The wear failure course of gas-valve/valve-seat in engine was investigated with a simulating tester. The results show that the failure of the contact conical surface is mainly caused by the elastic and plastic deforma...The wear failure course of gas-valve/valve-seat in engine was investigated with a simulating tester. The results show that the failure of the contact conical surface is mainly caused by the elastic and plastic deformation and the fatigue micro-crack and spalling. The creep-deformation and corrosion atmosphere accelerated wear failure course at the high temperature. The wear failure course of the gas-valve/valve-seat in engine follows general wear rules of mechanical elements, but the rate of wear in the sharp wear stage is faster.展开更多
时间表(T im etab ling)问题是NP-完全的,因此很难寻求一个有效的整体优化算法.分组作为重要的优化策略,可以将课程按优先等级逐次分组,每组再采用组合优化方法.通常认为课程的规模是优先等级的决定性因素.然而选课的模式允许学生在一...时间表(T im etab ling)问题是NP-完全的,因此很难寻求一个有效的整体优化算法.分组作为重要的优化策略,可以将课程按优先等级逐次分组,每组再采用组合优化方法.通常认为课程的规模是优先等级的决定性因素.然而选课的模式允许学生在一定的范围内选择课程,这就使得课程的关联关系更复杂.该文将课程的关联关系描述为一个M arkov链,进而给出了课程优先度(CourseR ank)的概念.通过对清华大学2002年度学生选课数据的分析和计算,结果表明课程的规模仍然是重要的因素,但并不完全是决定性的.展开更多
This paper presents an alternative design of postgraduate English writing course to meet the requirement of the current postgraduate English teaching reform.The author believes that efficiently-organized writing activ...This paper presents an alternative design of postgraduate English writing course to meet the requirement of the current postgraduate English teaching reform.The author believes that efficiently-organized writing activities based on practical needs could refresh teaching frame- work and consequently assist postgraduates in English writing.展开更多
Prof. Dr. Manfred Held will give a 7-day intro-ductive short course in Yellow Mountain of Anhui Province to the following topics: Shaped Charge Threat, KE Performance,
文摘The wear failure course of gas-valve/valve-seat in engine was investigated with a simulating tester. The results show that the failure of the contact conical surface is mainly caused by the elastic and plastic deformation and the fatigue micro-crack and spalling. The creep-deformation and corrosion atmosphere accelerated wear failure course at the high temperature. The wear failure course of the gas-valve/valve-seat in engine follows general wear rules of mechanical elements, but the rate of wear in the sharp wear stage is faster.
文摘This paper presents an alternative design of postgraduate English writing course to meet the requirement of the current postgraduate English teaching reform.The author believes that efficiently-organized writing activities based on practical needs could refresh teaching frame- work and consequently assist postgraduates in English writing.
文摘Prof. Dr. Manfred Held will give a 7-day intro-ductive short course in Yellow Mountain of Anhui Province to the following topics: Shaped Charge Threat, KE Performance,
