对瞬变电磁测深几个问题的思考(一)——瞬变电磁测深中偶极子源及其转换

偶极子源是电磁法研究的基本对象,是构成更复杂探测装置与资料解释的前提,也是电磁法勘探技术开发与创新的理论基础。从偶极子源的概念出发,导出了均匀大地表面上的主要偶极子源瞬变电磁场公式,并指明正垂直阶跃脉冲与负垂直阶跃脉冲激发的瞬变电磁场公式的异同,以加深认识。举例说明了相应于电性源与磁性源的场分量可根据电磁场的互易定理相互转换,便捷推导公式。重点阐述了由偶极子源的场强公式运用叠加原理可衍生更复杂的电磁场公式,诸如大回线源及其任意一点的瞬变电磁场公式,盘活了瞬变场的应用。     

变形体条件的土质边坡稳定性分析

基于能量法的上限定理,在定义滑体为变形体的条件下,采用能量法和强度折减法的有机结合,推导得出了土质边坡的能量法安全系数计算公式。能量法与传统刚体极限平衡法的区别在于：(1)前者使用的是能量平衡,而后者使用的是静力平衡;(2)前者将滑体视为变形体,而后者将滑体视为刚体。通过典型算例分析计算,结果显示,采用能量法进行土质边坡稳定性分析,得到的安全系数要比传统的瑞典圆弧法略小。     

二维梯形沉积盆地放大效应的数值模拟研究

盆地效应作为场地效应的一种特殊类型,其对地震动的影响仍在持续研究当中.建立二维梯形沉积盆地模型,模型边界采用透射人工边界,利用显式有限元法作为求解方法.根据Bucking-ham提出的π定理定义了多个影响盆地效应的无量纲参数,包括盆地深宽比、介质波速比、盆地深度与入射波长之比、盆地开口宽度与入射波长之比.以Ricker...     

NWP 模式热量系统误差的动力诊断分析

文章证明了模式在预报时段的位温误差,是由于在模式大气和真实大气中,该时段内位温变化过程的不同而造成的。还证明了原始方程的无加速定理对各强迫因子的线性分解同样适用于研究NWP模式热量误差的成因。对国家气象中心T42L9模式1992年1月和7月预报结果的动力诊断表明,模式对纬向位温分布具有较好的预报能力,但在各纬带也存在明显的误差。通过无加速定理的分解分析,研究了这些误差的成因及改善模式的可能途径。     

结构抗震可靠度二种简化解析表达式的一致性证明

结构抗震可靠度分析的解析求解一直是结构可靠度领域和地震工程领域研究者们的追求目标.解析表达式不仅有利于简化结构抗震可靠度分析这个极端困难的工作,而且也有利于进行基于可靠度的结构概率抗震性能设计与评定.从全概率定理的两种不同表达式出发,介绍了国际上流行的两种结构抗震可靠度解析表达式,过去一直认为这是两种理论基础不同的表达式.本文通过对地震易损性函数关系的解析推导,揭示了若干重要关系,证明了两种表达式的一致性.     

New distance measures: The route toward truly non-Gaussian geostatistics

The projection or minimum error norm algorithm does not require that the distance measure be a variogram. In non-Gaussian cases, the traditional variogram distance measure leading to minimization of an error variance offers no definite advantage. Other distance measures, more outlierresistant than the variogram, are proposed which fulfill the condition of the projection theorem. The resulting minimum error norms provide the same data configurations ranking as traditionally obtained from kriging variances. A case study based on actual digital terrain data is presented.This paper was presented by title at MGUS 87 Conference, Redwood City, California, 14 April 1987.     

在集合套的一类新的落影方式下的表现定理

本文给出了一类新的集合套的落影方式和表现定理,它是文献(2)、(4)、(5)中研究的有关问题的继续。作者推广了文献(2)的结果和给出了不同于文献(2)的证明方法。     

Hamilton's principle and the vorticity laws for a relativistic perfect fluid

Abstract

The equations for a relativistic perfect fluid result from the requirement that the total mass-energy be stationary with respect to variations δx^α(a, b, c, s) in the space-time location of the fluid particle identified by Lagrangian labels (a, b, c) at the point s on its world-line. By considering variations of the Lagrangian labels that leave the specific volume and entropy unchanged, we obtain a general covariant statement of vorticity conservation. The conservation laws for circulation, potential vorticity, and helicity are simple corollaries. This Noether-theorem derivation shows that the vorticity laws have no analogues in particle mechanics, where the corresponding particle labels cannot be continuously vaned.     

Magnetic field structure in differentially rotating discs

Abstract

In order to gain a better understanding of the processes that may give rise to non-axisymmetric magnetic fields in galaxies, we have calculated field decay rates for models with a realistic galactic rotation curve and including the effects of a locally enhanced turbulent magnetic diffusivity within the disc. In all cases we have studied, the differential rotation increases the decay rate of non-axisymmetric modes, whereas axisymmetric ones are unaffected. A stronger magnetic diffusivity inside the disc does not lead to a significant preference for non-axisymmetric modes. Although Elsasser's antidynamo theorem has not yet been proved for the present case of a non-spherical distribution of the magnetic diffusivity, we do not find any evidence for the theorem not to be valid in general.