2013年职称英语考试《理工类A级》考试真题_职称英语考试真题理工类

2013年职称英语考试《理工类A级》考试真题

16、请根据短文的内容，对16-23做出判断

New Understanding of Natural Silks Mysteries Natursl silk, as we all know, has a strength that manmade materials have long struggled tomatch. In a discovery that sounds more like an ancient Chinese proverb than a materials sciencebreakthrough, 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 froman unusual arrangement of hydrogen bonds that are inherently very weak but that work togetherto create a strong, flexible structure.

Most materials -- especially the ones we engineer for strength - get their toughness frombrittleness. As such, natural silks like those produced by spiders have long fascinated bothbiologists and engineers because of their light weight, ductility and high strength (pound forpOund, silk is stronger than steel and far less brittle). But on its face, it doesnt seem that silksshould be as strong as they are; molecularly, they are held together by hydrogen bonds, whichare far weaker than the covalent bonds found in other molecules.

To get a better understanding of how silk manages to produce such strength through suchweak bonds, the MIT team created a set of computer models that allowed them to observe theway silk behaves at the atomic level.They found that the arrangement of the tiny silknanocrystals is such that the hydrogen bonds are able to work cooperatively, reinforcing oneanother against external forces and failing slowly when they do fail, so as not so allow a suddenfracture to spread across a silk structure.