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Sample records for improved temperature stability

  1. Thermoelectric refrigerator having improved temperature stabilization means

    DOEpatents

    Falco, Charles M.

    1982-01-01

    A control system for thermoelectric refrigerators is disclosed. The thermoelectric refrigerator includes at least one thermoelectric element that undergoes a first order change at a predetermined critical temperature. The element functions as a thermoelectric refrigerator element above the critical temperature, but discontinuously ceases to function as a thermoelectric refrigerator element below the critical temperature. One example of such an arrangement includes thermoelectric refrigerator elements which are superconductors. The transition temperature of one of the superconductor elements is selected as the temperature control point of the refrigerator. When the refrigerator attempts to cool below the point, the metals become superconductors losing their ability to perform as a thermoelectric refrigerator. An extremely accurate, first-order control is realized.

  2. Improvements in X-band transmitter phase stability through Klystron body temperature regulation

    NASA Technical Reports Server (NTRS)

    Perez, R. M.

    1992-01-01

    This article describes the techniques used and experimental results obtained in improving transmitter stability by control of the klystron body temperature. Related work in the measurement of klystron phase control parameters (pushing factors) is also discussed. The contribution of wave guide temperature excursions to uplink phase stability is presented. Suggestions are made as to the direction of future work in this area.

  3. Improvements in X-band transmitter phase stability through klystron body temperature regulation

    NASA Technical Reports Server (NTRS)

    Perez, R. M.

    1992-01-01

    This article describes the techniques used and experimental results obtained in improving transmitter stability by control of the klystron body temperature. Related work in the measurement of klystron phase control parameters (pushing factors) is also discussed. The contribution of waveguide temperature excursions to uplink phase stability is presented. Suggestions are made as to the direction of future work in this area.

  4. Improvement in temperature stability of standard resistors using heat pipe technology

    NASA Astrophysics Data System (ADS)

    Yan, X.; Duan, Y.; Zhang, J. T.; Wang, W.; Wang, L.; Li, J.

    2013-09-01

    The temperature stability of standard resistors plays an important role in assuring the accuracy of resistance measurements that use resistance ratio bridges to calibrate standard platinum resistance thermometers (SPRTs) on the International Temperature Scale of 1990 (ITS-90). Therefore, during resistance measurements, the resistors are always kept in temperature controlled oil or air baths and enclosures to maintain a constant temperature. In order to achieve better temperature stability and reduce the effects of temperature fluctuations on the resistance of a standard resistor, an annular water heat pipe thermostat immersed in a mineral oil bath was developed to accommodate and stabilize a standard resistor. Also, the thermostat's performance was characterized. The results showed that the temperature stability of standard resistors was within 1 mK after using the heat pipe thermostat compared with that of 30 mK for the oil bath. Therefore, the temperature stability of standard resistors was improved by more than one order of magnitude, which was attributable to the good thermal self-regulating abilities of the water heat pipe.

  5. Technical ways to improve the temperature stability of fiber optic gyros

    NASA Astrophysics Data System (ADS)

    Song, Youshan; Zhou, Shiqin; Lu, Zheng

    2001-12-01

    Described in this paper are technical ways to improve the temperature stability of fiber optic gyroscopes. The fiber optic gyroscope consists of a super luminescent diode, an integrated optical circuit, a fiber coupler, a polarizing optical fiber coil, a detector and a signal-processing device. The peak wavelength of SLD is 1.3 micrometers . The multifunctional integrated optical circuit that includes a polarizater, a Y type junction coupler and a phase modulator, is manufactured with annealed proton exchange process. The polarizing optical fiber coil is fabricated by applying quadrupolar winding technology. The fiber optic gyroscope can work in high/low temperature, large acceleration, vibration, shock and other harsh environments. It is applied in strapdown inertial navigation systems, directional measuring system in oil-rigs and automobile positioning and guidance.

  6. Recent progress in improving low-temperature stability of infrared thin-film interference filters.

    PubMed

    Li, B; Zhang, S; Jiang, J; Liu, D Q; Zhang, F

    2005-08-22

    The degeneration of performance of an optical thin-film interference filter associated with the change of temperature is not acceptable. In this letter, we report a new progress in improving low-temperature performance of infrared narrow-band filters by using Pb(1-x)Ge(x)Te initial bulk alloy with appropriate Ge concentration x. It can be found that there exists a critical temperature for the investigated narrow-band filter, at which the temperature coefficient of filter is exactly zero. Therefore, by means of controlling the composition in (Pb(1-x)Ge(x))(1-y)Te(y) layers, the temperature coefficient of filter can be tunable at the designated low-temperature. In our present investigation, when temperature varies from 300 to 85 K, a shift of peak wavelength of 0.05935 nm.K-1 has been achieved.

  7. Use of Atomic Layer Deposition to Improve the Stability of Silver Substrates for In-Situ, High Temperature SERS Measurements

    SciTech Connect

    John, Joshy; Mahurin, Shannon Mark; Dai, Sheng; Sepaniak, Michael

    2010-01-01

    A method to stabilize silver surface-enhanced Raman spectroscopy (SERS) substrates for in-situ, high temperature applications is demonstrated. Silver island films grown by thermal evaporation were coated with a thin layer (from 2.5nm to 5nm) of alumina by atomic layer deposition (ALD), which protects and stabilizes the SERS-active substrate without eliminating the Raman enhancement. The temporal stability of the alumina-coated silver island films was examined by measurement of the Raman intensity of rhodamine 6G molecules deposited onto bare and alumina-coated silver substrates over the course of thirty-four days. The coated substrates showed almost no change in SERS enhancement while the uncoated substrates exhibited a significant decrease in Raman intensity. To demonstrate the feasibility of the alumina-coated silver substrate as a probe of adsorbates and reactions at elevated temperatures, an in-situ SERS measurement of calcium nitrate tetrahydrate on bare and alumina-coated silver was performed at temperatures ranging from 25 C to 400 C. ALD deposition of an ultrathin alumina layer significantly improved the thermal stability of the SERS substrate thus enabling in-situ detection of the dehydration of the calcium nitrate tetrahydrate at elevated temperature. Despite some loss of Raman signal, the coated substrate exhibited greater thermal stability compared to the uncoated substrate. These experiments show that ALD can be used to synthesize stable SERS substrates capable of measuring adsorbates and processes at high temperature.

  8. A facile approach to enhance the high temperature stability of magnetite nanoparticles with improved magnetic property

    NASA Astrophysics Data System (ADS)

    Pati, S. S.; Philip, John

    2013-01-01

    We study the effect of Zn2+ doping on crystal structure, magnetic properties, blocking and Curie temperatures, and the high temperature phase stability of magnetite nanoparticles under air and vacuum annealing. The Zn2+ doped nanoparticles (ZnxFe3-xO4 with x = 0, 0.2, 0.4, and 0.6) are prepared by simple co-precipitation technique and are characterized by high temperature X-ray powder diffraction (HTXRD), vibrating sample magnetometer, small angle X-ray scattering, thermogravimetry, differential scanning calorimetry (DSC), and transmission electron microscopy. Our HTXRD studies show that the decomposition temperature of pure magnetite (Fe3O4) in vacuum is increased by 300 °C (from 700 to 1000 °C), with 0.2 fraction of Zn2+ doping. The DSC studies under air environment also show that the γ-Fe2O3 to α-Fe2O3 phase transition temperature increases with the zinc fraction. The increase in transition temperature is attributed to the increase in the activation energy of the maghemite to hematite phase transition after the replacement of Fe3+ with larger diameter Zn2+ in the A site. Interestingly, the saturation magnetization increases from 61 to 69 emu/g upon 0.2 fraction of Zn2+, which augments the utility of the doped compound for practical applications. While the Curie temperature is found to increase with doping concentration, the blocking temperature shows an opposite trend. The blocking temperature values were found to be 262, 196, 144, and 153 K for 0, 0.2, 0.4, and 0.6 fraction of zinc, respectively. The reduction in TB is attributed to weak dipole-dipole interactions and local exchange coupling between nanoparticles. All the Zn2+ doped samples show superparamagnetic nature. These findings are extremely useful in producing superparamagnetic nanoparticles with enhanced magnetic properties for high temperature applications.

  9. Bio-lubricants derived from waste cooking oil with improved oxidation stability and low-temperature properties.

    PubMed

    Li, Weimin; Wang, Xiaobo

    2015-01-01

    Waste cooking oil (WCO) was chemically modified via epoxidation using H2O2 followed by transesterification with methanol and branched alcohols (isooctanol, isotridecanol and isooctadecanol) to produce bio-lubricants with improved oxidative stability and low temperature properties. Physicochemical properties of synthesized bio-lubricants such as pour point (PP), cloud point (CP), viscosity, viscosity index (VI), oxidative stability, and corrosion resistant property were determined according to standard methods. The synthesized bio-lubricants showed improved low temperature flow performances compared with WCO, which can be attributing to the introduction of branched chains in their molecular structures. What's more, the oxidation stability of the WCO showed more than 10 folds improvement due to the elimination of -C=C-bonds in the WCO molecule. Tribological performances of these bio-lubricants were also investigated using four-ball friction and wear tester. Experimental results showed that derivatives of WCO exhibited favorable physicochemical properties and tribological performances which making them good candidates in formulating eco-friendly lubricants.

  10. A temperature-dependent gain control system for improving the stability of Si-PM-based PET systems

    NASA Astrophysics Data System (ADS)

    Yamamoto, Seiichi; Satomi, Junkichi; Watabe, Tadashi; Watabe, Hiroshi; Kanai, Yasukazu; Imaizumi, Masao; Shimosegawa, Eku; Hatazawa, Jun

    2011-05-01

    The silicon-photomultiplier (Si-PM) is a promising photodetector for the development of new PET systems due to its small size, high gain and relatively low sensitivity to the static magnetic field. One drawback of the Si-PM is that it has significant temperature-dependent gain that poses a problem for the stability of the Si-PM-based PET system. To reduce this problem, we developed and tested a temperature-dependent gain control system for the Si-PM-based PET system. The system consists of a thermometer, analog-to-digital converter, personal computer, digital-to-analog converter and variable gain amplifiers in the weight summing board of the PET system. Temperature characteristics of the Si-PM array are measured and the calculated correction factor is sent to the variable gain amplifier. Without this correction, the temperature-dependent peak channel shifts of the block detector were -55% from 20 °C to 35 °C. With the correction, the peak channel variations were corrected within ±8%. The coincidence count rate of the Si-PM-based PET system was measured using a Na-22 point source while monitoring the room temperature. Without the correction, the count rate inversely changed with the room temperature by 10% for 1.5° C temperature changes. With the correction, the count rate variation was reduced to within 3.7%. These results indicate that the developed temperature-dependent gain control system can contribute to improving the stability of Si-PM-based PET systems.

  11. A temperature-dependent gain control system for improving the stability of Si-PM-based PET systems.

    PubMed

    Yamamoto, Seiichi; Satomi, Junkichi; Watabe, Tadashi; Watabe, Hiroshi; Kanai, Yasukazu; Imaizumi, Masao; Shimosegawa, Eku; Hatazawa, Jun

    2011-05-07

    The silicon-photomultiplier (Si-PM) is a promising photodetector for the development of new PET systems due to its small size, high gain and relatively low sensitivity to the static magnetic field. One drawback of the Si-PM is that it has significant temperature-dependent gain that poses a problem for the stability of the Si-PM-based PET system. To reduce this problem, we developed and tested a temperature-dependent gain control system for the Si-PM-based PET system. The system consists of a thermometer, analog-to-digital converter, personal computer, digital-to-analog converter and variable gain amplifiers in the weight summing board of the PET system. Temperature characteristics of the Si-PM array are measured and the calculated correction factor is sent to the variable gain amplifier. Without this correction, the temperature-dependent peak channel shifts of the block detector were -55% from 20 °C to 35 °C. With the correction, the peak channel variations were corrected within ±8%. The coincidence count rate of the Si-PM-based PET system was measured using a Na-22 point source while monitoring the room temperature. Without the correction, the count rate inversely changed with the room temperature by 10% for 1.5° C temperature changes. With the correction, the count rate variation was reduced to within 3.7%. These results indicate that the developed temperature-dependent gain control system can contribute to improving the stability of Si-PM-based PET systems.

  12. "Thermal Stabilization Effect" of Al2O3 nano-dopants improves the high-temperature dielectric performance of polyimide.

    PubMed

    Yang, Yang; He, Jinliang; Wu, Guangning; Hu, Jun

    2015-11-24

    Insulation performance of the dielectrics under extreme conditions always attracts widespread attention in electrical and electronic field. How to improve the high-temperature dielectric properties of insulation materials is one of the key issues in insulation system design of electrical devices. This paper studies the temperature-dependent corona resistance of polyimide (PI)/Al2O3 nanocomposite films under high-frequency square-wave pulse conditions. Extended corona resistant lifetime under high-temperature conditions is experimentally observed in the 2 wt% nanocomposite samples. The "thermal stabilization effect" is proposed to explain this phenomenon which attributes to a new kind of trap band caused by nanoparticles. This effect brings about superior space charge characteristics and corona resistance under high temperature with certain nano-doping concentration. The proposed theory is experimentally demonstrated by space charge analysis and thermally stimulated current (TSC) tests. This discovered effect is of profound significance on improving high-temperature dielectric properties of nanocomposites towards various applications.

  13. Temperature dependence of resonance characteristics of silicon resonators and thermal stability improvement by differential operation method

    NASA Astrophysics Data System (ADS)

    Sana, Amrita Kumar; Jun, Maeda; Yokoyama, Shuhei; Amemiya, Yoshiteru; Yokoyama, Shin

    2017-04-01

    In this paper, we describe the mechanism and solution for dominating temperature effects on refractive-index-based Si optical resonator sensors such as ring resonator and photonic crystal resonator sensors. The temperature change affects the silicon refractive index and also the resonator mechanical shape. As a result, it is reported that the refractive index change is marked, whereas the mechanical deformation effect is negligible. We also demonstrated that the differential operation is effective for suppressing the temperature effect for Si ring resonator sensors.

  14. Logarithmic current measurement circuit with improved accuracy and temperature stability and associated method

    DOEpatents

    Ericson, M. Nance; Rochelle, James M.

    1994-01-01

    A logarithmic current measurement circuit for operating upon an input electric signal utilizes a quad, dielectrically isolated, well-matched, monolithic bipolar transistor array. One group of circuit components within the circuit cooperate with two transistors of the array to convert the input signal logarithmically to provide a first output signal which is temperature-dependant, and another group of circuit components cooperate with the other two transistors of the array to provide a second output signal which is temperature-dependant. A divider ratios the first and second output signals to provide a resultant output signal which is independent of temperature. The method of the invention includes the operating steps performed by the measurement circuit.

  15. Improved stability of a phase change memory device using Ge-doped SbTe at varying ambient temperature

    NASA Astrophysics Data System (ADS)

    Wu, Zhe; Lee, Suyoun; Park, Young-Wook; Ahn, Hyung-Woo; Jeong, Doo Seok; Jeong, Jeung-hyun; No, Kwangsoo; Cheong, Byung-ki

    2010-03-01

    Ge-doped SbTe (Ge-ST) was compared with Ge2Sb2Te5 (GST) for its potential use in the phase-change memory with improved stability at varying ambient temperature (TA). Device characteristics such as RESET current, RESET resistance, and SET resistance of Ge-ST devices were found to vary significantly less with TA than those of GST devices. From measured carrier density, mobility, and optical band gaps, these findings are interpreted to derive from a metallic nature of the crystalline Ge-ST in contrast with a semiconducting nature of the crystalline GST as well as a relatively weaker covalent bonding in amorphous Ge-ST.

  16. Improved Glass Transition Temperature towards Thermal Stability via Thiols Solvent Additive versus DIO in Polymer Solar Cells.

    PubMed

    Yin, Jingping; Zhou, Weihua; Zhang, Lin; Xie, Yuanpeng; Yu, Zoukangning; Shao, Jun; Ma, Wei; Zeng, Jianrong; Chen, Yiwang

    2017-08-25

    The halogen-free solvent additive, 1,4-butanedithiol (BT) has been incorporated into PTB7-Th:PC71 BM, leading to higher power conversion efficiency (PCE) value as well as substantially enhanced thermal stability, as compared with the traditional 1,8-diiodooctane (DIO) additive. More importantly, the improved thermal stability after processing with BT contributes to a higher glass transition temperature (Tg ) of PTB7-Th, as determined by dynamic mechanical analysis. After thermal annealing at 130 °C in nitrogen atmosphere for 30 min, the PCE of the specimen processed with BT reduces from 9.3% to 7.1%, approaching to 80% of its original value. In contrast, the PCE of specimens processed with DIO seriously depresses from 8.3% to 3.8%. These findings demonstrate that smart utilization of low-boiling-point solvent additive is an effective and practical strategy to overcome thermal instability of organic solar cells via enhancing the Tg of donor polymer. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. Improving cyclic stability of lithium nickel manganese oxide cathode at elevated temperature by using dimethyl phenylphosphonite as electrolyte additive

    NASA Astrophysics Data System (ADS)

    Mai, Shaowei; Xu, Mengqing; Liao, Xiaolin; Xing, Lidan; Li, Weishan

    2015-01-01

    A novel electrolyte additive, dimethyl phenylphosphonite (DMPP), is reported in this paper to be able to improve significantly the cyclic stability of LiNi0.5Mn1.5O4 cathode of high voltage lithium ion battery at elevated temperature. When experiencing charge/discharge cycling at 50 °C with 1C (1C = 146.7 mAh g-1) rate in a standard (STD) electrolyte (1.0 M LiPF6 in ethylene carbonate (EC)/dimethyl carbonate (DMC), EC/DMC = 1/2 in volume), LiNi0.5Mn1.5O4 suffers serious discharge capacity decaying, with a capacity retention of 42% after 100 cycles. With adding 0.5% DMPP into the STD electrolyte, the capacity retention is increased to 91%. This improvement can be ascribed to the preferential oxidation of DMPP to the STD electrolyte and the subsequent formation of a protective film on LiNi0.5Mn1.5O4, which suppresses the electrolyte decomposition and protects LiNi0.5Mn1.5O4 from destruction. Theoretical calculations together with voltammetric analyses demonstrate the preferential oxidation of DMPP and the consequent suppression of electrolyte decomposition, while the observations from scanning electron microscopy, X-ray photoelectronic spectroscopy and Fourier transform infrared spectroscopy confirm the protection that DMPP provides for LiNi0.5Mn1.5O4.

  18. Improvement of high temperature stability of nickel contacts on n-type 6H SiC

    NASA Astrophysics Data System (ADS)

    Roccaforte, F.; La Via, F.; Raineri, V.; Calcagno, L.; Musumeci, P.

    2001-12-01

    The structural and electrical characterisation of nickel contacts on n-type silicon carbide was performed to improve the ohmic behaviour at high temperatures. The formation of nickel silicide (Ni 2Si) was observed after annealing in vacuum of Ni/SiC samples at 600 °C, as well as after rapid thermal annealing (RTA) in N 2 at 700 for 60 s. The carbon was almost uniformly distributed inside the Ni 2Si layer, as monitored by energy dispersion X-ray analysis (EDX). The specific contact resistance ρc was determined by the transmission line method (TLM) for different values of the substrate carrier concentration ND. Ohmic contacts with ρ c=3.9×10 -5 Ω cm 2 were obtained for substrates with N D=7.4×10 18 cm-3 after RTA in N 2 at 950 °C. The optimised contacts maintain their electrical stability even after annealing in N 2 up to 1000 °C.

  19. Temperature stability of nanocellulose dispersions.

    PubMed

    Heggset, Ellinor B; Chinga-Carrasco, Gary; Syverud, Kristin

    2017-02-10

    Cellulose nanofibrils (CNF) have potential as rheology modifiers of water based fluids, e.g. drilling fluids for use in oil wells or as additives in injection water for enhanced oil recovery (EOR). The temperature in oil wells can be high (>100°C), and the retention time long; days for drilling fluids and months for EOR fluids. Hence, it is important to assess the temperature stability over time of nanocellulose dispersions to clarify their suitability as rheology modifiers of water based fluids at such harsh conditions. Dispersions of CNF produced mechanically, by using TEMPO mediated oxidation and by using carboxymethylation as pretreatment, in addition to cellulose nanocrystals (CNC), have been subjected to heat aging. Temperature stability was best for CNC and for mechanically produced CNF that were stable after heating to 140°C for three days. The effect of additives was evaluated; cesium formate and sodium formate increased the temperature stability of the dispersions, while there was no effect of using phosphate buffer.

  20. Improved roof stabilization technologies

    SciTech Connect

    Ebadian, M.A.

    1998-01-01

    Decontamination and decommissioning (D and D) activities require that personnel have access to all areas of structures, some of which are more than 40 years old. In many cases, these structures have remained in a standby condition for up to 10 years; few preventative maintenance activities have been performed on them because of lack of funding or a defined future plan of action. This situation has led to deteriorated building conditions, resulting in potential personnel safety hazards. In addition, leaky roofs allow water to enter the buildings, which can cause the spread of contamination and increase building deterioration, worsening the already unsafe working conditions. To ensure worker safety and facilitate building dismantlement, the assessment of roof stabilization techniques applicable to US Department of Energy (DOE) structures has become an important issue. During Fiscal year 1997 (FY97), a comprehensive reliability-based model for the structural stabilization analysis of roof system in complex structures was developed. The model consists of three major components: a material testing method, a deterministic structural computer model, and a reliability-based optimization, and probabilistic analyses of roof structures can be implemented. Given site-specific needs, this model recommends the most appropriate roof stabilization system. This model will give not only an accurate evaluation of the existing roof system in complex structures, but it will also be a reliable method to aid the decision-making process. This final report includes in its appendix a Users` Manual for the Program of Deterministic and Reliability Analysis of Roof Structures.

  1. IMPROVED ROOF STABILIZATION TECHNOLOGIES

    SciTech Connect

    M.A. Ebadian, Ph.D.

    1999-01-01

    Many U.S. Department of Energy (DOE) remediation sites have performed roof repair and roof replacement to stabilize facilities prior to performing deactivation and decommissioning (D&D) activities. This project will review the decision criteria used by these DOE sites, along with the type of repair system used for each different roof type. Based on this information, along with that compiled from roofing experts, a decision-making tool will be generated to aid in selecting the proper roof repair systems. Where appropriate, innovative technologies will be reviewed and applied to the decision-making tool to determine their applicability. Based on the results, applied research and development will be conducted to develop a method to repair these existing roofing systems, while providing protection for the D and D worker in a cost-efficient manner.

  2. “Thermal Stabilization Effect” of Al2O3 nano-dopants improves the high-temperature dielectric performance of polyimide

    PubMed Central

    Yang, Yang; He, Jinliang; Wu, Guangning; Hu, Jun

    2015-01-01

    Insulation performance of the dielectrics under extreme conditions always attracts widespread attention in electrical and electronic field. How to improve the high-temperature dielectric properties of insulation materials is one of the key issues in insulation system design of electrical devices. This paper studies the temperature-dependent corona resistance of polyimide (PI)/Al2O3 nanocomposite films under high-frequency square-wave pulse conditions. Extended corona resistant lifetime under high-temperature conditions is experimentally observed in the 2 wt% nanocomposite samples. The “thermal stabilization effect” is proposed to explain this phenomenon which attributes to a new kind of trap band caused by nanoparticles. This effect brings about superior space charge characteristics and corona resistance under high temperature with certain nano-doping concentration. The proposed theory is experimentally demonstrated by space charge analysis and thermally stimulated current (TSC) tests. This discovered effect is of profound significance on improving high-temperature dielectric properties of nanocomposites towards various applications. PMID:26597981

  3. Improved stability of (+)-catechin and (-)-epicatechin by complexing with hydroxypropyl-β-cyclodextrin: Effect of pH, temperature and configuration.

    PubMed

    Liu, Min; Zheng, Yan; Wang, Chunmei; Xie, Jimin; Wang, Bingquan; Wang, Zhengping; Han, Jun; Sun, Dezhi; Niu, Meiju

    2016-04-01

    The stability and bioavailability of catechins, a kind of tea polyphenols with health benefit, could be improved by complexing with cyclodextrins. The aim of this study was to investigate the complexation of two geometrical isomers, (+)-catechin and (-)-epicatechin, with hydroxypropyl-β-cyclodextrin (HP-β-CD) in tris-HCl buffer solutions at pH 6.8-8.0 using isothermal titration calorimetry, fluorescence and proton nuclear magnetic resonance spectroscopy. Experimental results showed that these inclusion interactions are primarily enthalpy-driven processes. The complexation constant (KC) of EC+HP-β-CD complex was less than that of CA+HP-β-CD at the same temperature and pH value. Temperature and pH studies showed that the KC value decreased with the rise of temperature and pH. Stability study indicated that HP-β-CD showed a stronger protection effect on CA than that on EC. The different inclusion modes between CA and EC were discussed in terms of the discrepancy in their molecular structures. Copyright © 2015 Elsevier Ltd. All rights reserved.

  4. Raman spectra of single walled carbon nanotubes at high temperatures: pretreating samples in a nitrogen atmosphere improves their thermal stability in air.

    PubMed

    Molina-Duarte, J; Espinosa-Vega, L I; Rodríguez, A G; Guirado-López, R A

    2017-03-08

    We present a combined experimental and theoretical study dedicated to analyzing the structural stability and chemical reactivity of single walled carbon nanotubes (SWCNTs) in the presence of air and nitrogen atmospheres in the temperature interval of 300-1000 K. The temperature dependence of the radial breathing mode (RBM) region of the Raman spectra is irreversible in the presence of air, but it is reversible up to 1000 K in a nitrogen atmosphere. Our density functional theory (DFT) calculations reveal that irreversibility is due to partial degradation of SWCNTs produced by dissociative chemical adsorption of molecular oxygen on intrinsic defects of the nanotube surface. Oxygen partially opens the nanotubes forming semi-tubes with a non-uniform diameter distribution observed by Raman scattering. In contrast, heating CNTs in a nitrogen atmosphere seems to lead to the formation of nitrogen-doped SWCNTs. Our DFT calculations indicate that in general the most common types of nitrogen doping (e.g., pyridinic, pyrrolic, and substitutional) modify the location of the RBM frequency, leading also to frequency shifts and intensity changes of the surrounding modes. However, by performing a systematic comparison between calculated and measured spectra we have been able to infer the possible adsorbed configurations adopted by N species on the nanotube surface. Interestingly, by allowing previously nitrogen-exposed SWCNTs to interact with air at different temperatures (up to 1000 K) we note that the RBM region remains nearly unperturbed, defining thus our nitrogen-pretreated SWCNTs as more appropriate carbon nanostructures for high temperature applications in realistic environments. We believe that we have implemented a post-growth heat-treatment process that improves the stability of carbon nanotubes preserving their diameter and inducing a defect-healing process of the carbon wall.

  5. Improving Performance and Operational Stability of Porcine Interferon-α Production by Pichia pastoris with Combinational Induction Strategy of Low Temperature and Methanol/Sorbitol Co-feeding.

    PubMed

    Gao, Min-Jie; Zhan, Xiao-Bei; Gao, Peng; Zhang, Xu; Dong, Shi-Juan; Li, Zhen; Shi, Zhong-Ping; Lin, Chi-Chung

    2015-05-01

    Various induction strategies were investigated for effective porcine interferon-α (pIFN-α) production by Pichia pastoris in a 10 L fermenter. We found that pIFN-α concentration could be significantly improved with the strategies of low-temperature induction or methanol/sorbitol co-feeding. On this basis, a combinational strategy of induction at lower temperature (20 °C) with methanol/sorbitol co-feeding has been proposed for improvement of pIFN-α production. The results reveal that maximal pIFN-α concentration and antiviral activity reach the highest level of 2.7 g/L and 1.8 × 10(7) IU/mg with the proposed induction strategy, about 1.3-2.1 folds higher than those obtained with other sub-optimal induction strategies. Metabolic analysis and online multi-variable measurement results indicate that energy metabolic enrichment is responsible for the performance enhancement of pIFN-α production, as a large amount of ATP could be simultaneously produced from both formaldehyde oxidation pathway in methanol metabolism and tricarboxylic acid (TCA) cycle in sorbitol metabolism. In addition, the proposed combinational induction strategy enables P. pastoris to be resistant to high methanol concentration (42 g/L), which conceivably occur associating with the error-prone methanol over-feeding. As a result, the proposed combinational induction strategy simultaneously increased the targeted protein concentration and operational stability leading to significant improvement of pIFN-α production.

  6. Improvement of the long term stability in the high temperature solid oxide fuel cell using functional layers

    SciTech Connect

    Brueckner, B.; Guenther, C.; Ruckdaeschel, R.

    1996-12-31

    In the planar Siemens design of the solid oxide fuel cell a metallic interconnector is used to seperate the ceramic single cells. A disadvantage of the metallic bipolar plate which consists of a chromium alloy is the formation of high volatile Cr-oxides and hydroxides at the surface at the cathode side. The reaction products evaporate and are reduced at the cathode/electrolyte interface to form new crystalline phases. This process gives rise to long term cell degradation. Protective coatings might be successful in preventing the chromium oxide evaporation. The required properties of the protective layers are (I) high electrical conductivity, (II) similar coefficients of thermal expansion to the bipolar plate (III), chemical compatibility to the bipolar plate and cathode material, (IV) a low diffusion coefficient of Cr and (V) chemical stability up to 1223K under oxygen atmosphere. Furthermore, during operation at 1223K an electrical contact between the metallic plate and the electrodes has to be maintained. This problem could be solved using ceramic layer between the metallic plate and the single cells.

  7. Addition of SiC Particles to Ag Die-Attach Paste to Improve High-Temperature Stability; Grain Growth Kinetics of Sintered Porous Ag

    NASA Astrophysics Data System (ADS)

    Zhang, Hao; Nagao, Shijo; Suganuma, Katsuaki

    2015-10-01

    To improve the high-temperature reliability of sintered Ag joints, three types of silicon carbide particle (SiCp) of different size and morphology were added to Ag micron-flake paste. Quality sintered joints between Cu dummy chips and Cu substrate were obtained at a relatively low temperature (250°C), in air, under low load (0.4 MPa), and 35 MPa die-shear strength was achieved. High-temperature stability was investigated by means of aging tests at 150, 200, and 250°C for 500 h, and by thermal cycling between -50°C and 250°C for up to 170 cycles. The best distribution and compatibility with porous sintered Ag structures was observed for sub-micron SiC particles with an average diameter of 600 nm. After high-temperature storage for 500 h at 250°C, mean Ag grain size of the SiC-containing joints was unchanged whereas that for pure sintered Ag increased from 1.1 to 2.5 μm. Ag joints containing the optimum amount (2 wt.%) of SiCp retained their original strength (20 MPa) after storage at 250°C for 500 h. The shear strength of Ag joints without added SiCp decreased from 27 to 7 MPa after 500 h because of grain growth, which obeyed the classical parabolic law. Grain growth in pure Ag joints is discussed in terms of a temperature-dependent exponent n and activation energy Q. Our SiCp-containing joints resisted the grain growth that induces interfacial cracks during thermal cycling.

  8. Temperature Stabilization Requirements for Unchopped Thermal Detectors

    NASA Technical Reports Server (NTRS)

    Foote, Marc C.

    2000-01-01

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

  9. Localized temperature stability of low temperature cofired ceramics

    DOEpatents

    Dai, Steven Xunhu

    2013-11-26

    The present invention is directed to low temperature cofired ceramic modules having localized temperature stability by incorporating temperature coefficient of resonant frequency compensating materials locally into a multilayer LTCC module. Chemical interactions can be minimized and physical compatibility between the compensating materials and the host LTCC dielectrics can be achieved. The invention enables embedded resonators with nearly temperature-independent resonance frequency.

  10. The physical mechanism on the threshold voltage temperature stability improvement for GaN HEMTs with pre-fluorination argon treatment

    NASA Astrophysics Data System (ADS)

    Wang, Yun-Hsiang; Liang, Yung C.; Samudra, Ganesh S.; Huang, Chih-Fang; Kuo, Wei-Hung; Lo, Guo-Qiang

    2016-06-01

    In this paper, a normally-off AlGaN/GaN MIS-HEMT with improved threshold voltage (VTH) thermal stability is reported with investigations on its physical mechanism. The normally-off operation of the device is achieved from novel short argon plasma treatment (APT) prior to the fluorine plasma treatment (FPT) on Al2O3 gate dielectrics. For the MIS-HEMT with FPT only, its VTH drops from 4.2 V at room temperature to 0.5 V at 200 °C. Alternatively, for the device with APT-then-FPT process, its VTH can retain at 2.5 V at 200 °C due to the increased amount of deep-level traps that do not emit electrons at 200 °C. This thermally stable VTH makes this device suitable for high power applications. The depth profile of the F atoms in Al2O3, measured by the secondary ion mass spectroscopy, reveals a significant increase in the F concentration when APT is conducted prior to FPT. The X-ray photoelectron spectroscopy (XPS) analysis on the plasma-treated Al2O3 surfaces observes higher composition of Al-F bonds if APT was applied before FPT. The enhanced breaking of Al-O bonds due to Ar bombardment assisted in the increased incorporation of F radicals at the surface during the subsequent FPT process. The Schrödinger equation of Al2OxFy cells, with the same Al-F compositions as obtained from XPS, was solved by Gaussian 09 molecular simulations to extract electron state distribution as a function of energy. The simulation results show creation of the deeper trap states in the Al2O3 bandgap when APT is used before FPT. Finally, the trap distribution extracted from the simulations is verified by the gate-stress experimental characterization to confirm the physical mechanism described.

  11. Temperature Stability of the Sky Quality Meter

    PubMed Central

    Schnitt, Sabrina; Ruhtz, Thomas; Fischer, Jürgen; Hölker, Franz; Kyba, Christopher C.M.

    2013-01-01

    The stability of radiance measurements taken by the Sky Quality Meter (SQM) was tested under rapidly changing temperature conditions during exposure to a stable light field in the laboratory. The reported radiance was found to be negatively correlated with temperature, but remained within 7% of the initial reported radiance over a temperature range of −15°C to 35°C, and during temperature changes of −33°C/h and +70°C/h. This is smaller than the manufacturer's quoted unit-to-unit systematic uncertainty of 10%, indicating that the temperature compensation of the SQM is adequate under expected outdoor operating conditions. PMID:24030682

  12. The physical mechanism on the threshold voltage temperature stability improvement for GaN HEMTs with pre-fluorination argon treatment

    SciTech Connect

    Wang, Yun-Hsiang; Liang, Yung C.; Samudra, Ganesh S.; Huang, Chih-Fang; Kuo, Wei-Hung; Lo, Guo-Qiang

    2016-06-06

    In this paper, a normally-off AlGaN/GaN MIS-HEMT with improved threshold voltage (V{sub TH}) thermal stability is reported with investigations on its physical mechanism. The normally-off operation of the device is achieved from novel short argon plasma treatment (APT) prior to the fluorine plasma treatment (FPT) on Al{sub 2}O{sub 3} gate dielectrics. For the MIS-HEMT with FPT only, its V{sub TH} drops from 4.2 V at room temperature to 0.5 V at 200 °C. Alternatively, for the device with APT-then-FPT process, its V{sub TH} can retain at 2.5 V at 200 °C due to the increased amount of deep-level traps that do not emit electrons at 200 °C. This thermally stable V{sub TH} makes this device suitable for high power applications. The depth profile of the F atoms in Al{sub 2}O{sub 3}, measured by the secondary ion mass spectroscopy, reveals a significant increase in the F concentration when APT is conducted prior to FPT. The X-ray photoelectron spectroscopy (XPS) analysis on the plasma-treated Al{sub 2}O{sub 3} surfaces observes higher composition of Al-F bonds if APT was applied before FPT. The enhanced breaking of Al-O bonds due to Ar bombardment assisted in the increased incorporation of F radicals at the surface during the subsequent FPT process. The Schrödinger equation of Al{sub 2}O{sub x}F{sub y} cells, with the same Al-F compositions as obtained from XPS, was solved by Gaussian 09 molecular simulations to extract electron state distribution as a function of energy. The simulation results show creation of the deeper trap states in the Al{sub 2}O{sub 3} bandgap when APT is used before FPT. Finally, the trap distribution extracted from the simulations is verified by the gate-stress experimental characterization to confirm the physical mechanism described.

  13. Improved high-temperature resistant matrix resins

    NASA Technical Reports Server (NTRS)

    Green, H. E.; Chang, G. E.; Wright, W. F.; Ueda, K.; Orell, M. K.

    1989-01-01

    A study was performed with the objective of developing matrix resins that exhibit improved thermo-oxidative stability over state-of-the-art high temperature resins for use at temperatures up to 644 K (700 F) and air pressures up to 0.7 MPa (100 psia). The work was based upon a TRW discovered family of polyimides currently licensed to and marketed by Ethyl Corporation as EYMYD(R) resins. The approach investigated to provide improved thermo-oxidative properties was to use halogenated derivatives of the diamine, 2, 2-bis (4-(4-aminophenoxy)phenyl) hexafluoropropane (4-BDAF). Polyimide neat resins and Celion(R) 12,000 composites prepared from fluorine substituted 4-BDAF demonstrated unexpectedly lower glass transition temperatures (Tg) and thermo-oxidative stabilities than the baseline 4-BDAF/PMDA polymer.

  14. Stability Test for Transient-Temperature Calculations

    NASA Technical Reports Server (NTRS)

    Campbell, W.

    1984-01-01

    Graphical test helps assure numerical stability of calculations of transient temperature or diffusion in composite medium. Rectangular grid forms basis of two-dimensional finite-difference model for heat conduction or other diffusion like phenomena. Model enables calculation of transient heat transfer among up to four different materials that meet at grid point.

  15. Stability Test for Transient-Temperature Calculations

    NASA Technical Reports Server (NTRS)

    Campbell, W.

    1984-01-01

    Graphical test helps assure numerical stability of calculations of transient temperature or diffusion in composite medium. Rectangular grid forms basis of two-dimensional finite-difference model for heat conduction or other diffusion like phenomena. Model enables calculation of transient heat transfer among up to four different materials that meet at grid point.

  16. Protein stability and enzyme activity at extreme biological temperatures.

    PubMed

    Feller, Georges

    2010-08-18

    Psychrophilic microorganisms thrive in permanently cold environments, even at subzero temperatures. To maintain metabolic rates compatible with sustained life, they have improved the dynamics of their protein structures, thereby enabling appropriate molecular motions required for biological activity at low temperatures. As a consequence of this structural flexibility, psychrophilic proteins are unstable and heat-labile. In the upper range of biological temperatures, thermophiles and hyperthermophiles grow at temperatures > 100 °C and synthesize ultra-stable proteins. However, thermophilic enzymes are nearly inactive at room temperature as a result of their compactness and rigidity. At the molecular level, both types of extremophilic proteins have adapted the same structural factors, but in opposite directions, to address either activity at low temperatures or stability in hot environments. A model based on folding funnels is proposed accounting for the stability-activity relationships in extremophilic proteins.

  17. Improving the Stability of Fluorescent Silver Nanoclusters

    NASA Astrophysics Data System (ADS)

    Swanson, Nicholas; Stanko, Danielle; Campbell, Ian; Wittmershaus, Bruce

    The quantum mechanical nature of noble metal nanoparticles results in them having optical properties much different from the bulk metal. Silver nanoclusters (AgNC), groups of 4 to 20 atoms, are characterized by strong optical transitions in the visible part of the spectrum giving them an appearance like fluorescent organic dyes. These nanoclusters can also have fluorescence quantum yields over 90%. Following the analysis of published results of DNA templated nanoclusters, we created a procedure for synthesizing AgNC. The AgNC have a high fluorescence quantum yield but degrade with a lifetime of only a few days when in solution at room temperature. Our goal in this study was to increase the stability of the AgNC towards improving their value as a fluorescent material in various applications, such as luminescent solar concentrators. To increase their stability, we've chosen to modify our procedure by removing oxygen from the solution after the sample has reacted. Oxygen removal caused a significant increase in the stability of the clusters over a given period of time. This material is based upon work supported by the National Science Foundation under Grant Number NSF-ECCS-1306157.

  18. Dual role of boron in improving electrical performance and device stability of low temperature solution processed ZnO thin film transistors

    SciTech Connect

    Gandla, Srinivas; Gollu, Sankara Rao; Sharma, Ramakant; Sarangi, Venkateshwarlu; Gupta, Dipti

    2015-10-12

    In this paper, we have demonstrated the dual role of boron doping in enhancing the device performance parameters as well as the device stability in low temperatures (200 °C) sol-gel processed ZnO thin film transistors (TFTs). Our studies suggest that boron is able to act as a carrier generator and oxygen vacancy suppressor simultaneously. Boron-doped ZnO TFTs with 8 mol. % of boron concentration demonstrated field-effect mobility value of 1.2 cm{sup 2} V{sup −1} s{sup −1} and threshold voltage of 6.2 V, respectively. Further, these devices showed lower shift in threshold voltage during the hysteresis and bias stress measurements as compared to undoped ZnO TFTs.

  19. System evaluation of improved thermal stability jet fuels

    SciTech Connect

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

    1995-05-01

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

  20. Improved solubility and stability of 7-hydroxy-4-methylcoumarin at different temperatures and pH values through complexation with sulfobutyl ether-β-cyclodextrin.

    PubMed

    Liu, Min; Chen, Aiju; Wang, Yong; Wang, Chunmei; Wang, Bingquan; Sun, Dezhi

    2015-02-01

    The inclusion complex of 7-hydroxy-4-methylcoumarin (7H4MC) with sulfobutyl ether-β-cyclodextrin (SBE-β-CD) was investigated by means of UV-vis, circular dichroism and (1)H NMR spectroscopy in phosphate buffer solutions at different temperatures and pH values. The stoichiometric ratio of the complexation was found to be 1:1 and the stability constants (KC) were estimated from phase solubility analysis. The thermodynamic parameters of standard Gibbs free energy change, ΔG(o), enthalpy change, ΔH(o), and entropy change, ΔS(o), for the complexation process were obtained by using the van't Hoff equation and Gibbs-Helmholtz equation. The large negative ΔH(o) and the small negative or positive ΔS(o) (|ΔH(o)|>|TΔS(o)|) demonstrated that the inclusion interaction was an enthalpy-driven process. The positive signal of circular dichroism indicated that 7H4MC penetrated the cavity in such a way that the transition moment of the guest chromophore was parallel to the long axis of SBE-β-CD cavity. Moreover, the (1)H NMR spectrum showed that the entire 7H4MC molecule, except the hydroxyl group, was included in the SBE-β-CD cavity.

  1. Prop-fan with improved stability

    NASA Technical Reports Server (NTRS)

    Rothman, Edward A. (Inventor); Violette, John A. (Inventor)

    1988-01-01

    Improved prop-fan stability is achieved by providing each blade of the prop-fan with a leading edge which, outwardly, from a location thereon at the mid-span of the blade, occupy generally a single plane.

  2. DNA stability at temperatures typical for hyperthermophiles.

    PubMed Central

    Marguet, E; Forterre, P

    1994-01-01

    We have studied the fate of covalently-closed circular DNA in the temperature range from 95 to 107 degrees C. Supercoiled plasmid was not denatured up to the highest temperature tested. However, it was progressively transformed into open DNA by cleavage and then denatured. Thermodegradation was not dependent on the DNA supercoiling density. In particular, DNA made positively supercoiled by an archaeal reverse gyrase was not more resistant to depurination and thermodegradation than negatively supercoiled DNA. Thermodegradation was similar in aerobic or anaerobic conditions but strongly reduced in the presence of physiological concentrations of K+ or Mg2+. These results indicate that the major problem faced by covalently closed DNA in hyperthermophilic conditions is not thermodenaturation, but thermodegradation, and that intracellular salt concentration is important for stability of DNA primary structure. Our data suggest that reverse gyrase is not directly required to protect DNA against thermodegradation or thermodenaturation. Images PMID:8202372

  3. 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.

  4. High Temperature Stability of Potassium Beta Alumina

    NASA Technical Reports Server (NTRS)

    Williams, R. M.; Kisor, A.; Ryan, M. A.

    1996-01-01

    None. From Objectives section: Evaluate the stability of potassium beta alumina under potassium AMTEC operating conditions. Evaluate the stability regime in which potassium beta alumina can be fabricated.

  5. Improvement of Expansive Soils Using Chemical Stabilizers

    NASA Astrophysics Data System (ADS)

    Ikizler, S. B.; Senol, A.; Khosrowshahi, S. K.; Hatipoğlu, M.

    2014-12-01

    The aim of this study is to investigate the effect of two chemical stabilizers on the swelling potential of expansive soil. A high plasticity sodium bentonite was used as the expansive soil. The additive materials including fly ash (FA) and lime (L) were evaluated as potential stabilizers to decrease the swelling pressure of bentonite. Depending on the type of additive materials, they were blended with bentonite in different percentages to assess the optimum state and approch the maximum swell pressure reduction. According to the results of swell pressure test, both fly ash and lime reduce the swelling potential of bentonite but the maximum improvement occurs using bentonite-lime mixture while the swelling pressure reduction approaches to 49%. The results reveal a significant reduction of swelling potential of expansive soil using chemical stabilizers. Keywords: Expansive soil; swell pressure; chemical stabilization; fly ash; lime

  6. Lipid oxidation and improving the oxidative stability.

    PubMed

    Shahidi, Fereidoon; Zhong, Ying

    2010-11-01

    Lipids are a major component of food and important structural and functional constituents of cells in biological systems. However, this diverse group of substances is prone to oxidation through various pathways. Their oxidative stability depends on a number of intrinsic and extrinsic factors, including the unsaturation of their fatty acids, composition of minor components, environment conditions, delivery techniques and use of antioxidants, among others. Lipid oxidation has detrimental effects on both food quality and human health, and efforts must be made to minimize oxidation and improve oxidative stability of lipid products. Antioxidant strategy has been successfully employed in the food industry for quality preservation of the food products and in the medicinal industry for risk reduction of numerous oxidative stress-mediated diseases. This tutorial review will provide important knowledge about lipid oxidation, including the mechanism and factors involved in oxidation, as well as strategies for improving oxidative stability of lipids.

  7. Improvement of interfacial protein stability by CHAPS.

    PubMed

    Sah, Hongkee; Kim, Kil-Soo

    2006-04-01

    Emulsification of aqueous protein solutions in methylene chloride triggered the formation of water-insoluble aggregates at a water/methylene chloride interface. As a result, the amounts of beta-lactoglobulin and ovalbumin recovered in water were 36 and 44%, respectively. Addition of 5 mM: CHAPS in the aqueous phase raised the degree of beta-lactoglobulin recovery to 96%. Sodium taurocholate, however, failed to improve protein recovery. The stabilizing effect of CHAPS was also protein-specific and concentration-dependent: at >or=5 mM: , the surfactant caused unfolding of ovalbumin to make a water-soluble oligomer. CHAPS thus stabilizes proteins at an interface.

  8. Stability improvement in bleached phase holograms

    NASA Astrophysics Data System (ADS)

    Kumar, S.; Singh, K.

    1991-08-01

    An experimental study has been made of the influence of developer composition on the stability against the print-out effect of bleached, photographically recorded two-beam interference grating on Agfa-Gevaert 10E75 NAH plates. The diffraction efficiency has been increased by using potassium iodide and an iodine bleach process that converts a silver image into a dielectric image. An improvement in stability against the print-out effect has been observed by using two new developer compositions. Variation of the maximum diffraction efficiency against exposure to white light is shown graphically.

  9. Chemical stability of high-temperature superconductors

    NASA Technical Reports Server (NTRS)

    Bansal, Narottam P.

    1992-01-01

    A review of the available studies on the chemical stability of the high temperature superconductors (HTS) in various environments was made. The La(1.8)Ba(0.2)CuO4 HTS is unstable in the presence of H2O, CO2, and CO. The YBa2Cu3O(7-x) superconductor is highly susceptible to degradation in different environments, especially water. The La(2-x)Ba(x)CuO4 and Bi-Sr-Ca-Cu-O HTS are relatively less reactive than the YBa2Cu3O(7-x). Processing of YBa2Cu3O(7-x) HTS in purified oxygen, rather than in air, using high purity noncarbon containing starting materials is recommended. Exposure of this HTS to the ambient atmosphere should also be avoided at all stages during processing and storage. Devices and components made out of these oxide superconductors would have to be protected with an impermeable coating of a polymer, glass, or metal to avoid deterioration during use.

  10. Low-temperature improved-throughput method for analysis of brain fatty acids and assessment of their post-mortem stability.

    PubMed

    Fraser, Thomas; Tayler, Hannah; Love, Seth

    2008-03-30

    Deficiency of docosahexaenoic acid (DHA) and other omega-3 (omega3) fatty acids may constitute an alterable risk factor for Alzheimer's disease (AD). Mechanisms of potential involvement of DHA in the disease process have been postulated primarily from studies in vitro and in mouse models of AD. Information on the fatty acid profile of the brain in AD itself is limited and in some respects contradictory. Interpretation of the findings is complicated by the diversity of methods used in previous studies and a lack of information as to the effect of post-mortem delay on the results. Here we report the development of a simple and highly reproducible method that enables relatively high-throughput measurement of the fatty acid composition in samples of brain tissue and using this method we have demonstrated that there is no significant change in fatty acid composition under conditions designed to model post-mortem delay of up to 3 days at 4 degrees C (or even at room temperature). The development of this method and the observation that delay of up to 3 days has no effect on fatty acid content will facilitate further studies of fatty acid composition on large cohorts of post-mortem brains.

  11. Improved ferroelectric/piezoelectric properties and bright green/UC red emission in (Li,Ho)-doped CaBi4Ti4O15 multifunctional ceramics with excellent temperature stability and superior water-resistance performance.

    PubMed

    Xiao, Ping; Guo, Yongquan; Tian, Mijie; Zheng, Qiaoji; Jiang, Na; Wu, Xiaochun; Xia, Zhiguo; Lin, Dunmin

    2015-10-21

    Multifunctional materials based on rare earth ion doped ferro/piezoelectrics have attracted considerable attention in recent years. In this work, new lead-free multifunctional ceramics of Ca1-x(LiHo)x/2Bi4Ti4O15 were prepared by a conventional solid-state reaction method. The great multi-improvement in ferroelectricity/piezoelectricity, down/up-conversion luminescence and temperature stability of the multifunctional properties is induced by the partial substitution of (Li0.5Ho0.5)(2+) for Ca(2+) ions in CaBi4Ti4O15. All the ceramics possess a bismuth-layer structure, and the crystal structure of the ceramics is changed from a four layered bismuth-layer structure to a three-layered structure with the level of (Li0.5Ho0.5)(2+) increasing. The ceramic with x = 0.1 exhibits simultaneously, high resistivity (R = 4.51 × 10(11)Ω cm), good piezoelectricity (d33 = 10.2 pC N(-1)), high Curie temperature (TC = 814 °C), strong ferroelectricity (Pr = 9.03 μC cm(-2)) and enhanced luminescence. These behaviours are greatly associated with the contribution of (Li0.5Ho0.5)(2+) in the ceramics. Under the excitation of 451 nm light, the ceramic with x = 0.1 exhibits a strong green emission peak centered at 545 nm, corresponding to the transition of the (5)S2→(5)I8 level in Ho(3+) ions, while a strong red up-conversion emission band located at 660 nm is observed under the near-infrared excitation of 980 nm at room temperature, arising from the transition of (5)F5→(5)I8 levels in Ho(3+) ions. Surprisingly, the excellent temperature stability of ferroelectricity/piezoelectricity/luminescence and superior water-resistance behaviors of piezoelectricity/luminescence are also obtained in the ceramic with x = 0.1. Our study suggests that the present ceramics may have potential applications in advanced multifunctional devices at high temperature.

  12. Wing flexibility improves bumblebee flight stability.

    PubMed

    Mistick, Emily A; Mountcastle, Andrew M; Combes, Stacey A

    2016-11-01

    Insect wings do not contain intrinsic musculature to change shape, but rather bend and twist passively during flight. Some insect wings feature flexible joints along their veins that contain patches of resilin, a rubber-like protein. Bumblebee wings exhibit a central resilin joint (1m-cu) that has previously been shown to improve vertical force production during hovering flight. In this study, we artificially stiffened bumblebee (Bombus impatiens) wings in vivo by applying a micro-splint to the 1m-cu joint, and measured the consequences for body stability during forward flight in both laminar and turbulent airflow. In laminar flow, bees with stiffened wings exhibited significantly higher mean rotation rates and standard deviation of orientation about the roll axis. Decreasing the wing's flexibility significantly increased its projected surface area relative to the oncoming airflow, likely increasing the drag force it experienced during particular phases of the wing stroke. We hypothesize that higher drag forces on stiffened wings decrease body stability when the left and right wings encounter different flow conditions. Wing splinting also led to a small increase in body rotation rates in turbulent airflow, but this change was not statistically significant, possibly because bees with stiffened wings changed their flight behavior in turbulent flow. Overall, we found that wing flexibility improves flight stability in bumblebees, adding to the growing appreciation that wing flexibility is not merely an inevitable liability in flapping flight, but can enhance flight performance. © 2016. Published by The Company of Biologists Ltd.

  13. 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.

  14. Cyclodextrin polymer nanoassemblies: strategies for stability improvement.

    PubMed

    Wintgens, Véronique; Layre, Anne-Magali; Hourdet, Dominique; Amiel, Catherine

    2012-02-13

    The main goal of this work was to develop two strategies for stabilization of nanoassemblies made of β-cyclodextrin polymer and amphiphilic dextran associated through host-guest complexes. The first strategy was to coat the nanoassemblies with a dextran derivative bearing adamantyl anchoring groups and hydrophilic poly(ethylene oxide-co-propylene oxide) side chains to increase the steric repulsion between the nanoassemblies. The second strategy developed was to post-reticulate the nanoassemblies upon UV irradiation. Photo-cross-linkable nanoassemblies have been prepared from new host or guest polymers bearing allylether or methacrylate groups. The modified nanoassemblies have been characterized by dynamic light scattering as a function of time and for various salt and competitor concentrations. The results of the first strategy show an improvement of shelf stability and resistance at relatively low concentrations of competitors. The second strategy is the most efficient in providing good shelf stability, much larger than with the first strategy, together with a large resistance to dissociation in presence of competitors.

  15. Hydrogen-incorporation stabilization of metallic VO2(R) phase to room temperature, displaying promising low-temperature thermoelectric effect.

    PubMed

    Wu, Changzheng; Feng, Feng; Feng, Jun; Dai, Jun; Peng, Lele; Zhao, Jiyin; Yang, Jinlong; Si, Cheng; Wu, Ziyu; Xie, Yi

    2011-09-07

    Regulation of electron-electron correlation has been found to be a new effective way to selectively control carrier concentration, which is a crucial step toward improving thermoelectric properties. The pure electronic behavior successfully stabilized the nonambient metallic VO(2)(R) to room temperature, giving excellent thermoelectric performance among the simple oxides with wider working temperature ranges.

  16. DIFFUSED RESISTOR TEMPERATURE COEFFICIENT IMPROVEMENT.

    DTIC Science & Technology

    effects are found in both n and p-type silicon. In addition, it was found that using the optimum concentrations, the range of sheet resistance over which TCR improvement could be seen was 100 to 300 ohms per square. (Author)

  17. Temperature compensation via cooperative stability in protein degradation

    NASA Astrophysics Data System (ADS)

    Peng, Yuanyuan; Hasegawa, Yoshihiko; Noman, Nasimul; Iba, Hitoshi

    2015-08-01

    Temperature compensation is a notable property of circadian oscillators that indicates the insensitivity of the oscillator system's period to temperature changes; the underlying mechanism, however, is still unclear. We investigated the influence of protein dimerization and cooperative stability in protein degradation on the temperature compensation ability of two oscillators. Here, cooperative stability means that high-order oligomers are more stable than their monomeric counterparts. The period of an oscillator is affected by the parameters of the dynamic system, which in turn are influenced by temperature. We adopted the Repressilator and the Atkinson oscillator to analyze the temperature sensitivity of their periods. Phase sensitivity analysis was employed to evaluate the period variations of different models induced by perturbations to the parameters. Furthermore, we used experimental data provided by other studies to determine the reasonable range of parameter temperature sensitivity. We then applied the linear programming method to the oscillatory systems to analyze the effects of protein dimerization and cooperative stability on the temperature sensitivity of their periods, which reflects the ability of temperature compensation in circadian rhythms. Our study explains the temperature compensation mechanism for circadian clocks. Compared with the no-dimer mathematical model and linear model for protein degradation, our theoretical results show that the nonlinear protein degradation caused by cooperative stability is more beneficial for realizing temperature compensation of the circadian clock.

  18. Strategies for improved stability of Peste des Petits Ruminants Vaccine.

    PubMed

    Silva, Ana Carina; Carrondo, Manuel J T; Alves, Paula M

    2011-07-12

    The main focus of this work was the improvement of the stability of the current PPRV vaccine. First, new formulations based on the Tris buffer were tested, with and without the addition of sucrose and trehalose and compared with the formulation normally used to stabilize the vaccine, the Weybridge medium. The results show a virus half-life of 21 h at 37°C and 1 month at 4°C for the Tris/trehalose liquid formulation and, in the lyophilized form, the formulation was able to maintain the viral titer above the 1 × 10(4) TCID(50)/mL (>10 doses/mL) for at least 21 months at 4°C (0.6 log lost), 144 h at 37°C (0.6 log lost) and 120 h at 45°C (1 log lost). Secondly, a strategy based on culture medium composition manipulation aiming at improving the intrinsic PPRV vaccine stability was also evaluated. The addition of 25 mM fructose resulted in a higher virus production (1log increase) with higher stability (2.6-fold increase compared to glucose 25 mM) at 37°C. Increased concentrations of NaCl, improved virus release, reducing the cell-associated fraction of the virus produced. Moreover this harvesting strategy is scalable and more suitable for a larger scale production than the freeze/thaw cycles normally used. The information gathered in this work showed that it is possible for the PPRV vaccine to have adequate short-term stability at non-freezing temperatures to support manufacturing, short-term shipping and storage. The identification of a more stable formulation should significantly enhance the utility of the vaccine in the control of a PPRV outbreak.

  19. High temperature bias line stabilized current sources

    DOEpatents

    Patterson, R.B. III.

    1984-09-11

    A compensation device for the base of emitter follower configured bipolar transistors becoming operable at elevated temperatures including a bipolar transistor of a geometry of not more than half the geometry of the bipolar emitter follower having its collector connected to the base of the emitter follower and its base and emitter connected together and to the emitter of the emitter follower. 1 fig.

  20. High temperature bias line stabilized current sources

    DOEpatents

    Patterson, III, Raymond B.

    1984-01-01

    A compensation device for the base of emitter follower configured bipolar transistors becoming operable at elevated temperatures including a bipolar transistor of a geometry of not more than half the geometry of the bipolar emitter follower having its collector connected to the base of the emitter follower and its base and emitter connected together and to the emitter of the emitter follower.

  1. Nanowire Lasers of Formamidinium Lead Halide Perovskites and Their Stabilized Alloys with Improved Stability.

    PubMed

    Fu, Yongping; Zhu, Haiming; Schrader, Alex W; Liang, Dong; Ding, Qi; Joshi, Prakriti; Hwang, Leekyoung; Zhu, X-Y; Jin, Song

    2016-02-10

    The excellent intrinsic optoelectronic properties of methylammonium lead halide perovskites (MAPbX3, X = Br, I), such as high photoluminescence quantum efficiency, long carrier lifetime, and high gain coupled with the facile solution growth of nanowires make them promising new materials for ultralow-threshold nanowire lasers. However, their photo and thermal stabilities need to be improved for practical applications. Herein, we report a low-temperature solution growth of single crystal nanowires of formamidinium lead halide perovskites (FAPbX3) that feature red-shifted emission and better thermal stability compared to MAPbX3. We demonstrate optically pumped room-temperature near-infrared (∼820 nm) and green lasing (∼560 nm) from FAPbI3 (and MABr-stabilized FAPbI3) and FAPbBr3 nanowires with low lasing thresholds of several microjoules per square centimeter and high quality factors of about 1500-2300. More remarkably, the FAPbI3 and MABr-stabilized FAPbI3 nanowires display durable room-temperature lasing under ∼10(8) shots of sustained illumination of 402 nm pulsed laser excitation (150 fs, 250 kHz), substantially exceeding the stability of MAPbI3 (∼10(7) laser shots). We further demonstrate tunable nanowire lasers in wider wavelength region from FA-based lead halide perovskite alloys (FA,MA)PbI3 and (FA,MA)Pb(I,Br)3 through cation and anion substitutions. The results suggest that formamidinium lead halide perovskite nanostructures could be more promising and stable materials for the development of light-emitting diodes and continuous-wave lasers.

  2. Simultaneous stabilization of global temperature and precipitation through cocktail geoengineering

    NASA Astrophysics Data System (ADS)

    Cao, Long; Duan, Lei; Bala, Govindasamy; Caldeira, Ken

    2017-07-01

    Solar geoengineering has been proposed as a backup plan to offset some aspects of anthropogenic climate change if timely CO2 emission reductions fail to materialize. Modeling studies have shown that there are trade-offs between changes in temperature and hydrological cycle in response to solar geoengineering. Here we investigate the possibility of stabilizing both global mean temperature and precipitation simultaneously by combining two geoengineering approaches: stratospheric sulfate aerosol increase (SAI) that deflects sunlight to space and cirrus cloud thinning (CCT) that enables more longwave radiation to escape to space. Using the slab ocean configuration of National Center for Atmospheric Research Community Earth System Model, we simulate SAI by uniformly adding sulfate aerosol in the upper stratosphere and CCT by uniformly increasing cirrus cloud ice particle falling speed. Under an idealized warming scenario of abrupt quadrupling of atmospheric CO2, we show that by combining appropriate amounts of SAI and CCT geoengineering, global mean (or land mean) temperature and precipitation can be restored simultaneously to preindustrial levels. However, compared to SAI, cocktail geoengineering by mixing SAI and CCT does not markedly improve the overall similarity between geoengineered climate and preindustrial climate on regional scales. Some optimal spatially nonuniform mixture of SAI with CCT might have the potential to better mitigate climate change at both the global and regional scales.

  3. Stability of peatland carbon to rising temperatures

    NASA Astrophysics Data System (ADS)

    Wilson, R. M.; Hopple, A. M.; Tfaily, M. M.; Sebestyen, S. D.; Schadt, C. W.; Pfeifer-Meister, L.; Medvedeff, C.; McFarlane, K. J.; Kostka, J. E.; Kolton, M.; Kolka, R. K.; Kluber, L. A.; Keller, J. K.; Guilderson, T. P.; Griffiths, N. A.; Chanton, J. P.; Bridgham, S. D.; Hanson, P. J.

    2016-12-01

    Peatlands contain one-third of soil carbon (C), mostly buried in deep, saturated anoxic zones (catotelm). The response of catotelm C to climate forcing is uncertain, because prior experiments have focused on surface warming. We show that deep peat heating of a 2 m-thick peat column results in an exponential increase in CH4 emissions. However, this response is due solely to surface processes and not degradation of catotelm peat. Incubations show that only the top 20-30 cm of peat from experimental plots have higher CH4 production rates at elevated temperatures. Radiocarbon analyses demonstrate that CH4 and CO2 are produced primarily from decomposition of surface-derived modern photosynthate, not catotelm C. There are no differences in microbial abundances, dissolved organic matter concentrations or degradative enzyme activities among treatments. These results suggest that although surface peat will respond to increasing temperature, the large reservoir of catotelm C is stable under current anoxic conditions.

  4. Temperature stability of high Ge-doped fibre Bragg grating

    NASA Astrophysics Data System (ADS)

    Guo, Jiangtao; Tu, Feng; Wei, Huifeng; Deng, Tao; Tong, Weijun

    2010-12-01

    Temperature stability based on high Ge-doped fibre Bragg grating (FBG) is presented. A high Ge-doped photosensitive fibre (PSF) used for writing FBG was manufactured. Temperature characteristic of the FBG from 20 to 300°C had been researched. The transmission efficiency is about 75% at 300°C.

  5. Stability of peatland carbon to rising temperatures.

    PubMed

    Wilson, R M; Hopple, A M; Tfaily, M M; Sebestyen, S D; Schadt, C W; Pfeifer-Meister, L; Medvedeff, C; McFarlane, K J; Kostka, J E; Kolton, M; Kolka, R K; Kluber, L A; Keller, J K; Guilderson, T P; Griffiths, N A; Chanton, J P; Bridgham, S D; Hanson, P J

    2016-12-13

    Peatlands contain one-third of soil carbon (C), mostly buried in deep, saturated anoxic zones (catotelm). The response of catotelm C to climate forcing is uncertain, because prior experiments have focused on surface warming. We show that deep peat heating of a 2 m-thick peat column results in an exponential increase in CH4 emissions. However, this response is due solely to surface processes and not degradation of catotelm peat. Incubations show that only the top 20-30 cm of peat from experimental plots have higher CH4 production rates at elevated temperatures. Radiocarbon analyses demonstrate that CH4 and CO2 are produced primarily from decomposition of surface-derived modern photosynthate, not catotelm C. There are no differences in microbial abundances, dissolved organic matter concentrations or degradative enzyme activities among treatments. These results suggest that although surface peat will respond to increasing temperature, the large reservoir of catotelm C is stable under current anoxic conditions.

  6. Stability of peatland carbon to rising temperatures

    DOE PAGES

    Wilson, R. M.; Hopple, A. M.; Tfaily, M. M.; ...

    2016-12-13

    Peatlands contain one-third of soil carbon (C), mostly buried in deep, saturated anoxic zones (catotelm). The response of catotelm C to climate forcing is uncertain, because prior experiments have focused on surface warming. Here, we show that deep peat heating of a 2 m-thick peat column results in an exponential increase in CH4 emissions. But, this response is due solely to surface processes and not degradation of catotelm peat. Incubations show that only the top 20–30 cm of peat from experimental plots have higher CH4 production rates at elevated temperatures. Radiocarbon analyses demonstrate that CH4 and CO2 are produced primarilymore » from decomposition of surface-derived modern photosynthate, not catotelm C. Furthermore, there are no differences in microbial abundances, dissolved organic matter concentrations or degradative enzyme activities among treatments. Our results suggest that although surface peat will respond to increasing temperature, the large reservoir of catotelm C is stable under current anoxic conditions.« less

  7. Stability of peatland carbon to rising temperatures

    SciTech Connect

    Wilson, R. M.; Hopple, A. M.; Tfaily, M. M.; Sebestyen, S. D.; Schadt, C. W.; Pfeifer-Meister, L.; Medvedeff, C.; McFarlane, K. J.; Kostka, J. E.; Kolton, M.; Kolka, R. K.; Kluber, L. A.; Keller, J. K.; Guilderson, T. P.; Griffiths, N. A.; Chanton, J. P.; Bridgham, S. D.; Hanson, P. J.

    2016-12-13

    Peatlands contain one-third of soil carbon (C), mostly buried in deep, saturated anoxic zones (catotelm). The response of catotelm C to climate forcing is uncertain, because prior experiments have focused on surface warming. Here, we show that deep peat heating of a 2 m-thick peat column results in an exponential increase in CH4 emissions. But, this response is due solely to surface processes and not degradation of catotelm peat. Incubations show that only the top 20–30 cm of peat from experimental plots have higher CH4 production rates at elevated temperatures. Radiocarbon analyses demonstrate that CH4 and CO2 are produced primarily from decomposition of surface-derived modern photosynthate, not catotelm C. Furthermore, there are no differences in microbial abundances, dissolved organic matter concentrations or degradative enzyme activities among treatments. Our results suggest that although surface peat will respond to increasing temperature, the large reservoir of catotelm C is stable under current anoxic conditions.

  8. Stability of peatland carbon to rising temperatures

    PubMed Central

    Wilson, R. M.; Hopple, A. M.; Tfaily, M. M.; Sebestyen, S. D.; Schadt, C. W.; Pfeifer-Meister, L.; Medvedeff, C.; McFarlane, K. J.; Kostka, J. E.; Kolton, M.; Kolka, R.K.; Kluber, L. A.; Keller, J. K.; Guilderson, T. P.; Griffiths, N. A.; Chanton, J. P.; Bridgham, S. D.; Hanson, P. J.

    2016-01-01

    Peatlands contain one-third of soil carbon (C), mostly buried in deep, saturated anoxic zones (catotelm). The response of catotelm C to climate forcing is uncertain, because prior experiments have focused on surface warming. We show that deep peat heating of a 2 m-thick peat column results in an exponential increase in CH4 emissions. However, this response is due solely to surface processes and not degradation of catotelm peat. Incubations show that only the top 20–30 cm of peat from experimental plots have higher CH4 production rates at elevated temperatures. Radiocarbon analyses demonstrate that CH4 and CO2 are produced primarily from decomposition of surface-derived modern photosynthate, not catotelm C. There are no differences in microbial abundances, dissolved organic matter concentrations or degradative enzyme activities among treatments. These results suggest that although surface peat will respond to increasing temperature, the large reservoir of catotelm C is stable under current anoxic conditions. PMID:27958276

  9. Stabilization of Aspergillus parasiticus cytosine deaminase by immobilization on calcium alginate beads improved enzyme operational stability.

    PubMed

    Zanna, H; Nok, A J; Ibrahim, S; Inuwa, H M

    2013-12-01

    Cytosine deaminase (CD) from Aspergillus parasiticus, which has half-life of 1.10 h at 37°C, was stabilized by immobilization on calcium alginate beads. The immobilized CD had pH and temperature optimum of 5 and 50°C respectively. The immobilized enzyme also stoichiometrically deaminated Cytosine and 5-fluorocytosine (5-FC) with the apparent K(M) values of 0.60 mM and 0.65 mM respectively, displaying activation energy of 10.72 KJ/mol. The immobilization of native CD on calcium alginate beads gave the highest yield of apparent enzymatic activity of 51.60% of the original activity and the enzymatic activity was lost exponentially at 37°C over 12 h with a half-life of 5.80 h. Hence, the operational stability of native CD can be improved by immobilization on calcium alginate beads.

  10. Stability of peatland carbon to rising temperatures

    SciTech Connect

    Wilson, R. M.; Hopple, A. M.; Tfaily, M. M.; Sebestyen, S. D.; Schadt, C. W.; Pfeifer-Meister, L.; Medvedeff, C.; McFarlane, K. J.; Kostka, J. E.; Kolton, M.; Kolka, R. K.; Kluber, L. A.; Keller, J. K.; Guilderson, T. P.; Griffiths, N. A.; Chanton, J. P.; Bridgham, S. D.; Hanson, P. J.

    2016-12-13

    Peatlands contain one-third of the world’s soil carbon (C), mostly in the deep permanently saturated anoxic zone (i.e., catotelm)1 where C mineralization rates may be constrained, in part, by low temperatures; yet all soil warming experiments to date have focused on the response of peatland C degradation to surface warming2, 3. If the slow decomposition of deep peat C is due to kinetic constraints, then increasing temperatures at depth should cause parallel increases in carbon dioxide (CO2) and/or methane (CH4) production rates. Increasing CH4 emissions are of particular concern because CH4 has a sustained-flux global warming potential (SGWP) 45-times greater than CO2 over a 100- year timeframe4, creating a significant positive feedback to climate warming. Using a novel whole-ecosystem scale experiment in a regression-based design we show that ecosystem scale warming of deep peat exponentially increased CH4 emissions —but not ecosystem respiration of CO2— in the first year. Multiple lines of evidence, including laboratory incubations and in situ analyses of 14C, dissolved gases, and microbial community metabolic potential, indicate that CH4 emissions increased due to surface processes and not degradation of deep C. Our results indicate that rapid changes to the large bank of deep buried C in temperate peatlands may be minimal under future climatic warming.

  11. Elliptically Bent X-ray Mirrors with Active Temperature Stabilization

    SciTech Connect

    Yuan, Sheng; Church, Matthew; Yashchuk, Valeriy V.; Goldberg, Kenneth A.; Celestre, Rich; McKinney, Wayne R.; Kirschman, Jonathan; Morrison, Greg; Noll, Tino; Warwick, Tony; Padmore, Howard A.

    2010-01-31

    We present details of design of elliptically bent Kirkpatrick-Baez mirrors developed and successfully used at the Advanced Light Source for submicron focusing. A distinctive feature of the mirror design is an active temperature stabilization based on a Peltier element attached directly to the mirror body. The design and materials have been carefully optimized to provide high heat conductance between the mirror body and substrate. We describe the experimental procedures used when assembling and precisely shaping the mirrors, with special attention paid to laboratory testing of the mirror-temperature stabilization. For this purpose, the temperature dependence of the surface slope profile of a specially fabricated test mirror placed inside a temperature-controlled container was measured. We demonstrate that with active mirror-temperature stabilization, a change of the surrounding temperature by more than 3K does not noticeably affect the mirror figure. Without temperature stabilization, the surface slope changes by approximately 1.5 ?mu rad rms (primarily defocus) under the same conditions.

  12. Storage Stability and Improvement of Intermediate Moisture Foods, Phase 3

    NASA Technical Reports Server (NTRS)

    Labuza, T. P.

    1975-01-01

    Methods were determined for the improvement of shelf-life stability of intermediate moisture foods (IMF). Microbial challenge studies showed that protection against molds and Staphylococcus aureus could be achieved by a combination of antimicrobial agents, humectants and food acids. Potassium sorbate and propylene glycol gave the best results. It was also confirmed that the maximum in heat resistance shown by vegetative pathogens at intermediate water activities also occurred in a solid food. Glycols and sorbitol both achieve browning inhibition because of their action as a medium for reaction and effect on viscosity of the adsorbed phase. Chemical availability results showed rapid lysine loss before visual discoloration occurred. This is being confirmed with a biological test using Tetrahymena pyriformis W. Accelerated temperature tests show that effectiveness of food antioxidants against rancidity development can be predicted; however, the protection factor changes with temperature. BHA was found to be the best antioxidant for iron catalyzed oxidation.

  13. Localized temperature stability in Low Temperature Cofired Ceramics (LTCC).

    SciTech Connect

    Dai, Steven Xunhu; Hsieh, Lung-Hwa.

    2012-04-01

    The base dielectrics of commercial low temperature cofired ceramics (LTCC) systems have a temperature coefficient of resonant frequency ({tau}{sub f}) in the range -50 {approx} -80 ppm/C. In this research we explored a method to realize zero or near zero {tau}{sub f} resonators by incorporating {tau}{sub f} compensating materials locally into a multilayer LTCC structure. To select composition for {tau}{sub f} adjustment, {tau}{sub f} compensating materials with different amount of titanates were formulated, synthesized, and characterized. Chemical interactions and physical compatibility between the {tau}{sub f} modifiers and the host LTCC dielectrics were investigated. Studies on stripline (SL) resonator panels with multiple compensating dielectrics revealed that: 1) compositions using SrTiO{sub 3} provide the largest {tau}{sub f} adjustment among titanates, 2) the {tau}{sub f} compensation is proportional to the amount of SrTiO{sub 3} in compensating materials, as well as the thickness of the compensating layer, and 3) the most effective {tau}{sub f} compensation is achieved when the compensating dielectric is integrated next to the SL. Using the effective dielectric constant of a heterogeneous layered dielectric structure, results from Method of Momentum (MoM) electromagnetic simulations are consistent with the experimental observations.

  14. Phospholipid stabilized gold nanorods: towards improved colloidal stability and biocompatibility.

    PubMed

    Santhosh, Poornima Budime; Thomas, Neethu; Sudhakar, Swathi; Chadha, Anju; Mani, Ethayaraja

    2017-07-19

    Biocompatible and colloidally stable gold nanorods (GNRs) with well-defined plasmonic properties are essential for biomedical and theranostic applications. The as-synthesized GNRs using the seed-mediated method are stabilized by the surfactant, cetyltrimethylammonium bromide (CTAB), which is known for its cytotoxicity in many cell lines. Biocompatible GNRs synthesized using known protocols exhibit some extent of cytotoxicity and colloidal instability because of the incomplete removal of CTAB. We report a facile method for the efficient removal of CTAB molecules with 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) phospholipid molecules, which are naturally present in cell membranes. The kinetics of the ligand exchange process is studied using surface-enhanced Raman scattering (SERS) and corroborated with matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. From colloidal stability studies using dynamic light scattering (DLS) and UV-Vis spectroscopy, the optimal lipid concentration and duration required for the successful ligand exchange of CTAB by DMPC are reported. Using thermogravimetric analysis, the surface concentration of DMPC on colloidally stable GNRs is found to be approximately 9 molecules per nm(2). The 3-(4,5-dimethylthiozol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) and lactate dehydrogenase (LDH) assays show that the surface-modified DMPC-GNRs have significantly better biocompatibility than those of CTAB-GNRs. Studies on the ligand exchange, colloidal stability and biocompatibility of DMPC-GNRs with aspect ratios ranging from 2.2 to 4.2 demonstrate the robustness of the proposed method. The results provide insights into the important factors to be considered while designing biocompatible GNRs suitable for applications in nanomedicine.

  15. Room temperature skyrmion ground state stabilized through interlayer exchange coupling

    SciTech Connect

    Chen, Gong Schmid, Andreas K.; Mascaraque, Arantzazu; N'Diaye, Alpha T.

    2015-06-15

    Possible magnetic skyrmion device applications motivate the search for structures that extend the stability of skyrmion spin textures to ambient temperature. Here, we demonstrate an experimental approach to stabilize a room temperature skyrmion ground state in chiral magnetic films via exchange coupling across non-magnetic spacer layers. Using spin polarized low-energy electron microscopy to measure all three Cartesian components of the magnetization vector, we image the spin textures in Fe/Ni films. We show how tuning the thickness of a copper spacer layer between chiral Fe/Ni films and perpendicularly magnetized Ni layers permits stabilization of a chiral stripe phase, a skyrmion phase, and a single domain phase. This strategy to stabilize skyrmion ground states can be extended to other magnetic thin film systems and may be useful for designing skyrmion based spintronics devices.

  16. Increasing Crop Diversity Mitigates Weather Variations and Improves Yield Stability

    PubMed Central

    Gaudin, Amélie C. M.; Tolhurst, Tor N.; Ker, Alan P.; Janovicek, Ken; Tortora, Cristina; Martin, Ralph C.; Deen, William

    2015-01-01

    Cropping sequence diversification provides a systems approach to reduce yield variations and improve resilience to multiple environmental stresses. Yield advantages of more diverse crop rotations and their synergistic effects with reduced tillage are well documented, but few studies have quantified the impact of these management practices on yields and their stability when soil moisture is limiting or in excess. Using yield and weather data obtained from a 31-year long term rotation and tillage trial in Ontario, we tested whether crop rotation diversity is associated with greater yield stability when abnormal weather conditions occur. We used parametric and non-parametric approaches to quantify the impact of rotation diversity (monocrop, 2-crops, 3-crops without or with one or two legume cover crops) and tillage (conventional or reduced tillage) on yield probabilities and the benefits of crop diversity under different soil moisture and temperature scenarios. Although the magnitude of rotation benefits varied with crops, weather patterns and tillage, yield stability significantly increased when corn and soybean were integrated into more diverse rotations. Introducing small grains into short corn-soybean rotation was enough to provide substantial benefits on long-term soybean yields and their stability while the effects on corn were mostly associated with the temporal niche provided by small grains for underseeded red clover or alfalfa. Crop diversification strategies increased the probability of harnessing favorable growing conditions while decreasing the risk of crop failure. In hot and dry years, diversification of corn-soybean rotations and reduced tillage increased yield by 7% and 22% for corn and soybean respectively. Given the additional advantages associated with cropping system diversification, such a strategy provides a more comprehensive approach to lowering yield variability and improving the resilience of cropping systems to multiple environmental

  17. Increasing crop diversity mitigates weather variations and improves yield stability.

    PubMed

    Gaudin, Amélie C M; Tolhurst, Tor N; Ker, Alan P; Janovicek, Ken; Tortora, Cristina; Martin, Ralph C; Deen, William

    2015-01-01

    Cropping sequence diversification provides a systems approach to reduce yield variations and improve resilience to multiple environmental stresses. Yield advantages of more diverse crop rotations and their synergistic effects with reduced tillage are well documented, but few studies have quantified the impact of these management practices on yields and their stability when soil moisture is limiting or in excess. Using yield and weather data obtained from a 31-year long term rotation and tillage trial in Ontario, we tested whether crop rotation diversity is associated with greater yield stability when abnormal weather conditions occur. We used parametric and non-parametric approaches to quantify the impact of rotation diversity (monocrop, 2-crops, 3-crops without or with one or two legume cover crops) and tillage (conventional or reduced tillage) on yield probabilities and the benefits of crop diversity under different soil moisture and temperature scenarios. Although the magnitude of rotation benefits varied with crops, weather patterns and tillage, yield stability significantly increased when corn and soybean were integrated into more diverse rotations. Introducing small grains into short corn-soybean rotation was enough to provide substantial benefits on long-term soybean yields and their stability while the effects on corn were mostly associated with the temporal niche provided by small grains for underseeded red clover or alfalfa. Crop diversification strategies increased the probability of harnessing favorable growing conditions while decreasing the risk of crop failure. In hot and dry years, diversification of corn-soybean rotations and reduced tillage increased yield by 7% and 22% for corn and soybean respectively. Given the additional advantages associated with cropping system diversification, such a strategy provides a more comprehensive approach to lowering yield variability and improving the resilience of cropping systems to multiple environmental

  18. Stability of Materials in High Temperature Water Vapor: SOFC Applications

    NASA Technical Reports Server (NTRS)

    Opila, E. J.; Jacobson, N. S.

    2010-01-01

    Solid oxide fuel cell material systems require long term stability in environments containing high-temperature water vapor. Many materials in fuel cell systems react with high-temperature water vapor to form volatile hydroxides which can degrade cell performance. In this paper, experimental methods to characterize these volatility reactions including the transpiration technique, thermogravimetric analysis, and high pressure mass spectrometry are reviewed. Experimentally determined data for chromia, silica, and alumina volatility are presented. In addition, data from the literature for the stability of other materials important in fuel cell systems are reviewed. Finally, methods for predicting material recession due to volatilization reactions are described.

  19. Stability Curve Prediction of Homologous Proteins Using Temperature-Dependent Statistical Potentials

    PubMed Central

    Pucci, Fabrizio; Rooman, Marianne

    2014-01-01

    The unraveling and control of protein stability at different temperatures is a fundamental problem in biophysics that is substantially far from being quantitatively and accurately solved, as it requires a precise knowledge of the temperature dependence of amino acid interactions. In this paper we attempt to gain insight into the thermal stability of proteins by designing a tool to predict the full stability curve as a function of the temperature for a set of 45 proteins belonging to 11 homologous families, given their sequence and structure, as well as the melting temperature () and the change in heat capacity () of proteins belonging to the same family. Stability curves constitute a fundamental instrument to analyze in detail the thermal stability and its relation to the thermodynamic stability, and to estimate the enthalpic and entropic contributions to the folding free energy. In summary, our approach for predicting the protein stability curves relies on temperature-dependent statistical potentials derived from three datasets of protein structures with targeted thermal stability properties. Using these potentials, the folding free energies () at three different temperatures were computed for each protein. The Gibbs-Helmholtz equation was then used to predict the protein's stability curve as the curve that best fits these three points. The results are quite encouraging: the standard deviations between the experimental and predicted 's, 's and folding free energies at room temperature () are equal to 13 , 1.3 ) and 4.1 , respectively, in cross-validation. The main sources of error and some further improvements and perspectives are briefly discussed. PMID:25032839

  20. Stability curve prediction of homologous proteins using temperature-dependent statistical potentials.

    PubMed

    Pucci, Fabrizio; Rooman, Marianne

    2014-07-01

    The unraveling and control of protein stability at different temperatures is a fundamental problem in biophysics that is substantially far from being quantitatively and accurately solved, as it requires a precise knowledge of the temperature dependence of amino acid interactions. In this paper we attempt to gain insight into the thermal stability of proteins by designing a tool to predict the full stability curve as a function of the temperature for a set of 45 proteins belonging to 11 homologous families, given their sequence and structure, as well as the melting temperature (Tm) and the change in heat capacity (ΔCP) of proteins belonging to the same family. Stability curves constitute a fundamental instrument to analyze in detail the thermal stability and its relation to the thermodynamic stability, and to estimate the enthalpic and entropic contributions to the folding free energy. In summary, our approach for predicting the protein stability curves relies on temperature-dependent statistical potentials derived from three datasets of protein structures with targeted thermal stability properties. Using these potentials, the folding free energies (ΔG) at three different temperatures were computed for each protein. The Gibbs-Helmholtz equation was then used to predict the protein's stability curve as the curve that best fits these three points. The results are quite encouraging: the standard deviations between the experimental and predicted Tm's, ΔCP's and folding free energies at room temperature (ΔG25) are equal to 13° C, 1.3 kcal/(mol° C) and 4.1 kcal/mol, respectively, in cross-validation. The main sources of error and some further improvements and perspectives are briefly discussed.

  1. To improve the stability of combustion of low rank coal

    SciTech Connect

    Jing Bin Wei

    1995-03-01

    A new aerothermodynamic method, Bi-Flat Inlet Flow Precombustor with Control Jets, developed for flame stabilization of pulverized-coal and the improvement of the ignition condition of low grade coal is described in this paper. The BI-flat flow precombustor consists of a rectangular combustion chamber which can be installed in the location of the burner in the utility and industrial boilers to be used to advance ignition of fuel and primary air mixture and to increase combustion stability of the furnace flames. This type of precombustor simply constructs with two flattened primary air flow and control jets at the head end of the combustor. The velocity of control jets is higher than that of primary flow. A very large recirculation zone with high temperature burnt gases and high turbulent intensity as an ignition source is created in the center of combustion chamber based upon the principles of the actions of jets entraining and Coanda effect. Meanwhile, the higher velocity air layers with lower concentration of coal characteristics on preventing walls from slagging accumulation. Another very important feature is that coal particles could enter directly into the recirculation zone as their inertia and diffusion forces so that it shows a good compatibility of the flow paths of coal particles and high temperature gases. Finally, it is full of promise to be a low pollution emissions combustor since its staged flow and combustion structures.

  2. Design of DC-contact RF MEMS switch with temperature stability

    SciTech Connect

    Sun, Junfeng; Li, Zhiqun; Zhu, Jian; Yu, Yuanwei; Jiang, Lili

    2015-04-15

    In order to improve the temperature stability of DC-contact RF MEMS switch, a thermal buckle-beam structure is implemented. The stability of the switch pull-in voltage versus temperature is not only improved, but also the impact of stress and stress gradient on the drive voltage is suppressed. Test results show that the switch pull-in voltage is less sensitive to temperature between -20 °C and 100 °C. The variable rate of pull-in voltage to temperature is about -120 mV/°C. The RF performance of the switch is stable, and the isolation is almost independent of temperature. After being annealed at 280 °C for 12 hours, our switch samples, which are suitable for packaging, have less than 1.5% change in the rate of pull-in voltage.

  3. Improved temperature regulation of APS linac RF components.

    SciTech Connect

    Dortwegt, R.

    1998-09-21

    The temperature of the APS S-Band linac's high-power rf components is regulated by water from individual closed-loop deionized (DI) water systems. The rf components are all made of oxygen-free high-conductivity copper and respond quickly to temperature changes. The SLED cavities are especially temperature-sensitive and cause beam energy instabilities when the temperature is not well regulated. Temperature regulation better than {+-} 0.1 F is required to achieve good energy stability. Improvements in the closed-loop water systems have enabled them to achieve a regulation of {+-} 0.05 F over long periods. Regulation philosophy and equipment are discussed and numerical results are presented.

  4. High temperature stability multilayers for EUV condenser optics

    SciTech Connect

    Bajt, S; Stearns, D G

    2005-05-03

    We investigate the thermal stability of Mo/SiC multilayer coatings at elevated temperatures. Transmission electron microscopy and x-ray diffraction studies show that upon annealing a thermally-induced structural relaxation occurs that transforms the polycrystalline Mo and amorphous SiC layers in as-deposited multilayers into amorphous Mo-Si-C alloy and crystalline SiC, respectively. After this relaxation process is complete the multilayer is stable at temperatures up to 400 C.

  5. The stability of amino acids at submarine hydrothermal vent temperatures

    NASA Technical Reports Server (NTRS)

    Bada, Jeffrey L.; Miller, Stanley L.; Zhao, Meixun

    1995-01-01

    It has been postulated that amino acid stability at hydrothermal vent temperatures is controlled by a metastable thermodynamic equilibrium rather than by kinetics. Experiments reported here demonstrate that the amino acids are irreversibly destroyed by heating at 240 C and that quasi-equilibrium calculations give misleading descriptions of the experimental observations. Equilibrium thermodynamic calculations are not applicable to organic compounds under high-temperature submarine vent conditions.

  6. The stability of amino acids at submarine hydrothermal vent temperatures

    NASA Technical Reports Server (NTRS)

    Bada, Jeffrey L.; Miller, Stanley L.; Zhao, Meixun

    1995-01-01

    It has been postulated that amino acid stability at hydrothermal vent temperatures is controlled by a metastable thermodynamic equilibrium rather than by kinetics. Experiments reported here demonstrate that the amino acids are irreversibly destroyed by heating at 240 C and that quasi-equilibrium calculations give misleading descriptions of the experimental observations. Equilibrium thermodynamic calculations are not applicable to organic compounds under high-temperature submarine vent conditions.

  7. Improved Performance of a Temperature Compensated LN2 Cooled Sapphire Oscillator

    NASA Technical Reports Server (NTRS)

    Santiago, David G.; Wang, Rabi T.; Dick, G. John

    1995-01-01

    We report on improved stability in a whispering gallery sapphire resonator for which the dominant WGHn11 microwave mode family shows frequency-stable, compensated operation for temperatures above 77K. Several modifications during the past year have led to significant improvements in performance. Current tests with improved thermal stability provide Allan Deviation of frequency of 2.6 - 4 ? 10-13 for measurement times of 1#t#100 seconds. We project a frequency stability of 1014 for this resonator with stabilized housing temperature and with a mode Q of 107.!.

  8. Improved Wide Operating Temperature Range of Li-Ion Cells

    NASA Technical Reports Server (NTRS)

    Smart, Marshall C.; Bugga, Ratnakumar V.

    2013-01-01

    Future NASA missions aimed at exploring the Moon, Mars, and the outer planets require rechargeable batteries that can operate over a wide temperature range (-60 to +60 C) to satisfy the requirements of various applications including landers, rovers, penetrators, CEV, CLV, etc. This work addresses the need for robust rechargeable batteries that can operate well over a wide temperature range. The Department of Energy (DoE) has identified a number of technical barriers associated with the development of Liion rechargeable batteries for PHEVs. For this reason, DoE has interest in the development of advanced electrolytes that will improve performance over a wide range of temperatures, and lead to long life characteristics (5,000 cycles over a 10-year life span). There is also interest in improving the high-voltage stability of these candidate electrolyte systems to enable the operation of up to 5 V with high specific energy cathode materials. Currently, the state-of-the-art lithium-ion system has been demonstrated to operate over a wide range of temperatures (-40 to +40 C); however, the rate capability at the lower temperatures is very poor. In addition, the low-temperature performance typically deteriorates rapidly upon being exposed to high temperatures. A number of electrolyte formulations were developed that incorporate the use of electrolyte additives to improve the high-temperature resilience, low-temperature power capability, and life characteristics of methyl propionate (MP)-based electrolyte solutions. These electrolyte additives include mono-fluoroethylene carbonate (FEC), lithium oxalate, vinylene carbonate (VC), and lithium bis(oxalate borate) (LiBOB), which have previously been shown to result in improved high-temperature resilience of all carbonate-based electrolytes. These MP-based electrolytes with additives have been shown to have improved performance in experiments with MCMB-LiNiCoAlO2 cells.

  9. Thermal Improvement and Stability of Si3N4/GeNx/p- and n-Ge Structures Prepared by Electron-Cyclotron-Resonance Plasma Nitridation and Sputtering at Room Temperature

    NASA Astrophysics Data System (ADS)

    Fukuda, Yukio; Okamoto, Hiroshi; Iwasaki, Takuro; Izumi, Kohei; Otani, Yohei; Ishizaki, Hiroki; Ono, Toshiro

    2012-09-01

    This paper reports on the thermal improvement of Si3N4/GeNx/Ge structures. After the Si3N4 (5 nm)/GeNx (2 nm) stacks were prepared on Ge substrates by electron-cyclotron-resonance plasma nitridation and sputtering at room temperature, they were thermally annealed in atmospheric N2 + 10% H2 ambient at temperatures from 400 to 600 °C. It was demonstrated that the electronic properties of the GeNx/Ge interfaces were thermally improved at temperatures of up to 500 °C with a minimum interface trap density (Dit) of ˜1×1011 cm-2 eV-1 near the Ge midgap, whereas the interface properties were slightly degraded after annealing at 600 °C with a minimum Dit value of ˜4×1011 cm-2 eV-1.

  10. TOPICAL REVIEW: Protein stability and enzyme activity at extreme biological temperatures

    NASA Astrophysics Data System (ADS)

    Feller, Georges

    2010-08-01

    Psychrophilic microorganisms thrive in permanently cold environments, even at subzero temperatures. To maintain metabolic rates compatible with sustained life, they have improved the dynamics of their protein structures, thereby enabling appropriate molecular motions required for biological activity at low temperatures. As a consequence of this structural flexibility, psychrophilic proteins are unstable and heat-labile. In the upper range of biological temperatures, thermophiles and hyperthermophiles grow at temperatures > 100 °C and synthesize ultra-stable proteins. However, thermophilic enzymes are nearly inactive at room temperature as a result of their compactness and rigidity. At the molecular level, both types of extremophilic proteins have adapted the same structural factors, but in opposite directions, to address either activity at low temperatures or stability in hot environments. A model based on folding funnels is proposed accounting for the stability-activity relationships in extremophilic proteins.

  11. Improving calorimeter resolution using temperature compensation calculations

    NASA Astrophysics Data System (ADS)

    Smiga, Joseph; Purschke, Martin

    2017-01-01

    The sPHENIX experiment is an upgrade of the existing PHENIX apparatus at the Relativistic Heavy-Ion Collider (RHIC). The new detector improves upon measurements of various physical processes, such as jets of particles created during heavy-ion collisions. Prototypes of various calorimeter components were tested at the Fermilab Test Beam Facility (FTBF). This analysis tries to compensate the effects of temperature drifts in the silicon photomultipliers (SiPMs). Temperature data were used to calculate an appropriate compensation factor. This analysis will improve the achievable resolution and will also determine how accurately the temperature must be controlled in the final experiment. This will improve the performance of the calorimeters in the sPHENIX experiment. This project was supported in part by the U.S. Department of Energy, Office of Science, Office of Workforce Development for Teachers and Scientists (WDTS) under the Science Undergraduate Laboratory Internships Program (SULI).

  12. Passive Temperature Stabilization of Silicon Photonic Devices Using Liquid Crystals

    PubMed Central

    Ptasinski, Joanna; Khoo, Iam-Choon; Fainman, Yeshaiahu

    2014-01-01

    In this work we explore the negative thermo-optic properties of liquid crystal claddings for passive temperature stabilization of silicon photonic integrated circuits. Photonic circuits are playing an increasing role in communications and computing, but they suffer from temperature dependent performance variation. Most existing techniques aimed at compensation of thermal effects rely on power hungry Joule heating. We show that integrating a liquid crystal cladding helps to minimize the effects of a temperature dependent drift. The advantage of liquid crystals lies in their high negative thermo-optic coefficients in addition to low absorption at the infrared wavelengths. PMID:28788565

  13. Improved Low Temperature Performance of Supercapacitors

    NASA Technical Reports Server (NTRS)

    Brandon, Erik J.; West, William C.; Smart, Marshall C.; Gnanaraj, Joe

    2013-01-01

    Low temperature double-layer capacitor operation enabled by: - Base acetonitrile / TEATFB salt formulation - Addition of low melting point formates, esters and cyclic ethers center dot Key electrolyte design factors: - Volume of co-solvent - Concentration of salt center dot Capacity increased through higher capacity electrodes: - Zeolite templated carbons - Asymmetric cell designs center dot Continuing efforts - Improve asymmetric cell performance at low temperature - Cycle life testing Motivation center dot Benchmark performance of commercial cells center dot Approaches for designing low temperature systems - Symmetric cells (activated carbon electrodes) - Symmetric cells (zeolite templated carbon electrodes) - Asymmetric cells (lithium titanate/activated carbon electrodes) center dot Experimental results center dot Summary

  14. Improved Low Temperature Performance of Supercapacitors

    NASA Technical Reports Server (NTRS)

    Brandon, Erik J.; West, William C.; Smart, Marshall C.; Gnanaraj, Joe

    2013-01-01

    Low temperature double-layer capacitor operation enabled by: - Base acetonitrile / TEATFB salt formulation - Addition of low melting point formates, esters and cyclic ethers center dot Key electrolyte design factors: - Volume of co-solvent - Concentration of salt center dot Capacity increased through higher capacity electrodes: - Zeolite templated carbons - Asymmetric cell designs center dot Continuing efforts - Improve asymmetric cell performance at low temperature - Cycle life testing Motivation center dot Benchmark performance of commercial cells center dot Approaches for designing low temperature systems - Symmetric cells (activated carbon electrodes) - Symmetric cells (zeolite templated carbon electrodes) - Asymmetric cells (lithium titanate/activated carbon electrodes) center dot Experimental results center dot Summary

  15. Controlled Temperature Gradient Improves Freezing Alloy

    NASA Technical Reports Server (NTRS)

    Schmidt, Deborah; Alter, Wendy S.; Hamilton, William D.

    1991-01-01

    Controlled gradient of temperature in advancing zone of solidification increases fatigue life of directionally solidified nickel-base superalloy. Improved solidification process eliminates, reduces, or controls microstructure of deleterious brittle phases, including carbides and gamma/gamma prime eutectic. Also reduces microsegregation and makes discrete carbides (if present) become fine and blocky. Expected to improve properties of other alloys, of both directionally-solidified polycrystalline and single-crystal forms.

  16. Engineering autonomous error correction in stabilizer codes at finite temperature

    NASA Astrophysics Data System (ADS)

    Freeman, C. Daniel; Herdman, C. M.; Whaley, K. B.

    2017-07-01

    We present an error-correcting protocol that enhances the lifetime of stabilizer code-based qubits which are susceptible to the creation of pairs of localized defects (due to stringlike error operators) at finite temperature, such as the toric code. The primary tool employed is periodic application of a local, unitary operator, which exchanges defects and thereby translates localized excitations. Crucially, the protocol does not require any measurements of stabilizer operators and therefore can be used to enhance the lifetime of a qubit in the absence of such experimental resources.

  17. Improved high-temperature silicide coatings

    NASA Technical Reports Server (NTRS)

    Klopp, W. D.; Stephens, J. R.; Stetson, A. R.; Wimber, R. T.

    1969-01-01

    Special technique for applying silicide coatings to refractory metal alloys improves their high-temperature protective capability. Refractory metal powders mixed with a baked-out organic binder and sintered in a vacuum produces a porous alloy layer on the surface. Exposing the layer to hot silicon converts it to a silicide.

  18. Improved performance of silicon nitride-based high temperature ceramics

    NASA Technical Reports Server (NTRS)

    Ashbrook, R. L.

    1977-01-01

    Recent progress in the production of Si3N4 based ceramics is reviewed: (1) high temperature strength and toughness of hot pressed Si3N4 were improved by using high purity powder and a stabilized ZrO2 additive, (2) impact resistance of hot pressed Si3N4 was increased by the use of a crushable energy absorbing layer, (3) the oxidation resistance and strength of reaction sintered Si3N4 were increased by impregnating reaction sintered silicon nitride with solutions that oxidize to Al2O3 or ZrO2, (4) beta prime SiA1ON compositions and sintering aids were developed for improved oxidation resistance or improved high temperature strength.

  19. Improvement of fracture toughness of epoxy resins at cryogenic temperature

    SciTech Connect

    Nishijima, S.; Yamada, K.; Hussain, M.; Honda, Y.

    1997-06-01

    The improvement of the fracture toughness of epoxy resin has been tried to perform from the molecular level with an aim to improve the cryogenic properties of GFRP and/or the stability of superconducting magnets. The ceramic filler, which was formed by hydrolysis of alkoxide, was dispersed in the epoxy and cured. A coupling agent was also used to crosslink the filler and epoxy molecules. The positron annihilation lifetime was measured and the molecular state of the epoxies were evaluated. The thermal contraction and Vickers hardness were also measured. The thermal contraction and hardness were confirmed to reflect the molecular state as evaluated by positron annihilation lifetime. The fracture toughness was also measured down to cryogenic temperatures. It was found that the improvement of the fracture toughness at cryogenic temperatures is possible.

  20. Stability Issues in Ambient-Temperature Passive Magnetic Bearing Systems

    SciTech Connect

    Post, R.F.

    2000-02-17

    The ambient-temperature passive magnetic bearing system developed at the Lawrence Livermore National Laboratory achieves rotor-dynamic stability by employing special combinations of levitating and stabilizing elements. These elements, energized by permanent magnet material, create the magnetic and electrodynamic forces that are required for the stable levitation of rotating systems, such as energy-storage flywheels. Stability criteria, derived from theory, describe the bearing element parameters, i.e., stiffnesses and damping coefficients, that are required both to assure stable levitation (''Earnshaw-stability''), and stability against whirl-type rotor-dynamic instabilities. The work described in this report concerns experimental measurements and computer simulations that address some critical aspects of this overall stability problem. Experimentally, a test device was built to measure the damping coefficient of dampers that employ eddy currents induced in a metallic disc. Another test device was constructed for the purpose of measuring the displacement-dependent drag coefficient of annular permanent magnet bearing elements. In the theoretical developments a computer code was written for the purpose of simulating the rotor-dynamics of our passive bearing systems. This code is capable of investigating rotor-dynamic stability effects for both small-amplitude transient displacements (i.e., those within the linear regime), and for large-amplitude displacements, where non-linear effects can become dominant. Under the latter conditions a bearing system that is stable for small-amplitude displacements may undergo a rapidly growing rotor-dynamic instability once a critical displacement is exceeded. A new result of the study was to demonstrate that stiffness anisotropy of the bearing elements (which can be designed into our bearing system) is strongly stabilizing, not only in the linear regime, but also in the non-linear regime.

  1. Improved Seals for High Temperature Airframe Applications

    NASA Technical Reports Server (NTRS)

    DeMange, Jeffrey J.; Dunlap, Patrick H.; Steinetz, Bruce M.

    2006-01-01

    Current thermal barrier seals, such as those used on the Space Shuttle, are insufficient to fully meet the demands of future hypersonic vehicles and reentry spacecraft. Previous investigations have demonstrated limited usage temperatures, as evidenced by a decreased ability to maintain sealing effectiveness at high temperatures (i.e., inadequate resiliency). In order to improve resiliency at elevated temperatures, Rene 41 (Allvac) was substituted for Inconel X-750 (Special Metals Corp.) as the spring tube material in the existing seal design. A seal construction incorporating the Rene 41 spring tube was fabricated and tested against the baseline Inconel X-750 spring tube seal. Although resiliency improvements were not as dramatic as in previous tests with the spring tubes alone, seals incorporating the Rene 41 spring tube exhibited an average 20 percent resiliency enhancement up to 1750 F when compared to seals containing the Inconel spring tube. In addition, the seals with the Rene 41 spring tubes showed less reduction in resiliency as temperatures increased above 1200 F. Results also indicated the Saffil (Saffil Ltd.) insulation in the core of the seal contributed more to resiliency than previously thought. Leakage data did not demonstrate an improvement with the seal containing the Rene 41 spring tube. However, based upon resiliency results, one could reasonably expect the Rene 41 version of the seal to track gap openings over a wider range. Therefore it would exhibit lower leakage than the Inconel X-750 version as the seal gap opens during a typical mission.

  2. Stability of the high-temperature G-16 primer composition

    SciTech Connect

    Durand, N.A.; Weinmaster, R.R.; Massis, T.A.; Fleming, W.

    1988-01-01

    The stability of the G-16 pyrotechnic primer mixture of antimony sulfide, calcium silicide, and potassium chlorate was studied at temperatures up to 200/sup 0/C in sealed and open environments. Data have shown that this mixture is stable in open environments at 200/sup 0/C for up to 48 hours. However, in sealed, limited volume environments, the mixture completely decomposes within 24 hours at 200/sup 0/C. In sealed environments, the mixture shows stability with copper present. Both functional testing and chemical analysis were used to evaluate the primer composition after temperature exposure. The degree of degradation of the mixture was determined from the concentration of final reaction products (sulfate and chloride ions), using ion chromatography. When copper was present, the intermediate reaction products were scavenged by the copper, and the degradation was reduced. The role of copper in the reaction was verified with differential scanning calorimetry and surface analysis. 3 refs., 9 figs., 2 tabs.

  3. Diamond stabilization of ice multilayers at human body temperature.

    PubMed

    Wissner-Gross, Alexander D; Kaxiras, Efthimios

    2007-08-01

    Diamond is a promising material for wear-resistant medical coatings. Here we report a remarkable increase in the melting point of ice resting on a diamond (111) surface modified with a submonolayer of Na+. Our molecular dynamics simulations show that the interfacial ice bilayer melts at a temperature 130 K higher than in free ice, and relatively thick ice films (2.6 nm at 298 K and 2.2 nm at 310 K ) are stabilized by dipole interactions with the substrate. This unique physical effect may enable biocompatibility-enhancing ice overcoatings for diamond at human body temperature.

  4. Liquid crystal claddings for passive temperature stabilization of silicon photonics

    NASA Astrophysics Data System (ADS)

    Ptasinski, Joanna N.; Khoo, Iam-Choon; Fainman, Yeshaiahu

    2014-10-01

    Silicon photonics allows for high density component integration on a single chip and it brings promise for low-loss, high-bandwidth data processing in modern computing systems. Owing to silicon's high positive thermo-optic coefficient, temperature fluctuations tend to degrade the device performance. This work explores passive thermal stabilization of silicon photonic devices using nematic liquid crystal (NLC) claddings, as they possess large negative thermo-optic coefficients in addition to low absorption at the telecommunication wavelengths.

  5. Aircrew Stabilization Improvement Task Windblast Tests With Tekscan Evaluation

    DTIC Science & Technology

    2005-12-01

    ARLHFE-WP-TR-2OO6-OQO5 STINFO COPY AIR FORCE RESEARCH LABORATORY Airerew Stabilization Improvement Task Windblast Tests wi Tekscan Evaluation Joseph...Interim Report APRIL 2000 - MAY 2004 4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER Aircrew Stabilization Improvement Task Windblast Tests with Tekscan ...and test support to the ASIT effort during the testing of these deflector concepts, as well as an evaluation of the Tekscan pressure measurement system

  6. Method and apparatus for producing pyrolysis oil having improved stability

    DOEpatents

    Baird, Lance A.; Brandvold, Timothy A.; Muller, Stefan

    2016-12-27

    Methods and apparatus to improve hot gas filtration to reduce the liquid fuel loss caused by prolonged residence time at high temperatures are described. The improvement can be obtained by reducing the residence time at elevated temperature by reducing the temperature of the pyrolysis vapor, by reducing the volume of the pyrolysis vapor at the elevated temperature, by increasing the volumetric flow rate at constant volume of the pyrolysis vapor, or by doing a combination of these.

  7. Improved high temperature resistant matrix resins

    NASA Technical Reports Server (NTRS)

    Chang, G. E.; Powell, S. H.; Jones, R. J.

    1983-01-01

    The objective was to develop organic matrix resins suitable for service at temperatures up to 644 K (700 F) and at air pressures up to 0.4 MPa (60 psia) for time durations of a minimum of 100 hours. Matrix resins capable of withstanding these extreme oxidative environmental conditions would lead to increased use of polymer matrix composites in aircraft engines and provide significant weight and cost savings. Six linear condensation, aromatic/heterocyclic polymers containing fluorinated and/or diphenyl linkages were synthesized. The thermo-oxidative stability of the resins was determined at 644 K and compressed air pressures up to 0.4 MPa. Two formulations, both containing perfluoroisopropylidene linkages in the polymer backbone structure, exhibited potential for 644 K service to meet the program objectives. Two other formulations could not be fabricated into compression molded zero defect specimens.

  8. Stability of shock waves in high temperature plasmas

    SciTech Connect

    Das, Madhusmita; Bhattacharya, Chandrani; Menon, S. V. G.

    2011-10-15

    The Dyakov-Kontorovich criteria for spontaneous emission of acoustic waves behind shock fronts are investigated for high temperature aluminum and beryllium plasmas. To this end, the Dyakov and critical stability parameters are calculated from Rankine-Hugoniot curves using a more realistic equation of state (EOS). The cold and ionic contributions to the EOS are obtained via scaled binding energy and mean field theory, respectively. A screened hydrogenic model, including l-splitting, is used to calculate the bound electron contribution to the electronic EOS. The free electron EOS is obtained from Fermi-Dirac statistics. Predictions of the model for ionization curves and shock Hugoniot are found to be in excellent agreement with available experimental and theoretical data. It is observed that the electronic EOS has significant effect on the stability of the planar shock front. While the shock is stable for low temperatures and pressures, instability sets in as temperature rises. The basic reason is ionization of electronic shells and consequent increase in electronic specific heat. The temperatures and densities of the unstable region correspond to those where electronic shells get ionized. With the correct modeling of bound electrons, we find that shock instability for Al occurs at a compression ratio {approx}5.4, contrary to the value {approx}3 reported in the literature. Free electrons generated in the ionization process carry energy from the shock front, thereby giving rise to spontaneously emitted waves, which decay the shock front.

  9. Temperature-stabilized, narrowband tunable fiber-Bragg gratings for matched-filter receiver

    NASA Astrophysics Data System (ADS)

    Roth, Jeffrey M.; Kummer, Joseph W.; Minch, Jeffrey R.; Malinsky, Bryan G.; Scalesse, Vincent; Walther, Frederick G.

    2017-02-01

    We report on a 1550-nm matched filter based on a pair of fiber Bragg gratings (FBGs) that is actively stabilized over temperature. The filter is constructed of a cascaded pair of athermally-packaged FBGs. The tandem FBG pair produces an aggregate 3-dB bandwidth of 3.9-GHz that is closely matched to a return-to-zero, 2.880-GHz differential-phase-shift-keyed optical waveform. The FBGs comprising the filter are controlled in wavelength using a custom-designed, pulse-width modulation (PWM) heater controller. The controllers allow tuning of the FBGs over temperature to compensate and cancel out native temperature dependence of the athermal FBG (AFBG) package. Two heaters are bonded to each FBG device, one on each end. One heater is a static offset that biases the FBG wavelength positively. The second heater is a PWM controller that actively moves the FBG wavelength negatively. A temperature sensor measures the FBGs' temperature, and a feed-forward control loop adjusts the PWM signal to hold the wavelength within a desired range. This stabilization technique reduces the device's native temperature dependence from approximately 0.65 pm/°C to 0.06 pm/°C, improving the temperature stability by tenfold, while retaining some control for poten- tial long-term drifts. The technique demonstrates that the FBGs can be held to +/-1.5 pm (+/-188 MHz) of the target wavelength over a 0 to +50°C temperature range. The temperature-stabilized FBGs are integrated into a low-noise, optical pre-amplifier that operates over a wide temperature range for a laser communication system.

  10. Stabilization of solar films against hi temperature deactivation

    DOEpatents

    Jefferson, Clinton F.

    1984-03-20

    A multi-layer solar energy collector of improved stability comprising: (1) a solar absorptive film consisting essentially of copper oxide, cobalt oxide and manganese oxide; (2) a substrate of quartz, silicate glass or a stainless steel; and (3) an interlayer of platinum, plus a method for preparing a thermally stable multi-layered solar collector, in which the absorptive layer is undercoated with a thin film of platinum to obtain a stable conductor-dielectric tandem.

  11. Improved Estimation Model of Lunar Surface Temperature

    NASA Astrophysics Data System (ADS)

    Zheng, Y.

    2015-12-01

    Lunar surface temperature (LST) is of great scientific interest both uncovering the thermal properties and designing the lunar robotic or manned landing missions. In this paper, we proposed the improved LST estimation model based on the one-dimensional partial differential equation (PDE). The shadow and surface tilts effects were combined into the model. Using the Chang'E (CE-1) DEM data from the Laser Altimeter (LA), the topographic effect can be estimated with an improved effective solar irradiance (ESI) model. In Fig. 1, the highest LST of the global Moon has been estimated with the spatial resolution of 1 degree /pixel, applying the solar albedo data derived from Clementine UV-750nm in solving the PDE function. The topographic effect is significant in the LST map. It can be identified clearly the maria, highland, and craters. The maximum daytime LST presents at the regions with low albedo, i.g. mare Procellarum, mare Serenitatis and mare Imbrium. The results are consistent with the Diviner's measurements of the LRO mission. Fig. 2 shows the temperature variations at the center of the disk in one year, assuming the Moon to be standard spherical. The seasonal variation of LST at the equator is about 10K. The highest LST occurs in early May. Fig.1. Estimated maximum surface temperatures of the global Moon in spatial resolution of 1 degree /pixel

  12. Time and Temperature Test Results for PFP Thermal Stabilization Furnaces

    SciTech Connect

    COMPTON, J.A.

    2000-08-09

    The national standard for plutonium storage acceptability (standard DOE-STD-3013-99, generally known as ''the 3013 standard'') has been revised to clarify the requirement for processes that will produce acceptable storage materials. The 3013 standard (Reference 1) now states that ''Oxides shall be stabilized by heating the material in an oxidizing atmosphere to a Material Temperature of at least 950 C (1742 F) for not less than 2 hours.'' The process currently in use for producing stable oxides for storage at the Plutonium Finishing Plant (PFP) heats a furnace atmosphere to 1000 C and holds it there for 2 hours. The temperature of the material being stabilized is not measured directly during this process. The Plutonium Process Support Laboratories (PPSL) were requested to demonstrate that the process currently in use at PFP is an acceptable method of producing stable plutonium dioxide consistently. A spare furnace identical to the production furnaces was set up and tested under varying conditions with non-radioactive surrogate materials. Reference 2 was issued to guide the testing program. The process currently in use at the PFP for stabilizing plutonium-bearing powders was shown to heat all the material in the furnace to at least 950 C for at least 2 hours. The current process will work for (1) relatively pure plutonium dioxide, (2) dioxide powders mixed with up to 20 weight percent magnesium oxide, and (3) dioxide powders with up to 11 weight percent magnesium oxide and 20 weight percent magnesium nitrate hexahydrate. Time and temperature data were also consistent with a successful demonstration for a mixture containing 10 weight percent each of sodium and potassium chloride; however, the molten chloride salts destroyed the thermocouples in the powder and temperature data were unavailable for part of that run. These results assume that the current operating limits of no more than 2500 grams per furnace charge and a powder height of no more than 1.5 inches remain

  13. Improved high operating temperature MCT MWIR modules

    NASA Astrophysics Data System (ADS)

    Lutz, H.; Breiter, R.; Figgemeier, H.; Schallenberg, T.; Schirmacher, W.; Wollrab, R.

    2014-06-01

    High operating temperature (HOT) IR-detectors are a key factor to size, weight and power (SWaP) reduced IR-systems. Such systems are essential to provide infantrymen with low-weight handheld systems with increased battery lifetimes or most compact clip-on weapon sights in combination with high electro-optical performance offered by cooled IR-technology. AIM's MCT standard n-on-p technology with vacancy doping has been optimized over many years resulting in MWIR-detectors with excellent electro-optical performance up to operating temperatures of ~120K. In the last years the effort has been intensified to improve this standard technology by introducing extrinsic doping with Gold as an acceptor. As a consequence the dark current could considerably be suppressed and allows for operation at ~140K with good e/o performance. More detailed investigations showed that limitation for HOT > 140K is explained by consequences from rising dark current rather than from defective pixel level. Recently, several crucial parameters were identified showing great promise for further optimization of HOT-performance. Among those, p-type concentration could successfully be reduced from the mid 1016 / cm3 to the lower 1015/ cm3 range. Since AIM is one of the leading manufacturers of split linear cryocoolers, an increase in operating temperature will directly lead to IR-modules with improved SWaP characteristics by making use of the miniature members of its SX cooler family with single piston and balancer technology. The paper will present recent progress in the development of HOT MWIR-detector arrays at AIM and show electro-optical performance data in comparison to focal plane arrays produced in the standard technology.

  14. Stability of hydrocarbons at deep Earth pressures and temperatures

    PubMed Central

    Spanu, Leonardo; Donadio, Davide; Hohl, Detlef; Schwegler, Eric; Galli, Giulia

    2011-01-01

    Determining the thermochemical properties of hydrocarbons (HCs) at high pressure and temperature is a key step toward understanding carbon reservoirs and fluxes in the deep Earth. The stability of carbon-hydrogen systems at depths greater than a few thousand meters is poorly understood and the extent of abiogenic HCs in the Earth mantle remains controversial. We report ab initio molecular dynamics simulations and free energy calculations aimed at investigating the formation of higher HCs from dissociation of pure methane, and in the presence of carbon surfaces and transition metals, for pressures of 2 to 30 GPa and temperatures of 800 to 4,000 K. We show that for T≥2,000 K and P≥4 GPa HCs higher than methane are energetically favored. Our results indicate that higher HCs become more stable between 1,000 and 2,000 K and P≥4 GPa. The interaction of methane with a transition metal facilitates the formation of these HCs in a range of temperature where otherwise pure methane would be metastable. Our results provide a unified interpretation of several recent experiments and a detailed microscopic model of methane dissociation and polymerization at high pressure and temperature.

  15. Suspending loads decreases load stability but may slightly improve body stability.

    PubMed

    Ackerman, Jeffrey; Potwar, Karna; Seipel, Justin

    2017-02-08

    Here, we seek to determine how compliantly suspended loads could affect the dynamic stability of legged locomotion. We theoretically model the dynamic stability of a human carrying a load using a coupled spring-mass-damper model and an actuated spring-loaded inverted pendulum model, as these models have demonstrated the ability to correctly predict other aspects of locomotion with a load in prior work, such as body forces and energetic cost. We report that minimizing the load suspension natural frequency and damping ratio significantly reduces the stability of the load mass but may slightly improve the body stability of locomotion when compared to a rigidly attached load. These results imply that a highly-compliant load suspension could help stabilize body motion during human, animal, or robot load carriage, but at the cost of a more awkward (less stable) load.

  16. Improved Stratospheric Temperature Retrievals for Climate Reanalysis

    NASA Technical Reports Server (NTRS)

    Rokke, L.; Joiner, J.

    1999-01-01

    The Data Assimilation Office (DAO) is embarking on plans to generate a twenty year reanalysis data set of climatic atmospheric variables. One of the focus points will be in the evaluation of the dynamics of the stratosphere. The Stratospheric Sounding Unit (SSU), flown as part of the TIROS Operational Vertical Sounder (TOVS), is one of the primary stratospheric temperature sensors flown consistently throughout the reanalysis period. Seven unique sensors made the measurements over time, with individual instrument characteristics that need to be addressed. The stratospheric temperatures being assimilated across satellite platforms will profoundly impact the reanalysis dynamical fields. To attempt to quantify aspects of instrument and retrieval bias we are carefully collecting and analyzing all available information on the sensors, their instrument anomalies, forward model errors and retrieval biases. For the retrieval of stratospheric temperatures, we adapted the minimum variance approach of Jazwinski (1970) and Rodgers (1976) and applied it to the SSU soundings. In our algorithm, the state vector contains an initial guess of temperature from a model six hour forecast provided by the Goddard EOS Data Assimilation System (GEOS/DAS). This is combined with an a priori covariance matrix, a forward model parameterization, and specifications of instrument noise characteristics. A quasi-Newtonian iteration is used to obtain convergence of the retrieved state to the measurement vector. This algorithm also enables us to analyze and address the systematic errors associated with the unique characteristics of the cell pressures on the individual SSU instruments and the resolving power of the instruments to vertical gradients in the stratosphere. The preliminary results of the improved retrievals and their assimilation as well as baseline calculations of bias and rms error between the NESDIS operational product and col-located ground measurements will be presented.

  17. A Challenge to Improve High-Temperature Platinum Resistance Thermometer

    NASA Astrophysics Data System (ADS)

    Tanaka, Y.; Widiatmo, J. V.; Harada, K.; Kobayashi, T.; Yamazawa, K.

    2017-05-01

    High-temperature standard platinum resistance thermometers (HTSPRTs) are used to interpolate the international temperature scale of 1990 (ITS-90), especially for temperatures between the aluminum and the silver points. For this, long-term stability of the HTSPRT is essential. CHINO R800-3L type SPRT, which has a nominal resistance at the triple point of water (TPW) around 0.25 Ω , is the one developed earlier for the interpolation of the ITS-90 at this temperature range. Further development to this previous model has been carried out for the purpose of improving the thermal stability. The improvement was focused on reducing the effect coming from the difference in thermal expansion between platinum wire and the quartz frame on which the platinum wire is installed. New HTSPRTs were made by CHINO Corporation. Some series of tests were carried out at CHINO and at NMIJ. Initial tests after the HTSPRT fabrication were done at CHINO, where thermal cycles between 500°C and 980°C were applied to the HTSPRTs to see change in the resistances at the TPW (R_{TPW}) and at the gallium point (R_{Ga}). Repeated resistance measurements at the silver point (R_{Ag}) were performed after completing the thermal cycling test. Before and after every measurement at silver point, R_{TPW} was measured, while before and after every two silver point realization R_{Ga} were measured. After completing this test, the HTSPRTs were transported to NMIJ, where the same repeated measurements at the silver point were done at NMIJ. These were then repeated at CHINO and at NMIJ upon repeated transportation among the institutes, to evaluate some effect due to transportation. This paper reports the details of the above-mentioned tests, the results and the analysis.

  18. Improvement on the stabilization of a precision tracking system

    NASA Astrophysics Data System (ADS)

    Kuno, H.; Koshiba, T.

    A tracking system that operates from nonstationary platforms must be able to stabilize the tracking axis for precision tracking. Implementation of a free gyro pointing assembly which has a momentum wheel as an integral part of the inner gimbal assembly and that is oriented with its spin axis parallel to the line of sight, is the most widely used method for tactical missiles. The paper describes two methods to improve the stabilization of this tracking system by adjusting the gimbal balance during accelerated condition and adjusting gimbal friction torque at an optimium level appropriate to the applied torque. The results show a one-fifth improvement of the drift rate.

  19. Improving the Stability of Astaxanthin by Microencapsulation in Calcium Alginate Beads

    PubMed Central

    Lin, Shen-Fu; Chen, Ying-Chen; Chen, Ray-Neng; Chen, Ling-Chun; Ho, Hsiu-O; Tsung, Yu-Han; Sheu, Ming-Thau; Liu, Der-Zen

    2016-01-01

    There has been considerable interest in the biological functions of astaxanthin and its potential applications in the nutraceutical, cosmetics, food, and feed industries in recent years. However, the unstable structure of astaxanthin considerably limits its application. Therefore, this study reports the encapsulation of astaxanthin in calcium alginate beads using the extrusion method to improve its stability. This study also evaluates the stability of the encapsulated astaxanthin under different storage conditions. The evaluation of astaxanthin stability under various environmental factors reveals that temperature is the most influential environmental factor in astaxanthin degradation. Stability analysis shows that, regardless of the formulation used, the content of astaxanthin encapsulated in alginate beads remains above 90% of the original amount after 21 days of storage at 25°C. These results suggest that the proposed technique is a promising way to enhance the stability of other sensitive compounds. PMID:27093175

  20. Improving the Stability of Astaxanthin by Microencapsulation in Calcium Alginate Beads.

    PubMed

    Lin, Shen-Fu; Chen, Ying-Chen; Chen, Ray-Neng; Chen, Ling-Chun; Ho, Hsiu-O; Tsung, Yu-Han; Sheu, Ming-Thau; Liu, Der-Zen

    2016-01-01

    There has been considerable interest in the biological functions of astaxanthin and its potential applications in the nutraceutical, cosmetics, food, and feed industries in recent years. However, the unstable structure of astaxanthin considerably limits its application. Therefore, this study reports the encapsulation of astaxanthin in calcium alginate beads using the extrusion method to improve its stability. This study also evaluates the stability of the encapsulated astaxanthin under different storage conditions. The evaluation of astaxanthin stability under various environmental factors reveals that temperature is the most influential environmental factor in astaxanthin degradation. Stability analysis shows that, regardless of the formulation used, the content of astaxanthin encapsulated in alginate beads remains above 90% of the original amount after 21 days of storage at 25°C. These results suggest that the proposed technique is a promising way to enhance the stability of other sensitive compounds.

  1. Metallic radial head arthroplasty improves valgus stability of the elbow.

    PubMed

    King, G J; Zarzour, Z D; Rath, D A; Dunning, C E; Patterson, S D; Johnson, J A

    1999-11-01

    The stabilizing influence of radial head arthroplasty was studied in eight medial collateral ligament deficient anatomic specimen elbows. An elbow testing apparatus, which used computer controlled pneumatic actuators to apply tendon loading, was used to simulate active elbow flexion. The motion pathways of the elbow were measured using an electromagnetic tracking device, with the forearm in supination and pronation. As a measure of stability, the maximum varus to valgus laxity over the range of elbow flexion was determined from the difference between varus and valgus gravity loaded motion pathways. After transection of the medial collateral ligament, the radial head was excised and replaced with either a silicone or one of three metallic radial head prostheses. Medial collateral ligament transection caused a significant increase in the maximum varus to valgus laxity to 18.0 degrees +/- 3.2 degrees. After radial head excision, this laxity increased to 35.6 degrees +/- 10.3 degrees. The silicone implant conferred no increase in elbow stability, with a maximum varus to valgus laxity of 32.5 degrees +/- 15.5 degrees. All three metallic implants improved the valgus stability of the medial collateral ligament deficient elbow, providing stability similar to the intact radial head. The use of silicone arthroplasty to replace the radial head in the medial collateral ligament deficient elbow must be questioned. Metallic radial head arthroplasty provides improved valgus stability, approaching that of an intact radial head.

  2. High temperature stabilization of DNA in complexes with cationic lipids.

    PubMed Central

    Tarahovsky, Yury S; Rakhmanova, Vera A; Epand, Richard M; MacDonald, Robert C

    2002-01-01

    The influence on the melting of calf thymus and plasmid DNA of cationic lipids of the type used in gene therapy was studied by ultraviolet spectrophotometry and differential scanning calorimetry. It was found that various membrane-forming cationic lipids are able to protect calf thymus DNA against denaturation at 100 degrees C. After interaction with cationic lipids, the differential scanning calorimetry melting profile of both calf thymus and plasmid DNA revealed two major components, one corresponding to a thermolabile complex with transition temperature, T(m(labile)), close to that of free DNA and a second corresponding to a thermostable complex with a transition temperature, T(m(stable)), at 105 to 115 degrees C. The parameter T(m(stable)) did not depend on the charge ratio, R(+/-). Instead, the amount of thermostable DNA and the enthalpy ratio Delta H((stable))/Delta H((labile)) depended upon R(+/-) and conditions of complex formation. In the case of O-ethyldioleoylphosphatidylcholine, the cationic lipid that was the main subject of the investigation, the maximal stabilization of DNA exceeded 90% between R(+/-) = 1.5 and 3.0. Several other lipids gave at least 75% protection in the range R(+/-) = 1.5 to 2.0. Centrifugal separation of the thermostable and thermolabile fractions revealed that almost all the transfection activity was present at the thermostable fraction. Electron microscopy of the thermostable complex demonstrated the presence of multilamellar membranes with a periodicity 6.0 to 6.5 nm. This periodic multilamellar structure was retained at temperatures as high as 130 degrees C. It is concluded that constraint of the DNA molecules between oppositely charged membrane surfaces in the multilamellar complex is responsible for DNA stabilization. PMID:11751314

  3. Improving the alkaline stability of imidazolium cations by substitution.

    PubMed

    Dong, Huilong; Gu, Fenglou; Li, Min; Lin, Bencai; Si, Zhihong; Hou, Tingjun; Yan, Feng; Lee, Shuit-Tong; Li, Youyong

    2014-10-06

    Imidazolium cations are promising candidates for preparing anion-exchange membranes because of their good alkaline stability. Substitution of imidazolium cations is an efficient way to improve their alkaline stability. By combining density functional theory calculations with experimental results, it is found that the LUMO energy correlates with the alkaline stability of imidazolium cations. The results indicate that alkyl groups are the most suitable substituents for the N3 position of imidazolium cations, and the LUMO energies of alkyl-substituted imidazolium cations depend on the electron-donating effect and the hyperconjugation effect. Comparing 1,2-dimethylimidazolium cations (1,2-DMIm+) and 1,3-dimethylimidazolium cations (1,3-DMIm+) with the same substituents reveals that the hyperconjugation effect is more significant in influencing the LUMO energy of 1,3-DMIms. This investigation reveals that LUMO energy is a helpful aid in predicting the alkaline stability of imidazolium cations.

  4. INCREASING PROTEIN STABILITY BY IMPROVING BETA-TURNS

    PubMed Central

    Fu, Hailong; Grimsley, Gerald R.; Razvi, Abbas; Scholtz, J. Martin; Pace, C. Nick

    2009-01-01

    Our goal was to gain a better understanding of how protein stability can be increased by improving β-turns. We studied 22 β-turns in nine proteins with 66 to 370 residues by replacing other residues with proline and glycine and measuring the stability. These two residues are statistically preferred in some β-turn positions. We studied: Cold shock protein B (CspB), Histidine-containing phosphocarrier protein (HPr), Ubiquitin, Ribonucleases Sa2, Sa3, T1, and HI, Tryptophan synthetase α-subunit (TSα), and Maltose binding protein (MBP). Of the fifteen single proline mutations, 11increased stability (Average = 0.8 ± 0.3; Range = 0.3 – 1.5 kcal/mol), and the stabilizing effect of double proline mutants was additive. Based on this and our previous work, we conclude that proteins can generally be stabilized by replacing non-proline residues with proline residues at the i + 1 position of Type I and II β-turns and at the i position in Type II β-turns. Other turn positions can sometimes be used if the φ angle is near −60° for the residue replaced. It is important that the side chain of the residue replaced is less than 50% buried. Identical substitutions in β-turns in related proteins give similar results. Proline substitutions increase stability mainly by decreasing the entropy of the denatured state. In contrast, the large, diverse group of proteins considered here had almost no residues in β-turns that could be replaced by Gly to increase protein stability. Improving β-turns by substituting Pro residues is a generally useful way of increasing protein stability. PMID:19626709

  5. Stability of coronene at high temperature and pressure.

    PubMed

    Jennings, E; Montgomery, W; Lerch, Ph

    2010-12-09

    The infrared response of coronene (C(24)H(12)) under pressure and temperature conditions up to 10 GPa and 300 °C is examined in situ using a diamond anvil cell and synchrotron-source Fourier transform infrared (FTIR) spectroscopy. Coronene is a polycyclic aromatic hydrocarbon that is present in the interstellar medium and meteorites which may have contributed to the Earth's primordial carbon budget. It appears to undergo a reversible phase transition between 2 and 3.2 GPa at ambient temperature; new intramolecular bonds in the region 840-880 cm(-1) result from compression. We document the shift of spectral features to higher wavenumbers with increasing pressure but find this change suppressed by increased temperature. By investigating the stability of coronene over a range of naturally occurring conditions found in a range of environments, we assess the survival of the molecule through various terrestrial and extraterrestrial processes. Coronene has previously been shown to survive atmospheric entry during Earth accretion; this can now be extended to include survival through geological processes such as subduction and silicate melting of the rock cycle, opening the possibility of extraterrestrial coronene predating terrestrial accretion existing on Earth.

  6. Improvement in storage stability of infrared dried rough rice

    USDA-ARS?s Scientific Manuscript database

    The objective of this study was to develop infrared drying (IRD) method to improve the stability of physicochemical properties of rough rice during storage. The effect of IRD on the physicochemical properties of stored rough rice was compared with that of hot air drying (HAD) and ambient air drying ...

  7. Substituted silane-diol polymers have improved thermal stability

    NASA Technical Reports Server (NTRS)

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

    1966-01-01

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

  8. Chemical modification of L-asparaginase from Cladosporium sp. for improved activity and thermal stability.

    PubMed

    Mohan Kumar, N S; Kishore, Vijay; Manonmani, H K

    2014-01-01

    L-Asparaginase (ASNase), an antileukemia enzyme, is facing problems with antigenicity in the blood. Modification of L-asparaginase from Cladosporium sp. was tried to obtain improved stability and improved functionality. In our experiment, modification of the enzyme was tried with bovine serum albumin, ovalbumin by crosslinking using glutaraldehyde, N-bromosuccinimide, and mono-methoxy polyethylene glycol. Modified enzymes were studied for activity, temperature stability, rate constants (kd), and protection to proteolytic digestion. Modification with ovalbumin resulted in improved enzyme activity that was 10-fold higher compared to native enzyme, while modification with bovine serum albumin through glutaraldehyde cross-linking resulted in high stability of L-asparaginase that was 8.5- and 7.62-fold more compared to native enzyme at 28°C and 37°C by the end of 24 hr. These effects were dependent on the quantity of conjugate formed. Modification also markedly prolonged L-asparaginase half-life and serum stability. N-Bromosuccinimide-modified ASNase presented greater stability with prolonged in vitro half-life of 144 hr to proteolytic digestion relative to unmodified enzyme (93 h). The present work could be seen as producing a modified L-asparaginase with improved activity and stability and can be a potential source for developing therapeutic agents for cancer treatment.

  9. Radiation stability of some room temperature ionic liquids

    NASA Astrophysics Data System (ADS)

    Jagadeeswara Rao, Ch.; Venkatesan, K. A.; Tata, B. V. R.; Nagarajan, K.; Srinivasan, T. G.; Vasudeva Rao, P. R.

    2011-05-01

    Radiation stability of some room temperature ionic liquids (RTILs) that find useful electrochemical applications in nuclear fuel cycle has been evaluated. The ionic liquids such as protonated betaine bis(trifluoromethylsulfonyl)imide (HbetNTf 2), aliquat 336 (tri-n-octlymethylammonium chloride), 1-butyl-3-methylimidazolium chloride (bmimCl), 1-hexyl-3-methylimidazolium chloride (hmimCl), N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMPyNTf 2) and N-methyl-N-propylpiperidinium bis(trifluoromethylsulfonyl)imide (MPPiNTf 2) have been irradiated to various absorbed dose levels, up to 700 kGy. The effect of gamma radiation on these ionic liquids has been evaluated by determining the variations in the physical properties such as color, density, viscosity, refractive index and electrochemical window. The changes in density, viscosity and refractive index of these ionic liquids upon irradiation were insignificant; however, the color and electrochemical window varied significantly with increase of absorbed dose.

  10. Temperature and Microbial Activity Effects on Soil Carbon Stabilization

    NASA Astrophysics Data System (ADS)

    Fissore, C.; van Diepen, L.; Wixon, D.; Marin-Spiotta, E.; Giardina, C. P.

    2014-12-01

    Uncertainties on the importance of environmental controls on soil C stabilization and turnover limit accurate predictions of the rate and magnitude of the response of soils to climate change. Here we report results from a study of interactions among vegetation and soil microbial communities in North American forests across a highly constrained, 22OC gradient mean annual temperature (MAT) as a proxy for understanding changes with climate. Previous work indicated that turnover and amount of labile SOC responded negatively to MAT, whereas stable SOC was insensitive to temperature variation. Hardwood forests stored a larger amount of stable SOC, but with shorter mean residence times than paired pine forests. Our findings suggest that the interaction between vegetation composition and microbial communities may affect SOC accumulation and stabilization responses to rising temperature. To investigate these relationships, we characterized the microbial communities with Phospholipid Fatty Acid (PLFA) analysis. PLFA analyses indicate complex microbial responses to increased MAT and vegetation composition. Microbial biomass declined with MAT in conifer forests and increased in hardwood forests. Relative abundance of actinomycetes increased with MAT for both forest types, and was correlated with amount and turnover of active SOC. The relative abundance of fungi decreased with increasing MAT, while gram+ bacteria increased, such that fungi:bacteria ratio decreased with MAT, with this trend being more pronounced for hardwood cover type. These results are consistent with a long-term warming experiment in a hardwood forest at the Harvard Forest LTER site, where after 12 years of warming the relative abundance of gram positive bacteria and actinomycetes increased, while fungal biomass decreased. In contrast, relationships between microbial groups and the stable fraction of SOC along the gradient were only observed in conifers. Increases in mean residence time of stable SOC were

  11. Structural stability of high entropy alloys under pressure and temperature

    NASA Astrophysics Data System (ADS)

    Ahmad, Azkar S.; Su, Y.; Liu, S. Y.; Stâhl, K.; Wu, Y. D.; Hui, X. D.; Ruett, U.; Gutowski, O.; Glazyrin, K.; Liermann, H. P.; Franz, H.; Wang, H.; Wang, X. D.; Cao, Q. P.; Zhang, D. X.; Jiang, J. Z.

    2017-06-01

    The stability of high-entropy alloys (HEAs) is a key issue before their selection for industrial applications. In this study, in-situ high-pressure and high-temperature synchrotron radiation X-ray diffraction experiments have been performed on three typical HEAs Ni20Co20Fe20Mn20Cr20, Hf25Nb25Zr25Ti25, and Re25Ru25Co25Fe25 (at. %), having face-centered cubic (fcc), body-centered cubic (bcc), and hexagonal close-packed (hcp) crystal structures, respectively, up to the pressure of ˜80 GPa and temperature of ˜1262 K. Under the extreme conditions of the pressure and temperature, all three studied HEAs remain stable up to the maximum pressure and temperatures achieved. For these three types of studied HEAs, the pressure-dependence of the volume can be well described with the third order Birch-Murnaghan equation of state. The bulk modulus and its pressure derivative are found to be 88.3 GPa and 4 for bcc-Hf25Nb25Zr25Ti25, 193.9 GPa and 5.9 for fcc-Ni20Co20Fe20Mn20Cr20, and 304.6 GPa and 3.8 for hcp-Re25Ru25Co25Fe25 HEAs, respectively. The thermal expansion coefficient for the three studied HEAs is found to be in the order as follows: fcc-Ni20Co20Fe20Mn20Cr20 > bcc-Hf25Nb25Zr25Ti25 ≈ hcp-Re25Ru25Co25Fe25.

  12. Frequency stabilization of an external cavity diode laser: countermeasures against atmospheric temperature variations

    NASA Astrophysics Data System (ADS)

    Minabe, Yuta; Doi, Kohei; Sato, Takashi; Maruyama, Takeo; Ohkawa, Masashi; Tsubokawa, Tsuneya

    2008-02-01

    External cavity diode lasers (ECDL) are presently experiencing a surge in popularity, as laser light-sources for advanced optical measurement systems. While these devices normally require external optical-output controls, we simplified the setup, a bit, by adding a second external cavity. This technique boasts the added advantage of having a narrower oscillation-linewidth than would be achievable, using a single optical feedback. Because drive-current and atmospheric temperature directly impact the ECDL systems' oscillation frequency, during frequency stability checks, it was necessary, in this instance, to construct a slightly smaller ECDL system, which we mounted on a Super-Invar board, to minimize the influence of thermal expansion. Taking these and other aggressive and timely measures to prevent atmospheric temperature-related changes allowed us to achieve an improvement in oscillation-frequency stability, i.e., to obtain the square root of Allan variance σ =2×10 -10, at averaging time τ =10 -1. We introduced a vertical-cavity surface-emitting laser (VCSEL) to the setup, for the simple reason that its frequency is far less susceptible to changes in temperature, than other lasers of its type. And, because VCSELs are widely available, and the ECDL systems that use them improve frequency stability, we replaced the Fabry-Perot semiconductor laser with a VCSEL.

  13. Stability evaluation and improvement of adaptive optics systems by using the Lyapunov stability approach

    NASA Astrophysics Data System (ADS)

    Wang, Liang; Chen, Tao; Liu, Xin-yue; Lin, Xu-dong; Yang, Xiao-xia; Li, Hong-zhuang

    2016-02-01

    In this research, investigations on the closed-loop control stability of adaptive optics systems are conducted by using the Lyapunov approach. As an direct metric of the control stability, the error propagator includes the effects of both the integral gain and the influence matrix and is effective for control-stability evaluation. An experimental 97-element AO system is developed for the control-stability investigation, and the Southwell sensor-actuator configuration rather than the Fried geometry is adopted so as to suppress the potential waffle mode. Because filtering out small singular values of the influence matrix can be used to improve the control stability, the effect of the influence matrix and the effect of the integral gain are considered as a whole by using the error propagator. Then, the control stability of the AO system is evaluated for varying the integral gains and the number of filtered-out singular values. Afterwards, an analysis of the evaluations of the error propagator is made, and a conclusion can be drawn that the control stability can be improved by filtering out more singular values of the influence matrix when the integral gain is high. In other words, the error propagator is useful for trading off the bandwidth error and the fitting error of AO systems in a control-stability approach. Finally, a performance measurement of the experimental AO system is conducted when 13 smaller singular values of the influence matrix are filtered out, and the results show that filtering out a small fraction of the singular values has a minor influence on the performance of this AO system.

  14. Improved Stabilization Method for Lurie Networked Control Systems

    PubMed Central

    Zeng, Hong-Bing; Xiao, Shen-Ping; Yu, Fei

    2014-01-01

    The problem of stabilization of Lurie networked control systems (NCSs) is investigated in this paper. The network-induced delays in NCSs are assumed to be time-varying and bounded. By utilizing a reciprocally convex technique to consider the relationship between the network-induced delay and its varying interval, a new absolute stability condition is derived in terms of linear matrix inequalities (LMIs). Based on the obtained condition, an improved cone complementary linearisation (CCL) iteration algorithm is presented to design a state feedback controller. The effectiveness of the proposed method is verified by a numerical example. PMID:24892090

  15. Carbocation Stability in H-ZSM5 at High Temperature

    SciTech Connect

    Ferguson, Glen A.; Cheng, Lei; Bu, Lintao; Kim, Seonah; Robichaud, David J.; Nimlos, Mark R.; Curtiss, Larry A.; Beckham, Gregg T.

    2015-10-26

    Zeolites are common catalysts for multiple industrial applications, including alcohol dehydration to produce olefins, and given their commercial importance, reaction mechanisms in zeolites have long been proposed and studied. Some proposed reaction mechanisms for alcohol dehydration exhibit noncyclic carbocation intermediates or transition states that resemble carbocations, and several previous studies suggest that the tert-butyl cation is the only noncyclic cation more stable than the corresponding chemisorbed species with the hydrocarbon bound to the framework oxygen (i.e., an alkoxide). To determine if carbocations can exist at high temperatures in zeolites, where these catalysts are finding new applications for biomass vapor-phase upgrading (~500 °C), the stability of carbocations and the corresponding alkoxides were calculated with two ONIOM embedding methods (M06-2X/6-311G(d,p):M06-2X/3-21G) and (PBE-D3/6-311G(d,p):PBE-D3/3-21G) and plane-wave density functional theory (DFT) using the PBE functional corrected with entropic and Tkatchenko–Scheffler van der Waals corrections. Additionally, the embedding methods tested are unreliable at finding minima for primary carbocations, and only secondary or higher carbocations can be described with embedding methods consistent with the periodic DFT results. The relative energy between the carbocations and alkoxides differs significantly between the embedding and the periodic DFT methods. The difference is between ~0.23 and 14.30 kcal/mol depending on the molecule, the model, and the functional chosen for the embedding method. At high temperatures, the pw-DFT calculations predict that the allyl, isopropyl, and sec-butyl cations exhibit negligible populations while acetyl and tert-butyl cations exhibit significant populations (>10%). Furthermore, the periodic DFT results indicate that mechanisms including secondary and tertiary carbocations intermediates or carbocations stabilized by adjacent oxygen or double bonds are

  16. Carbocation Stability in H-ZSM5 at High Temperature

    SciTech Connect

    Ferguson, Glen A.; Cheng, Lei; Bu, Lintao; Kim, Seonah; Robichaud, David J.; Nimlos, Mark R.; Curtiss, Larry A.; Beckham, Gregg T.

    2015-10-26

    Zeolites are common catalysts for multiple industrial applications, including alcohol dehydration to produce olefins, and given their commercial importance, reaction mechanisms in zeolites have long been proposed and studied. Some proposed reaction mechanisms for alcohol dehydration exhibit noncyclic carbocation intermediates or transition states that resemble carbocations, and several previous studies suggest that the tert-butyl cation is the only noncyclic cation more stable than the corresponding chemisorbed species with the hydrocarbon bound to the framework oxygen (i.e., an alkoxide). To determine if carbocations can exist at high temperatures in zeolites, where these catalysts are finding new applications for biomass vapor-phase upgrading (~500 °C), the stability of carbocations and the corresponding alkoxides were calculated with two ONIOM embedding methods (M06-2X/6-311G(d,p):M06-2X/3-21G) and (PBE-D3/6-311G(d,p):PBE-D3/3-21G) and plane-wave density functional theory (DFT) using the PBE functional corrected with entropic and Tkatchenko-Scheffler van der Waals corrections. The embedding methods tested are unreliable at finding minima for primary carbocations, and only secondary or higher carbocations can be described with embedding methods consistent with the periodic DFT results. The relative energy between the carbocations and alkoxides differs significantly between the embedding and the periodic DFT methods. The difference is between ~0.23 and 14.30 kcal/mol depending on the molecule, the model, and the functional chosen for the embedding method. At high temperatures, the pw-DFT calculations predict that the allyl, isopropyl, and sec-butyl cations exhibit negligible populations while acetyl and tertbutyl cations exhibit significant populations (>10%). Moreover, the periodic DFT results indicate that mechanisms including secondary and tertiary carbocations intermediates or carbocations stabilized by adjacent oxygen or double bonds are possible at high

  17. Temperature after Arc Discharge Affected by Current Decrement Ratio in Wall Stabilized Arc

    NASA Astrophysics Data System (ADS)

    Sato, Ken; Suzuki, Daichi; Iwao, Toru

    2015-11-01

    Recently, the stable supply of electric power is indispensable in a power generation, and a transmission and distribution system of electric power. The GCB (Gas Circuit Breaker) has been researched for performance improvement of the arc interruption of abnormal fault current without the fail. The GCB has been researched for the high capacity and downsizing for development of practical use. Because the power network is expanded, the capacity of interruption current increased for reliability. The GCB should interrupt the arc of high current and voltage, shorten the time to interrupt, and become the high capability in order to improve the reliability and practicability. It is important to prevent the insulation of re-ignition and thermal re-ignition of arc after the arc interruption. It is mainly considered that the factor of thermal re-ignition is the arc temperature distribution after current zero. The temperature distribution has been elucidated by the current decrement ratio (di/dt). However, the variation of temperature distribution and decrement process of the temperature by the wall radius is also important in order to design the circuit breaker. In this paper, temperature after Arc Discharge Affected by Current Decrement Ratio in Wall Stabilized Arc was elucidated in order to know the effect on the temperature in the wall radius. As a result, when the wall radius decreases, the temperature at 0 A after 200 μs is lower.

  18. Improved Phase Stability of Formamidinium Lead Triiodide Perovskite by Strain Relaxation

    SciTech Connect

    Zheng, Xiaojia; Wu, Congcong; Jha, Shikhar K.; Li, Zhen; Zhu, Kai; Priya, Shashank

    2016-11-11

    Though formamidinium lead triiodide (FAPbI3) possesses a suitable band gap and good thermal stability, the phase transition from the pure black perovskite phase (a-phase) to the undesirable yellow nonperovskite polymorph (..delta..-phase) at room temperature, especially under humid air, hinders its practical application. Here, we investigate the intrinsic instability mechanism of the ..alpha..-phase at ambient temperature and demonstrate the existence of an anisotropic strained lattice in the (111) plane that drives phase transformation into the ..delta..-phase. Methylammonium bromide (MABr) alloying (or FAPbI3-MABr) was found to cause lattice contraction, thereby balancing the lattice strain. This led to dramatic improvement in the stability of ..alpha..-FAPbI3. Solar cells fabricated using FAPbI3-MABr demonstrated significantly enhanced stability under the humid air.

  19. Application of locked nucleic acids to improve aptamer in vivo stability and targeting function

    PubMed Central

    Schmidt, Kathrin S.; Borkowski, Sandra; Kurreck, Jens; Stephens, Andrew W.; Bald, Rolf; Hecht, Maren; Friebe, Matthias; Dinkelborg, Ludger; Erdmann, Volker A.

    2004-01-01

    Aptamers are powerful candidates for molecular imaging applications due to a number of attractive features, including rapid blood clearance and tumor penetration. We carried out structure–activity relationship (SAR) studies with the Tenascin-C binding aptamer TTA1, which is a promising candidate for application in tumor imaging with radioisotopes. The aim was to improve its in vivo stability and target binding. We investigated the effect of thermal stabilization of the presumed non-binding double-stranded stem region on binding affinity and resistance against nucleolytic degradation. To achieve maximal thermal stem stabilization melting experiments with model hexanucleotide duplexes consisting of unmodified RNA, 2′-O-methyl RNA (2′-OMe), 2′-Fluoro RNA (2′-F) or Locked Nucleic Acids (LNAs) were initially carried out. Extremely high melting temperatures have been found for an LNA/LNA duplex. TTA1 derivatives with LNA and 2′-OMe modifications within the non-binding stem have subsequently been synthesized. Especially, the LNA-modified TTA1 derivative exhibited significant stem stabilization and markedly improved plasma stability while maintaining its binding affinity to the target. In addition, higher tumor uptake and longer blood retention was found in tumor-bearing nude mice. Thus, our strategy to introduce LNA modifications after the selection procedure is likely to be generally applicable to improve the in vivo stability of aptamers without compromising their binding properties. PMID:15509871

  20. Brain temperature measurement: A study of in vitro accuracy and stability of smart catheter temperature sensors.

    PubMed

    Li, Chunyan; Wu, Pei-Ming; Wu, Zhizhen; Ahn, Chong H; LeDoux, David; Shutter, Lori A; Hartings, Jed A; Narayan, Raj K

    2012-02-01

    The injured brain is vulnerable to increases in temperature after severe head injury. Therefore, accurate and reliable measurement of brain temperature is important to optimize patient outcome. In this work, we have fabricated, optimized and characterized temperature sensors for use with a micromachined smart catheter for multimodal intracranial monitoring. Developed temperature sensors have resistance of 100.79 ± 1.19Ω and sensitivity of 67.95 mV/°C in the operating range from15-50°C, and time constant of 180 ms. Under the optimized excitation current of 500 μA, adequate signal-to-noise ratio was achieved without causing self-heating, and changes in immersion depth did not introduce clinically significant errors of measurements (<0.01°C). We evaluated the accuracy and long-term drift (5 days) of twenty temperature sensors in comparison to two types of commercial temperature probes (USB Reference Thermometer, NIST-traceable bulk probe with 0.05°C accuracy; and IT-21, type T type clinical microprobe with guaranteed 0.1°C accuracy) under controlled laboratory conditions. These in vitro experimental data showed that the temperature measurement performance of our sensors was accurate and reliable over the course of 5 days. The smart catheter temperature sensors provided accuracy and long-term stability comparable to those of commercial tissue-implantable microprobes, and therefore provide a means for temperature measurement in a microfabricated, multimodal cerebral monitoring device.

  1. Improved Optical-Fiber Temperature Sensors

    NASA Technical Reports Server (NTRS)

    Rogowski, Robert S.; Egalon, Claudio O.

    1993-01-01

    In optical-fiber temperature sensors of proposed type, phosphorescence and/or fluorescence in temperature-dependent coating layers coupled to photodetectors. Phosphorescent and/or fluorescent behavior(s) of coating material(s) depend on temperature; coating material or mixture of materials selected so one can deduce temperature from known temperature dependence of phosphorescence and/or fluorescence spectrum, and/or characteristic decay of fluorescence. Basic optical configuration same as that of optical-fiber chemical detectors described in "Making Optical-Fiber Chemical Detectors More Sensitive" (LAR-14525).

  2. Improved Dye Stability in Single-Molecule Fluorescence Experiments

    NASA Astrophysics Data System (ADS)

    EcheverrÍa Aitken, Colin; Marshall, R. Andrew; Pugi, Joseph D.

    Complex biological systems challenge existing single-molecule methods. In particular, dye stability limits observation time in singlemolecule fluorescence applications. Current approaches to improving dye performance involve the addition of enzymatic oxygen scavenging systems and small molecule additives. We present an enzymatic oxygen scavenging system that improves dye stability in single-molecule experiments. Compared to the currently-employed glucose-oxidase/catalase system, the protocatechuate-3,4-dioxygenase system achieves lower dissolved oxygen concentration and stabilizes single Cy3, Cy5, and Alexa488 fluorophores. Moreover, this system possesses none of the limitations associated with the glucose oxidase/catalase system. We also tested the effects of small molecule additives in this system. Biological reducing agents significantly destabilize the Cy5 fluorophore as a function of reducing potential. In contrast, anti-oxidants stabilize the Cy3 and Alexa488 fluorophores. We recommend use of the protocatechuate-3,4,-dioxygenase system with antioxidant additives, and in the absence of biological reducing agents. This system should have wide application to single-molecule fluorescence experiments.

  3. Improving storage stability of gasoline using elevated antioxidant concentrations

    SciTech Connect

    Sommer, S.; Luria, D.; Lavie, I.; Sufrin, J.; Weiss, A.; Shuftan, M.

    1995-04-01

    The purpose of this study was to examine the feasibility of increasing storage-stability of gasoline by blending it with elevated concentrations of standard antioxidants, normally added at low concentrations to gasolines. It was thought that, by raising the concentration of these additives in the gasoline from 25 ppm to 100 ppm, the storage stability of the fuel can be improved. In this study, two types of antioxidants (an aromatic diamine type and an alkylphenol type), and a mixture of the two, were added at different concentrations to two different gasoline blends. The various blends were stored in drums, simulating tank storage conditions, for a period of 25 months. Samples were drawn at varying intervals over the test duration and tested for Existent Gum, Potential Gum, Induction Period and other properties (according to standard ASTM test procedures). It was found that raising the concentrations of the aromatic amine antioxidant adversely effected the storage stability of the gasoline blends, whereas elevated concentrations of the alkylphenol antioxidant indeed improved the gasoline`s stability.

  4. Stability improvements for the NIST Yb optical lattice clock

    NASA Astrophysics Data System (ADS)

    Fasano, R. J.; Schioppo, M.; McGrew, W. F.; Brown, R. C.; Hinkley, N.; Yoon, T. H.; Beloy, K.; Oates, C. W.; Ludlow, A. D.

    2016-05-01

    To reach the fundamental limit given by quantum projection noise, optical lattice clocks require advanced laser stabilization techniques. The NIST ytterbium clock has benefited from several generations of extremely high finesse optical cavities, with cavity linewidths below 1 kHz. Characterization of the cavity drift rate has allowed compensation to the mHz/s level, improving the medium-term stability of the cavity. Based on recent measurements using Ramsey spectroscopy with synchronous interrogation, we report a fractional instability σy(1s) <=10-16 , dominated by atom number fluctuation noise. We also provide updates on our cryogenic sapphire cavity with a reduced thermal noise floor, which will improve our Dick-limited fractional instability at 1 s to below 10-16. Also at University of Colorado.

  5. Stability of a Crystal Oscillator, Type Si530, Inside and Beyond its Specified Operating Temperature Range

    NASA Technical Reports Server (NTRS)

    Patterson, Richard L.; Hammoud, Ahmad

    2011-01-01

    Data acquisition and control systems depend on timing signals for proper operation and required accuracy. These clocked signals are typically provided by some form of an oscillator set to produce a repetitive, defined signal at a given frequency. Crystal oscillators are commonly used because they are less expensive, smaller, and more reliable than other types of oscillators. Because of the inherent characteristics of the crystal, the oscillators exhibit excellent frequency stability within the specified range of operational temperature. In some cases, however, some compensation techniques are adopted to further improve the thermal stability of a crystal oscillator. Very limited data exist on the performance and reliability of commercial-off-the-shelf (COTS) crystal oscillators at temperatures beyond the manufacturer's specified operating temperature range. This information is very crucial if any of these parts were to be used in circuits designed for use in space exploration missions where extreme temperature swings and thermal cycling are encountered. This report presents the results of the work obtained on the operation of Silicon Laboratories crystal oscillator, type Si530, under specified and extreme ambient temperatures.

  6. 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.

  7. High critical temperature above T(g) may contribute to the stability of biological systems.

    PubMed

    Buitink, J; van den Dries, I J; Hoekstra, F A; Alberda, M; Hemminga, M A

    2000-08-01

    In this study, we characterized the molecular mobility around T(g) in sugars, poly-L-lysine and dry desiccation-tolerant biological systems, using ST-EPR, (1)H-NMR, and FTIR spectroscopy, to understand the nature and composition of biological glasses. Two distinct changes in the temperature dependence of the rotational correlation time (tau(R)) of the spin probe 3-carboxy-proxyl or the second moment (M(2)) were measured in sugars and poly-L-lysine. With heating, the first change was associated with the melting of the glassy state (T(g)). The second change (T(c)), at which tau(R) abruptly decreased over several orders of magnitude, was found to correspond with the so-called cross-over temperature, where the dynamics changed from solid-like to liquid-like. The temperature interval between T(g) and T(c) increased in the order of sucrose < trehalose < raffinose 50 degrees C, implying that the stability above T(g) improved in the same order. These differences in temperature-dependent mobilities above T(g) suggest that proteins rather than sugars play an important role in the intracellular glass formation. The exceptionally high T(c) of intracellular glasses is expected to provide excellent long-term stability to dry organisms, maintaining a slow molecular motion in the cytoplasm even at temperatures far above T(g).

  8. Noisy vestibular stimulation improves dynamic walking stability in bilateral vestibulopathy.

    PubMed

    Wuehr, Max; Nusser, Eva; Decker, Julian; Krafczyk, Siegbert; Straube, Andreas; Brandt, Thomas; Jahn, Klaus; Schniepp, Roman

    2016-06-07

    To examine the effects of imperceptible levels of white noise galvanic vestibular stimulation (nGVS) on dynamic walking stability in patients with bilateral vestibulopathy (BVP). Walking performance of 13 patients with confirmed BVP (mean age 50.1 ± 5.5 years) at slow, preferred, and fast speeds was examined during walking with zero-amplitude nGVS (sham trial) and nonzero-amplitude nGVS set to 80% of the individual cutaneous threshold for GVS (nGVS trial). Eight standard gait measures were analyzed: stride time, stride length, base of support, double support time percentage as well as the bilateral phase coordination index, and the coefficient of variation (CV) of stride time, stride length, and base of support. Compared to the sham trial, nGVS improved stride time CV by 26.0% ± 8.4% (p < 0.041), stride length CV by 26.0% ± 7.7% (p < 0.029), base of support CV by 27.8% ± 2.9% (p < 0.037), and phase coordination index by 8.4% ± 8.8% (p < 0.013). The nGVS effects on walking performance were correlated with subjective ratings of walking balance (ρ = 0.79, p < 0.001). Effect of nGVS on walking stability was most pronounced during slow walking. In patients with BVP, nGVS is effective in improving impaired gait performance, predominantly during slower walking speeds. It primarily targets the variability and bilateral coordination characteristics of the walking pattern, which are linked to dynamic walking stability. nGVS might present an effective treatment option to immediately improve walking performance and reduce the incidence of falls in patients with BVP. This study provides Class IV evidence that in patients with BVP, an imperceptible level of nGVS improves dynamic walking stability. © 2016 American Academy of Neurology.

  9. 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.

  10. THE STABILITY AND ELECTRICAL PROPERTIES OF HIGH TEMPERATURE PROTON CONDUCTORS

    SciTech Connect

    Brinkman, K.

    2010-07-06

    The morphological and electrical properties of Ba{sub 1-x}Sr{sub x}Ce{sub 0.8}Y{sub 0.2}O{sub 3-{delta}} with x varying from 0 to 1 prepared by a modified Pechini method were investigated as potential high temperature proton conductors. Dense microstructures were achieved for all the samples upon sintering at 1500 C for 5 h. The phase structure analysis indicated that perovskite phase was formed for 0 {le} x {le} 0.2, while for x larger than 0.5, impurity phases of Sr{sub 2}CeO{sub 4} and Y{sub 2}O{sub 3} appeared. The tolerance to H{sub 2}O for the samples improved with the increase in Sr content when exposed to boiling water, while the electrical conductivity decreased from x = 0 to 1. However, the resistance to CO{sub 2} attack at elevated temperatures was not improved within the whole x range studied.

  11. Connecting high-temperature and low-temperature protein stability and aggregation.

    PubMed

    Rosa, Mónica; Roberts, Christopher J; Rodrigues, Miguel A

    2017-01-01

    Protein aggregation is a long-standing problem for preservation of proteins in both laboratory settings and for commercial biotechnology products. It is well established that heating (cooling) can accelerate (slow) aggregation by populating (depopulating) unfolded or partially unfolded monomer states that are key intermediates in aggregation processes. However, there is a long-standing question of whether the same mechanism(s) that lead to aggregation under high-temperature stress are relevant for low-temperature stress such as in refrigerated or supercooled liquids. This report shows the first direct comparison of "hot" and "cold" aggregation kinetics and folding/unfolding thermodynamics, using bovine hemoglobin as a model system. The results suggest that the same mechanism for non-native aggregation holds from "hot" to "cold" temperatures, with an aggregation temperature-of-maximum-stability slightly below 0°C. This highlights that sub-zero temperatures can induce cold-mediated aggregation, even in the absence of freezing stresses. From a practical perspective, the results suggests the possibility that cold-stress may be a useful alternative to heat-stress for extrapolating predictions of protein shelf life at refrigerated conditions, as well as providing a foundation for more mechanistic studies of cold-stress conditions in future work. A comparison between isochoric and isobaric methods is also briefly discussed.

  12. Connecting high-temperature and low-temperature protein stability and aggregation

    PubMed Central

    Rosa, Mónica; Roberts, Christopher J.

    2017-01-01

    Protein aggregation is a long-standing problem for preservation of proteins in both laboratory settings and for commercial biotechnology products. It is well established that heating (cooling) can accelerate (slow) aggregation by populating (depopulating) unfolded or partially unfolded monomer states that are key intermediates in aggregation processes. However, there is a long-standing question of whether the same mechanism(s) that lead to aggregation under high-temperature stress are relevant for low-temperature stress such as in refrigerated or supercooled liquids. This report shows the first direct comparison of “hot” and “cold” aggregation kinetics and folding/unfolding thermodynamics, using bovine hemoglobin as a model system. The results suggest that the same mechanism for non-native aggregation holds from “hot” to “cold” temperatures, with an aggregation temperature-of-maximum-stability slightly below 0°C. This highlights that sub-zero temperatures can induce cold-mediated aggregation, even in the absence of freezing stresses. From a practical perspective, the results suggests the possibility that cold-stress may be a useful alternative to heat-stress for extrapolating predictions of protein shelf life at refrigerated conditions, as well as providing a foundation for more mechanistic studies of cold-stress conditions in future work. A comparison between isochoric and isobaric methods is also briefly discussed. PMID:28472066

  13. Comparison of Temperature and Additives Affecting the Stability of the Probiotic Weissella cibaria

    PubMed Central

    Kang, Mi-Sun; Kim, Youn-Shin; Lee, Hyun-Chul; Lim, Hoi-Soon

    2012-01-01

    Daily use of probiotic chewing gum might have a beneficial effect on oral health, and it is important that the viability of the probiotics be maintained in this food product. In this study, we examined the stability of probiotic chewing gum containing Weissella cibaria. We evaluated the effects of various factors, including temperature and additives, on the survival of freeze-dried probiotic W. cibaria powder. No changes in viability were detected during storage at 4℃ for 5 months, whereas the viability of bacteria stored at 20℃ decreased. The stability of probiotic chewing gum decreased steadily during storage at 20℃ for 4 weeks. The viability of the freeze-dried W. cibaria mixed with various additives, such as xylitol, sorbitol, menthol, sugar ester, magnesium stearate, and vitamin C, was determined over a 4-week storage period at 20℃. Most of the freeze-dried bacteria except for those mixed with menthol and vitamin C were generally stable during a 3-week storage period. Overall, our study showed that W. cibaria was more stable at 4℃ than that at 20℃. In addition, menthol and vitamin C had a detrimental effect on the storage stability of W. cibaria. This is the first study to examine the effects of various chewing gum additives on the stability of W. cibaria. Further studies will be needed to improve the stability of probiotic bacteria for developing a novel probiotic W. cibaria gum. PMID:23323221

  14. Stability of NiTi-Pd and NiTi-Hf high temperature shape memory alloys

    SciTech Connect

    Zhu, Y.R.; Pu, Z.J.; Li, C.; Wu, K.H.

    1994-09-28

    The thermal cycling tests and high temperature aging tests were performed to characterize the stability of NiTi-Pd and NiTi-Hf high temperature shape memory alloys. These alloys have better stability than NiTi during thermal cycling. In addition, it also found that the NiTi-Pd and NiTi-Hf alloy have a very good stability in high temperature aging.

  15. Note: Improving long-term stability of hot-wire anemometer sensors by means of annealing.

    PubMed

    Lundström, H

    2015-08-01

    Annealing procedures for hot-wire sensors of platinum and platinum-plated tungsten have been investigated experimentally. It was discovered that the two investigated sensor metals behave quite differently during the annealing process, but for both types annealing may improve long-term stability considerably. Measured drift of sensors both without and with prior annealing is presented. Suggestions for suitable annealing temperatures and times are given.

  16. Note: Improving long-term stability of hot-wire anemometer sensors by means of annealing

    NASA Astrophysics Data System (ADS)

    Lundström, H.

    2015-08-01

    Annealing procedures for hot-wire sensors of platinum and platinum-plated tungsten have been investigated experimentally. It was discovered that the two investigated sensor metals behave quite differently during the annealing process, but for both types annealing may improve long-term stability considerably. Measured drift of sensors both without and with prior annealing is presented. Suggestions for suitable annealing temperatures and times are given.

  17. Note: Improving long-term stability of hot-wire anemometer sensors by means of annealing

    SciTech Connect

    Lundström, H.

    2015-08-15

    Annealing procedures for hot-wire sensors of platinum and platinum-plated tungsten have been investigated experimentally. It was discovered that the two investigated sensor metals behave quite differently during the annealing process, but for both types annealing may improve long-term stability considerably. Measured drift of sensors both without and with prior annealing is presented. Suggestions for suitable annealing temperatures and times are given.

  18. Magnetic-divertor stabilization of an axisymmetric plasma with anisotropic temperature

    SciTech Connect

    Sasagawa, Y.; Katanuma, I.; Mizoguchi, Y.; Cho, T.; Pastukhov, V. P.

    2006-12-15

    Magnetohydrodynamic stabilization of an axisymmetric mirror plasma with a magnetic divertor is studied. An equation is found for the flute modes, which includes the stabilizing influence of ion temperature anisotropy and nonparaxial magnetic fields, as well as a finite ion Larmor radius. It is shown that if the density profile is sufficiently gentle, then the nonparaxial configuration can stabilize all modes as long as ion temperature is radially uniform. This can be demonstrated even when the density vanishes on the separatrix and even for small ion Larmor radii. It is found, however, that the ion temperature gradient makes the unstable region wider; high ion temperature is required to stabilize the flute mode.

  19. Improved Intrinsic Stability of CdTe Polycrystalline Thin Film Devices

    SciTech Connect

    Albin, D.; Berniard, T.; McMahon, T.; Noufi, R.; Demtsu, S.

    2005-01-01

    A systems-driven approach linking upstream solar cell device fabrication history with downstream performance and stability has been applied to CdS/CdTe small-area device research. The best resulting initial performance (using thinner CdS, thicker CdTe, no oxygen during VCC, and the use of NP etch) was shown to simultaneously correlate with poor stability. Increasing the CdS layer thickness significantly improved stability at only a slight decrease in overall performance. It was also determined that cell perimeter effects can accelerate degradation in these devices. A ''margined'' contact significantly reduces the contribution of edge shunting to degradation, and thus yields a more accurate determination of the intrinsic stability. Pspice discrete element models demonstrate how spatially localized defects can effectively dominate degradation. Mitigation of extrinsic shunting improved stabilized efficiency degradation levels (SEDL) to near 20% in 100 C tests. Further process optimization to reduce intrinsic effects improved SEDL to better than 10% at the same stress temperatures and times.

  20. Skin improvement and stability of Echinacea purpurea dermatological formulations.

    PubMed

    Yotsawimonwat, S; Rattanadechsakul, J; Rattanadechsakul, P; Okonogi, S

    2010-10-01

    Echinacea purpurea contains many beneficial constituents for protection of skin from oxidative stress and for improving hydration of skin. This study aimed to investigate the stability and dermatological efficacy of E. purpurea cream and gel. Echinacea purpurea extract was incorporated into suitable cream and gel bases. Stability of the extract in the formulations was investigated by determining its residual total phenolic content and antioxidant activity after storage at 4°C, 30°C and 40°C for 6 months. The effect of those formulations on skin irritation, hydration level and wrinkle reduction was evaluated in 10 healthy volunteers, aged 25-40 years. The shelf lives of E. purpurea cream and gel in terms of total phenolic content and antioxidant activity were only 2 and 4 months respectively at 4°C and could be extended up to 7 months by incorporation of α-tocopherol or disodium editate. The corneometer hydration indices increased up to 10.6 AU and 11.4 AU, and the wrinkles decreased 9.47% and 14.92% because of the application of E. purpurea cream and gel for 1 month. Both formulations showed no irritation to skin. Echinacea purpurea cream and gel developed in this study were effective in improving skin hydration and reducing wrinkle, but showed low storage stability.

  1. IMPROVED SYNTHESIS OF ROOM TEMPERATURE IONIC LIQUIDS

    EPA Science Inventory

    Room temperature ionic liquids (RTILs), molten salts comprised of N-alkylimidazolium cations and various anions, have received significant attention due to their commercial potential in a variety of chemical applications especially as substitutes for conventional volatile organic...

  2. IMPROVED SYNTHESIS OF ROOM TEMPERATURE IONIC LIQUIDS

    EPA Science Inventory

    Room temperature ionic liquids (RTILs), molten salts comprised of N-alkylimidazolium cations and various anions, have received significant attention due to their commercial potential in a variety of chemical applications especially as substitutes for conventional volatile organic...

  3. Improvement of stability of polidocanol foam for nonsurgical permanent contraception.

    PubMed

    Guo, Jian Xin; Lucchesi, Lisa; Gregory, Kenton W

    2015-08-01

    Polidocanol foam (PF), used clinically as a venous sclerosant, has recently been studied as a safe and inexpensive means for permanent contraception. Delivering the sclerosant to the fallopian tubes as a foam rather than a liquid increases the surface areas and thus enhances the desired epithelial disrupting activity of the agent. However, the foam is inherently unstable and degrades with time. Therefore, increasing foam stability and thus duration of the agent exposure time could increase epithelial effect while allowing reduction in agent concentration and potential toxicity. We studied methods to improve foam properties that might improve safety and efficacy of PF for intrauterine application. Several types of microporous filters adapted to a syringe-based foaming device were used to study the effect of pore structures on the formation of PF. The foam drainage time and bubble size were characterized. The addition of benzalkonium chloride (BZK) to polidocanol was also investigated for its effects on foam characteristics. A syringe-based foaming device adapted with an inline filter produced smaller bubble PF with a longer foam drainage time. PF generated with a circular pore filter lasts longer than with a noncircular pore filter. The addition of 0.01% of BZK also improved the stability of PF. The stability of PF is affected by the pore characteristics of the filter used for foam generation and enhanced by the presence of a small amount of BZK. The improved foam, if shown to be efficacious in animal models of contraception, could lead to a safe, simple and inexpensive method alternative to surgical contraception. Copyright © 2015 Elsevier Inc. All rights reserved.

  4. Stability improvement for coil position locking of joule balance

    NASA Astrophysics Data System (ADS)

    Bai, Yang; Liu, Yongmeng; Lu, Yunfeng; Hu, Pengcheng; Wang, Dawei; Li, Zhengkun; Tan, Jiubin; Zhang, Zhonghua

    2017-08-01

    The relative vertical position locking precision between the exciting and suspended coils is an important uncertainty for the Planck constant traceability in joule balance. In order to improve the relative vertical position locking precision, several stability experiments are conducted. The stability characteristics of the suspended and exciting coils are measured using a six-axis laser interferometer system; meanwhile, the effectiveness of the active vibration isolation table is measured using a vibration measurement sensor. The piezoelectric ceramic actuators with PID controller are used to compensate the relative vertical displacement drifts while a six-axis laser interferometer system is used to measure the positions of two coils. Experimental results show that the relative vertical position is stably locked.

  5. Oscillator frequency stability improvement by means of negative feedback.

    PubMed

    Goryachev, Maxim; Galliou, Serge; Abbé, Philippe; Komine, Vadim

    2011-11-01

    A novel, simple method is proposed to increase the frequency stability of an oscillator. An additional negative feedback is used in combination with the positive loop of the harmonic oscillator to decrease the phase sensitivity to fluctuations of parameters other than the resonator. The main advantage of the proposed correction approach is that it does not require expensive external elements such as mixers or resonators. The validity of the method is theoretically demonstrated on a Colpitts oscillator using the control system theory approach and numerical simulations, and is experimentally verified with phase noise measurements of an actual oscillator-mockup. It is shown that the medium-term frequency stability can be easily improved by a factor of ten.

  6. Pico-Kelvin thermometry and temperature stabilization using a resonant optical cavity.

    PubMed

    Tan, Si; Wang, Suwen; Saraf, Shailendhar; Lipa, John A

    2017-02-20

    Ultra-high sensitivity temperature sensing and stable thermal control are crucial for many science experiments testing fundamental theories to high precision. Here we report the first pico-kevin scale thermometer operating at room temperature with an exceptionally low theoretical noise figure of ~70pK/Hz at 1 Hz and a high dynamic range of ~500 K. We have experimentally demonstrated a temperature sensitivity of <3.8nK/Hz at 1 Hz near room temperature, which is an order of magnitude improvement over the state of the art. We have also demonstrated an ultra-high stability thermal control system using this thermometer, achieving 3.7 nK stability at 1 s and ∼ 120 pK at 104 s, which is 10-100 times more stable than the state of the art. With some upgrades to this proof-of-principle device, we can expect it to be used for very high resolution tests of special relativity and in critical point phenomena.

  7. Structural stability of E. coli transketolase to temperature and pH denaturation.

    PubMed

    Jahromi, Raha R F; Morris, Phattaraporn; Martinez-Torres, Ruben J; Dalby, Paul A

    2011-09-10

    We have previously shown that the denaturation of TK with urea follows a non-aggregating though irreversible denaturation pathway in which the cofactor binding appears to become altered but without dissociating, then followed at higher urea by partial denaturation of the homodimer prior to any further unfolding or dissociation of the two monomers. Urea is not typically present during biocatalysis, whereas access to TK enzymes that retain activity at increased temperature and extreme pH would be useful for operation under conditions that increase substrate and product stability or solubility. To provide further insight into the underlying causes of its deactivation in process conditions, we have characterised the effects of temperature and pH on the structure, stability, aggregation and activity of Escherichia coli transketolase. The activity of TK was initially found to progressively improve after pre-incubation at increasing temperatures. Loss of activity at higher temperature and low pH resulted primarily from protein denaturation and subsequent irreversible aggregation. By contrast, high pH resulted in the formation of a native-like state that was only partially inactive. The apo-TK enzyme structure content also increased at pH 9 to converge on that of the holo-TK. While cofactor dissociation was previously proposed for high pH deactivation, the observed structural changes in apo-TK but not holo-TK indicate a more complex mechanism.

  8. 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.

  9. Flexible all-carbon photovoltaics with improved thermal stability

    SciTech Connect

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

    2015-04-15

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

  10. Electrochemically polymerized conjugated polymer films: Stability improvement and surface functionalization

    NASA Astrophysics Data System (ADS)

    Wei, Bin

    Conjugated polymers have been widely used in various applications including organic solar cells, electrochromic devices, chemical sensors, and biomedical devices. Poly(3,4-ethylenedioxythiophene) (PEDOT) and its derivatives have received considerable interest because of their low oxidation potential, relatively high chemical stability, and high conductivity. Electrochemical deposition is a convenient method for precisely fabricating conjugated polymer thin films. Here, we report the stability improvement and surface functionalization of electrochemically polymerized PEDOT films. The long-term performance of PEDOT coatings is limited by their relatively poor stability on various inorganic substrates. Two different methods were used to improve the stability of PEDOT coatings, one involved using carboxylic acid functionalized EDOT (EDOT-acid) as adhesion promoter. EDOT-acid molecules were chemically bonded onto activated metal oxide substrates via chemisorption. PEDOT was then polymerized onto the EDOT-acid modified substrates, forming covalently bonded coatings. An aggressive ultrasonication test confirmed the significantly improved adhesion of the PEDOT films on electrodes with EDOT-acid treatment over those without treatment. The other method was to use an octa-ProDOT-functionalized POSS derivative (POSSProDOT) as cross-linker. PEDOT copolymer films were electrochemically deposited with various concentrations of POSS-ProDOT. The optical, morphological and electrochemical properties of the copolymer films could be systematically tuned with the incorporation of POSS-ProDOT. Significantly enhanced electrochemical and mechanical stability of the copolymers were observed at intermediate levels of POSS-ProDOT content (3.1 wt%) via chronic stimulation tests. Surface functionalization of conducting polymer films provides a potential means for systematically tailoring their chemical and physical properties. We have synthesized, polymerized and characterized a dialkene

  11. Tailless aircraft performance improvements with relaxed static stability

    NASA Technical Reports Server (NTRS)

    Ashkenas, Irving L.; Klyde, David H.

    1989-01-01

    The purpose is to determine the tailless aircraft performance improvements gained from relaxed static stability, to quantify this potential in terms of range-payload improvements, and to identify other possible operational and handling benefits or problems. Two configurations were chosen for the study: a modern high aspect ratio, short-chord wing proposed as a high-altitude long endurance (HALE) remotely piloted vehicle; a wider, lower aspect ratio, high volume wing suitable for internal stowage of all fuel and payload required for a manned long-range reconnaissance mission. Flying at best cruise altitude, both unstable configurations were found to have a 14 percent improvement in range and a 7 to 9 percent improvement in maximum endurance compared to the stable configurations. The unstable manned configuration also shows a 15 percent improvement in the 50 ft takeoff obstacle distance and an improved height response to elevator control. However, it is generally more deficient in control power due to its larger adverse aileron yaw and its higher takeoff and landing lift coefficient C(sub L), both due to the downward trimmed (vs. upward trimmed for stable configurations) trailing edge surfaces.

  12. Polyurethane adhesive with improved high temperature properties

    NASA Technical Reports Server (NTRS)

    Stuckey, J. M.

    1977-01-01

    A polyurethane resin with paste activator, capable of providing useful bond strengths over the temperature range of -184 C to 149 C, is described. The adhesive system has a pot life of over one hour. Tensile shear strength ratings are given for various adhesive formulations.

  13. Robust enzyme design: bioinformatic tools for improved protein stability.

    PubMed

    Suplatov, Dmitry; Voevodin, Vladimir; Švedas, Vytas

    2015-03-01

    The ability of proteins and enzymes to maintain a functionally active conformation under adverse environmental conditions is an important feature of biocatalysts, vaccines, and biopharmaceutical proteins. From an evolutionary perspective, robust stability of proteins improves their biological fitness and allows for further optimization. Viewed from an industrial perspective, enzyme stability is crucial for the practical application of enzymes under the required reaction conditions. In this review, we analyze bioinformatic-driven strategies that are used to predict structural changes that can be applied to wild type proteins in order to produce more stable variants. The most commonly employed techniques can be classified into stochastic approaches, empirical or systematic rational design strategies, and design of chimeric proteins. We conclude that bioinformatic analysis can be efficiently used to study large protein superfamilies systematically as well as to predict particular structural changes which increase enzyme stability. Evolution has created a diversity of protein properties that are encoded in genomic sequences and structural data. Bioinformatics has the power to uncover this evolutionary code and provide a reproducible selection of hotspots - key residues to be mutated in order to produce more stable and functionally diverse proteins and enzymes. Further development of systematic bioinformatic procedures is needed to organize and analyze sequences and structures of proteins within large superfamilies and to link them to function, as well as to provide knowledge-based predictions for experimental evaluation.

  14. Improved intravital microscopy via synchronization of respiration and holder stabilization

    NASA Astrophysics Data System (ADS)

    Lee, Sungon; Vinegoni, Claudio; Feruglio, Paolo Fumene; Weissleder, Ralph

    2012-09-01

    A major challenge in high-resolution intravital confocal and multiphoton microscopy is physiologic tissue movement during image acquisition. Of the various physiological sources of movement, respiration has arguably the largest and most wide-ranging effect. We describe a technique for achieving stabilized microscopy imaging using a dual strategy. First, we designed a mechanical stabilizer for constraining physical motion; this served to simultaneously increase the in-focus range over which data can be acquired as well as increase the reproducibility of imaging a certain position within each confocal imaging plane. Second, by implementing a retrospective breathing-gated imaging modality, we performed selective image extraction gated to a particular phase of the respiratory cycle. Thanks to the high reproducibility in position, all gated images presented a high degree of correlation over time. The images obtained using this technique not only showed significant improvements over images acquired without the stabilizer, but also demonstrated accurate in vivo imaging during longitudinal studies. The described methodology is easy to implement with any commercial imaging system, as are used by most biological imaging laboratories, and can be used for both confocal and multiphoton laser scanning microscopy.

  15. A simple method to improve the stability of docetaxel micelles

    PubMed Central

    Zhang, Lan; Tan, LiWei; Chen, LiJuan; Chen, XiaoXin; Long, ChaoFeng; Peng, JinRong; Qian, ZhiYong

    2016-01-01

    Self-assembled polymeric micelles have been widely applied in drug delivery systems. In this study, we found that pH value of micellar system solution was the decisive factor of physical stability. Furthermore, the weak basic solution could maintain the solution clarification for a relative long time. To investigate the stability of polymeric micelles in different pH solutions, the micellar particle size and the docetaxel content remaining in solution were detected at predetermined time points. The crystallographic assay of freeze-drying powder was characterized by an X-ray diffractometer. In vitro release results indicated that the PBS had little influence on the sustained-release effect of docetaxel-loaded polymeric micelles (DPM). Besides, the safety of micellar formulation was determined by an MTT assay on HEK293 cells, and the anti-tumor activity was tested on MCF-7 cells. The results demonstrated that DPM adjusted with PBS (DPM (PBS)) was of low toxicity and maintained the effectiveness of docetaxel. In vivo antitumor results indicated that DPM (PBS) had better antitumor efficacy than common docetaxel injection (DTX). Thus it was concluded that regulation of micellar solution PH by PBS is a safe and effective method to improve the physical stability of DPM. It might promote the application of micellar formulation in clinical applications. PMID:27833135

  16. Impact of different wort boiling temperatures on the beer foam stabilizing properties of lipid transfer protein 1.

    PubMed

    Van Nierop, Sandra N E; Evans, David E; Axcell, Barry C; Cantrell, Ian C; Rautenbach, Marina

    2004-05-19

    Beer consumers demand satisfactory and consistent foam stability; thus, it is a high priority for brewers. Beer foam is stabilized by the interaction between certain beer proteins, including lipid transfer protein 1 (LTP1), and isomerized hop alpha-acids, but destabilized by lipids. In this study it was shown that the wort boiling temperature during the brewing process was critical in determining the final beer LTP1 content and conformation. LTP1 levels during brewing were measured by an LTP1 ELISA, using antinative barley LTP1 polyclonal antibodies. It was observed that the higher wort boiling temperatures ( approximately 102 degrees C), resulting from low altitude at sea level, reduced the final beer LTP1 level to 2-3 microg/mL, whereas the lower wort boiling temperatures ( approximately 96 degrees C), resulting from higher altitudes (1800 m), produced LTP1 levels between 17 and 35 microg/mL. Low levels of LTP1 in combination with elevated levels of free fatty acids (FFA) resulted in poor foam stability, whereas beer produced with low levels of LTP1 and FFA had satisfactory foam stability. Previous studies indicated the need for LTP1 denaturing to improve its foam stabilizing properties. However, the results presented here show that LTP1 denaturation reduces its ability to act as a binding protein for foam-damaging FFA. These investigations suggest that wort boiling temperature is an important factor in determining the level and conformation of LTP1, thereby favoring satisfactory beer foam stability.

  17. Stability improvement of natural food colors: Impact of amino acid and peptide addition on anthocyanin stability in model beverages.

    PubMed

    Chung, Cheryl; Rojanasasithara, Thananunt; Mutilangi, William; McClements, David Julian

    2017-03-01

    Anthocyanins are prone to chemical degradation and color fading in the presence of vitamin C. The potential of three amino acids (l-phenylalanine, l-tyrosine, l-tryptophan) and a polypeptide (ε-poly-l-lysine) in prolonging the color stability of purple carrot anthocyanins (0.025%) in model beverages (0.05% l-ascorbic acid, citric acid, pH 3.0) stored at elevated temperature (40°C/7 days) was examined. In the absence of amino acids or peptides, anthocyanin degraded at first-order reaction rate. Addition of amino acids or peptide (0.1%) increased the color stability of anthocyanins, with the most significant improvement observed for l-tryptophan. The average half-life of anthocyanin color increased from 2 days to 6 days with l-tryptophan addition. Fluorescence quenching measurements revealed that the l-tryptophan interacted with anthocyanins mainly through hydrogen bonding, although some hydrophobic interaction may also have been involved. Overall, this study suggests that amino acid or peptide addition may prolong the color stability of anthocyanin in beverage products. Copyright © 2016 Elsevier Ltd. All rights reserved.

  18. Improved phase stability of formamidinium lead triiodide perovskite by strain relaxation

    DOE PAGES

    Zheng, Xiaojia; Wu, Congcong; Jha, Shikhar K.; ...

    2016-10-18

    Though formamidinium lead triiodide (FAPbI3) possesses a suitable band gap and good thermal stability, the phase transition from the pure black perovskite phase (α-phase) to the undesirable yellow nonperovskite polymorph (δ-phase) at room temperature, especially under humid air, hinders its practical application. Here, we investigate the intrinsic instability mechanism of the α-phase at ambient temperature and demonstrate the existence of an anisotropic strained lattice in the (111) plane that drives phase transformation into the δ-phase. Methylammonium bromide (MABr) alloying (or FAPbI3-MABr) was found to cause lattice contraction, thereby balancing the lattice strain. This led to dramatic improvement in the stabilitymore » of α-FAPbI3. As a result, solar cells fabricated using FAPbI3-MABr demonstrated significantly enhanced stability under the humid air.« less

  19. PMR polyimides with improved high temperature performance

    NASA Technical Reports Server (NTRS)

    Vannucci, R. D.; Alston, W. B.

    1975-01-01

    Studies were performed to investigate the effect of substituting a hexafluoro isopropyl idene connecting group for a carbonyl group of a PMR polyimide monomeric reactant on the thermo-mechanical properties processability of graphite fiber reinforced PMR polyimide composites. Composites were fabricated utilizing PMR methodology. Monomeric reactant solutions of various stoichiometric ratios were used to impregnate Hercules HTS graphite fiber. The processing characteristics and elevated temperature (600 F) mechanical properties of the composites are described.

  20. Improvement of test methodology for evaluating diesel fuel stability

    SciTech Connect

    Gutman, M.; Tartakovsky, L.; Kirzhner, Y.; Zvirin, Y.; Luria, D.; Weiss, A.; Shuftan, M.

    1995-05-01

    The storage stability of diesel fuel has been extensively investigated for many years under laboratory conditions. Although continuous efforts have been made to improve testing techniques, there does not yet exist a generally accepted correlation between laboratory methods (such as chemical analysis of the fuel) and actual diesel engine tests. A testing method was developed by the Technion Internal Combustion Engines Laboratory (TICEL), in order to address this problem. The test procedure was designed to simulate diesel engine operation under field conditions. It is based on running a laboratory-modified single cylinder diesel engine for 50 h under cycling operating conditions. The overall rating of each test is based on individual evaluation of the deposits and residue formation in the fuel filter, nozzle body and needle, piston head, piston rings, exhaust valve, and combustion chamber (six parameters). Two methods for analyzing the test results were used: objective, based on measured data, and subjective, based on visual evaluation results of these deposits by a group of experts. Only the residual level in the fuel filter was evaluated quantitatively by measured results. In order to achieve higher accuracy of the method, the test procedure was improved by introducing the measured results of nozzle fouling as an additional objective evaluating (seventh) parameter. This factor is evaluated on the basis of the change in the air flow rate through the nozzle before and after the complete engine test. Other improvements in the method include the use of the nozzle assembly photograph in the test evaluation, and representation of all seven parameters on a continuous scale instead of the discrete scale used anteriorly, in order to achieve higher accuracy. This paper also contains the results obtained by application of this improved fuel stability test for a diesel fuel stored for a five-year period.

  1. Improved high temperature creep resistant austenitic alloy

    DOEpatents

    Maziasz, P.J.; Swindeman, R.W.; Goodwin, G.M.

    1988-05-13

    An improved austenitic alloy having in wt% 19-21 Cr, 30-35 Ni, 1.5-2.5 Mn, 2-3 Mo, 0.1-0.4 Si, 0.3-0.5 Ti, 0.1-0.3 Nb, 0.1-0.5 V, 0.001-0.005 P, 0.08-0.12 C, 0.01-0.03 N, 0.005-0.01 B and the balance iron that is further improved by annealing for up to 1 hour at 1150-1200/degree/C and then cold deforming 5-15%. The alloy exhibits dramatically improved creep rupture resistance and ductility at 700/degree/C. 2 figs.

  2. Improved Refractometer for Measuring Temperatures of Drops

    NASA Technical Reports Server (NTRS)

    Naqwi, Amir A.

    2004-01-01

    The Dual Rainbow refractometer is an enhanced version of the Rainbow refractometer, which is added to, and extends the capabilities of, a phase Doppler particle analyzer (PDPA). A PDPA utilizes pairs of laser beams to measure individual components of velocity and sizes of drops in a spray. The Rainbow-refractometer addition measures the temperatures of individual drops. The designs of prior versions of the Rainbow refractometer have required substantial modifications of PDPA transmitting optics, plus dedicated lasers as sources of illumination separate from, and in addition to, those needed for PDPA measurements. The enhancement embodied in the Dual Rainbow refractometer eliminates the need for a dedicated laser and confers other advantages as described below. A dedicated laser is no longer needed because the Dual Rainbow refractometer utilizes one of the pairs of laser beams already present in a PDPA. Hence, the design of the Dual Rainbow refractometer simplifies the task of upgrading PDPA hardware to enable measurement of temperature. Furthermore, in a PDPA/Dual Rainbow refractometer system, a single argon-ion laser with three main wavelengths can be used to measure the temperatures, sizes, and all three components of velocity (in contradistinction to only two components of velocity in a prior PDPA/Rainbow refractometer system). In order to enable the Dual Rainbow refractometer to utilize a pair of PDPA laser beams, it was necessary to (1) find a location for the refractometer receiver, such that the combined rainbow patterns of two laser beams amount to a pattern identical to that of a single beam, (2) adjust the polarization of the two beams to obtain the strongest rainbow pattern, and (3) find a location for the PDPA receiver to obtain a linear relationship between the measured phase shift and drop size.

  3. A Review of Voltage Stability Assessment Techniques with an Improved Voltage Stability Indicator

    NASA Astrophysics Data System (ADS)

    Danish, Mir Sayed Shah; Yona, Atsushi; Senjyu, Tomonobu

    2015-04-01

    A blackout can take place in entire power system or a part of the system due to extreme voltage instability (voltage collapse) that can appear abruptly. Instability prediction and continuous monitoring of the power system performance is, therefore, known exigent. This paper is conducted with a broad overview of the voltage stability indices, which are previously studied in the literature, and have the same foundation during their formulation. Afterward, an improved voltage stability indicator is introduced as a result of the multi-criteria integration and enhancement of the original indices by employing linear algebra methods. It is found that the proposed algorithm can overcome on the probable limitations from calculating point view. Then comparative analysis of the indices is presented in order to reach a unique consensus about the typical techniques of modal analysis (sensitivity, eigenvalue, right eigenvectors, and bus participation factor) as a precise algorithm. Finally, the IEEE 14-bus, and 30-bus test systems are selected to verify the algorithm, and compare the performance of the improved indicator approach with the existing indices.

  4. Improving cabazitaxel chemical stability in parenteral lipid emulsions using cholesterol.

    PubMed

    Shao, Yanjie; Zhang, Chungang; Yao, Qing; Wang, Yueqi; Tian, Bin; Tang, Xing; Wang, Yanjiao

    2014-02-14

    Intravenous lipid emulsions of cabazitaxel (CLEs) with a high stability were prepared by adding cholesterol (CH) to provide a new and more suitable delivery system for its administration. The factors affecting CLEs, such as the solubility of cabazitaxel in various oils, different kinds of lecithin, pH, different types of oil phases, and different concentrations of lipoid E80®, CH and poloxamer 188 were investigated systematically. The degradation of cabazitaxel in aqueous solution and lipid emulsion both followed pseudo first-order kinetics. A degradation mechanism was suggested by the U-shaped pH-rate profile of cabazitaxel. A formulation containing 0.5% (w/v) CH and another formulation without CH were made to investigate the protective influence of CH on the chemical stability of CLEs. The activation energy of the two formulations was calculated to be 65.74±6.88 and 54.24±1.43 kJ/mol (n=3), respectively. Compared with the untreated CH, the shelf-life of cabazitaxel with added CH was longer, namely 134.0±23.4 days versus 831.4±204.4 days (n=3) at 4 °C. This indicates that the addition of CH significantly improved the lifetime of cabazitaxel in intravenous lipid emulsions. The hydrogen bonding that takes place between cabazitaxel and CH accounts for the protective effect of CH on the chemical stability of CLEs in two ways: preventing cabazitaxel from leaking and hydrolyzing in aqueous solution and hindering hydrolysis in the oil phase. Finally, the hypothesis was confirmed by LC/TOFMS and Fourier-transform infrared-spectroscopy. As a result, CLEs were obtained successfully by the addition of CH and were stable enough to allow further research.

  5. Hydrolytic Stability of 3-Aminopropylsilane Coupling Agent on Silica and Silicate Surfaces at Elevated Temperatures.

    PubMed

    Okhrimenko, Denis V; Budi, Akin; Ceccato, Marcel; Cárdenas, Marité; Johansson, Dorte B; Lybye, Dorthe; Bechgaard, Klaus; Andersson, Martin P; Stipp, Susan L S

    2017-03-08

    3-Aminopropylsilane (APS) coupling agent is widely used in industrial, biomaterial, and medical applications to improve adhesion of polymers to inorganic materials. However, during exposure to elevated humidity and temperature, the deposited APS layers can decompose, leading to reduction in coupling efficiency, thus decreasing the product quality and the mechanical strength of the polymer-inorganic material interface. Therefore, a better understanding of the chemical state and stability of APS on inorganic surfaces is needed. In this work, we investigated APS adhesion on silica wafers and compared its properties with those on complex silicate surfaces such as those used by industry (mineral fibers and fiber melt wafers). The APS was deposited from aqueous and organic (toluene) solutions and studied with surface sensitive techniques, including X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), streaming potential, contact angle, and spectroscopic ellipsometry. APS configuration on a model silica surface at a range of coverages was simulated using density functional theory (DFT). We also studied the stability of adsorbed APS during aging at high humidity and elevated temperature. Our results demonstrated that APS layer formation depends on the choice of solvent and substrate used for deposition. On silica surfaces in toluene, APS formed unstable multilayers, while from aqueous solutions, thinner and more stable APS layers were produced. The chemical composition and substrate roughness influence the amount of deposited APS. More APS was deposited and its layers were more stable on fiber melt than on silica wafers. The changes in the amount of adsorbed APS can be successfully monitored by streaming potential. These results will aid in improving industrial- and laboratory-scale APS deposition methods and increasing adhesion and stability, thus increasing the quality and effectiveness of materials where APS is used as a coupling agent.

  6. Highly conductive carbon nanotube buckypapers with improved doping stability via conjugational cross-linking.

    PubMed

    Chen, I-Wen Peter; Liang, Richard; Zhao, Haibo; Wang, Ben; Zhang, Chuck

    2011-12-02

    Carbon nanotube (CNT) sheets or buckypapers have demonstrated promising electrical conductivity and mechanical performance. However, their electrical conductivity is still far below the requirements for engineering applications, such as using as a substitute for copper mesh, which is currently used in composite aircraft structures for lightning strike protection. In this study, different CNT buckypapers were stretched to increase their alignment, and then subjected to conjugational cross-linking via chemical functionalization. The conjugationally cross-linked buckypapers (CCL-BPs) demonstrated higher electrical conductivity of up to 6200 S cm( - 1), which is more than one order increase compared to the pristine buckypapers. The CCL-BPs also showed excellent doping stability in over 300 h in atmosphere and were resistant to degradation at elevated temperatures. The tensile strength of the stretched CCL-BPs reached 220 MPa, which is about three times that of pristine buckypapers. We attribute these property improvements to the effective and stable conjugational cross-links of CNTs, which can simultaneously improve the electrical conductivity, doping stability and mechanical properties. Specifically, the electrical conductivity increase resulted from improving the CNT alignment and inter-tube electron transport capability. The conjugational cross-links provide effective 3D conductive paths to increase the mobility of electrons among individual nanotubes. The stable covalent bonding also enhances the thermal stability and load transfer. The significant electrical and mechanical property improvement renders buckypaper a multifunctional material for various applications, such as conducting composites, battery electrodes, capacitors, etc.

  7. Improving Separation Assurance Stability Through Trajectory Flexibility Preservation

    NASA Technical Reports Server (NTRS)

    Idris, Husni; Shen, Ni; Wing, David J.

    2010-01-01

    New information and automation technologies are enabling the distribution of tasks and decisions from the service providers to the users of the air traffic system, with potential capacity and cost benefits. This distribution of tasks and decisions raises the concern that independent user actions will decrease the predictability and increase the complexity of the traffic system, hence inhibiting and possibly reversing any potential benefits. One such concern is the adverse impact of uncoordinated actions by individual aircraft on the stability of separation assurance. For example, individual aircraft performing self-separation may resolve predicted losses of separation or conflicts with some traffic, only to result in secondary conflicts with other traffic or with the same traffic later in time. In answer to this concern, this paper proposes metrics for preserving user trajectory flexibility to be used in self-separation along with other objectives. The hypothesis is that preserving trajectory flexibility will naturally reduce the creation of secondary conflicts by bringing about implicit coordination between aircraft. The impact of using these metrics on improving self-separation stability is investigated by measuring the impact on secondary conflicts. The scenarios analyzed include aircraft in en route airspace with each aircraft meeting a required time of arrival in a twenty minute time horizon while maintaining separation from the surrounding traffic and using trajectory flexibility metrics to mitigate the risk of secondary conflicts. Preliminary experiments showed promising results in that the trajectory flexibility preservation reduced the potential for secondary conflicts.

  8. 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.

  9. Hot melt extrusion for amorphous solid dispersions: temperature and moisture activated drug-polymer interactions for enhanced stability.

    PubMed

    Sarode, Ashish L; Sandhu, Harpreet; Shah, Navnit; Malick, Waseem; Zia, Hossein

    2013-10-07

    Hot melt extrudates (HMEs) of indomethacin (IND) with Eudragit EPO and Kollidon VA 64 and those of itraconazole (ITZ) with HPMCAS-LF and Kollidon VA 64 were manufactured using a Leistritz twin screw extruder. The milled HMEs were stored at controlled temperature and humidity conditions. The samples were collected after specified time periods for 3 months. The stability of amorphous HMEs was assessed using moisture analysis, thermal evaluation, powder X-ray diffraction, FTIR, HPLC, and dissolution study. In general, the moisture content increased with time, temperature, and humidity levels. Amorphous ITZ was physically unstable at very high temperature and humidity levels, and its recrystallization was detected in the HMEs manufactured using Kollidon VA 64. Although physical stability of IND was better sustained by both Eudragit EPO and Kollidon VA 64, chemical degradation of the drug was identified in the stability samples of HMEs with Eudragit EPO stored at 50 °C. The dissolution rates and the supersaturation levels were significantly decreased for the stability samples in which crystallization was detected. Interestingly, the supersaturation was improved for the stability samples of IND:Eudragit EPO and ITZ:HPMCAS-LF, in which no physical or chemical instability was observed. This enhancement in supersaturation was attributed to the temperature and moisture activated electrostatic interactions between the drugs and their counterionic polymers.

  10. Improving Kinetic or Thermodynamic Stability of an Azoreductase by Directed Evolution

    PubMed Central

    Brissos, Vânia; Gonçalves, Nádia; Melo, Eduardo P.; Martins, Lígia O.

    2014-01-01

    Protein stability arises from a combination of factors which are often difficult to rationalise. Therefore its improvement is better addressed through directed evolution than by rational design approaches. In this study, five rounds of mutagenesis/recombination followed by high-throughput screening (≈10,000 clones) yielded the hit 1B6 showing a 300-fold higher half life at 50°C than that exhibited by the homodimeric wild type PpAzoR azoreductase from Pseudomonas putida MET94. The characterization using fluorescence, calorimetry and light scattering shows that 1B6 has a folded state slightly less stable than the wild type (with lower melting and optimal temperatures) but in contrast is more resistant to irreversible denaturation. The superior kinetic stability of 1B6 variant was therefore related to an increased resistance of the unfolded monomers to aggregation through the introduction of mutations that disturbed hydrophobic patches and increased the surface net charge of the protein. Variants 2A1 and 2A1-Y179H with increased thermodynamic stability (10 to 20°C higher melting temperature than wild type) were also examined showing the distinctive nature of mutations that lead to improved structural robustness: these occur in residues that are mostly involved in strengthening the solvent-exposed loops or the inter-dimer interactions of the folded state. PMID:24475252

  11. Storage stability and improvement of intermediate moisture foods, phase 2

    NASA Technical Reports Server (NTRS)

    Labuza, T. P.

    1975-01-01

    Methods for improvement of shelf-life stability of intermediate moisture foods are considered. It was found that vitamin C is the most limiting vitamin from a nutritional standpoint with its rate of destruction increasing with a sub w. Techniques for microbial challenge studies were developed. It was shown that organisms have a higher growth a sub w limit if the IMF is prepared by the adsorption process and long times are needed for challenge studies. Several alternative antimycotic systems were found. It was also found that the vegetative cells of pathogens have a maximum heat resistance in the IMF a sub w range. If glycols are in the formula, the IMF should have as high an a sub w as possible. The reverse is true if lipid oxidation occurs. In addition, to prevent rancidity, antioxidants and a low O2 atmosphere are necessary. The package also must be a good moisture barrier.

  12. Improvement of vehicle roll stability by varying suspension properties

    NASA Astrophysics Data System (ADS)

    Shim, Taehyun; Velusamy, Pradheep C.

    2011-02-01

    Vehicle roll dynamics are strongly influenced by suspension properties such as roll centre height, roll steer, and roll camber. In this paper, the effects of suspension properties on vehicle roll response have been investigated using a multi-body vehicle dynamics programme. Roll dynamics of a vehicle model with MacPherson (front) and multilink (rear) suspensions were evaluated for the fishhook manoeuvre and variations of its roll response due to changes in the suspension properties were assessed by quantitatively analysing the vehicle response through simulation. Critical suspension design parameters for vehicle roll dynamics were identified and adjusted to improve roll stability of the vehicle model with passive suspension. Design of experiments has been used for identifying critical hardpoints affecting the suspension parameters, and optimisation techniques were employed for parameter optimisation. This approach provides a viable alternative to costlier active control systems for economy-class vehicles.

  13. Low temperature stabilization process for production of carbon fiber having structural order

    DOEpatents

    Rios, Orlando; McGuire, Michael Alan; More, Karren Leslie; Tenhaeff, Wyatt Evan; Menchhofer, Paul A.; Paulauskas, Felix Leonard

    2017-08-15

    A method for producing a carbon fiber, the method comprising: (i) subjecting a continuous carbon fiber precursor having a polymeric matrix in which strength-enhancing particles are incorporated to a stabilization process during which the carbon fiber precursor is heated to within a temperature range ranging from the glass transition temperature to no less than 20.degree. C. below the glass transition temperature of the polymeric matrix, wherein the maximum temperature employed in the stabilization process is below 400.degree. C., for a processing time within said temperature range of at least 1 hour in the presence of oxygen and in the presence of a magnetic field of at least 1 Tesla, while said carbon fiber precursor is held under an applied axial tension; and (ii) subjecting the stabilized carbon fiber precursor, following step (i), to a carbonization process. The stabilized carbon fiber precursor, resulting carbon fiber, and articles made thereof are also described.

  14. Modeling Physical Stability of Amorphous Solids Based on Temperature and Moisture Stresses.

    PubMed

    Zhu, Donghua Alan; Zografi, George; Gao, Ping; Gong, Yuchuan; Zhang, Geoff G Z

    2016-09-01

    Isothermal microcalorimetry was utilized to monitor the crystallization process of amorphous ritonavir (RTV) and its hydroxypropylmethylcellulose acetate succinate-based amorphous solid dispersion under various stressed conditions. An empirical model was developed: ln(τ)=ln(A)+EaRT-b⋅wc, where τ is the crystallization induction period, A is a pre-exponential factor, Ea is the apparent activation energy, b is the moisture sensitivity parameter, and wc is water content. To minimize the propagation of errors associated with the estimates, a nonlinear approach was used to calculate mean estimates and confidence intervals. The physical stability of neat amorphous RTV and RTV in hydroxypropylmethylcellulose acetate succinate solid dispersions was found to be mainly governed by the nucleation kinetic process. The impact of polymers and moisture on the crystallization process can be quantitatively described by Ea and b in this Arrhenius-type model. The good agreement between the measured values under some less stressful test conditions and those predicted, reflected by the slope and R(2) of the correlation plot of these 2 sets of data on a natural logarithm scale, indicates its predictability of long-term physical stability of amorphous RTV in solid dispersions. To further improve the model, more understanding of the impact of temperature and moisture on the amorphous physical stability and fundamentals regarding nucleation and crystallization is needed.

  15. Stability of whey-protein-stabilized oil-in-water emulsions during chilled storage and temperature cycling.

    PubMed

    Kiokias, Sotirios; Reiffers-Magnani, Christel K; Bot, Arjen

    2004-06-16

    The stability of heat-treated and/or acidified, partly-crystalline-fat-based, whey-protein-stabilized oil-in-water (o/w) emulsions against partial coalescence was investigated during chilled storage (at 5 degrees C) and repeated temperature cycling (three times between 5 and 25 degrees C). Experiments focused on the evolution of firmness and droplet size (using pulsed field gradient NMR and scanning electron microscopy). Besides the effects of denaturation and/or acidification, the influence of the droplet size of the dispersed phase on emulsion stability was investigated also. It was found that heat treatment or acidification before emulsification led to unstable emulsions during temperature cycling, whereas heat treatment after acidification resulted in stable emulsions.

  16. Improved mass constraints in the MSSM from vacuum stability

    NASA Astrophysics Data System (ADS)

    Dasgupta, Indranil; Rademacher, Ricardo; Suranyi, Peter

    1999-02-01

    Using a simple numerical method, we compute the stability of the MSSM vacuum with respect to tunneling. The stability criterion is then used to put restrictions on the mass parameters. These restrictions are necessary conditions for the vacuum stability and complement the existing sufficiency conditions obtained analytically.

  17. Structural Stabilization and Functional Improvement of Horseradish Peroxidase upon Modification of Accessible Lysines: Experiments and Simulation

    PubMed Central

    Mogharrab, Navid; Ghourchian, Hedayatollah; Amininasab, Mehriar

    2007-01-01

    Horseradish peroxidase (HRP) is an important heme enzyme with enormous medical diagnostic, biosensing, and biotechnological applications. Thus, any improvement in the applicability and stability of the enzyme is potentially interesting. We previously reported that covalent attachment of an electron relay (anthraquinone 2-carboxylic acid) to the surface-exposed Lys residues successfully improves electron transfer properties of HRP. Here we investigated structural and functional consequences of this modification, which alters three accessible charged lysines (Lys-174, Lys-232, and Lys-241) to the hydrophobic anthraquinolysine residues. Thermal denaturation and thermoinactivation studies demonstrated that this kind of modification enhances the conformational and operational stability of HRP. The melting temperature increased 3°C and the catalytic efficiency enhanced by 80%. Fluorescence and circular dichroism investigations suggest that the modified HRP benefits from enhanced aromatic packing and more buried hydrophobic patches as compared to the native one. Molecular dynamics simulations showed that modification improves the accessibility of His-42 and the heme prosthetic group to the peroxide and aromatic substrates, respectively. Additionally, the hydrophobic patch, which functions as a binding site or trap for reducing aromatic substrates, is more extended in the modified enzyme. In summary, this modification produces a new derivative of HRP with enhanced electron transfer properties, catalytic efficiency, and stability for biotechnological applications. PMID:17114227

  18. Selection for Protein Kinetic Stability Connects Denaturation Temperatures to Organismal Temperatures and Provides Clues to Archaean Life

    PubMed Central

    Romero-Romero, M. Luisa; Risso, Valeria A.; Martinez-Rodriguez, Sergio; Gaucher, Eric A.; Ibarra-Molero, Beatriz; Sanchez-Ruiz, Jose M.

    2016-01-01

    The relationship between the denaturation temperatures of proteins (Tm values) and the living temperatures of their host organisms (environmental temperatures: TENV values) is poorly understood. Since different proteins in the same organism may show widely different Tm’s, no simple universal relationship between Tm and TENV should hold, other than Tm≥TENV. Yet, when analyzing a set of homologous proteins from different hosts, Tm’s are oftentimes found to correlate with TENV’s but this correlation is shifted upward on the Tm axis. Supporting this trend, we recently reported Tm’s for resurrected Precambrian thioredoxins that mirror a proposed environmental cooling over long geological time, while remaining a shocking ~50°C above the proposed ancestral ocean temperatures. Here, we show that natural selection for protein kinetic stability (denaturation rate) can produce a Tm↔TENV correlation with a large upward shift in Tm. A model for protein stability evolution suggests a link between the Tm shift and the in vivo lifetime of a protein and, more specifically, allows us to estimate ancestral environmental temperatures from experimental denaturation rates for resurrected Precambrian thioredoxins. The TENV values thus obtained match the proposed ancestral ocean cooling, support comparatively high Archaean temperatures, and are consistent with a recent proposal for the environmental temperature (above 75°C) that hosted the last universal common ancestor. More generally, this work provides a framework for understanding how features of protein stability reflect the environmental temperatures of the host organisms. PMID:27253436

  19. Factors affecting the stability of drug-loaded polymeric micelles and strategies for improvement

    NASA Astrophysics Data System (ADS)

    Zhou, Weisai; Li, Caibin; Wang, Zhiyu; Zhang, Wenli; Liu, Jianping

    2016-09-01

    Polymeric micelles (PMs) self-assembled by amphiphilic block copolymers have been used as promising nanocarriers for tumor-targeted delivery due to their favorable properties, such as excellent biocompatibility, prolonged circulation time, favorable particle sizes (10-100 nm) to utilize enhanced permeability and retention effect and the possibility for functionalization. However, PMs can be easily destroyed due to dilution of body fluid and the absorption of proteins in system circulation, which may induce drug leakage from these micelles before reaching the target sites and compromise the therapeutic effect. This paper reviewed the factors that influence stability of micelles in terms of thermodynamics and kinetics consist of the critical micelle concentration of block copolymers, glass transition temperature of hydrophobic segments and polymer-polymer and polymer-cargo interaction. In addition, some effective strategies to improve the stability of micelles were also summarized.

  20. Oxidation and low temperature stability of polymerized soybean oil-based lubricants

    USDA-ARS?s Scientific Manuscript database

    Oxidation and low temperature stability of polymerized soybean oil (PSO)-based lubricants have been investigated by the pressurized differential scanning calorimetry (PDSC) method. It was found that PSO samples have lower oxidative stability than their precursor, soybean oil. The main reason for the...

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

    NASA Astrophysics Data System (ADS)

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

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

  2. Ionic liquids and ionic liquid acids with high temperature stability for fuel cell and other high temperature applications, method of making and cell employing same

    DOEpatents

    Angell, C Austen [Mesa, AZ; Xu, Wu [Broadview Heights, OH; Belieres, Jean-Philippe [Chandler, AZ; Yoshizawa, Masahiro [Tokyo, JP

    2011-01-11

    Disclosed are developments in high temperature fuel cells including ionic liquids with high temperature stability and the storage of inorganic acids as di-anion salts of low volatility. The formation of ionically conducting liquids of this type having conductivities of unprecedented magnitude for non-aqueous systems is described. The stability of the di-anion configuration is shown to play a role in the high performance of the non-corrosive proton-transfer ionic liquids as high temperature fuel cell electrolytes. Performance of simple H.sub.2(g) electrolyte/O.sub.2(g) fuel cells with the new electrolytes is described. Superior performance both at ambient temperature and temperatures up to and above 200.degree. C. are achieved. Both neutral proton transfer salts and the acid salts with HSO.sup.-.sub.4 anions, give good results, the bisulphate case being particularly good at low temperatures and very high temperatures. The performance of all electrolytes is improved by the addition of a small amount of involatile base of pK.sub.a value intermediate between those of the acid and base that make the bulk electrolyte. The preferred case is the imidazole-doped ethylammonium hydrogensulfate which yields behavior superior in all respects to that of the industry standard phosphoric acid electrolyte.

  3. Development and stability during high temperature annealing of the cube texture in rolled Ni substrate materials

    NASA Astrophysics Data System (ADS)

    Zhou, Y.; Godfrey, A.; Liu, W.; Han, Z.; Liu, Q.

    2003-04-01

    The development and stability of the cube texture formed during annealing has been investigated, using rolled nickel sheets of 99.95% and 99.999% purity. Microstructure and texture were characterized using electron back-scatter pattern analysis in the scanning electron microscope. The texture following primary recrystallization in both materials showed cube volume fractions of up to 50% and 80% (99.95% and 99.999% Ni respectively). The average grain size of the cube textured grains during recrystallization was larger than for grains of other orientations. For both materials high temperature annealing resulted only in normal grain growth, leading to a significant strengthening of the cube texture. The results are discussed in terms of the relative effects of size, boundary mobility and boundary energy on the process of grain growth. For the 99.999% Ni material an annealing process using a continuous heating ramp to 1200 °C gave a further improvement in the cube texture.

  4. Mixture including hydrogen and hydrocarbon having pressure-temperature stability

    NASA Technical Reports Server (NTRS)

    Mao, Wendy L. (Inventor); Mao, Ho-Kwang (Inventor)

    2009-01-01

    The invention relates to a method of storing hydrogen that employs a mixture of hydrogen and a hydrocarbon that can both be used as fuel. In one embodiment, the method involves maintaining a mixture including hydrogen and a hydrocarbon in the solid state at ambient pressure and a temperature in excess of about 10 K.

  5. Rigidifying flexible sites: An approach to improve stability of chondroitinase ABC I.

    PubMed

    Kheirollahi, Asma; Khajeh, Khosro; Golestani, Abolfazl

    2017-04-01

    The stability of chondroitin ABC lyase I (cABC I) at physiological temperature is one of the current obstacles to its clinical application. In this study, we used a protein engineering approach; rigidify flexible sites, to improve stability of cABC I. B-factor analysis showed a flexible loop at the N-terminal domain of cABC I which may be involved in its thermal instability and five residues in this region were replaced with proline. Thermal inactivation and thermal denaturation analysis revealed that Glu138Pro mutation increased half-life and Tm of enzyme, respectively. The Km values of mutated enzymes were slightly increased compared to the wild type enzyme. The results of limited proteolysis indicated that Glu138Pro mutant was more resistant against trypsinolysis and this variant was less quenched in both acrylamide and KI quenching experiments. Moreover, intrinsic fluorescence intensity of Glu138Pro variant was increased and its ANS fluorescence intensity was decreased, whereas no considerable changes were observed in the far-UV CD spectra. The structural analyses indicated compactness of structure of Glu138Pro enzyme which can be related to moderately enhanced stability of this mutant. This study demonstrated that rigidifying flexible residues can be considered as a possible approach to increase the stability of the protein. Copyright © 2017 Elsevier B.V. All rights reserved.

  6. Improved Delay-Dependent Stability Conditions for MIMO Networked Control Systems with Nonlinear Perturbations

    PubMed Central

    2014-01-01

    This paper provides improved time delay-dependent stability criteria for multi-input and multi-output (MIMO) network control systems (NCSs) with nonlinear perturbations. Without the stability assumption on the neutral operator after the descriptor approach, the new proposed stability theory is less conservative than the existing stability condition. Theoretical proof is given in this paper to demonstrate the effectiveness of the proposed stability condition. PMID:24744679

  7. The research of improvements in Raman distributed temperature sensor

    NASA Astrophysics Data System (ADS)

    Zhang, Ge; Zhang, Li-na; Zhang, Shu-juan

    2014-12-01

    Temperature measurement system has been applied in industrial areas extensively. The fiber optic distributed temperature system is one of the most popular means. Measurement error is relatively large when using the distributed temperature sensors (DTS) based on Raman scattering to measure ambient temperature in harsh environments. In this paper, we propose a novel calibration technique to measure the temperature highly accurately over a wide range of temperatures. We also propose an improved double-ended configuration that is insusceptible to the differential loss change in the fiber. By using the improved double-ended configuration, through the anti-Stokes and Stokes signal intensity comparison, the differential mode signal loss in the temperature measurement can be suppressed in optical fiber. So, the measurement results of automatic calibration are irrespectively with the wastage of optical fiber sensors. The result shows that we can obtain the temperature parameters accuracy in wide temperature range, and temperature measurement system has high robustness in harsh environments, suitable for field use.

  8. Unforeseen high temperature and humidity stability of FeCl3 intercalated few layer graphene.

    PubMed

    Wehenkel, Dominique Joseph; Bointon, Thomas Hardisty; Booth, Tim; Bøggild, Peter; Craciun, Monica Felicia; Russo, Saverio

    2015-01-08

    We present the first systematic study of the stability of the structure and electrical properties of FeCl3 intercalated few-layer graphene to high levels of humidity and high temperature. Complementary experimental techniques such as electrical transport, high resolution transmission electron microscopy and Raman spectroscopy conclusively demonstrate the unforseen stability of this transparent conductor to a relative humidity up to 100% at room temperature for 25 days, to a temperature up to 150°C in atmosphere and to a temperature as high as 620°C in vacuum, that is more than twice higher than the temperature at which the intercalation is conducted. The stability of FeCl3 intercalated few-layer graphene together with its unique values of low square resistance and high optical transparency, makes this material an attractive transparent conductor in future flexible electronic applications.

  9. Unforeseen high temperature and humidity stability of FeCl3 intercalated few layer graphene

    PubMed Central

    Wehenkel, Dominique Joseph; Bointon, Thomas Hardisty; Booth, Tim; Bøggild, Peter; Craciun, Monica Felicia; Russo, Saverio

    2015-01-01

    We present the first systematic study of the stability of the structure and electrical properties of FeCl3 intercalated few-layer graphene to high levels of humidity and high temperature. Complementary experimental techniques such as electrical transport, high resolution transmission electron microscopy and Raman spectroscopy conclusively demonstrate the unforseen stability of this transparent conductor to a relative humidity up to 100% at room temperature for 25 days, to a temperature up to 150°C in atmosphere and to a temperature as high as 620°C in vacuum, that is more than twice higher than the temperature at which the intercalation is conducted. The stability of FeCl3 intercalated few-layer graphene together with its unique values of low square resistance and high optical transparency, makes this material an attractive transparent conductor in future flexible electronic applications. PMID:25567796

  10. Unforeseen high temperature and humidity stability of FeCl3 intercalated few layer graphene

    NASA Astrophysics Data System (ADS)

    Wehenkel, Dominique Joseph; Bointon, Thomas Hardisty; Booth, Tim; Bøggild, Peter; Craciun, Monica Felicia; Russo, Saverio

    2015-01-01

    We present the first systematic study of the stability of the structure and electrical properties of FeCl3 intercalated few-layer graphene to high levels of humidity and high temperature. Complementary experimental techniques such as electrical transport, high resolution transmission electron microscopy and Raman spectroscopy conclusively demonstrate the unforseen stability of this transparent conductor to a relative humidity up to 100% at room temperature for 25 days, to a temperature up to 150°C in atmosphere and to a temperature as high as 620°C in vacuum, that is more than twice higher than the temperature at which the intercalation is conducted. The stability of FeCl3 intercalated few-layer graphene together with its unique values of low square resistance and high optical transparency, makes this material an attractive transparent conductor in future flexible electronic applications.

  11. Improved temperature regulation of process water systems for the APS storage ring.

    SciTech Connect

    Putnam, C.; Dortwegt, R.

    2002-10-10

    Beam stability and operational reliability of critical mechanical systems are key performance issues for synchrotron accelerators such as the Advanced Photon Source (APS). Stability is influenced by temperature fluctuations of the process water (PW) used for cooling and/or temperature conditioning storage ring (SR) components such as vacuum chambers, magnets, absorbers, etc. Operational reliability is crucial in maintaining facility beam operations and remaining within downtime ''budgets.'' Water systems for the APS storage ring were originally provided with a distributive control system (DCS) capable of regulation to {+-}1.0 F, as specified by facility design requirements. After several years of operation, a particular mode of component mortality indicated a need for upgrade of the temperature control system. The upgrade that was implemented was chosen for both improved component reliability and temperature stability (now on the order of {+-}0.2 F for copper components and {+-}0.05 F for aluminum components). The design employs a network of programmable logic controllers (PLCs) for temperature control that functions under supervision of the existing DCS. The human-machine interface (HMI) of the PLC system employs RSView32 software. The PLC system also interfaces with the EPICS accelerator control system to provide monitoring of temperature control parameters. Eventual supervision of the PLC system by EPICS is possible with this design.

  12. Improvement of the positive bias stability of a-IGZO TFTs by the HCN treatment

    NASA Astrophysics Data System (ADS)

    Kim, Myeong-Ho; Choi, Myung-Jea; Kimura, Katsuya; Kobayashi, Hikaru; Choi, Duck-Kyun

    2016-12-01

    In recent years, many researchers have attempted to improve the bias stability of amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs). In this study, the hydrogen cyanide (HCN) treatment was carried out to improve the positive bias stability of bottom-gate a-IGZO TFTs. The HCN treatment was performed using a 0.1 M HCN solution with a pH of 10 at room temperature. Before applying the positive bias stress, there were no differences in the major electrical properties, including the saturation mobility (μsat), threshold voltage (Vth), and subthreshold swing (S/S), between HCN-treated and non-HCN-treated devices. However, after applying the positive bias stress, the HCN-treated device showed superior bias stability compared to the non-HCN-treated device. This difference is associated with the passivation of the defect states and the surface of the back-channel layer of the HCN-treated device by cyanide ions.

  13. Thermal and Chemical Stability of Baseline and Improved Crystalline Silicotitanate

    SciTech Connect

    Taylor, P.A.

    2002-01-23

    The Savannah River Site (SRS) has been evaluating technologies for removing radioactive cesium ({sup 137}Cs) from the supernate solutions stored in the high-level waste tanks at the site. Crystalline silicotitanate (CST) sorbent (IONSIV IE-911{reg_sign}, UOP LLC, Des Plaines, IL), which is very effective at removing cesium from high-salt solutions, was one of three technologies that were tested. Because of the extremely high inventory of {sup 137}Cs expected for the large columns of CST that would be used for treating the SRS supernate, any loss of flow or cooling to the columns could result in high temperatures from radiolytic heating. Also, even under normal operating conditions, the CST would be exposed to the supernates for up to a year before being removed. Small-scale batch and column tests conducted last year using samples of production batches of CST showed potential problems with CST clumping and loss of cesium capacity after extended contact with the simulant solutions. Similar tests-using samples of a baseline and improved granular CST and the CST powder used to make both granular samples-were performed this year to compare the performance of the improved CST. The column tests, which used recirculating supernate simulant, showed that the baseline CST generated more precipitates of sodium aluminosilicate than the improved CST. The precipitates were particularly evident in the tubing that carried the simulant solution to and from the column, but the baseline CST also showed higher concentrations of aluminum on the CST than were observed for the improved CST. Recirculating the simulant through just a section of the tubing (no contact with CST) also produced small amounts of precipitate, similar to the amounts seen for the improved CST column. The sodium aluminosilicate formed bridges between the CST granules, causing clumps of CST to form in the column. Clumps were visible in the baseline CST column after 1 month of operation and in the improved CST column

  14. Progress in Understanding Degradation Mechanisms and Improving Stability in Organic Photovoltaics.

    PubMed

    Mateker, William R; McGehee, Michael D

    2017-03-01

    Understanding the degradation mechanisms of organic photovoltaics is particularly important, as they tend to degrade faster than their inorganic counterparts, such as silicon and cadmium telluride. An overview is provided here of the main degradation mechanisms that researchers have identified so far that cause extrinsic degradation from oxygen and water, intrinsic degradation in the dark, and photo-induced burn-in. In addition, it provides methods for researchers to identify these mechanisms in new materials and device structures to screen them more quickly for promising long-term performance. These general strategies will likely be helpful in other photovoltaic technologies that suffer from insufficient stability, such as perovskite solar cells. Finally, the most promising lifetime results are highlighted and recommendations to improve long-term performance are made. To prevent degradation from oxygen and water for sufficiently long time periods, OPVs will likely need to be encapsulated by barrier materials with lower permeation rates of oxygen and water than typical flexible substrate materials. To improve stability at operating temperatures, materials will likely require glass transition temperatures above 100 °C. Methods to prevent photo-induced burn-in are least understood, but recent research indicates that using pure materials with dense and ordered film morphologies can reduce the burn-in effect.

  15. Studies for improved high temperature coatings for Space Shuttle application

    NASA Technical Reports Server (NTRS)

    Creedon, J.; Banas, R.; Garofalini, S. H.

    1979-01-01

    Improvement of the current Class 2 Space Shuttle Orbiter RCG coating was experimentally investigated.Coatings, which are applied to LI-900 or LI-2200 tiles, were prepared to provide increased performance in thermal expansion, impact, residual strain and increased viscosity. Turbulent duct arc-plasma tests at NASA/Ames Research Center are continuing on two candidates that show improved low residual strain and increased high temperature viscosity. A coating system with lower fusion-temperature (1950 F) was identified which has the potential of improving tile yield through reduced LI-900 shrinkage and distortion since it can be fused at 250 F lower than the present Class 2 coating.

  16. Miniature High Stability High Temperature Space Rated Blackbody Radiance Source

    NASA Astrophysics Data System (ADS)

    Jones, J. A.; Beswick, A. G.

    1987-09-01

    This paper presents the design and test performance of a conical cavity type blackbody radiance source that will meet the requirements of the Halogen Occultation Experiment (HALOE) on the NASA Upper Atmospheric Research Satellite program (UARS). Since a radiance source meeting the requirements of this experiment was unavailable in the commercial market, a development effort was undertaken by the HALOE Project. The blackbody radiance source operates in vacuum at 1300 K + 0.5 K over any 15-minute interval, uses less than 7.5 watts of power, maintains a 49°C outer case temperature, and fits within the 2.5 x 2.5 x 3.0 inch envelope allocated inside the HALOE instrument. Also, the unit operates in air, during ground testing of the HALOE instrument, where it uses 17 watts of power with an outer case temperature of 66°C. The thrust of this design effort was to minimize the heat losses, in order to keep the power usage under 7.5 watts, and to minimize the amount of silica in the materials. Silica in the presence of the platinum heater winding used in this design would cause the platinum to erode, changing the operating temperature set-point. The design required the development of fabrication techniques which would provide very small, close tolerance parts from extremely difficult-to-machine materials. Also, a space rated ceramic core and unique, low thermal conductance, ceramic-to-metal joint was developed, tested and incorporated in this design. The completed flight qualification hardware has undergone performance, environmental and life testing. The design configuration and test results are discussed in detail in this paper.

  17. Sensing disks for slug-type calorimeters have higher temperature stability

    NASA Technical Reports Server (NTRS)

    1967-01-01

    Graphite sensing disk for slug-type radiation calorimeters exhibits better performance at high temperatures than copper and nickel disks. The graphite is heat-soaked to stabilize its emittance and the thermocouple is protected from the graphite so repeated temperature cycling does not change its sensitivity.

  18. [Preservation and stability of corn tortillas at room temperature].

    PubMed

    Higuera-Ciapara, I; Nieblas, J M

    1995-06-01

    Three treatments with chemical preservative (sodium propionate, potassium sorbate-methylparaben and hydrogen peroxidemethyl paraben) were tested to delay microbial spoilage and extend shelf-life of corn tortillas at room temperature (25 degrees C). The treatment with the best results was selected for further studies using two types of packaging: Paper and high density polyethylene. Quality of corn tortillas during storage was assessed by measuring water content, microbial analysis (Total Plate Count, molds and yeast) and throguh sensory evaluation. Results were analyzed by covariance analysis and slope contrast between packaging materials at p<0.05. Spoilage of tortilla without preservative occurred within 24 hours due to a large number of gram negative bacteria, molds and yeasts, which were responsible for offensive odors. Only the combination of hydrogen peroxide-methyl paraben had a significant effect on retarding bacterial yeast spoilage. In addition, hydrogen peroxide residues could not [correction of no] be chemically detected after 2 days of storage. Results from this study show that tortilla can be kept for up to six days at room temperature with acceptable sensory properties with proper preservative treatment and packaging.

  19. Increasing viscosity storage stability of mannich base dispersant/VI-improvers

    SciTech Connect

    Fenoglio, D.J.; Song, Y.S.; Basalay, R.J.

    1990-10-16

    This patent describes a method for improving the viscosity stability upon storage of a Mannich base viscosity index improving composition. The composition comprising about 85 to 95 wt. % of low viscosity hydrocarbon oil and about 5 to 15 wt. % of a Mannich base condensation product of an oxidized polyolefin, an aliphatic aldehyde, and an aliphatic amine. It comprises combining the Mannich base viscosity index improving composition with an oxidizing material selected from the group consisting of a dialkyl peroxide, an alkyl hydroperoxide, an arylalkyl hydroperoxide, and a mixture thereof, wherein the alkyl moieties of the hydroperoxides contain seven carbons or less, and maintaining the resulting combination at a temperature of about 250{degrees}F to about 400{degrees}F for a time period of about 1 to about 5 hours. This patent also describes a method for operating an internal combustion engine. It comprises charging the crankcase of the engine with a lubricating oil composition containing a major amount of oil of lubricating viscosity and a minor viscosity-index improving amount of a Mannich base viscosity index improving composition, the viscosity index improving composition comprising about 85 to 95 wt. % of low viscosity hydrocarbon oil and about 5-15 wt. % of a Mannich base condensation product of an oxidized polyolefin, an aliphatic aldehyde and an aliphatic amine, wherein the Mannich base viscosity index improving composition is obtained by the process comprising the steps of and operating the engine with the crankcase so charged.

  20. Atmospheric Stability & Turbulence from Temperature Profiles over Sicily During Summer 2002 & 2003 HASI Balloon Campaigns

    NASA Technical Reports Server (NTRS)

    Colombatti, G.; Ferri, F.; Angrilli, F.; Fulchignoni, M.

    2005-01-01

    Experimental results and interpretation of the temperature measurements data retrieved during the balloon campaigns (in 2002 and in 2003) for testing HASI (Huygens Atmospheric Structure Instrument), launched from the Italian Space Agency Base in Trapani (Sicily), are presented. Both ascending and descending phases are analysed; data reveal interesting features near the tropopause (present in the region between 11km-14km), where temperature cooling can be related to layers with strong winds (2002 flight); in the troposphere a multistratified structure of the temperature field is observed and discussed (particularly in the 2003 flight) Finally, stability and turbulence of the atmosphere are analysed; the buoyancy N2 parameters for both the flights show lowers value respect to standard tropospheric values corresponding to a lower stability of the atmosphere; still there is a higher stability above the tropopause. The energy spectrum of temperature data is consistent with the Kolmogorov theory: the characteristic k(sup -5/3) behaviour is reproduced.

  1. Association of Yeast Alcohol Dehydrogenase with Superparamagnetic Nanoparticles: Improving the Enzyme Stability and Performance.

    PubMed

    Netto, Caterina G C Marques; Andrade, Leandro H; Freitas, Rafael S; Toma, Henrique E

    2015-12-01

    Alcohol dehydrogenase (ADH) from Saccharomyces cerevisiae was covalently attached, via glutaraldehyde, to magnetite nanoparticles (MagNP) previously coated with aminopropyltriethoxysilane (MagNP/APTS), or with a silica shell followed by the APTS coating (MagNP@SiO2/APTS). In both cases, a great improvement of enzymatic activity has been observed for the ethanol-acetaldehyde conversion. The MagNP@SiO2/APTS-ADH system exhibited the best stability with respect to pH and temperature. Its residual activity after 10 successive recovery cycles and 24 h storage, was maintained around 80% in comparison with 20% for the MagNP/APTS system, and a null activity for free ADH. Luminescence measurements for the immobilized enzyme indicated the occurrence of conformational changes on ADH, contributing for its improved catalytic performance.

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

    PubMed

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

    2017-02-01

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

  3. 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

  4. Soil Stabilization and Revegetation at the INEEL Recommendations for Improvement

    SciTech Connect

    Blew, R.D.; Jackson, M.R.; Forman, A.D.

    2003-03-24

    Soil stabilization for the INEEL Stormwater Pollution Prevention Plan (SWPPP) has mostly been by revegetation, but has experienced only limited success. The purpose of this report is to discuss issues associated with revegetation failures and to explore possible remedies.

  5. Improvement of Thermosensitive Liposome Stability by Cerasome Forming Lipid with Si-O-Si Network Structure.

    PubMed

    Su, Qin; Pu, Ximing; Bai, He; Chen, Xianchun; Liao, Xiaoming; Huang, Zhongbing; Yin, Guangfu

    2017-07-19

    Liposomes have been widely used in the gene transfection and the drug delivery systems due to their excellent biocompatibility and encapsulation ability, especially, the ability to deliver the gene/drug into the cells via the membrane fusion. Thermosensitive liposoems have been proven to be a precise and effective method for cancer treatment in many preclinical studies. But the imperfect crystalline arrangement between grains occurred, resulting in planar defects at the boundaries of membranes, compromising the stability of thermosensitive liposomes. In the present study, we developed a facile method to improve the stability of ordinary thermosensitive liposomes by introducing organic-inorganic hybrid materials with local Si-O-Si net. A cerasome forming lipid, N, N-Dihxadecyl-N'- [(3-triethoxysilyl) propyl] urea, was synthesized and then introduced into the thermosensitive lipids to form the composite liposomes (named as cera-liposomes). The effects of the cerasome forming lipid on the cera-liposomes characteristics, including the morphology, drug loading, Zeta potential and stability of vesicles, were investigated. Cera-liposomes were thermosensitive, and they had a loading efficiency over 2 folds more than conventional thermosensitive liposomes. With the enhanced sustain of Si-O-Si, cera-liposomes were able to avoid collapsing and fusing during storage, and had a good resistance to nonionic surfactant. More than 80% drug was still retained after storage of 15 days at room temperature. The cerasome forming lipid showed a potential in improving stability of thermosensitive liposomes. This novel kind of cera-liposomes could be a stable and effective drug carrier for anticancer applications. Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.

  6. Microstructural Stability and Oxidation Resistance of 9-12 Chromium Steels at Elevated Temperatures

    SciTech Connect

    Dogan, O.N.; Alman, D.E.; Jablonski, P.D.; Hawk, J.A.

    2006-05-01

    Various martensitic 9-12 Cr steels are utilized currently in fossil fuel powered energy plants for their good elevated temperature properties such as creep strength, steam side oxidation resistance, fire side corrosion resistance, and thermal fatigue resistance. Need for further improvements on the properties of 9-12 Cr steels for higher temperature (>600oC) use is driven by the environmental concerns (i.e., improve efficiency to reduce emissions and fossil fuel consumption). In this paper, we will discuss the results of the research done to explore new subsitutional solute solution and precipitate hardening mechanisms for improved strength of 9-12 Cr martensitic steels. Stability of the phases present in the steels will be evaluated for various temperature and time exposures. A comparison of microstructural properties of the experimental steels and commercial steels will also be presented.

    The influence of a Ce surface treatment on oxidation behavior of a commercial (P91) and several experimental steels containing 9 to 12 weight percent Cr was examined at 650ºC in flowing dry and moist air. The oxidation behavior of all the alloys without the Ce modification was significantly degraded by the presence of moisture in the air during testing. For instance the weight gain for P91 was two orders of magnitude greater in moist air than in dry air. This was accompanied by a change in oxide scale from the formation of Cr-based scales in dry air to the formation of Fe-based scales in moist air. The Ce surface treatment was very effective in improving the oxidation resistance of the experimental steels in both moist and dry air. For instance, after exposure to moist air at 650ºC for 2000 hours, an experimental alloy with the cerium surface modification had a weight gain three orders of magnitude lower than the alloy without the Ce modification and two orders of magnitude lower than P91. The Ce surface treatment suppressed the formation of Fe-based scales and

  7. Novel approaches for stability improvement in natural medicines.

    PubMed

    Thakur, Lovely; Ghodasra, Umang; Patel, Nilesh; Dabhi, Mahesh

    2011-01-01

    Natural product market has seen tremendous growth in the last few years. It results in the formulation of a number of proprietary herbal products, majority of them being multi-component formulations. With the advancement of herbal drug treatments, it has now been observed that many of the constituents present in the drug may react with each other, raising the serious concern about the stability of such formulations which is an important issue in the field of phytochemistry and natural medicines. Natural products are often prone to deterioration, especially during storage, leading to loss of active component, production of metabolites with no activity and, in extreme cases, production of toxic metabolites. This area needs to be addressed in order to determine the efficacy of the formulation. Understanding the problems related to natural product stability can give the idea of dealing with the stability issues. Modifications of the conventional herbal formulations can deal with the stability problems to a large extent. This article deals with the stability problems and is aimed to provide some tools and techniques to increase stability of natural medicines and herbal formulations.

  8. Novel approaches for stability improvement in natural medicines

    PubMed Central

    Thakur, Lovely; Ghodasra, Umang; Patel, Nilesh; Dabhi, Mahesh

    2011-01-01

    Natural product market has seen tremendous growth in the last few years. It results in the formulation of a number of proprietary herbal products, majority of them being multi-component formulations. With the advancement of herbal drug treatments, it has now been observed that many of the constituents present in the drug may react with each other, raising the serious concern about the stability of such formulations which is an important issue in the field of phytochemistry and natural medicines. Natural products are often prone to deterioration, especially during storage, leading to loss of active component, production of metabolites with no activity and, in extreme cases, production of toxic metabolites. This area needs to be addressed in order to determine the efficacy of the formulation. Understanding the problems related to natural product stability can give the idea of dealing with the stability issues. Modifications of the conventional herbal formulations can deal with the stability problems to a large extent. This article deals with the stability problems and is aimed to provide some tools and techniques to increase stability of natural medicines and herbal formulations. PMID:22096318

  9. Elevated body temperature in ischemic stroke associated with neurological improvement.

    PubMed

    Khanevski, A N; Naess, H; Thomassen, L; Waje-Andreassen, U; Nacu, A; Kvistad, C E

    2017-11-01

    Some studies suggest that high body temperature within the first few hours of ischemic stroke onset is associated with improved outcome. We hypothesized an association between high body temperature on admission and detectable improvement within 6-9 hours of stroke onset. Consecutive ischemic stroke patients with NIHSS scores obtained within 3 hours and in the interval 6-9 hours after stroke onset were included. Body temperature was measured on admission. A total of 315 patients with ischemic stroke were included. Median NIHSS score on admission was 6. Linear regression showed that NIHSS score 6-9 hours after stroke onset was inversely associated with body temperature on admission after adjusting for confounders including NIHSS score <3 hours after stroke onset (P<.001). The same result was found in patients with proximal middle cerebral occlusion on admission. We found an inverse association between admission body temperature and neurological improvement within few hours after admission. This finding may be limited to patients with documented proximal middle cerebral artery occlusion on admission and suggests a beneficial effect of higher body temperature on clot lysis within the first three hours. © 2017 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

  10. VCSEL's frequency stabilization of an external cavity diode laser: countermeasures against atmospheric temperature variations

    NASA Astrophysics Data System (ADS)

    Motojima, Mutsuki; Doi, Kohei; Sato, Takashi; Ohkawa, Masashi; Suzuki, Takamasa

    2010-02-01

    We introduced the vertical cavity surface emitting laser (VCSEL) as the laser diode in tour external cavity system. Because VCSELs are now commercially available, and the External cavity diode laser (ECDL) systems using them are expected to improve their frequency stability, we have replaced a Fabry-Perot type laser diode with a VCSEL, and examined its oscillation-frequency stability. Therefore we were able to expect that the VCSELs with our double optical feedback system have good oscillation frequency stability. The obtained VCSEL's oscillation-frequency stability, i.e., the square root of Allan variance σ was 4×10-10, at an averaging time of τ=1 sec.

  11. Measurement of improved pressure dependence of superconducting transition temperature

    NASA Astrophysics Data System (ADS)

    Karmakar, S.

    2013-06-01

    We describe a technique for making electrical transport measurements in a diamond anvil cell at liquid helium temperature having in situ pressure measurement option, permitting accurate pressure determination at any low temperature during the resistance measurement scan. In general, for four-probe resistivity measurements on a polycrystalline sample, four fine gold wires are kept in contact with the sample with the help of the compression from the soft solid (usually alkali halides such as NaCl, KCl, etc.) acting as a pressure-transmitting medium. The actual pressure on the sample is underestimated if not measured from a ruby sphere placed adjacent to the sample and at that very low temperature. Here, we demonstrate the technique with a quasi-four-probe resistance measurement on an Fe-based superconductor in the temperature range 1.2-300 K and pressures up to 8 GPa to find an improved pressure dependence of the superconducting transition temperature.

  12. A novel high pressure, high temperature vessel used to conduct long-term stability measurements of silicon MEMS pressure transducers

    NASA Astrophysics Data System (ADS)

    Wisniewiski, David

    2014-03-01

    The need to quantify and to improve long-term stability of pressure transducers is a persistent requirement from the aerospace sector. Specifically, the incorporation of real-time pressure monitoring in aircraft landing gear, as exemplified in Tire Pressure Monitoring Systems (TPMS), has placed greater demand on the pressure transducer for improved performance and increased reliability which is manifested in low lifecycle cost and minimal maintenance downtime through fuel savings and increased life of the tire. Piezoresistive (PR) silicon MEMS pressure transducers are the primary choice as a transduction method for this measurement owing to their ability to be designed for the harsh environment seen in aircraft landing gear. However, these pressure transducers are only as valuable as the long-term stability they possess to ensure reliable, real-time monitoring over tens of years. The "heart" of the pressure transducer is the silicon MEMS element, and it is at this basic level where the long-term stability is established and needs to be quantified. A novel High Pressure, High Temperature (HPHT) vessel has been designed and constructed to facilitate this critical measurement of the silicon MEMS element directly through a process of mechanically "floating" the silicon MEMS element while being subjected to the extreme environments of pressure and temperature, simultaneously. Furthermore, the HPHT vessel is scalable to permit up to fifty specimens to be tested at one time to provide a statistically significant data population on which to draw reasonable conclusions on long-term stability. With the knowledge gained on the silicon MEMS element, higher level assembly to the pressure transducer envelope package can also be quantified as to the build-effects contribution to long-term stability in the same HPHT vessel due to its accommodating size. Accordingly, a HPHT vessel offering multiple levels of configurability and robustness in data measurement is presented, along

  13. 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.

  14. Alkyl Caffeates Improve the Antioxidant Activity, Antitumor Property and Oxidation Stability of Edible Oil

    PubMed Central

    Wang, Jun; Gu, Shuang-Shuang; Pang, Na; Wang, Fang-Qin; Pang, Fei; Cui, Hong-Sheng; Wu, Xiang-Yang; Wu, Fu-An

    2014-01-01

    Caffeic acid (CA) is distributed widely in nature and possesses strong antioxidant activity. However, CA has lower solubility in non-polar media, which limits its application in fat-soluble food. To increase the lipophilicity of natural antioxidant CA, a series of alkyl caffeates were synthesized and their antioxidant and antitumor activities were investigated. The antioxidant parameters, including the induction period, acid value and unsaturated fatty acid content, of the alkyl caffeates in edible oil were firstly investigated. The results indicated that alkyl caffeates had a lower DPPH IC50 (14–23 µM) compared to CA, dibutyl hydroxy toluene (BHT) and Vitamin C (24–51 µM), and significantly inhibited four human cancer cells (SW620, SW480, SGC7901 and HepG2) with inhibition ratio of 71.4–78.0% by a MTT assay. With regard to the induction period and acid value assays, methyl and butyl caffeates had higher abilities than BHT to restrain the oxidation process and improve the stability of edible oil. The addition of ethyl caffeate to oil allowed maintenance of a higher unsaturated fatty acid methyl ester content (68.53%) at high temperatures. Overall, the alkyl caffeats with short chain length (n<5) assessed better oxidative stability than those with long chain length. To date, this is the first report to the correlations among the antioxidant activity, anticancer activity and oxidative stability of alkyl caffeates. PMID:24760050

  15. Improvement of the stability and activity of immobilized glucose oxidase on modified iron oxide magnetic nanoparticles

    NASA Astrophysics Data System (ADS)

    Abbasi, Mahboube; Amiri, Razieh; Bordbar, Abdol-Kalegh; Ranjbakhsh, Elnaz; Khosropour, Ahmad-Reza

    2016-02-01

    Immobilized proteins and enzymes are widely investigated in the medical field as well as the food and environmental fields. In this study, glucose oxidase (GOX) was covalently immobilized on the surface of modified iron oxide magnetic nanoparticles (MIMNs) to produce a bioconjugate complex. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) were used to the size, shape and structure characterization of the MIMNs. Binding of GOX to these MIMNs was confirmed by using FT-IR spectroscopy. The stability of the immobilized and free enzyme at different temperature and pH values was investigated by measuring the enzymatic activity. These studies reveal that the enzyme's stability is enhanced by immobilization. Further experiments showed that the storage stability of the enzyme is improved upon binding to the MIMNs. The results of kinetic measurements suggest that the effect of the immobilization process on substrate and product diffusion is small. Such bioconjugates can be considered as a catalytic nanodevice for accelerating the glucose oxidation reaction for biotechnological purposes.

  16. Development of a High Temperature Heater using an Yttria Stabilized Zirconia Cored Brick Matrix

    NASA Technical Reports Server (NTRS)

    Smith, K. W.; Decoursin, D. G.

    1971-01-01

    The Ames pilot heater is a ceramic regenerative heater that provides high temperature air for aerodynamic and combustion experiments. The development of this heater to provide a heat storage bed with temperature capability of about 4600 R is described. A bed was designed and installed having cored brick elements of yttria-stabilized zirconia. The bed dimensions were 14 inches in diameter by 10 feet high. The thermal stress limitations of the bed were studied and maximum air flow rates based upon these limits were established. A combustion reheat system was designed and installed to provide the necessary control over the bed temperature distribution. The revised heater system was successfully operated at a maximum bed temperature of 4600 R. The successful operation demonstrated that yttria-stabilized zirconia cored brick can satisfy the high temperature-long duration requirement for storage heater applications.

  17. Improvement of Stability and Antioxidant Activities by Using Phycocyanin - Chitosan Encapsulation Technique

    NASA Astrophysics Data System (ADS)

    Suzery, Meiny; Hadiyanto; Majid, Dian; Setyawan, Deny; Sutanto, Heri

    2017-02-01

    Encapsulation is a coating process to improve the stability of bioactive compounds. Phycocyanin with high antioxidant activity has been encapsulated with chitosan in microcapsules form. In this study aims to determine the best conditions in the encapsulation process using the extrusion method, characterization of the physicochemical properties of the microcapsules, antioxidant activity test using DPPH, in vitro release performance and evaluate the storage stability against temperature. The results of the encapsulation process is obtained: Na-TPP is better than Na-citrate as crosslinker and chitosan content 3% as a coating with ratio of chitosan to phycocyanin ratio 1: 1. Test of antioxidant activity also showed encapsulation with chitosan content 3% has the highest antioxidant activity. Morphological analysis microcapsules were found to have compact spherical shape with diameter range 900-1000 µm. In vitro release testing showed a quick release in an acidic environment (SGF) for 2 hours and slowly release under alkaline conditions (SIF) for 8 hours under mechanical stirring at 37°C. Phycocyanin much more stable against temperature during storage in microcapsules.

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

    PubMed

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

    2010-04-01

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

  19. Improved stability of nanocrystalline porous silicon after coating with a polymer

    NASA Astrophysics Data System (ADS)

    Mandal, N. P.; Sharma, Ashutosh; Agarwal, S. C.

    2006-07-01

    The effect of light soaking (LS) on nanocrystalline porous silicon (nc-Si) is found to depend on the ambient conditions. Light soaking in air decreases the photoluminescence (PL) intensity and increases the number of dangling bond density measured by electron spin resonance (ESR) monotonically as the exposure time is increased. In vacuum, however, short light exposures increase the PL intensity and decrease the ESR signal, but longer exposures have the opposite effect. Thus PL intensity has a maximum as a function of exposure time. The temperature dependence of LS in vacuum is measured at 300, 325, and 350K. We found that the maximum PL intensity occurs at smaller exposure times as the temperature is increased. These results are explained in terms of two kinds of photostructural changes having opposite LS effects on the PL. Coating nc-Si with a thin layer of polystyrene stabilizes PL against light soaking as well as water vapor, without affecting the PL intensity significantly. Modified bonding configurations at the nc-Si/polystyrene interface, as observed by Fourier transform infrared, seem responsible for the improved stability.

  20. Protein polymer conjugates: improving the stability of hemoglobin with poly(acrylic acid).

    PubMed

    Thilakarathne, Vindya; Briand, Victoria A; Zhou, Yuxiang; Kasi, Rajeswari M; Kumar, Challa V

    2011-06-21

    The synthesis, characterization, and evaluation of a novel polymer-protein conjugate are reported here. The covalent conjugation of high-molecular weight poly(acrylic acid) (PAA) to the lysine amino groups of met-hemoglobin (Hb) resulted in the covalent conjugation of Hb to PAA (Hb-PAA conjugate), as confirmed by dialysis and electrophoresis studies. The retention of native-like structure of Hb in Hb-PAA was established from Soret absorption, circular dichroism studies, and the redox activity of the iron center in Hb-PAA. The peroxidase-like activities of the Hb-PAA conjugate further confirmed the retention of Hb structure and biological activity. Thermal denaturation of the conjugate was investigated by differential scanning calorimetry and steam sterilization studies. The Hb-PAA conjugate indicated an improved denaturation temperature (T(d)) when compared to that of the unmodified Hb. One astonishing observation was that polymer conjugation significantly enhanced the Hb-PAA storage stability at room temperature. After 120 h of storage at room temperature in phosphate-buffered saline (PBS) at pH 7.4, for example, Hb-PAA retained 90% of its initial activity and unmodified Hb retained <60% of its original activity under identical conditions of buffer, pH, and temperature. Our conjugate demonstrates the key role of polymers in enhancing Hb stability via a very simple, efficient, general route. Water-swollen, lightly cross-linked, stable Hb-polymer nanogels of 100-200 nm were produced quickly and economically by this approach for a wide variety of applications.

  1. Slope stability improvement using low intensity field electrosmosis

    NASA Astrophysics Data System (ADS)

    Armillotta, Pasquale

    2014-05-01

    The electrosmosis technique has been introduced in the past for slope stabilization. However, its application to real cases has been scarce due to several drawbacks mostly related to the high intensity electric field needed (1.0 V/cm or higher): the rapid degradation of the electrodes, the high system management cost, the heating and cracking of the soil and the reduction of its colloidal fraction. Thanks to the introduction of new materials, the technique is currently applied to decrease the consolidation time of saturated clay soils (forcing the elimination of water), consequently improving its mechanical strength. In clay soils, the volume variation is influenced by the presence of smectites. The clay compressibility decreases with the increasing of electrolytes concentration. Soil containing smectites that have interacted with calcium showed a reduction or the absence of swelling during hydration with distilled water and a positive increase of their shear strength. The different values of pH between the anode (acid) and the cathode (basic), induced by the electrosmosis create the conditions for the precipitation of CaCO3 near the cathode. The injection of solutions containing calcium in soils and their diffusion induced by the electrosmosis, lead to calcium precipitation and consequential increase of the shear strength. The material technological advances and the laboratory experiences described in this paper, demonstrate that the use low electric field (0.1 V/cm or lower) intensity electrosmosis (LEFE in acronym) can be effective for soil dewatering and shear strength increase while reducing its adverse effect. The LEFE can be used to: reduce the potential for swelling of active clay minerals through the introduction of ions and the precipitation of hardening substances; induce the "dewatering" in cohesive soils. Several Lab activities were carried out, using custom made electrosmosis equipment. These activities can be divided in two phases: Phase 1

  2. [Improving recovery of body temperature after ablution in premature infants].

    PubMed

    Chiu, Shu-Yen; Huang, Hisu-Min; Tseng, Chi-Ying

    2007-06-01

    The purpose of this project was to improve the problem of decreased body temperature after ablution in premature infants, and increase the rate of recovery of body temperature. Before administration of this program, the rate of body temperature recovery was slow. The body temperatures of only 35% of premature infants' reached 36.5 degrees C at 30 minutes after bath, those of 43% did so at 60 minutes after bath, and those of 70 % did so at 120 minutes after bath. After a warmth maintenance nursing standard had been set, the bathing nursing standard corrected, standard interventions promoted and the system inspected, the percentage of body temperature recovery to 36.5 degrees C was raised from 35% to 74% at 30 minutes after bath and the body temperature became normal in all premature infants at 60 minutes after bath. This program not only solves the problem of low body temperature after ablution in premature infants, but also consolidates nursing staffs' knowledge and skills in maintaining body temperature in prematurity to promote the quality of premature care.

  3. Frequency stability improvement for piezoresistive micromechanical oscillators via synchronization

    NASA Astrophysics Data System (ADS)

    Pu, Dong; Huan, Ronghua; Wei, Xueyong

    2017-03-01

    Synchronization phenomenon first discovered in Huygens' clock shows that the rhythms of oscillating objects can be adjusted via an interaction. Here we show that the frequency stability of a piezoresistive micromechanical oscillator can be enhanced via synchronization. The micromechanical clamped-clamped beam oscillator is built up using the electrostatic driving and piezoresistive sensing technique and the synchronization phenomenon is observed after coupling it to an external oscillator. An enhancement of frequency stability is obtained in the synchronization state. The influences of the synchronizing perturbation intensity and frequency detuning applied on the oscillator are studied experimentally. A theoretical analysis of phase noise leads to an analytical formula for predicting Allan deviation of the frequency output of the piezoresistive oscillator, which successfully explains the experimental observations and the mechanism of frequency stability enhancement via synchronization.

  4. Improvements on the stability and operation of a magnetron H- ion source

    NASA Astrophysics Data System (ADS)

    Sosa, A.; Bollinger, D. S.; Karns, P. R.; Tan, C. Y.

    2017-05-01

    The magnetron H- ion sources developed in the 1970s currently in operation at Fermilab provide beam to the rest of the accelerator complex. A series of modifications to these sources have been tested in a dedicated off-line test stand with the aim of improving different operational issues. The solenoid type gas valve was tested as an alternative to the piezoelectric gas valve in order to avoid its temperature dependence. A new cesium oven was designed and tested in order to avoid glass pieces that were present with the previous oven, improve thermal insulation and fine-tune its temperature. A current-regulated arc modulator was developed to run the ion source at a constant arc current, providing very stable beam outputs during operations. In order to reduce beam noise, the addition of small amounts of N2 gas was explored, as well as testing different cathode shapes with increasing plasma volume. This paper summarizes the studies and modifications done in the source over the past three years with the aim of improving its stability, reliability and overall performance.

  5. Improving low-temperature activity of Sulfolobus acidocaldarius 2-keto-3-deoxygluconate aldolase.

    PubMed

    Wolterink-van Loo, Suzanne; Siemerink, Marco A J; Perrakis, Georgios; Kaper, Thijs; Kengen, Servé W M; van der Oost, John

    2009-03-02

    Sulfolobus acidocaldarius 2-keto-3-deoxygluconate aldolase (SacKdgA) displays optimal activity at 95 degrees C and is studied as a model enzyme for aldol condensation reactions. For application of SacKdgA at lower temperatures, a library of randomly generated mutants was screened for improved synthesis of 2-keto-3-deoxygluconate from pyruvate and glyceraldehyde at the suboptimal temperature of 50 degrees C. The single mutant SacKdgA-V193A displayed a threefold increase in activity compared with wild type SacKdgA. The increased specific activity at 40-60 degrees C of this mutant was observed, not only for the condensation of pyruvate with glyceraldehyde, but also for several unnatural acceptor aldehydes. The optimal temperature for activity of SacKdgA-V193A was lower than for the wild type enzyme, but enzymatic stability of the mutant was similar to that of the wild type, indicating that activity and stability were uncoupled. Valine193 has Van der Waals interactions with Lysine153, which covalently binds the substrate during catalysis. The mutation V193A introduced space close to this essential residue, and the increased activity of the mutant presumably resulted from increased flexibility of Lysine153. The increased activity of SacKdgA-V193A with unaffected stability demonstrates the potential for optimizing extremely thermostable aldolases for synthesis reactions at moderate temperatures.

  6. Effects of temperature and relative humidity on the stability of paper-immobilized antibodies.

    PubMed

    Wang, Jingyun; Yiu, Brian; Obermeyer, Jaclyn; Filipe, Carlos D M; Brennan, John D; Pelton, Robert

    2012-02-13

    The stability of a paper-immobilized antibody was investigated over a range of temperatures (40-140 °C) and relative humidities (RH, 30-90%) using both unmodified filter paper and the same paper impregnated with polyamide-epichlorohydrin (PAE) as supports. Antibody stability decreased with increasing temperature, as expected, but also decreased with increasing RH. At 40 °C, the half-life was more than 10 days, with little dependence on RH. However, at 80 °C, the half-life varied from ~3 days at low RH to less than half an hour at 90% RH, demonstrating that hydration of the antibody promotes unfolding. Antibody stability was not influenced by the PAE paper surface treatment. This work shows that antibodies are good candidates for development of bioactive paper as they have sufficient stability at high temperature to withstand printing and other roll-to-roll processing steps, and sufficient low temperature stability to allow long-term storage of bioactive paper materials.

  7. Manipulation of skin temperature improves nocturnal sleep in narcolepsy.

    PubMed

    Fronczek, R; Raymann, R J E M; Overeem, S; Romeijn, N; van Dijk, J G; Lammers, G J; Van Someren, E J W

    2008-12-01

    Besides excessive daytime sleepiness, disturbed nocturnal sleep is a major complaint of patients with narcolepsy. Previously, alterations in skin temperature regulation in narcoleptic patients have been shown to be related to increased sleepiness. This study tests the hypothesis that direct control of nocturnal skin temperature might be applied to improve the disturbed sleep of narcoleptic patients. Participants were eight patients (five males) diagnosed as having narcolepsy with cataplexy according to the ICSD-2 criteria, mean (SD) age 28.6 (6.4) years, range 18-35 years. During two nights, sleep was recorded polysomnographically while proximal and distal skin temperature were manipulated using a comfortable thermosuit that induced skin temperature to cycle slowly with an amplitude of only 0.4 degrees C within the comfortable range normally observed during sleep. Logistic regression was used to evaluate the effect of skin temperature manipulation on the probability of occurrence of different sleep stages and nocturnal wakefulness. Proximal skin warming significantly suppressed wakefulness and enhanced slow wave sleep (SWS). In contrast, distal skin warming enhanced wakefulness and stage 1 sleep at the cost of SWS and REM sleep. The optimal combination of proximal skin warming and distal skin cooling led to a 160% increase in SWS, a 50% increase in REM sleep and a 68% decrease in wakefulness, compared with the least beneficial combination of proximal skin cooling and distal skin warming. Subtle skin temperature manipulations under controlled conditions significantly improved the typical nocturnal sleep problems in narcolepsy.

  8. Temperature-Dependent Conformations of Model Viscosity Index Improvers

    SciTech Connect

    Ramasamy, Uma Shantini; Cosimbescu, Lelia; Martini, Ashlie

    2015-05-01

    Lubricants are comprised of base oils and additives where additives are chemicals that are deliberately added to the oil to enhance properties and inhibit degradation of the base oils. Viscosity index (VI) improvers are an important class of additives that reduce the decline of fluid viscosity with temperature [1], enabling optimum lubricant performance over a wider range of operating temperatures. These additives are typically high molecular weight polymers, such as, but not limited to, polyisobutylenes, olefin copolymer, and polyalkylmethacrylates, that are added in concentrations of 2-5% (w/w). Appropriate polymers, when dissolved in base oil, expand from a coiled to an uncoiled state with increasing temperature [2]. The ability of VI additives to increase their molar volume and improve the temperature-viscosity dependence of lubricants suggests there is a strong relationship between molecular structure and additive functionality [3]. In this work, we aim to quantify the changes in polymer size with temperature for four polyisobutylene (PIB) based molecular structures at the nano-scale using molecular simulation tools. As expected, the results show that the polymers adopt more conformations at higher temperatures, and there is a clear indication that the expandability of a polymer is strongly influenced by molecular structure.

  9. Effect of temperature and temperature shock on the stability of continuous cellulosic-hydrogen fermentation.

    PubMed

    Gadow, Samir I; Jiang, Hongyu; Watanabe, Ryoya; Li, Yu-You

    2013-08-01

    Three continuous stirred tank reactors (CSTR) were operated under mesophilic (37 ± 1°C), thermophilic (55 ± 1°C) and hyper-thermophilic (80 ± 1°C) temperatures for 164 days to investigate the effect of temperature and temperature shock on the cellulosic-dark hydrogen fermentation by mixed microflora. During steady state condition, the sudden decreases in the fermentation temperature occurred twice in each condition for 24h. The results show that the 55 ± 1 and 80 ± 1°C presented stable hydrogen yields of 12.28 and 9.72 mmol/g cellulose, respectively. However, the 37 ± 1°C presented low hydrogen yield of 3.56 mmol/g cellulose and methane yield of 5.4 mmol/g cellulose. The reactor performance under 55 ± 1 or 80 ± 1°C appeared to be more resilient to the sudden decreases in the fermentation temperature than 37 ± 1°C. The experimental analysis results indicated that the changing in soluble by-products could explain the effect of temperature and temperature shock, and the thermophilic temperature is expected having a better economic performance for cellulosic-hydrogen fermentation.

  10. Electronic correlations determine the phase stability of iron up to the melting temperature

    PubMed Central

    Leonov, I.; Poteryaev, A. I.; Gornostyrev, Yu. N.; Lichtenstein, A. I.; Katsnelson, M. I.; Anisimov, V. I.; Vollhardt, D.

    2014-01-01

    We present theoretical results on the high-temperature phase stability and phonon spectra of paramagnetic bcc iron which explicitly take into account many-body effects. Several peculiarities, including a pronounced softening of the [110] transverse (T1) mode and a dynamical instability of the bcc lattice in harmonic approximation are identified. We relate these features to the α-to-γ and γ-to-δ phase transformations in iron. The high-temperature bcc phase is found to be highly anharmonic and appears to be stabilized by the lattice entropy. PMID:24998330

  11. Effect of spatial inlet temperature and pressure distortion on turbofan engine stability

    NASA Technical Reports Server (NTRS)

    Mehalic, Charles M.

    1988-01-01

    The effects of circumferential and radial inlet temperature distortion, circumferential pressure distortion, and combined temperature and pressure distortion on the stability of an advanced turbofan engine were investigated experimentally at simulated altitude conditions. With circumferential and radial inlet temperature distortion, a flow instability generated by the fan operating near stall caused the high-pressure compressor to surge at, or near, the same time as the fan. The effect of combined distortion was dependent on the relative location of the high-temperature and low-pressure regions; high-pressure compressor stalls occurred when the regions coincided, and fan stalls occurred with the regions separated.

  12. The effect of annealing temperature on the stability of gallium tin zinc oxide thin film transistors

    NASA Astrophysics Data System (ADS)

    Nguyen, Ngoc; McCall, Briana; Alston, Robert; Collis, Ward; Iyer, Shanthi

    2015-10-01

    With the growing need for large area display technology and the push for a faster and cheaper alternative to the current amorphous indium gallium zinc oxide (a-IGZO) as the active channel layer for pixel-driven thin film transistors (TFTs) display applications, gallium tin zinc oxide (GSZO) has shown to be a promising candidate due to the similar electronic configuration of Sn4+ and In3+. In this work TFTs of GSZO sputtered films with only a few atomic % of Ga and Sn have been fabricated. A systematic and detailed comparison has been made of the properties of the GSZO films annealed at two temperatures: 140 °C and 450 °C. The electrical and optical stabilities of the respective devices have been studied to gain more insight into the degradation mechanism and are correlated with the initial TFT performance prior to the application of stress. Post deposition annealing at 450 °C of the films in air was found to lead to a higher atomic concentration of Sn4+ in these films and a superior quality of the film, as attested by the higher film density and less surface and interface roughness in comparison to the lower annealed temperature device. These result in significantly reduced shallow and deep interface traps with improved performance of the device exhibiting VON of -3.5 V, ION/IOFF of 108, field-effect mobility (μFE) of 4.46 cm2 V-1s-1, and sub-threshold swing of 0.38 V dec-1. The device is stable under both electrical and optical bias for wavelengths of 550 nm and above. Thus, this work demonstrates GSZO-based TFTs as a promising viable option to the IGZO TFTs by further tailoring the film composition and relevant processing temperatures.

  13. Surface functionalized LSMO nanoparticles with improved colloidal stability for hyperthermia applications

    NASA Astrophysics Data System (ADS)

    Thorat, N. D.; Khot, V. M.; Salunkhe, A. B.; Prasad, A. I.; Ningthoujam, R. S.; Pawar, S. H.

    2013-03-01

    LSMO (La0.7Sr0.3MnO3) magnetic nanoparticles (MNPs) coated with double layer oleic acid (OA) surfactant are prepared to make a water based magnetic nanofluid for hyperthermia application. Various experimental techniques are used for bilayer coating analysis. The effect of the bilayer coating on magnetic properties is studied by superconducting quantum interface device (SQUID). Colloidal behaviour of coated MNPs in aqueous medium is studied by the zeta potential and dynamic light scattering. The effects of pH and ionic strength on the colloidal stability of the MNPs are studied in detail. For the bilayer-coated LSMO MNPs aggregation is not observed even in high ionic strength and at physiological pH (7.4). For making the nanofluid of the bilayer-coated MNPs the colloidal stability is studied in physiological media like phosphate buffer solution. Under induction heating experiment, hyperthermia temperature (42-43 °C) could be achieved by the bilayer-coated sample at a magnetic field of 168-335 Oe and frequency of 267 kHz. The bilayer OA coating can hinder the agglomeration of MNPs significantly and produce stable suspension with improved hyperthermia properties. The bilayer OA coating also improves the specific absorption rate (SAR) of LSMO MNPs from 25 to 40 W g-1.

  14. Stabilization of Landslides for the Improvement of Aquatic Habitat

    Treesearch

    Michael J. Furniss

    1989-01-01

    Chronic surface and mass erosion from recent landslides often prevents the recovery of productive stream habitats following initial mass failure events. Low-cost methods that can accelerate recovery and stabilization processes have been employed on numerous failed slopes in the Six Rivers National Forest in the northwest corner of California, with notable success. Two...

  15. Making Stability Operations Less Complex While Improving Interoperability

    DTIC Science & Technology

    2008-06-01

    doctrine, organizations, training, education , exercises, materiel, leadership, personnel, facilities, and planning.” 3 “Stabil- ity operations are...is never context free, there are always aspects of community, culture, cognitive skills and technology evident. Accordingly, educational , cultural...Information sharing among systems is accomplished through interfaces with well-defined protocols, business rules and semantics (e.g., WSDL, SOAP and

  16. Creative Opportunities to Improve Young Children's Balance, Strength & Stability

    ERIC Educational Resources Information Center

    Mally, Kristi

    2008-01-01

    Strength, balance, and stability are important factors in performing movement skills, but are often overlooked by elementary schools when planning a quality physical education program for young children. These three interrelated structural characteristics are involved in all human movements. Movement is created by continually changing postures in…

  17. Creative Opportunities to Improve Young Children's Balance, Strength & Stability

    ERIC Educational Resources Information Center

    Mally, Kristi

    2008-01-01

    Strength, balance, and stability are important factors in performing movement skills, but are often overlooked by elementary schools when planning a quality physical education program for young children. These three interrelated structural characteristics are involved in all human movements. Movement is created by continually changing postures in…

  18. Modeling the effect of water activity and storage temperature on chemical stability of coffee brews.

    PubMed

    Manzocco, Lara; Nicoli, Maria Cristina

    2007-08-08

    This work was addressed to study the chemical stability of coffee brew derivatives as a function of water activity (aw) and storage temperature. To this purpose, coffee brew was freeze-dried, equilibrated at increasing aw values, and stored for up to 10 months at different temperatures from -30 to 60 degrees C. The chemical stability of the samples was assessed by measuring H3O+ formation during storage. Independently of storage temperature, the rate of H3O+ formation was considerably low only when aw was reduced below 0.5 (94% w/w). Beyond this critical boundary, the rate increased, reaching a maximum value at ca. 0.8 aw (78% w/w). Further hydration up to the aw of the freshly prepared beverage significantly increased chemical stability. It was suggested that mechanisms other than lactones' hydrolysis, probably related to nonenzymatic browning pathways, could contribute to the observed increase in acidity during coffee staling. The temperature dependence of H3O+ formation was well-described by the Arrhenius equation in the entire aw range considered. However, aw affected the apparent activation energy and frequency factor. These effects were described by simple equations that were used to set up a modified Arrhenius equation. This model was validated by comparing experimental values, not used to generate the model, with those estimated by the model itself. The model allowed efficient prediction of the chemical stability of coffee derivatives on the basis of only the aw value and storage temperature.

  19. Effects of temperature distribution on boundary layer stability for a circular cone at Mach 10

    NASA Astrophysics Data System (ADS)

    Rigney, Jeffrey M.

    A CFD analysis was conducted on a circular cone at 3 degrees angle of attack at Mach 10 using US3D and STABL 3D to determine the effect of wall temperature on the stability characteristics that lead to laminar-to-turbulent transition. Wall temperature distributions were manipulated while all other flow inputs and geometric qualities were held constant. Laminar-to-turbulent transition was analyzed for isothermal and adiabatic wall conditions, a simulated short-duration wind tunnel case, and several hot-nose temperature distributions. For this study, stability characteristics include maximum N-factor growth and the corresponding frequency range, disturbance spatial amplification rate and the corresponding modal frequency, and stability neutral point location. STABL 3D analysis indicates that temperature distributions typical of those in short-duration hypersonic wind tunnels do not result in any significant difference on the stability characteristics, as compared to an isothermal wall boundary condition. Hypothetical distributions of much greater temperatures at and past the nose tip do show a trend of dampening of second-mode disturbances, most notably on the leeward ray. The most pronounced differences existed between the isothermal and adiabatic cases.

  20. All Inorganic Cesium Lead Iodide Perovskite Nanowires with Stabilized Cubic Phase at Room Temperature and Nanowire Array-Based Photodetectors.

    PubMed

    Waleed, Aashir; Tavakoli, Mohammad Mahdi; Gu, Leilei; Hussain, Shabeeb; Zhang, Daquan; Poddar, Swapnadeep; Wang, Ziyi; Zhang, Rongjun; Fan, Zhiyong

    2017-08-09

    Alluring optical and electronic properties have made organometallic halide perovskites attractive candidates for optoelectronics. Among all perovskite materials, inorganic CsPbX3 (X is halide) in black cubic phase has triggered enormous attention recently owing to its comparable photovoltaic performance and high stability as compared to organic and hybrid perovskites. However, cubic phase stabilization at room temperature for CsPbI3 still survives as a challenge. Herein we report all inorganic three-dimensional vertical CsPbI3 perovskite nanowires (NWs) synthesized inside anodic alumina membrane (AAM) by chemical vapor deposition (CVD) method. It was discovered that the as-grown NWs have stable cubic phase at room temperature. This significant improvement on phase stability can be attributed to the effective encapsulation of NWs by AAM and large specific area of these NWs. To demonstrate device application of these NWs, photodetectors based on these high density CsPbI3 NWs were fabricated demonstrating decent performance. Our discovery suggests a novel and practical approach to stabilize the cubic phase of CsPbI3 material, which will have broad applications for optoelectronics in the visible wavelength range.

  1. Parameterized nonuniformity corrections (NUC) for non-temperature stabilized InGaAs SWIR sensing

    NASA Astrophysics Data System (ADS)

    Battaglia, Jesse; Burzi, Vincent; Moyer, Bruce; Sudol, Thomas; Passe, Joseph

    2010-04-01

    Military applications for conventional InGaAs SWIR sensing have been limited by the requirement of thermoelectric cooler (TEC) temperature stabilization for nonuniformity correction (NUC). TEC operation restricts the operating temperature range and size, weight, and power (SWAP) of these systems. For battery-powered man portable and micro UAV applications elimination of the TEC is critical. This paper discusses the advantages of our non-TEC temperature parameterized NUC corrections algorithms versus TEC stabilized architectures. The corrections algorithms enable performance-tuned polynomial order correction of both pixel uniformity and temperature parameterization for each SWIR sensor. These advances enable SWIR InGaAs sensing to meet the SWAP requirements of next generation military applications.

  2. Effect of Surface Aluminizing on Long-Term High-Temperature Thermal Stability of TC4 Titanium Alloy

    NASA Astrophysics Data System (ADS)

    Dai, Jingjie; Zhu, Jiyun; Zhuang, Lei; Li, Shouying

    2016-12-01

    Aluminum (Al)-rich titanium (Ti)-Al alloyed coating was fabricated on the surface of TC4 Ti alloy to improve the high-temperature stability of TC4 Ti alloy by means of arc-added glow discharge plasma technology. Microstructure, room-temperature properties and long-term high-temperature oxidation behavior of the alloyed sample were investigated. The results show that a uniform and compact Ti-Al alloyed coating with about 30μm thickness formed on the surface of TC4 Ti alloy. Microhardness and room-temperature wear resistance of the alloyed sample improved significantly. Long-term oxidation behaviors of the samples in air at 800∘C for 1000h show that the mass gain of the alloyed sample was 0.3686mg/cm2, while that of the substrate was 18.2095mg/cm2. Arc-added glow discharge plasma aluminizing improved high-temperature oxidation resistance of TC4 Ti alloy significantly.

  3. Lutein-enriched emulsion-based delivery systems: Influence of pH and temperature on physical and chemical stability.

    PubMed

    Davidov-Pardo, Gabriel; Gumus, Cansu Ekin; McClements, David Julian

    2016-04-01

    Lutein may be utilized in foods as a natural pigment or nutraceutical ingredient to improve eye health. Nevertheless, its use is limited by its poor water-solubility and chemical instability. We evaluated the effect of storage temperature and pH on the physical and chemical stability of lutein-enriched emulsions prepared using caseinate. The emulsions (initial droplet diameter=232 nm) remained physically stable at all incubation temperatures (5-70 °C); however the chemical degradation of lutein increased with increasing temperature (activation energy=38 kJ/mol). Solution pH had a major impact on the physical stability of the emulsions, causing droplet aggregation at pH 4 and 5. Conversely, the chemical stability of lutein was largely independent of the pH, with only a slight decrease in degradation at pH 8. This work provides important information for the rational design of emulsion-based delivery systems for a lipophilic natural dye and nutraceutical.

  4. Improving Small Signal Stability through Operating Point Adjustment

    SciTech Connect

    Huang, Zhenyu; Zhou, Ning; Tuffner, Francis K.; Chen, Yousu; Trudnowski, Daniel J.; Mittelstadt, William; Hauer, John F.; Dagle, Jeffery E.

    2010-09-30

    ModeMeter techniques for real-time small signal stability monitoring continue to mature, and more and more phasor measurements are available in power systems. It has come to the stage to bring modal information into real-time power system operation. This paper proposes to establish a procedure for Modal Analysis for Grid Operations (MANGO). Complementary to PSS’s and other traditional modulation-based control, MANGO aims to provide suggestions such as increasing generation or decreasing load for operators to mitigate low-frequency oscillations. Different from modulation-based control, the MANGO procedure proactively maintains adequate damping for all time, instead of reacting to disturbances when they occur. Effect of operating points on small signal stability is presented in this paper. Implementation with existing operating procedures is discussed. Several approaches for modal sensitivity estimation are investigated to associate modal damping and operating parameters. The effectiveness of the MANGO procedure is confirmed through simulation studies of several test systems.

  5. Improved in vivo stability of actinium-225 macrocyclic complexes.

    PubMed

    Deal, K A; Davis, I A; Mirzadeh, S; Kennel, S J; Brechbiel, M W

    1999-07-29

    The favorable nuclear properties of actinium-225 ((225)Ac) have led to proposal of this isotope for use in radioimmunotherapy. In an effort to reduce the toxicity of free (225)Ac, a series of ligands were evaluated for stability in vivo. Loss of (225)Ac from acyclic chelating agents resulted in high liver uptake and poor whole body clearance. The macrocyclic ligands c-DOTA, PEPA, and HEHA were evaluated, and (225)Ac-HEHA showed exceptional stability in vivo. (225)Ac chelated with EDTA, DTPA, DOTA, or PEPA permitted substantial accumulation of the radionuclide to the liver, while the (225)Ac-HEHA complex was essentially excreted within minutes of administration. The preparation of the ligands and radiolabeled complexes and the biodistribution results will be discussed.

  6. Improving electrokinetic microdevice stability by controlling electrolysis bubbles.

    PubMed

    Lee, Hwi Yong; Barber, Cedrick; Minerick, Adrienne R

    2014-07-01

    The voltage-operating window for many electrokinetic microdevices is limited by electrolysis gas bubbles that destabilize microfluidic system causing noise and irreproducible responses above ∼3 V DC and less than ∼1 kHz AC at 3 Vpp. Surfactant additives, SDS and Triton X-100, and an integrated semipermeable SnakeSkin® membrane were employed to control and assess electrolysis bubbles from platinum electrodes in a 180 by 70 μm, 10 mm long microchannel. Stabilized current responses at 100 V DC were observed with surfactant additives or SnakeSkin® barriers. Electrolysis bubble behaviors, visualized via video microscopy at the electrode surface and in the microchannels, were found to be influenced by surfactant function and SnakeSkin® barriers. Both SDS and Triton X-100 surfactants promoted smaller bubble diameters and faster bubble detachment from electrode surfaces via increasing gas solubility. In contrast, SnakeSkin® membranes enhanced natural convection and blocked bubbles from entering the microchannels and thus reduced current disturbances in the electric field. This data illustrated that electrode surface behaviors had substantially greater impacts on current stability than microbubbles within microchannels. Thus, physically blocking bubbles from microchannels is less effective than electrode functionalization approaches to stabilize electrokinetic microfluidic systems.

  7. Influence of Soil Organic Matter Stabilization Mechanisms on Temperature Sensitivity of Soil Respiration

    NASA Astrophysics Data System (ADS)

    Gillabel, J.; de Gryze, S.; Six, J.; Merckx, R.

    2007-12-01

    Knowledge on the sensitivity of soil organic matter (SOM) respiration to changes in temperature is crucial for predicting future impacts of climate change on soil C stocks. Temperature sensitivity of respiration is determined by the chemical structure of the compound to be decomposed and by the availability of the organic matter for decomposers. Biochemically recalcitrant SOM has a higher temperature sensitivity than biochemically labile SOM. However, it is hypothesized that the stabilization of SOM by interaction with the soil matrix could be an important attenuating control on temperature sensitivity. We investigated the effect of different SOM stabilization mechanisms on temperature sensitivity of SOM respiration. Two main mechanisms were considered: chemical interactions of SOM with clay and silt particles, and physical protection inside aggregates. Soil samples from an agricultural silt loam soil were fractionated by wet-sieving into macroaggregates, microaggregates and silt+clay fractions. SOM stabilization in the silt+clay fraction occurs mainly chemically, whereas in aggregates physical protection of SOM is more important. Samples of each fraction and of bulk soil were incubated at two temperatures (20°C and 30°C) for one month. After 2% of total soil carbon was respired, temperature sensitivity was determined for respiration of the next 0.5% of total soil carbon. This was done by calculating a Q10 value as the ratio of the times needed at each temperature to respire that fraction of the soil C. This method allows determination of temperature sensitivity independent of C quality. Calculated Q10 values decreased in the order bulk soil > macroaggregates > microaggregates > silt+clay, with the difference between macroaggregate Q10 and silt+clay Q10 being the only significant difference. These results indicate that protection of SOM attenuates temperature sensitivity, with chemical protection (silt+clay) having a larger effect than physical protection

  8. Ab Initio Simulations of Temperature Dependent Phase Stability and Martensitic Transitions in NiTi

    NASA Technical Reports Server (NTRS)

    Haskins, Justin B.; Thompson, Alexander E.; Lawson, John W.

    2016-01-01

    For NiTi based alloys, the shape memory effect is governed by a transition from a low-temperature martensite phase to a high-temperature austenite phase. Despite considerable experimental and computational work, basic questions regarding the stability of the phases and the martensitic phase transition remain unclear even for the simple case of binary, equiatomic NiTi. We perform ab initio molecular dynamics simulations to describe the temperature-dependent behavior of NiTi and resolve several of these outstanding issues. Structural correlation functions and finite temperature phonon spectra are evaluated to determine phase stability. In particular, we show that finite temperature, entropic effects stabilize the experimentally observed martensite (B19') and austenite (B2) phases while destabilizing the theoretically predicted (B33) phase. Free energy computations based on ab initio thermodynamic integration confirm these results and permit estimates of the transition temperature between the phases. In addition to the martensitic phase transition, we predict a new transition between the B33 and B19' phases. The role of defects in suppressing these phase transformations is discussed.

  9. Influence of Temperature and Grain Size on Austenite Stability in Medium Manganese Steels

    NASA Astrophysics Data System (ADS)

    Zhang, Yulong; Wang, Li; Findley, Kip O.; Speer, John G.

    2017-05-01

    With an aim to elucidate the influence of temperature and grain size on austenite stability, a commercial cold-rolled 7Mn steel was annealed at 893 K (620 °C) for times varying between 3 minutes and 96 hours to develop different grain sizes. The austenite fraction after 3 minutes was 34.7 vol pct, and at longer times was around 40 pct. An elongated microstructure was retained after shorter annealing times while other conditions exhibited equiaxed ferrite and austenite grains. All conditions exhibit similar temperature dependence of mechanical properties. With increasing test temperature, the yield and tensile strength decrease gradually, while the uniform and total elongation increase, followed by an abrupt drop in strength and ductility at 393 K (120 °C). The Olson-Cohen model was applied to fit the transformed austenite fractions for strained tensile samples, measured by means of XRD. The fit results indicate that the parameters α and β decrease with increasing test temperature, consistent with increased austenite stability. The 7Mn steels exhibit a distinct temperature dependence of the work hardening rate. Optimized austenite stability provides continuous work hardening in the temperature range of 298 K to 353 K (25 °C to 80 °C). The yield and tensile strengths have a strong dependence on grain size, although grain size variations have less effect on uniform and total elongation.

  10. Influence of Temperature and Grain Size on Austenite Stability in Medium Manganese Steels

    NASA Astrophysics Data System (ADS)

    Zhang, Yulong; Wang, Li; Findley, Kip O.; Speer, John G.

    2017-02-01

    With an aim to elucidate the influence of temperature and grain size on austenite stability, a commercial cold-rolled 7Mn steel was annealed at 893 K (620 °C) for times varying between 3 minutes and 96 hours to develop different grain sizes. The austenite fraction after 3 minutes was 34.7 vol pct, and at longer times was around 40 pct. An elongated microstructure was retained after shorter annealing times while other conditions exhibited equiaxed ferrite and austenite grains. All conditions exhibit similar temperature dependence of mechanical properties. With increasing test temperature, the yield and tensile strength decrease gradually, while the uniform and total elongation increase, followed by an abrupt drop in strength and ductility at 393 K (120 °C). The Olson-Cohen model was applied to fit the transformed austenite fractions for strained tensile samples, measured by means of XRD. The fit results indicate that the parameters α and β decrease with increasing test temperature, consistent with increased austenite stability. The 7Mn steels exhibit a distinct temperature dependence of the work hardening rate. Optimized austenite stability provides continuous work hardening in the temperature range of 298 K to 353 K (25 °C to 80 °C). The yield and tensile strengths have a strong dependence on grain size, although grain size variations have less effect on uniform and total elongation.

  11. Reactive Melt Extrusion To Improve the Dissolution Performance and Physical Stability of Naproxen Amorphous Solid Dispersions.

    PubMed

    Liu, Xu; Zhou, Lin; Zhang, Feng

    2017-03-06

    The purpose of this study was to investigate the reaction between naproxen (NPX) and meglumine (MEG) at elevated temperature and to study the effect of this reaction on the physical stabilities and in vitro drug-release properties of melt-extruded naproxen amorphous solid dispersions (ASDs). Differential scanning calorimetry, hot-stage polarized light microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy analyses demonstrated that in situ salt formation with proton transfer between NPX and MEG occurred at elevated temperature during the melt extrusion process. The amorphous NPX-MEG salt was physically most stable when two components were present at a 1:1 molar ratio. Polymeric carriers, including povidone, copovidone, and SOLUPLUS, did not interfere with the reaction between NPX and MEG during melt extrusion. Compared to the traditional NPX ASDs consisting of NPX and polymer only, NPX-MEG ASDs were physically more stable and remained amorphous following four months storage at 40 °C and 75% RH (relative humidity). Based on nonsink dissolution testing and polarized light microscopy analyses, we concluded that the conventional NPX ASDs composed of NPX and polymers failed to improve the NPX dissolution rate due to the rapid recrystallization of NPX in contact with aqueous medium. The dissolution rate of NPX-MEG ASDs was two times greater than the corresponding physical mixtures and conventional NPX ASDs. This study demonstrated that the acid-base reaction between NPX and MEG during melt extrusion significantly improved the physical stability and the dissolution rate of NPX ASDs.

  12. Improved performance of silicon nitride-based high temperature ceramics

    NASA Technical Reports Server (NTRS)

    Ashbrook, R. L.

    1977-01-01

    Results are presented regarding experiments intended for improving the strength and toughness of hot-pressed Si3N4 (HPSN), improving the strength and oxidation resistance of reaction-sintered Si3N4 (RSSN), and improving the strength and oxidation resistance of sinterable Si-Al-O-N compositions. It is shown that the use of ZrO2 instead of MgO as a sintering aid improved the room-temperature and high-temperature flexural strength of HPSN, in addition to enhancing the rupture strength and Charpy impact resistance. The use of crushable energy absorbing layers increased the impact resistance of HPSN. Impregnation of RSSN with solutions that oxidize to Al2O3 or ZrO2 resulted in increased bending strength at room temperature. Beta-prime Si-Al-O-N sintered to full density by means of the sintering aids CeO2, Y2O3, and ZrO2 yielded the greatest strength with Y2O3 and the greatest oxidation resistance with ZrO2.

  13. Improved Durability of SOEC Stacks for High Temperature Electrolysis

    SciTech Connect

    James E. O'Brien; Robert C. O'Brien; Xiaoyu Zhang; Joseph J. Hartvigsen; Greg Tao

    2013-01-01

    High temperature steam electrolysis is a promising technology for efficient and sustainable large-scale hydrogen production. Solid oxide electrolysis cells (SOECs) are able to utilize high temperature heat and electric power from advanced high-temperature nuclear reactors or renewable sources to generate carbon-free hydrogen at large scale. However, long term durability of SOECs needs to be improved significantly before commercialization of this technology can be realized. A degradation rate of 1%/khr or lower is proposed as a threshold value for commercialization of this technology. Solid oxide electrolysis stack tests have been conducted at Idaho National Laboratory to demonstrate recent improvements in long-term durability of SOECs. Electrolyte-supported and electrode-supported SOEC stacks were provided by Ceramatec Inc. and Materials and Systems Research Inc. (MSRI), respectively, for these tests. Long-term durability tests were generally operated for a duration of 1000 hours or more. Stack tests based on technologies developed at Ceramatec and MSRI have shown significant improvement in durability in the electrolysis mode. Long-term degradation rates of 3.2%/khr and 4.6%/khr were observed for MSRI and Ceramatec stacks, espectively. One recent Ceramatec stack even showed negative degradation (performance improvement) over 1900 hours of operation. Optimization of electrode materials, interconnect coatings, and electrolyte-electrode interface microstructures contribute to better durability of SOEC stacks.

  14. Improving the phase stability and oxidation resistance of β-NiAl

    SciTech Connect

    Brammer, Travis

    2011-01-01

    replacing Ni based superalloys. Modifications to NiAl were explored to increase the phase stability and oxidation resistance which would allow these alloys to be used at even higher temperatures yielding greater efficiencies. The extended Miedema model was an effective tool that screened all of the potential phase space for ternary substitutions to NiAl and found the few potential systems worth further investigation. After production of the alloys it was determined that Ir, Rh, and Pd were the top candidates for substitution on Ni site up to 12 at%. The melting temperature of NiAl could be increased as much as 150 C with 12 at% Ir and 130 C with 12 at% Rh substitution. Pall adium on the other hand decreased the melting temperature by 50 C at the 12 at% substitution level. The grain size was found to have a profound influence on the oxidation resistance. Both Ir and Rh substitutions resulted in finer grain sizes compared to Pd substitutions or base NiAl. The grain size increased drastically during high temperature annealing with the PGM substitutions hindering grain growth only slightly. However, the addition of 0.05 at% Hf limited the grain growth dramatically during high temperature annealing. NiAl inherently has respectable oxidation resistance up to 1100 C. It was found through experimental testing that both Ir and Rh substitutions improve the oxidation resistance of NiAl at ultra-high temperatures with Ir performing the best. Both PGM substitutions decreased the growth rate as well as forming a more adherent oxide scale. Pd substitutions appeared to have a negligible effect to the oxidation resistance of NiAl. Hafnium addition of 0.05 at% was found to decrease the oxidation rate as well as increase the scale adherence. The combination of both Ir substitution (6-9 at%) and Hf addition (0.05 at%) produced the alloy with the best oxidation resistance. Although improvements in phase stability and oxidation resistance have been made to the NiAl system, more development and

  15. Improved measurement of the rotor temperature in analytical ultracentrifugation.

    PubMed

    Zhao, Huaying; Balbo, Andrea; Metger, Howard; Clary, Robert; Ghirlando, Rodolfo; Schuck, Peter

    2014-04-15

    Sedimentation velocity is a classical method for measuring the hydrodynamic, translational friction coefficient of biological macromolecules. In a recent study comparing various analytical ultracentrifuges, we showed that external calibration of the scan time, radial magnification, and temperature is critically important for accurate measurements (Anal. Biochem. 440 (2013) 81-95). To achieve accurate temperature calibration, we introduced the use of an autonomous miniature temperature logging integrated circuit (Maxim Thermochron iButton) that can be inserted into an ultracentrifugation cell assembly and spun at low rotor speeds. In the current work, we developed an improved holder for the temperature sensor located in the rotor handle. This has the advantage of not reducing the rotor capacity and allowing for a direct temperature measurement of the spinning rotor during high-speed sedimentation velocity experiments up to 60,000rpm. We demonstrated the sensitivity of this approach by monitoring the adiabatic cooling due to rotor stretching during rotor acceleration and the reverse process on rotor deceleration. Based on this, we developed a procedure to approximate isothermal rotor acceleration for better temperature control.

  16. Improved Measurement of the Rotor Temperature in Analytical Ultracentrifugation

    PubMed Central

    Zhao, Huaying; Balbo, Andrea; Metger, Howard; Clary, Robert; Ghirlando, Rodolfo; Schuck, Peter

    2014-01-01

    Sedimentation velocity is a classical method for measuring the hydrodynamic, translational friction coefficient of biological macromolecules. In a recent study, comparing various analytical ultracentrifuges, we have shown that external calibration of the scan time, radial magnification, and temperature are critically important for accurate measurements (Anal. Biochem., 2013, doi: 10.1016/j.ab.2013.05.011). To achieve accurate temperature calibration, we have introduced the use of an autonomous miniature temperature logging integrated circuit (Maxim Thermochron iButton ™) that can be inserted in an ultracentrifugation cell assembly and spun at low rotor speeds. In the present work, we developed an improved holder for the temperature sensor located in the rotor handle. This has the advantage of not reducing the rotor capacity and allows for a direct temperature measurement of the spinning rotor during high-speed sedimentation velocity experiments up to 60,000 rpm. We demonstrate the sensitivity of this approach by monitoring the adiabatic cooling due to rotor stretching during rotor acceleration, and the reverse process upon rotor deceleration. Based on this, we developed a procedure to approximate isothermal rotor acceleration for better temperature control. PMID:24530285

  17. Room-temperature charge stability modulated by quantum effects in a nanoscale silicon island.

    PubMed

    Shin, S J; Lee, J J; Kang, H J; Choi, J B; Yang, S-R Eric; Takahashi, Y; Hasko, D G

    2011-04-13

    We report on transport measurement performed on a room-temperature-operating ultrasmall Coulomb blockade devices with a silicon island of sub5 nm. The charge stability at 300K exhibits a substantial change in slopes and diagonal size of each successive Coulomb diamond, but remarkably its main feature persists even at low temperature down to 5.3K except for additional Coulomb peak splitting. This key feature of charge stability with additional fine structures of Coulomb peaks are successfully modeled by including the interplay between Coulomb interaction, valley splitting, and strong quantum confinement, which leads to several low-energy many-body excited states for each dot occupancy. These excited states become enhanced in the sub5 nm ultrasmall scale and persist even at 300K in the form of cluster, leading to the substantial modulation of charge stability.

  18. Effects of crosslinking temperature and time on microstructure and stability of cassava starch microspheres.

    PubMed

    Puncha-Arnon, Santhanee; Jiranuntakul, Wittawat; Uttapap, Dudsadee

    2015-12-10

    Starch microspheres (SMs) were prepared by a water-in-water emulsion-crosslinking technique at 4 °C and 30 °C for 1, 6, 12 and 24h; the SMs obtained were analyzed for crosslinking density, morphology, crystalline structure, and stability against temperature, pH, and α-amylase hydrolysis. The crosslinking degree at 30 °C was considerably higher than that at 4 °C. SMs prepared at 4 °C for less than 12h incubation had larger size and more porous structure as compared with those prepared at 30 °C, but the morphology became comparable (spherical shape with smooth surface and dense structure) after 24h incubation. All SMs samples displayed amorphous structure. Stability tests revealed that the SMs were very stable under acidic and mild basic pH; however, stability against α-amylase hydrolysis varied depending on incubation temperature and time.

  19. Effect of surface morphology and temperature on the structural stability of nanoscale wavy films.

    PubMed

    Adnan, A; Sun, C T

    2008-08-06

    The atomic scale structural stability of freestanding wavy gold (Au) nanofilms was investigated using molecular dynamics simulations. The waviness in the Au film was formed by cleaving sinusoidal surfaces from a [Formula: see text] bulk crystal. The degree of waviness was varied by changing the wavelength of the sinusoidal surface profile. Films were then equilibrated at different temperatures (between 10 and 1080 K) and their structural stability was monitored. The MD simulation results revealed that the stability of films depends on temperature as well as the waviness of the film surface. It was shown that the size-dependent melting point depression of Au plays the dominant role in causing the structural instability of wavy films.

  20. Structure, electrical characteristics, and high-temperature stability of aerosol jet printed silver nanoparticle films

    NASA Astrophysics Data System (ADS)

    Rahman, Md Taibur; McCloy, John; Ramana, C. V.; Panat, Rahul

    2016-08-01

    Printed electronics has emerged as a versatile eco-friendly fabrication technique to create sintered nanoparticle (NP) films on arbitrary surfaces with an excellent control over the film microstructure. While applicability of such films for high-temperature applications is not explored previously, herein we report the high-temperature electrical stability of silver (Ag) metal NP films fabricated using an Aerosol Jet based printing technique and demonstrate that this behavior is dictated by changes in the film microstructure. In-situ high temperature (24-500 °C) impedance spectroscopy measurements show that the real part of the impedance increases with increasing temperature up to 150 °C, at which point a decreasing trend prevails until 300 °C, followed again by an increase in impedance. The electrical behavior is correlated with the in-situ grain growth of the Ag NP films, as observed afterwards by scanning electron microscopy and X-ray diffraction (XRD), and could be tailored by controlling the initial microstructure through sintering conditions. Using combined diffraction and spectroscopic analytical methods, it is demonstrated the Aerosol Jet printed Ag NP films exhibit enhanced thermal stability and oxidation resistance. In addition to establishing the conditions for stability of Ag NP films, the results provide a fundamental understanding of the effect of grain growth and reduction in grain boundary area on the electrical stability of sintered NP films.

  1. The role of temperature variability in stabilizing the mountain pine beetle-fungus mutualism.

    PubMed

    Addison, A L; Powell, J A; Six, D L; Moore, M; Bentz, B J

    2013-10-21

    As global climate patterns continue to change and extreme weather events become increasingly common, it is likely that many ecological interactions will be affected. One such interaction is the multipartite symbiosis that exists between the mountain pine beetle and two species of fungi, Grosmannia clavigera and Ophiostoma montium. In this mutualism, the fungi provide nutrition to the beetle, while the fungi benefit by being dispersed to new host trees. Multi-partite mutualisms are predicted to be unstable due to strong direct competition among symbionts or natural selection for superior over inferior mutualists. However, this mutualism has remained stable over long periods of evolutionary time. In this paper, we developed a temperature-based model for the spread of fungi within a tree and connected it to an existing model for mountain pine beetle development. Using this integrated model for fungal growth, we explored the possibility that temperature variability is a stabilizing mechanism for the mountain pine beetle-fungi mutualism. Of the three types of temperature variability we tested: intra-year, inter-year and variability due to transitioning between different thermal habitats (thermal migration), we found that thermal migration was the most robust stabilizing mechanism. Additionally, we found that the MPB attack density or spacing between fungal lesions also had a significant effect on the stability of the system. High attack densities or close lesion spacings also tended to stabilize the system, regardless of temperature.

  2. Structure, electrical characteristics, and high-temperature stability of aerosol jet printed silver nanoparticle films

    SciTech Connect

    Rahman, Md Taibur; McCloy, John; Panat, Rahul E-mail: rvchintalapalle@utep.edu; Ramana, C. V. E-mail: rvchintalapalle@utep.edu

    2016-08-21

    Printed electronics has emerged as a versatile eco-friendly fabrication technique to create sintered nanoparticle (NP) films on arbitrary surfaces with an excellent control over the film microstructure. While applicability of such films for high-temperature applications is not explored previously, herein we report the high-temperature electrical stability of silver (Ag) metal NP films fabricated using an Aerosol Jet based printing technique and demonstrate that this behavior is dictated by changes in the film microstructure. In-situ high temperature (24–500 °C) impedance spectroscopy measurements show that the real part of the impedance increases with increasing temperature up to 150 °C, at which point a decreasing trend prevails until 300 °C, followed again by an increase in impedance. The electrical behavior is correlated with the in-situ grain growth of the Ag NP films, as observed afterwards by scanning electron microscopy and X-ray diffraction (XRD), and could be tailored by controlling the initial microstructure through sintering conditions. Using combined diffraction and spectroscopic analytical methods, it is demonstrated the Aerosol Jet printed Ag NP films exhibit enhanced thermal stability and oxidation resistance. In addition to establishing the conditions for stability of Ag NP films, the results provide a fundamental understanding of the effect of grain growth and reduction in grain boundary area on the electrical stability of sintered NP films.

  3. High-temperature stabilization by air of a pyrophoric catalyst for the synthesis of ammonia

    SciTech Connect

    Krylova, A.V.; Ustimenko, G.A.

    1982-12-01

    The reaction of a catalyst for the synthesis of ammonia with air at 480 to 520/sup 0/C leads to the formation on the surface of a thin protective oxide structure that eliminates its pyrophoric character. High-temperature stabilization by air is a considerably faster process than passivation and leads to the production of catalysts with increased resistance to oxidation.

  4. OBSERVATIONS OF SIMILARITY THEORY STABILITY CORRECTION TERMS FOR MOMENTUM AND TEMPERATURE, OVER AGRICULTURAL FIELDS AND FORESTS.

    EPA Science Inventory

    Many observations of temperature and wind speed profiles have been taken over "ideal" terrain and analyzed to develop the stability correction terms which are commonly used in the application of similarity theory. Fewer observations have been taken and analyzed in this manner ov...

  5. OBSERVATIONS OF SIMILARITY THEORY STABILITY CORRECTION TERMS FOR MOMENTUM AND TEMPERATURE, OVER AGRICULTURAL FIELDS AND FORESTS.

    EPA Science Inventory

    Many observations of temperature and wind speed profiles have been taken over "ideal" terrain and analyzed to develop the stability correction terms which are commonly used in the application of similarity theory. Fewer observations have been taken and analyzed in this manner ov...

  6. Formaldehyde emission and high-temperature stability of cured urea-formaldehyde resins

    Treesearch

    Shin-ichiro Tohmura; Chung-Yun Hse; Mitsuo Higuchi

    2000-01-01

    A test method for measuring formaldehyde from urea-formaldehyde (UF) resins at high temperature was developed and used to assess the influence of the reaction pH on the formaldehyde emission and heat stability of the cured resins. Additionally, solid-state 13C CP/MAS nuclear magnetic resonance (NMR) techniques were used to investigate the...

  7. High-temperature strength stability of three forms of chemically vapor deposited tungsten

    NASA Technical Reports Server (NTRS)

    Bryant, W. A.

    1974-01-01

    Three types of CVD tungsten (fluoride-produced, chloride-produced, and a layered composite of the two-termed duplex) were evaluated to determine their high-temperature strength and microstructural stability following 5000-hr exposure to temperatures of 1540 and 1700 C. At the highest temperatures investigated (1540 and 1700 C), the tensile strengths of the two basic materials were essentially equal. At lower temperatures, chloride tungsten possessed lower yield strength but higher ultimate strength than fluoride tungsten while the behavior of the duplex material was generally intermediate. Apparent anomalies in high-temperature elongation behavior are explained on the basis of grain boundary cavity formation and recrystallization. The grain size of fluoride tungsten changed only slightly following 5000-h treatment at 1700 C. In contrast, chloride tungsten possessed both poor resistance to grain growth and an accompanying relatively high ductile-brittle transition temperature.

  8. Effect of high-temperature on high-performance liquid chromatography column stability and performance under temperature-programmed conditions.

    PubMed

    Marin, Stephanie J; Jones, Brian A; Felix, W Dale; Clark, Jody

    2004-03-19

    Six commercially available analytical (4.1 or 4.6 mm i.d.) columns were evaluated under temperature-programmed high-temperature liquid chromatography (HTLC) conditions to access their stability and performance at extreme temperatures. Seven components consisting of acidic, basic and neutral compounds were analyzed under temperature-programmed conditions and solvent gradient conditions using three different mobile phase compositions (acidic, basic and neutral). Each column was checked with a two-component test mix at various stages of the evaluation to look for signs of stationary phase collapse. Three zirconia based stationary phases studied exhibited column bleed under temperature-programmed conditions. The other three columns, a polydentate silica column, a polystyrene-divinylbenzene (PS-DVB) polymeric column, and a graphitic carbon column performed well with no evidence of stationary phase degradation. The R.S.D. for the retention times and efficiencies were less than 10% for most conditions, and not more than 15% during the course of the evaluation for each column. The polydentate silica stationary phase was temperature programmed to 100 degrees C, the PS-DVB stationary phase was temperature programmed up to 150 degrees C, and the graphitic carbon column was used with temperature programming up to 200 degrees C. Comparable peak capacities and similar retention behaviors were observed under solvent gradient and temperature-programmed conditions. Temperature programming with dynamic mobile phase preheating can replace solvent gradient analysis without a loss of peak capacity when used with 4.1 or 4.6 mm columns.

  9. Improvement in electrochromic stability of electrodeposited nickel hydroxide thin film

    SciTech Connect

    Natarajan, C.; Matsumoto, H.; Nogami, G.

    1997-01-01

    The electrochromic nickel hydroxide thin film was anodically deposited from an aqueous solution. The effect of solution temperature, postheat-treatment temperature, and addition of cadmium on the electrochromic behavior (color/bleach durability cycle, response time, and coloration efficiency of the nickel hydroxide films in NaOH) were investigated. A significant increase in the color/bleach durability cycle from 500 (for the as-deposited film) to more than 5000 cycles (for the heat-treated film) was observed. The addition of cadmium increased the utilization of the active materials. It was found that the coloration efficiency was 40 cm{sup 2}/C and coloration and bleaching response time were 20 to 30 s and 8 to 10 s, respectively. The change in the electrochromic properties with heat-treatment temperature is discussed based on the physical and electrochemical analysis.

  10. Evolution of stability in a cold-active enzyme elicits specificity relaxation and highlights substrate-related effects on temperature adaptation.

    PubMed

    Gatti-Lafranconi, Pietro; Natalello, Antonino; Rehm, Sascha; Doglia, Silvia Maria; Pleiss, Jürgen; Lotti, Marina

    2010-01-08

    Molecular aspects of thermal adaptation of proteins were studied by following the co-evolution of temperature dependence, conformational stability, and substrate specificity in a cold-active lipase modified via directed evolution. We found that the evolution of kinetic stability was accompanied by a relaxation in substrate specificity. Moreover, temperature dependence and selectivity turned out to be mutually dependent. While the wild-type protein was strictly specific for short-chain triglycerides (C4) in the temperature range 10-50 degrees C and displayed highest activity in the cold, its stabilized variant was able to accept C8 and C12 molecules and its selectivity was temperature dependent. We could not detect any improvement in the overall structural robustness of the mutant when the structure was challenged by temperature or chemical denaturants. There is, however, strong evidence for local stabilization effects in the active-site region provided by two independent approaches. Differential scanning fluorimetry revealed that the exposure of hydrophobic patches (as the active site is) precedes denaturation, and molecular dynamics simulations confirmed that stability was obtained by restriction of the mobility of the lid, a flexible structure that regulates the access to the enzyme active site and influences its stability. This reduction of lid movements is suggested to be accompanied by a concomitant increase in the mobility of other protein regions, thus accounting for the observed broadening of substrate specificity.

  11. Optimal placement of unified power flow controllers to improve dynamic voltage stability using power system variable based voltage stability indices.

    PubMed

    Albatsh, Fadi M; Ahmad, Shameem; Mekhilef, Saad; Mokhlis, Hazlie; Hassan, M A

    2015-01-01

    This study examines a new approach to selecting the locations of unified power flow controllers (UPFCs) in power system networks based on a dynamic analysis of voltage stability. Power system voltage stability indices (VSIs) including the line stability index (LQP), the voltage collapse proximity indicator (VCPI), and the line stability index (Lmn) are employed to identify the most suitable locations in the system for UPFCs. In this study, the locations of the UPFCs are identified by dynamically varying the loads across all of the load buses to represent actual power system conditions. Simulations were conducted in a power system computer-aided design (PSCAD) software using the IEEE 14-bus and 39- bus benchmark power system models. The simulation results demonstrate the effectiveness of the proposed method. When the UPFCs are placed in the locations obtained with the new approach, the voltage stability improves. A comparison of the steady-state VSIs resulting from the UPFCs placed in the locations obtained with the new approach and with particle swarm optimization (PSO) and differential evolution (DE), which are static methods, is presented. In all cases, the UPFC locations given by the proposed approach result in better voltage stability than those obtained with the other approaches.

  12. Optimal Placement of Unified Power Flow Controllers to Improve Dynamic Voltage Stability Using Power System Variable Based Voltage Stability Indices

    PubMed Central

    Albatsh, Fadi M.; Ahmad, Shameem; Mekhilef, Saad; Mokhlis, Hazlie; Hassan, M. A.

    2015-01-01

    This study examines a new approach to selecting the locations of unified power flow controllers (UPFCs) in power system networks based on a dynamic analysis of voltage stability. Power system voltage stability indices (VSIs) including the line stability index (LQP), the voltage collapse proximity indicator (VCPI), and the line stability index (Lmn) are employed to identify the most suitable locations in the system for UPFCs. In this study, the locations of the UPFCs are identified by dynamically varying the loads across all of the load buses to represent actual power system conditions. Simulations were conducted in a power system computer-aided design (PSCAD) software using the IEEE 14-bus and 39- bus benchmark power system models. The simulation results demonstrate the effectiveness of the proposed method. When the UPFCs are placed in the locations obtained with the new approach, the voltage stability improves. A comparison of the steady-state VSIs resulting from the UPFCs placed in the locations obtained with the new approach and with particle swarm optimization (PSO) and differential evolution (DE), which are static methods, is presented. In all cases, the UPFC locations given by the proposed approach result in better voltage stability than those obtained with the other approaches. PMID:25874560

  13. Improvement of transient stability using unified power flow controller

    SciTech Connect

    Mihalic, R.; Zunko, P.; Povh, D.

    1996-01-01

    The aim of the paper is to analyze the effect of an Unified Power Flow Controller (UPFC) on transient stability margin enhancement of a longitudinal system. To utilize the UPFC possibilities fully, the three controllable UPFC parameters were determined during the digital simulation process performed by the NETOMAC simulation program. The basis for determination of the suitable damping strategy and for determination of the optimal UPFC parameters is a mathematical model, which describes the interdependence between longitudinal transmission system parameters, operating conditions and UPFC parameters in the form of analytical equations. On the basis of the mathematical model, the theoretical UPFC limits were also detected, and their appearance explained.

  14. Improved Nominal Operating Cell Temperature (NOCT) test procedure

    NASA Technical Reports Server (NTRS)

    Wen, L.; Berns, D.

    1984-01-01

    A procedure is developed to improve testing of Nominal Operating Cell Temperature (NOCT) as it applies to solar energy conversion modules. NOCT is a direct reflection of module thermal design and is closely related to the representative ambient temperature. It is also a key to array energy production and estimates of module lifetimes. Present NOCT test and evaluation procedures are inconsistent, producing significant scatter. Test refinements would specify a clear sky, the addition of 10% to the insolation level for ground reflection, the addition of a ground emission factor of 0.8 (at 30C ground temperature), an effective wind direction of 135 degrees from the North, and a module tilt of 30 degrees from the horizon.

  15. Carbon--silicon coating alloys for improved irradiation stability

    DOEpatents

    Bokros, J.C.

    1973-10-01

    For ceramic nuclear fuel particles, a fission product-retaining carbon-- silicon alloy coating is described that exhibits low shrinkage after exposure to fast neutron fluences of 1.4 to 4.8 x 10/sup 21/ n/cm/sup 2/ (E = 0.18 MeV) at irradiation temperatures from 950 to 1250 deg C. Isotropic pyrolytic carbon containing from 18 to 34 wt% silicon is co-deposited from a gaseous mixiure of propane, helium, and silane at a temperature of 1350 to 1450 deg C. (Official Gazette)

  16. Iron aluminide alloys with improved properties for high temperature applications

    DOEpatents

    McKamey, C.G.; Liu, C.T.

    1990-10-09

    An improved iron aluminide alloy of the DO[sub 3] type is described that has increased room temperature ductility and improved high elevated temperature strength. The alloy system further is resistant to corrosive attack in the environments of advanced energy conversion systems such as those using fossil fuels. The resultant alloy is relatively inexpensive as contrasted to nickel based and high nickel steels currently utilized for structural components. The alloy system consists essentially of 26--30 at. % aluminum, 0.5--10 at. % chromium, 0.02--0.3 at. % boron plus carbon, up to 2 at. % molybdenum, up to 1 at. % niobium, up to 0.5 at. % zirconium, up to 0.1 at. % yttrium, up to 0.5 at. % vanadium and the balance iron. 3 figs.

  17. Iron aluminide alloys with improved properties for high temperature applications

    DOEpatents

    McKamey, Claudette G.; Liu, Chain T.

    1990-01-01

    An improved iron aluminide alloy of the DO.sub.3 type that has increased room temperature ductility and improved high elevated temperature strength. The alloy system further is resistant to corrosive attack in the environments of advanced energy corrosion systems such as those using fossil fuels. The resultant alloy is relatively inexpensive as contrasted to nickel based and high nickel steels currently utilized for structural components. The alloy system consists essentially of 26-30 at. % aluminum, 0.5-10 at. % chromium, 0.02-0.3 at. % boron plus carbon, up to 2 at. % molybdenum, up to 1 at. % niobium, up to 0.5 at. % zirconium, up to 0.1 at. % yttrium, up to 0.5 at. % vanadium and the balance iron.

  18. Effect of temperature and duration of storage on the stability of polyfluoroalkyl chemicals in human serum

    PubMed Central

    Kato, Kayoko; Wong, Lee-Yang; Basden, Brian J.; Calafat, Antonia M.

    2015-01-01

    We assessed the potential impact of temperature on the long-term stability of several polyfluoroalkyl chemicals in serum. We evaluated the concentrations of perfluorooctane sulfonate, perfluorohexane sulfonate, perfluorooctanoate and perfluorononanoate in 16 human serum samples stored at room temperature, 5 °C, −20 °C and −70 °C at several time points during an eight month period. Concentrations of the target analytes remained unchanged under all studied conditions, even when serum was kept at room temperature for 10 days. PMID:23232044

  19. Process for stabilizing dimensions of duplex stainless steels for service at elevated temperatures

    DOEpatents

    Hull, Frederick C.; Tobin, John C.

    1981-01-01

    Duplex stainless steel materials containing austenite plus delta ferrite, are dimensionally stabilized by heating the material to a reaction temperature between about 1050.degree.-1450.degree. F. (566.degree.-788.degree. C.), holding it at this temperature during transformation of delta ferrite to austenite plus sigma phase, and subsequently heating to a reversion temperature between about 1625.degree.-1750.degree. F. (885.degree.-954.degree. C.), whereby the sigma phase transforms back to ferrite, but the austenite remains dispersed in the ferrite phase. Final controlled cooling permits transformation of ferrite to austenite plus sigma and, later, precipitation of carbides.

  20. Ceramic Composite Intermediate Temperature Stress-Rupture Properties Improved Significantly

    NASA Technical Reports Server (NTRS)

    Morscher, Gregory N.; Hurst, Janet B.

    2002-01-01

    Silicon carbide (SiC) composites are considered to be potential materials for future aircraft engine parts such as combustor liners. It is envisioned that on the hot side (inner surface) of the combustor liner, composites will have to withstand temperatures in excess of 1200 C for thousands of hours in oxidizing environments. This is a severe condition; however, an equally severe, if not more detrimental, condition exists on the cold side (outer surface) of the combustor liner. Here, the temperatures are expected to be on the order of 800 to 1000 C under high tensile stress because of thermal gradients and attachment of the combustor liner to the engine frame (the hot side will be under compressive stress, a less severe stress-state for ceramics). Since these composites are not oxides, they oxidize. The worst form of oxidation for strength reduction occurs at these intermediate temperatures, where the boron nitride (BN) interphase oxidizes first, which causes the formation of a glass layer that strongly bonds the fibers to the matrix. When the fibers strongly bond to the matrix or to one another, the composite loses toughness and strength and becomes brittle. To increase the intermediate temperature stress-rupture properties, researchers must modify the BN interphase. With the support of the Ultra-Efficient Engine Technology (UEET) Program, significant improvements were made as state-of-the-art SiC/SiC composites were developed during the Enabling Propulsion Materials (EPM) program. Three approaches were found to improve the intermediate-temperature stress-rupture properties: fiber-spreading, high-temperature silicon- (Si) doped boron nitride (BN), and outside-debonding BN.

  1. Improved Magnetic Field Generation Efficiency and Higher Temperature Spheromak Plasmas

    SciTech Connect

    Wood, R D; Hill, D N; McLean, H S; Hooper, E B; Hudson, B F; Moller, J M; Romero-Talamas, C A

    2008-09-15

    New understanding of the mechanisms governing the observed magnetic field generation limits on the sustained spheromak physics experiment has been obtained. Extending the duration of magnetic helicity injection during the formation of a spheromak and optimizing the ratio of injected current to bias flux produce higher magnetic field plasmas with record spheromak electron temperatures. To explore magnetic field buildup efficiency limits, the confinement region geometry was varied resulting in improved field buildup efficiencies.

  2. Effect of low temperature on stability of theta-type plasmids in Carnobacterium maltaromaticum.

    PubMed

    Bohaychuk, Valerie M; van Belkum, Marco J; Stiles, Michael E; McMullen, Lynn M

    2008-03-01

    The heterologous production of useful peptides such as bacteriocins by lactic acid bacteria (LAB) has been studied for use in the biopreservation of foods. Recombinant plasmids can suffer drawbacks such as segregational instability affecting the production of these peptides in certain environments such as absence of selective pressure or low temperature. The link between growth temperature characteristics of parental strains and stability of theta-type plasmids at a low temperature was investigated. The growth of four parental strains at 4 degrees C and stability of five derivative theta-type plasmids transformed into Carnobacterium maltaromaticum UAL26 at 25 and 4 degrees C were determined. Two plasmids (pCD11 and pCaT) derived from psychrotrophic LAB and plasmid, pHW800, from Enterococcus faecium 226 with unknown growth temperature characteristics, had excellent stability when strains were grown at 4 degrees C. Plasmids (pTRKH2 and pUCB820) derived from LAB that did not grow at refrigeration temperatures were not stable at 4 degrees C. When a DNA fragment from pCD11 containing 22-bp repeats, a putative replication initiation site, and the gene for the RepA protein was inserted into pTRKH2, the resulting derivative plasmid was 100% stable at 4 degrees C.

  3. Improved stability and stabilization design for networked control systems using new quadruple-integral functionals.

    PubMed

    Li, Zhichen; Bai, Yan; Li, Tianqi

    2016-07-01

    This paper investigates stability analysis and stabilization for networked control systems. By a refined delay decomposition approach, slightly different Lyapunov-Krasovskii functionals (LKFs) with quadruple-integral terms and augmented vectors containing triple-integral forms of state are constructed. New integral inequalities are proposed to estimate the cross terms from derivatives of the LKFs, which can be proved to offer tighter bounds than what the Jensen one produces theoretically. Moreover, the non-strictly proper rational functions in deriving process are fully handled via reciprocally convex approach. A state feedback controller design approach is also developed. Numerical examples and applications to practical power and oscillator systems demonstrate the superiority of the proposed criteria in conservatism reduction compared to some existing ones. Copyright © 2016 ISA. Published by Elsevier Ltd. All rights reserved.

  4. Heat Sinking, Cross Talk, and Temperature Stability for Large, Close-Packed Arrays of Microcalorimeters

    NASA Technical Reports Server (NTRS)

    Imoto, Naoko; Bandler, SImon; Brekosky, Regis; Chervenak, James; Figueroa-Felicano, Enectali; Finkbeiner, Frederick; Kelley, Richard; Kilbourne, Caroline; Porter, Frederick; Sadleir, Jack; hide

    2007-01-01

    We are developing large, close-packed arrays of x-ray transition-edge sensor (TES) microcalorimeters. In such a device, sufficient heat sinking is important to to minimize thermal cross talk between pixels and to stabilize the bath temperature for all pixels. We have measured cross talk on out 8 x 8 arrays and studied the shape and amount of thermal crosstalk as a function of pixel location and efficiency of electrothermal feedback. In this presentation, we will compare measurements made on arrays with and without a backside, heat-sinking copper layer, as well as results of devices on silicon-nitride membranes and on solid substrates, and we will discuss the implications for energy resolution and maximum count rate. We will also discuss the dependence of pulse height upon bath temperature, and the measured and required stability of the bath temperature.

  5. Temperature and coverage effects on the stability of epitaxial silicene on Ag(111) surfaces

    NASA Astrophysics Data System (ADS)

    Liu, Hongsheng; Han, Nannan; Zhao, Jijun

    2017-07-01

    Silicene, the single layer of silicon atoms arranged in a honeycomb lattice, has been synthesized in recent experiments and attracted significant attentions. Silicene is promising in future nanoelectronic devices due to its outstanding electronic properties. In experiments, however, different silicene superstructures coexist on Ag(111) substrate. For the device applications, homogenous silicene sheet with large scale and high quality is highly desired. Here, for the first time, we investigate both the temperature and the coverage effects on the thermal stability of epitaxial silicene on Ag(111) surface by ab initio molecular dynamics simulations. The relationship between the stability of various silicene superstructures and the growth conditions, including temperature and coverage of silicon atoms, is revealed by plotting the chemical potential phase diagram of silicene on Ag(111) surfaces at different temperatures. Our results are helpful for understanding the observed diversity of silicene phases on Ag(111) surfaces and provide some useful guidance for the synthesis of homogenous silicene phase in experiments.

  6. The effects of wilting and storage temperatures on the fermentation quality and aerobic stability of stylo silage.

    PubMed

    Liu, Qinghua; Zhang, Jianguo; Shi, Shangli; Sun, Qizhong

    2011-08-01

    In order to clarify the ensiling characteristics of stylo (Stylosanthes guianensis Swartz), the effects of wilting (no wilting, light wilting and heavy wilting) and storage temperatures (10°C, 20°C, 30°C and 40°C) on the fermentation quality and aerobic stability of stylo silage were investigated. Wilting had no significant influence on the contents of crude protein, ether extract and acid detergent fiber, and numbers of lactic acid bacteria, aerobic bacteria, yeasts and mold (P > 0.05). Heavy wilted material, wilted for 12 h, had higher neutral detergent fiber content and lower water-soluble carbohydrate content than unwilted and light wilted materials (P < 0.05). Wilting and storage temperatures had significant effects on pH value, acetic acid, butyric acid and NH(3) -N contents of stylo silage (P < 0.01 or P < 0.05). Wilting tended to reduce acetic acid and NH(3) -N contents and improve the fermentation quality of stylo silage. In all the silages, no wilting silage ensiled at 30°C had the highest butyric acid content (P < 0.05). High temperature of 40°C markedly restricted the growth of lactic acid bacteria and aerobic bacteria in silage, irrespective of wilting. The wilted silage or silage stored at low temperature had poor aerobic stability.

  7. Additives for vaccine storage to improve thermal stability of adenoviruses from hours to months

    NASA Astrophysics Data System (ADS)

    Pelliccia, Maria; Andreozzi, Patrizia; Paulose, Jayson; D'Alicarnasso, Marco; Cagno, Valeria; Donalisio, Manuela; Civra, Andrea; Broeckel, Rebecca M.; Haese, Nicole; Jacob Silva, Paulo; Carney, Randy P.; Marjomäki, Varpu; Streblow, Daniel N.; Lembo, David; Stellacci, Francesco; Vitelli, Vincenzo; Krol, Silke

    2016-11-01

    Up to 80% of the cost of vaccination programmes is due to the cold chain problem (that is, keeping vaccines cold). Inexpensive, biocompatible additives to slow down the degradation of virus particles would address the problem. Here we propose and characterize additives that, already at very low concentrations, improve the storage time of adenovirus type 5. Anionic gold nanoparticles (10-8-10-6 M) or polyethylene glycol (PEG, molecular weight ~8,000 Da, 10-7-10-4 M) increase the half-life of a green fluorescent protein expressing adenovirus from ~48 h to 21 days at 37 °C (from 7 to >30 days at room temperature). They replicate the known stabilizing effect of sucrose, but at several orders of magnitude lower concentrations. PEG and sucrose maintained immunogenicity in vivo for viruses stored for 10 days at 37 °C. To achieve rational design of viral-vaccine stabilizers, our approach is aided by simplified quantitative models based on a single rate-limiting step.

  8. Additives for vaccine storage to improve thermal stability of adenoviruses from hours to months

    PubMed Central

    Pelliccia, Maria; Andreozzi, Patrizia; Paulose, Jayson; D'Alicarnasso, Marco; Cagno, Valeria; Donalisio, Manuela; Civra, Andrea; Broeckel, Rebecca M.; Haese, Nicole; Jacob Silva, Paulo; Carney, Randy P.; Marjomäki, Varpu; Streblow, Daniel N.; Lembo, David; Stellacci, Francesco; Vitelli, Vincenzo; Krol, Silke

    2016-01-01

    Up to 80% of the cost of vaccination programmes is due to the cold chain problem (that is, keeping vaccines cold). Inexpensive, biocompatible additives to slow down the degradation of virus particles would address the problem. Here we propose and characterize additives that, already at very low concentrations, improve the storage time of adenovirus type 5. Anionic gold nanoparticles (10−8–10−6 M) or polyethylene glycol (PEG, molecular weight ∼8,000 Da, 10−7–10−4 M) increase the half-life of a green fluorescent protein expressing adenovirus from ∼48 h to 21 days at 37 °C (from 7 to >30 days at room temperature). They replicate the known stabilizing effect of sucrose, but at several orders of magnitude lower concentrations. PEG and sucrose maintained immunogenicity in vivo for viruses stored for 10 days at 37 °C. To achieve rational design of viral-vaccine stabilizers, our approach is aided by simplified quantitative models based on a single rate-limiting step. PMID:27901019

  9. Additives for vaccine storage to improve thermal stability of adenoviruses from hours to months.

    PubMed

    Pelliccia, Maria; Andreozzi, Patrizia; Paulose, Jayson; D'Alicarnasso, Marco; Cagno, Valeria; Donalisio, Manuela; Civra, Andrea; Broeckel, Rebecca M; Haese, Nicole; Jacob Silva, Paulo; Carney, Randy P; Marjomäki, Varpu; Streblow, Daniel N; Lembo, David; Stellacci, Francesco; Vitelli, Vincenzo; Krol, Silke

    2016-11-30

    Up to 80% of the cost of vaccination programmes is due to the cold chain problem (that is, keeping vaccines cold). Inexpensive, biocompatible additives to slow down the degradation of virus particles would address the problem. Here we propose and characterize additives that, already at very low concentrations, improve the storage time of adenovirus type 5. Anionic gold nanoparticles (10(-8)-10(-6) M) or polyethylene glycol (PEG, molecular weight ∼8,000 Da, 10(-7)-10(-4) M) increase the half-life of a green fluorescent protein expressing adenovirus from ∼48 h to 21 days at 37 °C (from 7 to >30 days at room temperature). They replicate the known stabilizing effect of sucrose, but at several orders of magnitude lower concentrations. PEG and sucrose maintained immunogenicity in vivo for viruses stored for 10 days at 37 °C. To achieve rational design of viral-vaccine stabilizers, our approach is aided by simplified quantitative models based on a single rate-limiting step.

  10. Cesium Lead Halide Perovskites with Improved Stability for Tandem Solar Cells.

    PubMed

    Beal, Rachel E; Slotcavage, Daniel J; Leijtens, Tomas; Bowring, Andrea R; Belisle, Rebecca A; Nguyen, William H; Burkhard, George F; Hoke, Eric T; McGehee, Michael D

    2016-03-03

    A semiconductor that can be processed on a large scale with a bandgap around 1.8 eV could enable the manufacture of highly efficient low cost double-junction solar cells on crystalline Si. Solution-processable organic-inorganic halide perovskites have recently generated considerable excitement as absorbers in single-junction solar cells, and though it is possible to tune the bandgap of (CH3NH3)Pb(BrxI1-x)3 between 2.3 and 1.6 eV by controlling the halide concentration, optical instability due to photoinduced phase segregation limits the voltage that can be extracted from compositions with appropriate bandgaps for tandem applications. Moreover, these materials have been shown to suffer from thermal degradation at temperatures within the processing and operational window. By replacing the volatile methylammonium cation with cesium, it is possible to synthesize a mixed halide absorber material with improved optical and thermal stability, a stabilized photoconversion efficiency of 6.5%, and a bandgap of 1.9 eV.

  11. Basin-Wide Temperature Constraints On Gas Hydrate Stability In The Gulf Of Mexico

    NASA Astrophysics Data System (ADS)

    MacDonald, I. R.; Reagan, M. T.; Guinasso, N. L.; Garcia-Pineda, O. G.

    2012-12-01

    Gas hydrate deposits commonly occur at the seafloor-water interface on marine margins. They are especially prevalent in the Gulf of Mexico where they are associated with natural oil seeps. The stability of these deposits is potentially challenged by fluctuations in bottom water temperature, on an annual time-scale, and under the long-term influence of climate change. We mapped the locations of natural oil seeps where shallow gas hydrate deposits are known to occur across the entire Gulf of Mexico basin based on a comprehensive review of synthetic aperture radar (SAR) data (~200 images). We prepared a bottom water temperature map based on the archive of CTD casts from the Gulf (~6000 records). Comparing the distribution of gas hydrate deposits with predicted bottom water temperature, we find that a broad area of the upper slope lies above the theoretical stability horizon for structure 1 gas hydrate, while all sites where gas hydrate deposits occur are within the stability horizon for structure 2 gas hydrate. This is consistent with analytical results that structure 2 gas hydrates predominate on the upper slope (Klapp et al., 2010), where bottom water temperatures fluctuate over a 7 to 10 C range (approx. 600 m depth), while pure structure 1 hydrates are found at greater depths (approx. 3000 m). Where higher hydrocarbon gases are available, formation of structure 2 gas hydrate should significantly increase the resistance of shallow gas hydrate deposits to destabilizing effects variable or increasing bottom water temperature. Klapp, S.A., Bohrmann, G., Kuhs, W.F., Murshed, M.M., Pape, T., Klein, H., Techmer, K.S., Heeschen, K.U., and Abegg, F., 2010, Microstructures of structure I and II gas hydrates from the Gulf of Mexico: Marine and Petroleum Geology, v. 27, p. 116-125.Bottom temperature and pressure for Gulf of Mexico gas hydrate outcrops and stability horizons for sI and sII hydrate.

  12. Improving Forecast Skill by Assimilation of AIRS Temperature Soundings

    NASA Technical Reports Server (NTRS)

    Susskind, Joel; Reale, Oreste

    2010-01-01

    AIRS was launched on EOS Aqua on May 4, 2002, together with AMSU-A and HSB, to form a next generation polar orbiting infrared and microwave atmospheric sounding system. The primary products of AIRS/AMSU-A are twice daily global fields of atmospheric temperature-humidity profiles, ozone profiles, sea/land surface skin temperature, and cloud related parameters including OLR. The AIRS Version 5 retrieval algorithm, is now being used operationally at the Goddard DISC in the routine generation of geophysical parameters derived from AIRS/AMSU data. A major innovation in Version 5 is the ability to generate case-by-case level-by-level error estimates delta T(p) for retrieved quantities and the use of these error estimates for Quality Control. We conducted a number of data assimilation experiments using the NASA GEOS-5 Data Assimilation System as a step toward finding an optimum balance of spatial coverage and sounding accuracy with regard to improving forecast skill. The model was run at a horizontal resolution of 0.5 deg. latitude X 0.67 deg longitude with 72 vertical levels. These experiments were run during four different seasons, each using a different year. The AIRS temperature profiles were presented to the GEOS-5 analysis as rawinsonde profiles, and the profile error estimates delta (p) were used as the uncertainty for each measurement in the data assimilation process. We compared forecasts analyses generated from the analyses done by assimilation of AIRS temperature profiles with three different sets of thresholds; Standard, Medium, and Tight. Assimilation of Quality Controlled AIRS temperature profiles significantly improve 5-7 day forecast skill compared to that obtained without the benefit of AIRS data in all of the cases studied. In addition, assimilation of Quality Controlled AIRS temperature soundings performs better than assimilation of AIRS observed radiances. Based on the experiments shown, Tight Quality Control of AIRS temperature profile performs best

  13. Stabilized composite membranes and membrane electrode assemblies for high temperature/low relative humidity polymer electrolyte fuel cell operation

    NASA Astrophysics Data System (ADS)

    Ramani, Vijay Krishna

    Polymer electrolyte membrane fuel cells (PEMFCs) have a variety of applications in the stationary power, mobile power and automotive power sectors. Existing membrane technology presently permits fuel cell operation at temperatures less than 100°C under fully saturated conditions. However, several advantages such as easier heat rejection rates and improved impurities tolerance by the anode electrocatalyst result by operating a PEMFC at elevated temperatures (above 100°C) and lower relative humidities. In an attempt to extend the operating range of the polymer electrolyte membrane, perfluorosulfonic acid (NafionRTM) based organic/inorganic (heteropolyacid) composite membranes were investigated in terms of thermal and electrochemical stability, additive stability and conductivity. Tungsten based heteropolyacids (HPAs) were found to be electrochemically stable as opposed to molybdenum based additives. The stability of the inorganic heteropolyacid additive in aqueous environments was enhanced by ion exchanging the protons of the HPAs with larger counter ions. An additional stabilization technique developed involved improving the interaction of HPA with NafionRTM by linking the particles to the sulfonic acid clusters via a sol-gel induced metal oxide linkage. The proton conductivity of the composite membranes was found to depend on the particle size of the HPA additive. A two order of magnitude change in additive particle size was attained by modification of the membrane preparation technique. This modification resulted in a nearly 50% increase in conductivity. The membranes prepared were characterized by thermal analysis, spectroscopy and microscopy. A technique was developed to incorporate existing MEA preparation and HPA stabilization techniques to the composite membranes with small HPA particles. All MEAs prepared were evaluated at high temperatures (120°C) and low relative humidities (35%) in an operating fuel cell, with membrane resistance and hence conductivity

  14. Wavemeter measurements of frequency stability of an injection seeded alexandrite laser for pressure and temperature lidar

    NASA Technical Reports Server (NTRS)

    Prasad, C. R.; Schwemmer, G. K.; Korb, C. L.

    1992-01-01

    The GSFC pressure-temperature lidar is a differential absorption lidar operating in the oxygen A band absorption region (760 to 770 nm), and utilizes two tunable pulsed alexandrite lasers. For obtaining temperature measurements with an accuracy of less than or = 1 K, it has been determined that the stability of the online laser frequency over a period of time corresponding to a set of measurements, 0.1 to 30 min, has to be better than +/- 0.002/cm. In addition, the requirements on laser spectral bandwidth and spectral purity are less than or = 0.02/cm and greater than or = 99.9 percent, respectively. Injection seeding with a stabilized AlGaAs diode laser was used to achieve the required frequency stability and spectral bandwidth. A high resolution Fizeau wavemeter was employed to determine the frequency stability of the pulsed alexandrite laser and determine its bandwidth, mode structure. We present the results of measurements of the frequency stability and the spectrum of the injection seeded alexandrite laser.

  15. Polymer/Silicate Nanocomposites Developed for Improved Strength and Thermal Stability

    NASA Technical Reports Server (NTRS)

    Campbell, Sandi G.

    2003-01-01

    Over the past decade, polymer-silicate nanocomposites have been attracting considerable attention as a method of enhancing polymer properties. The nanometer dimensions of the dispersed silicate reinforcement can greatly improve the mechanical, thermal, and gas barrier properties of a polymer matrix. In a study at the NASA Glenn Research Center, the dispersion of small amounts (less than 5 wt%) of an organically modified layered silicate (OLS) into the polymer matrix of a carbon-fiber-reinforced composite has improved the thermal stability of the composite. The enhanced barrier properties of the polymer-clay hybrid are believed to slow the diffusion of oxygen into the bulk polymer, thereby slowing oxidative degradation of the polymer. Electron-backscattering images show cracking of a nanocomposite matrix composite in comparison to a neat resin matrix composite. The images show that dispersion of an OLS into the matrix resin reduces polymer oxidation during aging and reduces the amount of cracking in the matrix significantly. Improvements in composite flexural strength, flexural modulus, and interlaminar shear strength were also obtained with the addition of OLS. An increase of up to 15 percent in these mechanical properties was observed in composites tested at room temperature and 288 C. The best properties were seen with low silicate levels, 1 to 3 wt%, because of the better dispersion of the silicate in the polymer matrix.

  16. Long-term stability testing of optical fibre Fabry-Perot temperature sensors

    NASA Astrophysics Data System (ADS)

    Polyzos, Dimitrios; Jinesh, Mathew; MacPherson, William N.; Maier, Robert R. J.

    2016-05-01

    Applications of fibre optic sensors at high temperatures have gained a huge interest recently, as they appeared to be suitable for temperature recording in harsh environments. In this paper, we are demonstrating two intrinsic Fabry-Perot (F-P) fibre optic sensors for high temperature monitoring. The sensors are consisting of a 125μm diameter single mode fibre (SMF28) and a 125μm diameter PCF ESM-12B pure fused silica fibre spliced to a SMF28, respectively. The result was a low finesse optical SMF-Cr-SMF, and SMF-Cr-PCF, sensor with cavity lengths varying from 50μm to 100μm. Both types of Fabry-Perot sensors were tested in a tube furnace over a temperature range from room temperature up to 1100°C. Following a number of annealing cycles, between the above mentioned temperatures range, very good repeatability of the phase response was achieved. During the cycling process, thermal stress relief takes place which makes the sensors suitable for temperature testing at temperatures just in excess of 1000°C. After initial cycling the sensors are subjected to long term stability tests. The phase response is stable, less than 4°C, over a period of 5 days at a temperature of 1050°C for both sensors. The temperature resolution is around 3°C.

  17. Temperature stabilized effusion cell evaporation source for thin film deposition and molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Tiedje, H. F.; Brodie, D. E.

    2000-05-01

    A simple effusion cell evaporation source for thin film deposition and molecular-beam epitaxy is described. The source consists of a crucible with a thermocouple temperature sensor heated by a resistive crucible heater. Radiation heat transfer from the crucible to the thermocouple produces a consistent and reproducible thermocouple temperature for a given crucible temperature, without direct contact between the thermocouple and the crucible. The thermocouple temperature is somewhat less than the actual crucible temperature because of heat flow from the thermocouple junction along the thermocouple lead wires. In a typical case, the thermocouple temperature is 1007 °C while the crucible is at 1083 °C. The crucible temperature stability is estimated from the measured sensitivity of the evaporation rate of indium to temperature, and the observed variations in the evaporation rate for a fixed thermocouple temperature. The crucible temperature peak-to-peak variation over a one hour period is 1.2 °C. Machined molybdenum crucibles were used in the indium and copper sources for depositing CuInSe2 thin films for solar cells.

  18. Feasibility Study of Improved Methods for Riverbank Stabilization

    DTIC Science & Technology

    1964-11-01

    stabilization, that of sun drying, has been used for many cen- turies in making adobe . However, the hardening which o ccu1· s during this process is...lbwn • ••lty 0. tl4-0 "* ’ · otf.J, .)to ..... ,oo t O UO ... I r -o ... . ,. l lo:•t Stl 0 1’ •• hiCh d-~Uiy 0 t41·0.M-\\ 1, •oo. r., HIO )! • SOl > 10...This does not include an~r ballast to keep the mattress in place. The problem of impermeability is one that could be sol ved by mak- ing more

  19. Storage Stability and Improvement of Intermediate Moisture Foods

    NASA Technical Reports Server (NTRS)

    Labuza, T. P.

    1976-01-01

    Shelf life tests are used to estimate the rate of nonenzymatic browning; however, controlling the reducing sugar levels below 23:1 molar ratio to amines, slows the rate. In addition, liquid glycols surpress browning. The protozoan Tetrahymena pyriformis W can be used to estimate nutrition losses during browning. At high temperatures (80 to 120 C) used in processing intermediate moisture foods (IMF), vitamin C destruction shifts to a zero order mechanism. BHA and BHT are the most effective antioxidants against rancidity. In shelf life testing however, 45 C should be the maximum temperature used. Water binding agents are studied. The five isotherms of thirteen humectants were determined. The results show that neither the method of addition nor sequence of addition affects the a sub u lowering ability of these humectants. Results were used to formulate shelf stable IMF processed cheese foods with at least four months shelf life.

  20. Stability of colloidal silver nanoparticles trapped in lipid bilayer: effect of lecithin concentration and applied temperature.

    PubMed

    Barani, Hossein; Montazer, Majid; Braun, Hans-Georg; Dutschk, Victoria

    2014-12-01

    The use of silver nanoparticle on various substrates has been widespread because of its good antibacterial properties that directly depend on the stability of the silver nanoparticles in a colloidal suspension. In this study, the colloidal solutions of the silver nanoparticles were synthesised by a simple and safe method by using lecithin as a stabilising agent and their stability was examined at various temperatures. The effect of the lecithin concentrations on the stability of the synthesised silver nanoparticles was examined from 25 to 80°C at 5°C intervals, by recording the changes in the UV-vis absorption spectra, the hydrodynamic diameter and the light scattering intensity of the silver nanoparticles. In addition, the morphology of the synthesised silver nanoparticles was investigated with the low-voltage scanning electron microscopy and transmission electron microscopy. The results indicated that increasing temperature caused different changes in the size of the stabilised and the unstabilised silver nanoparticles. The size of the stabilised silver nanoparticles reduced from 38 to 36 nm during increasing temperature, which confirmed good stability.

  1. Methylated flavonoids have greatly improved intestinal absorption and metabolic stability.

    PubMed

    Wen, Xia; Walle, Thomas

    2006-10-01

    To better understand the relationship between the chemical structure and biological fate of dietary polyphenols, the hepatic metabolic stability and intestinal absorption of methylated polyphenols, in comparison with unmethylated polyphenols, were investigated in pooled human liver S9 fraction and human colon adenocarcinoma (Caco-2) cells. Consistent with previous in vivo studies, the two well known unmethylated polyphenols resveratrol (3,5,4'-trihydroxystilbene) and quercetin (3,5,7,3',4'-pentahydroxyflavone) were rapidly eliminated by the S9 fraction in the presence of the appropriate cofactors for conjugation and oxidation. In contrast, the methylated flavones, i.e., 7-methoxyflavone, 7,4'-dimethoxyflavone, 5,7-dimethoxyflavone, and 5,7,4'-trimethoxyflavone, were relatively stable, indicating high resistance to hepatic metabolism. The corresponding unmethylated flavones, i.e., 7-hydroxyflavone, 7,4'-dihydroxyflavone, chrysin (5,7-dihydroxyflavone), and apigenin (5,7,4'-trihydroxyflavone), were rapidly eliminated because of extensive glucuronidation and/or sulfation just as resveratrol and quercetin were. The rate of intestinal absorption was evaluated using Caco-2 cells grown in porous inserts. The methylated flavones showed approximately 5- to 8-fold higher apparent permeability (P(app), 22.6-27.6 x 10(-6) cm s(-1)) of apical to basolateral flux than the unmethylated flavones (P(app), 3.0-7.8 x 10(-6) cm s(-1)). The lower P(app) values for the unmethylated flavones correlated with their extensive metabolism in the Caco-2 cells. Thus, combined use of the hepatic S9 fraction and Caco-2 cells will be useful for predicting the oral bioavailability of dietary polyphenols. The higher hepatic metabolic stability and intestinal absorption of the methylated polyphenols make them more favorable than the unmethylated polyphenols to be developed as potential cancer chemopreventive agents.

  2. Electrical conductivity and electron-spin resonance in oxidatively stabilized polyacrylonitrile subjected to elevated temperature

    NASA Technical Reports Server (NTRS)

    Lerner, N. R.

    1981-01-01

    Electrical conductivity and electron spin resonance measurements are presented for oxidatively stabilized polyacrylonitrile (PAN) fibers subjected to heat treatment at temperatures ranging from 700 to 950 K. Conductivity measurements made at temperatures between 77 and 523 K reveal that PAN fibers heat treated in vacuum behave as semiconductors, with a room-temperature conductivity dominated by the contributions of impurity states, with an activation energy of 88 kcal/mole. A decrease in conductivity is observed upon air which is attributed to a decrease in the electron-phonon scattering time. ESR spectra indicate that conducting pathways having metallic properties are formed at temperatures as low as 715 K, although the contribution of these pathways to the room-temperature conductivity is extremely small next to the contribution of localized spin centers.

  3. Ultra-High Pressure Homogenization improves oxidative stability and interfacial properties of soy protein isolate-stabilized emulsions.

    PubMed

    Fernandez-Avila, C; Trujillo, A J

    2016-10-15

    Ultra-High Pressure Homogenization (100-300MPa) has great potential for technological, microbiological and nutritional aspects of fluid processing. Its effect on the oxidative stability and interfacial properties of oil-in-water emulsions prepared with 4% (w/v) of soy protein isolate and soybean oil (10 and 20%, v/v) were studied and compared to emulsions treated by conventional homogenization (15MPa). Emulsions were characterized by particle size, emulsifying activity index, surface protein concentration at the interface and by transmission electron microscopy. Primary and secondary lipid oxidation products were evaluated in emulsions upon storage. Emulsions with 20% oil treated at 100 and 200MPa exhibited the most oxidative stability due to higher amount of oil and protein surface load at the interface. This manuscript addresses the improvement in oxidative stability in emulsions treated by UHPH when compared to conventional emulsions.

  4. Silicon Carbide Temperature Monitor Processing Improvements. Status Report

    SciTech Connect

    Unruh, Troy Casey; Daw, Joshua Earl; Ahamad Al Rashdan

    2016-01-29

    could be performed in an MFC hot cell, further reducing the time and expense of lengthy decontaminations prior to processing. Sections of this report provide a general description of resistivity techniques currently used to infer peak irradiation temperature from silicon carbide temperature monitors along with some representative data, the proposed concepts to improve the process of analyzing irradiated SiC temperature monitors, the completed efforts to prove the proposed concepts, and future activities. The efforts detailed here succeeded in designing and developing a real-time automated SiC resistivity measurement system, and performed two initial test runs. Activities carried out include the assembly and integration of the system hardware; the design and development of a preliminary monitor fixture; the design of a technique to automate the data analysis and processing; the development of the communication, coordination, and user software; and the execution and troubleshooting of test run experiments using the box furnace. Although the automation system performed as required, the designed fixture did not succeed in establishing the needed electrical contacts with the SiC monitor.

  5. Stability improvement of an operational two-way satellite time and frequency transfer system

    NASA Astrophysics Data System (ADS)

    Huang, Yi-Jiun; Fujieda, Miho; Takiguchi, Hiroshi; Tseng, Wen-Hung; Tsao, Hen-Wai

    2016-04-01

    To keep national time accurately coherent with coordinated universal time, many national metrology institutes (NMIs) use two-way satellite time and frequency transfer (TWSTFT) to continuously measure the time difference with other NMIs over an international baseline. Some NMIs have ultra-stable clocks with stability better than 10-16. However, current operational TWSTFT can only provide frequency uncertainty of 10-15 and time uncertainty of 1 ns, which is inadequate. The uncertainty is dominated by the short-term stability and the diurnals, i.e. the measurement variation with a period of one day. The aim of this work is to improve the stability of operational TWSTFT systems without additional transmission, bandwidth or increase in signal power. A software-defined receiver (SDR) comprising a high-resolution correlator and successive interference cancellation associated with open-loop configuration as the TWSTFT receiver reduces the time deviation from 140 ps to 73 ps at averaging time of 1 h, and occasionally suppresses diurnals. To study the source of the diurnals, TWSTFT is performed using a 2  ×  2 earth station (ES) array. Consequently, some ESs sensitive to temperature variation are identified, and the diurnals are significantly reduced by employing insensitive ESs. Hence, the operational TWSTFT using the proposed SDR with insensitive ESs achieves time deviation to 41 ps at 1 h, and 80 ps for averaging times from 1 h to 20 h.

  6. Improvement in Thermal Stability of Sucralose by γ-Cyclodextrin Metal-Organic Frameworks.

    PubMed

    Lv, Nana; Guo, Tao; Liu, Botao; Wang, Caifen; Singh, Vikaramjeet; Xu, Xiaonan; Li, Xue; Chen, Dawei; Gref, Ruxandra; Zhang, Jiwen

    2017-02-01

    To explain thermal stability enhancement of an organic compound, sucralose, with cyclodextrin based metal organic frameworks. Micron and nanometer sized basic CD-MOFs were successfully synthesized by a modified vapor diffusion method and further neutralized with glacial acetic acid. Sucralose was loaded into CD-MOFs by incubating CD-MOFs with sucralose ethanol solutions. Thermal stabilities of sucralose-loaded basic CD-MOFs and neutralized CD-MOFs were investigated using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and high performance liquid chromatography with evaporative light-scattering detection (HPLC-ELSD). Scanning electron microscopy (SEM) and powder X-ray diffraction (PXRD) results showed that basic CD-MOFs were cubic crystals with smooth surface and uniform sizes. The basic CD-MOFs maintained their crystalline structure after neutralization. HPLC-ELSD analysis indicated that the CD-MOF crystal size had significant influence on sucralose loading (SL). The maximal SL of micron CD-MOFs (CD-MOF-Micro) was 17.5 ± 0.9% (w/w). In contrast, 27.9 ± 1.4% of sucralose could be loaded in nanometer-sized basic CD-MOFs (CD-MOF-Nano). Molecular docking modeling showed that sucralose molecules preferentially located inside the cavities of γ-CDs pairs in CD-MOFs. Raw sucralose decomposed fast at 90°C, with 86.2 ± 0.2% of the compound degraded within only 1 h. Remarkably, sucralose stability was dramatically improved after loading in neutralized CD-MOFs, with only 13.7 ± 0.7% degradation at 90°C within 24 h. CD-MOFs efficiently incorporated sucralose and maintained its integrity upon heating at elevated temperatures.

  7. Improving the Stability of the EC1 Domain of E-cadherin by Thiol Alkylation of the Cysteine Residue

    PubMed Central

    Trivedi, Maulik; Laurence, Jennifer S.; Williams, Todd D.; Middaugh, C. Russell; Siahaan, Teruna J.

    2012-01-01

    The objective of this work was to improve chemical and physical stability of the EC1 protein derived from the extracellular domain of E-cadherin. In solution, the EC1 protein has been shown to form a covalent dimer via a disulfide bond formation followed by physical aggregation and precipitation. To improve solution stability of the EC1 protein, the thiol group of the Cys13 residue in EC1 was alkylated with iodoacetate, iodoacetamide, and maleimide-PEG-5000 to produce thioether derivatives called EC1-IA, EC1-IN, and EC1-PEG. The physical and chemical stabilities of the EC1 derivatives and the parent EC1 were evaluated at various pHs (3.0, 7.0, and 9.0) and temperatures (0, 3, 70 °C). The structural characteristics of each molecule were analyzed by circular dichroism (CD) and fluorescence spectroscopy and the derivatives have similar secondary structure as the parent EC1 protein at pH 7.0. Both EC1-IN and EC1-PEG derivatives showed better chemical and physical stability profiles than did the parent EC1 at pH 7.0. EC1-PEG had the best stability profile compared to EC1-IN and EC1 in solution under various conditions. PMID:22531851

  8. Physical and Chemical Stability of Curcumin in Aqueous Solutions and Emulsions: Impact of pH, Temperature, and Molecular Environment.

    PubMed

    Kharat, Mahesh; Du, Zheyuan; Zhang, Guodong; McClements, David Julian

    2017-03-01

    The utilization of curcumin as a nutraceutical in food and supplement products is often limited because of its low water solubility, poor chemical stability, and low oral bioavailability. This study examined the impact of pH, storage temperature, and molecular environment on the physical and chemical stability of pure curcumin in aqueous solutions and in oil-in-water emulsions. Unlike naturally occurring curcuminoid mixtures (that contain curcumin, demethoxy-curcumin, and bisdemethoxy-curcumin), pure curcumin was highly unstable to chemical degradation in alkaline aqueous solutions (pH ≥7.0) and tended to crystallize out of aqueous acidic solutions (pH <7). These effects were attributed to changes in the molecular structure of curcumin under different pH conditions. The curcumin crystals formed were relatively large (10-50 μm), which made them prone to rapid sedimentation. The incorporation of curcumin into oil-in-water emulsions (30% MCT, 1 mg curcumin/g MCT, d32 ≈ 298 nm) improved its water dispersibility and chemical stability. After incubation at 37 °C for 1 month, >85% of curcumin was retained by emulsions stored under acidic conditions (pH <7), whereas 62, 60, and 53% was retained by emulsions stored at pH 7.0, 7.4, and 8.0, respectively. There was little change in the color of curcumin-loaded emulsions when stored under acidic conditions, but their yellow color faded when stored under alkaline conditions. There was no evidence of droplet aggregation or creaming in emulsions stored for 31 days at ambient temperature. These results suggest that emulsion-based delivery systems may be suitable for improving the water dispersibility and chemical stability of curcumin, which would facilitate its application in foods and supplements.

  9. High-temperature earth-storable propellant acoustic cavity technology. [for combustion stability

    NASA Technical Reports Server (NTRS)

    Oberg, C. L.; Hines, W. S.; Falk, A. Y.

    1974-01-01

    Design criteria, methods and data, were developed to permit effective design of acoustic cavities for use in regeneratively cooled OME-type engines. This information was developed experimentally from two series of motor firings with high-temperature fuel during which the engine stability was evaluated under various conditions and with various cavity configurations. Supplementary analyses and acoustic model testing were used to aid cavity design and interpretation of results. Results from this program clearly indicate that dynamic stability in regeneratively cooled OME-type engines can be ensured through the use of acoustic cavities. Moreover, multiple modes of instability were successfully suppressed with the cavity.

  10. Dietary glutamine supplementation improves growth performance, meat quality and colour stability of broilers under heat stress.

    PubMed

    Dai, S F; Wang, L K; Wen, A Y; Wang, L X; Jin, G M

    2009-05-01

    1. The present study was conducted to investigate the effects of dietary glutamine (Gln) supplementation on growth performance, carcase characteristics and meat quality in broilers exposed to high ambient temperature. 2. A total of 240 35-d-old male Arbor Acres broilers were randomly assigned to 4 treatment groups (three replicates of 20 birds per cage). The broilers were kept in a temperature-controlled room at either 23 degrees C (no-stress groups, NS) or 28 degrees C (heat stress groups, HS). The broilers were fed either on a basal diet (control, NS) or on the basal diet supplemented with 0, 0.5 or 1.0% Gln (HS). 3. Compared with the NS, the HS (0% Gln) group gained less weight and consumed less feed, had lower final body weight, gain-to-feed ratio, and abdominal fat yield. Breast meat in HS (0% Gln) had lower pH, water-holding capacity (WHC), a* value, ether extract (EE) content and crude protein (CP) content, and had higher shear force (SF) and L* value. 4. Linear increase were found in groups supplemented with Gln (0, 0.5% and 1.0%) for final body weight, weight gain, feed consumption, gain-to-feed ratio and abdominal fat yield. Supplementation with Gln improved breast meat pH, WHC, SF, L* value, a* value, EE content and CP content in broilers exposed to heat stress. No significant difference was observed in all the indices determined between the HS (1% Gln) and the NS. 5. Heat stress caused obvious breast meat discoloration in L*, a* and b* values. However, dietary supplementation with Gln gave a better colour stability. 6. The results indicated that dietary supplementation with Gln may alleviate heat stress-caused deterioration in growth performance, carcase characteristics, meat quality and meat colour stability of broilers.

  11. Effect of Temperature and Pressure on the Stability of Protein Microbubbles.

    PubMed

    Rovers, Tijs A M; Sala, Guido; van der Linden, Erik; Meinders, Marcel B J

    2016-01-13

    Protein microbubbles are air bubbles with a network of interacting proteins at the air-water interface. Protein microbubbles are commonly used in medical diagnostic and therapeutic research. They have also recently gained interest in the research area of food as they can be used as structural elements to control texture, allowing for the manufacture of healthier foods with increased consumer perception. For the application of microbubbles in the food industry, it is important to gain insights into their stability under food processing conditions. In this study, we tested the stability of protein microbubbles against heating and pressurization. Microbubbles could be heated to 50 °C for 2 min or pressurized to 100 kPa overpressure for 15 s without significantly affecting their stability. At higher pressures and temperatures, the microbubbles became unstable and buckled. Buckling was observed above a critical pressure and was influenced by the shell modulus. The addition of cross-linkers like glutaraldehyde and tannic acid resulted in microbubbles that were stable against all tested temperatures and overpressures, more specifically, up to 120 °C and 470 kPa, respectively. We found a relation between the storage temperatures of microbubble dispersions (4, 10, 15, and 21 °C) and a decrease in the number of microbubbles with the highest decrease at the highest storage temperature. The average rupture time of microbubbles stored at different storage temperatures followed an Arrhenius relation with an activation energy for rupture of the shell of approximately 27 kT. This strength ensures applicability of microbubbles in food processes only at moderate temperatures and storage for a moderate period of time. After the proteins in the shell are cross-linked, the microbubbles can withstand pressures and temperatures that are representative of food processes.

  12. High-Temperature, Thin-Film Strain Gages Improved

    NASA Technical Reports Server (NTRS)

    2005-01-01

    Conventional resistance strain gage technology uses "bonded" strain gages. These foil or wire gages are bonded onto the surface of the test article with glue, ceramic cements, or flame-sprayed ceramics. These bonding agents can, in some instances, limit both the degree of strain transmission from the test structure to the gage and the maximum working temperature of the gage. Also, the bulky, bonded gage normally disrupts aerodynamic gas flow on the surface of the test structure because of its intrusive character. To respond to the urgent needs in aeronautic and aerospace research where stress and temperature gradients are high, aerodynamic effects need to be minimized, and higher operational temperatures are required, the NASA Lewis Research Center developed a thin film strain gage. This gage, a vacuum-deposited thin film formed directly on the surface of a test structure, operates at much higher temperatures than commercially available gages do and with minimal disruption of the aerodynamic flow. The gage uses an alloy, palladium-13 wt % chromium (hereafter, PdCr), which was developed by United Technologies Research Center under a NASA contract. PdCr is structurally stable and oxidation resistant up to at least 1100 C (2000 F); its temperature-induced resistance change is linear, repeatable, and not sensitive to the rates of heating and cooling. An early strain gage, which was made of 25-micrometer-diameter PdCr wire and demonstrated to be useable to 800 C, won an R&D 100 award in 1991. By further improving the purity of the material and by developing gage fabrication techniques that use sputter-deposition, photolithography patterning, and chemical etching, we have made an 8- to 10-m PdCr thin-film strain gage that can measure dynamic and static strain to at least 1100 C. For static strain measurements, a 5-m-thick Pt element serves as a temperature compensator to further minimize the temperature effect of the gage. These thin-film gages provide the advantage of

  13. A visual physiological temperature sensor developed with gelatin-stabilized luminescent silver nanoclusters.

    PubMed

    Lan, Jing; Zou, Hongyan; Liu, Zexi; Gao, Mingxuan; Chen, Binbin; Li, Yuanfang; Huang, Chengzhi

    2015-10-01

    A visual physiological temperature sensor was successfully developed with newly hydrothermally prepared fluorescent silver nanoclusters (AgNCs) at room temperature using gelatin as the protective and reducing agent. The as-prepared gelatin-stabilized AgNCs was water-soluble, uniform and exhibited a narrow distribution with an average size of 1.16 nm, showing a maximum emission band at 552 nm (2.45 eV) when excited at 445 nm (2.79 eV). The large Stokes shift of 110 nm of the gelatin-stabilized AgNCs makes it actually applicable with very low background and light scattering interferences. It was found that the as-prepared gelatin-stabilized AgNCs is temperature-sensitive over the range from 5°C to 45°C, and thus a visual physiological temperature sensor could be developed with the gelatin-AgNCs as under the irradiation of visible light. Copyright © 2015 Elsevier B.V. All rights reserved.

  14. Mechanical stability analysis on spherical sandwich sheet at low temperature loading conditions

    NASA Astrophysics Data System (ADS)

    Wang, Shanshuai; Li, Shuhui; Li, Zhimin

    2013-12-01

    The spherical sandwich sheet (S-S-S) is generally used in the aerospace industry, for example, the airplane, the rocket's fairing, the spacecraft and the satellite for the purpose of heat-insulation, weight-saving and dimension-reducing. The stability of the S-S-S is of general concern because of its particularly thin but large size. For some S-S-S used in fuel tank storing liquid oxygen of the rocket, it must be facing low temperature down to about -183 °C. Low temperature condition affects the stability of the S-S-S and then causes buckling of the structure. In this paper, a finite element (FE) model is established for evaluating the stability of the S-S-S via the sequential coupling mode. The material mechanical properties related to temperature are concerned in the FE model. The buckling modes and critical buckling loading are predicted accurately, since the FE model includes heat transfer simulating, thermal stress computing, buckling and post buckling process. It is found that the thermal stress generated from the low temperature loading reduces the critical buckling loading and changes the buckling modes of the S-S-S.

  15. Inhomogeneous stability of bacteriorhodopsin in purple membrane against photobleaching at high temperature.

    PubMed

    Yokoyama, Yasunori; Sonoyama, Masashi; Mitaku, Shigeki

    2004-02-15

    Heterogeneity in the state of bacteriorhodopsin in purple membrane was studied through temperature jump experiments carried out in darkness and under illumination with visible light. The thermal denaturation, the irreversible component of spectral change at high temperature, had two decay components, suggesting that bacteriorhodopsin in purple membrane has heterogeneous stability. The temperature dependence of kinetic parameters under illumination revealed that the fast-decay component gradually increased at above 60 degrees C, indicating that the proportion of unstable bacteriorhodopsin increased. Significant change in the visible circular dichroism (CD) spectra was observed in darkness in the same temperature range as the increase of the fast-decay component under illumination. Denaturation experiments for C-terminal-cleaved bacteriorhodopsin showed that the C-terminal segment had some effect on the structural stability of bacteriorhodopsin under illumination. Dynamic and static models of the inhomogeneous stability of bacteriorhodopsin in purple membrane are discussed on the basis of the results of the denaturation kinetics and the visible CD spectra. Copyright 2004 Wiley-Liss, Inc.

  16. Stability of cobalt-carbon high temperature fixed points doped with iron and platinum

    NASA Astrophysics Data System (ADS)

    Kňazovická, L.; Lowe, D.; Machin, G.; Davies, H.; Rani, A.

    2015-04-01

    High temperature fixed points (HTFPs) are stable and repeatable and make comparison of temperature scales possible at a level of uncertainty not previously possible. However, they potentially lack objectivity if the fixed-point temperature is known. Five HTFPs were constructed, one pure Co-C, two Co-C doped with Fe and two Co-C doped with Pt of differing concentrations. The candidate dopants were identified through thermochemical modelling as likely to give maximum temperature shift with minimum increase in melting range. The temperature differences of the doped systems from the pure system were determined and it was found that the addition of Fe depressed the melting temperature and the addition of Pt elevated the melting temperature, qualitatively in line with the thermochemical modelling. The higher concentration doped HTFPs were then aged for approximately 100 h with continuous melting-freezing cycles and the difference to the undoped Co-C HTFP remeasured. These differences were found to agree with those of the unaged results within the measurement uncertainties, confirming artefact stability. It is clear that the doping of HTFPs is a powerful way of constructing stable and reliable high temperature scale comparison artefacts of unknown temperature.

  17. High Temperature Irradiation-Resistant Thermocouple Performance Improvements

    SciTech Connect

    Joshua Daw; Joy Rempe; Darrell Knudson; John Crepeau; S. Curtis Wilkins

    2009-04-01

    Traditional methods for measuring temperature in-pile degrade at temperatures above 1100 ºC. To address this instrumentation need, the Idaho National Laboratory (INL) developed and evaluated the performance of a high temperature irradiation-resistant thermocouple (HTIR-TC) that contains alloys of molybdenum and niobium. Data from high temperature (up to 1500 ºC) long duration (up to 4000 hours) tests and on-going irradiations at INL’s Advanced Test Reactor demonstrate the superiority of these sensors to commercially-available thermocouples. However, several options have been identified that could further enhance their reliability, reduce their production costs, and allow their use in a wider range of operating conditions. This paper presents results from on-going Idaho National Laboratory (INL)/University of Idaho (UI) efforts to investigate options to improve HTIR-TC ductility, reliability, and resolution by investigating specially-formulated alloys of molybdenum and niobium and alternate diameter thermoelements (wires). In addition, on-going efforts to evaluate alternate fabrication approaches, such as drawn and loose assembly techniques will be discussed. Efforts to reduce HTIR-TC fabrication costs, such as the use of less expensive extension cable will also be presented. Finally, customized HTIR-TC designs developed for specific customer needs will be summarized to emphasize the varied conditions under which these sensors may be used.

  18. Design of nanocatalysts for improved selectivity and stability

    NASA Astrophysics Data System (ADS)

    Zaera, Francisco

    2012-02-01

    Several examples from ongoing work in our laboratory on the use of self-assembly to prepare heterogeneous catalysts with novel architectures will be discussed in this presentation. In one case, catalysts consisting of dispersed platinum metal nanoparticles with narrow size distributions and well-defined shapes were prepared and tested for the selective promotion of carbon-carbon double-bond cis-trans isomerization reactions in olefins. It was shown that the selective formation of the cis isomer could be controlled by using tetrahedral particles with exposed (111) facets. In a second example, catalysts based on small platinum nanoparticles of well-defined sizes were made by using dendrimers as scaffolding structures. The organic framework in that case can provide new fuctionality, including chirality as a way to introduce enantioselectivity. The third example involves the control of metal nanoparticle sintering by covering those with a layer of mesoporous silica grown on top. The final case to be discussed is one where yolk@shell metal-semiconductor constructs are being developed for increase stability in oxidation and photocatalytic applications.

  19. Effects of Temperature on the Performance and Stability of Recent COTS Silicon Oscillators

    NASA Technical Reports Server (NTRS)

    Patterson, Richard L.; Hammoud, Ahmad

    2010-01-01

    Silicon oscillators have lately emerged to serve as potential replacement for crystal and ceramic resonators to provide timing and clock signals in electronic systems. These semiconductor-based devices, including those that are based on MEMS technology, are reported to be resistant to vibration and shock (an important criteria for systems to be deployed in space), immune to EMI, consume very low current, require few or no external components, and cover a wide range of frequency for analog and digital circuits. In this work, the performance of five recently-developed COTS silicon oscillator chips from different manufacturers was determined within a temperature range that extended beyond the individual specified range of operation. In addition, restart capability at extreme temperatures, i.e. power switched on while the device was soaking at extreme (hot or cold) temperature, and the effects of thermal cycling under a wide temperature range on the operation of these silicon oscillators were also investigated. Performance characterization of each oscillator was obtained in terms of its output frequency, duty cycle, rise and fall times, and supply current at specific test temperatures. The five different oscillators tested operated beyond their specified temperature region, with some displaying excellent stability throughout the whole test temperature range. Others experienced some instability at certain temperature test points as evidenced by fluctuation in the output frequency. Recovery from temperature-induced changes took place when excessive temperatures were removed. It should also be pointed out that all oscillators were able to restart at the extreme test temperatures and to withstand the limited thermal cycling without undergoing any significant changes in their characteristics. In addition, no physical damage was observed in the packaging material of any of these silicon oscillators due to extreme temperature exposure and thermal cycling. It is recommended

  20. Hydraulic design of Three Gorges right bank powerhouse turbine for improvement of hydraulic stability

    NASA Astrophysics Data System (ADS)

    Shi, Q.

    2010-08-01

    This paper presents the hydraulic design of Three Gorges Right Bank Powerhouse turbine for improvement of hydraulic stability. The technical challenges faced in the hydraulic design of the turbine are given. The method of hydraulic design for improving the hydraulic stability and particularly for eliminating the upper part load pressure pulsations is clarified. The final hydraulic design results of Three Gorges Right Bank Powerhouse turbine based on modern hydraulic design techniques are presented.

  1. Stability of CO2 hydrate under very high pressure and low temperature

    NASA Astrophysics Data System (ADS)

    Hirai, H.; Honda, M.; Kawamura, T.; Yamamoto, Y.; Yagi, T.

    2009-12-01

    CO2 hydrate is a clathrate compound and the crystal structure type is sI at low pressure. CO2-reduction in the atmosphere is one of the most urgent subjects for mankind. Some technical developments to seclude CO2 as CO2 hydrate in ocean floor have been proceeded. Looking around the solar system, existence of CO2 hydrate in and beneath Martian permafrost has been predicted from spacecraft probes and theoretical studies. Thus, its stability and properties under high pressures and low temperatures are of great interest for fundamental understanding of clathrate hydrate, for the ocean sequestration technology, and for planetary science. CO2 hydrate exhibits characteristic properties different from those of other gas hydrate such as methane hydrate. For example, phase boundary between hydrate and gas + water for many gas hydrates shows positive slope in pressure versus temperature field, and the gas hydrates are kept at pressures up to several GPa at room temperature. On the other hand, for CO2 hydrate, the phase boundary turns to negative slope from positive one at a certain critical point [Nakano et al., 1998], and it can exist only at low temperature regions. And, a theoretical study predicted that CO2 hydrate decompose at low temperature region [Longhi, 2005]. In this study, high pressure and low temperature experiments were performed to examine stability and phase changes of CO2 hydrate using diamond anvil cell in a pressure range from 0.1 to 2.5 GPa and a the temperature range from 65 to 265 K. X-ray diffractometry and Raman spectroscopy revealed that the known phase boundary was extended into lower temperature region, and that CO2 hydrate was kept at low temperature regions at least 65 K despite the theoretical prediction of decomposition. References [1] S. Nakano, M. Moritoki, K. Ohgaki, J. Chem. Eng. Data, 43, 807 (1998). [2] J. Longhi, Geochim. Cosmochim. Acta, 69, 529 (2005)

  2. Improvements of COMS Land Surface Temperature Retrieval Algorithm by considering diurnal variations of boundary layer temperature

    NASA Astrophysics Data System (ADS)

    Choi, Y. Y.; Suh, M. S.

    2015-12-01

    National Meteorological Satellite Centre in Republic of Korea retrieves operationally land surface temperature (LST) by applying the split-window LST algorithm (CSW_v1.0) from Communication, Ocean, and Meteorological Satellite (COMS) data. In order to improve COMS LST accuracy, Cho et al. (2015) developed six types of LST retrieval equations (CSW_v2.0) by considering temperature lapse rate and water vapor/aerosol effect. Similar to CSW_v1.0, the LST retrieved by CSW_v2.0 had a correlation coefficient of 0.99 with the prescribed LST and the root mean square error (RMSE) improved from 1.41 K to 1.39 K. However, CSW_v2.0 showed relatively poor performance, in particular, the temperature lapse rate is certainly large (superadiabatic cases during daytime or strong inversion cases during early morning). In this study, we upgraded the CSW_v2.0 by considering diurnal variations of boundary layer temperature to reduce the relatively large errors under the large lapse rate conditions. To achieve the goals, the diurnal variations of air temperature along with the land surface temperature are included during radiative transfer simulations for the generation of the pseudo-match-up database. The preliminary analysis results showed that RMSE and bias are reduced from 1.39K to 1.14K and from -0.03K to -0.01K. In this presentation, we will show the detailed results of LST retrieval using new algorithms according to the viewing geometry, temperature lapse rate condition, and water vapour amount along with the intercomparison results with MODIS LST data.

  3. Note: Improved heater design for high-temperature hollow cathodes

    NASA Astrophysics Data System (ADS)

    McDonald, M. S.; Gallimore, A. D.; Goebel, D. M.

    2017-02-01

    We present an improved heater design for thermionic cathodes using a rhenium filament encased in a boron nitride ceramic sleeve. This heater is relatively simple to fabricate, yet has been successfully used to reliably and repeatably light a lanthanum hexaboride (LaB6) hollow cathode based on a previously published design without noticeable filament degradation over hundreds of hours of operation. The high decomposition temperature of boron nitride (2800 C for inert environments) and melting point for rhenium (3180 C) make this heater especially attractive for use with LaB6, which may require operating temperatures upwards of 1700 C. While boron nitride decomposes in air above 1000 C, the heater was used only at vacuum with an inert gas discharge, and no degradation was observed. Limitations of current state of the art cathode heaters are also discussed and compared with the rhenium-boron nitride combination.

  4. Development of a stabilized low temperature infrared absorption cell for use in low temperature and collisional cooling experiments.

    PubMed

    Valentin, A; Henry, A; Claveau, C; Camy-Peyret, C; Hurtmans, D; Mantz, A W

    2004-12-01

    We have constructed a stabilized low temperature infrared absorption cell cooled by an open cycle refrigerator, which can run with liquid nitrogen from 250 to 80K or with liquid helium from 80K to a few kelvin. Several CO infrared spectra were recorded at low temperature using a tunable diode laser spectrometer. These spectra were analyzed taking into account the detailed effects of collisions on the line profile when the pressure increases. We also recorded spectra at very low pressure to accurately model the diode laser emission. Spectra of the R(2) line in the fundamental band of 13CO cooled by collisions with helium buffer gas at 10.5K and at pressures near 1 Torr have been recorded. The He-pressure broadening parameter (gamma(0) = 0.3 cm(-1) atm(-1)) has been derived from the simultaneous analysis of four spectra at different pressures.

  5. Improving the Numerical Stability of Fast Matrix Multiplication

    SciTech Connect

    Ballard, Grey; Benson, Austin R.; Druinsky, Alex; Lipshitz, Benjamin; Schwartz, Oded

    2016-10-04

    Fast algorithms for matrix multiplication, namely those that perform asymptotically fewer scalar operations than the classical algorithm, have been considered primarily of theoretical interest. Apart from Strassen's original algorithm, few fast algorithms have been efficiently implemented or used in practical applications. However, there exist many practical alternatives to Strassen's algorithm with varying performance and numerical properties. Fast algorithms are known to be numerically stable, but because their error bounds are slightly weaker than the classical algorithm, they are not used even in cases where they provide a performance benefit. We argue in this study that the numerical sacrifice of fast algorithms, particularly for the typical use cases of practical algorithms, is not prohibitive, and we explore ways to improve the accuracy both theoretically and empirically. The numerical accuracy of fast matrix multiplication depends on properties of the algorithm and of the input matrices, and we consider both contributions independently. We generalize and tighten previous error analyses of fast algorithms and compare their properties. We discuss algorithmic techniques for improving the error guarantees from two perspectives: manipulating the algorithms, and reducing input anomalies by various forms of diagonal scaling. In conclusion, we benchmark performance and demonstrate our improved numerical accuracy.

  6. Improving the Numerical Stability of Fast Matrix Multiplication

    DOE PAGES

    Ballard, Grey; Benson, Austin R.; Druinsky, Alex; ...

    2016-10-04

    Fast algorithms for matrix multiplication, namely those that perform asymptotically fewer scalar operations than the classical algorithm, have been considered primarily of theoretical interest. Apart from Strassen's original algorithm, few fast algorithms have been efficiently implemented or used in practical applications. However, there exist many practical alternatives to Strassen's algorithm with varying performance and numerical properties. Fast algorithms are known to be numerically stable, but because their error bounds are slightly weaker than the classical algorithm, they are not used even in cases where they provide a performance benefit. We argue in this study that the numerical sacrifice of fastmore » algorithms, particularly for the typical use cases of practical algorithms, is not prohibitive, and we explore ways to improve the accuracy both theoretically and empirically. The numerical accuracy of fast matrix multiplication depends on properties of the algorithm and of the input matrices, and we consider both contributions independently. We generalize and tighten previous error analyses of fast algorithms and compare their properties. We discuss algorithmic techniques for improving the error guarantees from two perspectives: manipulating the algorithms, and reducing input anomalies by various forms of diagonal scaling. In conclusion, we benchmark performance and demonstrate our improved numerical accuracy.« less

  7. Method for stabilizing low-level mixed wastes at room temperature

    SciTech Connect

    Wagh, A.S.; Singh, D.

    1997-07-08

    A method to stabilize solid and liquid waste at room temperature is provided comprising combining solid waste with a starter oxide to obtain a powder, contacting the powder with an acid solution to create a slurry, said acid solution containing the liquid waste, shaping the now-mixed slurry into a predetermined form, and allowing the now-formed slurry to set. The invention also provides for a method to encapsulate and stabilize waste containing cesium comprising combining the waste with Zr(OH){sub 4} to create a solid-phase mixture, mixing phosphoric acid with the solid-phase mixture to create a slurry, subjecting the slurry to pressure; and allowing the now pressurized slurry to set. Lastly, the invention provides for a method to stabilize liquid waste, comprising supplying a powder containing magnesium, sodium and phosphate in predetermined proportions, mixing said powder with the liquid waste, such as tritium, and allowing the resulting slurry to set. 4 figs.

  8. Method for stabilizing low-level mixed wastes at room temperature

    DOEpatents

    Wagh, Arun S.; Singh, Dileep

    1997-01-01

    A method to stabilize solid and liquid waste at room temperature is provided comprising combining solid waste with a starter oxide to obtain a powder, contacting the powder with an acid solution to create a slurry, said acid solution containing the liquid waste, shaping the now-mixed slurry into a predetermined form, and allowing the now-formed slurry to set. The invention also provides for a method to encapsulate and stabilize waste containing cesium comprising combining the waste with Zr(OH).sub.4 to create a solid-phase mixture, mixing phosphoric acid with the solid-phase mixture to create a slurry, subjecting the slurry to pressure; and allowing the now pressurized slurry to set. Lastly, the invention provides for a method to stabilize liquid waste, comprising supplying a powder containing magnesium, sodium and phosphate in predetermined proportions, mixing said powder with the liquid waste, such as tritium, and allowing the resulting slurry to set.

  9. STABILITY CONSTANTS OF NP(V) COMPLEXES WITH FLOURIDE AND SULFATE AT VARIABLE TEMPERATURES

    SciTech Connect

    Y. Xia; J.I. Friese; D.A. Moore; L. Rao

    2005-07-11

    A solvent extraction method was used to determine the stability constants of Np(V) complexes with fluoride and sulfate in 1.0 M NaClO{sub 4} from 25 C to 60 C. The distribution ratio of Np(V) between the organic and aqueous phases was found to decrease as the concentrations of fluoride and sulfate were increased. Stability constants of the 1:1 Np(V)-fluoride complexes and the 1:1 Np(V)-sulfate and 1:2 Np(V)-sulfate complexes, dominant in the aqueous phase under the experimental conditions, were calculated from the effect of [F{sup -}] and [SO{sub 4}{sup 2-}] on the distribution ratio. The enthalpy and entropy of complexation were calculated from the stability constants at different temperatures by using the Van't Hoff equation.

  10. Method for stabilizing low-level mixed wastes at room temperature

    DOEpatents

    Wagh, A.S.; Singh, D.

    1997-07-08

    A method to stabilize solid and liquid waste at room temperature is provided comprising combining solid waste with a starter oxide to obtain a powder, contacting the powder with an acid solution to create a slurry, said acid solution containing the liquid waste, shaping the now-mixed slurry into a predetermined form, and allowing the now-formed slurry to set. The invention also provides for a method to encapsulate and stabilize waste containing cesium comprising combining the waste with Zr(OH){sub 4} to create a solid-phase mixture, mixing phosphoric acid with the solid-phase mixture to create a slurry, subjecting the slurry to pressure; and allowing the now pressurized slurry to set. Lastly, the invention provides for a method to stabilize liquid waste, comprising supplying a powder containing magnesium, sodium and phosphate in predetermined proportions, mixing said powder with the liquid waste, such as tritium, and allowing the resulting slurry to set. 4 figs.

  11. 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.

  12. Evaluating Marie Byrd Land stability using an improved basal topography

    NASA Astrophysics Data System (ADS)

    Holschuh, N.; Pollard, D.; Alley, R. B.; Anandakrishnan, S.

    2014-12-01

    Prior understanding of the ice-sheet setting in Marie Byrd Land (MBL) was derived primarily from geologic and geochemical studies of the current nunataks, with very few geophysical surveys imaging the ice covered regions. The geologic context suggested that the ice rests on a broad regional high, in contrast to the deep basins and trenches that characterize the majority of West Antarctica. This assumed topography would favor long-term stability for the West Antarctic Ice Sheet (WAIS) in MBL. Airborne geophysical data collected in 2009 reveal a much deeper bed than previously estimated, including a significant trough underlying DeVicq Glacier and evidence for extensive glacial erosion. Using these data, we produce a new map of subglacial topography, with which we model the sensitivity of WAIS to a warming ocean using the ice-sheet model of Pollard and DeConto (2012b). We compare the results to estimates of ice loss during WAIS collapse using the previously defined subglacial topography, to determine the impact of the newly discovered subglacial features. Our results indicate that the topographic changes are not sufficient to destabilize the northern margin of MBL currently feeding the Getz Ice Shelf; the majority of ice loss occurs from flow toward the Siple Coast. However, despite only slight dynamic differences, using the new bed as a boundary condition results in an additional 8 cm of sea-level rise during major glacial retreat, an increase of just over 2%. Precise estimation of past and future ice retreat, as well as a complete understanding of the geologic history of the region, will require a higher resolution picture of the bed topography around the Executive Committee mountains.

  13. Improved Thermal-Insulation Systems for Low Temperatures

    NASA Technical Reports Server (NTRS)

    Fesmire, James E.; Augustynowicz, Stanislaw D.

    2003-01-01

    Improved thermal-insulation materials and structures and the techniques for manufacturing them are undergoing development for use in low-temperature applications. Examples of low-temperature equipment for which these thermal insulation systems could provide improved energy efficiency include storage tanks for cryogens, superconducting electric-power-transmission equipment, containers for transport of food and other perishable commodities, and cold boxes for low-temperature industrial processes. These systems could also be used to insulate piping used to transfer cryogens and other fluids, such as liquefied natural gas, refrigerants, chilled water, crude oil, or low-pressure steam. The present thermal-insulation systems are layer composites based partly on the older class of thermal-insulation systems denoted generally as multilayer insulation (MLI). A typical MLI structure includes an evacuated jacket, within which many layers of radiation shields are stacked or wrapped close together. Low-thermal-conductivity spacers are typically placed between the reflection layers to keep them from touching. MLI can work very well when a high vacuum level (less than 10(exp-4) torr) is maintained and utmost care is taken during installation, but its thermal performance deteriorates sharply as the pressure in the evacuated space rises into the soft vacuum range [pressures greater than 0.1 torr (greater than 13 Pa)]. In addition, the thermal performance of MLI is extremely sensitive to mechanical compression and edge effects and can easily decrease from one to two orders of magnitude from its ideal value even when the MLI is kept under high vacuum condition. The present thermal-insulation systems are designed to perform well under soft vacuum level, in particular the range of 1 to 10 torr. They are also designed with larger interlayer spacings to reduce vulnerability to compression (and consequent heat leak) caused by installation and use. The superiority of these systems is the

  14. High-Temperature Stability and Grain Boundary Complexion Formation in a Nanocrystalline Cu-Zr Alloy

    NASA Astrophysics Data System (ADS)

    Khalajhedayati, Amirhossein; Rupert, Timothy J.

    2015-12-01

    Nanocrystalline Cu-3 at.% Zr powders with ~20 nm average grain size were created with mechanical alloying and their thermal stability was studied from 550-950°C. Annealing drove Zr segregation to the grain boundaries, which led to the formation of amorphous intergranular complexions at higher temperatures. Grain growth was retarded significantly, with 1 week of annealing at 950°C, or 98% of the solidus temperature, only leading to coarsening of the average grain size to 54 nm. The enhanced thermal stability can be connected to both a reduction in grain boundary energy with doping as well as the precipitation of ZrC particles. High mechanical strength is retained even after these aggressive heat treatments, showing that complexion engineering may be a viable path toward the fabrication of bulk nanostructured materials with excellent properties.

  15. Preparation and Pore Structure Stability at High Temperature of Porous Fe-Al Intermetallics

    NASA Astrophysics Data System (ADS)

    Shen, P. Z.; Gao, H. Y.; Song, M.; He, Y. H.

    2013-12-01

    Porous Fe-Al intermetallics with different nominal compositions (from Fe-8 wt.% Al to Fe-50 wt.% Al) were fabricated by Fe and Al elemental powders through reaction synthesis. The effects of the Al content on the pore structure properties, and the comparison of pore structure stabilities at high-temperatures among the porous Fe-Al intermetallics and porous Ti, Ni, 316L stainless steel samples, were systematically studied. Results showed that the open porosity, maximum pore size, and permeability vary with the Al content. Porous Fe-(25-30 wt.%) Al intermetallics show good shape controllability and excellent pore structure stability at 1073 K in air, which suggests that these porous Fe-Al intermetallics could be used for filtration at high temperatures.

  16. Stability analysis of the high temperature thermal pebble bed nuclear reactor concept

    SciTech Connect

    Vondy, D.R.

    1981-02-01

    A study was made of the stability of the high temperature gas-cooled pebble bed core against xenon-driven oscillation. This generic study indicated that a core as large as 3000 MW(t) could be stable. Several aspects present a challenge to analysis including the void space above the pebble bed, the effects of possible control rod configurations, and the temperature feedback contribution. Special methods of analysis were developed in this effort. Of considerable utility was the scheme of including an azimuthal buckling loss term in the neturon balance equations admitting direct solution of the first azimuthal harmonic for a core having azimuthal symmetry. This technique allows the linear stability analysis to be done solving two-dimensional (RZ) problems instead of three-dimensional problems. A scheme for removing the fundamental source contribution was also implemented to allow direct iteration toward the dominant harmonic solution, treating up to three dimensions with diffusion theory.

  17. Laser safety and hazard analysis for the temperature stabilized BSLT ARES laser system.

    SciTech Connect

    Augustoni, Arnold L.

    2003-08-01

    A laser safety and hazard analysis was performed for the temperature stabilized Big Sky Laser Technology (BSLT) laser central to the ARES system based on the 2000 version of the American National Standards Institute's (ANSI) Standard Z136.1, for Safe Use of Lasers and the 2000 version of the ANSI Standard Z136.6, for Safe Use of Lasers Outdoors. As a result of temperature stabilization of the BSLT laser the operating parameters of the laser had changed requiring a hazard analysis based on the new operating conditions. The ARES laser system is a Van/Truck based mobile platform, which is used to perform laser interaction experiments and tests at various national test sites.

  18. Adaptive and freeze-tolerant heteronetwork organohydrogels with enhanced mechanical stability over a wide temperature range

    NASA Astrophysics Data System (ADS)

    Gao, Hainan; Zhao, Ziguang; Cai, Yudong; Zhou, Jiajia; Hua, Wenda; Chen, Lie; Wang, Li; Zhang, Jianqi; Han, Dong; Liu, Mingjie; Jiang, Lei

    2017-06-01

    Many biological organisms with exceptional freezing tolerance can resist the damages to cells from extra-/intracellular ice crystals and thus maintain their mechanical stability at subzero temperatures. Inspired by the freezing tolerance mechanisms found in nature, here we report a strategy of combining hydrophilic/oleophilic heteronetworks to produce self-adaptive, freeze-tolerant and mechanically stable organohydrogels. The organohydrogels can simultaneously use water and oil as a dispersion medium, and quickly switch between hydrogel- and organogel-like behaviours in response to the nature of the surrounding phase. Accordingly, their surfaces display unusual adaptive dual superlyophobic in oil/water system (that is, they are superhydrophobic under oil and superoleophobic under water). Moreover, the organogel component can inhibit the ice crystallization of the hydrogel component, thus enhancing the mechanical stability of organohydrogel over a wide temperature range (-78 to 80 °C). The organohydrogels may have promising applications in complex and harsh environments.

  19. Novel emulsions stabilized by pH and temperature sensitive microgels

    NASA Astrophysics Data System (ADS)

    Ngai, To; Auweter, Helmut; Behrens, Sven

    2006-03-01

    Poly(N-isopropylacrylamide-co-methacrylic acid) (PNIPAM-MAA) microgel particles in aqueous solution exhibit a volume phase transition that can be induced by changes of either pH or temperature. In the swollen state, these microgels self-assemble at an octanol-water interface and can be used to stabilize surfactant-free oil-in-water emulsions. This stabilizing efficiency is retained even in the collapsed state, provided that the microgels are fully charged. At very low charge (low pH), on the other hand, the microgels migrate completely into the oil phase, and the emulsion breaks. In an intermediate regime of practical interest the emulsion stability can be tuned by small adjustments of pH or temperature. Because of this unprecedented stability control, we believe that such stimulus-responsive charged microgels have a great potential for applications in the field of cosmetic or pharmaceutical formulations. Conceptually they belong to a new class of emulsifiers combining properties of both classical surfactants and solid particles.

  20. Effects of fan inlet temperature disturbances on the stability of a turbofan engine

    NASA Technical Reports Server (NTRS)

    Abdelwahab, M.

    1981-01-01

    The effects of steady-state and time-dependent fan inlet total temperature disturbances on the stability of a TF30-P-3 turbofan engine were determined. Disturbances were induced by a gaseous-hydrogen-fueled burner system installed upstream of the fan inlet. Data were obtained at a fan inlet Reynolds number index of 0.50 and at a low-pressure-rotor corrected speed of 90 percent of military speed. All tests were conducted with a 90 deg extent of the fan inlet circumference exposed to above-average temperatures.

  1. Analysis of a passive heat sink for temperature stabilization of high-power LED bulbs

    NASA Astrophysics Data System (ADS)

    Balvís, Eduardo; Bendaña, Ricardo; Michinel, Humberto; Fernández de Córdoba, Pedro; Paredes, Angel

    2015-04-01

    In this paper we present a numerical analysis and experimental measurements of the temperature stabilization of high-power LED chips that we have obtained by employing an aluminum passive heat sink, designed to be used in a compact light bulb configuration. We demonstrate that our system keeps the temperature of the LED chip well-below 70° C yielding long-term operation of the device. Our simulations have been performed for a low-cost device ready to install in public streetlights. The experimental measurements performed in different configurations show a nice agreement with the numerical calculations.

  2. Low-temperature electrochemical characterization of sputtered yttria-stabilized zirconia thin film on silicon substrate

    NASA Astrophysics Data System (ADS)

    Hua, Ching-Han; Chou, Chen-Chia

    2016-08-01

    The microstructure and electrical conductivity of yttria-stabilized zirconia (YSZ) thin films with Pt electrodes were evaluated through three configurations in the temperature range from 25 to 500 °C. Using ac-impedance spectra, the contribution of the Si substrate to resistance was separated by an equivalent-circuit analysis. The colossal ionic conductivity of YSZ thin films at temperatures higher than 125 °C was observed parallel to the interface. The total ionic conductivity of YSZ thin films increased significantly in comparison w the bulk YSZ electrolyte. An alternative conductive pathway ascribed to the homogeneous and heterogeneous interfaces with high strain and charge-containing defects was proposed.

  3. A high-stability non-contact dilatometer for low-amplitude temperature-modulated measurements

    SciTech Connect

    Luckabauer, Martin; Sprengel, Wolfgang; Würschum, Roland

    2016-07-15

    Temperature modulated thermophysical measurements can deliver valuable insights into the phase transformation behavior of many different materials. While especially for non-metallic systems at low temperatures numerous powerful methods exist, no high-temperature device suitable for modulated measurements of bulk metallic alloy samples is available for routine use. In this work a dilatometer for temperature modulated isothermal and non-isothermal measurements in the temperature range from room temperature to 1300 K is presented. The length measuring system is based on a two-beam Michelson laser interferometer with an incremental resolution of 20 pm. The non-contact measurement principle allows for resolving sinusoidal length change signals with amplitudes in the sub-500 nm range and physically decouples the length measuring system from the temperature modulation and heating control. To demonstrate the low-amplitude capabilities, results for the thermal expansion of nickel for two different modulation frequencies are presented. These results prove that the novel method can be used to routinely resolve length-change signals of metallic samples with temperature amplitudes well below 1 K. This high resolution in combination with the non-contact measurement principle significantly extends the application range of modulated dilatometry towards high-stability phase transformation measurements on complex alloys.

  4. Ultra-high temperature stability Joule-Thomson cooler with capability to accomodate pressure variations

    NASA Technical Reports Server (NTRS)

    Bard, Steven (Inventor); Wu, Jiunn-Jeng (Inventor); Trimble, Curtis A. (Inventor)

    1992-01-01

    A Joule-Thomson cryogenic refrigeration system capable of achieving high temperature stabilities in the presence of varying temperature, atmospheric pressure, and heat load is provided. The Joule-Thomson cryogenic refrigeration system includes a demand flow Joule-Thomson expansion valve disposed in a cryostat of the refrigeration system. The expansion valve has an adjustable orifice that controls the flow of compressed gas therethrough and induces cooling and partial liquefaction of the gas. A recuperative heat exchanger is disposed in the cryostat and coupled to the expansion valve. A thermostatically self-regulating mechanism is disposed in the cryostat and coupled to the J-T expansion valve. The thermostatically self-regulating mechanism automatically adjusts the cross sectional area of the adjustable valve orifice in response to environmental temperature changes and changes in power dissipated at a cold head. A temperature sensing and adjusting mechanism is coupled to a cold head for adjusting the temperature of the cold head in response to the change in heat flow in the cold head. The temperature sensing and adjusting mechanism comprises a temperature sensitive diode, a wound wire heater, and an electrical feedback control circuit coupling the diode to the heater. An absolute pressure relief valve is interposed between the output of the cryostat and an exhaust port for maintaining a constant exhaust temperature in the refrigerating system, independent of the changes in atmospheric pressure.

  5. A high-stability non-contact dilatometer for low-amplitude temperature-modulated measurements

    NASA Astrophysics Data System (ADS)

    Luckabauer, Martin; Sprengel, Wolfgang; Würschum, Roland

    2016-07-01

    Temperature modulated thermophysical measurements can deliver valuable insights into the phase transformation behavior of many different materials. While especially for non-metallic systems at low temperatures numerous powerful methods exist, no high-temperature device suitable for modulated measurements of bulk metallic alloy samples is available for routine use. In this work a dilatometer for temperature modulated isothermal and non-isothermal measurements in the temperature range from room temperature to 1300 K is presented. The length measuring system is based on a two-beam Michelson laser interferometer with an incremental resolution of 20 pm. The non-contact measurement principle allows for resolving sinusoidal length change signals with amplitudes in the sub-500 nm range and physically decouples the length measuring system from the temperature modulation and heating control. To demonstrate the low-amplitude capabilities, results for the thermal expansion of nickel for two different modulation frequencies are presented. These results prove that the novel method can be used to routinely resolve length-change signals of metallic samples with temperature amplitudes well below 1 K. This high resolution in combination with the non-contact measurement principle significantly extends the application range of modulated dilatometry towards high-stability phase transformation measurements on complex alloys.

  6. Computational tools help improve protein stability but with a solubility tradeoff.

    PubMed

    Broom, Aron; Jacobi, Zachary; Trainor, Kyle; Meiering, Elizabeth M

    2017-09-01

    Accurately predicting changes in protein stability upon amino acid substitution is a much sought after goal. Destabilizing mutations are often implicated in disease, whereas stabilizing mutations are of great value for industrial and therapeutic biotechnology. Increasing protein stability is an especially challenging task, with random substitution yielding stabilizing mutations in only ∼2% of cases. To overcome this bottleneck, computational tools that aim to predict the effect of mutations have been developed; however, achieving accuracy and consistency remains challenging. Here, we combined 11 freely available tools into a meta-predictor (meieringlab.uwaterloo.ca/stabilitypredict/). Validation against ∼600 experimental mutations indicated that our meta-predictor has improved performance over any of the individual tools. The meta-predictor was then used to recommend 10 mutations in a previously designed protein of moderate thermodynamic stability, ThreeFoil. Experimental characterization showed that four mutations increased protein stability and could be amplified through ThreeFoil's structural symmetry to yield several multiple mutants with >2-kcal/mol stabilization. By avoiding residues within functional ties, we could maintain ThreeFoil's glycan-binding capacity. Despite successfully achieving substantial stabilization, however, almost all mutations decreased protein solubility, the most common cause of protein design failure. Examination of the 600-mutation data set revealed that stabilizing mutations on the protein surface tend to increase hydrophobicity and that the individual tools favor this approach to gain stability. Thus, whereas currently available tools can increase protein stability and combining them into a meta-predictor yields enhanced reliability, improvements to the potentials/force fields underlying these tools are needed to avoid gaining protein stability at the cost of solubility. © 2017 by The American Society for Biochemistry and

  7. Effect of temperature variation and gas composition on the stability of the RPC operation

    NASA Astrophysics Data System (ADS)

    Ćwiok, M.; Dominik, W.; Górski, M.; Królikowski, J.

    2003-08-01

    An Inverted Double Gap Resistive Plate Chambers (RPC) made of bakelite of 5×10 9 Ωcm volume resistivity was tested at avalanche rates up to 1 kHz/cm2/ gap in the Gamma Irradiation Facility at CERN in 2001. The inner surfaces of the chamber electrodes were cladded using linseed oil varnish. Dependence of the intrinsic RPC noise and the stability of the gas gain on the gas temperature and the gas composition are discussed.

  8. Electrochemically prepared surface-enhanced Raman scattering-active silver substrates with improved stabilities

    NASA Astrophysics Data System (ADS)

    Yang, Kuang-Hsuan; Liu, Yu-Chuan; Yu, Chung-Chin; Chen, Bo-Chuen

    2011-01-01

    In this work, SiO 2 nanoparticles-modified surface-enhanced Raman scattering (SERS)-active silver substrates were prepared by electrochemical oxidation-reduction cycles (ORC) methods in 0.1 N HCl aqueous solutions containing 1 mM SiO 2 nanoparticles to improve their thermal stabilities and anti-aging abilities in SERS performances. Then these SERS-active substrates were further modified with different contents of SiO 2 nanoparticles to improve their corresponding SERS performances. Experimental results indicate that the operation temperature can be significantly raised from 125 to 175 °C based on this modified SERS-active Ag substrate. Also, the aging in SERS intensity is also depressed on this modified Ag substrate due to the contribution of SiO 2 nanoparticles. Moreover, the SERS enhancement capability on this modified Ag substrate is gradually raised from 25 °C to a maximum at 55 °C and monotonically decreased from 55 to 60 °C. This is a 10 °C delay as compared with the similar phenomenon observed on the unmodified Ag substrate.

  9. Encapsulation of catechin and epicatechin on BSA NPS improved their stability and antioxidant potential

    PubMed Central

    Yadav, Ramdhan; Kumar, Dharmesh; Kumari, Avnesh; Yadav, Sudesh Kumar

    2014-01-01

    Nanoencapsulation of antioxidant molecules on protein nanoparticles (NPs) could be an advanced approach for providing stable, better food nutraceuticals and anticancer drugs. The bioavailability and stability of catechin (CAT) and epicatechin (ECAT) were very poor. In the present study, the CAT and ECAT were loaded on bovine serum albumin (BSA) NPs following desolvation method. The transmission electron microscope (TEM) and atomic force microscope (AFM) recorded size of CAT-BSA NPs and ECAT-BSA NPs were 45 ± 5 nm and 48 ± 5 nm respectively. The encapsulation efficiency of CAT and ECAT on BSA NPs was found to be 60.5 and 54.5 % respectively. CAT-BSA NPs and ECAT-BSA NPs show slow and sustained in vitro release. The CAT-BSA NPs and ECAT-BSA NPs were stable in solution at various temperatures 37 °C, 47 °C and 57 °C. DPPH assay revealed that CAT and ECAT maintained their functional activity even after encapsulation on BSA NPs. Furthermore, the efficacy of CAT-BSA NPs and ECAT-BSA NPs determined against A549 cell lines was found to be improved. CAT and ECAT aptly encapsulated in BSA NPs, showed satisfactory sustained release, maintained antioxidant potential and found improved efficacy. This has thus suggested their more effective use in food and nutraceuticals as well as in medical field. PMID:26417264

  10. A method to stabilize the temperature dependent performance of G-APD arrays

    NASA Astrophysics Data System (ADS)

    Huh, Yoonsuk; Choi, Yong; Ho Jung, Jin; Jung, Jiwoong

    2015-02-01

    This paper presents a compensation method to stabilize the temperature dependent performance of Geiger-mode Avalanche Photodiode (G-APD) arrays for Positron Emission Tomography (PET). The compensation method is used to identify the bias voltage range that provides stable performance even at different temperatures using the G-APD's characteristics, and to control the photo-peak variation as a function of temperature using the preamplifier gain within the identified bias voltage range. A pair of G-APD detectors and temperature sensors were located in the temperature chamber and the preamplifiers which can control the gain of the detectors using the digital potentiometer were positioned outside the chamber. The performance of the G-APD detector, especially energy resolution and coincidence timing resolution, was characterized as a function of bias voltage at different temperatures from 20 °C to 40 °C at 5 °C increments; the energy resolution, coincidence timing resolution, and photo-peak position of all channels of G-APD PET detectors before and after the preamplifier gain correction were then measured and compared. The results of this study demonstrated that the optimal bias voltage range providing the good energy and coincidence timing resolution, 12.1±1.2% and 1.30±0.09 ns, respectively, could be identified at the temperature range and the photo-peak variation and the performance at different temperatures could be stabilized by adjusting the preamplifier gain within the identified bias voltage range. We concluded the proposed method to be reliable and useful for the development of the PET system using G-APD arrays.

  11. The improvement of phycocyanin stability extracted from Spirulina sp using extrusion encapsulation technique

    NASA Astrophysics Data System (ADS)

    Suzery, Meiny; Hadiyanto, Sutanto, Heri; Soetrisnanto, Danny; Majid, Dian; Setyawan, Deny; Azizah, Nur

    2015-12-01

    The stability of phycocyanin extracted from microalgae Spirulina has been evaluated and it showed that the stability of this antioxidant was affected by temperature and pH changes. The encapsulation technique was of the alternatives to overcome this stability changes. The objective of this paper was to investigate the effects of coating materials (alginate and chitosan) during encapsulation by using extrusion technique. The experiments were conducted with variation of alginate as coating materials. The size of each microcapsules was evaluated by using SEM/XRD for its size and homogeneity.

  12. The development of precipitated iron catalysts with improved stability

    SciTech Connect

    Not Available

    1990-01-01

    The goal of this program is to identify the chemical principles governing the deactivation of precipitated iron catalysts during Fischer-Tropsch synthesis and to use these chemical principles in the design of catalysts suitable for slurry reactors. This report covers testing an iron catalyst. During the last quarter, a new precipitated iron catalyst was prepared and tested in the slurry autoclave reactor at various conditions. This catalyst did not noticeably deactivate during 1250 hours of testing. This quarter, the test was extended to include performance evaluations at different conversion levels ranging from 35 to 88% at 265 and 275{degree}C. The conversion levels were varied by changing the feed rate. The catalytic performance at different conversion intervals was then integrated to approximately predict performance in a bubble column reactor. The run was shut down at the end of 1996 hours because of a 24-hour-power outage. When the power was back on, the run was restarted from room temperature. Catalytic performance during the first 300 hours after the restart-up was monitored. Overall product distributions are being tabulated as analytical laboratory data are obtained. 34 figs., 3 tabs.

  13. Random mutagenesis improves the low-temperature activity of the tetrameric 3-isopropylmalate dehydrogenase from the hyperthermophile Sulfolobus tokodaii.

    PubMed

    Sasaki, Michika; Uno, Mayumi; Akanuma, Satoshi; Yamagishi, Akihiko

    2008-12-01

    In general, the enzymes of thermophilic organisms are more resistant to thermal denaturation than are those of mesophilic or psychrophilic organisms. Further, as is true for their mesophilic and psychrophilic counterparts, the activities of thermophilic enzymes are smaller at temperatures that are less than the optimal temperature. In an effort to characterize the properties that would improve its activity at temperatures less than the optimal, we subjected the thermostable Sulfolobus tokodaii (S. tokodaii) 3-isopropylmalate dehydrogenase to two rounds of random mutagenesis and selected for improved low-temperature activity using an in vivo recombinant Escherichia coli system. Five dehydrogenase mutants were purified and their catalytic properties and thermostabilities characterized. The mutations favorably affect the K(m) values for NAD (nicotinamide adenine dinucleotide) and/or the k(cat) values. The results of thermal stability measurements show that, although the mutations somewhat decrease the stability of the enzyme, the mutants are still very resistant to heat. The locations and properties of the mutations found for the S. tokodaii enzyme are compared with those found for the previously isolated low-temperature adapted mutants of the homologous Thermus thermophilus enzyme. However, there are few, if any, common properties that enhance the low-temperature activities of both enzymes; therefore, there may be many ways to improve the low-temperature catalytic activity of a thermostable enzyme.

  14. Role of temperature in the radiation stability of yttria stabilized zirconia under swift heavy ion irradiation: A study from the perspective of nuclear reactor applications

    NASA Astrophysics Data System (ADS)

    Kalita, Parswajit; Ghosh, Santanu; Sattonnay, Gaël; Singh, Udai B.; Grover, Vinita; Shukla, Rakesh; Amirthapandian, S.; Meena, Ramcharan; Tyagi, A. K.; Avasthi, Devesh K.

    2017-07-01

    The search for materials that can withstand the harsh radiation environments of the nuclear industry has become an urgent challenge in the face of ever-increasing demands for nuclear energy. To this end, polycrystalline yttria stabilized zirconia (YSZ) pellets were irradiated with 80 MeV Ag6+ ions to investigate their radiation tolerance against fission fragments. To better simulate a nuclear reactor environment, the irradiations were carried out at the typical nuclear reactor temperature (850 °C). For comparison, irradiations were also performed at room temperature. Grazing incidence X-ray diffraction and Raman spectroscopy measurements reveal degradation in crystallinity for the room temperature irradiated samples. No bulk structural amorphization was however observed, whereas defect clusters were formed as indicated by transmission electron microscopy and supported by thermal spike simulation results. A significant reduction of the irradiation induced defects/damage, i.e., improvement in the radiation tolerance, was seen under irradiation at 850 °C. This is attributed to the fact that the rapid thermal quenching of the localized hot molten zones (arising from spike in the lattice temperature upon irradiation) is confined to 850 °C (i.e., attributed to the resistance inflicted on the rapid thermal quenching of the localized hot molten zones by the high temperature of the environment) thereby resulting in the reduction of the defects/damage produced. Our results present strong evidence for the applicability of YSZ as an inert matrix fuel in nuclear reactors, where competitive effects of radiation damage and dynamic thermal healing mechanisms may lead to a strong reduction in the damage production and thus sustain its physical integrity.

  15. Fusion Peptide Improves Stability and Bioactivity of Single Chain Antibody against Rabies Virus.

    PubMed

    Xi, Hualong; Zhang, Kaixin; Yin, Yanchun; Gu, Tiejun; Sun, Qing; Shi, Linqing; Zhang, Renxia; Jiang, Chunlai; Kong, Wei; Wu, Yongge

    2017-04-28

    The combination of rabies immunoglobulin (RIG) with a vaccine is currently effective against rabies infections, but improvements are needed. Genetic engineering antibody technology is an attractive approach for developing novel antibodies to replace RIG. In our previous study, a single-chain variable fragment, scFv57R, against rabies virus glycoprotein was constructed. However, its inherent weak stability and short half-life compared with the parent RIG may limit its diagnostic and therapeutic application. Therefore, an acidic tail of synuclein (ATS) derived from the C-terminal acidic tail of human alpha-synuclein protein was fused to the C-terminus of scFv57R in order to help it resist adverse stress and improve the stability and halflife. The tail showed no apparent effect on the preparation procedure and affinity of the protein, nor did it change the neutralizing potency in vitro. In the ELISA test of molecular stability, the ATS fusion form of the protein, scFv57R-ATS, showed an increase in thermal stability and longer half-life in serum than scFv57R. The protection against fatal rabies virus challenge improved after fusing the tail to the scFv, which may be attributed to the improved stability. Thus, the ATS fusion approach presented here is easily implemented and can be used as a new strategy to improve the stability and half-life of engineered antibody proteins for practical applications.

  16. Torque vectoring for improving stability of small electric vehicles

    NASA Astrophysics Data System (ADS)

    Grzegożek, W.; Weigel-Milleret, K.

    2016-09-01

    The electric vehicles solutions based on the individually controlled electric motors propel a single wheel allow to improve the dynamic properties of the vehicle by varying the distribution of the driving torque. Most of the literature refer to the vehicles with a track typical for passenger cars. This paper examines whether the narrow vehicle (with a very small track) torque vectoring bring a noticeable change of the understeer characteristics and whether torque vectoring is possible to use in securing a narrow vehicle from roll over (roll mitigation). The paper contains road tests of the steering characteristics (steady state understeer characteristic quasi-static acceleration with a fixed steering wheel (SH = const) and on the constant radius track (R = const)) of the narrow vehicle. The vehicle understeer characteristic as a function of a power distribution is presented.

  17. Thin-Film Reliability Trends Toward Improved Stability: Preprint

    SciTech Connect

    Jordan, D. C.; Kurtz, S. R.

    2011-07-01

    Long-term, stable performance of photovoltaic (PV) modules will be increasingly important to their successful penetration of the power grid. This paper summarizes more than 150 thin-film and more than 1700 silicon PV degradation rates (Rd) quoted in publications for locations worldwide. Partitioning the literature results by technology and date of installation statistical analysis shows an improvement in degradation rate especially for thin-film technologies in the last decade. A CIGS array deployed at NREL for more than 5 years that appears to be stable supports the literature trends. Indoor and outdoor data indicate undetectable change in performance (0.2+/-0.2 %/yr). One module shows signs of slight degradation from what appears to be an initial manufacturing defect, however it has not affected the overall system performance.

  18. Improved scaling of temperature-accelerated dynamics using localization.

    PubMed

    Shim, Yunsic; Amar, Jacques G

    2016-07-07

    While temperature-accelerated dynamics (TAD) is a powerful method for carrying out non-equilibrium simulations of systems over extended time scales, the computational cost of serial TAD increases approximately as N(3) where N is the number of atoms. In addition, although a parallel TAD method based on domain decomposition [Y. Shim et al., Phys. Rev. B 76, 205439 (2007)] has been shown to provide significantly improved scaling, the dynamics in such an approach is only approximate while the size of activated events is limited by the spatial decomposition size. Accordingly, it is of interest to develop methods to improve the scaling of serial TAD. As a first step in understanding the factors which determine the scaling behavior, we first present results for the overall scaling of serial TAD and its components, which were obtained from simulations of Ag/Ag(100) growth and Ag/Ag(100) annealing, and compare with theoretical predictions. We then discuss two methods based on localization which may be used to address two of the primary "bottlenecks" to the scaling of serial TAD with system size. By implementing both of these methods, we find that for intermediate system-sizes, the scaling is improved by almost a factor of N(1/2). Some additional possible methods to improve the scaling of TAD are also discussed.

  19. Stabilizing hybrid perovskites against moisture and temperature via non-hydrolytic atomic layer deposited overlayers

    DOE PAGES

    Kim, In Soo; Martinson, Alex B. F.

    2015-09-14

    We utilized a novel non-hydrolytic (nh) surface chemistry to allow the direct synthesis of pinhole-fee oxide overlayers directly on conventional hybrid perovskite halide absorbers without damage. By utilizing water- free ALD Al2O3 passivation, a minimum of ten-fold increase in stability against relative humidity (RH) 85% was achieved along with a dramatically improved thermal resistance (up to 250 °C). We extend this approach to synthesize nh-TiO2 directly on hybrid perovskites to establish its potential in inverted photovoltaic devices as a dual stabilizing and electron accepting layer, as evidenced by photoluminescence (PL) quenching.

  20. Hybrid R-Fe-B/R-Co Magnets with Improved Thermal Stability

    DTIC Science & Technology

    2009-12-23

    known that Nd2Fe14B -based magnets display excellent room temperature magnetic performance with (BH)max up to 50 MGOe. However, their low Curie... Nd2Fe14B - and Sm2Co17-based permanent magnets. This temperature range covers the exact temperatures that are very critical for many important...make a hybrid Nd2Fe14B /Sm2(Co,Fe,Cu,Zr)17 magnet that may combine the high magnetic performance of Nd2Fe14B and excellent high temperature stability

  1. Structure and stability of pyrophyllite edge surfaces: Effect of temperature and water chemical potential

    NASA Astrophysics Data System (ADS)

    Kwon, Kideok D.; Newton, Aric G.

    2016-10-01

    The surfaces of clay minerals, which are abundant in atmospheric mineral dust, serve as an important medium to catalyze ice nucleation. The lateral edge surface of 2:1 clay minerals is postulated to be a potential site for ice nucleation. However, experimental investigations of the edge surface structure itself have been limited compared to the basal planes of clay minerals. Density functional theory (DFT) computational studies have provided insights into the pyrophyllite edge surface. Pyrophyllite is an ideal surrogate mineral for the edge surfaces of 2:1 clay minerals as it possesses no or little structural charge. Of the two most-common hydrated edge surfaces, the AC edge, (1 1 0) surface in the monoclinic polytype notation, is predicted to be more stable than the B edge, (0 1 0) surface. These stabilities, however, were determined based on the total energies calculated at 0 K and did not consider environmental effects such as temperature and humidity. In this study, atomistic thermodynamics based on periodic DFT electronic calculations was applied to examine the effects of environmental variables on the structure and thermodynamic stability of the common edge surfaces in equilibrium with bulk pyrophyllite and water vapor. We demonstrate that the temperature-dependent vibrational energy of sorbed water molecules at the edge surface is a significant component of the surface free energy and cannot be neglected when determining the surface stability of pyrophyllite. The surface free energies were calculated as a function of temperature from 240 to 600 K and water chemical potential corresponding to conditions from ultrahigh vacuum to the saturation vapor pressure of water. We show that at lower water chemical potentials (dry conditions), the AC and B edge surfaces possessed similar stabilities; at higher chemical potentials (humid conditions) the AC edge surface was more stable than the B edge surface. At high temperatures, both surfaces showed similar stabilities

  2. Hot and Cold Drugs: National Park Service Medication Stability at the Extremes of Temperature.

    PubMed

    Armenian, Patil; Campagne, Danielle; Stroh, Geoff; Ives Tallman, Crystal; Zeng, William Z D; Lin, Thomas; Gerona, Roy R

    2017-01-01

    National Park Service (NPS) Parkmedics provide medical care in austere environments. The objective of this study was to evaluate the stability of specific medications used by Parkmedics at extremes of temperatures likely to be faced in the field. This is a bench research study conducted in the laboratory setting over a 4-week period. Parenteral medications were separated into 4 temperature exposure groups: A) 45°C (hot); B) -20°C (cold); C) hot then cold temperatures alternating weekly; and D) cold then hot temperatures alternating weekly. At study start and the end of each week, three aliquots from each group were sampled to determine the remaining drug concentration through liquid chromatography-quadrupole time-of-flight mass spectrometry (Agilent LC 1260- QTOF/MS 6550). Quantitative analysis was done using Agilent MassHunter Quantitative Analysis software. The mean drug concentration from triplicate aliquots was expressed as percentage of its baseline concentration to monitor the drug's stability during storage. Eight medications were analyzed (atropine, diphenhydramine, fentanyl, hydromorphone, midazolam, morphine, naloxone, ondansetron). Hydromorphone, morphine, and ondansetron showed the greatest stability, at above 90% of original concentration in all study arms. Diphenhydramine, fentanyl and midazolam showed heat independent degradation, degrading the same way regardless of heat exposure. By the end of the study period, 51-56% midazolam remained in all groups. Atropine and naloxone showed heat dependent degradation, degrading more when exposed to heat. Atropine had the most degradation, being undetectable after 4 weeks of heat exposure. We recommend that EMS providers replace atropine, naloxone, diphenhydramine, fentanyl, and midazolam frequently if they are practicing in low call volume or high-temperature environments. Further studies will be needed to determine if re-dosing midazolam, naloxone, and atropine is the appropriate clinical strategy in this

  3. Improved Blackbody Temperature Sensors for a Vacuum Furnace

    NASA Technical Reports Server (NTRS)

    Farmer, Jeff; Coppens, Chris; O'Dell, J. Scott; McKechnie, Timothy N.; Schofield, Elizabeth

    2009-01-01

    Some improvements have been made in the design and fabrication of blackbody sensors (BBSs) used to measure the temperature of a heater core in a vacuum furnace. Each BBS consists of a ring of thermally conductive, high-melting-temperature material with two tantalum-sheathed thermocouples attached at diametrically opposite points. The name "blackbody sensor" reflects the basic principle of operation. Heat is transferred between the ring and the furnace heater core primarily by blackbody radiation, heat is conducted through the ring to the thermocouples, and the temperature of the ring (and, hence, the temperature of the heater core) is measured by use of the thermocouples. Two main requirements have guided the development of these BBSs: (1) The rings should have as high an emissivity as possible in order to maximize the heat-transfer rate and thereby maximize temperature-monitoring performance and (2) the thermocouples must be joined to the rings in such a way as to ensure long-term, reliable intimate thermal contact. The problem of fabricating a BBS to satisfy these requirements is complicated by an application-specific prohibition against overheating and thereby damaging nearby instrumentation leads through the use of conventional furnace brazing or any other technique that involves heating the entire BBS and its surroundings. The problem is further complicated by another application-specific prohibition against damaging the thin tantalum thermocouple sheaths through the use of conventional welding to join the thermocouples to the ring. The first BBS rings were made of graphite. The tantalum-sheathed thermocouples were attached to the graphite rings by use of high-temperature graphite cements. The ring/thermocouple bonds thus formed were found to be weak and unreliable, and so graphite rings and graphite cements were abandoned. Now, each BBS ring is made from one of two materials: either tantalum or a molybdenum/titanium/zirconium alloy. The tantalum

  4. Improved granular activated carbon for the stabilization of wastewater PH

    SciTech Connect

    Farmer, R.W.; Dussert, B.W.; Kovacic, S.L.

    1996-12-31

    Laboratory studies have identified the cause of the pH rise, which occurs during water treatment with activated carbon, as an interaction between the naturally occurring anions and protons in the water and the carbon surface. The interaction can be described as an ion exchange type of phenomenon, in which the carbon surface sorbs the anions and corresponding hydronium ions from the water. These studies have shown that the anion sorption and resulting pH increase is independent of the raw material used for the activated carbon production, e.g. bituminous or subbituminous coal, peat, wood or coconut. Also, the pH excursions occur with virgin, reactivated, and acid washed granular carbons. Current pH control technologies focus on adjustment of the wastewater pH prior to discharge or recycle of the initial effluent water until the pH increase abates. However, improved water pH control options have been realized by altering the carbon surface through controlled oxidation rather than the water chemistry or extended preprocessing at the treatment site.

  5. Improvement of the stability of hydroxyapatite through glass ceramic reinforcement.

    PubMed

    Ha, Na Ra; Yang, Zheng Xun; Hwang, Kyu Hong; Kim, Tae Suk; Lee, Jong Kook

    2010-05-01

    Hydroxyapatite has achieved significant application in orthopedic and dental implants due to its excellent biocompatibility. Sintered hydroxyapatites showed significant dissolution, however, after their immersion in water or simulated body fluid (SBF). This grain boundary dissolution, even in pure hydroxyapatites, resulted in grain separation at the surfaces, and finally, in fracture. In this study, hydroxyapatite ceramics containing apatite-wollastonite (AW) or calcium silicate (SG) glass ceramics as additives were prepared to prevent the dissolution. AW and SG glass ceramics were added at 0-7 wt% and powder-compacted uniaxially followed by firing at moisture conditions. The glass phase was incorporated into the hydroxyapatite to act as a sintering aid, followed by crystallization, to improve the mechanical properties without reducing the biocompatibility. As seen in the results of the dissolution test, a significant amount of damage was reduced even after more than 14 days. TEM and SEM showed no decomposition of HA to the secondary phase, and the fracture toughness increased, becoming even higher than that of the commercial hydroxyapatite.

  6. Improving The Retrieval Of Atmospheric Stability Indices By Combining Ground-based And Satellite Remote Sensing

    NASA Astrophysics Data System (ADS)

    Loehnert, U.; Ebell, K.; Orlandi, E.

    2015-12-01

    A new generation of high-resolution (~1km) weather forecast models now becoming operational over Europe promises to revolutionize predictions of severe weather, specifically by explicitly resolving convection. For this, a dense observing network is required, focusing especially on the lowest few km of the atmosphere, so that forecast models have the most realistic state of the atmosphere for initialization, continuous assimilation and verification. In this context, the current European COST action TOPROF (ES1303) deals with operational networking of three existing but so far under-exploited, ground-based remote sensing instruments throughout Europe: i) Several hundreds of ceilometers, ii) more than 20 Doppler lidars, and iii) About 30 microwave profilers (MWP) giving profiles of temperature and humidity in the lowest few km every 10 minutes. Specifically, MWP are highly suited for continuously monitoring the temporal development of atmospheric stability (i.e. Cimini et al. 2015, AMT) before the initiation of deep convection. However, the vertical resolution of MWP temperature profiles is best in the lowest kilometer above the surface, decreasing rapidly with increasing height. In addition, humidity profile retrievals typically cannot be resolved with more than two degrees of freedom for signal, resulting in a rather poor vertical resolution throughout the troposphere. Typical stability indices (i.e. K-index, Lifted Index, Showalter Index, CAPE,..) rely on temperature and humidity values not only in the region of the boundary layer (850 hPa) but also at 700 hPa, 500 hPa, in between these levels or even higher above. In this study, for clear sky cases, satellite remote sensing (i.e. SEVIRI radiances from the geostationary METEOSAT ) is used to complement the ground-based MWP information. The theoretical basis of the combined retrieval is highlighted, error reductions resulting from the sensor synergy are discussed and applications to real data are shown. The study

  7. Improvements in Glucose Sensitivity and Stability of Trichoderma reesei β-Glucosidase Using Site-Directed Mutagenesis

    PubMed Central

    Amano, Yoshihiko

    2016-01-01

    Glucose sensitivity and pH and thermal stabilities of Trichoderma reesei Cel1A (Bgl II) were improved by site-directed mutagenesis of only two amino acid residues (L167W or P172L) at the entrance of the active site. The Cel1A mutant showed high glucose tolerance (50% of inhibitory concentration = 650 mM), glucose stimulation (2.0 fold at 50 mM glucose), and enhanced specific activity (2.4-fold) compared with those of the wild-type Cel1A. Furthermore, the mutant enzyme showed stability at a wide pH range of 4.5–9.0 and possessed high thermal stability up to 50°C with 80% of the residual activities compared with the stability seen at the pH range of 6.5–7.0 and temperatures of up to 40°C in the wild-type Cel1A. Kinetic studies for hydrolysis revealed that the Cel1A mutant was competitively inhibited by glucose at similar levels as the wild-type enzyme. Additionally, the mutant enzyme exhibited substrate inhibition, which gradually disappeared with an increasing glucose concentration. These data suggest that the glucose stimulation was caused by relieve the substrate inhibition in the presence of glucose. To conclude, all the properties improved by the mutagenesis would be great advantages in degradation of cellulosic biomass together with cellulases. PMID:26790148

  8. Evaluation of the Long-Term Stability and Temperature Coefficient of Dew-Point Hygrometers

    NASA Astrophysics Data System (ADS)

    Benyon, R.; Vicente, T.; Hernández, P.; De Rivas, L.; Conde, F.

    2012-09-01

    The continuous quest for improved specifications of optical dew-point hygrometers has raised customer expectations on the performance of these devices. In the absence of a long calibration history, users with a limited prior experience in the measurement of humidity, place reliance on manufacturer specifications to estimate long-term stability. While this might be reasonable in the case of measurement of electrical quantities, in humidity it can lead to optimistic estimations of uncertainty. This article reports a study of the long-term stability of some hygrometers and the analysis of their performance as monitored through regular calibration. The results of the investigations provide some typical, realistic uncertainties associated with the long-term stability of instruments used in calibration and testing laboratories. Together, these uncertainties can help in establishing initial contributions in uncertainty budgets, as well as in setting the minimum calibration requirements, based on the evaluation of dominant influence quantities.

  9. The combined effects of reactant kinetics and enzyme stability explain the temperature dependence of metabolic rates.

    PubMed

    DeLong, J P; Gibert, J P; Luhring, T M; Bachman, G; Reed, B; Neyer, A; Montooth, K L

    2017-06-01

    A mechanistic understanding of the response of metabolic rate to temperature is essential for understanding thermal ecology and metabolic adaptation. Although the Arrhenius equation has been used to describe the effects of temperature on reaction rates and metabolic traits, it does not adequately describe two aspects of the thermal performance curve (TPC) for metabolic rate-that metabolic rate is a unimodal function of temperature often with maximal values in the biologically relevant temperature range and that activation energies are temperature dependent. We show that the temperature dependence of metabolic rate in ectotherms is well described by an enzyme-assisted Arrhenius (EAAR) model that accounts for the temperature-dependent contribution of enzymes to decreasing the activation energy required for reactions to occur. The model is mechanistically derived using the thermodynamic rules that govern protein stability. We contrast our model with other unimodal functions that also can be used to describe the temperature dependence of metabolic rate to show how the EAAR model provides an important advance over previous work. We fit the EAAR model to metabolic rate data for a variety of taxa to demonstrate the model's utility in describing metabolic rate TPCs while revealing significant differences in thermodynamic properties across species and acclimation temperatures. Our model advances our ability to understand the metabolic and ecological consequences of increases in the mean and variance of temperature associated with global climate change. In addition, the model suggests avenues by which organisms can acclimate and adapt to changing thermal environments. Furthermore, the parameters in the EAAR model generate links between organismal level performance and underlying molecular processes that can be tested for in future work.

  10. Halide-stabilized LiBH4, a room-temperature lithium fast-ion conductor.

    PubMed

    Maekawa, Hideki; Matsuo, Motoaki; Takamura, Hitoshi; Ando, Mariko; Noda, Yasuto; Karahashi, Taiki; Orimo, Shin-ichi

    2009-01-28

    Solid state lithium conductors are attracting much attention for their potential applications to solid-state batteries and supercapacitors of high energy density to overcome safety issues and irreversible capacity loss of the currently commercialized ones. Recently, we discovered a new class of lithium super ionic conductors based on lithium borohydride (LiBH(4)). LiBH(4) was found to have conductivity as high as 10(-2) Scm(-1) accompanied by orthorhombic to hexagonal phase transition above 115 degrees C. Polarization to the lithium metal electrode was shown to be extremely low, providing a versatile anode interface for the battery application. However, the high transition temperature of the superionic phase has limited its applications. Here we show that a chemical modification of LiBH(4) can stabilize the superionic phase even below room temperature. By doping of lithium halides, high conductivity can be obtained at room temperature. Both XRD and NMR confirmed room-temperature stabilization of superionic phase for LiI-doped LiBH(4). The electrochemical measurements showed a great advantage of this material as an extremely lightweight lithium electrolyte for batteries of high energy density. This material will open alternative opportunities for the development of solid ionic conductors other than previously known lithium conductors.

  11. Thermocyclic stability of candidate Seebeck coefficient standard reference materials at high temperature

    NASA Astrophysics Data System (ADS)

    Martin, Joshua; Wong-Ng, Winnie; Caillat, Thierry; Yonenaga, I.; Green, Martin L.

    2014-05-01

    The Seebeck coefficient is the most widely measured property specific to thermoelectric materials. There is currently no consensus on measurement protocols, and researchers employ a variety of techniques to measure the Seebeck coefficient. The implementation of standardized measurement protocols and the use of reliable Seebeck Coefficient Standard Reference Materials (SRMs®) will allow the accurate interlaboratory comparison and validation of materials data, thereby accelerating the development and commercialization of more efficient thermoelectric materials and devices. To enable members of the thermoelectric materials community the means to calibrate Seebeck coefficient measurement equipment, NIST certified SRM® 3451 "Low Temperature Seebeck Coefficient Standard (10 K to 390 K)". Due to different practical requirements in instrumentation, sample contact methodology, and thermal stability, a complementary SRM® is required for the high temperature regime (300 K to 900 K). The principal requirement of a SRM® for the Seebeck coefficient at high temperature is thermocyclic stability. We therefore characterized the thermocyclic behavior of the Seebeck coefficient for a series of candidate materials: constantan, p-type single crystal SiGe, and p-type polycrystalline SiGe, by measuring the temperature dependence of the Seebeck coefficient as a function of 10 sequential thermal cycles, between 300 K and 900 K. We employed multiple regression analysis to interpolate and analyze the thermocyclic variability in the measurement curves.

  12. Stabilization of the Trigonal High-Temperature Phase of Formamidinium Lead Iodide.

    PubMed

    Binek, Andreas; Hanusch, Fabian C; Docampo, Pablo; Bein, Thomas

    2015-04-02

    Formamidinium lead iodide (FAPbI3) has the potential to achieve higher performance than established perovskite solar cells like methylammonium lead iodide (MAPbI3), while maintaining a higher stability. The major drawback for the latter material is that it can crystallize at room temperature in a wide bandgap hexagonal symmetry (P63mc) instead of the desired trigonal (P3m1) black phase formed at a higher temperature (130 °C). Our results show that employing a mixture of MAI and FAI in films deposited via a two-step approach, where the MAI content is <20%, results in the exchange of FA molecules with MA without any significant lattice shrinkage. Additionally, we show with temperature-dependent X-ray diffraction that the trigonal phase exhibits no phase changes in the temperature range studied (25 to 250 °C). We attribute the stabilization of the structure to stronger interactions between the MA cation and the inorganic cage. Finally, we show that the inclusion of this small amount of MA also has a positive effect on the lifetime of the photoexcited species and results in more efficient devices.

  13. Improved photoluminescence and sensing stability of porous silicon nanowires by surface passivation.

    PubMed

    Gan, Lu; He, Haiping; Sun, Luwei; Ye, Zhizhen

    2014-01-21

    Core-shell structured silicon nanowires (Si NWs) were obtained by coating Si NWs with an HfO2 layer. Enhanced photoluminescence (PL) and a slightly decreased PL lifetime are achieved by HfO2 coating. Furthermore, the sensing stability is strongly improved. The improvement of PL properties is interpreted in terms of surface passivation and the Purcell effect.

  14. Stability of phases at high temperatures in CoRe based alloys being developed for ultra-high temperature applications

    NASA Astrophysics Data System (ADS)

    Gilles, R.; Strunz, P.; Mukherji, D.; Hofmann, M.; Hoelzel, M.; Roesler, J.

    2012-02-01

    In the development of new high-temperature alloys for gas turbine applications various candidates are under consideration. This contribution deals with a CoRe based alloy strengthened by Cr23C6 type carbide and Cr2Re3 type σ phase precipitations (here designated as CoRe-1 alloy). High-temperature cycling experiments show how the influence of heating, cooling and the hcp<->fcc phase transformation of the Co-matrix on the stability of these phases. Neutron diffraction experiments with high-temperature vacuum furnace show that Cr23C6 carbides starts to dissolve around 1100°C and above 1250°C are almost completely dissolved. On the other hand σ phase is still present at 1300°C. This contribution describes the evolution of the different phases during the heating and cooling cycles which are repeated two times. Further, the influence of boron addition to CoRe-1 alloy was studied for samples in the first heating/cooling cycle. A newly developed tensile rig was also tested up to 980°C to combine in situ loading and heating for the neutron diffraction measurements.

  15. Microstructural stability of wrought, laser and electron beam glazed NARloy-Z alloy at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Singh, J.; Jerman, G.; Bhat, B.; Poorman, R.

    1993-01-01

    Microstructure of wrought, laser, and electron-beam glazed NARloy-Z(Cu-3 wt.% Ag-0.5 wt.% Zr) was investigated for thermal stability at elevated temperatures (539 to 760 C (1,100 to 1,400 F)) up to 94 h. Optical and scanning electron microscopy and electron probe microanalysis were employed for studying microstructural evolution and kinetics of precipitation. Grain boundary precipitation and precipitate free zones (PFZ's) were observed in the wrought alloy after exposing to temperatures above 605 C (1,120 F). The fine-grained microstructure observed in the laser and electron-beam glazed NARloy-Z was much more stable at elevated temperatures. Microstructural changes correlated well with hardness measurements.

  16. Distortions and Stabilization of Simple Cubic Calcium at High Pressure and Low Temperature

    SciTech Connect

    Veith, Alison A.

    2012-04-18

    Ca-III, the first superconducting calcium phase under pressure, was identified as simple-cubic (sc) by previous X-ray diffraction (XRD) experiments. In contrast, all previous theoretical calculations showed that sc had a higher enthalpy than many proposed structures and had an imaginary (unstable) phonon branch. By using our newly developed submicrometer high-pressure single-crystal XRD, cryogenic high-pressure XRD, and theoretical calculations, we demonstrate that Ca-III is neither exactly sc nor any of the lower-enthalpy phases, but sustains the sc-like, primitive unit by a rhombohedral distortion at 300 K and a monoclinic distortion below 30 K. This surprising discovery reveals a scenario that the high-pressure structure of calcium does not go to the zero-temperature global enthalpy minimum but is dictated by high-temperature anharmonicity and low-temperature metastability fine-tuned with phonon stability at the local minimum.

  17. Temperature dependence of hardness in yttria-stabilized zirconia single crystals

    NASA Technical Reports Server (NTRS)

    Morscher, Gregory N.; Pirouz, Pirouz; Heuer, Arthur H.

    1991-01-01

    The temperature dependence of hardness and microcracking in single-crystal 9.5-mol pct-Y2O3-fully-stabilized cubic-ZrO2 was studied as a function of orientation. Crack lengths increased with increased temperature up to 500 C; above 800 C, no cracks were found, indicating an indentation brittle-to-ductile transition of about 800 C. The temperature dependence of hardness was reduced around 500 C. Etching studies to delineate the plastic zone around and below indents identified the operative slip systems. The role of dislocations and their interactions within the plastic zone on the hardness and indentation fracture behavior of cubic-ZrO2 are discussed.

  18. Distortions and stabilization of simple-cubic calcium at high pressure and low temperature

    SciTech Connect

    Mao, Wendy L.; Wang, Lin; Ding, Yang; Yang, Wenge; Liu, Wenjun; Kim, Duck Young; Luo, Wei; Ahuja, R.; Meng, Yue; Sinogeikin, Stanislav V.; Shu, Jinfu; Mao, Ho-kwang

    2010-06-01

    Ca-III, the first superconducting calcium phase under pressure, was identified as simple-cubic (sc) by previous X-ray diffraction (XRD) experiments. In contrast, all previous theoretical calculations showed that sc had a higher enthalpy than many proposed structures and had an imaginary (unstable) phonon branch. By using our newly developed submicrometer high-pressure single-crystal XRD, cryogenic high-pressure XRD, and theoretical calculations, we demonstrate that Ca-III is neither exactly sc nor any of the lower-enthalpy phases, but sustains the sc-like, primitive unit by a rhombohedral distortion at 300 K and a monoclinic distortion below 30 K. This surprising discovery reveals a scenario that the high-pressure structure of calcium does not go to the zero-temperature global enthalpy minimum but is dictated by high-temperature anharmonicity and low-temperature metastability fine-tuned with phonon stability at the local minimum.

  19. Temperature dependence of hardness in yttria-stabilized zirconia single crystals

    NASA Technical Reports Server (NTRS)

    Morscher, Gregory N.; Pirouz, Pirouz; Heuer, Arthur H.

    1991-01-01

    The temperature dependence of hardness and microcracking in single-crystal 9.5-mol pct-Y2O3-fully-stabilized cubic-ZrO2 was studied as a function of orientation. Crack lengths increased with increased temperature up to 500 C; above 800 C, no cracks were found, indicating an indentation brittle-to-ductile transition of about 800 C. The temperature dependence of hardness was reduced around 500 C. Etching studies to delineate the plastic zone around and below indents identified the operative slip systems. The role of dislocations and their interactions within the plastic zone on the hardness and indentation fracture behavior of cubic-ZrO2 are discussed.

  20. 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

  1. Low temperature superplasticity and thermal stability of a nanostructured low-carbon microalloyed steel

    NASA Astrophysics Data System (ADS)

    Hu, J.; Du, L.-X.; Sun, G.-S.; Xie, H.; Misra, R. D. K.

    2015-12-01

    We describe here for the first time the low temperature superplasticity of nanostructured low carbon steel (microalloyed with V, N, Mn, Al, Si, and Ni). Low carbon nanograined/ultrafine-grained (NG/UFG) bulk steel was processed using a combination of cold-rolling and annealing of martensite. The complex microstructure of NG/UFG ferrite and 50-80 nm cementite exhibited high thermal stability at 500 °C with low temperature elongation exceeding 100% (at less than 0.5 of the absolute melting point) as compared to the conventional fine-grained (FG) counterpart. The low temperature superplasticity is adequate to form complex components. Moreover, the low strength during hot processing is favorable for decreasing the spring back and minimize die loss.

  2. Distortions and stabilization of simple-cubic calcium at high pressure and low temperature.

    PubMed

    Mao, Wendy L; Wang, Lin; Ding, Yang; Yang, Wenge; Liu, Wenjun; Kim, Duck Young; Luo, Wei; Ahuja, Rajeev; Meng, Yue; Sinogeikin, Stas; Shu, Jinfu; Mao, Ho-kwang

    2010-06-01

    Ca-III, the first superconducting calcium phase under pressure, was identified as simple-cubic (sc) by previous X-ray diffraction (XRD) experiments. In contrast, all previous theoretical calculations showed that sc had a higher enthalpy than many proposed structures and had an imaginary (unstable) phonon branch. By using our newly developed submicrometer high-pressure single-crystal XRD, cryogenic high-pressure XRD, and theoretical calculations, we demonstrate that Ca-III is neither exactly sc nor any of the lower-enthalpy phases, but sustains the sc-like, primitive unit by a rhombohedral distortion at 300 K and a monoclinic distortion below 30 K. This surprising discovery reveals a scenario that the high-pressure structure of calcium does not go to the zero-temperature global enthalpy minimum but is dictated by high-temperature anharmonicity and low-temperature metastability fine-tuned with phonon stability at the local minimum.

  3. Chemical Stability of Glass Seal Interfaces in Intermediate Temperature Solid Oxide Fuel Cells

    SciTech Connect

    Yang, Z Gary; Xia, Gordon; Meinhardt, Kerry D.; Weil, K. Scott; Stevenson, Jeffry W.

    2004-06-01

    In intermediate temperature planar SOFC stacks, the interconnect, which is typically made from cost-effective oxidation resistant high temperature alloys, is typically sealed to the ceramic PEN (Positive electrode-Electrolyte-Negative electrode) by a sealing glass. To maintain ther structural stability and minimize the degradation of stack performance, the sealing glass has to be chemically compatible with the PEN and alloy interconnects. In the present study, the chemical compatibility of a barium-calcium-aluminosilicate (BCAS) based glass-ceramic (specifically developed as a sealant in SOFC stacks) with a number of selected oxidation resistant high temperature alloys (and the YSZ electrolyte) was evaluated. This paper reports the results of that study, with a particular focus on Crofer22 APU, a new ferritic stainless steel that was developed specifically for SOFC interconnect applications.

  4. Stability of whey protein hydrolysate powders: effects of relative humidity and temperature.

    PubMed

    Zhou, Peng; Liu, Dasong; Chen, Xiaoxia; Chen, Yingjia; Labuza, Theodore P

    2014-05-01

    Whey protein hydrolysate (WPH) is now considered as an important and special dairy protein ingredient for its nutritional and functional properties. The objectives of the present study were to investigate the effect of environmental relative humidity (RH) and storage temperature on the physicochemical stability of three WPH powders with hydrolysis degrees (DH) of 5.2%, 8.8% and 14.9%, respectively. The water sorption isotherms of the three WPH powders fitted the Guggenheim-Andersson-DeBoer model well. An increase in water content leaded to a decrease in glass transition temperature (Tg), following a linear Tg vs log water content relationship. Moreover, an increase in DH caused the decrease in Tg at the same water content. Changes in microstructure and colour occurred significantly when the WPH powders were stored at high environmental RH or temperature, especially for those with high DH. Copyright © 2013 Elsevier Ltd. All rights reserved.

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

    NASA Astrophysics Data System (ADS)

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

    2013-10-01

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

  6. Radiative Transfer Modeling of AVHRR Brightness Temperatures for Improved Sea Surface Temperature Retrievals: Initial Results

    NASA Astrophysics Data System (ADS)

    Ignatov, A.; Dash, P.

    2007-05-01

    Operational Sea Surface Temperature (SST) products at NOAA/NESDIS have been derived from the Advanced Very High Resolution Radiometers (AVHRR) onboard NOAA satellites since the early 1980s. The two major SST algorithms, the multi-channel and non-linear SST (MC/NLSST), were initially introduced for the AVHRR in the mid- 1980s and mid-1990s, respectively. Both algorithms are based on solid physical principles but also include some empirical elements (such as for instance treatment of the view angle dependence in the SST equations and tuning their coefficients against in-situ SST), to account for approximations and assumptions in their derivation. The simple MC/NLSST formulations proved to be accurate and robust, and are still in use with the newer sensors, such as the Moderate Resolution Imaging Spectro-Radiometer (MODIS). They are also considered for the future sensors such as the Visible Infrared Imager and Radiometer Suite (VIIRS) onboard NPOESS, and the Advanced Baseline Imager (ABI) onboard GOES-R. Despite the apparent success and good accuracies, improved SST formulations should be explored based on improved and accurate Radiative Transfer Models (RTM). In order to be useful for inverse problem simulation (i.e., SST retrieval), the RTM should be able to adequately reproduce the top-of-the-atmosphere brightness temperatures. In this study, we use MODTRAN 4.2 model, coupled with two surface reflection models (black body and Fresnel), to simulate TOA brightness temperatures in the three thermal infrared AVHRR bands. Atmospheric profiles and SST come from the National Centers for Environmental Prediction (NCEP) Global Data Analysis System (GDAS) data as input, assuming aerosol- and cloud-free conditions. The simulation results are then convoluted with the respective relative spectral response functions of the individual sensors, and compared with collocated TOA brightness temperatures measured from NOAA-16, -17, and -18 satellites during nighttime. Initial results

  7. pH- and temperature-responsive aqueous foams stabilized by hairy latex particles.

    PubMed

    Fujii, Syuji; Akiyama, Ko; Nakayama, Saori; Hamasaki, Sho; Yusa, Shin-ichi; Nakamura, Yoshinobu

    2015-01-21

    Polystyrene (PS) particles carrying pH- and temperature-responsive poly[2-(dimethylamino)ethyl methacrylate] (PDMA) hairs (PDMA-PS particles) were synthesized by dispersion polymerization. The diameter, diameter distribution, morphology, chemical composition and surface chemistry of the particles were characterized using scanning electron microscopy (SEM), elemental microanalysis, dynamic light scattering and zeta potential measurements. The hydrophilicity-hydrophobicity balance of the PDMA could be tuned by varying both pH and temperature and therefore these sterically stabilized particles acted as doubly stimuli-responsive stabilizers for aqueous foams by adsorption and desorption to/from the air-water interface. At and above pH 6.0, in which range the PDMA hairs were either non-protonated or partially protonated, particle-stabilized foams were formed at both 23 and 55 °C. The foam prepared at 55 °C was the more stable of the two, lasting for at least 24 h, whereas the 23 °C foam destabilized within 24 h. SEM studies indicated that the particles adsorbed at the air-water interface as monolayers at 23 °C and as multilayers at 55 °C. At and below pH 5, in which range the hairs were cationic, hydrophilic and water-soluble, no foam was formed irrespective of temperature. Rapid defoaming could be induced by lowering the solution pH at both temperatures, due to rapid in situ protonation of the PDMA hairs, prompting the PDMA-PS particles to desorb from the air-water interface. The foaming and defoaming cycles could be repeated at least five times.

  8. Stability of dronabinol capsules when stored frozen, refrigerated, or at room temperature.

    PubMed

    Wempe, Michael F; Oldland, Alan; Stolpman, Nancy; Kiser, Tyree H

    2016-07-15

    Results of a study to determine the 90-day stability of dronabinol capsules stored under various temperature conditions are reported. High-performance liquid chromatography (HPLC) with ultraviolet (UV) detection was used to assess the stability of dronabinol capsules (synthetic delta-9-tetrahydrocannabinol [Δ9-THC] mixed with high-grade sesame oil and other inactive ingredients and encapsulated as soft gelatin capsules) that were frozen, refrigerated, or kept at room temperature for three months. The dronabinol capsules remained in the original foil-sealed blister packs until preparation for HPLC-UV assessment. The primary endpoint was the percentage of the initial Δ9-THC concentration remaining at multiple designated time points. The secondary aim was to perform forced-degradation studies under acidic conditions to demonstrate that the HPLC-UV method used was stability indicating. The appearance of the dronabinol capsules remained unaltered during frozen, cold, or room-temperature storage. Regardless of storage condition, the percentage of the initial Δ9-THC content remaining was greater than 97% for all evaluated samples at all time points over the three-month study. These experimental data indicate that the product packaging and the sesame oil used to formulate dronabinol capsules efficiently protect Δ9-THC from oxidative degradation to cannabinol; this suggests that pharmacies can store dronabinol capsules in nonrefrigerated automated dispensing systems, with a capsule expiration date of 90 days after removal from the refrigerator. Dronabinol capsules may be stored at room temperature in their original packaging for up to three months without compromising capsule appearance and with minimal reduction in Δ9-THC concentration. Copyright © 2016 by the American Society of Health-System Pharmacists, Inc. All rights reserved.

  9. Stability of cable thermocouples at the upper temperature limit of their working range

    NASA Astrophysics Data System (ADS)

    Ulanovskiy, A. A.; Zemba, E. S.; Belenkiy, A. M.; Chibizova, S. I.; Bursin, A. N.

    2013-09-01

    Experimental results of EMF stability research are presented for MIMS thermocouples of types K and N of external diameters 1.5; 3.0 and 5.0 mm. All thermocouples had heat resistant sheath and were not used before the tests. They were subjected to every-day cyclic heating and cooling. During each cycle there was 6 h annealing in air at the temperature 1200 °C Results shows, that stability of a cable thermocouple in air at the temperature 1200 °C depends, mainly, on its diameter, instead of on thermocouple type or metal sheath material. Acceptable time of operation in a thermal cycling mode for 1.5 mm cable thermocouples is limited by (15, 16) h, and for 3 mm thermocouples it is equal to (40, 45) h. Besides, the effect of signal shunting is shown in the work for a thermocouple under heating of its average part to the temperature 1200 °C Experiment has shown that use of long cable thermocouple of 1.5 mm diameter at the temperatures above 1000°C can lead to serious errors in temperature measurement. Heating of 400 mm thermocouple length to 1100 °C causes positive EMF in the 1.5 mm cable thermocouple equivalent to +3.4 °C and +18 °C at 1200°C. For 3 mm cable thermocouple EMF at 1200 °C reaches the value equivalent to +2.3 °C, but double increase in heating length makes the value greater to +13.5 °C. The given facts are necessary to consider while using of thin (1, 3) mm cable thermocouples at the temperatures (1100, 1200) °C.

  10. Characterizing the Chemical Stability of High Temperature Materials for Application in Extreme Environments

    NASA Technical Reports Server (NTRS)

    Opila, Elizabeth

    2005-01-01

    The chemical stability of high temperature materials must be known for use in the extreme environments of combustion applications. The characterization techniques available at NASA Glenn Research Center vary from fundamental thermodynamic property determination to material durability testing in actual engine environments. In this paper some of the unique techniques and facilities available at NASA Glenn will be reviewed. Multiple cell Knudsen effusion mass spectrometry is used to determine thermodynamic data by sampling gas species formed by reaction or equilibration in a Knudsen cell held in a vacuum. The transpiration technique can also be used to determine thermodynamic data of volatile species but at atmospheric pressures. Thermodynamic data in the Si-O-H(g) system were determined with this technique. Free Jet Sampling Mass Spectrometry can be used to study gas-solid interactions at a pressure of one atmosphere. Volatile Si(OH)4(g) was identified by this mass spectrometry technique. A High Pressure Burner Rig is used to expose high temperature materials in hydrocarbon-fueled combustion environments. Silicon carbide (SiC) volatility rates were measured in the burner rig as a function of total pressure, gas velocity and temperature. Finally, the Research Combustion Lab Rocket Test Cell is used to expose high temperature materials in hydrogen/oxygen rocket engine environments to assess material durability. SiC recession due to rocket engine exposures was measured as a function of oxidant/fuel ratio, temperature, and total pressure. The emphasis of the discussion for all techniques will be placed on experimental factors that must be controlled for accurate acquisition of results and reliable prediction of high temperature material chemical stability.

  11. 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

  12. Edge-emitting InGaAs/GaAs laser with high temperature stability of wavelength and threshold current

    NASA Astrophysics Data System (ADS)

    Gordeev, N. Yu; Novikov, I. I.; Chunareva, A. V.; Il'inskaya, N. D.; Shernyakov, Yu M.; Maximov, M. V.; Payusov, A. S.; Kalyuzhnyy, N. A.; Mintairov, S. A.; Lantratov, V. M.; Shchukin, V. A.; Ledentsov, N. N.

    2010-04-01

    We have investigated an edge-emitting tilted wave laser (TWL) with the active region based on GaInAs/GaAs quantum wells. In the TWL the wavelength stabilization is based on the coupling of the laser active waveguide cavity to a specially introduced thick epitaxial layer and the emission wavelength is defined by the combined cavity mode preferably by a single dominating mode. The TWL wafer has been grown by metal-organic chemical vapour deposition. Laser parameters have been investigated both in pulsed and CW mode in the temperature range of 15-60 °C. In the temperature window of 20-50 °C under CW excitation the lasers have shown high wavelength temperature stability with the temperature shift of 0.05 nm K-1 and threshold current stability with the characteristic temperature of 500 K. The data obtained prove the concept of thermal stability in tilted wave lasers.

  13. Divalent cations and molecular crowding buffers stabilize G-triplex at physiologically relevant temperatures

    PubMed Central

    Jiang, Hong-Xin; Cui, Yunxi; Zhao, Ting; Fu, Hai-Wei; Koirala, Deepak; Punnoose, Jibin Abraham; Kong, De-Ming; Mao, Hanbin

    2015-01-01

    G-triplexes are non-canonical DNA structures formed by G-rich sequences with three G-tracts. Putative G-triplex-forming sequences are expected to be more prevalent than putative G-quadruplex-forming sequences. However, the research on G-triplexes is rare. In this work, the effects of molecular crowding and several physiologically important metal ions on the formation and stability of G-triplexes were examined using a combination of circular dichroism, thermodynamics, optical tweezers and calorimetry techniques. We determined that molecular crowding conditions and cations, such as Na+, K+, Mg2+ and Ca2+, promote the formation of G-triplexes and stabilize these structures. Of these four metal cations, Ca2+ has the strongest stabilizing effect, followed by K+, Mg2+, and Na+ in a decreasing order. The binding of K+ to G-triplexes is accompanied by exothermic heats, and the binding of Ca2+ with G-triplexes is characterized by endothermic heats. G-triplexes formed from two G-triad layers are not stable at physiological temperatures; however, G-triplexes formed from three G-triads exhibit melting temperatures higher than 37°C, especially under the molecular crowding conditions and in the presence of K+ or Ca2+. These observations imply that stable G-triplexes may be formed under physiological conditions. PMID:25787838

  14. Divalent cations and molecular crowding buffers stabilize G-triplex at physiologically relevant temperatures.

    PubMed

    Jiang, Hong-Xin; Cui, Yunxi; Zhao, Ting; Fu, Hai-Wei; Koirala, Deepak; Punnoose, Jibin Abraham; Kong, De-Ming; Mao, Hanbin

    2015-03-19

    G-triplexes are non-canonical DNA structures formed by G-rich sequences with three G-tracts. Putative G-triplex-forming sequences are expected to be more prevalent than putative G-quadruplex-forming sequences. However, the research on G-triplexes is rare. In this work, the effects of molecular crowding and several physiologically important metal ions on the formation and stability of G-triplexes were examined using a combination of circular dichroism, thermodynamics, optical tweezers and calorimetry techniques. We determined that molecular crowding conditions and cations, such as Na(+), K(+), Mg(2+) and Ca(2+), promote the formation of G-triplexes and stabilize these structures. Of these four metal cations, Ca(2+) has the strongest stabilizing effect, followed by K(+), Mg(2+), and Na(+) in a decreasing order. The binding of K(+) to G-triplexes is accompanied by exothermic heats, and the binding of Ca(2+) with G-triplexes is characterized by endothermic heats. G-triplexes formed from two G-triad layers are not stable at physiological temperatures; however, G-triplexes formed from three G-triads exhibit melting temperatures higher than 37°C, especially under the molecular crowding conditions and in the presence of K(+) or Ca(2+). These observations imply that stable G-triplexes may be formed under physiological conditions.

  15. The stability of natural red/pink food colours in ultrahigh-temperature (UHT) products.

    PubMed

    Crinó, Michelle A; Heenan, Claire N; Nguyen, Minh H; Stathopoulos, Costas E

    2013-06-01

    The aim of this experiment was to select a pool of potential red/pink natural colour candidates and evaluate their stability during ultrahigh-temperature (UHT) processing and subsequent storage and to compare their behaviour against the artificial colour erythrosine. It was hypothesised that heat processing and post-treatment storage conditions would have a negative effect on the stability of the natural colourants. All colourants except fermented red rice showed significant colour loss post-UHT processing (α=0.05). Analysis of the colour parameters L*, a* and b* determined that lycopene was the least stable of the colourants and red radish the most stable under all conditions. Fermented red rice was observed to be heat-stable after exposure to UHT processing and also remained relatively stable during storage, as was black carrot. The variation across trials and the spoilage of some samples were attributed to the fluctuations in temperature (±5 °C) observed during processing. Heat processing and post-treatment storage conditions had a negative effect on the stability of the natural colourants. © 2012 Society of Chemical Industry.

  16. Improved thermal stability of polylactic acid (PLA) composite film via PLA-β-cyclodextrin-inclusion complex systems.

    PubMed

    Byun, Youngjae; Rodriguez, Katia; Han, Jung H; Kim, Young Teck

    2015-11-01

    The effects of the incorporation of PLA-β-cyclodextrin-inclusion complex (IC) and β-cyclodextrin (β-CD) on biopolyester PLA films were investigated. Thermal stability, surface morphology, barrier, and mechanical properties of the films were measured at varying IC (1, 3, 5, and 7%) and β-CD (1 and 5%) concentrations. The PLA-IC-composite films (IC-PLA-CFs) showed uniform morphological structure, while samples containing β-CD (β-CD-PLA-CFs) showed high agglomeration of β-CD due to poor interfacial interaction between β-CD and PLA moieties. According to the thermal property analysis, the 5% IC-PLA-CFs showed 6.6 times lower dimensional changes (6.5%) at the temperature range of 20-80°C than that of pure PLA film (43.0%). The increase of IC or β-CD content in the PLA-composite films shifted the glass transition and crystallization temperature to higher temperature regions. The crystallinity of both composite films improved by increasing IC or β-CD content. Both composite films had higher oxygen and water vapor permeability as IC or β-CD content increased in comparison to pure PLA film. All the composite films had less flexibility and lower tensile strength than the pure PLA film. In conclusion, this study shows that the IC technique is valuable to improve the thermal expansion stability of PLA-based films.

  17. Differential stability of photosynthetic membranes and fatty acid composition at elevated temperature in Symbiodinium

    NASA Astrophysics Data System (ADS)

    Díaz-Almeyda, E.; Thomé, P. E.; El Hafidi, M.; Iglesias-Prieto, R.

    2011-03-01

    Coral reefs are threatened by increasing surface seawater temperatures resulting from climate change. Reef-building corals symbiotic with dinoflagellates in the genus Symbiodinium experience dramatic reductions in algal densities when exposed to temperatures above the long-term local summer average, leading to a phenomenon called coral bleaching. Although the temperature-dependent loss in photosynthetic function of the algal symbionts has been widely recognized as one of the early events leading to coral bleaching, there is considerable debate regarding the actual damage site. We have tested the relative thermal stability and composition of membranes in Symbiodinium exposed to high temperature. Our results show that melting curves of photosynthetic membranes from different symbiotic dinoflagellates substantiate a species-specific sensitivity to high temperature, while variations in fatty acid composition under high temperature rather suggest a complex process in which various modifications in lipid composition may be involved. Our results do not support the role of unsaturation of fatty acids of the thylakoid membrane as being mechanistically involved in bleaching nor as being a dependable tool for the diagnosis of thermal susceptibility of symbiotic reef corals.

  18. High Temperature Stability of Dissimilar Metal Joints in Fission Surface Power Systems

    SciTech Connect

    Locci, Ivan E.; Nesbitt, James A.; Ritzert, Frank J.; Bowman, Cheryl L.

    2007-01-30

    Future generations of power systems for spacecraft and lunar surface systems will likely require a strong dependence on nuclear power. The design of a space nuclear power plant involves integrating together major subsystems with varying material requirements. Refractory alloys are repeatedly considered for major structural components in space power reactor designs because refractory alloys retain their strength at higher temperatures than other classes of metals. The relatively higher mass and lower ductility of the refractory alloys make them less attractive for lower temperature subsystems in the power plant such as the power conversion system. The power conversion system would consist more likely of intermediate temperature Ni-based superalloys. One of many unanswered questions about the use of refractory alloys in a space power plant is how to transition from the use of the structural refractory alloy to more traditional structural alloys. Because deleterious phases can form when complex alloys are joined and operated at elevated temperatures, dissimilar material diffusion analyses of refractory alloys and superalloys are needed to inform designers about options of joint temperature and operational lifetime. Combinations of four superalloys and six refractory alloys were bonded and annealed at 1150 K and 1300 K to examine diffusional interactions in this study. Joints formed through hot pressing and hot isostatic pressing were compared. Results on newer alloys compared favorably to historical data. Diffusional stability is promising for some combinations of Mo-Re alloys and superalloys at 1150 K, but it appears that lower joint temperatures would be required for other refractory alloy couples.

  19. Effect of temperature changes on the dimensional stability of elastomeric impression materials.

    PubMed

    Kambhampati, Sujan; Subhash, Vaddavalli; Vijay, Chellagulla; Das, Aruna

    2014-02-01

    The purpose of this study was to evaluate the changed dimensions of dies obtained from impressions made with different combinations of addition sillicones which were subjected to variations in storage temperature. 45 die stone models were obtained of 45 impressions of which 15 each were stored at three different storage temperatures(25°C, 37°C and 42°C). 15 impressions each were made using one impression technique. The measurements of the dies made from the impressions were measured with the help of Profile Projector with a accuracy of 0.001mm. The results were statistically analyzed. The results indicated the significant decrease in dimensions when the storage temperature reduced from the mouth temperature. As compared to this there was a marginal increase in overall dimensions of all variables when storage temperature increased. More changes were seen in putty/light body combination followed by monophase and least in heavy/light body combination. How to cite the article: Kambhampati S, Subhash V, Vijay C, Das A. Effect of temperature changes on the dimensional stability of elastomeric impression materials. J Int Oral Health 2014;6(1):12-9.

  20. Effect of temperature changes on the dimensional stability of elastomeric impression materials

    PubMed Central

    Kambhampati, Sujan; Subhash, Vaddavalli; Vijay, Chellagulla; Das, Aruna

    2014-01-01

    Background: The purpose of this study was to evaluate the changed dimensions of dies obtained from impressions made with different combinations of addition sillicones which were subjected to variations in storage temperature. Materials & Methods: 45 die stone models were obtained of 45 impressions of which 15 each were stored at three different storage temperatures(25°C, 37°C and 42°C). 15 impressions each were made using one impression technique. The measurements of the dies made from the impressions were measured with the help of Profile Projector with a accuracy of 0.001mm. Results: The results were statistically analyzed. The results indicated the significant decrease in dimensions when the storage temperature reduced from the mouth temperature. As compared to this there was a marginal increase in overall dimensions of all variables when storage temperature increased. Conclusion: More changes were seen in putty/light body combination followed by monophase and least in heavy/light body combination. How to cite the article: Kambhampati S, Subhash V, Vijay C, Das A. Effect of temperature changes on the dimensional stability of elastomeric impression materials. J Int Oral Health 2014;6(1):12-9. PMID:24653597

  1. Augmentation of peri-implant bone improves implant stability: quantification using simulated bone loss.

    PubMed

    Wirth, Andreas J; Müller, Ralph; van Lenthe, G Harry

    2012-02-01

    Low bone quality, such as induced by osteoporosis, is considered a main factor leading to failure of fracture fixations. Peri-implant bone augmentation has been proposed as a means of reducing failure rates in osteoporotic bone by improving implant stability. The beneficial effects of pharmacological augmentation of bone in the immediate vicinity of the implant have been demonstrated. Yet, a quantitative understanding of the role of peri-implant bone in implant stability is lacking. Therefore, the aim of our study was to quantify the effects of bone loss and peri-implant bone augmentation on implant stability using image-based finite element analyses. Using a validated model, we simulated how osteoporotic bone loss would affect implant stability in human humeral heads. We also quantified how augmentation of peri-implant bone can enhance implant stability. Our simulations revealed that a 30% reduction in bone mass led to a 50% decrease in implant stability. We also found that peri-implant bone augmentation increased implant stability and that the efficiency of bone augmentation decreased with increasing peri-implant distance. These findings highlight the strong effect that bone loss has on implant fixation and the potential of peri-implant bone augmentation for improving implant anchorage in low quality bone. Copyright © 2011 Orthopaedic Research Society.

  2. An Improved Estimation of COMS-based Sea Surface Temperature

    NASA Astrophysics Data System (ADS)

    Huh, M.; Seo, M.; Han, K. S.; Shin, J.; Shin, I.

    2016-12-01

    The objective of this paper is to implement retrieving Sea Surface Temperature (SST) using geostationary satellite of Korea, Communication, Ocean and Meteorological Satellite/Meteorological Imager (COMS/MI). In this study, IR channels of COMS are corrected using the Global Space-Based Inter-Calibration System (GSICS) that produces consistent accuracy of thermal infrared (IR) channels of satellite measurements. The new retrieval method is adopted the Multi-Channel Sea Surface Temperature (MCSST) `split-window' algorithm with First Guess and the quality controlled in-situ buoy data are used the reference data. The new MCSST_FG results are showed that RMSE is 0.85 ºC in day time (0.747 ºC in night time) by comparison with 0.92 ºC (0.827 ºC in night time) of MCSST which is the current operational retrieval method. We found the regional biases are reduced on MCSST_FG algorithm though, there are the skewness and outliers in the analysis of differences retrieved SST and in-situ. It is significant efforts reprocessing and improvement of the satellite COMS SST that expects the COMS SST is made use of thematic climate data record such as Global essential climate variables.

  3. Temperature Dependence Discontinuity in the Stability of Manganese doped Ceria Nanocrystals

    DOE PAGES

    Wu, Longjia; Dholabhai, Pratik; Uberuaga, Blas P.; ...

    2017-01-05

    CeO2 has strong potential for chemical-looping water splitting. It has been shown that manganese doping decreases interface energies of CeO2, allowing increased stability of high surface areas in this oxygen carrier oxide. The phenomenon is related to the segregation of Mn3+ at interfaces, which causes a measurable decrease in excess energy. Here in the present work, it is shown that, despite the stability of nanocrystals of manganese-doped CeO2 with relation to undoped CeO2, the effect is strongly dependent on the oxidation state of manganese, i.e., on the temperature. At temperatures below 800 °C, Mn is in the 3+ valence state,more » and coarsening is hindered by the reduced interface energetics, showing smaller crystal sizes with increasing Mn content. At temperatures above 800 °C, Mn is reduced to its 2+ valence state, and coarsening is enhanced with increasing Mn content. Atomistic simulations show the segregation of Mn to grain boundaries is relatively insensitive to the charge state of the dopant. However, point defect modeling finds that the reduced state causes a decrease in cation vacancy concentration and an increase in cation interstitials, reducing drag forces for grain boundary mobility and increasing growth rates.« less

  4. Long-term stability and temperature variability of Iris AO segmented MEMS deformable mirrors

    NASA Astrophysics Data System (ADS)

    Helmbrecht, M. A.; He, M.; Kempf, C. J.; Marchis, F.

    2016-07-01

    Long-term stability of deformable mirrors (DM) is a critical performance requirement for instruments requiring open-loop corrections. The effects of temperature changes in the DM performance are equally critical for such instruments. This paper investigates the long-term stability of three different Iris AO PTT111 DMs that were calibrated at different times ranging from 13 months to nearly 29 months prior to subsequent testing. Performance testing showed that only a small increase in positioning errors occurred from the initial calibration date to the test dates. The increases in errors ranged from as little as 1.38 nm rms after 18 months to 5.68 nm rms after 29 months. The paper also studies the effects of small temperature changes, up to 6.2°C around room temperature. For three different arrays, the errors ranged from 0.62-1.42 nm rms/°C. Removing the effects of packaging shows that errors are <=0.50 nm rms/°C. Finally, measured data showed that individual segments deformed <=0.11 nm rms/°C when heated.

  5. Tests of the Stability of Chinese RhFe Resistance Thermometers at Low Temperatures

    NASA Astrophysics Data System (ADS)

    Kowal, A.; Manuszkiewicz, H.; Kołodziej, B.; Szmyrka-Grzebyk, A.; Lin, Peng; Gao, Bo; Yu, Lihong

    2017-07-01

    Rhodium-iron resistance thermometers are recommended as precise thermometers at temperatures below 25 K. The thermometers were developed at the National Physical Laboratory and produced by H. Tinsley and Co Ltd almost 50 years ago. Later, they were made by other companies and institutes as well, but despite this, the availability of the thermometers decreased and a new source of supply was needed. Several years ago, the Technical Institute of Physics and Chemistry (TIPC), Chinese Academy of Sciences, developed its own technology for making wire of Rh-0.5 at% Fe alloy which was used in the production of new thermometers. These devices have been tested previously at INRIM (Italy) and later at INTiBS (Poland). INTiBS has carried out an investigation focused on the thermometers' stability after thermal cycling treatment. This paper presents the results of stability tests of about 30 thermometers produced by TIPC in two batches. The resistance of each thermometer was measured at temperatures of about 4.6 K and 7.2 K before and after 10, 30 and 50 thermal cycles from room temperature. The methods of measurement and the design of the cryostat used for the research are also presented.

  6. The Stability of Prostate-Specific Antigen in Semen Under Various Temperatures.

    PubMed

    Srettabunjong, Supawon; Betset, Parimol; Limawongpranee, Suvit; Ekpo, Pattama

    2015-11-01

    Prostate-specific antigen (PSA) is most commonly used for identifying semen, especially in the absence of sperm. However, PSA concentration varies according to storage temperature and duration, and little is known about its stability in semen. This study was therefore aimed to determine the stability under five different temperatures: -80, -20, 4, 25, and 37°C; and nine different durations: 1, 2, 3, 5, 7, 14, 30, 90, and 180 days. All samples were stored at -80°C after being secreted from the volunteers' body until analyzed. Results showed that the PSA concentration declined significantly over time under all temperatures studied except -80°C. At -20 and 4°C, PSA was still detectable on Day 180 with 50% and 70% decrease from its original concentration, respectively. At 25 and 37°C, PSA was detected up to Day 7 and 3, respectively. This information might assist forensic scientists understand more about PSA nature and integrate it into their works.

  7. Stability of the rate, state and temperature dependent friction model and its applications

    NASA Astrophysics Data System (ADS)

    Singh, Arun K.; Singh, Trilok N.

    2016-04-01

    In this paper, we study stability of the rate, state and temperature friction (RSTF) model. The Segall and Rice approach is used to model heat transfer at the sliding interface with its surroundings. The effect of pore pressure is not considered in the model to avoid the complex expression for critical stiffness. Linear stability analysis of the spring-mass sliding system is carried out with the ageing law under the quasistatic conditions in order to determine the critical stiffness above which sliding behaviour changes from unstable to stable or vice versa. Our numerical simulations establish that critical stiffness of the heated surface may increase or decrease from corresponding to the critical stiffness of the unheated surface depending on the relative values of two contradictory parameters related with velocity effect and temperature effect. Parametric studies are also carried out to understand shear velocity and temperature of the sliding surface dependence of steady friction. The RSTF model is also used to study the gravity induced failure of a creeping rock slope and the results are justified.

  8. 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).

  9. Lowering dialysate temperature improves sleep and alters nocturnal skin temperature in patients on chronic hemodialysis.

    PubMed

    Parker, Kathy P; Bailey, James L; Rye, David B; Bliwise, Donald L; Van Someren, Eus J W

    2007-03-01

    Hemodialysis (HD) induces physiological changes that may affect the ability to dissipate heat and adversely affect sleep. We studied the effects of altering dialysate temperature on polysomnographic measures of nocturnal sleep and the time course of proximal skin temperature. The sample included seven stable HD patients. The three-phase randomized trial was conducted in a research facility. After one acclimatization night, subjects were readmitted in the evening on two additional occasions for 42 h and received HD the next morning in the warm condition (dialysate 37 degrees C) and cool condition (dialysate 35 degrees C) in random order. Continuous proximal skin temperature (axillary, T(ax)) and polysomnographic measures of sleep were recorded the nights before and after HD was administered. Highly significant findings included that the time course of T(ax) was markedly affected by dialysis temperature. There was a greater drop of T(ax) in the early morning following the warm condition than during the baseline nights or in the cool condition. Logistic regression indicated that the odds for the occurrence of sleep and its deeper stages were strongly and positively associated with T(ax). Time of sleep onset was earlier in the cool condition (P = 0.03) with trends toward longer total sleep times (P = 0.09) and shorter rapid-eye-movement latencies (P = 0.09). These observations suggest that the use of cool dialysate during HD may improve nocturnal sleep by decreasing sympathetic activation and sustaining the normally elevated nocturnal skin temperature until later into the morning hours.

  10. Magnetite solubility and phase stability in alkaline media at elevated temperatures

    SciTech Connect

    Ziemniak, S.E.; Jones, M.E.; Combs, K.E.S.

    1994-05-01

    Magnetite, Fe{sub 3}O{sub 4}, is the dominant oxide constituent of the indigenous corrosion layers that form on iron base alloys in high purity, high temperature water. The apparent simultaneous stability of two distinct oxidation states of iron in this metal oxide is responsible for its unique solubility behavior. The present work was undertaken to extend the experimental and theoretical bases for estimating solubilities of an iron corrosion product (Fe{sub 3}O{sub 4}/Fe(OH){sub 2}) over a broader temperature range and in the presence of complexing, pH-controlling reagents. These results indicate that a surface layer of ferrous hydroxide controls magnetite solubility behavior at low temperatures in much the same manner as a surface layer of nickel(II) hydroxide was previously reported to control the low temperature solubility behavior of NiO. The importance of Fe(III) ion complexes implies not only that most previously-derived thermodynamic properties of the Fe(OH){sub 3}{sup {minus}} ion are incorrect, but that magnetite phase stability probably shifts to favor a sodium ferric hydroxyphosphate compound in alkaline sodium phosphate solutions at elevated temperatures. The test methodology involved pumping alkaline solutions of known composition through a bed of Fe{sub 3}O{sub 4} granules and analyzing the emerging solution for Fe. Two pH-controlling reagents were tested: sodium phosphate and ammonia. Equilibria for the following reactions were described in thermodynamic terms: (a) Fe(OH){sub 2}/Fe{sub 3}O{sub 4} dissolution and transformation, (b) Fe(II) and Fe(III) ion hydroxocomplex formation (hydrolysis), (c) Fe(II) ion amminocomplex formation, and (d) Fe(II) and Fe(III) ion phosphatocomplex formation. 36 refs.

  11. Engineering of isoamylase: improvement of protein stability and catalytic efficiency through semi-rational design.

    PubMed

    Li, Youran; Zhang, Liang; Ding, Zhongyang; Gu, Zhenghua; Shi, Guiyang

    2016-01-01

    Isoamylase catalyzes the hydrolysis of α-1,6-glycosidic linkages in glycogen, amylopectin and α/β-limit dextrins. A semi-rational design strategy was performed to improve catalytic properties of isoamylase from Bacillus lentus. Three residues in vicinity of the essential residues, Arg505, Asn513, and Gly608, were chosen as the mutation sites and were substituted by Ala, Pro, Glu, and Lys, respectively. Thermal stability of the mutant R505P and acidic stability of the mutant R505E were enhanced. The k cat /K m values of the mutant G608V have been promoted by 49%, and the specific activity increased by 33%. This work provides an effective strategy for improving the catalytic activity and stability of isoamylase, and the results obtained here may be useful for the improvement of catalytic properties of other α/β barrel enzymes.

  12. Stability of 21 Cocaine, Opioid and Benzodiazepine Drug Analytes in Spiked Meconium at Three Temperatures.

    PubMed

    Wu, Fang; Marin, Stephanie J; McMillin, Gwendolyn A

    2016-11-22

    In this study, the stability of 21 cocaine, opioid and benzodiazepine analytes in spiked meconium was investigated at three storage temperatures: 4°C, room temperature (RT), and 37°C (body temperature). The drugs/metabolites included were hydrocodone, hydromorphone, codeine, morphine, 6-acetylmorphine (6-AM), oxycodone, oxymorphone, cocaine, cocaethylene, benzoylecgonine, m-hydroxybenzoylecgonine, diazepam, oxazepam, temazepam, nordiazepam, chlordiazepoxide, lorazepam, alprazolam, alpha-hydroxyalprazolam, clonazepam, 7-aminoclonazepam, midazolam, alpha-hydroxymidazolam and zolpidem. Drug testing was performed using mass spectrometry methods that were validated for clinical use. After 2 weeks of storage, a substantial loss was observed in the concentrations of 7-aminoclonazepam (48.4% at 4°C and 71.5% at RT), and chlordiazepoxide (59.5% at RT). A slight decrease was observed in the concentrations of alprazolam (20.9% at 4°C), clonazepam (24.5% at 4°C), chlordiazepoxide (23.5% at 4°C), midazolam (20.8% at 4°C), nordiazepam (22.8% at RT), and alpha-hydroxyalprazolam (20.7% at 4°C). At 37°C, the concentrations of chlordiazepoxide, 7-aminoclonazepam, lorazepam, oxazepam, nordiazepam and temazepam decreased by 81.4%, 86.8%, 56.5%, 59.9%, 45.4% and 31.7%, respectively, after 2 weeks. 6-AM was observed to be unstable regardless of storage temperatures. For morphine, a 33.3% increase at 4°C and a 23.4% increase at RT were observed after 2 weeks, respectively, possibly due to 6-AM degradation, while no changes ≥20% were observed at 37°C. All other analytes were stable up to 2 weeks at all three storage temperatures (concentration changes <20%). The stability of select drug analytes in authentic clinical meconium specimens was consistent with that observed in spiked meconium. In conclusion, some drugs in meconium may not be stable for long periods of time. Sample storage conditions are an important consideration in the context of detection windows and

  13. Approaches to improve the stability of the antiviral agent UC781 in aqueous solutions.

    PubMed

    Damian, Festo; Fabian, Judit; Friend, David R; Kiser, Patrick F

    2010-08-30

    In this work, we evaluated the chemical stability profiles of UC781 based solutions to identify excipients that stabilize the microbicidal agent UC781. When different antioxidants were added to UC781 in sulfobutylether-beta-cyclodextrin (SBE-beta-CD) solutions and subjected to a 50 degrees C stability study, it was observed that EDTA was a better stabilizing agent than sodium metabisulfite, glutathione or ascorbic acid. Some antioxidants accelerated the degradation of UC781, suggesting metal-catalyzed degradation of UC781. Furthermore, we observed substantial degradation of UC781 when stored in 1% Tween 80 and 1% DMSO solutions alone or in those with 10mM EDTA. On the other hand, improved stability of UC781 in the presence of 100 and 200mM of EDTA was observed in these solutions. The addition of both EDTA and citric acid in the stock solutions resulted in recovery of more than 60% of UC781 after 12 weeks. Generally, 10% SBE-beta-CD in the presence of EDTA and citric acid stabilized UC781 solutions: the amount of UC781 recovered approaching 95% after 12 weeks of storage at 40 degrees C. We also showed that the desulfuration reaction of the UC781 thioamide involves oxygen by running solution stability studies in deoxygenated media. Improved stability of UC781 in the present study indicates that the incorporation of EDTA, citric acid and SBE-beta-CD and the removal of oxygen in formulations of this drug will aid in increasing the stability of UC781 where solutions of the drug are required.

  14. Effect of temperature on the mass and color stability of additional photoinitiatorcontaining composite resins.

    PubMed

    Kim, Tae-Hyung; García-Godoy, Franklin; Ko, Ching-Chang; Park, Jeong-Kil; Kim, Hyung-Il; Kwon, Yong-Hoon

    2013-01-01

    The purpose of this study was to evaluate how the temperature affects the stability of polymerized additional photoinitiator-containing composite resins. Five resin products were light-cured using a quartz-tungsten-halogen, and single and dual emission peaks lightemitting diodes. The degree of conversion (DC) and water sorption, solubility, and color change of the specimens were evaluated after immersion in the solutions of different temperatures (4, 37, and 60ºC) for 14 days. On the top surface, the light-curing units had no significant influence on DC of the tested specimens. On the bottom surface, the influence was inconsistent. As the solution temperature increased, water sorption also consistently increased in all specimens, whereas solubility changed inconsistently. Water sorption and solubility had a high linear correlation only at low temperature solution. Color change of the specimens was similar, mostly slight, and statistically inconsistent regardless of solution temperature. The restored composite resins are needed to avoid contact with hot solutions for durable dental restoration.

  15. Experimental Study of the Stability of Aircraft Fuels at Elevated Temperatures

    NASA Technical Reports Server (NTRS)

    Vranos, A.; Marteney, P. J.

    1980-01-01

    An experimental study of fuel stability was conducted in an apparatus which simulated an aircraft gas turbine fuel system. Two fuels were tested: Jet A and Number 2 Home Heating oil. Jet A is an aircraft gas turbine fuel currently in wide use. No. 2HH was selected to represent the properties of future turbine fuels, particularly experimental Reference Broad Specification, which, under NASA sponsorship, was considered as a possible next-generation fuel. Tests were conducted with varying fuel flow rates, delivery pressures and fuel pretreatments (including preheating and deoxygenation). Simulator wall temperatures were varied between 422K and 672K at fuel flows of 0.022 to 0.22 Kg/sec. Coking rate was determined at four equally-spaced locations along the length of the simulator. Fuel samples were collected for infrared analysis. The dependence of coking rate in Jet A may be correlated with surface temperature via an activation energy of 9 to 10 kcal/mole, although the results indicate that both bulk fluid and surface temperature affect the rate of decomposition. As a consequence, flow rate, which controls bulk temperature, must also be considered. Taken together, these results suggest that the decomposition reactions are initiated on the surface and continue in the bulk fluid. The coking rate data for No. 2 HH oil are very highly temperature dependent above approximately 533K. This suggests that bulk phase reactions can become controlling in the formation of coke.

  16. Activity-stability relationships revisited in blue oxidases catalyzing electron transfer at extreme temperatures.

    PubMed

    Roulling, Frédéric; Godin, Amandine; Cipolla, Alexandre; Collins, Tony; Miyazaki, Kentaro; Feller, Georges

    2016-09-01

    Cuproxidases are a subset of the blue multicopper oxidases that catalyze the oxidation of toxic Cu(I) ions into less harmful Cu(II) in the bacterial periplasm. Cuproxidases from psychrophilic, mesophilic, and thermophilic bacteria display the canonical features of temperature adaptation, such as increases in structural stability and apparent optimal temperature for activity with environmental temperature as well as increases in the binding affinity for catalytic and substrate copper ions. In contrast, the oxidative activities at 25 °C for both the psychrophilic and thermophilic enzymes are similar, suggesting that the nearly temperature-independent electron transfer rate does not require peculiar adjustments. Furthermore, the structural flexibilities of both the psychrophilic and thermophilic enzymes are also similar, indicating that the firm and precise bindings of the four catalytic copper ions are essential for the oxidase function. These results show that the requirements for enzymatic electron transfer, in the absence of the selective pressure of temperature on electron transfer rates, produce a specific adaptive pattern, which is distinct from that observed in enzymes possessing a well-defined active site and relying on conformational changes such as for the induced fit mechanism.

  17. Improved high temperature solar absorbers for use in Concentrating Solar Power central receiver applications.

    SciTech Connect

    Stechel, Ellen Beth; Ambrosini, Andrea; Hall, Aaron Christopher; Lambert, Timothy L.; Staiger, Chad Lynn; Bencomo, Marlene

    2010-09-01

    Concentrating solar power (CSP) systems use solar absorbers to convert the heat from sunlight to electric power. Increased operating temperatures are necessary to lower the cost of solar-generated electricity by improving efficiencies and reducing thermal energy storage costs. Durable new materials are needed to cope with operating temperatures >600 C. The current coating technology (Pyromark High Temperature paint) has a solar absorptance in excess of 0.95 but a thermal emittance greater than 0.8, which results in large thermal losses at high temperatures. In addition, because solar receivers operate in air, these coatings have long term stability issues that add to the operating costs of CSP facilities. Ideal absorbers must have high solar absorptance (>0.95) and low thermal emittance (<0.05) in the IR region, be stable in air, and be low-cost and readily manufacturable. We propose to utilize solution-based synthesis techniques to prepare intrinsic absorbers for use in central receiver applications.

  18. First-principles phase stability at high temperatures and pressure in Nb90Zr10 alloy

    DOE PAGES

    Landa, A.; Soderlind, P.

    2016-08-18

    The phase stability of Nb90Zr10 alloy at high temperatures and compression is explored by means of first-principles electronic-structure calculations. Utilizing the self-consistent ab initio lattice dynamics (SCAILD) approach in conjunction with density-functional theory, we show that pressure-induced mechanical instability of the body-centered cubic phase, which results in formation of a rhombohedral phase at around 50 GPa, will prevail significant heating. As a result, the body-centered cubic structure will recover before melting at ~1800 K.

  19. Stability and partial oligomerization of naphthalene under high pressure at room temperature

    NASA Astrophysics Data System (ADS)

    Shinozaki, Ayako; Mimura, Koichi; Nishida, Tamihito; Inoue, Toru; Nakano, Satoshi; Kagi, Hiroyuki

    2016-10-01

    The stability and pressure-induced chemical reactions of naphthalene were investigated at room temperature at pressures up to 23 GPa. In-situ X-ray diffraction (XRD) measurements indicated that naphthalene retained its crystal structure up to ∼20 GPa, whereas a solid amorphous phase was observed in the recovered samples. Based on microanalysis of the recovered samples using Gas Chromatograph Mass Spectrometer (GC/MS), naphthalene dimer and trimer isomers were observed at pressures exceeding 15 GPa. The dimers were classified as products of simple dimerization, naphthylation, and condensation, similar to the case of the pressure-induced dimerization of benzene, indicating a similar dimerization mechanism for naphthalene.

  20. Temperature-stabilized differential amplifier for low-noise DC measurements

    NASA Astrophysics Data System (ADS)

    Märki, P.; Braem, B. A.; Ihn, T.

    2017-08-01

    A tabletop low-noise differential amplifier with a bandwidth of 100 kHz is presented. Low voltage drifts of the order of 100 nV/day are reached by thermally stabilizing relevant amplifier components. The input leakage current is below 100 fA. Input-stage errors are reduced by extensive circuitry. Voltage noise, current noise, input capacitance, and input current are extraordinarily low. The input resistance is larger than 1 T Ω . The amplifiers were tested with and deployed for electrical transport measurements of quantum devices at cryogenic temperatures.

  1. Discovery of highly potent and selective Bruton's tyrosine kinase inhibitors: Pyridazinone analogs with improved metabolic stability.

    PubMed

    Young, Wendy B; Barbosa, James; Blomgren, Peter; Bremer, Meire C; Crawford, James J; Dambach, Donna; Eigenbrot, Charles; Gallion, Steve; Johnson, Adam R; Kropf, Jeffrey E; Lee, Seung H; Liu, Lichuan; Lubach, Joseph W; Macaluso, Jen; Maciejewski, Pat; Mitchell, Scott A; Ortwine, Daniel F; Di Paolo, Julie; Reif, Karin; Scheerens, Heleen; Schmitt, Aaron; Wang, Xiaojing; Wong, Harvey; Xiong, Jin-Ming; Xu, Jianjun; Yu, Christine; Zhao, Zhongdong; Currie, Kevin S

    2016-01-15

    BTK inhibitor GDC-0834 (1) was found to be rapidly metabolized in human studies, resulting in a suspension of clinical trials. The primary route of metabolism was through cleavage of the acyclic amide bond connecting the terminal tetrahydrobenzothiophene with the central linker aryl ring. SAR studies were focused on reducing metabolic cleavage of this amide, and resulted in the identification of several central aryl linker substituents that conferred improved stability. The most promising substituted aryl linkers were then incorporated into an optimized pyridazinone scaffold, resulting in the identification of lead analog 23, possessing improved potency, metabolic stability and preclinical properties. Copyright © 2015 Elsevier Ltd. All rights reserved.

  2. Solid-state nanoparticle coated emulsions for encapsulation and improving the chemical stability of all-trans-retinol.

    PubMed

    Ghouchi-Eskandar, Nasrin; Simovic, Spomenka; Prestidge, Clive A

    2012-02-28

    Submicron oil-in-water (o/w) emulsions stabilised with conventional surfactants and silica nanoparticles were prepared and freeze-dried to obtain free-flowing powders with good redispersibility and a three-dimensional porous matrix structure. Solid-state emulsions were characterised for visual appearance, particle size distribution, zeta potential and reconstitution properties after freeze-drying with various sugars and at a range of sugar to oil ratios. Comparative degradation kinetics of all-trans-retinol from freeze-dried and liquid emulsions was investigated as a function of storage temperatures. Optimum stability was observed for silica-coated oleylamine emulsions at 4 °C in their wet state. The half-life of all-trans-retinol was 25.66 and 22.08 weeks for silica incorporation from the oil and water phases respectively. This was ∼4 times higher compared to the equivalent solid-state emulsions with drug half-life of 6.18 and 6.06 weeks at 4 °C. Exceptionally, at a storage temperature of 40 °C, the chemical stability of the drug was 3 times higher in the solid-state compared to the wet emulsions which confirmed that freeze-drying is a promising approach to improve the chemical stability of water-labile compounds provided that the storage conditions are optimised.

  3. Atomic Layer Deposition Al2O3 Coatings Significantly Improve Thermal, Chemical, and Mechanical Stability of Anodic TiO2 Nanotube Layers

    PubMed Central

    2017-01-01

    We report on a very significant enhancement of the thermal, chemical, and mechanical stability of self-organized TiO2 nanotubes layers, provided by thin Al2O3 coatings of different thicknesses prepared by atomic layer deposition (ALD). TiO2 nanotube layers coated with Al2O3 coatings exhibit significantly improved thermal stability as illustrated by the preservation of the nanotubular structure upon annealing treatment at high temperatures (870 °C). In addition, a high anatase content is preserved in the nanotube layers against expectation of the total rutile conversion at such a high temperature. Hardness of the resulting nanotube layers is investigated by nanoindentation measurements and shows strongly improved values compared to uncoated counterparts. Finally, it is demonstrated that Al2O3 coatings guarantee unprecedented chemical stability of TiO2 nanotube layers in harsh environments of concentrated H3PO4 solutions. PMID:28291942

  4. Atomic Layer Deposition Al2O3 Coatings Significantly Improve Thermal, Chemical, and Mechanical Stability of Anodic TiO2 Nanotube Layers.

    PubMed

    Zazpe, Raul; Prikryl, Jan; Gärtnerova, Viera; Nechvilova, Katerina; Benes, Ludvik; Strizik, Lukas; Jäger, Ales; Bosund, Markus; Sopha, Hanna; Macak, Jan M

    2017-04-04

    We report on a very significant enhancement of the thermal, chemical, and mechanical stability of self-organized TiO2 nanotubes layers, provided by thin Al2O3 coatings of different thicknesses prepared by atomic layer deposition (ALD). TiO2 nanotube layers coated with Al2O3 coatings exhibit significantly improved thermal stability as illustrated by the preservation of the nanotubular structure upon annealing treatment at high temperatures (870 °C). In addition, a high anatase content is preserved in the nanotube layers against expectation of the total rutile conversion at such a high temperature. Hardness of the resulting nanotube layers is investigated by nanoindentation measurements and shows strongly improved values compared to uncoated counterparts. Finally, it is demonstrated that Al2O3 coatings guarantee unprecedented chemical stability of TiO2 nanotube layers in harsh environments of concentrated H3PO4 solutions.

  5. Evaluation of nucleic acid stabilization products for ambient temperature shipping and storage of viral RNA and antibody in a dried whole blood format.

    PubMed

    Dauner, Allison L; Gilliland, Theron C; Mitra, Indrani; Pal, Subhamoy; Morrison, Amy C; Hontz, Robert D; Wu, Shuenn-Jue L

    2015-07-01

    Loss of sample integrity during specimen transport can lead to false-negative diagnostic results. In an effort to improve upon the status quo, we used dengue as a model RNA virus to evaluate the stabilization of RNA and antibodies in three commercially available sample stabilization products: Whatman FTA Micro Cards (GE Healthcare Life Sciences, Pittsburgh, PA), DNAstāble Blood tubes (Biomātrica, San Diego, CA), and ViveST tubes (ViveBio, Alpharetta, GA). Both contrived and clinical dengue-positive specimens were stored on these products at ambient temperature or 37°C for up to 1 month. Antibody and viral RNA levels were measured by enzyme-linked immunosorbent assay (ELISA) and quantitative reverse transcription polymerase chain reaction (qRT-PCR) assays, respectively, and compared with frozen unloaded controls. We observed reduced RNA and antibody levels between stabilized contrived samples and frozen controls at our earliest time point, and this was particularly pronounced for the FTA cards. However, despite some time and temperature dependent loss, a 94.6-97.3% agreement was observed between stabilized clinical specimens and their frozen controls for all products. Additional considerations such as cost, sample volume, matrix, and ease of use should inform any decision to incorporate sample stabilization products into a diagnostic testing workflow. We conclude that DNAstāble Blood and ViveST tubes are useful alternatives to traditional filter paper for ambient temperature shipment of clinical specimens for downstream molecular and serological testing.

  6. Donor-Stabilized Silacyclobutanone: A Precursor of 1-Silaketene via Retro-[2 + 2]-Cycloaddition Reaction at Room Temperature.

    PubMed

    Troadec, Thibault; Lopez Reyes, Morelia; Rodriguez, Ricardo; Baceiredo, Antoine; Saffon-Merceron, Nathalie; Branchadell, Vicenç; Kato, Tsuyoshi

    2016-03-09

    The synthesis of donor-stabilized silacyclobutanone 2 was successfully realized by the reaction of silacyclopropylidene 1 with benzaldehyde in the presence of a Lewis acid catalyst. Of particular interest, silacyclobutanone 2 evolves at room temperature via a retro-[2 + 2]-cycloaddition reaction, leading to an original NHC-stabilized 1-silaketene 4 and cis-stilbene.

  7. Intensive unilateral core training improves trunk stability without preference for trunk left or right rotation.

    PubMed

    Kim, Yushin; Kim, Jungjin; Yoon, BumChul

    2015-01-01

    It is possible to increase multi-directional trunk stability using co-activation. However, it is unclear whether there is a preference for left or right trunk rotation after intensive unilateral stability training. The aim of this study was to examine the directional preference in trunk rotational stability after unilateral core training. This study was conducted on 16 female basketball players. For eight weeks, eight participants performed unilateral core training that focused on one side of the trunk. The remaining eight participants were not provided any additional training. To determine rotational trunk stability, all participants were requested to maintain an upright sitting posture against sudden, external, left or right rotational perturbations of the trunk. Angular displacement of the trunk was measured using a motion analyzer. At the end of the training period, the angular displacement in response to the perturbation was reduced for both rotational directions (left: −26%, right: −24%) in the trained group (p < 0.05). This study showed that trunk stability improved without particular directional preference in response to unilateral core training. This result adds to our understanding of the nature of trunk stability and multi-directional improvement. Intervention study, Level 1b.

  8. Effects of high temperature and e-beam irradiation on the stability of refractory thin films

    NASA Technical Reports Server (NTRS)

    Lee, E. H.; Poppa, H.

    1977-01-01

    Refractory thin films of Al2O3, ZrO2, MgO, ThO2, and BN have been investigated in situ in an UHV transmission electron microscope. The electron transparent refractory films were prepared by electron-beam evaporation, anodization, RF sputtering, and thinning of bulk crystal materials. The study concentrates on monitoring the thermal and mechanical stability of the films, phase and structural changes, and electron irradiation effects as a function of film-preparation conditions. With increasing temperatures, five different crystallographic phases were observed for both anodized and electron-beam-evaporated alumina films. Zirconia films exhibited two phase transitions upon heating to 1200 C and electron-irradiation-induced crystallization of ZrO2 even at room temperature. MgO, ThO2, and BN films did not undergo any noticeable phase transformation but ruptured due to sintering below 1200 C.

  9. Stability and corrosion testing of a high temperature phase change material for CSP applications

    NASA Astrophysics Data System (ADS)

    Liu, Ming; Bell, Stuart; Tay, Steven; Will, Geoffrey; Saman, Wasim; Bruno, Frank

    2016-05-01

    This paper presents the stability and corrosion testing results of a candidate high temperature phase change material (PCM) for potential use in concentrating solar power applications. The investigated PCM is a eutectic mixture of NaCl and Na2CO3 and both are low cost materials. This PCM has a melting temperature of 635 °C and a relatively high latent heat of fusion of 308.1 J/g. The testing was performed by means of an electric furnace subjected to 150 melt-freeze cycles between 600 °C and 650 °C. The results showed that this PCM candidate has no obvious decomposition up to 650 °C after 150 cycles and stainless steel 316 potentially can be used as the containment material under the minimized oxygen atmosphere.

  10. Stability Analysis of Thermoacoustic Gas Oscillations through Temperature Ratio Dependence of the Complex Frequency

    NASA Astrophysics Data System (ADS)

    Hyodo, Hiroaki; Muraoka, Keita; Biwa, Tetsushi

    2017-10-01

    The linear stability of a thermoacoustic system consisting of a looped tube having a regenerator and a branch resonator is studied numerically and experimentally as a function of the temperature ratio of the hot and cold parts of the regenerator. The characteristic complex angular frequency of the system is obtained as a solution of the basic equations of hydrodynamics. Results show that the system can possess two critical temperature ratios when the regenerator pore radius is smaller than the optimal value. Furthermore, the system can show a transition from a traveling-wave engine to a standing-wave engine as the pore size is increased. The experimental method for deriving the characteristic complex angular frequency of the system and the results are presented to support the validity of the numerical calculations.

  11. Thermodynamic analysis of chemical stability of ceramic materials in hydrogen-containing atmospheres at high temperatures

    NASA Technical Reports Server (NTRS)

    Misra, Ajay K.

    1990-01-01

    The chemical stability of several ceramic materials in hydrogen-containing environments was analyzed with thermodynamic considerations in mind. Equilibrium calculations were made as a function of temperature, moisture content, and total system pressure. The following ceramic materials were considered in this study: SiC, Si3N4, SiO2, Al2O3, mullite, ZrO2, Y2O3, CaO, MgO, BeO, TiB2, TiC, HfC, and ZrC. On the basis of purely thermodynamic arguments, upper temperature limits are suggested for each material for long-term use in H2-containing atmospheres.

  12. Effect of Charge, Size and Temperature on Stability of Charged Colloidal Nano Particles

    NASA Astrophysics Data System (ADS)

    Golchoobi, A.; Khosravi, A.; Modarress, H.; Ahmadzadeh, A.

    2012-10-01

    Molecular simulation of charged colloidal suspension is performed in NVT canonical ensemble using Monte Carlo method and primitive model. The well-known Derjaguin-Landau-Verwey-Overbeek theory is applied to account for effective interactions between particles. Effect of temperature, valance of micro-ions and the size of colloidal particles on the phase stability of the solution is investigated. The results indicate that the suspension is more stable at higher temperatures. On the other hand, for a more stable suspension to exist, lower micro-ion valance is favorable. For micro-ions of higher charge the number of aggregates and the number of particle in each of aggregate on average is higher. However for the best of our results larger colloidal particle are less stable. Comparing the results with theoretical formula considering the influence of surface curvature shows qualitative consistency.

  13. Linear stability of a compressible coaxial jet with continuous velocity and temperature profiles

    NASA Astrophysics Data System (ADS)

    Perrault-Joncas, Dominique; Maslowe, Sherwin A.

    2008-07-01

    This paper describes an investigation of the stability of a jet with velocity and temperature profiles characteristic of the exit region for a turbofan engine. Because the bypass stream mixes with both the exhaust and the ambient air, these profiles contain thin layers in which the velocity and temperature may vary rapidly. As a consequence, multiple instability modes are possible. In accordance with Rayleigh's theorem for axisymmetric incompressible shear flows, it turns out that there are three possible modes, only two of which are unstable. We consider the effect on spatial growth rates of varying the diameter and velocity ratios, compressibility, and azimuthal wavenumber. Radiating modes, that are possible when the primary jet is heated, are also studied.

  14. Deformation mechanisms for high-temperature creep of high yttria content stabilized zirconia single crystals

    SciTech Connect

    Gomez-Garcia, D.; Martinez-Fernandez, J.; Dominguez-Rodriguez, A.; Eveno, P.; Castaing, J.

    1996-03-01

    Creep of 21 mol.% yttria-stabilized zirconia single crystals has been studied between 1,400 and 1,800 C. The creep parameters have been determined indicating a change of the controlling mechanism around 1,500 C. At higher temperatures recovery creep is found to be the rate controlling mechanism, with a stress exponent {approx_equal} 3 and an activation energy {approx_equal} 6 eV. Transition to glide controlled creep occurs below 1,500 C, associated with larger stress exponents ({approx_equal} 5) and activation energies ({approx_equal} 8.5 eV). TEM observations of the dislocation microstructure confirm this transition. The influence of the high yttria content, which is at the origin of the high creep resistance of these crystals, is discussed for each range of temperatures.

  15. Tunneling stabilized magnetic force microscopy; Prospects for low temperature applications to superconductors

    SciTech Connect

    Moreland, J.; Rice, P. , Boulder, CO . Electromagnetic Technology Div.)

    1991-03-01

    The authors of this paper demonstrate an imaging technique referred to as tunneling stabilized magnetic force microscopy or TSMFM. TSMFM is performed using a scanning tunneling microscope (STM) with a flexible magnetic, tunneling tip in place of the usual rigid tunneling tip. TSMFM images are therefore combinations of topography and the magnetic forces between the tip and the sample. Room temperature TSMFM images of magnetic bit tracks on a hard disk have 100 nm resolution and are comparable to Bitter patterns made using a ferrofluid. We have built a low temperature STM with the hope of getting TSMFM images of the flux lattice in superconductors. Preliminary TSMFM images of a YBa{sub 2}Cu{sub c}O{sub x} (YBCO) film (T{sub c} {minus} 88 K) in a 5Q mT field show that relatively large magnetic forces are acting on the flexible tip while scanning at 48 K.

  16. Semiconductor lasers with asymmetric barrier layers: An approach to high temperature stability

    SciTech Connect

    Zhukov, A. E.; Kryzhanovskaya, N. V. Maximov, M. V.; Egorov, A. Yu.; Pavlov, M. M.; Zubov, F. I.; Asryan, L. V.

    2011-04-15

    A method for enhancing the temperature stability of injection lasers that is based on introducing asymmetric barrier layers on each side of the quantum-confined active region is suggested. The asymmetric barrier layers prevent electrons from escaping from the active region into the part of the waveguide region where holes are injected and prevent holes from escaping into the part of the waveguide region where electrons are injected. Parameters of the layers that allow implementation of the asymmetric-barrier design using pseudomorphic structures grown on GaAs substrates are determined. The calculation of the threshold characteristics of these laser structures demonstrates that suppression of electron-hole recombination outside the active region attained due to the use of asymmetric barrier layers leads to a significant decrease in the threshold current and an increase in the characteristic temperature of this type of lasers.

  17. [(68)Ga]NOTA-Galactosyl Human Serum Albumin: a Tracer for Liver Function Imaging with Improved Stability.

    PubMed

    Haubner, Roland; Schmid, Andreas M; Maurer, Andreas; Rangger, Christine; Roig, Llanos Geraldo; Pichler, Bernd J; Virgolini, Irene J

    2017-02-13

    Non-invasive techniques allowing quantitative determination of the functional liver mass are of great interest for patient management in a variety of clinical settings. Recently, we presented [(68)Ga]DTPA-GSA to target the hepatic asialoglycoprotein receptor for this purpose. Here, we introduce [(68)Ga]NOTA-GSA to improve metabolic stability of the radiopharmaceutical and compare the imaging properties with [(68)Ga]DTPA-GSA. Labeling of the compounds was carried out at room temperature using 1.9 M sodium acetate as buffer. For quality control, thin-layer, high-performance liquid, and size exclusion chromatographies were used. Metabolic stability was studied in rat and human serums. For in vivo evaluation, Fischer rats were scanned by positron emission tomography and magnetic resonance imaging and subsequently sacrificed for biodistribution studies. Time activity curves (TACs) for heart and liver were generated and corresponding parameters (T50, T90, LHL15, HH15) were calculated. [(68)Ga]NOTA-GSA can be produced in high radiochemical yield and purity (>95 %) within 15 min. Stability studies revealed almost no metabolite formation over the 2-h observation period. Analysis of the TACs showed comparable results for most of the investigated parameters. The only significant difference was found in the T90 value, where [(68)Ga]NOTA-GSA showed slower uptake in comparison with (68)Ga-DTPA-GSA (123 ± 10 vs. 89 ± 3 s, p < 0.01). [(68)Ga]NOTA-GSA showed a significant increase of the metabolic stability and in most organs lower background activity. However, comparison of LHL15 and HH15 indicates that the increased stability did not further improve the diagnostic value. Thus, [(68)Ga]NOTA-GSA and [(68)Ga]DTPA-GSA can be used equivalent for imaging hepatic function with positron emission tomography.

  18. Some like it hot, some like it cold: Temperature dependent biotechnological applications and improvements in extremophilic enzymes.

    PubMed

    Siddiqui, Khawar Sohail

    2015-12-01

    The full biotechnological exploitation of enzymes is still hampered by their low activity, low stability and high cost. Temperature-dependent catalytic properties of enzymes are a key to efficient and cost-effective translation to commercial applications. Organisms adapted to temperature extremes are a rich source of enzymes with broad ranging thermal properties which, if isolated, characterized and their structure-function-stability relationship elucidated, could underpin a variety of technologies. Enzymes from thermally-adapted organisms such as psychrophiles (low-temperature) and thermophiles (high-temperature) are a vast natural resource that is already under scrutiny for their biotechnological potential. However, psychrophilic and thermophilic enzymes show an activity-stability trade-off that necessitates the use of various genetic and chemical modifications to further improve their properties to suit various industrial applications. This review describes in detail the properties and biotechnological applications of both cold-adapted and thermophilic enzymes. Furthermore, the review critically examines ways to improve their value for biotechnology, concluding by proposing an integrated approach involving thermally-adapted, genetically and magnetically modified enzymes to make biocatalysis more efficient and cost-effective.

  19. 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.

  20. Silicone oil emulsions: strategies to improve their stability and applications in hair care products.

    PubMed

    Nazir, H; Zhang, W; Liu, Y; Chen, X; Wang, L; Naseer, M M; Ma, G

    2014-04-01

    Silicone oils have wide range of applications in personal care products due to their unique properties of high lubricity, non-toxicity, excessive spreading and film formation. They are usually employed in the form of emulsions due to their inert nature. Until now, different conventional emulsification techniques have been developed and applied to prepare silicone oil emulsions. The size and uniformity of emulsions showed important influence on stability of droplets, which further affect the application performance. Therefore, various strategies were developed to improve the stability as well as application performance of silicone oil emulsions. In this review, we highlight different factors influencing the stability of silicone oil emulsions and explain various strategies to overcome the stability problems. In addition, the silicone deposition on the surface of hair substrates and different approaches to increase their deposition are also discussed in detail. © 2013 Society of Cosmetic Scientists and the Société Française de Cosmétologie.

  1. Gait adaptability training improves obstacle avoidance and dynamic stability in patients with cerebellar degeneration.

    PubMed

    Fonteyn, Ella M R; Heeren, Anita; Engels, Jasper-Jan C; Boer, Jasper J Den; van de Warrenburg, Bart P C; Weerdesteyn, Vivian

    2014-01-01

    Balance and gait problems in patients with cerebellar degeneration lead to reduced mobility, loss of independence, and frequent falls. It is currently unclear, however, whether balance and gait capacities can be improved by training in this group of patients. Therefore, the aim of this study was to examine the effects of gait adaptability training on obstacle avoidance and dynamic stability during adaptive gait. Ten patients with degenerative cerebellar ataxia received 10 protocolized gait adaptability training sessions of 1 h each during 5 weeks. Training was performed on a treadmill with visual stepping targets and obstacles projected on the belt's surface. As the primary outcome, we used an obstacle avoidance task while walking on a treadmill. We determined avoidance success rates, as well as dynamic stability during the avoidance manoeuvre. Clinical ratings included the scale for the assessment of ataxia (SARA), 10 m walking test, timed up-and-go test, berg balance scale, and the obstacle subtask of the emory functional ambulation profile (EFAP). Following the intervention, success rates on the obstacle avoidance task had significantly improved compared to pre-intervention. For successful avoidance, participants allowed themselves smaller stability margins in the sagittal plane in the (shortened) pre-crossing step. However, in the subsequent steps they returned to baseline stability values more effectively than before training. SARA scores and the EFAP obstacle subtask improved significantly as well. This pilot study provides preliminary evidence of a beneficial effect of gait adaptability training on obstacle avoidance capacity and dynamic stability in patients with cerebellar degeneration.

  2. Transient Stability Improvement of Multi-Machine Power System with Large-Capacity Battery Systems

    NASA Astrophysics Data System (ADS)

    Kawabe, Ken-Ichi; Yokoyama, Akihiko

    An emergency control has been applied to power systems to avoid cascading outages by making the best use of existing equipment under severe fault conditions. Battery energy storage system (BESS) is one of the attractive equipment for the emergency control according to its growing installed capacity in the current grid. This paper investigates an effective use of BESS for transient stability improvement, and proposes a novel control scheme using wide-area information. The proposed control scheme adopts two stability indices, the energy function and rotor speed of the critical machine, to make it applicable to multi-machine power systems. Besides, it can control active and reactive power injection of the BESS coordinately to make the best use of its converter capacity for the stability enhancement. Digital simulations are conducted on the 32-machine meshed system with multiple BESSs. The results demonstrate that the BESSs controlled by the proposed method can improve the first swing stability and the system damping, and it is made clear how they improve the transient stability of the multi-machine power system. In addition, an impact of the reactive power control on the bus voltages around the installation sites is investigated to discuss a preferable way of their installation.

  3. 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.

  4. Designing Nanoscale Precipitates in Novel Cobalt-based Superalloys to Improve Creep Resistance and Operating Temperature

    SciTech Connect

    Dunand, David C.; Seidman, David N.; Wolverton, Christopher; Saal, James E.; Bocchini, Peter J.; Sauza, Daniel J.

    2014-10-01

    High-temperature structural alloys for aerospace and energy applications have long been dominated by Ni-base superalloys, whose strength and creep resistance can be attributed to microstructures consisting of a large volume fraction of ordered (L12) γ'-precipitates embedded in a disordered’(f.c.c.) γ-matrix. These alloys exhibit excellent mechanical behavior and thermal stability, but after decades of incremental improvement are nearing the theoretical limit of their operating temperatures. Conventional Co-base superalloys are solid-solution or carbide strengthened; although they see industrial use, these alloys are restricted to lower-stress applications because the absence of an ordered intermetallic phase places an upper limit on their mechanical performance. In 2006, a γ+γ' microstructure with ordered precipitates analogous to (L12) Ni3Al was first identified in the Co-Al-W ternary system, allowing, for the first time, the development of Co-base alloys with the potential to meet or even exceed the elevated-temperature performance of their Ni-base counterparts. The potential design space for these alloys is complex: the most advanced Ni-base superalloys may contain as many as 8-10 minor alloying additions, each with a specified purpose such as raising the γ' solvus temperature or improving creep strength. Our work has focused on assessing the effects of alloying additions on microstructure and mechanical behavior of γ'-strengthened Co-base alloys in an effort to lay the foundations for understanding this emerging alloy system. Investigation of the size, morphology, and composition of γ' and other relevant phases is investigated utilizing scanning electron microscopy (SEM) and 3-D picosecond ultraviolet local electrode atom probe tomography (APT). Microhardness, compressive yield stress at ambient and elevated temperatures, and compressive high-temperature creep measurements are employed to extract mechanical behavior

  5. Insights into the structural stability of Bax from molecular dynamics simulations at high temperatures.

    PubMed

    Rosas-Trigueros, Jorge Luis; Correa-Basurto, José; Benítez-Cardoza, Claudia Guadalupe; Zamorano-Carrillo, Absalom

    2011-12-01

    Bax is a member of the Bcl-2 protein family that participates in mitochondrion-mediated apoptosis. In the early stages of the apoptotic pathway, this protein migrates from the cytosol to the outer mitochondrial membrane, where it is inserted and usually oligomerizes, making cytochrome c-compatible pores. Although several cellular and structural studies have been reported, a description of the stability of Bax at the molecular level remains elusive. This article reports molecular dynamics simulations of monomeric Bax at 300, 400, and 500 K, focusing on the most relevant structural changes and relating them to biological experimental results. Bax gradually loses its α-helices when it is submitted to high temperatures, yet it maintains its globular conformation. The resistance of Bax to adopt an extended conformation could be due to several interactions that were found to be responsible for maintaining the structural stability of this protein. Among these interactions, we found salt bridges, hydrophobic interactions, and hydrogen bonds. Remarkably, salt bridges were the most relevant to prevent the elongation of the structure. In addition, the analysis of our results suggests which conformational movements are implicated in the activation/oligomerization of Bax. This atomistic description might have important implications for understanding the functionality and stability of Bax in vitro as well as within the cellular environment.

  6. Influence of temperature and preserving agents on the stability of cornelian cherries anthocyanins.

    PubMed

    Moldovan, Bianca; David, Luminiţa

    2014-06-17

    Cornelian cherry (Cornus mas L.) fruits are known for their significant amounts of anthocyanins which can be used as natural food colorants. The storage stability of anthocyanins from these fruit extracts, at different temperatures (2 °C, 25 °C and 75 °C), pH 3.02, in the presence of two of the most widely employed food preserving agents (sodium benzoate and potassium sorbate) was investigated. The highest stability was exhibited by the anthocyanin extract stored at 2 °C without any added preservative, with half-life and constant rate values of 1443.8 h and 0.48 × 10(-3) h(-1), respectively. The highest value of the degradation rate constant (82.76 × 10(-3)/h) was obtained in the case of anthocyanin extract stored at 75 °C without any added preservative. Experimental results indicate that the storage degradation of anthocyanins followed first-order reaction kinetics under each of the investigated conditions. In aqueous solution, the food preservatives used were found to have a slight influence on the anthocyanins' stability.

  7. A robust ambient temperature collection and stabilization strategy: Enabling worldwide functional studies of the human microbiome.

    PubMed

    Anderson, Ericka L; Li, Weizhong; Klitgord, Niels; Highlander, Sarah K; Dayrit, Mark; Seguritan, Victor; Yooseph, Shibu; Biggs, William; Venter, J Craig; Nelson, Karen E; Jones, Marcus B

    2016-08-25

    As reports on possible associations between microbes and the host increase in number, more meaningful interpretations of this information require an ability to compare data sets across studies. This is dependent upon standardization of workflows to ensure comparability both within and between studies. Here we propose the standard use of an alternate collection and stabilization method that would facilitate such comparisons. The DNA Genotek OMNIgene∙Gut Stool Microbiome Kit was compared to the currently accepted community standard of freezing to store human stool samples prior to whole genome sequencing (WGS) for microbiome studies. This stabilization and collection device allows for ambient temperature storage, automation, and ease of shipping/transfer of samples. The device permitted the same data reproducibility as with frozen samples, and yielded higher recovery of nucleic acids. Collection and stabilization of stool microbiome samples with the DNA Genotek collection device, combined with our extraction and WGS, provides a robust, reproducible workflow that enables standardized global collection, storage, and analysis of stool for microbiome studies.

  8. Room Temperature Stabilization of Oral, Live Attenuated Salmonella enterica serovar Typhi-Vectored Vaccines

    PubMed Central

    Ohtake, Satoshi; Martin, Russell; Saxena, Atul; Pham, Binh; Chiueh, Gary; Osorio, Manuel; Kopecko, Dennis; Xu, DeQi; Lechuga-Ballesteros, David; Truong-Le, Vu

    2011-01-01

    Foam drying, a modified freeze drying process, was utilized to produce a heat-stable, live attenuated Salmonella Typhi ‘Ty21a’ bacterial vaccine. Ty21a vaccine was formulated with pharmaceutically approved stabilizers, including sugars, plasticizers, amino acids, and proteins. Growth media and harvesting conditions of the bacteria were also studied to enhance resistance to desiccation stress encountered during processing as well as subsequent storage at elevated temperatures. The optimized Ty21a vaccine, formulated with trehalose, methionine, and gelatin, demonstrated stability for approximately 12 weeks at 37°C (i.e., time required for the vaccine to decrease in potency by 1log10 CFU) and no loss in titer at 4 and 25°C following storage for the same duration. Furthermore, the foam dried Ty21a elicited a similar immunogenic response in mice as well as protection in challenge studies compared to Vivotif™, the commercial Ty21a vaccine. The enhanced heat stability of the Ty21a oral vaccine, or Ty21a derivatives expressing foreign antigens (e.g. anthrax), could mitigate risks of vaccine potency loss during long term storage, shipping, delivery to geographical areas with warmer climates or during emergency distribution following a bioterrorist attack. Because the foam drying process is conducted using conventional freeze dryers and can be readily implemented at any freeze drying manufacturing facility, this technology appears ready and appropriate for large scale processing of foam dried vaccines. PMID:21300096

  9. Insights into the structural stability of Bax from molecular dynamics simulations at high temperatures

    PubMed Central

    Rosas-Trigueros, Jorge Luis; Correa-Basurto, José; Guadalupe Benítez-Cardoza, Claudia; Zamorano-Carrillo, Absalom

    2011-01-01

    Bax is a member of the Bcl-2 protein family that participates in mitochondrion-mediated apoptosis. In the early stages of the apoptotic pathway, this protein migrates from the cytosol to the outer mitochondrial membrane, where it is inserted and usually oligomerizes, making cytochrome c-compatible pores. Although several cellular and structural studies have been reported, a description of the stability of Bax at the molecular level remains elusive. This article reports molecular dynamics simulations of monomeric Bax at 300, 400, and 500 K, focusing on the most relevant structural changes and relating them to biological experimental results. Bax gradually loses its α-helices when it is submitted to high temperatures, yet it maintains its globular conformation. The resistance of Bax to adopt an extended conformation could be due to several interactions that were found to be responsible for maintaining the structural stability of this protein. Among these interactions, we found salt bridges, hydrophobic interactions, and hydrogen bonds. Remarkably, salt bridges were the most relevant to prevent the elongation of the structure. In addition, the analysis of our results suggests which conformational movements are implicated in the activation/oligomerization of Bax. This atomistic description might have important implications for understanding the functionality and stability of Bax in vitro as well as within the cellular environment. PMID:21936009

  10. A robust ambient temperature collection and stabilization strategy: Enabling worldwide functional studies of the human microbiome

    PubMed Central

    Anderson, Ericka L.; Li, Weizhong; Klitgord, Niels; Highlander, Sarah K.; Dayrit, Mark; Seguritan, Victor; Yooseph, Shibu; Biggs, William; Venter, J. Craig; Nelson, Karen E.; Jones, Marcus B.

    2016-01-01

    As reports on possible associations between microbes and the host increase in number, more meaningful interpretations of this information require an ability to compare data sets across studies. This is dependent upon standardization of workflows to ensure comparability both within and between studies. Here we propose the standard use of an alternate collection and stabilization method that would facilitate such comparisons. The DNA Genotek OMNIgene∙Gut Stool Microbiome Kit was compared to the currently accepted community standard of freezing to store human stool samples prior to whole genome sequencing (WGS) for microbiome studies. This stabilization and collection device allows for ambient temperature storage, automation, and ease of shipping/transfer of samples. The device permitted the same data reproducibility as with frozen samples, and yielded higher recovery of nucleic acids. Collection and stabilization of stool microbiome samples with the DNA Genotek collection device, combined with our extraction and WGS, provides a robust, reproducible workflow that enables standardized global collection, storage, and analysis of stool for microbiome studies. PMID:27558918

  11. Temporal stability of solid oxidizers at high temperature and humidity. Memorandum report

    SciTech Connect

    Pellenbarg, R.E.; Dotson, D.A.

    1985-09-30

    Chemical Warfare/Biological Warfare (CW/BW) decontamination operations may rely on aqueous solutions prepared from stored solid oxidizers. Needed are data defining the shipboard storage stability of candidate oxidizers. Therefore, the stability of a series of potential decontaminants has been examined at high temperature (90 + C) and humidity (95 + % R.H.). The loss of oxidizing capacity in aliquots of the oxidizers was followed with time by iodometric titration. Calcium hypochlorite lost over 99% of its oxidizing capacity in less than two days, whereas lithium hypochlorite retained one-third oxidizing capacity for approximately twenty days. Sodium perborate, and sodium persulfate were very hygroscopic and unstable with time. H-48 decomposed in approximately two days, while sodium isocyanurate lost about 80% of its oxidizing capacity in two weeks. The data presented documents severe stability problems of one sort or another with all the materials tested, although overall the sodium isocyanurate appeared to be the more stable candidate undr extreme conditions. In any case, packaging and storage considerations are shown to be important for any potential decontaminant to be stored under environmentally severe conditions.

  12. Optimization of ultrasound-assisted extraction of pectinase enzyme from guava (Psidium guajava) peel: Enzyme recovery, specific activity, temperature, and storage stability.

    PubMed

    Amid, Mehrnoush; Murshid, Fara Syazana; Manap, Mohd Yazid; Islam Sarker, Zaidul

    2016-01-01

    This study aimed to investigate the effects of the ultrasound-assisted extraction conditions on the yield, specific activity, temperature, and storage stability of the pectinase enzyme from guava peel. The ultrasound variables studied were sonication time (10-30 min), ultrasound temperature (30-50 °C), pH (2.0-8.0), and solvent-to-sample ratio (2:1 mL/g to 6:1 mL/g). The main goal was to optimize the ultrasound-assisted extraction conditions to maximize the recovery of pectinase from guava peel with the most desirable enzyme-specific activity and stability. Under the optimum conditions, a high yield (96.2%), good specific activity (18.2 U/mg), temperature stability (88.3%), and storage stability (90.3%) of the extracted enzyme were achieved. The optimal conditions were 20 min sonication time, 40 °C temperature, at pH 5.0, using a 4:1 mL/g solvent-to-sample ratio. The study demonstrated that optimization of ultrasound-assisted process conditions for the enzyme extraction could improve the enzymatic characteristics and yield of the enzyme.

  13. Stabilizing hybrid perovskites against moisture and temperature via non-hydrolytic atomic layer deposited overlayers

    SciTech Connect

    Kim, In Soo; Martinson, Alex B. F.

    2015-09-14

    We utilized a novel non-hydrolytic (nh) surface chemistry to allow the direct synthesis of pinhole-fee oxide overlayers directly on conventional hybrid perovskite halide absorbers without damage. By utilizing water- free ALD Al2O3 passivation, a minimum of ten-fold increase in stability against relative humidity (RH) 85% was achieved along with a dramatically improved thermal resistance (up to 250 °C). We extend this approach to synthesize nh-TiO2 directly on hybrid perovskites to establish its potential in inverted photovoltaic devices as a dual stabilizing and electron accepting layer, as evidenced by photoluminescence (PL) quenching.

  14. Improving tribological performance of gray cast iron by laser peening in dynamic strain aging temperature regime

    NASA Astrophysics Data System (ADS)

    Feng, Xu; Zhou, Jianzhong; Mei, Yufen; Huang, Shu; Sheng, Jie; Zhu, Weili

    2015-09-01

    A high and stable brake disc friction coefficient is needed for automobile safety, while the coefficient degrades due to elevated temperature during the braking process. There is no better solution except changes in material composition and shape design optimization. In the dynamic strain aging(DSA) temperature regime of gray cast iron, micro-dimples with different dimple depth over diameter and surface area density are fabricated on the material surface by laser peening(LP) which is an LST method. Friction behavior and wear mechanism are investigated to evaluate the effects of surface texturing on the tribological performance of specimens under dry conditions. Through LP impacts assisted by DSA, the friction coefficients of the LPed specimens increase noticeably both at room temperature and elevated temperature in comparison to untreated specimens. Moreover, the coefficient of specimen with dimple depth over diameter of 0.03 and surface area density of 30% is up to 0.351 at room temperature, which dramatically rises up to 1.33 times that of untextured specimen and the value is still up to 0.3305 at 400°C with an increasing ratio of 35% compared to that of untreated specimen. The surface of textured specimen shows better wear resistance compared to untreated specimen. Wear mechanism includes adhesive wear, abrasive wear and oxidation wear. It is demonstrated that LP assisted by DSA can substantially improve wear resistance, raise the friction coefficient as well as its stability of gray cast iron under elevated temperatures. Heat fade and premature wear can be effectively relieved by this surface modification method.

  15. Stability and solubility of trans-resveratrol are strongly influenced by pH and temperature.

    PubMed

    Zupančič, Špela; Lavrič, Zoran; Kristl, Julijana

    2015-06-01

    Recently trans-resveratrol (trans-RSV) has received great attention due to its prophylactic and therapeutic properties. Its limited bioavailability provides compelling evidence of the need for more suitable formulations in order to attain better clinical effectiveness. Some physicochemical properties of trans-RSV are still unknown or research findings are contradictory. Therefore, this paper presents newly determined trans-RSV solubility and stability at various pH and temperatures, and the importance of such data for the studies of novel trans-RSV-loaded nanofibers. In acidic pH trans-RSV was stable, whereas its degradation started to increase exponentially above pH 6.8. Consequently, it is worthwhile to note that special consideration has to be dedicated to long dissolution testing or biological assays on cell lines in order to obtain relevant data. Measurements were done by validated UV/VIS spectroscopy, HPLC, and newly developed UPLC methods. Specificity was confirmed for HPLC and UPLC method, whereas UV/VIS spectroscopy resulted in false higher trans-RSV concentrations in conditions under which it was not stable (alkaline pH, light, increased temperature). The study is of interest because it draws attention to the importance of careful selected experimental conditions, their influence on the trans-RSV stability and the implications this has for formulation development, storage, and maintenance of therapeutic doses.

  16. Carotenoid stability in fruits, vegetables and working standards - effect of storage temperature and time.

    PubMed

    Dias, M Graça; Camões, M Filomena G F C; Oliveira, Luísa

    2014-08-01

    The effects of freezing and storage temperature on the mass fraction of α- and β-carotene, β-cryptoxanthin, lutein, lycopene and zeaxanthin in minimally processed fresh food products, were evaluated after sample preparation, extraction and saponification (only when strictly necessary). Effects of freezing and long-term stability were studied at two temperatures, -20 and -70°C, using high performance liquid chromatography (reversed phase columns, UV-Vis diode array detector) at time points during storage; measurement uncertainty was included in the evaluation. Stability of working standard solutions was also examined. Freezing did not affect the carotenoid mass fraction under the conditions studied. Carotenoids in orange, cherry, peach, apple, and kale were stable (except α-carotene and zeaxanthin in peach) for 13, 9.7, 5.7, 2.5 and 7.5months, respectively. For these food sample matrices, no significant difference between the freezing/storage at -20 and -70°C was observed. Standard solutions (0.05-5μg/mL) were stable for at least 6months at -70°C, except lycopene which at 0.05μg/mL was apparently stable only for six weeks. Copyright © 2014 Elsevier Ltd. All rights reserved.

  17. Factors that impact the stability of vitamin C at intermediate temperatures in a food matrix.

    PubMed

    Herbig, Anna-Lena; Renard, Catherine M G C

    2017-04-01

    The study comprises a systematic and quantitative evaluation of potential intrinsic and extrinsic factors that impact vitamin C degradation in a real food matrix. The supernatant of centrifuged apple purée was fortified in vitamin C, and degradation was followed without stirring. Model discrimination indicated better fit for the zero order model than the first order model which was hence chosen for determination of rate constants. pH influenced strongly vitamin C degradation in citrate-phosphate buffer but not in the apple purée serum. To get an idea of the impact of the food matrix, stability in apple purée serum was compared with that in carrot purée. In the latter, stability was slightly higher. Vitamin C degradation rates were not influenced by its initial concentration. The temperature effect was only marked in the temperature range 40-60°C. In the range 60-80°C, filling height of tubes had the greatest impact. Copyright © 2016 Elsevier Ltd. All rights reserved.

  18. A mechanism for stabilization of membranes at low temperatures by an antifreeze protein.

    PubMed Central

    Tomczak, Melanie M; Hincha, Dirk K; Estrada, Sergio D; Wolkers, Willem F; Crowe, Lois M; Feeney, Robert E; Tablin, Fern; Crowe, John H

    2002-01-01

    Polar fish, cold hardy plants, and overwintering insects produce antifreeze proteins (AFPs), which lower the freezing point of solutions noncolligatively and inhibit ice crystal growth. Fish AFPs have been shown to stabilize membranes and cells in vitro during hypothermic storage, probably by interacting with the plasma membrane, but the mechanism of this stabilization has not been clear. We show here that during chilling to nonfreezing temperatures the alpha-helical AFP type I from polar fish inhibits leakage across model membranes containing an unsaturated chloroplast galactolipid. The mechanism involves binding of the AFP to the bilayer, which increases the phase transition temperature of the membranes and alters the molecular packing of the acyl chains. We suggest that this change in acyl chain packing results in the reduced membrane permeability. The data suggest a hydrophobic interaction between the peptide and the bilayer. Further, we suggest that the expression of AFP type I in transgenic plants may be significant for thermal adaptation of chilling-sensitive plants. PMID:11806929

  19. A mechanism for stabilization of membranes at low temperatures by an antifreeze protein.

    PubMed

    Tomczak, Melanie M; Hincha, Dirk K; Estrada, Sergio D; Wolkers, Willem F; Crowe, Lois M; Feeney, Robert E; Tablin, Fern; Crowe, John H

    2002-02-01

    Polar fish, cold hardy plants, and overwintering insects produce antifreeze proteins (AFPs), which lower the freezing point of solutions noncolligatively and inhibit ice crystal growth. Fish AFPs have been shown to stabilize membranes and cells in vitro during hypothermic storage, probably by interacting with the plasma membrane, but the mechanism of this stabilization has not been clear. We show here that during chilling to nonfreezing temperatures the alpha-helical AFP type I from polar fish inhibits leakage across model membranes containing an unsaturated chloroplast galactolipid. The mechanism involves binding of the AFP to the bilayer, which increases the phase transition temperature of the membranes and alters the molecular packing of the acyl chains. We suggest that this change in acyl chain packing results in the reduced membrane permeability. The data suggest a hydrophobic interaction between the peptide and the bilayer. Further, we suggest that the expression of AFP type I in transgenic plants may be significant for thermal adaptation of chilling-sensitive plants.

  20. Temperature Stability and Bioadhesive Properties of Δ9-Tetrahydrocannabinol Incorporated Hydroxypropylcellulose Polymer Matrix Systems

    PubMed Central

    Repka, Michael A.; Munjal, Manish; ElSohly, Mahmoud A.; Ross, Samir A.

    2010-01-01

    The purpose of this study was to determine and compare the bioadhesive profiles of hydroxypropylcellulose (HPC) polymer matrices as a function of Δ9-tetrahydrocannabinol (THC) content. In addition, the effect of processing temperature on the stability of THC and its extent of degradation to cannabinol (CBN) was investigated. A hot-melt cast molding method was used to prepare HPC polymer matrix systems incorporated with THC at 0, 4, 8, and 16 percent. Bioadhesive measurements including peak adhesive force, area under the curve, and elongation at adhesive failure were recorded utilizing the TA.XT2i Texture Analyzer™. Data obtained from these tests at various contact time intervals suggested that the incorporation of THC led to an increase in the bioadhesive strength of the HPC polymer matrices. To determine the stability of THC and the resulting CBN content in the matrices, three different processing temperatures were utilized (120, 160, and 200°C). Post-production High Performance Liquid Chromotography (HPLC) analysis revealed that the processed systems contained at least 94% of THC and the relative percent formation of CBN was 0.5% at 120°C and 0.4% at 160°C compared to 1.6% at 200°C. These findings indicate that the cannabinoid may be a plausible candidate for incorporation into systems utilizing hot-melt extrusion techniques for the development of an effective mucoadhesive transmucosal matrix system for delivery of THC. PMID:16455601

  1. Temperature and species concentration measurements in a swirl-stabilized combustor

    NASA Technical Reports Server (NTRS)

    Oven, M. J.; Gouldin, F. C.; Mclean, W. J.

    1979-01-01

    An experimental evaluation of a swirl-stabilized combustor is presented. The combustor is composed of two confined, concentric, swirling jets. The inner jet flow is lean premixed methane and air; the outer flow is air. Combustion is stabilized on a swirl-induced recirculation zone. Mean temperature and mean concentrations of major species are measured throughout the combustor, including the recirculation zone. Fine wire thermocouples are used to measure temperature. A gas chromatograph and a chemi-luminescence analyzer are employed to analyze samples extracted by a water-cooled gas-sampling probe. Results are presented in the form of isotherms and isopleths of species concentration in the combustor for two swirl conditions: co-swirl and counter-swirl. The effects of swirl on the combustion are discussed in light of flame quenching due to rapid dilution and cooling of the reacting inner jet flow by mixing with the outer flow. Evidence for probe induced perturbations of the combustion process is observed.

  2. Stabilization of temperature during magnetic hyperthermia by Ce substituted magnetite nanoparticles

    NASA Astrophysics Data System (ADS)

    Shaw, S. K.; Alla, S. K.; Meena, S. S.; Mandal, R. K.; Prasad, N. K.

    2017-07-01

    We report here magnetic hyperthermia using nanoparticles of CexFe3-xO4 (x = 0.01, 0.05, 0.1, 0.3 and 0.5) during which temperature was found to be stabilizing near 42 °C. This happens despite of their high saturation magnetization (MS) and Curie temperature (TC) values. It was observed that by selecting an appropriate magnetic field the temperature can be rose exactly near the therapeutic temperature and thus it will help to selectively kill the cancerous cells leaving normal cells unaffected. These nanoparticles (size around 8-15 nm) were produced by single step microwave refluxing technique. X-ray diffraction (XRD) analysis demonstrates that samples were essentially single phase except for x = 0.5 sample. The X-ray photoelectron spectroscopy (XPS) study for the samples demonstrated that Ce was present in both Ce3+ and Ce4+ states. The saturation magnetization value of the samples decreased sharply from 62 Am2/kg for x = 0.01 to 19 Am2/kg for x = 0.1. This value further decreased with increased Ce doping.

  3. Kinetic study of catechin stability: effects of pH, concentration, and temperature.

    PubMed

    Li, Na; Taylor, Lynne S; Ferruzzi, Mario G; Mauer, Lisa J

    2012-12-26

    The degradation behaviors of catechins in dilute aqueous systems, including tea beverages and catechin solutions, have been documented; however, their reaction kinetics in green tea concentrated solutions, and impacts of pH, concentration, and temperature thereon, have not yet been established. In this study, reactions were conducted at pH levels ranging from 1.5 to 7, concentrations ranging from 1 to 1666.7 mg/mL, and temperatures ranging from 25 to 120 °C. Catechin contents were determined using high-performance liquid chromatography. Catechins were found to be more stable at high concentrations around pH 4. An empirical model for catechin content was established as a function of pH and temperature and showed good correlation between green tea concentrated solutions and previous reports of catechin stability in powder systems. These results provide useful approaches for shelf life calculations and catechin loss predictions at given temperature and pH conditions in green tea concentrates.

  4. Surface Integrity and Structural Stability of Broached Inconel 718 at High Temperatures

    NASA Astrophysics Data System (ADS)

    Chen, Z.; Peng, R. Lin; Moverare, J.; Avdovic, P.; Zhou, J. M.; Johansson, S.

    2016-07-01

    The current study focused on the surface integrity issues associated with broaching of Inconel 718 and the structural stability of the broached specimen at high temperatures, mainly involving the microstructural changes and residual stress relaxation. The broaching operation was performed using similar cutting conditions as that used in turbo machinery industries for machining fir-tree root fixings on turbine disks. Thermal exposure was conducted at 723 K, 823 K, and 923 K (450 °C, 550 °C, and 650 °C) for 30, 300, and 3000 hours, respectively. Surface cavities and debris dragging, sub-surface cracks, high intensity of plastic deformation, as well as the generation of tensile residual stresses were identified to be the main issues in surface integrity for the broached Inconel 718. When a subsequent heating was applied, surface recrystallization and α-Cr precipitation occurred beneath the broached surface depending on the applied temperature and exposure time. The plastic deformation induced by the broaching is responsible for these microstructural changes. The surface tension was completely relaxed in a short time at the temperature where surface recrystallization occurred. The tensile layer on the sub-surface, however, exhibited a much higher resistance to the stress relief annealing. Oxidation is inevitable at high temperatures. The study found that the surface recrystallization could promote the local Cr diffusion on the broached surface.

  5. Requisite temperatures for the stabilization of atomic H in solid H2

    NASA Technical Reports Server (NTRS)

    Rosen, G.

    1978-01-01

    If an atomic hydrogen/molecular hydrogen propellant containing at least 15% free H atoms by weight may be used, values for the theoretical specific impulse near and above 750 s may be predicted. The tritium-impregnation concept has been applied to manufacturing such an H/H2 propellant, and a phenomenological rate process theory has been derived for the matrix-isolation storage and equilibrium stability of atomic H produced at such ultralow temperatures in tritium-impregnated H2. It is suggested that an energy storage efficiency greater than 0.30 may be obtained at temperatures below 100 mK. So that the storage of atomic H is stable with respect to arbitrary small perturbations, the surface temperature must be less than a critical value dependent on sample volume, tritium weight fraction, and energy storage efficiency. A derivation of the formula for this critical surface temperature is presented, noting that the energy storage efficiency is to be fixed by experiment.

  6. Combined networked switching output feedback control with ?-region stability for performance improvement

    NASA Astrophysics Data System (ADS)

    Nikolakopoulos, George; Dritsas, Leonidas; Delshad, Saleh S.

    2014-06-01

    In this article, a combined networked switching output feedback control scheme, with a ?-region stability performance improvement module is presented. The network induced time delays, that are considered to be time varying and integer multiples of the sampling period, are being embedded in the system model, by state augmentation. The resulting model of the overall networked closed-loop system is switching, with the current measured round-trip time delay acting as the switching rule. Based on this modelling approach, a Linear Matrix Inequality (LMI) tuned switching output feedback controller is designed. The proposed approach establishes robustness against time delays and is able to guarantee the overall stability of the switching closed-loop system. Integrated in the controlled synthesis phase, an LMI tuned performance improvement module is being introduced, based on ?-region stability. Multiple simulation results are being presented that prove the efficacy of the proposed scheme.

  7. The electronic image stabilization technology research based on improved optical-flow motion vector estimation

    NASA Astrophysics Data System (ADS)

    Wang, Chao; Ji, Ming; Zhang, Ying; Jiang, Wentao; Lu, Xiaoyan; Wang, Jiaoying; Yang, Heng

    2016-01-01

    The electronic image stabilization technology based on improved optical-flow motion vector estimation technique can effectively improve the non normal shift, such as jitter, rotation and so on. Firstly, the ORB features are extracted from the image, a set of regions are built on these features; Secondly, the optical-flow vector is computed in the feature regions, in order to reduce the computational complexity, the multi resolution strategy of Pyramid is used to calculate the motion vector of the frame; Finally, qualitative and quantitative analysis of the effect of the algorithm is carried out. The results show that the proposed algorithm has better stability compared with image stabilization based on the traditional optical-flow motion vector estimation method.

  8. Development of improved high temperature coatings for IN-792 + HF

    NASA Technical Reports Server (NTRS)

    Profant, D. D.; Naik, S. K.

    1981-01-01

    The development for t-55 l712 engine of high temperature for integral turbine nozzles with improved thermal fatigue resistance without sacrificing oxidation/corrosion protection is discussed. The program evaluated to coating systems which comprised one baseline plasma spray coating (12% Al-NiCoCrALY), three aluminide coatings including the baseline aluminide (701), two CoNiCrAly (6% Al) + aluminide systems and four NiCoCrY + aluminide coating were evaluated. The two-step coating processes were investigated since it offered the advantage of tailoring the composition as well as properly coating surfaces of an integral or segmented nozzle. Cyclic burner rig thermal fatigue and oxidation/corrosion tests were used to evaluate the candidate coating systems. The plasma sprayed 12% Al-NiCoCrAlY was rated the best coating in thermal fatigue resistance and outperformed all coatings by a factor between 1.4 to 2.5 in cycles to crack initiation. However, this coatings is not applicable to integral or segmented nozzles due to the line of sight limitation of the plasma spray process. The 6% Al-CoNiCrAlY + Mod. 701 aluminide (32 w/o Al) was rated the best coating in oxidation/corrosion resistance and was rated the second best in thermal fatigue resistance.

  9. An A-site-deficient perovskite offers high activity and stability for low-temperature solid-oxide fuel cells.

    PubMed

    Zhu, Yinlong; Chen, Zhi-Gang; Zhou, Wei; Jiang, Shanshan; Zou, Jin; Shao, Zongping

    2013-12-01

    Solid oxide fuel cells (SOFCs) directly convert fossil and/or renewable fuels into electricity and/or high-quality heat in an environmentally friendly way. However, high operating temperatures result in high cost and material issues, which have limited the commercialization of SOFCs. To lower their operating temperatures, highly active and stable cathodes are required to maintain a reasonable power output. Here, we report a layer-structured A-site deficient perovskite Sr0.95 Nb0.1 Co0.9 O3-δ (SNC0.95) prepared by solid-state reactions that shows not only high activity towards the oxygen reduction reaction (ORR) at operating temperatures below 600 °C, but also offers excellent structural stability and compatibility, and improved CO2 resistivity. An anode-supported fuel cell with SNC0.95 cathode delivers a peak power density as high as 1016 mW cm(-2) with an electrode-area-specific resistance of 0.052 Ω cm(2) at 500 °C.

  10. Quinone-rich polydopamine functionalization of yttria stabilized zirconia for apatite biomineralization: The effects of coating temperature

    NASA Astrophysics Data System (ADS)

    Zain, Norhidayu Muhamad; Hussain, Rafaqat; Abdul Kadir, Mohammed Rafiq

    2015-08-01

    The use of yttria stabilized zirconia (YSZ) as biomedical implants is often offset by its bioinert nature that prevents its osseointegration to occur. Therefore, the functionalization of YSZ surface by polydopamine to facilitate the biomineralization of apatite layer on top of the coated film has incessantly been studied. In this study YSZ discs were first immersed in 2 mg/mL of stirred dopamine solution at coating temperatures between 25 and 80 °C. The specimens were then incubated for 7d in 1.5 SBF. The effect of coating temperature on the properties (chemical compositions and wettability) and the apatite mineralization on top of the generated films was investigated. It was found that at 50 °C, the specimen displayed the highest intensity of Ca 2p peak (1.55 ± 0.42 cps) with Ca/P ratio of 1.67 due to the presence of abundant quinone groups (Cdbnd O). However, the hydrophilicity (40.9 ± 01.7°) was greatly improved at 60 °C accompanied by the highest film thickness of 306 nm. Therefore, it was concluded that the presence of high intensity of quinone groups (Cdbnd O) in polydopamine film at elevated temperature affects the chelation of Ca2+ ions and thus enhance the growth of apatite layer on top of the functionalized YSZ surface.

  11. Thermal Stability Study from Room Temperature to 1273 K (1000 °C) in Magnesium Silicide

    NASA Astrophysics Data System (ADS)

    Stefanaki, Eleni-Chrysanthi; Hatzikraniotis, Euripides; Vourlias, George; Chrissafis, Konstantinos; Kitis, George; Paraskevopoulos, Konstantinos M.; Polymeris, George S.

    2016-10-01

    Doped magnesium silicide has been identified as a promising and environmentally friendly advanced thermoelectric material in the temperature range between 500 K and 800 K (227 °C and 527 °C). Besides the plethora of magnesium silicide thermoelectric advantages, it is well known for its high sensitivity to oxidation. Oxidation is one of the primary instability mechanisms of degradation of high-temperature Mg2Si thermoelectric devices, as in the presence of O2, Mg2Si decomposes to form MgO and Si. In this work, commercial magnesium silicide in bulk form was used for thermal stability study from room temperature to 1273 K (1000 °C). Various techniques such as DTA-TG, PXRD, and FTIR have been applied. Moreover, the application of thermoluminescence (TL) as an effective and alternative probe for the study of oxidation and decomposition has been exploited. The latter provides qualitative but very helpful hints toward oxidation studies. The low-detection threshold of thermoluminescence, in conjunction with the chemical composition of the oxidation byproducts, consisting of MgO, Mg2SiO4, and SiO2, constitute two powerful motivations for further investigating its viable use as proxy for instability/decomposition studies of magnesium silicide. The partial oxidation reaction has been adopted due to the experimental fact that magnesium silicide is monitored throughout the heating temperature range of the present study. Finally, the role of silicon dioxide to the decomposition procedure, being in amorphous state and gradually crystallizing, has been highlighted for the first time in the literature. Mg2Si oxidation takes place in two steps, including a mild oxidation process with temperature threshold of 573 K (300 °C) and an abrupt one after 773 K (500 °C). Implications on the optimum operational temperature range for practical thermoelectric (TE) applications have also been briefly discussed.

  12. High Temperature Stability of Onion-Like Carbon vs Highly Oriented Pyrolytic Graphite

    PubMed Central

    Latini, Alessandro; Tomellini, Massimo; Lazzarini, Laura; Bertoni, Giovanni; Gazzoli, Delia; Bossa, Luigi; Gozzi, Daniele

    2014-01-01

    The thermodynamic stability of onion-like carbon (OLC) nanostructures with respect to highly oriented pyrolytic graphite (HOPG) was determined in the interval 765–1030 K by the electromotive force (emf) measurements of solid electrolyte galvanic cell: (Low) Pt|Cr3C2,CrF2,OLC|CaF2s.c.|Cr3C2,CrF2,HOPG|Pt (High). The free energy change of transformation HOPG = OLC was found positive below 920.6 K crossing the zero value at this temperature. Its trend with temperature was well described by a 3rd degree polynomial. The unexpected too high values of jointly to the HR-TEM, STEM and EELS evidences that showed OLC completely embedded in rigid cages made of a Cr3C2/CrF2 matrix, suggested that carbon in the electrodes experienced different internal pressures. This was confirmed by the evaluation under constant volume of by the ratio for OLC (0.5 MPa K−1) and HOPG (8 Pa K−1) where and are the isobaric thermal expansion and isothermal compressibility coefficients, respectively. The temperature dependency of the pressure was derived and utilized to calculate the enthalpy and entropy changes as function of temperature and pressure. The highest value of the internal pressure experienced by OLC was calculated to be about 7 GPa at the highest temperature. At 920.6 K, and values are 95.8 kJ mol−1 and 104.1 JK−1 mol−1, respectively. The surface contributions to the energetic of the system were evaluated and they were found negligible compared with the bulk terms. As a consequence of the high internal pressure, the values of the enthalpy and entropy changes were mainly attributed to the formation of carbon defects in OLC considered as multishell fullerenes. The change of the carbon defect fraction is reported as a function of temperature. PMID:25153181

  13. High Temperature Stability of Dissimilar Metal Joints in Fission Surface Power Systems

    NASA Technical Reports Server (NTRS)

    Locci, Ivan E.; Nesbitt, James A.; Ritzert, Frank J.; Bowman, Cheryl L.

    2007-01-01

    Future generations of power systems for spacecraft and lunar surface systems will likely require a strong dependence on nuclear power. The design of a space nuclear power plant involves integrating together major subsystems with varying materia1 requirements. Refractory alloys are repeatedly considered for major structural components in space power reactor designs because refractory alloys retain their strength at higher temperatures than other classes of metals. The relatively higher mass and lower ductility of the refractory alloys make them less attractive for lower temperature subsystems in the power plant such as the power conversion system. The power conversion system would consist more likely of intermediate temperature Ni-based superalloys. One of many unanswered questions about the use of refractory alloys in a space power plant is how to transition from the use of the structural refractory alloy to more traditional structural alloys. Because deleterious phases can form when complex alloys are joined and operated at elevated temperatures, dissimilar material diffusion analyses of refractory alloys and superalloys are needed to inform designers about options of joint temperature and operational lifetime. Combinations of four superalloys and six refractory alloys were bonded and annealed at 1150 K and 1300 K to examine diffusional interactions in this study. Joints formed through hot pressing and hot isostatic pressing were compared. Results on newer alloys compared favorably to historical data. Diffusional stability is promising for some combinations of Mo-Re alloys and superalloys at 1150 K, but it appears that lower joint temperatures would be required for other refractory alloy couples.

  14. Vapor-modulated heat pipe for improved temperature control

    NASA Technical Reports Server (NTRS)

    Edwards, D. K.; Eninger, J. E.; Ludeke, E. E.

    1978-01-01

    Dryout induced by vapor throttling makes control of equipment temperature less dependent on variations in sink environment. Mechanism controls flow of vapor in heat pipe by using valve in return path to build difference in pressure and also difference in saturation temperature of the vapor. In steady state, valve closes just enough to produce partial dryout that achieves required temperature drop.

  15. Vapor-modulated heat pipe for improved temperature control

    NASA Technical Reports Server (NTRS)

    Edwards, D. K.; Eninger, J. E.; Ludeke, E. E.

    1978-01-01

    Dryout induced by vapor throttling makes control of equipment temperature less dependent on variations in sink environment. Mechanism controls flow of vapor in heat pipe by using valve in return path to build difference in pressure and also difference in saturation temperature of the vapor. In steady state, valve closes just enough to produce partial dryout that achieves required temperature drop.

  16. Effect of synthetic temperature on the dispersion stability of gold nanocolloid produced via electrical explosion of wire.

    PubMed

    Yun, G S; Bac, L H; Kim, J S; Kwon, Y S; Choi, H S; Kim, J C

    2011-07-01

    In this study, gold nanocolloid was produced via the electrical explosion of wire in water, for the purpose of medical treatment. Thus, the use of other additives was avoided to stabilize the gold nanocolloid. The temperature of the water that was to be used for explosion was changed, and its effect on the stability of the gold nanocolloid was investigated. The synthetic temperature was varied from ice temperature to 80 degrees C. The morphology and particle size were studied using a transmission electron microscope. The UV-Vis spectra confirmed the formation of gold nanoparticles in the water. The stability of the gold nanocolloid was estimated using the zeta-potential and Turbiscan methods. The results showed that the synthetic temperature affected the stability of the gold nanocolloid. The TEM images of the gold nanoparticles prepared at low temperatures (0 and 20 degrees C) have several big particles. But, when the synthetic temperature was increased to 80 degrees C, most of the nanoparticles formed a spherical shape, without neck connection. Better stability was obtained in the gold nanocolloid sample prepared at a higher temperature. The gold nanocolloid that was synthesized at 80 degrees C was stable for more than three months, with small sedimentation.

  17. Improvement of helicopter attitude stability by active control of the conventional swash plate

    NASA Technical Reports Server (NTRS)

    Ham, Norman D.

    1993-01-01

    The Final Report on improvement of helicopter attitude stability by active control of the conventional swash plate covering the period from Nov. 1986 to Dec. 1993 is presented. A paper on the history, principles, and applications of helicopter individual-blade-control is included.

  18. Postural Stability in Parkinson's Disease Patients Is Improved after Stochastic Resonance Therapy.

    PubMed

    Kaut, Oliver; Brenig, Daniel; Marek, Milena; Allert, Niels; Wüllner, Ullrich

    2016-01-01

    Background. Postural instability in Parkinson's disease (PD) increases the risk of falls and is not improved by pharmacological therapy. Objective. We performed a double-blind, randomized sham-controlled study to test the effects of stochastic resonance (whole body vibration) therapy on postural stability in PD. Methods. Fifty-six PD participants were allocated to either experimental or sham groups. The experimental group received four series of vibration over eight days, with each series consisting of six stimulus trains of 60-second duration using a randomized whole body vibration. Participants allocated to the control group received a sham treatment. Results. Within-group analysis revealed that postural stability in the experimental group improved by 17.5% (p = 0.005) comparing experimental and sham groups. The between-group analysis of change after treatment comparing both groups also showed a significant improvement of postural stability (p = 0.03). Only in the within-group analysis several items were improved after Bonferroni correction, too, rigor 41.6% (p = 0.001), bradykinesia 23.7% (p = 0.001), tremor 30.8% (p = 0.006), and UPDRSIII sum score 23.9% (p = 0.000), but did not reach the level of significance in the between-group analysis. Conclusions. Stochastic resonance therapy significantly enhanced postural stability even in individuals with increased risk of falling. Thus it offers a potential supplementation to canonical treatments of PD.

  19. Cellulase variants with improved expression, activity and stability, and use thereof

    SciTech Connect

    Aehle, Wolfgang; Bott, Richard R.; Bower, Benjamin S.; Caspi, Jonathan; Goedegebuur, Frits; Hommes, Ronaldus Wilhelmus Joannes; Kaper, Thijs; Kelemen, Bradley R.; Kralj, Slavko; Van Lieshout, Johannes Franciscus Thomas; Nikolaev, Igor; Wallace, Louise; Van Stigt Thans, Sander; Vogtentanz, Gudrun; Sandgren, Mats

    2016-12-20

    The present disclosure relates to cellulase variants. In particular the present disclosure relates to cellulase variants having improved expression, activity and/or stability. Also described are nucleic acids encoding the cellulase variants, compositions comprising the cellulase variants, and methods of use thereof.

  20. Cellulase variants with improved expression, activity and stability, and use thereof

    DOEpatents

    Aehle, Wolfgang; Bott, Richard R; Bower, Benjamin; Caspi, Jonathan; Estell, David A; Goedegebuur, Frits; Hommes, Ronaldus W.J.; Kaper, Thijs; Kelemen, Bradley; Kralj, Slavko; Van Lieshout, Johan; Nikolaev, Igor; Van Stigt Thans, Sander; Wallace, Louise; Vogtentanz, Gudrun; Sandgren, Mats

    2014-03-25

    The present disclosure relates to cellulase variants. In particular the present disclosure relates to cellulase variants having improved expression, activity and/or stability. Also described are nucleic acids encoding the cellulase variants, compositions comprising the cellulase variants, and methods of use thereof.