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961.
The time dependence of the electron distribution function in helium afterglow, for pressures of 60–260 Pa, is calculated for the case in which metastable-metastable reactions are present. The time variation of the shape of the distribution function shows that careful consideration must be made of the time derivative of the distribution function in the Boltzmann equation for the calculation of the rate constant of such reactions from experimentally determined distribution function. 相似文献
962.
Experimental results of the study of superplastic behaviour in Zn-0·35 wt. % Al-0·25 wt. % Cd alloy are presented. The attention has been paid to the influence of temperature on stress-strain curves, ductility, strain rate sensitivy parameterm and activation energy of superplastic flow. The best superplastic properties have been established at temperatures T370 K (0·53 Tm): ductilityA=600% and parameterm=0·56. A fast grain growth observed at temperaturesT 380 K has been suggested to be responsible both for the decrease in ductility and parameterm values and for the origin of an anomaly in the decreasing temperature dependence of flow stress. The measurements of activation energy have shown an expected decrease in activation energy at the transition from the non-superplastic region at lower temperatures to the superplastic region at higher temperatures. Significant transient effects after strain rate changes have been observed. The experimental results obtained in the Zn-Al-Cd alloy have been compared with those obtained in binary Zn-1·1 wt. % Al alloy and discussed from the point of view of possible models of structural superplasticity. 相似文献
963.
964.
L. Havela P. Kratochvíl P. Lukáč B. Smola A. Svobodová 《Czechoslovak Journal of Physics》1988,38(4):384-387
The softening processes during and after the hot deformation (850–1180 C) in AISI 321 stainless steel were studied with respect to true strains
D and true strain rates
. The analysis of deformation curves indicates the occurrence of dynamic recrystallization for values of Zener-Hollomon parameterZ1015 s–1. The retardation of static recrystallization by fine Ti(N, C) precipitates is documented by microstructure studies and by variations of annealing conditions. 相似文献
965.
During ageing the Al-2·0 at. %Zn-1·0 at. % Mg alloy at elevated temperatures the width of the precipitation free zone (PFZ) at both sides of the grain boundaries (GB) is identical with that free of quenched-in dislocation loops (DL). After sufficiently long ageing a band of precipitates is growing inside the former PFZ and the DLs in the midgrain regions act as sites for the heterogeneous nucleation of the-phase. Two precipitation processes significantly affect the mechanical properties. TEM correlates grain boundary precipitate density and morphology with grain boundary misorientation. 相似文献
966.
P. J. Forrester 《Journal of statistical physics》1988,51(3-4):457-479
The Coulomb system consisting of an equal number of positive and negative charged rods confined to a one-dimensional lattice is studied. The grand partition function can be calculated exactly at two values of the coupling constant=q
2/k
B
T (q denoting the magnitude of the charges). The exact results lead to the conjecture that in the complex scaled fugacity plane, all the zeros of the grand partition function lie on the negative real axis for<2, on the point=–1 for=2, and on the unit circle for>2. In addition, for>4, we conjecture in general and prove at=4 that the zeros pinch the real axis in the thermodynamic limit, with an essential singularity in the pressure at the reduced density 1/2. 相似文献
967.
Z. M. Stadnik P. Griesbach P. Gütlich G. Stroink T. Kohara 《Hyperfine Interactions》1988,41(1):705-708
61Ni Mössbauer measurements have been performed at 4.2 K on spherical Ni particles with an average diameter of 100 and 30 Å, covered with a protective layer of SiO. Their spectra contain a surface component with a significantly reduced hyperfine magnetic field as compared with the field in the bulk. This result confirms recent theoretical predictions. 相似文献
968.
Dupieux P Alard JP Augerat J Babinet R Bastid N Brochard F Charmensat P De Marco N Fanet H Fodor Z Fraysse L Girard J Gorodetzky P Gosset J Laspalles C Lemaire MC L'Hôte D Lucas B Marroncle J Montarou G Parizet MJ Poitou J Qassoud D Racca C Schimmerling W 《Physics letters. [Part B]》1988,200(1-2):17-21
Proton-proton small angle correlations have been measured in neon-nucleus collisions, using the 4 pi detector Diogene, at 400 and 800 MeV per nucleon incident energies. Values of the size of the emitting region are obtained by comparison with the Koonin formula, taking into account the biases of the apparatus. The dependence of the density on target mass and incident energy is also analysed. 相似文献
969.
The organometallic complexes C5H5 Fe(I) C6(C2H5)6 and C5(CH3)5 Fe(I)C6 H(C2H5)5 have been studied by Mössbauer spectroscopy. Hyperfine data are typical for 19e? systems with one electron on the e 1 * orbital. The thermal variation of the quadrupole splittings indicates vibronic reduction of the spin-orbit constant, in agreement with previous analyses of similar 19e? systems. The quadrupole splitting and recoil-free fraction data give evidence for phase transitions, which are discussed with respect to cooperative Jahn-Teller distortion and hindered rotations of the ethyl groups. 相似文献
970.
Persistent currents in polycrystalline YBa2Cu3O7 rings have been investigated by measuring the spatial distribution of the magnetic flux trapped in field-cooled samples. The results unambiguously show that macroscopic persistent ring currents exist. The critical current density depends very sensitively on the sample quality, reachingj
c
250 A/cm2 at 77 K for our best samples. 相似文献