Polystyrene-supported Selenides and Selenoxide: Versatile Routes to Synthesize Allylic Alcohols

Combinatorial chemistry and solid phase synthesis have recently emerged as powerful tools for the drug discovery process1. It might be argued that selenoxide syn- elimination provided the principal impetus for the development of organoselenium chemistry. [2, 3] Sigmatropic rearrangement2 of allylic selenium compounds is the most fundamental reaction in the field of synthetic organoselenium chemistry as well as selenoxide syn-elimination. However, organic selenides are highly malodorous and …     

SEDIMENTATION OF CHARGED PARTICLES AT LARGE PéCLET NUMBER

1. Introduction Sedimentation of colloidal particles in dilute suspensionshas been investigated extensively during the last severaldecades due to its theoretical and practical importance(Russel et al., 1989; Wen, 1996; Dhont, 1996). The mostcommonly accepted theory seems to be that advanced byBatchelor and Batchelor and his co-workers (Batchelor,1972; Batchelor, 1982; Batchelor & Wen, 1982; Wen &Batchelor, 1985). In spite of the well-described settlingbehaviors of hard spheres, a review o…     

A New Triterpenoid Glycoside from Dichotomanthes tristaniaecarpa

Dichotomanthes tristaniaecarp ( Kurz.) belongs to the family Rosaceae. Its root bark is used as Chinese folk medicine for treatment of flu, cough, sore throat and nosebleed. Chemical constituents of this species have not been reported previously. Compound 1 was obtained as colorless needles, mp. 213-215 °C. The molecular formula was determined as C36H58O11 by its negative-ion FAB MS ([M]- at m/z 665) and 13C NMR DEPT spectrum. The analysis of 13C NMR spectrum showed 30 signals for …     

我国普通高等教育发展水平的全局主成分分析

本文根据 1995年、1997年和 1999年共同构成的关于我国普通高等教育发展水平的时序立体数据表 ,通过全局主成分分析得到公共主成分子空间L(F1,F2 ,… ,Fm) ,并在该子空间对我国高等教育发展背景和现状进行统计分析 ,给出了排名和变化趋势。     

一种“后部加载”型透平静叶的设计

“后部加载”形式载荷分布能有效降低叶片通道二次流损失，从而显著提高流动效率，为此，设计了一种具有“后部加载”特性的透平静叶叶型。数值分析和实验研究显示该叶型能够降低三维通道总损失，同时又具有高强度及大范围攻角适应性等特点。     

Two New Spirostanol Steroidal Sapogenins from Fermented Leaves of Agave americana

The genus Agave is well known as rich sources of steroidal saponins and sapogenins 1. More than ten steroidal sapogenins have been isolated from Agave americana L.2-4 In this paper, we describe the structural determination of two new steroidal sapogenins from fermented leaves of A. americana L. The methanolic extracts of dried residues of fermented leaves of A. americana L. produced in Ruili County of Yunnan Province at January 2000, were subjected to repeated column chromatography of …     

玻璃态聚合物银纹化过程的数值模拟

银纹化是玻璃态聚合物材料所特有的一种现象。本文在代表体积单元中嵌入能够刻划银纹萌生与生长的银纹单元，运用有限元方法对银纹化过程进行了数值模拟。银纹化过程中的最大主应力矢量图说明计算模型以及计算方法是比较合理的。而且，本文所揭示出来的银纹化过程的规律与实验中观察到的现象是吻合的。     

热斑分布方式对气冷双级涡轮气热性能影响研究

针对两种不同时序位置热斑在大冷气量燃气涡轮通道内的迁移对涡轮气动性能、叶片表面热负荷和气动激振力的影响开展了数值模拟研究,对比分析了涡轮效率、叶片表面温度分布、出口总温分布、非定常激振力时域/频域特征等,对进口热斑时序位置的选取方式进行了讨论。结果表明对于气冷燃气涡轮,与热斑正对通道中心相比,热斑正对导叶前缘可以有效降低动叶热负荷、改善第二级导叶温度分布均匀性、抑制效率下降、降低非定常激振力水平,有利于改善燃气涡轮气动热力性能。研究结果为大冷气量双级燃气涡轮热斑时序位置选取提供了依据。     

二次非线性粘弹性圆板的2/1+3/1超谐解

计及材料的非线性弹性和粘性性质，研究了圆板在简谐载荷作用下的2／1＋3／1超谐解，导出了相应的非线性动力方程。提出一类强非线性动力系统的叠加－叠代谐波平衡法。将描述动力系统的二阶常微分方程，化为基本解为未知函数的基本微分方程；及分岔解为未知函数的增量微分方程。通过叠加－迭代谐波平衡法得出了圆板的2／1＋3／1超谐解。对叠加迭代谐波平衡法和数值积分法进行了比较，两者结果吻合很高。并且讨论了2／1＋3／1超谐解的渐近稳定性。     

TENSILE STRENGTH FOR SPLITTING FAILURE OF BRITTLE PARTICLES WITH CONSIDERATION OF POISSON''''S RATIO

1. Introduction The core mechanism of comminution could be reduced to the breakage of individual particles that occurs through contact with other particles or with the grinding media, or with the solid walls of the mill (Potapov & Campbell, 1994). When a particle is subjected to a load, the nature of the stress field around and within the brittle particle, its material properties, and the size and distribution of micro-flaws within the particle govern the size and shape distribution of the fra…