Periodic change imposed on a controlled variable or a function by a controller.

通过控制器控制某一变量或函数进行周期性变化。

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A periodic change in the distribution of pressure between the North Pole and a circle at about 55degree.

在北极点与大约55度N纬圈之间气压分布的周期性变化。

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The phenology is the science studying mutual concern among plant, animal and the periodic change of ambient condition.

物候学是研究自然界的植物、动物与环境条件的周期变化之间相互关系的科学。

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Half a century is a long time, people want to see their families and help them in whatever measure they can, and since there is no periodic renewal of the government in Cuba, change being dependent only on the whims of biology, some relief is needed to ease the pain now, not whenever the inevitable finally happens.

CNN: Commentary: Obama should ask Cuba to lift restrictions