Temperature Dependence (temperature + dependence)

Distribution by Scientific Domains
Distribution within Physics and Astronomy

Kinds of Temperature Dependence

  • negative temperature dependence
  • strong temperature dependence


  • Selected Abstracts


    The Dual Mode Microwave Afterglow Apparatus for Measuring the Electron Temperature Dependence of the Electron-Ion Recombination

    CONTRIBUTIONS TO PLASMA PHYSICS, Issue 4 2008
    O. Miku
    Abstract Three dual mode microwave apparatus (one using S -band and two using X -band) have been developed to determine ambipolar diffusion and electron-ion recombination rates under conditions such that Tgas = 300K and Te is varied from 300 K to 6300 K, in the afterglow period of the dc glow discharge. TheTM010 cylindrical cavity (in S -band) and TM011 open cylindrical cavity (X -band) are used to determine the electron density during the afterglow period and a non-resonant waveguide mode is used to apply a constant microwave heating field to the electrons. To test the properties of the apparatus the neon afterglow plasma has been investigated. At Te = 300 K a value of , (Ne+2) = (1.7 0.2) 10,7cm3/s is obtained which is in good agreement with values of other investigators. Also similar variations of , as T,0.4e (S -band) and as T,0.42e (X -band) obeyed over the range 300 , Te , 6300K are in good agreement with some other previous measurements. The simplicity of the X-band microwave apparatus also allows the measurements of the gas temperature dependency and the study of electron attachment and may be used simultaneously with optical or mass spectrometry investigations. ( 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Patterns of Accelerated Junctional Rhythm During Slow Pathway Catheter Ablation for Atrioventricular Nodal Reentrant Tachycardia: Temperature Dependence, Prognostic Value, and Insights into the Nature of the Slow Pathway

    JOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 3 2000
    ALAN B. WAGSHAL M.D.
    Slow Pathway Accelerated Junctional Rhythm. Introduction: Although accelerated junctional rhythm (AJR) is a knuwn marker for successful slow pathway (SP) ablation sites. AJR may just be a regional effect of the anisotropic conduction properties of this area of the heart. We believe that detailed assessment of the AJR might provide insight into the SP specificity of this AJR and perhaps the nature of the SP itself. Methods and Results: Our ablation protocol consisted of 30-second, 70C temperature-controlled ablation pulses with assessment after each pulse. Serial booster ablations were performed at the original successful site and at least 2 to 3 nearby sites to assess for residual AJR after the procedure in 50 consecutive SP ablations. We defined three distinct patterns of AJR: continuous AJR that persisted until the end of energy delivery (group 1, 25 patients); alternating or "stuttering" AJR that persisted throughout energy delivery (group II, 9 patients); and AJR that ended abruptly during energy delivery (group III, 16 patients). Mean ablation temperatures in the three groups was 57 5C, 54 5C, and 63 5C, respectively (P = 0.0002 for groups I and II vs group III). Ten of 34 (29%) patients in groups I and II ("low-temperature ablation") exhibited residual SP (jump and/or single echo heats) despite tachycardia noninducibility, and 25 of 34 (73%) patients had residual AJR during the booster ablations, but neither of these was seen in any group III patients. Conclusion: Ablation temperature correlates with the pattern of AJR produced during SP ablation. That higher temperature lesions simultaneously abolish all SP activity as well as the focus of AJR suggests that this AJR is specific for the SP and is not a nonspecific regional effect. [source]


    Sintering Temperature Dependence of Thermoelectric Performance and Crystal Phase of Calcium Cobalt Oxides

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2010
    Masahiro Tahashi
    Polycrystalline samples were synthesized by a conventional solid-state reaction. As starting materials, Co3O4 and Ca(OH)2 were mixed in a molar ratio of Ca:Co=3:4 and sintered at 1073,1373 K. The compound phases and thermoelectric properties of the resulting products were dependent on the sintering temperature. X-ray diffraction analysis showed that the Ca3Co4O9 compound was stable up to 1193 K and that Ca3Co2O6 was formed at 1273 K. At 1373 K, the sample decomposed into cobalt oxide and calcium oxide. A maximum power factor of about 100 ,W/(K2m) at 873 K was obtained for the Ca3Co4O9 phase sintered at 1193 K. [source]


    Temperature Dependence of Tensile Strength for a Woven Boron-Nitride-Coated Hi-Nicalon SiC Fiber-Reinforced Silicon-Carbide-Matrix Composite

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2001
    Shuqi Guo
    The temperature dependence of tensile fracture behavior and tensile strength of a two-dimensional woven BN-coated Hi-Nicalon SiC fiber-reinforced SiC matrix composite fabricated by polymer infiltration pyrolysis (PIP) were studied. A tensile test of the composite was conducted in air at temperatures of 298 (room temperature), 1200, 1400, and 1600 K. The composite showed a nonlinear behavior for all the test temperatures; however, a large decrease in tensile strength was observed above 1200 K. Young's modulus was estimated from the initial linear regime of the tensile stress,strain curves at room and elevated temperatures, and a decrease in Young's modulus became significant above 1200 K. The multiple transverse cracking that occurred was independent of temperature, and the transverse crack density was measured from fractographic observations of the tested specimens at room and elevated temperatures. The temperature dependence of the effective interfacial shear stress was estimated from the measurements of the transverse crack density. The temperature dependence of in situ fiber strength properties was determined from fracture mirror size on the fracture surfaces of fibers. The decrease in the tensile strength of the composite up to 1400 K was attributed to the degradation in the strength properties of in situ fibers, and to the damage behavior exception of the fiber properties for 1600 K. [source]


    Temperature Dependence of Sol-Gel Conversion Kinetics in Gelatin-Water System

    MACROMOLECULAR BIOSCIENCE, Issue 4 2009
    Kai Chen
    Abstract The conversion kinetics of an aqueous gelatin solution to gel was studied by temperature modulated and regular DSC under isothermal and continuous cooling conditions. Isothermal runs revealed a decrease in the quasi-static heat capacity primarily associated with syneresis (phase separation) of the gel. Above 19,C the isothermal process demonstrated negative effective activation energy that turned positive below 14,C. Continuous cooling runs detected a reversing heat flow apparently related to the continuing formation and melting of new gel structures. Isoconversional kinetic analysis of continuous cooling measurements yielded negative activation energy for the whole range of conversions and temperatures suggesting that nucleation remained a rate controlling step throughout the whole gelation process. [source]


    Influence of Short-Chain Branching of Polyethylenes on the Temperature Dependence of Rheological Properties in Shear

    MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 22 2007
    Florian J. Stadler
    Abstract This contribution describes the influence of short-chain branching on the temperature dependence of rheological properties of polyethylene (PE) melts in shear. The materials investigated are linear and short-chain branched, metallocene-catalyzed PEs of narrow molecular mass distribution. The linear viscoelastic properties are determined by dynamic-mechanical analysis. Short-chain branching (SCB) leads to an increase of the flow activation energy. The activation energy was found to increase linearly with rising weight comonomer content. [source]


    Microwave and Ionic Liquids: Inverse Temperature Dependence of Viscosity in Aqueous Medium of Grafted Copolymers

    MACROMOLECULAR REACTION ENGINEERING, Issue 9 2009
    Ella Bezdushna
    Abstract We elaborated a route to the thermosensitive polyelectrolyte system composed of 1-methyl-3-vinylimidazolium salt with , -cyclodextrin complexed counterions and mono-(meth)acrylic functionalized poly(N -isopropylacrylamide) as grafted side chains via a three-step synthetic procedure. The aqueous solution of the polyelectrolyte displays partially inverse thermoresponsive behavior; it exhibits enhancement of shear viscosity up to body temperature. Furthermore, based on classically prepared poly(NIPAAm) bearing terminal amino groups, corresponding (meth-) acrylamide-type of macromonomers were easily obtained under microwave conditions. [source]


    Precipitates Temperature Dependence in Ion Beam Nitrited AISI H13 Tool Steel

    PLASMA PROCESSES AND POLYMERS, Issue S1 2007
    Luiz F. Zagonel
    Abstract AISI H13 tool steel samples were nitrided using broad nitrogen ion beams in a high-vacuum chamber at different temperatures. At 400,C, a thin , -Fe2-3N phase forms on the top of a shallow nitrided layer and the nitrogen distribution follows a complementary error function. At 500,C, deviations from this behavior are observed and a thick , -Fe2-3N layer is formed. At 600,C, no , -Fe2-3N phase is formed and the nitrogen profile is step-like. At such a temperature, coarse nitride precipitates are observed. Also, carbon losses (decarburizing) are observed upon nitriding at and above 500,C. [source]


    True and Apparent Temperature Dependence of Protein Adsorption Equilibrium in Reversed-Phase HPLC

    BIOTECHNOLOGY PROGRESS, Issue 6 2002
    Szabelski
    The adsorption behavior of bovine insulin on a C8 -bonded silica stationary phase was investigated at different column pressures and temperatures in isocratic reversed-phase HPLC. Changes in the molar volume of insulin (, Vm) upon adsorption were derived from the pressure dependence of the isothermal retention factor ( k,). The values of , Vm were found to be practically independent of the temperature between 25 and 50 C at ,96 mL/mol and to increase with increasing temperature, up to ,108 mL/mol reached at 50 C. This trend was confirmed by two separate series of measurements of the thermal dependence of ln( k,). In the first series the average column pressure was kept constant. The second series involved measurements of ln( k,) under constant mobile-phase flow rate, the average column pressure varying with the temperature. In both cases, a parabolic shape relationship was observed between ln( k,) and the temperature, but the values obtained for ln k, were higher in the first than in the second case. The relative difference in ln( k,), caused by the change in pressure drop induced by the temperature, is equivalent to a systematic error in the estimate of the Gibbs free energy of 12%. Thus, a substantial error is made in the estimates of the enthalpy and entropy of adsorption when neglecting the pressure effects associated with the change in the molar volume of insulin. This work proves that the average column pressure must be kept constant during thermodynamic measurements of protein adsorption constants, especially in RPLC and HIC. Our results show also that there is a critical temperature, Tc , 53 C, at which ln( k,) is maximum and the insulin adsorption process changes from an exothermic to an endothermic one. This temperature determines also the transition point in the molecular mechanism of insulin adsorption that involves successive unfolding of the protein chain. [source]


    7Li, 31P, and 1H Pulsed Gradient Spin-Echo (PGSE) Diffusion NMR Spectroscopy and Ion Pairing: On the Temperature Dependence of the Ion Pairing in Li(CPh3), Fluorenyllithium, and Li[N(SiMe3)2] amongst Other Salts

    CHEMISTRY - A EUROPEAN JOURNAL, Issue 5 2005
    Ignacio Fernndez
    Abstract 7Li, 31P, and 1H variable-temperature pulsed gradient spin-echo (PGSE) diffusion methods have been used to study ion pairing and aggregation states for a range of lithium salts such as lithium halides, lithium carbanions, and a lithium amide in THF solutions. For trityllithium (2) and fluorenyllithium (9), it is shown that ion pairing is favored at 299 K but the ions are well separated at 155 K. For 2-lithio-1,3-dithiane (13) and lithium hexamethyldisilazane (LiHMDS 16), low-temperature data show that the ions remain together. For the dithio anion 13, a mononuclear species has been established, whereas for the lithium amide 16, the PGSE results allow two different aggregation states to be readily recognized. For the lithium halides LiX (X = Br, Cl, I) in THF, the 7Li PGSE data show that all three salts can be described as well-separated ions at ambient temperature. The solid state structure of trityllithium (2) is described and reveals a solvent-separated ion pair formed by a [Li(thf)4]+ ion and a bare triphenylmethide anion. [source]


    Temperature Dependence of Interactions Between Stable Piperidine-1-yloxyl Derivatives and a Semicrystalline Ionic Liquid,

    CHEMPHYSCHEM, Issue 10 2010
    Veronika Strehmel Dr.
    Abstract The stable 2,2,6,6-tetramethylpiperidine-1-yloxyl and its derivatives with hydrogen-bond-forming (-OH, -OSO3H), anionic (-OSO3, bearing K+ or [K(18-crown-6)]+ as counter ion), or cationic (-N+(CH3)3 bearing I,, BF4,, PF6, or N,(SO2CF3)2 as counter ion) substituents are investigated in 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide over a wide temperature range. The temperature dependence of the viscosity of the ionic liquid is well described by the Vogel,Fulcher,Tammann equation. Interestingly, the temperature dependence of the rotational correlation time of the spin probes substituted with either a hydrogen-bond-forming group or an ionic substituent can be described using the Stokes,Einstein equation. In contrast, the temperature dependence of the rotational correlation time of the spin probe without an additional substituent at the 4-position to the nitroxyl group does not follow this trend. The activation energy for the mobility of the unsubstituted spin probe, determined from an Arrhenius plot of the spin-probe mobility in the ionic liquid above the melting temperature, is comparable with the activation energy for the viscous flow of the ionic liquid, but is higher for spin probes bearing an additional substituent at the 4-position. Quantum chemical calculations of the spin probes using the 6-31G+d method give information about the rotational volume of the spin probes and the spin density at the nitrogen atom of the radical structure as a function of the substituent at the spin probes in the presence and absence of a counter ion. The results of these calculations help in understanding the effect of the additional substituent on the experimentally determined isotropic hyperfine coupling constant. [source]


    Temperature Dependence of the Formation of Graphene and Subsurface Carbon on Ru(0001) and Its Effect on Surface Reactivity

    CHEMPHYSCHEM, Issue 5 2010
    Yi Cui
    Switching the surface structure: The formation of graphene and subsurface carbon on Ru(0001) is controlled by regulating the annealing temperature (see picture). A low annealing temperature (LT) drives bulk dissolved carbon onto the surface to form graphene. At high temperatures (HT), surface graphene carbon can diffuse into the subsurface or move into the bulk of the metal. [source]


    Temperature Dependence of the Dielectric Properties and Dynamics of Ionic Liquids

    CHEMPHYSCHEM, Issue 4 2009
    Johannes Hunger
    Abstract No solo dancers: The temperature dependence of dielectric spectra suggests that the lower-frequency relaxation dominating the dynamics of imidazolium-based room temperature ionic liquids cannot be solely due to independent rotational diffusion of the cations (see picture), but must also include cooperative motions of the surrounding particles. Dielectric spectra were measured for eight, mostly imidazolium-based, room temperature ionic liquids (RTILs) over a wide range of frequencies (0.2,,/GHz,89) and temperatures (5,,/C, 65). Detailed analysis of the spectra shows that the dominant low frequency process centred at ca. 0.06 to 10 GHz (depending on the salt and the temperature) is better described using a symmetrically broadened Cole,Cole model rather than the asymmetric Cole,Davidson models used previously. Evaluation of the temperature dependence of the static permittivities, effective dipole moments, volumes of rotation, activation energies, and relaxation times derived from the dielectric data indicates that the low frequency process cannot be solely due to rotational diffusion of the dipolar imidazolium cations, as has been thought, but must also include other contributions, probably from cooperative motions. Analysis of the Debye process observed at higher frequencies for these RTILs is not undertaken because it overlaps with even faster processes that lie outside the range of the present instrumentation. [source]


    Density and Temperature Dependence of Proton Diffusion in Water: A First-Principles Molecular Dynamics Study

    CHEMPHYSCHEM, Issue 9 2005
    Mauro Boero Prof.
    New insights into proton propagation: The authors present a detailed report on the diffusion of a proton in different thermodynamic states of water. At high temperature and intermediate density, the proton,which spends more time as an Eigen complex than as a Zundel complex (see figure),is destabilized, its migration is faster, and an incomplete Eigen complex acts as an acid with high chemical reactivity. [source]


    Temperature Dependences of Leakage Currents of ZnO Varistors Doped with Rare-Earth Oxides

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2010
    Jun Hu
    Rare-earth oxides are doped into ZnO varistors as grain growth inhibitors for increasing the varistors' voltage gradients. However, their leakage currents become large and their nonlinear coefficients decrease at the same time. The reasonable explanation for such a phenomenon has not yet been available. In this paper, the temperature dependences of varistor samples' leakage currents are investigated, which reveal that the increased leakage currents of ZnO varistors with Y2O3 doping are mainly due to the bypass paths through the intergranular materials at grain corners. [source]


    Temperature dependence of stress,lifetime fatigue curves

    FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 12 2000
    J. Kohout
    By analysing several finite-life fatigue curves obtained at various temperatures, a relation describing the temperature dependence of fatigue strength is proposed, based on the Basquin equation. Accordingly, an approximate inverse law between fatigue strength and the square root of absolute temperature is demonstrated. Moreover, a boundary temperature above which creep begins to play a significant role is estimated. A simple extension of the relationship to the low-cycle fatigue region, allows one to determine predictive curves describing fatigue behaviour at various temperatures, even in cases where only a single fatigue curve at a given temperature plus the temperature dependence of tensile strength are known. [source]


    Temperature dependence of stream benthic respiration in an Alpine river network under global warming

    FRESHWATER BIOLOGY, Issue 10 2008
    V. ACUA
    Summary 1. Global warming has increased the mean surface temperature of the Earth by 0.6 C in the past century, and temperature is probably to increase by an additional 3 C by 2100. Water temperature has also increased, which in turn can affect metabolic rate in rivers. Such an increase in metabolic rate could alter the role of river networks in the global C cycle, because the fraction of allochthonous organic C that is respired may increase. 2. Laboratory-based incubations at increasing water temperature were used to estimate the temperature dependence of benthic respiration in streams. These experiments were performed on stones taken from seven reaches with different thermal conditions (mean temperature ranging 8,19 C) within the pre-alpine Thur River network in Switzerland, June,October 2007. 3. The activation energy of respiration in different reaches along the river network (0.53 0.12 eV, n = 94) was similar, indicating that respiration was constrained by the activation energy of the respiratory complex (E = 0.62 eV). Water temperature and the thickness of the benthic biofilm influence the temperature dependence of respiration and our results suggest that an increase of 2.5 C will increase river respiration by an average of 20 1.6%. [source]


    Temperature dependence of Fe(III) and sulfate reduction rates and its effect on growth and composition of bacterial enrichments from an acidic pit lake neutralization experiment

    GEOBIOLOGY, Issue 4 2005
    J. MEIER
    ABSTRACT Microbial Fe(III) and sulfate reduction are important electron transport processes in acidic pit lakes and stimulation by the addition of organic substrates is a strategy to remove acidity, iron and sulfate. This principle was applied in a pilot-scale enclosure in pit lake 111 (Brandenburg, Germany). Because seasonal and spatial variation of temperature may affect the performance of in situ experiments considerably, the influence of temperature on Fe(III) and sulfate reduction was investigated in surface sediments from the enclosure in the range of 4,28 C. Potential Fe(III) reduction and sulfate reduction rates increased exponentially with temperature, and the effect was quantified in terms of the apparent activation energy Ea measuring 42,46 kJ mol,1 and 52 kJ mol,1, respectively. Relatively high respiration rates at 4 C and relatively low Q10 values (,2) indicated that microbial communities were well adapted to low temperatures. In order to evaluate the effect of temperature on growth and enrichment of iron and sulfate-reducing bacterial populations, MPN (Most Probable Number) dilution series were performed in media selecting for the different bacterial groups. While the temperature response of specific growth rates of acidophilic iron reducers showed mesophilic characteristics, the relatively high specific growth rates of sulfate reducers at the lowest incubation temperature indicated the presence of moderate psychrophilic bacteria. In contrast, the low cell numbers and low specific growth rates of neutrophilic iron reducers obtained in dilution cultures suggest that these populations play a less significant role in Fe and S cycling in these sediments. SSCP (Single-Strand Conformation Polymorphism) or DGGE (Denaturing Gradient Gel Electrophoresis) fingerprinting based on 16S rRNA genes of Bacteria indicated different bacterial populations in the MPN dilution series exhibiting different temperature ranges for growth. [source]


    Temperature dependence of structure and dynamics of the hydrated Ca2+ ion according to ab initio quantum mechanical charge field and classical molecular dynamics

    JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 6 2010
    Len Herald V. Lim
    Abstract Simulations using ab initio quantum mechanical charge field molecular dynamics (QMCF MD) and classical molecular dynamics using two-body and three-body potentials were performed to investigate the hydration of the Ca2+ ion at different temperatures. Results from the simulations demonstrate significant effects of temperature on solution dynamics and the corresponding composition and structure of hydrated Ca2+. Substantial increase in ligand exchange events was observed in going from 273.15 K to 368.15 K, resulting in a redistribution of coordination numbers to lower values. The effect of temperature is also visible in a red-shift of the ion-oxygen stretching frequencies, reflecting weakened ligand binding. Even the moderate increase from ambient to body temperature leads to significant changes in the properties of Ca2+ in aqueous environment. 2009 Wiley Periodicals, Inc. J Comput Chem, 2010 [source]


    Nisin Diffusion in Protein Films: Effects of Film Type and Temperature

    JOURNAL OF FOOD SCIENCE, Issue 8 2002
    A. Teerakarn
    ABSTRACT: Protein films [cast corn zein (CCZ), heat-pressed corn zein (HPCZ), cast wheat gluten (CWG), and heat-pressed wheat gluten (HPWG)] were studied at different exposure temperatures (5, 25, 35, and 45 C) to determine nisin diffusion in aqueous model systems. Kinetics of nisin diffusion in protein films followed a Fickian diffusion model. The CCZ had the lowest nisin diffusivity and highest nisin retention. Diffusivities in HPCZ, CWG, and HPWG films were not significantly different. Temperature dependence of nisin diffusion in all films followed an Arrhenius model, which indicated no morphological changes within 5 to 45 C. The activation energy for nisin diffusion in corn-zein films was higher than that in wheat-gluten films. [source]


    Study of the Segmental Dynamics in Semi-Crystalline Poly(lactic acid) using Mechanical Spectroscopies

    MACROMOLECULAR BIOSCIENCE, Issue 4 2005
    Joo F. Mano
    Abstract Summary: The glass transition of poly(L -lactic acid) (PLLA) occurs not far above typical service temperatures (room or body temperatures) which has consequences on the material properties during its use, such as damping or the occurrence of structural relaxation. This work aims at characterising the glass transition dynamics of a semi-crystalline PLLA using both dynamic mechanical analysis (DMA) and thermally stimulated recovery (TSR). The main viscoelastic parameters have been characterised at 1 Hz using DMA and the master curve obtained after isothermal experiments at different temperatures provided a full picture of the solid-state rheological behaviour throughout a wide frequency range. The activation energies calculated from the shift factors agree with the TSR ones, exhibiting a maximum near the Tg. Above the Tg, the results can be described with the WLF model. In the glassy state, the activation energy decreases with decreasing temperatures being always higher than the prediction of the Adam and Gibbs theory, at least down to temperatures 30,C below the Tg. This suggests the existence of non-arrested degrees of freedom in the glassy state, being consistent with the existence of a significant degree of cooperativity in the TSR results. Temperature dependence of the apparent activation energy across the glass transition. [source]


    The Influence of Hydrogen Bonding on the Propagation Rate Coefficient in Free-Radical Polymerizations of Hydroxypropyl Methacrylate

    MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 3 2003
    Sabine Beuermann
    Abstract The propagation rate coefficient kp was determined for hydroxypropyl methacrylate by applying pulsed laser initiated polymerizations and subsequent analysis of the polymer by size-exclusion chromatography. kp data were derived for polymerizations in bulk and in several solvents: toluene, tetrahydrofuran (THF), benzyl alcohol, and supercritical CO2. With the exception of THF, no solvent influence on kp was observed. For polymerizations in THF kp values 40% below the corresponding bulk data were obtained. In addition, the activation energy of kp for polymerizations in THF is higher than for the other systems. The results are explained by a complexation of the OH group contained in the ester group with THF. As a consequence, H bonds between OH groups and carbonyl O atoms, which occur in the other systems, are not formed in the presence of THF. This explanation is supported by Raman spectra, which show that association of carbonyl groups does not occur for systems containing THF, whereas for all other systems the occurrence of two peaks at 1,703 cm,1 and 1 720 cm,1 is indicative of the vibrations of two different , associated vs. not associated , types of carbonyl groups. Based on the change in activation energy it is suggested that a true kinetic solvent effect occurs. Temperature dependence of kp for HPMA polymerizations in bulk and in solution of THF. The literature data for bulk polymerizations are taken from ref. 22. Open symbols refer to ,rep,=,10 Hz and filled symbols to ,rep,=,25 Hz. [source]


    Thermally-Induced Phase Transitions in the Uniaxially-Oriented , Form of Syndiotactic Polystyrene

    MACROMOLECULAR SYMPOSIA, Issue 1 2006
    E. Bhoje Gowd
    Abstract The empty , (,e) form of uniaxially-oriented syndiotactic polystyrene (sPS) samples were obtained by extracting the solvent molecules from the , form of sPS and solvent complex in acetone and methanol. Temperature dependence of the X-ray fiber diagrams starting from the uniaxially-oriented ,e and , form has been measured successfully at various temperatures for the first time. The transition behavior was traced clearly by separating the equatorial and layer line reflections. The ,e form transformed to the , form via an intermediate form. The intermediate form is speculated to take disordered structure due to the empty cavities present in the ,e form. Calorimetric studies showed an endotherm followed by an exotherm during this phase transition, which is consistant with such a speculation. On the other hand the , form transformed to the , form directly without passing through the intermediate form or ,e form. During the , to , phase transition the solvent molecules evaporate through the columnar structure in a broad range of temperature, allowing the transition to occur smoothly. [source]


    Temperature dependence and resonance assignment of 13C NMR spectra of selectively and uniformly labeled fusion peptides associated with membranes

    MAGNETIC RESONANCE IN CHEMISTRY, Issue 2 2004
    Michele L. Bodner
    Abstract HIV-1 and influenza viral fusion peptides are biologically relevant model fusion systems and, in this study, their membrane-associated structures were probed by solid-state NMR 13C chemical shift measurements. The influenza peptide IFP-L2CF3N contained a 13C carbonyl label at Leu-2 and a 15N label at Phe-3 while the HIV-1 peptide HFP-UF8L9G10 was uniformly 13C and 15N labeled at Phe-8, Leu-9 and Gly-10. The membrane composition of the IFP-L2CF3N sample was POPC,POPG (4:1) and the membrane composition of the HFP-UF8L9G10 sample was a mixture of lipids and cholesterol which approximately reflects the lipid headgroup and cholesterol composition of host cells of the HIV-1 virus. In one-dimensional magic angle spinning spectra, labeled backbone 13C were selectively observed using a REDOR filter of the 13C,15N dipolar coupling. Backbone chemical shifts were very similar at ,50 and 20C, which suggests that low temperature does not appreciably change the peptide structure. Relative to ,50C, the 20C spectra had narrower signals with lower integrated intensity, which is consistent with greater motion at the higher temperature. The Leu-2 chemical shift in the IFP-L2CF3N sample correlates with a helical structure at this residue and is consistent with detection of helical structure by other biophysical techniques. Two-dimensional 13C,13C correlation spectra were obtained for the HFP-UF8L9G10 sample and were used to assign the chemical shifts of all of the 13C labels in the peptide. Secondary shift analysis was consistent with a ,-strand structure over these three residues. The high signal-to-noise ratio of the 2D spectra suggests that membrane-associated fusion peptides with longer sequences of labeled amino acids can also be assigned with 2D and 3D methods. Copyright 2004 John Wiley & Sons, Ltd. [source]


    Temperature dependence of the noise amplitude in graphene and graphene oxide

    PHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 6 2009
    B. R. Goldsmith
    Abstract Graphene and related materials such as carbon nanotubes and graphene oxide are promising materials for future applications in chemical sensing and electronics. Electronic noise in these materials is typically very high due to the low number of carriers and the inverse dependence of 1/f noise on the number of carriers. We have investigated the changes in 1/f noise amplitude with temperature in exfoliated graphene and reduced graphene oxide devices. We show that using reduced graphene oxide results in an intriguing environmental coupling to noise amplitude. ( 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Effects of correlated disorder on the magneto-transport in colossal magnetoresistance manganites

    PHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 4 2009
    M. Egilmez
    Abstract Monte-Carlo simulations predict that a local correlated disorder is responsible for many of the novel transport and magnetic properties of colossal magnetoresistance (CMR) materials such as manganites. One important prediction of these models is that the resistivity at the metal,insulator transition (MIT) in manganites depends strongly on the correlated quenched disorder. However, experimental confirmation has been challenging since it is difficult to control the amount of disorder in these compounds. We carried out experiments on Sm0.55Sr0.45MnO3, a prototypical CMR manganite with a sharp MIT, whereby the oxygen-related disorder is systematically enhanced by low temperature thermal activation. We observe dramatic changes in the temperature dependence of resistivity at the MIT as the amount of quenched disorder is increased, occurring in a manner that is in agreement with theoretical predictions. Temperature dependence of resistivity of Sm0.55Sr0.45MnO3 for different annealing times at 350 C in vacuum. ( 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Temperature dependence of thermally-carbonized porous silicon humidity sensor

    PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2005
    M. Bjrkqvist
    Abstract Thermal carbonization of porous silicon (PS) at 820 C under acetylene atmosphere is an appropriate method for humidity sensing purposes. It produces stable and hydrophilic surface still maintaining originally large specific surface area of PS. We report the temperature dependence of various electrical param- eters measured for the thermally-carbonized PS humidity sensor. Capacitance of the sensor in dry air (6 RH%) is almost constant at various temperatures, whereas in higher relative humidity values, the temperature dependence becomes evident. The resistance variation of the sensor is less dependent on RH as the temperature increases. While the capacitance showed linear behavior as a function of temperature, the resistance had a clear non-linear temperature dependence. In order to get information about the effects of frequency on capacitance values, we measured a phase angle and admittance of the sensor as a function of frequency at three different temperatures in low and high humidity. According to these results, it is preferable to operate this sensor construction using low frequency (<1 kHz). ( 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Temperature dependence of magnetic microstructure in Fe76Mo8Cu1B15 nanocrystalline alloy

    PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 15 2004
    M. Miglierini
    Abstract Fe76Mo8Cu1B15 nanocrystalline alloy featuring close-to-room Curie temperature of 310 K proves to be suitable for model case studies of complexity of magnetic interactions. Annealed samples with different contents of nanocrystallites are characterized by 57Fe transmission Mssbauer spectrometry performed in a wide temperature range (77,673 K). The validity of the temperature dependences of hyperfine parameters is discussed for all structural components including amorphous residual phase, bcc Fe nanocrystals and interface regions located in between the former two. Cautions which must be considered in deriving information about their relative contents are pointed out, because of the presence of static and dynamic effects at high temperatures due to non-interacting and weakly interacting single domain ferromagnetic grains dispersed into a paramagnetic amorphous matrix. ( 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Temperature dependence of tunnel magnetoresistance and magnetization of IrMn based MTJ

    PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2004
    P. Wi, niowski
    Abstract The temperature dependence of spin-polarized tunnel magnetoresistance (TMR) is investigated between 30 K and 300 K for annealed junctions with the structure of Ta(5)/Cu(10)/Ta(5)/NiFe(2)/Cu(5)/IrMn(10)/CoFe(2.5)/Al2O3(1.5)/CoFe(2.5)/NiFe(t)/Ta(5), where t = 10 and 100 nm. For the junction (t = 100 nm) annealed in 270 C we were able to separate electron polarization spin-dependent and spin-independent contributions of TMR temperature dependence. The thermally spin waves excitation constants determined from temperature dependence of magnetization and polarization are comparable. For junction with t = 10 nm annealed in 300 C electron spin polarization conductance is small in comparison to high conductance via trapped states, which arises from defects and magnetic impurities diffusion. ( 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Temperature dependence of elastic parameters and internal frictions for MnCu20Ni5Fe2 alloy

    PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 3 2004
    Mikio Fukuhara
    Abstract Using ultrasonics, MnCu20Ni5Fe2 (M2052) alloy's acoustic characteristics were observed in order to understand its high damping properties. Longitudinal and shear wave velocities, eight kinds of elastic parameters, and dilational and shear internal frictions were simultaneously measured as functions of temperature in cooling and heating runs between 218 and 373 K in M2052 alloy. A valley in Young and shear moduli, Debye temperature and internal friction peaks at around 345 K showed a M2052 fcc/fct trans-formation, accompanied by volume-nonpreserving lattice softening. The increment of dilational friction in the low temperature can be interpreted as boundary effect of the misfit domain, associated with nonharmonity of potential between pairs of atoms. The M2052 alloy shows highest elasticity below 300 K, indicating large resistance for volume-preserving distortion. ( 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]