共查询到20条相似文献,搜索用时 15 毫秒
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In weakly ionized astrophysical plasmas, shear flow induced plasma - neutral gas friction yields self-generated magnetic fields
of seed-field order. This process is of cosmological importance and relevant for protogalactic systems like Lyα-clouds. In
our contribution we illustrate this mechanism by the help of 3-dimensional 2-fluid simulations of primordial rotating gas
clumps in Lyα-clouds showing that plasma - neutral gas interactions cause large scale magnetic fields of the order of 10−15G on time scales of the order of 106yrs.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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N. Falcón 《Astrophysics and Space Science》1997,256(1-2):399-402
The plasma thermal stability condition under convection is discutided. Using Cattaneo law and mixing length theory before relaxation lets show a new thermal stability condition for plasmas in astrophysics. Application in neutron stars and low mass x-ray binaries stars is mentioned. 相似文献
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Kuniaki Masai 《Astrophysics and Space Science》2005,298(1-2):155-162
We discuss radiation properties of plasmas in high-energy astrophysics with a keyword nonequilibrium: non-LTE level populations, nonequilibrium ionization, and non-Maxwellian distribution function, beginning with radiative
transfer. We focus particularly on supernova remnants interacting with the circumstellar/interstellar matter, and also mention
line emission processes in accretion gas onto a neutron star or black hole, and in the X-ray afterglow of γ-ray bursts. 相似文献
5.
Anthony L. Peratt 《Astrophysics and Space Science》1997,256(1-2):51-75
Advances in the simulation of astrophysical and cosmic plasmas are the direct result of advances in computational capabilities, today consisting of new techniques such as multilevel concurrent simulation, multi-teraflop computational platforms and experimental facilities for producing and diagnosing plasmas under extreme conditions for the benchmarking of simulations. Examples of these are the treatment of mesoscalic plasma and the scaling to astrophysical and cosmic dimensions and the Accelerated Strategic Computing Initiative whose goal is to construct petaflop (1015 floating operations per second) computers, and pulsed power and laser inertial confinement plasmas where megajoules of energy are delivered to highly-diagnosed plasmas. This paper concentrates on the achievements to date in simulating and experimentally producing plasmas scaled to both astrophysical and cosmic plasma dimensions. A previous paper (Part I, Peratt, 1997) outlines the algorithms and computational growth. 相似文献
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The electron–ion inverse Bremsstrahlung is considered here as a factor of the influence on the opacity of the different stellar atmospheres and other astrophysical plasmas. It is shown that this process can be successfully described in the frames of cut-off Coulomb potential model within the regions of the electron densities and temperatures. The relevant quantum mechanical method of the calculation of the corresponding spectral coefficient processes is described and discussed. The results obtained for the plasmas with the electron densities from 1014 cm ?3 to 2?1019 cm ?3 and temperatures from 5?103 K to 3?104 K in the wavelength region 100 nm<λ<3000 nm are presented. Also, these results can be of interest for different laboratory plasmas. 相似文献
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In this paper we present a new class of exact reconnection solutions in cylindrical geometry. We point out that in the case of planar reconnection there is a natural cylindrical analog to the Cartesian Dawson function model for the magnetic field. Although the resistive energy release scalings of these solutions mimic the Cartesian models an important new feature is the presence of curvature in the current sheet. We go on to show that these solutions can be generalized to three dimensions. 相似文献
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王水 《紫金山天文台台刊》1994,13(3):181-188
Basic processes of magnetic reconnection and observations of coronal mass ejection are introduced. A possible mechanism of CME caused by magnetic rcconnection in the current sheet of solar corona is suggested. 相似文献
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A model of forced magnetic reconnection in a force-free magnetic field is considered, which allows calculation of the magnetic
energy release during the current sheet reconnection. The dependence of this energy on characteristics of the magnetic configuration
has been studied, and it was found that the released energy becomes very large when the field is near the marginal tearing
stability. A persistent plasma heating provided by ongoing external driving and internal reconnection is also derived. It
shows a typical relaxation-type dependence on the driving frequency, with dissipation becoming most efficient when the time-scales
of the driving and reconnection are comparable. Possible implications of the obtained results for the problem of solar coronal
heating are discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
13.
E.R. Priest 《Astrophysics and Space Science》1998,264(1-4):77-100
Here I review briefly the theory of magnetohydrodynamic reconnection and ask what observational evidence is there that it
is heating the corona. In particular, the new directions in which three-dimensional theory for reconnection is heading are
outlined. Part of the coronal heating problem has been solved with the identification of reconnection driven by converging
flux motions as the key for x-ray bright points. Furthermore, it has been shown that the large-scale diffuse corona is heated
rather uniformly, so that turbulent reconnection by braiding or ion-cyclotron waves driven by network micro-flares are prime
candidates. Finally, reconnection is the natural explanation for a wide variety of phenomena discovered by SOHO including
explosive events, blinkers, the magnetic carpet and even possibly tornadoes.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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Photoionization by stars cannot be the only cause for the diffuseionized gas component in the distant halos of galaxies.Quasistationary localized magnetic reconnection can efficientlycontribute to the ionization of the extraplanar halo gas. The gas isheated and re-ionized in numerous current filaments fast enough tocompensate recombination. The necessary magnetic energy is provided bythe disk activity. 相似文献
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Various topological features, for example magnetic null points and separators, have been inferred as likely sites of magnetic reconnection and particle acceleration in the solar atmosphere. In fact, magnetic reconnection is not constrained to solely take place at or near such topological features and may also take place in the absence of such features. Studies of particle acceleration using non-topological reconnection experiments embedded in the solar atmosphere are uncommon. We aim to investigate and characterise particle behaviour in a model of magnetic reconnection which causes an arcade of solar coronal magnetic field to twist and form an erupting flux rope, crucially in the absence of any common topological features where reconnection is often thought to occur. We use a numerical scheme that evolves the gyro-averaged orbit equations of single electrons and protons in time and space, and simulate the gyromotion of particles in a fully analytical global field model. We observe and discuss how the magnetic and electric fields of the model and the initial conditions of each orbit may lead to acceleration of protons and electrons up to 2 MeV in energy (depending on model parameters). We describe the morphology of time-dependent acceleration and impact sites for each particle species and compare our findings to those recovered by topologically based studies of three-dimensional (3D) reconnection and particle acceleration. We also broadly compare aspects of our findings to general observational features typically seen during two-ribbon flare events. 相似文献
17.
太阳大气中磁重联的MHD数值模拟 总被引:1,自引:0,他引:1
回顾了近30年太阳大气中磁重联过程的MHD数值模拟工作取得的进展。着重描述了在验证理论模型,解释观测现象,以及研究各种因素对重联的影响三个方面的成果,如快速磁重联,太阳耀斑机制及色球,日冕中的各种爆发现象等。指出了在数值模拟中应注意的几个问题,并对该领域今后的发展作了简要的展望。 相似文献
18.
Shou-Biao Zhang Jin-Lin Xie Guang-Hai Hu Hong Li Guang-Li Huang Wan-Dong Liu 《Chinese Astronomy and Astrophysics》2011,35(4):339-348
In the Linear Magnetized Plasma (LMP) device of University of Science and Technology of China and by exerting parallel currents on two parallel copper plates, we have realized the magnetic reconnection in laboratory plasma. With the emissive probes, we have measured the parallel (along the axial direction) electric field in the process of reconnection, and verified the dependence of reconnection current on passing particles. Using the magnetic probe, we have measured the time evolution of magnetic flux, and the measured result shows no pileup of magnetic flux, in consistence with the result of numerical simulation. 相似文献
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《Chinese Astronomy and Astrophysics》2007,31(2):117-127
By using the method of 2-dimensional, 3-component full particle simulation, collisionless magnetic reconnection in the presence of various initial guide fields and the Harris current sheet with 1-dimensional initial state are studied. The results show that strong guide fields with Bz0 > 0.5B0 can evidently alter not only the trajectory of the particles, but also the structure of the electric and velocity fields in the vicinity of the reconnection region, thereby affecting the rate of reconnection and the acceleration of electrons. The generalized Ohm's law is employed to interpret the structural characteristics of the electric fields with various guide fields. Also, via the tracing of the electron beam near he diffusion region, it is revealed that in the 2-D model, for both strong and weak guide fields, the induced electric field perpendicular to the simulation plane at the center of the diffusion region plays the major role in the acceleration of electrons. The contribution of the planar electric field outside the diffusion region is very small. 相似文献
20.
胡友秋 《中国天文和天体物理学报》1999,(2)
采用二维三分量磁流体力学模型,对日冕三重无力场电流片的磁场重联进行了数值研究,揭示了重联过程的基本物理特征.这类重联过程将加热和加速日冕等离子体,并导致多个高温、高密度、高磁螺度的磁岛的形成和向上喷发.这表明,多重无力场电流片的重联可能在日冕磁能释放、上行等离子体团的形成和太阳磁场螺度向行星际空间的逃逸方面起重要的作用. 相似文献