53 Nitinol
Nitinol is one of the most extraordinary metals to be discovered this century: A simple alloy of nickel and titanium, nitinol has some perplexing properties. A metal with a memory, it can be made to remember any shape into which it is fashioned, returning to that shape whenever it is heated. For example, a piece of nitinol wire bent to form a circle that is then heated and quenched will remember this shape. It may then be bent or crumpled, but on reheating, will violently untwist, reforming its original shape. This remarkable ability is called Shape Memory Effect ; other alloys, such as brasses, are known to possess it to a limited extent. No one fully understands SME, and nitinol remains particularly perplexing, for, whenever it performs this peculiar feat, it appears to be breaking the laws of thermodynamics by springing back into shape with greater force than was used to deform it in the first place. But not only is nitinol capable of remembering, it also has the ability to learn . If the heating-cooling-crumpling-reheating process is carried out sufficiently often, and the metal is always crumpled in exactly the same way, the nitinol will not only remember its original shape, but gradually it learns to remember its crumpled form as well, and will begin to return to the same crumpled shape every time it is cooled. Eventually, the metal will crumple and uncrumple, totally unaided, in response to changes in temperature and without any sign of metal fatigue. Engineers have produced prototype engines that are driven by the force of nitinol springing from one shape to another as it alternately encounters hot and cold water. The energy from these remarkable engines is, however, not entirely free: heat energy is required to produce the temperature differences needed to run the engine. But the optimum temperatures at which the metal reacts can be controlled by altering the proportions of nickel to titanium; some alloys will even perform at room temperature. The necessary temperature range between the warm and the cold can be as little as twelve degrees centigrade.
牛津小学六年级英语第五单元说课稿
初一新生入学英语摸底测试题
小学 Unit 1 Is it a dragon 说课稿
2013初一新生入学英语考试测试题
小学六年级英语Holidays说课稿
小学六年级英语Unit 8说课稿
初中二年级英语上册第6单元说课稿
八年级上册英语教学设计
小学英语六年级教学计划
2013高一新生英语入学考试摸底题
2013高一新生入学考试英语摸底题
2013年高一新生入学英语测试题
小学英语what does she do? 说课稿
牛津小学一年级英语说课稿
高一新生入学英语测试题
五年级英语上册Unit 2 Lesson 10说课稿
情人节送给男女朋友的金典礼物
四年级英语上册Unit 4第三课时说课稿
人教版小学一年级上册英语说课稿
2013年新生入学七年级英语测试题及答案
英语比较级
2013年初一新生入学英语测试题
高一新生入学英语摸底考试题
高一新生入学英语摸底测试题及答案
2013初一新生入学考试英语摸底试题
新生入学七年级英语考试试题
广州版小学一年级英语说课稿
小学六年级英语Book 4 Unit 4 Lesson 19说课稿
广州版小学六年级英语Where Is My Ruler说课稿
人教版小学一年级英语说课稿
不限 |
英语教案 |
英语课件 |
英语试题 |
不限 |
不限 |
上册 |
下册 |
不限 |