Showing papers on "Atmospheric temperature range published in 1988"

Entropic elastic processes in protein mechanisms. I. Elastic structure due to an inverse temperature transition and elasticity due to internal chain dynamics.

Abstract: Numerous physical characterizations clearly demonstrate that the polypentapeptide of elastin (Val1-Pro2-Gly3-Val4-Gly5)n in water undergoes an inverse temperature transition. Increase in order occurs both intermolecularly and intramolecularly on raising the temperature from 20 to 40 degrees C. The physical characterizations used to demonstrate the inverse temperature transition include microscopy, light scattering, circular dichroism, the nuclear Overhauser effect, temperature dependence of composition, nuclear magnetic resonance (NMR) relaxation, dielectric relaxation, and temperature dependence of elastomer length. At fixed extension of the cross-linked polypentapeptide elastomer, the development of elastomeric force is seen to correlate with increase in intramolecular order, that is, with the inverse temperature transition. Reversible thermal denaturation of the ordered polypentapeptide is observed with composition and circular dichroism studies, and thermal denaturation of the crosslinked elastomer is also observed with loss of elastomeric force and elastic modulus. Thus, elastomeric force is lost when the polypeptide chains are randomized due to heating at high temperature. Clearly, elastomeric force is due to nonrandom polypeptide structure. In spite of this, elastomeric force is demonstrated to be dominantly entropic in origin. The source of the entropic elastomeric force is demonstrated to be the result of internal chain dynamics, and the mechanism is called the librational entropy mechanism of elasticity. There is significant application to the finding that elastomeric force develops due to an inverse temperature transition. By changing the hydrophobicity of the polypeptide, the temperature range for the inverse temperature transition can be changed in a predictable way, and the temperature range for the development of elastomeric force follows. Thus, elastomers have been prepared where the development of elastomeric force is shifted over a 40 degrees C temperature range from a midpoint temperature of 30 degrees C for the polypentapeptide to 10 degrees C by increasing hydrophobicity with addition of a single CH2 moiety per pentamer and to 50 degrees C by decreasing hydrophobicity.(ABSTRACT TRUNCATED AT 400 WORDS)

Resistivity of a Simple Metal from Room Temperature to 10 6 K

Abstract: The resistivity of nearly solid-density Al was measured as a function of temperature over 4 orders of magnitudfe above ambient by observing the self-reflection of an intense, 0.5 psec, 308-nm light pulse incident on a planar Al target. As an increasing function of electron temperature, the resistivity is observed initially to increase, reach a maximum which is relatively constant over an extended temperature range, and then decrease at the highest temperatures. The broad maximum is interpreted as "resistivity saturation," a condition in which the mean free path of the conduction electrons reaches a minimum value as a function of temperature, regardless of the extent of any further disorder in the material.

Growth and Optical Properties of Li13Nd(GeO4)4 Single Crystal

Abstract: In this paper, single crystals of Li13Nd(GeO4)4 are grown by the Czochralski method. The unit cell dimensions and the crystal system are determined by an X-ray diffraction method. The principal refractive indices, na, nb and nc and the temperature dependence of birefringences, nc-nb, nc-na and na-nb, over the temperature range from room temperature to 500degC are measured. A fluorescence spectrum at around 1.06 µm is observed, and strong fluorescence is detected.

Wide temperature range IR spectroscopy cell for studies of adsorption and desorption on high area solids

Abstract: A new design for an infrared cell useful for studies of the spectrum of surface species on high area solids is presented. The cell is well suited over a wide temperature range (100–1000 K). Other demonstrated features of the cell include ultrahigh‐vacuum operation, temperature control to ±1 K, linear and rapid temperature programmability and low‐temperature gradients across the powdered sample. The method of sample preparation and support minimizes both heat and mass transport effects. A detailed literature search of previous infrared cell designs is included. Results of the application of the new cell design to the high‐temperature dehydroxylation of Al2O3 are given as an example of the performance.

Temperature dependence of photoluminescence from GaAs single and multiple quantum‐well heterostructures grown by molecular‐beam epitaxy

Abstract: The photoluminescence (PL) from GaAs/AlxGa1−xAs single and multiple quantum well (QW) heterostructures grown by molecular‐beam epitaxy (MBE) has been studied in the temperature range 10

Electrical Properties and Cation Valencies in Mn3O4

Abstract: The electrical conductivity and thermopower of Mn3O4 were measured in the temperature range 920° to 1530°C. Electrical conduction in cubic Mn3O4 is explained by the small polaron hopping of electron holes between Mn4+ and Mn3+ on octahedral sites. The concentrations of Mn4+ and Mn3+ are governed by the disproportionation equilibrium 2Mnoct3+⇄Mnoct4++ Mnoct2+. This model also explains the electrical behavior of NiMn2O4 and CuMn2O4.

Memory switching in bismuth‐vanadate glasses

Abstract: The electrical V‐I characteristics of thin blown films of V2O5‐Bi2O3 glasses with 95–70 mol % V2O5 were studied in the temperature range 200–400 K. It was observed that at lower fields, the bulk resistance controlled the current. At higher fields, all the glass compositions showed memory switching characteristics. The decrease in the threshold voltage and increase in the threshold current with the increase of V2O5 content in the glasses and also with increasing temperature were observed. The switching action was associated with a phase transition from a disordered glassy state to an ordered devitrified state due to self‐heating. The ideal thermal model was shown to be applicable to the present glasses.

Magnetic flux noise in thin‐film rings of YBa2Cu3O7−δ

Abstract: The low‐frequency magnetic flux noise in thin‐film rings of YBa2Cu3O7−δ (YBCO) is measured over the temperature range 1.3–125 K by means of a dc superconducting quantum interference device (SQUID) maintained at liquid‐helium temperatures. Below the transition temperature Tc of the YBCO, the spectral density of the noise scales as 1/f, where f is the frequency, and generally increases with increasing temperature. The magnitude of the noise depends strongly on the microstructure of the film, and is lowest for a sample which is predominantly oriented with its c axis perpendicular to the substrate. These results imply that SQUID’s and flux transformers of YBCO must be fabricated from highly oriented films to produce good resolution at low frequencies.

Thermal decomposition of 1,2 butadiene

Abstract: The thermal decomposition of 1,2 butadiene has been studied behind reflected shock waves over the temperature and total pressure ranges of 1300–2000 K and 0.20–0.55 atm using mixtures of 3% and 4.3% 1,2 butadiene in Ne. The major products of the pyrolysis are C2H2, C4H2, C2H4, CH4 and C6H6. Toluene was observed as a minor product in a narrow temperature range of 1500–1700 K. In order to model successfully the product profiles which were obtained by time-of-flight mass spectrometry, it was necessary to include the isomerization reaction of 1,2 to 1,3 butadiene. A reaction mechanism consisting of 74 reaction steps and 28 species was formulated to model the time and temperature dependence of major products obtained during the course of decomposition. The importance of C3H3 in the formation of benzene is demonstrated.

Shape-memory effect and pseudoelasticity associated with the R-phase transition in Ti-50·5 at.% Ni single crystals

Abstract: The rhombohedral phase (R-phase) transition and associated deformation behaviour in Ti-50·5 at.% Ni single crystals have been investigated systematically by tensile testing age-treated specimens in various orientations over a wide temperature range. Shape-memory effects and pseudoelasticity were observed in the first stage as well as in the second stage of the stress-strain curves; here we attempt to clarify the characteristics of the transition and deformation behaviour in the first-stage yielding. The strain in the first stage shows strong temperature and orientation dependences as follows: (1) the strain increases with decreasing temperature below the TR point, which is the critical temperature for the R-phase transition; (2) the strain is largest in the [111]B2 orientation and smallest in the [001]B2 orientation. Both the temperature and orientation dependences show excellent quantitative agreement with the calculated results based on the lattice distortion associated with the R-phase transit...

Novel technique to measure the microwave response of high Tc superconductors between 4.2 and 200 K

Abstract: This paper describes a novel technique for measurements of the complex surface impedance Z(s) of high-T(c) superconductors over an extremely wide range of temperature, from 4.2 K and at least 200 K. The technique uses a superconducting Pb-plated Cu high-Q-cavity resonator operated at an ambient temperature of 4.2 K, with the sample (typically a 3-mm-diam x 1-mm-thick disk) mounted on a sapphire rod in the center of cavity, at a high B-field and thermally insulated from the cavity walls, making it possible to control the sample temperature externally. Since the cavity characteristics are dominated by the sample properties (the contribution of the Pb-covered walls maintained at 4.2 K is negligible), measurement of the cavity Q and resonant frequency makes it possible to measure Zs as a function of the sample temperature. The Z(s) values for bulk Y1Ba2Cu3O(y) and La(1.85)Sr(0.15)CuO4 were measured over a temperature range 4.2-100 K.

Performance of a fiber-optic temperature sensor from −200 to 1050°C

Abstract: A reflectively monitored Fabry-Perot temperature sensor is characterized over a 1250 degrees C temperature range. Dielectric mirrors for the interferometer are incorporated into a continuous length of single-mode fiber by a fusionsplicing technique. The change in optical phase per unit temperature is nearly constant above room temperature but decreases at lower temperatures. Phase-shift data for the germania-doped silica fiber used in these experiments are compared with calculations based on previously reported information on the temperature dependence of refractive index and length in bulk fused silica.

Study on the substructure evolution and flow behaviour in type 316L stainless steel over the temperature range 21-900°C

Abstract: Tensile specimens of type 316L stainless steel with a grain size of 5.0 μm have been deformed at a constant strain rate of 10−3 s−1 over the temperature range 21–900°C and by differential strain-rate test technique over strain rates from about 10−5 to 10−3 s−1 at temperatures in the range 750–900°C. The normalized yield and flow stresses against temperature plots exhibit three regions. While in regions I and III the stresses decrease with increasing temperature, they increase with increasing temperature in region II. Transmission electron microscopy studies on deformed specimens show that at small strains the dislocations generated at grain boundaries have characteristic distributions: in region I the dislocations are confined to the vicinity of the grain boundary, in region II the dislocations are spread into the grain interior, and in region III the dislocations rearrange to form walls. The evolution of substructure and the work-hardening behaviour are explained by considering both intragranula...

XPS studies of the thermal behaviour of passivated Zircaloy‐4 surfaces

Abstract: The composition and the chemical states of components of Zircaloy-4 (zirconium alloy) surfaces were studied in the temperature range between room temperature and 500°C. Each sample was kept at constant temperature (25, 100, 200, 300, 400, 500°C) for up to 16 hours. The changes of composition and chemical states of the Zircaloy-4 surface during heating were monitored by x-ray photoelectron spectroscopy (XPS). Originally, the components form well-defined layers elucidated by angle-resolved x-ray photoelectron spectroscopy (ARXPS). In contrast to depth profiling using ion sputtering, ARXPS is non-destrutive. However, it is applicable for layers of up to a few nanometres thickness only. The experiments showed a decomposition of the ZrO2 coverage above 200°C accompanied by oxygen diffusion into the bulk. These processes lead to the reduction of ZrO2 to metallic zirconium on the surface at 300°C and higher temperatures. The oxygen diffusion into the bulk was indicated by AES depth profiles. The layered structure observed up to a heating temperature of 200°C could not be seen at higher temperatures. After Zr metal appears at the surface during the heating process, a reaction with the adsorbed hydrocarbons takes place, leading to the formation of zirconium carbide. Though the depth resolution of an AES depth profile does not permit identification of layers with thicknesses in the nanometre region, the temperature-dependent behaviour of oxyen is reflected by its AES profiles, showing features in accordance with the results from ARXPS, especially with respect to the fact that well-defined layers vanish above 200°C.

Titanium diffusion in silicon

Abstract: Titanium diffusion profiles in silicon were determined in the 950–1200 °C temperature range, with experimental conditions avoiding any oxygen or nitrogen contamination, which could perturb the boundary condition at the TiSi2/Si interface. Thus diffusivity values in the range 5×10−10–10−8 cm2 s−1 are obtained, and are about two orders of magnitude higher than previously reported.

Surface energy of liquid copper and single-crystal sapphire and the wetting behavior of copper on sapphire

Abstract: The wetting behavior of liquid copper on sapphire is affected by the crystallographic orientation of the sapphire surface, the oxygen partial pressure, and the temperature. The influences of each of these conditions have been studied by the sessile drop technique over the oxygen partial pressure range 10-2-10-20 atm at temperatures of 1100 and 1250°C. The effect of oxygen partial pressure on the liquid copper surface energy follows the Gibbs-Langmuir law. The contact angle varies with the crystallographic orientation of the sapphire surface. This variation is more significant at higher oxygen partial pressures, but is eliminated at higher temperatures. The liquid copper surface energy was determined to be γlv = 1.757-3.3 x 10-4T(°C) J/m2. The solid surface energy of sapphire was estimated as γsv = 1.961-4.7x 10-4T(°C) J/m2, which applies only to the temperature range 927-2077°C.