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分析了EA4T钢的性质特征以及传统调质处理工艺所存在的问题,系统地研究了正火、淬火及回火工艺对材料的组织及性能的影响规律。通过系统的实验,探索出了DJ4型机车车轴的最佳热处理工艺参数。 相似文献
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在以学习者为中心的语言教学研究中,监控和分析学习者的语言成为评估和指导教学的重要手段。本文运用错误分析理论,对轮机英语学习者在汉译英中出现的错误进行了分类、解释和评价,为轮机英语教学提供了一定的借鉴。 相似文献
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目的 探讨电针对慢性癫痫大鼠海马新生神经元生长抑素(SS)表达的影响.方法 应用免疫荧光双标记和激光共聚焦显微镜观察了电针慢性癫痫大鼠督脉穴位"大椎"与"百会"后海马新生神经元生长抑素的表达情况.结果 海马新生神经元有SS的表达,且电针后的癫痫大鼠表达比未电针的癫痫大鼠减少,差异有统计学意义(P<O.05).结论 电针可抑制海马新生神经元SS的表达,而SS有致痫作用.由此推测电针的抑痫机制可能是通过海马新生神经元SS的表达而实现的. 相似文献
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Two continuum approximation (CA) optimization models are formulated to design city-wide transit systems at minimum cost. Transit routes are assumed to lie atop a city’s street network. Model 1 assumes that the city streets are laid out in ring-radial fashion. Model 2 assumes that the city streets form a grid. Both models can furnish hybrid designs, which exhibit intersecting routes in a city’s central (downtown) district and only radial branching routes in the periphery. Model 1 allows the service frequency and the route spacing at a location to vary arbitrarily with the location’s distance from the center. Model 2 also allows such variation but in the periphery only.The paper shows how to solve these CA optimization problems numerically, and how the numerical results can be used to design actual systems. A wide range of scenarios is analyzed in this way. It is found among other things that in all cases and for both models: (i) the optimal headways and spacings in the periphery increase with the distance from the center; and (ii) at the boundary between the central district and the periphery both, the optimal service frequency and line spacing for radial lines decrease abruptly in the outbound direction. On the other hand Model 1 is distinguished from Model 2 in that the former produces in all cases: (i) a much smaller central district, and (ii) a high frequency circular line on the outer edge of that central district.Parametric tests with all the scenarios further show that Model 1 is consistently more favorable to transit than Model 2. Cost differences between the two designs are typically between 9% and 13%, but can top 21.5%. This is attributed to the manner in which ring-radial networks naturally concentrate passenger’s shortest paths, and to the economies of demand concentration that transit exhibits. Thus, it appears that ring-radial street networks are better for transit than grids.To illustrate the robustness of the CA design procedure to irregularities in real street networks, the results for all the test problems were then used to design and evaluate transit systems on networks of the “wrong” type – grid networks were outfilled with transit systems designed with Model 1 and ring-radial networks designed with Model 2. Cost increased on average by only 2.7%. The magnitude of these deviations suggests that the proposed CA procedures can be used to design transit systems over real street networks when they are not too different from the ideal and that the resulting costs should usually be very close to those predicted. 相似文献
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结合进化论和遗传理论的最新进展,提出基于学习算子的自学习进化算法;并将正态云模型引入进化过程中,提出云学习算子和基于云学习算子的自学习进化算法.最后的仿真实验表明,该算法具有精度高、收敛速度快等优点,能在很大程度上解决了现存进化算法的低效问题. 相似文献
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