90年代发展中国家国际资本流入的新特点及其影响

从1992年起,流向发展中国家的证券资本以较大的优势超过了国际直接投资。在全球经济一体化、金融市场自由化和国际化的背景下,国际资本跨国流动呈现出规模巨大化、运作方式机构化、流动形式多样化的特点。庞大证券资本的注入在给新兴市场国家带来益处的同时,也可能造成伤害,这一点在墨西哥和东南亚金融危机中已经得到证实。因此防范和化解国际资本的流入所带来的金融风险,是新兴市场国家当前所面临的严峻课题。     

Flow direction and magnetic mineralogy of lava flows from the central parts of the Peninsula of Baja California,Mexico

Magnetic properties of two apparently unrelated lava suites (one tholeiitic and the other alkalic) coexisting in the central parts of the Peninsula of Baja California, Mexico, were measured in this study. Macroscopic indicators and measurements of anisotropy of magnetic susceptibility (AMS) were combined to infer the flow direction on those lavas. These measurements were used to investigate the likelihood of the existence of an abnormally long tholeiitic lava flow in this part of the Peninsula. The obtained results indicate that the tholeiitic flows in the region constitute regular length flows, and are likely to have been issued through vents located within the area of study. Additionally, comparison of the magnetic signature of tholeiitic and alkalic lavas reveals a systematic difference in some of the magnetic parameters (bulk susceptibility and Curie temperatures). In particular, it is proposed that the narrow range of Curie temperatures characteristic of each lava type can be used as a reliable proxy for the identification of each lava type in the region. All of these findings show that the alkalic and tholeiitic lavas of the region are more closely related to each other than previously suspected.Editorial responsibility: R. Cioni     

通-南-巴三维地震采集参数设计方法

针对通-南-巴地区山地工区复杂的地表结构和地质构造造成的地震施工难题,结合表层结构调查进行了激发试验确定了激发岩性、激发井深及炸药量等参数,确保主要目的层的地震波反射主频,拓宽有效波频带,提高纵向分辨率,以获取高信噪比地震资料;同时进行了基于地质模型及地震正演模拟的观测系统参数的设计,最终达到了突出有效反射,得到复杂构造信息的目的。     

Morphological reactions of schematic alluvial rivers:Long simulations with a 0-D model

The paper presents a 0-D model of an alluvial watercourse schematized in two connected reaches, evolving at the long time-scale and under the hypothesis of Local Uniform Flow. Each reach is defined by its geometry (constant length and width, time-changing slope) and grain-size composition of the bed, while the sediment transport is computed using a sediment rating curve. The slope evolution is provided by a 0-D mass balance and the evolution of the bed composition is computed by a 0-D Hirano equation. A system of differential equations, solved with a predictor-corrector scheme, is derived and applied to the schematic watercourse to simulate the morphological response to changing initial conditions, and the evolution towards long-term equilibrium conditions. Differently from a single-reach 0-D schematization with uniform grain-size, besides the simplifications adopted, the model proposed here simulates the behaviour of alluvial rivers in a physically-based way, showing a grain-size fining in the downstream direction accompanied by milder slopes, and a tendency to develop concave longitudinal profiles.     

子像素匹配策略的对极几何估计算法

基本矩阵在计算机视觉中扮演着十分重要的角色,对极几何(即核线几何)的估计过程就是求解基本矩阵的过程,所以如何提高对极几何的估计精度一直是计算机视觉中的一个研究热点。本文通过提取子像素特征点,并经高精度影像匹配,最终用子像素匹配点来实现对极几何的稳健估计。实验表明,该计算法在平均余差和平均对级距离上都明显小于基于整像素级的对极几何估计结果,有效改善了对级几何的估计精度和稳定性。     

Axisymmetric wave propagation in multilayered poroelastic grounds due to a transient acoustic point source

This paper deals with the study of axisymmetric wave propagation in various acoustic/porous stratified media coupling configurations. It presents the theoretical developments of a semi-analytical method, its validation for a limit test-case half-space ground, and an extension to a realistic multilayered seabed, when spherical waves are emitted from a transient point source in water.     

Hydraulic geometry and maximum flow efficiency as products of the principle of least action

Basic flow relationships have previously been seen to be insufficient to explain the self‐adjusting mechanism of alluvial channels and as a consequence extremal hypotheses have been incorporated into the analyses. In contrast, this study finds that by introducing a channel form factor (width/depth ratio), the self‐adjusting mechanism of alluvial channels can be illustrated directly with the basic flow relations of continuity, resistance and sediment transport. Natural channel flow is able to reach an optimum state (Maximum Flow Efficiency (MFE), defined as the maximum sediment transporting capacity per unit available stream power) with regard to the adjustment of channel form such that rivers exhibit regular hydraulic geometry relations at dominant or bankfull stage. Within the context of MFE, this study offers support for the use of the concepts of maximum sediment transporting capacity (MSTC) and minimum stream power (MSP). Furthermore, this study indicates that the principle of least action is able to provide a physical explanation for the existence of MFE, MSTC and MSP. Potential energy is minimized and consequently sediment transport is maximized in alluvial channels. Copyright © 2000 John Wiley & Sons, Ltd.     

基于仙农熵理论的河相关系

在河流动力学理论研究中,已有的河相关系式大多是经验半经验性质的,往往不能明确地表达因素的影响,应用时具有很大的局限性.在能量均衡关系的基础上,利用仙农熵的理论,对影响沙质河床稳定河相关系的因素进行了探讨.通过理论分析,认为在取得所测河段上下边界测点相关资料后,用最大熵原理和变分法可以推导出稳定的河相关系式,最后通过试验对所得公式验证其合理性,认为其在计算试验区间任何时刻河相关系系数,均得到较好的吻合结果.