多粒子模拟方法分析北京正负电子对撞机储存环束团长度拉伸效应

采用多粒子模拟方法,分析了北京正负电子对撞机(BEPC)储存环纵向不稳定性,给出了BEPC储存环束团长度与单束流强的关系,得出了阈值流强.模拟结果与BEPC95年4月实测结果符合较好.     

具有弹性支承的圆管在内外部流激发下动力特性及实验研究

本文建立了具有弹性支承的圆管在内外部流激发下的力学模型.推导了内部流与静止外部流作用下圆管的耦联振动方程.提出了确定弹性系数的方法.采用振型叠加法分析圆管动力特性问题.对内部流与静止外部流情况下圆管固有频率进行了计算和测量,计算值与实验值吻合较好.另外,对内外流同时激发下圆管的固有频率进行了测量,得到若干对工程实际有用的结论.     

热传导方程三层并行差分格式初始条件的计算

给出二维热传导问题的三层差分格式初始条件的一种显式计算方法,对于由此形成的内边界预估校正三层并行差分算法,证明稳定性和收敛性定理.并行数值试验表明,方法稳定,且与通常采用隐式格式计算初始条件的方法相比,易于程序实现;与已有的扰动算法相比,能大幅度减小误差.     

Isomeric Effect on Optoelectronic Properties and Photovoltaic Performance of Anthraquinone-Core Perylene Diimide (PDI) and Helical PDI dimers

Isomerism heavily influences the optoelectronic properties and self-assembly behavior of compounds and subsequently affects their device performance. Herein, two pairs of isomeric perylene diimide (PDI) dimers, PDI and PDI2, were designed and synthesized. The electron-deficient 9,10-anthraquinone group was employed as the bridge, and thus, the resultant dimers exhibited an acceptor–acceptor–acceptor (A-A-A) structure. To determine the isomeric effects on the optoelectronic properties and photovoltaic performance of these dimers, their absorptivity, luminescence, and redox behavior were studied. Bulk heterojunction organic solar cells based on these four dimers were fabricated and measured. The two PDI dimers exhibited clear differences in photovoltaic performance, whereas the two PDI2 analogues showed similar power conversion efficiencies (PCEs). The PCEs of the two PDI2 dimers are much higher than those of the PDI dimers. These results illustrate that the isomeric effect of PDI dimers is much larger than that of PDI2 dimers on the device performance, and proper expansion of conjugation could improve the device performance.     

Analysis of the nonlinear scheme preserving the maximum principle for the anisotropic diffusion equation on distorted meshes

Science China Mathematics - In this paper, a nonlinear finite volume scheme preserving the discrete maximum principle for the anisotropic diffusion equation on distorted meshes is described. We...     

Zirconium-catalyzed methylalumination of heterosubstituted arylethynes: Factors affecting the regio-, stereo-, and chemoselectivities

The Zr-catalyzed methylalumination of heterosubstituted arylethynes containing O, S, Cl, and Si can proceed in high yields (>70%) and in a highly regio- and stereoselective manner (?98-99%), although SO₂Ph, Br, and Cl in a benzylic position present serious chemoselectivity-related problems. The low regioselectivity of 60% initially observed with o-ethynylphenol (1a) has been elevated to ?98% through the use of either a catalytic amount of Zr(ebi)Cl₂ or Zr(2-Me-Ind)₂Cl₂ or, more conveniently, the stoichiometric amount of ZrCp₂Cl₂, ZrCp₂MeCl, or ZrCp₂Me₂ in conjunction with the use of a deficient amount (0.9 molar equiv.) of I₂ for subsequent iodinolysis.     

Lewis acid-promoted three-component reactions of propargylic alcohols with 2-butynedioates and secondary amines

We report herein a three-component reaction of propargylic alcohols with 2-butynedioates and secondary amines, which furnished functionalized dihydroazepines. In the cases where benzylmethylamine and benzyl-i-propylamine were used as the secondary amine, the reaction afforded 2,5-dihydro-1H-pyrroles and 2,3-dihydro-1H-pyrroles, respectively, as the major product along with the desired dihydroazepines. The reaction mode depends on the electronic and steric effect of the substitutents on the secondary amines used. A tentative mechanism for this cascade process is postulated. The key intermediate is ascribed to 1,3,4-pentatrien-1-amine, which is formed by trapping the in situ generating allenic carbocation with enamine. Because of the reactivity of 1,3,4-pentatrien-1-amine formed, different products were thus formed.     

Electrochemical synthesis of CdS/ZnO nanotube arrays with excellent photoelectrochemical properties

A facile electrochemical method was developed to synthesize CdS/ZnO nanotube arrays. Implemented as the photoanode in a photoelectrochemical cell, the CdS/ZnO nanotube arrays exhibited a photocurrent as high as 10.64 mA cm(-2).     

An efficient and accurate reconstruction algorithm for the formulation of cell-centered diffusion schemes

A new reconstruction algorithm is proposed for constructing cell-centered diffusion schemes on distorted meshes. Its main feature is that edge unknowns are defined at certain balance points, the locations of which depend on the diffusion coefficient and the skewness of grid cells, so as to obtain a two-point reconstruction stencil. Implementing the new algorithm for the approximation of gradients, we extend the IDC (improved deferred correction) scheme, which was proposed by Traoré et al. [P. Traoré, Y. Ahipo, C. Louste, A robust and efficient finite volume scheme for the discretization of diffusive flux on extremely skewed meshes in complex geometries, J. Comput. Phys. 228 (2009) 5148–5159], to handle diffusion problems with discontinuous coefficients. Numerical results demonstrate the accuracy and efficiency of the extended scheme.     

CeO2/ZnO复合纳米管的制备及其光催化性能的研究

用纳米CeO2掺入ZnO纳米管制备了CeO2/ZnO复合纳米管,考察了复合纳米管的光学及其光催化性能,并运用X射线衍射、透射电镜、比表面积测定和紫外-可见漫反射光谱等技术对样品进行了表征.结果表明,与ZnO纳米管相比,CeO2/ZnO复合纳米管的比表面积虽有所降低,但光催化活性有所提高,随着复合纳米CeO2量的增加,催化剂的光催化活性相应降低,太阳光下CeO2/ZnO复合纳米管对甲基橙溶液也有较高的催化活性.