圆角化3∶1二维矩形柱体风压分布的雷诺数效应

在低紊流度的均匀场中,研究了4种圆角率(0,5%,10%和15%)的3∶1二维矩形柱体模型的风压分布随雷诺数的变化规律.从模型周围气流绕流的角度解释了圆角处理的矩形柱体模型的雷诺数效应的机理,并分析了雷诺数对各模型的背风面中点的风压系数的影响.试验雷诺数的变化范围为1.1×105~6.8×105.结果表明,四种圆角率模型的风压分布都受雷诺数的影响,但圆角率为0和5%的模型受雷诺数影响较小,圆角率为10%和15%的模型受雷诺数影响明显.圆角处理措施对矩形柱体模型雷诺数效应的影响主要是通过影响分离剪切层在模型侧面前缘的形成及其在侧面后部区域的再附,进而影响模型的气动特性,使模型更易受雷诺数的影响.     

应用订单教育实现高职双元制培养模式

采用双元制培养模式能加强学生实践能力的培养,有利于高职汽车整形技术专业人才培养目标的实现。在实施双元制培养模式的过程中会遇到很多困难,采用订单教育是克服这些困难的有效途径。     

用双棱镜在LiNbO3：Fe晶体中构造大面积光子晶格

推导了双棱镜干涉的强度,并用Matlab软件模拟了晶格图案.利用单个和正交双棱镜在LiNbO3：Fe中构造了一维和二维大面积光子晶格.通过CCD观测晶体内的晶格图案和衍射.选取不同的聚焦透镜,对比写入晶格的空间周期和衍射效率.实验结果表明,聚焦透镜焦距为450 mm时,空间周期最小,可达25.75μm,衍射效率为15.3%.     

Synthesis and properties of ZnO hexagonal prisms synthesized on MgO-coated Si (111) substrates

ZnO hexagonal prisms have grown on MgO-coated Si (111) substrates by chemical vapor deposition. The process has two steps : the preparation of MgO-coated Si (111) substrates and the preparation of uniform ZnO hexagonal prisms. Some nucleation sites are provided on the Si substrates by the MgO layers, which have the capability to improve the growth of ZnO prisms in the heteroepitaxy. The prisms are single crystals with a preferential growth along the c axis and they are well-faceted at both the end and side surfaces. Room-temperature photoluminescence measurement of these ZnO prisms have shown a strong ultraviolet (UV) emission band centered at 393 nm and a weak green emission band centered at 507 nm, which may be provide an improvement in novel ultraviolet light-emitting devices. In addition, a possible mechanism for the prism growth is proposed based on the analysis by electron microscopy.     

矩形截面线圈稳恒磁场的积分算法

从Biot-Savart定律和矢量叠加原理出发,发展了一种计算矩形截面不规则线圈稳恒磁场的积分算法.根据线圈的形状,将直流电流分割成直线段电流元和曲线段电流元,采用多个直线段电流元来拟合曲线段电流元,并将所有直线段电流元的磁场三重积分形式分别转化为一重积分;最后进行数值求解.为了快速求解这些积分,分别推导了梯形棱柱体电流元、三角形棱柱体电流元和梯形面电流元的磁场积分方程.模型验证表明,计算值与理论值符合良好.     

焊接结构应力场计算中的一类五面体可变节点等参单元

本文应用三维有限元理论，构造了一类五面体６～１５节点等参单元的形函数，提出了在五面体单元内的Ｇａｕｓｓ积分处理方法，建立了相应的单元刚度矩阵。这类单元的节点可以在６～１５之间任意选择。将其与ＳＡＰ５中的六面体８～２１节点等参单元匹配，计算了对接板接头的理论应力集中系数。经与有关文献结果比较表明：这类单元适合于计算焊接结构的应力场，并且具有良好的精度。     

Regular graphs are not universal fixers

For any permutation π of the vertex set of a graph G, the graph πG is obtained from two copies G^′ and G^″ of G by joining u∈V(G^′) and v∈V(G^″) if and only if v=π(u). Denote the domination number of G by γ(G). For all permutations π of V(G), γ(G)≤γ(πG)≤2γ(G). If γ(πG)=γ(G) for all π, then G is called a universal fixer. We prove that regular graphs and graphs with γ=4 are not universal fixers.     

垂直折射法测三棱镜的折射率

基于最小偏向角法和掠入射法测量三棱镜的折射率时,存在不易测准最小偏向角或明暗分界线的位置,测量量较多及测量原理复杂等缺点,本文提出了垂直折射法测量三棱镜折射率的理论公式和实验测量方法。采用此方法对两种不同顶角三棱镜进行测量,通过计算其折射率,验证了该方法的测量误差较小,可行度高。     

复合棱镜整形半导体激光束

根据半导体激光束的特点，考虑到光学元件加工及光路调节的难易程度，提出用复合棱镜对半导体激光束进行整形     

Microtopographical studies of prism faces of potassium dihydrogen phosphate crystals

Surface structures on prism faces of potassium dihydrogen phosphate crystals grown from aqueous solutions and also by gel method are described and illustrated. Density of growth centres increases as the supersaturation of the mother liquor is increased. Gel grown crystals predominantly show rectangular growth hillocks on their prism faces. In the needle shaped crystals further nucleation extends predominantly along theC axis than at right angles to it. Influence of misoriented guest microcrystals on the growth of the prism faces is described.