Collectively, these cycles are known as circadian rhythms and are generally tied to the 24-hour day-night cycle.

所有的这些周期被人们统称为昼夜节律，一般以24小时一昼夜为一个循环。

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Jet lag happens when your circadian rhythm is running on a different day-night cycle than the day-night cycle of the outside world.

当我们的生物钟周期与外部的昼夜交替周期不一致时，我们就有倒时差的感觉。

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Light will only stimulate your brain's day/night balance (circadian cycle).

光只能刺激你大脑的日夜平衡（生理节奏循环）。

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Based on computer modelling, the craft QinetiQ has developed thus far could complete a day-night cycle.

BBC: NEWS | Science/Nature | 'Eternal planes' to watch over us

The finding demonstrates that people have a day-night cycle that must be respected, even when they're doing the demanding work of space exploration.

MSN: Space station to get new insomnia-fighting light bulbs

Altered day-night cycle: the Antarctic winter involves a period of over three months of complete darkness where the sun does not rise above the horizon.

BBC: Viewpoint: The last great polar challenge