2013职称英语考试理工类A级阅读判断真题

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　　2013职称英语考试卫生类A级真题答案（网友版）

　　New Understanding of Natural Silk's Mysteries Could Lead to Stronger, Lighter Materials

　　By Clay Dillow

　　Natural silk, as we all know, has a strength that manmade 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 from an unusual arrangement of hydrogen bonds that are inherently 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 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 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, 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.

　　探索蚕丝的奥秘，制造更加结实而轻盈的材料

　　克雷·迪洛 著

　　我们都知道，蚕丝具有的韧性是人造织物长期奋力追求的目标。在一项研究中(该项研究成果听起来更像一则古代中国谚语，而不是材料科学的突破)，麻省理工学院的研究人员发现，蚕丝的力量源于其脆弱，或者，更具体地说，是它的多方面的脆弱。蚕丝的异常耐久性和延展性来自一种特别的氢键结构，这些氢键本质上非常脆弱，但它们共同创造了一种强壮而富有弹性的结构。

　　大多数材料(特别是那些要求硬度很高的材料)的韧性来自脆性。因此，和蜘蛛制造的蛛丝类似的蚕丝，因其重量轻，延展性强和韧性高，长期以来引起了生物学家和工程师的兴趣(同样重量，蚕丝比钢要壮，也不那么脆)。但表面上，蚕丝看起来却不那么强壮;从分子结构上看，它们是由氢键组成的，氢键比其他分子中发现的共价键要脆弱得多。

　　为了更好地了解蚕丝如何以如此脆弱的化学键产生这么强壮的力，麻省理工学院的研究小组创造了一套计算机模型，这种模型能够让他们在原子层次上观察蚕丝的活动方式。他们发现，微小蚕丝纳米晶体的结构使氢键能够齐心协力地合作，相互增援，对抗外力，同时，当外力减弱时也随之慢慢减弱，这样就不至于在蚕丝的整体结构上出现突然的断裂。

　　这样，天然丝能够既伸缩和弯曲，又能够保持极高的韧力。对于蜘蛛和蜜蜂之类的昆虫来说这也没什么，但对于蚕丝几何形状的这种了解，可能帮助人们制造出比我们面前能够制造的材料更结实而又更柔软的新材料。最好和最结实的材料通常是很昂贵而又难以制造的(需要高温处理，或者高能耗处理)。

　　通过研究蚕丝作为一个例子，研究人员有可能设计出制造材料的一种新方法，即用廉价材料和弱键，制造不那么坚硬而又柔软，但比目前所用的任何材料都结实的材料。如果你认为不研究碳纳米管的理论，就能从这一则材料学信息中获取制造方法，那请三思。麻省理工学院研究小组已经在实验室利用比蚕丝还结实的材料(比如碳纳米管)研究合成类似蚕丝一样的结构。超级蚕丝即将出现。

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