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。
2
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。
3
The number of GM decreased as the slope exposure turned from N to S, as slope increased, and as slope shape turned from convex to concave.