问题 问答题 简答题

在CDT循环式远动规约中,为什么遥信变位的传送采用信息字插入方式?

答案

参考答案:

电力系统中的遥信量一般很少变动,但一旦它发生变动,就是一个很重要的事件,应尽快向调度所报告,这就是遥信变位的传送。电力系统对遥信变位的总传送时间要求较高,不能大于3秒。遥信变位的传送不能采用循环传送的方式,因为循环传送一遍信息的时间太长;也不能采用帧插入传送的方式,因为帧插入传送最多要等待传送一帧所用的时间,这个时间也还是太长;只有采用信息字插入方式,才可以满足电力系统对遥信变位的总传送时间要求。因为这种方式不用等待的时间是传送一个或几个信息字所用的时间,等待时间很短,最适合传送象遥信变位这种实时性要求很高的情况。

判断题
阅读理解

A report, published in last week's Journal of the American Medical Association, offers a picture of how risky it is to get a lift from a teenage driver. Indeed, a 16-year-old driver with three or more passengers is three times as likely to have a fatal(致命)accident as a teenager driving alone. By contrast, the risk of death for drivers between 30 and 59 decreases with each additional passenger.

The author also found that the death rates for teenage drivers increased dramatically after 10 p. m.,and especially after midnight. With passengers in the car,the driver was even more likely to die in a late night accident.

Robert Foss, a scientist at the University of North Carolina Highway Safety Research Center, says the higher death rates for teenage drivers have less to do with "really stupid behavior" than with just a lack of driving experience. "The basic thing, "he says, "is that adults who are responsible for issuing(发放) licenses fail to recognize how skilled a task driving is. "

Both he and the author of the study believe that the way to reduce the harm is to have so-called graduated licensing systems, in which getting a license is a slower process. A graduated license requires that a teenager first prove himself capable of driving in the presence of an adult, followed by a period of driving at night with a limited number of passengers before graduating to get a full driving license.

Graduated licensing systems have reduced teenage driver crashes, according to recent studies. About half of the states now have some sort of graduated licensing system in place, but only 10 of those states have number limitation on passengers. California is the strictest, with a new driver prohibited from carrying any passenger under 20 for the first six months.

76.Which of the following situations is most dangerous according to the passage?

A. Adults giving a lift to teenagers on the highway after 10 p. m.

B. A teenager driving after midnight with passengers in the car.

C. Adults driving with three or more teenage passengers late at night.

D. A teenager getting a lift from a stranger on the highway at midnight.

77.According to Robert Foss, the high death rate of teenage drivers is mainly due to_______.

A. their frequent driving at night         B. their lack of driving experience

C. their improper way of driving         D. their driving with passengers

78.Which of the following statements is true according to Paragraph 3 ?  

A. Teenagers should spend more time learning to drive.

B. Driving is a skill too difficult for teenagers to learn.

C. Teenagers should be limited in taking driving lessons.

D. People issuing license are partly responsible for the accidents.

79.A suggested measure to be taken to reduce teenagers'driving accidents is that_______

A. driving in the presence of an adult should be made a rule.

B. they should be forbidden to take on passengers

C. they should not be allowed to drive after 10 p. m.

D. the licensing systems should be improved

80.The present situation in about half of the states is that the graduated licensing system_______.

A. is under discussion              B. is about to be set up

C. has been put into effect                 D. has been perfected