2015年12月英语六级听力暑期练习29
2015年6月的英语四六级考试已经告一段落，听力部分一直以来都是同学们考试时的难点，也是吐槽最多的部分。2015年12月份的四六级考试还离我们比较远，但是千里之行始于足下，没有积累很难有提升，想要早点为下半年的四六级考试做准备就来四六级考试网练习一下英语六级听力题吧。听力音频点击下载.mp3
听力材料：
Artificial limbs, including the most complex ofthem – the human hand – are getting more life-like and useful due to constant advances in tinyhydraulic, pneumatic and electric motors calledactuators. But now scientists in Germany saythe future of the prosthetic hand may be not inmotors, but in wires that can ‘remember’ their shape.
The human hand is one of the most mechanically complex systems in nature, so making anartificial replica is a daunting task. An ideal prosthesis should be light and flexible, with areasonably powerful grip and controlled by the owner’s mind.
Presently, prosthetics rely on relatively heavy hydraulic, electric or pneumatic actuators to flexartificial fingers, but scientists at Germany's Saarland University are experimenting with muchlighter fibers made of a nickel-titanium alloy that change shape when connected to a source ofelectricity.
“The movement of the hand is done by the wire. This wire, when activated, they contract. Andwe are able to exploit this contraction to make the finger move. And we can move eachphalanx independently,” said Filomena Simone, a PhD engineering student.
Artificial muscles, tendons
Bundles of memory wires could form more powerful yet lightweight artificial muscles andtendons. Their flexing can be controlled independently by measuring the electrical resistanceof the wires.
“We can monitor the position of the finger without adding any other sensor; only exploiting thisembedded feature of the wire,” said Simone.
Scientists believe that with further advances of so-called shape memory alloys, it will be possibleto build more natural-looking prosthetic hands.
“If you look down the road to future prostheses generations, you'd like to see this integratedwith the human body in a way that you can actually sense the nerve stimuli and then can feedthat into a micro-controller which there will be translated to a corresponding signal to activatethe muscle," said Stefan Seelecke at Saarland University.
Saarland University scientists are now looking into how natural patterns of hand movementscould be applied to memory alloy muscles.
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