Because there is no abrasion between the concave and convex, the nut is reusable.

由于凹面与凸面之间没有磨损，螺母可以重复使用。

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Water surges from the cells on the inside of the leaf to those on the outside, causing the leaf to rapidly flip in shape from convex to concave, like a soft contact lens.

水从叶子内部的细胞涌向外面的细胞，导致叶子迅速地从凸向凹翻转，就像一片柔软的隐形眼镜。

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Belt cupping, also called dishing, is characterized by an unintentional transversal concave or convex belt dishing over the whole belt width.

腰带拔罐，也被称为凹陷，特点是由无意的横向凹或凸的皮带在整个皮带宽度抛出。

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The result, in his final sketch of the Z4, was a roadster with edgier lines than its predecessor and intertwining concave and convex surfaces, echoing the geometry of a Cubist painting.

WSJ: Anders Warming: The Man Who Reinvents Wheels | Creating