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81.
José A. Ferrari 《General Relativity and Gravitation》1990,22(1):19-32
In this paper we investigate the (static) solution of the Kaluza-Klein equations for a cylindrically symmetric current distribution. Specifically, we are interested in the fields generated by a long, cylindrical solenoid. We shall examine in some detail the concept of effective mass of a charged test particle. We shall show that, for a certain charge-to(rest)mass ratio of the test particle, the effective mass becomes imaginary at a certain distance from the axis of our solenoid. 相似文献
82.
Summary Bhattacharya, Chernoff and Yang (1983) proposed a nonparametric estimate for the slope of a regression lineY =
o
X + V subjected to the truncationYy
0. The estimate corresponds to the zero-crossing of a random functionS
n
(). In this paper an estimate for the asymptotic variance of the estimate of the slope is proposed and the rate of convergence is given. The proofs rest heavily on the local behavior ofS
n
() in the neighborhood of the true value o. 相似文献
83.
A new class of expanding cosmological solutions is derived. The matter content of these models is a mixture of two interacting simple fluids: the first one, homogeneous and isotropic with equation of statep = (-1), the dynamics of which is given by the FRW equation and the second one an inhomogenous dust. The limiting case of two dusts corresponds to the Szekeres' universes of class II. A large subclass of the models evolve to a FRW phase for all physically meaningful values of the polytropic index and the curvature parameterk. A gauge condition, under which the metric is invariant, is shown to exist for k0. In particular, it explains why the parabolic model is a peculiar solution in the class found by Szekeres.On leave from Departamento de Fisica Teórica e Experimental Universidade Federal do Rio Grande do Norte, Natal, RN, Brazil. 相似文献
84.
A critical review of known results about the permanence conditions for the null character of the solutions to the (vacuum) Maxwell equations, is presented. Concomitants of the electromagnetic field and the metric tensor are constructed, which give the principal directions of the field in covariant form. The known permanence conditions are generalized in order to includeall the (local) null fields; the above concomitants allow these conditions to be explicitly formulated in terms of the electromagnetic field.Supported in part by Conselleria de Cultura, Educació i Ciència de la Generalitat Valenciana. 相似文献
85.
J. Kvapil B. Perner Jos Kvapil B. Mánek K. Hamal M. Košelja V. Kubeček 《Czechoslovak Journal of Physics》1988,38(11):1281-1287
YAP:Nd, Cr grown under Ar-H2 or Ar-He-H2 atmosphere possesses good energy transfer from Cr3+ to Nd3+ but suffers from the colour centre formation. The centre formation was completely prevented using further admixture of Ce3+ and 10–4–10–3 wt. % Fe. Small luminescence quenching of Cr3+ or Nd3+ due to iron ions is negligible in the presence of Ce3+. The crystals may be also heavily doped with Nd3+ because the increased pumping efficiency compensates the shortening of the luminescence lifetime. YAP: Nd, Ce, Cr, Fe is advisible active laser material particularly for all the types of pulsed lasers. 相似文献
86.
Reproducibility for successive determinations with a hanging mercury drop electrode is assessed in relation to solution stirring, drop size and back-diffusion to the mercury thread. The effect of experimental parameters such as drop size, deposition time and gallium concentration on the observed stripping current is investigated. The interference of zinc present in a 0.5M NaSCN + 4.2M NaClO(4) supporting electrolyte on the gallium detection limit and calibration plots is described. Formation of an intermetallic compound with a Zn:Ga ratio of 2:3 and its destruction by co-deposition of zinc with Sb are reported. A detection limit of 10(-8)M gallium was obtained in the presence of 10(-5)M Sb(III). 相似文献
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