亚洲一区二区三区不卡在线播放 ,91精品一区二区三区在线播放,国产综合久久一区二区三区

當前位置：

首頁 >> 外語類 >> 學位英語 >> 模擬試題>> 正文

2015年職稱英語考試綜合類模擬試題六：閱讀判斷

發表時間：2014/8/7 10:51:09 來源：互聯網點擊關注微信：

關注公眾號

New Understanding of Natural Silk’s Mysteries

Natural silk, as we all know, has a strength that man-made materials have long struggled to match. In a discovery that sounds more like an ancient Chinese proverb than a materials science breakthrough, MIT researchers have discovered that silk gets its strength from its weakness. Or, more specifically, its many weaknesses. Silk gets its extraordinary durability and ductility (柔韌性) from an unusual arrangement of hydrogen bonds that are intrinsically very weak but that work together to create a strong, flexible structure.

Most materials —especially the ones we engineer for strength —get their toughness from brittleness. As such, natural silks like those produced by spiders have long fascinated both biologists and engineers because of their light weight, ductility and high strength (pound for pound, silk is stronger than steel and far less brittle). But on its face, it doesn't seem that silks should be as strong as they are; molecularly, they are held together by hydrogen bonds, which are far weaker than the covalent (共價的) bonds found in other molecules.

To get a better understanding of how silk manages to produce such strength through such weak bonds, the MIT team created a set of computer models that allowed them to observe the way silk behaves at the atomic level. They found that the arrangement of the tiny silk nanocrystals (納米晶體) is such that the hydrogen bonds are able to work cooperatively, reinforcing one another against external forces and failing slowly when they do fail, so as not so allow a sudden fracture to spread across a silk structure.

The result is natural silks that can stretch and bend while retaining a high degree of strength. But while that's all well and good for spiders, bees and the like, this understanding of silk geometry could lead to new materials that are stronger and more ductile than those we can currently manufacture. Our best and strongest materials are generally expensive and difficult to produce (requiring high temperature treatments or energy-intensive processes).

By looking to silk as a model, researchers could potentially devise new manufacturing methods that rely on inexpensive materials and weak bonds to create less rigid, more forgiving materials that are nonetheless stronger than anything currently on offer. And if you thought you were going to get out of this materials science story without hearing about carbon nanotubes (納米碳管), think again.The MIT team is already in the lab looking into ways of synthesizing silk-like structures out of materials that are stronger than natural silk —like carbon nanotubes. Super-silks are on the horizon.

16. MIT researchers carry out the study to illustrate an ancient Chinese proverb.