近似法

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。

This makes more and more people pay more attention to studies and applications of numerical simulation in thermal recovery. In this research, we have developed a reliable mathematical model for thermal recovery, which takes a full consideration of the effect of viscos, gravitical and capillary forces on the three-phase flow of gas, water and oil, the effect of the temperature on the medium characteristics of liquid and solid, the phase equilibrium of gas-liquid in each component, heat transportation including connection, conduction and radiation as well as heat losses in both the overburn and underlying strata. In the space discreation of the mathematical model, we have proposed a new method based on the improvement of the conventional nine-points difference approximation, which has a higher difference accurancy.

本项研究以热力采油的主要机理为基础，充分考虑在粘性力、重力和毛管力作用下油水气三相流动，考虑温度对各种流体和固体介质物性的影响，考虑每一组分中汽液两相的相平衡，考虑热在地层中的传导、对流和辐射以及上下盖层的热损失，利用热力学第一定律、质量守恒定律和流体迁移定律，建立了正确可靠的注蒸汽数学模型；在对数学模型进行空间离散时，利用控制有限体积积分法，对以往的九点差分近似作了合理的改进，使其具有较高的差分近似精度：结果表明，该公式的近似精度要比以往文献中所给的九点差分近似精度高，可以认为，在油藏数值模拟中，如果遇到非均质情况，使用这种九点差分近似更合理。

Beginning with a general mean function, the model analyzes the distance between the arithmetic average and geometric average by Taylor's expanding.

第二章介绍了亚式期权定价研究中的市场结构、一般原理和若干重要的定价方法：PDE偏微分方程法；埃级沃斯级数展开近似定价；倒数分布近似定价；条件期望近似定价；执行价格调整近似定价，这些方法使亚式期权的定价得到了很大的发展。

A new SVM is presented in this paper to solve the approximately linear separable problem of pattern recognition:First,we transform the two convex hulls which are made up of the approximately separable training set to make them separable;Second,we can figure out a separating hyperplane by halving the nearest points method or maximal margin method;Then,we get the approximately linear SVM by solving the dual problem of maximal margin method.

对模式分类中的近似线性可分问题提出了一种新的近似线性支持向量机：先对近似线性分类中的训练集所形成的两类凸壳进行了相似变形，使变形后的凸壳线性可分，再用平分最近点和最大间隔法求出理想的分划超平面，然后再通过求解最大间隔法的对偶问题得到基于相似压缩的近似线性SVM。

Both LDPC codes and OFDM technology are studied in this paper. The working and the results obtained are summarized as follow:1. The definition of LDPC codes and its coding/decoding ideas are systematically summarized, a general algorithm of changing any parity-check matrix to lower triangular form, which is suitable for quick encoding, is given out, along with a girth checking algorithm. Absolutely random LDPC codes construction is improved, a new half random construction of LDPC codes with linear time coding and no 4-cycles is brought out.

系统地阐述了低密度校验码的定义及编译码原理，提出了一种将任何校验矩阵变换成适于快速编码的近似下三角形式的通用算法及一种围长检测算法，对完全随机的校验矩阵构造法进行了改进，提出了一类消除4环且可近似线性编码的校验矩阵半随机构造法，仿真表明，在高编码效率情况下，改进后的半随机构造法，其性能稍优于完全随机构造法，并可以线性时间编码，因此更适合实际应用。

At first, an approximated mathematical model is presented. Then, the system manager can compute the optimal control policy via the method of successive approximation. Based on the above-mentioned algorithm, we design an intelligent system with feedback control to regulate the allocation of limited channels of trunk circuit. This system will continuously detect the status of whole cellular network. Once the system parameters cross the predefined threshold, the recomputing mechanism will be activated.

首先针对系统的近似数学模型先將其定义出来，然后就可以用连续逼近法將最佳控管决策计算出来，这样的最佳决策演算法我们把它设计在一个有迴授机制的智慧型决策系统裹，此决策系统將不断地侦测行动通讯网路运作的情形，一旦网路参数变化超过某个预定的临界值时，整个最佳决策演算法將被启动，系统的近似数学模型將依新的参数重新定义，接下来同样地写出最佳方程式並用连续逼近法计算出新的最佳控管决策。

Secondly, the effectiveness and limitation of the classical perturbation, such as the method of multiple scales and the Poincare-Lindstedt method, are discussed in detail through a Duffing oscillator with delayed velocity feedback. It is shown that the two perturbation methods are effective only in solving the approximate solution of the first two orders. An ambiguity or paradox will be encountered when they are used to seeking for the third or higher order approximation of solution.

其次，以一具有时滞速度反馈的Duffing系统为例，研究了经典摄动法如多尺度法，Poincaré-Lindstedt法等在求解时滞微分方程级数解时的适用性和局限性问题，指出利用这些方法只能有效求得系统的前两阶近似解，而在求系统的三次以上近似解时会出现矛盾或二义性。

The direct calculation of the GaN/AlN super cell demonstrated that the GaN/AlN heterojunction was homotype and changed abruptly at the interface.

另外，通过使用常用的平均键能法、平均势法和芯态法三种近似方法对GaN/AlN带阶的计算，比较得出，超原胞法虽然计算量较大，但能够给出异质结界面附近更为详细的信息，这一点其他三种近似方法无法得到，但他们也能够得出与实验值基本一致的带阶参数。

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.

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。

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。

According to the clear water experiment, aeration performance of the new equipment is good with high total oxygen transfer coefficient and oxygen utilization ratio.

曝气设备的动力效率在叶轮转速为120rpm～150rpm时取得最大值，此时氧利用率和充氧能力也具有较高值。

The environmental stability of that world - including its crushing pressures and icy darkness - means that some of its most famous inhabitants have survived for eons as evolutionary throwbacks, their bodies undergoing little change.

稳定的海底环境─包括能把人压扁的压力和冰冷的黑暗─意谓海底某些最知名的栖居生物已以演化返祖的样态活了万世，形体几无变化。