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  • Corrole和Corrolazine的结构及其内氢迁移反应的理论研究

    采用B3LYP/6.31G**方法在Gaussian03程序下,对Corrole(CH3)和Corrolazine(C2H3)体系进行结构优化和振动分析.结果显示,CH3和C2H3的不同构型稳定性差异可忽略不计,结构参数的变化则说明中心空穴的大小顺序为PH2〉CH3〉PzH2〉C2H3.优化不同构型间相互转化的IHAT反应的过渡态,并进行相关的比较计算,发现CH3和C2H3的正反应速率都明显大于PH2和P2H2;同时CH3和C2H3的非平面构型的电子效应远大于PH2和P2H2的平面离域体系的平均化电子效应.
    廖玉婷,饶火瑜,王秋月,胡宝群 - 计算机与应用化学
    文章来源: 万方数据
  • It is a common phenomenon that the cracks originating from a hole can cause structural damage in engineering.However,the fracture mechanics studies of hole edge crack problems are not sufficient.The problem of an elliptical hole with two collinear edge cracks of unequal length in an infinite plate under uniform tension at infinity is investigated.Based on the complex variable method,the analytical solutions of stress functions and stress intensity factors are provided.The stress distribution along the axes and the edge of the elliptical hole is given graphically.The numerical results show that there is obvious stress concentration near the hole and cracks,and the stresses tend to applied loads at distances far from the defect,which conform to Saint-Venant's principle.Hence,the stress functions are proved to be right.Under special conditions,the present configuration becomes the Griffith crack,two symmetrical cracks emanating from an elliptical hole,two cracks of unequal length emanating from a circular hole,a crack at the edge of a circular hole,or a crack emanating from an elliptical hole.Compared with available results,stress intensity factors for these special shapes of ellipses and cracks show good coincidence.The stress intensity factor for two cracks of unequal length at the edge of an elliptical hole increases with the crack length and the major-to-minor axis ratio of the elliptical hole.The stress distribution in an infinite plate containing an elliptic hole with unsymmetrical cracks is given for the first time.
     - 中国机械工程学报
    文章来源: 万方数据
  • 基于PLC和变频技术的中央空调控制系统改造设计

    基于节能减排的目的,对中央空调控制系统实施改造.首先分析了中央空调系统的运行现状,阐述了中央空调系统的构成和变频节能原理,继而采用PLC和变频控制相结合的温差法控制方案对原有系统进行改造,给出了设计方案,进行了变频器的参数设置,并进行了节能分析.最后指出了中央空调采用变频调速控制具有较好的实用价值和发展前景.
    张涛,张丽,尚希 - 电机与控制应用
    文章来源: 万方数据
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