Preparation of chiral trans-5-substituted-acenaphthene-1,2-diols by baker’s yeast-mediated reduction of 5-substituted-acenaphthylene-1,2-diones

A series of trans-5-substituted-acenaphthene-1,2-diols were obtained in 21–72% yield with 97–100% ee by baker’s yeast-mediated reduction of the corresponding acenaphthylene-1,2-diones, in the presence of DMSO as a co-solvent and under vigorous agitation. The absolute configuration of (?)-trans-5-methoxy-acenaphthene-1,2-diol trans-3b and (?)-trans-5-bromo-acenaphthene-1,2-diol trans-3c was assigned as (S,S) and (?)-trans-5-thiomorpholin-acenaphthene-1,2-diol trans-3d was established as (R,R) by exciton-coupled circular dichroism.     

Probabilistic rough set over two universes and rough entropy

In this paper, we discuss the properties of the probabilistic rough set over two universes in detail. We present the parameter dependence or the continuous of the lower and upper approximations on parameters for probabilistic rough set over two universes. We also investigate some properties of the uncertainty measure, i.e., the rough degree and the precision, for probabilistic rough set over two universes. Meanwhile, we point out the limitation of the uncertainty measure for the traditional method and then define the general Shannon entropy of covering-based on universe. Then we discuss the uncertainty measure of the knowledge granularity and rough entropy for probabilistic rough set over two universes by the proposed concept. Finally, the validity of the methods and conclusions is tested by a numerical example.     

Microstructure and properties of high chrome steel roller after laser surface melting

Laser surface melting of high chrome steels was achieved by a 5 kW continuous wave CO₂ laser. The microstructure of the laser surface-melted steels was investigated by scanning electron microscopy, transmission electron microscopy and X-ray diffractometry, and the hardness profiles were determined by a Vickers hardness tester. The corrosion behavior in 3.5% NaCl solution was studied by electrochemical corrosion equipment. The large carbides of high chrome steels are completely dissolved and ultrafine dendrites of austenite with submicroscopic M₂₃C₆ carbides precipitation are formed in the melted zone. The austenite in the melted zone has a high tempering stability. The corrosion resistance of the laser surface-melted steels is significantly improved due to the dissolution of carbides and the increase of the alloying elements in the solid solution as well as the large amount of austenite.     

Preparation,Characterization and Thermal Decomposition of Polyimides with Main Chain Containing Cycloaliphatic Units

Two polyimides with main chain containing cycloaliphatic units were synthesized by conventional two‐step polycondensation of two diamines, 1,4‐bis (4‐aminophenoxymethylene) cyclohexane (BAMC) and 1,4‐bis (4‐aminobenzoyoloxymethyl) cyclohexane (BAZMC), with a dianhydride 3,3′, 4,4′‐benzophenonetetracarboxylic dianhydride (BTDA), respectively. The resulting polyimides showed exceptional thermal properties with glass transition temperatures of 212 and 178°C, and temperature for 5% weight loss of 461 and 421°C in nitrogen, respectively. Meanwhile, thermogravimetry coupled to Fourier transform infrared spectrometry (TG/FT‐IR) was used to study the thermal degradation behavior of the resulting polyimides. It was found that the thermal decomposition occurred by a double‐stage process; the major evolved products from the nonoxidative thermal degradation were hydrocarbon, CO, CO₂, H₂O, and aromatic compounds.     

Chain Conditions for Skew Polynomial Modules

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用络合转化法在甲壳胺膜上制备CdS、ZnS纳米微粒

结构单元上带有配位基团的天然高分子甲壳胺与Cd2+和Zn2+络合后,通过络合转化方法可以在高分子膜上制备CdS、ZnS等纳米微粒。用这种方法所得微粒尺寸可控、粒径均一、表面缺陷少。     

短路开关电感电阻的测量

短路开关是脉冲放电核聚变研究装置上的重要部件之一。根据需要,我们曾研制了一种性能优良的低电感场畸变型的短路开关。本文着重叙述该开关电感和电阻的测量方法及该开关的触发电路。