12,751 research outputs found
High-growth-rate magnetohydrodynamic instability in differentially rotating compressible flow
The transport of angular momentum in the outward direction is the fundamental
requirement for accretion to proceed in an accretion disc. This objective can
be achieved if the accretion flow is turbulent. Instabilities are one of the
sources for the turbulence. We study a differentially rotating compressive flow
in the presence of non vanishing radial and azimuthal magnetic field and
demonstrate the occurrence of a high growth rate instability. This instability
operates in a region where magnetic energy density exceeds the rotational
energy density
Skin effect with arbitrary specularity in Maxwellian plasma
The problem of skin effect with arbitrary specularity in maxwellian plasma
with specular--diffuse boundary conditions is solved. A new analytical method
is developed that makes it possible to to obtain a solution up to an arbitrary
degree of accuracy. The method is based on the idea of symmetric continuation
not only the electric field, but also electron distribution function. The
solution is obtained in a form of von Neumann series.Comment: 7 pages, 2 figure
Light diffraction by a strong standing electromagnetic wave
The nonlinear quantum interaction of a linearly polarized x-ray probe beam
with a focused intense standing laser wave is studied theoretically. Because of
the tight focusing of the standing laser pulse, diffraction effects arise for
the probe beam as opposed to the corresponding plane wave scenario. A
quantitative estimate for realistic experimental conditions of the ellipticity
and the rotation of the main polarization plane acquired by the x-ray probe
after the interaction shows that the implementation of such vacuum effects is
feasible with future X-ray Free Electron Laser light.Comment: 5 pages, 2 figures. Published versio
Superconductivity in the Sn-Ba-Sr-Y-Cu-O system
Since Bednorz and Muller discovered high-T(sub c) superconductivity in the La-Ba-Cu-O compound, several families of superconducting oxides have been synthesized. Here, researchers report the results of search for superconductivity in the compounds based on tin, which has a lone electron pair like Bi, Tl, Pb. The following compounds were synthesized: Sn1Ba1Sr1Cu3Ox, Sn1Ba1Ca1Cu3Ox, Sn1Ba1Mg1Cu3Ox, Sn1Sr1Ca1Cu3Ox, Sn1Sr1Mg1Cu3Ox, Sn1Ca1Mg1Cu3Ox. The initial components were oxides and carbonates of the appropriate elements. Standard firing-grinding procedure was used. Final heating was carried out at 960 C during 12 hours. Then the samples were cooled inside the furnace. All the synthesis cycles were carried out in air atmosphere. Among the synthesized compounds only Sn1Ba1Sr1Cu3Ox showed remarkable conductivity. Other compounds were practically dielectrics. Presence of a possible superconductivity in Sn1Ba1Sr1Cu3Ox was defined by using the Meissner effect. At low temperature a deviation from paramagnetic behavior is observed. The hysteresis loops obtained at lower temperatures undoubtly testify to the presence of a superconductive phase in the sample. However, the part of the superconductive phase in the Sn1Ba1Sr1Cu3Ox ceramic turned out to be small, less than 2 percent, which agrees with the estimation from magnetic data. In order to increase the content of the superconductive phase two-valent cations Ba, Sr were partially substituted by univalent (K) and three-valent ones (Y)
Effect of hypokinesia on blood microcirculation
Blood microcirculation in the region of the scleral bulbar conjunctiva and the nail folds on the fingers and toes was studied in 18 practically healthy men during 182 day antiorthostatic hypokinesia and 30 day rehabilitation period. Marked changes in microcirculation in the sclera and feet and less evident changes on the hands was revealed. A complex of special prophylactic physical exercises had a distinctly favorable effect on circulation in the hands
Geological-morphological description of the Ishtar Terra (photomap of the Venusian surface sheet B-5)
The main part of the Ishtar Terra east of the Maxwell Montes is covered with systems of areal dislocations of several directions, which are called Parquet. According to the structural patterns these may be divided into: (1) the central stable block; (2) the lesser peripheral blocks separated from the central one by gaps and grabens; (3) the zones of mobilized parquet, whose substance flowed downward at an incline in the directions away from the central block in the form of plastic flows; and (4) the partially parqueted lava sheets. The Maxwell Montes were formed as a result of the collision between the central parquet block and the Lakshmi Planum
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