我国首座卫星信道数字化地震台网落成

文章较为详细地介绍了我国第一座卫星信道数字化地震观测台网各配套仪器的性能,使用环境及整套系统的运行情况和目前在地震观测中所起的作用。作者展望了该系统的发展前景及其对我国地震观测事业的影响。     

地震前兆复杂性成因机理研究的讨论（一）：地震前兆复杂性的表现形式

通过国内外成功与失败的震例分析,介绍了地震前兆共性的一面,如在台网具有一定监测能力的地区,如果发生６级以上地震,震前总能或多或少地观测到异常现象。地震越大震前异常越多,分布越广,持续时间越长,异常幅度也较大,同时章着重对前兆复杂性的表现形式进行了较系统的归纳,整理,主要从以下几方面进行了分析,异常与地震关系的不确定性,主要表现在除了“有异常有地震”和“无异常无地震”的理论情况外,还存在“有异常无     

General absorbing boundary conditions for dynamic analysis of fluid-saturated porous media

General absorbing boundary conditions based on Biot's two-phase mixture theory and paraxial approximation is presented for the dynamic analysis of fluid-saturated porous media with isotropic, transverse isotropic, and anisotropic properties. For the last two cases, the equivalent Lame's constants, under conditions of uniqueness, are introduced to facilitate the analytical solutions. The numerical results show that the proposed absorbing boundary can greatly suppress spuriously reflected waves and efficiently model the far field of the system with sufficient accuracy.     

遗传规划在岩石力学中的应用

本文探讨了遗传规划这一新的优化方法在岩石力学参数确定中的应用。由于影响岩石力学性能的各因素之间关系不明确,而遗传规划特别适用于各影响因素之间因果关系不明确的复杂非线性问题。它为预测岩石力学性能提供了一条新的技术途径。通过例子,说明该方法的实用性。     

Interferometer phase calibration sources — II. The region 0° ≤ δB1950≤ +20°

We present a catalogue of 781 compact radio sources in the declination range 0° ≤ δ_B1950≤ +20° whose positions have been measured to an rms accuracy of about 14 mas with the Very Large Array (VLA). These sources are primarily intended for use as phase calibration sources for the Jodrell Bank MERLIN. However, they will also be suitable as phase calibrators for the VLA and can be considered as candidate phase calibrators for very long-baseline interferometry (VLBI) networks.     

Dynamical behaviour of the primitive asteroid belt

In this paper we consider the dynamical evolution and orbital stability of objects in the asteroid belt. A simple physical model, including full gravitational perturbations from both giant planets, is used to compute the dynamical evolution of 1000 test particles simulating the primitive asteroids. The criterion of planet crossing (or close approach in the case of resonant objects) is used to reject particles from the simulation. 44 per cent of the particles survived for the whole time-span covered by the numerical integration (∼10⁹ yr).
The 4:1, 3:1 and to a lesser extent the 2:1 Kirkwood gaps are formed in ∼10⁷ yr of evolution, representing direct numerical evidence about their gravitational origin.
We found that the rms eccentricity and inclination of the sample experience a fast increase during the first 10⁶ yr. The final rms eccentricity is 0.11, ∼60 per cent smaller than the present rms eccentricity (0.17). Nevertheless, the gravitational action of the giant planets suffices to prevent the formation of large objects, allowing catastrophic collisions and the subsequent depletion of material from this zone of the Solar system. The excited eccentricity by Jupiter and Saturn may favour mutual encounters and the further increase of the relative velocities up to their present values.     

Simulations of spheroidal systems with substructure: trees in fields

We present a hybrid technique of N -body simulation to deal with collisionless stellar systems having an inhomogeneous global structure. We combine a treecode and a self-consistent field code such that each of the codes models a different component of the system being investigated. The treecode is suited to treatment of dynamically cold or clumpy components, which may undergo significant evolution within a dynamically hot system. The hot system is appropriately evolved by the self-consistent field code. This combined code is particularly suited to a number of problems in galactic dynamics. Applications of the code to these problems are briefly discussed.     

Dynamical studies of cluster pairs in the Magellanic Clouds

We performed N -body simulations of star cluster encounters with Hernquist's TREECODE in a CRAY YMP-2E computer under different initial conditions (relative positions and velocities, cluster sizes, masses and concentration degrees). The total number of particles per simulation ranged from 1024 to 20480. These models are compared with a series of isodensity maps of cluster pairs in the Magellanic Clouds. Evidence is found that during the interactions, transient morphological effects such as an expanded halo, isophotal deformation and isophotal twisting can occur as a result of tidal effects and dynamical friction. The simulations also show that different outcomes are possible depending on the initial parameters: (i) long-standing changes of concentration degree can occur after the collision; (ii) one member can disaggregate; or (iii) the pair can coalesce into a single cluster with a distinct structure compared with the original ones. These simulations can reproduce a wide range of morphological structures in observed cluster pairs.     

Linear response of galactic haloes to adiabatic gravitational perturbations

We determine the response of a self-similar isothermal stellar system to small adiabatic gravitational perturbations. For odd spherical harmonics the response is identical to the response of the analogous isothermal fluid system. For even spherical harmonics the response can be regarded as an infinite series of wavetrains in log r , implying alternating compression and rarefaction in equal logarithmic radius intervals. Partly because of the oscillatory nature of the solutions, tidal fields from external sources are not strongly amplified by an intervening isothermal stellar system, except at radii ≲10^−3.5 times the satellite radius; at some radii the stellar system can even screen the external tidal field in a manner analogous to Debye screening. As Weinberg has pointed out, individual resonances in a stellar system can strongly amplify external tidal fields over a limited radial range, but we cannot address this possibility because we examine only adiabatic perturbations. We also discuss the application of our method to the halo response caused by the slow growth of an embedded thin disc.     

On a time-symmetric Hermite integrator for planetary N-body simulation

We describe a P(EC) ⁿ Hermite scheme for planetary N -body simulation. The fourth-order implicit Hermite scheme is a time-symmetric integrator that has no secular energy error for the integration of periodic orbits with time-symmetric time-steps. In general N -body problems, however, this advantage is of little practical significance, since it is difficult to achieve time-symmetry with individual variable time-steps. However, we can easily enjoy the benefit of the time-symmetric Hermite integrator in planetary N -body systems, where all bodies spend most of the time on nearly circular orbits. These orbits are integrated with almost constant time-steps even if we adopt the individual time-step scheme. The P(EC) ⁿ Hermite scheme and almost constant time-steps reduce the integration error greatly. For example, the energy error of the P(EC)² Hermite scheme is two orders of magnitude smaller than that of the standard PEC Hermite scheme in the case of an N  = 100,  m  = 10²⁵ g planetesimal system with the rms eccentricity 〈 e ²〉^1/2 ≲0.03.