Preparation and luminescence characteristics of Eu^2＋ activated silicate phosphor

This paper synthesizes the Sr2SiO4：Eu^2＋ phosphor by high temperature solid-state reaction. The emission spectrum of Sr2SiO4 ： Eu^2＋ shows two bands centred at 480 and 547 nm, which agree well with the calculation values of emission spectrum, and the location of yellow emission of Sr2SiO4 ： Eu^2＋ is influenced by the Eu^2＋ concentration. The excitation spectrum for 547 nm emission has two bands at 363 and 402 nm. The emission spectrum of white light emitting diodes （w-LEDs） based on Sr2SiO4 ： Eu^2＋ phosphor ＋ InGaN LED was investigated.     

圆孔与侧扩孔气膜冷却的大涡模拟

本文对圆孔和带有侧向扩散出口的侧扩孔气膜冷却进行了大涡模拟计算,对温度场和流场的发展进行了比较和分析.计算结果表明,圆孔形成的成股的冷却射流,与壁面分离明显,使得高温主流被卷席入气膜区域;侧扩孔所形成的冷却气膜没有脱离壁面,并且通过两侧的小股冷却气膜扩宽了横向扩散,可以很好地将高温主流排挤到气膜的两侧,因此可以获得更好的冷却保护效果.     

EVALUATION OF SINGULAR AND NEARLY SINGULAR INTEGRALS IN THE BEM WITH EXACT GEOMETRICAL REPRESENTATION＊

The geometries of many problems of practical interest are created from circular or ellip- tic arcs. Arc boundary elements can represent these boundaries exactly, and consequently, errors caused by representing such geometries using polynomial shape functions can be removed. To fully utilize the geometry of circular boundary, the non-singular boundary integral equations （BIEs） and a general nonlinear transformation technique available for arc elements are introduced to remove or damp out the singular or nearly singular proper- ties of the integral kernels. Several benchmark 2D elastostatic problems demonstrate that the present algorithm can effectively handle singular and nearly singular integrals occur- ring in the boundary element method （BEM） for boundary layer effect and thin-walled structural problems. Owing to the employment of exact geometrical representation, only a small number of elements need to be divided along the boundary and high accuracy can be achieved without increasing other more computational efforts.     

基于响应面法的五心底结构形状优化

三心底结构是国防、航空及航天等领域经常采用的结构,其旋转母线是由三段弧线组成的,对应着三个圆心,故得名三心底。三心底结构可调整的参数变量少,优化潜力小。根据三心底的形状推广出五心底结构,增加可调整的参数变量,然后对其进行优化。将响应面方法与模型参数化相结合,建立了以结构重量为目标及以结构强度为约束的形状优化模型。根据结...     

四次带参Ball曲线的形状分析

基于包络理论与拓扑映射的方法对四次带参Ball曲线进行了形状分析,得出了曲线上含有奇点,拐点和曲线为局部凸或全局凸的充分必要条件,这些条件完全由控制多边形和形状参数所决定;并进一步讨论了形状参数对形状分布图的影响及其对曲线形状的调节能力.研究表明,四次带参Ball曲线的形状调控能力要优于四次带参Bezier曲线.     

封堵物水中运动过程的数学模型研究

投放块石封堵物是溃口抢险的一项重要技术,研究的问题就是对封堵物水中运动过程进行运动系统辨识.利用牛顿运动定律和流体力学知识确定封堵物水中运动过程的模型结构,利用最小二乘原理进行模型参数估计,最终确定大实心方砖在水中的运动模型.通过MATLAB仿真求得不同试验条件下雷诺数与阻力系数间的关系,得到阻力系数试验曲线.最后,验证了所建模型和阻力系数试验曲线的合理性,并利用重力相似准则将所得结论应用于实际溃口封堵问题.     

三角形形状判断的三大策略

正确理解三角形的六要素间的关系和熟练运用三角形的正、余定理,才能迅速判断三角形的形状.一般有两种思路:其一是化边为角,求出三个角之间的关系式;其二是化角为边,求出三条边之间的关系式.实施转化的主     

A new type of the generalized Bézier curves

In this paper, we improve the generalized Bernstein basis functions introduced by Han, et al. The new basis functions not only inherit the most properties of the classical Bernstein basis functions, but also reserve the shape parameters that are similar to the shape parameters of the generalized Bernstein basis functions. The degree elevation algorithm and the conversion formulae between the new basis functions and the classical Bernstein basis functions are obtained. Also the new Q-Bézier curve and surface...