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Sample records for ability thermal stability

  1. 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

  2. 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.

  3. 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.

  4. Effect of Nb Concentration on Thermal Stability and Glass-Forming Ability of Soft Magnetic (Fe,Co)-Gd-Nb-B Glassy Alloys

    NASA Astrophysics Data System (ADS)

    Zhang, Wei; Jia, Fei; Zhang, Xingguo; Xie, Guoqiang; Inoue, Akihisa

    2010-07-01

    Addition of a small amount of Nb to the (Fe,Co)-Gd-B glassy alloy in (Fe0.9Co0.1)71.5- x Nb x Gd3.5B25 increased the stabilization of supercooled liquid. The largest supercooled liquid region of 104 K was obtained for the x = 2 alloy. A distinct two-stage-like glass transition was observed with further incresing Nb content. The nanoscale (Fe,Co)23B6 phase precipitated in the glassy matrix after annealing, while the two-stage-like glass transition disappeared, indicating that the anomalous glass transition behavior originates from the exothermic reaction for the formation of the (Fe,Co)23B6 phase in the supercooled liquid region. The glass-forming ability (GFA) also increased by addition of Nb, leading to formation of the bulk glass form for the Nb-doped alloys. The best GFA with a diameter of over 3 mm was achieved for the x = 4 alloy. The (Fe,Co)-Gd-Nb-B glassy alloys exhibited good magnetic properties, i.e., rather high saturation magnetization of 0.81 to 1.22 T, low coercive force of 2.5 to 5.8 A/m, and low saturated magnetostriction of 9 to 19 × 10-6. In addition, the glassy alloys also possessed very high compressive fracture strength of 3842 to 3916 MPa and high Vickers hardness of 1025 to 1076.

  5. 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.

  6. 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.

  7. 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.

  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. 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.

  10. 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.

  11. Longitudinal Stability of Cognitive Ability in the Colorado Adoption Project.

    ERIC Educational Resources Information Center

    Baker, Laura A.; And Others

    1983-01-01

    Measures of general cognitive ability in one- and two-year-old adopted and nonadopted infants and their parents were subjected to path analysis to estimate the contribution of genetic and environmental factors to short-term stability of mental ability. (Author/RH)

  12. 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).

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  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. 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

  13. Evaluation of muscular stabilization ability during a static workout.

    PubMed

    Staniszewski, Michał; Urbanik, Czesław; Staniszewski, Tadeusz

    2010-01-01

    The aim of this research was to determine the moving and stabilizing functions of selected groups of muscles during the process of static workout. 15 students of the Academy of Physical Education were tested in non-competitive training. Muscular torques achieved during flexing and extending big limb joints were used as the determinant of force. Comparative analysis of torque values achieved in passive stabilization (with support) and muscular stabilization (without support) in elbow and knee joints was carried out. The value of the force applied to the passively stabilizing element in a given measurement during the flexion of elbow and the extension of knee joint was tested. The results of these tests allowed us to learn the value of muscular torques and - after statistical analysis - the relationship between them in particular functions.

  14. 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.

  15. Enhancing enzyme stability and metabolic functional ability of β-galactosidase through functionalized polymer nanofiber immobilization.

    PubMed

    Misson, Mailin; Jin, Bo; Chen, Binghui; Zhang, Hu

    2015-10-01

    A functionalized polystyrene nanofiber (PSNF) immobilized β-galactosidase assembly (PSNF-Gal) was synthesized as a nanobiocatalyst aiming to enhance the biocatalyst stability and functional ability. The PSNF fabricated by electrospinning was functionalized through a chemical oxidation method for enzyme binding. The bioengineering performance of the enzyme carriers was further evaluated for bioconversion of lactose to galacto-oligosaccharides (GOS). The modified PSNF-Gal demonstrated distinguished performances to preserve the same activity as the free β-galactosidase at the optimum pH of 7.0, and to enhance the enzyme stability of PSNF-Gal in an alkaline condition up to pH 10. The PSNF assembly demonstrated improved thermal stability from 37 to 60 °C. The nanobiocatalyst was able to retain 30 % of its initial activity after ninth operation cycles comparing to four cycles with the unmodified counterpart. In contrast with free β-galactosidase, the modified PSNF-Gal enhanced the GOS yield from 14 to 28 %. These findings show the chemically modified PSNF-based nanobiocatalyst may be pertinent for various enzyme-catalysed bioprocessing applications.

  16. 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.

  17. 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

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. Calcium phosphate forming ability of thermally oxidized titanium implant

    NASA Astrophysics Data System (ADS)

    Hwang, Kyu-Seog; Yun, Yeon-Hum; Min, Seon-Suk; Lee, Yong-Ryeol; Park, Yeong-Joon

    2002-07-01

    Commercially pure titanium disks as-received and heat treated at 600°C in air for 10 min were used to investigate differences in calcium phosphate forming ability. Crystallinity and surface morphology were analyzed by X-ray diffraction and field emission scanning electron microscopy. Energy dispersive X-ray spectrometry and Fourier transform infrared reflection spectroscopy were used to collect information on chemical composition and chemical surface structure. TiO2 layers with a heterogeneous structure produced by heat treatment showed high in vitro calcium phosphate forming ability in contact with Eagle's minimum essential medium.

  4. 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.

  5. 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

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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

  17. 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.

  18. 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.

  19. 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.

  20. 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

  1. 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.

  2. Balance ability and postural stability among patients with painful shoulder disorders and healthy controls

    PubMed Central

    2013-01-01

    Background In therapeutic settings, patients with shoulder pain often exhibit deficient coordinative abilities in their trunk and lower extremities. The aim of the study was to investigate 1) if there is a connection between shoulder pain and deficits in balance ability and postural stability, 2) if pain intensity is related to balance ability and postural stability, and 3) if there is a connection between body mass index (BMI) and balance ability and postural stability. Methods In this case–control study, patients (n = 40) with pathological shoulder pain (> 4 months) were matched with a healthy controls (n = 40) and were compared with regard to their balance ability and postural stability. Outcome parameters were postural stability, balance ability and symmetry index which were measured using the S3-Check system. In addition, the influence of shoulder pain intensity and BMI on the outcome parameters was analysed. Results Patients with shoulder pain showed significantly worse results in measurements of postural stability right/left (p < 0.01) and front/back (p < 0.01) as well as balance ability right/left (p = 0.01) and front/back (p < 0.01) compared to healthy controls. There were no significant group differences with regard to symmetry index. However, there was a significant (p < 0.01) symmetry shift towards the affected side within the shoulder pain group. There was no correlation between pain intensity and measurements of balance ability or postural stability. Likewise, no correlation between BMI and deficiencies in balance ability and postural stability was established. Conclusions Patients with pathological shoulder pain (> 4 months) have deficiencies in balance ability and postural stability; however the underlying mechanisms for this remain unclear. Neither pain intensity nor BMI influenced the outcome parameters. Patients with shoulder pain shift their weight to the affected side. Further research is needed to determine if

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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

  18. 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.

  19. 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.

  20. How the local geometry of the Cu-binding site determines the thermal stability of blue copper proteins.

    PubMed

    Chaboy, Jesús; Díaz-Moreno, Sofía; Díaz-Moreno, I; De la Rosa, Miguel A; Díaz-Quintana, Antonio

    2011-01-28

    Identifying the factors that govern the thermal resistance of cupredoxins is essential for understanding their folding and stability, and for improving our ability to design highly stable enzymes with potential biotechnological applications. Here, we show that the thermal unfolding of plastocyanins from two cyanobacteria--the mesophilic Synechocystis and the thermophilic Phormidium--is closely related to the short-range structure around the copper center. Cu K-edge X-ray absorption spectroscopy shows that the bond length between Cu and the S atom from the cysteine ligand is a key structural factor that correlates with the thermal stability of the cupredoxins in both oxidized and reduced states. These findings were confirmed by an additional study of a site-directed mutant of Phormidium plastocyanin showing a reverse effect of the redox state on the thermal stability of the protein.

  1. 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

  2. A test of the transition-metal nanocluster formation and stabilization ability of the most common polymeric stabilizer, poly(vinylpyrrolidone), as well as four other polymeric protectants.

    PubMed

    Ott, Lisa Starkey; Hornstein, Brooks J; Finke, Richard G

    2006-10-24

    Following an introduction to the nanocluster stabilization literature and DLVO (Derjaugin-Landau-Verwey-Overbeek) theory of colloidal stability, the most common steric stabilizer of transition-metal nanoclusters, poly(vinylpyrrolidone) (PVP), has been examined for its efficacy in the formation, stabilization, and subsequent catalytic activity of prototype, test case Ir(0)n nanoclusters. First, the five criteria established previously for ranking nanocluster protectants for their nanocluster formation and stabilization ability were evaluated for 1 monomer equiv of 10000 average molecular weight (MWav) PVP in the absence, and then presence, of the traditionally weakly coordinating anion BF4- as well as the absence and presence of the strongly coordinating, superior anionic stabilizer P2W15Nb3O62(9-), all in propylene carbonate solvent. It is found that neither 1 equiv of BF4- in propylene carbonate nor 1 monomer equiv of (undried) PVP alone allows for isolable and redissolvable nanoclusters without bulk Ir(0)n metal formation. Careful predrying of the PVP, and by implication other polymers, is shown to be necessary for the formation and stabilization of the nanoclusters. Next, 40 monomer equiv of 10000 MWav PVP and 1 equiv of BF4- in propylene carbonate are shown to allow isolable, redissolvable nanoclusters. Control experiments reveal little difference on nanocluster stabilization by 3500 or 55000 (i.e., vs 10,000) MWav PVP, but yield interesting effects on nanocluster nucleation by the 3500 MWav PVP, as well as by the polymer poly(bis(ethoxy)phosphazene) (PBEP). Four other key polymers reported in the literature to be nanocluster stabilizers are tested by the five criteria method for their efficacy in the formation and stabilization of Ir0n nanoclusters (now in acetone due to the polymers' solubility) and in comparison to each other, specifically, poly(methyl methacrylate) (PMMA), poly(styrene) (PS), poly(methylhydrosilane) (PMHS), and PBEP. Only 40 monomer equiv

  3. Application of a Physics-Based Stabilization Criterion to Flight System Thermal Testing

    NASA Technical Reports Server (NTRS)

    Baker, Charles; Garrison, Matthew; Cottingham, Christine; Peabody, Sharon

    2010-01-01

    The theory shown here can provide thermal stability criteria based on physics and a goal steady state error rather than on an arbitrary "X% Q/mC(sub P)" method. The ability to accurately predict steady-state temperatures well before thermal balance is reached could be very useful during testing. This holds true for systems where components are changing temperature at different rates, although it works better for the components closest to the sink. However, the application to these test cases shows some significant limitations: This theory quickly falls apart if the thermal control system in question is tightly coupled to a large mass not accounted for in the calculations, so it is more useful in subsystem-level testing than full orbiter tests. Tight couplings to a fluctuating sink causes noise in the steady state temperature predictions.

  4. 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.

  5. 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

  6. 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

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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

  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. 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.

  18. 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.

  19. 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}.

  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. 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

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. "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.

  11. 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.

  12. 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.

  13. Effects of Pilates core stability exercises on the balance abilities of archers

    PubMed Central

    Park, Jeong-Min; Hyun, Gwang-Suk; Jee, Yong-Seok

    2016-01-01

    This study aimed to provide fundamental data contributing to archery performance improvement and stabilization of shooting posture in archers by examining the influence of Pilates core stability (PCS) exercises on dynamic and static balance. The study was conducted from December 2015 to March 2016 on high school archers who were registered as archers in the Korea Archery Association with 5 or more years of archery experience. Twenty voluntary subjects (exercise group n=10; control group n=10) with an understanding toward the aims of this study were selected and their body composition, static and dynamic balance abilities, before and after the PCS program, were measured. As for the static balance ability, there were no significant differences between pre- and postvalues in the exercise group after completing the PCS program. Similarly, these results were also represented in the control group. In the aspect of comparisons between postvalues in both groups, there were significant improvements in only the exercise group. As for the dynamic balance ability, there were significant differences between pre- and postvalues in the exercise group, except for up-right and left postures, whereas, there were no changes or decreases between pre- and postvalues in the control group after completing the PCS program. Meanwhile, in the aspect of comparisons between postvalues in both groups, there were significant improvements in up, and up right, and down right part and overall dynamic scores of the exercise groups. PMID:28119877

  14. Effects of Pilates core stability exercises on the balance abilities of archers.

    PubMed

    Park, Jeong-Min; Hyun, Gwang-Suk; Jee, Yong-Seok

    2016-12-01

    This study aimed to provide fundamental data contributing to archery performance improvement and stabilization of shooting posture in archers by examining the influence of Pilates core stability (PCS) exercises on dynamic and static balance. The study was conducted from December 2015 to March 2016 on high school archers who were registered as archers in the Korea Archery Association with 5 or more years of archery experience. Twenty voluntary subjects (exercise group n=10; control group n=10) with an understanding toward the aims of this study were selected and their body composition, static and dynamic balance abilities, before and after the PCS program, were measured. As for the static balance ability, there were no significant differences between pre- and postvalues in the exercise group after completing the PCS program. Similarly, these results were also represented in the control group. In the aspect of comparisons between postvalues in both groups, there were significant improvements in only the exercise group. As for the dynamic balance ability, there were significant differences between pre- and postvalues in the exercise group, except for up-right and left postures, whereas, there were no changes or decreases between pre- and postvalues in the control group after completing the PCS program. Meanwhile, in the aspect of comparisons between postvalues in both groups, there were significant improvements in up, and up right, and down right part and overall dynamic scores of the exercise groups.

  15. 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

  16. Habitat stability affects dispersal and the ability to track climate change.

    PubMed

    Hof, Christian; Brändle, Martin; Dehling, D Matthias; Munguía, Mariana; Brandl, Roland; Araújo, Miguel B; Rahbek, Carsten

    2012-08-23

    Habitat persistence should influence dispersal ability, selecting for stronger dispersal in habitats of lower temporal stability. As standing (lentic) freshwater habitats are on average less persistent over time than running (lotic) habitats, lentic species should show higher dispersal abilities than lotic species. Assuming that climate is an important determinant of species distributions, we hypothesize that lentic species should have distributions that are closer to equilibrium with current climate, and should more rapidly track climatic changes. We tested these hypotheses using datasets from 1988 and 2006 containing all European dragon- and damselfly species. Bioclimatic envelope models showed that lentic species were closer to climatic equilibrium than lotic species. Furthermore, the models over-predicted lotic species ranges more strongly than lentic species ranges, indicating that lentic species track climatic changes more rapidly than lotic species. These results are consistent with the proposed hypothesis that habitat persistence affects the evolution of dispersal.

  17. The effect of free radical inhibitor on the sensitized radiation crosslinking and thermal processing stabilization of polyurethane shape memory polymers.

    PubMed

    Hearon, Keith; Smith, Sarah E; Maher, Cameron A; Wilson, Thomas S; Maitland, Duncan J

    2013-02-01

    The effects of free radical inhibitor on the electron beam crosslinking and thermal processing stabilization of novel radiation crosslinkable polyurethane shape memory polymers (SMPs) blended with acrylic radiation sensitizers have been determined. The SMPs in this study possess novel processing capabilities-that is, the ability to be melt processed into complex geometries as thermoplastics and crosslinked in a secondary step using electron beam irradiation. To increase susceptibility to radiation crosslinking, the radiation sensitizer pentaerythritol triacrylate (PETA) was solution blended with thermoplastic polyurethane SMPs made from 2-butene-1,4-diol and trimethylhexamethylene diisocyanate (TMHDI). Because thermoplastic melt processing methods such as injection molding are often carried out at elevated temperatures, sensitizer thermal instability is a major processing concern. Free radical inhibitor can be added to provide thermal stabilization; however, inhibitor can also undesirably inhibit radiation crosslinking. In this study, we quantified both the thermal stabilization and radiation crosslinking inhibition effects of the inhibitor 1,4-benzoquinone (BQ) on polyurethane SMPs blended with PETA. Sol/gel analysis of irradiated samples showed that the inhibitor had little to no inverse effects on gel fraction at concentrations of 0-10,000 ppm, and dynamic mechanical analysis showed only a slight negative correlation between BQ composition and rubbery modulus. The 1,4-benzoquinone was also highly effective in thermally stabilizing the acrylic sensitizers. The polymer blends could be heated to 150°C for up to five hours or to 125°C for up to 24 hours if stabilized with 10,000 ppm BQ and could also be heated to 125°C for up to 5 hours if stabilized with 1000 ppm BQ without sensitizer reaction occurring. We believe this study provides significant insight into methods for manipulation of the competing mechanisms of radiation crosslinking and thermal stabilization

  18. The effect of free radical inhibitor on the sensitized radiation crosslinking and thermal processing stabilization of polyurethane shape memory polymers

    PubMed Central

    Hearon, Keith; Smith, Sarah E.; Maher, Cameron A.; Wilson, Thomas S.; Maitland, Duncan J.

    2012-01-01

    The effects of free radical inhibitor on the electron beam crosslinking and thermal processing stabilization of novel radiation crosslinkable polyurethane shape memory polymers (SMPs) blended with acrylic radiation sensitizers have been determined. The SMPs in this study possess novel processing capabilities—that is, the ability to be melt processed into complex geometries as thermoplastics and crosslinked in a secondary step using electron beam irradiation. To increase susceptibility to radiation crosslinking, the radiation sensitizer pentaerythritol triacrylate (PETA) was solution blended with thermoplastic polyurethane SMPs made from 2-butene-1,4-diol and trimethylhexamethylene diisocyanate (TMHDI). Because thermoplastic melt processing methods such as injection molding are often carried out at elevated temperatures, sensitizer thermal instability is a major processing concern. Free radical inhibitor can be added to provide thermal stabilization; however, inhibitor can also undesirably inhibit radiation crosslinking. In this study, we quantified both the thermal stabilization and radiation crosslinking inhibition effects of the inhibitor 1,4-benzoquinone (BQ) on polyurethane SMPs blended with PETA. Sol/gel analysis of irradiated samples showed that the inhibitor had little to no inverse effects on gel fraction at concentrations of 0-10,000 ppm, and dynamic mechanical analysis showed only a slight negative correlation between BQ composition and rubbery modulus. The 1,4-benzoquinone was also highly effective in thermally stabilizing the acrylic sensitizers. The polymer blends could be heated to 150°C for up to five hours or to 125°C for up to 24 hours if stabilized with 10,000 ppm BQ and could also be heated to 125°C for up to 5 hours if stabilized with 1000 ppm BQ without sensitizer reaction occurring. We believe this study provides significant insight into methods for manipulation of the competing mechanisms of radiation crosslinking and thermal

  19. The effect of free radical inhibitor on the sensitized radiation crosslinking and thermal processing stabilization of polyurethane shape memory polymers

    NASA Astrophysics Data System (ADS)

    Hearon, Keith; Smith, Sarah E.; Maher, Cameron A.; Wilson, Thomas S.; Maitland, Duncan J.

    2013-02-01

    The effects of free radical inhibitor on the electron beam crosslinking and thermal processing stabilization of novel radiation crosslinkable polyurethane shape memory polymers (SMPs) blended with acrylic radiation sensitizers have been determined. The SMPs in this study possess novel processing capabilities—that is, the ability to be melt processed into complex geometries as thermoplastics and crosslinked in a secondary step using electron beam irradiation. To increase susceptibility to radiation crosslinking, the radiation sensitizer pentaerythritol triacrylate (PETA) was solution blended with thermoplastic polyurethane SMPs made from 2-butene-1,4-diol and trimethylhexamethylene diisocyanate (TMHDI). Because the thermoplastic melt processing methods such as injection molding are often carried out at elevated temperatures, sensitizer thermal instability is a major processing concern. Free radical inhibitor can be added to provide thermal stabilization; however, inhibitor can also undesirably inhibit radiation crosslinking. In this study, we quantified both the thermal stabilization and radiation crosslinking inhibition effects of the inhibitor 1,4-benzoquinone (BQ) on polyurethane SMPs blended with PETA. Sol/gel analysis of irradiated samples showed that the inhibitor had little to no inverse effects on gel fraction at concentrations of 0-10,000 ppm, and dynamic mechanical analysis showed only a slight negative correlation between BQ composition and rubbery modulus. The 1,4-benzoquinone was also highly effective in thermally stabilizing the acrylic sensitizers. The polymer blends could be heated to 150 °C for up to 5 h or to 125 °C for up to 24 h if stabilized with 10,000 ppm BQ and could also be heated to 125 °C for up to 5 h if stabilized with 1000 ppm BQ without sensitizer reaction occurring. We believe this study provides significant insight into methods for manipulation of the competing mechanisms of radiation crosslinking and thermal stabilization of

  20. 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.

  1. 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.

  2. 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.

  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 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.

  5. 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

  6. 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.

  7. 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.

  8. Stability and Sugar Recognition Ability of Ricin-Like Carbohydrate Binding Domains

    SciTech Connect

    Yao, Jianzhuang; Nellas, Ricky B; Glover, Mary M; Shen, Tongye

    2011-01-01

    Lectins are a class of proteins known for their novel binding to saccharides. Understanding this sugar recognition process can be crucial in creating structure-based designs of proteins with various biological roles. We focus on the sugar binding of a particular lectin, ricin, which has two -trefoil carbohydrate-binding domains (CRDs) found in several plant protein toxins. The binding ability of possible sites of ricin-like CRD has been puzzling. The apo and various (multiple) ligand-bound forms of the sugar-binding domains of ricin were studied by molecular dynamics simulations. By evaluating structural stability, hydrogen bond dynamics, flexibility, and binding energy, we obtained a detailed picture of the sugar recognition of the ricin-like CRD. Unlike what was previously believed, we found that the binding abilities of the two known sites are not independent of each other. The binding ability of one site is positively affected by the other site. While the mean positions of different binding scenarios are not altered significantly, the flexibility of the binding pockets visibly decreases upon multiple ligand binding. This change in flexibility seems to be the origin of the binding cooperativity. All the hydrogen bonds that are strong in the monoligand state are also strong in the double-ligand complex, although the stability is much higher in the latter form due to cooperativity. These strong hydrogen bonds in a monoligand state are deemed to be the essential hydrogen bonds. Furthermore, by examining the structural correlation matrix, the two domains are structurally one entity. Galactose hydroxyl groups, OH4 and OH3, are the most critical parts in both site 1 and site 2 recognition.

  9. 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

  10. 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.

  11. 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.

  12. Thermal stability of lightweight graphite glass sandwich reflectors for far infrared astronomy

    NASA Technical Reports Server (NTRS)

    Bluege, J. H.; Mayor, R. A.; Hoffman, W. F.

    1986-01-01

    Graphite fiber-reinforced glass matrix composites are being developed for a variety of structural applications requiring excellent thermomechanical stability. These materials are ideally suited for lightweight, high strength, thermally stable infrared mirrors because of their low density, low thermal expansion, high strength and stiffness, and their ability to be machined, replicated and figured using standard polishing techniques. These properties are particularly promising for applications such as a 3-meter balloon-borne far-infrared and submillimeter telescope mirror which must be both very lightweight and able to retain its figure accuracy when cycled between room temperature and its operating temperature of -50 C. This paper presents the results of a set of low temperature optical tests conducted to determine the figure stability of a 30-cm diameter, frit-bonded graphite/glass mirror in the +20 to -60 C temperature range using a 10.6 micron laser interferometer. The results indicate that the residual change in figure was less than 0.3 microns, rms.

  13. Physicochemical properties and thermal stability of Lep w 1, the major allergen of whiff.

    PubMed

    Griesmeier, Ulrike; Bublin, Merima; Radauer, Christian; Vázquez-Cortés, Sonia; Ma, Yan; Fernández-Rivas, Montserrat; Breiteneder, Heimo

    2010-06-01

    Whiff (Lepidorhombus whiffiagonis) is a fish frequently consumed in Spain. Lep w 1, its major allergen, is a calcium-binding beta-parvalbumin. The resistance of Lep w 1 to heat denaturation and to digestion were studied by circular dichroism spectroscopy and by in vitro gastric digestion systems. Purified Lep w 1 was thermally stable up to 65 degrees C at neutral pH. Calcium depletion resulted in a change of its structure as determined by circular dichroism spectroscopy. A partial loss of structure was also observed at acidic pH; however, the allergen retained its full IgE-binding ability. The partially denatured Lep w 1 was easily digested by pepsin within 2 min. Further, the IgE reactivity of proteins extracted from cooked fish and their stability to proteolysis were analyzed. The extract revealed a higher number of IgE reactive bands than an extract from uncooked fish. IgE binding to these proteins could not be inhibited by an extract from uncooked fish. In contrast to a raw fish extract, the cooked extract showed higher resistance to pepsinolysis. The stability of Lep w 1 to thermal denaturation and digestion explains the high allergenicity of whiff.

  14. Gas uptake and thermal stability analysis of boron nitride and carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Guan, Mengyu

    Carbon nanotubes (CNTs) exist in many forms and can have critical pore diameters on the angstrom length scale, making them suitable for molecular capture. By combining the porous structure of CNTs with the chemical stability of carbide and/or nitride materials, one can create a more robust, nanoporous material for gas capture in high temperature conditions. Boron nitride nanotubes (BNNTs) are more chemically and thermally robust than pure CNTs, and were synthesized using CNTs as a structural precursor. However, this reaction mechanism was found to be unfavorable to produce high-yield and purity BNNTs. Adsorption tests using gases of interest (N2, He) were performed on commercial CNTs and BNNTs to determine their porosity and gas uptake abilities. Their thermal stability and oxidation resistance when heated up to 1773 K in air was also studied using differential scanning calorimetry and thermogravimetric analysis. While the CNTs began to oxidize between 450 °C and 750 °C, depending on the nanotube diameter, the BNNTs remained stable up until 1000 °C.

  15. Gait Adaptability Training Improves Both Postural Stability and Dual-Tasking Ability

    NASA Technical Reports Server (NTRS)

    Brady, Rachel A.; Batson, Crystal D.; Peters, Brian T.; Ploutz-Snyder, Robert J.; Mulavara, Ajitkumar P.; Bloomberg, Jacob J.

    2010-01-01

    After spaceflight, the process of readapting to Earth's gravity commonly presents crewmembers with a variety of locomotor challenges. Our recent work has shown that the ability to adapt to a novel discordant sensorimotor environment can be increased through preflight training, so one focus of our laboratory has been the development of a gait training countermeasure to expedite the return of normal locomotor function after spaceflight. We used a training system comprising a treadmill mounted on a motion base facing a virtual visual scene that provided a variety of sensory challenges. As part of their participation in a larger retention study, 10 healthy adults completed 3 training sessions during which they walked on a treadmill at 1.1 m/s while receiving discordant support-surface and visual manipulations. After a single training session, subjects stride frequencies improved, and after 2 training sessions their auditory reaction times improved, where improvement was indicated by a return toward baseline values. Interestingly, improvements in reaction time came after stride frequency improvements plateaued. This finding suggests that postural stability was given a higher priority than a competing cognitive task. Further, it demonstrates that improvement in both postural stability and dual-tasking can be achieved with multiple training exposures. We conclude that, with training, individuals become more proficient at walking in discordant sensorimotor conditions and are able to devote more attention to competing tasks.

  16. 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.

  17. 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

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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

    The synthesis of novel hexagonal ReB{sub 2}-type OsB{sub 2} ceramic powder was performed by high energy ball milling of elemental Os and B powders. Two different sources of B powder have been used for this mechanochemical synthesis. One B powder consisted of a mixture of amorphous and crystalline phases and a mixture of {sup 10}B and {sup 11}B isotopes with a fine particle size, while another B powder was a purely crystalline (rhombohedral) material consisting of enriched {sup 11}B isotope with coarse particle size. The same Os powder was used for the synthesis in both cases. It was established that, in the first case, the hexagonal OsB{sub 2} phase was the main product of synthesis with a small quantity of Os{sub 2}B{sub 3} phase present after synthesis as an intermediate product. In the second case, where coarse crystalline {sup 11}B powder was used as a raw material, only Os{sub 2}B{sub 3} boride was synthesized mechanochemically. The thermal stability of hexagonal OsB{sub 2} powder was studied by heating under argon up to 876 °C and cooling in vacuo down to −225 °C. During the heating, the sacrificial reaction 2OsB{sub 2}+3O{sub 2}→2Os+2B{sub 2}O{sub 3} took place due to presence of O{sub 2}/water vapor molecules in the heating chamber, resulting in the oxidation of B atoms and formation of B{sub 2}O{sub 3} and precipitation of Os metal out of the OsB{sub 2} lattice. As a result of such phase changes during heating, the lattice parameters of hexagonal OsB{sub 2} changed significantly. The shrinkage of the a lattice parameter was recorded in 276–426 °C temperature range upon heating, which was attributed to the removal of B atoms from the OsB{sub 2} lattice due to oxidation followed by the precipitation of Os atoms and formation of Os metal. While significant structural changes occurred upon heating due to presence of O{sub 2}, the hexagonal OsB{sub 2} ceramic demonstrated good phase stability upon cooling in vacuo with linear shrinkage of the lattice

  4. 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

  5. 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.

  6. 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.

  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. 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.

  9. 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.

  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. 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.

  12. 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

  13. 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.

  14. 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.

  15. 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.

  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

    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

  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. 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.

  20. Stability and Change in Executive Function Abilities from Late Adolescence to Early Adulthood: A Longitudinal Twin Study

    ERIC Educational Resources Information Center

    Friedman, Naomi P.; Miyake, Akira; Altamirano, Lee J.; Corley, Robin P.; Young, Susan E.; Rhea, Sally Ann; Hewitt, John K.

    2016-01-01

    Executive functions (EFs)--the higher level cognitive abilities that enable us to control our own thoughts and actions--continue to develop into early adulthood, yet no longitudinal study has examined their stability during the important life transition from late adolescence to young adulthood. In this twin study (total N = 840 individuals from…

  1. 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.

  2. 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.

  3. 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.

  4. Thermal Stability of Residual Stresses in Ti-6Al-4V components

    NASA Astrophysics Data System (ADS)

    Stanojevic, A.; Angerer, P.; Oberwinkler, B.

    2016-03-01

    The need for light weight design while maintaining a high safety is essential for many components, especially in the aircraft industry. Therefore, it's important to consider every aspect to reduce weight, improve fatigue life and maintain safety of crucial components. Residual stresses are a major factor which can positively influence components and fulfil all three requirements. However, due to the inconstancy of the behaviour of residual stresses during the life time of a component, residual stresses are often neglected. If the behaviour of residual stresses could be described reliably over the entire life time of a component, residual stresses could be taken into account and components could be optimized even further. Mechanical and thermal loads are the main reason for relaxation of residual stresses. This work covers the thermal stability of residual stresses in Ti-6Al-4V components. Therefore, exposure tests at raised temperatures were performed on specimens with different surface conditions. Residual stresses were measured by x-ray diffraction before and after testing. Creep tests were also carried out to describe the creep behaviour and thereby the ability for residual stress relaxation. A correlation between the creep rate and amount of relaxed stress was found. The creep behaviour of the material was described by using a combination of the Norton Power law and the Arrhenius equation. The Zener-Wert-Avrami model was used to describe the residual stress relaxation. With these models a satisfying correlation between measured and calculated data was found. Hence, the relaxation of residual stresses due to thermal load was described reliably.

  5. 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.

  6. Influence of the thickness on the morphology and sensing ability of thermally-deposited tellurium films

    NASA Astrophysics Data System (ADS)

    Hristova-Vasileva, T.; Bineva, I.; Dinescu, A.; Nesheva, D.; Arsova, D.; Pejova, B.

    2016-03-01

    Tellurium films with nominal thicknesses of 30, 90 and 300 nm were prepared by thermal evaporation in vacuum at a low deposition rate of 0.3 nm/s. The morphology evolution with the increase of the film thickness was observed by scanning electron microscopy and atomic force microscopy. Nanorods with a width of about 40 nm were observed on the thinnest films surface. On the 90 nm thick films, the formations grew in priority in the z-direction to nanoblades with the same width, but a length of about 100 nm. The further increase of the thickness led to an increase of the 2D nanoobjects' width and length and formation of a stacked nanosheet structure. The surface root-mean-square roughness (Sq) increased with the thickness of the films. Preliminary investigations of the sensing ability of the as-deposited tellurium films with different thicknesses towards water (H2O), ethanol (C2H5OH), acetone (C3H5OH), and ammonia (NH3) vapors were performed by measuring the vapor-induced changes in the film dark current. The films showed appreciable response only to ammonia vapors; their sensitivity was almost equal for the 30 and 90 nm thick films, and decreased significantly for the film tkness of 300 nm.

  7. The effect of physical parameters of inertial stabilization platform on disturbance rejection ability and its improvement method

    NASA Astrophysics Data System (ADS)

    Mao, Yao; Deng, Chao; Gan, Xun; Tian, Jing

    2015-10-01

    The development of space optical communication requires arcsecond precision or even higher precision of the tracking performance of ATP(Acquisition, Tracking and Pointing) system under the condition of base disturbance. ATP system supported by stabilized reference beam which is provided by inertial stabilization platform with high precision and high bandwidth, can effectively restrain the influence of base angular disturbance on the line of sight. To get better disturbance rejection ability, this paper analyzes the influence of transfer characteristics and physical parameters of stabilization platform on disturbance stabilization performance, the result shows that the stabilization characteristics of inertial stabilization platform equals to the product of rejection characteristics of control loop and disturbance transfer characteristics of the platform, and improving isolation characteristics of the platform or extending control bandwidth can both achieve the result of getting a better rejection ability. Limited by factors such as mechanical characteristics of stabilization platform, bandwidth/noise of the sensor, and so on, as the control bandwidth of the LOS stabilization platform is limited, and high frequency disturbance can not be effectively rejected, so the rejection of high frequency disturbance mainly depends on the isolation characteristics of the platform itself. This paper puts forward three methods of improving the isolation characteristics of the platform itself, which includes 1) changing mechanical structure, such as reducing elastic coefficient, increasing moment of inertia of the platform, and so on; 2) changing electrical structure of the platform, such as increasing resistance, adding current loop, and so on; 3)adding a passive vibration isolator between the inertial stabilization platform and the base. The result of the experiment shows that adding current loop or adding a passive vibration isolator can effectively reject high frequency

  8. 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

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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

  16. 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.

  17. 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.

  18. 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

  19. The effects of buffers and pH on the thermal stability, unfolding and substrate binding of RecA.

    PubMed

    Metrick, Michael A; Temple, Joshua E; MacDonald, Gina

    2013-12-31

    The Escherichia coli protein RecA is responsible for catalysis of the strand transfer reaction used in DNA repair and recombination. Previous studies in our lab have shown that high concentrations of salts stabilize RecA in a reverse-anionic Hofmeister series. Here we investigate how changes in pH and buffer alter the thermal unfolding and cofactor binding. RecA in 20mM HEPES, MES, Tris and phosphate buffers was studied in the pH range from 6.5 to 8.5 using circular dichroism (CD), infrared (IR) and fluorescence spectroscopies. The results show all of the buffers studied stabilize RecA up to 50°C above the Tris melting temperature and influence RecA's ability to nucleate on double-stranded DNA. Infrared and CD spectra of RecA in the different buffers do not show that secondary structural changes are associated with increased stability or decreased ability to nucleate on dsDNA. These results suggest the differences in stability arise from decreasing positive charge and/or buffer interactions.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. A single mutation within a Ca(2+) binding loop increases proteolytic activity, thermal stability, and surfactant stability.

    PubMed

    Okuda, Mitsuyoshi; Ozawa, Tadahiro; Tohata, Masatoshi; Sato, Tsuyoshi; Saeki, Katsuhisa; Ozaki, Katsuya

    2013-03-01

    We improved the enzymatic properties of the oxidatively stable alkaline serine protease KP-43 through protein engineering to make it more suitable for use in laundry detergents. To enhance proteolytic activity, the gene encoding KP-43 was mutagenized by error-prone PCR. Screening identified a Tyr195Cys mutant enzyme that exhibited increased specific activity toward casein between pH 7 and 11. At pH 10, the mutant displayed 1.3-fold higher specific activity for casein compared to the wild-type enzyme, but the activity of the mutant was essentially unchanged toward several synthetic peptides. Furthermore, the Tyr195Cys mutation significantly increased thermal stability and surfactant stability of the enzyme under oxidizing conditions. Examination of the crystal structure of KP-43 revealed that Tyr195 is a solvent exposed residue that forms part of a flexible loop that binds a Ca(2+) ion. This residue lies 15-20Å away from the residues comprising the catalytic triad of the enzyme. These results suggest that the substitution at position 195 does not alter the structure of the active center, but instead may affect a substrate-enzyme interaction. We propose that the Tyr195Cys mutation enhances the interaction with Ca(2+) and affects the packing of the Ca(2+) binding loop, consequently increasing protein stability. The simultaneously increased proteolytic activity, thermal stability, and surfactant stability of the Tyr195Cys mutant enzyme make the protein an ideal candidate for laundry detergent application.

  8. The Stability of IQ in People with Low Intellectual Ability: An Analysis of the Literature

    ERIC Educational Resources Information Center

    Whitaker, Simon

    2008-01-01

    A meta-analysis of the stability of low IQ (IQ less than 80) was performed on IQ tests that have been commonly used--tests that were derived by D. Wechsler (1949, 1955, 1974, 1981, 1991, 1997) and those based on the Binet scales (L. M. Terman, 1960; L. M. Terman & Merrill, 1972). Weighted-mean stability coefficients of 0.77 and 0.78 were found…

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. Stabilized FE simulation of prototype thermal-hydraulics problems with integrated adjoint-based capabilities

    NASA Astrophysics Data System (ADS)

    Shadid, J. N.; Smith, T. M.; Cyr, E. C.; Wildey, T. M.; Pawlowski, R. P.

    2016-09-01

    A critical aspect of applying modern computational solution methods to complex multiphysics systems of relevance to nuclear reactor modeling, is the assessment of the predictive capability of specific proposed mathematical models. In this respect the understanding of numerical error, the sensitivity of the solution to parameters associated with input data, boundary condition uncertainty, and mathematical models is critical. Additionally, the ability to evaluate and or approximate the model efficiently, to allow development of a reasonable level of statistical diagnostics of the mathematical model and the physical system, is of central importance. In this study we report on initial efforts to apply integrated adjoint-based computational analysis and automatic differentiation tools to begin to address these issues. The study is carried out in the context of a Reynolds averaged Navier-Stokes approximation to turbulent fluid flow and heat transfer using a particular spatial discretization based on implicit fully-coupled stabilized FE methods. Initial results are presented that show the promise of these computational techniques in the context of nuclear reactor relevant prototype thermal-hydraulics problems.

  16. Stabilized FE simulation of prototype thermal-hydraulics problems with integrated adjoint-based capabilities

    SciTech Connect

    Shadid, J.N.; Smith, T.M.; Cyr, E.C.; Wildey, T.M.; Pawlowski, R.P.

    2016-09-15

    A critical aspect of applying modern computational solution methods to complex multiphysics systems of relevance to nuclear reactor modeling, is the assessment of the predictive capability of specific proposed mathematical models. In this respect the understanding of numerical error, the sensitivity of the solution to parameters associated with input data, boundary condition uncertainty, and mathematical models is critical. Additionally, the ability to evaluate and or approximate the model efficiently, to allow development of a reasonable level of statistical diagnostics of the mathematical model and the physical system, is of central importance. In this study we report on initial efforts to apply integrated adjoint-based computational analysis and automatic differentiation tools to begin to address these issues. The study is carried out in the context of a Reynolds averaged Navier–Stokes approximation to turbulent fluid flow and heat transfer using a particular spatial discretization based on implicit fully-coupled stabilized FE methods. Initial results are presented that show the promise of these computational techniques in the context of nuclear reactor relevant prototype thermal-hydraulics problems.

  17. Stabilized FE simulation of prototype thermal-hydraulics problems with integrated adjoint-based capabilities

    SciTech Connect

    Shadid, J. N.; Smith, T. M.; Cyr, E. C.; Wildey, T. M.; Pawlowski, R. P.

    2016-05-20

    A critical aspect of applying modern computational solution methods to complex multiphysics systems of relevance to nuclear reactor modeling, is the assessment of the predictive capability of specific proposed mathematical models. The understanding of numerical error, the sensitivity of the solution to parameters associated with input data, boundary condition uncertainty, and mathematical models is critical. Additionally, the ability to evaluate and or approximate the model efficiently, to allow development of a reasonable level of statistical diagnostics of the mathematical model and the physical system, is of central importance. In our study we report on initial efforts to apply integrated adjoint-based computational analysis and automatic differentiation tools to begin to address these issues. The study is carried out in the context of a Reynolds averaged Navier–Stokes approximation to turbulent fluid flow and heat transfer using a particular spatial discretization based on implicit fully-coupled stabilized FE methods. We present the initial results that show the promise of these computational techniques in the context of nuclear reactor relevant prototype thermal-hydraulics problems.

  18. Stabilized FE simulation of prototype thermal-hydraulics problems with integrated adjoint-based capabilities

    DOE PAGES

    Shadid, J. N.; Smith, T. M.; Cyr, E. C.; ...

    2016-05-20

    A critical aspect of applying modern computational solution methods to complex multiphysics systems of relevance to nuclear reactor modeling, is the assessment of the predictive capability of specific proposed mathematical models. The understanding of numerical error, the sensitivity of the solution to parameters associated with input data, boundary condition uncertainty, and mathematical models is critical. Additionally, the ability to evaluate and or approximate the model efficiently, to allow development of a reasonable level of statistical diagnostics of the mathematical model and the physical system, is of central importance. In our study we report on initial efforts to apply integrated adjoint-basedmore » computational analysis and automatic differentiation tools to begin to address these issues. The study is carried out in the context of a Reynolds averaged Navier–Stokes approximation to turbulent fluid flow and heat transfer using a particular spatial discretization based on implicit fully-coupled stabilized FE methods. We present the initial results that show the promise of these computational techniques in the context of nuclear reactor relevant prototype thermal-hydraulics problems.« less

  19. 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

  20. Ability of Low-Cost Force-Feedback Device to Influence Postural Stability.

    PubMed

    Baud-Bovy, Gabriel; Tatti, Fabio; Borghese, Nunzio A

    2015-01-01

    Low-cost gaming technology offers promising devices for the rehabilitation of stroke patients at home. While several attempts have been made to use low-cost motion tracking devices (Kinect) or balance boards (Wii Board), the potential of low-cost haptic devices has yet to be explored in this context. The objective of this study was to investigate whether it is possible to influence postural stability with a low-cost device despite its technical limitations, and to explore the most promising modes of haptic interaction to increase and decrease postural stability. Two groups of younger subjects used a high-end (Omega.3) and a low-cost (Falcon) device respectively. A third group of older subjects used the Falcon. We show that light touch contact with the device improves stability, whereas the force tasks decrease it. The effects of the different tasks are consistent in the two age groups. Although there are differences in the participants' interaction with the two devices, the effect of the devices on postural stability is comparable. We conclude that a low-cost haptic device can be used to increase or decrease postural stability of healthy subjects with an age similar to that of typical stroke patients, in a safe and controllable way.

  1. 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

  2. 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.

  3. Thermal stability and 2.7 μm spectroscopic properties in Er3+ doped tellurite glasses

    NASA Astrophysics Data System (ADS)

    Tian, Ying; Li, Bingpeng; Chen, Rong; Xia, Jienan; Jing, Xufeng; Zhang, Junjie; Xu, Shiqing

    2016-10-01

    In present paper, the thermal stability and 2.7 μm spectroscopic properties in Er3+ doped tellurite glasses have been investigated by 980 nm laser diode pumping. Thermal analysis indicates that GeO2 modified tellurite glass has better thermal stability and anti-crystallization ability. Judd-Ofelt intensity parameters are calculated and discussed to examine the covalency characteristics based on absorption spectra. The 2.7 μm fluorescence is obtained and the lifetime can reach 124 ± 1 μs with the quantum efficiency of 61.5% in prepared samples. Moreover, higher effective emission bandwidth (136.67 nm), emission cross sections (12.75 × 10-21 cm2) and radiative transition probability (95.66s-1) at 2.7 μm are achieved. In addition, upconversion and near-infrared emission spectra are measured to elucidate energy transfer mechanism of Er3+. The results suggest that the present tellurite glass modified by GeO2 might have promising applications in mid-infrared fiber lasers.

  4. 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.

  5. 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.

  6. 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

  7. 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.

  8. 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.

  9. Effects of pH on the ability of flavonoids to act as Pickering emulsion stabilizers.

    PubMed

    Luo, Zijun; Murray, Brent S; Ross, Anne-Lise; Povey, Malcolm J W; Morgan, Michael R A; Day, Andrea J

    2012-04-01

    The flavonoids tiliroside, rutin and naringin have been investigated as stabilizers of Pickering oil-in-water (O/W) emulsions. The mean droplet size of tetradecane emulsions was considerably smaller at higher pH, especially for rutin. The solubility of flavonoids in the aqueous phase was 4-6 times higher at pH 8 compared to pH 2 for tiliroside and rutin, although all absolute solubilities remained low (<1 mM). This agreed with a slight increase in surface activity of tiliroside and rutin at the O-W interface at pH 8 compared to pH 2. However, improved emulsion stabilization at higher pH is better explained by the significant increase in ζ-potential of the flavonoid particles to more negative values at pH 8, which will improve particle dispersion and increase the charge on the droplets stabilized by them. A buckwheat tea extract, rich in rutin, was also shown to be an effective stabilizer of sunflower O/W emulsions.

  10. Stability of Caregiver-Reported Manual Ability and Gross Motor Function Classifications of Cerebral Palsy

    ERIC Educational Resources Information Center

    Imms, Christine; Carlin, John; Eliasson, Ann-Christin

    2010-01-01

    Aim: To examine the stability of caregiver-reported classifications of function of children with cerebral palsy (CP) measured 12 months apart. Method: Participants were 86 children (50 males, 36 females) with CP of all motor types and severities who were recruited into a population-based longitudinal study. Children were aged 11 years 8 months (SD…

  11. 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

  12. 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.

  13. 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.

  14. 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

  15. 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.

  16. 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.

  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. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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'.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. The Vane Kindergarten Test: Temporal Stability And Ability to Predict Behavioral Criteria

    ERIC Educational Resources Information Center

    Powers, Sandra M.

    1977-01-01

    The Vane Kindergarten Test (VKT) is judged to have limited usefulness in early detection of learning handicaps for two reasons: (a) Its reliability is too low to allow discrimination between individuals, and (b) The ability of the VKT to predict problem behaviors is quite limited. (Author)

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. The stability of IQ in people with low intellectual ability: an analysis of the literature.

    PubMed

    Whitaker, Simon

    2008-04-01

    A meta-analysis of the stability of low IQ (IQ < 80) was performed on IQ tests that have been commonly used--tests that were derived by D. Wechsler (1949, 1955, 1974, 1981, 1991, 1997) and those based on the Binet scales (L. M. Terman, 1960; L. M. Terman & Merrill, 1972). Weighted-mean stability coefficients of .77 and .78 were found for Verbal IQ (V IQ) and Performance IQ (P IQ) on the Wechsler tests and .82 for Full-Scale IQ (FS IQ) on both Wechsler and Binet tests, for a mean test-retest interval of 2.8 years. Although the majority of FS IQs changed by less than 6 points, 14% changed by 10 points or more. The author suggests that the results of IQ assessment should be treated with more caution than previously thought.

  15. 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

  16. 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.

  17. 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).

  18. 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.

  19. 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.

  20. Roles of subcutaneous fat and thermoregulatory reflexes in determining ability to stabilize body temperature in water.

    PubMed Central

    Hayward, M G; Keatinge, W R

    1981-01-01

    1. The lowest water temperature in which different young adults could stabilize body temperature was found to vary from 32 degrees C to less than 12 degrees C, because of large differences in both total body insulation and metabolic heat production. 2. Total body insulation per unit surface area, in the coldest water allowing stability, was quite closely determined by mean subcutaneous fat thickness measured ultrasonically (r = 0.92), regardless of differences in distribution of this fat between men and women. 3. Reactive individuals developed high metabolic rates, and often rather high insulations in relation to fat thickness, which enabled them to stabilize their body temperatures in water more than 10 degrees C colder than was possible for less reactive individuals of similar fat thickness. 4. Measurements of heat flux, after stabilization in the coldest water possible, showed that the trunk was the main site of heat loss and that over half of the internal insulation there could be accounted for by subcutaneous fat; by contrast, fat could account for less than a third of higher insulations found in muscular parts of the limbs, and for less than 3% of very high insulations in the hands and feet. 5. After stabilization of body temperature at rest in the coldest possible water, exercise reduced internal insulation only in muscular parts of the limbs. Exercise also increased heat loss elsewhere by exposing skin of protected regions such as flexural surfaces of joints. During exercise total heat production increased rather more than heat loss in unreactive subjects, but less than loss in subjects whose heat production had already risen to a high level when they were at rest in cold water. 6. In warm (37 degrees C) water, tissue insulations were lower and much more uniform between subjects and between different body regions than in the cold. Even in the warm, however, insulations remained rather higher in fat than thin subjects, higher at rest than during exercise

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. Physical stability of drugs after storage above and below the glass transition temperature: Relationship to glass-forming ability.

    PubMed

    Alhalaweh, Amjad; Alzghoul, Ahmad; Mahlin, Denny; Bergström, Christel A S

    2015-11-10

    Amorphous materials are inherently unstable and tend to crystallize upon storage. In this study, we investigated the extent to which the physical stability and inherent crystallization tendency of drugs are related to their glass-forming ability (GFA), the glass transition temperature (Tg) and thermodynamic factors. Differential scanning calorimetry was used to produce the amorphous state of 52 drugs [18 compounds crystallized upon heating (Class II) and 34 remained in the amorphous state (Class III)] and to perform in situ storage for the amorphous material for 12h at temperatures 20°C above or below the Tg. A computational model based on the support vector machine (SVM) algorithm was developed to predict the structure-property relationships. All drugs maintained their Class when stored at 20°C below the Tg. Fourteen of the Class II compounds crystallized when stored above the Tg whereas all except one of the Class III compounds remained amorphous. These results were only related to the glass-forming ability and no relationship to e.g. thermodynamic factors was found. The experimental data were used for computational modeling and a classification model was developed that correctly predicted the physical stability above the Tg. The use of a large dataset revealed that molecular features related to aromaticity and π-π interactions reduce the inherent physical stability of amorphous drugs.

  7. 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.

  8. 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

  9. 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

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  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. 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.

  16. The effect of phytosterol concentration on oxidative stability and thermal polymerization of heated oils

    Technology Transfer Automated Retrieval System (TEKTRAN)

    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...

  17. 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.

  18. Stability and Change in Executive Function Abilities From Late Adolescence to Early Adulthood: A Longitudinal Twin Study

    PubMed Central

    Friedman, Naomi P.; Miyake, Akira; Altamirano, Lee J.; Corley, Robin P.; Young, Susan E.; Rhea, Sally Ann; Hewitt, John K.

    2015-01-01

    Executive functions (EFs) –– the higher-level cognitive abilities that enable us to control our own thoughts and actions –– continue to develop into early adulthood, yet no longitudinal study has examined their stability during the important life transition from late adolescence to young adulthood. In this twin study (total N=840 individuals from 424 families), we examined the stability of individual differences in three EF components across a six-year period, from approximately age 17 years (Wave 1) to 23 years (Wave 2). Specifically, we address the following questions: 1) How stable are individual differences in multiple EFs across this time period? And 2) What (genetic and/or environmental) influences affect stability and change in EFs? Results indicated that individual differences in EFs are quite stable across this time 6-year period (phenotypic latent variable correlations ranged from 0.86 to 1.0). However, there was evidence for change, particularly in the factor common to multiple EFs (Common EF). Multivariate twin models suggested that stability was due almost entirely to high genetic correlations across time; there was no new genetic variance at Wave 2. Change in Common EF was due to small but significant nonshared environmental influences at Wave 2 (15%). The results suggest that individual differences in EFs are quite heritable and stable by late adolescence, yet are still sensitive to environmental influences. PMID:26619323

  19. 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.

  20. 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

  1. Ambient effect on thermal stability of amorphous InGaZnO thin film transistors

    NASA Astrophysics Data System (ADS)

    Xu, Jianeng; Wu, Qi; Xu, Ling; Xie, Haiting; Liu, Guochao; Zhang, Lei; Dong, Chengyuan

    2016-12-01

    The thermal stability of amorphous InGaZnO thin film transistors (a-IGZO TFTs) with various ambient gases was investigated. The a-IGZO TFTs in air were more thermally stable than the devices in the ambient argon. Oxygen, rather than nitrogen and moisture, was responsible for this improvement. Furthermore, the thermal stability of the a-IGZO TFTs improved with the increasing oxygen content in the surrounding atmosphere. The related physical mechanism was examined, indicating that the higher ambient oxygen content induced more combinations of the oxygen vacancies and adsorbed oxygen ions in the a-IGZO, which resulted in the larger defect formation energy. This larger defect formation energy led to the smaller variation in the threshold voltage for the corresponding TFT devices.

  2. 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.

  3. 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

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. Ability of nonperturbative density-functional theories to stabilize arbitrary solids

    NASA Astrophysics Data System (ADS)

    Kyrlidis, Agathagelos; Brown, Robert A.

    1991-12-01

    The effects of solid structure and interatomic potential are investigated for density-functional theories based on the definition of a weighted or effective density for approximating the solid phase in terms of the uniform liquid. The introduction of solidlike structure to the modified-weighted-density-approximation (MWDA) theory of Denton and Ashcroft [Phys. Rev. A 39, 4701 (1989)] leads to loss of existence of the weighted density for a system of hard spheres. This behavior is more pronounced for loose crystalline structures, such as the diamond lattice. By contrast, the generalized-effective-liquid-approximation theory (GELA) of Lutsko and Baus [Phys. Rev. A 41, 6647 (1990)] always predicts single-valued weighted densities in the cases studied here. The thermodynamic mapping, which is the core of both of the MWDA and GELA approximations, is ineffective for Lennard-Jones fluids, according to a criterion for the relative stability of the solid phase evaluated using liquid-state information.

  10. Relation between dynamics, activity and thermal stability within the cholinesterase family.

    PubMed

    Trovaslet, Marie; Trapp, Marcus; Weik, Martin; Nachon, Florian; Masson, Patrick; Tehei, Moeava; Peters, Judith

    2013-03-25

    Incoherent neutron scattering is one of the most powerful tools for studying dynamics in biological matter. Using the cold neutron backscattering spectrometer IN16 at the Institut Laue Langevin (ILL, Grenoble, France), temperature dependence of cholinesterases' dynamics (human butyrylcholinesterase from plasma: hBChE; recombinant human acetylcholinesterase: hAChE and recombinant mouse acetylcholinesterase: mAChE) was examined using elastic incoherent neutron scattering (EINS). The dynamics was characterized by the averaged atomic mean square displacement (MSD), associated with the sample flexibility at a given temperature. We found MSD values of hAChE above the dynamical transition temperature (around 200K) larger than for mAChE and hBChE, implying that hAChE is more flexible than the other ChEs. Activation energies for thermodynamical transition were extracted through the frequency window model (FWM) (Becker et al. 2004) [1] and turned out to increase from hBChE to mAChE and finally to hAChE, inversely to the MSDs relations. Between 280 and 316K, catalytic studies of these enzymes were carried out using thiocholine esters: at the same temperature, the hAChE activity was systematically higher than the mAChE or hBChE ones. Our results thus suggest a strong correlation between dynamics and activity within the ChE family. We also studied and compared the ChEs thermal inactivation kinetics. Here, no direct correlation with the dynamics was observed, thus suggesting that relations between enzyme dynamics and catalytic stability are more complex. Finally, the possible relation between flexibility and protein ability to grow in crystals is discussed.

  11. CHEMICALLY VAPOR DEPOSITED YTTRIA-STABILIZED ZIRCONIA (YSZ) FOR THERMAL AND ENVIRONMENTAL BARRIER COATING

    SciTech Connect

    Varanasi, V.G.; Besmann, T.M.; Lothian, J.L.; Xu, W.; Starr, T.L.

    2003-04-22

    Yttria-stabilized zirconia (YSZ) is used as a thermal barrier coating (TBC) to protect super-alloy blades such as Mar-M247 or Rene-N5 during engine operation. The current method for YSZ fabrication for TBC applications is by air-plasma spraying (APS) or electron beam physical vapor deposition (EB-PVD) (Haynes 1997). APS gives reasonable deposition rates, but has a limited life and aging effects due to its porous and lamellar structure. The EB-PVD coatings are more stable and can accommodate thermomechanical stresses due to their characteristic strain-tolerant, columnar microstructure. EB-PVD, however, is primarily line-of-sight, which often leaves ''hidden areas'' uncoated, has low throughput, and has high capital cost. The process of metal-organic chemical vapor deposition (MOCVD) is investigated here as an economical alternative to EB-PVD and APS, with the potential for better overall coverage as well as the ability to produce thick (100-250 {micro}m), strain-tolerant, columnar coatings. MOCVD of YSZ involves the use of zirconium and yttrium organometallic precursors reacting with an oxygen source. Previous researchers have used diketonate or chloride precursors and oxygen (Wahl et al. 2001a, Wahl et al. 2001b, Yamane and Harai 1989). These precursors have low transport rates due to their low carrier solvent solubility (Varanasi et al. 2003). Solvated zirconium and yttrium butoxide precursors were investigated here due to their higher vapor pressures and high solvent solubility. This work uses predictive equilibrium modeling and experiments involving butoxide precursors for tetragonal YSZ fabrication.

  12. 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.

  13. 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

  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 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.

  16. 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.

  17. 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.

  18. 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.

  19. Effects of solute methoxylation on glass-forming ability and stability of vitrification solutions

    PubMed

    Wowk; Darwin; Harris; Russell; Rasch

    1999-11-01

    The effects of replacing hydroxyl groups with methoxyl (OCH(3)) groups in the polyols ethylene glycol (EG), propylene glycol (PG), glycerol, and threitol were studied by differential scanning calorimetry (DSC) during cooling of aqueous solutions to -150 degrees C and subsequent rewarming. For 35% (w/w) PG, 40% EG, and 45% glycerol, a single substitution of a terminal hydroxyl group with a methoxyl group reduced the critical cooling rate necessary to avoid ice on cooling (vitrify) from approximately 500 to 50 degrees C/min. This reduction was approximately equivalent to increasing the parent polyol concentration by 5% (w/w). The critical warming rate calculated to avoid formation of ice on rewarming (devitrification) was also reduced by methoxyl substitution, typically by a factor of 10(4) for dilute solutions. Double methoxylation (replacement of both terminal hydroxyls) tended to result in hydrate formation, making these compounds less interesting. An exception was threitol, for which substituting both terminal hydroxyls by methoxyls reduced the critical rewarming rate of a 50% solution by a factor of 10(7) without any hydrate formation. These glass-forming and stability properties of methoxylated compounds, combined with their low viscosity, enhanced permeability, and high glass transition temperatures, make them interesting candidate cryoprotective agents for cryopreservation by vitrification or freezing. Copyright 1999 Academic Press.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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).

  10. Allometric dependence of the life span of mammal erythrocytes on thermal stability and sphingomyelin content of plasma membranes.

    PubMed

    Ivanov, Ivan Tanev

    2007-08-01

    Thermal stability of erythrocyte membrane is a measure for its ability to maintain permeability barrier at deleterious conditions. Hence, it could impact the resistance of erythrocytes against detrimental factors in circulation. In this study the thermostability of erythrocyte membranes was expressed by the temperature, T(go), at which the transmembrane gradient of ion concentration rapidly dissipated during transient heating. T(go) is the inducing temperature of the membrane transition that activated passive ion permeability at hyperthermia causing thermal hemolysis. A good allometric correlation of T(go) to the resistance against thermal hemolysis and the life span of erythrocytes were found for 13 mammals; sheep, cow, goat, dog, horse, man, rabbit, pig, cat, hamster, guinea pig, rat, and mouse. For the same group, the values of T(go) were strictly related to the sphingomyelin content of erythrocyte membranes. The residual ion permeability, P, was temperature activated from 38 to 57 degrees C with activation energy of 250+/-15 kJ/mol that strongly differed from that below 37 degrees C. The projected value of P at 37 degrees C was about half that of residual physiological permeability for Na+ and K+ that build ground for possible explanation of the life span vs membrane thermostability allometric correlation.

  11. 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.

  12. Synergistic thermal stabilization of ceramic/co-polyimide coated polypropylene separators for lithium-ion batteries

    NASA Astrophysics Data System (ADS)

    Lee, Yunju; Lee, Hoogil; Lee, Taejoo; Ryou, Myung-Hyun; Lee, Yong Min

    2015-10-01

    To improve the safety of lithium-ion batteries (LIBs), co-polyimide (PI) P84 was introduced as a polymeric binder for Al2O3/polymer composite surface coatings on polypropylene (PP) separators. By monitoring the dimensional shrinkage of the PP separators at high temperatures, we verified a synergistic thermal stabilization effect between the Al2O3 ceramic and the PI polymeric binder. Although PI was thermally stable up to 300 °C, a coating consisting solely of PI did not impede the PP separator dimensional changes (-22% at 150 °C). On the other hand, the Al2O3/PI-coated PP separators efficiently impeded the thermal shrinkage (-10% at 150 °C). In contrast, an Al2O3/poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) combination lowered the thermal stability of the PP separators (-33% at 150 °C). As a result, the Al2O3/PI-coated PP separators remarkably suppressed the internal short-circuit of the unit half-cells associated with separator thermal shrinkage (100 min at 160 °C), whereas the PVdF-HFP retained only 40 min under identical conditions. The Al2O3/PI-coated PP separators achieved rate capabilities and cell performances similar to those of the bare PP separators.

  13. Thermal Stability of Frozen Volatiles in the North Polar Region of Mercury

    NASA Technical Reports Server (NTRS)

    Paige, David A.; Siegler, Matthew A.; Harmon, John K.; Smith, David E.; Zuber, Maria T.; Neumann, Gregory A.; Solomon, Sean C.

    2012-01-01

    Earth-based radar observations have revealed the presence on Mercury of anomalously bright, depolarizing features that appear to be localized in the permanently shadowed regions of high-latitude impact craters [1]. Observations of similar radar signatures over a range of radar wavelengths implies that they correspond to deposits that are highly transparent at radar wavelengths and extend to depths of several meters below the surface [1]. Thermal models using idealized crater topographic profiles have predicted the thermal stability of surface and subsurface water ice at these same latitudes [2]. One of the major goals of the MESSENGER mission is to characterize the nature of radar-bright craters and presumed associated frozen volatile deposits at the poles of Mercury through complementary orbital observations by a suite of instruments [3]. Here we report on an examination of the thermal stability of water ice and other frozen volatiles in the north polar region of Mercury using topographic profiles obtained by the Mercury Laser Altimeter (MLA) instrument [4] in conjunction with a three-dimensional ray-tracing thermal model previously used to study the thermal environment of polar craters on the Moon [5].

  14. Structural features responsible for kinetic thermal stability of a carboxypeptidase from the archaebacterium Sulfolobus solfataricus.

    PubMed Central

    Villa, A; Zecca, L; Fusi, P; Colombo, S; Tedeschi, G; Tortora, P

    1993-01-01

    Investigations were performed on the structural features responsible for kinetic thermal stability of a thermostable carboxypeptidase from the thermoacidophilic archaebacterium Sulfolobus solfataricus which had been purified previously and identified as a zinc metalloprotease [Colombo, D'Auria, Fusi, Zecca, Raia and Tortora (1992) Eur. J. Biochem. 206, 349-357]. Removal of Zn2+ by dialysis led to reversible activity loss, which was promptly restored by addition of 80 microM ZnCl2 to the assay mixture. For the first-order irreversible thermal inactivation the metal-depleted enzyme showed an activation energy value of 205.6 kJ.mol-1, which is considerably lower than that of the holoenzyme (494.4 kJ.mol-1). The values of activation free energies, enthalpies and entropies also dropped with metal removal. Thermal inactivation of the apoenzyme was very quick at 80 degrees C, whereas the holoenzyme was stable at the same temperature. These findings suggest a major stabilizing role for the bivalent cation. Chaotropic salts strongly destabilized the holoenzyme, showing that hydrophobic interactions are involved in maintaining the native conformation of the enzyme. However, the inactivation rate was also increased by sodium sulphate, acetate and chloride, which are not chaotropes, indicating that one or more salt bridges concur in stabilizing the active enzyme. Furthermore, at the extremes of the pH-stability curve, NaCl did not affect the inactivation rate, confirming the stabilizing role of intramolecular ionic bonds, as a pH-dependent decrease in stability is likely to occur from breaking of salt bridges involved in maintaining the native conformation of the protein. PMID:8240298

  15. Structural features responsible for kinetic thermal stability of a carboxypeptidase from the archaebacterium Sulfolobus solfataricus.

    PubMed

    Villa, A; Zecca, L; Fusi, P; Colombo, S; Tedeschi, G; Tortora, P

    1993-11-01

    Investigations were performed on the structural features responsible for kinetic thermal stability of a thermostable carboxypeptidase from the thermoacidophilic archaebacterium Sulfolobus solfataricus which had been purified previously and identified as a zinc metalloprotease [Colombo, D'Auria, Fusi, Zecca, Raia and Tortora (1992) Eur. J. Biochem. 206, 349-357]. Removal of Zn2+ by dialysis led to reversible activity loss, which was promptly restored by addition of 80 microM ZnCl2 to the assay mixture. For the first-order irreversible thermal inactivation the metal-depleted enzyme showed an activation energy value of 205.6 kJ.mol-1, which is considerably lower than that of the holoenzyme (494.4 kJ.mol-1). The values of activation free energies, enthalpies and entropies also dropped with metal removal. Thermal inactivation of the apoenzyme was very quick at 80 degrees C, whereas the holoenzyme was stable at the same temperature. These findings suggest a major stabilizing role for the bivalent cation. Chaotropic salts strongly destabilized the holoenzyme, showing that hydrophobic interactions are involved in maintaining the native conformation of the enzyme. However, the inactivation rate was also increased by sodium sulphate, acetate and chloride, which are not chaotropes, indicating that one or more salt bridges concur in stabilizing the active enzyme. Furthermore, at the extremes of the pH-stability curve, NaCl did not affect the inactivation rate, confirming the stabilizing role of intramolecular ionic bonds, as a pH-dependent decrease in stability is likely to occur from breaking of salt bridges involved in maintaining the native conformation of the protein.

  16. 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

  17. Thermal and structural stability of medium energy target carrier assembly for NOvA at Fermilab

    SciTech Connect

    McGee, M.W.; Ader, C.; Anderson, K.; Hylen, J.; Martens, M.; /Fermilab

    2010-05-01

    The NOvA project will upgrade the existing Neutrino at Main Injector (NuMI) project beamline at Fermilab to accommodate beam power of 700 kW. The Medium Energy (ME) graphite target assembly is provided through an accord with the State Research Center of Russia Institute for High Energy Physics (IHEP) at Protvino, Russia. The effects of proton beam energy deposition within beamline components are considered as thermal stability of the target carrier assembly and alignment budget are critical operational issues. Results of finite element thermal and structural analysis involving the target carrier assembly is provided with detail regarding the target's beryllium windows.

  18. Use of Ramachandran plot for increasing thermal stability of bacterial formate dehydrogenase.

    PubMed

    Serov, A E; Odintzeva, E R; Uporov, I V; Tishkov, V I

    2005-07-01

    From analysis of Ramachandran plot for NAD+-dependent formate dehydrogenase from the methylotrophic bacterium Pseudomonas sp. 101 (FDH, EC 1.2.1.2), five amino acid residues with non-optimal values phi and psi have been located in beta- and pi-turns of the FDH polypeptide chain, e.g., Asn136, Ala191, Tyr144, Asn234, and His263. To clarify their role in the enzyme stability, the residues were replaced with Gly by means of site-directed mutagenesis. The His263Gly mutation caused FDH destabilization and a 1.3-fold increase in the monomolecular inactivation rate constant. The replacements Ala191Gly and Asn234Gly had no significant effect on the stability. The mutations Asn136Gly and Tyr144Gly resulted in higher thermal stability and decreased the inactivation rate by 1.2- and 1.4-fold, respectively. The stabilizing effect of the Tyr144Gly mutation was shown to be additive when introduced into the previously obtained mutant FDH with enhanced thermal stability.

  19. Superatom electron configuration predicts thermal stability of Au25(SR)18 nanoclusters.

    PubMed

    Tofanelli, Marcus A; Ackerson, Christopher J

    2012-10-17

    The exceptional stability of ligand-stabilized gold nanoclusters such as Au(25)(SC(6)H(13))(18)(-), Au(39)(PR(3))(14)X(6)(-), and Au(102)(SR)(44) arises from the total filling of superatomic electron shells, resulting in a "noble-gas superatom" electron configuration. Electrochemical manipulation of the oxidation state can add or remove electrons from superatom orbitals, creating species electronically analogous to atomic radicals. Herein we show that oxidizing the Au(25)(SR)(18)(-) superatom from the noble-gas-like 1S(2)1P(6) electron configuration to the open-shell radical 1S(2)1P(5) and diradical 1S(2)1P(4) configurations results in decreased thermal stability of the compound, as measured by differential scanning calorimetry. Similar experiments probing five oxidation states of the putatively geometrically stabilized Au(144)(SR)(60) cluster suggest a more complex relationship between oxidation state and thermal stability for this compound.

  20. Radiation and Thermal Stability of Solid Radwaste After Immobilization in Polymer Matrix - 13504

    SciTech Connect

    Pokhitonov, Yu.; Babain, V.; Strelkov, S.; Kuznetsov, D.; Kelley, Dennis

    2013-07-01

    The paper will illustrate results of the various experiments on radiation and thermal stability of polymer matrixes after solutions solidification including aqueous and organic solutions and mixed waste. It was shown that- after irradiation the specimen and after solidification the mixture with oil and TBP hydrogen has been observed (less 1%) and some others gases have been detected. Results of the performed experiments and the radiation stability data of the polymer compositions allow the conclusion that the technological process of immobilizing the above mentioned aqueous solutions and solutions with organic products into polymers at room temperature is the explosion- and flameproof as well as the storage thereof. (authors)

  1. 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.

  2. Effect of protein-encapsulation on thermal structural stability of liposome composed of glycosphingolipid/cholesterol/phospholipid.

    PubMed

    Hirai, Mitsuhiro; Sato, Shoki; Kimura, Ryota; Hagiwara, Yoshihiko; Kawai-Hirai, Rika; Ohta, Noboru; Igarashi, Noriyuki; Shimizu, Nobutaka

    2015-02-26

    We have studied the thermal structural stability of liposomes encapsulating proteins by using synchrotron radiation small- and wide-angle X-ray scattering (SR-SWAXS). Liposomes are known to be effective drug-delivery systems (DDSs) because they can reduce drug toxicity due to biodegradability and biocompatibility and can offer promising carriers of various types of drugs. However, in spite of numerous studies of liposomes, physicochemical characteristics of liposomes entrapping proteins are rarely known. The liposome studied is characterized by the lipid composition (mixture of acidic glycosphingolipid (ganglioside)/cholesterol/phospholipid). Gangliosides are one of the major constituents of so-called lipid rafts playing the role of a platform of cell-signaling. We have found that the encapsulation of proteins elevates the thermal transition temperature of the liposome membrane and suppresses the deformation of its shape. The present results suggest that not only membrane proteins, but also water-soluble proteins affect liposome stability through the revalence between osmotic pressure and membrane elasticity. In addition, we have found the presence of the size-effect depending on the molar content of gangliosides in the liposome, indicating the ability of ganglioside molecule controlling both the size and effective surface charge of the liposome. The present results would have significance from two different points of view. One is the confinement effect of proteins within a limited space like cell, and the other is a stability of a new type of DDS using gangliosides. Due to the intrinsic properties, gangliosides are expected to be promising agents for targeting and long-circulation properties of liposomal DDSs.

  3. Thermal stability of piezoelectric properties and infrared sensor performance of spin-coated polyurea thin films

    NASA Astrophysics Data System (ADS)

    Morimoto, Masahiro; Koshiba, Yasuko; Misaki, Masahiro; Ishida, Kenji

    2015-10-01

    We have investigated the temperature dependence of the piezoelectric coefficients and infrared sensor performance of spin-coated thin films of polyundecylurea (PUA11). The piezoelectric coefficients of the PUA11 films remained constant at temperatures above 180 °C and these films demonstrated thermal resistance superior to those of poly(vinylidene fluoride/trifluoroethylene) [P(VDF/TrFE)] films. The infrared sensor performance of the PUA11 films was measured after annealing at 125 °C for 500 h and was found to have retained 84% of its preannealing level. The thermal stability of the PUA11 films was higher than that of the P(VDF/TrFE) films; moreover, PUA11 is also expected to have superior electrothermal stability.

  4. Synthesis and thermal stability of selenium-doped hydroxyapatite with different substitutions

    NASA Astrophysics Data System (ADS)

    Liu, Yonghui; Ma, Jun; Zhang, Shengmin

    2015-12-01

    Selenium (Se) plays a specific role in human health, especially for its antitumor effect. Incorporation of selenium into biocompatible hydroxyapatite (HAP) may endow the materials with novel characteristics. In the current work, a series of seleniumdoped hydroxyapatite (Se-HAP) nanoparticles with different Se/P ratios were synthesized by a modified chemical precipitation. It was revealed that the powders with/without heattreatment were nano-sized needle-like HAP while the heat-treated samples have high crystallinity. The addition of selenium decreases the crystallinity of the synthesized apatite, and also takes a negative effect on the thermal stability of the as-prepared powders. The Se-HAP nanoparticles with Se/P molar ratio not more than 5% sintered at 900°C can achieve good crystallinity and thermal stability.

  5. Enhanced thermal oxidation stability of reduced graphene oxide by nitrogen doping.

    PubMed

    Sandoval, Stefania; Kumar, Nitesh; Sundaresan, A; Rao, C N R; Fuertes, Amparo; Tobias, Gerard

    2014-09-15

    Nitrogen-doped reduced graphene oxide (N-doped RGO) samples with a high level of doping, up to 13 wt. %, have been prepared by annealing graphene oxide under a flow of pure ammonia. The presence of nitrogen within the structure of RGO induces a remarkable increase in the thermal stability against oxidation by air. The thermal stability is closely related with the temperature of synthesis and the nitrogen content. The combustion reaction of nitrogen in different coordination environments (pyridinic, pyrrolic, and graphitic) is analyzed against a graphene fragment (undoped) from a thermodynamic point of view. In agreement with the experimental observations, the combustion of undoped graphene turns out to be more spontaneous than when nitrogen atoms are present.

  6. Improvement of thermal stability of insulation paper cellulose by modified polysiloxane grafting

    NASA Astrophysics Data System (ADS)

    Zhang, Song; Tang, Chao; Xie, Jingyu; Zhou, Qu

    2016-10-01

    We present a method for improving the thermal stability of insulation paper cellulose. A polysiloxane was grafted to the hydroxyl group connected to the C6 atom in the cellulose chain. The effects of the mass fraction of polysiloxane on the mechanical properties and glass-transition temperatures of model cellulose samples modified by polysiloxane grafting were investigated using molecular dynamics simulations. The results show that for four models, with polysiloxane mass fractions of 0%, 3.3%, 6.5%, and 12.2%, the best chain performance was achieved using a mass fraction of 6.5%. The glass-transition temperature of the modified cellulose with a 6.5% mass fraction of polysiloxane was 48 K higher than that of unmodified cellulose, which shows that modification improved the thermal stability of the cellulose.

  7. Thermal stability of sputter deposited nanomosaic rutile TiO{sub 2}

    SciTech Connect

    Aita, Carolyn Rubin

    2009-07-15

    A domain structure based on the rutile lattice with a large density of (1/2)<011>{l_brace}011{r_brace}-type stacking faults is found in sputter deposited TiO{sub 2} films [J. Vac. Sci. Technol. A 24, 2054 (2006)]. The thermal stability of nanomosaic rutile at moderate temperature is reported here. Films are annealed at 973 K for 0.25-15 h, characterized by x-ray diffraction. A Johnson-Mehl-Avrami-Kolmogorov analysis indicates impeded crystallite growth. A dislocation-locking mechanism is proposed for this behavior. Partial dislocations with (1/2)<011> Burgers vectors that bound the stacking faults glide on intersecting {l_brace}011{r_brace} slip planes and react to produce sessile stair rod dislocations. Without the high temperature required for dislocation climb, (1/2)<011>{l_brace}011{r_brace}-type faults inherent to nanomosaic rutile provide thermal stability against massive crystallite growth.

  8. Thermal Stability of Photosensitive Bragg Gratings in Sputter-Deposited Germanosilicate Glass

    SciTech Connect

    POTTER JR.,BARRETT G.; POTTER,KELLY SIMMONS; DUNBAR,TIMOTHY D.

    2000-07-24

    The thermal stability of photo-imprinted Bragg gratings formed in reactive-atmosphere, RF-magnetron sputtered germanosilicate thin films was evaluated in terms of point defect modifications observed during isochronal annealing. Optical and magnetic spectroscopes were utilized to evaluate structural relaxation in these sputtered glasses on both a local and medium-range size scale. Depending upon the substrate temperature used during deposition, significant structural rearrangement was found to occur with increasing post-deposition anneal temperature to 600 C. This resulted in changes in the photobleaching response of the material itself as the identity of optically active structural defects evolved. Based on a color center model for photosensitivity in these materials and measured changes in optical absorption with annealing, the thermal stability of a photo-imprinted Bragg grating was modeled. Good qualitative agreement with experiment was observed.

  9. Thermal stability of fission gas bubble superlattice in irradiated U–10Mo fuel

    SciTech Connect

    Gan, J.; Keiser, D. D.; Miller, B. D.; Robinson, A. B.; Wachs, D. M.; Meyer, M. K.

    2015-09-01

    To investigate the thermal stability of the fission gas bubble superlattice, a key microstructural feature in both irradiated U-7Mo dispersion and U-10Mo monolithic fuel plates, a FIB-TEM sample of the irradiated U-10Mo fuel with a local fission density of 3.5×1021 fissions/cm3 was used for an in-situ heating TEM experiment. The temperature of the heating holder was raised at a ramp rate of approximately 10 ºC/min up to ~700 ºC, kept at that temperature for about 34 min, continued to 850 ºC with a reduced rate of 5 ºC/min. The result shows a high thermal stability of the fission gas bubble superlattice. The implication of this observation on the fuel microstructural evolution and performance under irradiation is discussed.

  10. Applications of high pressure differential scanning calorimetry to aviation fuel thermal stability research

    NASA Technical Reports Server (NTRS)

    Neveu, M. C.; Stocker, D. P.

    1985-01-01

    High pressure differential scanning calorimetry (DSC) was studied as an alternate method for performing high temperature fuel thermal stability research. The DSC was used to measure the heat of reaction versus temperature of a fuel sample heated at a programmed rate in an oxygen pressurized cell. Pure hydrocarbons and model fuels were studied using typical DSC operating conditions of 600 psig of oxygen and a temperature range from ambient to 500 C. The DSC oxidation onset temperature was determined and was used to rate the fuels on thermal stability. Kinetic rate constants were determined for the global initial oxidation reaction. Fuel deposit formation is measured, and the high temperature volatility of some tetralin deposits is studied by thermogravimetric analysis. Gas chromatography and mass spectrometry are used to study the chemical composition of some DSC stressed fuels.

  11. Barrierless Cu-Ni-Mo Interconnect Films with High Thermal Stability Against Silicide Formation

    NASA Astrophysics Data System (ADS)

    Li, X. N.; Liu, L. J.; Zhang, X. Y.; Chu, J. P.; Wang, Q.; Dong, C.

    2012-12-01

    Cu-Ni-Mo alloys were investigated to increase thermal stability against silicide formation. The alloy compositions were chosen such that an insoluble element (Mo) solute was dissolved into Cu via a third element Ni which is soluble in both Cu and Ni. Thin-film Cu-Ni-Mo alloys were prepared by magnetron sputtering. The films with Mo/Ni ratio of 1/12 exhibited low electrical resistivities in combination with high thermal stabilities against silicide formation, in support of a tentative "cluster-plus-glue-atom" model for stable solid solutions. In particular, a (Mo1/13Ni12/13)0.3Cu99.7 sample reached a minimum resistivity of 2.6 μΩ cm after 400°C/1 h annealing and remained highly conductive with resistivities below 3 μΩ cm even after 400°C/40 h annealing. These alloys are promising candidates for future interconnect materials.

  12. Stability and color changes of thermally treated betanin, phyllocactin, and hylocerenin solutions.

    PubMed

    Herbach, Kirsten M; Stintzing, Florian C; Carle, Reinhold

    2006-01-25

    Thermal degradation of betanin, phyllocactin (malonyl-betanin), and hylocerenin (3' '-hydroxy-3' '-methyl-glutaryl-betanin) solutions isolated from purple pitaya (Hylocereus polyrhizus [Weber] Britton and Rose) was monitored by spectrophotometric and high-performance liquid chromatography-diode array detection (HPLC-DAD) analyses. For betanin and phyllocactin solutions, the color shift upon thermal treatment was found to be nearly identical, while hylocerenin samples exhibited an intelligibly higher chromatic steadiness. Betanin proved to be the most stable individual pigment structure, while the enhanced tinctorial stability of the integral phyllocactin and especially hylocerenin solutions was due to the formation of red degradation products exhibiting improved color retention as opposed to their respective genuine pigments. Individual structure-related stability characteristics can exclusively be assessed by HPLC-DAD analyses and may not be noticed by mere spectrophotometric assessment of color and tinctorial strength.

  13. 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

  14. 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

  15. Ordered domain lateral location, symmetry, and thermal stability in Ge:Si islands

    SciTech Connect

    Richard, M.-I.; Schülli, T. U.; Zhong, Z.; Metzger, T. H.; Renaud, G.

    2015-01-05

    Compositional atomic ordering is a crucial issue in the epitaxial growth of nanoparticles and thin films. Here, we report on a method based on x-ray diffuse scattering close to basis forbidden Bragg reflections to infer the lateral location, the symmetry, and the thermal stability of ordered domains in GeSi dome-shaped islands on Si(001) after growth and during annealing. We observe that atomic ordering does not disappear after annealing, demonstrating that it is a resilient metastable phenomenon.

  16. Thermal and photo-stability of the antioxidant potential of Spirulina platensis powder.

    PubMed

    Colla, L M; Bertol, C D; Ferreira, D J; Bavaresco, J; Costa, J A V; Bertolin, T E

    2016-09-26

    This work aimed to evaluate the thermal and photo stability of the antioxidant potential (AP) of the Spirulina platensis biomass. Thermal stability was established at 25ºC, 40ºC and 50ºC for 60 days, in the dark, protected from light. Photo stability was evaluated using UV (15 W, λ = 265 nm) and fluorescent (20 W, 0.16 A, power factor FP > 0.5, 50/60 Hz, 60 lm/w, 1200 lm) light for 90 days in capsules, glass and Petri dishes, at room temperature. The AP of the biomass in these conditions was determined at intervals (every 7 and 30 days in the studies of thermal and photo stability, respectively) using the induction of the oxidation of a lipid system by heat and aeration. In this lipid system, the biomass submitted to degradation was used as an antioxidant. The kinetics of the reaction was determined by the Arrhenius method. Thermal degradation was found to follow zero order kinetics, whereas photo degradation followed first order kinetics. The AP decreased 50% after 50 days at 25°C. At 40°C and 50°C, the AP decreased more than 50% after 35 and 21 days of exposition, respectively. The decrease of the AP of Spirulina was more sensible to UV and fluorescence light. After 30 days of exposition, the AP decreased more than 50% in all storage conditions tested. The antioxidant potential of Spirulina platensis is easily degraded when the biomass is exposed to heat and light, indicating the need for care to be taken in its storage.

  17. Novel PEG functionalized graphene nanosheets: enhancement of dispersibility and thermal stability

    NASA Astrophysics Data System (ADS)

    Zhang, Shupeng; Xiong, Pan; Yang, Xujie; Wang, Xin

    2011-05-01

    A series of polyethylene glycol (PEG) functionalized graphene sheet hybrid materials (FGHMs) have been successfully synthesized via ester linkages. Interestingly, our products can be dispersed in both polar/protic solvents and nonpolar/nonprotic ones, which differ significantly from previously reported systems and are of great value in the wide-spread application of these ``carbon nanosheet'' based materials by solution-phase processing. Furthermore, the addition of PEG-modified carbon nanosheets as nanofillers significantly improves the thermal stability of the bulk polymers. In our case, an increase of 35 K in thermal stability can be obtained for PEG4000 after filling with as low as 1 wt % of the PEG modified carbon sheets, suggesting their great potential as novel nanofillers in industry.A series of polyethylene glycol (PEG) functionalized graphene sheet hybrid materials (FGHMs) have been successfully synthesized via ester linkages. Interestingly, our products can be dispersed in both polar/protic solvents and nonpolar/nonprotic ones, which differ significantly from previously reported systems and are of great value in the wide-spread application of these ``carbon nanosheet'' based materials by solution-phase processing. Furthermore, the addition of PEG-modified carbon nanosheets as nanofillers significantly improves the thermal stability of the bulk polymers. In our case, an increase of 35 K in thermal stability can be obtained for PEG4000 after filling with as low as 1 wt % of the PEG modified carbon sheets, suggesting their great potential as novel nanofillers in industry. Electronic Supplementary Information (ESI) available: Table S1: Digital pictures of several typical hybrid materials dispersed in water and 22 organic solvents; Video 1: GO-PEG400 can be re-dispersed in the isooctane by simply turning the vials up and down. See DOI: 10.1039/c0nr00923g

  18. 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.

  19. Thermal stability of kudzu root (Pueraria Radix) isoflavones as additives to beef patties.

    PubMed

    Kumari, S; Raines, J M; Martin, J M; Rodriguez, J M

    2015-03-01

    Kudzu root, Pueraria radix, extracts are a rich source of isoflavones. This study investigates the thermal stability of Pueraria radix extracts as a natural nutraceutical supplement in beef patties. The extract contained puerarin, diadzin, genistin, ononin, daidzein, glycitein, calycosin, genistein, formononetin and biochanin A; however, puerarin, daidzein and glycitein were the main components. The isoflavones concentrations in the spiked beef patties with kudzu root extracts were unaffected by cooking.

  20. Design considerations of a thermally stabilized continuous flow electrophoresis chamber 2

    NASA Technical Reports Server (NTRS)

    Jandebeur, T. S.

    1982-01-01

    The basic adjustable parameters of a Beckman Continouous Particle Electrophoresis (CPE) Apparatus are investigated to determine the optimum conditions for ground based operation for comparison with space experiments. The possible application of electrically insulated copper/aluminum chamber walls is evaluated as a means to thermally stabilize or equilibrate lateral temperature gradients which exist on the walls of conventional plastic chambers and which distort the rectilinear base flow of buffer through the chamber, significantly affecting sample resolution.

  1. Resumption of thermal stabilization of plutonium oxide in Building 707, Rocky Flats Plant, Golden, Colorado. Environmental Assessment

    SciTech Connect

    Not Available

    1994-02-01

    The Department of Energy is proposing thermal stabilization to enhance the safe storage of plutonium at Rocky Flats Plant until decisions are made on long-term storage and disposition of the material. The proposed action is to resume thermal stabilization of pyrophoric plutonium in Building 707 at Rocky Flats Plant. Thermal stabilization would heat the pyrophoric plutonium under controlled conditions in a glovebox furnace to promote full oxidation and convert the material into stable plutonium oxide in the form of PuO{sub 2}. Other activities associated with thermal stabilization would include post-stabilization characterization of non-pyrophoric plutonium and on-site movement of pyrophoric and non-pyrophoric plutonium. This report covers; purpose and need; proposed action; alternatives to the proposed action; affected environment; environmental effects of proposed action and no action alternative; agencies and person consulted; and public participation.

  2. Thermal Stability of Co-Sputtered Ru Ti Alloy Electrodes for Dynamic Random Access Memory Applications

    NASA Astrophysics Data System (ADS)

    Horng, Ray-Hua; Wuu, Dong-Sing; Wu, Luh-Huei; Lee, Ming-Kwei; Chan, Shih-Hsiung; Leu, Ching-Chich; Huang, Tiao-Yuan; Sze, Simon

    1998-10-01

    Ru Ti alloy films were studied for use as a bottom electrode of ferroelectric/paraelectric thin film capacitors. These thin films with different Ru/Ti compositions were first prepared by co-sputtering. The Ru/Ti ratio in the alloy was found to strongly affect the resistivity, structure formation and thermal stability. The resistivity of the as-deposited films decreases and closes to that of pure Ru metal films as the amount of Ru atoms increasing. From X-ray diffraction measurement, it was found that the RuTi phase has formed for the as-deposited sample. There also exist Ru and Ti phases for Ru-enriched and Ti-enriched samples, respectively. As-deposited alloy films were also annealed by rapid thermal processing (RTP, 600 750°C, 1 min) in oxygen ambient to simulate the processing of ferroelectric/paraelectric thin film capacitors. It was found that the composition of the thin film has a large effect on the thermal stability. The resistivity of alloy thin films is thermally stable as the Ru composition varies from 0.68 to 0.81. It may be due to the RuTiO2 formation at the surface and play an important role in preventing further oxidation of the Ru-enriched layer. This oxide also presents conductive behavior. On the other hand, the interface between Ru-enriched alloys and Si substrate was still sharp for the RTP-treated sample at 600°C for 1 min. The alloy film with high Ru composition shows excellent thermal stability and barriers against interdiffusion of Si and oxygen. These results suggest that the Ru-enriched alloy films are suitable for the bottom electrode application in ferroelectric/paraelectric thin film capacitors.

  3. Thermal Conductivity and Water Vapor Stability of Ceramic HfO2-Based Coating Materials

    NASA Technical Reports Server (NTRS)

    Zhu, Dong-Ming; Fox, Dennis S.; Bansal, Narottam P.; Miller, Robert A.

    2004-01-01

    HfO2-Y2O3 and La2Zr2O7 are candidate thermal/environmental barrier coating materials for gas turbine ceramic matrix composite (CMC) combustor liner applications because of their relatively low thermal conductivity and high temperature capability. In this paper, thermal conductivity and high temperature phase stability of plasma-sprayed coatings and/or hot-pressed HfO2-5mol%Y2O3, HfO2-15mol%Y2O3 and La2Zr2O7 were evaluated at temperatures up to 1700 C using a steady-state laser heat-flux technique. Sintering behavior of the plasma-sprayed coatings was determined by monitoring the thermal conductivity increases during a 20-hour test period at various temperatures. Durability and failure mechanisms of the HfO2-Y2O3 and La2Zr2O7 coatings on mullite/SiC Hexoloy or CMC substrates were investigated at 1650 C under thermal gradient cyclic conditions. Coating design and testing issues for the 1650 C thermal/environmental barrier coating applications will also be discussed.

  4. Thermal stability of exchange-biased NiFe/FeMn multilayered thin films

    NASA Astrophysics Data System (ADS)

    Chen, H. Y.; Phuoc, Nguyen N.; Ong, C. K.

    2012-09-01

    A systematic study of the effect of ferromagnetic thickness on magnetic and microwave properties of exchange-biased NiFe/FeMn multilayered thin films was carried out with regards to thermal stability. The temperature-dependent microwave characteristics of the films were obtained from the near-field microwave microscopy technique and analysed based on Landau-Lifshitz-Gilbert equation. The complex microwave permeability spectra of the magnetic thin films up to 5 GHz in the temperature range from room temperature to 420 K were measured. It was found that thicker ferromagnetic layers helped to reduce the dependence of the magnetic properties on temperature, leading to better thermal stability. The saturation magnetization MS, dynamic magnetic anisotropy field HKdyn, and ferromagnetic resonance frequency fFMR were found to decrease with temperature, while the effective damping coefficient αeff was increased with temperature. We also investigate the rotational magnetic anisotropy field HKrot with temperature which gives a measure of the rotatable magnetization of the antiferromagnetic layers and its thermal stability.

  5. Thermal stability and mechanism of decomposition of emulsion explosives in the presence of pyrite.

    PubMed

    Xu, Zhi-Xiang; Wang, Qian; Fu, Xiao-Qi

    2015-12-30

    The reaction of emulsion explosives (ammonium nitrate) with pyrite was studied using techniques of TG-DTG-DTA. TG-DSC-MS was also used to analyze samples thermal decomposition process. When a mixture of pyrite and emulsion explosives was heated at a constant heating rate of 10K/min from room temperature to 350°C, exothermic reactions occurred at about 200°C. The essence of reaction between emulsion explosives and pyrite is the reaction between ammonium nitrate and pyrite. Emulsion explosives have excellent thermal stability but it does not mean it showed the same excellent thermal stability when pyrite was added. Package emulsion explosives were more suitable to use in pyrite shale than bulk emulsion explosives. The exothermic reaction was considered to take place between ammonium nitrate and pyrite where NO, NO2, NH3, SO2 and N2O gases were produced. Based on the analysis of the gaseous, a new overall reaction was proposed, which was thermodynamically favorable. The results have significant implication in the understanding of stability of emulsion explosives in reactive mining grounds containing pyrite minerals.

  6. Thermal Stabilization of Erwinia chrysanthemi Pectin Methylesterase A for Application in a Sugar Beet Pulp Biorefinery▿

    PubMed Central

    Chakiath, Chacko; Lyons, Margaret J.; Kozak, Robert E.; Laufer, Craig S.

    2009-01-01

    Directed evolution approaches were used to construct a thermally stabilized variant of Erwinia chrysanthemi pectin methylesterase A. The final evolved enzyme has four amino acid substitutions that together confer a Tm value that is approximately 11°C greater than that of the wild-type enzyme, while maintaining near-wild-type kinetic properties. The specific activity, with saturating substrate, of the thermally stabilized enzyme is greater than that of the wild-type enzyme when both are operating at their respective optimal temperatures, 60°C and 50°C. The engineered enzyme may be useful for saccharification of biomass, such as sugar beet pulp, with relatively high pectin content. In particular, the engineered enzyme is able to function in biomass up to temperatures of 65°C without significant loss of activity. Specifically, the thermally stabilized enzyme facilitates the saccharification of sugar beet pulp by the commercial pectinase preparation Pectinex Ultra SPL. Added pectin methylesterase increases the initial rate of sugar production by approximately 50%. PMID:19820151

  7. Thermal Stabilization of Erwinia chrysanthemi pectin methylesterase a for application in a sugar beet pulp biorefinery.

    PubMed

    Chakiath, Chacko; Lyons, Margaret J; Kozak, Robert E; Laufer, Craig S

    2009-12-01

    Directed evolution approaches were used to construct a thermally stabilized variant of Erwinia chrysanthemi pectin methylesterase A. The final evolved enzyme has four amino acid substitutions that together confer a T(m) value that is approximately 11 degrees C greater than that of the wild-type enzyme, while maintaining near-wild-type kinetic properties. The specific activity, with saturating substrate, of the thermally stabilized enzyme is greater than that of the wild-type enzyme when both are operating at their respective optimal temperatures, 60 degrees C and 50 degrees C. The engineered enzyme may be useful for saccharification of biomass, such as sugar beet pulp, with relatively high pectin content. In particular, the engineered enzyme is able to function in biomass up to temperatures of 65 degrees C without significant loss of activity. Specifically, the thermally stabilized enzyme facilitates the saccharification of sugar beet pulp by the commercial pectinase preparation Pectinex Ultra SPL. Added pectin methylesterase increases the initial rate of sugar production by approximately 50%.

  8. Improvement of thermal stability of amorphous CoFeSiB thin films

    SciTech Connect

    Jimbo, M. Shimizu, T.; Fujiwara, Y.

    2015-05-07

    The excellent soft magnetic properties of amorphous (a-) CoFeSiB films make it suited for use in the yoke of granular-in-gap sensors, but only if their thermal stability can be improved. To this end, this study investigated the effects of adding small amounts of other metals on the magnetic and structural properties of a-CoFeSiB films. It was found that adding metals with relatively large atomic radii is an effective way to increase thermal stability, with both Ta and Hf showing good thermal stability after annealing at temperatures of 473 to 573 K. Indeed, a -(CoFeSiB){sub 96.2}Hf{sub 3.8} film was found to maintain its initial coercivity of 0.2 Oe without very little decrease in magnetization after annealing at 623 K. Furthermore, even after annealing at 673 K a -(CoFeSiB){sub 93.0}Hf{sub 7.0} film still had a relatively low coercivity of approximately 0.5 Oe.

  9. Magnetic properties and thermal stability of MnBi/NdFeB hybrid bonded magnets

    NASA Astrophysics Data System (ADS)

    Cao, S.; Yue, M.; Yang, Y. X.; Zhang, D. T.; Liu, W. Q.; Zhang, J. X.; Guo, Z. H.; Li, W.

    2011-04-01

    Magnetic properties and thermal stability were investigated for the MnBi/NdFeB (MnBi = 0, 20, 40, 60, 80, and 100 wt.%) bonded hybrid magnets prepared by spark plasma sintering (SPS) technique. Effect of MnBi content on the magnetic properties of the hybrid magnets was studied. With increasing MnBi content, the coercivity of the MnBi/NdFeB hybrid magnets increases rapidly, while the remanence and maximum energy product drops simultaneously. Thermal stability measurement on MnBi magnet, NdFeB magnet, and the hybrid magnet with 20 wt.% MnBi indicates that both the NdFeB magnet and the MnBi/NdFeB hybrid magnet have a negative temperature coefficient of coercivity, while the MnBi magnet has a positive one. The (BH)max of the MnBi/NdFeB magnet (MnBi = 20 wt.%) is 5.71 MGOe at 423 K, which is much higher than 3.67 MGOe of the NdFeB magnet, indicating a remarkable improvement of thermal stability.

  10. Stability of Pin1 as revealed by thermal and spectroscopic studies

    NASA Astrophysics Data System (ADS)

    Wang, Jing-Zhang; Lin, Tao; Zhu, Guo-Fei; Du, Lin-Fang

    2010-06-01

    Pin1 is a two-domain enzyme which has peptidyl-prolyl cis/trans isomerase activity. Pin1 recognizes phospho-Ser/Thr-Pro motifs in cell-signaling proteins, and is both a cancer and an Alzheimer's disease target. The thermal stability of Pin1 was studied intensively by SDS-PAGE, enzymatic activity assay, intrinsic fluorescence spectroscopy and circular dichroism spectroscopy. The activity of Pin1 gradually decreased above 40 °C, and the Tm was 57.6 ± 1.0 °C. Fluorescence experiments indicated that heat treatment induced changes in the substructures in Pin1, resulting in that the polarity in the microenvironments of the tryptophan residues increased. It is assumed that the thermal denaturation of Pin1 involved a three-state transition. The intermediate state of Pin1 at about 60 °C was confirmed by fluorescence emission spectra, the synchronous fluorescence spectra and CD measurements. Decreases in α-helix and β-sheet appeared above 40 °C, which was balanced by an enhancement in unordered coil. The Tm values calculated from α-helix transition and β-sheet transition were 54.6 ± 0.6 °C and 70.7 ± 3.3 °C, respectively. Our results illustrated that Pin1 had a relatively high thermal stability and the WW domain had a higher stability than the PPIase domain.

  11. Structural Characterization of Mg/Al hydrotalcite-like Compounds and their Thermal Stability

    NASA Astrophysics Data System (ADS)

    Zhang, Shuhua; Yang, Siyuan; Wang, Cheng; Liu, Weijun; Gu, Xiaodan; Gan, Wenjun; Xue, Xiaoyu

    2014-03-01

    Hydrotalcite-like compounds, repersented by the formula [M1-x 2 + Mx3+ (OH)2]Xx/n n - . nH2O (M2+ = Ni2+, Mg2+, Cu2+,etc; M3+ = Al3+, Fe3+, etc; Xn- = CO32- , NO3-,etc) possess the brucite-like layers [Mg(OH)2] with positive charge and anionic compounds in the interlayer to form neutral materials. Catalytic effects to decompose NOx from automobile exhaust were highly related with the difference of M2+ and thermal stability because the catylists locate are about 200 ~ 500°. In this paper, Mg-Al-Cu and Mg-Al-Ni hydrotalcite-like compounds were characterized by XRD and FT-IR spectra and the thermal stability were analyzed by TGA and DTA. Even though they both have the typical diffraction peaks of hydrotalcites, but their interlayer spaces are different. Some weak chemical bonds were observed to be formed in Mg-Al-Ni hydrotalcites by FT-IR. Mg-Al-Ni hydrotalcite-like compound degraded at lower temperature, by contrast, Mg-Al-Cu hydrotalcite has the better structural stablilty and thermal stability.

  12. Carbon doped molybdenum disulfide nanosheets stabilized on graphene for the hydrogen evolution reaction with high electrocatalytic ability.

    PubMed

    Li, Yong; Wang, Jiao; Tian, Xike; Ma, Longlong; Dai, Chu; Yang, Chao; Zhou, Zhaoxin

    2016-01-21

    Fabricating a cost effective hydrogen evolution reaction catalyst without using precious metal elements is in crucial demand for environmentally-benign energy production. In this work, the thin and edge-rich molybdenum disulfide nanosheets, with carbon doped in the interlayers and decorated on graphene, were developed by a facile solvothermal process. The as-synthesized nanohybrids exhibited high catalytic ability for the hydrogen evolution electrochemical reaction with an onset overpotential of 0.165 mV and a Tafel slope of 46 mV dec(-1). Furthermore, the prepared nanohybrids also showed better durability and stability. Our work may lead to a potential method for in situ production of metal carbide-sulphur hybrid nanomaterials with promising applications for the hydrogen evolution reaction.

  13. Friction, wear, and thermal stability studies of some organotin and organosilicon compounds

    NASA Technical Reports Server (NTRS)

    Jones, W. R., Jr.

    1973-01-01

    Thermal decomposition temperatures were determined for a number of organotin and organosilicon compounds. A ball-on-disk sliding friction apparatus was used to determine the friction and wear characteristics of two representative compounds, (1) 3-tri-n-butylstannyl (diphenyl) and (2) 3-tri-n-butylsilyl (diphenyl). Friction and wear test conditions included a 1-kg load, 25 to 225 C disk temperatures, and a dry air atmosphere. The tin and silicon compounds yielded friction and wear results either lower than or similar to those obtained with a polyphenyl ether and a C-ether. The maximum thermal decomposition temperatures obtained in the silicon and tin series were 358 and 297 C, respectively. Increasing the steric hindrance around the silicon or tin atoms increased the thermal stability. Future work with these compounds will emphasize their use as antiwear additives rather than base fluids.

  14. Thermal properties of the optically transparent pore-free nanostructured yttria-stabilized zirconia

    SciTech Connect

    Ghosh, S.; Teweldebrhan, D.; Morales, J. R.; Garay, J. E.; Balandin, A. A.

    2009-12-01

    The authors report results of investigation of thermal conductivity of nanocrystalline yttria-stabilized zirconia. The optically transparent pore-free bulk samples were prepared via the spark plasma sintering process to ensure homogeneity. Thermal conductivity K was measured by two different techniques. It was found that the pore-free nanostructured bulk zirconia is an excellent thermal insulator with the room-temperature Kapprox1.7-2.0 W/m K. It was also shown that the 'phonon-hopping' model can accurately describe specifics of K dependence on temperature and the grain size. The obtained results are important for optimization of zirconia properties for specific applications in advanced electronics and coatings.

  15. Flame retardancy and thermal stability of polyurethane foam composites containing carbon additives

    NASA Astrophysics Data System (ADS)

    Lee, Pyoung-Chan; Kim, Bo-Ram; Jeoung, Sun Kyoung; Lee, Geesoo; Han, San Wook; Kim, Hyunchul; Lee, Ki-Dong; Han, Joo-Kwon

    2016-03-01

    Polyurethane (PU) is an important class of polymers that have wide application in a number of different industrial sectors. The goal of this work was the synthesis of flame-retarded PU foam with expandable graphite (EG) or commercial graphene. The flame retardancy and thermal stability of the foams has been studied through cone calorimeter analysis, the limited oxygen index and thermal conductivity. The presence of expandable graphite brings an improvement in fire behavior. In particular, the limited oxygen index increases in a linear way and the highest limited oxygen index values are obtained for EG-PU foams. The results from the cone calorimeter are in agreement with those of oxygen index; EG filled foams show a considerable decrease of maximum-heat release rate (M-HRR) with respect to unfilled foams. The results of thermal conductivity show that an increase in expandable graphite amount in PU foams lead to an increased conductivity.

  16. Thermal stability of the solid DNA as a novel optical material

    NASA Astrophysics Data System (ADS)

    Nizioł, Jacek; Makyła-Juzak, Katarzyna; Marzec, Mateusz M.; Ekiert, Robert; Marzec, Monika; Gondek, Ewa

    2017-04-01

    Deoxyribonucleic acid (DNA) has been extensively exploited for the past decade as the matrix material in organic electronics and nonlinear optics. In this work thermal stability of DNA in solid form was thoroughly studied, mainly by optical methods. Solid samples of low molecular mass DNA were subjected to heating according to different protocols and dissolved. The temperature effect was observed in the evolution of UV absorption and circular dichroism spectra. Thin films of DNA were deposited on polished silicon wafers. They were conditioned at consecutively raised temperature and simultaneously measured by spectroscopic ellipsometry. Changes in chemical composition of thermally treated films were studied by XPS. Below 100 °C all thermal effects were reversible. Melting occurred at c.a.140 °C. Irreversible chemical changes probably occurred at 170-180 °C.

  17. Thermally driven stability of octadecylphosphonic acid thin films grown on SS316L.

    PubMed

    Lim, Min Soo; Smiley, Katelyn J; Gawalt, Ellen S

    2010-01-01

    Stainless steel 316L is widely used as a biomedical implant material; however, there is concern about the corrosion of metallic implants in the physiological environment. The corrosion process can cause mechanical failure due to resulting cracks and cavities in the implant. Alkyl phosphonic acid forms a thin film by self-assembly on the stainless steel surface and this report conclusively shows that thermal treatment of the octadecylphosphonic acid (ODPA) film greatly enhances the stability of the ODPA molecules on the substrate surface. AFM images taken from the modified substrates revealed that thermally treated films remain intact after methanol, THF, and water flushes, whereas untreated films suffer substantial loss. Water contact angles also show that the hydrophobicity of thermally treated films does not diminish after being incubated in a dynamic flow of water for a 3-hour period, whereas the untreated film becomes increasingly hydrophilic due to loss of ODPA. IR spectra taken of both treated and untreated films after water and THF flushes show that the remaining film retains its initial crystallinity. A model is suggested to explain the stability of ODPA film enhanced by thermal treatment. An ODPA molecule is physisorbed to the surface weakly by hydrogen bonding. Heating drives away water molecules leading to the formation of strong monodentate or mixed mono/bi-dentate bonds of ODPA molecule to the surface.

  18. 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.

  19. Thermally Driven Stability of Octadecylphosphonic Acid Thin Films Grown on SS316L

    PubMed Central

    Lim, Min Soo; Smiley, Katelyn J.; Gawalt, Ellen S.

    2010-01-01

    Stainless steel 316L is widely used as a biomedical implant material; however, there is concern about the corrosion of metallic implants in the physiological environment. The corrosion process can cause mechanical failure due to resulting cracks and cavities in the implant. Alkyl phosphonic acid forms a thin film by self-assembly on the stainless steel surface and this report conclusively shows that thermal treatment of the octadecylphosphonic acid (ODPA) film greatly enhances the stability of the ODPA molecules on the substrate surface. AFM images taken from the modified substrates revealed that thermally treated films remain intact after methanol, THF and water flushes while untreated films suffer substantial loss. Water contact angles also show that the hydrophobicity of thermally treated films does not diminish after being incubated in a dynamic flow of water for a three hour period while the untreated film becomes increasingly hydrophilic due to loss of ODPA. IR spectra taken of both treated and untreated films after water and THF flushes show that the remaining film retains its initial crystallinity. A model is suggested to explain the stability of ODPA film enhanced by thermal treatment. An ODPA molecule is physisorbed to the surface weakly by hydrogen bonding. Heating drives away water molecules leading to the formation of strong monodentate or mixed mono/bi-dentate bonds of ODPA molecule to the surface. PMID:20648546

  20. 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.

  1. Feasibility of self-correcting quantum memory and thermal stability of topological order

    SciTech Connect

    Yoshida, Beni

    2011-10-15

    Recently, it has become apparent that the thermal stability of topologically ordered systems at finite temperature, as discussed in condensed matter physics, can be studied by addressing the feasibility of self-correcting quantum memory, as discussed in quantum information science. Here, with this correspondence in mind, we propose a model of quantum codes that may cover a large class of physically realizable quantum memory. The model is supported by a certain class of gapped spin Hamiltonians, called stabilizer Hamiltonians, with translation symmetries and a small number of ground states that does not grow with the system size. We show that the model does not work as self-correcting quantum memory due to a certain topological constraint on geometric shapes of its logical operators. This quantum coding theoretical result implies that systems covered or approximated by the model cannot have thermally stable topological order, meaning that systems cannot be stable against both thermal fluctuations and local perturbations simultaneously in two and three spatial dimensions. - Highlights: > We define a class of physically realizable quantum codes. > We determine their coding and physical properties completely. > We establish the connection between topological order and self-correcting memory. > We find they do not work as self-correcting quantum memory. > We find they do not have thermally stable topological order.

  2. Thermal stability of quadruplex primers for highly versatile isothermal DNA amplification.

    PubMed

    Mathias, Jordan; Okyere, Robert; Lomidze, Levan; Gvarjaladze, David; Musier-Forsyth, Karin; Kankia, Besik

    2014-01-01

    Quadruplex priming amplification (QPA) allows isothermal amplification of nucleic acids with improved yield and simplified detection. This assay is based on a DNA quadruplex, GGGTGGGTGGGTGGG (G3T), which in the presence of specific cations possesses unusually high thermal stability. QPA employs truncated G3T sequences as primers, which upon polymerase elongation, self-dissociate from the binding site and allow the next round of priming without thermal unfolding of amplicons. The rate of amplification strongly depends on the thermal stability of the primer/primer binding site (PBS) complex and to date QPA has been demonstrated to work over a narrow temperature range. To expand the capabilities of QPA, in the present study, we studied the fold and thermodynamic properties of the wild-type G3T and variants containing sequence modifications or extensions at the 5'-end. Circular dichroism studies demonstrate that the substitution of thymidines by other nucleotides or GC addition at the 5'-end does not change the parallel fold of G3T. Thermal unfolding experiments revealed that purine bases incorporated at loop positions and 5'-end dinucleotide extension significantly destabilize the quadruplex, while loop pyrimidines have almost no effect. Overall, the results of these studies suggest that linear isothermal QPA can be performed over a wide temperature range to accommodate both thermophilic and mesophilic DNA polymerases.

  3. Probing local thermal stabilities of bovine, horse, and tuna ferricytochromes c at pH 7.

    PubMed

    Filosa, A; English, A M

    2000-08-01

    Correlation between the flexibility of the Met80 loop (residues 75-86) and the local stabilities of native ferricytochromes c from horse, bovine, and tuna was examined. By monitoring the heme bands versus temperature, absorption changes associated with altered ligation in the alkaline isomers were observed. In addition, the intensity of the 695-nm absorption band, which is associated with the heme-crevice stability, decreased with increasing temperature and exhibited biphasic temperature dependence, with transition temperatures (Tc) at 35 degrees C in tuna c, 55 degrees C in horse c, and 58 C in bovine c. Since the heme crevice plays a key role in the thermal stabilities of cytochromes c, their susceptibility to proteolytic attack was examined as a function of temperature. Proteolytic digestion, which requires local conformational instability, revealed that the local stabilities of the cytochromes follow the order: bovine > horse > tuna, and increased digestion occurred at temperatures close to the 695-nm Tc for each protein. This is consistent with the actual substitution of the Met80 ligand above the 695-nm Tc, which is reflected in the thermodynamic parameters for the two phases. Also, tuna c, unlike horse and bovine c, exhibits different 695-nm (35 degrees C) and Soret (approximately 46 degrees C) Tc values, but its local stability is controlled by the transition detected at 695 nm. The combined spectroscopic and proteolysis results clearly indicate that the flexibility of the Met80 loop determines the local stability of cytochromes c.

  4. Shelf stability of nanofluids and its effect on thermal conductivity and viscosity

    NASA Astrophysics Data System (ADS)

    Haghighi, E. B.; Nikkam, N.; Saleemi, M.; Behi, M.; Mirmohammadi, S. A.; Poth, H.; Khodabandeh, R.; Toprak, M. S.; Muhammed, M.; Palm, B.

    2013-10-01

    This study proposes a method and apparatus to estimate shelf stability of nanofluids. Nanofluids are fabricated by dispersion of solid nanoparticles in base fluids, and shelf stability is a key issue for many practical applications of these fluids. In this study, shelf stability is evaluated by measuring the weight of settled solid particles on a suspended tray in a colloid versus time and correlated with the performance change of some nanofluid systems. The effects of solid particle concentration and bath sonication time were investigated for selected nanofluids. The results show the applicability of this simple method and the apparatus to evaluate nanofluid shelf stability. Furthermore, it shows that Stokes’ law is not valid for determining the settling time of the tested nanoparticles probably due to their complicated shape and presence of surface modifiers. The effect of shelf stability on thermal conductivity and viscosity was illustrated for some nanofluids. Experimental results show that water-based Al2O3 nanofluids have quite good shelf stability and can be good candidates for industrial applications.

  5. Evaluation of the JP-8+100 additive candidates in the extended duration thermal stability test system

    SciTech Connect

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

    1996-10-01

    The most promising JP-8+100 additive candidates consists of dispersants, detergents, antioxidants and metal deactivators. A series of tests were conducted in the Extended Duration Thermal Stability Test System to determine the thermal stability effects of the individual JP-8+100 additives and combinations of the additives. This paper will cover the test results and their relationship to future aircraft fuel systems. The Extended Duration Thermal Stability Test System was designed to conduct long duration tests at non-accelerated temperature conditions and resident times representative or aircraft/engine fuel systems. This system and its operating characteristics will also be covered in this paper.

  6. Vaccines with Aluminum-Containing Adjuvants: Optimizing Vaccine Efficacy and Thermal Stability

    PubMed Central

    Clapp, Tanya; Siebert, Paul; Chen, Dexiang; Braun, LaToya Jones

    2011-01-01

    Aluminum-containing adjuvants have been used to enhance the immune response against killed, inactivated and subunit antigens for over seven decades. Nevertheless, we are only beginning to gain important insight as to what may be some very fundamental parameters for optimizing their use. For example, there is evidence that the conventional approach of maximizing antigen binding (amount and/or strength) may not result in an optimal immune response. Adsorption of antigen onto the adjuvant has recently been suggested to decrease the thermal stability of some antigens; however, whether adsorption-induced alterations to the structure and/or stability of the antigen have consequences for the elicited immune response is unclear. Finally, the thermal stability of vaccines with aluminum-containing adjuvants is not robust. Optimizing the stability of these vaccines requires an understanding of the freeze sensitivity of the adjuvant, freeze and heat sensitivity of the antigen in the presence of the adjuvant, and perhaps most importantly, how (or whether) various approaches to formulation can be used to address these instabilities. This review attempts to summarize recent findings regarding issues that may dictate the success of vaccines with aluminum-containing adjuvants. PMID:20740674

  7. Prediction of salt effects on protein phase behavior by HIC retention and thermal stability.

    PubMed

    Baumgartner, Kai; Großhans, Steffen; Schütz, Juliane; Suhm, Susanna; Hubbuch, Jürgen

    2016-09-05

    In the biopharmaceutical industry it is mandatory to know and ensure the correct protein phase state as a critical quality attribute in every process step. Unwanted protein precipitation or crystallization can lead to column, pipe or filter blocking. In formulation, the formation of aggregates can even be lethal when injected into the patient. The typical methodology to illustrate protein phase states is the generation of protein phase diagrams. Commonly, protein phase behavior is shown in dependence of protein and precipitant concentration. Despite using high-throughput methods for the generation of phase diagrams, the time necessary to reach equilibrium is the bottleneck. Faster methods to predict protein phase behavior are desirable. In this study, hydrophobic interaction chromatography retention times were correlated to crystal size and form. High-throughput thermal stability measurements (melting and aggregation temperatures), using an Optim(®)2 system, were successfully correlated to glucose isomerase stability. By using hydrophobic interaction chromatography and thermal stability determinations, glucose isomerase conformational and colloidal stability were successfully predicted for different salts in a specific pH range.

  8. Phosphate buffer effects on thermal stability and H2O2-resistance of horseradish peroxidase.

    PubMed

    Asad, Sedigheh; Torabi, Seyed-Fakhreddin; Fathi-Roudsari, Mehrnoosh; Ghaemi, Nasser; Khajeh, Khosro

    2011-05-01

    Horseradish peroxidase (HRP) has attracted intense research interest due to its potential applications in biotechnological fields. However, inadequate stability under prevalent conditions such as elevated temperatures and H(2)O(2) exposure, has limited its industrial application. In this study, stability of HRP was investigated in the presence of different buffer systems (potassium phosphate and Tris-HCl) and additives. It was shown that the concentration of phosphate buffer severely affects enzyme thermostability in a way that in diluted potassium phosphate buffer (10mM) half-life (from 13 to 35 min at 80 °C) and T(m) (from 73 to 77.5 °C) increased significantly. Among additives tested, trehalose had the most thermostabilizing effect. Exploring the role of glycosylation in stabilizing effect of phosphate buffer, non-glycosylated recombinant HRP was also examined for its thermal and H(2)O(2) stability in both diluted and concentrated phosphate buffers. The recombinant enzyme was more thermally stable in diluted buffer in accordance to glycosylated HRP; but interestingly recombinant HRP showed higher H(2)O(2) tolerance in concentrated buffer.

  9. Additivity in both thermodynamic stability and thermal transition temperature for rubredoxin chimeras via hybrid native partitioning.

    PubMed

    LeMaster, David M; Hernández, Griselda

    2005-08-01

    Given any operational definition of pairwise interaction, the set of residues that differ between two structurally homologous proteins can be uniquely partitioned into subsets of clusters for which no such interactions occur between clusters. Although hybrid protein sequences that preserve such clustering are consistent with tertiary structures composed of only parental native-like interactions, the stability of such predicted structures will depend upon the physical robustness of the assumed interaction potential. A simple distance cutoff criterion was applied to the most thermostable protein known to predict such a seven-residue cluster in the metal binding site region of Pyrococcus furiosus rubredoxin and a mesophile homolog. Both conformational stability and thermal transition temperature measurements demonstrate that 39% of the differential stability arises from these seven residues.

  10. Stability of modulated-gravity-induced thermal convection in magnetic fields.

    PubMed

    Li, B Q

    2001-04-01

    A stability analysis is presented of modulated-gravity-induced thermal convection in a heated fluid layer subject to an applied magnetic field. The nearest correction to the critical Rayleigh number for both single and multiple frequency oscillating-gravity components is obtained by solving the linearized magnetohydrodynamic equations using the small parameter perturbation technique. The correction depends on both the applied magnetic field and the oscillating frequency. In the absence of an applied magnetic field, the correction depends on the Prandtl number only when the exciting frequency is small. However, it asymptotically approaches zero as the frequency increases, with or without the presence of a magnetic field. The heated fluid layer is more stable with gravity modulation than with any type of wall temperature modulation. The difference becomes smaller with decreasing Prandtl number Pr. This finding is of critical importance in that ground-based experiments with appropriate wall temperature modulations may be conducted to simulate the oscillating-gravity effects on the onset of thermal convection in lower-Prandtl-number fluids. For conducting melts considered for microgravity applications, it is possible to apply an external magnetic field to further inhibit the onset of modulated-gravity-induced thermal convection. This effectiveness increases with the Hartmann number Ha. For large Ha, the nearest correction term R02 approximately Ha2 as the magnetic Prandtl number Pm<1. However, R02 approximately Ha(4/3) for Ha>1 and Pm>1, provided that Ha<0.5pi(Pm/Pr(3/2)), which is satisfied by a majority of space melt experiments. Thus, under normal laboratory conditions applied magnetic fields are more effective in stabilizing a conducting fluid subject to an oscillating-gravity field than one subject to a constant field. If Ha>0.5pi(Pm/Pr(3/2)), R02 approximately -Ha2 for Ha>1 and Pm>1 and the magnetic field becomes less effective in stabilizing thermal convection

  11. Protein thermal stability enhancement by designing salt bridges: a combined computational and experimental study.

    PubMed

    Lee, Chi-Wen; Wang, Hsiu-Jung; Hwang, Jenn-Kang; Tseng, Ching-Ping

    2014-01-01

    Protein thermal stability is an important factor considered in medical and industrial applications. Many structural characteristics related to protein thermal stability have been elucidated, and increasing salt bridges is considered as one of the most efficient strategies to increase protein thermal stability. However, the accurate simulation of salt bridges remains difficult. In this study, a novel method for salt-bridge design was proposed based on the statistical analysis of 10,556 surface salt bridges on 6,493 X-ray protein structures. These salt bridges were first categorized based on pairing residues, secondary structure locations, and Cα-Cα distances. Pairing preferences generalized from statistical analysis were used to construct a salt-bridge pair index and utilized in a weighted electrostatic attraction model to find the effective pairings for designing salt bridges. The model was also coupled with B-factor, weighted contact number, relative solvent accessibility, and conservation prescreening to determine the residues appropriate for the thermal adaptive design of salt bridges. According to our method, eight putative salt-bridges were designed on a mesophilic β-glucosidase and 24 variants were constructed to verify the predictions. Six putative salt-bridges leaded to the increase of the enzyme thermal stability. A significant increase in melting temperature of 8.8, 4.8, 3.7, 1.3, 1.2, and 0.7°C of the putative salt-bridges N437K-D49, E96R-D28, E96K-D28, S440K-E70, T231K-D388, and Q277E-D282 was detected, respectively. Reversing the polarity of T231K-D388 to T231D-D388K resulted in a further increase in melting temperatures by 3.6°C, which may be caused by the transformation of an intra-subunit electrostatic interaction into an inter-subunit one depending on the local environment. The combination of the thermostable variants (N437K, E96R, T231D and D388K) generated a melting temperature increase of 15.7°C. Thus, this study demonstrated a novel

  12. High thermal stability of La2O3 and CeO2-stabilized tetragonal ZrO2

    DOE PAGES

    Wang, Shichao; Xie, Hong; Lin, Yuyuan; ...

    2016-02-15

    Catalyst support materials of tetragonal ZrO2, stabilized by either La2O3 (La2O3-ZrO2) or CeO2 (CeO2-ZrO2), were synthesized under hydrothermal conditions at 200 °C with NH4OH or tetramethylammonium hydroxide as the mineralizer. From In Situ synchrotron powder X-ray diffraction and small-angle X-ray scattering measurements, the calcined La2O3-ZrO2 and CeO2-ZrO2 supports were nonporous nanocrystallites that exhibited rectangular shapes with thermal stability up to 1000 °C in air. These supports had an average size of ~10 nm and a surface area of 59-97 m2/g. The catalysts Pt/La2O3-ZrO2 and Pt/CeO2-ZrO2 were prepared by using atomic layer deposition with varying Pt loadings from 6.3-12.4 wt %.more » Mono-dispersed Pt nanoparticles of ~3 nm were obtained for these catalysts. As a result, the incorporation of La2O3 and CeO2 into the t-ZrO2 structure did not affect the nature of the active sites for the Pt/ZrO2 catalysts for the water-gas-shift (WGS) reaction.« less

  13. Bone bonding ability of a chemically and thermally treated low elastic modulus Ti alloy: gum metal.

    PubMed

    Tanaka, Masashi; Takemoto, Mitsuru; Fujibayashi, Shunsuke; Kawai, Toshiyuki; Yamaguchi, Seiji; Kizuki, Takashi; Matsushita, Tomiharu; Kokubo, Tadashi; Nakamura, Takashi; Matsuda, Shuichi

    2014-03-01

    The gum metal with composition Ti-36Nb-2Ta-3Zr-0.3O, is free from cytotoxic elements and exhibits a low elastic modulus as well as high mechanical strength. We have previously demonstrated that this gum metal, once subjected to a series of surface treatments--immersion in 1 M NaOH (alkali treatment) and then 100 mM CaCl2, before heating at 700 °C (sample: ACaH-GM), with an optional final hot water immersion (sample: ACaHW-GM)--has apatite-forming ability in simulated body fluid. To confirm the in vivo bioactivity of these treated alloys, failure loads between implants and bone at 4, 8, 16, and 26 weeks after implantation in rabbits' tibiae were measured for untreated gum metal (UT-GM), ACaH-GM and ACaHW-GM, as well as pure titanium plates after alkali and heat treatment (AH-Ti). The ACaH-GM and UT-GM plates showed almost no bonding, whereas ACaHW-GM and AH-Ti plates showed successful bonding by 4 weeks, and their failure loads subsequently increased with time. The histological findings showed a large amount of new bone in contact with the surface of ACaHW-GM and AH-Ti plates, suggesting that the ACaHW treatment could impart bone-bonding bioactivity to a gum metal in vivo. Thus, with this improved bioactive treatment, these advantageous gum metals become useful candidates for orthopedic and dental devices.

  14. Thermal stability of poly(ethylene-co-vinyl acetate) based materials

    SciTech Connect

    Patel, Mogon; Pitts, Simon; Beavis, Peter; Robinson, Mathew; Morrell, Paul; Khan, Niaz; Khan, Imran; Pockett, Nicola; Letant, Sonia; Von White, Gregory; Labouriau, Andrea

    2013-03-26

    The thermal stability properties of poly (ethylene-co-vinyl acetate) composites have been studied in support of our core programmes in materials qualification and life assessment. The material is used as a binder phase for boron particles in highly filled (70 wt %) composites. Our studies show that the uncured resin readily accumulates acetic acid through hydrolysis of the pendent acetate groups which alters the acidity (pH) of the material. Thermal desorption studies in combination with gas-chromatography-mass spectrometry show that the resin readily evolves acetic acid when thermally aged to temperatures up to 75°C. Gel Permeation Chromatography (GPC) suggests that thermal ageing induces a gradual reduction in resin molecular weight and confirms the susceptibility of the material to chain scission. Heating at elevated temperatures in excess of 300oC is required to induce significant changes in the carbon skeleton through deacetylation and dehydration processes and the production of unsaturated main chain double bonds. Overall, the mechanical response of these filled composites are found to be relatively complex with the extent of polymer-filler interactions possibly playing an important role in determining key engineering properties. Mechanical property studies confirm a small but significant decrease in modulus presumably linked to thermally induced chain scission of the EVA binder.

  15. Thermal stability of poly(ethylene-co-vinyl acetate) based materials

    DOE PAGES

    Patel, Mogon; Pitts, Simon; Beavis, Peter; ...

    2013-03-26

    The thermal stability properties of poly (ethylene-co-vinyl acetate) composites have been studied in support of our core programmes in materials qualification and life assessment. The material is used as a binder phase for boron particles in highly filled (70 wt %) composites. Our studies show that the uncured resin readily accumulates acetic acid through hydrolysis of the pendent acetate groups which alters the acidity (pH) of the material. Thermal desorption studies in combination with gas-chromatography-mass spectrometry show that the resin readily evolves acetic acid when thermally aged to temperatures up to 75°C. Gel Permeation Chromatography (GPC) suggests that thermal ageingmore » induces a gradual reduction in resin molecular weight and confirms the susceptibility of the material to chain scission. Heating at elevated temperatures in excess of 300oC is required to induce significant changes in the carbon skeleton through deacetylation and dehydration processes and the production of unsaturated main chain double bonds. Overall, the mechanical response of these filled composites are found to be relatively complex with the extent of polymer-filler interactions possibly playing an important role in determining key engineering properties. Mechanical property studies confirm a small but significant decrease in modulus presumably linked to thermally induced chain scission of the EVA binder.« less

  16. Study of the thermal stability of studtite by in situ Raman spectroscopy and DFT calculations

    NASA Astrophysics Data System (ADS)

    Colmenero, Francisco; Bonales, Laura J.; Cobos, Joaquín; Timón, Vicente

    2017-03-01

    The design of a safe spent nuclear fuel repository requires the knowledge of the stability of the secondary phases which precipitate when water reaches the fuel surface. Studtite is recognized as one of the secondary phases that play a key-role in the mobilization of the radionuclides contained in the spent fuel. Thereby, it has been identified as a product formed under oxidation conditions at the surface of the fuel, and recently found as a corrosion product in the Fukushima-Daiichi nuclear plant accident. Thermal stability is one of the properties that should be determined due to the high temperature of the fuel. In this work we report a detailed analysis of the structure and thermal stability of studtite. The structure has been studied both by experimental techniques (SEM, TGA, XRD and Raman spectroscopy) and theoretical DFT electronic structure and spectroscopic calculations. The comparison of the results allows us to perform for the first time the Raman bands assignment of the whole spectrum. The thermal stability of studtite has been analyzed by in situ Raman spectroscopy, with the aim of studying the effect of the heating rate and the presence of water. For this purpose, a new cell has been designed. The results show that studtite is stable under dry conditions only at temperatures below 30 °C, in contrast with the higher temperatures published up to date ( 130 °C). Opposite behaviour has been found when studtite is in contact with water; under these conditions studtite is stable up to 90 °C, what is consistent with the encounter of this phase after the Fukushima-Daiichi accident.

  17. Study of the thermal stability of studtite by in situ Raman spectroscopy and DFT calculations.

    PubMed

    Colmenero, Francisco; Bonales, Laura J; Cobos, Joaquín; Timón, Vicente

    2017-03-05

    The design of a safe spent nuclear fuel repository requires the knowledge of the stability of the secondary phases which precipitate when water reaches the fuel surface. Studtite is recognized as one of the secondary phases that play a key-role in the mobilization of the radionuclides contained in the spent fuel. Thereby, it has been identified as a product formed under oxidation conditions at the surface of the fuel, and recently found as a corrosion product in the Fukushima-Daiichi nuclear plant accident. Thermal stability is one of the properties that should be determined due to the high temperature of the fuel. In this work we report a detailed analysis of the structure and thermal stability of studtite. The structure has been studied both by experimental techniques (SEM, TGA, XRD and Raman spectroscopy) and theoretical DFT electronic structure and spectroscopic calculations. The comparison of the results allows us to perform for the first time the Raman bands assignment of the whole spectrum. The thermal stability of studtite has been analyzed by in situ Raman spectroscopy, with the aim of studying the effect of the heating rate and the presence of water. For this purpose, a new cell has been designed. The results show that studtite is stable under dry conditions only at temperatures below 30°C, in contrast with the higher temperatures published up to date (~130°C). Opposite behaviour has been found when studtite is in contact with water; under these conditions studtite is stable up to 90°C, what is consistent with the encounter of this phase after the Fukushima-Daiichi accident.

  18. 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.

  19. 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.

  20. Effect of Au Content on Thermal Stability and Mechanical Properties of Au-Cu-Ag-Si Bulk Metallic Glasses

    NASA Astrophysics Data System (ADS)

    Guo, H.; Zhang, W.; Chen, M. W.; Saotome, Y.; Fukuhara, M.; Inoue, A.

    2011-06-01

    The thermal stability, glass-forming ability (GFA), and mechanical and electrical properties of Au-based Au x Si17Cu75.5- x Ag7.5 ( x = 40 to 75.5 at. pct) metallic glasses were investigated. The glass transition temperature ( T g ) and crystallization temperature ( T x ) decreased with increasing Au content. The ultralow T g values below 373 K (100 °C) were obtained for alloys with x = 55 to 75.5. The alloys with x = 45 to 70 exhibited a high stabilization of supercooled liquid and a high GFA, and the supercooled liquid region and critical sample diameter for glass formation were in the range of 31 K to 50 K and 2 to 5 mm, respectively. The compressive fracture strength ( σ c,f ), Young's modulus ( E), and Vicker's hardness ( H v ) of the bulk metallic glasses (BMGs) decreased with increasing Au content. A linear correlation between Au concentration and the characteristic temperature, i.e., T g and T x , and mechanical properties, i.e., σ c,f , E, and H v , as well as electrical resistivity can be found in the BMGs, which will be helpful for the composition design of the desirable Au-based BMGs with tunable physical properties.

  1. Thermal and hydrothermal stability of selected polymers in a nuclear reactor environment

    NASA Astrophysics Data System (ADS)

    Kim, Jinho

    The focus of this study is the development and understanding of polymer based burnable poison rod assemblies (BPRAs) in pressurized water reactors (PWRs). This material substitution reduces the water displacement penalty at the end of cycle (EOC) currently found with the B4C/Al 2O3 BPRAs that displace moderator water in PWRs. This gives rise to a longer fuel cycle due to the extra moderation from hydrogen in polymer structures. Finding synthetic polymers that endure a severe nuclear reactor circumstance is a challenge. Aside from the proper thermal stability at the range of 350--600°C in the core for a single cycle, the hydrothermal stability at near-critical water condition (350°C, 20.7MPa) is required to maintain the safe and controlled nuclear reaction because a danger comes if water might possibly penetrate inside the burnable poison rod by the failure of zircaloy cladding. There are two approaches to obtain a boron source (burnable position material) in hydrogen containing polymers. One is to utilize the boron source directly by synthesizing boron-containing polymers. A second approach is to find commercial polymers that have an appropriate thermal, hydrothermal, radiational stability and high hydrogen content; and then add an inorganic boron source such as B4C to form a composite material. Poly (diacetylene-siloxane-carborane)s and other silicon based precursor polymers were introduced to observe their thermal and hydrothermal stability. However, we found that the degradation of Si-O-Si, which was presented in the polymer, was an unfavorable disadvantage under near-critical water (350°C, 20.7MPa) even though they formed dense network structures. In addition, the Si-O bond is quite sensitive to variety of reagents, including base and acid. Therefore, the degradation rate might be accelerated by high H+ and OH- ion concentrations at the near-critical water condition. For the second approach, a number of candidate matrix polymers were screened for new

  2. 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.

  3. 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

  4. Refractory and Hard Materials in the Ti-Si-B-C-N System - Phase Equilibria, Phase Reactions and Thermal Stabilities

    DTIC Science & Technology

    2004-12-01

    1 REFRACTORY AND HARD MATERIALS IN THE Ti-Si-B-C-N SYSTEM – PHASE EQUILIBRIA , PHASE REACTIONS AND THERMAL STABILITIES Hans Jürgen Seifert...the underlying phase equilibria and reactions have to be known in detail. The main goal of this work was to study the thermal stability with...respect to the phase equilibria and the phase reactions of ceramics and refractory and hard materials in the Ti-Si-B-C-N system by means of CALPHAD

  5. Enhanced thermal stability of functionally graded sandwich cylindrical shells by shape memory alloys

    NASA Astrophysics Data System (ADS)

    Asadi, H.; Akbarzadeh, A. H.; Chen, Z. T.; Aghdam, M. M.

    2015-04-01

    The present paper deals with the nonlinear thermal instability of geometrically imperfect sandwich cylindrical shells under uniform heating. The sandwich shells are made of a shape memory alloy (SMA)-fiber-reinforced composite and functionally graded (FG) face sheets (FG/SMA/FG). The Brinson phenomenological model is used to express the constitutive characteristics of SMA fibers. The governing equations are established within the framework of the third-order shear deformation shell theory by taking into account the von Karman geometrical nonlinearity and initial imperfection. The material properties of constituents are assumed to be temperature dependent. The Galerkin technique is utilized to derive expressions of the bifurcation points and bifurcation paths of the sandwich cylindrical shells. Using the developed closed-form solutions, extensive numerical results are presented to provide an insight into the influence of the SMA fiber volume fraction, SMA pre-strain, core thickness, non-homogeneity index, geometrical imperfection, geometry parameters of sandwich shells and temperature dependency of materials on the stability of shells. The results reveal that proper application of SMA fibers postpones the thermal bifurcation point and dramatically decreases thermal post-buckling deflection. Moreover, the induced tensile recovery stress of SMA fibers could also stabilize the geometrically imperfect shells during the inverse martensite phase transformation.

  6. Composition, phase behavior and thermal stability of natural edible fat from rambutan (Nephelium lappaceum L.) seed.

    PubMed

    Solís-Fuentes, Julio A; Camey-Ortíz, Guadalupe; Hernández-Medel, María del Rosario; Pérez-Mendoza, Francisco; Durán-de-Bazúa, Carmen

    2010-01-01

    In this paper, the chemical composition, the main physicochemical properties, phase behavior and thermal stability of rambutan (Nephelium lappaceum L.) seed fat were studied. These results showed that the almond-like decorticated seed represents 6.1% of the wet weight fruit and is: 1.22% ash, 7.80% protein, 11.6% crude fiber, 46% carbohydrates, and 33.4% fat (d.b.). The main fatty acids in the drupe fat were 40.3% oleic, 34.5% arachidic, 6.1% palmitic, 7.1% stearic, 6.3% gondoic, and 2.9% behenic; the refraction, saponification and iodine values were 1.468, 186, and 47.0, respectively. The phase behavior analysis showed relatively simple crystallization and melting profiles: crystallization showed three well-differentiated groups of triglycerides around maximum peaks at +30.8, +15.6 and -18.1 degrees C; the fat-melting curve had a range between -14.5 and +51.8 degrees C with a fusion enthalpy of 124.3 J/g. The thermal stability analyzed in an inert atmosphere of N(2) and in a normal oxidizing atmosphere, showed that in the latter, fat decomposition begins at 237.3 degrees C and concludes at 529 degrees C, with three stages of decomposition. According to these results, rambutan seed fat has physicochemical and thermal characteristics that may become interesting for specific applications in several segments of the food industry.

  7. Stability of nickel-coated sand as gravel-pack material for thermal wells

    SciTech Connect

    Sacuta, A.; Nguyen, D.M.; Kissel, G.A. )

    1988-11-01

    Laboratory flow tests have been carried out to study the stability of various nickel-coated sands under aqueous steam temperature and pH conditions that may exist in thermal recovery operations. Other gravel-pack materials tested include Ottawa sand, sintered bauxite, cement clinker, zirconium oxide, and nickel pellets. A comparison was made between the performances of these materials after exposure to identical thermal and hydrolytic conditions. Test results indicate that nickel-coated sands are highly resistant to dissolution at temperatures as high as 300/sup 0/C (570/sup 0/F) and to solution pH's from 4.75 to 11. Weight losses measured after a 72-hour period were less than 1%. In contrast, weight losses from sintered bauxite, zirconium oxide, and Ottawa sand dissolution tests were 30 to 70 times higher under the same conditions. Cement clinker losses were in the intermediate range under alkaline conditions. API standard crushing and acid-solubility tests for proppants also were performed on nickel-coated sands. These results were favorable in that they exceeded the recommended standards. This study of nickel-coated sand stability and mechanical strength has demonstrated its high potential for application as either a gravel-pack material or proppant in thermal recovery operations.

  8. Cysteine residue is not essential for CPM protein thermal-stability assay.

    PubMed

    Wang, Zhaoshuai; Ye, Cui; Zhang, Xinyi; Wei, Yinan

    2015-05-01

    A popular thermal-stability assay developed especially for the study of membrane proteins uses a thiol-specific probe, 7-diethylamino-3-(4-maleimidophenyl)-4-methylcoumarin (CPM). The fluorescence emission of CPM surges when it forms a covalent bond with the side chain of a free Cys, which becomes more readily accessible upon protein thermal denaturation. Interestingly, the melting temperatures of membrane proteins determined using the CPM assay in literature are closely clustered in the temperature range 45-55 °C. A thorough understanding of the mechanism behind the observed signal change is critical for the accurate interpretation of the protein unfolding. Here we used two α-helical membrane proteins, AqpZ and AcrB, as model systems to investigate the nature of the fluorescence surge in the CPM assay. We found that the transition temperatures measured using circular-dichroism (CD) spectroscopy and the CPM assay were significantly different. To eliminate potential artifact that might arise from the presence of detergent, we monitored the unfolding of two soluble proteins. We found that, contrary to current understanding, the presence of a sulfhydryl group was not a prerequisite for the CPM thermal-stability assay. The observed fluorescence increase is probably caused by binding of the fluorophore to hydrophobic patches exposed upon protein unfolding.

  9. RP-2 Thermal Stability and Heat Transfer Investigation for Hydrocarbon Boost Engines

    NASA Technical Reports Server (NTRS)

    VanNoord, J. L.; Stiegemeier, B. R.

    2010-01-01

    A series of electrically heated tube tests were performed at the NASA Glenn Research Center s Heated Tube Facility to investigate the use of RP-2 as a fuel for next generation regeneratively cooled hydrocarbon boost engines. The effect that test duration, operating condition and test piece material have on the overall thermal stability and materials compatibility characteristics of RP-2 were evaluated using copper and 304 stainless steel test sections. The copper tests were run at 1000 psia, heat flux up to 6.0 Btu/in.2-sec, and wall temperatures up to 1180 F. Preliminary results, using measured wall temperature as an indirect indicator of the carbon deposition process, show that in copper test pieces above approximately 850 F, RP-2 begins to undergo thermal decomposition resulting in local carbon deposits. Wall temperature traces show significant local temperature increases followed by near instantaneous drops which have been attributed to the carbon deposition/shedding process in previous investigations. Data reduction is currently underway for the stainless steel test sections and carbon deposition measurements will be performed in the future for all test sections used in this investigation. 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-2.

  10. Viscosity and thermal conductivity of nanofluids containing multi-walled carbon nanotubes stabilized by chitosan

    SciTech Connect

    Phuoc, Tran X.; Massoudi, Mehrdad; Chen, Ruey-Hung

    2011-01-01

    Thermal conductivity, viscosity, and stability of nanofluids containing multi-walled carbon nanotubes (MWCNTs) stabilized by cationic chitosan were studied. Chitosan with weight fraction of 0.1%, 0.2 wt%, and 0.5 wt% was used to disperse stably MWCNTs in water. The measured thermal conductivity showed an enhancement from 2.3% to 13% for nanofluids that contained from 0.5 wt% to 3 wt% MWCNTs (0.24 to 1.43 vol %). These values are significantly higher than those predicted using the Maxwell's theory. We also observed that the enhancements were independent of the base fluid viscosity. Thus, use of microconvection effect to explain the anomalous thermal conductivity enhancement should be reconsidered. MWCNTs can be used either to enhance or reduce the fluid base viscosity depending on the weight fractions. In the viscosity-reduction case, a reduction up to 20% was measured by this work. In the viscosity-enhancement case, the fluid behaved as a non-Newtonian shear-thinning fluid. By assuming that MWCNT nanofluids behave as a generalized second grade fluid where the viscosity coefficient depends upon the rate of deformation, a theoretical model has been developed. The model was found to describe the fluid behavior very well.

  11. Thermal stability of proton conducting acid doped polybenzimidazole in simulated fuel cell environments

    SciTech Connect

    Samms, S.R.; Wasmus, S.; Savinell, R.F.

    1996-04-01

    Recently, polybenzimidazole membrane doped with phosphoric acid (PBI) was found to have promising properties for use as a polymer electrolyte in a high temperature (ca. 150 to 200 C) proton exchange membrane direct methanol fuel cell. However, operation at 200 C in strongly reducing and oxidizing environments introduces concerns of the thermal stability of the polymer electrolyte. To simulate the conditions in a high temperature fuel cell, PBI samples were loaded with fuel cell grade platinum black, doped with ca. 480 mole percent phosphoric acid (i.e., 4.8 H{sub 3}PO{sub 4} molecules per PBI repeat unit) and heated under atmospheres of either nitrogen, 5% hydrogen, or air in a thermal gravimetric analyzer. The products of decomposition were taken directly into a mass spectrometer for identification. In all cases weight loss below 400 C was found to be due to loss of water. Judging from the results of these tests, the thermal stability of PBI is more than adequate for use as a polymer electrolyte in a high temperature fuel cell.

  12. Enhanced thermal- and photo-stability of acid yellow 17 by incorporation into layered double hydroxides

    SciTech Connect

    Wang Qian; Feng Yongjun; Feng Junting; Li Dianqing

    2011-06-15

    2,5-dichloro-4-(5-hydroxy-3-methyl-4-(sulphophenylazo) pyrazol-1-yl) benzenesulphonate (DHSB) anions, namely acid yellow 17 anions, have been successfully intercalated into Zn-Al layered double hydroxides (LDH) to produce a novel organic-inorganic pigment by a simple method involving separate nucleation and aging steps (SNAS), and the dye-intercalated LDH was analyzed by various techniques, e.g., XRD, SEM, FT-IR, TG-DTA and ICP. The d-spacing of the prepared LDH is 2.09 nm. Furthermore, the incorporation of the DHSB aims to enhance the thermal- and photo-stability of the guest dye molecule, for example, the less color change after accelerated thermal- and photo-aging test. - Graphical abstract: Acid yellow anions were successfully assembled into ZnAl layered double hydroxides (LDH) to produce a novel organic-inorganic composite pigment by a simple method involving separate nucleation and aging steps (SNAS). Highlights: > Acid yellow 17 was directly intercalated into ZnAl-LDH to form a novel pigment. > The pigment was prepared by a method involving separate nucleation and aging steps. > The intercalation of dye anions enhances its thermal- and photo-stability.

  13. Thermal Design to Meet Stringent Temperature Gradient/Stability Requirements of SWIFT BAT Detectors

    NASA Technical Reports Server (NTRS)

    Choi, Michael K.

    2000-01-01

    The Burst Alert Telescope (BAT) is an instrument on the National Aeronautics and Space Administration (NASA) SWIFT spacecraft. It is designed to detect gamma ray burst over a broad region of the sky and quickly align the telescopes on the spacecraft to the gamma ray source. The thermal requirements for the BAT detector arrays are very stringent. The maximum allowable temperature gradient of the 256 cadmium zinc telluride (CZT) detectors is PC. Also, the maximum allowable rate of temperature change of the ASICs of the 256 Detector Modules (DMs) is PC on any time scale. The total power dissipation of the DMs and Block Command & Data Handling (BCDH) is 180 W. This paper presents a thermal design that uses constant conductance heat pipes (CCHPs) to minimize the temperature gradient of the DMs, and loop heat pipes (LHPs) to transport the waste heat to the radiator. The LHPs vary the effective thermal conductance from the DMs to the radiator to minimize heater power to meet the heater power budget, and to improve the temperature stability. The DMs are cold biased, and active heater control is used to meet the temperature gradient and stability requirements.

  14. A linear stability analysis for nonlinear, grey, thermal radiative transfer problems

    SciTech Connect

    Wollaber, Allan B.; Larsen, Edward W.

    2011-02-20

    We present a new linear stability analysis of three time discretizations and Monte Carlo interpretations of the nonlinear, grey thermal radiative transfer (TRT) equations: the widely used 'Implicit Monte Carlo' (IMC) equations, the Carter Forest (CF) equations, and the Ahrens-Larsen or 'Semi-Analog Monte Carlo' (SMC) equations. Using a spatial Fourier analysis of the 1-D Implicit Monte Carlo (IMC) equations that are linearized about an equilibrium solution, we show that the IMC equations are unconditionally stable (undamped perturbations do not exist) if {alpha}, the IMC time-discretization parameter, satisfies 0.5 < {alpha} {<=} 1. This is consistent with conventional wisdom. However, we also show that for sufficiently large time steps, unphysical damped oscillations can exist that correspond to the lowest-frequency Fourier modes. After numerically confirming this result, we develop a method to assess the stability of any time discretization of the 0-D, nonlinear, grey, thermal radiative transfer problem. Subsequent analyses of the CF and SMC methods then demonstrate that the CF method is unconditionally stable and monotonic, but the SMC method is conditionally stable and permits unphysical oscillatory solutions that can prevent it from reaching equilibrium. This stability theory provides new conditions on the time step to guarantee monotonicity of the IMC solution, although they are likely too conservative to be used in practice. Theoretical predictions are tested and confirmed with numerical experiments.

  15. Effect of Hofmeister ions on protein thermal stability: roles of ion hydration and peptide groups?

    PubMed

    Sedlák, Erik; Stagg, Loren; Wittung-Stafshede, Pernilla

    2008-11-01

    We have systematically explored the Hofmeister effects of cations and anions (0.3-1.75 M range) for acidic Desulfovibrio desulfuricans apoflavodoxin (net charge -19, pH 7) and basic horse heart cytochrome c (net charge +17, pH 4.5). The Hofmeister effect of the ions on protein thermal stability was assessed by the parameter dT trs/d[ion] (T trs; thermal midpoint). We show that dT trs/d[ion] correlates with ion partition coefficients between surface and bulk water and ion surface tension effects: this suggests direct interactions between ions and proteins. Surprisingly, the stability effects of the different ions on the two model proteins are similar, implying a major role of the peptide backbone, instead of charged groups, in mediation of the interactions. Upon assessing chemical/physical properties of the ions responsible for the Hofmeister effects on protein stability, ion charge density was identified as most important. Taken together, our study suggests key roles for ion hydration and the peptide group in facilitating interactions between Hofmeister ions and proteins.

  16. Novel LLM series high density energy materials: Synthesis, characterization, and thermal stability

    NASA Astrophysics Data System (ADS)

    Pagoria, Philip; Zhang, Maoxi; Tsyshevskiy, Roman; Kuklja, Maija

    Novel high density energy materials must satisfy specific requirements, such as an increased performance, reliably high stability to external stimuli, cost-efficiency and ease of synthesis, be environmentally benign, and be safe for handling and transportation. During the last decade, the attention of researchers has drifted from widely used nitroester-, nitramine-, and nitroaromatic-based explosives to nitrogen-rich heterocyclic compounds. Good thermal stability, the low melting point, high density, and moderate sensitivity make heterocycle materials attractive candidates for use as oxidizers in rocket propellants and fuels, secondary explosives, and possibly as melt-castable ingredients of high explosive formulations. In this report, the synthesis, characterization, and results of quantum-chemical DFT study of thermal stability of LLM-191, LLM-192 and LLM-200 high density energy materials are presented. Work performed under the auspices of the DOE by the LLNL (Contract DE-AC52-07NA27344). This research is supported in part by ONR (Grant N00014-12-1-0529) and NSF. We used NSF XSEDE (Grant DMR-130077) and DOE NERSC (Contract DE-AC02-05CH11231) resources.

  17. Diffusion mechanism and the thermal stability of fluorine ions in GaN after ion implantation

    SciTech Connect

    Wang, M. J.; Yuan, L.; Chen, K. J.; Xu, F. J.; Shen, B.

    2009-04-15

    The diffusion mechanisms of fluorine ions in GaN are investigated by means of time-of-flight secondary ion mass spectrometry. Instead of incorporating fluorine ions close to the sample surface by fluorine plasma treatment, fluorine ion implantation with an energy of 180 keV is utilized to implant fluorine ions deep into the GaN bulk, preventing the surface effects from affecting the data analysis. It is found that the diffusion of fluorine ions in GaN is a dynamic process featuring an initial out-diffusion followed by in- diffusion and the final stabilization. A vacancy-assisted diffusion model is proposed to account for the experimental observations, which is also consistent with results on molecular dynamic simulation. Fluorine ions tend to occupy Ga vacancies induced by ion implantation and diffuse to vacancy rich regions. The number of continuous vacancy chains can be significantly reduced by a dynamic thermal annealing process. As a result, strong local confinement and stabilization of fluorine ions can be obtained in GaN crystal, suggesting excellent thermal stability of fluorine ions for device applications.

  18. 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

  19. Thermal stability of Mn2+ ion luminescence in Mn-doped core-shell quantum dots

    NASA Astrophysics Data System (ADS)

    Yuan, Xi; Zheng, Jinju; Zeng, Ruosheng; Jing, Pengtao; Ji, Wenyu; Zhao, Jialong; Yang, Weiyou; Li, Haibo

    2013-12-01

    The thermal stability of luminescence is important for the application of quantum dots (QDs) in light-emitting devices. The temperature-dependent photoluminescence (PL) intensities and decay times of Mn-doped ZnS, ZnSe, and ZnSeS alloyed core-shell QD films were studied in the temperature range from 80 to 500 K by steady-state and time-resolved PL spectroscopy. It was found that the thermal stability of Mn-doped QD emissions was significantly dependent on the shell thickness and the host bandgap, which was higher than that of workhorse CdSe QDs. Nearly no PL quenching took place in Mn:ZnS QDs with a thick ZnS shell, which kept a high PL quantum yield (QY) of ~50% even at 500 K; and the thermally stable PL was also observed in highly luminescent Mn:ZnSe and Mn:ZnSeS QDs with a quenching temperature over 200 °C. Further, the stability of Mn-doped QDs with different shell thickness at high temperature was also examined through heating-cooling cycling experiments. The PL quenching in the thick shell-coated Mn-doped QDs was almost totally recovered. The PL quenching mechanisms of the Mn2+ ion emissions were discussed.The thermal stability of luminescence is important for the application of quantum dots (QDs) in light-emitting devices. The temperature-dependent photoluminescence (PL) intensities and decay times of Mn-doped ZnS, ZnSe, and ZnSeS alloyed core-shell QD films were studied in the temperature range from 80 to 500 K by steady-state and time-resolved PL spectroscopy. It was found that the thermal stability of Mn-doped QD emissions was significantly dependent on the shell thickness and the host bandgap, which was higher than that of workhorse CdSe QDs. Nearly no PL quenching took place in Mn:ZnS QDs with a thick ZnS shell, which kept a high PL quantum yield (QY) of ~50% even at 500 K; and the thermally stable PL was also observed in highly luminescent Mn:ZnSe and Mn:ZnSeS QDs with a quenching temperature over 200 °C. Further, the stability of Mn-doped QDs with

  20. Thermal stability and adhesion of low-emissivity electroplated Au coatings.

    SciTech Connect

    Jorenby, Jeff W.; Hachman, John T., Jr.; Yang, Nancy Y. C.; Chames, Jeffrey M.; Clift, W. Miles

    2010-12-01

    We are developing a low-emissivity thermal management coating system to minimize radiative heat losses under a high-vacuum environment. Good adhesion, low outgassing, and good thermal stability of the coating material are essential elements for a long-life, reliable thermal management device. The system of electroplated Au coating on the adhesion-enhancing Wood's Ni strike and 304L substrate was selected due to its low emissivity and low surface chemical reactivity. The physical and chemical properties, interface bonding, thermal aging, and compatibility of the above Au/Ni/304L system were examined extensively. The study shows that the as-plated electroplated Au and Ni samples contain submicron columnar grains, stringers of nanopores, and/or H{sub 2} gas bubbles, as expected. The grain structure of Au and Ni are thermally stable up to 250 C for 63 days. The interface bonding is strong, which can be attributed to good mechanical locking among the Au, the 304L, and the porous Ni strike. However, thermal instability of the nanopore structure (i.e., pore coalescence and coarsening due to vacancy and/or entrapped gaseous phase diffusion) and Ni diffusion were observed. In addition, the study also found that prebaking 304L in the furnace at {ge} 1 x 10{sup -4} Torr promotes surface Cr-oxides on the 304L surface, which reduces the effectiveness of the intended H-removal. The extent of the pore coalescence and coarsening and their effect on the long-term system integrity and outgassing are yet to be understood. Mitigating system outgassing and improving Au adhesion require a further understanding of the process-structure-system performance relationships within the electroplated Au/Ni/304L system.

  1. pH dependence of the stability of barstar to chemical and thermal denaturation.

    PubMed Central

    Khurana, R.; Hate, A. T.; Nath, U.; Udgaonkar, J. B.

    1995-01-01

    Equilibrium unfolding of barstar with guanidine hydrochloride (GdnHCl) and urea as denaturants as well as thermal unfolding have been carried out as a function of pH using fluorescence, far-UV and near-UV CD, and absorbance as probes. Both GdnHCl-induced and urea-induced denaturation studies at pH 7 show that barstar unfolds through a two-state F<->U mechanism and yields identical values for delta GU, the free energy difference between the fully folded (F) and unfolded (U) forms, of 5.0 +/- 0.5 kcal.mol-1 at 25 degrees C. Thermal denaturation of barstar also follows a two-state F<->U unfolding transition at pH 7, and the value of delta GU at 25 degrees C is similar to that obtained from chemical denaturation. The pH dependence of denaturation by GdnHCl is complex. The Cm value (midpoint of the unfolding transition) has been used as an index for stability in the pH range 2-10, because barstar does not unfold through a two-state transition on denaturation by GdnHCl at all pH values studied. Stability is maximum at pH 2-3, where barstar exists in a molten globule-like form that forms a large soluble oligomer. The stability decreases with an increase in pH to 5, the isoelectric pH of the protein. Above pH 5, the stability increases as the pH is raised to 7. Above pH 8, it again decreases as the pH is raised to 10. The decrease in stability from pH 7 to 5 in wild-type (wt) barstar, which is shown to be characterized by an apparent pKa of 6.2 +/- 0.2, is not observed in H17Q, a His 17-->Gln 17 mutant form of barstar. This decrease in stability has therefore been correlated with the protonation of His 17 in barstar. The decrease in stability beyond pH 8 in wt barstar, which is characterized by an apparent pKa of 9.2 +/- 0.2, is not detected in BSCCAA, the Cys 40 Cys 82-->Ala 40 Ala 82 double mutant form of barstar. Thus, this decrease in stability has been correlated with the deprotonation of at least one of the two cysteines present in wt barstar. The increase in

  2. [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.

  3. 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.

  4. Enhanced thermal- and photo-stability of acid yellow 17 by incorporation into layered double hydroxides

    NASA Astrophysics Data System (ADS)

    Wang, Qian; Feng, Yongjun; Feng, Junting; Li, Dianqing

    2011-06-01

    2,5-dichloro-4-(5-hydroxy-3-methyl-4-(sulphophenylazo) pyrazol-1-yl) benzenesulphonate (DHSB) anions, namely acid yellow 17 anions, have been successfully intercalated into Zn-Al layered double hydroxides (LDH) to produce a novel organic-inorganic pigment by a simple method involving separate nucleation and aging steps (SNAS), and the dye-intercalated LDH was analyzed by various techniques, e.g., XRD, SEM, FT-IR, TG-DTA and ICP. The d-spacing of the prepared LDH is 2.09 nm. Furthermore, the incorporation of the DHSB aims to enhance the thermal- and photo-stability of the guest dye molecule, for example, the less color change after accelerated thermal- and photo-aging test.

  5. Mechanical and Thermal Stability of Adhesive Membranes with Nonzero Bending Rigidity

    NASA Astrophysics Data System (ADS)

    Tallinen, T.; Åström, J. A.; Kekäläinen, P.; Timonen, J.

    2010-07-01

    Membranes at a microscopic scale are affected by thermal fluctuations and self-adhesion due to van der Waals forces. Methods to prepare membranes of even molecular scale, e.g., graphene, have recently been developed, and the question of their mechanical and thermal stability is of crucial importance. To this end we modeled microscopic membranes with an attractive interaction and applied Langevin dynamics. Their behavior was also analyzed under external loading. Even though these membranes folded during isotropic compression as a result of energy minimization, the process at high confinement was similar to crumpling of macroscopic nonadhesive sheets. The main difference appeared when the compression was released. In such cases, for membranes of sufficiently large size, folded or scrolled conformations emerged. At high temperature entropic effects made such conformations unfavorable, however.

  6. Mechanical and thermal stability of adhesive membranes with nonzero bending rigidity

    NASA Astrophysics Data System (ADS)

    Tallinen, Tuomas; Astrom, Jan; Kekalainen, Pekka; Timonen, Jussi

    2011-03-01

    Membranes at a microscopic scale are affected by thermal fluctuations and self-adhesion due to Van der Waals forces. Methods to prepare membranes of even molecular scale, e.g. graphene, have been recently developed, and the question of their mechanical and thermal stability is of crucial importance. To this end we modeled microscopic membranes with a short-range attractive interaction and applied Langevin dynamics. Their behavior was also analyzed under external loading. Even though these membranes folded during isotropic compression as a result of energy minimization, the process at high confinement did not differ much from crumpling of macroscopic thin sheets. The main difference appeared when the external load was released. In such cases, for membranes of sufficiently large size L , folded or scrolled conformations emerged. At high enough temperature T entropic effects made such conformations unfavorable, however. Possible conformations of free-standing membranes (``phase diagrams'') were determined in the TL -plane.

  7. DIAGNOSIS, ANALYSIS, AND RESOLUTION OF THERMAL STABILITY ISSUES WITH HOM COUPLERS ON PROTOTYPE CEBAF SRF CAVITIES

    SciTech Connect

    Charles Reece; Edward Daly; G. Davis; William Hicks; Timothy Rothgeb; H. Phillips; Joseph Preble; Haipeng Wang; Genfa Wu

    2008-02-12

    During initial testing of the prototype cavities incorporated into the developmental cryomodule Renascence severe thermal stability issues were encountered during CW operation. Additional diagnostic instrumentation was added. This enabled identification of an unanticipated thermal impedance between the HOM coupler probe feedthrough assembly and the cavity beamtube. Subsequent detailed FE analysis successfully modeled the situation and indicated the need for alternate cooling path for the couplers on those cavities. HOM damping was measured to be adequate employing only two of the four HOM couplers. The two pickup probes on the couplers at the input power coupler side of each cavity were removed, the remaining HOM probe feedthroughs were heat stationed to two-phase helium supply piping, and a novel heat sink was added to station both the inner and outer conductors of the remaining HOM rf cables. The characterization measurements, analysis, modifications, and resulting performance are presented.

  8. EXPANDED IRON UTA SPECTRA-PROBING THE THERMAL STABILITY LIMITS IN AGN CLOUDS

    SciTech Connect

    Ferland, G. J.; Lykins, M. L.; Kisielius, R.; Jonauskas, V.; Keenan, F. P.; Van Hoof, P. A. M.; Porter, R. L.; Williams, R. J. R.

    2013-04-20

    The Fe unresolved transition arrays (UTAs) produce prominent features in the {approx}15-17 A wavelength range in the spectra of active galactic nuclei (AGNs). Here, we present new calculations of the energies and oscillator strengths of inner-shell lines from Fe XIV, Fe XV, and Fe XVI. These are crucial ions since they are dominant at inflection points in the gas thermal stability curve, and UTA excitation followed by autoionization is an important ionization mechanism for these species. We incorporate these, and data reported in previous papers, into the plasma simulation code Cloudy. This updated physics is subsequently employed to reconsider the thermally stable phases in absorbing media in AGNs. We show how the absorption profile of the Fe XIV UTA depends on density, due to the changing populations of levels within the ground configuration.

  9. Thermal Stability of Austenite and Properties of Quenching & Partitioning (Q&P) Treated AHSS

    NASA Astrophysics Data System (ADS)

    Wu, R. M.; Wang, L.; Jin, X. J.

    A Fe-0.2C-1.87Mn-1.42Si-0.0405Al steel subjected to an appropriate Quenching & Partitioning treatment (Q&P) exhibits the combination of high tensile strength (1311 MPa) and high elongation (13.6%). The thermal decomposition of retained austenite in the as-treated steel has been studied at an elevated temperature of 500oC by means of differential scanning calorimetry (DSC). Activation energy has been obtained by performing a Kissinger analysis method. The DSC results show that the activation energy of thermal decomposition of the retained austenite in this Q&P steel is 221.3KJ/mol, which is in a good agreement with the result of retained austenite in similar chemical composition steel subjected to a TRansformation Induced Plasticity (TRIP) treatment. This investigation helps to investigate the stability of retained austenite in Q&P steels upon cooling or under external stress.

  10. Thermal stability and flammability of electrolytes for lithium-ion batteries

    NASA Astrophysics Data System (ADS)

    Arbizzani, Catia; Gabrielli, Giulio; Mastragostino, Marina

    2011-05-01

    Safety is the key-feature of large-size lithium-ion batteries and thermal stability of the electrolytes is crucial. We investigated the thermal and flammability properties of mixed electrolytes based on the conventional ethylene carbonate-dimethyl carbonate (1:1 wt/wt)-1 M LiPF6 and the hydrophobic ionic liquid N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr14TFSI). The results of thermogravimetric analyses and flammability tests of mixed electrolytes of different compositions are reported and discussed. An important finding is that though the mixtures with high contents of ionic liquid are more difficult to ignite, they burn for a longer time, once they are ignited.

  11. Dynamics and thermal stability of surface-confined metal-organic chains

    NASA Astrophysics Data System (ADS)

    Ecija, D.; Marschall, M.; Reichert, J.; Kasperski, A.; Nieckarz, D.; Szabelski, P.; Auwärter, W.; Barth, J. V.

    2016-01-01

    Understanding the dynamics and thermal stability of metallosupramolecular chains on surfaces is of relevance for the development of molecular connectors in nanoelectronics or other fields. Here we present a combined study using temperature-controlled STM and Monte Carlo simulations to explore the behavior of metal-organic porphyrin chains on Cu(111) based on two-fold pyridyl-Cu-pyridyl coordination motifs. We monitor their behavior in the 180-360 K range, revealing three thermal regimes: i) flexibility up to 240 K, ii) diffusion of chain fragments and partial dissociation into a fluid phase for T > 240 K, and iii) full dissolution with temperatures exceeding ~ 320 K. The experimentally estimated reaction enthalpy of the metal-organic bonding is ~ 0.6 eV. Monte Carlo simulations reproduce qualitatively our STM observations and reveal the preference for linear and extended supramolecular chains with reduced substrate temperatures.

  12. Thermal Stability of Cu/NiSi-Contacted p+n Shallow Junction

    NASA Astrophysics Data System (ADS)

    Wang, Chao-Chun; Lin, Hsin-Hung; Chen, Mao-Chieh

    2004-09-01

    The thermal stability of Cu/NiSi-contacted p+n shallow junction diodes was investigated with respect to their electrical characteristics and metallurgical reactions. The TaN/Cu/NiSi/p+n junction diode remained intact after 30 min thermal annealing at temperatures of up to 350°C. Upon annealing at 375°C, a marked increase in reverse bias leakage current occurred, and secondary ion mass spectrometry (SIMS) analysis indicated that Cu started to penetrate into the NiSi-contacted shallow junction region. After a higher temperature annealing at 425°C, a Cu3Si phase was formed. The failure of the TaN/Cu/NiSi/p+n junction diodes is attributed to the penetration of Cu through the NiSi layer into the junction region, leading to junction degradation by introducing deep-level trap states and the eventual formation of Cu3Si.

  13. 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.

  14. 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.

  15. Effect of Aromatic Concentration of a Fischer-Tropsch Fuel on Thermal Stability

    NASA Technical Reports Server (NTRS)

    Klettlinger, Jennifer Lindsey Suder

    2012-01-01

    Fischer-Tropsch (F-T) jet fuel composition differs from petroleum-based, conventional commercial jet fuel because of differences in feedstock and production methodology. Fischer­ Tropsch fuel typically has a lower aromatic and sulfur content and consists primarily of iso and normal parafins. 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 Fischer-Tropsch fuel. The testing completed in this report was supported by the NASA Fundamental Aeronautics Subsonics Fixed Wing Project.

  16. Thermal stability of Artemia HGPRT: effect of substrates on inactivation kinetics.

    PubMed

    Montero, C; Llorente, P; Argomaniz, L; Menendez, M

    1996-06-01

    Hypoxanthine-guanine phosphoribosyltransferase (HGPRT, E.C.2.4.2.8) from Artemia cysts exhibits maximum activity at 70 degrees C. Its thermal stability has been examined following enzymatic activity as a function of temperature. Cold-induced renaturation experiments of samples heated at increasing temperatures showed that reversibility of thermal inactivation depends on the incubation time and final temperature. Prolonged incubation of the thermoinactivated enzyme at 0 degree C did not afford any further increase of the catalytic activity at 37 degrees C. The complex substrate PRPP:Mg protects HGPRT from thermal inactivation. However, incubations with hypoxanthine rendered a less thermostable enzyme at any temperature tested. The irreversible inactivation of HGPRT proceeds in two exponential steps. The analysis of the apparent rate constants for the fast and the slow phases, lambda 1 and lambda 2 as per the Lumry and Eyring model suggests the existence of more than three states in the thermal denaturation pathway of the free enzyme. In the presence of PRPP:Mg the irreversible process follows a single exponential and proceeds very slowly below 70 degrees C. PRPP:Mg also protects the enzyme from inactivation by NEM and pCMB, suggesting that -SH groups may be in the vicinity of the active site.

  17. Linear and nonlinear stability of a thermally stratified magnetically driven rotating flow in a cylinder.

    PubMed

    Grants, Ilmars; Gerbeth, Gunter

    2010-07-01

    The stability of a thermally stratified liquid metal flow is considered numerically. The flow is driven by a rotating magnetic field in a cylinder heated from above and cooled from below. The stable thermal stratification turns out to destabilize the flow. This is explained by the fact that a stable stratification suppresses the secondary meridional flow, thus indirectly enhancing the primary rotation. The instability in the form of Taylor-Görtler rolls is consequently promoted. These rolls can only be excited by finite disturbances in the isothermal flow. A sufficiently strong thermal stratification transforms this nonlinear bypass instability into a linear one reducing, thus, the critical value of the magnetic driving force. A weaker temperature gradient delays the linear instability but makes the bypass transition more likely. We quantify the non-normal and nonlinear components of this transition by direct numerical simulation of the flow response to noise. It is observed that the flow sensitivity to finite disturbances increases considerably under the action of a stable thermal stratification. The capabilities of the random forcing approach to identify disconnected coherent states in a general case are discussed.

  18. Fabrication and characterization of poly (bisphenol A borate) with high thermal stability

    NASA Astrophysics Data System (ADS)

    Wang, Shujuan; Wang, Xiao; Jia, Beibei; Jing, Xinli

    2017-01-01

    In this work, poly (bisphenol A borate) (PBAB), which has excellent thermal resistance and a high char yield, was synthesized via a convenient A2 + B3 strategy by using bisphenol A (BPA) and boric acid (BA). The chemical reaction between BPA and BA and the chemical structure of PBAB were investigated. The results demonstrate that PBAB consists of aromatic, Ph-O-B and B-O-B structures, as well as a small number of boron hydroxyl groups and phenolic hydroxyl groups. The thermal properties of PBAB were studied by DMA and TGA. The results indicate that the glass transition temperature and char yield are gradually enhanced by increasing the boron content, where the char yield of PBAB at 800 °C in nitrogen (N2) reaches up to 71.3%. It is of particular importance that PBAB show excellent thermal resistance in N2 and air atmospheres. By analysing the pyrolysis of PBAB, the high char yield of PBAB can be attributed to the formation of boron oxide and boron carbide at high temperatures, which reduced the release of volatile carbon dioxide and improved the thermal stability of the carbonization products. This study provides a new perspective on the design of novel boron-containing polymers and possesses significant potential for the improvement of the comprehensive performance of thermosetting resins to broaden their applicability in the field of advanced composites.

  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. Structural characterization and thermal and chemical stability of bioactive molecule-hydrotalcite (LDH) nanocomposites.

    PubMed

    Conterosito, Eleonora; Croce, Gianluca; Palin, Luca; Pagano, Cinzia; Perioli, Luana; Viterbo, Davide; Boccaleri, Enrico; Paul, Geo; Milanesio, Marco

    2013-08-28

    Layered double hydroxides (LDH) are versatile materials used for intercalating bioactive molecules, both in pharmaceutical and cosmetic fields, with the purpose of protecting them from degradation, enhancing their water solubility to increase bioavailability, and/or obtaining modified release properties. The properties of the intercalation compounds of Mg/Al_LDH and Zn/Al_LDH with different drugs and sunscreens, namely diclofenac, ketoprofen, gliclazide, retinoic acid, furosemide, para-aminobenzoic acid and 2-phenylbenzimidazolsulfonic (Eusolex) acid, have been studied by crystallographic, spectroscopic and thermogravimetric techniques and by solid state NMR, to shed light on their structure, their molecular interactions and their stability from the thermal and chemical viewpoint. The structural features were described with particular attention to the interaction between the organic and inorganic components and to the stability of the intercalation products. For the first time two synchrotron radiation powder diffraction patterns of organic-containing LDH were solved and refined by Rietveld methods to obtain an experimental crystal structure.

  1. Use of whey protein soluble aggregates for thermal stability-a hypothesis paper.

    PubMed

    Ryan, Kelsey N; Zhong, Qixin; Foegeding, Edward A

    2013-08-01

    Forming whey proteins into soluble aggregates is a modification shown to improve or expand the applications in foaming, emulsification, gelation, film-formation, and encapsulation. Whey protein soluble aggregates are defined as aggregates that are intermediates between monomer proteins and an insoluble gel network or precipitate. The conditions under which whey proteins denature and aggregate have been extensively studied and can be used as guiding principles of producing soluble aggregates. These conditions are reviewed for pH, ion type and concentration, cosolutes, and protein concentration, along with heating temperature and duration. Combinations of these conditions can be used to design soluble aggregates with desired physicochemical properties including surface charge, surface hydrophobicity, size, and shape. These properties in turn can be used to obtain target macroscopic properties, such as viscosity, clarity, and stability, of the final product. A proposed approach to designing soluble aggregates with improved thermal stability for beverage applications is presented.

  2. Dielectric Coating Thermal Stabilization During GaAs-Based Laser Fabrication for Improved Device Yield

    NASA Astrophysics Data System (ADS)

    Connors, Michael K.; Millsapp, Jamal E.; Turner, George W.

    2016-06-01

    The quality and yield of GaAs-based ridge waveguide devices fabricated at MIT Lincoln Laboratory were negatively impacted by the random lot-to-lot appearance of blisters in the front-side contact metal. The blisters signaled compromised adhesion between the front-side contact metal, underlying SiO2 dielectric coating, and semiconductor surface. A thermal-anneal procedure developed for the fabrication of GaAs slab coupled optical waveguide (SCOW) ridge waveguide devices stabilizes the SiO2 dielectric coating by means of outgassing and stress reduction. This process eliminates a primary source of adhesion loss, as well as blister generation, and thereby significantly improves device yield. Stoney's equation was used to analyze stress-induced bow in device wafers fabricated using this stabilization procedure. This analysis suggests that changes in wafer bow contribute to the incidence of metal blisters in SCOW devices.

  3. Physico-chemical properties and thermal stability of microcrystalline cellulose isolated from Alfa fibres.

    PubMed

    Trache, Djalal; Donnot, André; Khimeche, Kamel; Benelmir, Riad; Brosse, Nicolas

    2014-04-15

    In this study, microcrystalline cellulose (Alfa-MCC) was extracted from Alfa fibres using acid hydrolysis method. The molecular weight of the cellulose samples was determined by gel permeation chromatography. The crystallinities were studied by means of X-ray diffraction and solid state cross polarization magic angle spinning (13)C nuclear magnetic resonance spectroscopy, revealing that Alfa-MCC was more crystalline than the native cellulose isolated from Alfa fibres. The morphology of the celluloses was investigated using scanning electron microscopy, showing a compact structure and a rough surface. Furthermore, a good thermal stability was shown for Alfa-MCC. Based on these analyses, Alfa-MCC showed tremendous potential use as composites reinforcing agent, foods stabilizer and pharmaceutical additive.

  4. Thermal stability of titanium nitride for shallow junction solar cell contacts

    NASA Astrophysics Data System (ADS)

    Cheung, N. W.; von Seefeld, H.; Nicolet, M.-A.; Ho, F.; Iles, P.

    1981-06-01

    To demonstrate the thermal stability of titanium nitride as a high-temperature diffusion barrier, the TiN-Ti-Ag metallization scheme has been tested on shallow-junction (2000 A) Si solar cells. Electrical measurements on reference samples with the Ti-Ag metallization scheme show serious degradation after a 600 C, 10-min annealing. With the TiN-Ti-Ag scheme, no degradation of cell performance is observed after the same heat treatment if the TiN layer is equal to or greater than 1700 A. The glass encapsulation of cells by electrostatic bonding requires such a heat treatment.

  5. Thermal-electrical properties and resistance stability of silver coated yarns

    NASA Astrophysics Data System (ADS)

    Li, Yafang; Liu, Hao; Li, Xiaojiu

    2017-03-01

    Thermal-electrical properties and resistance stability of silver yarns was researched to evaluate the performance be a heating element. Three samples of silver coated yarns with different linear density and electrical resistivity, which obtained by market. Silver coated yarns were placed at the high temperature condition for ageing. The electrical resistances of yarns were increased with the ageing process. The infrared photography instrument was used to measurement the temperature variation of silver coated yarns by applied different current on. The result shows that the temperature rise with the power increases.

  6. Heat pipe stability. 1: A preliminary investigation into thermally assisted cavitation

    NASA Technical Reports Server (NTRS)

    1973-01-01

    The notion is introduced of thermally assisted cavitation by localized fluctuations in capillary forces. Because cavitation in liquids can be closely approximated by an isothermal process, only momentum and mass balances are used to introduce the notion for liquids under mechanical tension. Brief attention is given to developing a stability theory in terms of the stiffness and compliance coefficients for a working fluid. Interestingly, the particular thermodynamic approach taken can be used to suggest experiments relating working fluid performance to meniscus behavior. A correction to the liquid flow equation is suggested.

  7. Thermal stability of the cellular structure of an austenitic alloy after selective laser melting

    NASA Astrophysics Data System (ADS)

    Bazaleeva, K. O.; Tsvetkova, E. V.; Balakirev, E. V.; Yadroitsev, I. A.; Smurov, I. Yu.

    2016-05-01

    The thermal stability of the cellular structure of an austenitic Fe-17% Cr-12% Ni-2% Mo-1% Mn-0.7% Si-0.02% C alloy produced by selective laser melting in the temperature range 20-1200°C is investigated. Metallographic analysis, transmission electron microscopy, and scanning electron microscopy show that structural changes in the alloy begin at 600-700°C and are fully completed at ~1150°C. Differential scanning calorimetry of the alloy with a cellular structure reveals three exothermic processes occurring upon annealing within the temperature ranges 450-650, 800-1000, and 1050-1200°C.

  8. Thermal domain stability of advanced digital recording (ADR) thin film heads

    NASA Astrophysics Data System (ADS)

    Bijker, M. D.; Draaisma, E. A.; Eisenberg, M.; Toonen, L.

    2002-04-01

    In this paper the thermal domain stability of electroplated Nickel-Iron flux guides is studied. During the thin film deposition process of ADR magnetic heads these magnetic structures are heated up to about 300°C on a few occasions and it is shown that this has a pronounced effect on the stress state of the deposited flux-guide layers. Domain observations are carried out on both NiFe strips of varying widths as well as on as-deposited test structures and annealed NiFe on product level of a data head.

  9. Effects of monohydric alcohols and polyols on the thermal stability of a protein

    NASA Astrophysics Data System (ADS)

    Murakami, Shota; Kinoshita, Masahiro

    2016-03-01

    The thermal stability of a protein is lowered by the addition of a monohydric alcohol, and this effect becomes larger as the size of hydrophobic group in an alcohol molecule increases. By contrast, it is enhanced by the addition of a polyol possessing two or more hydroxyl groups per molecule, and this effect becomes larger as the number of hydroxyl groups increases. Here, we show that all of these experimental observations can be reproduced even in a quantitative sense by rigid-body models focused on the entropic effect originating from the translational displacement of solvent molecules. The solvent is either pure water or water-cosolvent solution. Three monohydric alcohols and five polyols are considered as cosolvents. In the rigid-body models, a protein is a fused hard spheres accounting for the polyatomic structure in the atomic detail, and the solvent is formed by hard spheres or a binary mixture of hard spheres with different diameters. The effective diameter of cosolvent molecules and the packing fractions of water and cosolvent, which are crucially important parameters, are carefully estimated using the experimental data of properties such as the density of solid crystal of cosolvent, parameters in the pertinent cosolvent-cosolvent interaction potential, and density of water-cosolvent solution. We employ the morphometric approach combined with the integral equation theory, which is best suited to the physical interpretation of the calculation result. It is argued that the degree of solvent crowding in the bulk is the key factor. When it is made more serious by the cosolvent addition, the solvent-entropy gain upon protein folding is magnified, leading to the enhanced thermal stability. When it is made less serious, the opposite is true. The mechanism of the effects of monohydric alcohols and polyols is physically the same as that of sugars. However, when the rigid-body models are employed for the effect of urea, its addition is predicted to enhance the

  10. Effects of monohydric alcohols and polyols on the thermal stability of a protein.

    PubMed

    Murakami, Shota; Kinoshita, Masahiro

    2016-03-28

    The thermal stability of a protein is lowered by the addition of a monohydric alcohol, and this effect becomes larger as the size of hydrophobic group in an alcohol molecule increases. By contrast, it is enhanced by the addition of a polyol possessing two or more hydroxyl groups per molecule, and this effect becomes larger as the number of hydroxyl groups increases. Here, we show that all of these experimental observations can be reproduced even in a quantitative sense by rigid-body models focused on the entropic effect originating from the translational displacement of solvent molecules. The solvent is either pure water or water-cosolvent solution. Three monohydric alcohols and five polyols are considered as cosolvents. In the rigid-body models, a protein is a fused hard spheres accounting for the polyatomic structure in the atomic detail, and the solvent is formed by hard spheres or a binary mixture of hard spheres with different diameters. The effective diameter of cosolvent molecules and the packing fractions of water and cosolvent, which are crucially important parameters, are carefully estimated using the experimental data of properties such as the density of solid crystal of cosolvent, parameters in the pertinent cosolvent-cosolvent interaction potential, and density of water-cosolvent solution. We employ the morphometric approach combined with the integral equation theory, which is best suited to the physical interpretation of the calculation result. It is argued that the degree of solvent crowding in the bulk is the key factor. When it is made more serious by the cosolvent addition, the solvent-entropy gain upon protein folding is magnified, leading to the enhanced thermal stability. When it is made less serious, the opposite is true. The mechanism of the effects of monohydric alcohols and polyols is physically the same as that of sugars. However, when the rigid-body models are employed for the effect of urea, its addition is predicted to enhance the

  11. Enhancement of thermal stability of porous bodies comprised of stainless steel or an alloy

    DOEpatents

    Bischoff, Brian L.; Sutton, Theodore G.; Judkins, Roddie R.; Armstrong, Timothy R.; Adcock, Kenneth D.

    2010-11-09

    A method for treating a porous item constructed of metal powder, such as a powder made of Series 400 stainless steel, involves a step of preheating the porous item to a temperature of between about 700 and 900.degree. C. degrees in an oxidizing atmosphere and then sintering the body in an inert or reducing atmosphere at a temperature which is slightly below the melting temperature of the metal which comprises the porous item. The thermal stability of the resulting item is enhanced by this method so that the item retains its porosity and metallic characteristics, such as ductility, at higher (e.g. near-melting) temperatures.

  12. Achievement of thermal stability by varying metabolic heat production in flying honeybees.

    PubMed

    Harrison, J F; Fewell, J H; Roberts, S P; Hall, H G

    1996-10-04

    Thermoregulation of the thorax allows endothermic insects to achieve power outputs during flight that are among the highest in the animal kingdom. Flying endothermic insects, including the honeybee Apis mellifera, are believed to thermoregulate almost exclusively by varying heat loss. Here it is shown that a rise in air temperature from 20 degrees to 40 degrees C causes large decreases in metabolic heat production and wing-beat frequency in honeybees during hovering, agitated, or loaded flight. Thus, variation in heat production may be the primary mechanism for achieving thermal stability in flying honeybees, and this mechanism may occur commonly in endothermic insects.

  13. Heat Transfer and Thermal Stability of Alternative Aircraft Fuels. Volume 2. Appendices.

    DTIC Science & Technology

    1983-11-01

    AD-A137 405 HEAT TRANSFER AND THERMAL STABILITY OF ALTERNATIVE s AIRCRAFT FUELS VOLUME 2.-(U) PRATT AND WHITNEY AIRCRAFT GROUP WEST PALM BEACH FL...Whitney Aircraft PE63724N Government Products Division Project No. Z0838 P. O. Box 2691, West Palm Beach, FL 33402 Work Unit NAPC-617 11. CONTROLLING...Division, located in Palm Beach County, Florida. The work ws conducted under Contract No. N00140-80-C-0097, Lot III, for the Naval Air Propulsion Center

  14. Thermal Shock Tolerance of Ferroelectric Liquid Crystal Stabilized by Aligned Polymer Fibers

    NASA Astrophysics Data System (ADS)

    Fujikake, Hideo; Murashige, Takeshi; Sato, Hiroto; Fujisaki, Yoshihide; Kawakita, Masahiro; Kikuchi, Hiroshi; Kurita, Taiichiro

    2003-02-01

    In this paper, we report the marked enhancement of thermal shock tolerance of smectic layer structures of ferroelectric liquid crystal stabilized by aligned fine polymer fibers, which were formed by photopolymerization-induced phase separation. It was found that a smectic layer structure with such polymer fibers, which are aligned perpendicular to the smectic layer, generates no zigzag defects even after the composite film is cooled to -15°C, which is lower than the chiral smectic C-to-crystal phase-transition temperature, or heated to 100°C, which is above the chiral nematic-to-isotropic phase-transition temperature.

  15. Physical and molecular bases of protein thermal stability and cold adaptation.

    PubMed

    Pucci, Fabrizio; Rooman, Marianne

    2017-02-01

    The molecular bases of thermal and cold stability and adaptation, which allow proteins to remain folded and functional in the temperature ranges in which their host organisms live and grow, are still only partially elucidated. Indeed, both experimental and computational studies fail to yield a fully precise and global physical picture, essentially because all effects are context-dependent and thus quite intricate to unravel. We present a snapshot of the current state of knowledge of this highly complex and challenging issue, whose resolution would enable large-scale rational protein design.

  16. Thermal stability of hydrocarbons in nature: Limits, evidence, characteristics, and possible controls

    USGS Publications Warehouse

    Price, L.C.

    1993-01-01

    Numerous petroleum-geochemical analyses of deeply buried, high-rank, fine-grained rocks from ultra-deep wellbores by different investigators demonstrate that C15+ hydrocarbons (HCs) persist in moderate to high concentrations at vitrinite reflectance (R0) values of 2.0-5.0% and persist in measurable concentrations up to R0 = 7.0-8.0%, at which point the thermal deadline for C15+ HC's is finally approached. Qualitative analyses have been carried out on 1. (1) high-rank gas condensates which have been exposed to the HC-thermal-destructive phase, 2. (2) bitumens from high-temperature aqueous-pyrolysis experiments in the HC-thermal-destructive phase, and 3. (3) bitumens from high-rank, fine-grained rocks near the HC-thermal-destructive phase. These analyses clearly demonstrate that well-defined compositional suites are established in the saturated, aromatic, and sulfur-bearing aromatic HCs in and near the HC-thermal-destructive phase. On the other hand, accepted petroleum-geochemical paradigms place rigid limits on HC thermal stability: C15+ HCs begin thermal cracking at R0 values of 0.9% and are completely thermally destroyed by R0 = 1.35%; C2-C4 HC gases are thermally destroyed by R0 = 2.0% and methane is thermally destroyed by R0 = 4.0%. Furthermore, published data and observations in many HC basins worldwide support these models; for example, 1. (1) sharp basinal zonations of gas and oil deposits vs. maturation rank in HC basins and 2. (2) decreasing C15+ HC concentrations in some fine-grained rocks at ranks of R0 ??? 0.9%. The fact that observed data (C15+ HCs thermally stable to R0 = 7.0-8.0%) is so far removed from predicted behavior (C15+) HCs expected to be thermally destroyed by R0 = 1.35%) may be due to 1. (1) a lack of recognition of some important possible controlling parameters of organic matter (OM) metamorphism and too much importance given to other assumed controlling parameters; and 2. (2) assigning HC distribution patterns in petroleum basins to HC

  17. Donor-Acceptor Interface Stabilizer Based on Fullerene Derivatives toward Efficient and Thermal Stable Organic Photovoltaics.

    PubMed

    Li, Junli; Zhu, Xiaoguang; Yuan, Tao; Shen, Jiulin; Liu, Jikang; Zhang, Jian; Tu, Guoli

    2017-02-22

    An interface stabilizer based on alkylation-functionalized fullerene derivatives, [6, 6]-Phenyl-C61-butyric acid (3,5-bis(octyloxy)phenyl)methyl ester (PCB-C8oc), was successfully synthesized and applied for the active layer of Organic Photovoltaics (OPVs). The PCB-C8oc can replace part of the phenyl-C61-buty-ric acid methyl ester (PCBM) and be distributed on the interface of poly(3-hexylthiophene) (P3HT) and PCBM to form P3HT/PCBM/PCB-C8oc ternary blends, leading to thermally stable and efficient organic photovoltaics. The octyl groups of PCB-C8oc exhibit intermolecular interaction with the hexyl groups of P3HT, and the fullerene unit of PCB-C8oc are in tight contact with PCBM. The dual functions of PCB-C8oc will inhibit the phase separation between electron donor and acceptor, thereby improving the stability of devices under long-time thermal annealing at high temperature. When doped with 10 wt % PCB-C8oc, the power conversion efficiency (PCE) of the P3HT system decreased from 3.54% to 2.88% after 48 h of thermal treatment at 150 °C, whereas the PCE of the reference device without PCB-C8oc dramatically dropped from 3.53% to 0.73%. When doping 10 or 20 wt % PCB-C8oc, the unannealed P3HT/PCBM/PCB-C8oc device achieved a higher PCE than the P3HT/PCBM device without any annealing following the same fabricating condition. For the PTB7/PCBM-based devices, after adding only 5 wt % PCB-C8oc, the OPVs also exhibited thermally stable morphology and better device performances. All these results demonstrate that the utilization of alkyl interchain interactions is an effective and practical strategy to control morphological evolution.

  18. Thermal stability effects on the separated flow over a steep 2-D hill

    NASA Astrophysics Data System (ADS)

    Zhang, W.; Porte-Agel, F.

    2012-12-01

    Transport of momentum and scalars in turbulent boundary-layer flows over complex topography has been of great interest in the atmospheric sciences and wind engineering communities. Applications include but are not limited to weather forecasting, air pollution dispersion, aviation safety control, and wind energy project planning. Linear models have been well accepted to predict boundary-layer flows over topography with gentle slope. However, once the slope of the topography is sufficientlyo steep that flow separation occurs, linear models are not applicable. Modeling the turbulent transport of momentum and scalars in such flows has to be achieved through non-linear models, such as Reynolds-averaged Navier-Stokes solvers and large-eddy simulations (LES). Dynamics of the separated boundary-layer flows over steep topography is affected by the shape and size of the topography, surface characteristics (e.g., roughness and temperature) and atmospheric thermal stability. Most wind-tunnel experiments of boundary-layer flows over idealized topography (e.g. 2-D or 3-D hills, axisymmetric bumps) do not take thermal stability effects into account due to difficulty of physical simulation. We conducted comprehensive experimental investigation of stably- and unstably- stratified boundary layers over a steep 2-D hill in the thermally-controlled boundary-layer wind tunnel at the Saint Anthony Falls Laboratory. The 2-D model hill has a steepest slope of 0.73 and its shape follows a cosine square function: h=Hcos^2 (πx/L) for -L/2 ≤ x ≤ L/2 , where the maximum height H is 7 cm and the total width L is 15 cm. High-resolution Particle Image Velocimetry (PIV) provides dynamic information of the separated shear layer, the recirculation zone and flow reattachment. Turbulent momentum and scalar (heat) fluxes were characterized up to the top of the thermal boundary layer using a triple-wire (cross-wire and cold-wire) anemometer. Results indicate that promoted and suppressed turbulence

  19. 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.

  20. Correlation between calculated molecular descriptors of excipient amino acids and experimentally observed thermal stability of lysozyme.

    PubMed

    Meng-Lund, Helena; Friis, Natascha; van de Weert, Marco; Rantanen, Jukka; Poso, Antti; Grohganz, Holger; Jorgensen, Lene

    2017-03-21

    A quantitative structure-property relationship (QSPR) between protein stability and the physicochemical properties of excipients was investigated to enable a more rational choice of stabilizing excipients than prior knowledge. The thermal transition temperature and aggregation time were determined for lysozyme in combination with 13 different amino acids using high throughput fluorescence spectroscopy and kinetic static light scattering measurements. On the theoretical side, around 200 2D and 3D molecular descriptors were calculated based on the amino acids' chemical structure. Multivariate data analysis was applied to correlate the descriptors with the experimental results. It was possible to identify descriptors, i.e. amino acids properties, with a positive influence on either transition temperature or aggregation onset time, or both. A high number of hydrogen bond acceptor moieties was the most prominent stabilizing factor for both responses, whereas hydrophilic surface properties and high molecular mass density mostly had a positive influence on the unfolding temperature. A high partition coefficient (logP(o/w)) was identified as the most prominent destabilizing factor for both responses. The QSPR shows good correlation between calculated molecular descriptors and the measured stabilizing effect of amino acids on lysozyme.

  1. Stabilization of thin tungsten films on silicon during rapid thermal annealing in nitrogen

    SciTech Connect

    Smith, P.M.

    1991-01-01

    Thin W films on Si, deposited by electron-beam evaporation or sputtering, are shown to be stabilized against silicidation by a N[sub 2] ambient during rapid thermal annealing to temperatures of 1100[degree]C. The behavior of the W films in contact with Si was monitored following anneals in Ar and N[sub 2] ambients. Tungsten films annealed in an Ar ambient reacted fully to form the stable silicide, WSi[sub 2], while films annealed in N[sub 2] remained elemental W. The stability of W films with incorporated N was studied further by subsequent annealing in an Ar ambient. Complete stabilization of the W films was only achieved for N doses above 2.0 [times] 10[sup 17] N atoms/cm[sub 2]. At lower doses, a continual supply of N was necessary to maintain the stabilization by consumption of mobile Si at the interface. In contrast to films deposited by e-beam evaporation or sputtering, films deposited by chemical vapor deposition (CVD) reacted to form WSi[sub 2], regardless of the annealing ambient, at a substantially faster rate than the other samples. AES measurements show this reaction is the result of an absence of measurable O in the CVD films.

  2. Characterization, thermal stability studies, and analytical method development of Paromomycin for formulation development.

    PubMed

    Khan, Wahid; Kumar, Neeraj

    2011-06-01

    Paromomycin (PM) is an aminoglycoside antibiotic, first isolated in the 1950s, and approved in 2006 for treatment of visceral leishmaniasis. Although isolated six decades back, sufficient information essential for development of pharmaceutical formulation is not available for PM. The purpose of this paper was to determine thermal stability and development of new analytical method for formulation development of PM. PM was characterized by thermoanalytical (DSC, TGA, and HSM) and by spectroscopic (FTIR) techniques and these techniques were used to establish thermal stability of PM after heating PM at 100, 110, 120, and 130 °C for 24 h. Biological activity of these heated samples was also determined by microbiological assay. Subsequently, a simple, rapid and sensitive RP-HPLC method for quantitative determination of PM was developed using pre-column derivatization with 9-fluorenylmethyl chloroformate. The developed method was applied to estimate PM quantitatively in two parenteral dosage forms. PM was successfully characterized by various stated techniques. These techniques indicated stability of PM for heating up to 120 °C for 24 h, but when heated at 130 °C, PM is liable to degradation. This degradation is also observed in microbiological assay where PM lost ∼30% of its biological activity when heated at 130 °C for 24 h. New analytical method was developed for PM in the concentration range of 25-200 ng/ml with intra-day and inter-day variability of < 2%RSD. Characterization techniques were established and stability of PM was determined successfully. Developed analytical method was found sensitive, accurate, and precise for quantification of PM. Copyright © 2010 John Wiley & Sons, Ltd.

  3. A mechanistic analysis of the increase in the thermal stability of proteins in aqueous carboxylic acid salt solutions.

    PubMed Central

    Kaushik, J. K.; Bhat, R.

    1999-01-01

    The stability of proteins is known to be affected significantly in the presence of high concentration of salts and is highly pH dependent. Extensive studies have been carried out on the stability of proteins in the presence of simple electrolytes and evaluated in terms of preferential interactions and increase in the surface tension of the medium. We have carried out an in-depth study of the effects of a series of carboxylic acid salts: ethylene diamine tetra acetate, butane tetra carboxylate, propane tricarballylate, citrate, succinate, tartarate, malonate, and gluconate on the thermal stability of five different proteins that vary in their physico-chemical properties: RNase A, cytochrome c, trypsin inhibitor, myoglobin, and lysozyme. Surface tension measurements of aqueous solutions of the salts indicate an increase in the surface tension of the medium that is very strongly correlated with the increase in the thermal stability of proteins. There is also a linear correlation of the increase in thermal stability with the number of carboxylic groups in the salt. Thermal stability has been found to increase by as much as 22 C at 1 M concentration of salt. Such a high thermal stability at identical concentrations has not been reported before. The differences in the heat capacities of denaturation, deltaCp for RNase A, deduced from the transition curves obtained in the presence of varying concentrations of GdmCl and that of carboxylic acid salts as a function of pH, indicate that the nature of the solvent medium and its interactions with the two end states of the protein control the thermodynamics of protein denaturation. Among the physico-chemical properties of proteins, there seems to be an interplay of the hydrophobic and electrostatic interactions that lead to an overall stabilizing effect. Increase in surface free energy of the solvent medium upon addition of the carboxylic acid salts appears to be the dominant factor in governing the thermal stability of proteins

  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. The effects of certain glycols, substituted glycols and related organic solvents on the thermal stability of soluble collagen

    PubMed Central

    Hart, G. J.; Russell, A. E.; Cooper, D. R.

    1971-01-01

    The effects of a number of related diols, substituted diols and glycerol on the thermal stability of acid-soluble calf skin collagen were investigated. Thermal transition temperatures were determined by optical rotation measurement. Short-chain diols with terminal hydroxyl groups, i.e. ethylene glycol and propane-1,3-diol, stabilized the protein at all accessible concentrations. Stabilization was also observed with glycerol and diethylene glycol. Higher homologues in the diol series produced various effects, as did hydroxyl-group positional isomerism. Monoalkyl substitution of diols progressively lowered the denaturation temperature of collagen. Results are discussed in relation to possible mechanisms of perturbant action. PMID:5169191

  6. Modeling the Thermal Stability of Volatiles from Mercury to Pluto and Beyond (Invited)

    NASA Astrophysics Data System (ADS)

    Paige, D. A.

    2013-12-01

    Volatiles can be distinguished from non-volatile materials on the basis of their relative mobility. The solar system contains multiple sources of volatiles that can be trapped by solar system bodies either by gravity, by chemistry, or by the presence of suitable surface or subsurface cold traps. Thermal modeling has proven to be a very successful tool for studying the distribution and behavior of cold-trapped volatiles in the solar system. During the past few decades, we have acquired tremendous amounts of new observational data regarding the composition and distribution of planetary ices. We now have evidence for ices on every planetary body in our solar system, except for Venus. During this same period, we have also seen significant improvements in our capability to accurately model the global and local thermal environments of planets. Thermal modeling alone cannot predict the existence of a specific volatile compound. However, because of the strong dependence of volatile stability on temperature, thermal modeling can accurately predict the surface and subsurface regions where specific volatile compounds should be thermally stable in their solid and liquid forms. These models have been applied with notable success to understand polar water ice deposits on Mercury and the Moon, as well as the carbon-dioxide polar caps and water ice polar caps and ground ice on Mars. They have also been used to understand the behavior of various ices on comets, asteroids, and on moons, and on primitive bodies in the outer solar system, as well as seasonal variations in the behavior of nitrogen ices on Triton and Pluto. Despite these successes, many unsolved problems remain. We still do not understand the original sources of most of the ices that we find in the inner solar system, nor do we understand the processes that give rise to the accumulation of deep, but relatively pure subsurface water ice deposits on Mercury and on Mars. Looking beyond our own solar system, it is likely

  7. Use of thermal analysis techniques (TG-DSC) for the characterization of diverse organic municipal waste streams to predict biological stability prior to land application

    SciTech Connect

    Fernandez, Jose M.; Plaza, Cesar; Polo, Alfredo; Plante, Alain F.

    2012-01-15

    ) techniques. Total amounts of CO{sub 2} respired indicated that the organic matter in the TS was the least stable, while that in the CS was the most stable. This was confirmed by changes detected with the spectroscopic methods in the composition of the organic wastes due to C mineralization. Differences were especially pronounced for TS, which showed a remarkable loss of aliphatic and proteinaceous compounds during the incubation process. TG, and especially DSC analysis, clearly reflected these differences between the three organic wastes before and after the incubation. Furthermore, the calculated energy density, which represents the energy available per unit of organic matter, showed a strong correlation with cumulative respiration. Results obtained support the hypothesis of a potential link between the thermal and biological stability of the studied organic materials, and consequently the ability of thermal analysis to characterize the maturity of municipal organic wastes and composts.

  8. Investigation of the stability of paraffin-exfoliated graphite nanoplatelet composites for latent heat thermal storage systems

    SciTech Connect

    Abdelaziz, Omar; Mallow, Anne; Graham, Samuel; Kalaitzidou, Kyriaki

    2012-01-01

    Organic materials, such as paraffin wax, are sought as stable and environmentally friendly phase change materials (PCM) for thermal energy storage, but they suffer from low thermal conductivity which limits the rate at which thermal energy flows into and out of the material. A common method to improve the PCM thermal behavior is through loading with high thermal conductivity particulate fillers. However, the stability of these composites in the molten state is a concern as settling of the fillers will change the effective thermal conductivity. In this work, we investigate the stability of wax loaded with exfoliated graphite nanoplatelets either of 1 m (xGnP-1) or 15 m (xGnP-15) diameter. The effect of dispersants, oxidation of the wax, viscosity of the wax, mixing time, and hydrocarbon chain length on stability is reported. It was found that the addition of octadecylphosphonic acid (ODPA) is an effective dispersant for xGnP in paraffin and microcrystalline wax. In addition, mixing time, viscosity, and oxidation of the wax influence stability in the molten state. Overall, it was found that a mixing time of 24 hours for xGnP-15 along with ODPA mixed in a high viscosity, oxidized microcrystalline wax results in composite PCM systems with the greatest stability determined at 80 C in the molten state.

  9. Thermal Microstructural Stability of AZ31 Magnesium after Severe Plastic Deformation

    SciTech Connect

    Young, John P.; Askari, Hesam A.; Hovanski, Yuri; Heiden, Michael J.; Field, David P.

    2015-03-01

    Both equal channel angular pressing and friction stir processing have the ability to refine the grain size of twin roll cast AZ31 magnesium and potentially improve its superplastic properties. This work used isochronal and isothermal heat treatments to investigate the microstructural stability of twin roll cast, equal channel angular pressed and friction stir processed AZ31 magnesium. For both heat treatment conditions, it was found that the twin roll casted and equal channel angular pressed materials were more stable than the friction stir processed material. Calculations of the grain growth kinetics showed that severe plastic deformation processing decreased the activation energy for grain boundary motion with the equal channel angular pressed material having the greatest Q value of the severely plastically deformed materials and that increasing the tool travel speed of the friction stir processed material improved microstructural stability. The Hollomon-Jaffe parameter was found to be an accurate means of identifying the annealing conditions that will result in substantial grain growth and loss of potential superplastic properties in the severely plastically deformed materials. In addition, Humphreys’s model of cellular microstructural stability accurately predicted the relative microstructural stability of the severely plastically deformed materials and with some modification, closely predicted the maximum grain size ratio achieved by the severely plastically deformed materials.

  10. Eugenol-loaded chitosan nanoparticles: I. Thermal stability improvement of eugenol through encapsulation.

    PubMed

    Woranuch, Sarekha; Yoksan, Rangrong

    2013-07-25

    The objective of the present work was to improve the thermal stability of eugenol by encapsulating into chitosan nanoparticles via an emulsion-ionic gelation crosslinking method. The influences of the initial eugenol content and tripolyphosphate (TPP) concentration on the loading capacity (LC), encapsulation efficiency (EE), morphology and surface charge of the eugenol-loaded chitosan nanoparticles were also investigated. LC and EE tended to increase with increasing initial eugenol content and decreasing TPP concentration. Particles with LC of 12% and EE of 20% exhibited a spherical shape with an average size of less than 100 nm. Thermal stability of the encapsulated eugenol was verified through its extrusion at 155°C with a model plastic, i.e. thermoplastic flour (TPF). TPF containing encapsulated eugenol showed 8-fold higher remaining eugenol content and 2.7-fold greater radical scavenging activity than that containing naked eugenol. The results suggest the possible use of eugenol-loaded chitosan nanoparticles as antioxidants in bioactive plastics for food packaging.

  11. Thermal stability and phase transformations of martensitic Ti-Nb alloys

    NASA Astrophysics Data System (ADS)

    Bönisch, Matthias; Calin, Mariana; Waitz, Thomas; Panigrahi, Ajit; Zehetbauer, Michael; Gebert, Annett; Skrotzki, Werner; Eckert, Jürgen

    2013-10-01

    Aiming at understanding the governing microstructural phenomena during heat treatments of Ni-free Ti-based shape memory materials for biomedical applications, a series of Ti-Nb alloys with Nb concentrations up to 29 wt% was produced by cold-crucible casting, followed by homogenization treatment and water quenching. Despite the large amount of literature available concerning the thermal stability and ageing behavior of Ti-Nb alloys, only few studies were performed dealing with the isochronal transformation behavior of initially martensitic Ti-Nb alloys. In this work, the formation of martensites (α‧ and α″) and their stability under different thermal processing conditions were investigated by a combination of x-ray diffraction, differential scanning calorimetry, dilatometry and electron microscopy. The effect of Nb additions on the structural competition in correlation with stable and metastable phase diagrams was also studied. Alloys with 24 wt% Nb or less undergo a \\alpha '/\\alpha '' \\to \\alpha + \\beta \\to \\beta transformation sequence on heating from room temperature to 1155 K. In alloys containing >24 wt% Nb α″ martensitically reverts back to β0, which is highly unstable against chemical demixing by formation of isothermal ωiso. During slow cooling from the single phase β domain α precipitates and only very limited amounts of α″ martensite form.

  12. Thermal stability of NdBCO/YBCO/MgO thin film seeds

    NASA Astrophysics Data System (ADS)

    Volochová, D.; Kavečanský, V.; Antal, V.; Diko, P.; Yao, X.

    2016-04-01

    Thermal stability of the Nd1+x Ba2-x Cu3O7-δ (Nd-123 or NdBCO) thin films deposited on MgO substrate, with YBa2Cu3O7-δ (Y-123 or YBCO) buffer layer (NdBCO/YBCO/MgO thin film), has been experimentally studied in order to determine the optimal film thickness acting as seed for bulk YBCO growth. YBCO bulk superconductors with Y2BaCuO5 (Y-211) and CeO2 addition were prepared by the top seeded melt growth process in a chamber furnace using NdBCO/YBCO/MgO thin film seeds of different thicknesses (200-700 nm with 20 nm YBCO buffer layer) and different maximum temperatures, T max. The maximum temperatures varied in the range of 1040 °C-1125 °C. The highest thermal stability 1118 °C was observed in the case of NdBCO/YBCO/MgO thin film of 300 nm thickness. These results are corroborated with differential scanning calorimetry and high temperature x-ray diffraction measurements, as well as microstructure observations.

  13. Thermal Stability of MgyTi1-y Thin Films Investigated by Positron Annihilation Spectroscopy

    NASA Astrophysics Data System (ADS)

    Anastasopol, A.; Eijt, S. W. H.; Schut, H.; Mulder, F. M.; Plazaola, F.; Dam, B.

    Mg-Ti compounds are attractive candidates as hydrogen storage materials for their fast sorption kinetics and high storage capacity. In this context, an investigation of their thermal stability is of great importance. The thermal stability of MgyTi1-y thin films was investigated using positron annihilation spectroscopy. Despite the positive enthalpy of mixing of Mg and Ti, positron Doppler Broadening of Annihilation Radiation (DBAR) depth profiling showed that Mg0.9Ti0.1 films are stable up to 300°C. However, for Mg0.7Ti0.3 films, segregation of Mg and Ti was observed at 300oC by the appearance of a clear Ti signature in the S-W diagrams and in the Doppler broadening depth profiles analyzed using VEPFIT. The thickness of the 250-300 nm thin films remained unchanged during the heating treatments. We further present ab-initio calculations of positron lifetimes of the corresponding metal and metal hydride phases for comparison to our previous positron annihilation lifetime spectroscopy (PALS) study.

  14. History of Sulphur Content Effects on the Thermal Stability of RP-1 under Heated Conditions

    NASA Technical Reports Server (NTRS)

    Irvine, Solveig A.; Schoettmer, Amanda K.; Bates, Ronald W.; Meyer, Michael L.

    2004-01-01

    As technologies advance in the aerospace industry, a strong desire has emerged to design more efficient, longer life, reusable liquid hydrocarbon fueled rocket engines. To achieve this goal, a more complete understanding of the thermal stability and chemical makeup of the hydrocarbon propellant is needed. Since the main fuel used in modern liquid hydrocarbon systems is RP-1, there is concern that Standard Grade RP-1 may not be a suitable propellant for future-generation rocket engines due to concern over the outdated Mil-Specification for the fuel. This current specification allows high valued limits on contaminants such as sulfur compounds, and also lacks specification of required thermal stability qualifications for the fuel. Previous studies have highlighted the detrimental effect of high levels of mercaptan sulfur content (^50 ppm) on copper rocket engine materials, but the fuel itself has not been studied. While the role of sulfur in other fuels (e.g., aviation, diesel, and automotive fuels) has been extensively studied, little has been reported on the effects of sulfur levels in rocket fuels. Lower RP-1 sulfur concentrations need to be evaluated and an acceptable sulfur limit established before RP-1 can be recommended for use as the propellant for future launch vehicles. (5 tables, 8 figures, 9 refs.)

  15. High-temperature slurry reactors for synthesis gas reactions. 1: Liquid thermal stability

    SciTech Connect

    Roberts, G.W.; Marquez, M.A.; McCutchen, M.S.; Haney, C.A.; Shin, I.D.

    1997-10-01

    The use of slurry reactors has been limited to reactions that take place at temperatures below about 573 K because many of the liquids that have been used to suspend the solid catalyst are not stable above this temperature. The thermal stability of a number of organic liquids was evaluated at temperatures between 648 and 698 K and at H{sub 2} partial pressures of about 7 MPa. Certain saturated and partially-saturated, fused-ring compounds with no alkyl groups or bridges are quite stable at these conditions. Of the compounds tested, tetrahydronaphthalene, tetrahydroquinoline, and decahydronaphthalene were the most stable. Analysis of the liquids at the end of the thermal stability evaluation supports some speculation concerning possible degradation reactions. The motivation for this research was the desire to synthesize higher (C{sub 2}{minus}C{sub 6}) alcohols in a slurry reactor from a mixture of carbon monoxide (CO) and hydrogen (H{sub 2}), so-called synthesis gas. Alcohols such as isobutanol and isoamyl alcohol could be a source of the branched olefins that are needed to produce octane enhancers such as methyl tert-butyl ether (MTBE) and tert-amyl methyl ether (TAME).

  16. Dark and background response stability for the Landsat 8 Thermal Infrared Sensor

    USGS Publications Warehouse

    Vanderwerff, Kelly; Montanaro, Matthew

    2012-01-01

    The Thermal Infrared Sensor (TIRS) is a pushbroom sensor that will be a part of the Landsat Data Continuity Mission (LDCM), which is a joint mission between NASA and the USGS. The TIRS instrument will continue to collect the thermal infrared data that are currently being collected by the Thematic Mapper and the Enhanced Thematic Mapper Plus on Landsats 5 and 7, respectively. One of the key requirements of the new sensor is that the dark and background response be stable to ensure proper data continuity from the legacy Landsat instruments. Pre launch testing of the instrument has recently been completed at the NASA Goddard Space Flight Center (GSFC), which included calibration collects that mimic those that will be performed on orbit. These collects include images of a cold plate meant to simulate the deep space calibration source as viewed by the instrument in flight. The data from these collects give insight into the stability of the instrument’s dark and background response, as well as factors that may cause these responses to vary. This paper quantifies the measured background and dark response of TIRS as well as its stability.

  17. Effects of potential additives to promote seal swelling on the thermal stability of synthetic jet fuels

    SciTech Connect

    Lind, D.D.; Gormley, R.G.; Zandhuis, P.H.; Baltrus, J.P.

    2007-10-01

    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 of 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. These additives can include oxygenates and compounds containing other heteroatoms that may adversely affect thermal stability. In order to understand what additives will be the most beneficial, a comprehensive experimental and computational study of conventional and additized fuels has been undertaken. The experimental approach includes analysis of the trace oxygenate and nitrogen-containing compounds present in conventional petroleum-derived fuels and trying to relate their presence (or absence) to changes in the desired properties of the fuels. This paper describes the results of efforts to test the thermal stability of synthetic fuels and surrogate fuels containing single-component additives that have been identified in earlier research as the best potential additives for promoting seal swelling in synthetic fuels, as well as mixtures of synthetic and petroleum-derived fuels.

  18. 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.

  19. Studies on the thermal stability of BiCuSeO

    SciTech Connect

    Barreteau, Celine; Berardan, David Dragoe, Nita

    2015-02-15

    BiCuSeO based materials have been reported as very promising thermoelectric materials, with thermoelectric figure of merit values that make them among the best p-type Pb-free polycrystalline thermoelectric materials, and they could be suitable for applications in thermal to electrical power conversion modules in a 300–650 °C temperature range. In this paper, we report on the phase stability and thermal stability of these materials under inert and oxidizing atmosphere and we discuss their actual potential for wide scale applications. We show that although they are stable in inert atmosphere up to 650 °C, with very slow volatilization rate, it is not the case under oxidizing atmosphere, with a quick oxidation starting at a moderate temperature. - Graphical abstract: BiCuSeO oxidation under air, starting below 300 °C. - Highlights: • Decomposition and oxidation mechanisms of BiCuSeO were studied. • BiCuSeO does not volatilize in inert atmosphere up to 650 °C. • BiCuSeO starts oxidizing for temperatures as low as 200 °C.

  20. Molecular adaptation to an extreme environment: origin of the thermal stability of the pompeii worm collagen.

    PubMed

    Sicot, F X; Mesnage, M; Masselot, M; Exposito, J Y; Garrone, R; Deutsch, J; Gaill, F

    2000-09-29

    The annelid Alvinella pompejana is probably the most heat-tolerant metazoan organism known. Previous results have shown that the level of thermal stability of its interstitial collagen is significantly greater than that of coastal annelids and of vent organisms, such as the vestimentiferan Riftia pachyptila, living in colder parts of the deep-sea hydrothermal environment. In order to investigate the molecular basis of this thermal behavior, we cloned and sequenced a large cDNA molecule coding the fibrillar collagen of Alvinella, including one half of the helical domain and the entire C-propeptide domain. For comparison, we also cloned the 3' part of the homologous cDNA from Riftia. Comparison of the corresponding helical domains of these two species, together with that of the previously sequenced domain of the coastal lugworm Arenicola marina, showed that the increase in proline content and in the number of stabilizing triplets correlate with the outstanding thermostability of the interstitial collagen of A. pompejana. Phylogenetic analysis showed that triple helical and the C-propeptide parts of the same collagen molecule evolve at different rates, in favor of an adaptive mechanism at the molecular level.

  1. Thermal stability and phase transformations of martensitic Ti-Nb alloys.

    PubMed

    Bönisch, Matthias; Calin, Mariana; Waitz, Thomas; Panigrahi, Ajit; Zehetbauer, Michael; Gebert, Annett; Skrotzki, Werner; Eckert, Jürgen

    2013-10-01

    Aiming at understanding the governing microstructural phenomena during heat treatments of Ni-free Ti-based shape memory materials for biomedical applications, a series of Ti-Nb alloys with Nb concentrations up to 29 wt% was produced by cold-crucible casting, followed by homogenization treatment and water quenching. Despite the large amount of literature available concerning the thermal stability and ageing behavior of Ti-Nb alloys, only few studies were performed dealing with the isochronal transformation behavior of initially martensitic Ti-Nb alloys. In this work, the formation of martensites (α' and α″) and their stability under different thermal processing conditions were investigated by a combination of x-ray diffraction, differential scanning calorimetry, dilatometry and electron microscopy. The effect of Nb additions on the structural competition in correlation with stable and metastable phase diagrams was also studied. Alloys with 24 wt% Nb or less undergo a [Formula: see text] transformation sequence on heating from room temperature to 1155 K. In alloys containing >24 wt% Nb α″ martensitically reverts back to β0, which is highly unstable against chemical demixing by formation of isothermal ωiso. During slow cooling from the single phase β domain α precipitates and only very limited amounts of α″ martensite form.

  2. Structural and biochemical studies of GH family 12 cellulases: improved thermal stability, and ligand complexes.

    PubMed

    Sandgren, Mats; Ståhlberg, Jerry; Mitchinson, Colin

    2005-11-01

    In this review we will describe how we have gathered structural and biochemical information from several homologous cellulases from one class of glycoside hydrolases (GH family 12), and used this information within the framework of a protein-engineering program for the design of new variants of these enzymes. These variants have been characterized to identify some of the positions and the types of mutations in the enzymes that are responsible for some of the biochemical differences in thermal stability and activity between the homologous enzymes. In this process we have solved the three-dimensional structure of four of these homologous GH 12 cellulases: Three fungal enzymes, Humicola grisea Cel12A, Hypocrea jecorina Cel12A and Hypocrea schweinitzii Cel12A, and one bacterial, Streptomyces sp. 11AG8 Cel12A. We have also determined the three-dimensional structures of the two most stable H. jecorina Cel12A variants. In addition, four ligand-complex structures of the wild-type H. grisea Cel12A enzyme have been solved and have made it possible to characterize some of the interactions between substrate and enzyme. The structural and biochemical studies of these related GH 12 enzymes, and their variants, have provided insight on how specific residues contribute to protein thermal stability and enzyme activity. This knowledge can serve as a structural toolbox for the design of Cel12A enzymes with specific properties and features suited to existing or new applications.

  3. Thermal stability and phase transformations of martensitic Ti–Nb alloys

    PubMed Central

    Bönisch, Matthias; Calin, Mariana; Waitz, Thomas; Panigrahi, Ajit; Zehetbauer, Michael; Gebert, Annett; Skrotzki, Werner; Eckert, Jürgen

    2013-01-01

    Aiming at understanding the governing microstructural phenomena during heat treatments of Ni-free Ti-based shape memory materials for biomedical applications, a series of Ti–Nb alloys with Nb concentrations up to 29 wt% was produced by cold-crucible casting, followed by homogenization treatment and water quenching. Despite the large amount of literature available concerning the thermal stability and ageing behavior of Ti–Nb alloys, only few studies were performed dealing with the isochronal transformation behavior of initially martensitic Ti–Nb alloys. In this work, the formation of martensites (α′ and α″) and their stability under different thermal processing conditions were investigated by a combination of x-ray diffraction, differential scanning calorimetry, dilatometry and electron microscopy. The effect of Nb additions on the structural competition in correlation with stable and metastable phase diagrams was also studied. Alloys with 24 wt% Nb or less undergo a transformation sequence on heating from room temperature to 1155 K. In alloys containing >24 wt% Nb α″ martensitically reverts back to β0, which is highly unstable against chemical demixing by formation of isothermal ωiso. During slow cooling from the single phase β domain α precipitates and only very limited amounts of α″ martensite form. PMID:27877611

  4. Improvement of thermal stability of polypropylene using DOPO-immobilized silica nanoparticles

    PubMed Central

    Dong, Quanxiao; Ding, Yanfen; Wen, Bin; Wang, Feng; Dong, Huicong; Zhang, Shimin

    2014-01-01

    After the surface silylation with 3-methacryloxypropyltrimethoxysilane, silica nanoparticles were further modified by 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO). The immobilization of DOPO on silica nanoparticles was confirmed by Fourier transform infrared spectroscopy, UV–visible spectroscopy, magic angle spinning nuclear magnetic resonance, and thermogravimetric analysis. By incorporating the DOPO-immobilized silica nanoparticles (5 wt%) into polypropylene matrix, the thermal oxidative stability exhibited an improvement of 62 °C for the half weight loss temperature, while that was only 26 °C increment with incorporation of virgin silica nanoparticles (5 wt%). Apparent activation energies of the polymer nanocomposites were estimated via Flynn–Wall–Ozawa method. It was found that the incorporation of DOPO-immobilized silica nanoparticles improved activation energies of the degradation reaction. Based on the results, it was speculated that DOPO-immobilized silica nanoparticles could inhibit the degradation of polypropylene and catalyze the formation of carbonaceous char on the surface. Thus, thermal stability was significantly improved. PMID:24729654

  5. Update of S-NPP VIIRS thermal emissive bands radiometric calibration stability monitoring using the moon

    NASA Astrophysics Data System (ADS)

    Wang, Zhipeng; Xiong, Xiaoxiong; Li, Yonghong

    2016-10-01

    The Suomi-NPP VIIRS thermal emissive bands (TEB) are radiometrically calibrated on-orbit with reference to a blackbody (BB) regularly operated at approximately 292.5 K. The calibration stability at other temperature ranges can be evaluated based on the observations of remote targets with stable thermal properties, such as the Moon. VIIRS has scheduled viewings of the Moon on a nearly monthly basis at a phase angle of nearly -51 degrees. In this paper, the brightness temperatures (BT) of the lunar surface retrieved using the detector gain coefficients calibrated with the BB are trended to monitor the calibration stability of VIIRS TEB. Since the Lunar surface temperatures are spatially nonuniform and vary greatly with the solar illumination geometry, the BT trending must be based on the same regions of the Moon under the same solar illumination condition. Also, the TEB lunar images are always partially saturated because the highest lunar surface temperatures are beyond the dynamic range of all VIIRS TEB detectors. Therefore, a temporally dynamic mask is designed to clip a fraction of the lunar images corresponding to the regions of the Moon that may saturate the detector at any lunar event. The BT trending is then based on the hottest pixels not clipped by the mask. Results show that, since the launch of VIIRS to mid-2016, the radiometric calibration of all TEB detectors has been stable within +/-0.4 K at the BT range of as high as 350-260 K.

  6. Pressure effects on the thermal stability of SiC fibers

    NASA Technical Reports Server (NTRS)

    Jaskowiak, Martha H.; Dicarlo, James A.

    1986-01-01

    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.

  7. 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.

  8. Structural fluctuations and thermal stability of proteins in crowded environments: effects of the excluded volume

    NASA Astrophysics Data System (ADS)

    Starzyk, Anna; Wojciechowski, Michał; Cieplak, Marek

    2016-12-01

    We perform molecular dynamics simulations for a simple coarse-grained model of a protein placed inside of a softly repulsive sphere of radius R. The protein is surrounded either by a number of same molecules or a number of spherical crowding particles that immitate other biomolecules such as the osmolytes. The two descriptions are shown to lead to distinct results when testing thermal stability as assessed by studying the unfolding times as a function of temperature. We consider three examples of proteins and show that crowding increases the thermal stability provided the inter-protein or protein-crowder interactions are repulsive. On the other hand, an introduction of attraction between the proteins is found to destabilize the proteins. Crowding by repulsive crowder particles is seen to enhance the RMSF in certain exposed regions. The effect grows on decreasing the size of the crowding particles. In the absence of crowding the RMSF anticorrelates with the coordination number related to the residue-residue interaction.

  9. Application of vacuum stability test to determine thermal decomposition kinetics of nitramines bonded by polyurethane matrix

    NASA Astrophysics Data System (ADS)

    Elbeih, Ahmed; Abd-Elghany, Mohamed; Elshenawy, Tamer

    2017-03-01

    Vacuum stability test (VST) is mainly used to study compatibility and stability of energetic materials. In this work, VST has been investigated to study thermal decomposition kinetics of four cyclic nitramines, 1,3,5-trinitro-1,3,5-triazinane (RDX) and 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX), cis-1,3,4,6-tetranitrooctahydroimidazo-[4,5-d]imidazole (BCHMX), 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (ε-HNIW, CL-20), bonded by polyurethane matrix based on hydroxyl terminated polybutadiene (HTPB). Model fitting and model free (isoconversional) methods have been applied to determine the decomposition kinetics from VST results. For comparison, the decomposition kinetics were determined isothermally by ignition delay technique and non-isothermally by Advanced Kinetics and Technology Solution (AKTS) software. The activation energies for thermolysis obtained by isoconversional method based on VST technique of RDX/HTPB, HMX/HTPB, BCHMX/HTPB and CL20/HTPB were 157.1, 203.1, 190.0 and 176.8 kJ mol-1 respectively. Model fitting method proved that the mechanism of thermal decomposition of BCHMX/HTPB is controlled by the nucleation model while all the other studied PBXs are controlled by the diffusion models. A linear relationship between the ignition temperatures and the activation energies was observed. BCHMX/HTPB is interesting new PBX in the research stage.

  10. Enhancement of poly(3-hydroxybutyrate) thermal and processing stability using a bio-waste derived additive.

    PubMed

    Persico, Paola; Ambrogi, Veronica; Baroni, Antonio; Santagata, Gabriella; Carfagna, Cosimo; Malinconico, Mario; Cerruti, Pierfrancesco

    2012-12-01

    Poly(3-hydroxybutyrate) (PHB) is a biodegradable polymer, whose applicability is limited by its brittleness and narrow processing window. In this study a pomace extract (EP), from the bio-waste of winery industry, was used as thermal and processing stabilizer for PHB, aimed to engineer a totally bio-based system. The results showed that EP enhanced the thermal stability of PHB, which maintained high molecular weights after processing. This evidence was in agreement with the slower decrease in viscosity over time observed by rheological tests. EP also affected the melt crystallization kinetics and the overall crystallinity extent. Finally, dynamic mechanical and tensile tests showed that EP slightly improved the polymer ductility. The results are intriguing, in view of the development of sustainable alternatives to synthetic polymer additives, thus increasing the applicability of bio-based materials. Moreover, the reported results demonstrated the feasibility of the conversion of an agro-food by-product into a bio-resource in an environmentally friendly and cost-effective way.

  11. Effects of fluoride residue on thermal stability in Cu/porous low-k interconnects

    SciTech Connect

    Kobayashi, Y.; Ozaki, S.; Nakamura, T.

    2014-06-19

    We have investigated the effects of fluoride residue on the thermal stability of a Cu/barrier metal (BM)/porous low-k film (k < 2.3) structure. We confirmed that the Cu agglomerated more on a BM/inter layer dielectric (ILD) with a fluoride residue. To consider the effect of fluoride residue on Cu agglomeration, the structural state at the Cu/BM interface was evaluated with a cross-section transmission electron microscope (TEM) and atomic force microscope (AFM). In addition, the chemical bonding state at the Cu/BM interface was evaluated with the interface peeling-off method and X-ray photoelectron spectroscopy (XPS). Moreover, we confirmed the ionization of fluoride residue and oxidation of Cu with fluoride and moisture to clarify the effect of fluoride residue on Cu. Our experimental results indicated that the thermal stability in Cu/porous low-k interconnects was degraded by enhancement of Cu oxidation with fluoride ions diffusion as an oxidizing catalyst.

  12. Thermal stability of bimodal microstructure in magnesium alloy AZ91 processed by ECAP

    SciTech Connect

    Pantělejev, Libor

    2015-09-15

    The changes in microstructure of equal channel angular pressing (ECAP) processed magnesium alloy AZ91 during thermal exposure were studied in this paper. The microstructure stability was investigated by means of electron backscatter diffraction (EBSD), which allowed to measure the changes in grain size, mutual ratio of low-angle boundaries (LABs) to high-angle ones (HABs) and local lattice distortion evaluated by the kernel average misorientation (KAM) parameter. It was found experimentally that the threshold temperature at which significant grain coarsening takes place is 350 °C. No modification to mean grain diameter occurs below this temperature, nonetheless, some changes in LAB and HAB fraction, as well as in local lattice distortion, can be observed. - Highlights: • Thermal stability of bimodal UFG AZ91 alloy was assessed by means of EBSD. • Threshold temperature for pronounced grain coarsening was found at 350 °C. • Below 350 °C increase in LAB fraction and local lattice distortion takes place. • Local lattice distortion (LLD) can be well described using KAM approach. • LLD is influenced by coarsening and precipitation of Mg{sub 17}Al{sub 12} particles.

  13. 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.

  14. Effect of volumetric concentration of MWCNTs on the stability and thermal conductivity of nanofluids

    NASA Astrophysics Data System (ADS)

    Rehman, Wajid Ur; Bhat, A. H.; Suliamon, A. A.; Khan, Ihsan Ullah; Ullah, Hafeez

    2016-11-01

    Environmental concerns and running down of the fossil fuel deposits which are generally being used as base oil in Drilling Fluid/Mud have attended worldwide attention and thereby, researchers have focused on using environmentally friendly drilling fluids. This study demonstrates the preparation of drilling fluids and to explore the effect of increase in the volumetric concentration of nanoparticles on the stability and thermal conductivity of nanofluids. In this research, for the formation of nanofluids, Jatropha Seed Oil was used as the base oil with the addition of multi-walled carbon nanotubes as the nanoparticles using sonication technique. The raw multi-walled carbon nanotubes were characterized by using SEM for morphological examination. The prepared drilling fluid were characterized by using UV-Visible spectroscopic technique for analyzing the stability. Thermal Conductivity measurements were also carried out for heat transfer efficiency. It was observed that the heat transfer capability of the nanofluid ameliorates with the increase in the loading percentage of multi-walled carbon nanotubes.

  15. Changes in the color, chemical stability and antioxidant capacity of thermally treated anthocyanin aqueous solution over storage.

    PubMed

    Sui, Xiaonan; Bary, Solène; Zhou, Weibiao

    2016-02-01

    Many anthocyanin-containing foods are thermally processed to ensure their safety, and stored for some time before being consumed. However, the combination of thermal processing and subsequent storage has a significant impact on anthocyanins. This study aimed to investigate the color, chemical stability, and antioxidant capacity of thermally treated anthocyanin aqueous solutions during storage at 4, 25, 45, and 65 °C, respectively. Anthocyanin aqueous solutions were thermally treated before storage. Results showed that the degradation rate of anthocyanins in aqueous solutions was much faster than those in real food. The color of the anthocyanin aqueous solutions changed dramatically during storage. The anthocyanin aqueous solutions stored at 4 °C showed the best chemical stability. Interestingly, the antioxidant capacity of the anthocyanin aqueous solutions stored at lower temperatures remained the same; however, the antioxidant capacity of those thermally treated at 120 or 140 °C and stored at 45 or 65 °C significantly decreased.

  16. 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

  17. The Reference Ability Neural Network Study: Life-time stability of reference-ability neural networks derived from task maps of young adults.

    PubMed

    Habeck, C; Gazes, Y; Razlighi, Q; Steffener, J; Brickman, A; Barulli, D; Salthouse, T; Stern, Y

    2016-01-15

    Analyses of large test batteries administered to individuals ranging from young to old have consistently yielded a set of latent variables representing reference abilities (RAs) that capture the majority of the variance in age-related cognitive change: Episodic Memory, Fluid Reasoning, Perceptual Processing Speed, and Vocabulary. In a previous paper (Stern et al., 2014), we introduced the Reference Ability Neural Network Study, which administers 12 cognitive neuroimaging tasks (3 for each RA) to healthy adults age 20-80 in order to derive unique neural networks underlying these 4 RAs and investigate how these networks may be affected by aging. We used a multivariate approach, linear indicator regression, to derive a unique covariance pattern or Reference Ability Neural Network (RANN) for each of the 4 RAs. The RANNs were derived from the neural task data of 64 younger adults of age 30 and below. We then prospectively applied the RANNs to fMRI data from the remaining sample of 227 adults of age 31 and above in order to classify each subject-task map into one of the 4 possible reference domains. Overall classification accuracy across subjects in the sample age 31 and above was 0.80±0.18. Classification accuracy by RA domain was also good, but variable; memory: 0.72±0.32; reasoning: 0.75±0.35; speed: 0.79±0.31; vocabulary: 0.94±0.16. Classification accuracy was not associated with cross-sectional age, suggesting that these networks, and their specificity to the respective reference domain, might remain intact throughout the age range. Higher mean brain volume was correlated with increased overall classification accuracy; better overall performance on the tasks in the scanner was also associated with classification accuracy. For the RANN network scores, we observed for each RANN that a higher score was associated with a higher corresponding classification accuracy for that reference ability. Despite the absence of behavioral performance information in the

  18. Thermal stability of functional P(S-r-MMA) random copolymers for nanolithographic applications.

    PubMed

    Sparnacci, Katia; Antonioli, Diego; Gianotti, Valentina; Laus, Michele; Zuccheri, Giampaolo; Ferrarese Lupi, Federico; Giammaria, Tommaso Jacopo; Seguini, Gabriele; Ceresoli, Monica; Perego, Michele

    2015-02-25

    Two strategies are envisioned to improve the thermal stability of the grafted layer and to allow the processing of the random copolymer/block copolymer (RCP/BCP) system at high temperature. From one side, a high-temperature thermal treatment of a commercial α-hydroxyl ω-2,2,6,6-tetramethylpiperidinyloxy functional RCP, namely, TR58, leads to the formation of a stabilized layer able to induce the perpendicular orientation of a symmetric BCP to temperatures higher than 310 °C. On the other side, an α-hydroxyl ω-Br functional RCP, namely, BrR58, with the same molar mass and composition of TR58, was prepared by activator regenerated by electron transfer atom transfer radical polymerization. The resulting brush layer can sustain the self-assembly of the symmetric BCP for processing temperatures as high as 330 °C. In both systems, the disruption of the BCP film, deposited on the grafted RCP layer, occurs because of the formation of bubbles, due to a low-temperature evolution of monomers from the RCP layer. The extent of the low-temperature monomer evolution is higher for TR58 than it is for BrR58 and starts at lower temperatures. For both copolymers, the thermal treatment offsets the low-temperature monomer evolution while still maintaining surface characteristics suitable to induce the perpendicular orientation of the BCPs, thus ultimately extending the range of processing temperatures of the BCP film and consequently speeding the self-organization process.

  19. 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.

  20. Thermal behavior and stability of biodegradable spray-dried microparticles containing triamcinolone.

    PubMed

    da Silva, Arnóbio Antônio; de Matos, Jivaldo Rosário; Formariz, Thalita Pedroni; Rossanezi, Gustavo; Scarpa, Maria Virginia; do Egito, Eryvaldo Sócrates Tabosa; de Oliveira, Anselmo Gomes

    2009-02-23

    Thermal analysis has been widely used for obtaining information about drug-polymer interactions and for pre-formulation studies of pharmaceutical dosage forms. In this work, biodegradable microparticles of poly (d,L-lactide-co-glycolide) (PLGA) containing triamcinolone (TR) in various drug:polymer ratios were produced by spray drying. The main purpose of this study was to study the effect of the spray-drying process not only on the drug-polymer interactions but also on the stability of microparticles using differential scanning calorimetry (DSC), thermogravimetry (TG) and derivative thermogravimetry (DTG), X-ray analysis (XRD), and infrared spectroscopy (IR). The evaluation of drug-polymer interactions and the pre-formulation studies were assessed using the DSC, TG and DTG, and IR. The quantitative analysis of drugs entrapped in PLGA microparticles was performed by the HPLC method. The results showed high levels of drug-loading efficiency for all used drug:polymer ratio, and the polymorph used for preparing the microparticles was the form B. The DSC and TG/DTG profiles for drug-loaded microparticles were very similar to those for the physical mixtures of the components. Therefore, a correlation between drug content and the structural and thermal properties of drug-loaded PLGA microparticles was established. These data indicate that the spray-drying technique does not affect the physico-chemical stability of the microparticle components. These results are in agreement with the IR analysis demonstrating that no significant chemical interaction occurs between TR and PLGA in both physical mixtures and microparticles. The results of the X-ray analysis are in agreement with the thermal analysis data showing that the amorphous form of TR prevails over a small fraction of crystalline phase of the drug also present in the TR-loaded microparticles. From the pre-formulation studies, we have found that the spray-drying methodology is an efficient process for obtaining TR

  1. Use of fluorescence for the high-throughput evaluation of synergistic thermal and photo stabilizer interactions in poly (vinyl chloride)

    SciTech Connect

    Wu Chunyong; Wicks, Douglas A.

    2005-06-15

    The selection of thermal and photo stabilizers for poly (vinyl chloride) (PVC) using conventional methods is a time-consuming process. The high-throughput screening method developed in this research demonstrates rapid and efficient ways to quantify the effectiveness of PVC stabilizers with respect to raw plastic materials, stabilizers, levels of use, and testing conditions. An experimental protocol using liquid sampling and fluorescence measurement was developed to determine the effectiveness of formulations. This was used to evaluate the performance of stabilizers based on the change of fluorescence emission at 440 nm after thermal aging or ultraviolet (UV) radiation. The performance of PVC formulations using six different types of stabilizers was successfully mapped for both PVC resin and flexible PVC.

  2. Age-related thermal stability and susceptibility to proteolysis of rat bone collagen.

    PubMed Central

    Danielsen, C C

    1990-01-01

    The shrinkage temperature (Ts) and the pepsin-solubilizability of collagen fibrils in bone matrix obtained from decalcified femur diaphysis from 2-, 5-, 15- and 25-month-old rats were found to decrease with age. Digestion with human fibroblast collagenase dissolved less than half of the collagen, whereas sequential treatment by pepsin followed by collagenase resulted in its complete dissolution. This result shows that collagenase and a telopeptide-cleaving enzyme, when acting in an appropriate sequence, have a great potential for the degradation of bone collagen. The 'melting' profile of the pepsin-solubilized collagen showed a biphasic transition with transition peak at 35.9 degrees C and 40.8 degrees C. With increasing age an increasing proportion of the collagen 'melted' in the transition peak at 35.9 degrees C (pre-transition), and the 'melting' temperature (Tm) of the collagen decreased in parallel with Ts in relation to age. Both Ts and Tm decreased by 3 degrees C in the age span investigated. The age-related change in Ts could therefore be accounted for by the decrease in molecular stability. The collagenase-cleavage products of the bone collagen obtained by the sequential treatment with pepsin and collagenase showed only one peak transition (at 35.1 degrees C), and the Tm for the products was independent of age. The results indicate that the pre-transition for the pepsin-solubilized collagen is due to an age-related decrease in thermal stability may have implications for the mechanical strength and turnover of the bone collagen. In contrast with bone collagen, soft-tissue collagen showed neither the age-dependency of thermal stability nor the characteristic biphasic 'melting' profile. PMID:2176474

  3. Influence of shell thickness on thermal stability of bimetallic Al-Pd nanoparticles

    NASA Astrophysics Data System (ADS)

    Wen, John Z.; Nguyen, Ngoc Ha; Rawlins, John; Petre, Catalin F.; Ringuette, Sophie

    2014-07-01

    Aluminum-based bimetallic core-shell nanoparticles have shown promising applications in civil and defense industries. This study addresses the thermal stability of aluminum-palladium (Al-Pd) core/shell nanoparticles with a varying shell thickness of 5, 6, and 7 Å, respectively. The classic molecular dynamics (MD) simulations are performed in order to investigate the effects of the shell thickness on the ignition mechanism and subsequent energetic processes of these nanoparticles. The histograms of temperature change and structural evolution clearly show the inhibition role of the Pd shell during ignition. While the nanoparticle with a thicker shell is more thermally stable and hence requires more excess energy, stored as the potential energy of the nanoparticle and provided through numerically heating, to initiate the thermite reaction, a higher adiabatic temperature can be produced from this nanoparticle, thanks to its greater content of Pd. The two-stage thermite reactions are discussed with their activation energy based on the energy balance processes during MD heating and production. Analyses of the simulation results reveal that the inner pressure of the core-shell nanoparticle increases with both temperature and the absorbed thermal energy during heating, which may result in a breakup of the Pd shell.

  4. Effect of additives on jet fuel thermal stability determined using the gravimetric JFTOT

    SciTech Connect

    Pande, S.G.; Hardy, D.R.

    1996-10-01

    In an effort to address the need for improving the thermal stabilities of jet fuels, various additives are being examined. These include the antioxidant, BHT; a metal deactivator, MDA (N,N{prime}-Disalicylidene-1,2-propane diamine); a combination of BHT and MDA; and two dispersant/detergent additives, viz., a Betz and Mobil additive. In general, the additives were screened in three test fuels, viz., a refinery sampling blend (RSB), a JP-8, and a Jet A. Additive effectiveness on aging a fuel in the presence of 400 ppb copper was examined in the RSB fuel. Based on the studies conducted, the most effective additives were the MDA/BHT combination, the Betz, and the Mobil additive (when tested). For example, these additives significantly lowered the total thermal deposits formed for the copper-doped aged fuel. For the remaining two test fuels, differentiation in effectiveness among the additives screened was considerably less. These results, which are likely due to the test fuels being relatively thermally stable, focus on the necessity of using less stable fuels to better differentiate additive effectiveness.

  5. Evaluation of the thermal stability POHC incinerability ranking in a pilot-scale rotary kiln incinerator

    SciTech Connect

    Lee, J.W.; Waterland, L.R.; Whitworth, W.E.; Carroll, G.J.

    1991-01-01

    A series of pilot-scale incineration tests was performed at EPA's Incineration Research Facility to evaluate the thermal stability-based POHC incinerability ranking. In the tests, mixtures of 12 POHCs with predicted incinerability spanning the range of most to least difficult to incinerate class were combined with a clay-based sorbent and batch-fed to the facility's pilot-scale rotary kiln incinerator via a fiberpack drum ram feeder. Kiln operating conditions were varied to include a baseline operating condition, three modes of attempted incineration failure, and a worst case combination of the three failure modes. Kiln exit POHC DREs were in the 99.99 percent range for the volatile POHCs for the baseline, mixing failure (increased charge mass), and matrix failure (decreased feed H/C) tests. Semivolatile POHCs were not detected in the kiln exit for these tests; corresponding DREs were generally greater than 99.999 percent. The thermal failure (low kiln temperature) and worst case (combination of thermal, mixing, and matrix failure) tests resulted in substantially decreased kiln exit POHC DREs. These ranged from 99 percent or less for Freon 113 to greater than 99.999 percent for the less stable-ranked semivolatile POHCs. General agreement between relative kiln exit POHC DRE and predicted incinerability class was observed.

  6. Thermal stability and thermo-mechanical properties of magnetron sputtered Cr-Al-Y-N coatings

    SciTech Connect

    Rovere, Florian; Mayrhofer, Paul H.

    2008-01-15

    Cr{sub 1-x}Al{sub x}N coatings are promising candidates for advanced machining and high temperature applications due to their good mechanical and thermal properties. Recently the authors have shown that reactive magnetron sputtering using Cr-Al targets with Al/Cr ratios of 1.5 and Y contents of 0, 2, 4, and 8 at % results in the formation of stoichiometric (Cr{sub 1-x}Al{sub x}){sub 1-y}Y{sub y}N films with Al/Cr ratios of {approx}1.2 and YN mole fractions of 0%, 2%, 4%, and 8%, respectively. Here, the impact of Y on thermal stability, structural evolution, and thermo-mechanical properties is investigated in detail. Based on in situ stress measurements, thermal analyzing, x-ray diffraction, and transmission electron microscopy studies the authors conclude that Y effectively retards diffusional processes such as recovery, precipitation of hcp-AlN and fcc-YN, grain growth, and decomposition induced N{sub 2} release. Hence, the onset temperature of the latter shifts from {approx}1010 to 1125 deg. C and the hardness after annealing at T{sub a}=1100 deg. C increases from {approx}32 to 39 GPa with increasing YN mole fraction from 0% to 8%, respectively.

  7. Manganese complexes of curcumin analogues: evaluation of hydroxyl radical scavenging ability, superoxide dismutase activity and stability towards hydrolysis.

    PubMed

    Vajragupta, Opa; Boonchoong, Preecha; Berliner, Lawrence J

    2004-03-01

    In order to improve the antioxidant property of curcumin and its analogue, diacetylcurcumin, manganese was incorporated into the structures in order to enhance superoxide dismutase (SOD) activity. Manganese (Mn) complexes of curcumin (CpCpx) and diacetylcurcumin (AcylCpCpx) were synthesized and firstly investigated for SOD activity and hydroxyl radical (HO*) scavenging ability. SOD activity was evaluated by both the nitroblue tetrazolium (NBT) reduction assay and electron paramagnetic resonance (EPR) with 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a spin trapping agent. CpCpx and AcylCpCpx inhibited the NBT reduction and decreased the DMPO/OOH adduct much greater than corresponding antioxidants or ligands, with IC50 values of 29.9 and 24.7 microM (NBT), and 1.09 and 2.40 mM (EPR), respectively. For EPR, potassium superoxide (KO2) was used as a source of O2- where qualitative results suggested that CpCpx and AcylCpCpx were SOD mimics, which catalyze the conversion of O2- to dioxygen and hydrogen peroxide (H2O2). Additionally, CpCpx and AcylCpCpx exhibited the great inhibition of DMPO/OH adduct formation with an IC50 of 0.57 and 0.37mM, respectively, which were comparable to that of curcumin (IC50 of 0.64 mM), indicating that both Mn complexes are also an effective HO* scavenger. The stability against hydrolysis in water, various buffers and human blood/serum was carried out in vitro. It was found that both Mn complexes were pH and salt concentration dependent, being more stable in basic pH. In the human blood/serum test, CpCpx was more stable against hydrolysis than AcylCpCpx with about 10 and 20% of free Mn2+ releasing, respectively.

  8. Stabilization of type I collagen against collagenases (type I) and thermal degradation using iron complex.

    PubMed

    Fathima, Nishtar Nishad; Bose, Murugan Chandra; Rao, Jonnalagadda Raghava; Nair, Balachandran Unni

    2006-11-01

    The widespread application of collagen as a biomaterial warrants research in understanding the stabilization of the same. In this study, interaction of iron-tetrakis (hydroxymethyl) phosphonium (THP) complex with type I collagen has been investigated. DSC and hydrothermal measurement studies reveal that the shrinkage temperature of iron-THP treated rat tail tendon (RTT) collagen is 33 degrees C higher than that of native RTT collagen. Fe-THP complex also brings about high degree of enzymatic stability to type I collagen. The effect of Fe-THP on the conformation of collagen was studied using circular dichroism and it was found that no major alterations in the triple helical structure of collagen occur on treatment with Fe-THP. It is observed from viscosity experiment results that though Fe-THP complex is able to bring about long range ordering of collagen, as evident from the thermal and enzymatic stability imparted to collagen, this ordering does not lead to any aggregation of collagen. Since THPS is reducing in nature, it is expected to keep iron in the +2 state and if THP chelates to Fe(II), the hydrolytic behavior of iron can also be controlled.

  9. Thermal stability and molecular ordering of organic semiconductor monolayers: effect of an anchor group.

    PubMed

    Jones, Andrew O F; Knauer, Philipp; Resel, Roland; Ringk, Andreas; Strohriegl, Peter; Werzer, Oliver; Sferrazza, Michele

    2015-06-08

    The thermal stability and molecular order in monolayers of two organic semiconductors, PBI-PA and PBI-alkyl, based on perylene derivatives with an identical molecular structure except for an anchor group for attachment to the substrate in PBI-PA, are reported. In situ X-ray reflectivity measurements are used to follow the stability of these monolayers in terms of order and thickness as temperature is increased. Films have thicknesses corresponding approximately to the length of one molecule; molecules stand upright on the substrate with a defined structure. PBI-PA monolayers have a high degree of order at room temperature and a stable film exists up to 250 °C, but decomposes rapidly above 300 °C. In contrast, stable physisorbed PBI-alkyl monolayers only exist up to 100 °C. Above the bulk melting point at 200 °C no more order exists. The results encourage using anchor groups in monolayers for various applications as it allows enhanced stability at the interface with the substrate.

  10. Influences of the Structure of Lipids on Thermal Stability of Lipid Membranes

    NASA Astrophysics Data System (ADS)

    Hai, Nan-Nan; Zhou, Xin; Li, Ming

    2015-08-01

    The binding free energy (BFE) of lipid to lipid bilayer is a critical factor to determine the thermal or mechanical stability of the bilayer. Although the molecular structure of lipids has significant impacts on BFE of the lipid, there lacks a systematic study on this issue. In this paper we use coarse-grained molecular dynamics simulation to investigate this problem for several typical phospholipids. We find that both the tail length and tail unsaturation can significantly affect the BFE of lipids but in opposite way, namely, BFE decreases linearly with increasing length, but increases linearly with addition of unsaturated bonds. Inspired by the specific structure of cholesterol which is a crucial component of biomembrane, we also find that introduction of carbo-ring-like structures to the lipid tail or to the bilayer may greatly enhance the stability of the bilayer. Our simulation also shows that temperature can influence the bilayer stability and this effect can be significant when the bilayer undergoes phase transition. These results may be helpful to the design of liposome or other self-assembled lipid systems. Support by the National Natural Science Foundation of China under Grant Nos. 91027046 and 11105218.

  11. 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.

  12. Thermal stability of static coronal loops. I - Effects of boundary conditions

    NASA Technical Reports Server (NTRS)

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

    1985-01-01

    The linear stability of static coronal-loop models undergoing thermal perturbations was investigated. The effect of conditions at the loop base on the stability properties of the models was considered in detail. The question of appropriate boundary conditions at the loop base was considered and it was concluded that the most physical assumptions are that the temperature and density (or pressure) perturbations vanish there. However, if the base is taken to be sufficiently deep in the chromosphere, either several chromospheric scale heights or several coronal loop lengths in depth, then the effect of the boundary conditions on loop stability becomes negligible so that all physically acceptable conditions are equally appropriate. For example, one could as well assume that the velocity vanishes at the base. The growth rates and eigenmodes of static models in which gravity is neglected and in which the coronal heating is a relatively simple function, either constant per-unit mass or per-unit volume were calculated. It was found that all such models are unstable with a growth rate of the order of the coronal cooling time. The physical implications of these results for the solar corona and transition region are discussed.

  13. Thermal stability of static coronal loops: Part 1: Effects of boundary conditions

    NASA Technical Reports Server (NTRS)

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

    1985-01-01

    The linear stability of static coronal-loop models undergoing thermal perturbations was investigated. The effect of conditions at the loop base on the stability properties of the models was considered in detail. The question of appropriate boundary conditions at the loop base was considered and it was concluded that the most physical assumptions are that the temperature and density (or pressure) perturbations vanish there. However, if the base is taken to be sufficiently deep in the chromosphere, either several chromospheric scale heights or several coronal loop lengths in depth, then the effect of the boundary conditions on loop stability becomes negligible so that all physically acceptable conditions are equally appropriate. For example, one could as well assume that the velocity vanishes at the base. The growth rates and eigenmodes of static models in which gravity is neglected and in which the coronal heating is a relatively simple function, either constant per-unit mass or per-unit volume were calculated. It was found that all such models are unstable with a growth rate of the order of the coronal cooling time. The physical implications of these results for the solar corona and transition region are discussed.

  14. 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

  15. Role of Internal Water on Protein Thermal Stability: The Case of Homologous G Domains.

    PubMed

    Rahaman, Obaidur; Kalimeri, Maria; Melchionna, Simone; Hénin, Jérôme; Sterpone, Fabio

    2015-07-23

    In this work, we address the question of whether the enhanced stability of thermophilic proteins has a direct connection with internal hydration. Our model systems are two homologous G domains of different stability: the mesophilic G domain of the elongation factor thermal unstable protein from E. coli and the hyperthermophilic G domain of the EF-1α protein from S. solfataricus. Using molecular dynamics simulation at the microsecond time scale, we show that both proteins host water molecules in internal cavities and that these molecules exchange with the external solution in the nanosecond time scale. The hydration free energy of these sites evaluated via extensive calculations is found to be favorable for both systems, with the hyperthermophilic protein offering a slightly more favorable environment to host water molecules. We estimate that, under ambient conditions, the free energy gain due to internal hydration is about 1.3 kcal/mol in favor of the hyperthermophilic variant. However, we also find that, at the high working temperature of the hyperthermophile, the cavities are rather dehydrated, meaning that under extreme conditions other molecular factors secure the stability of the protein. Interestingly, we detect a clear correlation between the hydration of internal cavities and the protein conformational landscape. The emerging picture is that internal hydration is an effective observable to probe the conformational landscape of proteins. In the specific context of our investigation, the analysis confirms that the hyperthermophilic G domain is characterized by multiple states and it has a more flexible structure than its mesophilic homologue.

  16. Numerical investigation of CO{sub 2} emission and thermal stability of a convective and radiative stockpile of reactive material in a cylindrical pipe of variable thermal conductivity

    SciTech Connect

    Lebelo, Ramoshweu Solomon

    2014-10-24

    In this paper the CO{sub 2} emission and thermal stability in a long cylindrical pipe of combustible reactive material with variable thermal conductivity are investigated. It is assumed that the cylindrical pipe loses heat by both convection and radiation at the surface. The nonlinear differential equations governing the problem are tackled numerically using Runge-Kutta-Fehlberg method coupled with shooting technique method. The effects of various thermophysical parameters on the temperature and carbon dioxide fields, together with critical conditions for thermal ignition are illustrated and discussed quantitatively.

  17. Assessment and Stability of Early Learning Abilities in Preterm and Full-Term Infants across the First Two Years of Life

    ERIC Educational Resources Information Center

    Lobo, Michele A.; Galloway, James C.

    2013-01-01

    Infants born preterm have increased risk for learning disabilities yet we lack assessments to successfully detect these disabilities in early life. We followed 23 full-term and 29 preterm infants from birth through 24 months to assess for differences in and stability of learning abilities across time. Measures included the Bayley-III cognitive…

  18. 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.

  19. Effects of Mo addition on thermal stability and magnetic properties of a ferromagnetic Fe75P10C10B5 metallic glass

    NASA Astrophysics Data System (ADS)

    Zhang, Wei; Jia, Xingjie; Li, Yanhui; Fang, Canfeng

    2014-05-01

    The effects of Mo content on the thermal stability, glass-forming ability (GFA), magnetic and mechanical properties of Fe75-xMoxP10C10B5 (x = 0-10) metallic glasses were investigated. The stabilization of supercooled liquid and GFA were significantly enhanced by addition of Mo. Although the saturation magnetization (Is) of the alloys reduced with increasing Mo content, the coercive force (Hc) decreased. The metallic glasses with x = 2.5-7.5 exhibit low glass transition temperature of 733-749 K, large supercooled liquid region of 61-96 K, and high GFA with critical fully glassy sample diameters of 1.5-3.0 mm. They also possess rather high Is of 0.81-1.11 T, low Hc of 2.07-4.87 A/m, high Vicker's hardness of 860-992, high compressive yield strength of over 3000 MPa with a distinct plastic strain.

  20. Effect of compatible and noncompatible osmolytes on the enzymatic activity and thermal stability of bovine liver catalase.

    PubMed

    Sepasi Tehrani, H; Moosavi-Movahedi, A A; Ghourchian, H; Ahmad, F; Kiany, A; Atri, M S; Ariaeenejad, Sh; Kavousi, K; Saboury, A A

    2013-12-01

    Catalase is an important antioxidant enzyme that catalyzes the disproportionation of H2O2 into harmless water and molecular oxygen. Due to various applications of the enzyme in different sectors of industry as well as medicine, the enhancement of stability of the enzyme is important. Effect of various classes of compatible as well as noncompatible osmolytes on the enzymatic activity, disaggregation, and thermal stability of bovine liver catalase have been investigated. Compatible osmolytes, proline, xylitol, and valine destabilize the denatured form of the enzyme and, therefore, increase its disaggregation and thermal stability. The increase in the thermal stability is accompanied with a slight increase of activity in comparison to the native enzyme at 25 °C. On the other hand, histidine, a noncompatible osmolyte stabilizes the denatured form of the protein and hence causes an overall decrease in the thermal stability and enzymatic activity of the enzyme. Chemometric results have confirmed the experimental results and have provided insight into the distribution and number of mole fraction components for the intermediates. The increase in melting temperature (Tm) and enzymatic rate could be further amplified by the intrinsic effect of temperature enhancement on the enzymatic activity for the industrial purposes.

  1. Accelerated screening methods for determining chemical and thermal stability of refrigerant-lubricant mixtures, Part 1: Method assessment. Final report

    SciTech Connect

    Kauffman, R.

    1993-04-01

    This report presents results of a literature search performed to identify analytical techniques suitable for accelerated screening of chemical and thermal stabilities of different refrigerant/lubricant combinations. Search focused on three areas: Chemical stability data of HFC-134a and other non-chlorine containing refrigerant candidates; chemical stability data of CFC-12, HCFC-22, and other chlorine containing refrigerants; and accelerated thermal analytical techniques. Literature was catalogued and an abstract was written for each journal article or technical report. Several thermal analytical techniques were identified as candidates for development into accelerated screening tests. They are easy to operate, are common to most laboratories, and are expected to produce refrigerant/lubricant stability evaluations which agree with the current stability test ANSI/ASHRAE (American National Standards Institute/American Society of Heating, Refrigerating, and Air-Conditioning Engineers) Standard 97-1989, ``Sealed Glass Tube Method to Test the Chemical Stability of Material for Use Within Refrigerant Systems.`` Initial results of one accelerated thermal analytical candidate, DTA, are presented for CFC-12/mineral oil and HCFC-22/mineral oil combinations. Also described is research which will be performed in Part II to optimize the selected candidate.

  2. 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.

  3. Increasing the Thermal Stability of Aluminum Titanate for Solid Oxide Fuel Cell Anodes

    NASA Technical Reports Server (NTRS)

    Bender, Jeffrey B.

    2004-01-01

    Solid-oxide fuel cells (SOFCs) show great potential as a power source for future space exploration missions. Because SOFCs operate at temperatures significantly higher than other types of fuel cells, they can reach overall efficiencies of up to 60% and are able to utilize fossil fuels. The SOFC team at GRC is leading NASA's effort to develop a solid oxide fuel cell with a power density high enough to be used for aeronautics and space applications, which is approximately ten times higher than ground transport targets. layers must be able to operate as a single unit at temperatures upwards of 900'C for at least 40,000 hours with less than ten percent degradation. One key challenge to meeting this goal arises from the thermal expansion mismatch between different layers. The amount a material expands upon heating is expressed by its coefficient of thermal expansion (CTE). If the CTEs of adjacent layers are substantially different, thermal stresses will arise during the cell's fabrication and operation. These stresses, accompanied by thermal cycling, can fracture and destroy the cell. While this is not an issue at the electrolyte-cathode interface, it is a major concern at the electrolyte-anode interface, especially in high power anode-supported systems. electrolyte are nearly identical. Conventionally, this has been accomplished by varying the composition of the anode to match the CTE of the yittria-stabilized zirconia (YSZ) electrolyte (approx.10.8x10(exp -6/degC). A Ni/YSZ composite is typically used as a base material for the anode due to its excellent electrochemical properties, but its CTE is about 13.4x10(exp -6/degC). One potential way to lower the CTE of this anode is to add a small percentage of polycrystalline Al2TiO5, with a CTE of 0.68x10(exp -6/degC, to the Ni/YSZ base. However, Al2TiO5 is thermally unstable and loses its effectiveness as it decomposes to Al2O3 and TiO2 between 750 C and 1280 C. be used as additives to increase the thermal stability of Al2

  4. NaAlF{sub 4}: Preparation, crystal structure and thermal stability

    SciTech Connect

    Kirik, Sergei D.; Zaitseva, Julia N.

    2010-02-15

    The compound NaAlF{sub 4} has been obtained in the form of thin fibrous crystals or fine colorless powder by condensation at 18 deg. C of vapors arising over chiolite Na{sub 5}Al{sub 3}F{sub 14} or NaCaAlF{sub 6}, heated up to 800 deg. C. Thermal stability has been investigated by the methods of thermal analysis and high temperature X-ray diffraction. When heated in air, NaAlF{sub 4} is stable up to 390-400 deg. C, then there is an exothermal solid state decay into Na{sub 5}Al{sub 3}F{sub 14}(s) and AlF{sub 3}(s). At higher temperature Na{sub 5}Al{sub 3}F{sub 14}(s) decays into Na{sub 3}AlF{sub 6}(s) and NaAlF{sub 4}(g). The crystal structure (space group Cmcm, a=3.6124(1) A, b=14.9469(7) A, c=5.2617(3) A, V=284.10 A{sup 3}) has been determined by X-ray powder diffraction method. In the crystal structure of NaAlF{sub 4} the octahedrons [AlF{sub 6}] are joined through vertices and form corrugated layers, sodium ion layers being located between them. The distances between the atoms of Al-F are in the range 1.791-1.814 A, and those for Na...F are in the range 2.297-2.439 A. In spite of limited thermal stability of the crystal form, the compound NaAlF{sub 4} is the main component of the gas mixture over solid and molten salts in the ternary system NaF-AlF{sub 3}-CaF{sub 2} and participates in chemical transformations between the phases at high temperature. - Graphical abstract: The compound NaAlF{sub 4} was for the first time described 55 years ago, but until now it was not properly studied. Meantime the phase is responsible for the most low-melting part of the NaF-AlF{sub 3} system, which is the great importance for the aluminum production. The lack of information about NaAlF{sub 4} is due to narrow interval of stability which is close to liquid part of the system.

  5. Thermal and oxidative stability of Atlantic salmon oil (Salmo salar L.) and complexation with β-cyclodextrin

    PubMed Central

    Ünlüsayin, Mustafa; Gruia, Alexandra T; Birău (Mitroi), Cristina; Rusu, Gerlinde; Hădărugă, Nicoleta G

    2016-01-01

    Summary The thermal and oxidative stability of Atlantic salmon oil (Salmo salar L.) as well as its β-cyclodextrin (β-CD) complexation ability has been verified for the first time. The main omega-3 fatty acids, EPA and DHA, were significantly degraded, even at 50 °C. Their relative concentrations decrease from 6.1% for EPA and 4.1% for DHA to 1.7% and 1.5% after degradation at 150 °C, respectively. On the other hand, the relative concentrations of monounsaturated and saturated fatty acids remained constant or slightly increased by a few percent after degradation (e.g., from 10.7% to 12.9% for palmitic acid). Co-crystallization of ASO with β-CD at a host–guest ratio of 1:1 and 3:1 from an ethanol–water mixture and kneading methods has been used for the preparation of β-CD/ASO complexes. The analysis of the complexes by thermogravimetry, differential scanning calorimetry (DSC), and Karl Fischer titration (KFT) as well as the decrease of the “strongly-retained” water content confirm the formation of the inclusion compound. Furthermore, the DSC parameters correlate well with the KFT kinetic data for β-CD/ASO complexes. PMID:26977177

  6. Thermal aging stability of infiltrated solid oxide fuel cell electrode microstructures: A three-dimensional kinetic Monte Carlo simulation

    NASA Astrophysics Data System (ADS)

    Zhang, Yanxiang; Ni, Meng; Yan, Mufu; Chen, Fanglin

    2015-12-01

    Nanostructured electrodes are widely used for low temperature solid oxide fuel cells, due to their remarkably high activity. However, the industrial applications of the infiltrated electrodes are hindered by the durability issues, such as the microstructure stability against thermal aging. Few strategies are available to overcome this challenge due to the limited knowledge about the coarsening kinetics of the infiltrated electrodes and how the potentially important factors affect the stability. In this work, the generic thermal aging kinetics of the three-dimensional microstructures of the infiltrate electrodes is investigated by a kinetic Monte Carlo simulation model considering surface diffusion mechanism. Effects of temperature, infiltration loading, wettability, and electrode configuration are studied and the key geometric parameters are calculated such as the infiltrate particle size, the total and percolated quantities of three-phase boundary length and infiltrate surface area, and the tortuosity factor of infiltrate network. Through parametric study, several strategies to improve the thermal aging stability are proposed.

  7. Synthesis and enhanced thermal stability of albumins@alumina: towards injectable sol-gel materials.

    PubMed

    Rutenberg, Avi; Vinogradov, Vladimir V; Avnir, David

    2013-06-25

    A major obstacle to the introduction of bioactively-doped sol-gel based materials for medical applications has been the fact that silica - the most widely studied sol-gel material - despite being a GRAS material, which is widely used as an additive in foods and drug formulations, is still not approved by regulatory agencies for intramuscular injections. Here we point to a potential solution to this problem by shifting the weight to alumina, which is approved for injections as the most common immunization adjuvant. Towards the achievement of this goal we describe the development of protein entrapment methods tailored to alumina, and show high thermal stability of protein-dopants, using a newly developed DSC methodology for this purpose.

  8. Thermal stability of second generation carbosilane dendrimers with peripheral ammonia groups

    NASA Astrophysics Data System (ADS)

    Popescu, Maria-Cristina; Gómez, Rafael; de la Mata, Fco Javier; Rasines, Beatriz; Simionescu, Bogdan C.

    2013-10-01

    Thermal analysis has a wide range of applications in pharmaceutical industry, in designing new molecules, control of raw materials, stability, compatibility studies, and development of new formulations. This paper evaluates the thermodynamic properties of two second generation G2 carbosilane dendrimers with peripheral ammonia groups by differential scanning calorimetry and TG/FTIR coupled techniques. The physical transformations have been detected and their thermodynamic characteristics have been estimated and analyzed. Both dendrimers are stable up to 150 °C, have the Tg at 75 and 59 °C and melting temperatures at 113 and 128 °C, respectively. The decomposition process proved to be very complex and takes place in three steps in nitrogen atmosphere and four steps in air, for both types of dendrimers. IR spectroscopic analysis was used to observe the evolution of the gaseous products versus temperature.

  9. A neutron scattering study on the stability of trehalose mycolates under thermal stress

    NASA Astrophysics Data System (ADS)

    Migliardo, F.; Salmeron, C.; Bayan, N.

    2013-10-01

    The present paper is focused on the study of the dynamics of mycolic acids, which are fundamental components of the outer membrane (mycomembrane) of Mycobacterium tuberculosis. An elastic neutron scattering study of mycolic acid/H2O and lecithin/H2O mixtures as a function of temperature and exchanged wavevector Q has been carried out. This study provides an effective way for characterizing the dynamical properties, furnishing a set of parameters characterizing the different flexibility and rigidity of the investigated lipids. The behavior of the elastically scattered intensity profiles and the derived mean square displacements as a function of temperature shows a more marked temperature dependence for lecithin lipids in comparison with mycolic acids, so revealing a higher thermal stability of these latter. These findings could be useful for understanding the dynamics-function relation in the mycomembrane and then to relate it to the low permeability and high resistance of mycobacteria to many antibiotics.

  10. 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.

  11. 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

  12. Wettability Control of Gold Surfaces Modified with Benzenethiol Derivatives: Water Contact Angle and Thermal Stability.

    PubMed

    Tatara, Shingo; Kuzumoto, Yasutaka; Kitamura, Masatoshi

    2016-04-01

    The water wettability of Au surfaces has been controlled using various benzenethiol derivatives including 4-methylbenzenethiol, pentafluorobenzenethiol, 4-flubrobenzenethiol, 4-methoxy-benzenethiol, 4-nitrobenzenethiol, and 4-hydroxybenzenethiol. The water contact angle of the Au surface modified with the benzenethiol derivative was found to vary in the wide range of 30.9° to 88.3°. The contact angle of the modified Au films annealed was also measured in order to investigate their thermal stability. The change in the contact angle indicated that the modified surface is stable at temperatures below about 400 K. Meanwhile, the activation energy of desorption from the modified surface was estimated from the change in the contact angle. The modified Au surface was also examined using X-ray photoelectron spectroscopy.

  13. Static stability of a viscoelastically supported asymmetric sandwich beam with thermal gradient

    NASA Astrophysics Data System (ADS)

    Nayak, S.; Bisoi, A.; Dash, P. R.; Pradhan, P. K.

    2014-09-01

    The static stability of an asymmetric sandwich beam with viscoelastic core on viscoelastic supports at the ends and subjected to an axial pulsating load and a steady, one-dimensional temperature gradient is investigated by computational method. The equations of motion and associated boundary conditions are obtained using the Hamilton's energy principle. Then, these equations of motion and the associated boundary conditions are non-dimensionalised. A set of Hill's equations is obtained from the non-dimensional equations of motion by the application of the general Galerkin method. The static buckling loads are obtained from the Hill's equations. The effects of shear parameter, geometric parameters, core loss factors, and thermal gradient on the non-dimensional static buckling loads zones have been investigated.

  14. Local order origin of thermal stability enhancement in amorphous Ag doping GeTe

    SciTech Connect

    Xu, L.; Li, Y.; Yu, N. N.; Zhong, Y. P.; Miao, X. S.

    2015-01-19

    We demonstrate the impacts of Ag doping on the local atomic structure of amorphous GeTe phase-change material. The variations of phonon vibrational modes, boding nature, and atomic structure are shown by Raman, X-ray photoelectron spectroscopy, and ab initio calculation. Combining the experiments and simulations, we observe that the number of Ge atoms in octahedral site decreases and that in tetrahedral site increases. This modification in local order of GeTe originating from the low valence element will affect the crystallization behavior of amorphous GeTe, which is verified by differential scanning calorimetry and transmission electron microscope results. This work not only gives the analysis on the structural change of GeTe with Ag dopants but also provides a method to enhance the thermal stability of amorphous phase-change materials for memory and brain-inspired computing applications.

  15. Thermal stability of the oxygen ion conductor BICUVOX.10 in different gaseous atmospheres

    SciTech Connect

    Breiter, M.W.; Reiselhuber, K.; Dorner, G.

    1995-12-31

    A study of the thermal stability of the oxygen ion conductor BICUVOX.10 was carried out on small pieces of the polycrystalline material by combined TGA and DTA measurements in air, nitrogen, oxygen and helium. The TGA measurements demonstrated that the weight change was less than 0.1% in the different gases. The DTA curves were practically the same. There is evidence for the occurrence of a phase change. TGA curves were also taken on BICUVOX.10, the parent compound Bi{sub 4}V{sub 2}O{sub 11} and the oxides CuO, B{sub 2}O{sub 3}, V{sub 2}O{sub 5} under hydrogen. The comparison of the reduction curves shows that BICUVOX.10 is stable up to about 550 C with respect to a direct reduction by molecular hydrogen.

  16. Squeezing a thermal mechanical oscillator by stabilized parametric effect on the optical spring.

    PubMed

    Pontin, A; Bonaldi, M; Borrielli, A; Cataliotti, F S; Marino, F; Prodi, G A; Serra, E; Marin, F

    2014-01-17

    We report the confinement of an optomechanical micro-oscillator in a squeezed thermal state, obtained by parametric modulation of the optical spring. We propose and implement an experimental scheme based on parametric feedback control of the oscillator, which stabilizes the amplified quadrature while leaving the orthogonal one unaffected. This technique allows us to surpass the -3  dB limit in the noise reduction, associated with parametric resonance, with a best experimental result of -7.4  dB. While the present experiment is in the classical regime, in a moderately cooled system our technique may allow squeezing of a macroscopic mechanical oscillator below the zero-point motion.

  17. Thermal behavior of glassy phase stabilized ammonium nitrate (PSAN) thin films

    DOE PAGES

    Yeager, J. D.; Chellappa, R.; Singh, S.; ...

    2015-06-01

    Ammonium nitrate (AN) is a high interest material because of its wide usage in propellants and explosives but can be difficult to handle from a formulation standpoint. It is soluble in many common solvents and has complex phase behavior. Here, we formulate phase stabilized AN (PSAN) films in a polymer matrix and characterize thermal and phase behavior using neutron reflectometry and ellipsometry. Our PSAN films are generally stable up to 160 °C, though we observe small material loss between 60 and 100 °C, which we attribute to solvent interactions with the PSAN. Crystallization of AN from supersaturated polymer is mostmore » common at thicker regions of the film, suggesting a critical nucleation thickness for the AN which can be avoided by making very thin films.« less

  18. Thermal behavior of glassy phase stabilized ammonium nitrate (PSAN) thin films

    SciTech Connect

    Yeager, J. D.; Chellappa, R.; Singh, S.; Majewski, J.

    2015-06-01

    Ammonium nitrate (AN) is a high interest material because of its wide usage in propellants and explosives but can be difficult to handle from a formulation standpoint. It is soluble in many common solvents and has complex phase behavior. Here, we formulate phase stabilized AN (PSAN) films in a polymer matrix and characterize thermal and phase behavior using neutron reflectometry and ellipsometry. Our PSAN films are generally stable up to 160 °C, though we observe small material loss between 60 and 100 °C, which we attribute to solvent interactions with the PSAN. Crystallization of AN from supersaturated polymer is most common at thicker regions of the film, suggesting a critical nucleation thickness for the AN which can be avoided by making very thin films.

  19. 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.

  20. High thermal stability of magnetic tunnel junctions with oxide diffusion barrier layers

    NASA Astrophysics Data System (ADS)

    Fukumoto, Yoshiyuki; Shimura, Ken-ichi; Kamijo, Atsushi; Tahara, Shuichi; Yoda, Hiroaki

    2004-01-01

    We developed two types of magnetic tunnel junctions (MTJs) that showed high thermal stability. One is a PtMn exchange-biased spin-valve MTJ with a CoFe/Al-oxide (AlOx)/NiFe free layer and a CoFeTaOx/CoFe pinned layer, and the other is a pseudo-spin-valve (PSV) MTJ with a CoFe/AlOx/NiFe soft layer, where AlOx and CoFeTaOx act as barriers for Ni and Mn diffusion toward the tunnel barrier, respectively. After 390 °C-1H annealing, the PSV MTJs maintained 28% and the SV MTJs 39% of tunnel magnetoresistance. Transmission electron microscopy observation of the SV MTJs after 380 °C-1H annealing revealed that the migrated Mn atoms were trapped at the CoFeTaOx layer.