Secular frequencies of 3-D exoplanetary systems

Using a 12th order expansion of the perturbative potential in powers of the eccentricities and the inclinations, we study the secular effects of two non-coplanar planets which are not in mean–motion resonance. By means of Lie transformations (which introduce an action–angle formulation of the Hamiltonian), we find the four fundamental frequencies of the 3-D secular three-body problem and compute the long-term time evolutions of the Keplerian elements. To find the relations between these elements, the main combinations of the fundamental frequencies common to these evolutions are identified by frequency analysis. This study is performed for two different reference frames: a general one and the Laplace plane. We underline the known limitations of the linear Laplace–Lagrange theory and point out the great sensitivity of the 3-D secular three-body problem to its initial values. This analytical approach is applied to the exoplanetary system Andromedae in order to search whether the eccentricities evolutions and the apsidal configuration (libration of ) observed in the coplanar case are maintained for increasing initial values of the mutual inclination of the two orbital planes. Anne-Sophie Libert is FNRS Research Fellow.     

城市下垫面空气动力学参数的确定

分析近10年北京325m气象塔常年观测资料,研究城市化发展对城市大气边界层动力学结构和特征的影响.结果表明,空气动力学粗糙度和零平面位移总体是逐年递增的.气象塔西南方向的高层建筑群是20世纪90年代初期逐渐建成,在SW方向,空气动力学粗糙度和零平面位移在90年代增加明显,增加的幅度1997年和1999年之间较大,这一点与气象塔西南方向城市化的加快相符合.而在NE、SE和NW方向,从1987年到1994年空气动力学粗糙度和零平面位移增加明显,1994年以后变化较小.     

地面三维激光扫描技术在川藏铁路危岩落石勘察中的应用

危岩体结构面产状信息的获取是地质勘查中的重要内容。川藏铁路沿线山体陡峭,地质环境复杂,传统的人工测量方法受到很大限制。本文介绍了三维激光扫描技术在川藏铁路危岩体的扫描应用,阐述了三维激光扫描仪的数据获取及数据处理技术,并分析了如何利用三维激光扫描技术来获取危岩体结构面产状信息。     

多基准点和基准方向的面阵与线阵影像匹配方法

针对面阵影像与线阵影像之间存在的尺度、旋转等几何差异所导致的难以高效获得稳定可靠匹配点问题,该文提出了一种稳健的面阵影像与线阵影像匹配方法。算法分为3个阶段:(1)对影像进行尺度、旋转预处理,消除影像间的尺度和旋转差异;(2)用Harris算子提取特征点,进行逐层金字塔匹配,在最底层影像上进行最小二乘匹配获取精匹配点,利用随机抽样一致算法获取准确性较高的匹配点;(3)对准确性较高的匹配点分区,构建4块匹配区域,根据每块区域的匹配点计算重心,以此4块区域的重心作为匹配基准点和基准方向,重约束初始匹配结果。通过多组面阵影像与线阵影像数据实验结果,验证了该方法的可行性和有效性,可为后续空中三角测量及相关应用提供可靠的匹配点。     

Determination of the fault plane using a single near-field seismic station with a finite-dimension source model

We explore the possibility of determining the actual fault plane of an earthquake from the inversion of near-source displacement seismograms of one station when a finite-dimension source is used instead of a point source model and when the complete displacement is taken into account, including near-field waves. Tests on synthetic seismograms and real data recorded at local distances show that this is possible even with a single, three-component station. A single accelerogram available for the Erzincan, Turkey, 1992 March 13, M _s = 6.8 earthquake is inverted and the solution found is compatible with other seismological studies and with the mechanism expected for the North Anatolian Fault.     

土钉墙钉长确定和整体稳定性

土钉作为一种新型的挡土技术,已广泛地应用于边坡加固和基坑围护,但目前存在着土钉设计理论落后于实践的局面。本文就土钉的长度计算问题,结合目前土钉设计情况,谈谈如何就整体稳定性安全系数来确定土钉长度,使之既安全又合理。     

GPS工程控制网投影变形的处理

在ＧＰＳ工程控制网建立的内业处理中,为后续的方便必须设法高斯投影变形对坐标成果的影响,本文在简要介绍了常规投影变形处理方法之后,提出了尺度强制约束和投影面重新选择两种投影变形的处理方法。工程实践检验表明,两种方法不但可行而且可使处理后的坐标系统与国家坐标系统尽可能保持一致,方便了工程使用。     

节理岩体中地下洞室超挖预测

本文着重于岩体中洞室超挖-不稳定楔形体的预测。首先,论述洞室超挖的基本概念、主要原因及评价方法;其次分析和比较目前现有的针对洞室超挖的计算软件及其特征;然后介绍本文作者的计算软件;最后,简单介绍一个计算实例,即从野外地质调查着手,应用数理统计理论评价构成不稳定楔形体的主要地质参数及其模型,推导岩体中洞室超挖预测的一般公式;最后评价构成不稳定楔形体主要地质参数中的主要因素及次要因素,为节理岩体洞室防止超挖及其处理提供依据。     

Interaction between a circular opening and fractures originating from its boundary in a piecewise homogeneous plane

The complex variables boundary element method (CVBEM) is used to study interaction between a circular opening and fractures originating from its boundary in a piecewise homogeneous plane. A new complex hypersingular equation for piecewise homogeneous media with a circular opening is obtained. The equation is solved using the CVBEM technique with circular and straight boundary elements and polynomial approximations (with square root asymptotics for crack tip elements) for the unknown functions. The algorithm is verified through comparison with known semi‐analytical and numerical solutions that involve interaction between a circular opening and specific systems of cracks or other openings. New numerical results concerning the interaction of the circular opening with the cracks and circular inclusions are presented. The method is applied to an important problem in the petroleum industry: modelling propagation of hydraulic fractures in the vicinity of a borehole. Copyright © 2000 John Wiley & Sons, Ltd.