排序方式: 共有177条查询结果,搜索用时 15 毫秒
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A. R. Bell 《Monthly notices of the Royal Astronomical Society》2005,358(1):181-187
A large flux of cosmic rays streaming through a magnetized plasma creates cavities of low plasma density and low magnetic field. The magnetic field focuses the cosmic ray trajectories into the cavities with the possible formation of filaments or beams of high-energy cosmic rays. 相似文献
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F. M. Kerr A. Gouveia R. W. Lee P. K. Patel O. Renner S. J. Rose H. A. Scott J. S. Wark 《Astrophysics and Space Science》2005,298(1-2):171-176
An astrophysically relevant experiment is compared to the output of a multidimensional radiation transfer code in which populations
and radiation are self-consistently treated. Experimental Al Ly α spectra obtained with a very high-resolution spectrometer
are presented as quantitative evidence of dot plasma non-planar expansion. Analysis of these spectra using the code is performed,
in particular examining the effects of velocity gradients in directions other than that of the primary expansion. These calculations
are found to be in good agreement with the experimental results. Usage of the Ly α doublet as a planarity diagnostic is discussed. 相似文献
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Estelle Asseo David Khechinashvili 《Monthly notices of the Royal Astronomical Society》2002,334(4):743-759
We explore the role of complex multipolar magnetic fields in determining physical processes near the surface of rotation powered pulsars. We model the actual magnetic field as the sum of global dipolar and star-centred multipolar fields. In configurations involving axisymmetric and uniform multipolar fields, 'neutral points' and 'neutral lines' exist close to the stellar surface. Also, the curvature radii of magnetic field lines near the stellar surface can never be smaller than the stellar radius, even for very high-order multipoles. Consequently, such configurations are unable to provide an efficient pair-creation process above pulsar polar caps, necessary for plasma mechanisms of generation of pulsar radiation. In configurations involving axisymmetric and non-uniform multipoles, the periphery of the pulsar polar cap becomes fragmented into symmetrically distributed narrow subregions where curvature radii of complex magnetic field lines are less than the radius of the star. The pair-production process is only possible just above these 'favourable' subregions. As a result, the pair plasma flow is confined within narrow filaments regularly distributed around the margin of the open magnetic flux tube. Such a magnetic topology allows us to model the system of 20 isolated subbeams observed in PSR B0943+10 by Deshpande & Rankin. We suggest a physical mechanism for the generation of pulsar radio emission in the ensemble of finite subbeams, based on specific instabilities. We propose an explanation for the subpulse drift phenomenon observed in some long-period pulsars. 相似文献
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H.M. Wiechen 《Planetary and Space Science》2006,54(1):71-77
In partially ionized dusty space plasmas collisional momentum transfer between neutral and charged components of different inertia yields significant self-induced magnetic fields on remarkable short time scales of several dust Alfven times. Considering the proto-solar accretion disk previous first self-consistent plasma-neutral gas-dust simulations have shown, that this process yields a self-magnetization of 10-5- on time scales of about 100 days. Thus, this mechanism is able to explain the remanent magnetization of chondrite type meteorite matter. New simulations show the quantitative dependence of the self-magnetization on polarity and charge numbers of the dust grains. 相似文献
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Collapse calculations indicate that the hot young neutron stars rotate differentially so that strong toroidal magnetic field components should exist in the outer shell where also the Hall effect appears to be important when the Hall parameter = ωBτ exceeds unity. The amplitudes of the induced toroidal magnetic fields are limited by the current‐induced Tayler instability. An important characteristics of the Hall effect is its distinct dependence on the sign of the magnetic field. We find for fast rotation that positive (negative) Hall parameters essentially reduce (increase) the stability domain. It is thus concluded that the toroidal field belts in young neutron stars induced by their differential rotation should have different amplitudes in both hemispheres which later are frozen in. Due to the effect of magnetic suppression of the heat conductivity also the brightness of the two hemispheres should be different. As a possible example for our scenario the isolated neutron star RBS 1223 is considered which has been found to exhibit different X‐ray brightness at both hemispheres (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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Patrick Weltevrede Geoff Wright 《Monthly notices of the Royal Astronomical Society》2009,395(4):2117-2126
We present a geometric study of the radio and γ-ray pulsar B1055−52 based on recent observations at the Parkes radio telescope. We conclude that the pulsar's magnetic axis is inclined at an angle of 75° to its rotation axis and that both its radio main pulse and interpulse are emitted at the same height above their respective poles. This height is unlikely to be higher or much lower than 700 km, a typical value for radio pulsars.
It is argued that the radio interpulse arises from emission formed on open fieldlines close to the magnetic axis which do not pass through the magnetosphere's null (zero-charge) surface. However, the main pulse emission must originate from fieldlines lying well outside the polar cap boundary beyond the null surface, and farther away from the magnetic axis than those of the outer gap region where the single γ-ray peak is generated. This casts doubt on the common assumption that all pulsars have closed, quiescent, corotating regions stretching to the light cylinder. 相似文献
It is argued that the radio interpulse arises from emission formed on open fieldlines close to the magnetic axis which do not pass through the magnetosphere's null (zero-charge) surface. However, the main pulse emission must originate from fieldlines lying well outside the polar cap boundary beyond the null surface, and farther away from the magnetic axis than those of the outer gap region where the single γ-ray peak is generated. This casts doubt on the common assumption that all pulsars have closed, quiescent, corotating regions stretching to the light cylinder. 相似文献
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Yuri M. Shtemler Michael Mond Günther Rüdiger 《Monthly notices of the Royal Astronomical Society》2009,394(3):1379-1392
Axisymmetric steady-state weakly ionized Hall–magnetohydrodynamic (MHD) Keplerian thin discs are investigated by using asymptotic expansions in the small disc aspect ratio ε. The model incorporates the azimuthal and poloidal components of the magnetic fields in the leading order in ε. The disc structure is described by an appropriate Grad–Shafranov equation for the poloidal flux function ψ that involves two arbitrary functions of ψ for the toroidal and poloidal currents. The flux function is symmetric about the mid-plane and satisfies certain boundary conditions at the near-horizontal disc edges. The boundary conditions model the combined effect of the primordial as well as the dipole-like magnetic fields. An analytical solution for the Hall equilibrium is achieved by further expanding the relevant equations in an additional small parameter δ that is inversely proportional to the Hall parameter. It is thus found that the Hall equilibrium discs fall into two types: Keplerian discs with (i) small ( R d ∼δ0 ) and (ii) large ( R d ≳δ− k , k > 0) radius of the disc. The numerical examples that are presented demonstrate the richness and great variety of magnetic and density configurations that may be achieved under the Hall–MHD equilibrium. 相似文献