椭圆形裂纹扩展问题中一个变换式的证明

一、引言 在研究椭圆形裂纹扩展问题中,如果不考虑破裂的终止,则常常假定震源的滑移函数为     

基于树型小波变换和尺度共生矩阵的居民地提取

利用基于树型框架小波变换和尺度共生矩阵的方法对遥感影像中居民地进行识别提取。通过非完全树型框架小波变换把图像变换到不同的尺度层上,然后在不同尺度层之间,提取相互依存的尺度共生矩阵信息,进而形成居民地的纹理特征。实验结果表明,用基于小波的尺度共生矩阵的方法对居民地有较好的提取结果。     

拉普拉斯变换的两个新运算法则

推导出了拉普拉斯变换乘法运算法则和除法运算法则,进一步给出了线性系统增加闭环零点或闭环极点时时间响应的计算式,应用这些计算公式,分析了闭环零点和闭环极点对时间响应的影响。分析结果表明:增加闭环零点或实数闭环极点不会改变时间响应的振荡性,在线性系统中,离虚轴越远的闭环零点和闭环极点对时间响应影响越小。     

Solution of Generalized Fractional Reaction-Diffusion Equations

This paper deals with the investigation of a closed form solution of a generalized fractional reaction-diffusion equation. The solution of the proposed problem is developed in a compact form in terms of the H-function by the application of direct and inverse Laplace and Fourier transforms. Fractional order moments and the asymptotic expansion of the solution are also obtained.     

考虑地球扁率摄动影响的初轨计算方法

在二体问题意义下的短弧定轨,Laplace型方法是最主要最典型的一种初轨计算方法。若测角资料达到10^-4-10^-5精度(相当于2″—20″之间),那么要使定轨精度达到与其相应的程度,地球非球形引力位中的扁率项摄动应该考虑,在此前提下,同样可以采用相应的Laplace型定轨方法。即给出这种严格包含扁率摄动的初轨计算方法的原理和具体计算过程以及计算实例,除采用多资料定轨方法外,这种方法也是提高初轨计算精度的一种途径,它同样可用于多资料的情况,这种方法对于大扁率主天体(即中心天体)的卫星定轨将更有实用价值。     

土壤中溶质运移的数学模型及其解析解

首先给出了非均匀土壤中考虑水动力弥散尺度效应的一维溶质运移两区模型.然后在初始浓度为零,半无限一维空间内第一类边界条件下,推导出了可动区和不动区溶质浓度分布Cm(x,t),Cim(x,t)的解析表达式.     

Solution of the unsaturated soil moisture equation using repeated transforms

An alternative method of solution for the linearized ‘theta‐based’ form of the Richards equation of unsaturated flow is developed in two spatial dimensions. The Laplace and Fourier transformations are employed to reduce the Richards equation to an ordinary differential equation in terms of a transformed moisture content and the transform variables, s and ξ. Separate analytic solutions to the transformed equation are developed for initial states which are either in equilibrium or dis‐equilibrium. The solutions are assembled into a finite layer formulation satisfying continuity of soil suction, thereby facilitating the analysis of horizontally stratified soil profiles. Solution techniques are outlined for various boundary conditions including prescribed constant moisture content, prescribed constant flux and flux as a function of moisture change. Example solutions are compared with linearized finite element solutions. The agreement is found to be good. An adaptation of the method for treating the quasilinearized Richards equation with variable diffusivity is also described. Comparisons of quasilinear solutions with some earlier semi‐analytical, finite element and finite difference results are also favourable. Copyright © 2001 John Wiley & Sons, Ltd.     

Estimating Net Radiation from Air Temperature for Diffusion Modelling Applications in a Tropical Area

A simple and straightforward expression isproposed, which is based on the Fourier seriesdecomposition technique, for estimating hourly averagednet radiation from the corresponding values of airtemperature at a tropical location in West Africa. Thecomparisons made of the estimated net radiation withactual measurements (case studies) clearlydemonstrate that the scheme is efficient, both inclear and under cloudy weather conditions. Theestimates are also shown to be better than thosedetermined from an alternative relationship usingparametrizations for the shortwave and longwave components at the surface. The presentprocedure can easily be implemented in existingmeteorological preprocessors to calculate the sensibleheat flux for the Gaussian-based air pollutionmodels.