 (2002)]. The time-temperature shift factors for the thin films show weaker temperature dependence than seen in the macroscopic behavior, being near to Arrhenius-like in their temperature dependence. Furthermore, the Se films exhibit a "rubbery-like" stiffening that increases as film thickness decreases similar to prior observations [P. A. O'Connell et al., Macromolecules 45(5), 2453-2459 (2012)] for organic polymers. In spite of the differences from the macroscopic behavior in the temperature dependence of the viscoelastic response, virtually no change in Tg as determined from the thickness dependence of the retardation time defining Tg was observed in the bubble inflation creep experiments to thicknesses as small as 60 nm. We also find that the observed rubbery stiffening is consistent with the postulate of K. L. Ngai et al. [J. Polym. Sci., Part B: Polym. Phys. 51(3), 214-224 (2013)] that it should correlate with the change of the macroscopic segmental relaxation.

Active region dimensionality and quantum efficiencies of InGaN LEDs from temperature dependent photoluminescence transients

NASA Astrophysics Data System (ADS)

Can, Nuri; Okur, Serdal; Monavarian, Morteza; Zhang, Fan; Avrutin, Vitaliy; Morkoç, Hadis; Teke, Ali; Özgür, Ümit

2015-03-01

Temperature dependent recombination dynamics in c-plane InGaN light emitting diodes (LEDs) with different well thicknesses, 1.5, 2, and 3 nm, were investigated to determine the active region dimensionality and its effect on the internal quantum efficiencies. It was confirmed for all LEDs that the photoluminescence (PL) transients are governed by radiative recombination at low temperatures while nonradiative recombination dominates at room temperature. At photoexcited carrier densities of 3 - 4.5 x 1016 cm-3 , the room-temperature Shockley-Read-Hall (A) and the bimolecular (B) recombination coefficients (A, B) were deduced to be (9.2x107 s-1, 8.8x10-10 cm3s-1), (8.5x107 s-1, 6.6x10-10 cm3s-1), and (6.5x107 s-1, 1.4x10-10 cm3s-1) for the six period 1.5, 2, and 3 nm well-width LEDs, respectively. From the temperature dependence of the radiative lifetimes, τrad α Tn/2, the dimensionality n of the active region was found to decrease consistently with decreasing well width. The 3 nm wide wells exhibited ~T1.5 dependence, suggesting a three-dimensional nature, whereas the 1.5 nm wells were confirmed to be two-dimensional (~T1) and the 2 nm wells close to being two-dimensional. We demonstrate that a combination of temperature dependent PL and time-resolved PL techniques can be used to evaluate the dimensionality as well as the quantum efficiencies of the LED active regions for a better understanding of the relationship between active-region design and the efficiency limiting processes in InGaN LEDs.

Clear-Sky Longwave Irradiance at the Earth's Surface--Evaluation of Climate Models.

NASA Astrophysics Data System (ADS)

Garratt, J. R.

2001-04-01

An evaluation of the clear-sky longwave irradiance at the earth's surface (LI) simulated in climate models and in satellite-based global datasets is presented. Algorithm-based estimates of LI, derived from global observations of column water vapor and surface (or screen air) temperature, serve as proxy `observations.' All datasets capture the broad zonal variation and seasonal behavior in LI, mainly because the behavior in column water vapor and temperature is reproduced well. Over oceans, the dependence of annual and monthly mean irradiance upon sea surface temperature (SST) closely resembles the observed behavior of column water with SST. In particular, the observed hemispheric difference in the summer minus winter column water dependence on SST is found in all models, though with varying seasonal amplitudes. The analogous behavior in the summer minus winter LI is seen in all datasets. Over land, all models have a more highly scattered dependence of LI upon surface temperature compared with the situation over the oceans. This is related to a much weaker dependence of model column water on the screen-air temperature at both monthly and annual timescales, as observed. The ability of climate models to simulate realistic LI fields depends as much on the quality of model water vapor and temperature fields as on the quality of the longwave radiation codes. In a comparison of models with observations, root-mean-square gridpoint differences in mean monthly column water and temperature are 4-6 mm (5-8 mm) and 0.5-2 K (3-4 K), respectively, over large regions of ocean (land), consistent with the intermodel differences in LI of 5-13 W m2 (15-28 W m2).

High-temperature magnetostructural transition in van der Waals-layered α - MoCl 3

DOE PAGES

McGuire, Michael A.; Yan, Jiaqiang; Lampen-Kelley, Paula; ...

2017-11-07

Here, the crystallographic and magnetic properties of the cleavable 4d 3 transition metal compound α–MoCl 3 are reported, with a focus on the behavior above room temperature. Crystals were grown by chemical vapor transport and characterized using temperature dependent x-ray diffraction, Raman spectroscopy, and magnetization measurements. A structural phase transition occurs near 585 K, at which the Mo-Mo dimers present at room temperature are broken. A nearly regular honeycomb net of Mo is observed above the transition, and an optical phonon associated with the dimerization instability is identified in the Raman data and in first-principles calculations. The crystals are diamagneticmore » at room temperature in the dimerized state, and the magnetic susceptibility increases sharply at the structural transition. Moderately strong paramagnetism in the high-temperature structure indicates the presence of local moments on Mo. This is consistent with results of spin-polarized density functional theory calculations using the low- and high-temperature structures. Above the magnetostructural phase transition the magnetic susceptibility continues to increase gradually up to the maximum measurement temperature of 780 K, with a temperature dependence that suggests two-dimensional antiferromagnetic correlations.« less

High-temperature magnetostructural transition in van der Waals-layered α -MoCl3

NASA Astrophysics Data System (ADS)

McGuire, Michael A.; Yan, Jiaqiang; Lampen-Kelley, Paula; May, Andrew F.; Cooper, Valentino R.; Lindsay, Lucas; Puretzky, Alexander; Liang, Liangbo; KC, Santosh; Cakmak, Ercan; Calder, Stuart; Sales, Brian C.

2017-11-01

The crystallographic and magnetic properties of the cleavable 4 d3 transition metal compound α -MoCl3 are reported, with a focus on the behavior above room temperature. Crystals were grown by chemical vapor transport and characterized using temperature dependent x-ray diffraction, Raman spectroscopy, and magnetization measurements. A structural phase transition occurs near 585 K, at which the Mo-Mo dimers present at room temperature are broken. A nearly regular honeycomb net of Mo is observed above the transition, and an optical phonon associated with the dimerization instability is identified in the Raman data and in first-principles calculations. The crystals are diamagnetic at room temperature in the dimerized state, and the magnetic susceptibility increases sharply at the structural transition. Moderately strong paramagnetism in the high-temperature structure indicates the presence of local moments on Mo. This is consistent with results of spin-polarized density functional theory calculations using the low- and high-temperature structures. Above the magnetostructural phase transition the magnetic susceptibility continues to increase gradually up to the maximum measurement temperature of 780 K, with a temperature dependence that suggests two-dimensional antiferromagnetic correlations.

Temperature dependent dielectric properties and ion transportation in solid polymer electrolyte for lithium ion batteries

NASA Astrophysics Data System (ADS)

Sengwa, R. J.; Dhatarwal, Priyanka; Choudhary, Shobhna

2016-05-01

Solid polymer electrolyte (SPE) film consisted of poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) blend matrix with lithium tetrafluroborate (LiBF4) as dopant ionic salt and poly(ethylene glycol) (PEG) as plasticizer has been prepared by solution casting method followed by melt pressing. Dielectric properties and ionic conductivity of the SPE film at different temperatures have been determined by dielectric relaxation spectroscopy. It has been observed that the dc ionic conductivity of the SPE film increases with increase of temperature and also the decrease of relaxation time. The temperature dependent relaxation time and ionic conductivity values of the electrolyte are governed by the Arrhenius relation. Correlation observed between dc conductivity and relaxation time confirms that ion transportation occurs with polymer chain segmental dynamics through hopping mechanism. The room temperature ionic conductivity is found to be 4 × 10-6 S cm-1 which suggests the suitability of the SPE film for rechargeable lithium batteries.

Temperature dependent dielectric properties and ion transportation in solid polymer electrolyte for lithium ion batteries

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

Sengwa, R. J., E-mail: rjsengwa@rediffmail.com; Dhatarwal, Priyanka, E-mail: dhatarwalpriyanka@gmail.com; Choudhary, Shobhna, E-mail: shobhnachoudhary@rediffmail.com

2016-05-06

Solid polymer electrolyte (SPE) film consisted of poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) blend matrix with lithium tetrafluroborate (LiBF{sub 4}) as dopant ionic salt and poly(ethylene glycol) (PEG) as plasticizer has been prepared by solution casting method followed by melt pressing. Dielectric properties and ionic conductivity of the SPE film at different temperatures have been determined by dielectric relaxation spectroscopy. It has been observed that the dc ionic conductivity of the SPE film increases with increase of temperature and also the decrease of relaxation time. The temperature dependent relaxation time and ionic conductivity values of the electrolyte are governedmore » by the Arrhenius relation. Correlation observed between dc conductivity and relaxation time confirms that ion transportation occurs with polymer chain segmental dynamics through hopping mechanism. The room temperature ionic conductivity is found to be 4 × 10{sup −6} S cm{sup −1} which suggests the suitability of the SPE film for rechargeable lithium batteries.« less

Extended investigation of intermartensitic transitions in Ni-Mn-Ga magnetic shape memory alloys: A detailed phase diagram determination

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

Çakir, Asli; Aktürk, Selçuk; Righi, Lara

2013-11-14

Martensitic transitions in shape memory Ni-Mn-Ga Heusler alloys take place between a high temperature austenite and a low temperature martensite phase. However, intermartensitic transformations have also been encountered that occur from one martensite phase to another. To examine intermartensitic transitions in magnetic shape memory alloys in detail, we carried out temperature dependent magnetization, resistivity, and x-ray diffraction measurements to investigate the intermartensitic transition in Ni{sub 50}Mn{sub 50–x}Ga{sub x} in the composition range 12≤x≤25 at. %. Rietveld refined x-ray diffraction results are found to be consistent with magnetization and resistivity data. Depending on composition, we observe that intermartensitic transitions occur inmore » the sequences 7M→L1{sub 0}, 5M→7M, and 5M→7M→L1{sub 0} with decreasing temperature. The L1{sub 0} non-modulated structure is most stable at low temperature.« less

Temperature-driven topological transition in 1T'-MoTe2

NASA Astrophysics Data System (ADS)

Berger, Ayelet Notis; Andrade, Erick; Kerelsky, Alexander; Edelberg, Drew; Li, Jian; Wang, Zhijun; Zhang, Lunyong; Kim, Jaewook; Zaki, Nader; Avila, Jose; Chen, Chaoyu; Asensio, Maria C.; Cheong, Sang-Wook; Bernevig, Bogdan A.; Pasupathy, Abhay N.

2018-01-01

The topology of Weyl semimetals requires the existence of unique surface states. Surface states have been visualized in spectroscopy measurements, but their connection to the topological character of the material remains largely unexplored. 1T'-MoTe2, presents a unique opportunity to study this connection. This material undergoes a phase transition at 240 K that changes the structure from orthorhombic (putative Weyl semimetal) to monoclinic (trivial metal), while largely maintaining its bulk electronic structure. Here, we show from temperature-dependent quasiparticle interference measurements that this structural transition also acts as a topological switch for surface states in 1T'-MoTe2. At low temperature, we observe strong quasiparticle scattering, consistent with theoretical predictions and photoemission measurements for the surface states in this material. In contrast, measurements performed at room temperature show the complete absence of the scattering wavevectors associated with the trivial surface states. These distinct quasiparticle scattering behaviors show that 1T'-MoTe2 is ideal for separating topological and trivial electronic phenomena via temperature-dependent measurements.

Modelling and measurement of bandgap behaviour in medium-wavelength IR InAs/InAs0.815Sb0.185 strained-layer superlattices

NASA Astrophysics Data System (ADS)

Letka, Veronica; Keen, James; Craig, Adam; Marshall, Andrew R. J.

2017-10-01

InAs/InAs1-xSbx type-II strained-layer superlattices (SLS) are a structure with potential infrared detection applications, owing to its tunable bandgap and suppressed Auger recombination. A series of medium-wavelength infrared (MWIR) InAs/InAs0.815Sb0.185 SLS structures, grown as undoped absorption epilayers on GaAs, were fabricated using molecular beam epitaxy in order to study the dependence of the ground state transitions on temperature and superlattice period thickness. Photoluminescence peaks at 4 K were obtained with the use of a helium-cooled micro-PL system and an InSb detector, and temperature-dependent absorption spectra were measured in the range 77 K - 300 K on a Fourier Transform Infrared (FTIR) spectrometer, equipped with a 1370 K blackbody source and a DTGS detector. An nBn device sample with the absorber structure identical to one of the undoped samples was also grown and processed with the goal of measuring temperature-dependent spectral response. A model for superlattice band alignment was also devised, incorporating the Bir-Pikus transformation results for uniaxial and biaxial strain, and the Einstein oscillator model for bandgap temperature dependence. Absorption coefficients of several 1000 cm-1 throughout the entire MWIR range are found for all samples, and temperature dependence of the bandgaps is extracted and compared to the model. This and photoluminescence data also demonstrate bandgap shifts consistent with the different superlattice periods of the three samples.

Abiotic factors influencing embryonic development, egg hatching, and larval orientation in the reindeer warble fly, Hypoderma tarandi.

PubMed

Karter, A J; Folstad, I; Anderson, J R

1992-10-01

Wild-caught, tethered females of the reindeer warble fly, Hypoderma tarandi (L.) (= Oedemagena tarandi (L.)), (Diptera, Oestridae) were stimulated to oviposit on hairs of a reindeer hide. Newly laid eggs incubated at constant temperatures and relative humidities hatched within 3 days to 2 weeks, depending on the experimental conditions. Over a range of 7-40 degrees C, hatching only occurred between 20 and 37 degrees C. Eggs held at 100% relative humidity had lower hatchability and longer time to hatch relative to eggs held at 77% relative humidity. The average number of degree-days for hatching was 50.35. Between 20 and 33 degrees C there was a temperature-dependent linear trend in developmental rate, and the proportion of eggs hatching was highest, and least variable, at the mid-temperature ranges. The temperature range found in the natural host micro-habitat where H. tarandi commonly affix their eggs (close to the skin at the base of a host hair) was consistent with the experimental temperature treatments that produced the highest hatching rate. Newly emerged larvae displayed positive thermotaxis, while showing no phototaxic or geotaxic behaviour. Results indicate that constraints of the host environment, coupled with temperature-dependent hatching success, may impose a selective pressure on oviposition behaviour.

Temperature dependence of positron annihilation parameters in Tl-Ba-Ca-Cu-O superconductors

NASA Astrophysics Data System (ADS)

Sundar, C. S.; Bharathi, A.; Ching, W. Y.; Jean, Y. C.; Hor, P. H.; Meng, R. L.; Huang, Z. J.; Chu, C. W.

1990-08-01

The results of positron lifetime and Doppler broadened line-shape parameter measurements as a function of temperature, across Tc, in the Tl-Ba-Ca-Cu-O superconductors are presented. The bulk lifetime in the normal state is found to decrease with the increase in the number of CuO2 layers. Different temperature dependencies of the annihilation parameters are observed in the various Tl systems containing different numbers of CuO2 layers. In the Tl2Ba2Ca2Cu3O10 system, an increase in lifetime is observed below Tc, whereas in Tl2Ba2CaCu2O8, a decrease in lifetime is seen below Tc. In the Tl2Ba2CuO6 system, the lifetime is observed to be temperature independent. The different temperature variations of positron annihilation parameters are discussed in the light of the positron density distribution, obtained with use of the results of the self-consistent orthogonalized linear combination of atomic orbitals band-structure calculations. It is argued that the different temperature dependencies of the annihilation parameters is related to the positron density distribution within the unit cell and arise due to local charge transfer in the vicinity of the CuO2 layer in the superconducting state.

Magneto-optical properties of semi-parabolic plus semi-inverse squared quantum wells

NASA Astrophysics Data System (ADS)

Tung, Luong V.; Vinh, Pham T.; Phuc, Huynh V.

2018-06-01

We theoretically study the optical absorption in a quantum well with the semi-parabolic potential plus the semi-inverse squared potential (SPSIS) in the presence of a static magnetic field in which both one- and two-photon absorption processes have been taken into account. The expression of the magneto-optical absorption coefficient (MOAC) is expressed by the second-order golden rule approximation including the electron-LO phonon interaction. We also use the profile method to obtain the full width at half maximum (FWHM) of the absorption peaks. Our numerical results show that either MOAC or FWHM strongly depends on the confinement frequency, temperature, and magnetic field but their dependence on the parameter β is very weak. The temperature dependence of FWHM is consistent with the previous theoretical and experimental works.

Semi-empirical calculations of line-shape parameters and their temperature dependences for the ν6 band of CH3D perturbed by N2

NASA Astrophysics Data System (ADS)

Dudaryonok, A. S.; Lavrentieva, N. N.; Buldyreva, J.

2018-06-01

(J, K)-line broadening and shift coefficients with their temperature-dependence characteristics are computed for the perpendicular (ΔK = ±1) ν6 band of the 12CH3D-N2 system. The computations are based on a semi-empirical approach which consists in the use of analytical Anderson-type expressions multiplied by a few-parameter correction factor to account for various deviations from Anderson's theory approximations. A mathematically convenient form of the correction factor is chosen on the basis of experimental rotational dependencies of line widths, and its parameters are fitted on some experimental line widths at 296 K. To get the unknown CH3D polarizability in the excited vibrational state v6 for line-shift calculations, a parametric vibration-state-dependent expression is suggested, with two parameters adjusted on some room-temperature experimental values of line shifts. Having been validated by comparison with available in the literature experimental values for various sub-branches of the band, this approach is used to generate massive data of line-shape parameters for extended ranges of rotational quantum numbers (J up to 70 and K up to 20) typically requested for spectroscopic databases. To obtain the temperature-dependence characteristics of line widths and line shifts, computations are done for various temperatures in the range 200-400 K recommended for HITRAN and least-squares fit procedures are applied. For the case of line widths strong sub-branch dependence with increasing K is observed in the R- and P-branches; for the line shifts such dependence is stated for the Q-branch.

Bottomonium above deconfinement in lattice nonrelativistic QCD.

PubMed

Aarts, G; Kim, S; Lombardo, M P; Oktay, M B; Ryan, S M; Sinclair, D K; Skullerud, J-I

2011-02-11

We study the temperature dependence of bottomonium for temperatures in the range 0.4T(c) < T < 2.1T(c), using nonrelativistic dynamics for the bottom quark and full relativistic lattice QCD simulations for Nf = 2 light flavors on a highly anisotropic lattice. We find that the Υ is insensitive to the temperature in this range, while the χb propagators show a crossover from the exponential decay characterizing the hadronic phase to a power-law behavior consistent with nearly free dynamics at T ≃ 2T(c).

Temperature and doping dependence of the high-energy kink in cuprates.

PubMed

Zemljic, M M; Prelovsek, P; Tohyama, T

2008-01-25

It is shown that spectral functions within the extended t-J model, evaluated using the finite-temperature diagonalization of small clusters, exhibit the high-energy kink in single-particle dispersion consistent with recent angle-resolved photoemission results on hole-doped cuprates. The kink and waterfall-like features persist up to large doping and to temperatures beyond J; hence, the origin can be generally attributed to strong correlations and incoherent hole propagation at large binding energies. In contrast, our analysis predicts that electron-doped cuprates do not exhibit these phenomena in photoemission.

Temperature shift of intraband absorption peak in tunnel-coupled QW structure

NASA Astrophysics Data System (ADS)

Akimov, V.; Firsov, D. A.; Duque, C. A.; Tulupenko, V.; Balagula, R. M.; Vinnichenko, M. Ya.; Vorobjev, L. E.

2017-04-01

An experimental study of the intersubband light absorption by the 100-period GaAs/Al0.25Ga0.75As double quantum well heterostructure doped with silicon is reported and interpreted. Small temperature redshift of the 1-3 intersubband absorption peak is detected. Numerical calculations of the absorption coefficient including self-consistent Hartree calculations of the bottom of the conduction band show good agreement with the observed phenomena. The temperature dependence of energy gap of the material and the depolarization shift should be accounted for to explain the shift.

Far-infrared spectra of acetanilide revisited

NASA Astrophysics Data System (ADS)

Spire, A.; Barthes, M.; Kellouai, H.; De Nunzio, G.

2000-03-01

A new investigation of the temperature dependence of the far-infrared spectra of acetanilide and some isotopomers is presented. Four absorption bands are considered at 31, 42, 64, and 80 cm-1, and no significant change of their integrated intensity is observed when reducing the temperature. The temperature induced frequency shift values and other properties of these bands are consistent with an assignment as anharmonic lattice phonons. These results rule out the assignment of the 64, 80, and 106 cm-1 bands as normal modes of the polaronic excitation, as previously suggested.

Age Spreads and the Temperature Dependence of Age Estimates in Upper Sco

NASA Astrophysics Data System (ADS)

Fang, Qiliang; Herczeg, Gregory J.; Rizzuto, Aaron

2017-06-01

Past estimates for the age of the Upper Sco Association are typically 11–13 Myr for intermediate-mass stars and 4–5 Myr for low-mass stars. In this study, we simulate populations of young stars to investigate whether this apparent dependence of estimated age on spectral type may be explained by the star formation history of the association. Solar and intermediate mass stars begin their pre-main sequence evolution on the Hayashi track, with fully convective interiors and cool photospheres. Intermediate-mass stars quickly heat up and transition onto the radiative Henyey track. As a consequence, for clusters in which star formation occurs on a timescale similar to that of the transition from a convective to a radiative interior, discrepancies in ages will arise when ages are calculated as a function of temperature instead of mass. Simple simulations of a cluster with constant star formation over several Myr may explain about half of the difference in inferred ages versus photospheric temperature; speculative constructions that consist of a constant star formation followed by a large supernova-driven burst could fully explain the differences, including those between F and G stars where evolutionary tracks may be more accurate. The age spreads of low-mass stars predicted from these prescriptions for star formation are consistent with the observed luminosity spread of Upper Sco. The conclusion that a lengthy star formation history will yield a temperature dependence in ages is expected from the basic physics of pre-main sequence evolution, and is qualitatively robust to the large uncertainties in pre-main sequence evolutionary models.

Quality aspects of the Wegener Center multi-satellite GPS radio occultation record OPSv5.6

NASA Astrophysics Data System (ADS)

Angerer, Barbara; Ladstädter, Florian; Scherllin-Pirscher, Barbara; Schwärz, Marc; Steiner, Andrea K.; Foelsche, Ulrich; Kirchengast, Gottfried

2017-12-01

The demand for high-quality atmospheric data records, which are applicable in climate studies, is undisputed. Using such records requires knowledge of the quality and the specific characteristics of all contained data sources. The latest version of the Wegener Center (WEGC) multi-satellite Global Positioning System (GPS) radio occultation (RO) record, OPSv5.6, provides globally distributed upper-air satellite data of high quality, usable for climate and other high-accuracy applications. The GPS RO technique has been deployed in several satellite missions since 2001. Consistency among data from these missions is essential to create a homogeneous long-term multi-satellite climate record. In order to enable a qualified usage of the WEGC OPSv5.6 data set we performed a detailed analysis of satellite-dependent quality aspects from 2001 to 2017. We present the impact of the OPSv5.6 quality control on the processed data and reveal time-dependent and satellite-specific quality characteristics. The highest quality data are found for MetOp (Meteorological Operational satellite) and GRACE (Gravity Recovery and Climate Experiment). Data from FORMOSAT-3/COSMIC (Formosa Satellite mission-3/Constellation Observing System for Meteorology, Ionosphere, and Climate) are also of high quality. However, comparatively large day-to-day variations and satellite-dependent irregularities need to be taken into account when using these data. We validate the consistency among the various satellite missions by calculating monthly mean temperature deviations from the multi-satellite mean, including a correction for the different sampling characteristics. The results are highly consistent in the altitude range from 8 to 25 km, with mean temperature deviations less than 0.1 K. At higher altitudes the OPSv5.6 RO temperature record is increasingly influenced by the characteristics of the bending angle initialization, with the amount of impact depending on the receiver quality.

Corrigendum to "Measurement and computations for temperature dependences of self-broadened carbon dioxide transitions in the 30012←00001 and 30013←00001 bands" [J. Quant. Spectrosc. Radiat. Transf., 111 (9) (2010) 1065-1079

NASA Astrophysics Data System (ADS)

Predoi-Cross, Adriana; Liu, W.; Murphy, Reba; Povey, Chad; Gamache, R.; Laraia, A.; McKellar, A. R. W.; Hurtmans, Daniel; Devi, V. M.

2015-10-01

The group of authors would like to make the following clarification: the retrievals of self-broadened temperature dependence coefficients were performed by the authors both using the multispectrum fit program from Ref. [14] and using the multispectrum fit program of D. Chris Benner [Benner DC, Rinsland CP, Devi VM, Smith MAH, Atkins D. A multispectrum nonlinear least-squares fitting technique. J. Quant. Spectrosc. Radiat. Transf. 1995;53:705-21.). To retrieve the room temperature self-broadening parameters, the authors have used the values in Ref. [4]. For reasons of consistency with the results published for air-broadening and air-shift temperature dependence coefficients in A. Predoi-Cross, A.R.W. McKellar, D. Chris Benner, V. Malathy Devi, R.R. Gamache, C.E. Miller, R.A. Toth, L.R. Brown, Temperature dependences for air-broadened Lorentz half width and pressure-shift coefficients in the 30013←00001 and 30012←00001 bands of CO2near 1600 μm, Canadian Journal of Physics, 87 (5) (2009) 517-535, Tables 2 and 3, and Figures 2 and 4 contain only the values retrieved using the multispectrum fit program of D. Chris Benner. We would like to thank D. Chris Benner for allowing us to use his fitting software.

Molecular evolution of Dmrt1 accompanies change of sex-determining mechanisms in reptilia.

PubMed

Janes, Daniel E; Organ, Christopher L; Stiglec, Rami; O'Meally, Denis; Sarre, Stephen D; Georges, Arthur; Graves, Jennifer A M; Valenzuela, Nicole; Literman, Robert A; Rutherford, Kim; Gemmell, Neil; Iverson, John B; Tamplin, Jeffrey W; Edwards, Scott V; Ezaz, Tariq

2014-12-01

In reptiles, sex-determining mechanisms have evolved repeatedly and reversibly between genotypic and temperature-dependent sex determination. The gene Dmrt1 directs male determination in chicken (and presumably other birds), and regulates sex differentiation in animals as distantly related as fruit flies, nematodes and humans. Here, we show a consistent molecular difference in Dmrt1 between reptiles with genotypic and temperature-dependent sex determination. Among 34 non-avian reptiles, a convergently evolved pair of amino acids encoded by sequence within exon 2 near the DM-binding domain of Dmrt1 distinguishes species with either type of sex determination. We suggest that this amino acid shift accompanied the evolution of genotypic sex determination from an ancestral condition of temperature-dependent sex determination at least three times among reptiles, as evident in turtles, birds and squamates. This novel hypothesis describes the evolution of sex-determining mechanisms as turnover events accompanied by one or two small mutations. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

Antiferromagnetic Interlayer Exchange Coupling in All-Semiconducting EuS/PbS/EuS Trilayers

NASA Technical Reports Server (NTRS)

Smits, C. J. P.; Filip, A. T.; Swagten, H. J. M.; Koopmans, B.; deJonge, W. J. M.; Chernyshova, M.; Kowalczyk, L.; Grasza, K.; Szczerbakow, A.; Story, T.

2003-01-01

A comprehensive experimental study on the antiferromagnetic interlayer exchange coupling in high quality epitaxial all-semiconducting EuSPbSEuS trilayers is reported. The influence of substrates, the thickness of the non-magnetic PbS spacer layer, and of temperature, was investigated by means of SQUID magnetometry. In trilayers with a PbS thickness between 4 and 12 deg A the low temperature hysteresis loops showed the signature of antiferromagnetic coupling. The value of the interlayer exchange coupling energy was determined by simulating the data with a modified Stoner model, including Zeeman, anisotropy, and exchange coupling energies. An important observation was of a strong dependence of the interlayer exchange coupling energy on temperature, consistent with a power law dependence of the exchange coupling constant on the saturation magnetization of the EuS layers. While no theoretical description is readily available, we conjecture that the observed behavior is due to a dependence of the interlayer exchange coupling energy on the exchange splitting of the EuS conduction band.

Theoretical calculation of CH3F/N2-broadening coefficients and their temperature dependence

NASA Astrophysics Data System (ADS)

Jellali, C.; Maaroufi, N.; Aroui, H.

2018-07-01

Using Robert and Bonamy formalism (with parabolic and exact trajectories) based on the semi-classical impact theory, N2-broadening coefficients of methyl fluoride CH3F were calculated for transitions belonging to the PP-, PQ-, PR-, RP-, RQ- and RR- sub-branches of the ν6 perpendicular band near 8.5 μm. The calculations showed the predominance of the dipole-quadruple interaction. The J and K rotational quantum numbers dependencies of the computed coefficients that are consistent with previous measurements were clearly observed in this study. For a fixed value of J, we noticed a decrease in the broadening coefficients, which was more significant at lower J values. In order to deduce the temperature exponent, the N2-broadening coefficients of CH3F were calculated at various temperatures of atmospheric interest between 183 and 296 K with J ≤ 60 and K ≤ 10. These exponents were, in general, J-dependent and K-independent, except for K close to J.

Molecular evolution of Dmrt1 accompanies change of sex-determining mechanisms in reptilia

PubMed Central

Janes, Daniel E.; Organ, Christopher L.; Stiglec, Rami; O'Meally, Denis; Sarre, Stephen D.; Georges, Arthur; Graves, Jennifer A. M.; Valenzuela, Nicole; Literman, Robert A.; Rutherford, Kim; Gemmell, Neil; Iverson, John B.; Tamplin, Jeffrey W.; Edwards, Scott V.; Ezaz, Tariq

2014-01-01

In reptiles, sex-determining mechanisms have evolved repeatedly and reversibly between genotypic and temperature-dependent sex determination. The gene Dmrt1 directs male determination in chicken (and presumably other birds), and regulates sex differentiation in animals as distantly related as fruit flies, nematodes and humans. Here, we show a consistent molecular difference in Dmrt1 between reptiles with genotypic and temperature-dependent sex determination. Among 34 non-avian reptiles, a convergently evolved pair of amino acids encoded by sequence within exon 2 near the DM-binding domain of Dmrt1 distinguishes species with either type of sex determination. We suggest that this amino acid shift accompanied the evolution of genotypic sex determination from an ancestral condition of temperature-dependent sex determination at least three times among reptiles, as evident in turtles, birds and squamates. This novel hypothesis describes the evolution of sex-determining mechanisms as turnover events accompanied by one or two small mutations. PMID:25540158

Dependence of SOL widths on plasma current and density in NSTX H-mode plasmas

NASA Astrophysics Data System (ADS)

Ahn, J.-W.; Maingi, R.; Boedo, J. A.; Soukhanovskii, V.; NSTX Team

2009-06-01

The dependence of various SOL widths on the line-averaged density ( n) and plasma current ( Ip) for the quiescent H-mode plasmas with Type-V ELMs in the National Spherical Torus Experiment (NSTX) was investigated. It is found that the heat flux SOL width ( λq), measured by the IR camera, is virtually insensitive to n and has a strong negative dependence on Ip. This insensitivity of λq to n¯e is consistent with the scaling law from JET H-mode plasmas that shows a very weak dependence on the upstream density. The electron temperature, ion saturation current density, electron density, and electron pressure decay lengths ( λTe, λjsat, λne, and λpe, respectively) measured by the probe showed that λTe and λjsat have strong negative dependence on Ip, whereas λne and λpe revealed only a little or no dependence. The dependence of λTe on Ip is consistent with the scaling law in the literature, while λne and λpe dependence shows a different trend.

Molecular dynamics simulations of methane hydrate decomposition.

PubMed

Myshakin, Evgeniy M; Jiang, Hao; Warzinski, Robert P; Jordan, Kenneth D

2009-03-12

Molecular dynamics simulations have been carried out to study decomposition of methane hydrate at different cage occupancies. The decomposition rate is found to depend sensitively on the hydration number. The rate of the destruction of the cages displays Arrhenius behavior, consistent with an activated mechanism. During the simulations, reversible formation of partial water cages around methane molecules in the liquid was observed at the interface at temperatures above the computed hydrate decomposition temperature.

Role of temperature-dependent O-p-Fe-d hybridization parameter in the metal-insulator transition of Fe3O4: a theoretical study

NASA Astrophysics Data System (ADS)

Fauzi, A. D.; Majidi, M. A.; Rusydi, A.

2017-04-01

We propose a simple tight-binding based model for Fe3O4 that captures the preference of ferrimagnetic over ferromagnetic spin configuration of the system. Our model is consistent with previous theoretical and experimental studies suggesting that the system is half metallic, in which spin polarized electrons hop only among the Fe B sites. To address the metal-insulator transition (MIT) we propose that the strong correlation among electrons, which may also be influenced by the electron-phonon interactions, manifest as the temperature-dependence of the O-p-Fe-d hybridization parameter, particularly Fe-d belonging to one of the Fe B sites (denoted as {t}{{FeB}-{{O}}}(2)). By proposing that this parameter increases as the temperature decreases, our density-of-states calculation successfully captures a gap opening at the Fermi level, transforming the system from half metal to insulator. Within this model along with the corresponding choice of parameters and a certain profile of the temperature dependence of {t}{{FeB}-{{O}}}(2), we calculate the resistivity of the system as a function of temperature. Our calculation result reveals the drastic uprising trend of the resistivity profile as the temperature decreases, with the MIT transition temperature located around 100 K, which is in agreement with experimental data.

Influence of Temperature and Grain Size on Austenite Stability in Medium Manganese Steels

NASA Astrophysics Data System (ADS)

Zhang, Yulong; Wang, Li; Findley, Kip O.; Speer, John G.

2017-05-01

With an aim to elucidate the influence of temperature and grain size on austenite stability, a commercial cold-rolled 7Mn steel was annealed at 893 K (620 °C) for times varying between 3 minutes and 96 hours to develop different grain sizes. The austenite fraction after 3 minutes was 34.7 vol pct, and at longer times was around 40 pct. An elongated microstructure was retained after shorter annealing times while other conditions exhibited equiaxed ferrite and austenite grains. All conditions exhibit similar temperature dependence of mechanical properties. With increasing test temperature, the yield and tensile strength decrease gradually, while the uniform and total elongation increase, followed by an abrupt drop in strength and ductility at 393 K (120 °C). The Olson-Cohen model was applied to fit the transformed austenite fractions for strained tensile samples, measured by means of XRD. The fit results indicate that the parameters α and β decrease with increasing test temperature, consistent with increased austenite stability. The 7Mn steels exhibit a distinct temperature dependence of the work hardening rate. Optimized austenite stability provides continuous work hardening in the temperature range of 298 K to 353 K (25 °C to 80 °C). The yield and tensile strengths have a strong dependence on grain size, although grain size variations have less effect on uniform and total elongation.

South Pole Hydrogen Distribution for Present Lunar Conditions: Implications for Past Impacts

NASA Technical Reports Server (NTRS)

Elphic, R. C.; Paige, D. A.; Siegler, M. A.; Vasavada, A. R.; Eke, V. R.; Teodoro, L. F. A.; Lawrence, D. J.

2010-01-01

It has been known since the Lunar Prospector mission that the poles of the Moon evidently harbor enhanced concentrations of hydrogen [1,2]. The physical and chemical form of the hydrogen has been much debated. Using imagery from Clementine it was possible to roughly estimate permanently-shadowed regions (PSRs), and to perform image reconstructions of the Lunar Prospector epithermal neutron flux maps [3,4]. The hydrogen concentrations resulting from these reconstructions were consistent with a few weight percent water ice in selected locations. With the LCROSS impact, we now know that hydrogen in the form of ice does exist in lunar polar cold traps [5]. Armed with this information, and new data from LRO/Diviner, we can examine whether the pre-sent-day distribution of hydrogen in the form of water ice is consistent with a past large impact that delivered a large mass of volatiles to the lunar surface. These volatiles, mixed with solid impact ejecta, would then be lost from locations having high mean temperatures but would otherwise remain trapped in locations with sufficiently low mean annual temperatures [6]. The time scales for loss would depend on the location-dependent temperatures as well as impact history.

Free-standing nanocomposites with high conductivity and extensibility.

PubMed

Chun, Kyoung-Yong; Kim, Shi Hyeong; Shin, Min Kyoon; Kim, Youn Tae; Spinks, Geoffrey M; Aliev, Ali E; Baughman, Ray H; Kim, Seon Jeong

2013-04-26

The prospect of electronic circuits that are stretchable and bendable promises tantalizing applications such as skin-like electronics, roll-up displays, conformable sensors and actuators, and lightweight solar cells. The preparation of highly conductive and highly extensible materials remains a challenge for mass production applications, such as free-standing films or printable composite inks. Here we present a nanocomposite material consisting of carbon nanotubes, ionic liquid, silver nanoparticles, and polystyrene-polyisoprene-polystyrene having a high electrical conductivity of 3700 S cm(-1) that can be stretched to 288% without permanent damage. The material is prepared as a concentrated dispersion suitable for simple processing into free-standing films. For the unstrained state, the measured thermal conductivity for the electronically conducting elastomeric nanoparticle film is relatively high and shows a non-metallic temperature dependence consistent with phonon transport, while the temperature dependence of electrical resistivity is metallic. We connect an electric fan to a DC power supply using the films to demonstrate their utility as an elastomeric electronic interconnect. The huge strain sensitivity and the very low temperature coefficient of resistivity suggest their applicability as strain sensors, including those that operate directly to control motors and other devices.

Signals of strong electronic correlation in ion scattering processes

NASA Astrophysics Data System (ADS)

Bonetto, F.; Gonzalez, C.; Goldberg, E. C.

2016-05-01

Previous measurements of neutral atom fractions for S r+ scattered by gold polycrystalline surfaces show a singular dependence with the target temperature. There is still not a theoretical model that can properly describe the magnitude and the temperature dependence of the neutralization probabilities found. Here, we applied a first-principles quantum-mechanical theoretical formalism to describe the time-dependent scattering process. Three different electronic correlation approaches consistent with the system analyzed are used: (i) the spinless approach, where two charge channels are considered (S r0 and S r+ ) and the spin degeneration is neglected; (ii) the infinite-U approach, with the same charge channels (S r0 and S r+ ) but considering the spin degeneration; and (iii) the finite-U approach, where the first ionization and second ionization energy levels are considered very, but finitely, separated. Neutral fraction magnitudes and temperature dependence are better described by the finite-U approach, indicating that e -correlation plays a significant role in charge-transfer processes. However, none of them is able to explain the nonmonotonous temperature dependence experimentally obtained. Here, we suggest that small changes in the surface work function introduced by the target heating, and possibly not detected by experimental standard methods, could be responsible for that singular behavior. Additionally, we apply the same theoretical model using the infinite-U approximation for the Mg-Au system, obtaining an excellent description of the experimental neutral fractions measured.

Ozone Depletion at Mid-Latitudes: Coupling of Volcanic Aerosols and Temperature Variability to Anthropogenic Chlorine

NASA Technical Reports Server (NTRS)

Solomon, S.; Portmann, R. W.; Garcia, R. R.; Randel, W.; Wu, F.; Nagatani, R.; Gleason, J.; Thomason, L.; Poole, L. R.; McCormick, M. P.

1998-01-01

Satellite observations of total ozone at 40-60 deg N are presented from a variety of instruments over the time period 1979-1997. These reveal record low values in 1992-3 (after Pinatubo) followed by partial but incomplete recovery. The largest post-Pinatubo reductions and longer-term trends occur in spring, providing a critical test for chemical theories of ozone depletion. The observations are shown to be consistent with current understanding of the chemistry of ozone depletion when changes in reactive chlorine and stratospheric aerosol abundances are considered along with estimates of wave-driven fluctuations in stratospheric temperatures derived from global temperature analyses. Temperature fluctuations are shown to make significant contributions to model calculated northern mid-latitude ozone depletion due to heterogeneous chlorine activation on liquid sulfate aerosols at temperatures near 200-210 K (depending upon water vapor pressure), particularly after major volcanic eruptions. Future mid-latitude ozone recovery will hence depend not only on chlorine recovery but also on temperature trends and/or variability, volcanic activity, and any trends in stratospheric sulfate aerosol.

Temperature-dependence of stress and elasticity in wet-transferred graphene membranes

NASA Astrophysics Data System (ADS)

De Alba, Roberto; Abhilash, T. S.; Hui, Aaron; Storch, Isaac R.; Craighead, Harold G.; Parpia, Jeevak M.

2018-03-01

We report measurements of the mechanical properties of two suspended graphene membranes in the temperature range of 80 K to 550 K. For this entire range, the resonant frequency and quality factor of each device were monitored continuously during cooling and heating. Below 300 K, we have additionally measured the resonant frequency's tunability via electrostatic force, and modeled this data to determine graphene's tension and elastic modulus; both of these parameters are found to be strongly temperature-dependent in this range. Above 300 K, we observe a resonant frequency (and therefore tension) minimum near room temperature. This suggests that the thermal expansion coefficient is positive for temperatures below roughly 315 K, and negative for higher temperatures. Lastly, we observe a large, reproducible hysteresis in the resonant frequency as our graphene devices are cycled between 300 K and 550 K. After returning to 300 K, the measured frequency evolves exponentially in time with a time constant of ˜24 h. Our results clash with expectations for pristine graphene membranes, but are consistent with expectations for composite membranes composed of graphene coated by a thin layer of polymer residue.

Quantum dot-containing polymer particles with thermosensitive fluorescence.

PubMed

Generalova, Alla N; Oleinikov, Vladimir A; Sukhanova, Alyona; Artemyev, Mikhail V; Zubov, Vitaly P; Nabiev, Igor

2013-01-15

Composite polymer particles consisting of a solid poly(acrolein-co-styrene) core and a poly(N-vinylcaprolactam) (PVCL) polymer shell doped with CdSe/ZnS semiconductor quantum dots (QDs) were fabricated. The temperature response of the composite particles was observed as a decrease in their hydrodynamic diameter upon heating above the lower critical solution temperature of the thermosensitive PVCL polymer. Embedding QDs in the PVCL shell yields particles whose fluorescence is sensitive to temperature changes. This sensitivity was determined by the dependence of the QD fluorescence intensity on the distances between them in the PVCL shell, which reversibly change as a result of the temperature-driven conformational changes in the polymer. The QD-containing thermosensitive particles were assembled with protein molecules in such a way that they retained their thermosensitive properties, including the completely reversible temperature dependence of their fluorescence response. The composite particles developed can be used as local temperature sensors, as carriers for biomolecules, as well as in biosensing and various bioassays employing optical detection schemes. Copyright © 2012 Elsevier B.V. All rights reserved.

Physical properties of ionic liquids consisting of the 1-butyl-3-methylimidazolium cation with various anions and the bis(trifluoromethylsulfonyl)imide anion with various cations.

PubMed

Jin, Hui; O'Hare, Bernie; Dong, Jing; Arzhantsev, Sergei; Baker, Gary A; Wishart, James F; Benesi, Alan J; Maroncelli, Mark

2008-01-10

Physical properties of 4 room-temperature ionic liquids consisting of the 1-butyl-3-methylimidazolium cation with various perfluorinated anions and the bis(trifluoromethylsulfonyl)imide (Tf2N-) anion with 12 pyrrolidinium-, ammonium-, and hydroxyl-containing cations are reported. Electronic structure methods are used to calculate properties related to the size, shape, and dipole moment of individual ions. Experimental measurements of phase-transition temperatures, densities, refractive indices, surface tensions, solvatochromic polarities based on absorption of Nile Red, 19F chemical shifts of the Tf2N- anion, temperature-dependent viscosities, conductivities, and cation diffusion coefficients are reported. Correlations among the measured quantities as well as the use of surface tension and molar volume for estimating Hildebrand solubility parameters of ionic liquids are also discussed.

The effects of plasma inhomogeneity on the nanoparticle coating in a low pressure plasma reactor

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

Pourali, N.; Foroutan, G.

2015-10-15

A self-consistent model is used to study the surface coating of a collection of charged nanoparticles trapped in the sheath region of a low pressure plasma reactor. The model consists of multi-fluid plasma sheath module, including nanoparticle dynamics, as well as the surface deposition and particle heating modules. The simulation results show that the mean particle radius increases with time and the nanoparticle size distribution is broadened. The mean radius is a linear function of time, while the variance exhibits a quadratic dependence. The broadening in size distribution is attributed to the spatial inhomogeneity of the deposition rate which inmore » turn depends on the plasma inhomogeneity. The spatial inhomogeneity of the ions has strong impact on the broadening of the size distribution, as the ions contribute both in the nanoparticle charging and in direct film deposition. The distribution width also increases with increasing of the pressure, gas temperature, and the ambient temperature gradient.« less

The mobility of Nb in rutile-saturated NaCl- and NaF-bearing aqueous fluids from 1–6.5 GPa and 300–800 °C

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

Tanis, Elizabeth A.; Simon, Adam; Tschauner, Oliver

Rutile (TiO 2) is an important host phase for high field strength elements (HFSE) such as Nb in metamorphic and subduction zone environments. The observed depletion of Nb in arc rocks is often explained by the hypothesis that rutile sequesters HFSE in the subducted slab and overlying sediment, and is chemically inert with respect to aqueous fluids evolved during prograde metamorphism in the forearc to subarc environment. However, field observations of exhumed terranes, and experimental studies, indicate that HFSE may be soluble in complex aqueous fluids at high pressure (i.e., >0.5 GPa) and moderate to high temperature (i.e., >300 °C).more » In this study, we investigated experimentally the mobility of Nb in NaCl- and NaF-bearing aqueous fluids in equilibrium with Nb-bearing rutile at pressure-temperature conditions applicable to fluid evolution in arc environments. Niobium concentrations in aqueous fluid at rutile saturation were measured directly by using a hydrothermal diamond-anvil cell (HDAC) and synchrotron X-ray fluorescence (SXRF) at 2.1 to 6.5 GPa and 300-500 °C, and indirectly by performing mass loss experiments in a piston-cylinder (PC) apparatus at similar to 1 GPa and 700-800 °C. The concentration of Nb in a 10 wt% NaCl aqueous fluid increases from 6 to 11 mu g/g as temperature increases from 300 to 500 °C, over a pressure range from 2.1 to 2.8 GPa, consistent with a positive temperature dependence. The concentration of Nb in a 20 wt% NaCl aqueous fluid varies from 55 to 150 mu g/g at 300 to 500 °C, over a pressure range from 1.8 to 6.4 GPa; however, there is no discernible temperature or pressure dependence. Here, the Nb concentration in a 4 wt% NaF-bearing aqueous fluid increases from 180 to 910 mu g/g as temperature increases from 300 to 500 °C over the pressure range 2.1 to 6.5 GPa. The data for the F-bearing fluid indicate that the Nb content of the fluid exhibits a dependence on temperature between 300 and 500 °C at ≥ 2 GPa, but there is no observed dependence on pressure. Together, the data demonstrate that the hydrothermal mobility of Nb is strongly controlled by the composition of the fluid, consistent with published data for Ti. At all experimental conditions, however, the concentration of Nb in the fluid is always lower than coexisting rutile, consistent with a role for rutile in moderating the Nb budget of arc rocks.« less

The mobility of Nb in rutile-saturated NaCl- and NaF-bearing aqueous fluids from 1–6.5 GPa and 300–800 °C

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

Tanis, Elizabeth A.; Simon, Adam; Tschauner, Oliver

Rutile (TiO₂) is an important host phase for high field strength elements (HFSE) such as Nb in metamorphic and subduction zone environments. The observed depletion of Nb in arc rocks is often explained by the hypothesis that rutile sequesters HFSE in the subducted slab and overlying sediment, and is chemically inert with respect to aqueous fluids evolved during prograde metamorphism in the forearc to subarc environment. However, field observations of exhumed terranes, and experimental studies, indicate that HFSE may be soluble in complex aqueous fluids at high pressure (i.e., >0.5 GPa) and moderate to high temperature (i.e., >300 °C). Inmore » this study, we investigated experimentally the mobility of Nb in NaCl- and NaF-bearing aqueous fluids in equilibrium with Nb-bearing rutile at pressure-temperature conditions applicable to fluid evolution in arc environments. Niobium concentrations in aqueous fluid at rutile saturation were measured directly by using a hydrothermal diamond-anvil cell (HDAC) and synchrotron X-ray fluorescence (SXRF) at 2.1 to 6.5 GPa and 300–500 °C, and indirectly by performing mass loss experiments in a piston-cylinder (PC) apparatus at ~1 GPa and 700–800 °C. The concentration of Nb in a 10 wt% NaCl aqueous fluid increases from 6 to 11 μg/g as temperature increases from 300 to 500 °C, over a pressure range from 2.1 to 2.8 GPa, consistent with a positive temperature dependence. The concentration of Nb in a 20 wt% NaCl aqueous fluid varies from 55 to 150 μg/g at 300 to 500 °C, over a pressure range from 1.8 to 6.4 GPa; however, there is no discernible temperature or pressure dependence. The Nb concentration in a 4 wt% NaF-bearing aqueous fluid increases from 180 to 910 μg/g as temperature increases from 300 to 500 °C over the pressure range 2.1 to 6.5 GPa. The data for the F-bearing fluid indicate that the Nb content of the fluid exhibits a dependence on temperature between 300 and 500 °C at ≥2 GPa, but there is no observed dependence on pressure. Together, the data demonstrate that the hydrothermal mobility of Nb is strongly controlled by the composition of the fluid, consistent with published data for Ti. At all experimental conditions, however, the concentration of Nb in the fluid is always lower than coexisting rutile, consistent with a role for rutile in moderating the Nb budget of arc rocks.« less

The mobility of Nb in rutile-saturated NaCl- and NaF-bearing aqueous fluids from 1–6.5 GPa and 300–800 °C

DOE PAGES

Tanis, Elizabeth A.; Simon, Adam; Tschauner, Oliver; ...

2015-07-01

Rutile (TiO 2) is an important host phase for high field strength elements (HFSE) such as Nb in metamorphic and subduction zone environments. The observed depletion of Nb in arc rocks is often explained by the hypothesis that rutile sequesters HFSE in the subducted slab and overlying sediment, and is chemically inert with respect to aqueous fluids evolved during prograde metamorphism in the forearc to subarc environment. However, field observations of exhumed terranes, and experimental studies, indicate that HFSE may be soluble in complex aqueous fluids at high pressure (i.e., >0.5 GPa) and moderate to high temperature (i.e., >300 °C).more » In this study, we investigated experimentally the mobility of Nb in NaCl- and NaF-bearing aqueous fluids in equilibrium with Nb-bearing rutile at pressure-temperature conditions applicable to fluid evolution in arc environments. Niobium concentrations in aqueous fluid at rutile saturation were measured directly by using a hydrothermal diamond-anvil cell (HDAC) and synchrotron X-ray fluorescence (SXRF) at 2.1 to 6.5 GPa and 300-500 °C, and indirectly by performing mass loss experiments in a piston-cylinder (PC) apparatus at similar to 1 GPa and 700-800 °C. The concentration of Nb in a 10 wt% NaCl aqueous fluid increases from 6 to 11 mu g/g as temperature increases from 300 to 500 °C, over a pressure range from 2.1 to 2.8 GPa, consistent with a positive temperature dependence. The concentration of Nb in a 20 wt% NaCl aqueous fluid varies from 55 to 150 mu g/g at 300 to 500 °C, over a pressure range from 1.8 to 6.4 GPa; however, there is no discernible temperature or pressure dependence. Here, the Nb concentration in a 4 wt% NaF-bearing aqueous fluid increases from 180 to 910 mu g/g as temperature increases from 300 to 500 °C over the pressure range 2.1 to 6.5 GPa. The data for the F-bearing fluid indicate that the Nb content of the fluid exhibits a dependence on temperature between 300 and 500 °C at ≥ 2 GPa, but there is no observed dependence on pressure. Together, the data demonstrate that the hydrothermal mobility of Nb is strongly controlled by the composition of the fluid, consistent with published data for Ti. At all experimental conditions, however, the concentration of Nb in the fluid is always lower than coexisting rutile, consistent with a role for rutile in moderating the Nb budget of arc rocks.« less

Ultra-High Q Acoustic Resonance in Superfluid ^4He

NASA Astrophysics Data System (ADS)

De Lorenzo, L. A.; Schwab, K. C.

2017-02-01

We report the measurement of the acoustic quality factor of a gram-scale, kilohertz-frequency superfluid resonator, detected through the parametric coupling to a superconducting niobium microwave cavity. For temperatures between 400 mK and 50 mK, we observe a T^{-4} temperature dependence of the quality factor, consistent with a 3-phonon dissipation mechanism. We observe Q factors up to 1.4× 10^8, consistent with the dissipation due to dilute ^3He impurities, and expect that significant further improvements are possible. These experiments are relevant to exploring quantum behavior and decoherence of massive macroscopic objects, the laboratory detection of continuous gravitational waves from pulsars, and the probing of possible limits to physical length scales.

The significance of temperature dependence on the piezoelectric energy harvesting by using a phononic crystal

NASA Astrophysics Data System (ADS)

Aly, Arafa H.; Nagaty, Ahmed; Khalifa, Zaki; Mehaney, Ahmed

2018-05-01

In this study, an acoustic energy harvester based on a two-dimensional phononic crystal has been constructed. The present structure consists of silicon cylinders in the air background with a polyvinylidene fluoride cylinder as a defect to confine the acoustic energy. The presented energy harvester depends on the piezoelectric effect (using the piezoelectric material polyvinylidene fluoride) that converts the confined acoustic energy to electric energy. The maximum output voltage obtained equals 170 mV. Moreover, the results revealed that the output voltage can be increased with increasing temperature. In addition, the effects of the load resistance and the geometry of the piezoelectric material on the output voltage have been studied theoretically. Based on these results, all previous studies about energy harvesting in phononic structures must take temperature effects into account.

In-depth analysis and modelling of self-heating effects in nanometric DGMOSFETs

NASA Astrophysics Data System (ADS)

Roldán, J. B.; González, B.; Iñiguez, B.; Roldán, A. M.; Lázaro, A.; Cerdeira, A.

2013-01-01

Self-heating effects (SHEs) in nanometric symmetrical double-gate MOSFETs (DGMOSFETs) have been analysed. An equivalent thermal circuit for the transistors has been developed to characterise thermal effects, where the temperature and thickness dependency of the thermal conductivity of the silicon and oxide layers within the devices has been included. The equivalent thermal circuit is consistent with simulations using a commercial technology computer-aided design (TCAD) tool (Sentaurus by Synopsys). In addition, a model for DGMOSFETs has been developed where SHEs have been considered in detail, taking into account the temperature dependence of the low-field mobility, saturation velocity, and inversion charge. The model correctly reproduces Sentaurus simulation data for the typical bias range used in integrated circuits. Lattice temperatures predicted by simulation are coherently reproduced by the model for varying silicon layer geometry.

Temperature-programmed technique accompanied with high-throughput methodology for rapidly searching the optimal operating temperature of MOX gas sensors.

PubMed

Zhang, Guozhu; Xie, Changsheng; Zhang, Shunping; Zhao, Jianwei; Lei, Tao; Zeng, Dawen

2014-09-08

A combinatorial high-throughput temperature-programmed method to obtain the optimal operating temperature (OOT) of gas sensor materials is demonstrated here for the first time. A material library consisting of SnO2, ZnO, WO3, and In2O3 sensor films was fabricated by screen printing. Temperature-dependent conductivity curves were obtained by scanning this gas sensor library from 300 to 700 K in different atmospheres (dry air, formaldehyde, carbon monoxide, nitrogen dioxide, toluene and ammonia), giving the OOT of each sensor formulation as a function of the carrier and analyte gases. A comparative study of the temperature-programmed method and a conventional method showed good agreement in measured OOT.

Tunneling effects in the kinetics of helium and hydrogen isotopes desorption from single-walled carbon nanotube bundles

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

Danilchenko, B. A., E-mail: danil@iop.kiev.ua; Yaskovets, I. I.; Uvarova, I. Y.

2014-04-28

The kinetics of desorption both helium isotopes and molecules of hydrogen and deuterium from open-ended or γ-irradiated single-walled carbon nanotube bundles was investigated in temperature range of 10–300 K. The gases desorption rates obey the Arrhenius law at high temperatures, deviate from it with temperature reduction and become constant at low temperatures. These results indicate the quantum nature of gas outflow from carbon nanotube bundles. We had deduced the crossover temperature below which the quantum corrections to the effective activation energy of desorption become significant. This temperature follows linear dependence against the inverse mass of gas molecule and is consistent withmore » theoretical prediction.« less

Hydrodynamics in a Degenerate, Strongly Attractive Fermi Gas

NASA Technical Reports Server (NTRS)

Thomas, John E.; Kinast, Joseph; Hemmer, Staci; Turlapov, Andrey; O'Hara, Ken; Gehm, Mike; Granade, Stephen

2004-01-01

In summary, we use all-optical methods with evaporative cooling near a Feshbach resonance to produce a strongly interacting degenerate Fermi gas. We observe hydrodynamic behavior in the expansion dynamics. At low temperatures, collisions may not explain the expansion dynamics. We observe hydrodynamics in the trapped gas. Our observations include collisionally-damped excitation spectra at high temperature which were not discussed above. In addition, we observe weakly damped breathing modes at low temperature. The observed temperature dependence of the damping time and hydrodynamic frequency are not consistent with collisional dynamics nor with collisionless mean field interactions. These observations constitute the first evidence for superfluid hydrodynamics in a Fermi gas.

Pressure Dependence of Coherence-Incoherence Crossover Behavior in KFe 2As 2 Observed by Resistivity and 75As-NMR/NQR.

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

Wiecki, P.; Taufour, V.; Chung, D. Y.

We present the results of 75As nuclear magnetic resonance (NMR), nuclear quadrupole resonance (NQR), and resistivity measurements in KFe 2As 2 under pressure (p). The temperature dependence of the NMR shift, nuclear spin-lattice relaxation time (T1), and resistivity show a crossover between a high-temperature incoherent, local-moment behavior and a low-temperature coherent behavior at a crossover temperature (T *). T * is found to increase monotonically with pressure, consistent with increasing hybridization between localized 3d orbitalderived bands with the itinerant electron bands. No anomaly in T * is seen at the critical pressure pc = 1.8 GPa where a change ofmore » slope of the superconducting (SC) transition temperature Tc(p) has been observed. In contrast, Tc(p) seems to correlate with antiferromagnetic spin fluctuations in the normal state as measured by the NQR 1/T1 data, although such a correlation cannot be seen in the replacement effects of A in the KFe 2As 2 (A = K, Rb, Cs) family. In the superconducting state, two T1 components are observed at low temperatures, suggesting the existence of two distinct local electronic environments. The temperature dependence of the short T1s indicates a nearly gapless state below Tc. On the other hand, the temperature dependence of the long component 1/T1L implies a large reduction in the density of states at the Fermi level due to the SC gap formation. These results suggest a real-space modulation of the local SC gap structure in KFe 2As 2 under pressure.« less

Pressure dependence of coherence-incoherence crossover behavior in KFe 2 As 2 observed by resistivity and As 75 -NMR/NQR

DOE PAGES

Wiecki, P.; Taufour, V.; Chung, D. Y.; ...

2018-02-13

We present the results of 75As nuclear magnetic resonance (NMR), nuclear quadrupole resonance (NQR), and resistivity measurements in KF e2 As 2 under pressure (p). The temperature dependence of the NMR shift, nuclear spin-lattice relaxation time (T 1), and resistivity show a crossover between a high-temperature incoherent, local-moment behavior and a low-temperature coherent behavior at a crossover temperature (T*). T* is found to increase monotonically with pressure, consistent with increasing hybridization between localized 3d orbital-derived bands with the itinerant electron bands. No anomaly in T* is seen at the critical pressure p c= 1.8 GPa where a change of slopemore » of the superconducting (SC) transition temperature T c( p ) has been observed. In contrast, T c( p ) seems to correlate with antiferromagnetic spin fluctuations in the normal state as measured by the NQR 1/T 1 data, although such a correlation cannot be seen in the replacement effects of A in the AFe 2As 2 (A=K,Rb,Cs) family. In the superconducting state, two T 1 components are observed at low temperatures, suggesting the existence of two distinct local electronic environments. The temperature dependence of the short T 1s indicates a nearly gapless state below T c. On the other hand, the temperature dependence of the long component 1/T 1Limplies a large reduction in the density of states at the Fermi level due to the SC gap formation. These results suggest a real-space modulation of the local SC gap structure in KFe 2As 2 under pressure.« less

Pressure dependence of coherence-incoherence crossover behavior in KFe 2 As 2 observed by resistivity and As 75 -NMR/NQR

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

Wiecki, P.; Taufour, V.; Chung, D. Y.

We present the results of 75As nuclear magnetic resonance (NMR), nuclear quadrupole resonance (NQR), and resistivity measurements in KF e2 As 2 under pressure (p). The temperature dependence of the NMR shift, nuclear spin-lattice relaxation time (T 1), and resistivity show a crossover between a high-temperature incoherent, local-moment behavior and a low-temperature coherent behavior at a crossover temperature (T*). T* is found to increase monotonically with pressure, consistent with increasing hybridization between localized 3d orbital-derived bands with the itinerant electron bands. No anomaly in T* is seen at the critical pressure p c= 1.8 GPa where a change of slopemore » of the superconducting (SC) transition temperature T c( p ) has been observed. In contrast, T c( p ) seems to correlate with antiferromagnetic spin fluctuations in the normal state as measured by the NQR 1/T 1 data, although such a correlation cannot be seen in the replacement effects of A in the AFe 2As 2 (A=K,Rb,Cs) family. In the superconducting state, two T 1 components are observed at low temperatures, suggesting the existence of two distinct local electronic environments. The temperature dependence of the short T 1s indicates a nearly gapless state below T c. On the other hand, the temperature dependence of the long component 1/T 1Limplies a large reduction in the density of states at the Fermi level due to the SC gap formation. These results suggest a real-space modulation of the local SC gap structure in KFe 2As 2 under pressure.« less

Local Nanomechanical Motion of the Cell Wall of Saccharomyces cerevisiae

NASA Astrophysics Data System (ADS)

Pelling, Andrew E.; Sehati, Sadaf; Gralla, Edith B.; Valentine, Joan S.; Gimzewski, James K.

2004-08-01

We demonstrate that the cell wall of living Saccharomyces cerevisiae (baker's yeast) exhibits local temperature-dependent nanomechanical motion at characteristic frequencies. The periodic motions in the range of 0.8 to 1.6 kHz with amplitudes of ~3 nm were measured using the cantilever of an atomic force microscope (AFM). Exposure of the cells to a metabolic inhibitor causes the periodic motion to cease. From the strong frequency dependence on temperature, we derive an activation energy of 58 kJ/mol, which is consistent with the cell's metabolism involving molecular motors such as kinesin, dynein, and myosin. The magnitude of the forces observed (~10 nN) suggests concerted nanomechanical activity is operative in the cell.

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

Usman, Muhammad; Mumtaz, Arif, E-mail: arif@qau.edu.pk; Raoof, Sobia

We report the relaxor behavior of the zirconium doped barium titanate BaZr{sub x}Ti{sub 1−x}O{sub 3} solid solutions and discuss the temperature, frequency, and concentration dependence in terms of correlations among the polar nanoregions. The relaxor behavior is analyzed within the mean field theory by estimating the Edward-Anderson order parameter q{sub EA}. Additionally, we find that q{sub EA} calculated for the different concentrations obeys a scaling behavior q{sub EA}=1−(T/T{sub m}){sup n}, where T{sub m} are the respective dielectric maxima temperatures and n = 2.0 ± 0.1. The frequency dependence of the q{sub EA} also shows results consistent with the above mentioned picture.

Penetration depth of MgB2 measured using Josephson junctions and SQUIDs

NASA Astrophysics Data System (ADS)

Cunnane, Daniel; Zhuang, Chenggang; Chen, Ke; Xi, X. X.; Yong, Jie; Lemberger, T. R.

2013-02-01

The penetration depth of MgB2 was measured using two methods of different mechanisms. The first method used MgB2 Josephson junctions and the magnetic field dependence of the junction critical current. The second method deduced the penetration depth from the inductance of a MgB2 microstrip used to modulate the voltage of a MgB2 DC SQUID. The two methods showed a consistent value of the low-temperature penetration depth for MgB2 to be about 40 nm. Both the small penetration depth value and its temperature dependence are in agreement with a microscopic theory for MgB2 in the clean limit.

Low-dimensional ordering and fluctuations in methanol-{beta}-hydroquinone clathrate studied by x-ray and neutron diffraction

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

Rheinstaedter, Maikel C.; Enderle, Mechthild; Kloepperpieper, Axel

2005-01-01

Methanol-{beta}-hydroquinone clathrate has been established as a model system for dielectric ordering and fluctuations and is conceptually close to magnetic spin systems. In x-ray and neutron diffraction experiments, we investigated the ordered structure, the one-dimensional (1D) and the three-dimensional critical scattering in the paraelectric phase, and the temperature dependence of the lattice constants. Our results can be explained by microscopic models of the methanol pseudospin in the hydroquinone cage network, in consistency with previous dielectric investigations. A coupling of the 1D fluctuations to local strains leads to an anomalous temperature dependence of the 1D lattice parameter in the paraelectric regime.

Transport and thermoelectric properties of the LaAlO3/SrTiO3 interface

NASA Astrophysics Data System (ADS)

Jost, A.; Guduru, V. K.; Wiedmann, S.; Maan, J. C.; Zeitler, U.; Wenderich, S.; Brinkman, A.; Hilgenkamp, H.

2015-01-01

The transport and thermoelectric properties of the interface between SrTiO3 and a 26-monolayer-thick LaAlO3 layer grown at high oxygen pressure have been investigated at temperatures from 4.2 to 100 K and in magnetic fields up to 18 T. For T >4.2 K , two different electronlike charge carriers originating from two electron channels which contribute to transport are observed. We probe the contributions of a degenerate and a nondegenerate band to the thermoelectric power and develop a consistent model to describe the temperature dependence of the thermoelectric tensor. Anomalies in the data point to an additional magnetic field dependent scattering.

Strengths of serpentinite gouges at elevated temperatures

USGS Publications Warehouse

Moore, Diane E.; Lockner, D.A.; Ma, S.; Summers, R.; Byerlee, J.D.

1997-01-01

Serpentinite has been proposed as a cause of both low strength and aseismic creep of fault zones. To test these hypotheses, we have measured the strength of chrysotile-, lizardite-, and antigorite-rich serpentinite gouges under hydrothermal conditions, with emphasis on chrysotile, which has thus far received little attention. At 25??C, the coefficient of friction, ??, of chrysotile gouge is roughly 0.2, whereas the lizardite- and antigorite-rich gouges are at least twice as strong. The very low room temperature strength of chrysotile is a consequence of its unusually high adsorbed water content. When the adsorbed water is removed, chrysotile is as strong as pure antigorite gouge at room temperature. Heating to ???200??C causes the frictional strengths of all three gouges to increase. Limited data suggest that different polytypes of a given serpentine mineral have similar strengths; thus deformation-induced changes in polytype should not affect fault strength. At 25??C, the chrysotile gouge has a transition from velocity strengthening at low velocities to velocity weakening at high velocities, consistent with previous studies. At temperatures up to ???200??C, however, chrysotile strength is essentially independent of velocity at low velocities. Overall, chrysotile has a restricted range of velocity-strengthening behavior that migrates to higher velocities with increasing temperature. Less information on velocity dependence is available for the lizardite and antigorite gouges, but their behavior is consistent with that outlined for chrysotile. The marked changes in velocity dependence and strength of chrysotile with heating underscore the hazards of using room temperature data to predict fault behavior at depth. The velocity behavior at elevated temperatures does not rule out serpentinite as a cause of aseismic slip, but in the presence of a hydrostatic fluid pressure gradient, all varieties of serpentine are too strong to explain the apparent weakness of faults such as the San Andreas.

Determining temperature limits of drilling fluids

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

Thuren, J.B.; Chenevert, M.E.; Huang, W.T.W.

A capillary three tube viscometer has been designed which allows the measurement of rheological properties of time dependent non-Newtonian fluids in laminar flow at high temperture and pressure. The objective of this investigation is to determine the temperature stability of clay-water suspensions containing various drilling fluid additives. The additives studied consisted of viscosifiers, filtrate reducers, and chemical thinners. The temperature range studied is from room temperature to 550{sup 0}F. The system pressure is consistently maintained above the vapor pressure. The Bentonite and water standardized base mud used is equivalent to a 25 ppB fluid. Stabilization of the base mud ismore » necessary to obtain steady state laminar flow conditions and to obtain reliable temperature thinning effects with each temperature interval under investigation. Generally the temperature levels are maintained for one hour until 550{sup 0}F is attained. The last interval is then maintained until system fluid degradation occurs. Rheological measurements are obtained from differential pressure transducers located in a three diameter tube test section and externally at ambient conditions from a Baroid Rotational Viscometer. The power law model for non-Newtonian fluids is used to correlate the data.« less

Direct measurements of temperature-dependent laser absorptivity of metal powders

DOE PAGES

Rubenchik, A.; Wu, S.; Mitchell, S.; ...

2015-08-12

Here, a compact system is developed to measure laser absorptivity for a variety of powder materials (metals, ceramics, etc.) with different powder size distributions and thicknesses. The measured results for several metal powders are presented. The results are consistent with those from ray tracing calculations.

Nonlinear saturation of tearing mode islands.

PubMed

Hastie, R J; Militello, F; Porcelli, F

2005-08-05

New, rigorous results for the tearing island saturation problem are presented. These results are valid for the realistic case where the magnetic island structure is non-symmetric about the reconnection surface and the electron temperature, on which the electrical resistivity depends, is evolved self-consistently with the island growth.

Direct measurements of temperature-dependent laser absorptivity of metal powders

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

Rubenchik, A.; Wu, S.; Mitchell, S.

Here, a compact system is developed to measure laser absorptivity for a variety of powder materials (metals, ceramics, etc.) with different powder size distributions and thicknesses. The measured results for several metal powders are presented. The results are consistent with those from ray tracing calculations.

Female turtles from hot nests: is it duration of incubation or proportion of development at high temperatures that matters?

PubMed

Georges, Arthur

1989-11-01

Mean daily temperature in natural nests of freshwater turtles with temperature-dependent sex determination is known to be a poor predictor of hatchling sex ratios when nest temperatures fluctuate. To account for this, a model was developed on the assumption that females will emerge from eggs when more than half of embryonic development occurs above the threshold temperature for sex determination rather than from eggs that spend more than half their time above the threshold. The model is consistent with previously published data and in particular explains the phenomenon whereby the mean temperature that best distinguishes between male and female nests decreases with increasing variability in nest temperature. The model, if verified by controlled experiments, has important implications for our understanding of temperature-dependent sex determination in natural nests. Both mean nest temperature and "hours spent above the threshold" will be poor predictors of hatchling sex ratios. Studies designed to investigate latitudinal trends and inter-specific differences in the threshold temperature will need to consider latitudinal and inter-specific variation in the magnitude of diel fluctuations in nest temperature, and variation in factors influencing the magnitude of those fluctuations, such as nest depth. Furthermore, any factor that modifies the relationship between developmental rate and temperature can be expected to influence hatchling sex ratios in natural nests, especially when nest temperatures are close to the threshold.

Development of NTD Ge Sensors for Superconducting Bolometer

NASA Astrophysics Data System (ADS)

Garai, A.; Mathimalar, S.; Singh, V.; Dokania, N.; Nanal, V.; Pillay, R. G.; Ramakrishnan, S.; Shrivastava, A.; Jagadeesan, K. C.; Thakare, S. V.

2016-08-01

Neutron transmutation-doped (NTD) Ge sensors have been prepared by irradiating device-grade Ge with thermal neutrons at Dhruva reactor, BARC, Mumbai. These sensors are intended to be used for the study of neutrinoless double beta decay in ^{124}Sn with a superconducting Tin bolometer. Resistance measurements are performed on NTD Ge sensors in the temperature range 100-350 mK. The observed temperature dependence is found to be consistent with the variable-range hopping mechanism.

Critical scaling of a jammed system after a quench of temperature.

PubMed

Otsuki, Michio; Hayakawa, Hisao

2012-09-01

Critical behavior of soft repulsive particles after quench of temperature near the jamming transition is numerically investigated. It is found that the plateau of the mean-square displacement of tracer particles and the pressure satisfy critical scaling laws. The critical density for the jamming transition depends on the protocol to prepare the system, while the values of the critical exponents which are consistent with the prediction of a phenomenology are independent of the protocol.

Potential of energy harvesting in barium titanate based laminates from room temperature to cryogenic/high temperatures: measurements and linking phase field and finite element simulations

NASA Astrophysics Data System (ADS)

Narita, Fumio; Fox, Marina; Mori, Kotaro; Takeuchi, Hiroki; Kobayashi, Takuya; Omote, Kenji

2017-11-01

This paper studies the energy harvesting characteristics of piezoelectric laminates consisting of barium titanate (BaTiO3) and copper (Cu) from room temperature to cryogenic/high temperatures both experimentally and numerically. First, the output voltages of the piezoelectric BaTiO3/Cu laminates were measured from room temperature to a cryogenic temperature (77 K). The output power was evaluated for various values of load resistance. The results showed that the maximum output power density is approximately 2240 nW cm-3. The output voltages of the BaTiO3/Cu laminates were also measured from room temperature to a higher temperature (333 K). To discuss the output voltages of the BaTiO3/Cu laminates due to temperature changes, phase field and finite element simulations were combined. A phase field model for grain growth was used to generate grain structures. The phase field model was then employed for BaTiO3 polycrystals, coupled with the time-dependent Ginzburg-Landau theory and the oxygen vacancies diffusion, to calculate the temperature-dependent piezoelectric coefficient and permittivity. Using these properties, the output voltages of the BaTiO3/Cu laminates from room temperature to both 77 K and 333 K were analyzed by three dimensional finite element methods, and the results are presented for several grain sizes and oxygen vacancy densities. It was found that electricity in the BaTiO3 ceramic layer is generated not only through the piezoelectric effect caused by a thermally induced bending stress but also by the temperature dependence of the BaTiO3 piezoelectric coefficient and permittivity.

Biomechanics of ant adhesive pads: frictional forces are rate- and temperature-dependent.

PubMed

Federle, Walter; Baumgartner, Werner; Hölldobler, Bert

2004-01-01

Tarsal adhesive pads enable insects to hold on to smooth plant surfaces. Using a centrifuge technique, we tested whether a "wet adhesion" model of a thin film of liquid secreted between the pad and the surface can explain adhesive and frictional forces in Asian Weaver ants (Oecophylla smaragdina). When forces are acting parallel to the surface, pads in contact with the surface can slide smoothly. Force per unit pad contact area was strongly dependent on sliding velocity and temperature. Seemingly consistent with the effect of a thin liquid film in the contact zone, (1) frictional force linearly increased with sliding velocity, (2) the increment was greater at lower temperatures and (3) no temperature dependence was detected for low-rate perpendicular detachment forces. However, we observed a strong, temperature-independent static friction that was inconsistent with a fully lubricated contact. Static friction was too large to be explained by the contribution of other (sclerotized) body parts. Moreover, the rate-specific increase of shear stress strongly exceeded predictions derived from estimates of the adhesive liquid film's thickness and viscosity. Both lines of evidence indicate that the adhesive secretion alone is insufficient to explain the observed forces and that direct interaction of the soft pad cuticle with the surface ("rubber friction") is involved.

Frequency-dependent dynamic magnetic properties of the Ising bilayer system consisting of spin-3/2 and spin-5/2 spins

NASA Astrophysics Data System (ADS)

Keskin, Mustafa; Ertaş, Mehmet

2018-04-01

Dynamic magnetic properties of the Ising bilayer system consisting of the mixed (3/2, 5/2) Ising spins with a crystal-field interaction in an oscillating field on a two-layer square lattice is studied by the use of dynamic mean-field theory based on the Glauber-type stochastic. Dynamic phase transition temperatures are obtained and dynamic phase diagrams are presented in three different planes. The frequency dependence of dynamic hysteresis loops is also investigated in detail. We compare the results with some available theoretical and experimental works and observe a quantitatively good agreement with some theoretical and experimental results.

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.

Sealing Materials for Use in Vacuum at High Temperatures

NASA Technical Reports Server (NTRS)

Pettit, Donald R.; Camarda, Charles J.; Lee Vaughn, Wallace

2012-01-01

Sealing materials that can be applied and left in place in vacuum over a wide range of temperatures (especially temperatures of a few thousand degrees Celsius) have been conceived and investigated for potential utility in repairing thermal-protection tiles on the space shuttles in orbit before returning to Earth. These materials are also adaptable to numerous terrestrial applications that involve vacuum processing and/or repair of structures that must withstand high temperatures. These materials can be formulated to have mechanical handling characteristics ranging from almost freely flowing liquid-like consistency through paste-like consistency to stiff puttylike consistency, and to retain these characteristics in vacuum until heated to high curing temperatures. A sealing material of this type can be formulated to be used in any of several different ways for example, to be impregnated into a high-temperature-fabric patch, impregnated into a high-temperature-fabric gasket for sealing a patch, applied under a patch, or applied alone in the manner of putty or wallboard compound. The sealing material must be formulated to be compatible with, and adhere to, the structural material(s) to be repaired. In general, the material consists of a vacuum-compatible liquid containing one or more dissolved compound(s) and/or mixed with suspended solid particles. Depending on the intended application, the liquid can be chosen to be of a compound that can remain in place in vacuum for a time long enough to be useful, and/or to evaporate or decompose in a controlled way to leave a useful solid residue behind. The evaporation rate is determined by proper choice of vapor pressure, application of heat, and/or application of ultraviolet light or other optical radiation. The liquid chosen for the original space shuttle application is a commercial silicone vacuum-pump oil.

Temperature Dependence and Energetics of Single Ions at the Aqueous Liquid-Vapor Interface

PubMed Central

Ou, Shuching; Patel, Sandeep

2014-01-01

We investigate temperature-dependence of free energetics with two single halide anions, I− and Cl−, crossing the aqueous liquid-vapor interface through molecular dynamics simulations. The result shows that I− has a modest surface stability of 0.5 kcal/mol at 300 K and the stability decreases as the temperature increases, indicating the surface adsorption process for the anion is entropically disfavored. In contrast, Cl− shows no such surface state at all temperatures. Decomposition of free energetics reveals that water-water interactions provide a favorable enthalpic contribution, while the desolvation of ion induces an increase in free energy. Calculations of surface fluctuations demonstrate that I− generates significantly greater interfacial fluctuations compared to Cl−. The fluctuation is attributed to the malleability of the solvation shells, which allows for more long-ranged perturbations and solvent density redistribution induced by I− as the anion approaches the liquid-vapor interface. The increase in temperature of the solvent enhances the inherent thermally-excited fluctuations and consequently reduces the relative contribution from anion to surface fluctuations, which is consistent with the decrease in surface-stability of I−. Our results indicate a strong correlation with induced interfacial fluctuations and anion surface stability; moreover, resulting temperature dependent behavior of induced fluctuations suggests the possibility of a critical level of induced fluctuations associated with surface stability. PMID:23537166

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

Kim, Kyung Hwan; Pathak, Harshad; Spah, Alexander

Nuclear quantum effects (NQEs) have a significant influence on the hydrogen bonds in water and aqueous solutions and have thus been the topic of extensive studies. However, the microscopic origin and the corresponding temperature dependence of NQEs have been elusive and still remain the subject of ongoing discussion. Previous x-ray scattering investigations indicate that NQEs on the structure of water exhibit significant temperature dependence. Here, by performing wide-angle x-ray scattering of H 2O and D 2O droplets at temperatures from 275 K down to 240 K, we determine the temperature dependence of NQEs on the structure of water down tomore » the deeply supercooled regime. The data reveal that the magnitude of NQEs on the structure of water is temperature independent, as the structure factor of D 2O is similar to H 2O if the temperature is shifted by a constant 5 K, valid from ambient conditions to the deeply supercooled regime. Analysis of the accelerated growth of tetrahedral structures in supercooled H 2O and D 2O also shows similar behavior with a clear 5 K shift. The results indicate a constant compensation between NQEs delocalizing the proton in the librational motion away from the bond and in the OH stretch vibrational modes along the bond. In conclusion, this is consistent with the fact that only the vibrational ground state is populated at ambient and supercooled conditions.« less

Microstructural indicators of transition mechanisms in time-dependent fatigue crack growth in nickel base superalloys

NASA Astrophysics Data System (ADS)

Heeter, Ann E.

Gas turbine engines are an important part of power generation in modern society, especially in the field of aerospace. Aerospace engines are design to last approximately 30 years and the engine components must be designed to survive for the life of the engine or to be replaced at regular intervals to ensure consumer safety. Fatigue crack growth analysis is a vital component of design for an aerospace component. Crack growth modeling and design methods date back to an origin around 1950 with a high rate of accuracy. The new generation of aerospace engines is designed to be efficient as possible and require higher operating temperatures than ever seen before in previous generations. These higher temperatures place more stringent requirements on the material crack growth performance under creep and time dependent conditions. Typically the types of components which are subject to these requirements are rotating disk components which are made from advanced materials such as nickel base superalloys. Traditionally crack growth models have looked at high temperature crack growth purely as a function of temperature and assumed that all crack growth was either controlled by a cycle dependent or time dependent mechanism. This new analysis is trying to evaluate the transition between cycle-dependent and time-dependent mechanism and the microstructural markers that characterize this transitional behavior. The physical indications include both the fracture surface morphology as well as the shape of the crack front. The research will evaluate whether crack tunneling occurs and whether it consistently predicts a transition from cycle-dependent crack growth to time-dependent crack growth. The study is part of a larger research program trying to include the effects of geometry, mission profile and environmental effects, in addition to temperature effects, as a part of the overall crack growth system. The outcome will provide evidence for various transition types and correlate those physical attributes back to the material mechanisms to improve predictive modeling capability.

Doping-dependent charge order correlations in electron-doped cuprates

PubMed Central

da Silva Neto, Eduardo H.; Yu, Biqiong; Minola, Matteo; Sutarto, Ronny; Schierle, Enrico; Boschini, Fabio; Zonno, Marta; Bluschke, Martin; Higgins, Joshua; Li, Yangmu; Yu, Guichuan; Weschke, Eugen; He, Feizhou; Le Tacon, Mathieu; Greene, Richard L.; Greven, Martin; Sawatzky, George A.; Keimer, Bernhard; Damascelli, Andrea

2016-01-01

Understanding the interplay between charge order (CO) and other phenomena (for example, pseudogap, antiferromagnetism, and superconductivity) is one of the central questions in the cuprate high-temperature superconductors. The discovery that similar forms of CO exist in both hole- and electron-doped cuprates opened a path to determine what subset of the CO phenomenology is universal to all the cuprates. We use resonant x-ray scattering to measure the CO correlations in electron-doped cuprates (La2−xCexCuO4 and Nd2−xCexCuO4) and their relationship to antiferromagnetism, pseudogap, and superconductivity. Detailed measurements of Nd2−xCexCuO4 show that CO is present in the x = 0.059 to 0.166 range and that its doping-dependent wave vector is consistent with the separation between straight segments of the Fermi surface. The CO onset temperature is highest between x = 0.106 and 0.166 but decreases at lower doping levels, indicating that it is not tied to the appearance of antiferromagnetic correlations or the pseudogap. Near optimal doping, where the CO wave vector is also consistent with a previously observed phonon anomaly, measurements of the CO below and above the superconducting transition temperature, or in a magnetic field, show that the CO is insensitive to superconductivity. Overall, these findings indicate that, although verified in the electron-doped cuprates, material-dependent details determine whether the CO correlations acquire sufficient strength to compete for the ground state of the cuprates. PMID:27536726

Doping-dependent charge order correlations in electron-doped cuprates.

PubMed

da Silva Neto, Eduardo H; Yu, Biqiong; Minola, Matteo; Sutarto, Ronny; Schierle, Enrico; Boschini, Fabio; Zonno, Marta; Bluschke, Martin; Higgins, Joshua; Li, Yangmu; Yu, Guichuan; Weschke, Eugen; He, Feizhou; Le Tacon, Mathieu; Greene, Richard L; Greven, Martin; Sawatzky, George A; Keimer, Bernhard; Damascelli, Andrea

2016-08-01

Understanding the interplay between charge order (CO) and other phenomena (for example, pseudogap, antiferromagnetism, and superconductivity) is one of the central questions in the cuprate high-temperature superconductors. The discovery that similar forms of CO exist in both hole- and electron-doped cuprates opened a path to determine what subset of the CO phenomenology is universal to all the cuprates. We use resonant x-ray scattering to measure the CO correlations in electron-doped cuprates (La2-x Ce x CuO4 and Nd2-x Ce x CuO4) and their relationship to antiferromagnetism, pseudogap, and superconductivity. Detailed measurements of Nd2-x Ce x CuO4 show that CO is present in the x = 0.059 to 0.166 range and that its doping-dependent wave vector is consistent with the separation between straight segments of the Fermi surface. The CO onset temperature is highest between x = 0.106 and 0.166 but decreases at lower doping levels, indicating that it is not tied to the appearance of antiferromagnetic correlations or the pseudogap. Near optimal doping, where the CO wave vector is also consistent with a previously observed phonon anomaly, measurements of the CO below and above the superconducting transition temperature, or in a magnetic field, show that the CO is insensitive to superconductivity. Overall, these findings indicate that, although verified in the electron-doped cuprates, material-dependent details determine whether the CO correlations acquire sufficient strength to compete for the ground state of the cuprates.

Characterisation of retention properties of charge-trapping memory cells at low temperatures

NASA Astrophysics Data System (ADS)

Yurchuk, E.; Bollmann, J.; Mikolajick, T.

2009-09-01

The density of states of deep level centers in silicon oxynitride layer of SONOS memory cells are calculated from temperature dependent retention measurement. The dominating charge loss mechanisms are direct trap-to-band tunneling (TB) and thermally stimulated emission (TE). Retention measurements at low temperatures (80 - 300K) will be dominated by TE from more "shallow" traps with energies below 1eV and by TB. Taking into account both independent and rival processes the density of states could be calculated self consisting. The results are in excellent agreement with elsewhere published data.

Enhanced thermoelectric transport in modulation-doped GaN/AlGaN core/shell nanowires.

PubMed

Song, Erdong; Li, Qiming; Swartzentruber, Brian; Pan, Wei; Wang, George T; Martinez, Julio A

2016-01-08

The thermoelectric properties of unintentionally n-doped core GaN/AlGaN core/shell N-face nanowires are reported. We found that the temperature dependence of the electrical conductivity is consistent with thermally activated carriers with two distinctive donor energies. The Seebeck coefficient of GaN/AlGaN nanowires is more than twice as large as that for the GaN nanowires alone. However, an outer layer of GaN deposited onto the GaN/AlGaN core/shell nanowires decreases the Seebeck coefficient at room temperature, while the temperature dependence of the electrical conductivity remains the same. We attribute these observations to the formation of an electron gas channel within the heavily-doped GaN core of the GaN/AlGaN nanowires. The room-temperature thermoelectric power factor for the GaN/AlGaN nanowires can be four times higher than the GaN nanowires. Selective doping in bandgap engineered core/shell nanowires is proposed for enhancing the thermoelectric power.

Small-angle neutron scattering study of magnetic ordering and inhomogeneity across the martensitic phase transformation in Ni 50–xCo xMn₄₀Sn₁₀ alloys

DOE PAGES

Bhatti, Kanwal Preet; El-Khatib, S.; Srivastava, Vijay; ...

2012-04-27

The Heusler-derived multiferroic alloy Ni 50–xCo xMn₄₀Sn₁₀ has recently been shown to exhibit, at just above room temperature, a highly reversible martensitic phase transformation with an unusually large magnetization change. In this work the nature of the magnetic ordering above and below this transformation has been studied in detail in the critical composition range x = 6–8 via temperature-dependent (5–600 K) magnetometry and small-angle neutron scattering (SANS). We observe fairly typical paramagnetic to long-range-ordered ferromagnetic phase transitions on cooling to 420–430 K, with the expected critical spin fluctuations, followed by first-order martensitic phase transformations to a nonferromagnetic state below 360–390more » K. The static magnetization reveals complex magnetism in this low-temperature nonferromagnetic phase, including a Langevin-like field dependence, distinct spin freezing near 60 K, and significant exchange bias effects, consistent with superparamagnetic blocking of ferromagnetic clusters of nanoscopic dimensions. We demonstrate that these spin clusters, whose existence has been hypothesized in a variety of martensitic alloys exhibiting competition between ferromagnetic and antiferromagnetic exchange interactions, can be directly observed by SANS. The scattering data are consistent with a liquidlike spatial distribution of interacting magnetic clusters with a mean center-to-center spacing of 12 nm. Considering the behavior of the superparmagnetism, cooling-field and temperature-dependent exchange bias, and magnetic SANS, we discuss in detail the physical form and origin of these spin clusters, their intercluster interactions, the nature of the ground-state magnetic ordering in the martensitic phase, and the implications for our understanding of such alloy systems.« less

Temperature-dependent responses of the photosynthetic and chlorophyll fluorescence attributes of apple (Malus domestica) leaves during a sustained high temperature event.

PubMed

Greer, Dennis H

2015-12-01

The objective of this study was to follow changes in the temperature-dependent responses of photosynthesis and photosystem II performance in leaves of field-grown trees of Malus domestica (Borkh.) cv. 'Red Gala' before and after exposure to a long-term heat event occurring late in the growing season. Light-saturated photosynthesis was optimal at 25 °C before the heat event. The high temperatures caused a reduction in rates at low temperatures (15-20 °C) but increased rates at high temperatures (30-40 °C) and a shift in optimum to 30 °C. Rates at all temperatures increased after the heat event and the optimum shifted to 33 °C, indicative of some acclimation to the high temperatures occurring. Photosystem II attributes were all highly temperature-dependent. The operating quantum efficiency of PSII during the heat event declined, but mostly at high temperatures, partly because of decreased photochemical quenching but also from increased non-photochemical quenching. However, a further reduction in PSII operating efficiency occurred after the heat event subsided. Non-photochemical quenching had subsided, whereas photochemical quenching had increased in the post-heat event period and consistent with a greater fraction of open PSII reaction centres. What remained uncertain was why these effects on PSII performance appeared to have no effect on the process of light-saturated photosynthesis. However, the results provide an enhanced understanding of the impacts of sustained high temperatures on the photosynthetic process and its underlying reactions, notably photochemistry. Copyright © 2015 Elsevier Masson SAS. All rights reserved.

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

Mun, Eundeok; Bud'ko, Sergey L.; Canfield, Paul C.

We present the magnetic field dependencies of transport properties for RPtBi ( R = Gd, Dy, Tm, and Lu) half-Heusler compounds. Temperature- and field-dependent resistivity measurements of high-quality RPtBi single crystals reveal an unusually large, nonsaturating magnetoresistance (MR) up to 300 K under a moderate magnetic field of H = 140 kOe. At 300 K, the large MR effect decreases as the rare earth is traversed from Gd to Lu and the magnetic field dependence of MR shows a deviation from the conventional H2 behavior. The Hall coefficient ( RH) for R = Gd indicates a sign change around 120more » K, whereas RH curves for R = Dy, Tm, and Lu remain positive for all measured temperatures. At 300 K, the Hall resistivity reveals a deviation from the linear field dependence for all compounds. Thermoelectric power measurements on this family show strong temperature and magnetic field dependencies which are consistent with resistivity measurements. A highly enhanced thermoelectric power under applied magnetic field is observed as high as ~100 μV/K at 140 kOe. Furthermore, analysis of the transport data in this series reveals that the rare-earth-based half-Heusler compounds provide opportunities to tune MR effect through lanthanide contraction and to elucidate the mechanism of nontrivial MR.« less

Temperature and depth dependence of positron annihilation parameters in YBa2Cu3O7-x and La1.85Sr0.15CuO4

NASA Astrophysics Data System (ADS)

Lynn, K. G.; Usmar, S. G.; Nielsen, B.; van der Kolk, G. J.; Kanazawa, I.; Sferlazzo, P.; Moodenbaugh, A. R.

1988-02-01

The temperature dependence of the positron annihilation parameters for YBa2Cu3O7-x x=0.7, 0.4 and 0.0 and La1.85Sr0.15CuO4 were measured. The depth dependence of the YBa2Cu3O7 was studied using a variable-energy positron beam showing a strong depth dependence in the Doppler line-shape extending up to an average depth of ˜5.0 μm. It was found that a transition in the Doppler line-shape parameter, ``S'', was associated with the superconducting transition temperature (Tc) in YBa2Cu3O7-x x=0.4 and 0.0 while no transition was observed in the nonsuperconducting YBa2Cu3O6.3. Positron lifetime parameters in YBa2Cu3O7 were found to be consistent with positrons localized at open volume regions (probably unoccupied crystallographic sites) in this material with a lifetime of 210 psec at 300 K. These results indicate that the electron density at these unoccupied sites increases, using a free electron model, approximately 9% between 100 and 12 K.

Precise new shock temperatures in forsterite and in silicate liquids: phase transitions and heat capacity at high pressure

NASA Astrophysics Data System (ADS)

Asimow, P. D.; Fat'yanov, O. V.; Su, C.; Ma, X. J.

2017-12-01

Shock temperature measurements in transparent samples provide key constraints on the phase transitions and thermodynamic properties of materials at high pressure and temperature. Such measurements are necessary, for example, to allow equation of state measurements taken along the Hugoniot to be translated to P-V-T space. We have recently completed a detailed study of the accuracy and reproducibility of calibration of our 6-channel fast pyrometer. We have also introduced improved analysis procedures of the time-dependent multi-wavelength radiance signal that avoid the need for a greybody assumption and therefore have better precision than earlier results. This has motivated (a) renewed study of the shock temperature of forsterite in the superheating, partial melting, and complete melting regimes, (b) pre-heated diopside-anorthite glass shock temperature experiments for comparison to pre-heated silicate liquid equation of state results, and (c) new soda-lime glass shock temperature experiments. Single-crystal synthetic forsterite samples were shocked along (100) to pressures between 120 and 210 GPa on the Caltech two-stage light gas gun. Uncertainties on most results are 50 K. Results above the onset of partial melting at 130 GPa are consistent with Lyzenga and Ahrens (1980) data and show a low P-T slope consistent with a partial melting interval. Complete melting may occur, given sufficient time, at about 210 GPa. The experiment at 120-130 GPa is anomalous, showing two-wave structure and time- and wavelength-dependent scattering suggesting a subsolidus phase transition behind the shock front. The amount of super-heating, if any, is far smaller than claimed by Holland and Ahrens (1997). Steady radiation profiles, high emissivity, and consistency from channel to channel provide high precision (±40 K) in diopside-anorthite liquid shocked from just above the glass transition to high pressure. Temperatures are colder than expected for a model with constant heat capacity, providing direct evidence that multicomponent silicate liquids show a major increase in heat capacity in the P-T range appropriate to terrestrial magma oceans (<150 GPa, <5000 K).

Novel models on fluid's variable thermo-physical properties for extensive study on convection heat and mass transfer

NASA Astrophysics Data System (ADS)

Shang, De-Yi; Zhong, Liang-Cai

2017-01-01

Our novel models for fluid's variable physical properties are improved and reported systematically in this work for enhancement of theoretical and practical value on study of convection heat and mass transfer. It consists of three models, namely (1) temperature parameter model, (2) polynomial model, and (3) weighted-sum model, respectively for treatment of temperature-dependent physical properties of gases, temperature-dependent physical properties of liquids, and concentration- and temperature-dependent physical properties of vapour-gas mixture. Two related components are proposed, and involved in each model for fluid's variable physical properties. They are basic physic property equations and theoretical similarity equations on physical property factors. The former, as the foundation of the latter, is based on the typical experimental data and physical analysis. The latter is built up by similarity analysis and mathematical derivation based on the former basic physical properties equations. These models are available for smooth simulation and treatment of fluid's variable physical properties for assurance of theoretical and practical value of study on convection of heat and mass transfer. Especially, so far, there has been lack of available study on heat and mass transfer of film condensation convection of vapour-gas mixture, and the wrong heat transfer results existed in widespread studies on the related research topics, due to ignorance of proper consideration of the concentration- and temperature-dependent physical properties of vapour-gas mixture. For resolving such difficult issues, the present novel physical property models have their special advantages.

Glass transition temperature of polymer nano-composites with polymer and filler interactions

NASA Astrophysics Data System (ADS)

Hagita, Katsumi; Takano, Hiroshi; Doi, Masao; Morita, Hiroshi

2012-02-01

We systematically studied versatile coarse-grained model (bead spring model) to describe filled polymer nano-composites for coarse-grained (Kremer-Grest model) molecular dynamics simulations. This model consists of long polymers, crosslink, and fillers. We used the hollow structure as the filler to describe rigid spherical fillers with small computing costs. Our filler model consists of surface particles of icosahedra fullerene structure C320 and a repulsive force from the center of the filler is applied to the surface particles in order to make a sphere and rigid. The filler's diameter is 12 times of beads of the polymers. As the first test of our model, we study temperature dependence of volumes of periodic boundary conditions under constant pressures through NPT constant Andersen algorithm. It is found that Glass transition temperature (Tg) decrease with increasing filler's volume fraction for the case of repulsive interaction between polymer and fillers and Tg weakly increase for attractive interaction.

Magnetic phase transition in Heisenberg antiferromagnetic films with easy-axis single-ion anisotropy

NASA Astrophysics Data System (ADS)

Pan, Kok-Kwei

2012-03-01

The staggered susceptibility of spin-1 and spin-3/2 Heisenberg antiferromagnet with easy-axis single-ion anisotropy on the cubic lattice films consisting of n=2, 3, 4, 5 and 6 interacting square lattice layers is studied by high-temperature series expansions. Sixth order series in J/kBT have been obtained for free-surface boundary conditions. The dependence of the Néel temperature on film thickness n and easy-axis anisotropy D has been investigated. The shifts of the Néel temperature from the bulk value can be described by a power law n with a shift exponent λ, where λ is the inverse of the bulk correlation length exponent. The effect of easy-axis single-ion anisotropy on shift exponent of antiferromagnetic films has been studied. A comparison is made with related works. The results obtained are qualitatively consistent with the predictions of finite-size scaling theory.

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

Atypically small temperature-dependence of the direct band gap in the metastable semiconductor copper nitride Cu 3 N

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

Birkett, Max; Savory, Christopher N.; Fioretti, Angela N.

The temperature-dependence of the direct band gap and thermal expansion in the metastable anti-ReO 3 semiconductor Cu 3N are investigated between 4.2 and 300 K by Fourier-transform infrared spectroscopy and x-ray diffraction. Complementary refractive index spectra are determined by spectroscopic ellipsometry at 300K. A direct gap of 1.68eV is associated with the absorption onset at 300K, which strengthens continuously and reaches a magnitude of 3.5 x 10 5cm -1 at 2.7eV, suggesting potential for photovoltaic applications. Notably, the direct gap redshifts by just 24meV between 4.2 and 300K, giving an atypically small band-gap temperature coefficient dE g/dT of -0.082meV/K. Additionally,more » the band structure, dielectric function, phonon dispersion, linear expansion, and heat capacity are calculated using density functional theory; remarkable similarities between the experimental and calculated refractive index spectra support the accuracy of these calculations, which indicate beneficially low hole effective masses and potential negative thermal expansion below 50K. To assess the lattice expansion contribution to the band-gap temperature-dependence, a quasiharmonic model fit to the observed lattice contraction finds a monotonically decreasing linear expansion (descending past 10 -6K -1 below 80K), while estimating the Debye temperature, lattice heat capacity, and Gruneisen parameter. Accounting for lattice and electron-phonon contributions to the observed band-gap evolution suggests average phonon energies that are qualitatively consistent with predicted maxima in the phonon density of states. Furthermore, as band-edge temperature-dependence has significant consequences for device performance, copper nitride should be well suited for applications that require a largely temperature-invariant band gap.« less

Atypically small temperature-dependence of the direct band gap in the metastable semiconductor copper nitride Cu 3 N

DOE PAGES

Birkett, Max; Savory, Christopher N.; Fioretti, Angela N.; ...

2017-03-06

The temperature-dependence of the direct band gap and thermal expansion in the metastable anti-ReO 3 semiconductor Cu 3N are investigated between 4.2 and 300 K by Fourier-transform infrared spectroscopy and x-ray diffraction. Complementary refractive index spectra are determined by spectroscopic ellipsometry at 300K. A direct gap of 1.68eV is associated with the absorption onset at 300K, which strengthens continuously and reaches a magnitude of 3.5 x 10 5cm -1 at 2.7eV, suggesting potential for photovoltaic applications. Notably, the direct gap redshifts by just 24meV between 4.2 and 300K, giving an atypically small band-gap temperature coefficient dE g/dT of -0.082meV/K. Additionally,more » the band structure, dielectric function, phonon dispersion, linear expansion, and heat capacity are calculated using density functional theory; remarkable similarities between the experimental and calculated refractive index spectra support the accuracy of these calculations, which indicate beneficially low hole effective masses and potential negative thermal expansion below 50K. To assess the lattice expansion contribution to the band-gap temperature-dependence, a quasiharmonic model fit to the observed lattice contraction finds a monotonically decreasing linear expansion (descending past 10 -6K -1 below 80K), while estimating the Debye temperature, lattice heat capacity, and Gruneisen parameter. Accounting for lattice and electron-phonon contributions to the observed band-gap evolution suggests average phonon energies that are qualitatively consistent with predicted maxima in the phonon density of states. Furthermore, as band-edge temperature-dependence has significant consequences for device performance, copper nitride should be well suited for applications that require a largely temperature-invariant band gap.« less

Thermal diffusivity of electrical insulators at high temperatures: Evidence for diffusion of bulk phonon-polaritons at infrared frequencies augmenting phonon heat conduction

NASA Astrophysics Data System (ADS)

Hofmeister, Anne M.; Dong, Jianjun; Branlund, Joy M.

2014-04-01

We show that laser-flash analysis measurements of the temperature (T) dependence of thermal diffusivity (D) for diverse non-metallic (e.g., silicates) single-crystals is consistently represented by D(T) = FT-G + HT above 298 K, with G ranging from 0.3 to 2, depending on structure, and H being ˜10-4 K-1 for 51 single-crystals, 3 polycrystals, and two glasses unaffected by disorder or reconstructive phase transitions. Materials exhibiting this behavior include complex silicates with variable amounts of cation disorder, perovskite structured materials, and graphite. The high-temperature term HT becomes important by ˜1300 K, above which temperature its contribution to D(T) exceeds that of the FT-G term. The combination of the FT-G and HT terms produces the nearly temperature independent high-temperature region of D previously interpreted as the minimal phonon mean free path being limited by the finite interatomic spacing. Based on the simplicity of the fit and large number of materials it represents, this finding has repercussions for high-temperature models of heat transport. One explanation is that the two terms describing D(T) are associated with two distinct microscopic mechanisms; here, we explore the possibility that the thermal diffusivity of an electrical insulator could include both a contribution of lattice phonons (the FT-G term) and a contribution of diffusive bulk phonon-polaritons (BPP) at infrared (IR) frequencies (the HT term). The proposed BPP diffusion exists over length scales smaller than the laboratory sample sizes, and transfers mixed light and vibrational energy at a speed significantly smaller than the speed of light. Our diffusive IR-BPP hypothesis is consistent with other experimental observations such as polarization behavior, dependence of D on the number of IR peaks, and H = 0 for Ge and Si, which lack IR fundamentals. A simple quasi-particle thermal diffusion model is presented to begin understanding the contribution from bulk phonon-polaritons to overall heat conduction.

Temperature-Independent Nuclear Quantum Effects on the Structure of Water

DOE PAGES

Kim, Kyung Hwan; Pathak, Harshad; Spah, Alexander; ...

2017-08-14

Nuclear quantum effects (NQEs) have a significant influence on the hydrogen bonds in water and aqueous solutions and have thus been the topic of extensive studies. However, the microscopic origin and the corresponding temperature dependence of NQEs have been elusive and still remain the subject of ongoing discussion. Previous x-ray scattering investigations indicate that NQEs on the structure of water exhibit significant temperature dependence. Here, by performing wide-angle x-ray scattering of H 2O and D 2O droplets at temperatures from 275 K down to 240 K, we determine the temperature dependence of NQEs on the structure of water down tomore » the deeply supercooled regime. The data reveal that the magnitude of NQEs on the structure of water is temperature independent, as the structure factor of D 2O is similar to H 2O if the temperature is shifted by a constant 5 K, valid from ambient conditions to the deeply supercooled regime. Analysis of the accelerated growth of tetrahedral structures in supercooled H 2O and D 2O also shows similar behavior with a clear 5 K shift. The results indicate a constant compensation between NQEs delocalizing the proton in the librational motion away from the bond and in the OH stretch vibrational modes along the bond. In conclusion, this is consistent with the fact that only the vibrational ground state is populated at ambient and supercooled conditions.« less

Experiments on the contact angle of n-propanol on differently prepared silver substrates at various temperatures and implications for the properties of silver nanoparticles

NASA Astrophysics Data System (ADS)

Pinterich, T.; Winkler, P. M.; Vrtala, A. E.; Wagner, P. E.

2011-08-01

In this paper we present the results of contact angle measurements between n-propanol and silver substrates in the temperature range from -10 °C to 30 °C. The interest in a potential temperature dependence of contact angles originates from recent experiments by S. Schobesberger et al. (Schobesberger S., Strange temperature dependence observed for heterogeneous nucleation of n-propanol vapor on NaCl particles. Master's thesis, University of Vienna, 2008; Schobesberger S. et al., Experiments on the temperature dependence of heterogeneous nucleation on NaCl and Ag particles. In preparation.) investigating the temperature dependence for heterogeneous nucleation of n-propanol vapour on NaCl and on silver particles. We determined dynamic advancing θ a and receding θ r angles on variously prepared silver probes. The Dynamic Wilhelmy method (Wilhelmy L., Über die Abhängigkeit der Capillaritäts-Constanten des Alkohols von Substanz und Gestalt des benetzten festen Körpers. Ann. Phys. Chem., 199:177-217, 1863) was applied using a Krüss K12 Tensiometer, with a refrigerated double-walled glass top. With respect to its potential influence on heterogeneous nucleation mainly the advancing angle is of interest. The uniform probe geometry required was achieved by accurate cutting and by multiple polishing stages up to the accomplishment of a 0.04 μm grain size. The original probes consist of 925 sterling silver including a 7.5% copper content. Additional coating with silver pro Analysi (p.A.) was applied making use of pure silver powder evaporation process via Physical Vapour Deposition (PVD). Results show that a surface contamination by copper cannot be neglected for the specification of contact angles. It turned out that additional PVD coatings not only change the values of θa but also their temperature dependence. With increasing the number of coatings of a plate the contact angle decreases and its temperature dependence inverts. Since the contact angle hysteresis θhyst. obtained for the variously often coated probes remained practically constant possible changes in surface roughness with increasing number of PVD layers could be excluded.

Sintering behavior of U 80 at.%Zr powder compacts in a vacuum environment

NASA Astrophysics Data System (ADS)

Kim, Tae-Kyu; Lee, Chong-Tak; Sohn, Dong-Seong

2008-01-01

Sintering behavior of U-80 at.%Zr powder compacts in a temperature range from 1100 to 1500 °C in a vacuum of 1 × 10 -4 Pa was evaluated. The sintered density depended more on the sintering temperature than on the sintering time. The sintered specimens consisted of the δ-UZr 2 matrix with acicular α-Zr precipitates, but it still had un-reacted zirconium when the sintering temperature was 1100 °C. The uranium depletion near the surface of the specimens sintered at temperatures above 1300 °C was detected. Massive Zr(O) grains in the sintered specimen were found, and their formation was restrained when the cooling rate from the sintering temperature was increased.

Hydrophobicity within the three-dimensional Mercedes-Benz model: potential of mean force.

PubMed

Dias, Cristiano L; Hynninen, Teemu; Ala-Nissila, Tapio; Foster, Adam S; Karttunen, Mikko

2011-02-14

We use the three-dimensional Mercedes-Benz model for water and Monte Carlo simulations to study the structure and thermodynamics of the hydrophobic interaction. Radial distribution functions are used to classify different cases of the interaction, namely, contact configurations, solvent separated configurations, and desolvation configurations. The temperature dependence of these cases is shown to be in qualitative agreement with atomistic models of water. In particular, while the energy for the formation of contact configurations is favored by entropy, its strengthening with increasing temperature is accounted for by enthalpy. This is consistent with our simulated heat capacity. An important feature of the model is that it can be used to account for well-converged thermodynamics quantities, e.g., the heat capacity of transfer. Microscopic mechanisms for the temperature dependence of the hydrophobic interaction are discussed at the molecular level based on the conceptual simplicity of the model.

Hydrophobicity within the three-dimensional Mercedes-Benz model: Potential of mean force

NASA Astrophysics Data System (ADS)

Dias, Cristiano L.; Hynninen, Teemu; Ala-Nissila, Tapio; Foster, Adam S.; Karttunen, Mikko

2011-02-01

We use the three-dimensional Mercedes-Benz model for water and Monte Carlo simulations to study the structure and thermodynamics of the hydrophobic interaction. Radial distribution functions are used to classify different cases of the interaction, namely, contact configurations, solvent separated configurations, and desolvation configurations. The temperature dependence of these cases is shown to be in qualitative agreement with atomistic models of water. In particular, while the energy for the formation of contact configurations is favored by entropy, its strengthening with increasing temperature is accounted for by enthalpy. This is consistent with our simulated heat capacity. An important feature of the model is that it can be used to account for well-converged thermodynamics quantities, e.g., the heat capacity of transfer. Microscopic mechanisms for the temperature dependence of the hydrophobic interaction are discussed at the molecular level based on the conceptual simplicity of the model.

A Computer Program for the Computation of Running Gear Temperatures Using Green's Function

NASA Technical Reports Server (NTRS)

Koshigoe, S.; Murdock, J. W.; Akin, L. S.; Townsend, D. P.

1996-01-01

A new technique has been developed to study two dimensional heat transfer problems in gears. This technique consists of transforming the heat equation into a line integral equation with the use of Green's theorem. The equation is then expressed in terms of eigenfunctions that satisfy the Helmholtz equation, and their corresponding eigenvalues for an arbitrarily shaped region of interest. The eigenfunction are obtalned by solving an intergral equation. Once the eigenfunctions are found, the temperature is expanded in terms of the eigenfunctions with unknown time dependent coefficients that can be solved by using Runge Kutta methods. The time integration is extremely efficient. Therefore, any changes in the time dependent coefficients or source terms in the boundary conditions do not impose a great computational burden on the user. The method is demonstrated by applying it to a sample gear tooth. Temperature histories at representative surface locatons are given.

Polaron physics and crossover transition in magnetite probed by pressure-dependent infrared spectroscopy.

PubMed

Ebad-Allah, J; Baldassarre, L; Sing, M; Claessen, R; Brabers, V A M; Kuntscher, C A

2013-01-23

The optical properties of magnetite at room temperature were studied by infrared reflectivity measurements as a function of pressure up to 8 GPa. The optical conductivity spectrum consists of a Drude term, two sharp phonon modes, a far-infrared band at around 600 cm(-1) and a pronounced mid-infrared absorption band. With increasing pressure both absorption bands shift to lower frequencies and the phonon modes harden in a linear fashion. Based on the shape of the MIR band, the temperature dependence of the dc transport data, and the occurrence of the far-infrared band in the optical conductivity spectrum, the polaronic coupling strength in magnetite at room temperature should be classified as intermediate. For the lower energy phonon mode an abrupt increase of the linear pressure coefficient occurs at around 6 GPa, which could be attributed to minor alterations of the charge distribution among the different Fe sites.

Pressure and temperature dependence of the Ce valence and c -f hybridization gap in Ce T2In5(T =Co ,Rh ,Ir ) heavy-fermion superconductors

NASA Astrophysics Data System (ADS)

Yamaoka, H.; Yamamoto, Y.; Schwier, E. F.; Honda, F.; Zekko, Y.; Ohta, Y.; Lin, J.-F.; Nakatake, M.; Iwasawa, H.; Arita, M.; Shimada, K.; Hiraoka, N.; Ishii, H.; Tsuei, K.-D.; Mizuki, J.

2015-12-01

Pressure- and temperature-induced changes in the Ce valence and c -f hybridization of the Ce115 superconductors have been studied systematically. Resonant x-ray-emission spectroscopy indicated that the increase of the Ce valence with pressure was significant for CeCoIn5, and moderate for CeIr (In0.925Cd0.075)5 . We found no abrupt change of the Ce valence in the Kondo regime for CeIr (In0.925Cd0.075)5 , which suggests that valence fluctuations are unlikely to mediate the superconductivity in this material. X-ray-diffraction results were consistent with the pressure-induced change in the Ce valence. High-resolution photoelectron spectroscopy revealed a temperature-dependent reduction of the spectral intensity at the Fermi level, indicating enhanced c -f hybridization on cooling.

Temperature- and composition-dependent hydrogen diffusivity in palladium from statistically-averaged molecular dynamics

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

Zhou, Xiaowang; Heo, Tae Wook; Wood, Brandon C.

Solid-state hydrogen storage materials undergo complex phase transformations whose kinetics is often limited by hydrogen diffusion. Among metal hydrides, palladium hydride undergoes a diffusional phase transformation upon hydrogen uptake, during which the hydrogen diffusivity varies with hydrogen composition and temperature. Here we perform robust statistically-averaged molecular dynamics simulations to obtain a well-converged analytical expression for hydrogen diffusivity in bulk palladium that is valid throughout all stages of the reaction. Our studies confirm significant dependence of the diffusivity on composition and temperature that elucidate key trends in the available experimental measurements. Whereas at low hydrogen compositions, a single process dominates, atmore » high hydrogen compositions, diffusion is found to exhibit behavior consistent with multiple hopping barriers. Further analysis, supported by nudged elastic band computations, suggests that the multi-barrier diffusion can be interpreted as two distinct mechanisms corresponding to hydrogen-rich and hydrogen-poor local environments.« less

Temperature- and composition-dependent hydrogen diffusivity in palladium from statistically-averaged molecular dynamics

DOE PAGES

Zhou, Xiaowang; Heo, Tae Wook; Wood, Brandon C.; ...

2018-03-09

Solid-state hydrogen storage materials undergo complex phase transformations whose kinetics is often limited by hydrogen diffusion. Among metal hydrides, palladium hydride undergoes a diffusional phase transformation upon hydrogen uptake, during which the hydrogen diffusivity varies with hydrogen composition and temperature. Here we perform robust statistically-averaged molecular dynamics simulations to obtain a well-converged analytical expression for hydrogen diffusivity in bulk palladium that is valid throughout all stages of the reaction. Our studies confirm significant dependence of the diffusivity on composition and temperature that elucidate key trends in the available experimental measurements. Whereas at low hydrogen compositions, a single process dominates, atmore » high hydrogen compositions, diffusion is found to exhibit behavior consistent with multiple hopping barriers. Further analysis, supported by nudged elastic band computations, suggests that the multi-barrier diffusion can be interpreted as two distinct mechanisms corresponding to hydrogen-rich and hydrogen-poor local environments.« less

Nanostructured ZnO films for potential use in LPG gas sensors

NASA Astrophysics Data System (ADS)

Latyshev, V. M.; Berestok, T. O.; Opanasyuk, A. S.; Kornyushchenko, A. S.; Perekrestov, V. I.

2017-05-01

The aim of the work was to obtain ZnO nanostructures with heightened surface area and to study relationship between formation method and gas sensor properties towards propane-butane mixture (LPG). In order to synthesize ZnO nanostructures chemical and physical formation methods have been utilized. The first one was chemical bath deposition technology and the second one magnetron sputtering of Zn followed by oxidation. Optimal method and technological parameters corresponding to formation of material with the highest sensor response have been determined experimentally. Dynamical gas sensor response at different temperature values and dependencies of the sensor sensitivity on the temperature at different LPG concentrations in air have been investigated. It has been found, that sensor response depends on the sample morphology and has the highest value for the structure consisting of thin nanowires. The factors that lead to the decrease in the gas sensor operating temperature have been determined.

CCl 4 chemistry on the magnetite selvedge of single-crystal hematite: competitive surface reactions

NASA Astrophysics Data System (ADS)

Adib, K.; Camillone, N., III; Fitts, J. P.; Rim, K. T.; Flynn, G. W.; Joyce, S. A.; Osgood, R. M., Jr.

2002-01-01

Temperature programmed reaction/desorption (TPR/D) studies were undertaken to characterize the surface chemistry which occurs between CCl 4 and the Fe 3O 4 (1 1 1) selvedge of single crystal α-Fe 2O 3 (0 0 0 1). Six separate desorption events are clearly observed and four desorbing species are identified: CCl 4, OCCl 2, C 2Cl 4 and FeCl 2. It is proposed that OCCl 2, CCl 4 and C 2Cl 4 are produced in reactions involving the same precursor, CCl 2. Three reaction paths compete for the CCl 2 precursor: oxygen atom abstraction (for OCCl 2), molecular recombinative desorption (for CCl 4) and associative desorption (for C 2Cl 4). During the TPR/D temperature ramp, the branching ratio is observed to depend upon temperature and the availability of reactive sites. The data are consistent with a rich site-dependent chemistry.

Simultaneous in situ electron temperature comparisons using Alouette 2 probe and plasma resonance data

NASA Technical Reports Server (NTRS)

Benson, R. F.

1973-01-01

The electron temperatures deduced from Alouette 2 diffuse resonance observations are compared with the temperature obtained from the Alouette 2 cylindrical electrostatic probe experiment using data from 5 mid-to-high latitude telemetry stations. The probe temperature is consistently higher than the diffuse resonance temperature. The average difference ranged from approximately 10% to 40% with the lower values occurring at the lowest altitudes sampled (near 500 km) and at high latitudes (dip latitude greater than 55 deg), and the larger values occurring at high altitudes and lower latitudes. The discrepancy appears to be of geophysical origin since it is dependent on the location of the data sample. The present observations support the view that the often observed radar backscatter - probe electron temperature discrepancy is also of geophysical origin.

Temperature-dependent MR signals in cortical bone: potential for monitoring temperature changes during high-intensity focused ultrasound treatment in bone.

PubMed

Ramsay, Elizabeth; Mougenot, Charles; Kazem, Mohammad; Laetsch, Theodore W; Chopra, Rajiv

2015-10-01

Because existing magnetic resonance thermometry techniques do not provide temperature information within bone, high-intensity focused ultrasound (HIFU) exposures in bone are monitored using temperature changes in adjacent soft tissues. In this study, the potential to monitor temperature changes in cortical bone using a short TE gradient echo sequence is evaluated. The feasibility of this proposed method was initially evaluated by measuring the temperature dependence of the gradient echo signal during cooling of cortical bone samples implanted with fiber-optic temperature sensors. A subsequent experiment involved heating a cortical bone sample using a clinical MR-HIFU system. A consistent relationship between temperature change and the change in magnitude signal was observed within and between cortical bone samples. For the two-dimensional gradient echo sequence implemented in this study, a least-squares linear fit determined the percentage change in signal to be (0.90 ± 0.01)%/°C. This relationship was used to estimate temperature changes observed in the HIFU experiment and these temperatures agreed well with those measured from an implanted fiber-optic sensor. This method appears capable of displaying changes related to temperature in cortical bone and could improve the safety of MR-HIFU treatments. Further investigations into the sensitivity of the technique in vivo are warranted. © 2014 Wiley Periodicals, Inc.

Genetic variation of temperature-regulated curd induction in cauliflower: elucidation of floral transition by genome-wide association mapping and gene expression analysis

PubMed Central

Matschegewski, Claudia; Zetzsche, Holger; Hasan, Yaser; Leibeguth, Lena; Briggs, William; Ordon, Frank; Uptmoor, Ralf

2015-01-01

Cauliflower (Brassica oleracea var. botrytis) is a vernalization-responsive crop. High ambient temperatures delay harvest time. The elucidation of the genetic regulation of floral transition is highly interesting for a precise harvest scheduling and to ensure stable market supply. This study aims at genetic dissection of temperature-dependent curd induction in cauliflower by genome-wide association studies and gene expression analysis. To assess temperature-dependent curd induction, two greenhouse trials under distinct temperature regimes were conducted on a diversity panel consisting of 111 cauliflower commercial parent lines, genotyped with 14,385 SNPs. Broad phenotypic variation and high heritability (0.93) were observed for temperature-related curd induction within the cauliflower population. GWA mapping identified a total of 18 QTL localized on chromosomes O1, O2, O3, O4, O6, O8, and O9 for curding time under two distinct temperature regimes. Among those, several QTL are localized within regions of promising candidate flowering genes. Inferring population structure and genetic relatedness among the diversity set assigned three main genetic clusters. Linkage disequilibrium (LD) patterns estimated global LD extent of r2 = 0.06 and a maximum physical distance of 400 kb for genetic linkage. Transcriptional profiling of flowering genes FLOWERING LOCUS C (BoFLC) and VERNALIZATION 2 (BoVRN2) was performed, showing increased expression levels of BoVRN2 in genotypes with faster curding. However, functional relevance of BoVRN2 and BoFLC2 could not consistently be supported, which probably suggests to act facultative and/or might evidence for BoVRN2/BoFLC-independent mechanisms in temperature-regulated floral transition in cauliflower. Genetic insights in temperature-regulated curd induction can underpin genetically informed phenology models and benefit molecular breeding strategies toward the development of thermo-tolerant cultivars. PMID:26442034

London penetration depth measurements in Ba (Fe 1-xT x) 2As 2(T=Co,Ni,Ru,Rh,Pd,Pt,Co+Cu) superconductors

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

Gordon, Ryan T.

2011-01-01

The London penetration depth has been measured in various doping levels of single crystals of Ba(Fe 1-xT x) 2As 2 (T=Co,Ni,Ru,Rh,Pd,Pt,Co+Cu) superconductors by utilizing a tunnel diode resonator (TDR) apparatus. All in-plane penetration depth measurements exhibit a power law temperature dependence of the form Δλ ab(T) = CT n, indicating the existence of low-temperature, normal state quasiparticles all the way down to the lowest measured temperature, which was typically 500 mK. Several different doping concentrations from the Ba(Fe 1-xT x) 2As 2 (T=Co,Ni) systems have been measured and the doping dependence of the power law exponent, n, is compared tomore » results from measurements of thermal conductivity and specific heat. In addition, a novel method has been developed to allow for the measurement of the zero temperature value of the in-plane penetration depth, λ ab(0), by using TDR frequency shifts. By using this technique, the doping dependence of λ ab(0) has been measured in the Ba(Fe 1-xCo x) 2As 2 series, which has allowed also for the construction of the doping-dependent superfluid phase stiffness, ρ s(T) = [λ(0)/λ(T)] 2. By studying the effects of disorder on these superconductors using heavy ion irradiation, it has been determined that the observed power law temperature dependence likely arises from pair-breaking impurity scattering contributions, which is consistent with the proposed s±-wave symmetry of the superconducting gap in the dirty scattering limit. This hypothesis is supported by the measurement of an exponential temperature dependence of the penetration depth in the intrinsically clean LiFeAs, indicative of a nodeless superconducting gap.« less

Permittivity of ice and water at millimeter wavelengths

NASA Technical Reports Server (NTRS)

Blue, M. D.

1980-01-01

Measurements of reflectivity of water and ice at 100 GHz, 140 GHz, and 180 GHz are reported. Measurements on water covered the temperature range 0 C to 50 C. No anomalies in the dielectric properties of water due to the presence of either salts or organic matter were found. The reflectivity of water and its temperature dependence are consistent with recent dielectric property models derived from data at other wavelengths. The index of refraction of fresh ice is constant at 1.78 throughout this regions.

Nernst effect from fluctuating pairs in the pseudogap phase of the cuprates.

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

Levchenko, A.; Norman, M. R.; Varlamov, A. A.

2011-01-31

The observation of a large Nernst signal in cuprates above the superconducting transition temperature has attracted much attention. A potential explanation is that it originates from superconducting fluctuations. Although the Nernst signal is indeed consistent with Gaussian fluctuations for overdoped cuprates, Gaussian theory fails to describe the temperature dependence seen for underdoped cuprates. Here, we consider the vertex correction to Gaussian theory resulting from the pseudogap. This yields a Nernst signal in good agreement with the data.

Fourier transform infrared and Raman spectroscopic characterization of homogeneous solution concentration gradients near a container wall at different temperatures

NASA Technical Reports Server (NTRS)

Loo, B. H.; Burns, D. H.; Lee, Y. G. L.; Emerson, M. T.

1991-01-01

Fourier transform infrared (FTIR) and Raman spectroscopic techniques were used to study the solution concentration gradient in succino nitrile-rich and water-rich homogeneous solutions. The spectroscopic data shows significant concentration dependency. Although FTIR-attenuated total reflectance could not yield surface spectra since the evanescent infrared wave penetrated deep into the bulk solution, it showed that water-rich clusters were decreased at higher temperatures. This result is consistent with the calorimetric results reported earlier.

-Sb Glasses at Low Temperatures

NASA Astrophysics Data System (ADS)

Souri, Dariush; Azizpour, Parvin; Zaliani, Hamideh

2014-09-01

Semiconducting glasses of the type 40TeO2-(60 - x) V2O5- xSb were prepared by rapid melt quenching and their dc electrical conductivity was measured in the temperature range 180-296 K. For these glassy samples, the dc electrical conductivity ranged from 2.26 × 10-7 S cm-1 to 1.11 × 10-5 S cm-1 at 296 K, indicating the conductivity is enhanced by increasing the V2O5 content. These experimental results could be explained on the basis of different mechanisms (based on polaron-hopping theory) in the different temperature regions. At temperatures above Θ D/2 (where Θ D is the Debye temperature), the non-adiabatic small polaron hopping (NASPH) model is consistent with the data, whereas at temperatures below Θ D/2, a T -1/4 dependence of the conductivity indicative of the variable range hopping (VRH) mechanism is dominant. For all these glasses crossover from SPH to VRH conduction was observed at a characteristic temperature T R ≤ Θ D/2. In this study, the hopping carrier density and carrier mobility were determined at different temperatures. N ( E F), the density of states at (or near) the Fermi level, was also determined from the Mott variables; the results were dependent on V2O5 content.

Temperature and parasite life-history are important modulators of the outcome of Trypanosoma rangeli-Rhodnius prolixus interactions.

PubMed

Rodrigues, Juliana DE O; Lorenzo, Marcelo G; Martins-Filho, Olindo A; Elliot, Simon L; Guarneri, Alessandra A

2016-09-01

Trypanosoma rangeli is a protozoan parasite, which does not cause disease in humans, although it can produce different levels of pathogenicity to triatomines, their invertebrate hosts. We tested whether infection imposed a temperature-dependent cost on triatomine fitness using T. rangeli with different life histories. Parasites cultured only in liver infusion tryptose medium (cultured) and parasites exposed to cyclical passages through mice and triatomines (passaged) were used. We held infected insects at four temperatures between 21 and 30 °C and measured T. rangeli growth in vitro at the same temperatures in parallel. Overall, T. rangeli infection induced negative effects on insect fitness. In the case of cultured infection, parasite effects were temperature-dependent. Intermoult period, mortality rates and ecdysis success were affected in those insects exposed to lower temperatures (21 and 24 °C). For passaged-infected insects, the effects were independent of temperature, intermoult period being prolonged in all infected groups. Trypanosoma rangeli seem to be less tolerant to higher temperatures since cultured-infected insects showed a reduction in the infection rates and passaged-infected insects decreased the salivary gland infection rates in those insects submitted to 30 °C. In vitro growth of T. rangeli was consistent with these results.

Temperature-dependent electrical characteristics and carrier transport mechanism of p-Cu2ZnSnS4/n-GaN heterojunctions

NASA Astrophysics Data System (ADS)

Niteesh Reddy, Varra; Reddy, M. Siva Pratap; Gunasekhar, K. R.; Lee, Jung-Hee

2018-04-01

This work explores the temperature-dependent electrical characteristics and carrier transport mechanism of Au/p-Cu2ZnSnS4/n-type GaN heterojunction (HJ) diodes with a CZTS interlayer. The electrical characteristics were examined by current-voltage-temperature, turn-on voltage-temperature and series resistance-temperature in the high-temperature range of 300-420 K. It is observed that an exponential decrease in the series resistance ( R S) and increase in the ideality factor ( n) and barrier height ( ϕ b) with increase in temperature. The thermal coefficient ( K j) is determined to be - 1.3 mV K-1 at ≥ 300 K. The effective ϕ b is determined to be 1.21 eV. This obtained barrier height is consistent with the theoretical one. The characteristic temperature ( T 0) resulting from the Cheung's functions [d V/d(ln I) vs. I and H( I) vs. I], is seen that there is good agreement between the T 0 values from both Cheung's functions. The relevant carrier transport mechanisms of Au/p-CZTS/n-type GaN HJ are explained based on the thermally decreased energy band gap of n-type GaN layers, thermally activated deep donors and increased further activated shallow donors.

Working Towards Deep-Ocean Temperature Monitoring by Studying the Acoustic Ambient Noise Field in the South Pacific Ocean

NASA Astrophysics Data System (ADS)

Sambell, K.; Evers, L. G.; Snellen, M.

2017-12-01

Deriving the deep-ocean temperature is a challenge. In-situ observations and satellite observations are hardly applicable. However, knowledge about changes in the deep ocean temperature is important in relation to climate change. Oceans are filled with low-frequency sound waves created by sources such as underwater volcanoes, earthquakes and seismic surveys. The propagation of these sound waves is temperature dependent and therefore carries valuable information that can be used for temperature monitoring. This phenomenon is investigated by applying interferometry to hydroacoustic data measured in the South Pacific Ocean. The data is measured at hydrophone station H03 which is part of the International Monitoring System (IMS). This network consists of several stations around the world and is in place for the verification of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). The station consists of two arrays located north and south of Robinson Crusoe Island separated by 50 km. Both arrays consist of three hydrophones with an intersensor distance of 2 km located at a depth of 1200 m. This depth is in range of the SOFAR channel. Hydroacoustic data measured at the south station is cross-correlated for the time period 2014-2017. The results are improved by applying one-bit normalization as a preprocessing step. Furthermore, beamforming is applied to the hydroacoustic data in order to characterize ambient noise sources around the array. This shows the presence of a continuous source at a backazimuth between 180 and 200 degrees throughout the whole time period, which is in agreement with the results obtained by cross-correlation. Studies on source strength show a seasonal dependence. This is an indication that the sound is related to acoustic activity in Antarctica. Results on this are supported by acoustic propagation modeling. The normal mode technique is used to study the sound propagation from possible source locations towards station H03.

Temperature Dependence of Molecular Line Strengths and Fei 1565 nm Zeeman Splitting in a Sunspot

NASA Astrophysics Data System (ADS)

Penn, M. J.; Walton, S.; Chapman, G.; Ceja, J.; Plick, W.

2003-03-01

Spectroscopic observations at 1565 nm were made in the eastern half of the main umbra of NOAA 9885 on 1 April 2002 using the National Solar Observatory McMath-Pierce Telescope at Kitt Peak with a tip-tilt image stabilization system and the California State University Northridge-National Solar Observatory infrared camera. The line depth of the OH blend at 1565.1 nm varies with the observed continuum temperature; the variation fits previous observations except that the continuum temperature is lower by 600 K. The equivalent width of the OH absorption line at 1565.2 nm shows a temperature dependence similar to previously published umbral molecular observations at 640 nm. A simple model of expected OH abundance based upon an ionization analogy to molecular dissociation is produced and agrees well with the temperature variation of the line equivalent width. A CN absorption line at 1564.6 nm shows a very different temperature dependence, likely due to complicated formation and destruction processes. Nonetheless a numerical fit of the temperature variation of the CN equivalent width is presented. Finally a comparison of the Zeeman splitting of the Fei 1564.8 nm line with the sunspot temperature derived from the continuum intensity shows an umbra somewhat cooler for a given magnetic field strength than previous comparisons using this infrared 1564.8 nm line, but consistent with these previous infrared measurements the umbra is hotter for a given magnetic field strength than magnetic and temperature measurements at 630.2 nm would suggest. Differences between the 630.2 nm and 1564.8 nm umbral temperature and magnetic field relations are explained with the different heights of formation of the lines and continua at these wavelengths.

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

Conversion treatment of thin titanium layer deposited on carbon steel

NASA Astrophysics Data System (ADS)

Benarioua, Younes; Wendler, Bogdan; Chicot, Didier

2018-05-01

The present study has been conducted in order to obtain titanium carbide layer using a conversion treatment consisting of two main steps. In the first step a thin pure titanium layer was deposited on 120C4 carbon steel by PVD. In the second step, the carbon atoms from the substrate diffuse to the titanium coating due to a vacuum annealing treatment and the Ti coating transforms into titanium carbide. Depending on the annealing temperature a partial or complete conversion into TiC is obtained. The hardness of the layer can be expected to differ depending on the processing temperatures. By a systematic study of the hardness as a function of the applied load, we confirm the process of growth of the layer.

Analysis of the normal-state magnetic susceptibility of La sub 2 minus x Sr sub x CuO sub 4+ y (abstract) (US)

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

Filipkowski, M.E.; Budnick, J.I.

1991-11-15

We describe a quantitative analysis of the low-temperature ({ital T}{lt}300 K) susceptibility ({chi}({ital T})) of La{sub 2{minus}x}Sr{sub x}CuO{sub 4+y} for dopant concentrations in the vicinity of the superconducting phase boundary (SPB) at {ital x}=0.055. This analysis is based on a phenomenological model for the temperature dependence consisting of a Curie-like 1/{ital T} term plus a term linear in {ital T}. We find that the former exhibits nontrivial doping dependence at the SPB, while the {ital T}-linear part accepts decomposition into a Pauli contribution and a portion which can be understood using spin-wave theory.

On the temperature-dependent exchange splitting in the quasiparticle bandstructure of Ni

NASA Astrophysics Data System (ADS)

Borgiel, W.; Nolting, W.; Donath, M.

1989-11-01

A theoretical model for the bandferromagnet Ni is proposed, which takes into account the intraatomic electron interactions within the d band complex. After introducing effective spin operators the model-Hamiltonian consists of a one-particle part, an intraband interaction of Hubbard-type, and an interband exchange, formally describing electron magnon scattering (s-f model). The one particle energies are taken from a realistic bandstructure calculation for paramagnetic Ni. We use a many body procedure for a detailed inspection of the quasiparticle bandstructure in KX and XW directions, present the corresponding spectral densities, and compare the temperature dependent exchange splittings near the X and W point with recent results from spin resolved photoemission (PE) - and inverse photoemission (IPE) - experiments.

Electroless controllable growth of ZnO films and their morphology-dependent antimicrobial properties.

PubMed

Ruíz-Gómez, M A; Figueroa-Torres, M Z; Alonso-Lemus, I L; Vega-Becerra, O E; González-López, J R; Zaldívar-Cadena, A A

2018-04-05

An electroless deposition process was used to synthesize with a controlled morphology, polycrystalline ZnO on glass substrates as antimicrobial coatings. The influence of deposition temperature (T dep ) on the physicochemical and antimicrobial properties of the ZnO films was analyzed. The results indicated that a change in deposition temperature greatly affected the morphology and the degree of crystallinity of the films. Scanning electron microscope images show that the film surface is porous at a deposition temperature of 40 and 50 °C, whereas hexagonal-plate shaped morphology predominated at 60 °C and finally at 70 and 80 °C the films consisted of rod-like particles. The films showed good transparency in the visible region. All ZnO films presented notable antimicrobial activity against the gram-negative bacteria Escherichia coli (E. coli) and the gram-positive Staphylococcus aureus (S. aureus). It was found that the antimicrobial efficiency is strongly dependent on morphology and structural properties. The best antimicrobial performance was recorded for the films consisting of rod-like morphology with a high degree of crystallinity. The procedure used in this investigation is strongly recommended for the development of functional surfaces. Copyright © 2017 Elsevier B.V. All rights reserved.

Temperature-dependent poroelastic and viscoelastic effects on microscale-modelling of seismic reflections in heavy oil reservoirs

NASA Astrophysics Data System (ADS)

Ciz, Radim; Saenger, Erik H.; Gurevich, Boris; Shapiro, Serge A.

2009-03-01

We develop a new model for elastic properties of rocks saturated with heavy oil. The heavy oil is represented by a viscoelastic material, which at low frequencies and/or high temperatures behaves as a Newtonian fluid, and at high frequencies and/or low temperatures as a nearly elastic solid. The bulk and shear moduli of a porous rock saturated with such viscoelastic material are then computed using approximate extended Gassmann equations of Ciz and Shapiro by replacing the elastic moduli of the pore filling material with complex and frequency-dependent moduli of the viscoelastic pore fill. We test the proposed model by comparing its predictions with numerical simulations based on a direct finite-difference solution of equations of dynamic viscoelasticity. The simulations are performed for the reflection coefficient from an interface between a homogeneous fluid and a porous medium. The numerical tests are performed both for an idealized porous medium consisting of alternating solid and viscoelastic layers, and for a more realistic 3-D geometry of the pore space. Both sets of numerical tests show a good agreement between the predictions of the proposed viscoelastic workflow and numerical simulations for relatively high viscosities where viscoelastic effects are important. The results confirm that application of extended Gassmann equations in conjunction with the complex and frequency-dependent moduli of viscoelastic pore filling material, such as heavy oil, provides a good approximation for the elastic moduli of rocks saturated with such material. By construction, this approximation is exactly consistent with the classical Gassmann's equation for sufficiently low frequencies or high temperature when heavy oil behaves like a fluid. For higher frequencies and/or lower temperatures, the predictions are in good agreement with the direct numerical solution of equations of dynamic viscoelasticity on the microscale. This demonstrates that the proposed methodology provides realistic estimates of elastic properties of heavy oil rocks.

Fibre systems for future astronomy: anomalous wavelength-temperature effects

NASA Astrophysics Data System (ADS)

Poppett, C. L.; Allington-Smith, J. R.

2007-07-01

Focal ratio degradation is an important property of optical fibres that determines the design and cost of instruments using fibres. Motivated by the importance of fibres in feeding instruments on Extremely Large Telescopes, the need for cryogenic-cooling to reduce thermal background and the desire for broad-band performance, we have studied the dependency of focal ratio degradation (FRD) on both temperature and wavelength. This shows a small but significant reduction in performance when cooled as expected from previous work. We also find an increase in FRD with wavelength broadly consistent with theory at room temperature but this dependency reverses in sign when the fibres are cooled to 77K, contrary to existing theory. We parameterize the wavelength dependency by an ad hoc extension to an existing model but it is clear that existing theory does not provide a good description of the operation of fibres in astronomical systems. This unexpected behaviour, which may relate to frozen-in stress from the manufacturing process, will need to be taken into account when designing future fibre systems.

Single-particle stochastic heat engine.

PubMed

Rana, Shubhashis; Pal, P S; Saha, Arnab; Jayannavar, A M

2014-10-01

We have performed an extensive analysis of a single-particle stochastic heat engine constructed by manipulating a Brownian particle in a time-dependent harmonic potential. The cycle consists of two isothermal steps at different temperatures and two adiabatic steps similar to that of a Carnot engine. The engine shows qualitative differences in inertial and overdamped regimes. All the thermodynamic quantities, including efficiency, exhibit strong fluctuations in a time periodic steady state. The fluctuations of stochastic efficiency dominate over the mean values even in the quasistatic regime. Interestingly, our system acts as an engine provided the temperature difference between the two reservoirs is greater than a finite critical value which in turn depends on the cycle time and other system parameters. This is supported by our analytical results carried out in the quasistatic regime. Our system works more reliably as an engine for large cycle times. By studying various model systems, we observe that the operational characteristics are model dependent. Our results clearly rule out any universal relation between efficiency at maximum power and temperature of the baths. We have also verified fluctuation relations for heat engines in time periodic steady state.

Anisotropic physical properties and pressure dependent magnetic ordering of CrAuTe 4

DOE PAGES

Jo, Na Hyun; Kaluarachchi, Udhara S.; Wu, Yun; ...

2016-11-11

Systematic measurements of temperature-dependent magnetization, resistivity, and angle-resolved photoemission spectroscopy (ARPES) at ambient pressure as well as resistivity under pressures up to 5.25 GPa were conducted on single crystals of CrAuTe 4. Magnetization data suggest that magnetic moments are aligned antiferromagnetically along the crystallographic c axis below T N = 255 K. ARPES measurements show band reconstruction due to the magnetic ordering. Magnetoresistance data show clear anisotropy, and, at high fields, quantum oscillations. The Néel temperature decreases monotonically under pressure, decreasing to T N = 236 K at 5.22 GPa. The pressure dependencies of (i) T N, (ii) the residualmore » resistivity ratio, and (iii) the size and power-law behavior of the low-temperature magnetoresistance all show anomalies near 2 GPa suggesting that there may be a phase transition (structural, magnetic, and/or electronic) induced by pressure. Lastly, for pressures higher than 2 GPa a significantly different quantum oscillation frequency emerges, consistent with a pressure induced change in the electronic states.« less

Free oscillations in a climate model with ice-sheet dynamics

NASA Technical Reports Server (NTRS)

Kallen, E.; Crafoord, C.; Ghil, M.

1979-01-01

A study of stable periodic solutions to a simple nonlinear model of the ocean-atmosphere-ice system is presented. The model has two dependent variables: ocean-atmosphere temperature and latitudinal extent of the ice cover. No explicit dependence on latitude is considered in the model. Hence all variables depend only on time and the model consists of a coupled set of nonlinear ordinary differential equations. The globally averaged ocean-atmosphere temperature in the model is governed by the radiation balance. The reflectivity to incoming solar radiation, i.e., the planetary albedo, includes separate contributions from sea ice and from continental ice sheets. The major physical mechanisms active in the model are (1) albedo-temperature feedback, (2) continental ice-sheet dynamics and (3) precipitation-rate variations. The model has three-equilibrium solutions, two of which are linearly unstable, while one is linearly stable. For some choices of parameters, the stability picture changes and sustained, finite-amplitude oscillations obtain around the previously stable equilibrium solution. The physical interpretation of these oscillations points to the possibility of internal mechanisms playing a role in glaciation cycles.

Cryogenic Refractive Indices of S-LAH55, S-LAH55V, S-LAH59, S-LAM3, S-NBM51, S-NPH2, S-PHM52, and S-TIH14 Glasses

NASA Technical Reports Server (NTRS)

Miller, Kevin H.; Quijada, Manuel A.; Leviton, Douglas B.

2015-01-01

The Transiting Exoplanet Survey Satellite (TESS) is an explorer-class planet finder, whose principal goal is to detect small planets with bright host starts in the solar neighborhood. The TESS payload consists of four identical cameras and a Data Handling Unit (DHU) fitted with CCD detectors and associated electronics. Each camera consist of a lens assembly with seven optical elements that include various types of Ohara glass substrates. The successful implementation of a panchromatic and a thermal lens assembly design for these cameras requires a fairly accurate (up to 0.000001 (1e-6)) knowledge of the temperature- and wavelength-dependent of the refractive index in the wavelength and temperature range of operation. Hence, this paper is devoted to report on measurements of the refractive index over the wavelength range of 0.42-1.15 micrometers and temperature range of 110-300 K for the following Ohara glasses: S-LAH55, S-LAH55V, S-LAH59, S-LAM3, S-NBM51, S-NPH2, S-PHM52, and S-TIH14. The measurements were performed utilizing the Cryogenic High Accuracy Refraction Measuring System (CHARMS) facility at NASA's Goddard Space Flight Center. A dense coverage of the absolute refractive index for all these substrates in the aforementioned wavelength and temperature ranges was used to determine the thermo-optic coefficient (dndT) and dispersion relation (dnd) as a function of wavelength and temperature. A comparison of the measured indices with literature values, specifically the temperature-dependent refractive indices of S-PHM52 and S-TIH14 reported by Yamamuro et al. [Yamamuro et al., Opt. Eng. 45(8), 083401 (2006)], will be presented.

Effect of 50 MeV Li3 + irradiation on structural and electrical properties of Mn-doped ZnO

NASA Astrophysics Data System (ADS)

Neogi, S. K.; Chattopadhyay, S.; Banerjee, Aritra; Bandyopadhyay, S.; Sarkar, A.; Kumar, Ravi

2011-05-01

The present work aims to study the effect of ion irradiation on structural and electrical properties and their correlation with the defects in the Zn1 - xMnxO-type system. Zn1 - xMnxO (x = 0.02, 0.04) samples have been synthesized by the solid-state reaction method and have been irradiated with 50 MeV Li3 + ions. The concomitant changes have been probed by x-ray diffraction (XRD), temperature-dependent electrical resistivity and positron annihilation lifetime (PAL) spectroscopy. The XRD result shows a single-phase wurtzite structure for Zn0.98Mn0.02O, whereas for the Zn0.96Mn0.04O sample an impurity phase has been found, apart from the usual peaks of ZnO. Ion irradiation removes this impurity peak. The grain size of the samples is found to be uniform. For Zn0.98Mn0.02O, the observed sharp decrease in room temperature resistivity (ρRT) with irradiation is consistent with the lowering of the full width at half maximum of the XRD peaks. However, for Zn0.96Mn0.04O, ρRT decreases for the initial fluence but increases for a further increase in fluence. All the irradiated Zn0.98Mn0.02O samples show a metal-semiconductor transition in temperature-dependent resistivity measurements at low temperature. But all the irradiated Zn0.96Mn0.04O samples show a semiconducting nature in the whole range of temperatures. Results of room temperature resistivity, XRD and PAL measurements are consistent with each other.

Effect of 50 MeV Li3+ irradiation on structural and electrical properties of Mn-doped ZnO.

PubMed

Neogi, S K; Chattopadhyay, S; Banerjee, Aritra; Bandyopadhyay, S; Sarkar, A; Kumar, Ravi

2011-05-25

The present work aims to study the effect of ion irradiation on structural and electrical properties and their correlation with the defects in the Zn(1 - x)Mn(x)O-type system. Zn(1 - x)Mn(x)O (x = 0.02, 0.04) samples have been synthesized by the solid-state reaction method and have been irradiated with 50 MeV Li(3+) ions. The concomitant changes have been probed by x-ray diffraction (XRD), temperature-dependent electrical resistivity and positron annihilation lifetime (PAL) spectroscopy. The XRD result shows a single-phase wurtzite structure for Zn(0.98)Mn(0.02)O, whereas for the Zn(0.96)Mn(0.04)O sample an impurity phase has been found, apart from the usual peaks of ZnO. Ion irradiation removes this impurity peak. The grain size of the samples is found to be uniform. For Zn(0.98)Mn(0.02)O, the observed sharp decrease in room temperature resistivity (ρ(RT)) with irradiation is consistent with the lowering of the full width at half maximum of the XRD peaks. However, for Zn(0.96)Mn(0.04)O, ρ(RT) decreases for the initial fluence but increases for a further increase in fluence. All the irradiated Zn(0.98)Mn(0.02)O samples show a metal-semiconductor transition in temperature-dependent resistivity measurements at low temperature. But all the irradiated Zn(0.96)Mn(0.04)O samples show a semiconducting nature in the whole range of temperatures. Results of room temperature resistivity, XRD and PAL measurements are consistent with each other.

Transport properties of glass-forming liquids suggest that dynamic crossover temperature is as important as the glass transition temperature.

PubMed

Mallamace, Francesco; Branca, Caterina; Corsaro, Carmelo; Leone, Nancy; Spooren, Jeroen; Chen, Sow-Hsin; Stanley, H Eugene

2010-12-28

It is becoming common practice to partition glass-forming liquids into two classes based on the dependence of the shear viscosity η on temperature T. In an Arrhenius plot, ln η vs 1/T, a strong liquid shows linear behavior whereas a fragile liquid exhibits an upward curvature [super-Arrhenius (SA) behavior], a situation customarily described by using the Vogel-Fulcher-Tammann law. Here we analyze existing data of the transport coefficients of 84 glass-forming liquids. We show the data are consistent, on decreasing temperature, with the onset of a well-defined dynamical crossover η(×), where η(×) has the same value, η(×) ≈ 10(3) Poise, for all 84 liquids. The crossover temperature, T(×), located well above the calorimetric glass transition temperature T(g), marks significant variations in the system thermodynamics, evidenced by the change of the SA-like T dependence above T(×) to Arrhenius behavior below T(×). We also show that below T(×) the familiar Stokes-Einstein relation D/T ∼ η(-1) breaks down and is replaced by a fractional form D/T ∼ η(-ζ), with ζ ≈ 0.85.

Transport properties of glass-forming liquids suggest that dynamic crossover temperature is as important as the glass transition temperature

PubMed Central

Mallamace, Francesco; Branca, Caterina; Corsaro, Carmelo; Leone, Nancy; Spooren, Jeroen; Chen, Sow-Hsin; Stanley, H. Eugene

2010-01-01

It is becoming common practice to partition glass-forming liquids into two classes based on the dependence of the shear viscosity η on temperature T. In an Arrhenius plot, ln η vs 1/T, a strong liquid shows linear behavior whereas a fragile liquid exhibits an upward curvature [super-Arrhenius (SA) behavior], a situation customarily described by using the Vogel–Fulcher–Tammann law. Here we analyze existing data of the transport coefficients of 84 glass-forming liquids. We show the data are consistent, on decreasing temperature, with the onset of a well-defined dynamical crossover η×, where η× has the same value, η× ≈ 103 Poise, for all 84 liquids. The crossover temperature, T×, located well above the calorimetric glass transition temperature Tg, marks significant variations in the system thermodynamics, evidenced by the change of the SA-like T dependence above T× to Arrhenius behavior below T×. We also show that below T× the familiar Stokes–Einstein relation D/T ∼ η-1 breaks down and is replaced by a fractional form D/T ∼ η-ζ, with ζ ≈ 0.85. PMID:21148100

Embedded Gold Nanorods as Microscale Thermochromic Temperature Sensors

NASA Astrophysics Data System (ADS)

Kennedy, W. Joshua; Slinker, Keith; Koerner, Hilmar; Ehlert, Gregory; Baur, Jeffery

2015-03-01

Gold nanorods (AuNRs) are known to undergo a shape transformation via surface melting at temperatures far below the bulk melting temperature of gold. Because the optical scattering by the AuNRs depends on both particle morphology and the surrounding local dielectric constant the opto-thermal properties of polymer-AuNR nanocomposites depend strongly on the chemical and mechanical characteristics of the polymer host. We have measured the optical absorption of polymer nanocomposites consisting of AuNRs in a variety of polymer systems as a function of temperature, time, molecular weight, and crosslink density. Our results show that the shape transformation of the AuNRs is not well described by a simple kinetic model, and that multiple contributors to the surface energy play significant roles in the process. We show that the dynamics of the shape transformation may be calibrated in a nanocomposite such that the optical absorption spectrum of the material may be used as a local sensor of both temperature history and degree of cure. We demonstrate the usefulness of this technique by measuring (ex situ) the temperature of an internally heated epoxy resin with a lateral spatial resolution of < 10 μm. Principal Investigator.

Modelling of Continental Lithosphere Breakup and Rifted Margin Formation in Response to an Upwelling Divergent Flow Field Incorporating a Temperature Dependent Rheology

NASA Astrophysics Data System (ADS)

Tymms, V. J.; Kusznir, N. J.

2005-05-01

We numerically model continental lithosphere deformation leading to breakup and sea floor spreading initiation in response to an imposed upwelling and divergent flow field applied to continental lithosphere and asthenosphere. The model is used to predict rifted continental margin lithosphere thinning and temperature structure. Model predictions are compared with observed rifted margin structure for four diverse case studies. Prior to application of the upwelling divergent flow field the continental lithosphere is undeformed with a uniform temperature gradient. The upwelling divergent flow field is defined kinematically using boundary conditions consisting of the upwelling velocity Vz at the divergence axis and the half divergence rate Vx . The resultant velocity field throughout the continuum is computed using finite element (FE) code incorporating a Newtonian temperature dependent rheology. The flow field is used to advect the continental lithosphere material and lithospheric and asthenospheric temperatures. Viscosity structure is hence modified and the velocities change correspondingly in a feedback loop. We find the kinematic boundary conditions Vz and Vx to be of first order importance. A high Vz/Vx (greater than10), corresponding to buoyancy assisted flow, leads to minimal mantle exhumation and a well defined continent ocean transition consistent with observations at volcanic margins. For Vz/Vx near unity, corresponding to plate boundary driven divergence, mantle exhumation over widths of up to 100 km is predicted which is consistent with observations at non-volcanic margins. The FE method allows the upwelling velocity Vz to be propagated upwards from the top of the asthenosphere to the Earth's surface without the requirement of imposing Vx. When continental breakup is achieved the half divergence velocity Vx can be applied at the lithosphere surface and the upwelling velocity Vz left free. We find this time and space dependent set of boundary conditions is more plausible than a constant corner flow type solution and predicts levels of depth dependent stretching and continent ocean transitions consistent with observation. Depth dependent lithosphere stretching, which is observed at rifted continental margins, is predicted to occur before continental breakup and sea-floor spreading initiation. The model may be used to predict surface heat flow and bathymetry, and to provide estimates of melt production rates and cumulative thickness. We compare model predictions with observed margin structure for four diverse rifted margins: the Lofoten Margin (a mature volcanic margin), Goban Spur (a mature non-volcanic margin), the Woodlark Basin (a neotectonic young ocean basin) and the Faroe-Shetland Basin (a failed attempt at continental breakup). This work forms part of the NERC Margins iSIMM project. iSIMM investigators are from Liverpool and Cambridge Universities, Badley Geoscience & Schlumberger Cambridge Research supported by the NERC, the DTI, Agip UK, BP, Amerada Hess Ltd, Anadarko, Conoco¬Phillips, Shell, Statoil and WesternGeco. The iSIMM team comprises NJ Kusznir, RS White, AM Roberts, PAF Christie, A Chappell, J Eccles, R Fletcher, D Healy, N Hurst, ZC Lunnon, CJ Parkin, AW Roberts, LK Smith, V Tymms & R Spitzer.

Parametric dependence of density limits in the Tokamak Experiment for Technology Oriented Research (TEXTOR): Comparison of thermal instability theory with experiment

NASA Astrophysics Data System (ADS)

Kelly, F. A.; Stacey, W. M.; Rapp, J.

2001-11-01

The observed dependence of the TEXTOR [Tokamak Experiment for Technology Oriented Research: E. Hintz, P. Bogen, H. A. Claassen et al., Contributions to High Temperature Plasma Physics, edited by K. H. Spatschek and J. Uhlenbusch (Akademie Verlag, Berlin, 1994), p. 373] density limit on global parameters (I, B, P, etc.) and wall conditioning is compared with the predicted density limit parametric scaling of thermal instability theory. It is necessary first to relate the edge parameters of the thermal instability theory to n¯ and the other global parameters. The observed parametric dependence of the density limit in TEXTOR is generally consistent with the predicted density limit scaling of thermal instability theory. The observed wall conditioning dependence of the density limit can be reconciled with the theory in terms of the radiative emissivity temperature dependence of different impurities in the plasma edge. The thermal instability theory also provides an explanation of why symmetric detachment precedes radiative collapse for most low power shots, while a multifaceted asymmetric radiation from the edge MARFE precedes detachment for most high power shots.

Geometry-dependent penetration fields of superconducting Bi2Sr2CaCu2O8+δ platelets

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

Curran, P. J.; Clem, J. R.; Bending, S. J.

Magneto-optical imaging has been used to study vortex penetration into regular polygon-shaped Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} platelets with various geometries (disks, pentagons, squares, and triangles) but known fixed areas. In all cases we observe an exponential dependence of the field of first penetration, H{sub p}, on temperature, consistent with a dominant Bean-Livingston barrier for pancake vortices at our measurement temperatures (45-80 K). However, the penetration field consistently decreases with decreasing degree of sample symmetry, in stark contrast to conventional estimates of demagnetization factors using equivalent ellipsoids based on inscribed circles, which predict the reverse trend. Surprisingly, this observation doesmore » not appear to have been reported in the literature before. We demonstrate empirically that estimates using equivalent ellipsoids based on circumscribed circles predict the correct qualitative experimental trend in Hp. Our work has important implications for the estimation of appropriate effective demagnetization factors for flux penetration into arbitrarily shaped superconducting bodies.« less

Geometry-dependent penetration fields in superconducting Bi2Sr2CaCu2O8+δ platelets

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

By: Curran, P. J.; Clem, J. R.; Bending, S. J.

Magneto-optical imaging has been used to study vortex penetration into regular polygon-shaped Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} platelets with various geometries (disks, pentagons, squares, and triangles) but known fixed areas. In all cases we observe an exponential dependence of the field of first penetration, H{sub p}, on temperature, consistent with a dominant Bean-Livingston barrier for pancake vortices at our measurement temperatures (45-80 K). However, the penetration field consistently decreases with decreasing degree of sample symmetry, in stark contrast to conventional estimates of demagnetization factors using equivalent ellipsoids based on inscribed circles, which predict the reverse trend. Surprisingly, this observation doesmore » not appear to have been reported in the literature before. We demonstrate empirically that estimates using equivalent ellipsoids based on circumscribed circles predict the correct qualitative experimental trend in H{sub p}. Our work has important implications for the estimation of appropriate effective demagnetization factors for flux penetration into arbitrarily shaped superconducting bodies.« less

Theory of the water vapor continuum and validations

NASA Technical Reports Server (NTRS)

Tipping, Richard H.; Ma, Q.

1995-01-01

A far-wing line shape theory based on the binary collision and quasistatic approximations that is applicable for both the low- and high-frequency wings of the vibration-rotational bands has been developed. This theory has been applied in order to calculate the frequency and temperature dependence of the continuous absorption coefficient for frequencies up to 10,000 cm(exp -1) for pure H2O and for H2O-N2 mixtures. The calculations were made assuming an interaction potential consisting of an isotropic Lennard-Jones part with two parameters that are consistent with values obtained from other data, and the leading long-range anisotropic part, together with the measured line strengths and transition frequencies. The results, obtained without the introduction of adjustable parameters, compare well with the existing laboratory data, both in magnitude and in temperature dependence. This leads us to the conclusion that the water continuum can be explained in terms of far-wing absorption. Current work in progress to extend the theory and to validate the theoretically calculated continuum will be discussed briefly.

Order in dense hydrogen at low temperatures

PubMed Central

Edwards, B.; Ashcroft, N. W.

2004-01-01

By increase in density, impelled by pressure, the electronic energy bands in dense hydrogen attain significant widths. Nevertheless, arguments can be advanced suggesting that a physically consistent description of the general consequences of this electronic structure can still be constructed from interacting but state-dependent multipoles. These reflect, in fact self-consistently, a disorder-induced localization of electron states partially manifesting the effects of proton dynamics; they retain very considerable spatial inhomogeneity (as they certainly do in the molecular limit). This description, which is valid provided that an overall energy gap has not closed, leads at a mean-field level to the expected quadrupolar coupling, but also for certain structures to the eventual emergence of dipolar terms and their coupling when a state of broken charge symmetry is developed. A simple Hamiltonian incorporating these basic features then leads to a high-density, low-temperature phase diagram that appears to be in substantial agreement with experiment. In particular, it accounts for the fact that whereas the phase I–II phase boundary has a significant isotope dependence, the phase II–III boundary has very little. PMID:15028839

Idealized modeling of convective organization with changing sea surface temperatures using multiple equilibria in weak temperature gradient simulations

NASA Astrophysics Data System (ADS)

Sentić, Stipo; Sessions, Sharon L.

2017-06-01

The weak temperature gradient (WTG) approximation is a method of parameterizing the influences of the large scale on local convection in limited domain simulations. WTG simulations exhibit multiple equilibria in precipitation; depending on the initial moisture content, simulations can precipitate or remain dry for otherwise identical boundary conditions. We use a hypothesized analogy between multiple equilibria in precipitation in WTG simulations, and dry and moist regions of organized convection to study tropical convective organization. We find that the range of wind speeds that support multiple equilibria depends on sea surface temperature (SST). Compared to the present SST, low SSTs support a narrower range of multiple equilibria at higher wind speeds. In contrast, high SSTs exhibit a narrower range of multiple equilibria at low wind speeds. This suggests that at high SSTs, organized convection might occur with lower surface forcing. To characterize convection at different SSTs, we analyze the change in relationships between precipitation rate, atmospheric stability, moisture content, and the large-scale transport of moist entropy and moisture with increasing SSTs. We find an increase in large-scale export of moisture and moist entropy from dry simulations with increasing SST, which is consistent with a strengthening of the up-gradient transport of moisture from dry regions to moist regions in organized convection. Furthermore, the changes in diagnostic relationships with SST are consistent with more intense convection in precipitating regions of organized convection for higher SSTs.

Olivine friction at the base of oceanic seismogenic zones

USGS Publications Warehouse

Boettcher, M.S.; Hirth, G.; Evans, B. M.

2007-01-01

We investigate the strength and frictional behavior of olivine aggregates at temperatures and effective confining pressures similar to those at the base of the seismogenic zone on a typical ridge transform fault. Triaxial compression tests were conducted on dry olivine powder (grain size ???60 ??m) at effective confining pressures between 50 and 300 MPa (using Argon as a pore fluid), temperatures between 600??C and 1000??C, and axial displacement rates from 0.06 to 60 ??m/s (axial strain rates from 3 ?? 10-6 to 3 ?? 10-3 s-1). Yielding shows a negative pressure dependence, consistent with predictions for shear enhanced compaction and with the observation that samples exhibit compaction during the initial stages of the experiments. A combination of mechanical data and microstructural observations demonstrate that deformation was accommodated by frictional processes. Sample strengths were pressure-dependent and nearly independent of temperature. Localized shear zones formed in initially homogeneous aggregates early in the experiments. The frictional response to changes in loading rate is well described by rate and state constitutive laws, with a transition from velocity-weakening to velocity-strengthening at 1000??C. Microstructural observations and physical models indicate that plastic yielding of asperities at high temperatures and low axial strain rates stabilizes frictional sliding. Extrapolation of our experimental data to geologic strain rates indicates that a transition from velocity weakening to velocity strengthening occurs at approximately 600??C, consistent with the focal depths of earthquakes in the oceanic lithosphere. Copyright 2007 by the American Geophysical Union.

Study of vaporization of sodium metaborate by transpiration thermogravimetry and Knudsen effusion mass spectrometry.

PubMed

Narasimhan, T S Lakshmi; Viswanathan, R; Nalini, S

2011-11-17

The vaporization of solid sodium metaborate NaBO(2)(s) was studied by transpiration thermogravimetry (TTG) and Knudsen effusion mass spectrometry (KEMS). The transpiration measurements, performed for the first time on NaBO(2)(s), involved use of argon as the carrier gas for vapor transport and derivation of vapor pressure of NaBO(2)(g) (by assuming it as the sole vapor species) through many flow-dependence runs and temperature-dependence runs in the temperature range 1075-1218 K. The KEMS measurements performed in the temperature range 1060-1185 K confirmed NaBO(2)(g) as the principal vapor species over NaBO(2)(s), in accord with the previously reported KEMS studies. The values of p(NaBO(2)) obtained by both TTG and KEMS are consistent within the uncertainties associated with each method and so are the second- and third-law values of enthalpy of sublimation, the latter aspect consistently missing in all previous vaporization studies. The results of both TTG and KEMS were combined to recommend the following thermodynamic parameters pertinent to the sublimation reaction, NaBO(2)(s) = NaBO(2)(g): Log{p(NaBO(2))/Pa} = -(17056 ± 441)/(T/K) + (14.73 ± 0.35) for the temperature range 1060-1218 K; Δ(r)H°(m)(298.15 K) = (346.3 ± 9.4) kJ·mol(-1); and Δ(r)S°(m)(298.15 K) = (210.2 ± 6.8) J·mol(-1)·K(-1).

Non-arrhenius behavior in the unfolding of a short, hydrophobic alpha-helix. Complementarity of molecular dynamics and lattice model simulations.

PubMed

Collet, Olivier; Chipot, Christophe

2003-05-28

The unfolding of the last, C-terminal residue of AcNH(2)-(l-Leu)(11)-NHMe in its alpha-helical form has been investigated by measuring the variation of free energy involved in the alpha(R) to beta conformational transition. These calculations were performed using large-scale molecular dynamics simulations in conjunction with the umbrella sampling method. For different temperatures ranging from 280 to 370 K, the free energy of activation was estimated. Concurrently, unfolding simulations of a homopolypeptide formed by twelve hydrophobic residues were carried out, employing a three-dimensional lattice model description of the peptide, with a temperature-dependent interaction potential. Using a Monte Carlo approach, the lowest free energy conformation, an analogue of a right-handed alpha-helix, was determined in the region where the peptide chain is well ordered. The free energy barrier separating this state from a distinct, compact conformation, analogue to a beta-strand, was determined over a large enough range of temperatures. The results of these molecular dynamics and lattice model simulations are consistent and indicate that the kinetics of the unfolding of a hydrophobic peptide exhibits a non-Arrhenius behavior closely related to the temperature dependence of the hydrophobic effect. These results further illuminate the necessity to include a temperature dependence in potential energy functions designed for coarse-grained models of proteins.

Strong anharmonicity in the phonon spectra of PbTe and SnTe from first principles

NASA Astrophysics Data System (ADS)

Ribeiro, Guilherme A. S.; Paulatto, Lorenzo; Bianco, Raffaello; Errea, Ion; Mauri, Francesco; Calandra, Matteo

2018-01-01

At room temperature, PbTe and SnTe are efficient thermoelectrics with a cubic structure. At low temperature, SnTe undergoes a ferroelectric transition with a critical temperature strongly dependent on the hole concentration, while PbTe is an incipient ferroelectric. By using the stochastic self-consistent harmonic approximation, we investigate the anharmonic phonon spectra and the occurrence of a ferroelectric transition in both systems. We find that vibrational spectra strongly depend on the approximation used for the exchange-correlation kernel in density-functional theory. If gradient corrections and the theoretical volume are employed, then the calculation of the phonon frequencies as obtained from the diagonalization of the free-energy Hessian leads to phonon spectra in good agreement with experimental data for both systems. In PbTe we evaluate the linear thermal expansion coefficient γ =2.3 ×10-5K-1 , finding it to be in good agreement with experimental value of γ =2.04 ×10-5K-1 . Furthermore, we study the phonon spectrum and we do reproduce the transverse optical mode phonon satellite detected in inelastic neutron scattering and the crossing between the transverse optical and the longitudinal acoustic modes along the Γ X direction. The phonon satellite becomes broader at high temperatures but its energy is essentially temperature independent, in agreement with experiments. We decompose the self-consistent harmonic free energy in second-, third-, and fourth-order anharmonic terms. We find that the third- and fourth-order terms are small. However, treating the third-order term perturbatively on top of the second-order self-consistent harmonic free energy overestimates the energy of the satellite associated with the transverse optical mode. On the contrary, a perturbative treatment on top of the harmonic Hamiltonian breaks down and leads to imaginary phonon frequencies already at 300 K. In the case of SnTe, we describe the occurrence of a ferroelectric transition from the high-temperature F m 3 ¯m structure to the low-temperature R 3 m one. The transition temperature is, however, underestimated with respect to the experimental one. No satellites are present in the SnTe phonon spectra despite a not negligible anharmonic broadening of the zone-center TO mode.

Effects of temperature and particles on nitrification in a eutrophic coastal bay in southern China

NASA Astrophysics Data System (ADS)

Zheng, Zhen-Zhen; Wan, Xianhui; Xu, Min Nina; Hsiao, Silver Sung-Yun; Zhang, Yao; Zheng, Li-Wei; Wu, Yanhua; Zou, Wenbin; Kao, Shuh-Ji

2017-09-01

Despite being the only link between reduced and oxidized nitrogen, the impact of environmental factors on nitrification, temperature and particles, in particular, remains unclear for coastal zones. By using the 15NH4+-labeling technique, we determined nitrification rates in bulk (NTRB) and free-living (NTRF, after removing particles >3 μm) for water samples with varying particle concentrations (as sampled at different tidal stages) during autumn, winter, and summer in a eutrophic coastal bay in southern China. The highest NTRB occurred in autumn, when particle concentrations were highest. In general, particle-associated nitrification rates (NTRP, >3 μm) were higher than NTRF and increased with particle abundance. Regardless of seasonally distinctive temperature and particle concentrations, nitrification exhibited consistent temperature dependence in all cases (including bulk, particle-associated, and free-living) with a Q10 value of 2.2. Meanwhile, the optimum temperature for NTRP was 29°C, 5°C higher than that for NTRF although the causes for such a difference remained unclear. Strong temperature dependence and particle association suggest that nitrification is sensitive to temperature change (seasonality and global warming) and to ocean dynamics (wave and tide). Our results can potentially be applied to biogeochemical models of the nitrogen cycle for future predictions.

Temperature dependent infrared nano-imaging of La0.67Sr0.33MnO3 thin film

NASA Astrophysics Data System (ADS)

Xu, Peng; Huffman, T. J.; Hae Kwak, In; Biswas, Amlan; Qazilbash, M. M.

2018-01-01

We investigate the temperature dependence of infrared properties at nanometer length scales in La0.67Sr0.33MnO3 (LSMO) thin film with a thickness of 47 unit cells grown on SrTiO3 substrate. The infrared nano-imaging experiments were performed using a near-field optical microscope in conjunction with a variable temperature heating stage. The near-field infrared data is consistent with the bulk of the LSMO film undergoing the thermally-driven non-percolative second-order transition from a metallic, ferromagnetic phase to an insulating, paramagnetic phase. We find persistent infrared contrast on the nanoscale that is independent of temperature and which we attribute to two novel phases with different conductivities coexisting in the vicinity of the film-substrate interface. These two coexisting phases at the film-substrate interface do not undergo the metal-insulator transition (MIT) and hence are different from the metallic, ferromagnetic and insulating, paramagnetic phases in the bulk of the film. At temperatures approaching the nominal MIT temperature, repeated scans of the same microscopic area at constant temperature reveal bimodal fluctuation of the near-field infrared amplitude. We interpret this phenomenon as slow, critical fluctuations of the conductivity in the bulk of the LSMO film.

Fatigue life characterization for piezoelectric macrofiber composites

NASA Astrophysics Data System (ADS)

Henslee, Isaac A.; Miller, David A.; Tempero, Tyler

2012-10-01

In an effort to aid the investigation into lightweight and reliable materials for actuator design, a study was developed to characterize the temperature-dependent lifetime performance of a piezoelectric macrofiber composite (MFC). MFCs are thin rectangular patches of polyimide film, epoxy and a single layer of rectangular lead zirconium titanate (PZT) fibers. In this study, the useful life of the MFC is characterized to determine the effect of temperature on the performance of the composite as it is fatigued by cyclic piezoelectric excitation. The test specimen consists of the MFC laminated to a cantilevered stainless steel beam. Beam strain and tip displacement measurements are used as a basis for determining the performance of the MFC as it is cyclically actuated under various operating temperatures. The temperature of the beam laminate is held constant and then cycled to failure, or 250 million cycles, in order to determine the useful life of the MFC over a temperature range from - 15 to 145 °C. The results of the experiments show a strong temperature dependence of the operational life for the MFC. Damage inside the composite was identified through in situ visual inspection and during post-test microstructural observation; however, no degradation in operational performance was identified as it was cyclically actuated up to the point of failure, regardless of temperature or actuation cycle number.

The Effect of Temperature on Faceplate/Core Delamination in Composite/Titanium Sandwich Plates

NASA Technical Reports Server (NTRS)

Liechti, Kenneth M.; Marton, Balazs

2000-01-01

A study was made of the delamination behavior of sandwich beams made of titanium core bonded to face-plates that consisted of carbon fiber reinforced polymer composite. Nominally mode I behavior was considered at 23C and 180C, by making use of a specially reinforced double cantilever (DCB) specimens. The toughness of the bond between the faceplate and the core was determined on the basis of a beam on elastic foundation analysis. The specimen compliance, and toughness were all independent of temperature in these relatively short-term experiments. The fracture mechanism showed temperature dependence, due to the hygrothermal sensitivity of the adhesive.

Flow effects in a vertical CVD reactor

NASA Technical Reports Server (NTRS)

Young, G. W.; Hariharan, S. I.; Carnahan, R.

1992-01-01

A model is presented to simulate the non-Boussinesq flow in a vertical, two-dimensional, chemical vapor deposition reactor under atmospheric pressure. Temperature-dependent conductivity, mass diffusivity, viscosity models, and reactive species mass transfer to the substrate are incorporated. In the limits of small Mach number and small aspect ratio, asymptotic expressions for the flow, temperature, and species fields are developed. Soret diffusion effects are also investigated. Analytical solutions predict an inverse relationship between temperature field and concentration field due to Soret effects. This finding is consistent with numerical simulations, assisting in the understanding of the complex interactions amongst the flow, thermal, and species fields in a chemically reacting system.

When the Heat Is On: The Effect of Temperature on Voter Behavior in Presidential Elections

PubMed Central

Van Assche, Jasper; Van Hiel, Alain; Stadeus, Jonas; Bushman, Brad J.; De Cremer, David; Roets, Arne

2017-01-01

Hot temperatures lead to heightened arousal. According to excitation transfer theory, arousal can increase both antisocial and prosocial behavior, depending on the context. Although many studies have shown that hot temperatures can increase antisocial behavior, very few studies have investigated the relationship between temperature and prosocial behavior. One important prosocial behavior is voting. We analyzed state-level data from the United States presidential elections (N = 761). Consistent with excitation transfer theory, which proposes that heat-induced arousal can transfer to other activities and strengthen those activities, changes in temperature and voter turnout were positively related. Moreover, a positive change in temperature was related to a positive change in votes for the incumbent party. These findings add to the literature on the importance of non-ideological and non-rational factors that influence voting behavior. PMID:28642723

When the Heat Is On: The Effect of Temperature on Voter Behavior in Presidential Elections.

PubMed

Van Assche, Jasper; Van Hiel, Alain; Stadeus, Jonas; Bushman, Brad J; De Cremer, David; Roets, Arne

2017-01-01

Hot temperatures lead to heightened arousal. According to excitation transfer theory, arousal can increase both antisocial and prosocial behavior, depending on the context. Although many studies have shown that hot temperatures can increase antisocial behavior, very few studies have investigated the relationship between temperature and prosocial behavior. One important prosocial behavior is voting. We analyzed state-level data from the United States presidential elections ( N = 761). Consistent with excitation transfer theory, which proposes that heat-induced arousal can transfer to other activities and strengthen those activities, changes in temperature and voter turnout were positively related. Moreover, a positive change in temperature was related to a positive change in votes for the incumbent party. These findings add to the literature on the importance of non-ideological and non-rational factors that influence voting behavior.

Effects of Cd vacancies and unconventional spin dynamics in the Dirac semimetal Cd3As2

NASA Astrophysics Data System (ADS)

Koumoulis, Dimitrios; Taylor, Robert E.; McCormick, Jeffrey; Ertas, Yavuz N.; Pan, Lei; Che, Xiaoyu; Wang, Kang L.; Bouchard, Louis-S.

2017-08-01

Cd3As2 is a Dirac semimetal that is a 3D analog of graphene. We investigated the local structure and nuclear-spin dynamics in Cd3As2 via 113Cd NMR. The wideline spectrum of the static sample at 295 K is asymmetric and its features are well described by a two-site model with the shielding parameters extracted via Herzfeld-Berger analysis of the magic-angle spinning spectrum. Surprisingly, the 113Cd spin-lattice relaxation time (T1) is extremely long (T1 = 95 s at 295 K), in stark contrast to conductors and the effects of native defects upon semiconductors; but it is similar to that of 13C in graphene (T1 = 110 s). The temperature dependence of 1/T1 revealed a complex bipartite mechanism that included a T2 power-law behavior below 330 K and a thermally activated process above 330 K. In the high-temperature regime, the Arrhenius behavior is consistent with a field-dependent Cd atomic hopping relaxation process. At low temperatures, a T2 behavior consistent with a spin-1/2 Raman-like process provides evidence of a time-dependent spin-rotation magnetic field caused by angular oscillations of internuclear vectors due to lattice vibrations. The observed mechanism does not conform to the conventional two-band model of semimetals, but is instead closer to a mechanism observed in high-Z element ionic solids with large magnetorotation constant [A. J. Vega et al., Phys. Rev. B 74, 214420 (2006)].

Impact of Langmuir Turbulence on Upper Ocean Response to Hurricane Edouard: Model and Observations

NASA Astrophysics Data System (ADS)

Blair, A.; Ginis, I.; Hara, T.; Ulhorn, E.

2017-12-01

Tropical cyclone intensity is strongly affected by the air-sea heat flux beneath the storm. When strong storm winds enhance upper ocean turbulent mixing and entrainment of colder water from below the thermocline, the resulting sea surface temperature cooling may reduce the heat flux to the storm and weaken the storm. Recent studies suggest that this upper ocean turbulence is strongly affected by different sea states (Langmuir turbulence), which are highly complex and variable in tropical cyclone conditions. In this study, the upper ocean response under Hurricane Edouard (2014) is investigated using a coupled ocean-wave model with and without an explicit sea state dependent Langmuir turbulence parameterization. The results are compared with in situ observations of sea surface temperature and mixed layer depth from AXBTs, as well as satellite sea surface temperature observations. Overall, the model results of mixed layer deepening and sea surface temperature cooling under and behind the storm are consistent with observations. The model results show that the effects of sea state dependent Langmuir turbulence can be significant, particularly on the mixed layer depth evolution. Although available observations are not sufficient to confirm such effects, some observed trends suggest that the sea state dependent parameterization might be more accurate than the traditional (sea state independent) parameterization.

Low temperature structural and transport studies of La{sub 0.175}Pr{sub 0.45}Ca{sub 0.375}MnO{sub 3-δ}

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

Sharma, Shivani; Shahee, Aga; Singh, Kiran

2016-05-23

The temperature (T) dependent x-ray diffraction (XRD) and resistivity measurements of La{sub 0.175}Pr{sub 0.45}Ca{sub 0.375}MnO{sub 3-δ} (LPCMO) have been performed down to 2 K to understand the structural and transport properties. From room temperature down to 220 K, LPCMO exists in orthorhombic phase with Pnma structure and at T~220 K, it transforms to charge ordered (CO) monoclinic phase with P2{sub 1}/m structure and remains as it is down to 2 K. The CO phase is evident from the occurrence of weak but well defined superlattice peaks in the XRD pattern. This structural transformation is of first order in nature asmore » evident from the phase coexistence across the transition region. These results thus clearly illustrate that LPCMO undergoes a first order structural phase transition from charge disordered orthorhombic phase to CO monoclinic phase at ~220 K, consistent with temperature dependent resistivity results. Our structural analysis of T dependent XRD data using Rietveld refinement infers that below 220 K, LPCMO forms commensurate CO monoclinic P2{sub 1}/m structure with four times structural modulation.« 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

Mechanisms of Thermosensation in TRP Channels

NASA Astrophysics Data System (ADS)

Talavera, Karel; Voets, Thomas; Nilius, Bernd

The transient receptor potential (TRP) superfamily encompasses a large number of cationic channels that are modulated by a wide variety of physical and chemical stimuli. A notorious subgroup of TRP channels, dubbed thermoTRPs, shows a dramatic dependence on temperature, which can be up to tenfold higher than that of classical ionic channels. Consequently, some thermoTRPs are thought to have a prominent role in the mechanisms of thermosensation and thermoregulation. However, the mechanisms underlying the high temperature sensitivity of thermoTRP activation are, for the most part, obscure. Only four out of the nine thermoTRPs known so far are sufficiently well characterised to allow a comprehensive model to be put forward. Temperature modulates the gating of TRPM8, TRPV1, TRPM4 and TRPM5 by shifting the voltage dependence of channel activation towards more negative potentials, which can be accounted for by a model in which voltage-dependent gating is directly affected by temperature. Heat activation of TRPV3 seems to be consistent with this mechanism, although a modification of the pore may also take place. For TRPV4, it has been proposed that an, as yet unidentified, diffusible ligand mediates activation by heat. The mechanisms for TRPV2, TRPA1 and TRPM2 are still unknown.

Deformation modeling and constitutive modeling for anisotropic superalloys

NASA Technical Reports Server (NTRS)

Milligan, Walter W.; Antolovich, Stephen D.

1989-01-01

A study of deformation mechanisms in the single crystal superalloy PWA 1480 was conducted. Monotonic and cyclic tests were conducted from 20 to 1093 C. Both (001) and near-(123) crystals were tested, at strain rates of 0.5 and 50 percent/minute. The deformation behavior could be grouped into two temperature regimes: low temperatures, below 760 C; and high temperatures, above 820 to 950 C depending on the strain rate. At low temperatures, the mechanical behavior was very anisotropic. An orientation dependent CRSS, a tension-compression asymmetry, and anisotropic strain hardening were all observed. The material was deformed by planar octahedral slip. The anisotropic properties were correlated with the ease of cube cross-slip, as well as the number of active slip systems. At high temperatures, the material was isotropic, and deformed by homogeneous gamma by-pass. It was found that the temperature dependence of the formation of superlattice-intrinsic stacking faults was responsible for the local minimum in the CRSS of this alloy at 400 C. It was proposed that the cube cross-slip process must be reversible. This was used to explain the reversible tension-compression asymmetry, and was used to study models of cross-slip. As a result, the cross-slip model proposed by Paidar, Pope and Vitek was found to be consistent with the proposed slip reversibility. The results were related to anisotropic viscoplastic constitutive models. The model proposed by Walter and Jordan was found to be capable of modeling all aspects of the material anisotropy. Temperature and strain rate boundaries for the model were proposed, and guidelines for numerical experiments were proposed.

Iterative matrix algorithm for high precision temperature and force decoupling in multi-parameter FBG sensing.

PubMed

Hopf, Barbara; Dutz, Franz J; Bosselmann, Thomas; Willsch, Michael; Koch, Alexander W; Roths, Johannes

2018-04-30

A new iterative matrix algorithm has been applied to improve the precision of temperature and force decoupling in multi-parameter FBG sensing. For the first time, this evaluation technique allows the integration of nonlinearities in the sensor's temperature characteristic and the temperature dependence of the sensor's force sensitivity. Applied to a sensor cable consisting of two FBGs in fibers with 80 µm and 125 µm cladding diameter installed in a 7 m-long coiled PEEK capillary, this technique significantly reduced the uncertainties in friction-compensated temperature measurements. In the presence of high friction-induced forces of up to 1.6 N the uncertainties in temperature evaluation were reduced from several degrees Celsius if using a standard linear matrix approach to less than 0.5°C if using the iterative matrix approach in an extended temperature range between -35°C and 125°C.

Robust tunability of magnetoresistance in half-Heusler R PtBi ( R = Gd , Dy, Tm, and Lu) compounds

DOE PAGES

Mun, Eundeok; Bud'ko, Sergey L.; Canfield, Paul C.

2016-03-15

We present the magnetic field dependencies of transport properties for RPtBi ( R = Gd, Dy, Tm, and Lu) half-Heusler compounds. Temperature- and field-dependent resistivity measurements of high-quality RPtBi single crystals reveal an unusually large, nonsaturating magnetoresistance (MR) up to 300 K under a moderate magnetic field of H = 140 kOe. At 300 K, the large MR effect decreases as the rare earth is traversed from Gd to Lu and the magnetic field dependence of MR shows a deviation from the conventional H2 behavior. The Hall coefficient ( RH) for R = Gd indicates a sign change around 120more » K, whereas RH curves for R = Dy, Tm, and Lu remain positive for all measured temperatures. At 300 K, the Hall resistivity reveals a deviation from the linear field dependence for all compounds. Thermoelectric power measurements on this family show strong temperature and magnetic field dependencies which are consistent with resistivity measurements. A highly enhanced thermoelectric power under applied magnetic field is observed as high as ~100 μV/K at 140 kOe. Furthermore, analysis of the transport data in this series reveals that the rare-earth-based half-Heusler compounds provide opportunities to tune MR effect through lanthanide contraction and to elucidate the mechanism of nontrivial MR.« less

High temperature electromagnetic characterization of thermal protection system tile materials

NASA Technical Reports Server (NTRS)

Heil, Garrett G.

1993-01-01

This study investigated the impact of elevated temperatures on the electromagnetic performance of the LI-2200 thermal protection system. A 15-kilowatt CO2 laser was used to heat an LI-2200 specimen to 3000 F while electromagnetic measurements were performed over the frequency range of l9 to 21 GHz. The electromagnetic measurement system consisted of two Dual-Lens Spot-Focusing (DLSF) antennas, a sample support structure, and an HP-8510B vector network analyzer. Calibration of the electromagnetic system was accomplished with a Transmission-Reflection-Line (TRL) procedure and was verified with measurements on a two-layer specimen of known properties. The results of testing indicated that the LI-2200 system's electromagnetic performance is slightly temperature dependent at temperatures up to 3000 F.

Isochoric Burn, an Internally Consistent Method for the Reactant to Product Transformation in Reactive Flow

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

Reaugh, J E; Lee, E L

2002-07-01

Mixture rules for partially reacted explosives differ amongst various models. For instance, JWL++ uses a partial pressure addition to compute an average zonal pressure, Ignition and Growth requires pressure equilibration and thermal equilibration of temperature dependent JWL EOSs, CHEETAH In Line RF also assumes temperature and pressure equilibration. It has been suggested in the past that a more realistic equilibration scheme should comprise isentropic pressure equilibration of the separate reacted and unreacted phases. This turns out not to be a proper path for equilibration. Rather, we find that the only internally consistent method is the evaluation of the equilibrium pressuremore » that satisfies the particular conditions of reactant and product resulting from deflagration in a fixed volume.« less

Low-temperature mechanical properties of superconducting radio frequency cavity materials

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

Byun, Thak Sang; Kim, Sang-Ho; Mammosser, John

2009-01-01

Low temperature mechanical behaviors have been investigated for the constituent materials of superconducting radio frequency cavities. Test materials consist of small grain Nb, single crystal Nb, large grain Nb (bicrystal), Ti45Nb-Nb weld joint (e-beam welded), and Ti-316L bimetal joint (explosion welded). The strength of all test metals displayed strong temperature dependence and the Ti-316L bimetal showed the highest strength and lowest ductility among the test materials. The fracture toughness of the small grain Nb metals decreased with decreasing test temperature and reached the lower shelf values (30 40 MPa m) at or above 173 K. The Ti45Nb base and Ti45Nb-Nbmore » weld metals showed much higher fracture toughness than the small grain Nb. An extrapolation and comparison with existing data showed that the fracture toughness of the small grain Nb metals at 4 K was expected to be similar to those at 173 K and 77 K. The results from optical photography at a low magnification and fractography by a scanning electron microscope were consistent with corresponding mechanical properties.« less

Growth of pentacene on α -Al2O3 (0001) studied by in situ optical spectroscopy

NASA Astrophysics Data System (ADS)

Zhang, Lei; Fu, X.; Hohage, M.; Zeppenfeld, P.; Sun, L. D.

2017-09-01

The growth of pentacene thin films on a sapphire α -Al2O3 (0001) surface was investigated in situ using differential reflectance spectroscopy (DRS). Two different film structures are observed depending on the substrate temperature. If pentacene is deposited at room temperature, a wetting layer consisting of flat-lying molecules is formed after which upright-standing molecular layers with a herringbone structure start to grow. At low substrate temperature of 100 K, the long molecular axis of the pentacene molecules remains parallel to the surface plane throughout the entire growth regime up to rather large thicknesses. Heating thin films deposited at 100 K to room temperature causes the pentacene molecules beyond the wetting layer to stand up and assemble into a herringbone structure. Another interesting observation is the dewetting of the first flat-lying monolayer upon exposure to air, leading to the condensation of islands consisting of upright-standing molecules. Our results emphasize the interplay between growth kinetics and thermodynamics and its influence on the molecular orientation in organic thin films.

Electrode effects in dielectric spectroscopy measurements on (Nb+In) co-doped TiO2

NASA Astrophysics Data System (ADS)

Crandles, D. A.; Yee, S. M. M.; Savinov, M.; Nuzhnyy, D.; Petzelt, J.; Kamba, S.; Prokeš, J.

2016-04-01

Recently, several papers reported the discovery of giant permittivity and low dielectric loss in (Nb+In) co-doped TiO2. A series of tests was performed which included the measurement of the frequency dependence of the dielectric permittivity and alternating current (ac) conductivity of co-doped (Nb+In)TiO2 as a function of electrode type, sample thickness, and temperature. The data suggest that the measurements are strongly affected by the electrodes. The consistency between four-contact van der Pauw direct current conductivity measurements and bulk conductivity values extracted from two-contact ac conductivity measurements suggest that the values of colossal permittivity are, at least in part, a result of Schottky barrier depletion widths that depend on electrode type and temperature.

Electrode effects in dielectric spectroscopy measurements on (Nb +In) co-doped TiO2

NASA Astrophysics Data System (ADS)

Crandles, David; Yee, Susan; Savinov, Maxim; Nuzhnyy, Dimitri; Petzelt, Jan; Kamba, Stanislav; Prokes, Jan

Recently, several papers reported the discovery of giant permittivity and low dielectric loss in (Nb+In) co-doped TiO2. A series of tests was performed which included the measurement of the frequency dependence of the dielectric permittivity and ac conductivity of co-doped (Nb+In)TiO2 as a function of electrode type, sample thickness and temperature. The data suggest that the measurements are strongly affected by the electrodes. The consistency between four contact van der Pauw dc conductivity measurements and bulk conductivity values extracted from two contact ac conductivity measurements suggest that the values of colossal permittivity are, at least in part, a result of Schottky barrier depletion widths that depend on electrode type and temperature. Nserc, Czech Science Foundation (Project 15-08389S).

Time-Dependent Hartree-Fock Approach to Nuclear Pasta at Finite Temperature

NASA Astrophysics Data System (ADS)

Schuetrumpf, B.; Klatt, M. A.; Iida, K.; Maruhn, J. A.; Mecke, K.; Reinhard, P.-G.

2013-03-01

We present simulations of neutron-rich matter at subnuclear densities, like supernova matter, with the time-dependent Hartree-Fock approximation at temperatures of several MeV. The initial state consists of α particles randomly distributed in space that have a Maxwell-Boltzmann distribution in momentum space. Adding a neutron background initialized with Fermi distributed plane waves the calculations reflect a reasonable approximation of astrophysical matter. This matter evolves into spherical, rod-like, and slab-like shapes and mixtures thereof. The simulations employ a full Skyrme interaction in a periodic three-dimensional grid. By an improved morphological analysis based on Minkowski functionals, all eight pasta shapes can be uniquely identified by the sign of only two valuations, namely the Euler characteristic and the integral mean curvature.

[Bioacoustic of the advertisement call of Ceratophrys cranwelli (Anura: Ceratophryidae)].

PubMed

Valetti, Julián Alonso; Salas, Nancy Edith; Martino, Adolfo Ludovico

2013-03-01

The advertisement call plays an important role in the life history of anuran amphibians, mainly during the breeding season. Call features represent an important character to discriminate species, and sound emissions are very effective to assure or reinforce genetic incompatibility, especially in the case of sibling species. Since frogs are ectotherms, acoustic properties of their calls will vary with temperature. In this study, we described the advertisement call of C. cranwelli, quantifying the temperature effect on its components. The acoustic emissions were recorded during 2007 using a DAT record Sony TCD-100 with stereo microphone ECM-MS907 Sony and tape TDK DAT-RGX 60. As males emit their calls floating in temporary ponds, water temperatures were registered after recording the advertisement calls with a digital thermometer TES 1300+/-0.1 degreeC. Altogether, 54 calls from 18 males were analyzed. The temporal variables of each advertisement call were measured using oscillograms and sonograms and the analyses of dominant frequency were performed using a spectrogram. Multiple correlation analysis was used to identify the temperature-dependent acoustic variables and the temperature effect on these variables was quantified using linear regression models. The advertisement call of C. cranwelli consists of a single pulse group. Call duration, Pulse duration and Pulse interval decreased with the temperature, whereas the Pulse rate increased with temperature. The temperature-dependent variables were standardized at 25 degreeC according to the linear regression model obtained. The acoustic variables that were correlated with the temperature are the variables which emissions depend on laryngeal muscles and the temperature constraints the contractile properties of muscles. Our results indicated that temperature explains an important fraction of the variability in some acoustic variables (79% in the Pulse rate), and demonstrated the importance of considering the effect of temperature in acoustic components. The results suggest that acoustic variables show geographic variation to compare data with previous works.

Enhanced thermoelectric transport in modulation-doped GaN/AlGaN core/shell nanowires

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

Song, Erdong; Li, Qiming; Swartzentruber, Brian

2015-11-25

The thermoelectric properties of unintentionally n-doped core GaN/AlGaN core/shell N-face nanowires are reported. We found that the temperature dependence of the electrical conductivity is consistent with thermally activated carriers with two distinctive donor energies. The Seebeck coefficient of GaN/AlGaN nanowires is more than twice as large as that for the GaN nanowires alone. However, an outer layer of GaN deposited onto the GaN/AlGaN core/shell nanowires decreases the Seebeck coefficient at room temperature, while the temperature dependence of the electrical conductivity remains the same. We attribute these observations to the formation of an electron gas channel within the heavily-doped GaN coremore » of the GaN/AlGaN nanowires. The room-temperature thermoelectric power factor for the GaN/AlGaN nanowires can be four times higher than the GaN nanowires. As a result, selective doping in bandgap engineered core/shell nanowires is proposed for enhancing the thermoelectric power.« less

Superconducting and magnetic properties of Sr 3 Ir 4 Sn 13

DOE PAGES

Biswas, P. K.; Amato, A.; Khasanov, R.; ...

2014-10-10

In this research, magnetization and muon spin relaxation or rotation (µSR) measurements have been performed to study the superconducting and magnetic properties of Sr₃Ir₄Sn₁₃. From magnetization measurements the lower and upper critical fields of Sr₃Ir₄Sn₁₃ are found to be 81(1) Oe and 14.4(2) kOe, respectively. Zero-field µSR data show no sign of any magnetic ordering or weak magnetism in Sr₃Ir₄Sn₁₃. Transverse-field µSR measurements in the vortex state provided the temperature dependence of the magnetic penetration depth λ. The dependence of λ⁻² with temperature is consistent with the existence of single s-wave energy gap in the superconducting state of Sr₃Ir₄Sn₁₃ withmore » a gap value of 0.82(2) meV at absolute zero temperature. The magnetic penetration depth at zero temperature λ(0) is 291(3) nm. The ratio Δ(0)/k BT c = 2.1(1) indicates that Sr₃Ir₄Sn₁₃ should be considered as a strong-coupling superconductor.« less

Electroforming and Switching in Oxides of Transition Metals: The Role of Metal Insulator Transition in the Switching Mechanism

NASA Astrophysics Data System (ADS)

Chudnovskii, F. A.; Odynets, L. L.; Pergament, A. L.; Stefanovich, G. B.

1996-02-01

Electroforming and switching effects in sandwich structures based on anodic films of transition metal oxides (V, Nb, Ti, Fe, Ta, W, Zr, Hf, Mo) have been studied. After being electroformed, some materials exhibited current-controlled negative resistance with S-shapedV-Icharacteristics. For V, Fe, Ti, and Nb oxides, the temperature dependences of the threshold voltage have been measured. As the temperature increased,Vthdecreased to zero at a critical temperatureT0, which depended on the film material. Comparison of theT0values with the temperatures of metal-insulator phase transition for some compounds (Tt= 120 K for Fe3O4, 340 K for VO2, ∼500 K for Ti2O3, and 1070 K for NbO2) showed that switching was related to the transition in the applied electric field. Channels consisting of the above-mentioned lower oxides were formed in the initial anodic films during the electroforming. The possibility of formation of these oxides with a metal-insulator transition was confirmed by thermodynamic calculations.

Continuing upward trend in Mt Read Huon pine ring widths - Temperature or divergence?

NASA Astrophysics Data System (ADS)

Allen, K. J.; Cook, E. R.; Buckley, B. M.; Larsen, S. H.; Drew, D. M.; Downes, G. M.; Francey, R. J.; Peterson, M. J.; Baker, P. J.

2014-10-01

To date, no attempt has been made to assess the presence or otherwise of the “Divergence Problem” (DP) in existing multi-millennial Southern Hemisphere tree-ring chronologies. We have updated the iconic Mt Read Huon pine chronology from Tasmania, southeastern Australia, to now include the warmest decade on record, AD 2000-2010, and used the Kalman Filter (KF) to examine it for signs of divergence against four different temperature series available for the region. Ring-width growth for the past two decades is statistically unprecedented for the past 1048 years. Although we have identified a decoupling between temperature and growth in the past two decades, the relationship between some of the temperature records and growth has varied over time since the start of instrumental records. Rather than the special case of ‘divergence', we have identified a more general time-dependence between growth and temperature over the last 100 years. This time-dependence appears particularly problematic at interdecadal time scales. Due to the time-dependent relationships, and uncertainties related to the climate data, the use of any of the individual temperature series examined here potentially complicates temperature reconstruction. Some of the uncertainty in the climate data may be associated with changing climatic conditions, such as the intensification of the sub-tropical ridge (STR) and its impact on the frequency of anticyclonic conditions over the Mt Read site. Increased growth at the site, particularly in the last decade, over and above what would be expected based on a linear temperature model alone, may be consistent with a number of hypotheses. Existing uncertainties in the climate data need to be resolved and independent physiological information obtained before a range of hypotheses for this increased growth can be effectively evaluated.

Orientational ordering of a banana-shaped solute molecule in a nematic calamitic solvent by {sup 2}H-NMR spectroscopy: An indication of glasslike behavior

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

Cinacchi, Giorgio; Domenici, Valentina

The Saupe ordering matrix of a banana-shaped mesogenic molecule as a solute in a common nematic calamitic solvent has been determined by {sup 2}H-NMR spectroscopy as a function of temperature. The temperature dependence of the Saupe ordering matrix element associated with the principal molecular axis is consistent with a glassy behavior in the reorientational motion of this particular solute molecule. The Haller expression, appropriately modified, provides a good fit to the experimental data.

Solid-phase equilibria on Pluto's surface

NASA Astrophysics Data System (ADS)

Tan, Sugata P.; Kargel, Jeffrey S.

2018-03-01

Pluto's surface is covered by volatile ices that are in equilibrium with the atmosphere. Multicomponent phase equilibria may be calculated using a thermodynamic equation of state and, without additional assumptions, result in methane-rich and nitrogen-rich solid phases. The former is formed at temperature range between the atmospheric pressure-dependent sublimation and condensation points, while the latter is formed at temperatures lower than the sublimation point. The results, calculated for the observed 11 μbar atmospheric pressure and composition, are consistent with recent work derived from observations by New Horizons.

Molecular dynamics simulation study of hydrogen bonding in aqueous poly(ethylene oxide) solutions.

PubMed

Smith, G D; Bedrov, D; Borodin, O

2000-12-25

A molecular dynamics simulation study of hydrogen bonding in poly(ethylene oxide) (PEO)/water solutions was performed. PEO-water and water-water hydrogen bonding manifested complex dependence on both composition and temperature. Strong water clustering in concentrated solutions was seen. Saturation of hydrogen bonding at w(p) approximately equal to 0.5 and a dramatic decrease in PEO-water hydrogen bonding with increasing temperature, consistent with experimentally observed closed-loop phase behavior, were observed. Little tendency toward intermolecular bridging of PEO chains by water molecules was seen.

Evidence of Electron-Hole Imbalance in WTe2 from High-Resolution Angle-Resolved Photoemission Spectroscopy

NASA Astrophysics Data System (ADS)

Wang, Chen-Lu; Zhang, Yan; Huang, Jian-Wei; Liu, Guo-Dong; Liang, Ai-Ji; Zhang, Yu-Xiao; Shen, Bing; Liu, Jing; Hu, Cheng; Ding, Ying; Liu, De-Fa; Hu, Yong; He, Shao-Long; Zhao, Lin; Yu, Li; Hu, Jin; Wei, Jiang; Mao, Zhi-Qiang; Shi, You-Guo; Jia, Xiao-Wen; Zhang, Feng-Feng; Zhang, Shen-Jin; Yang, Feng; Wang, Zhi-Min; Peng, Qin-Jun; Xu, Zu-Yan; Chen, Chuang-Tian; Zhou, Xing-Jiang

2017-08-01

WTe2 has attracted a great deal of attention because it exhibits extremely large and nonsaturating magnetoresistance. The underlying origin of such a giant magnetoresistance is still under debate. Utilizing laser-based angle-resolved photoemission spectroscopy with high energy and momentum resolutions, we reveal the complete electronic structure of WTe2. This makes it possible to determine accurately the electron and hole concentrations and their temperature dependence. We find that, with increasing the temperature, the overall electron concentration increases while the total hole concentration decreases. It indicates that the electron-hole compensation, if it exists, can only occur in a narrow temperature range, and in most of the temperature range there is an electron-hole imbalance. Our results are not consistent with the perfect electron-hole compensation picture that is commonly considered to be the cause of the unusual magnetoresistance in WTe2. We identified a flat band near the Brillouin zone center that is close to the Fermi level and exhibits a pronounced temperature dependence. Such a flat band can play an important role in dictating the transport properties of WTe2. Our results provide new insight on understanding the origin of the unusual magnetoresistance in WTe2.

Modeling of surface temperature effects on mixed material migration in NSTX-U

NASA Astrophysics Data System (ADS)

Nichols, J. H.; Jaworski, M. A.; Schmid, K.

2016-10-01

NSTX-U will initially operate with graphite walls, periodically coated with thin lithium films to improve plasma performance. However, the spatial and temporal evolution of these films during and after plasma exposure is poorly understood. The WallDYN global mixed-material surface evolution model has recently been applied to the NSTX-U geometry to simulate the evolution of poloidally inhomogenous mixed C/Li/O plasma-facing surfaces. The WallDYN model couples local erosion and deposition processes with plasma impurity transport in a non-iterative, self-consistent manner that maintains overall material balance. Temperature-dependent sputtering of lithium has been added to WallDYN, utilizing an adatom sputtering model developed from test stand experimental data. Additionally, a simplified temperature-dependent diffusion model has been added to WallDYN so as to capture the intercalation of lithium into a graphite bulk matrix. The sensitivity of global lithium migration patterns to changes in surface temperature magnitude and distribution will be examined. The effect of intra-discharge increases in surface temperature due to plasma heating, such as those observed during NSTX Liquid Lithium Divertor experiments, will also be examined. Work supported by US DOE contract DE-AC02-09CH11466.

The Effect of Specimen Size on the Results of Concrete Adiabatic Temperature Rise Test with Commercially Available Equipment.

PubMed

Lee, Byung Jae; Bang, Jin Wook; Shin, Kyung Joon; Kim, Yun Yong

2014-12-08

In this study, adiabatic temperature rise tests depending on binder type and adiabatic specimen volume were performed, and the maximum adiabatic temperature rises and the reaction factors for each mix proportion were analyzed and suggested. The results indicated that the early strength low heat blended cement mixture had the lowest maximum adiabatic temperature rise ( Q ∞ ) and the ternary blended cement mixture had the lowest reaction factor ( r ). Also, Q and r varied depending on the adiabatic specimen volume even when the tests were conducted with a calorimeter, which satisfies the recommendations for adiabatic conditions. Test results show a correlation: the measurements from the 50 L specimens were consistently higher than those from the 6 L specimens. However, the Q ∞ and r values of the 30 L specimen were similar to those of the 50 L specimen. Based on the above correlation, the adiabatic temperature rise of the 50 L specimen could be predicted using the results of the 6 L and 30 L specimens. Therefore, it is thought that this correlation can be used for on-site concrete quality control and basic research.

Resource Supply Overrides Temperature as a Controlling Factor of Marine Phytoplankton Growth

PubMed Central

Marañón, Emilio; Cermeño, Pedro; Huete-Ortega, María; López-Sandoval, Daffne C.; Mouriño-Carballido, Beatriz; Rodríguez-Ramos, Tamara

2014-01-01

The universal temperature dependence of metabolic rates has been used to predict how ocean biology will respond to ocean warming. Determining the temperature sensitivity of phytoplankton metabolism and growth is of special importance because this group of organisms is responsible for nearly half of global primary production, sustains most marine food webs, and contributes to regulate the exchange of CO2 between the ocean and the atmosphere. Phytoplankton growth rates increase with temperature under optimal growth conditions in the laboratory, but it is unclear whether the same degree of temperature dependence exists in nature, where resources are often limiting. Here we use concurrent measurements of phytoplankton biomass and carbon fixation rates in polar, temperate and tropical regions to determine the role of temperature and resource supply in controlling the large-scale variability of in situ metabolic rates. We identify a biogeographic pattern in phytoplankton metabolic rates, which increase from the oligotrophic subtropical gyres to temperate regions and then coastal waters. Variability in phytoplankton growth is driven by changes in resource supply and appears to be independent of seawater temperature. The lack of temperature sensitivity of realized phytoplankton growth is consistent with the limited applicability of Arrhenius enzymatic kinetics when substrate concentrations are low. Our results suggest that, due to widespread resource limitation in the ocean, the direct effect of sea surface warming upon phytoplankton growth and productivity may be smaller than anticipated. PMID:24921945

Development of numerical model for predicting heat generation and temperatures in MSW landfills.

PubMed

Hanson, James L; Yeşiller, Nazli; Onnen, Michael T; Liu, Wei-Lien; Oettle, Nicolas K; Marinos, Janelle A

2013-10-01

A numerical modeling approach has been developed for predicting temperatures in municipal solid waste landfills. Model formulation and details of boundary conditions are described. Model performance was evaluated using field data from a landfill in Michigan, USA. The numerical approach was based on finite element analysis incorporating transient conductive heat transfer. Heat generation functions representing decomposition of wastes were empirically developed and incorporated to the formulation. Thermal properties of materials were determined using experimental testing, field observations, and data reported in literature. The boundary conditions consisted of seasonal temperature cycles at the ground surface and constant temperatures at the far-field boundary. Heat generation functions were developed sequentially using varying degrees of conceptual complexity in modeling. First a step-function was developed to represent initial (aerobic) and residual (anaerobic) conditions. Second, an exponential growth-decay function was established. Third, the function was scaled for temperature dependency. Finally, an energy-expended function was developed to simulate heat generation with waste age as a function of temperature. Results are presented and compared to field data for the temperature-dependent growth-decay functions. The formulations developed can be used for prediction of temperatures within various components of landfill systems (liner, waste mass, cover, and surrounding subgrade), determination of frost depths, and determination of heat gain due to decomposition of wastes. Copyright © 2013 Elsevier Ltd. All rights reserved.

Role of rheology in reconstructing slab morphology in global mantle models

NASA Astrophysics Data System (ADS)

Bello, Léa; Coltice, Nicolas; Tackley, Paul; Müller, Dietmar

2015-04-01

Reconstructing the 3D structure of the Earth's mantle has been a challenge for geodynamicists for about 40 years. Although numerical models and computational capabilities have incredibly progressed, parameterizations used for modeling convection forced by plate motions are far from being Earth-like. Among the set of parameters, rheology is fundamental because it defines in a non-linear way the dynamics of slabs and plumes, and the organization of the lithosphere. Previous studies have employed diverse viscosity laws, most of them being temperature and depth dependent with relatively small viscosity contrasts. In this study, we evaluate the role of the temperature dependence of viscosity (variations up to 6 orders of magnitude) on reconstructing slab evolution in 3D spherical models of convection driven by plate history models. We also investigate the importance of pseudo-plasticity in such models. We show that strong temperature dependence of viscosity combined with pseudo-plasticity produce laterally and vertically continuous slabs, and flat subduction where trench retreat is fast (North, Central and South America). Moreover, pseudo-plasticity allows a consistent coupling between imposed plate motions and global convection, which is not possible with temperature-dependent viscosity only. However, even our most sophisticated model is not able to reproduce unambiguously stagnant slabs probably because of the simplicity of material properties we use here. The differences between models employing different viscosity laws are very large, larger than the differences between two models with the same rheology but using two different plate reconstructions or initial conditions.

Water vapor self-continuum absorption measurements in the 4.0 and 2.1 μm transparency windows

NASA Astrophysics Data System (ADS)

Richard, L.; Vasilchenko, S.; Mondelain, D.; Ventrillard, I.; Romanini, D.; Campargue, A.

2017-11-01

In a recent contribution [A. Campargue, S. Kassi, D. Mondelain, S. Vasilchenko, D. Romanini, Accurate laboratory determination of the near infrared water vapor self-continuum: A test of the MT_CKD model. J. Geophys. Res. Atmos., 121,13,180-13,203, doi:10.1002/2016JD025531], we reported accurate water vapor absorption continuum measurements by Cavity Ring-down Spectroscopy (CRDS) and Optical-Feedback-Cavity Enhanced Absorption Spectroscopy (OF-CEAS) at selected spectral points of 4 near infrared transparency windows. In the present work, the self-continuum cross-sections, CS, are determined for two new spectral points. The 2491 cm-1 spectral point in the region of maximum transparency of the 4.0 μm window was measured by OF-CEAS in the 23-52 °C temperature range. The 4435 cm-1 spectral point of the 2.1 μm window was measured by CRDS at room temperature. The self-continuum cross-sections were determined from the pressure squared dependence of the continuum absorption. Comparison to the literature shows a reasonable agreement with 1970 s and 1980 s measurements using a grating spectrograph in the 4.0 μm window and a very good consistency with our previous laser measurements in the 2.1 μm window. For both studied spectral points, our values are much smaller than previous room temperature measurements by Fourier Transform Spectroscopy. Significant deviations (up to about a factor 4) are noted compared to the widely used semi empirical MT_CKD model of the absorption continuum. The measured temperature dependence at 2491 cm-1 is consistent with previous high temperature measurements in the 4.0 μm window and follows an exp(D0/kT) law, D0 being the dissociation energy of the water dimer.

Long term evolution of temperature in the venus upper atmosphere at the evening and morning terminators

NASA Astrophysics Data System (ADS)

Krause, P.; Sornig, M.; Wischnewski, C.; Kostiuk, T.; Livengood, T. A.; Herrmann, M.; Sonnabend, G.; Stangier, T.; Wiegand, M.; Pätzold, M.; Mahieux, A.; Vandaele, A. C.; Piccialli, A.; Montmessin, F.

2018-01-01

This paper contains a comprehensive dataset of long-term observations between 2009 and 2015 at the upper mesosphere/lower thermosphere providing temperature values at different locations of the morning and evening side of the terminator of Venus. Temperature information is obtained by line-resolved spectroscopy of Doppler broadened CO2 transitions features. Results are restricted to a pressure level of 1 μbar, ∼110 km altitude due the nature of the addressed non-LTE CO2 emission line at 10 μm. The required high spectral resolution of the instrumentation is provided by the ground-based spectrometers THIS (University of Cologne) and HIPWAC (NASA GSFC). For the first time upper mesosphere/lower thermosphere temperatures at the Venusian terminator derived from IR-het spectroscopy between 2009 and 2015 are investigated in order to clarify the local-time dependences, latitudinal dependences and the long-term trend. Measured temperatures were distributed in the range between 140 K and 240 K, with mean values equal to 199 K ± 17 K for the morning side of the terminator and 195 K ± 19 K for the evening side of the terminator. Within the uncertainty no difference between the averaged morning and evening terminator side temperature is found. In addition, no strong latitudinal dependency is observed at these near terminator local times. In contrast IR-het data from 2009 show a strong latitudinal dependency at noon, with a temperature difference of around 60 K between the equatorial and polar region (Sonnabend et al., 2012). Accord with the instruments of the Venus Express mission a northern-southern hemispherical symmetry is observed (Mahieux et al., 2012; Piccialli et al., 2015). The data shows no consistent long-term temperature trend throughout the six years of observation, but a variability in the order of tens of Kelvin for the different observing runs representing a time step of few month to two years. This is about the same order of magnitude as the variability within a single run with a typically time range of 2-10 days. This variation is not connected to the solar cycle. Sub-millimeter observations by Clancy et al. found a relation between temperatures and long-term variation in mesospheric water vapor, SO2, and sulfate aerosols (Clancy and Muhleman, 1991; Clancy et al., 2012). SO2 column densities observed by SOIR at the terminator are fairly stable over the time period of 2006-2011 (Mahieux et al., 2015), supporting the hypothesis of a relation between SO2 and temperature variations. The temperatures derived from the infrared heterodyne spectroscopy (IR-het) are compared to results from the Venus Express space mission (VEx). A consistence with the temperatures from the VEx instruments SOIR, VIRTIS and SPICAV is found. As the instruments probe different local time, SPICAV probes the pure nightside, SOIR across the terminator and IR-het the pure dayside atmosphere it is not surprising that the IR-het temperatures are mostly on the warmer side compared to results from SPICAV and SOIR.

Temperature-Dependent Growth Modeling of Environmental and Clinical Legionella pneumophila Multilocus Variable-Number Tandem-Repeat Analysis (MLVA) Genotypes

PubMed Central

Sharaby, Yehonatan; Rodríguez-Martínez, Sarah; Oks, Olga; Pecellin, Marina; Mizrahi, Hila; Peretz, Avi; Brettar, Ingrid; Höfle, Manfred G.

2017-01-01

ABSTRACT Legionella pneumophila causes waterborne infections resulting in severe pneumonia. High-resolution genotyping of L. pneumophila isolates can be achieved by multiple-locus variable-number tandem-repeat analysis (MLVA). Recently, we found that different MLVA genotypes of L. pneumophila dominated different sites in a small drinking-water network, with a genotype-related temperature and abundance regime. The present study focuses on understanding the temperature-dependent growth kinetics of the genotypes that dominated the water network. Our aim was to model mathematically the influence of temperature on the growth kinetics of different environmental and clinical L. pneumophila genotypes and to compare it with the influence of their ecological niches. Environmental strains showed a distinct temperature preference, with significant differences among the growth kinetics of the three studied genotypes (Gt4, Gt6, and Gt15). Gt4 strains exhibited superior growth at lower temperatures (25 and 30°C), while Gt15 strains appeared to be best adapted to relatively higher temperatures (42 and 45°C). The temperature-dependent growth traits of the environmental genotypes were consistent with their distribution and temperature preferences in the water network. Clinical isolates exhibited significantly higher growth rates and reached higher maximal cell densities at 37°C and 42°C than the environmental strains. Further research on the growth preferences of L. pneumophila clinical and environmental genotypes will result in a better understanding of their ecological niches in drinking-water systems as well as in the human body. IMPORTANCE Legionella pneumophila is a waterborne pathogen that threatens humans in developed countries. The bacteria inhabit natural and man-made freshwater environments. Here we demonstrate that different environmental L. pneumophila genotypes have different temperature-dependent growth kinetics. Moreover, Legionella strains that belong to the same species but were isolated from environmental and clinical sources possess adaptations for growth at different temperatures. These growth preferences may influence the bacterial colonization at specific ecological niches within the drinking-water network. Adaptations for growth at human body temperatures may facilitate the abilities of some L. pneumophila strains to infect and cause illness in humans. Our findings may be used as a tool to improve Legionella monitoring in drinking-water networks. Risk assessment models for predicting the risk of legionellosis should take into account not only Legionella concentrations but also the temperature-dependent growth kinetics of the isolates. PMID:28159784

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 animals. We suggest that maternal thermoregulatory behaviour in marine turtles, and many other reptiles, is consistent with a strategy of adaptively increasing body temperatures to accelerate egg maturation. © 2011 The Authors. Journal of Animal Ecology © 2011 British Ecological Society.

Assessing trait-based scaling theory in tropical and temperate forests spanning a broad temperature gradients

NASA Astrophysics Data System (ADS)

Enquist, B. J.

2017-12-01

Tropical and temperate elevation gradients are natural laboratories to assess how changing climate can influence tropical forests. However, there is a need for theory and integrated data collection to scale from traits to ecosystems. We assess predictions of a novel trait-based metabolic scaling theory including whether observed shifts in forest traits across a broad tropical temperature gradient is consistent with local phenotypic optima and adaptive compensation for temperature. We tested a new anaytical theory - Trait Driver Theory - that is capable of scaling from traits to entire stands and ecosystems across several elevation gradients spanning 3300m. Each gradient consists of thousands of tropical and temperate tree trait measures taken from forest plots. In several of these plots, in particular in southern Perú, gross and net primary productivity (GPP and NPP) were measured. We measured multiple traits linked to variation in tree growth and assessed their frequency distributions within and across the elevation gradient. We paired these trait measures across individuals within forests with simultaneous measures of ecosystem net and gross primary productivity. Consistent with theory, variation in forest NPP and GPP primarily scaled with forest biomass but the secondary effect of temperature on productivity was much less than expected. This weak temperature dependency appears to reflect directional shifts in several mean community traits that underlie tree growth with decreases in site temperature. The observed shift in traits of trees that dominant more cold environments appear to reflect `adaptive/acclimatory' compensation for the kinetic effects of temperature on leaf photosynthesis and tree growth. Forest trait distributions across the gradient showed peaked and skewed distributions, consistent with the importance of local filtering of optimal growth traits and recent shifts in species composition and dominance due to warming from climate change. Trait-based metabolic scaling theory provides a basis to predict how shifts in climate have and will influence the trait composition and ecosystem functioning of temperate and tropical forests.

Influence of deep level intrinsic defects on the carrier transport in p-type Hg1- xCdxTe

NASA Astrophysics Data System (ADS)

Hoerstel, W.; Klimakow, A.; Kramer, R.

1990-04-01

The magnetic field dependence of the Hall effect in p-type Hg1- xCdxTe is analysed for determining the carrier densities and their mobilities in the mixed conduction range T = 70-250 K. A consistent description of the temperature dependence of the concentrations and mobilities of electrons and holes succeeds by taking into account energy-dependent momentum scattering times in the transport coefficients. Using this formalism, an energy level near 0.7 Eg above the valence band edge caused by intrinsic defects which were influenced by thermal treament is determined and discussed.

Water temperature of streams in the Cook Inlet basin, Alaska, and implications of climate change

USGS Publications Warehouse

Kyle, Rebecca E.; Brabets, Timothy P.

2001-10-02

Water-temperature data from 32 sites in the Cook Inlet Basin, south-central Alaska, indicate various trends that depend on watershed characteristics. Basins with 25 percent or more of their area consisting of glaciers have the coldest water temperatures during the open-water season, mid-May to mid-October. Streams and rivers that drain lowlands have the warmest water temperatures. A model that uses air temperature as input to predict water temperature as output was utilized to simulate future trends in water temperature based on increased air temperatures due to climate warming. Based on the Nash-Sutcliffe coefficient, the model produced acceptable results for 27 sites. For basins with more than 25 percent glacial coverage, the model was not as accurate. Results indicate that 15 sites had a predicted water-temperature change of 3 degrees Celsius or more, a magnitude of change that is considered significant for the incidence of disease in fish populations.

Sequential vortex hopping in an array of artificial pinning centers

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

Keay, J. C.

2010-02-24

We use low-temperature magnetic force microscopy (MFM) to study the hopping motion of vortices in an array of artificial pinning centers (APCs). The array consists of nanoscale holes etched in a niobium thin film by Ar-ion sputtering through an anodic aluminum-oxide template. Variable-temperature magnetometry shows a transition temperature of 7.1 K and an enhancement of the magnetization up to the third matching field at 5 K. Using MFM with attractive and repulsive tip-vortex interaction, we measure the vortex-pinning strength and investigate the motion of individual vortices in the APC array. The depinning force for individual vortices at low field rangedmore » from 0.7 to 1.2 pN. The motion of individual vortices was found to be reproducible and consistent with movement between adjacent holes in the film. The movements are repeatable but the sequence of hops depends on the scan direction. This asymmetry in the motion indicates nonuniform local pinning, a consequence of array disorder and hole-size variation.« less

Magnetic properties of co-precipitated hexaferrite powders with Sm-Co substitutions optimized with the molten flux method

NASA Astrophysics Data System (ADS)

Serletis, C.; Litsardakis, G.; Pavlidou, E.; Efthimiadis, K. G.

2017-11-01

In this work, using the chemical coprecipitation method, Sr1-xSmxFe12-xCoxO19 (x = 0, 0.1, 0.2) hexaferrite powders were prepared. Major magnetization loops were recorded at room temperature in order to determine the correct calcination temperature for optimum hard magnetic properties. It is found that a small degree of substitution increases substantially the coercive field. Also, the use of the molten flux calcination method increases the remanent magnetization. SEM/EDXS and XRD measurements were performed at the calcined powders: the results show that a single hexaferrite phase is formed and that the substituted powders consist of an assembly of grains with a mean diameter of 40 nm. Measurements of minor magnetization loops and of the temperature and time dependence of the magnetization confirm that the powders consist of a non-oriented single domain magnetic particles assembly. The results indicate that Sm could be a viable replacement for La in the manufacturing of hexaferrites with a high-energy product.

Self-consistent electro-opto-thermal model of quantum cascade lasers with coupled electron and phonon interactions far from equilibrium

NASA Astrophysics Data System (ADS)

Yousefvand, Hossein Reza

2017-12-01

A self-consistent model of quantum cascade lasers (QCLs) is presented here for the study of the QCL's behavior in the far from equilibrium conditions. The approach is developed by employing a number of physics-based models such as the carrier and photon rate equations, the energy balance equation, the heat transfer equation and a simplified rate equation for the creation and annihilation of nonequilibrium optical phonons. The temperature dependency of the relevant physical effects such as stimulated gain cross section, longitudinal optical (LO) phonons and hot-phonon generation rates are included in the model. Using the presented model, the static and transient device characteristics are calculated and analyzed for a wide range of heat sink temperatures. Besides the output characteristics, this model also provides a way to study the hot-phonon dynamics in the device, and to explore the electron temperature and thermal roll-over in the QCLs.

Exogenous application of estradiol to eggs unexpectedly induces male development in two turtle species with temperature-dependent sex determination.

PubMed

Warner, Daniel A; Addis, Elizabeth; Du, Wei-guo; Wibbels, Thane; Janzen, Fredric J

2014-09-15

Steroid hormones affect sex determination in a variety of vertebrates. The feminizing effects of exposure to estradiol and the masculinizing effects of aromatase inhibition during development are well established in a broad range of vertebrate taxa, but paradoxical findings are occasionally reported. Four independent experiments were conducted on two turtle species with temperature-dependent sex determination (Chrysemys picta and Chelydra serpentina) to quantify the effects of egg incubation temperature, estradiol, and an aromatase inhibitor on offspring sex ratios. As expected, the warmer incubation temperatures induced female development and the cooler temperatures produced primarily males. However, application of an aromatase inhibitor had no effect on offspring sex ratios, and exogenous applications of estradiol to eggs produced male offspring across all incubation temperatures. These unexpected results were remarkably consistent across all four experiments and both study species. Elevated concentrations of estradiol could interact with androgen receptors or inhibit aromatase expression, which might result in relatively high testosterone concentrations that lead to testis development. These findings add to a short list of studies that report paradoxical effects of steroid hormones, which addresses the need for a more comprehensive understanding of the role of sex steroids in sexual development. Copyright © 2014 Elsevier Inc. All rights reserved.

Resonant and Inelastic Andreev Tunneling Observed on a Carbon Nanotube Quantum Dot.

PubMed

Gramich, J; Baumgartner, A; Schönenberger, C

2015-11-20

We report the observation of two fundamental subgap transport processes through a quantum dot (QD) with a superconducting contact. The device consists of a carbon nanotube contacted by a Nb superconducting and a normal metal contact. First, we find a single resonance with position, shape, and amplitude consistent with the theoretically predicted resonant Andreev tunneling (AT) through a single QD level. Second, we observe a series of discrete replicas of resonant AT at a separation of ~145 μeV, with a gate, bias, and temperature dependence characteristic for boson-assisted, inelastic AT, in which energy is exchanged between a bosonic bath and the electrons. The magnetic field dependence of the replica's amplitudes and energies suggest that two different bosons couple to the tunnel process.

Quasiparticle self-consistent GW study of cuprates: electronic structure, model parameters, and the two-band theory for Tc

PubMed Central

Jang, Seung Woo; Kotani, Takao; Kino, Hiori; Kuroki, Kazuhiko; Han, Myung Joon

2015-01-01

Despite decades of progress, an understanding of unconventional superconductivity still remains elusive. An important open question is about the material dependence of the superconducting properties. Using the quasiparticle self-consistent GW method, we re-examine the electronic structure of copper oxide high-Tc materials. We show that QSGW captures several important features, distinctive from the conventional LDA results. The energy level splitting between and is significantly enlarged and the van Hove singularity point is lowered. The calculated results compare better than LDA with recent experimental results from resonant inelastic xray scattering and angle resolved photoemission experiments. This agreement with the experiments supports the previously suggested two-band theory for the material dependence of the superconducting transition temperature, Tc. PMID:26206417

Asymmetry of projected increases in extreme temperature distributions

PubMed Central

Kodra, Evan; Ganguly, Auroop R.

2014-01-01

A statistical analysis reveals projections of consistently larger increases in the highest percentiles of summer and winter temperature maxima and minima versus the respective lowest percentiles, resulting in a wider range of temperature extremes in the future. These asymmetric changes in tail distributions of temperature appear robust when explored through 14 CMIP5 climate models and three reanalysis datasets. Asymmetry of projected increases in temperature extremes generalizes widely. Magnitude of the projected asymmetry depends significantly on region, season, land-ocean contrast, and climate model variability as well as whether the extremes of consideration are seasonal minima or maxima events. An assessment of potential physical mechanisms provides support for asymmetric tail increases and hence wider temperature extremes ranges, especially for northern winter extremes. These results offer statistically grounded perspectives on projected changes in the IPCC-recommended extremes indices relevant for impacts and adaptation studies. PMID:25073751

The effect of polymer composition on the gelation behavior of PLGA-g-PEG biodegradable thermoreversible gels.

PubMed

Tarasevich, B J; Gutowska, A; Li, X S; Jeong, B-M

2009-04-01

Graft copolymers consisting of a poly(D,L-lactic acid-co-glycolic acid) backbone grafted with polyethylene glycol side chains were synthesized and formed thermoreversible gels in aqueous solutions that exhibited solution behavior at low temperature and sol-to-gel transitions at higher temperature. The composition of the polymer and relative amounts of polylactic acid, glycolic acid, and ethylene glycol were varied by controlling the precursor concentrations and reaction temperature. The gelation temperature could be systematically tailored from 15 to 34 degrees C by increasing the concentration of polyethylene glycol in the graft copolymer. The gelation temperature also depended on the polymer molecular weight and concentration. This work has importance for the development of water soluble gels with tailored compositions and gelation temperatures for use in tissue engineering and as injectable depots for drug delivery. Copyright 2008 Wiley Periodicals, Inc.

Photobleaching of chromophoric dissolved organic matter (CDOM) in the Yangtze River estuary: kinetics and effects of temperature, pH, and salinity.

PubMed

Song, Guisheng; Li, Yijie; Hu, Suzheng; Li, Guiju; Zhao, Ruihua; Sun, Xin; Xie, Huixiang

2017-06-21

The kinetics and temperature-, pH- and salinity-dependences of photobleaching of chromophoric dissolved organic matter (CDOM) in the Yangtze River estuary (YRE) were evaluated using laboratory solar-simulated irradiation and compared to those of Suwannee River humic substances (SRHSs). Nearly all CDOM in water at the head of the estuary (headwater herein) was photobleachable in both summer and winter, while significant fractions of CDOM (13-29%) were resistant to photobleaching in saltier waters. The photobleaching rate constant in the headwater was 25% higher in summer than that in winter. The absorbed photon-based photobleaching efficiency (PE) increased with temperature following the linear Arrhenius equation. For a 20 °C increase in temperature, PE increased by ∼45% in the headwater and by 70-81% in the saltier waters. PE for YRE samples exhibited minima at pH from 6 to 7 and increased with both lower and higher pH values, contrasting the consistent increase in PE with pH shown by SRHSs. No consistent effect of salinity on PE was observed for both SRHSs and YRE samples. Photobleaching increased the spectral slope coefficient between 275 nm and 295 nm in summer, consistent with the behavior of SRHSs, but decreased it in winter, implying a difference in the molecular composition of chromophores between the two seasons. Temperature, salinity, and pH modified the photoalteration of the spectral shape but their effects varied spatially and seasonally. This study demonstrates that CDOM quality, temperature, and pH should be incorporated into models involving quantification of photobleaching.

Exploring connections between statistical mechanics and Green's functions for realistic systems: Temperature dependent electronic entropy and internal energy from a self-consistent second-order Green's function

NASA Astrophysics Data System (ADS)

Welden, Alicia Rae; Rusakov, Alexander A.; Zgid, Dominika

2016-11-01

Including finite-temperature effects from the electronic degrees of freedom in electronic structure calculations of semiconductors and metals is desired; however, in practice it remains exceedingly difficult when using zero-temperature methods, since these methods require an explicit evaluation of multiple excited states in order to account for any finite-temperature effects. Using a Matsubara Green's function formalism remains a viable alternative, since in this formalism it is easier to include thermal effects and to connect the dynamic quantities such as the self-energy with static thermodynamic quantities such as the Helmholtz energy, entropy, and internal energy. However, despite the promising properties of this formalism, little is known about the multiple solutions of the non-linear equations present in the self-consistent Matsubara formalism and only a few cases involving a full Coulomb Hamiltonian were investigated in the past. Here, to shed some light onto the iterative nature of the Green's function solutions, we self-consistently evaluate the thermodynamic quantities for a one-dimensional (1D) hydrogen solid at various interatomic separations and temperatures using the self-energy approximated to second-order (GF2). At many points in the phase diagram of this system, multiple phases such as a metal and an insulator exist, and we are able to determine the most stable phase from the analysis of Helmholtz energies. Additionally, we show the evolution of the spectrum of 1D boron nitride to demonstrate that GF2 is capable of qualitatively describing the temperature effects influencing the size of the band gap.

The impact of anisotropy and interaction range on the self-assembly of Janus ellipsoids

NASA Astrophysics Data System (ADS)

Ruth, D. P.; Gunton, J. D.; Rickman, J. M.; Li, Wei

2014-12-01

We assess the roles of anisotropy and interaction range on the self-assembly of Janus colloidal particles. In particular, Monte Carlo simulation is employed to investigate the propensity for the formation of aggregates in a spheroidal model of a colloid having a relatively short-ranged interaction that is consistent with experimentally realizable systems. By monitoring the equilibrium distribution of aggregates as a function of temperature and density, we identify a "micelle" transition temperature and discuss its dependence on particle shape. We find that, unlike systems with longer ranged interactions, this system does not form micelles below a transition temperature at low density. Rather, larger clusters comprising 20-40 particles characterize the transition. We then examine the dependence of the second virial coefficient on particle shape and well width to determine how these important system parameters affect aggregation. Finally, we discuss possible strategies suggested by this work to promote self-assembly for the encapsulation of particles.

Developing Lathing Parameters for PBX 9501

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

Woodrum, Randall Brock

This thesis presents the work performed on lathing PBX 9501 to gather and analyze cutting force and temperature data during the machining process. This data will be used to decrease federal-regulation-constrained machining time of the high explosive PBX 9501. The effects of machining parameters depth of cut, surface feet per minute, and inches per revolution on cutting force and cutting interface were evaluated. Cutting tools of tip radius 0.005 -inches and 0.05 -inches were tested to determine what effect the tool shape had on the machining process as well. A consistently repeatable relationship of temperature to changing depth of cutmore » and surface feet per minute is found, while only a weak dependence was found to changing inches per revolution. Results also show the relation of cutting force to depth of cut and inches per revolution, while weak dependence on SFM is found. Conclusions suggest rapid, shallow cuts optimize machining time for a billet of PBX 9501, while minimizing temperature increase and cutting force.« less

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

Mukherjee, Rupam; Huang, Zhi-Feng; Nadgorny, Boris

Multiple percolation transitions are observed in a binary system of RuO{sub 2}-CaCu{sub 3}Ti{sub 4}O{sub 12} metal-semiconductor nanoparticle composites near percolation thresholds. Apart from a classical percolation transition, associated with the appearance of a continuous conductance path through RuO{sub 2} metal oxide nanoparticles, at least two additional tunneling percolation transitions are detected in this composite system. Such behavior is consistent with the recently emerged picture of a quantum conductivity staircase, which predicts several percolation tunneling thresholds in a system with a hierarchy of local tunneling conductance, due to various degrees of proximity of adjacent conducting particles distributed in an insulating matrix.more » Here, we investigate a different type of percolation tunneling staircase, associated with a more complex conductive and insulating particle microstructure of two types of non-spherical constituents. As tunneling is strongly temperature dependent, we use variable temperature measurements to emphasize the hierarchical nature of consecutive tunneling transitions. The critical exponents corresponding to specific tunneling percolation thresholds are found to be nonuniversal and temperature dependent.« less

Solvation enthalpies and heat capacities of n-alkanes in four polymer phases by capillary gas chromatography.

PubMed

Görgenyi, Miklós; Héberger, Károly

2005-04-01

Molar solvation enthalpy (deltasol H(o)298) and molar heat capacity changes (deltasol C(o)p) were determined by gas chromatography for the C6-C12 n-alkanes on four preferred stationary phases (100% polydimethyl siloxane, 50% diphenyl-50% dimethyl polysiloxane, 50% trifluoropropyl methylsiloxane, and polyethylene glycol) in commercial FSOT. Statistical evaluation indicated the temperature independence of deltasol C(o)p in the range 303-393 K. Deltasol H(o)298 depends linearly on the number of carbon atoms in the n-alkanes, but no linearity could be established for deltasol C(o)p of higher homologues on polar columns, which may be due to a more ordered state on the liquid phase. The homologues for which a linear temperature dependence exists demonstrated that deltasol C(o)p is related linearly to the van der Waals volume and the temperature derivative of the density of the stationary phase. The results are consistent with a simple physical explanation at the molecular level.

Superconductivity with extremely large upper critical fields in Nb2Pd0.81S5

PubMed Central

Zhang, Q.; Li, G.; Rhodes, D.; Kiswandhi, A.; Besara, T.; Zeng, B.; Sun, J.; Siegrist, T.; Johannes, M. D.; Balicas, L.

2013-01-01

Here, we report the discovery of superconductivity in a new transition metal-chalcogenide compound, i.e. Nb2Pd0.81S5, with a transition temperature Tc ≅ 6.6 K. Despite its relatively low Tc, it displays remarkably high and anisotropic superconducting upper critical fields, e.g. μ0Hc2 (T → 0 K) > 37 T for fields applied along the crystallographic b-axis. For a field applied perpendicularly to the b-axis, μ0Hc2 shows a linear dependence in temperature which coupled to a temperature-dependent anisotropy of the upper critical fields, suggests that Nb2Pd0.81S5 is a multi-band superconductor. This is consistent with band structure calculations which reveal nearly cylindrical and quasi-one-dimensional Fermi surface sheets having hole and electron character, respectively. The static spin susceptibility as calculated through the random phase approximation, reveals strong peaks suggesting proximity to a magnetic state and therefore the possibility of unconventional superconductivity. PMID:23486091

Thermal conductivity of nanocrystalline silicon: importance of grain size and frequency-dependent mean free paths.

PubMed

Wang, Zhaojie; Alaniz, Joseph E; Jang, Wanyoung; Garay, Javier E; Dames, Chris

2011-06-08

The thermal conductivity reduction due to grain boundary scattering is widely interpreted using a scattering length assumed equal to the grain size and independent of the phonon frequency (gray). To assess these assumptions and decouple the contributions of porosity and grain size, five samples of undoped nanocrystalline silicon have been measured with average grain sizes ranging from 550 to 64 nm and porosities from 17% to less than 1%, at temperatures from 310 to 16 K. The samples were prepared using current activated, pressure assisted densification (CAPAD). At low temperature the thermal conductivities of all samples show a T(2) dependence which cannot be explained by any traditional gray model. The measurements are explained over the entire temperature range by a new frequency-dependent model in which the mean free path for grain boundary scattering is inversely proportional to the phonon frequency, which is shown to be consistent with asymptotic analysis of atomistic simulations from the literature. In all cases the recommended boundary scattering length is smaller than the average grain size. These results should prove useful for the integration of nanocrystalline materials in devices such as advanced thermoelectrics.

Different storage conditions influence biocompatibility and physicochemical properties of iron oxide nanoparticles.

PubMed

Zaloga, Jan; Janko, Christina; Agarwal, Rohit; Nowak, Johannes; Müller, Robert; Boccaccini, Aldo R; Lee, Geoffrey; Odenbach, Stefan; Lyer, Stefan; Alexiou, Christoph

2015-04-24

Superparamagnetic iron oxide nanoparticles (SPIONs) have attracted increasing attention in many biomedical fields. In magnetic drug targeting SPIONs are injected into a tumour supplying artery and accumulated inside the tumour with a magnet. The effectiveness of this therapy is thus dependent on magnetic properties, stability and biocompatibility of the particles. A good knowledge of the effect of storage conditions on those parameters is of utmost importance for the translation of the therapy concept into the clinic and for reproducibility in preclinical studies. Here, core shell SPIONs with a hybrid coating consisting of lauric acid and albumin were stored at different temperatures from 4 to 45 °C over twelve weeks and periodically tested for their physicochemical properties over time. Surprisingly, even at the highest storage temperature we did not observe denaturation of the protein or colloidal instability. However, the saturation magnetisation decreased by maximally 28.8% with clear correlation to time and storage temperature. Furthermore, the biocompatibility was clearly affected, as cellular uptake of the SPIONs into human T-lymphoma cells was crucially dependent on the storage conditions. Taken together, the results show that the particle properties undergo significant changes over time depending on the way they are stored.

Quantitative characterization of the viscosity of a microemulsion

NASA Technical Reports Server (NTRS)

Berg, Robert F.; Moldover, Michael R.; Huang, John S.

1987-01-01

The viscosity of the three-component microemulsion water/decane/AOT has been measured as a function of temperature and droplet volume fraction. At temperatures well below the phase-separation temperature the viscosity is described by treating the droplets as hard spheres suspended in decane. Upon approaching the two-phase region from low temperature, there is a large (as much as a factor of four) smooth increase of the viscosity which may be related to the percolation-like transition observed in the electrical conductivity. This increase in viscosity is not completely consistent with either a naive electroviscous model or a simple clustering model. The divergence of the viscosity near the critical point (39 C) is superimposed upon the smooth increase. The magnitude and temperature dependence of the critical divergence are similar to that seen near the critical points of binary liquid mixtures.

Non-equilibrium phase transitions in a liquid crystal

NASA Astrophysics Data System (ADS)

Dan, K.; Roy, M.; Datta, A.

2015-09-01

The present manuscript describes kinetic behaviour of the glass transition and non-equilibrium features of the "Nematic-Isotropic" (N-I) phase transition of a well known liquid crystalline material N-(4-methoxybenzylidene)-4-butylaniline from the effects of heating rate and initial temperature on the transitions, through differential scanning calorimetry (DSC), Fourier transform infrared and fluorescence spectroscopy. Around the vicinity of the glass transition temperature (Tg), while only a change in the baseline of the ΔCp vs T curve is observed for heating rate (β) > 5 K min-1, consistent with a glass transition, a clear peak for β ≤ 5 K min-1 and the rapid reduction in the ΔCp value from the former to the latter rate correspond to an order-disorder transition and a transition from ergodic to non-ergodic behaviour. The ln β vs 1000/T curve for the glass transition shows convex Arrhenius behaviour that can be explained very well by a purely entropic activation barrier [Dan et al., Eur. Phys. Lett. 108, 36007 (2014)]. Fourier transform infrared spectroscopy indicates sudden freezing of the out-of-plane distortion vibrations of the benzene rings around the glass transition temperature and a considerable red shift indicating enhanced coplanarity of the benzene rings and, consequently, enhancement in the molecular ordering compared to room temperature. We further provide a direct experimental evidence of the non-equilibrium nature of the N-I transition through the dependence of this transition temperature (TNI) and associated enthalpy change (ΔH) on the initial temperature (at fixed β-values) for the DSC scans. A plausible qualitative explanation based on Mesquita's extension of Landau-deGennes theory [O. N. de Mesquita, Braz. J. Phys. 28, 257 (1998)] has been put forward. The change in the molecular ordering from nematic to isotropic phase has been investigated through fluorescence anisotropy measurements where the order parameter, quantified by the anisotropy, goes to zero from nematic to isotropic phase. To a point below the transition temperature, the order parameter is constant but decreases linearly with increase in temperature below that indicating the dependence of nematic ordering on the initial temperature during heating consistent with the non-equilibrium nature of nematic-isotropic phase transition.

Optical probe of Heisenberg-Kitaev magnetism in α -RuCl3

NASA Astrophysics Data System (ADS)

Sandilands, Luke J.; Sohn, C. H.; Park, H. J.; Kim, So Yeun; Kim, K. W.; Sears, Jennifer A.; Kim, Young-June; Noh, Tae Won

2016-11-01

We report a temperature-dependent optical spectroscopic study of the Heisenberg-Kitaev magnet α -RuCl3 . Our measurements reveal anomalies in the optical response near the magnetic ordering temperature. At higher temperatures, we observe a redistribution of spectral weight over a broad energy range that is associated with nearest-neighbor spin-spin correlations. This finding is consistent with highly frustrated magnetic interactions and in agreement with theoretical expectations for this class of material. The optical data also reveal significant electron-hole interaction effects, including a bound excitonic state. These results demonstrate a clear coupling between charge and spin degrees of freedom and provide insight into the properties of thermally disordered Heisenberg-Kitaev magnets.

Electron drift velocity and mobility in graphene

NASA Astrophysics Data System (ADS)

Dong, Hai-Ming; Duan, Yi-Feng; Huang, Fei; Liu, Jin-Long

2018-04-01

We present a theoretical study of the electric transport properties of graphene-substrate systems. The drift velocity, mobility, and temperature of the electrons are self-consistently determined using the Boltzmann equilibrium equations. It is revealed that the electronic transport exhibits a distinctly nonlinear behavior. A very high mobility is achieved with the increase of the electric fields increase. The electron velocity is not completely saturated with the increase of the electric field. The temperature of the hot electrons depends quasi-linearly on the electric field. In addition, we show that the electron velocity, mobility, and electron temperature are sensitive to the electron density. These findings could be employed for the application of graphene for high-field nano-electronic devices.

Liquid Hydrogenation of Maleic Anhydride with Pd/C Catalyst at Low Pressure and Temperature in Batch Reactor.

PubMed

Kim, Ji Sun; Baek, Jae Ho; Ryu, Young Bok; Hong, Seong-Soo; Lee, Man Sig

2015-01-01

Succinic acid (SA) produced from hydrogenation of maleic anhydride (MAN) is used widely in manufacturing of pharmaceuticals, agrochemicals, surfactants and detergent, green solvent and biodegradable plastic. In this study, we performed that liquid hydrogenation of MAN to SA with 5 wt% Pd supported on activated carbon (Pd/C) at low pressure and temperature. The synthesis of SA was performed in aqueous solution while varying temperature, pressure, catalytic amount and agitation speed. We confirmed that the composition of the products consisting of SA, maleic acid (MA), fumaric acid (FA) and malic acid (MLA) depends on the process. The catalytic characteristics were analyzed by TGA, TEM.

Dynamics of quantum turbulence of different spectra

PubMed Central

Walmsley, Paul; Zmeev, Dmitry; Pakpour, Fatemeh; Golov, Andrei

2014-01-01

Turbulence in a superfluid in the zero-temperature limit consists of a dynamic tangle of quantized vortex filaments. Different types of turbulence are possible depending on the level of correlations in the orientation of vortex lines. We provide an overview of turbulence in superfluid 4He with a particular focus on recent experiments probing the decay of turbulence in the zero-temperature regime below 0.5 K. We describe extensive measurements of the vortex line density during the free decay of different types of turbulence: ultraquantum and quasiclassical turbulence in both stationary and rotating containers. The observed decays and the effective dissipation as a function of temperature are compared with theoretical models and numerical simulations. PMID:24704876

Superconducting gamma and fast-neutron spectrometers with high energy resolution

DOEpatents

Friedrich, Stephan; , Niedermayr, Thomas R.; Labov, Simon E.

2008-11-04

Superconducting Gamma-ray and fast-neutron spectrometers with very high energy resolution operated at very low temperatures are provided. The sensor consists of a bulk absorber and a superconducting thermometer weakly coupled to a cold reservoir, and determines the energy of the incident particle from the rise in temperature upon absorption. A superconducting film operated at the transition between its superconducting and its normal state is used as the thermometer, and sensor operation at reservoir temperatures around 0.1 K reduces thermal fluctuations and thus enables very high energy resolution. Depending on the choice of absorber material, the spectrometer can be configured either as a Gamma-spectrometer or as a fast-neutron spectrometer.

Disorder induced magnetism and electrical conduction in La doped Ca2FeMoO6 double perovskite

NASA Astrophysics Data System (ADS)

Poddar, Asok; Bhowmik, R. N.; Muthuselvam, I. Panneer

2010-11-01

We report the magnetism and electrical transport properties of La doped Ca2FeMoO6 double perovskite. Reduction in magnetic moment, nonmonotonic variation in magnetic ordering temperature (TC), increasing magnetic hardness, low temperature resistivity upturn, and loss of metallic conductivity are some of the major changes that we observed due to La doping induced disorder in double perovskite structure. The increase in magnetic disorder in La doped samples and its effect on TC is more consistent with the mean field theory. The modification in electronic band structure due to La doping is understood by establishing a correlation between the temperature dependence of electrical conductivity and thermoelectric power.

Parental thermal environment alters offspring sex ratio and fitness in an oviparous lizard.

PubMed

Schwanz, Lisa E

2016-08-01

The environment experienced by parents can impact the phenotype of their offspring (parental effects), a critical component of organismal ecology and evolution in variable or changing environments. Although temperature is a central feature of the environment for ectotherms, its role in parental effects has been little explored until recently. Here, parental basking opportunity was manipulated in an oviparous lizard with temperature-dependent sex determination, the jacky dragon (Amphibolurus muricatus). Eggs were incubated at a temperature that typically produces a 50:50 sex ratio, and hatchlings were reared in a standard thermal environment. Offspring of parents in short bask conditions appeared to have better fitness outcomes in captive conditions than those of parents in long bask conditions - they had greater growth and survival as a function of their mass. In addition, the sex of offspring (male or female) depended on the interaction between parental treatment and egg mass, and treatment impacted whether sons or daughters grew larger in their first season. The interactive effects of treatment on offspring sex and growth are consistent with adaptive explanations for the existence of temperature-dependent sex determination in this species. Moreover, the greater performance recorded in short bask offspring may represent an anticipatory parental effect to aid offspring in predicted conditions of restricted thermal opportunity. Together, these responses constitute a crucial component of the population response to spatial or temporal variation in temperature. © 2016. Published by The Company of Biologists Ltd.

Synthesis and piezoelectric properties of (1 - x)Bi0.5(Na0.8K0.2)0.5TiO3-xSr2ZrTiO6 ceramics

NASA Astrophysics Data System (ADS)

Onishi, Ryo; Ogawa, Hirotaka; Iida, Daiki; Kan, Akinori

2017-10-01

The effects of Sr2ZrTiO6 (SZT) addition on the piezoelectric properties of (1 - x)Bi0.5(Na0.8K0.2)0.5TiO3 (BNKT)-xSZT ceramics were characterized in this study. The X-ray powder diffraction (XRPD) profiles and Raman spectra of the ceramics in the composition range of 0-0.02 implies the presence of morphotropic phase boundary (MPB) which consists of the rhombohedral and tetragonal phases. Moreover, the temperature dependence of dielectric loss indicated a presence of the ferroelectric-relaxor transition temperature (T F-R) of around 75 °C for x = 0.005 and the temperature dependence shifted to a lower temperature at x = 0.01. The temperature dependence of the P-E hysteresis loop of the ceramics at the compositions of x = 0.005-0.02 showed pinched hysteresis loops above T F-R. Regarding the piezoelectric constant (d 33), it was increased by SZT addition in the MPB region (x = 0-0.01) and the highest d 33 of 202 pC/N was obtained at the composition of x = 0.0025. The S-E unipolar loop was also evaluated, the strain of the ceramic increased up to x = 0.02; and the highest d33* = 436 pm/V was obtained at the composition of x = 0.02.

Temperature mapping of laser-induced hyperthermia in an ocular phantom using magnetic resonance thermography.

PubMed

Maswadi, Saher M; Dodd, Stephen J; Gao, Jia-Hong; Glickman, Randolph D

2004-01-01

Laser-induced heating in an ocular phantom is measured with magnetic resonance thermography (MRT) using temperature-dependent phase changes in proton resonance frequency. The ocular phantom contains a layer of melanosomes isolated from bovine retinal pigment epithelium. The phantom is heated by the 806-nm output of a continuous wave diode laser with an irradiance of 2.4 to 21.6 W/cm2 in a beam radius of 0.8 or 2.4 mm, depending on the experiment. MRT is performed with a 2 T magnet, and a two-turn, 6-cm-diam, circular radio frequency coil. Two-dimensional temperature gradients are measured within the plane of the melanin layer, as well as normal to it, with a temperature resolution of 1 degrees C or better. The temperature gradients extending within the melanin layer are broader than those orthogonal to the layer, consistent with the higher optical absorption and consequent heating in the melanin. The temperature gradients in the phantom measured by MRT closely approximate the predictions of a classical heat diffusion model. Three-dimensional temperature maps with a spatial resolution of 0.25 mm in all directions are also made. Although the temporal resolution is limited in the prototype system (22.9 s for a single image "slice"), improvements in future implementations are likely. These results indicate that MRT has sufficient spatial and temperature resolution to monitor target tissue temperature during transpupillary thermotherapy in the human eye.

Temperature Dependence of Thin Film Spiral Inductors on Alumina Over a Temperature Range of 25 to 475 C

NASA Technical Reports Server (NTRS)

Ponchak, George E.; Jordan, Jennifer L.; Scardelletti, Maximilian C.

2010-01-01

In this paper, we present an analysis of inductors on an Alumina substrate over the temperature range of 25 to 475 C. Five sets of inductors, each set consisting of a 1.5, 2.5, 3.5, and a 4.5 turn inductor with different line width and spacing, were measured on a high temperature probe station from 10 MHz to 30 GHz. From these measured characteristics, it is shown that the inductance is nearly independent of temperature for low frequencies compared to the self resonant frequency, the parasitic capacitances are independent of temperature, and the resistance varies nearly linearly with temperature. These characteristics result in the self resonant frequency decreasing by only a few percent as the temperature is increased from 25 to 475 C, but the maximum quality factor decreases by a factor of 2 to 3. These observations based on measured data are confirmed through 2D simulations using Sonnet software.

Cross spectra between pressure and temperature in a constant-area duct downstream of a hydrogen-fueled combustor

NASA Technical Reports Server (NTRS)

Miles, J. H.; Wasserbauer, C. A.; Krejsa, E. A.

1983-01-01

Pressure temperature cross spectra are necessary in predicting noise propagation in regions of velocity gradients downstream of combustors if the effect of convective entropy disturbances is included. Pressure temperature cross spectra and coherences were measured at spatially separated points in a combustion rig fueled with hydrogen. Temperature-temperature and pressure-pressure cross spectra and coherences between the spatially separated points as well as temperature and pressure autospectra were measured. These test results were compared with previous results obtained in the same combustion rig using Jet A fuel in order to investigate their dependence on the type of combustion process. The phase relationships are not consistent with a simple source model that assumes that pressure and temperature are in phase at a point in the combustor and at all other points downstream are related to one another by only a time delay due to convection of temperature disturbances. Thus these test results indicate that a more complex model of the source is required.

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.

Infrared study of OH(-) defects in KTiOPO4 crystals

NASA Astrophysics Data System (ADS)

Morris, P. A.; Crawford, M. K.; Jones, B.

1992-12-01

Variations in the concentrations and distributions of the OH(-) defects present in flux and hydrothermal KTiOPO4 (KTP) crystals, measured by infrared spectroscopy of single crystals, are attributed to differences in the growth environments and other nonhydrogenic defects present in the crystals. The concentrations of OH(-) have been estimated from the infrared data to be approximately 400 ppma (parts per million atomic) (3.0 x 10 exp 19/cu cm) in the flux crystals, 1100-1500 ppma (0.74-1.1 x 10 exp 20/cu cm) in the high-temperature hydrothermal and 600 ppma (4.3 x 10 exp 19/cu cm) in the low-temperature hydrothermal crystals. A 3566/cm peak and a 3575/cm band are observed in all crystals. The integrated intensity of the OH(-) absorption band at 3566/cm increases at the expense of the 3575/cm band at higher temperatures in the high-temperature hydrothermal crystals. Several OH(-) peaks (3490, 3455, 3428, 3420, and 3333/cm), which have strongly temperature-dependent linewidths, are present in the hydrothermally grown KTP crystals. The temperature dependencies of their peak frequencies and widths are consistent with the presence of mobile protons in the lattice. The protons located in the 3490 and 3428/cm sites are believed to contribute to the ionic conductivity of the high-conductivity high-temperature hydrothermal crystals.

Self-Consistency of the Lauritzen-Hoffman and Strobl Models of Polymer Crystallization Evaluated for Poly(epsilon-caprolactone) Fractions and Effect of Composition on the Phenomenon of Concurrent Crystallization in Polyethylene Blends

NASA Astrophysics Data System (ADS)

Sheth, Swapnil Suhas

Narrow molecular weight fractions of poly(epsilon-caprolactone) were successfully obtained using the successive precipitation fractionation technique with toluene/n-heptane as a solvent/nonsolvent pair. Calorimetric studies of the melting behavior of fractions that were crystallized either isothermally or under constant cooling rate conditions suggested that the isothermal crystallization of the samples should be used for a proper evaluation of the molecular weight dependence of the observed melting temperature and degree of crystallinity in PCL. The molecular weight and temperature dependence of the spherulitic growth rate of fractions was studied in the context of the Lauritzen-Hoffman two-phase model and the Strobl three-phase model of polymer crystallization. The zero-growth rate temperatures, determined from spherulitic growth rates using four different methods, are consistent with each other and increase with chain length. The concomitant increase in the apparent secondary nucleation constant was attributed to two factors. First, for longer chains there is an increase in the probability that crystalline stems belong to loose chain-folds, hence, an increase in fold surface free energy. It is speculated that the increase in loose folding and resulting decrease in crystallinity with increasing chain length are associated with the ester group registration requirement in PCL crystals. The second contribution to the apparent nucleation constant arises from chain friction associated with segmental transport across the melt/crystal interface. These factors were responsible for the much stronger chain length dependence of spherulitic growth rates at fixed undercooling observed here with PCL than previously reported for PE and PEO. In the case of PCL, the scaling exponent associated with the chain length dependence of spherulitic growth rates exceeds the upper theoretical bound of 2 predicted from the Brochard- DeGennes chain pullout model. Observation that zero-growth and equilibrium melting temperature values are identical with each other within the uncertainty of their determinations casts serious doubt on the validity of Strobl three-phase model. A novel method is proposed to determine the Porod constant necessary to extrapolate the small angle X-ray scattering intensity data to large scattering vectors. The one-dimensional correlation function determined using this Porod constant yielded the values of lamellar crystal thickness, which were similar to these estimated using the Hosemann-Bagchi Paracrystalline Lattice model. The temperature dependence of the lamellar crystal thickness was consistent with both LH and the Strobl model of polymer crystallization. However, in contrast to the predictions of Strobl's model, the value of the mesomorph-to-crystal equilibrium transition temperature was very close to the zero-growth temperature. Moreover, the lateral block sizes (obtained using wide angle X-ray diffraction) and the lamellar thicknesses were not found to be controlled by the mesomorph-to-crystal equilibrium transition temperature. Hence, we concluded that the crystallization of PCL is not mediated by a mesophase. Metallocene-catalyzed linear low-density (m-LLDPE with 3.4 mol% 1-octene) and conventional low-density (LDPE) polyethylene blends of different compositions were investigated for their melt-state miscibility and concurrent crystallization tendency. Differential scanning calorimetric studies and morphological studies using atomic force microscopy confirm that these blends are miscible in the melt-state for all compositions. LDPE chains are found to crystallize concurrently with m-LLDPE chains during cooling in the m-LLDPE crystallization temperature range. While the extent of concurrent crystallization was found to be optimal in .. .. iv blends with highest m-LLDPE content studied, strong evidence was uncovered for the existence of a saturation effect in the concurrent crystallization behavior. This observation leads us to suggest that co-crystallization, rather than mere concurrent crystallization, of LDPE with m- LLDPE can indeed take place. Matching of the respective sequence length distributions in LDPE and m-LLDPE is suggested to control the extent of co-crystallization.

Early establishment of trees at the alpine treeline: idiosyncratic species responses to temperature-moisture interactions

PubMed Central

Loranger, Hannah; Zotz, Gerhard; Bader, Maaike Y.

2016-01-01

On a global scale, temperature is the main determinant of arctic and alpine treeline position. However on a local scale, treeline form and position vary considerably due to other climatic factors, tree species ecology and life-stage-dependent responses. For treelines to advance poleward or uphill, the first steps are germination and seedling establishment. These earliest life stages may be major bottlenecks for treeline tree populations and will depend differently on climatic conditions than adult trees. We investigated the effect of soil temperature and moisture on germination and early seedling survival in a field experiment in the French Alps near the local treeline (2100 m a.s.l.) using passive temperature manipulations and two watering regimes. Five European treeline tree species were studied: Larix decidua, Picea abies, Pinus cembra, Pinus uncinata and Sorbus aucuparia. In addition, we monitored the germination response of three of these species to low temperatures under controlled conditions in growth chambers. The early establishment of these trees at the alpine treeline was limited either by temperature or by moisture, the sensitivity to one factor often depending on the intensity of the other. The results showed that the relative importance of the two factors and the direction of the effects are highly species-specific, while both factors tend to have consistent effects on both germination and early seedling survival within each species. We show that temperature and water availability are both important contributors to establishment patterns of treeline trees and hence to species-specific forms and positions of alpine treelines. The observed idiosyncratic species responses highlight the need for studies including several species and life-stages to create predictive power concerning future treeline dynamics. PMID:27402618

Early establishment of trees at the alpine treeline: idiosyncratic species responses to temperature-moisture interactions.

PubMed

Loranger, Hannah; Zotz, Gerhard; Bader, Maaike Y

2016-01-01

On a global scale, temperature is the main determinant of arctic and alpine treeline position. However on a local scale, treeline form and position vary considerably due to other climatic factors, tree species ecology and life-stage-dependent responses. For treelines to advance poleward or uphill, the first steps are germination and seedling establishment. These earliest life stages may be major bottlenecks for treeline tree populations and will depend differently on climatic conditions than adult trees. We investigated the effect of soil temperature and moisture on germination and early seedling survival in a field experiment in the French Alps near the local treeline (2100 m a.s.l.) using passive temperature manipulations and two watering regimes. Five European treeline tree species were studied: Larix decidua, Picea abies, Pinus cembra, Pinus uncinata and Sorbus aucuparia In addition, we monitored the germination response of three of these species to low temperatures under controlled conditions in growth chambers. The early establishment of these trees at the alpine treeline was limited either by temperature or by moisture, the sensitivity to one factor often depending on the intensity of the other. The results showed that the relative importance of the two factors and the direction of the effects are highly species-specific, while both factors tend to have consistent effects on both germination and early seedling survival within each species. We show that temperature and water availability are both important contributors to establishment patterns of treeline trees and hence to species-specific forms and positions of alpine treelines. The observed idiosyncratic species responses highlight the need for studies including several species and life-stages to create predictive power concerning future treeline dynamics. © The Authors 2016. Published by Oxford University Press on behalf of the Annals of Botany Company.

Calibration and Evaluation of Ultrasound Thermography using Infrared Imaging

PubMed Central

Hsiao, Yi-Sing; Deng, Cheri X.

2015-01-01

Real-time monitoring of the spatiotemporal evolution of tissue temperature is important to ensure safe and effective treatment in thermal therapies including hyperthermia and thermal ablation. Ultrasound thermography has been proposed as a non-invasive technique for temperature measurement, and accurate calibration of the temperature-dependent ultrasound signal changes against temperature is required. Here we report a method that uses infrared (IR) thermography for calibration and validation of ultrasound thermography. Using phantoms and cardiac tissue specimens subjected to high-intensity focused ultrasound (HIFU) heating, we simultaneously acquired ultrasound and IR imaging data from the same surface plane of a sample. The commonly used echo time shift-based method was chosen to compute ultrasound thermometry. We first correlated the ultrasound echo time shifts with IR-measured temperatures for material-dependent calibration and found that the calibration coefficient was positive for fat-mimicking phantom (1.49 ± 0.27) but negative for tissue-mimicking phantom (− 0.59 ± 0.08) and cardiac tissue (− 0.69 ± 0.18 °C-mm/ns). We then obtained the estimation error of the ultrasound thermometry by comparing against the IR measured temperature and revealed that the error increased with decreased size of the heated region. Consistent with previous findings, the echo time shifts were no longer linearly dependent on temperature beyond 45 – 50 °C in cardiac tissues. Unlike previous studies where thermocouples or water-bath techniques were used to evaluate the performance of ultrasound thermography, our results show that high resolution IR thermography provides a useful tool that can be applied to evaluate and understand the limitations of ultrasound thermography methods. PMID:26547634

Calibration and Evaluation of Ultrasound Thermography Using Infrared Imaging.

PubMed

Hsiao, Yi-Sing; Deng, Cheri X

2016-02-01

Real-time monitoring of the spatiotemporal evolution of tissue temperature is important to ensure safe and effective treatment in thermal therapies including hyperthermia and thermal ablation. Ultrasound thermography has been proposed as a non-invasive technique for temperature measurement, and accurate calibration of the temperature-dependent ultrasound signal changes against temperature is required. Here we report a method that uses infrared thermography for calibration and validation of ultrasound thermography. Using phantoms and cardiac tissue specimens subjected to high-intensity focused ultrasound heating, we simultaneously acquired ultrasound and infrared imaging data from the same surface plane of a sample. The commonly used echo time shift-based method was chosen to compute ultrasound thermometry. We first correlated the ultrasound echo time shifts with infrared-measured temperatures for material-dependent calibration and found that the calibration coefficient was positive for fat-mimicking phantom (1.49 ± 0.27) but negative for tissue-mimicking phantom (-0.59 ± 0.08) and cardiac tissue (-0.69 ± 0.18°C-mm/ns). We then obtained the estimation error of the ultrasound thermometry by comparing against the infrared-measured temperature and revealed that the error increased with decreased size of the heated region. Consistent with previous findings, the echo time shifts were no longer linearly dependent on temperature beyond 45°C-50°C in cardiac tissues. Unlike previous studies in which thermocouples or water bath techniques were used to evaluate the performance of ultrasound thermography, our results indicate that high-resolution infrared thermography is a useful tool that can be applied to evaluate and understand the limitations of ultrasound thermography methods. Copyright © 2016 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

Entanglement of solid vortex matter: a boomerang-shaped reduction forced by disorder in interlayer phase coherence in Bi2Sr2CaCu2O8+y.

PubMed

Kato, T; Shibauchi, T; Matsuda, Y; Thompson, J R; Krusin-Elbaum, L

2008-07-11

We present evidence for entangled solid vortex matter in a glassy state in a layered superconductor Bi2Sr2CaCu2O8+y containing randomly splayed linear defects. The interlayer phase coherence--probed by the Josephson plasma resonance--is enhanced at high temperatures, reflecting the recoupling of vortex liquid by the defects. At low temperatures in the vortex solid state, the interlayer coherence follows a boomerang-shaped reentrant temperature path with an unusual low-field decrease in coherence, indicative of meandering vortices. We uncover a distinct temperature scaling between in-plane and out-of-plane critical currents with opposing dependencies on field and time, consistent with the theoretically proposed "splayed-glass" state.

Spectroscopic study of shock-induced decomposition in ammonium perchlorate single crystals.

PubMed

Gruzdkov, Y A; Winey, J M; Gupta, Y M

2008-05-01

Time-resolved Raman scattering measurements were performed on ammonium perchlorate (AP) single crystals under stepwise shock loading. For particular temperature and pressure conditions, the intensity of the Raman spectra in shocked AP decayed exponentially with time. This decay is attributed to shock-induced chemical decomposition in AP. A series of shock experiments, reaching peak stresses from 10-18 GPa, demonstrated that higher stresses inhibit decomposition while higher temperatures promote it. No orientation dependence was found when AP crystals were shocked normal to the (210) and (001) crystallographic planes. VISAR (velocity interferometer system for any reflector) particle velocity measurements and time-resolved optical extinction measurements carried out to verify these observations are consistent with the Raman data. The combined kinetic and spectroscopic results are consistent with a proton-transfer reaction as the first decomposition step in shocked AP.

Biphasic Kinetic Behavior of E. coli WrbA, an FMN-Dependent NAD(P)H:Quinone Oxidoreductase

PubMed Central

Kishko, Iryna; Harish, Balasubramanian; Zayats, Vasilina; Reha, David; Tenner, Brian; Beri, Dhananjay; Gustavsson, Tobias; Ettrich, Rüdiger; Carey, Jannette

2012-01-01

The E. coli protein WrbA is an FMN-dependent NAD(P)H:quinone oxidoreductase that has been implicated in oxidative defense. Three subunits of the tetrameric enzyme contribute to each of four identical, cavernous active sites that appear to accommodate NAD(P)H or various quinones, but not simultaneously, suggesting an obligate tetramer with a ping-pong mechanism in which NAD departs before oxidized quinone binds. The present work was undertaken to evaluate these suggestions and to characterize the kinetic behavior of WrbA. Steady-state kinetics results reveal that WrbA conforms to a ping-pong mechanism with respect to the constancy of the apparent Vmax to Km ratio with substrate concentration. However, the competitive/non-competitive patterns of product inhibition, though consistent with the general class of bi-substrate reactions, do not exclude a minor contribution from additional forms of the enzyme. NMR results support the presence of additional enzyme forms. Docking and energy calculations find that electron-transfer-competent binding sites for NADH and benzoquinone present severe steric overlap, consistent with the ping-pong mechanism. Unexpectedly, plots of initial velocity as a function of either NADH or benzoquinone concentration present one or two Michaelis-Menten phases depending on the temperature at which the enzyme is held prior to assay. The effect of temperature is reversible, suggesting an intramolecular conformational process. WrbA shares these and other details of its kinetic behavior with mammalian DT-diaphorase, an FAD-dependent NAD(P)H:quinone oxidoreductase. An extensive literature review reveals several other enzymes with two-plateau kinetic plots, but in no case has a molecular explanation been elucidated. Preliminary sedimentation velocity analysis of WrbA indicates a large shift in size of the multimer with temperature, suggesting that subunit assembly coupled to substrate binding may underlie the two-plateau behavior. An additional aim of this report is to bring under wider attention the apparently widespread phenomenon of two-plateau Michaelis-Menten plots. PMID:22952804

Iron oxide particles in large pore zeolites

NASA Astrophysics Data System (ADS)

García, J. L.; López, A.; Lázaro, F. J.; Martínez, C.; Corma, A.

1996-05-01

The magnetic properties of iron-containing ETS-10 zeolite and its calcined variety have been studied by magnetic measurements. The results are consistent with the presence of paramagnetic ions and superparamagnetic clusters. Calcination results in a shift of the blocking temperatures, although their frequency dependence cannot be ascribed to non-interacting clusters. The hypothesis of cluster-glass like behaviour is discussed.

Phonons in quantum solids with defects. [lattice vacancies and interstitials in solid helium and metallic hydrogen

NASA Technical Reports Server (NTRS)

Jacobi, N.; Zmuidzinas, J. S.

1974-01-01

A formalism was developed for temperature-dependent, self-consistent phonons in quantum solids with defects. Lattice vacancies and interstitials in solid helium and metallic hydrogen, as well as electronic excitations in solid helium, were treated as defects that modify properties of these systems. The information to be gained from the modified phonon spectrum is discussed.

Performance and temperature dependencies of proton irradiated n/p and p/n GaAs and n/p silicon cells

NASA Technical Reports Server (NTRS)

Weinberg, I.; Swartz, C. K.; Hart, R. E., Jr.

1985-01-01

n/p homojunction GaAs cells are found to be more radiation resistant than p/n heteroface GaAs under 10 MeV proton irradiation. Both GaAs cell types outperform conventional silicon n/p cells under the same conditions. An increased temperature dependency of maximum power for the GaAs n/p cells is attributed to differences in Voc between the two GaAs cell types. These results and diffusion length considerations are consistent with the conclusion that p-type GaAs is more radiation resistant than n-type and therefore that the n/p configuration is possibly favored for use in the space radiation environment. However, it is concluded that additional work is required in order to choose between the two GaAs cell configurations.

Performance and temperature dependencies of proton irradiated n/p GaAs and n/p silicon cells

NASA Technical Reports Server (NTRS)

Weinberg, I.; Swartz, C. K.; Hart, R. E., Jr.

1985-01-01

The n/p homojunction GaAs cell is found to be more radiation resistant than p/nheteroface GaAs under 10 MeV proton irradiation. Both GaAs cell types outperform conventional silicon n/p cells under the same conditions. An increase temperature dependency of maximum power for the GaAs n/p cells is attributed largely to differences in Voc between the two GaAs cell types. These results and diffusion length considerations are consistent with the conclusion that p-type GaAs is more radiation resistant than n-type and therefore that the n/p configuration is possibly favored for use in the space radiation environment. However, it is concluded that additional work is required in order to choose between the two GaAs cell configurations.

Flux pinning characteristics in cylindrical ingot niobium used in superconducting radio frequency cavity fabrication

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

Dhavale Ashavai, Pashupati Dhakal, Anatolii A Polyanskii, Gianluigi Ciovati

We present the results of from DC magnetization and penetration depth measurements of cylindrical bulk large-grain (LG) and fine-grain (FG) niobium samples used for the fabrication of superconducting radio frequency (SRF) cavities. The surface treatment consisted of electropolishing and low temperature baking as they are typically applied to SRF cavities. The magnetization data were fitted using a modified critical state model. The critical current density Jc and pinning force Fp are calculated from the magnetization data and their temperature dependence and field dependence are presented. The LG samples have lower critical current density and pinning force density compared to FGmore » samples which implies a lower flux trapping efficiency. This effect may explain the lower values of residual resistance often observed in LG cavities than FG cavities.« less

Spectral characteristics of the microwave emission from a wind-driven foam-covered sea

NASA Technical Reports Server (NTRS)

Webster, W. J., Jr.; Wilheit, T. T.; Gloersen, P.; Ross, D. B.

1976-01-01

Aircraft observations of the microwave emission from the wind-driven foam-covered Bering Sea substantiate earlier results and show that the combination of surface roughness and white water yields a significant microwave brightness temperature dependence on wind speed over a wide range of microwave wavelengths, with a decreasing dependence for wavelengths above 6 cm. The spectral characteristic of brightness temperature as a function of wind speed is consistent with a foam model in which the bubbles give rise to a cusped surface between the foam and the sea. In the fetch-limited situation the contribution of the wave structure at the surface appears to increase as the foam coverage decreases. Although the data show that the thin streaks are the most important part of the white water signature, there is some evidence for the contribution of whitecaps.

Testing the Reliability of Cluster Mass Indicators with a Systematics Limited Dataset

NASA Technical Reports Server (NTRS)

Juett, Adrienne M.; Davis, David S.; Mushotzky, Richard

2009-01-01

We present the mass X-ray observable scaling relationships for clusters of galaxies using the XMM-Newton cluster catalog of Snowden et al. Our results are roughly consistent with previous observational and theoretical work, with one major exception. We find 2-3 times the scatter around the best fit mass scaling relationships as expected from cluster simulations or seen in other observational studies. We suggest that this is a consequence of using hydrostatic mass, as opposed to virial mass, and is due to the explicit dependence of the hydrostatic mass on the gradients of the temperature and gas density profiles. We find a larger range of slope in the cluster temperature profiles at radii 500 than previous observational studies. Additionally, we find only a weak dependence of the gas mass fraction on cluster mass, consistent with a constant. Our average gas mass fraction results also argue for a closer study of the systematic errors due to instrumental calibration and modeling method variations between analyses. We suggest that a more careful study of the differences between various observational results and with cluster simulations is needed to understand sources of bias and scatter in cosmological studies of galaxy clusters.

Nuclear Pasta at Finite Temperature with the Time-Dependent Hartree-Fock Approach

NASA Astrophysics Data System (ADS)

Schuetrumpf, B.; Klatt, M. A.; Iida, K.; Maruhn, J. A.; Mecke, K.; Reinhard, P.-G.

2016-01-01

We present simulations of neutron-rich matter at sub-nuclear densities, like supernova matter. With the time-dependent Hartree-Fock approximation we can study the evolution of the system at temperatures of several MeV employing a full Skyrme interaction in a periodic three-dimensional grid [1]. The initial state consists of α particles randomly distributed in space that have a Maxwell-Boltzmann distribution in momentum space. Adding a neutron background initialized with Fermi distributed plane waves the calculations reflect a reasonable approximation of astrophysical matter. The matter evolves into spherical, rod-like, connected rod-like and slab-like shapes. Further we observe gyroid-like structures, discussed e.g. in [2], which are formed spontaneously choosing a certain value of the simulation box length. The ρ-T-map of pasta shapes is basically consistent with the phase diagrams obtained from QMD calculations [3]. By an improved topological analysis based on Minkowski functionals [4], all observed pasta shapes can be uniquely identified by only two valuations, namely the Euler characteristic and the integral mean curvature. In addition we propose the variance in the cell-density distribution as a measure to distinguish pasta matter from uniform matter.

[Thermal tolerance, diel variation of body temperature, and thermal dependence of locomotor performance of hatchling soft-shelled turtles, Trionyx sinensis].

PubMed

Sun, Pingyue; Xu, Xiaoyin; Chen, Huili; Ji, Xiang

2002-09-01

The thermal tolerance, body temperature, and influence of temperature on locomotor performance of hatchling soft-shelled turtles (Trionyx sinensis) were studied under dry and wet conditions, and the selected body temperature of hatchlings was 28.0 and 30.3 degrees C, respectively. Under wet condition, the critical thermal maximum and minimum averaged 40.9 and 7.8 degrees C, respectively. In the environments without thermal gradients, the diel variation of body temperature was highly consistent with the variation of both air and water temperatures, and the body temperature was more directly affected by water temperature than by air temperature, which implied that the physiological thermoregulation of hatchling T. sinensis was very weak. In the environments with thermal gradients, hatchling turtles could maintain relatively high and constant body temperatures, primarily through behavioral thermoregulation. The locomotor performance of hatchling turtles was highly dependent on their body temperature. Within a certain range, the locomotor performance increased with increasing body temperature. In our study, the optimal body temperature for locomotor performance was 31.5 degrees C, under which, the maximum continuous running distance, running distance per minute, and number of stops per minute averaged 1.87 m, 4.92 m.min-1, and 6.2 times.min-1, respectively. The correspondent values at 33.0 degrees C averaged 1.30 m, 4.28 m.min-1, and 7.7 times.min-1, respectively, which indicated that the locomotor performance of hatchling turtles was impaired at 33.0 degrees C. Therefore, extremely high body temperatures might have an adverse effect on locomotor performance of hatchling turtles.

Environmental signals modulate ToxT-dependent virulence factor expression in Vibrio cholerae.

PubMed

Schuhmacher, D A; Klose, K E

1999-03-01

The regulatory protein ToxT directly activates the transcription of virulence factors in Vibrio cholerae, including cholera toxin (CT) and the toxin-coregulated pilus (TCP). Specific environmental signals stimulate virulence factor expression by inducing the transcription of toxT. We demonstrate that transcriptional activation by the ToxT protein is also modulated by environmental signals. ToxT expressed from an inducible promoter activated high-level expression of CT and TCP in V. cholerae at 30 degrees C, but expression of CT and TCP was significantly decreased or abolished by the addition of 0.4% bile to the medium and/or an increase of the temperature to 37 degrees C. Also, expression of six ToxT-dependent TnphoA fusions was modulated by temperature and bile. Measurement of ToxT-dependent transcription of genes encoding CT and TCP by ctxAp- and tcpAp-luciferase fusions confirmed that negative regulation by 37 degrees C or bile occurs at the transcriptional level in V. cholerae. Interestingly, ToxT-dependent transcription of these same promoters in Salmonella typhimurium was relatively insensitive to regulation by temperature or bile. These data are consistent with ToxT transcriptional activity being modulated by environmental signals in V. cholerae and demonstrate an additional level of complexity governing the expression of virulence factors in this pathogen. We propose that negative regulation of ToxT-dependent transcription by environmental signals prevents the incorrect temporal and spatial expression of virulence factors during cholera pathogenesis.

Temperature dependence and GABA modulation of (TH)triazolam binding in the rat brain

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

Earle, M.E.; Concas, A.; Wamsley, J.K.

1987-07-27

The hypnotic triazolam (TZ), a triazolobenzodiazepine displays a short physiological half life and has been used for the treatment of insomnia related to anxiety states. The authors major objectives were the direct measurement of the temperature dependence and the gamma-aminobutyric acid (GABA) effect of (TH)TZ binding in the rat brain. Saturation studies showed a shift to lower affinity with increasing temperatures (K/sub d/ = 0.27 +/- 08 nM at 0C; K/sub d/ = 1.96 +/- 0.85 nM at 37C) while the B/sub max/ values remained unchanged (1220 +/- 176 fmoles/mg protein at 0C and 1160 +/- 383 fmoles/mg protein atmore » 37C). Saturation studies of (TH)TZ binding in the presence or absence of GABA (100 M) showed a GABA-shift. At 0C the K/sub d/ values were (K/sub d/ = 0.24 +/- 0.03 nM/-GABA; K/sub d/ = 0.16 +/- 0.04/+GABA) and at 37C the K/sub d/ values were (K/sub d/ = 1.84 +/- 0.44 nM/-GABA; K/sub d/ = 0.95 +/- 0.29 nM/+GABA). In contrast to reported literature, the authors findings show that TZ interacts with benzodiazepine receptors with a temperature dependence and GABA-shift consistent with predicted behavior for benzodiazepine agonists. 20 references, 3 tables.« less

Diffusive and subdiffusive dynamics of indoor microclimate: a time series modeling.

PubMed

Maciejewska, Monika; Szczurek, Andrzej; Sikora, Grzegorz; Wyłomańska, Agnieszka

2012-09-01

The indoor microclimate is an issue in modern society, where people spend about 90% of their time indoors. Temperature and relative humidity are commonly used for its evaluation. In this context, the two parameters are usually considered as behaving in the same manner, just inversely correlated. This opinion comes from observation of the deterministic components of temperature and humidity time series. We focus on the dynamics and the dependency structure of the time series of these parameters, without deterministic components. Here we apply the mean square displacement, the autoregressive integrated moving average (ARIMA), and the methodology for studying anomalous diffusion. The analyzed data originated from five monitoring locations inside a modern office building, covering a period of nearly one week. It was found that the temperature data exhibited a transition between diffusive and subdiffusive behavior, when the building occupancy pattern changed from the weekday to the weekend pattern. At the same time the relative humidity consistently showed diffusive character. Also the structures of the dependencies of the temperature and humidity data sets were different, as shown by the different structures of the ARIMA models which were found appropriate. In the space domain, the dynamics and dependency structure of the particular parameter were preserved. This work proposes an approach to describe the very complex conditions of indoor air and it contributes to the improvement of the representative character of microclimate monitoring.

Design, Analysis and Implementation of an Experimental System to Harvest Energy From Atmospheric Temperature Variations Using Ethyl Chloride Filled Bellows

NASA Astrophysics Data System (ADS)

Ali, Gibran

The increase in global warming and the dwindling supplies of fossil fuels have shifted the focus from traditional to alternate sources of energy. This has resulted in a concerted effort towards finding new energy sources as well as better understanding traditional renewable energy sources such as wind and solar power. In addition to the shift in focus towards alternate energy, the last two decades have offered a dramatic rise in the use of digital technologies such as wireless sensor networks that require small but isolated power supplies. Energy harvesting, a method to gather energy from ambient sources including sunlight, vibrations, heat, etc., has provided some success in powering these systems. One of the unexplored areas of energy harvesting is the use of atmospheric temperature variations to obtain usable energy. This thesis investigates an innovative mechanism to extract energy from atmospheric variations using ethyl chloride filled mechanical bellows. The energy harvesting process was divided into two parts. The first part consisted of extracting energy from the temperature variations and converting it into the potential energy stored in a linear coil spring. This was achieved by designing and fabricating an apparatus that consisted of an ethyl chloride filled bellows working against a mechanical spring in a closed and controlled environment. The bellows expanded/contracted depending upon the ambient temperature and the energy harvested was calculated as a function of the bellows' length. The experiments showed that 6 J of potential energy may be harvested for a 23°C change in temperature. The numerical results closely correlated to the experimental data with an error magnitude of 1%. In regions with high diurnal temperature variation, such an apparatus may yield approximately 250 microwatts depending on the diurnal temperature range. The second part of the energy harvesting process consisted of transforming linear expansion of the bellows into electric power. A system was designed and simulated using Mathworks Simulink and SimDriveline packages that converted the linear oscillations of the bellows into electric power. This was achieved in two steps; a gear train was designed that would convert the linear displacement of the bellows into potential energy stored in a spiral spring. The spiral spring would then periodically engage to a small generator producing electric power. The electrical power generated was found to depend solely on the potential energy stored in the spring. It was discovered that for a sinusoidal force with constant amplitude and frequency, the potential energy stored in the spring depended on the duration of force input and the parameters of the drivetrain such as the spring stiffness, the gear ratios, and the pinion radii. After simulating the system for different parameters, an optimal set of values was presented to maximize the electrical energy output for a given duration of time. For constant amplitude (120 N) sinusoidal force input with a time period of T seconds, the system stored 37 J, 65 J, and 90 J after a time of 3T, 5T, and 7T, respectively. The electric power output was 7.14 microwatts for a conversion efficiency of 5%. The next step is building a physical geartrain generator assembly based on the design presented in the thesis. The physical system will first be verified by simulating the force input using a pneumatic cylinder. The two parts of the research experiment can then be integrated into one system that would generate electric power directly from temporal temperature and pressure variations.

Thermal acclimation of leaf photosynthetic traits in an evergreen woodland, consistent with the coordination hypothesis

NASA Astrophysics Data System (ADS)

Fürstenau Togashi, Henrique; Prentice, Iain Colin; Atkin, Owen K.; Macfarlane, Craig; Prober, Suzanne M.; Bloomfield, Keith J.; Evans, Bradley John

2018-06-01

Ecosystem models commonly assume that key photosynthetic traits, such as carboxylation capacity measured at a standard temperature, are constant in time. The temperature responses of modelled photosynthetic or respiratory rates then depend entirely on enzyme kinetics. Optimality considerations, however, suggest this assumption may be incorrect. The coordination hypothesis (that Rubisco- and electron-transport-limited rates of photosynthesis are co-limiting under typical daytime conditions) predicts, instead, that carboxylation (Vcmax) capacity should acclimate so that it increases somewhat with growth temperature but less steeply than its instantaneous response, implying that Vcmax when normalized to a standard temperature (e.g. 25 °C) should decline with growth temperature. With additional assumptions, similar predictions can be made for electron-transport capacity (Jmax) and mitochondrial respiration in the dark (Rdark). To explore these hypotheses, photosynthetic measurements were carried out on woody species during the warm and the cool seasons in the semi-arid Great Western Woodlands, Australia, under broadly similar light environments. A consistent proportionality between Vcmax and Jmax was found across species. Vcmax, Jmax and Rdark increased with temperature in most species, but their values standardized to 25 °C declined. The ci : ca ratio increased slightly with temperature. The leaf N : P ratio was lower in the warm season. The slopes of the relationships between log-transformed Vcmax and Jmax and temperature were close to values predicted by the coordination hypothesis but shallower than those predicted by enzyme kinetics.

Environmental Effects on the Metallicities of Early-Type Galaxies

NASA Technical Reports Server (NTRS)

Jones, Christine; Oliversen, Ronald (Technical Monitor)

2004-01-01

We completed and published two papers in the Astrophysical Journal based on research from grant. In the first paper we analyzed nine X-ray-bright Virgo early-type galaxies observed by both ASCA and ROSAT. Through spatially resolved spectroscopy, we determined the radial temperature profiles and abundances of Mg, Si, and Fe for six galaxies. The temperature profiles are consistent with isothermal temperatures outside of cooler regions at the galaxies' centers. We present new evidence for iron abundance gradients in NGC 4472 and NGC 4649 and confirm the previous results on NGC 4636. Mg and Si abundance gradients on average are flatter than those of iron and correspond to an underabundance of α-process elements at high Fe values, while at low iron the element ratios favor enrichment by Type II supernovae (SNe). We explain the observed trend using the metallicity dependence of SN Ia metal production and present constraints on the available theoretical modeling for low-metallicity inhibition of SNe Ia. In the second paper We analyzed nine X-ray-bright Virgo early-type galaxies observed by both ASCA and ROSAT. Through spatially resolved spectroscopy, we determined the radial temperature profiles and abundances of Mg, Si, and Fe for six galaxies. The temperature profiles are consistent with isothermal temperatures outside of cooler regions at the galaxies' centers. We present new evidence for iron abundance gradients in NGC 4472 and NGC 4649 and confirm the previous results on NGC 4636. Mg and Si abundance gradients on average are flatter than those of iron and correspond to an underabundance of α-process elements at high Fe values, while at low iron the element ratios favor enrichment by Type I1 supernovae (SNe). We explain the observed trend using the metallicity dependence of SN Ia metal production and present constraints on the available theoretical modeling for low-metallicity inhibition of SNe Ia.

Pulse echo and combined resonance techniques: a full set of LGT acoustic wave constants and temperature coefficients.

PubMed

Sturtevant, Blake T; Davulis, Peter M; da Cunha, Mauricio Pereira

2009-04-01

This work reports on the determination of langatate elastic and piezoelectric constants and their associated temperature coefficients employing 2 independent methods, the pulse echo overlap (PEO) and a combined resonance technique (CRT) to measure bulk acoustic wave (BAW) phase velocities. Details on the measurement techniques are provided and discussed, including the analysis of the couplant material in the PEO technique used to couple signal to the sample, which showed to be an order of magnitude more relevant than the experimental errors involved in the data extraction. At room temperature, elastic and piezoelectric constants were extracted by the PEO and the CRT methods and showed results consistent to within a few percent for the elastic constants. Both raw acquired data and optimized constants, based on minimization routines applied to all the modes involved in the measurements, are provided and discussed. Comparison between the elastic constants and their temperature behavior with the literature reveals the recent efforts toward the consistent growth and characterization of LGT, in spite of significant variations (between 1 and 30%) among the constants extracted by different groups at room temperature. The density, dielectric permittivity constants, and respective temperature coefficients used in this work have also been independently determined based on samples from the same crystal boule. The temperature behavior of the BAW modes was extracted using the CRT technique, which has the advantage of not relying on temperature dependent acoustic couplants. Finally, the extracted temperature coefficients for the elastic and piezoelectric constants between room temperature and 120 degrees C are reported and discussed in this work.

Temperature dependence of structure, bending rigidity, and bilayer interactions of dioleoylphosphatidylcholine bilayers.

PubMed

Pan, Jianjun; Tristram-Nagle, Stephanie; Kucerka, Norbert; Nagle, John F

2008-01-01

X-ray diffuse scattering was measured from oriented stacks and unilamellar vesicles of dioleoylphosphatidylcholine lipid bilayers to obtain the temperature dependence of the structure and of the material properties. The area/molecule, A, was 75.5 A(2) at 45 degrees C, 72.4 A(2) at 30 degrees C, and 69.1 A(2) at 15 degrees C, which gives the area expansivity alpha(A) = 0.0029/deg at 30 degrees C, and we show that this value is in excellent agreement with the polymer brush theory. The bilayer becomes thinner with increasing temperature; the contractivity of the hydrocarbon portion was alpha(Dc) = 0.0019/deg; the difference between alpha(A) and alpha(Dc) is consistent with the previously measured volume expansivity alpha(Vc) = 0.0010/deg. The bending modulus K(C) decreased as exp(455/T) with increasing T (K). Our area compressibility modulus K(A) decreased with increasing temperature by 5%, the same as the surface tension of dodecane/water, in agreement again with the polymer brush theory. Regarding interactions between bilayers, the compression modulus B as a function of interbilayer water spacing D'(W) was found to be nearly independent of temperature. The repulsive fluctuation pressure calculated from B and K(C) increased with temperature, and the Hamaker parameter for the van der Waals interaction was nearly independent of temperature; this explains why the fully hydrated water spacing, D'(W), that we obtain from our structural results increases with temperature.

Temperature optimum of insulin-stimulated 2-deoxy-D-glucose uptake in rat adipocytes. Correlation of cellular transport with membrane spin-label and fluorescence-label data.

PubMed Central

Hyslop, P A; Kuhn, C E; Sauerheber, R D

1984-01-01

The effects of temperature alterations between 22 degrees C and 48 degrees C on basal and insulin-stimulated 2-deoxy-D-[1-14C]glucose uptake were examined in isolated rat adipocytes. A distinct optimum was found near physiological temperature for uptake in the presence of maximally effective insulin concentrations where insulin stimulation and hexose uptake were both conducted at each given assay temperature. Basal uptake was only subtly affected. Control and maximally insulin-stimulated cells incubated at 35 degrees C subsequently exhibited minimal temperature-sensitivity of uptake measured between 30 and 43 degrees C. The data are mostly consistent with the concept that insulin-sensitive glucose transporters are, after stimulation by insulin, functionally similar to basal transporters. Adipocyte plasma membranes were labelled with various spin- and fluorescence-label probes in lipid structural studies. The temperature-dependence of the order parameter S calculated from membranes labelled with 5-nitroxide stearate indicated the presence of a lipid phase change at approx. 33 degrees C. Membranes labelled with the fluorescence label 1,6-diphenylhexa-1,3,5-triene, or the cholesterol-like spin label nitroxide cholestane, reveal sharp transitions at lower temperatures. We suggest that a thermotropic lipid phase separation occurs in the adipocyte membrane that may be correlated with the temperature-dependence of hexose transport and insulin action in the intact cells. PMID:6324752

Process for forming retrograde profiles in silicon

DOEpatents

Weiner, K.H.; Sigmon, T.W.

1996-10-15

A process is disclosed for forming retrograde and oscillatory profiles in crystalline and polycrystalline silicon. The process consisting of introducing an n- or p-type dopant into the silicon, or using prior doped silicon, then exposing the silicon to multiple pulses of a high-intensity laser or other appropriate energy source that melts the silicon for short time duration. Depending on the number of laser pulses directed at the silicon, retrograde profiles with peak/surface dopant concentrations which vary are produced. The laser treatment can be performed in air or in vacuum, with the silicon at room temperature or heated to a selected temperature.

Nearly Perfect Triplet-Triplet Energy Transfer from Wannier Excitons to Naphthalene in Organic-Inorganic Hybrid Quantum-Well Materials

NASA Astrophysics Data System (ADS)

Ema, K.; Inomata, M.; Kato, Y.; Kunugita, H.; Era, M.

2008-06-01

We report the observation of extremely efficient energy transfer (greater than 99%) in an organic-inorganic hybrid quantum-well structure consisting of perovskite-type lead bromide well layers and naphthalene-linked ammonium barrier layers. Time-resolved photoluminescence measurements confirm that the transfer is triplet-triplet Dexter-type energy transfer from Wannier excitons in the inorganic well to the triplet state of naphthalene molecules in the organic barrier. Using measurements in the 10 300 K temperature range, we also investigated the temperature dependence of the energy transfer.

Effect of electron beam on the properties of electron-acoustic rogue waves

NASA Astrophysics Data System (ADS)

El-Shewy, E. K.; Elwakil, S. A.; El-Hanbaly, A. M.; Kassem, A. I.

2015-04-01

The properties of nonlinear electron-acoustic rogue waves have been investigated in an unmagnetized collisionless four-component plasma system consisting of a cold electron fluid, Maxwellian hot electrons, an electron beam and stationary ions. It is found that the basic set of fluid equations is reduced to a nonlinear Schrodinger equation. The dependence of rogue wave profiles and the associated electric field on the carrier wave number, normalized density of hot electron and electron beam, relative cold electron temperature and relative beam temperature are discussed. The results of the present investigation may be applicable in auroral zone plasma.

μ SR and magnetometry study of superconducting 5% Pt-doped IrTe 2

DOE PAGES

Wilson, M. N.; Medina, T.; Munsie, T. J.; ...

2016-11-11

In this paper, we present magnetometry and muon spin rotation ( SR) measurements of the superconducting dichalcogenide Ir 0.95Pt 0.05Te 2. From both sets of measurements we calculate the penetration depth and thence superfluid density as a function of temperature. The temperature dependence of the superfluid densities from both sets of data indicate fully gapped superconductivity that can be fit to a conventional s-wave model and yield fitting parameters consistent with a BCS weak coupling superconductor. Finally, we therefore see no evidence for exotic superconductivity in Ir 0.95Pt 0.05Te 2.

μ SR and magnetometry study of superconducting 5% Pt-doped IrTe2

NASA Astrophysics Data System (ADS)

Wilson, M. N.; Medina, T.; Munsie, T. J.; Cheung, S. C.; Frandsen, B. A.; Liu, L.; Yan, J.; Mandrus, D.; Uemura, Y. J.; Luke, G. M.

2016-11-01

We present magnetometry and muon spin rotation (μ SR ) measurements of the superconducting dichalcogenide Ir0.95Pt0.05Te2 . From both sets of measurements, we calculate the penetration depth and thence superfluid density as a function of temperature. The temperature dependence of the superfluid densities from both sets of data indicate fully gapped superconductivity that can be fit to a conventional s -wave model and yield fitting parameters consistent with a BCS weak coupling superconductor. We therefore see no evidence for exotic superconductivity in Ir0.95Pt0.05Te2 .

Formation of quasi-single crystalline porous ZnO nanostructures with a single large cavity

NASA Astrophysics Data System (ADS)

Cho, Seungho; Kim, Semi; Jung, Dae-Won; Lee, Kun-Hong

2011-09-01

We report a method for synthesizing quasi-single crystalline porous ZnO nanostructures containing a single large cavity. The microwave-assisted route consists of a short (about 2 min) temperature ramping stage (from room temperature to 120 °C) and a stage in which the temperature is maintained at 120 °C for 2 h. The structures produced by this route were 200-480 nm in diameter. The morphological yields of this method were very high. The temperature- and time-dependent evolution of the synthesized powders and the effects of an additive, vitamin C, were studied. Spherical amorphous/polycrystalline structures (70-170 nm in diameter), which appeared transitorily, may play a key role in the formation of the single crystalline porous hollow ZnO nanostructures. Studies and characterization of the nanostructures suggested a possible mechanism for formation of the quasi-single crystalline porous ZnO nanostructures with an interior space.We report a method for synthesizing quasi-single crystalline porous ZnO nanostructures containing a single large cavity. The microwave-assisted route consists of a short (about 2 min) temperature ramping stage (from room temperature to 120 °C) and a stage in which the temperature is maintained at 120 °C for 2 h. The structures produced by this route were 200-480 nm in diameter. The morphological yields of this method were very high. The temperature- and time-dependent evolution of the synthesized powders and the effects of an additive, vitamin C, were studied. Spherical amorphous/polycrystalline structures (70-170 nm in diameter), which appeared transitorily, may play a key role in the formation of the single crystalline porous hollow ZnO nanostructures. Studies and characterization of the nanostructures suggested a possible mechanism for formation of the quasi-single crystalline porous ZnO nanostructures with an interior space. Electronic supplementary information (ESI) available: TEM images and the corresponding SAED image of a ZnO nanostructure synthesized from the reaction without l(+)-ascorbic acid at the 85 °C time point (Fig. S1). See DOI: 10.1039/c1nr10609k

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

PubMed Central

Hatakeyama, Tetsuhiro S.; Kaneko, Kunihiko

2012-01-01

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

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

PubMed

Hatakeyama, Tetsuhiro S; Kaneko, Kunihiko

2012-05-22

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

Half-life of the electron-capture decay of {sup 97}Ru: Precision measurement shows no temperature dependence

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

Goodwin, J. R.; Golovko, V. V.; Iacob, V. E.

2009-10-15

We have measured the half-life of the electron-capture (ec) decay of {sup 97}Ru in a metallic environment, both at low temperature (19 K), and also at room temperature. We find the half-lives at both temperatures to be the same within 0.1%. This demonstrates that a recent claim that the ec decay half-life for {sup 7}Be changes by 0.9%{+-}0.2% under similar circumstances certainly cannot be generalized to other ec decays. Our results for the half-life of {sup 97}Ru, 2.8370(14) d at room temperature and 2.8382(14) d at 19 K, are consistent with, but much more precise than, previous room-temperature measurements. Inmore » addition, we have also measured the half-lives of the {beta}{sup -}-emitters {sup 103}Ru and {sup 105}Rh at both temperatures, and found them also to be unchanged.« less

Creep of Ni(3)Al in the temperature regime of anomalous flow behavior

NASA Astrophysics Data System (ADS)

Uchic, Michael David

Much attention has been paid to understanding the dynamics of dislocation motion and substructure formation in Ni3Al in the anomalous flow regime. However, most of the experimental work that has been performed in the lowest temperatures of the anomalous flow regime has been under constant-strain-rate conditions. An alternative and perhaps more fundamental way to probe the plastic behavior of materials is a monotonic creep test, in which the stress and temperature are held constant while the time-dependent strain is measured. The aim of this study is to use constant-stress experiments to further explore the plastic flow anomaly in L12 alloys at low temperatures. Tension creep experiments have been carried out on <123> oriented single crystals of Ni75Al24Ta1 at temperatures between 293 and 473 K. We have observed primary creep leading to exhaustion at all temperatures and stresses, with creep rates declining faster than predicted by the logarithmic creep law. The total strain and creep strain have an anomalous dependence on temperature, which is consistent with the flow stress anomaly. We have also observed other unusual behavior in our creep experiments; for example, the reinitiation of plastic flow at low temperatures after a modest increment in applied stress shows a sigmoidal response, i.e., there is a significant time delay before the plastic strain rate accelerates to a maximum value. We also examined the ability to reinitiate plastic flow in samples that have been crept to exhaustion by simply lowering the test temperature. In addition, we have also performed conventional constant-displacement-rate experiments in the same temperature range. From these experiments, we have discovered that unlike most metals, Ni3Al displays a negative dependence of the work hardening rate (WHR) with increasing strain rate. For tests at intermediate temperatures (373 and 423 K), the WHRs of crystals tested at moderately high strain rates (10-2 s-1) are half the WHRs of crystals tested at conventional strain rates (10 -5 s-1), and this anomalous dependence has also been shown to be reversible with changes in strain rate. The implications of all results are discussed in light of our efforts to model plastic deformation in these alloys.

SiC JFET Transistor Circuit Model for Extreme Temperature Range

NASA Technical Reports Server (NTRS)

Neudeck, Philip G.

2008-01-01

A technique for simulating extreme-temperature operation of integrated circuits that incorporate silicon carbide (SiC) junction field-effect transistors (JFETs) has been developed. The technique involves modification of NGSPICE, which is an open-source version of the popular Simulation Program with Integrated Circuit Emphasis (SPICE) general-purpose analog-integrated-circuit-simulating software. NGSPICE in its unmodified form is used for simulating and designing circuits made from silicon-based transistors that operate at or near room temperature. Two rapid modifications of NGSPICE source code enable SiC JFETs to be simulated to 500 C using the well-known Level 1 model for silicon metal oxide semiconductor field-effect transistors (MOSFETs). First, the default value of the MOSFET surface potential must be changed. In the unmodified source code, this parameter has a value of 0.6, which corresponds to slightly more than half the bandgap of silicon. In NGSPICE modified to simulate SiC JFETs, this parameter is changed to a value of 1.6, corresponding to slightly more than half the bandgap of SiC. The second modification consists of changing the temperature dependence of MOSFET transconductance and saturation parameters. The unmodified NGSPICE source code implements a T(sup -1.5) temperature dependence for these parameters. In order to mimic the temperature behavior of experimental SiC JFETs, a T(sup -1.3) temperature dependence must be implemented in the NGSPICE source code. Following these two simple modifications, the Level 1 MOSFET model of the NGSPICE circuit simulation program reasonably approximates the measured high-temperature behavior of experimental SiC JFETs properly operated with zero or reverse bias applied to the gate terminal. Modification of additional silicon parameters in the NGSPICE source code was not necessary to model experimental SiC JFET current-voltage performance across the entire temperature range from 25 to 500 C.

Decay constants of the charmed tensor mesons at finite temperature

NASA Astrophysics Data System (ADS)

Azizi, K.; Sundu, H.; Türkan, A.; Veliev, E. Veli

2016-01-01

Investigation of the thermal properties of the mesons with higher spin is one of the important problems in the hadron physics. At finite temperature, the Lorentz invariance is broken by the choice of a preferred frame of reference and some new operators appear in the Wilson expansion. Taking into account these additional operators, we calculate the thermal two-point correlation function for D2*(2460 ) and Ds2 *(2573 ) tensor mesons. In order to perform the numerical analysis, we use the fermionic part of the energy density obtained both from lattice QCD and Chiral perturbation theory. We also use the temperature dependent continuum threshold and show that the values of the decay constants decrease considerably near to the critical temperature compared to their values in the vacuum. Our results at zero temperature are in good consistency with predictions of other nonperturbative models.

Effects of cycling temperatures on the voltage fade phenomenon in 0.5Li 2 MnO 3 ·0.5LiNi 0.375 Mn 0.375 Co 0.25 O 2 cathodes

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

Vu, Anh; Walker, Lee K.; Bareño, Javier

2015-04-01

The rate of voltage fade in 0.5Li2MnO3•0.5LiNi0.375Mn0.375Co0.25O2 cathodes was measured in half-cells in a temperature range of 25 to 55°C. On the basis of the dependence of the values of the open-circuit potential with cycle count and temperature, the voltage fade phenomenon seems to consist of two chemical processes: one that can be described using a parabolic rate law and another that uses a linear-with-time law. As the cycling temperature increased, the relative contributions of the two processes changed. On the basis of the overall rate versus temperature data, we believe the two processes may be in competition with onemore » another.« less

Site Redistribution, Partial Frozen-in Defect Chemistry, and Electrical Properties of Ba1-x(Zr,Pr)O3-δ.

PubMed

Antunes, Isabel; Mikhalev, Sergey; Mather, Glenn Christopher; Kharton, Vladislav Vadimovich; Figueiras, Fábio Gabriel; Alves, Adriana; Rodrigues, Joana; Correia, Maria Rosário; Frade, Jorge Ribeiro; Fagg, Duncan Paul

2016-09-06

Changes in nominal composition of the perovskite (ABO3) solid solution Ba1-x(Zr,Pr)O3-δ and adjusted firing conditions at very high temperatures were used to induce structural changes involving site redistribution and frozen-in point defects, as revealed by Raman and photoluminescence spectroscopies. Complementary magnetic measurements allowed quantification of the reduced content of Pr. Weak dependence of oxygen stoichiometry with temperature was obtained by coulometric titration at temperatures below 1000 °C, consistent with a somewhat complex partial frozen-in defect chemistry. Electrical conductivity measurements combined with transport number and Seebeck coefficient measurements showed prevailing electronic transport and also indicated trends expected for partial frozen-in conditions. Nominal Ba deficiency and controlled firing at very high temperatures allows adjustment of structure and partial frozen-in defect chemistry, opening the way to engineer relevant properties for high-temperature electrochemical applications.

Development of an instrumentation system for measurement of degradation of lubricating oil using optical fiber sensor

NASA Astrophysics Data System (ADS)

Laskar, S.; Bordoloi, S.

2016-01-01

This paper presents an instrumentation system to measure the degradation in lubricating oil using a bare, tapered and bent multi-mode optical fiber (BTBMOF) sensor probe and a temperature probe. The sensor system consists of (i) a bare, tapered and bent multi-mode optical fiber (BTBMOF) as optical sensor along with a laser source and a LDR (Light Dependent Resistor) as detector (ii) a temperature sensor (iii) a ATmega microcontroller based data acquisition system and (iv) a trained ANN for processing and calibration. The BTBMOF sensor and the temperature sensor are used to provide the measure of refractive index (RI) and the temperature of a lubricating oil sample. A microcontroller based instrumentation system with trained ANN algorithm has been developed to determine the degradation of the lubricating oil sample by sampling the readings of the optical fiber sensor, and the temperature sensor.

The cosmological Higgstory of the vacuum instability

DOE PAGES

Espinosa, José R.; Giudice, Gian F.; Morgante, Enrico; ...

2015-09-24

We report that the Standard Model Higgs potential becomes unstable at large field values. After clarifying the issue of gauge dependence of the effective potential, we study the cosmological evolution of the Higgs field in presence of this instability throughout inflation, reheating and the present epoch. We conclude that anti-de Sitter patches in which the Higgs field lies at its true vacuum are lethal for our universe. From this result, we derive upper bounds on the Hubble constant during inflation, which depend on the reheating temperature and on the Higgs coupling to the scalar curvature or to the inflaton. Finallymore » we study how a speculative link between Higgs meta-stability and consistence of quantum gravity leads to a sharp prediction for the Higgs and top masses, which is consistent with measured values.« less

Quasiparticle self-consistent GW study of cuprates: electronic structure, model parameters, and the two-band theory for Tc.

PubMed

Jang, Seung Woo; Kotani, Takao; Kino, Hiori; Kuroki, Kazuhiko; Han, Myung Joon

2015-07-24

Despite decades of progress, an understanding of unconventional superconductivity still remains elusive. An important open question is about the material dependence of the superconducting properties. Using the quasiparticle self-consistent GW method, we re-examine the electronic structure of copper oxide high-Tc materials. We show that QSGW captures several important features, distinctive from the conventional LDA results. The energy level splitting between d(x(2)-y(2)) and d(3z(2)-r(2)) is significantly enlarged and the van Hove singularity point is lowered. The calculated results compare better than LDA with recent experimental results from resonant inelastic xray scattering and angle resolved photoemission experiments. This agreement with the experiments supports the previously suggested two-band theory for the material dependence of the superconducting transition temperature, Tc.

First-Principles Momentum-Dependent Local Ansatz Wavefunction and Momentum Distribution Function Bands of Iron

NASA Astrophysics Data System (ADS)

Kakehashi, Yoshiro; Chandra, Sumal

2016-04-01

We have developed a first-principles local ansatz wavefunction approach with momentum-dependent variational parameters on the basis of the tight-binding LDA+U Hamiltonian. The theory goes beyond the first-principles Gutzwiller approach and quantitatively describes correlated electron systems. Using the theory, we find that the momentum distribution function (MDF) bands of paramagnetic bcc Fe along high-symmetry lines show a large deviation from the Fermi-Dirac function for the d electrons with eg symmetry and yield the momentum-dependent mass enhancement factors. The calculated average mass enhancement m*/m = 1.65 is consistent with low-temperature specific heat data as well as recent angle-resolved photoemission spectroscopy (ARPES) data.

Evidence for pressure-tuned quantum structural fluctuations in KCuF3

NASA Astrophysics Data System (ADS)

Yuan, S.; Kim, M.; Seeley, J.; Lal, S.; Abbamonte, P.; Cooper, S. L.

2012-02-01

Frustrated magnetic systems are currently of great interest because of the possibility that these materials exhibit novel ground states such as orbital and spin liquids. We provide evidence in the orbital-ordering material KCuF3 for pressure-tuned quantum melting of a static structural phase to a phase that dynamically fluctuates even near T ˜ 0K.[1] Pressure-dependent Raman scattering measurements show that applied pressure above P* ˜ 7kbar reverses a low temperature structural distortion in KCuF3, resulting in the development of a φ ˜ 0 fluctuational (quasielastic) response near T ˜ 0K. This pressure-induced fluctuational response is temperature independent and exhibits a characteristic fluctuation rate that is much larger than the temperature, γ >> KBT, consistent with quantum fluctuations of the CuF6 octahedra. We show that a previous developed model of pseudospin-phonon coupling qualitatively describes both the temperature- and pressure-dependent evolution of the Raman spectra of KCuF3. Work supported by the U.S. Department of Energy under Award No. DE-FG02-07ER46453 and by the National Science Foundation under Grant NSF DMR 08-56321. [4pt] [1] S. Yuan et al., arXiv:1107.1433 (2011).

Temperature dependence of excitonic emission in [(CH3)2NH2]3[BiI6] organic-inorganic natural self assembled bimodal quantum dots

NASA Astrophysics Data System (ADS)

Abid, Haitham; Samet, Amira; Mlayah, Adnen; Boughzala, Habib; Abid, Younes

2017-11-01

This paper reports on the optical properties of organic - inorganic natural self assembled bimodal quantum dots (dimetylammonium) hexa-iodobismuthate [(CH3)2NH2]3[BiI6]. The crystal structure consists of isolated BiI6 octahedra, as inorganic ions, surrounded by dimethylamine cations. At room temperature, we investigate the optical properties by: UV/Vis absorption, ellipsometry, diffuse reflectance and photoluminescence. A broad Gaussian-shape luminescence band with a large stokes shift is observed in the red spectral range at 2.15 eV, due to radiative recombination of confined excitons in BiI quantum dots, suggesting that excitons are self trapped. The temperature-dependence of the PL emission is investigated. The observed S-shaped emission behavior is explained by thermal escape occurring at lower temperatures for high-energy dots and carriers being recaptured by dots emitting on the low-energy side of the distribution. A rate equation model, showing agreement with the experimental results, is used to investigate the thermal redistribution of the charge carriers. Exciton binding energies of 149.125 and 295.086 meV were determined from the modified Arrhenius analysis.

Electronic Asymmetry by Compositionally Braking Inversion Symmetry

NASA Astrophysics Data System (ADS)

Warusawithana, Maitri

2005-03-01

By stacking molecular layers of 3 different perovskite titanate phases, BaTiO3, SrTiO3 and CaTiO3 with atomic layer control, we construct nanostructures where global inversion symmetry is broken. With the structures clamped to the substrate, the stacking order gives rise to asymmetric strain fields. The dielectric response show asymmetric field tuning consistent with the symmetry of the stacking order. By analyzing the temperature and frequency dependence of the complex dielectric constant, we show that the response comes from activated switching of dipoles between two asymmetric states separated by an energy barrier. We find the size of average dipole units from the temperature dependence of the linewidth of field tuning curves to be around 10 unit cells in all the different nanostructures we investigate. At low temperatures we observe a deviation from the kinetic response suggesting a further growth in correlations. Pyrocurrent measurements confirm this observation indicating a phase transition to a ferro-like state. We explain the high temperature dipoles as single unit cell cross sectional columns correlated via the strain fields in the stacking direction, with the height somewhat short of the film thickness possibly due to some form of weak disorder.

MOCVD growth and characterization of gallium nitride and gallium antimonide nanowires

NASA Astrophysics Data System (ADS)

Burke, Robert Alan

Group-III nitride and group-III antimonide thin films have been used for years in optoelectronic, high-speed applications, and high power/high temperature applications such as light emitting diodes (LEDs), microwave power devices, and thermovoltaics. In recent years, nanowires have gained interest due to the ability to take advantage of their geometry for increased light absorption and the synthesis of radial heterostructures. Several growth techniques have been explored for the growth of GaN and GaSb nanowires. Metal-organic chemical vapor deposition (MOCVD) is of particular interest due to its use in the commercial growth and fabrication of GaN-based and GaSb-based devices. The first part of this thesis focused on addressing several key issues related to the growth of GaN nanowires by MOCVD. Preliminary studies investigated the effect of growth conditions on GaN nanowire formation in a hot wall MOCVD reactor. A computational fluid dynamics-based model was developed to predict the gas phase velocity, temperature and concentration profiles in the reactor. The results demonstrate a strong dependence of GaN nanowire growth on substrate position within the reactor which is due to the rapid reaction and depletion of precursors near the gas inlet of the reactor. Ni-catalyzed GaN nanowire growth was observed to occur over the temperature range of 800-900°C, which is significantly lower than typical GaN thin film temperatures. The nanowires, however, exhibited a tapered diameter due to thin film deposition which occurred simultaneously with nanowire growth. Based on the low growth temperatures, TEM characterization was carried out to investigate the nature of the catalyst. Through these studies, the catalyst was found to consist of Ni3Ga, indicating the presence of a vapor-solid-solid growth mechanism. In an attempt to improve the nanowire growth selectivity, GeCl4 was added during growth resulting in a drastic increase in nanowire density and a reduction in the tapering of the nanowires. Upon further inspection with TEM, the nanowires were found to consist of two morphologies: smooth nanowires and serrated nanowires. The smooth nanowires were found to consist of the wurtzite crystal structure, while the serrated nanowires were determined to have a wurtzite core with zinc blende faceted islands protruding from the wurtzite core. The second half of this thesis focused on the growth and characterization of GaSb nanowires. An extensive amount of work has been carried out on GaSb thin films, however only a few reports exist on GaSb nanowire growth. As a result, it was necessarily to complete a systematic study to determine a growth window for GaSb nanowires. A narrow range of growth conditions were found for Au-catalyzed GaSb nanowire growth. Vertically oriented nanowires were observed over a pressure range of 150-300 Torr depending on the substrate. Based on these findings, additional characterization was carried out to investigate the structural properties of the nanowires along with chemical analysis of the catalyst to determine the nature of the catalyst as a function of the growth conditions. The catalyst was found to consist of Ga, Sb, and Au consistent with that expected for vapor-liquidsolid growth, however the concentrations varied depending on the growth conditions and nanowire sample. For one set of nanowires, the seed particle contained a Au-Sb solid solution (1-15 at.% Sb). For the other set of nanowires, the particle consisted of an AuSb2 grain and an AuGa or Au2Ga grain that resulted in the formation of a bicrystalline nanowire. Photoluminescence measurements were also obtained on these samples and compared to the thin film literature. Samples grown on Si (111) were found to possess good optical properties, while samples grown on sapphire substrates were dominated by native defect transitions. The optical quality of the nanowire sample was also found to have a significant dependence on the V/III ratio.

Rotational dynamics in supercooled water from nuclear spin relaxation and molecular simulations.

PubMed

Qvist, Johan; Mattea, Carlos; Sunde, Erik P; Halle, Bertil

2012-05-28

Structural dynamics in liquid water slow down dramatically in the supercooled regime. To shed further light on the origin of this super-Arrhenius temperature dependence, we report high-precision (17)O and (2)H NMR relaxation data for H(2)O and D(2)O, respectively, down to 37 K below the equilibrium freezing point. With the aid of molecular dynamics (MD) simulations, we provide a detailed analysis of the rotational motions probed by the NMR experiments. The NMR-derived rotational correlation time τ(R) is the integral of a time correlation function (TCF) that, after a subpicosecond librational decay, can be described as a sum of two exponentials. Using a coarse-graining algorithm to map the MD trajectory on a continuous-time random walk (CTRW) in angular space, we show that the slowest TCF component can be attributed to large-angle molecular jumps. The mean jump angle is ∼48° at all temperatures and the waiting time distribution is non-exponential, implying dynamical heterogeneity. We have previously used an analogous CTRW model to analyze quasielastic neutron scattering data from supercooled water. Although the translational and rotational waiting times are of similar magnitude, most translational jumps are not synchronized with a rotational jump of the same molecule. The rotational waiting time has a stronger temperature dependence than the translation one, consistent with the strong increase of the experimentally derived product τ(R) D(T) at low temperatures. The present CTRW jump model is related to, but differs in essential ways from the extended jump model proposed by Laage and co-workers. Our analysis traces the super-Arrhenius temperature dependence of τ(R) to the rotational waiting time. We present arguments against interpreting this temperature dependence in terms of mode-coupling theory or in terms of mixture models of water structure.

Results of scalp cooling during anthracycline containing chemotherapy depend on scalp skin temperature.

PubMed

Komen, M M C; Smorenburg, C H; Nortier, J W R; van der Ploeg, T; van den Hurk, C J G; van der Hoeven, J J M

2016-12-01

The success of scalp cooling in preventing or reducing chemotherapy induced alopecia (CIA) is highly variable between patients undergoing similar chemotherapy regimens. A decrease of the scalp skin temperature seems to be an important factor, but data on the optimum temperature reached by scalp cooling to prevent CIA are lacking. This study investigated the relation between scalp skin temperature and its efficacy to prevent CIA. In this explorative study, scalp skin temperature was measured during scalp cooling in 62 breast cancer patients undergoing up to six cycles of anthracycline containing chemotherapy. Scalp skin temperature was measured by using two thermocouples at both temporal sides of the head. The primary end-point was the need for a wig or other head covering. Maximal cooling was reached after 45 min and was continued for 90 min after chemotherapy infusion. The scalp skin temperature after 45 min cooling varied from 10 °C to 31 °C, resulting in a mean scalp skin temperature of 19 °C (SEM: 0,4). Intrapersonal scalp skin temperatures during cooling were consistent for each chemotherapy cycle (ANOVA: P = 0,855). Thirteen out of 62 patients (21%) did not require a wig or other head covering. They appeared to have a significantly lower mean scalp skin temperature (18 °C; SEM: 0,7) compared to patients with alopecia (20 °C; SEM: 0,5) (P = 0,01). The efficacy of scalp cooling during chemotherapy is temperature dependent. A precise cut-off point could not be detected, but the best results seem to be obtained when the scalp temperature decreases below 18 °C. TRIALREGISTER. 3082. Copyright © 2016 Elsevier Ltd. All rights reserved.

Heat transfer analysis of skin during thermal therapy using thermal wave equation.

PubMed

Kashcooli, Meisam; Salimpour, Mohammad Reza; Shirani, Ebrahim

2017-02-01

Specifying exact geometry of vessel network and its effect on temperature distribution in living tissues is one of the most complicated problems of the bioheat field. In this paper, the effects of blood vessels on temperature distribution in a skin tissue subjected to various thermal therapy conditions are investigated. Present model consists of counter-current multilevel vessel network embedded in a three-dimensional triple-layered skin structure. Branching angles of vessels are calculated using the physiological principle of minimum work. Length and diameter ratios are specified using length doubling rule and Cube law, respectively. By solving continuity, momentum and energy equations for blood flow and Pennes and modified Pennes bioheat equations for the tissue, temperature distributions in the tissue are measured. Effects of considering modified Pennes bioheat equation are investigated, comprehensively. It is also observed that blood has an impressive role in temperature distribution of the tissue, especially at high temperatures. The effects of different parameters such as boundary conditions, relaxation time, thermal properties of skin, metabolism and pulse heat flux on temperature distribution are investigated. Tremendous effect of boundary condition type at the lower boundary is noted. It seems that neither insulation nor constant temperature at this boundary can completely describe the real physical phenomena. It is expected that real temperature at the lower levels is somewhat between two predicted values. The effect of temperature on the thermal properties of skin tissue is considered. It is shown that considering temperature dependent values for thermal conductivity is important in the temperature distribution estimation of skin tissue; however, the effect of temperature dependent values for specific heat capacity is negligible. It is seen that considering modified Pennes equation in processes with high heat flux during low times is significant. Copyright © 2016 Elsevier Ltd. All rights reserved.

Electronic transport properties of single-crystal bismuth nanowire arrays

NASA Astrophysics Data System (ADS)

Zhang, Zhibo; Sun, Xiangzhong; Dresselhaus, M. S.; Ying, Jackie Y.; Heremans, J.

2000-02-01

We present here a detailed study of the electrical transport properties of single-crystal bismuth nanowire arrays embedded in a dielectric matrix. Measurements of the resistance of Bi nanowire arrays with different wire diameters (60-110 nm) have been carried out over a wide range of temperatures (2.0-300 K) and magnetic fields (0-5.4 T). The transport properties of a heavily Te-doped Bi nanowire array have also been studied. At low temperatures, we show that the wire boundary scattering is the dominant scattering process for carriers in the undoped single-crystal Bi nanowires, while boundary scattering is less important for a heavily Te-doped sample, consistent with general theoretical considerations. The temperature dependences of the zero-field resistivity and of the longitudinal magneto-coefficient of the Bi nanowires were also studied and were found to be sensitive to the wire diameter. The quantum confinement of carriers is believed to play an important role in determining the overall temperature dependence of the zero-field resistivity. Theoretical considerations of the quantum confinement effects on the electronic band structure and on the transport properties of Bi nanowires are discussed. Despite the evidence for localization effects and diffusive electron interactions at low temperatures (T<=4.0 K), localization effects are not the dominant mechanisms affecting the resistivity or the magnetoresistance in the temperature range of this study.

Diffusion of GPI-anchored proteins is influenced by the activity of dynamic cortical actin

PubMed Central

Saha, Suvrajit; Lee, Il-Hyung; Polley, Anirban; Groves, Jay T.; Rao, Madan; Mayor, Satyajit

2015-01-01

Molecular diffusion at the surface of living cells is believed to be predominantly driven by thermal kicks. However, there is growing evidence that certain cell surface molecules are driven by the fluctuating dynamics of cortical cytoskeleton. Using fluorescence correlation spectroscopy, we measure the diffusion coefficient of a variety of cell surface molecules over a temperature range of 24–37°C. Exogenously incorporated fluorescent lipids with short acyl chains exhibit the expected increase of diffusion coefficient over this temperature range. In contrast, we find that GPI-anchored proteins exhibit temperature-independent diffusion over this range and revert to temperature-dependent diffusion on cell membrane blebs, in cells depleted of cholesterol, and upon acute perturbation of actin dynamics and myosin activity. A model transmembrane protein with a cytosolic actin-binding domain also exhibits the temperature-independent behavior, directly implicating the role of cortical actin. We show that diffusion of GPI-anchored proteins also becomes temperature dependent when the filamentous dynamic actin nucleator formin is inhibited. However, changes in cortical actin mesh size or perturbation of branched actin nucleator Arp2/3 do not affect this behavior. Thus cell surface diffusion of GPI-anchored proteins and transmembrane proteins that associate with actin is driven by active fluctuations of dynamic cortical actin filaments in addition to thermal fluctuations, consistent with expectations from an “active actin-membrane composite” cell surface. PMID:26378258

Heat transfer from Atlantic waters to sea ice in the Arctic Ocean: Evidence from dissolved argon

NASA Astrophysics Data System (ADS)

Moore, R. M.; Spitzer, W.

1990-11-01

In an attempt to determine whether the temperature and salinity properties of Arctic Ocean waters above the Atlantic water temperature maximum are the result of heat transfer to sea-ice, dissolved Ar has been measured as a temperature tracer. Consistent with such a hypothesis, it is found that there is a transition from supersaturation of Ar in the upper waters to undersaturation below a depth of 275m. Using the known dependence of the solubility of Ar on T and S, and assuming that the water was originally equilibrated with the atmosphere at 760mm Hg, it has been calculated that ca. 0.6° C of cooling can be attributed to transfer of heat to sea-ice.

Computer codes for the evaluation of thermodynamic and transport properties for equilibrium air to 30000 K

NASA Technical Reports Server (NTRS)

Thompson, Richard A.; Lee, Kam-Pui; Gupta, Roop N.

1991-01-01

The computer codes developed here provide self-consistent thermodynamic and transport properties for equilibrium air for temperatures from 500 to 30000 K over a temperature range of 10 (exp -4) to 10 (exp -2) atm. These properties are computed through the use of temperature dependent curve fits for discrete values of pressure. Interpolation is employed for intermediate values of pressure. The curve fits are based on mixture values calculated from an 11-species air model. Individual species properties used in the mixture relations are obtained from a recent study by the present authors. A review and discussion of the sources and accuracy of the curve fitted data used herein are given in NASA RP 1260.

Photoluminescence of ZnTe/ZnMgTe multiple quantum well structures grown on ZnTe substrates by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Tanaka, Tooru; Ohshita, Hiroshi; Saito, Katsuhiko; Guo, Qixin

2018-02-01

Photoluminescence (PL) properties of ZnTe/ZnMgTe quantum well (QW) structures grown by molecular beam epitaxy (MBE) were investigated systematically with respect to well widths and Mg contents. Observed PL peak energies were consistent well with the calculated emission energies of the QWs considering a lattice distortion in the ZnTe well. From the temperature dependence of PL intensity, it was found that a suppression of a carrier escape from QW is crucial to obtain a PL at higher temperature in the ZnTe/ZnMgTe QW. Based on the results, multiple quantum well structures were designed and fabricated, which exhibited a green PL at room temperature.

The International Conference on Low Temperature Physics (14th), Helsinki University of Technology, Otaniemi, Finland, 14-20 August 1975

DTIC Science & Technology

1975-12-30

that is consistent with other calculations and experiments- (H.-009). W. F. Brinkman and H. Smith (Bell Laboratories, ’Murray Hill, N.J.) presented...can depend on details of the Pd (part) of the phonon spectrum,"(S.010). D. S. Mac Lachlan , et al. (Universite de Paris-Sud, Orsay) reported in (S.011

In situ time-series measurements of subseafloor sediment properties

USGS Publications Warehouse

Wheatcroft, R.A.; Stevens, A.W.; Johnson, R.V.

2007-01-01

The capabilities and diversity of subsurface sediment sensors lags significantly from what is available for the water column, thereby limiting progress in understanding time-dependent seabed exchange and high-frequency acoustics. To help redress this imbalance, a new instrument, the autonomous sediment profiler (ASP), is described herein. ASP consists of a four-electrode, Wenner-type resistivity probe and a thermistor that log data at 0.1-cm vertical intervals over a 58-cm vertical profile. To avoid resampling the same spot on the seafloor, the probes are moved horizontally within a 20 times 100-cm-2 area in one of three preselected patterns. Memory and power capacities permit sampling at hourly intervals for up to 3-mo duration. The system was tested in a laboratory tank and shown to be able to resolve high-frequency sediment consolidation, as well as changes in sediment roughness. In a field test off the southern coast of France, the system collected resistivity and temperature data at hourly intervals for 16 d. Coupled with environmental data collected on waves, currents, and suspended sediment, the ASP is shown to be useful for understanding temporal evolution of subsurface sediment porosity, although no large depositional or erosional events occurred during the deployment. Following a rapid decrease in bottom-water temperature, the evolution of the subsurface temperature field was consistent with the 1-D thermal diffusion equation coupled with advection in the upper 3-4 cm. Collectively, the laboratory and field tests yielded promising results on time-dependent seabed change.

The interacting effects of temperature and food chain length on trophic abundance and ecosystem function.

PubMed

Beveridge, Oliver S; Humphries, Stuart; Petchey, Owen L

2010-05-01

1. While much is known about the independent effects of trophic structure and temperature on density and ecosystem processes, less is known about the interaction(s) between the two. 2. We manipulated the temperature of laboratory-based bacteria-protist communities that contained communities with one, two, or three trophic levels, and recorded species' densities and bacterial decomposition. 3. Temperature, food chain length and their interaction produced significant responses in microbial density and bacterial decomposition. Prey and resource density expressed different patterns of temperature dependency during different phases of population dynamics. The addition of a predator altered the temperature-density relationship of prey, from a unimodal trend to a negative one. Bacterial decomposition was greatest in the presence of consumers at higher temperatures. 4. These results are qualitatively consistent with a recent model of direct and indirect temperature effects on resource-consumer population dynamics. Results highlight and reinforce the importance of indirect effects of temperature mediated through trophic interactions. Understanding and predicting the consequences of environmental change will require that indirect effects, trophic structure, and individual species' tolerances be incorporated into theory and models.

Global Temperature Measurement of Supercooled Water under Icing Conditions using Two-Color Luminescent Images and Multi-Band Filter

NASA Astrophysics Data System (ADS)

Tanaka, Mio; Morita, Katsuaki; Kimura, Shigeo; Sakaue, Hirotaka

2012-11-01

Icing occurs by a collision of a supercooled-water droplet on a surface. It can be seen in any cold area. A great attention is paid in an aircraft icing. To understand the icing process on an aircraft, it is necessary to give the temperature information of the supercooled water. A conventional technique, such as a thermocouple, is not valid, because it becomes a collision surface that accumulates ice. We introduce a dual-luminescent imaging to capture a global temperature distribution of supercooled water under the icing conditions. It consists of two-color luminescent probes and a multi-band filter. One of the probes is sensitive to the temperature and the other is independent of the temperature. The latter is used to cancel the temperature-independent luminescence of a temperature-dependent image caused by an uneven illumination and a camera location. The multi-band filter only selects the luminescent peaks of the probes to enhance the temperature sensitivity of the imaging system. By applying the system, the time-resolved temperature information of a supercooled-water droplet is captured.

Low-temperature elastic properties of YbSbPt probed by ultrasound measurements

NASA Astrophysics Data System (ADS)

Nakanishi, Y.; Takahashi, S.; Ohyama, R.; Hasegawa, J.; Nakamura, M.; Suzuki, H.; Yoshizawa, M.

2018-03-01

The elastic properties of a single crystal of the half-Heusler compound YbSbPt have been investigated by means of the ultrasonic measurement. In particular, careful measurements of the temperature (T) dependent elastic constant C 11(T) was performed in the vicinity of its phase transition point near T N of 0.5 K. A clear step-like anomaly accompanied by spin-density-wave type antiferromagnetic (AFM) phase transition was found in the C 11(T) curve. The low-temperature magnetic phase diagram is proposed on the basis of the results. The phase diagram consists of, at least two main distinct phases: a low-field and high-field regime with a transition field of approximately 0.6 T at zero field. We discuss the low-temperature elastic property based on analysis of Landau-type free energy.

Interpenetrating polymer networks from acetylene terminated materials

NASA Technical Reports Server (NTRS)

Connell, J. W.; Hergenrother, P. M.

1989-01-01

As part of a program to develop high temperature/high performance structural resins for aerospace applications, the chemistry and properties of a novel class of interpenetrating polymer networks (IPNs) were investigated. These IPNs consist of a simple diacetylenic compound (aspartimide) blended with an acetylene terminated arylene ether oligomer. Various compositional blends were prepared and thermally cured to evaluate the effect of crosslink density on resin properties. The cured IPNs exhibited glass transition temperatures ranging from 197 to 254 C depending upon the composition and cure temperature. The solvent resistance, fracture toughness and coefficient of thermal expansion of the cured blends were related to the crosslink density. Isothermal aging of neat resin moldings, adhesive and composite specimens showed a postcure effect which resulted in improved elevated temperature properties. The chemistry, physical and mechanical properties of these materials will be discussed.

Spongy Raney nickel hydrogen electrodes for alkaline fuel cells

NASA Astrophysics Data System (ADS)

Tomida, Tahei; Nakabayashi, Ichiro

1989-11-01

Spongy Raney nickel catalysts for use as hydrogen electrodes of fuel cells were prepared by a new method. In this method molten aluminum was sprayed on both sides of a spongy plate of nickel as substrate with an acetylene-oxygen flame gun. Then, the spongy nickel electrodes were activated by alloying at a given temperature of from 550 to 750 C, and leaching the aluminum from the alloy in alkaline solution. This type of catalyst showed good thermal and electrical conductivity and also mechanical strength by itself. Its polarization resistance was very low, and the characteristics of the electrodes improved with increase in the temperature of heat-treatment for alloying. The finding that activity depended on the alloying temperature was consistent with observations by scanning electron microscope on the surface textures of catalysts alloyed at different temperatures.

Simulation study on nitrogen vibrational and translational temperature in air breakdown plasma generated by 110 GHz focused microwave pulse

NASA Astrophysics Data System (ADS)

Yang, Wei; Zhou, Qianhong; Dong, Zhiwei

2017-01-01

We report a simulation study on nitrogen vibrational and translational temperature in 3 μs pulse 110 GHz microwave air breakdown at pressure from 1 Torr to 100 Torr. The one-dimensional model is based on a self-consistent solution to Helmholtz equation for microwave field, electron density equation, and the average energy equation for electrons, nitrogen vibrational, and translational degrees. The breakdown threshold is calculated from the transmitted microwave profile, and it agrees well with that from experiment. The spatio-temporal characteristics of vibrational and translational temperature are shown, and the peak values at the end of pulse are compared to the results fitted from optical emission spectroscopy. The dependences of vibrational and translational temperature on normalized microwave fields and gas pressure are investigated, and the underlying mechanisms are unveiled.

In vivo optoacoustic temperature imaging for image-guided cryotherapy of prostate cancer

NASA Astrophysics Data System (ADS)

Petrova, E. V.; Brecht, H. P.; Motamedi, M.; Oraevsky, A. A.; Ermilov, S. A.

2018-03-01

The objective of this study is to demonstrate in vivo the feasibility of optoacoustic temperature imaging during cryotherapy of prostate cancer. We developed a preclinical prototype optoacoustic temperature imager that included pulsed optical excitation at a wavelength of 805 nm, a modified clinical transrectal ultrasound probe, a parallel data acquisition system, image processing and visualization software. Cryotherapy of a canine prostate was performed in vivo using a commercial clinical system, Cryocare® CS, with an integrated ultrasound imaging. The universal temperature-dependent optoacoustic response of blood was employed to convert reconstructed optoacoustic images to temperature maps. Optoacoustic imaging of temperature during prostate cryotherapy was performed in the longitudinal view over a region of 30 mm (long)  ×  10 mm (deep) that covered the rectum, the Denonvilliers fascia, and the posterior portion of the treated gland. The transrectal optoacoustic images showed high-contrast vascularized regions, which were used for quantitative estimation of local temperature profiles. The constructed temperature maps and their temporal dynamics were consistent with the arrangement of the cryoprobe and readouts of the thermal needle sensors. The temporal profiles of the readouts from the thermal needle sensors and the temporal profile estimated from the normalized optoacoustic intensity of the selected vascularized region showed significant resemblance, except for the initial overshoot, that may be explained as a result of the physiological thermoregulatory compensation. The temperature was mapped with errors not exceeding  ±2 °C (standard deviation) consistent with the clinical requirements for monitoring cryotherapy of the prostate. In vivo results showed that the optoacoustic temperature imaging is a promising non-invasive technique for real-time imaging of tissue temperature during cryotherapy of prostate cancer, which can be combined with transrectal ultrasound—the current standard for guiding clinical cryotherapy procedure.

Compensation for Time-Dependent Star Tracker Thermal Deformation on the Aqua Spacecraft

NASA Technical Reports Server (NTRS)

Hashmall, Joseph A.; Natanson, Gregory; Glickman, Jonathan; Sedlak, Joseph

2004-01-01

Analysis of attitude sensor data from the Aqua mission showed small but systematic differences between batch least-squares and extended Kalman filter attitudes. These differences were also found to be correlated with star tracker residuals, gyro bias estimates, and star tracker baseplate temperatures. This paper describes the analysis that shows that these correlations are all consistent with a single cause: time-dependent thermal deformation of star tracker alignments. These varying alignments can be separated into relative and common components. The relative misalignments can be determined and compensated for. The common misalignments can only be determined in special cases.

Positive magnetoresistance in Fe3Se4 nanowires

NASA Astrophysics Data System (ADS)

Li, D.; Jiang, J. J.; Liu, W.; Zhang, Z. D.

2011-04-01

We report the magnetotransport properties of Fe3Se4 nanowire arrays in anodic aluminum oxide (AAO) porous membrane. The temperature dependence of resistance of Fe3Se4 nanowires at a zero field shows thermal activated behavior below 295 K. The exponential relationship in resistance is consistent with the model of strong localization with variable-range hopping (VRH) for a finite one-dimensional wire. Resistance versus magnetic field curves below 100 K show small positive magnetoresistance (MR). The field dependencies of log[R(H)/R(0)] explain the positive MR as the effect of magnetic field on the VRH conduction.

Spreading of mercury droplets on thin silver films at room temperature.

PubMed

Be'er, Avraham; Lereah, Yossi; Frydman, Aviad; Taitelbaum, Haim

2007-05-01

We study the spreading characteristics of a reactive-wetting system of mercury (Hg) droplets on silver (Ag) films in room temperature. This is done using our recently developed method for reconstructing the dynamical three-dimensional shape of spreading droplets from two-dimensional microscope images [A. Be'er and Y. Lereah, J. Microsc. 208, 148 (2002)]. We study the time evolution of the droplet radius and its contact angle, and find that the spreading process consists of two stages: (i) the "bulk propagation" regime, controlled by chemical reaction on the surface, and (ii) the "fast-flow" regime, which occurs within the metal film as well as on the surface and consists of both reactive and diffusive propagation. We show that the transition time between the two main time regimes depends solely on the thickness of the Ag film. We also discuss the chemical structure of the intermetallic compound formed in this process.

Thermal Conductivity Measurement of Synthesized Mantle Minerals

NASA Astrophysics Data System (ADS)

Asimow, P. D.; Luo, S.; Mosenfelder, J. L.; Liu, W.; Staneff, G. D.; Ahrens, T. J.; Chen, G.

2002-12-01

Direct thermal conductivity (k) measurement of mantle minerals is crucial to constrain the thermal profile of the Earth as well as geodynamic studies of the mantle (e.g., to determine the Rayleigh number). We have embarked on systematic multi-anvil syntheses of dense polycrystalline specimens of mantle phases of adequate size and zero porosity for precise thermal conductivity measurements by the 3ω method (\\textit{Cahill and Pohl, Phys. Rev. B, 1987}) under elevated temperatures (T). Coesite and stishovite (see \\textit{Luo et al., GRL, 2002}) as well as majorite and wadsleyite have been synthesized; ringwoodite and perovskite are scheduled. Preliminary thermal conductivity measurements at ambient pressure on coesite (120 - 300 K, 9.53 Wm-1K-1 at 300 K) are consistent with prior room temperature data (\\textit{Yukutake & Shimada, PEPI, 1978}), while our stishovite data at 300 K appear to be low (1.96 Wm-1K-1). Efforts are being made to extend the measurement to higher temperatures (e.g., above Debye temperature Θ D), thus allowing determination of k(T) relationship (say, k~ T-n); success will depend on the decomposition kinetics of these metastable phases. The pressure dependence of k of these synthesized samples can also be measured (\\textit{e.g., Osako et al., HPMPS-6, 2002; Xu et al., EOS, 2001}). Recent thermal conductivity measurement on LiF and Al2O_3 from shock wave loading (\\textit{Holland & Ahrens, 1998}) is consistent with the modeling on MgO and Al2O_3 (\\textit{Manga & Jeanloz, JGR, 1997}) with classical theories. Thus, k values at modest pressures and T (say, above Θ D) would allow extrapolation of k to appropriate mantle conditions.

Energy budget, oxidative stress and antioxidant in striped hamster acclimated to moderate cold and warm temperatures.

PubMed

Chen, Ke-Xin; Wang, Chun-Ming; Wang, Gui-Ying; Zhao, Zhi-Jun

2014-08-01

The mechanism of the rate of living-free radical theory suggests that higher rate of oxidative metabolism results from greater rate of mitochondria oxidative phosphorylation, leading to a consequent increase in production of free radicals. However, the relation between metabolic rate and oxidative stress is tissue dependent in animals acclimated to cold temperatures. Here we examined oxidative stress, reflected by changes of antioxidant activity and other related markers, in striped hamsters acclimated to moderate cold (15°C), room (23°C) or warm temperature (30°C) for 6 weeks, by which either higher or lower metabolic rate was induced experimentally. Energy intake and the rate of metabolism and nonshivering thermogenesis were increased at 15°C, but decreased at 30°C compared with that at 23°C. Effects of temperatures on the markers of both oxidative stress and antioxidant activities were rarely significant. The percentages of positive correlation between the 11 tissues (brain, BAT, liver, heart, lung, kidneys, stomach, small and large intestine, caecum and skeletal muscle) were 14.5% (8/55) for catalase (CAT), 7.3% (4/55) for the capacity of inhibition of hydroxyl free radical (CIH), 5.5% (3/55) for activities of superoxide dismutase (SOD), 1.8% (1/55) for total antioxidant capacity (T-AOC), 4.3% (2/46) for H2O2 and 11.1% (4/36) for the capacity of inhibition of hydroxyl free radical (CIH). This indicated that the tissue-dependent changes of both oxidative stress and antioxidant activity were less consistent among the different tissues. Finally the data from this study were less consistent with the prediction of the mechanism of the rate of living-free radical theory. Copyright © 2014 Elsevier Ltd. All rights reserved.

Symmetry Energy and Its Components in Finite Nuclei

NASA Astrophysics Data System (ADS)

Antonov, A. N.; Gaidarov, M. K.; Kadrev, D. N.; Sarriguren, P.; Moya de Guerra, E.

2018-05-01

We derive the volume and surface components of the nuclear symmetry energy (NSE) and their ratio within the coherent density fluctuation model. The estimations use the results of the model for the NSE in finite nuclei based on the Brueckner and Skyrme energy-density functionals for nuclear matter. The obtained values of the volume and surface contributions to the NSE and their ratio for the Ni, Sn, and Pb isotopic chains are compared with estimations of other approaches which have used available experimental data on binding energies, neutron-skin thicknesses, and excitation energies to isobaric analog states (IAS). Apart from the density dependence investigated in our previous works, we study also the temperature dependence of the symmetry energy in finite nuclei in the framework of the local density approximation combining it with the self-consistent Skyrme-HFB method using the cylindrical transformed deformed harmonic-oscillator basis. The results for the thermal evolution of the NSE in the interval T = 0–4 MeV show that its values decrease with temperature. The investigations of the T-dependence of the neutron and proton root-mean-square radii and the corresponding neutron skin thickness point out that the effect of temperature leads mainly to a substantial increase of the neutron radii and skins, especially in nuclei which are more rich of neutrons.

Potentially exploitable supercritical geothermal resources in the ductile crust

USGS Publications Warehouse

Watanabe, Noriaki; Numakura, Tatsuya; Sakaguchi, Kiyotoshi; Saishu, Hanae; Okamoto, Atsushi; Ingebritsen, Steven E.; Tsuchiya, Noriyoshi

2017-01-01

The hypothesis that the brittle–ductile transition (BDT) drastically reduces permeability implies that potentially exploitable geothermal resources (permeability >10−16 m2) consisting of supercritical water could occur only in rocks with unusually high transition temperatures such as basalt. However, tensile fracturing is possible even in ductile rocks, and some permeability–depth relations proposed for the continental crust show no drastic permeability reduction at the BDT. Here we present experimental results suggesting that the BDT is not the first-order control on rock permeability, and that potentially exploitable resources may occur in rocks with much lower BDT temperatures, such as the granitic rocks that comprise the bulk of the continental crust. We find that permeability behaviour for fractured granite samples at 350–500 °C under effective confining stress is characterized by a transition from a weakly stress-dependent and reversible behaviour to a strongly stress-dependent and irreversible behaviour at a specific, temperature-dependent effective confining stress level. This transition is induced by onset of plastic normal deformation of the fracture surface (elastic–plastic transition) and, importantly, causes no ‘jump’ in the permeability. Empirical equations for this permeability behaviour suggest that potentially exploitable resources exceeding 450 °C may form at depths of 2–6 km even in the nominally ductile crust.

Electron Spin Relaxation Rates for High-Spin Fe(III) in Iron Transferrin Carbonate and Iron Transferrin Oxalate

PubMed Central

Gaffney, Betty Jean; Eaton, Gareth R.; Eaton*, Sandra S.

2005-01-01

To optimize simulations of CW EPR spectra for high-spin Fe(III) with zero-field splitting comparable to the EPR quantum, information is needed on the factors that contribute to the line shapes and line widths. Continuous wave electron paramagnetic resonance (EPR) spectra obtained for iron transferrin carbonate from 4 to 150 K and for iron transferrin oxalate from 4 to 100 K did not exhibit significant temperature dependence of the line shape, which suggested that the line shapes were not relaxation determined. To obtain direct information concerning the electron spin relaxation rates, electron spin echo and inversion recovery EPR were used to measure T1 and Tm for the high-spin Fe(III) in iron transferrin carbonate and iron transferrin oxalate between 5 and 20–30 K. For comparison with the data for the transferrin complexes, relaxation times were obtained for tris(oxalato)ferrate(III). The relaxation rates are similar for the three complexes and do not exhibit a strong dependence on position in the spectrum. Extrapolation of the observed temperature dependence of the relaxation rates to higher temperatures gives values consistent with the conclusion that the CW line shapes are not relaxation determined up to 150 K. PMID:16429607

Wide temperature range (T = 295 K and 770-1305 K) study of the kinetics of the reactions HCO + NO and HCO + NO2 using frequency modulation spectroscopy.

PubMed

Dammeier, J; Colberg, M; Friedrichs, G

2007-08-21

The rate constants for , HCO + NO --> HNO + CO, and , HCO + NO(2)--> products, have been measured at temperatures between 770 K < T < 1305 K behind reflected shock waves and, for the purpose of a consistency check, in a slow flow reactor at room temperature. HCO radicals were generated by 193 nm excimer laser photolysis of diluted gas mixtures containing glyoxal, (CHO)(2), and NO or NO(2) in argon and were monitored using frequency modulation (FM) absorption spectroscopy. Kinetic simulations based on a comprehensive reaction mechanism showed that the rate constants for the title reactions could be sensitively extracted from the measured HCO profiles. The determined high temperature rate constants are k(1)(769-1307 K) = (7.1 +/- 2.7) x 10(12) cm(3) mol(-1) s(-1) and k(2)(804-1186 K) = (3.3 +/- 1.8) x 10(13) cm(3) mol(-1) s(-1). The room temperature values were found to be in very good agreement with existing literature data and show that both reactions are essentially temperature independent. The weak temperature dependence of can be explained by the interplay of a dominating direct abstraction pathway and a complex-forming mechanism. Both pathways yield the products HNO + CO. In contrast to , no evidence for a significant contribution of a direct high temperature abstraction channel was found for . Here, the observed temperature independent overall rate constant can be described by a complex-forming mechanism with several product channels. Detailed information on the strongly temperature dependent channel branching ratios is provided. Moreover, the high temperature rate constant of , OH + (CHO)(2), has been determined to be k(7) approximately 1.1 x 10(13) cm(3) mol(-1) s(-1).

Mechanical, Dielectric, and Spectroscopic Characteristics of "Micro/Nanocellulose + Oxide" Composites.

PubMed

Nedielko, Maksym; Hamamda, Smail; Alekseev, Olexander; Chornii, Vitalii; Dashevskii, Mykola; Lazarenko, Maksym; Kovalov, Kostiantyn; Nedilko, Sergii G; Tkachov, Sergii; Revo, Sergiy; Scherbatskyi, Vasyl

2017-12-01

The set of composite materials that consist of micro/nanocellulose and complex K 2 Eu(MoO 4 )(PO 4 ) luminescent oxide particles was prepared. The composites were studied by means of scanning electron microscopy, XRD analysis, dilatometry, differential scanning calorimetry and thermogravimetric analysis, and dielectric and luminescence spectroscopy.Dependencies of density, crystallinity, relative extension, thermal extension coefficient, dielectric relaxation parameters, intensity and shape of photoluminescence bands on temperature, and content of oxide component were studied. The structure of the composite without oxide is formed by grains of nearly 5-50 μm in size (crystallinity is about ~56%). Structure of the micro/nanocellulose samples which contain oxide particles is similar, but the cellulose grains are deformed by oxide particles. Dependencies of the abovementioned properties on temperature and oxide content were analyzed together with data on the size distribution of oxide particles for the samples for various oxide and molecules of water concentrations.

Corrected Implicit Monte Carlo

DOE PAGES

Cleveland, Mathew Allen; Wollaber, Allan Benton

2018-01-02

Here in this work we develop a set of nonlinear correction equations to enforce a consistent time-implicit emission temperature for the original semi-implicit IMC equations. We present two possible forms of correction equations: one results in a set of non-linear, zero-dimensional, non-negative, explicit correction equations, and the other results in a non-linear, non-negative, Boltzman transport correction equation. The zero-dimensional correction equations adheres to the maximum principle for the material temperature, regardless of frequency-dependence, but does not prevent maximum principle violation in the photon intensity, eventually leading to material overheating. The Boltzman transport correction guarantees adherence to the maximum principle formore » frequency-independent simulations, at the cost of evaluating a reduced source non-linear Boltzman equation. Finally, we present numerical evidence suggesting that the Boltzman transport correction, in its current form, significantly improves time step limitations but does not guarantee adherence to the maximum principle for frequency-dependent simulations.« less

Calculating the Magnetic Anisotropy of Rare-Earth-Transition-Metal Ferrimagnets

NASA Astrophysics Data System (ADS)

Patrick, Christopher E.; Kumar, Santosh; Balakrishnan, Geetha; Edwards, Rachel S.; Lees, Martin R.; Petit, Leon; Staunton, Julie B.

2018-03-01

Magnetocrystalline anisotropy, the microscopic origin of permanent magnetism, is often explained in terms of ferromagnets. However, the best performing permanent magnets based on rare earths and transition metals (RE-TM) are in fact ferrimagnets, consisting of a number of magnetic sublattices. Here we show how a naive calculation of the magnetocrystalline anisotropy of the classic RE-TM ferrimagnet GdCo5 gives numbers that are too large at 0 K and exhibit the wrong temperature dependence. We solve this problem by introducing a first-principles approach to calculate temperature-dependent magnetization versus field (FPMVB) curves, mirroring the experiments actually used to determine the anisotropy. We pair our calculations with measurements on a recently grown single crystal of GdCo5 , and find excellent agreement. The FPMVB approach demonstrates a new level of sophistication in the use of first-principles calculations to understand RE-TM magnets.

Magnetic pinning in a superconducting film by a ferromagnetic layer with stripe domains

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

Mancusi, D.; Di Giorgio, C.; Bobba, F.

2014-10-31

A magnetic study of superconductor/ferromagnet bilayers was performed by hysteresis loops and temperature-dependent magnetization measurements. The superconductor/ferromagnet bilayers consist of a Nb film deposited on a Py film with weak perpendicular magnetic anisotropy. By comparing the temperature-dependent magnetization data obtained on samples with different ferromagnetic layer thickness, a decrease of the magnetic pinning with increasing thickness of the ferromagnetic layer has been found. This is confirmed by the reduction of the Nb film critical current density at low fields extracted by using the magnetic irreversibility of the hysteresis loops. As the ferromagnetic layer exhibits a magnetic structure with stripe domains,more » whose width increases for increasing thickness as observed by magnetic force microscopy (MFM) measurements, we relate the reduction of the superconducting critical current in samples with thicker ferromagnetic layers to a weaker interaction between the vortices guided by the underlying magnetic template.« less

Calculating the Magnetic Anisotropy of Rare-Earth-Transition-Metal Ferrimagnets.

PubMed

Patrick, Christopher E; Kumar, Santosh; Balakrishnan, Geetha; Edwards, Rachel S; Lees, Martin R; Petit, Leon; Staunton, Julie B

2018-03-02

Magnetocrystalline anisotropy, the microscopic origin of permanent magnetism, is often explained in terms of ferromagnets. However, the best performing permanent magnets based on rare earths and transition metals (RE-TM) are in fact ferrimagnets, consisting of a number of magnetic sublattices. Here we show how a naive calculation of the magnetocrystalline anisotropy of the classic RE-TM ferrimagnet GdCo_{5} gives numbers that are too large at 0 K and exhibit the wrong temperature dependence. We solve this problem by introducing a first-principles approach to calculate temperature-dependent magnetization versus field (FPMVB) curves, mirroring the experiments actually used to determine the anisotropy. We pair our calculations with measurements on a recently grown single crystal of GdCo_{5}, and find excellent agreement. The FPMVB approach demonstrates a new level of sophistication in the use of first-principles calculations to understand RE-TM magnets.

The Electronic Structure Signature of the Spin Cross-Over Transition of [Co(dpzca)2

NASA Astrophysics Data System (ADS)

Zhang, Xin; Mu, Sai; Liu, Yang; Luo, Jian; Zhang, Jian; N'Diaye, Alpha T.; Enders, Axel; Dowben, Peter A.

2018-05-01

The unoccupied electronic structure of the spin crossover molecule cobalt (II) N-(2-pyrazylcarbonyl)-2-pyrazinecarboxamide, [Co(dpzca)2] was investigated, using X-ray absorption spectroscopy (XAS) and compared with magnetometry (SQUID) measurements. The temperature dependence of the XAS and molecular magnetic susceptibility χmT are in general agreement for [Co(dpzca)2], and consistent with density functional theory (DFT). This agreement of magnetic susceptibility and X-ray absorption spectroscopy provides strong evidence that the changes in magnetic moment can be ascribed to changes in electronic structure. Calculations show the choice of Coulomb correlation energy U has a profound effect on the electronic structure of the low spin state, but has little influence on the electronic structure of the high spin state. In the temperature dependence of the XAS, there is also evidence of an X-ray induced excited state trapping for [Co(dpzca)2] at 15 K.

Corrected implicit Monte Carlo

NASA Astrophysics Data System (ADS)

Cleveland, M. A.; Wollaber, A. B.

2018-04-01

In this work we develop a set of nonlinear correction equations to enforce a consistent time-implicit emission temperature for the original semi-implicit IMC equations. We present two possible forms of correction equations: one results in a set of non-linear, zero-dimensional, non-negative, explicit correction equations, and the other results in a non-linear, non-negative, Boltzman transport correction equation. The zero-dimensional correction equations adheres to the maximum principle for the material temperature, regardless of frequency-dependence, but does not prevent maximum principle violation in the photon intensity, eventually leading to material overheating. The Boltzman transport correction guarantees adherence to the maximum principle for frequency-independent simulations, at the cost of evaluating a reduced source non-linear Boltzman equation. We present numerical evidence suggesting that the Boltzman transport correction, in its current form, significantly improves time step limitations but does not guarantee adherence to the maximum principle for frequency-dependent simulations.

Time-dependent Hartree-Fock approach to nuclear ``pasta'' at finite temperature

NASA Astrophysics Data System (ADS)

Schuetrumpf, B.; Klatt, M. A.; Iida, K.; Maruhn, J. A.; Mecke, K.; Reinhard, P.-G.

2013-05-01

We present simulations of neutron-rich matter at subnuclear densities, like supernova matter, with the time-dependent Hartree-Fock approximation at temperatures of several MeV. The initial state consists of α particles randomly distributed in space that have a Maxwell-Boltzmann distribution in momentum space. Adding a neutron background initialized with Fermi distributed plane waves the calculations reflect a reasonable approximation of astrophysical matter. This matter evolves into spherical, rod-like, and slab-like shapes and mixtures thereof. The simulations employ a full Skyrme interaction in a periodic three-dimensional grid. By an improved morphological analysis based on Minkowski functionals, all eight pasta shapes can be uniquely identified by the sign of only two valuations, namely the Euler characteristic and the integral mean curvature. In addition, we propose the variance in the cell density distribution as a measure to distinguish pasta matter from uniform matter.

Basic electronic properties of iron selenide under variation of structural parameters

NASA Astrophysics Data System (ADS)

Guterding, Daniel; Jeschke, Harald O.; Valentí, Roser

2017-09-01

Since the discovery of high-temperature superconductivity in the thin-film FeSe /SrTiO3 system, iron selenide and its derivates have been intensively scrutinized. Using ab initio density functional theory calculations we review the electronic structures that could be realized in iron selenide if the structural parameters could be tuned at liberty. We calculate the momentum dependence of the susceptibility and investigate the symmetry of electron pairing within the random phase approximation. Both the susceptibility and the symmetry of electron pairing depend on the structural parameters in a nontrivial way. These results are consistent with the known experimental behavior of binary iron chalcogenides and, at the same time, reveal two promising ways of tuning superconducting transition temperatures in these materials: on one hand by expanding the iron lattice of FeSe at constant iron-selenium distance and, on the other hand, by increasing the iron-selenium distance with unchanged iron lattice.

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

Cleveland, Mathew Allen; Wollaber, Allan Benton

Here in this work we develop a set of nonlinear correction equations to enforce a consistent time-implicit emission temperature for the original semi-implicit IMC equations. We present two possible forms of correction equations: one results in a set of non-linear, zero-dimensional, non-negative, explicit correction equations, and the other results in a non-linear, non-negative, Boltzman transport correction equation. The zero-dimensional correction equations adheres to the maximum principle for the material temperature, regardless of frequency-dependence, but does not prevent maximum principle violation in the photon intensity, eventually leading to material overheating. The Boltzman transport correction guarantees adherence to the maximum principle formore » frequency-independent simulations, at the cost of evaluating a reduced source non-linear Boltzman equation. Finally, we present numerical evidence suggesting that the Boltzman transport correction, in its current form, significantly improves time step limitations but does not guarantee adherence to the maximum principle for frequency-dependent simulations.« less

Relaxation Dynamics in Heme Proteins.

NASA Astrophysics Data System (ADS)

Scholl, Reinhard Wilhelm

A protein molecule possesses many conformational substates that are likely arranged in a hierarchy consisting of a number of tiers. A hierarchical organization of conformational substates is expected to give rise to a multitude of nonequilibrium relaxation phenomena. If the temperature is lowered, transitions between substates of higher tiers are frozen out, and relaxation processes characteristic of lower tiers will dominate the observational time scale. This thesis addresses the following questions: (i) What is the energy landscape of a protein? How does the landscape depend on the environment such as pH and viscosity, and how can it be connected to specific structural parts? (ii) What relaxation phenomena can be observed in a protein? Which are protein specific, and which occur in other proteins? How does the environment influence relaxations? (iii) What functional form best describes relaxation functions? (iv) Can we connect the motions to specific structural parts of the protein molecule, and are these motions important for the function of the protein?. To this purpose, relaxation processes after a pressure change are studied in carbonmonoxy (CO) heme proteins (myoglobin-CO, substrate-bound and substrate-free cytochrome P450cam-CO, chloroperoxidase-CO, horseradish peroxidase -CO) between 150 K and 250 K using FTIR spectroscopy to monitor the CO bound to the heme iron. Two types of p -relaxation experiments are performed: p-release (200 to ~eq40 MPa) and p-jump (~eq40 to 200 MPa) experiments. Most of the relaxations fall into one of three groups and are characterized by (i) nonexponential time dependence and non-Arrhenius temperature dependence (FIM1( nu), FIM1(Gamma)); (ii) exponential time dependence and non-Arrhenius temperature dependence (FIM0(A_{i}to A_{j})); exponential time dependence and Arrhenius temperature dependence (FIMX( nu)). The influence of pH is studied in myoglobin-CO and shown to have a strong influence on the substate population of the highest tier, tier 0, but not on the relaxation rates. Two different viscosities in myoglobin-CO are compared. The dependence of relaxations on the thermodynamic history of a sample is shown. For substrate-free P450cam-CO, relaxations after a p-jump are observed far above the glass transition of the protein-solvent system.

Canted antiferromagnetism in phase-pure CuMnSb

NASA Astrophysics Data System (ADS)

Regnat, A.; Bauer, A.; Senyshyn, A.; Meven, M.; Hradil, K.; Jorba, P.; Nemkovski, K.; Pedersen, B.; Georgii, R.; Gottlieb-Schönmeyer, S.; Pfleiderer, C.

2018-05-01

We report the low-temperature properties of phase-pure single crystals of the half-Heusler compound CuMnSb grown by means of optical float zoning. The magnetization, specific heat, electrical resistivity, and Hall effect of our single crystals exhibit an antiferromagnetic transition at TN=55 K and a second anomaly at a temperature T*≈34 K. Powder and single-crystal neutron diffraction establish an ordered magnetic moment of (3.9 ±0.1 ) μB/f .u . , consistent with the effective moment inferred from the Curie-Weiss dependence of the susceptibility. Below TN, the Mn sublattice displays commensurate type-II antiferromagnetic order with propagation vectors and magnetic moments along <111 > (magnetic space group R [I ]3 c ). Surprisingly, below T*, the moments tilt away from <111 > by a finite angle δ ≈11∘ , forming a canted antiferromagnetic structure without uniform magnetization consistent with magnetic space group C [B ]c . Our results establish that type-II antiferromagnetism is not the zero-temperature magnetic ground state of CuMnSb as may be expected of the face-centered cubic Mn sublattice.

Large scale Direct Numerical Simulation of premixed turbulent jet flames at high Reynolds number

NASA Astrophysics Data System (ADS)

Attili, Antonio; Luca, Stefano; Lo Schiavo, Ermanno; Bisetti, Fabrizio; Creta, Francesco

2016-11-01

A set of direct numerical simulations of turbulent premixed jet flames at different Reynolds and Karlovitz numbers is presented. The simulations feature finite rate chemistry with 16 species and 73 reactions and up to 22 Billion grid points. The jet consists of a methane/air mixture with equivalence ratio ϕ = 0 . 7 and temperature varying between 500 and 800 K. The temperature and species concentrations in the coflow correspond to the equilibrium state of the burnt mixture. All the simulations are performed at 4 atm. The flame length, normalized by the jet width, decreases significantly as the Reynolds number increases. This is consistent with an increase of the turbulent flame speed due to the increased integral scale of turbulence. This behavior is typical of flames in the thin-reaction zone regime, which are affected by turbulent transport in the preheat layer. Fractal dimension and topology of the flame surface, statistics of temperature gradients, and flame structure are investigated and the dependence of these quantities on the Reynolds number is assessed.

pn junctions based on a single transparent perovskite semiconductor BaSnO3

NASA Astrophysics Data System (ADS)

Kim, Hoon Min; Kim, Useong; Park, Chulkwon; Kwon, Hyukwoo; Lee, Woongjae; Kim, Tai Hoon; Kim, Kee Hoon; Char, Kookrin; Mdpl, Department Of Physics; Astronomy Team; Censcmr, Department Of Physics; Astronomy Team

2014-03-01

Successful p doping of transparent oxide semiconductor will further increase its potential, especially in the area of optoelectronic applications. We will report our efforts to dope the BaSnO3 (BSO) with K by pulsed laser deposition. Although the K doped BSO exhibits rather high resistivity at room temperature, its conductivity increases dramatically at higher temperatures. Furthermore, the conductivity decreases when a small amount of oxygen was removed from the film, consistent with the behavior of p type doped oxides. We have fabricated pn junctions by using K doped BSO as a p type and La doped BSO as an n type material. I_V characteristics of these devices show the typical rectifying behavior of pn junctions. We will present the analysis of the junction properties from the temperature dependent measurement of their electrical properties, which shows that the I_V characteristics are consistent with the material parameters such as the carrier concentration, the mobility, and the bandgap. Our demonstration of pn junctions based on a single transparent perovskite semiconductor further enhances the potential of BSO system with high mobility and stability.

Gyrokinetic Studies of Turbulence Reduction with Reverse Shear ETG Transport Barriers or Lithium Walls

NASA Astrophysics Data System (ADS)

Hammett, G. W.; Peterson, J. L.; Granstedt, E. M.; Bell, R.; Guttenfelder, W.; Kaye, S.; Leblanc, B.; Mikkelsen, D. R.; Smith, D. R.; Yuh, H. Y.; Candy, J.

2012-03-01

The National Spherical Torus Experiment (NSTX) can achieve high electron confinement regimes that are super-critically unstable to the electron temperature gradient (ETG) instability. These electron internal transport barriers (e-ITBs) occur when the magnetic shear becomes strongly negative. Using the gyrokinetic code GYRO, the first nonlinear ETG simulations of NSTX e-ITB plasmas demonstrate reduced turbulence consistent with this observation. This is qualitatively consistent with a secondary instability picture of reduced ETG turbulence at negative shear (Jenko and Dorland PRL 2002). Local simulations identify a strongly upshifted nonlinear critical gradient for thermal transport that depends on magnetic shear. Global simulations show that ETG-driven turbulence outside of the barrier is large enough to be experimentally relevant, but cannot propagate very far into the barrier. We also use GYRO to study turbulence in regimes that might be expected in the Lithium Torus eXperiment (LTX). While lithium has experimentally been shown to raise the edge temperature and improve performance, there can still be some turbulence from density-gradient-driven trapped electron modes, and a temperature pinch is found in some cases. (Supported by DOE.)

Organic photochemical storage of solar energy. Progress report, February 1, 1979-January 31, 1980

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

Jones, G. II

1980-02-01

Study of valence isomerization of organic compounds has focused on two mechanisms of photosensitization involving either electron donor-acceptor interaction or energy transfer. The quenching of fluorescent sensitizers by isomerizable substrates results in the formation of excited complexes. These sensitizer-substrate pairs are highly polarized, leading to changes in bond order for the substrates. For several substrates such as quadricyclene, hexamethyldewarbenzene, and a nonbornadiene derivative, this perturbation results in efficient valence isomerization. Isomerization observed on irradiation of charge transfer complexes of isomerizable substrates is consistent with a similar exciplex - template mechanism. The energy transfer mechanism of photosensitization has been studied bymore » measuring the temperature dependence of quantum yield for isomerization of dimethyl norbornadiene-2,3-dicarboxylate sensitized by benzanthrone. From temperature and quencher concentration profiles quenching constants have been obtained which are consistent with an endoergic triplet energy transfer mechanism. The thermal upconversion of the low energy triplet of benzanthrone results in a threefold increase in isomerization quantum yield over a 90/sup 0/ temperature range.« less

High-throughput powder diffraction measurement system consisting of multiple MYTHEN detectors at beamline BL02B2 of SPring-8

NASA Astrophysics Data System (ADS)

Kawaguchi, S.; Takemoto, M.; Osaka, K.; Nishibori, E.; Moriyoshi, C.; Kubota, Y.; Kuroiwa, Y.; Sugimoto, K.

2017-08-01

In this study, we developed a user-friendly automatic powder diffraction measurement system for Debye-Scherrer geometry using a capillary sample at beamline BL02B2 of SPring-8. The measurement system consists of six one-dimensional solid-state (MYTHEN) detectors, a compact auto-sampler, wide-range temperature control systems, and a gas handling system. This system enables to do the automatic measurement of temperature dependence of the diffraction patterns for multiple samples. We introduced two measurement modes in the MYTHEN system and developed new attachments for the sample environment such as a gas handling system. The measurement modes and the attachments can offer in situ and/or time-resolved measurements in an extended temperature range between 25 K and 1473 K and various gas atmospheres and pressures. The results of the commissioning and performance measurements using reference materials (NIST CeO2 674b and Si 640c), V2O3 and Ti2O3, and a nanoporous coordination polymer are presented.

Rubber friction: The contribution from the area of real contact.

PubMed

Tiwari, A; Miyashita, N; Espallargas, N; Persson, B N J

2018-06-14

There are two contributions to the friction force when a rubber block is sliding on a hard and rough substrate surface, namely, a contribution F ad = τ f A from the area of real contact A and a viscoelastic contribution F visc from the pulsating forces exerted by the substrate asperities on the rubber block. Here we present experimental results obtained at different sliding speeds and temperatures, and we show that the temperature dependency of the shear stress τ f , for temperatures above the rubber glass transition temperature T g , is weaker than that of the bulk viscoelastic modulus. The physical origin of τ f for T > T g is discussed, and we propose that its temperature dependency is determined by the rubber molecule segment mobility at the sliding interface, which is higher than in the bulk because of increased free-volume effect due to the short-wavelength surface roughness. This is consistent with the often observed reduction in the glass transition temperature in nanometer-thick surface layers of glassy polymers. For temperatures T < T g , the shear stress τ f is nearly velocity independent and of similar magnitude as observed for glassy polymers such as PMMA or polyethylene. In this case, the rubber undergoes plastic deformations in the asperity contact regions and the contact area is determined by the rubber penetration hardness. For this case, we propose that the frictional shear stress is due to slip at the interface between the rubber and a transfer film adsorbed on the concrete surface.

Rubber friction: The contribution from the area of real contact

NASA Astrophysics Data System (ADS)

Tiwari, A.; Miyashita, N.; Espallargas, N.; Persson, B. N. J.

2018-06-01

There are two contributions to the friction force when a rubber block is sliding on a hard and rough substrate surface, namely, a contribution Fad = τf A from the area of real contact A and a viscoelastic contribution Fvisc from the pulsating forces exerted by the substrate asperities on the rubber block. Here we present experimental results obtained at different sliding speeds and temperatures, and we show that the temperature dependency of the shear stress τf, for temperatures above the rubber glass transition temperature Tg, is weaker than that of the bulk viscoelastic modulus. The physical origin of τf for T > Tg is discussed, and we propose that its temperature dependency is determined by the rubber molecule segment mobility at the sliding interface, which is higher than in the bulk because of increased free-volume effect due to the short-wavelength surface roughness. This is consistent with the often observed reduction in the glass transition temperature in nanometer-thick surface layers of glassy polymers. For temperatures T < Tg, the shear stress τf is nearly velocity independent and of similar magnitude as observed for glassy polymers such as PMMA or polyethylene. In this case, the rubber undergoes plastic deformations in the asperity contact regions and the contact area is determined by the rubber penetration hardness. For this case, we propose that the frictional shear stress is due to slip at the interface between the rubber and a transfer film adsorbed on the concrete surface.

Examination of the temperature dependent electronic behavior of GeTe for switching applications

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

Champlain, James G.; Ruppalt, Laura B.; Guyette, Andrew C.

2016-06-28

The DC and RF electronic behaviors of GeTe-based phase change material switches as a function of temperature, from 25 K to 375 K, have been examined. In its polycrystalline (ON) state, GeTe behaved as a degenerate p-type semiconductor, exhibiting metal-like temperature dependence in the DC regime. This was consistent with the polycrystalline (ON) state RF performance of the switch, which exhibited low resistance S-parameter characteristics. In its amorphous (OFF) state, the GeTe presented significantly greater DC resistance that varied considerably with bias and temperature. At low biases (<1 V) and temperatures (<200 K), the amorphous GeTe low-field resistance dramatically increased, resulting in exceptionally highmore » amorphous-polycrystalline (OFF-ON) resistance ratios, exceeding 10{sup 9} at cryogenic temperatures. At higher biases and temperatures, the amorphous GeTe exhibited nonlinear current-voltage characteristics that were best fit by a space-charge limited conduction model that incorporates the effect of a defect band. The observed conduction behavior suggests the presence of two regions of localized traps within the bandgap of the amorphous GeTe, located at approximately 0.26–0.27 eV and 0.56–0.57 eV from the valence band. Unlike the polycrystalline state, the high resistance DC behavior of amorphous GeTe does not translate to the RF switch performance; instead, a parasitic capacitance associated with the RF switch geometry dominates OFF state RF transmission.« less

Seasonal- and temperature-dependent variation in CNS ascorbate and glutathione levels in anoxia-tolerant turtles.

PubMed

Pérez-Pinzón, M A; Rice, M E

1995-12-24

We determined the ascorbic acid (ascorbate) and glutathione (GSH) contents of eight regions of the CNS from anoxia-tolerant turtles collected in summer and in winter. Ascorbate was of special interest because it is found in exceptionally high levels in the turtle CNS. The temperature-dependence of CNS ascorbate content was established by comparing levels in animals collected from two geographic zones with different average winter temperatures and in animals re-acclimated to different temperatures in the laboratory. The analytical method was liquid chromatography with electrochemical detection. Turtle ascorbate levels were 30-40% lower in animals acclimatized to winter (2 degrees C) than to summer (23 degrees C) in all regions of the CNS. Similarly, GSH levels were 20-30% lower in winter than in summer. Winter ascorbate levels were higher in turtles from Louisiana (19 degrees C) than in turtles acclimatized to winter in Wisconsin (2 degrees C). Summer and winter levels of ascorbate could be reversed by re-acclimating animals to cold (1 degree C) or warm (23 degrees C) temperatures for at least one week. CNS water content did not differ between cold- and warm-acclimated turtles. Taken together, the data indicated that ascorbate and GSH undergo significant seasonal variation and that the catalyst for change is environmental temperature. Steady-state ascorbate content showed a linear dependence on temperature, with a slope of 1.5% per degree C that was independent of CNS region. Lower levels of cerebral antioxidants in turtles exposed to colder temperatures were consistent with the decreased rate of cerebral metabolism that accompanies winter hibernation. Cerebral ascorbate and GSH levels in the turtle remained similar to or higher than those in mammals, even during winter, however. These findings support the notion that unique mechanisms of antioxidant regulation in the turtle contribute to their tolerance of the hypoxia-reoxygenation that characterizes diving behavior.

Air temperature sensors: dependence of radiative errors on sensor diameter in precision metrology and meteorology

NASA Astrophysics Data System (ADS)

de Podesta, Michael; Bell, Stephanie; Underwood, Robin

2018-04-01

In both meteorological and metrological applications, it is well known that air temperature sensors are susceptible to radiative errors. However, it is not widely known that the radiative error measured by an air temperature sensor in flowing air depends upon the sensor diameter, with smaller sensors reporting values closer to true air temperature. This is not a transient effect related to sensor heat capacity, but a fluid-dynamical effect arising from heat and mass flow in cylindrical geometries. This result has been known historically and is in meteorology text books. However, its significance does not appear to be widely appreciated and, as a consequence, air temperature can be—and probably is being—widely mis-estimated. In this paper, we first review prior descriptions of the ‘sensor size’ effect from the metrological and meteorological literature. We develop a heat transfer model to describe the process for cylindrical sensors, and evaluate the predicted temperature error for a range of sensor sizes and air speeds. We compare these predictions with published predictions and measurements. We report measurements demonstrating this effect in two laboratories at NPL in which the air flow and temperature are exceptionally closely controlled. The results are consistent with the heat-transfer model, and show that the air temperature error is proportional to the square root of the sensor diameter and that, even under good laboratory conditions, it can exceed 0.1 °C for a 6 mm diameter sensor. We then consider the implications of this result. In metrological applications, errors of the order of 0.1 °C are significant, representing limiting uncertainties in dimensional and mass measurements. In meteorological applications, radiative errors can easily be much larger. But in both cases, an understanding of the diameter dependence allows assessment and correction of the radiative error using a multi-sensor technique.

Characterization of the Hole Transport and Electrical Properties in the Small-Molecule Organic Semiconductors

NASA Astrophysics Data System (ADS)

Wang, L. G.; Zhu, J. J.; Liu, X. L.; Cheng, L. F.

2017-10-01

In this paper, we investigate the hole transport and electrical properties in a small-molecule organic material N, N'-bis(1-naphthyl)- N, N'-diphenyl-1,1'-biphenyl-4,4'-diamine (NPB), which is frequently used in organic light-emitting diodes. It is shown that the thickness-dependent current density versus voltage ( J- V) characteristics of sandwich-type NPB-based hole-only devices cannot be described well using the conventional mobility model without carrier density or electric field dependence. However, a consistent and excellent description of the thickness-dependent and temperature-dependent J- V characteristics of NPB hole-only devices can be obtained with a single set of parameters by using our recently introduced improved model that take into account the temperature, carrier density, and electric field dependence of the mobility. For the small-molecule organic semiconductor studied, we find that the width of the Gaussian distribution of density of states σ and the lattice constant a are similar to the values reported for conjugated polymers. Furthermore, we show that the boundary carrier density has an important effect on the J- V characteristics. Both the maximum of carrier density and the minimum of electric field appear near the interface of NPB hole-only devices.

Seafloor age dependence of Rayleigh wave phase velocities in the Indian Ocean

NASA Astrophysics Data System (ADS)

Godfrey, Karen E.; Dalton, Colleen A.; Ritsema, Jeroen

2017-05-01

Variations in the phase velocity of fundamental-mode Rayleigh waves across the Indian Ocean are determined using two inversion approaches. First, variations in phase velocity as a function of seafloor age are estimated using a pure-path age-dependent inversion method. Second, a two-dimensional parameterization is used to solve for phase velocity within 1.25° × 1.25° grid cells. Rayleigh wave travel time delays have been measured between periods of 38 and 200 s. The number of measurements in the study area ranges between 4139 paths at a period of 200 s and 22,272 paths at a period of 40 s. At periods < 100 s, the phase velocity variations are strongly controlled by seafloor age and shown to be consistent with temperature variations predicted by the half-space-cooling model for a mantle potential temperature of 1400°C. The inferred thermal structure beneath the Indian Ocean is most similar to the structure of the Pacific upper mantle, where phase velocities can also be explained by a half-space-cooling model. The thermal structure is not consistent with that of the Atlantic upper mantle, which is best fit by a plate-cooling model and requires a thin plate. Removing age-dependent phase velocity from the 2-D maps of the Indian Ocean highlights anomalously high velocities at the Rodriguez Triple Junction and the Australian-Antarctic Discordance and anomalously low velocities immediately to the west of the Central Indian Ridge.

Crystal cryocooling distorts conformational heterogeneity in a model Michaelis complex of DHFR

PubMed Central

Keedy, Daniel A.; van den Bedem, Henry; Sivak, David A.; Petsko, Gregory A.; Ringe, Dagmar; Wilson, Mark A.; Fraser, James S.

2014-01-01

Summary Most macromolecular X-ray structures are determined from cryocooled crystals, but it is unclear whether cryocooling distorts functionally relevant flexibility. Here we compare independently acquired pairs of high-resolution datasets of a model Michaelis complex of dihydrofolate reductase (DHFR), collected by separate groups at both room and cryogenic temperatures. These datasets allow us to isolate the differences between experimental procedures and between temperatures. Our analyses of multiconformer models and time-averaged ensembles suggest that cryocooling suppresses and otherwise modifies sidechain and mainchain conformational heterogeneity, quenching dynamic contact networks. Despite some idiosyncratic differences, most changes from room temperature to cryogenic temperature are conserved, and likely reflect temperature-dependent solvent remodeling. Both cryogenic datasets point to additional conformations not evident in the corresponding room-temperature datasets, suggesting that cryocooling does not merely trap pre-existing conformational heterogeneity. Our results demonstrate that crystal cryocooling consistently distorts the energy landscape of DHFR, a paragon for understanding functional protein dynamics. PMID:24882744

Application of SEAWAT to select variable-density and viscosity problems

USGS Publications Warehouse

Dausman, Alyssa M.; Langevin, Christian D.; Thorne, Danny T.; Sukop, Michael C.

2010-01-01

SEAWAT is a combined version of MODFLOW and MT3DMS, designed to simulate three-dimensional, variable-density, saturated groundwater flow. The most recent version of the SEAWAT program, SEAWAT Version 4 (or SEAWAT_V4), supports equations of state for fluid density and viscosity. In SEAWAT_V4, fluid density can be calculated as a function of one or more MT3DMS species, and optionally, fluid pressure. Fluid viscosity is calculated as a function of one or more MT3DMS species, and the program also includes additional functions for representing the dependence of fluid viscosity on temperature. This report documents testing of and experimentation with SEAWAT_V4 with six previously published problems that include various combinations of density-dependent flow due to temperature variations and/or concentration variations of one or more species. Some of the problems also include variations in viscosity that result from temperature differences in water and oil. Comparisons between the results of SEAWAT_V4 and other published results are generally consistent with one another, with minor differences considered acceptable.

Physical properties of i-R-Cd quasicrystals(R = Y, Gd-Tm)

NASA Astrophysics Data System (ADS)

Kong, Tai; Bud'Ko, Sergey L.; Jesche, Anton; Goldman, Alan I.; Kreyssig, Andreas; Dennis, Kevin W.; Ramazanoglu, Mehmet; Canfield, Paul C.; McArthur, John

2014-03-01

Detailed characterization of recently discovered i-R-Cd (R = Y, Gd-Tm) binary quasicrystals by means of room-temperature powder x-ray diffraction, dc and ac magnetization, resistivity and specific heat measurements will be presented. i-Y-Cd is weakly diamagnetic. The dc magnetization of i-R-Cd (R = Gd, Ho-Tm) shows typical spin-glass type splitting between field-cooled (FC) and zero-field-cooled (ZFC) data. i-Tb-Cd and i-Dy-Cd do not show a clear cusp in their ZFC dc magnetization. ac magnetization measured on i-Gd-Cd indicates a clear frequency-dependence and the third-order non-linear magnetization, χ3, is consistent with a spin-glass transition. The resistivity for i-R-Cd is of order 100 μΩ cm and weakly temperature-dependent. No feature that can be associated with long-range magnetic order was observed in any of the measurements. Characteristic freezing temperatures for i-R-Cd (R = Gd-Tm) deviate from ideal de Gennes scaling. This work is supported by the US DOE, Basic Energy Sciences under Contract No. DE-AC02-07CH11358.

Temperature dependence of proton NMR relaxation times at earth's magnetic field

NASA Astrophysics Data System (ADS)

Niedbalski, Peter; Kiswandhi, Andhika; Parish, Christopher; Ferguson, Sarah; Cervantes, Eduardo; Oomen, Anisha; Krishnan, Anagha; Goyal, Aayush; Lumata, Lloyd

The theoretical description of relaxation processes for protons, well established and experimentally verified at conventional nuclear magnetic resonance (NMR) fields, has remained untested at low fields despite significant advances in low field NMR technology. In this study, proton spin-lattice relaxation (T1) times in pure water and water doped with varying concentrations of the paramagnetic agent copper chloride have been measured from 6 to 92oC at earth's magnetic field (1700 Hz). Results show a linear increase of T1 with temperature for each of the samples studied. Increasing the concentration of the copper chloride greatly reduced T1 and reduced dependence on temperature. The consistency of the results with theory is an important confirmation of past results, while the ability of an ultra-low field NMR system to do contrast-enhanced magnetic resonance imaging (MRI) is promising for future applicability to low-cost medical imaging and chemical identification. This work is supported by US Dept of Defense Award No. W81XWH-14-1-0048 and the Robert A. Welch Foundation Grant No. AT-1877.

The interaction of atomic oxygen with thin copper films

NASA Technical Reports Server (NTRS)

Gibson, B. C.; Williams, J. R.; Fromhold, A. T., Jr.; Bozack, M. J.; Neely, W. C.; Whitaker, Ann F.

1992-01-01

A source of thermal, ground-state atomic oxygen has been used to expose thin copper films at a flux of 1.4 x 10 exp 17 atoms/sq cm s for times up to 50 min for each of five temperatures between 140 and 200 C. Rutherford backscattering spectroscopy was used to characterize the oxide formed during exposure. The observations are consistent with the oxide phase Cu2O. The time dependence and the temperature dependence of the oxide layer thickness can be described using oxide film growth theory based on rate limitation by diffusion. Within the time and temperature ranges of this study, the growth of the oxide layers is well described by the equation L(T,t) = 3.6 x 10 to 8th exp(- 1.1/2k sub B T)t exp 1/2, where L,T, and t are measured in angstroms, degrees Kelvin, and minutes, respectively. The deduced activation energy is 1.10 +/- 0.15 eV, with the attendant oxidation rate being greater than that for the corresponding reaction in molecular oxygen.

Experimental investigation of the glass transition of polystyrene thin films in a broad frequency range

NASA Astrophysics Data System (ADS)

Inoue, Rintaro; Kanaya, Toshiji; Yamada, Takeshi; Shibata, Kaoru; Fukao, Koji

2018-01-01

In this study, we investigate the α process of a polystyrene thin film using inelastic neutron scattering (INS), dielectric relaxation spectroscopy (DRS), and thermal expansion spectroscopy (TES). The DRS and TES measurements exhibited a decrease in glass transition temperature (Tg) with film thickness. On the other hand, an increase in Tg was observed in INS studies. In order to interpret this contradiction, we investigated the temperature dependence of the peak frequency (fm) of the α process probed by DRS and TES. The experiments revealed an increase in the peak frequency (fm) with decreasing film thickness in the frequency region. This observation is consistent with the observed decrease in Tg with thickness. Interestingly, the increase in Tg with film thickness was confirmed by fitting the temperature dependence measurements of the peak frequency with the Vogel-Fulcher-Tammann equation, within the frequency region probed by INS. The discrepancy between INS and DRS or TES descriptions of the α process is likely to be attributed to a decrease in the apparent activation energy with film thickness and reduced mobility, due to the impenetrable wall effect.

A combined temperature-dependent electron and single-crystal X-ray diffraction study of the fresnoite compound Rb 2V 4+V 25+O 8

NASA Astrophysics Data System (ADS)

Withers, Ray L.; Höche, Thomas; Liu, Yun; Esmaeilzadeh, Saeid; Keding, Ralf; Sales, Brian

2004-10-01

High-purity Rb2V3O8 has been grown and temperature-dependent electron and single-crystal X-ray diffraction used to carefully investigate its fresnoite-type reciprocal lattice. In contrast to other recently investigated representatives of the fresnoite family of compounds, Rb2V3O8 is not incommensurately modulated with an incommensurate basal plane primary modulation wave vector given by q∼0.3 <110>*. A careful low-temperature electron diffraction study has, however, revealed the existence of weak incommensurate satellite reflections characterized by the primitive primary modulation wave vector q1∼0.16c*. The reciprocal space positioning of these incommensurate satellite reflections, the overall (3+1)-d superspace group symmetry, as well as the shapes of the refined displacement ellipsoids determined from single-crystal XRD refinement, are all consistent with their arising from a distinct type of condensed rigid unit modes (RUMs) of distortion of the Rb2V3O8 parent structure.

Folding of the 25 residue Abeta(12-36) peptide in TFE/water: temperature-dependent transition from a funneled free-energy landscape to a rugged one.

PubMed

Kamiya, Narutoshi; Mitomo, Daisuke; Shea, Joan-Emma; Higo, Junichi

2007-05-17

The free-energy landscape of the Alzheimer beta-amyloid peptide Abeta(12-36) in a 40% (v/v) 2,2,2-trifluoroethanol (TFE)/water solution was determined by using multicanonical molecular dynamics simulations. Simulations using this enhanced conformational sampling technique were initiated from a random unfolded polypeptide conformation. Our simulations reliably folded the peptide to the experimental NMR structure, which consists of two linked helices. The shape of the free energy landscape for folding was found to be strongly dependent on temperature: Above 325 K, the overall shape was funnel-like, with the bottom of the funnel coinciding exactly with the NMR structure. Below 325 K, on the other hand, the landscape became increasingly rugged, with the emergence of new conformational clusters connected by low free-energy pathways. Finally, our simulations reveal that water and TFE solvate the polypeptide in different ways: The hydrogen bond formation between TFE and Abeta was enhanced with decreasing temperature, while that between water and Abeta was depressed.

Explicit expressions of self-diffusion coefficient, shear viscosity, and the Stokes-Einstein relation for binary mixtures of Lennard-Jones liquids

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

Ohtori, Norikazu, E-mail: ohtori@chem.sc.niigata-u.ac.jp; Ishii, Yoshiki

Explicit expressions of the self-diffusion coefficient, D{sub i}, and shear viscosity, η{sub sv}, are presented for Lennard-Jones (LJ) binary mixtures in the liquid states along the saturated vapor line. The variables necessary for the expressions were derived from dimensional analysis of the properties: atomic mass, number density, packing fraction, temperature, and the size and energy parameters used in the LJ potential. The unknown dependence of the properties on each variable was determined by molecular dynamics (MD) calculations for an equimolar mixture of Ar and Kr at the temperature of 140 K and density of 1676 kg m{sup −3}. The scalingmore » equations obtained by multiplying all the single-variable dependences can well express D{sub i} and η{sub sv} evaluated by the MD simulation for a whole range of compositions and temperatures without any significant coupling between the variables. The equation for D{sub i} can also explain the dual atomic-mass dependence, i.e., the average-mass and the individual-mass dependence; the latter accounts for the “isotope effect” on D{sub i}. The Stokes-Einstein (SE) relation obtained from these equations is fully consistent with the SE relation for pure LJ liquids and that for infinitely dilute solutions. The main differences from the original SE relation are the presence of dependence on the individual mass and on the individual energy parameter. In addition, the packing-fraction dependence turned out to bridge another gap between the present and original SE relations as well as unifying the SE relation between pure liquids and infinitely dilute solutions.« less

Self-Consistent Thermal Accretion Disk Corona Models for Compact Objects. I: Properties of the Corona and the Spectrum of Escaping Radiation

NASA Technical Reports Server (NTRS)

Dove, James B.; Wilms, Jorn; Begelman, Mitchell C.

1997-01-01

We present the properties of accretion disk corona (ADC) models in which the radiation field, the temperature, and the total opacity of the corona are determined self-consistently. We use a nonlinear Monte Carlo code to perform the calculations. As an example, we discuss models in which the corona is situated above and below a cold accretion disk with a plane-parallel (slab) geometry, similar to the model of Haardt & Maraschi. By Comptonizing the soft radiation emitted by the accretion disk, the corona is responsible for producing the high-energy component of the escaping radiation. Our models include the reprocessing of radiation in the accretion disk. Here the photons either are Compton-reflected or photoabsorbed, giving rise to fluorescent line emission and thermal emission. The self- consistent coronal temperature is determined by balancing heating (due to viscous energy dissipation) with Compton cooling, determined using the fully relativistic, angle-dependent cross sections. The total opacity is found by balancing pair productions with annihilations. We find that, for a disk temperature kT(sub BB) approx. less than 200 eV, these coronae are unable to have a self-consistent temperature higher than approx. 140 keV if the total optical depth is approx. less than 0.2, regardless of the compactness parameter of the corona and the seed opacity. This limitation corresponds to the angle-averaged spectrum of escaping radiation having a photon index approx. greater than 1.8 within the 5-30 keV band. Finally, all models that have reprocessing features also predict a large thermal excess at lower energies. These constraints make explaining the X-ray spectra of persistent black hole candidates with ADC models very problematic.

Effect of Time and Temperature on Thickened Infant Formula.

PubMed

Gosa, Memorie M; Dodrill, Pamela

2017-04-01

Unlike adult populations, who primarily depend on liquids for hydration alone, infants rely on liquids to provide them with hydration and nutrition. Speech-language pathologists working within pediatric medical settings often identify dysphagia in patients and subsequently recommend thickened liquids to reduce aspiration risk. Caregivers frequently report difficulty attempting to prepare infant formula to the prescribed thickness. This study was designed to determine (1) the relationship between consistencies in modified barium swallow studies and thickened infant formulas and (2) the effects of time and temperature on the resulting thickness of infant formula. Prepackaged barium consistencies and 1 standard infant formula that was thickened with rice cereal and with 2 commercially available thickening agents were studied. Thickness was determined via a line spread test after various time and temperature conditions were met. There were significant differences between the thickened formula and barium test consistencies. Formula thickened with rice cereal separated over time into thin liquid and solid residue. Formula thickened with a starch-based thickening agent was thicker than the desired consistency immediately after mixing, and it continued to thicken over time. The data from this project suggest that nectar-thick and honey-thick infant formulas undergo significant changes in flow rates within 30 minutes of preparation or if refrigerated and then reheated after 3 hours. Additional empirical evidence is warranted to determine the most reliable methods and safest products for thickening infant formula when necessary for effective dysphagia management.

Beyond the classical kinetic model for chronic graphite oxidation by moisture in high temperature gas-cooled reactors

DOE PAGES

Contescu, Cristian I.; Mee, Robert W.; Lee, Yoonjo; ...

2017-11-03

Four grades of nuclear graphite with various microstructures were subjected to accelerated oxidation tests in helium with traces of moisture and hydrogen in order to evaluate the effects of chronic oxidation on graphite components in high temperature gas cooled reactors. Kinetic analysis showed that the Langmuir-Hinshelwood (LH) model cannot consistently reproduce all results. In particular, at high temperatures and water partial pressures oxidation was always faster than the LH model predicts, with stronger deviations for superfine grain graphite than for medium grain grades. It was also found empirically that the apparent reaction order for water has a sigmoid-type variation withmore » temperature which follows the integral Boltzmann distribution function. This suggests that the apparent activation with temperature of graphite reactive sites that causes deviations from the LH model is rooted in specific structural and electronic properties of surface sites on graphite. A semi-global kinetic model was proposed, whereby the classical LH model was modified with a temperature-dependent reaction order for water. The new Boltzmann-enhanced model (BLH) was shown to consistently predict experimental oxidation rates over large ranges of temperature (800-1100 oC) and partial pressures of water (3-1200 Pa) and hydrogen (0-300 Pa), not only for the four grades of graphite but also for the historic grade H-451. The BLH model offers as more reliable input for modeling the chemical environment effects during the life-time operation of new grades of graphite in advanced nuclear reactors operating at high and very high temperatures.« less

Beyond the classical kinetic model for chronic graphite oxidation by moisture in high temperature gas-cooled reactors

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

Contescu, Cristian I.; Mee, Robert W.; Lee, Yoonjo

Four grades of nuclear graphite with various microstructures were subjected to accelerated oxidation tests in helium with traces of moisture and hydrogen in order to evaluate the effects of chronic oxidation on graphite components in high temperature gas cooled reactors. Kinetic analysis showed that the Langmuir-Hinshelwood (LH) model cannot consistently reproduce all results. In particular, at high temperatures and water partial pressures oxidation was always faster than the LH model predicts, with stronger deviations for superfine grain graphite than for medium grain grades. It was also found empirically that the apparent reaction order for water has a sigmoid-type variation withmore » temperature which follows the integral Boltzmann distribution function. This suggests that the apparent activation with temperature of graphite reactive sites that causes deviations from the LH model is rooted in specific structural and electronic properties of surface sites on graphite. A semi-global kinetic model was proposed, whereby the classical LH model was modified with a temperature-dependent reaction order for water. The new Boltzmann-enhanced model (BLH) was shown to consistently predict experimental oxidation rates over large ranges of temperature (800-1100 oC) and partial pressures of water (3-1200 Pa) and hydrogen (0-300 Pa), not only for the four grades of graphite but also for the historic grade H-451. The BLH model offers as more reliable input for modeling the chemical environment effects during the life-time operation of new grades of graphite in advanced nuclear reactors operating at high and very high temperatures.« less

Hot-carrier trap-limited transport in switching chalcogenides

NASA Astrophysics Data System (ADS)

Piccinini, Enrico; Cappelli, Andrea; Buscemi, Fabrizio; Brunetti, Rossella; Ielmini, Daniele; Rudan, Massimo; Jacoboni, Carlo

2012-10-01

Chalcogenide materials have received great attention in the last decade owing to their application in new memory systems. Recently, phase-change memories have, in fact, reached the early stages of production. In spite of the industrial exploitation of such materials, the physical processes governing the switching mechanism are still debated. In this paper, we work out a complete and consistent model for transport in amorphous chalcogenide materials based on trap-limited conduction accompanied by carrier heating. A previous model is here extended to include position-dependent carrier concentration and field, consistently linked by the Poisson equation. The results of the new model reproduce the experimental electrical characteristics and their dependences on the device length and temperature. Furthermore, the model provides a sound physical interpretation of the switching phenomenon and is able to give an estimate of the threshold condition in terms of the material parameters, a piece of information of great technological interest.

Cystic fibrosis transmembrane conductance regulator: temperature-dependent cysteine reactivity suggests different stable conformers of the conduction pathway.

PubMed

Liu, Xuehong; Dawson, David C

2011-11-29

Cysteine scanning has been widely used to identify pore-lining residues in mammalian ion channels, including the cystic fibrosis transmembrane conductance regulator (CFTR). These studies, however, have been typically conducted at room temperature rather than human body temperature. Reports of substantial effects of temperature on gating and anion conduction in CFTR channels as well as an unexpected pattern of cysteine reactivity in the sixth transmembrane segment (TM6) prompted us to investigate the effect of temperature on the reactivity of cysteines engineered into TM6 of CFTR. We compared reaction rates at temperatures ranging from 22 to 37 °C for cysteines placed on either side of an apparent size-selective accessibility barrier previously defined by comparing reactivity toward channel-permeant and channel-impermeant, thiol-directed reagents. The results indicate that the reactivity of cysteines at three positions extracellular to the position of the accessibility barrier, 334, 336, and 337, is highly temperature-dependent. At 37 °C, cysteines at these positions were highly reactive toward MTSES(-), whereas at 22 °C, the reaction rates were 2-6-fold slower to undetectable. An activation energy of 157 kJ/mol for the reaction at position 337 is consistent with the hypothesis that, at physiological temperature, the extracellular portion of the CFTR pore can adopt conformations that differ significantly from those that can be accessed at room temperature. However, the position of the accessibility barrier defined empirically by applying channel-permeant and channel-impermeant reagents to the extracellular aspect of the pore is not altered. The results illuminate previous scanning results and indicate that the assay temperature is a critical variable in studies designed to use chemical modification to test structural models for the CFTR anion conduction pathway.

Quantum entanglement at high temperatures? Bosonic systems in nonequilibrium steady state

NASA Astrophysics Data System (ADS)

Hsiang, Jen-Tsung; Hu, B. L.

2015-11-01

This is the second of a series of three papers examining how viable it is for entanglement to be sustained at high temperatures for quantum systems in thermal equilibrium (Case A), in nonequilibrium (Case B) and in nonequilibrium steady state (NESS) conditions (Case C). The system we analyze here consists of two coupled quantum harmonic oscillators each interacting with its own bath described by a scalar field, set at temperatures T 1 > T 2. For constant bilinear inter-oscillator coupling studied here (Case C1) owing to the Gaussian nature, the problem can be solved exactly at arbitrary temperatures even for strong coupling. We find that the valid entanglement criterion in general is not a function of the bath temperature difference, in contrast to thermal transport in the same NESS setting [1]. Thus lowering the temperature of one of the thermal baths does not necessarily help to safeguard the entanglement between the oscillators. Indeed, quantum entanglement will disappear if any one of the thermal baths has a temperature higher than the critical temperature T c, defined as the temperature above which quantum entanglement vanishes. With the Langevin equations derived we give a full display of how entanglement dynamics in this system depends on T 1, T 2, the inter-oscillator coupling and the system-bath coupling strengths. For weak oscillator-bath coupling the critical temperature T c is about the order of the inverse oscillator frequency, but for strong oscillator-bath coupling it will depend on the bath cutoff frequency. We conclude that in most realistic circumstances, for bosonic systems in NESS with constant bilinear coupling, `hot entanglement' is largely a fiction.

Recent advancements in 2D-materials interface based magnetic junctions for spintronics

NASA Astrophysics Data System (ADS)

Iqbal, Muhammad Zahir; Qureshi, Nabeel Anwar; Hussain, Ghulam

2018-07-01

Two-dimensional (2D) materials comprising of graphene, hexagonal boron nitride (hBN) and transition metal dichalcogenides (TMDs) have revealed fascinating properties in various spintronic architectures. Here, we review spin valve effect in lateral and vertical magnetic junctions incorporating 2D materials as non-magnetic layer between ferromagnetic (FM) electrodes. The magnetic field dependent spin transport properties are studied by measuring non-local resistance (RNL) and relative magnetoresistance ratio (MR) for lateral and vertical structures, respectively. The review consists of (i) studying spin lifetimes and spin diffusion length thereby exploring the effect of tunneling and transparent contacts in lateral spin valve structures, temperature dependence, gate tunability and contrasting mechanisms of spin relaxation in single layer graphene (SLG) and bilayer graphene (BLG) devices. (ii) Perpendicular spin valve devices are thoroughly investigated thereby studying the role of different 2D materials in vertical spin dynamics. The dependence of spin valve signal on interface quality, temperature and various other parameters is also investigated. Furthermore, the spin reversal in graphene-hBN hybrid system is examined on the basis of Julliere model.

Host polymer influence on dilute polystyrene segmental dynamics

NASA Astrophysics Data System (ADS)

Lutz, T. R.

2005-03-01

We have utilized deuterium NMR to investigate the segmental dynamics of dilute (2%) d3-polystyrene (PS) chains in miscible polymer blends with polybutadiene, poly(vinyl ethylene), polyisoprene, poly(vinyl methylether) and poly(methyl methacrylate). In the dilute limit, we find qualitative differences depending upon whether the host polymer has dynamics that are faster or slower than that of pure PS. In blends where PS is the fast (low Tg) component, segmental dynamics are slowed upon blending and can be fit by the Lodge-McLeish model. When PS is the slow (high Tg) component, PS segmental dynamics speed up upon blending, but cannot be fit by the Lodge-McLeish model unless a temperature dependent self-concentration is employed. These results are qualitatively consistent with a recent suggestion by Kant, Kumar and Colby (Macromolecules, 2003, 10087), based upon data at higher concentrations. Furthermore, as the slow component, we find the segmental dynamics of PS has a temperature dependence similar to that of its host. This suggests viewing the high Tg component dynamics in a miscible blend as similar to a polymer in a low molecular weight solvent.

Non-linear dielectric signatures of entropy changes in liquids subject to time dependent electric fields

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

Richert, Ranko

2016-03-21

A model of non-linear dielectric polarization is studied in which the field induced entropy change is the source of polarization dependent retardation time constants. Numerical solutions for the susceptibilities of the system are obtained for parameters that represent the dynamic and thermodynamic behavior of glycerol. The calculations for high amplitude sinusoidal fields show a significant enhancement of the steady state loss for frequencies below that of the low field loss peak. Also at relatively low frequencies, the third harmonic susceptibility spectrum shows a “hump,” i.e., a maximum, with an amplitude that increases with decreasing temperature. Both of these non-linear effectsmore » are consistent with experimental evidence. While such features have been used to conclude on a temperature dependent number of dynamically correlated particles, N{sub corr}, the present result demonstrates that the third harmonic susceptibility display a peak with an amplitude that tracks the variation of the activation energy in a model that does not involve dynamical correlations or spatial scales.« less

Low temperature and high pressure thermoelastic and crystallographic properties of SrZrO3 perovskite in the Pbnm phase

NASA Astrophysics Data System (ADS)

Knight, Kevin S.; Bull, Craig L.

2016-12-01

The thermoelastic and structural properties of SrZrO3 perovskite in the Pnma (Pbnm) phase have been studied using neutron powder diffraction at 82 temperatures between 11 K and 406 K at ambient pressure, and at sixteen pressures between 0.07 and 6.7 GPa at ambient temperature. The bulk modulus, derived by fitting the equation of state to a second order Birch-Murnaghan equation-of-state, 157(5) GPa, is in excellent agreement with that deduced in a recent resonant ultrasound investigation. Experimental axial compressional moduli are in agreement with those calculated from the elastic stiffness coefficients derived by ab-initio calculation, although the experimental bulk modulus is significantly softer than that calculated. Following low temperature saturation for temperatures less than 40 K, the unit cell monotonically increases with a predicted high temperature limit in the volume expansivity of ∼2.65 × 10-5 K-1. Axial linear thermal expansion coefficients are found to be in the order αb < αc < αa for all temperatures greater than 20 K with the b axis indicating a weak, low temperature negative expansion coefficient at low temperatures. The thermoelastic properties of SrZrO3 can be approximated by a two-term Debye model for the phonon density of states with Debye temperatures of 238(4) K and 713(6) K derived in a self-consistent manner by simultaneously fitting the isochoric heat capacity and the unit cell volume. Atomic displacement parameters have been fitted to a modified Debye model in which the zero-point term is an additional refinable variable and shows the cations and anions have well separated Debye temperatures, mirroring the need for two Debye-like distributions in the vibrational density of states. The temperature dependence of the crystal structure is presented in terms of the amplitudes of the seven symmetry-adapted basis vectors of the aristotype phase that are consistent with space group Pbnm, thus permitting a direct measure of the order parameter evolution in SrZrO3. The temperature variation of the in-phase tilt, which is lost at the phase transition at 973 K, is consistent with tricritical behaviour, in agreement with published results based on high temperature crystallographic data.

Explaining observed red and blue-shifts using multi-stranded coronal loops

NASA Astrophysics Data System (ADS)

Regnier, S.; Walsh, R. W.; Pearson, J.

2012-03-01

Magnetic plasma loops have been termed the building blocks of the solar atmosphere. However, it must be recognised that if the range of loop structures we can observe do consist of many ''sub-resolution'' elements, then current one-dimensional hydrodynamic models are really only applicable to an individual plasma element or strand. Thus a loop should be viewed is an amalgamation of these strands. They could operate in thermal isolation from one another with a wide range of temperatures occurring across the structural elements. This scenario could occur when the energy release mechanism consists of localised, discrete bursts of energy that are due to small scale reconnection sites within the coronal magnetic field- the nanoflare coronal heating mechanism. These energy bursts occur in a time-dependent manner, distributed along the loop/strand length, giving a heating function that depends on space and time. An important observational discovery with the Hinode/EIS spectrometer is the existence of red and blue-shifts in coronal loops depending on the location of the footpoints (inner or outer parts of the active region), and the temperature of the emission line in which the Doppler shifts are measured. Based on the multi-stranded model developed by Sarkar and Walsh (2008, ApJ, 683, 516), we show that red and blue-shifts exist in different simulated Hinode/EIS passbands: cooler lines (OV-SiVII) being dominated by red-shifts, whilst hotter lines (FeXV-CaXVII) are a combination of both. The distribution of blue-shifts depends on the energy input and not so much on the heating location. Characteristic Doppler shifts generated fit well with observed values. We also simulate the Hinode/EIS rasters to closely compare our simulation with the observations. Even if not statistically significant, loops can have footpoints with opposite Doppler shifts.

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 to characterize the temperature dependent refractive index relationship, n(T), for phosphate buffered saline. Phosphate buffered saline (PBS) is a water-based solution used with our biological cells because it maintains an ion concentration similar to that found in body fluids. The n(T) characterization was performed using a custom-built isothermal apparatus in which the temperature could be controlled. To check for the accuracy of the PBS refractive index measurements, water was also measured and compared with known values in the literature. The literature source of choice has affiliations to NIST and a formulation of refractive index involving temperature and wavelength dependence, two parameters which are necessary for our specialized infrared wavelength range. From the NIST formula, linear approximations were found to be dn/dT = -1.4x10-4 RIU °C-1 and dn/dlambda = -1.5x10-5 RIU nm-1 for water. A comparison with the formulated refractive indices of water indicated the measured values were off. This was attributed to the fact that light penetration into the HfO2/SiO2 dielectric mirrors had not been considered. Once accounted for, the refractive indices of water were consistent with the literature, and the values for PBS are believed to be accurate. A further discovery was the refractive index values at the discrete resonant wavelengths were monotonically decreasing, such that the dn/dlambda slope for water was considerably close to the NIST formula. Thus, n(T,lambda) was characterized for both water and PBS. A refractive index relationship for PBS with spatial, temperature, and wavelength dependence is particularly useful for non-uniform temperature distributions caused by DEP electrodes. First, a maximum temperature can be inferred, which is the desired measurement for cell viability concerns. In addition, a lateral refractive index distribution can be measured to help quantify the gradient index lenses that are formed by the energized electrodes. The non-uniform temperature distribution was also simulated with a finite element analysis software package. This simulated temperature distribution was converted to a refractive index distribution, and focal lengths were calculated for positive and negative gradient index lenses to a smallest possible length of about 10mm.

Fuel cladding behavior under rapid loading conditions

NASA Astrophysics Data System (ADS)

Yueh, K.; Karlsson, J.; Stjärnsäter, J.; Schrire, D.; Ledergerber, G.; Munoz-Reja, C.; Hallstadius, L.

2016-02-01

A modified burst test (MBT) was used in an extensive test program to characterize fuel cladding failure behavior under rapid loading conditions. The MBT differs from a normal burst test with the use of a driver tube to simulate the expansion of a fuel pellet, thereby producing a partial strain driven deformation condition similar to that of a fuel pellet expansion in a reactivity insertion accident (RIA). A piston/cylinder assembly was used to pressurize the driver tube. By controlling the speed and distance the piston travels the loading rate and degree of sample deformation could be controlled. The use of a driver tube with a machined gauge section localizes deformation and allows for continuous monitoring of the test sample diameter change at the location of maximum hoop strain, during each test. Cladding samples from five irradiated fuel rods were tested between 296 and 553 K and loading rates from 1.5 to 3.5/s. The test rods included variations of Zircaloy-2 with different liners and ZIRLO, ranging in burn-up from 41 to 74 GWd/MTU. The test results show cladding ductility is strongly temperature and loading rate dependent. Zircaloy-2 cladding ductility degradation due to operational hydrogen pickup started to recover at approximately 358 K for test condition used in the study. This recovery temperature is strongly loading rate dependent. At 373 K, ductility recovery was small for loading rates less than 8 ms equivalent RIA pulse width, but longer than 8 ms the ductility recovery increased exponentially with increasing pulse width, consistent with literature observations of loading rate dependent brittle-to-ductile (BTD) transition temperature. The cladding ductility was also observed to be strongly loading rate/pulse width dependent for BWR cladding below the BTD temperature and Pressurized Water Reactor (PWR) cladding at both 296 and 553 K.

Thermochemical and Kinetics of Hydrazine Dehydrogenation by an Oxygen Atom in Hydrazine-Rich Systems: A Dimer Model.

PubMed

Spada, Rene F K; Ferrão, Luiz F A; Roberto-Neto, Orlando; Lischka, Hans; Machado, Francisco B C

2015-12-24

The kinetics of the reaction of N2H4 with oxygen depends sensitively on the initial conditions used. In oxygen-rich systems, the rate constant shows a conventional positive temperature dependence, while in hydrazine-rich setups the dependence is negative in certain temperature ranges. In this study, a theoretical model is presented that adequately reproduces the experimental results trend and values for hydrazine-rich environment, consisting of the hydrogen abstraction from the hydrazine (N2H4) dimer by an oxygen atom. The thermochemical properties of the reaction were computed using two quantum chemical approaches, the coupled cluster theory with single, double, and noniterative triple excitations (CCSD(T)) and the M06-2X DFT approach with the aug-cc-pVTZ and the maug-cc-pVTZ basis sets, respectively. The kinetic data were calculated with the improved canonical variational theory (ICVT) using a dual-level methodology to build the reaction path. The tunneling effects were considered by means of the small curvature tunneling (SCT) approximation. Potential wells on both sides of the reaction ((N2H4)2 + O → N2H4···N2H3 + OH) were determined. A reaction path with a negative activation energy was found leading, in the temperature range of 250-423 K, to a negative dependence of the rate constant on the temperature, which is in good agreement with the experimental measurements. Therefore, the consideration of the hydrazine dimer model provides significantly improved agreement with the experimental data and should be included in the mechanism of the global N2H4 combustion process, as it can be particularly important in hydrazine-rich systems.

Coupling heat and chemical tracer experiments for estimating heat transfer parameters in shallow alluvial aquifers.

PubMed

Wildemeersch, S; Jamin, P; Orban, P; Hermans, T; Klepikova, M; Nguyen, F; Brouyère, S; Dassargues, A

2014-11-15

Geothermal energy systems, closed or open, are increasingly considered for heating and/or cooling buildings. The efficiency of such systems depends on the thermal properties of the subsurface. Therefore, feasibility and impact studies performed prior to their installation should include a field characterization of thermal properties and a heat transfer model using parameter values measured in situ. However, there is a lack of in situ experiments and methodology for performing such a field characterization, especially for open systems. This study presents an in situ experiment designed for estimating heat transfer parameters in shallow alluvial aquifers with focus on the specific heat capacity. This experiment consists in simultaneously injecting hot water and a chemical tracer into the aquifer and monitoring the evolution of groundwater temperature and concentration in the recovery well (and possibly in other piezometers located down gradient). Temperature and concentrations are then used for estimating the specific heat capacity. The first method for estimating this parameter is based on a modeling in series of the chemical tracer and temperature breakthrough curves at the recovery well. The second method is based on an energy balance. The values of specific heat capacity estimated for both methods (2.30 and 2.54MJ/m(3)/K) for the experimental site in the alluvial aquifer of the Meuse River (Belgium) are almost identical and consistent with values found in the literature. Temperature breakthrough curves in other piezometers are not required for estimating the specific heat capacity. However, they highlight that heat transfer in the alluvial aquifer of the Meuse River is complex and contrasted with different dominant process depending on the depth leading to significant vertical heat exchange between upper and lower part of the aquifer. Furthermore, these temperature breakthrough curves could be included in the calibration of a complex heat transfer model for estimating the entire set of heat transfer parameters and their spatial distribution by inverse modeling. Copyright © 2014 Elsevier B.V. All rights reserved.

State-dependent climate sensitivity in past warm climates and its implications for future climate projections.

PubMed

Caballero, Rodrigo; Huber, Matthew

2013-08-27

Projections of future climate depend critically on refined estimates of climate sensitivity. Recent progress in temperature proxies dramatically increases the magnitude of warming reconstructed from early Paleogene greenhouse climates and demands a close examination of the forcing and feedback mechanisms that maintained this warmth and the broad dynamic range that these paleoclimate records attest to. Here, we show that several complementary resolutions to these questions are possible in the context of model simulations using modern and early Paleogene configurations. We find that (i) changes in boundary conditions representative of slow "Earth system" feedbacks play an important role in maintaining elevated early Paleogene temperatures, (ii) radiative forcing by carbon dioxide deviates significantly from pure logarithmic behavior at concentrations relevant for simulation of the early Paleogene, and (iii) fast or "Charney" climate sensitivity in this model increases sharply as the climate warms. Thus, increased forcing and increased slow and fast sensitivity can all play a substantial role in maintaining early Paleogene warmth. This poses an equifinality problem: The same climate can be maintained by a different mix of these ingredients; however, at present, the mix cannot be constrained directly from climate proxy data. The implications of strongly state-dependent fast sensitivity reach far beyond the early Paleogene. The study of past warm climates may not narrow uncertainty in future climate projections in coming centuries because fast climate sensitivity may itself be state-dependent, but proxies and models are both consistent with significant increases in fast sensitivity with increasing temperature.

Electrical characteristics of multilayer MoS2 FET's with MoS2/graphene heterojunction contacts.

PubMed

Kwak, Joon Young; Hwang, Jeonghyun; Calderon, Brian; Alsalman, Hussain; Munoz, Nini; Schutter, Brian; Spencer, Michael G

2014-08-13

The electrical properties of multilayer MoS2/graphene heterojunction transistors are investigated. Temperature-dependent I-V measurements indicate the concentration of unintentional donors in exfoliated MoS2 to be 3.57 × 10(11) cm(-2), while the ionized donor concentration is determined as 3.61 × 10(10) cm(-2). The temperature-dependent measurements also reveal two dominant donor levels, one at 0.27 eV below the conduction band and another located at 0.05 eV below the conduction band. The I-V characteristics are asymmetric with drain bias voltage and dependent on the junction used for the source or drain contact. I-V characteristics of the device are consistent with a long channel one-dimensional field-effect transistor model with Schottky contact. Utilizing devices, which have both graphene/MoS2 and Ti/MoS2 contacts, the Schottky barrier heights of both interfaces are measured. The charge transport mechanism in both junctions was determined to be either thermionic-field emission or field emission depending on bias voltage and temperature. On the basis of a thermionic field emission model, the barrier height at the graphene/MoS2 interface was determined to be 0.23 eV, while the barrier height at the Ti/MoS2 interface was 0.40 eV. The value of Ti/MoS2 barrier is higher than previously reported values, which did not include the effects of thermionic field emission.

Evolution of Combustion-Generated Particles at Tropospheric Conditions

NASA Technical Reports Server (NTRS)

Tacina, Kathleen M.; Heath, Christopher M.

2012-01-01

This paper describes particle evolution measurements taken in the Particulate Aerosol Laboratory (PAL). The PAL consists of a burner capable of burning jet fuel that exhausts into an altitude chamber that can simulate temperature and pressure conditions up to 13,700 m. After presenting results from initial temperature distributions inside the chamber, particle count data measured in the altitude chamber are shown. Initial particle count data show that the sampling system can have a significant effect on the measured particle distribution: both the value of particle number concentration and the shape of the radial distribution of the particle number concentration depend on whether the measurement probe is heated or unheated.

In-place recalibration technique applied to a capacitance-type system for measuring rotor blade tip clearance

NASA Technical Reports Server (NTRS)

Barranger, J. P.

1978-01-01

The rotor blade tip clearance measurement system consists of a capacitance sensing probe with self contained tuning elements, a connecting coaxial cable, and remotely located electronics. Tests show that the accuracy of the system suffers from a strong dependence on probe tip temperature and humidity. A novel inplace recalibration technique was presented which partly overcomes this problem through a simple modification of the electronics that permits a scale factor correction. This technique, when applied to a commercial system significantly reduced errors under varying conditions of humidity and temperature. Equations were also found that characterize the important cable and probe design quantities.

Myelin basic protein reduces molecular motions in DMPA, an elastic neutron scattering study

NASA Astrophysics Data System (ADS)

Natali, F.; Gliozzi, A.; Rolandi, R.; Cavatorta, P.; Deriu, A.; Fasano, A.; Riccio, P.

2001-07-01

We have studied the effect of physiological amounts of myelin basic protein (MBP) on pure dimyristoyl L- α-phosphatidic acid (DMPA) vesicles using the elastic neutron scattering technique. Elastic scans have been performed in a wide temperature range (20-300 K). In the lower temperature region the behaviour of the integrated elastic intensity was the typical one of harmonic systems. The analysis of the Q and T dependence performed in terms of an asymmetric double well potential clearly showed that the effect of the protein consisted in a significant reduction of the conformational mobility of the DMPA bilayers and in the stabilisation of the membrane.

Charge and spin transport in metal-graphene-metal vertical junctions

NASA Astrophysics Data System (ADS)

Cobas, Enrique; van't Erve, Olaf; Cheng, Shu-Fan; Culbertson, James; Jernigan, Glenn; Bussman, Konrad; Jonker, Berry

We observe negative magnetoresistance(MR) in metallic NiFe(111)|multi-layer graphene|Fe heterostructures consistent with minority spin filtering. The MR is -5 percent at room temperature and -12 percent at 10 K. The transport properties and temperature dependence are metallic. We further investigate the out-of-plane (c-axis) resistivity and magnetoresistance of multi-layer graphene between metal surfaces. We fabricate various metal-graphene-metal vertical heterostructures via chemical vapor deposition directly on lattice-matched crystalline metal films including NiFe(111) and Co(0002) and in-situ electron beam evaporation of NiFe, Co, Ni, Fe, Cu and Au.

Single particle excitations in RbAg/sub 4/I/sub 5/

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

Shapiro, S.M.; Salamon, M.B.

1979-01-01

In an inelastic neutron experiment on RbAg/sub 4/I/sub 5/ a broad quasielastic peak was observed throughout Q-space. As the temperature was lowered, the quasielastic peak became a broad propagating excitation with dirac constant ..omega.. approx. 2.2 meV. This excitation was measured along several symmetry directions and it exhibited little dispersion. This confirms that the original idea of a single particle excitation corresponding to the Ag/sup +/ ions moving within a potential well created by the rest of the lattice. The temperature dependence of this excitation is consistent with recent calculations of neutron scattering in superionic conductors.