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Sample records for substrate thermal resistance

  1. Thermal resistance optimization of GaN/substrate stacks considering thermal boundary resistance and temperature-dependent thermal conductivity

    NASA Astrophysics Data System (ADS)

    Park, K.; Bayram, C.

    2016-10-01

    Here, we investigate the effects of thermal boundary resistance (TBR) and temperature-dependent thermal conductivity on the thermal resistance of GaN/substrate stacks. A combination of parameters such as substrates {diamond, silicon carbide, silicon, and sapphire}, thermal boundary resistance {10-60 m2K/GW}, heat source lengths {10 nm-20 μm}, and power dissipation levels {1-8 W} are studied by using technology computer-aided design (TCAD) software Synopsys. Among diamond, silicon carbide, silicon, and sapphire substrates, the diamond provides the lowest thermal resistance due to its superior thermal conductivity. We report that due to non-zero thermal boundary resistance and localized heating in GaN-based high electron mobility transistors, an optimum separation between the heat source and substrate exists. For high power (i.e., 8 W) heat dissipation on high thermal conductive substrates (i.e., diamond), the optimum separation between the heat source and substrate becomes submicron thick (i.e., 500 nm), which reduces the hotspot temperature as much as 50 °C compared to conventional multi-micron thick case (i.e., 4 μm). This is attributed to the thermal conductivity drop in GaN near the heat source. Improving the TBR between GaN and diamond increases temperature reduction by our further approach. Overall, we provide thermal management design guidelines for GaN-based devices.

  2. Reduced thermal resistance of the silicon-synthetic diamond composite substrates at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Goyal, V.; Subrina, S.; Nika, D. L.; Balandin, A. A.

    2010-07-01

    The authors report results of experimental investigation of thermal conductivity of synthetic diamond-silicon composite substrates. Although composite substrates are more thermally resistive than silicon at room temperature they outperform conventional wafers at elevated temperatures owing to different thermal conductivity dependence on temperature. The crossover point is reached near ˜360 K and can be made even lower by tuning the polycrystalline-grain size, film thickness, and interface quality. The reduction of thermal resistance of composite wafers at temperatures, typical for operation of electronic chips, may lead to better thermal management and new phonon-engineered methods for the electron mobility enhancement.

  3. Oxidation resistant high temperature thermal cycling resistant coatings on silicon-based substrates and process for the production thereof

    DOEpatents

    Sarin, V.K.

    1990-08-21

    An oxidation resistant, high temperature thermal cycling resistant coated ceramic article for ceramic heat engine applications is disclosed. The substrate is a silicon-based material, i.e. a silicon nitride- or silicon carbide-based monolithic or composite material. The coating is a graded coating of at least two layers: an intermediate AlN or Al[sub x]N[sub y]O[sub z] layer and an aluminum oxide or zirconium oxide outer layer. The composition of the coating changes gradually from that of the substrate to that of the AlN or Al[sub x]N[sub y]O[sub z] layer and further to the composition of the aluminum oxide or zirconium oxide outer layer. Other layers may be deposited over the aluminum oxide layer. A CVD process for depositing the graded coating on the substrate is also disclosed.

  4. Oxidation resistant high temperature thermal cycling resistant coatings on silicon-based substrates and process for the production thereof

    DOEpatents

    Sarin, Vinod K.

    1990-01-01

    An oxidation resistant, high temperature thermal cycling resistant coated ceramic article for ceramic heat engine applications. The substrate is a silicon-based material, i.e. a silicon nitride- or silicon carbide-based monolithic or composite material. The coating is a graded coating of at least two layers: an intermediate AlN or Al.sub.x N.sub.y O.sub.z layer and an aluminum oxide or zirconium oxide outer layer. The composition of the coating changes gradually from that of the substrate to that of the AlN or Al.sub.x N.sub.y O.sub.z layer and further to the composition of the aluminum oxide or zirconium oxide outer layer. Other layers may be deposited over the aluminum oxide layer. A CVD process for depositing the graded coating on the substrate is also disclosed.

  5. Impact of substrate and thermal boundary resistance on the performance of AlGaN/GaN HEMTs analyzed by means of electro-thermal Monte Carlo simulations

    NASA Astrophysics Data System (ADS)

    García, S.; Íñiguez-de-la-Torre, I.; Mateos, J.; González, T.; Pérez, S.

    2016-06-01

    In this paper, we present results from the simulations of a submicrometer AlGaN/GaN high-electron-mobility transistor (HEMT) by using an in-house electro-thermal Monte Carlo simulator. We study the temperature distribution and the influence of heating on the transfer characteristics and the transconductance when the device is grown on different substrates (sapphire, silicon, silicon carbide and diamond). The effect of the inclusion of a thermal boundary resistance (TBR) is also investigated. It is found that, as expected, HEMTs fabricated on substrates with high thermal conductivities (diamond) exhibit lower temperatures, but the difference between hot-spot and average temperatures is higher. In addition, devices fabricated on substrates with higher thermal conductivities are more sensitive to the value of the TBR because the temperature discontinuity is greater in the TBR layer.

  6. Composite plasma electrolytic oxidation to improve the thermal radiation performance and corrosion resistance on an Al substrate

    NASA Astrophysics Data System (ADS)

    Kim, Donghyun; Sung, Dahye; Lee, Junghoon; Kim, Yonghwan; Chung, Wonsub

    2015-12-01

    A composite plasma electrolytic oxidation (PEO) was performed for enhancing the thermal radiation performance and corrosion resistance on an Al alloy by dispersing cupric oxide (CuO) particles in a conventional PEO electrolyte. Cu-based oxides (CuO and Cu2O) formed by composite PEO increased the emissivity of the substrate to 0.892, and made the surface being dark color, similar to a black body, i.e., an ideal radiator. In addition, the corrosion resistance was analyzed using potentio-dynamic polarization and electrochemical impedance spectroscopy tests in 3.5 wt.% NaCl aqueous solution. An optimum condition of 10 ampere per square decimeter (ASD) current density and 30 min processing time produced appropriate surface morphologies and coating thicknesses, as well as dense Cu- and Al-based oxides that constituted the coating layers.

  7. Method for improving the oxidation-resistance of metal substrates coated with thermal barrier coatings

    DOEpatents

    Thompson, Anthony Mark; Gray, Dennis Michael; Jackson, Melvin Robert

    2002-01-01

    A method for providing a protective coating on a metal-based substrate is disclosed. The method involves the application of an aluminum-rich mixture to the substrate to form a discontinuous layer of aluminum-rich particles, followed by the application of a second coating over the discontinuous layer of aluminum-rich particles. Aluminum diffuses from the aluminum-rich layer into the substrate, and into any bond coat layer which is subsequently applied. Related articles are also described.

  8. The Impact of GaN/Substrate Thermal Boundary Resistance on a HEMT Device

    DTIC Science & Technology

    2011-11-01

    stack between the GaN and Substrate layers. The University of Bristol recently reported that this TBR in commercial devices on Silicon Carbide ( SiC ...Circuit RF Radio Frequency PA Power Amplifier SiC Silicon Carbide FEA Finite Element Analysis heff Effective Heat transfer Coefficient (W/m 2 K...substrate material switched from sapphire to silicon , and by another factor of two from silicon to SiC . TABLE 1: SAMPLE RESULTS FROM DOUGLAS ET AL. FOR

  9. Method For Improving The Oxidation Resistance Of Metal Substrates Coated With Thermal Barrier Coatings

    DOEpatents

    Thompson, Anthony Mark; Gray, Dennis Michael; Jackson, Melvin Robert

    2003-05-13

    A method for providing a protective coating on a metal-based substrate is disclosed. The method involves the application of an aluminum-rich mixture to the substrate to form a discontinuous layer of aluminum-rich particles, followed by the application of a second coating over the discontinuous layer of aluminum-rich particles. Aluminum diffuses from the aluminum-rich layer into the substrate, and into any bond coat layer which is subsequently applied. Related articles are also described. A method for providing a protective coating on a metal-based substrate is disclosed. The method involves the application of an aluminum-rich mixture to the substrate to form a discontinuous layer of aluminum-rich particles, followed by the application of a second coating over the discontinuous layer of aluminum-rich particles. Aluminum diffuses from the aluminum-rich layer into the substrate, and into any bond coat layer which is subsequently applied. Related articles are also described.

  10. Substrate effect in chemically amplified resist

    NASA Astrophysics Data System (ADS)

    Mori, Shigeyasu; Watanabe, Takeo; Adachi, Kouichirou; Fukushima, Takashi; Uda, Keichiro; Sato, Yuichi

    1996-06-01

    SiN substrate effect in chemically amplified (CA) resist has been investigated by surface analysis and evaluating the pattern profile of CA negative tone resist. Fine profile can be replicated on SiN substrate treated with oxygen plasma optimized condition. Undercut profile can be affected by adsorbed materials on SiN substrate from thermal desorption spectroscopy (TDS) analysis results. From the results of electron spectroscopy for chemical analysis (ESCA), it is found that Si-N bonding is replaced to Si-O bonding while SiN substrate is treated with oxygen plasma. Relations between footing length and oxygen plasma treatment condition suggest that undercut profile due to the concentration of nitrogen on the surface of SiN substrate. At the interface between the SiN substrate and the CA resist, the SiN substrate works as base existing water, and quenches photo-generated-acids. The mechanism of substrate effect of SiN is clarified. Reducing the SiN-substrate effect by treating the surface with oxygen plasma, fine resist pattern without undercut and footing is formed on SiN substrate.

  11. Intensified magneto-resistance by rapid thermal annealing in magnetite (Fe3O4) thin film on SiO2 glass substrate

    NASA Astrophysics Data System (ADS)

    Kobori, H.; Morii, K.; Yamasaki, A.; Sugimura, A.; Taniguchi, T.; Horie, T.; Naitoh, Y.; Shimizu, T.

    2012-12-01

    We have observed large magneto-resistance (MR) intensified by rapid thermal annealing (RTA) in magnetite (Fe3O4) thin film (MTF) on SiO2 glass (a-SiO2) substrate. The MTF was produced by the RF magnetron sputtering method by using a magnetite target. The electrical resistivity (ER) of as-grown MTF (AG-MTF) showed the Mott's variable range hopping behavior, which implies that the AG-MTF is amorphous-like. Although the magneto-resistance (MR) ratio of bulk single crystal is very small except around the Verwey transition temperature (VTT), that of the AG-MTF showed moderately large below room temperature. Due to RTA of the AG-MTF by use of an IR image furnace, the MR ratio of MTFs was intensified, and especially by the annealing around the Curie temperature (585°C) of magnetite. Furthermore the ER of the rapid thermally annealed MTF (RTA-MTF) showed a slight kink at around the VTT, which indicates that the crystallinity of the RTA-MTF is higher than that of the AG-MTF The MTF produced by the RF magnetron sputtering method are composed of magnetite fine particles (MFPs). We consider that the directions of magnetic moments of MFPs in the MTF were spatially randomized by the RTA and the strong spin scattering of itinerant electrons transferring between adjacent MFPs caused the intensification of the MR ratio.

  12. Ink for Ink-Jet Printing of Electrically Conductive Structures on Flexible Substrates with Low Thermal Resistance

    NASA Astrophysics Data System (ADS)

    Mościcki, A.; Smolarek-Nowak, A.; Felba, J.; Kinart, A.

    2017-02-01

    The development of new technologies in electronics related to flexible polymeric substrates forces the industry to introduce suitable tools (special type of dispensers) and modern conductive materials for printing electronic circuits. Moreover, due to the wide use of inexpensive polymeric foils (polyethene, PE, or poly(ethylene terephthalate), PET), there is a need to develop materials with the lowest possible processing temperatures. The present paper presents the selection criteria of suitable components and their preparation for obtaining electrically conductive ink with a special nanosilver base. In the case of the discussed solution, all components allow to make circuits in relatively low sintering temperature (even below 130°C). Additionally, the authors show the most significant ink parameters that should be taken into consideration during Research and Development (R&D) works with electrically conductive inks. Moreover, ink stability parameters are discussed and some examples of printed circuits are presented.

  13. Thermally Stable, Piezoelectric and Pyroelectric Polymeric Substrates

    NASA Technical Reports Server (NTRS)

    Simpson, Joycely O. (Inventor); St.Clair, Terry L. (Inventor)

    1999-01-01

    A thermally stable, piezoelectric and pyroelectric polymeric substrate was prepared. This thermally stable, piezoelectric and pyroelectric polymeric substrate may be used to prepare electromechanical transducers, thermomechanical transducers, accelerometers. acoustic sensors, infrared sensors, pressure sensors, vibration sensors, impact sensors, in-situ temperature sensors, in-situ stress/strain sensors, micro actuators, switches, adjustable fresnel lenses, speakers, tactile sensors. weather sensors, micro positioners, ultrasonic devices, power generators, tunable reflectors, microphones, and hydrophones. The process for preparing these polymeric substrates includes: providing a polymeric substrate having a softening temperature greater than 1000 C; depositing a metal electrode material onto the polymer film; attaching a plurality of electrical leads to the metal electrode coated polymeric substrate; heating the metal electrode coated polymeric substrate in a low dielectric medium; applying a voltage to the heated metal electrode coated polymeric substrate to induce polarization; and cooling the polarized metal electrode coated polymeric electrode while maintaining a constant voltage.

  14. Empirical model building based on Weibull distribution to describe the joint effect of pH and temperature on the thermal resistance of Bacillus cereus in vegetable substrate.

    PubMed

    Fernández, A; Collado, J; Cunha, L M; Ocio, M J; Martínez, A

    2002-07-25

    A mathematical model based on Weibull parameters was built to describe the joint effect of temperature and pH on thermal inactivation of Bacillus cereus spores (strain INRA TZ415). The effect of these factors on Weibull model parameters (beta, 1/alpha) was also studied. Heat inactivation tests were carried out in acidified carrot broth as vegetable substrate, following a full factorial design at four levels for temperature (80, 85, 90 and 95 degrees C) and pH (6.2, 5.8, 5.2 and 4.7). The Weibull distribution model provided good individual fits for the different combinations of temperature-pH tested, with discrepancy factors, Df, coming close to 25% for most cases. The temperature and pH did not have a significant effect on the shape parameter (beta), which yielded a mean value of 0.88. The scale parameter (alpha) decreased with pH, and its inverse (1/alpha) followed an Arrhenius-type relationship with temperature. A global model was built, including the dependence of the alpha parameter on temperature and pH, and the model parameters were estimated by using a one-step nonlinear least-squares regression to improve the precision of the estimates. Results indicated that the global model provides a satisfactory description of the thermal inactivation of B. cereus spores, with R2 equal to 0.983.

  15. Substrate size mediates thermal stress in the rocky intertidal.

    PubMed

    Gedan, Keryn B; Bernhardt, Joanna; Bertness, Mark D; Leslie, Heather M

    2011-03-01

    Variation in physical factors, such as slope, orientation, and wind exposure, shapes thermal conditions. Variation in substrate size is common in many habitats, but its thermal consequences for organisms are not well characterized. Larger substrates should remain more thermally stable and act as thermal refuges for associated organisms during short, thermally stressful periods such as midday temperature peaks or tidal exposure. In observations and a transplant and thermal integration experiment, we found that larger rock substrates stayed cooler and facilitated greater survival of the barnacle Semibalanus balanoides in the high intertidal relative to small substrates during the hot summer months in southern New England, USA. However, in thermally benign northern New England, rock substrate size had no effect on barnacle distributions, indicating that the thermal effects of substrate size are mediated by regional climate.

  16. Low thermal resistance power module assembly

    DOEpatents

    Hassani, Vahab; Vlahinos, Andreas; Bharathan, Desikan

    2007-03-13

    A power module assembly with low thermal resistance and enhanced heat dissipation to a cooling medium. The assembly includes a heat sink or spreader plate with passageways or openings for coolant that extend through the plate from a lower surface to an upper surface. A circuit substrate is provided and positioned on the spreader plate to cover the coolant passageways. The circuit substrate includes a bonding layer configured to extend about the periphery of each of the coolant passageways and is made up of a substantially nonporous material. The bonding layer may be solder material which bonds to the upper surface of the plate to provide a continuous seal around the upper edge of each opening in the plate. The assembly includes power modules mounted on the circuit substrate on a surface opposite the bonding layer. The power modules are positioned over or proximal to the coolant passageways.

  17. Measuring thermal conductivity of thin films by Scanning Thermal Microscopy combined with thermal spreading resistance analysis.

    PubMed

    Juszczyk, J; Kaźmierczak-Bałata, A; Firek, P; Bodzenta, J

    2017-01-27

    While measuring the thermal properties of a thin film, one of the most often encountered problems is the influence of the substrate thermal properties on measured signal and the need for its separation. In this work an approach for determining the thermal conductivity κ of a thin layer is presented. It bases on Scanning Thermal Microscopy (SThM) measurement combined with thermal spreading resistance analysis for a system consisting of a single layer on a substrate. Presented approach allows to take into account the influence of the substrate thermal properties on SThM signal and to estimate the true value of a thin film κ. It is based on analytical solution of the problem being a function of dimensionless parameters and requires numerical solution of relatively simple integral equation. As the analysis utilizes a solution in dimensionless parameters it can be used for any substrate-layer system. As an example, the method was applied for determination of the thermal conductivities of 4 different thin layers of thicknesses from 12 to 100nm. The impact of model parameters on the uncertainty of the estimated final κ value was analyzed.

  18. Temperature Dependent Thermal Conductivity and Thermal Interface Resistance of Pentacene Thin Films with Varying Morphology.

    PubMed

    Epstein, Jillian; Ong, Wee-Liat; Bettinger, Christopher J; Malen, Jonathan A

    2016-07-27

    Temperature dependent thermal conductivities and thermal interface resistances of pentacene (Pn) thin films deposited on silicon substrates and self-assembled monolayer-modified [octadecyltrichlorosilane (OTS) and (3-aminopropyl)triethoxysilane (APTES)] silicon substrates were measured using frequency domain thermoreflectance. Atomic force microscopy images were used to derive an effective film thickness for thermal transport that accounts for surface roughness. Data taken over a temperature range of 77-300 K for various morphologies and film thicknesses show that the thermal conductivity increases with increasing Pn grain size. The sum of the substrate-Pn and Pn-gold thermal interface resistances was isolated from the intrinsic thermal resistance of the Pn films and found to be independent of surface chemistry. Corresponding Kapitza lengths of approximately 150 nm are larger than the physical thicknesses of typical Pn thin films and indicate that the interfaces play a dominant role in the total thermal resistance. This study has implications for increasing the performance and effective thermal management of small molecule electronic and energy conversion devices.

  19. Thermal Shock-resistant Cement

    SciTech Connect

    Sugama T.; Pyatina, T.; Gill, S.

    2012-02-01

    We studied the effectiveness of sodium silicate-activated Class F fly ash in improving the thermal shock resistance and in extending the onset of hydration of Secar #80 refractory cement. When the dry mix cement, consisting of Secar #80, Class F fly ash, and sodium silicate, came in contact with water, NaOH derived from the dissolution of sodium silicate preferentially reacted with Class F fly ash, rather than the #80, to dissociate silicate anions from Class F fly ash. Then, these dissociated silicate ions delayed significantly the hydration of #80 possessing a rapid setting behavior. We undertook a multiple heating -water cooling quenching-cycle test to evaluate the cement’s resistance to thermal shock. In one cycle, we heated the 200 and #61616;C-autoclaved cement at 500 and #61616;C for 24 hours, and then the heated cement was rapidly immersed in water at 25 and #61616;C. This cycle was repeated five times. The phase composition of the autoclaved #80/Class F fly ash blend cements comprised four crystalline hydration products, boehmite, katoite, hydrogrossular, and hydroxysodalite, responsible for strengthening cement. After a test of 5-cycle heat-water quenching, we observed three crystalline phase-transformations in this autoclaved cement: boehmite and #61614; and #61543;-Al2O3, katoite and #61614; calcite, and hydroxysodalite and #61614; carbonated sodalite. Among those, the hydroxysodalite and #61614; carbonated sodalite transformation not only played a pivotal role in densifying the cementitious structure and in sustaining the original compressive strength developed after autoclaving, but also offered an improved resistance of the #80 cement to thermal shock. In contrast, autoclaved Class G well cement with and without Class F fly ash and quartz flour failed this cycle test, generating multiple cracks in the cement. The major reason for such impairment was the hydration of lime derived from the dehydroxylation of portlandite formed in the autoclaved

  20. Method of Making Thermally Stable, Piezoelectric and Proelectric Polymeric Substrates

    NASA Technical Reports Server (NTRS)

    Simpson, Joycelyn O. (Inventor); St.Clair, Terry L. (Inventor)

    1999-01-01

    A thermally stable, piezoelectric and pyroelectric polymeric substrate was prepared. This thermally stable, piezoelectric and pyroelectric polymeric substrate may be used to prepare electromechanical transducers, thermomechanical transducers, accelerometers, acoustic sensors, infrared sensors, pressure sensors, vibration sensors, impact sensors. in-situ temperature sensors, in-situ stress/strain sensors, micro actuators, switches, adjustable fresnel lenses, speakers, tactile sensors, weather sensors, micro positioners, ultrasonic devices, power generators, tunable reflectors, microphones, and hydrophones. The process for preparing these polymeric substrates includes: providing a polymeric substrate having a softening temperature greater than 100 C; depositing a metal electrode material onto the polymer film; attaching a plurality of electrical leads to the metal electrode coated polymeric substrate; heating the metal electrode coated polymeric substrate in a low dielectric medium: applying a voltage to the heated metal electrode coated polymeric substrate to induce polarization; and cooling the polarized metal electrode coated polymeric electrode while maintaining a constant voltage.

  1. Thermal effects of the substrate on water droplet evaporation

    NASA Astrophysics Data System (ADS)

    Sobac, B.; Brutin, D.

    2012-08-01

    We experimentally investigate the behavior of a pinned water droplet evaporating into air. The influence of the substrate temperature and substrate thermal properties on the evaporation process are studied in both hydrophilic and hydrophobic conditions. Our objective is to understand the effect of thermal mechanisms on the droplet evaporation process. The experimental results are compared with the quasisteady, diffusion-driven evaporation model, which is implemented under the influence of the temperature; the model assumes the isothermia of the droplet at the substrate temperature. The results highlight a favorable correlation between the model and the experimental data at ambient temperatures for most situations considered here. The model works to qualitatively describe the influence of the substrate temperature on the evaporation process. However, with an increase in the substrate temperature, the role of the thermal-linked mechanisms becomes increasingly important; this experiment highlights the need for more accurate models to account for the buoyant convection in vapor transport and the evaporative cooling and heat conduction between the droplet and the substrate. Finally, the experimental data reveal the modification of contact angle evolution as the temperature increases and the crucial role played by the nature of the substrate in the evaporation of a sessile droplet. The influence of the substrate thermal properties on the global evaporation rate is explained by the parallel thermal effusivity of the liquid and solid phases.

  2. Thermal Effects of the Substrate on Water Droplet Evaporation

    NASA Astrophysics Data System (ADS)

    Sobac, Benjamin; Brutin, David

    2012-11-01

    Since a few decades, the evaporation of a drop deposited onto a substrate has been subject to numerous research activities due to the increase of the range of applications underpinned by this phenomenon. However, this process today is always a challenging problem in soft matter physics due to the complexity of present couplings: fluid dynamic, physical chemistry of the substrate, heat and mass transfer. The originality of the presented experiment is to decouple the effects of wetting properties and thermal properties of the substrate. Thus, whereas we previously presented the role of wetting properties on evaporation by changing the surface energy and the roughness while maintaining the thermal properties constant thanks to nanoscale coatings on the substrate surface (B. Sobac and D. Brutin, Langmuir 27, 14999 (2011)), we investigate here the influence of the thermal properties of the substrate while keeping the wetting properties the same (B. Sobac and D. Brutin, Phys. Rev. E, underpress). We experimentally investigate the behavior of a pinned droplet evaporating into air. The influences of the substrate temperature and substrate thermal properties on the evaporation process are studied in both hydrophilic and hydrophobic conditions. Experimental data are compared to the quasi-steady diffusion-driven evaporation model assuming the isothermia of the drop at the substrate temperature. This comparison permits to highlights several thermal mechanisms linked to evaporation and their respective contributions in regard of pure mass diffusion mechanism. The range of validity of the classical evaporation model is also discussed.

  3. Low thermal resistance power module assembly

    DOEpatents

    Hassani, Vahab; Vlahinos, Andreas; Bharathan, Desikan

    2010-12-28

    A power module assembly (400) with low thermal resistance and enhanced heat dissipation to a cooling medium. The assembly includes a heat sink or spreader plate (410) with passageways or openings (414) for coolant that extend through the plate from a lower surface (411) to an upper surface (412). A circuit substrate (420) is provided and positioned on the spreader plate (410) to cover the coolant passageways. The circuit substrate (420) includes a bonding layer (422) configured to extend about the periphery of each of the coolant passageways and is made up of a substantially nonporous material. The bonding layer (422) may be solder material which bonds to the upper surface (412) of the plate to provide a continuous seal around the upper edge of each opening (414) in the plate. The assembly includes power modules (430) mounted on the circuit substrate (420) on a surface opposite the bonding layer (422). The power modules (430) are positioned over or proximal to the coolant passageways.

  4. An aluminum resist substrate for microfabrication by LIGA.

    SciTech Connect

    Kelly, James J.; Boehme, Dale R.; Hauck, Cheryl A.; Yang, Chu-Yeu Peter; Hunter, Luke L.; Griffiths, Stewart K.; McLean, Dorrance E.; Aigeldinger, Georg; Hekmaty, Michelle A.; Hachman, John T.; Losey, Matthew W.; Skala, Dawn M.; Korellis, John S.; Friedmann, Thomas Aquinas; Yang, Nancy Y. C.; Lu, Wei-Yang

    2005-04-01

    Resist substrates used in the LIGA process must provide high initial bond strength between the substrate and resist, little degradation of the bond strength during x-ray exposure, acceptable undercut rates during development, and a surface enabling good electrodeposition of metals. Additionally, they should produce little fluorescence radiation and give small secondary doses in bright regions of the resist at the substrate interface. To develop a new substrate satisfying all these requirements, we have investigated secondary resist doses due to electrons and fluorescence, resist adhesion before exposure, loss of fine features during extended development, and the nucleation and adhesion of electrodeposits for various substrate materials. The result of these studies is a new anodized aluminum substrate and accompanying methods for resist bonding and electrodeposition. We demonstrate successful use of this substrate through all process steps and establish its capabilities via the fabrication of isolated resist features down to 6 {micro}m, feature aspect ratios up to 280 and electroformed nickel structures at heights of 190 to 1400 {micro}m. The minimum mask absorber thickness required for this new substrate ranges from 7 to 15 {micro}m depending on the resist thickness.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  6. Thermal shock resistance ceramic insulator

    DOEpatents

    Morgan, Chester S.; Johnson, William R.

    1980-01-01

    Thermal shock resistant cermet insulators containing 0.1-20 volume % metal present as a dispersed phase. The insulators are prepared by a process comprising the steps of (a) providing a first solid phase mixture of a ceramic powder and a metal precursor; (b) heating the first solid phase mixture above the minimum decomposition temperature of the metal precursor for no longer than 30 minutes and to a temperature sufficiently above the decomposition temperature to cause the selective decomposition of the metal precursor to the metal to provide a second solid phase mixture comprising particles of ceramic having discrete metal particles adhering to their surfaces, said metal particles having a mean diameter no more than 1/2 the mean diameter of the ceramic particles, and (c) densifying the second solid phase mixture to provide a cermet insulator having 0.1-20 volume % metal present as a dispersed phase.

  7. Thermal contact resistance across a copper-silicon interface

    SciTech Connect

    Khounsary, A.M.; Chojnowski, D.; Assoufid, L.; Worek, W.M.

    1997-10-01

    The issue of thermal contact resistance across metallic interfaces has been investigated for many situations over the past several decades. The application in the present case is contact cooling of high heat load optical substrates. High heat load x-ray mirrors and other optical components used at the Advanced Photon Source (APS) are either internally cooled or contact cooled. In the internally cooled mirrors, a coolant flows through passages configured in the optical substrate. In the contact-cooled case, cooling is provided by placing cooling plates in contact with the mirror to extract the heat. Here, an experimental setup to measure the thermal contact conductance across a silicon-copper (Si-Cu) interface is described, and the results obtained are presented. The resulting thermal contact resistance data are used in estimating the thermo-mechanical and optical performance of optical substrates cooled by interfaced copper cooling blocks. Several factors influence the heat transfer across solid interfaces. These include the material properties, interface pressure, flatness and roughness of the contacting surfaces, temperature, and interstitial material, if any. Results presented show the variation of thermal contact conductance as a function of applied interface pressure for a Cu-Si interface. Various interstitial materials investigated include indium foil, silver foil and a liquid eutectic (Ga-In-Sn). As expected, thermal contact resistance decreases as interface pressure increases, except in the case of the eutectic, in which it was nearly constant. The softer the interstitial material, the lower the thermal contact resistance. Liquid metal provides the lowest thermal contact resistance across the Cu-Si interface, followed by the indium foil, and then the silver foil.

  8. Thermally tunable water-substrate broadband metamaterial absorbers

    NASA Astrophysics Data System (ADS)

    Pang, Yongqiang; Wang, Jiafu; Cheng, Qiang; Xia, Song; Zhou, Xiao Yang; Xu, Zhuo; Cui, Tie Jun; Qu, Shaobo

    2017-03-01

    The naturally occurring water has frequency dispersive permittivity at microwave frequencies and thus is a promising constituent material for broadband absorbers. Here, we develop water as the dielectric spacer in the substrate of metal-backed metamaterial (MM) absorbers. The designed substrate is a hybrid of water and a low-permittivity dielectric material. Such a design allows tight packaging of water and easy fabrication of the absorber. We obtain broadband absorption at temperatures of interest by designing the hybrid substrate and MM inclusions. Additionally, the absorption performance of the water-substrate MM absorbers could be tunable according to the environment temperature. We experimentally demonstrate the broadband and thermally tunable absorption performance. We expect that water could replace dielectric layers in other structural MM absorbers to achieve the broadband and thermally tunable absorption performance.

  9. Evaluation of thermal barrier coating systems on novel substrates

    NASA Astrophysics Data System (ADS)

    Pint, B. A.; Wright, I. G.; Brindley, W. J.

    2000-06-01

    Testing was conducted on both plasma-sprayed (PS) and electron beam-physical vapor deposited (EB-PVD) Y2O3-stabilized ZrO2 (YSZ) thermal barrier coatings (TBCs) applied directly to oxidation-resistant substrates such as β-NiAl, oxide-dispersed FeCrAl, and NiCr. On an alloy that forms a very adherent alumina scale, β-NiAl+Zr, the coating lifetime of YSZ in furnace cyclic tests was 6 or more times longer than on state-of-the-art, YSZ coatings on single-crystal Ni-base superalloys with MCrAlY or Pt aluminide bond coats. Coatings on FeCrAl alloys appear to be a viable option for applications such as the external skin of the X-33, single stage to orbit, reusable launch vehicle. Model chromia-forming bond coat compositions also show promise for power generation applications at temperatures where hot corrosion may be a major problem. In general, while this work examined unique materials systems, many of the same fundamental failure mechanisms observed in conventional TBCs were observed.

  10. Thermal boundary resistance from transient nanocalorimetry: A multiscale modeling approach

    NASA Astrophysics Data System (ADS)

    Caddeo, Claudia; Melis, Claudio; Ronchi, Andrea; Giannetti, Claudio; Ferrini, Gabriele; Rurali, Riccardo; Colombo, Luciano; Banfi, Francesco

    2017-02-01

    The thermal boundary resistance at the interface between a nanosized Al film and an Al2O3 substrate is investigated at an atomistic level. The thermal dynamics occurring in time-resolved thermoreflectance experiments is then modeled via macrophysics equations upon insertion of the materials parameters obtained from atomistic simulations. Electrons and phonons nonequilibrium and spatiotemporal temperatures inhomogeneities are found to persist up to the nanosecond time scale. These results question the validity of the commonly adopted lumped thermal capacitance model in interpreting transient nanocalorimetry experiments. The strategy adopted in the literature to extract the thermal boundary resistance from transient reflectivity traces is revised in the light of the present findings. The results are of relevance beyond the specific system, the physical picture being general and readily extendable to other heterojunctions.

  11. RESISTIVITY OF A THIN FILM DEPOSITED ON A CONDUCTIVE SUBSTRATE

    NASA Technical Reports Server (NTRS)

    Oberle, L. G.

    1994-01-01

    Resistivity of a Thin Film Deposited on a Conductive Substrate is a computer program developed to aid in the solution of the class of problems where resistivity measurements are needed for a substance deposited on a substrate of higher resistivity than the deposited layer. One of the ways in which a semiconductor material is characterized is by measurement of its resistivity. In the development of silicon carbide (SiC) for use as a semiconductor material for high temperature applications, it became necessary to measure the resistivity of the thin SiC film while it was still attached to the silicon upon which it had been grown epitaxially. The problem is that the presence of the silicon substrate will introduce error in the measured resistivity of the SiC. This program assumes that the resistivity of a thin film of conducting material deposited on another layer of conducting material is measured using the four-point probe. Using the four-point probe measurements, this program calculates the "true" resistivity of the deposited layer on a substrate of finite and different resistivity. Starting from basic principles, an expression for the ratio of measured voltage difference to injected current is developed. This expression involves the probe spacing, relative thicknesses of the layers, and the substrate resistivity as parameters, as well as the unknown resistivity of the deposited layer. The unknown resistivity can be found by iteratively evaluating the theoretical expression. This must be done numerically. The program is written in FORTRAN 77 and targeted for use on an IBM PC or compatible. It can be modified for use on any machine with a FORTRAN 77 compiler. It requires 46K of memory and has been implemented under MS-DOS 3.2.1. The program was developed in 1986.

  12. Thermal transport across a substrate-thin-film interface: effects of film thickness and surface roughness.

    PubMed

    Liang, Zhi; Sasikumar, Kiran; Keblinski, Pawel

    2014-08-08

    Using molecular dynamics simulations and a model AlN-GaN interface, we demonstrate that the interfacial thermal resistance R(K) (Kapitza resistance) between a substrate and thin film depends on the thickness of the film and the film surface roughness when the phonon mean free path is larger than film thickness. In particular, when the film (external) surface is atomistically smooth, phonons transmitted from the substrate can travel ballistically in the thin film, be scattered specularly at the surface, and return to the substrate without energy transfer. If the external surface scatters phonons diffusely, which is characteristic of rough surfaces, R(K) is independent of film thickness and is the same as R(K) that characterizes smooth surfaces in the limit of large film thickness. At interfaces where phonon transmission coefficients are low, the thickness dependence is greatly diminished regardless of the nature of surface scattering. The film thickness dependence of R(K) is analogous to the well-known fact of lateral thermal conductivity thickness dependence in thin films. The difference is that phonon-boundary scattering lowers the in-plane thermal transport in thin films, but it facilitates thermal transport from the substrate to the thin film.

  13. Graphene photoconductors fabricated on the substrates with different resistivity

    NASA Astrophysics Data System (ADS)

    Ruta, Lukasz; Wozny, Janusz; Lisik, Zbigniew; Podgorski, Jacek; Piotrowski, Jozef; Pawluczyk, Jaroslaw; Stepien, Dawid; Zeranska, Klaudia

    2016-12-01

    In this paper, the results of the initial work on determining the photoelectric properties of graphene detector operating in a photoconductive mode are presented. Graphene is considered as a material for uncooled fast detectors. The investigation has been done by electrical and optical characterization. Two values of substrate resistivity have been used in the project - below 1 Ωcm and higher than 1.6 kΩcm. Measurements of detectors response to short, strong light pulses were conducted. Presented studies show that the use of high resistivity substrates is necessary to prevent capacitive shorting of the signal to the substrate, causing signal losses and increasing response time.

  14. Smoother Turbine Blades Resist Thermal Shock Better

    NASA Technical Reports Server (NTRS)

    Czerniak, Paul; Longenecker, Kent; Paulus, Don; Ullman, Zane

    1991-01-01

    Surface treatment increases resistance of turbine blades to low-cycle fatigue. Smoothing removes small flaws where cracks start. Intended for blades in turbines subject to thermal shock of rapid starting. No recrystallization occurs at rocket-turbine operating temperatures.

  15. Gas microstrip detectors on resistive plastic substrates

    SciTech Connect

    Dixit, M.S.; Oakham, F.G.; Armitage, J.C.

    1993-12-31

    Plastics are desirable as substrates for gas microstrip detectors (GMDs) because of their flexibility, low density and long radiation length. GMDs have been fabricated on white Tedlar which has bulk electrical conductivity and ion-implanted Upilex which has a thin electrically conductive layer on the surface of an insulator. The effect of back plane voltage on the gain of such GMDs is investigated. Three 200 {mu}m pitch, ion-implanted Upilex GMDs were recently tested in a high intensity beam at CERN. The anode signals were read out using fast, low noise, high gain amplifiers. Preliminary results of the test are presented.

  16. Thermal Fracture and Thermal Shock Resistance of Functionally Graded Materials

    NASA Astrophysics Data System (ADS)

    Jin, Z.-H.; Batra, R. C.

    We first analyze thermal stresses and thermal cracking in a strip of a functionally graded material (FGM) subjected to sudden cooling. It is assumed that the shear modulus of the material decreases hyperbolically with the higher value occurring at the surface exposed to the thermal shock and that thermal conductivity varies exponentially. It is shown that the maximum tensile thermal stress induced in the strip is substantially reduced by the presumed thermal conductivity gradient. Thermal stress intensity factors (TSIFs) are also calculated for an edge crack at the surface exposed to the thermal shock and results show that while the TSIF is relatively insensitive to the shear modulus gradient, it is significantly reduced by the thermal conductivity gradient. The crack growth resistance curve of a ceramic-metal FGM is also studied and it is found that the FGM exhibits strong R-curve behavior when a crack grows from the ceramic-rich region into the metalrich region. Finally, the thermal shock resistance of FGMs is discussed.

  17. Quantitative scanning thermal microscopy of graphene devices on flexible polyimide substrates

    NASA Astrophysics Data System (ADS)

    Sadeghi, Mir Mohammad; Park, Saungeun; Huang, Yu; Akinwande, Deji; Yao, Zhen; Murthy, Jayathi; Shi, Li

    2016-06-01

    A triple-scan scanning thermal microscopy (SThM) method and a zero-heat flux laser-heated SThM technique are investigated for quantitative thermal imaging of flexible graphene devices. A similar local tip-sample thermal resistance is observed on both the graphene and metal areas of the sample, and is attributed to the presence of a polymer residue layer on the sample surface and a liquid meniscus at the tip-sample junction. In addition, it is found that the tip-sample thermal resistance is insensitive to the temperature until it begins to increase as the temperature increases to 80 °C and exhibits an abrupt increase at 110 °C because of evaporation of the liquid meniscus at the tip-sample junction. Moreover, the variation in the tip-sample thermal resistance due to surface roughness is within the experimental tolerance except at areas with roughness height exceeding tens of nanometers. Because of the low thermal conductivity of the flexible polyimide substrate, the SThM measurements have found that the temperature rise in flexible graphene devices is more than one order of magnitude higher than those reported for graphene devices fabricated on a silicon substrate with comparable dimensions and power density. Unlike a graphene device on a silicon substrate where the majority of the electrical heating in the graphene device is conducted vertically through the thin silicon dioxide dielectric layer to the high-thermal conductivity silicon substrate, lateral heat spreading is important in the flexible graphene devices, as shown by the observed decrease in the average temperature rise normalized by the power density with decreasing graphene channel length from about 30 μm to 10 μm. However, it is shown by numerical heat transfer analysis that this trend is mainly caused by the size scaling of the thermal spreading resistance of the polymer substrate instead of lateral heat spreading by the graphene. In addition, thermoelectric effects are found to be negligible

  18. Thermal interaction between WC-Co coating and steel substrate in process of HVOF spraying

    SciTech Connect

    Guilemany, J.M.; Sobolev, V.V.; Nutting, J.; Dong, Z.; Calero, J.A. . Metalurgia Fisica-Ciencia de Materials)

    1994-10-01

    The WC-Co powders can be used to produce good adhesive and wear resistant HVOF thermal spray coatings on steel and light alloys substrates. In order to understand the properties of this kind of coating, the phases which are present in the coatings and structure changes during post heat treatments have been investigated. Although the coating properties depend very much on the structure developed in the substrate-coating interfacial region it has not been yet investigated in detail. The present study is devoted to the experimental and theoretical analysis of this interfacial region. The structure characterization has been performed mainly through the use of transmission electron microscopy. To provide a theoretical investigation a realistic prediction model of the process has been developed and on its base the mathematical simulation of the substrate-coating thermal interaction has been undertaken.

  19. Thermal conductivity measurement and interface thermal resistance estimation using SiO2 thin film.

    PubMed

    Chien, Heng-Chieh; Yao, Da-Jeng; Huang, Mei-Jiau; Chang, Tien-Yao

    2008-05-01

    In this paper, we describe an easy-to-use method to measure the thermal conductivity of thin films based on an electrical heating/sensing mechanism and a steady-state technique. The method used relative commonly used instruments, and without any signal processing circuit, is easy to be used in such thin-film thermal conductivity measurement. The SiO2 thin-film samples, prepared by thermal oxidation, plasma enhanced chemical vapor deposition (PECVD), and E-beam evaporator, were deposited on a silicon substrate. The apparent thermal conductivity, the intrinsic thermal conductivity of SiO2 films, and the total interface thermal resistance of the heater/SiO2/silicon system were evaluated. Our data showed agreement with those data obtained from previous literatures and from the 3 omega method. Furthermore, by using a sandwiched structure, the interface thermal resistance of Cr/PECVD SiO2 and PECVD SiO2/silicon were also separately evaluated in this work. The data showed that the interface thermal resistance of Cr/PECVD SiO2 (metal/dielectric) is about one order of magnitude larger than that of PECVD SiO2/silicon (dielectric/dielectric).

  20. Performance Analysis and Modeling of Thermally Sprayed Resistive Heaters

    NASA Astrophysics Data System (ADS)

    Lamarre, Jean-Michel; Marcoux, Pierre; Perrault, Michel; Abbott, Richard C.; Legoux, Jean-Gabriel

    2013-08-01

    Many processes and systems require hot surfaces. These are usually heated using electrical elements located in their vicinity. However, this solution is subject to intrinsic limitations associated with heating element geometry and physical location. Thermally spraying electrical elements directly on surfaces can overcome these limitations by tailoring the geometry of the heating element to the application. Moreover, the element heat transfer is maximized by minimizing the distance between the heater and the surface to be heated. This article is aimed at modeling and characterizing resistive heaters sprayed on metallic substrates. Heaters were fabricated by using a plasma-sprayed alumina dielectric insulator and a wire flame-sprayed iron-based alloy resistive element. Samples were energized and kept at a constant temperature of 425 °C for up to 4 months. SEM cross-sectional observations revealed the formation of cracks at very specific locations in the alumina layer after thermal use. Finite-element modeling shows that these cracks originate from high local thermal stresses and can be predicted according to the considered geometry. The simulation model was refined using experimental parameters obtained by several techniques such as emissivity and time-dependent temperature profile (infra-red camera), resistivity (four-probe technique), thermal diffusivity (laser flash method), and mechanical properties (micro and nanoindentation). The influence of the alumina thickness and the substrate material on crack formation was evaluated.

  1. Thermal Barrier Coatings on Copper Substrates for Rocket Applications

    NASA Astrophysics Data System (ADS)

    Schloesser, Jana; Fedorova, Tatiana; Bäker, Martin; Rösler, Joachim

    Currently a new generation of relaunchable space transportation system using liquid hydrogen/ liquid oxygen rocket engines is under development. The inner combustion chamber is exposed to extreme thermal loads and environmental attack during starts. To prevent failure of the cooling channels, a thermal barrier coating to provide thermal and oxidation protection could be applied. Thermal barrier coatings are state of the art for gas turbines and this concept should be transferred to copper substrates in rocket engine applications. The thermomechanical loading conditions are quite different from the gas turbine applications as heat fluxes and temperature gradients are much higher while overall service time is much shorter. As a start for optimization of a suitable coating, a material system known for gas turbines is employed. In this work a thermal barrier coating system is applied by atmospheric plasma spraying to the copper-based high strength alloy Cu-1%Cr-0.3%Zr. The bond coat consists of a NiCrAlY alloy, while partially stabilized zirconia is used as a top coat. Spraying parameter optimization for the new substrate is described. The reached coating system is tested in thermal cycling experiments, where no failure of the coating could be detected. In oxidation experiments good environmental protection of the coating is shown.

  2. Developing a dissimilar metal foil-to-substrate resistance welding process.

    SciTech Connect

    Knorovsky, Gerald Albert

    2010-10-01

    Materials changes occurring upon redesign caused redevelopment of the multiple spot resistance weld procedure employed to join a 23 micrometer thick foil of 15-7PH to a thick substrate and (at a separate location) a second, smaller thermal mass substrate. Both substrates were 304L. To avoid foil wrinkling, minimal heat input was used. The foil/thick substrate weld was solid-state, though the foil/small substrate weld was not. Metallographic evidence indicated occasional separation of the solid-state weld, hence a fusion weld was desired at both locations. In the redesign, a Co-Cr-Fe-Ni alloy was substituted for the foil, and a Ni-Cr-Mo alloy was evaluated for the small substrate. Both materials are substantially more resistive than their predecessors. This study reports development of weld schedules to accommodate the changes, yet achieve the fusion weld goal. Thermal analysis was employed to understand the effects caused by the various weld schedule parameters, and guide their optimization.

  3. Substrate-induced reduction of graphene thermal conductivity

    NASA Astrophysics Data System (ADS)

    Koniakhin, S. V.; Utesov, O. I.; Terterov, I. N.; Nalitov, A. V.

    2017-01-01

    We develop a theory of heat conductivity in supported graphene, accounting for coherent phonon scattering on disorder induced by an amorphous substrate. We derive spectra for in-plane and out-of-plane phonons in the framework of Green's function approach. The energy parameters of the theory are obtained using molecular dynamics simulations for graphene on a SiO2 substrate. The heat conductivity is calculated by the Boltzmann transport equation. We find that the interaction with the substrate drastically reduces the phonon lifetime and completely suppresses the contribution of flexural (ZA) phonons to the heat conductivity. As a result, the total heat conductivity is reduced by several times, which matches with the tendency observed in the available experimental data. The considered effect is important for managing the thermal properties of graphene-based electronic devices.

  4. Spin-dependent heat transport and thermal boundary resistance

    NASA Astrophysics Data System (ADS)

    Jeong, Taehee

    in thin film structures. A transient theraroreflectance (TTR) technique can be used for measuring the thermal conductivity of thin films in cross-sectional direction. In this study, a pump-probe scheme was employed for the TTR technique. We built an optical pump-probe system by using a nanosecond pulse laser for pumping and a continuous-wave laser for probing. A short-time heating event occured at the surface of a sample by shining a laser pulse on the surface. Then the time-resolved thermoreflectance signals were detected using a photodetector and an oscilloscope. The increased temperature decreases slowly and its thermal decay depends on the thermal properties of a sample. Since the reflectivity is linearly proportional to the temperature, the time-resolved thermoreflectance signals have the information of the thermal properties of a sample. In order to extract the thermal properties of a sample, a thermal analysis was performed by fitting the experimental data with thermal models. We developed 2-layered and 3-layered thermal models using the analogies between thermal conduction and electric conduction and a transmission-line concept. We used two sets of sample structures: Au/SiNx/Si substrate and Au/CoFe/SiNx/Si substrate with various thickness of SiN x layer. Using the pump-probe system, we measured the time-resolved thermoreflectance signals for each sample. Then, the thermal conductivity and thermal boundary resistance were obtained by fitting the experimental data with the thermal models. The thermal conductivity of SiNx films was measured to be 2.0 W/mK for both structures. In the case of the thermal boundary resistance, it was 0.81x10-5 m 2K/W at the Au/SiNx interface and 0.54x10 -5 m2K/W at the CoFe/SiNx interface, respectively. The difference of the thermal boundary resistance between Au/SiNx and CoFe/SiNx might be came from the different phonon dispersion of Au and CoFe. The thermal conductivity did not depend on the thickness of SiNx films in the

  5. Corrosion-resistant ceramic thermal barrier coating

    NASA Technical Reports Server (NTRS)

    Hodge, P. E.; Levine, S. R.; Miller, R. A.

    1980-01-01

    Two-layer thermal barrier coating, consisting of metal-CrA1Y bond coating and calcium silicate ceramic outer layer, greatly improves resistance of turbine parts to hot corrosion from fuel and air impurities. Both layers can be plasma sprayed, and ceramic layer may be polished to reduce frictional losses. Ceramic provides thermal barrier, so parts operate cooler metal temperatures, coolant flow can be reduced, or gas temperatures increased. Lower grade fuels also can be used.

  6. Deposition of thermal and hot-wire chemical vapor deposition copper thin films on patterned substrates.

    PubMed

    Papadimitropoulos, G; Davazoglou, D

    2011-09-01

    In this work we study the hot-wire chemical vapor deposition (HWCVD) of copper films on blanket and patterned substrates at high filament temperatures. A vertical chemical vapor deposition reactor was used in which the chemical reactions were assisted by a tungsten filament heated at 650 degrees C. Hexafluoroacetylacetonate Cu(I) trimethylvinylsilane (CupraSelect) vapors were used, directly injected into the reactor with the aid of a liquid injection system using N2 as carrier gas. Copper thin films grown also by thermal and hot-wire CVD. The substrates used were oxidized silicon wafers on which trenches with dimensions of the order of 500 nm were formed and subsequently covered with LPCVD W. HWCVD copper thin films grown at filament temperature of 650 degrees C showed higher growth rates compared to the thermally ones. They also exhibited higher resistivities than thermal and HWCVD films grown at lower filament temperatures. Thermally grown Cu films have very uniform deposition leading to full coverage of the patterned substrates while the HWCVD films exhibited a tendency to vertical growth, thereby creating gaps and incomplete step coverage.

  7. Effects of thermal inhomogeneity on 4m class mirror substrates

    NASA Astrophysics Data System (ADS)

    Jedamzik, Ralf; Kunisch, Clemens; Westerhoff, Thomas

    2016-07-01

    The new ground based telescope generation is moving to a next stage of performance and resolution. Mirror substrate material properties tolerance and homogeneity are getting into focus. The coefficient of thermal expansion (CTE) homogeneity is even more important than the absolute CTE. The error in shape of a mirror, even one of ZERODUR, is affected by changes in temperature, and by gradients in temperature. Front to back gradients will change the radius of curvature R that in turn will change the focus. Some systems rely on passive athermalization and do not have means to focus. Similarly changes in soak temperature will result in surface changes to the extent there is a non-zero coefficient of thermal expansion. When there are in-homogeneities in CTE, the mirror will react accordingly. Results of numerical experiments are presented discussing the impact of CTE in-homogeneities on the optical performance of 4 m class mirror substrates. Latest improvements in 4 m class ZERODUR CTE homogeneity and the thermal expansion metrology are presented as well.

  8. Thermal shock resistance of silicon oxynitride

    NASA Technical Reports Server (NTRS)

    Glandus, J. C.; Boch, P.

    1981-01-01

    The thermal shock resistance of Si2N2O refractory material was studied. The thermal expansion coeff. is 3.55x10 to the -6th power at 20 to 800 C and 2.86x10 to the -6th power m/m/deg at 20 to 200 C. The breaking loads are high at high stress. Young's modulus E and the shear modulus G decrease linearly with increasing porosity. For dense material E sub o approx. = 216,500 N/mm2 and G approx = 90,600 N/mm2. The Vickers hardness of the dense material is comparable to that of sapphire. The results on thermal shock show that R, the breaking load, stays constant for T T sub c, the first cracks appear and R decreases sharply for T=T sub c. As the severity of the thermal shock is increased at T T sub c, a small no. of new, large-size cracks appears. The shock's cumulative effect is negligible, and repeated shocks do not change the cracks. The low values of the thermal expansion coefficient and Young's modulus and the high tension breaking load are considered. Sintered Si2N2O with 5% MgO shows excellent cracking resistance under thermal shock.

  9. Heat resistant substrates and battery separators made therefrom

    NASA Technical Reports Server (NTRS)

    Langer, Alois (Inventor); Scala, Luciano C. (Inventor); Ruffing, Charles R. (Inventor)

    1976-01-01

    A flexible substrate having a caustic resistant support and at least one membrane comprising a solid polymeric matrix containing a network of interconnected pores and interdispersed inorganic filler particles with a ratio of filler: polymer in the polymeric matrix of between about 1:1 to 5:1, is made by coating at least one side of the support with a filler:coating formulation mixture of inorganic filler particles and a caustic resistant, water insoluble polymer dissolved in an organic solvent, and removing the solvent from the mixture to provide a porous network within the polymeric matrix.

  10. Multiharmonics Method Characterizing In-Plane Thermal Conductivity and TBR of Semiconductor Nanofilm on Substrate: Theoretical Analysis

    NASA Astrophysics Data System (ADS)

    Wang, Zhaoliang; Xu, Zhe; Du, Xiaoli; Tang, Dawei

    2017-02-01

    The in-plane thermal conductivity of semiconductor nanofilm is difficult to be tested due to suspension problem. The thermal boundary resistance (TBR) plays a key role in semiconductor nanoscale structures and nanoscale thermal experiments. By applying alternating current and direct current currents simultaneously on the semiconducting nanofilm on highly insulated substrate, multiharmonics including 1ω, 2ω and 3ω signals originating from the self-heating of nanofilm are measured. The thermal boundary resistance is introduced into the heat diffusion equation in in-plane direction. The expression of temperature oscillation and theoretical analysis of heat transport process show that the in-plane thermal conductivity and TBR can be decoupled from the multiharmonics in frequency domain. Thermal analysis justifies the multiharmonics method according to the effect of in-plane thermal conductivity, TBR between nanofilm and insulated substrate, resistance coefficient of semiconductor nanofilm on temperature oscillation at low frequency. Results show the multiharmonic method sensitivity variations depending on the TBR, the in-plane thermal conductivity, and the electric current frequency.

  11. Thermal singularity and droplet motion in one-component fluids on solid substrates with thermal gradients

    NASA Astrophysics Data System (ADS)

    Xu, Xinpeng; Qian, Tiezheng

    2012-06-01

    Using a continuum model capable of describing the one-component liquid-gas hydrodynamics down to the contact line scale, we carry out numerical simulation and physical analysis for the droplet motion driven by thermal singularity. For liquid droplets in one-component fluids on heated or cooled substrates, the liquid-gas interface is nearly isothermal. Consequently, a thermal singularity occurs at the contact line and the Marangoni effect due to temperature gradient is suppressed. Through evaporation or condensation in the vicinity of the contact line, the thermal singularity makes the contact angle increase with the increasing substrate temperature. This effect on the contact angle can be used to move the droplets on substrates with thermal gradients. Our numerical results for this kind of droplet motion are explained by a simple fluid dynamical model at the droplet length scale. Since the mechanism for droplet motion is based on the change of contact angle, a separation of length scales is exhibited through a comparison between the droplet motion induced by a wettability gradient and that by a thermal gradient. It is shown that the flow field at the droplet length scale is independent of the statics or dynamics at the contact line scale.

  12. Thermal singularity and droplet motion in one-component fluids on solid substrates with thermal gradients.

    PubMed

    Xu, Xinpeng; Qian, Tiezheng

    2012-06-01

    Using a continuum model capable of describing the one-component liquid-gas hydrodynamics down to the contact line scale, we carry out numerical simulation and physical analysis for the droplet motion driven by thermal singularity. For liquid droplets in one-component fluids on heated or cooled substrates, the liquid-gas interface is nearly isothermal. Consequently, a thermal singularity occurs at the contact line and the Marangoni effect due to temperature gradient is suppressed. Through evaporation or condensation in the vicinity of the contact line, the thermal singularity makes the contact angle increase with the increasing substrate temperature. This effect on the contact angle can be used to move the droplets on substrates with thermal gradients. Our numerical results for this kind of droplet motion are explained by a simple fluid dynamical model at the droplet length scale. Since the mechanism for droplet motion is based on the change of contact angle, a separation of length scales is exhibited through a comparison between the droplet motion induced by a wettability gradient and that by a thermal gradient. It is shown that the flow field at the droplet length scale is independent of the statics or dynamics at the contact line scale.

  13. Thermal barrier coating resistant to sintering

    DOEpatents

    Subramanian, Ramesh; Sabol, Stephen M.

    2001-01-01

    A device (10) having a ceramic thermal barrier coating layer (16) characterized by a microstructure having gaps (18) with a sintering inhibiting material (22) disposed on the columns (20) within the gaps (18). The sintering resistant material (22) is stable over the range of operating temperatures of the device (10) and is not soluble with the underlying ceramic layer (16). For a YSZ ceramic layer (16) the sintering resistant layer (22) may preferably be aluminum oxide or yttrium aluminum oxide, deposited as a continuous layer or as nodules.

  14. Method for applying photographic resists to otherwise incompatible substrates

    NASA Technical Reports Server (NTRS)

    Fuhr, W. (Inventor)

    1981-01-01

    A method for applying photographic resists to otherwise incompatible substrates, such as a baking enamel paint surface, is described wherein the uncured enamel paint surface is coated with a non-curing lacquer which is, in turn, coated with a partially cured lacquer. The non-curing lacquer adheres to the enamel and a photo resist material satisfactorily adheres to the partially cured lacquer. Once normal photo etching techniques are employed the lacquer coats can be easily removed from the enamel leaving the photo etched image. In the case of edge lighted instrument panels, a coat of uncured enamel is placed over the cured enamel followed by the lacquer coats and the photo resists which is exposed and developed. Once the etched uncured enamel is cured, the lacquer coats are removed leaving an etched panel.

  15. Thermal engineering of non-local resistance in lateral spin valves

    NASA Astrophysics Data System (ADS)

    Kasai, S.; Hirayama, S.; Takahashi, Y. K.; Mitani, S.; Hono, K.; Adachi, H.; Ieda, J.; Maekawa, S.

    2014-04-01

    We study the non-local spin transport in Permalloy/Cu lateral spin valves (LSVs) fabricated on thermally oxidized Si and MgO substrates. While these LSVs show the same magnitude of spin signals, significant substrate dependence of the baseline resistance was observed. The baseline resistance shows much weaker dependence on the inter-electrode distance than that of the spin transport observed in the Cu wires. A simple analysis of voltage-current characteristics in the baseline resistance indicates the observed result can be explained by a combination of the Peltier and Seebeck effects at the injector and detector junctions, suggesting the usage of high thermal conductivity substrate (or under-layer) is effective to reduce the baseline resistance.

  16. Thermal engineering of non-local resistance in lateral spin valves

    SciTech Connect

    Kasai, S. Takahashi, Y. K.; Hirayama, S.; Mitani, S.; Hono, K.; Adachi, H.; Ieda, J.; Maekawa, S.

    2014-04-21

    We study the non-local spin transport in Permalloy/Cu lateral spin valves (LSVs) fabricated on thermally oxidized Si and MgO substrates. While these LSVs show the same magnitude of spin signals, significant substrate dependence of the baseline resistance was observed. The baseline resistance shows much weaker dependence on the inter-electrode distance than that of the spin transport observed in the Cu wires. A simple analysis of voltage-current characteristics in the baseline resistance indicates the observed result can be explained by a combination of the Peltier and Seebeck effects at the injector and detector junctions, suggesting the usage of high thermal conductivity substrate (or under-layer) is effective to reduce the baseline resistance.

  17. Properties of topological insulator Bi2Se3 films prepared by thermal evaporation growth on different substrates

    NASA Astrophysics Data System (ADS)

    Zhang, Min.

    2017-02-01

    Topological insulator Bi2Se3 thin films were grown by the thermal evaporation deposition on different substrates and their phase structures and magneto-transport properties were discussed. The films growth is along the c-axis, and their surfaces exhibited terrace-like quintuple layers. Resistivity upturn as well as weak anti-localization was observed only in the film with Si and LAO substrates. The linear magneto-resistance (LMR) under high field was found, which was associated with the gapless topological surface states and the quantum origin. The results indicate that the films are highly uniform.

  18. 49 CFR Appendix D to Part 178 - Thermal Resistance Test

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 49 Transportation 2 2010-10-01 2010-10-01 false Thermal Resistance Test D Appendix D to Part 178.... 178, App. D Appendix D to Part 178—Thermal Resistance Test 1. Scope. This test method evaluates the thermal resistance capabilities of a compressed oxygen generator and the outer packaging for a cylinder...

  19. Thermally resistant polymers for fuel tank sealants

    NASA Technical Reports Server (NTRS)

    Webster, J. A.

    1973-01-01

    Imide-linked perfluoroalkylene ether polymers, that were developed for the high temperature fuel tank sealant application, are discussed. Modifications of polymer structure and properties were realized through use of a new aromatic dianhydride intermediate containing an ether-linked perfluoroalkylene segment. Tests of thermal, oxidative and hydrolytic stability, fuel resistance, and adhesion are discussed along with tensile strength and elongation results. Efforts to effect a low temperature condensation of amic acid prepolymer to form imide links inside are described.

  20. Thermal barrier coating resistant to sintering

    DOEpatents

    Subramanian, Ramesh; Seth, Brij B.

    2004-06-29

    A device (10) is made, having a ceramic thermal barrier coating layer (16) characterized by a microstructure having gaps (18) with a sintering inhibiting material (22) disposed on the columns (20) within the gaps (18). The sintering resistant material (22) is stable over the range of operating temperatures of the device (10), is not soluble with the underlying ceramic layer (16) and is applied by a process that is not an electron beam physical vapor deposition process.

  1. Substrate-dependent thermal conductivity of aluminum nitride thin-films processed at low temperature

    SciTech Connect

    Belkerk, B. E.; Bensalem, S.; Soussou, A.; Carette, M.; Djouadi, M. A.; Scudeller, Y.; Al Brithen, H.

    2014-12-01

    In this paper, we report on investigation concerning the substrate-dependent thermal conductivity (k) of Aluminum Nitride (AlN) thin-films processed at low temperature by reactive magnetron sputtering. The thermal conductivity of AlN films grown at low temperature (<200 °C) on single-crystal silicon (Si) and amorphous silicon nitride (SiN) with thicknesses ranging from 100 nm to 4000 nm was measured with the transient hot-strip technique. The k values for AlN films on SiN were found significantly lower than those on Silicon consistently with their microstructures revealed by X-ray diffraction, high resolution scanning electron microscopy, and transmission electron microscopy. The change in k was due to the thermal boundary resistance found to be equal to 10 × 10{sup −9} Km{sup 2}W{sup −1} on SiN against 3.5 × 10{sup −9} Km{sup 2}W{sup −1} on Si. However, the intrinsic thermal conductivity was determined with a value as high as 200 Wm{sup −1}K{sup −1} whatever the substrate.

  2. The study of crack resistance of TiAlN coatings under mechanical loading and thermal cycle testing

    SciTech Connect

    Akulinkin, Alexandr Shugurov, Artur Sergeev, Viktor; Panin, Alexey; Cheng, C.-H.

    2015-10-27

    The effect of preliminary ion bombardment of 321 stainless steel substrate on crack resistance of TiAlN coatings at uniaxial tension and thermal cycling is studied. The ion-beam treatment of the substrate is shown to substantially improve the adhesion strength of the coatings that prevents their delamination and spalling under uniaxial tension. The resistance to crack propagation and spalling by the thermal shock is higher in the TiAlN coating deposited onto the substrate subjected to Ti ion bombardment as compared to that in the TiAlN coating deposited onto the initial substrate.

  3. Reduction of substrate dependency of chemically amplified resist

    NASA Astrophysics Data System (ADS)

    Chun, Jun-Sung; Bok, Cheol-Kyu; Baik, Ki-Ho

    1996-06-01

    In the case of silicon nitride films acid pretreatment can eliminate resist scum so that we can get clean resist profiles. The acid used, called Clean D treatment for photoresist strip, normally consists of a mixture of sulfuric acid (80% water) and hydrogen peroxide (80% water). ESCA (electron spectroscopy by chemical analysis) was used to examine the surface of the films after cleaning with acid and to monitor the changes in atomic percents of the films with time. Considering all the analytical data, this acid treatment to silicon nitride makes the film surface oxide-rich resulting in forming barrier layer between substrates and protons from PAG (photo acid generator). For BPSG boro-phosphorous silicate glass) films the mechanism of the formation of resist foot is quite different from that of silicon nitride. Improved resist profiles on BPSG were obtained by the dehydration bake. Therefore it could be speculated that the formation of resist scums on silicon nitride films are due to the nitrogen in films and on the BPSG moisture. O2 plasma surface pretreatment was also reviewed. It is quite certain that these two methods, acid and O2 plasma treatments are very effective, economical and simple process. However, there are delay time effects after pretreating films unlike other conventional oxide capping layers. This problem is also discussed in detail.

  4. Thermal constriction resistance of sphere/layered flat contacts: Theory and experiment

    SciTech Connect

    Fisher, N.J. ); Yovanovich, M.M. )

    1989-05-01

    The effect of surface layers on the thermal constriction resistance of contacts is of interest to the thermal analyst. This paper investigates analytically and experimentally the thermomechanical problem of a sphere in elastic contact with a flat plate coated with a layer. An approximate solution is developed that utilizes the solution to the thermal portion of the problem and the Hertzian limits of the mechanical portion. The approximation shows good agreement with the full solution for two examples that represent extremes in elastic properties for common metallics. Thermal constriction resistance measurements for a steel sphere contacting a nickel flat coated with a silver layer are compared to theoretical predictions. Resistance predictions from both full and approximate solutions show good agreement with measurements for light loads within the elastic load range. For heavy loads, the resistance is over-predicted due to plastic yielding of the nickel substrate.

  5. Sustainably Sourced, Thermally Resistant, Radiation Hard Biopolymer

    NASA Technical Reports Server (NTRS)

    Pugel, Diane

    2011-01-01

    This material represents a breakthrough in the production, manufacturing, and application of thermal protection system (TPS) materials and radiation shielding, as this represents the first effort to develop a non-metallic, non-ceramic, biomaterial-based, sustainable TPS with the capability to also act as radiation shielding. Until now, the standing philosophy for radiation shielding involved carrying the shielding at liftoff or utilizing onboard water sources. This shielding material could be grown onboard and applied as needed prior to different radiation landscapes (commonly seen during missions involving gravitational assists). The material is a bioplastic material. Bioplastics are any combination of a biopolymer and a plasticizer. In this case, the biopolymer is a starch-based material and a commonly accessible plasticizer. Starch molecules are composed of two major polymers: amylase and amylopectin. The biopolymer phenolic compounds are common to the ablative thermal protection system family of materials. With similar constituents come similar chemical ablation processes, with the potential to have comparable, if not better, ablation characteristics. It can also be used as a flame-resistant barrier for commercial applications in buildings, homes, cars, and heater firewall material. The biopolymer is observed to undergo chemical transformations (oxidative and structural degradation) at radiation doses that are 1,000 times the maximum dose of an unmanned mission (10-25 Mrad), indicating that it would be a viable candidate for robust radiation shielding. As a comparison, the total integrated radiation dose for a three-year manned mission to Mars is 0.1 krad, far below the radiation limit at which starch molecules degrade. For electron radiation, the biopolymer starches show minimal deterioration when exposed to energies greater than 180 keV. This flame-resistant, thermal-insulating material is non-hazardous and may be sustainably sourced. It poses no hazardous

  6. 49 CFR Appendix D to Part 178 - Thermal Resistance Test

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 49 Transportation 3 2011-10-01 2011-10-01 false Thermal Resistance Test D Appendix D to Part 178 Transportation Other Regulations Relating to Transportation (Continued) PIPELINE AND HAZARDOUS MATERIALS SAFETY... to Part 178—Thermal Resistance Test 1. Scope. This test method evaluates the thermal...

  7. 49 CFR Appendix D to Part 178 - Thermal Resistance Test

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 49 Transportation 3 2012-10-01 2012-10-01 false Thermal Resistance Test D Appendix D to Part 178 Transportation Other Regulations Relating to Transportation (Continued) PIPELINE AND HAZARDOUS MATERIALS SAFETY... to Part 178—Thermal Resistance Test 1. Scope. This test method evaluates the thermal...

  8. 49 CFR Appendix D to Part 178 - Thermal Resistance Test

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 49 Transportation 3 2014-10-01 2014-10-01 false Thermal Resistance Test D Appendix D to Part 178 Transportation Other Regulations Relating to Transportation (Continued) PIPELINE AND HAZARDOUS MATERIALS SAFETY... to Part 178—Thermal Resistance Test 1. Scope. This test method evaluates the thermal...

  9. 49 CFR Appendix D to Part 178 - Thermal Resistance Test

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 49 Transportation 3 2013-10-01 2013-10-01 false Thermal Resistance Test D Appendix D to Part 178 Transportation Other Regulations Relating to Transportation (Continued) PIPELINE AND HAZARDOUS MATERIALS SAFETY... to Part 178—Thermal Resistance Test 1. Scope. This test method evaluates the thermal...

  10. 40 CFR 90.427 - Catalyst thermal stress resistance evaluation.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 21 2013-07-01 2013-07-01 false Catalyst thermal stress resistance... Gaseous Exhaust Test Procedures § 90.427 Catalyst thermal stress resistance evaluation. (a) The purpose of... catalyst conversion efficiency for Phase 1 engines. The thermal stress is imposed on the test catalyst...

  11. 40 CFR 90.427 - Catalyst thermal stress resistance evaluation.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 20 2014-07-01 2013-07-01 true Catalyst thermal stress resistance... Gaseous Exhaust Test Procedures § 90.427 Catalyst thermal stress resistance evaluation. (a) The purpose of... catalyst conversion efficiency for Phase 1 engines. The thermal stress is imposed on the test catalyst...

  12. 40 CFR 91.427 - Catalyst thermal stress resistance evaluation.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 20 2010-07-01 2010-07-01 false Catalyst thermal stress resistance... Procedures § 91.427 Catalyst thermal stress resistance evaluation. (a)(1) The purpose of the evaluation procedure specified in this section is to determine the effect of thermal stress on catalyst...

  13. 40 CFR 91.427 - Catalyst thermal stress resistance evaluation.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 21 2013-07-01 2013-07-01 false Catalyst thermal stress resistance... Procedures § 91.427 Catalyst thermal stress resistance evaluation. (a)(1) The purpose of the evaluation procedure specified in this section is to determine the effect of thermal stress on catalyst...

  14. 40 CFR 90.427 - Catalyst thermal stress resistance evaluation.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 20 2010-07-01 2010-07-01 false Catalyst thermal stress resistance... Gaseous Exhaust Test Procedures § 90.427 Catalyst thermal stress resistance evaluation. (a) The purpose of... catalyst conversion efficiency for Phase 1 engines. The thermal stress is imposed on the test catalyst...

  15. 40 CFR 90.427 - Catalyst thermal stress resistance evaluation.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 20 2011-07-01 2011-07-01 false Catalyst thermal stress resistance... Gaseous Exhaust Test Procedures § 90.427 Catalyst thermal stress resistance evaluation. (a) The purpose of... catalyst conversion efficiency for Phase 1 engines. The thermal stress is imposed on the test catalyst...

  16. 40 CFR 91.427 - Catalyst thermal stress resistance evaluation.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 20 2014-07-01 2013-07-01 true Catalyst thermal stress resistance... Procedures § 91.427 Catalyst thermal stress resistance evaluation. (a)(1) The purpose of the evaluation procedure specified in this section is to determine the effect of thermal stress on catalyst...

  17. 40 CFR 91.427 - Catalyst thermal stress resistance evaluation.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 21 2012-07-01 2012-07-01 false Catalyst thermal stress resistance... Procedures § 91.427 Catalyst thermal stress resistance evaluation. (a)(1) The purpose of the evaluation procedure specified in this section is to determine the effect of thermal stress on catalyst...

  18. 40 CFR 91.427 - Catalyst thermal stress resistance evaluation.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 20 2011-07-01 2011-07-01 false Catalyst thermal stress resistance... Procedures § 91.427 Catalyst thermal stress resistance evaluation. (a)(1) The purpose of the evaluation procedure specified in this section is to determine the effect of thermal stress on catalyst...

  19. 40 CFR 90.427 - Catalyst thermal stress resistance evaluation.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 21 2012-07-01 2012-07-01 false Catalyst thermal stress resistance... Gaseous Exhaust Test Procedures § 90.427 Catalyst thermal stress resistance evaluation. (a) The purpose of... catalyst conversion efficiency for Phase 1 engines. The thermal stress is imposed on the test catalyst...

  20. Thermal shock and thermal cycling behaviour of amorphous a-C:H films on molybdenum substrates

    NASA Astrophysics Data System (ADS)

    Kny, E.; Winter, J.; Littmark, U.; Friedbacher, G.; Grasserbauer, M.; Waelbroeck, F.

    1988-07-01

    The thermal behaviour of a-C: H films (a stands for amorphous) deposited by the TEXTOR carbonization technique on molybdenum substrates was investigated in high power electron beam testing device for single and multiple shot sequences. The stationary thermal behaviour was also measured. The results for single shot testing are presented in a threshold damage diagram and show that the stability of a-C: H films on molybdenum is superior to that on steel. At higher or repeated loadings the films are converted gradually to molybdenum carbide. AES and SIMS depth profiling was used to investigate the concentration profiles and interface compositions of the films after various heat treatments. Their 1-h thermal stability on molybdenum extends to approximately 700°C in a stationary test. Results show that a-C: H films on molybdenum should be effective in shielding the molybdenum substrate from the plasma in a fusion device as long as the stated loading limits are not exceeded.

  1. Thermal Resistance of Transferred-Silicon-Nanomembrane Interfaces.

    PubMed

    Schroeder, D P; Aksamija, Z; Rath, A; Voyles, P M; Lagally, M G; Eriksson, M A

    2015-12-18

    We report measurements of the interfacial thermal resistance between mechanically joined single crystals of silicon, the results of which are up to a factor of 5 times lower than any previously reported thermal resistances of mechanically created interfaces. Detailed characterization of the interfaces is presented, as well as a theoretical model incorporating the critical properties determining the interfacial thermal resistance in the experiments. The results demonstrate that van der Waals interfaces can have very low thermal resistance, with important implications for membrane-based micro- and nanoelectronics.

  2. Final Project Report for "Interfacial Thermal Resistance of Carbon Nanotubes”

    SciTech Connect

    Cumings, John

    2016-04-15

    This report describes an ongoing project to comprehensively study the interfacial thermal boundary resistance (Kapitza resistance) of carbon nanotubes. It includes a list of publications, personnel supported, the overall approach, accomplishments and future plans.

  3. Evaluation of Erosion Resistance of Advanced Turbine Thermal Barrier Coatings

    NASA Technical Reports Server (NTRS)

    Zhu, Dongming; Kuczmarski, Maria A.; Miller, Robert A.; Cuy, Michael D.

    2007-01-01

    The erosion resistant turbine thermal barrier coating system is critical to aircraft engine performance and durability. By demonstrating advanced turbine material testing capabilities, we will be able to facilitate the critical turbine coating and subcomponent development and help establish advanced erosion-resistant turbine airfoil thermal barrier coatings design tools. The objective of this work is to determine erosion resistance of advanced thermal barrier coating systems under simulated engine erosion and/or thermal gradient environments, validating advanced turbine airfoil thermal barrier coating systems based on nano-tetragonal phase toughening design approaches.

  4. Improvement of thermal contact resistance by carbon nanotubes and nanofibers

    NASA Technical Reports Server (NTRS)

    Chuang, Helen F.; Cooper, Sarah M.; Meyyappan, M.; Cruden, Brett A.

    2004-01-01

    Interfacial thermal resistance results of various nanotube and nanofiber coatings, prepared by chemical vapor deposition (CVD) methods, are reported at relatively low clamping pressures. The five types of samples examined include multi-walled and single-walled nanotubes growth by CVD, multi-walled nanotubes grown by plasma enhanced CVD (PECVD) and carbon nanofibers of differing aspect ratio grown by PECVD. Of the samples examined, only high aspect ratio nanofibers and thermally grown multi-walled nanotubes show an improvement in thermal contact resistance. The improvement is approximately a 60% lower thermal resistance than a bare Si-Cu interface and is comparable to that attained by commercially available thermal interface materials.

  5. Thermal barrier coating resistant to sintering

    DOEpatents

    Subramanian, Ramesh; Seth, Brig B.

    2005-08-23

    A device (10) is made, having a ceramic thermal barrier coating layer (16) characterized by a microstructure having gaps (18) with a sintering inhibiting material (22) disposed on the columns (20) within the gaps (18). The sintering resistant material (22) is stable over the range of operating temperatures of the device (10), is not soluble with the underlying ceramic layer (16) and is applied by a process that is not an electron beam physical vapor deposition process. The sintering inhibiting material (22) has a morphology adapted to improve the functionality of the sintering inhibiting material (22), characterized as continuous, nodule, rivulet, grain, crack, flake and combinations thereof and being disposed within at least some of the vertical and horizontal gaps.

  6. Development of a protective decorative fire resistant low smoke emitting, thermally stable coating material

    NASA Technical Reports Server (NTRS)

    1976-01-01

    The development of suitable electrocoatings and subsequent application to nonconductive substrates are discussed. Substrates investigated were plastics or resin-treated materials such as FX-resin (phenolic-type resin) impregnated fiberglass mat, polyphenylene sulfide, polyether sulfone and polyimide-impregnated unidirectional fiberglass. Efforts were aimed at formulating a fire-resistant, low smoke emitting, thermally stable, easily cleaned coating material. The coating is to be used for covering substrate panels, such as aluminum, silicate foam, polymeric structural entities, etc., all of which are applied in the aircraft cabin interior and thus subject to the spillages, scuffing, spotting and the general contaminants which prevail in aircraft passenger compartments.

  7. Investigation of thermal spray coatings on austenitic stainless steel substrate to enhance corrosion protection

    NASA Astrophysics Data System (ADS)

    Rogers, Daniel M.

    The research is aimed to evaluate thermal spray coatings to address material issues in supercritical and ultra-supercritical Rankine cycles. The primary purpose of the research is to test, evaluate, and eventually implement a coating to improve corrosion resistance and increase efficiency of coal fired power plants. The research is performed as part of a comprehensive project to evaluate the ability of titanium, titanium carbide, or titanium diboride powders to provide fireside corrosion resistance in supercritical and ultra-supercritical steam boilers, specifically, coal driven boilers in Illinois that must utilize high sulfur and high chlorine content coal. [1] The powder coatings that were tested are nano-sized titanium carbide (TiC) and titanium di-boride (TiB2) powders that were synthesized by a patented process at Southern Illinois University. The powders were then sent to Gas Technology Institute in Chicago to coat steel coupons by HVOF (High Velocity Oxy-Fuel) thermal spray technique. The powders were coated on an austenitic 304H stainless steel substrate which is commonly found in high temperature boilers, pipelines, and heat exchangers. The samples then went through various tests for various lengths of time under subcritical, supercritical, and ultra-supercritical conditions. The samples were examined using a scanning electron microscope and x-ray diffraction techniques to study microstructural changes and then determined which coating performed best.

  8. Theoretical analysis of thermal shock resistance of ceramic foam coatings

    NASA Astrophysics Data System (ADS)

    Zhang, Y. X.; Wang, B. L.

    2017-01-01

    Ceramic foams have a high resistance to corrosion and wear. They also have a good thermal insulation performance because of their high melting point and low thermal conductivity. The thermal shock resistance of a ceramic foam coating with an edge crack under a sudden temperature variation is investigated. The dynamic thermal stress fields in the ceramic foam coating are obtained. Using the superposition principle, the crack problem of the ceramic foam coating is reduced to the solution of a set of singular integral equations. Propagation of the edge crack is analyzed. Effects of the relative density and thermal properties of the ceramic foam and of crack length on the thermal shock resistance are identified. The results obtained can be useful in designing thermal protective ceramic materials for thermal barrier coatings.

  9. Thermally Stable, Piezoelectric and Pyroelectric Polymeric Substrates and Method Relating Thereto

    NASA Technical Reports Server (NTRS)

    Simpson, Joycelyn O. (Inventor); St.Claire, Terry L. (Inventor)

    2002-01-01

    A thermally stable, piezoelectric and pyroelectric polymeric substrate was prepared, This thermally stable, piezoelectric and pyroelectric polymeric substrate may be used to prepare electromechanical transducers, thermomechanical transducers, accelerometers, acoustic sensors, infrared sensors, pressure sensors, vibration sensors, impact sensors. in-situ temperature sensors, in-situ stress/strain sensors, micro actuators, switches. adjustable fresnel lenses, speakers, tactile sensors, weather sensors, micro positioners, ultrasonic devices, power generators, tunable reflectors, microphones, and hydrophones. The process for preparing these polymeric substrates includes: providing a polymeric substrate having a softening temperature greater than 100 C; depositing a metal electrode material onto the polymer film; attaching a plurality of electrical leads to the metal electrode coated polymeric substrates; heating the metal electrode coated polymeric substrate in a low dielectric medium; applying a voltage to the heated metal electrode coated polymeric substrate to induce polarization; and cooling the polarized metal electrode coated polymeric electrode while maintaining a constant voltage.

  10. Monolithic pixels on moderate resistivity substrate and sparsifying readout architecture

    NASA Astrophysics Data System (ADS)

    Giubilato, P.; Battaglia, M.; Bisello, D.; Caselle, M.; Chalmet, P.; Demaria, L.; Ikemoto, Y.; Kloukinas, K.; Mansuy, S. C.; Mattiazzo, S.; Marchioro, A.; Mugnier, H.; Pantano, D.; Potenza, A.; Rivetti, A.; Rousset, J.; Silvestrin, L.; Snoeys, W.

    2013-12-01

    The LePix projects aim realizing a new generation monolithic pixel detectors with improved performances at lesser cost with respect to both current state of the art monolithic and hybrid pixel sensors. The detector is built in a 90 nm CMOS process on a substrate of moderate resistivity. This allows charge collection by drift while maintaining the other advantages usually offered by MAPS, like having a single piece detector and using a standard CMOS production line. The collection by drift mechanism, coupled to the low capacitance design of the collecting node made possible by the monolithic approach, provides an excellent signal to noise ratio straight at the pixel cell together with a radiation tolerance far superior to conventional un-depleted MAPS. The excellent signal-to-noise performance is demonstrated by the device ability to separate the 6 keV 55Fe double peak at room temperature. To achieve high granularity (10-20 μm pitch pixels) over large detector areas maintaining high readout speed, a completely new compressing architecture has been devised. This architecture departs from the mainstream hybrid pixel sparsification approach, which uses in-pixel logic to reduce data, by using topological compression to minimize pixel area and power consumption.

  11. Silicon based substrate with calcium aluminosilicate/thermal barrier layer

    NASA Technical Reports Server (NTRS)

    Eaton, Jr., Harry Edwin (Inventor); Allen, William Patrick (Inventor); Miller, Robert Alden (Inventor); Jacobson, Nathan S. (Inventor); Smialek, James L. (Inventor); Opila, Elizabeth J. (Inventor); Lee, Kang N. (Inventor); Nagaraj, Bangalore A. (Inventor); Wang, Hongyu (Inventor); Meschter, Peter Joel (Inventor)

    2001-01-01

    A barrier layer for a silicon containing substrate which inhibits the formation of gaseous species of silicon when exposed to a high temperature aqueous environment comprises a calcium alumino silicate.

  12. Silicon based substrate with environmental/ thermal barrier layer

    NASA Technical Reports Server (NTRS)

    Eaton, Jr., Harry Edwin (Inventor); Allen, William Patrick (Inventor); Jacobson, Nathan S. (Inventor); Bansal, Nanottam P. (Inventor); Opila, Elizabeth J. (Inventor); Smialek, James L. (Inventor); Lee, Kang N. (Inventor); Spitsberg, Irene T. (Inventor); Wang, Hongyu (Inventor); Meschter, Peter Joel (Inventor)

    2002-01-01

    A barrier layer for a silicon containing substrate which inhibits the formation of gaseous species of silicon when exposed to a high temperature aqueous environment comprises a barium-strontium alumino silicate.

  13. Experimental and numerical study of the effective thermal conductivity of silica nanocomposites with thermal boundary resistance

    SciTech Connect

    Kothari, Rushabh M; Dinwiddie, Ralph Barton; Wang, Hsin

    2013-01-01

    The thermal interface resistance at the macro scale is mainly described by the physical gap between two interfaces and constriction resistance due to this gap. The small gaps between the two material faces makes up the majority of thermal interface resistance at the macro scale. So, most of the studies have been focused on characterizing effect of surface geometry and material properties to thermal interface resistance. This resistance is more widely known as thermal contact resistance, represented with Rc. There are various models to predict thermal contact resistance at macro scale. These models predict thermal resistance Rc for given two materials by utilizing their bulk thermomechanical properties. Although, Rc represents thermal resistance accurately for macro size contacts between two metals, it is not suitable to describe interface resistance of particles in modern TIMs, aka particulate composites. The particles inside recently available TIMs are micron size and with effort to further increase surface area this particle size is approaching nano scale. At this small scale, Rc does not accurately predict thermal interface, as it is very difficult to characterize the surface topography. The thermal discontinuity at perfectly bonded interface of two dissimilar materials is termed as thermal boundary resistance (Rb) or Kapitza resistance. The macroscopic assumptions that thermal discontinuity only exists due to gaps and surface geometry leads to substantial error in determining interface thermal properties at micron and nano scale. The phenomenon of thermal boundary resistance is an inherent material property and arises due to fundamental mechanism of thermal transport. For metal-matrix particulate composites, Rb plays more important role than Rc. The free flowing nature of the polymer would eliminate most of the gaps between the two materials at their interface. This means almost all of the thermal resistance at particle/matrix interface would occur due to Rb

  14. Bilateral substrate effect on the thermal conductivity of two-dimensional silicon.

    PubMed

    Zhang, Xiaoliang; Bao, Hua; Hu, Ming

    2015-04-14

    Silicene, the silicon-based counterpart of graphene, has received exceptional attention from a wide community of scientists and engineers in addition to graphene, due to its unique and fascinating physical and chemical properties. Recently, the thermal transport of the atomic thin Si layer, critical to various applications in nanoelectronics, has been studied; however, to date, the substrate effect has not been investigated. In this paper, we present our nonequilibrium molecular dynamics studies on the phonon transport of silicene supported on different substrates. A counter-intuitive phenomenon, in which the thermal conductivity of silicene can be either enhanced or suppressed by changing the surface crystal plane of the substrate, has been observed. This phenomenon is fundamentally different from the general understanding of supported graphene, a representative two-dimensional material, in which the substrate always has a negative effect on the phonon transport of graphene. By performing phonon polarization and spectral energy density analysis, we explain the underlying physics of the new phenomenon in terms of the different impacts on the dominant phonons in the thermal transport of silicene induced by the substrate: the dramatic increase in the thermal conductivity of silicene supported on the 6H-SiC substrate is due to the augmented lifetime of the majority of the acoustic phonons, while the significant decrease in the thermal conductivity of silicene supported on the 3C-SiC substrate results from the reduction in the lifetime of almost the entire phonon spectrum. Our results suggest that, by choosing different substrates, the thermal conductivity of silicene can be largely tuned, which paves the way for manipulating the thermal transport properties of silicene for future emerging applications.

  15. Evaporative Droplets in One-Component Fluids Driven by Thermal Gradients on Solid Substrates

    NASA Astrophysics Data System (ADS)

    Xu, Xinpeng; Qian, Tiezheng

    2013-03-01

    A continuum hydrodynamic model is presented for one-component liquid-gas flows on nonisothermal solid substrates. Numerical simulations are carried out for evaporative droplets moving on substrates with thermal gradients. For droplets in one-component fluids on heated/cooled substrates, the free liquid-gas interfaces are nearly isothermal. Consequently, a thermal singularity occurs at the contact line while the Marangoni effect due to interfacial temperature variation is suppressed. Through evaporation/condensation near the contact line, the thermal singularity makes the contact angle increase with the increasing substrate temperature. Due to this effect, droplets will move toward the cold end on substrates with thermal gradients. The droplet migration velocity is found to be proportional to the change of substrate temperature across the droplet. It follows that for two droplets of different sizes on a substrate with temperature gradient, the larger droplet moves faster and will catch up with the smaller droplet ahead. As soon as they touch, they coalesce rapidly into an even larger droplet that will move even faster.

  16. Thermal analysis of resin composites with ellipsoidal filler considering thermal boundary resistance

    NASA Astrophysics Data System (ADS)

    Asakuma, Yusuke; Yamamoto, Tsuyoshi

    2016-10-01

    The effective thermal conductivity of composites with ellipsoidal fillers is analyzed by using a homogenization method that is able to represent the microstructure precisely. In this study, various parameters such as the volume fraction, shape, and distribution of the filler are quantitatively estimated to understand the mechanisms of heat transfer in the composite. First, thermal boundary resistance between resin and filler is important for obtaining composites with higher thermal conductivity. Second, the anisotropy of the effective thermal conductivity arises from contact between filler in the case of ellipsoidal filler and produces lower thermal resistance. Finally, the filler network and thermal resistance are essential for the heat transfer in composites because the path of thermal conduction is improved by contact between neighboring filler particles.

  17. Thermal contact resistance in solid oxide fuel cell stacks

    NASA Astrophysics Data System (ADS)

    Dillig, Marius; Biedermann, Thomas; Karl, Jürgen

    2015-12-01

    For detailed thermal modelling of SOFC stacks, in particular research of improved thermal management, start-up and shut-down processes, thermal contact resistances (TCR) are required input parameters. These parameters are difficult to access analytically and strongly depend on temperature, geometry and material properties of the contact. Therefore, this work presents an experimental study of thermal contact resistance between different components of one SOFC stack repeating unit at varying temperatures up to typical operating temperatures (800 °C). Heat transfer rates are obtained for full repeating units, cell only, contact mesh only and sealing set-ups. Thermal interface resistances between interconnector and Ni-mesh, Ni-mesh and anode, cathode and interconnector as well as between interconnector and sealing are computed based on the measured data and provide information for numerical SOFC stack modelling.

  18. Method and apparatus for thermal processing of semiconductor substrates

    DOEpatents

    Griffiths, Stewart K.; Nilson, Robert H.; Mattson, Brad S.; Savas, Stephen E.

    2000-01-01

    An improved apparatus and method for thermal processing of semiconductor wafers. The apparatus and method provide the temperature stability and uniformity of a conventional batch furnace as well as the processing speed and reduced time-at-temperature of a lamp-heated rapid thermal processor (RTP). Individual wafers are rapidly inserted into and withdrawn from a furnace cavity held at a nearly constant and isothermal temperature. The speeds of insertion and withdrawal are sufficiently large to limit thermal stresses and thereby reduce or prevent plastic deformation of the wafer as it enters and leaves the furnace. By processing the semiconductor wafer in a substantially isothermal cavity, the wafer temperature and spatial uniformity of the wafer temperature can be ensured by measuring and controlling only temperatures of the cavity walls. Further, peak power requirements are very small compared to lamp-heated RTPs because the cavity temperature is not cycled and the thermal mass of the cavity is relatively large. Increased speeds of insertion and/or removal may also be used with non-isothermal furnaces.

  19. Method and apparatus for thermal processing of semiconductor substrates

    DOEpatents

    Griffiths, Stewart K.; Nilson, Robert H.; Mattson, Brad S.; Savas, Stephen E.

    2002-01-01

    An improved apparatus and method for thermal processing of semiconductor wafers. The apparatus and method provide the temperature stability and uniformity of a conventional batch furnace as well as the processing speed and reduced time-at-temperature of a lamp-heated rapid thermal processor (RTP). Individual wafers are rapidly inserted into and withdrawn from a furnace cavity held at a nearly constant and isothermal temperature. The speeds of insertion and withdrawal are sufficiently large to limit thermal stresses and thereby reduce or prevent plastic deformation of the wafer as it enters and leaves the furnace. By processing the semiconductor wafer in a substantially isothermal cavity, the wafer temperature and spatial uniformity of the wafer temperature can be ensured by measuring and controlling only temperatures of the cavity walls. Further, peak power requirements are very small compared to lamp-heated RTPs because the cavity temperature is not cycled and the thermal mass of the cavity is relatively large. Increased speeds of insertion and/or removal may also be used with non-isothermal furnaces.

  20. Measurement and thermal modeling of sapphire substrate temperature at III-Nitride MOVPE conditions

    SciTech Connect

    Creighton, J. Randall; Coltrin, Michael E.; Figiel, Jeffrey J.

    2016-11-17

    Here, growth rates and alloy composition of AlGaN grown by MOVPE is often very temperature dependent due to the presence of gas-phase parasitic chemical processes. These processes make wafer temperature measurement highly important, but in fact such measurements are very difficult because of substrate transparency in the near- IR (~900 nm) where conventional pyrometers detect radiation. The transparency problem can be solved by using a mid-IR pyrometer operating at a wavelength (~7500 nm) where sapphire is opaque. We employ a mid- IR pyrometer to measure the sapphire wafer temperature and simultaneously a near-IR pyrometer to measure wafer pocket temperature, while varying reactor pressure in both a N2 and H2 ambient. Near 1300 °C, as the reactor pressure is lowered from 300 Torr to 10 Torr the wafer temperature drops dramatically, and the ΔT between the pocket and wafer increases from ~20 °C to ~250 °C. Without the mid-IR pyrometer the large wafer temperature change with pressure would not have been noted. In order to explain this behavior we have developed a quasi-2D thermal model that includes a proper accounting of the pressure-dependent thermal contact resistance, and also accounts for sapphire optical transmission. The model and experimental results demonstrate that at most growth conditions the majority of the heat is transported from the wafer pocket to the wafer via gas conduction, in the free molecular flow limit. In this limit gas conductivity is independent of gap size but first order in pressure, and can quantitatively explain results from 20 to 300 Torr. Further analysis yields a measure of the thermal accommodation coefficients; α(H2) =0.23, α(N2) =0.50, which are in the range typically measured.

  1. Measurement and thermal modeling of sapphire substrate temperature at III-Nitride MOVPE conditions

    NASA Astrophysics Data System (ADS)

    Creighton, J. Randall; Coltrin, Michael E.; Figiel, Jeffrey J.

    2017-04-01

    Growth rates and alloy composition of AlGaN grown by MOVPE is often very temperature dependent due to the presence of gas-phase parasitic chemical processes. These processes make wafer temperature measurement highly important, but in fact such measurements are very difficult because of substrate transparency in the near-IR ( 900 nm) where conventional pyrometers detect radiation. The transparency problem can be solved by using a mid-IR pyrometer operating at a wavelength ( 7500 nm) where sapphire is opaque. We employ a mid-IR pyrometer to measure the sapphire wafer temperature and simultaneously a near-IR pyrometer to measure wafer pocket temperature, while varying reactor pressure in both a N2 and H2 ambient. Near 1300 °C, as the reactor pressure is lowered from 300 Torr to 10 Torr the wafer temperature drops dramatically, and the ∆T between the pocket and wafer increases from 20 °C to 250 °C. Without the mid-IR pyrometer the large wafer temperature change with pressure would not have been noted. In order to explain this behavior we have developed a quasi-2D thermal model that includes a proper accounting of the pressure-dependent thermal contact resistance, and also accounts for sapphire optical transmission. The model and experimental results demonstrate that at most growth conditions the majority of the heat is transported from the wafer pocket to the wafer via gas conduction, in the free molecular flow limit. In this limit gas conductivity is independent of gap size but first order in pressure, and can quantitatively explain results from 20 to 300 Torr. Further analysis yields a measure of the thermal accommodation coefficients; α(H2) =0.23, α(N2) =0.50, which are in the range typically measured.

  2. Measurement and thermal modeling of sapphire substrate temperature at III-Nitride MOVPE conditions

    DOE PAGES

    Creighton, J. Randall; Coltrin, Michael E.; Figiel, Jeffrey J.

    2017-04-01

    Here, growth rates and alloy composition of AlGaN grown by MOVPE is often very temperature dependent due to the presence of gas-phase parasitic chemical processes. These processes make wafer temperature measurement highly important, but in fact such measurements are very difficult because of substrate transparency in the near- IR (~900 nm) where conventional pyrometers detect radiation. The transparency problem can be solved by using a mid-IR pyrometer operating at a wavelength (~7500 nm) where sapphire is opaque. We employ a mid- IR pyrometer to measure the sapphire wafer temperature and simultaneously a near-IR pyrometer to measure wafer pocket temperature, whilemore » varying reactor pressure in both a N2 and H2 ambient. Near 1300 °C, as the reactor pressure is lowered from 300 Torr to 10 Torr the wafer temperature drops dramatically, and the ΔT between the pocket and wafer increases from ~20 °C to ~250 °C. Without the mid-IR pyrometer the large wafer temperature change with pressure would not have been noted. In order to explain this behavior we have developed a quasi-2D thermal model that includes a proper accounting of the pressure-dependent thermal contact resistance, and also accounts for sapphire optical transmission. The model and experimental results demonstrate that at most growth conditions the majority of the heat is transported from the wafer pocket to the wafer via gas conduction, in the free molecular flow limit. In this limit gas conductivity is independent of gap size but first order in pressure, and can quantitatively explain results from 20 to 300 Torr. Further analysis yields a measure of the thermal accommodation coefficients; α(H2) =0.23, α(N2) =0.50, which are in the range typically measured.« less

  3. Thermal resistance of ultra-small-diameter disk microlasers

    SciTech Connect

    Zhukov, A. E. Kryzhanovskaya, N. V.; Maximov, M. V.; Lipovskii, A. A.; Savelyev, A. V.; Shostak, I. I.; Moiseev, E. I.; Kudashova, Yu. V.; Kulagina, M. M.; Troshkov, S. I.

    2015-05-15

    The thermal resistance of AlGaAs/GaAs microlasers of the suspended-disk type with a diameter of 1.7–4 μm and InAs/InGaAs quantum dots in the active region is inversely proportional to the squared diameter of the microdisk. The proportionality factor is 3.2 × 10{sup −3} (K cm{sup 2})/W, and the thermal resistance is 120–20°C/mW.

  4. Towards an Accurate Measurement of Thermal Contact Resistance at Chemical Vapor Deposition-Grown Graphene/SiO2 Interface Through Null Point Scanning Thermal Microscopy.

    PubMed

    Chung, Jaehun; Hwang, Gwangseok; Kim, Hyeongkeun; Yang, Wooseok; Kwon, Ohmyoung

    2015-11-01

    In the development of graphene-based electronic devices, it is crucial to characterize the thermal contact resistance between the graphene and the substrate precisely. In this study, we demonstrate that the thermal contact resistance between CVD-grown graphene and SiO2 substrate can be obtained by measuring the temperature drop occurring at the graphene/SiO2 interface with null point scanning thermal microscopy (NP SThM), which profiles the temperature distribution quantitatively with nanoscale spatial resolution (-50 nm) without the shortcomings of the conventional SThM. The thermal contact resistance between the CVD-grown graphene and SiO2 substrate is measured as (1.7 ± 0.27) x 10(-6) M2K/W. This abnormally large thermal contact resistance seems to be caused by extrinsic factors such as ripples and metal-based contamination, which inevitably form in CVD-grown graphene during the production and transfer processes.

  5. Integrated Fresnel lens on thermally oxidized silicon substrate.

    PubMed

    Mottier, P; Valette, S

    1981-05-01

    Thin film Fresnel lenses have been achieved on SiO(2)/Si substrates covered with a waveguide layer of Si(3)N(4) grown by low pressure chemical vapor deposition (LPCVD). The phase shift between the different zones is induced by a SiO(2) top layer chemically etched. The use of this additional layer having a smaller refractive index than the waveguide results in a saturation of the lens characteristics vs the thickness of the SiO(2) layer; this feature associated with the good reproducibility of the LPCVD technology allows good control of the lens characteristics.

  6. Research of surface activating influence on formation of adhesion between gas-thermal coating and steel substrate

    NASA Astrophysics Data System (ADS)

    Kovalevskaya, Z.; Klimenov, V.; Zaitsev, K.

    2015-09-01

    Estimation of influence of physical and thermal activating on adhesion between steel substrates and thermal coatings has been performed. The substrates with surfaces obtained by and ultrasonic surface plastic deformation were used. To evaluate physical activating, preheating of the substrates to 600°C was performed. To evaluate the effect of thermal activating, the substrate surfaces after interfacial detachment were examined. Bonded areas on the substrate surfaces were measured by means of optical profilometry. The experiments have shown that surface physical activating is the main factor in formation of the adhesive bond between the coating and the substrate processed with the proposed methods.

  7. Surface morphology changes of graphene on flexible PET substrate upon thermal annealing.

    PubMed

    Samal, Monica; Lee, Jong Min; Park, Won Il; Yi, Dong Kee; Paik, Ungyu; Lee, Chang-Lyoul

    2011-11-01

    The performance of a polymer photovoltaic device using multilayered graphene on an amorphous PET substrate as the electrode was studied. The changes in surface morphology of graphene coated polyethylene terephthalate (PETG) substrate upon thermal annealing were investigated by atomic force microscopy (AFM), field emission scanning electron microscope (FE-SEM) and current-voltage characteristics. The root mean square (RMS) roughness of PETG substrate before annealing was 36.5 nm that decreased to 11.5 nm after 10 min thermal annealing at 110 degrees C. The mean grain size of the substrate decreased from 2301 nm2 to 848 nm2. The PETG surface became smooth when thermally annealed as the voids created by the bubbles in the graphene layer were filled up with thermal expansion of the PET substrate. However, cracks present initially on the graphene due to surface stress between the graphene and PET layer grew further upon annealing that deteriorated the device performance. This study on the graphene surface morphology change upon annealing and the consequent drop in device performance vis-à-vis an ITO glass electrode shows potential drawback of solar cell device fabrication on such flexible substrates.

  8. Thermal characterization methodology of packages and substrates intended for power electronics

    NASA Astrophysics Data System (ADS)

    Ratolojanahary, Faniry Emilson

    1993-12-01

    An analytical method, which will assist in thermal design problems, and whose formalism is analogous to that of two port network theory, is presented. This method addresses the frequent case of the heating elements being cooled by conduction toward a heat sink through a plane multilayered substrate (for example hybrid power technologies). The method permits thermal characterization of the packaging elements, as well as the formulation of the laws that govern the matching of materials and the evaluation of the package's thermal performance, with reduced computational means. The developed theory also indicates the means needed to measure the thermal parameters of the materials, packages, substrates, coolers, etc., as required by temperature computation. Thus a thermal characterization and measuring set up which is more particularly suited for the power hybrid devices is presented.

  9. Arrayed SU-8 polymer thermal actuators with inherent real-time feedback for actively modifying MEMS’ substrate warpage

    NASA Astrophysics Data System (ADS)

    Wang, Xinghua; Xiao, Dingbang; Chen, Zhihua; Wu, Xuezhong

    2016-09-01

    This paper describes the design, fabrication and characterization of a batch-fabricated micro-thermal actuators array with inherent real-time self-feedback, which can be used to actively modify micro-electro-mechanical systems’ (MEMS’) substrate warpage. Arrayed polymer thermal actuators utilize SU-8 polymer (a thick negative photoresist) as a functional material with integrated Ti/Al film-heaters as a microscale heat source. The electro-thermo-mechanical response of a micro-fabricated actuator was measured. The resistance of the Al/Ti film resistor varies obviously with ambient temperature, which can be used as inherent feedback for observing real-time displacement of activated SU-8 bumps (0.43 μm Ω-1). Due to the high thermal expansion coefficient, SU-8 bumps tend to have relatively large deflection at low driving voltage and are very easily integrated with MEMS devices. Experimental results indicated that the proposed SU-8 polymer thermal actuators (array) are able to achieve accurate rectification of MEMS’ substrate warpage, which might find potential applications for solving stress-induced problems in MEMS.

  10. Vendor Capability for Low Thermal Expansion Mask Substrates for EUV Lithography

    SciTech Connect

    Blaedel, K L; Taylor, J S; Hector, S D; Yan, P Y; Ramamoorthy, A; Brooker, P D

    2002-04-12

    Development of manufacturing infrastructure is required to ensure a commercial source of mask substrates for the timely introduction of EUVL. Improvements to the low thermal expansion materials that compose the substrate have been made, but need to be scaled to production quantities. We have been evaluating three challenging substrate characteristics to determine the state of the infrastructure for the finishing of substrates. First, surface roughness is on track and little risk is associated with achieving the roughness requirement as an independent specification. Second, with new flatness-measuring equipment just coming on line, the vendors are poised for improvement toward the SEMI P37 flatness specification. Third, significant acceleration is needed in the reduction of defect levels on substrates. The lack of high-sensitivity defect metrology at the vendors' sites is limiting progress in developing substrates for EWL.

  11. Significance of thermal contact resistance in two-layer thermal-barrier-coated turbine vanes

    NASA Technical Reports Server (NTRS)

    Liebert, C. H.; Gaugler, R. E.

    1980-01-01

    The importance of thermal contact resistance between layers in heat transfer through two layer, plasma sprayed, thermal barrier coatings applied to turbine vanes was investigated. Results obtained with a system of NiCrAlY bond and yttria stabilized zirconia ceramic show that thermal contact resistance between layers is negligible. These results also verified other studies which showed that thermal contact resistance is negligible for a different coating system of NiCr bond calcia stabilized zirconia ceramic. The zirconia stabilized ceramic thermal conductivity data scatter presented in the literature is ?20 to -10 percent about a curve fit of the data. More accurate predictions of heat transfer and metal wall temperatures are obtained when the thermal conductivity values are used at the ?20 percent level.

  12. Substrate-bound structure of the E. coli multidrug resistance transporter MdfA

    PubMed Central

    Heng, Jie; Zhao, Yan; Liu, Ming; Liu, Yue; Fan, Junping; Wang, Xianping; Zhao, Yongfang; Zhang, Xuejun C

    2015-01-01

    Multidrug resistance is a serious threat to public health. Proton motive force-driven antiporters from the major facilitator superfamily (MFS) constitute a major group of multidrug-resistance transporters. Currently, no reports on crystal structures of MFS antiporters in complex with their substrates exist. The E. coli MdfA transporter is a well-studied model system for biochemical analyses of multidrug-resistance MFS antiporters. Here, we report three crystal structures of MdfA-ligand complexes at resolutions up to 2.0 Å, all in the inward-facing conformation. The substrate-binding site sits proximal to the conserved acidic residue, D34. Our mutagenesis studies support the structural observations of the substrate-binding mode and the notion that D34 responds to substrate binding by adjusting its protonation status. Taken together, our data unveil the substrate-binding mode of MFS antiporters and suggest a mechanism of transport via this group of transporters. PMID:26238402

  13. Substrate control of anisotropic resistivity in heteroepitaxial nanostructured arrays of cryptomelane manganese oxide on strontium titanate.

    PubMed

    Espinal, Anais E; Yan, Yonggao; Zhang, Lichun; Espinal, Laura; Morey, Aimee; Wells, Barrett O; Aindow, Mark; Suib, Steven L

    2014-01-15

    Resistivity and resistance measurements have been carried out for thin films of cryptomelane-type manganese oxide (OMS-2) grown onto (001), (110), and (111)STO single crystals substrates via pulsed laser deposition. While the symmetries of the (001) and (111)STO substrate surfaces give deposits consisting of multiple nanofiber arrays with isotropic in-plane resistivities, only a single nanofiber array is formed on (110)STO giving highly anisotropic electrical properties with very low resistivity values measured parallel to the fibers and similar to the lowest value ever reported.

  14. Thermal transport in bismuth telluride quintuple layer: mode-resolved phonon properties and substrate effects

    PubMed Central

    Shao, Cheng; Bao, Hua

    2016-01-01

    The successful exfoliation of atomically-thin bismuth telluride (Bi2Te3) quintuple layer (QL) attracts tremendous research interest in this strongly anharmonic quasi-two-dimensional material. The thermal transport properties of this material are not well understood, especially the mode-wise properties and when it is coupled with a substrate. In this work, we have performed molecular dynamics simulations and normal mode analysis to study the mode-resolved thermal transport in freestanding and supported Bi2Te3 QL. The detailed mode-wise phonon properties are calculated and the accumulated thermal conductivities with respect to phonon mean free path (MFP) are constructed. It is shown that 60% of the thermal transport is contributed by phonons with MFP longer than 20 nm. Coupling with a-SiO2 substrate leads to about 60% reduction of thermal conductivity. Through varying the interfacial coupling strength and the atomic mass of substrate, we also find that phonon in Bi2Te3 QL is more strongly scattered by interfacial potential and its transport process is less affected by the dynamics of substrate. Our study provides an in-depth understanding of heat transport in Bi2Te3 QL and is helpful in further tailoring its thermal property through nanostructuring. PMID:27263656

  15. Thermally resistant polymers for fuel tank sealants

    NASA Technical Reports Server (NTRS)

    Webster, J. A.

    1972-01-01

    Conversion of fluorocarbon dicarboxylic acid to intermediates whose terminal functional groups permit polymerization is discussed. Resulting polymers are used as fuel tank sealers for jet fuels at elevated temperatures. Stability and fuel resistance of the prototype polymers is explained.

  16. Effects of substrate properties on the hydraulic and thermal behavior of a green roof

    NASA Astrophysics Data System (ADS)

    Sandoval, V. P.; Suarez, F. I.; Victorero, F.; Bonilla, C.; Gironas, J. A.; Vera, S.; Bustamante, W.; Rojas, V.; Pasten, P.

    2014-12-01

    Green roofs are a sustainable urban development solution that incorporates a growing media (also known as substrate) and vegetation into infrastructures to reach additional benefits such as the reduction of: rooftop runoff peak flows, roof surface temperatures, energy utilized for cooling/heating buildings, and the heat island effect. The substrate is a key component of the green roof that allows achieving these benefits. It is an artificial soil that has an improved behavior compared to natural soils, facilitating vegetation growth, water storage and typically with smaller densities to reduce the loads over the structures. Therefore, it is important to study the effects of substrate properties on green roof performance. The objective of this study is to investigate the physical properties of four substrates designed to improve the behavior of a green roof, and to study their impact on the efficiency of a green roof. The substrates that were investigated are: organic soil; crushed bricks; a mixture of mineral soil with perlite; and a mixture of crushed bricks and organic soil. The thermal properties (thermal conductivity, volumetric heat capacity and thermal diffusivity) were measured using a dual needle probe (Decagon Devices, Inc.) at different saturation levels, and the hydraulic properties were measured with a constant head permeameter (hydraulic conductivity) and a pressure plate extractor (water retention curve). This characterization, combined with numerical models, allows understanding the effect of these properties on the hydraulic and thermal behavior of a green roof. Results show that substrates composed by crushed bricks improve the thermal insulation of infrastructures and at the same time, retain more water in their pores. Simulation results also show that the hydraulic and thermal behavior of a green roof strongly depends on the moisture content prior to a rainstorm.

  17. Thermally assisted peeling of an elastic strip in adhesion with a substrate via molecular bonds

    NASA Astrophysics Data System (ADS)

    Qian, Jin; Lin, Ji; Xu, Guang-Kui; Lin, Yuan; Gao, Huajian

    A statistical model is proposed to describe the peeling of an elastic strip in adhesion with a flat substrate via an array of non-covalent molecular bonds. Under an imposed tensile peeling force, the interfacial bonds undergo diffusion-type transition in their bonding state, a process governed by a set of probabilistic equations coupled to the stretching, bending and shearing of the elastic strip. Because of the low characteristic energy scale associated with molecular bonding, thermal excitations are found to play an important role in assisting the escape of individual molecular bonds from their bonding energy well, leading to propagation of the peeling front well below the threshold peel-off force predicted by the classical theories. Our study establishes a link between the deformation of the strip and the spatiotemporal evolution of interfacial bonds, and delineates how factors like the peeling force, bending rigidity of the strip and binding energy of bonds influence the resultant peeling velocity and dimensions of the process zone. In terms of the apparent adhesion strength and dissipated energy, the bond-mediated interface is found to resist peeling in a strongly rate-dependent manner.

  18. Microfluidic devices obtained by thermal toner transferring on glass substrate.

    PubMed

    do Lago, Claudimir L; Neves, Carlos A; Pereira de Jesus, Dosil; da Silva, Heron D T; Brito-Neto, José G A; Fracassi da Silva, José A

    2004-11-01

    A new process for the manufacture of microfluidic devices based on deposition of laser-printing toner on glass substrates is described. It is an alternative method to the toner on polyester film (toner-polyester) one, previously introduced. Commercial laser printers cannot print directly on glass, thus the toner must first be printed on a special paper and then transferred by heating under pressure to the glass surface. Although this procedure is more complex than the toner-polyester one, it can be repeated several times, yielding multiple toner layers. Even without special alignment equipment, up to four layers could be satisfactorily piled up. Characterization tests revealed that the toner-glass devices have similar behavior as toner-polyester ones regarding the toner layer porosity. The main advantages of the toner-glass technology are improved mechanical stability, possibility of multiple toner layers, augmented electroosmotic flow (EOF), and improved heat transfer. On the other hand, toner adhesion to glass is weaker than to polyester, which limits the device lifetime and usable liquid media. The measured EOF mobility (3.5 x 10(-4) cm2.V(-1).s(-1) for pH 7) suggests that it is mainly determined by the glass surface, being little influenced by the toner walls. Microchip electrophoresis with contactless conductivity detection and photometric detection were implemented using toner-glass devices.

  19. Structural and optical properties of copper-coated substrates for solar thermal absorbers

    NASA Astrophysics Data System (ADS)

    Pratesi, Stefano; De Lucia, Maurizio; Meucci, Marco; Sani, Elisa

    2016-10-01

    Spectral selectivity, i.e. merging a high absorbance at sunlight wavelengths to a low emittance at the wavelengths of thermal spectrum, is a key characteristics for materials to be used for solar thermal receivers. It is known that spectrally selective absorbers can raise the receiver efficiency for all solar thermal technologies. Tubular sunlight receivers for parabolic trough collector (PTC) systems can be improved by the use of spectrally selective coatings. Their absorbance is increased by deposing black films, while the thermal emittance is minimized by the use of properly-prepared substrates. In this work we describe the intermediate step in the fabrication of black-chrome coated solar absorbers, namely the fabrication and characterization of copper coatings on previously nickel-plated stainless steel substrates. We investigate the copper surface features and optical properties, correlating them to the coating thickness and to the deposition process, in the perspective to assess optimal conditions for solar absorber applications.

  20. Effect of Cu Addition to Zn-12Al Alloy on Thermal Properties and Wettability on Cu and Al Substrates

    NASA Astrophysics Data System (ADS)

    Gancarz, Tomasz; Pstruś, Janusz; Mosińska, Sylwia; Pawlak, Sylwia

    2016-01-01

    The thermal properties, electrical resistivity, thermal linear expansion and tensile strength of a new high-temperature lead-free solder based on a eutectic Zn-Al alloy with 0.5, 1.0, or 1.5 at. pct Cu added were studied. Wettability studies on Cu substrate were performed with flux at 773 K (500 °C) for 60, 180, 240, 900, 1800, and 3600 seconds, and for 480 seconds at 733 K, 753 K, 773 K, 793 K, and 823 K (460 °C, 480 °C, 500 °C, 520 °C, and 550 °C, respectively). The experiment was designed to demonstrate the effect of the addition of Cu on the kinetics of the formation and growth of the CuZn, Cu5Zn8, CuZn4, and Al4Cu9 phases, which were identified by X-ray diffraction analysis. Wetting tests were also performed on the Al substrate, for 15 and 30 seconds at 773 K and 793 K (500 °C and 520 °C, respectively). Very low contact angles on Al pads were obtained. The electrical resistivity of Zn-Al-Cu alloys was slightly higher than that of the ZnAl eutectic alloy. The present results are discussed with respect to the available literature on Zn-Al and Zn-Al-Cu alloys.

  1. Thermal resistance of Saccharomyces yeast ascospores in beers.

    PubMed

    Milani, Elham A; Gardner, Richard C; Silva, Filipa V M

    2015-08-03

    The industrial production of beer ends with a process of thermal pasteurization. Saccharomyces cerevisiae and Saccharomyces pastorianus are yeasts used to produce top and bottom fermenting beers, respectively. In this research, first the sporulation rate of 12 Saccharomyces strains was studied. Then, the thermal resistance of ascospores of three S. cerevisiae strains (DSMZ 1848, DSMZ 70487, Ethanol Red(®)) and one strain of S. pastorianus (ATCC 9080) was determined in 4% (v/v) ethanol lager beer. D60 °C-values of 11.2, 7.5, 4.6, and 6.0 min and z-values of 11.7, 14.3, 12.4, and 12.7 °C were determined for DSMZ 1848, DSMZ 70487, ATCC 9080, and Ethanol Red(®), respectively. Lastly, experiments with 0 and 7% (v/v) beers were carried out to investigate the effect of ethanol content on the thermal resistance of S. cerevisiae (DSMZ 1848). D55 °C-values of 34.2 and 15.3 min were obtained for 0 and 7% beers, respectively, indicating lower thermal resistance in the more alcoholic beer. These results demonstrate similar spore thermal resistance for different Saccharomyces strains and will assist in the design of appropriate thermal pasteurization conditions for preserving beers with different alcohol contents.

  2. Coral Thermal Tolerance: Tuning Gene Expression to Resist Thermal Stress

    PubMed Central

    Bellantuono, Anthony J.; Granados-Cifuentes, Camila; Miller, David J.; Hoegh-Guldberg, Ove; Rodriguez-Lanetty, Mauricio

    2012-01-01

    The acclimatization capacity of corals is a critical consideration in the persistence of coral reefs under stresses imposed by global climate change. The stress history of corals plays a role in subsequent response to heat stress, but the transcriptomic changes associated with these plastic changes have not been previously explored. In order to identify host transcriptomic changes associated with acquired thermal tolerance in the scleractinian coral Acropora millepora, corals preconditioned to a sub-lethal temperature of 3°C below bleaching threshold temperature were compared to both non-preconditioned corals and untreated controls using a cDNA microarray platform. After eight days of hyperthermal challenge, conditions under which non-preconditioned corals bleached and preconditioned corals (thermal-tolerant) maintained Symbiodinium density, a clear differentiation in the transcriptional profiles was revealed among the condition examined. Among these changes, nine differentially expressed genes separated preconditioned corals from non-preconditioned corals, with 42 genes differentially expressed between control and preconditioned treatments, and 70 genes between non-preconditioned corals and controls. Differentially expressed genes included components of an apoptotic signaling cascade, which suggest the inhibition of apoptosis in preconditioned corals. Additionally, lectins and genes involved in response to oxidative stress were also detected. One dominant pattern was the apparent tuning of gene expression observed between preconditioned and non-preconditioned treatments; that is, differences in expression magnitude were more apparent than differences in the identity of genes differentially expressed. Our work revealed a transcriptomic signature underlying the tolerance associated with coral thermal history, and suggests that understanding the molecular mechanisms behind physiological acclimatization would be critical for the modeling of reefs in impending climate

  3. Coral thermal tolerance: tuning gene expression to resist thermal stress.

    PubMed

    Bellantuono, Anthony J; Granados-Cifuentes, Camila; Miller, David J; Hoegh-Guldberg, Ove; Rodriguez-Lanetty, Mauricio

    2012-01-01

    The acclimatization capacity of corals is a critical consideration in the persistence of coral reefs under stresses imposed by global climate change. The stress history of corals plays a role in subsequent response to heat stress, but the transcriptomic changes associated with these plastic changes have not been previously explored. In order to identify host transcriptomic changes associated with acquired thermal tolerance in the scleractinian coral Acropora millepora, corals preconditioned to a sub-lethal temperature of 3°C below bleaching threshold temperature were compared to both non-preconditioned corals and untreated controls using a cDNA microarray platform. After eight days of hyperthermal challenge, conditions under which non-preconditioned corals bleached and preconditioned corals (thermal-tolerant) maintained Symbiodinium density, a clear differentiation in the transcriptional profiles was revealed among the condition examined. Among these changes, nine differentially expressed genes separated preconditioned corals from non-preconditioned corals, with 42 genes differentially expressed between control and preconditioned treatments, and 70 genes between non-preconditioned corals and controls. Differentially expressed genes included components of an apoptotic signaling cascade, which suggest the inhibition of apoptosis in preconditioned corals. Additionally, lectins and genes involved in response to oxidative stress were also detected. One dominant pattern was the apparent tuning of gene expression observed between preconditioned and non-preconditioned treatments; that is, differences in expression magnitude were more apparent than differences in the identity of genes differentially expressed. Our work revealed a transcriptomic signature underlying the tolerance associated with coral thermal history, and suggests that understanding the molecular mechanisms behind physiological acclimatization would be critical for the modeling of reefs in impending climate

  4. Optimal Substrate Preheating Model for Thermal Spray Deposition of Thermosets onto Polymer Matrix Composites

    NASA Technical Reports Server (NTRS)

    Ivosevic, M.; Knight, R.; Kalidindi, S. R.; Palmese, G. R.; Tsurikov, A.; Sutter, J. K.

    2003-01-01

    High velocity oxy-fuel (HVOF) sprayed, functionally graded polyimide/WC-Co composite coatings on polymer matrix composites (PMC's) are being investigated for applications in turbine engine technologies. This requires that the polyimide, used as the matrix material, be fully crosslinked during deposition in order to maximize its engineering properties. The rapid heating and cooling nature of the HVOF spray process and the high heat flux through the coating into the substrate typically do not allow sufficient time at temperature for curing of the thermoset. It was hypothesized that external substrate preheating might enhance the deposition behavior and curing reaction during the thermal spraying of polyimide thermosets. A simple analytical process model for the deposition of thermosetting polyimide onto polymer matrix composites by HVOF thermal spray technology has been developed. The model incorporates various heat transfer mechanisms and enables surface temperature profiles of the coating to be simulated, primarily as a function of substrate preheating temperature. Four cases were modeled: (i) no substrate preheating; (ii) substrates electrically preheated from the rear; (iii) substrates preheated by hot air from the front face; and (iv) substrates electrically preheated from the rear and by hot air from the front.

  5. Impact of substrate surface scratches on the laser damage resistance of multilayer coatings

    SciTech Connect

    Qiu, S; Wolfe, J; Monterrosa, A; Teslich, N; Feit, M; Pistor, T; Stolz, C

    2010-11-03

    Substrate scratches can limit the laser resistance of multilayer mirror coatings on high-peak-power laser systems. To date, the mechanism by which substrate surface defects affect the performance of coating layers under high power laser irradiation is not well defined. In this study, we combine experimental approaches with theoretical simulations to delineate the correlation between laser damage resistance of coating layers and the physical properties of the substrate surface defects including scratches. A focused ion beam technique is used to reveal the morphological evolution of coating layers on surface scratches. Preliminary results show that coating layers initially follow the trench morphology on the substrate surface, and as the thickness increases, gradually overcoat voids and planarize the surface. Simulations of the electrical-field distribution of the defective layers using the finite-difference time-domain (FDTD) method show that field intensification exists mostly near the top surface region of the coating near convex focusing structures. The light intensification could be responsible for the reduced damage threshold. Damage testing under 1064 nm, 3 ns laser irradiation over coating layers on substrates with designed scratches show that damage probability and threshold of the multilayer depend on substrate scratch density and width. Our preliminary results show that damage occurs on the region of the coating where substrate scratches reside and etching of the substrate before coating does not seem to improve the laser damage resistance.

  6. Design and Construction of a Thermal Contact Resistance and Thermal Conductivity Measurement System

    DTIC Science & Technology

    2015-09-01

    systems to improve fuel efficiency and performance. Comprehensive details of the design, construction, and operation of the experimental device are... heat transfer issues facing the Department of Defense. 14. SUBJECT TERMS Thermal contact resistance, thermal conductivity, measurement system 15...analyze component interfaces and advanced material applications within Department of Defense’s energy systems to improve fuel efficiency and

  7. Modeling the electrical resistance of gold film conductors on uniaxially stretched elastomeric substrates

    NASA Astrophysics Data System (ADS)

    Cao, Wenzhe; Görrn, Patrick; Wagner, Sigurd

    2011-05-01

    The electrical resistance of gold film conductors on polydimethyl siloxane substrates at stages of uniaxial stretching is measured and modeled. The surface area of a gold conductor is assumed constant during stretching so that the exposed substrate takes up all strain. Sheet resistances are calculated from frames of scanning electron micrographs by numerically solving for the electrical potentials of all pixels in a frame. These sheet resistances agree sufficiently well with values measured on the same conductors to give credence to the model of a stretchable network of gold links defined by microcracks.

  8. Ultra low thermal expansion, highly thermal shock resistant ceramic

    DOEpatents

    Limaye, Santosh Y.

    1996-01-01

    Three families of ceramic compositions having the given formula: .phi..sub.1+X Zr.sub.4 P.sub.6-2X Si.sub.2X O.sub.24, .phi..sub.1+X Zr.sub.4-2X Y.sub.2X P.sub.6 O.sub.24 and .phi..sub.1+X Zr.sub.4-X Y.sub.X P.sub.6-2X Si.sub.X O.sub.24 wherein .phi. is either Strontium or Barium and X has a value from about 0.2 to about 0.8 have been disclosed. Ceramics formed from these compositions exhibit very low, generally near neutral, thermal expansion over a wide range of elevated temperatures.

  9. Ultra low thermal expansion, highly thermal shock resistant ceramic

    DOEpatents

    Limaye, S.Y.

    1996-01-30

    Three families of ceramic compositions having the given formula: {phi}{sub 1+X}Zr{sub 4}P{sub 6{minus}2X}Si{sub 2X}O{sub 24}, {phi}{sub 1+X}Zr{sub 4{minus}2X}Y{sub 2X}P{sub 6}O{sub 24} and {phi}{sub 1+X}Zr{sub 4{minus}X}Y{sub X}P{sub 6{minus}2X}Si{sub X}O{sub 24} wherein {phi} is either strontium or barium and X has a value from about 0.2 to about 0.8 have been disclosed. Ceramics formed from these compositions exhibit very low, generally near neutral, thermal expansion over a wide range of elevated temperatures. 7 figs.

  10. High-gain phototransistors on high-resistivity silicon substrate

    NASA Astrophysics Data System (ADS)

    Batignani, G.; Bisogni, M. G.; Boscardin, M.; Bosisio, L.; Dalla Betta, G. F.; Del Guerra, A.; Dittongo, S.; Forti, F.; Giorgi, M.; Han, D. J.; Linsalata, S.; Marchiori, G.; Piemonte, C.; Rachevskaia, I.; Ronchin, S.

    2004-02-01

    NPN phototransistors have been fabricated on high-purity silicon substrate. The devices have been produced by ITC-IRST in the framework of a National Research Project funded by the Italian Education, University and Research Ministry (MIUR). The phototransistor emitter is composed of a phosphorus n + implant, the base is a diffused high-energy boron implant, and the collector is the 300 μm thick silicon bulk. Several devices have been investigated. Results with 22 keV X-ray from a 109Cd-radioactive source and visible light irradiation are presented.

  11. Pattern transfer from the e-beam resist, over the nanoimprint resist and to the final silicon substrate

    NASA Astrophysics Data System (ADS)

    He, Jian; Howitz, S.; Richter, K.; Bartha, J. W.; Moench, J. I.

    2012-03-01

    We developed Fluor-based RIE processes to fabricate nanoimprint template in silicon and to transfer patterns from the imprint resist to the silicon substrate. The etched silicon patterns have slightly tapered and smooth sidewalls. The sidewall angle can be controlled between 85° and 90° by varying the ratio of the used gas. The dimension of the etched structures is identical with the patterns in the resist. We demonstrated line structures in silicon substrate down to 50 nm. The etching rate is over 100 nm per minute and the maximal achieved aspect ratio is more than 10.

  12. Modeling Penicillium expansum resistance to thermal and chlorine treatments.

    PubMed

    Salomão, Beatriz C M; Churey, John J; Aragão, Gláucia M F; Worobo, Randy W

    2009-12-01

    Apples and apple products are excellent substrates for Penicillium expansum to produce patulin. In an attempt to avoid excessive levels of patulin, limiting or reducing P. expansum contamination levels on apples designated for storage in packinghouses and/or during apple juice processing is critical. The aim of this work was (i) to determine the thermal resistance of P. expansum spores in apple juice, comparing the abilities of the Bigelow and Weibull models to describe the survival curves and (ii) to determine the inactivation of P. expansum spores in aqueous chlorine solutions at varying concentrations of chlorine solutions, comparing the abilities of the biphasic and Weibull models to fit the survival curves. The results showed that the Bigelow and Weibull models were similar for describing the heat inactivation data, because the survival curves were almost linear. In this case, the concept of D- and z-values could be used, and the D-values obtained were 10.68, 6.64, 3.32, 1.14, and 0.61 min at 50, 52, 54, 56, and 60 degrees C, respectively, while the z-value was determined to be 7.57 degrees C. For the chlorine treatments, although the biphasic model gave a slightly superior performance, the Weibull model was selected, considering the parsimony principle, because it has fewer parameters than the biphasic model has. In conclusion, the typical pasteurization regimen used for refrigerated apple juice (71 degrees C for 6 s) is capable of achieving a 6-log reduction of P. expansum spores.

  13. Techniques for Reducing Thermal Contact Resistance in Steady-State Thermal Conductivity Measurements on Polymer Composites

    NASA Astrophysics Data System (ADS)

    Stacey, C.; Simpkin, A. J.; Jarrett, R. N.

    2016-11-01

    The National Physical Laboratory (NPL) has developed a new variation on the established guarded hot plate technique for steady-state measurements of thermal conductivity. This new guarded hot plate has been specifically designed for making measurements on specimens with a thickness that is practical for advanced industrial composite materials and applications. During the development of this new guarded hot plate, NPL carried out an experimental investigation into methods for minimising the thermal contact resistance between the test specimen and the plates of the apparatus. This experimental investigation included tests on different thermal interface materials for use in another NPL facility based on a commercial guarded heat flow meter apparatus conforming to standard ASTM E1530-11. The results show the effect of applying different quantities of the type of heat transfer compound suggested in ASTM E1530-11 (clause 10.7.3) and also the effect on thermal resistance of alternative types of thermal interface products. The optimum quantities of two silicone greases were determined, and a silicone grease filled with copper was found to offer the best combination of repeatability, small hysteresis effect and a low thermal contact resistance. However, two products based on a textured indium foil and pyrolytic graphite sheet were found to offer similar or better reductions in thermal contact resistance, but with quicker, easier application and the advantages of protecting the apparatus plates from damage and being useable with specimen materials that would otherwise absorb silicone grease.

  14. SOFI/Substrate integrity testing for cryogenic propellant tanks at extreme thermal gradient conditions

    NASA Astrophysics Data System (ADS)

    Haynes, M.; Fabian, P.

    2015-12-01

    Liquid propellant tank insulation for space flight requires low weight as well as high insulation factors. Use of Spray-On Foam Insulation (SOFI) is an accepted, cost effective technique for insulating a single wall cryogenic propellant tank and has been used extensively throughout the aerospace industry. Determining the bond integrity of the SOFI to the metallic substrate as well as its ability to withstand the in-service strains, both mechanical and thermal, is critical to the longevity of the insulation. This determination has previously been performed using highly volatile, explosive cryogens, which increases the test costs enormously, as well as greatly increasing the risk to both equipment and personnel. CTD has developed a new test system, based on a previous NASA test that simulates the mechanical and thermal strains associated with filling a large fuel tank with a cryogen. The test enables a relatively small SOFI/substrate sample to be monitored for any deformations, delaminations, or disjunctures during the cooling and mechanical straining process of the substrate, and enables the concurrent application of thermal and physical strains to two specimens at the same time. The thermal strains are applied by cooling the substrate to the desired cryogen temperature (from 4 K to 250 K) while maintaining the outside surface of the SOFI foam at ambient conditions. Multiple temperature monitoring points are exercised to ensure even cooling across the substrate, while at the same time, surface temperatures of the SOFI can be monitored to determine the heat flow. The system also allows for direct measurement of the strains in the substrate during the test. The test system as well as test data from testing at 20 K, for liquid Hydrogen simulation, will be discussed.

  15. Surface modification of several dental substrates by non-thermal, atmospheric plasma brush

    PubMed Central

    Chen, Mingsheng; Zhang, Ying; Driver, M. Sky; Caruso, Anthony N.; Yu, Qingsong; Wang, Yong

    2013-01-01

    Objective The purpose of this study was to reveal the effectiveness of non-thermal atmospheric plasma brush in surface wettability and modification of four dental substrates. Methods Specimens of dental substrates including dentin, enamel, and two composites Filtek Z250, Filtek LS Silorane were prepared (~2 mm thick, ~10 mm diameter). The prepared surfaces were treated for 5–45 s with a non-thermal atmospheric plasma brush working at temperatures from 36 to 38 °C. The plasma-treatment effects on these surfaces were studied with contact-angle measurement, X-ray photoemission spectroscopy (XPS) and scanning electron microscopy (SEM). Results The non-thermal atmospheric argon plasma brush was very efficient in improving the surface hydrophilicity of four substrates studied. The results indicated that water contact angle values decreased considerably after only 5 s plasma treatment of all these substrates. After 30 s treatment, the values were further reduced to <5°, which was close to a value for super hydrophilic surfaces. XPS analysis indicated that the percent of elements associated with mineral in dentin/enamel or fillers in the composites increased. In addition, the percent of carbon (%C) decreased while %O increased for all four substrates. As a result, the O/C ratio increased dramatically, suggesting that new oxygen-containing polar moieties were formed on the surfaces after plasma treatment. SEM surface images indicated that no significant morphology change was induced on these dental substrates after exposure to plasmas. Significance Without affecting the bulk properties, a super-hydrophilic surface could be easily achieved by the plasma brush treatment regardless of original hydrophilicity/hydrophobicity of dental substrates tested. PMID:23755823

  16. Thermal instability of a radiative and resistive coronal plasma

    NASA Technical Reports Server (NTRS)

    Sparks, L.; Van Hoven, G.

    1988-01-01

    Thermal instability is believed to determine the evolution and formation of cool structures in the solar atmosphere such as the transition region and prominences (or filaments). The linear modes that arise in a sheared, force-free, magnetic field due to thermal instability are studied numerically. Previous studies have considered separately modes that arise due to the effects of radiation, compression, anisotropic thermal conduction, and ohmic heating. Here the results of such studies are integrated, first by presenting simple arguments that illustrate the essential physics of ideal, sheared-field, condensation modes, and second by showing numerically how finite resistivity affects the condensational instability in parameter regimes applicable to the solar corona.

  17. High temperature resistant cermet and ceramic compositions. [for thermal resistant insulators and refractory coatings

    NASA Technical Reports Server (NTRS)

    Phillips, W. M. (Inventor)

    1978-01-01

    High temperature oxidation resistance, high hardness and high abrasion and wear resistance are properties of cermet compositions particularly to provide high temperature resistant refractory coatings on metal substrates, for use as electrical insulation seals for thermionic converters. The compositions comprise a sintered body of particles of a high temperature resistant metal or metal alloy, preferably molybdenum or tungsten particles, dispersed in and bonded to a solid solution formed of aluminum oxide and silicon nitride, and particularly a ternary solid solution formed of a mixture of aluminum oxide, silicon nitride and aluminum nitride. Ceramic compositions comprising a sintered solid solution of aluminum oxide, silicon nitride and aluminum nitride are also described.

  18. Ambient cure polyimide foams. [thermal resistant foams

    NASA Technical Reports Server (NTRS)

    Sawko, P. M.; Riccitiello, S. R.; Hamermesh, C. L. (Inventor)

    1978-01-01

    Flame and temperature resistant polyimide foams are prepared by the reaction of an aromatic dianhydride, (pyromellitic dianhydride) with an aromatic polyisocyanate, (polymethylene polyphenylisocyanate), in the presence of an inorganic acid and furfuryl alcohol. Usable acids include dilute sulfuric acid, dilute nitric acid, hydrochloric acid, polyphosphoric acid, and phosphoric acid, with the latter being preferred. The dianhydride and the isocyanate in about equimolar proportions constitute about 50% of the reaction mixture, the rest being made up with the acid and the alcohol in a ratio of about 1:10. An exothermic reaction between the acid and the alcohol provides the heat necessary for the other components to polymerize without recourse to external heat sources. The mixture can be sprayed on any surface to form polymeric foam in locations where the application of heat is not practical or possible, for instance, between walls or on mine tunnel surfaces.

  19. Substrate effect on thermal stability of superconductor thin films in the peritectic melting.

    PubMed

    Chen, Y Y; Fang, T F; Yan, S B; Yao, X; Tao, B W

    2012-05-31

    Systematic experiments were performed by in situ observation of the YBa(2)Cu(3)O(z) (Y123 or YBCO) melting. Remarkably, the superheating phenomenon was identified to exist in all commonly used YBCO thin films, that is, films deposited on MgO, LaAlO(3) (LAO), and SrTiO(3) (STO) substrates, suggesting a universal superheating mode of the YBCO film. Distinctively, YBCO/LAO films were found to possess the highest level of superheating, over 100 K, mainly attributed to the lattice match effect of LAO substrate, that is, its superior lattice fit with Y123 delaying the Y123 dissolving and inferior lattice matching with Y(2)BaCuO(5) (Y211) delaying the Y211 nucleation. Moreover, strong dependence of the thermal stability on the substrate material for Y123 films was also found to be associated with the substrate wettability by the liquid and the potential element doping from the substrate. Most importantly, the understanding of the superheating behavior is widely valid for more film/substrate constructions that have the same nature as the YBCO film/substrate.

  20. Interface thermal conductance of van der Waals monolayers on amorphous substrates

    NASA Astrophysics Data System (ADS)

    Correa, Gabriela C.; Foss, Cameron J.; Aksamija, Zlatan

    2017-03-01

    Heterostructures based on atomic monolayers are emerging as leading materials for future energy efficient and multifunctional electronics. Due to the single atom thickness of monolayers, their properties are strongly affected by interactions with the external environment. We develop a model for interface thermal conductance (ITC) in an atomic monolayer van der Waals bonded to a disordered substrate. Graphene on SiO2 is initially used in our model and contrasted against available experimental data; the model is then applied to monolayer molybdenum disulfide (MoS2) on SiO2 substrate. Our findings show the dominant carrier of heat in both graphene and MoS2 in the cross-plane direction is the flexural (ZA) phonon mode, owing to the large overlap between graphene ZA and substrate vibrational density of states. The rate of phonon transfer across the interface depends quadratically on the substrate coupling constant K a , but this interaction also causes a lifting of the lowest flexural phonon modes. As a result, ITC depends roughly linearly on the strength of the coupling between a monolayer and its substrate. We conclude that, in both graphene and MoS2 on SiO2, substrate adhesion plays a strong role in determining ITC, requiring further study of substrate coupling in TMDCs.

  1. Interface thermal conductance of van der Waals monolayers on amorphous substrates.

    PubMed

    Correa, Gabriela C; Foss, Cameron J; Aksamija, Zlatan

    2017-03-01

    Heterostructures based on atomic monolayers are emerging as leading materials for future energy efficient and multifunctional electronics. Due to the single atom thickness of monolayers, their properties are strongly affected by interactions with the external environment. We develop a model for interface thermal conductance (ITC) in an atomic monolayer van der Waals bonded to a disordered substrate. Graphene on SiO2 is initially used in our model and contrasted against available experimental data; the model is then applied to monolayer molybdenum disulfide (MoS2) on SiO2 substrate. Our findings show the dominant carrier of heat in both graphene and MoS2 in the cross-plane direction is the flexural (ZA) phonon mode, owing to the large overlap between graphene ZA and substrate vibrational density of states. The rate of phonon transfer across the interface depends quadratically on the substrate coupling constant K a , but this interaction also causes a lifting of the lowest flexural phonon modes. As a result, ITC depends roughly linearly on the strength of the coupling between a monolayer and its substrate. We conclude that, in both graphene and MoS2 on SiO2, substrate adhesion plays a strong role in determining ITC, requiring further study of substrate coupling in TMDCs.

  2. Thermal resistance of ridge-waveguide lasers mounted upside down

    SciTech Connect

    Amann, M.

    1987-01-05

    The heat dissipation in upside down mounted ridge-waveguide lasers equipped with a double-channel structure is analyzed by a simplified device model. Assuming an isothermal active region, the thermal resistance is obtained by means of conformal mapping. A comparison to published experimental results shows good agreement.

  3. Thermal and Microstructure Characterization of Zn-Al-Si Alloys and Chemical Reaction with Cu Substrate During Spreading

    NASA Astrophysics Data System (ADS)

    Berent, Katarzyna; Pstruś, Janusz; Gancarz, Tomasz

    2016-08-01

    The problems associated with the corrosion of aluminum connections, the low mechanical properties of Al/Cu connections, and the introduction of EU directives have forced the potential of new materials to be investigated. Alloys based on eutectic Zn-Al are proposed, because they have a higher melting temperature (381 °C), good corrosion resistance, and high mechanical strength. The Zn-Al-Si cast alloys were characterized using differential scanning calorimetry (DSC) measurements, which were performed to determine the melting temperatures of the alloys. Thermal linear expansion and electrical resistivity measurements were performed at temperature ranges of -50 to 250 °C and 25 to 300 °C, respectively. The addition of Si to eutectic Zn-Al alloys not only limits the growth of phases at the interface of liquid solder and Cu substrate but also raises the mechanical properties of the solder. Spreading test on Cu substrate using eutectic Zn-Al alloys with 0.5, 1.0, 3.0, and 5.0 wt.% of Si was studied using the sessile drop method in the presence of QJ201 flux. Spreading tests were performed with contact times of 1, 8, 15, 30, and 60 min, and at temperatures of 475, 500, 525, and 550 °C. After cleaning the flux residue from solidified samples, the spreadability of Zn-Al-Si on Cu was determined. Selected, solidified solder/substrate couples were cross-sectioned, and the interfacial microstructures were studied using scanning electron microscopy and energy dispersive x-ray spectroscopy. The growth of the intermetallic phase layer was studied at the solder/substrate interface, and the activation energy of growth of Cu5Zn8, CuZn4, and CuZn phases were determined.

  4. Estimating the thermal expansion coefficient of graphene: the role of graphene-substrate interactions.

    PubMed

    Shaina, P R; George, Lijin; Yadav, Vani; Jaiswal, Manu

    2016-03-02

    The temperature-dependent thermal expansion coefficient of graphene is estimated for as-grown chemical vapor deposited graphene using temperature-dependent Raman spectroscopy. For as-grown graphene on copper, the extent of thermal expansion mismatch between substrate and the graphene layer is significant across the entire measured temperature interval, T  =  90-300 K. This mismatch induces lattice strain in graphene. However, graphene grown on copper substrates has a unique morphology in the form of quasi-periodic nanoripples. This crucially influences the profile of the strain in the graphene membrane, which is uniaxial. An estimate of the thermal expansion coefficient of grapheme α(T) is obtained after consideration of this strain profile and after incorporating temperature-dependent Grüneisen parameter corrections. The value of α(T), is found to be negative (average value, -3.75  ×  10(-6) K(-1)) for the entire temperature range and it approaches close to zero for T  <  150 K. For graphene wet-transferred to three kinds of substrates: copper, poly-dimethylsiloxane, and SiO2/Si, the Raman shifts can largely be modeled with lattice expansion and anharmonic contributions, and the data suggests limited interfacial interaction with the substrate.

  5. Modeling of nonlinear thermal resistance in FinFETs

    NASA Astrophysics Data System (ADS)

    Krishna Kompala, Bala; Kushwaha, Pragya; Agarwal, Harshit; Khandelwal, Sourabh; Duarte, Juan-Pablo; Hu, Chenming; Singh Chauhan, Yogesh

    2016-04-01

    In this paper, self-consistent three-dimensional (3D) device simulations for exact analysis of thermal transport in FinFETs are performed. We analyze the temperature rise in FinFET devices with the variation in the number of fins (N fin), shape of fins and fin pitch (F pitch). We investigate that the thermal resistance R th has nonlinear dependency on N fin and F pitch. We formulate a model for thermal resistance behavior correctly with N fin and F pitch variation. The proposed formulation is implemented in industry standard Berkeley short-channel independent gate FET model for common multi-gate transistors (BSIM-CMG) and validated with both experimental data and TCAD simulations.

  6. Steady-state low thermal resistance characterization apparatus: The bulk thermal tester

    SciTech Connect

    Burg, Brian R.; Kolly, Manuel; Blasakis, Nicolas; Gschwend, Dominic; Zürcher, Jonas; Brunschwiler, Thomas

    2015-12-15

    The reliability of microelectronic devices is largely dependent on electronic packaging, which includes heat removal. The appropriate packaging design therefore necessitates precise knowledge of the relevant material properties, including thermal resistance and thermal conductivity. Thin materials and high conductivity layers make their thermal characterization challenging. A steady state measurement technique is presented and evaluated with the purpose to characterize samples with a thermal resistance below 100 mm{sup 2} K/W. It is based on the heat flow meter bar approach made up by two copper blocks and relies exclusively on temperature measurements from thermocouples. The importance of thermocouple calibration is emphasized in order to obtain accurate temperature readings. An in depth error analysis, based on Gaussian error propagation, is carried out. An error sensitivity analysis highlights the importance of the precise knowledge of the thermal interface materials required for the measurements. Reference measurements on Mo samples reveal a measurement uncertainty in the range of 5% and most accurate measurements are obtained at high heat fluxes. Measurement techniques for homogeneous bulk samples, layered materials, and protruding cavity samples are discussed. Ultimately, a comprehensive overview of a steady state thermal characterization technique is provided, evaluating the accuracy of sample measurements with thermal resistances well below state of the art setups. Accurate characterization of materials used in heat removal applications, such as electronic packaging, will enable more efficient designs and ultimately contribute to energy savings.

  7. Thermal forming of substrates for the x-ray surveyor telescope

    NASA Astrophysics Data System (ADS)

    Cotroneo, Vincenzo; Allured, Ryan; Reid, Paul B.; DeRoo, Casey T.; Schwartz, Daniel A.; Marquez, Vanessa; Vikhlinin, Alexey A.; Civitani, Marta; Salmaso, Bianca; Pareschi, Giovanni

    2016-09-01

    In this paper we review the progress and current status of thermal forming activities at SAO, highlighting the most relevant technical problems and the way to solve them. These activities are devoted to the realization of mirror substrates for the X-ray surveyor mission concept, an observatory with Chandra-like angular resolution and 30 times more effective area or larger. The technology under development at SAO is based on the deposition of piezoelectric material on the back of the substrates. About 8000 mirror segments, with initial quality of 10 arcseconds or better are required for the telescope.

  8. Thermal Catalytic Oxidation of Airborne Contaminants by a Reactor Using Ultra-Short Channel Length, Monolithic Catalyst Substrates

    NASA Technical Reports Server (NTRS)

    Perry, J. L.; Tomes, K. M.; Tatara, J. D.

    2005-01-01

    Contaminated air, whether in a crewed spacecraft cabin or terrestrial work and living spaces, is a pervasive problem affecting human health, performance, and well being. The need for highly effective, economical air quality processes spans a wide range of terrestrial and space flight applications. Typically, air quality control processes rely on absorption-based processes. Most industrial packed-bed adsorption processes use activated carbon. Once saturated, the carbon is either dumped or regenerated. In either case, the dumped carbon and concentrated waste streams constitute a hazardous waste that must be handled safely while minimizing environmental impact. Thermal catalytic oxidation processes designed to address waste handling issues are moving to the forefront of cleaner air quality control and process gas decontamination processes. Careful consideration in designing the catalyst substrate and reactor can lead to more complete contaminant destruction and poisoning resistance. Maintenance improvements leading to reduced waste handling and process downtime can also be realized. Performance of a prototype thermal catalytic reaction based on ultra-short waste channel, monolith catalyst substrate design, under a variety of process flow and contaminant loading conditions, is discussed.

  9. Interfacial thermal resistance and thermal rectification in carbon nanotube film-copper systems.

    PubMed

    Duan, Zheng; Liu, Danyang; Zhang, Guang; Li, Qingwei; Liu, Changhong; Fan, Shoushan

    2017-03-02

    Thermal rectification occurring at interfaces is an important research area, which contains deep fundamental physics and has extensive application prospects. In general, the measurement of interfacial thermal rectification is based on measuring interfacial thermal resistance (ITR). However, ITRs measured via conventional methods cannot avoid extra thermal resistance asymmetry due to the contact between the sample and the thermometer. In this study, we employed a non-contact infrared thermal imager to monitor the temperature of super-aligned carbon nanotube (CNT) films and obtain the ITRs between the CNT films and copper. The ITRs along the CNT-copper direction and the reverse direction are in the ranges of 2.2-3.6 cm(2) K W(-1) and 9.6-11.9 cm(2) K W(-1), respectively. The obvious difference in the ITRs of the two directions shows a significant thermal rectification effect, and the rectifying coefficient ranges between 0.57 and 0.68. The remarkable rectification factor is extremely promising for the manufacture of thermal transistors with a copper/CNT/copper structure and further thermal logic devices. Moreover, our method could be extended to other 2-dimensional materials, such as graphene and MoS2, for further explorations.

  10. Stress generation in thermally grown oxide films. [oxide scale spalling from superalloy substrates

    NASA Technical Reports Server (NTRS)

    Kumnick, A. J.; Ebert, L. J.

    1981-01-01

    A three dimensional finite element analysis was conducted, using the ANSYS computer program, of the stress state in a thin oxide film thermally formed on a rectangular piece of NiCrAl alloy. The analytical results indicate a very high compressive stress in the lateral directions of the film (approximately 6200 MPa), and tensile stresses in the metal substrate that ranged from essentially zero to about 55 MPa. It was found further that the intensity of the analytically determined average stresses could be approximated reasonably well by the modification of an equation developed previously by Oxx for stresses induced into bodies by thermal gradients.

  11. Thermally driven classical Heisenberg chain with a spatially varying magnetic field: thermal rectification and negative differential thermal resistance

    NASA Astrophysics Data System (ADS)

    Bagchi, Debarshee

    2015-02-01

    Thermal rectification and negative differential thermal resistance are two important features that have direct technological relevance. Here, we study the classical one-dimensional Heisenberg model, driven thermally by heat baths attached at the two ends of the system and in the presence of an external magnetic field that varies monotonically in space. Heat conduction in this system is studied using a local energy conserving dynamics. It is found that by suitably tuning the spatially varying magnetic field, the structurally homogeneous symmetric system exhibits both thermal rectification and negative differential thermal resistance. Thermal rectification, in some parameter ranges, shows interesting dependencies on the average temperature T and the system size N—rectification improves as T and N are increased. Using the microscopic dynamics of the spins we present a physical picture to understand thermal rectification as exhibited by this system and provide supporting numerical evidence. Emergence of the negative response in this system can be controlled by tuning the external magnetic field alone, which can have possible applications in the fabrication of novel thermal devices.

  12. Magneto-transport properties of oriented Mn{sub 2}CoAl films sputtered on thermally oxidized Si substrates

    SciTech Connect

    Xu, G. Z.; Du, Y.; Zhang, X. M.; Liu, E. K.; Wang, W. H. Wu, G. H.; Zhang, H. G.

    2014-06-16

    Spin gapless semiconductors are interesting family of materials by embracing both magnetism and semiconducting due to their unique band structure. Its potential application in future spintronics requires realization in thin film form. In this Letter, we report fabrication and transport properties of spin gapless Mn{sub 2}CoAl films prepared on thermally oxidized Si substrates by magnetron sputtering deposition. The films deposited at 673 K are well oriented to (001) direction and display a uniform-crystalline surface. Magnetotransport measurements on the oriented films reveal a semiconducting-like resistivity, small anomalous Hall conductivity, and linear magnetoresistance representative of the transport signatures of spin gapless semiconductors. The magnetic properties of the films have also been investigated and compared to that of bulk Mn{sub 2}CoAl, showing small discrepancy induced by the composition deviation.

  13. Electric and thermal resistivities in dense high-Z plasmas

    NASA Astrophysics Data System (ADS)

    Kitamura, Hikaru; Ichimaru, Setsuo

    1995-06-01

    Analytic expressions for the electric and thermal resistivities in dense high-Z plasmas have been obtained. The expressions incorporate phase-shift calculations of high-Z ion-sphere-model cross sections as well as existing quantum-mechanical transport calculations for hydrogen plasmas, and are applicable to fluid plasmas with 1<=Z<=26 strong-coupling effects between electrons and ions are particularly clarified. It has been shown that the heat capacity for a dense plasma may have a considerable effect, modifying the rate of thermal conduction. The results are compared with other theoretical predictions for those plasma parameters appropriate to degenerate stars.

  14. Thermal rectification and negative differential thermal resistance in a driven two segment classical Heisenberg chain

    NASA Astrophysics Data System (ADS)

    Bagchi, Debarshee

    2013-12-01

    Using computer simulation we investigate thermal transport in a two segment classical Heisenberg spin chain with nearest neighbor interaction and in the presence of an external magnetic field. The system is thermally driven by heat baths attached at the two ends and transport properties are studied using energy conserving dynamics. We demonstrate that by properly tuning the parameters thermal rectification can be achieved—the system behaves as a good conductor of heat along one direction but becomes a bad conductor when the thermal gradient is reversed, and crucially depends on nonlinearity and spatial asymmetry. Moreover, suitable tuning of the system parameters gives rise to the counterintuitive and technologically important feature known as negative differential thermal resistance (NDTR). We find that the crucial factor responsible for the emergence of NDTR is a suitable mechanism for impeding the current in the bulk of the system.

  15. Dynamic thermal characteristics of heat pipe via segmented thermal resistance model for electric vehicle battery cooling

    NASA Astrophysics Data System (ADS)

    Liu, Feifei; Lan, Fengchong; Chen, Jiqing

    2016-07-01

    Heat pipe cooling for battery thermal management systems (BTMSs) in electric vehicles (EVs) is growing due to its advantages of high cooling efficiency, compact structure and flexible geometry. Considering the transient conduction, phase change and uncertain thermal conditions in a heat pipe, it is challenging to obtain the dynamic thermal characteristics accurately in such complex heat and mass transfer process. In this paper, a ;segmented; thermal resistance model of a heat pipe is proposed based on thermal circuit method. The equivalent conductivities of different segments, viz. the evaporator and condenser of pipe, are used to determine their own thermal parameters and conditions integrated into the thermal model of battery for a complete three-dimensional (3D) computational fluid dynamics (CFD) simulation. The proposed ;segmented; model shows more precise than the ;non-segmented; model by the comparison of simulated and experimental temperature distribution and variation of an ultra-thin micro heat pipe (UMHP) battery pack, and has less calculation error to obtain dynamic thermal behavior for exact thermal design, management and control of heat pipe BTMSs. Using the ;segmented; model, the cooling effect of the UMHP pack with different natural/forced convection and arrangements is predicted, and the results correspond well to the tests.

  16. Improving the Resistance Profile of Hepatitis C NS3/4A Inhibitors: Dynamic Substrate Envelope Guided Design

    PubMed Central

    Özen, Ayşegül; Sherman, Woody; Schiffer, Celia A.

    2014-01-01

    Drug resistance is a principal concern in the treatment of quickly evolving diseases. The viral protease NS3/4A is a primary drug target for the hepatitis C virus (HCV) and is known to evolve resistance mutations in response to drug therapy. At the molecular level, drug resistance reflects a subtle change in the balance of molecular recognition by NS3/4A; the drug resistant protease variants are no longer effectively inhibited by the competitive active site inhibitors but can still process the natural substrates with enough efficiency for viral survival. In previous works we have developed the “substrate envelope” hypothesis, which posits that inhibitors should be less susceptible to drug resistance if they better mimic the natural substrate molecular recognition features. In this work, we perform molecular dynamics simulations on four native substrates bound to NS3/4A and discover a clearly conserved dynamic substrate envelope. We show that the most severe drug resistance mutations in NS3/4A occur at residues that are outside the substrate envelope. Comparative analysis of three NS3/4A inhibitors reveals structural and dynamic characteristics of inhibitors that could lead to resistance. We also suggest inhibitor modifications to improve resistance profiles based on the dynamic substrate envelope. This study provides a general framework for guiding the development of novel inhibitors that will be more robust against resistance by mimicking the static and dynamic binding characteristics of natural substrates. PMID:24587770

  17. Experimental determination of satellite bolted joints thermal resistance

    NASA Technical Reports Server (NTRS)

    Mantelli, Marcia Barbosa Henriques; Basto, Jose Edson

    1990-01-01

    The thermal resistance was experimentally determined of the bolted joints of the first Brazilian satellite (SCD 01). These joints, used to connect the satellite structural panels, are reproduced in an experimental apparatus, keeping, as much as possible, the actual dimensions and materials. A controlled amount of heat is forced to pass through the joint and the difference of temperature between the panels is measured. The tests are conducted in a vacuum chamber with liquid nitrogen cooled walls, that simulates the space environment. Experimental procedures are used to avoid much heat losses, which are carefully calculated. Important observations about the behavior of the joint thermal resistance with the variation of the mean temperature are made.

  18. Thermal shock and erosion resistant tantalum carbide ceramic material

    NASA Technical Reports Server (NTRS)

    Honeycutt, L., III; Manning, C. R. (Inventor)

    1978-01-01

    Ceramic tantalum carbide artifacts with high thermal shock and mechanical erosion resistance are provided by incorporating tungsten-rhenium and carbon particles in a tantalum carbide matrix. The mix is sintered by hot pressing to form the ceramic article which has a high fracture strength relative to its elastic modulus and thus has an improved thermal shock and mechanical erosion resistance. The tantalum carbide is preferable less than minus 100 mesh, the carbon particles are preferable less than minus 100 mesh, and the tungsten-rhenium particles are preferable elongate, having a length to thickness ratio of at least 2/1. Tungsten-rhenium wire pieces are suitable as well as graphite particles.

  19. Thermal conductivity and electrical resistivity of porous material

    NASA Technical Reports Server (NTRS)

    Koh, J. C. Y.; Fortini, A.

    1971-01-01

    Thermal conductivity and electrical resistivity of porous materials, including 304L stainless steel Rigimesh, 304L stainless steel sintered spherical powders, and OFHC sintered spherical powders at different porosities and temperatures are reported and correlated. It was found that the thermal conductivity and electrical resistivity can be related to the solid material properties and the porosity of the porous matrix regardless of the matrix structure. It was also found that the Wiedermann-Franz-Lorenz relationship is valid for the porous materials under consideration. For high conductivity materials, the Lorenz constant and the lattice component of conductivity depend on the material and are independent of the porosity. For low conductivity, the lattice component depends on the porosity as well.

  20. Thermal Inactivation of Bacillus anthracis Spores Using Rapid Resistive Heating

    DTIC Science & Technology

    2016-03-24

    microbiological study sought to obtain a correlation between exposure time, temperature , and spore viability. This information is invaluable when...of the spores were found using rapid resistive heating at short duration exposure times from 0.26 to 7 seconds at temperatures ranging from 73.5 to...ranging from 0.1 to 10 seconds. Higher temperatures were needed to thermally inactivate the B.a. spores as exposure times decreased. vi

  1. Transported Substrate Determines Exchange Rate in the Multidrug Resistance Transporter EmrE*

    PubMed Central

    Morrison, Emma A.; Henzler-Wildman, Katherine A.

    2014-01-01

    EmrE, a small multidrug resistance transporter, serves as an ideal model to study coupling between multidrug recognition and protein function. EmrE has a single small binding pocket that must accommodate the full range of diverse substrates recognized by this transporter. We have studied a series of tetrahedral compounds, as well as several planar substrates, to examine multidrug recognition and transport by EmrE. Here we show that even within this limited series, the rate of interconversion between the inward- and outward-facing states of EmrE varies over 3 orders of magnitude. Thus, the identity of the bound substrate controls the rate of this critical step in the transport process. The binding affinity also varies over a similar range and is correlated with substrate hydrophobicity within the tetrahedral substrate series. Substrate identity influences both the ground-state and transition-state energies for the conformational exchange process, highlighting the coupling between substrate binding and transport required for alternating access antiport. PMID:24448799

  2. Transported substrate determines exchange rate in the multidrug resistance transporter EmrE.

    PubMed

    Morrison, Emma A; Henzler-Wildman, Katherine A

    2014-03-07

    EmrE, a small multidrug resistance transporter, serves as an ideal model to study coupling between multidrug recognition and protein function. EmrE has a single small binding pocket that must accommodate the full range of diverse substrates recognized by this transporter. We have studied a series of tetrahedral compounds, as well as several planar substrates, to examine multidrug recognition and transport by EmrE. Here we show that even within this limited series, the rate of interconversion between the inward- and outward-facing states of EmrE varies over 3 orders of magnitude. Thus, the identity of the bound substrate controls the rate of this critical step in the transport process. The binding affinity also varies over a similar range and is correlated with substrate hydrophobicity within the tetrahedral substrate series. Substrate identity influences both the ground-state and transition-state energies for the conformational exchange process, highlighting the coupling between substrate binding and transport required for alternating access antiport.

  3. Low conductivity and sintering-resistant thermal barrier coatings

    NASA Technical Reports Server (NTRS)

    Zhu, Dongming (Inventor); Miller, Robert A. (Inventor)

    2004-01-01

    A thermal barrier coating composition comprising a base oxide, a primary stabilizer oxide, and at least one dopant oxide is disclosed. Preferably, a pair of group A and group B defect cluster-promoting oxides is used in conjunction with the base and primary stabilizer oxides. The new thermal barrier coating is found to have significantly lower thermal conductivity and better sintering resistance. The base oxide is selected from the group consisting of zirconia and hafnia and combinations thereof. The primary stabilizing oxide is selected from the group consisting of yttria, dysprosia, erbia and combinations thereof. The dopant or group A and group B cluster-promoting oxide dopants are selected from the group consisting of rare earth metal oxides, transitional metal oxides, alkaline earth metal oxides and combinations thereof. The dopant or dopants preferably have ionic radii different from those of the primary stabilizer and/or the base oxides.

  4. Low conductivity and sintering-resistant thermal barrier coatings

    NASA Technical Reports Server (NTRS)

    Zhu, Dongming (Inventor); Miller, Robert A. (Inventor)

    2007-01-01

    A thermal barrier coating composition is provided. The composition has a base oxide, a primary stabilizer, and at least two additional cationic oxide dopants. Preferably, a pair of group A and group B defect cluster-promoting oxides is used in conjunction with the base and primary stabilizer oxides. The new thermal barrier coating is found to have significantly lower thermal conductivity and better sintering resistance. In preferred embodiments, the base oxide is selected from zirconia and hafnia. The group A and group B cluster-promoting oxide dopants preferably are selected such that the group A dopant has a smaller cationic radius than the primary stabilizer oxide, and so that the primary stabilizer oxide has a small cationic radius than that of the group B dopant.

  5. Low conductivity and sintering-resistant thermal barrier coatings

    NASA Technical Reports Server (NTRS)

    Zhu, Dongming (Inventor); Miller, Robert A. (Inventor)

    2006-01-01

    A thermal barrier coating composition is provided. The composition has a base oxide, a primary stabilizer, and at least two additional cationic oxide dopants. Preferably, a pair of group A and group B defect cluster-promoting oxides is used in conjunction with the base and primary stabilizer oxides. The new thermal barrier coating is found to have significantly lower thermal conductivity and better sintering resistance. In preferred embodiments, the base oxide is selected from zirconia and hafnia. The group A and group B cluster-promoting oxide dopants preferably are selected such that the group A dopant has a smaller cationic radius than the primary stabilizer oxide, and so that the primary stabilizer oxide has a small cationic radius than that of the group B dopant.

  6. Long-range ordering of block copolymer cylinders driven by combining thermal annealing and substrate functionalization.

    PubMed

    She, Ming-Shiuan; Lo, Ting-Ya; Ho, Rong-Ming

    2013-03-26

    This work presents a new method for forming well-defined nanostructured thin films from self-assembled polystyrene-block-poly(l-lactide) (PS-PLLA) on Si wafers with a functionalized SiO2 surface. Large, well-ordered, perpendicular PLLA cylinders in PS-PLLA thin films can be formed using the functionalized substrate. In contrast to random copolymers, a neutral substrate for the PS and PLLA blocks is formed by functionalizing a substrate with hydroxyl-terminated PS (PS-OH) followed by hydroxyl-terminated PLLA (PLLA-OH). The heterogeneous grafting of PS-OH and PLLA-OH can be substantially alleviated using this two-step functionalization. Accordingly, the surface properties can be fine-tuned by controlling the ratio of grafted PS-OH to PLLA-OH to control the orientation of the PLLA cylinders on the functionalized SiO2. Nevertheless, the orientation that is driven by the neutral substrate is surprisingly limited in that the effective length of orienting cylinders is less than twice the interdomain spacing. Thermal annealing at high temperature can yield a neutral air surface, rendering perpendicular PLLA cylinders that stand sub-micrometers from the air surface. Consequently, the neutral substrate can be used to enable truly film-spanning perpendicular cylinders in films to be fabricated using the high-temperature thermal treatment. In addition, the perpendicular cylinders can be laterally ordered by further increasing the annealing temperature. The ability to create these film-spanning perpendicular cylinders in films with a well-ordered texture and sub-micrometer thickness opens up possible applications in nanotechnology.

  7. Development of Conformation Independent Computational Models for the Early Recognition of Breast Cancer Resistance Protein Substrates

    PubMed Central

    Gantner, Melisa Edith; Di Ianni, Mauricio Emiliano; Ruiz, María Esperanza; Bruno-Blanch, Luis E.

    2013-01-01

    ABC efflux transporters are polyspecific members of the ABC superfamily that, acting as drug and metabolite carriers, provide a biochemical barrier against drug penetration and contribute to detoxification. Their overexpression is linked to multidrug resistance issues in a diversity of diseases. Breast cancer resistance protein (BCRP) is the most expressed ABC efflux transporter throughout the intestine and the blood-brain barrier, limiting oral absorption and brain bioavailability of its substrates. Early recognition of BCRP substrates is thus essential to optimize oral drug absorption, design of novel therapeutics for central nervous system conditions, and overcome BCRP-mediated cross-resistance issues. We present the development of an ensemble of ligand-based machine learning algorithms for the early recognition of BCRP substrates, from a database of 262 substrates and nonsubstrates compiled from the literature. Such dataset was rationally partitioned into training and test sets by application of a 2-step clustering procedure. The models were developed through application of linear discriminant analysis to random subsamples of Dragon molecular descriptors. Simple data fusion and statistical comparison of partial areas under the curve of ROC curves were applied to obtain the best 2-model combination, which presented 82% and 74.5% of overall accuracy in the training and test set, respectively. PMID:23984415

  8. The effects of co-substrate and thermal pretreatment on anaerobic digestion performance.

    PubMed

    Amiri, Leyla; Abdoli, Mohammad Ali; Gitipour, Saeid; Madadian, Edris

    2016-11-29

    The influence of anaerobic co-digestion of leachate and sludge with organic fraction of municipal solid waste (OFMSW) under mesophilic condition in three batch digesters of 5 L capacity has been studied. OFMSW was mixed with leachate and sludge at three different ratios. Experimental results illustrated that the digester with a ratio of 2000/2500 (leachate (mL) or sludge/OFMSW (mL)) had significantly higher performance. Furthermore, this study compared the performance of anaerobic digestion of different substrates with three different mixing ratios with and without thermal pretreatment at low temperature (65°C) in terms of biogas production, chemical oxygen demand (COD) elimination as well as hydraulic retention time. In addition, to predict the biogas yield and evaluate the kinetic parameters, the modified Gompertz model was applied. Based on the results, the maximum biogas yield from adding different leachate and sludge ratios to OFMSW was recorded to be 0.45 and 0.38 m(3 )kg(-1) COD which was higher about 7% in comparison with co-digestion original OFMSW without thermal pretreatment. In addition, thermal pretreatment accelerated the hydrolysis step. Moreover, the total COD elimination was relatively stable in the range of 52-60% at all types of substrate mixtures. Also, the modified Gompertz model demonstrated a good fit to the experimental results.

  9. Substrate system for spray forming

    DOEpatents

    Chu, Men G.; Chernicoff, William P.

    2002-01-01

    A substrate system for receiving a deposit of sprayed metal droplets including a movable outer substrate on which the sprayed metal droplets are deposited. The substrate system also includes an inner substrate disposed adjacent the outer substrate where the sprayed metal droplets are deposited on the outer substrate. The inner substrate includes zones of differing thermal conductivity to resist substrate layer porosity and to resist formation of large grains and coarse constituent particles in a bulk layer of the metal droplets which have accumulated on the outer substrate. A spray forming apparatus and associated method of spray forming a molten metal to form a metal product using the substrate system of the invention is also provided.

  10. Substrate system for spray forming

    DOEpatents

    Chu, Men G.; Chernicoff, William P.

    2000-01-01

    A substrate system for receiving a deposit of sprayed metal droplets including a movable outer substrate on which the sprayed metal droplets are deposited. The substrate system also includes an inner substrate disposed adjacent the outer substrate where the sprayed metal droplets are deposited on the outer substrate. The inner substrate includes zones of differing thermal conductivity to resist substrate layer porosity and to resist formation of large grains and coarse constituent particles in a bulk layer of the metal droplets which have accumulated on the outer substrate. A spray forming apparatus and associated method of spray forming a molten metal to form a metal product using the substrate system of the invention is also provided.

  11. Metal-Organic-Inorganic Nanocomposite Thermal Interface Materials with Ultralow Thermal Resistances.

    PubMed

    Yegin, Cengiz; Nagabandi, Nirup; Feng, Xuhui; King, Charles; Catalano, Massimo; Oh, Jun Kyun; Talib, Ansam J; Scholar, Ethan A; Verkhoturov, Stanislav V; Cagin, Tahir; Sokolov, Alexei V; Kim, Moon J; Matin, Kaiser; Narumanchi, Sreekant; Akbulut, Mustafa

    2017-03-22

    As electronic devices get smaller and more powerful, energy density of energy storage devices increases continuously, and moving components of machinery operate at higher speeds, the need for better thermal management strategies is becoming increasingly important. The removal of heat dissipated during the operation of electronic, electrochemical, and mechanical devices is facilitated by high-performance thermal interface materials (TIMs) which are utilized to couple devices to heat sinks. Herein, we report a new class of TIMs involving the chemical integration of boron nitride nanosheets (BNNS), soft organic linkers, and a copper matrix-which are prepared by the chemisorption-coupled electrodeposition approach. These hybrid nanocomposites demonstrate bulk thermal conductivities ranging from 211 to 277 W/(m K), which are very high considering their relatively low elastic modulus values on the order of 21.2-28.5 GPa. The synergistic combination of these properties led to the ultralow total thermal resistivity values in the range of 0.38-0.56 mm(2) K/W for a typical bond-line thickness of 30-50 μm, advancing the current state-of-art transformatively. Moreover, its coefficient of thermal expansion (CTE) is 11 ppm/K, forming a mediation zone with a low thermally induced axial stress due to its close proximity to the CTE of most coupling surfaces needing thermal management.

  12. Mechanically robust, thermally stable, broadband antireflective, and superhydrophobic thin films on glass substrates.

    PubMed

    Xu, Ligang; Geng, Zhi; He, Junhui; Zhou, Gang

    2014-06-25

    In this study, we developed a simple and versatile strategy to fabricate hierarchically structured lotus-leaf-like superhydrophobic thin films. The thin films are broadband antireflective, and the average transmittance of coated glass substrates reached greater than 95% in the wavelength range of 530-1340 nm, in contrast to 92.0% for bare glass substrate. The thin film surface shows a static water contact angle of 162° and a sliding angle less than 4°. Moreover, the thin film is thermally stable up to 300 °C, and shows remarkable stability against strong acid, strong alkali, water drop impact, and sand impact abrasion, while retaining its superhydrophobicity. Further, the thin film can pass the 3H pencil hardness test. The current approach may open a new avenue to a variety of practical applications, including windshields, eyeglasses, windows of high rise buildings and solar cells, etc.

  13. Correlation of physical properties of ceramic materials with resistance to fracture by thermal shock

    NASA Technical Reports Server (NTRS)

    Lidman, W G; Bobrowsky, A R

    1949-01-01

    An analysis is made to determine which properties of materials affect their resistance to fracture by thermal stresses.From this analysis, a parameter is evaluated that is correlated with the resistance of ceramic materials to fracture by thermal shock as experimentally determined. This parameter may be used to predict qualitatively the resistance of a material to fracture by thermal shock. Resistance to fracture by thermal shock is shown to be dependent upon the following material properties: thermal conductivity, tensile strength, thermal expansion, and ductility modulus. For qualitative prediction of resistance of materials to fracture by thermal shock, the parameter may be expressed as the product of thermal conductivity and tensile strength divided by the product of linear coefficient of thermal expansion and ductility modulus of the specimen.

  14. Thermal resistance at a solid/superfluid helium interface

    NASA Astrophysics Data System (ADS)

    Ramiere, Aymeric; Volz, Sebastian; Amrit, Jay

    2016-05-01

    Kapitza in 1941 discovered that heat flowing across a solid in contact with superfluid helium (<2 K) encounters a strong thermal resistance at the interface. Khalatnikov demonstrated theoretically that this constitutes a general phenomenon related to all interfaces at all temperatures, given the dependence of heat transmission on the acoustic impedance (sound velocity × density) of each medium. For the solid/superfluid interface, the measured transmission of heat is almost one hundred times stronger than the Khalatnikov prediction. This discrepancy could be intuitively attributed to diffuse scattering of phonons at the interface but, despite several attempts, a detailed quantitative comparison between theoretical and experimental findings to explain the occurrence of scattering and its contribution to heat transmission had been lacking. Here we show that when the thermal wavelength λ of phonons of the less dense medium (liquid 4He) becomes comparable to the r.m.s. surface roughness σ, the heat flux crossing the interface is amplified; in particular when σ ~ 0.33λ, a spatial resonant mechanism occurs, as proposed by Adamenko and Fuks. We used a silicon single crystal whose surface roughness was controlled and characterized. The thermal boundary resistance measurements were performed from 0.4 to 2 K at different superfluid pressures ranging from saturated vapour pressure (SVP) to above 4He solidification, to eliminate all hypothetical artefact mechanisms. Our results demonstrate the physical conditions necessary for resonant phonon scattering to occur at all interfaces, and therefore constitute a benchmark in the design of nanoscale devices for heat monitoring.

  15. Diode-laser based scanning laser thermoelectric microscope for thermal diffusivity characterization of thin films on semiconductor substrates

    SciTech Connect

    Borca-Tasciuc, T.; Chen, G.

    1999-07-01

    This work presents new experimental results in the characterization of thermophysical properties for dielectric thin films on semiconductor substrates using the Scanning Laser Thermoelectric Microscope (SLTM) measurement technique. The new improved SLTM employs a modulated laser beam from a 1.55 {micro}m IR diode laser. The laser is used to create a micro-scale thermal wave in the film by focusing the light through the substrate. At this laser wavelength, the technique can be used to determine the thermal diffusivity for films deposited on semiconductor substrates with the band-gap larger than 0.8eV. The generated thermal wave is detected by a fast responding thermocouple formed between the film surface and the tip of a sharp probe. By scanning the laser beam around the thermocouple, the amplitude and phase distributions of the thermal wave are obtained. The film thermal diffusivity is obtained by fitting the detected phase profile of the thermal wave with a three-dimensional heat conduction model. Experimental results are presented for a film-on-substrate system composed of a two-layer thin film on the silicon substrate. The two-layer film is a 4.65{micro}m silicon dioxide film on which a 100nm thick gold film is deposited in order to provide an absorption layer for the laser light and also to facilitate the thermoelectric detection of the thermal wave.

  16. Preparation and modification of VO2 thin film on R-sapphire substrate by rapid thermal process

    NASA Astrophysics Data System (ADS)

    Zhu, Nai-Wei; Hu, Ming; Xia, Xiao-Xu; Wei, Xiao-Ying; Liang, Ji-Ran

    2014-04-01

    The VO2 thin film with high performance of metal-insulator transition (MIT) is prepared on R-sapphire substrate for the first time by magnetron sputtering with rapid thermal process (RTP). The electrical characteristic and THz transmittance of MIT in VO2 film are studied by four-point probe method and THz time domain spectrum (THz-TDS). X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and search engine marketing (SEM) are employed to analyze the crystalline structure, valence state, surface morphology of the film. Results indicate that the properties of VO2 film which is oxidized from the metal vanadium film in oxygen atmosphere are improved with a follow-up RTP modification in nitrogen atmosphere. The crystallization and components of VO2 film are improved and the film becomes compact and uniform. A better phase transition performance is shown that the resistance changes nearly 3 orders of magnitude with a 2-°C hysteresis width and the THz transmittances are reduced by 64% and 60% in thermal and optical excitation respectively.

  17. Uptake inhibitors but not substrates induce protease resistance in extracellular loop two of the dopamine transporter.

    PubMed

    Gaffaney, Jon D; Vaughan, Roxanne A

    2004-03-01

    Changes in protease sensitivity of extracellular loop two (EL2) of the dopamine transporter (DAT) during inhibitor and substrate binding were examined using trypsin proteolysis and epitope-specific immunoblotting. In control rat striatal membranes, proteolysis of DAT in a restricted region of EL2 was produced by 0.001 to 10 microg/ml trypsin. However, in the presence of the dopamine uptake blockers [2-(diphenylmethoxyl) ethyl]-4-(3phenylpropyl) piperazine (GBR 12909), mazindol, 2beta-carbomethoxy-3beta-(4-flourophenyl)tropane (beta-CFT), nomifensine, benztropine, or (-)-cocaine, 100- to 1000-fold higher concentrations of trypsin were required to produce comparable levels of proteolysis. Protease resistance induced by ligands was correlated with their affinity for DAT binding, was not observed with Zn2+, (+)-cocaine, or inhibitors of norepinephrine or serotonin transporters, and was not caused by altered catalytic activity of trypsin. Together, these results support the hypothesis that the interaction of uptake inhibitors with DAT induces a protease-resistant conformation in EL2. In contrast, binding of substrates did not induce protease resistance in EL2, suggesting that substrates and inhibitors interact with DAT differently during binding. To assess the effects of EL2 proteolysis on DAT function, the binding and transport properties of trypsin-digested DAT were assayed with [3H]CFT and [3H]dopamine. Digestion decreased the Bmax for binding and the Vmax for uptake in amounts that were proportional to the extent of proteolysis, indicating that the structural integrity of EL2 is required for maintenance of both DAT binding and transport functions. Together this data provides novel information about inhibitor and substrate interactions at EL2, possibly relating the protease resistant DAT conformation to a mechanism of transport inhibition.

  18. A protease substrate profiling method that links site-specific proteolysis with antibiotic resistance.

    PubMed

    Sandersjöö, Lisa; Kostallas, George; Löfblom, John; Samuelson, Patrik

    2014-01-01

    Proteases are involved in many biological processes and have become important tools in biomedical research and industry. Technologies for engineering and characterization of, for example, proteolytic activity and specificity are essential in protease research. Here, we present a novel method for assessment of site-specific proteolysis. The assay utilizes plasmid-encoded reporters that, upon processing by a co-expressed protease, confer antibiotic resistance to bacteria in proportion to the cleavage efficiency. We have demonstrated that cells co-expressing cleavable reporters together with tobacco etch virus protease (TEVp) could be discriminated from cells with non-cleavable reporters by growth in selective media. Importantly, the resistance to antibiotics proved to correlate with the substrate processing efficiency. Thus, by applying competitive growth of a mock library in antibiotic-containing medium, we could show that the substrate preferred by TEVp was enriched relative to less-efficient substrates. We believe that this simple methodology will facilitate protease substrate identification, and hold great promise for directed evolution of proteases and protease recognition sequences towards improved or even new functionality.

  19. Thermal fatigue resistance of cobalt-modified UDIMET 700

    NASA Technical Reports Server (NTRS)

    Bizon, P. T.

    1982-01-01

    The determination of comparative thermal fatigue resistances of five cobalt composition modifications of UDIMET 700 from fluidized bed tests is described. Cobalt compositional levels of 0.1, 4.3, 8.6, 12.8, 17.0 percent were being investigated in both the bare and coated (NiCrAlY overlay) conditions. Triplicate tests of each variation including duplicate tests of three control alloys are under investigation. Fluidized beds were maintained at 550 and 1850 F for the first 5500 cycles at which time the hot bed was increased to 1922 F. Immersion time in each bed is always 3 minutes. Upon the completion of 10,000 cycles, it appears that the 8.6 percent cobalt level gives the best thermal fatigue life. Considerable deformation of the test bars was observed.

  20. Thermally evaporated conformal thin films on non-traditional/non-planar substrates

    NASA Astrophysics Data System (ADS)

    Pulsifer, Drew Patrick

    Conformal thin films have a wide variety of uses in the microelectronics, optics, and coatings industries. The ever-increasing capabilities of these conformal thin films have enabled tremendous technological advancement in the last half century. During this period, new thin-film deposition techniques have been developed and refined. While these techniques have remarkable performance for traditional applications which utilize planar substrates such as silicon wafers, they are not suitable for the conformal coating of non-traditional substrates such as biological material. The process of thermally evaporating a material under vacuum conditions is one of the oldest thin-film deposition techniques which is able to produce functional film morphologies. A drawback of thermally evaporated thin films is that they are not intrinsically conformal. To overcome this, while maintaining the advantages of thermal evaporation, a procedure for varying the substrates orientation with respect to the incident vapor flux during deposition was developed immediately prior to the research undertaken for this doctoral dissertation. This process was shown to greatly improve the conformality of thermally evaporated thin films. This development allows for several applications of thermally evaporated conformal thin films on non-planar/non-traditional substrates. Three settings in which to evaluate the improved conformal deposition of thermally evaporated thin films were investigated for this dissertation. In these settings the thin-film morphologies are of different types. In the first setting, a bioreplication approach was used to fabricate artificial visual decoys for the invasive species Agrilus planipennis, commonly known as the emerald ash borer (EAB). The mating behavior of this species involves an overflying EAB male pouncing on an EAB female at rest on an ash leaflet before copulation. The male spots the female on the leaflet by visually detecting the iridescent green color of the

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

    PubMed

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

    1996-06-01

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

  2. Thermal transport across graphene/SiC interface: effects of atomic bond and crystallinity of substrate

    NASA Astrophysics Data System (ADS)

    Li, Man; Zhang, Jingchao; Hu, Xuejiao; Yue, Yanan

    2015-05-01

    The effect of interatomic interaction between graphene and 4H-SiC on their interfacial thermal transport is investigated by empirical molecular dynamics simulation. Two magnitudes of interfacial thermal conductance (ITC) improvement are observed for graphene/4H-SiC interface interacting through covalent bonds than through van der Waals interaction, which can be explained by the bond strength and the number of covalent bonds. Besides, it is found that the ITC of covalent graphene/C-terminated SiC is larger than that Si-terminated SiC, which is due to the stronger bond strength of C-C than that of C-Si. The effect of crystallinity of the substrate is studied, and the result shows that the ITC of graphene/a-SiC is higher than that of graphene/c-SiC. These results are crucial to the understanding of thermal transport across graphene interfaces, which are useful for thermal design in graphene-based transistors.

  3. Enhanced mesophilic anaerobic digestion of food waste by thermal pretreatment: Substrate versus digestate heating.

    PubMed

    Ariunbaatar, Javkhlan; Panico, Antonio; Yeh, Daniel H; Pirozzi, Francesco; Lens, Piet N L; Esposito, Giovanni

    2015-12-01

    Food waste (FW) represents a source of high potential renewable energy if properly treated with anaerobic digestion (AD). Pretreating the substrates could yield a higher biomethane production in a shorter time. In this study, the effects of thermal (heating the FW in a separate chamber) and thermophilic (heating the full reactor content containing both FW and inoculum) pretreatments at 50, 60, 70 and 80°C prior to mesophilic AD were studied through a series of batch experiments. Pretreatments at a lower temperature (50°C) and a shorter time (<12h) had a positive effect on the AD process. The highest enhancement of the biomethane production with an increase by 44-46% was achieved with a thermophilic pretreatment at 50°C for 6-12h or a thermal pretreatment at 80°C for 1.5h. Thermophilic pretreatments at higher temperatures (>55°C) and longer operating times (>12h) yielded higher soluble chemical oxygen demand (CODs), but had a negative effect on the methanogenic activity. The thermal pretreatments at the same conditions resulted in a lower solubilization of COD. Based on net energy calculations, the enhanced biomethane production is sufficient to heat up the FW for the thermal, but not for the thermophilic pretreatment.

  4. A prediction model of substrates and non-substrates of breast cancer resistance protein (BCRP) developed by GA-CG-SVM method.

    PubMed

    Zhong, Lei; Ma, Chang-Ying; Zhang, Hui; Yang, Li-Jun; Wan, Hua-Lin; Xie, Qing-Qing; Li, Lin-Li; Yang, Sheng-Yong

    2011-11-01

    Breast cancer resistance protein (BCRP) is one of the key multi-drug resistance proteins, which significantly influences the therapeutic effects of many drugs, particularly anti-cancer drugs. Thus, distinguishing between substrates and non-substrates of BCRP is important not only for clinical use but also for drug discovery and development. In this study, a prediction model of the substrates and non-substrates of BCRP was developed using a modified support vector machine (SVM) method, namely GA-CG-SVM. The overall prediction accuracy of the established GA-CG-SVM model is 91.3% for the training set and 85.0% for an independent validation set. For comparison, two other machine learning methods, namely, C4.5 DT and k-NN, were also adopted to build prediction models. The results show that the GA-CG-SVM model is significantly superior to C4.5 DT and k-NN models in terms of the prediction accuracy. To sum up, the prediction model of BCRP substrates and non-substrates generated by the GA-CG-SVM method is sufficiently good and could be used as a screening tool for identifying the substrates and non-substrates of BCRP.

  5. Method of applying a bond coating and a thermal barrier coating on a metal substrate, and related articles

    DOEpatents

    Hasz, Wayne Charles; Borom, Marcus Preston

    2002-01-01

    A method for applying at least one bond coating on a surface of a metal-based substrate is described. A foil of the bond coating material is first attached to the substrate surface and then fused thereto, e.g., by brazing. The foil is often initially prepared by thermally spraying the bond coating material onto a removable support sheet, and then detaching the support sheet. Optionally, the foil may also include a thermal barrier coating applied over the bond coating. The substrate can be a turbine engine component.

  6. Optical device with low electrical and thermal resistance bragg reflectors

    DOEpatents

    Lear, Kevin L.

    1996-01-01

    A compound-semiconductor optical device and method. The optical device is provided with one or more asymmetrically-graded heterojunctions between compound semiconductor layers for forming a distributed Bragg reflector mirror having an improved electrical and thermal resistance. Efficient light-emitting devices such as light-emitting diodes, resonant-cavity light-emitting diodes, and vertical-cavity surface-emitting lasers may be formed according to the present invention, which may be applied to the formation of resonant-cavity photodetectors.

  7. Optical device with low electrical and thermal resistance Bragg reflectors

    DOEpatents

    Lear, K.L.

    1996-10-22

    A compound-semiconductor optical device and method are disclosed. The optical device is provided with one or more asymmetrically-graded heterojunctions between compound semiconductor layers for forming a distributed Bragg reflector mirror having an improved electrical and thermal resistance. Efficient light-emitting devices such as light-emitting diodes, resonant-cavity light-emitting diodes, and vertical-cavity surface-emitting lasers may be formed according to the present invention, which may be applied to the formation of resonant-cavity photodetectors. 16 figs.

  8. Highly defective oxides as sinter resistant thermal barrier coating

    DOEpatents

    Subramanian, Ramesh

    2005-08-16

    A thermal barrier coating material formed of a highly defective cubic matrix structure having a concentration of a stabilizer sufficiently high that the oxygen vacancies created by the stabilizer interact within the matrix to form multi-vacancies, thereby improving the sintering resistance of the material. The concentration of stabilizer within the cubic matrix structure is greater than that concentration of stabilizer necessary to give the matrix a peak ionic conductivity value. The concentration of stabilizer may be at least 30 wt. %. Embodiments include a cubic matrix of zirconia stabilized by at least 30-50 wt. % yttria, and a cubic matrix of hafnia stabilized by at least 30-50 wt. % gadolinia.

  9. Anomalous thermally induced pinning of a liquid drop on a solid substrate.

    PubMed

    Mettu, Srinivas; Kanungo, Mandakini; Law, Kock-Yee

    2013-08-27

    The effect of substrate temperature on the wetting and spreading behavior of a UV ink monomer has been studied as a surrogate for the ink on four different substrates: DTC (digital top coat)-coated BOPP (biaxial oriented polypropylene), Flexo-coated BOPP, DTC-coated SGE (semigloss elite) paper, and Flexo-coated SGE paper. Results show that the dynamic contact angles of the monomer decrease exponentially over time after contacting the surface, and the rate of spreading is consistently higher at 95 °C than at 22 °C. This observation indicates that spreading is controlled by the viscosity of the monomer as it decreases with temperature. An anomalous temperature effect is observed for the static contact angle on the DTC-coated BOPP substrate. The static contact angle at 95 °C is significantly larger than that at 22 °C (52° versus 30°). This is counterintuitive, as the surface tension of the monomer is shown to decease with increasing temperature. Microscopy (SEM and AFM) studies suggest that there is little interaction between the DTC coating solution and the BOPP substrate during the fast-drying coating process. This results in a smooth coated surface and, more importantly, voids between the BOPP nanofibers underneath the DTC coating. As the DTC-BOPP substrate is heated to 95 °C, fiber expansions occur. Microscopy results show that nanosized protrusions are formed on the DTC surface. We attribute it to fiber expansions in the vertical direction. Fiber expansions in the lateral direction causes little surface morphology change as the expanded materials only fill the voids laterally between the nanofiber network. We suggest that the protrusions on the surface create strong resistance to the wetting process and pin the monomer drop into a metastable wetting state. This interpretation is supported by the sliding angle and sessile drop height experiments.

  10. Laser-resistance sensitivity to substrate pit size of multilayer coatings

    PubMed Central

    Chai, Yingjie; Zhu, Meiping; Wang, Hu; Xing, Huanbin; Cui, Yun; Sun, Jian; Yi, Kui; Shao, Jianda

    2016-01-01

    Nanosecond laser-resistance to dielectric multilayer coatings on substrate pits was examined with respect to the electric-field (E-field) enhancement and mechanical properties. The laser-induced damage sensitivity to the shape of the substrate pits has not been directly investigated through experiments, thus preventing clear understanding of the damage mechanism of substrate pits. We performed a systematic and comparative study to reveal the effects of the E-field distributions and localized stress concentration on the damage behaviour of coatings on substrates with pits. To obtain reliable results, substrate pits with different geometries were fabricated using a 520-nm femtosecond laser-processing platform. By using the finite element method, the E-field distribution and localized stress of the pitted region were well simulated. The 1064-nm damage morphologies of the coated pit were directly compared with simulated E-field intensity profiles and stress distributions. To enable further understanding, a simplified geometrical model was established, and the damage mechanism was introduced. PMID:27252016

  11. Evaluation of the nanotube intrinsic resistance across the tip-carbon nanotube-metal substrate junction by Atomic Force Microscopy

    PubMed Central

    2011-01-01

    Using an atomic force microscope (AFM) at a controlled contact force, we report the electrical signal response of multi-walled carbon nanotubes (MWCNTs) disposed on a golden thin film. In this investigation, we highlight first the theoretical calculation of the contact resistance between two types of conductive tips (metal-coated and doped diamond-coated), individual MWCNTs and golden substrate. We also propose a circuit analysis model to schematize the «tip-CNT-substrate» junction by means of a series-parallel resistance network. We estimate the contact resistance R of each contribution of the junction such as Rtip-CNT, RCNT-substrate and Rtip-substrate by using the Sharvin resistance model. Our final objective is thus to deduce the CNT intrinsic radial resistance taking into account the calculated electrical resistance values with the global resistance measured experimentally. An unwished electrochemical phenomenon at the tip apex has also been evidenced by performing measurements at different bias voltages with diamond tips. For negative tip-substrate bias, a systematic degradation in color and contrast of the electrical cartography occurs, consisting of an important and non-reversible increase of the measured resistance. This effect is attributed to the oxidation of some amorphous carbon areas scattered over the diamond layer covering the tip. For a direct polarization, the CNT and substrate surface can in turn be modified by an oxidation mechanism. PMID:21711904

  12. Determining the Thermal Conductivity of Nanocrystalline Bismuth Telluride Thin Films Using the Differential 3 ω Method While Accounting for Thermal Contact Resistance

    NASA Astrophysics Data System (ADS)

    Kudo, S.; Hagino, H.; Tanaka, S.; Miyazaki, K.; Takashiri, M.

    2015-06-01

    We have estimated the thermal conductivity of nanocrystalline bismuth telluride thin films using the differential 3 ω method, taking into account the thermal contact resistance (TCR) between the substrate and thin-film layers. The thin films were prepared on alumina substrates by radio-frequency (RF) magnetron sputtering at temperature of 200°C. Film thickness varied between 0.8 μm and 3.1 μm. The structural properties of the films were analyzed using x-ray diffraction analysis. Their electrical conductivity, Seebeck coefficient, and power factor were evaluated. For measurement of thermal properties by the differential 3 ω method, SiO2 thin films were deposited onto the samples, to act as insulating layers. Thin aluminum wire was then patterned onto the SiO2 layer. The observed variations in temperature amplitude as a function of film thickness indicated that the TCR contribution was very small and could therefore be neglected when estimating the thermal conductivity of the thin films. The thermal conductivity of the nanocrystalline bismuth telluride thin films with thickness of 0.8 μm and 2.1 μm were determined to be 0.55 W/(m K) and 0.48 W/(m K), respectively.

  13. Response of wetland herbaceous communities to gradients of light and substrate following disturbance by thermal pollution

    USGS Publications Warehouse

    Dunn, Christopher P.; Scott, Michael L.

    1987-01-01

    The influence of thermal disturbance and site characteristics on distribution of herbs was studied in portions of a 3020 ha wetland in the southeastern USA. Presence-absence of 52 species in 130 0.25 m2 plots was determined from four sites with different disturbance histories and from an undisturbed site. Data from the four disturbed sites were ordinated by detrended correspondence analysis. Differences in species composition among sites (coarse scale) were associated with water depth, light, and substrate type. Within a site (at a fine scale), correlation of environmental variables with ordination scores at a chronically disturbed site was weakly correlated with light (r=0.50). At two sites with episodic disturbance, species composition correlated significantly and positively with substrate and water depth. At a recovering site, vegetation patterns were moderately correlated with water depth (r=−0.52). Species richness was correlated with substrate type along the disturbance gradient. Our results are consistent the intermediate disturbance hypothesis and the subsidy-stress gradient concept.

  14. Effect of headgroup-substrate interactions on the thermal behavior of long-chain amphiphiles

    NASA Astrophysics Data System (ADS)

    Singla, Saranshu; Zhu, He; Dhinojwala, Ali

    The structure of amphiphilic molecules at liquid/solid and solid/solid interfaces is relevant in understanding lubrication, colloid stabilization, chromatography, and nucleation. Here, we characterize the interfacial structures of long chain amphiphilic molecules with different head groups (OH, COOH, NH2) using interface-sensitive sum frequency generation (SFG) spectroscopy. The behavior of these self-assembled monolayers (SAMs) on sapphire substrate is recorded in situ as a function of temperature (above and below bulk Tm) using SFG. Previous studies using synchrotron X-ray reflectivity and SFG show that the melting point of an ordered hexadecanol monolayer is around 30°C above its bulk Tm. The thermal stability of the monolayer is explained due to strong hydrogen bonding interactions between the head-group and the sapphire substrate. The strength of these hydrogen-bonding interactions between substrate and different head groups is calculated using the Badger-Bauer equation. Below Tm, the ordered monolayer influenced the structure of the interfacial crystalline layer, and the transition from monolayer to the bulk crystalline phases. The results with different head groups will be presented.

  15. Transient thermal deformation of alumina (A12O3) substrate during laser drilling

    NASA Astrophysics Data System (ADS)

    Halter, Ryan; Jayaraman, Subash B.; Tittmann, Bernhard R.

    2001-08-01

    The cracking and failure in ceramic substrates during the laser drilling process has been acknowledged as a major problem by designers and manufacturers in the electronic component industries. The cracking and failure is due to large localized thermal stresses within the narrow heat-affected zone on the ceramics. Although the knowledge of the stress distribution in the ceramic substrate is important in understanding and solving the cracking/failure problem, it is impossible to measure the stress directly. The physical parameters of the laser drilling process such as temperatures or displacements, which can be directly related to stresses, can however be measured. That is why, in this research, an electronic speckle pattern interferometer (ESPI) system was designed and used to take speckle pattern images of the ceramic surface during the laser drilling process. Using commercial software, the speckle fringe images were image processed to quantify whole-field transient out-of-plane displacement measurements. A deformation history of the ceramic surface during the laser shaping process with millisecond temporal resolution was obtained, restricted only by the camera frame rate, camera resolution and laser power available. A finite difference model was developed to compare the deformation measurements with the predicted strain calculations. The experimental study and the analysis show that the designed in-situ electronic speckle pattern interferometer system provides an excellent experimental basis for whole- field, transient deformation measurements of ceramic substrates during the laser drilling process.

  16. Binding Induced RNA Conformational Changes Control Substrate Recognition and Catalysis by the Thiostrepton Resistance Methyltransferase (Tsr)*

    PubMed Central

    Kuiper, Emily G.; Conn, Graeme L.

    2014-01-01

    Ribosomal RNA (rRNA) post-transcriptional modifications are essential for ribosome maturation, translational fidelity, and are one mechanism used by both antibiotic-producing and pathogenic bacteria to resist the effects of antibiotics that target the ribosome. The thiostrepton producer Streptomyces azureus prevents self-intoxication by expressing the thiostrepton-resistance methyltransferase (Tsr), which methylates the 2′-hydroxyl of 23 S rRNA nucleotide adenosine 1067 within the thiostrepton binding site. Tsr is a homodimer with each protomer containing an L30e-like amino-terminal domain (NTD) and a SPOUT methyltransferase family catalytic carboxyl-terminal domain (CTD). We show that both enzyme domains are required for high affinity RNA substrate binding. The Tsr-CTD has intrinsic, weak RNA affinity that is necessary to direct the specific high-affinity Tsr-RNA interaction via NTDs, which have no detectable RNA affinity in isolation. RNA structure probing experiments identify the Tsr footprint on the RNA and structural changes in the substrate, induced specifically upon NTD binding, which are necessary for catalysis by the CTD. Additionally, we identify a key amino acid in each domain responsible for CTD-RNA binding and the observed NTD-dependent RNA structural changes. These studies allow us to develop a model for Tsr-RNA interaction in which the coordinated substrate recognition of each Tsr structural domain is an obligatory pre-catalytic recognition event. Our findings underscore the complexity of substrate recognition by RNA modification enzymes and the potential for direct involvement of the RNA substrate in controlling the process of its modification. PMID:25086036

  17. Transparent bipolar resistive switching memory on a flexible substrate with indium-zinc-oxide electrodes

    NASA Astrophysics Data System (ADS)

    Yeom, Seung-Won; Ha, Hyeon Jun; Park, Junsu; Shim, Jae Won; Ju, Byeong-Kwon

    2016-12-01

    We fabricated transparent indium zinc oxide (IZO)/TiO2/IZO devices on flexible polyethylene phthalate (PET) substrates. These devices demonstrate bipolar resistive switching behavior, exhibit a transmittance greater than 80 % for visible light, and have stable resistive switching properties, including long retention and good endurance. In addition, the devices were investigated based on their temperature dependence; the results show metallic properties in the low-resistance state (LRS) and semiconducting properties in the high-resistance state (HRS). The conduction mechanism for resistive switching in our device was well-fitted with Ohmic conduction in the LRS and Poole-Frenkel emission in the HRS. The mechanism could be explained by the formation and the rupture of the conduction paths formed by the movement of oxygen ions and vacancies. Moreover, acute bending of the devices did not affect the memory characteristics because of the pliability of both the IZO electrodes and the thin oxide layer. These results indicate potential applications as resistive random access memories in future flexible, transparent electronic devices.

  18. Graphite having improved thermal stress resistance and method of preparation

    DOEpatents

    Kennedy, Charles R.

    1980-01-01

    An improved method for fabricating a graphite article comprises the steps of impregnating a coke article by first heating the coke article in contact with a thermoplastic pitch at a temperature within the range of 250.degree.-300.degree. C. at a pressure within the range of 200-2000 psig for at least 4-10 hours and then heating said article at a temperature within the range of 450.degree.-485.degree. C. at a pressure of 200-2000 psig for about 16-24 hours to provide an impregnated article; heating the impregnated article for sufficient time to carbonize the impregnant to provide a second coke article, and graphitizing the second coke article. A graphite having improved thermal stress resistance results when the coke to be impregnated contains 1-3 wt.% sulfur and no added puffing inhibitors. An additional improvement in thermal stress resistance is achieved when the second coke article is heated above about 1400.degree. C. at a rate of at least 10.degree. C./minute to a temperature above the puffing temperature.

  19. Phonon impedance matching: minimizing interfacial thermal resistance of thin films

    NASA Astrophysics Data System (ADS)

    Polanco, Carlos; Zhang, Jingjie; Ghosh, Avik

    2014-03-01

    The challenge to minimize interfacial thermal resistance is to allow a broad band spectrum of phonons, with non-linear dispersion and well defined translational and rotational symmetries, to cross the interface. We explain how to minimize this resistance using a frequency dependent broadening matrix that generalizes the notion of acoustic impedance to the whole phonon spectrum including symmetries. We show how to ``match'' two given materials by joining them with a single atomic layer, with a multilayer material and with a graded superlattice. Atomic layer ``matching'' requires a layer with a mass close to the arithmetic mean (or spring constant close to the harmonic mean) to favor high frequency phonon transmission. For multilayer ``matching,'' we want a material with a broadening close to the geometric mean to maximize transmission peaks. For graded superlattices, a continuous sequence of geometric means translates to an exponentially varying broadening that generates a wide-band antireflection coating for both the coherent and incoherent limits. Our results are supported by ``first principles'' calculations of thermal conductance for GaAs / Gax Al1 - x As / AlAs thin films using the Non-Equilibrium Greens Function formalism coupled with Density Functional Perturbation Theory. NSF-CAREER (QMHP 1028883), NSF-IDR (CBET 1134311), XSEDE.

  20. Fly ash based geopolymer thin coatings on metal substrates and its thermal evaluation.

    PubMed

    Temuujin, Jadambaa; Minjigmaa, Amgalan; Rickard, William; Lee, Melissa; Williams, Iestyn; van Riessen, Arie

    2010-08-15

    Class F fly ash based Na-geopolymer formulations have been applied as fire resistant coatings on steel. The main variables for the coating formulations were Si: Al molar and water: cement weight ratios. We have determined that the adhesive strength of the coatings strongly depend on geopolymer composition. The ease with which geopolymer can be applied onto metal surfaces and the resultant thickness depend on the water content of the formulation. Adhesive strengths of greater than 3.5 MPa have been achieved on mild steel surfaces for compositions with Si:Al of 3.5. Microstructure evolution and thermal properties of the optimised coating formulations show that they have very promising fire resistant characteristics.

  1. Positive/Negative Mid Uv Resists With High Thermal Stability

    NASA Astrophysics Data System (ADS)

    Ito, Hiroshi; Wilson, C. G.; Frechet, Jean M.

    1987-08-01

    New mid UV resist systems based on poly(p-vinylbenzoates) sensitized with diphenyl-4-thiophenoxyphenylsulfonium hexafluoroantimonate are described. t-Butyl, cyclohexenyl, a-methylbenzyl, and a-methylallyl esters are converted upon postbake to poly(p-vinylbenzoic acid) through thermolysis reaction catalyzed by the photochemically generated Bronsted acid, inducing a large change in the polarity of the repeating units. Thus, development in aqueous base such as MF312/water or alcohol provides a positive tone image of the mask, while the use of a nonpolar organic developer allows a negative tone imaging. Because the glass transition temperature of poly(p-vinylbenzoic acid) is ca. 250° C, the negative image is devoid of thermal flow to this temperature even without any hardening processes. Another interesting feature of the benzoate resists is their high opacity in the deep UV region. The optical density of a 1μ thick film of poly(p-vinylbenzoic acid) is 3.5 at 254 nm and the benzoate polymers are as absorbing as the acid polymer. This high deep UV absorption of the resin necessitates the imaging above 300 nm for good light penetration (or by e-beam or X-ray) and makes the use of this resist as an imaging layer in the PCM scheme very attractive. This imaging layer is especially useful when employed in conjunction with a planarizing layer absorbing above 240 nm (for example, PMGI) as addition of a dye is not required.

  2. Entropic effects of thermal rippling on van der Waals interactions between monolayer graphene and a rigid substrate

    NASA Astrophysics Data System (ADS)

    Wang, Peng; Gao, Wei; Huang, Rui

    2016-02-01

    Graphene monolayer, with extremely low flexural stiffness, displays spontaneous rippling due to thermal fluctuations at a finite temperature. When a graphene membrane is placed on a solid substrate, the adhesive interactions between graphene and the substrate could considerably suppress thermal rippling. On the other hand, the statistical nature of thermal rippling adds an entropic contribution to the graphene-substrate interactions. In this paper, we present a statistical mechanics analysis on thermal rippling of monolayer graphene supported on a rigid substrate, assuming a generic form of van der Waals interactions between graphene and substrate at T = 0 K. The rippling amplitude, the equilibrium average separation, and the average interaction energy are predicted simultaneously and compared with molecular dynamics (MD) simulations. While the amplitude of thermal rippling is reduced by adhesive interactions, the entropic contribution leads to an effective repulsion. As a result, the equilibrium average separation increases and the effective adhesion energy decreases with increasing temperature. Moreover, the effect of a biaxial pre-strain in graphene is considered, and a buckling instability is predicted at a critical compressive strain that depends on both the temperature and the adhesive interactions. Limited by the harmonic approximations, the theoretical predictions agree with MD simulations only for relatively small rippling amplitudes but can be extended to account for the anharmonic effects.

  3. Process for producing a well-adhered durable optical coating on an optical plastic substrate. [abrasion resistant polymethyl methacrylate lenses

    NASA Technical Reports Server (NTRS)

    Kubacki, R. M. (Inventor)

    1978-01-01

    A low temperature plasma polymerization process is described for applying an optical plastic substrate, such as a polymethyl methacrylate lens, with a single layer abrasive resistant coating to improve the durability of the plastic.

  4. Differential hepatic distribution of insulin receptor substrates causes selective insulin resistance in diabetes and obesity

    PubMed Central

    Kubota, Naoto; Kubota, Tetsuya; Kajiwara, Eiji; Iwamura, Tomokatsu; Kumagai, Hiroki; Watanabe, Taku; Inoue, Mariko; Takamoto, Iseki; Sasako, Takayoshi; Kumagai, Katsuyoshi; Kohjima, Motoyuki; Nakamuta, Makoto; Moroi, Masao; Sugi, Kaoru; Noda, Tetsuo; Terauchi, Yasuo; Ueki, Kohjiro; Kadowaki, Takashi

    2016-01-01

    Hepatic insulin signalling involves insulin receptor substrates (Irs) 1/2, and is normally associated with the inhibition of gluconeogenesis and activation of lipogenesis. In diabetes and obesity, insulin no longer suppresses hepatic gluconeogenesis, while continuing to activate lipogenesis, a state referred to as ‘selective insulin resistance'. Here, we show that ‘selective insulin resistance' is caused by the differential expression of Irs1 and Irs2 in different zones of the liver. We demonstrate that hepatic Irs2-knockout mice develop ‘selective insulin resistance', whereas mice lacking in Irs1, or both Irs1 and Irs2, develop ‘total insulin resistance'. In obese diabetic mice, Irs1/2-mediated insulin signalling is impaired in the periportal zone, which is the primary site of gluconeogenesis, but enhanced in the perivenous zone, which is the primary site of lipogenesis. While hyperinsulinaemia reduces Irs2 expression in both the periportal and perivenous zones, Irs1 expression, which is predominantly in the perivenous zone, remains mostly unaffected. These data suggest that ‘selective insulin resistance' is induced by the differential distribution, and alterations of hepatic Irs1 and Irs2 expression. PMID:27708333

  5. Factors influencing the ballistic impact resistance of elastomer-coated metal substrates

    NASA Astrophysics Data System (ADS)

    Roland, C. M.; Fragiadakis, D.; Gamache, R. M.; Casalini, R.

    2013-02-01

    An experimental study was carried out of various factors affecting the ballistic penetration resistance of elastomer/steel bilayers. For blunt penetrators, the contribution of the coating to performance is optimized using the hardest substrates, front surface placement of the elastomer, and (when normalizing by added weight) thin, ca. 2-3 mm, coatings. These results, none of which are predicted by existing models, evince the marked coupling of coating and substrate in the impact response of the bilayer. We also show that nanoparticle fillers have a modest effect on ballistic performance of polyurea coatings, changing the penetration velocity by a few percent or less. This contrasts with the linear dynamic mechanical behavior, which shows much more significant increases in energy absorption due to nano-reinforcement.

  6. Titanium nickel silver and gold die backside metalization for Quad Flat Nolead package thermal resistance reduction

    NASA Astrophysics Data System (ADS)

    Chau, Hung

    Thermal resistance of a Quad Flat Nolead (QFN) package, comprised of the bulk material resistance of a die attach with its two interfaces, is measured by thermal transient technique. Two die attach chemistries (Ag filled and Boron Nitride filled) and three die-backside coatings (TiNiAg, Au, and bare Si) were investigated to understand their contribution to the thermal resistance. Of the tests conducted, the most effective combination was a metalized layer of TiNiAg with the Ag filled epoxy system. In order to further improve the thermal resistance reduction, electron to phonon and phonon to phonon transport must be better understood.

  7. Thermal resistance between crossed carbon nanotubes: Molecular dynamics simulations and analytical modeling

    NASA Astrophysics Data System (ADS)

    Hu, Guo-Jie; Cao, Bing-Yang

    2013-12-01

    A nonequilibrium molecular dynamics (MD) method is used to calculate the thermal resistance between crossed carbon nanotubes (CNTs). The thermal resistance is predicted to be of the order of 109-1011 K/W. The effects of the crossing angle, nanotube length, and initial nanotube spacing on the thermal resistance are studied in detail with the fixed boundary condition applied in the axial direction of each CNT. The thermal resistance is found to increase with the increasing crossing angle while decrease with the increasing nanotube length and converge to a constant eventually. An increase in the thermal resistance is observed for nanotubes with larger initial spacing and the increase becomes abrupt as the initial spacing is increased to the van der Waals diameter. Between the crossed CNTs the phonon transport is constricted through the contact. The thermal resistance between the crossed CNTs calculated by MD is found to be close to the ballistic constriction resistance, which indicates that the constriction thermal resistance plays a major role in the inter-tube thermal resistance and the ballistic transport of phonons is dominant in the thermal transport between the crossed CNTs.

  8. Advanced thermal barrier system bond coatings for use on Ni, Co-, and Fe-base alloy substrates

    NASA Technical Reports Server (NTRS)

    Stecura, S.

    1985-01-01

    New and improved Ni-, Co-, and Fe-base bond coatings have been identified for the ZrO2-Y2O3 thermal barrier coatings to be used on NI-, Co-, and Fe-base alloy substrates. These bond coatings were evaluated in a cyclic furnace between 1120 and 1175 C. It was found that MCrAlYb (where M = Ni, Co, or Fe) bond coating thermal barrier systems. The longest life was obtained with the FeCrAlYb thermal barrier system followed by NiCrAlYb and CoCrAlYb thermal barrier systems in that order.

  9. Investigation of nanocrystalline thin cobalt films thermally evaporated on Si(100) substrates

    NASA Astrophysics Data System (ADS)

    Kozłowski, W.; Balcerski, J.; Szmaja, W.; Piwoński, I.; Batory, D.; Miękoś, E.; Cichomski, M.

    2017-03-01

    We have made a quantitative study of the morphological and magnetic domain structures of 100 nm thick nanocrystalline cobalt films thermally evaporated on naturally oxidized Si(100) substrates. The morphological structure is composed of densely packed grains with the average grain size (35.6±0.8) nm. The grains exhibit no geometric alignment and no preferred elongation on the film surface. In the direction perpendicular to the film surface, the grains are aligned in columns. The films crystallize mainly in the hexagonal close-packed phase of cobalt and possess a crystallographic texture with the hexagonal axis perpendicular to the film surface. The magnetic domain structure consists of domains forming a maze stripe pattern with the average domain size (102±6) nm. The domains have their magnetizations oriented almost perpendicularly to the film surface. The domain wall energy, the domain wall thickness and the critical diameter for single-domain particle were determined.

  10. Activation energy of thermal desorption of silicon oxide layers on silicon substrates

    NASA Astrophysics Data System (ADS)

    Enta, Yoshiharu; Osanai, Shodai; Ogasawara, Takahito

    2017-02-01

    Thermal desorption rates of silicon oxide layers, from 20 to 120 nm in thickness, on silicon substrates in vacuum have been accurately obtained from intervals between ring structures formed inside voids on the oxide layers. From the temperature dependence of the desorption rate, the activation energy and frequency factor of the desorption reaction have been derived as a function of the oxide thickness. The obtained values are compared with the previous studies, and as a result, the activation energy is found to be almost constant ( 4 eV) in a wide range of the oxide thickness. The frequency factor decreases as the inverse square of the oxide thickness. The decomposition kinetics of the oxide layer is also discussed from the obtained results.

  11. Basic thermal-mechanical properties and thermal shock, fatigue resistance of swaged + rolled potassium doped tungsten

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaoxin; Yan, Qingzhi; Lang, Shaoting; Xia, Min; Ge, Changchun

    2014-09-01

    The potassium doped tungsten (W-K) grade was achieved via swaging + rolling process. The swaged + rolled W-K alloy exhibited acceptable thermal conductivity of 159.1 W/m K and ductile-to-brittle transition temperature of about 873 K while inferior mechanical properties attributed to the coarse pores and small deformation degree. Then the thermal shock, fatigue resistance of the W-K grade were characterized by an electron beam facility. Thermal shock tests were conducted at absorbed power densities varied from 0.22 to 1.1 GW/m2 in a step of 0.22 GW/m2. The cracking threshold was in the range of 0.44-0.66 GW/m2. Furthermore, recrystallization occurred in the subsurface of the specimens tested at 0.66-1.1 GW/m2 basing on the analysis of microhardness and microstructure. Thermal fatigue tests were performed at 0.44 GW/m2 up to 1000 cycles and no cracks emerged throughout the tests. Moreover, recrystallization occurred after 1000 cycles.

  12. Multiferroic YCrO3 thin films grown on glass substrate: Resistive switching characteristics

    NASA Astrophysics Data System (ADS)

    Seo, Jeongdae; Ahn, Yoonho; Son, Jong Yeog

    2016-01-01

    Polycrystalline YCrO3 thin films were deposited on (111) Pt/Ta/glass substrates by pulsed laser deposition. The YCrO3 thin films exhibited good ferroelectric properties with remnant polarization of about 5 µC/cm2. Large leakage current was observed by I- V curve and ferroelectric hysteresis loop. The YCrO3 resistive random access memory (RRAM) capacitor showed unipolar switching behaviors with SET and RESET voltages higher than those of general NiO RRAM capacitors. [Figure not available: see fulltext.

  13. Integrated Thermal Protection Systems and Heat Resistant Structures

    NASA Technical Reports Server (NTRS)

    Pichon, Thierry; Lacoste, Marc; Glass, David E.

    2006-01-01

    In the early stages of NASA's Exploration Initiative, Snecma Propulsion Solide was funded under the Exploration Systems Research & Technology program to develop integrated thermal protection systems and heat resistant structures for reentry vehicles. Due to changes within NASA's Exploration Initiative, this task was cancelled early. This presentation provides an overview of the work that was accomplished prior to cancellation. The Snecma team chose an Apollo-type capsule as the reference vehicle for the work. They began with the design of a ceramic aft heatshield (CAS) utilizing C/SiC panels as the capsule heatshield, a C/SiC deployable decelerator and several ablators. They additionally developed a health monitoring system, high temperature structures testing, and the insulation characterization. Though the task was pre-maturely cancelled, a significant quantity of work was accomplished.

  14. Thermal stability of Pr2O3 films grown on Si(100) substrate

    NASA Astrophysics Data System (ADS)

    Goryachko, A.; Liu, J. P.; Krüger, D.; Osten, H. J.; Bugiel, E.; Kurps, R.; Melnik, V.

    2002-11-01

    We have investigated the effect of thermal annealing on uncapped and Si-capped Pr2O3 films deposited on Si(100) substrate by Auger electron spectroscopy, x-ray photoelectron spectroscopy, and transmission electron microscopy. A rapid diffusion of Si out of the substrate was found for uncapped films at temperatures starting from 700 °C. The diffused Si is oxidized, forming a Pr2O3-Prx- Oy- Siz mixture. The excess Si diffuses through the film, forming a SiO2 rich layer on the surface. Annealing of uncapped films in vacuum has qualitatively similar effects as annealing in N2, which is not the case for Si-capped films. The latter were transformed into a Pr2O3-Prx- Oy- Siz mixture when annealed in N2 starting from 900 °C and into PrSix when annealed in vacuum starting from 700 °C. Two distinct PrSix phases were found, with Si-richer phases corresponding to higher annealing temperature.

  15. Dynamics of ultrathin metal films on amorphous substrates under fast thermal processing

    NASA Astrophysics Data System (ADS)

    Favazza, Christopher; Kalyanaraman, Ramki; Sureshkumar, Radhakrishna

    2007-11-01

    A mathematical model is developed to analyze the growth/decay rate of surface perturbations of an ultrathin metal film on an amorphous substrate (SiO2). The formulation combines the approach of Mullins [W. W. Mullins, J. Appl. Phys. 30, 77 (1959)] for bulk surfaces, in which curvature-driven mass transport and surface deformation can occur by surface/volume diffusion and evaporation-condensation processes, with that of Spencer etal . [B. J. Spencer, P. W. Voorhees, and S. H. Davis, Phys. Rev. Lett. 67, 26 (1991)] to describe solid-state transport in thin films under epitaxial strain. Modifications of the Mullins model to account for thin-film boundary conditions result in qualitatively different dispersion relationships especially in the limit as kho≪1, where k is the wavenumber of the perturbation and ho is the unperturbed film height. The model is applied to study the relative rate of solid-state mass transport as compared to that of liquid phase dewetting in a thin film subjected to a fast thermal pulse. Specifically, we have recently shown that multiple cycles of nanosecond (ns) pulsed laser melting and resolidification of ultrathin metal films on amorphous substrates can lead to the formation of various types of spatially ordered nanostructures [J. Trice, D. Thomas, C. Favazza, R. Sureshkumar, and R. Kalyanaraman, Phys. Rev. B 75, 235439 (2007)]. The pattern formation has been attributed to the dewetting of the thin film by a hydrodynamic instability. In such experiments the film is in the solid state during a substantial fraction of each thermal cycle. However, results of a linear stability analysis based on the aforementioned model suggest that solid-state mass transport has a negligible effect on morphological changes of the surface. Further, a qualitative analysis of the effect of thermoelastic stress, induced by the rapid temperature changes in the film-substrate bilayer, suggests that stress relaxation does not appreciably contribute to surface

  16. Some effects of metallic substrate composition on degradation of thermal barrier coatings

    SciTech Connect

    Wright, I.G.; Pint, B.A.; Lee, W.Y.; Alexander, K.B.; Pruessner, K.

    1997-12-31

    Comparisons have been made in laboratory isothermal and cyclic oxidation tests of the degradation of oxide scales grown on single crystal superalloy substrates and bond coating alloys intended for use in thermal barrier coatings systems. The influence of desulfurization of the superalloy and bond coating, of reactive element addition to the bond coating alloy, and of oxidation temperature on the spallation behavior of the alumina scales formed was assessed from oxidation kinetics and from SEM observations of the microstructure and composition of the oxide scales. Desulfurization of nickel-base superalloy (in the absence of a Y addition) resulted in an increase in the lifetime of a state-of-the-art thermal barrier coating applied to it compared to a Y-free, non-desulfurized version of the alloy. The lifetime of the same ceramic coating applied without a bond coating to a non-desulfurized model alloy that formed an ideal alumina scale was also found to be at least four times longer than on the Y-doped superalloy plus state-of-the-art bond coating combination. Some explanations are offered of the factors controlling the degradation of such coatings.

  17. Residual Stresses in Thermal Barrier Coatings for a Cu-8Cr-4Nb Substrate System

    NASA Technical Reports Server (NTRS)

    Ghosn, Louis J.; Raj, Sai V.

    2002-01-01

    Analytical calculations were conducted to determine the thermal stresses developed in a coated copper-based alloy, Cu-8%(at.%)Cr-4%Nb (designated as GRCop-84), after plasma spraying and during heat-up in a simulated rocket engine environment. Finite element analyses were conducted for two coating systems consisting of a metallic top coat, a pure copper bond coat and the GRCop-84. The through thickness temperature variations were determined as a function of coating thickness for two metallic coatings, a Ni-17%(wt%)Cr-6%Al-0.5%Y alloy and a Ni-50%(at.%)Al alloy. The residual stresses after low-pressure plasma spraying of the NiCrAlY and NiAl coatings on GRCop-84 substrate were also evaluated. These analyses took into consideration a 50.8 mm copper bond coat and the effects of an interface coating roughness. The through the thickness thermal stresses developed in coated liners were also calculated after 15 minutes of exposure in a rocket environment with and without an interfacial roughness.

  18. Anion exchanger and the resistance against thermal haemolysis.

    PubMed

    Ivanov, I T; Zheleva, A; Zlatanov, I

    2011-01-01

    4,4'-Diiso-thiocyanato stilbene-2,2'-disulphonic acid (DIDS) is a membrane-impermeable, highly specific covalent inhibitor and powerful thermal stabiliser of the anion exchanger (AE1), the major integral protein of erythrocyte membrane (EM). Suspensions of control and DIDS-treated (15 µM, pH 8.2) human erythrocytes were heated from 20° to 70°C using various but constant heating rates (1-8°C/min). The cellular electrolyte leakage exhibited a sigmoidal response to temperature as detected by conductometry. The critical midpoint temperature of leakage, T(mo), extrapolated to low heating rate (0.5°C/min) was used as a measure for EM thermostability. T(mo) was greater for DIDS-treated erythrocytes, 63.2° ± 0.3°C, than for intact erythrocytes, 60.7° ± 0.2°C. The time, t(1/2), for 50% haemolysis of erythrocytes, exposed to 53°C was used as a measure for the resistance of erythrocytes against thermal haemolysis. The t(1/2) was also greater for DIDS-treated erythrocytes, 63 ± 3 min, than for intact erythrocytes, 38 ± 2 min. The fluorescent label N-(3-pyrenyl)maleimide and EPR spin label 3-maleimido-proxyl, covalently bound to sulphydryl groups of major EM proteins, were used to monitor the changes in molecular motions during transient heating. Both labels reported an intensification of the motional dynamics at the denaturation temperatures of spectrin (50°C) and AE1 (67°C), and, surprisingly, immobilisation of a major EM protein, presumably the AE1, at T(mo). The above results are interpreted in favour of the possible involvement of a predenaturational rearrangement of AE1 copies in the EM thermostability and the resistance against thermal haemolysis.

  19. The influence of the thermal diffusivity of the substrates on fabrication of metal nanostructures by femtosecond laser irradiation

    NASA Astrophysics Data System (ADS)

    Takami, Akihiro; Nakajima, Yasutaka; Nedyalkov, Nikolay; Terakawa, Mitsuhiro

    2017-02-01

    We demonstrate the fabrication of nanowire gratings by irradiation of femtosecond laser pulses to platinum thin films on various substrates: silicon carbide, aluminum nitride, silicon and fused silica. Scanning electron microscopy showed that many cracks were formed on the nanowire surfaces formed on silicon carbide, aluminum nitride and silicon substrates, while few cracks were formed on a fused silica substrate. Elemental analysis by energy-dispersive X-ray spectroscopy indicated that melting or evaporation of the platinum thin film could hardly occur in the case of the silicon carbide and aluminum nitride substrates. Calculated results by two temperature models revealed that the lattice temperature within the platinum thin films after laser irradiation depends on the thermal diffusivity of the substrates, which could influence the melting phase existence time. From the experimental and the calculated results, melting of the metal thin film could have influenced metal nanowire grating formation.

  20. Finite dipole model for extreme near-field thermal radiation between a tip and planar SiC substrate

    NASA Astrophysics Data System (ADS)

    Jarzembski, Amun; Park, Keunhan

    2017-04-01

    Recent experimental studies have measured the infrared (IR) spectrum of tip-scattered near-field thermal radiation for a SiC substrate and observed up to a 50cm-1 redshift of the surface phonon polariton (SPhP) resonance peak [1,2]. However, the observed spectral redshift cannot be explained by the conventional near-field thermal radiation model based on the point dipole approximation. In the present work, a heated tip is modeled as randomly fluctuating point charges (or fluctuating finite dipoles) aligned along the primary axis of a prolate spheroid, and quasistatic tip-substrate charge interactions are considered to formulate the effective polarizability and self-interaction Green's function. The finite dipole model (FDM), combined with fluctuational electrodynamics, allows the computation of tip-plane thermal radiation in the extreme near-field (i.e., H / R ≲ 1 , where H is the tip-substrate gap distance and R is the tip radius), which cannot be calculated with the point dipole approximation. The FDM provides the underlying physics on the spectral redshift of tip-scattered near-field thermal radiation as observed in experiments. In addition, the SPhP peak in the near-field thermal radiation spectrum may split into two peaks as the gap distance decreases into the extreme near-field regime. This observation suggests that scattering-type spectroscopic measurements may not convey the full spectral features of tip-plane extreme near-field thermal radiation.

  1. Elastic modulus and thermal stress in coating during heat cycling with different substrate shapes

    NASA Astrophysics Data System (ADS)

    Gaona, Daniel; Valarezo, Alfredo

    2015-09-01

    The elastic modulus of a deposit ( E d) can be obtained by monitoring the temperature (Δ T) and curvature (Δ k) of a one-side coated long plate, namely, a onedimensional (1D) deformation model. The aim of this research is to design an experimental setup that proves whether a 1D deformation model can be scaled for complex geometries. The setup includes a laser displacement sensor mounted on a robotic arm capable of scanning a specimen surface and measuring its deformation. The reproducibility of the results is verified by comparing the present results with Stony Brook University Laboratory's results. The Δ k-Δ T slope error is less than 8%, and the E d estimation error is close to 2%. These values reveal the repeatability of the experiments. Several samples fabricated with aluminum as the substrate and 100MXC nanowire (Fe and Cr alloy) as the deposit are analyzed and compared with those in finite element (FE) simulations. The linear elastic behavior of 1D (flat long plate) and 2D (squared plate) specimens during heating/cooling cycles is demonstrated by the high linearity of all Δ k-Δ T curves (over 97%). The E d values are approximately equal for 1D and 2D analyses, with a median of 96 GPa and standard deviation of 2 GPa. The correspondence between the experimental and simulated results for the 1D and 2D specimens reveals that deformation and thermal stress in coated specimens can be predicted regardless of specimen geometry through FE modeling and by using the experimental value of E d. An example of a turbine-bladeshaped substrate is presented to validate the approach.

  2. The pathogenesis of insulin resistance: integrating signaling pathways and substrate flux

    PubMed Central

    Samuel, Varman T.; Shulman, Gerald I.

    2016-01-01

    Insulin resistance arises when the nutrient storage pathways evolved to maximize efficient energy utilization are exposed to chronic energy surplus. Ectopic lipid accumulation in liver and skeletal muscle triggers pathways that impair insulin signaling, leading to reduced muscle glucose uptake and decreased hepatic glycogen synthesis. Muscle insulin resistance, due to ectopic lipid, precedes liver insulin resistance and diverts ingested glucose to the liver, resulting in increased hepatic de novo lipogenesis and hyperlipidemia. Subsequent macrophage infiltration into white adipose tissue (WAT) leads to increased lipolysis, which further increases hepatic triglyceride synthesis and hyperlipidemia due to increased fatty acid esterification. Macrophage-induced WAT lipolysis also stimulates hepatic gluconeogenesis, promoting fasting and postprandial hyperglycemia through increased fatty acid delivery to the liver, which results in increased hepatic acetyl-CoA content, a potent activator of pyruvate carboxylase, and increased glycerol conversion to glucose. These substrate-regulated processes are mostly independent of insulin signaling in the liver but are dependent on insulin signaling in WAT, which becomes defective with inflammation. Therapies that decrease ectopic lipid storage and diminish macrophage-induced WAT lipolysis will reverse the root causes of type 2 diabetes. PMID:26727229

  3. Performance Evaluation and Modeling of Erosion Resistant Turbine Engine Thermal Barrier Coatings

    NASA Technical Reports Server (NTRS)

    Miller, Robert A.; Zhu, Dongming; Kuczmarski, Maria

    2008-01-01

    The erosion resistant turbine thermal barrier coating system is critical to the rotorcraft engine performance and durability. The objective of this work was to determine erosion resistance of advanced thermal barrier coating systems under simulated engine erosion and thermal gradient environments, thus validating a new thermal barrier coating turbine blade technology for future rotorcraft applications. A high velocity burner rig based erosion test approach was established and a new series of rare earth oxide- and TiO2/Ta2O5- alloyed, ZrO2-based low conductivity thermal barrier coatings were designed and processed. The low conductivity thermal barrier coating systems demonstrated significant improvements in the erosion resistance. A comprehensive model based on accumulated strain damage low cycle fatigue is formulated for blade erosion life prediction. The work is currently aiming at the simulated engine erosion testing of advanced thermal barrier coated turbine blades to establish and validate the coating life prediction models.

  4. The Development of Erosion and Impact Resistant Turbine Airfoil Thermal Barrier Coatings

    NASA Technical Reports Server (NTRS)

    Zhu, Dongming; Miller, Robert A.

    2007-01-01

    Thermal barrier coatings are used in gas turbine engines to protect engine hot-section components in the harsh combustion environments and extend component lifetimes. For thermal barrier coatings designed for turbine airfoil applications, further improved erosion and impact resistance are crucial for engine performance and durability. Advanced erosion resistant thermal barrier coatings are being developed, with a current emphasis on the toughness improvements using a combined rare earth- and transition metal-oxide doping approach. The performance of the doped thermal barrier coatings has been evaluated in burner rig and laser heat-flux rig simulated engine erosion and thermal gradient environments. The results have shown that the coating composition optimizations can effectively improve the erosion and impact resistance of the coating systems, while maintaining low thermal conductivity and cyclic durability. The erosion and impact damage mechanisms of the thermal barrier coatings will also be discussed.

  5. Large-scale uniform ZnO tetrapods on catalyst free glass substrate by thermal evaporation method

    SciTech Connect

    Alsultany, Forat H.; Hassan, Z.; Ahmed, Naser M.

    2016-07-15

    Highlights: • Investigate the growth of ZnO-Ts on glass substrate by thermal evaporation method. • Glass substrate without any catalyst or a seed layer. • The morphology was controlled by adjusting the temperature of the material and the substrate. • Glass substrate was placed vertically in the quartz tube. - Abstract: Here, we report for the first time the catalyst-free growth of large-scale uniform shape and size ZnO tetrapods on a glass substrate via thermal evaporation method. Three-dimensional networks of ZnO tetrapods have needle–wire junctions, an average leg length of 2.1–2.6 μm, and a diameter of 35–240 nm. The morphology and structure of ZnO tetrapods were investigated by controlling the preparation temperature of each of the Zn powder and the glass substrate under O{sub 2} and Ar gases. Studies were carried out on ZnO tetrapods using X-ray diffraction, field emission scanning electron microscopy, UV–vis spectrophotometer, and a photoluminescence. The results showed that the sample grow in the hexagonal wurtzite structure with preferentially oriented along (002) direction, good crystallinity and high transmittance. The band gap value is about 3.27 eV. Photoluminescence spectrum exhibits a very sharp peak at 378 nm and a weak broad green emission.

  6. Thermal oxidation of amorphous germanium thin films on SiO2 substrates

    NASA Astrophysics Data System (ADS)

    de los Santos Valladares, L.; Bustamante Dominguez, A.; Ionescu, A.; Brown, A.; Sepe, A.; Steiner, U.; Avalos Quispe, O.; Holmes, S.; Majima, Y.; Langford, R.; Barnes, C. H. W.

    2016-12-01

    In this work we report the thermal oxidation of amorphous germanium (a-Ge) thin films (140 nm thickness) in air. Following fabrication by conventional thermal evaporation on SiO2 substrates, the samples were annealed in air at different temperatures ranging from 300 to 1000 °C. By means of x-ray diffraction, x-ray reflectivity, synchrotron grazing-incidence wide-angle x-ray scattering and cross-sectional transmission electron microscopy analysis it is found that the a-Ge films abruptly crystallize at 475 °C, while simultaneously increasing the thickness of the oxide (GeO2) in a layer by layer fashion. X-ray photoemission spectroscopy reveals that the oxidation state of the Ge atoms in the GeO2 layer is 4+. However, a reaction at the GeO2/Ge interface occurs between 500 and 550 °C reducing the oxide layer to GeO x (x < 2) and containing Ge2+ and Ge+. The thickness of the oxide layer grows with the annealing temperature following an Arrhenius behavior with an activation energy of 0.82 ± 0.09 eV up to 500 °C. Remarkably, we observed simultaneous enhancement of the oxidation and crystallization of the a-Ge in the temperature interval 450 °C-500 °C, in which the oxidation rate reaches a maximum of around 0.8 nm °C-1 at around 500 °C.

  7. Comparative thermal fatigue resistances of twenty-six nickel and cobalt base alloys

    NASA Technical Reports Server (NTRS)

    Bizon, P. T.; Spera, D. A.

    1975-01-01

    Thermal fatigue resistances were determined from fluidized bed tests. Cycles to cracking differed by almost three orders of magnitude for these materials with directional solidification and surface protection of definite benefit. The alloy-coating combination with the highest thermal fatigue resistance was directionally solidified NASA TAZ-8A with an RT-XP coating. It oxidation resistance was excellent, showing almost no weight change after 15 000 fluidized bed cycles.

  8. Geopolymer Porous Nanoceramics for Structural Smart and Thermal Shock Resistant Applications

    DTIC Science & Technology

    2011-02-02

    1 FINAL REPORT for GEOPOLYMER POROUS NANOCERAMICS FOR STRUCTURAL, FOR SMART AND THERMAL SHOCK RESISTANT APPLICATIONS AFOSR - Grant No. (FA9550...Potential applications were explored in the area of refractory adhesives between metal, corrosion resistant coatings on steel, glass and ceramics...THERMAL SHOCK RESISTANT APPLICATIONS 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) Waltraud Kriven 5d. PROJECT NUMBER

  9. Geopolymer Porous Nanoceramics for Structural, for Smart and Thermal Shock Resistant Applications

    DTIC Science & Technology

    2011-02-02

    1 FINAL REPORT for GEOPOLYMER POROUS NANOCERAMICS FOR STRUCTURAL, FOR SMART AND THERMAL SHOCK RESISTANT APPLICATIONS AFOSR - Grant No. (FA9550...Potential applications were explored in the area of refractory adhesives between metal, corrosion resistant coatings on steel, glass and ceramics...STRUCTURAL, FOR SMART AND THERMAL SHOCK RESISTANT APPLICATIONS 5a. CONTRACT NUMBER FA9550-06-1-0221 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6

  10. Advanced thermal barrier system bond coatings for use on nickel-, cobalt- and iron-base alloy substrates

    NASA Technical Reports Server (NTRS)

    Stecura, S.

    1986-01-01

    New and improved Ni-, Co-, and Fe-base bond coatings have been identified for the ZrO2-Y2O3 thermal barrier coatings to be used on Ni-, Co-, and Fe-base alloy substrates. These bond coatings were evaluated in a cyclic furnace between 1120 and 1175 C. It was found that MCrAlYb (where M = Ni, Co, or Fe) bond coating thermal barrier systems have significantly longer lives than MCrAlY bond coating thermal barrier systems. The longest life was obtained with the FeCrAlYb thermal barrier system followed by NiCrAlYb and CoCrAlYb thermal barrier systems in that order.

  11. Thermal preference, thermal resistance, and metabolic rate of juvenile Chinese pond turtles Mauremys reevesii acclimated to different temperatures.

    PubMed

    Xu, Wei; Dang, Wei; Geng, Jun; Lu, Hong-Liang

    2015-10-01

    The thermal acclimatory capacity of a particular species may determine its resilience to environmental change. Evaluating the physiological acclimatory responses of economically important species is useful for determining their optimal culture conditions. Here, juvenile Chinese three-keeled pond turtles (Mauremys reevesii) were acclimated to one of three different temperatures (17, 25 or 33°C) for four weeks to assess the effects of thermal acclimation on some physiological traits. Thermal acclimation significantly affected thermal resistance, but not thermal preference, of juvenile M. reevesii. Turtles acclimated to 17°C were less resistant to high temperatures than those acclimated to 25°C and 33°C. However, turtles increased resistance to low temperatures with decreasing acclimation temperature. The acclimation response ratio of the critical thermal minimum (CTMin) was lower than that of the critical thermal maximum (CTMax) for acclimation temperatures between 17 and 25°C, but slightly higher between 25 and 33°C. The thermal resistance range (i.e., the difference between CTMax and CTMin) was widest in turtles acclimated to the intermediate temperature (25°C), and narrowest in those acclimated to low temperature (17°C). The standard metabolic rate increased as body temperature and acclimation temperature increased, and the temperature quotient (Q10) between acclimation temperatures 17 and 25°C was higher than the Q10 between 25 and 33°C. Our results suggest that juvenile M. reevesii may have a greater resistance under mild thermal conditions resembling natural environments, and better physiological performance at relatively warm temperatures.

  12. Analytical investigations on the thermal properties of microscale inorganic light-emitting diodes on an orthotropic substrate

    NASA Astrophysics Data System (ADS)

    Li, Y.; Chen, J.; Xing, Y.; Song, J.

    2017-03-01

    The microscale inorganic light-emitting diodes (μ-ILEDs) create novel opportunities in biointegrated applications such as wound healing acceleration and optogenetics. Analytical expressions, validated by finite element analysis, are obtained for the temperature increase of a rectangular μ-ILED device on an orthotropic substrate, which could offer an appealing advantage in controlling the heat flow direction to achieve the goal in thermal management. The influences of various parameters (e.g., thermal conductivities of orthotropic substrate, loading parameters) on the temperature increase of the μ-ILED are investigated based on the obtained closed-form solutions. These results provide a novel route to control the temperature distribution in the μ-ILED system and provide easily interpretable guidelines to minimize the adverse thermal effects.

  13. Thermal Resistance Variations of Fly Ash Geopolymers: Foaming Responses

    PubMed Central

    Cheng-Yong, Heah; Yun-Ming, Liew; Abdullah, Mohd Mustafa Al Bakri; Hussin, Kamarudin

    2017-01-01

    This paper presents a comparative study of the characteristic of unfoamed and foamed geopolymers after exposure to elevated temperatures (200–800 °C). Unfoamed geopolymers were produced with Class F fly ash and sodium hydroxide and liquid sodium silicate. Porous geopolymers were prepared by foaming with hydrogen peroxide. Unfoamed geopolymers possessed excellent strength of 44.2 MPa and degraded 34% to 15 MPa in foamed geopolymers. The strength of unfoamed geopolymers decreased to 5 MPa with increasing temperature up to 800 °C. Foamed geopolymers behaved differently whereby they deteriorated to 3 MPa at 400 °C and increased up to 11 MPa at 800 °C. Even so, the geopolymers could withstand high temperature without any disintegration and spalling up to 800 °C. The formation of crystalline phases at higher temperature was observed deteriorating the strength of unfoamed geopolymers but enhance the strength of foamed geopolymers. In comparison, foamed geopolymer had better thermal resistance than unfoamed geopolymers as pores provide rooms to counteract the internal damage. PMID:28345643

  14. Preparing Al-Mg Substrate for Thermal Spraying: Evaluation of Surface State After Different Pretreatments

    NASA Astrophysics Data System (ADS)

    Lukauskaitė, R.; Valiulis, A. V.; Černašėjus, O.; Škamat, J.; Rębiś, J. A.

    2016-08-01

    The article deals with the pretreatment technique for preparing the surface of aluminum alloy EN AW 5754 before thermal spray. The surface after different pretreatments, including degreasing with acetone, chemical etching with acidic and alkali solutions, grit-blasting, cathodic cleaning, and some combinations of these techniques, has been studied. The investigation of pre-treated surfaces covered the topographical study (using scanning electron microscopy, atomic force microscopy, and 3D profilometry), the chemical analysis by x-ray photoelectron spectroscopy, the evaluation of surface wettability (sessile drop method), and the assessment of surface free energy. Compared with all the techniques used in present work, the cathodic cleaning and its combination with grit-blasting provide the most preferable chemistry of the surface. Due to the absence of hydroxides at the surface and, possible, due to the diffusion of magnesium to the surface of substrate, the surface wettability and the surface free energy have been significantly improved. No direct correlation between the surface topography and the surface wettability has been established.

  15. Development of chlorine resistant membrane, asymmetric polyimide membrane and porous substrates. Final report

    SciTech Connect

    Sudak, R.G.; Chirrick, J.M.; Fox, R.L.; McKee, M.E.; Bott, J.B.; Tomaschke, J.E.

    1980-09-01

    The development of chlorine resistant membrane, asymmetric polymide membrane, and porous substrates was studied. The development of supports with different polymeric materials was undertaken to increase: (1) the number of possible solvents for use in membrane barrier layer formation, and (2) the allowable temperature for such formation. The materials were developed with pore size variations for use in ultrafiltration/ microfiltration applications as well as hyperfiltration. It was found that cellulose acetate is stable to low residual chlorine concentrations in feedwaters, but polymide in sheet composite membrane or asymmetric hollow fine fibers was not. The mechanism of residual chlorine degradation of various polymers which caused synthesis of several polymers and their subsquent reaction to form polyimide membrane layers was also investigated.

  16. Thermal resistance of indium coated sapphire-copper contacts below 0.1 K

    NASA Astrophysics Data System (ADS)

    Eisel, T.; Bremer, J.; Koettig, T.

    2014-11-01

    High thermal resistances exist at ultra-low temperatures for solid-solid interfaces. This is especially true for pressed metal-sapphire joints, where the heat is transferred by phonons only. For such pressed joints it is difficult to achieve good physical, i.e. thermal contacts due to surface irregularities in the microscopic or larger scale. Applying ductile indium as an intermediate layer reduces the thermal resistance of such contacts. This could be proven by measurements of several researchers. However, the majority of the measurements were performed at temperatures higher than 1 K. Consequently, it is difficult to predict the thermal resistance of pressed metal-sapphire joints at temperatures below 1 K. In this paper the thermal resistances across four different copper-sapphire-copper sandwiches are presented in a temperature range between 30 mK and 100 mK. The investigated sandwiches feature either rough or polished sapphire discs (Ø 20 mm × 1.5 mm) to investigate the phonon scattering at the boundaries. All sandwiches apply indium foils as intermediate layers on both sides of the sapphire. Additionally to the indium foils, thin indium films are vapour deposited onto both sides of one rough and one polished sapphire in order to improve the contact to the sapphire. Significantly different thermal resistances have been found amongst the investigated sandwiches. The lowest total thermal resistivity (roughly 26 cm2 K4/W at 30 mK helium temperature) is achieved across a sandwich consisting of a polished sapphire with indium vapour deposition. The thermal boundary resistance between indium and sapphire is estimated from the total thermal resistivity by assuming the scattering at only one boundary, which is the warm sapphire boundary where phonons impinge, and taking the scattering in the sapphire bulk into account. The so derived thermal boundary resistance agrees at low temperatures very well with the acoustic mismatch theory.

  17. Effect of Substrates on the Resistivity and Adhesion of Copper Nanoparticle Ink

    NASA Astrophysics Data System (ADS)

    Poddar, Pritam

    Printed electronics processes have the potential to make electronics manufacturing more flexible by providing a wider choice of materials and easier processing steps. In traditional electronics manufacturing techniques, corrosive etching steps limit the choice of materials and also require advanced infrastructure for process implementation. High speed low cost printing processes (e.g. inkjet) can be used, and the printed tracks can then be cured to conductive circuits that meet the needs of electronic devices like radio frequency identification (RFID) tags, sensors, etc. In this work, intense flashes of broad spectrum light from Xenon lamps are used to cure inkjet printed metal nanoparticle inks. This technique is known as photonic curing. Paper, polyethylene terephthalate (PET), and polyimide have been used as substrates with the aim of determining how different substrates affect the behavior of the ink and the photonic curing parameters. A statistical approach was employed for the experiments, and significant control variables determining curing of the ink were identified. Experiments were also conducted to obtain prints conforming to dimensional tolerances. Using the results from the experiments, standard curing parameters for low resistance and good adhesion of the ink were obtained. The results have been statistically validated and used to study the interaction between the control variables and individual effects of each control variable on the response variable.

  18. Microstructure and Properties of Thermally Sprayed Functionally Graded Coatings for Polymeric Substrates

    NASA Technical Reports Server (NTRS)

    Ivosevic, M.; Knight, R.; Kalidindi, S. R.; Palmese, G. R.; Sutter, J. K.

    2003-01-01

    The use of polymer matrix composites (PMCs) in the gas flow path of advanced turbine engines offers significant benefits for aircraft engine performance but their useful lifetime is limited by their poor erosion resistance. High velocity oxy-fuel (HVOF) sprayed polymer/cermet functionally graded (FGM) coatings are being investigated as a method to address this technology gap by providing erosion and oxidation protection to polymer matrix composites. The FGM coating structures are based on a polyimide matrix filled with varying volume fractions of WC-Co. The graded coating architecture was produced using a combination of internal and external feedstock injection, via two computer-controlled powder feeders and controlled substrate preheating. Porosity, coating thickness and volume fraction of the WC-Co filler retained in the coatings were determined using standard metallographic techniques and computer image analysis. The pull-off strength (often referred to as the adhesive strength) of the coatings was evaluated according to the ASTM D 4541 standard test method, which measured the greatest normal tensile force that the coating could withstand. Adhesive/cohesive strengths were determined for three different types of coating structures and compared based on the maximum indicated load and the surface area loaded. The nature and locus of the fractures were characterized according to the percent of adhesive and/or cohesive failure, and the tested interfaces and layers involved were analyzed by Scanning Electron Microscopy.

  19. Simulating the effects of bake process parameters on resist thermal reflow

    NASA Astrophysics Data System (ADS)

    Lee, Jae-Won; Feng, Zhaohua; Engelstad, Roxann L.; Lovell, Edward G.

    2004-12-01

    Producing smaller feature sizes by extending current and near-term lithographic printing tools is a cost-effective strategy for high-volume production of integrated circuits. The hardbake process, as an annealing step to strengthen resist structures, includes a desirable thermal reflow that can facilitate this objective. Thermal reflow of polymer-based resists is a phase-dependent phenomenon in which a polymeric material with recyclable / reversible thermal characteristics experiences dimensional changes through relaxation during thermal cycling at hardbake. Unlike polymer melts, resist reflow is accompanied by a continuous change in the physical state of the resist over a specific temperature range, so it can be described on the basis of the relaxation modulus-temperature relation. Resist behavior during thermal transitions (e.g., glassy, leathery, rubbery plateau, etc.) can effectively be classified into either solid or viscous, depending on whether the resist material is below or above the characteristic glass transition temperature. In general, resist contact hole size can be significantly reduced by optimizing the principal factors driving resist reflow, i.e., temperature-dependent material properties, bake cycle parameters, contact-hole dimensions, and the type of contact array. Recognizable size reduction of the contact hole appears as the resist passes through the leathery state, and its maximum permanent deformation after thermal cycling completely depends on the resist material used. This research focuses on a bake profile of the resist described by the parameters in typical three-stage proximity contact wafer processing. Simulation programs were developed to characterize the primary thermal properties and process parameters affecting the bake profile, and to identify their relative effects on the resist contact-hole response.

  20. Measuring the thermal boundary resistance of van der Waals contacts using an individual carbon nanotube.

    PubMed

    Hirotani, Jun; Ikuta, Tatsuya; Nishiyama, Takashi; Takahashi, Koji

    2013-01-16

    Interfacial thermal transport via van der Waals interaction is quantitatively evaluated using an individual multi-walled carbon nanotube bonded on a platinum hot-film sensor. The thermal boundary resistance per unit contact area was obtained at the interface between the closed end or sidewall of the nanotube and platinum, gold, or a silicon dioxide surface. When taking into consideration the surface roughness, the thermal boundary resistance at the sidewall is found to coincide with that at the closed end. A new finding is that the thermal boundary resistance between a carbon nanotube and a solid surface is independent of the materials within the experimental errors, which is inconsistent with a traditional phonon mismatch model, which shows a clear material dependence of the thermal boundary resistance. Our data indicate the inapplicability of existing phonon models when weak van der Waals forces are dominant at the interfaces.

  1. Role of thermal resistance on the performance of superconducting radio frequency cavities

    NASA Astrophysics Data System (ADS)

    Dhakal, Pashupati; Ciovati, Gianluigi; Myneni, Ganapati Rao

    2017-03-01

    Thermal stability is an important parameter for the operation of the superconducting radio frequency (SRF) cavities used in particle accelerators. The rf power dissipated on the inner surface of the cavities is conducted to the helium bath cooling the outer cavity surface and the equilibrium temperature of the inner surface depends on the thermal resistance. In this manuscript, we present the results of direct measurements of thermal resistance on 1.3 GHz single cell SRF cavities made from high purity large-grain and fine-grain niobium as well as their rf performance for different treatments applied to outer cavity surface in order to investigate the role of the Kapitza resistance to the overall thermal resistance and to the SRF cavity performance. The results show no significant impact of the thermal resistance to the SRF cavity performance after chemical polishing, mechanical polishing or anodization of the outer cavity surface. Temperature maps taken during the rf test show nonuniform heating of the surface at medium rf fields. Calculations of Q0(Bp) curves using the thermal feedback model show good agreement with experimental data at 2 and 1.8 K when a pair-braking term is included in the calculation of the Bardeen-Cooper-Schrieffer surface resistance. These results indicate local intrinsic nonlinearities of the surface resistance, rather than purely thermal effects, to be the main cause for the observed field dependence of Q0(Bp) .

  2. Method for preparation of thermally and mechanically stable metal/porous substrate composite membranes

    DOEpatents

    Damle, Ashok S.

    2004-07-13

    A method is provided for the preparation of metal/porous substrate composite membranes by flowing a solution of metal to be plated over a first surface of a porous substrate and concurrently applying a pressure of gas on a second surface of the porous substrate, such that the porous substrate separates the solution of metal from the gas, and the use of the resulting membrane for the production of highly purified hydrogen gas.

  3. Effects of eccentric and concentric resistance training on skeletal muscle substrates, enzyme activities and capillary supply.

    PubMed

    Tesch, P A; Thorsson, A; Colliander, E B

    1990-12-01

    This study compared the skeletal muscle metabolic adaptations in response to combined eccentric and concentric or concentric resistance training regimens. Twenty-six physically active males were assigned to either the combined eccentric and concentric group (n = 10), the concentric group (n = 10) or the control group (n = 6). The combined eccentric and concentric and the concentric groups performed four to five sets of maximal, voluntary bilateral quadriceps muscle actions at 1.05 rad s-1 using a speed-controlled dynamometer three times per week for 12 weeks. The concentric group performed 12 concentric actions per set, whereas the combined eccentric and concentric group performed six coupled eccentric and concentric actions per set. Bilateral percutaneous muscle biopsies were obtained from m. vastus lateralis at rest pre- and post-training. Tissue samples were analysed for contents of adenosine triphosphate, creatine phosphate and creatine and for enzyme activities of citrate synthase, lactate dehydrogenase, myokinase, phosphofructokinase, hexokinase and Mg2(+)-ATPase using fluorometric techniques. Histochemical staining procedures were employed to determine capillary supply. The overall increase (P less than 0.05) in muscle strength was greater (P less than 0.05) for the combined eccentric and concentric group than for the concentric group. Enzyme or substrate contents and capillary supply were unaltered after either type of training. It is suggested that substantial increases in muscle strength may occur in response to resistance training without enhancing or compromising metabolic function of skeletal muscle.

  4. Transparent, superhydrophobic, and wear-resistant surfaces using deep reactive ion etching on PDMS substrates.

    PubMed

    Ebert, Daniel; Bhushan, Bharat

    2016-11-01

    Surfaces that simultaneously exhibit superhydrophobicity, low contact angle hysteresis, and high transmission of visible light are of interest for many applications, such as optical devices, solar panels, and self-cleaning windows. Superhydrophobicity could also find use in medical devices where antifouling characteristics are desirable. These applications also typically require mechanical wear resistance. The fabrication of such surfaces is challenging due to the competing goals of superhydrophobicity and transmittance in terms of the required degree of surface roughness. In this study, deep reactive ion etching (DRIE) was used to create rough surfaces on PDMS substrates using a O2/CF4 plasma. Surfaces then underwent an additional treatment with either octafluorocyclobutane (C4F8) plasma or vapor deposition of perfluorooctyltrichlorosilane (PFOTCS) following surface activation with O2 plasma. The effects of surface roughness and the additional surface modifications were examined with respect to the contact angle, contact angle hysteresis, and optical transmittance. To examine wear resistance, a sliding wear experiment was performed using an atomic force microscope (AFM).

  5. Transparent resistive switching memory using aluminum oxide on a flexible substrate.

    PubMed

    Yeom, Seung-Won; Shin, Sang-Chul; Kim, Tan-Young; Ha, Hyeon Jun; Lee, Yun-Hi; Shim, Jae Won; Ju, Byeong-Kwon

    2016-02-19

    Resistive switching memory (ReRAM) has attracted much attention in recent times owing to its fast switching, simple structure, and non-volatility. Flexible and transparent electronic devices have also attracted considerable attention. We therefore fabricated an Al2O3-based ReRAM with transparent indium-zinc-oxide (IZO) electrodes on a flexible substrate. The device transmittance was found to be higher than 80% in the visible region (400-800 nm). Bended states (radius = 10 mm) of the device also did not affect the memory performance because of the flexibility of the two transparent IZO electrodes and the thin Al2O3 layer. The conduction mechanism of the resistive switching of our device was explained by ohmic conduction and a Poole-Frenkel emission model. The conduction mechanism was proved by oxygen vacancies in the Al2O3 layer, as analyzed by x-ray photoelectron spectroscopy analysis. These results encourage the application of ReRAM in flexible and transparent electronic devices.

  6. Stress-strain state in "coating-substrate" system after coating stability loss induced by impact of thermal stresses

    NASA Astrophysics Data System (ADS)

    Lyukshin, P. A.; Bochkareva, S. A.; Grishaeva, N. Yu.; Lyukshin, B. A.; Matolygina, N. Yu.; Panin, S. V.

    2016-11-01

    Thermal barrier coatings (TBC) are aimed at protection of machine parts working under extremely high temperatures. One of the major problems at their exploitation is related to delamination of the coating from the substrate. In this concern, investigation of the patterns and evolution of the stress-strain state (SSS) at their interface is of particular interest. The main reasons of the delamination are associated with the distinction of thermo-physical properties (first of all, thermal expansion coefficient) of the interfaced material, as well as by the difference in heating conditions (heat supply and abstraction). The latter is of particular importance when the transient regimes take place under the heat impact, i.e. the TBC becomes rapidly heated, while the substrate has much lower temperature. In order to analyze and simulate the processes that give rise to the delamination, a number of problems is to be solved. At the first stage, the temperature variation induced by the thermal impact both in the coating and the substrate is to be determined. At the second stage, the distribution of the Stress Strain State (SSS) in the coating and the substrate are to be found. Based on the values of the calculated stresses, the stability loss patterns of the coating might be revealed. In doing so, the latter is regarded as a plate rested on Winkler elastic foundation. By defining the plate deflections in concern of its interaction with the substrate, the distribution of the SSS parameters at the contact surface can be found. Finally, the conditions to determine the TBC delamination from the substrate are estimated.

  7. Attachable and flexible aluminum oxide resistive non-volatile memory arrays fabricated on tape as the substrate

    NASA Astrophysics Data System (ADS)

    Lee, Woocheol; Jang, Jingon; Song, Younggul; Cho, Kyungjune; Yoo, Daekyoung; Kim, Youngrok; Chung, Seungjun; Lee, Takhee

    2017-03-01

    We fabricated 8 × 8 arrays of non-volatile resistive memory devices on commercially available Scotch® Magic™ tape as a flexible substrate. The memory devices consist of double active layers of Al2O3 with a structure of Au/Al2O3/Au/Al2O3/Al (50 nm/20 nm/20 nm/20 nm/50 nm) on attachable tape substrates. Because the memory devices were fabricated using only dry and low temperature processes, the tape substrate did not suffer from any physical or chemical damage during the fabrication. The fabricated memory devices were turned to the low resistance state at ∼3.5 V and turned to the high resistance state at ∼10 V with a negative differential resistance region after ∼5 V, showing typical unipolar non-volatile resistive memory behavior. The memory devices on the tape substrates exhibited reasonable electrical performances including a high ON/OFF ratio of 104, endurance over 200 cycles of reading/writing processes, and retention times of over 104 s in both the flat and bent configurations.

  8. Attachable and flexible aluminum oxide resistive non-volatile memory arrays fabricated on tape as the substrate.

    PubMed

    Lee, Woocheol; Jang, Jingon; Song, Younggul; Cho, Kyungjune; Yoo, Daekyoung; Kim, Youngrok; Chung, Seungjun; Lee, Takhee

    2017-03-01

    We fabricated 8 × 8 arrays of non-volatile resistive memory devices on commercially available Scotch(®) Magic(™) tape as a flexible substrate. The memory devices consist of double active layers of Al2O3 with a structure of Au/Al2O3/Au/Al2O3/Al (50 nm/20 nm/20 nm/20 nm/50 nm) on attachable tape substrates. Because the memory devices were fabricated using only dry and low temperature processes, the tape substrate did not suffer from any physical or chemical damage during the fabrication. The fabricated memory devices were turned to the low resistance state at ∼3.5 V and turned to the high resistance state at ∼10 V with a negative differential resistance region after ∼5 V, showing typical unipolar non-volatile resistive memory behavior. The memory devices on the tape substrates exhibited reasonable electrical performances including a high ON/OFF ratio of 10(4), endurance over 200 cycles of reading/writing processes, and retention times of over 10(4) s in both the flat and bent configurations.

  9. Undoped InOx films deposited by radio frequency plasma enhanced reactive thermal evaporation at room temperature: importance of substrate.

    PubMed

    Parreira, P; Lavareda, G; Valente, J; Nunes, F T; Amaral, A; de Carvalho, C Nunes

    2010-04-01

    Conductive and transparent undoped thin films of indium oxide (InOx ), 120 nm average thick, were deposited by radio frequency plasma enhanced reactive thermal evaporation (rf-PERTE) of indium in the presence of oxygen at room temperature. Several substrates were used in order to study their influence on the main properties of these films: alkali free (AF) glass, fused silica, crystalline silicon and polyethylene terephthalate (PET). Surface morphology of the InOx films as a function of the substrates was observed by SEM and showed that the undoped InOx films obtained are nanostructured. For the c-Si substrate, InOx films with increased grain size are obtained, induced by the crystalline substrate. Films deposited on fused silica and AF glass substrates show a nano-grainy surface with similar surface morphologies. The InOx films deposited on AF glass show the highest values of both: electrical conductivity of about 1100 (omega cm)(-1) and visible transmittance of 85%. The substrate has a greater influence on the surface morphology of the films when a polymer (PET) is used. InOx films deposited on PET show a decrease in the electrical conductivity (90 (omega cm)(-1)) and a slight decrease in the average visible transmittance (78%).

  10. Thermal contact resistance at the Nb/Cu interface as a limiting factor for sputtered thin film RF superconducting cavities

    NASA Astrophysics Data System (ADS)

    Palmieri, V.; Vaglio, R.

    2016-01-01

    The ‘Q-slope’ problem has so far strongly limited the application of niobium thin film sputtered copper cavities in high field accelerators. In the present paper, based on experimental evidence, we consider the hypothesis that the Q-slope is related to enhanced thermal boundary resistance R Nb/Cu at the Nb/Cu interface, due to poor thermal contact between film and substrate. We have developed a simple model that directly connects the Q versus E acc curves to the distribution function f(R Nb/Cu) of R Nb/Cu values at the Nb/Cu interface over the cavity surface. Starting from different Q versus E acc experimental curves from different sources, using typical ‘inverse problem’ methods, we deduce the corresponding distribution functions generating those curves. The results show, for all the examined cases, very similar functional dependences of f(R Nb/Cu) and prove that, to describe the experimental Q versus E acc curves, it is sufficient to assume that only a small fraction of the film over the cavity surface is in poor thermal contact with the substrate. The whole body of information and data reported seems to indicate that the main origin of the Q-slope in thin film cavities is related to bad adhesion at the Nb/Cu interface. Strategies to solve the Q-slope problem improving the film adhesion are finally delineated.

  11. Aphidicolin resistance in herpes simplex virus type 1 appears to alter substrate specificity in the DNA polymerase

    SciTech Connect

    Hall, J.D.; Woodward, S.

    1989-06-01

    The authors describe novel mutants of herpes simplex virus which are resistant to aphidicolin. Their mutant phenotypes suggest that they encode DNA polymerases with altered substrate recognition. This conclusion is based on their abnormal sensitivity to polymerase inhibitors and to the abnormal mutation rates exhibited by two of the mutants.

  12. Galvanomagnetic properties of thin films of bismuth and bismuth-antimony alloys on substrates with different thermal expansions

    NASA Astrophysics Data System (ADS)

    Grabov, V. M.; Komarov, V. A.; Kablukova, N. S.

    2016-03-01

    Temperature dependences of the galvanomagnetic properties of films of bismuth and Bi100 - x Sb x ( x ≤ 12) on substrates with different temperature expansion coefficients were studied in the temperature range of 77-300 K. The block films were prepared through thermal deposition, and single-crystal Bi100 - x Sb x were grown by zone recrystallization under a coating. It was found that the temperature expansion coefficient of a substrate substantially influenced the galvanomagnetic properties of Bi and Bi100 - x Sb x films. Using the experimental data, the change in the charge-carrier concentration in the Bi and Bi100 - x Sb x films on different substrates at 77 K was estimated.

  13. Influence of Substrate Surfaces on Thermal Behavior of Photopolymerization-Induced Phase Separation of Liquid Crystal and Polymer

    NASA Astrophysics Data System (ADS)

    Murashige, Takeshi; Fujikake, Hideo; Ikehata, Seiichiro; Sato, Fumio

    2003-01-01

    We studied photopolymerization-induced phase separation (P-PIPS) of polymer fibers and liquid crystal (LC) formed at various thicknesses between glass substrates using a differential scanning calorimeter to find the influence of substrates on the P-PIPS phenomenon. In this case, the energy of ultraviolet light adsorbed by the solution film of the LC and monomer was kept constant in a unit area even when the solution thickness was changed. As an experimental result, the thermal phase-transition sequence behavior of the LC component in the formed composite film of smaller thickness approached that of the original pure LC. The total reaction heat for the polymerization in any thickness solutions did not make meaningful difference. These indicate that the phase separation can be promoted by decreasing the distance between the substrates even under constant polymerization degree, which depends on the polymerization reaction.

  14. The Effect of HVOF Particle-Substrate Interactions on Local Variations in the Coating Microstructure and the Corrosion Resistance

    NASA Astrophysics Data System (ADS)

    Racek, Ondrej

    2010-09-01

    Splashing and redeposition of droplets occur during thermal spray processing, which affects the coating porosity and morphology. Therefore, this phenomenon is important from a practical point of view such as corrosion. Particle interaction with substrate is a function of the particle velocity, viscosity, temperature, as well as the substrate temperature, chemistry, roughness, and geometry. In the present study, the splashing phenomenon was studied on CrC-NiCr and stainless steel materials deposited using the high velocity oxygen fuel process. The effect of particle splashing on the coating microstructure was investigated with respect to the corrosion properties. Particle behavior during impact was explained based on in-flight particle velocity and temperature measurements. It was found that the conditions that favor particle splashing promote occurrence of localized porosity. The localized porosity was a strong function of the substrate curvature and originated from the substrate asperities.

  15. Analysis of dual-phase-lag thermal behaviour in layered films with temperature-dependent interface thermal resistance

    NASA Astrophysics Data System (ADS)

    Liu, Kuo-Chi

    2005-10-01

    This work analyses theoretically the dual-phase-lag thermal behaviour in two-layered thin films with an interface thermal resistance, which is predicted by the radiation boundary condition model. The effect of the interface thermal resistance on the transmission-reflection phenomenon, induced by a pulsed volumetric source adjacent to the exterior surface of one layer, is investigated. Due to the difference between the two layers in the relaxation times, τq and τT, and the nonlinearity of the interfacial boundary condition, complexity is introduced and some mathematical difficulties are involved in solving the present problem. A hybrid application of the Laplace transform method and a control-volume formulation are used along with the linearization technique. The results show that the effect of the thermophysical properties on the behaviour of the energy passing across the interface gradually reduces with increasing interface thermal resistance. The lagging thermal behaviour depends on the magnitude of τT and τq more than on the ratio of τT/τq.

  16. Characterization of Contact and Bulk Thermal Resistance of Laminations for Electric Machines

    SciTech Connect

    Cousineau, J. Emily; Bennion, Kevin; DeVoto, Doug; Mihalic, Mark; Narumanchi, Sreekant

    2015-06-30

    The ability to remove heat from an electric machine depends on the passive stack thermal resistances within the machine and the convective cooling performance of the selected cooling technology. This report focuses on the passive thermal design, specifically properties of the stator and rotor lamination stacks. Orthotropic thermal conductivity, specific heat, and density are reported. Four materials commonly used in electric machines were tested, including M19 (29 and 26 gauge), HF10, and Arnon 7 materials.

  17. Corrosion resistant thermal barrier coating. [protecting gas turbines and other engine parts

    NASA Technical Reports Server (NTRS)

    Levine, S. R.; Miller, R. A.; Hodge, P. E. (Inventor)

    1981-01-01

    A thermal barrier coating system for protecting metal surfaces at high temperature in normally corrosive environments is described. The thermal barrier coating system includes a metal alloy bond coating, the alloy containing nickel, cobalt, iron, or a combination of these metals. The system further includes a corrosion resistant thermal barrier oxide coating containing at least one alkaline earth silicate. The preferred oxides are calcium silicate, barium silicate, magnesium silicate, or combinations of these silicates.

  18. Thermal and substrate color-induced melanization in laboratory reared red-eared sliders (Trachemys scripta elegans).

    PubMed

    Rowe, John W; Clark, David L; Mortensen, Rebecca A; Commissaris, Carolyn V; Wittle, Lawrence W; Tucker, John K

    2016-10-01

    Color and pigmentation patterns of the integument can facilitate crypsis, thermoregulation, and social signaling. According to the "thermal melanism hypothesis", cold environmental temperature should increase the quantity of melanin that is deposited in the integument thereby facilitating radiative warming. We studied the influences of water temperature (26°C or 31°C) and substrate color (black or white) on the degree of melanization in the red-eared slider, Trachemys scripta elegans, under laboratory conditions. Turtles reared on a black substrate, or in 26°C water, for 120 days were darker than those reared on a white substrate or in 31°C water. A potential tradeoff between the fitness benefits of crypsis and the benefits of radiative warming through melanism was detected because turtles reared in 26°C water and on a white substrate were darker than those reared on a white substrate and in 31°C water. Low temperatures limited metabolic processes because turtles reared in 26°C water grew more slowly than those reared in 31°C water. However, histological analyses revealed that melanization was a dynamic process in all treatments confirming that the degree of melanization in the cool water treatment was not influenced by the initial and relatively dark hatchling coloration in individuals that grew relatively slowly.

  19. Effects of substrate deformation and sip thickness on tile/sip interface stresses for shuttle thermal protection

    NASA Technical Reports Server (NTRS)

    Shore, C. P.; Garcia, R.

    1980-01-01

    A nonlinear analysis was used to study the effects of substrate deformation characteristics and strain isolator pad (SIP) thickness on TILE/SIP interface stresses for the space shuttle thermal protection system. The configuration analyzed consisted of a 5.08 cm thick, 15.24 cm square tile with a 12.7 cm square SIP footprint bordered by a 1.27 cm wide filler bar and was subjected to forces and moments representative of a 20.7 kPa aerodynamic shock passing over the tile. The SIP stress deflection curves were obtained after a 69 kPa proof load and 100 cycles conditioning at 55 kPa. The TILE/SIP interface stresses increase over flat substrate values for zero to peak substrate deformation amplitudes up to 0.191 cm by up to a factor of nearly five depending on deformation amplitude, half wave length, and location. Stresses for a 0.23 cm thick SIP found to be up to 60 percent greater than for a 0.41 cm thick SIP for identical loads and substrate deformation characteristics. A simplified method was developed for approximating the substrate location which produces maximum TILE/SIP interface stresses.

  20. In situ study of dislocation behavior in columnar Al thin film on Si substrate during thermal cycling

    SciTech Connect

    Allen, C. W.; Schroeder, H.; Hiller, J. M.

    1999-12-13

    In situ transmission electron microscopy (150 kV) has been employed to study the evolution of dislocation microstructure during relatively rapid thermal cycling of a 200 nm Al thin film on Si substrate. After a few thermal cycles between 150 and 500 C, nearly stable Al columnar grain structure is established with average grain less than a {micro}m. On rapid cooling (3--30+ C/s) from 500 C, dislocations first appear at a nominal temperature of 360--380 C, quickly multiplying and forming planar glide plane arrays on further cooling. From a large number of such experiments the authors have attempted to deduce the dislocation evolution during thermal cycling in these polycrystalline Al films and to account qualitatively for the results on a simple dislocation model.

  1. Effect of posture positions on the evaporative resistance and thermal insulation of clothing.

    PubMed

    Wu, Y S; Fan, J T; Yu, W

    2011-03-01

    Evaporative resistance and thermal insulation of clothing are important parameters in the design and engineering of thermal environments and functional clothing. Past work on the measurement of evaporative resistance of clothing was, however, limited to the standing posture with or without body motion. Information on the evaporative resistance of clothing when the wearer is in a sedentary or supine posture and how it is related to that when the wearer is in a standing posture is lacking. This paper presents original data on the effect of postures on the evaporative resistance of clothing, thermal insulation and permeability index, based on the measurements under three postures, viz. standing, sedentary and supine, using the sweating fabric manikin-Walter. Regression models are also established to relate the evaporative resistance and thermal insulation of clothing under sedentary and supine postures to those under the standing posture. The study further shows that the apparent evaporated resistances of standing and sedentary postures measured in the non-isothermal condition are much lower than those in the isothermal condition. The apparent evaporative resistances measured using the mass loss method are generally lower than those measured using the heat loss method due to moisture absorption or condensation within clothing. STATEMENT OF RELEVANCE: The thermal insulation and evaporative resistance values of clothing ensembles under different postures are essential data for the ergonomics design of thermal environments (e.g. indoors or a vehicle's interior environment) and functional clothing. They are also necessary for the prediction of thermal comfort or duration of exposure in different environmental conditions.

  2. Effect of Ni content on thermal and radiation resistance of VVER RPV steel

    NASA Astrophysics Data System (ADS)

    Shtrombakh, Ya. I.; Gurovich, B. A.; Kuleshova, E. A.; Frolov, A. S.; Fedotova, S. V.; Zhurko, D. A.; Krikun, E. V.

    2015-06-01

    In this paper thermal stability and radiation resistance of VVER-type RPV steels for pressure vessels of advanced reactors with different nickel content were studied. A complex of microstructural studies and mechanical tests of the steels in different states (after long thermal exposures, provoking embrittling heat treatment and accelerated neutron irradiation) was carried out. It is shown that nickel content (other things being equal) determines the extent of materials degradation under influence of operational factors: steels with a lower nickel concentration demonstrate a higher thermal stability and radiation resistance.

  3. Termite Resistance of Thermally-Modified Dendrocalamus asper (Schultes f.) Backer ex Heyne.

    PubMed

    Manalo, Ronniel D; Garcia, Carlos M

    2012-03-27

    The effects of thermal modification on the resistance of Dendrocalamus asper against Microcerotermes losbañosensis were investigated after exposure to virgin coconut oil at 140-200 °C for 30-120 min. The results showed that heat treatment significantly improved bamboo's resistance to termites based on mass losses and visual observations. The enhancement was highest at 200 °C. Prolonged treatment had a positive effect on the resistance at lower temperatures only.

  4. Improving the Adhesion Resistance of the Boride Coatings to AISI 316L Steel Substrate by Diffusion Annealing

    NASA Astrophysics Data System (ADS)

    Campos-Silva, I.; Bernabé-Molina, S.; Bravo-Bárcenas, D.; Martínez-Trinidad, J.; Rodríguez-Castro, G.; Meneses-Amador, A.

    2016-09-01

    In this study, new results about the practical adhesion resistance of boride coating/substrate system formed at the surface of AISI 316 L steel and improved by means of a diffusion annealing process are presented. First, the boriding of AISI 316 L steel was performed by the powder-pack method at 1173 K with different exposure times (4-8 h). The diffusion annealing process was conducted on the borided steels at 1273 K with 2 h of exposure using a diluent atmosphere of boron powder mixture. The mechanical behavior of the boride coating/substrate system developed by both treatments was established using Vickers and Berkovich tests along the depth of the boride coatings, respectively. Finally, for the entire set of experimental conditions, the scratch tests were performed with a continuously increasing normal force, in which the practical adhesion resistance of the boride coating/substrate system was represented by the critical load. The failure mechanisms developed over the surface of the scratch tracks were analyzed; the FeB-Fe2B/substrate system exhibited an adhesive mode, while the Fe2B/substrate system obtained by the diffusion annealing process showed predominantly a cohesive failure mode.

  5. Heat Flow Pattern and Thermal Resistance Modeling of Anisotropic Heat Spreaders

    NASA Astrophysics Data System (ADS)

    Falakzaadeh, F.; Mehryar, R.

    2017-01-01

    To ensure safe operating temperatures of the ever smaller heat generating electronic devices, drastic measures should be taken. Heat spreaders are used to increase surface area, by spreading the heat without necessarily transferring it to the ambient in the first place. The heat flow pattern is investigated in heat spreaders and the fundamental differences regarding how heat conducts in different materials is addressed. Isotropic materials are compared with anisotropic ones having a specifically higher in-plane thermal conductivity than through plane direction. Thermal resistance models are proposed for anisotropic and isotropic heat spreaders in compliance with the order of magnitude of dimensions used in electronics packaging. After establishing thermal resistance models for both the isotropic and anisotropic cases, numerical results are used to find a correlation for predicting thermal resistance in anisotropic heat spreaders with high anisotropy ratios.

  6. Silicon based substrate with calcium aluminosilicate environmental/thermal barrier layer

    NASA Technical Reports Server (NTRS)

    Eaton, Jr., Harry Edwin (Inventor); Allen, William Patrick (Inventor); Miller, Robert Alden (Inventor); Jacobson, Nathan S. (Inventor); Smialek, James L. (Inventor); Opila, Elizabeth J. (Inventor); Lee, Kang N. (Inventor); Nagaraj, Bangalore A. (Inventor); Wang, Hongyu (Inventor); Meschter, Peter Joel (Inventor)

    2001-01-01

    A barrier layer for a silicon containing substrate which inhibits the formation of gaseous species of silicon when exposed to a high temperature aqueous environment comprises a calcium alumino silicate.

  7. Enhanced thermal resistance of Salmonella in marinated whole muscle compared with ground pork.

    PubMed

    Velasquez, Adriana; Breslin, Tasha J; Marks, Bradley P; Orta-Ramirez, Alicia; Hall, Nicole O; Booren, Alden M; Ryser, Elliot T

    2010-02-01

    The internal muscle environment may enhance thermal resistance of bacterial pathogens. Based on the migration of pathogens into whole muscle products during marination, the validity of current thermal inactivation models for whole muscle versus ground products has been questioned. Consequently, the objective of this work was to compare thermal resistance of Salmonella in whole muscle versus ground pork. Irradiated samples of whole and ground pork loin (5.5 to 7.5 g) were exposed to a Salmonella-inoculated (10(8) CFU/ml) marinade (eight serovar cocktail) for 20 min, placed in sterile brass tubes (12.7 mm diameter), sealed, and heated isothermally at 55, 58, 60, 62, or 63 degrees C, and surviving salmonellae were enumerated on Petrifilm aerobic count plates. The thermal lag times and initial bacterial counts were similar for both whole muscle and ground samples (P > 0.05), with all samples having equivalent compositions, inocula, and thermal histories. Heating temperature and physical state of the meat (whole versus ground muscle) affected Salmonella inactivation, with greater thermal resistance observed in whole than in ground muscle (P < 0.05). Assuming log-linear inactivation kinetics, Salmonella was 0.64 to 2.96 times more heat resistant in whole muscle than in ground pork. Therefore, thermal process validations for pork products should also account for the physical state of the product to ensure microbial safety.

  8. Using High-Resolution Hand-Held Radiometers To Measure In-Situ Thermal Resistance

    NASA Astrophysics Data System (ADS)

    Burch, Douglas M.; Krintz, Donald F.

    1984-03-01

    A field study was carried out to investigate the accuracy of using high-resolution radiometers to determine the in situ thermal resistance of building components having conventional residential construction. Two different types of radiometers were used to determine the thermal resistances of the walls of six test buildings located at the National Bureau of Standards. These radiometer thermal resistance measurements were compared to reference thermal resistance values determined from steady-state series resistance predictions, time-averaged heat-flow-sensor measurements, and guarded-hot-box measurements. When measurements were carried out 5 hours after sunset when the outdoor temperature was relatively steady and the heating plant was operated in a typical cyclic fashion, the following results were obtained: for lightweight wood-frame cavity walls, the radiometer procedures were found to distinguish wall thermal resistance 4.4 h.ft2- °F/Btu (0.77 m2•K/W) systematically higher than corresponding reference values. Such a discrimination will per-mit insulated and uninsulated walls to be distinguished. However, in the case of walls having large heat capacity (e.g., masonry and log), thermal storage effects produced large time lags between the outdoor diurnal temperature variation and the heat-flow response at the inside surface. This phenomenon caused radiometer thermal resistances to deviate substantially from corresponding reference values. This study recommends that the ANSI/ASHRAE Standard 101-1981 be modified requiring the heating plant to be operated in a typical cyclic fashion instead of being turned off prior to and during radiometer measurements.

  9. Assessing the thermoelectric properties of single InSb nanowires: the role of thermal contact resistance

    NASA Astrophysics Data System (ADS)

    Yazji, S.; Swinkels, M. Y.; De Luca, M.; Hoffmann, E. A.; Ercolani, D.; Roddaro, S.; Abstreiter, G.; Sorba, L.; Bakkers, E. P. A. M.; Zardo, I.

    2016-06-01

    The peculiar shape and dimensions of nanowires (NWs) have opened the way to their exploitation in thermoelectric applications. In general, the parameters entering into the thermoelectric figure of merit are strongly interdependent, which makes it difficult to realize an optimal thermoelectric material. In NWs, instead, the power factor can be increased and the thermal conductivity reduced, thus boosting the thermoelectric efficiency compared to bulk materials. However, the assessment of all the thermoelectric properties of a NW is experimentally very challenging. Here, we focus on InSb NWs, which have proved to be promising thermoelectric materials. The figure of merit is accurately determined by using a novel method based on a combination of Raman spectroscopy and electrical measurements. Remarkably, this type of experiment provides a powerful approach allowing us to neglect the role played by thermal contact resistance. Furthermore, we compare the thermal conductivity determined by this novel method to the one determined on the same sample by the thermal bridge method. In this latter approach, the thermal contact resistance is a non-negligible parameter, especially in NWs with large diameters. We provide experimental evidence of the crucial role played by thermal contact resistance in the assessment of the thermal properties of nanostructures, using two different measurement methods of the thermal conductivity.

  10. Bidirectional negative differential thermal resistance in three-segment Frenkel-Kontorova lattices

    NASA Astrophysics Data System (ADS)

    Ou, Ya-li; Lu, Shi-cai; Hu, Cai-tian; Ai, Bao-quan

    2016-12-01

    By coupling three nonlinear 1D lattice segments, we demonstrate a thermal insulator model, where the system acts like an insulator for large temperature bias and a conductor for very small temperature bias. We numerically investigate the parameter range of the thermal insulator and find that the nonlinear response (the role of on-site potential), the weakly coupling interaction between each segment, and the small system size collectively contribute to the appearance of bidirectional negative differential thermal resistance (BNDTR). The corresponding exhibition of BNDTR can be explained in terms of effective phonon-band shifts. Our results can provide a new perspective for understanding the microscopic mechanism of negative differential thermal resistance and also would be conducive to further developments in designing and fabricating thermal devices and functional materials.

  11. Improved resistance of chemically-modified nanocellulose against thermally-induced depolymerization.

    PubMed

    Agustin, Melissa B; Nakatsubo, Fumiaki; Yano, Hiroyuki

    2017-05-15

    The study demonstrated the improvement in the resistance of nanocellulose against thermally-induced depolymerization by esterification with benzoyl (BNZ) and pivaloyl (PIV). The change in the degree of polymerization (DP) and molecular weight distribution (MWD) after thermal treatment in nitrogen and in air was investigated using viscometry and gel permeation chromatography. BNZ and PIV nanocellulose esters without α-hydrogens gave higher DP and narrower MWD than pure bacterial cellulose; and the acetyl and myristoyl esters, which possess α-hydrogens. Results also showed that when depolymerization is suppressed, thermal discoloration is also reduced. Resistance against depolymerization inhibits the formation of reducing ends which can be active sites for thermal discoloration. Finally, the findings suggest that benzoylation and pivaloylation can be an excellent modification technique to improve the thermal stability of nanocellulose.

  12. Thermal-Cycling Behavior of Plasma-Sprayed Partially Stabilized Zirconia Coatings on High-Density Graphite Substrate

    NASA Astrophysics Data System (ADS)

    Sure, Jagadeesh; Thyagarajan, K.; Mallika, C.; Mudali, U. Kamachi

    2015-08-01

    The thermal cycling behavior of partially stabilized zirconia (PSZ)-coated by plasma-spray process on NiCrAlY bond-coated high-density (HD) graphite substrate was investigated. Thermal cycling was carried out at 600 and 750 °C under vacuum, up to 200 cycles. Each cycle comprised a 10-min heating followed by forced air cooling for 10 min down to room temperature. Characterization of the microstructure and the phase analysis of thermal-cycled PSZ coatings by scanning electron microscopy, energy dispersive x-ray spectroscopy, x-ray diffraction (XRD), and Raman spectroscopy revealed the correlation between the microstructural/crystallographic phases and the mechanical integrity of the coating up to 200 cycles. Segmented and vertical cracks generated on the coating during thermal cycling were observed to propagate with increase in the number of cycles. Macrocracks and variations in elemental compositions were not observed until 200 cycles at 600 and 750 °C. XRD and Raman spectroscopic analysis confirmed the presence of nontransformable tetragonal phase only in all the thermal-cycled PSZ coatings, irrespective of temperature up to 200 cycles.

  13. Fabrication of extremely thermal-stable GaN template on Mo substrate using double bonding and step annealing process

    NASA Astrophysics Data System (ADS)

    Qing, Wang; Yang, Liu; Yongjian, Sun; Yuzhen, Tong; Guoyi, Zhang

    2016-08-01

    A new layer transfer technique which comprised double bonding and a step annealing process was utilized to transfer the GaN epilayer from a sapphire substrate to a Mo substrate. Combined with the application of the thermal-stable bonding medium, the resulting two-inch-diameter GaN template showed extremely good stability under high temperature and low stress state. Moreover, no cracks and winkles were observed. The transferred GaN template was suitable for homogeneous epitaxial, thus could be used for the direct fabrication of vertical LED chips as well as power electron devices. It has been confirmed that the double bonding and step annealing technique together with the thermal-stable bonding layer could significantly improve the bonding strength and stress relief, finally enhancing the thermal stability of the transferred GaN template. Project supported by the Guangdong Innovative Research Team Program (No. 2009010044), the China Postdoctoral Science Foundation (No. 2014M562233), the National Natural Science Foundation of Guangdong, China (No. 2015A030312011), and the Opened Fund of the State Key Laboratory on Integrated Optoelectronics (No. IOSKL2014KF17).

  14. Cellular mechanisms of insulin resistance: role of stress-regulated serine kinases and insulin receptor substrates (IRS) serine phosphorylation.

    PubMed

    Tanti, Jean-François; Jager, Jennifer

    2009-12-01

    Insulin receptor substrates (IRS) serine phosphorylation is a time-controlled physiological feedback mechanism in insulin signaling that is hijacked by metabolic and inflammatory stresses to promote insulin resistance. Kinases, including IKKbeta, JNK, ERK, mTOR, and S6K, activated by the inducers of insulin resistance induce uncontrolled IRS serine phosphorylation. Studies with genetically modified mice reveal that these kinases integrate signals from metabolic and inflammatory stresses in adipose tissue, liver, and hypothalamus leading to peripheral and central insulin resistance. Moreover, IKKbeta/NF-kappaB and JNK1 pathways in myeloid cells represent a core mechanism involved in inflammation linked to obesity. These kinases are thus potential drug targets against insulin resistance and the targeting of the IKKbeta/NF-kappaB or the JNK pathway may evolve into future diabetes medication.

  15. Flexible transparent memory cell: bipolar resistive switching via indium-tin oxide nanowire networks on a poly(dimethylsiloxane) substrate

    NASA Astrophysics Data System (ADS)

    Li, Qiang; Tian, Zhenhuan; Shang, Geng; Wang, Jiangteng; Li, Yufeng; Yun, Feng

    2016-11-01

    This report describes the fabrication and resistive switching (RS) characteristics of a novel flexible transparent (FT) resistive random access memory (ReRAM) device with a Ag/indium-tin oxide (ITO) nanowire network/ITO capacitor deposited on a PDMS substrate. The transmittance of the device is ˜70% in the visible region, and it exhibits a stable high-resistance state (HRS) to low-resistance state (LRS) ratio (HRS/LRS ratio) in different bending states. The RS characteristics are attributed to the congregate state of oxygen vacancies at different voltages, and the difference between positive and negative bending is mainly contributed by the effect of stress on the conductive layer. The FT-ReRAM can be used as nonvolatile memory element in future flexible transparent devices.

  16. Investigation of thermal and hot-wire chemical vapor deposition copper thin films on TiN substrates using CupraSelect as precursor.

    PubMed

    Papadimitropoulos, G; Davazoglou, D

    2011-09-01

    Copper films were deposited on oxidized Si substrates covered with TiN using a novel chemical vapor deposition reactor in which reactions were assisted by a heated tungsten filament (hot-wire CVD, HWCVD). Liquid at room temperature hexafluoroacetylacetonate Cu(I) trimethylvinylsilane (CupraSelect) was directly injected into the reactor with the aid of a direct-liquid injection (DLI) system using N2 as carrier gas. The deposition rates of HWCVD Cu films obtained on TiN covered substrates were found to increase with filament temperature (65 and 170 degrees C were tested). The resistivities of HWCVD Cu films were found to be higher than for thermally grown films due to the possible presence of impurities into the Cu films from the incomplete dissociation of the precursor and W impurities caused by the presence of the filament. For HWCVD films grown at a filament temperature of 170 degrees C, smaller grains are formed than at 65 degrees C as shown from the taken SEM micrographs. XRD diffractograms taken on Cu films deposited on TiN could not reveal the presence of W compounds originating from the filament because the relative peak was masked by the TiN [112] peak.

  17. Platelet adhesion-resistance of titanium substrate with mussel-inspired adhesive polymer bearing phosphorylcholine group

    NASA Astrophysics Data System (ADS)

    Yao, Ye; Fukazawa, Kyoko; Ma, Wenyong; Ishihara, Kazuhiko; Huang, Nan

    2012-05-01

    To make improvement of hemocompatibility on the titanium (Ti) substrate, mussel-inspired adhesive polymer (PMDP) with both catechol groups for surface anchoring and phosphorylcholine groups for obtaining biocompatibility was synthesized. Only 10 s-immersion of Ti substrate into an aqueous solution of PMDP resulted in reliable coating, because the coating was stable during one month rinsing. The PMDP-coated Ti substrate showed significant reduction of amount of proteins and number of platelets adhered on the surface compared with the non-treated Ti substrate. For this immobilization method, no chemical pretreatment of the substrates is necessary, and a stable and hemocompatible coating can be prepared by a simple, one-step procedure. Thus, we concluded that the proposed PMDP immobilization method has promising approach for improving hemocompatibility of Ti substrate for cardiovascular implant application.

  18. Effect of substrate temperature on structural and optical properties of ZnO nanostructures grown by thermal evaporation method

    NASA Astrophysics Data System (ADS)

    Tu, Nguyen; Trung, Do Quang; Kien, N. D. T.; Huy, P. T.; Nguyen, D. H.

    2017-01-01

    In this study, ZnO nanostructures were synthesized on SiO2/Si substrate by thermal evaporation method. The dependence of the crystalline phase, morphologies and chemical composition of the samples grown at different substrate temperatures were systematically studied. The XRD, Raman spectra, FTIR spectra and XPS results reveal the existence of Zn2SiO4 phase, beside the ZnO phase. The Zn2SiO4 phase dominates at high substrate temperature and vise versa. Under UV excitation at room temperature, the samples show three distinct emission bands namely UV ( 380 nm), green ( 525 nm), and NIR (730 nm). The increase of the PL intensity of the NIR emission with increasing substrate temperature, indicates the relation between this emission and the higher Zn2SiO4 phase content in the samples. Origin of the rarely observed NIR emission band is attributed to the energy transition from non-bridging oxygen hole centers of SiO2 to the Zni and Vo states of Zn2SiO4.

  19. Comparison of Stress Relief Mechanisms of Metal Films Deposited on Liquid Substrates by Thermal Evaporating and Sputtering

    NASA Astrophysics Data System (ADS)

    Yu, Sen-Jiang; Zhang, Yong-Ju; Chen, Miao-Gen

    Various metal film systems, deposited on liquid (silicone oil) substrates by thermal evaporating and DC-magnetron sputtering methods, have been successfully fabricated and the stress relief mechanisms are systematically studied by analyzing the characteristic surface morphologies. The experiment shows that the evaporating metal films can move on silicone oil surfaces freely due to the nearly zero adhesion of solid-liquid interface, which results in spontaneous formation of ordered surface patterns with a characteristic sandwiched structure driven by the internal stress. For the sputtering metal film system, however, the top surface of silicone oil can be modified to form an elastomeric polymer layer on the liquid substrate during deposition. Subsequent cooling of the system creates a higher compressive stress in the film, which is relieved by buckling of the film to form periodic wavy structures because the adhesion of solid-elastomer interface is quite strong.

  20. Low resistance tungsten films on GaAs deposited by means of rapid thermal low pressure chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Katz, A.; Feingold, A.; Nakahara, S.; Pearton, S. J.; Lane, E.

    1992-08-01

    Low resistance tungsten (W) films were deposited onto GaAs substrates by means of rapid thermal low pressure chemical vapor deposition (RT-LPCVD), using tungsten hexafluoride (WF6) gas reduced by hydrogen (H2). Deposition temperatures up to 550 °C for durations of up to 30 s were explored, resulting in deposition of relatively pure W films (containing less than 2% O2 and C). Post-deposition sintering of the layers led to significant reduction of the resistivity to values as low as 50 μΩ cm. The efficiency of the deposition improved upon increasing the H2 flow rate up to 1250 sccm resulting in a deposition rate of about 10 nm/s at a total chamber pressure of 3.5 Torr and temperature of 500 °C. The films appeared to be polycrystalline with a very fine grain structure, regardless of the deposition temperature with good morphology and underwent a limited reaction with the underlying GaAs substrates.

  1. Impact of thermal stress on the piezoelectric and dielectric properties of PbTiO{sub 3} thick films on various substrates

    SciTech Connect

    Bai, Gang; Liu, Zhiguo; Yan, Xiaobing; Zhang, Changchun

    2014-08-07

    The impact of thermal stress on the polarization, as well as dielectric and piezoelectric properties of (001) oriented PbTiO{sub 3} (PTO) thick films deposited on various substrates was investigated based on Landau-Devonshire thermodynamic model. The results showed that dielectric and piezoelectric properties of PTO films depend strongly on the thermal stress in PTO films decided by the deposition temperature T{sub G} and the thermal expansion coefficients' difference between PTO films and substrates. For IC-compatible substrates such as Si, c-sapphire, and a-sapphire that induce tensile in-plane thermal stresses, the dielectric and piezoelectric responses and tunabilities of PTO films were enhanced. Whereas for PTO films on MgO, compressive thermal in-plane stresses can degraded the dielectric and piezoelectric responses and tunabilities of the films.

  2. Treating Surfaces To Obtain Narrowband Thermal Emission

    NASA Technical Reports Server (NTRS)

    Burger, Dale R.; Ong, Tiong P.

    1993-01-01

    Surfaces emitting electromagnetic radiation predominantly in desired narrow spectral bands when heated made more durable, and fabricated less expensively, according to proposal. Narrowband thermal emitters made by polishing metal substrates to specularity, then coating specular surfaces with films of rare-earth oxides approximately less than 1 micrometer thick. Metal substrates inherently resistant to mechanical shock. Resistance to thermal shock achieved by choosing metals and rare-earth oxides having equal or nearly equal coefficients of thermal expansion.

  3. The antiepileptic drug lamotrigine is a substrate of mouse and human breast cancer resistance protein (ABCG2).

    PubMed

    Römermann, Kerstin; Helmer, Renate; Löscher, Wolfgang

    2015-06-01

    Resistance to antiepileptic drugs (AEDs) is the major problem in the treatment of epilepsy. One hypothesis to explain AED resistance suggests that seizure-induced overexpression of efflux transporters at the blood-brain barrier (BBB) restricts AEDs to reach their brain targets. Various studies examined whether AEDs are substrates of P-glycoprotein (Pgp; MDR1; ABCB1), whereas information about the potential role of breast cancer resistance protein (BCRP; ABCG2) is scanty. We used a highly sensitive in vitro assay (concentration equilibrium transport assay; CETA) with MDCKII cells transduced with murine Bcrp1 or human BCRP to evaluate whether AEDs are substrates of this major efflux transporter. Six of 7 AEDs examined, namely phenytoin, phenobarbital, carbamazepine, levetiracetam, topiramate, and valproate, were not transported by Bcrp at therapeutic concentrations, whereas lamotrigine exhibited a marked asymmetric, Bcrp-mediated transport in the CETA, which could be almost completely inhibited with the Bcrp inhibitor Ko143. Significant but less marked transport of lamotrigine was determined in MDCK cells transfected with human BCRP. Lamotrigine is also a substrate of human Pgp, so that this drug is the first AED that has been identified as a dual substrate of the two major human efflux transporters at the BBB. Previous in vivo studies have demonstrated a synergistic or cooperative role of Pgp and Bcrp in the efflux of dual substrates at the BBB, so that transport of lamotrigine by Pgp and BCRP may be an important mechanism of pharmacoresistance in epilepsy patients in whom both transporters are overexpressed.

  4. The Measurement and Uncertainty Analysis of Thermal Resistance in Cryogenic Temperature Sensor Installation

    NASA Astrophysics Data System (ADS)

    Li, K. R.; Zhou, G.; Dong, B.; Liu, L. Q.; Xiong, L. Y.; Meng, R.; Li, Q.

    2017-02-01

    The choice of the appropriate installation method plays an important role for accurate temperature measurement. In the cryogenic and high vacuum environment, due to poor contact between the cryogenic temperature sensor and the surroundings that the sensor is installed and intended to measure, the self-heating from sensor measuring current brings about temperature difference and creates a potential temperature measurement error. The self-heating temperature difference is directly proportional to the thermal resistance for a mounted sensor, which means that lower installation thermal resistance of sensors is advantageous to obtain better measurement results. In this paper, a measurement model for the installation thermal resistance of sensor is built in terms of two currents method which is always used to measure self-heating effect. A cryostat that can provide variable temperature in the accurate temperature measurement and control experiments is designed and manufactured. This cryostat can reach 3K in a few hours and the sample temperature can reach as high as 20 K. Based on the experimental results, the measurement uncertainty of the thermal resistance are also analyzed and calculated. To obtain the best measurement results in our cryostat, the thermal resistances of sensors with two installation methods are measured and compared.

  5. Thermal resistance across a copper/Kapton/copper interface at cryogenic temperatures

    SciTech Connect

    Zhao, L.; Phelan, P.E.; Niemann, R.C.; Weber, B.R.

    1997-09-01

    The high-{Tc} superconductor current lead heat intercept connection, which is utilized as a thermal intercept to remove the Joule heat from the upper stage lead to a heat sink operating at 50--77 K, consists of a structure where a 152-{micro}m film is sandwiched between two concentric copper cylinders. The material chosen for the insulating film is Kapton MT, a composite film which has a relatively low thermal resistance, but yet a high voltage standoff capability. Here, the measured thermal conductance of a copper/Kapton MT/copper junction in a flat-plate geometry is compared to the results obtained from the actual heat intercept connection. Increasing the contact pressure reduces the thermal resistance to a minimum value determined by the film conduction resistance. A comparison between the resistance of the copper/Kapton MT/copper junction and a copper/G-10/copper junction demonstrates that the Kapton MT layer yields a lower thermal resistance while still providing adequate electrical isolation.

  6. Molecular Dynamics Studies on Ballistic Thermal Resistance of Graphene Nano-Junctions

    NASA Astrophysics Data System (ADS)

    Yao, Wen-Jun; Cao, Bing-Yang

    2015-05-01

    Ballistic thermal resistance of graphene nano-junctions is investigated using non-equilibrium molecular dynamics simulation. The simulation system is consisted of two symmetrical trapezoidal or rectangular graphene nano-ribbons (GNRs) and a connecting nanoscale constriction in between. From the simulated temperature profile, a big temperature jump resulted from the constriction is found, which is proportional to the heat current and corresponds to a local ballistic thermal resistance. Fixing the constriction width and the length of GNRs, this ballistic thermal resistance is independent of the width of the GNRs bottom layer, i.e., the convex angle. But interestingly, this thermal resistance has obvious size effect. It is inversely proportional to the constriction width and will disappear with the constriction being wider. Moreover, based on the phonon dynamics theory, a theoretical model of the ballistic thermal resistance in two-dimensional nano-systems is developed, which gives a good explanation on microcosmic level and agrees well with the simulation result quantitatively and qualitatively. Supported by the National Natural Science Foundation of China under Grant Nos. 51322603, 51136001, 51356001, Science Fund for Creative Research Groups (No. 51321002), the Program for New Century Excellent Talents in University, Tsinghua University Initiative Scientific Research Program, the Tsinghua National Laboratory for Information Science and Technology of China

  7. Microstructure, bonding strength and thermal shock resistance of ceramic coatings on steels prepared by plasma electrolytic oxidation

    NASA Astrophysics Data System (ADS)

    Wang, Yunlong; Jiang, Zhaohua; Yao, Zhongping

    2009-11-01

    Ceramic coatings were successfully prepared on steel by plasma electrolytic oxidation (PEO) in aluminate electrolyte and silicate electrolyte, respectively. The microstructure of the coatings including surface morphology, phase and element composition were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The bonding strength between the ceramic coating and the substrate was tested using different methods including tensile tests and shearing tests. The thermal shock resistance of the coatings was also evaluated. The results indicated that coatings obtained in both electrolytes were porous and coarse. The average diameters of the pores were below 10 μm. PEO coatings obtained in aluminate electrolyte were composed of Fe 3O 4 and FeAl 2O 4, while those obtained in silicate electrolyte were in a noncrystal state. PEO coatings obtained in aluminate electrolyte showed similar change trend of tensile strength and shearing strength with increasing treating time, namely, a relatively high values with middle time treating and low value with short and long time treating. The best coating was the samples treated with 30 min, whose tensile strength was 20.6 MPa and shearing strength was 16 MPa. The tensile strength and shearing strength of coatings obtained in silicate electrolyte were not strongly influenced by the treating time, the values of which were range in 14 ± 2 MPa and 11 ± 2 MPa, respectively. Coatings obtained in both electrolytes showed the best thermal shock resistance with middle time treating. Coatings obtained in silicate electrolyte show a little better thermal shock resistance than those obtained in aluminate electrolyte.

  8. Small molecules that dramatically alter multidrug resistance phenotype by modulating the substrate specificity of P-glycoprotein

    PubMed Central

    Kondratov, Roman V.; Komarov, Pavel G.; Becker, Yigal; Ewenson, Ariel; Gudkov, Andrei V.

    2001-01-01

    By screening a chemical library for the compounds protecting cells from adriamycin (Adr), a series of small molecules was isolated that interfered with the accumulation of Adr in mouse fibroblasts by enhancing efflux of the drug. Isolated compounds also stimulated efflux of Rhodamine 123 (Rho-123), another substrate of multidrug transporters. Stimulation of drug efflux was detectable in the cells expressing P-glycoprotein (P-gp), but not in their P-gp-negative variants, and was completely reversible by the P-gp inhibitors. A dramatic stimulation of P-gp activity against Adr and Rho-123 by the identified compounds was accompanied by suppression of P-gp-mediated efflux of other substrates, such as Taxol (paclitaxel) or Hoechst 33342, indicating that they act as modulators of substrate specificity of P-gp. Consistently, P-gp modulators dramatically altered the pattern of cross-resistance of P-gp-expressing cells to different P-gp substrates: an increase in resistance to Adr, daunorubicin, and etoposide was accompanied by cell sensitization to Vinca alkaloids, gramicidin D, and Taxol with no effect on cell sensitivity to colchicine, actinomycin D, puromycin, and colcemid, as well as to several non-P-gp substrates. The relative effect of P-gp modulators against different substrates varied among the isolated compounds that can be used as fine tools for analyzing mechanisms of drug selectivity of P-gp. These results raise the possibility of a rational control over cell sensitivity to drugs and toxins through modulation of P-gp activity by small molecules. PMID:11707575

  9. Thermal fluctuations of a liquid film on a heterogeneous solid substrate

    NASA Astrophysics Data System (ADS)

    Pierre-Louis, Olivier

    2016-09-01

    The dynamics of the fluctuations of a liquid film on a heterogeneous substrate is analyzed. We consider the case of a viscous liquid in the Stokes limit, with small variations of substrate height and a small varying slip length. We discuss the possibility of extracting the topographic profile or the slip length profile at the liquid-solid interface from the measurement of the fluctuations of the free liquid surface. Our results, therefore, explore the theoretical basis of a strategy for a fluctuation-induced microscopy of immersed solids at the micrometer scale.

  10. Modification of fluorous substrates with oligo(ethylene glycol) via "click" chemistry for long-term resistance of cell adhesion.

    PubMed

    Contreras-Caceres, Rafael; Santos, Catherine M; Li, Siheng; Kumar, Amit; Zhu, Zhiling; Kolar, Satya S; Casado-Rodriguez, Miguel A; Huang, Yongkai; McDermott, Alison; Lopez-Romero, Juan Manuel; Cai, Chengzhi

    2015-11-15

    In this work perfluorinated substrates fabricated from SiO2 glass slides are modified with oligo(ethylene glycol) (OEG) units for long-term resistance of cell adhesion purposes, based on fluorous interactions and click chemistry. Specifically, fluorous substrates, prepared by treatment of glass slides with 1H, 1H, 2H, 2H-perfluorodecyltrimethoxysilane (FAS17), were coated with ethynyl-OEG-C8F17, followed by covalent attachment of an azido-OEG via copper-catalyzed azide-alkyne cycloaddition (CuAAC) "click" reaction. We demonstrate that the resultant surface avoid fibrinogen adsorption and resisted cell adhesion for over 14days. X-ray photoemission spectroscopy (XPS) analysis and contact angle goniometry measurements confirm the presence of the OEG molecules on the fluorous substrates. Bright field optical images show total absence of 3T3 fibroblast cells on the OEG modified fluorinated substrate for 1 and 5days, and a remarkably decrease of cell adhesion at 14days.

  11. Location of hot spots in integrated circuits by monitoring the substrate thermal-phase lag with the mirage effect.

    PubMed

    Perpiñà, Xavier; Altet, Josep; Jordà, Xavier; Vellvehi, Miquel; Mestres, Narcís

    2010-08-01

    This Letter presents a solution for locating hot spots in active integrated circuits (IC) and devices. This method is based on sensing the phase lag between the power periodically dissipated by a device integrated in an IC (hot spot) and its corresponding thermal gradient into the chip substrate by monitoring the heat-induced refractive index gradient with a laser beam. The experimental results show a high accuracy and prove the suitability of this technique to locate and characterize devices behaving as hot spots in current IC technologies.

  12. Changes in the Chemical Composition and Decay Resistance of Thermally-Modified Hevea brasiliensis Wood

    PubMed Central

    2016-01-01

    In this study the effect of thermal treatment on the equilibrium moisture content, chemical composition and biological resistance to decay fungi of juvenile and mature Hevea brasiliensis wood (rubber wood) was evaluated. Samples were taken from a 53-year-old rubber wood plantation located in Tabapuã, Sao Paulo, Brazil. The samples were thermally-modified at 180°C, 200°C and 220°C. Results indicate that the thermal modification caused: (1) a significant increase in the extractive content and proportional increase in the lignin content at 220°C; (2) a significant decrease in the equilibrium moisture content, holocelluloses, arabinose, galactose and xylose content, but no change in glucose content; and (3) a significant increase in wood decay resistance against both Pycnoporus sanguineus (L.) Murrill and Gloeophyllum trabeum (Pers.) Murrill decay fungi. The greatest decay resistance was achieved from treatment at 220°C which resulted in a change in wood decay resistance class from moderately resistant to resistant. Finally, this study also demonstrated that the influence of thermal treatment in mature wood was lower than in juvenile wood. PMID:26986200

  13. Changes in the Chemical Composition and Decay Resistance of Thermally-Modified Hevea brasiliensis Wood.

    PubMed

    Severo, Elias Taylor Durgante; Calonego, Fred Willians; Sansígolo, Cláudio Angeli; Bond, Brian

    2016-01-01

    In this study the effect of thermal treatment on the equilibrium moisture content, chemical composition and biological resistance to decay fungi of juvenile and mature Hevea brasiliensis wood (rubber wood) was evaluated. Samples were taken from a 53-year-old rubber wood plantation located in Tabapuã, Sao Paulo, Brazil. The samples were thermally-modified at 180°C, 200°C and 220°C. Results indicate that the thermal modification caused: (1) a significant increase in the extractive content and proportional increase in the lignin content at 220°C; (2) a significant decrease in the equilibrium moisture content, holocelluloses, arabinose, galactose and xylose content, but no change in glucose content; and (3) a significant increase in wood decay resistance against both Pycnoporus sanguineus (L.) Murrill and Gloeophyllum trabeum (Pers.) Murrill decay fungi. The greatest decay resistance was achieved from treatment at 220°C which resulted in a change in wood decay resistance class from moderately resistant to resistant. Finally, this study also demonstrated that the influence of thermal treatment in mature wood was lower than in juvenile wood.

  14. Aqueously dispersed silver nanoparticle-decorated boron nitride nanosheets for reusable, thermal oxidation-resistant surface enhanced Raman spectroscopy (SERS) devices.

    PubMed

    Lin, Yi; Bunker, Christopher E; Fernando, K A Shiral; Connell, John W

    2012-02-01

    The impurity-free aqueous dispersions of boron nitride nanosheets (BNNS) allowed the facile preparation of silver (Ag) nanoparticle-decorated BNNS by chemical reduction of an Ag salt with hydrazine in the presence of BNNS. The resultant Ag-BNNS nanohybrids remained dispersed in water, allowing convenient subsequent solution processing. By using substrate transfer techniques, Ag-BNNS nanohybrid thin film coatings on quartz substrates were prepared and evaluated as reusable surface enhanced Raman spectroscopy (SERS) sensors that were robust against repeated solvent washing. In addition, because ofthe unique thermal oxidation-resistant properties of the BNNS, the sensor devices may be readily recycled by short-duration high temperature air oxidation to remove residual analyte molecules in repeated runs. The limiting factor associated with the thermal oxidation recycling process was the Ostwald ripening effect of Ag nanostructures.

  15. Aqueously Dispersed Silver Nanoparticle-Decorated Boron Nitride Nanosheets for Reusable, Thermal Oxidation-Resistant Surface Enhanced Raman Spectroscopy (SERS) Devices

    NASA Technical Reports Server (NTRS)

    Lin, Yi; Bunker, Christopher E.; Fernandos, K. A. Shiral; Connell, John W.

    2012-01-01

    The impurity-free aqueous dispersions of boron nitride nanosheets (BNNS) allowed the facile preparation of silver (Ag) nanoparticle-decorated BNNS by chemical reduction of an Ag salt with hydrazine in the presence of BNNS. The resultant Ag-BNNS nanohybrids remained dispersed in water, allowing convenient subsequent solution processing. By using substrate transfer techniques, Ag-BNNS nanohybrid thin film coatings on quartz substrates were prepared and evaluated as reusable surface enhanced Raman spectroscopy (SERS) sensors that were robust against repeated solvent washing. In addition, because of the unique thermal oxidation-resistant properties of the BNNS, the sensor devices may be readily recycled by short-duration high temperature air oxidation to remove residual analyte molecules in repeated runs. The limiting factor associated with the thermal oxidation recycling process was the Ostwald ripening effect of Ag nanostructures.

  16. Thermal-Interaction Matrix For Resistive Test Structure

    NASA Technical Reports Server (NTRS)

    Buehler, Martin G.; Dhiman, Jaipal K.; Zamani, Nasser

    1990-01-01

    Linear mathematical model predicts increase in temperature in each segment of 15-segment resistive structure used to test electromigration. Assumption of linearity based on fact: equations that govern flow of heat are linear and coefficients in equations (heat conductivities and capacities) depend only weakly on temperature and considered constant over limited range of temperature.

  17. Thermal singularity and contact line motion in pool boiling: Effects of substrate wettability.

    PubMed

    Taylor, M T; Qian, Tiezheng

    2016-03-01

    The dynamic van der Waals theory [Phys. Rev. E 75, 036304 (2007)] is employed to model the growth of a single vapor bubble in a superheated liquid on a flat homogeneous substrate. The bubble spreading dynamics in the pool boiling regime has been numerically investigated for one-component van der Waals fluids close to the critical point, with a focus on the effect of the substrate wettability on bubble growth and contact line motion. The substrate wettability is found to control the apparent contact angle and the rate of bubble growth (the rate of total evaporation), through which the contact line speed is determined. An approximate expression is derived for the contact line speed, showing good agreement with the simulation results. This demonstrates that the contact line speed is primarily governed by (1) the circular shape of interface (for slow bubble growth), (2) the constant apparent contact angle, and (3) the constant bubble growth rate. It follows that the contact line speed has a sensitive dependence on the substrate wettability via the apparent contact angle which also determines the bubble growth rate. Compared to hydrophilic surfaces, hydrophobic surfaces give rise to a thinner shape of bubble and a higher rate of total evaporation, which combine to result in a much faster contact line speed. This can be linked to the earlier formation of a vapor film and hence the onset of boiling crisis.

  18. Thermal singularity and contact line motion in pool boiling: Effects of substrate wettability

    NASA Astrophysics Data System (ADS)

    Taylor, M. T.; Qian, Tiezheng

    2016-03-01

    The dynamic van der Waals theory [Phys. Rev. E 75, 036304 (2007), 10.1103/PhysRevE.75.036304] is employed to model the growth of a single vapor bubble in a superheated liquid on a flat homogeneous substrate. The bubble spreading dynamics in the pool boiling regime has been numerically investigated for one-component van der Waals fluids close to the critical point, with a focus on the effect of the substrate wettability on bubble growth and contact line motion. The substrate wettability is found to control the apparent contact angle and the rate of bubble growth (the rate of total evaporation), through which the contact line speed is determined. An approximate expression is derived for the contact line speed, showing good agreement with the simulation results. This demonstrates that the contact line speed is primarily governed by (1) the circular shape of interface (for slow bubble growth), (2) the constant apparent contact angle, and (3) the constant bubble growth rate. It follows that the contact line speed has a sensitive dependence on the substrate wettability via the apparent contact angle which also determines the bubble growth rate. Compared to hydrophilic surfaces, hydrophobic surfaces give rise to a thinner shape of bubble and a higher rate of total evaporation, which combine to result in a much faster contact line speed. This can be linked to the earlier formation of a vapor film and hence the onset of boiling crisis.

  19. Factors affecting the thermal shock resistance of several hafnia based composites containing graphite or tungsten. M.S. Thesis

    NASA Technical Reports Server (NTRS)

    Lineback, L. D.

    1974-01-01

    The thermal shock resistance of hafnia based composites containing graphite powder or tungsten fibers was investigated in terms of material properties which include thermal expansion, thermal conductivity, compressive fracture stress, modulus of elasticity, and phase stability in terms of the processing parameters of hot pressing pressure and/or density, degree of stabilization of the hafnia, and composition. All other parameters were held constant or assumed constant. The thermal shock resistance was directly proportional to the compressive fracture stress to modulus of elasticity ratio and was not affected appreciably by the small thermal expansion or thermal conductivity changes. This ratio was found to vary strongly with the composition and density such that the composites containing graphite had relatively poor thermal shock resistance, while the composites containing tungsten had superior thermal shock resistance.

  20. Characterization of Thermal Oxides on 4H-SiC Epitaxial Substrates Using Fourier-Transform Infrared Spectroscopy.

    PubMed

    Seki, Hirofumi; Yoshikawa, Masanobu; Kobayashi, Takuma; Kimoto, Tsunenobu; Ozaki, Yukihiro

    2016-07-12

    Fourier transform infrared (FT-IR) spectra were measured for thermal oxides with different electrical properties grown on 4H-SiC substrates. The peak frequency of the transverse optical (TO) phonon mode was blue-shifted by 5 cm(-1) as the oxide-layer thickness decreased to 3 nm. The blue shift of the TO mode indicates interfacial compressive stress in the oxide. Comparison of data for the oxide on a SiC substrate with that for similar oxides on a Si substrate implies that the peak shift of the TO mode at the SiO2/SiC interface is larger than that of SiO2/Si, which suggests that the interfacial stress for the oxide on the SiC substrate is larger than that on the Si substrate. For the SiO2/SiC interfacial region (<3 nm oxide thickness), despite the fact that the blue shift of the TO modes becomes larger while approaching the oxide/SiC interface, the peak frequency of the TO modes red-shifts at the oxide/SiC interface. The peak-frequency shift of the TO mode for the sample without post-oxidation annealing was larger than that for the samples post-annealed in a nitric oxide atmosphere. The channel mobilities are correlated with the degree of shift of the TO mode when the oxide thickness is <3 nm. It appears that the compressive stress at the SiO2/SiC interface generates silicon suboxide components and weakens the Si-O bonds. As the result, the TO mode was red-shifted and the oxygen deficiency increased to relax the compressive stress in the oxide with <3 nm thickness. Fourier transform infrared spectroscopy measurements provide unique and useful information about stress and inhomogeneity at the oxide/SiC interface.

  1. Design and performance of low-thermal-resistance, high-electrical-isolation heat intercept connections

    NASA Astrophysics Data System (ADS)

    Niemann, R. C.; Gonczy, J. D.; Phelan, P. E.; Nicol, T. H.

    Electrical conductors often require the removal of heat produced by normal operation. The heat can be removed by mechanical connection of the conductor to a refrigeration source. Such connections require both effective heat removal (low thermal resistance) and effective electrical isolation (high electrical resistance and high dielectric strength). Fabrication of these connections should be straightforward, and performance must be reliable and independent of operating temperature. The connection method described here involves clamping (by thermal interference fit) an electrically insulating cylinder between an outer metallic ring and an inner metallic disc. Material candidates for insulating cylinders include composites, e.g. epoxy/fibreglass, and ceramics, e.g. alumina. Design factors, including geometry, materials and thermal contact resistance are discussed. The design, construction experience and performance measurements of a heat intercept connection in a high-temperature superconducting lead assembly is presented.

  2. Assessing thermal conductivity of composting reactor with attention on varying thermal resistance between compost and the inner surface.

    PubMed

    Wang, Yongjiang; Niu, Wenjuan; Ai, Ping

    2016-12-01

    Dynamic estimation of heat transfer through composting reactor wall was crucial for insulating design and maintaining a sanitary temperature. A model, incorporating conductive, convective and radiative heat transfer mechanisms, was developed in this paper to provide thermal resistance calculations for composting reactor wall. The mechanism of thermal transfer from compost to inner surface of structural layer, as a first step of heat loss, was important for improving insulation performance, which was divided into conduction and convection and discussed specifically in this study. It was found decreasing conductive resistance was responsible for the drop of insulation between compost and reactor wall. Increasing compost porosity or manufacturing a curved surface, decreasing the contact area of compost and the reactor wall, might improve the insulation performance. Upon modeling of heat transfers from compost to ambient environment, the study yielded a condensed and simplified model that could be used to conduct thermal resistance analysis for composting reactor. With theoretical derivations and a case application, the model was applicable for both dynamic estimation and typical composting scenario.

  3. Synthesis of thermal and chemical resistant oxygen barrier starch with reinforcement of nano silicon carbide.

    PubMed

    Dash, Satyabrata; Swain, Sarat K

    2013-09-12

    Starch/silicon carbide (starch/SiC) bionanocomposites were synthesized by solution method using different wt% of silicon carbide with starch matrix. The interaction between starch and silicon carbide was studied by Fourier transform infrared (FTIR) spectroscopy. The structure of the bionanocomposites was investigated by X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM). Thermal property of starch/SiC bionanocomposites was measured and a significant enhancement of thermal resistance was noticed. The oxygen barrier property of the composites was studied and a substantial reduction in permeability was observed as compared to the virgin starch. The reduction of oxygen permeability with enhancement of thermal stability of prepared bionanocomposites may enable the materials suitable for thermal resistant packaging and adhesive applications.

  4. Development and Life Prediction of Erosion Resistant Turbine Low Conductivity Thermal Barrier Coatings

    NASA Technical Reports Server (NTRS)

    Zhu, Dongming; Miller, Robert A.; Kuczmarski, Maria A.

    2010-01-01

    Future rotorcraft propulsion systems are required to operate under highly-loaded conditions and in harsh sand erosion environments, thereby imposing significant material design and durability issues. The incorporation of advanced thermal barrier coatings (TBC) in high pressure turbine systems enables engine designs with higher inlet temperatures, thus improving the engine efficiency, power density and reliability. The impact and erosion resistance of turbine thermal barrier coating systems are crucial to the turbine coating technology application, because a robust turbine blade TBC system is a prerequisite for fully utilizing the potential coating technology benefit in the rotorcraft propulsion. This paper describes the turbine blade TBC development in addressing the coating impact and erosion resistance. Advanced thermal barrier coating systems with improved performance have also been validated in laboratory simulated engine erosion and/or thermal gradient environments. A preliminary life prediction modeling approach to emphasize the turbine blade coating erosion is also presented.

  5. On the early and developed stages of surface condensation: competition mechanism between interfacial and condensate bulk thermal resistances

    NASA Astrophysics Data System (ADS)

    Sun, Jie; Wang, Hua Sheng

    2016-10-01

    We use molecular dynamics simulation to investigate the early and developed stages of surface condensation. We find that the liquid-vapor and solid-liquid interfacial thermal resistances depend on the properties of solid and fluid, which are time-independent, while the condensate bulk thermal resistance depends on the condensate thickness, which is time-dependent. There exists intrinsic competition between the interfacial and condensate bulk thermal resistances in timeline and the resultant total thermal resistance determines the condensation intensity for a given vapor-solid temperature difference. We reveal the competition mechanism that the interfacial thermal resistance dominates at the onset of condensation and holds afterwards while the condensate bulk thermal resistance gradually takes over with condensate thickness growing. The weaker the solid-liquid bonding, the later the takeover occurs. This competition mechanism suggests that only when the condensate bulk thermal resistance is reduced after it takes over the domination can the condensation be effectively intensified. We propose a unified theoretical model for the thermal resistance analysis by making dropwise condensation equivalent to filmwise condensation. We further find that near a critical point (contact angle being ca. 153°) the bulk thermal resistance has the least opportunity to take over the domination while away from it the probability increases.

  6. On the early and developed stages of surface condensation: competition mechanism between interfacial and condensate bulk thermal resistances.

    PubMed

    Sun, Jie; Wang, Hua Sheng

    2016-10-10

    We use molecular dynamics simulation to investigate the early and developed stages of surface condensation. We find that the liquid-vapor and solid-liquid interfacial thermal resistances depend on the properties of solid and fluid, which are time-independent, while the condensate bulk thermal resistance depends on the condensate thickness, which is time-dependent. There exists intrinsic competition between the interfacial and condensate bulk thermal resistances in timeline and the resultant total thermal resistance determines the condensation intensity for a given vapor-solid temperature difference. We reveal the competition mechanism that the interfacial thermal resistance dominates at the onset of condensation and holds afterwards while the condensate bulk thermal resistance gradually takes over with condensate thickness growing. The weaker the solid-liquid bonding, the later the takeover occurs. This competition mechanism suggests that only when the condensate bulk thermal resistance is reduced after it takes over the domination can the condensation be effectively intensified. We propose a unified theoretical model for the thermal resistance analysis by making dropwise condensation equivalent to filmwise condensation. We further find that near a critical point (contact angle being ca. 153°) the bulk thermal resistance has the least opportunity to take over the domination while away from it the probability increases.

  7. On the early and developed stages of surface condensation: competition mechanism between interfacial and condensate bulk thermal resistances

    PubMed Central

    Sun, Jie; Wang, Hua Sheng

    2016-01-01

    We use molecular dynamics simulation to investigate the early and developed stages of surface condensation. We find that the liquid-vapor and solid-liquid interfacial thermal resistances depend on the properties of solid and fluid, which are time-independent, while the condensate bulk thermal resistance depends on the condensate thickness, which is time-dependent. There exists intrinsic competition between the interfacial and condensate bulk thermal resistances in timeline and the resultant total thermal resistance determines the condensation intensity for a given vapor-solid temperature difference. We reveal the competition mechanism that the interfacial thermal resistance dominates at the onset of condensation and holds afterwards while the condensate bulk thermal resistance gradually takes over with condensate thickness growing. The weaker the solid-liquid bonding, the later the takeover occurs. This competition mechanism suggests that only when the condensate bulk thermal resistance is reduced after it takes over the domination can the condensation be effectively intensified. We propose a unified theoretical model for the thermal resistance analysis by making dropwise condensation equivalent to filmwise condensation. We further find that near a critical point (contact angle being ca. 153°) the bulk thermal resistance has the least opportunity to take over the domination while away from it the probability increases. PMID:27721397

  8. An excellent candidate for largely reducing interfacial thermal resistance: a nano-confined mass graded interface

    NASA Astrophysics Data System (ADS)

    Zhou, Yanguang; Zhang, Xiaoliang; Hu, Ming

    2016-01-01

    Pursuing extremely low interfacial thermal resistance has long been the task of many researchers in the area of nano-scale heat transfer, in particular pertaining to improve heat dissipation performance in electronic cooling. While it is well known and documented that confining a macroscopic third layer between two dissimilar materials usually increases the overall interfacial thermal resistance, no research has realized the fundamental decrease in resistance so far. By performing nonequilibrium molecular dynamics simulations, we report that the overall interfacial thermal resistance can be reduced by 6 fold by confining mass graded materials with thickness of the order of nanometers. As comparison we also studied the thermal transport across the perfectly abrupt interface and the widely used alloyed (rough) interface, which shows an opposing and significantly large increase in the overall thermal resistance. With the help of frequency dependent interfacial thermal conductance and wave packet dynamics simulation, different mechanisms governing the heat transfer across these three types of interfaces are identified. It is found that for the rough interface there are two different regimes of interfacial heat transfer, which originates from the competition between phonon scattering and the thickness of the interface. The mechanism of dramatically improved interfacial heat transfer across the nano-confined mass graded interface resides in the minor phonon reflection when the phonons first reach the mass graded area and the rare occurrence of phonon scattering in the subsequent interior region. The phonons are found to be gradually truncated by the geometric interfaces and can travel through the mass graded layer with a high transmission coefficient, benefited from the small mass mismatch between two neighboring layers in the interfacial region. Our findings provide deep insight into the phonon transport across nano-confined mass graded layers and also offer significant

  9. A computer program to calculate the resistivity of a thin film deposited on a conductive substrate from four-point probe measurements

    NASA Technical Reports Server (NTRS)

    Oberle, L. G.; Fralick, G. C.

    1986-01-01

    A series of FORTRAN-77 programs is described which correct for the effect of a conducting substrate when a linear four-point probe is used to measure the resistivity of a thin film. The resistivity of the film is given in terms of the thicknesses of the film and substrate, the known resistivity of the substrate, and the measured delta V/I. A full development is given as well as a complete description of the operation of the programs. The programs themselves can be obtained through COSMIC, and are identified as LEW No. 14381.

  10. Characterization of Contact and Bulk Thermal Resistance of Laminations for Electric Machines

    SciTech Connect

    Cousineau, Emily; Bennion, Kevin; Devoto, Douglas; Naramanchi, Sreekant

    2015-07-06

    Thermal management for electric motors is important as the automotive industry continues to transition to more electrically dominant vehicle propulsion systems. The transition to more electrically dominant propulsion systems leads to higher-power duty cycles for electric-drive systems. Thermal constraints place significant limitations on how electric motors ultimately perform. As thermal management improves, there will be a direct trade-off among motor performance, efficiency, cost, and the sizing of electric motors to operate within the thermal constraints. During the development of thermal finite element analysis models and computational fluid dynamics models for electric motors, it was found that there was a lack of open literature detailing the thermal properties of key materials common in electric motors that are significant in terms of heat removal. The lack of available literature, coupled with the strong interest from industry in the passive-stack thermal measurement results, led to experiments to characterize the thermal contact resistance between motor laminations. We examined four lamination materials, including the commonly used 26 gauge and 29 gauge M19 materials, the HF10 and Arnon 7 materials. These latter two materials are thinner and reduce eddy currents responsible for core losses. We measured the thermal conductivity of the lamination materials and the thermal contact resistance between laminations in a stack, as well as investigated factors affecting contact resistance between laminations such as the contact pressure and surface finish. Lamination property data will be provided and we also develop a model to estimate the through-stack thermal conductivity for materials beyond those that were directly tested in this work. For example, at a clamping pressure of 138 kPa, the 29 gauge M19 material has a through-stack thermal conductivity of 1.68 W/m-K, and the contact resistance between laminations was measured to be 193 mm^2-K/W. The measured bulk

  11. FT-IR standoff detection of thermally excited emissions of trinitrotoluene (TNT) deposited on aluminum substrates.

    PubMed

    Castro-Suarez, John R; Pacheco-Londoño, Leonardo C; Vélez-Reyes, Miguel; Diem, Max; Tague, Thomas J; Hernandez-Rivera, Samuel P

    2013-02-01

    A standoff detection system was assembled by coupling a reflecting telescope to a Fourier transform infrared spectrometer equipped with a cryo-cooled mercury cadmium telluride detector and used for detection of solid-phase samples deposited on substrates. Samples of highly energetic materials were deposited on aluminum substrates and detected at several collector-target distances by performing passive-mode, remote, infrared detection measurements on the heated analytes. Aluminum plates were used as support material, and 2,4,6-Trinitrotoluene (TNT) was used as the target. For standoff detection experiments, the samples were placed at different distances (4 to 55 m). Several target surface temperatures were investigated. Partial least squares regression analysis was applied to the analysis of the intensities of the spectra obtained. Overall, standoff detection in passive mode was useful for quantifying TNT deposited on the aluminum plates with high confidence up to target-collector distances of 55 m.

  12. Thermal compression chip interconnection using organic solderability preservative etched substrate by plasma processing.

    PubMed

    Cho, Sung-Won; Choi, JoonYoung; Chung, Chin-Wook

    2014-12-01

    The solderability of copper organic solderbility preservative (CuOSP) finished substrate was enhanced by the plasma etching. To improve the solderability of TC interconnection with the CuOSP finished substrate, the plasma etching process is used. An Oxygen-Hydrogen plasma treatment process is performed to remove OSP material. To prevent the oxidation by oxygen plasma treatment, hydrogen reducing process is also performed before TC interconnection process. The thickness of OSP material after plasma etching is measured by optical reflection method and the component analysis by Auger Electron Spectroscopy is performed. From the lowered thickness, the bonding force of TC interconnection after OSP etching process is lowered. Also the electrical open/short test was performed after assembling the completed semiconductor packaging. The improved yield due to the plasma etching process is achieved.

  13. Thermal cycling and high power density hydrogen ion beam irradiation of tungsten layers on tungsten substrate

    NASA Astrophysics Data System (ADS)

    Airapetov, A. A.; Begrambekov, L. B.; Gretskaya, I. Yu; Grunin, A. V.; Dyachenko, M. Yu; Puntakov, N. A.; Sadovskiy, Ya A.

    2016-09-01

    Tungsten layers with iron impurity were deposited on tungsten substrates modeling re-deposited layers in a fusion device. The samples were tested by thermocycling and hydrogen ion beam tests. Thermocycling revealed globule formation on the surface. The size of the globules depended on iron impurity content in the coating deposited. Pore formation was observed which in some cases lead to exfoliation of the coatings. Hydrogen ion irradiation lead to formation of blisters on the coating and finally its exfoliation.

  14. Multiple adaptive mechanisms affect asparagine synthetase substrate availability in asparaginase-resistant MOLT-4 human leukaemia cells.

    PubMed Central

    Aslanian, A M; Kilberg, M S

    2001-01-01

    Childhood acute lymphoblastic leukaemia is treated by combination chemotherapy with a number of drugs, almost always including the enzyme L-asparaginase (ASNase). Although the initial remission rate is quite high, relapse and associated drug resistance remain a problem. In vitro studies have demonstrated an adaptive increase in asparagine synthetase (AS) expression in ASNase-resistant cells, which is believed to permit ASNase-resistant human leukaemia cells to survive in vivo. The present results, obtained with ASNase-sensitive and -resistant human MOLT-4 leukaemia cell lines, illustrate that several other adaptive processes occur to provide sufficient amounts of the AS substrates, aspartate and glutamine, required to support this increased enzymic activity. In both cell populations, aspartate is derived almost exclusively from intracellular sources, whereas the necessary glutamine arises from both intracellular and extracellular sources. Transport of glutamine into ASNase-resistant cells is significantly enhanced compared with the parental cells, whereas amino acid efflux (e.g. asparagine) is reduced. Most of the adaptive change for the amino acid transporters, Systems A, ASC and L, is rapidly (12 h) reversed following ASNase removal. The enzymic activity of glutamine synthetase is also enhanced in ASNase-resistant cells by a post-transcriptional mechanism. The results demonstrate that there are several sites of metabolic adaptation in ASNase-treated leukaemia cells that serve to promote the replenishment of both glutamine and asparagine. PMID:11485552

  15. The thermal fatigue resistance of H-13 Die Steel for aluminum die casting dies

    NASA Technical Reports Server (NTRS)

    1982-01-01

    The effects of welding, five selected surface coatings, and stress relieving on the thermal fatigue resistance of H-13 Die Steel for aluminum die casting dies were studied using eleven thermal fatigue specimens. Stress relieving was conducted after each 5,000 cycle interval at 1050 F for three hours. Four thermal fatigue specimens were welded with H-13 or maraging steel welding rods at ambient and elevated temperatures and subsequently, subjected to different post-weld heat treatments. Crack patterns were examined at 5,000, 10,000, and 15,000 cycles. The thermal fatigue resistance is expressed by two crack parameters which are the average maximum crack and the average cracked area. The results indicate that a significant improvement in thermal fatigue resistance over the control was obtained from the stress-relieving treatment. Small improvements were obtained from the H-13 welded specimens and from a salt bath nitrogen and carbon-surface treatment. The other surface treatments and welded specimens either did not affect or had a detrimental influence on the thermal fatigue properties of the H-13 die steel.

  16. Osteogenic potential of in situ TiO2 nanowire surfaces formed by thermal oxidation of titanium alloy substrate

    NASA Astrophysics Data System (ADS)

    Tan, A. W.; Ismail, R.; Chua, K. H.; Ahmad, R.; Akbar, S. A.; Pingguan-Murphy, B.

    2014-11-01

    Titanium dioxide (TiO2) nanowire surface structures were fabricated in situ by a thermal oxidation process, and their ability to enhance the osteogenic potential of primary osteoblasts was investigated. Human osteoblasts were isolated from nasal bone and cultured on a TiO2 nanowires coated substrate to assess its in vitro cellular interaction. Bare featureless Ti-6Al-4V substrate was used as a control surface. Initial cell adhesion, cell proliferation, cell differentiation, cell mineralization, and osteogenic related gene expression were examined on the TiO2 nanowire surfaces as compared to the control surfaces after 2 weeks of culturing. Cell adhesion and cell proliferation were assayed by field emission scanning electron microscope (FESEM) and Alamar Blue reduction assay, respectively. The nanowire surfaces promoted better cell adhesion and spreading than the control surface, as well as leading to higher cell proliferation. Our results showed that osteoblasts grown onto the TiO2 nanowire surfaces displayed significantly higher production levels of alkaline phosphatase (ALP), extracellular (ECM) mineralization and genes expression of runt-related transcription factor (Runx2), bone sialoprotein (BSP), ostoepontin (OPN) and osteocalcin (OCN) compared to the control surfaces. This suggests the potential use of such surface modification on Ti-6Al-4V substrates as a promising means to improve the osteointegration of titanium based implants.

  17. Increased Water Activity Reduces the Thermal Resistance of Salmonella enterica in Peanut Butter

    PubMed Central

    He, Yingshu; Li, Ye; Salazar, Joelle K.; Yang, Jingyun; Tortorello, Mary Lou

    2013-01-01

    Increased water activity in peanut butter significantly (P < 0.05) reduced the heat resistance of desiccation-stressed Salmonella enterica serotypes treated at 90°C. The difference in thermal resistance was less notable when strains were treated at 126°C. Using scanning electron microscopy, we observed minor morphological changes of S. enterica cells resulting from desiccation and rehydration processes in peanut oil. PMID:23728806

  18. Low thermal resistance of a GaN-on-SiC transistor structure with improved structural properties at the interface

    NASA Astrophysics Data System (ADS)

    Chen-Tai, Jr.; Pomeroy, James W.; Rorsman, Niklas; Xia, Chao; Virojanadara, Chariya; Forsberg, Urban; Kuball, Martin; Janzén, Erik

    2015-10-01

    The crystalline quality of AlGaN/GaN heterostructures was improved by optimization of surface pretreatment of the SiC substrate in a hot-wall metal-organic chemical vapor deposition reactor. X-ray photoelectron spectroscopy measurements revealed that oxygen- and carbon-related contaminants were still present on the SiC surface treated at 1200 °C in H2 ambience, which hinders growth of thin AlN nucleation layers with high crystalline quality. As the H2 pretreatment temperature increased to 1240 °C, the crystalline quality of the 105 nm thick AlN nucleation layers in the studied series reached an optimal value in terms of full width at half-maximum of the rocking curves of the (002) and (105) peaks of 64 and 447 arcsec, respectively. The improvement of the AlN growth also consequently facilitated a growth of the GaN buffer layers with high crystalline quality. The rocking curves of the GaN (002) and (102) peaks were thus improved from 209 and 276 arcsec to 149 and 194 arcsec, respectively. In addition to a correlation between the thermal resistance and the structural quality of an AlN nucleation layer, we found that the microstructural disorder of the SiC surface and the morphological defects of the AlN nucleation layers to be responsible for a substantial thermal resistance. Moreover, in order to decrease the thermal resistance in the GaN/SiC interfacial region, the thickness of the AlN nucleation layer was then reduced to 35 nm, which was shown sufficient to grow AlGaN/GaN heterostructures with high crystalline quality. Finally, with the 35 nm thick high-quality AlN nucleation layer a record low thermal boundary resistance of 1.3×10-8 m2 K/W, measured at an elevated temperature of 160 °C, in a GaN-on-SiC transistor structure was achieved.

  19. A study on structural, optical, electrical and microstructural properties of thin TiO x films upon thermal oxidation: Effect of substrate temperature and oxidation temperature

    NASA Astrophysics Data System (ADS)

    Sreemany, Monjoy; Bose, Ankita; Sen, Suchitra

    2010-01-01

    Influences of both substrate temperature, Ts (∼305, 473 K) and oxidation temperature, Ta (∼623-973 K) on the structural, optical, electrical and microstructural properties of thin TiO x ( x≤2) films obtained by thermal oxidation of sputtered titanium thin films have been investigated. Ts is found to be an important parameter that affects both the as deposited film morphology and phase evolution of TiO x films during oxidation. As deposited and oxidized films processed at Ta∼623 K exist in TiO form. Formation of anatase (TiO 2) phase takes place at Ta∼723 K. As the Ta increases above 723 K, degree of crystallinity of the film improves and rutile (TiO 2) phase appears along with anatase phase at Ta∼873 K. Further increase in the Ta enhances the contribution of rutile phase at the expense of anatase contribution. Apparent crystallite size, L, and refractive index of the TiO x ( x≈2) films increase with Ta but band gap energy, Eg decreases from ∼3.4 to 3.35 eV. Scanning electron microscopic study reveals that both film densification and grain size improve with Ta. As the Ta increases above 873 K, rutile phase contribution as well as grains of the oxidized films deposited at a lower Ts grow at a faster rate than that of the TiO x films prepared at a higher Ts. Room temperature resistivity of the as deposited films is found to be dependent on Ts. Film-resistivity increases with oxidation temperature and at Ta∼723 K, resistivity of the film increases drastically. Temperature coefficient of resistivity (TCR) for all the as deposited and oxidized films processed at Ta∼623 K is found to be negative and lie between ∼1.2×10 -3-2.1×10 -3 K -1. Thermal activation energy, Ea, of the as deposited and oxidized ( Ta∼623 K) TiO x ( x≈1) films is estimated to vary over the range ∼0.015-0.027 eV. Observed change in the film electrical properties with Ta is discussed in the light of oxygen incorporation in the TiO x structure.

  20. Generalized Procedure for Improved Accuracy of Thermal Contact Resistance Measurements for Materials With Arbitrary Temperature-Dependent Thermal Conductivity

    SciTech Connect

    Sayer, Robert A.

    2014-06-26

    Thermal contact resistance (TCR) is most commonly measured using one-dimensional steady-state calorimetric techniques. In the experimental methods we utilized, a temperature gradient is applied across two contacting beams and the temperature drop at the interface is inferred from the temperature profiles of the rods that are measured at discrete points. During data analysis, thermal conductivity of the beams is typically taken to be an average value over the temperature range imposed during the experiment. Our generalized theory is presented and accounts for temperature-dependent changes in thermal conductivity. The procedure presented enables accurate measurement of TCR for contacting materials whose thermal conductivity is any arbitrary function of temperature. For example, it is shown that the standard technique yields TCR values that are about 15% below the actual value for two specific examples of copper and silicon contacts. Conversely, the generalized technique predicts TCR values that are within 1% of the actual value. The method is exact when thermal conductivity is known exactly and no other errors are introduced to the system.

  1. Optimization of low-diffusion EUV resist for linewidth roughness and pattern collapse on various substrates

    NASA Astrophysics Data System (ADS)

    Thackeray, James W.; Cameron, James F.; Wagner, Michael; Coley, Suzanne; Ongayi, Owendi; Montgomery, Warren; Lovell, Dave; Biafore, John; Chakrapani, Vidhya; Ko, Akiteru

    2012-03-01

    This paper will report on our development of low diffusion EUV resists based on polymer-bound PAG technology. With our low diffusion resist, a wide process window for 30-nm hp of 280nm DOF over a 10% exposure range is achieved on a prototype ADT fullfield scanner. Linewidth roughness of 3.1nm is also achieved. Excellent resist profiles can be achieved on organic ULs or Si hardmask materials. This resist also shows only 1.1 nm carbon growth on witness plate mirrors for cleanables, and no reflectivity loss after mirror cleaning. These results clearly pass for use on all NXE exposure tools. We also have shown good pattern transfer for a Si HM stack using this resist. Finally, we report 17-nm hp resolution at a dose of 14.5mj for a higher absorption resist.

  2. Dependences of microwave surface resistance of HTS thin films on applied dc magnetic fields parallel and normal to the substrate

    NASA Astrophysics Data System (ADS)

    Sato, K.; Sato, S.; Ichikawa, K.; Watanabe, M.; Honma, T.; Tanaka, Y.; Oikawa, S.; Saito, A.; Ohshima, S.

    2014-05-01

    We investigated the dc magnetic field and temperature dependences of microwave surface resistance (Rs) of high-temperature superconductor (HTS) films. Previously, we reported that the surface resistance RsRs(n) under a dc magnetic field applied normaly to the substrate increased when increasing the applied magnetic field. For NMR application, we have to examine the Rs(p) under the dc magnetic field parallel to the substrate. We measured the Rs(p) of the YBCO and DyBCO thin films with a thickness of 500 nm deposited on a MgO (100) substrate using the dielectric resonator method at 21.8 GHz, and a dc magnetic field of up to 5 T. In a zero magnetic field, the values of Rs(n) and Rs(p) were 0.35 mQ at 20 K. Under the dc magnetic field, the Rs(n) and the Rs(p) also increased with increasing magnetic field, however, the Rs(p) had a lower magnetic field dependence and the value was about 1/10 of that of the Rs(n). The Rs(p) at 16.4 T and at 700 MHz could be estimated by the two-fluid model. The Rs(p) value was about 1/2600 compared with that of copper at 20 K. As a result, we clarified that 500 nm thick YBCO and DyBCO thin films could provide advantages for NMR application.

  3. Thermoelectric study of Y-Ba-Cu-O thin film on MgO substrate prepared by resistive evaporation

    NASA Astrophysics Data System (ADS)

    Pekala, M.; Pekala, K.; Lapsker, I.; Verdyan, A.; Azoulay, J.

    1993-04-01

    Thermoelectric measurements were carried out on Y-Ba-Cu-O thin film deposited on MgO substrate by resistive evaporation technique. A pulverized mixture of Y, BaF 2 and Cu weighed in the atomic proportion was evaporated from resistively heated source onto a MgO substrate kept at 400°C using a simple vacuum system. The substrate temperature was then raised to 700°C for insitu heat treatment. Oxygen was injected through a nozzle placed close to subtrate surface, thus raising the pressure to about 7 Pa during the heat treatment, which lasted for about 15 minutes. The film was then gradually cooled down to room temperature and the pressure raised to atmospheric pressure. The films thus obtained were measured and the values of thermoelectric power measurements in the plane of the film were found to be close to the typical thermoelectric power values of crystalline Y-Ba-Cu-O superconductors. As expected, vanishing values of the thermoelectric power have been observed below 80 K. If the relation observed for sintered Y-Ba-Cu-O is applied for thin films, it suggests an extremely low oxygen deficiency.

  4. Metalorganic chemical vapor deposition of hexagonal boron nitride on (001) sapphire substrates for thermal neutron detector applications

    NASA Astrophysics Data System (ADS)

    Ahmed, K.; Dahal, R.; Weltz, A.; Lu, James J.-Q.; Danon, Y.; Bhat, I. B.

    2017-03-01

    This paper reports on the growth and characterization of hexagonal boron nitride (hBN) and its use for solid-state thermal neutron detection. The hBN epilayers were grown by metalorganic chemical vapor deposition on sapphire substrates at a temperature of 1350 C. X-ray diffraction peak from the (002) hBN plane at a 2theta angle of 26.7 deg exhibited the c-lattice constant of 6.66 {\\AA} for these films. A strong peak corresponding to the high frequency Raman active mode of hBN was found for the films at 1370.5/cm. hBN-based solid-state neutron detectors were fabricated and tested with a metal-semiconductor-metal configuration with an electrode spacing of 1 mm and hBN thickness of 2.5 micron. Fabricated detectors showed strong response to deep UV light as well. An intrinsic thermal neutron detection efficiency of 0.86% was measured, which is close to the theoretically expected efficiency of 0.87%. These results demonstrate that epitaxial hBN films are promising for thermal neutron detection applications.

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

    NASA Astrophysics Data System (ADS)

    Li, Yafang; Liu, Hao; Li, Xiaojiu

    2017-03-01

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

  6. New approach to improve LER of EUV resist pattern by chemical and thermal treatment

    NASA Astrophysics Data System (ADS)

    Nagahara, Tatsuro; Yamamoto, Kazuma; Matsuura, Yuriko; Sekito, Takashi

    2015-03-01

    In this paper, we discuss a new approach to improve the resist roughness, which is applied after the lithography process. The ERC (Edge Roughness Controller) process is composed of two steps, 1) To deliver resist softening material at the resist surface 2) To give thermal flow at that region in the bake step. Several samples were prepared based on this concept and consistent improvement was observed. Finally, by optimizing ERC chemistry using HSP (Hansen Solubility Parameter), LWR improvement of 14.8% could be achieved.

  7. Analysis of thermal shock resistance of CVD ZnS dome

    NASA Astrophysics Data System (ADS)

    Zhang, Daijun; Luo, Haibo; Zhou, Peipei; Hou, Xinglin

    2016-10-01

    Since the dome experiences the convective heat loading, thermal stress will be generated in the thickness direction. Thus, estimation of the thermal shock and analysis of the thermal shock resistance of the dome are the key to the design of the dome. In this paper, thermal shock resistance of CVD ZnS dome is analysed based on the flight condition of 6000m altitude and 3.0 Mach. We obtained the critical Reynolds number through a rockets pry experiment, which deduced that there exists a transition from laminar flow to turbulent flow at somewhere over the dome. We calculated the heat transfer coefficient over dome through heat transfer coefficient engineering formula of high-speed sphere with turbulent boundary layer near the stagnation point. The largest heat transfer coefficient is 2590W/(m2.K). Then, we calculated the transient thermal stress of dome by using the finite element method. Then we obtained the temperature and thermal stress distribution of different time through the direction of thickness. In order to obtain the mechanical properties of CVD ZnS at high temperatures, the 3-point bending method was used to test the flexure strength of CVD ZnS at different temperature. When compared the maximum thermal stress with flexure strength at different temperature, we find that the safety factors were not less than 1.75. The result implied that the dome has good safety margin under the proposed application condition. Through the above test and analysis, we can get the conclusion that the thermal shock resistance of the CVD ZnS dome satisfied the requirements of flight conditions.

  8. A theoretical study of electrical and thermal response in resistance spot welding

    SciTech Connect

    Na, S.J.; Park, S.W.

    1996-08-01

    The effect of contact resistance including constriction and contamination resistance has been a major hurdle for the thermoelectrical analysis of the resistance spot welding process. In this paper, a simple model was suggested and used for calculating the electrical and thermal response of the resistance spot welding process to investigate the influence of contacting forces on the formation of weld nuggets. The electrode surface of the contact interface was assumed to be axisymmetric and its microasperities to have a trapezoidal cross-section. These microasperities were considered as the one-dimensional contact resistance elements in the finite element formulation. The contamination film was assumed to be a nonconducting oxide layer, which is very brittle, so that it is broken to some number of pieces when a contacting pressure is being applied. The crushed films were assumed to be distributed at regular intervals and to conserve their size and number during the welding process. The simulation results revealed that the proposed model can be successfully used to predict the effect of the contact resistance on the electrical and thermal response of the resistance spot welding process.

  9. Resist profile and CD control improvement by using optimized resist thickness and substrate film stack ratio for 0.35-um logic process

    NASA Astrophysics Data System (ADS)

    Fan, Ming H.; Yu, Raymond; Chu, Ronfu; Lim, Chet Ping

    1997-08-01

    LOCOS is the most widely used method for 0.35 micrometers process isolation. 2000 angstrom silicon nitride on 200 angstrom padoxide was selected as oxidation barrier before process optimization for the need of control the bird's beak and stress which affects the subsequent gate oxide quality. However, resist profile is prone to footing at this film stack. Severe footing could make minimum space CD too small, even not opened, to cause isolation failure. Experiment data shows that if nitride thickness varies from 1.9 K to 2.1 K, line CD variation can be up to 0.08 micrometers for a 0.6 micrometers line, which is about 80 percent of CD variation budget. Based on simulation results, 8 different nitride thickness in the range of 1750 angstrom to 2100 angstrom with step of 50 angstrom were deposited on 200 angstrom padoxide. Swing curve, CD versus nitride thickness for resist Emax and Emin, CD versus different exposure dose charts were obtained. Resist profile cross-sectional SEM pictures were also done to confirm simulation and in-line CD SEM measurement. An optimum combination of substrate film stack and resist thickness was selected. After implementation of this optimization, the sensitivity of CD to the nitride thickness was greatly reduced. Better resist profile and CD control were obtained. This was well confirmed by in-line monitoring data.

  10. Electrochemical depositing rGO-Ti-rGO heterogeneous substrates with higher thermal conductivity and heat transfer performance compared to pure Ti

    NASA Astrophysics Data System (ADS)

    Wang, Jing; Wang, Huatao; Zhang, Wenying; Yang, Xinyi; Wen, Guangwu; Wang, Yijie; Zhou, Weiwei

    2017-02-01

    Titanium (Ti) and its alloys are widely applied in many high strength, light weight applications, but their thermal conductivity is lower compared to that of other metals, which limits their further applications. In this paper, we demonstrated experimentally that rGO-Ti-rGO heterogeneous substrates with higher thermal conductivity, up to ˜38.8% higher than Ti, could be fabricated by electrochemical depositing rGO on their surface. The rGO layers are grown on the surface of Ti substrates, with appearance of bedclothes on the beds. The thickness of rGO layers is around 300-500 nm and around 600-1000 nm when deposited for 5 cycles and 10 cycles, respectively. According to the cooling experiment results, as-prepared Ti + rGO substrates can present excellent thermal conduction performance, and reduce the chip temperature close to 3.2 °C-13.1 °C lower than Ti alloy substrates with the heat flow density of 0.4-3.6 W cm-2. Finally, the approach to electro-chemically deposit hundreds of nanometer rGO layers on the surface of Ti substrates can improve their thermal conductivity and heat transfer performance, which may have further application in the increasing thermal conduction of other metal-alloys, ceramics and polymers.

  11. Electrochemical depositing rGO-Ti-rGO heterogeneous substrates with higher thermal conductivity and heat transfer performance compared to pure Ti.

    PubMed

    Wang, Jing; Wang, Huatao; Zhang, Wenying; Yang, Xinyi; Wen, Guangwu; Wang, Yijie; Zhou, Weiwei

    2017-02-17

    Titanium (Ti) and its alloys are widely applied in many high strength, light weight applications, but their thermal conductivity is lower compared to that of other metals, which limits their further applications. In this paper, we demonstrated experimentally that rGO-Ti-rGO heterogeneous substrates with higher thermal conductivity, up to ∼38.8% higher than Ti, could be fabricated by electrochemical depositing rGO on their surface. The rGO layers are grown on the surface of Ti substrates, with appearance of bedclothes on the beds. The thickness of rGO layers is around 300-500 nm and around 600-1000 nm when deposited for 5 cycles and 10 cycles, respectively. According to the cooling experiment results, as-prepared Ti + rGO substrates can present excellent thermal conduction performance, and reduce the chip temperature close to 3.2 °C-13.1 °C lower than Ti alloy substrates with the heat flow density of 0.4-3.6 W cm(-2). Finally, the approach to electro-chemically deposit hundreds of nanometer rGO layers on the surface of Ti substrates can improve their thermal conductivity and heat transfer performance, which may have further application in the increasing thermal conduction of other metal-alloys, ceramics and polymers.

  12. Enhanced thermal and combustion resistance of cotton linked to natural inorganic salt components

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Cotton is most commonly scoured or scoured and bleached before being used for commercial purposes, but, due to its propensity to burn, cotton's use is limited and protective chemistry is needed in applications where resistance to heat and flame is required. A comparison of the thermal decomposition ...

  13. Structure Analysis Of Corrosion Resistant Thermal Sprayed Coatings On Low Alloy Steels

    SciTech Connect

    Chaliampalias, D.; Vourlias, G.; Pistofidis, N.; Pavlidou, E.; Stergiou, A.; Stergioudis, G.; Polychroniadis, E. K.

    2007-04-23

    Metallic coatings have been proved to reduce the rate of corrosion of steel in various atmospheres. In this work the structure of Al, Cu-Al and Zn thermal sprayed coatings is examined. The as formed coatings are extremely rough, and they are composed of several phases which increase corrosion resistance as it was determined Salt Spray Chamber tests.

  14. Thermally oxidized titania nanotubes enhance the corrosion resistance of Ti6Al4V.

    PubMed

    Grotberg, John; Hamlekhan, Azhang; Butt, Arman; Patel, Sweetu; Royhman, Dmitry; Shokuhfar, Tolou; Sukotjo, Cortino; Takoudis, Christos; Mathew, Mathew T

    2016-02-01

    The negative impact of in vivo corrosion of metallic biomedical implants remains a complex problem in the medical field. We aimed to determine the effects of electrochemical anodization (60V, 2h) and thermal oxidation (600°C) on the corrosive behavior of Ti-6Al-4V, with serum proteins, at physiological temperature. Anodization produced a mixture of anatase and amorphous TiO2 nanopores and nanotubes, while the annealing process yielded an anatase/rutile mixture of TiO2 nanopores and nanotubes. The surface area was analyzed by the Brunauer-Emmett-Teller method and was estimated to be 3 orders of magnitude higher than that of polished control samples. Corrosion resistance was evaluated on the parameters of open circuit potential, corrosion potential, corrosion current density, passivation current density, polarization resistance and equivalent circuit modeling. Samples both anodized and thermally oxidized exhibited shifts of open circuit potential and corrosion potential in the noble direction, indicating a more stable nanoporous/nanotube layer, as well as lower corrosion current densities and passivation current densities than the smooth control. They also showed increased polarization resistance and diffusion limited charge transfer within the bulk oxide layer. The treatment groups studied can be ordered from greatest corrosion resistance to least as Anodized+Thermally Oxidized > Anodized > Smooth > Thermally Oxidized for the conditions investigated. This study concludes that anodized surface has a potential to prevent long term implant failure due to corrosion in a complex in-vivo environment.

  15. Resistive switching of Pt/TiO x /Pt devices fabricated on flexible Parylene-C substrates

    NASA Astrophysics Data System (ADS)

    Khiat, Ali; Cortese, Simone; Serb, Alexander; Prodromakis, Themistoklis

    2017-01-01

    Pt/TiO x /Pt resistive switching (RS) devices are considered to be amongst the most promising candidates in memristor family and the technology transfer to flexible substrates could open the way to new opportunities for flexible memory implementations. Hence, an important goal is to achieve a fully flexible RS memory technology. Nonetheless, several fabrication challenges are present and must be solved prior to achieving reliable device fabrication and good electronic performances. Here, we propose a fabrication method for the successful transfer of Pt/TiO x /Pt stack onto flexible Parylene-C substrates. The devices were electrically characterised, exhibiting both digital and analogue memory characteristics, which are obtained by proper adjustment of pulsing schemes during tests. This approach could open new application possibilities of these devices in neuromorphic computing, data processing, implantable sensors and bio-compatible neural interfaces.

  16. Fabrication of thermal-resistant gratings for high-temperature measurements using geometric phase analysis

    NASA Astrophysics Data System (ADS)

    Zhang, Q.; Liu, Z.; Xie, H.; Ma, K.; Wu, L.

    2016-12-01

    Grating fabrication techniques are crucial to the success of grating-based deformation measurement methods because the quality of the grating will directly affect the measurement results. Deformation measurements at high temperatures entail heating and, perhaps, oxidize the grating. The contrast of the grating lines may change during the heating process. Thus, the thermal-resistant capability of the grating becomes a point of great concern before taking measurements. This study proposes a method that combines a laser-engraving technique with the processes of particle spraying and sintering for fabricating thermal-resistant gratings. The grating fabrication technique is introduced and discussed in detail. A numerical simulation with a geometric phase analysis (GPA) is performed for a homogeneous deformation case. Then, the selection scheme of the grating pitch is suggested. The validity of the proposed technique is verified by fabricating a thermal-resistant grating on a ZrO2 specimen and measuring its thermal strain at high temperatures (up to 1300 °C). Images of the grating before and after deformation are used to obtain the thermal-strain field by GPA and to compare the results with well-established reference data. The experimental results indicate that this proposed technique is feasible and will offer good prospects for further applications.

  17. Experimental investigation and characterization of micro resistance welding with an electro-thermal actuator

    NASA Astrophysics Data System (ADS)

    Chang, Chun-Wei; Yeh, Cheng-Chi; Hsu, Wensyang

    2009-02-01

    Resistance welding is a common scheme of assembly on the macro scale by pressing together two workpieces with current passing through them to generate joule heating at the contact region due to high contact resistance. However, micro assembly by resistance welding is seldom reported. Here, resistance welding with an electro-thermal microactuator to assemble micro Ni structures is experimentally investigated and characterized. The bent-beam electro-thermal microactuator is designed to provide the necessary displacements and pressing forces. The two-mask metal-based surface micromachining process is adopted to fabricate the micro Ni structures. The calibrated initial contact resistance is shown to decrease with increasing contact pressure. Furthermore, stronger welding strength is achieved at a smaller initial contact resistance, which indicates that a larger clamping force would enhance the welding strength as large as 3.09 MPa (74.4 µN) at a contact resistance of 2.7 Ω here. The input welding energy is also found to be a critical factor. In our tests, when welding energy is below the threshold limit of 0.05 J, the welding trials all fail. For the energy between 0.05 J and 1 J, there is a transition from a lower yield of 33.3% to a higher yield of 58.3%. At high welding energy, between 1 and 10 J, 100% yield is achieved. With the demonstration and characterization of micro resistance welding by the electro-thermal microactuator, the scheme proposed here would be helpful in the automation of micro assembly.

  18. Thermal resistance and compressive strain of underwater aerogel syntactic foam hybrid insulation at atmospheric and elevated hydrostatic pressure

    NASA Astrophysics Data System (ADS)

    Bardy, Erik; Mollendorf, Joseph; Pendergast, David

    2006-05-01

    The purpose of this study was to present a new underwater thermal insulation designed for flexibility and high thermal resistance. The insulation was a hybrid composite of two constituents: syntactic foam and an insulating aerogel blanket. Methods for treating and combining the constituents into a hybrid insulation of several designs are presented. A final configuration was selected based on high thermal resistance and was tested for thermal resistance and compressive strain to a pressure of 1.2 MPa (107 msw, meters of sea water) for five continuous pressure cycles. The thermal resistance and compressive strain results were compared to foam neoprene and underwater pipeline insulation. It was found that the hybrid insulation has a thermal resistance significantly higher than both foam neoprene and underwater pipeline insulation at atmospheric and elevated hydrostatic pressures (1.2 MPa). The total thermal resistance of the hybrid insulation decreased 32% at 1.2 MPa and returned to its initial value upon decompression. It was concluded that the hybrid insulation, with modifications, could be used for wetsuit construction, shallow underwater pipeline insulation, or any underwater application where high thermal resistance, flexibility, and resistance to compression are desired.

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

    SciTech Connect

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

    2014-11-15

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

  20. Thermal fatigue resistance of NASA WAZ-20 alloy with three commercial coatings

    NASA Technical Reports Server (NTRS)

    Bizon, P. T.; Oldrieve, R. E.

    1975-01-01

    Screening tests using three commercial coatings (Jocoat, HI-15, and RT-1A) on the nickel-base alloy NASA WAZ-20 were performed by cyclic exposure in a Mach 1 burner facility. These tests showed Jocoated WAZ-20 to have the best cracking resistance. The thermal fatigue resistance of Jocoated WAZ-20 in both the random polycrystalline and directionally solidified polycrystalline forms relative to that of other superalloys was then evaluated in a fluidized-bed facility. This investigation showed that Jocoated random polycrystalline WAZ-20 ranked approximately in midrange in thermal fatigue life. The thermal fatigue life of directionally solidified Jocoated WAZ-20 was shorter than that of other directionally solidified alloys but still longer than that of all alloys in the random polycrystalline form.

  1. Molecular dynamics simulations of grain boundary thermal resistance in UO2

    SciTech Connect

    Tianyi Chen; Di Chen; Bulent H. Sencer; Lin Shao

    2014-09-01

    By means of molecular dynamics (MD) simulations, we have calculated Kaptiza resistance of UO2 with or without radiation damage. For coincident site lattice boundaries of different configurations, the boundary thermal resistance of unirradiated UO2 can be well described by a parameter-reduced formula by using boundary energies as variables. We extended the study to defect-loaded UO2 by introducing damage cascades in close vicinity to the boundaries. Following cascade annealing and defect migrations towards grain boundaries, the boundary energy increases and so does Kaptiza resistance. The correlations between these two still follow the same formula extracted from the unirradiated UO2. The finding will benefit multi-scale modeling of UO2 thermal properties under extreme radiation conditions by combining effects from boundary configurations and damage levels.

  2. Thermal method for fabricating a hydrogen separation membrane on a porous substrate

    DOEpatents

    Song, Sun-Ju; Lee, Tae H.; Chen, Ling; Dorris, Stephen E.; Balachandran, Uthamalingam

    2009-10-20

    A thermal method of making a hydrogen permeable composition is disclosed. A mixture of metal oxide powder and ceramic oxide powder and optionally a pore former is formed and pressed to form an article. The article is dried at elevated temperatures and then sintered in a reducing atmosphere to provide a dense hydrogen permeable portion near the surface of the sintered mixture. The dense hydrogen permeable portion has a higher initial concentration of metal than the remainder of the sintered mixture and is present in the range of from about 20 to about 80 percent by volume of the dense hydrogen permeable portion.

  3. Fully Electrical Modeling of Thermoelectric Generators with Contact Thermal Resistance Under Different Operating Conditions

    NASA Astrophysics Data System (ADS)

    Siouane, Saima; Jovanović, Slaviša; Poure, Philippe

    2017-01-01

    The Seebeck effect is used in thermoelectric generators (TEGs) to supply electronic circuits by converting the waste thermal into electrical energy. This generated electrical power is directly proportional to the temperature difference between the TEG module's hot and cold sides. Depending on the applications, TEGs can be used either under constant temperature gradient between heat reservoirs or constant heat flow conditions. Moreover, the generated electrical power of a TEG depends not only on these operating conditions, but also on the contact thermal resistance. The influence of the contact thermal resistance on the generated electrical power have already been extensively reported in the literature. However, as reported in Park et al. (Energy Convers Manag 86:233, 2014) and Montecucco and Knox (IEEE Trans Power Electron 30:828, 2015), while designing TEG-powered circuit and systems, a TEG module is mostly modeled with a Thévenin equivalent circuit whose resistance is constant and voltage proportional to the temperature gradient applied to the TEG's terminals. This widely used simplified electrical TEG model is inaccurate and not suitable under constant heat flow conditions or when the contact thermal resistance is considered. Moreover, it does not provide realistic behaviour corresponding to the physical phenomena taking place in a TEG. Therefore, from the circuit designer's point of view, faithful and fully electrical TEG models under different operating conditions are needed. Such models are mainly necessary to design and evaluate the power conditioning electronic stages and the maximum power point tracking algorithms of a TEG power supply. In this study, these fully electrical models with the contact thermal resistance taken into account are presented and the analytical expressions of the Thévenin equivalent circuit parameters are provided.

  4. Silver conductive features on flexible substrates from a thermally accelerated chain reaction at low sintering temperatures.

    PubMed

    Chen, Shih-Pin; Kao, Zhen-Kai; Lin, Jeng-Lung; Liao, Ying-Chih

    2012-12-01

    In this study, a simple and effective silver ink formulation was developed to generate silver tracks with high electrical conductivity on flexible substrates at low sintering temperatures. Diethanolamine (DEA), a self-oxidizing compound at moderate temperatures, was mixed with a silver ammonia solution to form a clear and stable solution. After inkjet-printed or pen-written on plastic sheets, DEA in the silver ink decomposes at temperatures higher than 50 °C and generates formaldehyde, which reacts spontaneously with silver ammonia ions to form silver thin films. The electrical conductivity of the inkjet-printed silver films can be 26% of the bulk silver after heating at 75 °C for 20 min and show great adhesion on plastic sheets.

  5. Generalized Procedure for Improved Accuracy of Thermal Contact Resistance Measurements for Materials With Arbitrary Temperature-Dependent Thermal Conductivity

    DOE PAGES

    Sayer, Robert A.

    2014-06-26

    Thermal contact resistance (TCR) is most commonly measured using one-dimensional steady-state calorimetric techniques. In the experimental methods we utilized, a temperature gradient is applied across two contacting beams and the temperature drop at the interface is inferred from the temperature profiles of the rods that are measured at discrete points. During data analysis, thermal conductivity of the beams is typically taken to be an average value over the temperature range imposed during the experiment. Our generalized theory is presented and accounts for temperature-dependent changes in thermal conductivity. The procedure presented enables accurate measurement of TCR for contacting materials whose thermalmore » conductivity is any arbitrary function of temperature. For example, it is shown that the standard technique yields TCR values that are about 15% below the actual value for two specific examples of copper and silicon contacts. Conversely, the generalized technique predicts TCR values that are within 1% of the actual value. The method is exact when thermal conductivity is known exactly and no other errors are introduced to the system.« less

  6. Surface studies on aluminized and thermally oxidized superalloy 690 substrates interacted with simulated nuclear waste and sodium borosilicate melt

    SciTech Connect

    Yusufali, C. Sengupta, P.; Dutta, R. S.; Dey, G. K.; Kshirsagar, R. J.; Mishra, R. K.; Kaushik, C. P.

    2014-04-24

    Aluminized and thermally oxidized Ni-Cr-Fe based superalloy 690 substrates with Al{sub 2}O{sub 3} layer on top have been exposed in nitrate based environment (simulated high level nuclear liquid waste) at 373 K for 216 hours and sodium borosilicate melt at 1248 K for 192 hours. The surfaces of exposed samples have been characterized by using Electron probe micro-analyzer (EPMA). Elemental X-ray mapping on coated specimen that exposed in simulated nuclear waste solution revealed that the surface is enriched with Ni, Cr and Al. X-ray mapping on surface of the specimen that interacted with sodium borosilicate melt indicated that the surface is composed of Al, Fe, Ni and Cr.

  7. Comparison of the properties of Pb thin films deposited on Nb substrate using thermal evaporation and pulsed laser deposition techniques

    NASA Astrophysics Data System (ADS)

    Perrone, A.; Gontad, F.; Lorusso, A.; Di Giulio, M.; Broitman, E.; Ferrario, M.

    2013-11-01

    Pb thin films were prepared at room temperature and in high vacuum by thermal evaporation and pulsed laser deposition techniques. Films deposited by both the techniques were investigated by scanning electron microscopy to determine their surface topology. The structure of the films was studied by X-ray diffraction in θ-2θ geometry. The photoelectron performances in terms of quantum efficiency were deduced by a high vacuum photodiode cell before and after laser cleaning procedures. Relatively high quantum efficiency (>10-5) was obtained for all the deposited films, comparable to that of corresponding bulk. Finally, film to substrate adhesion was also evaluated using the Daimler-Benz Rockwell-C adhesion test method. Weak and strong points of these two competitive techniques are illustrated and discussed.

  8. A study for the detection of ionizing particles with phototransistors on thick high-resistivity silicon substrates

    NASA Astrophysics Data System (ADS)

    Batignani, G.; Angelini, C.; Bisogni, M. G.; Boscardin, M.; Bettarini, S.; Bondioli, M.; Bosisio, L.; Bucci, F.; Calderini, G.; Carpinelli, M.; Ciacchi, M.; Dalla Betta, G. F.; Dittongo, S.; Forti, F.; Giorgi, M. A.; Gregori, P.; Han, D. J.; Manfredi, P. F.; Manghisoni, M.; Marchiori, G.; Neri, N.; Novelli, M.; Paoloni, E.; Piemonte, C.; Rachevskaia, I.; Rama, M.; Ratti, L.; Re, V.; Rizzo, G.; Ronchin, S.; Rosso, V.; Simi, G.; Speziali, V.; Stefanini, A.; Zorzi, N.

    2004-09-01

    We report on bipolar NPN phototransistors fabricated at ITC-IRST on thick high-resistivity silicon substrates. The phototransistor emitter is composed of a phosphorus n+ implant, the base is a diffused high-energy boron implant, and the collector is the 600-800 μm thick silicon bulk, contacted on the backplane. We have studied the current amplification for two different doping profiles of the emitter, obtaining values of β ranging from 60 to 3000. For various emitter and base configurations, we measured the static device characteristics and extracted the leakage currents and the base resistance, verifying the fundamental relationship between them and the total base capacitances. The use of such phototransistors to detect ionizing particles is exploited and discussed.

  9. The effects of precursor concentration and thermal annealing on the growth of zinc oxide nanostructures grown on silicon substrate

    NASA Astrophysics Data System (ADS)

    Paculba, H. M. D.; Alguno, A. C.; Vequizo, R. M.

    2015-06-01

    This study focuses on the growth of Zinc Oxide (ZnO) nanostructures on SiO2/Si(100) substrate via chemical bath deposition (CBD) with varying NH4OH concentration and annealing temperature. The grown ZnOnanostructures were characterized via SEM-EDS for the surface morphology and elemental composition and UV-Vis spectroscopy for the reflectance measurement. Increasing the concentration of NH4OH produced denser ZnOnanostructures composed of rods having smaller diameter. It is believed that at higher concentration of NH4OH, more Zn(OH)2 seed will act as nucleation site for ZnOformation which suggests higher probability of ZnOgrowth. Thermal annealing increased the average diameter of ZnOnanorods. Annealing provided enough energy for unstable atoms to rearrange into a more suitable position. This would result to larger rods that have been formed in expense of the smaller rods. Furthermore, it is confirmed in the UV-Vis spectroscopy results that ZnOnanostructures were successfully grown on SiO2/Si(100) substrate. This successful growth of ZnOnanostructures is a promising material for solar cell technology.

  10. Thermal boundary resistance in Si/Ge interfaces determined by approach-to-equilibrium simulations

    NASA Astrophysics Data System (ADS)

    Puligheddu, Marcello; Hahn, Konstanze; Melis, Claudio; Colombo, Luciano

    2015-03-01

    Nanostructured materials hold great promises as efficient thermoelectrics. In such materials, the propagation of phonons is hindered by the internal interfaces (grain boundaries), leading to a reduced overall thermal conductivity and, therefore, to a larger figure of merit. Any further improvement in this field does, however, require a better fundamental understanding of the specific interface effects on thermal transport. In the present work we use approach-to-equilibrium molecular dynamics simulations (AEMD) to investigate the interfacial thermal resistance (ITR) of Si/Ge interfaces, occurring in very promising nanostructured SiGe alloys. We discuss how ITR depends on the thickness of the interface layer, as well as on its composition. Furthermore, the effect of the heat flux direction has been investigated at ambient temperature showing lower ITR for thermal transport from Si to Ge than vice versa. This feature is discussed in connection to possible rectification effects. Present address: The Institute for Molecular Engineering, University of Chicago.

  11. Thermal conductivity in large residual resistance ratio MgB2 wire

    NASA Astrophysics Data System (ADS)

    Pope, A. L.; Tritt, T. M.; Canfield, P. C.; Bud'ko, S. L.; Liebenberg, D. H.

    2003-05-01

    We measured the thermal conductivity in MgB2 wires, with Tc=39.5 K, in both the superconducting and normal state regimes between 10-70 K. As expected, the thermal conductivity is increased for this sample, which has a residual resistance ratio (RRR) of about 32, as compared with earlier measurements on bulk samples with much lower RRR values. Over the measured temperature range, this more metallic material exhibits a temperature dependence of the thermal conductivity in the superconducting state that is different from that in previous reports and can be ascribed primarily to defect scattering. Unusual results are presented for the magnetic field dependence of the thermal conductivity around Tc for fields up to 9 T.

  12. Temperature coefficient of resistance and thermal conductivity of Vanadium oxide 'Big Mac' sandwich structure

    NASA Astrophysics Data System (ADS)

    Abdel-Rahman, M.; Ilahi, S.; Zia, M. F.; Alduraibi, M.; Debbar, N.; Yacoubi, N.; Ilahi, B.

    2015-07-01

    In this paper, we synthesize and characterize a thin film thermometer structure for infrared microbolometers. The structure is composed of alternating multilayers of Vanadium pentoxide (V2O5), 25 nm, and Vanadium (V), 5 nm, thin films deposited by rf magnetron and dc magnetron sputtering respectively and annealed for 20, 30 and 40 min at 300 °C in Nitrogen (N2) atmosphere. The best achieved temperature coefficient of resistance (TCR) was found to be -2.57%/K for 40 min annealed samples. Moreover, we apply, for the first time, the photo-thermal deflection (PTD) technique for measuring the thermal conductivity of the synthesized thin films. The thermal conductivity of the developed thin films reveals an increase in thermal conductivity from 2 W/m K to 5.8 W/m K for as grown and 40 min annealed samples respectively.

  13. Fabrication of Fe nanowires on yittrium-stabilized zirconia single crystal substrates by thermal CVD methods

    SciTech Connect

    Kawahito, A.; Yanase, T.; Endo, T.; Nagahama, T.; Shimada, T.

    2015-05-07

    Magnetic nanowires (NWs) are promising as material for use in spintronics and as the precursor of permanent magnets because they have unique properties due to their high aspect ratio. The growth of magnetic Fe whiskers was reported in the 1960s, but the diameter was not on a nanoscale level and the growth mechanism was not fully elucidated. In the present paper, we report the almost vertical growth of Fe NWs on a single crystal yttrium-stabilized zirconia (Y{sub 0.15}Zr{sub 0.85}O{sub 2}) by a thermal CVD method. The NWs show a characteristic taper part on the bottom growing from a trigonal pyramidal nucleus. The taper angle and length can be controlled by changing the growth condition in two steps, which will lead to obtaining uniformly distributed thin Fe NWs for applications.

  14. Substrate Inhibition of VanA by d-Alanine Reduces Vancomycin Resistance in a VanX-Dependent Manner

    PubMed Central

    van der Aart, Lizah T.; Lemmens, Nicole; van Wamel, Willem J.

    2016-01-01

    The increasing resistance of clinical pathogens against the glycopeptide antibiotic vancomycin, a last-resort drug against infections with Gram-positive pathogens, is a major problem in the nosocomial environment. Vancomycin inhibits peptidoglycan synthesis by binding to the d-Ala–d-Ala terminal dipeptide moiety of the cell wall precursor lipid II. Plasmid-transferable resistance is conferred by modification of the terminal dipeptide into the vancomycin-insensitive variant d-Ala–d-Lac, which is produced by VanA. Here we show that exogenous d-Ala competes with d-Lac as a substrate for VanA, increasing the ratio of wild-type to mutant dipeptide, an effect that was augmented by several orders of magnitude in the absence of the d-Ala–d-Ala peptidase VanX. Liquid chromatography-mass spectrometry (LC-MS) analysis showed that high concentrations of d-Ala led to the production of a significant amount of wild-type cell wall precursors, while vanX-null mutants produced primarily wild-type precursors. This enhanced the efficacy of vancomycin in the vancomycin-resistant model organism Streptomyces coelicolor, and the susceptibility of vancomycin-resistant clinical isolates of Enterococcus faecium (VRE) increased by up to 100-fold. The enhanced vancomycin sensitivity of S. coelicolor cells correlated directly to increased binding of the antibiotic to the cell wall. Our work offers new perspectives for the treatment of diseases associated with vancomycin-resistant pathogens and for the development of drugs that target vancomycin resistance. PMID:27270282

  15. Finite-size effects on molecular dynamics interfacial thermal-resistance predictions

    NASA Astrophysics Data System (ADS)

    Liang, Zhi; Keblinski, Pawel

    2014-08-01

    Using molecular dynamics simulations, we study the role of finite size effects on the determination of interfacial thermal resistance between two solids characterized by high phonon mean free paths. In particular, we will show that a direct, heat source-sink method leads to strong size effect, associated with ballistic phonon transport to and from, and specular reflections at the simulation domain boundary. Lack of proper account for these effects can lead to incorrect predictions about the role of interfacial bonding and structure on interfacial thermal resistance. We also show that the finite size effect can be dramatically reduced by introduction of rough external boundaries leading to diffuse phonon scattering, as explicitly demonstrated by phonon wave-packet simulations. Finally, we demonstrate that when careful considerations are given to the effects associated with the finite heat capacity of the simulation domains and phonon scattering from the external surfaces, a size-independent interfacial resistance can be properly extracted from the time integral of the correlation function of heat power across the interface. Our work demonstrates that reliable and consistent values of the interfacial thermal resistance can be obtained by equilibrium and nonequilibrium methods with a relatively small computational cost.

  16. Facile and scalable preparation of highly wear-resistance superhydrophobic surface on wood substrates using silica nanoparticles modified by VTES

    NASA Astrophysics Data System (ADS)

    Jia, Shanshan; Liu, Ming; Wu, Yiqiang; Luo, Sha; Qing, Yan; Chen, Haibo

    2016-11-01

    In this study, an efficient, facile method has been developed for fabricating superhydrophobic surfaces on wood substrates using silica nanoparticles modified by VTES. The as-prepared superhydrophobic wood surface had a water contact angle of 154° and water slide angle close to 0°. Simultaneously, this superhydrophobic wood showed highly durable and robust wear resistance when having undergone a long period of sandpaper abrasion or being scratched by a knife. Even under extreme conditions of boiling water, the superhydrophobicity of the as-prepared wood composite was preserved. Characterizations by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy showed that a typical and tough hierarchical micro/nanostructure was created on the wood substrate and vinyltriethoxysilane contributed to preventing the agglomeration of silica nanoparticles and serving as low-surface-free-energy substances. This superhydrophobic wood was easy to fabricate, mechanically resistant and exhibited long-term stability. Therefore, it is considered to be of significant importance in the industrial production of functional wood, especially for outdoor applications.

  17. Facile fabrication of superhydrophobic surface with excellent mechanical abrasion and corrosion resistance on copper substrate by a novel method.

    PubMed

    Su, Fenghua; Yao, Kai

    2014-06-11

    A novel method for controllable fabrication of a superhydrophobic surface with a water contact angle of 162 ± 1° and a sliding angle of 3 ± 0.5° on copper substrate is reported in this Research Article. The facile and low-cost fabrication process is composed from the electrodeposition in traditional Watts bath and the heat-treatment in the presence of (heptadecafluoro-1,1,2,2-tetradecyl) triethoxysilane (AC-FAS). The superhydrophobicity of the fabricated surface results from its pine-cone-like hierarchical micro-nanostructure and the assembly of low-surface-energy fluorinated components on it. The superhydrophobic surface exhibits high microhardness and excellent mechanical abrasion resistance because it maintains superhydrophobicity after mechanical abrasion against 800 grit SiC sandpaper for 1.0 m at the applied pressure of 4.80 kPa. Moreover, the superhydrophobic surface has good chemical stability in both acidic and alkaline environments. The potentiodynamic polarization and electrochemical impedance spectroscopy test shows that the as-prepared superhydrophobic surface has excellent corrosion resistance that can provide effective protection for the bare Cu substrate. In addition, the as-prepared superhydrophobic surface has self-cleaning ability. It is believed that the facile and low-cost method offer an effective strategy and promising industrial applications for fabricating superhydrophobic surfaces on various metallic materials.

  18. Process for the deposition of high temperature stress and oxidation resistant coatings on silicon-based substrates

    DOEpatents

    Sarin, V.K.

    1991-07-30

    A process is disclosed for depositing a high temperature stress and oxidation resistant coating on a silicon nitride- or silicon carbide-based substrate body. A gas mixture is passed over the substrate at about 900--1500 C and about 1 torr to about ambient pressure. The gas mixture includes one or more halide vapors with other suitable reactant gases. The partial pressure ratios, flow rates, and process times are sufficient to deposit a continuous, fully dense, adherent coating. The halide and other reactant gases are gradually varied during deposition so that the coating is a graded coating of at least two layers. Each layer is a graded layer changing in composition from the material over which it is deposited to the material of the layer and further to the material, if any, deposited thereon, so that no clearly defined compositional interfaces exist. The gases and their partial pressures are varied according to a predetermined time schedule and the halide and other reactant gases are selected so that the layers include (a) an adherent, continuous intermediate layer about 0.5-20 microns thick of an aluminum nitride or an aluminum oxynitride material, over and chemically bonded to the substrate body, and (b) an adherent, continuous first outer layer about 0.5-900 microns thick including an oxide of aluminum or zirconium over and chemically bonded to the intermediate layer.

  19. Process for the deposition of high temperature stress and oxidation resistant coatings on silicon-based substrates

    DOEpatents

    Sarin, Vinod K.

    1991-01-01

    A process for depositing a high temperature stress and oxidation resistant coating on a silicon nitride- or silicon carbide-based substrate body. A gas mixture is passed over the substrate at about 900.degree.-1500.degree. C. and about 1 torr to about ambient pressure. The gas mixture includes one or more halide vapors with other suitable reactant gases. The partial pressure ratios, flow rates, and process times are sufficient to deposit a continuous, fully dense, adherent coating. The halide and other reactant gases are gradually varied during deposition so that the coating is a graded coating of at least two layers. Each layer is a graded layer changing in composition from the material over which it is deposited to the material of the layer and further to the material, if any, deposited thereon, so that no clearly defined compositional interfaces exist. The gases and their partial pressures are varied according to a predetermined time schedule and the halide and other reactant gases are selected so that the layers include (a) an adherent, continuous intermediate layer about 0.5-20 microns thick of an aluminum nitride or an aluminum oxynitride material, over and chemically bonded to the substrate body, and (b) an adherent, continuous first outer layer about 0.5-900 microns thick including an oxide of aluminum or zirconium over and chemically bonded to the intermediate layer.

  20. The Vickers indentation technique used to evaluate thermal shock resistance of brittle materials

    SciTech Connect

    Tancret, F.; Osterstock, F.

    1997-08-15

    The establishment of transient thermal stresses during quenching brittle materials involves a number of parameters, such as Young`s modulus E, Poisson`s ratio v, coefficient of thermal expansion {alpha}, thermal conductivity of the material k, the size and shape of the sample, the quenching temperature difference {Delta}T, and the coefficient of heat transfer in the quenching medium h. The damage resulting from a critical thermal shock is governed by the toughness, the statistical distribution of initial surface flaws and thus by the rupture stress. It is shown here that, additionally to the preliminary determination of the material`s toughness and the quantification of the maximum value of the thermal transient stress, the combination of toughness and these thermal stresses yields descriptions of a new thermal shock resistance parameter for temperature differences {Delta}T lower than the critical one {Delta}{Tc}. The derivations will be verified on various microstructures of high-temperature superconducting ceramics, YBaCuO, and on alumina.

  1. Thermal barrier coatings for thermal insulation and corrosion resistance in industrial gas turbine engines

    NASA Technical Reports Server (NTRS)

    Vogan, J. W.; Hsu, L.; Stetson, A. R.

    1981-01-01

    Four thermal barrier coatings were subjected to a 500-hour gas turbine engine test. The coatings were two yttria stabilized zirconias, calcium ortho silicate and calcium meta titanate. The calcium silicate coating exhibited significant spalling. Yttria stabilized zirconia and calcium titanate coatings showed little degradation except in blade leading edge areas. Post-test examination showed variations in the coating due to manual application techniques. Improved process control is required if engineering quality coatings are to be developed. The results indicate that some leading edge loss of the coating can be expected near the tip.

  2. [The enhancement of human thermal resistance by the single use of bemitil and fenibut].

    PubMed

    Makarov, V I; Tiurenkov, I N; Klauchek, S V; Nalivaĭko, I Iu; Antipova, A Iu

    1997-01-01

    The authors studied the effect of single intake of bymetil (0.5 g) and phenibut (0.25 g) on the thermal state, gas-energy exchange, blood oxygenation, working capacity, and the subjective status of man in intensive physical exertion in isolating means of individual protection. The drugs under study increased thermal resistance, promoted normal supply of the organism with oxygen, and provided the maintenance of man's high working capacity under conditions which lead to his overheating. The best protective effects was produced in this case with phenibut.

  3. Novel Resistance Measurement Method: Analysis of Accuracy and Thermal Dependence with Applications in Fiber Materials.

    PubMed

    Casans, Silvia; Rosado-Muñoz, Alfredo; Iakymchuk, Taras

    2016-12-14

    Material resistance is important since different physicochemical properties can be extracted from it. This work describes a novel resistance measurement method valid for a wide range of resistance values up to 100 GΩ at a low powered, small sized, digitally controlled and wireless communicated device. The analog and digital circuits of the design are described, analysing the main error sources affecting the accuracy. Accuracy and extended uncertainty are obtained for a pattern decade box, showing a maximum of 1 % accuracy for temperatures below 30 ∘ C in the range from 1 MΩ to 100 GΩ. Thermal analysis showed stability up to 50 ∘ C for values below 10 GΩ and systematic deviations for higher values. Power supply V i applied to the measurement probes is also analysed, showing no differences in case of the pattern decade box, except for resistance values above 10 GΩ and temperatures above 35 ∘ C. To evaluate the circuit behaviour under fiber materials, an 11-day drying process in timber from four species (Oregon pine-Pseudotsuga menziesii, cedar-Cedrus atlantica, ash-Fraxinus excelsior, chestnut-Castanea sativa) was monitored. Results show that the circuit, as expected, provides different resistance values (they need individual conversion curves) for different species and the same ambient conditions. Additionally, it was found that, contrary to the decade box analysis, V i affects the resistance value due to material properties. In summary, the proposed circuit is able to accurately measure material resistance that can be further related to material properties.

  4. Novel Resistance Measurement Method: Analysis of Accuracy and Thermal Dependence with Applications in Fiber Materials

    PubMed Central

    Casans, Silvia; Rosado-Muñoz, Alfredo; Iakymchuk, Taras

    2016-01-01

    Material resistance is important since different physicochemical properties can be extracted from it. This work describes a novel resistance measurement method valid for a wide range of resistance values up to 100 GΩ at a low powered, small sized, digitally controlled and wireless communicated device. The analog and digital circuits of the design are described, analysing the main error sources affecting the accuracy. Accuracy and extended uncertainty are obtained for a pattern decade box, showing a maximum of 1% accuracy for temperatures below 30 ∘C in the range from 1 MΩ to 100 GΩ. Thermal analysis showed stability up to 50 ∘C for values below 10 GΩ and systematic deviations for higher values. Power supply Vi applied to the measurement probes is also analysed, showing no differences in case of the pattern decade box, except for resistance values above 10 GΩ and temperatures above 35 ∘C. To evaluate the circuit behaviour under fiber materials, an 11-day drying process in timber from four species (Oregon pine-Pseudotsuga menziesii, cedar-Cedrus atlantica, ash-Fraxinus excelsior, chestnut-Castanea sativa) was monitored. Results show that the circuit, as expected, provides different resistance values (they need individual conversion curves) for different species and the same ambient conditions. Additionally, it was found that, contrary to the decade box analysis, Vi affects the resistance value due to material properties. In summary, the proposed circuit is able to accurately measure material resistance that can be further related to material properties. PMID:27983652

  5. The Equivalent Thermal Resistance of Tile Roofs with and without Batten Systems

    SciTech Connect

    Miller, William A

    2013-01-01

    Clay and concrete tile roofs were installed on a fully instrumented attic test facility operating in East Tennessee s climate. Roof, attic and deck temperatures and heat flows were recorded for each of the tile roofs and also on an adjacent attic cavity covered with a conventionally pigmented and direct-nailed asphalt shingle roof. The data were used to benchmark a computer tool for simulation of roofs and attics and the tool used to develop an approach for computing an equivalent seasonal R-value for sub-tile venting. The approach computed equal heat fluxes through the ceilings of roofs having different combinations of surface radiation properties and or building constructions. A direct nailed shingle roof served as a control for estimating the equivalent thermal resistance of the air space. Simulations were benchmarked to data in the ASHRAE Fundamentals for the thermal resistance of inclined and closed air spaces.

  6. Effect of oxide films on the thermal resistance between contacting zirconium alloys

    SciTech Connect

    Schankula, M.H.; Patterson, D.W.; Yovanovich, M.M.

    1982-01-01

    The resistance to heat flow at interfaces formed between contacting solids plays a key role in nuclear reactor systems. In many instances, these contacts occur at elevated temperatures and in oxidizing or corrosive environments. These environments normally lead to increased thermal resistance (decreased conductance), which recent theoretical predictions have related to (i) thermal conductivity of the oxide layer, (ii) layer thickness, (iii) effective hardness of the surface, and (iv) surface microtopography. Experiments with oxidized zirconium specimens have confirmed these predictions and revealed that the contact conductance in vacuum increases as the ratio of layer thickness to contact-spot radius increases. This study is of particular importance in our efforts to predict the rate of heat flow from an overheated CANDU pressure tube when it comes into contact with the surrounding calandria tube during a postulated loss-of-coolant accident. 12 references, 6 figures, 3 tables.

  7. Variations of Strength, Resistivity and Thermal Parameters of Clay after High Temperature Treatment

    NASA Astrophysics Data System (ADS)

    Sun, Qiang; Zhang, Weiqiang; Zhang, Yuliang; Yang, Lining

    2016-12-01

    This paper reports the variations of strength, resistivity and thermal parameters of clay after high-temperature heating. Experiments were carried out to test the physical properties of clay heated at temperatures ranging from room temperature to 800°C in a furnace. The experiment results show that below 400°C the uniaxial compressive strength and resistivity change very little. However, above 400°C, both increase rapidly. At a temperature under 400°C, the thermal conductivity and specific heat capacity decrease significantly. The thermogravimetric analysis (TG) and differential scanning calorimeter (DSC) test indicate that a series of changes occur in kaolinite at temperatures from 400 to 600°C, which is considered the primary cause of the variation of physical and mechanical properties of clay under high temperatures.

  8. Direct Deposition of Low Resistance Thermally Stable Ohmic Contacts to n-SiC

    DTIC Science & Technology

    2001-06-01

    Direct Deposition of Low Resistance Thermally Stable Ohmic Contacts to n-SiC by M. W. Cole, P. C. Joshi, M. H . Ervin, J. D. Demaree, M...SiC M. W. Cole, P. C. Joshi, J. D. Demaree, C. W. Hubbard, and J. K. Hirvonen Weapons and Materials Research Directorate, ARL M. H . Ervin and...device operation. ii Acknowledgments The authors would like to acknowledge H . Kim, A. Pique, D. B. Chrisey, C. K. Richardson, and M. H . Wisnioski

  9. Silicon nitride: A ceramic material with outstanding resistance to thermal shock and corrosion

    NASA Technical Reports Server (NTRS)

    Huebner, K. H.; Saure, F.

    1983-01-01

    The known physical, mechanical and chemical properties of reaction-sintered silicon nitride are summarized. This material deserves interest especially because of its unusually good resistance to thermal shock and corrosion at high temperatures. Two types are distinguished: reaction-sintered (porous) and hot-pressed (dense) Si3N4. Only the reaction-sintered material which is being produced today in large scale as crucibles, pipes, nozzles and tiles is considered.

  10. Experimental DC extraction of the thermal resistance of bipolar transistors taking into account the Early effect

    NASA Astrophysics Data System (ADS)

    d'Alessandro, Vincenzo

    2017-01-01

    This paper presents three methods to experimentally extract the thermal resistance of bipolar transistors taking into account the Early effect. The approaches are improved variants of recently-proposed techniques relying on common-base DC measurements. The accuracy is numerically verified by making use of a compact model calibrated on I-V characteristics of state-of-the-art SOG BJTs and SiGe:C HBTs.

  11. Nondestructive measurement of thermal contact resistance for the power vertical double-diffused metal-oxide-semiconductor

    NASA Astrophysics Data System (ADS)

    Li, Rui; Guo, Chun-Sheng; Feng, Shi-Wei; Shi, Lei; Zhu, Hui; Wang, Lin

    2015-07-01

    To obtain thermal contact resistance (TCR) between the vertical double-diffused metal-oxide-semiconductor (VDMOS) and the heat sink, we derived the relationship between the total thermal resistance and the contact force imposed on the VDMOS. The total thermal resistance from the chip to the heat sink is measured under different contact forces, and the TCR can be extracted nondestructively from the derived relationship. Finally, the experimental results are compared with the simulation results. Project supported by the National Natural Science Foundation of China (Grant No. 61204081).

  12. Crystallinity and thermal resistance of microcrystalline cellulose prepared from manau rattan (Calamusmanan)

    NASA Astrophysics Data System (ADS)

    Rizkiansyah, Raden Reza; Mardiyati, Steven, Suratman, R.

    2016-04-01

    The objective of this study was to prepare microcrystalline cellulose from Manau rattan (Calamusmanan) and to investigate the influence of concentration of sulfuric acid and hydrolysis time on crystallinity and thermal resistance of the microcrystalline cellulose (MCC). In this research, MCC was extracted through two stages, which is alkalization and acid hydrolysis. Alkalization was prepared by soaking manau rattan powder into sodium hydroxide (NaOH) 17.5wt% at 100°C for 8 hours. Acid hydrolysis was prepared by using sulfuric acid with concentration 0.1 M; 0.3 M; and 0.5 M for 4, 6, 8 and 10 hours. Crystallinity of MCC was measured by XRD, and thermal resistance was characterized by TGA. MCC was successfully extracted from manau rattan. The highest crystallinity of MCC obtained was 72.42% which prepared by acid hydrolysis with concentration 0.5 M for 10 hours. MCC prepared by acid hydrolysis with concentration 0.5 M for 10 hours not only resulted the highest crystallinity but also the best thermal resistance.

  13. Characterization of GaN nanowires grown on PSi, PZnO and PGaN on Si (111) substrates by thermal evaporation

    SciTech Connect

    Shekari, Leila; Hassan, Haslan Abu; Thahab, Sabah M.; Hassan, Zainuriah

    2012-06-20

    In this research, we used an easy and inexpensive method to synthesize highly crystalline GaN nanowires (NWs); on different substrates such as porous silicon (PSi), porous zinc oxide (PZnO) and porous gallium nitride (PGaN) on Si (111) wafer by thermal evaporation using commercial GaN powder without any catalyst. Micro structural studies by scanning electron microscopy and transmission electron microscope measurements reveal the role of different substrates in the morphology, nucleation and alignment of the GaN nanowires. The degree of alignment of the synthesized nanowires does not depend on the lattice mismatch between wires and their substrates. Further structural and optical characterizations were performed using high resolution X-ray diffraction and energy-dispersive X-ray spectroscopy. Results indicate that the nanowires are of single-crystal hexagonal GaN. The quality and density of grown GaN nanowires for different substrates are highly dependent on the lattice mismatch between the nanowires and their substrates and also on the size of the porosity of the substrates. Nanowires grown on PGaN have the best quality and highest density as compared to nanowires on other substrates. By using three kinds of porous substrates, we are able to study the increase in the alignment and density of the nanowires.

  14. A quasi-physical model for predicting the thermal insulation and moisture vapour resistance of clothing.

    PubMed

    Qian, Xiaoming; Fan, Jintu

    2009-07-01

    Based on the improved understanding of the effects of wind and walking motion on the thermal insulation and moisture vapour resistance of clothing induced by air ventilation in the clothing system, a new model has been derived based on fundamental mechanisms of heat and mass transfer, which include conduction, diffusion, radiation and natural convection, wind penetration and air ventilation. The model predicts thermal insulation of clothing under body movement and windy conditions from the thermal insulation of clothing measured when the person is standing in the still air. The effects of clothing characteristics such as fabric air permeability, garment style, garment fitting and construction have been considered in the model through the key prediction parameters. With the new model, an improved prediction accuracy is achieved with a percentage of fit being as high as 0.96.

  15. Effect of Thermal Oxidation on Corrosion Resistance of Commercially Pure Titanium in Acid Medium

    NASA Astrophysics Data System (ADS)

    Jamesh, M.; Kumar, Satendra; Sankara Narayanan, T. S. N.

    2012-06-01

    This article addresses the characteristics of commercially pure titanium (CP-Ti) subjected to thermal oxidation in air at 650 °C for 48 h and its corrosion behavior in 0.1 and 4 M HCl and HNO3 mediums. Thermal oxidation of CP-Ti leads to the formation of thick oxide scales (~20 μm) throughout its surface without any spallation. The oxide layer consists of rutile- and oxygen-diffused titanium as predominant phases with a hardness of 679 ± 43 HV1.96. Electrochemical studies reveal that the thermally oxidized CP-Ti offers a better corrosion resistance than its untreated counterpart in both HCl and HNO3 mediums. The uniform surface coverage and compactness of the oxide layer provide an effective barrier toward corrosion of CP-Ti. The study concludes that thermal oxidation is an effective approach to engineer the surface of CP-Ti so as to increase its corrosion resistance in HCl and HNO3 mediums.

  16. Corrosion resistance of stainless steels during thermal cycling in alkali nitrate molten salts.

    SciTech Connect

    Bradshaw, Robert W.; Goods, Steven Howard

    2001-09-01

    The corrosion behavior of three austenitic stainless steels was evaluated during thermal cycling in molten salt mixtures consisting of NaNO{sub 3} and KNO{sub 3}. Corrosion tests were conducted with Types 316, 316L and 304 stainless steels for more than 4000 hours and 500 thermal cycles at a maximum temperature of 565 C. Corrosion rates were determined by chemically descaling coupons. Metal losses ranged from 5 to 16 microns and thermal cycling resulted in moderately higher corrosion rates compared to isothermal conditions. Type 316 SS was somewhat more corrosion resistant than Type 304 SS in these tests. The effect of carbon content on corrosion resistance was small, as 316L SS corroded only slightly slower than 316 SS. The corrosion rates increased as the dissolved chloride content of the molten salt mixtures increased. Chloride concentrations approximating 1 wt.%, coupled with thermal cycling, resulted in linear weight loss kinetics, rather than parabolic kinetics, which described corrosion rates for all other conditions. Optical microscopy and electron microprobe analysis revealed that the corrosion products consisted of iron-chromium spinel, magnetite, and sodium ferrite, organized as separate layers. Microanalysis of the elemental composition of the corrosion products further demonstrated that the chromium content of the iron-chromium spinel layer was relatively high for conditions in which parabolic kinetics were observed. However, linear kinetics were observed when the spinel layer contained relatively little chromium.

  17. High thermal shock resistance of the hot rolled and swaged bulk W-ZrC alloys

    NASA Astrophysics Data System (ADS)

    Xie, Z. M.; Liu, R.; Miao, S.; Yang, X. D.; Zhang, T.; Fang, Q. F.; Wang, X. P.; Liu, C. S.; Lian, Y. Y.; Liu, X.; Luo, G. N.

    2016-02-01

    The thermal shock (single shot) resistance and mechanical properties of the W-0.5wt% ZrC (WZC) alloys manufactured by ordinary sintering followed by swaging or rolling process were investigated. No cracks or surface melting were detected on the surface of the rolled WZC alloy plates after thermal shock at a power density of 0.66 GW/m2 for 5 ms, while primary intergranular cracks appear on the surface of the swaged WZC samples after thermal shock at a power density of 0.44 GW/m2 for 5 ms. Three point bending tests indicate that the rolled WZC alloy has a flexural strength of ˜2.4 GPa and a total strain of 1.8% at room temperature, which are 100% and 260% higher than those of the swaged WZC, respectively. The fracture energy density of the rolled WZC alloy is 3.23 × 107 J/m3, about 10 times higher than that of the swaged WZC (2.9 × 106 J/m3). The high thermal shock resistance of the rolled WZC alloys can be ascribed to their extraordinary ductility and plasticity.

  18. Phosphoproteomics Reveals HMGA1, a CK2 Substrate, as a Drug-Resistant Target in Non-Small Cell Lung Cancer

    PubMed Central

    Wang, Yi-Ting; Pan, Szu-Hua; Tsai, Chia-Feng; Kuo, Ting-Chun; Hsu, Yuan-Ling; Yen, Hsin-Yung; Choong, Wai-Kok; Wu, Hsin-Yi; Liao, Yen-Chen; Hong, Tse-Ming; Sung, Ting-Yi; Yang, Pan-Chyr; Chen, Yu-Ju

    2017-01-01

    Although EGFR tyrosine kinase inhibitors (TKIs) have demonstrated good efficacy in non-small-cell lung cancer (NSCLC) patients harboring EGFR mutations, most patients develop intrinsic and acquired resistance. We quantitatively profiled the phosphoproteome and proteome of drug-sensitive and drug-resistant NSCLC cells under gefitinib treatment. The construction of a dose-dependent responsive kinase-substrate network of 1548 phosphoproteins and 3834 proteins revealed CK2-centric modules as the dominant core network for the potential gefitinib resistance-associated proteins. CK2 knockdown decreased cell survival in gefitinib-resistant NSCLCs. Using motif analysis to identify the CK2 core sub-network, we verified that elevated phosphorylation level of a CK2 substrate, HMGA1 was a critical node contributing to EGFR-TKI resistance in NSCLC cell. Both HMGA1 knockdown or mutation of the CK2 phosphorylation site, S102, of HMGA1 reinforced the efficacy of gefitinib in resistant NSCLC cells through reactivation of the downstream signaling of EGFR. Our results delineate the TKI resistance-associated kinase-substrate network, suggesting a potential therapeutic strategy for overcoming TKI-induced resistance in NSCLC. PMID:28290473

  19. Bioindicator production with Bacillus atrophaeus' thermal-resistant spores cultivated by solid-state fermentation.

    PubMed

    Sella, Sandra Regina B R; Guizelini, Belquis P; Vandenberghe, Luciana P S; Medeiros, Adriane B P; Soccol, Carlos Ricardo

    2009-04-01

    Bacillus atrophaeus' spores are used in the preparation of bioindicators to monitor the dry heat, ethylene oxide, and plasma sterilization processes and in tests to assess sterilizing products. Earlier production methods involved culture in chemically defined medium to support sporulation with the disadvantage of requiring an extended period of time (14 days) besides high cost of substrates. The effect of cultivation conditions by solid-state fermentation (SSF) was investigated aiming at improving the cost-productivity relation. Initial SSF parameters such as the type of substrate were tested. Process optimization was carried out using factorial experimental designs and response surface methodology in which the influence of different variables--particle size, moisture content, incubation time, pH, inoculum size, calcium sources, and medium composition--was studied. The results have suggested that soybean molasses and sugarcane bagasse are potential substrate and support, respectively, contributing to a 5-day reduction in incubation time. Variables which presented significant effects and optimum values were mean particle size (1.0 mm), moisture content (93%), initial substrate pH (8.0), and water as a solution base. The high-yield spore production was about 3 logs higher than the control and no significant difference in dry heat resistance was observed.

  20. Robust superhydrophobic surface on Al substrate with durability, corrosion resistance and ice-phobicity

    NASA Astrophysics Data System (ADS)

    Wang, Guoyong; Liu, Shuai; Wei, Sufeng; Liu, Yan; Lian, Jianshe; Jiang, Qing

    2016-02-01

    Practical application of superhydrophobic surfaces is limited by the fragility of nanoscale asperities. Combining chemical etching and anodization, microscale pits and nanoscale pores, instead of the micro and nano protrusions on traditional superhydrophobic surfaces mimicking Lutos leaves, were fabricated on commercially pure aluminum surfaces. After modified by FDTS, the surfaces were superhydrophobic and self-cleaning. The ultrahigh hardness and electrochemical stability of Al2O3 coating endowed the surface excellent mechanical durability and good corrosion resistance. Because the method is scalable, it may find practical application on body panels of automobiles and aircrafts and so on.

  1. Robust superhydrophobic surface on Al substrate with durability, corrosion resistance and ice-phobicity

    PubMed Central

    Wang, Guoyong; Liu, Shuai; Wei, Sufeng; Liu, Yan; Lian, Jianshe; Jiang, Qing

    2016-01-01

    Practical application of superhydrophobic surfaces is limited by the fragility of nanoscale asperities. Combining chemical etching and anodization, microscale pits and nanoscale pores, instead of the micro and nano protrusions on traditional superhydrophobic surfaces mimicking Lutos leaves, were fabricated on commercially pure aluminum surfaces. After modified by FDTS, the surfaces were superhydrophobic and self-cleaning. The ultrahigh hardness and electrochemical stability of Al2O3 coating endowed the surface excellent mechanical durability and good corrosion resistance. Because the method is scalable, it may find practical application on body panels of automobiles and aircrafts and so on. PMID:26853810

  2. Robust superhydrophobic surface on Al substrate with durability, corrosion resistance and ice-phobicity.

    PubMed

    Wang, Guoyong; Liu, Shuai; Wei, Sufeng; Liu, Yan; Lian, Jianshe; Jiang, Qing

    2016-02-08

    Practical application of superhydrophobic surfaces is limited by the fragility of nanoscale asperities. Combining chemical etching and anodization, microscale pits and nanoscale pores, instead of the micro and nano protrusions on traditional superhydrophobic surfaces mimicking Lutos leaves, were fabricated on commercially pure aluminum surfaces. After modified by FDTS, the surfaces were superhydrophobic and self-cleaning. The ultrahigh hardness and electrochemical stability of Al2O3 coating endowed the surface excellent mechanical durability and good corrosion resistance. Because the method is scalable, it may find practical application on body panels of automobiles and aircrafts and so on.

  3. Microscopic Theory of Resistive Switching in Ordered Insulators: Electronic vs. Thermal Mechanism.

    PubMed

    Li, Jiajun; Aron, Camille; Kotliar, Gabriel; Han, Jong E

    2017-04-10

    We investigate the dramatic switch of resistance in ordered correlated insulators, when driven out of equilibrium by a strong voltage bias. Microscopic calculations on a driven-dissipative lattice of interacting electrons explain the main experimental features of resistive switching (RS), such as the hysteretic $I$-$V$ curves and the formation of hot conductive filaments. The energy-resolved electron distribution at the RS reveals the underlying nonequilibrium electronic mechanism, namely Landau-Zener tunneling, and also justifies a thermal description where the hot-electron temperature, estimated from the first moment of the distribution, matches the equilibrium phase transition temperature. We discuss the tangled relationship between filament growth and negative differential resistance, and the influence of crystallographic structure and disorder in the RS.

  4. LL-37-derived peptides eradicate multidrug-resistant Staphylococcus aureus from thermally wounded human skin equivalents.

    PubMed

    Haisma, Elisabeth M; de Breij, Anna; Chan, Heelam; van Dissel, Jaap T; Drijfhout, Jan W; Hiemstra, Pieter S; El Ghalbzouri, Abdoelwaheb; Nibbering, Peter H

    2014-08-01

    Burn wound infections are often difficult to treat due to the presence of multidrug-resistant bacterial strains and biofilms. Currently, mupirocin is used to eradicate methicillin-resistant Staphylococcus aureus (MRSA) from colonized persons; however, mupirocin resistance is also emerging. Since we consider antimicrobial peptides to be promising candidates for the development of novel anti-infective agents, we studied the antibacterial activities of a set of synthetic peptides against different strains of S. aureus, including mupirocin-resistant MRSA strains. The peptides were derived from P60.4Ac, a peptide based on the human cathelicidin LL-37. The results showed that peptide 10 (P10) was the only peptide more efficient than P60.4Ac, which is better than LL-37, in killing MRSA strain LUH14616. All three peptides displayed good antibiofilm activities. However, both P10 and P60.4Ac were more efficient than LL-37 in eliminating biofilm-associated bacteria. No toxic effects of these three peptides on human epidermal models were detected, as observed morphologically and by staining for mitochondrial activity. In addition, P60.4Ac and P10, but not LL-37, eradicated MRSA LUH14616 and the mupirocin-resistant MRSA strain LUH15051 from thermally wounded human skin equivalents (HSE). Interestingly, P60.4Ac and P10, but not mupirocin, eradicated LUH15051 from the HSEs. None of the peptides affected the excretion of interleukin 8 (IL-8) by thermally wounded HSEs upon MRSA exposure. In conclusion, the synthetic peptides P60.4Ac and P10 appear to be attractive candidates for the development of novel local therapies to treat patients with burn wounds infected with multidrug-resistant bacteria.

  5. Functional network alterations and their structural substrate in drug-resistant epilepsy

    PubMed Central

    Caciagli, Lorenzo; Bernhardt, Boris C.; Hong, Seok-Jun; Bernasconi, Andrea; Bernasconi, Neda

    2014-01-01

    The advent of MRI has revolutionized the evaluation and management of drug-resistant epilepsy by allowing the detection of the lesion associated with the region that gives rise to seizures. Recent evidence indicates marked chronic alterations in the functional organization of lesional tissue and large-scale cortico-subcortical networks. In this review, we focus on recent methodological developments in functional MRI (fMRI) analysis techniques and their application to the two most common drug-resistant focal epilepsies, i.e., temporal lobe epilepsy related to mesial temporal sclerosis and extra-temporal lobe epilepsy related to focal cortical dysplasia. We put particular emphasis on methodological developments in the analysis of task-free or “resting-state” fMRI to probe the integrity of intrinsic networks on a regional, inter-regional, and connectome-wide level. In temporal lobe epilepsy, these techniques have revealed disrupted connectivity of the ipsilateral mesiotemporal lobe, together with contralateral compensatory reorganization and striking reconfigurations of large-scale networks. In cortical dysplasia, initial observations indicate functional alterations in lesional, peri-lesional, and remote neocortical regions. While future research is needed to critically evaluate the reliability, sensitivity, and specificity, fMRI mapping promises to lend distinct biomarkers for diagnosis, presurgical planning, and outcome prediction. PMID:25565942

  6. Transparent, superhydrophobic, and wear-resistant coatings on glass and polymer substrates using SiO2, ZnO, and ITO nanoparticles.

    PubMed

    Ebert, Daniel; Bhushan, Bharat

    2012-08-07

    It is of significant interest to create surfaces that simultaneously exhibit high water contact angle, low contact angle hysteresis, and high transmission of visible light, as well as mechanical wear resistance for industrial applications. The fabrication of such surfaces has often involved complex or expensive processes, required techniques that were not suitable for a variety of substrates and particles, required surface post-treatment, or lacked wear resistance. A systematic study has been performed in which transparent superhydrophobic surfaces were created on glass, polycarbonate, and poly(methyl methacrylate) (PMMA) substrates using surface-functionalized SiO(2), ZnO, and indium tin oxide (ITO) nanoparticles. The contact angle, contact angle hysteresis, and optical transmittance were measured for samples using all particle-substrate combinations. To examine wear resistance, multiscale wear experiments were performed using an atomic force microscope (AFM) and a water jet apparatus.

  7. Excretion of fluorescent substrates of mammalian multidrug resistance-associated protein (MRP) in the Schistosoma mansoni excretory system.

    PubMed

    Sato, H; Kusel, J R; Thornhill, J

    2004-01-01

    The protonephridium of platyhelminths including Schistosoma mansoni plays a pivotal role in their survival by excretion of metabolic wastes as well as xenobiotics, and can be revealed in the living adult parasite by certain fluorescent compounds which are concentrated in excretory tubules and collecting ducts. To determine the presence of the multidrug resistance-associated protein (MRP) as a possible transporter in protonephridial epithelium, adult schistosomes were exposed to a fluorescent Ca2+ indicator, fluo-3 acetyloxymethyl ester, which is a potential substrate of mammalian MRP. Specific fluorescence related to fluo-3/Ca2+ chelate delineated the whole length of the protonephridial system. Simultaneously, a fluorescent substance was accumulated in the posterior part of collecting ducts and the excretory bladder. Similarly, when other fluorogenic substrates for mammalian MRP such as monoclorobimane, fluorescein diacetate, and 5(6)-carboxyfluorescein diacetate were applied to adult schistosomes, these fluorescent markers were observed in the excretory tubules through to the excretory bladder. The excretory system of mechanically-transformed schistosomula was not labelled with any of these 4 fluorescent markers. These findings suggest that the protonephridial epithelium of adult schistosomes, but not schistosomula, might express the homologue of the mammalian MRP transporting organic anionic conjugates with glutathione, glucuronate or sulphate as well as unconjugated amphiphilic organic anions.

  8. Liquid jet impingement cooling with diamond substrates for extremely high heat flux applications

    NASA Astrophysics Data System (ADS)

    Lienhard V, John H.; Khounsary, Ali M.

    1993-11-01

    This paper considers the potential of jet/diamond systems for removing localized high heat fluxes. Diamond substrates are compared to other candidate materials. Limits on usable thermal resistances and heat transfer rates are estimated.

  9. Cyclic Thermal Stress-Induced Degradation of Cu Metallization on Si3N4 Substrate at -40°C to 300°C

    NASA Astrophysics Data System (ADS)

    Lang, Fengqun; Yamaguchi, Hiroshi; Nakagawa, Hiroshi; Sato, Hiroshi

    2015-01-01

    The high-temperature reliability of active metal brazed copper (AMC) on Si3N4 ceramic substrates used for fabricating SiC high-temperature power modules was investigated under harsh environments. The AMC substrate underwent isothermal storage at 300°C for up to 3000 h and a thermal cycling test at -40°C to 300°C for up to 3000 cycles. During isothermal storage at 300°C, the AMC substrate exhibited high reliability, characterized by very little deformation of the copper (Cu) layer, low crack growth, and low oxidation rate of the Cu layer. Under thermal cycling conditions at -40°C to 300°C, no detachment of the Cu layer was observed even after the maximum 3000 cycles of the experiment. However, serious deformation of the Cu layer occurred and progressed as the number of thermal cycles increased, thus significantly roughening the surface of the Cu metallized layer. The cyclic thermal stress led to a significant increase in the crack growth and oxidation of the Cu layer. The maximum depth of the copper oxides reached up to 5/6 of the Cu thickness. The deformation of the Cu layer was the main cause of the decrease of the bond strength under thermal cycling conditions. The shear strength of the SiC chips bonded on the AMC substrate with a Au-12 wt.%Ge solder decreased from the original 83 MPa to 14 MPa after 3000 cycles. Therefore, the cyclic thermal stress destroyed the Cu oxides and enhanced the oxidation of the Cu layer.

  10. Structural and electronic properties of ZnO nanoparticles grown on p-Si and Al2O3 substrates by using spin coating and thermal treatment.

    PubMed

    No, Young Soo; Son, Dong Ick; Leem, Jae Hyeon; Kim, Su Youn; Oh, Do Hyun; Kim, Tae Whan

    2008-10-01

    ZnO nanoparticles were formed on p-Si and Al2O3 substrates by using spin coating and thermal treatment method. Scanning electron microscopy images and X-ray energy dispersive spectrometry profiles showed that ZnO nanoparticles were formed on p-Si and Al2O3 substrates. X-ray diffraction patterns showed that ZnO nanoparticles formed on the p-Si substrates had polycrystalline hexagonal wurtzite structures and that those formed on the Al2O3 substrates had a c-axis preferential orientation. X-ray photoelectron spectroscopy profiles showed that the O 1s and the Zn 2p peaks corresponding to the ZnO nanoparticles were observed.

  11. The Effects of Thermal Annealing on ZnO Thin Films Produced by Spin-Coating Method on Quartz Substrates

    NASA Astrophysics Data System (ADS)

    Ertek, Özlem; Okur, İbrahim

    2015-07-01

    In this work, zinc oxide (ZnO) thin films on quartz substrates were fabricated using the spin-coating method. Thermal annealings from to have been performed in increments and for two annealing durations (0.5 h and 8 h). X-ray diffraction (XRD) spectra, scanning electron microscopy micrographs, and UV-Vis absorption spectra of all the samples have been elucidated from mechanical and optical points of view. It has been observed that for all annealing temperatures, the crystal phase has been obtained. After annealings, a new crystal phase related to (willemite) has also been appeared in XRD spectra. This phase remained stable up to annealing together with the ZnO crystal phase. It has been found that the nano/micro rod diameters of the ZnO crystals reach to a maximum at the annealing for both annealing durations. For annealings, ZnO nanorods appeared to be split into two homogeneous nanorods of length of and of width of (350 nm) which was not the case for all other annealing temperatures. After annealings, ZnO nano/micro rods started to disappear and formed homogeneous ZnO thin films.

  12. Design of a Resistively Heated Thermal Hydraulic Simulator for Nuclear Rocket Reactor Cores

    NASA Technical Reports Server (NTRS)

    Litchford, Ron J.; Foote, John P.; Ramachandran, Narayanan; Wang, Ten-See; Anghaie, Samim

    2007-01-01

    A preliminary design study is presented for a non-nuclear test facility which uses ohmic heating to replicate the thermal hydraulic characteristics of solid core nuclear reactor fuel element passages. The basis for this testing capability is a recently commissioned nuclear thermal rocket environments simulator, which uses a high-power, multi-gas, wall-stabilized constricted arc-heater to produce high-temperature pressurized hydrogen flows representative of reactor core environments, excepting radiation effects. Initially, the baseline test fixture for this non-nuclear environments simulator was configured for long duration hot hydrogen exposure of small cylindrical material specimens as a low cost means of evaluating material compatibility. It became evident, however, that additional functionality enhancements were needed to permit a critical examination of thermal hydraulic effects in fuel element passages. Thus, a design configuration was conceived whereby a short tubular material specimen, representing a fuel element passage segment, is surrounded by a backside resistive tungsten heater element and mounted within a self-contained module that inserts directly into the baseline test fixture assembly. With this configuration, it becomes possible to create an inward directed radial thermal gradient within the tubular material specimen such that the wall-to-gas heat flux characteristics of a typical fuel element passage are effectively simulated. The results of a preliminary engineering study for this innovative concept are fully summarized, including high-fidelity multi-physics thermal hydraulic simulations and detailed design features.

  13. Thermal and Thermoelectric Transport in Highly Resistive Single Sb2Se3 Nanowires and Nanowire Bundles

    NASA Astrophysics Data System (ADS)

    Ko, Ting-Yu; Shellaiah, Muthaiah; Sun, Kien Wen

    2016-10-01

    In this study, we measured the thermal conductivity and Seebeck coefficient of single Sb2Se3 nanowires and nanowire bundles with a high resistivity (σ ~ 4.37 × 10‑4 S/m). Microdevices consisting of two adjacent suspended silicon nitride membranes were fabricated to measure the thermal transport properties of the nanowires in vacuum. Single Sb2Se3 nanowires with different diameters and nanowire bundles were carefully placed on the device to bridge the two membranes. The relationship of temperature difference on each heating/sensing suspension membranes with joule heating was accurately determined. A single Sb2Se3 nanowire with a diameter of ~ 680 nm was found to have a thermal conductivity (kNW) of 0.037 ± 0.002 W/m·K. The thermal conductivity of the nanowires is more than an order of magnitude lower than that of bulk materials (k ~ 0.36–1.9 W/m·K) and highly conductive (σ ~ 3 × 104 S/m) Sb2Se3 single nanowires (k ~ 1 W/m·K). The measured Seebeck coefficient with a positive value of ~ 661 μV/K is comparable to that of highly conductive Sb2Se3 single nanowires (~ 750 μV/K). The thermal transport between wires with different diameters and nanowire bundles was compared and discussed.

  14. Thermal and Thermoelectric Transport in Highly Resistive Single Sb2Se3 Nanowires and Nanowire Bundles.

    PubMed

    Ko, Ting-Yu; Shellaiah, Muthaiah; Sun, Kien Wen

    2016-10-07

    In this study, we measured the thermal conductivity and Seebeck coefficient of single Sb2Se3 nanowires and nanowire bundles with a high resistivity (σ ~ 4.37 × 10(-4) S/m). Microdevices consisting of two adjacent suspended silicon nitride membranes were fabricated to measure the thermal transport properties of the nanowires in vacuum. Single Sb2Se3 nanowires with different diameters and nanowire bundles were carefully placed on the device to bridge the two membranes. The relationship of temperature difference on each heating/sensing suspension membranes with joule heating was accurately determined. A single Sb2Se3 nanowire with a diameter of ~ 680 nm was found to have a thermal conductivity (kNW) of 0.037 ± 0.002 W/m·K. The thermal conductivity of the nanowires is more than an order of magnitude lower than that of bulk materials (k ~ 0.36-1.9 W/m·K) and highly conductive (σ ~ 3 × 10(4) S/m) Sb2Se3 single nanowires (k ~ 1 W/m·K). The measured Seebeck coefficient with a positive value of ~ 661 μV/K is comparable to that of highly conductive Sb2Se3 single nanowires (~ 750 μV/K). The thermal transport between wires with different diameters and nanowire bundles was compared and discussed.

  15. Thermal and Thermoelectric Transport in Highly Resistive Single Sb2Se3 Nanowires and Nanowire Bundles

    PubMed Central

    Ko, Ting-Yu; Shellaiah, Muthaiah; Sun, Kien Wen

    2016-01-01

    In this study, we measured the thermal conductivity and Seebeck coefficient of single Sb2Se3 nanowires and nanowire bundles with a high resistivity (σ ~ 4.37 × 10−4 S/m). Microdevices consisting of two adjacent suspended silicon nitride membranes were fabricated to measure the thermal transport properties of the nanowires in vacuum. Single Sb2Se3 nanowires with different diameters and nanowire bundles were carefully placed on the device to bridge the two membranes. The relationship of temperature difference on each heating/sensing suspension membranes with joule heating was accurately determined. A single Sb2Se3 nanowire with a diameter of ~ 680 nm was found to have a thermal conductivity (kNW) of 0.037 ± 0.002 W/m·K. The thermal conductivity of the nanowires is more than an order of magnitude lower than that of bulk materials (k ~ 0.36–1.9 W/m·K) and highly conductive (σ ~ 3 × 104 S/m) Sb2Se3 single nanowires (k ~ 1 W/m·K). The measured Seebeck coefficient with a positive value of ~ 661 μV/K is comparable to that of highly conductive Sb2Se3 single nanowires (~ 750 μV/K). The thermal transport between wires with different diameters and nanowire bundles was compared and discussed. PMID:27713527

  16. Microstructure and Wear Resistance of Composite Coating by Laser Cladding Al/TiN on the Ti-6Al-4V Substrate

    NASA Astrophysics Data System (ADS)

    Zhang, H. X.; Yu, H. J.; Chen, C. Z.

    2015-05-01

    The composite coatings were fabricated by laser cladding Al/TiN pre-placed powders on Ti-6Al-4V substrate for enhancing wear resistance and hardness of the substrate. The composite coatings were analyzed by means of X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). The sliding wear tests were performed by MM200 wear test machine. The hardness of the coatings was tested by HV-1000 hardness tester. After laser cladding, it was found that there was a good metallurgical bond between the coating and the substrate. The composite coatings were mainly composed of the matrix of β-Ti (Al) and the reinforcements of titanium nitride (TiN), Ti3Al, TiAl and Al3Ti. The hardness and wear resistance of the coatings on four samples were greatly improved, among which sample 4 exhibited the highest hardness and best wear resistance. The hardness of the coating on sample 4 was approximately 2.5 times of the Ti-6Al-4V substrate. And the wear resistance of sample 4 was four times of the substrate.

  17. Thermal stability and oxidation resistance of Ti–Al–N coatings

    PubMed Central

    Chen, Li; Paulitsch, Jörg; Du, Yong; Mayrhofer, Paul H.

    2012-01-01

    Ti1 − xAlxN coatings are widely used for wear resistant applications due to their excellent mechanical and thermal properties, which depend to a great extent on the Al content. Here, we concentrate on a comparative study of the effect of Al content on crystal structure, thermal stability and oxidation resistance of Ti1 − xAlxN coatings. In agreement to earlier studies, thermal annealing of the individual cubic (c) and wurtzite (w) structured metastable Ti1 − xAlxN coatings induces decomposition into their stable phases c-TiN and w-AlN. The decomposition process for c-Ti1 − xAlxN involves an intermediate formation of cubic Al-rich and Ti-rich domains which results in a hardness increase to 34.7 and 34.4 GPa for x = 0.52 and 0.62 when annealed at 950 and 900 °C, respectively. In general, coatings with an Al content closer to the solubility limit, exhibit an earlier decomposition process, and hence an earlier peak-hardness. During exposure of the Ti1 − xAlxN coatings to ambient air at elevated temperatures Al2O3, TiO2 and Al2TiO5 are formed. The oxidation resistance of as-deposited single-phase Ti1 − xAlxN coatings, cubic or wurtzite structured, increases with increasing Al content. However, coatings containing Al contents at the metastable solubility limit, which result in a mixed cubic–wurtzite structure, have the worst oxidation resistance of the Al-containing coatings investigated. The single phase wurtzite structured coating w-Ti0.25Al0.75N shows the best oxidation resistance, with only ~0.7 μm oxide scale thickness, after thermal exposure for 20 h at 850 °C in ambient air. PMID:23471551

  18. Calculation of Local Stress and Fatigue Resistance due to Thermal Stratification on Pressurized Surge Line Pipe

    NASA Astrophysics Data System (ADS)

    Bandriyana, B.; Utaja

    2010-06-01

    Thermal stratification introduces thermal shock effect which results in local stress and fatique problems that must be considered in the design of nuclear power plant components. Local stress and fatique calculation were performed on the Pressurize Surge Line piping system of the Pressurize Water Reactor of the Nuclear Power Plant. Analysis was done on the operating temperature between 177 to 343° C and the operating pressure of 16 MPa (160 Bar). The stagnant and transient condition with two kinds of stratification model has been evaluated by the two dimensional finite elements method using the ANSYS program. Evaluation of fatigue resistance is developed based on the maximum local stress using the ASME standard Code formula. Maximum stress of 427 MPa occurred at the upper side of the top half of hot fluid pipe stratification model in the transient case condition. The evaluation of the fatigue resistance is performed on 500 operating cycles in the life time of 40 years and giving the usage value of 0,64 which met to the design requirement for class 1 of nuclear component. The out surge transient were the most significant case in the localized effects due to thermal stratification.

  19. Calculation of Local Stress and Fatigue Resistance due to Thermal Stratification on Pressurized Surge Line Pipe

    SciTech Connect

    Bandriyana, B.; Utaja

    2010-06-22

    Thermal stratification introduces thermal shock effect which results in local stress and fatigue problems that must be considered in the design of nuclear power plant components. Local stress and fatigue calculation were performed on the Pressurize Surge Line piping system of the Pressurize Water Reactor of the Nuclear Power Plant. Analysis was done on the operating temperature between 177 to 343 deg. C and the operating pressure of 16 MPa (160 Bar). The stagnant and transient condition with two kinds of stratification model has been evaluated by the two dimensional finite elements method using the ANSYS program. Evaluation of fatigue resistance is developed based on the maximum local stress using the ASME standard Code formula. Maximum stress of 427 MPa occurred at the upper side of the top half of hot fluid pipe stratification model in the transient case condition. The evaluation of the fatigue resistance is performed on 500 operating cycles in the life time of 40 years and giving the usage value of 0,64 which met to the design requirement for class 1 of nuclear component. The out surge transient were the most significant case in the localized effects due to thermal stratification.

  20. Water resistance and thermal properties of polyvinyl alcohol-starch fiber blend film

    NASA Astrophysics Data System (ADS)

    Salleh, M. S. N.; Nor, N. N. Mohamed; Mohd, N.; Draman, S. F. Syed

    2017-02-01

    The growing attention of starch fiber (SF) has led to the innovation of Polyvinyl Alcohol-SF (PVA-SF) blends. This blend is regarded as the biodegradable material which aims to reduce the accumulation of synthetic polymer solid waste derived from petroleum. In this study, the thermal blending characterizations of PVA-SF were investigated by differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The water resistance of the blend was also evaluated to study the polarity of the blends. The blend was prepared by plasticizing the polyvinyl alcohol with glycerol and distilled water with the addition of starch fiber. The incorporation of SF to the blends was at 10 wt% to 50 wt% composition. Based on the thermal analysis, PVA-SF blends were suitable for processing at high temperatures, which can be seen by the shifted onset degradation temperature to a higher temperature. This is because cyclic hemiacetals which were provided by SF can act to prevent the thermal attacks. Conversely, increasing the starch fiber proportion to the film blend reduce the endothermic peak amplitude in the DSC thermogram. It was found that PVA-SF blend at the higher composition of SF had the highest water resistance. This may be attributed to the content of fibre in SF which is hydrophilic.

  1. Evidence for thermal boundary resistance effects on superconducting radiofrequency cavity performances

    NASA Astrophysics Data System (ADS)

    Palmieri, Vincenzo; Rossi, Antonio Alessandro; Stark, Sergey Yu; Vaglio, Ruggero

    2014-08-01

    The majority of the literature on superconducting cavities for particle accelerators concentrates on the interaction of a radiofrequency (RF) electromagnetic field with a superconductor cooled in liquid helium, generally either at a fixed temperature of 4.2 K or 1.8 K, basing the analysis of experimental results on the assumption that the superconductor is at the same temperature as the infinite reservoir of liquid helium. Only a limited number of papers have extended their analysis to the more complex overall system composed of an RF field, a superconductor and liquid helium. Only a few papers have analyzed, for example, the problem of the Kapitza resistance, i.e. the thermal boundary resistance between the superconductor and the superfluid helium. Among them, the general conclusion is that the Kapitza resistance, one of the most controversial and less understood topics in physics, is generally negligible, or not relevant for the performance enhancement of cavities. In our work presented here, studying the performance of 6 GHz niobium (Nb) test cavities, we have discovered and studied a new effect consisting of an abrupt change in the surface resistance versus temperature at the superfluid helium lambda transition Tλ. This abrupt change (or ‘jump’) clearly appears when the RF measurement of a cavity is performed at constant power rather than at a constant field. We have correlated this jump to a change in the thermal exchange regime across the lambda transition, and, through a simple thermal model and further reasonable assumptions, we have calculated the thermal boundary resistance between niobium and liquid helium in the temperature range between 4.2 K and 1.8 K. We find that the absolute values of the thermal resistance both above and below the lambda point are fully compatible with the data reported in the literature for heat transfer to pool boiling helium I (HeI) above Tλ and for the Kapitza interface resistance (below Tλ) between a polished metal

  2. A Substrate Radical Intermediate in Catalysis by the Antibiotic Resistance Protein Cfr

    PubMed Central

    Grove, Tyler L.; Livada, Jovan; Schwalm, Erica L.; Green, Michael T.; Booker, Squire J.; Silakov, Alexey

    2013-01-01

    Cfr-dependent methylation of C8 of adenosine 2503 (A2503) in 23S rRNA confers bacterial resistance to an array of clinically important antibiotics that target the large subunit of the ribosome, including the synthetic oxazolidinone antibiotic linezolid. The key element of the proposed mechanism for Cfr, a radical S-adenosylmethionine (SAM) enzyme, is the addition of a methylene radical — generated by hydrogen-atom abstraction from the methyl group of an S-methylated cysteine residue (mCys) — onto C8 of A2503 to form a protein – nucleic acid cross-linked species containing an unpaired electron. Herein we use continuous-wave and pulsed electron paramagnetic resonance (EPR) techniques to provide direct spectroscopic evidence for this intermediate, showing a spin-delocalized radical with maximum spin density at N7 of the adenine ring. In addition, we use rapid-freeze quench EPR to show that the radical forms and decays with rate constants that are consistent with the rate of formation of the methylated product. PMID:23644479

  3. Synthesis of organic-inorganic hybrid sols with nano silica particles and organoalkoxysilanes for transparent and high-thermal-resistance coating films using sol-gel reaction.

    PubMed

    Na, Moonkyong; Park, Hoyyul; Ahn, Myeongsang; Lee, Hyeonhwa; Chung, Ildoo

    2010-10-01

    Organic-inorganic hybrid sols were synthesized from nano silica particles dispersed in water and from organoalkoxysilanes, using the sol-gel reaction. This work focuses on the effects of the three multifunctional organoalkoxysilanes dimethyldimethoxysilane (DMDMS), methyltrimethoxysilane (MTMS), and tetramethoxysilane (TMOS) to form a transparent and high-thermal-resistance coating film. The stability of the hybrid sol was evaluated as a function of the reaction time for 10 d through the variation of the viscosity. The viscosity of the silica/DMDMS and silica/MTMS sol was slightly increased for 10 d. The multifunctional organoalkoxysilanes formed dense silica networks through hydrolysis and condensation reaction, which enhanced the thermal resistance of the coating films. No thermal degradation of the silica/DMDMS sample occurred up to 600 degrees C, and none of the silica/MTMS and silica/TMOS samples occurred either up to 700 degrees C. The organic-inorganic hybrid sols were coated on the glass substrate using a spin-coating procedure. The organic-inorganic hybrid sols formed flat coating films without cracks. The transmittance of the hybrid sol coating films using MTMS and DMDMS was shown to be over 90%. The transmittance of the silica/TMOS sol coating film reacted for 10 d abruptly decreased due to faster gelation. The silica/DMDMS and silica/MTMS hybrid sols formed smooth coating films while the surface roughness of the silica/TMOS coating film markedly increased when the hybrid sol reacted for 10 d. The increase of the surface roughness of the silica/TMOS coating film can be attributed to the degradation of the stability of the hybrid sol and to the loss of transmittance of the coating film. It was confirmed in this study that the use of organic-inorganic hybrid sol can yield transparent and high-thermal-resistance coating films.

  4. Characterization and Effect of Thermal Annealing on InAs Quantum Dots Grown by Droplet Epitaxy on GaAs(111)A Substrates.

    PubMed

    Bietti, Sergio; Esposito, Luca; Fedorov, Alexey; Ballabio, Andrea; Martinelli, Andrea; Sanguinetti, Stefano

    2015-12-01

    We report the study on formation and thermal annealing of InAs quantum dots grown by droplet epitaxy on GaAs (111)A surface. By following the changes in RHEED pattern, we found that InAs quantum dots arsenized at low temperature are lattice matched with GaAs substrate, becoming almost fully relaxed when substrate temperature is increased. Morphological characterizations performed by atomic force microscopy show that annealing process is able to change density and aspect ratio of InAs quantum dots and also to narrow size distribution.

  5. Formalising a mechanistic linkage between heterotrophic feeding and thermal bleaching resistance

    NASA Astrophysics Data System (ADS)

    Wooldridge, Scott A.

    2014-12-01

    In this paper, I utilise the CO2 (sink) limitation model of coral bleaching to propose a new biochemical framework that explains how certain (well-adapted) coral species can utilise heterotrophic carbon acquisition to combat the damaging algal photoinhibition response sequence that underpins thermal bleaching, thereby increasing thermal bleaching resistance. This mechanistic linkage helps to clarify a number of previously challenging experimental responses arising from feeding (versus starved) temperature stress experiments, and isotope labelling (tracer) experiments with heterotrophic carbon sources (e.g., zooplankton). In an era of rapidly warming surface ocean temperatures, the conferred fitness benefits arising from such a mechanistic linkage are considerable. Yet, various ecological constraints are outlined which caution against the ultimate benefit of the mechanism for raising bleaching thresholds at the coral community (reef) scale. Future experiments are suggested that can strengthen these proposed arguments.

  6. Blanch Resistant and Thermal Barrier NiAl Coating Systems for Advanced Copper Alloys

    NASA Technical Reports Server (NTRS)

    Raj, Sai V. (Inventor)

    2005-01-01

    A method of forming an environmental resistant thermal barrier coating on a copper alloy is disclosed. The steps include cleansing a surface of a copper alloy, depositing a bond coat on the cleansed surface of the copper alloy, depositing a NiAl top coat on the bond coat and consolidating the bond coat and the NiAl top coat to form the thermal barrier coating. The bond coat may be a nickel layer or a layer composed of at least one of copper and chromium-copper alloy and either the bond coat or the NiAl top coat or both may be deposited using a low pressure or vacuum plasma spray.

  7. Thermal shock and fatigue resistance of tungsten materials under transient heat loading

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaoxin; Yan, Qingzhi; Lang, Shaoting; Xia, Min; Liu, Xiang; Ge, Changchun

    2014-12-01

    Transient heat loading tests were performed on rolled pure tungsten (PW) and lanthanum oxide doped tungsten (WL10) as well as swaged + rolled potassium doped tungsten (W-K) samples using an electron beam. In thermal shock tests, the cracking threshold was 0.44-0.66, 0.17-0.22 and 0.44-0.66 GW/m2 for PW, WL10 and W-K, respectively. The melting threshold was over 1.1 GW/m2 for PW and W-K while 0.66-0.88 GW/m2 for WL10. In thermal fatigue tests, the obvious roughening threshold was over 1000 cycles for PW and WL10 while 1-100 cycles for W-K. The cracking threshold was 100-1000 cycles for PW, 1-100 cycles for WL10 and over 1000 cycles for W-K alloy. WL10 displayed worse thermal and fatigue resistance while W-K exhibited better properties compared with PW, which was attributed to differences in thermal-mechanical properties of the three tungsten alloys, in addition to the size and number density of La2O3 particles and potassium bubbles.

  8. Laser Welded versus Resistance Spot Welded Bone Implants: Analysis of the Thermal Increase and Strength

    PubMed Central

    Fornaini, Carlo; Meleti, Marco; Bonanini, Mauro; Lagori, Giuseppe; Vescovi, Paolo; Merigo, Elisabetta; Nammour, Samir

    2014-01-01

    Introduction. The first aim of this “ex vivo split mouth” study was to compare the thermal elevation during the welding process of titanium bars to titanium implants inserted in pig jaws by a thermal camera and two thermocouples. The second aim was to compare the strength of the joints by a traction test with a dynamometer. Materials and Methods. Six pigs' jaws were used and three implants were placed on each side of them for a total of 36 fixtures. Twelve bars were connected to the abutments (each bar on three implants) by using, on one side, laser welding and, on the other, resistance spot welding. Temperature variations were recorded by thermocouples and by thermal camera while the strength of the welded joint was analyzed by a traction test. Results. For increasing temperature, means were 36.83 and 37.06, standard deviations 1.234 and 1.187, and P value 0.5763 (not significant). For traction test, means were 195.5 and 159.4, standard deviations 2.00 and 2.254, and P value 0.0001 (very significant). Conclusion. Laser welding was demonstrated to be able to connect titanium implant abutments without the risk of thermal increase into the bone and with good results in terms of mechanical strength. PMID:25110731

  9. Resistance of fly ash-Portland cement blends to thermal shock

    SciTech Connect

    Pyatina, Tatiana; Sugama, Toshifumi

    2015-09-11

    Thermal-shock resistance of high-content fly ash-Portland cement blends was tested in the following ways. Activated and non-activated blends with 80-90 % fly ash F (FAF) were left to set at room temperature, then hydrated for 24 hours at 85°C and 24-more hours at 300°C and tested in five thermal-shock cycles (600°C heat - 25°C water quenching). XRD, and thermal gravimetric analyses, along with calorimetric measurements and SEM-EDX tests demonstrated that the activated blends form more hydrates after 24 hours at 300°C, and achieve a higher short-term compressive strength than do non-activated ones. Sodium meta-silicate and sodaash engendered the concomitant hydration of OPC and FAF, with the formation of mixed crystalline FAF-OPC hydrates and FAF hydrates, such as garranite, analcime, and wairakite, along with the amorphous FAF hydration products. In SS-activated and non-activated blends separate OPC (tobermorite) and FAF (amorphous gel) hydrates with no mixed crystalline products formed. The compressive strength of all tested blends decreased by nearly 50% after 5 thermal-shock test cycles. These changes in the compressive strength were accompanied by a marked decrease in the intensities of XRD patterns of the crystalline hydrates after the thermalshock. As a result, there was no significant difference in the performance of the blends with different activators

  10. Resistance of fly ash-Portland cement blends to thermal shock

    DOE PAGES

    Pyatina, Tatiana; Sugama, Toshifumi

    2015-09-11

    Thermal-shock resistance of high-content fly ash-Portland cement blends was tested in the following ways. Activated and non-activated blends with 80-90 % fly ash F (FAF) were left to set at room temperature, then hydrated for 24 hours at 85°C and 24-more hours at 300°C and tested in five thermal-shock cycles (600°C heat - 25°C water quenching). XRD, and thermal gravimetric analyses, along with calorimetric measurements and SEM-EDX tests demonstrated that the activated blends form more hydrates after 24 hours at 300°C, and achieve a higher short-term compressive strength than do non-activated ones. Sodium meta-silicate and sodaash engendered the concomitant hydrationmore » of OPC and FAF, with the formation of mixed crystalline FAF-OPC hydrates and FAF hydrates, such as garranite, analcime, and wairakite, along with the amorphous FAF hydration products. In SS-activated and non-activated blends separate OPC (tobermorite) and FAF (amorphous gel) hydrates with no mixed crystalline products formed. The compressive strength of all tested blends decreased by nearly 50% after 5 thermal-shock test cycles. These changes in the compressive strength were accompanied by a marked decrease in the intensities of XRD patterns of the crystalline hydrates after the thermalshock. As a result, there was no significant difference in the performance of the blends with different activators« less

  11. Thermal boundary resistance predictions from molecular dynamics simulations and theoretical calculations

    NASA Astrophysics Data System (ADS)

    Landry, E. S.; McGaughey, A. J. H.

    2009-10-01

    The accuracies of two theoretical expressions for thermal boundary resistance are assessed by comparing their predictions to independent predictions from molecular dynamics (MD) simulations. In one expression (RE) , the phonon distributions are assumed to follow the equilibrium, Bose-Einstein distribution, while in the other expression (RNE) , the phonons are assumed to have nonequilibrium, but bulk-like distributions. The phonon properties are obtained using lattice dynamics-based methods, which assume that the phonon interface scattering is specular and elastic. We consider (i) a symmetrically strained Si/Ge interface, and (ii) a series of interfaces between Si and “heavy-Si,” which differs from Si only in mass. All of the interfaces are perfect, justifying the assumption of specular scattering. The MD-predicted Si/Ge thermal boundary resistance is temperature independent and equal to 3.1×10-9m2-K/W below a temperature of ˜500K , indicating that the phonon scattering is elastic, as required for the validity of the theoretical calculations. At higher-temperatures, the MD-predicted Si/Ge thermal boundary resistance decreases with increasing temperature, a trend we attribute to inelastic scattering. For the Si/Ge interface and the Si/heavy-Si interfaces with mass ratios greater than two, RE is in good agreement with the corresponding MD-predicted values at temperatures where the interface scattering is elastic. When applied to a system containing no interface, RE is erroneously nonzero due to the assumption of equilibrium phonon distributions on either side of the interface. While RNE is zero for a system containing no interface, it is 40%-60% less than the corresponding MD-predicted values for the Si/Ge interface and the Si/heavy-Si interfaces at temperatures where the interface scattering is elastic. This inaccuracy is attributed to the assumption of bulk-like phonon distributions on either side of the interface.

  12. The thermal flash technique: the inconsequential effect of contact resistance and the characterization of carbon nanotube clusters.

    PubMed

    Mahanta, Nayandeep K; Abramson, Alexis R

    2012-05-01

    This article presents a comprehensive mathematical treatment of the theory behind the thermal flash technique used to measure the thermal diffusivity of nanostructures. Analytical expressions predicting the temperature and its rate of change for various combinations of sample length and diffusivity confirmed that the presence of contact resistance between the heat sink/source or within a cluster of materials does not influence the measurement. Measurements on multi-walled carbon nanotube clusters provide further experimental evidence supporting the claim that contact resistance is inconsequential to this technique and yield a thermal conductivity of 2665 W/m K, which corresponds to an isolated nanotube and not the overall cluster.

  13. Evaluation of thermal and evaporative resistances in cricket helmets using a sweating manikin.

    PubMed

    Pang, Toh Yen; Subic, Aleksandar; Takla, Monir

    2014-03-01

    The main objective of this study is to establish an approach for measuring the dry and evaporative heat dissipation cricket helmets. A range of cricket helmets has been tested using a sweating manikin within a controlled climatic chamber. The thermal manikin experiments were conducted in two stages, namely the (i) dry test and (ii) wet test. The ambient air temperature for the dry tests was controlled to ~ 23 °C, and the mean skin temperatures averaged ~ 35 °C. The thermal insulation value measured for the manikin with helmet ensemble ranged from 1.0 to 1.2 clo. The results showed that among the five cricket helmets, the Masuri helmet offered slightly more thermal insulation while the Elite helmet offered the least. However, under the dry laboratory conditions and with minimal air movement (air velocity = 0.08 ± 0.01 ms(-1)), small differences exist between the thermal resistance values for the tested helmets. The wet tests were conducted in an isothermal condition, with an ambient and skin mean temperatures averaged ~ 35 °C, the evaporative resistance, Ret, varied between 36 and 60 m(2) Pa W(-1). These large variations in evaporative heat dissipation values are due to the presence of a thick layer of comfort lining in certain helmet designs. This finding suggests that the type and design of padding may influence the rate of evaporative heat dissipation from the head and face; hence the type of material and thickness of the padding is critical for the effectiveness of evaporative heat loss and comfort of the wearer. Issues for further investigations in field trials are discussed.

  14. Development of fire-resistant, low smoke generating, thermally stable end items for aircraft and spacecraft

    NASA Technical Reports Server (NTRS)

    Gagliani, J.; Sorathia, U. A. K.; Wilcoxson, A. L.

    1977-01-01

    Materials were developed to improve aircraft interior materials by modifying existing polymer structures, refining the process parameters, and by the use of mechanical configurations designed to overcome specific deficiencies. The optimization, selection, and fabrication of five fire resistant, low smoke emitting open cell foams are described for five different types of aircraft cabin structures. These include: resilient foams, laminate floor and wall paneling, thermal/acoustical insulation, molded shapes, and coated fabrics. All five have been produced from essentially the same polyimide precursor and have resulted in significant benefits from transfer of technology between the various tasks.

  15. Thermal resistance of attic loose-fill insulations decreases under simulated winter conditions

    SciTech Connect

    Graves, R.S.; Wilkes, K.E.; McElroy, D.L.

    1994-05-01

    Two absolute techniques were used to measure the thermal resistance of attic loose-fill insulations: the Large Scale Climate Simulator (LSCS) and the Unguarded Thin-Heater Apparatus (UTHA). Two types of attic loose-fill insulations (unbonded and bonded/cubed) were tested under simulated winter conditions. To simulate winter conditions for an attic insulation, the specimens were tested with heat flow up, large temperature differences, and an air gap. The specimens were tested either with a constant mean temperature (30 or 21{degrees}C) and an increasing temperature difference or with a constant base temperature (21{degrees}C) and an increasing temperature difference (i.e., a decreasing mean temperature). The UTHA test specimens had a nominal thickness of 0.2 m of loose-fill insulation. The LSCS test specimens had a nominal thickness of 0.3 m of loose-fill insulation contained in a 4.2 by 5 m attic test module with a gypsum board base. The module had a gabled attic with a 5 in 12 slope roof. The tests yielded the surface-to-surface thermal resistance, R, which includes the thermal resistance due to gypsum, insulation, and any wood joists. Tests with and without an air gap were conducted in the UTHA. Surface-to-surface thermal resistance results from the LSCS and the UTHA show similar trends for these two types of loose-fill insulation when tested under simulated winter conditions. Tests with no air gap gave values of R that agreed with the bag label R-value for the insulations; R increased with lower mean temperatures. These no-gap values of R were 2 to 5% greater than the values of R obtained with an air gap for temperature differences of less than 22{degrees}C. For larger temperature differences R decreased, and at temperature differences of over 40{degrees}C, the R values were 50% less than those at small temperature differences.

  16. Thermal-resistive current filamentation in the cathode plasma of a pinch-reflex diode

    SciTech Connect

    Tripathi, V.K.; Ottinger, P.F.; Guillory, J.

    1983-06-01

    Electron current flow drawn off a hollow cylindrical cathode in a pinch-reflex ion diode is observed to have a filamentary structure. Such filamentation can lead to nonuniform anode turn on and ion emission. Consequently, ion beam brightness is degraded. In this context a purely growing thermal-resistive instability in the cathode plasma is examined. The instability causes current filamentation and grows on a time scale comparable to the electron--ion energy equilibration time. Electron inelastic collisions have a stabilizing influence on the instability.

  17. Investigation of thermal sensitivity and radiation resistance of SiOx metal-dielectric films

    NASA Astrophysics Data System (ADS)

    Shepeliavyi, P. E.; Indutnyi, I. Z.; Dan'ko, V. A.; Neimash, V. B.; Povarchuk, V. Yu.

    2014-03-01

    In this investigation the composite SiOx films were prepared by the thermal evaporation of a mixture of silicon oxide (SiO2) and Тi powders. The optical transmission of the films in the IR spectral range and their temperature-sensitive properties are studied. By varying the contents of the metal in vaporizer and time of evaporation it is possible to obtain SiOx layers with resistance (for monopixel of 0.8 × 1 mm) from tens kOhms to MOhms and a value of the temperature coefficient of resistance (TCR) is equal to -2.22% K-1. IR spectrum of SiOx film is characterized by a broad absorption band in the range of 8-12 μm which is associated with the Si-O-Si stretching mode.

  18. Thermal stress resistance and aging effects of Panax notoginseng polysaccharides on Caenorhabditis elegans.

    PubMed

    Feng, Shiling; Cheng, Haoran; Xu, Zhou; Shen, Shian; Yuan, Ming; Liu, Jing; Ding, Chunbang

    2015-11-01

    Panax notoginseng attract public attention due to their potential biomedical properties and corresponding health benefits. The present study investigated the anti-aging and thermal stress resistance effects of polysaccharides from P. notoginseng on Caenorhabditis elegans. Results showed polysaccharides had little scavenging ability of reactive oxygen species (ROS) in vitro, but significantly extended lifespan of C. elegans, especially the main root polysaccharide (MRP) which prolongs the mean lifespan of wild type worms by 21%. Further study demonstrated that the heat stress resistance effect of polysaccharides on C. elegans might be attributed to the elevation of antioxidant enzyme activities (both superoxide dismutase (SOD) and catalase (CAT)) and the reduction lipid peroxidation of malondialdehyde (MDA) level. Taken together, the results provided a scientific basis for the further exploitation of the mechanism of longer lifespan controlled by P. notoginseng polysaccharides on C. elegans. The P. notoginseng polysaccharides might be considered as a potential source to delay aging.

  19. Resist-free antireflective nanostructured film fabricated by thermal-NIL

    NASA Astrophysics Data System (ADS)

    Kang, Young Hun; Han, Jae Hyung; Cho, Song Yun; Choi, Choon-Gi

    2014-05-01

    Resist-free antireflective (AR) nanostructured films are directly fabricated on polycarbonate (PC) film using thermal-nanoimprint lithography (T-NIL) and the moth-eye shape of AR nanostructure is elaborately optimized with different oxygen reactive ion etching conditions. Anodic aluminum oxide (AAO) templates are directly used as master molds of T-NIL for preparation of AR nanostructures on PC film without an additional T-NIL resist. AR nanostructures are well arranged with a period of about 200 nm and diameter of about 150 nm, which corresponds to those of the AAO template mold. The moth-eye AR nanostructures exhibit the average reflectance of 2% in wavelength range from 400 to 800 nm. From the results, highly enhanced AR properties with simple direct imprinting on PC film demonstrate the potential for panel application in the field of flat display, touch screen, and solar cells.

  20. Chromium-niobium co-doped vanadium dioxide films: Large temperature coefficient of resistance and practically no thermal hysteresis of the metal-insulator transition

    NASA Astrophysics Data System (ADS)

    Miyazaki, Kenichi; Shibuya, Keisuke; Suzuki, Megumi; Sakai, Kenichi; Fujita, Jun-ichi; Sawa, Akihito

    2016-05-01

    We investigated the effects of chromium (Cr) and niobium (Nb) co-doping on the temperature coefficient of resistance (TCR) and the thermal hysteresis of the metal-insulator transition of vanadium dioxide (VO2) films. We determined the TCR and thermal-hysteresis-width diagram of the V1-x-yCrxNbyO2 films by electrical-transport measurements and we found that the doping conditions x ≳ y and x + y ≥ 0.1 are appropriate for simultaneously realizing a large TCR value and an absence of thermal hysteresis in the films. By using these findings, we developed a V0.90Cr0.06Nb0.04O2 film grown on a TiO2-buffered SiO2/Si substrate that showed practically no thermal hysteresis while retaining a large TCR of 11.9%/K. This study has potential applications in the development of VO2-based uncooled bolometers.

  1. Trade-off between thermal tolerance and insecticide resistance in Plutella xylostella

    PubMed Central

    Zhang, Lin Jie; Wu, Zhao Li; Wang, Kuan Fu; Liu, Qun; Zhuang, Hua Mei; Wu, Gang

    2015-01-01

    Fitness costs associated with resistance to insecticides have been well documented, usually at normal temperature conditions, in many insect species. In this study, using chlorpyrifos-resistant homozygote (RR) and chlorpyrifos-susceptible homozygote (SS) of resistance ace1 allele of Plutella xylostella (DBM), we confirmed firstly that high temperature experience in pupal stage influenced phenotype of wing venation in insecticide-resistant and insecticide-susceptible Plutella xylostella, and SS DBM showed significantly higher thermal tolerance and lower damages of wing veins under heat stress than RR DBM. As compared to SS DBM, RR DBM displayed significantly lower AChE sensitivity to chlorpyrifos, higher basal GSTs activity and P450 production at 25°C, but higher inhibitions on the enzyme activities and P450 production as well as reduced resistance to chlorpyrifos under heat stress. Furthermore, RR DBM displayed significantly higher basal expressions of hsp69s, hsp72s, hsp20,hsp90,Apaf-1, and caspase-7 at 25°C, but lower induced expressions of hsps and higher induced expressions of Apaf-1,caspase-9, and caspase-7 under heat stress. These results suggest that fitness costs of chlorpyrifos resistance in DBM may partly attribute to excess consumption of energy caused by over production of detoxification enzymes and hsps when the proteins are less demanded at conducive environments but reduced expressions when they are highly demanded by the insects to combat environmental stresses, or to excess expressions of apoptotic genes under heat stress, which results in higher apoptosis. The evolutionary and ecological implications of these findings at global warming are discussed. PMID:25691976

  2. Applying thermosettable zwitterionic copolymers as general fouling-resistant and thermal-tolerant biomaterial interfaces.

    PubMed

    Chou, Ying-Nien; Chang, Yung; Wen, Ten-Chin

    2015-05-20

    We introduced a thermosettable zwitterionic copolymer to design a high temperature tolerance biomaterial as a general antifouling polymer interface. The original synthetic fouling-resistant copolymer, poly(vinylpyrrolidone)-co-poly(sulfobetaine methacrylate) (poly(VP-co-SBMA)), is both thermal-tolerant and fouling-resistant, and the antifouling stability of copolymer coated interfaces can be effectively controlled by regulating the VP/SBMA composition ratio. We studied poly(VP-co-SBMA) copolymer gels and networks with a focus on their general resistance to protein, cell, and bacterial bioadhesion, as influenced by the thermosetting process. Interestingly, we found that the shape of the poly(VP-co-SBMA) copolymer material can be set at a high annealing temperature of 200 °C while maintaining good antifouling properties. However, while the zwitterionic PSBMA polymer gels were bioinert as expected, control of the fouling resistance of the PSBMA polymer networks was lost in the high temperature annealing process. A poly(VP-co-SBMA) copolymer network composed of PSBMA segments at 32 mol % showed reduced fibrinogen adsorption, tissue cell adhesion, and bacterial attachment, but a relatively higher PSBMA content of 61 mol % was required to optimize resistance to platelet adhesion and erythrocyte attachment to confer hemocompatibility to human blood. We suggest that poly(VP-co-SBMA) copolymers capable of retaining stable fouling resistance after high temperature shaping have a potential application as thermosettable materials in a bioinert interface for medical devices, such as the thermosettable coating on a stainless steel blood-compatible metal stent investigated in this study.

  3. Improvements in contact resistivity and thermal stability of Au-contacted InP solar cells

    NASA Technical Reports Server (NTRS)

    Fatemi, Navid S.; Weizer, Victor G.

    1991-01-01

    Specific contact resistivities for as-fabricated Au contacts on n-p InP solar cells are typically in the 10(exp -3) ohm/sq cm range, but contact resistivities in the 10(exp -6) ohm/sq cm range can be obtained if the cells are heat treated at 400 C for a few minutes. This heat treatment, however, results in a dramatic drop in the open circuit voltage of the cell due to excessive dissolution of the emitter into the metallization. It was found that low values of contact resistivity can be secured without the accompanying drop in the open circuit voltage by adding Ga and In in the Au metallization. It is shown that Au contacts containing as little as 1 percent atomic Ga can suppress the reaction that takes place at the metal-InP interface during heat treatment, while exhibiting contact resistivity values in the low 10(exp -5) ohm/sq cm. Detailed explanations for the observed superior thermal stability of these contacts are presented.

  4. Applications in the Nuclear Industry for Corrosion-Resistant Amorphous-Metal Thermal-Spray Coatings

    SciTech Connect

    Farmer, J; Choi, J

    2007-07-18

    Amorphous metal and ceramic thermal spray coatings have been developed that can be used to enhance the corrosion resistance of containers for the transportation, aging and disposal of spent nuclear fuel and high-level radioactive wastes. Fe-based amorphous metal formulations with chromium, molybdenum and tungsten have shown the corrosion resistance believed to be necessary for such applications. Rare earth additions enable very low critical cooling rates to be achieved. The boron content of these materials, and their stability at high neutron doses, enable them to serve as high efficiency neutron absorbers for criticality control. Ceramic coatings may provide even greater corrosion resistance for container applications, though the boron-containing amorphous metals are still favored for criticality control applications. These amorphous metal and ceramic materials have been produced as gas atomized powders and applied as near full density, non-porous coatings with the high-velocity oxy-fuel process. This paper summarizes the performance of these coatings as corrosion-resistant barriers, and as neutron absorbers. Relevant corrosion models are also discussed, as well as a cost model to quantify the economic benefits possible with these new materials.

  5. Measurements of thermal effusivity of a fine wire and contact resistance of a junction using a T type probe.

    PubMed

    Wang, Jianli; Gu, Ming; Zhang, Xing; Wu, Gangping

    2009-07-01

    The thermal effusivity of a fine wire and the thermal contact resistance of a junction have been measured by a modified T type probe using a periodic heating method. The modified T type probe is made of a short periodic heated platinum wire and a test wire with one end contacting to the midpoint of the hot wire. Dimensionless expressions for the temperature responses of the hot wire with respect to the thermal effusivity of the test wire and the thermal contact resistance of the junction between the test wire and the hot wire were presented. A measurement system based on a flexible resolution A/D board and a LABVIEW-based virtual lock-in was setup. The probe was further verified by measuring four kinds of commercially available metallic wires at room temperature. The obtained thermal contact resistances were repeatable, with the calculated thicknesses of about 1 to 2 microm. The present method can further be applied to measure the thermal effusivity of nonconductive wires, and to analyze the thermal contact resistance of nano/microscale junction.

  6. Development of a Laboratory Experiment to Derivate the Thermal Conductivity based on Electrical Resistivity Measurments

    NASA Astrophysics Data System (ADS)

    Vienken, T.; Firmbach, L.; Dietrich, P.

    2014-12-01

    In the course of the energy transition, the number of shallow geothermal systems is constantly growing. These systems allow the exploitation of renewable energy from the subsurface, reduced CO2 emission and additionally, energy storage. An efficient performance of geothermal systems strongly depends upon the availability of exploration data (e.g. thermal conductivity distribution). However, due to high exploration costs, the dimensioning of smaller plants (< 30 kW) is generally based on literature values. While standard in-situ-tests are persistent for larger scale projects, they yield only integral values, e.g. entire length of a borehole heat exchanger. Hence, exploring the distribution of the thermal conductivity as important soil parameter requires the development of new cost-efficient technologies. The general relationship between the electrical (RE) and the thermal resistivity (RT) can be described as log(RE) = CR log(RT) with CRas a multiplier depending on additional soil parameter (e.g. water content, density, porosity, grain size and distribution). Knowing the influencing factor of these additional determining parameters, geoelectrical measurements could provide a cost-efficient exploration strategy of the thermal conductivity for shallow geothermal sites. The aim of this study now is to define the multiplier CRexperimentally to conclude the exact correlation of the thermal and electrical behavior. The set-up consists of an acrylic glass tube with two current electrodes installed at the upper and lower end of the tube. Four electrode chains (each with eight electrodes) measure the potential differences in respect to an induced heat flux initiated by a heat plate. Additional, eight temperature sensors measure the changes of the temperature differences. First, we use this set-up to analyze the influence of soil properties based on differing homogenous sediments with known chemical and petro-physical properties. Further, we analyze the influence of the water

  7. Quantum Dots: Growth of InAs Quantum Dots on GaAs (511)A Substrates: The Competition between Thermal Dynamics and Kinetics (Small 31/2016).

    PubMed

    Wen, Lei; Gao, Fangliang; Zhang, Shuguang; Li, Guoqiang

    2016-08-01

    On page 4277, G. Li and co-workers aim to promote III-V compound semiconductors and devices for a broad range of applications with various technologies. The growth process of InAs quantum dots on GaAs (511)A substrates is systematically studied. By carefully controlling the competition between growth thermal-dynamics and kinetics, InAs quantum dots with high size uniformity are prepared, which are highly desirable for the fabrication of high-efficiency solar cells.

  8. Design and Performance Optimizations of Advanced Erosion-Resistant Low Conductivity Thermal Barrier Coatings for Rotorcraft Engines

    NASA Technical Reports Server (NTRS)

    Zhu, Dongming; Miller, Robert A.; Kuczmarski, Maria A.

    2012-01-01

    Thermal barrier coatings will be more aggressively designed to protect gas turbine engine hot-section components in order to meet future rotorcraft engine higher fuel efficiency and lower emission goals. For thermal barrier coatings designed for rotorcraft turbine airfoil applications, further improved erosion and impact resistance are crucial for engine performance and durability, because the rotorcraft are often operated in the most severe sand erosive environments. Advanced low thermal conductivity and erosion-resistant thermal barrier coatings are being developed, with the current emphasis being placed on thermal barrier coating toughness improvements using multicomponent alloying and processing optimization approaches. The performance of the advanced thermal barrier coatings has been evaluated in a high temperature erosion burner rig and a laser heat-flux rig to simulate engine erosion and thermal gradient environments. The results have shown that the coating composition and architecture optimizations can effectively improve the erosion and impact resistance of the coating systems, while maintaining low thermal conductivity and cyclic oxidation durability

  9. Real time investigation of the effect of thermal expansion coefficient mismatch on film-substrate strain partitioning in Ag/Si systems

    NASA Astrophysics Data System (ADS)

    Das, Debolina; Banu, Nasrin; Bisi, Bhaskar; Mahato, J. C.; Srihari, V.; Halder, Rumu; Dev, B. N.

    2016-10-01

    We have used X-ray diffraction (XRD) to investigate strain partitioning between an epitaxial layer and the substrate as a function of temperature, where the substrate (Si) and the epilayer material (Ag) have large thermal expansion coefficient (α) mismatch. The Ag/Si(111) system undergoes morphological changes upon heating, and the larger and taller islands are formed exposing more substrate surfaces. Sample heating was carried out under nitrogen flow. At >300 °C, the Si(111) diffraction peak splits into three. One of these components conforms to the thermal expansion of bulk Si. The other two components correspond to a highly nonlinear decrease and increase of Si-d(111) planar spacing. The decreasing component has been associated with strained Si under Ag and the increasing component with strained Si under SiO2, which has been formed partly prior to the XRD experiment and partly during sample heating. The opposite trends of these two Si-d(111) components are because of the larger value of α for Ag (7 times) and smaller for SiO2 (1/5th) compared to Si. The out-of-plane strain partitioning has been such that at room temperature, the Si substrate is unstrained and the strain in Ag is ˜0.3%. At 800 °C, Ag is practically relaxed, while Si under Ag is ˜-0.7% strained. A temperature dependent strain partitioning factor has been introduced to fit the data.

  10. High-Resistivity Semi-insulating AlSb on GaAs Substrates Grown by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Vaughan, E. I.; Addamane, S.; Shima, D. M.; Balakrishnan, G.; Hecht, A. A.

    2016-04-01

    Thin-film structures containing AlSb were grown using solid-source molecular beam epitaxy and characterized for material quality, carrier transport optimization, and room-temperature radiation detection response. Few surface defects were observed, including screw dislocations resulting from shear strain between lattice-mismatched layers. Strain was also indicated by broadening of the AlSb peak in x-ray diffraction measurements. Threading dislocations and interfacial misfit dislocations were seen with transmission electron microscopy imaging. Doping of the AlSb layer was introduced during growth using GaTe and Be to determine the effect on Hall transport properties. Hall mobility and resistivity were largest for undoped AlSb samples, at 3000 cm2/V s and 106 Ω cm, respectively, and increased doping levels progressively degraded these values. To test for radiation response, p-type/intrinsic/ n-type (PIN) diode structures were grown using undoped AlSb on n-GaAs substrates, with p-GaSb cap layers to protect the AlSb from oxidation. Alpha-particle radiation detection was achieved and spectra were produced for 241Am, 252Cf, and 239Pu sources. Reducing the detector surface area increased the pulse height observed, as expected based on voltage-capacitance relationships for diodes.

  11. Multifunctional substrate of Al alloy based on general hierarchical micro/nanostructures: superamphiphobicity and enhanced corrosion resistance

    NASA Astrophysics Data System (ADS)

    Li, Xuewu; Shi, Tian; Liu, Cong; Zhang, Qiaoxin; Huang, Xingjiu

    2016-10-01

    Aluminum alloys are vulnerable to penetrating and peeling failures in seawater and preparing a barrier coating to isolate the substrate from corrosive medium is an effective anticorrosion method. Inspired by the lotus leaves effect, a wetting alloy surface with enhanced anticorrosion behavior has been prepared via etch, deposition, and low-surface-energy modification. Results indicate that excellent superamphiphobicity has been achieved after the modification of the constructed hierarchical labyrinth-like microstructures and dendritic nanostructures. The as-prepared surface is also found with good chemical stability and mechanical durability. Furthermore, superior anticorrosion behaviors of the resultant samples in seawater are investigated by electrochemical measurements. Due to trapped air in micro/nanostructures, the newly presented solid-air-liquid contacting interface can help to resist the seawater penetration by greatly reducing the interface interaction between corrosive ions and the superamphiphobic surface. Finally, an optimized two-layer perceptron artificial neural network is set up to model and predict the cause-and-effect relationship between preparation conditions and the anticorrosion parameters. This work provides a great potential to extend the applications of aluminum alloys especially in marine engineering fields.

  12. Multifunctional substrate of Al alloy based on general hierarchical micro/nanostructures: superamphiphobicity and enhanced corrosion resistance

    PubMed Central

    Li, Xuewu; Shi, Tian; Liu, Cong; Zhang, Qiaoxin; Huang, Xingjiu

    2016-01-01

    Aluminum alloys are vulnerable to penetrating and peeling failures in seawater and preparing a barrier coating to isolate the substrate from corrosive medium is an effective anticorrosion method. Inspired by the lotus leaves effect, a wetting alloy surface with enhanced anticorrosion behavior has been prepared via etch, deposition, and low-surface-energy modification. Results indicate that excellent superamphiphobicity has been achieved after the modification of the constructed hierarchical labyrinth-like microstructures and dendritic nanostructures. The as-prepared surface is also found with good chemical stability and mechanical durability. Furthermore, superior anticorrosion behaviors of the resultant samples in seawater are investigated by electrochemical measurements. Due to trapped air in micro/nanostructures, the newly presented solid-air-liquid contacting interface can help to resist the seawater penetration by greatly reducing the interface interaction between corrosive ions and the superamphiphobic surface. Finally, an optimized two-layer perceptron artificial neural network is set up to model and predict the cause-and-effect relationship between preparation conditions and the anticorrosion parameters. This work provides a great potential to extend the applications of aluminum alloys especially in marine engineering fields. PMID:27775053

  13. Thermally-induced transition of lamellae orientation in block-copolymer films on ‘neutral’ nanoparticle-coated substrates

    SciTech Connect

    Yager, Kevin G.; Forrey, Christopher; Singh, Gurpreet; Satija, Sushil K.; Page, Kirt A.; Patton, Derek L.; Jones, Ronald L.; Karin, Alamgir; Douglas, Jack F.

    2015-06-01

    Block-copolymer orientation in thin films is controlled by the complex balance between interfacial free energies, including the inter-block segregation strength, the surface tensions of the blocks, and the relative substrate interactions. While block-copolymer lamellae orient horizontally when there is any preferential affinity of one block for the substrate, we recently described how nanoparticle-roughened substrates can be used to modify substrate interactions. We demonstrate how such ‘neutral’ substrates can be combined with control of annealing temperature to generate vertical lamellae orientations throughout a sample, at all thicknesses. We observe an orientational transition from vertical to horizontal lamellae upon heating, as confirmed using a combination of atomic force microscopy (AFM), neutron reflectometry (NR) and rotational small-angle neutron scattering (RSANS). Using molecular dynamics (MD) simulations, we identify substrate-localized distortions to the lamellar morphology as the physical basis of the novel behavior. In particular, under strong segregation conditions, bending of horizontal lamellae induce a large energetic cost. At higher temperatures, the energetic cost of conformal deformations of lamellae over the rough substrate is reduced, returning lamellae to the typical horizontal orientation. Thus, we find that both surface interactions and temperature play a crucial role in dictating block-copolymer lamellae orientation. As a result, our combined experimental and simulation findings suggest that controlling substrate roughness should provide a useful and robust platform for controlling block-copolymer orientation in applications of these materials.

  14. Thermally-induced transition of lamellae orientation in block-copolymer films on ‘neutral’ nanoparticle-coated substrates

    DOE PAGES

    Yager, Kevin G.; Forrey, Christopher; Singh, Gurpreet; ...

    2015-06-01

    Block-copolymer orientation in thin films is controlled by the complex balance between interfacial free energies, including the inter-block segregation strength, the surface tensions of the blocks, and the relative substrate interactions. While block-copolymer lamellae orient horizontally when there is any preferential affinity of one block for the substrate, we recently described how nanoparticle-roughened substrates can be used to modify substrate interactions. We demonstrate how such ‘neutral’ substrates can be combined with control of annealing temperature to generate vertical lamellae orientations throughout a sample, at all thicknesses. We observe an orientational transition from vertical to horizontal lamellae upon heating, as confirmedmore » using a combination of atomic force microscopy (AFM), neutron reflectometry (NR) and rotational small-angle neutron scattering (RSANS). Using molecular dynamics (MD) simulations, we identify substrate-localized distortions to the lamellar morphology as the physical basis of the novel behavior. In particular, under strong segregation conditions, bending of horizontal lamellae induce a large energetic cost. At higher temperatures, the energetic cost of conformal deformations of lamellae over the rough substrate is reduced, returning lamellae to the typical horizontal orientation. Thus, we find that both surface interactions and temperature play a crucial role in dictating block-copolymer lamellae orientation. As a result, our combined experimental and simulation findings suggest that controlling substrate roughness should provide a useful and robust platform for controlling block-copolymer orientation in applications of these materials.« less

  15. Measurement of effective bulk and contact resistance of gas diffusion layer under inhomogeneous compression - Part II: Thermal conductivity

    NASA Astrophysics Data System (ADS)

    Roy Chowdhury, Prabudhya; Vikram, Ajit; Phillips, Ryan K.; Hoorfar, Mina

    2016-07-01

    The gas diffusion layer (GDL) is a thin porous layer sandwiched between a bipolar plate (BPP) and a catalyst coated membrane in a fuel cell. Besides providing passage for water and gas transport from and to the catalyst layer, it is responsible for electron and heat transfer from and to the BPP. In this paper, a method has been developed to measure the GDL bulk thermal conductivity and the contact resistance at the GDL/BPP interface under inhomogeneous compression occurring in an actual fuel cell assembly. Toray carbon paper GDL TGP-H-060 was tested under a range of compression pressure of 0.34 to 1.71 MPa. The results showed that the thermal contact resistance decreases non-linearly (from 3.8 × 10-4 to 1.17 × 10-4 Km2 W-1) with increasing pressure due to increase in microscopic contact area between the GDL and BPP; while the effective bulk thermal conductivity increases (from 0.56 to 1.42 Wm-1 K-1) with increasing the compression pressure. The thermal contact resistance was found to be greater (by a factor of 1.6-2.8) than the effective bulk thermal resistance for all compression pressure ranges applied here. This measurement technique can be used to identify optimum GDL based on minimum bulk and contact resistances measured under inhomogeneous compression.

  16. Thermal resistance of Listeria monocytogenes Scott A in ultrafiltered milk as related to the effect of different milk components.

    PubMed

    Szlachta, Kinga; Keller, Susanne E; Shazer, Arlette; Chirtel, Stuart

    2010-11-01

    Pasteurization parameters for grade A milk are well established and set by regulation. However, as solids levels increase, an increased amount of heat is required to destroy any pathogens present. This effect is not well characterized. In this work, the effect of increased dairy solids levels on the thermal resistance of Listeria monocytogenes was examined through the use of ultrafiltered (UF) milk, reconstituted milk powder, and the milk components lactose and caseinate. From the results obtained, lactose and caseinate did not appear to affect thermal resistance. In addition, the level of milk fat, up to 10% of the total solids in UF whole milk, did not result in statistically significant changes to thermal resistance when compared with UF skim milk. Reconstituted skim milk powder at 27% total solids (D⁶²-value = 1.16 ± 0.2 [SD] min, z = 5.7) did result in increased thermal resistance, as compared with reconstituted skim milk powder at 17.5% (D⁶²-value = 0.86 ± 0.02 min, z = 5.57) and UF whole milk at 27% total solids (D⁶²-value = 0.66 ± 0.07 min, z = 5.16). However, that increase appeared to be due to the increase in salt levels, not to increases in caseinate, fat, or lactose. Consequently, total solids, as a single measure, could not be used to predict increased thermal resistance of L. monocytogenes in concentrated milk.

  17. Method for collecting naturally occurring airborne bacterial spores for determining their thermal resistance.

    PubMed

    Puleo, J R; Favero, M S; Oxborrow, G S; Herring, C M

    1975-11-01

    The ability to determine the thermal resistance of naturally occurring airborne bacterial spores associated with spacecraft and their assembly areas has been hindered by lack of an effective collecting system. Efforts to collect and concentrate spores with air samplers or from air filters have not been successful. A fallout method was developed for this purpose and tested. Sterile Teflon ribbons (7.6 by 183 cm) were exposed in pertinent spacecraft assembly areas and subsequently treated with dry heat. Thermal inactivation experiments were conducted at 125 and 113 C. Heating intervals ranged from 1 to 12 h at 125 C and 6, 12, 18, and 24 h at 113 C. Eight hours was the longest heating time yielding survivors at 125 C, whereas survivors were recovered at all of the heating intervals at 113 C. D125C values were calculated using the fractional-replicate-unit-negative technique of Pflug and Schmidt (1968) and ranged from 25 to 126 min. This variation indicated that the most probable number of survivors at each heating interval did not fall on a straight line passing through the initial spore population. However, the most-probable-number values taken alone formed a straight line suggesting logarithmic thermal destruction of a subpopulation of spores with a D125C value of 6.3 h.

  18. Improvements of Thermal, Mechanical, and Water-Resistance Properties of Polybenzoxazine/Boron Carbide Nanocomposites

    NASA Astrophysics Data System (ADS)

    Ramdani, Noureddine; Derradji, Mehdi; Wang, Jun; Mokhnache, El-Oualid; Liu, Wen-Bin

    2016-09-01

    Novel kinds of nanocomposites based on bisphenol A-aniline based polybenzoxazine matrix P(BA-a) and 0 wt.%-20 wt.% boron carbide (B4C) nanoparticles were produced and their properties were evaluated in terms of the nano-B4C content. The thermal conductivity of the P(BA-a) matrix was improved approximately three times from 0.18 W/m K to 0.86 W/m K at 20 wt.% nano-B4C loading, while its coefficient of thermal expansion (CTE) was deceased by 47% with the same nanofiller content. The microhardness properties were significantly improved by adding the B4C nanoparticles. At 20 wt.% of nano-B4C content, dynamic mechanical analysis (DMA) revealed a marked increase in the storage modulus and the glass transition temperature ( T g) of the nanocomposites, reaching 3.9 GPa and 204°C, respectively. Hot water uptake tests showed that the water-resistance of the polybenzoxazine matrix was increased by filling with nano-B4C nano-filler. The morphological analysis reflected that the improvements obtained in the mechanical and thermal properties are related to the uniform dispersion of the nano-B4C particles and their strong adhesion to the P(BA-a) matrix.

  19. Thermal Hysteresis in Resistivity and Magnetization of PrCa(Sr)MnO

    NASA Astrophysics Data System (ADS)

    Mollah, S.

    Thermal hysteresis in resistivity and magnetization of Pr0.65Ca0.35-xSrxMnO3 (x = 0-0.35) manganites has been systematically studied to establish the interplay of their charge and spin-ordering. The increasing Sr concentration (x) transforms the charge-ordered (CO)/antiferromagnetic (AFM) insulating system (for x = 0) into a mixed-phased one (for x = 0.1) with sharp metal-insulator (MI) transition and finally leads to a ferromagnetic (FM) metallic (for x = 0.35) system. It has been found that the interplay of charge and spin-ordering is higher in mixed-phased state and the thermal hysteresis loop area is bigger. It increases with the increase of sharpness of MI transition. Interplay of charge and spin-ordering decreases with the increase of either CO/AFM insulating or FM metallic phase and is almost absent in completely CO/AFM insulating (with x = 0) or FM metallic (with x = 0.35) states bringing about zero thermal hysteresis loop.

  20. Resistive switching characteristics and mechanism of thermally grown WOx thin films

    NASA Astrophysics Data System (ADS)

    Biju, Kuyyadi P.; Liu, Xinjun; Siddik, Manzar; Kim, Seonghyun; Shin, Jungho; Kim, Insung; Ignatiev, Alex; Hwang, Hyunsang

    2011-09-01

    Resistive switching characteristics of thermally oxidized tungsten thin films and their switching mechanism were investigated, modifying thickness of the active layer (WOx) by varying oxidation conditions. Two types of switching were observed in Pt/WOx/W memory devices. Thinner film (t ≤ 15 nm) exhibits clockwise switching (CWS) with filamentary characteristics, whereas thicker film (t ≥ 25 nm) exhibits counter-clockwise switching (CCWS) with more homogeneous conduction. Both switching modes are highly reliable and show good cycling endurance. The conduction phenomena in two different switching modes were examined. In the case of CWS, the conduction mechanism changes from Schottky emission to ohmic conduction due to the local bypass of Schottky barrier formed at Pt/WOx interface by oxygen vacancies. Contrary to CWS, CCWS showed a completely different conduction mechanism. The high resistance state is dominated by the Schottky emission at low electric field and by Poole-Frenkel emission at high electric field, whereas the low resistance state exhibits the Schottky emission. Different types of switching behavior might be attributed to the non-homogenous defect distribution across the active layer. A possible conduction sketch for two types switching behaviors is also discussed.

  1. Nanoscale characterization of the thermal interface resistance of a heat-sink composite material by in situ TEM

    NASA Astrophysics Data System (ADS)

    Kawamoto, Naoyuki; Kakefuda, Yohei; Mori, Takao; Hirose, Kenji; Mitome, Masanori; Bando, Yoshio; Golberg, Dmitri

    2015-11-01

    We developed an original method of in situ nanoscale characterization of thermal resistance utilizing a high-resolution transmission electron microscope (HRTEM). The focused electron beam of the HRTEM was used as a contact-free heat source and a piezo-movable nanothermocouple was developed as a thermal detector. This method has a high flexibility of supplying thermal-flux directions for nano/microscale thermal conductivity analysis, and is a powerful way to probe the thermal properties of complex or composite materials. Using this method we performed reproducible measurements of electron beam-induced temperature changes in pre-selected sections of a heat-sink α-Al2O3/epoxy-based resin composite. Observed linear behavior of the temperature change in a filler reveals that Fourier’s law holds even at such a mesoscopic scale. In addition, we successfully determined the thermal resistance of the nanoscale interfaces between neighboring α-Al2O3 fillers to be 1.16 × 10-8 m2K W-1, which is 35 times larger than that of the fillers themselves. This method that we have discovered enables evaluation of thermal resistivity of composites on the nanoscale, combined with the ultimate spatial localization and resolution sample analysis capabilities that TEM entails.

  2. Nanoscale characterization of the thermal interface resistance of a heat-sink composite material by in situ TEM.

    PubMed

    Kawamoto, Naoyuki; Kakefuda, Yohei; Mori, Takao; Hirose, Kenji; Mitome, Masanori; Bando, Yoshio; Golberg, Dmitri

    2015-11-20

    We developed an original method of in situ nanoscale characterization of thermal resistance utilizing a high-resolution transmission electron microscope (HRTEM). The focused electron beam of the HRTEM was used as a contact-free heat source and a piezo-movable nanothermocouple was developed as a thermal detector. This method has a high flexibility of supplying thermal-flux directions for nano/microscale thermal conductivity analysis, and is a powerful way to probe the thermal properties of complex or composite materials. Using this method we performed reproducible measurements of electron beam-induced temperature changes in pre-selected sections of a heat-sink α-Al(2)O(3)/epoxy-based resin composite. Observed linear behavior of the temperature change in a filler reveals that Fourier's law holds even at such a mesoscopic scale. In addition, we successfully determined the thermal resistance of the nanoscale interfaces between neighboring α-Al(2)O(3) fillers to be 1.16 × 10(-8) m(2)K W(-1), which is 35 times larger than that of the fillers themselves. This method that we have discovered enables evaluation of thermal resistivity of composites on the nanoscale, combined with the ultimate spatial localization and resolution sample analysis capabilities that TEM entails.

  3. High-Temperature Oxidation-Resistant and Low Coefficient of Thermal Expansion NiAl-Base Bond Coat Developed for a Turbine Blade Application

    NASA Technical Reports Server (NTRS)

    2003-01-01

    Many critical gas turbine engine components are currently made from Ni-base superalloys that are coated with a thermal barrier coating (TBC). The TBC consists of a ZrO2-based top coat and a bond coat that is used to enhance the bonding between the superalloy substrate and the top coat. MCrAlY alloys (CoCrAlY and NiCrAlY) are currently used as bond coats and are chosen for their very good oxidation resistance. TBC life is frequently limited by the oxidation resistance of the bond coat, along with a thermal expansion mismatch between the metallic bond coat and the ceramic top coat. The aim of this investigation at the NASA Glenn Research Center was to develop a new longer life, higher temperature bond coat by improving both the oxidation resistance and the thermal expansion characteristics of the bond coat. Nickel aluminide (NiAl) has excellent high-temperature oxidation resistance and can sustain a protective Al2O3 scale to longer times and higher temperatures in comparison to MCrAlY alloys. Cryomilling of NiAl results in aluminum nitride (AlN) formation that reduces the coefficient of thermal expansion (CTE) of the alloy and enhances creep strength. Thus, additions of cryomilled NiAl-AlN to CoCrAlY were examined as a potential bond coat. In this work, the composite alloy was investigated as a stand-alone substrate to demonstrate its feasibility prior to actual use as a coating. About 85 percent of prealloyed NiAl and 15 percent of standard commercial CoCrAlY alloys were mixed and cryomilled in an attritor with stainless steel balls used as grinding media. The milling was carried out in the presence of liquid nitrogen. The milled powder was consolidated by hot extrusion or by hot isostatic pressing. From the consolidated material, oxidation coupons, four-point bend, CTE, and tensile specimens were machined. The CTE measurements were made between room temperature and 1000 C in an argon atmosphere. It is shown that the CTE of the NiAl-AlN-CoCrAlY composite bond coat

  4. Hyper-resistivity and electron thermal conductivity due to destroyed magnetic surfaces in axisymmetric plasma equilibria

    SciTech Connect

    Weening, R. H.

    2012-06-15

    In order to model the effects of small-scale current-driven magnetic fluctuations in a mean-field theoretical description of a large-scale plasma magnetic field B(x,t), a space and time dependent hyper-resistivity {Lambda}(x,t) can be incorporated into the Ohm's law for the parallel electric field E Dot-Operator B. Using Boozer coordinates, a theoretical method is presented that allows for a determination of the hyper-resistivity {Lambda}({psi}) functional dependence on the toroidal magnetic flux {psi} for arbitrary experimental steady-state Grad-Shafranov axisymmetric plasma equilibria, if values are given for the parallel plasma resistivity {eta}({psi}) and the local distribution of any auxiliary plasma current. Heat transport in regions of plasma magnetic surfaces destroyed by resistive tearing modes can then be modeled by an electron thermal conductivity k{sub e}({psi})=({epsilon}{sub 0}{sup 2}m{sub e}/e{sup 2}){Lambda}({psi}), where e and m{sub e} are the electron charge and mass, respectively, while {epsilon}{sub 0} is the permittivity of free space. An important result obtained for axisymmetric plasma equilibria is that the {psi}{psi}-component of the metric tensor of Boozer coordinates is given by the relation g{sup {psi}{psi}}({psi}){identical_to}{nabla}{psi} Dot-Operator {nabla}{psi}=[{mu}{sub 0}G({psi})][{mu}{sub 0}I({psi})]/{iota}({psi}), with {mu}{sub 0} the permeability of free space, G({psi}) the poloidal current outside a magnetic surface, I({psi}) the toroidal current inside a magnetic surface, and {iota}({psi}) the rotational transform.

  5. Elevated [CO2] magnifies isoprene emissions under heat and improves thermal resistance in hybrid aspen.

    PubMed

    Sun, Zhihong; Hüve, Katja; Vislap, Vivian; Niinemets, Ülo

    2013-12-01

    Isoprene emissions importantly protect plants from heat stress, but the emissions become inhibited by instantaneous increase of [CO2], and it is currently unclear how isoprene-emitting plants cope with future more frequent and severe heat episodes under high [CO2]. Hybrid aspen (Populus tremula x Populus tremuloides) saplings grown under ambient [CO2] of 380 μmol mol(-1) and elevated [CO2] of 780 μmol mol(-1) were used to test the hypothesis that acclimation to elevated [CO2] reduces the inhibitory effect of high [CO2] on emissions. Elevated-[CO2]-grown plants had greater isoprene emission capacity and a stronger increase of isoprene emissions with increasing temperature. High temperatures abolished the instantaneous [CO2] sensitivity of isoprene emission, possibly due to removing the substrate limitation resulting from curbed cycling of inorganic phosphate. As a result, isoprene emissions were highest in elevated-[CO2]-grown plants under high measurement [CO2]. Overall, elevated growth [CO2] improved heat resistance of photosynthesis, in particular, when assessed under high ambient [CO2] and the improved heat resistance was associated with greater cellular sugar and isoprene concentrations. Thus, contrary to expectations, these results suggest that isoprene emissions might increase in the future.

  6. Wear Resistant Carbide-based Thermal Sprayed Coatings: Process, Properties, Mechanical Degradation and Wear

    NASA Astrophysics Data System (ADS)

    Ghabchi, Arash

    Thermally sprayed ceramic-metallic composite (CerMet) materials consist of ceramic particles mainly in form of carbides reinforced by metallic binder exhibit unique microstructural and mechanical characteristics. Such structure brings in a novel combination of hardness and toughness enabling application of this class of material in wear resistant surfaces. Final deposit microstructure that defines the mechanical properties and wear performance of material depends on process parameters and starting material characteristics. Complex interaction of in-flight particles with supersonic flame, formation of complex defective deposit structure comprising of pores, cracks and splat boundaries make comprehending of interrelation of process, microstructure, properties and performance a difficult task. Additional challenge is development of systematic understanding on mechanical degradation, damage and wear mechanisms of cermet coatings due to their complex structure. This dissertation attempts to address these issues first by taking a systematic step by step approach, process map, to establish a correlation between process, particle state, microstructure and properties. Different strategies were proposed and examined to control the high velocity thermal spray process. This strategy assessment enabled a better control over in-flight particles state in high velocity thermal spray process and provided better understanding on interaction of in-flight particles with the flame. Further, possible advantages of reducing the carbide particle size from micron to nano in terms of mechanical properties and different wear performance were explored. It was suggested that poor wear performance of nano-structured coating is due to presence of brittle phases and less available binder promotes the excessive stress detrimental to load carrying capability of material. Material damage and wear mechanisms of coating under different tribological conditions were examined. The results suggest a

  7. Short-term in vivo inhibition of insulin receptor substrate-1 expression leads to insulin resistance, hyperinsulinemia, and increased adiposity.

    PubMed

    Araújo, Eliana P; De Souza, Cláudio T; Gasparetti, Alessandra L; Ueno, Mirian; Boschero, Antonio C; Saad, Mário J A; Velloso, Lício A

    2005-03-01

    Insulin receptor substrate-1 (IRS-1) has an important role as an early intermediary between the insulin and IGF receptors and downstream molecules that participate in insulin and IGF-I signal transduction. Here we employed an antisense oligonucleotide (IRS-1AS) to inhibit whole-body expression of IRS-1 in vivo and evaluate the consequences of short-term inhibition of IRS-1 in Wistar rats. Four days of treatment with IRS-1AS reduced the expression of IRS-1 by 80, 75, and 65% (P < 0.05) in liver, skeletal muscle, and adipose tissue, respectively. This was accompanied by a 40% (P < 0.05) reduction in the constant of glucose decay during an insulin tolerance test, a 78% (P < 0.05) reduction in glucose consumption during a hyperinsulinemic-euglycemic clamp, and a 90% (P < 0.05) increase in basal plasma insulin level. The metabolic effects produced by IRS-1AS were accompanied by a significant reduction in insulin-induced [Ser (473)] Akt phosphorylation in liver (85%, P < 0.05), skeletal muscle (40%, P < 0.05), and adipose tissue (85%, P < 0.05) and a significant reduction in insulin-induced tyrosine phosphorylation of ERK in liver (20%, P < 0.05) and skeletal muscle (30%, P < 0.05). However, insulin-induced tyrosine phosphorylation of ERK was significantly increased (60%, P < 0.05) in adipose tissue of IRS-1AS-treated rats. In rats treated with IRS-1AS for 8 d, a 100% increase (P < 0.05) in relative epididymal fat weight and a 120% (P < 0.05) increase in nuclear expression of peroxisome proliferator-activated receptor-gamma were observed. Thus, acute inhibition of IRS-1 expression in rats leads to insulin resistance accompanied by activation of a growth-related pathway exclusively in white adipose tissue.

  8. Center wavelength shift dependence on substrate coefficient of thermal expansion for optical thin-film interference filters deposited by ion-beam sputtering.

    PubMed

    Brown, Jeffrey T

    2004-08-10

    Single-layer films of Ta2O5 and multilayer thin-film filters of Ta2O5 and SiO2 were deposited by ion-beam-sputter deposition. Postdeposition annealing of the structures resulted in increased optical thickness of the films, resulting in an upward shift in the wavelength of the transmission-reflection spectra. Modeling of the single-layer films by means of the effective media approximation indicates an increase in the void fraction of the film after annealing. This increase is consistent with an observed decrease in refractive index and an increase in physical film thickness. The multilayer structures, deposited on substrates of varying coefficient of thermal expansion (CTE), were annealed at various temperatures, and the change in the center wavelength was measured. The measured change is dependent on the annealing temperature and the substrate CTE, indicating that the increase in the void fraction is caused in part by thermally induced stress during the annealing process. A simple model is proposed that relates the void fraction present in the films after annealing with the substrate CTE and the annealing temperature.

  9. Diffusion in liquid metal systems. [information on electrical resistivity and thermal conductivity

    NASA Technical Reports Server (NTRS)

    Ukanwa, A. O.

    1975-01-01

    Physical properties of twenty liquid metals are reported; some of the data on such liquid metal properties as density, electrical resistivity, thermal conductivity, and heat capacity are summarized in graphical form. Data on laboratory handling and safety procedure are summarized for each metal; heat-transfer-correlations for liquid metals under various conditions of laminar and turbulent flow are included. Where sufficient data were available, temperature equations of properties were obtained by the method of least-squares fit. All values of properties given are valid in the given liquid phase ranges only. Additional tabular data on some 40 metals are reported in the appendix. Included is a brief description of experiments that were performed to investigate diffusion in liquid indium-gallium systems.

  10. Enhancing the Thermal Resistance of a Novel Acidobacteria-Derived Phytase by Engineering of Disulfide Bridges.

    PubMed

    Tan, Hao; Miao, Renyun; Liu, Tianhai; Cao, Xuelian; Wu, Xiang; Xie, Liyuan; Huang, Zhongqian; Peng, Weihong; Gan, Bingcheng

    2016-10-28

    A novel phytase of Acidobacteria was identified from a soil metagenome, cloned, overexpressed, and purified. It has low sequence similarity (<44%) to all the known phytases. At the optimum pH (2.5), the phytase shows an activity level of 1,792 μmol/min/mg at physiological temperature (37°C) and could retain 92% residual activity after 30 min, indicating the phytase is acidophilic and acidostable. However the phytase shows poor stability at high temperatures. To improve its thermal resistance, the enzyme was redesigned using Disulfide by Design 2.0, introducing four additional disulfide bridges. The half-life time of the engineered phytase at 60°C and 80°C, respectively, is 3.0× and 2.8× longer than the wild-type, and its activity and acidostability are not significantly affected.

  11. Molecular mechanisms of thermal resistance of the insect trypanosomatid Crithidia thermophila

    PubMed Central

    Ishemgulova, Aygul; Butenko, Anzhelika; Kortišová, Lucie; Boucinha, Carolina; Grybchuk-Ieremenko, Anastasiia; Morelli, Karina A.; Tesařová, Martina; Kraeva, Natalya; Grybchuk, Danyil; Pánek, Tomáš; Flegontov, Pavel; Lukeš, Julius; Votýpka, Jan; Pavan, Márcio Galvão; Opperdoes, Fred R.; Spodareva, Viktoria; d'Avila-Levy, Claudia M.; Kostygov, Alexei Yu.

    2017-01-01

    In the present work, we investigated molecular mechanisms governing thermal resistance of a monoxenous trypanosomatid Crithidia luciliae thermophila, which we reclassified as a separate species C. thermophila. We analyzed morphology, growth kinetics, and transcriptomic profiles of flagellates cultivated at low (23°C) and elevated (34°C) temperature. When maintained at high temperature, they grew significantly faster, became shorter, with genes involved in sugar metabolism and mitochondrial stress protection significantly upregulated. Comparison with another thermoresistant monoxenous trypanosomatid, Leptomonas seymouri, revealed dramatic differences in transcription profiles of the two species with only few genes showing the same expression pattern. This disparity illustrates differences in the biology of these two parasites and distinct mechanisms of their thermotolerance, a prerequisite for living in warm-blooded vertebrates. PMID:28328988

  12. Molecular mechanisms of thermal resistance of the insect trypanosomatid Crithidia thermophila.

    PubMed

    Ishemgulova, Aygul; Butenko, Anzhelika; Kortišová, Lucie; Boucinha, Carolina; Grybchuk-Ieremenko, Anastasiia; Morelli, Karina A; Tesařová, Martina; Kraeva, Natalya; Grybchuk, Danyil; Pánek, Tomáš; Flegontov, Pavel; Lukeš, Julius; Votýpka, Jan; Pavan, Márcio Galvão; Opperdoes, Fred R; Spodareva, Viktoria; d'Avila-Levy, Claudia M; Kostygov, Alexei Yu; Yurchenko, Vyacheslav

    2017-01-01

    In the present work, we investigated molecular mechanisms governing thermal resistance of a monoxenous trypanosomatid Crithidia luciliae thermophila, which we reclassified as a separate species C. thermophila. We analyzed morphology, growth kinetics, and transcriptomic profiles of flagellates cultivated at low (23°C) and elevated (34°C) temperature. When maintained at high temperature, they grew significantly faster, became shorter, with genes involved in sugar metabolism and mitochondrial stress protection significantly upregulated. Comparison with another thermoresistant monoxenous trypanosomatid, Leptomonas seymouri, revealed dramatic differences in transcription profiles of the two species with only few genes showing the same expression pattern. This disparity illustrates differences in the biology of these two parasites and distinct mechanisms of their thermotolerance, a prerequisite for living in warm-blooded vertebrates.

  13. Interlaced, Nanostructured Interface with Graphene Buffer Layer Reduces Thermal Boundary Resistance in Nano/Microelectronic Systems.

    PubMed

    Tao, Lei; Theruvakkattil Sreenivasan, Sreeprasad; Shahsavari, Rouzbeh

    2017-01-11

    Improving heat transfer in hybrid nano/microelectronic systems is a challenge, mainly due to the high thermal boundary resistance (TBR) across the interface. Herein, we focus on gallium nitride (GaN)/diamond interface-as a model system with various high power, high temperature, and optoelectronic applications-and perform extensive reverse nonequilibrium molecular dynamics simulations, decoding the interplay between the pillar length, size, shape, hierarchy, density, arrangement, system size, and the interfacial heat transfer mechanisms to substantially reduce TBR in GaN-on-diamond devices. We found that changing the conventional planar interface to nanoengineered, interlaced architecture with optimal geometry results in >80% reduction in TBR. Moreover, introduction of conformal graphene buffer layer further reduces the TBR by ∼33%. Our findings demonstrate that the enhanced generation of intermediate frequency phonons activates the dominant group velocities, resulting in reduced TBR. This work has important implications on experimental studies, opening up a new space for engineering hybrid nano/microelectronics.

  14. Modeling of the effects of different substrate materials on the residual thermal stresses in the aluminum nitride crystal grown by sublimation

    NASA Astrophysics Data System (ADS)

    Lee, R. G.; Idesman, A.; Nyakiti, L.; Chaudhuri, J.

    2009-02-01

    A three-dimensional numerical finite element modeling method is applied to compare interfacial residual thermal stress distribution in AlN single crystals grown by using different substrates such as silicon carbide, boron nitride, tungsten, tantalum carbide, and niobium carbide. A dimensionless coordinate system is used which reduces the numbers of computations and hence simplifies the stress analysis. All components of the stress distribution, both in the film and in the substrate, including the normal stress along the growth direction as well as in-plane normal stresses and shear stresses are fully investigated. This information about the stress distribution provides insight into understanding and controlling the AlN single crystal growth by the sublimation technique. The normal stress in the film at the interface along the growth direction and the shear stresses are zero except at the edges, whereas in-plane stresses are nonzero. The in-plane stresses are compressive when TaC and NbC substrates are used. A small compressive stress might be beneficial in prohibiting crack growth in the film. The compressive stress in the AlN is lower for the TaC substrate than that for the NbC. Tensile in-plane stresses are formed in the AlN for 6H-SiC, BN, and W substrates. This tensile stress in the film is detrimental as it will assist in the crack growth. The stress concentration at the edges of the AlN film at the interface is compressive in nature when TaC and NbC are used as a substrate. This causes the film to bend downward (i.e., convex shape) and assist it to adhere to the substrate. The AlN film curves upward or in a concave shape when SiC, BN, and W substrates are used since the stress concentration at the edges of the AlN film is tensile at the interface and this may cause detachment of the film from the substrate.

  15. Temperate and virulent Lactobacillus delbrueckii bacteriophages: comparison of their thermal and chemical resistance.

    PubMed

    Ebrecht, Ana C; Guglielmotti, Daniela M; Tremmel, Gustavo; Reinheimer, Jorge A; Suárez, Viviana B

    2010-06-01

    The aim of this work was to study the efficiency of diverse chemical and thermal treatments usually used in dairy industries to control the number of virulent and temperate Lactobacillus delbrueckii bacteriophages. Two temperate (Cb1/204 and Cb1/342) and three virulent (BYM, YAB and Ib3) phages were studied. The thermal treatments applied were: 63 degrees C for 30 min (low temperature--long time, LTLT), 72 degrees C for 15 s (high temperature--short time, HTST), 82 degrees C for 5 min (milk destined to yogurt elaboration) and 90 degrees C for 15 min (FIL-IDF). The chemical agents studied were: sodium hypochlorite, ethanol, isopropanol, peracetic acid, biocides A (quaternary ammonium chloride), B (hydrogen peroxide, peracetic acid and peroctanoic acid), C (alkaline chloride foam), D (p-toluensulfonchloroamide, sodium salt) and E (ethoxylated nonylphenol and phosphoric acid). The kinetics of inactivation were drew and T(99) (time necessary to eliminate the 99% of phage particles) calculated. Results obtained showed that temperate phages revealed lower resistance than the virulent ones to the treatment temperatures. Biocides A, C, E and peracetic acid showed a notable efficiency to inactivate high concentrations of temperate and virulent L. delbrueckii phages. Biocide B evidenced, in general, a good capacity to eliminate the phage particles. Particularly for this biocide virulent phage Ib3 showed the highest resistance in comparison to the rest of temperate and virulent ones. On the contrary, biocide D and isopropanol presented a very low capacity to inactivate all phages studied. The efficiency of ethanol and hypochlorite was variable depending to the phages considered. These results allow a better knowledge and give useful information to outline more effective treatments to reduce the phage infections in dairy plants.

  16. Two orders of magnitude reduction in the temperature dependent resistivity of Ga1-xMnxAs grown on (6 3 1) GaAs insulating substrates

    NASA Astrophysics Data System (ADS)

    Rangel-Kuopp, Victor-Tapio; Martinez-Velis, Isaac; Gallardo-Hernandez, Salvador; Lopez-Lopez, Maximo

    2013-12-01

    The temperature dependent van der Pauw (T-Pauw) technique was used to investigate the resistivity of three Ga1-xMnxAs layers grown on (6 3 1) GaAs semi-insulating substrates. The samples had Mn concentration of 3.52×l020 cm-3, 5.05×1020 cm-3 and 1.12×l021 cm-3, corresponding to Mn cell effusion temperature TMn of 700 °C, 715 °C and 745 °C, respectively. They were compared to samples grown under the same conditions but on (0 0 1) GaAs semi-insulating substrates. For the sample grown at TMn=700 °C on a (6 3 1) substrate, a two orders of magnitude decrease in the resistivity is observed, when compared with the sample grown on a (0 0 1) substrate. For the sample grown at TMn=715 °C the decrease is approximately four times, while for the sample grown at TMn=745 °C the decrease is approximately forty times. We plotted the resistivities as a function of temperature in Arrhenius plots, where we extracted two activation energies, the smallest one between 6 and 11 meV, and the largest one between 25 and 183 meV. Both activation energies increased as TMn increased. These results are in agreement with SIMS analysis where we observed that manganese concentration in the (6 3 1) orientation growth is around two order of magnitude larger than in the samples grown in the (0 0 1) orientation substrate.

  17. Investigations on crack generation mechanism and crack reduction by buffer layer insertion in thermal-plasma-jet crystallization of amorphous silicon films on glass substrate

    NASA Astrophysics Data System (ADS)

    Tanaka, Keisuke; Hayashi, Shohei; Morisaki, Seiji; Higashi, Seiichiro

    2015-01-01

    The crack generation mechanism and the effect of crack reduction by buffer SiO2 layer insertion in thermal-plasma-jet (TPJ) crystallization of an amorphous silicon film on a glass substrate have been investigated. The crack generation was clearly observed 13.7 s after TPJ irradiation using a high-speed camera, which indicates that cracks are generated not during heating, but during cooling. From the measurement and simulation of substrate deformations, it was clarified that the substrate deformed convexly during heating and it consequently deformed concavely after cooling owing to the substrate surface densification. This result indicated that the tensile stress generated by the concave deformation is the origin of cracks. The deposition of the buffer SiO2 layer generated compressive stress, which minimizes accumulation of tensile stress after TPJ annealing. The number of cracks in unit length significantly decreased owing to the decrease in tensile stress with the increase in the thickness of the buffer SiO2 layer.

  18. Thermal-fatigue and oxidation resistance of cobalt-modified Udimet 700 alloy

    NASA Technical Reports Server (NTRS)

    Bizon, P. T.; Barrow, B. J.

    1986-01-01

    Comparative thermal-fatigue and oxidation resistances of cobalt-modified wrought Udimet 700 alloy (obtained by reducing the cobalt level by direct substitution of nickel) were determined from fluidized-bed tests. Bed temperatures were 1010 and 288 C (1850 and 550 C) for the first 5500 symmetrical 6-min cycles. From cycle 5501 to the 14000-cycle limit of testing, the heating bed temperature was increased to 1050 C (1922 F). Cobalt levels between 0 and 17 wt% were studied in both the bare and NiCrAlY overlay coated conditions. A cobalt level of about 8 wt% gave the best thermal-fatigue life. The conventional alloy specification is for 18.5% cobalt, and hence, a factor of 2 in savings of cobalt could be achieved by using the modified alloy. After 13500 cycles, all bare cobalt-modified alloys lost 10 to 13 percent of their initial weight. Application of the NiCrAlY overlay coating resulted in weight losses of 1/20 to 1/100 of that of the corresponding bare alloy.

  19. Extreme resistance to thermally induced DNA backbone breaks in the hyperthermophilic archaeon Pyrococcus furiosus.

    PubMed Central

    Peak, M J; Robb, F T; Peak, J G

    1995-01-01

    Pyrococcus furiosus is a hyperthermophilic archaeon that grows optimally at 100 degrees C. It is not conceivable that these organisms could survive with genomic DNA that was subject to thermal destruction, yet the mechanisms protecting the genomes of this and other hyperthermophiles against such destruction are obscure. We have determined the effect of elevated temperatures up to 110 degrees C on the molecular weight of DNA in intact P. furiosus cells, compared with the effect of elevated temperatures on DNA in the mesothermophilic bacterium Escherichia coli. At 100 degrees C, DNA in P. furiosus cells is about 20 times more resistant to thermal breakage than that in E. coli cells, and six times fewer breaks were found in P. furiosus DNA after exposure to 110 degrees C for 30 min than in E. coli DNA at 95 degrees C. Our hypothesis for this remarkable stability of DNA in a hyperthermophile is that this hyperthermophile possesses DNA-binding proteins that protect against hydrolytic damage, as well as other endogenous protective mechanisms and DNA repair enzyme systems. PMID:7592404

  20. Development of silane-hydrolysate binder for UV-resistant thermal control coatings

    NASA Technical Reports Server (NTRS)

    Patterson, W. J.

    1981-01-01

    Detailed characterizaton and formulation studies were performed on a methyltriakoxysilane hydrolysate as a binder for thermal control coatings. The binder was optimized by varying hydrolysis temperature, time, catalyst type, and water concentration. The candidate coating formulations, based on this binder with TiO2 pigment, were optimized via a detailed series of sprayed test panels that included the parameters of binder/pigment ratio, ethanol content, pigment particle size, coating thickness and cure conditions. A typical optimized coating was prepared by acetic acid catalyzed hydrolysis of methyltriethoxysilane with 3.25 mol-equivalents of water over a 24 hour period at room temperature. The resulting hydrolysate was directly mixed with pre-milled TiO2 (12 grams pigment/26 grams binder) to yield a sprayable consistency. Panels were sprayed to result in a nominal cure coating thickness of 2 mils. Cure was affected by air drying for 24 hr at room temperature plus 72 hr at 150 F. These coatings are typically extremely tough and abrasion-resistant, with an absorptance (alpha) of 0.20 and emittance (e) of 0.89. No significant coating damage was observed in the mandrel bend test, even after exposure to thermal cycling from -160 to 160 F. Vacuum exposure of the coatings for 930 hours at 1 equivalent UV sun resulted in no visible degradation and no significant increase in absorptance.

  1. MBE growth of ALGaN/GaN HEMTS on resistive Si(1 1 1) substrate with RF small signal and power performances

    NASA Astrophysics Data System (ADS)

    Cordier, Y.; Semond, F.; Lorenzini, P.; Grandjean, N.; Natali, F.; Damilano, B.; Massies, J.; Hoël, V.; Minko, A.; Vellas, N.; Gaquière, C.; DeJaeger, J. C.; Dessertene, B.; Cassette, S.; Surrugue, M.; Adam, D.; Grattepain, J.-C.; Aubry, R.; Delage, S. L.

    2003-04-01

    In this paper, we report on the properties of GaN films and AlGaN/GaN HEMT structures grown by molecular beam epitaxy on resistive Si(1 1 1) substrates. The properties of the GaN buffer layer and the AlGaN/GaN HEMTs are presented. Finally, both static and high-frequency performances of sub-micron gate length devices are analyzed demonstrating their RF power capability.

  2. Performance improvement of GaN-based metal-semiconductor-metal photodiodes grown on Si(111) substrate by thermal cycle annealing process

    NASA Astrophysics Data System (ADS)

    Lin, Jyun-Hao; Huang, Shyh-Jer; Su, Yan-Kuin

    2014-01-01

    A simple thermal cycle annealing (TCA) process was used to improve the quality of GaN grown on a Si substrate. The X-ray diffraction (XRD) and etch pit density (EPD) results revealed that using more process cycles, the defect density cannot be further reduced. However, the performance of GaN-based metal-semiconductor-metal (MSM) photodiodes (PDs) prepared on Si substrates showed significant improvement. With a two-cycle TCA process, it is found that the dark current of the device was only 1.46 × 10-11 A, and the photo-to-dark-current contrast ratio was about 1.33 × 105 at 5 V. Also, the UV/visible rejection ratios can reach as high as 1077.

  3. Substrate-mediated strain effect on the role of thermal heating and electric field on metal-insulator transition in vanadium dioxide nanobeams

    PubMed Central

    Kim, Min-Woo; Jung, Wan-Gil; Hyun-Cho; Bae, Tae-Sung; Chang, Sung-Jin; Jang, Ja-Soon; Hong, Woong-Ki; Kim, Bong-Joong

    2015-01-01

    Single-crystalline vanadium dioxide (VO2) nanostructures have recently attracted great attention because of their single domain metal-insulator transition (MIT) nature that differs from a bulk sample. The VO2 nanostructures can also provide new opportunities to explore, understand, and ultimately engineer MIT properties for applications of novel functional devices. Importantly, the MIT properties of the VO2 nanostructures are significantly affected by stoichiometry, doping, size effect, defects, and in particular, strain. Here, we report the effect of substrate-mediated strain on the correlative role of thermal heating and electric field on the MIT in the VO2 nanobeams by altering the strength of the substrate attachment. Our study may provide helpful information on controlling the properties of VO2 nanobeam for the device applications by changing temperature and voltage with a properly engineered strain. PMID:26040637

  4. Correlation of the nanostructure with optoelectronic properties during rapid thermal annealing of Ga(NAsP) quantum wells grown on Si(001) substrates

    SciTech Connect

    Wegele, Tatjana; Beyer, Andreas; Gies, Sebastian; Zimprich, Martin; Heimbrodt, Wolfram; Stolz, Wolfgang; Volz, Kerstin

    2016-01-14

    Ga(NAsP) quantum wells grown pseudomorphically on Si substrate are promising candidates for optically active light sources in future optoelectronically integrated circuits on Si substrates. As the material is typically grown at low temperatures, it has to be thermally annealed after growth to remove defects and optimize optoelectronic properties. Here we show by quantitative transmission electron microscopy that two different kinds of structural development are associated with the annealing. First of all, the quantum well homogeneity improves with increasing annealing temperature. For annealing temperatures above 925 °C the composition becomes less homogeneous again. Second, voids form in the quantum well for annealing temperatures above 850 °C. Their density and size increase continuously with increasing annealing temperature. These results are correlated to the optical properties of the samples, where we find from temperature-dependent photoluminescence measurements two scales of disorder, which show the same temperature dependence as the structural properties.

  5. The effect of thermal damage on the electrical resistivity of sandstone

    NASA Astrophysics Data System (ADS)

    Zhang, Weiqiang; Sun, Qiang; Zhu, Shuyun; Hao, Shuqing

    2017-03-01

    In order to study the effect of thermal damage on the electrical property of sandstone, an electrical resistivity test is carried out with an electrical instrument. The prepared cylindrical samples are successively heated to target temperatures (i.e. 100 °C, 200 °C, 300 °C, 400 °C, 500 °C, 600 °C, 700 °C and 800 °C) at a fixed slow rate and gradually cooled down to room temperature at the same rate. The test results show that the resistivity of the sandstone samples increases gradually with the increasing temperature, and increases drastically between 300 °C and 350 °C. The wave velocity of the samples at different temperatures is also investigated and the results show that the wave velocity reduces gradually with the increasing temperature. Special attention is paid to the fact that the wave velocity reduces more quickly at certain temperatures between 300 °C and 350 °C. It can be speculated that there is a threshold temperature between 300 °C and 350 °C.

  6. Low- and high-resistivity silicon substrate characterization using the Al/silicon-rich oxide/Si structure with comparison to the metal oxide semiconductor technique

    NASA Astrophysics Data System (ADS)

    Luna-López, A.; Aceves-Mijares, M.; Malik, O.; Glaenzer, R.

    2005-05-01

    High-resistivity silicon substrates (HRS, NB<1014 cm-3) are commonly used, especially in optoelectronic integrated circuits. However, standard metal oxide semiconductor (MOS) characterization methods fail to predict correctly the dopant concentration and lifetime. This is due to the high resistance in series with the MOS capacitor, which causes an erroneous capacitance measurement at high frequency. To overcome this restriction, a different characterization method is proposed, using the electronic transport property of silicon-rich oxide (SRO) films, with aluminum/silicon-rich oxide (Al/SRO/Si) devices and using capacitance-voltage (C-V) and current-voltage (I-V) characteristics, the dopant concentration and lifetime can be estimated with these method. In addition, using low/high-frequency C-V measurements in MOS structure on HRS can be used to determine the dopant concentration. In this work, low-resistivity silicon and HRS substrates are characterized. The results for both type of substrates and for the different methods are compared. It is shown that the results are similar and any of these methods produce reliable results, but the Al/SRO/Si structure has the advantage that the generation lifetime is easily obtained.

  7. Thermal residual stresses near the interface between plasma-sprayed hydroxyapatite coating and titanium substrate: finite element analysis and synchrotron radiation measurements.

    PubMed

    Cofino, B; Fogarassy, P; Millet, P; Lodini, A

    2004-07-01

    Plasma-sprayed hydroxyapatite (HA) coatings on titanium alloy are often used in prosthetic implants. The metallic substrate gives the implant good mechanical strength which is combined with good biocompatibility and osteointegration of the ceramic coating. However, the interface between the HA coating and titanium alloy substrate is an area of critical weakness when compared with the interlamellar cohesive strength of the HA coating structure. Knowledge of the stresses in materials near the interface seems to be an important step in understanding why failure occurs. Synchrotron radiation, using Beamline BM16 at the European Synchrotron Radiation Facility (Grenoble, France), has been used to determine local stresses near the interface, down to 10 microm in resolution, between a plasma-sprayed HA coating and a titanium alloy substrate. This experimental determination of residual stresses is compared with the results found by a finite element analysis modeling the thermal effects of the plasma-spraying process. Residual stresses have been found in deposited ceramic near the interface due to a thermal properties mismatch of the materials. If the plane stress state is assumed, meaning the perpendicular component of residual stress is ignored (sigma(z) = 0), then the synchrotron residual stress measurements should be interpreted as mainly compressive in the ceramic coating. This is in contradiction with the coefficient of thermal expansion mismatch; therefore, the simplified plane stresses assumption seems to be inappropriate for the deposited morphology characterized by pores and a network of microcracks. The detailed finite element analysis model, taking into account the real morphology of the coating and the real three-dimensional stress field distribution, allowed the estimation of sigma(z), leading to a more accurate interpretation of synchrotron measurements, which is validated by the experimental results.

  8. Altering the thermal resistance of foodborne bacterial pathogens with an eggshell membrane waste by-product.

    PubMed

    Poland, A L; Sheldon, B W

    2001-04-01

    Eggshells from egg-breaking operations are a significant waste disposal problem. Thus, the development of value-added by-products from this waste would be welcomed by the industry. The ability of extracted eggshell membranes containing, several bacteriolytic enzymes (i.e., lysozyme and beta-N-acetylglucosaminidase) or other membrane components to alter the thermal resistance of gram-positive and gram-negative bacterial pathogens was evaluated. Mid-log phase cells of Salmonella Enteritidis (SE), Salmonella Typhimurium (ST), Escherichia coli O157:H7 (EC), Listeria monocytogenes Scott A (LM), and Staphylococcus aureus (SA) were suspended in 100 ml of 0.1% peptone water (pH 6.9, 10(7-8) CFU/ml) containing either 0 (control) or 10 g of an eggshell membrane extract and incubated at 37 degrees C for 45 min. Following exposure, membrane-free samples (1.5 ml) were heated in a 56 degrees C (LM, SA), 54 degrees C (SE, ST), or 52 degrees C (EC) water bath from 0 to 14 min in sealed glass reaction vials (12 by 32 mm), and the survivors were recovered on brain heart infusion agar. Population reductions ranging from 27.6% (SA) to 99.8% (LM) (ST, 43.8%; SE, 47.5%; EC, 71.8%) were observed for cells treated for 45 min with extracted membrane, as compared to controls. D-value reductions ranging from 0 (LM) to 87.2% (SE) (SA, 36.7%; EC, 83.3%; ST, 86.3%) were observed when membrane-treated cells were subsequently heat inactivated. The effects of exposure pH, time, temperature, and organic load on membrane activity were also evaluated with Salmonella Typhimurium. Exposure pH (5.0 versus 6.9), time (15 versus 45 min), and temperature (4 degrees C versus 37 degrees C) did not significantly reduce the impact of eggshell membranes on D-values. However, the presence of organic matter (0.1% peptone water versus skim milk) significantly reduced the thermal resistance-reducing capacity of the membranes. These preliminary findings provide information on the potential use of extracted eggshell

  9. High-speed thermal imaging of yttria-stabilized zirconia droplet impinging on substrate in plasma spraying

    SciTech Connect

    Shinoda, Kentaro; Murakami, Hideyuki; Kuroda, Seiji; Oki, Sachio; Takehara, Kohsei; Etoh, Takeharu Goji

    2007-05-07

    The authors have developed an in situ monitoring system that captures the impacting phenomena of plasma-sprayed particles at 1x10{sup 6} frames/s. The system clearly captured deformation and cooling processes of an yttria-stabilized zirconia droplet of 50 {mu}m in diameter impinging at 170 m/s on a smooth quartz glass substrate kept at room temperature. The images show that the liquid sheet jetting out sideways from the droplet detached from the substrate and kept on spreading without disintegration until its maximum extent. While the sheet was spreading, the center region of the flattened droplet cooled down much more rapidly.

  10. Effects of Chicken Litter Storage Time and Ammonia Content on Thermal Resistance of Desiccation-Adapted Salmonella spp.

    PubMed Central

    Chen, Zhao; Wang, Hongye; Ionita, Claudia; Luo, Feng

    2015-01-01

    Broiler chicken litter was kept as a stacked heap on a poultry farm, and samples were collected up to 9 months of storage. Chicken litter inoculated with desiccation-adapted Salmonella cells was heat-treated at 75, 80, 85, and 150°C. Salmonella populations decreased in all these samples during heat treatment, and the inactivation rates became lower in chicken litter when storage time was extended from 0 to 6 months. There was no significant difference (P > 0.05) in thermal resistance of Salmonella in 6- and 9-month litter samples, indicating that a threshold for thermal resistance was reached after 6 months. Overall, the thermal resistance of Salmonella in chicken litter was affected by the storage time of the litter. The changes in some chemical, physical, and microbiological properties during storage could possibly contribute to this difference. Moisture and ammonia could be two of the most significant factors influencing the thermal resistance of Salmonella cells in chicken litter. Our results emphasize the importance of adjusting time and temperature conditions for heat processing chicken litter when it is removed from the chicken house at different time intervals. PMID:26209673

  11. Effects of Chicken Litter Storage Time and Ammonia Content on Thermal Resistance of Desiccation-Adapted Salmonella spp.

    PubMed

    Chen, Zhao; Wang, Hongye; Ionita, Claudia; Luo, Feng; Jiang, Xiuping

    2015-10-01

    Broiler chicken litter was kept as a stacked heap on a poultry farm, and samples were collected up to 9 months of storage. Chicken litter inoculated with desiccation-adapted Salmonella cells was heat-treated at 75, 80, 85, and 150°C. Salmonella populations decreased in all these samples during heat treatment, and the inactivation rates became lower in chicken litter when storage time was extended from 0 to 6 months. There was no significant difference (P > 0.05) in thermal resistance of Salmonella in 6- and 9-month litter samples, indicating that a threshold for thermal resistance was reached after 6 months. Overall, the thermal resistance of Salmonella in chicken litter was affected by the storage time of the litter. The changes in some chemical, physical, and microbiological properties during storage could possibly contribute to this difference. Moisture and ammonia could be two of the most significant factors influencing the thermal resistance of Salmonella cells in chicken litter. Our results emphasize the importance of adjusting time and temperature conditions for heat processing chicken litter when it is removed from the chicken house at different time intervals.

  12. Thermally aware, durable nanoengineered surfaces with high speed liquid impalement resistance

    NASA Astrophysics Data System (ADS)

    Tiwari, Manish; Peng, Chaoyi; Chen, Zhuyang

    2016-11-01

    Highly hydrophobic nanoengineered surfaces delaying freezing down to -20 degrees Centigrade for a day, sustaining dropwise steam condensation under high rate steam shear for several days, sustaining mechanical abrasion and high strains have attracted strong interest recently. Particularly, anti-icing and dropwise condensation promotion require thermally conductive surfaces with careful nucleation control - of ice germs or droplets, respectively - using precise surface nanotexture. Scalability of surface manufacture is an additional challenge. In the current presentation, we will demonstrate a pathway to address these needs. Anodisation of metallic substrate is first used to obtain nanotextured surfaces with a precision of approx. 200 nm. Next, rationally formulated nanocomposites comprising solution processed fluorinated copolymers and nanoparticle dispersions were spray coated on the anodized metals. The resulting nanocomposite coatings were superhydrophobic with approx. 20 nm precision in surface texture. The surface durability is assessed using tape peel, sand abrasion, and droplet and water jet impact tests up to 30 m/s. High speed jet splashing is recorded at speeds >10 m/s to demonstrate the influence of jet diameter on splashing characteristics. This work was partly supported by EPSRC Grant EP/N006577/1.

  13. Electrostatic Assembly Preparation of High-Toughness Zirconium Diboride-Based Ceramic Composites with Enhanced Thermal Shock Resistance Performance.

    PubMed

    Zhang, Baoxi; Zhang, Xinghong; Hong, Changqing; Qiu, Yunfeng; Zhang, Jia; Han, Jiecai; Hu, PingAn

    2016-05-11

    The central problem of using ceramic as a structural material is its brittleness, which associated with rigid covalent or ionic bonds. Whiskers or fibers of strong ceramics such as silicon carbide (SiC) or silicon nitride (Si3N4) are widely embedded in a ceramic matrix to improve the strength and toughness. The incorporation of these insulating fillers can impede the thermal flow in ceramic matrix, thus decrease its thermal shock resistance that is required in some practical applications. Here we demonstrate that the toughness and thermal shock resistance of zirconium diboride (ZrB2)/SiC composites can be improved simultaneously by introducing graphene into composites via electrostatic assembly and subsequent sintering treatment. The incorporated graphene creates weak interfaces of grain boundaries (GBs) and optimal thermal conductance paths inside composites. In comparison to pristine ZrB2-SiC composites, the toughness of (2.0%) ZrB2-SiC/graphene composites exhibited a 61% increasing (from 4.3 to 6.93 MPa·m(1/2)) after spark plasma sintering (SPS); the retained strength after thermal shock increased as high as 74.8% at 400 °C and 304.4% at 500 °C. Present work presents an important guideline for producing high-toughness ceramic-based composites with enhanced thermal shock properties.

  14. Electrical resistivity and thermal conductivity of liquid Fe alloys at high P and T, and heat flux in Earth's core.

    PubMed

    de Koker, Nico; Steinle-Neumann, Gerd; Vlcek, Vojtech

    2012-03-13

    Earth's magnetic field is sustained by magnetohydrodynamic convection within the metallic liquid core. In a thermally advecting core, the fraction of heat available to drive the geodynamo is reduced by heat conducted along the core geotherm, which depends sensitively on the thermal conductivity of liquid iron and its alloys with candidate light elements. The thermal conductivity for Earth's core is very poorly constrained, with current estimates based on a set of scaling relations that were not previously tested at high pressures. We perform first-principles electronic structure computations to determine the thermal conductivity and electrical resistivity for Fe, Fe-Si, and Fe-O liquid alloys. Computed resistivity agrees very well with existing shock compression measurements and shows strong dependence on light element concentration and type. Thermal conductivity at pressure and temperature conditions characteristic of Earth's core is higher than previous extrapolations. Conductive heat flux near the core-mantle boundary is comparable to estimates of the total heat flux from the core but decreases with depth, so that thermally driven flow would be constrained to greater depths in the absence of an inner core.

  15. The naphthoquinones, vitamin K3 and its structural analog plumbagin, are substrates of the multidrug resistance-linked ABC drug transporter ABCG2

    PubMed Central

    Shukla, Suneet; Wu, Chung-Pu; Nandigama, Krishnamachary; Ambudkar, Suresh V.

    2008-01-01

    Vitamin K3 (Menadione; 2-methyl-1,4-naphthoquinone) is a structural precursor of vitamins K1 and K2 which are essential for blood clotting. The naturally occurring structural analog of this vitamin, plumbagin (5-hydroxy-menadione), is known to modulate cellular proliferation, apoptosis, carcinogenesis, and radioresistance. We, here, report that both vitamin K3 and plumbagin are substrates of the multidrug resistance-linked ATP binding cassette (ABC) drug transporter, ABCG2. Vitamin K3 and plumbagin specifically inhibited the ABCG2-mediated efflux of mitoxantrone, but did not have any effect on the ABCB1-mediated efflux of rhodamine 123. This inhibition of ABCG2 function was due to their interaction at the substrate-binding site(s). They inhibited the binding of [125I]-Iodoarylazidoprazosin (IAAP), a substrate of ABCG2, to this transporter in a concentration-dependent manner with IC50 values of 7.3 and 22.6 μM, respectively, but had no effect on the binding of this photoaffinity analog to ABCB1. Both compounds stimulated ABCG2-mediated ATP hydrolysis and also inhibited the mitoxantrone-stimulated ATPase activity of this transporter, but did not have any significant effect on the ATPase activity of ABCB1. In a cytotoxicity assay, ABCG2-expressing HEK cells were 2.8- and 2.3-fold resistant to plumbagin and vitamin K3, respectively, compared to the control cells, suggesting that they are substrates of this transporter. Collectively, these data demonstrate for the first time that vitamin K3 is a substrate of the ABCG2 transporter. Thus, ABCG2 may have a role in the regulation of vitamin K3 levels in the body. In addition, vitamin K3 and its structural derivative, plumbagin, could potentially be used to modulate ABCG2 function. PMID:18065489

  16. Evidence of a Substrate-Discriminating Entrance Channel in the Lower Porter Domain of the Multidrug Resistance Efflux Pump AcrB

    PubMed Central

    Vavra, Martina; Kern, Winfried V.

    2016-01-01

    Efflux pumps of the resistance nodulation cell division (RND) transporter family, such as AcrB of Escherichia coli, play an important role in the development of multidrug resistance, but the molecular basis for their substrate promiscuity is not yet completely understood. From a collection of highly clarithromycin-resistant AcrB periplasmic domain mutants derived from in vitro random mutagenesis, we identified variants with an unusually altered drug resistance pattern characterized by increased susceptibility to many drugs of lower molecular weight, including fluoroquinolones, tetracyclines, and oxazolidinones, but unchanged or increased resistance to drugs of higher molecular weight, including macrolides. Sequencing of 14 such “divergent resistance” phenotype mutants and 15 control mutants showed that this unusual phenotype was associated with mutations at residues I38 and I671 predominantly to phenylalanine and threonine, respectively, both conferring a similar susceptibility pattern. Reconstructed I38F and I671T single mutants as well as an engineered I38F I671T double mutant with proved efflux competence revealed an equivalent phenotype with enhanced or unchanged resistance to many large AcrB substrates but increased susceptibility to several lower-molecular-weight drugs known to bind within the distal binding pocket. The two isoleucines located in close vicinity to each other in the lower porter domain of AcrB beneath the bottom of the proximal binding pocket may be part of a preferential small-drug entrance pathway that is compromised by the mutations. This finding supports recent indications of distinct entrance channels used by compounds with different physicochemical properties, of which molecular size appears to play a prominent role. PMID:27161641

  17. Flexible crossbar-structured resistive memory arrays on plastic substrates via inorganic-based laser lift-off.

    PubMed

    Kim, Seungjun; Son, Jung Hwan; Lee, Seung Hyun; You, Byoung Kuk; Park, Kwi-Il; Lee, Hwan Keon; Byun, Myunghwan; Lee, Keon Jae

    2014-11-26

    Crossbar-structured memory comprising 32 × 32 arrays with one selector-one resistor (1S-1R) components are initially fabricated on a rigid substrate. They are transferred without mechanical damage via an inorganic-based laser lift-off (ILLO) process as a result of laser-material interaction. Addressing tests of the transferred memory arrays are successfully performed to verify mitigation of cross-talk on a plastic substrate.

  18. Thermal and irradiation induced interdiffusion in magnetite thin films grown on magnesium oxide (0 0 1) substrates

    NASA Astrophysics Data System (ADS)

    Kim-Ngan, N.-T. H.; Balogh, A. G.; Meyer, J. D.; Brötz, J.; Zając, M.; Ślęzak, T.; Korecki, J.

    2009-05-01

    Epitaxial Fe 3O 4(0 0 1) thin films (with a thickness in the range of 10-20 nm) grown on MgO substrates were characterized using low-energy electron diffraction (LEED), conversion electron Mössbauer spectroscopy (CEMS) and investigated using Rutherford backscattering spectrometry (RBS), channeling (RBS-C) experiments and X-ray reflectometry (XRR). The Mg out-diffusion from the MgO substrate into the film was observed for the directly-deposited Fe 3O 4/MgO(0 0 1) films. For the Fe 3O 4/Fe/MgO(0 0 1) films, the Mg diffusion was prevented by the Fe layer and the surface layer is always a pure Fe 3O 4 layer. Annealing and ion beam mixing induced a very large interface zone having a spinel and/or wustite formula in the Fe 3O 4-on-Fe film system.

  19. Multiscale simulation of thermal disruption in resistance switching process in amorphous carbon

    NASA Astrophysics Data System (ADS)

    Popov, A. M.; Shumkin, G. N.; Nikishin, N. G.

    2015-09-01

    The switching of material atomic structure and electric conductivity is used in novel technologies of making memory on the base of phase change. The possibility of making memory on the base of amorphous carbon is shown in experiment [1]. Present work is directed to simulation of experimentally observed effects. Ab initio quantum calculations were used for simulation of atomic structure changes in amorphous carbon [2]. These simulations showed that the resistance change is connected with thermally induced effects. The temperature was supposed to be the function of time. In present paper we propose a new multiscale, self-consistent model which combines three levels of simulation scales and takes into account the space and time dependencies of the temperature. On the first level of quantum molecular dynamic we provide the calculations of phase change in atomic structure with space and time dependence of the temperature. Nose-Hover thermostats are used for MD simulations to reproduce space dependency of the temperature. It is shown that atomic structure is localized near graphitic layers in conducting dot. Structure parameter is used then on the next levels of the modeling. Modified Ehrenfest Molecular Dynamics is used on the second level. Switching evolution of electronic subsystem is obtained. In macroscopic scale level the heat conductivity equation for continuous media is used for calculation space-time dependence of the temperature. Joule heat source depends on structure parameter and electric conductivity profiles obtained on previous levels of modeling. Iterative procedure is self-consistently repeated combining three levels of simulation. Space localization of Joule heat source leads to the thermal disruption. Obtained results allow us to explain S-form of the Volt-Ampere characteristic observed in experiment. Simulations were performed on IBM Blue Gene/P supercomputer at Moscow State University.

  20. Increasing activity and thermal resistance of Bacillus gibsonii alkaline protease (BgAP) by directed evolution.

    PubMed

    Martinez, Ronny; Jakob, Felix; Tu, Ran; Siegert, Petra; Maurer, Karl-Heinz; Schwaneberg, Ulrich

    2013-03-01

    Bacillus gibsonii Alkaline Protease (BgAP) is a recently reported subtilisin protease exhibiting activity and stability properties suitable for applications in laundry and dish washing detergents. However, BgAP suffers from a significant decrease of activity at low temperatures. In order to increase BgAP activity at 15°C, a directed evolution campaign based on the SeSaM random mutagenesis method was performed. An optimized microtiter plate expression system in B. subtilis was established and classical proteolytic detection methods were adapted for high throughput screening. In parallel, the libraries were screened for increased residual proteolytic activity after incubation at 58°C. Three iterative rounds of directed BgAP evolution yielded a set of BgAP variants with increased specific activity (K(cat)) at 15°C and increased thermal resistance. Recombination of both sets of amino acid substitutions resulted finally in variant MF1 with a 1.5-fold increased specific activity (15°C) and over 100 times prolonged half-life at 60°C (224 min compared to 2 min of the WT BgAP). None of the introduced amino acid substitutions were close to the active site of BgAP. Activity-altering amino acid substitutions were from non-charged to non-charged or from sterically demanding to less demanding. Thermal stability improvements were achieved by substitutions to negatively charged amino acids in loop areas of the BgAP surface which probably fostered ionic and hydrogen bonds interactions.

  1. Influence of electrical current variance and thermal resistances on optimum working conditions and geometry for thermoelectric energy harvesting

    NASA Astrophysics Data System (ADS)

    Gomez, Miguel; Reid, Rachel; Ohara, Brandon; Lee, Hohyun

    2013-05-01

    Recent reports on enhanced thermoelectric figure of merits based on nanoscale effects have revived interest in potential applications of thermoelectric modules for waste heat recovery and distributed power generation. However, studies of optimized working conditions have not been thoroughly investigated. The majority of the previous studies on optimum load resistance for maximum power output or maximum efficiency assume temperatures at the ends of thermoelectric materials are known and constant. In reality, temperature should be determined by the energy conservation equations, which are functions of the load resistance, as well as the thermal resistances of the heat source, heat sink, and contact pads. This work exploits a numerical method to determine the actual temperature of thermoelectric materials, and optimum working conditions for thermoelectric energy harvesting are presented. The proposed model considers the effect of thermal resistances between a thermoelectric module and heat reservoirs, and the electrical current variation with respect to load resistance. The optimum condition for load resistance ratio was observed to occur at larger values than those obtained from traditional optimization work. Additionally, optimum geometry for a thermoelectric module is suggested for energy harvesting methods, where forced convection or oversized heat sinks cannot be used. Experimental results obtained from a commercial thermoelectric module are also presented to validate the proposed model. This work forms a basis to predict optimum working conditions in various thermoelectric energy harvesting applications.

  2. A wave-dominated heat transport mechanism for negative differential thermal resistance in graphene/hexagonal boron nitride heterostructures

    NASA Astrophysics Data System (ADS)

    Chen, Xue-Kun; Liu, Jun; Peng, Zhi-Hua; Du, Dan; Chen, Ke-Qiu

    2017-02-01

    Nonlinear thermal transport in graphene/hexagonal boron nitride (h-BN) heterostructure is investigated by the nonequilibrium molecular dynamics method. It is found that negative differential thermal resistance (NDTR) will appear as the applied temperature difference increases. Detailed phonon spectra analysis reveals that the excited out-of-plane acoustic wave plays an important role in the heat transport across such interface. That is, the mechanical wave results in a significant mismatch between the lattice vibrations of graphene and h-BN domains and hinders interfacial thermal transport. In addition, NDTR can be tuned through the temperature parameter. Interestingly, the regime of NDTR becomes smaller and eventually vanishes with increasing the heterostructure length. However, NDTR is insensitive to the variation of system width. The work may be useful for nanoscale thermal managements utilizing the graphene/h-BN heterostructure.

  3. Improving the Thermal Shock Resistance of Thermal Barrier Coatings Through Formation of an In Situ YSZ/Al2O3 Composite via Laser Cladding

    NASA Astrophysics Data System (ADS)

    Soleimanipour, Zohre; Baghshahi, Saeid; Shoja-razavi, Reza

    2017-03-01

    In the present study, laser cladding of alumina on the top surface of YSZ thermal barrier coatings (TBC) was conducted via Nd:YAG pulsed laser. The thermal shock behavior of the TBC before and after laser cladding was modified by heating at 1000 °C for 15 min and quenching in cold water. Phase analysis, microstructural evaluation and elemental analysis were performed using x-ray diffractometry, scanning electron microscopy (SEM), and energy-dispersive spectroscopy. The results of thermal shock tests indicated that the failure in the conventional YSZ (not laser clad) and the laser clad coatings happened after 200 and 270 cycles, respectively. The SEM images of the samples showed that delamination and spallation occurred in both coatings as the main mechanism of failure. Formation of TGO was also observed in the fractured cross section of the samples, which is also a main reason for degradation. Thermal shock resistance in the laser clad coatings improved about 35% after cladding. The improvement is due to the presence of continuous network cracks perpendicular to the surface in the clad layer and also the thermal stability and high melting point of alumina in Al2O3/ZrO2 composite.

  4. The R-curve behavior and thermal shock resistance for Al2O3 + ZrO2 laminated nanoceramics.

    PubMed

    Chen, Bei; Hu, Xiaohua; Cheng, Chuan

    2014-05-01

    The properties of thermal shock resistances of Al2O3 + ZrO2 monolayer and laminated ceramics are determined by the indentation method. The relationships between the R-curve, the thermal shock resistance properties and the mechanism of strengthening and toughening are also studied in this paper. The Al2O3 + ZrO2 laminated ceramics have an R-curve feature and a decrease in the sensitivity of the strength to the size of surface cracks. Indentation thermal shock test shows that the critical temperature difference of the Al2O3 + ZrO2 laminated ceramics is 400 degrees C, 150 degrees C higher than that of the monolayer ceramics. Under the condition of the surface compressive stress, the surface fracture appearance is more uneven and the fracture mechanism is different along the interface. The R-curve and thermal shock resistance properties are improved by strengthening the transformation effect resulting from the surface compressive stress.

  5. Rapid thermal annealing effect on the spatial resistivity distribution of AZO thin films deposited by pulsed-direct-current sputtering for solar cells applications

    NASA Astrophysics Data System (ADS)

    Ayachi, Boubakeur; Aviles, Thomas; Vilcot, Jean-Pierre; Sion, Cathy

    2016-03-01

    Room temperature deposited aluminium-doped zinc oxide thin films on glass substrate, using pulsed-DC magnetron sputtering, have shown high optical transmittance and low electrical resistivity with high uniformity of its spatial distribution after they were exposed to a rapid thermal annealing process at 400 °C under N2H2 atmosphere. It is particularly interesting to note that such an annealing process of AZO thin films for only 30 s was sufficient, on one hand to improve their optical transmittance from 73% to 86%, on the other hand to both decrease their resistivity from 1.7 × 10-3 Ω cm to 5.1 × 10-4 Ω cm and achieve the highest uniformity spatial distribution. To understand the mechanisms behind such improvements of the optoelectronic properties, electrical, optical, structural and morphological changes as a function of annealing time have been investigated by using hall measurement, UV-visible spectrometry, X-ray diffraction and scanning electron microscope imaging, respectively.

  6. Thermal conductivity of a graphite bipolar plate (BPP) and its thermal contact resistance with fuel cell gas diffusion layers: Effect of compression, PTFE, micro porous layer (MPL), BPP out-of-flatness and cyclic load

    NASA Astrophysics Data System (ADS)

    Sadeghifar, Hamidreza; Djilali, Ned; Bahrami, Majid

    2015-01-01

    This paper reports on measurements of thermal conductivity of a graphite bipolar plate (BPP) as a function of temperature and its thermal contact resistance (TCR) with treated and untreated gas diffusion layers (GDLs). The thermal conductivity of the BPP decreases with temperature and its thermal contact resistance with GDLs, which has been overlooked in the literature, is found to be dominant over a relatively wide range of compression. The effects of PTFE loading, micro porous layer (MPL), compression, and BPP out-of-flatness are also investigated experimentally. It is found that high PTFE loadings, MPL and even small BPP out-of-flatness increase the BPP-GDL thermal contact resistance dramatically. The paper also presents the effect of cyclic load on the total resistance of a GDL-BPP assembly, which sheds light on the behavior of these materials under operating conditions in polymer electrolyte membrane fuel cells.

  7. High temperature coefficient of resistance of low-temperature-grown VO2 films on TiO2-buffered SiO2/Si (100) substrates

    NASA Astrophysics Data System (ADS)

    Miyazaki, Kenichi; Shibuya, Keisuke; Suzuki, Megumi; Wado, Hiroyuki; Sawa, Akihito

    2015-08-01

    The introduction of a TiO2 buffer layer significantly improved the temperature coefficient of resistance (TCR), a measure of the sharpness of the metal-insulator transition, for films of VO2 grown on SiO2/Si (100) substrates at growth temperatures below 670 K. X-ray diffraction and Raman scattering measurements revealed that polycrystalline VO2 films were formed on the TiO2-buffered substrates at low temperatures below 600 K, whereas amorphous films were formed at these temperatures on SiO2/Si (100) substrates without a TiO2 buffer layer. Electron microscopy studies confirmed that the TiO2 buffer layer enhanced the grain growth of VO2 films at low growth temperatures. The VO2 films grown at 600 K on TiO2-buffered substrates showed a large TCR of more than 80%/K as a result of the improved crystallinity and grain size of the VO2 films. Our results provide an effective approach toward the integration of VO2-based devices onto Si platforms at process temperatures below 670 K.

  8. Fracture Resistance of K3 Nickel-Titanium Files Made from Different Thermal Treatments.

    PubMed

    Choi, JinWook; Oh, Soram; Kim, Yu-Chan; Jee, Kwang-Koo; Kum, KeeYeon; Chang, SeokWoo

    2016-01-01

    The purpose of this study was to compare fracture resistances of K3 nickel-titanium files made from different thermal treatments. K3 (SybronEndo, Orange, CA), K3XF (SybronEndo), and experimentally heat treated K3 (K3H) were used. For the cyclic fatigue test, the samples were rotated with up-and-down motion in the artificial canal with the curvature of 60 degrees until the fracture occurred. The number of cycles to fracture (NCF) was measured. For the torsional fracture test, the samples were tightly bound and rotated until the fracture occurred. Elastic modulus (EM), ultimate torsional strength (UTS), and angle of rotation to fracture (ARF) were measured. The results were statistically analyzed by one-way ANOVA. The NCF of K3H was higher than those of K3 and K3XF (P < 0.05). The EM of K3XF and K3H was lower than that of K3 (P < 0.05). There was no significant difference in UTS. The ARF of K3XF was higher than that of K3 (P < 0.05). K3XF and K3H showed more flexibility than K3. The maximum torsional angle of K3XF was higher than that of K3, but there was no significant difference on the UTS in all three groups.

  9. Thermal resistance of naturally occurring airborne bacterial spores. [Viking spacecraft dry heat decontamination simulation

    NASA Technical Reports Server (NTRS)

    Puleo, J. R.; Bergstrom, S. L.; Peeler, J. T.; Oxborrow, G. S.

    1978-01-01

    Simulation of a heat process used in the terminal dry-heat decontamination of the Viking spacecraft is reported. Naturally occurring airborne bacterial spores were collected on Teflon ribbons in selected spacecraft assembly areas and subsequently subjected to dry heat. Thermal inactivation experiments were conducted at 105, 111.7, 120, 125, 130, and 135 C with a moisture level of 1.2 mg of water per liter. Heat survivors were recovered at temperatures of 135 C when a 30-h heating cycle was employed. Survivors were recovered from all cycles studied and randomly selected for identification. The naturally occurring spore population was reduced an average of 2.2 to 4.4 log cycles from 105 to 135 C. Heating cycles of 5 and 15 h at temperature were compared with the standard 30-h cycle at 111.7, 120, and 125 C. No significant differences in inactivation (alpha = 0.05) were observed between 111.7 and 120 C. The 30-h cycle differs from the 5- and 15-h cycles at 125 C. Thus, the heating cycle can be reduced if a small fraction (about 0.001 to 0.0001) of very resistant spores can be tolerated.

  10. A new model for thermal contact resistance between fuel cell gas diffusion layers and bipolar plates

    NASA Astrophysics Data System (ADS)

    Sadeghifar, Hamidreza; Djilali, Ned; Bahrami, Majid

    2014-11-01

    A new analytical model is developed to predict the thermal contact resistance (TCR) between fibrous porous media such as gas diffusion layers (GDLs) of polymer electrolyte membrane fuel cells (PEMFCs) and flat surfaces (bipolar plates). This robust model accounts for the salient geometrical parameters of GDLs, mechanical deformation, and thermophysical properties of the contacting bodies. The model is successfully validated against experimental data, and is used to perform in a comprehensive parametric study to investigate the effects of fiber parameters such as waviness and GDL properties on the TCR. Fiber waviness, diameter and surface curvature, as well as GDL porosity, are found to have a strong influence on TCR whereas fiber length does not affect the TCR when the porosity is kept constant. Such findings provide useful guidance for design and manufacturing of more effective GDLs for PEMFC heat management. The analytic model can be readily implemented in simulation and modeling of PEMFCs, and can be extended with minor modifications to other fibrous porous media such as fibrous catalysts, insulating media and sintered metals.

  11. Fracture Resistance of K3 Nickel-Titanium Files Made from Different Thermal Treatments

    PubMed Central

    Choi, JinWook; Oh, Soram; Kim, Yu-Chan; Jee, Kwang-Koo

    2016-01-01

    The purpose of this study was to compare fracture resistances of K3 nickel-titanium files made from different thermal treatments. K3 (SybronEndo, Orange, CA), K3XF (SybronEndo), and experimentally heat treated K3 (K3H) were used. For the cyclic fatigue test, the samples were rotated with up-and-down motion in the artificial canal with the curvature of 60 degrees until the fracture occurred. The number of cycles to fracture (NCF) was measured. For the torsional fracture test, the samples were tightly bound and rotated until the fracture occurred. Elastic modulus (EM), ultimate torsional strength (UTS), and angle of rotation to fracture (ARF) were measured. The results were statistically analyzed by one-way ANOVA. The NCF of K3H was higher than those of K3 and K3XF (P < 0.05). The EM of K3XF and K3H was lower than that of K3 (P < 0.05). There was no significant difference in UTS. The ARF of K3XF was higher than that of K3 (P < 0.05). K3XF and K3H showed more flexibility than K3. The maximum torsional angle of K3XF was higher than that of K3, but there was no significant difference on the UTS in all three groups. PMID:27965526

  12. In vivo non-thermal irreversible electroporation impact on rat liver galvanic apparent internal resistance

    NASA Astrophysics Data System (ADS)

    Golberg, A.; Laufer, S.; Rabinowitch, H. D.; Rubinsky, B.

    2011-02-01

    Non-thermal irreversible electroporation (NTIRE) is a biophysical phenomenon which involves application of electric field pulses to cells or tissues, causing certain rearrangements in the membrane structure leading to cell death. The treated tissue ac impedance changes induced by electroporation were shown to be the indicators for NTIRE efficiency. In a previous study we characterized in vitro tissue galvanic apparent internal resistance (GAIR) changes due to NTIRE. Here we describe an in vivo study in which we monitored the GAIR changes of a rat liver treated by NTIRE. Electrical pulses were delivered through the same Zn/Cu electrodes by which GAIR was measured. GAIR was measured before and for 3 h after the treatment at 15 min intervals. The results were compared to the established ac bioimpedance measurement method. A decrease of 33% was measured immediately after the NTIRE treatment and a 40% decrease was measured after 3 h in GAIR values; in the same time 40% and 47% decrease respectively were measured by ac bioimpedance analyses. The temperature increase due to the NTIRE was only 0.5 °C. The results open the way for an inexpensive, self-powered in vivo real-time NTIRE effectiveness measurement.

  13. Junction-to-Case Thermal Resistance of a Silicon Carbide Bipolar Junction Transistor Measured

    NASA Technical Reports Server (NTRS)

    Niedra, Janis M.

    2006-01-01

    Junction temperature of a prototype SiC-based bipolar junction transistor (BJT) was estimated by using the base-emitter voltage (V(sub BE)) characteristic for thermometry. The V(sub BE) was measured as a function of the base current (I(sub B)) at selected temperatures (T), all at a fixed collector current (I(sub C)) and under very low duty cycle pulse conditions. Under such conditions, the average temperature of the chip was taken to be the same as that of the temperature-controlled case. At increased duty cycle such as to substantially heat the chip, but same I(sub C) pulse height, the chip temperature was identified by matching the V(sub BE) to the thermometry curves. From the measured average power, the chip-to-case thermal resistance could be estimated, giving a reasonable value. A tentative explanation for an observed bunching with increasing temperature of the calibration curves may relate to an increasing dopant atom ionization. A first-cut analysis, however, does not support this.

  14. Evaluating the thermal damage resistance of graphene/carbon nanotube hybrid composite coatings

    NASA Astrophysics Data System (ADS)

    David, L.; Feldman, A.; Mansfield, E.; Lehman, J.; Singh, G.

    2014-03-01

    We study laser irradiation behavior of multiwalled carbon nanotubes (MWCNT) and chemically modified graphene (rGO)-composite spray coatings for use as a thermal absorber material for high-power laser calorimeters. Spray coatings on aluminum test coupon were exposed to increasing laser irradiance for extended exposure times to quantify their damage threshold and optical absorbance. The coatings, prepared at varying mass % of MWCNTs in rGO, demonstrated significantly higher damage threshold values at 2.5 kW laser power at 10.6 μm wavelength than carbon paint or MWCNTs alone. Electron microscopy and Raman spectroscopy of irradiated specimens show that the coating prepared at 50% CNT loading endure at least 2 kW.cm-2 for 10 seconds without significant damage. The improved damage resistance is attributed to the unique structure of the composite in which the MWCNTs act as an efficient absorber of laser light while the much larger rGO sheets surrounding them, dissipate the heat over a wider area.

  15. Improving Metallic Thermal Protection System Hypervelocity Impact Resistance Through Design of Experiments Approach

    NASA Technical Reports Server (NTRS)

    Poteet, Carl C.; Blosser, Max L.

    2001-01-01

    A design of experiments approach has been implemented using computational hypervelocity impact simulations to determine the most effective place to add mass to an existing metallic Thermal Protection System (TPS) to improve hypervelocity impact protection. Simulations were performed using axisymmetric models in CTH, a shock-physics code developed by Sandia National Laboratories, and validated by comparison with existing test data. The axisymmetric models were then used in a statistical sensitivity analysis to determine the influence of five design parameters on degree of hypervelocity particle dispersion. Several damage metrics were identified and evaluated. Damage metrics related to the extent of substructure damage were seen to produce misleading results, however damage metrics related to the degree of dispersion of the hypervelocity particle produced results that corresponded to physical intuition. Based on analysis of variance results it was concluded that the most effective way to increase hypervelocity impact resistance is to increase the thickness of the outer foil layer. Increasing the spacing between the outer surface and the substructure is also very effective at increasing dispersion.

  16. Evaluating the thermal damage resistance of graphene/carbon nanotube hybrid composite coatings

    PubMed Central

    David, L.; Feldman, A.; Mansfield, E.; Lehman, J.; Singh, G.

    2014-01-01

    We study laser irradiation behavior of multiwalled carbon nanotubes (MWCNT) and chemically modified graphene (rGO)-composite spray coatings for use as a thermal absorber material for high-power laser calorimeters. Spray coatings on aluminum test coupon were exposed to increasing laser irradiance for extended exposure times to quantify their damage threshold and optical absorbance. The coatings, prepared at varying mass % of MWCNTs in rGO, demonstrated significantly higher damage threshold values at 2.5 kW laser power at 10.6 μm wavelength than carbon paint or MWCNTs alone. Electron microscopy and Raman spectroscopy of irradiated specimens show that the coating prepared at 50% CNT loading endure at least 2 kW.cm−2 for 10 seconds without significant damage. The improved damage resistance is attributed to the unique structure of the composite in which the MWCNTs act as an efficient absorber of laser light while the much larger rGO sheets surrounding them, dissipate the heat over a wider area. PMID:24603681

  17. Spin-dependent Seebeck Effect, Thermal Colossal Magnetoresistance and Negative Differential Thermoelectric Resistance in Zigzag Silicene Nanoribbon Heterojunciton

    NASA Astrophysics Data System (ADS)

    Fu, Hua-Hua; Wu, Dan-Dan; Zhang, Zu-Quan; Gu, Lei

    2015-05-01

    Spin-dependent Seebeck effect (SDSE) is one of hot topics in spin caloritronics, which examine the relationships between spin and heat transport in materials. Meanwhile, it is still a huge challenge to obtain thermally induced spin current nearly without thermal electron current. Here, we construct a hydrogen-terminated zigzag silicene nanoribbon heterojunction, and find that by applying a temperature difference between the source and the drain, spin-up and spin-down currents are generated and flow in opposite directions with nearly equal magnitudes, indicating that the thermal spin current dominates the carrier transport while the thermal electron current is much suppressed. By modulating the temperature, a pure thermal spin current can be achieved. Moreover, a thermoelectric rectifier and a negative differential thermoelectric resistance can be obtained in the thermal electron current. Through the analysis of the spin-dependent transport characteristics, a phase diagram containing various spin caloritronic phenomena is provided. In addition, a thermal magnetoresistance, which can reach infinity, is also obtained. Our results put forward an effective route to obtain a spin caloritronic material which can be applied in future low-power-consumption technology.

  18. Spin-dependent Seebeck Effect, Thermal Colossal Magnetoresistance and Negative Differential Thermoelectric Resistance in Zigzag Silicene Nanoribbon Heterojunciton

    PubMed Central

    Fu, Hua-Hua; Wu, Dan-Dan; Zhang, Zu-Quan; Gu, Lei

    2015-01-01

    Spin-dependent Seebeck effect (SDSE) is one of hot topics in spin caloritronics, which examine the relationships between spin and heat transport in materials. Meanwhile, it is still a huge challenge to obtain thermally induced spin current nearly without thermal electron current. Here, we construct a hydrogen-terminated zigzag silicene nanoribbon heterojunction, and find that by applying a temperature difference between the source and the drain, spin-up and spin-down currents are generated and flow in opposite directions with nearly equal magnitudes, indicating that the thermal spin current dominates the carrier transport while the thermal electron current is much suppressed. By modulating the temperature, a pure thermal spin current can be achieved. Moreover, a thermoelectric rectifier and a negative differential thermoelectric resistance can be obtained in the thermal electron current. Through the analysis of the spin-dependent transport characteristics, a phase diagram containing various spin caloritronic phenomena is provided. In addition, a thermal magnetoresistance, which can reach infinity, is also obtained. Our results put forward an effective route to obtain a spin caloritronic material which can be applied in future low-power-consumption technology. PMID:26000658

  19. Spin-dependent Seebeck Effect, Thermal Colossal Magnetoresistance and Negative Differential Thermoelectric Resistance in Zigzag Silicene Nanoribbon Heterojunciton.

    PubMed

    Fu, Hua-Hua; Wu, Dan-Dan; Zhang, Zu-Quan; Gu, Lei

    2015-05-22

    Spin-dependent Seebeck effect (SDSE) is one of hot topics in spin caloritronics, which examine the relationships between spin and heat transport in materials. Meanwhile, it is still a huge challenge to obtain thermally induced spin current nearly without thermal electron current. Here, we construct a hydrogen-terminated zigzag silicene nanoribbon heterojunction, and find that by applying a temperature difference between the source and the drain, spin-up and spin-down currents are generated and flow in opposite directions with nearly equal magnitudes, indicating that the thermal spin current dominates the carrier transport while the thermal electron current is much suppressed. By modulating the temperature, a pure thermal spin current can be achieved. Moreover, a thermoelectric rectifier and a negative differential thermoelectric resistance can be obtained in the thermal electron current. Through the analysis of the spin-dependent transport characteristics, a phase diagram containing various spin caloritronic phenomena is provided. In addition, a thermal magnetoresistance, which can reach infinity, is also obtained. Our results put forward an effective route to obtain a spin caloritronic material which can be applied in future low-power-consumption technology.

  20. Thermal Resistance Formulation of Fourier Equation and Its Application in the Study of Inhomogeneous Materials and Inverse Problems

    NASA Astrophysics Data System (ADS)

    Alvarado-Leaños, J. J.; Ordonez-Miranda, J.; Alvarado-Gil, J. J.

    2013-09-01

    In this work, considering that all the thermal properties of a sample depend on the position, it is shown that the Fourier heat transport equation can be written in terms of just the square of the thermal effusivity, by introducing the thermal resistance as a new variable. The conditions, in which analytical solutions of this equation can be obtained, are discussed. Based on these results, an inversion method is proposed to retrieve the profile of the thermal property profiles, if the surface temperature is provided. The method requires the assumption of a local thermal-effusivity profile, such that the temperature profile can be analytically obtained, to generate a global thermal-effusivity profile, which is independent of the initial assumed profile. Applying this method to a pair of simple but representative cases of one-dimensional layered systems, the accuracy and stability of the method is verified. In particular, the noise sensitivity is investigated by carrying out the inversion procedure with white Gaussian noise added to the simulated experimental data. The proposed approach could be useful for the development of methodologies to interpret experimental data and to retrieve the in-depth variations of thermal properties of materials.