问题 问答题 简答题

简述干式缸套和湿式缸套特点。

答案

参考答案:

湿式汽缸套:在气缸体上设有封闭的水套,铸造方便,容易拆卸更换,冷却效果小号。但是气缸的刚度差,易于漏水漏气。

干式汽缸套:机体刚度大,气缸中心距小、质量轻和加工工艺简单。但是散热较差,温度分布不均匀、容易发生局部变形。

单项选择题
单项选择题

Modern industrial society grants little status to old people. In fact, such a society has a system of built-in obsolescence. There is no formal system for continuing our education throughout our life in order to keep up with rapidly changing knowledge. When our education and job skills have grown obsolete, we are treated exactly like those who have never gained an education or job skills and are not encouraged or given the opportunity to begin anew.As a society becomes more highly developed, the overall status of older people diminishes. Improved health technology creates a large pool of old people, who compete for jobs with the young. However, economic technology lowers the demand for workers and creates new jobs for which the skills of the aged are obsolete, forcing older people into retirement. At the same time, young people are being educated in the new technology and are keeping pace with rapid changes in knowledge. Finally, urbanization creates age-segregated neighborhoods. Because the old live on fixed incomes, they must often live in inferior housing. All these factors — retirement, obsolete knowledge and skills, inferior standards of living — lower the status of the aged in society.A century ago, when one could expect to live only to 50 or so, the life span more or less coincided with the occupation and family cycle. But today the average life span allows for fifteen to twenty years of life after these cycles. It appears that our life span is outpacing our usefulness in society.

Which of the following would be the best title for this passage

A.The Problem of Aging

B.Social Structures

C.Economic Technology

D.Continuing Education