近似方法

Firstly, the isotropic difference templates were introduced to approximate the differential in the ADI-FDTD method, and the weighting coefficients of difference terms were determined for implementing isotropic numerical dispersion; Then the permittivity and permeability were adjusted manually to reduce the numerical dispersion error in any directions. Therefore the simulation accuracy and efficiency can be improved effectively for time domain problems with some finite bandwidths.

该方法在ADI-FDTD方法的差分近似微分中引入各向同性差分模板，并通过确定各向同性差分的加权系数来近似实现各向同性，然后人为修正空间的介质参数来减少各个方向上的数值色散误差，因此在模拟一定带宽的时域问题时可有效提高计算精度和计算效率。

Diffusion approximation theory is often used as basis of the experiments and methods in determining the optical properties of biological tissues.

漫射近似理论经常被用来作为测量生物组织光学特性参数实验和方法的理论基础，但是漫射近似理论只是一种对辐射传输理论的近似结果，在一定条件下有其特定的适用范围。

This article consists of:(1) a brief review of the previous work concerning this subject,(2) the various methods of studying the arrangement of fibers in yarns, and (3)two basic forms of fiber arrangement——approximate cylindrical helix and approximat conical helix——in ordinary cotton yarns, spun by the roller-drafting system The reasons of formation of such arrangement and their influence on yarn strength are also analyzed.

本文分三部分，第一部分引述了国外以往对细纱中纤维排列形态的研究结果，从而引出本文研究目的；第二部分主要介绍了研究棉纱中纤维排列形态的方法；第三部分根据所采用之方法得出试验结果，表明在一般棉纱中纤维排列成近似圆柱形螺旋线与近似圆锥形的复什的螺旋线二种基本形态。

With the use of absorption chiller performance model, an approximate calculation method was derived for the absorption chiller unit with a quantitative analysis of the effect of operating parameters on the absorption chiller performance. The formula is simple, physically clear and accurate enough. Its correctness was verified by calculation examples and model predictions were compared against performance data from experiments with favorable results.

给出单效吸收式制冷机局部定量分析近似计算方法，解决了工程上吸收式制冷机局部定量分析计算时的简化计算问题，提出的近似计算方法在精度和计算量方面均具有一定的优势，既解决了吸收式制冷机变工况计算问题，又满足实际机组经济性诊断的需要，实例计算证明了理论模型和诊断方法的准确、简捷性。

Numerical differentiation is that derivative value of a function at a certain point is approximately solved in discrete method.

中文摘要：数值微分就是用离散方法近似地求出函数在某点的导数值，关于数值微分已有许多求解方法，但这些方法都有各自的局限性，并且关于高阶导数近似逼近的方法研究相对较少。

The influence of the bark layer and trunk radial and height and the ratio of interior radius and exterior radius and ground elevation angle on scattering pattern is investigated.

第二，基于Monte-Carlo模拟技术，用相干叠加近似、树的独立散射近似和独立散射近似等方法，计算了倾斜或水平粗糙地面上分形树的电磁散射。

Hamilton modeling and generating function method for relative motion were introduced. Approximation of Hamilton function for relative motion of satellite formation and its impact on modeling accuracy were interviewed.

采用分析力学方法研究DSS卫星间的相对运动，讨论了DSS相对运动的Hamilton力学建模与生成函数近似求解方法，分析了相对运动的Hamilton函数近似阶数对求解精度的影响。

Based on chapter two, In chapter three, the method of multiple scales is introduced to the study of the multiple-dimensional nonlinear stochastic systems under random external excitation. Using method of multiple scales, we strictly deduce the equation of modulation of amplitude and phase. The effects of random excitations are analyzed; numerical simulations verify the results. Theoretical and numerical simulations show that when the intensity of the random excitation increases, the nontrivial steady state solution may be changed from a limit cycle to a diffused limit cycle.

在第二章基础上，第三章将多尺度法引入到相应的随机系统的研究中；严格推导了系统的约简方程，用矩方法求出稳态解应满足的方程，获得一些结果；并且数值模拟结果与理论推导的结果是一致的；并注意到，与其对应的确定性系统相比较，系统响应从周期解变为近似周期解，系统的相轨线从极限环变为扩大的近似极限环；随着激励带宽的增大，此扩大的近似极限环的宽度将增大。

Three approximate methods (called as scaling, rectangle and trapezia methods respectively) for performance analysis of orthogonal space-time block code with M-ary phase shift keying and M-ary quadrature amplitude modulation over flat Rayleigh fading channels are proposed, and their approximate performance expressions are given-The analysis of approximate results shows that OSTBC can obtain full diversity orders.

在平坦瑞利衰落信道下，提出了3种正交空时分组码在MPSK和MQAM调制下的近似性能分析方法（分别称为放缩法、矩形法和梯形法），并给出其近似表达式。通过对近似结果的分析，OSTBC能获得满分集增益。

The method includes dividing a digital image, formed from M rows and N columns of pixels, into a plurality of band-shaped areas by partitioning at each of a prescribed number of rows; averaging, for each column, the gradation values of pixels in said band-shaped areas for each of said plurality of band-shaped areas; computing an approximation line which approximates, in each of said plurality of band-shaped areas, a distribution of said average of gradation values; and judging whether there exists a succession of d columns at which the difference between said gradation value derived from said approximation line and said average of gradation values for each column exceeds a prescribed threshold.

该方法包括：通过以规定行数为单位进行分割，将由M行N列个像素形成的数字图像划分为多个带状区域；对于所述多个带状区域的每一个，针对各列来对所述带状区域中的像素的浓淡值求平均；计算近似线，该近似线在所述多个带状区域的每一个中近似于所述浓淡值的平均值的分布；并且判断是否存在如下连续的d个列，在所述连续的d个列中，从所述近似线得到的所述浓淡值与针对各列的所述浓淡值的平均值之间的差值超出一指定阈值。

The split between the two groups can hardly be papered over.

这两个团体间的分歧难以掩饰。

This approach not only encourages a greater number of responses, but minimizes the likelihood of stale groupthink.

这种做法不仅鼓励了更多的反应，而且减少跟风的可能性。