中文摘要：

应用阿基米德copula刻画随机变量间的相依性结构,对于由两个元件组成的并联系统,比较了由旧元件组成的新系统的寿命与旧系统的剩余寿命的随机大小,得到了似然比序存在的充分条件.对于由两个元件组成的并（串）联系统,比较了新元件组成的系统的休止时间与在给定两相似元件已损坏条件下系统休止时间的最大（最小）值之间的随机大小,得到了失效率序、似然比序存在的充分条件,也给出几个数值例子进一步说明得到的主要结论.

英文摘要：

In this paper,we employ the Archimedean copula to characterize the dependence structure between random variables.For two-unit parallel systems,we compare the lifetime of a parallel system composed of two used units with the residual lifetime of the parallel system composed of a similar pair of new units,and obtain a sufficient condition for the existence of likelihood ratio order.as for two-unit series （parallel）systems,we compare the inactivity time of a series （parallel）system with two new unitsand the mini-mum （maximum）of a similar pair of units＆#39;inactivity time given that both units have failed,and obtain several sufficient conditions for the existence of hazard rate order and likelihood ratio order.Several numerical examples are also presented to illustrate the main results.