Temperature Axis Research Articles

908 鉄基形状記憶合金の逆変態条件におよぼす非比例負荷の影響

Austenite-start condition is studied experimentally under tension/compression-torsion stress state in an Fe-Mn-Si polycrystalline SMA after non-proportional pre-loading. When the specimen is subjected to a successive axial and shear loads, the martensite variants induced during loading transform back to the parent phase in the subsequent heating process. The austenite-start temperature, determined by monitoring the dilatation curves during heating, can be represented as an austenite-start plane in the axial hold stress-shear hold stress-temperature space. The austenite-start plane rotates around the temperature axis while the shear preload increases. The position of the plane in the stress-temperature space also changes, depending on the amount of shear load.

Study of cryostructuration of polymer systems:: XIII. Some characteristic features of the behaviour of macromolecular thiols in frozen aqueous solutions

Thiol-containing derivatives of linear poly(acrylamide) (SH-PAAm) were synthesized through the free-radical copolymerization of acrylamide with bis-N-acryloyl-cystamine followed by the reduction of SS-bridges in the formed gel and separation of the solubilized polymeric products from the low-molecular admixtures. The polymer thus prepared, was used to study the peculiarities of the processes of cryotropic gel formation of water-soluble macromolecular thiols. It was shown that cryogenic treatment (freezing—frozen storage—thawing) of SH-PAAm water solutions containing soluble oxidants results in the formation of polymeric cryogels cross-linked with intermolecular disulphide bonds. The dependence of the oxidation rate of thiol groups on the temperature of a frozen system showed an extreme character due to the competition between the accelerating and decelerating factors; the major accelerating factor being an increase in the concentration of solutes in the unfrozen microphase after the crystallization of most part of the solvent. The position of the extreme points on the temperature axis and the absolute magnitude of the reaction rate were controlled, along with other factors, by the freezing mode used, i.e. by the thermal history of the system during its transition to the frozen storage conditions. The implementation of the low-temperature quenching procedure to the freezing of a polymer solution altered the respective kinetic curves giving rise to the appearance of lag-periods, whose duration depended on the particular temperature of frozen storage. With the use of 2H NMR spectroscopy, the amount of unfrozen liquid microphase in macrofrozen solid samples was evaluated, and the time-dependent distinctions in the characteristics of these unfrozen inclusions were demonstrated for samples frozen using different methods.

A Study of Heavy Rainfall Events during the Great Midwest Flood of 1993

A synoptic–dynamic climatology was constructed using all 24-h 2-in. (50.8 mm) or greater rainfall events in nine states affected by heavy rains and flooding from June through September 1993 using 6- or 12-h gridded analyses from the Regional Data Assimilation System and geostationary satellite imagery. Each of the 85 events was assigned a category (0–4) based on the areal coverage of the 3-in. (76.2 mm) or greater observed precipitation isohyet. A variety of meteorological fields and rules of thumb used by forecasters at the Hydrometeorological Prediction Center are investigated that may help identify the most likely location and scale of a convective precipitation event. The heaviest rain usually fell to the north (downwind) of the axis of highest 850-mb winds and moisture flux in an area of 850-mb warm temperature and equivalent potential temperature advection. The rainfall maximum also usually occurred to the north or northeast of the axis of highest 850-mb equivalent potential temperature. The scale and intensity of the rainfall appeared to be related to 1) the magnitude of the warm advection, 2) the 1000–500-mb mean relative humidity, 3) the breadth of the axis of stronger values of moisture transport feeding northward into a surface boundary, 4) the strength of low-level moisture flux convergence, and 5) the length of the low-level moisture flux convergence that was aligned along the mean flow upstream from the location of the rainfall maximum. The latter finding suggests that propagation plays an important role in modulating the scale and intensity of rainfall events.

Universality, frustration, and conformal invariance in two-dimensional random Ising magnets

We consider long, finite-width strips of Ising spins with randomly distributed couplings. Frustration is introduced by allowing both ferromagnetic and antiferromagnetic interactions. Free energy and spin-spin correlation functions are calculated by transfer-matrix methods. Numerical derivatives and finite-size scaling concepts allow estimates of the usual critical exponents $\ensuremath{\gamma}/\ensuremath{\nu},$ $\ensuremath{\alpha}/\ensuremath{\nu},$ and $\ensuremath{\nu}$ to be obtained, whenever a second-order transition is present. Low-temperature ordering persists for suitably small concentrations of frustrated bonds, with a transition governed by pure-Ising exponents. Contrary to the unfrustrated case, subdominant terms do not fit a simple, logarithmic-enhancement form. Our analysis also suggests a vertical critical line at and below the Nishimori point. Approaching this point along either the temperature axis or the Nishimori line, one finds nondiverging specific heats. A percolationlike ratio $\ensuremath{\gamma}/\ensuremath{\nu}$ is found upon analysis of the uniform susceptibility at the Nishimori point. Our data are also consistent with frustration inducing a breakdown of the relationship between correlation-length amplitude and critical exponents, predicted by conformal invariance for pure systems.

Chemometrics on thermochromatography of inorganic salts: decomposition of thermochromatograms to chromatograms and thermograms using EFA and peak shape constraints

A low volume thermal furnace, interfaced to a capillary gas chromatograph (GC) via a computer controlled, pneumatic sample inlet device, permits temperature resolved high speed GC analysis of the evolved components. The method is called thermochromatography (ThGC). The results of such an evolved gas analysis (EGA) can be conveniently represented as a thermochromatogram: a two-way detector response surface in the axes of sample temperature and chromatographic retention time. It is demonstrated that such thermochromatograms, if subjected to the specific chemometrics analysis — evolving factor analysis (EFA) — provide information about independent thermal processes that happened during the sample heating. The data is decomposed to matrixes of chromatograms and thermal evolution curves, thermograms, in a manner which connects each thermal decomposition step to the products evolved at that temperature region. Chromatographic peak shapes of the evolved gases are used as additional constraints in the analysis. The EFA performance is evaluated by ThGC of several inorganic salts and apatites. As a reference to EFA the direct deconvolution of thermochromatograms to the gas chromatograms and temperature dependent thermograms was performed. This comparison demonstrated that EFA gives confident results if essential constraints of non-negativity to chromatograms and thermograms have been applied.

Time and temperature based gellability zones in modified titanium alkoxide sols

Titanium hydroxide derived from stoichiometrically hydrolysed modified precursors usually takes as much as 14 days to gel under ambient conditions. These systems can however be made to gel within a few hours by raising the sol temperature to above 80°C or alternatively, by lowering it to below 10°C. A gellability zone has been identified between 10°C and 80°C on the temperature axis and between 0 and 14 days on the time axis, for all chelate ratios up to 1:4. The spread of the acetyl acetone gellability zone is wider than that for ethyl acetoacetate leading to a wider range of microstructural controls that may be imposed upon such systems. The locus of gel points on the gellability zone separates the sol state from the precipitated state. Thermoreversible gelling is seen within the titania gellability zone. ©

Temperature dependence of the retention index for perfumery compounds on a SE-30 glass capillary column: II. The hyperbolic equation

The Antoine-type hyperbolic equation of the retention index temperature dependence was reported for 82 perfumery solutes on a SE-30 capillary column. The precision was compared with that of the linear equation. The thermodynamic significance of the parameters was reconsidered and discussed. The methylene increments of the thermodynamic functions of solution were used for the prediction of the vertical asymptote position on the temperature axis at about 400–500°C, in agreement with the experimental data. Therefore, only two particular cases of this type of hyperbola should exist in a pure gas–liquid partition process.

Crystallinity and amorphous segmental properties in random propylene-ethylene copolymers: NMR correlation

We present a characterization of the state of semi-crystallization of random propylene–ethylene copolymers, observing the transverse relaxation of protons attached to the chains. The degree of crystallinity was determined step by step, from NMR, during the progressive annealing of the copolymers, quenched at room temperature from the melt. The ethylene content varied over the range 0–4.7 (w/w). It is shown that the empirical temperature dependence of the degree of crystallinity, as detected by NMR, obeys a single curve; this curve is translated along the temperature axis in accordance with the melting point depression when the ethylene content varies. The degree of crystallinity is primarily a function of the undercooling, whatever the ethylene content. Considering any state of semi-crystallization, a strong correlation between the degree of crystallinity and the relaxation rate of the protons attached to amorphous segments is established; the NMR sensitivity to crystallinity is considerably enhanced when detected by amorphous properties. © 1999 Society of Chemical Industry

Comparing dielectric measurements on poly(ethylene terephthalate) at constant heating rates with isothermal measurements

In this study, dielectric relaxation spectroscopy experiments were carried out during heating in the α relaxation region of PET. The results for low heating rates were consistent with isothermal measurements. Moreover, the results expressed as a function of temperature were much clearer than those expressed as a function of frequency. However, the loss peaks obtained in these non-isothermal experiments showed a systematic shift on the temperature axis when the heating rate increased. A significant but nearly constant thermal lag was observed in experiments with heating at 1 K min −1 when using different equipment. It appears that isothermal data obtained in a well calibrated apparatus can be used to adjust the temperature axis of dielectric results obtained in ramp temperature experiments.

Ab initiocalculation of the lattice dynamics and phase diagram of boron nitride

We present a detailed study of the lattice dynamics and of the phase stability of cubic zincblende (c-BN) and hexagonal (h-BN) boron nitrides. The phonon-dispersion relations at different densities are calculated using a first-principles force-constant method. The calculated eigenfrequencies and phonon Gr\"uneisen parameters are in good agreement with experimental findings. From the electronic and vibrational energies as a function of volume we calculate the phase $(p,T)$ diagram of boron nitride in a quasiharmonic approximation. At low temperature c-BN is the stable modification; the c-BN/h-BN coexistence line intersects the temperature axis at 1440 K. In experiments this temperature lies between 1200 and 1800 K. Anharmonic corrections improve the agreement between the calculation and experiment for high pressure and temperature.

Starting dates and basic temperatures in phenological observations of plants

Several methods have been used in plant phenology to find the best starting date in spring and the best threshold or basic temperature for growth and development of perennial plants. In the present paper the date giving the highest correlation coefficient for development to various phenophases, in relation to 24-hourly mean air temperatures was chosen as the best starting value in further analyses. For many woody plants this date was very often found to be 1 April based on phenological and climatological observations at about 60 sites in western Norway (at about 61°N). The early flowering species Corylus avellana and Salix caprea and the early leaf-bud breaking Prunus padus seemed to start development earlier in Spring, while the late sprouting Fraxinus excelsior showed the highest correlation coefficient using 15 April. If daytime temperatures were used in the calculations, the ”best” starting date was generally found to be later than for the 24-hour mean temperatures. This variation must be seen as resulting from the different basic temperatures for the development of various species. Estimates of basic temperatures in various species and periods may be given, for example by finding the value having the least variance in heat sums or by various regression analyses. A technique has been developed to minimise the influence of significance of correlation, using the intercept with the temperature axis by merging the two least squares rectilinear regression lines that can be found between plant development and mean air temperature (from the estimated best starting date) at r=+1 or –1. The basic temperature seemed to vary from –5.9°C for leaf-bud break of P. padus to 5.5°C for leaf-bud break of F. excelsior, with basic temperatures of several other woody plants having intermediate values. These values are compared with those found by other methods.

Effect of temperature on the lifetime of stabilized and unstabilized PP films

Unstabilized and phenolic antioxidant stabilized PP films were aged in draft air ovens at temperatures between 150 and 40°C. The Arrhenius plots of the failure times reveal quite distinctive features. Thus, unstabilized PP films show a marked downward curvature of the plot at temperatures below 80°C. The role of Ti catalyst residues in this behavior is discussed.Phenolic antioxidant stabilized films show a similar bent in the Arrhenius plot at significantly higher temperatures. Furthermore, these plots can be superposed onto the curve obtained for the unstabilized film by a shift parallel to the reciprocal absolute temperature axis. The numerical value of the shift is a function of the chemical nature of the phenolic antioxidant and of its concentration. Remarkably, the phenol stabilized films show a second curvature in the Arrhenius plot at temperatures below 80°C. This second curvature is an upward bent so that the Arrhenius plot becomes a typical sigmoid. This low temperature curvature depends also on the nature of the phenolic antioxidant and its concentration. It is attributed to some kind of complexation of the Ti catalyst residues by the phenols. Comparison with PP films stabilized with Hindered Amine Stabilizers (HAS) and with PE-LD films lends additional support to the conclusions concerning the role of transition metals.

Small-signal deep level transient spectroscopy on hydrogenated amorphous silicon based metal/insulator/semiconductor structures

The high-temperature tail of small-signal deep level transient spectroscopy (DLTS) spectra of hydrogenated amorphous silicon (a-Si:H) based metal/insulator/semiconductor structures has been analyzed in terms of oxidation of some negatively charged mobile hydrogen species at the Al/a-Si:H interface, the excitation pulses of an amplitude of 0.1 V being applied repetitively between the top Al and the bottom (gate) electrodes. The concentration of the mobile hydrogen in the a-Si:H layer has been estimated to an amount up to ≈2×1020 cm−3, taking the earlier published data on the diffusion coefficient. Having chosen an appropriate polarity of the excitation pulses, one could observe a DLTS peak moving with applied bias on the temperature axis. The latter is pointing to an energy distribution of states at the Al/a-Si:H interface. The interface state density increases with increasing energy depth of the states. At the ultimate experimentally observable energy of E≈0.95 eV below the electron mobility edge Ec a corresponding areal density Na(E) of these states amounted up to 1.5×1011 cm−2 eV−1.

Fisher zeros and singular behaviour of the two-dimensional Potts model in the thermodynamic limit

The duality transformation is applied to the Fisher zeros near the ferromagnetic critical point in the q>4 state two-dimensional Potts model. A requirement that the locus of the duals of the zeros be identical to the dual of the locus of zeros in the thermodynamic limit (i) recovers the ratio of specific heat to internal energy discontinuity at criticality and the relationships between the discontinuities of higher cumulants and (ii) identifies duality with complex conjugation for the zeros near the ferromagnetic critical point. The conjecture that all zeros governing ferromagnetic singular behaviour satisfy the latter requirement gives the full locus of such Fisher zeros to be a circle. This locus, together with the density of zeros is then shown to be sufficient to recover the singular part of the thermodynamic functions in the thermodynamic limit, their regular parts coming from separate loci of zeros not crossing the positive real temperature axis.

On the Deformation Term in the Quasigeostrophic Omega Equation

It is a common diagnostic, synoptic practice to consider the Trenberth–Sutcliffe approximation to the quasigeostrophic (QG) omega equation, which relates upward vertical motion to regions of cyclonic vorticity advection by the thermal wind. Use of this approximate form of the QG omega equation requires the neglect of the so-called deformation term, which is often described as important only in frontal regions. Here, an alternative expression for the deformation term is derived that clearly illustrates its relationship to the mathematical forcing function in the Q-vector form of the QG omega equation. The magnitude of the deformation term in the middle troposphere is traced throughout the life cycle of a typical midlatitude cyclone. It is found that this term is generally small at midlevels in the early stages of the cyclone life cycle. As the cyclone approaches and passes its mature stage, however, the deformation term exerts a comparable, locally predominant influence on the total QG forcing for vertical motion. Particularly interesting is the large magnitude this term acquires in the axis of high potential temperature, characteristic of a post–mature stage cyclone’s horizontal thermal structure. The large magnitude of the deformation term in such regions demonstrates that there are nonfrontal, midtropospheric regions within cyclones in which the deformation term may not be small.

A study of the perfectly oriented Gay–Berne model of a nematic liquid crystal via perturbation theory and molecular dynamics

A perturbation theory for the Gay–Berne interaction potential has been developed and selected results are compared with those of molecular dynamics simulations for the same model. The perturbation method can be regarded as a generalization to oriented molecular fluids of the Weeks–Chandler–Andersen perturbation scheme. The properties of the soft repulsive reference system are related to a system of hard ellipsoids of revolution by the introduction of temperature and density dependent ellipsoidal axes. For the sake of simplicity and clarity both methods are applied to the perfectly ordered nematic phase, in which all particles are oriented in the same direction. Compressibility factors and structure factors were calculated via both routes for different temperatures and show remarkable agreement. Benefits and drawbacks of the two methods are discussed.

On the phase diagram of the attractive Hubbard model: Crossover and quantum critical phenomena

We explore the phase diagram of the attractive Hubbard model from the point of view of phase transition theory. Using the quantum Monte-Carlo technique, the scaling theory of quantum critical phenomena and the mapping to the XY model we investigate the critical properties along the temperature, band filling and coupling strength axes of the phase diagram. Particular emphasis is devoted to the insulator to superconductor and superconductor to normal metal transitions driven by the variation of the coupling strength U. We also discuss the particular similarities between this simple lattice model and the high-Tc cuprates: both systems exhibit a phase transition along a certain critical line as a function of a particular control parameter, which is e.g. the strength of the attractive coupling |U| in the case of the Hubbard model and the electron doping in the copper oxide planes for the cuprates; both show a remarkable crossover along this phase transition line with similar consequences. At one end point (overdoped/small-U regime) we find a behavior similar to a conventional BCS-type superconductor, the system undergoes a normal metal to superconductor transition (NS), whereas at the other end (underdoped/large-U limit) a description in terms of Bose-Einstein condensation (BEC) of preformed pairs is more adequate, with a superconductor to insulator critical endpoint (SI). There superconductivity occurs when the phases of the pairs become coherent, not when the pairs are initially formed. In addition to the fixed electron density, interaction driven crossover the Hubbard model undergoes a further T=0 quantum transition from a (super-) conductor to an insulator for \(\rho \to 0\).

Phase decomposition and hardening of Ag-modified L12Al3Ti

Abstract Transmission electron microscopy examinations of Ag-modified Al3Ti with an L12-ordered structure have revealed the various modes of precipitation of Al2Ti upon aging after quenching from higher temperatures. A fine uniform precipitation of Al2Ti occurs when the supersaturation is sufficiently high. On the other hand, a preferential precipitation at the antiphase boundaries can be observed in alloy with a low supersaturation. When L12Al3Ti is supersaturated with DO22Al3Ti, DO23Al11Ti5 with a multidomain structure is formed during aging. The L12 phase field in the TiAlAg system is severely skewed with respect to the temperature axis and is restricted into a much smaller field at lower temperatures. Appreciable hardening and overage softening during aging can be explained in terms of microstructural variations.

A group II self-splicing intron from the brown alga Pylaiella littoralis is active at unusually low magnesium concentrations and forms populations of molecules with a uniform conformation

We have investigated the reactivity of three of the seven group II introns encoded by the mitochondrial genome of the brown alga Pylaiella littoralis. While the first intron in the protein-coding cox1 gene could not be induced to self-splice under any of the conditions tested, the first two introns in the gene encoding the large ribosomal subunit are reactive in vitro and splice primarily by the standard group II two-step transesterification pathway. Intron 2 proved to be of exceptional interest, because in contrast to all group II molecules known so far, its optimal magnesium concentration is less than 10 mM and it still carries out accurate splicing at concentrations as low as 0.1 mM magnesium. Analysis of reaction products under optimal conditions showed no evidence of hydrolysis at the 5′ splice site and up to 90% of precursor molecules could be converted into excised lariat intron, which migrated as a single band on non-denaturing polyacrylamide gels. Absorbance versus temperature profiles generated from the lariat form of intron 2 reveal the existence of an early melting component, the amplitude of which does not depend on the way the molecules were purified, i.e. with or without a denaturation step. This highly cooperative transition, whose position along the temperature axis changes with the concentration of magnesium, is proposed to consist of the unfolding of the tertiary structure of the molecule. We conclude that group II introns, which are the largest known ribozymes, can form conformationally homogeneous populations of molecules suitable for physical-chemical studies of higher-order structure.

Phase equilibria for binary n-alkanenitrile- n-alkane mixtures IV. Liquid-liquid phase equilibria for propanenitrile with C 5C 8 and C 10n-alkanes

The orthobaric liquid-liquid phase diagrams for the five binary mixtures of propanenitrile with the n-alkanes C 5C 8 and C 10 have been determined by visual observation of the separation temperatures of mixtures of known mass composition. The results have been fitted to a conventional modern expression incorporating where needed Wegner extended-scaling terms. Various aspects of coexistence curve symmetry have been explored, particularly symmetry of the critical composition, i.e., whether it falls close to 0.5, and symmetry of the diameter, i.e., whether it falls parallel to the temperature axis. Neither mole fraction nor volume fraction fully meets either requirement. A new variable τ based on a forced fit to τ c = 0.5 reveals both kinds of symmetry and the data for all five mixtures when expressed in terms of a reduced temperature T T c as a function of τ fall on a universal curve. The implications of this for the coexistence curves for bihomologous mixtures are briefly discussed.