Science.gov

Sample records for comparing thermal stability

  1. A comparative study of thermal and mechanical stabilities of gamma irradiated PMMA, PP and PVC

    NASA Astrophysics Data System (ADS)

    Güven, O.; Uzun, C.

    1993-10-01

    In this comparative study it has been tried to find a correlation between the thermal and mechanical stabilities of some γ-irradiated polymers. Among various mechanical properties evaluated, the best correlation was found between the toughness (energy to break point) and the time required for 10% weight loss (isothermally). Among three polymers irradiated up to 100 kGy in the form of thin films, the best fit was observed to be for PMMA while PVC and PP has shown poorer correlation.

  2. Comparative evaluation of thermal decomposition behavior and thermal stability of powdered ammonium nitrate under different atmosphere conditions.

    PubMed

    Yang, Man; Chen, Xianfeng; Wang, Yujie; Yuan, Bihe; Niu, Yi; Zhang, Ying; Liao, Ruoyu; Zhang, Zumin

    2017-09-05

    In order to analyze the thermal decomposition characteristics of ammonium nitrate (AN), its thermal behavior and stability under different conditions are studied, including different atmospheres, heating rates and gas flow rates. The evolved decomposition gases of AN in air and nitrogen are analyzed with a quadrupole mass spectrometer. Thermal stability of AN at different heating rates and gas flow rates are studied by differential scanning calorimetry, thermogravimetric analysis, paired comparison method and safety parameter evaluation. Experimental results show that the major evolved decomposition gases in air are H2O, NH3, N2O, NO, NO2 and HNO3, while in nitrogen, H2O, NH3, NO and HNO3 are major components. Compared with nitrogen atmosphere, lower initial and end temperatures, higher heat flux and broader reaction temperature range are obtained in air. Meanwhile, higher air gas flow rate tends to achieve lower reaction temperature and to reduce thermal stability of AN. Self-accelerating decomposition temperature of AN in air is much lower than that in nitrogen. It is considered that thermostability of AN is influenced by atmosphere, heating rate and gas flow rate, thus changes of boundary conditions will influence its thermostability, which is helpful to its safe production, storage, transportation and utilization. Copyright © 2017 Elsevier B.V. All rights reserved.

  3. THERMAL STABILITY OF GLASS PLASTICS.

    DTIC Science & Technology

    COMPOSITE MATERIALS, THERMAL STABILITY), (* GLASS TEXTILES, THERMAL STABILITY), (*LAMINATED PLASTICS , THERMAL STABILITY), HEATING, COOLING, MECHANICAL PROPERTIES, FATIGUE(MECHANICS), FLEXURAL STRENGTH, THERMAL STRESSES, USSR

  4. Comparative thermal stability characteristics and isothermal oxidation behavior of an aluminized and a Pt-aluminized Ni-base superalloy

    SciTech Connect

    Tawancy, H.M.; Sridhar, N.; Abbas, N.M.; Rickerby, D.

    1995-11-01

    It is the objective of this paper to compare the thermal stability characteristics and isothermal oxidation behavior of an aluminide coating and a Pt-aluminide coating of the same Al content on a Ni-base superalloy. Addition of Pt to an aluminide coating was found to improve its thermal stability as well as its capability for selective oxidation of Al resulting in a purer scale of slower growth rate. This was correlated with the greater diffusional stability of the Pt-aluminide coating restricting the transport of substrate elements into the outer coating layers.

  5. Thermal Stabilization Blend Plan

    SciTech Connect

    RISENMAY, H.R.

    2000-05-02

    This Blend Plan documents the feed material items that are stored in 2736-2 vaults, the 2736-ZB 638 cage, the 192C vault, and the 225 vault that will be processed through the thermal stabilization furnaces. The purpose of thermal stabilization is to heat the material to 1000 degrees Celsius to drive off all water and leave the plutonium and/or uranium as oxides. The stabilized material will be sampled to determine the Loss On Ignition (LOI) or percent water. The stabilized material must meet water content or LOI of less than 0.5% to be acceptable for storage under DOE-STD-3013-99 specifications. Out of specification material will be recycled through the furnaces until the water or LOI limits are met.

  6. Comparative effects of cryosolvents on tubulin association, thermal stability, and binding of microtubule-associated proteins.

    PubMed

    Pajot-Augy, E

    1993-06-01

    Organic cryosolvents essential for cryopreservation of living cells have a colligative effect on water properties, but also affect cellular structures such as the membrane, actin, or tubulin cytoskeleton. The effects of cryosolvents on actin and its binding proteins are starting to be well investigated. In parallel, tubulin assembly characteristics were investigated comparatively, with 0-30% 1,2-propanediol, dimethyl sulfoxide, or glycerol, and with or without microtubule-associated proteins, at 37 or 4 degrees C. Tubulin association was monitored by spectrometry and sedimentation, providing the concentration in free protein, cold-depolymerizable microtubules, and cold-resistant associations. At 37 degrees C, 1,2-propanediol and dimethyl sulfoxide induce a similar association level and cold stability of the assemblies. Glycerol yields a lower level of tubulin association. Cold stability of the assemblies requires the presence of solvent, the amount of which is modulated by microtubule-associated proteins (MAPs): 15% 1,2-propanediol or dimethyl sulfoxide, decreasing down to 10% with MAPs, or 10% glycerol with MAPs only. At 4 degrees C, some cold-stable association is promoted by 1,2-propanediol or dimethyl sulfoxide above 10-15%, in the presence or absence of MAPs, but not with glycerol. In addition, protein content of the various fractions obtained with MAPs and 30% solvent was examined by densitometry of electrophoresis gels. Cold-labile associations obtained at 37 degrees C with 1,2-propanediol or dimethyl sulfoxide are lacking in tubulin and enriched in tau proteins relative to control or glycerol. Associations formed at 37 degrees C and stable to subsequent cold treatment, or at 4 degrees C, regardless of the solvent, present a large tubulin content, as well as few tau proteins and high-molecular-weight MAPs.

  7. Comparing the thermal stability of NbTi and Nb3Sn wires

    NASA Astrophysics Data System (ADS)

    Breschi, M.; Trevisani, L.; Bottura, L.; Devred, A.; Trillaud, F.

    2009-02-01

    The investigation of quenching in low temperature superconducting wires is of great relevance for a proper design of superconductive cables and magnets. This paper reports the experimental results of a vast measurement campaign of quench induced by laser pulses on NbTi and Nb3Sn wires in pool boiling helium I. A comparison of the quench behavior of two typical NbTi and Nb3Sn wires is shown from different standpoints. Different qualitative behaviors of the voltage traces recorded during quenches and recoveries on NbTi and Nb3Sn wires are reported and analyzed. It is shown that the Nb3Sn wire exhibits a quench or no-quench behavior, whereas quenches and recoveries are exhibited by the NbTi wire. The two wires are also compared by considering the behaviors of the two main parameters describing quench, i.e. quench energies and quench velocities, with respect to operating current, pulse duration, and magnetic field. It is shown that the Nb3Sn wire exhibits a 'kink' of the quench energy versus current curve that makes the quench energy of Nb3Sn lower than that of NbTi at some intermediate current levels. Both the qualitative differences of the voltage traces and the different behaviors of quench energies and velocities are interpreted through a coupled electromagnetic-thermal model, with special emphasis on the detailed description of heat exchange with liquid helium.

  8. Steam generation in line-focus solar collectors: a comparative assessment of thermal performance, operating stability, and cost issues

    SciTech Connect

    Murphy, L.M.; May, E.K.

    1982-04-01

    The engineering and system benefits of using direct steam (in situ) generation in line-focus collectors are assessed. The major emphasis of the analysis is a detailed thermal performance comparison of in situ systems (which utilize unfired boilers). The analysis model developed for this study is discussed in detail. An analysis of potential flow stability problems is also provided along with a cursory cost analysis and an assessment of freeze protection, safety, and control issues. Results indicated a significant thermal performance advantage over the more conventional oil and flash systems and the flow stability does not appear to be a significant problem. In particular, at steam temperatures of 220/sup 0/C (430/sup 0/F) under the chosen set of assumptions, annual delivered energy predictions indicate that the in situ system can deliver 15% more energy than an oil system and 12% more energy than a flash system, with all of the systems using the same collector field. Further, the in situ system may result in a 10% capital cost reduction. Other advantages include improvement in simpler control when compared with flash systems, and fluid handling and safety enhancement when compared with oil systems.

  9. A comparative study of the thermal stability of oligodeoxyribonucleotides containing 5-substituted 2'-deoxyuridines.

    PubMed Central

    Ahmadian, M; Zhang, P; Bergstrom, D E

    1998-01-01

    Two series of modified oligonucleotides based on the self-complementary dodecamer d(CGCTAATTAGCG) were synthesized. The first contained the -C identical withCCH2R linker at C5 of deoxyuridine at position 4 (T*) of d(CGCT*AATTAGCG) and the second contained the -SR linker. The goal of the study was to evaluate and compare these two types of side chains for suitability as tethers for linking reporter groups to oligonucleotides. Our primary concern was how these tethers would effect duplex stability. The modified nucleosides were synthesized by palladium-mediated coupling reactions between the substituted alkyne and 5'-(4, 4'-dimethoxytrityl)-5-iodo-2'-deoxyuridine and between a disulfide and 5-chloromercurio-2'-deoxyuridine. The C5 deoxyuridine side chains evaluated included C identical with CCH3, C identical with CCH2NHC(O)CH3, C identical with CCH2N(CH3)2, C identical with CCH2N-HC(O)C5H4N, C identical with CCH2NHC(O)C10H15, SCH3, SC6H5 and SCH2CH2NHC(O)CH3. The nucleosides containing these substituents were incorporated into oligo-deoxyribonucleotides by standard phosphoramidite methodology. Melting studies demonstrated that the sequence containing the C identical with CCH3side chain had the highest T m value (59.1 degrees C) in comparison with the control sequence (T m = 55.2 degrees C) and that any additional substituent on C3 of the propynyl group lowered the T m value relative to propynyl. Nevertheless, even the most destabilizing substituent, adamantylcarbamoyl, yielded an oligodeoxyribonucleotide that dissociated with a T m of 54 degrees C, which is only 1.2 degrees C less than the control sequence. In contrast, the thioether substituents led to lower T m values, ranging from as low as 45.1 degrees C for SPh up to 52.2 degrees C for SMe. Replacing the methyl of the SMe substituent with a CH2CH2NHC(O)CH3 tether led to no further reduction in melting temperature. The T m value of the CH2CH2NHC(O)CH3-containing oligonucleotide was less than the natural sequence

  10. A comparative study of the thermal stability of oligodeoxyribonucleotides containing 5-substituted 2'-deoxyuridines.

    PubMed

    Ahmadian, M; Zhang, P; Bergstrom, D E

    1998-07-01

    Two series of modified oligonucleotides based on the self-complementary dodecamer d(CGCTAATTAGCG) were synthesized. The first contained the -C identical withCCH2R linker at C5 of deoxyuridine at position 4 (T*) of d(CGCT*AATTAGCG) and the second contained the -SR linker. The goal of the study was to evaluate and compare these two types of side chains for suitability as tethers for linking reporter groups to oligonucleotides. Our primary concern was how these tethers would effect duplex stability. The modified nucleosides were synthesized by palladium-mediated coupling reactions between the substituted alkyne and 5'-(4, 4'-dimethoxytrityl)-5-iodo-2'-deoxyuridine and between a disulfide and 5-chloromercurio-2'-deoxyuridine. The C5 deoxyuridine side chains evaluated included C identical with CCH3, C identical with CCH2NHC(O)CH3, C identical with CCH2N(CH3)2, C identical with CCH2N-HC(O)C5H4N, C identical with CCH2NHC(O)C10H15, SCH3, SC6H5 and SCH2CH2NHC(O)CH3. The nucleosides containing these substituents were incorporated into oligo-deoxyribonucleotides by standard phosphoramidite methodology. Melting studies demonstrated that the sequence containing the C identical with CCH3side chain had the highest T m value (59.1 degrees C) in comparison with the control sequence (T m = 55.2 degrees C) and that any additional substituent on C3 of the propynyl group lowered the T m value relative to propynyl. Nevertheless, even the most destabilizing substituent, adamantylcarbamoyl, yielded an oligodeoxyribonucleotide that dissociated with a T m of 54 degrees C, which is only 1.2 degrees C less than the control sequence. In contrast, the thioether substituents led to lower T m values, ranging from as low as 45.1 degrees C for SPh up to 52.2 degrees C for SMe. Replacing the methyl of the SMe substituent with a CH2CH2NHC(O)CH3 tether led to no further reduction in melting temperature. The T m value of the CH2CH2NHC(O)CH3-containing oligonucleotide was less than the natural sequence

  11. Jet Fuel Thermal Stability

    NASA Technical Reports Server (NTRS)

    Taylor, W. F. (Editor)

    1979-01-01

    Various aspects of the thermal stability problem associated with the use of broadened-specification and nonpetroleum-derived turbine fuels are addressed. The state of the art is reviewed and the status of the research being conducted at various laboratories is presented. Discussions among representatives from universities, refineries, engine and airframe manufacturers, airlines, the Government, and others are presented along with conclusions and both broad and specific recommendations for future stability research and development. It is concluded that significant additional effort is required to cope with the fuel stability problems which will be associated with the potentially poorer quality fuels of the future such as broadened specification petroleum fuels or fuels produced from synthetic sources.

  12. Thermal stability of grafted fibers. [Gamma radiation

    SciTech Connect

    Sundardi, F.; Kadariah; Marlianti, I.

    1983-10-01

    Presented the experimental results on the study of thermal stability of grafted fibers, i.e., polypropylene-, polyester-, and rayon-grafted fibers. These fibers were obtained by radiation grafting processes using hydrophylic monomers such as 1-vinyl 2-pyrolidone, acrylic acid, N-methylol acrylamide, and acrylonitrile. The thermal stability of the fibers was studied using a Shimadzu Thermal Analyzer DT-30. The thermal stability of the fibers, which can be indicated by the value of the activation energy for thermal degradation, was not improved by radiation grafting. The degree of improvement depends on the thermal stability of the monomers used for grafting. The thermal stability of a polypropylene fiber, either a grafted or an ungrafted one, was found to be inferior compared to the polyester of a rayon fiber, which may be due to the lack of C=O and C=C bonds in the polypropylene molecules. The thermal stability of a fiber grafted with acrylonitrile monomer was found to be better than that of an ungrafted one. However, no improvement was detected in the fibers grafted with 1-vinyl 2-pyrrolidone monomer, which may be due to the lower thermal stability of poly(1-vinyl-2-pyrrolidone), compared to the polypropylene or polyester fibers. 17 figures, 3 tables.

  13. Thermal Stability Of Formohydroxamic Acid

    SciTech Connect

    Fondeur, F. F.; Rudisill, T. S.

    2011-10-21

    The thermal stability of formohydroxamic acid (FHA) was evaluated to address the potential for exothermic decomposition during storage and its use in the uranium extraction process. Accelerating rate calorimetry showed rapid decomposition at a temperature above 65 {degree}C; although, the rate of pressure rise was greater than two orders of magnitude less than the lower bound for materials which have no explosive properties with respect to transportation. FHA solutions in water and nitric acid did not reach runaway conditions until 150 {degree}C. Analysis by differential scanning calorimetry showed that FHA melted at 67 {degree}C and thermally decomposed at 90 {degree}C with an enthalpy of -1924 J/g. The energics of the FHA thermal decomposition are comparable to those measured for aqueous solutions of hydroxylamine nitrate. Solid FHA should be stored in a location where the temperature does not exceed 20-25 {degree}C. As a best practice, the solid material should be stored in a climate-controlled environment such as a refrigerator or freezer. FHA solutions in water are not susceptible to degradation by acid hydrolysis and are the preferred way to handle FHA prior to use.

  14. Thermally stabilized heliostat

    DOEpatents

    Anderson, Alfred J.

    1983-01-01

    An improvement in a heliostat having a main support structure and pivoting and tilting motors and gears and a mirror module for reflecting solar energy onto a collector, the improvement being characterized by an internal support structure within each mirror module and front and back sheets attached to the internal support structure, the front and back sheets having the same coefficient of thermal expansion such that no curvature is induced by temperature change, and a layer of adhesive adhering the mirror to the front sheet. The adhesive is water repellent and has adequate set strength to support the mirror but has sufficient shear tolerance to permit the differential expansion of the mirror and the front sheet without inducing stresses or currature effect. The adhesive also serves to dampen fluttering of the mirror and to protect the mirror backside against the adverse effects of weather. Also disclosed are specific details of the preferred embodiment.

  15. Thermal stability of DNA.

    PubMed Central

    Blake, R D; Delcourt, S G

    1998-01-01

    Tij and Delta Hij for stacking of pair i upon j in DNA have been obtained over the range 0.034-0.114 M Na+from high-resolution melting curves of well-behaved synthetic tandemly repeating inserts in recombinant pN/MCS plasmids. Results are consistent with neighbor-pair thermodynamic additivity, where the stability constant, sij , for different domains of length N depend quantitatively on the product of stability constants for each individual pair in domains, sijN . Unit transition enthalpies with average errors less than +/-5%, were determined by analysis of two-state equilibria associated with the melting of internal domains and verified from variations of Tij with [Na+]. Enthalpies increase with Tij , in close agreement with the empirical function: Delta Hij = 52.78@ Tij - 9489, and in parallel with a smaller increase in Delta Sij . Delta Hij and Delta Sij are in good agreement with the results of an extensive compilation of published Delta Hcal and Delta Scal for synthetic and natural DNAs. Neighbor-pair additivity was also observed for (dA@dT)-tracts at melting temperatures; no evidence could be detected of the familiar and unusual structural features that characterize tracts at lower temperatures. The energetic effects of loops were determined from the melting behavior of repeating inserts installed between (G+C)-rich barrier domains in the pN/MCS plasmids. A unique set of values for the cooperativity, loop exponent and stiffness parameters were found applicable to internal domains of all sizes and sequences. Statistical mechanical curves calculated with values of Tij([Na+]) , Delta Hij and these loop parameters are in good agreement with observation. PMID:9649614

  16. Comparative Study of Thermal Stability of NiFe and NiFeTa Thin Films Grown by Cosputtering Technique

    NASA Astrophysics Data System (ADS)

    Phuoc, Nguyen N.; Ong, C. K.

    2016-08-01

    A comparative study of the thermal behavior of dynamic permeability spectra for compositionally graded NiFeTa and uniform-composition NiFe thin films has been carried out. We found that the resonance frequency of the compositionally graded NiFeTa film increased with increasing temperature, while it decreased for the case of the uniform-composition NiFe thin film. This finding unambiguously suggests that the compositional gradient of the film is the only reason for the increase of the magnetic anisotropy with temperature due to its stress-induced origin, while the cosputtering technique does not play any role in this peculiar behavior. The temperature dependence of the frequency linewidth is also presented and discussed.

  17. Thermal stability of bioactive enzymatic papers.

    PubMed

    Khan, Mohidus Samad; Li, Xu; Shen, Wei; Garnier, Gil

    2010-01-01

    The thermal stability of two enzymes adsorbed on paper, alkaline phosphatase (ALP) and horseradish peroxidase (HRP), was measured using a colorimetric technique quantifying the intensity of the product complex. The enzymes adsorbed on paper retained their functionality and selectivity. Adsorption on paper increased the enzyme thermal stability by 2-3 orders of magnitude compared to the same enzyme in solution. ALP and HRP enzymatic papers had half-lives of 533 h and 239 h at 23 degrees C, respectively. The thermal degradation of adsorbed enzyme was found to follow two sequential first-order reactions, indication of a reaction system. A complex pattern of enzyme was printed on paper using a thermal inkjet printer. Paper and inkjet printing are ideal material and process to manufacture low-cost-high volume bioactive surfaces.

  18. The role of stabilization centers in protein thermal stability

    SciTech Connect

    Magyar, Csaba; Gromiha, M. Michael; Sávoly, Zoltán; Simon, István

    2016-02-26

    The definition of stabilization centers was introduced almost two decades ago. They are centers of noncovalent long range interaction clusters, believed to have a role in maintaining the three-dimensional structure of proteins by preventing their decay due to their cooperative long range interactions. Here, this hypothesis is investigated from the viewpoint of thermal stability for the first time, using a large protein thermodynamics database. The positions of amino acids belonging to stabilization centers are correlated with available experimental thermodynamic data on protein thermal stability. Our analysis suggests that stabilization centers, especially solvent exposed ones, do contribute to the thermal stabilization of proteins. - Highlights: • Stabilization centers contribute to thermal stabilization of protein structures. • Stabilization center content correlates with melting temperature of proteins. • Exposed stabilization center content correlates with stability even in hyperthermophiles. • Stability changing mutations are frequently found at stabilization centers.

  19. Thermal Stability of Dopamine Transporters.

    PubMed

    Kukk, Siim; Stepanov, Vladimir; Järv, Jaak

    2015-08-01

    The thermal stabilities of the rat and mouse dopamine transporter (DAT) proteins were studied within the temperature range of 0-37°C. The inactivation of the protein was followed by monitoring changes in radioligand-specific binding. We found that the process followed a rate equation with first-order kinetics and was characterized by having a single rate constant k inact. The activation energies (E a) that were calculated from the Arrhenius plots (ln k inact vs. 1/T) were 43 ± 5 and 45 ± 6 kJ/mol for the rat (rDAT) and mouse (mDAT) transporters, respectively, and 44 ± 7 kJ/mol for rDAT from PC-6.3 cell line. These E a values were similar to the E a values of thermal inactivation of the muscarinic receptor from rat brain cortex and to the thermal inactivation of other transmembrane proteins. However, all of these activation energy values were significantly lower than the E a values for soluble single-subunit proteins of similar size. These results therefore suggest that the thermal stability of transmembrane proteins may be governed to a significant extent by cell membrane properties and by interactions between the membrane components and the protein. In contrast, the stability of soluble proteins seems to be mostly governed by protein structure and size, which determine the sum of the stabilizing intramolecular interactions within the protein molecule. It is therefore not surprising that cell membrane properties and composition may have significant effects on the functional properties of transmembrane proteins.

  20. Thermal stability of sulfonated polymers

    SciTech Connect

    Audibert, A.; Argillier, J.F.

    1995-11-01

    Polyacrylamides which are used in oil applications i.e. polymer flooding and water based muds, are hydrolyzed versus time and temperature. This leads to a lack of tolerance towards electrolyte contamination and to a rapid degradation inducing a loss of their properties. Modifications of polyacrylamide structure have been proposed to postpone their thermal stability to higher temperatures. Monomers such as acrylamido methylpropane sulfonate (AMPS) or sulfonated styrene/maleic anhydride can be used to prevent acrylamide comonomer from hydrolysis. The aim of this work is to study under controlled conditions, i.e. anaerobic atmosphere, neutral pH, the stability of sulfonated polymers in order to distinguish between hydrolysis and radical degradation reactions. It has been observed that up to 100 C, the AMPS group is stable and protects the acrylamide function from hydrolysis up to 80%. At higher temperature, even the hydrolysis of the AMPS group occurs, giving acrylate and {beta},{beta} dimethyl taurine, with a kinetics that depends on temperature and time. Degradation in terms of molecular weight then occurs indicating that it follows a radical decarboxylation reaction. It can be limited either by the use of free radical scavenger or when the polymer is in the presence of a mineral phase such as bentonite. These results provide valuable data for the determination of the limits of use of sulfonated copolymers and guidelines for optimizing chemical structure of sulfonated polymers used in water based formulation, in particular to enhance their thermal stability.

  1. Comparing blends and blocks: Synthesis of partially fluorinated diblock polythiophene copolymers to investigate the thermal stability of optical and morphological properties

    PubMed Central

    Boufflet, Pierre; Wood, Sebastian; Wade, Jessica; Fei, Zhuping; Kim, Ji-Seon

    2016-01-01

    Summary The microstructure of the active blend layer has been shown to be a critically important factor in the performance of organic solar devices. Block copolymers provide a potentially interesting avenue for controlling this active layer microstructure in solar cell blends. Here we explore the impact of backbone fluorination in block copolymers of poly(3-octyl-4-fluorothiophene)s and poly(3-octylthiophene) (F-P3OT-b-P3OT). Two block co-polymers with varying block lengths were prepared via sequential monomer addition under Kumada catalyst transfer polymerisation (KCTP) conditions. We compare the behavior of the block copolymer to that of the corresponding homopolymer blends. In both types of system, we find the fluorinated segments tend to dominate the UV–visible absorption and molecular vibrational spectral features, as well as the thermal behavior. In the block copolymer case, non-fluorinated segments appear to slightly frustrate the aggregation of the more fluorinated block. However, in situ temperature dependent Raman spectroscopy shows that the intramolecular order is more thermally stable in the block copolymer than in the corresponding blend, suggesting that such materials may be interesting for enhanced thermal stability of organic photovoltaic active layers based on similar systems. PMID:27829922

  2. Multifunctional Composites for Improved Polyimide Thermal Stability

    NASA Technical Reports Server (NTRS)

    Miller, Sandi G.

    2007-01-01

    The layered morphology of silicate clay provides an effective barrier to oxidative degradation of the matrix resin. However, as resin thermal stability continues to reach higher limits, development of an organic modification with comparable temperature capabilities becomes a challenge. Typically, phyllosilicates used in polymer nanocomposites are modified with an alkyl ammonium ion. Such organic modifiers are not suited for incorporation into high temperature polymers as they commonly degrade below 200oC. Therefore, the development of nanoparticle specifically suited for high temperature applications is necessary. Several nanoparticles were investigated in this study, including pre-exfoliated synthetic clay, an organically modified clay, and carbon nanofiber. Dispersion of the layered silicate increases the onset temperature of matrix degradation as well as slows oxidative degradation. The thermally stable carbon nanofibers are also observed to significantly increase the resin thermal stability.

  3. Comparative analysis of the structure and thermal stability of sea urchin peristome and rat tail tendon collagen.

    PubMed

    Mayne, Janice; Robinson, John J

    2002-01-01

    We have purified collagen from two distinct sources; the vertebrate, rat tail tendon and an invertebrate, sea urchin adult tissue, the peristome. The collagenous nature of the purification products was confirmed by amino acid compositional analysis. Both preparations had high contents of glycine and proline residues and hydroxyproline was also present. The total pyrrolidine (proline+hydroxyproline) content decreased from 17.9 mole% in rat tail collagen to 12.9 mole% in peristome collagen. Distinctly different circular dichroic spectra were measured for these collagens. Analyses of spectra, measured as a function of temperature, revealed distinct thermal denaturation profiles. The melting temperature for rat tail collagen was 38.5 degrees C, while the corresponding value for peristome collagen was significantly lower at 27 degrees C. A similar thermal denaturation profile was obtained for rat tail collagen in digestion experiments using a 41-kDa gelatinase activity, isolated from sea urchin eggs. These results identify structural differences between a typical, vertebrate type I fibrillar collagen and an echinoderm collagen which serves as a constituent of a mutable connective tissue. These differences may relate to the functional roles played by collagen in these distinctly different tissues.

  4. Thermal stability of strained nanowires.

    PubMed

    Nisoli, Cristiano; Abraham, Douglas; Lookman, Turab; Saxena, Avadh

    2009-06-19

    Stranski-Krastanow strained islands undergo a shape anisotropy transition as they grow in size, finally evolving toward nanowires. This effect has been explained until now via simple energetic models that neglect thermodynamics. We investigate theoretically the stability of strained nanowires under thermal fluctuations of the long side. We find phase transitions from nanowires back to nanoislands as the temperature is increased and as the height of the nanostructure is raised or lowered, and we predict regions of phase coexistence. Our results are general, but explain recent data on the growth of erbium silicide on a vicinal Si surface.

  5. The role of stabilization centers in protein thermal stability.

    PubMed

    Magyar, Csaba; Gromiha, M Michael; Sávoly, Zoltán; Simon, István

    2016-02-26

    The definition of stabilization centers was introduced almost two decades ago. They are centers of noncovalent long range interaction clusters, believed to have a role in maintaining the three-dimensional structure of proteins by preventing their decay due to their cooperative long range interactions. Here, this hypothesis is investigated from the viewpoint of thermal stability for the first time, using a large protein thermodynamics database. The positions of amino acids belonging to stabilization centers are correlated with available experimental thermodynamic data on protein thermal stability. Our analysis suggests that stabilization centers, especially solvent exposed ones, do contribute to the thermal stabilization of proteins.

  6. Thermal oxidation stability of aviation turbine fuels

    SciTech Connect

    Hazlett, R.N.

    1991-01-01

    This paper documents the 35 year history of fuel thermal stability problems and remedies in jet aircraft. Specifically, Monograph 1: Discusses the chemical and physical aspects that are critical factors in thermal stability; Describes the great variety of test devices---from small scale fuel specification testers to large scale engineering simulators---that have been used in defining thermal stability; and Presents information on the thermal environment in jet aircraft and engines, the role of oxidation and trace metals in insolubles formation, the use of additives to modify stability behavior, and the possible characteristics of future fuels.

  7. Jet Fuel Thermal Stability Investigations Using Ellipsometry

    NASA Technical Reports Server (NTRS)

    Nash, Leigh; Vasu, Subith S.; Klettlinger, Jennifer Lindsey

    2017-01-01

    Jet fuels are typically used for endothermic cooling in practical engines where their thermal stability is very important. In this work the thermal stability of Sasol IPK (a synthetic jet fuel) with varying levels of naphthalene has been studied on stainless steel substrates using spectroscopic ellipsometry in the temperature range 385-400 K. Ellipsometry is an optical technique that measures the changes in a light beam’s polarization and intensity after it reflects off of a thin film to determine the film’s thickness and optical properties. All of the tubes used were rated as thermally unstable by the color standard portion of the Jet Fuel Thermal Oxidation Test, and this was confirmed by the deposit thicknesses observed using ellipsometry. A new amorphous model on a stainless steel substrate was used to model the data and obtain the results. It was observed that, as would be expected, increasing the temperature of the tube increased the overall deposit amount for a constant concentration of naphthalene. The repeatability of these measurements was assessed using multiple trials of the same fuel at 385 K. Lastly, the effect of increasing the naphthalene concentration in the fuel at a constant temperature was found to increase the deposit thickness.In conclusion, ellipsometry was used to investigate the thermal stability of jet fuels on stainless steel substrate. The effects of increasing temperature and addition of naphthalene on stainless steel tubes with Sasol IPK fuel were investigated. It was found, as expected, that increasing temperature lead to an increase in deposit thickness. It wasAmerican Institute of Aeronautics and Astronautics6also found that increasing amounts of naphthalene increased the maximum deposit thickness. The repeatability of these measurements was investigated using multiple tests at the same conditions. The present work provides as a better quantitative tool compared to the widely used JFTOT technique. Future work will expand on the

  8. Fuels research: Fuel thermal stability overview

    NASA Technical Reports Server (NTRS)

    Cohen, S. M.

    1980-01-01

    Alternative fuels or crude supplies are examined with respect to satisfying aviation fuel needs for the next 50 years. The thermal stability of potential future fuels is discussed and the effects of these characteristics on aircraft fuel systems are examined. Advanced fuel system technology and design guidelines for future fuels with lower thermal stability are reported.

  9. High Reynolds Number Thermal Stability Experiments

    NASA Technical Reports Server (NTRS)

    Emens, Jessica M.; Brown, Sarah P.; Frederick Robert A., Jr.; Wood, A. John

    2004-01-01

    This work represents preliminary thermal stability results for liquid hydrocarbon fuels. High Reynolds Number Thermal Stability experiments with Jet A and RP-1 resulted in a quantitative measurement of the thermal stability. Each fuel flowed through a heated capillary tube that held the outlet temperature at 290 C. An optical pyrometer measured the surface temperature of the tube at 12 locations as a function of time. The High Reynolds Number Thermal Stability number was then determined using standards published by the American Society for Testing and Materials. The results for Jet A showed lower thermal stability than similar tests conducted at another facility. The RP-1 results are the first reported using this technique. Because the temperature rise on the capillary tube during testing for the RP-1 fuels was not significant, a new standard for the testing conditions should be developed for these types of fuels.

  10. On the remarkable thermal stability of nanocrystalline cobalt via alloying

    PubMed Central

    Bachmaier, A.; Motz, C.

    2015-01-01

    Nanostructured Co materials are produced by severe plastic deformation via alloying with small amounts of C and larger amounts of Cu. The thermal stability of the different nanostructured Co materials is studied through isothermal annealing at different temperatures for various times and compared to the stability of severe plastically deformed high-purity nanocrystalline Co. The microstructural changes taking place during annealing are evaluated by scanning electron microscopy, transmission electron microscopy and microhardness measurements. In the present work it is shown that the least stable nanostructured material is the single-phase high purity Co. Alloying with C improves the thermal stability to a certain extent. A remarkable thermal stability is achieved by alloying Co with Cu resulting in stabilized nanostructures even after annealing for long times at high temperatures. The essential reason for the enhanced thermal stability is to be found in the immiscibility of both components of the alloy. PMID:25892849

  11. Protein thermal stabilization in aqueous solutions of osmolytes.

    PubMed

    Bruździak, Piotr; Panuszko, Aneta; Jourdan, Muriel; Stangret, Janusz

    2016-01-01

    Proteins' thermal stabilization is a significant problem in various biomedical, biotechnological, and technological applications. We investigated thermal stability of hen egg white lysozyme in aqueous solutions of the following stabilizing osmolytes: Glycine (GLY), N-methylglycine (NMG), N,N-dimethylglycine (DMG), N,N,N-trimethylglycine (TMG), and trimethyl-N-oxide (TMAO). Results of CD-UV spectroscopic investigation were compared with FTIR hydration studies' results. Selected osmolytes increased lysozyme's thermal stability in the following order: Gly>NMG>TMAO≈DMG>TMG. Theoretical calculations (DFT) showed clearly that osmolytes' amino group protons and water molecules interacting with them played a distinctive role in protein thermal stabilization. The results brought us a step closer to the exact mechanism of protein stabilization by osmolytes.

  12. Thermal and pH Stability of Feline Calicivirus

    PubMed Central

    Lee, Kyu M.; Gillespie, J. H.

    1973-01-01

    Molar concentration of sodium chloride partially stabilized feline calicivirus against thermal inactivation at 50 C. One strain of feline calicivirus was relatively acid labile compared to another. PMID:4762115

  13. Influence of specific mutations on the thermal stability of the td group I intron in vitro and on its splicing efficiency in vivo: a comparative study.

    PubMed

    Brion, P; Schroeder, R; Michel, F; Westhof, E

    1999-07-01

    Group I introns constitute excellent systems for analyzing the relationship between RNA tertiary folding and catalysis. Within a hierarchical framework interpretation of RNA folding, secondary structure motifs subtend RNA three-dimensional (3D) architecture. Thus, mutations in two-dimensional motifs are expected to have effects different from those disrupting 3D contacts. Using UV spectroscopy, we have studied the influence of nucleotide substitutions, in both secondary and tertiary structure elements, on the thermal stability of the tertiary folding of the bacteriophage T4 td group I intron. Further, we present a quantitative analysis of the relationship between the splicing efficiency in vivo and the stability of the intron structure as monitored by UV melting curves. We conclude that the stability of the tertiary structure of a group I intron as measured by UV melting is generally a good indication of its ability to splice in vivo.

  14. Thermal stability enhancement of rubbery ormosils

    SciTech Connect

    Kramer, S.J.; Mackenzie, J.D.

    1994-12-31

    Thermal stability of a novel rubbery ORMOSIL of condensed tetraethoxysilane (TEOS) and polydimethylsiloxane (PDMS) was investigated along with methods by which to improve this stability. Based upon literature review of siloxane systems, modifications of the base ORMOSIL system was made which included substitution of polydimethyldiphenylsiloxane (PDMDPS) for PDMS, adding antioxidant, and adding iron compounds. Relative enhancement was investigated in terms of resilience measurements, and was also analyzed with thermo-gravimetric analysis (TGA) and differential thermal analysis (DTA).

  15. High stability buffered phase comparator

    NASA Technical Reports Server (NTRS)

    Adams, W. A.; Reinhardt, V. S. (Inventor)

    1984-01-01

    A low noise RF signal phase comparator comprised of two high stability driver buffer amplifiers driving a double balanced mixer which operate to generate a beat frequency between the two RF input signals coupled to the amplifiers from the RF sources is described. The beat frequency output from the mixer is applied to a low noise zero crossing detector which is the phase difference between the two RF inputs. Temperature stability is provided by mounting the amplifiers and mixer on a common circuit board with the active circuit elements located on one side of a circuit board and the passive circuit elements located on the opposite side. A common heat sink is located adjacent the circuit board. The active circuit elements are embedded into the bores of the heat sink which slows the effect of ambient temperature changes and reduces the temperature gradients between the active circuit elements, thus improving the cancellation of temperature effects. The two amplifiers include individual voltage regulators, which increases RF isolation.

  16. Thermal stability of petroleum pitches

    SciTech Connect

    Sorensen, I.W.

    1982-01-01

    Petroleum pitches and similar materials are becoming increasingly important as raw materials for the production of various types of carbons and graphites. Most recently, significant interest in such materials as low cost precursors for carbon fiber has developed. Crucial to success in this regard is the behavior of pitches and related substances as they pass through a mesophase or liquid crystalline form during heat treatment to form carbonaceous material. There is limited understanding of this phenomenon as well as the effects of pitch modification on it. An effort was made to elucidate the mesophase formation mechanisms by comparison of thermally-formed mesophase with that formed more rapidly in solvent-separated narrower pitch fractions. Specifically, selected pitches are subjected to heat treatment and characterized in terms of their composition, microstructural development, and rheology. Independent study was made of the effects of shearing field on composition, mesophase development, and molecular weight distributions for CTP-240 pitch. Complementary work is described for the thermal decomposition of pitch fractions obtained by solvent extraction. Several important technical advances are described that will assist in further study of these materials.

  17. Thermal and thermal-oxidative stability of trichloroethanol sulfide

    SciTech Connect

    Kalyavina, S.I.; Borshchevskii, S.B.; Medvedovskaya, I.I.; Stepanova, O.N.; Veselovskaya, L.F.; Zorina, E.F.

    1984-03-01

    This article reports on an investigation of the thermal and thermal-oxidative stability of bis(2,2,2-trichloro-1-hydroxyethyl) sulfide CCl/sub 3/-CHOHO-S-CHOH-CCl/sub 3/, which contains trichloromethyl and sulfide groups. The antiscoring effectiveness of this compound in TSp-14.5 oil is considerably better than that given by oils with the presently used commercial additives. The thermal stabilities of the sulfide additive and the IS-45 oil were tested in a stream of nitrogen at 100-150/sup 0/C, analyzing the reaction products by iodometric and mercurimetric titration to determine the quantities of sulfur and chlorine ions and the degree to which the additive had been converted to these ions. The thermal decomposition of the additive begins at 118/sup 0/C and increases with increasing temperature, whether it is tested by itself or in a 1.25% solution in IS-45 oil. The additive and the hydrocarbon oil with and without the additive were oxidized with atmospheric oxygen in a thin layer in a series of sealed ampuls, which were removed sequentially from the thermostat at predetermined time intervals for analysis of the gas phase by gas chromatography. It is concluded that the sulfide, which was studied as an extreme-pressure additive, when blended in IS-45 oil, has a lower thermal stability but a higher thermaloxidative stability in comparison with the straight hydrocarbon oil IS-45.

  18. Comparative studies on the thermal stability and corrosion resistance of CrN, CrSiN, and CrSiN/AlN coatings

    SciTech Connect

    Kim, Gwang Seok; Kim, Sung Min; Lee, Sang Yul; Lee, Bo Young

    2009-07-15

    In this work, three kinds of Cr-based nitride coatings such as monolithic CrN, CrSiN coatings, and multilayered CrSiN/AlN coating with bilayer period of 3.0 nm were deposited on both Si (100) wafer and AISI H13 steel substrates by unbalanced magnetron sputtering. Thermal stability of these coatings was evaluated by annealing the coatings at temperatures between 600 and 1000 degree sign C for 30 min in air. In addition, the corrosion behaviors of these coatings were investigated by potentiodynamic polarization tests in a deaerated 3.5 wt. % NaCl solution at 40 degree sign C. Results from annealing test show the monolithic CrN and CrSiN coatings were completely oxidized after annealed at 800 and 900 degree sign C, and their cross sectional images and atomic force microscopy showed a loose and very porous morphology due to the oxidation. Also, the hardness values of the monolithic CrN and CrSiN coatings were decreased significantly from 22 and 27 GPa to 8 and 14 GPa, respectively. However, the multilayered CrSiN/AlN coating still exhibited a dense microstructure without visible change after annealed at 1000 degree sign C, and moreover, the relatively high hardness of 25 GPa was maintained. The superior thermal stability of the CrSiN/AlN multilayer coating could be attributed to the formation of the dense and stable oxidation barrier consisted of the Al{sub 2}O{sub 3}, Cr{sub 2}O{sub 3}, and amorphous SiO{sub 2} phases near the surface region, which retard the diffusion of oxygen into the coating. In the potentiodynamic polarization test results, it was found that the significantly improved corrosion resistance of the multilayered CrSiN/AlN coating was observed in comparison with those from the monolithic CrN and CrSiN coatings, and its corrosion current density (i{sub corr}) and protective efficiency were measured to be approximately 4.21 {mu}A/cm{sup 2} and 95%, respectively.

  19. Thermal Stability of Rhodopsin and Progression of Retinitis Pigmentosa

    PubMed Central

    Liu, Monica Yun; Liu, Jian; Mehrotra, Devi; Liu, Yuting; Guo, Ying; Baldera-Aguayo, Pedro A.; Mooney, Victoria L.; Nour, Adel M.; Yan, Elsa C. Y.

    2013-01-01

    Over 100 point mutations in the rhodopsin gene have been associated with retinitis pigmentosa (RP), a family of inherited visual disorders. Among these, we focused on characterizing the S186W mutation. We compared the thermal properties of the S186W mutant with another RP-causing mutant, D190N, and with WT rhodopsin. To assess thermal stability, we measured the rate of two thermal reactions contributing to the thermal decay of rhodopsin as follows: thermal isomerization of 11-cis-retinal and hydrolysis of the protonated Schiff base linkage between the 11-cis-retinal chromophore and opsin protein. We used UV-visible spectroscopy and HPLC to examine the kinetics of these reactions at 37 and 55 °C for WT and mutant rhodopsin purified from HEK293 cells. Compared with WT rhodopsin and the D190N mutant, the S186W mutation dramatically increases the rates of both thermal isomerization and dark state hydrolysis of the Schiff base by 1–2 orders of magnitude. The results suggest that the S186W mutant thermally destabilizes rhodopsin by disrupting a hydrogen bond network at the receptor's active site. The decrease in the thermal stability of dark state rhodopsin is likely to be associated with higher levels of dark noise that undermine the sensitivity of rhodopsin, potentially accounting for night blindness in the early stages of RP. Further studies of the thermal stability of additional pathogenic rhodopsin mutations in conjunction with clinical studies are expected to provide insight into the molecular mechanism of RP and test the correlation between rhodopsin's thermal stability and RP progression in patients. PMID:23625926

  20. Thermal stabilization of levoglucosan in aromatic substances.

    PubMed

    Hosoya, Takashi; Kawamoto, Haruo; Saka, Shiro

    2006-09-25

    Thermal degradation of levoglucosan (1,6-anhydro-beta-D-glucopyranose) was shown to be substantially suppressed in the presence of some aromatic compounds under the conditions of N2/240-340 degrees C/15 min. This stabilization effect is also discussed with CH-pi interaction between levoglucosan and pi-electrons in the benzene ring.

  1. Temperature Stabilization Requirements for Unchopped Thermal Detectors

    NASA Technical Reports Server (NTRS)

    Foote, Marc C.

    2000-01-01

    The temperature stabilization requirements of unchopped thermistor bolometers and thermopile detectors are analyzed. The detector temperature, on which the bolometer output signal depends, is quite sensitive to changes in instrument temperature but relatively insensitive to changes in scene temperature. In contrast, the difference in temperature between detector and substrate (instrument), on which the thermopile signal depends, is equally sensitive to changes in instrument and scene temperature. Expressions for these dependencies are derived based on a simplified instrument model. It is shown that for a typical uncooled thermal imager, the temperature stabilization requirements for a bolometer are two orders of magnitude more stringent than those for a thermopile detector. Keywords: thermistor, bolometer, thermopile, detector, IR, thermal, temperature stabilization

  2. On the cause of low thermal stability of ethyl halodiazoacetates

    PubMed Central

    Mortén, Magnus; Hennum, Martin

    2016-01-01

    Summary Rates for the thermal decomposition of ethyl halodiazoacetates (halo = Cl, Br, I) have been obtained, and reported herein are their half-lives. The experimental results are supported by DFT calculations, and we provide a possible explanation for the reduced thermal stability of ethyl halodiazoacetates compared to ethyl diazoacetate and for the relative decomposition rates between the chloro, bromo and iodo analogs. We have also briefly studied the thermal, non-catalytic cyclopropanation of styrenes and compared the results to the analogous Rh(II)-catalyzed reactions. PMID:27559411

  3. Thermal stability of collagen triple helix.

    PubMed

    Xu, Yujia

    2009-01-01

    Chief among the challenges of characterizing the thermal stability of the collagen triple helix are the lack of the reversibility of the thermal transition and the presence of multiple folding-unfolding steps during the thermal transition which rarely follows the simple two-state, all-or-none mechanism. Despite of the difficulties inherited in the quantitative depiction of the thermal transition of collagen, biophysical studies combined with proteolysis and mutagenesis approaches using full-chain collagens, short synthetic peptides, and recombinant collagen fragments have revealed molecular features of the thermal unfolding of the subdomains of collagen and led to a better understanding of the diverse biological functions of this versatile protein. The subdomain of collagen generally refers to a segment of the long, rope-like triple helical molecule that can unfold cooperatively as an independent unit whose properties (their size, location, and thermal stability) are considered essential for the molecular recognition during the self-assembly of collagen and during the interactions of collagen with other macromolecules. While the unfolding of segments of the triple helix at temperatures below the apparent melting temperature of the molecule has been used to interpret much of the features of the thermal unfolding of full-chain collagens, the thermal studies of short, synthetic peptides have firmly established the molecular basis of the subdomains by clearly demonstrating the close dependence of the thermal stability of a triple helix on the constituent amino acid residues at the X and the Y positions of the characteristic Gly-X-Y repeating sequence patterns of the triple helix. Studies using recombinant collagen fragments further revealed that in the context of the long, linear molecule, the stability of a segment of the triple helix is also modulated by long-range impact of the local interactions such as the interchain salt bridges. Together, the combined approaches

  4. CHEMICAL REACTIVITY TEST: Assessing Thermal Stability and Chemical Compatibility

    SciTech Connect

    Koerner, J; Tran, T; Gagliardi, F; Fontes, A

    2005-04-21

    The thermal stability of high explosive (HE) and its compatibility with other materials are of critical importance in storage and handling practices. These properties are measured at Lawrence Livermore National Laboratory using the chemical reactivity test (CRT). The CRT measures the total amount of gas evolved from a material or combination of materials after being heat treated for a designated period of time. When the test result is compared to a threshold value, the relative thermal stability of an HE or the compatibility of an HE with other materials is determined. We describe the CRT testing apparatus, the experimental procedure, and the comparison methodology and provide examples and discussion of results.

  5. Stabilizing the thermal lattice Boltzmann method by spatial filtering

    NASA Astrophysics Data System (ADS)

    Gillissen, J. J. J.

    2016-10-01

    We propose to stabilize the thermal lattice Boltzmann method by filtering the second- and third-order moments of the collision operator. By means of the Chapman-Enskog expansion, we show that the additional numerical diffusivity diminishes in the low-wavnumber limit. To demonstrate the enhanced stability, we consider a three-dimensional thermal lattice Boltzmann system involving 33 discrete velocities. Filtering extends the linear stability of this thermal lattice Boltzmann method to 10-fold smaller transport coefficients. We further demonstrate that the filtering does not compromise the accuracy of the hydrodynamics by comparing simulation results to reference solutions for a number of standardized test cases, including natural convection in two dimensions.

  6. Stabilizing the thermal lattice Boltzmann method by spatial filtering.

    PubMed

    Gillissen, J J J

    2016-10-01

    We propose to stabilize the thermal lattice Boltzmann method by filtering the second- and third-order moments of the collision operator. By means of the Chapman-Enskog expansion, we show that the additional numerical diffusivity diminishes in the low-wavnumber limit. To demonstrate the enhanced stability, we consider a three-dimensional thermal lattice Boltzmann system involving 33 discrete velocities. Filtering extends the linear stability of this thermal lattice Boltzmann method to 10-fold smaller transport coefficients. We further demonstrate that the filtering does not compromise the accuracy of the hydrodynamics by comparing simulation results to reference solutions for a number of standardized test cases, including natural convection in two dimensions.

  7. Thermal stabilization FY 1999 blend plan

    SciTech Connect

    RISENMAY, H.R.

    1999-06-01

    This Blend Plan documents the alternate feed material items for the thermal stabilization process that will be used in place of the metal items that were originally planned to be processed. Problems with resolution of the safety basis for the metal items resulted in the decision to run material that already had an established safety basis. Various in process and scrap recovery items stored in gloveboxes, plutonium oxide and plutonium oxide mixed with uranium oxide stored in 2736-2 vaults will be processed through the stabilization furnaces until the safety basis for the metal items has been resolved. The purpose of thermal stabilization is to heat the material to 1000 degrees Celsius to drive off all volatile materials and leave the plutonium and/or uranium as oxides. The stabilized material will be sampled to determine the Loss On Ignition (LOI). The stabilized material must meet LOI of less than 0.5% to be acceptable for storage under DOE-STD-3013-94 specifications. Out of specification material will be recycled through the furnaces until the LOI limits are met.

  8. Thermal Stabilization FY 1999 blend plan

    SciTech Connect

    RISENMAY, H.R.

    1999-02-23

    This Blend Plan documents the alternate feed material items for the thermal stabilization process that will be used in place of the metal items that were originally planned to be processed. Problems with resolution of the safety basis for the metal items resulted in the decision to run material that already had an established safety basis. Various in process and scrap recovery items stored in gloveboxes, plutonium oxide and plutonium oxide mixed with uranium oxide stored in 2736-Z vaults will be processed through the stabilization furnaces until the safety basis for the metal items has been resolved. The purpose of thermal stabilization is to heat the material to 1000 degrees Celsius to drive off all volatile materials and leave the plutonium and/or uranium as oxides. The stabilized material will be sampled to determine the Loss On Ignition (LOI). The stabilized material must meet LOI of less than 0.5% to be acceptable for storage under DOE-STD-3013-94 specifications. Out of specification material will be recycled through the furnaces until the LOI limits are met.

  9. Determination of the thermal stability of perfluoroalkylethers

    NASA Technical Reports Server (NTRS)

    Helmick, Larry S.; Jones, William R., Jr.

    1990-01-01

    The thermal decomposition temperatures of several commercial and custom synthesized perfluoroalkylether fluids were determined with a computerized tensimeter. In general, the decomposition temperatures of the commercial fluids were all similar and significantly higher than those for custom synthesized fluids. Correlation of the decomposition temperatures with the molecular structures of the primary components of the commercial fluids revealed that the stability of the fluids is not affected by intrinsic factors such as carbon chain length, branching, or cumulated difluoroformal groups. Instead, correlation with extrinsic factors revealed that the stability may be limited by the presence of small quantities of thermally unstable material and/or chlorine-containing material arising from the use of chlorine-containing solvents during synthesis. Finally, correlation of decomposition temperatures with molecular weights for Demnum and Krytox fluids supports a chain cleavage reaction mechanism for Demnum fluids and an unzipping reaction mechanism for Krytox fluids.

  10. Thermal stability of polyvinyl alcohol/nanocrystalline cellulose composites.

    PubMed

    Voronova, Marina I; Surov, Oleg V; Guseinov, Sabir S; Barannikov, Vladimir P; Zakharov, Anatoly G

    2015-10-05

    Thermal stability of polyvinyl alcohol/cellulose nanocrystals (PVA/CNCs) composites prepared with solution casting technique was studied. The PVA/CNCs composites were characterized by Fourier transform infrared spectrometry, X-ray diffraction, differential scanning calorimeter (DSC) and thermogravimetric (TG) analysis. Due to the presence of CNCs nanoparticles, thermal degradation of the composites occurs at much higher temperatures compared to that of the neat PVA. Thermal stability of the PVA/CNCs composites is maximally enhanced with CNCs content of 8-12 wt%. Some thermal degradation products of the PVA/CNCs composites were identified by mass spectrometric analysis. TG measurements with synchronous recording of mass spectra revealed that the thermal degradation of both CNCs and PVA in the composites with CNCs content of 8-12 wt% occurs simultaneously at a much higher temperature than that of CNCs or the neat PVA. However, with increasing CNCs content more than 12 wt% the thermal stability of the composites decreases. In this case, the degradation of CNCs comes first followed by the degradation of PVA. Copyright © 2015 Elsevier Ltd. All rights reserved.

  11. Can green solvents be alternatives for thermal stabilization of collagen?

    PubMed

    Mehta, Ami; Rao, J Raghava; Fathima, Nishter Nishad

    2014-08-01

    "Go Green" campaign is gaining light for various industrial applications where water consumption needs to be reduced. To resolve this, industries have adopted usage of green, organic solvents, as an alternative to water. For leather making, tanning industry consumes gallons of water. Therefore, for adopting green solvents in leather making, it is necessary to evaluate its influence on type I collagen, the major protein present in the skin matrix. The thermal stability of collagen from rat tail tendon fiber (RTT) treated with seven green solvents namely, ethanol, ethyl lactate, ethyl acetate, propylene carbonate, propylene glycol, polyethylene glycol-200 and heptane was determined using differential scanning calorimetry (DSC). Crosslinking efficiency of basic chromium sulfate and wattle on RTT in green solvents was determined. DSC thermograms show increase in thermal stability of RTT collagen against heat with green solvents (>78°C) compared to water (63°C). In the presence of crosslinkers, RTT demonstrated thermal stability >100°C in some green solvents, resulting in increased intermolecular forces between collagen, solvent and crosslinkers. The significant improvement in thermal stability of collagen potentiates the capability of green solvents as an alternative for water. Copyright © 2014 Elsevier B.V. All rights reserved.

  12. Fluctuations of thermal conductivity and morphological stability

    NASA Technical Reports Server (NTRS)

    Mazuruk, K.; Gillies, D. C.; Lehoczky, S. L.

    1995-01-01

    Compositional fluctuations of the binary alloy result in the corresponding fluctuations of the thermal conductivity of the material. During crystal growth, these fluctuations can significantly modify the local temperature fields at the liquid-solid interface. This, in turn, will affect the morphological stability of the growing interface. In this work, the temperature dependence of the thermal conductivity of the solid phase has been included into the Mullins-Sekerka formalism. A significant effect on the onset of the instability of planar interface has been predicted. It has been found, in particular, that for binary systems with the segregation coefficient above unity a flat interface is always unstable. The shape of the interface fluctuation should have a single harmonic character with a well defined wavelength.

  13. Thermal Stability of Chelated Indium Activable Tracers

    SciTech Connect

    Chrysikopoulos, Costas; Kruger, Paul

    1986-01-21

    The thermal stability of indium tracer chelated with organic ligands ethylenediaminetetraacetic acid (EDTA) and nitrilotriacetic acid (NTA) was measured for reservoir temperatures of 150, 200, and 240 C. Measurements of the soluble indium concentration was made as a function of time by neutron activation analysis. From the data, approximate thermal decomposition rates were estimated. At 150 C, both chelated tracers were stable over the experimental period of 20 days. At 200 C, the InEDTA concentration remained constant for 16 days, after which the thermal decomposition occurred at a measured rate constant of k = 0.09 d{sup -1}. The thermal decomposition of InNTA at 200 C showed a first order reaction with a measured rate constant of k = 0.16 d{sup -1}. At 240 C, both indium chelated tracers showed rapid decomposition with rate constants greater than 1.8 d{sup -1}. The data indicate that for geothermal reservoir with temperatures up to about 200 C, indium chelated tracers can be used effectively for transit times of at least 20 days. These experiments were run without reservoir rock media, and do not account for concomitant loss of indium tracer by adsorption processes.

  14. Radiation and thermal stabilities of adenine nucleotides.

    PubMed

    Demidov, V V; Potaman, V N; Solyanina, I P; Trofimov, V I

    1995-03-01

    We have investigated in detail radiation and thermal stabilities and transformations of adenosine mono- and triphosphates in liquid and frozen solid aqueous solutions within a wide range of absorbed radiation dose (up to 75 kGy) and temperature (up to 160 degrees C). Dephosphorylation is the main pathway of high temperature hydrolysis of adenine nucleotides. Basic thermodynamic and kinetic parameters of this process have been determined. Radiolysis of investigated compounds at room temperature results in scission of N-glycosidic bond with a radiation yield about of 1 mol/100 eV. Solution freezing significantly enhances radiation stability of nucleotides as well as other biomolecules. This circumstance is essential in the discussion of panspermia concepts.

  15. Ceramic membranes with enhanced thermal stability

    DOEpatents

    Anderson, Marc A.; Xu, Qunyin; Bischoff, Brian L.

    1993-01-01

    A method of creating a ceramic membrane with enhanced thermal stability is disclosed. The method involves combining quantities of a first metal alkoxide with a second metal, the quantities selected to give a preselected metal ratio in the resultant membrane. A limited amount of water and acid is added to the combination and stirred until a colloidal suspension is formed. The colloid is dried to a gel, and the gel is fired at a temperature greater than approximately 400.degree. C. The porosity and surface area of ceramic membranes formed by this method are not adversely affected by this high temperature firing.

  16. The Thermal Stability of Unsymmetrical Dimethylhydrazine

    NASA Technical Reports Server (NTRS)

    Spakowski, Adolph E.

    1958-01-01

    The thermal stability of unsymmetrical dimethylhydrazine was investigated in a static system simulating conditions in an almost-empty fuel tank. The self-ignition temperature and spontaneous decomposition temperature of the pure fuel were determined at atmospheric pressure to be 454 and 740 F. respectively, with the larger (740 F) value, obtained in an inert atmosphere of nitrogen, representing the minimum temperature that would cause a rapid exothermic reaction. The addition of 40 weight percent dimethylenetriamine to unsymmetrical dimethylhydrazine did not significantly affect these properties.

  17. PID feedback control of monochromator thermal stabilization

    NASA Astrophysics Data System (ADS)

    Yoder, Derek W.; Makarov, Oleg; Corcoran, Stephen; Fischetti, Robert F.

    2011-09-01

    The desire for increasingly smaller X-ray beams for macromolecular crystallography experiments also stimulates the need for improvements in beam stability. There are numerous sources of instability, which influence beam quality on the micron-size scale. Typically, the most problematic source is thermal drift within the double crystal monochromators. In addition to using liquid nitrogen to indirectly cool both the first and second crystals, GM/CA-CAT previously used a combination of flowing water at constant temperature and copper braiding to stabilize the mechanics, mounts, and the Compton scatter shielding. However, the copper braids inefficiently stabilized the temperature of components that were distant from the water lines. Additionally, vibrations in the water lines propagated throughout the vibrationally dampened monochromator, thereby introducing both positional and intensity instabilities in the transmitted X-ray beam. To address these problems, heating pads were placed directly onto the temperature-sensitive components, with output controlled by a PID-feedback loop. As a result, there is negligible temperature change in the first crystal radiation shielding over the entire range of operational heat loads. Additionally, the angular drift in the second crystal induced by temperature changes in other components is dramatically decreased.

  18. Enhanced thermal stability of phosphate capped magnetite nanoparticles

    SciTech Connect

    Muthukumaran, T.; Philip, John

    2014-06-14

    We have studied the effect of phosphate capping on the high temperature thermal stability and magnetic properties of magnetite (Fe{sub 3}O{sub 4}) nanoparticles synthesized through a single-step co-precipitation method. The prepared magnetic nanoparticles are characterized using various techniques. When annealed in air, the phosphate capped nanoparticle undergoes a magnetic to non-magnetic phase transition at a temperature of 689 °C as compared to 580 °C in the uncoated nanoparticle of similar size. The observed high temperature phase stability of phosphate capped nanoparticle is attributed to the formation of a phosphocarbonaceous shell over the nanoparticles, which acts as a covalently attached protective layer and improves the thermal stability of the core material by increasing the activation energy. The phosphocarbonaceous shell prevents the intrusion of heat, oxygen, volatiles, and mass into the magnetic core. At higher temperatures, the coalescence of nanoparticles occurs along with the restructuring of the phosphocarbonaceous shell into a vitreous semisolid layer on the nanoparticles, which is confirmed from the small angle X-ray scattering, Fourier transform infra red spectroscopy, and transmission electron microscopy measurements. The probable mechanism for the enhancement of thermal stability of phosphocarbonaceous capped nanoparticles is discussed.

  19. Plasma-Enhanced Chemical Vapor Deposition (PE-CVD) yields better Hydrolytical Stability of Biocompatible SiOx Thin Films on Implant Alumina Ceramics compared to Rapid Thermal Evaporation Physical Vapor Deposition (PVD).

    PubMed

    Böke, Frederik; Giner, Ignacio; Keller, Adrian; Grundmeier, Guido; Fischer, Horst

    2016-07-20

    Densely sintered aluminum oxide (α-Al2O3) is chemically and biologically inert. To improve the interaction with biomolecules and cells, its surface has to be modified prior to use in biomedical applications. In this study, we compared two deposition techniques for adhesion promoting SiOx films to facilitate the coupling of stable organosilane monolayers on monolithic α-alumina; physical vapor deposition (PVD) by thermal evaporation and plasma enhanced chemical vapor deposition (PE-CVD). We also investigated the influence of etching on the formation of silanol surface groups using hydrogen peroxide and sulfuric acid solutions. The film characteristics, that is, surface morphology and surface chemistry, as well as the film stability and its adhesion properties under accelerated aging conditions were characterized by means of X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), inductively coupled plasma-optical emission spectroscopy (ICP-OES), and tensile strength tests. Differences in surface functionalization were investigated via two model organosilanes as well as the cell-cytotoxicity and viability on murine fibroblasts and human mesenchymal stromal cells (hMSC). We found that both SiOx interfaces did not affect the cell viability of both cell types. No significant differences between both films with regard to their interfacial tensile strength were detected, although failure mode analyses revealed a higher interfacial stability of the PE-CVD films compared to the PVD films. Twenty-eight day exposure to simulated body fluid (SBF) at 37 °C revealed a partial delamination of the thermally deposited PVD films whereas the PE-CVD films stayed largely intact. SiOx layers deposited by both PVD and PE-CVD may thus serve as viable adhesion-promoters for subsequent organosilane coupling agent binding to α-alumina. However, PE-CVD appears to be favorable for long-term direct film exposure to aqueous

  20. On the stability of subsonic thermal fronts

    SciTech Connect

    Ibanez S, Miguel H.; Shchekinov, Yuri; Bessega L, Maria C.

    2005-08-15

    The stability of subsonic thermal fronts against corrugation is analyzed and an exact dispersion relation is obtained taking into account the compressibility of the gas. For heat fronts, this dispersion equation has an unstable root ({omega}{sub ex}) corresponding to the Landau-Darrieus unstable mode ({omega}{sub 0}) modified by the compressional effects. In particular, the exact solution shows a conspicuous maximum very close to the value of the intake Mach number M{sub 1} at which a Chapman-Jouguet deflagration wave behind the heat front is formed. Cooling fronts are stable for corrugation-like disturbances. A maximum damping as well as a maximum in the frequency occur at a value of M{sub 1} depending on the value of the normalized cooling q.

  1. Thermal stability analysis of the fine structure of solar prominences

    NASA Technical Reports Server (NTRS)

    Demoulin, Pascal; Malherbe, Jean-Marie; Schmieder, Brigitte; Raadu, Mickael A.

    1986-01-01

    The linear thermal stability of a 2D periodic structure (alternatively hot and cold) in a uniform magnetic field is analyzed. The energy equation includes wave heating (assumed proportional to density), radiative cooling and both conduction parallel and orthogonal to magnetic lines. The equilibrium is perturbed at constant gas pressure. With parallel conduction only, it is found to be unstable when the length scale 1// is greater than 45 Mn. In that case, orthogonal conduction becomes important and stabilizes the structure when the length scale is smaller than 5 km. On the other hand, when the length scale is greater than 5 km, the thermal equilibrium is unstable, and the corresponding time scale is about 10,000 s: this result may be compared to observations showing that the lifetime of the fine structure of solar prominences is about one hour; consequently, our computations suggest that the size of the unresolved threads could be of the order of 10 km only.

  2. System evaluation of improved thermal stability jet fuels

    SciTech Connect

    Binns, K.E.; Dieterle, G.L.; Williams, T.

    1995-05-01

    A single-pass, single-tube heat exchanger device called the Phoenix rig and a single-pass, dual-heat exchanger system called the Extended Duration Thermal Stability Test system are specific devices/systems developed for evaluating jet fuel thermal stability. They have been used extensively in the evaluation of various jet fuels and thermal stability additives. The test results have indicated that additives can substantially improve the thermal stability of conventional jet fuels. Relationships of oxygen consumption, residence time, bulk, and wetted wall temperatures on coking deposits that form in the heated tubes have also been investigated.

  3. Thermal stability of tagatose in solution.

    PubMed

    Luecke, Katherine J; Bell, Leonard N

    2010-05-01

    Tagatose, a monosaccharide similar to fructose, has been shown to behave as a prebiotic. To deliver this prebiotic benefit, tagatose must not degrade during the processing of foods and beverages. The objective of this study was to evaluate the thermal stability of tagatose in solutions. Tagatose solutions were prepared in 0.02 and 0.1 M phosphate and citrate buffers at pHs 3 and 7, which were then held at 60, 70, and 80 degrees C. Pseudo-1st-order rate constants for tagatose degradation were determined. In citrate and phosphate buffers at pH 3, minimal tagatose was lost and slight browning was observed. At pH 7, tagatose degradation rates were enhanced. Degradation was faster in phosphate buffer than citrate buffer. Higher buffer concentrations also increased the degradation rate constants. Enhanced browning accompanied tagatose degradation in all buffer solutions at pH 7. Using the activation energies for tagatose degradation, less than 0.5% and 0.02% tagatose would be lost under basic vat and HTST pasteurization conditions, respectively. Although tagatose does breakdown at elevated temperatures, the amount of tagatose lost during typical thermal processing conditions would be virtually negligible. Practical Application: Tagatose degradation occurs minimally during pasteurization, which may allow for its incorporation into beverages as a prebiotic.

  4. Thermal stability of simvastatin under different atmospheres.

    PubMed

    Simões, Ricardo G; Diogo, Hermínio P; Dias, Ana; Oliveira, Maria Conceição; Cordeiro, Carlos; Bernardes, Carlos E S; Minas Da Piedade, Manuel E

    2014-01-01

    Simvastatin (SV) is a widely used drug for the treatment of hypercholesterolemia in humans. Nevertheless, serious efforts are still being made to develop new SV formulations with, for example, improved tabletability or bioavailability properties. These efforts frequently involve heating the compound well above ambient temperature or even fusion. In this work, the thermal stability of solid SV under different atmospheres was investigated by using isothermal tests in glass ampules, differential scanning calorimetry, and Calvet-drop microcalorimetry experiments. These tests were combined with analytical data from diffuse reflectance infrared Fourier-transform spectroscopy and liquid chromatography coupled with tandem mass spectrometry or Fourier transform ion cyclotron resonance mass spectrometry (LC-FT-ICR-MS). No decomposition was observed when the sample was kept at a temperature ≤373 K under N2 or reduced pressure (13.3 Pa) atmospheres. Thermal degradation was, however, observed for temperatures ≥353 K in the presence of pure or atmospheric oxygen. The nature of the two main oxidative degradation products was determined through MS/MS experiments and accurate mass measurements of the precursor ions using FT-ICR-MS. The obtained results indicated that the decomposition process involves the oxidation of the hexahydronaphthalene fragment of SV.

  5. Thermal stability of self-assembled peptide vaccine materials.

    PubMed

    Sun, Tao; Han, Huifang; Hudalla, Gregory A; Wen, Yi; Pompano, Rebecca R; Collier, Joel H

    2016-01-01

    The majority of current vaccines depend on a continuous "cold chain" of storage and handling between 2 and 8°C. Vaccines experiencing temperature excursions outside this range can suffer from reduced potency. This thermal sensitivity results in significant losses of vaccine material each year and risks the administration of vaccines with diminished protective ability, issues that are heightened in the developing world. Here, using peptide self-assemblies based on the fibril-forming peptide Q11 and containing the epitopes OVA323-339 from ovalbumin or ESAT651-70 from Mycobacterium tuberculosis, the chemical, conformational, and immunological stability of supramolecular peptide materials were investigated. It was expected that these materials would exhibit advantageous thermal stability owing to their adjuvant-free and fully synthetic construction. Neither chemical nor conformational changes were observed for either peptide when stored at 45°C for 7days. ESAT651-70-Q11 was strongly immunogenic whether it was stored as a dry powder or as aqueous nanofibers, showing undiminished immunogenicity even when stored as long as six months at 45°C. This result was in contrast to ESAT651-70 conjugated to a protein carrier and adjuvanted with alum, which demonstrated marked thermal sensitivity in these conditions. Antibody titers and affinities were undiminished in mice for OVA323-339-Q11 if it was stored as assembled nanofibers, yet some diminishment was observed for material stored as a dry powder. The OVA study was done in a different mouse strain and with a different prime/boost regimen, and so it should not be compared directly with the study for the ESAT epitope. This work indicates that peptide self-assemblies can possess attractive thermal stability properties in the context of vaccine development. Almost all current vaccines must be maintained within a tight and refrigerated temperature range, usually between 2 and 8°C. This presents significant challenges for their

  6. Enhanced thermal stability of the thylakoid membranes from spruce. A comparison with selected angiosperms.

    PubMed

    Karlický, Václav; Kurasová, Irena; Ptáčková, Božena; Večeřová, Kristýna; Urban, Otmar; Špunda, Vladimír

    2016-12-01

    Recently, we have found that thermal stability of photosystem II (PSII) photochemistry in spruce needles is higher than in other plants (barley, beech) cultivated under the same temperatures. In this work, temperature dependences of various characteristics of PSII organization were studied in order to obtain complex information on the thermal stability of PSII function and organization in spruce. Temperature dependency of circular dichroism spectra revealed by about 6 °C higher thermal stability of macrodomain organization in spruce thylakoid membranes in comparison with Arabidopsis and barley ones; however, thermal disintegration of light-harvesting complex of PSII did not significantly differ among the species studied. These results thus indicate that thermal stability of PSII macro-organization in spruce thylakoid membranes is enhanced to a similar extent as thermal stability of PSII photochemistry. Clear-native polyacrylamide gel electrophoresis of preheated thylakoids demonstrated that among the separated pigment-protein complexes, only PSII supercomplexes (SCs) revealed considerably higher thermal stability in spruce thylakoids as compared to Arabidopsis and barley ones. Hence we suggest that higher thermal stability of PSII macro-organization of spruce is influenced by the maintenance of PSII SCs in the thylakoid membrane. In addition, we discuss possible effects of different PSII organizations and lipid compositions on the thermal stability of spruce thylakoid membranes.

  7. Thermal Stability of Nanocrystalline Copper Alloyed with Antimony

    NASA Astrophysics Data System (ADS)

    Atwater, Mark A.; Mula, Suhrit; Scattergood, Ronald O.; Koch, Carl C.

    2013-12-01

    Nanocrystalline copper (Cu) was generated by cryogenic, high-energy ball milling. Antimony (Sb) was added to investigate its utility in stabilizing the grain structure during annealing up to a maximum temperature of 1073 K (800 °C). When alloyed with Sb in quantities up to 1 at. pct, thermal stability was maintained up to 673 K (400 °C). Cu and Sb have very different molar volumes which can drive segregation of the solute due to the elastic strain energy and hence stabilize the grain size by reducing grain boundary energy. The elastic mismatch of Sb in Cu is calculated to be quite large (113 kJ/mol) when molar volume is used, but when an equivalent equation using atomic radius is applied, the driving force is nearly an order of magnitude lower (~12 kJ/mol). The low elastic mismatch is corroborated by the large equilibrium solubility of Sb in Cu. The results for the Cu-Sb system are compared to the nanocrystalline Ni-W system and the large amount of equilibrium solubility of the solute in both cases is thought to hinder thermal stabilization since segregation is not strongly favored.

  8. System Design Description PFP Thermal Stabilization

    SciTech Connect

    RISENMAY, H.R.

    2000-01-27

    DOE has authorized in their letter of August 2, 1999, the operation of these three furnaces, quote ''Operation of the three uncompleted muffle furnaces (No.3, No.4, and No.5) located in Room 235B is authorized, using the same feed charge limits as the two existing furnaces (No.1, and No.2) located in Room 230C,''. The above statement incorrectly refers to Room 230C whereas the correct location is Room 230A. The current effort is directed to initiate the operation and to complete the design activities DOE authorized the operation of the furnaces based on their Safety Evaluation Report (SER). Based on analogy and the principle of similarity, the risks and consequences of accidents both onsite and offsite due to operation of three furnaces are not significantly larger than those already evaluated with the two operating furnaces. Thermal stabilization operations and the material of feed for furnaces in Glovebox HA-21 I are essentially the same as those currently being stabilized in furnaces in Glovebox HC-21 C. Therefore the accident analysis has utilized identical accident scenarios in evaluation and no additional failure modes are introduced by HA-21 I muffle furnace operation that would enhance the consequences of accidents. Authorization Basis documents as referenced below (PFP FSAR and DOE Letter authorizing the operation) appear to contradict each other, i.e. one allows and authorizes the operation and the other imposes the restriction on the operation. The purpose of the PFP FSAR restrictions was to review thoroughly the design and installation of three furnaces and perform acceptance testing before approving the startup for operation. With the experience of operating the two furnaces in Glovebox HC-21C, and the knowledge of risks and hazards the facility operation, the plant is adequately prepared to operate these additional furnaces. ECN 653595 has been prepared to incorporate operation of the muffle furnaces in Glovebox HA-21 I into the PFP FSAR.

  9. Thermal stability of brushite with chitosan samples

    NASA Astrophysics Data System (ADS)

    Chikanova, E. S.; Golovanova, O. A.; Malikova, T. V.; Kuimova, M. V.

    2017-01-01

    In this paper, the powders of brushite from an aqueous solution of Ca(NO3)2- (NH4)2HPO4 with different content of chitosan were synthesized. XRD data revealed that all samples are single-phase and are brushite (CaHPO4·2H2O). By FT-IR spectroscopy and BET methods, it was found that chitosan adsorbs onto the surface of powders. With increase of the content of the additive, the average size of crystallites increases 4.0 – 4.8 – 11.8 μm, respectively, and the dissolution rate in isotonic solution also decreases. The thermal stability of the composite powders was studied. It was established that the highest destruction of samples occurs in the range 473-673 K by removing of adsorption and crystallization water and partial change of the structure of the mineral and chitosan. At a temperature of 873 K, carbonization of the organic additive occurs.

  10. In situ observation of the thermal stability of black phosphorus

    NASA Astrophysics Data System (ADS)

    Lin, Shenghuang; Li, Yanyong; Lu, Wei; San Chui, Ying; Rogée, Lukas; Bao, Qiaoliang; Lau, Shu Ping

    2017-06-01

    Two-dimensional (2D) layered black phosphorus (BP), with a direct band gap and high carrier mobility, has shown great potential for next generation electronics and optoelectronics. However, 2D materials always show different thermal properties when compared to its bulk counterpart. Therefore, it is necessary to understand the thermal process of BP to reveal its natural physical properties. Herein, an atomic-scale microscopic and spectroscopic study is performed to characterize the thermal degradation and re-deposition of solution-exfoliated BP. The in situ decomposition temperature of the BP is observed to be greater than 400 °C. The residual gaseous BP would be re-deposited to form amorphous phosphorus when the chamber was cooled down to room temperature. Moreover, the thickness of the BP flakes can be moderately controlled through thermal thinning process. Our study provides an insight into the thermal stability of 2D BP in vacuum and opens an avenue in fabricating large-area ultra-thin BP films.

  11. Thermal stability of marks gold nanoparticles: A molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Jia, Yanlin; Li, Siqi; Qi, Weihong; Wang, Mingpu; Li, Zhou; Wang, Zhixing

    2017-03-01

    Molecular dynamics (MDs) simulations were used to explore the thermal stability of Au nanoparticles (NPs) with decahedral, cuboctahedral, icosahedral and Marks NPs. According to the calculated cohesive energy and melting temperature, the Marks NPs have a higher cohesive energy and melting temperature compared to these other shapes. The Lindemann index, radial distribution function, deformation parameters, mean square displacement and self-diffusivity have been used to characterize the structure variation during heating. This work may inspire researchers to prepare Marks NPs and apply them in different fields.

  12. Thermal Decomposition of RP-2 with Stabilizing Additives

    DTIC Science & Technology

    2010-04-01

    RP-2 are that the allowed sulfur content is much lower in RP-2 (0.1 mg/kg, compared to 30 mg/kg in RP-1), the allowed olefin concentration is lower...28,30-35 decahydronaphthalene (decalin), 33,35 and benzyl alcohol . 28,36-38 In related work, a major research effort initiated by the U.S. Air Force...additives (e.g., benzyl alcohol ). We would also like to test the effect of different reactor materials, particularly copper, on the thermal stability of

  13. Off-set stabilizer for comparator output

    DOEpatents

    Lunsford, James S.

    1991-01-01

    A stabilized off-set voltage is input as the reference voltage to a comparator. In application to a time-interval meter, the comparator output generates a timing interval which is independent of drift in the initial voltage across the timing capacitor. A precision resistor and operational amplifier charge a capacitor to a voltage which is precisely offset from the initial voltage. The capacitance of the reference capacitor is selected so that substantially no voltage drop is obtained in the reference voltage applied to the comparator during the interval to be measured.

  14. Enhanced Thermal Stability of Polylactide by Terminal Conjugation Groups

    NASA Astrophysics Data System (ADS)

    Tran, Hang Thi; Matsusaki, Michiya; Akashi, Mitsuru; Vu, Ngo Dinh

    2016-05-01

    Various acids such as aliphatic or carbocyclic fatty or aromatic acids were successfully conjugated into the ending hydroxyl group of poly( l-lactide) (PLLA). The chemical structures of various acid-PLLAs were confirmed by Fourier transform infrared and proton nuclear magnetic resonance analysis. The crystallinity and solubility of the original PLLA were maintained after the terminal conjugation of various acids. The thermal properties were significantly improved, especially the 10% weight-loss temperature that showed an increase of over 80°C for conjugation of aliphatic or aromatic acids as compared to that of the corresponding original PLLA. In addition, more than 60 wt.% of the aliphatic acid-PLLAs was pyrolyzed, and aromatic acid-PLLAs degraded only about 10 wt.% for 150 min, although the original PLLA was pyrolyzed completely at 250°C for 7 min. The thermal stability of PLLA was controlled by the conjugation of aliphatic or aromatic acids into a chain end. These acid-PLLAs may be useful as materials with high thermal stability for various application fields.

  15. The effects of thermally reversible agents on PVC stability properties

    NASA Astrophysics Data System (ADS)

    Wang, J.; Yao, J.; Xiong, X. H.; Jia, C. X.; Ren, R.; Chen, P.; Liu, X. M.

    2016-07-01

    One kind of thermally reversible cross-linking agents for improving PVC thermally stability was synthesized. The chemical structure and thermally reversible characteristics of cross-linking agents were investigated by FTIR and DSC analysis, respectively. FTIR results confirmed that the cyclopentadienyl barium mercaptides ((CPD-C2H4S)2Ba) were successfully synthesized. DSC results showed it has thermally reversible characteristics and the depolymerization temperature was between 170 °C and 205 °C. The effects of cross-linking reaction time on gel content of Poly(vinyl chloride) compounds was evaluated. The gel content value arrived at 42% after being cross-linked for 25 min at 180 C. The static thermally stability measurement proved that the thermally stability of PVC compounds was improved.

  16. RP-1 Thermal Stability and Copper Based Materials Compatibility Study

    NASA Technical Reports Server (NTRS)

    Stiegemeier, B. R.; Meyer, M. L.; Driscoll, E.

    2005-01-01

    A series of electrically heated tube tests was performed at the NASA Glenn Research Center s Heated Tube Facility to investigate the effect that sulfur content, test duration, and tube material play in the overall thermal stability and materials compatibility characteristics of RP-1. Scanning-electron microscopic (SEM) analysis in conjunction with energy dispersive spectroscopy (EDS) were used to characterize the condition of the tube inner wall surface and any carbon deposition or corrosion formed during these runs. Results of the parametric study indicate that tests with standard RP-1 (total sulfur -23 ppm) and pure copper tubing are characterized by a depostion/deposit shedding process producing local wall temperature swings as high as 500 F. The effect of this shedding is to keep total carbon deposition levels relatively constant for run times from 20 minutes up to 5 hours, though increasing tube pressure drops were observed in all runs. Reduction in the total sulfur content of the fuel from 23 ppm to less than 0.1 ppm resulted in the elimination of deposit shedding, local wall temperature variation, and the tube pressure drop increases that were observed in standard sulfur level RP-1 tests. The copper alloy GRCop-84, a copper alloy developed specifically for high heat flux applications, was found to exhibit higher carbon deposition levels compared to identical tests performed in pure copper tubes. Results of the study are consistent with previously published heated tube data which indicates that small changes in fuel total sulfur content can lead to significant differences in the thermal stability of kerosene type fuels and their compatibility with copper based materials. In conjunction with the existing thermal stability database, these findings give insight into the feasibility of cooling a long life, high performance, high-pressure liquid rocket combustor and nozzle with RP-1.

  17. Silphenylene elastomers have high thermal stability and tensile strength

    NASA Technical Reports Server (NTRS)

    1969-01-01

    Two polymeric silphenylene ethers, when cured by reactions with ethyl silicates and metal salts at room temperature, form elastomers having excellent thermal stability and tensile properties. The highest tensile strength obtained in a reinforced elastomer was 2800 psi.

  18. Development of thermal stability additive packages for JP-8

    SciTech Connect

    Anderson, S.D.; Harrison, W.E. III; Edwards, T.; Morris, R.W.; Shouse, D.T.

    1995-05-01

    Advanced military aircraft use fuel as the primary heat sink to cool engine and airframe components. As the fuel is thermally stressed, thermal oxidative reactions take place that result in the formation of deposits. These deposits degrade aircraft performance and ultimately lead to premature servicing of the affected components. The frequency of these incidents, coupled with the projected cooling requirements for future systems, demonstrates that current thermal stability limits are inadequate. In response to this situation, the United States Air Force (USAF) has embarked on a program to improve thermal stability using specially formulated additive packages. Results indicate that additives offer significant thermal stability improvement. This paper describes the USAF program to develop and deploy an improved JP-8 for fleet-wide use by 1998.

  19. Stabilization of supercooled fluids by thermal hysteresis proteins.

    PubMed Central

    Wilson, P W; Leader, J P

    1995-01-01

    It has been reported that thermal hysteresis proteins found in many cold-hardy, freeze-avoiding arthropods stabilize their supercooled body fluids. We give evidence that fish antifreeze proteins, which also produce thermal hysteresis, bind to and reduce the efficiency of heterogenous nucleation sites, rather than binding to embryonic ice nuclei. We discuss both possible mechanisms for stabilization of supercooled body fluids and also describe a new method for measuring and defining the supercooling point of small volumes of liquid. PMID:7612853

  20. Optimal control theory applied to fusion plasma thermal stabilization

    SciTech Connect

    Sager, G.; Miley, G.; Maya, I.

    1985-01-01

    Many authors have investigated stability characteristics and performance of various burn control schemes. The work presented here represents the first application of optimal control theory to the problem of fusion plasma thermal stabilization. The objectives of this initial investigation were to develop analysis methods, demonstrate tractability, and present some preliminary results of optimal control theory in burn control research.

  1. Thermal Stability of Otto Fuel Prepolymer

    NASA Technical Reports Server (NTRS)

    Tompa, Albert S.; Sandagger, Karrie H.; Bryant, William F., Jr.; McConnell, William T.; Lacot, Fernando; Carr, Walter A.

    2000-01-01

    Otto Fuel II contains a nitrate ester, plasticizer, and 2-NPDA as a stabilizer. Otto Fuel with stabilizers from three vendors was investigated by dynamic and isothermal differential scanning calorimetry (DSC) using samples sealed in a glass ampoule and by Isothermal Microcalorimetry (IMC) using 10 gram samples aged at 75 C for 35 days. DSC kinetics did not show differences between the stabilizer; the samples had an activation energy of 36.7 +/- 0.6 kcal/mol. However, IMC analysis was sensitive enough to detect small differences between the stabilizer, namely energy of interaction values of 7 to 14 Joules. DSC controlled cooling and heating at 5 C/min from 30 to -60 to 40 C experiments were similar and showed a crystallization peak at -48 +/- 1 C during cooling, and upon heating there was a glass transition temperature step at approx. -54 +/- 0.5 C and a melting peak at -28 +/- 0.4 C.

  2. Thermal Stability of Otto Fuel Prepolymer

    NASA Technical Reports Server (NTRS)

    Tompa, Albert S.; Sandagger, Karrie H.; Bryant, William F., Jr.; McConnell, William T.; Lacot, Fernando; Carr, Walter A.

    2000-01-01

    Otto Fuel II contains a nitrate ester, plasticizer, and 2-NDPA as a stabilizer. Otto Fuel with stabilizers from three vendors was investigated by dynamic and isothermal DSC using samples sealed in a glass ampoule and by Isothermal Microcalorimetry (IMC) using 10 gram samples aged at 75 C for 35 days. DSC kinetics did not show differences between the stabilizer; the samples had an activation energy of 36.7 +/- 0.6 kcal/mol. However, IMC analysis was sensitive enough to detect small differences between the stabilizer, namely energy of interaction values of 7 to 14 Joules. DSC controlled cooling and heating at 5 C/min from 30 to -60 to 40 C experiments were similar and showed a crystallization peak at -48 +/- 1 C during cooling, and upon heating there was a glass transition temperature step at approx. -54 +/- 0.5 C and a melting peak at -28 +/- 0.4 C.

  3. Thermal Stability of Otto Fuel Prepolymer

    NASA Technical Reports Server (NTRS)

    Tompa, Albert S.; Sandagger, Karrie H.; Bryant, William F., Jr.; McConnell, William T.; Lacot, Fernando; Carr, Walter A.

    2000-01-01

    Otto Fuel II contains a nitrate ester, plasticizer, and 2-NPDA as a stabilizer. Otto Fuel with stabilizers from three vendors was investigated by dynamic and isothermal differential scanning calorimetry (DSC) using samples sealed in a glass ampoule and by Isothermal Microcalorimetry (IMC) using 10 gram samples aged at 75 C for 35 days. DSC kinetics did not show differences between the stabilizer; the samples had an activation energy of 36.7 +/- 0.6 kcal/mol. However, IMC analysis was sensitive enough to detect small differences between the stabilizer, namely energy of interaction values of 7 to 14 Joules. DSC controlled cooling and heating at 5 C/min from 30 to -60 to 40 C experiments were similar and showed a crystallization peak at -48 +/- 1 C during cooling, and upon heating there was a glass transition temperature step at approx. -54 +/- 0.5 C and a melting peak at -28 +/- 0.4 C.

  4. Micellar Enzymology for Thermal, pH, and Solvent Stability.

    PubMed

    Minteer, Shelley D

    2017-01-01

    This chapter describes methods for enzyme stabilization using micellar solutions. Micellar solutions have been shown to increase the thermal stability, as well as the pH and solvent tolerance of enzymes. This field is traditionally referred to as micellar enzymology. This chapter details the use of ionic and nonionic micelles for the stabilization of polyphenol oxidase, lipase, and catalase, although this method could be used with any enzymatic system or enzyme cascade system.

  5. Effect of stabilizer on dynamic thermal transport property of ZnO nanofluid

    PubMed Central

    2013-01-01

    In this paper, we investigate the effect of adding a stabilizer on the dynamic thermal properties of ZnO nanofluid (containing 5 to 10 nm diameter of ZnO nanocrystals) measured using a 3ω method. Addition of the stabilizer leads to the stabilization of the nanofluid and also substantial reduction of the enhancement of thermal transport compared to that seen in the bare ZnO nanofluid. This also alters the frequency dependence of the thermal transport and the characteristic time scale associated with it. It is suggested that the addition of the stabilizer inhibits the thermodiffusion-assisted local aggregation thus leading to substantial reduction of the enhancement of thermal transport properties of the bare nanofluid as proposed in some recent models, and this also alters the characteristic time scales by altering the scale of aggregation. PMID:23497347

  6. Effect of stabilizer on dynamic thermal transport property of ZnO nanofluid.

    PubMed

    Neogy, Rajesh Kumar; Raychaudhuri, Arup Kumar

    2013-03-14

    In this paper, we investigate the effect of adding a stabilizer on the dynamic thermal properties of ZnO nanofluid (containing 5 to 10 nm diameter of ZnO nanocrystals) measured using a 3ω method. Addition of the stabilizer leads to the stabilization of the nanofluid and also substantial reduction of the enhancement of thermal transport compared to that seen in the bare ZnO nanofluid. This also alters the frequency dependence of the thermal transport and the characteristic time scale associated with it. It is suggested that the addition of the stabilizer inhibits the thermodiffusion-assisted local aggregation thus leading to substantial reduction of the enhancement of thermal transport properties of the bare nanofluid as proposed in some recent models, and this also alters the characteristic time scales by altering the scale of aggregation.

  7. Thermal Stability Comparison of Nanocrystalline Fe-Based Binary Alloy Pairs

    NASA Astrophysics Data System (ADS)

    Clark, B. G.; Hattar, K.; Marshall, M. T.; Chookajorn, T.; Boyce, B. L.; Schuh, C. A.

    2016-06-01

    The widely recognized property improvements of nanocrystalline (NC) materials have generated significant interest; yet, they have been difficult to realize in engineering applications due to the propensity for grain growth in these interface-dominated systems. Although traditional pathways to thermal stabilization can slow the mobility of grain boundaries, recent theories suggest that solute segregation in NC alloys can reduce the grain boundary energy such that thermodynamic stabilization is achieved. Following the predictions of Murdoch et al., here we compare for the first time the thermal stability of a predicted NC stable alloy (Fe-10 at.% Mg) with a predicted non-NC stable alloy (Fe-10 at.% Cu) using the same processing and characterization methodologies. Results show improved thermal stability of the Fe-Mg alloy in comparison with the Fe-Cu, and thermally-evolved microstructures that are consistent with those predicted by Monte Carlo simulations.

  8. Thermal stability of octadecyltrimethylammonium bromide modified montmorillonite organoclay.

    PubMed

    Xi, Yunfei; Zhou, Qin; Frost, Ray L; He, Hongping

    2007-07-15

    Organoclays are significant for providing a mechanism for the adsorption of organic molecules from potable water. As such their thermal stability is important. A combination of thermogravimetric analysis and infrared emission spectroscopy was used to determine this stability. Infrared emission spectroscopy (IES) was used to investigate the changes in the structure and surface characteristics of water and surfactant molecules in montmorillonite, octadecyltrimethylammonium bromide and organoclays prepared with the surfactant octadecyltrimethylammonium bromide with different surfactant loadings. These spectra collected at different temperatures give support to the results obtained from the thermal analysis and also provide additional evidence for the dehydration which is difficult to obtain by normal thermoanalytical techniques. The spectra provide information on the conformation of the surfactant molecules in the clay layers and the thermal decomposition of the organoclays. Infrared emission spectroscopy proved to be a useful tool for the study of the thermal stability of the organoclays.

  9. Thermal stability in exchange-spring chains of spins

    NASA Astrophysics Data System (ADS)

    Pellicelli, Raffaele; Solzi, Massimo

    2016-02-01

    Thermal stability and switching behaviour have been compared in pure-hard and soft-hard Heisenberg linear spin chains of the same total length and equal magnetic parameters (except for magnetic anisotropy) with the anisotropy axis and external magnetic field parallel to the chain direction. The zero-temperature energy barriers and finite-temperature transition rates between remanent equilibrium states have been calculated by utilizing the string method and the forward flux sampling (FFS) method, respectively. Depending on the assumed interfaces, the FFS method could in fact fail to correctly sample the characteristic transition paths at interfaces at which these paths have probabilities much lower than those associated with other non-characteristic transition paths. This can especially occur in the case of the asymmetric energy landscapes and multiple asymmetric minimum energy paths (MEPs) of soft-hard systems. Therefore, a proper interface definition is needed in order to deduce the correct transition rates. In particular, we show that the thermal switching of soft-hard chains starting in the soft or in the hard part turns out to occur with an equal rate provided that the interfaces of the FFS method are defined on the basis of the corresponding zero-temperature MEPs. The thermal stability of a soft-hard chain in the remanent equilibrium state could be to some extent lower with respect to that of a pure-hard chain, due to the shorter hard-part length crossed by the domain wall formed in the chain and also to the related slightly smaller energy barrier. However, its switching field at zero temperature is verified to be widely lower than that of the pure-hard chain. Analytical expressions of switching fields and energy barriers have been deduced in various cases.

  10. Comprehensive stabilization mechanism of electron-beam irradiated polyacrylonitrile fibers to shorten the conventional thermal treatment

    PubMed Central

    Park, Sejoon; Yoo, Seung Hwa; Kang, Ha Ri; Jo, Seong Mu; Joh, Han-Ik; Lee, Sungho

    2016-01-01

    An electron beam was irradiated on polyacrylonitrile (PAN) fibers prior to thermal stabilization. The electron-beam irradiation effectively shortened the thermal stabilization process by one fourth compared with the conventional thermal stabilization process. A comprehensive mechanistic study was conducted regarding this shortening of the thermal stabilization by electron-beam irradiation. Various species of chain radicals were produced in PAN fibers by electron-beam irradiation and existed for a relatively long duration, as observed by electron spin resonance spectroscopy. Subsequently, these radicals were gradually oxidized to peroxy radicals in the presence of oxygen under storage or heating. We found that these peroxy radicals (CO) enabled such an effective shortcut of thermal stabilization by acting as intermolecular cross-linking and partial aromatization points in the low temperature range (100–130 °C) and as earlier initiation seeds of successive cyclization reactions in the next temperature range (>130–140 °C) of thermal stabilization. Finally, even at a low irradiation dose (200 kGy), followed by a short heat treatment (230 °C for 30 min), the PAN fibers were sufficiently stabilized to produce carbon fibers with tensile strength and modulus of 2.3 and 216 GPa, respectively, after carbonization. PMID:27349719

  11. Comprehensive stabilization mechanism of electron-beam irradiated polyacrylonitrile fibers to shorten the conventional thermal treatment.

    PubMed

    Park, Sejoon; Yoo, Seung Hwa; Kang, Ha Ri; Jo, Seong Mu; Joh, Han-Ik; Lee, Sungho

    2016-06-28

    An electron beam was irradiated on polyacrylonitrile (PAN) fibers prior to thermal stabilization. The electron-beam irradiation effectively shortened the thermal stabilization process by one fourth compared with the conventional thermal stabilization process. A comprehensive mechanistic study was conducted regarding this shortening of the thermal stabilization by electron-beam irradiation. Various species of chain radicals were produced in PAN fibers by electron-beam irradiation and existed for a relatively long duration, as observed by electron spin resonance spectroscopy. Subsequently, these radicals were gradually oxidized to peroxy radicals in the presence of oxygen under storage or heating. We found that these peroxy radicals (CO) enabled such an effective shortcut of thermal stabilization by acting as intermolecular cross-linking and partial aromatization points in the low temperature range (100-130 °C) and as earlier initiation seeds of successive cyclization reactions in the next temperature range (>130-140 °C) of thermal stabilization. Finally, even at a low irradiation dose (200 kGy), followed by a short heat treatment (230 °C for 30 min), the PAN fibers were sufficiently stabilized to produce carbon fibers with tensile strength and modulus of 2.3 and 216 GPa, respectively, after carbonization.

  12. Comprehensive stabilization mechanism of electron-beam irradiated polyacrylonitrile fibers to shorten the conventional thermal treatment

    NASA Astrophysics Data System (ADS)

    Park, Sejoon; Yoo, Seung Hwa; Kang, Ha Ri; Jo, Seong Mu; Joh, Han-Ik; Lee, Sungho

    2016-06-01

    An electron beam was irradiated on polyacrylonitrile (PAN) fibers prior to thermal stabilization. The electron-beam irradiation effectively shortened the thermal stabilization process by one fourth compared with the conventional thermal stabilization process. A comprehensive mechanistic study was conducted regarding this shortening of the thermal stabilization by electron-beam irradiation. Various species of chain radicals were produced in PAN fibers by electron-beam irradiation and existed for a relatively long duration, as observed by electron spin resonance spectroscopy. Subsequently, these radicals were gradually oxidized to peroxy radicals in the presence of oxygen under storage or heating. We found that these peroxy radicals (CO) enabled such an effective shortcut of thermal stabilization by acting as intermolecular cross-linking and partial aromatization points in the low temperature range (100-130 °C) and as earlier initiation seeds of successive cyclization reactions in the next temperature range (>130-140 °C) of thermal stabilization. Finally, even at a low irradiation dose (200 kGy), followed by a short heat treatment (230 °C for 30 min), the PAN fibers were sufficiently stabilized to produce carbon fibers with tensile strength and modulus of 2.3 and 216 GPa, respectively, after carbonization.

  13. Thermal barrier coating having high phase stability

    DOEpatents

    Subramanian, Ramesh

    2002-01-01

    A device (10) comprising a substrate (22) having a deposited ceramic thermal barrier coating characterized by a microstructure having gaps (28) where the thermal barrier coating comprises a first thermal barrier layer (40), and a second thermal barrier layer (30) with a pyrochlore crystal structure having a chemical formula of A.sup.n+.sub.2-x B.sup.m+.sub.2+x O.sub.7-y, where A is selected from the group of elements consisting of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and mixtures thereof, where B is selected from the group of elements consisting of Zr, Hf, Ti and mixtures thereof, where n and m are the valence of A and B respectively, and for -0.5.ltoreq.x.ltoreq.0.5, ##EQU1## and excluding the following combinations for x=0, y=0: A=La and B=Zr; A=La and B=Hf; A=Gd and B=Hf; and A=Yb and B=Ti.

  14. Thermal stability of diesel fuels by quantitative gravimetric JFTOT

    SciTech Connect

    Beal, E.J.; Hardy, D.R.

    1995-04-01

    The gravimetric jet fuel total oxidation tester (JFTOT) was developed several years ago to provide JFTOT conditions which measure quantitatively the solid/deposit products formed in aviation fuels. The gravimetric JFTOT has now been used to measure these products in a small set of typical diesel fuels. These baseline data are compared to a much larger data base of jet fuels and also several pure compounds. Results from the diesels indicate that the gravimetric JFTOT is a useful concept for ranking fuels for their thermal stability. The diesels ranged from quite low (better than jet) to quite high (an order of magnitude greater than jet fuel) in their deposit forming tendencies. Properly ranked fuels can be used in device tests such as diesel injectors and gas turbine nozzles to assess deposition. In addition, diesels with appropriate viscosities may be able to be used as aviation fuels provided the gravimetric JFTOT gives a low deposition rating.

  15. Analytic tests and their relation to jet fuel thermal stability

    SciTech Connect

    Heneghan, S.P.; Kauffman, R.E.

    1995-05-01

    The evaluation of jet fuel thermal stability (TS) by simple analytic procedures has long been a goal of fuels chemists. The reason is obvious: if the analytic chemist can determine which types of material cause his test to respond, the refiners will know which materials to remove to improve stability. Complicating this quest is the lack of an acceptable quantitative TS test with which to compare any analytic procedures. To circumvent this problem, we recently compiled the results of TS tests for 12 fuels using six separate test procedures. The results covering a range of flow and temperature conditions show that TS is not as dependent on test conditions as previously thought. Also, comparing the results from these tests with several analytic procedures shows that either a measure of the number of phenols or the total sulfur present in jet fuels is strongly indicative of the TS. The phenols have been measured using a cyclic voltammetry technique and the polar material by gas chromatography (atomic emission detection) following a solid phase extraction on silica gel. The polar material has been identified as mainly phenols (by mass spectrometry identification). Measures of the total acid number or peroxide concentration have little correlation with TS.

  16. Thermal self-stability, multi-stability, and memory effects in Brillouin fiber lasers

    NASA Astrophysics Data System (ADS)

    Kotlicki, Omer; Scheuer, Jacob

    2017-02-01

    We demonstrate an inherently self-stable Brillouin fiber laser in telecom wavelengths, stemming from a natural thermal feedback mechanism. Such lasers demonstrate great stability which significantly overcomes the hampering drift often associated with fiber lasers.

  17. Thermal stability of idealized folded carbyne loops

    PubMed Central

    2013-01-01

    Self-unfolding items provide a practical convenience, wherein ring-like frames are contorted into a state of equilibrium and subsequently  pop up’ or deploy when perturbed from a folded structure. Can the same process be exploited at the molecular scale? At the limiting scale is a closed chain of single atoms, used here to investigate the limits of stability of such folded ring structures via full atomistic molecular dynamics. Carbyne is a one-dimensional carbon allotrope composed of sp-hybridized carbon atoms. Here, we explore the stability of idealized carbyne loops as a function of chain length, curvature, and temperature, and delineate an effective phase diagram between folded and unfolded states. We find that while overall curvature is reduced, in addition to torsional and self-adhesive energy barriers, a local increase in curvature results in the largest impedance to unfolding. PMID:24252156

  18. A Physics-Based Temperature Stabilization Criterion for Thermal Testing

    NASA Technical Reports Server (NTRS)

    Rickman, Steven L.; Ungar, Eugene K.

    2009-01-01

    Spacecraft testing specifications differ greatly in the criteria they specify for stability in thermal balance tests. Some specify a required temperature stabilization rate (the change in temperature per unit time, dT/dt), some specify that the final steady-state temperature be approached to within a specified difference, delta T , and some specify a combination of the two. The particular values for temperature stabilization rate and final temperature difference also vary greatly between specification documents. A one-size-fits-all temperature stabilization rate requirement does not yield consistent results for all test configurations because of differences in thermal mass and heat transfer to the environment. Applying a steady-state temperature difference requirement is problematic because the final test temperature is not accurately known a priori, especially for powered configurations. In the present work, a simplified, lumped-mass analysis has been used to explore the applicability of these criteria. A new, user-friendly, physics-based approach is developed that allows the thermal engineer to determine when an acceptable level of temperature stabilization has been achieved. The stabilization criterion can be predicted pre-test but must be refined during test to allow verification that the defined level of temperature stabilization has been achieved.

  19. Chemical, thermal and mechanical stabilities of metal-organic frameworks

    NASA Astrophysics Data System (ADS)

    Howarth, Ashlee J.; Liu, Yangyang; Li, Peng; Li, Zhanyong; Wang, Timothy C.; Hupp, Joseph T.; Farha, Omar K.

    2016-03-01

    The construction of thousands of well-defined, porous, metal-organic framework (MOF) structures, spanning a broad range of topologies and an even broader range of pore sizes and chemical functionalities, has fuelled the exploration of many applications. Accompanying this applied focus has been a recognition of the need to engender MOFs with mechanical, thermal and/or chemical stability. Chemical stability in acidic, basic and neutral aqueous solutions is important. Advances over recent years have made it possible to design MOFs that possess different combinations of mechanical, thermal and chemical stability. Here, we review these advances and the associated design principles and synthesis strategies. We focus on how these advances may render MOFs effective as heterogeneous catalysts, both in chemically harsh condensed phases and in thermally challenging conditions relevant to gas-phase reactions. Finally, we briefly discuss future directions of study for the production of highly stable MOFs.

  20. Thermal stability of a magnetic domain wall in nanowires

    NASA Astrophysics Data System (ADS)

    Fukami, S.; Ieda, J.; Ohno, H.

    2015-06-01

    We study the thermal stability of a magnetic domain wall pinned in nanowires with various widths and thicknesses made of Co/Ni multilayers and analyze the effective volume that governs the thermal stability. We find that, above a critical wire width, the domain wall depinning is initiated by a subvolume excitation and that the critical width is dependent on the wire thickness. The obtained findings are supported by the distribution of critical current density for domain wall depinning and are qualitatively described by an analytical model in which the balance between the Zeeman energy and domain wall elastic energy is considered. We also show a different behavior between the device size dependence of the thermal stability and that of critical current, leading to an enhancement of domain wall motion efficiency with decreasing the device size.

  1. Thermal and mechanical stability of zeolitic imidazolate frameworks polymorphs

    SciTech Connect

    Bouëssel du Bourg, Lila; Ortiz, Aurélie U.; Coudert, François-Xavier; Boutin, Anne

    2014-12-01

    Theoretical studies on the experimental feasibility of hypothetical Zeolitic Imidazolate Frameworks (ZIFs) have focused so far on relative energy of various polymorphs by energy minimization at the quantum chemical level. We present here a systematic study of stability of 18 ZIFs as a function of temperature and pressure by molecular dynamics simulations. This approach allows us to better understand the limited stability of some experimental structures upon solvent or guest removal. We also find that many of the hypothetical ZIFs proposed in the literature are not stable at room temperature. Mechanical and thermal stability criteria thus need to be considered for the prediction of new MOF structures. Finally, we predict a variety of thermal expansion behavior for ZIFs as a function of framework topology, with some materials showing large negative volume thermal expansion.

  2. Thermal barrier coating having high phase stability

    DOEpatents

    Subramanian, Ramesh

    2001-01-01

    A device (10) comprising a substrate (22) having a deposited ceramic thermal barrier coating layer (20) characterized by a microstructure having gaps (28) where the thermal barrier coating (20) consists essentially of a pyrochlore crystal structure having a chemical formula consisting essentially of A.sup.n+.sub.2-x B.sup.m+.sub.2+x O.sub.7-y, where A is selected from the group of elements selected from La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and mixtures thereof; where B is selected from the group of elements selected from Zr, Hf, Ti and mixtures thereof; n and m are the valence of A and B respectively, and for -0.5.ltoreq.x.ltoreq.0.5, ##EQU1## and excluding the following combinations for x=0, y=0: A=La and B=Zr; A=La and B=Hf; A=Gd and B=Hf; and A=Yb and B=Ti.

  3. Thermalization Time Bounds for Pauli Stabilizer Hamiltonians

    NASA Astrophysics Data System (ADS)

    Temme, Kristan

    2017-03-01

    We prove a general lower bound to the spectral gap of the Davies generator for Hamiltonians that can be written as the sum of commuting Pauli operators. These Hamiltonians, defined on the Hilbert space of N-qubits, serve as one of the most frequently considered candidates for a self-correcting quantum memory. A spectral gap bound on the Davies generator establishes an upper limit on the life time of such a quantum memory and can be used to estimate the time until the system relaxes to thermal equilibrium when brought into contact with a thermal heat bath. The bound can be shown to behave as {λ ≥ O(N^{-1} exp(-2β overline{ɛ}))}, where {overline{ɛ}} is a generalization of the well known energy barrier for logical operators. Particularly in the low temperature regime we expect this bound to provide the correct asymptotic scaling of the gap with the system size up to a factor of N -1. Furthermore, we discuss conditions and provide scenarios where this factor can be removed and a constant lower bound can be proven.

  4. A numerical study of the thermal stability of solar loops

    NASA Technical Reports Server (NTRS)

    Klimchuk, J. A.; Antiochos, S. K.; Mariska, J. T.

    1987-01-01

    An important property of all loops is their thermal stability. If low lying hot loops were thermally unstable, for example, a great majority of the low loops on the Sun might be expected to be cool. How small perturbations evolve in low lying, linearly unstable hot loops was determined and how high lying, linearly stable hot loops respond to large amplitude disturbances such as might be expected on the Sun were examined. Only general descriptions and results are given.

  5. Synthesis and thermal stability of carborane containing phosphazenes

    NASA Technical Reports Server (NTRS)

    Fewell, L. L.; Basi, R. J.; Parker, J. A.

    1983-01-01

    Carborane substituted polyphosphazenes were prepared by the thermal polymerization of phenyl-carboranyl penta chlorocyclotriphosphazene. Successive isothermal vacuum pyrolyses were conducted on the polymer and examined for structural changes by infrared spectroscopy. The degradation products were ascertained by gas chromatography-mass spectrometric analysis. It was found that the presence of the carborane group improves the thermal stability of the polymer by retarding the ring chain equilibrium processes of decomposition.

  6. Local Topological Order Inhibits Thermal Stability in 2D

    NASA Astrophysics Data System (ADS)

    Landon-Cardinal, Olivier; Poulin, David

    2013-03-01

    We study the robustness of quantum information stored in the degenerate ground space of a local, frustration-free Hamiltonian with commuting terms on a 2D spin lattice. On one hand, a macroscopic energy barrier separating the distinct ground states under local transformations would protect the information from thermal fluctuations. On the other hand, local topological order would shield the ground space from static perturbations. Here we demonstrate that local topological order implies a constant energy barrier, thus inhibiting thermal stability.

  7. Thermal Stability Analysis for a Heliocentric Gravitational Radiation Detection Mission

    NASA Technical Reports Server (NTRS)

    Folkner, W.; McElroy, P.; Miyake, R.; Bender, P.; Stebbins, R.; Supper, W.

    1994-01-01

    The Laser Interferometer Space Antenna (LISA) mission is designed for detailed studies of low-frequency gravitational radiation. The mission is currently a candidate for ESA's post-Horizon 2000 program. Thermal noise affects the measurement in at least two ways. Thermal variation of the length of the optical cavity to which the lasers are stabilized introduces phase variations in the interferometer signal, which have to be corrected for by using data from the two arms separately.

  8. Thermal stability of corrugated epitaxial graphene grown on Re(0001).

    PubMed

    Miniussi, E; Pozzo, M; Baraldi, A; Vesselli, E; Zhan, R R; Comelli, G; Menteş, T O; Niño, M A; Locatelli, A; Lizzit, S; Alfè, D

    2011-05-27

    We report on a novel approach to determine the relationship between the corrugation and the thermal stability of epitaxial graphene grown on a strongly interacting substrate. According to our density functional theory calculations, the C single layer grown on Re(0001) is strongly corrugated, with a buckling of 1.6 Å, yielding a simulated C 1s core level spectrum which is in excellent agreement with the experimental one. We found that corrugation is closely knit with the thermal stability of the C network: C-C bond breaking is favored in the strongly buckled regions of the moiré cell, though it requires the presence of diffusing graphene layer vacancies.

  9. Optimal control theory applied to fusion plasma thermal stabilization

    SciTech Connect

    Sager, G.; Maya, I.; Miley, G.H.

    1985-07-01

    Optimal control theory is applied to determine feedback control for thermal stability of a driven, subingnition tokamak controlled by fuel injection and additional heating. It was found that the simplifications of the plasma burn dynamics and the control figure of merit required for the synthesis of optimal feedback laws were valid. Control laws were determined which allowed thermal stability in plasmas subject to 10% offset in temperature. The minimum ignition margin (defined as the difference between ignition temperature and the subignition operating point) was found to be 0.95 keV, corresponding to steady state heating requirements of less than 2% of fusion power.

  10. Enhanced thermal stability of Ag nanorods through capping

    SciTech Connect

    Bachenheimer, Lou; Elliott, Paul; Stagon, Stephen; Huang, Hanchen

    2014-11-24

    Ag nanorods may serve as sensors in the detection of trace amounts of chemical agents, even single molecules, through surface enhanced Raman spectroscopy (SERS). However, thermal coarsening of Ag nanorods near room temperature limits their applications. This letter proposes the use of a thin oxide capping layer to enhance the thermal stability of Ag nanorods beyond 100 °C. Using electron microscopy characterization and SERS tests, the authors show that the proposed method is effective in stabilizing both morphology and sensitivity of Ag nanorods. The results of this work extend the applicability of Ag nanorods as chemical sensors to higher temperatures.

  11. Effects of sugars on the thermal stability of a protein

    NASA Astrophysics Data System (ADS)

    Oshima, Hiraku; Kinoshita, Masahiro

    2013-06-01

    It is experimentally known that the heat-denaturation temperature of a protein is raised (i.e., its thermal stability is enhanced) by sugar addition. In earlier works, we proposed a physical picture of thermal denaturation of proteins in which the measure of the thermal stability is defined as the solvent-entropy gain upon protein folding at 298 K normalized by the number of residues. A multipolar-model water was adopted as the solvent. The polyatomic structures of the folded and unfolded states of a protein were taken into account in the atomic detail. A larger value of the measure implies higher thermal stability. First, we show that the measure remains effective even when the model water is replaced by the hard-sphere solvent whose number density and molecular diameter are set at those of real water. The physical picture is then adapted to the elucidation of the effects of sugar addition on the thermal stability of a protein. The water-sugar solution is modeled as a binary mixture of hard spheres. The thermal stability is determined by a complex interplay of the diameter of sugar molecules dC and the total packing fraction of the solution η: dC is estimated from the volume per molecule in the sugar crystal and η is calculated using the experimental data of the solution density. We find that the protein is more stabilized as the sucrose or glucose concentration becomes higher and the stabilization effect is stronger for sucrose than for glucose. These results are in accord with the experimental observations. Using a radial-symmetric integral equation theory and the morphometric approach, we decompose the change in the measure upon sugar addition into two components originating from the protein-solvent pair and protein-solvent many-body correlations, respectively. Each component is further decomposed into the excluded-volume and solvent-accessible-surface terms. These decompositions give physical insights into the microscopic origin of the thermal-stability

  12. Unusual Thermal Stability of High-Entropy Alloy Amorphous Structure

    DTIC Science & Technology

    2012-06-20

    1    REPORT Unusual Thermal Stability of High - Entropy Alloy Amorphous Structure Basic research for AOARD 114009 Award No. FA2386-11-1...stability of high - entropy alloy amorphous structure 5a. CONTRACT NUMBER FA23861114009 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) Jien-Wei...at least 3 h. If substrate effect could be eliminated, the crystallization temperature would be higher. 15. SUBJECT TERMS high entropy alloys 16

  13. A Novel Test Method for Fuel Thermal Stability

    DTIC Science & Technology

    1993-02-01

    H., Knight, K., Bates, S.C., Solomon, P.R., "in-Situ FT-IR Diagnostics for Coal Liquefaction Processes," Final Report to U.S. DOE, under Contract No... supercritical fuels, and development of on-board fuel stability monitors. 14. SUBJECT TERMS 15. NUMnER OF PAGES Thermal Stability, Aviation Fuels...capabilities and operation in a user’e manual. Make assessment of system capabilities for other applications such as : 1) evaluation of supercritical aviation

  14. Thermal stability of intralipid optical phantoms.

    PubMed

    Rowe, Philip I; Künnemeyer, Rainer; McGlone, Andrew; Talele, Sadhana; Martinsen, Paul; Oliver, Richard

    2013-08-01

    We investigated the stability of light transmission through Intralipid-based optical phantoms in the wavelength range of 400-950 nm at temperatures between 35 and 70 °C. Optical phantoms are materials commonly used to simulate the light scattering and absorption properties of biological materials. These simulations require the phantom to be optically stable. We demonstrate that the scattering properties of Intralipid remain stable at higher temperatures, varying less than 0.5%. We also present results that show this is not the case for absorption below 700 nm at 35 and 70 °C, with greater instability at 70 °C. For example, at 500 nm, the light intensity transmitted through 15 mm of Intralipid dropped 39% over 12 h. We demonstrate that oxidation of fatty acids in Intralipid could account for this effect and show, by flushing the system continuously with nitrogen gas, the instability is reduced.

  15. Thermal stability comparison of nanocrystalline Fe-based binary alloy pairs

    SciTech Connect

    Clark, Blythe G.; Hattar, Khalid Mikhiel; Marshall, Michael Thomas; Chookajorn, Tonghai; Boyce, Brad L.; Schuh, Christopher A.

    2016-03-24

    Here, the widely recognized property improvements of nanocrystalline (NC) materials have generated significant interest, yet have been difficult to realize in engineering applications due to the propensity for grain growth in these interface-dense systems. While traditional pathways to thermal stabilization can slow the mobility of grain boundaries, recent theories suggest that solute segregation in NC alloy can reduce the grain boundary energy such that thermodynamic stabilization is achieved. Following the predictions of Murdock et al., here we compare for the first time the thermal stability of a predicted NC stable alloy (Fe-10at.% Mg) with a predicted non-NC stable alloy (Fe-10at.% Cu) using the same processing and characterization methodologies. Results indicate improved thermal stability of the Fe-Mg alloy in comparison to the Fe-Cu, and observed microstructures are consistent with those predicted by Monte Carlo simulations.

  16. Thermal stability comparison of nanocrystalline Fe-based binary alloy pairs

    DOE PAGES

    Clark, Blythe G.; Hattar, Khalid Mikhiel; Marshall, Michael Thomas; ...

    2016-03-24

    Here, the widely recognized property improvements of nanocrystalline (NC) materials have generated significant interest, yet have been difficult to realize in engineering applications due to the propensity for grain growth in these interface-dense systems. While traditional pathways to thermal stabilization can slow the mobility of grain boundaries, recent theories suggest that solute segregation in NC alloy can reduce the grain boundary energy such that thermodynamic stabilization is achieved. Following the predictions of Murdock et al., here we compare for the first time the thermal stability of a predicted NC stable alloy (Fe-10at.% Mg) with a predicted non-NC stable alloy (Fe-10at.%more » Cu) using the same processing and characterization methodologies. Results indicate improved thermal stability of the Fe-Mg alloy in comparison to the Fe-Cu, and observed microstructures are consistent with those predicted by Monte Carlo simulations.« less

  17. Thermal stability of phenolic based binders and frictional performance of brake composite materials

    NASA Astrophysics Data System (ADS)

    Pudhota, Madhuri

    To enhance frictional performance, wear and to obtain improved thermal stability with a reduction of noise, vibration, and harshness (NVH) and provide environment friendly brakes for the increasing needs of the population's comfort and safety requirements this study was initiated. The thermal stability of two different phenolic resins as binder on the frictional performance of brake composite material was studied. The two phenolic resins used are Durite phenolic resin and Bakelite phenolic resins. They were tested for friction, wear, thermal stability and degradation. This was executed by using a universal friction tester (UFT) for testing friction and wear, then on thermo gravimetric analysis (TGA) and the TGA results indicate more mass loss of NB samples contrary to test results. When individual materials were heated, Bakelite lost less mass compared to Durite. The friction test indicates more friction when used the NB samples but they had less wear and more stability nevertheless this could vary for other compositions and conditions.

  18. The thermal stability of organic acids in sedimentary basins

    SciTech Connect

    Crossey, L.J. )

    1991-03-01

    Water-soluble organic compounds in subsurface brines directly affect the evolution of porosity and permeability during sedimentary diagenesis. Recent examination of the aqueous thermal degradation of oxalic acid (a naturally occurring dicarboxylic acid) and its anions has implications for the thermal stability of dicarboxylic acids under sedimentary basin conditions. Because the thermal stability of these compounds is pH-dependent, consideration of the dissociation behavior of carboxylic acids as a function of temperature is essential for estimating the longevity of difunctional carboxylic acids. Results of burial history models suggest that dicarboxylic acid species may be long-lived in formation waters. Comparison with other experimental studies of carboxylic acids and their anion indicates that acetate stability is greater than formate stability, which is greater than oxalate stability, which is greater than gallate and malonate stability. In addition to the implications of natural systems, the aqueous degradation behavior is critical in evaluating other types of experimental results; notably mineral dissolution studies performed at elevated temperatures in the presence of organic materials and hydrous pyrolysis experiments involving kerogens.

  19. Thermal stability of ceramic coated thermal protection materials in a simulated high-speed earth entry

    NASA Technical Reports Server (NTRS)

    Stewart, David A.; Leiser, Daniel B.

    1988-01-01

    The dimensional stability of ceramic coated thermal protection materials developed for use on advanced entry vehicles is evaluated. Dimensional stability of these ceramic materials were studied as a function of temperature and pressure during exposure to simulated atmospheric entry in an arc-jet facility.

  20. Thermal stabilization of glucose oxidase and glucoamylase by physical entrapment.

    PubMed Central

    Basaveswara Rao, V; Sastri, N V; Subba Rao, P V

    1981-01-01

    Physical entrapment was used as an approach to achieve thermal stabilization of enzymes. The t 1/2 values for the thermoinactivation of glucose oxidase and glucoamylase were increased several-fold by their entrapment in polyacrylamide gels. In polyacrylate gels the individual enzymes behaved differently, probably owing to microenvironmental effects arising by the polyelectrolyte nature of the carrier. PMID:6796045

  1. Substituted silane-diol polymers have improved thermal stability

    NASA Technical Reports Server (NTRS)

    Byrd, J. D.; Curry, J. E.

    1966-01-01

    Organosilicon polymers were synthesized to produce improved physical and chemical properties, including high thermal stability. Of the polymers produced, poly/4, 4 prime-bisoxybi- phenylene/diphenylsilane, formed from bis/anilino/diphenylsilane and p, p prime-biphenol, was found to have the most desirable properties.

  2. Boundary lubrication, thermal and oxidative stability of a fluorinated polyether and a perfluoropolyether triazine

    NASA Technical Reports Server (NTRS)

    Jones, W. R., Jr.; Snyder, C. E., Jr.

    1979-01-01

    Boundary lubricating characteristics, thermal stability, and oxidation-corrosion stability were determined for a fluorinated polyether and a perfluoropolyether triazine. A ball-on-disk apparatus, a tensimeter, and oxidation-corrosion apparatus were used. Results were compared to data for a polyphenyl ether and a C-ether. The polyether and triazine yielded better boundary lubricating characteristics than either the polyphenyl ether or C-ether. The polyphenyl ether had the greatest thermal stability (443 C) while the other fluids had stabilities in the range 389 to 397 C. Oxidation-corrosion results indicated the following order of stabilities: perfluoropolyether trizine greater than polyphenyl ether greater than C-ether greater than fluorinated polyether.

  3. RP-1 and JP-8 Thermal Stability Experiments

    NASA Technical Reports Server (NTRS)

    Brown, Sarah P.; Emens, Jessica M.; Frederick, Robert A., Jr.

    2005-01-01

    This work experimentally investigates the effect of fuel composition changes on jet and rocket fuel thermal stability. A High Reynolds Number Thermal Stability test device evaluated JP-8 and RP-1 fuels. The experiment consisted of an electrically heated, stainless steel capillary tube with a controlled fuel outlet temperature. An optical pyrometer monitored the increasing external temperature profiles of the capillary tube as deposits build inside during each test. Multiple runs of each fuel composition provided results on measurement repeatability. Testing a t two different facilities provided data on measurement reproducibility. The technique is able to distinguish between thermally stable and unstable compositions of JP-8 and intermediate blends made by combining each composition. The technique is also able to distinguish among standard RP-1 rocket fuels and those having reduced sulfur levels. Carbon burn off analysis of residue in the capillary tubes on the RP-1 fuels correlates with the external temperature results.

  4. Thermal stability of sintered and bonded rare-earth magnets

    NASA Astrophysics Data System (ADS)

    Kato, Yoshio

    1999-04-01

    One of most important issues of magnets for automobiles is thermal stability. The aim of the present work is to make clear the available temperature limit of sintered and bonded magnets for automobile applications. Thermal stability was determined by the critical temperature of 3% irreversible flux loss (T-3%φ) under thermal cycles. For instance, the T-3%φ of sintered NdFeB magnets (Pc=0.5) with the intrinsic coercivity of 1600, 1920, and 2240 kA/m, were 393, 423, and 453 K, respectively. On the other hand, the T-3%φ of HDDR-NdFeB (HcJ=960 kA/m) and SmFeN (HcJ=560 kA/m) bonded magnets (Pc=2) were about 353 K.

  5. Effect of some nitrogen compounds thermal stability of jet A

    NASA Technical Reports Server (NTRS)

    Antoine, A. C.

    1982-01-01

    The effect of known concentrations of some nitrogen containing compounds on the thermal stability of a conventional fuel, namely, Jet A was investigated. The concentration range from 0.01 to 0.1 wt% nitrogen was examined. Solutions were made containing, individually, pyrrole, indole, quinoline, pyridine, and 4 ethylpyridine at 0.01, 0.03, 0.06, and 0.1 wt% nitrogen concentrations in Jet A. The measurements were all made by using a standard ASTM test for evaluating fuel thermal oxidation behavior, namely, ASTM D3241, 'thermal oxidation stability of turbine fuels (JFTOT procedure).' Measurements were made at two temperature settings, and 'breakpoint temperatures' were determined. The results show that the pyrrole and indole solutions have breakpoint temperatures substantially lower than those of the Jet A used.

  6. Thermal analysis and stability of commercially available endodontic obturation materials.

    PubMed

    Roberts, H W; Kirkpatrick, T C; Bergeron, B E

    2017-02-10

    The purpose of this study was to evaluate the thermal stability of 23 commercially-available endodontic obturation materials. Specimens (n = 10) were sealed in aluminum differential scanning calorimetry (DSC) crucibles and subjected to thermal scan series consisting of a 25 to 70 °C at 5 °C/min followed by a rapid increase to 230 °C, followed by a second scan from 25 to 70 °C at 5 °C/min. The first scan evaluated the materials as-received followed by a worse-case-scenario thermal challenge simulating temperatures involved with warm vertical condensation obturation techniques. The second thermal scan observed any phase changes from the high temperature challenge. This two-scan process was repeated twice to observe changes encountered by repeat high heat exposure during obturation. Mean thermal enthalpies were analyzed with Kruskal-Wallis and Games-Howell post-hoc test. (p = 0.05). Thermal behavior was material dependent. During the first thermal scan, materials typically demonstrated broad endothermic enthalpy curves suggesting either a gutta-percha phase mixture and/or an alpha crystalline phase. The first high-heat challenge produced definitive alpha/beta thermal phase signatures usually associated with gutta-percha. Changes in beta-phase enthalpies were noted with Therarmafil Plus and UltraFil Firmset while increase in alpha-phases was observed with GuttaCore, K3, Lexicon, and Schein Accessory Points. Commercial endodontic gutta-percha obturation materials displayed thermal characteristics that were material dependent. However, all demonstrated stability at temperatures in excess to that experienced during warm vertical condensation techniques. The gutta-percha obturation materials evaluated in this evaluation can be used successfully in warm vertical condensation techniques without fear of degradation.

  7. Evaluation of Next Generation Thermal Stability-Improving Additives for JP-8, Phase 1, Thermal Stability Impact Characterization

    DTIC Science & Technology

    2012-04-01

    thermal stability effects. The FCOC represents the engine lube oil cooler. It consists of an induction heater and a steel manifold with three 3/8” tubes...2 3.3.3.3. Fuel-Cooled Oil Cooler (FCOC...and P47 ..............................27 Figure 28. Fuel Cooled Oil Cooler Carbon Deposition

  8. Organic underlayer materials with exceptionally high thermal stability

    NASA Astrophysics Data System (ADS)

    Cheon, Hwan-Sung; Yoon, Kyong-Ho; Kim, Min-Soo; Oh, Sung Bae; Song, Jee-Yun; Tokareva, Nataliya; Kim, Jong-Seob; Chang, Tuwon

    2009-03-01

    Multilayer hardmask (MLHM) schemes have been implemented as an indispensable process for ArF lithography which continues to demand thinner photoresist films. There are many variations of MLHM and semiconductor manufacturers choose to adopt their own designs, depending on their specific needs and technical advances. The quad-layer stack consisting of photoresist, organic ARC, CVD Si hardmask, and spin-on carbon underlayer is one of them. Despite the need for wafer transporting between the spin track and CVD equipment, this scheme is attractive because it can avoid laborious elaboration of sophisticated etching chemistries for spin-on Si-ARC and carbon underlayer. One of the issues arising from the mixed film forming process is the thermal stability of carbon underlayer at high temperatures during the CVD process of the Si hardmask. Organic underlayer which shows high thermal stability is crucial for this mixed hardmask process. These types of thermally stable organic film can also be used for other applications such as the spacer patterning technique for pitch size shrinkage. In this paper, we discuss the development of organic resins with high thermal stability, their physical properties, and their lithographic behaviors in the MLHM schemes.

  9. Interplay between Protein Thermal Flexibility and Kinetic Stability.

    PubMed

    Quezada, Andrea G; Díaz-Salazar, A Jessica; Cabrera, Nallely; Pérez-Montfort, Ruy; Piñeiro, Ángel; Costas, Miguel

    2017-01-03

    Kinetic stability is a key parameter to comprehend protein behavior and it plays a central role to understand how evolution has reached the balance between function and stability in cell-relevant timescales. Using an approach that includes simulations, protein engineering, and calorimetry, we show that there is a clear correlation between kinetic stability determined by differential scanning calorimetry and protein thermal flexibility obtained from a novel method based on temperature-induced unfolding molecular dynamics simulations. Thermal flexibility quantitatively measures the increment of the conformational space available to the protein when energy in provided. The (β/α)8 barrel fold of two closely related by evolution triosephosphate isomerases from two trypanosomes are used as model systems. The kinetic stability-thermal flexibility correlation has predictive power for the studied proteins, suggesting that the strategy and methodology discussed here might be applied to other proteins in biotechnological developments, evolutionary studies, and the design of protein based therapeutics.

  10. The thermal stability of amorphous nickel-niobium alloys

    SciTech Connect

    Farrens, S.N.

    1989-01-01

    Amorphous metallic alloys have been found to have features that make them exciting candidate materials for the electron device industry. Some of these features include resistance to electromigration and interdiffusion with other component materials. These features are primarily the result of the absence of grain boundaries in the amorphous alloy. However, if these materials are to be used in devices exposed to elevated temperatures it is important to understand the thermal stability of the amorphous alloy. The thermal stability of amorphous nickel niobium alloys was investigated in this work. The assessment of thermal performance was based on crystallization temperature, diffusion properties, and interface stability of the amorphous alloys with metallic overlayers and silicon substrates. Thermal treatments spanned the temperature range from 400{degree}C to 850{degree}C for times of 5 minutes to 96 hours. The primary experimental methods included x-ray diffraction, Rutherford backscattering spectroscopy, and electron microscopy. The alloys studied had compositions of 60, 65, 70 and 75 atomic percent nickel and are listed in order of their thermal stability. The 60 at% alloys have the highest one hour crystallization temperatures of 700{degree}C. All alloys are very stable until crystallization occurs. This is evidenced by the sluggish diffusion rates (10{sup {minus}19} cm{sup 2}/sec) measured at the overlayer/glass interface. Similarly, substrate interactions are not observed until crystallization has began. Once the grain boundaries develop with the initiation of crystallization interdiffusion of Ni and Si proceeds and eventual silicide formation is observed. Combining the results of the silicide reaction kinetics and the x-ray diffraction data allowed the estimation of the time-temperature-transformation curve.

  11. Changes in the Thermal and Dimensional Stability of the Structure of a Polymer Composite After Carbonization

    NASA Astrophysics Data System (ADS)

    Gaidachuk, V. E.; Kondratiev, A. V.; Chesnokov, A. V.

    2017-01-01

    Based on the theory of reinforcement of polymer composites, approximate relations for the physicomechanical and strength properties of a carbon-carbon composite material are synthesized, which are used to perform a finite-element analysis of the degree and character of changes in the thermal and dimensional stability of its structure after carbonization. Using approximate criteria of structural optimization of carbon-carbon composites ensuring their maximum dimensional stability, a [0/±45/90] package of thermally nonquilibrium layers is investigated and compared with an analogous carbon-fiber-reinforced plastic.

  12. Deformation-enhanced thermal stability of an amorphous Fe80B20 alloy

    NASA Astrophysics Data System (ADS)

    Fan, G. J.; Quan, M. X.; Hu, Z. Q.

    1996-11-01

    By means of differential scanning calorimeter (DSC) measurements, the thermal stability of an amorphous Fe80B20 alloy after various periods of low-energy ball milling has been studied. The results indicate that the thermal stability of the amorphous Fe80B20 ribbons can be enhanced upon mechanical deformation with a low milling intensity. The crystallization temperature Tp, the crystallization enthalpy ΔH, and the crystallization activation energy Ex increase with milling time. The above observations will be compared with our previous findings that extensive mechanical deformation with a high milling intensity can otherwise induce a structural relaxation in an amorphous Fe80B20 alloy. Based on conventional thermodynamic and kinetic arguments, a reasonable interpretation will be made to explain the enhanced thermal stability of the amorphous Fe80B20 alloy after mechanical deformation.

  13. Modifications to improve entrance slit thermal stability for grasshopper monochromators

    NASA Astrophysics Data System (ADS)

    Wallace, Daniel J.; Rogers, Gregory C.; Crossley, Sherry L.

    1994-08-01

    As new monochromators are designed for high-flux storage rings, computer modeling and thermal engineering can be done to process increased heat loads and achieve mechanical stability. Several older monochromators, such as the Mark 2 and Mark 5 Grasshopper monochromators, which were designed in 1974, have thermal instabilities in their entrance slit mechanisms. The Grasshoppers operating with narrow slits experience closure of the entrance slit from thermal expansion. In extreme cases, the thermal expansion of the precision components has caused permanent mechanical damage, leaving the slit uncalibrated and/or inoperable. For the Mark 2 and Mark 5 Grasshopper monochromators at the Synchrotron Radiation Center, the original 440 stainless steel entrance slit jaws were retrofitted with an Invar (low expansion Fe, Ni alloy) slit jaw. To transfer the heat from the critical components, two flexible heat straps of Cu were attached. These changes allow safe operation with a 10 μm entrance slit width where the previous limit was 30 μm. After an initial 2 min equilibration, the slit remains stable to 10%, with 100 mA of beam current. Additional improvements in slit thermal stability are planned for a third Grasshopper.

  14. Thermal stability of nanocrystalline layers fabricated by surface nanocrystallization

    NASA Astrophysics Data System (ADS)

    Mai, Yong-jin; Jie, Xiao-hua; Liu, Li-li; Yu, Neng; Zheng, Xiang-xin

    2010-01-01

    A nanocrystalline layer with ultrafine grains (about 30-40 nm) on the surface of 7050 aluminum alloy was fabricated by a new technique called High Pressure Shot Peening (HPSP) which is the combination of common Shot Peening equipment with a pressurizing vessel. Relationship between hot flow and temperature was observed by Differential Scanning Calorimetry (DSC) and the activation energy, calculated by Kisssinger equation, of the as-treated sample increased 26.6 kJ/mol when it is compared with the as-reserved sample. The Bragg peaks of the as-prepared samples, respectively treated with various annealing treatments were characterized by XRD and the microhardness distribution along the depth from the treated surface were measured at the same time, which indicated that the broadening of Bragg peaks decreased with the increasing of anneal temperature; the grain size, calculated by Scherrer-Wilson equation, increased obviously during 180-220 °C, accordingly, the microhardness obviously decreased. According to the results of DSC, XRD and microhardness, it is reasonable to deduce that the temperature range of thermal stability for aluminum alloy nanocrystalline layer is lower than 200 °C.

  15. Thermal stabilization of low level RF distribution systems at SLAC

    SciTech Connect

    McCormick, D.; Ross, M.; Himel, T.; Spencer, N.

    1993-07-01

    Analysis of SLC accelerator operator activity, in particular control system knob turns, indicated poor thermal stability performance of the low level RF distribution system in the SLC injector and positron production complex. Daily drifts of up to 15 S-band delay, about 30 times the tolerance, were observed. In this paper we describe the tool used to track down and quantify operator knob turn activity, the low level RF distribution stabilization systems, and some fixes used to correct the problem. In order to identify poorly performing components, a beam timing or phase monitor diagonstic has been developed. Initial results from it will be presented.

  16. Thermal stability studies of Li-ion cells and components

    SciTech Connect

    Maleki, H.; Deng, G.; Anani, A.; Howard, J.

    1999-09-01

    A Li-ion cell consists of a carbon-based negative electrode (NE); a porous polymer membrane separator (high density polypropylene and/or polyethylene); and positive electrode (PE) containing lithium transition metal oxides (LiMo{sub 2}, M = Co, Ni, or Mn); and a mixture of lithium salt and organic solvents provides an electrolytic medium for Li-ions to shuttle between the PE and NE. Electrodes are produced by coating slurries of active PE or NE material, polymer binder, most commonly polyvinylidene difluoride (PVDF), and small amounts of high surface area carbon onto a metallic current collectors. Thermal stability of fully charged 550 mAh prismatic Li-ion cells (Sn-doped LiCoO{sub 2}/graphitic carbon) and their components are investigated. Accelerating rate calorimetry (ARC) is used to determine the onset temperature of exothermic chemical reactions that force the cell into thermal runaway. Differential scanning calorimetry (DSC) and thermogravimetry analysis are used to determine the thermal stability of the cell's positive electrode (PE) and negative electrode (NE) materials from 35 to 400 C. The cell self-heating exothermic reactions start at 123 C, and thermal runaway occurs near 167 C. The total exothermic heat generation of the NE and PE materials are 697 and 407 J/g, respectively. Heat generations of the NE and PE materials, washed in diethyl carbonate (DEC) and dried at {approx}65 C under vacuum, are significantly lower than unwashed samples. Lithium plating increases the heat generation of the NE material at temperatures near the lithium melting point. Comparison of the heat generation profiles from DSC and ARC tests indicates that thermal runaway of this cell is close to the decomposition temperature range of the unwashed PE material. The authors conclude that the heat generation from the decomposition of PE material and reaction of that with electrolyte initiates thermal runaway in a Li-ion cell, under thermally or abusive conditions.

  17. Stabilization of the ionization overheating thermal instability in atmospheric pressure microplasmas

    SciTech Connect

    Staack, D.; Farouk, B.; Gutsol, A.; Fridman, A.

    2009-07-01

    Stable direct current atmospheric pressure plasmas can regularly be generated in air using microplasma systems, and rapid cooling due to the small size is typically suggested as the thermally stabilizing mechanism. However, temperatures of the stable discharges are significantly higher than ambient, and stable operation is not easily achieved in all gases at similar sizes. Revisiting a traditional analysis of the thermal instability, we find that the inclusion of the simple ballasted external circuit in the analysis leads to additional stabilizing mechanisms. This stabilization occurs in microplasmas due to the characteristic times of the external circuit and the instability being comparable, which allows the electric field to change during the time frame of the instability. Experimentally this is implemented by reducing the stray capacitance of the external circuit. This stabilizing mechanism is verified in several gases and its application in a plasma enhanced chemical vapor deposition system leads to a more uniform film deposition.

  18. Thermal phase stability of some simulated Defense waste glasses

    SciTech Connect

    May, R.P.

    1981-04-01

    Three simulated defense waste glass compositions developed by Savannah River Laboratories were studied to determine viscosity and compositional effects on the comparative thermal phase stabilities of these glasses. The glass compositions are similar except that the 411 glasses are high in lithium and low in sodium compared to the 211 glass, and the T glasses are high in iron and low in aluminum compared to the C glass. Specimens of these glasses were heat treated using isothermal anneals as short as 10 min and up to 15 days over the temperature range of 450/sup 0/C to 1100/sup 0/C. Additionally, a specimen of each glass was cooled at a constant cooling rate of 7/sup 0/C/hour from an 1100/sup 0/C melt down to 500/sup 0/C where it was removed from the furnace. The following were observed. The slow cooling rate of 7/sup 0/C/hour is possible as a canister centerline cooling rate for large canisters. Accordingly, it is important to note that a short range diffusion mechanism like cooperative growth phenomena can result in extensive devitrification at lower temperatures and higher yields than a long-range diffusion mechanism can; and can do it without the growth of large crystals that can fracture the glass. Refractory oxides like CeO/sub 2/ and (Ni, Mn, Fe)/sub 2/O/sub 4/ form very rapidly at higher temperatures than silicates and significant yields can be obtained at sufficiently high temperatures that settling of these dense phases becomes a major microstructural feature during slow cooling of some glasses. These annealing studies further show that below 500/sup 0/C there is but little devitrification occurring implying that glass canisters stored at 300/sup 0/C may be kinetically stable despite not being thermodynamically so.

  19. Thermal Stability of Aqueous Polyurethanes Depending on the Applied Catalysts

    PubMed Central

    Cakic, Suzana; Nikolic, Goran; Lacnjevac, Caslav; Gligoric, Miladin; Stamenkovic, Jakov; Rajkovic, Milos B.; Barac, Miroljub

    2006-01-01

    The thermal stability of aqueous polyurethanes has been measured applying the thermogravimetric analysis. The aqueous polyurethanes (aqPUR) with catalysts of different selectivity have been studied by use of the dynamic method. To obtain degradations of 0.025, 0.05, and 0.10, employing the dynamic method, the heating rates of 0.5, 1, 2, 5, and 10 °C min-1 have been used in the range of 30-500 °C. Using the more selective catalysts in the aqueous polyurethanes, the total resulting time of the decompositon has been on the increase at all degrees of the degradation and at the particular starting temperature. This paper shows that the dynamic method based on the thermogravimetric analysis can be used to assess the thermal stability of the aqueous polyurethanes using the catalysts of different selectivity.

  20. Exceptional chemical and thermal stability of zeolitic imidazolate frameworks

    PubMed Central

    Park, Kyo Sung; Ni, Zheng; Côté, Adrien P.; Choi, Jae Yong; Huang, Rudan; Uribe-Romo, Fernando J.; Chae, Hee K.; O’Keeffe, Michael; Yaghi, Omar M.

    2006-01-01

    Twelve zeolitic imidazolate frameworks (ZIFs; termed ZIF-1 to -12) have been synthesized as crystals by copolymerization of either Zn(II) (ZIF-1 to -4, -6 to -8, and -10 to -11) or Co(II) (ZIF-9 and -12) with imidazolate-type links. The ZIF crystal structures are based on the nets of seven distinct aluminosilicate zeolites: tetrahedral Si(Al) and the bridging O are replaced with transition metal ion and imidazolate link, respectively. In addition, one example of mixed-coordination imidazolate of Zn(II) and In(III) (ZIF-5) based on the garnet net is reported. Study of the gas adsorption and thermal and chemical stability of two prototypical members, ZIF-8 and -11, demonstrated their permanent porosity (Langmuir surface area = 1,810 m2/g), high thermal stability (up to 550°C), and remarkable chemical resistance to boiling alkaline water and organic solvents. PMID:16798880

  1. Thermal stability of poly(3-hydroxybutyrate)/vegetable fiber composites

    NASA Astrophysics Data System (ADS)

    Cipriano, Pâmela Bento; de Sá, Mayelli Dantas; Andrade, André L. Simões; de Carvalho, Laura Hecker; Canedo, Eduardo Luis

    2015-05-01

    The present work deals with the thermal stability during and after processing of composites of poly(3-hydroxybutyrate) (PHB) - a fully biodegradable semi-crystalline thermoplastic obtained from renewable resources through low-impact biotechnological process, biocompatible and non-toxic - and vegetable fiber from the fruit (coconut) of babassu palm tree. PHB/babassu composites with 0, 5, 10 and 20% w/w load were prepared in a laboratory internal mixer. Two fractions of the mesocarp of babassu with different particle sizes were compounded with PHB and test specimens molded by compression. The effect of loading level and processing conditions on torque, temperature and mechanical energy dissipation were studied using a new engineering model. It was found that PHB degrades during processing at temperatures slightly above the melting point. To minimize thermal degradation stabilizer and chain extender additives were incorporated, with mixed results. These findings were confirmed by the dependence of the melt flow rate on the processing temperature.

  2. Determination of the thermal stability of perfluoropolyalkyl ethers by tensimetry

    NASA Technical Reports Server (NTRS)

    Helmick, Larry A.; Jones, William R., Jr.

    1992-01-01

    The thermal decomposition temperatures of several perfluoropolyalkyl ether fluids were determined with a computerized tensimeter. In general, the decomposition temperatures of the commercial fluids were all similar and significantly higher than those for noncommercial fluids. Correlation of the decomposition temperatures with the molecular structures of the primary components of the commercial fluids revealed that the stability of the fluids was not affected by carbon chain length, branching, or adjacent difluoroformal groups. Instead, stability was limited by the presence of small quantities of thermally unstable material and/or chlorine-containing material arising from the use of chlorine containing solvents during synthesis. Finally, correlation of decomposition temperatures with molecular weights for two fluids supports a chain cleavage reaction mechanism for one and an unzipping reaction mechanism for the other.

  3. On the thermal stability of coronal loop plasma

    NASA Technical Reports Server (NTRS)

    Antiochos, S. K.; Emslie, A. G.; Shoub, E. C.; An, C. H.

    1982-01-01

    The stability to thermal perturbation of static models of coronal loops is considered including the effects of cool, radiatively stable material at the loop base. The linear stability turns out to be sensitive only to the boundary conditions assumed on the velocity at the loop base. The question of the appropriate boundary conditions is discussed, and it is concluded that the free surface condition (the pressure perturbation vanishes), rather than the rigid wall (the velocity vanishes), is relevant to the solar case. The static models are found to be thermally unstable, with a growth time of the order of the coronal cooking time. The physical implications of these results for the solar corona and transition region are examined.

  4. Dependence of thermal stability of lithiated Si on particle size

    NASA Astrophysics Data System (ADS)

    Li, Chao; Shi, Tongfei; Li, Decheng; Yoshitake, Hideya; Wang, Hongyu

    2016-12-01

    Thermal properties of the component materials are key issues in lithium ion batteries (LIBs). Si-based anodes are one of the most promising materials, but its thermal evolution have received much less attention than its electrochemical performance. In this article, the thermal behavior of various of Si material has been studied by differential scanning calorimetry (DSC). Three kinds of Si-particles, ranging from nano-to micro-sizes was subject to thermal analysis. It has been found that the thermal stability increases with the rise in particle-size. For the nanoparticles of 20 nm, both characteristic peaks of A and B regions in the heating process are stronger than the large-diameter particles. For three kinds of Si particles, the starting temperature of thermal reaction demonstrates a similar trend, gradually becoming lower with the increasing of the lithiation extent. At last, the ex situ XPS has also been conducted to explore the causes of surface state after temperature elevation. In A region, the heating decomposition of SEI with electrolyte, mainly consisting of a variety of esterification compounds, produces high content of lithium carbonate below 180 °C. When lithium in the inner phase of Si particles loses the protection of SEI film, the severe exothermic reaction occurred between lithium and the solvent species.

  5. Flexible all-carbon photovoltaics with improved thermal stability

    SciTech Connect

    Tang, Chun; Ishihara, Hidetaka; Sodhi, Jaskiranjeet; Chen, Yen-Chang; Siordia, Andrew; Martini, Ashlie; Tung, Vincent C.

    2015-04-15

    The structurally robust nature of nanocarbon allotropes, e.g., semiconducting single-walled carbon nanotubes (SWCNTs) and C{sub 60}s, makes them tantalizing candidates for thermally stable and mechanically flexible photovoltaic applications. However, C{sub 60}s rapidly dissociate away from the basal of SWCNTs under thermal stimuli as a result of weak intermolecular forces that “lock up” the binary assemblies. Here, we explore use of graphene nanoribbons (GNRs) as geometrically tailored protecting layers to suppress the unwanted dissociation of C{sub 60}s. The underlying mechanisms are explained using a combination of molecular dynamics simulations and transition state theory, revealing the temperature dependent disassociation of C{sub 60}s from the SWCNT basal plane. Our strategy provides fundamental guidelines for integrating all-carbon based nano-p/n junctions with optimized structural and thermal stability. External quantum efficiency and output current–voltage characteristics are used to experimentally quantify the effectiveness of GNR membranes under high temperature annealing. Further, the resulting C{sub 60}:SWCNT:GNR ternary composites display excellent mechanical stability, even after iterative bending tests. - Graphical abstract: The incorporation of solvent resistant, mechanically flexible and electrically addressable 2-D soft graphene nanoribbons facilitates the assembly of photoconductive carbon nano-p/n junctions for thermally stable and flexible photovoltaic cells.

  6. Dispersion interactions govern the strong thermal stability of a protein.

    PubMed

    Vondrásek, Jirí; Kubar, Tomás; Jenney, Francis E; Adams, Michael W W; Kozísek, Milan; Cerný, Jirí; Sklenár, Vladimír; Hobza, Pavel

    2007-01-01

    Rubredoxin from the hyperthermophile Pyrococcus furiosus (Pf Rd) is an extremely thermostable protein, which makes it an attractive subject of protein folding and stability studies. A fundamental question arises as to what the reason for such extreme stability is and how it can be elucidated from a complex set of interatomic interactions. We addressed this issue first theoretically through a computational analysis of the hydrophobic core of the protein and its mutants, including the interactions taking place inside the core. Here we show that a single mutation of one of phenylalanine's residues inside the protein's hydrophobic core results in a dramatic decrease in its thermal stability. The calculated unfolding Gibbs energy as well as the stabilization energy differences between a few core residues follows the same trend as the melting temperature of protein variants determined experimentally by microcalorimetry measurements. NMR spectroscopy experiments have shown that the only part of the protein affected by mutation is the reasonably rearranged hydrophobic core. It is hence concluded that stabilization energies, which are dominated by London dispersion, represent the main source of stability of this protein.

  7. Applications of differential scanning calorimetry for thermal stability analysis of proteins: qualification of DSC.

    PubMed

    Wen, Jie; Arthur, Kelly; Chemmalil, Letha; Muzammil, Salman; Gabrielson, John; Jiang, Yijia

    2012-03-01

    Differential scanning calorimetry (DSC) has been used to characterize protein thermal stability, overall conformation, and domain folding integrity by the biopharmaceutical industry. Recently, there have been increased requests from regulatory agencies for the qualification of characterization methods including DSC. Understanding the method precision can help determine what differences between samples are significant and also establish the acceptance criteria for comparability and other characterization studies. In this study, we identify the parameters for the qualification of DSC for thermal stability analysis of proteins. We use these parameters to assess the precision and sensitivity of DSC and demonstrate that DSC is suitable for protein thermal stability analysis for these purposes. Several molecules from different structural families were studied. The experiments and data analyses were performed by different analysts using different instruments at different sites. The results show that the (apparent) thermal transition midpoint (T(m)) values obtained for the same protein by same and different instruments and/or analysts are quite reproducible, and the profile similarity values obtained for the same protein from the same instrument are also high. DSC is an appropriate method for assessing protein thermal stability and conformational changes.

  8. Scandia-and-Yttria-Stabilized Zirconia for Thermal Barriers

    NASA Technical Reports Server (NTRS)

    Mess, Derek

    2003-01-01

    yttria in suitable proportions has shown promise of being a superior thermal- barrier coating (TBC) material, relative to zirconia stabilized with yttria only. More specifically, a range of compositions in the zirconia/scandia/yttria material system has been found to afford increased resistance to deleterious phase transformations at temperatures high enough to cause deterioration of yttria-stabilized zirconia. Yttria-stabilized zirconia TBCs have been applied to metallic substrates in gas turbine and jet engines to protect the substrates against high operating temperatures. These coatings have porous and microcracked structures, which can accommodate strains induced by thermal-expansion mismatch and thermal shock. The longevity of such a coating depends upon yttria as a stabilizing additive that helps to maintain the zirconia in an yttria-rich, socalled non-transformable tetragonal crystallographic phase, thus preventing transformation to the monoclinic phase with an associated deleterious volume change. However, at a temperature greater than about 1,200 C, there is sufficient atomic mobility that the equilibrium, transformable zirconia phase is formed. Upon subsequent cooling, this phase transforms to the monoclinic phase, with an associated volume change that adversely affects the integrity of the coating. Recently, scandia was identified as a stabilizer that could be used instead of, or in addition to, yttria. Of particular interest are scandia-and-yttria-stabilized zirconia (SYSZ) compositions of about 6 mole percent scandia and 1 mole percent yttria, which have been found to exhibit remarkable phase stability at a temperature of 1,400 C in simple aging tests. Unfortunately, scandia is expensive, so that the problem becomes one of determining whether there are compositions with smaller proportions of scandia that afford the required high-temperature stability. In an attempt to solve this problem, experiments were performed on specimens made with reduced

  9. Graphene oxide immobilized enzymes show high thermal and solvent stability

    NASA Astrophysics Data System (ADS)

    Hermanová, Soňa; Zarevúcká, Marie; Bouša, Daniel; Pumera, Martin; Sofer, Zdeněk

    2015-03-01

    The thermal and solvent tolerance of enzymes is highly important for their industrial use. We show here that the enzyme lipase from Rhizopus oryzae exhibits exceptionally high thermal stability and high solvent tolerance and even increased activity in acetone when immobilized onto a graphene oxide (GO) nanosupport prepared by Staudenmaier and Brodie methods. We studied various forms of immobilization of the enzyme: by physical adsorption, covalent attachment, and additional crosslinking. The activity recovery was shown to be dependent on the support type, enzyme loading and immobilization procedure. Covalently immobilized lipase showed significantly better resistance to heat inactivation (the activity recovery was 65% at 70 °C) in comparison with the soluble counterpart (the activity recovery was 65% at 40 °C). Physically adsorbed lipase achieved over 100% of the initial activity in a series of organic solvents. These findings, showing enhanced thermal stability and solvent tolerance of graphene oxide immobilized enzyme, will have a profound impact on practical industrial scale uses of enzymes for the conversion of lipids into fuels.The thermal and solvent tolerance of enzymes is highly important for their industrial use. We show here that the enzyme lipase from Rhizopus oryzae exhibits exceptionally high thermal stability and high solvent tolerance and even increased activity in acetone when immobilized onto a graphene oxide (GO) nanosupport prepared by Staudenmaier and Brodie methods. We studied various forms of immobilization of the enzyme: by physical adsorption, covalent attachment, and additional crosslinking. The activity recovery was shown to be dependent on the support type, enzyme loading and immobilization procedure. Covalently immobilized lipase showed significantly better resistance to heat inactivation (the activity recovery was 65% at 70 °C) in comparison with the soluble counterpart (the activity recovery was 65% at 40 °C). Physically adsorbed

  10. Structural stability vs. thermal performance: old dilemma, new solutions

    SciTech Connect

    Kosny, J.; Christian, J.E.

    1996-10-01

    In many building envelopes, actual thermal performance falls quite a bit short of nominal design parameters given in standards. Very often only windows, doors, and a small part of the wall area meet standards requirements. In the other parts of the building envelope, unaccounted thermal bridges reduce the effective thermal resistance of the insulation material. Such unaccounted heat losses compromise the thermal performance of the whole building envelope. For the proper analysis of the thermal performance of most wall and roof details, measurements and three-dimensional thermal modeling are necessary. For wall thermal analysis the whole-wall R-value calculation method can be very useful. In ties method thermal properties of all wall details are incorporated as an area weighted average. For most wall systems, the part of the wall that is traditionally analyzed, is the clear wall, that is, the flat part of the wall that is uninterrupted by details. It comprises only 50 to 80% of the total area of the opaque wall. The remaining 20 to 50% of the wall area is not analyzed nor are its effects incorporated in the thermal performance calculations. For most of the wall technologies, traditionally estimated R-values are 20 to 30% higher than whole-wall R-values. Such considerable overestimation of wall thermal resistance leads to significant errors in building heating and cooling load estimations. In this paper several examples are presented of the use of the whole-wall R-value procedure for building envelope components. The advantages of the use of the whole wall R-value calculation procedure are also discussed. For several building envelope components, traditional clear-wall R-values are compared with the results of whole-wall thermal analysis to highlight significant limits on the use of the traditional methods and the advantages of advanced computer modeling.

  11. Thermal stability of hexagonal OsB{sub 2}

    SciTech Connect

    Xie, Zhilin; Blair, Richard G.; Orlovskaya, Nina; Cullen, David A.; Andrew Payzant, E.

    2014-11-15

    parameters and no phase changes detected during cooling. - Graphical abstract: The in situ high temperature XRD contour plot (A) and XRD patterns (B) of h-OsB{sub 2} upon heating and cooling under an argon atmosphere. - Highlights: • Different boron sources were compared for the synthesis of h-OsB{sub 2}. • The phase stability and thermal behavior of h-OsB{sub 2} were studied by in situ XRD. • Shrinkage of the a lattice parameter was observed from 276 °C to 426 °C upon heating. • Oxidation of OsB{sub 2} produced B vacancies led to the shrinkage of a lattice parameter.

  12. Effect of graphene oxide sheet size on the curing kinetics and thermal stability of epoxy resins

    NASA Astrophysics Data System (ADS)

    Wang, Xiao; Jin, Jie; Song, Mo; Lin, Yue

    2016-10-01

    This work revealed the influences of graphene oxide (GO) sheet size on the curing kinetics and thermal stability of epoxy resins. A series of GO/epoxy nanocomposites were prepared by the incorporation of three different sized GO sheets, namely GO-1, GO-2 and GO-3, the average size of which was 10.79 μm, 1.72 μm and 0.70 μm, respectively. The morphologies of the nanocomposites were observed by field emission gun scanning electron microscope. The dispersion quality of each sized GO was comparable in the epoxy matrix. The curing kinetics was investigated by means of differential scanning calorimetry and analyzed based on kinetics model. Addition of a small amount of GO (0.1 wt%) exhibited strong catalytic effect on the curing reaction of epoxy resin. The activation energy was reduced by 18.9%, 28.8% and 14.6% with addition of GO-1, GO-2 and GO-3, respectively. GO-2 with medium size (1.72 μm) showed the most effective catalysis on the cure. The thermal stability of the cured resins was evaluated based on thermogravimetric analysis. GO/epoxy nanocomposites showed improved thermal stability in the range of 420 °C-500 °C, compared with the pure resin. A ˜ 4% more residue was obtained in each of the incorporated system. The variations of GO sheet size did not influence the enhancement effect on the thermal stability.

  13. Thermal Stability of RP-2 for Hydrocarbon Boost Regenerative Cooling

    NASA Technical Reports Server (NTRS)

    Kleinhenz, Julie E.; Deans, Matthew C.; Stiegemeier, Benjamin R.; Psaras, Peter M.

    2013-01-01

    A series of tests were performed in the NASA Glenn Research Centers Heated Tube Facility to study the heat transfer and thermal stability behavior of RP-2 under conditions similar to those found in rocket engine cooling channels. It has long been known that hydrocarbon fuels, such as RP-2, can decompose at high temperature to form deposits (coke) which can adversely impact rocket engine cooling channel performance. The heated tube facility provides a simple means to study these effects. Using resistively heated copper tubes in a vacuum chamber, flowing RP-2 was heated to explore thermal effects at a range of test conditions. Wall temperature (850-1050F) and bulk fluid temperature (300-500F) were varied to define thermal decomposition and stability at each condition. Flow velocity and pressure were fixed at 75 fts and 1000 psia, respectively. Additionally, five different batches of RP-2 were tested at identical conditions to examine any thermal stability differences resulting from batch to batch compositional variation. Among these tests was one with a potential coke reducing additive known as 1,2,3,4-Tetrahydroquinoline (THQ). While copper tubes were used for the majority of tests, two exploratory tests were performed with a copper alloy known as GRCop-42. Each tube was instrumented with 15 thermocouples to examine the temperature profile, and carbon deposition at each thermocouple location was determined post-test in an oxidation furnace. In many tests, intermittent local temperature increases were observed visually and in the thermocouple data. These hot spots did not appear to correspond with a higher carbon deposition.

  14. General stability analysis of composite sandwich plates under thermal load

    NASA Astrophysics Data System (ADS)

    Abdallah, Shaher A.

    In structures subjected to high temperature change such as high-speed aircraft the panels are stressed more significantly under thermal loading than mechanical loading. This can produce instability within the structure; therefore, the thermal loading may become the primary factor in the design of the structure. For example, buckling and facesheet wrinkling are two major failure modes of the composite sandwich plates subjected to various loadings. The goal of this dissertation is to study the stability analysis of composite sandwich plates due to buckling and wrinkling subjected to thermal loading. The primary objective is to find out the critical failure mode and the associated critical temperature change causing it. For thermal buckling and wrinkling analysis, the critical temperature change Delta Tcr, is of more interest than the critical thermal load. In this study, two different approaches of the stability problem of the composite sandwich plate subjected to thermally induced load are developed. In the first approach, the wrinkling analysis and buckling analysis are performed separately to evaluate their associated critical wrinkling and buckling temperature changes. For the face-wrinkling problem, two different models, the linear decaying Hoff model and exponential decaying Chen model are employed. The global buckling analysis is based on the energy method. The second approach is based on the unified theory of Benson and Mayers. In such an approach, the critical temperature change for both the global buckling and face wrinkling can be evaluated simultaneously. A potential energy based variation principle has been applied to formulate the problem. The Lagrange multipliers are used to satisfy the face-core continuity conditions. The buckling and wrinkling can be analyzed and calculated simultaneously. Therefore, the critical wrinkling temperature and the critical buckling temperature are found in a single analysis. The critical buckling and wrinkling stresses

  15. Three-dimensional self-assembled photonic crystals with high temperature stability for thermal emission modification

    NASA Astrophysics Data System (ADS)

    Arpin, Kevin A.; Losego, Mark D.; Cloud, Andrew N.; Ning, Hailong; Mallek, Justin; Sergeant, Nicholas P.; Zhu, Linxiao; Yu, Zongfu; Kalanyan, Berç; Parsons, Gregory N.; Girolami, Gregory S.; Abelson, John R.; Fan, Shanhui; Braun, Paul V.

    2013-10-01

    Selective thermal emission in a useful range of energies from a material operating at high temperatures is required for effective solar thermophotovoltaic energy conversion. Three-dimensional metallic photonic crystals can exhibit spectral emissivity that is modified compared with the emissivity of unstructured metals, resulting in an emission spectrum useful for solar thermophotovoltaics. However, retention of the three-dimensional mesostructure at high temperatures remains a significant challenge. Here we utilize self-assembled templates to fabricate high-quality tungsten photonic crystals that demonstrate unprecedented thermal stability up to at least 1,400 °C and modified thermal emission at solar thermophotovoltaic operating temperatures. We also obtain comparable thermal and optical results using a photonic crystal comprising a previously unstudied material, hafnium diboride, suggesting that refractory metallic ceramic materials are viable candidates for photonic crystal-based solar thermophotovoltaic devices and should be more extensively studied.

  16. Thermal stability of spent coffee ground polysaccharides: galactomannans and arabinogalactans.

    PubMed

    Simões, Joana; Maricato, Elia; Nunes, Fernando M; Domingues, M Rosário; Coimbra, Manuel A

    2014-01-30

    In order to better understand the thermal stability of spent coffee grounds (SCG) galactomannans and arabinogalactans and the reactions that can occur upon roasting, long term isothermal exposures, up to 3h, were performed at 160, 180, 200, 220, and 240 °C. The resultant products were analysed according to the sugars and linkage composition and also by electrospray mass spectrometry. Galactomannans did not loss mass at T ≤ 200 °C during exposures up to 3h whereas the arabinogalactans showed that thermal stability only for T ≤ 180 °C. This was in accordance with the estimated activation energies of their thermal decomposition of 138 kJ/mol and 94 kJ/mol, respectively. The roasting of galactomannans promoted the formation of new glycosidic linkages, with occurrence of 2-, 6-, 2,3-, 2,6-, 3,6-, 2,3,6-, 3,4,6-linked mannose residues, 3,4,6-linked galactose residues, and terminally-linked glucose residues, observed by methylation analysis. Depolymerisation and formation of anhydrohexose residues at the reducing end and mannose-glucose isomerisation were also observed. The roasting of galactomannans at 200 °C promoted their solubility in water upon alkali extraction and neutralisation.

  17. Autoxidation of jet fuels: Implications for modeling and thermal stability

    SciTech Connect

    Heneghan, S.P.; Chin, L.P.

    1995-05-01

    The study and modeling of jet fuel thermal deposition is dependent on an understanding of and ability to model the oxidation chemistry. Global modeling of jet fuel oxidation is complicated by several facts. First, liquid jet fuels are hard to heat rapidly and fuels may begin to oxidize during the heat-up phase. Non-isothermal conditions can be accounted for but the evaluation of temperature versus time is difficult. Second, the jet fuels are a mixture of many compounds that may oxidize at different rates. Third, jet fuel oxidation may be autoaccelerating through the decomposition of the oxidation products. Attempts to model the deposition of jet fuels in two different flowing systems showed the inadequacy of a simple two-parameter global Arrhenius oxidation rate constant. Discarding previous assumptions about the form of the global rate constants results in a four parameter model (which accounts for autoacceleration). This paper discusses the source of the rate constant form and the meaning of each parameter. One of these parameters is associated with the pre-exponential of the autoxidation chain length. This value is expected to vary inversely to thermal stability. We calculate the parameters for two different fuels and discuss the implication to thermal and oxidative stability of the fuels. Finally, we discuss the effect of non-Arrhenius behavior on current modeling of deposition efforts.

  18. Flexible all-carbon photovoltaics with improved thermal stability

    NASA Astrophysics Data System (ADS)

    Tang, Chun; Ishihara, Hidetaka; Sodhi, Jaskiranjeet; Chen, Yen-Chang; Siordia, Andrew; Martini, Ashlie; Tung, Vincent C.

    2015-04-01

    The structurally robust nature of nanocarbon allotropes, e.g., semiconducting single-walled carbon nanotubes (SWCNTs) and C60s, makes them tantalizing candidates for thermally stable and mechanically flexible photovoltaic applications. However, C60s rapidly dissociate away from the basal of SWCNTs under thermal stimuli as a result of weak intermolecular forces that "lock up" the binary assemblies. Here, we explore use of graphene nanoribbons (GNRs) as geometrically tailored protecting layers to suppress the unwanted dissociation of C60s. The underlying mechanisms are explained using a combination of molecular dynamics simulations and transition state theory, revealing the temperature dependent disassociation of C60s from the SWCNT basal plane. Our strategy provides fundamental guidelines for integrating all-carbon based nano-p/n junctions with optimized structural and thermal stability. External quantum efficiency and output current-voltage characteristics are used to experimentally quantify the effectiveness of GNR membranes under high temperature annealing. Further, the resulting C60:SWCNT:GNR ternary composites display excellent mechanical stability, even after iterative bending tests.

  19. Growth morphology and thermal stability of metal islands on graphene

    NASA Astrophysics Data System (ADS)

    Liu, Xiaojie; Hupalo, Myron; Wang, Cai-Zhuang; Lu, Wen-Cai; Thiel, Patricia A.; Ho, Kai-Ming; Tringides, Michael C.

    2012-08-01

    We performed an experiment to study the thermal stability of metal on graphene. We show that Fe, Gd, Dy, and Eu on graphene exhibit island growth morphology. The 3D islands of Fe, Gd, and Dy show a small decrease in island density and an increase in the height/width aspect ratio upon thermal annealing. By contrast, coarsening of Eu islands to a close flat film is observed after annealing to 365 K. By investigating the fundamental interactions (i.e., adsorption energies and diffusion barriers) between the metal adatoms and graphene using ab initio calculations, we predict that most of the 3d and group 10 transition metals, noble metals, as well as rare earth metals on graphene should exhibit a 3D growth mode as observed in experiment. Most of the metal nanostructures on graphene should also be stable against aggregation. The 3D morphology and strong thermal stability of Fe, Co, Ni, Pt, and Gd islands on graphene can serve as good candidates for surface-supported catalysis applications.

  20. Thermal Stability Analysis for Superconducting Coupling Coil in MICE

    SciTech Connect

    Wu, Hong; Wang, Li; Pan, Heng; Guo, XingLong; Green, M.A.

    2010-06-28

    The superconducting coupling coil to be used in the Muon Ionization Cooling Experiment (MICE) with inner radius of 750 mm, length of 285 mm and thickness of 110.4 mm will be cooled by a pair of 1.5 W at 4.2 K cryo-coolers. When the coupling coil is powered to 210 A, it will produce about 7.3 T peak magnetic field at the conductor and it will have a stored energy of 13 MJ. A key issue for safe operation of the coupling coil is the thermal stability of the coil during a charge and discharge. The magnet and its cooling system are designed for a rapid discharge where the magnet is to be discharged in 5400 seconds. The numerical simulation for the thermal stability of the MICE coupling coil has been done using ANSYS. The analysis results show that the superconducting coupling coil has a good stability and can be charged and discharged safely.

  1. Influence of polarity on GaN thermal stability

    NASA Astrophysics Data System (ADS)

    Mastro, M. A.; Kryliouk, O. M.; Anderson, T. J.; Davydov, A.; Shapiro, A.

    2005-01-01

    A comparative study of the stability of Ga- and N-polar GaN films was made in different gas ambients (N 2, H 2, NH 3, HCl). The Ga-polar films were observed to undergo a dissociative sublimation, while the N-polar films formed condensed Ga in addition to the gaseous species. The difference in polarity affects the morphology and bonding on the surface, and thus, stability of the atoms bonded to the surface.

  2. Thermal stability of lipid-depleted purple membranes at neutral and low pH values.

    PubMed

    Taneva, S G; Koynova, R; Tenchov, B

    1994-05-30

    Differential scanning calorimetry was used to compare the thermal behavior of native and delipidated purple membrane fragments at pH values corresponding to purple, blue and acid-purple forms. At neutral pH, delipidation results in a 2.5- to 3-times increase in the cooperativity of the denaturational transition, accompanied by a minor increase in its temperature. At pH values below 5 the delipidated membranes exhibit considerably higher thermal stability than the native membranes. The reversible predenaturational transition observed in the native state is not detectable upon delipidation. There is no strict correlation between color changes upon acidification and deionization of either native or delipidated purple membranes and their thermal stability.

  3. Chemical and thermal stability of core-shelled magnetite nanoparticles and solid silica

    NASA Astrophysics Data System (ADS)

    Cendrowski, Krzysztof; Sikora, Pawel; Zielinska, Beata; Horszczaruk, Elzbieta; Mijowska, Ewa

    2017-06-01

    Pristine nanoparticles of magnetite were coated by solid silica shell forming core/shell structure. 20 nm thick silica coating significantly enhanced the chemical and thermal stability of the iron oxide. Chemical and thermal stability of this structure has been compared to the magnetite coated by mesoporous shell and pristine magnetite nanoparticles. It is assumed that six-membered silica rings in a solid silica shell limit the rate of oxygen diffusion during thermal treatment in air and prevent the access of HCl molecules to the core during chemical etching. Therefore, the core/shell structure with a solid shell requires a longer time to induce the oxidation of iron oxide to a higher oxidation state and, basically, even strong concentrated acid such as HCl is not able to dissolve it totally in one month. This leads to the desired performance of the material in potential applications such as catalysis and environmental protection.

  4. Enhancement of Aviation Fuel Thermal Stability Characterization Through Application of Ellipsometry

    NASA Technical Reports Server (NTRS)

    Browne, Samuel Tucker; Wong, Hubert; Hinderer, Cameron Branch; Klettlinger, Jennifer

    2012-01-01

    ASTM D3241/Jet Fuel Thermal Oxidation Tester (JFTOT) procedure, the standard method for testing thermal stability of conventional aviation turbine fuels is inherently limited due to the subjectivity in the color standard for tube deposit rating. Quantitative assessment of the physical characteristics of oxidative fuel deposits provides a more powerful method for comparing the thermal oxidation stability characteristics of fuels, especially in a research setting. We propose employing a Spectroscopic Ellipsometer to determine the film thickness and profile of oxidative fuel deposits on JFTOT heater tubes. Using JP-8 aviation fuel and following a modified ASTM D3241 testing procedure, the capabilities of the Ellipsometer will be demonstrated by measuring oxidative fuel deposit profiles for a range of different deposit characteristics. The testing completed in this report was supported by the NASA Fundamental Aeronautics Subsonics Fixed Wing Project

  5. Synthesis, characterization and application of enrofloxacin complexes as thermal stabilizers for rigid poly(vinyl chloride).

    PubMed

    el-Gamel, Nadia E A; Mohamed, Riham R; Zayed, M A

    2012-02-14

    Synthesis and characterization of both binary Co(II)- (1), Ni(II)- (2) complexes with enrofloxacin drug (HL(1)) and ternary Co(II)- (3), Ni(II)- (4) complexes in presence of DL-alanine (H(2)L(2)) are reported using physico-chemical techniques. The antimicrobial activity of these complexes has been screened against two gram-positive and two gram-negative bacteria. Antifungal activity against two different fungi has been evaluated and compared with reference drug. All the binary and ternary complexes showed remarkable potential antimicrobial activity higher than the recommended standard agents. Ni(II)-complexes exhibited higher potency as compared to the parent drug against bacterial and fungal strain. In addition, it was of interest to investigate the reported complexes as thermal stabilizers and co-stabilizers for rigid PVC in air at 180 °C. Their high stabilizing efficiency is detected by their high induction period values (T(s)) compared with some of the common reference stabilizers used industrially, such as dibasic lead carbonate (DBLC) and calcium-zinc soap. Blending these complexes with some of the reference stabilizers in different ratios had a synergistic effect on both induction period as it gave better thermal stability and lower extent of discoloration. The stabilizing efficiency is attributed at least partially to the ability of the metal complex stabilizer to be incorporated in the polymeric chains, thus disrupting the chain degradation and replace the labile chlorine atoms on PVC chains by a relatively more s moiety of the inorganic stabilizer. Their amenability to use as a biomedical additives for PVC, has afforded them great potential for various medical applications.

  6. Synthesis, antibacterial and thermal studies of cellulose nanocrystal stabilized ZnO-Ag heterostructure nanoparticles.

    PubMed

    Azizi, Susan; Ahmad, Mansor Bin Hj; Hussein, Mohd Zobir; Ibrahim, Nor Azowa

    2013-05-28

    Synthesis of ZnO-Ag heterostructure nanoparticles was carried out by a precipitation method with cellulose nanocrystals (CNCs) as a stabilizer for antimicrobial and thermal studies. ZnO-Ag nanoparticles were obtained from various weight percentages of added AgNO₃ relative to Zn precursors for evaluating the best composition with enhanced functional properties. The ZnO-Ag/CNCs samples were characterized systematically by TEM, XRD, UV, TGA and DTG. From the TEM studies we observed that ZnO-Ag heterostructure nanoparticles have spherical shapes with size diameters in a 9-35 nm range. The antibacterial activities of samples were assessed against the bacterial species Salmonella choleraesuis and Staphylococcus aureus. The CNC-stabilized ZnO-Ag exhibited greater bactericidal activity compared to cellulose-free ZnO-Ag heterostructure nanoparticles of the same particle size. The incorporation of ZnO-Ag hetreostructure nanoparticles significantly increased the thermal stability of cellulose nanocrystals.

  7. Magnetic thermal stability of permalloy microstructures with shape-induced bi-axial anisotropy

    NASA Astrophysics Data System (ADS)

    Telepinsky, Yevgeniy; Sinwani, Omer; Mor, Vladislav; Schultz, Moty; Klein, Lior

    2016-02-01

    We study the thermal stability of the magnetization states in permalloy microstructures in the form of two crossing elongated ellipses, a shape which yields effective bi-axial magnetic anisotropy in the overlap area. We prepare the structure with the magnetization along one of the easy axes of magnetization and measure the waiting time for switching when a magnetic field favoring the other easy axis is applied. The waiting time for switching is measured as a function of the applied magnetic field and temperature. We determine the energy barrier for switching and estimate the thermal stability of the structures. The experimental results are compared with numerical simulations. The results indicate exceptional stability which makes such structures appealing for a variety of applications including magnetic random access memory based on the planar Hall effect.

  8. A comparative kinetics study of thermal degradation of some novel ABA block copolymers

    NASA Astrophysics Data System (ADS)

    Blanco, Ignazio; Cicala, Gianluca; Mamo, Antonino; Latteri, Alberta; Recca, Antonino

    2012-07-01

    Some novel ABA block copolymers, synthesized with three different molecular weights, where the block A is a PPO while the block B is a random copoly(aryl ether sulfone), were studied by TGA and DTA techniques, in both flowing nitrogen and static air atmosphere, in order to draw useful information about their resistance to thermal degradation. The results obtained for the various compounds investigated were discussed and compared with each other and a thermal stability classifications in the studied environments were made.

  9. On the thermal stability of radiation-dominated accretion disks

    SciTech Connect

    Jiang, Yan-Fei; Stone, James M.; Davis, Shane W.

    2013-11-20

    We study the long-term thermal stability of radiation-dominated disks in which the vertical structure is determined self-consistently by the balance of heating due to the dissipation of MHD turbulence driven by magneto-rotational instability (MRI) and cooling due to radiation emitted at the photosphere. The calculations adopt the local shearing box approximation and utilize the recently developed radiation transfer module in the Athena MHD code based on a variable Eddington tensor rather than an assumed local closure. After saturation of the MRI, in many cases the disk maintains a steady vertical structure for many thermal times. However, in every case in which the box size in the horizontal directions are at least one pressure scale height, fluctuations associated with MRI turbulence and dynamo action in the disk eventually trigger a thermal runaway that causes the disk to either expand or contract until the calculation must be terminated. During runaway, the dependence of the heating and cooling rates on total pressure satisfy the simplest criterion for classical thermal instability. We identify several physical reasons why the thermal runaway observed in our simulations differ from the standard α disk model; for example, the advection of radiation contributes a non-negligible fraction to the vertical energy flux at the largest radiation pressure, most of the dissipation does not happen in the disk mid-plane, and the change of dissipation scale height with mid-plane pressure is slower than the change of density scale height. We discuss how and why our results differ from those published previously. Such thermal runaway behavior might have important implications for interpreting temporal variability in observed systems, but fully global simulations are required to study the saturated state before detailed predictions can be made.

  10. Design of Ag nanorods for sensitivity and thermal stability of surface-enhanced Raman scattering

    NASA Astrophysics Data System (ADS)

    Ma, Lingwei; Zhang, Zhengjun; Huang, Hanchen

    2017-10-01

    The technology of surface-enhanced Raman scattering (SERS) has found many applications and may find more if it can possess both sensitivity and thermal stability. This paper reports a rational design of Ag nanorods to simultaneously achieve two competing goals: the sensitivity and the thermal stability of SERS substrates. The Ag nanorods are designed and synthesized using physical vapor deposition under the condition of glancing angle incidence. The working pressure of the vacuum chamber is controlled so the mean free path of depositing atoms is comparable to the dimension of the chamber, so as to grow Ag nanorods with small diameter, and small but clear separation for optimal SERS sensitivity. Such Ag nanorods are further capped with Al2O3 on their top surfaces to reduce the diffusion-induced coarsening at high temperatures, and thereby to improve the thermal stability for SERS detections. Meanwhile, since the side surfaces of Ag nanorods are not coated with oxides in this approach, the SERS sensitivity is largely preserved while good thermal stability is achieved.

  11. Design of Ag nanorods for sensitivity and thermal stability of surface-enhanced Raman scattering.

    PubMed

    Ma, Lingwei; Zhang, Zhengjun; Huang, Hanchen

    2017-10-06

    The technology of surface-enhanced Raman scattering (SERS) has found many applications and may find more if it can possess both sensitivity and thermal stability. This paper reports a rational design of Ag nanorods to simultaneously achieve two competing goals: the sensitivity and the thermal stability of SERS substrates. The Ag nanorods are designed and synthesized using physical vapor deposition under the condition of glancing angle incidence. The working pressure of the vacuum chamber is controlled so the mean free path of depositing atoms is comparable to the dimension of the chamber, so as to grow Ag nanorods with small diameter, and small but clear separation for optimal SERS sensitivity. Such Ag nanorods are further capped with Al2O3 on their top surfaces to reduce the diffusion-induced coarsening at high temperatures, and thereby to improve the thermal stability for SERS detections. Meanwhile, since the side surfaces of Ag nanorods are not coated with oxides in this approach, the SERS sensitivity is largely preserved while good thermal stability is achieved.

  12. Study of thermal stability of Cu2Se thermoelectric material

    NASA Astrophysics Data System (ADS)

    Bohra, Anil; Bhatt, Ranu; Bhattacharya, Shovit; Basu, Ranita; Ahmad, Sajid; Singh, Ajay; Aswal, D. K.; Gupta, S. K.

    2016-05-01

    Sustainability of thermoelectric parameter in operating temperature range is a key consideration factor for fabricating thermoelectric generator or cooler. In present work, we have studied the stability of thermoelectric parameter of Cu2Se within the temperature range of 50-800°C. Temperature dependent Seebeck coefficients and electrical resistivity measurement are performed under three continuous thermal cycles. X-ray diffraction pattern shows the presence of mixed cubic-monoclinic Cu2Se phase in bare pellet which transforms to pure α-Cu2Se phase with repeating thermal cycle. Significant enhancement in Seebeck coefficient and electrical resistivity is observed which may be attributed to (i) Se loss observed in EDS and (ii) the phase transformation from mixed cubic-monoclinic structure to pure monoclinic α-Cu2Se phase.

  13. Thermal stability of carbon nanotubes probed by anchored tungsten nanoparticles

    NASA Astrophysics Data System (ADS)

    Wei, Xianlong; Wang, Ming-Sheng; Bando, Yoshio; Golberg, Dmitri

    2011-08-01

    The thermal stability of multiwalled carbon nanotubes (CNTs) was studied in high vacuum using tungsten nanoparticles as miniaturized thermal probes. The particles were placed on CNTs inside a high-resolution transmission electron microscope equipped with a scanning tunneling microscope unit. The setup allowed manipulating individual nanoparticles and heating individual CNTs by applying current to them. CNTs were found to withstand high temperatures, up to the melting point of 60-nm-diameter W particles (~3400 K). The dynamics of W particles on a hot CNT, including particle crystallization, quasimelting, melting, sublimation and intradiffusion, were observed in real time and recorded as a video. Graphite layers reel off CNTs when melted or premelted W particles revolve along the tube axis.

  14. Thermal stability of carbon nanotubes probed by anchored tungsten nanoparticles

    PubMed Central

    Wei, Xianlong; Wang, Ming-Sheng; Bando, Yoshio; Golberg, Dmitri

    2011-01-01

    The thermal stability of multiwalled carbon nanotubes (CNTs) was studied in high vacuum using tungsten nanoparticles as miniaturized thermal probes. The particles were placed on CNTs inside a high-resolution transmission electron microscope equipped with a scanning tunneling microscope unit. The setup allowed manipulating individual nanoparticles and heating individual CNTs by applying current to them. CNTs were found to withstand high temperatures, up to the melting point of 60-nm-diameter W particles (∼3400 K). The dynamics of W particles on a hot CNT, including particle crystallization, quasimelting, melting, sublimation and intradiffusion, were observed in real time and recorded as a video. Graphite layers reel off CNTs when melted or premelted W particles revolve along the tube axis. PMID:27877413

  15. Thermal stability of the midgap acceptor rhodium in indium phosphide

    NASA Astrophysics Data System (ADS)

    Näser, A.; Dadgar, A.; Kuttler, M.; Heitz, R.; Bimberg, D.; Hyeon, J. Y.; Schumann, H.

    1995-07-01

    We investigated the thermally induced redistribution of Rh in low pressure MOCVD grown InP structures by means of secondary-ion-mass-spectroscopy. Analogous measurements for InP:Fe structures serve as reference. On alternately Rh-doped/undoped InP structures an upper limit for the diffusion coefficient of DRh(800 °C)≤1×10-14 cm2/s is established much smaller than DFe(750 °C)=1×10-11 cm2/s. No exchange reactions are observed at the interface of p-InP/InP:Rh structures. Only Rh implanted into InP shows defect induced redistribution into amorphous areas. Rh is superior to Fe as far as thermal stability is concerned.

  16. Thermal Stability of Distillate Hydrocarbon Fuels. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Reddy, Kishenkumar Tadisina; Cernansky, Nicholas P.

    1987-01-01

    Thermal stability of fuels is expected to become a severe problem in the future due to the anticipated use of broadened specification and alternative fuels. Future fuels will have higher contents of heteroatomic species which are reactive constituents and are known to influence fuel degradation. To study the degradation chemistry of selected model fuels, n-dodecane and n-dodecane plus heteroatoms were aerated by bubbling air through the fuels amd stressed on a modified Jet Fuel Thermal Oxidation Tester facility operating at heater tube temperatures between 200 to 400 C. The resulting samples were fractionated to concentrate the soluble products and then analyzed using gas chromatographic and mass spectrometric techniques to quantify and identify the stable reaction intermediate and product specifically. Heteroatom addition showed that the major soluble products were always the same, with and without heteroatoms, but their distributions varied considerably.

  17. Organic transistors with high thermal stability for medical applications

    NASA Astrophysics Data System (ADS)

    Kuribara, Kazunori; Wang, He; Uchiyama, Naoya; Fukuda, Kenjiro; Yokota, Tomoyuki; Zschieschang, Ute; Jaye, Cherno; Fischer, Daniel; Klauk, Hagen; Yamamoto, Tatsuya; Takimiya, Kazuo; Ikeda, Masaaki; Kuwabara, Hirokazu; Sekitani, Tsuyoshi; Loo, Yueh-Lin; Someya, Takao

    2012-03-01

    The excellent mechanical flexibility of organic electronic devices is expected to open up a range of new application opportunities in electronics, such as flexible displays, robotic sensors, and biological and medical electronic applications. However, one of the major remaining issues for organic devices is their instability, especially their thermal instability, because low melting temperatures and large thermal expansion coefficients of organic materials cause thermal degradation. Here we demonstrate the fabrication of flexible thin-film transistors with excellent thermal stability and their viability for biomedical sterilization processes. The organic thin-film transistors comprise a high-mobility organic semiconductor, dinaphtho[2,3-b:2‧,3‧-f]thieno[3,2-b]thiophene, and thin gate dielectrics comprising a 2-nm-thick self-assembled monolayer and a 4-nm-thick aluminium oxide layer. The transistors exhibit a mobility of 1.2 cm2 V-1s-1 within a 2 V operation and are stable even after exposure to conditions typically used for medical sterilization.

  18. Si-substituted hydroxyapatite nanopowders: Synthesis, thermal stability and sinterability

    SciTech Connect

    Bianco, Alessandra Cacciotti, Ilaria; Lombardi, Mariangela Montanaro, Laura

    2009-02-04

    Synthetic hydroxyapatites incorporating small amounts of Si have shown improved biological performances in terms of enhanced bone apposition, bone in-growth and cell-mediated degradation. This paper reports a systematic investigation on Si-substituted hydroxyapatite (Si 1.40 wt%) nanopowders produced following two different conventional wet methodologies: (a) precipitation of Ca(NO{sub 3}){sub 2}.4H{sub 2}O and (b) titration of Ca(OH){sub 2}. The influence of the synthesis process on composition, thermal behaviour and sinterability of the resulting nanopowders is studied. Samples were characterised by electron microscopy, induced coupled plasma atomic emission spectroscopy, thermal analysis, infrared spectroscopy, N{sub 2} adsorption measurements, X-ray diffraction and dilatometry. Semicrystalline Si-substituted hydroxyapatite powders made up of needle-like nanoparticles were obtained, the specific surface area ranged between 84 and 110 m{sup 2}/g. Pure and Si-substituted hydroxyapatite nanopowders derived from Ca(NO{sub 3}){sub 2}.4H{sub 2}O decomposed around 1000 deg. C. Si-substituted hydroxyapatite nanopowders obtained from Ca(OH){sub 2} were thermally stable up to 1200 deg. C and showed a distinct decreased thermal stability with respect to the homologous pure sample. Si-substituted hydroxyapatites exhibited higher sintering temperature and increased total shrinkage with respect to pure powders. Nanostructured dense ceramics were obtained by sintering at 1100 deg. C Si-substituted hydroxyapatites derived from Ca(OH){sub 2}.

  19. Substituted Cyclohexene Endcaps for Polymers with Thermal-Oxidative Stability

    NASA Technical Reports Server (NTRS)

    2005-01-01

    This invention relates to polyimides having improved thermal-oxidative stability, to the process of preparing said polyimides, and the use of polyimide prepolymers in the preparation of prepregs and composites. The polyimides are particularly usefull in the preparation of fiber-reinforced, high-temperature composites for use in various engine parts including inlets, fan ducts, exit flaps and other parts of high speed aircraft. The polyimides are derived from the polymerization of effective amounts of at least one tetracarboxylic dianhydride, at least one polyamine and a novel dicarboxylic endcap having the formula presented.

  20. Thermal Stabilization in a High Vacuum Cryogenic Optical System

    NASA Astrophysics Data System (ADS)

    Wallace, Rosa; Cripe, Jonathan; Corbitt, Thomas

    2016-03-01

    The existing technology for gravitational wave detection is limited in part by quantum noise. In our tabletop experiments, we are attempting to lower the noise floor to the quantum limit through the use of a seismically isolated cryogenic high vacuum environment, with the intention of exploring different methods to reduce quantum noise. In the development phase of this environment, we have implemented a customized strategy of ultraviolet irradiation combined with cryogenically cooled radiation shielding to reduce the impact of water vapor and blackbody radiation on the thermal stability of the cryogenic micro-components. Supported by National Science Foundation REU Site #1262890 and CAREER Award #1150531.

  1. Water-soluble Au25(Capt)18 nanoclusters: synthesis, thermal stability, and optical properties

    NASA Astrophysics Data System (ADS)

    Kumar, Santosh; Jin, Rongchao

    2012-06-01

    This work was motivated by the unsatisfactory stability of Au25(SG)18 in solution under thermal conditions (e.g. 70-90 °C for DNA melting). Thus, we searched for a better, water-soluble thiol ligand. Herein, we report a one-pot synthesis and investigation of the stability and optical properties of captopril (abbreviated Capt)-protected Au25(Capt)18 nanoclusters. The Au25(Capt)18 (anionic, counterion: Na+) nanoclusters were formed via size focusing under ambient conditions. Significantly, Au25(Capt)18 nanoclusters exhibit largely improved thermal stability compared to the glutathione (HSG) capped Au25(SG)18. Both Au25(Capt)18 and Au25(SG)18 nanoclusters show fluorescence centered at ~700 nm. The chiral ligands (Capt, SG, as well as chirally modified phenylethanethiol (PET*)) give rise to distinct chiroptical features. The high thermal stability and distinct optical properties of Au25(Capt)18 nanoclusters render this material quite promising for biological applications.This work was motivated by the unsatisfactory stability of Au25(SG)18 in solution under thermal conditions (e.g. 70-90 °C for DNA melting). Thus, we searched for a better, water-soluble thiol ligand. Herein, we report a one-pot synthesis and investigation of the stability and optical properties of captopril (abbreviated Capt)-protected Au25(Capt)18 nanoclusters. The Au25(Capt)18 (anionic, counterion: Na+) nanoclusters were formed via size focusing under ambient conditions. Significantly, Au25(Capt)18 nanoclusters exhibit largely improved thermal stability compared to the glutathione (HSG) capped Au25(SG)18. Both Au25(Capt)18 and Au25(SG)18 nanoclusters show fluorescence centered at ~700 nm. The chiral ligands (Capt, SG, as well as chirally modified phenylethanethiol (PET*)) give rise to distinct chiroptical features. The high thermal stability and distinct optical properties of Au25(Capt)18 nanoclusters render this material quite promising for biological applications. Electronic supplementary

  2. Layered and intercalated hydrotalcite-like materials as thermal stabilizers in PVC resin

    NASA Astrophysics Data System (ADS)

    Lin, Yanjun; Wang, Jianrong; Evans, David G.; Li, Dianqing

    2006-05-01

    In the light of the accepted mechanism of thermal stabilization of PVC by layered double hydroxides (LDHs), the layer cations and interlayer counterions in LDHs were tailored to give MgZnAl-CO3-LDH and MgZnAl-maleate-LDH. These materials were characterized by XRD, FT-IR, and TG DTA. The thermal stability of PVC composites containing different LDH additives was tested in sheets having a thickness of about 1 mm. The results showed that compared with MgAl-CO3-LDH, MgZnAl-CO3-LDH enhances the thermal stability of PVC in terms of both long-term stability and early coloring. After intercalation of maleate in the LDH by reaction of maleic acid with the MgZnAl-CO3-LDH precursor, the interlayer distance increases from 0.75 to 1.11 nm. Since Cl- promotes the autocatalytic dehydrochlorination of PVC, which is responsible for its degradation, an increased interlayer distance should facilitate entry of Cl- into the interlayer galleries and inhibit the decomposition of PVC. In addition, maleic acid has a conjugated C=C double bond which can react with double bond formed in the dehydrochlorination of PVC and thus further inhibit the autocatalytic degradation reaction. The results show that the early coloring of PVC is markedly improved and the long-term stability slightly reduced by addition of the MgZnAl-maleate-LDH.

  3. Differential scanning fluorimetry based assessments of the thermal and kinetic stability of peptide-MHC complexes.

    PubMed

    Hellman, Lance M; Yin, Liusong; Wang, Yuan; Blevins, Sydney J; Riley, Timothy P; Belden, Orrin S; Spear, Timothy T; Nishimura, Michael I; Stern, Lawrence J; Baker, Brian M

    2016-05-01

    Measurements of thermal stability by circular dichroism (CD) spectroscopy have been widely used to assess the binding of peptides to MHC proteins, particularly within the structural immunology community. Although thermal stability assays offer advantages over other approaches such as IC50 measurements, CD-based stability measurements are hindered by large sample requirements and low throughput. Here we demonstrate that an alternative approach based on differential scanning fluorimetry (DSF) yields results comparable to those based on CD for both class I and class II complexes. As they require much less sample, DSF-based measurements reduce demands on protein production strategies and are amenable for high throughput studies. DSF can thus not only replace CD as a means to assess peptide/MHC thermal stability, but can complement other peptide-MHC binding assays used in screening, epitope discovery, and vaccine design. Due to the physical process probed, DSF can also uncover complexities not observed with other techniques. Lastly, we show that DSF can also be used to assess peptide/MHC kinetic stability, allowing for a single experimental setup to probe both binding equilibria and kinetics. Copyright © 2016 Elsevier B.V. All rights reserved.

  4. Thermal-Mechanical Stability of Single Crystal Oxide Refractive Concentrators for High-Temperature Solar Thermal Propulsion

    NASA Technical Reports Server (NTRS)

    Zhu, Dongming; Jacobson, Nathan S.; Miller, Robert A.

    1999-01-01

    Single crystal oxides such as yttria-stabilized zirconia (Y2O3-ZrO2), yttrium aluminum garnet (Y3Al5O12, or YAG), magnesium oxide (MgO) and sapphire (Al2O3) are candidate refractive secondary concentrator materials for high temperature solar propulsion applications. However, thermo-mechanical reliability of these components in severe thermal environments during the space mission sun/shade transition is of great concern. Simulated mission tests are important for evaluating these candidate oxide materials under a variety of transient and steady-state heat flux conditions, and thus provide vital information for the component design. In this paper, a controlled heat flux thermal shock test approach is established for the single crystal oxide materials using a 3.0 kW continuous wave CO2 laser, with a wavelength 10.6 micron. Thermal fracture behavior and failure mechanisms of these oxide materials are investigated and critical temperature gradients are determined under various temperature and heating conditions. The test results show that single crystal sapphire is able to sustain the highest temperature gradient and heating-cooling rate, and thus exhibit the best thermal shock resistance, as compared to the yttria-stabilized zirconia, yttrium aluminum garnet, and magnesium oxide.

  5. Thermal-Mechanical Stability of Single Crystal Oxide Refractive Concentrators for High-Temperature Solar Thermal Propulsion

    NASA Technical Reports Server (NTRS)

    Zhu, Dongming; Jacobson, Nathan S.; Miller, Robert A.

    1999-01-01

    Single crystal oxides such as yttria-stabilized zirconia (Y2O3-ZrO2), yttrium aluminum garnet (Y3Al5O12, or YAG), magnesium oxide (MgO) and sapphire (Al2O3) are candidate refractive secondary concentrator materials for high temperature solar propulsion applications. However, thermo-mechanical reliability of these components in severe thermal environments during the space mission sun/shade transition is of great concern. Simulated mission tests are important for evaluating these candidate oxide materials under a variety of transient and steady-state heat flux conditions, and thus provide vital information for the component design. In this paper, a controlled heat flux thermal shock test approach is established for the single crystal oxide materials using a 3.0 kW continuous wave CO2 laser, with a wavelength 10.6 micron. Thermal fracture behavior and failure mechanisms of these oxide materials are investigated and critical temperature gradients are determined under various temperature and heating conditions. The test results show that single crystal sapphire is able to sustain the highest temperature gradient and heating-cooling rate, and thus exhibit the best thermal shock resistance, as compared to the yttria-stabilized zirconia, yttrium aluminum garnet and magnesium oxide.

  6. Thermal-mechanical stability of single crystal oxide refractive concentrators for high-temperature solar thermal propulsion

    SciTech Connect

    Zhu, D.; Jacobson, S.; Miller, R.A.

    1999-07-01

    Single crystal oxides such as yttria-stabilized zirconia (Y{sub 2}O{sub 3}-ZrO{sub 2}), yttrium aluminum garnet (Y{sub 3}Al{sub 5}O{sub 12}, or YAG), magnesium oxide (MgO) and sapphire (Al{sub 2}O{sub 3}) are candidate refractive secondary concentrator materials for high temperature solar propulsion applications. However, thermo-mechanical reliability of these components in severe thermal environments during the space mission sun/shade transition is of great concern. Simulated mission tests are important for evaluating these candidate oxide materials under a variety of transient and steady-state heat flux conditions, and thus provide vital information for the component design. In this paper, a controlled heat flux thermal shock test approach is established for the single crystal oxide materials using a 3.0 kW continuous wave CO{sub 2} laser, with a wavelength 10.6 micron. Thermal fracture behavior and failure mechanisms of these oxide materials are investigated and critical temperature gradients are determined under various temperature and heating conditions. The test results show that single crystal sapphire is able to sustain the highest temperature gradient and heating-cooling rate, and thus exhibit the best thermal shock resistance, as compared to the yttria-stabilized zirconia, yttrium aluminum garnet and magnesium oxide.

  7. On the thermal stability of a radiating plasma subject to nonlocal thermal conduction. I - Linear analysis

    NASA Technical Reports Server (NTRS)

    Chun, E.; Rosner, R.

    1993-01-01

    We study the linear stability of an optically thin uniform radiating plasma subject to nonlocal heat transport. We derive the dispersion relation appropriate to this problem, and the marginal wavenumbers for instability. Our analysis indicates that nonlocal heat transport acts to reduce the stabilizing influence of thermal conduction, and that there are critical values for the electron mean free path such that the plasma is always unstable. Our results may be applied to a number of astrophysical plasmas, one such example being the halos of clusters of galaxies.

  8. On the thermal stability of a radiating plasma subject to nonlocal thermal conduction. I - Linear analysis

    NASA Technical Reports Server (NTRS)

    Chun, E.; Rosner, R.

    1993-01-01

    We study the linear stability of an optically thin uniform radiating plasma subject to nonlocal heat transport. We derive the dispersion relation appropriate to this problem, and the marginal wavenumbers for instability. Our analysis indicates that nonlocal heat transport acts to reduce the stabilizing influence of thermal conduction, and that there are critical values for the electron mean free path such that the plasma is always unstable. Our results may be applied to a number of astrophysical plasmas, one such example being the halos of clusters of galaxies.

  9. Thermal stability of corn oil flavoured with Thymus capitatus under heating and deep-frying conditions.

    PubMed

    Karoui, Iness Jabri; Dhifi, Wissal; Jemia, Meriam Ben; Marzouk, Brahim

    2011-03-30

    The thermal stability of corn oil flavoured with thyme flowers was determined and compared with that of the original refined corn oil (control). The oxidative stability index (OSI) was measured and samples were exposed to heating (30 min at 150, 180 and 200 °C) and deep-frying (180 °C). Changes in peroxide value (PV), free fatty acid (FFA) content, specific absorptivity values (K(232) and K(270)), colour and chlorophyll, carotenoid and total phenol contents were monitored. The OSI and heating results showed that thyme incorporation was effective against thermal oxidation based on the increased induction time observed for the flavoured oil (6.48 vs 4.36 h), which was characterised by lower PV, FFA content, K(232) and K(270) than the control oil after heating from 25 to 200 °C, with higher red and yellow colour intensities and chlorophyll, carotenoid and total phenol contents. The deep-frying test showed the accelerated deterioration of both oils in the presence of French fries. Compared with the control oil, the thyme-flavoured oil showed improved thermal stability after heating. This could be attributed to the presence of thyme pigments and antioxidant compounds allowing extended oil thermal resistance. Copyright © 2011 Society of Chemical Industry.

  10. Factors affecting the microstructural stability and durability of thermal barrier coatings fabricated by air plasma spraying

    SciTech Connect

    Helminiak, M. A.; Yanar, N. M.; Pettit, F. S.; Taylor, T. A.; Meier, G. H.

    2012-10-01

    The high-temperature behavior of high-purity, low-density (HP-LD) air plasma sprayed (APS) thermal barrier coatings (TBCs) with NiCoCrAlY bond coats deposited by argon-shrouded plasma spraying is described. The high purity yttria-stabilized zirconia resulted in top coats which are highly resistant to sintering and transformation from the metastable tetragonal phase to the equilibrium mixture of monoclinic and cubic phases. The thermal conductivity of the as-processed TBC is low but increases during high temperature exposure even before densification occurs. The porous topcoat microstructure also resulted in good spallation resistance during thermal cycling. The actual failure mechanisms of the APS coatings were found to depend on topcoat thickness, topcoat density, and the thermal cycle frequency. The failure mechanisms are described and the durability of the HP-LD coatings is compared with that of state-of-the-art electron beam physical vapor deposition TBCs.

  11. Pressure effects on the thermal stability of silicon carbide fibers

    NASA Technical Reports Server (NTRS)

    Jaskowiak, Martha H.; Dicarlo, James A.

    1989-01-01

    Commercially available polymer derived SiC fibers were treated at temperatures from 1000 to 2200 C in vacuum and argon gas pressure of 1 and 1360 atm. Effects of gas pressure on the thermal stability of the fibers were determined through property comparison between the pressure treated fibers and vacuum treated fibers. Investigation of the thermal stability included studies of the fiber microstructure, weight loss, grain growth, and tensile strength. The 1360 atm argon gas treatment was found to shift the onset of fiber weight loss from 1200 to above 1500 C. Grain growth and tensile strength degradation were correlated with weight loss and were thus also inhibited by high pressure treatments. Additional heat treatment in 1 atm argon of the fibers initially treated at 1360 atm argon caused further weight loss and tensile strength degradation, thus indicating that high pressure inert gas conditions would be effective only in delaying fiber strength degradation. However, if the high gas pressure could be maintained throughout composite fabrication, then the composites could be processed at higher temperatures.

  12. Speciation of copper in the thermally stabilized slag

    NASA Astrophysics Data System (ADS)

    Tuan, Y.-J.; Paul Wang, H.; Chang, J.-E.; Chao, C.-C.; Tsai, C.-K.

    2010-07-01

    The Taiwan universities laboratory hazardous wastes have been treated by incineration at the temperature range of 1173-1273 K. By X-ray absorption near edge structure (XANES) spectroscopy, mainly CuO and CuSO 4 are found in the incineration bottom and fly ashes. The incineration fly ash can be stabilized thermally at 1773 K in the plasma melting reaction chamber (integrated with the incinerator), and converted to slag. The concentration of leachable copper in the slag is reduced significantly mainly due to the fact that copper is encapsulated in the SiO 2 matrix. In addition, the refined extended X-ray adsorption fine structure (EXAFS) spectra of copper also indicate formation of the Cu-O-Si species in the slag as the bond distances of 1.95 Å for Cu-O and 2.67 Å for O-Si are observed. This work exemplifies utilization of the synchrotron X-ray absorption spectroscopy to facilitate the thermal stabilization treatments of the fly ash hazardous waste using the plasma melting method.

  13. Thermal stabilization of collagen molecules in bone tissue.

    PubMed

    Trebacz, Hanna; Wójtowicz, Krzysztof

    2005-12-30

    Differential thermal calorimetry (DSC) analysis of partially dehydrated bovine bone, demineralized bone and bovine tendon collagen was performed up to 300 degrees C to determine factors influencing stability of mineralized collagen in bone tissue. Two endothermal regions were recognized. The first, attributed to denaturation of collagen triple helix, was hydration dependent and had a peak at 155-165 degrees C in bone, 118-137 degrees C in tendon and 131-136 degrees C in demineralized bone. The second region extended from 245 to 290 degrees C in bone and from 200 to 280 degrees C in tendon and was connected with melting and decomposition of collagen. Differences in thermodynamic parameters between cortical and trabecular bone tissue were stated. Activation energy of collagen unfolding in native bone tissue increased with dehydration of the bone. From the results of the present study we conclude that dehydrated bone collagen is thermally very stable both in native and in demineralized bone. Presence of mineral additionally stabilizes bone tissue.

  14. Preliminary hazards analysis of thermal scrap stabilization system. Revision 1

    SciTech Connect

    Lewis, W.S.

    1994-08-23

    This preliminary analysis examined the HA-21I glovebox and its supporting systems for potential process hazards. Upon further analysis, the thermal stabilization system has been installed in gloveboxes HC-21A and HC-21C. The use of HC-21C and HC-21A simplified the initial safety analysis. In addition, these gloveboxes were cleaner and required less modification for operation than glovebox HA-21I. While this document refers to glovebox HA-21I for the hazards analysis performed, glovebox HC-21C is sufficiently similar that the following analysis is also valid for HC-21C. This hazards analysis document is being re-released as revision 1 to include the updated flowsheet document (Appendix C) and the updated design basis (Appendix D). The revised Process Flow Schematic has also been included (Appendix E). This Current revision incorporates the recommendations provided from the original hazards analysis as well. The System Design Description (SDD) has also been appended (Appendix H) to document the bases for Safety Classification of thermal stabilization equipment.

  15. Thermal stability of biodegradable plasmonic nanoclusters in photoacoustic imaging

    PubMed Central

    Yoon, Soon Joon; Murthy, Avinash; Johnston, Keith P.; Sokolov, Konstantin V.; Emelianov, Stanislav Y.

    2012-01-01

    The photothermal stability of plasmonic nanoparticles is critically important to perform reliable photoacoustic imaging and photothermal therapy. Recently, biodegradable nanoclusters composed of sub-5 nm primary gold particles and a biodegradable polymer have been reported as clinically-translatable contrast agents for photoacoustic imaging. After cellular internalization, the nanoclusters degrade into 5 nm primary particles for efficient excretion from the body. In this paper, three different sizes of biodegradable nanoclusters were synthesized and the optical properties and photothermal stability of the nanoclusters were investigated and compared to that of gold nanorods. The results of our study indicate that 40 nm and 80 nm biodegradable nanoclusters demonstrate higher photothermal stability compared to gold nanorods. Furthermore, 40 nm nanoclusters produce higher photoacoustic signal than gold nanorods at a given concentration of gold. Therefore, the biodegradable plasmonic nanoclusters can be effectively used for photoacoustic imaging and photothermal therapy. PMID:23388774

  16. Thermal stability of biodegradable plasmonic nanoclusters in photoacoustic imaging.

    PubMed

    Yoon, Soon Joon; Murthy, Avinash; Johnston, Keith P; Sokolov, Konstantin V; Emelianov, Stanislav Y

    2012-12-31

    The photothermal stability of plasmonic nanoparticles is critically important to perform reliable photoacoustic imaging and photothermal therapy. Recently, biodegradable nanoclusters composed of sub-5 nm primary gold particles and a biodegradable polymer have been reported as clinically-translatable contrast agents for photoacoustic imaging. After cellular internalization, the nanoclusters degrade into 5 nm primary particles for efficient excretion from the body. In this paper, three different sizes of biodegradable nanoclusters were synthesized and the optical properties and photothermal stability of the nanoclusters were investigated and compared to that of gold nanorods. The results of our study indicate that 40 nm and 80 nm biodegradable nanoclusters demonstrate higher photothermal stability compared to gold nanorods. Furthermore, 40 nm nanoclusters produce higher photoacoustic signal than gold nanorods at a given concentration of gold. Therefore, the biodegradable plasmonic nanoclusters can be effectively used for photoacoustic imaging and photothermal therapy.

  17. Thermal and mechanical stability of nanograined FCC metals

    NASA Astrophysics Data System (ADS)

    Hattar, Khalid Mikhiel

    The mechanisms governing and factors controlling the thermal and mechanical stability of nanograined free-standing face-centered cubic thin films were investigated through in situ transmission electron microscopy annealing and straining experiments. A variety of sample preparation techniques were developed to investigate the active mechanisms. The results obtained from the select face-centered cubic metals studied were used to develop a general understanding of face-centered cubic metals with microstructure limited to the nanometer scale. The films were analyzed, both prior to and following the in situ transmission electron microscopy experiments, via a range of analytical techniques in order to characterize chemical and microstructural details. The mechanisms observed were compared to the pertinent theories and models. In situ transmission electron microscopy heating and annealing experiments were performed on free-standing pulsed-laser deposited Au, Cu, and Ni thin films. The grain growth of pulsed-laser deposited Ni films was studied and the growth rate was found to be a function of time, temperature, film thickness, and surface abnormalities. The grain growth was classified as abnormal in nature resulting in a bimodal grain size distribution. Abnormal grain growth was found to increase with an increase in film thickness. This increase was attributed to the presence of a higher density of preferred nanograins for abnormal grain growth in thicker films, although the mechanisms that induce the rapid growth were not determined. A higher percentage of abnormal large grains were found along ridges templated from the substrate, and in regions with extensive electron beam exposure. Post-annealing analysis of pulsed-laser deposited Ni films revealed an unexpected myriad of microstructural defects including dislocations, twins, stacking faults, dislocation loops, and stacking-fault tetrahedra, as well as a metastable hexagonal closed-packed phase. The production of these

  18. Thermal stability of sputtered intermetallic Al-Au coatings

    SciTech Connect

    Moser, M.; Mayrhofer, P. H.; Ross, I. M.; Rainforth, W. M.

    2007-09-15

    Recently, the authors have shown that single-phase Al{sub 2}Au coatings, prepared by unbalanced magnetron sputtering, exhibit a dense columnar structure and highest hardness and indentation moduli of 8 and 144 GPa, respectively, within the Al-Au films investigated. This study focuses on the thermal stability of Al{sub 2}Au with respect to films containing more Al and Au having Al/Au at. % ratios of 4.32 and 1.85, respectively. Single-phase Al{sub 2}Au has the highest onset temperature for recovery of 475 deg. C and recrystallization of 575 deg. C. Upon annealing Au- and Al-rich films, their stresses deviate from the linear thermoelastic behavior at temperatures (T) above 200 and 450 deg. C, respectively, due to pores and metallic phases present. Metastable Au within the as-deposited Au-rich film is consumed by the growing intermetallic AlAu and AlAu{sub 2} phases at T{>=}450 deg. C, which themselves melt at {approx}625 deg. C. Due to nanometer scale segregations of Al, encapsulated by Al{sub 2}Au in Al-rich coatings, their melting point is reduced by {approx}85 deg. C to 575 deg. C. Dynamic thermal analyses up to 1100 deg. C in synthetic air reveal the single-phase Al{sub 2}Au films with a superior thermal stability and only negligible oxidation. At 750 deg. C, the mass gain is {approx}1.5 mg/cm{sup 2} after 50 h isothermal exposure. Based on the investigations, the authors can conclude that single-phase intermetallic Al{sub 2}Au films have a high potential for oxidation protection of sensitive materials.

  19. Thermal stabilization of static single-mirror Fourier transform spectrometers

    NASA Astrophysics Data System (ADS)

    Schardt, Michael; Schwaller, Christian; Tremmel, Anton J.; Koch, Alexander W.

    2017-05-01

    Fourier transform spectroscopy has become a standard method for spectral analysis of infrared light. With this method, an interferogram is created by two beam interference which is subsequently Fourier-transformed. Most Fourier transform spectrometers used today provide the interferogram in the temporal domain. In contrast, static Fourier transform spectrometers generate interferograms in the spatial domain. One example of this type of spectrometer is the static single-mirror Fourier transform spectrometer which offers a high etendue in combination with a simple, miniaturized optics design. As no moving parts are required, it also features a high vibration resistance and high measurement rates. However, it is susceptible to temperature variations. In this paper, we therefore discuss the main sources for temperature-induced errors in static single-mirror Fourier transform spectrometers: changes in the refractive index of the optical components used, variations of the detector sensitivity, and thermal expansion of the housing. As these errors manifest themselves in temperature-dependent wavenumber shifts and intensity shifts, they prevent static single-mirror Fourier transform spectrometers from delivering long-term stable spectra. To eliminate these shifts, we additionally present a work concept for the thermal stabilization of the spectrometer. With this stabilization, static single-mirror Fourier transform spectrometers are made suitable for infrared process spectroscopy under harsh thermal environmental conditions. As the static single-mirror Fourier transform spectrometer uses the so-called source-doubling principle, many of the mentioned findings are transferable to other designs of static Fourier transform spectrometers based on the same principle.

  20. "Thermal Stability of Anodic Hafnium Oxide Nanotube Arrays"

    SciTech Connect

    Qiu, Xiaofeng; Howe, Jane Y; Mayer, Harry A; Paranthaman, Mariappan Parans; Tuncer, Enis

    2011-01-01

    Thermal stability of highly ordered Hafnium oxide, HfO2 nanotube arrays prepared through electrochemical anodization approach in the presence of ammonium fluoride is investigated in a temperature range of room temperature to 900 C in flowing Argon atmosphere. The formation of the HfO2 nanotube arrays was monitored by current density transient characteristics during anodization of hafnium metal foil. Morphologies of the as grown and post-annealed HfO2 nanotube arrays were analyzed by X-ray powder diffraction (XRD), Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM). Although monoclinic HfO2 is thermally stable up to 2000K in bulk, the morphology HfO2 nanotube arrays degraded at 900 C. Detailed X-ray photoelectron spectroscopy (XPS) study revealed that the thermal treatment significantly impact the composition and chemical environment of the core elements (Hf, O and F) of HfO2. Possible reasons for the degradation of the nanotube morphology were discussed based on XPS study and possible future improvements were suggested briefly.

  1. Thermal stability studies of diamond-like carbon films

    SciTech Connect

    Parmeter, J.E.; Tallant, D.R.; Siegal, M.P.

    1994-04-01

    Thin films of amorphous carbon/hydrogen, also known as diamond-like carbon or DLC, are of interest as an economical alternative to diamond in a variety of coatings applications. We have investigated the thermal stability of DLC films deposited onto tungsten and aluminum substrates via plasma CVD of methane. These films contain approximately 40 atom % hydrogen, and based on Auger spectra the carbon in the films is estimated to be 60% sp{sup 3} hybridized and 40% sp{sup 2} hybridized. Thermal desorption, Auger, and Raman measurements all indicate that the DLC films are stable to 250--300C. Between 300 and 500C, thermal evolution of hydrogen from the films is accompanied by the conversion of carbon from sp{sup 3} to sp{sup 2} hybridization, and Raman spectra indicate the conversion of the overall film structure from DLC to micro-crystalline graphite or so called ``glassy`` carbon. These results suggest that DLC of this type is potentially useful for applications in which the temperature does not exceed 250C.

  2. Thermal stability of HfO2 nanotube arrays

    SciTech Connect

    Qiu, Xiaofeng; Howe, Jane Y; Meyer III, Harry M; Tuncer, Enis; Paranthaman, Mariappan Parans

    2010-01-01

    Thermal stability of highly ordered hafnium oxide (HfO2) nanotube arrays prepared through an electrochemical anodization method in the presence of ammonium fluoride is investigated in a temperature range of room temperature to 900 C in flowing argon atmosphere. The formation of the HfO2 nanotube arrays was monitored by current density transient characteristics during anodization of hafnium metal foil. Morphologies of the as-grown and post-annealed HfO2 nanotube arrays were analyzed by powder Xray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Although monoclinic HfO2 is thermally stable up to 2000K in bulk, the morphology of HfO2 nanotube arrays degraded at 900 C. A detailed X-ray photoelectron spectroscopy (XPS) study revealed that the thermal treatment significantly impacted the composition and the chemical environment of the core elements (Hf and O), as well as F content coming from the electrolyte. Possible reasons for the degradation of the nanotube at high temperature were discussed based on XPS study and possible future improvements have also been suggested. Moreover, dielectric measurements were carried out on both the as-grown amorphous film and 500 C post-annealed crystalline film. This study will help us to understand the temperature impact on the morphology of nanotube arrays, which is important to its further applications at elevated temperatures.

  3. Thermal stabilization of anti-α-cobratoxin single domain antibodies.

    PubMed

    Anderson, George P; Liu, Jessica H; Zabetakis, Dan; Liu, Jinny L; Goldman, Ellen R

    2017-04-01

    There is an unmet need for snake antivenoms that can be stored ready to use near the point of care. To address that need we have taken two anti-α-cobratoxin single domain antibodies and increased their thermal stability to improve their ambient temperature shelf-life. The anti-α-cobratoxin single domain antibodies C2 and C20 were first isolated, and demonstrated to be toxin neutralizing by Richard et al., 2013 (Richard, G., Meyers, A.J., McLean, M.D., Arbabi-Ghahroudi, M., MacKenzie, R., Hall, J.C., 2013. In vivo neutralization of alpha-cobratoxin with high-affinity llama single-domain antibodies (VHHs) and a VHH-Fc antibody. PLoS One 8, e69495). To thermal stabilize C2 and C20, we first made changes to their frame work 1 region that we had previously identified to be stabilizing, as well as reverted to the hallmark amino acids highly conserved in VHH domains; these changes improved their melting temperature (Tm) by 2 and 6 °C respectively. The further addition of a non-canonical disulfide bond raised the Tm an additional 13 and 9 °C respectively; giving final Tm values of 86 and 75 °C. Testing these mutants at 1 mg/mL at a range of elevated temperatures for an hour; we found that at 65 °C the wild type C2 and C20 had lost 35 and 95% of their binding activity respectively, while the mutants with the added disulfide bond retained nearly 100% of their initial binding activity. While significant work remains to formulate and field a shelf-stable antivenom, our results indicate such a product should be attainable in the near future.

  4. Interferometric measurement of dimensional and thermal stability of joints

    NASA Astrophysics Data System (ADS)

    Lorenz, Hagen; Schödel, René

    2014-08-01

    In this work we demonstrate how absolute length measurements by interferometry, as used for regular gauge block calibration, can be applied to measure the dimensional drift behavior of connections joined by gluing or screwing and how these joining techniques are influenced by thermal treatment. While it is common to investigate the intrinsic stability of material samples by repeated length measurements, there exist growing demands in precision engineering to characterize the stability of assemblies, i.e. of joined material pieces. In order to enable investigation of joining techniques representative joints were fabricated by a number of methods as wringing, screwing and gluing. By using gauge block shaped samples as joining parts parallelism and flatness could be achieved which is needed for interferometric length measurements. The stability of the joints has been investigated longitudinally and laterally to the connection interface, and also mutual tilting of the parts was detected by analysis of the phase topographies. With the use of sample joints, the behavior of connection elements used in ultrahigh-precision instruments can now be examined on an accuracy level of about one nanometer. Results of approximately one year of observation show that screwed joints do not exhibit a significant change of length or orientation. They also did not show response to temperature variations of +/-10°C, which is different for adhesive joints where dimensional changes of up to 100 nm were observed.

  5. Interlayer exchange coupling dependence of thermal stability parameters in synthetic antiferromagnetic free layers

    NASA Astrophysics Data System (ADS)

    Saito, Y.; Sugiyama, H.; Inokuchi, T.; Inomata, K.

    2006-08-01

    We conducted a detailed comparative study of thermal stability properties over a thermal excitation of switching of the free layer in a magnetic tunnel junction (MTJ) with Ni 81Fe 19, Co 90Fe 10, and synthetic antiferromagnetic (Syn-AF) free layers with several strengths of interlayer exchange coupling ( JEX). The thermal stability properties were investigated using the junction magnetoresistance of current-perpendicular MTJ devices with a word line as probes. The observed sweep-rate-dependent coercivities were analyzed using the Sharrock formula. The results confirmed strong JEX dependence on thermal stability parameters (KV/kT) in Syn-AF free layers. The values of KV/kT for MTJs with Syn-AF free layers decreased with a decrease in the strength of JEX, and the increase in the effective volume of the Syn-AF free layer disappeared at J⩽0.52 erg/cm. The Syn-AF free layer with JEX>0.52 erg/cm 2 is relevant for high-density spin electronic nanodevices with a low aspect ratio.

  6. Transient thermal conductivity and colloidal stability measurements of nanofluids by using the 3omega method.

    PubMed

    Oh, Dong-Wook; Kwon, Ohmyoung; Lee, Joon Sik

    2008-10-01

    Nanofluid is a mixture of nanoscale particles of metal, metal oxide or carbon nanotube and heat transfer fluids such as water and ethylene glycol. This work presents the application of the 3-omega (3omega) method for measuring the colloidal stability and the transient thermal conductivity of multi-wall carbon nanotube (MWCNT), Al2O3 and TiO2 nanoparticles suspended in water or ethylene glycol. The microfabricated 3omega device is verified by comparing the measured thermal conductivities of pure fluids with the table values. After the validation, the transient thermal responses of the nanofluids are measured to evaluate the colloidal stability. All of Al2O3 nanofluid samples show a clear sign of sedimentation while the acid-treated MWCNT (tMWCNT) nanofluid and a couple of TiO2 nanofluids with pH control or surfactant addition are found to have excellent colloidal stability. The thermal conductivities of tMWCNT nanofluids in the de-ionized water and ethylene glycol are measured, which are found to be in good agreement with previous data.

  7. Comparative thermal inactivation analysis of Aspergillus oryzae and Thiellavia terrestris cutinase: Role of glycosylation.

    PubMed

    Shirke, Abhijit N; Su, An; Jones, J Andrew; Butterfoss, Glenn L; Koffas, Mattheos A G; Kim, Jin Ryoun; Gross, Richard A

    2017-01-01

    Cutinase thermostability is important so that the enzymes can function above the glass transition of what are often rigid polymer substrates. A detailed thermal inactivation analysis was performed for two well-characterized cutinases, Aspergillus oryzae Cutinase (AoC) and Thiellavia terrestris Cutinase (TtC). Both AoC and TtC are prone to thermal aggregation upon unfolding at high temperature, which was found to be a major reason for irreversible loss of enzyme activity. Our study demonstrates that glycosylation stabilizes TtC expressed in Pichia pastoris by inhibiting its thermal aggregation. Based on the comparative thermal inactivation analyses of non-glycosylated AoC, glycosylated (TtC-G), and non-glycosylated TtC (TtC-NG), a unified model for thermal inactivation is proposed that accounts for thermal aggregation and may be applicable to other cutinase homologues. Inspired by glycosylated TtC, we successfully employed glycosylation site engineering to inhibit AoC thermal aggregation. Indeed, the inhibition of thermal aggregation by AoC glycosylation was greater than that achieved by conventional use of trehalose under a typical condition. Collectively, this study demonstrates the excellent potential of implementing glycosylation site engineering for thermal aggregation inhibition, which is one of the most common reasons for the irreversible thermal inactivation of cutinases and many proteins. Biotechnol. Bioeng. 2017;114: 63-73. © 2016 Wiley Periodicals, Inc.

  8. Study on the influence of moisture content on thermal stability of propellant.

    PubMed

    Guo, Song; Wang, Qingsong; Sun, Jinhua; Liao, Xin; Wang, Ze-shan

    2009-08-30

    This paper studies the influence of moisture content on the thermal stabilities of double-base propellant and multi-nitro ester propellant. The thermal behaviors and chemical kinetic parameters of the above two propellants and their mixtures with water were analyzed by using a CALVET heat flux calorimeter, C80. The thermal decomposition mechanisms of these two propellants with water were conjectured based on the tests. And then, the self-accelerating decomposition temperatures (SADT) of these two propellants and their mixtures with water were calculated and compared according to the kinetic parameters and Semenov model. The results show that the thermal decomposition mechanism of double-base propellant with water may be changing with the varying moisture content by transferring hydrogen proton (H(+)). However, the thermal decomposition mechanism of multi-nitro ester propellant with water may be unchanging due to the excess of formaldehyde (HCHO). Water plays the external physical factor on the thermal decomposition of multi-nitro ester propellant, and it plays both the physical and the chemical factors on the thermal decomposition of double-base propellant. The SADTs of their mixtures with water are much lower than that of pure propellants, and keep decreasing with the increasing of moisture content.

  9. Increasing Type 1 Poliovirus Capsid Stability by Thermal Selection

    PubMed Central

    Adeyemi, Oluwapelumi O.; Nicol, Clare

    2016-01-01

    ABSTRACT Poliomyelitis is a highly infectious disease caused by poliovirus (PV). It can result in paralysis and may be fatal. Integrated global immunization programs using live-attenuated oral (OPV) and/or inactivated (IPV) PV vaccines have systematically reduced its spread and paved the way for eradication. Immunization will continue posteradication to ensure against reintroduction of the disease, but there are biosafety concerns for both OPV and IPV. They could be addressed by the production and use of virus-free virus-like particle (VLP) vaccines that mimic the “empty” capsids (ECs) normally produced in viral infection. Although ECs are antigenically indistinguishable from mature virus particles, they are less stable and readily convert into an alternative conformation unsuitable for vaccine purposes. Stabilized ECs, expressed recombinantly as VLPs, could be ideal candidate vaccines for a polio-free world. However, although genome-free PV ECs have been expressed as VLPs in a variety of systems, their inherent antigenic instability has proved a barrier to further development. In this study, we selected thermally stable ECs of type 1 PV (PV-1). The ECs are antigenically stable at temperatures above the conversion temperature of wild-type (wt) virions. We have identified mutations on the capsid surface and in internal networks that are responsible for EC stability. With reference to the capsid structure, we speculate on the roles of these residues in capsid stability and postulate that such stabilized VLPs could be used as novel vaccines. IMPORTANCE Poliomyelitis is a highly infectious disease caused by PV and is on the verge of eradication. There are biosafety concerns about reintroduction of the disease from current vaccines that require live virus for production. Recombinantly expressed virus-like particles (VLPs) could address these inherent problems. However, the genome-free capsids (ECs) of wt PV are unstable and readily change antigenicity to a form not

  10. Stabilization of gold nanoparticle films on glass by thermal embedding.

    PubMed

    Karakouz, Tanya; Maoz, Ben M; Lando, Gilad; Vaskevich, Alexander; Rubinstein, Israel

    2011-04-01

    The poor adhesion of gold nanoparticles (NPs) to glass has been a known obstacle to studies and applications of NP-based systems, such as glass/Au-NP optical devices. Here we present a simple scheme for obtaining stable localized surface plasmon resonance (LSPR) transducers based on Au NP films immobilized on silanized glass and annealed. The procedure includes high-temperature annealing of the Au NP film, leading to partial embedding in the glass substrate and stabilization of the morphology and optical properties. The method is demonstrated using citrate-stabilized Au NPs, 20 and 63 nm mean diameter, immobilized electrostatically on glass microscope cover slides precoated with an aminosilane monolayer. Partial thermal embedding of the Au NPs in the glass occurs at temperatures in the vicinity of the glass transition temperature of the substrate. Upon annealing in air the Au NPs gradually settle into the glass and become encircled by a glass rim. In situ transmission UV-vis spectroscopy carried out during the annealing in a specially designed optical oven shows three regions: The most pronounced change of the surface plasmon (SP) band shape occurs in the first ca. 15 min of annealing; this is followed by a blue-shift of the SP band maximum (up to ca. 5 h), after which a steady red-shift of the SP band is observed (up to ca. 70 h, when the experiment was terminated). The development of the SP extinction spectrum was correlated to changes in the system structure, including thermal modification of the NP film morphology and embedding in the glass. The partially embedded Au NP films pass successfully the adhesive-tape test, while their morphology and optical response are stable toward immersion in solvents, drying, and thiol self-assembly. The enhanced adhesion is attributed to the metal NP embedding and rim formation. The stabilized NP films display a refractive index sensitivity (RIS) of 34-48 nm/RIU and 0.1-0.4 abs.u./RIU in SP band shift and extinction change

  11. Thermal stability of radiating fluids: The scattering problem

    NASA Astrophysics Data System (ADS)

    Bakan, Stephan

    1984-12-01

    The problem of convective instability of a radiating fluid layer with scattering is treated with an extension of the Eddington aproximation that allows the inclusion of anisotropic scattering into the solution of the radiative transfer equation. Introduction of scattering by keeping the optical depth of absorption constant reduces the critical Rayleigh number as well as the wavenumber, and thus, reduces the stabilizing influence of thermal radiation. It is shown that in cases of a narrow radiative boundary layer with a large temperature gradient, higher-order expansion terms are sometimes necessary to approximate the solution properly. In certain cases a two layer convection mode with a large critical wavenumber up to 50 sets in the first layer has two cells developing in and near the two radiative boundary layers.

  12. Thermal stability of low dielectric constant porous silica films

    NASA Astrophysics Data System (ADS)

    Esposito, L.; Ottaviani, G.; Carollo, E.; Bacchetta, M.

    2005-12-01

    Thermal stability of porous-silica-based low dielectric constant, k, material deposited by chemical vapor deposition has been investigated in a wide temperature range. The films as-deposited and after heat treatments up to 600°C have Si1O1.6C1.4H2.3 composition, permittivity k ≈2.8, and porosity h ≈0.25. A skeleton of silicon dioxide and empty pores justifies the permittivity and porosity values. Permeation experiments with deuterated water vapor indicate that pores are interconnected. At 700°C, the film has Si1O1.6C1.4H1.4 composition, k ≈2.4, and h ≈0.21. Bonds with lower polarizability could be responsible for the decrease of k. Above 800°C, carbon segregation and nanoclusters formation occur.

  13. Synthesis and characterization of processable polyimides with enhanced thermal stability

    NASA Technical Reports Server (NTRS)

    Harris, Frank W.

    1987-01-01

    Many of the emerging applications of polymers on space vehicles require materials with outstanding thermal stability. These polymers must also be readily processable in order to facilitate their use. The syntheses and polymerization of a cardo dianhydride were investigated. This monomer was prepared via the reaction of N-methyl 4-nitrophthalimide with a cardo diol. Polyimides containing oxyalkylene linkages were studied. The effects of two additional structural modifications on the polymers' properties were investigated. The effects of carrying out the preparation of poly(amic acid)s under non-equilibrium conditions were examined. Approaches that were investigated included the in-situ neutralization of the generated amic acid and its in-situ esterification.

  14. Stability of mixed time integration schemes for transient thermal analysis

    NASA Technical Reports Server (NTRS)

    Liu, W. K.; Lin, J. I.

    1982-01-01

    A current research topic in coupled-field problems is the development of effective transient algorithms that permit different time integration methods with different time steps to be used simultaneously in various regions of the problems. The implicit-explicit approach seems to be very successful in structural, fluid, and fluid-structure problems. This paper summarizes this research direction. A family of mixed time integration schemes, with the capabilities mentioned above, is also introduced for transient thermal analysis. A stability analysis and the computer implementation of this technique are also presented. In particular, it is shown that the mixed time implicit-explicit methods provide a natural framework for the further development of efficient, clean, modularized computer codes.

  15. Joule-Thomson cryogenic cooler with extremely high thermal stability

    NASA Technical Reports Server (NTRS)

    Bard, Steven; Wu, J. J.; Trimble, Curt

    1991-01-01

    An 80-K Joule-Thomson (J-T) cooling system designed for the Probe Infrared Laser Spectrometer (PIRLS) proposed for the Huygens Titan Probe of the Cassini Saturn orbiter mission is presented. The cryogenic cooling requirements of the PIRLS instrument are listed, and the cooler system design including details of a J-T cryostat, cold head, and dewar design is described along with the results of a thermal modeling effort and lab cooler performance testing. It is shown that by using active feedback temperature control of the cold head in combination with the self-regulating action of the J-T cryostat, a temperature stability of less than 0.1 mK/min is achieved by the cooler weighting 1.8 kg.

  16. Joule-Thomson cryogenic cooler with extremely high thermal stability

    NASA Technical Reports Server (NTRS)

    Bard, Steven; Wu, J. J.; Trimble, Curt

    1991-01-01

    An 80-K Joule-Thomson (J-T) cooling system designed for the Probe Infrared Laser Spectrometer (PIRLS) proposed for the Huygens Titan Probe of the Cassini Saturn orbiter mission is presented. The cryogenic cooling requirements of the PIRLS instrument are listed, and the cooler system design including details of a J-T cryostat, cold head, and dewar design is described along with the results of a thermal modeling effort and lab cooler performance testing. It is shown that by using active feedback temperature control of the cold head in combination with the self-regulating action of the J-T cryostat, a temperature stability of less than 0.1 mK/min is achieved by the cooler weighting 1.8 kg.

  17. High physiological thermal triplex stability optimization of twisted intercalating nucleic acids (TINA).

    PubMed

    Bomholt, Niels; Osman, Amany M A; Pedersen, Erik B

    2008-10-21

    The structure of the monomer (R)-1-O-[4-(1-pyrenylethynyl)phenylmethyl]glycerol () in twisted intercalating nucleic acids (TINA) was optimized for stabilizing interactions between the intercalator and surrounding nucleobases when used as a triplex forming oligonucleotide (TFO). Enhancement of pi-pi interactions with nucleobases of the TFO was achieved by increasing the aromatic surface using the (R)-1-O-[4-(1-pyrenylethynyl)naphthylmethyl]glycerol monomer (). Bulge insertion of in the middle of a Hoogsteen-type triplex increased the triplex thermal stability, DeltaT(m) = +2.0 degrees C compared with at pH 7.2. Syntheses and thermal denaturation studies of triplexes and duplexes are described for three novel TINA monomers. The influence of pi-pi interactions, link length and the positioning of the ether in the linker in the TINA derivatives are described.

  18. Size-dependent thermal stability analysis of graded piezomagnetic nanoplates on elastic medium subjected to various thermal environments

    NASA Astrophysics Data System (ADS)

    Ebrahimi, Farzad; Barati, Mohammad Reza

    2016-10-01

    This paper investigates the thermal stability of magneto-electro-thermo-elastic functionally graded (METE-FG) nanoplates based on the nonlocal theory and a refined plate model. The METE-FG nanoplate is subjected to the external electric potential, magnetic potential and different temperature rises. Interaction of elastic medium with the METE-FG nanoplate is modeled via Winkler-Pasternak foundation model. The governing equations are derived by using the Hamilton principle and solved by using an analytical method to determine the critical buckling temperatures. To verify the validity of the developed model, the results of the present work are compared with those available in the literature. A detailed parametric study is conducted to study the influences of the nonlocal parameter, foundation parameters, temperature rise, external electric and magnetic potentials on the size-dependent thermal buckling characteristics of METE-FG nanoplates.

  19. Chasing the Patagonian sun: comparative thermal biology of Liolaemus lizards.

    PubMed

    Azócar, Débora Lina Moreno; Vanhooydonck, Bieke; Bonino, Marcelo F; Perotti, M Gabriela; Abdala, Cristian S; Schulte, James A; Cruz, Félix B

    2013-04-01

    The importance of the thermal environment for ectotherms and its relationship with thermal physiology and ecology is widely recognized. Several models have been proposed to explain the evolution of the thermal biology of ectotherms, but experimental studies have provided mixed support. Lizards from the Liolaemus goetschi group can be found along a wide latitudinal range across Argentina. The group is monophyletic and widely distributed, and therefore provides excellent opportunities to study the evolution of thermal biology. We studied thermal variables of 13 species of the L. goetschi group, in order to answer three questions. First, are aspects of the thermal biology of the L. goetschi group modelled by the environment or are they evolutionarily conservative? Second, have thermal characteristics of these animals co-evolved? And third, how do the patterns of co-evolution observed within the L. goetschi group compare to those in a taxonomically wider selection of species of Liolaemus? We collected data on 13 focal species and used species information of Liolaemus lizards available in the literature and additional data obtained by the authors. We tackled these questions using both conventional and phylogenetically based analyses. Our results show that lizards from the L. goetschi group and the genus Liolaemus in general vary in critical thermal minimum in relation to mean air temperature, and particularly the L. goetschi group shows that air temperature is associated with critical thermal range, as well as with body temperature. Although the effect of phylogeny cannot be ignored, our results indicate that these thermal biology aspects are modelled by cold environments of Patagonia, while other aspects (preferred body temperature and critical thermal maximum) are more conservative. We found evidence of co-evolutionary patterns between critical thermal minimum and preferred body temperature at both phylogenetic scales (the L. goetschi group and the extended sample of

  20. Detector stability of the Terra MODIS thermal emissive bands

    NASA Astrophysics Data System (ADS)

    Xiong, Xiaoxiong; Chiang, Kwo-Fu; Chen, Na; Xiong, S.; Wu, Aisheng; Adimi, Farida; Barnes, William L.

    2003-11-01

    The MODerate Resolution Imaging Spectroradiometer (MODIS) is one of the key instruments for the NASA"s Earth Observing System (EOS). The MODIS ProtoFlight Model (PFM) was launched on-board the EOS Terra spacecraft on December 18, 1999. The science data acquisition started on February 24, 2000. Since then it has been providing the science community and public users unprecedented amount of data sets for the global monitoring of the Earth"s land, oceans, and atmosphere. MODIS has 36 spectral bands with wavelengths ranging from 0.41 micrometer to 14.5 micrometers. Its 16 thermal emissive bands (TEB) range from 3.7 to 14.2 micrometers and have a total of 160 individual detectors (10 detectors per band). The thermal emissive bands are calibrated on-orbit by an on-board calibrator blackbody (OBC BB) on a scan by scan basis. The detectors responses to the BB source track their operational stability and therefore their noise characteristics as well. In this paper, we provide a brief review of the MODIS TEB on-orbit calibration algorithm with a focus on detector stability using over three years of on-orbit calibration data sets. The on-orbit changes in detectors responses from one operational configuration to another, the changes within the same operational condition, and the impact of these changes on the calibration and on the Earth scene observations are carefully examined. Except for a few detectors that were identified from pre-launch or became noisy on-orbit, the overall performance of MODIS TEB detectors is very satisfactory according to the design specifications.

  1. Thermal Stability and Material Balance of Nanomaterials in Waste Incineration

    NASA Astrophysics Data System (ADS)

    Paur, H.-R.; Baumann, W.; Hauser, M.; Lang, I.; Teuscher, N.; Seifert, H.; Stapf, D.

    2017-06-01

    Nanostructured materials are widely used to improve the properties of consumer products such as tires, cosmetics, light weight equipment etc. Due to their complex composition these products are hardly recycled and thermal treatment is preferred. In this study we investigated the thermal stability and material balance of nanostructured metal oxides in flames and in an industrial waste incinerator. We studied the size distribution of nanostructured metal oxides (CeO2, TiO2, SiO2) in a flame reactor and in a heated reaction tube. In the premixed ethylene/air flame, nano-structured CeO2 partly evaporates forming a new particle mode. This is probably due to chemical reactions in the flame. In addition sintering of agglomerates takes place in the flame. In the electrically heated reaction tube however only sintering of the agglomerated nanomaterials is observed. Ceria has a low background in waste incinerators and is therefore a suitable tracer for investigating the fate of nanostructured materials. Low concentrations of Ceria were introduced by a two-phase nozzle into the post-combustion zone of a waste incinerator. By the incineration of coal dust in a burning chamber the Ceria nanoparticles are mainly found in the size range of the fly ash (1 - 10 µm) because of agglomeration. With gas as a fuel less agglomeration was observed and the Ceria nanoparticles were in the particle size range below 1 µm.

  2. Thermal Stability and Vertical Structure of Radiation Dominated Accretion Disks

    NASA Astrophysics Data System (ADS)

    Jiang, Yanfei; Stone, J. M.; Davis, S.

    2013-01-01

    Standard thin disk model predicts that radiation dominated accretion disk is thermally unstable. However, using a radiation MHD code based on flux-limited diffusion (FLD) approximation, Hirose et al. (2009) finds that when the accretion stress provided by Magneto-rotational instability (MRI) is calculated self-consistently, the disk is actually stable. We check this surprising result with our recently developed radiation transfer module in Athena. We modify the Godunov method to include the radiation source terms and close the radiation momentum equations with variable Eddington tensor. In this way, it works in both optically thin and thick regimes, and works for both radiation or gas pressure dominated flows. As a general purpose radiation MHD code, it can also be used to study other systems, where radiation field plays an important role, such as feedback effects of stars on the interstellar medium. I will show a set of tests to demonstrate that the code is working accurately as expected for different regimes. I will describe in detail our results on the thermal stability of accretion disks in both the gas pressure dominated regime and radiation pressure dominated regime. Detailed studies of the vertical structures of the accretion disk will also be presented. I will also comment on the differences between our results and the results from FLD calculations.

  3. The thermal stability of a castor bean seed acid phosphatase.

    PubMed

    Granjeiro, Paulo Afonso; Cavagis, Alexandre Donizeti Martins; de Campos Leite, Luciana; Ferreira, Carmen Veríssima; Granjeiro, José Mauro; Aoyama, Hiroshi

    2004-11-01

    The effect of temperature on the activity and structural stability of an acid phosphatase (EC 3.1.3.2.) purified from castor bean (Ricinus communis L.) seeds have been examined. The enzyme showed high activity at 45 degrees C using p-nitrophenylphosphate (p-NPP) as substrate. The activation energy for the catalyzed reaction was 55.2 kJ mol(-1) and the enzyme maintained 50% of its activity even after 30 min at 55 degrees C. Thermal inactivation studies showed an influence of pH in the loss of enzymatic activity at 60 degrees C. A noticeable protective effect from thermal inactivation was observed when the enzyme was preincubated, at 60 degrees C, with the reaction products inorganic phosphate-P (10 mM) and p-nitrophenol-p-NP(10 mM). Denaturation studies showed a relatively high transition temperature (Tm) value of 75 degrees C and an influence of the combination of Pi (10 mM) and p-NP (10 mM) was observed on the conformational behaviour of the macromolecule.

  4. Thermal stability of a thin disk with magnetically driven winds

    SciTech Connect

    Li, Shuang-Liang; Begelman, Mitchell C. E-mail: mitch@jila.colorado.edu

    2014-05-01

    The absence of thermal instability in the high/soft state of black hole X-ray binaries, in disagreement with the standard thin disk theory, has been a long-standing riddle for theoretical astronomers. We have tried to resolve this question by studying the thermal stability of a thin disk with magnetically driven winds in the M-dot −Σ plane. It is found that disk winds can greatly decrease the disk temperature and thus help the disk become more stable at a given accretion rate. The critical accretion rate, M-dot {sub crit}, corresponding to the thermal instability threshold, is significantly increased in the presence of disk winds. For α = 0.01 and B {sub φ} = 10B {sub p}, the disk is quite stable even for a very weak initial poloidal magnetic field [β{sub p,0}∼2000,β{sub p}=(P{sub gas}+P{sub rad})/(B{sub p}{sup 2}/8π)]. However, when B {sub φ} = B {sub p} or B {sub φ} = 0.1B {sub p}, a somewhat stronger (but still weak) field (β{sub p,} {sub 0} ∼ 200 or β{sub p,} {sub 0} ∼ 20) is required to make the disk stable. Nevertheless, despite the great increase of M-dot {sub crit}, the luminosity threshold, corresponding to instability, remains almost constant or decreases slowly with increasing M-dot {sub crit} due to decreased gas temperature. The advection and diffusion timescales of the large-scale magnetic field threading the disk are also investigated in this work. We find that the advection timescale can be smaller than the diffusion timescale in a disk with winds, because the disk winds take away most of the gravitational energy released in the disk, resulting in the decrease of the magnetic diffusivity η and the increase of the diffusion timescale.

  5. Thermal Stability of Jet Fuels: Kinetics of Forming Deposit Precursors

    NASA Technical Reports Server (NTRS)

    Naegeli, David W.

    1997-01-01

    The focus of this study was on the autoxidation kinetics of deposit precursor formation in jet fuels. The objectives were: (1) to demonstrate that laser-induced fluorescence is a viable kinetic tool for measuring rates of deposit precursor formation in jet fuels; (2) to determine global rate expressions for the formation of thermal deposit precursors in jet fuels; and (3) to better understand the chemical mechanism of thermal stability. The fuels were isothermally stressed in small glass ampules in the 120 to 180 C range. Concentrations of deposit precursor, hydroperoxide and oxygen consumption were measured over time in the thermally stressed fuels. Deposit precursors were measured using laser-induced fluorescence (LIF), hydroperoxides using a spectrophotometric technique, and oxygen consumption by the pressure loss in the ampule. The expressions, I.P. = 1.278 x 10(exp -11)exp(28,517.9/RT) and R(sub dp) = 2.382 x 10(exp 17)exp(-34,369.2/RT) for the induction period, I.P. and rate of deposit precursor formation R(sub dp), were determined for Jet A fuel. The results of the study support a new theory of deposit formation in jet fuels, which suggest that acid catalyzed ionic reactions compete with free radical reactions to form deposit precursors. The results indicate that deposit precursors form only when aromatics are present in the fuel. Traces of sulfur reduce the rate of autoxidation but increase the yield of deposit precursor. Free radical chemistry is responsible for hydroperoxide formation and the oxidation of sulfur compounds to sulfonic acids. Phenols are then formed by the acid catalyzed decomposition of benzylic hydroperoxides, and deposit precursors are produced by the reaction of phenols with aldehydes, which forms a polymer similar to Bakelite. Deposit precursors appear to have a phenolic resin-like structure because the LIF spectra of the deposit precursors were similar to that of phenolic resin dissolved in TAM.

  6. Thermal stability of water ice in Ceres' crater Oxo

    NASA Astrophysics Data System (ADS)

    Formisano, Michelangelo; Federico, Costanzo; De Sanctis, Maria Cristina; Frigeri, Alessandro; Magni, Gianfranco; Tosi, Federico

    2016-10-01

    Dwarf planet Ceres, target of the NASA Dawn mission, exhibits evidences of ammoniated phyllosilicates on its surface [1], compatible with a likely outer Solar System origin. Considerable amounts of water ice have recently been detected in some craters by the Visible InfraRed mapping spectrometer (VIR) onboard Dawn in some small fresh crater, such as Oxo, located at about 40° N. The exposure mechanism of water ice is unknown: cryovolcanism, cometary type sublimation/recondensation [2]or impacts with other bodies are likely mechanisms. The evaluation of the time stability of the water ice is crucial to understand the plausible mechanism for its existence. For this purpose, we developed a 3D finite-elements model (FEM) by using the topography given by the shape model of Ceres derived on the basis of images acquired by the Framing Camera in the Survey mission phase. The illumination conditions are provided by the SPICE toolkit. We performed several simulations by analyzing the effect of thermal inertia and albedo on the temperature and rate of ice sublimation. The results of the simulations about the stability of water ice will be presented.[1] De Sanctis et al. NATURE, doi:10.1038/nature16172[2] Formisano et al. MNRAS, doi: 10.1093/mnras/stv2344

  7. Thermal stability of horizontally superposed porous and fluid layers

    SciTech Connect

    Taslim, M.E.; Narusawa, U. )

    1989-05-01

    The results of stability analyses for the onset of convective motion are reported for the following three horizontally superposed systems of porous and fluid layers: (a) a porous layer sandwiched between two fluid layers with rigid top and bottom boundaries, (b) a fluid layer overlying a layer of porous medium, and (c) a fluid layer sandwiched between two porous layers. By changing the depth radio d from zero to infinity, a set of stability criteria (i.e., the critical Rayleigh number Ra{sub c} and the critical wave number a{sub c}) is obtained, ranging from the case of a fluid layer between two rigid boundaries to the case of a porous layer between two impermeable boundaries. The effects of k/k{sub m} (the thermal conductivity ratio), {delta} (the square root of the Darcy number), and {alpha} (the nondimensional proportionality constant in the slip condition) on Ra{sub c} and a{sub c} are also examined in detail. The results in this paper combined with those reported previously for Case (a) (Pillatsis et al., 1987), will provide a comprehensive picture of the interaction between a porous and a fluid layer.

  8. An experimental study on thermal stability of biodiesel fuel

    NASA Astrophysics Data System (ADS)

    Zhu, Yiying

    Biodiesel fuel, as renewable energy, has been used in conventional diesel engines in pure form or as biodiesel/diesel blends for many years. However, thermal stability of biodiesel and biodiesel/diesel blends has been minimally explored. Aimed to shorten this gap, thermal stability of biodiesel is investigated at high temperatures. In this study, batch thermal stressing experiments of biodiesel fuel were performed in stainless steel coils at specific temperature and residence time range from 250 to 425 °C and 3 to 63 minutes, respectively. Evidence of different pathways of biodiesel fuel degradation is demonstrated chromatographically. It was found that biodiesel was stable at 275 °C for a residence time of 8 minutes or below, but the cis-trans isomerization reaction was observed at 28 minutes. Along with isomerization, polymerization also took place at 300 °C at 63 minutes. Small molecular weight products were detected at 350 °C at 33 minutes resulting from pyrolysis reactions and at 360 °C for 33 minutes or above, gaseous products were produced. The formed isomers and dimers were not stable, further decomposition of these compounds was observed at high temperatures. These three main reactions and the temperature ranges in which they occurred are: isomerization, 275--400 °C; polymerization (Diels-Alder reaction), 300--425 °C; pyrolysis reaction, ≥350 °C. The longer residence time and higher temperature resulted in greater decomposition. As the temperature increased to 425 °C, the colorless biodiesel became brownish. After 8 minutes, almost 84% of the original fatty acid methyl esters (FAMEs) disappeared, indicating significant fuel decomposition. A kinetic study was also carried out subsequently to gain better insight into the biodiesel thermal decomposition. A three-lump model was proposed to describe the decomposition mechanism. Based on this mechanism, a reversible first-order reaction kinetic model for the global biodiesel decomposition was shown to

  9. Investigation of thermal and electrical stabilities of a GdBCO coil using grease as an insulation material for practical superconducting applications.

    PubMed

    Kang, D H; Kim, K L; Kim, Y G; Park, Y J; Kim, W J; Kim, S H; Lee, H G

    2014-09-01

    This paper presents the effects of thermal grease on the electrical and thermal characteristics of GdBCO pancake coils, observed through charge-discharge, sudden discharge, over-current, and thermal quench testing. In charge-discharge and sudden discharge tests, a coil using thermal grease as an insulation material demonstrated faster charging/discharging rates compared to a coil without turn-to-turn insulation. In the case of over-current tests, the coil using thermal grease exhibited the highest electrical stability. Furthermore, thermal quench testing showed the coil employing thermal grease to possess superior thermal characteristics, with rapid cooling and low temperature rise. Overall, the use of thermal grease as an insulation material may be a potential solution to the problems observed with the existing insulation materials, possessing fast charging/discharging rates with superior thermal and electrical stabilities.

  10. Thermal-stability studies of electrode materials for lithium-ion batteries

    NASA Astrophysics Data System (ADS)

    Jiang, Junwei

    2005-07-01

    The thermal stability of lithium-ion batteries has recently attracted attention for two major reasons. (1) Attempts to make large-size cells used in power tools, E-bikes and EVs. Large cells have lower surface area to volume ratios and hence heat dissipation is more problematic than 18650-size cells. Safety problems, therefore, for large cells are more serious. (2) Next generation high-capacity electrodes will increase the energy density of lithium-ion cells meaning even an 18650-size cell may face safety concerns. This thesis presents studies of the thermal stability of electrode materials in electrolytes to understand their reactivity. A search for new positive electrode materials with high thermal stability was made. The thermal stability of two common electrode materials (Li0.81 C6 and Li0.5CoO2) in lithium-ion cells was studied by Accelerating Rate Calorimeter (ARC). Li0.81C 6 has much lower reactivity with lithium bis(oxalato)borate (LiBOB) electrolyte compared to LiPF6 electrolyte. It is not the case, however, for Li0.5CoO2. Oven tests of full LiCoO 2/C 18650-size cells with LiBOB or LiPF6 electrolytes, confirmed the ARC results. ARC was then used to study the reactivity of existing electrode materials. The thermal stability of a negative electrode material was found to increase with the binding energy of Li atoms hosted in the material. Li0.5VO 2 (B) has a higher lithium binding energy (2.45 eV vs. Li) than Li 0.81C6 (0.1 eV vs. Li) and Li7Ti5O 12 (1.55 eV) and it shows the highest thermal stability in EC/DEC among the three materials. The reactivity of two existing positive electrode materials, LiMn2O4 and LiFePO4, was studied. Cell systems expected to be highly tolerant to thermal abuse were suggested: LiFePO 4/C or Li4Ti5O12 in LiBOB electrolytes. The system, x Li[Ni1/2Mn1/2]O2 • y LiCoO2 • z Li[Li1/3Mn2/3]O2 (x + y + z = 1), was explored for new positive electrode materials with large capacity and high thermal stability. Li[(Ni0.5Mn0.5) xCo1-x]O2 (0

  11. Thermal analysis and test of SUNLITE reference cavity for laser frequency stabilization

    NASA Technical Reports Server (NTRS)

    Amundsen, R. M.

    1992-01-01

    SUNLITE is a space-based experiment which uses a reference cavity to provide a stable frequency reference for a terahertz laser oscillator. Thermal stability of the cavity is a key factor in attaining a stable narrow-linewidth laser beam. This paper describes the thermal stability requirements on the cavity design and detailed thermal analysis performed, as well as thermal testing that was performed on a prototype. Analytical thermal models were correlated to the test data and additional modeling of the current design is presented. Suggestions for improving similar high-precision thermal tests are given.

  12. Comparative evaluation of the stability of seven-transmembrane microbial rhodopsins to various physicochemical stimuli

    NASA Astrophysics Data System (ADS)

    Honda, Naoya; Tsukamoto, Takashi; Sudo, Yuki

    2017-08-01

    Rhodopsins are seven-transmembrane proteins that function as photoreceptors for a variety of biological processes. Their characteristic visible colors make rhodopsins a good model for membrane-embedded proteins. In this study, by utilizing their color changes, we performed comparative studies on the stability of five microbial rhodopsins using the same instruments, procedures and media. As denaturants, we employed four physicochemical stimuli: (i) thermal perturbation, (ii) the water-soluble reagent hydroxylamine, (iii) the detergent sodium dodecyl sulfate, and (iv) the organic solvent ethanol. On the basis of the results, models for stabilization mechanisms in rhodopsins against each stimulus is proposed.

  13. Comparison of stabilization by Vitamin E and 2,6-di-tert-butylphenols during polyethylene radio-thermal-oxidation

    NASA Astrophysics Data System (ADS)

    Richaud, Emmanuel

    2014-10-01

    This paper reports a compilation of data for PE+Vitamin E and 2,6-di-tert-butylphenols oxidation in radio-thermal ageing. Data unambiguously show that Vitamin E reacts with Prad and POOrad whereas 2,6-di-tert-butyl phenols only react with POOrad. Kinetic parameters of the stabilization reactions for both kinds of antioxidants were tentatively extracted from phenol depletion curves, and discussed regarding the structure of the stabilizer. They were also used for completing an existing kinetic model used for predicting the stabilization by antioxidants. This one permits to compare the efficiency of stabilizer with dose rate or sample thickness.

  14. Oxidative stability, thermal stability and acceptability of coconut oil flavored with essential oils from black pepper and ginger.

    PubMed

    Chandran, Janu; Nayana, N; Roshini, N; Nisha, P

    2017-01-01

    The present study investigates the oxidative and thermal stability of flavoured oils developed by incorporating essential oils from black pepper and ginger to coconut oil (CNO) at concentrations of 0.1 and 1.0% (CNOP-0.1, CNOP-1, CNOG-0.1, CNOG-1). The stability of oils were assessed in terms of free fatty acids, peroxide, p-anisidine, conjugated diene and triene values and compared with CNO without any additives and a positive control with synthetic antioxidant TBHQ (CNOT). It was found that the stability of CNOP-1 and CNOG-1 were comparable with CNOT at both study conditions. The possibility of flavoured oil as a table top salad oil was explored by incorporating the same in vegetable salad and was found more acceptable than the control, on sensory evaluation. The synergetic effect of essential oil as a flavour enhancer and a powerful natural antioxidant that can slow down the oxidation of fats was established in the study.

  15. Thermal Stability Improvement of Rice Bran Albumin Protein Incorporated with Epigallocatechin Gallate.

    PubMed

    Zhou, Zhongkai; Xu, Jingjing; Liu, Yuqian; Meng, Demei; Sun, Xiaoli; Yi, Hong; Gao, Yunjing; Sun, Guoyu; Strappe, Padraig; Blanchard, Chris; Yang, Rui

    2017-02-01

    Rice bran albumin protein (RAP) is sensitive to thermal changes and tends to degrade when exposed to high-temperature processing. In this work, RAP-epigallocatechin-3-gallate (EGCG) complex (RAPE) was prepared and the thermal stability was evaluated. Fluorescence results showed that EGCG could interact with RAP with a binding number n of 0.0885:1 (EGCG:RAP, w/w) and a binding constant K of 1.02 (± 0.002) ×10(4) /M, suggesting both hydrogen bonding and van der Waals forces played an important role. FTIR analysis demonstrated that EGCG could induce secondary structural changes in RAP above a ratio of 1.6:1 (EGCG:RAP, w/w). Interestingly, the secondary structure changes of RAPE at different temperatures (25, 50, 60, 70, and 80 °C) were inhibited compared with that for RAP, suggesting RAPE was more resistant and stable to the heat treatment. In addition, a dense porous structure of RAPE was achieved due to the EGCG binding after thermal treatment. Furthermore, the Tpeak temperature of RAPE increased significantly from 64.58 to 74.16 °C and the enthalpy also increased from 85.53 to 138.52 J/g with a mass ratio increasing from 0 to 3.2 (EGCG:RAP, w/w), demonstrating the thermal stability of RAPE. In addition, the valine, methionine, and lysine content in RAPE were significantly higher than RAP following 80 °C treatment for 20 min (P < 0.05), exhibiting enhanced amino acid profiles, which might be due to EGCG-RAP interactions and microenvironment changes around relevant amino acids. These findings demonstrate that EGCG has the potential to improve the thermal stability of sensitive proteins and is beneficial for usage in the food industry. © 2017 Institute of Food Technologists®.

  16. Formulation and thermal sterile stability of a less painful intravenous clarithromycin emulsion containing vitamin E.

    PubMed

    Lu, Yan; Wang, YanJiao; Tang, Xing

    2008-01-04

    The purpose of this study is to develop a less painful intravenous clarithromycin emulsion (ClaE) and investigate its thermal sterile stability. The formulation of ClaE is composed of clarithromycin 0.25% (w/v), vitamin E 5% (w/v), medium chain triglyceride (MCT) 10% (w/v), egg lecithin 1.0% (w/v), Cremophor EL-40 (EL-40) 2% (w/v), Pluronic F-68 (F-68) 0.2% (w/v), Tween80 0.2% (w/v), glycerol 2.5% (w/v) and L-cysteine 0.05% (w/v) in water. High-pressure homogenization, photon correlation spectroscopy (PCS) and electrophoretic light scattering (ELS) technology, light microscopy and high-performance liquid chromatography (HPLC) methods were used in the preparation and evaluation of ClaE. Investigation of thermal sterile stability included the effects of different thermal sterile methods, thermal sterile time, drug concentrations and pH values. Sterilization in a 100 degrees C rotating water bath for 30 min was finally adopted as the sterilization method. The drug remaining was 98.6% and 96.5%, respectively, before and after thermal sterilization. Moreover, the pH value, particle size distribution (PSD), zeta-potential and entrapment efficiency (EE) of ClaE after sterilization were 7.95, 213.6 nm, -22.29 mV and 96.35%, respectively. This showed that ClaE had sufficient physicochemical stability to resist the sterilization process. Tests using animal models demonstrated that there was a marked pain reduction following the injection of ClaE compared with clarithromycin solution. Overall, ClaE described in this paper may be very suitable for industrial-scale production and clinical application.

  17. Thermal Stability of a 4 Meter Primary Reflector for the Scanning Microwave Limb Sounder

    NASA Technical Reports Server (NTRS)

    Cofield, Richard E.; Kasl, Eldon P.

    2011-01-01

    The Scanning Microwave Limb Sounder (SMLS) is a space-borne heterodyne radiometer which will measure pressure, temperature and atmospheric constituents from thermal emission in [180,680] GHz. SMLS, planned for the NRC Decadal Survey's Global Atmospheric Composition Mission, uses a novel toric Cassegrain antenna to perform both elevation and azimuth scanning. This provides better horizontal and temporal resolution and coverage than were possible with elevation-only scanning in the two previous MLS satellite instruments. SMLS is diffraction-limited in the vertical plane but highly astigmatic in the horizontal (beam aspect ratio approx. 1:20). Nadir symmetry ensures that beam shape is nearly invariant over plus or minus 65 deg azimuth. A low-noise receiver FOV is swept over the reflector system by a small azimuth-scanning mirror. We describe the fabrication and thermal-stability test of a composite demonstration primary reflector, having full 4m height and 1/3 the width planned for flight. Using finite-element models of reflectors and structure, we evaluate thermal deformations and optical performance for 4 orbital environments and isothermal soak. We compare deformations with photogrammetric measurements made during soak tests in a chamber. The test temperature range exceeds predicted orbital ranges by large factors, implying in-orbit thermal stability of 0.21 micron rms (root mean square)/C, which meets SMLS requirements.

  18. Improving the thermal dimensional stability of flexible polymer composite backing materials for ultrasound transducers.

    PubMed

    State, Mihai; Brands, Peter J; van de Vosse, Frans N

    2010-04-01

    Novel ultrasound backing materials based on polymer composites with improved dimensional stability and low coefficient of thermal expansion are being developed and analyzed. For this purpose a filled epoxy resin (Stycast(1265)), a commonly used backing material, was considered reference material and polyurethane composites (PU(2305), PU(2350)) were proposed as better alternatives. When compared to the reference, the PU(2350) filled with a mixture of Al(2)O(3) and tungsten exhibited an approximately 15 times lower glassy transition temperature and a 2.5 time lower longitudinal thermal expansion at 20 degrees C. This ensures that within the entire operational temperature range the backing material is flexible, minimizing the thermal stresses induced onto transducer elements soldered joints and piezoceramic core. For the same material, the attenuation at 5MHz was similar to the reference material while at 7 and 8.5MHz it was 33% and 54% higher respectively. From these analyses it is concluded that the newly developed polyurethane composites outperform the reference backing with respect to the thermal dimensional stability as well as to the damping properties. An integrated rigorous mechano-acoustical approach is being proposed as an appropriate passive material design path. It can be easily extended to any other passive materials used for ultrasound transducer conception.

  19. On the physics of thermal-stability changes upon mutations of a protein

    NASA Astrophysics Data System (ADS)

    Murakami, Shota; Oshima, Hiraku; Hayashi, Tomohiko; Kinoshita, Masahiro

    2015-09-01

    It is of great interest from both scientific and practical viewpoints to theoretically predict the thermal-stability changes upon mutations of a protein. However, such a prediction is an intricate task. Up to now, significantly many approaches for the prediction have been reported in the literature. They always include parameters which are adjusted so that the prediction results can be best fitted to the experimental data for a sufficiently large set of proteins and mutations. The inclusion is necessitated to achieve satisfactorily high prediction performance. A problem is that the resulting values of the parameters are often physically meaningless, and the physicochemical factors governing the thermal-stability changes upon mutations are rather ambiguous. Here, we develop a new measure of the thermal stability. Protein folding is accompanied by a large gain of water entropy (the entropic excluded-volume (EV) effect), loss of protein conformational entropy, and increase in enthalpy. The enthalpy increase originates primarily from the following: The energy increase due to the break of protein-water hydrogen bonds (HBs) upon folding cannot completely be cancelled out by the energy decrease brought by the formation of protein intramolecular HBs. We develop the measure on the basis of only these three factors and apply it to the prediction of the thermal-stability changes upon mutations. As a consequence, an approach toward the prediction is obtained. It is distinguished from the previously reported approaches in the following respects: The parameters adjusted in the manner mentioned above are not employed at all, and the entropic EV effect, which is ascribed to the translational displacement of water molecules coexisting with the protein in the system, is fully taken into account using a molecular model for water. Our approach is compared with one of the most popular approaches, FOLD-X, in terms of the prediction performance not only for single mutations but also for

  20. On the physics of thermal-stability changes upon mutations of a protein.

    PubMed

    Murakami, Shota; Oshima, Hiraku; Hayashi, Tomohiko; Kinoshita, Masahiro

    2015-09-28

    It is of great interest from both scientific and practical viewpoints to theoretically predict the thermal-stability changes upon mutations of a protein. However, such a prediction is an intricate task. Up to now, significantly many approaches for the prediction have been reported in the literature. They always include parameters which are adjusted so that the prediction results can be best fitted to the experimental data for a sufficiently large set of proteins and mutations. The inclusion is necessitated to achieve satisfactorily high prediction performance. A problem is that the resulting values of the parameters are often physically meaningless, and the physicochemical factors governing the thermal-stability changes upon mutations are rather ambiguous. Here, we develop a new measure of the thermal stability. Protein folding is accompanied by a large gain of water entropy (the entropic excluded-volume (EV) effect), loss of protein conformational entropy, and increase in enthalpy. The enthalpy increase originates primarily from the following: The energy increase due to the break of protein-water hydrogen bonds (HBs) upon folding cannot completely be cancelled out by the energy decrease brought by the formation of protein intramolecular HBs. We develop the measure on the basis of only these three factors and apply it to the prediction of the thermal-stability changes upon mutations. As a consequence, an approach toward the prediction is obtained. It is distinguished from the previously reported approaches in the following respects: The parameters adjusted in the manner mentioned above are not employed at all, and the entropic EV effect, which is ascribed to the translational displacement of water molecules coexisting with the protein in the system, is fully taken into account using a molecular model for water. Our approach is compared with one of the most popular approaches, FOLD-X, in terms of the prediction performance not only for single mutations but also for

  1. Thermal stability and melt rheology of poly(p-dioxanone).

    PubMed

    Liu, Changdeng; Andjelić, Sasa; Zhou, Jack; Xu, Yunmei; Vailhe, Christophe; Vetrecin, Robert

    2008-12-01

    Melt viscosities of poly(p-dioxanone) (PPDO) samples having different molecular weights were studied using a controlled-strain rotational rheometer under a nitrogen atmosphere. First, PPDO's thermal stability was evaluated by recording changes in its viscosity with time. The result, that samples' viscosities decreased with time when heated, demonstrated that PPDO is thermally unstable: its degradation activation energy, obtained by using a modified MacCallum equation, was a relatively low 71.8 kJ/mol K. Next, viscoelastic information was acquired through dynamic frequency measurements, which showed a shear thinning behavior among high molecular weight PPDOs, but a Newtonian flow behavior in a low molecular weight polymer (Mw = 18 kDa). Dynamic viscosity values were transferred to steady shear viscosities according to the Cox-Merz rule, and zero shear viscosities were derived according to the Cross model with a shear thinning index of 0.80. Then flow activation energy (48 kJ/mol K) was extrapolated for PPDO melts using an Arrhenius type equation. This activation energy is independent of polymer molecular weight. A linear relationship between zero shear viscosity and molecular weight was obtained using a double-logarithmic plot with a slope of 4.0, which is near the usually observed value of 3.4 for entangled linear polymers. Finally, the rheological behaviors of PPDO polymer blends having bimodal molecular weight distributions were investigated, with the results indicating that the relationship between zero shear viscosity and low molecular weight composition fraction can be described with a Christov model.

  2. Evaluation of electrodeposited ternary Ni-alloys for thermal stability

    NASA Astrophysics Data System (ADS)

    Kim, Myong Jin; Kim, Joung Soo; Kim, Dong Jin; Kim, Hong Pyo

    2011-04-01

    Electroplating methods for ternary Ni-alloys, such as Ni-P-Fe and Ni-P-B, in a Ni sulfamate solution on the inner wall surfaces of Alloy 600 tubing have been developed in order to use them to repair steam generator tubes damaged by a variety of corrosion mechanisms, in particular, by stress corrosion cracking. In this study, the stability of their microstructures and mechanical properties were evaluated to check if they could be used for a long period of time at the operating temperature of a PWR (pressurized water reactor) in nuclear power plants. The specimens were heat treated at 325 °C and 400 °C for 10, 20 and 30 days, followed by observation of their microstructures and measurement of their microhardness and tensile property. According to the experiment results, there was no noticeable change in their microstructures or microhardness with the heat treatment temperature and time conditions used in this study. For a Ni-P-B deposit, the ultimate tensile strength (UTS) slightly increased with the heat treatment time, while their elongation decreased. In the case of a Ni-P-Fe deposit, however, its tensile property varied with the applied current density. For a Ni-P-Fe deposit plated at an applied current density of 50 mA/cm2, its UTS slightly decreased, but its elongation slightly increased with the heat treatment time. We concluded that the thermal stability of the ternary Ni-alloy deposits used in this study is good enough to be used with the materials of operating nuclear power plants.

  3. Comparative Study of the Thermal Conductivity of Solid Biomass Fuels

    PubMed Central

    2016-01-01

    The thermal conductivity of solid biomass fuels is useful information in the investigation of biomass combustion behavior and the development of modeling especially in the context of large scale power generation. There are little published data on the thermal conductivity of certain types of biomass such as wheat straw, miscanthus, and torrefied woods. Much published data on wood is in the context of bulk materials. A method for determining the thermal conductivities of small particles of biomass fuels has been developed using a custom built test apparatus. Fourteen different samples of various solid biomass fuel were processed to form a homogenized pellet for analysis. The thermal conductivities of the pelletized materials were determined and compared against each other and to existing data. PMID:27041819

  4. Thermal stability of ladderane lipids as determined by hydrous pyrolysis

    USGS Publications Warehouse

    Jaeschke, A.; Lewan, M.D.; Hopmans, E.C.; Schouten, S.; Sinninghe, Damste J.S.

    2008-01-01

    Anaerobic ammonium oxidation (anammox) has been recognized as a major process resulting in loss of fixed inorganic nitrogen in the marine environment. Ladderane lipids, membrane lipids unique to anammox bacteria, have been used as markers for the detection of anammox in marine settings. However, the fate of ladderane lipids after sediment burial and maturation is unknown. In this study, anammox bacterial cell material was artificially matured by hydrous pyrolysis at constant temperatures ranging from 120 to 365 ??C for 72 h to study the stability of ladderane lipids during progressive dia- and catagenesis. HPLC-MS/MS analysis revealed that structural alterations of ladderane lipids already occurred at 120 ??C. At temperatures >140 ??C, ladderane lipids were absent and only more thermally stable products could be detected, i.e., ladderane derivatives in which some of the cyclobutane rings were opened. These diagenetic products of ladderane lipids were still detectable up to temperatures of 260 ??C using GC-MS. Thus, ladderane lipids are unlikely to occur in ancient sediments and sedimentary rocks, but specific diagenetic products of ladderane lipids will likely be present in sediments and sedimentary rocks of relatively low maturity (i.e., C31 hopane 22S/(22S + 22R) ratio 0.5). ?? 2008 Elsevier Ltd.

  5. Thermal Stability of MnBi Magnetic Materials

    SciTech Connect

    Cui, Jun; Choi, Jung-Pyung; Li, Guosheng; Polikarpov, Evgueni; Darsell, Jens T.; Overman, Nicole R.; Olszta, Matthew J.; Schreiber, Daniel K.; Bowden, Mark E.; Droubay, Timothy C.; Kramer, Matthew J.; Zarkevich, Nikolai; Wang, L. L.; Johnson, Duane D.; Marinescu, Melania; Takeuchi, Ichiro; Huang, Qingzhen; Wu, Hui; Reeve, Hayden; Vuong, Nguyen V.; Liu, J.Ping

    2014-01-01

    MnBi attracts great attention in recent years for its great potential as permanent magnet materials. It is unique because its coercivity increases with increasing temperature, which makes it a good hard phase for exchange coupling nanocomposite magnet. MnBi phase is difficult to obtain, partly because the reaction between Mn and Bi is peritectic, and partly because Mn is easy to react with oxygen. MnO formation is irreversible and causes degradation to the magnetic properties. In this paper, we report our effort on developing MnBi permanent magnet. High purity MnBi (>90%) can be routinely produced in large quantity. The obtained powder exhibit 74 emu/g saturation magnetization at room temperature with 9 T applied field. After alignment, the powder exhibits 11.6 MGOe, and the sintered bulk magnet exhibit 7.8 MGOe at room temperature. Thermal stability study shows that the MnBi is stable up to 473 K in air.

  6. Thermal stability of DNA adducts induced by cyanomorpholinoadriamycin in vitro.

    PubMed Central

    Cullinane, C; Phillips, D R

    1993-01-01

    The Adriamycin derivative, cyanomorpholinoadriamycin (CMA) was reacted with DNA in vitro to form apparent interstrand crosslinks. The extent of interstrand crosslink formation was monitored by a gel electrophoresis assay and maximal crosslinking of DNA was observed within 1 hr with 5 microM of drug. The interstrand crosslinks were heat labile, with a midpoint melting temperature of 70 degrees C (10 min exposure to heat) in 45% formamide. When CMA-induced adducts were detected as blockages of lambda-exonuclease, 12 blockage sites were observed with 8 being prior to 5'-GG sequences, one prior to 5'-CC, one prior to 5'-GC and 2 at unresolved combinations of these sequences. These exonuclease-detected blockages reveal the same sites of CMA-induced crosslinking as detected by in vitro transcription footprinting and primer-extension blockages on single strand DNA, where the blockages at 5'-GG and 5'-CC were identified as sites of intrastrand crosslinking and the 5'-GC blockage as a probable site of interstrand crosslinking. The thermal stability of both types of crosslink (10 min exposure to heat) ranged from 63-70 degrees C at individual sites. High levels of adduct were detected with poly (dG-dC) but not with poly (dI-dC). These results suggest adduct formation involving an aminal linkage between the 3 position of the morpholino moiety and N2 of guanine. Images PMID:8493102

  7. Controlled synthesis and thermal stability of hydroxyapatite hierarchical microstructures

    SciTech Connect

    Sun, Ruixue; Chen, Kezheng; Liao, Zhongmiao; Meng, Nan

    2013-03-15

    Highlights: ► Hydroxyapatite hierarchical microstructures have been synthesized by a facile method. ► The morphology and size of the building units of 3D structures can be controlled. ► The hydroxyapatite with 3D structure is morphologically and structurally stable up to 800 °C. - Abstract: Hydroxyapatite (HAp) hierarchical microstructures with novel 3D morphology were prepared through a template- and surfactant-free hydrothermal homogeneous precipitation method. Field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), and X-ray diffraction (XRD) were used to characterize the morphology and composition of the synthesized products. Interestingly, the obtained HAp with 3D structure is composed of one-dimensional (1D) nanorods or two-dimensional (2D) nanoribbons, and the length and morphology of these building blocks can be controlled through controlling the pH of the reaction. The building blocks are single crystalline and have different preferential orientation growth under different pH conditions. At low pH values, octacalcium phosphate (OCP) phase formed first and then transformed into HAp phase due to the increased pH value caused by the decomposition of urea. The investigation on the thermal stability reveals that the prepared HAp hierarchical microstructures are morphologically and structurally stable up to 800 °C.

  8. Experimental study of the thermal stability of hydrocarbon fuels

    NASA Technical Reports Server (NTRS)

    Marteney, P. J.; Colket, M. B.; Vranos, A.

    1982-01-01

    The thermal stability of two hydrocarbon fuels (premium diesel and regular diesel) was determined in a flow reactor under conditions representing operation of an aircraft gas turbine engine. Temperature was varied from 300 to 750 F (422 to 672 K) for fuel flows of 2.84 to 56.8 liters/hr (corresponding to 6.84 x 0.00010 to 1.63 x 0.010 kg/sec for regular diesel fuel and 6.55 x 0.00010 to 1.37 x 0.010 kg/sec for premium diesel fuel); test times varied between 1 and 8 hr. The rate of deposition was obtained through measurement of weight gained by metal discs fixed along the channel wall. The rate of deposit formation is best correlated by an Arrhenius expression. The sample discs in the flow reactor were varied among stainless steel, aluminum and brass; fuels were doped with quinoline, indole, and benzoyl perioxide to yield nitrogen or oxygen concentrations of approximately 1000 ppm. The most substantial change in rate was an increase in deposits for brass discs; other disc materials or the additives caused only small perturbations. Tests were also conducted in a static reactor at temperatures of 300 to 800 F for times of 30 min to 2 1/2 hr. Much smaller deposition was found, indicating the importance of fluid transport in the mechanism.

  9. Synthesis, thermal stability, and photocatalytic activity of nanocrystalline titanium carbide

    SciTech Connect

    Chen, Youjian; Zhang, Hong; Ma, DeKun; Ma, Jianhua; Ye, Hongnan; Qian, Gaojin; Ye, Yi

    2011-11-15

    Highlights: {yields} The synthesized temperature is lower than some conventional methods. {yields} These raw materials are safe; all manipulations are rather safe and convenient. {yields} The product exhibits photocatalytic activity in degradation of Rhodamine-B. -- Abstract: Titanium carbide (TiC) was prepared via one simple route by the reaction of metallic magnesium powders with titanium dioxide (TiO{sub 2}) and potassium acetate (CH{sub 3}COOK) in an autoclave at 600 {sup o}C and 8 h. Phase structure and morphology were characterized by X-ray powder diffraction (XRD) and Scanning electron microscopy (SEM). The results indicated that the product was cubic TiC, which consisted of particles with an average size of about 100 nm in diameter. The product was also studied by the thermogravimetric analysis (TGA) and its photocatalysis. It had good thermal stability and oxidation resistance below 350 {sup o}C in air. In addition, we discovered that the cubic TiC powders exhibited photocatalytic activity in degradation of Rhodamine-B (RhB) under 500 W mercury lamp light irradiation.

  10. The thermal stability of radiation-induced defects in illite

    NASA Astrophysics Data System (ADS)

    Riegler, T.; Allard, T.; Beaufort, D.; Cantin, J.-L.; von Bardeleben, H. J.

    2016-01-01

    High-purity illite specimens from the Mesoproterozoic unconformity-related uranium deposits of Kiggavik, Thelon basin, Nunavut (Canada), and Shea Creek (Athabasca basin, Saskatchewan, Canada) have been studied using electron paramagnetic resonance spectroscopy to determine the thermal stability of the main radiation-induced defects and question the potential of using illite as a natural dosimeter. The observed spectra are complex as they can show in the same region several contributions: (1) an unstable native defect, (2) the main stable defect named Ai by reference to a previous study (Morichon et al. in Phys Chem Minerals 35:339-346, 2008), (3) a signal at g = 2.063 assigned to a new defect, not yet fully characterized, named Ai2 center and (4) impurities such as vanadyl complex or divalent manganese. Isochronal heating shows that the new signal corresponds to a stable species. Isothermal heating experiments at 400 and 450 °C provide values of half-life extrapolated at room temperature and activation energy of 1.9-29,109 years and 1.3-1.4 eV, respectively, corresponding to the Ai center. These parameters allow the use of stable radiation-induced defects as a record of radioactivity down to the Paleoproterozoic period.

  11. Zirconia coating for enhanced thermal stability of gold nanoparticles

    NASA Astrophysics Data System (ADS)

    Pastre, A.; Cristini-Robbe, O.; Bois, L.; Chassagneux, F.; Branzea, D.; Boé, A.; Kinowski, C.; Raulin, K.; Rolland, N.; Bernard, R.

    2016-01-01

    This paper describes a rapid, simple and one-step method for the preparation of 2-4 nm diameter zirconia-coated gold nanoparticles at room temperature. These nanoparticles were synthesized by two simultaneous processes: the chemical reduction of tetrachloroauric acid with sodium borohydride and the formation of zirconia sol-gel matrices. All the gold nanoparticle sols were characterized by UV-visible absorption and transmission electron microscopy to determine the nanoparticle size and shape. The synthesis method is a combination of a polymeric structure of the amorphous zirconia and the use of a strong reducing agent, and it yields to very small quasi-spherical gold nanoparticles at room temperature. The thermal stability up to 1200 °C of the coated nanoparticles was studied by x-ray diffraction. The metastable tetragonal phase of the zirconia coating was obtained at 400 °C, and a progressive transformation from tetragonal to monoclinic phases of the zirconia coating was observed up to 1100 °C. After the heat treatment at 400 °C, the crystallite size of the gold nanoparticles was about 29 nm, and it remained unchanged from 400 °C to 1200 °C. These results are promising for the development of such materials as doping elements for optical fiber applications.

  12. Thermal stability of wild type and disulfide bridge containing mutant of poplar plastocyanin.

    PubMed

    Guzzi, Rita; Andolfi, Laura; Cannistraro, Salvatore; Verbeet, Martin Ph; Canters, Gerard W; Sportelli, Luigi

    2004-12-01

    A comparative study of the thermal stability of wild type poplar plastocyanin and of a mutant form containing a disulfide bridge between residues 21 and 25 was performed using differential scanning calorimetry and optical spectroscopic techniques. For wild type plastocyanin the transition temperature, determined from the calorimetric profiles, is 62.7 degrees C at the scan rate of 60 degrees C/h, whereas for the mutant it is reduced to 58.0 degrees C. In both cases, the endothermic peak is followed by an exothermic one at higher temperatures. The unfolding process monitored by optical absorption at 596 nm also reveals a reduced thermal stability of the mutated plastocyanin compared to the wild type protein, with transition temperatures of 54.8 and 58.0 degrees C, respectively. For both proteins, the denaturation process was found to be irreversible and dependent on the scan rate preventing the thermodynamic analysis of the unfolding process. In parallel, small conformational changes between wild type and mutant plastocyanin emerge from fluorescence spectroscopy measurements. Here, a difference in the interaction of the two proteins between the microenvironment surrounding the fluorophores and the solvent was proposed. The destabilization observed in the disulfide containing mutant of plastocyanin suggests that the double mutation, Ile21Cys and Glu25Cys, introduces strain into the protein which offsets the stabilizing effect expected from the formation of a covalent crosslink.

  13. Stability of the DMF-protected Au nanoclusters: photochemical, dispersion, and thermal properties.

    PubMed

    Kawasaki, Hideya; Yamamoto, Hiroko; Fujimori, Hiroaki; Arakawa, Ryuichi; Iwasaki, Yasuhiko; Inada, Mitsuru

    2010-04-20

    We have reported the synthesis of dimethylformamide (DMF)-protected gold nanoclusters using a surfactant-free DMF reduction method. DMF-protected gold nanoclusters (Au NCs) are obtained without the formation of gold nanoparticles and bulk metals as byproducts using a hot injection process for the homogeneous reduction. The as-prepared DMF-protected Au NCs were a mixture of various-sized Au NCs with a cluster number of less than 20 including at least Au(8) and Au(13). The photoluminescence emission from Au(8) and Au(13) was confirmed in the photoluminescence spectra. The Au NCs are stabilized with DMF molecules through the interaction of amide groups of DMF with Au NCs. DMF-protected Au NCs in solution were found to have high thermal stability, high dispersion stability in various solvents, and high photochemical stability. The DMF-protected Au NCs dispersed well for at least a month in various solvents such as water, acid (pH 2), alkali (pH 12) and 0.5 M NaCl aqueous solution, and methanol without further surface modification. The thermal stability of DMF-protected Au NCs was approximately 150 degrees C, which was comparable to that of thiolate-protected Au NCs. The photobleaching of Au NCs in water gradually occurred under UV light irradiation (356 nm, 1.3 mW/cm(2)) because of the photoinduced oxidation of Au NCs. After 8 h irradiation, the fluorescence intensity slowly decreased to approximately 50% of the maximum and to approximately 20% after 96 h under the present condition, compared to the photobleaching of CdSe semiconductor quantum dots. We also found that the fluorescence intensity remained to be about 30% of the maximum even in the presence of concentrated 30% H(2)O(2). These findings demonstrate that the photobleaching process under the UV irradiation is effectively suppressed for DMF-protected Au NCs.

  14. Silica, Hybrid Silica, Hydride Silica and Non-Silica Stationary Phases for Liquid Chromatography. Part II: Chemical and Thermal Stability.

    PubMed

    Borges, Endler M; Volmer, Dietrich A

    2015-08-01

    In the first part of this review, stationary phases (silica, hybrid silica, hydride silica and non-silica stationary phases) were characterized and compared with respect to selectivity, efficiency, resolution, solvent consumption and analysis time. The present review focuses on the thermal and chemical stability of stationary phases. Stationary phases of high chemical and thermal stability are required for separations that are carried over a wide pH and/or temperature range. © The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

  15. Comparative Thermal Degradation Patterns of Natural Yellow Colorants Used in Foods.

    PubMed

    Giménez, Pedro J; Fernández-López, José A; Angosto, José M; Obón, José M

    2015-12-01

    There is a great interest in natural yellow colorants due to warnings issued about certain yellow food colorings of synthetic origin. However, no comparative studies have been reported of their thermal stability. For this reason, the thermal stabilities of six natural yellow colorants used in foods--lutein, riboflavin, curcumin, ß-carotene, gardenia yellow and Opuntia betaxanthins--were studied in simple solutions over a temperature range 30-90 °C. Spectral properties and visual color were investigated during 6 h of heat treatment. Visual color was monitored from the CIEL*a*b* parameters. The remaining absorbance at maximum wavelength and the total color difference were used to quantify color degradation. The rate of color degradation increased as the temperature rose. The results showed that the thermal degradation of the colorants followed a first-order reaction kinetics. The reaction rate constants and half-life periods were determined as being central to understanding the color degradation kinetics. The temperature-dependent degradation was adequately modeled on the Arrhenius equation. Activation energies ranged from 3.2 kJmol(-1) (lutein) to 43.7 kJmol(-1) (Opuntia betaxanthins). ß-carotene and lutein exhibited high thermal stability, while betaxanthins and riboflavin degraded rapidly as temperature increased. Gardenia yellow and curcumin were in an intermediate position.

  16. Effect of thermal expansion on the stability of two-reactant flames

    NASA Technical Reports Server (NTRS)

    Jackson, T. L.

    1986-01-01

    The full problem of flame stability for the two-reactant model, which takes into account thermal expansion effects for all disturbance wave lengths, is examined. It is found that the stability problem for the class of two-reactant flames is equivalent to the stability problem for the class of one-reactant flames with an appropriate interpretation of Lewis numbers.

  17. SiC-dopped MCM-41 materials with enhanced thermal and hydrothermal stabilities

    SciTech Connect

    Wang, Yingyong; Jin, Guoqiang; Tong, Xili; Guo, Xiangyun

    2011-11-15

    Graphical abstract: Novel SiC-dopped MCM-41 materials were synthesized by adding silicon carbide suspension in the molecular sieve precursor solvent followed by in situ hydrothermal synthesis. The dopped materials have a wormhole-like mesoporous structure and exhibit enhanced thermal and hydrothermal stabilities. Highlights: {yields} SiC-dopped MCM-41 was synthesized by in situ hydrothermal synthesis of molecular sieve precursor combined with SiC. {yields} The dopped MCM-41 materials show a wormhole-like mesoporous structure. {yields} The thermal stability of the dopped materials have an increment of almost 100 {sup o}C compared with the pure MCM-41. {yields} The hydrothermal stability of the dopped materials is also better than that of the pure MCM-41. -- Abstract: SiC-dopped MCM-41 mesoporous materials were synthesized by the in situ hydrothermal synthesis, in which a small amount of SiC was added in the precursor solvent of molecular sieve before the hydrothermal treatment. The materials were characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, N{sub 2} physical adsorption and thermogravimetric analysis, respectively. The results show that the thermal and hydrothermal stabilities of MCM-41 materials can be improved obviously by incorporating a small amount of SiC. The structure collapse temperature of SiC-dopped MCM-41 materials is 100 {sup o}C higher than that of pure MCM-41 according to the differential scanning calorimetry analysis. Hydrothermal treatment experiments also show that the pure MCM-41 will losses it's ordered mesoporous structure in boiling water for 24 h while the SiC-dopped MCM-41 materials still keep partial porous structure.

  18. Modification of proteins with cyclodextrins prevents aggregation and surface adsorption and increases thermal stability.

    PubMed

    Prashar, Deepali; Cui, DaWei; Bandyopadhyay, Debjyoti; Luk, Yan-Yeung

    2011-11-01

    This work describes a general approach for preventing protein aggregation and surface adsorption by modifying proteins with β-cyclodextrins (βCD) via an efficient water-driven ligation. As compared to native unmodified proteins, the cyclodextrin-modified proteins (lysozyme and RNase A) exhibit significant reduction in aggregation, surface adsorption and increase in thermal stability. These results reveal a new chemistry for preventing protein aggregation and surface adsorption that is likely of different mechanisms than that by modifying proteins with poly(ethylene glycol).

  19. Phase evolution and thermal properties of yttria-stabilized hafnia nano-coatings deposited on alumina

    NASA Astrophysics Data System (ADS)

    Rubio, Ernesto Javier

    High-temperature coatings are critical to the future power-generation systems and industries. Thermal barrier coatings (TBCs), which are usually the ceramic materials applied as thin coatings, protect engine components and allow further increase in engine temperatures for higher efficiency. Thus, the durability and reliability of the coating systems have to be more robust compared to current natural gas based engines. While a near and mid-term target is to develop TBC architecture with a 1300 °C surface temperature tolerance, a deeper understanding of the structure evolution and thermal behavior of the TBC-bond coat interface, specifically the thermally grown oxide (TGO), is of primary importance. In the present work, attention is directed towards yttria-stabilized hafnia (YSH) coatings on alumina (α-Al2O 3) to simulate the TBC-TGO interface and understand the phase evolution, microstructure and thermal oxidation of the coatings. YSH coatings were grown on α-Al2O3 substrates by sputter deposition by varying coating thickness in a wide range ˜30-1000 nm. The effect of coating thickness on the structure, morphology and the residual stress has been investigated using X-ray diffraction (XRD) and high resolution scanning electron microscopy (SEM). Thermal oxidation behavior of the coatings has been evaluated using the isothermal oxidation measurements under static conditions. X-ray diffraction analyses revealed the existence of monoclinic hafnia phase for relatively thin coatings indicating that the interfacial phenomena are dominant in phase stabilization. The evolution towards pure stabilized cubic phase of hafnia with the increasing coating thickness is observed. The SEM results indicate the changes in morphology of the coatings; the average grain size increases from 15 to 500 nm with increasing thickness. Residual stress was calculated employing XRD using the variable ψ-angle. Relation between residual stress and structural change is also studied. The results

  20. Thermal Stability of Ice on Ceres with Rough Topography

    NASA Astrophysics Data System (ADS)

    Hayne, Paul O.; Aharonson, Oded

    2015-11-01

    The dwarf planet Ceres may have an ice-rich crust, and subsurface ice exposed by impacts or endogenic activity would be subject to sublimation. The “bright spots” recently discovered by the Dawn mission on the illuminated surface of Ceres have prompted speculation regarding their possible icy composition and the youthful age this might imply. Furthermore, sublimation of ice at the surface or in the interior of Ceres could explain water vapor observed on more than one occasion in the exosphere. We investigated the possible distribution and lifetimes of water ice and other volatiles on Ceres using detailed thermal models, including realistic thermophysical properties and surface roughness.Topographic shadowing creates polar cold traps where a small, but non-negligible fraction (~0.4%) of Ceres' surface is perennially below the ~110 K criterion for 1 Gyr of H2O ice stability. These areas are found above 60° latitude. Other molecules (CH3OH, NH3, SO2, CO2) may be cold-trapped in smaller abundances. A model for the transport, gravitational escape and photoionization of H2O molecules suggests net accumulation in the cold traps. At latitudes 0° - 30°, ice is stable under solar illumination only briefly (~10-100 yr), unless it has high albedo and thermal inertia, in which case lifetimes of > 104 yr are possible.Buried ice is stable within a meter for > 1 Gyr at latitudes higher than ~50°. An illuminated polar cap of water ice would be stable within a few degrees of the poles only if it maintained a high albedo (> 0.5) at present obliquity. If the obliquity exceeded 5° in the geologically recent past, then a putative polar cap would have been erased. Finally, a small hemispheric asymmetry exists due to the timing of Ceres' perihelion passage, which would lead to a detectable enhancement of ice in the northern hemisphere if the orbital elements vary slowly relative to the ice accumulation rate. Our model results are potentially testable during the Dawn science

  1. Thermal Stability of a 4 Meter Primary Reflector for the Scanning Microwave Limb Sounder

    NASA Technical Reports Server (NTRS)

    Cofield, Richard; Kasl, Eldon P.

    2010-01-01

    We describe the fabrication and thermal-stability analysis and test of a composite demonstration model of the Scanning Microwave Limb Sounder (SMLS) primary reflector, having full 4m height and 1/3 the width planned for flight. SMLS is a space-borne heterodyne radiometer which will measure pressure, temperature and atmospheric constituents from thermal emission between 180 and 660 GHz. Current MLS instruments in low Earth orbit scan pencil-beam antennas (sized to resolve about one scale height) vertically over the atmospheric limb. SMLS, planned for the Global Atmospheric Composition Mission of the NRC Decadal Survey, adds azimuthal scanning for better horizontal and temporal resolution and coverage than typical orbit spacing provides. SMLS combines the wide scan range of the parabolic torus with unblocked offset Cassegrain optics. The resulting system is diffraction-limited in the vertical plane but highly astigmatic in the horizontal, having a beam aspect ratio [tilde operator]1:20. Symmetry about the nadir axis ensures that beam shape is nearly invariant over +/-65(white bullet) azimuth. The a feeds a low-noise SIS receiver whose FOV is swept over the reflector system by a small scanning mirror. Using finiteelement models of antenna reflectors and structure, we evaluate thermal deformations and the resulting optical performance for 4 orbital environments and isothermal soak. We compare deformations with photogrammetric measurements made during wide-range (ambient+[-97,+75](white bullet) C) thermal soak tests of the primary in a chamber. This range exceeds predicted orbital soak ranges by large factors, implying in-orbit thermal stability of 0.21(mu)m rms/(white bullet)C, which meets SMLS requirements.

  2. Thermal Stability of a 4 Meter Primary Reflector for the Scanning Microwave Limb Sounder

    NASA Technical Reports Server (NTRS)

    Cofield, Richard; Kasl, Eldon P.

    2010-01-01

    We describe the fabrication and thermal-stability analysis and test of a composite demonstration model of the Scanning Microwave Limb Sounder (SMLS) primary reflector, having full 4m height and 1/3 the width planned for flight. SMLS is a space-borne heterodyne radiometer which will measure pressure, temperature and atmospheric constituents from thermal emission between 180 and 660 GHz. Current MLS instruments in low Earth orbit scan pencil-beam antennas (sized to resolve about one scale height) vertically over the atmospheric limb. SMLS, planned for the Global Atmospheric Composition Mission of the NRC Decadal Survey, adds azimuthal scanning for better horizontal and temporal resolution and coverage than typical orbit spacing provides. SMLS combines the wide scan range of the parabolic torus with unblocked offset Cassegrain optics. The resulting system is diffraction-limited in the vertical plane but highly astigmatic in the horizontal, having a beam aspect ratio [tilde operator]1:20. Symmetry about the nadir axis ensures that beam shape is nearly invariant over +/-65(white bullet) azimuth. The a feeds a low-noise SIS receiver whose FOV is swept over the reflector system by a small scanning mirror. Using finiteelement models of antenna reflectors and structure, we evaluate thermal deformations and the resulting optical performance for 4 orbital environments and isothermal soak. We compare deformations with photogrammetric measurements made during wide-range (ambient+[-97,+75](white bullet) C) thermal soak tests of the primary in a chamber. This range exceeds predicted orbital soak ranges by large factors, implying in-orbit thermal stability of 0.21(mu)m rms/(white bullet)C, which meets SMLS requirements.

  3. The chemical stability of abasic RNA compared to abasic DNA.

    PubMed

    Küpfer, Pascal A; Leumann, Christian J

    2007-01-01

    We describe the synthesis of an abasic RNA phosphoramidite carrying a photocleavable 1-(2-nitrophenyl)ethyl (NPE) group at the anomeric center and a triisopropylsilyloxymethyl (TOM) group as 2'-O-protecting group together with the analogous DNA and the 2'-OMe RNA abasic building blocks. These units were incorporated into RNA-, 2'-OMe-RNA- and DNA for the purpose of studying their chemical stabilities towards backbone cleavage in a comparative way. Stability measurements were performed under basic conditions (0.1 M NaOH) and in the presence of aniline (pH 4.6) at 37 degrees C. The kinetics and mechanisms of strand cleavage were followed by High pressure liquid chromotography and ESI-MS. Under basic conditions, strand cleavage at abasic RNA sites can occur via beta,delta-elimination and 2',3'-cyclophosphate formation. We found that beta,delta-elimination was 154-fold slower compared to the same mechanism in abasic DNA. Overall strand cleavage of abasic RNA (including cyclophosphate formation) was still 16.8 times slower compared to abasic DNA. In the presence of aniline at pH 4.6, where only beta,delta-elimination contributes to strand cleavage, a 15-fold reduced cleavage rate at the RNA abasic site was observed. Thus abasic RNA is significantly more stable than abasic DNA. The higher stability of abasic RNA is discussed in the context of its potential biological role.

  4. The chemical stability of abasic RNA compared to abasic DNA

    PubMed Central

    Küpfer, Pascal A.; Leumann, Christian J.

    2007-01-01

    We describe the synthesis of an abasic RNA phosphoramidite carrying a photocleavable 1-(2-nitrophenyl)ethyl (NPE) group at the anomeric center and a triisopropylsilyloxymethyl (TOM) group as 2′-O-protecting group together with the analogous DNA and the 2′-OMe RNA abasic building blocks. These units were incorporated into RNA-, 2′-OMe-RNA- and DNA for the purpose of studying their chemical stabilities towards backbone cleavage in a comparative way. Stability measurements were performed under basic conditions (0.1 M NaOH) and in the presence of aniline (pH 4.6) at 37°C. The kinetics and mechanisms of strand cleavage were followed by High pressure liquid chromotography and ESI-MS. Under basic conditions, strand cleavage at abasic RNA sites can occur via β,δ-elimination and 2′,3′-cyclophosphate formation. We found that β,δ-elimination was 154-fold slower compared to the same mechanism in abasic DNA. Overall strand cleavage of abasic RNA (including cyclophosphate formation) was still 16.8 times slower compared to abasic DNA. In the presence of aniline at pH 4.6, where only β,δ-elimination contributes to strand cleavage, a 15-fold reduced cleavage rate at the RNA abasic site was observed. Thus abasic RNA is significantly more stable than abasic DNA. The higher stability of abasic RNA is discussed in the context of its potential biological role. PMID:17151071

  5. Thermal stability of anthocyanin extract of Hibiscus sabdariffa L. in the presence of beta-cyclodextrin.

    PubMed

    Mourtzinos, Ioannis; Makris, Dimitris P; Yannakopoulou, Konstantina; Kalogeropoulos, Nick; Michali, Iliana; Karathanos, Vaios T

    2008-11-12

    The thermal stability of anthocyanin extract isolated from the dry calyces of Hibiscus sabdariffa L. was studied over the temperature range 60-90 degrees C in aqueous solutions in the presence or absence of beta-cyclodextrin (beta-CD). The results indicated that the thermal degradation of anthocyanins followed first-order reaction kinetics. The temperature-dependent degradation was adequately modeled by the Arrhenius equation, and the activation energy for the degradation of H. sabdariffa L. anthocyanins during heating was found to be approximately 54 kJ/mol. In the presence of beta-CD, anthocyanins degraded at a decreased rate, evidently due to their complexation with beta-CD, having the same activation energy. The formation of complexes in solution was confirmed by nuclear magnetic resonance studies of beta-CD solutions in the presence of the extract. Moreover, differential scanning calorimetry revealed that the inclusion complex of H. sabdariffa L. extract with beta-CD in the solid state was more stable against oxidation as compared to the free extract, as the complex remained intact at temperatures 100-250 degrees C where the free extract was oxidized. The results obtained clearly indicated that the presence of beta-CD improved the thermal stability of nutraceutical antioxidants present in H. sabdariffa L. extract, both in solution and in solid state.

  6. Advanced study of thermal behaviour of CSZ comparing with the classic YSZ coating

    NASA Astrophysics Data System (ADS)

    Dragomirescu, A.; Constantin, N.; Ştefan, A.; Manoliu, V.; Truşcă, R.

    2017-01-01

    Thermal barrier coatings (TBC) are advanced materials typically applied to metal surfaces subjected to extreme temperatures to protect them and increase their lifetime. Ceria stabilized zirconia ceramic layer (CSZ) is increasingly used as an alternative improved as replace for classical TBC system - yttria stabilized zirconia - thanks to superior properties, including mechanical and high resistance to thermal corrosion. The paper describes the thermal shock testing of two types of thermal barrier coatings used to protect a nickel super alloy. For the experimental procedure, it was used plate samples from nickel super alloy with a bond coat and a ceramic top coat. The top coat was different: on some samples, it was used YSZ and on others CSZ. Ni based super alloys have good corrosion resistance in reducing environments action, but poor in oxidizing conditions. Extreme environments can lead to loss of material by oxidation / corrosion, along with decreased mechanical properties of the substrate due to damaging elements which diffuses into the substrate at high temperatures. Using laboratory equipment, the TBC systems were exposed repeatedly to extreme high temperatures for a short time and then cooled. After the thermal shock tests, the samples were morph-structured characterized using electronic microscopy to analyze the changes. The experimental results were compared to rank the TBC systems in order of performance.

  7. An algorithm to stabilize a sequence of thermal brain images

    NASA Astrophysics Data System (ADS)

    Kovalerchuk, Boris; Lemley, Joseph; Gorbach, Alexander M.

    2007-03-01

    Complex challenges of optical imaging in diagnostics and surgical treatment require accurate image registration/stabilization methods that remove only unwanted motions. An SIAROI algorithm is proposed for real-time subpixel registration sequences of intraoperatively acquired infrared (thermal) brain images. SIAROI algorithm is based upon automatic, localized Subpixel Image Autocorrelation and a user-selected Region of Interest (ROI). Human expertise about unwanted motions is added through a user-outlined ROI, using a low-accuracy free-hand paintbrush. SIAROI includes: (a) propagating the user-outlined ROI by selecting pixels in the second image of the sequence, using the same ROI; (b) producing SROI (sub-pixel ROI) by converting each pixel to k=NxN subpixels; (c) producing new SROI in the second image by shifting SROI within plus or minus 6k subpixels; (d) finding an optimal autocorrelation shift (x,y) within 12N that minimizes the Standard Deviation of Differences of Pixel Intensities (SDDPI) between corresponding ROI pixels in both images, (e) shifting the second image by (x,y), repeating (a)-(e) for successive images (t,t1). In experiments, a user quickly outlined non-deformable ROI (such as bone) in the first image of a sequence. Alignment of 100 brain images (25600x25600 pixel search, after every pixel was converted to 100 sub-pixels), took ~3 minutes, which is 200 times faster (with a 0.1=ROI/image ratio) than global auto-correlation. SIAROI improved frame alignment by a factor of two, relative to a Global Auto-correlation and Tie-points-based registration methods, as measured by reductions in the SDDPI.

  8. Conjugation of D-glucosamine to bovine trypsin increases thermal stability and alters functional properties.

    PubMed

    Gizurarson, Jóhann Grétar Kröyer; Filippusson, Hörður

    2015-01-01

    D-Glucosamine was conjugated to bovine trypsin by carbodiimide chemistry, involving a water-soluble carbodiimide and a succinimide ester, with the latter being to increase the yield of the conjugation. Mass spectrometric data suggested that several glycoforms were formed, with around 12 D-glucosamine moieties coupled to each trypsin molecule on average. The moieties were probably coupled to eight carboxyl groups (of glutamyl and aspartyl residues) and to four tyrosyl residues on the surface of the enzyme. The glycated trypsin possessed increased thermal stability. When compared with its unmodified counterpart, T50% was increased by 7 °C, thermal inactivation of the first step was increased 34%, and long-term stability assay revealed 71-times higher residual activity at 25 °C (without stabilizing Ca(2+) ions in aqueous buffer) after 67 days. Furthermore, resistance against autolysis was increased almost two-fold. Altered functional properties of the glycated trypsin were also observed. The glycated trypsin was found to become increasingly basophilic, and was found to be slightly structurally altered. This was indicated by 1.2 times higher catalytic efficiency (k(cat)/K(m)) than unmodified trypsin against the substrate N-α-benzoyl-L-arginine-p-nitroanilide. Circular dichroism spectropolarimetry suggested a minor change in spatial arrangement of α-helix/helices, resulting in an increased affinity of the glycated trypsin for this small synthetic substrate. Copyright © 2015 Elsevier Inc. All rights reserved.

  9. Thermal and Trophic Stability of Deeper Maine Lakes in Granite Watersheds Impacted by Acid Deposition

    NASA Astrophysics Data System (ADS)

    Stauffer, Robert E.; Wittchen, Bruce D.

    1990-09-01

    Acid deposition can lead to lake and watershed acidification, increases in lake transparency, and reductions in thermal stability and hypolimnetic oxygen deficits. On the basis of lake surveys during August-September 1985, we determined to what extent the deeper (maximum depth zm > 17 m) Maine lakes in acid-sensitive granitic watersheds have registered changes in temperature and oxygen stratification, as compared to 1938-1942, when G. P. Cooper performed the earliest scientific surveys of the state's lakes. After correcting for small but geographically consistent interannual differences in summer hypolimnetic temperatures related to spring turnover, and weather-dependent differences in mixed layer depth, there has been no significant change in thermal stratification in these Maine lakes over approximately 43 years. On the basis of specific historical contrasts in the late summer metalimnetic, hypolimnetic, and bathylimnetic oxygen concentrations there has been no significant change in lake trophic state or transparency.

  10. Thermal stabilization of thin gold nanowires by surfactant-coating: a molecular dynamics study.

    PubMed

    Huber, Stefan E; Warakulwit, Chompunuch; Limtrakul, Jumras; Tsukuda, Tatsuya; Probst, Michael

    2012-01-21

    The thermal stabilization of thin gold nanowires with a diameter of about 2 nm by surfactants is investigated by means of classical molecular dynamics simulations. While the well-known melting point depression leads to a much lower melting of gold nanowires compared to bulk gold, coating the nanowires with surfactants can reverse this, given that the attractive interaction between surfactant molecules and gold atoms lies beyond a certain threshold. It is found that the melting process of coated nanowires is dominated by surface instability patterns, whereas the melting behaviour of gold nanowires in a vacuum is dominated by the greater mobility of atoms with lower coordination numbers that are located at edges and corners. The suppression of the melting by surfactants is explained by the isotropic pressure acting on the gold surface (due to the attractive interaction) which successfully suppresses large-amplitude thermal motions of the gold atoms.

  11. Study of phase transformation and microstructure of alcohol washed titania nanoparticles for thermal stability

    SciTech Connect

    Kaur, Manpreet Singh, Gaganjot; Bimbraw, Keshav; Uniyal, Poonam

    2015-08-28

    Nanostructured titania have been successfully synthesized by hydrolysis of alkoxide at calcination temperatures 500 °C, 600 °C and 700 °C. As the calcination temperature increases, alcohol washed samples show lesser rutile content as compared to water washed samples. Morphology and Particle sizes was determined by field emission scanning electron microscopy (FESEM), while thermogravimetric-differential scanning calorimetry (TG-DSC) was used to determine thermal stability. Alcohol washed samples undergo 30% weight loss whereas 16% in water washed samples was observed. The mean particle sizes were found to be increase from 37 nm to 100.9 nm and 35.3 nm to 55.2 nm for water and alcohol washed samples respectively. Hydrolysis of alkoxide was shown to be an effective means to prepare thermally stable titania by using alcohol washed samples as a precursor.

  12. Thermal stability of electrodeposited platinum nanowires and morphological transformations at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Rauber, M.; Muench, F.; Toimil-Molares, M. E.; Ensinger, W.

    2012-11-01

    Pt nanowires were prepared by template electrodeposition using ion track etched polymer membranes and analysed with respect to their thermal stability. Driven by Rayleigh instability, the polycrystalline Pt nanostructures experienced structural transformations and finally fragmented into linear chains of nanospheres at temperatures much below the melting point of bulk Pt. Morphological changes were systematically studied by electron microscopy and compared with previously reported results on other metal nanowires and theoretical predictions. In addition, nanowires could readily be interconnected to two-dimensional assemblies by taking advantage of the rapid diffusion processes. This study will help to predict the durability of integrated nanowires and contributes to the understanding of thermal-induced transformations for polycrystalline nanowires.

  13. Thermal stability of electrodeposited platinum nanowires and morphological transformations at elevated temperatures.

    PubMed

    Rauber, M; Muench, F; Toimil-Molares, M E; Ensinger, W

    2012-11-30

    Pt nanowires were prepared by template electrodeposition using ion track etched polymer membranes and analysed with respect to their thermal stability. Driven by Rayleigh instability, the polycrystalline Pt nanostructures experienced structural transformations and finally fragmented into linear chains of nanospheres at temperatures much below the melting point of bulk Pt. Morphological changes were systematically studied by electron microscopy and compared with previously reported results on other metal nanowires and theoretical predictions. In addition, nanowires could readily be interconnected to two-dimensional assemblies by taking advantage of the rapid diffusion processes. This study will help to predict the durability of integrated nanowires and contributes to the understanding of thermal-induced transformations for polycrystalline nanowires.

  14. [Thermal stability of lactate dehydrogenase and alcohol dehydrogenase incorporated into highly concentrated gels].

    PubMed

    Kulis, Iu Iu

    1979-03-01

    The rate constants for inactivation of lactate dehydrogenase and alcohol dehydrogenase in solution at 65 degrees C (pH 7,5) are 0,72 and 0,013 min-1, respectively. The enzyme incorporation into acrylamide gels results in immobilized enzymes, whose residual activity is 18--25% of the original one. In 6,7% gels the rate of thermal inactivation for lactate dehydrogenase is decreased nearly 10-fold, whereas the inactivation rate for alcohol dehydrogenase is increased 4,6-fold as compared to the soluble enzymes. In 14% and 40% gels the inactivation constants for lactate dehydrogenase are 6,3.10(-3) and 5,9.10(-4) min-1, respectively. In 60% gels the thermal inactivation of lactate dehydrogenase is decelerated 3600-fold as compared to the native enzyme. The enthalpy and enthropy for the inactivation of the native enzyme are equal to 62,8 kcal/mole and 116,9 cal/(mole.grad.) for the native enzyme and those of gel-incorporated (6,7%) enzyme -- 38,7 kcal/mole and 42 cal/(mole.grad.), respectively. The thermal stability of alcohol dehydrogenase in 60% gels is increased 12-fold. To prevent gel swelling, methacrylic acid and allylamine were added to the matrix, with subsequent treatment by dicyclohexylcarbodiimide. The enzyme activity of the modified gels is 2,7--3% of that for the 6,7% gels. The stability of lactate dehydrogenase in such gels is significantly increased. A mechanism of stabilization of the subunit enzymes in highly concentrated gels is discussed.

  15. Phosphorus-Assisted Biomass Thermal Conversion: Reducing Carbon Loss and Improving Biochar Stability

    PubMed Central

    Zhao, Ling; Cao, Xinde; Zheng, Wei; Kan, Yue

    2014-01-01

    There is often over 50% carbon loss during the thermal conversion of biomass into biochar, leading to it controversy for the biochar formation as a carbon sequestration strategy. Sometimes the biochar also seems not to be stable enough due to physical, chemical, and biological reactions in soils. In this study, three phosphorus-bearing materials, H3PO4, phosphate rock tailing (PRT), and triple superphosphate (TSP), were used as additives to wheat straw with a ratio of 1: 0.4–0.8 for biochar production at 500°C, aiming to alleviate carbon loss during pyrolysis and to increase biochar-C stabilization. All these additives remarkably increased the biochar yield from 31.7% (unmodified biochar) to 46.9%–56.9% (modified biochars). Carbon loss during pyrolysis was reduced from 51.7% to 35.5%–47.7%. Thermogravimetric analysis curves showed that the additives had no effect on thermal stability of biochar but did enhance its oxidative stability. Microbial mineralization was obviously reduced in the modified biochar, especially in the TSP-BC, in which the total CO2 emission during 60-d incubation was reduced by 67.8%, compared to the unmodified biochar. Enhancement of carbon retention and biochar stability was probably due to the formation of meta-phosphate or C-O-PO3, which could either form a physical layer to hinder the contact of C with O2 and bacteria, or occupy the active sites of the C band. Our results indicate that pre-treating biomass with phosphors-bearing materials is effective for reducing carbon loss during pyrolysis and for increasing biochar stabilization, which provides a novel method by which biochar can be designed to improve the carbon sequestration capacity. PMID:25531111

  16. Phosphorus-assisted biomass thermal conversion: reducing carbon loss and improving biochar stability.

    PubMed

    Zhao, Ling; Cao, Xinde; Zheng, Wei; Kan, Yue

    2014-01-01

    There is often over 50% carbon loss during the thermal conversion of biomass into biochar, leading to it controversy for the biochar formation as a carbon sequestration strategy. Sometimes the biochar also seems not to be stable enough due to physical, chemical, and biological reactions in soils. In this study, three phosphorus-bearing materials, H3PO4, phosphate rock tailing (PRT), and triple superphosphate (TSP), were used as additives to wheat straw with a ratio of 1: 0.4-0.8 for biochar production at 500°C, aiming to alleviate carbon loss during pyrolysis and to increase biochar-C stabilization. All these additives remarkably increased the biochar yield from 31.7% (unmodified biochar) to 46.9%-56.9% (modified biochars). Carbon loss during pyrolysis was reduced from 51.7% to 35.5%-47.7%. Thermogravimetric analysis curves showed that the additives had no effect on thermal stability of biochar but did enhance its oxidative stability. Microbial mineralization was obviously reduced in the modified biochar, especially in the TSP-BC, in which the total CO2 emission during 60-d incubation was reduced by 67.8%, compared to the unmodified biochar. Enhancement of carbon retention and biochar stability was probably due to the formation of meta-phosphate or C-O-PO3, which could either form a physical layer to hinder the contact of C with O2 and bacteria, or occupy the active sites of the C band. Our results indicate that pre-treating biomass with phosphors-bearing materials is effective for reducing carbon loss during pyrolysis and for increasing biochar stabilization, which provides a novel method by which biochar can be designed to improve the carbon sequestration capacity.

  17. Comparative study of thermal conductivity in crystalline and amorphous nanocomposite

    NASA Astrophysics Data System (ADS)

    Juangsa, Firman Bagja; Muroya, Yoshiki; Ryu, Meguya; Morikawa, Junko; Nozaki, Tomohiro

    2017-06-01

    Silicon nanocrystals (SiNCs)/polystyrene (PS) nanocomposite has been observed to have a significant decrease in thermal conductivity in terms of the SiNC fraction with unspecified factors remained unclear. In this paper, amorphous silicon nanoparticles (a-SiNPs) with a mean diameter of 6 nm and PS nanocomposites were synthesized, and their thermal conductivity, including the density and specific heat, was compared with our previous work which investigated well-crystalized SiNPs (6 nm) and PS nanocomposite. The difference between amorphous and crystalline structure is insignificant, but phonon scattering at SiNPs and PS boundary is the key influencing factor of thermal conductivity reduction. The effective thermal conductivity models for nanocomposite revealed that the thermal boundary resistance, explained by Kapitza principle, is estimated to be 4 × 10-7 m2K/W, showing the significant effect of nanostructured heterogenic surface resistance on overall heat transfer behavior. Preservation of unique properties nanoscale materials and low-cost fabrication by silicon inks process at room temperature give the promising potential of SiNPs based heat transfer management.

  18. Thermal stability studies of short period Sc/Cr and Sc/B₄C/Cr multilayers.

    PubMed

    Prasciolu, Mauro; Leontowich, Adam F G; Beyerlein, Kenneth R; Bajt, Saša

    2014-04-01

    The stability of short period Sc/Cr and Sc/B₄C/Cr multilayers was investigated over a large temperature range. The aim was to find a stable reflective coating for an off-axis parabola for focusing x rays from a soft x-ray free-electron laser. Normal incidence reflectivity, surface roughness, and intrinsic stress were investigated as a function of annealing temperature and two samples were also studied with a high-resolution transmission electron microscope (TEM), a scanning TEM, and through electron energy loss spectroscopy (EELS). Interface-engineered Sc/B₄C/Cr multilayers showed increased thermal stability and higher reflectivity as compared to pure Sc/Cr multilayers.

  19. Enhanced superhydrophilicity and thermal stability of ITO surface with patterned ceria coatings

    NASA Astrophysics Data System (ADS)

    Xue, Mingshan; Peng, Na; Li, Changquan; Ou, Junfei; Wang, Fajun; Li, Wen

    2015-02-01

    Surface wettability of solid materials is significant for both fundamental research and engineering applications. Compared with most existing fabrication methods of superhydrophilic surfaces by UV exposure or chemical modification, in this work, a superhydrophilic ceria coating on ITO substrate is developed by a fast, simple one-step method. It is found that the superhydrophilicity of ceria coatings is strongly dependent on both the patterned microstructures benefiting the capillary effect and the peculiar chemical composition of ceria inducing numerous oxygen vacancies and large surface free energy. Owing to the inherent physical stability of ceria, such a superhydrophilic ceria coating exhibits an excellently thermal stability at both room temperature and higher temperature. These results open up new avenues for the underlying applications of superhydrophilic coatings, such as heat transfer/dissipation.

  20. Thermal Stability of Nanocrystalline Alloys by Solute Additions and A Thermodynamic Modeling

    NASA Astrophysics Data System (ADS)

    Saber, Mostafa

    an example, model predictions are compared to experimental results for Fe-Cr-Zr and Fe-Ni-Zr alloy systems. Consistency between the experimental results and the present model predictions provide a more rigorous criterion for investigating thermal stabilization. However, other possible contributions for grain growth stabilization should still be considered.

  1. Thermal stability of structurally different viruses with proven or potential relevance to food safety.

    PubMed

    Tuladhar, E; Bouwknegt, M; Zwietering, M H; Koopmans, M; Duizer, E

    2012-05-01

    To collect comparative data on thermal stability of structurally different viruses with proven or potential relevance to food safety. Suspensions with poliovirus Sabin1, adenovirus type5, parechovirus1, human norovirus (NoV) GII.4, murine NoV (MNV1) and human influenza A (H1N1) viruses were heated at 56 and 73°C. Infectivity was tested by culture assay for all but human NoV GII.4 that cannot be cultivated in vitro. Time to first log(10) reduction (TFL-value) was calculated based on best fit using the monophasic, biphasic or Weibull models. The Weibull model provided the best fit at 56°C for all viruses except influenza virus. The TFL at 56°C varied between a high of 27 min (parechovirus) to a low of 10 s (adenovirus) and ranked parechovirus > influenza > MNV1 > poliovirus > adenovirus. The monophasic model best described the behaviour of the viruses at 73°C, in which case the TFL was MNV1(62s) > influenza > adenovirus > parechovirus > poliovirus(14s). Viruses do not follow log-linear thermal inactivation kinetics and the thermostability of parechovirus and influenza virus is similar to that of proven foodborne viruses. Resistant fractions of viruses may remain infectious in thermal inactivation processes and inactivation of newly discovered or enveloped viruses in thermal food preparation processes should not be assumed without further testing. © 2012 The Authors. Journal of Applied Microbiology © 2012 The Society for Applied Microbiology.

  2. STABILIZING SELECTION AND THE COMPARATIVE ANALYSIS OF ADAPTATION.

    PubMed

    Hansen, Thomas F

    1997-10-01

    Comparative studies tend to differ from optimality and functionality studies in how they treat adaptation. While the comparative approach focuses on the origin and change of traits, optimality studies assume that adaptations are maintained at an optimum by stabilizing selection. This paper presents a model of adaptive evolution on a macroevolutionary time scale that includes the maintenance of traits at adaptive optima by stabilizing selection as the dominant evolutionary force. Interspecific variation is treated as variation in the position of adaptive optima. The model illustrates how phylogenetic constraints not only lead to correlations between phylogenetically related species, but also to imperfect adaptations. From this model, a statistical comparative method is derived that can be used to estimate the effect of a selective factor on adaptive optima in a way that would be consistent with an optimality study of adaptation to this factor. The method is illustrated with an analysis of dental evolution in fossil horses. The use of comparative methods to study evolutionary trends is also discussed. © 1997 The Society for the Study of Evolution.

  3. Factors affecting the microstructural stability and durability of thermal barrier coatings fabricated by air plasma spraying: TBC microstructural stability and durability

    SciTech Connect

    Helminiak, M. A.; Yanar, N. M.; Pettit, F. S.; Taylor, T. A.; Meier, G. H.

    2012-07-23

    The high-temperature behavior of high-purity, low-density (HP-LD) air plasma sprayed (APS) thermal barrier coatings (TBCs) with NiCoCrAlY bond coats deposited by argon-shrouded plasma spraying is described. The high purity yttria-stabilized zirconia resulted in top coats which are highly resistant to sintering and transformation from the metastable tetragonal phase to the equilibrium mixture of monoclinic and cubic phases. The thermal conductivity of the as-processed TBC is low but increases during high temperature exposure even before densification occurs. The porous topcoat microstructure also resulted in good spallation resistance during thermal cycling. The actual failure mechanisms of the APS coatings were found to depend on topcoat thickness, topcoat density, and the thermal cycle frequency. The failure mechanisms are described and the durability of the HP-LD coatings is compared with that of state-of-the-art electron beam physical vapor deposition TBCs.

  4. Development and evaluation of suspension plasma sprayed yttria stabilized zirconia coatings as thermal barriers

    NASA Astrophysics Data System (ADS)

    van Every, Kent J.

    The insulating effects from thermal barrier coatings (TBCs) in gas turbine engines allow for increased operational efficiencies and longer service lifetimes. Consequently, improving TBCs can lead to enhanced gas turbine engine performance. This study was conducted to investigate if yttria-stabilized zirconia (YSZ) coatings, the standard industrial choice for TBCs, produced from nano-sized powder could provide better thermal insulation than current commericial YSZ coatings generated using micron-sized powders. The coatings for this research were made via the recently developed suspension plasma spraying (SPS) process. With SPS, powders are suspended in a solvent containing dispersing agents; the suspension is then injected directly into a plasma flow that evaporates the solvent and melts the powder while transporting it to the substrate. Although related to the industrial TBC production method of air plasma spraying (APS), SPS has two important differences---the ability to spray sub-micron diameter ceramic particles, and the ability to alloy the particles with chemicals dissolved in the solvent. These aspects of SPS were employed to generate a series of coatings from suspensions containing ˜100 nm diameter YSZ powder particles, some of which were alloyed with neodymium and ytterbium ions from the solvent. The SPS coatings contained columnar structures not observed in APS TBCs; thus, a theory was developed to explain the formation of these features. The thermal conductivity of the coatings was tested to evaluate the effects of these unique microstructures and the effects of the alloying process. The results for samples in the as-sprayed and heat-treated conditions were compared to conventional YSZ TBCs. This comparison showed that, relative to APS YSZ coatings, the unalloyed SPS samples typically exhibited higher as-sprayed and lower heat-treated thermal conductivities. All thermal conductivity values for the alloyed samples were lower than conventional YSZ TBCs

  5. Thermal Stability of Goethite-Bound Natural Organic Matter Is Impacted by Carbon Loading.

    PubMed

    Feng, Wenting; Klaminder, Jonatan; Boily, Jean-François

    2015-12-24

    Dissolved natural organic matter (NOM) sorption at mineral surfaces can significantly affect the persistence of organic carbon in soils and sediments. Consequently, determining the mechanisms that stabilize sorbed NOM is crucial for predicting the persistence of carbon in nature. This study determined the effects of loadings and pH on the thermal stability of NOM associated with synthetic goethite (α-FeOOH) particle surfaces, as a proxy for NOM-mineral interactions taking place in nature. NOM thermal stability was investigated using temperature-programmed desorption (TPD) in the 30-700 °C range to collect vibration spectra of thermally decomposing goethite-NOM assemblages, and to concomitantly analyze evolved gases using mass spectrometry. Results showed that NOM thermal stability, indicated by the range of temperatures in which CO2 evolved during thermal decomposition, was greatest in unbound NOM and lowest when NOM was bound to goethite. NOM thermal stability was also loading dependent. It decreased when loadings were in increased the 0.01 to 0.42 mg C m(-2) range, where the upper value corresponds to a Langmuirian adsorption maximum. Concomitant Fourier transform infrared (FTIR) spectroscopy measurement showed that these lowered stabilities could be ascribed to direct NOM-goethite interactions that dominated the NOM binding environment. Mineral surface interactions at larger loadings involved, on the contrary, a smaller fraction of the sorbed NOM, thus increasing thermal stability toward that of its unbound counterpart. This study thus identifies a sorption threshold below which NOM sorption to goethite decreases NOM thermal stability, and above which no strong effects are manifested. This should likely influence the fate of organic carbon exposed to thermal gradients in natural environments.

  6. Acacia gum as modifier of thermal stability, solubility and emulsifying properties of α-lactalbumin.

    PubMed

    de Oliveira, Fabíola Cristina; Dos Reis Coimbra, Jane Sélia; de Oliveira, Eduardo Basílio; Rodrigues, Marina Quadrio Raposo Branco; Sabioni, Rachel Campos; de Souza, Bartolomeu Warlene Silva; Santos, Igor José Boggione

    2015-03-30

    Protein-polysaccharide conjugates often display improved techno-functional properties when compared to their individual involved biomolecules. α-Lactalbumin:acacia gum (α-la:AG) conjugates were prepared via Maillard reaction by the dry-heating method. Conjugate formation was confirmed using results of absorbance, o-phthalaldehyde test, sodium dodecyl sulfate-polyacrilamide gel electrophoresis (SDS-PAGE) and size exclusion chromatography. Techno-functional properties (emulsifying characteristics, solubility, and thermal stability) were evaluated for α-la, α-la/AG mixtures and α-la:AG conjugates. Conjugate thermal stability was improved compared to pure α-la treated at the same conditions of conjugate formation. Response surface methodology was used to establish models to predict solubility and emulsifying activity as functions of the salt concentration, pH and reaction time. α-la:AG conjugate solubility is affected in a complex manner by the three factors analyzed. Emulsifying activity index (EAI) of α-la is significantly affected by pH, while the α-la:AG EAI is affected by the three analyzed factors. Both solubility and EAI are maximized with pH 8.0, NaCl concentration of 0.3 mol L(-1) and two days of Maillard reaction.

  7. Thermal stability enhanced ZDSF proposal for ultra high-speed long haul communication systems

    NASA Astrophysics Data System (ADS)

    Makouei, S.; Makouei, F.

    2017-04-01

    In this article, thermal stability enhanced triangular graded-index single-mode zero-dispersion shifted fiber (ZDSF) is designed and the effect of temperature variation on its characteristics is investigated. The zero-dispersion wavelength (λZD) adjustment is accomplished through minimization of the broadening factor at the wavelength of 1.55 μm. The simulation results admit that the dispersion and its slope at 1.55 μm are 0.0051 ps/km/nm and 0.038 ps/km/nm2, respectively. This small slope of the structure results in the bit rate of 133 Gb/s in the 100 km distance. In addition, compared to the bell-shaped electrical mode distribution structures, the proposed structure holds an extended effective area (Aeff), which leads to elimination of the nonlinear effects. The λZD in the designed fiber exhibits a lower thermal coefficient compared to the reports previously presented which provides a better stability. This satisfactory feature is the direct result of small dispersion slope in the introduced structure. Furthermore, a temperature compensation system based on tensile strain induction, for the first time to the best of our knowledge, is proposed that preserves the effective refractive index (neff) profile versus wavelength not only in λZD but also in all communication bands of S+C+L. This accomplishment compensates the temperature impact on parameters such as dispersion and zero-dispersion wavelength.

  8. Thermal stability of disordered carbon negative-electrode materials prepared from peanut shells

    NASA Astrophysics Data System (ADS)

    Watanabe, Izumi; Doi, Takayuki; Yamaki, Jun-ichi; Lin, Y. Y.; Fey, George Ting-Kuo

    The thermal stability of electrochemically lithiated disordered carbon with a poly(vinylidene difluoride) binder and 1 mol dm -3 LiPF 6 dissolved in a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) was investigated by differential scanning calorimetry (DSC) using a hermetically sealed pan. The disordered carbon used was prepared by pyrolyzing peanut shells with porogen at temperatures above 500 °C. The disordered carbon gave much larger charge and discharge capacities than graphite when a weight ratio of porogen to peanut shells was set at 5. In DSC curves, several exothermic peaks were observed at temperatures ranging from 120 to 310 °C. This behavior was similar to that for electrochemically lithiated graphite, except for an exothermic peak at around 250 °C. However, the lithiated disordered carbon had a higher heat value, which was evaluated by integrating a DSC curve, compared to lithiated graphite. The heat values increased with an increase in accumulated irreversible capacities. These results suggest that heat generation at elevated temperatures should increase as an amount of irreversibly trapped lithium-ion increases. On the other hand, heat values per reversible capacities for disordered carbon, which showed larger capacities than graphite, were almost comparable to that for graphite. These results indicate that several types of disordered carbon showed larger capacity than graphite, while their thermal stability was lowered accordingly.

  9. Effects of actin-binding proteins on the thermal stability of monomeric actin.

    PubMed

    Pivovarova, Anastasia V; Chebotareva, Natalia A; Kremneva, Elena V; Lappalainen, Pekka; Levitsky, Dmitrii I

    2013-01-08

    Differential scanning calorimetry (DSC) was applied to investigate the thermal unfolding of rabbit skeletal muscle G-actin in its complexes with actin-binding proteins, cofilin, twinfilin, and profilin. The results show that the effects of these proteins on the thermal stability of G-actin depend on the nucleotide, ATP or ADP, bound in the nucleotide-binding cleft between actin subdomains 2 and 4. Interestingly, cofilin binding stabilizes both ATP-G-actin and ADP-G-actin, whereas twinfilin increases the thermal stability of the ADP-G-actin but not that of the ATP-G-actin. By contrast, profilin strongly decreases the thermal stability of the ATP-G-actin but has no appreciable effect on the ADP-G-actin. Comparison of these DSC results with literature data reveals a relationship between the effects of actin-binding proteins on the thermal unfolding of G-actin, stabilization or destabilization, and their effects on the rate of nucleotide exchange in the nucleotide-binding cleft, decrease or increase. These results suggest that the thermal stability of G-actin depends, at least partially, on the conformation of the nucleotide-binding cleft: the actin molecule is more stable when the cleft is closed, while an opening of the cleft leads to significant destabilization of G-actin. Thus, DSC studies of the thermal unfolding of G-actin can provide new valuable information about the conformational changes induced by actin-binding proteins in the actin molecule.

  10. Kinetic analysis of enhanced thermal stability of an alkaline protease with engineered twin disulfide bridges and calcium-dependent stability.

    PubMed

    Ikegaya, Kazuo; Sugio, Shigetoshi; Murakami, Kohji; Yamanouchi, Kouichi

    2003-01-20

    The thermal stability of a cysteine-free alkaline protease (Alp) secreted by the eukaryote Aspergillus oryzae was improved both by the introduction of engineered twin disulfide bridges (Cys-69/Cys-101 and Cys-169/Cys-200), newly constructed as part of this study, and by the addition of calcium ions. We performed an extensive kinetic analysis of the increased thermal stability of the mutants as well as the role of calcium dependence. The thermodynamic activation parameters for irreversible thermal inactivation, the activation free energy (deltaG), the activation enthalpy (deltaH), and the activation entropy (deltaS) were determined from absolute reaction rate theory. The values of deltaH and deltaS were significantly and concomitantly increased as a result of introducing the twin disulfide bridges, for which the increase in the value of deltaH outweighed that of deltaS, resulting in significant increases in the value of deltaG. The enhancement of the thermal stability obtained by introducing the twin disulfide bridges is an example of the so-called low-temperature stabilization of enzymes. The stabilizing effect of calcium ions on wild-type Alp is similar to the results we obtained by introducing the engineered twin disulfide bridges.

  11. Experimentation and Modeling of Jet A Thermal Stability in a Heated Tube

    NASA Technical Reports Server (NTRS)

    Khodabandeh, Julia W.

    2005-01-01

    High performance aircraft typically use hydrocarbon fuel to regeneratively cool the airframe and engine components. As the coolant temperatures increase, the fuel may react with dissolved oxygen forming deposits that limit the regenerative cooling system performance. This study investigates the deposition of Jet A using a thermal stability experiment and computational fluid dynamics (CFD) modeling. The experimental portion of this study is performed with a high Reynolds number thermal stability (HiRets) tester in which fuel passes though an electrically heated tube and the fuel outlet temperature is held constant. If the thermal stability temperature of the fuel is exceeded, deposits form and adhere to the inside of the tube creating an insulating layer between the tube and the fuel. The HiRets tester measures the tube outer wall temperatures near the fuel outlet to report the effect of deposition occurring inside the tube. Final deposits are also estimated with a carbon burn off analysis. The CFD model was developed and used to simulate the fluid dynamics, heat transfer, chemistry, and transport of the deposit precursors. The model is calibrated to the experiment temperature results and carbon burn-off deposition results. The model results show that the dominant factor in deposition is the heated wall temperature and that most of the deposits are formed in the laminar sublayer. The models predicted a 7.0E-6 kilograms per square meter-sec deposition rate, which compared well to the carbon burn-off analysis deposition rate of 1.0E-6 kilograms per square meter-sec.

  12. Phase stability of thermal barrier oxides based on t'-zirconia with trivalent oxide additions

    NASA Astrophysics Data System (ADS)

    Rebollo Franco, Noemi Rosa

    Zirconia stabilized with 7+/-1 wt.% addition of yttria (7YSZ) is widely used for thermal barrier coatings (TBC's) on actively cooled gas turbine components, selected partly because of its superior durability under thermal cyclic conditions. As deposited, 7YSZ occurs as a metastable single-phase tetragonal solid solution (t') that is thermodynamically stable against the deleterious transformation to monoclinic upon cooling. However, at high temperatures t' is driven to decompose diffusionally into an equilibrium mixture of high-Y cubic and low-Y tetragonal; the latter becomes transformable to monoclinic compromising the mechanical integrity of the system. This dissertation explores the effects of trivalent stabilizers, including Y, Sc and selected rare-earth oxides (REO's), on the phase stability of the resulting solid solutions in zirconia. The REO additions are of interest because they can potentially enhance the insulation efficiency on the coating allowing higher operating temperatures. However, understanding of their effects on phase stability and potentially on cyclic durability at the projected use temperature in next generation engines (1200-1400°C) is insufficient to guide the design of coatings with the desirable combination of lower thermal conductivity and acceptable durability. Sc was also investigated because of previous reports on the higher phase stability of materials doped with Sc, and Y served as the baseline. The experimental approach is based on powders synthesized by reverse co-precipitation of precursor solutions, usually compacted and then subjected to a variety of heat treatments, following their evolution by means of X-ray diffractometry, dilatometry, transmission electron microscopy and Raman spectroscopy. The use of powders facilitated the synthesis of a wider range of compositions that would not have been possible by coating deposition approaches, and because the synthesis occurs at low temperature, it also enabled the starting

  13. Improving thermal stability of thermophilic L-threonine aldolase from Thermotoga maritima.

    PubMed

    Wieteska, Lukasz; Ionov, Maksim; Szemraj, Janusz; Feller, Claudia; Kolinski, Andrzej; Gront, Dominik

    2015-04-10

    Threonine aldolase (TA) catalyzes a reversible reaction, in which threonine is decomposed into glycine and acetaldehyde. The same enzyme can be used to catalyze aldol reaction between glycine and a variety of aromatic and aliphatic aldehydes, thus creating various alpha-amino-alcohols. Therefore, TA is a very promising enzyme that could be used to prepare biologically active compounds or building blocks for pharmaceutical industry. Rational design was applied to thermophilic TA from Thermotoga maritima to improve thermal stability by the incorporation of salt and disulfide bridges between subunits in the functional tetramer. An activity assay together with CD analysis and Western-blot detection was used to evaluate mutants. Except one, each of the designed mutants preserved activity toward the natural substrate. One of the 10 proposed single point mutants, P56C, displayed significantly enhanced stability compared to the wild type (WT). Its initial activity was not affected and persisted longer than WT, proportionally to increased stability. Additionally one of the mutants, W86E, displayed enhanced activity, with stability similar to WT. Higher activity may be explained by a subtle change in active site availability. Salt bridge formation between glutamic acid at position 86 and arginine at position 120 in the neighboring chain may be responsible for the slight shift of the chain fragment, thus creating wider access to the active site both for the substrate and PLP.

  14. Flammability, odor, offgassing, thermal vacuum stability, and compatibility with aerospace fluids of wire insulations

    NASA Technical Reports Server (NTRS)

    Hirsch, David; Johnson, Harry

    1994-01-01

    The NASA Lewis Research Center requested NASA Johnson Space Center White Sands Test Facility to conduct flammability, odor, offgassing, thermal vacuum stability, and compatibility tests with aerospace fluids of several wire insulations.

  15. Engineering Interface Structures and Thermal Stabilities via SPD Processing in Bulk Nanostructured Metals

    PubMed Central

    Zheng, Shijian; Carpenter, John S.; McCabe, Rodney J.; Beyerlein, Irene J.; Mara, Nathan A.

    2014-01-01

    Nanostructured metals achieve extraordinary strength but suffer from low thermal stability, both a consequence of a high fraction of interfaces. Overcoming this tradeoff relies on making the interfaces themselves thermally stable. Here we show that the atomic structures of bi-metal interfaces in macroscale nanomaterials suitable for engineering structures can be significantly altered via changing the severe plastic deformation (SPD) processing pathway. Two types of interfaces are formed, both exhibiting a regular atomic structure and providing for excellent thermal stability, up to more than half the melting temperature of one of the constituents. Most importantly, the thermal stability of one is found to be significantly better than the other, indicating the exciting potential to control and optimize macroscale robustness via atomic-scale bimetal interface tuning. Taken together, these results demonstrate an innovative way to engineer pristine bimetal interfaces for a new class of simultaneously strong and thermally stable materials. PMID:24573355

  16. Engineering interface structures and thermal stabilities via SPD processing in bulk nanostructured metals.

    PubMed

    Zheng, Shijian; Carpenter, John S; McCabe, Rodney J; Beyerlein, Irene J; Mara, Nathan A

    2014-02-27

    Nanostructured metals achieve extraordinary strength but suffer from low thermal stability, both a consequence of a high fraction of interfaces. Overcoming this tradeoff relies on making the interfaces themselves thermally stable. Here we show that the atomic structures of bi-metal interfaces in macroscale nanomaterials suitable for engineering structures can be significantly altered via changing the severe plastic deformation (SPD) processing pathway. Two types of interfaces are formed, both exhibiting a regular atomic structure and providing for excellent thermal stability, up to more than half the melting temperature of one of the constituents. Most importantly, the thermal stability of one is found to be significantly better than the other, indicating the exciting potential to control and optimize macroscale robustness via atomic-scale bimetal interface tuning. Taken together, these results demonstrate an innovative way to engineer pristine bimetal interfaces for a new class of simultaneously strong and thermally stable materials.

  17. Engineering Interface Structures and Thermal Stabilities via SPD Processing in Bulk Nanostructured Metals

    SciTech Connect

    Zheng, Shijian; Carpenter, John S.; McCabe, Rodney J.; Beyerlein, Irene J.; Mara, Nathan A.

    2014-02-27

    Nanostructured metals achieve extraordinary strength but suffer from low thermal stability, both a consequence of a high fraction of interfaces. Overcoming this tradeoff relies on making the interfaces themselves thermally stable. In this paper, we show that the atomic structures of bi-metal interfaces in macroscale nanomaterials suitable for engineering structures can be significantly altered via changing the severe plastic deformation (SPD) processing pathway. Two types of interfaces are formed, both exhibiting a regular atomic structure and providing for excellent thermal stability, up to more than half the melting temperature of one of the constituents. Most importantly, the thermal stability of one is found to be significantly better than the other, indicating the exciting potential to control and optimize macroscale robustness via atomic-scale bimetal interface tuning. As a result, we demonstrate an innovative way to engineer pristine bimetal interfaces for a new class of simultaneously strong and thermally stable materials.

  18. Engineering Interface Structures and Thermal Stabilities via SPD Processing in Bulk Nanostructured Metals

    DOE PAGES

    Zheng, Shijian; Carpenter, John S.; McCabe, Rodney J.; ...

    2014-02-27

    Nanostructured metals achieve extraordinary strength but suffer from low thermal stability, both a consequence of a high fraction of interfaces. Overcoming this tradeoff relies on making the interfaces themselves thermally stable. In this paper, we show that the atomic structures of bi-metal interfaces in macroscale nanomaterials suitable for engineering structures can be significantly altered via changing the severe plastic deformation (SPD) processing pathway. Two types of interfaces are formed, both exhibiting a regular atomic structure and providing for excellent thermal stability, up to more than half the melting temperature of one of the constituents. Most importantly, the thermal stability ofmore » one is found to be significantly better than the other, indicating the exciting potential to control and optimize macroscale robustness via atomic-scale bimetal interface tuning. As a result, we demonstrate an innovative way to engineer pristine bimetal interfaces for a new class of simultaneously strong and thermally stable materials.« less

  19. Comparative evaluation of different thermally modified wood samples finishing with UV-curable and waterborne coatings

    NASA Astrophysics Data System (ADS)

    Herrera, René; Muszyńska, Monika; Krystofiak, Tomasz; Labidi, Jalel

    2015-12-01

    Thermally modified wood has been developed as an industrial method to improve durability and dimensional stability of wood and thus extends the range of uses and service life of wood-based products. Despite the improvements gained by treatment, surface finishing using coatings prevents esthetical changes such as color degradation or occasional growth of mold adding protection in outdoor use and extending the service life of products. The wood finishing process was carried out with commercially available waterborne and UV-curable coatings on industrially modified at 192, 200, 212 °C and unmodified European ash (Fraxinus excelsior L.) wood, using an industrial rollers system and a laboratory brushing system. Changes caused by thermal treatment which could affect the surface finish were measured and compared with control samples, such as water uptake, wettability and acidity. Following the wood finishing, surface properties and esthetic changes were evaluated; as well as the coatings performance. Thermally modified wood presented improved adherence compared with unmodified wood with a significant improvement in samples modified at 212 °C, which also present the highest hardness when UV-cured. Finishes with UV-curing maintain the hydrophobic effect of thermally modified wood, whereas waterborne finishes increase the surface wettability. Thermal modification did not negatively influence on the elastic properties of the coated substrate and thus allows this material to be finished with different coating systems in the same conditions as unmodified wood.

  20. Fibre Bragg Gratings, towards a Better Thermal Stability at High Temperatures

    NASA Astrophysics Data System (ADS)

    de Oliveira, Valmir; Abe, Ilda; Alberto, Nelia Jordão; Kalinowski, Hypolito José

    Regenerated fibre Bragg gratings (RFBG) are obtained by heating an original seed grating until its reflection practically vanishes, which is followed by the growth of a new reflection band. Advantages of RFBG for sensing purposes are the longer lifetime and higher thermal stability at higher temperatures, as they have been observed to survive temperatures in the range 1300-1500 °C. The thermal stability of the RFBG permits several applications not attained by standard Bragg gratings.

  1. Thermal Stability Threshold for Amyloid Formation in Light Chain Amyloidosis

    PubMed Central

    Poshusta, Tanya L.; Katoh, Nagaaki; Gertz, Morie A.; Dispenzieri, Angela; Ramirez-Alvarado, Marina

    2013-01-01

    Light chain (AL) amyloidosis is a devastating disease characterized by amyloid deposits formed by immunoglobulin light chains. Current available treatments involve conventional chemotherapy and autologous stem cell transplant. We have recently concluded a phase III trial comparing these two treatments. AL amyloidosis patients who achieve hematological complete response (CR) do not necessarily achieve organ response regardless of the treatment they received. In order to investigate the possible correlation between amyloid formation kinetics and organ response, we selected AL amyloidosis patients from the trial with kidney involvement and CR after treatment. Six patients were selected and their monoclonal immunoglobulin light chains were characterized. The proteins showed differences in their stability and their kinetics of amyloid formation. A correlation was detected at pH 7.4, showing that less stable proteins are more likely to form amyloid fibrils. AL-T03 is too unstable to form amyloid fibrils at pH 7.4. This protein was found in the only patient in the study that had organ response, suggesting that partially folded species are required for amyloid formation to occur in AL amyloidosis. PMID:24248061

  2. Correlation between iron self-diffusion and thermal stability in doped iron nitride thin films

    NASA Astrophysics Data System (ADS)

    Tayal, Akhil; Gupta, Mukul; Kumar, D.; Reddy, V. R.; Gupta, Ajay; Amir, S. M.; Korelis, Panagiotis; Stahn, Jochen

    2014-12-01

    Nanocrystalline Fe-X-N thin films (with doping X = 0, 3.1 at. % Al, 1.6 at. % Zr), were deposited using reactive ion beam sputtering. Magnetization study reveals that the deposited films exhibit a perpendicular magnetic anisotropy. Thermal stability of the films was investigated systematically and it was observed that the structural and the magnetic stability gets significantly enhanced with Al doping, whereas Zr doping has only a marginal effect. Fe self-diffusion, obtained using polarized neutron reflectivity, shows a suppression with both additives. A correlation between the thermal stability and the diffusion process gives a direct evidence that the enhancement in the thermal stability is primarily diffusion controlled. A combined picture of diffusion, structural, and magnetic stability has been drawn to understand the obtained results.

  3. Correlation between iron self-diffusion and thermal stability in doped iron nitride thin films

    SciTech Connect

    Tayal, Akhil; Gupta, Mukul E-mail: dr.mukul.gupta@gmail.com; Kumar, D.; Reddy, V. R.; Gupta, Ajay; Amir, S. M.; Korelis, Panagiotis; Stahn, Jochen

    2014-12-14

    Nanocrystalline Fe-X-N thin films (with doping X = 0, 3.1 at. % Al, 1.6 at. % Zr), were deposited using reactive ion beam sputtering. Magnetization study reveals that the deposited films exhibit a perpendicular magnetic anisotropy. Thermal stability of the films was investigated systematically and it was observed that the structural and the magnetic stability gets significantly enhanced with Al doping, whereas Zr doping has only a marginal effect. Fe self-diffusion, obtained using polarized neutron reflectivity, shows a suppression with both additives. A correlation between the thermal stability and the diffusion process gives a direct evidence that the enhancement in the thermal stability is primarily diffusion controlled. A combined picture of diffusion, structural, and magnetic stability has been drawn to understand the obtained results.

  4. Comparative performance of solar thermal power generation concepts

    NASA Technical Reports Server (NTRS)

    Wen, L.; Wu, Y. C.

    1976-01-01

    A performance comparison is made between the central receiver system (power tower) and a distributed system using either dishes or troughs and lines to transport fluids to the power station. These systems were analyzed at a rated capacity of 30 MW of thermal energy delivered in the form of superheated steam at 538 C (1000 F) and 68 atm (1000 psia), using consistent weather data, collector surface waviness, pointing error, and electric conversion efficiency. The comparisons include technical considerations for component requirements, land utilization, and annual thermal energy collection rates. The relative merits of different representative systems are dependent upon the overall conversion as expressed in the form of performance factors in this paper. These factors are essentially indices of the relative performance effectiveness for different concepts based upon unit collector area. These performance factors enable further economic tradeoff studies of systems to be made by comparing them with projected production costs for these systems.

  5. Thermal stability of ricin in orange and apple juices.

    PubMed

    Jackson, Lauren S; Zhang, Zhe; Tolleson, William H

    2010-05-01

    Ricin is a potent protein toxin that could be exploited for bioterrorism. Although ricin may be detoxified using heat, inactivation conditions in foods are not well characterized. Two brands of pulp-free orange juice and 2 brands of single-strength apple juice (one clarified and the other unclarified) containing 100 microg/mL added ricin were heated at 60 to 90 degrees C for up to 2 h. With increasing heating times and temperatures the heat-treated juices exhibited decreasing detectability of ricin by enzyme-linked immunosorbent assay (ELISA) and cytotoxicity to cultured cells. Z-values for ricin inactivation in orange juices were 14.4 +/- 0.8 degrees C and 17 +/- 4 degrees C using cytotoxicity assays, compared to 13.4 +/- 1.5 degrees C and 14 +/- 2 degrees C determined by ELISA. Although insignificant differences were apparent for z-values measured for the 2 orange juice brands, significant differences were found in the z-values for the 2 brands of apple juice. The z-values for ricin inactivation in the clarified and unclarified apple juices were 21 +/- 4 degrees C and 9.5 +/- 1.1 degrees C, determined by cytotoxicity assays, and 20 +/- 2 degrees C and 11.6 +/- 0.7 degrees C, respectively, using ELISA. Overall, there were no significant differences between results measured with ELISA and cytotoxicity assays. Ricin stability in orange juice and buffer was evaluated at 25 degrees C. Half-lives of 10 +/- 3 d and 4.9 +/- 0.4 d, respectively, indicated that active ricin in juice could reach consumers. These results indicate that ricin in apple and orange juices can remain toxic under some processing and product storage conditions. Ricin is a potent toxin that is abundant in castor beans and is present in the castor bean mash by-product after cold-press extraction of castor oil. U.S. Health and Human Services recognizes that ricin could be used for bioterrorism. This study reports the stability of ricin in apple and orange fruit juices at temperatures ranging from 60 to

  6. Potential Additives to Promote Seal Swell in Synthetic Fuels and Their Effect on Thermal Stability

    SciTech Connect

    Link, D.D.; Gormley, R.J.; Baltrus, J.P.; Anderson, R.R.; Zandhuis, P.H.

    2008-03-01

    Synthetic fuels derived from the Fischer–Tropsch (F-T) process using natural gas or coal-derived synthesis gas as feedstocks can be used for powering ground vehicles, aircraft, and ships. Because of their chemical and physical properties, F-T fuels will probably require additives in order to meet specifications with respect to lubricity and seal swell capability for use in ground and air vehicles. Using both experimental and computational studies, the propensity of certain species to enhance the seal swell characteristics of synthetic fuels and surrogates has been determined, and promising additives have been identified. Important structural characteristics for potential additives, namely an aromatic ring along with a polar constituent, are described. The thermal stability of synthetic and surrogate fuels containing the single-component additive benzyl alcohol, which is representative of this structural class, has been determined by batch stressing of the mixtures at 350 °C for up to 12 h. Synthetic fuels spiked with benzyl alcohol at concentrations (vol %) of 1.0, 0.75, and 0.5 have demonstrated the ability to swell nitrile rubber o-rings to a comparable degree as petroleum jet fuel. Further, batch reactor studies have shown that addition of benzyl alcohol does not degrade the thermal oxidative stability of the fuel based on gravimetric analysis of the solid deposits after stressing. GC-MS was used to characterize the products from thermal stressing of neat and additized surrogate jet fuel, and their compositions were compared with respect to the creation of certain species and their potential effect on deposition.

  7. Insights into thermal stability of thermophilic nitrile hydratases by molecular dynamics simulation.

    PubMed

    Liu, Jie; Yu, Huimin; Shen, Zhongyao

    2008-11-01

    Thermal stability is of great importance for industrial enzymes. Here we explored the thermal-stable mechanism of thermophilic nitrile hydratases (NHases) utilizing a molecular dynamic simulation. At a nanosecond timescale, profiles of root mean square fluctuation (RMSF) of two thermophilic NHases, 1UGQ and 1V29, under enhancing thermal stress were carried out at 300 K, 320 K, 350 K and 370 K, respectively. Results showed that the region A1 (211-231 aa) and A2 (305-316 aa) in 1UGQ, region B1 (186-192 aa) in 1V29, and most of terminal ends in both enzymes are hyper-sensitive. Salt-bridge analyses revealed that in one hand, salt-bridges contributed to maintaining the rigid structure and stable performance of the thermophilic 1UGQ and 1V29; in the other hand, salt-bridges involved in thermal sensitive regions are relatively weak and prone to be broken at elevated temperature, thereby cannot hold the stable conformation of the spatial neighborhood. In 1V29, region A1 was stabilized by a well-organized hook-hook like cluster with multiple salt-bridge interactions, region A2 was stabilized by two strong salt-bridge interactions of GLU52-ARG332 and GLU334-ARG332. In 1UGQ, the absence of a charged residue decreased its thermal sensitivity of region B1, and the formation of a small beta-sheet containing a stable salt-bridge in C-beta-terminal significantly enhanced its thermal stability. By radius of gyration calculation containing or eliminating the thermal sensitive regions, we quantified the contribution of thermal sensitive regions for thermal sensitivity of 1UGQ and 1V29. Consequently, we presented strategies to improve thermal stability of the industrialized mesophilic NHase by introducing stable salt-bridge interactions into its thermal sensitive regions.

  8. Specific cleavage of the DNase-I binding loop dramatically decreases the thermal stability of actin.

    PubMed

    Pivovarova, Anastasia V; Khaitlina, Sofia Yu; Levitsky, Dmitrii I

    2010-09-01

    Differential scanning calorimetry was used to investigate the thermal unfolding of actin specifically cleaved within the DNaseI-binding loop between residues Met47-Gly48 or Gly42-Val43 by two bacterial proteases, subtilisin or ECP32/grimelysin (ECP), respectively. The results obtained show that both cleavages strongly decreased the thermal stability of monomeric actin with either ATP or ADP as a bound nucleotide. An even more pronounced difference in the thermal stability between the cleaved and intact actin was observed when both actins were polymerized into filaments. Similar to intact F-actin, both cleaved F-actins were significantly stabilized by phalloidin and aluminum fluoride; however, in all cases, the thermal stability of the cleaved F-actins was much lower than that of intact F-actin, and the stability of ECP-cleaved F-actin was lower than that of subtilisin-cleaved F-actin. These results confirm that the DNaseI-binding loop is involved in the stabilization of the actin structure, both in monomers and in the filament subunits, and suggest that the thermal stability of actin depends, at least partially, on the conformation of the nucleotide-binding cleft. Moreover, an additional destabilization of the unstable cleaved actin upon ATP/ADP replacement provides experimental evidence for the highly dynamic actin structure that cannot be simply open or closed, but rather should be considered as being able to adopt multiple conformations. © 2010 The Authors Journal compilation © 2010 FEBS.

  9. Comparative study on heat stability and functionality of camel and bovine milk whey proteins.

    PubMed

    Laleye, L C; Jobe, B; Wasesa, A A H

    2008-12-01

    Heat stability, emulsifying, and foaming properties of camel whey have been investigated and compared with that of bovine whey. Camel whey is similar to bovine whey in composition, but is deficient in beta-lactoglubulin (beta-LG), a major component of bovine whey. Whether the deficiency in beta-LG will affect stability and functional properties is not yet known. Substantial information on the functional properties of bovine milk whey proteins is available; however, there is little research done on functional properties of camel whey proteins. Therefore, the objective of this study was to investigate the heat stability, emulsifying, and foaming characteristics of camel whey proteins. Calorimetric studies showed no significant difference in heat stability between bovine and camel whey proteins in liquid form. Upon drying, thermograms indicated that the 2 proteins are different in composition and thermal stability. The difference is represented in the absence of beta-LG and the occurrence of protein denaturation peak at a lesser temperature in camel whey. The first marginal thermal transition in bovine whey appeared at 81 degrees C, followed by 2 other transitions at 146 and 198 degrees C. For camel whey, the transitions appeared at 139, 180, and 207 degrees C respectively. The first marginal denaturation peak in bovine whey is due to beta-LG, which is essentially absent in camel whey, while the second peak is due to the mixture of alpha-lactalbumin, serum albumin, and possibly part of the partially stabilized beta-LG structure during the denaturation process. Because camel whey is deficient in beta-LG, the denaturation peak at 139 must be due to the mixture of alpha-lactalbumin and camel serum albumin. In both proteins, the highest thermal transition is due to sugars such as lactose. The solubility study has shown that camel whey is more sensitive to pH than bovine milk whey and that heat stability is lowest near the isoelectric point of the proteins at pH 4.5. The

  10. The effect of chemical modification with pyromellitic anhydride on structure, function, and thermal stability of horseradish peroxidase.

    PubMed

    Hassani, Leila

    2012-06-01

    The stability of enzymes remains a critical issue in biotechnology. Compared with the strategies for obtaining stable enzymes, chemical modification is a simple and effective technique. In the present study, chemical modification of horseradish peroxidase (HRP) was carried out with pyromellitic anhydride. HRP has achieved a prominent position in the pharmaceutical, chemical, and biotechnological industries. In this study, the effect of chemical modification on thermal stability, structure, and function of the enzyme was studied by fluorescence, circular dichroism, and absorbance measurements. The results indicated a decrease in compactness of the structure and a considerable enhancement in thermal stability of HRP below 60 °C. It seems the charge replacement and introduction of the bulky group bring about the observed structural and the functional changes.

  11. Thermal stability of bimetallic Au/Fe nanoparticles in silica matrix

    SciTech Connect

    Pannu, Compesh Singh, Udai B. Hooda, Sonu Kabiraj, D. Avasthi, D. K.

    2014-04-24

    Thin silica film containing Au and Fe bimetallic nanoparticles were prepared by atom beam cosputtering. The samples were annealed at different temperatures from 400 to 800° C to study the thermal stability of bimetallic nanoparticles using X ray diffraction. It is observed that at 800° C strong structural rearrangement took place leading to thermal decomposition of bimetallic nanoparticles.

  12. Enhanced thermal stability of carbon nanotubes by plasma surface modification in Al2O3 composites

    NASA Astrophysics Data System (ADS)

    Cho, Hoonsung; Shi, Donglu; Guo, Yan; Lian, Jie; Ren, Zhifeng; Poudel, Bed; Song, Yi; Abot, Jandro L.; Singh, Dileep; Routbort, Jules; Wang, Lumin; Ewing, Rodney C.

    2008-10-01

    A plasma polymerization method was employed to deposit an ultrathin pyrrole film of 3 nm onto the surfaces of single wall carbon nanotubes (SWCNTs) and Al2O3 nanoparticles for developing high-strength nanocomposites. The surfaces of plasma coated SWCNTs and Al2O3 nanoparticles were studied by high resolution transmission electron microscopy (TEM) and time-of-flight secondary ion mass spectroscopy. After sintering the SWCNTs-Al2O3 composites at different temperatures (maximum of 1200 °C), the thermal stability of plasma-coated SWCNTs was significantly increased, compared to their uncoated counterparts. After hot-press sintering, the SWCNTs without plasma coating were essentially decomposed into amorphous clusters in the composites, leading to degraded mechanical properties. However, under the same sintering conditions, the plasma surface modified SWCNTs were well preserved and distributed in the composite matrices. The effects of plasma surface coating on the thermal stability of SWCNTs and mechanical behavior of the nanocomposites are discussed.

  13. Thermal Stability and Magnetic Properties of Polyvinylidene Fluoride/Magnetite Nanocomposites

    PubMed Central

    Ouyang, Zen-Wei; Chen, Erh-Chiang; Wu, Tzong-Ming

    2015-01-01

    This work describes the thermal stability and magnetic properties of polyvinylidene fluoride (PVDF)/magnetite nanocomposites fabricated using the solution mixing technique. The image of transmission electron microscopy for PVDF/magnetite nanocomposites reveals that the 13 nm magnetite nanoparticles are well distributed in PVDF matrix. The electroactive β-phase and piezoelectric responses of PVDF/magnetite nanocomposites are increased as the loading of magnetite nanoparticles increases. The piezoelectric responses of PVDF/magnetite films are extensively increased about five times in magnitude with applied strength of electrical field at 35 MV/m. The magnetic properties of PVDF/magnetite nanocomposites exhibit supermagnetism with saturation magnetization in the range of 1.6 × 10−3–3.1 × 10−3 emu/g, which increases as the amount of magnetite nanoparticles increases. The incorporation of 2 wt % magnetite nanoparticles into the PVDF matrix improves the thermal stability about 25 °C as compared to that of PVDF. The effect of magnetite particles on the isothermal degradation behavior of PVDF is also investigated. PMID:28793456

  14. Thermal Shock Resistance of Stabilized Zirconia/Metal Coat on Polymer Matrix Composites by Thermal Spraying Process

    NASA Astrophysics Data System (ADS)

    Zhu, Ling; Huang, Wenzhi; Cheng, Haifeng; Cao, Xueqiang

    2014-12-01

    Stabilized zirconia/metal coating systems were deposited on the polymer matrix composites by a combined thermal spray process. Effects of the thicknesses of metal layers and ceramic layer on thermal shock resistance of the coating systems were investigated. According to the results of thermal shock lifetime, the coating system consisting of 20 μm Zn and 125 μm 8YSZ exhibited the best thermal shock resistance. Based on microstructure evolution, failure modes and failure mechanism of the coating systems were proposed. The main failure modes were the formation of vertical cracks and delamination in the outlayer of substrate, and the appearance of coating spallation. The residual stress, thermal stress and oxidation of substrate near the substrate/metal layer interface were responsible for coating failure, while the oxidation of substrate near the substrate/coating interface was the dominant one.

  15. Methods for thermal stability enhancement of leaf essential oils and their main constituents from indigenous cinnamon (Cinnamomum osmophloeum).

    PubMed

    Yeh, Hsin-Fu; Luo, Chi-Yuan; Lin, Chun-Ya; Cheng, Sen-Sung; Hsu, Yen-Ray; Chang, Shang-Tzen

    2013-07-03

    The thermal stability of leaf essential oils from various Cinnamomum osmophloeum and their constituents was investigated for the first time. The results indicated that trans-cinnamaldehyde (Cin) content in eugenol-free essential oil from C. osmophloeum was affected by high temperatures. The retention of Cin (RC) decreased to 17.4% after the essential oil was incubated for 8 h at 100 °C. In contrast, essential oils containing eugenol showed greater thermal stability. Seven kinds of antioxidants were added to Cin to improve its thermal stability. Among them, eugenol endowed Cin with the best thermal stability. We also investigated the influence of various amounts of eugenol on the thermal stability of both essential oil and Cin. Both essential oil and Cin showed excellent thermal stability when 0.62 and 2.60% (v/v) eugenol were added. In short, the thermal stability of essential oil and Cin could be effectively improved by adding appropriate amounts of eugenol.

  16. High shear homogenization of lignin to nanolignin and thermal stability of nanolignin-polyvinyl alcohol blends.

    PubMed

    Nair, Sandeep S; Sharma, Sudhir; Pu, Yunqiao; Sun, Qining; Pan, Shaobo; Zhu, J Y; Deng, Yulin; Ragauskas, Art J

    2014-12-01

    A new method to prepare nanolignin using a simple high shear homogenizer is presented. The kraft lignin particles with a broad distribution ranging from large micron- to nano-sized particles were completely homogenized to nanolignin particles with sizes less than 100 nm after 4 h of mechanical shearing. The (13) C nuclear magnetic resonance (NMR) and (31) P NMR analysis showed that there were no major changes in the chemical composition between the starting kraft lignin particles and the nanolignin obtained after 4 h of mechanical treatment. The nanolignin particles did not show any change in molecular weight distribution and polydispersity compared to the original lignin particles. The nanolignin particles when used with polyvinyl alcohol (PVA) increased the thermal stability of nanolignin/PVA blends more effectively compared to the original lignin/PVA blends. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. Thermal Stability of Platinum-Cobalt Bimetallic Nanoparticles: Chemically Disordered Alloys, Ordered Intermetallics, and Core-Shell Structures.

    PubMed

    Huang, Rao; Shao, Gui-Fang; Zhang, Yang; Wen, Yu-Hua

    2017-04-12

    Pt-Co bimetallic nanoparticles are promising candidates for Pt-based nanocatalysts and magnetic-storage materials. By using molecular dynamics simulations, we here present a detailed examination on the thermal stabilities of Pt-Co bimetallic nanoparticles with three configurations including chemically disordered alloy, ordered intermetallics, and core-shell structures. It has been revealed that ordered intermetallic nanoparticles possess better structural and thermal stability than disordered alloyed ones for both Pt3Co and PtCo systems, and Pt3Co-Pt core-shell nanoparticles exhibit the highest melting points and the best thermal stability among Pt-Co bimetallic nanoparticles, although their meltings all initiate at the surface and evolve inward with increasing temperatures. In contrast, Co-Pt core-shell nanoparticles display the worst thermal stability compared with the aforementioned nanoparticles. Furthermore, their melting initiates in the core and extends outward surface, showing a typical two-stage melting mode. The solid-solid phase transition is discovered in Co core before its melting. This work demonstrates the importance of composition distribution to tuning the properties of binary nanoparticles.

  18. Contrasting tropical estuarine ecosystem functioning and stability: A comparative study

    NASA Astrophysics Data System (ADS)

    Villanueva, Maria Ching

    2015-03-01

    A comparative study of the Sine-saloum (Senegal) and Gambia (The Gambia) estuaries was performed based on trophic model outputs that describe the system structure and functioning. These trophic models were constructed such as to differentiate main energetic flows in the systems and express how climate change may have impacted ecosystem resilience to change. Estuarine fish assemblages are highly resilient despite exposure to vast hydrodynamic variations and stress. Coupled with strong anthropogenic-driven stresses such as fisheries and climate change, ecosystems may undergo severe regime shifts that may weaken their resilience and stability. Taxonomically related and morphologically similar species do not necessarily play similar ecological roles in these two ecosystems. Biomass and production in the Sine-saloum are concentrated at trophic levels (TLs) 2 and 3, while for the Gambia, both are concentrated at TL3. Higher TL biomasses in Gambia compared to Sine-Saloum may be explained by the latter ecosystem being characterized by inverse hypersalinity. Higher TL of production in Sine-Saloum is due to higher exploitations compared to Gambia where fishing activities are still less developed. High production and consumption rates of some groups in both ecosystems indicate high system productivity. Elevated productivity may be due to higher abundance of juvenile fishes in most groups that utilize the latter as refuge and/or nursery zones. Both ecosystems are phytoplankton-driven. Differences in group trophic and ecological roles are mainly due to adaptive responses of these species to seasonal and long-term climate and anthropogenic stressors. System indicators suggest different levels of ecosystem resilience and stability as a function of biodiversity. Relevance of other observations on ecosystem functioning and indicators in relation to perturbation is discussed.

  19. The stability of second sound waves in a rotating Darcy-Brinkman porous layer in local thermal non-equilibrium

    NASA Astrophysics Data System (ADS)

    Eltayeb, I. A.; Elbashir, T. B. A.

    2017-08-01

    The linear and nonlinear stabilities of second sound waves in a rotating porous Darcy-Brinkman layer in local thermal non-equilibrium are studied when the heat flux in the solid obeys the Cattaneo law. The simultaneous action of the Brinkman effect (effective viscosity) and rotation is shown to destabilise the layer, as compared to either of them acting alone, for both stationary and overstable modes. The effective viscosity tends to favour overstable modes while rotation tends to favour stationary convection. Rapid rotation invokes a negative viscosity effect that suppresses the stabilising effect of porosity so that the stability characteristics resemble those of the classical rotating Benard layer. A formal weakly nonlinear analysis yields evolution equations of the Landau-Stuart type governing the slow time development of the amplitudes of the unstable waves. The equilibrium points of the evolution equations are analysed and the overall development of the amplitudes is examined. Both overstable and stationary modes can exhibit supercritical stability; supercritical instability, subcritical instability and stability are not possible. The dependence of the supercritical stability on the relative values of the six dimensionless parameters representing thermal non-equilibrium, rotation, porosity, relaxation time, thermal diffusivities and Brinkman effect is illustrated as regions in regime diagrams in the parameter space. The dependence of the heat transfer and the mean heat flux on the parameters of the problem is also discussed.

  20. Comparison of methods for evaluating the thermal stability of human enteric viruses.

    PubMed

    Arthur, Sabastine E; Gibson, Kristen E

    2015-03-01

    Human enteric viruses have been identified as one of the predominant causative agents of food-borne illnesses in developed countries, and it is estimated that human norovirus accounts for a majority of these illnesses each year. Not all of these viruses can be cultured and hence relatively little is known about their pathogenesis and physicochemical properties. To overcome this, researchers have utilized different virus surrogates for the study of non-cultivable human enteric viruses. In this review, we discuss various methods utilized for the evaluation of the thermal stability of human enteric viruses, compare the results of these methods, and examine how researchers may move toward a single standard approach (i.e., temperatures, virus concentrations, volume/weight of matrices, etc.) for determining thermal inactivation profiles of human enteric viruses and their surrogates. Based on our review, we found that temperature, time of exposure, type of matrix, analysis type, type of heat application, and the concentration and volume of virus used in the experiments were highly variable across virus surrogates even for the same surrogates. Because of these differences-along with the inherent limitations of using surrogate viruses-comparison of these methods and how the results may be extrapolated to human enteric viruses is quite challenging. As a result, we discuss how researchers may move toward a single standard approach for determining thermal inactivation profiles of human enteric viruses and their surrogates.

  1. Numerical analysis of propagation of thermal disturbances in brass-stabilized REBCO tapes

    NASA Astrophysics Data System (ADS)

    Brighenti, A.; Bonifetto, R.; Drotziger, S.; Heller, R.; Savoldi, L.; Zanino, R.

    2016-12-01

    An extensive characterization of commercially available High-Temperature Superconducting (HTS) REBCO tapes has been recently performed at KIT. The main thermo-physical properties of the tapes have been measured, and heat slug and quench propagation have been investigated in vacuum at LN2 temperature, using a resistive heater as driver and recording the voltage and temperature evolution after the pulse at several locations along the tapes. In this paper, we present a study of thermal disturbance propagation in a HTS tape with brass stabilizer. The experimental data are analyzed first, to identify the phenomena that influence heat propagation in the tape, and namely the heat loss to the sample holder and the non-ideal efficiency of the resistive heater. A numerical tool is then developed, which solves the 1D transient heat conduction equation in each layer of the tape and accounts for the thermal coupling between layers. The heat loss to the sample holder and the non-ideal efficiency of the resistive heater are taken into account in the model. A first validation of the thermal part of the model against an extended database of heat slug propagation tests is then performed: the comparison between simulation and experiment confirms the very good capability of the model to reproduce the measured temperature evolution. Finally, the results of the simulations of quench propagation are compared with experimental data, showing the capability of the model to reproduce the experiment, within the uncertainty in the input parameters.

  2. THERMAL STABILITY OF MAGNETIZED, OPTICALLY THIN, RADIATIVE COOLING-DOMINATED ACCRETION DISKS

    SciTech Connect

    Yu, Xiao-Fei; Gu, Wei-Min; Liu, Tong; Ma, Ren-Yi; Lu, Ju-Fu

    2015-03-01

    We investigate the thermal stability of optically thin, two-temperature, radiative cooling-dominated accretion disks. Our linear analysis shows that the disk is thermally unstable without magnetic fields, which agrees with previous stability analysis on the Shapiro-Lightman-Eardley disk. By taking into account the effects of magnetic fields, however, we find that the disk can be, or partly be, thermally stable. Our results may be helpful to understand the outflows in optically thin flows. Moreover, such radiative cooling-dominated disks may provide a new explanation of the different behaviors between black hole and neutron star X-ray binaries on the radio/X-ray correlation.

  3. Effect of Filler Concentration on Thermal Stability of Vinyl Copolymer Elastomer (VCE) Composites

    SciTech Connect

    Yang, Dali; Hubbard, Kevin Mark; Devlin, David James; Henderson, Kevin C.; Pacheco, Robin Montoya

    2015-03-06

    To study the thermal stability of vinyl copolymer elastomer (VCE) in its composite form, systematic TGA characterizations were conducted in both nonisothermal and isothermal modes. The effects of filler concentration on the aging behaviors of the VCE/filler composites were investigated under nitroplasticizer (NP) environment. FTIR characterization was used to probe the structural changes in the VCE polymer before and after the thermal treatments. This study suggests that the filler concentration significantly deteriorates the thermal stability of NP at a moderate temperature (< 70 °C). The degradation of NP, in turn, accelerates the aging process of the VCE polymer in its composite form.

  4. Kinetic analysis about the effects of neutral salts on the thermal stability of yeast alcohol dehydrogenase.

    PubMed

    Ikegaya, Kazuo

    2005-03-01

    The effects of salts on the rate constants of inactivation by heat of yeast alcohol dehydrogenase (YADH) at 60.0 degrees C were measured. Different effects were observed at low and high salt concentrations. At high concentrations, some salts had stabilizing effects, while others were destabilizing. The effects of salts in the high concentration range examined can be described as follows: (decreased thermal stability) NaClO(4) < NaI = (C(2)H(5))(4)NBr < NH(4)Br < NaBr = KBr = CsBr = (no addition) < (CH(3))(4)NBr < KCl < KF < Na(2)SO(4) (increased thermal stability). The decreasing effect of NaClO(4) on YADH controlled the thermal stability of the enzyme absolutely and was not compensated by the addition of Na(2)SO(4), a salt which stabilized the enzyme. However, Na(2)SO(4) compensation did occur in response to the decrease in thermal stability caused by (C(2)H(5))(4)NBr. The rate constants of inactivation by heat (k (in)) of the enzyme were measured at various temperatures. Effective values of the thermodynamic activation parameters of thermal inactivation, activation of free energy (DeltaG (double dagger)), activation enthalpy (DeltaH (double dagger)), and activation entropy (DeltaS (double dagger)), were determined. The thermal stability of YADH in 0.8 M Na(2)SO(4) increased more than that of pyruvate kinase from Bacillus stearothermophilus, a moderate thermophile. The changes in the values of DeltaH (double dagger) and DeltaS (double dagger) were great and showed a general compensatory tendency, with the exception of in the case of NaClO(4). The temperature for the general compensation effect (T (c)) was approximately 123 degrees C. With Na(2)SO(4), the thermal stability of YADH at a temperature below T (c) was greater than that in the absence of salt due to the higher values of DeltaH (double dagger) and DeltaS (double dagger), respectively, and thus was an example of low-temperature enzymatic stabilization. With (C(2)H(5))(4)NBr, the thermal stability of YADH

  5. Coaxial carbon@boron nitride nanotube arrays with enhanced thermal stability and compressive mechanical properties

    NASA Astrophysics Data System (ADS)

    Jing, Lin; Tay, Roland Yingjie; Li, Hongling; Tsang, Siu Hon; Huang, Jingfeng; Tan, Dunlin; Zhang, Bowei; Teo, Edwin Hang Tong; Tok, Alfred Iing Yoong

    2016-05-01

    Vertically aligned carbon nanotube (CNT) arrays have aroused considerable interest because of their remarkable mechanical properties. However, the mechanical behaviour of as-synthesized CNT arrays could vary drastically at a macro-scale depending on their morphologies, dimensions and array density, which are determined by the synthesis method. Here, we demonstrate a coaxial carbon@boron nitride nanotube (C@BNNT) array with enhanced compressive strength and shape recoverability. CNT arrays are grown using a commercially available thermal chemical vapor deposition (TCVD) technique and an outer BNNT with a wall thickness up to 1.37 nm is introduced by a post-growth TCVD treatment. Importantly, compared to the as-grown CNT arrays which deform almost plastically upon compression, the coaxial C@BNNT arrays exhibit an impressive ~4-fold increase in compressive strength with nearly full recovery after the first compression cycle at a 50% strain (76% recovery maintained after 10 cycles), as well as a significantly high and persistent energy dissipation ratio (~60% at a 50% strain after 100 cycles), attributed to the synergistic effect between the CNT and outer BNNT. Additionally, the as-prepared C@BNNT arrays show an improved structural stability in air at elevated temperatures, attributing to the outstanding thermal stability of the outer BNNT. This work provides new insights into tailoring the mechanical and thermal behaviours of arbitrary CNT arrays which enables a broader range of applications.Vertically aligned carbon nanotube (CNT) arrays have aroused considerable interest because of their remarkable mechanical properties. However, the mechanical behaviour of as-synthesized CNT arrays could vary drastically at a macro-scale depending on their morphologies, dimensions and array density, which are determined by the synthesis method. Here, we demonstrate a coaxial carbon@boron nitride nanotube (C@BNNT) array with enhanced compressive strength and shape recoverability

  6. Dimensional stability of fused silica, Invar, and several ultralow thermal expansion materials

    NASA Technical Reports Server (NTRS)

    Berthold, J. W., III; Jacobs, S. F.; Norton, M. A.

    1976-01-01

    A method is developed for testing the long-term dimensional stability of an iodine-stabilized He-Ne laser, using a technique whereby thermal expansion coefficients are measured by forming a Fabry-Perot etalon from the sample and monitoring the optical resonant frequencies with tunable sidebands impressed on a laser beam from a frequency-stabilized He-Ne laser. A change of 1 ppm over a 3-yr period on the part of fused silica dimensions and the differential thermal expansion of Invar LR-35 and Super Invar materials are noted. The method is of interest for the metrology of extremely stable structures such as telescopes and optical resonators.

  7. Thermal stability of chimeric isopropylmalate dehydrogenase genes constructed from a thermophile and a mesophile.

    PubMed

    Numata, K; Muro, M; Akutsu, N; Nosoh, Y; Yamagishi, A; Oshima, T

    1995-01-01

    Chimeric isopropylmalate dehydrogenases were constructed by connecting the genes isolated from an extreme thermophile, Thermus thermophilus, and a mesophile, Bacillus subtilis. These genes were expressed in Escherichia coli. The enzymes were purified and analysed. Enzymes of T.thermophilus and B.subtilis and chimeric enzymes showed similar enzymological characteristics except for thermal stability. The stability of each enzyme was approximately proportional to the content of the amino acid sequence from the T.thermophilus enzyme. The results suggested that amino acid residues contributing the thermal stability distribute themselves, in general, evenly at least in the N-terminal half of the amino acid sequence of T.thermophilus isopropylmalate dehydrogenase.

  8. The study of the thermal stability of Ni3Al nanoneedles using computer simulation

    NASA Astrophysics Data System (ADS)

    Poletaev, G. M.; Starostenkov, M. D.; Novoselova, D. V.; Tsellermaer, V. Y.

    2016-02-01

    The study of the thermal stability of Ni3Al nanoneedles in the dependence on the sharpness and crystallography orientation of the needle axis was held using molecular dynamics method. It is shown that the most stability nanoneedles in the conditions of thermal influence are the nanoneedles with the axis along [111] direction. Violation of the nanoneedles stability associated with their blunting, which is caused by surface diffusion. Stable radius of curvature of the needles depends on the angle of the tip and orientation of the needle axis. It is 0.6-1 nm at low temperatures.

  9. A thermally baffled device for highly stabilized convective PCR

    PubMed Central

    Chang, Hsiao-Fen Grace; Tsai, Yun-Long; Tsai, Chuan-Fu; Lin, Ching-Ko; Lee, Pei-Yu; Teng, Ping-Hua; Su, Chen; Jeng, Chien-Chung

    2012-01-01

    Rayleigh-Bénard convective PCR is a simple and effective design for amplification of DNA. Convective PCR is, however, extremely sensitive to environmental temperature fluctuations, especially when using small- diameter test tubes. Therefore, this method is inherently unstable with limited applications. Here, we present a convective PCR device that has been modified by adding thermal baffles. With this thermally baffled device the influence from fluctuations in environmental temperature were significantly reduced, even in a wind tunnel (1 m/s). The thermally baffled PCR instrument described here has the potential to be used as a low-cost, point-of-care device for PCR-based molecular diagnostics in the field. PMID:22241586

  10. ITO/ATO bilayer transparent electrodes with enhanced light scattering, thermal stability and electrical conductance

    NASA Astrophysics Data System (ADS)

    Guillén, C.; Montero, J.; Herrero, J.

    2016-10-01

    Transparent electrodes based on In2O3:Sn (ITO) and SnO2:Sb (ATO) thin films have been deposited by sputtering at room temperature on soda lime glass (SLG) substrates. The preparation conditions were adjusted to obtain 250 nm-thick ITO layers with high conductivity and textured ATO coatings with various thicknesses from 80 to 200 nm. These ITO and ATO films have been combined to enhance the optical scattering and the electrical conductivity of the bilayer electrodes. Besides, a suitable ATO coating can prevent the oxidation of the ITO underlayer, thus increasing the stability of the overall electrical performance. With this purpose the structure, morphology, optical and electrical properties have been analysed comparatively for SLG/ITO, SLG/ATO and SLG/ITO/ATO samples after heating in air at 500 °C, studying the influence of the ATO layer thickness on the light scattering and thermal stability of the electrodes. In this way, a minimum sheet resistance of 8 Ω/sq has been achieved with a 120 nm-thick ATO film deposited on the 250 nm-thick ITO layer; such stacked electrode has visible transmittance near 80% and average haze HT = 10%, showing superior stability, light scattering and electrical performance than the isolated ITO and ATO films.

  11. Calcium Binding and Disulfide Bonds Regulate the Stability of Secretagogin towards Thermal and Urea Denaturation

    PubMed Central

    Weiffert, Tanja; Ní Mhurchú, Niamh; O’Connell, David; Linse, Sara

    2016-01-01

    Secretagogin is a calcium-sensor protein with six EF-hands. It is widely expressed in neurons and neuro-endocrine cells of a broad range of vertebrates including mammals, fishes and amphibia. The protein plays a role in secretion and interacts with several vesicle-associated proteins. In this work, we have studied the contribution of calcium binding and disulfide-bond formation to the stability of the secretagogin structure towards thermal and urea denaturation. SDS-PAGE analysis of secretagogin in reducing and non-reducing conditions identified a tendency of the protein to form dimers in a redox-dependent manner. The denaturation of apo and Calcium-loaded secretagogin was studied by circular dichroism and fluorescence spectroscopy under conditions favoring monomer or dimer or a 1:1 monomer: dimer ratio. This analysis reveals significantly higher stability towards urea denaturation of Calcium-loaded secretagogin compared to the apo protein. The secondary and tertiary structure of the Calcium-loaded form is not completely denatured in the presence of 10 M urea. Reduced and Calcium-loaded secretagogin is found to refold reversibly after heating to 95°C, while both oxidized and reduced apo secretagogin is irreversibly denatured at this temperature. Thus, calcium binding greatly stabilizes the structure of secretagogin towards chemical and heat denaturation. PMID:27812162

  12. Comprehensive analysis of surface charged residues involved in thermal stability in Alicyclobacillus acidocaldarius esterase 2.

    PubMed

    Pezzullo, Margherita; Del Vecchio, Pompea; Mandrich, Luigi; Nucci, Roberto; Rossi, Mosè; Manco, Giuseppe

    2013-01-01

    Here we report a comprehensive analysis through alanine-scanning mutagenesis of the contribution of surface ion pairs to the thermal stability of Alicyclobacillus acidocaldarius esterase 2 (EST2). We produced 16 single mutants, 4 double mutants corresponding to selected ion pairs R31/E118, E43/K102, R58/D130, D145/R148, 2 double mutants (R63A/R98A and E50A/D94A) involving residues of a large ion network on the protein surface and the double-mutant R98A/R148A meant to disrupt the R98 interactions within the said network and, contextually, the interaction between R148 and D145. The double-mutant E43A/E273K was obtained by chance. All selected residues were replaced with alanine except E91, which was mutated to a glycine and K102, which was changed to a glutamine. All 24 proteins were over-expressed in Escherichia coli, purified and characterized with respect to the main features. Structural stability data were compared with an in silico prediction of ΔΔG values. Our study of the individual factors involved in thermostability and their structural interpretation reveals that the great stability of this thermophilic protein can be explained by the contribution of a few residues at the protein surface.

  13. Evidence for formation of a PAN analogue of pinonic structure and investigation of its thermal stability

    NASA Astrophysics Data System (ADS)

    NozièRe, Barbara; Barnes, Ian

    1998-10-01

    The first evidence and laboratory study of a peroxyacetyl nitrate (PAN) analogue produced by the photooxidation of a terpene, α-pinene, is presented. This PAN analogue, assigned to 3-acetyl-2,2-dimethyl-cyclobutane-acetyl peroxynitrate and referred to as "α-pinonyl peroxynitrate" (αP-PAN) was synthesized in the gas phase from the radical (OH, Cl, Br, or NO3) initiated oxidation of pinonaldehyde (3-acetyl-2,2-dimethyl-cyclobutyl-ethanal) in the presence of excess NO2 and evidenced by Fourier transform-infrared (FT-IR) spectroscopy. Another reaction channel producing PAN was also observed for some of the radical initiators. Of particular atmospheric interest, the experiments with OH radicals demonstrated that αP-PAN is the main product of pinonaldehyde under NOx-rich conditions with a yield of (81.3±16)%, while an upper limit of the PAN yield for this reaction is around 8%. The further photooxidation of αP-PAN was also observed to produce PAN directly. The thermal stability of αP-PAN was studied between 303 and 281 K. The rate constant of thermal dissociation was found to be k-1 = 10(9.25±0.33) × exp [-(72.0±1.9)/RT] where the activation energy is in kJ mol-1. Distortions of the kinetic profiles attributed to aerosol formation were observed and led to large errors in the above estimation of k-1. Within the uncertainties, the observed thermal stability of αP-PAN is comparable to that of PAN. The tropospheric importance of pinonaldehyde and of αP-PAN are discussed.

  14. Toward Improved Lifetimes of Organic Solar Cells under Thermal Stress: Substrate-Dependent Morphological Stability of PCDTBT:PCBM Films and Devices

    NASA Astrophysics Data System (ADS)

    Li, Zhe; Ho Chiu, Kar; Shahid Ashraf, Raja; Fearn, Sarah; Dattani, Rajeev; Cheng Wong, Him; Tan, Ching-Hong; Wu, Jiaying; Cabral, João T.; Durrant, James R.

    2015-10-01

    Morphological stability is a key requirement for outdoor operation of organic solar cells. We demonstrate that morphological stability and lifetime of polymer/fullerene based solar cells under thermal stress depend strongly on the substrate interface on which the active layer is deposited. In particular, we find that the stability of benchmark PCDTBT/PCBM solar cells under modest thermal stress is substantially increased in inverted solar cells employing a ZnO substrate compared to conventional devices employing a PEDOT:PSS substrate. This improved stability is observed to correlate with PCBM nucleation at the 50 nm scale, which is shown to be strongly influenced by different substrate interfaces. Employing this approach, we demonstrate remarkable thermal stability for inverted PCDTBT:PC70BM devices on ZnO substrates, with negligible (<2%) loss of power conversion efficiency over 160 h under 85 °C thermal stress and minimal thermally induced “burn-in” effect. We thus conclude that inverted organic solar cells, in addition to showing improved environmental stability against ambient humidity exposure as widely reported previously, can also demonstrate enhanced morphological stability. As such we show that the choice of suitable substrate interfaces may be a key factor in achieving prolonged lifetimes for organic solar cells under thermal stress conditions.

  15. Toward Improved Lifetimes of Organic Solar Cells under Thermal Stress: Substrate-Dependent Morphological Stability of PCDTBT:PCBM Films and Devices.

    PubMed

    Li, Zhe; Ho Chiu, Kar; Shahid Ashraf, Raja; Fearn, Sarah; Dattani, Rajeev; Cheng Wong, Him; Tan, Ching-Hong; Wu, Jiaying; Cabral, João T; Durrant, James R

    2015-10-15

    Morphological stability is a key requirement for outdoor operation of organic solar cells. We demonstrate that morphological stability and lifetime of polymer/fullerene based solar cells under thermal stress depend strongly on the substrate interface on which the active layer is deposited. In particular, we find that the stability of benchmark PCDTBT/PCBM solar cells under modest thermal stress is substantially increased in inverted solar cells employing a ZnO substrate compared to conventional devices employing a PSS substrate. This improved stability is observed to correlate with PCBM nucleation at the 50 nm scale, which is shown to be strongly influenced by different substrate interfaces. Employing this approach, we demonstrate remarkable thermal stability for inverted PCDTBT:PC70BM devices on ZnO substrates, with negligible (<2%) loss of power conversion efficiency over 160 h under 85 °C thermal stress and minimal thermally induced "burn-in" effect. We thus conclude that inverted organic solar cells, in addition to showing improved environmental stability against ambient humidity exposure as widely reported previously, can also demonstrate enhanced morphological stability. As such we show that the choice of suitable substrate interfaces may be a key factor in achieving prolonged lifetimes for organic solar cells under thermal stress conditions.

  16. Effect of deoxygenation and prestressing on hydrocarbon fuel thermal stability

    NASA Technical Reports Server (NTRS)

    Bittker, D. A.

    1983-01-01

    A jet fuel thermal oxidation tester was used to study the effect of deoxygenation and deoxygenated prestressing on deposit formation when hydrocarbon fuels are thermally stressed. Four pure hydrocarbons (n-decane, cyclohexane, benzene and 1-hexene) and two mixtures (10 percent tetralin in n-dodecane and commercial Jet A) were used at temperatures of 250 C to 400 C. Deoxygenation decreased deposit formation for cycloheaxane but increased it for benzene. Deoxygenation decreased deposit formation for the two fuel mixtures at 250 C but had no effect at 350 C. Deoxygenated prestressing either increased or decreased deposit formation depending on the fuel used and the temperature.

  17. Effect of Si additions on thermal stability and the phase transition sequence of sputtered amorphous alumina thin films

    SciTech Connect

    Bolvardi, H.; Baben, M. to; Nahif, F.; Music, D. Schnabel, V.; Shaha, K. P.; Mráz, S.; Schneider, J. M.; Bednarcik, J.; Michalikova, J.

    2015-01-14

    Si-alloyed amorphous alumina coatings having a silicon concentration of 0 to 2.7 at. % were deposited by combinatorial reactive pulsed DC magnetron sputtering of Al and Al-Si (90-10 at. %) split segments in Ar/O{sub 2} atmosphere. The effect of Si alloying on thermal stability of the as-deposited amorphous alumina thin films and the phase formation sequence was evaluated by using differential scanning calorimetry and X-ray diffraction. The thermal stability window of the amorphous phase containing 2.7 at. % of Si was increased by more than 100 °C compared to that of the unalloyed phase. A similar retarding effect of Si alloying was also observed for the α-Al{sub 2}O{sub 3} formation temperature, which increased by more than 120 °C. While for the latter retardation, the evidence for the presence of SiO{sub 2} at the grain boundaries was presented previously, this obviously cannot explain the stability enhancement reported here for the amorphous phase. Based on density functional theory molecular dynamics simulations and synchrotron X-ray diffraction experiments for amorphous Al{sub 2}O{sub 3} with and without Si incorporation, we suggest that the experimentally identified enhanced thermal stability of amorphous alumina with addition of Si is due to the formation of shorter and stronger Si–O bonds as compared to Al–O bonds.

  18. The effect of an anisotropic pressure of thermal particles on resistive wall mode stability

    SciTech Connect

    Berkery, J. W. Sabbagh, S. A.; Betti, R.; Guazzotto, L.; Manickam, J.

    2014-11-15

    The effect of an anisotropic pressure of thermal particles on resistive wall mode stability in tokamak fusion plasmas is derived through kinetic theory and assessed through calculation with the MISK code [B. Hu et al., Phys. Plasmas 12, 0 57301 (2005)]. The fluid anisotropy is treated as a small perturbation on the plasma equilibrium and modeled with a bi-Maxwellian distribution function. A complete stability treatment without an assumption of high frequency mode rotation leads to anisotropic kinetic terms in the dispersion relation in addition to anisotropy corrections to the fluid terms. With the density and the average pressure kept constant, when thermal particles have a higher temperature perpendicular to the magnetic field than parallel, the fluid pressure-driven ballooning destabilization term is reduced. Additionally, the stabilizing kinetic effects of the trapped thermal ions can be enhanced. Together these two effects can lead to a modest increase in resistive wall mode stability.

  19. High thermal stability and sluggish crystallization kinetics of high-entropy bulk metallic glasses

    NASA Astrophysics Data System (ADS)

    Yang, M.; Liu, X. J.; Ruan, H. H.; Wu, Y.; Wang, H.; Lu, Z. P.

    2016-06-01

    Metallic glasses are metastable and their thermal stability is critical for practical applications, particularly at elevated temperatures. The conventional bulk metallic glasses (BMGs), though exhibiting high glass-forming ability (GFA), crystallize quickly when being heated to a temperature higher than their glass transition temperature. This problem may potentially be alleviated due to the recent developments of high-entropy (or multi-principle-element) bulk metallic glasses (HE-BMGs). In this work, we demonstrate that typical HE-BMGs, i.e., ZrTiHfCuNiBe and ZrTiCuNiBe, have higher kinetic stability, as compared with the benchmark glass Vitreoy1 (Zr41.2Ti13.8Cu12.5Ni10Be22.5) with a similar chemical composition. The measured activation energy for glass transition and crystallization of the HE-BMGs is nearly twice that of Vitreloy 1. Moreover, the sluggish crystallization region ΔTpl-pf, defined as the temperature span between the last exothermic crystallization peak temperature Tpl and the first crystallization exothermic peak temperature Tpf, of all the HE-BMGs is much wider than that of Vitreloy 1. In addition, high-resolution transmission electron microscopy characterization of the crystallized products at different temperatures and the continuous heating transformation diagram which is proposed to estimate the lifetime at any temperature below the melting point further confirm high thermal stability of the HE-BMGs. Surprisingly, all the HE-BMGs show a small fragility value, which contradicts with their low GFA, suggesting that the underlying diffusion mechanism in the liquid and the solid of HE-BMGs is different.

  20. High thermal stability and sluggish crystallization kinetics of high-entropy bulk metallic glasses

    SciTech Connect

    Yang, M.; Liu, X. J.; Wu, Y.; Wang, H.; Lu, Z. P.; Ruan, H. H.

    2016-06-28

    Metallic glasses are metastable and their thermal stability is critical for practical applications, particularly at elevated temperatures. The conventional bulk metallic glasses (BMGs), though exhibiting high glass-forming ability (GFA), crystallize quickly when being heated to a temperature higher than their glass transition temperature. This problem may potentially be alleviated due to the recent developments of high-entropy (or multi-principle-element) bulk metallic glasses (HE-BMGs). In this work, we demonstrate that typical HE-BMGs, i.e., ZrTiHfCuNiBe and ZrTiCuNiBe, have higher kinetic stability, as compared with the benchmark glass Vitreoy1 (Zr{sub 41.2}Ti{sub 13.8}Cu{sub 12.5}Ni{sub 10}Be{sub 22.5}) with a similar chemical composition. The measured activation energy for glass transition and crystallization of the HE-BMGs is nearly twice that of Vitreloy 1. Moreover, the sluggish crystallization region ΔT{sub pl-pf}, defined as the temperature span between the last exothermic crystallization peak temperature T{sub pl} and the first crystallization exothermic peak temperature T{sub pf}, of all the HE-BMGs is much wider than that of Vitreloy 1. In addition, high-resolution transmission electron microscopy characterization of the crystallized products at different temperatures and the continuous heating transformation diagram which is proposed to estimate the lifetime at any temperature below the melting point further confirm high thermal stability of the HE-BMGs. Surprisingly, all the HE-BMGs show a small fragility value, which contradicts with their low GFA, suggesting that the underlying diffusion mechanism in the liquid and the solid of HE-BMGs is different.

  1. Investigating the Thermal and Phase Stability of Nanocrystalline Ni-W Produced by Electrodeposition, Sputtering, and Mechanical Alloying

    NASA Astrophysics Data System (ADS)

    Marvel, Christopher Jonathan

    The development of nanocrystalline materials has been increasingly pursued over the last few decades. They have been shown to exhibit superior properties compared to their coarse-grain counterparts, and thus present a tremendous opportunity to revolutionize the performance of nanoscale devices or bulk structural materials. However, nanocrystalline materials are highly prone to grain growth, and if the nanocrystalline grains coarsen, the beneficial properties are lost. There is a strong effort to determine the most effective thermal stability mechanisms to avoid grain growth, but the physical nature of nanocrystalline grain growth is still unclear due to a lack of detailed understanding of nanocrystalline microstructures. Furthermore, the influence of contamination has scarcely been explored with advanced transmission electron microscopy techniques, nor has there been a direct comparison of alloys fabricated with different bulk processes. Therefore, this research has applied aberration-corrected scanning transmission electron microscopy to characterize nanocrystalline Ni-W on the atomic scale and elucidate the physical grain growth behavior. Three primary objectives were pursued: (1) explore the thermal stability mechanisms of nanocrystalline Ni-W, (2) evaluate the phase stability of Ni-W and link any findings to grain growth behavior, and (3) compare the influences of bulk fabrication processing, including electrodeposition, DC magnetron sputtering, and mechanical alloying, on the thermal stability and phase stability of Ni-W. Several thermal stability mechanisms were identified throughout the course of this research. First and foremost, W-segregation was scarcely observed to grain boundaries, and it is unclear if W-segregation improves thermal stability contrary to most reports in the 2 literature. Long-range Ni4W chemical ordering was observed in alloys with more than 20 at.% W, and it is likely Ni4W domains reduce grain boundary mobility. In addition, lattice

  2. Stabilization of immobilized glucose oxidase against thermal inactivation by silanization for biosensor applications.

    PubMed

    Sarath Babu, V R; Kumar, M A; Karanth, N G; Thakur, M S

    2004-05-15

    An important requirement of immobilized enzyme based biosensors is the thermal stability of the enzyme. Studies were carried out to increase thermal stability of glucose oxidase (GOD) for biosensor applications. Immobilization of the enzyme was carried out using glass beads as support and the effect of silane concentration (in the range 1-10%) during the silanization step on the thermal stability of GOD has been investigated. Upon incubation at 70 degrees C for 3h, the activity retention with 1% silane was only 23%, which increased with silane concentration to reach a maximum up to 250% of the initial activity with 4% silane. Above this concentration the activity decreased. The increased stability of the enzyme in the presence of high silane concentrations may be attributed to the increase in the surface hydrophobicity of the support. The decrease in the enzyme stability for silane concentrations above 4% was apparently due to the uneven deposition of the silane layer on the glass bead support. Further work on thermal stability above 70 degrees C was carried out by using 4% silane and it was found that the enzyme was stable up to 75 degrees C with an increased activity of 180% after 3-h incubation. Although silanization has been used for the modification of the supports for immobilization of enzymes, the use of higher concentrations to stabilize immobilized enzymes is being reported for the first time.

  3. Influence of structure on chemical and thermal stability of aliphatic diesters.

    PubMed

    Raghunanan, Latchmi; Narine, Suresh S

    2013-11-27

    Ester group interactions with each other and with the atoms between them were investigated in order to determine dependence of chemical and thermal stabilities of aliphatic diesters on structure. Novel glycol-derived diesters with chemical formula (C17H33COO)2C(n)H(2n) were used as model systems. Chemical stability was determined using (1)H NMR and FTIR, and thermal stability and weight-loss kinetics were examined using nonisothermal TGA. Chemical stability increased with the number of methylene units (n, carbon) between the ester groups until n = 6, and no significant improvement was observed past n > 6. It is argued that other ester-dense materials, including polyesters, would behave similarly. Evidence of a strong dependence of thermal stability on chemical stability is also provided. This work shows that the chemical and thermal stabilities of ester-dense functional materials such as diesters, oligo-esters, and polyesters can be manipulated by varying the distance between the ester groups, and hence the interactions of the electron-withdrawing ester groups with its neighbors.

  4. Stabilized thermally beneficiated low rank coal and method of manufacture

    DOEpatents

    Viall, Arthur J.; Richards, Jeff M.

    2000-01-01

    A process for reducing the spontaneous combustion tendencies of thermally beneficiated low rank coals employing heat, air or an oxygen containing gas followed by an optional moisture addition. Specific reaction conditions are supplied along with knowledge of equipment types that may be employed on a commercial scale to complete the process.

  5. Stabilized thermally beneficiated low rank coal and method of manufacture

    DOEpatents

    Viall, Arthur J.; Richards, Jeff M.

    1999-01-01

    A process for reducing the spontaneous combustion tendencies of thermally beneficiated low rank coals employing heat, air or an oxygen containing gas followed by an optional moisture addition. Specific reaction conditions are supplied along with knowledge of equipment types that may be employed on a commercial scale to complete the process.

  6. Stabilized thermally beneficiated low rank coal and method of manufacture

    DOEpatents

    Viall, A.J.; Richards, J.M.

    1999-01-26

    A process is described for reducing the spontaneous combustion tendencies of thermally beneficiated low rank coals employing heat, air or an oxygen containing gas followed by an optional moisture addition. Specific reaction conditions are supplied along with knowledge of equipment types that may be employed on a commercial scale to complete the process. 3 figs.

  7. Limited thermal stability of imidazolium and pyrrolidinium ionic liquids

    SciTech Connect

    Del Sesto, Rico E; Mccleskey, T; Macomber, Clay; Ott, Kevin; Koppisch, Andrew; Baker, Gary A; Burrell, Anthony K

    2009-01-01

    Ionic liquids, with their vast applications, have been touted as being thermally stable to very high temperatures. However, decomposition not detected by standard TGA and NMR techniques are observed with spectroscopic techniques sensitive enough to see small amounts of impurities. Decomposition temperatures of common ionic liquids appear to occur at hundreds of degrees below those temperatures previously reported.

  8. Thermal stability of electrodes in Lithium-ion cells

    SciTech Connect

    ROTH,EMANUEL P.; NAGASUBRAMANIAN,GANESAN

    2000-02-07

    Differential scanning calorimetry (DSC) analysis was used to identify thermal reactions in Sony-type lithium-ion cells and to correlate these reactions with interactions of cell constituents and reaction products. An electrochemical half-cell was used to cycle the anode and cathode materials and to set the state-of-charge (SOC). Three temperature regions of interaction were identified and associated with the SOC (degree of Li intercalation) of the cell. Anodes were shown to undergo exothermic reactions as low as 80 C involving decomposition of the solid electrolyte interphase (SEI) layer. The LiPF{sub 6} salt in the electrolyte (EC:PC:DEC/1M LiPF{sub 6}) was seen to play an essential role in this reaction. DSC analysis of the anodes from disassembled Sony cells showed similar behavior to the half-cell anodes with a strong exotherm beginning in the 80 C--90 C range. Exothermic reactions were also observed in the 200 C--300 C region between the intercalated lithium anodes, the LiPF{sub 6} salt, and the PVDF binder. These reactions were followed by a high-temperature reaction region, 300 C--400 C, also involving the PVDF binder and the intercalated lithium anodes. Cathode exothermic reactions with the PVDF binder were observed above 200 C and increased with the SOC (decreasing Li content in the cathode). No thermal reactions were seen at lower temperatures suggesting that thermal runaway reactions in this type of cell are initiated at the anode. An Accelerating Rate Calorimeter (ARC) was used to perform measurements of thermal runaway on commercial Sony Li-ion cells as a function of SOC. The cells showed sustained thermal output as low as 80 C in agreement with the DSC observations of anode materials but the heating rate was strongly dependent on the SOC.

  9. Heat Transfer and Thermal Stability Research for Advanced Hydrocarbon Fuel Technologies

    NASA Technical Reports Server (NTRS)

    DeWitt, Kenneth; Stiegemeier, Benjamin

    2005-01-01

    In recent years there has been increased interest in the development of a new generation of high performance boost rocket engines. These efforts, which will represent a substantial advancement in boost engine technology over that developed for the Space Shuttle Main Engines in the early 1970s, are being pursued both at NASA and the United States Air Force. NASA, under its Space Launch Initiative s Next Generation Launch Technology Program, is investigating the feasibility of developing a highly reliable, long-life, liquid oxygen/kerosene (RP-1) rocket engine for launch vehicles. One of the top technical risks to any engine program employing hydrocarbon fuels is the potential for fuel thermal stability and material compatibility problems to occur under the high-pressure, high-temperature conditions required for regenerative fuel cooling of the engine combustion chamber and nozzle. Decreased heat transfer due to carbon deposits forming on wetted fuel components, corrosion of materials common in engine construction (copper based alloys), and corrosion induced pressure drop increases have all been observed in laboratory tests simulating rocket engine cooling channels. To mitigate these risks, the knowledge of how these fuels behave in high temperature environments must be obtained. Currently, due to the complexity of the physical and chemical process occurring, the only way to accomplish this is empirically. Heated tube testing is a well-established method of experimentally determining the thermal stability and heat transfer characteristics of hydrocarbon fuels. The popularity of this method stems from the low cost incurred in testing when compared to hot fire engine tests, the ability to have greater control over experimental conditions, and the accessibility of the test section, facilitating easy instrumentation. These benefits make heated tube testing the best alternative to hot fire engine testing for thermal stability and heat transfer research. This investigation

  10. Factors affecting the thermal shock behavior of yttria stabilized hafnia based graphite and tungsten composites.

    NASA Technical Reports Server (NTRS)

    Lineback, L. D.; Manning, C. R.

    1971-01-01

    Hafnia-based composites containing either graphite or tungsten were investigated as rocket nozzle throat inserts in solid propellant rocket engines. The thermal shock resistance of these materials is considered in terms of macroscopic thermal conductivity, thermal expansion, modulus of elasticity, and compressive fracture stress. The effect of degree of hafnia stabilization, density, and graphite or tungsten content upon these parameters is discussed. The variation of the ratio of elastic modulus to compressive fracture stress with density and its effect upon thermal shock resistance of these materials are discussed in detail.

  11. Thermal Stability and Kinetic Studies of LMH-1

    DTIC Science & Technology

    was extracted from AlH3 - 1451 and is believed to be responsible for nucleation sites which result in the decomposition of AlH3 . Pound quantities of stabilized AlH3 have been successfully used in high energy propellant formulations.

  12. High Temperature Thermal Properties of Columnar Yttria Stabilized Zirconia Thermal Barrier Coating Performed by Suspension Plasma Spraying

    NASA Astrophysics Data System (ADS)

    Bernard, B.; Schick, V.; Remy, B.; Quet, A.; Bianchi, L.

    2016-09-01

    Performance enhancement of gas turbines is a main issue for the aircraft industry. Over many years, a large part of the effort has been focused on the development of more insulating Thermal Barrier Coatings (TBCs). In this study, Yttria Stabilized Zirconia (YSZ) columnar structures are processed by Suspension Plasma Spraying (SPS). These structures have already demonstrated abilities to get improved thermal lifetime, similarly to standard YSZ TBCs performed by EB-PVD. Thermal diffusivity measurements coupled with differential scanning calorimetry analysis are performed from room temperature up to 1100 °C, first, on HastelloyX substrates and then, on bilayers including a SPS YSZ coating. Results show an effective thermal conductivity for YSZ performed by SPS lower than 1 W.m-1K-1 whereas EB- PVD YSZ coatings exhibit a value of 1.5 W.m-1K-1.

  13. Thermal stability and spectroscopic properties of Er 3+-doped antimony-borosilicate glasses

    NASA Astrophysics Data System (ADS)

    Qian, Q.; Zhao, C.; Yang, G. F.; Yang, Z. M.; Zhang, Q. Y.; Jiang, Z. H.

    2008-11-01

    This paper reports on the optical spectroscopic properties and thermal stability of Er 3+-doped antimony-borosilicate glasses for developing 1.5 μm optical amplifiers. Upon excitation at 980 nm laser diode, an intense 1.5 μm infrared fluorescence has been observed with the maximum full width at half maximum (FWHM) of 90 nm for Er 3+-doped antimony-borosilicate glasses. The emission cross-section and the lifetime of the 4I13/2 level of Er 3+ ions are 6.3 × 10 -21 cm 2 and 0.30 ms, respectively. It is noted that the product of the emission cross-section and FWHM of the glass studied is as great as 567 × 10 -21 cm 2 nm, which is comparable or higher than that of bismuthate and tellurite glasses.

  14. The antioxidant activity and thermal stability of lemon verbena (Aloysia triphylla) infusion.

    PubMed

    Abderrahim, Fatima; Estrella, Seyer; Susín, Cristina; Arribas, Silvia M; González, M Carmen; Condezo-Hoyos, Luis

    2011-05-01

    Because of its good sensorial attributes, lemon verbena is used as a primary ingredient in infusions and nonalcoholic drinks. The present study was designed to assess the antioxidant activity (AA) of lemon verbena infusion (LVI) as well as the thermal stability of its AA and the content of polyphenolic compounds. The values reflecting the AA of LVI, including AA index, fast scavenging rate against 2,2-diphenyl-1-picrylhydrazyl, Trolox equivalent antioxidant capacity, and hydroxyl radical scavenging, are higher than those of many herbal infusions and antioxidant drinks estimated from reported data. In addition, the slope lag time and specific oxyradical antioxidant capacity values of LVI are comparable to those of a commercial antioxidant drink based on green tea. Hence, LVI is a source of bifunctional antioxidants, and thus in vivo studies of the antioxidant capacity of LVI would be useful to evaluate its potential as an ingredient in antioxidant drinks.

  15. Thermal stability and spectroscopic properties of Er3+-doped antimony-borosilicate glasses.

    PubMed

    Qian, Q; Zhao, C; Yang, G F; Yang, Z M; Zhang, Q Y; Jiang, Z H

    2008-11-01

    This paper reports on the optical spectroscopic properties and thermal stability of Er3+-doped antimony-borosilicate glasses for developing 1.5 microm optical amplifiers. Upon excitation at 980 nm laser diode, an intense 1.5 microm infrared fluorescence has been observed with the maximum full width at half maximum (FWHM) of 90 nm for Er3+-doped antimony-borosilicate glasses. The emission cross-section and the lifetime of the 4I13/2 level of Er3+ ions are 6.3 x 10(-21) cm2 and 0.30 ms, respectively. It is noted that the product of the emission cross-section and FWHM of the glass studied is as great as 567 x 10(-21) cm2 nm, which is comparable or higher than that of bismuthate and tellurite glasses.

  16. Low temperature superplasticity and thermal stability of a nanostructured low-carbon microalloyed steel

    PubMed Central

    Hu, J.; Du, L.-X.; Sun, G.-S.; Xie, H.; Misra, R.D.K.

    2015-01-01

    We describe here for the first time the low temperature superplasticity of nanostructured low carbon steel (microalloyed with V, N, Mn, Al, Si, and Ni). Low carbon nanograined/ultrafine-grained (NG/UFG) bulk steel was processed using a combination of cold-rolling and annealing of martensite. The complex microstructure of NG/UFG ferrite and 50–80 nm cementite exhibited high thermal stability at 500 °C with low temperature elongation exceeding 100% (at less than 0.5 of the absolute melting point) as compared to the conventional fine-grained (FG) counterpart. The low temperature superplasticity is adequate to form complex components. Moreover, the low strength during hot processing is favorable for decreasing the spring back and minimize die loss. PMID:26687012

  17. Low temperature superplasticity and thermal stability of a nanostructured low-carbon microalloyed steel

    NASA Astrophysics Data System (ADS)

    Hu, J.; Du, L.-X.; Sun, G.-S.; Xie, H.; Misra, R. D. K.

    2015-12-01

    We describe here for the first time the low temperature superplasticity of nanostructured low carbon steel (microalloyed with V, N, Mn, Al, Si, and Ni). Low carbon nanograined/ultrafine-grained (NG/UFG) bulk steel was processed using a combination of cold-rolling and annealing of martensite. The complex microstructure of NG/UFG ferrite and 50-80 nm cementite exhibited high thermal stability at 500 °C with low temperature elongation exceeding 100% (at less than 0.5 of the absolute melting point) as compared to the conventional fine-grained (FG) counterpart. The low temperature superplasticity is adequate to form complex components. Moreover, the low strength during hot processing is favorable for decreasing the spring back and minimize die loss.

  18. Improved thermal oxidation stability of solution-processable silver nanowire transparent electrode by reduced graphene oxide.

    PubMed

    Ahn, Yumi; Jeong, Youngjun; Lee, Youngu

    2012-12-01

    Solution-processable silver nanowire-reduced graphene oxide (AgNW-rGO) hybrid transparent electrode was prepared in order to replace conventional ITO transparent electrode. AgNW-rGO hybrid transparent electrode exhibited high optical transmittance and low sheet resistance, which is comparable to ITO transparent electrode. In addition, it was found that AgNW-rGO hybrid transparent electrode exhibited highly enhanced thermal oxidation and chemical stabilities due to excellent gas-barrier property of rGO passivation layer onto AgNW film. Furthermore, the organic solar cells with AgNW-rGO hybrid transparent electrode showed good photovoltaic behavior as much as solar cells with AgNW transparent electrode. It is expected that AgNW-rGO hybrid transparent electrode can be used as a key component in various optoelectronic application such as display panels, touch screen panels, and solar cells.

  19. A new technique for marginal linear stability analysis of thermal convection using propagator matrix method

    NASA Astrophysics Data System (ADS)

    Liu, X.; Zhong, S.

    2011-12-01

    Critical Rayleigh number, Ra_c, is the Rayleigh number at the onset of thermal convection. Classic linear analysis provides a way to solve for Ra_c, but this method is mostly used for incompressible fluid with uniform properties. Here we report a new technique for linear stability analysis using propagator matrix method. This new technique can solve for Ra_c for both incompressible and compressible fluids, with depth dependent viscosity, thermal expansion and thermal diffusivity. This technique determines Ra_c for fundamental mode as well as higher modes. We found that results from this new technique agree well with those from the classic analysis for incompressible fluid with uniform properties. We have compared results of Ra_c from the new method with that of finite element code Citcom( Leng and Zhong, 2008 ). For incompressible fluid, they agree with each other very well, including fundamental and higher modes. For compressible fluid, the agreement is not as good, but relative difference remains less than a couple of percent, especially for fundamental mode at small dissipation number Di (e.g., less than 1). Our results show that Ra_c for compressible fluid are similar to that of incompressible fluid, but are significantly different from that of Jarvis & Mckenzie (1981). Given that much higher Rayleigh number is needed in compressible fluid to generate a given heat flux, our results from the new method have implications for the Nusselt-Rayleigh number relation for compressible thermal convection.

  20. Al-Ti Particulate Composite: Processing and Studies on Particle Twinning, Microstructure, and Thermal Stability

    NASA Astrophysics Data System (ADS)

    Yadav, Devinder; Bauri, Ranjit; Kauffmann, Alexander; Freudenberger, Jens

    2016-08-01

    The present investigation shows that alternate to the ceramic particles, hard metallic particles can be used as reinforcement in an aluminum matrix to achieve a good strength-ductility combination in a composite. Titanium particles were incorporated into aluminum by friction stir processing (FSP) to process an Al-Ti particulate composite. FSP led to uniform distribution of the particles in the stir zone without any particle-matrix reaction, thereby retaining the particles in their elemental state. Fracture and twinning of the Ti particles with different frequency of occurrence on the advancing and retreating sides of the stir zone was observed. Twinning of the particles was studied by focused ion beam-assisted transmission electron microscopy. The processed Al-Ti composite exhibited a significant improvement in strength and also retained appreciable amount of ductility. The thermal stability of the fine-grained structure against abnormal grain growth (AGG) was improved by the Ti particles. The AGG in the Al-Ti composite occurred at 713 K (440 °C) compared to 673 K (400 °C) in the unreinforced aluminum processed under the same conditions. On the other hand, the particle-matrix reaction occurred only at 823 K (550 °C), and hence the Ti particles were thermally more stable compared to the matrix grain structure.

  1. Invaded grassland communities have altered stability-maintenance mechanisms but equal stability compared to native communities.

    PubMed

    Wilsey, Brian J; Daneshgar, Pedram P; Hofmockel, Kirsten; Polley, H Wayne

    2014-01-01

    Theory predicts that stability should increase with diversity via several mechanisms. We tested predictions in a 5-year experiment that compared low-diversity exotic to high-diversity native plant mixtures under two irrigation treatments. The study included both wet and dry years. Variation in biomass across years (CV) was 50% lower in mixtures than monocultures of both native and exotic species. Growth among species was more asynchronous and overyielding values were greater during and after a drought in native than exotic mixtures. Mean-variance slopes indicated strong portfolio effects in both community types, but the intercept was higher for exotics than for natives, suggesting that exotics were inherently more variable than native species. However, this failed to result in higher CV's in exotic communities because species that heavily dominated plots tended to have lower than expected variance. Results indicate that diversity-stability mechanisms are altered in invaded systems compared to native ones they replaced. © 2013 John Wiley & Sons Ltd/CNRS.

  2. Correlation of aging and thermal stability of commercial 18650-type lithium ion batteries

    NASA Astrophysics Data System (ADS)

    Börner, M.; Friesen, A.; Grützke, M.; Stenzel, Y. P.; Brunklaus, G.; Haetge, J.; Nowak, S.; Schappacher, F. M.; Winter, M.

    2017-02-01

    Established safety of lithium ion batteries is key for the vast diversity of applications. The influence of aging on the thermal stability of individual cell components and complete cells is of particular interest. Commercial 18650-type lithium ion batteries based on LiNi0.5Co0.2Mn0.3O2/C are investigated after cycling at different temperatures. The variations in the electrochemical performance are mainly attributed to aging effects on the anode side considering the formation of an effective solid-electrolyte interphase (SEI) during cycling at 45 °C and a thick decomposition layer on the anode surface at 20 °C. The thermal stability of the anodes is investigated including the analysis of the evolving gases which confirmed the severe degradation of the electrolyte and active material during cycling at 20 °C. In addition, the presence of metallic lithium deposits could strongly affect the thermal stability. Thermal safety tests using quasi-adiabatic conditions show variations in the cells response to elevated temperatures according to the state-of-charge, i.e. a reduced reactivity in the discharged state. Furthermore, it is revealed that the onset of exothermic reactions correlates with the thermal stability of the SEI, while the thermal runaway is mainly attributed to the decomposition of the cathode and the subsequent reactions with the electrolyte.

  3. Thermal stability of antiferromagnetically coupled multilayers with Ru/Co and Cu/Co interfaces

    NASA Astrophysics Data System (ADS)

    Bal, K.; van den Berg, H. A. M.; Deck, D.; Rasing, Th.

    2001-11-01

    The long-term thermal stability of the hard artificial antiferromagnetic subsystem (AAF) found in giant magnetoresistance (GMR) and tunnel magnetoresistance sensors based on Cu/Co/Ru/Co/Cu has been investigated using the complete sensor stack as well as of selected single layers. A striking asymmetry between both types of Co layers in the single Co layer samples with respect to magnetic and transport properties is observed, which show a different dynamics for each upon annealing. Directly after deposition, the Co/Ru interface is stronger mixed as compared to the Ru/Co interface, due to difference in sputter energies and order of growth. The different behavior upon annealing has been interpreted by the difference in concentration gradients and lattice mismatch at the interfaces. Despite the strong mixing found at the Co/Ru interface, the impact on the characteristics of the AAF, like the GMR signal and the rigidity is limited. Several causes, like the cohesion in the AAF induced by its Co seed layer on the Cu and the limited availability of Ru, are pointed out as likely origins of the improved stability of the AAF as compared to the single Co layers. Possibilities to even further improve the rigidity by carefully matching of anneal procedure and layer thicknesses are discussed.

  4. Comprehensive transient-state study for CARMENES NIR high-thermal stability

    NASA Astrophysics Data System (ADS)

    Becerril, Santiago; Sánchez, Miguel A.; Cárdenas, M. C.; Rabaza, Ovidio; Ramón, Alejandro; Abril, Miguel; Costillo, Luis P.; Morales, Rafael; Rodríguez, Alicia; Amado, Pedro J.

    2010-07-01

    CARMENES has been proposed as a next-generation instrument for the 3.5m Calar Alto Telescope. Its objective is finding habitable exoplanets around M dwarfs through radial velocity measurements (m/s level) in the near-infrared. Consequently, the NIR spectrograph is highly constraint regarding thermal/mechanical requirements. Indeed, the requirements used for the present study limit the thermal stability to +/-0.01K (within year period) over a working temperature of 243K in order to minimise radial velocity drifts. This can be achieved by implementing a solution based on several temperature-controlled rooms (TCR), whose smallest room encloses the vacuum vessel which houses the spectrograph's optomechanics. Nevertheless, several options have been taken into account to minimise the complexity of the thermal design: 1) Large thermal inertia of the system, where, given a thermal instability of the environment (typically, +/-0.1K), the optomechanical system remains stable within +/-0.01K in the long run; 2) Environment thermal control, where thermal stability is ensured by controlling the temperature of the environment surrounding the vacuum vessel. The present article also includes the comprehensive transient-state thermal analyses which have been implemented in order to make the best choice, as well as to give important inputs for the thermal layout of the instrument.

  5. Pump power stability range of single-mode solid-state lasers with rod thermal lensing

    SciTech Connect

    De Silvestri, S.; La Porta, P.; Magni, V.

    1987-11-01

    The pump power stability range of solid-state laser resonators operating in the TEM/sub 00/ mode has been thoroughly investigated. It has been shown that, for a very general resonator containing intracavity optical systems, rod thermal lensing engenders a pump power stability range which is a characteristic parameter of laser material and pump cavity, but is independent of resonator configuration. Stability ranges have been calculated and critically discussed for Nd:YAG, Nd:Glasses, Nd:Cr:GSGG, and alexandrite. The independence of the pump power stability range from the resonator configuration has been experimentally demonstrated for a CW Nd:YAG laser.

  6. Thermal stability improvements to the ESPaDOnS spectrograph with the addition of a thermal enclosure

    NASA Astrophysics Data System (ADS)

    Barrick, Gregory; Benedict, Tom; Moutou, Claire; Malo, Lison; White, John; Chene, André-Nicolas; Lundquist, Michael

    2016-08-01

    As part of GRACES (Gemini Remote Access to CFHT ESPaDOnS Spectrograph), a project to link the Gemini-North telescope to the ESPaDOnS (Echelle Polarimetric Device for the Observation of Stars) spectrograph at CFHT (Canada- France-Hawaii Telescope), the original thermal enclosure of the spectrograph needed to be modified. Although the modifications were slight, there was a significant possibility that the thermal stability of ESPaDOnS would be somewhat compromised. To eliminate this risk, a walk-in thermal enclosure was purchased and installed around the ESPaDOnS spectrograph as part of the GRACES project. The thermal impact of these modifications to the ESPaDOnS environment will be analyzed and the effect of the changes on the amplitude and behavior of the spectral drift for the ESPaDOnS and GRACES instruments will be examined. While the outer enclosure has reduced the extremes in thermal variation, this has not had a direct effect on the stability of the spectra.

  7. Stability of absorption phenomena in laser-thermal propulsion

    NASA Technical Reports Server (NTRS)

    Merkle, C. L.; Tsai, Y.-L. P.

    1984-01-01

    The mean flow and stability characteristics of laser absorption phenomena in a choked converging-diverging nozzle are considered. Calculations are presented for a given nozzle geometry and a series of laser intensities. Gas absorptivities corresponding to a hydrogen-cesium mixture are used with different initial temperatures being selected to investigate the effects of changes in the shape of the k-T curve. Both stability and mean flow calculations are limited to the one-dimensional case. The mean flow results show a decrease in mass flow as laser power is increased, along with increasingly steep temperature profiles. Calculations span regions of partial and complete absorption. One region is found where multiple solutions exist. Local stability results indicate the u-c characteristic is the only unstable mode in the unheated case. Laser heat addition makes this mode more unstable and also destabilizes the u-characteristic. Numerical calculations of disturbance propagation show that the instability of the u-c disturbances is counteracted by their reflection to u + c disturbances at the upstream end. The growth of the u-disturbances is localized in regions where the temperature profile is steep and they are damped in other regions. The increasing destabilization that is observed with increased laser power is probably the reason for difficulty in obtaining converged mean flow solutions at high laser intensities.

  8. Thermal stability relationships between PMR-15 resin and its composites

    NASA Technical Reports Server (NTRS)

    Bowles, Kenneth J.; Jayne, Douglas; Leonhardt, Todd A.; Bors, Dennis

    1993-01-01

    A study was conducted to investigate the relationship between the thermo-oxidative stability of PMR-15 matrix resin and the stability of graphite-fiber-reinforced composites that contain this resin as the matrix material. Three areas were investigated. The first was the effect of fiber/matrix interfacial bond strength on the isothermal aging weight loss of composites. By using type-A graphite fibers produced by Hercules, it was possible to study composites reinforced with fibers that were processed to receive different surface treatments. One of the fibers was untreated, a second fiber was treated by oxidation to enhance fiber/matrix bonding, and the third type of fiber was coated with an epoxy sizing. These treatments produced three significantly different interfacial bond strengths. The epoxy sizing on the third fiber was quickly oxidized from the bare fiber surfaces at 288, 316, and 343 C. The weight loss due to the removal of the sizing was constant at 1.5 percent. This initial weight loss was not observed in thermo-oxidative stability studies of composites. The PMR-15 matrix satisfactorily protected the reinforcemnt at all three temperatures.

  9. Effects of Protein Stabilizing Agents on Thermal Backbone Motions: A Disulfide Trapping Study†

    PubMed Central

    Butler, Scott L.; Falke, Joseph J.

    2010-01-01

    Chemical stabilizers are widely used to enhance protein stability, both in nature and in the laboratory. Here, the molecular mechanism of chemical stabilizers is studied using a disulfide trapping assay to measure the effects of stabilizers on thermal backbone dynamics in the Escherichia coli galactose/glucose binding protein. Two types of backbone fluctuations are examined: (a) relative movements of adjacent surface α-helices within the same domain and (b) interdomain twisting motions. Both types of fluctuations are significantly reduced by all six stabilizers tested (glycerol, sucrose, trehalose, l-glucose, d-glucose, and d-galactose), and in each case larger amplitude motions are inhibited more than smaller ones. Motional inhibition does not require a high-affinity stabilizer binding site, indicating that the effects of stabilizers are nonspecific. Overall, the results support the theory that effective stabilizing agents act by favoring the most compact structure of a protein, thereby reducing local backbone fluctuations away from the fully folded state. Such inhibition of protein backbone dynamics may be a general mechanism of protein stabilization in extreme thermal or chemical environments. PMID:8718847

  10. Comparative Solid-State Stability of Perindopril Active Substance vs. Pharmaceutical Formulation

    PubMed Central

    Buda, Valentina; Andor, Minodora; Ledeti, Adriana; Ledeti, Ionut; Vlase, Gabriela; Vlase, Titus; Cristescu, Carmen; Voicu, Mirela; Suciu, Liana; Tomescu, Mirela Cleopatra

    2017-01-01

    This paper presents the results obtained after studying the thermal stability and decomposition kinetics of perindopril erbumine as a pure active pharmaceutical ingredient as well as a solid pharmaceutical formulation containing the same active pharmaceutical ingredient (API). Since no data were found in the literature regarding the spectroscopic description, thermal behavior, or decomposition kinetics of perindopril, our goal was the evaluation of the compatibility of this antihypertensive agent with the excipients in the tablet under ambient conditions and to study the effect of thermal treatment on the stability of perindopril erbumine. ATR-FTIR (Attenuated Total Reflectance Fourier Transform Infrared) spectroscopy, thermal analysis (thermogravimetric mass curve (TG—thermogravimetry), derivative thermogravimetric mass curve (DTG), and heat flow (HF)) and model-free kinetics were chosen as investigational tools. Since thermal behavior is a simplistic approach in evaluating the thermal stability of pharmaceuticals, in-depth kinetic studies were carried out by classical kinetic methods (Kissinger and ASTM E698) and later with the isoconversional methods of Friedman, Kissinger-Akahira-Sunose and Flynn-Wall-Ozawa. It was shown that the main thermal degradation step of perindopril erbumine is characterized by activation energy between 59 and 69 kJ/mol (depending on the method used), while for the tablet, the values were around 170 kJ/mol. The used excipients (anhydrous colloidal silica, microcrystalline cellulose, lactose, and magnesium stearate) should be used in newly-developed generic solid pharmaceutical formulations, since they contribute to an increased thermal stability of perindopril erbumine. PMID:28098840

  11. Thermal Mechanical Stability of Single-Crystal-Oxide Refractive Concentrators Evaluated for High-Temperature Solar-Thermal Propulsion

    NASA Technical Reports Server (NTRS)

    Jacobson, Nathan S.; Jacobson, Nathan S.; Miller, Robert A.

    1999-01-01

    Recently, refractive secondary solar concentrator systems were developed for solar thermal power and propulsion (ref. 1). Single-crystal oxides-such as yttria-stabilized zirconia (Y2O3-ZrO2), yttrium aluminum garnet (Y3Al5O12, or YAG), magnesium oxide (MgO), and sapphire (Al2O3)-are candidate refractive secondary concentrator materials. However, the refractive concentrator system will experience high-temperature thermal cycling in the solar thermal engine during the sun/shade transition of a space mission. The thermal mechanical reliability of these components in severe thermal environments is of great concern. Simulated mission tests are important for evaluating these candidate oxide materials under a variety of transient and steady-state heat flux conditions. In this research at the NASA Lewis Research Center, a controlled heat flux test approach was developed for investigating the thermal mechanical stability of the candidate oxide. This approach used a 3.0-kW continuous-wave (wavelength, 10.6 mm) carbon dioxide (CO2) laser (ref. 2). The CO2 laser is especially well-suited for single-crystal thermal shock tests because it can directly deliver well-characterized heat energy to the oxide surfaces. Since the oxides are opaque at the 10.6-mm wavelength of the laser beam, the light energy is absorbed at the surfaces rather than transmitting into the crystals, and thus generates the required temperature gradients within the specimens. The following figure is a schematic diagram of the test rig.

  12. Microstructure and thermal oxidation behavior of yttria-stabilized hafnia nanostructured coatings deposited on alumina

    SciTech Connect

    Rubio, E. J.; Martinez, G.; Noor-A-Alam, M.; Stafford, S. W.; Shutthanandan, V.; Ramana, C. V.

    2013-12-01

    Nanostructured yttria-stabilized hafnia (YSH) coatings were grown on α-Al2O3 substrates with variable coating thickness in a wide range of ~50 nm to 1 μm. Microstructure and thermal oxidation behavior of the grown YSH coatings were studied employing X-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS), scanning electron microscopy (SEM) and isothermal furnace oxidation testing. The effect of coating thickness on the crystal structure, surface/interface morphology and thermal oxidation was investigated. X-ray diffraction analyses revealed the formation of monoclinic phase for relatively thin coatings (b100 nm) indicating that the interfacial phenomena play a dominant role in phase stabilization. The evolution towards stabilized cubic phase with increasing coating thickness is observed. The SEM results indicate the dense, columnar structure of YSH coatings as a function of thickness. Thermal oxidation measurements indicate the enhanced hightemperature oxidation resistance of cubic YSH coatings.

  13. The thermal stability of the Fusarium solani pisi cutinase as a function of pH

    PubMed Central

    2001-01-01

    We have investigated the thermal stability of the Fusarium solani pisi cutinase as a function of pH, in the range from pH 2–12. Its highest enzymatic activity coincides with the pH-range at which it displays its highest thermal stability. The unfolding of the enzyme as a function of pH was investigated by microcalorimetry. The ratio between the calorimetric enthalpy (ΔHcal) and the van't Hoff enthalpy (ΔHv) obtained, is far from unity, indicating that cutinase does not exhibit a simple two state unfolding behaviour. The role of pH on the electrostatic contribution to the thermal stability was assessed using TITRA. We propose a molecular interpretation for the pH-variation in enzymatic activity. PMID:12488611

  14. Thermal stability of an ultrathin hafnium oxide film on plasma nitrided Si(100)

    NASA Astrophysics Data System (ADS)

    Skaja, K.; Schönbohm, F.; Weier, D.; Lühr, T.; Keutner, C.; Berges, U.; Westphal, C.

    2013-10-01

    We report on the thermal stability of an ultrathin hafnium oxide film on a plasma nitrided Si(100) surface. The ultrathin silicon nitride buffer layer was produced by an ECR-plasma ion source. Onto this buffer layer a thin hafnium oxide film was prepared by electron beam evaporation. The thermal stability of the layer stack was checked by systematic annealing steps. A detailed angle resolved X-ray photoelectron spectroscopy study of the interfaces is presented. For chemical surface studies high-resolution spectra of the Si 2p and Hf 4f signals were taken. It is demonstrated that the thermal stability of hafnium oxide thin films can be increased by a smooth and homogenous buffer layer of silicon nitride.

  15. An in situ SEM experimental study of the thermal stability of a LAST thermoelectric material

    SciTech Connect

    Ren, Fei; Howe, Jane Y; Walker, Larry R; Case, Eldon D; Lara-Curzio, Edgar

    2011-01-01

    Thermal stability is a key factor affecting the deployment of thermoelectric (TE) materials in the application of power generation. LAST (Lead-Antimony-Silver-Tellurium) is an emerging material with promising TE properties. The current study focused on the thermal stability of a LAST composition Ag0.86Pb19SbTe20 fabricated from a cast ingot. Using a customized heating stage, the morphology of LAST particles was studied via scanning electron microscopy (SEM) in situ, between room temperature and 575oC. The LAST material included in this study was stable below 550oC. The inclusion phase, which was antimony-rich, has a lower thermal stability than the PbTe-rich matrix. The SEM finding was also consistent with a thermogravimetrtic analysis.

  16. Multicore-shell nanofiber architecture of polyimide/polyvinylidene fluoride blend for thermal and long-term stability of lithium ion battery separator.

    PubMed

    Park, Sejoon; Son, Chung Woo; Lee, Sungho; Kim, Dong Young; Park, Cheolmin; Eom, Kwang Sup; Fuller, Thomas F; Joh, Han-Ik; Jo, Seong Mu

    2016-11-11

    Li-ion battery, separator, multicoreshell structure, thermal stability, long-term stability. A nanofibrous membrane with multiple cores of polyimide (PI) in the shell of polyvinylidene fluoride (PVdF) was prepared using a facile one-pot electrospinning technique with a single nozzle. Unique multicore-shell (MCS) structure of the electrospun composite fibers was obtained, which resulted from electrospinning a phase-separated polymer composite solution. Multiple PI core fibrils with high molecular orientation were well-embedded across the cross-section and contributed remarkable thermal stabilities to the MCS membrane. Thus, no outbreaks were found in its dimension and ionic resistance up to 200 and 250 °C, respectively. Moreover, the MCS membrane (at ~200 °C), as a lithium ion battery (LIB) separator, showed superior thermal and electrochemical stabilities compared with a widely used commercial separator (~120 °C). The average capacity decay rate of LIB for 500 cycles was calculated to be approximately 0.030 mAh/g/cycle. This value demonstrated exceptional long-term stability compared with commercial LIBs and with two other types (single core-shell and co-electrospun separators incorporating with functionalized TiO2) of PI/PVdF composite separators. The proper architecture and synergy effects of multiple PI nanofibrils as a thermally stable polymer in the PVdF shell as electrolyte compatible polymers are responsible for the superior thermal performance and long-term stability of the LIB.

  17. Multicore-shell nanofiber architecture of polyimide/polyvinylidene fluoride blend for thermal and long-term stability of lithium ion battery separator

    NASA Astrophysics Data System (ADS)

    Park, Sejoon; Son, Chung Woo; Lee, Sungho; Kim, Dong Young; Park, Cheolmin; Eom, Kwang Sup; Fuller, Thomas F.; Joh, Han-Ik; Jo, Seong Mu

    2016-11-01

    Li-ion battery, separator, multicoreshell structure, thermal stability, long-term stability. A nanofibrous membrane with multiple cores of polyimide (PI) in the shell of polyvinylidene fluoride (PVdF) was prepared using a facile one-pot electrospinning technique with a single nozzle. Unique multicore-shell (MCS) structure of the electrospun composite fibers was obtained, which resulted from electrospinning a phase-separated polymer composite solution. Multiple PI core fibrils with high molecular orientation were well-embedded across the cross-section and contributed remarkable thermal stabilities to the MCS membrane. Thus, no outbreaks were found in its dimension and ionic resistance up to 200 and 250 °C, respectively. Moreover, the MCS membrane (at ~200 °C), as a lithium ion battery (LIB) separator, showed superior thermal and electrochemical stabilities compared with a widely used commercial separator (~120 °C). The average capacity decay rate of LIB for 500 cycles was calculated to be approximately 0.030 mAh/g/cycle. This value demonstrated exceptional long-term stability compared with commercial LIBs and with two other types (single core-shell and co-electrospun separators incorporating with functionalized TiO2) of PI/PVdF composite separators. The proper architecture and synergy effects of multiple PI nanofibrils as a thermally stable polymer in the PVdF shell as electrolyte compatible polymers are responsible for the superior thermal performance and long-term stability of the LIB.

  18. Thermal stability of interconnected a-Si:H solar modules

    NASA Astrophysics Data System (ADS)

    Willing, F.; Bennett, M.; Newton, J.

    Interconnected solar modules with cell structures of glass/transparent-conducting-oxide (TCO)/piNa-Si/aluminum were heat-treated at a series of elevated temperatures in order to accelerate two degradation modes: interdiffusion at the aluminum/a-Si back contact, and conductivity loss at the aluminum/TCO contacts which serve as connections between individual cells in a module. Plots of device lifetime vs. 1/T extrapolated to normal operating temperatures showed that neither degradation mode would significantly effect module stability over the projected lifetime of the device.

  19. Thermal stability of dopants in laser annealed silicon

    NASA Astrophysics Data System (ADS)

    Takamura, Y.; Jain, S. H.; Griffin, P. B.; Plummer, J. D.

    2002-07-01

    As semiconductor device dimensions continue to decrease, the main challenge in the area of junction formation involves decreasing the junction depth while simultaneously decreasing the sheet resistance. Laser annealing is being investigated as an alternative to rapid thermal annealing to repair the damage from ion implantation and to activate the dopants. With this technique, uniform, box-shaped profiles are obtained, with dopant concentrations that can exceed equilibrium solubility limits at normal processing temperatures. Unfortunately, these super-saturated dopant concentrations exist in a metastable state and deactivate upon further thermal processing. In this article, we describe a comprehensive study of the deactivation kinetics of common dopants (P, B, and Sb) across a range of concentrations and annealing conditions. For comparison, As deactivation data from the literature is also presented. P and As deactivate substantially at temperatures as low as 500 degC, while Sb at moderate concentrations and B remain fully active until 700 to 800 degC. It is proposed that As and P deactivate through the formation of small dopant-defect clusters while B deactivates through precipitation. The proximity to the surface is shown to be a second-order effect.

  20. Thermal stability and optical properties of Si-Ge nanoparticles.

    PubMed

    Bonham, Brandon; Guisbiers, Grégory

    2017-06-16

    Silicon-germanium is an important alloy mainly used in thermoelectricity and electronics. However, its thermal and optical properties still need further investigation at the nanoscale. That is why in this study, the size and shape effect on the silicon-germanium phase diagram is investigated through the nano-thermodynamics methodology. As expected, the phase diagram undergoes a shift down in temperature when the size decreases. However, it is demonstrated and explained why the size effect on the solidus-liquidus curves is much stronger than the one on the miscibility gap. Moreover, the shape effect is investigated for various faceted polyhedral nanoparticles as well as for the sphere. Phase maps are then provided as a function of the number of facets, at 4 and 10 nm, in order to determine the structure of the alloy. Furthermore, the size and shape effects on the energy bandgap are also studied. The energy bandgap increases when the size is reduced. The cube and tetrahedral shapes exhibit the largest size effect on the thermal and optical properties of the silicon-germanium alloy. Finally, this paper provides a useful roadmap for experimentalists willing to tune the properties of this alloy.

  1. Thermal stability of soils and detectability of intrinsic soil features

    NASA Astrophysics Data System (ADS)

    Siewert, Christian; Kucerik, Jiri

    2014-05-01

    Soils are products of long term pedogenesis in ecosystems. They are characterized by a complex network of interactions between organic and inorganic constituents, which influence soil properties and functions. However, the interrelations cannot easily be determined. Our search for unifying principles of soil formation focuses on water binding. This approach was derived from water-dependent soil formation. It considers the importance of water binding in theories about the origin of genes, in the structural arrangement and functionality of proteins, and in the co-evolution of organism species and the biosphere during the history of earth. We used thermogravimetry as a primary experimental technique. It allows a simple determi-nation of bound water together with organic and inorganic components in whole soil samples without a special preparation. The primary goal was to search for fingerprinting patterns using dynamics of thermal mass losses (TML) caused by water vaporization from natural soils, as a reference base for soil changes under land use. 301 soil samples were collected in biosphere reserves, national parks and other areas as-sumingly untouched by human activity in Siberia, North and South America, Antarctica, and in several long term agricultural experiments. The results did not support the traditional data evaluation procedures used in classical differ-ential thermogravimetry. For example, peak positions and amplitudes did not provide useful information. In contrast, using thermal mass losses (TML) in prefixed smaller, e.g. 10 °C temperature intervals allowed the determination of the content of carbon, clay, nitrogen and carbonates with high accuracy. However, this approach was applicable for soils and neither for soil-like carbon containing mineral substrates without pedogenetic origin, nor for plant residues or soils containing ashes, cinder, or charcoal. Therefore, intrinsic soil regulation processes are discussed as a possible factor causing

  2. High thermal stability solution-processable narrow-band gap molecular semiconductors.

    PubMed

    Liu, Xiaofeng; Hsu, Ben B Y; Sun, Yanming; Mai, Cheng-Kang; Heeger, Alan J; Bazan, Guillermo C

    2014-11-19

    A series of narrow-band gap conjugated molecules with specific fluorine substitution patterns has been synthesized in order to study the effect of fluorination on bulk thermal stability. As the number of fluorine substituents on the backbone increase, one finds more thermally robust bulk structures both under inert and ambient conditions as well as an increase in phase transition temperatures in the solid state. When integrated into field-effect transistor devices, the molecule with the highest degree of fluorination shows a hole mobility of 0.15 cm(2)/V·s and a device thermal stability of >300 °C. Generally, the enhancement in thermal robustness of bulk organization and device performance correlates with the level of C-H for C-F substitution. These findings are relevant for the design of molecular semiconductors that can be introduced into optoelectronic devices to be operated under a wide range of conditions.

  3. Enhancement of thermal stability and water resistance in yttrium-doped GeO{sub 2}/Ge gate stack

    SciTech Connect

    Lu, Cimang Hyun Lee, Choong; Zhang, Wenfeng; Nishimura, Tomonori; Nagashio, Kosuke; Toriumi, Akira

    2014-03-03

    We have systematically investigated the material and electrical properties of yttrium-doped GeO{sub 2} (Y-GeO{sub 2}) on Germanium (Ge). A significant improvement of both thermal stability and water resistance were demonstrated by Y-GeO{sub 2}/Ge stack, compared to that of pure GeO{sub 2}/Ge stack. The excellent electrical properties of Y-GeO{sub 2}/Ge stacks with low D{sub it} were presented as well as enhancement of dielectric constant in Y-GeO{sub 2} layer, which is beneficial for further equivalent oxide thickness scaling of Ge gate stack. The improvement of thermal stability and water resistance are discussed both in terms of the Gibbs free energy lowering and network modification of Y-GeO{sub 2}.

  4. Evaluation of the Impact of Kerojet (trademark) Aquarius Water Scavenger Additive on the Thermal Stability of Jet A Fuels

    DTIC Science & Technology

    2014-12-01

    SUBJECT TERMS water separation, water coalescence, water contamination , thermal stability, API/EI 5th Edition 16. SECURITY CLASSIFICATION OF: 17...AFRL-RQ-WP-TR-2015-0014 EVALUATION OF THE IMPACT OF KEROJET™ AQUARIUS WATER SCAVENGER ADDITIVE ON THE THERMAL STABILITY OF JET A FUELS Robert W...IMPACT OF KEROJET™ AQUARIUS WATER SCAVENGER ADDITIVE ON THE THERMAL STABILITY OF JET A FUELS 5a. CONTRACT NUMBER CRADA 14-016-RQ-01 and In-house

  5. Thermal Stability Limits of Imidazolium Ionic Liquids Immobilized on Metal-Oxides.

    PubMed

    Babucci, Melike; Akçay, Aslı; Balci, Volkan; Uzun, Alper

    2015-08-25

    Thermal stability limits of 33 imidazolium ionic liquids (ILs) immobilized on three of the most commonly used high surface area metal-oxides, SiO2, γ-Al2O3, and MgO, were investigated. ILs were chosen from a family of 13 cations and 18 anions. Results show that the acidity of C2H of an imidazolium ring is one of the key factors controlling the thermal stability. An increase in C2H bonding strength of ILs leads to an increase in their stability limits accompanied by a decrease in interionic energy. Systematic changes in IL structure, such as changes in electronic structure and size of anion/cation, methylation on C2 site, and substitution of alkyl groups on the imidazolium ring with functional groups have significant effects on thermal stability limits. Furthermore, thermal stability limits of ILs are influenced strongly by acidic character of the metal-oxide surface. Generally, as the point of zero charge (PZC) of the metal-oxide increases from SiO2 to MgO, the interactions of IL and metal-oxide dominate over interionic interactions, and metal-oxide becomes the significant factor controlling the stability limits. However, thermal stability limits of some ILs show the opposite trend, as the chemical activities of the cation functional group or the electron donating properties of the anion alter IL/metal-oxide interactions. Results presented here can help in choosing the most suitable ILs for materials involving ILs supported on metal-oxides, such as for supported ionic liquid membranes (SILM) in separation applications or for solid catalyst with ionic liquid layer (SCILL) and supported ionic liquid phase (SILP) catalysts in catalysis.

  6. Microparticles containing lemongrass volatile oil: preparation, characterization and thermal stability.

    PubMed

    Weisheimer, V; Miron, D; Silva, C B; Guterres, S S; Schapoval, E E S

    2010-12-01

    Lemongrass volatile oil (LVO) is an important ingredient in cosmetics, presenting antimicrobial properties, in particular antifungal activity, and it is a promising raw material for the development of pharmaceutical products. However, its volatility and susceptibility to degradation are the major drawbacks for the use of Cymbopogon citratus oil in pharmaceutical compounding. Thus, the aim of this work was to develop and to characterize microparticles containing this oil viewing the stabilization of LVO. Two techniques of preparation were evaluated; spray drying and precipitation, and two encapsulation materials, beta-cyclodextrin (beta-CD) and hydroxypropyl-beta-cyclodextrin (HP-beta-CD) were tested. The microparticles were characterized in terms of content of water, yield, percentage of inclusion, infrared spectroscopy. Morphology was evaluated by scanning electronic microscopy. Studies of stability were also conducted. The content of citral (neral and geranial), major component of the oil, present in microparticles was assayed by a validated HPLC method. The percentage of inclusion of LVO into the microparticles was 56-60% and 26-29% using beta-CD and HP-beta-CD, respectively. The results showed that the use of the beta-CD as encapsulant material was more efficient. Additionally, an increased inclusion of lemongrass oil was observed with the precipitation technique.

  7. Size effect on thermal stability of nanocrystalline anatase TiO2

    NASA Astrophysics Data System (ADS)

    Wang, Junwei; Mishra, Ashish Kumar; Zhao, Qing; Huang, Liping

    2013-06-01

    Thermal stability of nanocrystalline anatase TiO2 against coarsening and anatase-rutile phase transformation was studied using both a pyroprobe heater and a conventional furnace. The pyroprobe heater, because of the programmable control and the ultra-fast heating rate (up to 20 000 °C s-1), for the first time, allows us to access the very early stage of the sintering and phase-transformation processes. Our short time (0-30 s) heat treatments reveal that rapid grain growth takes place first in anatase nanoparticles (NPs) upon the initial heating due to the lower activation energy compared with that for the anatase-rutile phase transformation. Meanwhile, rutile-like structural elements develop at the interface between anatase NPs during the fast grain growth period, which evolve into rutile nuclei with time, followed by nuclei growth, to convert nanocrystalline anatase into rutile rapidly in the temperature range where the phase transformation does not occur in coarse anatase TiO2. Overall, both grain growth and phase transformation in smaller anatase NPs happen at lower temperatures and faster than in bigger ones. The coupled sintering-phase-transformation mechanism can be exploited to design thermally stable nanocrystalline anatase TiO2 by reducing the sintering kinetics, for example, via minority additives.

  8. Pickering emulsions with α-cyclodextrin inclusions: Structure and thermal stability.

    PubMed

    Diaz-Salmeron, Raul; Chaab, Ismail; Carn, Florent; Djabourov, Madeleine; Bouchemal, Kawthar

    2016-11-15

    This paper explores structural, interfacial and thermal properties of two types of Pickering emulsions containing α-cyclodextrin inclusion complexes: on one hand, emulsions were obtained between aqueous solutions of α-cyclodextrin and different oils (fatty acids, olive oil, silicone oil) and on the other hand, emulsions were obtained between these oils, water and micro or nano-platelet suspensions with inclusion complexes of hydrophobically-modified polysaccharides. The emulsions exhibit versatile properties according to the molecular architecture of the oils. Experiments were performed by microcalorimetry, X-ray diffraction and confocal microscopy. The aptitude of oil molecules to be threaded in α-cyclodextrin cavity is a determining parameter in emulsification and thermal stability. The heat flow traces and images showed dissolution, cooperative melting and de-threading of inclusion complexes which take place progressively, ending at high temperatures, close or above 100°C. Another important feature observed in the emulsions with micro-platelets is the partial substitution of the guest molecules occurring at room temperature at the oil/water interfaces without dissolution, possibly by a diffusion mechanism of the oil. Accordingly, the dissolution and the cooperative melting temperatures of the inclusion crystals changed, showing marked differences upon the type of guest molecules. The enthalpies of dissolution of crystals were measured and compared with soluble inclusions. Copyright © 2016 Elsevier Inc. All rights reserved.

  9. Optimized interatomic potential for silicon and its application to thermal stability of silicene

    NASA Astrophysics Data System (ADS)

    Pun, G. P. Purja; Mishin, Y.

    2017-06-01

    An optimized interatomic potential has been constructed for silicon using a modified Tersoff model. The potential reproduces a wide range of properties of Si and improves over existing potentials with respect to point defect structures and energies, surface energies and reconstructions, thermal expansion, melting temperature, and other properties. The proposed potential is compared with three other potentials from the literature. The potentials demonstrate reasonable agreement with first-principles binding energies of small Si clusters as well as single-layer and bilayer silicenes. The four potentials are used to evaluate the thermal stability of free-standing silicenes in the form of nanoribbons, nanoflakes, and nanotubes. While single-layer silicene is found to be mechanically stable at zero Kelvin, it is predicted to become unstable and collapse at room temperature. By contrast, the bilayer silicene demonstrates a larger bending rigidity and remains stable at and even above room temperature. The results suggest that bilayer silicene might exist in a free-standing form at ambient conditions.

  10. Novel Ceramic-Grafted Separator with Highly Thermal Stability for Safe Lithium-Ion Batteries.

    PubMed

    Jiang, Xiaoyu; Zhu, Xiaoming; Ai, Xinping; Yang, Hanxi; Cao, Yuliang

    2017-08-09

    The separator is a critical component of lithium-ion batteries (LIBs), which not only allows ionic transport while it prevents electrical contact between electrodes but also plays a key role for thermal safety performance of LIBs. However, commercial separators for LIBs are typically microporous polyolefin membranes that pose challenges for battery safety, due to shrinking and melting at elevated temperature. Here, we demonstrate a strategy to improve the thermal stability and electrolyte affinity of polyethylene (PE) separators. By simply grafting the vinylsilane coupling reagent on the surface of the PE separator by electron beam irradiation method and subsequent hydrolysis reaction into the Al(3+) solution, an ultrathin Al2O3 layer is grafted on the surface of the porous polymer microframework without sacrificing the porous structure and increasing the thickness. The as-synthesized Al2O3 ceramic-grafted separator (Al2O3-CGS) shows almost no shrinkage at 150 °C and decreases the contact angle of the conventional electrolyte compared with the bare PE separator. Notably, the full cells with the Al2O3-CGSs exhibit better cycling performance and rate capability and also provide stable open circuit voltage even at 170 °C, indicating its promising application in LIBs with high safety and energy density.

  11. Infrared Radiative Properties of Yttria-Stabilized Zirconia Thermal Barrier Coatings

    NASA Technical Reports Server (NTRS)

    Eldridge, Jeff I.; Spuckler, Charles M.; Street, Ken W.; Markham, Jim R.; Gray, Hugh R. (Technical Monitor)

    2002-01-01

    The infrared (IR) transmittance and reflectance of translucent thermal barrier coatings (TBCs) have important implications for both the performance of these coatings as radiation barriers and emitters as well as affecting measurements of TBC thermal conductivity, especially as TBCs are being pushed to higher temperatures. In this paper, the infrared spectral directional-hemispherical transmittance and reflectance of plasma-sprayed 8wt% yttria-stabilized zirconia (8YSZ) TBCs are reported. These measurements are compared to those for single crystal YSZ specimens to show the effects of the plasma-sprayed coating microstructure. It is shown that the coatings exhibit negligible absorption at wavelengths up to about 5 micrometers, and that internal scattering rather than surface reflections dominates the hemispherical reflectance. The translucent nature of the 8YSZ TBCs results in the absorptance/emittance and reflectance of TBC-coated substrates depending on the TBC thickness, microstructure, as well as the radiative properties of the underlying substrate. The effects of these properties on TBC measurements and performance are discussed.

  12. Tuneable enhancement of the salt and thermal stability of polymeric micelles by cyclized amphiphiles

    PubMed Central

    Honda, Satoshi; Yamamoto, Takuya; Tezuka, Yasuyuki

    2013-01-01

    Cyclic molecules provide better stability for their aggregates. Typically in nature, the unique cyclic cell membrane lipids allow thermophilic archaea to inhabit extreme conditions. By mimicking the biological design, the robustness of self-assembled synthetic nanostructures is expected to be improved. Here we report topology effects by cyclized polymeric amphiphiles against their linear counterparts, demonstrating a drastic enhancement in the thermal, as well as salt stability of self-assembled micelles. Furthermore, through coassembly of the linear and cyclic amphiphiles, the stability was successfully tuned for a wide range of temperatures and salt concentrations. The enhanced thermal/salt stability was exploited in a halogen exchange reaction to stimulate the catalytic activity. The mechanism for the enhancement was also investigated. These topology effects by the cyclic amphiphiles offer unprecedented opportunities in polymer materials design unattainable by traditional means. PMID:23481382

  13. Improved thermal stability of oxide-supported naked gold nanoparticles by ligand-assisted pinning

    SciTech Connect

    Moreno, C; Divins, N. J.; Gazquez, Jaume; Varela, Maria; Angurell, I; Llorca, J

    2012-01-01

    We report a method to improve the thermal stability, up to 900 C, of bare-metal (naked) gold nanoparticles supported on top of SiO{sub 2} and SrTiO{sub 3} substrates via ligand-assisted pinning. This approach leads to monodisperse naked gold nanoparticles without significant sintering after thermal annealing in air at 900 C. The ligand-assisted pinning mechanism is described.

  14. Thermal stability of polyacetal/ethylene-octene copolymer/zinc oxide nanocomposites

    NASA Astrophysics Data System (ADS)

    Grigalovica, A.; Merijs Meri, R.; Zicans, J.; Ivanova, T.; Grabis, J.

    2013-12-01

    In this work we investigate binary blends of polyoxymethylene and ethylene octene copolymer (EOC) and their composites with nanostructured zinc oxide (ZnO). EOC content in the composites varies from 0 to 50 wt. %. The amount of ZnO filler in the composites is changed in the interval from 0 to 5 wt. %. Thermal properties of composites are investigated with thermogravimetric analysis and differential scanning calorimetry. It is observed that ZnO addition increases thermal stability of the investigated composites.

  15. Thermal Stability of Annealed Germanium-Tin Alloys Grown by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Bhargava, Nupur; Gupta, Jay Prakash; Faleev, Nikolai; Wielunski, Leszek; Kolodzey, James

    2017-01-01

    The thermal stability of undoped and boron-doped germanium tin (Ge1-x Sn x ) alloys grown by molecular beam epitaxy with varying composition and layer thickness was investigated. The alloys were annealed in forming gas at various temperatures up to 800°C for 1 min using rapid thermal processing, and were characterized using high-resolution x-ray diffraction and Rutherford backscattering spectrometry. It was found that the Ge1-x Sn x alloys were stable to well above the growth temperature, but the stability decreased with increasing thickness, Sn content, and doping. Ge1-x Sn x alloys with low Sn composition (x ˜ 0.025) were stable up to 700°C, and for a given Sn composition, the undoped alloys were more thermally stable than the doped alloys. As the thickness of the Ge0.975Sn0.025 alloys increased to about 950 nm, the temperature of thermal stability dropped to 500°C. As the Sn composition of the 90 nm-Ge1-x Sn x alloys increased up to x = 0.08, the temperature of thermal stability dropped to 300°C. At higher annealing temperatures, the Ge1-x Sn x alloy degraded with lower crystal quality, and a gradient in the Sn composition appeared, which may be due to Sn diffusion or segregation.

  16. Thermal stability increase in metallic nanoparticles-loaded cellulose nanocrystal nanocomposites.

    PubMed

    Goikuria, U; Larrañaga, A; Vilas, J L; Lizundia, E

    2017-09-01

    Due to the potential of CNC-based flexible materials for novel industrial applications, the aim of this work is to improve the thermal stability of cellulose nanocrystals (CNC) films through a straightforward and scalable method. Based of nanocomposite approach, five different metallic nanoparticles (ZnO, SiO2, TiO2, Al2O3 and Fe2O3) have been co-assembled in water with CNCs to obtain free-standing nanocomposite films. Thermogravimetric analysis (TGA) reveals an increased thermal stability upon nanoparticle. This increase in the thermal stability reaches a maximum of 75°C for the nanocomposites having 10wt% of Fe2O3 and ZnO. The activation energies of thermodegradation process (Ea) determined according to Kissinger and Ozawa-Flynn-Wall methods further confirm the delayed degradation of CNC nanocomposites upon heating. Finally, the changes induced in the crystalline structure during thermodegradation were followed by wide angle X-ray diffraction (WAXD). It is also observed that thermal degradation proceeds at higher temperatures for nanocomposites having metallic nanoparticles. Overall, experimental findings here showed make nanocomposite approach a simple low-cost environmentally-friendly strategy to overcome the relatively poor thermal stability of CNCs when extracted via sulfuric acid assisted hydrolysis of cellulose. Copyright © 2017 Elsevier Ltd. All rights reserved.

  17. Thermal Stability of Annealed Germanium-Tin Alloys Grown by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Bhargava, Nupur; Gupta, Jay Prakash; Faleev, Nikolai; Wielunski, Leszek; Kolodzey, James

    2017-03-01

    The thermal stability of undoped and boron-doped germanium tin (Ge1- x Sn x ) alloys grown by molecular beam epitaxy with varying composition and layer thickness was investigated. The alloys were annealed in forming gas at various temperatures up to 800°C for 1 min using rapid thermal processing, and were characterized using high-resolution x-ray diffraction and Rutherford backscattering spectrometry. It was found that the Ge1- x Sn x alloys were stable to well above the growth temperature, but the stability decreased with increasing thickness, Sn content, and doping. Ge1- x Sn x alloys with low Sn composition ( x ˜ 0.025) were stable up to 700°C, and for a given Sn composition, the undoped alloys were more thermally stable than the doped alloys. As the thickness of the Ge0.975Sn0.025 alloys increased to about 950 nm, the temperature of thermal stability dropped to 500°C. As the Sn composition of the 90 nm-Ge1- x Sn x alloys increased up to x = 0.08, the temperature of thermal stability dropped to 300°C. At higher annealing temperatures, the Ge1- x Sn x alloy degraded with lower crystal quality, and a gradient in the Sn composition appeared, which may be due to Sn diffusion or segregation.

  18. PMR-15/Layered Silicate Nanocomposites For Improved Thermal Stability And Mechanical Properties

    NASA Technical Reports Server (NTRS)

    Campbell, Sandi; Scheiman, Daniel; Faile, Michael; Papadopoulos, Demetrios; Gray, Hugh R. (Technical Monitor)

    2002-01-01

    Montmorillonite clay was organically modified by co-exchange of an aromatic diamine and a primary alkyl amine. The clay was dispersed into a PMR (Polymerization of Monomer Reactants)-15 matrix and the glass transition temperature and thermal oxidative stability of the resulting nanocomposites were evaluated. PMR-15/ silicate nanocomposites were also investigated as a matrix material for carbon fabric reinforced composites. Dispersion of the organically modified silicate into the PMR-15 matrix enhanced the thermal oxidative stability, the flexural strength, flexural modulus, and interlaminar shear strength of the polymer matrix composite.

  19. Effects of curvature and compressibility on the stability of thermal fronts

    SciTech Connect

    Ibanez S, Miguel H.; Bessega L, Maria C.; Shchekinov, Yuri

    2006-06-15

    The stability of subsonic thermal fronts against corrugation is analyzed and an exact dispersion relation is obtained taking into account the effects of the curvature of the distorted front as well as the compressibility of the gas. At a certain value of the Mach number ahead of the thermal front, unstable rates show a maximum; these rates drop to zero when a Chapman-Jouguet regime is established behind heat fronts. It is shown that curvature effects tend to stabilize conductive heat fronts propagating in a compressible gas.

  20. Effect of nitrogenous bases on the thermal stability of jet fuels

    NASA Technical Reports Server (NTRS)

    Englin, B. A.; Alekseyeva, M. P.; Gasanova, Z. I.; Isaev, A. V.; Skovorodin, G. B.; Borisova, S. M.

    1977-01-01

    Fuels from naphthenic petroleums were evaluated, and it was found that they had more N bases than those paraffinic ones (0.00024 and 0.000009% N, respectively). The removal of the N bases improved significantly the thermal stability and reduced the residue formation during oxidation of the fuel. The improvement depended on both content and composition of the bases. Thus, fuels with similar content of N bases (0.00058% N) and thermal stability had oxidation residues of 17.5 and 5.6 and sol. gum of 13 and 1.5 mg/100 ml, before and after removing the N bases, respectively.

  1. Surge discharge capability and thermal stability of a metal oxide surge arrester

    SciTech Connect

    Kan, M.; Kojima, S.; Nishiwaki, S.; Sato, T.; Yanabu, S.

    1983-02-01

    The surge discharge capability and the thermal stability of a metal oxide surge arrester were examined experimentally. It was found that the breakdown energy is nearly the same against the switching surge and the temporary overvoltage of various peak values and time durations. Heat dissipation capability of an 84kV porcelain-type model arrester was examined and found to be less than that of a small model unit, while this relation of the value had been considered opposite in a previously published paper. From these experimental data, the limit at high operation stress was found to be determined by the thermal stability rather than by the discharge capability

  2. Thermal stability and thermal expansion studies of cubic fluorite-type MgF{sub 2} up to 135 GPa

    SciTech Connect

    Sun, X.W.; Song, T.; Wei, X.P.; Quan, W.L.; Liu, X.B.; Su, W.F.

    2014-04-01

    Highlights: • The thermal expansion of MgF{sub 2} with a fluorite-type structure has been investigated. • The quasi-harmonic Debye model is applied to take into account the thermal effect. • Particular attention is paid to the prediction of thermal expansion for the first time. - Abstract: The thermal expansion of MgF{sub 2} with a fluorite structure has been investigated at high pressures using plane-wave pseudopotential scheme within the local density approximation correction in the frame of density functional theory based on the analysis of thermal stability using classical molecular dynamics simulations up to 6500 K. To investigate the thermodynamic properties like as the P–V–T equation of state and volumetric thermal expansion coefficient α{sub V} of cubic fluorite-type MgF{sub 2} at extended pressure and temperature ranges, we apply the quasi-harmonic Debye model in which the phononic effects are considered. The P–V relationship and α{sub V} dependence of the pressure up to 135 GPa at different temperatures, and the V–T relationship and α{sub V} dependence of the temperature up to the melting temperature 1500 K at different pressures have been obtained.

  3. Thermal and pH changes, and dimensional stability in irreversible hydrocolloid impression material during setting.

    PubMed

    Bayindir, Funda; Yanikoğlu, Nuran; Duymuş, Zeynep

    2002-06-01

    Present study the relation between pH, thermal changes and dimensional stability during setting of irreversible hydrocolloid impression materials was investigated. Ten specimens of each product were prepared for different measurements: Thermal, pH changes and dimensional stability (mass and linear). Thermal and pH readings for 20 min and dimensional measurements for a 2 hr period were taken after mixing. It was observed that pH and thermal values changed in relation to different materials, while they did not change with the time according to variance analysis results. On the other hand, dimensional stability showed significant differences with time in all tested impression materials. A continuous pH change was observed with the time of gelation in all irreversible hydrocolloid impression materials tested. Dimensional stability also showed significant differences with time in all impression material and as a result hydrocolloids with a high pH showed better dimensional stability than those with a low pH.

  4. Differential Scanning Calorimetry - A Method for Assessing the Thermal Stability and Conformation of Protein Antigen.

    PubMed

    Durowoju, Ibrahim B; Bhandal, Kamaljit S; Hu, Jian; Carpick, Bruce; Kirkitadze, Marina

    2017-03-04

    Differential scanning calorimetry (DSC) is an analytical technique that measures the molar heat capacity of samples as a function of temperature. In the case of protein samples, DSC profiles provide information about thermal stability, and to some extent serves as a structural "fingerprint" that can be used to assess structural conformation. It is performed using a differential scanning calorimeter that measures the thermal transition temperature (melting temperature; Tm) and the energy required to disrupt the interactions stabilizing the tertiary structure (enthalpy; ∆H) of proteins. Comparisons are made between formulations as well as production lots, and differences in derived values indicate differences in thermal stability and structural conformation. Data illustrating the use of DSC in an industrial setting for stability studies as well as monitoring key manufacturing steps are provided as proof of the effectiveness of this protocol. In comparison to other methods for assessing the thermal stability of protein conformations, DSC is cost-effective, requires few sample preparation steps, and also provides a complete thermodynamic profile of the protein unfolding process.

  5. Differential Scanning Calorimetry — A Method for Assessing the Thermal Stability and Conformation of Protein Antigen

    PubMed Central

    Durowoju, Ibrahim B.; Bhandal, Kamaljit S.; Hu, Jian; Carpick, Bruce; Kirkitadze, Marina

    2017-01-01

    Differential scanning calorimetry (DSC) is an analytical technique that measures the molar heat capacity of samples as a function of temperature. In the case of protein samples, DSC profiles provide information about thermal stability, and to some extent serves as a structural “fingerprint” that can be used to assess structural conformation. It is performed using a differential scanning calorimeter that measures the thermal transition temperature (melting temperature; Tm) and the energy required to disrupt the interactions stabilizing the tertiary structure (enthalpy; ∆H) of proteins. Comparisons are made between formulations as well as production lots, and differences in derived values indicate differences in thermal stability and structural conformation. Data illustrating the use of DSC in an industrial setting for stability studies as well as monitoring key manufacturing steps are provided as proof of the effectiveness of this protocol. In comparison to other methods for assessing the thermal stability of protein conformations, DSC is cost-effective, requires few sample preparation steps, and also provides a complete thermodynamic profile of the protein unfolding process. PMID:28287565

  6. Improved insights into protein thermal stability: from the molecular to the structurome scale.

    PubMed

    Pucci, Fabrizio; Rooman, Marianne

    2016-11-13

    Despite the intense efforts of the last decades to understand the thermal stability of proteins, the mechanisms responsible for its modulation still remain debated. In this investigation, we tackle this issue by showing how a multiscale perspective can yield new insights. With the help of temperature-dependent statistical potentials, we analysed some amino acid interactions at the molecular level, which are suggested to be relevant for the enhancement of thermal resistance. We then investigated the thermal stability at the protein level by quantifying its modification upon amino acid substitutions. Finally, a large scale analysis of protein stability-at the structurome level-contributed to the clarification of the relation between stability and natural evolution, thereby showing that the mutational profile of proteins differs according to their thermal properties. Some considerations on how the multiscale approach could help in unravelling the protein stability mechanisms are briefly discussed.This article is part of the themed issue 'Multiscale modelling at the physics-chemistry-biology interface'. © 2016 The Author(s).

  7. Differential Thermal Stability and Oxidative Vulnerability of the Hemoglobin Variants, HbA2 and HbE

    PubMed Central

    Chakrabarti, Abhijit; Bhattacharya, Dipankar; Deb, Sanghamitra; Chakraborty, Madhumita

    2013-01-01

    Apart from few early biophysical studies, the relative thermal instability of HbE has been only shown by clinical investigations. We have compared in vitro thermal stability of HbE with HbA2 and HbA using optical spectroscopy. From absorption measurements in the soret region, synchronous fluorescence spectroscopy and dynamic light scattering experiments, we have found thermal stability of the three hemoglobin variants following the order HbE11.0 in all the three variants. Under oxidative stress conditions in presence of hydrogen peroxide, HbE has been found to be more vulnerable to aggregation compared to HbA and HbA2. Taken together, these studies have shown thermal and oxidative instability of HbE and points towards the role of HbE in the upregulation of redox regulators and chaperone proteins in erythrocyte proteome of patients suffering from HbEbeta thalassemia. PMID:24244748

  8. Thermal stability of porcine circovirus type 2 in cell culture.

    PubMed

    O'Dea, Mark A; Hughes, Andrew P; Davies, Linda J; Muhling, Jillian; Buddle, Ross; Wilcox, G E

    2008-01-01

    International trade in pig meat has resulted in some countries placing restrictions on the importation of pig meat, with requirements for cooking of imported meat to destroy viral agents. This study investigated the in vitro resistance of an Australian strain of porcine circovirus type 2 (PCV2), the causative agent of post-weaning multisystemic wasting syndrome (PMWS), to heat treatment. The viability of the virus in cell cultures was determined by a combination of reverse transcriptase polymerase chain reaction (RT-PCR) to detect viral transcripts, and immunohistochemistry (IHC) to visualize viral capsid antigen. PCV2 retained infectivity when heated at 75 degrees C for 15 min but was inactivated by heating at 80 degrees C and above for 15 min. The results provide important information on the thermal tolerance of PCV2, which can be taken into account in risk assessments for trade in pig meat and porcine-derived biological products.

  9. Hafnia-plugged microcavities for thermal stability of selective emitters

    NASA Astrophysics Data System (ADS)

    Lee, Heon-Ju; Smyth, Katherine; Bathurst, Stephen; Chou, Jeffrey; Ghebrebrhan, Michael; Joannopoulos, John; Saka, Nannaji; Kim, Sang-Gook

    2013-06-01

    Two-dimensional arrays of micro-cavities effectively control photon motion and selectively emit radiation tailored to the preferred bandgap of photovoltaic (PV) cells, thus enhancing the efficiency of thermophotovoltaic energy conversion. At the high operating temperatures, however, the micro- and nano-patterned structures of the selective emitters quickly lose their integrity--obliterating the tight tolerances required for precise spectral control. Even if oxidation, recrystallization, and grain growth could be avoided with single-crystal tungsten (W) selective emitters with vacuum packaging, surface diffusion, evaporation, and re-condensation are not avoidable in long-term operation at high temperatures. The concept of a planar array of plugged micro-cavities to suppress the curvature-dependent thermal degradation modes is proposed and tested. Based on scale-accelerated failure tests of silicon devices, the lifetime of W selective emitters operating at 1100 K is estimated to be at least 30 yr.

  10. The analysis of thermal stability of detonation nanodiamond

    NASA Astrophysics Data System (ADS)

    Efremov, V. P.; Zakatilova, E. I.

    2016-11-01

    The detonation nanodiamond is a new perspective material. Ammunition recycling with use of high explosives and obtaining nanodiamond as the result of the detonation synthesis have given a new motivation for searching of their application areas. In this work nanodiamond powder has been investigated by the method of synchronous thermal analysis. Experiments have been carried out at atmospheric pressure in the environment of argon. Nanodiamond powder has been heated in the closed corundum crucible at the temperature range of 30-1500 °C. The heating rates were varied from 2 K/min to 20 K/min. After the heat treatment, the samples have been studied by the x-ray diffraction and the electron microscopy. As one of the results of this work, it has been found that the detonation nanodiamond has not started the transition into graphite at the temperature below 800 °C.

  11. Fiber support technology for thermal isolation and mechanical stability

    NASA Astrophysics Data System (ADS)

    Jensen, Scott M.; Batty, J. Clair; McLain, David

    1996-10-01

    Conventional methods for supporting cold components in optical systems and instruments often lead to excessive conductive heat loads. The need for better thermal isolation while maintaining structural rigidity motivated work on a tension system utilizing high performance fibers to support a focal plane assembly in an instrument to be flown in space. Utilizing Kevlar 49 fibers in an approach referred to as fiber support technology, we were able to reduce the conducted parasitic heat loads from 85 mW to less than 2 mW while increasing the 1st resonant frequency form about 50 Hz to 700 Hz. Various radiation suppression and wiring schemes were necessary to further reduce the total parasitic heat loads on this system. This paper outlines the details of this development effort making the use of a low input power miniature mechanical cooler possible. This approach seems consistent with the 'smaller', better, cheaper, faster' attitude of the nineties.

  12. Examining the stability of thermally fissile Th and U isotopes

    NASA Astrophysics Data System (ADS)

    Kumar, Bharat; Biswal, S. K.; Singh, S. K.; Patra, S. K.

    2015-11-01

    The properties of recently predicted thermally fissile Th and U isotopes are studied within the framework of the relativistic mean-field approach using the axially deformed basis. We calculate the ground, first intrinsic excited state for highly neutron-rich thorium and uranium isotopes. The possible modes of decay such as α decay and β decay are analyzed. We found that neutron-rich isotopes are stable against α decay, however, they are very unstable against β decay. The lifetime of these nuclei is predicted to be tens of seconds against β decay. If these nuclei are utilized before their decay time, a lot of energy can be produced with the help of multifragmentation fission. Also, these nuclei have great implications from the astrophysical point of view. In some cases, we found that the isomeric states with energy range from 2 to 3 MeV and three maxima in the potential energy surface of Th-230228 and U-234228 isotopes.

  13. Thermal stability and magnetic properties of MgFe2O4@ZnO nanoparticles

    NASA Astrophysics Data System (ADS)

    Mallesh, S.; Prabu, D.; Srinivas, V.

    2017-05-01

    Magnesium ferrite, MgFe2O4, (MgFO) nanoparticles (NPs) have been synthesized through sol-gel process. Subsequently, as prepared particles were coated with Zinc-oxide (ZnO) layer(s) through ultrasonication process. Thermal stability, structure and magnetic properties of as-prepared (AP) and annealed samples in the temperature range of 350 °C-1200 °C have been investigated. Structural data suggests that AP MgFO NPs and samples annealed below 500 °C in air exhibit stable ferrite phase. However, α-Fe2O3 and a small fraction of MgO secondary phases appear along with ferrite phase on annealing in the temperatures range 500 °C- 1000 °C. This results in significant changes in magnetic moment for AP NPs 0.77 μB increases to 0.92 μB for 1200 °C air annealed sample. The magnetic properties decreased at intermediate temperatures due to the presence of secondary phases. On the other hand, pure ferrite phase could be stabilized with an optimum amount of ZnO coated MgFO NPs for samples annealed in the temperature range 500 °C-1000 °C with improvement in magnetic behavior compared to that of MgFO samples.

  14. Polyacrylamide-metal nanocomposites: one-pot synthesis, antibacterial properties, and thermal stability

    NASA Astrophysics Data System (ADS)

    Li, Cuiyan; Cai, Yanling; Zhu, Yihua; Ma, Mingguo; Zheng, Wei; Zhu, Jiefang

    2013-09-01

    The incorporation of inorganic nanoparticles into polymers is a hot research spot, since it endows the nanocomposites with new or improved properties by exploiting synergistic effects. Here we report a facile one-pot synthesis of polyacrylamide (PAM)-metal (M = Au, Ag, or Pd) nanocomposites in ethylene glycol (EG). The simultaneous polymerization of the acylamide (AM) monomer and formation of metal nanoparticles lead to a homogeneous distribution of metal nanoparticles in the PAM matrix. The sizes of Au, Ag, and Pd nanoparticles are 55.50 ± 10.6, 14.15 ± 2.57, and 7.74 ± 1.82 nm, respectively. The reaction system only includes EG, AM monomer, and corresponding metal salt. EG acts as both the solvent and the reducing reagent. Also, no initiator for AM polymerization and no surfactant for stabilization of metal nanoparticles are used. Furthermore, this simple synthetic route does not rely on any special or expensive equipment, thus can be exploited to the synthesis of similar polymer-inorganic nanocomposites. Compared to PAM, the PAM-metal nanocomposites showed enhanced thermal stability and antibacterial properties.

  15. Thermal stability of hydrogen and sulfur atoms in a-SiSx:H films

    NASA Astrophysics Data System (ADS)

    Itoh, Takashi; Nitta, Shoji; Wang, S. L.; Taylor, P. C.

    1996-11-01

    The thermal stability of hydrogen and sulfur atoms in a-SiSx:H films is studied using gas effusion spectra and electron spectroscopy for chemical analysis. Two evolution peaks of hydrogen are found above 400 °C in gas effusion spectra of a-SiSx:H films. Sulfur atoms are evolved only above 550 °C. The stability of sulfur and the relationship of dangling bonds to sulfur effusion are discussed.

  16. Time and Temperature Test Results for PFP Thermal Stabilization Furnaces

    SciTech Connect

    COMPTON, J.A.

    2000-08-09

    The national standard for plutonium storage acceptability (standard DOE-STD-3013-99, generally known as ''the 3013 standard'') has been revised to clarify the requirement for processes that will produce acceptable storage materials. The 3013 standard (Reference 1) now states that ''Oxides shall be stabilized by heating the material in an oxidizing atmosphere to a Material Temperature of at least 950 C (1742 F) for not less than 2 hours.'' The process currently in use for producing stable oxides for storage at the Plutonium Finishing Plant (PFP) heats a furnace atmosphere to 1000 C and holds it there for 2 hours. The temperature of the material being stabilized is not measured directly during this process. The Plutonium Process Support Laboratories (PPSL) were requested to demonstrate that the process currently in use at PFP is an acceptable method of producing stable plutonium dioxide consistently. A spare furnace identical to the production furnaces was set up and tested under varying conditions with non-radioactive surrogate materials. Reference 2 was issued to guide the testing program. The process currently in use at the PFP for stabilizing plutonium-bearing powders was shown to heat all the material in the furnace to at least 950 C for at least 2 hours. The current process will work for (1) relatively pure plutonium dioxide, (2) dioxide powders mixed with up to 20 weight percent magnesium oxide, and (3) dioxide powders with up to 11 weight percent magnesium oxide and 20 weight percent magnesium nitrate hexahydrate. Time and temperature data were also consistent with a successful demonstration for a mixture containing 10 weight percent each of sodium and potassium chloride; however, the molten chloride salts destroyed the thermocouples in the powder and temperature data were unavailable for part of that run. These results assume that the current operating limits of no more than 2500 grams per furnace charge and a powder height of no more than 1.5 inches remain

  17. Thermal Stability of Magnesium Silicide/Nickel Contacts

    NASA Astrophysics Data System (ADS)

    de Boor, J.; Droste, D.; Schneider, C.; Janek, J.; Mueller, E.

    2016-10-01

    Magnesium silicide-based materials are a very promising class of thermoelectric materials with excellent potential for thermoelectric waste heat recovery. For the successful application of magnesium silicide-based thermoelectric generators, the development of long-term stable contacts with low contact resistance is as important as material optimization. We have therefore studied the suitability of Ni as a contact material for magnesium silicide. Co-sintering of magnesium silicide and Ni leads to the formation of a stable reaction layer with low electrical resistance. In this paper we show that the contacts retain their low electrical contact resistance after annealing at temperatures up to 823 K for up to 168 h. By employing scanning electron microscope analysis and time-of-flight (ToF)-secondary ion mass spectrometry, we can further show that elemental diffusion is occurring to a very limited extent. This indicates long-term stability under practical operation conditions for magnesium silicide/nickel contacts.

  18. Developing Multilayer Thin Film Strain Sensors With High Thermal Stability

    NASA Technical Reports Server (NTRS)

    Wrbanek, John D.; Fralick, Gustave C.; Gonzalez, Jose M., III

    2006-01-01

    A multilayer thin film strain sensor for large temperature range use is under development using a reactively-sputtered process. The sensor is capable of being fabricated in fine line widths utilizing the sacrificial-layer lift-off process that is used for micro-fabricated noble-metal sensors. Tantalum nitride films were optimized using reactive sputtering with an unbalanced magnetron source. A first approximation model of multilayer resistance and temperature coefficient of resistance was used to set the film thicknesses in the multilayer film sensor. Two multifunctional sensors were fabricated using multilayered films of tantalum nitride and palladium chromium, and tested for low temperature resistivity, TCR and strain response. The low temperature coefficient of resistance of the films will result in improved stability in thin film sensors for low to high temperature use.

  19. Effect of Selective Contacts on the Thermal Stability of Perovskite Solar Cells.

    PubMed

    Zhao, Xing; Kim, Hui-Seon; Seo, Ja-Young; Park, Nam-Gyu

    2017-03-01

    Thermal stability of CH3NH3PbI3 (MAPbI3)-based perovskite solar cells was investigated for normal structure including the mesoporous TiO2 layer and spiro-MeOTAD and the inverted structure with PCBM and NiO. MAPbI3 was found to be intrinsically stable from 85 °C to 120 °C in the absence of moisture. However, fast degradation was observed for the encapsulated device including spiro-MeOTAD upon thermal stress at 85 °C. Photoluminescence (PL) intensity and the time constant for charge separation increased with thermal exposure time, which is indicative of inhibition of charge separation from MAPbI3 into spiro-MeOTAD. A full recovery of photovoltaic performance was observed for the 85 °C-aged device after renewal with fresh spiro-MeOTAD, which clearly indicates that thermal instability of the normal structured device is mainly due to spiro-MeOTAD, and MAPbI3 is proved to be thermally stable. Spiro-MeOTAD with additives was crystallized at 85 °C due to a low glass transition temperature, and hole mobility was significantly deteriorated, which was responsible for the thermal instability. Thermal stability was significantly improved for the inverted structure with the NiO hole transporting layer, where the power conversion efficiency (PCE) was maintained at 74% of its initial PCE of 14.71% after the 80th thermal cycle (one cycle: heating at 85 °C for 2 h and cooling at 25 °C for 2 h). This work implies that the thermal stability of perovskite solar cells depends on selective contacts.

  20. Thermal instability of silicon fullerenes stabilized with hydrogen: Computer simulation

    SciTech Connect

    Galashev, A. E.

    2008-05-15

    The structure and kinetic properties of a hollow single-layer fullerene-structured Si{sub 60} cluster are treated theoretically by molecular dynamic simulation in the temperature range 10 K {<=} T {<=} 1760 K. Five series of calculations are conducted, with simulation of several media inside and outside the Si{sub 60} cluster, specifically, vacuum and interior spaces filled with 30 and 60 hydrogen atoms with and without the exterior hydrogen environment of 60 atoms. The average radius of the silicon cluster, R-bar {sub cl}increases with increasing temperature, reaching a maximal value in the absence of hydrogen near the cluster and taking smaller values if the unpaired bonds of silicon atoms are fully compensated with hydrogen atoms located inside the cluster and there is no exterior hydrogen 'coat.' An increase in temperature yields a decrease in the average number of Si-Si bonds per atom in the silicon cluster, n-bar{sub b}, and in the average length L-bar{sub b} of the Si-Si bonds. The higher stability of the quantities n-bar {sub b} and L-bar{sub b} in the entire temperature region under consideration is characteristic of the Si{sub 60} fullerene surrounded by a hydrogen 'coat' and containing 60 hydrogen atoms in the interior space. Such clusters have smaller self-diffusion coefficients at high temperatures. The fullerene stabilized with hydrogen is stable to the formation of linear atomic chains up to the temperatures 270-280 K.

  1. Enhanced thermal stability of lysosomal beta-D-galactosidase in parenchymal cells of tumour bearing mice.

    PubMed Central

    Lenti, L.; Lipari, M.; Lombardi, D.; Zicari, A.; Dotta, A.; Pontieri, G. M.

    1986-01-01

    The thermal stability of the enzyme beta-D-galactosidase varies among different organs in normal C57Bl/6 mice, and increases in the same organs in mice with Lewis Lung carcinoma. Thermal stability of this enzyme is also increased by treatment of the mice with cell-free extracts of tumour cells or with inflammatory compounds such as carrageenan or orosomucoid. After desialylation, orosomucoid more effectively increases the heat stability of the enzyme. By contrast talc, which has no galactosyl groups, is without effect on the stability of the enzyme in vivo. Macrophages of tumour bearing mice release into the culture medium a more heat resistant enzyme than macrophages from control mice. In both cases the heat resistance of the secreted enzyme is higher when fetal calf serum is present in the culture medium. Bovine serum does not modify the thermal stability of beta-D-galactosidase in this system. Incubation of lysosomal fractions of various organs with the synthetic beta-D-galactosidase substrate, p-nitrophenyl-galactopyranoside, also strongly increases the heat resistance of the enzyme. The results suggest that one factor influencing the heat resistance of this enzyme may be complex formation between the enzyme and its substrates, an example of substrate protection of the enzyme. This may not be the only factor involved in enzyme stabilization in vivo. PMID:3099822

  2. Comparison of the wild-type alpha-amylase and its variant enzymes in Bacillus amyloliquefaciens in activity and thermal stability, and insights into engineering the thermal stability of bacillus alpha-amylase.

    PubMed

    Lee, Seunjae; Mouri, Yoshiki; Minoda, Masashi; Oneda, Hiroshi; Inouye, Kuniyo

    2006-06-01

    The starch hydrolysis activity and thermal stability of Bacillus amyloliquefaciens alpha-amylase (wild-type enzyme or WT) and its variant enzymes, designated as M77, M111, and 21B, were compared. All have an optimal pH at around 6, as well as almost the same reaction rates and Km and kcat values. The optimal temperature in the absence of Ca2+ ions is 60 degrees C for WT and M77 and 40 degrees C for M111 and 21B. Those of M111 and 21B rose to 50-60 degrees C upon the addition of 5 mM CaCl2, while those of WT and M77 did not change. The dissociation constants Kd for Ca2+ to WT and M77 are much lower than those of M111 and 21B. Asp233 in WT is replaced by Asn in M111 and 21B, while it is retained in M77, suggesting that Asp233 is involved in the thermal stability of the enzyme through Ca2+ ion binding. These findings provide insight into engineering the thermal stability of B. amyloliquefaciens alpha-amylase, which would be useful for its applications in the baking industry and in glucose manufacturing.

  3. Experimental Study of Turbine Fuel Thermal Stability in an Aircraft Fuel System Simulator

    NASA Technical Reports Server (NTRS)

    Vranos, A.; Marteney, P. J.

    1980-01-01

    The thermal stability of aircraft gas turbines fuels was investigated. The objectives were: (1) to design and build an aircraft fuel system simulator; (2) to establish criteria for quantitative assessment of fuel thermal degradation; and (3) to measure the thermal degradation of Jet A and an alternative fuel. Accordingly, an aircraft fuel system simulator was built and the coking tendencies of Jet A and a model alternative fuel (No. 2 heating oil) were measured over a range of temperatures, pressures, flows, and fuel inlet conditions.

  4. Thermal stability study for candidate stainless steels of GEN IV reactors

    NASA Astrophysics Data System (ADS)

    Simeg Veternikova, J.; Degmova, J.; Pekarcikova, M.; Simko, F.; Petriska, M.; Skarba, M.; Mikula, P.; Pupala, M.

    2016-11-01

    Candidate stainless steels for GEN IV reactors were investigated in term of thermal and corrosion stability at high temperatures. New austenitic steel (NF 709), austenitic ODS steel (ODS 316) and two ferritic ODS steels (MA 956 and MA 957) were exposed to around 1000 °C in inert argon atmosphere at pressure of ∼8 MPa. The steels were further studied in a light of vacancy defects presence by positron annihilation spectroscopy and their thermal resistance was confronted to classic AISI steels. The thermal strain supported a creation of oxide layers observed by scanning electron microscopy (SEM).

  5. Diffusion and the Thermal Stability of Amorphous Copper-Zirconium

    NASA Astrophysics Data System (ADS)

    Stelter, Eric Carl

    Measurements have been made of diffusion and thermal relaxation in amorphous Cu(,50)Zr(,50). Samples were prepared by melt-spinning under vacuum. Diffusion measurements were made over the temperature range from 317 to 385 C, using Ag and Au as substitutional impurities, by means of Auger electron spectrometry (AES) and Rutherford backscattering spectrometry (RBS). Thermal measurements were made by differential scanning calorimetry (DSC) up to 550 C. The diffusion coefficients of Ag and Au in amorphous Cu(,50)Zr(,50) are found to be somewhat higher than, but very close in magnitude to the coefficient of self-diffusion in crystalline Cu at the same temperatures. The activation energies for diffusion in the amorphous alloy are 0.72 to 1.55 eV/atom, much closer to the activation energy for self-diffusion in liquid Cu, 0.42 eV/atom, than that for the crystalline solid, 2.19 eV/atom. The mechanism for diffusion in the amorphous metal is presumably quite different from the monovacancy mechanism dominant in the crystalline solid. The pre-exponential terms are found to be extremely small, on the order of 10('-10) to 10('-11) cm('2)/sec for Ag diffusion. This indicates that diffusion in amorphous Cu(,50)Zr(,50) may involve an extended defect of 10 or more atoms. Analysis of the data in terms of the free -volume model also lends strength to this conclusion and indicates that the glass is composed of liquid-like clusters of 15 to 20 atoms. The initial stage of relaxation in amorphous CuZr occurs with a spectrum of activation energies. The lowest activation energy involved, 0.78 eV/atom, is almost identical to the average activation energy of Ag diffusion in the glass, 0.77 eV/atom, indicating that relaxation occurs primarily through diffusion. The activation energy of crystallization, determined by Kissinger's method, is 3.10 eV/atom. The large difference, on the order of 2.3 eV/atom, between the activation energies of crystallization and diffusion is attributed to the energy

  6. Thermal/chemical stability of ceramic cross flow filter materials

    SciTech Connect

    Alvin, M.A.; Bahovchin, D.M.; Lippert, T.E.; Tressler, R.E.; McNerney, K.B.

    1992-01-01

    Westinghouse has undertaken a two phase program to determine possible long-term, high temperature influence that advanced coal-based power system environments may have on the stability of the ceramic cross flow filter elements. During the past year, we have principally focused our efforts on developing an understanding of the stability of the alumina/mullite filter material at high temperature (i.e., 870, 980, and 1100[degrees]C) under oxidizing conditions which contain gas phase alkali species. The alumina/mullite cross flow liter material that has consistently been used throughout the flow-through gas phase alkali testing segment of this program, consists of mullite rods or needles that are embedded within an amorphous phase which contains corundum (Al[sub 2]O[sub 3]) and anorthite (CaAl[sub 2]Si[sub 2]O[sub 8]). Due to the rapid cooling rate that was used to produce the alumina/mullite filter disc material from high fire, the matrix consists of 59.6 wt% mullite, 30.5 wt% amorphous, 5.1 wt% anorthite, and 4.8 wt% alumina. The relatively low, as-fabricated, hot strength of this material (841[plus minus]259 psi at 870[degrees]C) is a direct result of the high amorphous content which softens at temperatures of 870[degrees]C. Load versus deflection curves as a function of temperature indicate that this material is relatively brittle up to temperatures of 600[degrees]C. Both a loss of strength, as well as plastic deformation of the matrix occurs at [approximately]700[degrees]C. If cross flow filters are manufactured from an alumina/mullite matrix that contains an [approximately]30.5 wt% amorphous content, we suspect that the plastic nature of the glass phase could potentially serve as a substrate for fines collection during initial filter operation at 700[degrees]C. Similarly the plastic nature could potentially cause deformation of the liter under load.

  7. Thermal/chemical stability of ceramic cross flow filter materials

    SciTech Connect

    Alvin, M.A.; Bahovchin, D.M.; Lippert, T.E.; Tressler, R.E.; McNerney, K.B.

    1992-11-01

    Westinghouse has undertaken a two phase program to determine possible long-term, high temperature influence that advanced coal-based power system environments may have on the stability of the ceramic cross flow filter elements. During the past year, we have principally focused our efforts on developing an understanding of the stability of the alumina/mullite filter material at high temperature (i.e., 870, 980, and 1100{degrees}C) under oxidizing conditions which contain gas phase alkali species. The alumina/mullite cross flow liter material that has consistently been used throughout the flow-through gas phase alkali testing segment of this program, consists of mullite rods or needles that are embedded within an amorphous phase which contains corundum (Al{sub 2}O{sub 3}) and anorthite (CaAl{sub 2}Si{sub 2}O{sub 8}). Due to the rapid cooling rate that was used to produce the alumina/mullite filter disc material from high fire, the matrix consists of 59.6 wt% mullite, 30.5 wt% amorphous, 5.1 wt% anorthite, and 4.8 wt% alumina. The relatively low, as-fabricated, hot strength of this material (841{plus_minus}259 psi at 870{degrees}C) is a direct result of the high amorphous content which softens at temperatures of 870{degrees}C. Load versus deflection curves as a function of temperature indicate that this material is relatively brittle up to temperatures of 600{degrees}C. Both a loss of strength, as well as plastic deformation of the matrix occurs at {approximately}700{degrees}C. If cross flow filters are manufactured from an alumina/mullite matrix that contains an {approximately}30.5 wt% amorphous content, we suspect that the plastic nature of the glass phase could potentially serve as a substrate for fines collection during initial filter operation at 700{degrees}C. Similarly the plastic nature could potentially cause deformation of the liter under load.

  8. Positive/Negative Mid Uv Resists With High Thermal Stability

    NASA Astrophysics Data System (ADS)

    Ito, Hiroshi; Wilson, C. G.; Frechet, Jean M.

    1987-08-01

    New mid UV resist systems based on poly(p-vinylbenzoates) sensitized with diphenyl-4-thiophenoxyphenylsulfonium hexafluoroantimonate are described. t-Butyl, cyclohexenyl, a-methylbenzyl, and a-methylallyl esters are converted upon postbake to poly(p-vinylbenzoic acid) through thermolysis reaction catalyzed by the photochemically generated Bronsted acid, inducing a large change in the polarity of the repeating units. Thus, development in aqueous base such as MF312/water or alcohol provides a positive tone image of the mask, while the use of a nonpolar organic developer allows a negative tone imaging. Because the glass transition temperature of poly(p-vinylbenzoic acid) is ca. 250° C, the negative image is devoid of thermal flow to this temperature even without any hardening processes. Another interesting feature of the benzoate resists is their high opacity in the deep UV region. The optical density of a 1μ thick film of poly(p-vinylbenzoic acid) is 3.5 at 254 nm and the benzoate polymers are as absorbing as the acid polymer. This high deep UV absorption of the resin necessitates the imaging above 300 nm for good light penetration (or by e-beam or X-ray) and makes the use of this resist as an imaging layer in the PCM scheme very attractive. This imaging layer is especially useful when employed in conjunction with a planarizing layer absorbing above 240 nm (for example, PMGI) as addition of a dye is not required.

  9. Thermal stabilization of collagen in skin and decalcified bone

    NASA Astrophysics Data System (ADS)

    Miles, Christopher A.; Avery, Nicholas C.

    2011-04-01

    The state of collagen molecules in the fibres of tail tendon, skin and demineralized bone has been investigated in situ using differential scanning calorimetry (DSC). Hydroxyproline analysis and tissue digestion with bacterial collagenase and trypsin were used to confirm that the common cause of all the DSC endotherms was collagen denaturation. This occurred within a narrow temperature range in tendons, but over a wide temperature range in demineralized bone and old skin and demonstrated that in tendon and demineralized bone at least the same type I collagen molecule exists in different thermal states. Hypothesizing that this might be caused by different degrees of confinement within the fibre lattice, experiments were performed to measure the effect of changing the lattice dimensions by extracting the collagen into dilute solution with pepsin, swelling the lattice in acetic acid, and contracting the lattice by dehydration. A theoretical analysis was undertaken to predict the effect of dehydration. Results were consistent with the hypothesis, demonstrating that collagen molecules within the natural fibres of bone and old skin are located at different intermolecular spacings, revealing differences between molecules in the magnitude of either the attractive or repulsive forces controlling their separation. One potential cause of such variation is known differences in covalent cross-linking.

  10. Optical and Thermal Stability of Oligofluorene/Rubber Luminescent Blend.

    PubMed

    Barbosa, Camila G; Faez, Roselena; Péres, Laura O

    2016-09-01

    This paper proposes to obtain homogeneous and stable blends of oligo(9,9-dioctylfluorene)-co-phenylene (OF), a conjugated oligomer with strong tendency of formation of excimers in the solid state, and nitrile rubber (NBR). This rubber protection reduces the formation of polymer excimers in the films. The fluorene oligomer was synthesized via Suzuki reaction and incorporated in the nitrile rubber. The films were formed by spin coating and casting techniques on the proportions of 1, 5, 10, 20 and 50 % (w/w) of OF in the nitrile rubber (NBR). The structural, optical and thermal properties of the films were evaluated with infrared, UV-Vis, fluorescence and thermogravimetry, respectively. The nitrile rubber proved to be essential for the preparation of homogeneous and stable films, since it was not possible to obtain films with only fluorene using the above-mentioned techniques. Furthermore, luminescent properties of OF are unchanged and the excimers formation in the solid state decrease suggesting the efficiency of nitrile rubber as the matrix for making films.

  11. Thermal stabilization of collagen in skin and decalcified bone.

    PubMed

    Miles, Christopher A; Avery, Nicholas C

    2011-04-01

    The state of collagen molecules in the fibres of tail tendon, skin and demineralized bone has been investigated in situ using differential scanning calorimetry (DSC). Hydroxyproline analysis and tissue digestion with bacterial collagenase and trypsin were used to confirm that the common cause of all the DSC endotherms was collagen denaturation. This occurred within a narrow temperature range in tendons, but over a wide temperature range in demineralized bone and old skin and demonstrated that in tendon and demineralized bone at least the same type I collagen molecule exists in different thermal states. Hypothesizing that this might be caused by different degrees of confinement within the fibre lattice, experiments were performed to measure the effect of changing the lattice dimensions by extracting the collagen into dilute solution with pepsin, swelling the lattice in acetic acid, and contracting the lattice by dehydration. A theoretical analysis was undertaken to predict the effect of dehydration. Results were consistent with the hypothesis, demonstrating that collagen molecules within the natural fibres of bone and old skin are located at different intermolecular spacings, revealing differences between molecules in the magnitude of either the attractive or repulsive forces controlling their separation. One potential cause of such variation is known differences in covalent cross-linking.

  12. Rigidity versus flexibility: the dilemma of understanding protein thermal stability.

    PubMed

    Karshikoff, Andrey; Nilsson, Lennart; Ladenstein, Rudolf

    2015-10-01

    The role of fluctuations in protein thermostability has recently received considerable attention. In the current literature a dualistic picture can be found: thermostability seems to be associated with enhanced rigidity of the protein scaffold in parallel with the reduction of flexible parts of the structure. In contradiction to such arguments it has been shown by experimental studies and computer simulation that thermal tolerance of a protein is not necessarily correlated with the suppression of internal fluctuations and mobility. Both concepts, rigidity and flexibility, are derived from mechanical engineering and represent temporally insensitive features describing static properties, neglecting that relative motion at certain time scales is possible in structurally stable regions of a protein. This suggests that a strict separation of rigid and flexible parts of a protein molecule does not describe the reality correctly. In this work the concepts of mobility/flexibility versus rigidity will be critically reconsidered by taking into account molecular dynamics calculations of heat capacity and conformational entropy, salt bridge networks, electrostatic interactions in folded and unfolded states, and the emerging picture of protein thermostability in view of recently developed network theories. Last, but not least, the influence of high temperature on the active site and activity of enzymes will be considered. © 2015 FEBS.

  13. Air, aqueous and thermal stabilities of Ce3+ ions in cerium oxide nanoparticle layers with substrates

    NASA Astrophysics Data System (ADS)

    Naganuma, Tamaki; Traversa, Enrico

    2014-05-01

    Abundant oxygen vacancies coexisting with Ce3+ ions in fluorite cerium oxide nanoparticles (CNPs) have the potential to enhance catalytic ability, but the ratio of unstable Ce3+ ions in CNPs is typically low. Our recent work, however, demonstrated that the abundant Ce3+ ions created in cerium oxide nanoparticle layers (CNPLs) by Ar ion irradiation were stable in air at room temperature. Ce valence states in CNPs correlate with the catalytic ability that involves redox reactions between Ce3+ and Ce4+ ions in given application environments (e.g. high temperature in carbon monoxide gas conversion and immersion conditions in biomedical applications). To better understand the mechanism by which Ce3+ ions achieve stability in CNPLs, we examined (i) extra-long air-stability, (ii) thermal stability up to 500 °C, and (iii) aqueous stability of Ce3+ ions in water, buffer solution and cell culture medium. It is noteworthy that air-stability of Ce3+ ions in CNPLs persisted for more than 1 year. Thermal stability results showed that oxidation of Ce3+ to Ce4+ occurred at 350 °C in air. Highly concentrated Ce3+ ions in ultra-thin CNPLs slowly oxidized in water within 1 day, but stability was improved in the cell culture medium. Ce3+ stability of CNPLs immersed in the medium was associated with phosphorus adsorption on the Ce3+ sites. This study also illuminates the potential interaction mechanisms of stable Ce3+ ions in CNPLs. These findings could be utilized to understand catalytic mechanisms of CNPs with abundant oxygen vacancies in their application environments.Abundant oxygen vacancies coexisting with Ce3+ ions in fluorite cerium oxide nanoparticles (CNPs) have the potential to enhance catalytic ability, but the ratio of unstable Ce3+ ions in CNPs is typically low. Our recent work, however, demonstrated that the abundant Ce3+ ions created in cerium oxide nanoparticle layers (CNPLs) by Ar ion irradiation were stable in air at room temperature. Ce valence states in CNPs

  14. Thermal Noise Limit in Frequency Stabilization of Lasers with Rigid Cavities

    NASA Technical Reports Server (NTRS)

    Numata, Kenji; Kemery, Amy; Camp, Jordan

    2004-01-01

    We evaluated thermal noise (Brownian motion) in a rigid reference cavity used for frequency stabilization of lasers, based on the mechanical loss of cavity materials and the numerical analysis of the mirror-spacer mechanics with t.he direct application of the fluctuation dissipation theorem. This noise sets a fundamental limit for the frequency stability achieved with a rigid frequency- reference cavity of order 1 Hz/square root Hz(0.01 Hz/square root Hz) at 10 mHz (100 Hz) at room temperature. This level coincides with the world-highest level stabilization results.

  15. Thermal Noise Limit in Frequency Stabilization of Lasers with Rigid Cavities

    NASA Technical Reports Server (NTRS)

    Numata, Kenji; Kemery, Amy; Camp, Jordan

    2005-01-01

    We evaluated thermal noise (Brownian motion) in a rigid reference cavity Used for frequency stabilization of lasers, based on the mechanical loss of cavity materials and the numerical analysis of the mirror-spacer mechanics with the direct application of the fluctuation dissipation theorem. This noise sets a fundamental limit for the frequency stability achieved with a rigid frequency-reference cavity of order 1 Hz/rtHz at 10mHz at room temperature. This level coincides with the world-highest level stabilization results.

  16. Thermal Noise Limit in Frequency Stabilization of Lasers with Rigid Cavities

    NASA Technical Reports Server (NTRS)

    Numata, Kenji; Kemery, Amy; Camp, Jordan

    2004-01-01

    We evaluated thermal noise (Brownian motion) in a rigid reference cavity used for frequency stabilization of lasers, based on the mechanical loss of cavity materials and the numerical analysis of the mirror-spacer mechanics with t.he direct application of the fluctuation dissipation theorem. This noise sets a fundamental limit for the frequency stability achieved with a rigid frequency- reference cavity of order 1 Hz/square root Hz(0.01 Hz/square root Hz) at 10 mHz (100 Hz) at room temperature. This level coincides with the world-highest level stabilization results.

  17. Thermal Noise Limit in Frequency Stabilization of Lasers with Rigid Cavities

    NASA Technical Reports Server (NTRS)

    Numata, Kenji; Kemery, Amy; Camp, Jordan

    2005-01-01

    We evaluated thermal noise (Brownian motion) in a rigid reference cavity Used for frequency stabilization of lasers, based on the mechanical loss of cavity materials and the numerical analysis of the mirror-spacer mechanics with the direct application of the fluctuation dissipation theorem. This noise sets a fundamental limit for the frequency stability achieved with a rigid frequency-reference cavity of order 1 Hz/rtHz at 10mHz at room temperature. This level coincides with the world-highest level stabilization results.

  18. Thermal Reaction of Cinnamate Oligomers and Their Effect on the Orientational Stability of Liquid Crystals

    NASA Astrophysics Data System (ADS)

    Hah, Hyundae; Sung, Shi‑Joon; Park, Jung‑Ki

    2006-08-01

    Cinnamate groups are well-known for a dimerization reaction upon exposure to ultraviolet irradiation and a thermal reaction after being heated. In this study, to verify the thermal reaction of the cinnamate group in detail, we investigated the thermal crosslinking of cinnamate oligomers. The thermal reaction of cinnamate oligomers of low molecular weight is induced more readily by thermal energy compared with that of cinnamate polymers. This reaction is attributed to a radical reaction involving the carbon-carbon double bond in the cinnamate group. The orientation of the liquid crystal depended on the length of the spacers in the cinnamate oligomers.

  19. Thermal Stability: The Next Frontier for Nanocrystalline Materials

    SciTech Connect

    Mathaudhu, Suveen; Boyce, Brad L.

    2015-11-06

    For the past quarter decade, the science and technology of nanocrystalline materials (materials with grain sizes less than 100 nm) has been an extremely rich and diverse field of study.1,2 Generally, it has been observed that tremendous improvements in physical and mechanical properties, including order-of-magnitude increases in yield strength, are possible.2 As predicted by the Hall– Petch equation,3,4 a reduction in grain size should be accompanied by an increase in strength. But, despite the promise of nanocrystalline materials for a host of structural and functional applications, their use has been severely limited by their lack of microstructural stability at elevated temperatures5 or under mechanical loads.6,7 In the case of pure metals, this coarsening often occurs even at ambient temperatures.5 Ironically, the same features that often result in the enhancement of properties in nanocrystalline materials, namely the high volume fraction of high-energy grain boundaries, are responsible for the observed grain growth or phase transformation.8

  20. Stability of thermal convection in a rotating cylindrical container

    NASA Astrophysics Data System (ADS)

    Herrada, Miguel; Shtern, Vladimir

    2016-08-01

    The rotation and an axial gradient of temperature drive the meridional circulation of a fluid filling a sealed cylindrical container. This numerical study explains why the flow remains stable up to the Grashof number Gr around 1011; Gr characterizes the circulation strength. The shear-layer instability, occurring in a rotating pipe for small values of the Prandtl number Pr [M. A. Herrada and V. N. Shtern, "Stability of centrifugal convection in a rotating pipe," Phys. Fluids 27, 064106 (2015)], is suppressed here even for the cylinder length-to-radius ratio being ten. The cold end disk enhances the fluid circulation near the sidewall and diminishes it near the axis. The inflection point in the radial profile of axial velocity shifts to the sidewall vicinity where the stable centrifugal stratification and the no-slip condition prevent the disturbance growth. The cases Pr = 0, 0.015 (mercury), 0.7 (air), and 5.8 (water) are particularly analyzed. At Pr > 0, the stable density stratification develops and helps to suppress the disturbances. The obtained results are of fundamental interest and might be important for the development of efficient heat exchangers.

  1. Research on the stability of heavy metals (Cu, Zn) in excess sludge with the pretreatment of thermal hydrolysis.

    PubMed

    Wu, Huimin; Li, Meng; Zhang, Lei; Sheng, Chao

    2016-01-01

    Thermal hydrolysis (TH) has been used to improve anaerobic digestion performance as well as the stability of heavy metals in sludge. Because the toxicity of heavy metals is closely related to both the concentration and the chemical speciation, more exhaustive studies on speciation distribution are urgently needed. This research aimed to investigate the effects of TH treatment (especially the time and temperature) on the concentration and stability of heavy metals in sludge, and to define the optimal TH conditions. The TH experiment indicated that the content of the stable form of Cu and Zn reached 83% and 47.4%, respectively, with TH at 210°C and 30 min. Compared with the raw sludge, the proportion of Cu and Zn increased by 11.88% and 7.3%, respectively. Results indicated that the heavy metals were combined with sludge in a more stable form with the pretreatment of TH, which improved the stability of heavy metals.

  2. The Effect of Homogenization Heat Treatment on Thermal Expansion Coefficient and Dimensional Stability of Low Thermal Expansion Cast Irons

    NASA Astrophysics Data System (ADS)

    Chen, Li-Hao; Liu, Zong-Pei; Pan, Yung-Ning

    2016-08-01

    In this paper, the effect of homogenization heat treatment on α value [coefficient of thermal expansion (10-6 K-1)] of low thermal expansion cast irons was studied. In addition, constrained thermal cyclic tests were conducted to evaluate the dimensional stability of the low thermal expansion cast irons with various heat treatment conditions. The results indicate that when the alloys were homogenized at a relatively low temperature, e.g., 1023 K (750 °C), the elimination of Ni segregation was not very effective, but the C concentration in the matrix was moderately reduced. On the other hand, if the alloys were homogenized at a relatively high temperature, e.g., 1473 K (1200 °C), opposite results were obtained. Consequently, not much improvement (reduction) in α value was achieved in both cases. Therefore, a compound homogenization heat treatment procedure was designed, namely 1473 K (1200 °C)/4 hours/FC/1023 K (750 °C)/2 hours/WQ, in which a relatively high homogenization temperature of 1473 K (1200 °C) can effectively eliminate the Ni segregation, and a subsequent holding stage at 1023.15 K (750 °C) can reduce the C content in the matrix. As a result, very low α values of around (1 to 2) × 10-6 K-1 were obtained. Regarding the constrained thermal cyclic testing in 303 K to 473 K (30 °C to 200 °C), the results indicate that regardless of heat treatment condition, low thermal expansion cast irons exhibit exceedingly higher dimensional stability than either the regular ductile cast iron or the 304 stainless steel. Furthermore, positive correlation exists between the α 303.15 K to 473.15 K value and the amount of shape change after the thermal cyclic testing. Among the alloys investigated, Heat I-T3B (1473 K (1200 °C)/4 hours/FC/1023 K (750 °C)/2 hours/WQ) exhibits the lowest α 303 K to 473 K value (1.72 × 10-6 K-1), and hence has the least shape change (7.41 μm) or the best dimensional stability.

  3. Solute-Derived Thermal Stabilization of Nano-sized Grains in Melt-Spun Aluminum

    NASA Astrophysics Data System (ADS)

    Baker, A. H.; Sanders, P. G.; Lass, E. A.; Kapoor, Deepak; Kampe, S. L.

    2016-08-01

    Thermal stabilization of nanograined metallic microstructures (or nanostructures) can be difficult due to the large driving force for growth that arises from the inherently significant boundary area. Kinetic approaches for stabilization of the nanostructure effective at low homologous temperatures often fail at higher homologous temperatures. Alternatively, thermodynamic approaches for thermal stabilization may offer higher temperature stability. In this research, modest alloying of aluminum with solute (1 pct by mole Sc, Yb, or Sr) was examined as a means to thermodynamically stabilize a bulk nanostructure at elevated temperatures. Following 1-hour annealing treatments at 673 K (400 °C) (0.72 Tm), 773 K (500 °C) (0.83 Tm), and 873 K (600 °C) (0.94 Tm), the alloys remain nanocrystalline (<100 nm) as measured by Warren-Averbach Fourier analysis of X-ray diffraction peaks and direct observation of TEM dark-field micrographs, with the efficacy of stabilization: Sr ≈ Yb > Sc. The disappearance of intermetallic phases in the Sr- and Yb-containing alloys in the X-ray diffraction spectra is observed to occur coincident with the stabilization after annealing, suggesting that precipitates dissolve and the boundaries are enriched with solute.

  4. Solution-processed silver nanowire/indium-tin-oxide nanoparticle hybrid transparent conductors with high thermal stability.

    PubMed

    Hong, Sung-Jei; Kim, Jong-Woong; Kim, Yong-Hoon

    2014-12-01

    In this study, solution-processed hybrid structure transparent conductors consisting of silver nanowires (AgNWs) and indium-tin-oxide nanoparticle (ITO-NP) layers are investigated. Fabricated transparent conductors had stacked structures of ITO-NP/AgNW and ITO-NP/AgNW/ITO-NP, and a successful integration was possible on glass substrates. Compared to a single-layered ITO-NP film which has a sheet resistance value of 1.31 k Ω/⟂, a remarkable enhancement in sheet resistance was achieved from the hybrid structures, showing sheet resistance values of 44.74 Ω/⟂ and 28.07 Ω/⟂ for ITO-NP/AgNW and ITO-NP/AgNW/ITO-NP structures, respectively. In addition, the ITO-NP/AgNW/ITO-NP triple-layered transparent conductor showed greatly enhanced thermal stability in terms of sheet resistance and transmittance against a high-temperature environment up to 300 degrees C. Based on these results, it can be suggested that the hybrid structure has advantages of enhancing both electrical properties of ITO-NP layer and thermal stability of AgNW layer, and we believe the hybrid structure transparent conductors can be a suitable option for applications which require high electrical conductivity, transmittance, and thermal stability.

  5. Core-shell structured titanium-nitrogen alloys with high strength, high thermal stability and good plasticity.

    PubMed

    Zhang, Y S; Zhao, Y H; Zhang, W; Lu, J W; Hu, J J; Huo, W T; Zhang, P X

    2017-01-06

    Multifunctional materials with more than two good properties are widely required in modern industries. However, some properties are often trade-off with each other by single microstructural designation. For example, nanostructured materials have high strength, but low ductility and thermal stability. Here by means of spark plasma sintering (SPS) of nitrided Ti particles, we synthesized bulk core-shell structured Ti alloys with isolated soft coarse-grained Ti cores and hard Ti-N solid solution shells. The core-shell Ti alloys exhibit a high yield strength (~1.4 GPa) comparable to that of nanostructured states and high thermal stability (over 1100 °C, 0.71 of melting temperature), contributed by the hard Ti-N shells, as well as a good plasticity (fracture plasticity of 12%) due to the soft Ti cores. Our results demonstrate that this core-shell structure offers a design pathway towards an advanced material with enhancing strength-plasticity-thermal stability synergy.

  6. Encapsulation of β-carotene within ferritin nanocages greatly increases its water-solubility and thermal stability.

    PubMed

    Chen, Lingli; Bai, Guangling; Yang, Rui; Zang, Jiachen; Zhou, Ting; Zhao, Guanghua

    2014-04-15

    Carotenoids may play a number of potential health benefits for human. However, their use in food industry is limited mostly because of their poor water-solubility and low thermal stability. Ferritins are widely distributed in nature with a shell-like structure which offers a great opportunity to improve the water-solubility and thermal stability of the carotenoids by encapsulation. In this work, recombinant human H-chain ferritin (rHuHF) was prepared and used to encapsulate β-carotene, a typical compound among carotenoids, by taking advantage of the reversible dissociation and reassembly characteristic of apoferritin in different pH environments. Results from high-performance liquid chromatography (HPLC), UV/Vis spectroscopy and transmission electron microscope (TEM) indicated that β-carotene molecules were successfully encapsulated within protein cages with a β-carotene/protein molar ratio of 12.4-1. Upon such encapsulation, these β-carotene-containing apoferritin nanocomposites were water-soluble. Interestingly, the thermal stability of the β-carotene encapsulated within apoferritin nanocages was markedly improved as compared to free β-carotene. These new properties might be favourable to the utilisation of β-carotene in food industry.

  7. Effects of terbium sulfide addition on magnetic properties, microstructure and thermal stability of sintered Nd-Fe-B magnets

    NASA Astrophysics Data System (ADS)

    Xiang-Bin, Li; Shuo, Liu; Xue-Jing, Cao; Bei-Bei, Zhou; Ling, Chen; A-Ru, Yan; Gao-Lin, Yan

    2016-07-01

    To increase coercivity and thermal stability of sintered Nd-Fe-B magnets for high-temperature applications, a novel terbium sulfide powder is added into (Pr0.25Nd0.75)30.6Cu0.15FebalB1 (wt.%) basic magnets. The effects of the addition of terbium sulfide on magnetic properties, microstructure, and thermal stability of sintered Nd-Fe-B magnets are investigated. The experimental results show that by adding 3 wt.% Tb2S3, the coercivity of the magnet is remarkably increased by about 54% without a considerable reduction in remanence and maximum energy product. By means of the electron probe microanalyzer (EPMA) technology, it is observed that Tb is mainly present in the outer region of 2:14:1 matrix grains and forms a well-developed Tb-shell phase, resulting in enhancement of H A, which accounts for the coercivity enhancement. Moreover, compared with Tb2S3-free magnets, the reversible temperature coefficients of remanence (α) and coercivity (β) and the irreversible flux loss of magnetic flow (h irr) values of Tb2S3-added magnets are improved, indicating that the thermal stability of the magnets is also effectively improved. Project supported by the Science Funds from the Ministry of Science and Technology, China (Grant Nos. 2014DFB50130 and 2011CB612304) and the National Natural Science Foundation of China (Grant Nos. 51172168 and 51072139).

  8. Core-shell structured titanium-nitrogen alloys with high strength, high thermal stability and good plasticity

    PubMed Central

    Zhang, Y. S.; Zhao, Y. H.; Zhang, W.; Lu, J. W.; Hu, J. J.; Huo, W. T.; Zhang, P. X.

    2017-01-01

    Multifunctional materials with more than two good properties are widely required in modern industries. However, some properties are often trade-off with each other by single microstructural designation. For example, nanostructured materials have high strength, but low ductility and thermal stability. Here by means of spark plasma sintering (SPS) of nitrided Ti particles, we synthesized bulk core-shell structured Ti alloys with isolated soft coarse-grained Ti cores and hard Ti-N solid solution shells. The core-shell Ti alloys exhibit a high yield strength (~1.4 GPa) comparable to that of nanostructured states and high thermal stability (over 1100 °C, 0.71 of melting temperature), contributed by the hard Ti-N shells, as well as a good plasticity (fracture plasticity of 12%) due to the soft Ti cores. Our results demonstrate that this core-shell structure offers a design pathway towards an advanced material with enhancing strength-plasticity-thermal stability synergy. PMID:28059150

  9. Core-shell structured titanium-nitrogen alloys with high strength, high thermal stability and good plasticity

    NASA Astrophysics Data System (ADS)

    Zhang, Y. S.; Zhao, Y. H.; Zhang, W.; Lu, J. W.; Hu, J. J.; Huo, W. T.; Zhang, P. X.

    2017-01-01

    Multifunctional materials with more than two good properties are widely required in modern industries. However, some properties are often trade-off with each other by single microstructural designation. For example, nanostructured materials have high strength, but low ductility and thermal stability. Here by means of spark plasma sintering (SPS) of nitrided Ti particles, we synthesized bulk core-shell structured Ti alloys with isolated soft coarse-grained Ti cores and hard Ti-N solid solution shells. The core-shell Ti alloys exhibit a high yield strength (~1.4 GPa) comparable to that of nanostructured states and high thermal stability (over 1100 °C, 0.71 of melting temperature), contributed by the hard Ti-N shells, as well as a good plasticity (fracture plasticity of 12%) due to the soft Ti cores. Our results demonstrate that this core-shell structure offers a design pathway towards an advanced material with enhancing strength-plasticity-thermal stability synergy.

  10. Thermal stability and spontaneous breakdown of free-standing metal nanowires

    NASA Astrophysics Data System (ADS)

    Michailov, Michail; Ranguelov, Bogdan; Giazitzidis, Paraskevas; Argyrakis, Panos

    2017-01-01

    We present a model for vacancy-mediated spontaneous breakdown of free-standing monatomic nanowire based on exclusively random, thermally activated motion of atoms. The model suggests a new two-step vacancy-mediated mechanism for nanowire rupture compared to the more complex three-step hole-mediated mechanism driving the disintegration of nanowire on crystalline surface. It also demonstrates that a free-standing nanowire breaks down much more rapidly than a nanowire on a substrate, because it cannot experience the stabilizing effect of the nanowire/substrate interactions. The rupture mechanism includes single atomic vacancy generation, preceded by appearance of weakly bonded active atoms. The analysis of the simulation data indicates that the active atoms act as a precursor of vacancy formation. These two successive events in the temporal evolution of the nanowire morphology bring the free-standing nanowire into irreversible unstable state, leading to its total disintegration. The present study also manifests an unexpected substantial increase of the nanowire lifetime with diminishing the strength of the atomic interactions between the nanowire atoms. The simulation data reveal three energy regions where a large oscillatory variation of nanowire lifetime is realized. The first region of strong atomic interactions is characterized by tight nanowire rigidity and short lifetime. The next, second region in the consecutive step-down of the attractive interatomic force is characterized by generation of wave-shaped morphology of the atomic chain, enhanced flexibility and dramatic increase of nanowire lifetime. In the last, third region, further weakening of the interactions returns the nanowire again to unstable, short-lifetime state. The observed phenomenon is considered as a "stick-like" to "polymer-like" transition in the nanowire atomic structure as a result of interaction energy variation. The enhanced flexibility reduces the nanowire free energy since it favors and

  11. New class of thermosetting plastics has improved strength, thermal and chemical stability

    NASA Technical Reports Server (NTRS)

    Burns, E. A.; Dubrow, B.; Lubowitz, H. R.

    1967-01-01

    New class of thermosetting plastics has high hydrocarbon content, high stiffness, thermal stability, humidity resistance, and workability in the precured state. It is designated cyclized polydiene urethane, and is applicable as matrices to prepare chemically stable ablative materials for rocket nose cones of nozzles.

  12. Photochemical and thermal stability of green and blue proteorhodopsins: implications for protein-based bioelectronic devices.

    PubMed

    Ranaghan, Matthew J; Shima, Sumie; Ramos, Lavosier; Poulin, Daniel S; Whited, Gregg; Rajasekaran, Sanguthevar; Stuart, Jeffery A; Albert, Arlene D; Birge, Robert R

    2010-11-11

    The photochemical and thermal stability of the detergent-solubilized blue- and green-absorbing proteorhodpsins, BPR and GPR, respectively, are investigated to determine the viability of these proteins for photonic device applications. Photochemical stability is studied by using pulsed laser excitation and differential UV-vis spectroscopy to assign the photocyclicity. GPR, with a cyclicity of 7 × 10(4) photocycles protein(-1), is 4-5 times more stable than BPR (9 × 10(3) photocycles protein(-1)), but is less stable than native bacteriorhodopsin (9 × 10(5) photocycles protein(-1)) or the 4-keto-bacteriorhodopsin analogue (1 × 10(5) photocycles protein(-1)). The thermal stabilities are assigned by using differential scanning calorimetry and thermal bleaching experiments. Both proteorhodopsins display excellent thermal stability, with melting temperatures above 85 °C, and remain photochemically stable up to 75 °C. The biological relevance of our results is also discussed. The lower cyclicity of BPR is found to be adequate for the long-term biological function of the host organism at ocean depths of 50 m or more.

  13. The effect of phytosterol concentration on oxidative stability and thermal polymerization of heated oils

    USDA-ARS?s Scientific Manuscript database

    This study determined the effect of adding mixed phytosterols, at various concentrations, on the thermal polymerization and oxidative stability index (OSI) of soybean and high-oleic sunflower oils. The indigenous tocopherols and phytosterols were removed from the oils by molecular distillation. Pu...

  14. Thermal and Chemical Stability of Crystalline Silicotitanate Sorbent

    SciTech Connect

    Taylor, P.A.

    2000-10-04

    The Savannah River Site (SRS) is evaluating technologies for removing radioactive cesium ({sup 137}Cs) from the supernate solutions stored in the high-level waste tanks at the site. Crystalline silicotitanate sorbent (IONSIV IE-911,{reg_sign} UOP LLC, Des Plaines, IL), which is very effective at removing cesium from high-salt solution, is one of three technologies currently being tested. Because of the extremely high inventory of {sup 137}Cs expected for the large columns of crystalline silicotitanate (CST) that would be used for treating the SRS supernate, any loss of flow or cooling to the columns could result in high temperatures from radiolytic heating. Also, even for normal operation, the CST would be exposed to the supernates for up to a year before being removed. Small-scale tests using simulant solutions were used to determine the long-term stability of the CST to the solutions at various temperatures. In the tests performed in this study, the cesium capacity of the CST decreased significantly (76%) as the temperature of the simulant and CST during loading was increased from 23 to 80 C. CST exposed to recirculating SRS average simulant solution at room temperature in a column test showed a slow decrease in cesium loading capacity (measured at 23 C), with a drop of 30% for CST from the top of the bed and 13% for CST from the bottom of the bed after a 12-month period of exposure. A similar column test using a high-pH salt solution did not show any change in the cesium capacity of the CST. An increase was noted in pressure drop through the column using average simulant, but no change was observed for the column using high-pH salt solution.

  15. Improved Glass Transition Temperature towards Thermal Stability via Thiols Solvent Additive versus DIO in Polymer Solar Cells.

    PubMed

    Yin, Jingping; Zhou, Weihua; Zhang, Lin; Xie, Yuanpeng; Yu, Zoukangning; Shao, Jun; Ma, Wei; Zeng, Jianrong; Chen, Yiwang

    2017-08-25

    The halogen-free solvent additive, 1,4-butanedithiol (BT) has been incorporated into PTB7-Th:PC71 BM, leading to higher power conversion efficiency (PCE) value as well as substantially enhanced thermal stability, as compared with the traditional 1,8-diiodooctane (DIO) additive. More importantly, the improved thermal stability after processing with BT contributes to a higher glass transition temperature (Tg ) of PTB7-Th, as determined by dynamic mechanical analysis. After thermal annealing at 130 °C in nitrogen atmosphere for 30 min, the PCE of the specimen processed with BT reduces from 9.3% to 7.1%, approaching to 80% of its original value. In contrast, the PCE of specimens processed with DIO seriously depresses from 8.3% to 3.8%. These findings demonstrate that smart utilization of low-boiling-point solvent additive is an effective and practical strategy to overcome thermal instability of organic solar cells via enhancing the Tg of donor polymer. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Subhertz linewidth diode lasers by stabilization to vibrationally and thermally compensated ultralow-expansion glass Fabry-Pérot cavities

    NASA Astrophysics Data System (ADS)

    Alnis, J.; Matveev, A.; Kolachevsky, N.; Udem, Th.; Hänsch, T. W.

    2008-05-01

    We achieved a 0.5 Hz optical beat note linewidth with ˜0.1Hz/s frequency drift at 972 nm between two external cavity diode lasers independently stabilized to two vertically mounted Fabry-Pérot (FP) reference cavities with a finesse of 400 000. Vertical FP reference cavities are suspended in midplane such that the influence of vertical vibrations to the mirror separation is significantly suppressed. This makes the setup virtually immune for vertical vibrations that are more difficult to isolate than horizontal vibrations. To compensate for thermal drifts the FP spacers are made from ultralow-expansion (ULE) glass which possesses a zero linear expansion coefficient. A design using Peltier elements in vacuum allows operation at an optimal temperature where the quadratic temperature expansion of ULE could be eliminated as well. The measured linear drift of such ULE FP cavity of 63 mHz/s was due to material aging and the residual frequency fluctuations were less than ±20Hz during 16 h of measurement. Some part of the temperature-caused drift is attributed to the thermal expansion of the mirror coatings. Thermally induced fluctuations that cause vibrations of the mirror surfaces limit the stability of our cavity. By comparing two similar laser systems we obtain an Allan instability of 2×10-15 between 0.1 and 10 s averaging time, which is close to the theoretical thermal noise limit.

  17. The Universal Thermal Climate Index UTCI compared to ergonomics standards for assessing the thermal environment.

    PubMed

    Bröde, Peter; Błazejczyk, Krzysztof; Fiala, Dusan; Havenith, George; Holmér, Ingvar; Jendritzky, Gerd; Kuklane, Kalev; Kampmann, Bernhard

    2013-01-01

    The growing need for valid assessment procedures of the outdoor thermal environment in the fields of public weather services, public health systems, urban planning, tourism & recreation and climate impact research raised the idea to develop the Universal Thermal Climate Index UTCI based on the most recent scientific progress both in thermo-physiology and in heat exchange theory. Following extensive validation of accessible models of human thermoregulation, the advanced multi-node 'Fiala' model was selected to form the basis of UTCI. This model was coupled with an adaptive clothing model which considers clothing habits by the general urban population and behavioral changes in clothing insulation related to actual environmental temperature. UTCI was developed conceptually as an equivalent temperature. Thus, for any combination of air temperature, wind, radiation, and humidity, UTCI is defined as the air temperature in the reference condition which would elicit the same dynamic response of the physiological model. This review analyses the sensitivity of UTCI to humidity and radiation in the heat and to wind in the cold and compares the results with observational studies and internationally standardized assessment procedures. The capabilities, restrictions and potential future extensions of UTCI are discussed.

  18. Age and thermal stability of particulate organic matter fractions indicate the presence of black carbon in soil

    NASA Astrophysics Data System (ADS)

    Leifeld, Jens; Heiling, Maria; Hajdas, Irka

    2014-05-01

    Black carbon (BC) from incomplete combustion is abundant in many soils. The age of black carbon is often higher than that of typical soil organic carbon (SOC) owing to its higher recalcitrance against microbial decomposition compared to plant residues. Also fossil BC may contribute to the high age of SOC. At the same time, the oxidative thermal stability of BC is known to be higher than that of SOC due to its chemical and physical structure. For a meaningful application of radiocarbon as an indicator for soil carbon age and turnover, the relative contribution of BC needs to be known but BC is difficult to separate physically from soil. Here we analyze particulate organic carbon (POC) fractions from four different field sites in Europe for their thermal stability using oxidative differential scanning calorimetry (DSC) and for their radiocarbon signature. POC may be particularly sensitive to BC 'contamination' because it was gained using a combination of size and density separation. One of these sites is essentially free of measurable amounts of BC. Each of the four sites comprised between five and eight individual POC samples taken from different spots. The radiocarbon signature and the calculated POC mean residence time of samples from three out of four sites indicated the presence of very old carbon, resulting in mean residence times (MRT) of several hundreds and up to 3700 years. In contrast, MRT's of POC from the virtually BC-free site were between 50 and 100 years. Two indicators for thermal stability of the POC fractions, i) the amount of heat released at temperatures > 450 °C and ii) the amount of heat released at 500 °C (where the latter represents the peak temperature of charcoal isolated from one of the samples) correlated both significantly and non-linearly with the samples MRT, indicating that samples with high BC content are older. Hence we can conclude that for an individual site with increasing abundance of BC both the age and the thermal stability

  19. The influence of alkaline treatment on thermal stability of flax fibres

    NASA Astrophysics Data System (ADS)

    Chaishome, J.; Rattanapaskorn, S.

    2017-04-01

    The paper pursued the hypothesis that alkaline treatment removed hemicellulose and pectin from the flax fibres, the fibre thermal stability will be improved. The use of plant fibres as reinforcement in thermoplastic composites comes with the detrimental effect of thermal degradation on the tensile performance of fibres and composites, particularly during long consolidation times at high temperature. SEM was used to observe the treated fibre surface. The micrographs show that the treatment with a higher concentration of NaOH solution results in a more obviously rough fibre surface. Moreover, FTIR and TGA were used to examine the chemical decomposition and thermal stability, respectively. The spectra of treated materials indicate that both hemicellulose and pectin were dissolved from the fibre surface following treatment. Finally, TGA results revealed that the loss of mass belonging to hemicellulose and pectin in treated fibres results in a shift of the main degradation temperature to higher temperature.

  20. Co-solvent mediated thermal stabilization of chondroitinase ABC I form Proteus vulgaris.

    PubMed

    Nazari-Robati, Mahdieh; Khajeh, Khosro; Aminian, Mahdi; Fathi-Roudsari, Mehrnoosh; Golestani, Abolfazl

    2012-04-01

    Chondroitinase ABC I (cABC I) from Proteus vulgaris cleaves glycosaminoglycan chains which are responsible for most of the inhibition of axon regrowth in spinal cord injury. The clinical utilization of this enzyme is mainly limited by its thermal instability. This study has been undertaken to determine the effects of glycerol, sorbitol and trehalose on cABC I activity and thermal stability. The results indicated that the enzyme catalytic activity and intrinsic fluorescence intensity increased in the presence of these cosolvents whereas no considerable conformational changes observed in far-UV CD spectra. Thermal CD experiment revealed an increase in T(m) of cABC I in the presence of cosolvents which was significant for trehalose. Our results support the idea that cABC I has stabilized in the presence of glycerol, sorbitol and trehalose. Therefore, the use of these cosolvents seems to be promising for improvement in shelf-life and clinical applications of this drug enzyme.

  1. Effect of supramolecular organization of a cartilaginous tissue on thermal stability of collagen II

    NASA Astrophysics Data System (ADS)

    Ignat'eva, N. Yu.; Averkiev, S. V.; Lunin, V. V.; Grokhovskaya, T. E.; Obrezkova, M. V.

    2006-08-01

    The thermal stability of collagen II in various cartilaginous tissues was studied. It was found that heating a tissue of nucleus pulposus results in collagen II melting within a temperature range of 60-70°C; an intact tissue of hyaline cartilage (of nasal septum and cartilage endplates) is a thermally stable system, where collagen II is not denatured completely up to 100°C. It was found that partial destruction of glycosaminoglycans in hyaline cartilage leads to an increase in the degree of denaturation of collagen II upon heating, although a significant fraction remains unchanged. It was shown that electrostatic interactions of proteoglycans and collagen only slightly affect the thermal stability of collagen II in the tissues. Evidently, proteoglycan aggregates play a key role: they create topological hindrances for moving polypeptide chains, thereby reducing the configurational entropy of collagen macromolecules in the state of a random coil.

  2. Influence of the neutralization step on the oxidative and thermal stability of acid olive oil.

    PubMed

    Essid, Kamel; Chtourou, Manef; Trabelsi, Mahmoud; Frikha, Mohamed Hédi

    2009-01-01

    This study elucidate the modification on oxidative and thermal stability of acid olive oils during the neutralization step. The neutralization of an acidified olive oil, chosen as model, was carried out by substituting lime (calcium hydroxide) for soda (sodium hydroxide) as the neutralizing agent. Resulting olive oil preserved almost 95% of their alpha-tocopherol content and had higher temperatures of thermal decomposition than oils neutralized with soda. Oils neutralized with lime had better oxidative stability since the losses of their natural antioxidants, particularly tocopherols, were very limited. The neutralization with soda was accompanied by a passage of epoxides and hydroperoxides (products of first stage of oxidation) to alpha, beta-unsaturated aldehydes and ketones (products of second stage of oxidation). These purposes were confirmed by thermal spectrophotometric analyses and the increase of the carbonyl value after neutralization.

  3. Effect of electrolytical hydrogenation on the thermal stability and crystallization kinetics of METGLASS MBF-50

    NASA Astrophysics Data System (ADS)

    Górecki, Cz; Górecki, T.

    2007-08-01

    The effect of electrolytical hydrogenation on both the surface and volume crystallization kinetics and thermal stability of amorphous alloy METGLASS MBF-50 has been investigated. The surface crystallization has been investigated by the exoelectron emission (EEE) technique, whereas the volume crystallization has been followed by differential thermal analysis (DTA). It has been found that both the surface and volume crystallization of investigated material occur in two stages. The surface crystallization occurs at temperature lower and with activation energy distinctly smaller than the volume crystallization. Hydrogenation of the investigated metallic glass enhances its thermal stability by increasing the activation energies for both the surface and volume crystallization. The results of DTA measurements indicate that hydrogenation causes an increase in the enthalpy of both stages of volume crystallization.

  4. Photodegradation of oxytocin and thermal stability of photoproducts.

    PubMed

    Mozziconacci, Olivier; Schöneich, Christian

    2012-09-01

    Photodegradation of oxytocin at λ = 253.7 nm and λ ≥ 290 nm results in the transformation of the intrachain disulfide bond into predominantly dithiohemiacetal and thioether. Especially the dithiohemiacetal is sensitive to further degradation by light and/or elevated temperature, implying that the combination of an initial photostress and a subsequent heat stress can yield products significantly different compared with those observed under heat stress only. Copyright © 2012 Wiley Periodicals, Inc.

  5. Direct laser writing of thermally stabilized channel waveguides with Bragg gratings.

    PubMed

    Nishiyama, Hiroaki; Miyamoto, Isamu; Matsumoto, Shin-Ichi; Saito, Mitsunori; Kintaka, Kenji; Nishii, Junji

    2004-09-20

    Thermally stabilized photo-induced channel waveguides with Bragg gratings were fabricated in Ge-B-SiO2 thin glass films by exposure with KrF excimer laser and successive annealing at 600 degrees C. The annealing reversed the photo-induced refractive index pattern and also enhanced its thermal stability. The stabilized channel waveguide with a Bragg grating showed diffraction efficiency of 18.0 dB and 18.7 dB for TE- and TM-like modes, respectively. The diffraction efficiencies and wavelengths for both modes never changed after heat treatment at 500 degrees C, whereas the conventional photo-induced grating decayed even at 200 degrees C.

  6. Direct laser writing of thermally stabilized channel waveguides with Bragg gratings

    NASA Astrophysics Data System (ADS)

    Nishiyama, Hiroaki; Miyamoto, Isamu; Matsumoto, Shin-Ichi; Saito, Mitsunori; Kintaka, Kenji; Nishii, Junji

    2004-09-01

    Thermally stabilized photo-induced channel waveguides with Bragg gratings were fabricated in Ge-B-SiO2 thin glass films by exposure with KrF excimer laser and successive annealing at 600°C. The annealing reversed the photo-induced refractive index pattern and also enhanced its thermal stability. The stabilized channel waveguide with a Bragg grating showed diffraction efficiency of 18.0 dB and 18.7 dB for TE- and TM-like modes, respectively. The diffraction efficiencies and wavelengths for both modes never changed after heat treatment at 500°C, whereas the conventional photo-induced grating decayed even at 200°C.

  7. Thermal stability and energy harvesting characteristics of Au nanorods: harsh environment chemical sensing

    NASA Astrophysics Data System (ADS)

    Karker, Nicholas; Dharmalingam, Gnanaprakash; Carpenter, Michael A.

    2015-05-01

    Monitoring the levels of polluting gases such as CO and NOx from high temperature (500°C and higher) combustion environments requires materials with high thermal stability and resilience that can withstand harsh oxidizing and reducing environments. Au nanorods (AuNRs) have shown potential in plasmonic gas sensing due to their catalytic activity, high oxidation stability, and absorbance sensitivity to changes in the surrounding environment. By using electron beam lithography, AuNR geometries can be patterned with tight control of the rod dimensions and spacings, allowing tunability of their optical properties. Methods such as NR encapsulation within an yttria-stabilized zirconia overcoat layer with subsequent annealing procedures will be shown to improve temperature stability within a simulated harsh environment. Since light sources and spectrometers are typically required to obtain optical measurements, integration is a major barrier for harsh environment sensing. Plasmonic sensing results will be presented where thermal energy is harvested by the AuNRs, which replaces the need for an external incident light source. Results from gas sensing experiments that utilize thermal energy harvesting are in good agreement with experiments which use an external incident light source. Principal component analysis results demonstrate that by selecting the most "active" wavelengths in a plasmonic band, the wavelength space can be reduced from hundreds of monitored wavelengths to just four, without loss of information about selectivity of the AuNRs. By combining thermal stability, the thermal energy harvesting capability, and the selectivity in gas detection (achieved through multivariate analysis), integration of plasmonic sensors into combustion environments can be greatly simplified.

  8. Evaluation of VIIRS and MODIS Thermal Emissive Band Calibration Stability Using Ground Target

    NASA Technical Reports Server (NTRS)

    Madhavan, Sriharsha; Brinkmann, Jake; Wenny, Brian N.; Wu, Aisheng; Xiong, Xiaoxiong

    2017-01-01

    The S-NPP Visible Infrared Imaging Radiometer Suite (VIIRS) instrument, a polar orbiting Earth remote sensing instrument built using a strong MODIS background, employs a similarly designed on-board calibrating source - a V-grooved blackbody for the thermal emissive bands (TEB). The central wavelengths of most VIIRS TEBs are very close to those of MODIS with the exception of the 10.7 micron channel. To ensure the long term continuity of climate data records derived using VIIRS and MODIS TEB, it is necessary to assess any systematic differences between the two instruments, including scenes with temperatures significantly lower than blackbody operating temperatures at approximately 290 K. Previous work performed by the MODIS Characterization Support Team (MCST) at NASAGSFC used the frequent observations of the Dome Concordia site located in Antarctica to evaluate the calibration stability and consistency of Terra and Aqua MODIS over the mission lifetime. The near-surface temperature measurements from an automatic weather station (AWS) provide a direct reference useful for tracking the stability and determining the relative bias between the two MODIS instruments. In this study, the same technique is applied to the VIIRS TEB and the results are compared with those from the matched MODIS TEB. The results of this study show a small negative bias when comparing the matching VIIRS and Aqua MODIS TEB, implying a higher scene temperature retrieval for S-VIIRS at the cold end. Statistically no significant drift is observed for VIIRS TEB performance over the first 3.5 years of the mission.

  9. On the formation of phases and their influence on the thermal stability and thermoelectric properties of nanostructured zinc antimonide

    NASA Astrophysics Data System (ADS)

    Balasubramanian, Priyadarshini; Battabyal, Manjusha; Sivaprahasam, Duraiswamy; Gopalan, Raghavan

    2017-01-01

    To investigate the thermal reliability of the structure and thermoelectric properties of the zinc antimony compounds, undoped (Zn4Sb3) and doped (Zn4Sb2.95Sn0.05 and Co0.05Zn3.95Sb3) zinc antimonide samples were processed using the powder metallurgy route. It was observed that the as-prepared undoped sample contains a pure β-Zn4Sb3 phase, whereas the doped samples consist of Ω-ZnSb as the major phase and β-Zn4Sb3 as the minor phase. Differential scanning calorimetry analysis confirms the stability of the β-Zn4Sb3 phase up to 600 K. X-ray diffraction data of the undoped and doped samples show that the nanocrystallinity of the as-prepared samples is retained after one thermal cycle. The thermal bandgap, thermopower and thermal conductivity are not affected by the thermal cycle for the doped samples. A maximum power factor of 0.6 mW m-1 K-2 was achieved in the Sn-doped sample (Zn4Sb2.95Sn0.05). This is enhanced to 0.72 mW m-1 K-2 after one thermal cycle at 650 K under Ar atmosphere and slightly decreases after the third thermal cycle. In the case of the Co-doped sample (Co0.05Zn3.95Sb3), the power factor increases from 0.4 mW m-1 K-2 to 0.7 mW m-1 K-2 after the third thermal cycle. A figure of merit of ~0.3 is achieved at 573 K in the Zn4Sb2.95Sn0.05 sample. The results from the nanoindentation experiment show that Young’s modulus of the Sn-doped sample (Zn4Sb2.95Sn0.05) after the thermal cycle is enhanced (96 GPa) compared to the as-prepared sample (~76 GPa). These important findings on the thermal stability of the thermoelectric and mechanical properties of Sn-doped samples (Zn4Sb2.95Sn0.05) confirm that Sn-doped zinc antimonide samples can be used as efficient thermoelectric materials for device applications.

  10. Carbohydrates and thermal analysis reflects changes in soil organic matter stability after forest expansion on abandoned grassland

    NASA Astrophysics Data System (ADS)

    Guidi, Claudia; Vesterdal, Lars; Cannella, David; Leifeld, Jens; Gianelle, Damiano; Rodeghiero, Mirco

    2014-05-01

    Grassland abandonment, followed by progressive forest expansion, is the dominant land-use change in the Southern Alps, Europe. Land-use change can affect not only the amount of organic matter (OM) in soil but also its composition and stability. Our objective was to investigate changes in organic matter properties after forest expansion on abandoned grasslands, combining analysis of carbohydrates, indicative of labile OM compounds with prevalent plant or microbial origin, with thermal analysis. Thermal analysis was used as a rapid assessment method for the characterization of SOM stability. A land-use gradient was investigated in four land-use types in the subalpine area of Trentino region, Italy: i) managed grassland, mown and fertilized for the past 100 years; ii) grassland abandoned since 10 years, with sparse shrubs and Picea abies saplings; iii) early-stage forest, dominated by P. abies and established on a grassland abandoned around 1970; iv) old forest, dominated by Fagus sylvatica and P. abies. Mineral soil was sampled at three subplots in each land use type with eight soil cores, which were subsequently pooled by depth (0-5 cm, 5-10 cm, 10-20 cm). Sugars were extracted from bulk soil samples through acid hydrolysis with H2SO4 (0.5 M). The analytical composition of sugar monomers was performed with HPAEC technology (Dionex ICS5000), equipped with PAD-detection. Thermal stability was assessed with a differential scanning calorimeter DSC100, heating soil samples up to 600°C at a heating rate of 10°C min-1 in synthetic air. Peak height (W g OC-1) of 1st DSC exotherm, dominated by burning of labile OM compounds, was used as thermal stability index. In the abandoned grassland, carbohydrates compounds accounted for a greater proportion of soil OC than in other land use types. Microbially derived sugars, as rhamnose and galactose, were more abundant in managed and abandoned grasslands compared with early-stage and old forest. The amount of thermally labile sugars

  11. Thermal stability and oxidation resistance of Ti–Al–N coatings

    PubMed Central

    Chen, Li; Paulitsch, Jörg; Du, Yong; Mayrhofer, Paul H.

    2012-01-01

    Ti1 − xAlxN coatings are widely used for wear resistant applications due to their excellent mechanical and thermal properties, which depend to a great extent on the Al content. Here, we concentrate on a comparative study of the effect of Al content on crystal structure, thermal stability and oxidation resistance of Ti1 − xAlxN coatings. In agreement to earlier studies, thermal annealing of the individual cubic (c) and wurtzite (w) structured metastable Ti1 − xAlxN coatings induces decomposition into their stable phases c-TiN and w-AlN. The decomposition process for c-Ti1 − xAlxN involves an intermediate formation of cubic Al-rich and Ti-rich domains which results in a hardness increase to 34.7 and 34.4 GPa for x = 0.52 and 0.62 when annealed at 950 and 900 °C, respectively. In general, coatings with an Al content closer to the solubility limit, exhibit an earlier decomposition process, and hence an earlier peak-hardness. During exposure of the Ti1 − xAlxN coatings to ambient air at elevated temperatures Al2O3, TiO2 and Al2TiO5 are formed. The oxidation resistance of as-deposited single-phase Ti1 − xAlxN coatings, cubic or wurtzite structured, increases with increasing Al content. However, coatings containing Al contents at the metastable solubility limit, which result in a mixed cubic–wurtzite structure, have the worst oxidation resistance of the Al-containing coatings investigated. The single phase wurtzite structured coating w-Ti0.25Al0.75N shows the best oxidation resistance, with only ~0.7 μm oxide scale thickness, after thermal exposure for 20 h at 850 °C in ambient air. PMID:23471551

  12. Thermal Stability and Fire Properties of Salen and Metallosalens as Fire Retardants in Thermoplastic Polyurethane (TPU).

    PubMed

    Ramgobin, Aditya; Fontaine, Gaëlle; Penverne, Christophe; Bourbigot, Serge

    2017-06-17

    This study deals with the synthesis and evaluation of salen based derivatives as fire retardants in thermoplastic polyurethane. Salens, hydroxysalens and their first row transition metal complexes (salen-M) were synthesized (Copper, Manganese, Nickel and Zinc). They were then incorporated in thermoplastic polyurethane (TPU) with a loading as low as 10:1 weight ratio. The thermal stability as well as the fire properties of the formulations were evaluated. Thermogravimetric analysis (TGA) showed that different coordination metals on the salen could induce different decomposition pathways when mixed with TPU. The Pyrolysis Combustion Flow Calorimetry (PCFC) results showed that some M-salen have the ability to significantly decrease the peak heat release rate (-61% compared to neat TPU) and total heat released (-63% compared to neat TPU) when formulated at 10:1 wt % ratio in TPU. Mass Loss Cone Calorimetry (MLC) results have shown that some additives (salen-Cu and salen-Mn) exhibit very promising performance and they are good candidates as flame-retardants for TPU.

  13. Microwave Irradiation Effect on the Dispersion and Thermal Stability of RGO Nanosheets within a Polystyrene Matrix.

    PubMed

    Alsharaeh, Edreese H; Othman, Ali A; Aldosari, Mohammad A

    2014-07-18

    Polystyrene-reduced graphene oxide (PSTY/RGO) composites were prepared via the in situ bulk polymerization method using two different preparation techniques. The general approach is to use microwave irradiation (MWI) to enhance the exfoliation and the dispersion of RGO nanosheets within the PSTY matrix. In the first approach, a mixture of GO and styrene monomers (STY) were polymerized using a bulk polymerization method facilitated by microwave irradiation (MWI) to obtain R-(GO-PSTY) composites. In the second approach, a mixture of RGO and STY monomers were polymerized using a bulk polymerization method to obtain RGO-(PSTY) composites. The two composites were characterized by FTIR, ¹H-NMR, XRD, SEM, HRTEM, TGA and DSC. The results indicate that the composite obtained using the first approach, which involved MWI, had a better morphology and dispersion with enhanced thermal stability, compared with the composites prepared without MWI. Moreover, DSC results showed that the Tg value of the composites after loading the RGO significantly increased by 24.6 °C compared to the neat polystyrene.

  14. Examination of lignocellulosic fibers for chemical, thermal, and separations properties: Addressing thermo-chemical stability issues

    NASA Astrophysics Data System (ADS)

    Johnson, Carter David

    Natural fiber-plastic composites incorporate thermoplastic resins with fibrous plant-based materials, sometimes referred to as biomass. Pine wood mill waste has been the traditional source of natural fibrous feedstock. In anticipation of a waste wood shortage other fibrous biomass materials are being investigated as potential supplements or replacements. Perennial grasses, agricultural wastes, and woody biomass are among the potential source materials. As these feedstocks share the basic chemical building blocks; cellulose, hemicellulose, and lignin, they are collectively called lignocellulosics. Initial investigation of a number of lignocellulosic materials, applied to fiber-plastic composite processing and material testing, resulted in varied results, particularly response to processing conditions. Less thermally stable lignocellulosic filler materials were physically changed in observable ways: darkened color and odor. The effect of biomass materials' chemical composition on thermal stability was investigated an experiment involving determination of the chemical composition of seven lignocellulosics: corn hull, corn stover, fescue, pine, soy hull, soy stover, and switchgrass. These materials were also evaluated for thermal stability by thermogravimetric analysis. The results of these determinations indicated that both chemical composition and pretreatment of lignocellulosic materials can have an effect on their thermal stability. A second study was performed to investigate what effect different pretreatment systems have on hybrid poplar, pine, and switchgrass. These materials were treated with hot water, ethanol, and a 2:1 benzene/ethanol mixture for extraction times of: 1, 3, 6, 12, and 24 hours. This factorial experiment demonstrated that both extraction time and medium have an effect on the weight percent of extractives removed from all three material types. The extracted materials generated in the above study were then subjected to an evaluation of thermal

  15. Thermal Stabilization of Dihydrofolate Reductase Using Monte Carlo Unfolding Simulations and Its Functional Consequences

    PubMed Central

    Whitney, Anna; Shakhnovich, Eugene I.

    2015-01-01

    Design of proteins with desired thermal properties is important for scientific and biotechnological applications. Here we developed a theoretical approach to predict the effect of mutations on protein stability from non-equilibrium unfolding simulations. We establish a relative measure based on apparent simulated melting temperatures that is independent of simulation length and, under certain assumptions, proportional to equilibrium stability, and we justify this theoretical development with extensive simulations and experimental data. Using our new method based on all-atom Monte-Carlo unfolding simulations, we carried out a saturating mutagenesis of Dihydrofolate Reductase (DHFR), a key target of antibiotics and chemotherapeutic drugs. The method predicted more than 500 stabilizing mutations, several of which were selected for detailed computational and experimental analysis. We find a highly significant correlation of r = 0.65–0.68 between predicted and experimentally determined melting temperatures and unfolding denaturant concentrations for WT DHFR and 42 mutants. The correlation between energy of the native state and experimental denaturation temperature was much weaker, indicating the important role of entropy in protein stability. The most stabilizing point mutation was D27F, which is located in the active site of the protein, rendering it inactive. However for the rest of mutations outside of the active site we observed a weak yet statistically significant positive correlation between thermal stability and catalytic activity indicating the lack of a stability-activity tradeoff for DHFR. By combining stabilizing mutations predicted by our method, we created a highly stable catalytically active E. coli DHFR mutant with measured denaturation temperature 7.2°C higher than WT. Prediction results for DHFR and several other proteins indicate that computational approaches based on unfolding simulations are useful as a general technique to discover stabilizing

  16. Impact of revised thermal stability on pollutant transport time in a deep reservoir

    NASA Astrophysics Data System (ADS)

    Wu, Binbin; Wang, Guoqiang; Jiang, Hong; Wang, Jingfu; Liu, Changming

    2016-04-01

    Thermal stability (Schmidt stability) and water age, which are significantly related to water quality and algae bloom in deep reservoirs, are two crucial indicators of stratification strength and pollutant transport time, respectively. Here, the original Schmidt stability, which was derived from a one-dimensional assumption, was theoretically extended to a three-dimensional water body. In addition, a three-dimensional model was verified for the case study of Hongfeng Reservoir in China based on data from 2009 and 2010. Although the revised stability was similar to the original stability of Hongfeng Reservoir, which occurred at a relatively low level, the greater stratification in other deep water bodies would enhance their difference. Air temperature and water depth were the most important factors of the temporal variation in stability and the spatial variation in stability, respectively. The pollutant transport processes in the Hongfeng Reservoir was very complex with alternate appearances of overflow, interflow and underflow, depending on the season. The spatial water age was primarily determined by the morphometry and the inflow/outflow (with the highest water age in North Lake), whereas the vertical difference in the water age among the layers was primarily controlled by thermal stratification. Negative linear relationships between the average stability and the water ages of the bottom layers in three representative sites during summer were observed. Positive linear relationships between the average stability and the water ages of the surface layers were also observed. These findings enable a better understanding of the hydrodynamic and pollutant transport processes in a deep reservoir.

  17. Thermal stability of Trichoderma reesei c30 cellulase and aspergillus niger; -glucosidase after ph and chemical modification

    SciTech Connect

    Woodward, J.; Whaley, K.S.; Zachry, G.S.; Wohlpart, D.L.

    1981-01-01

    Treatment of Trichoderma reesei C30 cellulase at pH 10.0 for 1 h at room temperature increased its pH and thermal stability. Chemical modification of the free epsilon-amino groups of cellulase at pH 10.0 resulted in no further increase in stability. Such chemical modification, however, decreased the thermal stability of the cellulose-cellulase complex. On the contrary, the chemical modification of Aspergillus niger glucosidase with glutaraldehyde at pH 8.0 increased the thermal stability of this enzyme.

  18. Thermal stability of Trichoderma reesei C30 cellulase and Aspergillus niger. beta. -glucosidase after pH and chemical modification

    SciTech Connect

    Woodward, J.; Whaley, K.S.; Zachry, G.S.; Wohlpart, D.L.

    1981-01-01

    Treatment of Trichoderma reesei C30 cellulase at pH 10.0 for 1 h at room temperature increased its pH and thermal stability. Chemical modification of the free epsilon-amino groups of cellulase at pH 10.0 resulted in no further increase in stability. Such chemical modification, however, decreased the thermal stability of the cellulose-cellulase complex. On the contrary, the chemical modification of Aspergillus niger ..beta..-glucosidase with glutaraldehyde at pH 8.0 increased the thermal stability of this enzyme.

  19. Data on blueberry peroxidase kinetic characterization and stability towards thermal and high pressure processing.

    PubMed

    Terefe, Netsanet Shiferaw; Delon, Antoine; Versteeg, Cornelis

    2017-08-01

    The data presented in this article are related to a research article entitled 'Thermal and high pressure inactivation kinetics of blueberry peroxidase' (Terefe et al., 2017) [1]. In this article, we report original data on the activity of partially purified blueberry peroxidase at different concentrations of hydrogen peroxide and phenlylenediamine as substrates and the effects of thermal and high pressure processing on the activity of the enzyme. Data on the stability of the enzyme during thermal (at temperatures ranging from 40 to 80 °C) and combined thermal-high pressure processing (100-690 MPa, 30-90 °C) are included in this report. The data are presented in this format in order to facilitate comparison with data from other researchers and allow statistical analyses and modeling by others in the field.

  20. Thermal stability and flame resistance of cotton fabrics treated with whey proteins.

    PubMed

    Bosco, Francesca; Carletto, Riccardo Andrea; Alongi, Jenny; Marmo, Luca; Di Blasio, Alessandro; Malucelli, Giulio

    2013-04-15

    It is well described in the literature that whey proteins are able to form coatings, which exhibit high mechanical and oxygen barrier properties, notwithstanding a great water vapour adsorption. These peculiarities have been exploited for applying a novel protein-based finishing treatment to cotton and for assessing the protein effect on the thermal and thermo-oxidative stability and on the flame retardant properties of the cellulosic fabric. Indeed, the deposited whey protein coatings have turned out to significantly affect the thermal degradation of cotton in inert and oxidative atmosphere, and to somehow modify its combustion when a flame has been applied. Furthermore, the influence of the secondary and tertiary structure of these proteins on the morphology of the deposited coating, and thus on the thermal and flame retardant properties of the treated fabrics, has been evaluated by performing a denaturation thermal treatment before the protein application.

  1. Expanded polytetrafluoroethylene reinforced polyvinylidenefluoride-hexafluoropropylene separator with high thermal stability for lithium-ion batteries

    NASA Astrophysics Data System (ADS)

    Xiong, Ming; Tang, Haolin; Wang, Yadong; Lin, Yu; Sun, Meiling; Yin, Zhuangfei; Pan, Mu

    2013-11-01

    PVDF-HFP/ePTFE composite separator with high thermal stability and low thermal shrinkage characteristic has been developed. The PVDF-HFP acts to absorb the electrolyte and shutdown at elevated temperature. The thermally stable ePTFE matrix is adopted to improve the mechanical strength and sustain the insulation after the shutdown. This novel separator presents good ion conductivity (up to 1.29 mS cm-1) and has a low thermal shrinkage of 8.8% at 162 °C. The composite separator shutdown at 162 °C and keep its integrity before 329 °C. Cells based on the composite separator show excellent capacities at high rate discharge and stable cycling performance.

  2. Multifunctional cyclotriphosphazene/hexagonal boron nitride hybrids and their flame retarding bismaleimide resins with high thermal conductivity and thermal stability.

    PubMed

    Jin, Wenqin; Yuan, Li; Liang, Guozheng; Gu, Aijuan

    2014-09-10

    A novel hybridized multifunctional filler (CPBN), cyclotriphosphazene/hexagonal boron nitride (hBN) hybrid, was synthesized by chemically coating hBN with hexachlorocyclotriphosphazene and p-phenylenediamine, its structure was systemically characterized. Besides, CPBN was used to develop new flame retarding bismaleimide/o,o'-diallylbisphenol A (BD) resins with simultaneously high thermal conductivity and thermal stability. The nature of CPBN has a strong influence on the flame behavior of the composites. With the addition of only 5 wt % CPBN to BD resin, the thermal conductivity increases 2 times; meanwhile the flame retardancy of BD resin is remarkably increased, reflected by the increased limited oxygen index, much longer time to ignition, significantly reduced heat release rate. The thermogravimetric kinetics, structures of chars and pyrolysis gases, and cone calorimeter tests were investigated to reveal the unique flame retarding mechanism of CPBN/BD composites. CPBN provides multieffects on improving the flame retardancy, especially in forming a protective char layer, which means a more thermally stable and condensed barrier for heat and mass transfer, and thus protecting the resin from further combustion.

  3. Thermal and Chemical Stability of Baseline and Improved Crystalline Silicotitanate

    SciTech Connect

    Taylor, P.A.

    2002-01-23

    The Savannah River Site (SRS) has been evaluating technologies for removing radioactive cesium ({sup 137}Cs) from the supernate solutions stored in the high-level waste tanks at the site. Crystalline silicotitanate (CST) sorbent (IONSIV IE-911{reg_sign}, UOP LLC, Des Plaines, IL), which is very effective at removing cesium from high-salt solutions, was one of three technologies that were tested. Because of the extremely high inventory of {sup 137}Cs expected for the large columns of CST that would be used for treating the SRS supernate, any loss of flow or cooling to the columns could result in high temperatures from radiolytic heating. Also, even under normal operating conditions, the CST would be exposed to the supernates for up to a year before being removed. Small-scale batch and column tests conducted last year using samples of production batches of CST showed potential problems with CST clumping and loss of cesium capacity after extended contact with the simulant solutions. Similar tests-using samples of a baseline and improved granular CST and the CST powder used to make both granular samples-were performed this year to compare the performance of the improved CST. The column tests, which used recirculating supernate simulant, showed that the baseline CST generated more precipitates of sodium aluminosilicate than the improved CST. The precipitates were particularly evident in the tubing that carried the simulant solution to and from the column, but the baseline CST also showed higher concentrations of aluminum on the CST than were observed for the improved CST. Recirculating the simulant through just a section of the tubing (no contact with CST) also produced small amounts of precipitate, similar to the amounts seen for the improved CST column. The sodium aluminosilicate formed bridges between the CST granules, causing clumps of CST to form in the column. Clumps were visible in the baseline CST column after 1 month of operation and in the improved CST column

  4. Thermal and Chemical Stability of Crystalline Silicotitanate Sorbent

    SciTech Connect

    Taylor, P.A.; Mattus, C.H.

    1999-10-01

    The Savannah River Site (SRS) is evaluating technologies for removing cesium-137 (137Cs) from the supemate solutions stored in the high-level waste tanks at the site. Crystalline silicotitanate sorbent (IONSIV IE-9 1 lo, UOP Molecular Sieves; Mount Laurel, NJ) is very effective for removing cesium from high-salt solution, such as the SRS supemates, and is currently being used at Oak Ridge National Laboratory to remove radioactive cesium from similar solutions, Because of the extremely high loading of 137Cs that would be expected for the large columns of crystalline silicotitanate (CST) that would be used for treating the SRS supemate, any loss of flow or cooling to the columns could result in high temperatures within the column from radiolytic heating. The ability of CST to retain previously loaded cesium while in contact with SRS tank supemates at various temperatures was determined by performing bench scale simulant tests using CST samples that were loaded with stable cesium and radi oactive cesium tracer. These results were compared with those obtained from loading tests at the same temperatures.

  5. Purification, characterization, and solvent-induced thermal stabilization of ficin from Ficus carica.

    PubMed

    Devaraj, Kamsagara Basavarajappa; Kumar, Parigi Ramesh; Prakash, Vishweshwaraiah

    2008-12-10

    Ficin (EC 3.4.22.3), a cysteine proteinase isolated from the latex of a Ficus tree, is known to occur in multiple forms. Although crude ficin is of considerable commercial importance, ficin as such has not been fully characterized. A major ficin from the commercial crude proteinase mixture preparation of Ficus carica was purified and characterized. The purified enzyme was homogeneous in both sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and gel-filtration chromatography and is a single polypeptide chain protein with a molecular mass of 23 100 +/- 300 Da as determined by matrix-assisted laser desorption ionization-time of flight (MALDI-TOF). The enzyme was active in the pH range of 6.5-8.5, and maximum activity was observed at pH 7.0. The N-terminal core sequence of ficin has homology with N-terminal sequences of plant cysteine proteinases. The enzyme contains three disulfide bonds and a single free cysteine residue at the active site. The effect of co-solvents, such as sorbitol, trehalose, sucrose, and xylitol, on the thermal stability of ficin was determined by activity measurements, fluorescence, and thermal denaturation studies. The apparent thermal denaturation temperature (T(m)) of ficin was significantly increased from the control value of 72 +/- 1 degrees C in the presence of all co-solvents. However, the maximum stabilization effect was observed in terms of thermal stabilization by the co-solvent trehalose.

  6. Enhancement of thermal reversibility and stability of human carbonic anhydrase II by mesoporous nanoparticles.

    PubMed

    Khatibi, Ali; Ma'mani, Leila; Khodarahmi, Reza; Shafiee, Abbas; Maghami, Parvaneh; Ahmad, Faizan; Sheibani, Nader; Moosavi-Movahedi, Ali Akbar

    2015-04-01

    Aminopropyl functionalized PEGylated mesoporous silica nanoparticles [H2N-Pr@PEGylated SBA-15] were synthesized and evaluated as a promising biocompatible additive to study the activity and thermal reversibility and stability of human carbonic anhydrase II (HCA II). For this purpose, the additive was prepared by covalent amino propyl functionalization of mesoporous silica nanoparticles (MSNs) bearing PEG moiety as linker. The MSNs was fully characterized using different techniques including transmission electron microscopy, N2 adsorption-desorption measurements, thermal gravimetric analysis, Fourier transform infrared spectroscopy and dynamic light scattering. The average particle size of [H2N-Pr@PEGylated SBA-15] was about 80 nm and showed high loading capacity for HCA II at pH 7.75 as a target protein. The efficiency of [H2N-Pr@PEGylated SBA-15] in improving reversibility of HCA II was investigated by various techniques including UV-vis, 1,8-Anilinonaphtalene Sulfonate (ANS) fluorescence, circular dichroism (CD), and differential scanning calorimetry. Our results showed that [H2N-Pr@PEGylated SBA-15] can increase the protein thermal reversibility and stability. Herein, kinetic studies were applied to confirm the ability of [H2N-Pr@PEGylated SBA-15] in increasing the activity of HCA II at high temperatures. Together our results present the [H2N-Pr@PEGylated SBA-15] as a water-dispersible and efficient additive for improving the activity, and thermal reversibility and stability of enzyme. Copyright © 2015 Elsevier B.V. All rights reserved.

  7. Enhanced thermal stability of RuO2/polyimide interface for flexible device applications

    NASA Astrophysics Data System (ADS)

    Music, Denis; Schmidt, Paul; Chang, Keke

    2017-09-01

    We have studied the thermal stability of RuO2/polyimide (Kapton) interface using experimental and theoretical methods. Based on calorimetric and spectroscopic analyses, this inorganic–organic system does not exhibit any enthalpic peaks as well as all bonds in RuO2 and Kapton are preserved up to 500 °C. In addition, large-scale density functional theory based molecular dynamics, carried out in the same temperature range, validates the electronic structure and points out that numerous Ru–C and a few Ru–O covalent/ionic bonds form across the RuO2/Kapton interface. This indicates strong adhesion, but there is no evidence of Kapton degradation upon thermal excitation. Furthermore, RuO2 does not exhibit any interfacial bonds with N and H in Kapton, providing additional evidence for the thermal stability notion. It is suggested that the RuO2/Kapton interface is stable due to aromatic architecture of Kapton. This enhanced thermal stability renders Kapton an appropriate polymeric substrate for RuO2 containing systems in various applications, especially for flexible microelectronic and energy devices.

  8. Thermal Stability Results of a Fischer-Tropsch Fuel With Various Blends of Aromatic Solution

    NASA Technical Reports Server (NTRS)

    Lindsey, Jennifer; Klettlinger, Suder

    2013-01-01

    Fischer-Tropsch (F-T) jet fuel composition differs from petroleum-based, conventional commercial jet fuel because of differences in feedstock and production methodology. F-T fuel typically has a lower aromatic and sulfur content and consists primarily of iso and normal paraffins. The ASTM D3241 specification for Jet Fuel Thermal Oxidation Test (JFTOT) break point testing method was used to test the breakpoint of a baseline commercial grade F-T jet fuel, and various blends of this F-T fuel with an aromatic solution. The goal of this research is to determine the effect of aromatic content on the thermal stability of F-T fuel. The testing completed in this report was supported by the NASA Fundamental Aeronautics Subsonic Fixed Wing Project. Two different aromatic content fuels from Rentech, as well as these fuels with added aromatic blend were analyzed for thermal stability using the JFTOT method. Preliminary results indicate a reduction in thermal stability occurs upon increasing the aromatic content to 10% by adding an aromatic blend to the neat fuel. These results do not specify a failure based on pressure drop, but only on tube color. It is unclear whether tube color correlates to more deposition on the tube surface or not. Further research is necessary in order to determine if these failures are true failures based on tube color. Research using ellipsometry to determine tube deposit thickness rather than color will be continued in follow-up of this study.

  9. Thermal stability of vapor-deposited stable glasses of an organic semiconductor

    SciTech Connect

    Walters, Diane M.; Ediger, M. D.; Richert, Ranko

    2015-04-07

    Vapor-deposited organic glasses can show enhanced kinetic stability relative to liquid-cooled glasses. When such stable glasses of model glassformers are annealed above the glass transition temperature T{sub g}, they lose their thermal stability and transform into the supercooled liquid via constant velocity propagating fronts. In this work, we show that vapor-deposited glasses of an organic semiconductor, N,N′-bis(3-methylphenyl)-N,N′-diphenylbenzidine (TPD), also transform via propagating fronts. Using spectroscopic ellipsometry and a new high-throughput annealing protocol, we measure transformation front velocities for TPD glasses prepared with substrate temperatures (T{sub Substrate}) from 0.63 to 0.96 T{sub g}, at many different annealing temperatures. We observe that the front velocity varies by over an order of magnitude with T{sub Substrate}, while the activation energy remains constant. Using dielectric spectroscopy, we measure the structural relaxation time of supercooled TPD. We find that the mobility of the liquid and the structure of the glass are independent factors in controlling the thermal stability of TPD films. In comparison to model glassformers, the transformation fronts of TPD have similar velocities and a similar dependence on T{sub Substrate}, suggesting universal behavior. These results may aid in designing active layers in organic electronic devices with improved thermal stability.

  10. Structure-Activity Relationship Analysis of the Thermal Stabilities of Nitroaromatic Compounds Following Different Decomposition Mechanisms.

    PubMed

    Li, Jiazhong; Liu, Huanxiang; Huo, Xing; Gramatica, Paola

    2013-02-01

    The decomposition behavior of energetic materials is very important for the safety problems concerning their production, transportation, use and storage, because molecular decomposition is intimately connected to their explosive properties. Nitroaromatic compounds, particularly nitrobenzene derivatives, are often considered as prototypical energetic molecules, and some of them are commonly used as high explosives. Quantitative structure-activity relationship (QSAR) represents a potential tool for predicting the thermal stability properties of energetic materials. But it is reported that constructing general reliable models to predict their stability and their potential explosive properties is a very difficult task. In this work, we make our efforts to investigate the relationship between the molecular structures and corresponding thermal stabilities of 77 nitrobenzene derivatives with various substituent functional groups (in ortho, meta and/or para positions). The proposed best MLR model, developed by the new software QSARINS, based on Genetic Algorithm for variable selection and with various validation tools, is robust, stable and predictive with R(2) of 0.86, QLOO (2) of 0.79 and CCC of 0.90. The results indicated that, though difficult, it is possible to build predictive, externally validated QSAR models to estimate the thermal stability of nitroaromatic compounds. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Using thermal and spectroscopic (XANES) indices to understand the biological stability of soil organic matter.

    NASA Astrophysics Data System (ADS)

    Gillespie, A. W.; Sanei, H.; Diochon, A.; Tarnocai, C.; Janzen, H.; Regier, T. Z.; Gregorich, E.

    2014-12-01

    Soil organic matter (SOM) composition is a key property that underpins ecosystem productivity. Understanding its physical, chemical and biological properties is important for evaluating its role in carbon (C) and nutrient cycling in terrestrial ecosystems. In particular, the stability of SOM (i.e., resistance to microbial degradation) has important implications in ecosystem processes, including nutrient cycling, emission of greenhouse gases from soil, and C sequestration. Thus there is interest in developing new ways to measure and quantify the labile and stable forms of soil organic carbon. In this presentation, we describe the combined use of thermal decomposition methods based on pyrolysis, and chemical properties using X-ray absorption spectroscopy (XAS), to describe the stability of soil organic matter. Soils (n=81) for this study were obtained from a wide geographical range and management practices. Controlled respiration studies were conducted on the soils to determine the biodegradability of organic C after 98 days. In the thermal analysis, the sample is subjected to a temperature ramp and pyrolyzed/volatilized organic C was recorded as a function of temperature. Analysis by XAS provided information on the types of C functional groups present in a soil sample. We show that biological stability is well described using a two component model which included thermal stability and C composition chemistry.

  12. Thermal stability of vapor-deposited stable glasses of an organic semiconductor

    NASA Astrophysics Data System (ADS)

    Walters, Diane M.; Richert, Ranko; Ediger, M. D.

    2015-04-01

    Vapor-deposited organic glasses can show enhanced kinetic stability relative to liquid-cooled glasses. When such stable glasses of model glassformers are annealed above the glass transition temperature Tg, they lose their thermal stability and transform into the supercooled liquid via constant velocity propagating fronts. In this work, we show that vapor-deposited glasses of an organic semiconductor, N,N'-bis(3-methylphenyl)-N,N'-diphenylbenzidine (TPD), also transform via propagating fronts. Using spectroscopic ellipsometry and a new high-throughput annealing protocol, we measure transformation front velocities for TPD glasses prepared with substrate temperatures (TSubstrate) from 0.63 to 0.96 Tg, at many different annealing temperatures. We observe that the front velocity varies by over an order of magnitude with TSubstrate, while the activation energy remains constant. Using dielectric spectroscopy, we measure the structural relaxation time of supercooled TPD. We find that the mobility of the liquid and the structure of the glass are independent factors in controlling the thermal stability of TPD films. In comparison to model glassformers, the transformation fronts of TPD have similar velocities and a similar dependence on TSubstrate, suggesting universal behavior. These results may aid in designing active layers in organic electronic devices with improved thermal stability.

  13. Thermal Stability of Intermetallic Phases in Fe-rich Fe-Cr-Ni-Mo Alloys

    NASA Astrophysics Data System (ADS)

    Yang, Ying; Tan, Lizhen; Busby, Jeremy T.

    2015-09-01

    Understanding the thermal stability of intermetallic phases in Fe-rich Fe-Cr-Ni-Mo alloys is critical to alloy design and application of Mo-containing austenitic steels. Coupled with thermodynamic modeling, the thermal stability of intermetallic Chi and Laves phases in two Fe-Cr-Ni-Mo alloys was investigated at 1273 K, 1123 K, and 973 K (1000 °C, 850 °C, and 700 °C) for different annealing times. The morphologies, compositions, and crystal structures of the precipitates of the intermetallic phases were carefully examined by scanning electron microscopy, electron probe microanalysis, X-ray diffraction, and transmission electron microscopy. Two key findings resulted from this study. First, the Chi phase is stable at high temperature, and with the decreasing temperature it transforms into the Laves phase that is stable at low temperature. Secondly, Cr, Mo, and Ni are soluble in both the Chi and Laves phases, with the solubility of Mo playing a major role in the relative stability of the intermetallic phases. The thermodynamic models that were developed were then applied to evaluating the effect of Mo on the thermal stability of intermetallic phases in type 316 and NF709 stainless steels.

  14. Fabrication of protective over layer for enhanced thermal stability of zinc oxide based TCO films

    NASA Astrophysics Data System (ADS)

    Ravichandran, K.; Ravikumar, P.; Sakthivel, B.

    2013-12-01

    To prevent the loss of oxygen vacancies in aluminium doped zinc oxide (AZO) thin films at high temperature process, and to enhance the thermal stability a protective tin oxide (TO) over layer has been realized. To investigate the protective nature of doped tin oxide layer, fluorine doped tin oxide (FTO) and antimony doped tin oxide (ATO) layers have also been coated on AZO layer. Then, to confirm its stability of opto-electrical properties under high temperature process, structural, optical and electrical studies of AZO single layer, TO/AZO, FTO/AZO and ATO/AZO double layered films were carried out before and after annealing and the results are reported. The XRD results showed that the crystalline nature of double layered films remains unchanged, even after the heat treatment. The UV results depicted that, in all the double layer films the transmission spectra remain unchanged or changed negligibly after annealing, indicating the thermal stability of double layered films. The photoluminescence results also strongly supported the improvement in the thermal stability of double layered films. The electrical studies suggested that the double layered films exhibited better electrical resistivity with bare AZO films.

  15. Thermal stability and energetics of 15-mer DNA duplex interstrand crosslinked by trans-diamminedichloroplatinum(II).

    PubMed

    Hofr, Ctirad; Brabec, Viktor

    2005-03-01

    The effect of the location of the interstrand cross-link formed by trans-diamminedichloroplatinum(II) (transplatin) on the thermal stability and energetics of 15-mer DNA duplex has been investigated. The duplex containing single, site-specific cross-link, thermodynamically equivalent model structures (hairpins) and nonmodified duplexes were characterized by differential scanning calorimetry, temperature-dependent uv absorption, and circular dichroism. The results demonstrate that the formation of the interstrand cross-link of transplatin does not affect pronouncedly thermodynamic stability of DNA: the cross-link induces no marked changes not only in enthalpy, but also in "reduced" (concentration independent) monomolecular transition entropy. These results are consistent with the previous observations that interstrand cross-links of transplatin structurally perturb DNA only to a relatively small extent. On the other hand, constraining the duplex with the interstrand cross-link of transplatin results in a significant increase in thermal stability that is primarily due to entropic effects: the cross-link reduces the molecularity of the oligomer system from bimolecular to monomolecular. Importantly, the position of the interstrand cross-link within the duplex modulates cooperativity of the melting transition of the duplex and consequently its thermal stability.

  16. Study of fuzzy adaptive PID controller on thermal frequency stabilizing laser with double longitudinal modes

    NASA Astrophysics Data System (ADS)

    Mo, Qingkai; Zhang, Tao; Yan, Yining

    2016-10-01

    There are contradictions among speediness, anti-disturbance performance, and steady-state accuracy caused by traditional PID controller in the existing light source systems of thermal frequency stabilizing laser with double longitudinal modes. In this paper, a new kind of fuzzy adaptive PID controller was designed by combining fuzzy PID control technology and expert system to make frequency stabilizing system obtain the optimal performance. The experiments show that the frequency stability of the designed PID controller is similar to the existing PID controller (the magnitude of frequency stability is less than 10-9 in constant temperature and 10-7 in open air). But the preheating time is shortened obviously (from 10 minutes to 5 minutes) and the anti-disturbance capability is improved significantly (the recovery time needed after strong interference is reduced from 1 minute to 10 seconds).

  17. ALD Functionalized Nanoporous Gold: Thermal Stability, Mechanical Properties, and Catalytic Activity

    SciTech Connect

    Biener, M M; Biener, J; Wichmann, A; Wittstock, A; Baumann, T F; Baeumer, M; Hamza, A V

    2011-03-24

    Nanoporous metals have many technologically promising applications but their tendency to coarsen limits their long-term stability and excludes high temperature applications. Here, we demonstrate that atomic layer deposition (ALD) can be used to stabilize and functionalize nanoporous metals. Specifically, we studied the effect of nanometer-thick alumina and titania ALD films on thermal stability, mechanical properties, and catalytic activity of nanoporous gold (np-Au). Our results demonstrate that even only one-nm-thick oxide films can stabilize the nanoscale morphology of np-Au up to 1000 C, while simultaneously making the material stronger and stiffer. The catalytic activity of np-Au can be drastically increased by TiO{sub 2} ALD coatings. Our results open the door to high temperature sensor, actuator, and catalysis applications and functionalized electrodes for energy storage and harvesting applications.

  18. Quantitation of protein–protein interactions by thermal stability shift analysis

    PubMed Central

    Layton, Curtis J; Hellinga, Homme W

    2011-01-01

    Thermal stability shift analysis is a powerful method for examining binding interactions in proteins. We demonstrate that under certain circumstances, protein–protein interactions can be quantitated by monitoring shifts in thermal stability using thermodynamic models and data analysis methods presented in this work. This method relies on the determination of protein stabilities from thermal unfolding experiments using fluorescent dyes such as SYPRO Orange that report on protein denaturation. Data collection is rapid and straightforward using readily available real-time polymerase chain reaction instrumentation. We present an approach for the analysis of the unfolding transitions corresponding to each partner to extract the affinity of the interaction between the proteins. This method does not require the construction of a titration series that brackets the dissociation constant. In thermal shift experiments, protein stability data are obtained at different temperatures according to the affinity- and concentration-dependent shifts in unfolding transition midpoints. Treatment of the temperature dependence of affinity is, therefore, intrinsic to this method and is developed in this study. We used the interaction between maltose-binding protein (MBP) and a thermostable synthetic ankyrin repeat protein (Off7) as an experimental test case because their unfolding transitions overlap minimally. We found that MBP is significantly stabilized by Off7. High experimental throughput is enabled by sample parallelization, and the ability to extract quantitative binding information at a single partner concentration. In a single experiment, we were able to quantify the affinities of a series of alanine mutants, covering a wide range of affinities (∼ 100 nM to ∼ 100 μM). PMID:21674662

  19. Predicting thermal stability of organic solar cells through real-time capacitive techniques (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Tessarolo, Marta; Guerrero, Antonio; Seri, Mirko; Prosa, Mario; Bolognesi, Margherita; Garcia Belmonte, Germà

    2015-10-01

    Bulk Heterojunction (BHJ) solar cells have reached Power Conversion Efficiencies (PCE) over 10% but to be a competitive product long lifetimes are mandatory. In this view, guidelines for the prediction and optimization of the device stability are crucial to generate improved materials for efficient and stable BHJ devices. For encapsulated cells, degradation mechanisms can be mainly ascribed to external agents such as light and temperature. In particular, thermal degradation appears to be related not only to the BHJ morphology but also to the adjacent interfaces. Therefore, in order to have a complete description of the thermal stability of a BHJ cell, it is necessary to consider the entire stack degradation processes by using techniques enabling a direct investigation on working devices. Here, five different donor polymers were selected and the OPV performance of the corresponding BHJ devices were monitored during the thermal degradation at 85°C, showing an exponential decay of the corresponding PCEs. In parallel, we measured the geometrical capacitance of analogous OPV devices as a function of temperature and we observed that at a defined temperature (TMAX), typical for each polymer-based device, the capacitance starts to decrease. Combining all these results we found an evident and direct correlation between TMAX and the PCE decay parameters (obtained from capacitance-temperature an thermal measurements, respectively). This implies that the capacitance-method here presented is a fast, reliable and relatively simple method to predict the thermal stability of BHJ solar cells without the need to perform time-consuming thermal degradation tests.

  20. Thermal stability of higher plant biomarkers evaluated through pyrolysis; geologic implications in thermally-mature sediment

    NASA Astrophysics Data System (ADS)

    Longbottom, T. L.; Hockaday, W. C.; Von Bargen, J.

    2013-12-01

    The organic molecules known as n-alkanes, n-alkanoic acids, and sterols are widely used biomarkers in paleoecological and organic matter source-apportionment studies, and are complementary to traditional bulk organic matter proxies (organic carbon stable isotopes and C/N ratios). These organic matter parameters are hindered by early and late diagenesis, through a combination of biotic and abiotic factors, which can lead to uncertainty in sediments on geologic timescales. This study seeks to use modern central Texas plants and soils as tools for our understanding and interpretation of biomarker patterns deep time, specifically in thermally mature sediment and paleosols. Bulk leaf and soil samples were heat treated to a range of temperatures in a muffle furnace in the absence of oxygen in order to clarify the role of abiotic degradation (thermal cracking) on bulk SOM and biomarker distributions. Preliminary results for unaltered n-alkane distributions of Southern Cattail (Typha domingensis) biomass shows a strong odd-over-even predominance, where the most abundant n-alkanes are nC23, nC25, nC27, and nC29. The biomass exposed to slow pyrolysis temperature of 300°C had n-alkanes ranging from nC11-nC29, with no odd-over-even predominance. The high abundance of lower molecular weight n-alkanes (thermal cracking of high molecular weight alkanes into smaller fragments. It is evident that the n-alkane distributions of modern plant material is severely disrupted by modest heating, an observation that must be taken into account when interpreting these biomarkers in deeply-buried geological samples.