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1.
本文讨论半简并费密子自引力系统的平衡位形,将基于热力学量级数展开的计算结果与直接计算Fermi积分得到的精确值作了对比,指出了级数展开法的适用范围。对温度T不为零的任何值,不论中心密度如何,远离中心处的密度总是按r~(-2)降低,位形的质量和半径总是无限的。 相似文献
2.
木星的四颗大卫星都是同步轨旋卫星，常被称为伽利略卫星，美国发射的伽利略飞船自1995年12月抵达木星系统后，的几年来对木星的四颗伽利略卫星进行了一系列的探测，利用飞船探测的最新资料作为约束条件，建立了伽利略卫星的一组内部结构模型，然后按照同步轨旋卫星的形态理论公式计算了它们的平衡形太参数及潮汐耗散因子等。 相似文献
3.
等离子体弧是日冕中的一种基本结构,其高温观测特性意味着它有较高的等离子体压力。本文在二维近似下,讨论了等离子体拱被两个强磁场区域所约束时的平衡。对于较大的等离子体标高,等离子体具有近似圆弧形的结构。通过求出强磁场区域中的磁场位形,可以得到孤立的等离子体拱的平衡状态。由于总压守恒的边界条件是高度非线性的,整个问题是一类非线性的自由边界问题。在近圆弧形近似下,其基态是一维的非线性问题,而相对于基态的偏离是二维的线性问题。这样,整个问题可以给出分析解。 相似文献
4.
比较了12个日冕物质抛射(CME)事件, 发现它们可以分为两类, 其中分别是快速(＞1000 km/s)和慢速(≤800 km/s)各6个事件, 发现这2类CME事件分别对应于不同的多波段射电辐射类型和不同的日冕磁位形.本文定性地分析了这二个类型的射电爆发的产生过程,指出多重磁极和双磁极结构可能是分别产生二类CME和二类多波段射电爆发类型的原因,并涉及到"磁崩溃"模型与多重磁结构的关系.讨论了CME的不同速度可能是造成多波段不同射电爆发的主要因素,并指出快速或慢速的CME可能取决于日冕的多重或双重磁结构. 相似文献
5.
本文用一阶微扰理论讨论了有核的转动多层球平衡结构,并给出数值解。结果表明,核的质量越大,多层球转动的临界中心角速度Ω_(ocrl)就越小。而在相同的中心自转角速度下,核的质量越大,旋转棉球的扁率ξ_a/ξ_p也越大。本文还讨论了较差转动参数b对有核多层球平衡结构的影响。 相似文献
6.
利用国家天文台(北京和昆明)的射电频谱仪(频段为0.65~7.6 GHz)和相关的NoRH/17GHz射电以及TRACE/171 EUV和Yohkoh/SXT的观测资料,分析了2001/04/10和10/19的2个共生精细时间结构的稀有事件,这2个事件的射电爆发时间轮廓和观测特征相似,通过这2个事件的微波(17GHz)偏振观测资料的比较,发现这2个射电爆发均由包含多重(4极)磁结构的复杂活动区引起,特别指出这2个耀斑最后都导致了耀斑后相的分米波射电爆发(第二次触发耀斑),这可能是后环引起的射电爆发。它们都分别对应于双极磁位形,表明这两次触发耀斑是由相似的耀斑模型产生。2个分米波爆发可能是相似(homologous)耀斑的射电表现,可以推测这两次耀斑的驱动器可能皆是磁流浮现或对消(因为源区有新的单或双极出现或消失),而它们的触发器皆是由双极反向Y型位形(具有一个双极拱的单磁流系统)的磁重联,耀斑后环的演化是导致耀斑后相分米波射电爆发的必要条件。我们认为,这双带耀斑对应的宽带射电爆发辐射机制是回旋同步加速辐射过程,而耀斑后相的窄带分米波爆发的辐射机制是等离子体辐射过程。 相似文献
7.
用时间缓变的非线性无力场模拟超级活动区（弧岛式大型δ黑子）的磁场位形。这个复杂磁场包含了向量磁场的主要观测特征：正负磁流极端不平衡性（正负磁流之比为１：６）,Ｕ形磁反变线,局域磁场的二极子、四极子差异性。模拟结果厅用来解释一些观测结果：（１）大耀斑主要产生在Ｕ形中性线的磁性混杂区或四极子区（２）Ｕ形反变线的准双极性区几乎没有大耀斑很小。（３）活动区内部的大型旋转运动和磁沲运动会导致四极子场磁拓扑分 相似文献
8.
伽利略探测器对木星深部的大气测量，进一步增加了木星大气的平均带状交替快速环流是由其深部大气运动产生的可能性。由于木星高速自转，所以此带状流的基本动力学特征是地转流，即主要动力学平衡是科里奥利力和压力。基于近两维和非轴对称地转慢波的非线性相互作用，描述了一个新的带状交替环流的分析理论，并给出了地转波动的一个显函数关系分析表达式，以及它对应于弱非线性问题的首阶解。对考虑非线性效应的高阶解问题，推导出了一个运动方向交替的快速环流的分析表达式。也对该理论在木星和其他行星的大气动力学研究方面作了讨论。 相似文献
9.
本文在细长柱位形下数值研究了具有剪切流动的电流片中电阻撕裂模不稳定性的非线性演化。结果表明，电流片附近Ｓｅｃｈ形式的剪切流动，将导致电阻撕裂模不稳定性的发展，且不稳定性增长率随着剪切参数Ｒｒ的增加而增长，导致磁岛的形成和快速的磁能释放。这种剪切流动和撕裂模的耦合过程以及超热不稳定性的相互作用，改变了磁拱中的磁场剪切强度或者说电流密度梯度，从而驱动电阻撕裂模不稳定性的发展，这种过程对于等离子体电流密 相似文献
10.
本文用Harrison-Wheeler物态方程,通过“自洽场方法”,对Einstein场方程和广义相对论流体静力学平衡方程作数值求解,研究了快速旋转致密天体的平衡位形及其某些引力效应。结果表明:其平衡位形是扁的旋转椭球,当角速度大于3.0×10~2/秒时,偏心率和天体质量随角速度的增加而迅速增大,在极限情况下,偏心率可达0.7,质量增大可达10％—35％;旋转引起的天体表面引力红移的差异,光线顺逆旋转方向通过天体表面时的偏转角差异都是相当显著的。 相似文献
11.
We have derived a similarity solution in the form of a power series of the nonlinear magnetostatic equilibrium equation and identified the region of convergence in the parameter space. Within this region we have equilibrium configurations, outside it, non-equilibrium configurations. An example of nonlinear equilibrium configuration is shown graphically.
Our results can be used to explain the generation of multi-ribbon flares, the two-arch structures and the structures of the magnetic fields above elongated sunspot groups. 相似文献
12.
We present a novel numerical method that allows the calculation of nonlinear force-free magnetostatic solutions above a boundary
surface on which only the distribution of the normal magnetic field component is given. The method relies on the theory of
force-free electrodynamics and applies directly to the reconstruction of the solar coronal magnetic field for a given distribution
of the photospheric radial field component. The method works as follows: we start with any initial magnetostatic global field
configuration (e.g. zero, dipole), and along the boundary surface we create an evolving distribution of tangential (horizontal) electric fields
that, via Faraday’s equation, give rise to a respective normal-field distribution approaching asymptotically the target distribution.
At the same time, these electric fields are used as boundary condition to numerically evolve the resulting electromagnetic
field above the boundary surface, modeled as a thin ideal plasma with non-reflecting, perfectly absorbing outer boundaries.
The simulation relaxes to a nonlinear force-free configuration that satisfies the given normal-field distribution on the boundary.
This is different from existing methods relying on a fixed boundary condition – the boundary evolves toward the a priori given
one, at the same time evolving the three-dimensional field solution above it. Moreover, this is the first time that a nonlinear
force-free solution is reached by using only the normal field component on the boundary. This solution is not unique, but
it depends on the initial magnetic field configuration and on the evolutionary course along the boundary surface. To our knowledge,
this is the first time that the formalism of force-free electrodynamics, used very successfully in other astrophysical contexts,
is applied to the global solar magnetic field. 相似文献
13.
F. H. Busse 《Solar physics》1973,33(2):413-423
An analytical solution is derived for the nonlinear magnetostatic balance between the Lorentz forces on one side and the pressure and gravitational forces induced by the magnetic inhibition of granular convection in a sunspot on the other. In order to exhibit the mathematical structure of the problem it has been reduced to the simplest case which still contains the basic physical features. Although the results of a model with a two-dimensional periodic magnetic field are not quantitatively comparable with sunspot observations the conclusion can be drawn that an upper limit on the size of sunspots exists. The results suggest that this upper limit is close to the size of observed large sunspots. 相似文献
14.
M. K. Das 《Astrophysics and Space Science》1985,114(2):295-302
The nonlinear pseudo-radial mode of oscillation of a rotating magnetic star is studied. It is shown that for a general rotational field, the coupling between magnetic field and rotation tends to reduce the average rotational energy parameterT. This result in a lowering of the maximum pulsation amplitudeq
max, which depends on strength of rotation and magnetic field. The configuration tends, therefore, to a new equilibrium state at lower value ofq
max. The analytic solution of the pulsation equation for the case ofy=5/3 in the presence of rotation and magnetic field has also been derived in the Appendix. 相似文献
15.
B. C. Low 《Solar physics》1985,100(1-2):309-331
This article describes recent developments in the theoretical investigation of magnetostatic equilibrium in the presence of gravity, nonequilibrium in hydromagnetics, and classical problems in hydromagnetic stability. The construction of magnetostatic equilibria has progressed beyond geometrically idealized systems, such as the axisymmetric system, to fully three-dimensional systems capable of modelling realistic solar structures. Nonequilibrium in a magnetic field with an arbitrary interweaving of lines of force due to random footpoint motion is a novel and subtle property with important implications for the solar atmosphere. Work begun by Parker and subsequent developments are described. To the extent quasi-static solar structures are approximated by stable equilibrium, ideal hydromagnetic stability theory provides a first insight into how stability is achieved in the solar environment. A qualitative physical picture based on recent stability analyses is given. The article places emphasis on understanding basic principles and issues rather than detailed results which can be found in the published literature.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
16.
We present a theoretical model of quiescent prominences in the form of an infinite vertical sheet. Self-consistent solutions are obtained by integrating simultaneously the set of nonlinear equations of magnetostatic equilibrium and thermal balance. The basic features of the models are: (1) The prominence matter is confined to a sheet and supported against gravity by a bowed magnetic field. (2) The thermal flux is channelled along magnetic field lines. (3) The thermal flux is everywhere balanced by Low's (1975b) hypothetical heat sink which is proportional to the local density. (4) A constant component of the magnetic field along the length of the prominence shields the cool plasma from the hot surrounding. We assume that the prominence plasma emits more radiation than it absorbs from the radiation fields of the photosphere, chromosphere and corona, and we interpret the above hypothetical heat sink to represent the amount of radiative loss that must be balanced by a nonradiative energy input. Using a central density and temperature of 1011 particles cm–3 and 5000 K respectively, a magnetic field strength between 2 to 10 gauss and a thermal conductivity that varies linearly with temperature, we discuss the physical properties implied by the model. The analytic treatment can also be carried out for a class of more complex thermal conductivities. These models provide a useful starting point for investigating the combined requirements of magnetostatic equilibrium and thermal balance in the quiescent prominence. 相似文献
17.
The properties of the magnetostatic structures in a collisionless relativistic plasma found by exactly solving the nonlinear
self-consistent kinetic and Maxwell equations using the method of invariants of particle motion are analyzed. These structures
include individual neutral current sheets and cylindrically symmetric filaments as well as their ensembles, admitting a wide
variety of types of particle energy distribution functions. Relationships are established between the possible parameters
of the current sheets and filaments—their sizes, currents and magnetic fields, and the degree of anisotropy of the particle
momentum distribution. The extent to which these parameters are conditioned by the properties of the Weibel instability that
can produce these structure is also discussed. The spectral peculiarities of the synchrotron radiation from the particles
that form the current sheets and filaments are investigated in the special case of power-law energy distribution functions. 相似文献
18.
B. C. Low 《Solar physics》1982,75(1-2):119-131
We present a simple magnetostatic theory of the thin vertical filaments that make up the quiescent prominence plasma as revealed by fine spatial resolution H photographs. A class of exact equilibrium solutions is obtained describing a horizontal row of long vertical filaments whose weights are supported by bowed magnetic field lines. A free function is available to generate different assortments of filament sizes and spacings, as well as different density and temperature variations. The classic Kippenhahn-Schlüter solution for a long sheet without filamentary structures is a particular member of this class of solutions. The role of the magnetic field in supporting and thermally shielding the filament plasma is illustrated. It is found that the filament can have a sharp transition perpendicular to the local field, whereas the transition in the direction of the local field is necessarily diffuse. A consequence of the filamentary structure is that its support by the Lorentz force requires the electric current to have a component along the magnetic field. This electric current flowing into the rarefied region around the prominence can contain substantial energy stored in the form of force-free magnetic fields. This novel feature has implications for the heating and the disruption of prominences. 相似文献
19.
A set of nonlinear equations governing the dynamics of finite amplitude drift-ion acoustic-waves is derived for sheared ion flows parallel and perpendicular to the ambient magnetic field in the presence of Cairns and Kappa distributed electrons. It is shown that stationary solution of the nonlinear equations can be represented in the form of a tripolar vortex for specific profiles of the equilibrium sheared flows. The tripolar vortices are, however, observed to form on a scale of the order of ion Larmor radius ρ i which is calculated to be around a Kilometer for the plasma parameters found in the Saturn’s E-ring. The relevance of the present investigation in planetary environments is also pointed out. 相似文献
20.
A normal-polarity prominence is modelled as a series of cool fibrils set in the hotter corona. Equations of magnetostatic equilibrium are solved and each fibril corresponds to a dip in the mgnetic field. The ratio of fibril width to interfibril spacing is dependent on the prominence-coronal temperature ratio and the ratio of plasma to magnetic pressure. The prominence mass is found to depend on the square of the magnetic field strength. When variations along the prominence are allowed in addition to those across the prominence, an apparently random pattern of fibrils results. 相似文献