差分法

Therefore scientists have been engaged in research on approximate solutions of the partial differential equations,e.g.,the difference methods,the methods of characteristic curve and MWR method etc.,i.e., by using approx...

因此不少研究分布参数系统的科学工作者对这方程式近似方法进行了大量的研究，如差分法，特性曲线法和MWR法等；或者把分布参数系统近似成集中参数系统，或者把高价方程简化为低阶方程等。

Spectral element methods for partial differencial equation is introduced in this study from viewpoint of the collocation approximation of Chebyshev polynomial. Wave Equation and its space discretization are deduced. Two time integral methods, central difference method and implicit Newmark method, are introduced, and their stability and applicability are also discussed in some details. The significance of absorbing boundary conditions in spectral element methods for Aeroacoustics is explained, and Clayton-Engquist-Majda absorbing boundary conditions is emphasized and introduced, then the discrete scheme of this boundary conditions is deduced and applied to spectral element methods for wave equation.

本文从Chebyshev多项式逼近理论出发，详细介绍了谱元方法求解偏微分方程的过程；推导了流体中的声波动方程并在空间上对其进行了谱元离散；详细讨论了两种时间积分方法──中心差分法和Newmark方法，分析了它们的稳定性条件，并从理论上对比了两种方法的优缺点和适用范围；将吸收边界条件推广应用于谱元方法求解气动声学问题中，重点介绍了Clayton-Engquist-Majda吸收边界条件的原理和公式，推导了该吸收边界条件的变分形式，并将其引入波动方程的离散形式中。

On the other hand, finite difference and finite element methods use bases with small compact support but poor continuity properties.

小波基函数在空间域和频率域中都具有局部性特征，它的性质优于有限差分法、有限元法和伪谱法中所用的基函数。

An electromagnetic numerical analysis, set finite difference method, finite element method and the method of moments as one basis for teaching materials.

详细说明：一本的电磁数值分析方面的，集有限差分法，有限元法和矩量法为一体的基础教材。

Since any approximations, such as numerical Laplace inversion, backward differentiation formula, nonlinear model of switch, do not exist, the new algorithms are accurate.

由于该方法不存在任何极限近似问题（数值拉普拉斯反变换法，后向差分法，非线性开关模型法等），因而它是一种精确计算方法。

The principles of FEM, finite difference method , numerical mode method and integral equation method are elaborately described.

详细阐述了非均匀介质问题中常用的有限元法、有限差分法、数值模式匹配法和积分方程方法的基本原理和各自的优缺点。

Up to now, finite difference method, finite element method and boundary element method are common numerical methods to obtain numerical solutions of parabolic partial differential equation.

目前求解抛物型偏微分方程的数值方法有有限差分法、有限元法和边界元法等。

This dissertation has finished algorithm analysis and has designed the ship target detection system.

传统的帧间差分法算法简单、便于硬件实现，但在信噪比较低时抗噪性能较差。

According to the diffraction theory used in DVD system, we propose a new theory to analyze the RF signal and tracking error signal of Super-RENS disk. Then we use simulate the tracking error signal under beam aberration. Finally we use FDTD method to simulate the tracking error signal at defocus.

我们亦根据传统光碟片的绕射理论，提出一新的架构用於分析此近场结构，并用此理论进行射频及偏轨信号的模拟；接著探讨在有像差产生的情形下，其对偏轨信号的影响，最后用有限时域差分法验证在失焦下，偏轨信号的变化。

In the program, on theoretically we have studied the effects of configuration, the arranged periodic length and the refractive index ratio on PBG using finite difference time dormain method; on experimental, we have synthesized monodispersed silaca microspheres with size of 150-320 nm by colloidal chemical methods. And 3D perfect photonic crystals were prepared using the evaporating of acetone self-assembling the monodispersed SiO2 microspheres on quartzes by and horizontal and vertical deposition methods.

在本项目的研究中，理论上我们应用有限时阈差分法研究了光子晶体光子带隙形成与空间构型、排列的周期长度及折射率比之间的关系；实验上，我们应用胶体化学方法制备了150-320 nm的SiO2胶体微球，以丙酮为挥发溶剂，通过水平重力沉积法和垂直自然吸附法制备了各种粒度、排列完美的面心立方光子晶体。

Cynanchum Lingtai apricot production in the average weight 65 grams, the brightly-colored fruit, juicy rich, sweet-sour taste, sweet from the nucleolus, when the late Qing Dynasty famous Shaanxi, Gansu provinces, the Qing imperial court Tongzhi tribute for years.

灵台生产的牛心杏平均单果重65克，果实色泽鲜艳，汁多味浓，甜酸适口，离核仁甜，清末时就驰名陕、甘两省，清同治年间曾为朝廷贡品。

Chenopodium album,Solanum nigrum, and Amaranthus retroflexus were very susceptible to the herbicides. Polygonum persicaria and Abutilon theophrasti were relatively less susceptible to the herbicides, and Lycopersicon esculentum was not susceptible to it. The relationship between reduction rates of weed biomass and PPM values of weed leaves 2,4, and 6 days after treatment was established.

供试的6种杂草对该混剂的敏感性存在显著差异：红心藜Chenopodium album、龙葵Solanum nigrum和反枝苋Amaranthus retroflexus对该混剂最敏感，ED90值分别为47.65、71.67和29.17g/hm2；春蓼Polygonum persicaria和苘麻Abutilon theophrasti敏感，ED90值分别为96.91、114.20g/hm2；而番茄不敏感。