A new polymer material that can repeatedly heal itself at room temperature when exposed to ultraviolet light presents the tantalizing possibility of products that can repair themselves when damaged.

一种新的聚合物材料在室温紫外光照射下可以不断地进行自我恢复，这一特性表示日后的产品在受损后也可以自我修复。

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Exposed steel used in automobiles can't be made with recycled material and has to be treated to withstand the elements.

汽车暴露在外部分所用的钢材不能用回收材料生产，它们必须能够经受风雨的侵蚀。

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The rim of the plugs is usually not exposed and the enveloping material cannot be ascertained.

岩栓的边缘通常是不露出的，因而不能确定其包裹的物质是什么。

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The exterior is completely metal and the only other exposed material on the outside is concrete.

BBC: California faces up to year-round forest fires

"Ending the exemptions from age classification for hard copy music videos will be an important step forward in making sure that children are not inadvertently exposed to unsuitable material, " said Mr Bailey.

BBC: Age-ratings call for music DVDs

The material is exposed to ultraviolet light through a mask patterned with the outlines of cells.

ECONOMIST: REPORTS