体积的涨缩变化产生了地震道上的正、负振幅。

These changes in volume contribute to the positive and negative amplitudes of a seismic trace.

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旋击盘周边均布100 ~ 120个旋击头和多个涨缩槽。

Around rotating plate there are 100-120 rotating heads and many collapsible grooves.

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四个明袋采用涨缩自如、颇具弹性的“琴袋”式样，旨在便于放置书本、笔记本等必需品之用。

The flexible and elastic style is adopted for the four visual pockets for the purpose of putting book, notebook and other necessities inside.

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