Asymmetric synthesis XXVII: Asymmetric catalytic trimethylsilylcyanation of aldehydes by novel Ti-chiral Schiff base complexes

Enantioselective catalytic trimethylsilylcyanations of aldehydes with 48% to 92% e.e. have been studied using the novel Ti-chiral Schiff base complexes. We have found that the catalyst led to high enantoselectivity when the molar ratio of the Schiff base 1 to Ti(O-i-Pr)₄ was 2:1.     

Variation of geometric invariant theory quotients

Geometric Invariant Theory gives a method for constructing quotients for group actions on algebraic varieties which in many cases appear as moduli spaces parameterizing isomorphism classes of geometric objects (vector bundles, polarized varieties, etc.). The quotient depends on a choice of an ample linearized line bundle. Two choices are equivalent if they give rise to identical quotients. A priori, there are infinitely many choices since there are infinitely many isomorphism classes of linearized ample line bundles. Hence several natural questions arise. Is the set of equivalence classes, and hence the set of non-isomorphic quotients, finite? How does the quotient vary under change of the equivalence class? In this paper we give partial answers to these questions in the case of actions of reductive algebraic groups on nonsingular projective algebraic varieties. We shall show that among ample line bundles which give projective geometric quotients there are only finitely many equivalence classes. These classes span certain convex subsets (chambers) in a certain convex cone in Euclidean space, and when we cross a wall separating one chamber from another, the corresponding quotient undergoes a birational transformation which is similar to a Mori flip.     

沉淀法制备CeO2超微粉末

采用过氧化氢－－氨水沉淀法在较低温度下制备ＣｅＯ２超微粉末。试验表明，溶液起始浓度及焙烧温度以形成粉素晶体粒径有一定影响。焙烧温度在２２０－８５０℃，所得ＣｅＯ２微粉均为立方晶系，透射电测试表明，粒子基本呈球形，晶体平均粒径随焙烧温度升高而增大。控制适当条件，可制得粒径范围在５－１３ｎｍ，比表面积１１１．８ｍ＾２／ｇ的ＣｅＯ２超微粉末。     

Kantorovich-type inequalities and the measures of inefficiency of the glse

In this paper we introduce some Kantorovich inequalities for the Euclidean norm of a matrix, that is, the upper bounds to (X'B ^–1 X) ^–1 X'B ^–1 AB ^–1 X(X'B ^–1X)^–1 X' BX(X'AX) ^–1 X'CX² are given, where A²=trace (A'A). In terms of these inequalities the upper bounds to the three measures of inefficiency of the generalized least squares estimator (GLSE) in general Gauss-Markov models are also established.Project supported partially by the Third World Academy of Sciences under contract TWASRG 87-46 and by the National Natural Science Foundation.     

Linear mode conversion of waves near the maxima or minima of the density in a warm magnetized plasma

Behaviour of the h. f. electrostatic waves near the plasma or upper hybrid resonances was studied in the case that these resonances are situated at the maxima or minima of the plasma density. Supposing the parabolic density profile in these regions we obtained the connection formulae for the WKB solutions. In a weakly inhomogeneous magnetoplasma the effect of the parabolic profile manifests itself only in narrow frequency band centred at the resonance frequency corresponding to the extreme value of the density. The whole process can be then described by only two coefficients, viz. the power conversion and power transmission coefficients.     

Improved method for analyzing estrogens in water by liquid chromatography-electrospray mass spectrometry

An improved LC-electrospray ionization MS method was established for four estrogens (17beta-estradiol (E2), estriol (E3), estrone (E1), and ethynyl estradiol (EE)) in environmental water. Almost complete separation of all estrogens was achieved on a phenyl column with methanol/water as the mobile phase. Quantification was achieved in the negative ionization mode using selected ion monitoring. The instrumental detection limits were 20-30 ng/l for the four analytes. In Milli-Q spiked water, the recoveries of the four estrogens were 72-81%, which was similar to those found for river water spiked with the corresponding deuterated estrogens. The detection limits for the four estrogens in river water were 0.1-0.2 ng/l. The method was used to detect residual estrogens in the Tonghui River, which receives water from a municipal sewage treatment plant in Beijing; E1 (1.1 ng/l) and E2 (0.2 ng/l) were detected.     

电位滴定法测定模拟高放废液中的游离酸

本文研究了用电位滴定法测定模拟高放废液中游离酸的方法。用草酸钾做络合剂以消除Ｆｅ＾３＋、Ａｌ＾３＋、Ｎｄ＾３＋等多种水解离子的影响，用标准碱直接进行电位滴定，即可快速准确地测定模拟高放废液中游离酸的含量。方法的相对标准偏差为１．８％，标准加入回收率为１００－１０１％，能为放射性废物固化试验提供可靠的分析数据。     

膨润土对结晶紫的吸附

用分光光度、显微电泳和ｘ－射线衍射等方法研究了膨润土对结晶紫的吸附；实验表明，钙型膨润土在吸收结晶紫溶液时，加入钠盐可明显改善吸附效果。