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991.
Th. Friedrich I. Kath A. Moroianu U. Semmelmann 《Journal of Geometry and Physics》1997,23(3-4):259-286
A nearly parallel G2-structure on a seven-dimensional Riemannian manifold is equivalent to a spin structure with a Killing spinor. We prove general results about the automorphism group of such structures and we construct new examples. We classify all nearly parallel G2-manifolds with large symmetry group and in particular all homogeneous nearly parallel G2-structures. 相似文献
992.
V. I. Psarev 《Russian Physics Journal》1991,34(12):1110-1113
A method is proposed for determining the similarities and differences between the experimental distribution of particles in a disperse system with respect to a significant feature-particle size (sample) and the corresponding distribution (likeness), selected from the diversity of theoretical distributions with positive and negative asymmetry. The aim of the comparison is to extract the necessary information about the nature of the internal processes in the disperse system evolving as a result of the Ostwald reaction coagulation of microparticles. The procedure of comparing the distributions is illustrated on the example of the histogram of disperse Al3Mg2 particles of an aluminum-magnesium alloy heated isothermally at 430°C.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 80–84, December, 1991. 相似文献
993.
The paraelectric resonance spectrum of non-central impurity ions situated in crystal fields of icosahedral symmetry is predicted.
A multiwell potential is considered that corresponds to the displacement of the ions from the center of symmetry toward the
vertices of the icosahedron, the faces of a dodecahedron, and the pentagonal faces of a fullerene molecule. The effective
Hamiltonian of endohedral complexes in external electric fields with arbitrary orientation is obtained, its eigenvalues are
found, and the line intensities of different transitions between the tunnelling levels are calculated.
Fiz. Tverd. Tela (St. Petersburg) 39, 1693–1698 (September 1997) 相似文献
994.
We investigate some issues of minimax estimation of spectral intensity of acoustic sources in cases when the noise and the spectral amplitudes satisfy quadratic constraints. Recursive minimax filters are obtained.Translated from Vychislitel'naya i Prikladnaya Matematika, No. 58, pp. 116–119, 1986. 相似文献
995.
V. Shikin 《JETP Letters》2002,76(6):355-359
The origin of the specific activation-type behavior of the mobility of electrons on liquid-helium films with different kinds of substrates is discussed. The characteristic feature of the activation energy E a observed in the experiment is its dependence on the effective film thickness d in the form E a∝d ?2. A scenario of this effect is proposed with consideration for the roughness of the substrate underlying the liquid-helium film. 相似文献
996.
997.
V. A. Batanov V. S. Petriv A. O. Radkevich A. L. Telyatnikov A. Yu. Volkov 《International Journal of Infrared and Millimeter Waves》1991,12(7):703-715
High power IR pumping beams self focusing and defocusing in NH3 Raman laser is investigated by numerical methods on the basis of the solution of nonlinear quasioptical equations. The analysis of self focusing have been done for a wide range of parameters of radiation and of active medium. Spatial evolution of the beam configuration have been investigated for different regimes of nonlinear diffraction. Developed model enables to allow exactly for the spectroscopic features of active molecules and may be applied to the analysis of the properties of powerful optically pumped FIR lasers. 相似文献
998.
It was studied the tin phase composition of the electrodeposited alloys produced at different temperatures and current densities from an acid chloride/fluoride electrolyte and an acid chloride bath. Mössbauer spectra were consistent with a Ni3Sn4 intermetallic compound, dissolved tin, and a Cu?Sn intermetallic compound formed at the interface of the copper substrate. 相似文献
999.
I. V. Yakushin 《Russian Physics Journal》1991,34(12):1090-1094
The contribution of the interacting vector and pseudovector torsion components to the interaction of polarized photons in an atomic sodium vapor is investigated. Estimates are obtained for the parameters of the gauge-theoretical model of gravitation.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 50–55, December, 1991. 相似文献
1000.
D. D. Bainov S. I. Kostadinov P. P. Zabreiko 《International Journal of Theoretical Physics》1992,31(8):1521-1526
Necessary and sufficient conditions for the existence of an exponential dichotomy of impulsive differential equations in a Hilbert space are found. 相似文献