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与线路交换相比，分组交换最大的优点是 (1) ，最大的缺点是 (2) 。设待传送数据总长度为L位分组长度为P位，其中头部开销长度为H位，源节点到目的节点之间的链路数为h，每个键路上的延迟时间为D秒，数据传输率为B bit/s，线路交换和虚电路建立连接的时间都为Ss，在分组交换方式下每个中间节点产生d bit的延迟时间，则传送所有数据，线路交换需时间为 (3) s，虚电路分组交换所需时间为 (4) s，数据报分组交换所需时间为 (5) s。([X]表示对X向上取整) 5（）
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An awkward-looking character such as Cyrano de Bergerac might sniff at the suggestion, but recent scientific research shows beauty, brains and brawn may in fact all be allied, writes Dr. Raj Persaud.(46) Psychologists have concluded that we may be drawn to the stereotypically attractive because of what their faces reveal about their intelligence and success in later life. In America, research led by Professor Leslie Zebrowitz, of Brandeis University, has shown an association between facial attractive and IQ. Strangers briefly exposed to a target’s face were able to correctly judge intelligence at levels significantly better than chance.The same team also researched how a person’s attractiveness might bear relation to their intelligence. They found that good-looking people did better in IQ tests as they aged. (47) Their research sought to prove that how a person perceived himself and was perceived by others predicted how intelligent he apparently became more accurately than his past intelligence. (48) Perhaps because the more attractive people were treated as more intelligent, they ended up having more stimulating and, therefore, intelligence-enhancing lives.Does this mean that your face really could be your destiny Sociologists Dr. Ulrich Mueller and Dr. Allan Mazur, of the University of Marburg in Germany, recently analyzed the final-year photographs of the 1950’s graduates of West Point in the United States. Dominant facial appearances turned out to be a consistent predictor of later-rank attainment.Again, they believed there could be a self-fulfilling effect. (49) Because some men looked more authoritative, they naturally drew respect and obedience from others which, in turn, assisted their rise through the ranks.A team at the Royal College of Surgeons in Dublin has been investigating the sensitive subject of links between physical and mental abnormalities. Led by Doctors Robin Hennessy and John Waddington, the team used a new laser surface-scanning technique to make a 3-D analysis of how facial shape might vary with brain structure. Their findings showed that in early fetal life, brain and face development are intimately connected. From this they concluded that abnormalities in brain elaboration probably also affect face development.This, according to them, explains the striking facial features of some one with Down’s syndrome. (50) Using similar techniques, the team also demonstrated how other disorders linked to brain aberrations could be associated with facial alterations.So the very latest scientific research suggests that nobody should try to look too obviously different from average. Using similar techniques, the team also demonstrated how other disorders linked to brain aberrations could be associated with facial alterations.
设信道带宽为3000Hz，根据尼奎斯特(Nyquist)定理，理想信道的波特率为 (1) 波特，若采用QPSK调制，其数据速率应为 (2) ，如果该信道信噪比为30dB，则该信道的带宽约为 (3) 。设信道误码率为10-5，帧长为10Kb，差错为单个错，则帧出错的概率为 (4) 。若整个报文被分成5个帧，帧出错的概率为0.1，纠错重发以报文为单位，则整个报文的平均发送次数约为 (5) 次。 2（）
帧中继网的虚电路建立在 (1) ，在用户层面采用的协议是 (2) 。这种网络没有流量控制功能，但增加了拥塞控制功能。如果沿着帧传送方向出现了拥塞，则把帧地址字段中的 (3) 位设置为1，这样接收方就可通过 (4) 协议要求发送方降低数据速率。最适合提供帧中继业务的网络是 (5) 。 3（）
与线路交换相比，分组交换最大的优点是 (1) ，最大的缺点是 (2) 。设待传送数据总长度为L位分组长度为P位，其中头部开销长度为H位，源节点到目的节点之间的链路数为h，每个键路上的延迟时间为D秒，数据传输率为B bit/s，线路交换和虚电路建立连接的时间都为Ss，在分组交换方式下每个中间节点产生d bit的延迟时间，则传送所有数据，线路交换需时间为 (3) s，虚电路分组交换所需时间为 (4) s，数据报分组交换所需时间为 (5) s。([X]表示对X向上取整) 2（）
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