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Reliability Comparison Between Parallel and Cold-standby Two-unit System Under Poisson shock

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南京邮电大学学报（自然科学版） 2012年第2期32卷 118-120页

作者： TANG Jia-shan LANG Man ZHAO Xiao-ling College of Science Nanjing University of Posts and Telecommunications Nanjing 210046 China

This paper investigates the comparison problem of the reliability index between a parallel and a cold-standby system,both of which are consisting of two identical *** the contrary to the general intuitive result,we proved that,under the condition that the system is shocked by a Poisson stream,the life time of the parallel system is longer than that of the cold-standby one in the sense of probability.

关键词： parallel system cold-standby system shock model Poisson process reliablity index

Crashworthiness design of density-graded cellular metals

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Theoretical & Applied Mechanics Letters 2013年第3期3卷 9-13页

作者： Xiaokai Wang Zhijun Zheng Jilin Yu CAS Key Laboratory of Mechanical Behavior and Design of Materials University of Science and Technology of China

Crashworthiness of cellular metals with a linear density gradient was analyzed by using cell-based finite element models and shock models. Mechanisms of energy absorption and deformation of graded cellular metals were explored by shock wave propagation analysis. Results show that a positive density gradient is a good choice for protecting the impacting object because it can meet the crashworthiness requirements of high energy absorption, stable impact resistance and low peak stress.

关键词： functionally graded materials deformation localization shock model crashworthiness

The NBEE and NWEE classes of lifetime distributions and their properties

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Journal of Southeast University(English Edition) 2012年第2期28卷 251-255页

作者：王冠军东南大学数学系南京211189

A class of lifetime distributions, new better than equilibrium in expectation （NBEE）, and its dual, new worse than equilibrium in expectation （NWEE）, are studied based on the comparison of the expectations of lifetime X and its equilibrium Xo. The relationships of the NBEE （NWEE） and other lifetime distribution classes are discussed. It is proved that the NBEE is very large, and increasing failure rate （IFR）, new better than used （NBU） and the L class are its subclasses. The closure properties under two kinds of reliability operations, namely, convolution and mixture, are investigated. Furthermore, a Poisson shock model and a special cumulative model are also studied, in which the necessary and sufficient conditions for the NBEE （NWEE） lifetime distribution of the systems are established. In the homogenous Poisson shock model, the system lifetime belongs to NBEE（NWEE） if and only if the corresponding discrete failure distribution belongs to the discrete NBEE（NWEE）. While in the cumulative model, the system has an NBEE lifetime if and only if the stochastic threshold of accumulated damage is NBEE.

关键词： lifetime distribution survival function closure property new better than equilibrium in expectation (NBEE) equilibrium distribution shock model cumulative damage model