The age replacement decision for the system with intermittently used equipment is studied in this paper.

研究了设备间歇使用系统的年龄替换决策。

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The expected cost per unit -time for infinite time span is analyzed strictly under the mathematical model constructed, and the optimum age replacement decision is also discussed.

在建立数学模型的基础上，分析了系统长期单位时间内的期望费用，并讨论了最优年龄替换决策。

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Scientists believe the secret to the clams' longevity is a slowed cell-replacement process. But why they age so slowly is unknown.

科学家们认为蛤蜊长寿的秘诀在于其细胞代谢过程的缓慢，但是仍然不知道它为何如此缓慢。

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The team studied over 2, 500 women involved in hormone replacement therapy - whose average age was 66.

BBC: Annual post-menopause smears 'unnecessary'

Prolonged oestrogen secretion would certainly keep a woman fertile longer, and it might also keep her healthier in old age as those who use hormone-replacement therapy are well aware.

ECONOMIST: Ageing

But another explanation could be changes in lifestyle factors which increase the risk of hormone-dependent tumours, such as women having babies at an older age, obesity after menopause and use of hormone replacement therapy.

BBC: Breast cancer biology 'changing'