Computer Physics Reports最新文献

An overview of the phenomena known to be of importance in molecule-surface scattering is presented and a detailed description of dynamical models and theories which can be used to study chemical reactions at or with solid surfaces are given. We have mainly focused upon the presentation of timedependent models and theories — the reason being that the time-dependent approach offers the necessary flexibility for a description of the vast amount of relevant processes in molecule-surface scattering.

A knowldge-based project, the GRAPE system(Group Representation and Application in Physics Environment), is described in this paper. The GRAPE system is designed to provide physicists with a group theoretical environment to help them solve problems in group theory and representation. The user can communicate with GRAPE in plain English. At the present stage, it contains the knowledge of crystallography point groups, space groups as well as magnetic space groups both in group structure and group representations. The GRAPE system consists of five modules besides the knowledge base and the data base: a natural language interface, a computation module, a tutprial module, a bibliography module, and a program library. Group theoretical analysis for the Landau theory of continuous phase transitions has been the first application of the GRAPE system. The calculation for determining directions of phase transition at the Γ point for 230 space groups, 230 grey space groups and 674 black and white magnetic space groups has been performed.

Accretion disks in close binary systems originate when mass overflow occurs from the primary star onto the compact star. When the compact star is a neutron star or a black hole the inner parts of the thin disk extend to the Alfvén radius respectively a few times the Schwarzchild radius. In the Keplerian rotating highly turbulent inner parts of the accretion disk magnetic fields are strongly amplified and expelled from the disk thus leading to the formation of a magnetically structured accretion disk corona, sandwiching the disk to which it is electrodynamically coupled. The magnetic energy supplied to the corona is radiated by inverse Compton scattering of soft X-ray photons produced in the disk by the viscous heating of the accreting matter. This may explain why certain X-ray sources show a very large fluctuating hard X-ray component. The interaction of the inner parts of an accretion disk with the magnetosphere around a neutron star leads to channeled accretion onto the magnetic poles, resulting in the phenomenon of X-ray pulsars with the associated spin variations due to angular momentum transfer. The interaction of disk coronal structures with the relatively weak magnetic fields of old fast spinning neutron stars lead to a new form of interaction around the so called beat frequency that can be used as a model for quasiperiodic oscillations in low-mass X-ray binaries.

A personal review of the structure and stability of solar coronal plasmas is given. Firstly the structure of the corona is presented in two parts, namely models for coronal arcades and coronal loops. Each topic is dealt with using two different approaches. One approach is to solve the equilibrium equations directly and the other is to solve the time dependent equations with a slow photospheric motion prescribed. In this latter approach, the plasma evolves through a sequence of approximate equilibria with dynamic behaviour occurring only when the photospheric field distribution is sufficiently complex. The evolution of coronal loops shows that the internal magnetic field tends to contract whereas the external field tends to expand. Here it is interesting to note that the simple twisting of a straight cylindrical field generates substantial structuring in the coronal field, with a strong current concentration on the magnetic axis. Secondly, the stability of the above equilibrium structures is discussed. Three-dimensional disturbances are considered and some of the numerical methods used are described. The main focus of attention here is the ideal and resistive MHD stability properties of the magnetic field. General results are hard to come but numerical results have suggested that all force-free coronal arcades are stable unless a magnetic island exists. Some references to other non-ideal instabilities, in particular thermal instabilities, are mentioned.

There are several important astrophysical questions that might be answered by numerical modelling. These involve the kinematic effects of motion on magnetic fields, the dynamics of magnetoconvection, the stucture and scale of convection and the global dynamo problem. This review will focus on detailed modelling of nonlinear compressible convection in a strong vertical magnetic field. Techniques range from heuristic models, which may be relatively primitive, through idealized numerical experiments to large scale simulations and each approach has its proponents. Early studies of nonlinear convection relied on the Boussinesq or anelastic approximations but recently there have been systematic investigations of fully compressible two- and three-dimensional convection as well as ambitious simulations. Detailed studies of two-dimensional behaviour reveal complicated bifurcation structures, involving changes of scale and transitions from steady to oscillatory solutions and from standing waves to travelling waves. Such behaviour is sensitive to assumptions built into the numerical model. Models of large-scale behaviour throughout the convection zone of a star like the sun show that dynamo action can occur but are still far from being able to reproduce the observed patterns of differential rotation or magnetic activity.