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991.
The interference of light in a medium with optical memory is discussed within the framework of a nonassociative algebra. It
is shown that it is possible to introduce an energy coefficient of useful action Ke, an information coefficient of useful action Kint, and a coefficient characterizing the size of the memory of the medium D. The problem of optimizing the process over these
parameters is considered. Graphs are given for Ke, Kint, and D as functions of a free parameter β that accounts for experimental conditions.
Tbilisi State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 29–32, August, 1997. 相似文献
992.
We discuss the nature of the pairing mechanism and the physical properties associated with the normal as well as the superconducting state of cubic perovskites Ba0.6K0.4BiO3using the strong coupling theory. An interaction potential which includes the Coulomb, electron–optical phonon and electron–plasmon interactions is developed to elucidate the superconducting state. A model dielectric function is constructed with these interactions fulfilling thef-sum rule. The screening parameter (μ* = 0.26) infers the poor screening of charge carriers. The electron–optical phonon strength (λ) estimated as 0.98 is consistent with an attractive electron–electron interaction and supports the moderate to strong coupling theory. The superconducting transition temperature of Ba0.6K0.4BiO3is then estimated as 32 K. Ziman's formula of resistivity is employed to analyse and compare this with the temperature-dependent resistivity of a single crystal. The estimated contribution from the electron–optical phonon together with the residual resistivity clearly infers a difference when a comparison is made with experimental data. The subtracted data infer a quadratic temperature dependence in the temperature domain (30 ≤ T ≤ 200 K). The quadratic temperature dependence of ρ [ = ρexp − (ρ0 + ρe–ph)] is understood in terms of 3D electron–electron inelastic scattering. The presence of these el–el and el–ph interactions allows a coherent interpretation of the physical properties. Analysis reveals that a moderate to strong coupling exists in the Ba0.6K0.4BiO3system and the coupling of electrons with the high-energy optical phonons of the oxygen breathing mode will be a reason for superconductivity. The implications of the above analysis are discussed. 相似文献
993.
L. J. Cowen D. J. Kleitman F. Lasaga D. E. Sussman 《Studies in Applied Mathematics》1996,96(3):339-350
A full graph on n vertices, as defined by Fulkerson, is a representation of the intersection and containment relations among a system of n sets. It has an undirected edge between vertices representing intersecting sets and a directed edge from a to b if the corresponding set A contains B;. Kleitman, Lasaga, and Cowen gave a unified argument to show that asymptotically, almost all full graphs can be obtained by taking an arbitrary undirected graph on the n vertices, distinguishing a clique in this graph, which need not be maximal, and then adding directed edges going out from each vertex in the clique to all vertices to which there is not already an existing undirected edge. Call graphs of this type members of the dominant class. This article obtains the first upper and lower bounds on how large n has to be, so that the asymptotic behavior is indeed observed. It is shown that when n > 170, the dominant class predominates, while when n < 17, the full graphs in the dominant class compose less than half of the total number of realizable full graphs on n vertices. 相似文献
994.
995.
J.P. Contour A. Défossez D. Ravelosona A. Abert P. Ziemann 《Zeitschrift für Physik B Condensed Matter》1996,100(2):185-190
An energy model has been used to calculate the critical thickness h c of YBaCuO thin films and YBaCuO based superlattices within an isotropic or anisotropic approximation. The critical thickness of single layers calculated from the anisotropic model (16 nm) is in good agreement with the previously published experimental values which are spread out from 4 to 20 nm. In the case of superlattices, relaxation appears to be governed by the critical thickness of the elementary sub-layers and is then better evaluated through the calculation performed for YBaCuO single layers. XRD measurements on YBa2Cu3O7/PrBa2Cu3?xGaxO7 superlattices grown on {100{ SrTiO3 have evidenced a tetragonal stress in the YBaCuO ab plane which remains expanded when the YBaCuO elementary layer thickness is lower than 4.8 nm (4 YBaCuO cells). However the critical temperature of the shortest period superlattices is only slightly affected by this expanded stress in contrast to the effect of an elastic stress externally applied along the ab plane of YBaCuO thin films. 相似文献
996.
The resistance to slow crack growth (SCG) was measured in binary blends of high density polyethylene (HDPE) and 5–10% concentrations of model ethylene-butene random copolymers by measuring the time to failure (tf) under a constant stress intensity. An increase of tf with the addition of the copolymer if the copolymer could crystallize and the increase was greater the higher branch density. The copolymer with 117 branches/1000C could not crystallize and therefore its blend had a tf that was less than that of the HDPE. The fracture energies of the blends as determined by their resistance to SCG were compared with the energy by rapid fracture, Jc, as previously measured by Rhee and Crist. It is concluded that SCG is more sensitive to variations in the microstructure than is rapid fracture and that the differences in SCG behavior can be qualitatively explained in terms of the differences in microstructure of the blends. ©1995 John Wiley & Sons, Inc. 相似文献
997.
B. D. Symeopoulos P. G. Koutsoukos 《Journal of Radioanalytical and Nuclear Chemistry》1993,173(1):23-36
The formation of barium sulfate in aqueous media causes problems of insoluble scale formation. On the other hand, the coprecipitation of uranium and transuranium elements with barium sulfate has been suggested for the determination of these elements in environmental monitoring processes. Therefore, the study of barium sulfate crystal growth is required. The investigations done so far suffer from the low sensitivity of the analytical methods used. In the present work we have overcome this problem by using131Ba for the preparation of supersaturated solutions. Thus kinetics parameters such as induction time and precipitation rates were measured. The polynuclear mechanism was found to be operative at high and the spiral growth at low supersaturations. 相似文献
998.
Stanley D. Rasberry 《Fresenius' Journal of Analytical Chemistry》1993,345(2-4):87-89
Summary Sales and use of analytical instruments have expanded in the United States over the past two years, despite the recessionary nature of the economy. Interest in increasing the quality of analytical measurements seems to be undiminished, if not growing. Trends in several measurement areas, including health, environment, manufacturing, and commerce, are described as they bear on this growth of interest in reliably accurate measurements. The paper also considers trends in the development of reference materials and accreditation of laboratories in the USA. United States of America participation in efforts of the International Organization for Standardization, and a study by the International Bureau of Weights and Measures of how to provide for international traceability for analytical chemical measurements are mentioned. 相似文献
999.
I. S. Dubenko I. V. Golosovsky E. Gratz R. Z. Levitin A. S. Markosyan I. Mirebeau S. V. Sharygin 《Journal of magnetism and magnetic materials》1995,150(3):304-310
The present neutron diffraction studies have confirmed that TmCo2 represents an exception within the RCo2 series. It was found that, in contrast with other heavy RCo2 compounds, the Co sublattice in TmCo2 does not order magnetically below the Curie temperature (Tc = 3.9 K). This is assumed to be due the fact that in TmCo2 the intersublattice (f-d) molecular field is smaller than the critical field necessary to induce magnetic order within the Co sublattice, as is the case in other RCo2 compounds. Furthermore, we show that the magnetic structure and the onset of long-range order in TmCo2 depend sensitively on the sample preparation, which partly explains the differing results published earlier. 相似文献
1000.
P. A. Bokhan T. Ya. Dubnishcheva D. E. Zakrevskii Yu. V. Nastaushev 《Journal of Russian Laser Research》1995,16(2):164-171
A gas-discharge gold-vapor laser on self-terminating transitions with operating wavelength λ=312.2 nm has been used to develop a highly efficient system for image transfer. An optical scheme and all its parameters have been chosen optimal for image quality. It has been found both theoretically and experimentally that the best results on micron-structure image transfer are obtained with 2–5-times image reduction. Various types of masks have been used. A 1-µm structure has been resolved due to the choice of optimal exposure time of 10 ms under a period of pulse repetition (0.6 – 0.8) ms; in this case, the minimal fringe dimension was ≈2 µm with an image dimension of 2 mm for a laser tube 1.8 cm in diameter. 相似文献