In the downstream direction, the PON is a broadcast medium.

在下行方向，PON是一种广播介质。

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The author based on the above results designed a model of downstream direction bileaflet mechanical valve and used finite bulk method to calculate the velocity and shear stress profiles of this valve.

作者提出了一种顺向双叶机械瓣的设计模型，并用有限体积法对这种模型进行流场和剪应力分布的数值模拟。

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