General relativistic self-similar solutions in cosmology

We present general relativistic solutions for self-similar spherical perturbations in an expanding cosmological background of cold pressure-less gas. We focus on solutions having shock discontinuities propagating in the surrounding cold gas. The pressure, p , and energy density, μ, in the shock-heated matter are assumed to obey   p = w μ  , where w is a positive constant. Consistent solutions are found for shocks propagating from the symmetry centre of a region of a positive density excess over the background. In these solutions, shocks exist outside the radius marking the event horizon of the black hole which would be present in a shock-less collapse. For large jumps in the energy density at the shock, a black hole is avoided altogether and the solutions are regular at the centre. The shock-heated gas does not contain any sonic points, provided the motion of the cold gas ahead of the shock deviates significantly from the Hubble flow. For shocks propagating in the uniform background, sonic points always appear for small jumps in the energy density. We also discuss self-similar solutions without shocks in fluids with   w < −1/3  .     

Bianchi type-IX cosmic strings in a scalar-tensor theory of gravitation

Bianchi type-IX space-time is considered in the presence of cosmic string source in the frame work of a scalar- tensor theory of gravitation proposed by Saez and Ballester (Phys. Lett. A 113:467, 1985). Exact cosmological models representing geometric (Nambu) string, p string and baratropic string are discussed in this theory. Some physical and kinematical properties of the models are also studied.     

地球轨道根数变化与第四纪冰期

介绍了米兰柯维奇（Milankovitch)天文气候学理论和第四纪地质时期以来冰期的研究进展。研究结果表明，地球上的冰体积具有近10万yr的变化周期，并伴有近4万yr和2万yr的变化周期，它们是由于地球的轨道根数变化导致的气候变迁所致；不同的地球物理资料中均存在上述类似的变化周期，表明气候变迁所导致的变化是全球性效应，证实米兰柯维奇天文理论是基本正确的；对天文气候学理论作了简要介绍，指出了米兰柯维奇天文气候学理论的可能不足，对引起最近百万yr以来的近10万yr气候变化周期的可能天文机制也作了介绍。     

解流体动力弥散问题的等参数溶质质量均衡有限元法

本文根据流体动力弥散理论,按照地下水中溶质局部质量守恒原理,采用非线性基函数,导出了求解流体动力弥散问题的一种新的数值法,即等参数溶质质量均衡有限元法。该法与采用同样非线性基函数的等参数里茨(Ritz)法或伽辽全法相比,具有物理意义明确、能准确反映局部质量均衡关系、计算公式简单和易于应用等优点。