试分析遮热板的原理及其在削弱辐射传热中的作用。
参考答案：
可从遮热板能增加系统热阻角度加以说明。A.在辐射换热表面之间插入金属（或固体）薄板，称为遮热板。B.其原理是，遮热板的存在增大了系统中的辐射换热热阻，使辐射过程的总热阻增大，系统黑度减少，使辐射换热量减少。C.遮热板对于削弱辐射换热具有显著作用，如在两个平行辐射表面之间插入一块同黑度的遮热板，可使辐射换热量减少为原来的1／2，若采用黑度较小的遮热板，则效果更为显著。
| 阅读下列短文，从四个选项中选出能回答所提问题或完成所给句子的最佳答案。 |
| The computer age is making an army of robots-machines that are directed by electronic (电子的) brains and which replace human labor in industrial operations. Many are man-made arms which reach into areas man enters only at the cost of his life, such as the inside of a nuclear reactor (核反应堆). Already in 1980, there were over 8000 such robots working in industrial plants throughout the world. The big change over to the robot, however, is likely to come only when their costs go down while workers' wages continue to rise. |
| 1. Sentence 1 means that robots are used mainly____. |
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| Ａ：to fight wars Ｂ：to operate computers Ｃ：to direct electronic brains Ｄ：to take the place of human workers |
| 2. The shape of many robots already in use looks like a human____. |
[ ] |
| Ａ：brain Ｂ：arm Ｃ：hand Ｄ：eye |
| 3. The passage makes it clear that a very valuable use of many robots is to _____ . |
[ ] |
| Ａ：act as a teacher to children Ｂ：replace the human brain in making computers Ｃ：help doctors in medical operations Ｄ：do tasks very dangerous for humans to do |
| 4. Which of the following about the last sentence is true? |
[ ] |
| Ａ：Robots are becoming cheaper all the time. Ｂ：Robots are becoming more and more expensive. Ｃ：The cost of a human worker is higher than that of the average (普通的) robot. Ｄ：The cost of the average robot is higher than that of a human worker. |
| 5. The writer thinks that the widespread replacement of human labor by industrial robots _____. |
[ ] |
| Ａ：has already begun worldwide Ｂ：is starting especially in the developing nations Ｃ：is being put off mainly for economic (经济的) reasons Ｄ：will not take place before the end of this century |