近似方法

The following are main contents studied: A finite element method for Navier-Stokes equation with ALE formulation is considered and by combined with theNewmark method of numerical intergration a pressure correction scheme is obtained for the solution of the FE formulation of N-S equation. Because the incompressibility condition can be satisfied approximately in this scheme, the interpolation functions of elements can be equalorder for the velocity field and pressure field. In the ALE formulation the fluid-solid interaction analysis became a three-field coupling problem of the fluid field, the solid field and the fluid dynamic mesh. The properties and charactiristices of this three-field coupling problem are deeply discussed.

研究的主要内容有：主容器中流体大晃动是一种强非线性问题，文中研究了求解ALE描述的粘性流体N-S方程的有限元方法，以有利于大晃动自由液面的跟踪和流体大晃动中非线性现象的描述；并结合Newmark数值积分法推出了求解ALE型N-S方程的压力修正解法，由于这种解法可以近似满足不可压条件，因此可以采用速度场和压力场等阶插值的有限元离散格式，从而较好地解决了普遍采用的不等阶插值解法中，速度场和压力场数值精度不一致、程序编制不便等的不足。

In order to study the changing process of Barium strontium titanate Ba(subscript xSr(subscript 1-x) TiO3, BST from cubic phase to the tetragonal phase with Ba doping and the ferroelectric characteristic of BST, the total energy of BST with different mole ratio of Ba/Sr when Ba doped was calculated and the fine structure determined, based on general gradient approximation, by means of ultrasoft pseudopotentials plane wave method.

为了研究钛酸锶(SrTiO3， ST)中随Ba的掺入，其晶体从顺电相到铁电相的变化过程及四方相钛酸锶钡Ba(下标 xSr(下标 1-x)TiO3， BST的铁电性。在广义梯度近似下，利用超软赝势平面波方法计算了不同Ba/Sr摩尔比BST的总能量，确定了BST的精细结构。

Unfortunately, however, the simple WKB approximation may be inapplicable to steep-sided profiles (e.g., proton exchanged or epitaxially grown) where, for these almost square cases, it is more appropriate to use a perturbation theory approach.

但不幸的是，简单的WKB近似可能不适用于陡峭片面概况情况下，这些几乎平方米情况下，它更适合使用微扰理论方法。

The calculation method also included a stair-step representation of the shroud, staggered grid system, the k-ε turbulence model and wall function method on the shroud.

计算方法还包括涵道壁的阶梯型近似，原始变量的交错网格，k-ε湍流模型和涵道壁上的壁面函数法等措施。

More importantly, we propose a data-dependent parameterization method in which optimal parameterization in the lighting and viewing space that minimizes the modeling error is obtained.

我们使用了多变量的球面迳向基底函数核心当作我们双向贴图函数模型的核心并且使用了资料相关的重新参数化方法得到在光源及视点空间的最佳参数以增进我们双向贴图函数模型的近似度。

The approximate analytic solution for the plane problem of semi infinite elastic solid subjected to a concentrated force at the midpoint of bottom of a groove is given by means of complex stress function.

运用复变函数方法，求出了半无限弹性体通过刻槽之底施以集中力的平面弹性应力场的近似解析解，并进行了光弹性试验，理论上求得的应力分布与试验结果相吻合

The band structures and the band gaps of some single-walled carbon nanotubes were calculated and their ...

但是，一方面，那些结论大多数是对孤立的单壁碳纳米管而言的，而且跟实验没有很好的吻合；另一方面，采用的方法大多数是紧束缚计算和基于局域密度近似的第一性原理计算。

Chirp scaling algorithm is considered more efficient and widely applicable when the bistatic SAR system is in side-look or small squint angle mode,but in large squint angle case,the errors caused by Taylor expansion are so large that the algorithm could lose its precision.In such a case,an equivalent mono-static SAR range mode which has fewer errors than Taylor expansion with large squint angle is proposed to substitute the range history of bistatic SAR.Then bistatic SAR images with large squint angles are gotten by common Nonlinear CS algorithm.The effectivity of the method is verified by Matlab simulation.

在正侧视或小斜视情况下，CS算法具有较好的聚焦性能和广泛的适用性，但在斜视角较大的情况下，该算法将散焦而不能成像，因而提出了用等效的单基地距离模型来代替双基地距离历史的方法，解决了大斜视角情况下距离模型二阶近似误差较大的问题，并结合单基地非线性CS算法，实现了在大斜视角情况下的基于GPS反射信号的双基地SAR高精度成像，最后通过Matlab仿真进行了验证。

a system of along-track mode sar based on the gps is established.by seeing the gps signal as a chirp,chirp scaling algorithm of this mode with large squint angle is investigated.chirp scaling algorithm is considered more efficient and widely applicable when the bistatic sar system is in side-look or small squint angle mode,but in large squint angle case,the errors caused by taylor expansion are so large that the algorithm could lose its precision.in such a case,an equivalent mono-static sar range mode which has fewer errors than taylor expansion with large squint angle is proposed to substitute the range history of bistatic sar.then bistatic sar images with large squint angles are gotten by common nonlinear cs algorithm.the effectivity of the method is verified by matlab simulation.

摘 要：建立了基于gps的顺轨sar系统模型，通过将gps信号等效为chirp信号，研究了在该模式下的大斜视角chirp scaling算法。在正侧视或小斜视情况下，cs算法具有较好的聚焦性能和广泛的适用性，但在斜视角较大的情况下，该算法将散焦而不能成像，因而提出了用等效的单基地距离模型来代替双基地距离历史的方法，解决了大斜视角情况下距离模型二阶近似误差较大的问题，并结合单基地非线性cs算法，实现了在大斜视角情况下的基于gps反射信号的双基地sar高精度成像，最后通过matlab仿真进行了验证。

We describe the GW approximation which has turned out to be a fruitful approximation to the self-energy.

通过理论的推导和计算试验将表明GW方法能很好地近似求解自能。

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。