“三位水平法”快速调节分光计

分光计构造精密,它的调节技术是光学实验中的基本技术之一。应用分光计测定棱镜折射率时,仪器的调节存在两个难点。在此介绍借助圆水准泡,应用"三位水平法"快速解决这两个难点,方法简单、易操作,可在物理实验教学中应用。     

DNS of heat transfer in turbulent and transitional channel flow obstructed by rectangular prisms

Direct numerical simulation (DNS) of heat transfer in a channel flow obstructed by rectangular prisms has been performed for Re_τ = 80–20, where Re_τ is based on the friction velocity, the channel half width and the kinematic viscosity. The molecular Prandtl number is set to be 0.71. The flow remains unsteady down to Re_τ = 40 owing to the disturbance induced by the prism. For Re_τ = 30 and 20, the flow results in a steady laminar flow. In the vicinity of the prism, the three-dimensional complex vortices are generated and heat transfer is enhanced. The Reynolds number effect on the time-averaged vortex structure and the local Nusselt number are investigated. The mechanism of the heat transfer enhancement is discussed. In addition, the mean flow parameters such as the friction factor and the Nusselt number are examined in comparison with existing DNS and experimental data.     

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.     

用分光计测量三棱镜的折射率的几个问题

本文对分光计的调整、三棱镜的折射率的测量及数据处理过程中常出现的几个问题作详细的分析,提出了最简单的调节方法,澄清了一些易混淆的问题,可以避免盲目的操作,达到该实验的训练目的。     

Tris-(thiocyanato)-bis-(hexamethylenetetramine)-nona-(aquo) lanthanum(III): synthesis, crystal structure, IR and Raman characterization

The title compound (LaC₁₅H₄₂N₁₁O₉S₃) was prepared and characterized by means of X-ray, IR and Raman measurements. The crystals are orthorhombic: Pnma (No. 62), a = 21.117(2), b = 14.736(2), c = 10.082(1) Å, and Z = 4. The structure consists of polyhedra with a La(III) ion in the center of them and hexamethylene molecules, which link these polyhedra. Each La(III) ion coordinates seven molecules of water and two thiocyanate ions via nitrogen atoms. The IR and Raman spectra, which have been obtained and interpreted, are in good agreement with X-ray results.     

Tc6三棱柱原子簇电子结构探讨

本文用SCC-DV-Xα方法计算了Tc_6Cl_(12)~(2-)、Tc_6Cl_(14)~(3-)、Tc_6Br_(12)等三棱柱原子簇.结果表明,Tc_6Cl_(12)~(2-)与Tc_6Cl_(14)~(3-)金属键轨道大体相似,只是Tc_6Cl_(14)~(3-)较前者多一个反键轨道.Tc_8Br_(12)有22个金属键轨道,分别由2个、4个或8个Tc原子组成,形式有双中心键,多中心键或离域键.过渡金属原子簇众多的d轨道与三棱柱构型的特点,使金属键变得多种多样。文中附有部分金属键轨道图。     

Synthesis and Crystal Structure of a Heptanuclear Trigonal Prismatic Cluster {PrCu_6} with Glycine and Imidazole as Ligands

A new heptanuclear trigonal prismatic cluster [PrCu6(μ3-OH)3(Gly)6im6](ClO4)6 was synthesized through the self-assembly of Pr^3 , Cu^2 , glycine and imidazole in aqueous solution and characterized by X-ray structure analysis. The compound belongs to the trigonal R3 space groupwith a=b=15.8761(2), c=23.4943(5) A, V=5128.4(1)A^3, Z=3, Dc=1.965 g/cm^3,μ=2.869mm^-1 F(000)=3012, the final R=0.0332 and wR=0.0844 for 3596 independent reflections. In the cation, the Pr3 ion is situated at the center of a prism formed by six copper atoms and coordinates to nine oxygen atoms with a tricapped trigonal prismatic coordination polyhedron. Six glycine ligands and six imidazole terminal ligands participate in constructing the cluster.     

冰洲石-玻璃组合e光超高透偏光棱镜

为了既节省稀有昂贵的冰洲石晶体材料，又尽量提高偏光棱镜的透射比，设计了一种冰洲石晶体与光学玻璃组合的方法。叙述以布儒斯特角入射来提高偏光棱镜e光透射比的设计方案。该棱镜可用甘油或有机硅胶将FK 2玻璃与冰洲石晶体胶合而成。理论分析和实验测试表明，该棱镜的透射比高于96％，消光比优于10-5，在一定情况下可以取代纯冰洲石晶体材料的偏光棱镜。     

微棱镜阵列型定向反射器特性

介绍了微棱镜阵列型定向反射器的材料折射率对入射孔径角的限制,定向反射率随入射角的变化关系,特别是提出了单元有效反射面积的计算方法,并进行了计算机模拟和实验,为该元件的设计和制作提供了理论依据。