公共英語五級閲讀文章《鎳鈦合金》

公共英語五級的難度較大，考生需要平時在多加練習。下面是小編整理的一篇公共英語五級閲讀文章，歡迎閲讀。

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 (SME); 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 thecold can be as little as twelve degrees centigrade.

鎳鈦諾是這個世紀所發現的最不尋常的金屬之一，作為鎳和鈦的簡單的一種合金，鎳鈦諾具有一些令人驚歎的特徵。這是一種有記憶力的金屬，人們可以使它記住它被塑成的任何形狀，並在加熱後恢復這一形狀。

比如，一節鎳鈦諾線圈在加熱冷卻後會記住圓圈這形狀。隨後它可能被彎折成其它形狀，但一旦再次加熱，就會迅速地自動恢復成最初的圓圈狀。這種不尋常的能力被稱為形狀記憶效果(SME)。其它一些合金如黃銅在一定程度上也具有這種特性。目前人們對SME 這一特性尚缺乏透徹的認識，而鎳鈦諾尤其使人驚奇，因為每當它展現這一驚人的功能時，似乎都違背了熱力學原理。因為它在恢復原有形狀時所釋放的力比人們使它變形所施加的力大得多。

鎳鈦諾不僅有記憶力，還能"學習"。如果加熱-冷卻-彎曲-再加熱這一過程重複一定次數，且每次冷卻後它都被絲毫不差地彎成同一形狀，它不僅可以記住最初的形狀，還能逐漸記住它被彎成的形狀，並開始在每次冷卻時恢復這一形狀。最終，它會自動地隨温度變化而彎曲和恢復這些形狀，並且沒有任何疲勞跡象。工程師們已製造出一些發動機樣機，利用鎳鈦合金在交替遇熱水和冷水時迅速改變形狀所產生的力做推動力。然而這些神奇的發動機工作時並非完全不耗能，因為必須有熱能來製造温差才能使機器運轉。但人們可以通過改變合金中鎳鈦的比例來控制使它反應的最佳温度。有的'鎳鈦合金甚至能在室温下做出反應，冷暖之間的最小温差只有12℃。

　附：公共英語五級閲讀如何猜詞義?

　　一、利用所出現生詞的上下文與其意義上的聯繫或下文進一步的敍述，猜測詞義。

例一：the female mosquito is a vampire and lives on blood.如不知道vampire的詞義，從下文lives on blood(靠吸血而生存)則可得知其詞義為吸血昆蟲。

例二：the old man put on his spectacles and began to read.如不知道spectacles的詞義，從下文"戴上'spectacles'後開始閲讀"可以猜得其詞義"眼鏡".

　二、利用文中的舉例猜測詞義

例三：some artists plan their paintings around geometric forms like squares， circles and triangles.如不知道geometric forms的意思，可從文中所列舉的三角形，正方形、圓形來猜得其意義為"幾何圖形".

today young couples who are just starting their households often spend lots of their money on appliances for instance， washing machines， refrigerators and color televisions.如不知道appliances的意思，從文中的舉例"washing-machines(洗衣機)，refrigerator(冰箱)，televisions(電視機)"可以猜得該詞的意思為"家用電器".