Cosmic structure growth and dark energy     

E. V. Linder  A. Jenkins 《Monthly notices of the Royal Astronomical Society》2003,346(2):573-583

Dark energy has a dramatic effect on the dynamics of the Universe, causing the recently discovered acceleration of the expansion. The dynamics are also central to the behaviour of the growth of large-scale structure, offering the possibility that observations of structure formation provide a sensitive probe of the cosmology and dark energy characteristics. In particular, dark energy with a time-varying equation of state can have an influence on structure formation stretching back well into the matter-dominated epoch. We analyse this impact, first calculating the linear perturbation results, including those for weak gravitational lensing. These dynamical models possess definite observable differences from constant equation of state models. Then we present a large-scale numerical simulation of structure formation, including the largest volume to date involving a time-varying equation of state. We find the halo mass function is well described by the Jenkins et al. mass function formula. We also show how to interpret modifications of the Friedmann equation in terms of a time-variable equation of state. The results presented here provide steps toward realistic computation of the effect of dark energy in cosmological probes involving large-scale structure, such as cluster counts, the Sunyaev–Zel'dovich effect or weak gravitational lensing.  相似文献   

Numerical Stabilization of Orbital Motion     

Victor A. Avdyushev 《Celestial Mechanics and Dynamical Astronomy》2003,87(4):383-409

Mainly, the author focuses on Baumgarte's method and its applications in satellite, asteroid, stellar and planetary problems. In the paper arguments are given for the use of energy relations for stabilization in the elliptical two-body problem. Stabilizing properties of Baumgarte's equations and others are discussed. A simple approach is proposed for stabilizing the equations of almost circular motion. By using Baumgarte's technique, the author derives stabilized equations of perturbed restricted three-body problem. It is shown experimentally that stabilization in the problems mentioned above can raise the accuracy of numerical integration by several orders.  相似文献   

The effect of radiative feedback on Bondi–Hoyle flow around a massive star     

Richard Edgar  Cathie Clarke 《Monthly notices of the Royal Astronomical Society》2004,349(2):678-686

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Chaotic Diffusion And Effective Stability of Jupiter Trojans     

Kleomenis Tsiganis  Harry Varvoglis  Rudolf Dvorak 《Celestial Mechanics and Dynamical Astronomy》2005,92(1-3):71-87

It has recently been shown that Jupiter Trojans may exhibit chaotic behavior, a fact that has put in question their presumed long term stability. Previous numerical results suggest a slow dispersion of the Trojan swarms, but the extent of the ‘effective’ stability region in orbital elements space is still an open problem. In this paper, we tackle this problem by means of extensive numerical integrations. First, a set of 3,200 fictitious objects and 667 numbered Trojans is integrated for 4 Myrs and their Lyapunov time, T_L, is estimated. The ones following chaotic orbits are then integrated for 1 Gyr, or until they escape from the Trojan region. The results of these experiments are presented in the form of maps of T_Land the escape time, T_E, in the space of proper elements. An effective stability region for 1 Gyr is defined on these maps, in which chaotic orbits also exist. The distribution of the numbered Trojans follows closely the T_E=1 Gyr level curve, with 86% of the bodies lying inside and 14% outside the stability region. This result is confirmed by a 4.5 Gyr integration of the 246 chaotic numbered Trojans, which showed that 17% of the numbered Trojans are unstable over the age of the solar system. We show that the size distributions of the stable and unstable populations are nearly identical. Thus, the existence of unstable bodies should not be the result of a size-dependent transport mechanism but, rather, the result of chaotic diffusion. Finally, in the large chaotic region that surrounds the stability zone, a statistical correlation between T_LandT_E is found.  相似文献   

Coronal Holes and Icosahedral Symmetry     

Wolfram Neutsch  Herbert Kalisch  Horst Fichtner  S. Ranga Sreenivasan  Maurice Shevalier 《Astrophysics and Space Science》2003,288(3):391-408

The study of the expansion of the solar wind out of a system of coronal holes is continued. To this end, we consider the numerical integration of partial differential equations for problems with icosahedral symmetry, in general. First, employing Weyl theory, orbifold coordinates are introduced. Second, the icosahedral coordinates are discussed in detail. Third, following an analysis of the properties of these coordinates and the derivation of a few expressions useful for grid construction, various alternatives for the distribution of lattice points required for numerical integration are considered. A comparison of these numerical grids motivates the choice of a specific grid optimized for the numerical integration carried out in the accompanying paper by Kalish et al.(2002). This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

A new stereo‐analytical method for determination of removal blocks in discontinuous rock masses     

Zixin Zhang  P. H. S. W. Kulatilake 《国际地质力学数值与分析法杂志》2003,27(10):791-811

The paper provides a new stereo‐analytical method, which is a combination of the stereographic method and analytical methods, to separate finite removable blocks from the infinite and tapered blocks in discontinuous rock masses. The methodology has applicability to both convex and concave blocks. Application of the methodology is illustrated through examples. Addition of this method to the existing block theory procedures available in the literature improves the capability of block theory in solving practical problems in rock engineering. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

MONITORING THE DIFFUSION OF SUSPENDED SEDIMENTS AND STABILITY OF TIDAL RADIAL SAND RIDGES AREA USING MULTI-SATELLITE REMOTE SENSING DATA     

黄海军  何宜军 《中国海洋湖沼学报》2001,19(4):361-367

Nine Landsat TM tapes and images and MSS images, 10 NOAA tapes and images and 1 SAR image from 1973 to 1997 were used to analyse the diffusion of suspended sediments and the change of tidal radial sand ridges in the northern part of the Changjiang River delta, the South Yellow Sea. The results showed that the diffusion of suspended sediments was controlled by the tide, net current, and submarine topography in this area. The distribution of suspended sediments had close relationship with thesubmarine topography. The old Huanghe River delta and the Changjiang River comprise the main sediment supply for the formation of radial sand ridges, whose evolution can be divided into three stages since the Huangbe River changed its course and flowed northward into the Bohai Sea.  相似文献   

介质横向不均匀对震后地表位移场的影响     

朱桂芝  王庆良  李辉  唐文 《大地测量与地球动力学》2003,23(4):54-59

利用三维有限元模拟两层地球模型(包括弹性层和粘弹性层)介质的横向不均匀和断层错动的复杂性对震后地表位移场的影响，其数值结果包括弹性解和粘弹性解。结果表明，震后位移场的分布特征不仅与粘弹性层的流变特性有关，还与弹性层介质的剪切模量以及断层的同震错动有关。  相似文献   

海拉尔盆地乌尔逊凹陷古流体动力场数值模拟   总被引：5，自引：0，他引：5  

杨金侠 《地球科学与环境学报》2003,25(3):41-47

首先对地下水动力场进行数学描述,以水动力为主线,建立适合该地区的数学模型,选择正确的地质模型参数,主要采用数值计算和模拟等手段,在恢复出乌尔逊凹陷主要目的层在不同地质历史时期古水动力的基础上又恢复出古流体势的演化历史。整体上,在乌尔逊凹陷,各主要地质时期的油势演化特征为西部地区大于东部地区,乌南大于乌北,且低势区的发育有较好的继承性。最后,依据油气聚集理论,进行油气运移聚集系统的划分、油气运移方向的分析,从而得出有关研究区油气运移聚集条件的认识,主要从流体动力的角度考虑,指出有利聚集区,认为在乌尔逊凹陷苏4～苏18井区、苏132～苏17～铜2井区及巴1～巴2～巴4井区为有利油气运移聚集区。  相似文献   

Constraints on the ultraviolet metagalactic emissivity using the Lyα forest     

Avery Meiksin  Martin White 《Monthly notices of the Royal Astronomical Society》2003,342(4):1205-1214

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