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Wide Temperature Range (wide + temperature_range)
Selected AbstractsMethanogenesis and methanogenic pathways in a peat from subarctic permafrostENVIRONMENTAL MICROBIOLOGY, Issue 4 2007Martina Metje Summary Few studies have dealt so far with methanogenic pathways and populations in subarctic and arctic soils. We studied the effects of temperature on rates and pathways of CH4 production and on the relative abundance and structure of the archaeal community in a mildly acidic peat from a permafrost region in Siberia (67°N). We monitored the production of CH4 and CO2 over time and measured the consumption of Fe(II), ethanol and volatile fatty acids. All experiments were performed with and without specific inhibitors [2-bromoethanesulfonate (BES) for methanogenesis and CH3F for acetoclastic methanogenesis]. The optimum temperature for methanogenesis was between 26°C and 28°C [4.3 ,mol CH4 (g dry weight),1 day,1], but the activity was high even at 4°C [0.75 ,mol CH4 (g dry weight),1 day,1], constituting 17% of that at 27°C. The population structure of archaea was studied by terminal restriction fragment length polymorphism analysis and remained constant over a wide temperature range. Acetoclastic methanogenesis accounted for about 70% of the total methanogenesis. Most 16S rRNA gene sequences clustered with Methanosarcinales, correlating with the prevalence of acetoclastic methanogenesis. In addition, sequences clustering with Methanobacteriales were recovered. Fe reduction occurred in parallel to methanogenesis. At lower and higher temperatures Fe reduction was not affected by BES. Because butyrate was consumed during methanogenesis and accumulated when methanogenesis was inhibited (BES and CH3F), it is proposed to serve as methanogenic precursor, providing acetate and H2 by syntrophic oxidation. In addition, ethanol and caproate occurred as intermediates. Because of thermodynamic constraints, homoacetogenesis could not compete with hydrogenotrophic methanogenesis. [source] Heteroleptic Guanidinate- and Amidinate-Based Complexes of Hafnium as New Precursors for MOCVD of HfO2EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 11 2010Ke Xu Abstract The synthesis and characterization of four new heteroleptic complexes [Hf{,2 -(iPrN)2CNMe2}2Cl2] (1), [Hf{,2 -(iPrN)2CNMe2}2Me2] (2), [Hf{,2 -(iPrN)2CMe}2Cl2] (3), and [Hf{,2 -(iPrN)2CMe}2Me2] (4) are reported. All the complexes were characterized by spectroscopic methods, while compounds 1,3 were further examined by single-crystal X-ray diffraction, revealing that the complexes are monomers with the hafnium center in a distorted octahedral geometry. The thermal properties of the chlorine-free complexes (2, 4) were examined to determine their suitability for metalorganic chemical vapor deposition (MOCVD) applications, and compound 2 showed good volatility and thermal stability. On the basis of these results, compound 2 was selected for MOCVD of HfO2 with oxygen as oxidant. Depositions were carried out on Si(100) substrates in the temperature range 300,700 °C. The as-deposited HfO2 films crystallized in the monoclinic phase at temperatures above 500 °C, and the composition analysis determined by Rutherford back-scattering (RBS) and X-ray photoelectron spectroscopy (XPS) revealed that the films were stoichiometric and free of carbon. Thus, alkylguanidinatohafnium complex 2 is a promising precursor for growing HfO2 films in a wide temperature range with the desired stoichiometry, because of its adequate volatility, sufficient temperature window between vaporization and decomposition, as well as its ability to decompose cleanly in the presence of oxygen. [source] Oxidation Resistant Coatings for Ultrahigh Temperature Refractory Mo-Base Alloys,ADVANCED ENGINEERING MATERIALS, Issue 11 2009John H. Perepezko The use of Mo base alloys is limited by severe oxidation above about 650,°C. While MoSi2 coatings offer protection at high temperature, they are ineffective at low temperature. An integrated coating design has been developed based upon (B,+,Si) co-deposition and an in-situ diffusion barrier that offers robust, long term oxidation protection and self-healing for Mo alloys over a wide temperature range to over 1600,°C. [source] Towards a methodology for the characterization of fire resistive materials with respect to thermal performance models,FIRE AND MATERIALS, Issue 4 2006Dale P. Bentz Abstract A methodology is proposed for the characterization of fire resistive materials with respect to thermal performance models. Typically in these models, materials are characterized by their densities, heat capacities, thermal conductivities, and any enthalpies (of reaction or phase changes). For true performance modelling, these thermophysical properties need to be determined as a function of temperature for a wide temperature range from room temperature to over 1000°C. Here, a combined experimental/theoretical/modelling approach is proposed for providing these critical input parameters. Particularly, the relationship between the three-dimensional microstructure of the fire resistive materials and their thermal conductivities is highlighted. Published in 2005 by John Wiley & Sons, Ltd. [source] Preparation of Oriented Aluminum Nitride Thin Films on Polyimide Films and Piezoelectric Response with High Thermal Stability and FlexibilityADVANCED FUNCTIONAL MATERIALS, Issue 3 2007M. Akiyama Abstract c -Axis oriented aluminum nitride (AlN) thin films are successfully prepared on amorphous polyimide films by radiofrequency magnetron reactive sputtering at room temperature. Structural analysis shows that the AlN films have a wurtzite structure and consist of c -axis oriented columnar grains about 100,nm wide. The full width at half maximum of the X-ray diffraction rocking curves and piezoelectric coefficient d33 of the AlN films are 8.3° and 0.56,pC,N,1, respectively. The AlN films exhibit a piezoelectric response over a wide temperature range, from ,196 to 300,°C, and can measure pressure within a wide range, from pulse waves of hundreds of pascals to 40,MPa. Moreover, the sensitivity of the AlN films increases with the number of times it was folded, suggesting that we can control the sensitivity of the AlN films by changing the geometric form. These results were achieved by a combination of preparing the oriented AlN thin films on polyimide films, and sandwiching the AlN and polymer films between top and bottom electrodes, such as Pt/AlN/polyimide/Pt. They are thin (less than 10,,m), self powered, adaptable to complex contours, and available in a variety of configurations. Although AlN is a piezoelectric ceramic, the AlN films are flexible and excellent in mechanical shock resistance. [source] Recent Progress in Exploring Magnetocaloric MaterialsADVANCED MATERIALS, Issue 45 2009B. G. Shen Abstract The magnetic refrigeration technique based on the magnetocaloric effect (MCE) has attracted increasing interest because of its high efficiency and environment friendliness. In this article, our recent progress in exploring effective MCE materials is reviewed with emphasis on the MCE in the LaFe13,xSixbased alloys discovered by us. These alloys show large entropy changes over a wide temperature range near room temperature. The effects of magnetic rare-earth doping, interstitial atoms and high pressure on the MCE have been systematically studied. Special issues, such as appropriate approaches to determining the MCE associated with the first-order magnetic transition, the depression of magnetic and thermal hysteresis, and the key factors determining the magnetic exchange in alloys of this kind, are discussed. The applicability of giant MCE materials to magnetic refrigeration near ambient temperature is evaluated. A brief review of other materials with significant MCE is also presented. [source] Direct dynamic study on the hydrogen abstraction reaction of H2CO with NCOINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 6 2009Hao Sun A direct ab initio dynamics method is used to investigate the hydrogen-abstraction reaction of H2CO with NCO. The potential energy surface information is obtained at the MP2/6-311G(d,p) level. More accurate single-point energy is refined at the G3(MP2)//MP2/6-311G(d,p) level. Furthermore, the rate constants of reaction H2CO + NCO are evaluated by using the canonical variational transition state theory with small-curvature tunneling contributions over a wide temperature range of 200,2000 K. The calculated reaction enthalpy and rate constants are in good agreement with the available experimental values. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 394,400, 2009 [source] Kinetics of the thermal isomerization of 1,1,2,2-tetramethylcyclopropaneINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 8 2006David K. Lewis Reaction rates for the structural isomerization of 1,1,2,2-tetramethylcyclopropane to 2,4-dimethyl-2-pentene have been measured over a wide temperature range, 672,750 K in a static reactor and 1000,1120 K in a single-pulse shock tube. The combined data from the two temperature regions give Arrhenius parameters Ea=64.7 (±0.5) kcal/mol and log10(A, s,1) = 15.47 (±0.13). These values lie at the upper end of the ranges of Ea and log A values (62.2,64.7 kcal/mol and 14.82,15.55, respectively) obtained from three previous experimental studies, each of which covered a narrower temperature range. The previously noted trend toward lower Ea values for structural isomerization of methylcyclopropanes as methyl substitution increases extends only through the dimethylcyclopropanes (1,1- and 1,2-); Ea then appears to increase with further methyl substitution. In contrast, the pre-exponential factors for isomerization of cyclopropane and all of the methylcyclopropanes through tetramethylcyclopropane lie within ±0.3 of log10(A, s,1) = 15.2 and show no particular trend with increasing substitution. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 483,488, 2006 [source] Trans-admittance control for eliminating the temperature effect of piezoelectric transformer in the CCFL backlight moduleINTERNATIONAL JOURNAL OF CIRCUIT THEORY AND APPLICATIONS, Issue 8 2008Yu-Kang Lo Abstract A half-bridge (HB) resonant inverter for driving a cold cathode fluorescent lamp (CCFL) backlight module with a piezoelectric transformer (PT) is analyzed in this paper. The resonant inductance of the HB inverter is expressed as a function of the load current, the load resistance and the PT circuit parameters. Also, the trans-admittance of the PT-CCFL combination network is measured to track the operating frequency for the HB resonant inverter, which may be varied due to the temperature rise of PT. The lamp driving current and power can thus remain almost constant in a wide temperature range. Experiments show that the observed results match the theoretical analyses. Copyright © 2008 John Wiley & Sons, Ltd. [source] An effective iodide formulation for killing Bacillus and Geobacillus spores over a wide temperature rangeJOURNAL OF APPLIED MICROBIOLOGY, Issue 2 2004N. Kida Abstract Aims:, To develop a sporicidal reagent which shows potent activity against bacterial spores not only at ambient temperatures but also at low temperatures. Methods and Results:, Suspension tests on spores of Bacillus and Geobacillus were conducted with the reagent based on a previously reported agent (N. Kida, Y. Mochizuki and F. Taguchi, Microbiology and Immunology 2003; 47: 279,283). The modified reagent (tentatively designated as the KMT reagent) was composed of 50 mmol l,1 EDTA-2Na, 50 mmol l,1 ferric chloride hexahydrate (FeCl3·6H2O), 50 mmol l,1 potassium iodide (KI) and 50% ethanol in 0·85% NaCl solution at pH 0·3. The KMT reagent showed significant sporicidal activity against three species of Bacillus and Geobacillus spores over a wide range of temperature. The KMT reagent had many practical advantages, i.e. activity was much less affected by organic substances than was sodium hypochlorite, it did not generate any harmful gas and it was stable for a long period at ambient temperatures. The mechanism(s) of sporicidal activity of the KMT reagent was considered to be based on active iodine species penetrating the spores with enhanced permeability of the spore cortex by a synergistic effect of acid, ethanol and generated active oxygen. Conclusions:, The data suggest that the KMT reagent shows potent sporicidal activity over a wide range temperatures and possesses many advantages for practical applications. Significance and Impact of the Study:, The results indicate development of a highly applicable sporicidal reagent against Bacillus and Geobacillus spores. [source] Electrical characteristics of Al/polyindole Schottky barrier diodes.JOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2009Abstract In this study, the forward and reverse bias current,voltage (I,V), capacitance,voltage (C,V), and conductance,voltage (G/,,V) characteristics of Al/polyindole (Al/PIN) Schottky barrier diodes (SBDs) were studied over a wide temperature range of 140,400 K. Zero-bias barrier height ,B0(I,V), ideality factor (n), ac electrical conductivity (,ac), and activation energy (Ea), determined by using thermionic emission (TE) theory, were shown fairly large temperature dispersion especially at lower temperatures due to surface states and series resistance of Al/PIN SBD. I,V characteristics of the Al/PIN SBDs showed an almost rectification behavior, but the reverse bias saturation current (I0) and n were observed to be high. This high value of n has been attributed to the particular distribution of barrier heights due to barrier height inhomogeneities and interface states that present at the Al/PIN interface. The conductivity data obtained from G/,V measurements over a wide temperature range were fitted to the Arrhenius and Mott equations and observed linear behaviors for ,ac vs. 1/T and ln ,ac vs. 1/T1/4 graphs, respectively. The Mott parameters of T0 and K0 values were determined from the slope and intercept of the straight line as 3.8 × 107 and 1.08 × 107 Scm,1K1/2, respectively. Assuming a value of 6 × 1012 s,1 for ,0, the decay length ,,1 and the density states at the Fermi energy level, N(EF) are estimated to be 8.74 Å and 1.27 × 1020 eV,1cm,3, respectively. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Morphology and thermal and dielectric behavior of cycloaliphatic epoxy/trimethacrylate interpenetrating polymer networks for vacuum-pressure-impregnation electrical insulationJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008Jingkuan Duan Abstract Vacuum pressure impregnation has been known as the most advanced impregnation technology that has ever been developed for large and medium high-voltage electric machines and apparatuses. We developed one new type of vacuum-pressure-impregnation resin with excellent properties by means of a novel approach based on in situ sequential interpenetrating polymer networks resulting from the curing of trimethacrylate monomer [trimethylol-1,1,1-propane trimethacrylate (TMPTMA)] and cycloaliphatic epoxy resin (CER). In this study, the influence of the concentrations of the components and their microstructures on their thermal and dielectric behaviors were investigated for the cured CER/TMPTMA systems via atomic force microscopy, dynamic mechanical analysis, thermogravimetric analysis, and dielectric analysis. The investigation results show that the addition of TMPTMA to the CER,anhydride system resulted in the formation of a uniform and compact microstructure in the cured epoxy system. This led the cured CER/TMPTMA systems to show much higher moduli in comparison with the pure CER,anhydride system. The thermogravimetric analysis results show that there existed a decreasing tendency in the maximum thermal decomposition rates of the cured CER/TMPTMA systems, which implies that the thermal stability properties improved to some extent. The dielectric analysis results show that the cured CER/TMPTMA systems displayed quite different dielectric behaviors in the wide frequency range 0.01 Hz,1 MHz and in the wide temperature range 27,250°C compared with the cured CER,anhydride system. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Microstructure dependent properties of polypropylene-clay nanocompositesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2007Y. Fan Abstract The mechanical properties of melt processed polypropylene-montmorillonite nanocomposites were studied as a function of clay content. The measurement of tensile properties at room temperature and dynamic mechanical properties over a wide temperature range reveal a decrease in modulus and tensile strength of the composite with increasing clay content. The origins of this anomalous result were examined in detail using X-ray diffraction and differential scanning calorimeter, which averaged the microstructure over reasonable specimen volumes. Micromechanical models could be used to adequately describe the composite properties, provided appropriate properties for the matrix and particle were used. The matrix properties were found to affect the average properties significantly. © Wiley Periodicals, Inc. J Appl Polym Sci 103: 204,210, 2007 [source] Theoretical and kinetic study of the H + C2H5CN reactionJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 6 2010Jingyu Sun Abstract The reaction of H radical with C2H5CN has been studied using various quantum chemistry methods. The geometries were optimized at the B3LYP/6-311+G(d,p) and B3LYP/6-311++G(2d,2p) levels. The single-point energies were calculated using G3 and BMC-CCSD methods based on B3LYP/6-311++G(2d,2p) geometries. Four mechanisms were investigated, namely, hydrogen abstraction, C-addition/elimination, N-addition/elimination and substitution. The kinetics of this reaction were studied using the transition state theory and multichannel Rice-Ramsperger-Kassel-Marcus methodologies over a wide temperature range of 200,3000 K. The calculated results indicate that C-addition/elimination channel is the most feasible over the whole temperature range. The deactivation of initial adduct C2H5CHN is dominant at lower temperature with bath gas H2 of 760 Torr; whereas C2H5+HCN is the dominant product at higher temperature. Our calculated rate constants are in good agreement with the available experimental data. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010 [source] FLOW PROPERTIES AND TUBE FRICTION FACTOR OF MILK CREAM: INFLUENCE OF TEMPERATURE AND FAT CONTENTJOURNAL OF FOOD PROCESS ENGINEERING, Issue 5 2010RODRIGO DIAZ FLAUZINO ABSTRACT The rheological behavior of milk cream was studied for different fat contents (0.10 to 0.31) and for a wide temperature range (2 and 87C) using a rotational rheometer. Newtonian behavior was observed, except for fat content between 0.20 and 0.31 and temperature between 2 and 33C, where viscoplastic behavior was remarkable. The rheological parameters (Newtonian viscosity, plastic viscosity and yield stress) and density were well correlated to temperature and fat content. Tube friction factor during flow of cream was experimentally obtained at various flow rates, temperatures and tube diameters (86 , Re , 2.3 × 104, 38 , ReB , 8.8 × 103, 1.1 × 103 , He , 6.7 × 103). The proposed correlations for density and rheological parameters were applied for the prediction of friction factor for laminar and turbulent flow of cream using well-known equations for Newtonian and viscoplastic flow. The good agreement between experimental and predicted values confirms the reliability of the proposed correlations for describing the flow behavior of cream. PRACTICAL APPLICATIONS This paper presents correlations for the calculation of density and rheological parameters (Newtonian viscosity, Bingham plastic viscosity and yield stress) of milk cream as functions of temperature (2,87C) and fat content (0.10,0.31). Because of the large temperature range, the proposed correlations are useful for process design and optimization in dairy processing. An example of practical application is presented in the text, where the correlations were applied for the prediction of friction factor for laminar and turbulent tube flow of cream using well-known equations for Newtonian and viscoplastic flow, which are summarized in the text. The comparison with experimental data obtained at various flow rates, temperatures and tube diameters showed a good agreement, which confirms the reliability of the proposed correlations. [source] EFFECTS OF ORGANIC ACIDS, NISIN, LYZOZYME AND EDTA ON THE SURVIVAL OF YERSINIA ENTEROCOLITICA POPULATION IN INOCULATED ORANGE BEVERAGESJOURNAL OF FOOD SAFETY, Issue 1 2010CECILIA S.M. LUCERO ESTRADA ABSTRACT Inactivation of a Yersinia enterocolitica strain by 3.4% ascorbic acid (AA), 0.5% citric acid (CA), 0.2% lactic acid, 100 IU/mL nisin, 2,400 IU/mL lysozyme and 20 mM ethylenediaminetetraacetic acid disodium salt (EDTA ), alone and combined, was studied at different temperatures (4 and 25C) in commercial and laboratory-prepared orange beverages. In laboratory-prepared juice, highest reductions (between 3.06 and 4.07 log units) were obtained with acid mixtures at 25C after 20 min of incubation. At 24 h of incubation, EDTA was bactericidal and the mixtures with nisin or lysozyme resulted in count reductions of 6.03 and 5.98 log units, respectively. In commercial orange beverage, AA and CA gave reductions of 5.43 and 4.26 log units, respectively. The three acid mixtures were bactericidal within the first 10 min. EDTA alone or mixed completely inhibited Y. enterocolitica strain at 6 and 24 h of incubation. At 4C, all the results were significantly lower than at 25C. PRACTICAL APPLICATIONS Yersinia enterocolitica is a common cause of gastrointestinal disorders and may lead to sequelae. This pathogen can maintain its virulence in a wide temperature range and under adverse conditions such as pH lower than 4. There are reports describing the isolation of Y. enterocolitica from water and ice in Brazil and Latin America. The sale of unpasteurized drinks is a common practice in our region and their consumption has increased over the past years. In the present work, chemical compounds and biological inhibitors were studied. Some of these compounds showed to be efficient for reducing Y. enterocolitica populations. Furthermore, they did not modify the organoleptic characteristics of the beverages and they are not toxic for human beings. [source] Thermal Effects on Fast Skeletal Myosins from Alaska Pollock, White Croaker, and Rabbit in Relation to Gel FormationJOURNAL OF FOOD SCIENCE, Issue 5 2003H. Fukushima ABSTRACT Thermodynamic properties in differential scanning calorimetry (DSC) and changes in viscoelasticity upon heating of myosins from white croaker, Alaska pollock, and rabbit fast muscles were investigated in relation to their thermal gel formation abilities. Alaska pollock myosin unfolded in a wide temperature range of 19 to 69°C as revealed by DSC, whereas rabbit myosin unfolded in very narrow range of 32 to 56°C. Thermal unfolding of white croaker myosin occurred in an intermediate temperature range of 30 to 60°C. Viscoelastic properties determined as storage modulus, G,, and loss modulus, G,, reflected differences observed in DSC for the 3 myosins. [source] Characteristics of ammonia permeation through porous silica membranesAICHE JOURNAL, Issue 5 2010Masakoto Kanezashi Abstract A sol,gel method was applied for the preparation of silica membranes with different average pore sizes. Ammonia (NH3) permeation/separation characteristics of the silica membranes were examined in a wide temperature range (50,400°C) by measurement of both single and binary component separation. The order of gas permeance through the silica membranes, which was independent of membrane average pore size, was as follows: He > H2 > NH3 > N2. These results suggest that, for permeation through silica membranes, the molecular size of NH3 is larger than that of H2, despite previous reports that the kinetic diameter of NH3 is smaller than that of H2. At high temperatures, there was no effect of NH3 adsorption on H2 permeation characteristics, and silica membranes were highly stable in NH3 at 400°C (i.e., gas permeance remained unchanged). On the other hand, at 50°C NH3 molecules adsorbed on the silica improved NH3 -permselectivity by blocking permeation of H2 molecules without decreasing NH3 permeance. The maximal NH3/H2 permeance ratio obtained during binary component separation was ,30 with an NH3 permeance of ,10,7 mol m,2 s,1 Pa,1 at an H2 permeation activation energy of ,6 kJ mol,1. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Prediction of phase equilibria and excess properties for systems with sulfonesAICHE JOURNAL, Issue 2 2003Roland Wittig The group contribution method modified UNIFAC (Dortmund) has become very popular because of its broad applications, and reliable predictions for vapor-liquid equilibria, solid-liquid equilibria, liquid-liquid equilibria, activity coefficients at infinite dilution, azeotropic data and excess enthalpies in a wide temperature range. Therefore, the existing parameter matrix for the modified UNIFAC method is continuously extended with the help of the Dortmund Data Bank and by carrying out systematic measurements. The new main group for sulfones, such as that required to describe systems with the selective solvent sulfolane, is introduced, as well as ten new pairs of group interaction parameters for modified UNIFAC. [source] Methane hydrate equilibria in silica gels with broad pore-size distributionsAICHE JOURNAL, Issue 2 2002Duane H. Smith Equilibrium pressures for the dissociation of methane hydrates confined in silica gel pores of nominal radii 7.5, 5.0 and 3.0 nm were measured over a wide temperature range, and were observed to be higher than those for bulk methane hydrate. A model is presented that allows the pore radius involved in each equilibrium to be determined from these data, so that the model exactly reproduces the experimental equilibrium pressure. Based on this model, pore volume distributions were reconstructed and found to be in good agreement with those obtained from nitrogen desorption isotherms, indicating that hydrate formed nearly uniformly in the available pores. [source] Synthesis and white electroluminescent properties of multicomponent copolymers containing polyfluorene, oligo(phenylenevinylene), and porphyrin derivativesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2009Hui Li Abstract Two novel multicomponent copolymers (P1 and P2) containing polyfluorene (PF), oligo(phenylenevinylene) (OPV), and porphyrin (Por) derivatives were synthesized according to the Suzuki polymerization method. The structures, optical, and electrochemical properties of the two model compounds (OPV and Por) and multicomponent copolymers were characterized by 1H NMR, FTIR, elemental analysis, UV,vis spectroscopy, photoluminescence, and cyclic voltammetry, respectively. Both of the copolymers exhibit thermotropic liquid crystalline properties and represent the characteristic Schlieren textures in a wide temperature range. Electroluminescence spectra of these copolymers exhibit broadband emissions covering the entire visible region from 400 to 700 nm. The single layer polymer light emitting diodes device based on P2 with a configuration of indium tin oxide/poly(ethylenedioxythiophene):poly(styrenesulfonic acid)/polymers/Ca/Al emits white light with the Commission Internationale de l,Eclairage chromaticity coordinates of (0.29, 0.30), maximum brightness of 443 cd/m2. The white-light-emitting devices based on the novel multicomponent copolymers exhibit low turn-on voltage, and good color stability at different driving voltages as well. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5291,5303, 2009 [source] Synthesis and characterization of side-chain liquid crystalline ABC triblock copolymers with p -methoxyazobenzene moieties by atom transfer radical polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 13 2008Xiaohua He Abstract A series of novel side-chain liquid crystalline ABC triblock copolymers composed of poly(ethylene oxide) (PEO), polystyrene (PS), and poly[6-(4-methoxy-4,-oxy-azobenzene) hexyl methacrylate] (PMMAZO) were synthesized by atom transfer radical polymerization (ATRP) using CuBr/1,1,4,7,7-pentamethyldiethylenetriamine (PMDETA) as a catalyst system. First, the bromine-terminated diblock copolymer poly(ethylene oxide)- block -polystyrene (PEO-PS-Br) was prepared by the ATRP of styrene initiated with the macro-initiator PEO-Br, which was obtained from the esterification of PEO and 2-bromo-2-methylpropionyl bromide. An azobenzene-containing block of PMMAZO with different molecular weights was then introduced into the diblock copolymer by a second ATRP to synthesize the novel side-chain liquid crystalline ABC triblock copolymer poly(ethylene oxide)- block -polystyrene- block -poly[6-(4-methoxy-4,-oxy-azobenzene) hexyl methacrylate] (PEO-PS-PMMAZO). These block copolymers were characterized using proton nuclear magnetic resonance (1H NMR) and gel permeation chromatograph (GPC). Their thermotropic phase behaviors were investigated using differential scanning calorimetry (DSC) and polarized optical microscope (POM). These triblock copolymers exhibited a smectic phase and a nematic phase over a relatively wide temperature range. At the same time, the photoresponsive properties of these triblock copolymers in chloroform solution were preliminarily studied. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4442,4450, 2008 [source] Poly[1-(trimethylgermyl)-1-propyne] and poly[1-(trimethylsilyl)-1-propyne] with various geometries: Their synthesis and propertiesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 14 2003V. S. Khotimsky Abstract The polymerization of 1,2-disubstituted acetylenes [1-(trimethylgermyl)-1-propyne and 1-(trimethylsilyl)-1-propyne] initiated by Nb- and Ta-based catalytic systems was studied within a wide temperature range (,10 to +80 °C) with solvents (cyclohexane, CCl4, toluene, anisol, and n -chlorobutane) with variable dielectric constants (2.023,7.390). Conditions ensuring the synthesis of poly[1-(trimethylsilyl)-1-propyne] (PTMSP) containing 20,80% cis units and poly[1-(trimethylgermyl)-1-propyne] (PTMGP) containing 3,65% cis units were determined. The PTMSP and PTMGP samples were amorphous, exhibited a two-phase structure characterized by the presence of less ordered regions and regions with an enhanced level of ordering, and differed in solubility. A correlation was found between the cis/trans ratio and the morphology, the geometrical density of PTMSP and PTMGP films, and the gas permeability of the polymers. The gas permeability and solubility behavior of PTMSP and PTMGP were examined in terms of the molecular characteristics of the polymer samples (the thermodynamic Kuhn segment and the Kerr electrooptic effect). It was demonstrated that the gas permeability, as well as the solubility of the polymers, was defined by their supramolecular ordering, which depended on the lengths of continuous sequences composed of units of analogous microstructures and on the flexibility of macrochains. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2133,2155, 2003 [source] Critical Factors Affecting the Wettability of ,-Alumina by Molten AluminumJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2004Ping Shen The wetting behaviors of ,-Al2O3 single crystals with three different faces,R(0112), A(01120), and C(0001),and polycrystals (PC) by molten aluminum were studied over a wide temperature range using both a conventional and an improved sessile-drop method. The critical factors affecting the wettability, such as temperature, atmosphere, substrate surface roughness, and crystallographic orientation, and the influence from the experimental technique, were thoroughly investigated. The results show that the aluminum surface oxidation and the thickness of the oxide film have a pronounced effect on the wettability, especially at low temperatures. To eliminate this effect, the experimental temperature must be over a critical value. Vacuum favors lowering this value compared with atmosphere, and the improved sessile-drop method, particularly using an impingement-dropping mode (I-mode), helps to weaken this effect by mechanical disruption and removal of the oxide film. However, the dropping distance and the dropping force must be controlled to prevent an overspreading of the drop. The effects of the substrate surface roughness and temperature are not significant in the case of a clean aluminum surface and a fine-prepared alumina surface. On the other hand, the effect of the alumina surface crystallographic orientation is noticeable and the wettability is in the order of R > A > PC > C. The intrinsic contact angles of the Al/,-Al2O3 system in the temperature range of 1000°,1500°C were estimated to be 76°,85° for the R and A faces, 88°,100° for the C face, and 77°,90° for the polycrystal, depending on the temperature. [source] Microstructures and Pyroelectric Properties of Multicomposition 0.9PbZrO3·xPbTiO3·(0.1,x)Pb(Zn1/3Nb2/3)O3 CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2002Yong Jun Wu The microstructures and pyroelectric properties of multicomposition 0.9PbZrO3·xPbTiO3·(0.1,x)Pb(Zn1/3Nb2/3)O3 (PZ,PT,PZN) ceramics were investigated. The PZ,PT,PZN ceramics with nearly theoretical density were prepared by spark plasma sintering at low temperature (800°C) for a very short time (10 min) from two original compositions with x= 0.025 and x= 0.050. The heat treatment was successfully used to control the diffusion between the different compositions in such ceramics. For ceramics heat-treated at 900°C, two pyroelectric peaks corresponding to the original compositions were observed. When the heat-treatment temperature was increased to 1200°C, these two pyroelectric peaks combined into one sharp pyroelectric peak, which corresponds to average composition. When the spark-plasma-sintered ceramics were heat-treated at 950°C, a high and stable pyroelectric coefficient (>100 nC·cm,2·K,1) over a wide temperature range (23°,47°C) was obtained. It was found that the pyroelectric properties strongly depended on the microstructures. [source] Viscometric properties of viscosity index improvers in lubricant base oil over a wide temperature range.LUBRICATION SCIENCE, Issue 2 2000Part I: Group II base oil Capillary viscometry has been employed to measure the viscosities of dilute polymer solutions over the temperature range -10 to 150 °C. A Group II base oil containing 95% saturates was used as solvent for an olefin copolymer (OCP), a hydrogenated diene copolymer (HDP), and a polymethacrylate (PMA). These three polymers represent the three major families of viscosity index (VI) improvers used nowadays in lubricant formulations. Intrinsic viscosities and Huggins' constants were also determined. The thickening effects of the olefin copolymer and the hydrogenated diene copolymer were found to be higher at low temperatures (e.g., 40 °C) than at higher ones (e.g., 100 °C), which phenomenon was attributed to stronger intermolecular hydrodynamic interactions at low temperatures, as indicated by the Huggins constants. For the hydrogenated diene copolymer and the polymethacrylate polymer, the viscosity increased abruptly when the temperature went below 10 °C. This unusual observation was attributed to the crystallisation of a small fraction of the base oil. Based on the intrinsic viscosity data, it was concluded that at temperatures between 10 and 150 °C, the polymer coil dimension remains a constant for the olefin copolymer and the hydrogenated diene copolymer VI improvers, but increases with increasing temperature for the polymethacrylate VI improver. [source] Hydrolytic Degradation and Monomer Recovery of Poly(butylene succinate) and Poly(butylene succinate/adipate) in the MeltMACROMOLECULAR REACTION ENGINEERING, Issue 6 2008Hideto Tsuji Abstract Aliphatic dicarboxylic acid/aliphatic diol-derived polyesters, poly(butylene succinate) and poly(butylene succinate/adipate), have been hydrolytically degraded in the melt in high-temperature and high-pressure water over a wide temperature range of 180,300,°C for periods of up to 30 min. The formation/decomposition of succinic acid (SA), adipic acid (AA), and butane-1,4-diol (BD), plus the molecular weight change of PBS and PBSA were then investigated. SA and AA were recovered at maximum yields of 65,80%, whereas BD was recovered at a maximum yield of only 30%, probably because of its decomposition. The obtained results were compared with those reported for aliphatic hydroxycarboxylic acid-derived polyesters and aromatic dicarboxylic acid/aliphatic diol-derived polyesters. [source] Subtraction of scattering parameters for adiabatic intrinsic responses of semiconductor lasersMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 4 2008S. J. Zhang Abstract Thermal effects will make chip temperature change with bias current of semiconductor lasers, which results in inaccurate intrinsic response by the conventional subtraction method. In this article, an extended subtraction method of scattering parameters for characterizing adiabatic responses of laser diode is proposed. The pulsed injection operation is used to determine the chip temperature of packaged semiconductor laser, and an optimal injection condition is obtained by investigating the dependence of the lasing wavelength on the width and period of the injection pulse in a relatively wide temperature range. In this case, the scattering parameters of laser diode are measured on adiabatic condition and the adiabatic intrinsic responses of packaged laser diode are first extracted. It is found that the adiabatic intrinsic responses are evidently superior to those without thermal consideration. The analysis results indicate that inclusion of thermal effects is necessary to acquire accurate intrinsic responses of semiconductor lasers. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 992,995, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23278 [source] Magnetic field-dependence study of the magnetocaloric properties of a superparamagnetic nanoparticle system: a Monte Carlo simulationPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2008D. Serantes Abstract The influence of the applied magnetic field on the magnetocaloric properties of a fine magnetic particle system has been studied using a Monte Carlo technique. By simulating zero field cooling (ZFC) curves under different strengths of the applied magnetic field, we have analyzed the variation of the entropy for temperatures above the maximum of the ZFC curves, where the process is reversible. The entropy curves have been observed to behave in a different fashion at low values of the magnetic field, where the peak only slightly shifts to higher temperatures with increasing fields. For larger fields, the peak rapidly shifts to higher temperatures, while the overall shape of the curve broadens over a wide temperature range. It is also observed that the blocking temperature as a function of the magnetic field shows the feature of a change from a bell-like shape to a monotonically decreasing function, resembling what is found experimentally for intermediate values of the sample concentration. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Temperature dependence of magnetic microstructure in Fe76Mo8Cu1B15 nanocrystalline alloyPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 15 2004M. 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 Mössbauer 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] | ||||||||||||||||||||||||||||||||||