High Thermal (high + thermal)

Distribution by Scientific Domains

Terms modified by High Thermal

  • high thermal conductivity
  • high thermal stability

  • Selected Abstracts

    High thermal and chemical stability of Thermus thermophilus seven-iron ferredoxin

    FEBS JOURNAL, Issue 23 2003
    Linear clusters form at high pH on polypeptide unfolding
    To probe the stability of the seven-iron ferredoxin from Thermus thermophilus (FdTt), we investigated its chemical and thermal denaturation processes in solution. As predicted from the crystal structure, FdTt is extremely resistant to perturbation. The guanidine hydrochloride-induced unfolding transition shows a midpoint at 6.5 m (pH 7, 20 °C), and the thermal midpoint is above boiling, at 114 °C. The stability of FdTt is much lower at acidic pH, suggesting that electrostatic interactions are important for the high stability at higher pH. On FdTt unfolding at alkaline pH, new absorption bands at 520 nm and 610 nm appear transiently, resulting from rearrangement of the cubic clusters into linear three-iron species. A range of iron,sulfur proteins has been found to accommodate these novel clusters in vitro, although no biological function has yet been assigned. [source]

    Cationic polymerization of L,L -lactide

    gorzata Ba
    Abstract Cationic bulk polymerization of L,L- lactide (LA) initiated by trifluromethanesulfonic acid [triflic acid (TfA)] has been studied. At temperatures 120,160 °C, polymerization proceeded to high conversion (>90% within ,8 h) giving polymers with Mn , 2 × 104 and relatively high dispersity. Thermogravimetric analysis of resulting polylactide (PLA) indicated that its thermal stability was considerably higher than the thermal stability of linear PLA of comparable molecular weight obtained with ROH/Sn(Oct)2 initiating system. Also hydrolytic stability of cationically prepared PLA was significantly higher than hydrolytic stability of linear PLA. Because thermal or hydrolytic degradation of PLA starting from end-groups is considerably faster than random chain scission, both thermal and hydrolytic stability depend on molecular weight of the polymer. High thermal and hydrolytic stability, in spite of moderate molecular weight of cationically prepared PLA, indicate that the fraction of end-groups is considerably lower than in linear PLA of comparable molecular weight. According to proposed mechanism of cationic LA polymerization growing macromolecules are fitted with terminal OH and C(O)OSO2CF3 end-groups. The presence of those groups allows efficient end-to-end cyclization. Cyclic nature of resulting PLA explains its higher thermal and hydrolytic stability as compared with linear PLA. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2650,2658, 2010 [source]

    Low-Threshold Distributed-Feedback Lasers Based on Pyrene-Cored Starburst Molecules with 1,3,6,8-Attached Oligo(9,9-Dialkylfluorene) Arms

    Ruidong Xia
    Abstract Here, a detailed characterization of the optical gain properties of sky-blue-light-emitting pyrene-cored 9,9-dialkylfluorene starbursts is reported; it is shown that these materials possess encouragingly low laser thresholds and relatively high thermal and environmental stability. The materials exhibit high solid-state photoluminescence (PL) quantum efficiencies (>90%) and near-single-exponential PL decay transients with excited state lifetimes of ,1.4,ns. The thin-film slab waveguide amplified spontaneous emission (ASE)-measured net gain reaches 75,78,cm,1. The ASE threshold energy is found to remain unaffected by heating at temperatures up to 130,°C, 40 to 50,°C above Tg. The ASE remained observable for annealing temperatures up to 170 or 200,°C. 1D distributed feedback lasers with 75% fill factor and 320,nm period show optical pumping thresholds down to 38,65,Wcm,2, laser slope efficiencies up to 3.9%, and wavelength tuning ranges of ,40,nm around 471,512,nm. In addition, these lasers have relatively long operational lifetimes, with N1/2,,,1.1,×,105,pulses for unencapsulated devices operated at ten times threshold in air. [source]

    High-Performance Field-Effect Transistor Based on Dibenzo[d,d,]thieno[3,2- b;4,5- b,]dithiophene, an Easily Synthesized Semiconductor with High Ionization Potential,

    ADVANCED MATERIALS, Issue 19 2007
    H. Gao
    Three simple, controlled steps are all it takes to synthesize the title pentacene analogue DBTDT (see figure). The material's high ionization potential, high thermal and photostability, high mobilities, and an on/off ratio larger than 106 at a substrate temperature of ca.,36,°C, as reported here, suggest that DBTDT will be extremely valuable for applications in plastic organic electronics. [source]

    Catalytic porous ceramic prepared in-situ by sol-gelation for butane-to-syngas processing in microreactors

    AICHE JOURNAL, Issue 7 2009
    Nico Hotz
    Abstract In this study, a novel flow-based method is presented to place catalytic nanoparticles into a reactor by sol-gelation of a porous ceramic consisting of Rh/ceria/zirconia nanoparticles, silica sand, ceramic binder, and a gelation agent. This method allows for the placement of a liquid precursor containing the catalyst into the final reactor geometry without the need of impregnating or coating of a substrate with the catalytic material. The so generated foam-like porous ceramic shows properties highly appropriate for use as catalytic reactor material, e.g., reasonable pressure drop due to its porosity, high thermal and catalytic stability, and excellent catalytic behavior. To investigate the catalytic activity, microreactors containing this foam-like ceramic are employed for the production of hydrogen and carbon monoxide-rich syngas from butane. The effect of operating parameters such as the inlet flow rate on the hydrocarbon processing is analyzed and the limitation of the reactor by diffusion mass transport is investigated. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]

    New method for bonding an adsorbent film to the walls of capillary columns

    Abstract A new method for immobilisation of an adsorbent on the wall of a capillary column ensures high thermal and mechanical stability of the resulting coating. The method can be applied to a variety of adsorbents of natural or synthetic origin. Its effectiveness is illustrated by results obtained for coating with modified silica or molecular sieve 13X. [source]

    Highly Thermal Stable Main-Chain Nonlinear Optical Polyimide Based on Two-Dimensional Carbazole Chromophores

    Hsieh-Chih Tsai
    Abstract Summary: A new NLO-active lambda-shaped main-chain polyimide that comprises a two-dimensional carbazole chromophore was synthesized. This polyimide exhibits high thermal and temporal stability. It can endure temperatures of up to 240,°C for a transient time and maintain a large SH signal at 100,°C for a long time because embedding the two-dimensional chromophores into the polymer backbone effectively suppresses the randomization of the oriented dipole at high temperatures. [source]

    New vanadium(IV) and titanium(IV) oxyfluorotellurates(IV): V2Te2O7F2 and TiTeO3F2

    Jean Paul Laval
    As part of a continuing study of oxyfluorotellurates(IV), materials likely to present interesting nonlinear optical properties, two new phases, titanium(IV) tellurium(IV) trioxide difluoride, TiTeO3F2, and divanadium(IV) ditellurium(IV) heptaoxide difluoride, V2Te2O7F2, have been characterized and present, respectively, titanium and vanadium in the tetravalent state. The TiTeO3F2 structure is based on linear double rows of TiO3F3 polyhedra sharing vertices. These rows are connected to adjacent rows via two vertices of Te2O5 bipolyhedra. The Te, Ti, one F and two O atoms are on general positions, with one O and F statistically occupying the same site with half-occupancy for each anion. One O and one F occupy sites with .m. symmetry. The V2Te2O7F2 structure consists of zigzag chains of VO4F2 octahedra alternately sharing O,O and F,F edges. These chains are connected via Te2O5 bipolyhedra, forming independent mixed layers. The Te, V, one F and three O atoms are on general positions while one O atom occupies a site of symmetry. In both phases, the electronic lone pair E of the TeIV atom is stereochemically active. A full O/F anionic ordering is observed in V2Te2O7F2, but in TiTeO3F2 one of the six anionic sites is occupied by half oxygen and half fluorine, all the others being strictly ordered. These compounds represent new members of a growing family of oxyfluorotellurates(IV), including the recently characterized members of formula MTeO3F, M being a trivalent cation. As was true for the previous members, they are characterized by an unusually high thermal and chemical stability in relation to the absence of direct Te,F bonds. [source]

    Acenaphtho[1,,2- c]phosphole P -Oxide: A Phosphole,Naphthalene ,-Conjugated System with High Electron Mobility

    Arihiro Saito
    One order of magnitude: Naphthalene- and acenaphthene-fused phosphole P -oxides (see figure) are shown to have reasonably high thermal and electrochemical stabilities and electron-accepting ability. The electron mobility of the naphthalene-fused phosphole P -oxide is about one order higher than that of tris(8-hydroxyquinoline)aluminium(III) Alq3 at any given electric field. [source]

    Studies on Stereoselective [2+2] Cycloadditions between N,N-Dialkylhydrazones and Ketenes

    Eloísa Martín-Zamora Dr.
    Abstract Staudinger-like cycloadditions between chiral, non-racemic N,N-dialkylhydrazones 1 and functionalized ketenes constitute an efficient methodology for the stereoselective construction of the ,-lactam ring. The potential for fine tuning of the dialkylamino auxiliary structure, the availability of a high-yielding deprotection method for the release of the free azetidinones, and the high thermal and chemical stability of hydrazones as N-dialkylamino imines are highlighted as the key elements for the success of the strategy. This last aspect is of particular importance concerning generality: even hydrazones from easily enolizable aldehydes or from formaldehyde reacted to afford the corresponding cycloadducts with high chemical and stereochemical yields. The syntheses of the ,-amino-,-hydroxyacids (2R,3S)-phenylisoserine (42) and (2R,3S)-norstatin (45) were accomplished as illustrative examples of the synthetic utility of this procedure. A model system for the cycloaddition of g series auxiliaries was studied by ab initio computational methods. The collected results support a two-step mechanism through zwitterionic intermediates, and explain the observed absolute and relative stereochemistry in terms of the preferred outward cycloaddition to the Re face of the hydrazone. La reacción de cicloadición [2+2] de tipo Staudinger entre cetenas funcionalizadas y las hidrazonas quirales 1 constituye un método eficiente para la construcción estereoselectiva del anillo de azetidinona. La modulación de la estructura del grupo dialquilamino empleado como auxiliar, la disponibilidad de un procedimiento eficiente para la desprotección de las , -lactamas libres y la alta estabilidad química y térmica de las hidrazonas como N-dialquilamino iminas son los puntos clave para el éxito de la estrategia. Este último aspecto es de particular importancia por su implicación en la generalidad del método: hidrazonas derivadas de aldehídos fácilmente enolizables o incluso las derivadas de formaldehído reaccionan para dar lugar a los correspondientes cicloaductos con excelentes rendimientos químicos y estereoquímicos. La síntesis de los , -amino- , -hidroxiácidos (2R,3S)-fenilisoserina (42) y (2R,3S)-norestatina (45) se llevaron a cabo como ejemplos ilustrativos del potencial sintético del método. Estudios computacionales ab initio realizados sobre una reacción modelo basada en los auxiliares de la serie g sugieren un mecanismo en dos pasos a través de intermedios zwitteriónicos. Los resultados obtenidos explican la estereoquímica absoluta y relativa, así como el alto grado de inducción observado para estos auxiliares, por la preferencia de la aproximación "outward" de la cetena sobre la cara Re de la hidrazona. [source]